Inflammation and elevation of C-reactive protein: does magnesium play a key role?

The adverse role played by inflammation in the etiology of humankind's most prevalent chronic diseases compels researchers to work diligently to explore its biologic basis. Recent research supports the concept of an important relationship between dietary factors and inflammation, and in particular the role of magnesium deficiency, however, the specifics of this association are not completely understood. Recent findings from epidemiologic studies support that magnesium intake is inversely associated with C-reactive protein concentration, an important marker of inflammation strongly associated with cardiovascular disease risk. Animal studies have provided many mechanistic possibilities to explain the link between magnesium and inflammation. Further research is needed to understand more completely the role of magnesium in inflammation.

Relation between potassium, magnesium and cardiac arrhythmias

Magnesium may influence the incidence of cardiac arrhythmias by 1) a direct effect 2) an effect on potassium metabolism 3) an effect as a calcium blocking agent. In the event of a magnesium deficiency the cell cannot attract potassium against the transmembrane concentration gradient. The reason may be that a magnesium deficiency interferes with the function of membrane ATPase, and thus the pumping of sodium out from the cell and potassium into the cell is impaired. The interference from a magnesium deficiency on the equilibrium of potassium between the intra- and extracellular spaces may result in changes in the resting membrane potential, changes in potassium conductance across the cell membrane as well as disturbances in the repolarization phase.

Magnesium and potassium interrelationships, experimental and clinical

1) Coexisting Mg and K deficiency may occur with greater frequency than has been previously appreciated. 2) Profound hypokalemia, or refractoriness to K repletion or coexisting hypokalemia and hypocalcemia should suggest the possibility of concurrent Mg and K depletion. 3) The identification and treatment of concurrent K and Mg depletion is especially important in patients with congestive heart failure because of problem of digitalis toxicity. 4) We believe that the role of magnesium in optimizing cardiac function remains to be elucidated, identification and treatment of coexisting Mg and K depletion will be facilitated by making serum Mg a routine electrolyte determination together with Na, K, Cl, CO2.

The heart cell--electrophysiological aspects

A short review is given of the ionic fluxes associated with the action potential in Purkinje fibres, and in sinus and AV-node, and of the influence of variations in the extracellular concentrations of K+, Na+, Ca2+ and Mg2+ on basic electrophysiological parameters. Variations in serum potassium concentration often plays an important role in the genesis of arrhythmias by changing several electrophysiological parameters, whereas only extreme variations in the serum calcium level produce electrophysiological effects of clinical importance. Hypo- and hypernatremia within the ranges observed clinically most probably do not produce significant electrophysiological changes. Variations in extracellular magnesium concentration seem to have effects on electrophysiological parameters particularly when they occur simultaneously with changes in the concentrations of calcium and potassium.

Biomimetic study of the Ca(2+)-Mg2+ and K(+)-Li+ antagonism on biologically active sites: new methodology to study potential dependent ion exchange

Competitive divalent (magnesium and calcium) or monovalent (potassium, lithium and sodium) ion exchange and its influence on a membrane potential formation was studied at biological ligands (BL) such as adenosine triphosphate (ATP), asparagine (Asn) and glutamine (Gln) sites. The sites are dispersed electrochemically in membranes made of the conducting polymers (CPs)--poly(N-methylpyrrole) (PMPy) and poly(pyrrole) (PPy). The membranes are made sensitive to calcium and magnesium or to potassium, sodium and lithium by optimized electrodeposition and soaking procedures supported by the study of membrane topography and morphology. Distinctively different electrochemical responses, i.e. electrical potential transients or currents, are observed in the case of "antagonistic" calcium and magnesium or potassium and sodium/lithium ion pairs. Dissimilarity in the responses is ascribed to a difference between on site vs. bulk concentrations of ions, and is dictated by different transport properties of the ions, as shown by using the Nernst-Planck-Poisson (NPP) model and the diffusion-layer model (DLM). The method described allows inspecting potential-dependent competitive ion-exchange processes at the biologically active sites. It is suggested that this approach could be used as an auxiliary tool in study of potential dependent block in realistic membrane channels, such as Mg block in the N-methyl D-aspartate receptor channel (NMDA).

