Effects of Testosterone Undecanoate vs Placebo on Intrahepatic Fat Content in Overweight/Obese Men With T2DM or Prediabetes and Hypogonadism

Background The epidemics of obesity, metabolic syndrome, type 2 diabetes, and atherosclerosis are increasing worldwide. Non-alcoholic fatty liver disease (NAFLD), for a long time unnoted in the metabolic field, is becoming recognized as a condition possibly involved in the pathogenesis of these diseases. Support for this hypothesis emerges from studies revealing that NAFLD precedes the manifestation of the metabolic derangements. NAFLD includes the whole spectrum from non-evolutive simple steatosis to progressive non-alcoholic steatohepatitis (NASH) with/without cirrhosis and hepatocellular carcinoma in individuals without relevant alcohol consumption. NAFLD is a relevant issue in public health owing to its' epidemiologic burden. It represents the most common chronic liver disease in the general population and is expected to increase in the future as a result of an ageing population, the improving control of other major causes of chronic liver disease and the epidemics of obesity and diabetes. The prevalence of NAFLD varies according to age, gender and ethnicity. In the general population, the prevalence of NAFLD is about 25% and the incidence is of two new cases/100 people/year. 2-3% of individuals in the general population will suffer from NASH. Furthermore, up to 15-20% of patients with NASH may develop cirrhosis and 30-40%of these patients who develop cirrhosis may suffer from liver-related mortality. NAFLD is tightly associated with the metabolic syndrome. The metabolic syndrome is a condition characterized by a cluster of alterations including glucose intolerance/ insulin resistance, abdominal obesity, atherogenic dyslipidemia (low concentrations of high density lipoprotein- cholesterol and high concentrations of triglycerides), elevated blood pressure, a proinflammatory and a prothrombotic state. It increases morbidity and mortality, especially due to cardiovascular disease. The prevailing hypothesis for NAFLD pathogenesis is the 'two-hit' model, with insulin resistance and hyperinsulinemia playing essential roles. Insulin resistance and hyperinsulinemia have a plethora of effects on hepatic lipid metabolism and can lead to accumulation of excess triglycerides in hepatocytes. The progression to NASH entails a 'second hit', which is believed to be due to oxidative stress, upregulation of inflammatory mediators, and dysregulated apoptosis, resulting in inflammation (producing NASH) and fibrosis. Currently, the only accepted treatment for NAFLD regardless of stage is lifestyle modifications. These include weight loss by a combination of decreased caloric intake and increased physical activity.

Study rationale Many patients worldwide are suffering from type 2 diabetes with steeply rising numbers predicted for the next decades. Although much progress can be seen in the field of diabetic research and new treatment modalities, new approaches have to be found to cure the disease and underlying risk factors. As men and women show sex specific differences especially in risk factors of T2DM, a sex- and gender-sensitive approach might be considered. Sex hormones might play an important role in the development and possibly the treatment of T2DM. In women higher but in men lower than normal testosterone concentrations predispose for a higher diabetes risk making evident that sex hormones and sex hormone equilibrium are relevant in disease progression. Especially in men low testosterone levels have deteriorating effects on glucose levels, which is aggravated in obesity as aromatization of testosterone to estrogen is enhanced. Due to this mechanism changes in energy homeostasis are reported which lead to changes in lipid accumulation, as described for visceral obesity. Testosterone deficiency is related to increases of visceral fat accumulation. Furthermore testosterone deficiency is associated with the development of non alcoholic fatty liver disease (NAFLD), a well known risk factor for progression of metabolic syndrome (MEtSy), T2DM and cardiovascular disease. Thus, testosterone replacement might be a successful way in hypogonadal men to treat obesity and counteract the further progression of MEtSy, T2DM or cardiovascular disease mainly driven by visceral fat accumulation and NAFLD and are able to improve quality of life.

Testosterone and changes in metabolism:

Whether low testosterone levels have direct effects on hyperglycaemia or testosterone deficiency is caused by chronic diseases such as type 2 diabetes is not yet fully understood and needs further clarification.

Studies are showing that the link between hypogonadism and the metabolic syndrome is bidirectional. On the one hand MetSy and obesity are associated with a higher risk of hypogonadism in the future but on the other hand low testosterone levels and SHBG levels are strong predictors for the development of MetSy and T2DM. It is further hypothesized that hypoandrogenism is an early marker for disturbances in glucose metabolism. Many studies proved that low testosterone levels may aggravate hyperglycaemia and also may deteriorate other metabolic parameters such as insulin levels and sensitivity, lipid levels, hepatic, myocardial and visceral fat content or body composition in general. Just recently the ADA recommends to test for testosterone deficiency (morning testosterone levels) in all men with T2DM with symptoms or signs of hypogonadism, which are decreased sexual desire or erectile dysfunction.

