the effect of exercise on DNA methylation in human skeletal muscle and provide evidence that acute exercise alters promoter methylation of exercise-responsive genes in a dose-dependent manner
DNA methylation was unaltered 48 hr after a 3-week exercise training program, whereas RNA expression of PGC-1α and TFAM promoters was elevated (data not shown), further suggesting that DNA hypomethylation is a transient mechanism involved in mRNA synthesis
Our findings that ionomycin, AICAR, or ROS production increased mRNA expression without altering promoter methylation may support the notion that DNA methylation does not exclusively control exercise-induced gene expression
acute exercise leads to transient changes in DNA methylation in adult skeletal muscle
Small study finds acute exercise is associated with epigenetic alteration of muscle through methylation. This study found a hypomethylation of the genes PGC-1alpha, PDK4, and PPAR-delta with a respondent increase in expression. The methylation activity was in the promoter region of these genes.
In a cohort of well-trained athletes, we demonstrated that intense endurance exercise causes an acute reduction in RV function that increases with race duration and correlates with increases in biomarkers of myocardial injury
no relationship between LV function and biomarker levels
focal gadolinium enhancement and increased RV remodelling were more prevalent in those athletes with a longer history of competitive sport, suggesting that repetitive ultra-endurance exercise may lead to more extensive RV change and possible myocardial fibrosis
he cardiac impact of both acute and cumulative exercise is greatest on the RV.
Greater reductions in RV function occurred in those athletes competing for a longer duration, suggesting that the heart has a finite capacity to maintain the increased work demands of exercise
cardiac injury is greatest in the least trained
Previous investigators have documented reductions in RV function in less trained subjects over the marathon distance
We enrolled elite and subelite athletes and found a significant association between fitness (VO2max) and the reduction in post-race RVEF
Even after many years of detraining, cardiac dilation may not completely regress in elite athletes
The focus on well-trained athletes may be of particular relevance, given that they perform exercise of highest intensity and duration most frequently, and, thus, may be at a greater risk of cumulative injury.
The lack of correlation between increases in troponin and changes in LV function seen in this study has been previously interpreted as evidence that post-exercise elevations in cardiac biomarkers are benign.
a significant correlation between changes in RVEF and post-race biomarker levels and this relationship was even stronger in the athletes who completed the race of longest duration, the ultra-triathlon
The correlations with RVEF, but not LVEF, provide further evidence of the differential effects of intense exercise on RV and LV function
BNP release during intense exercise is associated with greater relative increases in RV systolic pressures, but not LV pressures
BNP may provide a measure of both acute RV load and the resultant fatigue which occurs when this load is sustained
It has been demonstrated that ventricular load increases with exercise intensity and is greater for the RV than the LV,29 thus potentially explaining why the RV is more susceptible to fatigue after prolonged exercise.
This study demonstrates, for the first time, an association between endurance exercise of increasing duration and structural, functional, and biochemical markers of cardiac dysfunction in highly trained athletes
Functional abnormalities were confined to the RV and were largely reversible 1 week following the event
there remained a significant minority of athletes in whom there was evidence of myocardial fibrosis in the interventricular septum
RV abnormalities may be acquired through cumulative bouts of intense exercise and provides direction for prospective investigations aimed at elucidating whether extreme exercise may promote arrhythmias in some athletes.
the acute injury and chronic remodelling of the myocardium both disproportionately affect the RV and it remains possible that the two are linked.
focal DGE was confined to the interventricular septum and commonly at the site of RV attachment
emerging evidence that intense endurance exercise may be associated with an excess in arrhythmic disorders, the mechanisms for which remain unexplained
RVEF (and not LVEF) was reduced in athletes with complex ventricular arrhythmias when compared with healthy athletes and non-athletes without arrhythmias
it is premature to conclude that these changes may represent a proarrhythmic substrate
Study finds endurance racing results in reduce Right ventricle ejection fraction even in elite athletes. This post-race RVEF reduction is associated with VO2max.
low vitamin D associated with poor outcomes in hematologic cancers. This chapter reviews several studies that highlight the link with low vitamin D and poor outcomes in AML patients.