Making sense of a missense mutation: characterization of MutT2, a Nudix hydrolase from Mycobacterium tuberculosis, and the G58R mutant encoded in W-Beijing strains of M. tuberculosis

Recent polymorphism analyses of Mycobacterium tuberculosis strains have identified missense mutations unique to the W-Beijing lineage in genes belonging to the Nudix hydrolase superfamily. This study investigates the structure and function of one of these Nudix hydrolases, MutT2, and examines the effect that the W-Beijing mutation (G58R) has on enzyme characteristics. MutT2 has a preference for cytidine triphosphates, and although the G58R mutation does not alter nucleotide specificity, it reduces the protein's affinity for divalent cations. The K(D) of free Mg(2+) is 79-fold higher for the G58R mutant (3.30 +/- 0.19 mM) compared with that for the wild-type (41.7 +/- 1.4 microM). Circular dichroism and nuclear magnetic resonance spectroscopy measurements show that while the mutation does not perturb the overall structure of the protein, protein stability is significantly compromised by the presence of the arginine with DeltaG (H(2)O), the free-energy of unfolding, being reduced by 2.48 kcal mol(-1) in the G58R mutant. Homology modeling of MutT2 shows that Gly-58 is in close proximity (10.8 A) to the Mg(2+) binding site formed by the highly conserved Nudix box residues and hydrogen bonds with Ala-54 in the preceding alpha-helix. This may explain the increased divalent cation requirement and decreased stability observed when an arginine is substituted for glycine at this position. A role for MutT2 in the regulation of cytidine-triphosphates available for nucleotide-dependent reactions is postulated, and the impact that the G58R mutation may have on these reactions is discussed.

Physiology of calcium, phosphate and magnesium

The physiology of calcium and the other minerals involved in its metabolism is complex and intimately tied in with the physiology of bone. Five principal humoral factors are involved in maintaining plasma levels of calcium, magnesium and phosphate and coordinating the balance between these and their content in bone. The transmembrane transport of these elements is dependent on a series of complex mechanisms that are controlled by these hormones. The plasma concentration of calcium is initially sensed by a calcium-sensing receptor which then sets up a cascade of events that initially determines parathyroid hormone secretion and eventually results in a specific action within the target organs, mainly bone and kidney. This chapter describes the physiology of these humoral factors and relates them to the pathological processes that give rise to disorders of calcium and bone metabolism. It details the stages in the calcium cascade and describes the effects on the various target organs. The pathology of disorders of bone and calcium metabolism is described in detail in the relevant chapters.

Specificity of ligand binding to transport sites: Ca2+ binding to the Ca2+ transport ATPase and its dependence on H+ and Mg2+

Ligand binding to transport sites constitutes the initial step in the catalytic cycle of transport ATPases. Here, we consider the well characterized Ca2+ ATPase of sarcoplasmic reticulum (SERCA) and describe a series of Ca2+ binding isotherms obtained by equilibrium measurements in the presence of various H+ and Mg2+ concentrations. We subject the isotherms to statistical mechanics analysis, using a model based on a minimal number of mechanistic steps. The analysis allows satisfactory fits and yields information on occupancy of the specific Ca2+ sites under various conditions. It also provides a fundamental method for analysis of binding specificity to transport sites under equilibrium conditions that lead to tightly coupled catalytic activation.

Potassium, magnesium, and calcium: their role in both the cause and treatment of hypertension

Despite advances in the prevention and treatment of hypertension over the past decade, hypertension remains an important public health challenge. Recent efforts to reduce the prevalence of hypertension have focused on nonpharmacologic means, specifically diet. An increased intake of minerals such as potassium, magnesium, and calcium by dietary means has been shown in some but not all studies to reduce blood pressure in patients with hypertension. This review will discuss the roles of potassium, magnesium, and calcium in the prevention and treatment of essential hypertension with specific emphasis on clinical trial evidence, mechanism of action, and recommendations for dietary intake of these minerals. A high intake of these minerals through increased consumption of fruits and vegetables may improve blood pressure levels and reduce coronary heart disease and stroke.

Long-term effects of maternal magnesium restriction on adiposity and insulin resistance in rat pups

OBJECTIVE

We investigated the long-term effects of maternal/postnatal magnesium (Mg) restriction on adiposity, glucose tolerance, and insulin secretion in the offspring and the probable biochemical mechanisms associated with them.

METHODS AND PROCEDURES

Female weanling Wistar/NIN (WNIN) rats received a control diet or 70% Mg-restricted (MgR) diet for 9 weeks and mated with control males. A third of the restricted dams were shifted to control diet from parturition. Half of the pups born to the remaining restricted dams were weaned on to control diet, while the other half continued on MgR diet. Various parameters were determined in the offspring at 18 months of age.

