Induction of peroxisomal beta-oxidation enzymes by dehydroepiandrosterone and its sulfate in primary cultures of rat hepatocytes

Involvement of endogenous testosterone in hepatic steatosis in women with polycystic ovarian syndrome

AIMS

The prevalence of nonalcoholic fatty liver disease (NAFLD) is higher in women with polycystic ovarian syndrome (PCOS) than that in healthy women. This association can be explained in part by the resistance to insulin and the prevalence of obesity, which are fueled by high androgen levels. However, there is little evidence of the involvement of endogenous testosterone in hepatic steatosis in women with PCOS. Here, we treated Sprague Dawley rats with the aromatase inhibitor, letrozole, to increase the endogenous testosterone level and to decrease the estradiol levels. We also quantified the testosterone levels in human serum specimens and HepG2 cells to investigate the effects of androgens on hepatic steatosis and liver dysfunction.

RESULTS

Twenty-nine PCOS patients and twenty healthy women were enrolled. Alanine transaminase and aspartate transaminase (AST) levels were increased in women with PCOS, and a strong correlation between testosterone and AST levels was observed. After letrozole treatment for 90 days, rats were significantly more obese, with animals developing hepatic steatosis and moderate insulin resistance. Additional experiments revealed that excess androgen inhibited the AMP-activated protein kinase alpha pathway in letrozole-treated livers and dihydrotestosterone (DHT)-treated HepG2 cells, thereby causing steatosis.

INNOVATION AND CONCLUSION

Our results show that an elevated endogenous testosterone level can induce hepatic steatosis. Decreasing the endogenous testosterone level in hepatocytes may represent a new approach in the treatment of NAFLD in PCOS patients.

Dehydroepiandrosterone reduced lipid droplet accumulation via inhibiting cell proliferation and improving mitochondrial function in primary chicken hepatocytes

Dehydroepiandrosterone (DHEA) possesses fat-reducing effect, while little information is available on whether DHEA regulates cell proliferation and mitochondrial function, which would, in turn, affect lipid droplet accumulation in the broiler. In the present study, the lipid droplet accumulation, cell proliferation, cell cycle and mitochondrial membrane potential were analysis in primary chicken hepatocytes after DHEA treated. The results showed that total area and counts of lipid droplets were significantly decreased in hepatocytes treated with DHEA. The cell viability was significantly increased, while cell proliferation was significantly inhibited in a dose dependent manner in primary chicken hepatocytes after DHEA treated. DHEA treatment significantly increased the cell population in S phase and decreased the population in G2/M in primary chicken hepatocytes. Meanwhile, the cyclin A and cyclin-dependent kinases 2 (CDK2) mRNA abundance were significantly decreased in hepatocytes after DHEA treated. No significant differences were observed in the number of mitochondria, while the mitochondrial membrane permeability and succinate dehydrogenase (SDH) activity were significantly increased in hepatocytes after DHEA treated. In conclusion, our results demonstrated that DHEA reduced lipid droplet accumulation by inhibiting hepatocytes proliferation and enhancing mitochondrial function in primary chicken hepatocytes.

Dehydroepiandrosterone sulfate and cytochrome P450 inducers alleviate fatty liver in male rats fed an orotic acid-supplemented diet

The effects of the peroxisome proliferator, dehydroepiandrosterone sulfate (DHEAS), and the typical cytochrome P450 (CYP) inducers phenobarbital (PB) and 3-methylcholanthrene (3-MC) on fatty liver were examined in rats. Treating rats with orotic acid caused marked accumulation of lipid droplets in the liver. This effect of orotic acid was almost eradicated by co-treatment with DHEAS and PB. While DHEAS or PB alone also alleviated fatty liver, treatment with 3-MC caused little effect on a reduction in lipid droplets. Histopathological examinations revealed numerous peroxisomes in the liver of rats treated with DHEAS. In addition, a significant increase in the expression on hepatic CYPs was observed in rats the fatty liver of which was attenuated. Regarding other enzymes associated with hepatic fatty acid oxidation, the expression levels of sirtuin 1, sirtuin 6, and carnitine palmitoyltransferase 1 were also upregulated most markedly by treatment with DHEAS alone. Thus, the attenuation in fatty liver observed in the present study is likely due to peroxisome proliferation and the induction of fatty acid-metabolizing enzymes by DHEAS and typical CYP inducers.