Testosterone has beneficial
effects on several cardiovascular risk factors, which include cholesterol, endothelial dysfunction and inflammation
In clinical studies, acute and chronic testosterone administration increases coronary artery diameter and flow, improves
cardiac ischaemia and symptoms in men with chronic stable angina and reduces peripheral vascular resistance in chronic heart
failure.
testosterone is an L-calcium channel blocker and induces potassium
channel activation in vascular smooth muscle cells
Animal studies have consistently demonstrated that testosterone is atheroprotective,
whereas testosterone deficiency promotes the early stages of atherogenesis
there is no compelling evidence that testosterone replacement to levels within the normal healthy range contributes
adversely to the pathogenesis of CVD (Carson & Rosano 2011) or prostate cancer (Morgentaler & Schulman 2009)
bidirectional effect between decreased testosterone
concentrations and disease pathology exists as concomitant cardiovascular risk factors (including inflammation, obesity and
insulin resistance) are known to reduce testosterone levels and that testosterone confers beneficial effects on these cardiovascular
risk factors
Achieving a normal physiological testosterone concentration through the administration
of testosterone replacement therapy (TRT) has been shown to improve risk factors for atherosclerosis including reducing central
adiposity and insulin resistance and improving lipid profiles (in particular, lowering cholesterol), clotting and inflammatory
profiles and vascular function
It is well known that impaired erectile function and CVD are closely
related in that ED can be the first clinical manifestation of atherosclerosis often preceding a cardiovascular event by 3–5
years
no decrease in the response (i.e. no tachyphylaxis) of testosterone and that patient benefit persists in the long term.
free testosterone
levels within the physiological range, has been shown to result in a marked increase in both flow- and nitroglycerin-mediated
brachial artery vasodilation in men with CAD
Clinical studies, however, have revealed either small reductions of 2–3 mm in diastolic pressure or no significant effects
when testosterone is replaced within normal physiological limits in humans
Endothelium-independent mechanisms of testosterone
are considered to occur primarily via the inhibition of voltage-operated Ca2+ channels (VOCCs) and/or activation of K+ channels (KCs) on smooth muscle cells (SMCs)
Testosterone shares the same molecular binding site as nifedipine
Testosterone increases the expression of endothelial nitric oxide synthase (eNOS)
and enhances nitric oxide (NO) production
Testosterone also inhibited
the Ca2+ influx response to PGF2α
one of the major actions of testosterone is on NO and its signalling pathways
In addition to direct effects on NOS expression, testosterone may also affect phosphodiesterase type 5 (PDE5 (PDE5A)) gene expression, an enzyme controlling the degradation of cGMP, which acts as a vasodilatory second messenger
the significance of the action of testosterone on VSMC apoptosis and proliferation in atherosclerosis is difficult
to delineate and may be dependent upon the stage of plaque development
Several human studies have shown that carotid IMT (CIMT) and aortic calcification negatively correlate
with serum testosterone
t long-term testosterone treatment reduced CIMT in men with low testosterone levels
and angina
neither intracellular nor membrane-associated
ARs are required for the rapid vasodilator effect
acute responses appear to be AR independent, long-term AR-mediated effects on the vasculature have also been described,
primarily in the context of vascular tone regulation via the modulation of gene transcription
Testosterone and DHT increased the expression of eNOS in HUVECs
oestrogens have been shown to activate eNOS and stimulate NO production in an ERα-dependent manner
Several studies, however, have demonstrated that the vasodilatory actions of testosterone are not reduced by aromatase
inhibition
non-aromatisable DHT elicited similar vasodilation to testosterone treatment in arterial smooth muscle
increased endothelial NOS (eNOS) expression and phosphorylation were observed in testosterone- and DHT-treated
human umbilical vein endothelial cells
Androgen deprivation leads to a reduction in neuronal NOS expression associated with a decrease of intracavernosal pressure
in penile arteries during erection, an effect that is promptly reversed by androgen replacement therapy
Observational evidence suggests that several pro-inflammatory cytokines (including interleukin 1β (IL1β), IL6, tumour necrosis
factor α (TNFα), and highly sensitive CRP) and serum testosterone levels are inversely associated in patients with CAD, T2DM
and/or hypogonadism
patients with the
highest IL1β concentrations had lower endogenous testosterone levels