RESULTS

The percentage of body fat increased, lean body mass (LBM) and fat free mass (FFM) decreased in restricted offspring and were irreversible by rehabilitation. While glucose tolerance and insulin resistance (IR) were comparable among groups, glucose-stimulated insulin secretion and basal glucose uptake by the diaphragm were significantly decreased in restricted offspring and not corrected by rehabilitation. Plasma leptin was lower, and tumor necrosis factor-alpha (TNF-alpha) was higher in restricted offspring, whereas expression of fatty acid synthase (FAS) and fatty acyl transport protein 1 (FATP 1) was higher in liver and adipose tissue. While changes in FAS and FATP 1 were not correctible by rehabilitation, those in leptin and TNF-alpha were corrected by rehabilitation from parturition but not from weaning. Tissue oxidative stress and antioxidant status were comparable among groups.

DISCUSSION

Results indicate that maternal and postnatal Mg status is important in the long-term programming of body adiposity and insulin secretion in rat offspring.

TRP channels: an overview

The TRP ("transient receptor potential") family of ion channels now comprises more than 30 cation channels, most of which are permeable for Ca2+, and some also for Mg2+. On the basis of sequence homology, the TRP family can be divided in seven main subfamilies: the TRPC ('Canonical') family, the TRPV ('Vanilloid') family, the TRPM ('Melastatin') family, the TRPP ('Polycystin') family, the TRPML ('Mucolipin') family, the TRPA ('Ankyrin') family, and the TRPN ('NOMPC') family. The cloning and characterization of members of this cation channel family has exploded during recent years, leading to a plethora of data on the roles of TRPs in a variety of tissues and species, including mammals, insects, and yeast. The present review summarizes the most pertinent recent evidence regarding the structural and functional properties of TRP channels, focusing on the regulation and physiology of mammalian TRPs.

Correlations suggest low magnesium may lead to higher rates of type 2 diabetes in Indigenous Australians

INTRODUCTION

Diabetes accounts for a significant part of the morbidity and mortality experienced by Australian Aboriginal and Torres Strait Islander populations. Research over the past two decades has provided evidence of a clinical correlation between diabetes and low magnesium intake. Hypomagnesaemia is the most common electrolyte abnormality in diabetic outpatients and may be linked to the development of both macrovascular and microvascular diabetic complications. A diabetes risk reduction of 33%-34% has been found among those with diets highest in magnesium.

OBJECTIVE

This study examines the case for magnesium as a potential contributor to diabetes in Australia, especially among Aboriginal and Torres Strait Islander peoples. Specifically explored are associations between diabetes and the magnesium content of drinking water and diet, as well as climatic and socioeconomic factors that may impact on magnesium status including temperature, rainfall, education, employment and income.

METHODS

Queensland age-standardized death rates due to diabetes were correlated with the magnesium content of drinking water, maximum average temperature, rainfall, unemployment rate, proportion of population with post-school qualification, weekly income, and the percentage population identified as Indigenous. Multiple-pass 24-hour recalls from a convenience sample of 100 Indigenous patients at a regional centre were also analyzed to estimate dietary magnesium intake. The Indigenous nutrient intake was then compared with the Australian National Nutrition Survey estimates.

RESULTS

Diabetes related mortality was significantly correlated to the percentage of the population identified as Indigenous (r = 0.675), to water magnesium levels (r = -.414), and to average maximum daily temperature (r = 0.579). The average daily magnesium intake in an Indigenous cohort from a regional centre was 248 mg (men: 267 mg +/- 17; women: 245 mg +/- 6 mg), significantly less than intakes observed in the 1995 National Nutrition Survey (p<.001).

CONCLUSIONS

Although not representative of all Indigenous people, this study identified low dietary magnesium intake among an Indigenous cohort from a regional centre. We also found a significant correlation between the magnesium content of municipal water supplies and age-standardized deaths due to diabetes. We hypothesise that low magnesium dietary intake, compounded by inadequate magnesium replenishment in drinking water, may increase the risk of hypomagnesaemia in the Indigenous population of Queensland. The associations identified in this study support the hypothesis that magnesium may be a potential contributor to diabetes in Australia, especially among Indigenous people, and confirm the need for further research.

