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Nathan Goodyear

Testosterone and the Cardiovascular System: A Comprehensive Review of the Clinical Lite... - 0 views

  • Low endogenous bioavailable testosterone levels have been shown to be associated with higher rates of all‐cause and cardiovascular‐related mortality.39,41,46–47 Patients suffering from CAD,13–18 CHF,137 T2DM,25–26 and obesity27–28
  • have all been shown to have lower levels of endogenous testosterone compared with those in healthy controls. In addition, the severity of CAD15,17,29–30 and CHF137 correlates with the degree of testosterone deficiency
  • In patients with CHF, testosterone replacement therapy has been shown to significantly improve exercise tolerance while having no effect on LVEF
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  • testosterone therapy causes a shift in the skeletal muscle of CHF patients toward a higher concentration of type I muscle fibers
  • Testosterone replacement therapy has also been shown to improve the homeostatic model of insulin resistance and hemoglobin A1c in diabetics26,68–69 and to lower the BMI in obese patients.
  • Lower levels of endogenous testosterone have been associated with longer duration of the QTc interval
  • testosterone replacement has been shown to shorten the QTc interval
  • negative correlation has been demonstrated between endogenous testosterone levels and IMT of the carotid arteries, abdominal aorta, and thoracic aorta
  • These findings suggest that men with lower levels of endogenous testosterone may be at a higher risk of developing atherosclerosis.
  • Current guidelines from the Endocrine Society make no recommendations on whether patients with heart disease should be screened for hypogonadism and do not recommend supplementing patients with heart disease to improve survival.
  • The Massachusetts Male Aging Study also projects ≈481 000 new cases of hypogonadism annually in US men within the same age group
  • since 1993 prescriptions for testosterone, regardless of the formulation, have increased nearly 500%
  • Testosterone levels are lower in patients with chronic illnesses such as end‐stage renal disease, human immunodeficiency virus, chronic obstructive pulmonary disease, type 2 diabetes mellitus (T2DM), obesity, and several genetic conditions such as Klinefelter syndrome
  • A growing body of evidence suggests that men with lower levels of endogenous testosterone are more prone to develop CAD during their lifetimes
  • There are 2 major potential confounding factors that the older studies generally failed to account for. These factors are the subfraction of testosterone used to perform the analysis and the method used to account for subclinical CAD.
  • The biologically inactive form of testosterone is tightly bound to SHBG and is therefore unable to bind to androgen receptors
  • The biologically inactive fraction of testosterone comprises nearly 68% of the total testosterone in human serum
  • The biologically active subfraction of testosterone, also referred to as bioavailable testosterone, is either loosely bound to albumin or circulates freely in the blood, the latter referred to as free testosterone
  • It is estimated that ≈30% of total serum testosterone is bound to albumin, whereas the remaining 1% to 3% circulates as free testosterone
  • it can be argued that using the biologically active form of testosterone to evaluate the association with CAD will produce the most reliable results
  • English et al14 found statistically significant lower levels of bioavailable testosterone, free testosterone, and free androgen index in patients with catheterization‐proven CAD compared with controls with normal coronary arteries
  • patients with catheterization‐proven CAD had statistically significant lower levels of bioavailable testosterone
  • In conclusion, existing evidence suggests that men with CAD have lower levels of endogenous testosterone,13–18 and more specifically lower levels of bioavailable testosterone
  • low testosterone levels are associated with risk factors for CAD such as T2DM25–26 and obesity
  • In a meta‐analysis of these 7 population‐based studies, Araujo et al41 showed a trend toward increased cardiovascular mortality associated with lower levels of total testosterone, but statistical significance was not achieved (RR, 1.25
  • the authors showed that a decrease of 2.1 standard deviations in levels of total testosterone was associated with a 25% increase in the risk of cardiovascular mortality
  • the relative risk of all‐cause mortality in men with lower levels of total testosterone was calculated to be 1.35
  • higher risk of cardiovascular mortality is associated with lower levels of bioavailable testosterone
  • Existing evidence seems to suggest that lower levels of endogenous testosterone are associated with higher rates of all‐cause mortality and cardiovascular mortality
  • studies have shown that lower levels of endogenous bioavailable testosterone are associated with higher rates of all‐cause and cardiovascular mortality
  • It may be possible that using bioavailable testosterone to perform mortality analysis will yield more accurate results because it prevents the biologically inactive subfraction of testosterone from playing a potential confounding role in the analysis
  • The earliest published material on this matter dates to the late 1930s
  • the concept that testosterone replacement therapy improves angina has yet to be proven wrong
  • In more recent studies, 3 randomized, placebo‐controlled trials demonstrated that administration of testosterone improves myocardial ischemia in men with CAD
  • The improvement in myocardial ischemia was shown to occur in response to both acute and chronic testosterone therapy and seemed to be independent of whether an intravenous or transdermal formulation of testosterone was used.
  • testosterone had no effect on endothelial nitric oxide activity
  • There is growing evidence from in vivo animal models and in vitro models that testosterone induces coronary vasodilation by modulating the activity of ion channels, such as potassium and calcium channels, on the surface of vascular smooth muscle cells
  • Experimental studies suggest that the most likely mechanism of action for testosterone on vascular smooth muscle cells is via modulation of action of non‐ATP‐sensitive potassium ion channels, calcium‐activated potassium ion channels, voltage‐sensitive potassium ion channels, and finally L‐type calcium ion channels
  • Corona et al confirmed those results by demonstrating that not only total testosterone levels are lower among diabetics, but also the levels of free testosterone and SHBG are lower in diabetic patients
  • Laaksonen et al65 followed 702 Finnish men for 11 years and demonstrated that men in the lowest quartile of total testosterone, free testosterone, and SHBG were more likely to develop T2DM and metabolic syndrome.
  • Vikan et al followed 1454 Swedish men for 11 years and discovered that men in the highest quartile of total testosterone were significantly less likely to develop T2DM
  • authors demonstrated a statistically significant increase in the incidence of T2DM in subjects receiving gonadotropin‐releasing hormone antagonist therapy. In addition, a significant increase in the rate of myocardial infarction, stroke, sudden cardiac death, and development of cardiovascular disease was noted in patients receiving antiandrogen therapy.67
  • Several authors have demonstrated that the administration of testosterone in diabetic men improves the homeostatic model of insulin resistance, hemoglobin A1c, and fasting plasma glucose
  • Existing evidence strongly suggests that the levels of total and free testosterone are lower among diabetic patients compared with those in nondiabetics
  • insulin seems to be acting as a stimulant for the hypothalamus to secret gonadotropin‐releasing hormone, which consequently results in increased testosterone production. It can be argued that decreased stimulation of the hypothalamus in diabetics secondary to insulin deficiency could result in hypogonadotropic hypogonadism
  • BMI has been shown to be inversely associated with testosterone levels
  • This interaction may be a result of the promotion of lipolysis in abdominal adipose tissue by testosterone, which may in turn cause reduced abdominal adiposity. On the other hand, given that adipose tissue has a higher concentration of the enzyme aromatase, it could be that increased adipose tissue results in more testosterone being converted to estrogen, thereby causing hypogonadism. Third, increased abdominal obesity may cause reduced testosterone secretion by negatively affecting the hypothalamus‐pituitary‐testicular axis. Finally, testosterone may be the key factor in activating the enzyme 11‐hydroxysteroid dehydrogenase in adipose tissue, which transforms glucocorticoids into their inactive form.
  • increasing age may alter the association between testosterone and CRP. Another possible explanation for the association between testosterone level and CRP is central obesity and waist circumference
  • Bai et al have provided convincing evidence that testosterone might be able to shorten the QTc interval by augmenting the activity of slowly activating delayed rectifier potassium channels while simultaneously slowing the activity of L‐type calcium channels
  • consistent evidence that supplemental testosterone shortens the QTc interval.
  • Intima‐media thickness (IMT) of the carotid artery is considered a marker for preclinical atherosclerosis
  • Studies have shown that levels of endogenous testosterone are inversely associated with IMT of the carotid artery,126–128,32,129–130 as well as both the thoracic134 and the abdominal aorta
  • 1 study has demonstrated that lower levels of free testosterone are associated with accelerated progression of carotid artery IMT
  • another study has reported that decreased levels of total and bioavailable testosterone are associated with progression of atherosclerosis in the abdominal aorta
  • These findings suggest that normal physiologic testosterone levels may help to protect men from the development of atherosclerosis
  • Czesla et al successfully demonstrated that the muscle specimens that were exposed to metenolone had a significant shift in their composition toward type I muscle fibers
  • Type I muscle fibers, also known as slow‐twitch or oxidative fibers, are associated with enhanced strength and physical capability
  • It has been shown that those with advanced CHF have a higher percentage of type II muscle fibers, based on muscle biopsy
  • Studies have shown that men with CHF suffer from reduced levels of total and free testosterone.137 It has also been shown that reduced testosterone levels in men with CHF portends a poor prognosis and is associated with increased CHF mortality.138 Reduced testosterone has also been shown to correlate negatively with exercise capacity in CHF patients.
  • Testosterone replacement therapy has been shown to significantly improve exercise capacity, without affecting LVEF
  • the results of the 3 meta‐analyses seem to indicate that testosterone replacement therapy does not cause an increase in the rate of adverse cardiovascular events
  • Data from 3 meta‐analyses seem to contradict the commonly held belief that testosterone administration may increase the risk of developing prostate cancer
  • One meta‐analysis reported an increase in all prostate‐related adverse events with testosterone administration.146 However, when each prostate‐related event, including prostate cancer and a rise in PSA, was analyzed separately, no differences were observed between the testosterone group and the placebo group
  • the existing data from the 3 meta‐analyses seem to indicate that testosterone replacement therapy does not increase the risk of adverse cardiovascular events
  • the authors correctly point out the weaknesses of their study which include retrospective study design and lack of randomization, small sample size at extremes of follow‐up, lack of outcome validation by chart review and poor generalizability of the results given that only male veterans with CAD were included in this study
    • Nathan Goodyear
       