Dehydroepiandrosterone protects endothelial cells against inflammatory events induced by urban particulate matter and titanium dioxide nanoparticles

Particulate matter (PM) and nanoparticles (NPs) induce activation and dysfunction of endothelial cells characterized by inhibition of proliferation, increase of adhesion and adhesion molecules expression, increase of ROS production, and death. DHEA has shown anti-inflammatory and antioxidant properties in HUVEC activated with proinflammatory agents. We evaluated if DHEA could protect against some inflammatory events produced by PM10 and TiO2 NPs in HUVEC. Adhesion was evaluated by a coculture with U937 cells, proliferation by crystal violet staining, and oxidative stress through DCFDA and Griess reagent. PM10 and TiO2 NPs induced adhesion and oxidative stress and inhibited proliferation of HUVEC; however, when particles were added in combination with DHEA, the effects previously observed were abolished independently from the tested concentrations and the time of addition of DHEA to the cultures. These results indicate that DHEA exerts significant anti-inflammatory and antioxidative effects on the damage induced by particles in HUVEC, suggesting that DHEA could be useful to counteract the harmful effects and inflammatory diseases induced by PM and NPs.

Upregulation of fatty acyl-CoA thioesterases in the heart and skeletal muscle of rats fed a high-fat diet

In rodent models of diet-induced obesity, prolonged high-fat feeding increases the cellular uptake of fatty acids and causes lipotoxicity in the heart and skeletal muscle, where substrate overload to beta-oxidation generates mitochondrial stress. We examined the hypothesis that, because of its catalytic properties, acyl-CoA thioesterase (ACOT) would counteract these detrimental situations by modulating intracellular acyl-CoA levels. Rats were fed a low- or high-fat diet for up to 20 weeks, and the expressions of ACOT isoforms and fatty acid beta-oxidation enzymes were analyzed by western blotting. The expressions of ACOT1, ACOT2 and ACOT7 proteins in the heart and soleus muscle were significantly increased, by 2.0-7.6-fold, in rats fed the high-fat diet as compared with the low-fat diet group. These effects were accompanied by increases in carnitine palmitoyltransferase and acyl-CoA oxidase expression. However, ACOT was not induced in the extensor digitorum longus muscle or the liver. Subcellular fractionation of heart and soleus muscle homogenates confirmed expression of both the cytosolic and mitochondrial ACOT isoforms. These results underscore the functional relationship between ACOT and fatty acid oxidation, and suggest adaptive upregulation of ACOT to protect against fatty acid oversupply in the heart and skeletal muscle.

Endocrine effects of oral dehydroepiandrosterone in men with HIV infection: a prospective, randomized, double-blind, placebo-controlled trial

Dehydroepiandrosterone (DHEA) is commonly used by HIV-infected men, but its endocrine effects in this population are not well defined. We conducted an 8-week randomized, placebo-controlled trial to determine the effects of escalating doses (100-400 mg/d) of DHEA on the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes, and on a number of metabolic parameters in 69 HIV-positive men (31 in DHEA-treated group, 38 in placebo group). High-dose (250 microg) corticotropin and luteinizing hormone-releasing hormone stimulation tests were carried out in all subjects. Fifty-four subjects (26 in the DHEA-treated group and 28 in the placebo group) also underwent optional corticotropin-releasing hormone test, and 67 subjects (31 in DHEA-treated group and 36 in placebo group) underwent optional low-dose (1 microg) corticotropin stimulation test. All tests were performed at baseline and at the end of week 8. Repeated-measures analysis of variance was used to analyze the data. We observed significant increases in circulating levels of DHEA, DHEA-sulfate, free testosterone, dihydrotestosterone, androstenedione, and estrone, and a decline in the serum concentration of sex hormone-binding globulin in the DHEA-treated group but not in the placebo group (P < .001). There were no differences between the groups in other endocrine or metabolic parameters or in the results of the stimulation tests. In conclusion, oral DHEA therapy in HIV-positive men significantly increases circulating levels of DHEA and DHEA-sulfate, free testosterone, dihydrotestosterone, androstenedione, and estrone and suppresses circulating concentration of sex hormone-binding globulin. Long-term studies are needed to assess the clinical significance of these hormonal changes in subjects with HIV infection receiving oral DHEA therapy.

Dehydroepiandrosterone and human adipose tissue

OBJECTIVE

The aim of this study was to investigate whether DHEA alters the proliferation and differentiation of human sc and visceral adipose cells in primary cultures.

METHOD

Sc and omental adipose tissue was obtained from 10 female donors aged 36+/-3.6 yr with a body mass index (BMI) of 33+/-3.21 kg/m2. Stromal vascular cells were isolated and cultured using modified procedures described by Entenmann and Hauner. For the proliferation assay, stromal-vascular cells from sc and visceral adipose tissue cultures were fed with proliferation media containing 0, 25 or 100 microM DHEA for 3 days. At the end of this treatment period, two type cultures were prepared for determining their metabolic activity using the sulforhodamine B staining procedure.

