C Manso

DIFFERENT EFFECTS OF THIOL AND NONTHIOL ACE INHIBITORS ON COPPER-INDUCED LIPID AND PROTEIN OXIDATIVE MODIFICATION

Differences among angiotensin-converting enzyme inhibitors (ACEI) in scavenging reactive oxygen species were described and mainly attributed to the presence or absence of a thiol group. Plasma constituents and red cells are known targets for oxidative damage. Transition metals, like copper, are well known catalizers of free radical generation. In the present study we compared the abilities of captopril (a thiol ACEI), enalaprilat, and lisinopril (two nonthiol ACEI) for inhibiting copper-induced thiobarbituric acid reactive substances (TBARS) formation and fluorescence generation in whole human plasma and low-density lipoprotein. The effects of those ACEI on copper/hydrogen peroxide-induced fluorescence development and electrophoretic mobility modification in albumin and on copper-induced TBARS formation and hemolysis in human red cells were also compared. Captopril was more effective than the two nonthiol ACEI in inhibiting plasma and LDL lipid peroxidation, but it was ineffective in inhibiting the albumin oxidative modification that was moderately inhibited by enalaprilat and lisinopril. On the contrary, the inhibitory effects of the three ACEI on copper-induced lipid peroxidation and hemolysis in red cell suspensions were more uniform. This as yet unreported red cell protective effect may deserve pharmacological evaluation. Our results show that captopril is a more effective antioxidant than the nonthiol ACEI in some systems. However, the nonthiol ACEI also have the ability to partially protect some targets against oxidative damage. These observations suggest that the presence of a thiol group in the ACEI structure is not the only determinant for the antioxidant properties.

Superoxide Radical Generation by Amadori Compounds

Several D-sugars were incubated with L-lysine or with L-arginine for 10 days. The resulting compounds are able to reduce nitrobluetetrazolium (NBT). This is prevented by superoxide dismutase (SOD), indicating that the superoxide radical is generated by the resulting Amadori compounds. The formation of superoxide radical in vivo, as a result of nonenzymatic glycosylation of proteins, may be considered to be a contributory factor to the appearance of chronic complications of diabetes.

Mechanisms of hemolysis induced by copper.

An excess of copper is the cause of hemolysis in a number of clinical conditions. Incubation of human erythrocyte (RBC) suspensions with copper (II) causes the formation of methemoglobin, lipid peroxidation and hemolysis. A new variant of the thiobarbituric acid (TBA) method, which minimizes the formation of interfering chromophores, was used to detect lipid peroxidation. Lipid peroxidation precedes hemolysis and the antioxidant vitamins C and E, which inhibit lipid peroxidation, also inhibit hemolysis. Consequently lipid peroxidation appears to be the cause of RBC destruction. Lipid peroxidation arises mostly from the oxidation of oxyhemoglobin by copper as it is inhibited in RBCs with carbon monoxyhemoglobin or methemoglobin. A direct interaction of copper with the red cell membrane seems to play only a minor role. Copper effects depend on the presence of free SH groups. Lipid peroxidation is probably initiated by activated forms of oxygen as it is increased by an inhibitor of catalase and reduced by hydroxyl radical scavengers. With higher copper concentrations hemolysis is greater: its mechanism appears different as lipid peroxidation is smaller but hemoglobin alterations, namely precipitation, are more pronounced.

Protective effects of a 21-aminosteroid against copper-induced erythrocyte and plasma lipid peroxidation.

The 21-aminosteroids, or lazaroids, are a novel class of antioxidant drugs designed to inhibit iron-dependent lipid peroxidation in biological lipid environments. They have been shown to be of therapeutic value in several animal models of traumatic, ischemic and hemorrhagic injury of the central nervous system. Our purpose was to evaluate the ability of 21-aminosteroids to protect human erythrocytes and plasma against oxidative damage in vitro. We found that the 21-aminosteroid U74500A inhibited erythrocyte and plasma lipid peroxidation. U74500A at 1 microM significantly reduced copper-induced and hydrogen peroxide-induced erythrocyte lipid peroxidation by 76.5 and 27.6%, respectively. The inhibition of erythrocyte lipid peroxidation was accompanied by an inhibition of hemolysis. Copper-induced plasma lipid peroxidation was also significantly reduced by as little as 1 microM U74500A. These results suggest that 21-aminosteroids may prove useful in preventive or therapeutic interventions in situations where erythrocyte or plasma components are subjected to oxidative stress and in situations related to copper-induced oxidative damage.