      The authors here present Total Testosterone as a "confounding" value
    • Nathan Goodyear
       
      This would be HSD-II
  • the studies that failed to find an association between testosterone and CRP used an older population group
  • low testosterone may influence the severity of CAD by adversely affecting the mediators of the inflammatory response such as high‐sensitivity C‐reactive protein, interleukin‐6, and tumor necrosis factor–α
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    Good review of Testosterone and CHD.  Low T is associated with increased all cause mortality and cardiovascular mortality, CAD, CHF, type II diabetes, obesity, increased IMT,  increased severity of CAD and CHF.  Testosterone replacement in men with low T has been shown to improve exercise tolerance in CHF, improve insulin resistance, improve HgbA1c and lower BMI in the obese.
Nathan Goodyear

Testosterone level in men with type 2 diabetes mellitus and related metabolic... - 0 views

  • defined by consistent symptoms and signs of androgen deficiency, and an unequivocally low serum testosterone level
  • the threshold serum testosterone level below which adverse clinical outcomes occur in the general population is not known
  • most population-based studies use the serum testosterone level corresponding to the lower limit, quoted from 8.7 to 12.7 nmol/L, of the normal range for young Caucasian men as the threshold
    • Nathan Goodyear
       
      this equals 251 to 366 in serum Total Testosterone
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  • Researchers tried to examine whether serum total or free testosterone would be a better/more reliable choice when studying the effect of testosterone. The results were mixed. Some reported significant associations of both serum total and free testosterone level with clinical parameters25, whereas others reported that only serum free testosterone26 or only serum total testosterone6 showed significant associations.
  • −0.124 nmol/L/year in serum total testosterone
    • Nathan Goodyear
       
