Inhibition of spontaneous testicular Leydig cell tumor development in F-344 rats by dehydroepiandrosterone

Methionine restriction delays aging-related urogenital diseases in male Fischer 344 rats

Dietary methionine restriction (MR) has been found to enhance longevity across many species. We hypothesized that MR might enhance longevity in part by delaying or inhibiting age-related disease processes. To this end, male Fischer 344 rats were fed control (CF, 0.86% methionine) or MR (0.17% methionine) diets throughout their life until sacrifice at approximately 30 months of age, and histopathology was performed to identify the incidence and progression of two important aging-related pathologies, namely, chronic progressive nephropathy (CPN) and testicular tumorigenesis. Although kidney pathology was observed in 87% CF rats and CPN in 62% of CF animals, no evidence of kidney disease was observed in MR rats. Consistent with the absence of renal pathology, urinary albumin levels were lower in the MR group compared to controls throughout the study, with over a six-fold difference between the groups at 30 months of age. Biomarkers associated with renal disease, namely, clusterin, cystatin C, and β-2 microglobulin, were reduced following 18 months of MR. A reduction in testicular tumor incidence from 88% in CF to 22% in MR rats was also observed. These results suggest that MR may lead to metabolic and cellular changes providing protection against age-related diseases.

Carcinogenicity of Monochloro-1,2-Propanediol (α-Chlorohydrin, 3-MCPD)

3-Monochloro-1,2-propanediol (3-MCPD) is a by-product found in trace amounts, generally less than 1 mg/kg (<1 ppm), in hydrolyzed vegetable protein produced through acid hydrolysis. In a chronic study with F344 rats, high doses of 3-MCPD produced benign renal tumors in both sexes and Leydig-cell and mammary tumors in males. 3-MCPD is genotoxic in vitro, but there is no evidence of genotoxicity in vivo. There is some question about the mechanism responsible for the carcinogenicity of 3-MCPD in certain species. Here we present a critical review of the toxicological, metabolic, and mechanistic data on 3-MCPD. On the basis of this review, the tumors reported in F344 rats are concluded to have developed as a result of nongenotoxic mechanisms and are considered not to be relevant to humans exposed to trace amounts of 3-MCPD. This conclusion was based on the lack of carcinogenicity of 3-MCPD in mice or Sprague-Dawley rats; the benign nature of the tumors involved; the dependence of the Leydig-cell and mammary tumors on species-and strain-dependent mechanisms involving chronic changes in hormone balance; the association of the renal tumors with chronic nephropathy and nephrotoxicity; and differences between bacterial and mammalian systems in the metabolism of 3-MCPD that likely account for its genotoxic activity in certain in vitro test systems. At trace levels in foods, 3 MCPD is considered not to pose a carcinogenic risk to humans.

Relationship between serum DHEAS and oxidative stress levels of body mass index in healthy postmenopausal women

OBJECTIVES

Menopause is a natural step in the process of aging. Postmenopausal women have decreased levels of antioxidants and increased oxidative stress, the latter of which plays an important role in atherogenesis. The aim of the present study was to evaluate the relationship of the body mass index (BMI) with serum catalase activity, malondialdehyde (MDA), and dehydroepiandrosterone sulfate (DHEAS) levels in healthy postmenopausal women and estimate whether the MDA/DHEAS ratio is a possible marker of oxidative stress for determining cardiovascular risk in these women.

METHODS

We investigated serum catalase activity, MDA, and DHEAS levels, parity history, age, and BMI in 96 healthy postmenopausal women aged 50-82 years. The serum MDA levels and catalase activity were measured spectrophotometrically. The serum DHEAS levels were measured using an enzyme-linked immunosorbent assay. The ratio percentage of the serum DHEAS levels to serum MDA levels was designated as a biomarker for oxidative stress.

