V. E. Kagan

Formation of α-tocopherol complexes with fatty acids. A hypothetical mechanism of stabilization of biomembranes by vitamin E

The formation of alpha-tocopherol complexes with saturated and unsaturated fatty acids in ethanol has been demonstrated. The values of equilibrium constants for alpha-tocopherol interactions with fatty acids have been determined. These values do not depend in practice on the number of carbon atoms in saturated fatty acid molecules (from 7:0 to 24:0) and are equal to about 40-50 M-1. For unsaturated fatty acids the values of equilibrium constants are increased exponentially with an increase in the number of double bonds in the fatty acid molecule (1.25 X 10(4) M-1 for arachidonic acid). alpha-Tocopherol can form complexes with free fatty acids incorporated into phosphatidylcholine liposomes or into skeletal muscle sarcoplasmic reticulum membranes. The formation of alpha-tocopherol complexes with free fatty acids is regarded as a molecular mechanism of membrane stabilization by vitamin E against the damaging action of free fatty acids.

Light-induced free radical oxidation of membrane lipids in photoreceptors of frog retina

Abstract Exposure to light of frog retinae and rod outer segments results in accumulation of free radical oxidation products (hydroperoxides) in the lipid phase of photoreceptors. The action spectrum of this process is similar to the absorption spectrum of the visual pigment rhodopsin and the spectral sensitivity curve of frog retina, indicating that the photosensitive pigment participates in the induction of lipid photooxidation.

Formation of α-tocopherol complexes with fatty acids. Nature of complexes

Abstract Using ultraviolet spectrophotometry and 1 H-NMR high-resolution spectroscopy, it has been demonstrated that the formation of α-tocopherol complexes with free fatty acids occurs via two types of interaction, namely (i) formation of a hydrogen bond between the α-tocopherol chromanol nucleus hydroxyl and the carboxyl group of a fatty acid, and (ii) interaction of the fatty acid acyl chains with the chromanol nucleus methyl groups. The second interaction is significantly enhanced by an increase in the number of double bonds in the fatty acid molecule, which results in restriction of the molecular mobility of α-tocopherol. The proposed structural model of α-tocopherol-fatty acid complexes has been confirmed by the use of molecular models. It has been assumed that the efficiency of complex formation of natural tocopherols with fatty acids is correlated with their biological activity.

Lipid peroxidation and electric activity of the retina.

Abstract The induction of lipid peroxidation (LPO) by the Fe2+ + ascorbate system in the frog retina decreases the magnitude of the electroretinographic waves and eliminates intracellular rod light responses. The addition of antioxidants (α-tocopherol, BHT) exerts a powerful protective effect against electroretinogram suppression and simultaneous inhibition of LPO. Preincubation of the retina in a medium with α-tocopherol allows us to record intracellular rod light responses for 20–25 min, irrespective of the presence of LPO inducers. Under the effect of LPO products the photoreceptor cell membrane potentials remain unchanged despite the elimination of the light response, whereas the values of the dark membrane potential in the inner nuclear layer cells are higher than in the controls.

Accumulation of lipid peroxidation products and depression of retinal electrical activity in vitamin E-deficient rats exposed to high-intensity light

: It was shown in experiments on dogs that after 4-hour hypovolemic hypotension the content of total RNA in brain cortex and myocardium homogenates decreased. In the liver, there was a significant decrease both in RNA and DNA content. In the postresuscitation period, the content of nucleic acids in the myocardium returned to normal after 14--21 days, and that in the liver after 3--4 months. The gray matter of the brain manifested a delayed lowering of DNA content (after 14--21 days), and the level of nucleic acid did not return ot normal over 3--4 months after resuscitation.

Protection of Ca++ transport by carnosine against disturbances induced by lipid peroxidation

Carnosine, an endogenous component of the muscle cell whose concentration in the myoplasm amounts to some tens of millimoles, is evidently important for muscular function. It has recently been shown that it has a stabilizing action on the system of the sarcoplasmic reticulum (SR), and also increases the working capacity of fatigued muscle [2, 6, 12]. However, the molecular mechanism of the increase in the efficiency of work of the Ca pump of the SR produced by carnosine have not been explained. We know that during exhausting physical exertion lipid peroxidation (LPO) processes in the membranous structures of the muscle cell are activated [8, 9]. It has also been recentIy shown that accumulation of LPO products in the membranes of SR results in inhibition of their Ca-transporting ability [4]. It has accordingly been suggested that the stabilizing action of carnosine may be due to its ability to inhibit LPO. The ability of carnosine to inhibit accumulation of LPO products interacting with 2-thiobarbituric acid was demonstrated previously on suspensions of mitochondria [5].

LIPID PEROXIDATION IN CHILDREN WITH DUCHENNE'S HEREDITARY MUSCULAR DYSTROPHY

(1976), p. 8. 5. V. I. Kulinskii, in: Theoretical and Practical Problems of Temperature Regulation [in Russian], Ashkhabad (1982), p. 125. 6. V. V. Khaskin, Energetics of Heat Formation and Adaptation to Cold [in Russian], Novosibirsk (1975). 7. S. Kerpel-Pronius and F. Hajos, Histochemie, 14, 343 (1968)~ 8. J. Leblanc, Am. J. Physiol., 212, 530 (1967). 9. S. Lo, J. C. Russell, and A. W. Taylor, J. Appl. Physiolo, 28, 234 (1970). i0. O. H. Lowry et al., J. Biol. Chem., 239, 18 (1964).

Calcium and lipid peroxidation in mitochondrial and microsomal membranes of the heart

It has recently been shown that in lesions of the heart of varied etiology (myocardial infarction, ischemia, severe stress) the key stages in the pathogenetic chain of irreversible changes in the myocardium are two simultaneously occurring processes: activation of peroxidation in phospholipids of membranous structures of the cardiomyocytes and damage to enzyme systems responsible for transmembrane transport of Ca++ [2, 3, 6].

Ischemic damage to the sarcoplasmic reticulum of skeletal muscles: The role of lipid peroxidation

The development of ischemia was shown to be accompanied by inhibition of the Ca2+ enzyme transport system (ETS) (a decrease in the Ca2+/ATP ratio and in activity of Ca2+-dependent ATPase), which correlates with accumulation of the primary and secondary molecular lipid peroxidation products (POL) in vivo and in the membranes of the sarcoplasmic reticulum (SR) of the skeletal muscles. Administration of antioxidants (2,6-di-tert-butyl-4-methylphenol, α-tocopherol) prevents activation of POL in the ischemic muscle and partially protects the Ca2+ ETS against injury. Restoration of the blood flow after prolonged ischemia leads to further inhibition of the Ca2+ ETS while the concentration of POL products remains unchanged.

Effects of products of phospholipid hydrolysis by phospholipases on rhodopsin thermal stability in photoreceptor membranes

Abstract The decrease in the thermal stability of rhodopsin in sea teleost fish ( Theragra chalcogramma ) retinal rod outer segments (ROS) is strictly correlated with the increase in the amount of phospholipid hydrolysis products. The addition of exogenous unsaturated fatty acids to the ROS suspensions cause an increase of the rhodopsin thermal denaturation rate constants and a decrease of the E a value. On the other hand, saturated fatty acids at temperatures below their melting points and lysophosphatidylcholine produce practically no effect. The thermal stability of T. chalcogramma rhodopsin may be considerably enhanced when endogenous or exogenous fatty acids are eliminated by washing the ROS suspensions with a solution of fatty acid free bovine serum albumin. The role of phospholipids and their hydrolysis products in the thermal stability of rhodopsin is discussed.