Biological activity of novel synthetic derivatives of carnosine.

Two novel derivatives of carnosine--(S)-trolox-L-carnosine (STC) and (R)-trolox-L-carnosine (RTC) are characterized in terms of their antioxidant and membrane-stabilizing activities as well as their resistance to serum carnosinase. STC and RTC were synthesized by N-acylation of L-carnosine with (S)- and (R)-trolox, respectively. STC and RTC were found to react more efficiently with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and protect serum lipoproteins from Fe(2+)-induced oxidation more successfully than carnosine and trolox. At the same time, STC, RTC and trolox suppressed oxidative hemolysis of red blood cells (RBC) less efficiently than carnosine taken in the same concentration. When oxidative stress was induced in suspension of cerebellum granule cells by their incubation with N-methyl-D-aspartate (NMDA), or hydrogen peroxide (H(2)O(2)), both STC and RTC more efficiently decreased accumulation of reactive oxygen species (ROS) than carnosine and trolox. Both STC and RTC were resistant toward hydrolytic degradation by human serum carnosinase. STC and RTC were concluded to demonstrate higher antioxidant capacity and better ability to prevent cerebellar neurons from ROS accumulation than their precursors, carnosine and trolox.

Effect of homocysteine and homocysteic acid on glutamate receptors on rat lymphocytes.

Homocysteine and homocysteic acid increased the stationary level of reactive oxygen species in rat lymphocytes, homocysteic acid being more potent in this respect. The effect of this compound was realized via ionotropic NMDA receptors and group III metabotropic glutamate receptors. Incubation of lymphocytes with homocysteic acid increased intracellular Ca(2+)concentration, activated of protein kinase C, and induced accumulation of reactive oxygen species, which reflected the involvement of homocysteic acid into cell signaling mechanisms.

Effect of carnosine on immunocompetent cells from alcoholic patients.

We studied the effect of natural dipeptide carnosine on phagocytosis, respiratory burst in neutrophils, and subpopulation composition of lymphocytes from healthy donors and alcoholic patients. Carnosine in vitro produced different effects on immunocompetent cells from healthy donors and patients with alcoholism. In patients with alcoholism phagocytic activity of leukocytes and generation of reaction oxygen species increased under the influence of carnosine in a concentration of 0.01 mM, but decreased after treatment with this compound in a concentration of 1 mM. Carnosine in both concentrations stimulated the respiratory burst, but had no effect on the count of phagocytic cells in healthy donors. Carnosine in a concentration of 0.01 mM increased the number of lymphocytes carrying apoptosis markers (CD95+) in patients with alcoholism not receiving therapy. Our results indicate that carnosine holds much promise for the therapy of alcoholism.

In vitro effects of ethanol, acetaldehyde and fatty acid ethyl esters on human erythrocytes.

In vitro experiments were performed to determine if ethanol was metabolized by human erythrocytes and to investigate if ethanol or its metabolites, acetaldehyde and fatty acid ethyl esters, affected erythrocyte morphology and stability. No detectable metabolism of ethanol was found in erythrocytes, although ethanol itself caused an elevated rate of spontaneous haemolysis in erythrocyte preparations. Physiologically attainable levels of ethanol were found to stabilize erythrocytes against haemolysis induced by sodium hypochlorite, and the presence of ethanol caused a decrease in erythrocyte reactive oxygen species levels, although the mechanism for such a process is unknown. Both physiologically attainable and higher levels of acetaldehyde had no effects on erythrocyte morphology and stability even after a 16 h exposure. Fatty acid ethyl esters caused structural changes and instability in erythrocytes in vitro, but whether such changes occur in vivo has not been established. The results of these studies suggest that the deleterious effects of ethanol consumption on erythrocytes in vivo may be, at least in part, the result of direct effects of unmetabolized ethanol on erythrocyte components.

Does ethanol metabolism affect erythrocyte hemolysis?

The effects of ethanol and acetaldehyde on the hemolytic stability of rabbit erythrocytes have been compared. Incubation of normal erythrocytes with ethanol facilitated both acidic and oxidative hemolysis and increased the percentages of cells that were hemolyzed at maximal rate. Acetaldehyde exerted a similar destabilizing effect on erythrocytes only in the case of oxidative hemolysis. The destabilizing effect of ethanol was observed in catalase-inactivated erythrocytes under acidic, but not oxidative, hemolysis conditions. It is concluded that the destabilizing effect of unmetabolized ethanol occurs under conditions of acidic hemolysis, whereas the destabilizing effect of the oxidation of ethanol to acetaldehyde takes place only under the conditions of oxidative hemolysis.

