Frequent occurrence of hypogonadotropic hypogonadism in type 2 diabetes

Influence of testosterone replacement therapy on metabolic disorders in male patients with type 2 diabetes mellitus and androgen deficiency

Background

Multiple epidemiological studies have shown that low testosterone levels are associated with and predict the future development of type 2 diabetes mellitus and the metabolic syndrome.

The aim of our study was to show the influence of testosterone replacement therapy on obesity, HbA1c level, hypertension and dyslipidemia in patients with diabetes mellitus and androgen deficiency.

Methods

One hundred and twenty-five male patients with diabetes mellitus were screened; 85 subjects aged 41 to 65 years, with BMI from 27.0 to 48.0 kg/m², were randomized in a placebo-controlled study. They also underwent a routine physical examination and selected by free testosterone examination. We divided patients into two groups: 1) treatment group, where we used diet, physical activity, patient’s antidiabetic therapy and testosterone replacement therapy; 2) placebo group, where we used diet, physical activity, patient’s antidiabetic therapy and placebo.

Results

After 6 months of treatment we repeated the diagnostic assessments: lipid profile was improved in both groups but in first group it was clinically significant. Free testosterone level increased in all groups, but in group I was clinically significant. HbA1c decreased in both groups, but in group I we obtained the best result. Leptin level after treatment was approximately the same in both groups. Also, blood pressure was reduced in both groups but results were similar.

Conclusions

Our study demonstrated that it is possible to break this metabolic vicious circle by raising testosterone levels in diabetic men with androgen deficiency. Re-instituting physiological levels of testosterone, as the study has shown, has an important role in reducing the prevalence of diabetic complications.

Diabetic complications in obese type 2 diabetic rat models

We overviewed the pathophysiological features of diabetes and its complications in obese type 2 diabetic rat models: Otsuka Long-Evans Tokushima fatty (OLETF) rat, Wistar fatty rat, Zucker diabetic fatty (ZDF) rat and Spontaneously diabetic Torii (SDT) fatty rat. Pancreatic changes with progression of diabetes were classified into early changes, such as islet hypertrophy and degranulation of β cells, and degenerative changes, such as islet atrophy and fibrosis of islet with infiltration of inflammatory cells. Renal lesions in tubuli and glomeruli were observed, and nodular lesions in glomeruli were notable changes in OLETF and SDT fatty rats. Among retinal changes, folding and thickening were interesting findings in SDT fatty rats. A decrease of motor nerve conduction velocity with progression of diabetes was presented in obese diabetic rats. Other diabetic complications, osteoporosis and sexual dysfunction, were also observed. Observation of bone metabolic abnormalities, including decrease of osteogenesis and bone mineral density, and sexual dysfunction, including hypotestosteronemia and erectile dysfunction, in obese type 2 diabetic rats have been reported.

Testosterone and weight loss: the evidence

PURPOSE OF REVIEW

The purpose of this article is to examine the contemporary data linking testosterone therapy in overweight and obese men with testosterone deficiency to increased lean body mass, decreased fat mass, improvement in overall body composition and sustained weight loss. This is of paramount importance because testosterone therapy in obese men with testosterone deficiency represents a novel and a timely therapeutic strategy for managing obesity in men with testosterone deficiency.

RECENT FINDINGS

Long-term testosterone therapy in men with testosterone deficiency produces significant and sustained weight loss, marked reduction in waist circumference and BMI and improvement in body composition. Further, testosterone therapy ameliorates components of the metabolic syndrome. The aforementioned improvements are attributed to improved mitochondrial function, increased energy utilization, increased motivation and vigor resulting in improved cardio-metabolic function and enhanced physical activity.

SUMMARY

The implication of testosterone therapy in management of obesity in men with testosterone deficiency is of paramount clinical significance, as it produces sustained weight loss without recidivism. On the contrary, alternative therapeutic approaches other than bariatric surgery failed to produce significant and sustained outcome and exhibit a high rate of recidivism. These findings represent strong foundations for testosterone therapy in obese men with testosterone deficiency and should spur clinical research for better understanding of usefulness of testosterone therapy in treatment of underlying pathophysiological conditions of obesity.

Adverse health effects of testosterone deficiency (TD) in men

Testosterone and its metabolite, 5α-dihydrotestosterone are critical metabolic and vascular hormones, which regulate a host of biochemical pathways including carbohydrate, lipid and protein metabolism and modulate vascular function. Testosterone deficiency (TD) is a well-recognized medical condition with important health implications. TD is associated with a number of co-morbidities including increased body weight, adiposity and increased waist circumference, insulin resistance (IR) and type 2 diabetes mellitus (T2DM), hypertension, inflammation, atherosclerosis and cardiovascular disease, erectile dysfunction (ED) and increased incidence of mortality. In this review, we summarize the data in the literature on the prevalence of TD and its association with the various co-morbidities and suggest that T therapy is necessary to improve health outcomes in men with TD.

Diet-induced obesity and low testosterone increase neuroinflammation and impair neural function

BACKGROUND

Low testosterone and obesity are independent risk factors for dysfunction of the nervous system including neurodegenerative disorders such as Alzheimer's disease (AD). In this study, we investigate the independent and cooperative interactions of testosterone and diet-induced obesity on metabolic, inflammatory, and neural health indices in the central and peripheral nervous systems.

METHODS

Male C57B6/J mice were maintained on normal or high-fat diet under varying testosterone conditions for a four-month treatment period, after which metabolic indices were measured and RNA isolated from cerebral cortex and sciatic nerve. Cortices were used to generate mixed glial cultures, upon which embryonic cerebrocortical neurons were co-cultured for assessment of neuron survival and neurite outgrowth. Peripheral nerve damage was determined using paw-withdrawal assay, myelin sheath protein expression levels, and Na+,K+-ATPase activity levels.

RESULTS

Our results demonstrate that detrimental effects on both metabolic (blood glucose, insulin sensitivity) and proinflammatory (cytokine expression) responses caused by diet-induced obesity are exacerbated by testosterone depletion. Mixed glial cultures generated from obese mice retain elevated cytokine expression, although low testosterone effects do not persist ex vivo. Primary neurons co-cultured with glial cultures generated from high-fat fed animals exhibit reduced survival and poorer neurite outgrowth. In addition, low testosterone and diet-induced obesity combine to increase inflammation and evidence of nerve damage in the peripheral nervous system.

CONCLUSIONS

Testosterone and diet-induced obesity independently and cooperatively regulate neuroinflammation in central and peripheral nervous systems, which may contribute to observed impairments in neural health. Together, our findings suggest that low testosterone and obesity are interactive regulators of neuroinflammation that, in combination with adipose-derived inflammatory pathways and other factors, increase the risk of downstream disorders including type 2 diabetes and Alzheimer's disease.

Metabolic effects of testosterone replacement therapy on hypogonadal men with type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials

This systematic review was aimed at assessing the metabolic effects of testosterone replacement therapy (TRT) on hypogonadal men with type 2 diabetes mellitus (T2DM). A literature search was performed using the Cochrane Library, EMBASE and PubMed. Only randomized controlled trials (RCTs) were included in the meta-analysis. Two reviewers retrieved articles and evaluated the study quality using an appropriate scoring method. Outcomes including glucose metabolism, lipid parameters, body fat and blood pressure were pooled using a random effects model and tested for heterogeneity. We used the Cochrane Collaboration's Review Manager 5.2 software for statistical analysis. Five RCTs including 351 participants with a mean follow-up time of 6.5-months were identified that strictly met our eligibility criteria. A meta-analysis of the extractable data showed that testosterone reduced fasting plasma glucose levels (mean difference (MD): −1.10; 95% confidence interval (CI) (−1.88, −0.31)), fasting serum insulin levels (MD: −2.73; 95% CI (−3.62, −1.84)), HbA1c % (MD: −0.87; 95% CI (−1.32, −0.42)) and triglyceride levels (MD: −0.35; 95% CI (−0.62, −0.07)). The testosterone and control groups demonstrated no significant difference for other outcomes. In conclusion, we found that TRT can improve glycemic control and decrease triglyceride levels of hypogonadal men with T2DM. Considering the limited number of participants and the confounding factors in our systematic review; additional large, well-designed RCTs are needed to address the metabolic effects of TRT and its long-term influence on hypogonadal men with T2DM.

