Induction of 5-aminolaevulinate synthase by two- to five-carbon alcohols in cultured chick-embryo hepatocytes. Relationship to induction of cytochrome P-450

Abstract

The induction of 5-aminolaevulinate synthase and of cytochrome P-450 by short-chain aliphatic alcohols was compared in primary cultures of chicken-embryo hepatocytes. Isopropyl alcohol, isobutanol, pentan-1-ol and isopentanol alone caused up to a 4-fold increase in 5-aminolaevulinate synthase, whereas ethanol and propan-1-ol did not. Induction of the synthase by isopentanol was maximal at 8 h, and reached a plateau thereafter, whereas the activity induced by 2-propyl-2-isopropylacetamide continued to increase for 20 h. In the presence of 3,4,3',4'-tetrachlorobiphenyl, an inhibitor of haem synthesis at the uroporphyrinogen decarboxylase step, synergistic induction of 5-aminolaevulinate synthase was observed with all the alcohols except ethanol. Ethanol, but not isopentanol, decreased the extent of induction of 5-aminolaevulinate synthase by 2-propyl-2-isopropylacetamide and 3,4,3',4'-tetrachlorobiphenyl (50% decrease at 112 mM-ethanol). Total protein synthesis was not inhibited by ethanol in these cells. The composition of porphyrins was determined after treatment of cells with ethanol, isopentanol or 2-propyl-2-isopropylacetamide. Untreated cells, when incubated with 5-aminolaevulinate for 6 h, accumulated mainly protoporphyrin. However, when cells were pretreated with ethanol, isopentanol or 2-propyl-2-isopropylacetamide for 20 h, and 5-aminolaevulinate was added, 8- and 7-carboxyporphyrins increased, whereas protoporphyrin decreased. The dose responses for induction of either 5-aminolaevulinate synthase or cytochrome P-450 after a 20 h exposure to 3- to 5-carbon alcohols were identical. The results indicate that: simple alcohols can induce both enzymes; hydrophobicity increases their effectiveness; and induction of both enzymes are probably mediated by a common mechanism.

Haem synthesis from exogenous 5-aminolaevulinate in cultured chick-embryo hepatocytes. Effects of inducers of cytochromes P-450

“…The increase in uroporphyrin accumulation observed in PIA-and 3-MC-treated cultures (Figs. 4 and 5) agrees with previous observations (Marks de Verneuil et al, 1983;Ferioli et al, 1984;Sinclair et al, 1986;). This accumulation occurs despite the increases in the amounts of cellular haem (Table 1), and therefore could not represent a substantial inhibition of the haem pathway at uroporphyrinogen decarboxylase.…”

“…The increased accumulation of uroporphyrin is perhaps due to the oxidation of uroporphyrinogen, the substrate of uroporphyrinogen decarboxylase, to uroporphyrin, which is not a substrate for the decarboxylase. Other data, previously discussed (Sinclair et al, 1986), suggest that uroporphyrinogen oxidation in chick hepatocyte cultures can be caused by action of some species of cytochrome P-450, perhaps by forming a reactive oxygen radical.…”

Effects of acute ethanol administration on rat liver 5-aminolaevulinate synthase activity

“…The drug is also known to increase the activity of the enzyme in rat liver after chronic (Rubin et al, 1970;Teschke et al, 1987), and in human leukocytes after acute (McColl et al, 1980), administration. In isolated cell systems, however, the effects of the drug are variable, with inhibition in isolated rabbit reticulocytes (Ibrahim et al, 1979) and cultured chick-embryo hepatocytes (Sinclair et al, 1986) and induction in this latter system (Geiger & Meyer, 1980) and in cultured rat hepatocytes (Lane & Stewart, 1983). These controversial findings also clearly require further experimental scrutiny.…”