Estado oxidativo/antioxidante y biodisponibilidad de cobre y zinc en la recuperación de la anemia ferropénica nutricional con dietas basadas en leche (cabra o vaca) fortificadas en hierro y ácido fólico

Resumen

La investigación llevada a cabo estudia algunos parámetros bioquímicos relacionados con la fisiología hepática, los mecanismos de peroxidación lipídica y la defensa enzimática antioxidante durante la recuperación de la anemia ferropénica nutricional tras el consumo de dietas basadas en leche de cabra o vaca con un contenido normal o con sobrecarga crónica de Fe y suplementadas o no en ácido fólico. Los animales se sometieron a un periodo pre¿experimental (PPE) de 40 días en el que un grupo control se alimenta con una dieta estándar con contenido normal de Fe (45 mg/Kg dieta), y otro grupo se alimenta con una dieta con bajo contenido en Fe (5 mg/Kg dieta) para inducir experimentalmente la anemia ferropénica nutricional, realizándose un estudio hematológico en ambos grupos al final de dicho periodo. Posteriormente, ambos grupos de animales se someten a un periodo experimental (PE) en el que son alimentados ¿pair feed¿ durante 30 días con dietas basadas en leche de cabra o vaca (elaboradas con un 10% de grasa y un 20% de proteína, aportada por cada tipo de leche), con un contenido normal (45 mg/kg dieta) o sobrecarga de Fe (450 mg/Kg dieta) y contenido normal (2 mg/Kg dieta) o suplemento de ácido fólico (40 mg/Kg dieta). En los últimos 7 días de este PE se recogen por separado heces y orina para la determinación la utización y metabólica de Cu y Zn. Al final del PE, se determinan parámetros hematológicos, transaminasas, creatina, creatin¿kinasa, TBARS y las principales enzimas antioxidantes (SOD, CAT y GPx) en plasma y citosol de hígado, cerebro y eritrocito. After analyzing the data obtained, we have reached the following CONCLUSIONS: FIRST CONCLUSION Cow milk¿based diet with iron¿overload increased alanine transferase and aspartate transaminase plasma levels in control and anaemic rats, indicating hepatocellular damage and subsequently release of both transaminases into the bloodstream. Dietary folate supplementation in goat milk¿s diet reduced plasma transaminases levels, suggesting a hepatoprotective effect under basal conditions and more noticeably in situation of Feoverload. This fact can be explained by the better zinc bioavailability and nutritive utilisation of goat milk fat, which provides lower substrate for hepatic lipid peroxidation and consequently reduces free radicals production in the animals consuming this type of milk. SECOND CONCLUSION Folic acid supplementation in goat and cow milk¿based diets with normal or ironoverload increased creatinine and creatin¿kinase plasma levels in the control and anaemic groups, because of high production of creatine, which is a major consumer of methyl groups. From an oxidative point of view, the increase in plasma creatinine would be negative because the oxidative degradation of xenobiotics via thiodiglycolic acid formation decreases the plasma glutathione, one of the main intracellular antioxidant; therefore, this fact lead to a decrease of all metabolic pathways dependent on glutathione. However, it can be postulated that folate supplementation reduces the glutathione consumption and also improves hepatic antioxidant capacity, scavenging the excessive free radicals produced in the course of creatine metabolism, finding supported by the activities of superoxide dismutase, catalase and glutathione peroxidase recorded in the current study. THIRD CONCLUSION Cow milk¿based diet with iron¿overload increased lipid peroxidation products levels (TBARS) in control and anaemic groups, suggesting an imbalance in the functioning of the enzymatic antioxidant defence system. On the other hand, folate supplement in goat and cow milk¿based diets has beneficial effects on antioxidant status, avoiding lipid peroxidation in liver, brain and erythrocyte. FOURTH CONCLUSION Cow milk¿based diet either with normal¿iron or iron¿overload provoked a remarkable increase in the superoxide dismutase and catalase activity in liver, brain and erythrocyte, especially with folate supplementation for catalase, inducing a concomitant augmentation in the formation of hydroperoxides. The increased activity of both enzymes recorded with cow milk¿based diet and iron¿overload is a compensatory mechanism of the body to cope with the increase in oxidative stress. The lower levels of glutathione peroxidase in the groups fed ironoverload diets, especially in liver and erythrocyte of the animals fed cow milk, can be explained by the reduction of the enzyme in the process of neutralisation of free radicals generated. FIFTH CONCLUSION Folate¿supplementation in the diets led to a reduction in the peroxide dismutase, catalase and glutathione peroxidase activities in brain and erythrocyte, which suggest that the functions of the key intracellular antioxidant enzymes may be interdependent. This finding could be due to the antioxidant effects of folate and the capacity of scavenging the excessive free radicals output, a fact that can be directly correlated with the lower increase in superoxide dismutase activity in these tissues, reducing the formation of hydroperoxides. The unchanged activities of superoxide dismutase, catalase and glutathione peroxidase in the nervous tissue, revealed that it is relatively independent of the iron variations in the organism. SIXTH CONCLUSION In groups fed with goat milk¿based diet under all experimental conditions, it exists a higher digestive and metabolic utilization of copper and zinc due to beneficial nutritional characteristics of this milk. Furthermore, folic acid supplement in goat or cow milk¿based diets highly enhanced copper absorption due to the reducing and antioxidant character of this vitamin, provoking the transformation of Cu2+ into Cu1+, influencing positively the enzymatic activity of SOD, fact that can be attributed to its role as a cofactor. This finding is not observed with zinc digestive and metabolic utilization, since this mineral is absorbed mainly via DMT1 uptake as a divalent cation. OVERALL CONCLUSION Folate¿supplemented goat milk¿based diet consumption in situation of iron¿overload leads to a reduction of alanine transferase and aspartate transaminase plasma levels, suggesting a hepatoprotective effect with beneficial effects, protecting cell from free radicals oxidative damage, improving the antioxidant enzymes activities and limiting lipid peroxidation. Therefore, it would be reccomendable the consumption of folate¿supplemented caprine milk in populations suffering from nutritional ferropenic anaemia and intaking oral Fe supplements.