Francisco Alba

Plasma lipid peroxidation in sporadic Parkinson's disease. Role of the l-dopa

Oxidative stress plays an important role in the pathogenesis of neurodegenerative diseases, such as Parkinsons disease (PD). There are several methods to measure oxidative stress, being lipid peroxidation (LPO) one of the most frequently used. Endogenous plasma LPO was determined by a spectrofluorimetric method in fifty two patients with sporadic PD and in forty controls. To know the maximum capacity of lipids to peroxidate, LPO was also measured after co-incubation with Fe2+/H2O2 (exogenous LPO). All PD patients were taken L-dopa and the effect of this treatment on LPO levels was additionally studied. Urine catecholamines and their main metabolites were also analyzed, and their possible correlation to LPO statistically studied. Endogenous plasma LPO levels were 33% higher in PD group than in control group (P<0.001). Exogenous plasma or oxidizability was also higher in PD patients compared to controls (20%, P<0.05). The intake of L-dopa was negatively dose-related to endogenous and exogenous plasma LPO. In conclusion, plasma of PD patients has elevated levels of LPO and also is more prone to peroxidation than that in the control group. The results also suggest an antioxidant effect of L-dopa.

Review: Brain Aminopeptidases and Hypertension

The brain aminopeptidases that participate in the enzymatic cascade of the renin-angiotensin system play a major role in blood pressure (BP) control, and their study offers new perspectives for the understanding of central BP control and the treatment of hypertension. In this system, angiotensin II is converted to angiotensin III (Ang III) by glutamyl aminopeptidase (GluAP) and Ang III is further metabolised to angiotensin IV by alanyl aminopeptidase or arginine-aminopeptidase. It is now clear that Ang III is the key active form of the central angiotensins, exerting tonic stimulatory control over BP Therefore, the development of GluAP inhibitors as potential antihypertensive agents offers new perspectives for therapy. Brain aspartyl JR aminopeptidase, which converts angiotensin I to angiotensin 2-10, is also a possible target for antihypertensive therapy because of its potential role in BP control. Finally, since changes in BP levels, that paralleled changes in brain and plasma aminopeptidase activities, were observed after unilateral lesions of the nigrostriatal system, brain asymmetry, aminopeptidase activities and BP control appear to be related, resulting their interplay in an asymmetrical neuroendocrine response that differentially affect BP control.The study of this interaction may contribute to our understanding of how the brain controls BP

Sex Differences and In Vitro Effects of Steroids on Serum Aminopeptidase Activities

We studied the possible existence of physiological sex differences in serum aminopeptidase activities in mice, by evaluating the effect of gonadectomy and the in vitro response to the presence in the medium of cholesterol or steroid hormones. Alanyl- and glutamyl-aminopeptidase activities were measured in sera from male, female, orchiectomized and ovariectomized mice, incubated with substrate solutions, and compared with the same groups of serum incubated with substrate solutions including cholesterol, 17-beta-estradiol, testosterone, progesterone or hydrocortisone. Our results demonstrated highly significant sex differences, and an influence of cholesterol and steroid hormones on aminopeptidase activity. Depending on the nature of the aminopeptidase, these enzymes responded in different ways to the presence of these substances and also responded differently to gonadectomy. For alanyl-aminopeptidase activity, but not for glutamyl-aminopeptidase activity, there was a clear difference in response between males and females to incubation of the serum with steroid hormones.

Neuropeptides, neuropeptidases and brain asymmetry.

Brain asymmetry is understood as an anatomical, functional or neurochemical difference between the two hemispheres. It is not a static but rather a dynamic phenomenon in which both environmental and endogenous factors act as modulators. Aging modifies brain asymmetry, and an imbalance in specific asymmetries characterizes some brain disorders such as schizophrenia, depression, infantile autism or Alzheimers disease. However, it is not clear whether these changes are a cause or a consequence of these disorders. Although this phenomenon has been extensively studied, its functional significance is not yet clear, and the neurochemical basis underlying anatomical or functional asymmetries in the brain is still poorly understood. In recent decades intensive research on the behaviour of neuropeptides has revealed asymmetries in their distribution in the brain, and there is evidence that the lateralized patterns of distribution are involved in the regulatory control of some neuropeptidase activities. Therefore, if these enzymatic activities are distributed asymmetrically, their endogenous substrates would presumably be affected in an asymmetrical way, as would the functions they are involved in. Here we review the most significant literature regarding human and animal brain asymmetry involving neuropeptides such as corticotropin-releasing hormone, cholecystokinin, luteinizing hormone-releasing hormone, thyrotropin-releasing hormone and angiotensin II, as well as their neuropeptidases.