TRT has been reported to significantly
reduce TNFα and elevate the circulating anti-inflammatory IL10 in hypogonadal men with CVD
testosterone treatment to normalise levels in hypogonadal men with the MetS
resulted in a significant reduction in the circulating CRP, IL1β and TNFα, with a trend towards lower IL6 compared with placebo
parenteral testosterone undecanoate, CRP decreased significantly in hypogonadal elderly
men
Higher levels of serum adiponectin have been shown to lower cardiovascular risk
Research suggests that the expression of VCAM-1, as induced by pro-inflammatory cytokines such as TNFα or interferon γ (IFNγ
(IFNG)) in endothelial cells, can be attenuated by treatment with testosterone
Testosterone also inhibits the production of pro-inflammatory cytokines such as IL6, IL1β and TNFα in a range of cell types
including human endothelial cells
decreased inflammatory response to TNFα and lipopolysaccharide (LPS) in
human endothelial cells when treated with DHT
The key to unravelling the link between testosterone
and its role in atherosclerosis may lay in the understanding of testosterone signalling and the cross-talk between receptors
and intracellular events that result in pro- and/or anti-inflammatory actions in athero-sensitive cells.
testosterone
functions through the AR to modulate adhesion molecule expression
pre-treatment with DHT reduced the cytokine-stimulated inflammatory response
DHT inhibited NFκB activation
DHT could inhibit an LPS-induced upregulation of MCP1
Both NFκB and
AR act at the transcriptional level and have been experimentally found to be antagonistic to each other
As the AR and NFκB are mutual antagonists, their interaction and influence on functions can be bidirectional, with inflammatory
agents that activate NFκB interfering with normal androgen signalling as well as the AR interrupting NFκB inflammatory transcription
prolonged exposure of vascular cells to the inflammatory activation of NFκB associated with atherosclerosis
may reduce or alter any potentially protective effects of testosterone
DHT and IFNγ also modulate each other's signalling through interaction at the transcriptional
level, suggesting that androgens down-regulate IFN-induced genes
(Simoncini et al. 2000a,b). Norata et al. (2010) suggest that part of the testosterone-mediated atheroprotective effects could depend on ER activation mediated by the testosterone/DHT
3β-derivative, 3β-Adiol
TNFα-induced induction of ICAM-1, VCAM-1 and E-selectin as well as MCP1 and IL6 was significantly
reduced by a pre-incubation with 3β-Adiol in HUVECs
3β-Adiol also reduced LPS-induced gene expression
of IL6, TNFα, cyclooxygenase 2 (COX2 (PTGS2)), CD40, CX3CR1, plasminogen activator inhibitor-1, MMP9, resistin, pentraxin-3 and MCP1 in the monocytic cell line U937 (Norata et al. 2010)
This study suggests that testosterone metabolites, other than those generated through aromatisation, could exert anti-inflammatory
effects that are mediated by ER activation.
The authors suggest that DHT differentially
effects COX2 levels under physiological and pathophysiological conditions in human coronary artery smooth muscle cells and
via AR-dependent and -independent mechanisms influenced by the physiological state of the cell
There are, however, a number of systematic meta-analyses of clinical trials of TRT that have not demonstrated
an increased risk of adverse cardiovascular events or mortality
The TOM trial, which was designed to investigate the effect of TRT on frailty in elderly men, was terminated prematurely
as a result of an increased incidence of cardiovascular-related events after 6 months in the treatment arm
trials of TRT in men with either chronic stable angina or chronic cardiac failure have also found no increase
in either cardiovascular events or mortality in studies up to 12 months
Evidence may therefore suggest that low testosterone levels and testosterone levels above the normal range have an adverse
effect on CVD, whereas testosterone levels titrated to within the mid- to upper-normal range have at least a neutral effect
or, taking into account the knowledge of the beneficial effects of testosterone on a series of cardiovascular risk factors,
there may possibly be a cardioprotective action
The effect of testosterone on human vascular function is a complex issue and may be dependent upon the underlying androgen
and/or disease status.
the majority of studies suggest that testosterone may display both acute and
chronic vasodilatory effects upon various vascular beds at both physiological and supraphysiological concentrations and via
endothelium-dependent and -independent mechanisms
A Sore Throat is a painful feeling in the throat aggravated by swallowing. A sore throat can also feel dry and scratchy and makes it hard to talk. A sore throat is a frequent symptom of the common cold or other acute respiratory tract ...
