Plasma Metabonomics in Insulin-Resistant Hypogonadic Patients Induced by Testosterone Treatment

Abstract

Hypogonadic subjects with insulin resistance (IR) showed different metabonomic profiles compared to normo-insulinemic subjects (IS). Testosterone replacement therapy (TRT) may have a different impact on the metabolisms of those with the presence or absence of insulin resistance. We evaluated the changes in the metabolism of IR hypogonadic patients before and after 60 days of TRT. The metabonomic plasma profiles from 20 IR hypogonadal patients were recorded using ultra-high-performance liquid chromatography (UHPLC) and high-resolution mass spectrometry (HRMS). Plasma metabolites, before and after 60 days of TRT, were compared. In hypogonadic patients, carnosine, which is important for improving performance during exercise, increased. Conversely, proline and lysine—amino acids involved in the synthesis of collagen—reduced. Triglycerides decreased and fatty acids (FFAs) increased in the blood as a consequence of reduced FFA β-oxidation. Glycolysis slightly improved, while the Krebs cycle was not activated. Gluconeogenesis (which is the main energy source for hypogonadal IR before TRT) stopped after treatment. As a consequence, lactate and acetyl CoA increased significantly. Both lactate and acetyl CoA were metabolized into ketone bodies which increased greatly, also due to leucine/isoleucine degradation. Ketone bodies were derived predominantly from acetyl CoA because the reaction of acetyl CoA into ketone bodies is catalyzed by mtHMGCoA synthase. This enzyme is inhibited by insulin, which is absent in IR patients but overexpressed following testosterone administration. Ketosis is an alternative route for energy supply and provides the same metabolic effects as insulin but at the metabolic or primitive control level, which bypasses the complex signaling pathway of insulin. After treatment, the hypogonadic patients showed clinical symptoms related to ketonuria. They presented similarly to those following a ketogenic diet, the so-called ‘keto flu’. This must be taken into account before the administration of TRT to hypogonadic patients.

On the Need to Distinguish between Insulin-Normal and Insulin-Resistant Patients in Testosterone Therapy

“…Finally, higher concentrations of proline and lysine were also recorded in both IS and IR, suggesting a positive influence of testosterone on the synthesis of collagen fibers, independently of the presence or absence of insulin. Reduced bone loss and excretion of bone-degradation parameters, such as hydroxyproline, were also recorded [ 54 ], in agreement with Tenover [ 69 ] and Wang et al [ 70 ].…”

“…Upon the administration of TRT for three months, testosterone levels were restored in both IS and IR hypogonadal patients [ 53 , 54 ], but in IR insulin was slightly reduced (decreasing from 17 to 15 µU/mL), in agreement with Kapoor [ 23 ]. Since synergic and/or antagonistic action between testosterone and insulin exists [ 55 , 56 ], it is not surprising that this partial insulin reduction can limit the total restoration of all metabolisms, except for those in muscle and adipose tissue, which were shown to benefit.…”

“…Interestingly, in both IS and IR, after TRT there were significant increases in lactate and acetyl-CoA production ( Figure 4 ), which were much (ten times) higher in IR [ 53 , 54 ].…”

“…Consequently, the rate of conversion of pyruvate to lactate is decreased and pyruvate is converted into acetyl-CoA by PDH enzymes (see below), commonly downregulated by insulin [ 63 ]. Finally, in IR the degradation of leucine/isoleucine also contributes to increase in acetyl-CoA [ 54 ], these being two well-known ketogenic amino acids [ 64 , 65 ]. Since leucine/isoleucine and valine account for nearly 35% of the essential amino acids in muscle proteins, after TRT, a higher protein catabolism of skeletal proteins occurred, causing a decrease in muscle mass.…”

“…In IR, a higher protein catabolism of skeletal proteins was recorded after TRT [ 54 ], causing a decrease in muscle mass. A recent metabolome profiling study revealed a correlation between BCAA and insulin resistance [ 40 , 46 ], which remains after TRT.…”