      this equates to a 4 ng/dl decline annually in total Testosterone.
  • In experimental studies, androgen receptor knockout mice developed significant insulin resistance rapidly
  • In mouse models, testosterone promoted differentiation of pluripotent stem cells to the myogenic lineage
  • testosterone decreased insulin resistance by enhancing catecholamine induced lipolysis in vitro, and reducing lipoprotein lipase activity and triglyceride uptake in human abdominal tissue in vivo
  • by promoting lipolysis and myogenesis, testosterone might lead to improved insulin resistance
  • testosterone regulated skeletal muscle genes involved in glucose metabolism that led to decreased systemic insulin resistance
  • In the liver, hepatic androgen receptor signaling inhibited development of insulin resistance in mice
  • independent and inverse association of testosterone with hepatic steatosis shown in a cross-sectional study carried out in humans
  • In short, androgen improves insulin resistance by changing body composition and reducing body fat.
  • Although a low serum testosterone level could contribute to the development of obesity and type 2 diabetes through changes in body composition, obesity might also alter the metabolism of testosterone
  • In obese men, the peripheral conversion from testosterone to estrogen could attenuate the amplitude of luteinizing hormone pulses and centrally inhibit testosterone production
  • leptin, an adipokine, has been shown to be inversely correlated with serum testosterone level in men
  • Leydig cells expressed leptin receptors and leptin has been shown to inhibit testosterone secretion, suggesting a role of obesity and leptin in the pathogenesis of low testosterone
    • Nathan Goodyear
       
      So what is "unequivocal"?
  • Baltimore Longitudinal Study of Aging (BLSA) cohort made up of 3,565 middle-class, mostly Caucasian men from the USA, the incidence of low serum total testosterone increased from approximately 20% of men aged over 60 years, 30% over 70 years, to 50% over 80 years-of-age
  • 30–44% sex hormone binding globulin (SHBG)-bound testosterone and 54–68% albumin-bound testosterone
  • As the binding of testosterone to albumin is non-specific and therefore not tight, the sum of free and albumin-bound testosterone is named bioavailable testosterone, which reflects the hormone available at the cellular level
  • Serum total testosterone is composed of 0.5–3.0% of free testosterone unbound to plasma proteins
  • alterations in SHBG concentration might affect total serum testosterone level without altering free or bioavailable testosterone
  • listed in Table​T
  • A significant, independent and longitudinal effect of age on testosterone has been observed with an average change of −0.124 nmol/L/year in serum total testosterone28. The same trend has been shown in Europe and Australia
  • Asian men residing in HK and Japan, but not those living in the USA, had 20% higher serum total testosterone than in Caucasians living in the USA, as shown in a large multinational observational prospective cohort of the Osteoporotic Fractures in Men Study
  • subjects with chronic diseases consistently had a 10–15% lower level compared with age-matched healthy subjects
  • In Caucasians, the mean serum total testosterone level for men in large epidemiological studies has been reported to range from 15.1 to 16.6 nmol/L
  • Asians, higher values, ranging from 18.1 to 19.1 nmol/L, were seen in Korea and Japan
  • Chinese middle-aged men reported a similar mean serum testosterone level of 17.1 nmol/L in 179 men who had a family history of type 2 diabetes and 17.8 nmol/L in 128 men who had no family history of type 2 diabetes
  • The reduction of total testosterone was 0.4% per year in both groups
  • HK involving a cohort of 1,489 community-dwelling men with a mean age of 72 years, a mean serum total testosterone of 19.0 nmol/L was reported
  • pro-inflammatory factors, such as tumor necrosis factor-α in the testes, could locally inhibit testosterone biosynthesis in Leydig cells47, and testosterone treatment in men was shown to reduce the level of tumor necrosis factor-α
  • In Asians, a genetic deletion polymorphism of uridine diphosphate-glucuronosyltransferase UGT2B17 was associated with reduced androgen glucuronidation. This resulted in higher level of active androgen in Asians as compared to Caucasians, as Caucasians' androgen would be glucuronidated into inactive forms faster.
  • Compared with Caucasians, the frequency of this deletion polymorphism of UGT2B17 was 22-fold higher in Asian subjects
  • Other researchers have suggested that environmental, but not genetic, factors influenced serum total testosterone
  • The basal and ligand-induced activity of the AR is inversely associated with the length of the CAG repeat chain
  • In the European Male Aging Study, increased estrogen/androgen ratio in association with longer AR CAG repeat was observed
  • a smaller number of AR CAG repeat had been shown to be associated with benign prostate hypertrophy and faster prostate growth during testosterone treatment
  • In India, men with CAG ≤19 had increased risk of prostate cancer
  • the odds of having a short CAG repeat (≤17) were substantially higher in patients with lymph node-positive prostate cancer than in those with lymph node-negative disease or in the general population
  • assessing the polymorphism at the AR level could be a potential tool towards individualized assessment and treatment of hypogonadism.
  • In elderly men, there was reduced testicular response to gonadotropins with suppressed and altered pulsatility of the hypothalamic pulse generator
  • a significant, independent and longitudinal effect of age on serum total testosterone level had been observed
  • A significant graded inverse association between serum testosterone level and insulin levels independent of age has also been reported in Caucasian men
  • Low testosterone is commonly associated with a high prevalence of MES
  • most studies showed that changes in serum testosterone level led to changes in body composition, insulin resistance and the presence of MES, the reverse might also be possible
  • MES predicted a 2.6-fold increased risk of development of low serum testosterone level independent of age, smoking and other potential confounders
  • Other prospective studies have shown that development of MES accelerated the age-related decline in serum testosterone level
  • In men with type 2 diabetes, changes in serum testosterone level over time correlated inversely with changes in insulin resistance
  • weight loss by either diet control or bariatric surgery led to a substantial increase in total testosterone, especially in morbidly obese men, and the rise in serum testosterone level was proportional to the amount of weight lost
  • To date, published clinical trials are small, of short duration and often used pharmacological, not physiological, doses of testosterone
  • In the population-based Osteoporotic Fractures in Men Study cohort from Sweden, men in the highest quartile of serum testosterone level had the lowest risk of cardiovascular events compared with men in the other three quartiles (hazard ratio [HR] 0.70
  • low serum total testosterone was associated with a significant fourfold higher risk of cardiovascular events when comparing men from the lowest testosterone tertile with those in the highest tertile
  • Shores et al. were the first to report that low serum testosterone level, including both serum total and free testosterone, was associated with increased mortality
  • low serum total testosterone predicted increased risk of cardiovascular mortality with a HR of 1.38
  • low serum total testosterone increased all-cause (HR 1.35, 95% CI 1.13–1.62, P < 0.001) and cardiovascular mortality (HR 1.25
  • European Association for the Study of Diabetes 2013 suggested there was an inverse relationship between serum testosterone level and acute myocardial infarction
  • Diabetic men in the highest quartile of serum total testosterone had a significantly reduced risk of acute MI when compared with those in the lower quartiles
  • serum total testosterone level in the middle two quartiles at baseline predicted reduced incidence of death compared with having the highest and lowest levels
  •  
    Nice review of Testosterone levels and some of the evidence linking Diabetes with low T.  However, the conclusion by the authors regarding what is causing the low T in men with Diabetes is baffling.  The literature does not point to one cause, it is clearly multifactorial--obesity, inflammation, high aromatase activity...I would suggest the authors continue their readings in the manner.
Nathan Goodyear

