Growth hormone and insulin-like growth factor-I counteracts established steroid catabolism in rats by effects on hepatic amino-N degradation

A potent liver-mediated mechanism for loss of muscle mass during androgen deprivation therapy

CONTEXT

Androgen deprivation therapy (ADT) in prostate cancer results in muscular atrophy, due to loss of the anabolic actions of testosterone. Recently, we discovered that testosterone acts on the hepatic urea cycle to reduce amino acid nitrogen elimination. We now hypothesize that ADT enhances protein oxidative losses by increasing hepatic urea production, resulting in muscle catabolism. We also investigated whether progressive resistance training (PRT) can offset ADT-induced changes in protein metabolism.

OBJECTIVE

To investigate the effect of ADT on whole-body protein metabolism and hepatic urea production with and without a home-based PRT program.

DESIGN

A randomized controlled trial.

PATIENTS AND INTERVENTION

Twenty-four prostate cancer patients were studied before and after 6 weeks of ADT. Patients were randomized into either usual care (UC) (n = 11) or PRT (n = 13) starting immediately after ADT.

MAIN OUTCOME MEASURES

The rate of hepatic urea production was measured by the urea turnover technique using 15N2-urea. Whole-body leucine turnover was measured, and leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, was calculated.

RESULTS

ADT resulted in a significant mean increase in hepatic urea production (from 427.6 ± 18.8 to 486.5 ± 21.3; P < 0.01) regardless of the exercise intervention. Net protein loss, as measured by Lox/Lra, increased by 12.6 ± 4.9% (P < 0.05). PRT preserved lean body mass without affecting hepatic urea production.

CONCLUSION

As early as 6 weeks after initiation of ADT, the suppression of testosterone increases protein loss through elevated hepatic urea production. Short-term PRT was unable to offset changes in protein metabolism during a state of profound testosterone deficiency.

Hepatic actions of androgens in the regulation of metabolism

PURPOSE OF REVIEW

The purpose of this review is to summarize recent findings on hepatic actions of androgens in the regulation of protein, lipid and glucose metabolism. The rationale for liver-targeted testosterone use will be provided.

RECENT FINDINGS

Liver-targeted testosterone administration, via the oral route, induces protein anabolic effect by reducing the rate of protein oxidation to a similar extent to that of systemic testosterone administration. Recent evidence indicates that testosterone exerts whole-body anabolic effect through inhibition of nitrogen loss via the hepatic urea cycle. Several hepatic effects of androgens, particularly on glucose metabolism, are direct and take place before any changes in body composition occur. This includes an increase in insulin secretion and sensitivity, and reduction in hepatic glucose output by testosterone. Furthermore, lack of testosterone in the liver exacerbates diet-induced impairment in glucose metabolism. In the liver, androgens induce the full spectrum of metabolic changes through interaction with growth hormone or aromatization to estradiol.

SUMMARY

Liver-targeted testosterone therapy may open up a new approach to achieve whole-body anabolism without systemic side-effects. Aromatizable androgens may be superior to nonaromatizable androgens in inducing a complex spectrum of direct, estrogen-mediated and other hormone-mediated effects of androgens.

Testosterone prevents protein loss via the hepatic urea cycle in human

CONTEXT

The urea cycle is a rate-limiting step for amino acid nitrogen elimination. The rate of urea synthesis is a true indicator of whole-body protein catabolism. Testosterone reduces protein and nitrogen loss. The effect of testosterone on hepatic urea synthesis in humans has not been studied.

OBJECTIVE

To determine whether testosterone reduces hepatic urea production.

DESIGN

An open-label study.

PATIENTS AND INTERVENTION

Eight hypogonadal men were studied at baseline, and after two weeks of transdermal testosterone replacement (Testogel, 100 mg/day).

MAIN OUTCOMES MEASURES

The rate of hepatic urea synthesis was measured by the urea turnover technique using stable isotope methodology, with ¹⁵N₂-urea as tracer. Whole-body leucine turnover was measured, from which leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, were calculated.

RESULTS

Testosterone administration significantly reduced the rate of hepatic urea production (from 544.4 ± 71.8 to 431.7 ± 68.3 µmol/min; P < 0.01), which was paralleled by a significant reduction in serum urea concentration. Testosterone treatment significantly reduced net protein loss, as measured by percent Lox/LRa, by 19.3 ± 5.8% (P < 0.05). There was a positive association between Lox and hepatic urea production at baseline (r² = 0.60, P < 0.05) and after testosterone administration (r² = 0.59, P < 0.05).

CONCLUSION

Testosterone replacement reduces protein loss and hepatic urea synthesis. We conclude that testosterone regulates whole-body protein metabolism by suppressing the urea cycle.