RESULTS

The mean BMI of the patients was 31.72 ± 6.16 kg/m(2) (range = 20.5-47.94). The MDA/DHEAS ratio was significantly decreased in patients with a BMI over 30 compared to that of patients with a BMI between 25 and 30 (P = 0.025). Moreover, BMI was positively correlated with serum DHEAS levels (r = 0.285, P < 0.01) and negatively correlated with the MDA/DHEAS ratio (r = -0.241, P < 0.05) in postmenopausal women. Furthermore, BMI was observed to be a potential predictor of the MDA/DHEAS ratio based on covariance analysis (P = 0.039).

CONCLUSIONS

Our results indicate that healthy, obese, postmenopausal women have a decreased MDA/DHEAS ratio. Additionally, BMI was observed to be a potential predictor of the MDA/DHEAS ratio.

Antiviral effect of dehydroepiandrosterone on Japanese encephalitis virus infection

Japanese encephalitis virus (JEV), which causes neurological disorders, completes its life cycle and triggers apoptotic cell death in infected cells. Dehydroepiandrosterone (DHEA), an adrenal-derived steroid, has been implicated in protection against neurotoxicity and protection of animals from viral-induced encephalitis, resulting in an increased survival rate of the animals. Currently, the mechanisms underlying the beneficial effects of DHEA against the virus are largely unknown. In this study, DHEA suppression of JEV replication and virus-induced apoptosis in murine neuroblastoma (N18) cells was investigated. It was found that DHEA suppressed JEV-induced cytopathic effects, JEV-induced apoptotic cell death and JEV propagation in a concentration-dependent manner. Antiviral activity was more efficient in cultures treated with DHEA immediately after viral adsorption compared with that in cultures receiving delayed administration after adsorption or transient exposure before adsorption. JEV-induced cytotoxicity was accompanied by the inactivation of extracellular signal-regulated protein kinase (ERK). Inactivation of ERK by JEV infection was reversed by DHEA. When cells were treated with the ERK inhibitor U0126, DHEA lost its antiviral effect. Activation of ERK by anisomycin mimicked the action of DHEA in suppressing JEV-induced cytotoxicity. DHEA-related compounds, such as its sulfate ester (DHEAS) and pregnenolone, were unable to suppress JEV-induced cytotoxicity and ERK inactivation. The hormone-receptor antagonists ICI 182780 and flutamide failed to abrogate the antiviral effect of DHEA. These findings suggest that the antiviral effect of DHEA is not linked directly to the genomic steroid-receptor pathways and suggest that the signalling pathways of ERK play a role in the antiviral action of DHEA.

High-performance liquid chromatographic analysis of dehydroepiandrosterone

Qualitative and quantitative analysis of dehydroepiandrosterone and its conjugates in biological matrices and establishment of their relationships with physiological functions is a very active field. This review article discusses methods of separation and quantification of dehydroepiandrosterone and its conjugates using high-performance liquid chromatographic techniques.

Effects of ubiquinone and mevalonic acid on hepatic peroxisomal enzymes induced by dehydroepiandrosterone

The adrenal steroid, dehydroepiandrosterone (DHEA) has been identified as a peroxisome proliferator. We examined the effects of the cellular antioxidant ubiquinone and its precursor mevalonic acid on the induction of enzymes associated with DHEA-mediated peroxisome proliferation in male F-344 rats. Upon treatment with DHEA (300 mg/kg orally for 14 days), there was a significant increase in hepatic activities of peroxisomal beta-oxidation (3 fold), 3-ketoacyl-CoA thiolase (4 fold) and catalase (1.8 fold). Co-administration of either mevalonic acid (100 mg/kg intraperitoneally) or ubiquinone (50 mg/kg orally) with DHEA significantly attenuated the DHEA-mediated induction of these enzymes. However, neither ubiquinone nor mevalonic acid alone significantly altered peroxisomal enzyme activities in rat liver. These data suggest that exogenous administration of ubiquinone or mevalonic acid can modulate the induction of the enzymes involved in peroxisome proliferation.