Testosterone and glucose metabolism in men: current concepts and controversies - 0 views

  • Around 50% of ageing, obese men presenting to the diabetes clinic have lowered testosterone levels relative to reference ranges based on healthy young men
  • The absence of high-level evidence in this area is illustrated by the Endocrine Society testosterone therapy in men with androgen deficiency clinical practice guidelines (Bhasin et al. 2010), which are appropriate for, but not specific to men with metabolic disorders. All 32 recommendations made in these guidelines are based on either very low or low quality evidence.
  • A key concept relates to making a distinction between replacement and pharmacological testosterone therapy
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  • The presence of symptoms was more closely linked to increasing age than to testosterone levels
  • Findings similar to type 2 diabetes were reported for men with the metabolic syndrome, which were associated with reductions in total testosterone of −2.2 nmol/l (95% CI −2.41 to 1.94) and in free testosterone
  • low testosterone is more predictive of the metabolic syndrome in lean men
  • Cross-sectional studies uniformly show that 30–50% of men with type 2 diabetes have lowered circulating testosterone levels, relative to references based on healthy young men
  • In a recent cross-sectional study of 240 middle-aged men (mean age 54 years) with either type 2 diabetes, type 1 diabetes or without diabetes (Ng Tang Fui et al. 2013b), increasing BMI and age were dominant drivers of low total and free testosterone respectively.
  • both diabetes and the metabolic syndrome are associated with a modest reduction in testosterone, in magnitude comparable with the effect of 10 years of ageing
  • In a cross-sectional study of 490 men with type 2 diabetes, there was a strong independent association of low testosterone with anaemia
  • In men, low testosterone is a marker of poor health, and may improve our ability to predict risk
    • Nathan Goodyear
       
      probably the most important point made in this article
  • low testosterone identifies men with an adverse metabolic phenotype
  • Diabetic men with low testosterone are significantly more likely to be obese or insulin resistant
  • increased inflammation, evidenced by higher CRP levels
  • Bioavailable but not free testosterone was independently predictive of mortality
  • It remains possible that low testosterone is a consequence of insulin resistance, or simply a biomarker, co-existing because of in-common risk factors.
  • In prospective studies, reviewed in detail elsewhere (Grossmann et al. 2010) the inverse association of low testosterone with metabolic syndrome or diabetes is less consistent for free testosterone compared with total testosterone
  • In a study from the Framingham cohort, SHBG but not testosterone was prospectively and independently associated with incident metabolic syndrome
  • low SHBG (Ding et al. 2009) but not testosterone (Haring et al. 2013) with an increased risk of future diabetes
  • In cross-sectional studies of men with (Grossmann et al. 2008) and without (Bonnet et al. 2013) diabetes, SHBG but not testosterone was inversely associated with worse glycaemic control
  • SHBG may have biological actions beyond serving as a carrier protein for and regulator of circulating sex steroids
  • In men with diabetes, free testosterone, if measured by gold standard equilibrium dialysis (Dhindsa et al. 2004), is reduced
    • Nathan Goodyear
       