RESULTS

The metabolic activity of proliferating human visceral adipose tissue was higher than sc adipose tissue. The activity of proliferating human visceral tissue cultures decreased more than the sc tissue as the level of DHEA in the cultures was increased.

CONCLUSIONS

These data suggest that DHEA predominantly influences the proliferation and differentiation of human omental adipose tissue.

Evidence for the involvement of the fatty acid and peroxisomal beta-oxidation pathways in the inhibition by dehydroepiandrosterone (DHEA) and induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benz(a)anthracene (BA) of cytochrome P4501B1 (CYP1B1) in mouse embryo fibroblasts (C3H10T1/2 cells)

Treatment of intact C3H10T1/2 cells or microsomes therefrom with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzanthracene (BA) enhanced CYP1B1 activity and CYP1B1 expression as revealed by elevations of CYP1B1-catalyzed DMBA metabolism, CYP1B1 apoprotein level and CYP1B1 gene expression. One hundred microM DHEA caused an 80-90% inhibition of cellular DMBA metabolism without inflicting cell death. Cytosolic glucose-6-phosphate dehydrogenase (G6PDH) was also inhibited in DHEA-treated cells, presumably due to the inhibition of NADP reduction. In contrast, neither DMBA metabolism nor CYP1B1 apoprotein was inhibited by DHEA in the microsomes isolated from these cells. DHEA (100 microM), TCDD (10 nM) and BA (10 microM) stimulated the activities and increased the apoprotein levels of two peroxisomal enzymes, namely, acyl CoA oxidase (ACOX) and acyl CoA hydrolase (ACH2) and also induced the expression of CYP1B1 and ACOX genes. Cytosolic fatty acyl-CoA beta-oxidation was also stimulated by DHEA, TCDD and BA. In corroboratory experiments, it was found that concomitant with the stimulation of the activity of a key enzyme regulator of fatty acid homeostasis, namely, glycerol-3-phosphate dehydrogenase (G3PDH), these agents enhanced arachidonic acid (AA) metabolism as judged by the release of [3H] from AA into the culture medium. Collectively, these data suggest that DHEA mediates the regulation of CYP1B1 and inhibits BA and TCDD-induced CYP1B1-catalyzed carcinogen (DMBA) activation in 10T1/2 cells through metabolic interactions that involve the activation of the peroxisomal and fatty acid beta-oxidation signaling pathways. These results also present evidence for the first time, for the possible peroxisomal effects of TCDD and BA which are similar to those of DHEA in this mouse embryo fibroblast cell line.

Dehydroepiandrosterone and related steroids alter 3T3-L1 preadipocyte proliferation and differentiation

The purpose of the present study was to determine if the anti-adipogenic effects of dehydroepiandrosterone (DHEA) are mediated solely by DHEA or by one or more of its downstream metabolites. In Experiment 1, preconfluent proliferating cultures of 3T3-L1 preadipocytes were incubated for either 24 or 72 h with 0, 1, 5 or 25 microM DHEA, DHEA sulfate (DHEAS), testosterone, estrone and 17beta-estradiol. Pregnenolone, a precursor of DHEA(S), was also tested at these concentrations. After 24 h of incubation, DHEAS, 17beta-estradiol and estrone at the 1 microM level stimulated preadipocyte proliferation. In contrast, DHEA and 17beta-estradiol at the 25 microM level attenuated proliferation to a greater extent than all other steroids. After 72 h of incubation, DHEA and 17beta-estradiol at the 25 microM level attenuated proliferation to a greater extent than all other steroids. In Experiment 2, post-confluent cultures of differentiating 3T3-L1 preadipocytes were incubated for 6 days with 0, 5, 30, or 60 microM levels of these steroids. Preadipocyte differentiation, as assessed by lipid content and glycerol-3-phosphate dehydrogenase activity, decreased markedly when treated with 30 and 60 microM DHEA, 17beta-estradiol, estrone and pregnenolone. In contrast, DHEAS had no impact on preadipocyte proliferation or differentiation. These results suggest that the anti-adipogenic actions of DHEA in adipose tissue may be mediated, in part, by one or more of its distal metabolites, including 17beta-estradiol.

