Role of magnesium in patho-physiological processes and the clinical utility of magnesium ion selective electrodes

High Magnesium Promotes the Recovery of Binocular Vision from Amblyopia via TRPM7

Abnormal visual experience during the critical period can cause deficits in visual function, such as amblyopia. High magnesium (Mg2+) supplementary can restore ocular dominance (OD) plasticity, which promotes the recovery of amblyopic eye acuity in adults. However, it remains unsolved whether Mg2+ could recover binocular vision in amblyopic adults and what the molecular mechanism is for the recovery. We found that in addition to the recovery of OD plasticity, binocular integration can be restored under the treatment of high Mg2+ in amblyopic mice. Behaviorally, Mg2+-treated amblyopic mice showed better depth perception. Moreover, the effect of high Mg2+ can be suppressed with transient receptor potential melastatin-like 7 (TRPM7) knockdown. Collectively, our results demonstrate that high Mg2+ could restore binocular visual functions from amblyopia. TRPM7 is required for the restoration of plasticity in the visual cortex after high Mg2+ treatment, which can provide possible clinical applications for future research and treatment of amblyopia.

Understanding How Minerals Contribute to Optimal Immune Function

Sufficient mineral supply is vital not only for the innate immune system but also for the components of the adaptive immune defense, which encompass defense mechanisms against pathogens and the delicate balance of pro- and anti-inflammatory regulation in the long term. Generally, a well-balanced diet is capable of providing the necessary minerals to support the immune system. Nevertheless, specific vulnerable populations should be cautious about obtaining adequate amounts of minerals such as magnesium, zinc, copper, iron, and selenium. Inadequate levels of these minerals can temporarily impair immune competence and disrupt the long-term regulation of systemic inflammation. Therefore, comprehending the mechanisms and sources of these minerals is crucial. In exceptional circumstances, mineral deficiencies may necessitate supplementation; however, excessive intake of supplements can have adverse effects on the immune system and should be avoided. Consequently, any supplementation should be approved by medical professionals and administered in recommended doses. This review emphasizes the crucial significance of minerals in promoting optimal functioning of the immune system. It investigates the indispensable minerals required for immune system function and the regulation of inflammation. Moreover, it delves into the significance of maintaining an optimized intake of minerals from a nutritional standpoint.

Role of Magnesium in the Intensive Care Unit and Immunomodulation: A Literature Review

Both the role and the importance of magnesium in clinical practice have grown considerably in recent years. Emerging evidence suggests an association between loss of magnesium homeostasis and increased mortality in the critical care setting. The underlying mechanism is still unclear, but an increasing number of in vivo and in vitro studies on magnesium's immunomodulating capabilities may shed some light on the matter. This review aims to discuss the evidence behind magnesium homeostasis in critically ill patients, and its link with intensive care unit mortality via a likely magnesium-induced dysregulation of the immune response. The underlying pathogenetic mechanisms, and their implications for clinical outcomes, are discussed. The available evidence strongly supports the crucial role of magnesium in immune system regulation and inflammatory response. The loss of magnesium homeostasis has been associated with an elevated risk of bacterial infections, exacerbated sepsis progression, and detrimental effects on the cardiac, respiratory, neurological, and renal systems, ultimately leading to increased mortality. However, magnesium supplementation has been shown to be beneficial in these conditions, highlighting the importance of maintaining adequate magnesium levels in the intensive care setting.

A chemically modified solid-state sensor for magnesium(ii) ions and esomeprazole magnesium potentiometric assay

The use of electrochemical sensors offers a simple, affordable solution with great reliability. Magnesium is a mineral that the body requires to function properly. It encourages preserving a stable pulse, strong bones, and healthy blood pressure. Herein, a novel ion-selective electrode using esomeprazole magnesium trihydrate as an ion-association complex was developed for magnesium(ii) ion determination in mineral water, drug substances, and pharmaceutical formulations. The electrode response was optimized in terms of plasticizer type, ion exchanger concentration, and membrane composition. To find the best sensor combination, the initial optimization research was performed using eight different sensors. A membrane containing 20% esomeprazole magnesium trihydrate, 36% carbon, and 44% o-Nitrophenyl Octyl Ether (NPOE) as a plasticizer yielded the best potentiometric response. The developed sensor demonstrated a Nernstian response with a slope of 29.93 ± 0.1 mV per decade in the concentration range of 1.41 × 10^-5 mol L^-1 to 1 × 10^-2 mol L^-1. Within a pH range of 5-8, it had a low detection limit of 4.13 × 10^-6 mol L^-1. When compared to the official method, there are no statistically significant differences.