      expensive, laborious process filled with variables
  • Low free testosterone remains inversely associated with insulin resistance, independent of SHBG (Grossmann et al. 2008). This suggests that the low testosterone–dysglycaemia association is not solely a consequence of low SHBG.
  • Experimental evidence reviewed below suggests that visceral adipose tissue is an important intermediate (rather than a confounder) in the inverse association of testosterone with insulin resistance and metabolic disorders.
  • testosterone promotes the commitment of pluripotent stem cells into the myogenic lineage and inhibits their differentiation into adipocytes
  • testosterone regulates the metabolic functions of mature adipocytes (Xu et al. 1991, Marin et al. 1995) and myocytes (Pitteloud et al. 2005) in ways that reduce insulin resistance.
  • Pre-clinical evidence (reviewed in Rao et al. (2013)) suggests that at the cellular level, testosterone may improve glucose metabolism by modulating the expression of the glucose-transported Glut4 and the insulin receptor, as well as by regulating key enzymes involved in glycolysis.
  • More recently testosterone has been shown to protect murine pancreatic β cells against glucotoxicity-induced apoptosis
  • Interestingly, a reciprocal feedback also appears to exist, given that not only chronic (Cameron et al. 1990, Allan 2013) but also, as shown more recently (Iranmanesh et al. 2012, Caronia et al. 2013), acute hyperglycaemia can lower testosterone levels.
  • There is also evidence that testosterone regulates insulin sensitivity directly and acutely
  • In men with prostate cancer commencing androgen deprivation therapy, both total as well as, although not in all studies (Smith 2004), visceral fat mass increases (Hamilton et al. 2011) within 3 months
  • More prolonged (>12 months) androgen deprivation therapy has been associated with increased risk of diabetes in several large observational registry studies
  • Testosterone has also been shown to reduce the concentration of pro-inflammatory cytokines in some, but not all studies, reviewed recently in Kelly & Jones (2013). It is not know whether this effect is independent of testosterone-induced changes in body composition.
  • the observations discussed in this section suggest that it is the decrease in testosterone that causes insulin resistance and diabetes. One important caveat remains: the strongest evidence that low testosterone is the cause rather than consequence of insulin resistance comes from men with prostate cancer (Grossmann & Zajac 2011a) or biochemical castration, and from mice lacking the androgen receptor.
  • Several large prospective studies have shown that weight gain or development of type 2 diabetes is major drivers of the age-related decline in testosterone levels
  • there is increasing evidence that healthy ageing by itself is generally not associated with marked reductions in testosterone
  • Circulating testosterone, on an average 30%, is lower in obese compared with lean men
  • increased visceral fat is an important component in the association of low testosterone and insulin resistance
  • The vast majority of men with metabolic disorders have functional gonadal axis suppression with modest reductions in testosterone levels
  • obesity is a dominant risk factor
  • men with Klinefelter syndrome have an increased risk of metabolic disorders. Interestingly, greater body fat mass is already present before puberty
  • Only 5% of men with type 2 diabetes have elevated LH levels
  • inhibition of the gonadal axis predominantly takes place in the hypothalamus, especially with more severe obesity
  • Metabolic factors, such as leptin, insulin (via deficiency or resistance) and ghrelin are believed to act at the ventromedial and arcuate nuclei of the hypothalamus to inhibit gonadotropin-releasing hormone (GNRH) secretion from GNRH neurons situated in the preoptic area
  • kisspeptin has emerged as one of the most potent secretagogues of GNRH release
  • hypothesis that obesity-mediated inhibition of kisspeptin signalling contributes to the suppression of the HPT axis, infusion of a bioactive kisspeptin fragment has been recently shown to robustly increase LH pulsatility, LH levels and circulating testosterone in hypotestosteronaemic men with type 2 diabetes
  • A smaller study with a similar experimental design found that acute testosterone withdrawal reduced insulin sensitivity independent of body weight, whereas oestradiol withdrawal had no effects
  • suppression of the diabesity-associated HPT axis is functional, and may hence be reversible
  • Obesity and dysglycaemia and associated comorbidities such as obstructive sleep apnoea (Hoyos et al. 2012b) are important contributors to the suppression of the HPT axis
  • weight gain and development of diabetes accelerate the age-related decline in testosterone
  • Modifiable risk factors such as obesity and co-morbidities are more strongly associated with a decline in circulating testosterone levels than age alone
  • 55% of symptomatic androgen deficiency reverted to a normal testosterone or an asymptomatic state after 8-year follow-up, suggesting that androgen deficiency is not a stable state
  • Weight loss can reactivate the hypothalamic–pituitary–testicular axis
  • Leptin treatment resolves hypogonadism in leptin-deficient men
  • The hypothalamic–pituitary–testicular axis remains responsive to treatment with aromatase inhibitors or selective oestrogen receptor modulators in obese men
  • Kisspeptin treatment increases LH secretion, pulse frequency and circulating testosterone levels in hypotestosteronaemic men with type 2 diabetes
  • change in BMI was associated with the change in testosterone (Corona et al. 2013a,b).
  • weight loss can lead to genuine reactivation of the gonadal axis by reversal of obesity-associated hypothalamic suppression
  • There is pre-clinical and observational evidence that chronic hyperglycaemia can inhibit the HPT axis
  • in men who improved their glycaemic control over time, testosterone levels increased. By contrast, in those men in whom glycaemic control worsened, testosterone decreased
  • testosterone levels should be measured after successful weight loss to identify men with an insufficient rise in their testosterone levels. Such men may have HPT axis pathology unrelated to their obesity, which will require appropriate evaluation and management.
  •  
    Article discusses the expanding evidence of low T and Metabolic syndrome.
Nathan Goodyear

Testosterone Deficiency, Cardiac Health, and Older Men - 0 views

  • Studies have shown pharmacological doses of testosterone to relax coronary arteries when injected intraluminally [39] and to produce modest but consistent improvement in exercise-induced angina and reverse associated ECG changes [40]. The mechanism of action is via blockade of calcium channels with effect of similar magnitude to nifedipine
    • Nathan Goodyear
       
      This directly refutes the recent studies (3) that Testosterone therapy increases cardiovascular events.
    • Nathan Goodyear
       
      Testosterone acts as a calcium channel blocker inducing vasodilation.
  • men with chronic stable angina pectoris, the ischaemic threshold increased after 4 weeks of TRT and a recent study demonstrates improvement continuing beyond 12 months [
  • Exercise capacity in men with chronic heart failure increased after 12 weeks
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  • Studies have shown an inverse relationship between serum testosterone and fasting blood glucose and insulin levels
  • Medications such as chronic analgesics, anticonvulsants, 5ARIs, and androgen ablation therapy are associated with increased risk of testosterone deficiency and insulin resistance
  • Women with T2D or metabolic syndrome characteristically have low SHBG and high free testosterone
    • Nathan Goodyear
       