Preventive effects of dehydroepiandrosterone acetate on the fatty liver induced by orotic acid in male rats

Preventive effects of dehydroepiandrosteone acetate (DHEA-A) and clofibrate (positive control substance) on the fatty liver induced by orotic acid (OA) were examined on the male Sprague-Dawley rats fed a high sucrose based diet containing 1% OA and this diet further mixed with 0.5% DHEA-A or 0.5% clofibrate for 2 weeks. Numerous lipid droplets were observed in the hepatocytes of the rats treated with OA alone, but not in those treated with DHEA-A or clofibrate. In comparison to the group with OA alone, the DHEA-A or clofibrate treated rats showed a larger relative liver weight (to body weight) which was accompanied by increased peroxisomes in the hepatocytes. These results indicate that DHEA-A, as well as clofibrate, may prevent OA-induced fatty liver.

Dehydroepiandrosterone attenuates preadipocyte growth in primary cultures of stromal-vascular cells

The purpose of this study was to determine whether the antiobesity actions of dehydroepiandrosterone (DHEA) are due to an influence on preadipocyte proliferation and/or differentiation in primary cultures of pig and rat stromal-vascular (SV) cells. Pig SV cells were isolated from dorsal subcutaneous adipose tissue of 7-day-old pigs. For the proliferation assays, pig SV cells were grown for 4 days in plating medium containing DHEA at 0, 15, 50, or 150 microM. For the differentiation assays, pig SV cells were grown in plating medium for 3 days and then switched to a serum-free medium containing DHEA at 0, 15, 50, or 150 microM for the next 6 days. Rat SV cells were isolated from inguinal fat pads of 5-wk-old male rats. Rat SV cells were exposed to DHEA at 0, 5, 25, or 75 microM during proliferation. For the differentiation assays, rat SV cells were grown for 8 days in a serum-free medium containing DHEA at 0, 5, 25, or 75 microM. Preadipocyte differentiation [lipid staining, glycerol-3-phosphate dehydrogenase (GPDH) activity] and proliferation (preadipocyte-specific antigen staining) decreased with increasing levels of DHEA in cultures of pig SV cells. In cultures of rat SV cells, preadipocyte differentiation (lipid staining, GPDH activity) and proliferation ([3H]thymidine incorporation) were decreased in the 25 and 75 microM DHEA groups compared with the control and 5 microM DHEA groups. The level of expression of CCAAT enhancer binding protein-alpha, a master regulator of adipogenesis, in cultures of pig SV cells treated with 150 microM DHEA was 38% of control cultures. These data support the hypothesis that DHEA directly attenuates adipogenesis via attenuation of preadipocyte proliferation and differentiation.

Prevention of orotic-acid-induced fatty liver in male rats by dehydroepiandrosterone and/or phenobarbital

Dehydroepiandrosterone (DHEA) is a steroid hormone which induces the peroxisome proliferation in rodents. The fatty liver induced by orotic acid and a high sucrose diet in male rats was prevented by the administration of DHEA and/or phenobarbital (PB). A significant increase in the liver weight was induced in the DHEA group (relative weight) and the DHEA + PB group (absolute and relative weight). The liver weight increased more conspicuously in the DHEA + PB group than in the DHEA group. The increase in the liver weight was caused by an increase in the cell size and peroxisome number. In addition, the administration of DHEA alone and the combination of DHEA and PB prevented the lipid droplet accumulation in hepatocytes. The administration of PB alone also prevented the accumulation of lipid droplets without any increase in the liver weight.

Dehydroepiandrosterone (DHEA) and DHEA-S interact with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to stimulate human osteoblastic cell differentiation

DHEA, an adrenocortical steroid, and its sulfate derivative (DHEA-S), have been implicated in many biological functions, including the regulation of bone mass. In this study, we examined whether DHEA/DHEA-S are capable of directly affecting bone cell proliferation and differentiation, and compared this with the effects of, and interaction with, the established bone cell modulating steroid, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Two in vitro models of human osteoblastic cells were used, viz. MG63 osteosarcoma cell line and normal primary osteoblast-like cells (HOB). Our results show that DHEA and DHEA-S failed on their own to exert direct, independent significant effects on the growth and differentiation of human osteoblastic cells, but treating the cells in conjunction with 1,25(OH)2D3 resulted in enhancement of specific A1P activity. Moreover, 1,25(OH)2D3-induced osteocalcin production was potentiated by the adrenal steroids in both cell models. DHEA-S proved in general to be more potent than DHEA. In conclusion, this study shows that the effects of DHEA/DHEA-S on osteoblastic cell growth and differentiation are likely to be mediated via an effect on 1,25(OH)2D3-induced changes in bone cells, suggesting a distinctive role for these steroids in the regulation of bone metabolism.

