Manuel Bicho

Role of cellular magnesium in health and human disease.

The aim of this paper is to discuss, on the basis of an extensive literature review, the role of magnesium in health and disease. Magnesium is an essential cation playing a crucial role in many physiological functions. It is critical in energy-requiring metabolic processes, in protein synthesis, membrane integrity, nervous tissue conduction, neuromuscular excitability, muscle contraction, hormone secretion, and in intermediary metabolism. Serum magnesium concentration is maintained within a narrow range by the small intestine and kidney which both increase their fractional magnesium absorption under conditions of magnesium deprivation. If magnesium depletion continues, the bone store helps to maintain serum magnesium concentration by exchanging part of its content with extracellular fluid. The abundance of magnesium within cells is consistent with its relevant role in regulating tissue and cell functions. Recent data suggest that large fluxes of magnesium can cross the cell plasma membrane in either direction following a variety of hormonal and non-hormonal stimuli, resulting in major changes in total and, to a lesser extent, in free magnesium content within tissues. Imbalances of magnesium are common and are associated with a great number of pathological situations responsible for human morbidity and mortality. A large part of the population may have an inadequate magnesium intake, and in particular elderly subjects and athletes may be prone to chronic latent magnesium deficiency. Magnesium deficit is frequently observed in alcoholics and diabetic patients, in whom a combination of factors contributes to its pathogenesis. We will discuss some of the aspects of the involvement of magnesium in the etiology of some pathological situations, such as cardiovascular diseases, diabetes, pre-eclampsia, eclampsia, sickle cell disease and chronic alcoholism.

Magnesium, Insulin Resistance and Body Composition in Healthy Postmenopausal Women

Objective: This study was conducted to determine the association between magnesium (Mg), body composition and insulin resistance in 136 sedentary postmenopausal women, 50 to 77 years of age. Methods: Diabetics, hypertensives and women on hormonal replacement therapy were excluded and the remaining 74 were divided according to BMI≥25 (obese: OG) and BMI<25 kg/m2 (non-obese: NOG). Nutritional data disclosed that intakes were high for protein and saturated fat, low for carbohydrates, polyunsaturated fat and Mg and normal for the other nutrients, according to recommended dietary allowances (RDA). Mg values in red blood cells (RBC-Mg) and plasma (P-Mg), were determined, as were fasting glucose, and insulin levels, Homeostasis Model Assessment (HOMA), body mass index (BMI), body fat percent (BF %), abdominal fat (AF) and free fat mass (FFM). Results: RBC-Mg values were low in both groups when compared with normal values. There were significant differences in body composition parameters, HOMA and insulin levels, with higher basal insulin levels in OG. RBC-Mg was directly correlated with insulin, HOMA and FFM in both groups, according to Pearson correlations. HOMA in OG was also directly correlated with BMI, FFM and AF. In NOG, HOMA was only correlated with FFM. The low RBC-Mg levels observed were probably due to low Mg intake and to deregulation of factors that control Mg homeostasis during menopause. Conclusions: Both Mg deficit and obesity may independently lead to a higher risk for insulin resistance and cardiovascular disease.

ACP1 genotype, glutathione reductase activity, and riboflavin uptake affect cardiovascular risk in the obese

Erythrocyte acid phosphatase (ACP locus 1), also known as low-molecular-weight protein tyrosine phosphatase, has previously been associated to glycemia, dyslipidemia, and obesity. In this study, ACP1 genotype and activity were tested in 318 women aged 19 to 83 (mean, 51.74 +/- 13.44) years. ACP1 genotype was found to directly correlate to glutathione reductase activity (P < .001) and levels of low-density lipoprotein cholesterol (P = .038). Glutathione reductase activity was in turn found to correlate to a series of cardiovascular risk factors such as systolic arterial pressure (P < .001), total cholesterol levels (P = .018), and low-density lipoprotein cholesterol levels (P = .039). A possible protective effect of ACP1 genotype AA against these cardiovascular risk factors was observed in this study. Furthermore, this work hypothesizes that nutritional riboflavin uptake becomes more crucial as body mass index increases, to counteract oxidative stress and minimize cardiovascular risk. This might be especially true in ACP1 genotypes AC, BC, and CC, which might possibly show the least endogenous protection against oxidative stress.

Activation of a NADH Dehydrogenase in the Human Erythrocyte by Beta-Adrenergic Agonists: Possible Involvement of a G Protein in Enzyme Activation

