Wojciech Nowacki

Inflammatory response following acute magnesium deficiency in the rat

The importance of inflammatory processes in the pathology of Mg deficiency has been recently reconsidered but the sequence of events leading to the inflammatory response remains unclear. Thus, the purpose of the present study was to characterize more precisely the acute phase response following Mg deficiency in the rat. Weaning male Wistar rats were pair-fed either a Mg-deficient or a control diet for either 4 or 8 days. The characteristic allergy-like crisis of Mg-deficient rats was accompanied by a blood leukocyte response and changes in leukocytes subpopulations. A significant increase in interleukin-6 (IL-6) plasma level was observed in Mg-deficient rats compared to rats fed a control diet. The inflammatory process was accompanied by an increase in plasma levels of acute phase proteins. The concentrations of alpha2-macroglobulin and alpha1-acid glycoprotein in the plasma of Mg-deficient rats were higher than in control rats. This was accompanied in the liver by an increase in the level of mRNA coding for these proteins. Moreover, Mg-deficient rats showed a significant increase in plasma fibrinogen and a significant decrease in albumin concentrations. Macrophages found in greater number in the peritoneal cavity of Mg-deficient rats were activated endogenously and appeared to be primed for superoxide production following phorbol myristate acetate stimulation. A high plasma level of IL-6 could be detected as early as day 4 for the Mg-deficient diet. Substance P does not appear to be the initiator of inflammation since IL-6 increase was observed without plasma elevation of this neuropeptide. The fact that the inflammatory response was an early consequence of Mg deficiency suggests that reduced extracellular Mg might be responsible for the activated state of immune cells.

Accelerated thymus involution in magnesium-deficient rats is related to enhanced apoptosis and sensitivity to oxidative stress

Experimental Mg deficiency leads to alterations in the immune response. Reduction of thymus weight and histological changes were previously observed in Mg-deficient rats after several weeks on a deficient diet, suggesting that functions of this immune organ may be affected by Mg deficiency. More recently, changes in the immune system during early Mg deficiency were shown. Thus, in the present study we examined modifications in the thymus during the early stages of Mg deficiency in weanling rats. From our results, it appears that Mg deficiency accelerates thymus involution. The assessment of apoptosis (enumeration of apoptotic cells on the basis of morphological criteria and intranucleosomal degradation of genomic DNA) showed greater values in thymuses from Mg-deficient rats as compared with controls. This was observed very early, since a significant difference was shown on the second day of deficiency, before reduced weight of thymus, which was recorded in the later period. These results indicate the relationship of accelerated thymus involution with an active process of cell death. Mg deficiency led to histological changes in the thymus. In the early stage of deficiency (second day) the presence of inflammatory cells was shown, suggesting that the inflammatory process was already occurring in the tissue studied. Later (eighth day) an increased proportion of epithelial reticular cells in the cortex was shown, indicating a remodelling process occurring in this period. Enhanced susceptibility to peroxidation also occurred very early during Mg deficiency. It may be hypothesized that disturbances in Mg status of short duration could have cellular effects with various deleterious consequences.

Enhanced tumor necrosis factor-α production following endotoxin challenge in rats is an early event during magnesium deficiency

Magnesium (Mg) plays an essential role in fundamental cellular reactions and the importance of the immuno-inflammatory processes in the pathology of Mg deficiency has been recently reconsidered. The purpose of the present study was to assess the effect of different stages of Mg deficiency on endotoxin response and tumor necrosis factor-alpha (TNF alpha) production. Weaning male Wistar rats were pair fed either a Mg-deficient or a control diet. At day 7, lipopolysaccharide (LPS) induced no lethal effects in control rats but resulted in 70% mortality in Mg-deficient rats within 3 h. The vulnerability of Mg-deficient rats to LPS was associated with higher TNF alpha plasma values. Mg-deficient animals that received magnesium supplementation before endotoxin challenge had significantly increased survival. At day 2, control and Mg-deficient rats were also subjected to endotoxin challenge with or without magnesium pre-treatment. A significant increase in TNF alpha plasma level was observed in Mg-deficient rats compared to rats fed the control diet. Mg-deficient rats that received magnesium replacement therapy before endotoxin challenge had significantly lower TNF alpha plasma values than those receiving saline before endotoxin. Thus, the results of this experiment suggest that the activated or primed state of immune cells is an early event occurring in Mg deficiency.

Magnesium deficiency and metabolic syndrome: stress and inflammation may reflect calcium activation

