Metabolic Abnormalities of Erythrocytes as a Risk Factor for Alzheimer's Disease

Alzheimer's disease (AD) is a slowly progressive, neurodegenerative disorder of uncertain etiology. According to the amyloid cascade hypothesis, accumulation of non-soluble amyloid β peptides (Aβ) in the Central Nervous System (CNS) is the primary cause initiating a pathogenic cascade leading to the complex multilayered pathology and clinical manifestation of the disease. It is, therefore, not surprising that the search for mechanisms underlying cognitive changes observed in AD has focused exclusively on the brain and Aβ-inducing synaptic and dendritic loss, oxidative stress, and neuronal death. However, since Aβ depositions were found in normal non-demented elderly people and in many other pathological conditions, the amyloid cascade hypothesis was modified to claim that intraneuronal accumulation of soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, is the first step of a fatal cascade in AD. Since a characteristic reduction of cerebral perfusion and energy metabolism occurs in patients with AD it is suggested that capillary distortions commonly found in AD brain elicit hemodynamic changes that alter the delivery and transport of essential nutrients, particularly glucose and oxygen to neuronal and glial cells. Another important factor in tissue oxygenation is the ability of erythrocytes (red blood cells, RBC) to transport and deliver oxygen to tissues, which are first of all dependent on the RBC antioxidant and energy metabolism, which finally regulates the oxygen affinity of hemoglobin. In the present review, we consider the possibility that metabolic and antioxidant defense alterations in the circulating erythrocyte population can influence oxygen delivery to the brain, and that these changes might be a primary mechanism triggering the glucose metabolism disturbance resulting in neurobiological changes observed in the AD brain, possibly related to impaired cognitive function. We also discuss the possibility of using erythrocyte biochemical aberrations as potential tools that will help identify a risk factor for AD.

Impacts of lisinopril and lisinopril plus simvastatin on erythrocyte and plasma arginase, nitrite, and nitrate in hypertensive patients

Angiotensin-converting enzyme inhibitors are effective at reducing blood pressure, whereas statins decrease plasma cholesterol, impeding atherosclerosis. The authors hypothesize that these medications may improve blood pressure by modifying the arginase-nitric oxide synthase system of erythrocytes. In this study, the effects of lisinopril alone versus lisinopril + simvastatin on erythrocyte and plasma arginase enzyme and nitric oxide metabolites are compared. Patients with atherosclerosis and hypertension are randomly assigned to receive lisinopril 10 to 20 mg/d or lisinopril 10 to 20 mg/d plus simvastatin 20 mg/d for 24 weeks. Higher arginase activity is observed in erythrocytes from 100% of patients and mainly recovered after 12 and 24 weeks of treatment with lisinopril or lisinopril + simvastatin. Plasma arginase activity is 3 orders of magnitude lower than erythrocyte arginase activity in all participants, suggesting a lack of its clinical significance. Both treatments cause the increase in plasma $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ , $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ , and $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ in 100% of patients. Erythrocyte $$\hbox{ N }{\hbox{ O }}_{2}^{-}$$ + $$\hbox{ N }{\hbox{ O }}_{3}^{-}$$ concentration is greatly decreased in hypertensive patients but recovers after monotherapy and combined therapy. The results show for the first time that lisinopril monotherapy and combined lisinopril + simvastatin therapy exhibit pronounced and equipotential normalizing effects on erythrocyte arginase and nitric oxide synthase activities.

Specific and pronounced impacts of lisinopril and lisinopril plus simvastatin on erythrocyte antioxidant enzymes

Angiotensin-converting enzyme inhibitors are effective at reducing blood pressure, whereas statins decrease plasma cholesterol impeding atherosclerosis. It is hypothesized that these medications may improve blood pressure and serum cholesterol by modifying the antioxidative status and energy metabolism of erythrocytes. In this study, the effects of 2 treatments are compared: lisinopril alone versus lisinopril + simvastatin, on erythrocyte antioxidant and energy metabolic enzymes. Patients with atherosclerosis and moderate hypertension are randomly assigned to receive lisinopril 10 to 20 mg/d or lisinopril 10 to 20 mg/d plus simvastatin 20 mg/d for 24 weeks. Higher catalase activity and lower glutathione peroxidase activity are observed in 94% to 100% patients from both groups after 12 and 24 weeks of treatment. Superoxide dismutase activity is increased significantly only after 24 weeks. No changes of glutathione reductase, lactate dehydrogenase, and phosphofructokinase activities are found under any conditions indicated. Both treatments decrease systolic and diastolic blood pressure equally. Only lisinopril + simvastatin treatment decreases plasma total cholesterol and low-density lipoprotein cholesterol. The results show for the first time that lisinopril monotherapy and combined lisinopril + simvastatin therapy exhibit specific and pronounced effects on antioxidant and energy metabolic enzyme activities in erythrocytes of hypertensive patients.