Magnesium–calcium signalling in rat parotid acinar cells: effects of acetylcholine

This study investigated the effects of extracellular Mg(2+) ([Mg(2+)](o)) on basal and acetylcholine (ACh)-evoked amylase secretion and intracellular free Ca(2+) ([Ca(2+)](i)) in rat parotid acinar cells. In a medium containing 1.1 mM [Mg(2+)](o), ACh evoked significant increases in amylase secretion and [Ca(2+)](i). Either low (0 mM) or elevated (5 and 10 mM) [Mg(2+)](o) attenuated ACh-evoked responses. In a nominally Ca(2+) free medium, elevated [Mg(2+)](o) attenuated basal and ACh-evoked amylase secretion and [Ca(2+)](i). In parotid acinar cells incubated with either 0, 1.1, 5 or 10 mM [Mg(2+)](o), ACh evoked a gradual decrease in [Mg(2+)](i). These results indicate that the ACh-evoked Mg(2+) efflux is an active process since Mg(2+) has to move against its gradient. Either lidocaine, amiloride, N-methyl-D: -glucamine, quinidine, dinitrophenol or bumetanide can elevate [Mg(2+)](i) above basal level. In the presence of these membrane transport inhibitors, ACh still evoked a decrease in [Mg(2+)](i) but the response was less pronounced with either [Na(+)](o) removal or in the presence of either amiloride or quinidine. These results indicate marked interactions between Ca(2+) and Mg(2+) signalling in parotid acinar cells and that ACh-evoked Mg(2+) transport was not dependent upon [Na(+)](o).

[Hypomagnesemia and hypoparathyroidism]

Magnesium (Mg) is the second most abundant intracellular cation in human and is involved in numerous biological processes. The kidney and intestinal tract are the principal organs involved in Mg homeostasis. Although calcium (Ca) is considered to be the major regulator of PTH secretion, a number of studies have demonstrated that Mg can modulate PTH secretion in a manner similar to Ca. Especially, it has been suggested that intracellular Mg depletion impairs the ability of the parathyroid to secrete PTH resulting in a fall in the serum PTH levels, and subsequently a fall in the serum Ca concentration.

The use of magnesium in bronchial asthma: a new approach to an old problem

Magnesium deficiency is a common electrolyte disorder in patients with acute severe asthma, but intracellular magnesium content better reflects its homeostasis than does its serum concentration. Magnesium takes part in many metabolic processes in the organism, including energy metabolism, protein and nucleic acid synthesis, cell cycle, the binding of substances to the plasma membrane, and maintenance of cytoskeletal and mitochondrial integrity. It also modulates ion transport and influences intracellular calcium concentration. Maintenance of the cells' transmembrane gradient depends on the presence of magnesium, and hypomagnesemia may result in an increase in neuromuscular cell excitability. Magnesium is a cation modulating the smooth muscle contractility of different tissues: hypomagnesemia causes their contraction and hypermagnesemia their relaxation. Suggestions of a positive influence of magnesium in the treatment of asthma exacerbation have been known for a long time, but research results differ. A single dose of intravenous magnesium sulfate given to patients with acute asthma exacerbation has been shown to be safe, but its efficiency is still under discussion. According to the Global Initiative for Asthma GINA-2005, magnesium sulfate administration is not recommended for routine treatment, but it is permitted in patients with severe asthma exacerbation not responding to treatment (evidence category A). Recommendations of the British Thoracic Society allow one dose of magnesium sulfate to patients with acute severe asthma exacerbation and inadequate initial response to broncho-dilating inhalation treatment (evidence category A). Future investigations should help to establish the indications for magnesium use in the treatment of acute asthma exacerbations as well as the magnesium dose and the scheme of its administration.

Magnesium disturbances in critically ill patients

Magnesium alterations can have a noticeable effect on the neuromuscular cardiovascular, and metabolic systems. With recent advances in point-of-care testing, it is now easier to monitor for changes in the serum magnesium concentration and implement therapies in the critical care setting. This article reviews the normal homeostatic mechanisms, clinical abnormalities, and therapeutic strategies for magnesium disturbances in critically ill patients.