The inducible and cytochrome P450-containing dehydroepiandrosterone 7alpha-hydroxylating enzyme system of Fusarium moniliforme

7Alpha-hydroxylation of DHEA by Fusarium moniliforme was investigated with regard to inducibility and characterization of the responsible enzyme system. Using GC/MS, the 7-hydroxylated metabolites of DHEA produced after biotransformation by Fusarium moniliforme mycelia were identified. The strain of Fusarium moniliforme hydroxylated DHEA predominantly at the 7alpha-position, with minor hydroxylation occurring at the 7beta-position. Constitutive 7alpha-hydroxylation activity was low, but DHEA induced the enzyme complex responsible for 7alpha-hydroxylation via an increase in protein synthesis. DHEA 7alpha-hydroxylase was found to be mainly microsomal, and the best production yields of 7alpha-hydroxy-DHEA (28.5 +/- 3.51 pmol/min/mg protein) were obtained with microsomes prepared from 18-h-induced mycelia. Kinetic parameters (KM=1.18 +/- 0.035 microM and Vmax=909 +/- 27 pmol/min/mg protein) were determined. Carbon monoxide inhibited 7alpha-hydroxylation of DHEA by microsomes of Fusarium moniliforme. Also, exposure of mycelia to DHEA increased microsomal P450 content. These results demonstrated that: (i) DHEA is 7alpha-hydroxylated by microsomes of Fusarium moniliforme; (ii) DHEA induces Fusarium moniliforme 7alpha-hydroxylase; (iii) this enzyme complex contains a cytochrome P450.

Photoaffinity labeling of peroxisome proliferator binding proteins in rat hepatocytes; dehydroepiandrosterone sulfate- and bezafibrate-binding proteins

To detect the cellular sites which directly interact with peroxisome proliferators (PPs) and mediate their inducing effect on peroxisomal enzymes in rat hepatocytes, two kinds of radiolabeled ligands, AD12 (7alpha-N-(4-azido-2-hydroxy-5-iodo[125I]benzyl)-aminomethyl-5-and rostene-3beta-ol-17-one-O-3-sulfate) and BZ5 (2-[p-[2-(4'-azido-3',5'-diiodo[125I]benzamido-2'-hydroxy)ethyl]phenoxy] -2-methylpropionic acid), were developed for photoaffinity labeling. These compounds were derivatives of dehydroepiandrosterone sulfate (DHEAS) and bezafibrate, respectively, with an azido group as the photoreactive functional group. Upon UV-irradiation following incubation with rat liver cytosol and nuclei, both the ligands effectively radiolabeled several proteins analyzed by SDS-polyacrylamide gel electrophoresis/radioluminography. When [125I]AD12 was used at a concentration of 0.2 microM, two cytosolic proteins with molecular masses of 55 and 28 kDa and a nuclear protein of 40 kDa were specifically labeled, as coincubation with a 1000-fold excess of DHEAS inhibited labeling. Photoaffinity labeling of the cytosolic 28-kDa protein was also affected by Wy-14,643, but not by unsulfated dehydroepiandrosterone or androsterone sulfate, consistent with our previous findings obtained in competitive binding studies of [3H]DHEAS-binding detected in rat liver cytosol (Yamada et al. (1994) Biochim. Biophys. Acta 1224, 139-146). On the other hand, [125I]BZ5 specifically labeled a cytosolic protein of 31 kDa, which was inhibited by coincubation with bezafibrate, clofibric acid and Wy-14,643, but not with DHEAS. Thus, [125I]AD12 and [125I]BZ5 labeled several proteins which recognized DHEAS and bezafibrate, respectively, in rat liver cytosol and nuclei, providing a useful means to investigate PP-binding proteins.

Effect of dehydroepiandrosterone sulfate on carnitine acetyl transferase activity and L-carnitine levels in oophorectomized rats

Alteration in energy metabolism of postmenopausal women might be related to the reduction of dehydroepiandrosterone sulfate (DHEAS). DHEA and DHEAS decline with age, leveling at their nadir near menopause. DHEA and DHEAS modulate fatty acid metabolism by regulating carnitine acyltransferases and CoA. The purpose of this study was to determine whether dietary supplementation with DHEAS would also increase tissue L-carnitine levels, carnitine acetyltransferase (CAT) activity and mitochondrial respiration in oophorectomized rats. Plasma L-carnitine levels rose following oophorectomy in all groups (P < 0.0001). Supplementation with DHEAS was not associated with further elevation of plasma L-carnitine levels, but with increased hepatic total and free L-carnitine (P = 0.021 and P < 0.0001, respectively) and cardiac total L-carnitine concentrations (P = 0.045). In addition, DHEAS supplementation increased both hepatic and cardiac CAT activities (P < 0.0001 and P = 0.05 respectively). CAT activity positively correlated with the total and free carnitine levels in both liver and heart (r = 0.764, r = 0.785 and r = 0.700, r = 0.519, respectively). Liver mitochondrial respiratory control ratio, ADP:O ratio and oxygen uptake were similar in both control and supplemented groups. These results demonstrate that in oophorectomized rats, dietary DHEAS supplementation increases the liver and heart L-carnitine levels and CAT activities. In conclusion, DHEAS may modulate L-carnitine level and CAT activity in estrogen deficient rats. The potential role of DHEAS in the regulation of fatty acid oxidation in postmenopausal women is worthy of investigation.