Effect of continuous positive airway pressure therapy on sexual function and serum testosterone in males with type 2 diabetes and obstructive sleep apnoea

OBJECTIVE

There have been no studies of the effect of continuous positive airway pressure (CPAP) therapy on erectile dysfunction (ED) and serum testosterone in men with type 2 diabetes and obstructive sleep apnoea (OSA), a patient group at increased risk of ED and hypogonadism. The aim of this study was to determine whether CPAP improves sexual and gonadal function in males with type 2 diabetes and a pre-CPAP apnoea-hypopnoea index >15/h.

DESIGN

Substudy of a trial assessing the effect of 3 months of CPAP on cardiovascular risk in type 2 diabetes.

PATIENTS

Of 35 males starting CPAP, 27 (mean ± SD age 65.4 ± 9.6 years, median [interquartile range] diabetes duration 12.1 [5.2-15.3] years) completed the trial.

MEASUREMENTS

Serum total and free testosterone, responses to the Androgen Deficiency in the Aging Aale (ADAM) and Sexual Health Inventory for Men (SHIM) questionnaires.

RESULTS

There were no significant changes in mean total or free testosterone (baseline concentrations 12.7 ± 4.5 nm and 0.26 ± 0.07 pm, respectively), or SHIM score (baseline 13 [5-17]), after 3 months of CPAP (P > 0.20). The ADAM score (baseline 6.2 ± 2.1) fell after 1 month (to 5.0 ± 2.6) and was maintained at this level at 3 months (P = 0.015). The Epworth Sleepiness Scale score decreased and self-reported physical activity increased over 3 months (P ≤ 0.017) without a change in body mass index (P = 1.00).

CONCLUSIONS

These findings imply that CPAP therapy improves somnolence and promotes exercise in men with type 2 diabetes, but that there is no direct benefit for gonadal or sexual function.

Effect of testosterone treatment on glucose metabolism in men with type 2 diabetes: a randomized controlled trial

OBJECTIVE

To determine whether testosterone therapy improves glucose metabolism in men with type 2 diabetes (T2D) and lowered testosterone.

RESEARCH DESIGN AND METHODS

We conducted a randomized, double-blind, parallel, placebo-controlled trial in 88 men with T2D, aged 35-70 years with an HbA1c ≤8.5% (69 mmol/mol), and a total testosterone level, measured by immunoassay, of ≤12.0 nmol/L (346 ng/dL). Participants were randomly assigned to 40 weeks of intramuscular testosterone undecanoate (n = 45) or matching placebo (n = 43). All study subjects were included in the primary analysis. Seven men assigned to testosterone and six men receiving placebo did not complete the study. Main outcome measures were insulin resistance by homeostatic model assessment (HOMA-IR, primary outcome) and glycemic control by HbA1c (secondary outcome).

RESULTS

Testosterone therapy did not improve insulin resistance (mean adjusted difference [MAD] for HOMA-IR compared with placebo -0.08 [95% CI -0.31 to 0.47; P = 0.23]) or glycemic control (MAD HbA1c 0.36% [0.0-0.7]; P = 0.05), despite a decrease in fat mass (MAD -2.38 kg [-3.10 to -1.66]; P < 0.001) and an increase in lean mass (MAD 2.08 kg [1.52-2.64]; P < 0.001). Testosterone therapy reduced subcutaneous (MAD -320 cm(3) [-477 to -163]; P < 0.001) but not visceral abdominal adipose tissue (MAD 140 cm(3) [-89 to 369]; P = 0.90).

CONCLUSIONS

Testosterone therapy does not improve glucose metabolism or visceral adiposity in obese men with moderately controlled T2D and modest reductions in circulating testosterone levels typical for men with T2D.

Systematic Literature Review of the Epidemiology of Nongenetic Forms of Hypogonadism in Adult Males

This study summarizes the literature on the prevalence, incidence, and proportion of patients receiving treatment for male hypogonadism and a systematic literature search was performed for articles published in the last 20 years. Of the 97 studies identified, 96 examined the prevalence, 2 examined the incidence, and 4 examined the proportion of males with hypogonadism patients receiving treatment. Based on studies conducted in Europe and USA, the prevalence of hypogonadism in the general population ranged from 2.1% to 12.8% of middle-aged to older men, with an estimated incidence of 12 new cases per 1,000 person-years. Prevalence was higher among patients with comorbid conditions, such as type 2 diabetes mellitus and obesity. Approximately 10–12% of men with hypogonadism were receiving testosterone treatment. This literature review suggests that there is potentially a significant burden of hypogonadism in the general population. Burden seems to increase with age and in the presence of certain disease conditions. Data suggests that many hypogonadal men who may benefit from testosterone replacement are not receiving treatment. This may be the result of underdiagnosis of the disease, lack of awareness by patients or physicians, irregularities surrounding the diagnostic criteria, and deficiency of long-term safety studies.

Significantly increased risk of cancer in diabetes mellitus patients: A meta-analysis of epidemiological evidence in Asians and non-Asians

Aims/Introduction:  Emerging evidence from observational studies suggests that diabetes mellitus affects the cancer risk. However, whether there are differences in the magnitude of the influence of diabetes among ethnic groups is unknown.

Materials and Methods:  We searched MEDLINE and the Cochrane Library for pertinent articles that had been published as of 4 April 2011, and included them in a meta‐analysis of the risk of all‐cancer mortality and incidence in diabetic subjects.

Results:  A total of 33 studies were included in the meta‐analysis, and they provided 156,132 diabetic subjects for the mortality analysis and 993,884 for the incidence analysis. Cancer mortality was approximately 3%, and cancer incidence was approximately 8%. The pooled adjusted risk ratio (RR) of all‐cancer mortality was significantly higher than for non‐diabetic people (RR 1.32 [CI 1.20–1.45] for Asians; RR 1.16 [CI 1.01–1.34] for non‐Asians). Diabetes was also associated with an increased RR of incidence across all cancer types (RR 1.23 [CI 1.09–1.39] for Asians; RR 1.15 [CI 0.94–1.43] for non‐Asians). The RR of incident cancer for Asian men was significantly higher than for non‐Asian men (P = 0.021).

Conclusions:  Diabetes is associated with a higher risk for incident cancer in Asian men than in non‐Asian men. In light of the exploding global epidemic of diabetes, particularly in Asia, a modest increase in the cancer risk will translate into a substantial socioeconomic burden. Our current findings underscore the need for clinical attention and better‐designed studies of the complex interactions between diabetes and cancer. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00183.x, 2012)

Androgen deficiency and type 2 diabetes mellitus

The rising incidence of T2DM is well recognised and associated with trends in obesity and ageing. It is estimated that 2.8% of the world population had a diagnosis of diabetes mellitus in 2000, which is projected to rise to 4.3% by 2030. Diabetes, obesity and ageing are also associated with an increased risk of isolated male hypogonadotropic hypogonadism, often labelled 'late onset hypogonadism' (LOH) to distinguish it from hypogonadism secondary to distinct hypothalamopituitary pathology. Whether the incidence of hypogonadism is increasing is open to question; the past decade, however, has witnessed a marked increase in the prescription of testosterone replacement therapy. Testosterone deficiency appears to be particularly common in type 2 diabetes with a prevalence of 33% observed in one cohort of 103 men (mean age 54.7). However, the diagnosis of androgen deficiency states is not necessarily straightforward, depending amongst other factors, upon whether a biochemical threshold or a syndromic approach (mandating the presence of certain key clinical features) is employed. The pathogenic mechanisms underlying obesity and diabetes related hypogonadism remain unclear with several competing theories, most of which are not mutually exclusive. Whilst a large body of epidemiological evidence associates testosterone deficiency with increased risk of cardiovascular disease and mortality, little evidence exists to support a protective effect of testosterone replacement. The benefits of androgen replacement in younger men with pituitary disease are well established, however, the potential benefits and safety of androgen replacement in older men is much less well developed. At present, replacement therapy in older men is advocated principally for the amelioration of sexual symptoms. This review will seek to explore issues around the pathogenesis, diagnosis, clinical consequences and management of male hypogonadism as it relates to T2DM.

