Nutr Res Pract.  2008 Jun;2(2):80-84.

Dehydroepiandrosterone supplement increases malate dehydrogenase activity and decreases NADPH-dependent antioxidant enzyme activity in rat hepatocellular carcinogenesis

• Kim J
• Kim SH
• Choi H

Abstract

Beneficial effects of dehydroepiandrosterone (DHEA) supplement on age-associated chronic diseases such as cancer, cardiovascular disease, insulin resistance and diabetes, have been reported. However, its mechanism of action in hepatocellular carcinoma in vivo has not been investigated in detail. We have previously shown that during hepatocellular carcinogenesis, DHEA treatment decreases formation of preneoplastic glutathione S-transferase placental form-positive foci in the liver and has antioxidant effects. Here we aimed to determine the mechanism of actions of DHEA, in comparison to vitamin E, in a chemically-induced hepatocellular carcinoma model in rats. Sprague-Dawley rats were administered with control diet without a carcinogen, diets with 1.5% vitamin E, 0.5% DHEA and both of the compounds with a carcinogen for 6 weeks. The doses were previously reported to have anti-cancer effects in animals without known toxicities. With DHEA treatment, cytosolic malate dehydrogenase activities were significantly increased by ~5 fold and glucose 6-phosphate dehydrogenase activities were decreased by ~25% compared to carcinogen treated group. Activities of Se-glutathione peroxidase in the cytotol was decreased significantly with DHEA treatment, confirming its antioxidative effect. However, liver microsomal cytochrome P-450 content and NADPH-dependent cytochrome P-450 reductase activities were not altered with DHEA treatment. Vitamin E treatment decreased cytosolic Se-glutathione peroxidase activities in accordance with our previous reports. However, vitamin E did not alter glucose 6-phosphate dehydrogenase or malate dehydrogenase activities. Our results suggest that DHEA may have decreased tumor nodule formation and reduced lipid peroxidation as previously reported, possibly by increasing the production of NADPH, a reducing equivalent for NADPH-dependent antioxidant enzymes. DHEA treatment tended to reduce glucose 6-phosphate dehydrogenase activities, which may have resulted in limited supply for de novo synthesis of DNA via inhibiting the hexose monophophaste pathway. Although both DHEA and vitamin E effectively reduced preneoplastic foci in this model, they seemed to function in different mechanisms. In conclusion, DHEA may be used to reduce hepatocellular carcinoma growth by targeting NADPH synthesis, cell proliferation and anti-oxidant enzyme activities during tumor growth.

Keyword

Hepatocellular carcinoma; DHEA; malate dehydrogenase; NADPH and glucose 6-phosphate dehydrogenase

MeSH Terms

Animals
Antioxidants
Carcinoma, Hepatocellular
Cardiovascular Diseases
Cell Proliferation
Chronic Disease
Cytochrome P-450 Enzyme System
Cytosol
Dehydroepiandrosterone
Diet
DNA
Glucose
Glutathione Transferase
Insulin Resistance
Lipid Peroxidation
Liver
Malate Dehydrogenase
Malates
NADP
NADPH-Ferrihemoprotein Reductase
Oxidoreductases
Peroxidase
Rats
Rats, Sprague-Dawley
Vitamin E
Vitamins
Antioxidants
Cytochrome P-450 Enzyme System
DNA
Dehydroepiandrosterone
Glucose
Glutathione Transferase
Malate Dehydrogenase
Malates
NADP
NADPH-Ferrihemoprotein Reductase
Oxidoreductases
Peroxidase
Vitamin E
Vitamins

Figure

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  Fig. 1 DHEA treament increases cytosolic malate dehydrogenase activities. The level of cytosolic malate dehydrogenase activity was determined by biochmical enzymatic assay. Hepatocellular carcinoma was induced with diethylnitrosamine, 2-acetylaminofluorene and ~70% partial hepatectomy using male Sprague-Dawley rats. The animals were treated with control diet without a carcinogen, carcinogen diets with 1.5% vitamin E, 0.5% dehydroepiandrosterone (DHEA) and both 1.5% vitamin E and 0.5% DHEA. After ultracentrifugation of freshly-obtained liver, cytosolic fraction was obtained and used to measure malate dehydrogenase activities. Activities were normlaized against protein concentration. One-way ANOVA test was used to determine significance (n=6~9 each). Means with different subscripts are significantly different at p<0.05 by Duncan's multiple range test.

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  Fig. 2 Activities of cytosolic glucose 6-phosphate dehydrogenase tended to decrease with DHEA treatment. The level of glucose 6-phosphate dehydrogenase activity was determined by biochmical enzymatic assay. Similar to the malate dehydrogenase, after ultracentrifugation of freshly-obtained liver, cytosolic fraction was obtained and used to measure glucose 6-phosphate dehydrogenase activities. Activities were normalized against protein concentration. One-way ANOVA test was used to determine significance (n=6~9 each). Means with different subscripts are significantly different at p<0.05 by Duncan's multiple range test.

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  Fig. 3 DHEA treatment decreased hepatic cytosolic Se-glutathione peroxidase activities. Activities of Se-glutathione peroxidase activities were measured in the hepatic cytosolic fractions as mentioned above, using hydrogen peroxide as substrate. Means with different subscripts are significantly different at p<0.05 by Duncan's multiple range test.

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  Fig. 4 Hepatic microsomal cytochrome P-450 content was not different with DHEA treatment. Content of cytochrome P-450 was measured in the hepatic microsomal fractions using reduced carbon monoxide. Microsomal fraction was obtained as described in the methods. One-way ANOVA test was used to determine significance (n=6~9 each).

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