Sex differences and age-related changes in human serum aminopeptidase A activity

Given that aminopeptidase A is primarily responsible for cleaving aspartic acid and converting angiotensin II to angiotensin III, the purpose of the present study was to evaluate the activity of aminopeptidase A by determination of glutamate aminopeptidase activity (GluAP) and aspartate aminopeptidase activity (AspAP) (reported respectively as aminopeptidase A and angiotensinase A activities) in human serum during development and ageing, in an apparently healthy population of 139 male and 148 female subjects. To measure GluAP and AspAP we used glutamyl- and aspartyl-2-naphthylamide as substrates. Significant age-related increases were observed in GluAP activity in males and females and in AspAP activity in females. In males, there were no age-related differences in AspAP activity. A significant correlation was observed between age and GluAP activity in the population analysed as a whole or according to sex. No correlation was demonstrated between age and AspAP activity either in the whole population or according to sex. These results may reflect the evolution of the functional status of susceptible circulating substrates during development and ageing.

Asymmetrical response of aminopeptidase A and nitric oxide in plasma of normotensive and hypertensive rats with experimental hemiparkinsonism.

Aminopeptidases and dopamine (DA) exhibit asymmetries in the brain that are reflected in the peripheral response to unilateral striatal DA depletions (experimental hemiparkinsonism). This might be due to asymmetries in the autonomic innervation of the peripheral vessels. Nitric oxide (NO) is released through vascular sympathetic activation. A similar pathway could be postulated for aminopeptidases. Angiotensin II, metabolized by aminopeptidase A (AP A), interacts with NO and dopamine in the control of blood pressure. Moreover, plasma AP A activity and NO concentrations are elevated in hypertensive rats in which sympathetic activity is increased. We hypothesize that plasma AP A activity and NO concentrations may reflect a central asymmetry of the sympathetic activity. Therefore, we analyzed the effect of unilateral depletions of brain DA by injecting 6-hydroxydopamine into the left or right striatum and measuring plasma AP A, NO and systolic blood pressure (SBP) in normotensive and hypertensive rats. Changes in plasma AP A and NO in opposite directions may reflect an asymmetry in the function of the nigrostriatal system. Our results also revealed an inverse correlation between AP A and NO, in normotensive rats lesioned or sham operated in the right side and hypertensive rats lesioned in the left one. We concluded that the observed changes in plasma NO and AP A after left or right striatal DA depletions may be due to asymmetries in the peripheral autonomic innervation of the vessels.

Role of central and peripheral aminopeptidase activities in the control of blood pressure: a working hypothesis

Although there is a large body of knowledge on protein synthesis, the available data on protein catabolism, although quite substantial, are still inadequate. This is due to the marked differences in the activity of proteolytic enzymes, compounded by different substrate specificities and multiple environmental factors. Understanding enzyme behavior under physiological and pathological conditions requires the identification of specific proteolytic activities, such as aminopeptidases, as able to degrade certain peptidergic hormones or neuropeptides. Another requirement is the isolation, purification and characterization of the enzymes involved. In addition, systematic studies are needed to determine each enzyme’s subcellular location, tissue distribution, and the influence of environmental factors such as diurnal rhythm, age, gender, diet, cholesterol, or steroids. Central and peripheral aminopeptidases may play a role in the control of blood pressure by coordinating the effect of the different peptides of the renin–angiotensin system cascade, acting through the AT1, AT2, and AT4 receptors. Our review of the available data suggests the hypothesis that cholesterol or steroids, particularly testosterone, significantly influence aminopeptidase activities, their substrate availability and consequently their functions. These observations may have relevant clinical implications for a better understanding of the pathophysiology of cardiovascular diseases, and thus for their treatment with aminopeptidase inhibitors.