Elevated mitochondrial biogenesis in skeletal muscle is associated with testosterone-induced body weight loss in male mice

Androgen reduces fat mass, although the underlying mechanisms are unknown. Here, we examined the effect of testosterone on heat production and mitochondrial biogenesis. Testosterone-treated mice exhibited elevated heat production. Treatment with testosterone increased the expression level of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), ATP5B and Cox4 in skeletal muscle, but not that in brown adipose tissue and liver. mRNA levels of genes involved in mitochondrial biogenesis were elevated in skeletal muscle isolated from testosterone-treated male mice, but were down-regulated in androgen receptor deficient mice. These results demonstrated that the testosterone-induced increase in energy expenditure is derived from elevated mitochondrial biogenesis in skeletal muscle.

Male hypogonadism

Male hypogonadism is a clinical syndrome that results from failure to produce physiological concentrations of testosterone, normal amounts of sperm, or both. Hypogonadism may arise from testicular disease (primary hypogonadism) or dysfunction of the hypothalamic-pituitary unit (secondary hypogonadism). Clinical presentations vary dependent on the time of onset of androgen deficiency, whether the defect is in testosterone production or spermatogenesis, associated genetic factors, or history of androgen therapy. The clinical diagnosis of hypogonadism is made on the basis of signs and symptoms consistent with androgen deficiency and low morning testosterone concentrations in serum on multiple occasions. Several testosterone-replacement therapies are approved for treatment and should be selected according to the patient's preference, cost, availability, and formulation-specific properties. Contraindications to testosterone-replacement therapy include prostate and breast cancers, uncontrolled congestive heart failure, severe lower-urinary-tract symptoms, and erythrocytosis. Treatment should be monitored for benefits and adverse effects.

Obesity and Testosterone Levels in Ghanaian Men With Type 2 Diabetes

Testosterone plays a vital role in obesity, glucose homeostasis, and lipid metabolism. The aim of this study was to investigate androgen levels and its association with obesity in Ghanaian men with type 2 diabetes. The study showed that serum total and free testosterone concentrations were lower in male patients with type 2 diabetes and that obesity was strongly associated with low levels of total and free testosterone in Ghanaian men with type 2 diabetes.

Prevalence of low testosterone levels in men with type 2 diabetes mellitus: a cross-sectional study

Background:

A high prevalence of low serum testosterone (LST) in men with type 2 diabetes have been reported worldwide. The aim of this study was to determine the prevalence and associated factors of LST in men with type 2 diabetes.

Materials and Methods:

This was a cross-sectional study, conducted among 1,089 men (aged 30-70 years) with type 2 diabetes who consecutively attended a major diabetes center in Amman, Jordan, between August 2008 and February 2009. The patients’ demographic characteristics were collected using a prestructured questionnaire. Duration of diabetes, smoking habits, presence of retinopathy, neuropathy, and nephropathy were collected from the medical records. All participants were asked to complete the Androgen Deficiency in Ageing Male (ADAM) questionnaire. Venous blood sample was collected to test for total testosterone (TT), free testosterone (FT), sex hormone binding globulin (SHBG), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), serum lipids, and glycosylated hemoglobin (HbA1c). LST was defined as TT <3 ng/ml.

Results:

Overall, 36.5% of patients with diabetes had TT level <3 ng/ml and 29% had symptoms of androgen deficiency. Of those with serum testosterone level <3 ng/ml, 80.2% had symptoms of androgen deficiency, 16.9% had primary hypogonadism (HG), and 83.1% had secondary HG. Univariate analysis showed a significant relationship between age, income, education, body mass index (BMI), smoking, duration of diabetes, diabetic nephropathy, diabetic neuropathy, and HbA1c. Multivariate logistic regression analysis indicated age, income, BMI, and diabetic neuropathy as the independent risk factors of LST.

Conclusions:

The prevalence of LST among men with type 2 diabetes is high. Age, income, BMI, and diabetic neuropathy were found to be the independent risk factors for LST.

The prevalence of Hypogonadism among diabetic and non-diabetic men in Jordan

OBJECTIVE

Determine the prevalence of hypogonadism among diabetic and non-diabetic men in Jordan.

RESEARCH DESIGN AND METHODS

A cross-sectional study of 1717 men (1089 participants with type 2 diabetes and 628 non-diabetic subjects). Both groups were inquired to answer the Androgen Deficiency for aging male (ADAM) questionnaire. Early morning Total testosterone, prolactin, sex hormone binding globulin, follicle stimulating hormone, leutinizing hormone, HbA1c and fasting blood sugar were measured. Hypogonadism was defined as total testosterone <3 ng/ml and calculated free testosterone <5 ng/dl.

RESULTS

The prevalence of Hypogonadism among all study participants was 18.5%. The prevalence of Hypogonadism in diabetic and non-diabetic men was 24.3% and 8.3%, respectively. The mean (SD) total testosterone concentration of diabetic and non-diabetic men was 3.78 ng/ml (1.7) and 4.92 ng/ml (2.5), respectively (P- value <0.005). In response to (ADAM) questionnaire, 19.8% of diabetics and 3% of the non-diabetics had symptomatic androgen deficiency (P value <0.005). Hypogonadism and symptomatic androgen deficiency were negatively and significantly related to diabetes, monthly income and age (P value <0.005).

CONCLUSION

Hypogonadism is a prevalent disorder among Jordanian diabetic population. Symptoms of androgen deficiency should be corroborated with testosterone level to establish a multidisciplinary approach for management of hypogonadism.

Long-term testosterone therapy in hypogonadal men ameliorates elements of the metabolic syndrome: an observational, long-term registry study

AIM

The goal of this study was to determine if long-term testosterone (T) therapy in men with hypogonadism, henceforth referred to as testosterone deficiency (TD), ameliorates or improves metabolic syndrome (MetS) components.

METHODS

We performed a cumulative registry study of 255 men, aged between 33 and 69 years (mean 58.02 ± 6.30) with subnormal plasma total T levels (mean: 9.93 ± 1.38; range: 5.89-12.13 nmol/l) as well as at least mild symptoms of TD assessed by the Aging Males' symptoms scale. All men received treatment with parenteral T undecanoate 1000 mg (Nebido(®) , Bayer Pharma, Berlin, Germany), administered at baseline and 6 weeks and thereafter every 12 weeks for up to 60 months. Lipids, glucose, liver enzymes and haemoglobin A1c analyses were carried out in a commercial laboratory. Anthropometric measurements were also made throughout the study period.

RESULTS

Testosterone therapy restored physiological T levels and resulted in reductions in total cholesterol (TC) [7.29 ± 1.03 to 4.87 ± 0.29 mmol/l (281.58 ± 39.8 to 188.12 ± 11.31 mg/dl)], low-density lipoprotein cholesterol [4.24 ± 1.07 to 2.84 ± 0.92 mmol/l (163.79 ± 41.44 to 109.84 ± 35.41 mg/dl)], triglycerides [3.14 ± 0.58 to 2.16 ± 0.13 mmol/l (276.16 ± 51.32 to 189.78 ± 11.33 mg/dl)] and increased high-density lipoprotein levels [1.45 ± 0.46 to 1.52 ± 0.45 mmol/l (56.17 ± 17.79 to 58.85 ± 17.51 mg/dl)] (p < 0.0001 for all). There were marked reductions in systolic and diastolic blood pressure, blood glucose, haemoglobin A1c , C-reactive protein (6.29 ± 7.96 to 1.03 ± 1.87 U/l), alanine aminotransferase and aspartate aminotransferase (p < 0.0001 for all).