      This stands in polar opposite of that with men.
  • Hypogonadism is a common feature of the metabolic syndrome
  • The precise interaction between insulin resistance, visceral adiposity, and hypogonadism is, as yet, unclear but the important mechanisms are through increased aromatase production, raised leptin levels, and increase in inflammatory kinins
  • levels of testosterone are reduced in proportion to degree of obesity
  • Men should be encouraged to combine aerobic exercise with strength training. As muscle increases, glucose will be burned more efficiently and insulin levels will fall. A minimum of 30 minutes exercise three times weekly should be advised
  • Testosterone increases levels of fast-twitch muscle fibres
  • By increasing testosterone, levels of type 2 fibres increase and glucose burning improves
  • Weight loss will increase levels of testosterone
  • studies now clearly show that low testosterone leads to visceral obesity and metabolic syndrome and is also a consequence of obesity
  • In the case of MMAS [43], a baseline total testosterone of less than 10.4 nmol/L was associated with a greater than 4-fold incidence of type 2 diabetes over the next 9 years
  • There is high level evidence that TRT improves insulin resistance
  • Low testosterone predicts increased mortality and testosterone therapy improves survival in 587 men with type 2 diabetes
  • A similar retrospective US study involved 1031 men with 372 on TRT. The cumulative mortality was 21% in the untreated group versus 10% ( ) in the treated group with the greatest effect in younger men and those with type 2 diabetes
  • the presence of ED has been shown to be an independent risk factor, particularly in hypogonadal men, increasing the risk of cardiac events by over 50%
  • A recent online publication on ischaemic heart disease mortality in men concluded optimal androgen levels are a biomarker for survival
  • inverse associations between low TT or FT (Table 2) and the severity of CAD
  • A recent 10 year study from Western Australia involving 3690 men followed up from 2001–2010 concluded that TT and FT levels in the normal range were associated with decreased all-cause and cardiovascular mortality, for the first time suggesting that both low and DHT are associated with all-cause mortality and higher levels of DHT reduced cardiovascular risk
  • TDS is associated with increased cardiovascular and all-cause mortality
  • The effect of treatment with TRT reduced the mortality rate of treated cohort (8.4%) to that of the eugonadal group whereas the mortality for the untreated remained high at 19.2%
  • hypogonadal men had slightly increased triglycerides and HDL
  • Men with angiographically proven CAD (coronary artery disease) have significantly lower testosterone levels [29] compared to controls ( ) and there was a significant inverse relationship between the degree of CAD and TT (total testosterone) levels
  • TRT has also been shown to reduce fibrinogen to levels similar to fibrates
  • men treated with long acting testosterone showed highly significant reductions in TC, LDL, and triglycerides with increase in HDL, associated with significant reduction in weight, BMI, and visceral fat
  • Low androgen levels are associated with an increase in inflammatory markers
  • In the Moscow study, C-reactive protein was reduced by TRT at 30 weeks versus placebo
  • In some studies, a decline in diastolic blood pressure has been observed, after 3–9 months [24, 26] and in systolic blood pressure
  • A decline was noted in IL6 and TNF-alpha
  • No studies to date show an increase in LUTS/BPH symptoms with higher serum testosterone levels
  • TRT has been shown to upregulate PDE5 [65] and enhance the effect of PDE5Is (now an accepted therapy for both ED and LUTS), it no longer seems logical to advice avoidance of TRT in men with mild to moderate BPH.
    • Nathan Goodyear
       
      What about just starting with normalization of Testosterone levels first.
  • Several meta-analyses have failed to show a link between TRT and development of prostate cancer [66] but some studies have shown a tendency for more aggressive prostate cancer in men with low testosterone
    • Nathan Goodyear
       
      And if one would have looked at their estrogen levels, I guarantee they would have been found to be elevated.
  • low bioavailable testosterone and high SHBG were associated with a 4.9- and 3.2-fold risk of positive biopsy
  • Current EAU, ISSAM, and BSSM guidance [1, 2] is that there is “no evidence TRT is associated with increased risk of prostate cancer or activation of subclinical cancer.”
  • Men with prostate cancer, treated with androgen deprivation, develop an increase of fat mass with an altered lipid profile
  • Erectile dysfunction is an established marker for future cardiovascular risk and the major presenting symptom leading to a diagnosis of low testosterone
Nathan Goodyear

Testosterone deficiency syndrome and cardiovascular health: An assessment of beliefs, k... - 0 views

  • The vast majority (88%) did not screen cardiac patients for TDS.
  • Testosterone deficiency has a prevalence of 7% in the general population, rising to 20% in elderly males
  • Males with CAD have lower testosterone levels than those with normal coronary angiograms of the same age,5 suggesting that the prevalence of testosterone deficiency is much higher in the CAD population
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  • Men with hypertension, another established risk factor for CAD, have lower testosterone compared to normotensive men
  • Recent meta-analyses showed that testosterone levels are generally lower among patients with metabolic syndrome, regardless of the various definitions of metabolic syndrome that are used
  • Testosterone (total and bioavailable) and sex-hormone binding globulin (SHBG) are inversely associated with the prevalence of metabolic syndrome in men between the ages of 40 and 80, and this association persists across racial and ethnic backgrounds
  • ower levels of testosterone and SHBG predict a higher incidence of metabolic syndrome.
  • Low testosterone levels have been related to increased insulin resistance and cardiovascular mortality,12 even in the absence of overt type 2 diabetes mellitus.
  • testosterone levels (total and bioavailable) in middle-aged men are inversely correlated with insulin resistance
  • The Massachusetts Male Aging Study (MMAS) demonstrated that low levels of testosterone and SHBG are independent risk factors for the development of type 2 diabetes,
  • Andropausal men (age 58 ± 7 years) have a higher maximal carotid artery intima-media thickness
  • There is an inverse linear correlation between body mass index (BMI) and wait-to-hip ratio with testosterone and insulin-like growth factor-1 levels.
  • Testosterone supplementation for 1 year in hypogonadal men has been shown to cause a significant improvement in body weight, BMI, waist size, lipid profile, and C-reactive protein levels
  • TRT for 3 months in hypogonadal men with type 2 diabetes significantly improved fasting insulin sensitivity, fasting blood glucose and glycated hemoglobin.
  • Testosterone replacement can improve angina symptoms and delay the onset of cardiac ischemia, likely through a coronary vasodilator mechanism
  • ADT is associated with an increased risk of cardiovascular events, including myocardial infarction and cardiovascular mortality.
  • ADT significantly increases fat mass, decreases lean body mass,29,30 increases fasting plasma insulin and decreases insulin sensitivity31 and increases serum cholesterol and triglyceride levels
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    Startling study on the knowledge of Testosterone and cardiovascular disease in general practitioners and cardiologists in Canada.  Eight-eight percent did not screen patients with cardiovascular disease for low Testosterone.  A whopping 67% of physicians did not know that low T was a risk factor for cardiovascular disease, yet 62% believed Testosterone would increase exercise tolerance. The lack of knowledge displayed by physicians today is staggering and is an indictment of the governing bodies.  This was a survey conducted in Canada so there are obvious limitations to the strength/conclusion of this study.
Nathan Goodyear

