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Lipogenic enzyme activities in primary cultures of adult mouse hepatocytes
Author(s) -
Hillyard Lewis A.,
Lin C. Y.,
Abraham S.
Publication year - 1988
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02535465
Subject(s) - linoleic acid , hepatocyte , malic enzyme , biochemistry , arachidonic acid , polyunsaturated fatty acid , dehydrogenase , biology , fatty acid , oleic acid , enzyme assay , enzyme , lipogenesis , lactate dehydrogenase , medicine , metabolism , in vitro
The effects of various unsaturated fatty acids such as oleic (18∶1n−9), linoleic (18∶2n−6) and arachidonic (20∶4n−6) on the activities of fatty acid synthetase (FAS), malic enzyme (ME), glucose‐6‐phosphate dehydrogenase (G6PDH) and 6‐phosphogluconate dehydrogenase (6PGDH) all were determined in primary cultures of mouse hepatocytes. Activities of FAS and ME were found to decrease with time in culture regardless of whether hepatocyte donors were fed diets containing polyunsaturated fatty acid‐free hydrogenated cottonseed oil (HCTO) or corn oil (CO). On the other hand, while G6PDH activity also declined in cultured hepatocytes obtained from HCTO‐fed mice, the activity of this enzyme increased in cells cultured from CO‐fed mice. 6PGDH activity was found to increase in hepatocytes obtained from both diet groups. Neither 18∶2 nor 20∶4 when added to media could alter FAS or ME activities compared with those observed with either 18∶1‐containing or fatty acid‐free media. Since lactic dehydrogenase activity and the rate of incorporation of [ 3 H] leucine into FAS protein were unaltered with time in hepatocyte cultures, the decreased activities of FAS and ME cannot be attributed to a loss in cell viability during culture but rather appear to be specific for those enzymes which respond to diet hormones in vivo. Examination of the fatty acid contents of the cells after the culture period showed that the values for the ratios of 16∶0/16∶1 and of 18∶0/18∶1 were elevated when either 18∶2 or 20∶4 was added to the medium even though there was no evidence for elongation of the added 18∶2 or for 20∶4 being converted to 22∶4. This result suggest that Δ9‐desaturase activity was inhibited by these polyunsaturated fatty acids and that conversion of 18∶2 to 20∶4 was not required for such action. The rate of synthesis determined by the relative rate of incorporation of [ 3 H]leucine into FAS was two to five times higher in hepatocytes prepared from mice fed the HCTO diet than in hepatocytes from mice fed the CO diet. We have concluded that the mechanisms for long‐term regulation may not be contained entirely within the liver.