Magnesium (Mg) intake is inadequate in the western diet and metabolic syndrome is highly prevalent in populations around the world. Epidemiological studies suggest that high Mg intake may reduce the risk but the possibility of confounding factors exists, given the strong association between Mg and other beneficial nutriments (vegetables, fibers, cereals). The concept that metabolic syndrome is an inflammatory condition may explain the role of Mg.Mg deficiency results in a stress effect and increased susceptibility to physiological damage produced by stress. Stress activates the hypothalamic-pituitary-adrenal axis (HPA) axis and the sympathetic nervous system. The activation of the renin-angiotensin-aldosterone system is a factor in the development of insulin resistance by increasing oxidative stress. In both humans and rats, aldosteronism results in an immunostimulatory state and leads to an inflammatory phenotype. Stress response induces the release of large quantities of excitatory amino acids and activates the nuclear factor NFkappaB, promoting translation of molecules involved in cell regulation, metabolism and apoptosis. The rise in neuropeptides is also well documented. Stress-induced HPA activation has been identified to play an important role in the preferential body fat accumulation but evidence that Mg is involved in body weight regulation is lacking. One of the earliest events in the acute response to stress is endothelial dysfunction. Endothelial cells actively contribute to inflammation by elaborating cytokines, synthesizing chemical mediators and expressing adhesion molecules. Experimental Mg deficiency in rats induces a clinical inflammatory syndrome characterized by leukocyte and macrophage activation, synthesis of inflammatory cytokines and acute phase proteins, extensive production of free radicals. An increase in extracellular Mg concentration decreases inflammatory effects, while reduction in extracellular Mg results in cell activation. The effect of Mg deficiency in the development of insulin resistance in the rat model is well documented. Inflammation occurring during experimental Mg deficiency is the mechanism that induces hypertriglyceridemia and pro-atherogenic changes in lipoprotein metabolism. The presence of endothelial dysfunction and dyslipidemia triggers platelet aggregability, thus increasing the risk of thrombotic events. Oxidative stress contributes to the elevation of blood pressure. The inflammatory syndrome induces activation of several factors, which are dependent on cytosolic Ca activation. Recent findings support the hypothesis that the Mg effect on intracellular Ca2+ homeostasis may be a common link between stress, inflammation and a possible relationship to metabolic syndrome.

EXACERBATED IMMUNE STRESS RESPONSE DURING EXPERIMENTAL MAGNESIUM DEFICIENCY RESULTS FROM ABNORMAL CELL CALCIUM HOMEOSTASIS

The aim of this study was to assess the potential mechanism underlying the enhanced inflammatory processes during magnesium deficit. In this study, exacerbated response to live bacteria and platelet activating factors was shown in rats fed a magnesium-deficient diet. Peritoneal cells from these animals also showed enhanced superoxide anion production and calcium mobilising potency following in vitro stimulation. The latter effect occurred very early in the course of magnesium deficiency. These studies first showed that an abnormal calcium handling induced by extracellular magnesium depression in vivo may be at the origin of exacerbated inflammatory response.

Extracellular Mg concentration and Ca blockers modulate the initial steps of the response of Th2 lymphocytes in co-culture with macrophages and dendritic cells.

Magnesium is highly involved in the metabolic network such that even subtle disturbances in its homeostasis affect many cellular functions, including calcium homeostasis, signal transduction, energy metabolism, membrane stability and cell proliferation. Recently, magnesium level has been proposed to modulate the priming and activity of immune cells. We studied the behavior of antigen-presenting cells (APCs) and T lymphocytes after altering the magnesium/calcium balance. We used two different populations of primary APCs, i.e. bone marrowderived dendritic cells and bone marrow-derived macrophages, while D10.G4.1 cells served as a model of responding Th2 cells. Our principal findings are the following: (i) the extracellular magnesium concentration had no significant impact on endocytosis by bone marrow-derived APCs, (ii) high concentrations of extracellular magnesium, with or without calcium antagonists, significantly decreased IL-4 and IL-10 secretion by Th2 cells in a co-culture system of APCsandTh2lymphocytes, (iii) proliferation ofTh2cells in co-culture systems was significantly inhibited by calcium antagonists independently from extracellular magnesium concentrations. Our results suggest that alterations of magnesium and calcium homeostasis impact on some crucial steps of the immune response.

Extracellular magnesium and calcium blockers modulate macrophage activity.

Magnesium (Mg) possesses anti-inflammatory properties, partly because it antagonizes calcium (Ca) and inhibits L-type Ca channels. Our aim was to determine the effects of different concentrations of extracellular Mg, with or without Ca-channel blockers, in macrophages. A macrophage-like cell line J774.E was cultured in different concentrations of extracellular Mg and exposed to i) the phorbol ester PMA to induce the production of reactive oxygen species ii) lipopolysaccharide to induce the production of pro-inflammatory cytokines, or iii) ovalbumin to study endocytosis. The Ca antagonists verapamil and/or TMB-8 were used to interfere with Ca homeostasis. Different concentrations of extracellular Mg did not impact on endocytosis, while Ca antagonists markedly decreased it. Low extracellular Mg exacerbated, whereas Ca antagonists inhibited, PMA-induced production of free radicals. Ca blockers prevented lipopolysaccharide-induced transcription and release of IL-1β, IL-6 and TNF-α, while extracellular Mg had only a marginal effect. Ca channel inhibitors markedly reduced the activity of J774.E cells, thus underscoring the critical role of Ca in the non-specific immune response, a role which was, in some instances, also modulated by extracellular Mg.

Increased Apoptosis and Free Radical Production in Thymus of Magnesium-Deficient Rats: Implications to Enhanced Thymus Involution and Immunity

Magnesium plays an important role in the maintenance of host regulatory mechanisms in inflammation and immunity. It is well known that dietary magnesium deficiency in rodents, and especially in rats, causes inflammation (for review[l,2]). This inflammatory reaction is characterized by peripheral vasodilatation, splenomegaly and leukocytosis. Elevated levels of proinflammatory cytokines and acute phase proteins have also been observed during magnesium deficiency [1,2]. On the other hand several observations on the modifications in the immune response during this deficiency have been reported [3]. Since T lymphocytes play a key role in the immune response in the present study we examined modifications occurred in the thymic gland during experimental magnesium deficiency. The thymus presents marked variations in its structure depending on the age and the condition of the organism as a whole. This organ is largest in embryos and gradually and continuously involutes throughout life. However, this process of normal or age involution may be complicated by the rapid changes of “accidental involution”[4]. Since the pioneering work of Selye (1936) it is known that following noxious stimuli, stress results in thymic involution and lymphopenia.