A Sore Throat is a painful feeling in the throat aggravated by swallowing. A sore throat can also feel dry and scratchy and makes it hard to talk. A sore throat is a frequent symptom of the common cold or other acute respiratory tract ...
Thyroid hormone plays significant role in cardiac remodeling after acute myocardial infarction. Thyroid hormone, particularly T3 as the vast majority of T3 is produced in heart tissue via D1 enzymatic activity, improves cardiac contractility, reduces systemic vascular resistance, reduces cardiac work load, decreases blood pressure, improves cardiac metabolism, and thus improves outcomes post MI.
National Athletic Trainers’ Association recommends that athletes prone to muscle cramping add 0.3 to 0.7 g/L of salt to their drinks to stave off muscle cramps
Others have recommended adding higher amounts of sodium (about 3.0 to 6.0 g/L) to sports drinks based on the frequency of EAMC
intravenous infusion of fluids removes this delay, and it has been used to aid athletes who develop acute EAMC
maintaining hydration and adequate electrolyte levels is a good prevention strategy for individuals susceptible to EAMC
Fluid volumes of 1.8 L per hour have been well tolerated by tennis athletes who are susceptible to EAMC
Monitoring an athlete’s body weight is an easy method of ensuring adequate fluid replacement and individualizes each athlete’s fluid needs
the National Athletic Trainers’ Association and the American College of Sports Medicine recommend a volume of fluid that allows for less than a 2% body weight reduction
Endurance training may also serve as an effective means of preventing EAMC by expanding plasma volume and the extracellular fluid compartment15 and delaying neuromuscular fatigue
Exercise associated muscle cramps or EAMC is not worked out. The theories include dehydration, mineral/electrolyte deficiencies, and neuromuscular activity.
Long-chain polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are highly enriched in neuronal synaptosomal plasma membranes and vesicles
The predominant CNS polyunsaturated fatty acid is DHA
effective supplementation and/or increased ingestion of dietary sources rich in EPA and DHA, such as cold-water fish species and fish oil, may help improve a multitude of neuronal functions, including long-term potentiation and cognition.
multiple preclinical studies have suggested that DHA and/or EPA supplementation may have potential benefit through a multitude of diverse, but complementary mechanisms
pre-injury dietary supplementation with fish oil effectively reduces post-traumatic elevations in protein oxidation
The benefits of pre-traumatic DHA supplementation have not only been independently confirmed,[150] but DHA supplementation has been shown to significantly reduce the number of swollen, disconnected and injured axons when administered following traumatic brain injury.