NADH dehydrogenase in the plasma membrane transfers electrons from NADH to external oxidants like ferricyanide, through pathways which are linked to metabolic processes in the cell. Hormone binding to specific sites (receptors) can modify the enzyme activity, suggesting a direct or indirect coupling between the redox system and the hormone receptors. Reduction of external ferricyanide to ferrocyanide by human erythrocytes was stimulated by beta-adrenergic agonists (adrenaline, ritodrine and isoxsuprine), this effect being dependent upon concentration and pH. The agonist-stimulatory effect was attenuated in the presence of metoprolol (10(-4) M), a beta-adrenergic antagonist, and was not modified in the presence of prazosin, an alpha-adrenergic antagonist, suggesting that modification of the redox activity is mediated by binding of the agonists to beta-adrenergic receptors present in the human erythrocytes. Basal and agonist-dependent activities were inhibited in the presence of sulfhydryl reagents p-chloromercuribenzoate (PCMB, 10(-5) M) and N-ethylmaleimide (NEM, 10(-3) M), indicating the involvement of -SH groups. Inactivation by NEM was reversed by washing the cells with GTP (10(-3) M) and GTP gamma S (10(-4) M), suggesting that the specific alkylated -SH group(s) is located on a G protein in the hormone-receptor-G-protein complex. The human erythrocytes contain G proteins, displaying both guanine-nucleotide-binding properties and GTPase activity. Fluoride (10(-2) M) and fluoroaluminate (AlF4- (F-, 10(-2) M + Al3+, 10(-5) M), G protein activators, enhanced the basal and agonist-dependent activities, suggesting the involvement of G proteins in this system. The overall results indicated that one of the coupling components between the hormonal receptors and the redox system is probably a G protein, and the mechanism of enzyme activation after hormone binding to the receptor is based on the redox state of cysteine residues probably within the receptor-G-protein complex.

Validation and clinical application of an UHPLC method for simultaneous analysis of total homocysteine and cysteine in human plasma

Several studies indicate that high levels of homocysteine (Hcy) and L-cysteine (L-Cys) are independent risk factors for cardiovascular disease. The validation and clinical application of an ultra HPLC method for analysis of Hcy and L-Cys is described. The reported method is simple, sensitive, rapid, precise, and less aggressive than other previously reported methods. The effect of the derivatization reaction time, pH, and organic solvent contents in the mobile phase are described and discussed. Optimized conditions resulted in excellent peak shapes. Results of method validation showed a good linearity (r(2) ≥ 0.993) over the investigated concentration ranges and were observed for both compounds. The LOD and LOQ were 0.05 μM and 0.15 μM for Hcy and 0.24 μM and 0.80 μM for L-Cys, respectively. Validation results proved that the method precision was good and the accuracy was satisfactory. This validated method was successfully applied in an epidemiological study to measure and compare the prevalence of Hcy and L-Cys high levels in plasma of Portuguese type 2 diabetic patients with and without angiopathy. The study results showed that prevalence of hyperhomocysteinemia and hypercysteinemia were at least two times higher in diabetic patients with angiopathy compared to diabetics without angiopathy.

The role of low-molecular-weight protein tyrosine phosphatase (LMW-PTP ACP1) in oncogenesis

Protein tyrosine phosphorylation is a crucial cellular event that is involved in the most important processes of cellular metabolism. Low-molecular-weight protein tyrosine phosphatase (LMW-PTP) is a tyrosine phosphatase that presents two active distinct isoforms and is regulated through cysteine oxidation and tyrosine phosphorylation. This enzyme has been linked to tumorigenesis, but its role is considered controversial: it may be considered oncogenic or anti-oncogenic depending on its interaction with different substrates. Furthermore, recent studies have demonstrated that LMW-PTP is involved in epithelial cell migration, a characteristic of tumor cells. This fact strengthens the importance of this enzyme in the oncogenic process and opens new avenues for future research. The study of LMW-PTP and its pathways may enhance therapeutic strategies that target tyrosine phosphorylation and its substrates. In this review, we try to clarify the importance of this protein in carcinogenesis through the analysis of LMW-PTP interaction with different substrates.

Genetic and environmental factors regulating blood pressure in childhood: prospective study from 0 to 3 years

Objectives: Blood pressure (BP) regulation depends on the interaction between multiple environmental and genetic factors. Of these, BP sensitivity to dietary sodium intake has been one that has been investigated in adults but not in children. The aim of the present study was to investigate, prospectively, the BP profile in relation to different genetic and hormonal factors, in the first 3 years of life. Population and methods: Thirty-nine children born at term following normal pregnancies, with uncomplicated neonatal periods, were randomly selected to take part in the study. BP, weight and length were evaluated every 3 months from birth to 3 years. At the age of 12 months, haptoglobin phenotypes and plasma active renin concentration were determined as well as random urine evaluation of aldosterone, cAMP, dopamine and digoxin-like immunoreactive substances (DLIS). Family history of cardio-vascular diseases was also recorded. Results: Systolic BP (SBP) demonstrated a gradual increase until the age of 6 months with little variation up to 36 months. Tracking of SBP values was also observed from the first year as infants with high values (above the 75 percentile) maintained this tendency up to, at least, the age of 36 months. The comparison between SBP and diastolic BP (DBP) according haptoglobin phenotypes demonstrated that SBP was systematically higher in allele 1, with apparently an increasing tendency with age, although the differences did not have statistical significance. The comparative study between haptoglobin phenotypes, with correction for the covariates fractional excretion of sodium and potassium, showed that allele 1 carriers had significantly lower plasma renin and urine aldosterone and cAMP concentrations than allele 2, but dopamine excretion was found to be higher in allele 1 than in allele 2. There were no differences among variables relating to family history of cardiovascular disease. Conclusions: There was an early tracking process of BP values from the first 6 months of life which persists through, at least, to the age of 36 months. Differences in sodium handling between haptoglobin 1 and 2 phenotypes were already present in early childhood, although no significant repercussion in BP values could be demonstrated in the 3-year duration of this study.