Stress Influences Brain Enkephalinase, Oxytocinase and Angiotensinase Activities: A New Hypothesis

Brain enkephalin and oxytocin are anxiolytic agents involved in the response mechanism to stress. Degrading enzymes such as enkephalinase and oxytocinase could also be associated with this response. The effect of acute immobilization stress on enkephalinase and oxytocinase activities was determined in the soluble and membrane fractions of the medial prefrontal cortex, hippocampus and amygdala using alanyl- and leucyl-beta-naphthylamide as substrates, the latter in the presence and absence of 20 mML-methionine. No change in aminopeptidase activities was observed in the prefrontal cortex of stressed rats. In contrast, enkephalinase activity decreased in the soluble fraction of the hippocampus but increased in the membrane fraction. In the amygdala, soluble oxytocinase and membrane enkephalinase activities decreased in stressed animals. These results show that acute immobilization stress affects differentially enkephalinase and oxytocinase activities depending on the fraction and brain region analyzed. A reduction in the activity of soluble enkephalinase in the hippocampus and soluble oxytocinase as well as membrane enkephalinase in the amygdala may suggest higher availability/longer action of enkephalin and oxytocin at these locations. This may explain the relative importance of these enzymatic activities in the anxiolytic properties proposed for enkephalins and oxytocin in the hippocampus and amygdala during stress conditions. This interpretation is not applicable to membrane enkephalinase activity in the hippocampus. However, alanyl-beta-naphthylamide hydrolyzing activity not only measures enkephalinase activity, it also reflects the angiotensinase-induced metabolism of angiotensin III to angiotensin IV. Therefore, our results may also mirror an increase in the formation of Ang IV in hippocampus and a decrease in the amygdala in acute stress. In conclusion, aminopeptidase activities in the hippocampus and amygdala may affect enkephalin, oxytocin and angiotensin III metabolism during acute immobilization stress and therefore be involved in the anxiolytic response.

Angiotensinase activities in the kidney of renovascular hypertensive rats

In spite of the well-known contribution of angiotensin II (Ang II) in the pathogenesis of Goldblatt two-kidney one clip (G2K1C) hypertension, the importance of other Ang peptides, such as Ang III, Ang IV or Ang 2-10, is scarcely understood. The functional status of these peptides depends on the action of several aminopeptidases called angiotensinases. The metabolism of Ang III to Ang IV by aminopeptidase M (AlaAP) and of Ang I to Ang 2-10 by aspartyl aminopeptidase (AspAP) was evaluated in the renal cortex and medulla of normotensive (Sham-operated) and hypertensive (G2K1C) rats, treated or not with the AT(1) receptor antagonist valsartan. The results demonstrated a highly significant increase of membrane-bound (MEMB) AlaAP in the cortex of the non-ischemic kidney of G2K1C rats compared with the kidney of normal rats and with the clipped kidney of G2K1C rats. This suggests an increased formation of Ang IV in the non-clipped kidney of G2R1C rats. Valsartan reduced MEMB AlaAP and AspAP activities in the renal cortex of normotensive and in the clipped kidney of hypertensive rats. The reduced metabolism of Ang III may prolong its half-life in valsartan-treated animals. These results suggest a role for AlaAP in renovascular hypertension. In addition, the higher AspAP activity of the renal cortex compared to medulla reflects its relative functional difference between both locations.

Plasma Aminopeptidase Activities in Rats after Left and Right Intrastriatal Administration of 6-Hydroxydopamine

Asymmetries in the neuroendocrine system extend from central structures to paired endocrine glands and their innervation. In addition to the well-known asymmetry in the function of brain dopamine, there are also asymmetries in the peripheral response to experimental hemi-parkinsonism, performed by means of lesions of the nigrostriatal system with 6-hydroxydopamine (6-OHDA) injections into the left or right hemisphere. Therefore, it is speculated that the neuroendocrine system would also be asymmetrically affected in experimental hemi-parkinsonism. Aminopeptidases (AP) play a major role in the control of peptide concentration at both central and peripheral levels in tissues and blood, thus reflecting the functional status of their endogenous substrates. Therefore, to evaluate the peripheral response of hemi-parkinsonism, we have performed a comprehensive study of plasma AP activities after lesions of the nigrostriatal system with 6-OHDA administered into either left or right striatum of adult male rats. Saline was injected into control groups. AlaAP, CysAP, AspAP and GluAP activities were determined in plasma, using specific arylamides as substrates. Plasma AlaAP activity increased 3-fold (p < 0.001) whereas AspAP activity decreased by 30% (p < 0.05) after lesion of the right hemisphere. In contrast, CysAP and GluAP activities increased significantly after lesion of the left hemisphere by 200 and 50%, respectively (p < 0.05). The main discovery of the present results demonstrates that experimental hemi-parkinsonism affects differentially the plasma AP activities depending on the hemisphere in which the lesion is performed. This suggests that the circulating hormones, susceptible to be hydrolyzed by these enzymatic activities, are also modified.