DHA has provided neuroprotection in experimental models of both focal and diffuse traumatic brain injury
potential mechanisms of neuroprotection, in addition to DHA and EPA's well-established anti-oxidant and anti-inflammatory properties
Despite abundant laboratory evidence supporting its neuroprotective effects in experimental models, the role of dietary DHA and/or EPA supplementation in human neurological diseases remains uncertain
Several population-based, observational studies have suggested that increased dietary fish and/or omega-3 polyunsaturated fatty acid consumption may reduce risk for ischemic stroke in several populations
Randomized control trials have also demonstrated significant reductions in ischemic stroke recurrence,[217] relative risk for ischemic stroke,[2] and reduced incidence of both symptomatic vasospasm and mortality following subarachnoid hemorrhage
Clinical trials in Alzheimer's disease have also been largely ineffective
The clinical evidence thus far appears equivocal
curcumin has gained much attention from Western researchers for its potential therapeutic benefits in large part due to its potent anti-oxidant[128,194,236] and anti-inflammatory properties
Curcumin is highly lipophilic and crosses the blood-brain barrier enabling it to exert a multitude of different established neuroprotective effects
in the context of TBI, a series of preclinical studies have suggested that pre-traumatic and post-traumatic curcumin supplementation may bolster the brain's resilience to injury and serve as a valuable therapeutic option
Curcumin may confer significant neuroprotection because of its ability to act on multiple deleterious post-traumatic, molecular cascades
studies demonstrated that both pre- and post-traumatic curcumin administration resulted in a significant reduction of neuroinflammation via inhibition of the pro-inflammatory molecules interleukin 1β and nuclear factor kappa B (NFκB)
no human studies have been conducted with respect to the effects of curcumin administration on the treatment of TBI, subarachnoid or intracranial hemorrhage, epilepsy or stroke
studies have demonstrated that resveratrol treatment reduces brain edema and lesion volume, as well as improves neurobehavioral functional performance following TBI
green tea consumption or supplementation with its derivatives may bolster cognitive function acutely and may slow cognitive decline
At least one population based study, though, did demonstrate that increased green tea consumption was associated with a reduced risk for Parkinson's disease independent of total caffeine intake
a randomized, placebo-controlled trial demonstrated that administration of green tea extract and L-theanine, over 16 weeks of treatment, improved indices of memory and brain theta wave activity on electroencephalography, suggesting greater cognitive alertness
Other animal studies have also demonstrated that theanine, another important component of green tea extract, exerts a multitude of neuroprotective benefits in experimental models of ischemic stroke,[63,97] Alzheimer's disease,[109] and Parkinson's disease
Theanine, like EGCG, contains multiple mechanisms of neuroprotective action including protection from excitotoxic injury[97] and inhibition of inflammation
potent anti-oxidant EGCG which is capable of crossing the blood-nerve and blood-brain barrier,
Epigallocatechin-3-gallate also displays neuroprotective properties
More recent research has suggested that vitamin D supplementation and the prevention of vitamin D deficiency may serve valuable roles in the treatment of TBI and may represents an important and necessary neuroprotective adjuvant for post-TBI progesterone therapy
Progesterone is one of the few agents to demonstrate significant reductions in mortality following TBI in human patients in preliminary trials
in vitro and in vivo studies have suggested that vitamin D supplementation with progesterone administration may significantly enhance neuroprotection
Vitamin D deficiency may increase inflammatory damage and behavioral impairment following experimental injury and attenuate the protective effects of post-traumatic progesterone treatment.[37]
emerging evidence has suggested that daily intravenous administration of vitamin E following TBI significantly decreases mortality and improves patient outcomes
high dose vitamin C administration following injury stabilized or reduced peri-lesional edema and infarction in the majority of patients receiving post-injury treatment
it has been speculated that combined vitamin C and E therapy may potentiate CNS anti-oxidation and act synergistically with regards to neuroprotection
one prospective human study has found that combined intake of vitamin C and E displays significant treatment interaction and reduces the risk of stroke
Pycnogenol has demonstrated the ability to slow or reduce the pathological processes associated with Alzheimer's disease
Pcynogenol administration, in a clinical study of elderly patients, led to improved cognition and reductions in markers of lipid peroxidase
One other point of consideration is that in neurodegenerative disease states like Alzheimer's disease and Parkinson's disease, where there are high levels of reactive oxygen species generation, vitamin E can tend to become oxidized itself. For maximal effectiveness and to maintain its anti-oxidant capacity, vitamin E must be given in conjunction with other anti-oxidants like vitamin C or flavonoids
These various factors might account for the null effects of alpha-tocopherol supplementation in patients with MCI and Alzheimer's disease