PLOS ONE: Probiotic Microbes Sustain Youthful Serum Testosterone Levels and Testicular ... - 0 views

  • Studies in both humans and rodents, however, suggest that low testosterone is due to age-related lesions in testes rather than irregular luteinizing hormone metabolism
  • Various dietary factors and diet-induced obesity have been shown to increase the risk for late onset male hypogonadism and low testosterone production in both humans and mice
  • Testosterone deficiency and metabolic diseases such as obesity appear to inter-digitate in complex cause-and-effect relationships
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  • dietary supplementation of aged mice with the probiotic bacterium Lactobacillus reuteri makes them appear to be younger than their matched untreated sibling mice
  • These results indicate that gut microbiota induce modulation of local gastrointestinal immunity resulting in systemic effects on the immune system which activate metabolic pathways that restore tissue homeostasis and overall health
  • all these studies we consistently observed that young and aged mice consuming purified L. reuteri organisms had particularly large testes and a dominant male behavior.
  • The testes of probiotic-fed aged mice were rescued from both seminiferous tubule atrophy and interstitial Leydig cell area reduction typical of the normal aging process. Preservation of testicular architecture despite advanced age or high-fat diet coincided with remarkably high levels of circulating testosterone. The beneficial effects of probiotic consumption were recapitulated by the depletion of the pro-inflammatory cytokine Il-17.
  • feeding of L. reuteri consistently increased the gonadal weights, consumption of a non-pathogenic strain of Escherichia coli (E. coli) K12 organisms did not affect testicular weight
  • mice with dietary L. reuteri supplements were rescued from diet-induced obesity and had normal body weight and lean physique
  • Despite the comparable numbers of ST profiles, we determined that testes from L. reuteri-treated mice had increased ST cross-sectioned profiles
  • the probiotic organism induced prominent Leydig cell accumulations in the interstitial tissue between the ST's
  • The probiotic-associated increase of interstitial Leydig cell areas was sustained with advancing age at 7 (CD vs CD+LR, P = 0.0025; CD+E.coli vs CD+LR, P = 0.0251) and 12 months
  • mice eating L. reuteri had profoundly increased levels of circulating testosterone regardless of the type of diet they consumed
  • blocking pro-inflammatory Il-17 signaling entirely recapitulates the beneficial effects of probiotics
  • previous studies we found that dietary probiotics counteract obesity [19] and age-related integumentary pathology [18] at least in part by down-regulating systemic pro-inflammatory IL-17A-dependent signaling
  • Testes histomorphometry and serum androgen concentration data were both suggestive of a probiotic-associated up-regulation of spermatogenesis in mice
  • Lactobacillus reuteri we discovered that aging male animals had larger testes compared to their age-matched controls
  • xamined testes of probiotic microbe-fed mice and found that they had less testicular atrophy coinciding with higher levels of circulating testosterone compared to their age-matched controls
  • Similar testicular health benefits were produced using systemic depletion of the pro-inflammatory cytokine Il-17 alone, implicating a chronic inflammatory pathway in hypogonadism
  • One specific aspect of this paradigm is reciprocal activities of pro-inflammatory Th-17 and anti-inflammatory Treg cells
  • Feeding of L. reuteri organisms was previously shown to up-regulate IL-10 levels and reduce levels of IL-17 [19] serving to lower systemic inflammation
  • insufficient levels of IL-10 may increase the risk for autoimmunity, obesity, and other inflammatory disease syndromes
  • Westernized diets are also low in vitamin D, a nutrient that when present normally works together with IL-10 to protect against inflammatory disorders
  • Physiological feedback loops apparently exist between microbes, host hormones, and immunity
  • The hormone testosterone has been shown to act directly through androgen receptors on CD4+ cells to increase IL-10 expression
  • studies in both humans and rodents suggest that hypogonadism is due to age-related lesions in testes rather than irregular LH metabolism
  • We postulate that probiotic gut microbes function symbiotically with their mammalian hosts to impart immune homeostasis to maintain systemic and testicular health [34]–[35] despite suboptimal dietary conditions.
  • Dietary factors and diet-induced obesity were previously shown to increase risk for age-associated male hypogonadism, reduced spermatogenesis, and low testosterone production in both humans and mice [2]–[4], [8]–[11], [14]–[17], phenotypic features that in this study were inhibited by oral probiotic therapy absent milk sugars, extra protein, or vitamin D supplied in yogurt.
  • Similar beneficial effects of probiotic microbes on testosterone levels and sperm indices were reported in male mice that had been simultaneously supplemented with selenium
  • L. reuteri-associated prevention of age- and diet-related testicular atrophy correlates with increased numbers and size of Leydig cells
  • the initial changes of testicular atrophy begin to occur in mice from the age of 6 moths onwards [7] and indicates that the trophic effect of L. reuteri on Leydig cells is a key event which precedes and prevents age-related changes in the testes of mice. This effect is reminiscent of earlier studies describing Leydig cell hyperplasia and/or hypertrophy in the mouse and the rat testis that were achievable by the administration of gonadotropins, including human chorionic gonadotropin, FSH and LH
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    Fascinating study on how the addition of Lactobacillus reuteri increased Testicular size, prevented testicular atrophy, increased serum Testosterone production and protected against diet-induced/obesity-induced hypogonadism.  This was a mouse model
Nathan Goodyear

Redefining Metabolic Syndrome in Men (July 2012) Townsend Letter for Doctors & Patients - 0 views

