Background: Ethanol increases histone H3 acetylation in the rat liver. However, the effect of other carbon chain length alcohols, consumed as surrogate alcohols and used in industry, on H3 acetylation is unknown. Hence, we investigated the effect of these alcohols on histone H3 acetylation, cell toxicity and HAT and HDAC activity.
Methods: Primary cultures of rat hepatocytes were incubated with selected concentration (40 mM) of different chain length alcohols with or without inhibitors of alcohol metabolizing enzymes. Cells were also treated with low concentration (2.5 mM) of 1-propanol or 1-butanol or isopentanol, with or without 40 mM ethanol for 24 hours. Effects of the metabolites of these alcohols were also studied. Cytotoxicity was determined by lactate dehydrogenase (LDH) release and mitochondrial activity (MTT assay). The degree of histone H3 acetylation at specific lysine residues were monitored by western bloting using site specific antibodies. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) activities were measured by enzyme-linked immunosorbent assay (ELISA) and colorimetric assay respectively.
Results: Alcohols with increasing carbon chain length exhibited a variable effect on the ratio of acetylated lys9 histone H3 to β-actin. A graded increase (methanol < ethanol < 1-propanol < 1-butanol) followed by a gradual decrease (1-butanol > 1-pentanol > 1-hexanol > 1-octanol) in the ratio was observed. Other lysine sites were not affected. HAT activation also corresponded to the acetylation profile. These alcohols or their metabolites did not significantly alter HDAC activity in the hepatocytes. Low concentration (2.5 mM) of 1-propanol alone did not affect acetylation, but sensitized the ethanol induced H3 acetylation at lysine 9 (H3AcK9). 1-Butanol and isopentanol also increased the response of ethanol induced H3AcK9. Alcohol metabolizing inhibitors attenuated ethanol and propanol induced increase in H3AcK9. Carboxylic acid metabolites of these alcohols also increased HAT activity and histone H3 acetylation at lysine 9. Propionate and butyrate modestly inhibited HDAC activity in an in vitro assay.
Conclusions: Surrogate alcohols modulate H3AcK9 via increasing HAT activity and this is dependent on their metabolism. Furthermore, alcohol metabolites also increased H3AcK9, but in contrast, exhibit both HAT activation and HDAC inhibition.