Coordinated Peripheral Neuronal Activities Among the Different Regions of the Digestive Tract in Aplysia

Peripheral neuronal somata are scattered throughout the enteric nervous system (ENS) in Aplysia. We found that somata on the outer surface of the digestive tract were more densely distributed on the stomatogastric ring and the posterior gizzard than on other regions. In preparations with or without the central nervous system, two types of synchronous bursting activity were recorded from the nerves of the ENS. Some of the synchronous bursts were recorded from nerves on the crop and stomatogastric ring, whereas others were recorded from nerves on the crop, stomatogastric ring, and gizzard. Experiments using preparations in which the different regions were separated suggested that the former bursts originated in neurons on the crop and the latter originated in neurons on the gizzard. Axonal projections of neurons on the different regions were examined by backfilling and analysis of the direction of impulse conduction. Blocking chemical synapses in separated gizzards depressed EPSP-like potentials and eliminated the bursting activities. When chemical synapses on the crop and stomatogastric ring but not on the gizzard were blocked in a whole digestive tract preparation, bursting activity recorded from nerves on all the regions was decreased, although the frequency of the bursting rhythm did not change. Stimulation of a neuron on the crop elicited bursts in nerves on the gizzard. These results suggest that chemical synaptic connections and a feedback loop along the digestive tract coordinate the synchrony of bursting activity originating in the gizzard.

Ionic effects on viral DNA packaging and portal motor function in bacteriophage phi 29

In many viruses, DNA is confined at such high density that its bending rigidity and electrostatic self-repulsion present a strong energy barrier in viral assembly. Therefore, a powerful molecular motor is needed to package the DNA into the viral capsid. Here, we investigate the role of electrostatic repulsion on single DNA packaging dynamics in bacteriophage phi 29 via optical tweezers measurements. We show that ionic screening strongly affects the packing forces, confirming the importance of electrostatic repulsion. Separately, we find that ions affect the motor function. We separate these effects through constant force measurements and velocity versus load measurements at both low and high capsid filling. Regarding motor function, we find that eliminating free Mg(2+) blocks initiation of packaging. In contrast, Na(+) is not required, but it increases the motor velocity by up to 50% at low load. Regarding internal resistance, we find that the internal force was lowest when Mg(2+) was the dominant ion or with the addition of 1 mM Co(3+). Forces resisting DNA confinement were up to approximately 80% higher with Na(+) as the dominant counterion, and only approximately 90% of the genome length could be packaged in this condition. The observed trend of the packing forces is in accord with that predicted by DNA charge-screening theory. However, the forces are up to six times higher than predicted by models that assume coaxial spooling of the DNA and interaction potentials derived from DNA condensation experiments. The forces are also severalfold higher than ejection forces measured with bacteriophage lambda.

Magnesium physiology and pathogenic mechanisms that contribute to the development of the metabolic syndrome

The clinical and public health impact of the metabolic syndrome (MetS) has increased substantially in recent years. MetS is defined by a constellation of cardiovascular disease risk factors including: insulin resistance, elevated blood pressure, impaired glucose tolerance, central obesity, and atherogenic dyslipidemia as well as impaired clotting, increased inflammatory burden, and oxidative stress. Recently, there has been burgeoning experimental, clinical, and epidemiological data that provides strong evidence that dietary magnesium intake and supplementation are inversely associated with the risk for MetS and its components. In this review, we describe and discuss the myriad of integrated physiological mechanisms through which magnesium deficiency and the resultant altered magnesium status may lead to the development of the MetS and each of its components.

Protective effect of magnesium and potassium ions on the permeability of the external mitochondrial membrane

The data reported are fully consistent with the well-known observation that exogenous cytochrome c (cyto-c) molecules do not permeate through the outer membrane of mitochondria (MOM) incubated in isotonic medium (250 mM sucrose). Cyto-c is unable to accept electrons from the sulfite/cyto-c oxido-reductase (Sox) present in the intermembrane space, unless mitochondria are solubilized. Mitochondria incubated in a very high hypotonic medium (25 mM sucrose), in contrast to any expectation, continue to be not permeable to added cyto-c even if Sox and adenylate kinase are released into the medium. The succinate/exogenous cyto-c reductase activity, very low in isotonic medium, is greatly increased decreasing the osmolarity of the medium but in both cases remains insensitive to proteolysis by added trypsin. In hypotonic medium, magnesium and potassium ions have a protective effect on the release of enzymes and on the reactivity of cyto-c as electron acceptor from both sulfite and succinate; results which are consistent with the view that MOM preserves its identity and remains not permeable to exogenous cyto-c. This report strengthens the proposal, supported by previously published data that in isotonic medium the exogenous NADH/cyto-c electron transport system is catalyzed by intact mitochondria, not permeable to added cyto-c.