  • Approximately 95% to 98% of testosterone is bound to a carrier protein at any given time, leaving just the remaining 2% to 5% as completely unbound and available for tissues to use
  • most serum laboratories offer a free testosterone level, which is a calculated value based on SHBG levels or determined with equilibrium dialysis
  • the hormone enters the salivary gland by passive diffusion
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  • Testosterone has a known age-related decline, and total levels typically drop by approximately 1.6% per year beginning for most men in their 30s
  • As estrogen levels rise, they prompt the body to produce more SHBG, which in turn has a higher binding affinity for testosterone, and drives the unbound fraction of the testosterone pool down even further
  • When the increase in SHBG is taken into account, the age-related decline in the level of hormone that can be used by the body is closer to 2% to 3% per year.
  • Stinging nettle (Urtica dioica), an herb commonly used for allergies, can also be employed to bind to SHBG, which leaves more testosterone available to tissues
  • Leptin, an adipose-derived peptide hormone that regulates appetite and metabolism, has been shown to directly inhibit testosterone production in animal models
  • tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) further inhibit Leydig cell testosterone production
  • Natural aromatase inhibitors include the bioflavonoids chrysin and luteolin
  • Zinc deficiency causes an upregulation of the aromatase enzyme
  • Testosterone reduces lipoprotein lipase (LPL) activity
  • there are several herbs that can work to boost testosterone levels, including longjack (Eurycoma longifolia), horny goat weed (Epimedium grandiflorum), and tribulus (Tribulus terrestris).
  • the majority of the hormone is bound to carrier proteins including sex hormone binding globulin (SHBG) and albumin
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    nice and short review on testosterone and men's  health.
Nathan Goodyear

Effect of Testosterone Replacement Therapy on Cognitive Performance and Depression in M... - 0 views

  • Azad et al [15] used single photon emission computed tomography and showed that, after 3~5 weeks of TRT, cerebral perfusion was increased in the midbrain and the superior frontal gyrus in seven men with hypogonadism
  • After 12~14 weeks, increased perfusion was still observed in the midbrain as well as in the midcingulate gyrus
  • TDS patients who received TRT showed significant improvement in cognitive function only if mild cognitive impairment was present at baseline
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  • Cherrier et al [17] evaluated a sample of 32 subjects, which included 17 men with mild cognitive impairment and 15 with Alzheimer's disease. At the 6-week follow-up, patients who received TRT showed significantly better scores regarding spatial memory, constructional abilities, and verbal memory compared to those noted in the placebo group. Taken together, these results suggest that TRT has a beneficial effect on cognitive function
  • TRT improved mood and well-being, and reduced fatigue and irritability in hypogonadal men
  • The study by Pope et al [20] involved men with depression refractory to standard anti-depressants, and found that TRT lowered the Hamilton Depression score,
  • depression tends to increase as testosterone levels decrease [21], it is highly likely that TRT improved symptoms of depression by increasing testosterone levels.
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    men with Testosterone <300 ng/dl with levels after 8 months of therapy achieving +680 ng/dl.
Nathan Goodyear

Testosterone Deficiency, Cardiac Health, and Older Men - 0 views

  • 2.1 standard deviations in total testosterone was associated with a 25% increase in mortality
  • Erectile dysfunction is an established marker for future cardiovascular risk and the major presenting symptom leading to a diagnosis of low testosterone
  • There is a considerable body of evidence that low testosterone is associated with increased cardiovascular and cancer mortality
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  • There is considerable evidence of modest cardiac and metabolic benefits that are shown to reduce cardiovascular risk plus sexual, mood, and quality of life changes associated with restoring testosterone levels
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    low Testosterone is associated with increased mortality in men and Testosterone therapy in men with low T is associated with a reduction in mortality in men.
Nathan Goodyear

Testosterone Replacement Alone for Testosterone Deficiency Syndrome Improves Moderate L... - 0 views

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    Study finds that Testosterone therapy reduces LUTS in men with low T.  The definition of low T is a little wide in this study.  Another study that contradicts the belief that Testosterone contributes to LUTS through the prostate.
Nathan Goodyear

Testosterone Therapy in Men with Androgen Deficiency Syndromes: An Endocrine Society Cl... - 0 views

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    androgen deficiency and guidelines for Testosterone therapy.  Nice review of statistics and symptoms.  Many symptoms of low T go unrecognized.
Nathan Goodyear

Access : Testosterone deficiency, insulin resistance and the metabolic syndrome : Natur... - 1 views

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    testosterone replacement in those with low T shown to improve insulin sensitivity, diabetes control, and metabolic syndrome in men.
Nathan Goodyear

The Dark Side of Testosterone Deficiency: II. Type 2 Diabetes and Insulin Resistance - ... - 0 views

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    low Testosterone linked to insulin resistance, type II Diabetes, and increased  metabolic syndrome.  Low T is linked to increased visceral fat in this study.  
Nathan Goodyear

PLOS ONE: Prediabetes Is Associated with an Increased Risk of Testosterone Deficiency, ... - 0 views

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    This study found that low T was clearly associated with "pre diabetes" independent of weight and MetS.  All men that are overweight, obese, with metabolic syndrome, "pre diabetic" need evaluation of hormones, not just Testosterone.
Nathan Goodyear

Testosterone as Potential Effective Therapy in Treatment of Obesity in Men with Testost... - 0 views

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    Testosterone therapy in men with low T will improve lean body mass, some reduction in abdominal obesity, yet little effect in visceral obesity.
Nathan Goodyear

The Dark Side of Testosterone Deficiency: II. Type 2 Diabetes and Insulin Resistance --... - 1 views

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    low Testosterone associated with insulin resistance, type II diabetes, metabolic syndrome, and increased fat.  These will all translate to increased mortality.
Nathan Goodyear

Perspectives for metabolomics in testosterone replacement therapy - 0 views

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    androgen deficiency syndrome and metabolomics
Nathan Goodyear

The Dark Side of Testosterone Deficiency: I. Metabolic Syndrome and Erectile Dysfunctio... - 0 views

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    Article reviews the link between obesity, low T, metabolic syndrome and ED.  ED has been shown to be predictive of CVD by 3-5 years.  
Nathan Goodyear

Marked Testosterone Deficiency-Related Symptoms Ma... [J Sex Med. 2014] - PubMed - NCBI - 0 views

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    The more severe the symptoms, the more the increased risk of CVD in men with low T.
Nathan Goodyear

Low Sex Hormone-Binding Globulin, Total Testosterone, and Symptomatic Androgen Deficien... - 0 views

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    Low Total Testosterone, low SHBG, and symptoms of low T are associated with an increase risk (relative) of Mets, especially in normal weight men.
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