Effect of ethanol on the hemolytic stability of erythrocytes.

The stability of rabbit erythrocytes to hemolysis induced by different compounds in the presence or absence of ethanol or acetaldehyde has been analyzed. Ethanol slightly reduced erythrocyte stability against acidic hemolysis only after long-term preincubation, but the effect of ethanol on stability to oxidative hemolysis manifested itself immediately after its addition to the cells. Ethanol decreased both stability of cells to oxidative damage and dispersion of the hemolytic curve. Comparison of the effects of ethanol and acetaldehyde showed that the destabilizing effect of ethanol might be caused by either its direct action or the effect of its metabolites formed during preincubation of ethanol with erythrocytes. Possible mechanisms of ethanol and acetaldehyde effects on erythrocyte stability are discussed.

Oxidative resistance of Na/K-ATPase.

1. Oxidative modification of Na/K-ATPase from brain and kidney has been studied. Brain enzyme has been found to be more sensitive than kidney enzyme to inhibition by both H2O2 and NaOCl. 2. The inhibition of Na/K-ATPase correlates well with the decrease in a number of SH groups, suggesting that the latter belong mainly to ATPase protein and are essential for the enzyme activity. We suggest that the differences in the number, location, and accessibility of SH groups in Na/K-ATPase isozymes predict their oxidative stability. 3. The hydrophilic natural antioxidant carnosine, the hydrophobic natural antioxidant alpha-tocopherol, and the synthetic antioxidant ionol as well as the ferrous ion chelating agent deferoxamine were found to protect Na/K-ATPase from oxidation by different concentrations of H2O2. The data suggest that these antioxidants are effective due to their ability to neutralize or to prevent formation of hydroxyl radicals.

Evidence for a direct interaction of superoxide anion radical with carnosine.

Using photochemiluminescence, the interaction between carnosine and superoxide anion was measured directly. Carnosine at physiological concentrations decreased the amplitude of luminol chemiluminescence like superoxide dismutase (SOD) did, and prolonged the lag-period of the chemiluminescence similar to the effect of ascorbic acid. From the interaction of nitro blue tetrazolium with superoxide anion generated by the xanthine oxidase system, the constant for interaction of carnosine with 02-. was calculated to be 10(5) M-1.sec-1. The possible biological significance of the quenching of superoxide anion by carnosine is discussed.

Biochemical and physiological evidence that carnosine is an endogenous neuroprotector against free radicals.

1. Carnosine, anserine, and homocarnosine are endogenous dipeptides concentrated in brain and muscle whose biological functions remain in doubt. 2. We have tested the hypothesis that these compounds function as endogenous protective substances against molecular and cellular damage from free radicals, using two isolated enzyme systems and two models of ischemic brain injury. Carnosine and homocarnosine are both effective in activating brain Na, K-ATPase measured under optimal conditions and in reducing the loss of its activity caused by incubation with hydrogen peroxide. 3. In contrast, all three endogenous dipeptides cause a reduction in the activity of brain tyrosine hydroxylase, an enzyme activated by free radicals. In hippocampal brain slices subjected to ischemia, carnosine increased the time to loss of excitability. 4. In in vivo experiments on rats under experimental hypobaric hypoxia, carnosine increased the time to loss of ability to stand and breath and decreased the time to recovery. 5. These actions are explicable by effects of carnosine and related compounds which neutralize free radicals, particularly hydroxyl radicals. In all experiments the effective concentration of carnosine was comparable to or lower than those found in brain. These observations provide further support for the conclusion that protection against free radical damage is a major role of carnosine, anserine, and homocarnosine.

Effects of carnosine and related compounds on generation of free oxygen species: a comparative study.

The effect of carnosine and related compounds on the luminol- and lucigenin-dependent luminescence of rabbit leukocytes, activated by BaSO4, has been studied. Carnosine was found to modify BaSO4-induced chemiluminescence of leukocytes via suppression of hypochlorous anion generation with simultaneous stimulation the system of oxygen superoxide anion. Additionally to this effect carnosine prevents enzymic dismutation of O2.. Anserine, acetylanserine, and homocarnosine also possess the ability to activate O.2 production by leukocytes. The effect is not inherent to imidazole used in the same concentrations. Suppression of myeloperoxidase reaction by carnosine and related compounds is explained by both inhibiting action on the enzyme itself, and direct neutralization of hypochlorous anion due to formation of stable chloroamine complexes. Methylation of carnosine at N1 nitrogen of imidazole ring, leading to anserine, forced inhibition of myeloperoxidase system, whereas its acetylation at the free beta-amino group weakened this effect.