preliminary results obtained in a pediatric population have suggested that post-traumatic oral creatine administration (0.4 g/kg) given within four hours of traumatic brain injury and then daily thereafter, may improve both acute and long-term outcomes
Acutely, post-traumatic creatine administration seemed to reduce duration of post-traumatic amnesia, length of time spent in the intensive care unit, and duration of intubation
At three and six months post-injury, subjects in the creatine treatment group demonstrated improvement on indices of self care, communication abilities, locomotion, sociability, personality or behavior and cognitive function when compared to untreated controls
patients in the creatine-treatment group were less likely to experience headaches, dizziness and fatigue over six months of follow-up
CNS creatine is derived from both its local biosynthesis from the essential amino acids methionine, glycine and arginine
Studies of patients with CNS creatine deficiency and/or murine models with genetic ablation of creatine kinase have consistently demonstrated significant neurological impairment in the absence of proper creatine, phosphocreatine, or creatine kinase function; thus highlighting its functional importance
chronic dosing may partially reverse neurological impairments in human CNS creatine deficiency syndromes
Several studies have suggested that creatine supplementation may also reduce oxidative DNA damage and brain glutamate levels in Huntington disease patients
Another study highlighted that creatine supplementation marginally improved indices of mood and reduced the need for increased dopaminergic therapy in patients with Parkinson's disease
vitamin D supplementation found to be beneficial in reducing the risk of acute respiratory tract infections. This study found more benefit in those with D levels < 25 nmol/L
GCs induce increased cellular expression of receptors for several pro-inflammatory cytokines including interleukin (IL)-1 (Spriggs et al. 1990), IL-2 (Wiegers et al. 1995), IL-4 (Paterson et al. 1994), IL-6 (Snyers et al. 1990), and IFN-g (Strickland et al. 1986), as well as GM-CSF
GCs have also been shown to stimulate effector cell functions including phagocytosis by monocytes (van der Goes et al. 2000), effector cell proliferative responses (Spriggs et al. 1990), macrophage activation (Sorrells and Sapolsky 2010), and a delay of neutrophil apoptosis
a concentration- and time-dependent range of GC effects that are both pro- and anti-inflammatory
basal (diurnal) concentrations of cortisol do not exert an anti-inflammatory effect on several pro-and anti-inflammatory mediators of the human immune inflammatory response
withdrawal of cortisol activity in vivo did not lead to increased inflammatory responsiveness of immune effector cells
maximal suppression of inflammation was achieved by a stress-associated, but still physiologic, cortisol concentration. There was no greater anti-inflammatory effect at higher cortisol concentrations (Yeager et al. 2005) although IL-10 concentrations continued to increase with increasing cortisol concentrations as we and others have shown
acutely, physiological cortisol concentrations are anti-inflammatory and, as proposed, act to limit over expression of an inflammatory response that could lead to tissue damage
Acutely, cortisol has anti-inflammatory effects following a systemic inflammatory stimulus (Figure 4). However, a cortisol concentration that acts acutely to suppress systemic inflammation also has a delayed effect of augmenting the inflammatory response to subsequent, delayed stimulu
1) GCs can exert pro-inflammatory effects on key inflammatory processes and, 2) GC regulation of inflammation can vary from anti- to a pro-inflammatory in a time-dependent manner
The immediate in vivo effect of both stress-induced and pharmacological GC concentrations is to suppress concurrent inflammation and protect the organism from an excessive or prolonged inflammatory response
GCs alone, in the absence of an inflammatory stimulus, up-regulate monocyte mRNA and/or receptors for several molecules that participate in pro-inflammatory signaling, as noted above and in the studies presented here.
In humans, as shown here, if in vivo GC concentrations are elevated concurrent with an inflammatory stimulus, anti-inflammatory effects are observed
In sharp contrast, with a time delay of 12 or more hours between an increased GC concentration and the onset of an inflammatory stimulus, enhancing effects on inflammation are observed. These effects have been shown to persist in humans for up to 6 days
GC-induced enhancement of inflammatory responses is maximal at an intermediate concentration, in our studies at a concentration that approximates that observed in vivo following a major systemic inflammatory stimulus
In addition to enhanced responses to LPS, recently identified pro-inflammatory effects of GCs also show enhanced localization of effector cells at inflammatory sites
we hypothesize that pre-exposure to stress-associated cortisol concentrations “prime” effector cells of the monocyte/macrophage lineage for an augmented pro-inflammatory response by; a) inducing preparative changes in key regulators of LPS signal transduction, and b) enhancing localization of inflammatory effector cells at potential sites of injury
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
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
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
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.