CONCLUSIONS

Long-term T therapy, at physiological levels, ameliorates MetS components. These findings strongly suggest that T therapy in hypogonadal men may prove useful in reducing the risk of cardiometabolic diseases.

Testosterone and glucose metabolism in men: current concepts and controversies

A wealth of observational studies show that low testosterone is associated with insulin resistance and with an increased risk of diabetes and the metabolic syndrome. Experimental studies have identified potential mechanisms by which low testosterone may lead to insulin resistance. Visceral adipose tissue is an important intermediate in this relationship. Actions of testosterone or its metabolite oestradiol on other tissues such as muscle, liver, bone or the brain, and body composition-independent effects may also play a role. However, definitive evidence from randomised controlled trials (RCTs) to clarify whether the association of low testosterone with disordered glucose metabolism is causative is currently lacking. It therefore remains possible that this association is due to reverse causation, or simply originates by association with common health and lifestyle factors. RCTs of testosterone therapy in men with or without diabetes consistently show modest metabolically favourable changes in body composition. Despite this, testosterone effects on glucose metabolism have been inconsistent. Recent evidence suggests that the hypothalamic-pituitary-testicular axis suppression in the majority of obese men with metabolic disorders is functional, and may be, at least in part, reversible with weight loss. Until further evidence is available, lifestyle measures with emphasis on weight reduction, treatment of comorbidities and optimisation of diabetic control should remain the first-line treatment in these men. Such measures, if successful, may be sufficient to normalise testosterone levels in men with metabolic disorders, who typically have only modest reductions in circulating testosterone levels.

The response to testosterone undecanoate in men with type 2 diabetes is dependent on achieving threshold serum levels (the BLAST study)

BACKGROUND

The association between testosterone deficiency and insulin resistance in men with type 2 diabetes is well established. Current Endocrine Society and European Association of Urology guidelines recommend the measurement of testosterone levels in all men with type 2 diabetes and in men suffering from erectile dysfunction. It is recognised that a range of physical symptoms appear as the testosterone level falls but few studies have addressed the threshold at which symptoms improve with physiological replacement. We report the first double-blind placebo-controlled study conducted exclusively in a male type 2 diabetes population to assess the metabolic changes with testosterone replacement.

METHODS

The type 2 diabetes registers of seven general practices were screened to establish the prevalence of low testosterone and the associations with diabetes control. Of 550 eligible patients approached, 488 men (mean age 62.6) consented to take part in screening with a morning testosterone level, assessed between 8 and 11 am. This identified 211 patients for a double-blind placebo-controlled study of long acting testosterone undecanoate (TU) 1000 mg lasting 30 weeks followed by 52 weeks of open label use. The population was divided into a SEVERE group with either total testosterone (TT) of 8 nmol/l or less or free testosterone (FT) 180 pmol/l or less or a MILD group with TT 8.1-12 nmol/l or FT 181-250 pmol/l.

RESULTS

Men in the SEVERE group increased mean through TT from 7.73 nmol/l at baseline to 9.93 at 30 weeks and the MILD group from 10.47 to 11.94. The SEVERE group showed marked improvement in sexual function, but no significant improvement in metabolic parameters. The MILD group showed no improvement in sexual function, but significant improvement in weight, body mass index, waist circumference and Hospital Anxiety and Depression Scale. Improvement was seen in all parameters during 52 weeks open label treatment where trough TT levels approached 15 nmol/l. Baseline prostate-specific antigen (PSA) was lower in the SEVERE group and increased with TU for 30 weeks and then stabilised. There was no increase in PSA with treatment in the MILD group.

CONCLUSIONS

Testosterone undecanoate significantly improves sexual parameters and Ageing Male Symptom Score, but not metabolic factors at 30 weeks in men with SEVERE testosterone deficiency syndrome (TDS). In men with MILD TDS, significant improvements in metabolic but not sexual parameters were seen, suggesting that there are threshold levels for response to testosterone replacement therapy and that trials of therapy need to achieve sustained therapeutic levels to be effective. PSA showed minor rises, but only for 30 weeks in the SEVERE group.

Diabetes and sexual dysfunction: current perspectives

Diabetes mellitus is one of the most common chronic diseases in nearly all countries. It has been associated with sexual dysfunction, both in males and in females. Diabetes is an established risk factor for sexual dysfunction in men, as a threefold increased risk of erectile dysfunction was documented in diabetic men, as compared with nondiabetic men. Among women, evidence regarding the association between diabetes and sexual dysfunction are less conclusive, although most studies have reported a higher prevalence of female sexual dysfunction in diabetic women as compared with nondiabetic women. Female sexual function appears to be more related to social and psychological components than to the physiological consequence of diabetes. Hyperglycemia, which is a main determinant of vascular and microvascular diabetic complications, may participate in the pathogenetic mechanisms of sexual dysfunction in diabetes. Moreover, diabetic people may present several clinical conditions, including hypertension, overweight and obesity, metabolic syndrome, cigarette smoking, and atherogenic dyslipidemia, which are themselves risk factors for sexual dysfunction, both in men and in women. The adoption of healthy lifestyles may reduce insulin resistance, endothelial dysfunction, and oxidative stress - all of which are desirable achievements in diabetic patients. Improved well-being may further contribute to reduce and prevent sexual dysfunction in both sexes.

Effects of long-term testosterone therapy on patients with "diabesity": results of observational studies of pooled analyses in obese hypogonadal men with type 2 diabetes

To investigate effects of long-term testosterone (T) therapy in obese men with T deficiency (TD) and type 2 diabetes mellitus (T2DM), data were collected from two observational, prospective, and cumulative registry studies of 561 men with TD receiving T therapy for up to 6 years. A subgroup of obese hypogonadal men with T2DM was analyzed. Weight, height, waist circumference (WC), fasting blood glucose (FBG), glycated haemoglobin (HbA1c) blood pressure, lipid profile, C-reactive protein (CRP), and liver enzymes were measured. A total of 156 obese, diabetic men with T deficiency, aged 61.17 ± 6.18 years, fulfilled selection criteria. Subsequent to T therapy, WC decreased by 11.56 cm and weight declined by 17.49 kg (15.04%). Fasting glucose declined from 7.06 ± 1.74 to 5.59 ± 0.94 mmol/L (P < 0.0001 for all). HbA1c decreased from 8.08 to 6.14%, with a mean change of 1.93%. Systolic and diastolic blood pressure, lipid profiles including total cholesterol: HDL ratio, CRP, and liver enzymes all improved (P < 0.0001). Long-term T therapy for up to 6 years resulted in significant and sustained improvements in weight, T2DM, and other cardiometabolic risk factors in obese, diabetic men with TD and this therapy may play an important role in the management of obesity and diabetes (diabesity) in men with T deficiency.

Hypogonadism and metabolic syndrome in nigerian male patients with both type 2 diabetes and hypertension

BACKGROUND

The association between testosterone level and the components of metabolic syndrome remains controversial. Relevant studies from Sub-Saharan Africa are few and incohesive.

OBJECTIVES

The current study was designed to investigate the level of testosterone in patients with both diabetes and hypertension and the association of low testosterone with metabolic syndrome in these patients.

MATERIALS AND METHODS

In this prospective case-control study, 83 male subjects (49 newly diagnosed men with both diabetes and hypertension and 34 apparently healthy controls) were recruited from Ladoke Akintola University of Technology Teaching Hospital, Osogbo, Nigeria and University College Hospital Ibadan, Ibadan, Nigeria. Demographic, anthropometric and sexual characteristics were obtained using structured questionnaires and standard methods. Blood plasma glucose (BPG), total cholesterol (TC), triglycerides (TG), high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) were measured by conventional methods. Testosterone (T) was analyzed by enzyme immunoassay. Data obtained were statically analyzed with the SPSS 15.0 software, and results were expressed as mean ± SEM.