Induction of peroxisomal enzymes in rat liver by dehydroepiandrosterone sulfate

Male F-344 rats, when treated with either 150 mg/kg or 300 mg/kg body weight of DHEAS for 14 days, produced a dose-dependent increase in liver weight and peroxisomal beta-oxidation activity, characteristic of peroxisomal proliferation. Contrary to previous observations in vitro, we also found a significant increase in catalase activity in rat liver with the higher dose of the steroid. Furthermore, the in vivo induction of peroxisomal beta-oxidation by DHEAS observed in our study was significantly less than reported in vitro, and also unlike previously reported in vitro results, was approximately equivalent to DHEA administered in vivo.

Dehydroepiandrosterone markedly inhibits the accumulation of cholesteryl ester in mouse macrophage J774-1 cells

To clarify the antiatherogenic mechanism of action of dehydroepiandrosterone (DHEA), we investigated the effects of DHEA on the accumulation of cholesteryl ester (CE) in cultured mouse macrophage J774-1 cells. The accumulation of CE in J774-1 cells in the presence of acetyl low density lipoprotein (AcLDL) and 10(-5) mol/l DHEA was significantly reduced to 30% of the control values for 24 h. The marked effect of DHEA was observed as early as 6 h and continued at least for 48 h. This reduction by DHEA was dose-dependent and occurred starting at a DHEA dose of 5 x 10(-7) mol/1 for 24 h. DHEA treatment did not induced any changes in the cell surface binding, cell-association, or degradation of AcLDL. In comparison, the DHEA analogues, 8354 and 8356, which are known to be much stronger inhibitors of glucose 6-phosphate dehydrogenase than DHEA, did not show as marked an effect as DHEA on the accumulation of CE during the first 6 h. However, after 24-48 h of incubation, both 8354 and 8356 caused a marked reduction in the accumulation of CE similar to that observed with DHEA. A quantitative analysis of the cellular cholesterol content revealed that DHEA caused a marked reduction in CE with a concomitant continuous increase in free cholesterol (FC), while the DHEA analogues caused a marked reduction in CE with no change in FC. DHEA demonstrated little inhibitory effect on 25-hydroxycholesterol-driven esterification. Moreover, 10(-5) mol/1 DHEA induced a CE reduction in the foam cells induced by AcLDL. The CE-reducing capacity was also observed in the DHEA analogues. This CE-reducing capacity disappeared, however, when acyl CoA:cholesterol acyltransferase inhibitor, 58-035, was also present. Based on these findings, it can be concluded that the inhibitory effect of DHEA on the CE storage in response to AcLDL can be explained, at least in part, by two mechanisms. First, a recently published mechanism, namely, the inhibitory action of DHEA on lysosomal cholesterol transport, correlates well with the inhibition against foam cell transformation by DHEA in the early phase (at 6 h) observed in our study. With regard to the second mechanism, the CE-reducing capacity of DHEA from CE-laden foam cells, which appears to be related to a decreased cholesteryl ester cycle, may contribute to the inhibitory effect on the CE storage in the late phase (at 24 h and 48 h). These phase-specific inhibitory mechanisms of DHEA on the CE-storage may therefore partly explain the antiatherogenic action of DHEA.

Dehydroepiandrosterone-induced lipid peroxidation in rat liver mitochondria

Administration of dehydroepiandrosterone (DHEA), a steroid hormone of the adrenal cortex which acts as a peroxisome proliferator and hepatocarcinogen in the rat, caused an increase in NADPH-dependent lipid peroxidation in mitochondria isolated from the liver, kidney and heart, but not from the brain. The effect of DHEA on rat liver mitochondrial lipid peroxidation became discernible after feeding steroid-containing diet (0.6% w/w) for 3 days, and reached maximal levels between 1 and 2 weeks. DHEA in the concentration range 0.001-0.02% did not significantly increase lipid peroxidation compared to the control. Lipid peroxidation was significantly enhanced in animals given a diet containing > or = 0.05% DHEA. The addition of DHEA in the concentration range 0.1-100 microM to mitochondria isolated from control rats had no effect on lipid peroxidation. It seems, therefore, that the steroid effect is mediated by an intracellular process. Our data indicate that induction of mitochondrial membrane lipid peroxidation is an early effect of DHEA administration at pharmacological doses.