Plasma-Ionized Magnesium in Hospitalized Horses with Gastrointestinal Disorders and Systemic Inflammatory Response Syndrome

Simple Summary

Gastrointestinal diseases are the most prevalent diseases in hospitalized horses. One of the predisposing factors of decreased intestinal motility in horses with colic could be low plasma calcium concentration and related magnesium imbalances. Magnesium and calcium disturbances can predispose to decreased intestinal motility in horses with colic after abdominal surgery. Plasma ionized magnesium concentrations were measured in hospitalized horses with different types of gastrointestinal disorders (i.e., colic), horses with non-gastrointestinal diseases, horses with systemic inflammatory conditions and control horses; our results allowed us to conclude that hypomagnesemia was more prevalent in horses with obstructive gastrointestinal lesions. Surprisingly, no association was found with systemic inflammatory conditions nor with mortality. These valuable results suggest to us that magnesium concentrations in horses presenting obstructive colic should be monitored. Further research is needed to evaluate the effects of intravenous magnesium supplementation in horses with gastrointestinal diseases.

Abstract

Magnesium disorders in horses with gastrointestinal disorders or systemic inflammatory response syndrome (SIRS) are scarcely characterized. The purpose of the study was to explore the association of magnesium disorders with diagnosis, SIRS and mortality in horses admitted to a referral equine hospital. In total, 75 sick horses were included in an observational prospective study and classified as: obstructive (n = 17), inflammatory (n = 10) and ischemic gastrointestinal disorders (n = 12), and other non-gastrointestinal systemic disorders (n = 36). All sick horses were also divided according to the presence (n = 26) or absence of SIRS, and survival to discharge from hospital (survivors (n = 61) and non-survivors (n = 14). In addition, 26 horses were included as controls. On admission, mean (iMg) (95% confidence interval (CI)) in the SIRS group (0.47 (0.43–0.50 mmol/L)) was within the normal range (0.4–0.6 mmol/L). The obstructive group had lower (iMg) compared to the control group (0.44 (0.38–0.51 mmol/L) vs. 0.56 (0.50–0.61 mmol/L); p = 0.001). In total, 8 out of 17 (47%) horses with obstructive lesions presented with hypomagnesemia compared to controls (4% (1/26)) (p = 0.001). In conclusion, hypomagnesemia was more prevalent on admission in horses in the obstructive group, and to a lesser extent, in the inflammatory and ischemic groups. In contrast to human ICU patients, the proportion of hospitalized horses with hypomagnesemia was not associated with mortality.

Nuclear Magnetic Resonance-Measured Ionized Magnesium Is Inversely Associated with Type 2 Diabetes in the Insulin Resistance Atherosclerosis Study

The aims were to optimize a nuclear magnetic resonance (NMR)-based assay for quantifying ionized or free magnesium and investigate its association with type 2 diabetes (T2D). A high-throughput, ionized magnesium assay was optimized and evaluated. Plasma magnesium was quantified, and associations with T2D were ascertained in Insulin Resistance Atherosclerosis Study (IRAS) participants. Coefficients of variation for the ionized magnesium assay ranged from 0.7−1.5% for intra-assay and 4.2−4.7% for inter-assay precision. In IRAS (n = 1342), ionized magnesium was significantly lower in subjects with prediabetes and T2D than in normoglycemic subjects, and lower in participants with T2D than those with prediabetes (p < 0.0001). Cross-sectional regression analyses revealed that magnesium was associated with T2D at baseline in models adjusted for multiple clinical risk factors (p = 0.032). This association appeared to be modified by sex, in such a way that the associations were present in women (OR = 0.54 (95% CI 0.37−0.79), p = 0.0015) and not in men (OR = 0.98 (95% CI 0.71−1.35), p = 0.90). Longitudinal regression analyses revealed an inverse association between magnesium and future T2D in the total population (p = 0.035) that was attenuated by LP-IR (p = 0.22). No interactions were detected between magnesium and age, race, BMI, glucose, insulin, triglycerides, or LPIR for the prospective association with future T2D. However, a significant interaction between magnesium and sex was present, now with a trend for an association in men (OR = 0.75 (95% CI 0.55−1.02), p = 0.065 and absence of an association in women (OR = 1.01 (0.76−1.33), p = 0.97). Conclusions: lower ionized magnesium, as measured by an NMR-based assay optimized for accuracy and precision, was associated cross-sectionally with T2D at baseline and longitudinally with incident T2D in IRAS.

In vivo and in vitro performances of chitosan-coated Mg-Zn-Zr-Gd-Ca alloys as bone biodegradable materials in rat models

Mg alloys have attracted significant attention as promising biomedical materials, specifically as fixation materials for promoting fracture healing. However, their unsatisfactory corrosion resistances hinder further clinical applications and thus require attention. This study aims to determine the performance of novel chitosan-coated Mg-1Zn-0.3Zr-2Gd-1Ca alloy and its ability to promote the healing of osteoporotic fractures. Moreover, its corrosion resistance and biocompatibility were assessed. Performance degradations of the samples were measured via electrochemical tests, weight loss test and morphological analysis, and the uncoated and chitosan-coated fixations were compared based on their effects on biocompatibility via the cytotoxicity test, X-rays, and hematoxylin and eosin staining. The effect of bone growth and healing was investigated via immunohistochemical test. Results of the electrochemical tests indicated that compared with the bare body, chitosan-coated Mg-Zn-Ca-Zr-Gd alloys improved by one order of magnitude. Additionally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and weight loss test demonstrated that the corrosion resistance of the chitosan-coated Mg alloy is better than that of the uncoated alloy. In addition, cytotoxicity analysis indicated that the viability and morphology of the chitosan-coated alloy groups were superior to the uncoated groups in vitro. During in vivo analysis, chitosan-coated and uncoated Mg-1Zn-0.3Zr-2Gd-1Ca alloys were implanted into ovariectomized SD female rats with osteoporotic fractures for 1, 2, and 3 weeks. No displacement and shedding were observed through X-rays, and pathological analyses proved that the material was not harmful for liver and kidney tissues. Immunohistochemistry revealed that the chitosan-coated Mg-Zn-Ca-Zr-Gd alloy material contributed to the healing of osteoporotic fractures in the SD rat models. In conclusion, this study demonstrated the chitosan-coated Mg-Zn-Ca-Zr-Gd alloys have improved corrosion resistance and biocompatibility. Moreover, the alloy was found to accelerate the healing of osteoporotic fractures in SD rat models. Therefore, it has significant potential as a fixation material for osteoporotic fractures.