RESULTS

This study showed significantly lowered concentrations of testosterone (3.11 nm/L ± 0.34) and HDL (0.39 mmol/L ± 0.02), in addition to the expected increased concentrations of fasting plasma glucose (9.61 mmol/L ± 0.37) in the subjects compared to controls (P < 0.05). An inverse significant correlation was observed between the serum testosterone concentration and metabolic syndrome (BMI, r = -0.477; waist/Hip ratio, r = -0.376 and dyslipidemia, r = -0.364, P < 0.05). Also, the testosterone level decreased with increase in central obesity (P < 0.05).

CONCLUSIONS

This study established a strong association between low serum testosterone and metabolic syndrome in subjects with both type 2 diabetes and hypertension. It may therefore be advisable to include routine measurement of the testosterone level in the management of patients presented with both diabetes and hypertension. Furthermore, these patients may benefit from testosterone replacement therapy.

Characterization of the male ApcMin/+ mouse as a hypogonadism model related to cancer cachexia

Cancer cachexia, the unintentional loss of lean body mass, is associated with decreased quality of life and poor patient survival. Hypogonadism, involving a reduction in circulating testosterone, is associated with the cachectic condition. At this time there is a very limited understanding of the role of hypogonadism in cancer cachexia progression. This gap in our knowledge is related to a lack of functional hypogonadal models associated with cancer cachexia. The Apc^Min/+ mouse is an established colorectal cancer model that develops an IL-6 dependent cachexia which is physiologically related to human disease due to the gradual progression of tumor development and cachexia. The purpose of this study was to assess the utility of the Apc^Min/+ mouse for the examination of hypogonadism during cancer cachexia and to investigate if IL-6 has a role in this process. We report that Apc^Min/+ mice that are weight stable have comparable testosterone levels and gonad size compared to wild type mice. Cachectic Apc^Min/+ mice exhibit a reduction in circulating testosterone and gonad size, which has a significant association with the degree of muscle mass and functional strength loss. Circulating testosterone levels were also significantly associated with the suppression of myofibrillar protein synthesis. Skeletal muscle and testes androgen receptor expression were decreased with severe cachexia. Although testes STAT3 phosphorylation increased with severe cachexia, systemic IL-6 over-expression for 2 weeks was not sufficient to reduce either testes weight or circulating testosterone. Inhibition of systemic IL-6 signaling by an IL-6 receptor antibody to Apc^Min/+ mice that had already initiated weight loss was sufficient to attenuate a reduction in testes size and circulating testosterone. In summary, the Apc^Min/+ mouse becomes hypogonadal with the progression of cachexia severity and elevated circulating IL-6 levels may have a role in the development of hypogonadism during cancer cachexia.

Testosterone replacement therapy improves metabolic parameters in hypogonadal men with type 2 diabetes but not in men with coexisting depression: the BLAST study

INTRODUCTION

The association between testosterone deficiency and insulin resistance in men with type 2 diabetes is well established and current endocrine society guidelines recommend the measurement of testosterone levels in all men with type 2 diabetes or erectile dysfunction.

AIM

We report the first double-blind, placebo-controlled study conducted exclusively in a male type 2 diabetes population to assess metabolic changes with long-acting testosterone undecanoate (TU).

METHODS

The type 2 diabetes registers of seven general practices identified 211 patients for a 30-week double-blind, placebo-controlled study of long-acting TU 1,000 mg followed by 52 weeks of open-label use. Because of the established impact of age, obesity, and depression on sexual function, these variables were also assessed for influence on metabolic parameters.

MAIN OUTCOME MEASURE

Changes in glycated hemoglobin (HbA1c) and the level of testosterone at which response are achieved.

RESULTS

Treatment with TU produced a statistically significant reduction in HbA1c at 6 and 18 weeks and after a further 52 weeks of open-label medication most marked in poorly controlled patients with baseline HbA1c greater than 7.5 where the reduction was 0.41% within 6 weeks, and a further 0.46% after 52 weeks of open-label use. There was significant reduction in waist circumference, weight, and body mass index in men without depression, and improvements were related to achieving adequate serum levels of testosterone. There were no significant safety issues.

CONCLUSIONS

Testosterone replacement therapy significantly improved HbA1c, total cholesterol, and waist circumference in men with type 2 diabetes. Improvements were less marked in men with depression at baseline, and therapeutic responses were related to achieving adequate serum testosterone levels. Current advice on 3- to 6-month trials of therapy may be insufficient to achieve maximal response. Patients reported significant improvements in general health.

Testosterone deficiency is associated with increased risk of mortality and testosterone replacement improves survival in men with type 2 diabetes

OBJECTIVE

Men with type 2 diabetes are known to have a high prevalence of testosterone deficiency. No long-term data are available regarding testosterone and mortality in men with type 2 diabetes or any effect of testosterone replacement therapy (TRT). We report a 6-year follow-up study to examine the effect of baseline testosterone and TRT on all-cause mortality in men with type 2 diabetes and low testosterone.

RESEARCH DESIGN AND METHODS

A total of 581 men with type 2 diabetes who had testosterone levels performed between 2002 and 2005 were followed up for a mean period of 5.81.3 S.D. years. mortality rates were compared between total testosterone 10.4nmol/l (300ng/dl; n=343) and testosterone 10.4nmol/l (n=238). the effect of TRT (as per normal clinical practise: 85.9% testosterone gel and 14.1% intramuscular testosterone undecanoate) was assessed retrospectively within the low testosterone group.

RESULTS

Mortality was increased in the low testosterone group (17.2%) compared with the normal testosterone group (9%; P=0.003) when controlled for covariates. In the Cox regression model, multivariate-adjusted hazard ratio (HR) for decreased survival was 2.02 (P=0.009, 95% CI 1.2-3.4). TRT (mean duration 41.6±20.7 months; n=64) was associated with a reduced mortality of 8.4% compared with 19.2% (P=0.002) in the untreated group (n=174). The multivariate-adjusted HR for decreased survival in the untreated group was 2.3 (95% CI 1.3-3.9, P=0.004).

CONCLUSIONS

Low testosterone levels predict an increase in all-cause mortality during long-term follow-up. Testosterone replacement may improve survival in hypogonadal men with type 2 diabetes.

Andropause: Current concepts

Andropause or late-onset hypogonadism is a common disorder which increases in prevalence with advancing age. Diagnosis of late-onset of hypogonadism is based on presence of symptoms suggestive of testosterone deficiency - prominent among them are sexual symptoms like loss of libido, morning penile erection and erectile dysfunction; and demonstration of low testosterone levels. Adequate therapeutic modalities are currently available, but disparate results of clinical trial suggest further evaluation of complex interaction between androgen deficiency and ageing. Before initiating therapy benefits and risk should be discussed with patients and in case of poor response, alternative cause should be investigated.

[Androgenic treatment of male hypogonadism]

The diagnosis of male hypogonadism should be clearly established on a clinical and biological basis before considering the initiation of a substitutive treatment with androgens. A careful evaluation of advantages, constraints and limitations of the treatment should be done previously. The potential advantages of an androgenic substitution include an improvement of the symptoms of hypogonadism and the prevention of its bone and metabolic consequences. Absolute (namely prostatic) or relative contraindications should be detected before starting any substitution. The modalities of treatment will be adapted to both the patient's age and the goals to reach. The different available formulations do not induce a similar pattern of plasma testosterone levels. Patches, gel applications and long-acting intramuscular formulations [injected every 3 months] result in stable plasma levels in the physiologic range. The main limitation to their use is linked to a financial aspect as they are not the object of any refund. A careful survey (on clinical, biological and radiological basis) should be established after starting the substitutive treatment with androgens.