Incidence of pancreatic and testicular tumors in rats treated with ciprofibrate, a peroxisome proliferator

It is hypothesized that hepatic tumors in rats induced by peroxisome proliferators is dependent on peroxisome proliferative effect of these compounds and the resulting oxidative stress. However, it is argued that since these compounds also induce tumors in pancreas and testes, the two organs in which there is no proliferation of peroxisomes, the carcinogenic effect is unlikely to be related to oxidative stress. To clarify this controversy we have systematically analyzed the incidence of pancreatic acinar cell foci and nodules, and testicular Leydig cell tumors in ciprofibrate treated and control rats. In animals treated with 0.025% ciprofibrate for 22 months the incidence of Leydig cell tumors and acinar cell lesions was 100% and 66%, respectively. In age-matched controls the incidence of testicular and pancreatic lesions was 93% and 66%, respectively. These findings clearly demonstrate that the Leydig cell tumors and pancreatic lesions develop spontaneously and are not induced by ciprofibrate.

Ergosteroids: induction of thermogenic enzymes in liver of rats treated with steroids derived from dehydroepiandrosterone

Dehydroepiandrosterone (DHEA), an intermediate in the biosynthesis of testosterone and estrogens, exerts several physiological effects not involving the sex hormones. When fed to rats it induces the thermogenic enzymes mitochondrial sn-glycerol-3-phosphate dehydrogenase and cytosolic malic enzyme in their livers. Animals and humans, and their excised tissues, are known to hydroxylate DHEA at several positions and to interconvert 7 alpha-hydroxy-DHEA, 7 beta-hydroxy-DHEA, 7-oxo-DHEA, and the corresponding derivatives of androst-5-enediol. We report here that these 7-oxygenated derivatives are active inducers of these thermogenic enzymes in rats and that the 7-oxo derivatives are more active than the parent steroids. We postulate that the 7 alpha-hydroxy and 7-oxo derivatives are on a metabolic pathway from DHEA to more active steroid hormones. These 7-oxo steroids have potential as therapeutic agents because of their increased activity and because they are not convertible to either testosterone or estrogens.

Prevention of carbon tetrachloride-induced lipid peroxidation in liver microsomes from dehydroepiandrosterone-pretreated rats

Dehydroepiandrosterone (DHEA), a lipid soluble steroid, administered to rats (100 mg/kg b.wt) by a single intraperitoneal injection, increases to twice its normal level in the liver microsomes. Microsomes so enriched become resistant to lipid peroxidation induced by incubation with carbon tetrachloride in the presence of a NADPH-regenerating system: also the lipid peroxidation-dependent inactivation of glucose-6-phosphatase and gamma-glutamyl transpetidase due to the haloalkane are prevented. Noteworthy, the liver microsomal drug-metabolizing enzymes and in particular the catalytic activity of cytochrome P450IIE1, responsible for the CCl4-activation, are not impaired by the supplementation with the steroid. Consistently, in DHEA-pretreated microsomes the protein covalent binding of the trichloromethyl radical (CCl3 degrees), is similar to that of not supplemented microsomes treated with CCl4. It thus seems likely that DHEA protects liver microsomes from oxidative damage induced by carbon tetrachloride through its own antioxidant properties rather than inhibiting the metabolism of the toxin.

Comparative effects of dehydroepiandrosterone and related steroids on peroxisome proliferation in rat liver

Dehydroepiandrosterone (DHEA) is known to induce peroxisome proliferation and peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (PBE) mRNA in the rat liver. We have compared the effects of 6 intermediate metabolites of DHEA on the induction of peroxisome proliferation and PBE mRNA. Administration of epiandrosterone, etiocholanolone, androstenedione, estrone or estradiol for 2 weeks in the diet at 0.45% concentration to adult male F-344 rats failed to induce significant increases in peroxisome proliferation and PBE mRNA when compared to the parent compound DHEA. Dietary administration of 5-androstene-3 beta,17 beta-diol (ADIOL) for 2 weeks at 0.45% concentration caused an increase in PBE mRNA and peroxisome proliferation but to a lesser extent than DHEA. Following a single intragastric dose of DHEA an increase in PBE mRNA level was observed in the liver at 1 hr and continued to 16 hrs., but not with its metabolites. These results strongly suggest that DHEA or possibly another yet to be identified metabolite might be responsible for peroxisome proliferation.