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Biomedical subjects

T S Stoytchev

Publications and source records attributed to T S Stoytchev.

5 recordsLinked to original sources
PubMed1992

Combined effect of fascioliasis and diethylnitrosamine carcinogenesis on the activity of the rat liver monooxygenase system.

1. The activity of the rat liver monooxygenase system after single and combined treatment with Fasciola hepatica and diethylnitrosamine (DENA) has been studied in a 27-week experiment. 2. The changes in lever drug metabolism were due mainly to F. hepatica with DENA having a modulating effect only. 3. The results are discussed with reference to earlier data of ours concerning the effects of stimulation or inhibition of DENA-induced liver carcinogenesis against a background of acute or chronic fascioliasis.

Animals↗
PubMed1990

Mechanisms of stabilization of biomembranes by alpha-tocopherol. The role of the hydrocarbon chain in the inhibition of lipid peroxidation.

The effects of alpha-tocopherol and its homologues with different chain lengths (6-hydroxy-chromanes: C1, C6, C11) on lipid peroxidation in natural membranes (liver microsomes and mitochondria, brain synaptosomes) and liposomes were studied. It was shown that the antioxidant activity of alpha-tocopherol homologues decreased in the order: C1 greater than C6 greater than C11 greater than alpha-tocopherol (C16). Using fluorescent measurements, the possible reasons underlying these differences were investigated: (i) the distribution between the aqueous media and nonpolar phase of the membrane, which predetermines the binding of alpha-tocopherol homologues to membranes; (ii) the incorporation of alpha-tocopherol homologues into lipid bilayer; (iii) non-uniform distribution (formation of the clusters) of tocopherol homologues in the lipid bilayer; and (iv) transbilayer mobility of alpha-tocopherol homologues and accessibility of the inhibitors for radical-generating centres under enzymically and non-enzymically induced lipid peroxidation. It was demonstrated that: (i) binding of C1 with membranes was less efficient than that of longer-chain homologues (C6, C11, C16); (ii) the level of incorporation of alpha-tocopherol homologues into membranes decreased in a succession alpha-tocopherol C11 greater than C6 greater than C1; (iii) all alpha-tocopherol homologues existed in the lipid bilayer not only in a monomeric form but also associated in clusters thus decreasing the efficiency of radical scavenging; (iv) the short-chain alpha-tocopherol homologue, C1, exhibited a high transbilayer mobility whereas the long-chain one, C16, underwent no transbilayer migration within tens of minutes. The inhibiting effect of alpha-tocopherol esters and C1-acetate was predetermined by their hydrolysis in biomembranes; a strong correlation exists between the rate of the ester hydrolysis and their antioxidant activity in the membrane. In liposomes, in which the esterase activity was absent, alpha-tocopherol esters and C1-acetate exhibited very low lipid peroxidation inhibition.

Animals↗
PubMed1990

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes.

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q0 to Q10) in preventing (Fe2+ + ascorbate)-dependent or (Fe2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQn, possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q1-Q4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q5-Q10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q1 greater than Q2 greater than Q3 greater than Q4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q5 greater than Q6 greater than Q7 greater than Q8 greater than Q9 greater than Q10 and iii) the antioxidant efficiency of Q0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q1-Q4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q6-Q10 exert no effect. In contrast to ubiquinol Q10 (ubiquinone Q10) ubiquinone Q1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.

Animals↗
PubMed1989

Lipid peroxidation activation and cytochrome P-450 decrease in rat liver endoplasmic reticulum under oxidative stress.

Iron loading was associated with development of oxidative stress, viz, decrease in tocopherol content and an increase in amount of lipid peroxidation products but only slight, if any, decrease in cytochrome P-450 content. Combinations of iron loading with other stress-inducing treatments (exhaustive physical exercise and hyperoxia) caused marked decreases in cytochrome P-450 content. Thus, a combination of factors favoring development of oxidative stress, but insufficient to exert a damaging effect on the cytochrome P-450-dependent detoxification system when acting alone, may become quite potent when acting in concert.

Animals↗