Evaluation of the hypothalamic-pituitary-gonadal axis in eugonadal men with type 2 diabetes mellitus

Men with type 2 diabetes mellitus (DM2) have lower testosterone levels and a higher prevalence of hypogonadism. It still remains unclear the mechanism by which there is a relationship between hypogonadism and DM2. The objective was to evaluate the hypothalamic-pituitary-gonadal axis at different levels in eugonadal patients with DM2. Fourteen patients with DM2 (DM2 group) and 15 subjects without DM2 (normal glucose tolerance test) as control group (CG) were included. We assessed: (i) fasting glucose, insulin, Homeostasis Model Assessment (HOMA); (ii) luteinizing hormone (LH) pulsatility through blood collections every 10 min for 4 h; (iii) gonadotropin-releasing hormone (GnRH) test: basal LH and 30, 60 and 90 min after 100 μg of i.v. GnRH; (iv) human chorionic gonadotropin (hCG) test: basal total testosterone (TT), bioavailable testosterone (BT), free testosterone (FT), estradiol (E2), bioavailable E2 (BE2) and sex hormone-binding globulin (SHBG) and 72 h post 5000 IU of i.m. hCG. There were no differences in age, body mass index and waist circumference between groups. Glucose was higher in the DM2 group vs. CG: 131.1 ± 25.5 vs. 99.1 ± 13.6 mg/dL, p = 0.0005. There were no difference in basal insulin, HOMA, TT, BT, FT, E2, BE2, SHBG and LH levels between groups. The DM2 group had lower LH pulse frequency vs. CG: 0.8 ± 0.8 vs. 1.5 ± 0.5 pulses, p = 0.009. Differences in LH pulse amplitude were not found. A negative correlation was found between the number of LH pulses and glucose, r: -0.39, p = 0.03. There were no differences in the response of LH to GnRH between groups nor in the response of sexual steroids and SHBG to hCG. Patients with DM2 showed lower hypothalamic pulse frequency without changes in the pituitary response to GnRH nor testicular response to hCG. Glucose levels negatively correlated with the number of LH pulses which suggests a negative effect of hyperglycaemia in the hypothalamic secretion of GnRH.

[Plasma testosterone, obesity, metabolic syndrome and diabetes]

The frequency of diabetes and/or metabolic syndrome rises concurrently with that of body mass index (BMI). In adult men, plasma testosterone level changes evolve inversely to that of BMI. Plasma total testosterone, sex hormone-binding globulin (SHBG) and free testosterone are significantly lower in adult men with a clinical and biological pattern of metabolic syndrome (MetS) than in those without such a pattern. After adjustment for confounding factors, diabetes type 2 (DT2) remains associated with a significant decrease of plasma testosterone level. The androgenic blockade, used as a treatment for disseminated prostate cancer, induces a metabolic pattern similar to MetS. In men older than 65 years, a decrease of plasma testosterone level is associated with an increased risk of stroke or of death linked to a cardiovascular event. After exclusion of contraindications, the substitution with androgens of a demonstrated hypogonadism in a obese patient, notably when obesity is associated with a pattern of MetS and/or a DT2, could have some metabolic and cardiovascular advantages.

The incidence of hypogonadotropic hypogonadism in type 2 diabetic men in Polish population

The aim of this study was to investigate the incidence of hypogonadotropic hypogonadism (HH) in type 2 diabetic men (T2DM) in population of Polish men and examine the possible influence of estradiol levels and glycemic control. We evaluated TT, cfT, estradiol, and glycemic control (HbA1c) in 184 diabetic men and in 149 nondiabetic control group. The mean HbA1c was 8.6 ± 0.2% and 6.1 ± 0.3% and cfT concentration was 0.315 ± 0.08 nmol/L and 0.382 ± 0.07 nmol/L, respectively. T2DM had higher E2 concentration than nonobese control men (29.4 ± 3.7 pg/mL versus 24.5 ± 2.9 pg/mL). Forty-six percent of T2DM were hypogonadal and 93% had HH. We observed inverse relationship between BMI and cfT (r = -0.341, P < 0.01) and positive between BMI and E2 (r = 0.329, P < 0.01). E2 concentration was higher in T2DM with HH versus T2DM with normal TT/cfT concentration (34.5 ± 5.2 versus 27.4 ± 3.4 pg/mL). We observed negative correlation between HbA1c and cfT (r = -0.336, P < 0.005) but positive between HbA1c and E2 levels (r = 0.337, P < 0.002). The prevalence of obesity, hypertension, and CVD was higher in men with hypogonadism. High incidence of hypogonadotropic hypogonadism in type 2 diabetic men in Polish population is associated with poor glycemic control and can be secondary to an increase in estradiol concentrations.

Long-term treatment of hypogonadal men with testosterone produces substantial and sustained weight loss

OBJECTIVE

This study analyzed the effects of normalization of serum testosterone (T) levels on anthropometric parameters in hypogonadal men.

DESIGN AND METHODS

Open-label, single-center, cumulative, prospective registry study of 255 men (aged 33-69 years, mean 58.02 ± 6.30 years), with T levels below 12.13 nmol/L (mean: 9.93±1.38). 215 men for at least 2 years, 182 for 3 years, 148 for 4, and 116 for at least 5 years were studied. They received parenteral T undecanoate 1,000 mg/12 weeks after an initial interval of 6 weeks.

RESULTS

Body weight (BW) decreased from 106.22 ± 16.93 kg to 90.07 ± 9.51 kg. Waist circumference (WC) reduced from 107.24 ± 9.14 cm to 98.46 ± 7.39 cm. BMI (m/kg(2) ) declined from 33.9 ± 5.51 m/kg(2) to 29.13 ± 3.09 m/kg(2) . All parameters examined were statistically significant with P < 0.0001 versus baseline and versus the previous year over 5 years indicating a continuous weight loss over the full observation period. The mean per cent weight loss after 1 year was 4.16 ± 0.31%, after 2 years 7.54 ± 0.32%, after 3 years 9.23 ± 0.33%, after 4 years 11.42 ± 0.35% and after 5 years 13.57 ± 0.37%.

CONCLUSIONS

In an uncontrolled, observational cohort, normalizing serum T to normal physiological levels produced consistent loss of BW, WC, and BMI. These improvements were progressive over the full 5 years of the study.

Obesity and age as dominant correlates of low testosterone in men irrespective of diabetes status

Although men with type 2 diabetes (T2D) frequently have lowered testosterone levels, it is not well established whether this is ascribable to the diabetic state per se, or because of other factors, such as obesity. Our objective was to determine the prevalence and correlates of low testosterone in middle-aged men with diabetes. We conducted a cross-sectional study in 240 men including 80 men with type 1 diabetes (T1D), 80 men with T2D and 80 men without diabetes. Prevalence of a total testosterone ≤8 nmol/L was low, occurring in none of the men with T1D, 6.2% of men with T2D and 2.5% of men without diabetes. Men with T1D had higher testosterone levels compared with men without diabetes (p < 0.001), even after adjustment for body mass index (BMI) and age (p < 0.02). While men with T2D had lower testosterone compared with controls (p = 0.03), this was no longer significant when BMI and age were taken into account (p = 0.16). In the entire cohort, TT remained inversely associated with BMI independent of age, sex hormone-binding globulin and diabetic status (p = 0.01), whereas calculated free testosterone (cFT) was independently and inversely associated with age (p < 0.001), but not with BMI (p = 0.47). These results suggest that marked reductions in circulating testosterone are uncommon in middle-aged men with diabetes. Increasing BMI and age are dominant drivers of lowered total and cFT, respectively, independent of the presence or absence of diabetes.

Prediabetes is associated with an increased risk of testosterone deficiency, independent of obesity and metabolic syndrome

OBJECTIVE

The association between type 2 diabetes and low testosterone has been well recognized. However, testosterone levels in men with prediabetes have been rarely reported. We aimed to investigate whether prediabetes was associated with an increased risk of testosterone deficiency.