Treatment in asymptomatic men is controversial. Supplementation of testosterone in diabetic men with hypogonadism was reported to increase insulin sensitivity and to significantly reduce HbA1c, which was also reported in a long time observational study including men with T2DM with an amelioration of glycemic control as well as other cardiovascular and cardiometabolic parameters. Furthermore, total and LDL cholesterol, as well as lipoprotein a were lowered, and body composition, libido, and sexual function improved, whereas frequencies of adverse events (AEs) or serious AEs between groups were comparable after 6 months of transdermal testosterone application. These results were corroborated by a systematic review including five RCTs with 350 diabetic hypogonadal men showing improvements in fasting glucose, fasting insulin, HbA1c and triglyceride levels. In a recent study depression was found to have confounding effects with alleviated success in reduction in waist circumference, weight, and body mass index as well as improvements in glycaemic control in men with psychiatric disorders. Testosterone is an important regulator of central and peripheral adipose tissue and shows many inhibitory effects such as triglyceride uptake in fat tissue or lipoprotein lipase activity, as well as a higher lipolytic activity triggered by β-adrenergic receptors. An RCT found that in men with hypogonadism subcutaneous fat mass decreases, lean mass and insulin sensitivity increase and the expression of insulin signaling genes is upregulated after testosterone treatment. Furthermore, inflammatory parameters as well as FFA decrease after testosterone treatment. Interestingly in this study a decrease in hepatic lipids in the treatment group was found, which was not significant in a 24 weeks treatment period. However, treatment groups were inhomogenous regarding baseline hepatic lipid content, the lipid content was relatively low for a collective of subjects with T2DM and the treatment period was relatively short. Another recent RCT found significant reductions in HOMA-IR, HbA1c by 0.94 +- 0.88% and an increase in flow-mediated dilatation, which indicates improved endothelial function in a hypogonadal male population with obesity and diabetes.

Testosterone and cardiovascular risk:

The influence of testosterone on cardiovascular risk factors is not well investigated as prospective data are widely missing but evidence shows that testosterone application in men does not increase cardiovascular risk. Furthermore androgen deficiency is associated with a higher risk in cardiovascular mortality. Recent epidemiological data suspect testosterone replacement therapy to increase cardiovascular risk. However, FDA experts find that data is insufficient to make clear suggestions and that there is a need for clinical trials assessing safety of testosterone replacement in people at high risk for cardiovascular risk, like older men, men with T2DM or obesity. After this FDA statement a retrospectively assessed observational study with over 80000 male veterans with documented low total testosterone levels was published reporting a reduction of all cause mortality, myocardial infarction and stroke in men with testosterone replacement therapy. A reduction of MACE was also reported in a further study in male subjects with low testosterone levels substituted to normal levels compared to those with persistent low levels. Men with high testosterone levels had similar MACE risk but a trend for higher stroke risk.

Especially in an obese population with T2DM and hypogonadism the mortality and morbidity caused by coronary artery disease is expected to be high, as CAD is the leading cause of death in subjects with T2DM and often progresses asymptomatic until an infarction or sudden cardiac death occur. Recent conducted MPI (=myocardial perfusion imaging) studies in T2DM patients have shown higher prevalence of abnormal MPI, with more extensive ischemia, compared with subjects without T2DM. The DIAD trial did not show any benefit in prevention of cardiac events comparing MPI screening at regular intervals with a non-screened diabetic population up to nearly 5 years. However, it remains uncertain whether asymptomatic patients with type 2 diabetes benefit from revascularization after the identification of inducible ischemia, as was suggested in a prior retrospective database analysis and a small randomized pilot study. Currently in obese men with hypogonadism and T2DM it is largely unknown whether testosterone replacement has any effects on cardiac perfusion. According to appropriate use criteria (AUC) for the detection a risk assessment of stable ischemic heart disease MPI is a potential diagnostic method to detect CHD at stages of high global coronary artery disease risk [42]. According to NCEP ATP III criteria, the recommended tool of the AUC, the patient collective of TEST2FUNC featuring male subjects with hypogonadism, diabetes mellitus, overweight/obesity, hypertension and dyslipidemia are at high risk for coronary heart disease, as diabetes is seen as a CHD risk equivalent and confers to a high risk of new CHD within 10 years.

Study objective:

This study wants to investigate the direct effects of intramuscular testosterone replacement versus placebo in changing the intrahepatic fat content, myocardial fat content, visceral and abdominal fat content as well as pancreatic fat content of poorly controlled men suffering from T2DM and secondary hypogonadism. Furthermore, the effects of testosterone on glycaemic control and cardiovascular safety will be investigated. The effect of testosterone on cardiac perfusion will be tested in this high risk collective.

For studying long-term effects, an open-label extension of the study by an additional 2 years is intended.