Growth hormone and growth hormone secretagogue effects on nitrogen balance and urea synthesis in steroid treated rats

OBJECTIVES

Growth hormone (GH) reduces the catabolic side effects of steroid treatment via effects on the amino-nitrogen metabolism. Ipamorelin is a synthetic peptide with GH releasing properties. We wished to study the metabolic effects of Ipamorelin and GH on selected hepatic measures of alpha-amino-nitrogen conversion during steroid-induced catabolism.

DESIGN

Five groups of rats were included: (1) free-fed controls (2) pair-fed controls (3) prednisolone (delcortol, 4 mg x kg(-1) x day(-1)) (4) prednisolone and GH (1 mg x kg(-1) x day(-1)) (5) prednisolone and Ipamorelin (0.5 mg x kg(-1) x day(-1)). After seven days the hepatic capacity of urea-N synthesis (CUNS) was determined in parallel with measurements of liver mRNA levels of urea cycle enzymes, whole-body N-balance, and N-contents of various organs.

RESULTS

Compared to pair-fed controls, prednisolone increased CUNS (p<0.01) as well as the expression of urea cycle genes (p<0.01), and decreased N-balance (p<0.01) as well as organ N-contents (p<0.05). Compared to prednisolone treated animals, co-administration of GH reduced CUNS by 33% (p<0.01), normalized urea cycle gene expression, improved N-balance 2.5-fold, and normalized or improved organ N-contents. In prednisolone treated rats Ipamorelin reduced CUNS by 20% (p<0.05), decreased the expression of urea cycle enzymes, neutralised N-balance, and normalized or improved organ N-contents.

CONCLUSION

Accelerated nitrogen wasting in the liver and other organs caused by prednisolone treatment was counteracted by treatment with either GH or its secretagogue Ipamorelin, though at the doses given less efficiently by the latter. This functional study of animals confirms that the GH secretagogue exerts GH related metabolic effects and may be useful in the treatment of steroid-induced catabolism.

Bovine Somatotropin Increases Hepatic Phosphoenolpyruvate Carboxykinase mRNA in Lactating Dairy Cows,

Somatotropin (ST) increases milk production and through coordinated changes in hepatic glucose synthesis and amino acid metabolism in dairy cows. The objective of this study was to determine the effects of ST on hepatic mRNA expression for phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC), enzymes that are critical to the synthesis of glucose in liver and hepatic mRNA expression for carbamylphosphate synthetase I (CPS-I), argininosuccinate synthetase (AS), and ornithine transcarbamylase (OTC), critical enzymes of the urea cycle. Eighteen cows were randomly allocated to 2 treatment groups and received either recombinant bovine ST (Posilac; Monsanto, St. Louis, MO) or saline injections at 14-d intervals during a 42-d period. Expression of mRNA was determined using Northern blot analysis. Nuclei, isolated from liver biopsy samples, were used to determine effects of ST on transcription rate of PEPCK. Milk production was increased with ST (37.3 vs. 35.1+/-0.6 kg/ d). Plasma NEFA was increased with ST (299 vs. 156+/-34 microM). There were no differences in the expression of CPS-I, AS, and OTC mRNA with ST. Expression of PEPCK and IGF-I mRNA were increased with ST but PC mRNA was unchanged. The data indicate increased PEPCK mRNA in cows given ST and indicates a greater capacity for gluconeogenesis from gluconeogenic precursors that form oxaloacetate. The effects of ST to elevate PEPCK mRNA expression require chronic administration and involve increased transcription of the PEPCK gene.

A potent human C5a receptor antagonist protects against disease pathology in a rat model of inflammatory bowel disease

The complement system is implicated in the pathogenesis of human inflammatory bowel disease, but the specific role of C5a has never been examined. We have compared the efficacy of an orally active human C5a receptor antagonist (AcPhe[Orn-Pro-D-cyclohexylalanine-Trp-Arg]), prednisolone, and infliximab against trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. The drugs were administered either 2 days before or 24 h after TNBS instillation, and rats were then examined after 8 days. Drug-free colitis control rats showed severe disease pathology with significant mortality (39%). Rats pre or posttreated with the C5a antagonist (10 mg/kg/day peroral, 0.3 mg/kg/day s.c.) had reduced mortality and significantly improved macroscopic scores, colon edema, colon myeloperoxidase levels, reduced concentrations of TNF-alpha levels in the colon and serum, and had greater food intake resulting in greater weight gains than colitis-only rats. Rats pretreated with prednisolone (1 mg/kg/day s.c.) displayed significant improvement in parameters measured, but posttreatment was ineffective. Single dose pretreatment with the TNF-alpha inhibitor infliximab (3 mg/kg i.v.) also had significant improvements in the parameters measured. Rats pretreated with a combination of the C5a antagonist and prednisolone showed no greater improvements than either drug alone. These findings suggest a central role for complement, particularly C5a, in the pathology of TNBS-induced colitis in rats, indicating a possible therapeutic role for C5a antagonists in inflammatory bowel disease.