Increase of lipid peroxidation in rat liver microsomes by dehydroepiandrosterone feeding

Oral administration of the adrenal steroid dehydroepiandrosterone (DHEA), a peroxisome proliferator and hepatocarcinogen in the rat, caused an increase in NADPH-dependent lipid peroxidation in microsomes isolated from rat liver and kidney cortex, but not from brain. The increase of liver microsomal lipid peroxidation was greater in male than in female rats. the effect of DHEA on lipid peroxidation became discernible after feeding steroid-containing diet (0.6%) to male and female rats for 2 and 3 days and reached maximal levels at 1 and 2 weeks, respectively. The increase of microsomal lipid peroxidation reached a plateau stimulation at 0.05% in the diet. The addition of DHEA in the concentration range 0.1-100 microM to microsomes isolated from control rats had no effect on lipid peroxidation. Furthermore, a significant increase of the endogenous concentration of thiobarbituric acid reactive substances was found in microsomes after DHEA-administration at 0.05% in the diet. These results provide in vivo evidence that DHEA can cause lipid peroxidation in rat liver. Administration of DHEA at 0.6% in the diet for 7 consecutive days also significantly enhanced NADH- and ascorbate-dependent lipid peroxidation in liver microsomes. The DHEA-stimulated rat liver microsomal lipid peroxidation was completely inhibited by EDTA but not by superoxide dismutase, catalase or mannitol applied as OH-radical scavenger. The findings indicate that membrane lipid peroxidation is an early effect of DHEA, and that this process may be involved in the steroid-induced carcinogenesis in rats.

Pleotropic effects of dietary DHEA

We present data pertaining to some of the in vivo effects associated with dietary DHEA administration to mice and rats. Dietary DHEA leads to: (1) decrease in body weight gain; (2) relative increases in liver weight; (3) liver color change; (4) induction of hepatic peroxisomal enzymes; (5) proliferation of hepatic peroxisomes with increased cross-sectional area; (6) decreased hepatic mitochondrial cross-sectional area; (7) elevated levels of hepatic cytosolic malic enzyme; (8) slight decreases, significant decreases, or significant increases in serum triglyceride levels, depending on mouse strain; (9) increases in total serum cholesterol levels; (10) significant decreases in the hepatic rates of fatty acid synthesis; (11) significant increases in the hepatic rates of cholesterol synthesis; (12) decreases in both protein content and specific activity of hepatic mitochondrial carbamoyl phosphate synthetase-I without concomitant changes in serum urea nitrogen; (13) induction of glutathione S-transferase activity in liver; (14) decrease in hepatic endogenous protein phosphorylation; (15) increase in hepatic AMPase and GTPase activities; (16) formation of 5-androstene-3 beta,17 beta-diol as a major metabolite of DHEA by subcellular fractions of liver, which is reflected in serum and tissue levels; and (17) reduction in serum prolactin levels.

Specific binding of dehydroepiandrosterone sulfate to rat liver cytosol: a possible association with peroxisomal enzyme induction

Incubation of [3H]dehydroepiandrosterone sulfate (DHEAS) with rat liver cytosol demonstrated its specific binding with a dissociation constant of 72 +/- 14 nM and a maximal binding capacity of 312 +/- 105 fmol/mg cytosol protein. The binding correlated with the amount of cytosol protein, and depended on time, temperature and pH, with equilibrium being reached after 6 h at 0 degrees C and pH 7.5. Boiling or treatment of the cytosol with proteases or sulfhydryl-blocking reagents affected the binding. The apparent molecular mass of the binding entity was estimated to be 160-230 kDa by HPLC gel filtration. In competitive binding studies, free steroids, including dehydroepiandrosterone (DHEA), sulfatase substrates and ligands of organic anion binders such as ligandin and fatty acid binding protein, had no effect on the [3H]DHEAS binding. Peroxisome proliferators also had no effect, except Wy-14,643. Competition with various steroids related to DHEAS revealed strict structural requirements for DHEAS binding, in which epiandrosterone sulfate was almost as effective as unlabeled DHEAS in inhibiting [3H]DHEAS binding. These findings indicated the presence of a binding protein highly specific to DHEAS in rat liver cytosol. The DHEAS binding in liver cytosol was 2-fold higher in male than in female rats. The cytosolic DHEAS binding was highest in the liver, followed by the kidney and heart. The possibility of association between the DHEAS binding and DHEA induction of peroxisomal beta-oxidation is discussed.