Magnesium and strength in elite judo athletes according to intracellular water changes

Magnesium (Mg) deficiency strongly affects muscle performance. In judo, many athletes often undergo impressive weight changes associated with severe dehydration. Common practices used by athletes to achieve a target weight can lead to Mg deficit. This study aimed to understand the impact of Mg changes on strength from periods of weight stability to prior to competition in a sample of elite judo athletes who differentially changed their intracellular water (ICW). The sample consisted of 20 elite male judo athletes. Subjects were divided according to ICW changes: losses below 2% and losses equal to or above 2%. Mg was measured in serum, red blood cells and urine by atomic absorption spectrophotometry. ICW was calculated as the difference between total-body water and extracellular water using dilution techniques. Maximal handgrip strength was evaluated using Jamar Hydraulic Hand Dynamometer. Upper-body power was determined in a bench press. Higher ICW decreases were associated with higher strength reductions, though our results suggest that an increase in red blood cell Mg might attenuate those strength reductions in athletes who decrease the ICW compartment. As Mg losses can be considerable and intake is frequently insufficient, athletes should consider supplementation, especially during periods of weight reduction.

The Relationship between Dehydroepiandrosterone (DHEA), Working Memory and Distraction – A Behavioral and Electrophysiological Approach

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulphate (DHEAS) have been reported to have memory enhancement effects in humans. A neuro-stimulatory action and an anti-cortisol mechanism of action may contribute to that relation. In order to study DHEA, DHEAS and cortisol relations to working memory and distraction, we recorded the electroencephalogram of 23 young women performing a discrimination (no working memory load) or 1-back (working memory load) task in an audio-visual oddball paradigm. We measured salivary DHEA, DHEAS and cortisol both before each task and at 30 and 60 min. Under working memory load, a higher baseline cortisol/DHEA ratio was related to higher distraction as indexed by an enhanced novelty P3. This suggests that cortisol may lead to increased distraction whereas DHEA may hinder distraction by leading to less processing of the distractor. An increased DHEA production with consecutive cognitive tasks was found and higher DHEA responses attributed to working memory load were related to enhanced working memory processing as indexed by an enhanced visual P300. Overall, the results suggest that in women DHEA may oppose cortisol effects reducing distraction and that a higher DHEA response may enhance working memory at the electrophysiological level.

Insulin and high glucose modulation of phosphatase and reductase enzymes in the human erythrocytes: a comparative analysis in normal and diabetic states

The ability of insulin to influence activities of various protein kinases and protein phosphatases, that are thought to mediate insulin action, are limited in patients with insulin resistance. Because numerous responses to insulin are affected, we undertook studies to determine whether protein tyrosine phosphatases (PTPs) activities are altered in patients with diabetes syndrome. In order to evaluate abnormal PTP activities, we done a comparative study using erythrocytes from normal and diabetic patients. We determined the activity of the cytosolic acid PTP in basal and insulin-dependent states. Mean basal PTP activities, were found to be significantly higher in diabetics than in normal subjects (type 1 diabetics: 0.36 +/- 0.01 vs 0.28 +/- 0.01 mmol p-nitrophenolate/h per g hemoglobin (Hb), P < 0.001; type 2 diabetics: 0.35 +/- 0.01 vs 0.28 +/- 0.01 mmol p-nitrophenolate/h per g Hb, P < 0.001). Insulin, at concentrations above physiological levels (1 mIU/ml), inhibited the PTP activities in erythrocytes from normal subjects (-15 +/- 4.1%, P < 0.01). Insulin could also modulate glycolysis, probably as a consequence of receptor tyrosine kinase activation, inducing phosphorylation of protein band 3 and hence the release of glycolytic enzymes. We have previously reported that a reductase enzyme in human erythrocytes is dependent on glycolysis being significantly activated (+28 +/- 3.1%, P < 0.001) by high insulin levels (1 mIU/ml). Mean basal reductase activities were found to be significantly lower in diabetics than in normal subjects (type 1 diabetics: 0.77 +/- 0.03 vs 0.97 +/- 0.02 mmol ferrocyanide/20 min per l cells, P < 0.001; type 2 diabetics: 0.77 +/- 0.04 vs 0.97 +/- 0.02 mmol ferrocyanide/20 min per l cells, P < 0.001), indicating altered erythrocyte metabolism in the diabetic patients. High glucose levels were used to mimic hyperglycemia condition, using erythrocytes from normal subjects. At 30 mM glucose, erythrocytic phosphatase activity was stimulated (+32 +/- 4.2%, P < 0.0001), although no effect was observed on the reductase enzyme at the same glucose levels. Results indicated that diabetic disorders appear to be associated with quantitative alterations of erythrocyte acid phosphatase activity and other enzymes that depend on the glycolytic rate (reductase). The overall data suggest that erythrocyte acid phosphatase may have a role in the modulation of glycolytic rates through the control of insulin receptor phosphorylation.