Derivatives of 1,4-dihydropyridines as modulators of ascorbate-induced lipid peroxidation and high-amplitude swelling of mitochondria, caused by ascorbate, sodium linoleate and sodium pyrophosphate

Abstract

A group of 26 2,6-dimethyl-3,5-disubstituted and 2,6-dimethyl-3,4,5-trisubstituted-1,4-dihpdropyridines (1,4-H2Py = 1.4-DHPs) and five related pyridines were studied as inhibitors of rat liver mitochondrial swelling and O2 uptake by ascorbic acid-dependent lipid peroxidation (LP) and as modulators of mitochondrial swelling induced by Na+-linoleate or Na+-pyrophosphate. 1,4-DHPs studied include 4-unsubstituted and 4-methyl- and 4-phenyl-substituted 3,5-dialkoxycarbonylderivatives of 2,6-dimethyl-1,4-DHP with variations in alkoxy chain length and composition, 4-unsubstituted and 4-methyl-, 4-aryl- and 4-pyridyl-substituted 3,5-dianilidocarbonylderivatives, and a structurally related group of 3,5-dipyridylamidocarbonylderivatives. Many 1,4-DHPs possess marked antioxidant (AO) and membrane stabilizing activity, expressed as the mitochondrial swelling (ΔA520/t) and/or O2 uptake rate decrease (V(O)/V) as well as prolongation of the induction period (τ/τ0) of mitochondrial swelling and/or O2 uptake at ascorbic acid-dependent LP of rat liver mitochondria. 4-Unsubstituted 3,5-dialkoxycarbonyl-2,6-dimethyl-1,4-DHPs, as well as 4-unsubstituted or those possessing lipophylic 4-aryl- groups 3,5-diamido-2,6-dimethyl-1,4-DHPs, reveal marked AO and membrane stabilizing properties. Oxidized (heteroaromatized) derivatives have minimal activity. Perhaps 1,4-DHPs preferably act as antioxidants on stages of initiation and prolongation of LP chain reactions at low concentrations: IC50 (when V(O)/V or τ/τ(O)2 = 2) are 0.1 μM to 100 μM. At 100 μM 3,5-di-p-hydroxyphenoxycarbonyl- and 3,5-di-p-tolyloxycarbonyl-2,6-dimethyl-1,4-DHPs, as well as 3,5-diethoxycarbonyl-2,6-dimethylpyridine (oxidized form of Hantzsch ester) and 3,5-diamyloxycarbonyl-2,6-dimethylpyridine alter the mitochondrial swelling rate in the presence of natural protonophore Na+-linoleate (0.063 mM and 0.125 mM). 3,5-Di-n-butyloxycarbonyl-2 6-dimethyl-1,4-DHP at 100 μM completely stops mitochondrial swelling in the presence of 0.8 mM Na+-pyrophosphate. In the presence of many of the 1,4-DHPs, the lipid peroxidation process was inhibited. However, the swelling process could be prolonged, promoted, accelerated or inhibited - depending on 1,4-DHPs concentration, the type of initiators of the swelling process and the medium composition.