Dehydroepiandrosterone 3 beta-sulphate is an endogenous activator of the peroxisome-proliferation pathway: induction of cytochrome P-450 4A and acyl-CoA oxidase mRNAs in primary rat hepatocyte culture and inhibitory effects of Ca(2+)-channel blockers

The role of steroids related to the adrenal androgen dehydroepiandrosterone (5-androstene-3 beta-ol-17-one; DHEA) in regulating the expression of peroxisomal and cytochrome P-450 4A (CYP4A) enzymes active in fatty acid metabolism was assessed using a primary rat hepatocyte culture system. Exposure of hepatocytes to the peroxisome proliferator, clofibric acid (10-250 microM), for 48-96 h led to substantial increases in CYP4A protein, CYP4A1, CYP4A2 and CYP4A3 mRNAs, and the mRNAs encoding both forms of peroxisomal acyl-CoA oxidase (ACOX-I and ACOX-II), as judged by Northern-blot analysis using gene-specific oligonucleotide probes. Although DHEA treatment in vivo is effective in inducing these mRNAs in rat liver, it had no effect in the cultured hepatocytes. In contrast, treatment of the cells with DHEA 3 beta-sulphate (DHEA-S; 10-250 microM) stimulated major increases in CYP4A and ACOX mRNA levels. Examination of several analogues indicated a preference for 3 beta-sulphate over 17 beta-sulphated steroids and the inactivity of a 3 alpha-hydroxy-17 beta-sulphate derivative (DHEA-S > 5-androstene-3 beta,17 beta-diol 3-sulphate approximately 5 alpha-androstene-3 beta-ol-17-one 3-sulphate > 5-androstene-3 beta, 17 beta,17 beta-diol 17-sulphate approximately 5 beta-androstane-3 alpha-ol-17-one 3-sulphate >> 5 alpha-androstane-3 alpha, 17 beta-diol 17-sulphate). Induction of CYP4A mRNAs by either DHEA-S or clofibric acid was partially blocked by structurally diverse Ca(2+)-channel antagonists (nicardipine, nifedipine and diltiazem; 50 microM), suggesting that both the steroidal and fibrate classes of CYP4A inducers stimulate peroxisomal-proliferative responses via a Ca(2+)-dependent pathway. Retinoic acid alone slightly induced CYP4A mRNAs but did not enhance the induction by clofibrate or DHEA-S. As DHEA-S corresponds to a physiologically important major circulating androgen, these findings suggest that it may serve as an endogenous regulator of hepatic peroxisome enzyme levels. They further suggest that Ca(2+)-channel blockers may be useful pharmacological tools for the further study of the underlying cellular mechanism whereby endogenous steroids and fibrate drugs induce peroxisome proliferation, and the relationship of these events to activation of the peroxisome proliferator-activated receptor.

Fatty-acid metabolism and the pathogenesis of hepatocellular carcinoma: review and hypothesis

Despite increasing understanding of the genetic control of cell growth and the identification of several involved chemical and infectious factors, the pathogenesis of clinical and experimental hepatocellular carcinoma remains unknown. Available evidence is consistent with the possibility that selected changes in the hepatocellular metabolism of long-chain fatty acids may contribute significantly to this, process. Specifically, studies of the peroxisome proliferators, a diverse group of xenobiotics that includes the fibrate class of hypolipidemic drugs, suggest that increased fatty acid oxidation by way of extramitochondrial pathways (i.e., omega-oxidation in the smooth endoplasmic reticulum and beta-oxidation in the peroxisomes) results in a corresponding increase in the generation of hydrogen peroxide and, thus, oxidative stress. This in turn leads to alterations in gene expression and in DNA itself. We also review evidence supporting a potentially decisive influence of particular aspects of hepatocellular fatty acid metabolism in determining the activity of the extramitochondrial pathways. Moreover, certain intermediates of extramitochondrial fatty acid oxidation (e.g., the long-chain dicarboxylic fatty acids) impair mitochondrial function and are implicated as modulators of gene expression through their interaction with the peroxisome proliferator-activated receptor. Finally, the occurrence of hepatic tumors in type I glycogen storage disease (glucose-6-phosphatase deficiency) may exemplify this general mechanism, which may also contribute to nonneoplastic liver injury and to tumorigenesis in other tissues.