The inhibition of lipid peroxidation by cinnarizine. Possible implications to its therapeutic and side-effects.

Cinnarizine has antivasoconstrictor properties and improves red-cell deformability. Its major side-effects are the induction of extrapyramidal reactions. It is a calcium antagonist, but it was suggested that its effects may depend on other mechanisms, namely on antiperoxidant properties. We have studied these properties in different biological systems, intact red-cells included. The occurrence of lipid peroxidation was determined by the formation of 2-thiobarbituric acid reactive products. Cinnarizine was found to inhibit spontaneous lipid peroxidation in rat liver homogenates, copper-induced lipid peroxidation in human plasma and copper-induced and hydrogen peroxide-induced lipid peroxidation in human red-cells. In red-cells, the inhibition of lipid peroxidation is accompanied by the inhibition of hemolysis. Copper-induced red-cell lipid peroxidation is 85% inhibited by as little as 5 microM cinnarizine. The antioxidant activity of cinnarizine may contribute to explain some of the effects of this drug.

Erythrocyte acetylcholinesterase in essential hypertension

Red cell acetylcholinesterase activity (AChE) has been studied in 58 patients suffering from essential hypertension; diastolic blood pressure values were about 130mm or higher in 45 patients (group A) and lower in 13 (group B). The very significant increase (p<0.001) of AChE activity in group A has been forced by the severity of systemic lesions. Meanwhile, the AChE values have been slightly increased, but not statistically significant in the patients of group B. These results are supporting the hypothesis that the blood pressure control can be mediated or normalized, at least in part, by cholinergic mechanisms.

Plasma dopamine-beta-hydroxylase and erythrocyte acetylcholinesterase in a group of patients with Parkinson disease.

In a group of patients with Parkinson disease there was no difference in plasma DBH activity between cases treated with L-Dopa and not treated. These patients tend to have an elevated activity of erythrocyte AChE.

Oxygen radical generation by Maillard compounds

Amino sugars such as galactosamine are hepatotoxic. It has been verified that toxic hepatitis induced by galactosamine is similar to that of CCl4 poisoning, and that both were inhibited by O2* scavengers. Fructosamine results from the union of glucose with the epsilon-amine of lysine. A test for fructosamine quantification is based on nitroblue tetrazolium (NBT) reduction, in which O2- is involved, the reduction being inhibited in the presence of superoxide dismutase (SOD). Given these facts, we attempted to elucidate if galactosamine and glucosamine reduce NBT and if that reduction is inhibited by SOD. This was confirmed. Subsequently, we incubated aminoacids (glycine, lysine, alanine) with glucose and galactose for 7 days and studied the action of the incubation products on NBT, using amino acids and sugars as controls. We found that NBT reduction increases proportionally to the length of incubation time of glucose/galactose with lysine, but not with other amino acids. Reduction of NBT by the Amadori compounds formed is inhibited by SOD. We suggest that oxygen radical generation by Amadori compounds must be taken into consideration as one cause of damage in diabetes of long duration.

Inhibitory effect of drugs used in the treatment of Parkinson's disease on plasma monoamine oxidase activity

The plasma amine oxidase (benzylamine oxidase, BzAO) of patients with Parkinsons disease is sometimes decreased in activity, when compared to normal controls. This is the result of therapy with DOPA decarboxylase inhibitors. The Authors suggest that complications due to prolonged therapy with these drugs may be, at least in part, the result of an interference with BzAO capacity to catabolize circulating amines.

Behavior of human erythrocytes under stress induced by a superoxide generator.

Na presenca de hidroquinona gera-se superoxido no sangue que pode ser detectado por nitroazul de tetrazolio. Existe um factor limitante que provavelmente resulta de modificacao da estrutura quimica da propria hidroquinona. Um extracto de favas tem uma capacidade geradora de superoxido, em contacto com o sangue, semelhante a hidroquinona. Admite-se que este facto resulte da presenca de substâncias como a vicina e convicina, com estrutura parecida. Apos a incubacao com hidroquinona, o espectro de absorcao da oxihemoglobina sofre alteracoes caracteristicas, que se interpretam como resultantes da formacao de metahemoglobina, coleglobina e hemicromios. Estas alteracoes parecem ser mais precoces em individuos com carencia de desidrogenase da glucose-6-fosfato.