METHODS

This study included 1,306 men whose sex hormones was measured during a medical examination. Serum total testosterone and sex hormone-binding globulin were measured; free and bioavailable testosterone concentrations were calculated by Vermeulen's formula. Prediabetes was defined by impaired fasting glucose (IFG), impaired postprandial glucose (IPG), or glycated hemoglobin (HbA1c) 5.7%-6.4%. Logistic regression was performed to obtain the odds ratios (OR) for subnormal total testosterone (<300 ng/dL) or free testosterone (<6 ng/dL) in prediabetic and diabetic men compared with normoglycemic individuals, while adjusting for age, BMI, waist circumference, and metabolic syndrome (MetS).

RESULTS

Normoglycemia, prediabetes, and diabetes were diagnosed in 577 (44.2%), 543 (41.6%), and 186 (14.2%) men, respectively. Prediabetes was associated with an increased risk of subnormal total testosterone compared to normoglycemic individuals (age-adjusted OR=1.87; 95%CI=1.38-2.54). The risk remained significant in all multivariate analyses. After adjusting for MetS, the OR in prediabetic men equals that of diabetic patients (1.49 versus 1.50). IFG, IPG, and HbA1c 5.7%-6.4% were all associated with an increased risk of testosterone deficiency, with different levels of significance in multivariate analyses. However, neither prediabetes nor diabetes was associated with subnormal free testosterone in multivariate analyses.

CONCLUSIONS

Prediabetes is associated with an increased risk of testosterone deficiency, independent of obesity and MetS. After adjusting for MetS, the risk equals that of diabetes. Our data suggest that testosterone should be measured routinely in men with prediabetes.

The Relationship between Testosterone Deficiency and Men's Health

Testosterone is important in the physiology of various organs and tissues. The serum testosterone concentration gradually declines as one of the processes of aging. Thus, the concept of late-onset hypogonadism has gained increasing attention in the last few years. Reported symptoms of late-onset hypogonadism are easily recognized and include diminished sexual desire and erectile quality, particularly in nocturnal erections, changes in mood with concomitant decreases in intellectual activity and spatial orientation, fatigue, depression and anger, a decrease in lean body mass with associated decreases in muscle volume and strength, a decrease in body hair and skin alterations, and decreased bone mineral density resulting in osteoporosis. Among these various symptoms, sexual dysfunction has been the most common and necessary to treat in the field of urology. It is well known that a low serum testosterone level is associated with erectile dysfunction and hypoactive sexual libido and that testosterone replacement treatment can improve these symptoms in patients with hypogonadism. Recently, in addition to sexual dysfunction, a close relationship between metabolic syndrome, characterized by central obesity, insulin resistance, dyslipidemia, and hypertension, and late-onset hypogonadism has been highlighted by several epidemiologic studies. Several randomized control trials have shown that testosterone replacement treatment significantly decreases insulin resistance in addition to its advantage for obesity. Furthermore, metabolic syndrome is one of the major risk factors for cardiovascular disease, and a low serum testosterone level is closely related to the development of atherosclerosis. Presently, it is speculated that a low serum testosterone level may increase the risk for cardiovascular disease. Thus, testosterone is a key molecule in men's health, especially that of elderly men.

Testosterone and insulin resistance in the metabolic syndrome and T2DM in men

Obesity, type 2 diabetes mellitus and the metabolic syndrome are major risk factors for cardiovascular disease. Studies have demonstrated an association between low levels of testosterone and the above insulin-resistant states, with a prevalence of hypogonadism of up to 50% in men with type 2 diabetes mellitus. Low levels of testosterone are also associated with an increased risk of all-cause and cardiovascular mortality. Hypogonadism and obesity share a bidirectional relationship as a result of the complex interplay between adipocytokines, proinflammatory cytokines and hypothalamic hormones that control the pituitary-testicular axis. Interventional studies have shown beneficial effects of testosterone on components of the metabolic syndrome, type 2 diabetes mellitus and other cardiovascular risk factors, including insulin resistance and high levels of cholesterol. Biochemical evidence indicates that testosterone is involved in promoting glucose utilization by stimulating glucose uptake, glycolysis and mitochondrial oxidative phosphorylation. Testosterone is also involved in lipid homeostasis in major insulin-responsive target tissues, such as liver, adipose tissue and skeletal muscle.

Exploring the pathophysiology of hypogonadism in men with type 2 diabetes: kisspeptin-10 stimulates serum testosterone and LH secretion in men with type 2 diabetes and mild biochemical hypogonadism

RATIONALE

Low serum testosterone is commonly observed in men with type 2 diabetes (T2DM), but the neuroendocrine pathophysiology remains to be elucidated.

OBJECTIVES

The hypothalamic neuropeptide kisspeptin integrates metabolic signals with the reproductive axis in animal models. We hypothesized that administration of exogenous kisspeptin-10 will restore luteinizing hormone (LH) and testosterone secretion in hypotestosteronaemic men with T2DM.

PARTICIPANTS

Five hypotestosteronaemic men with T2DM (age 33·6 ± 3 years, BMI 40·6 ± 6·3, total testosterone 8·5 ± 1·0 nmol/l, LH 4·7 ± 0·7 IU/l, HbA1c 7·4±2%, duration of diabetes <5 years) and seven age-matched healthy men. EXPERIMENT 1: Mean LH increased in response to intravenous administration of kisspeptin-10 (0·3 mcg/kg bolus) both in healthy men (5·5 ± 0·8 to 13·9 ± 1·7 IU/l P < 0·001) and in men with T2DM (4·7 ± 0·7 to 10·7 ± 1·2 IU/l P = 0·02) with comparable ΔLH (P = 0·18). EXPERIMENT 2: Baseline 10-min serum sampling for LH and hourly testosterone measurements were performed in four T2DM men over 12 h. An intravenous infusion of kisspeptin-10 (4 mcg/kg/h) was administered for 11 h, 5 days later. There were increases in LH (3·9 ± 0·1 IU/l to 20·7 ± 1·1 IU/l P = 0·03) and testosterone (8·5 ± 1·0 to 11·4 ± 0·9 nmol/l, P = 0·002). LH pulse frequency increased from 0·6 ± 0·1 to 0·9 ± 0 pulses/h (P = 0·05) and pulsatile component of LH secretion from 32·1 ± 8·0 IU/l to 140·2 ± 23·0 IU/l (P = 0·007).

CONCLUSIONS

Kisspeptin-10 administration increased LH pulse frequency and LH secretion in hypotestosteronaemic men with T2DM in this proof-of-concept study, with associated increases in serum testosterone. These data suggest a potential novel therapeutic role for kisspeptin agonists in enhancing endogenous testosterone secretion in men with T2DM and central hypogonadism.

Risks and benefits of testosterone therapy in older men

In young men (defined as age<50 years) with classic hypogonadism caused by known diseases of the hypothalamus, pituitary or testes, testosterone replacement therapy induces a number of beneficial effects, for example, the development of secondary sex characteristics, improvement and maintenance of sexual function, and increases in skeletal muscle mass and BMD. Moreover, testosterone treatment in this patient population is associated with a low frequency of adverse events. Circulating testosterone levels decline progressively with age, starting in the second and third decade of life, owing to defects at all levels of the hypothalamic-pituitary-testicular axis. In cohort studies, testosterone levels are associated weakly but consistently with muscle mass, strength, physical function, anaemia, BMD and bone quality, visceral adiposity, and with the risk of diabetes mellitus, coronary artery disease, falls, fractures and mortality. However, the clinical benefits and long-term risks of testosterone therapy--especially prostate-related and cardiovascular-related adverse events--have not been adequately assessed in large, randomized clinical trials involving older men (defined as age>65 years) with androgen deficiency. Therefore, a general policy of testosterone replacement in all older men with age-related decline in testosterone levels is not justified.

Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis

OBJECTIVE

Few randomized clinical studies have evaluated the impact of diet and physical activity on testosterone levels in obese men with conflicting results. Conversely, studies on bariatric surgery in men generally have shown an increase in testosterone levels. The aim of this study is to perform a systematic review and meta-analysis of available trials on the effect of body weight loss on sex hormones levels.

DESIGN

Meta-analysis.

METHODS

An extensive Medline search was performed including the following words: 'testosterone', 'diet', 'weight loss', 'bariatric surgery', and 'males'. The search was restricted to data from January 1, 1969 up to August 31, 2012.

RESULTS

Out of 266 retrieved articles, 24 were included in the study. Of the latter, 22 evaluated the effect of diet or bariatric surgery, whereas two compared diet and bariatric surgery. Overall, both a low-calorie diet and bariatric surgery are associated with a significant (P<0.0001) increase in plasma sex hormone-binding globulin-bound and -unbound testosterone levels (total testosterone (TT)), with bariatric surgery being more effective in comparison with the low-calorie diet (TT increase: 8.73 (6.51-10.95) vs 2.87 (1.68-4.07) for bariatric surgery and the low-calorie diet, respectively; both P<0.0001 vs baseline). Androgen rise is greater in those patients who lose more weight as well as in younger, non-diabetic subjects with a greater degree of obesity. Body weight loss is also associated with a decrease in estradiol and an increase in gonadotropins levels. Multiple regression analysis shows that the degree of body weight loss is the best determinant of TT rise (B=2.50±0.98, P=0.029).

CONCLUSIONS

These data show that weight loss is associated with an increase in both bound and unbound testosterone levels. The normalization of sex hormones induced by body weight loss is a possible mechanism contributing to the beneficial effects of surgery in morbid obesity.

Testosterone: a metabolic hormone in health and disease

Testosterone is a hormone that plays a key role in carbohydrate, fat and protein metabolism. It has been known for some time that testosterone has a major influence on body fat composition and muscle mass in the male. Testosterone deficiency is associated with an increased fat mass (in particular central adiposity), reduced insulin sensitivity, impaired glucose tolerance, elevated triglycerides and cholesterol and low HDL-cholesterol. All these factors are found in the metabolic syndrome (MetS) and type 2 diabetes, contributing to cardiovascular risk. Clinical trials demonstrate that testosterone replacement therapy improves the insulin resistance found in these conditions as well as glycaemic control and also reduces body fat mass, in particular truncal adiposity, cholesterol and triglycerides. The mechanisms by which testosterone acts on pathways to control metabolism are not fully clear. There is, however, an increasing body of evidence from animal, cell and clinical studies that testosterone at the molecular level controls the expression of important regulatory proteins involved in glycolysis, glycogen synthesis and lipid and cholesterol metabolism. The effects of testosterone differ in the major tissues involved in insulin action, which include liver, muscle and fat, suggesting a complex regulatory influence on metabolism. The cumulative effects of testosterone on these biochemical pathways would account for the overall benefit on insulin sensitivity observed in clinical trials. This review discusses the current knowledge of the metabolic actions of testosterone and how testosterone deficiency contributes to the clinical disease states of obesity, MetS and type 2 diabetes and the role of testosterone replacement.

The prevalence and predictors of androgen deficiency in Taiwanese men with type 2 diabetes

OBJECTIVE

To evaluate the prevalence and predictors of androgen deficiency (AD) in Taiwanese men with type 2 diabetes mellitus (T2DM).

METHODS

A recent hospital-based series of Western populations showed that 30%-50% of men with T2DM have low testosterone, and AD links to DM and obesity bidirectionally. However, data of AD from other ethnicities with character of less obesity are rarely reported. AD was defined as having a total testosterone level less than 300 ng/dL. The clinical variables and diabetes-associated complications of the risk of AD were evaluated.

RESULTS

Of 766 consecutive subjects (mean age 62.2 years, mean body mass index [BMI] 26.0) attending out-patient diabetic clinics, 32.5% have AD. The AD group was older, had higher BMI, waist circumference, higher proportion of metabolic syndrome and stroke, higher levels of triglyceride, high sensitivity C-reactive protein (hsCRP), uric acid, and lower levels of total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) than the normal testosterone group. After age adjustment, AD was positively associated with metabolic syndrome (odds ratio [OR] = 2.142), serum high sensitivity C-reactive protein (OR = 1.120), uric acid (OR = 1.118), BMI (OR = 1.083), waist circumference (OR = 1.038), triglyceride (OR = 1.028), and inversely associated with serum low-density lipoprotein (OR = 0.931) and high-density lipoprotein (OR = 0.826) in logistic regression analysis. There were no significant differences in retinopathy, neuropathy, nephropathy, or coronary artery disease between patients with or without AD.

CONCLUSION

One third of Taiwanese men with T2DM have AD. The major predictors of AD are linked to obesity, which is a potentially modifiable risk factor, and may represent an important avenue for intervention.

Total testosterone levels, metabolic parameters, cardiac remodeling and exercise capacity in coronary artery disease patients with different stages of glucose tolerance

OBJECTIVE AND METHODS

The correlation between total testosterone levels, exercise capacity, and metabolic and echocardiographic parameters was studied in 1097 male subjects with coronary artery disease (CAD) and different stages of glucose tolerance.

RESULTS

Testosterone level was the lowest among diabetics as compared to prediabetics or controls (P < 0.001). Total and abdominal adiposity were the highest in the subjects with the lowest testosterone. Independent of adiposity, fasting glucose, insulin, and leptin were higher (P < 0.03 to < 0.001) among diabetic and control groups in the lowest, and HbA1c values (P < 0.001) higher among diabetics in the lowest, than in the highest testosterone tertile. Controls and prediabetic subjects with the lowest testosterone levels had the lowest HDL-cholesterol levels, and controls also the highest triglycerides. An association between low testosterone level and low maximal exercise capacity was observed in diabetics (P < 0.001) and controls (P < 0.03). Independent of adiposity and metabolic parameters, low testosterone levels were associated with the highest septal wall thickness (P < 0.03) among diabetics.

CONCLUSION

A negative correlation between low testosterone and dysmetabolic features was observed. Independent of metabolic status, low plasma testosterone seems to be an indicator of impaired maximal exercise capacity and cardiac hypertrophy among CAD patients with type II diabetes.

Insulin directly regulates steroidogenesis via induction of the orphan nuclear receptor DAX-1 in testicular Leydig cells

Testosterone level is low in insulin-resistant type 2 diabetes. Whether this is due to negative effects of high level of insulin on the testes caused by insulin resistance has not been studied in detail. In this study, we found that insulin directly binds to insulin receptors in Leydig cell membranes and activates phospho-insulin receptor-β (phospho-IR-β), phospho-IRS1, and phospho-AKT, leading to up-regulation of DAX-1 (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1) gene expression in the MA-10 mouse Leydig cell line. Insulin also inhibits cAMP-induced and liver receptor homolog-1 (LRH-1)-induced steroidogenic enzyme gene expression and steroidogenesis. In contrast, knockdown of DAX-1 reversed insulin-mediated inhibition of steroidogenesis. Whether insulin directly represses steroidogenesis through regulation of steroidogenic enzyme gene expression was assessed in insulin-injected mouse models and high fat diet-induced obesity. In insulin-injected mouse models, insulin receptor signal pathway was activated and subsequently inhibited steroidogenesis via induction of DAX-1 without significant change of luteinizing hormone or FSH levels. Likewise, the levels of steroidogenic enzyme gene expression and steroidogenesis were low, but interestingly, the level of DAX-1 was high in the testes of high fat diet-fed mice. These results represent a novel regulatory mechanism of steroidogenesis in Leydig cells. Insulin-mediated induction of DAX-1 in Leydig cells of testis may be a key regulatory step of serum sex hormone level in insulin-resistant states.