The Role of Minerals in the Optimal Functioning of the Immune System

Minerals fulfil a wide variety of functions in the optimal functioning of the immune system. This review reports on the minerals that are essential for the immune system’s function and inflammation regulation. We also discuss nutritional aspects of optimized mineral supply. The supply of minerals is important for the optimal function of the innate immune system as well as for components of adaptive immune defense; this involves defense mechanisms against pathogens in addition to the long-term balance of pro- and anti-inflammatory regulation. Generally, a balanced diet is sufficient to supply the required balance of minerals to help support the immune system. Although a mineral deficiency is rare, there are nevertheless at-risk groups who should pay attention to ensure they are receiving a sufficient supply of minerals such as magnesium, zinc, copper, iron, and selenium. A deficiency in any of these minerals could temporarily reduce immune competence, or even disrupt systemic inflammation regulation in the long term. Therefore, knowledge of the mechanisms and supply of these minerals is important. In exceptional cases, a deficiency should be compensated by supplementation; however, supplement over-consumption may be negative to the immune system, and should be avoided. Accordingly, any supplementation should be medically clarified and should only be administered in prescribed concentrations.

Elevation of brain magnesium with Swiss chard and buckwheat extracts in an animal model of reduced magnesium dietary intake

OBJECTIVES

Inadequate dietary magnesium (Mg) intake is a growing public health concern. Mg is critical for diverse metabolic processes including energy production, macromolecule biosynthesis, and electrolyte homeostasis. Inadequate free Mg²⁺ ion concentration ([Mg²⁺]) in the brain is associated with several neurological and behavioral disorders. Elevating [Mg²⁺]in the brain using oral Mg supplementation has proven to be challenging due to the tight regulation of Mg²⁺ transport to the brain. This study explored the effect of short-term moderate reduction in dietary Mg intake (87% of normal Mg diet for 30 days) on [Mg²⁺] in the cerebrospinal fluid (CSF) ([Mg²⁺]_CSF) and red blood cells (RBCs) ([Mg²⁺]_RBC) in adult male rats. In addition, we investigated the effectiveness of magnesium-rich blend of Swiss chard and buckwheat extracts (SC/BW extract) in increasing brain [Mg²⁺] compared to various Mg salts commonly used as dietary supplements.

METHODS

Animals were assigned to either normal or low Mg diet for 30 - 45 days. Following this, animals maintained on low Mg diet were supplemented with various Mg compounds. [Mg²⁺]_CSF and [Mg²⁺]_RBC were measured at baseline and following Mg administration. Anxiety-like behavior and cognitive function were also evaluated.

RESULTS

The present study showed that a short-term and moderate reduction in Mg dietary intake results in a significant decline in [Mg²⁺]_CSF and [Mg²⁺]_RBC and the emergence of anxiety-like behavior in comparison to animals maintained on normal Mg diet. Supplementation with SC/BW extract significantly elevated [Mg²⁺]_CSF and improved animal performance in the novel object recognition test in comparison with animals maintained on reduced Mg intake and supplemented with various Mg compounds.

DISCUSSION

These observations indicate that brain [Mg²⁺] is more sensitive to a short-term and moderate reduction in Mg dietary intake than previously thought and emphasizes the importance of dietary Mg in replenishing brain Mg²⁺ reserves.

Circulating Ionized Magnesium as a Measure of Supplement Bioavailability: Results from a Pilot Study for Randomized Clinical Trial

Oral supplementation may improve the dietary intake of magnesium, which has been identified as a shortfall nutrient. We conducted a pilot study to evaluate appropriate methods for assessing responses to the ingestion of oral magnesium supplements, including ionized magnesium in whole blood (iMg²⁺) concentration, serum total magnesium concentration, and total urinary magnesium content. In a single-blinded crossover study, 17 healthy adults were randomly assigned to consume 300 mg of magnesium from MgCl₂ (ReMag^®, a picosized magnesium formulation) or placebo, while having a low-magnesium breakfast. Blood and urine samples were obtained for the measurement of iMg²⁺, serum total magnesium, and total urine magnesium, during 24 h following the magnesium supplement or placebo dosing. Bioavailability was assessed using area-under-the-curve (AUC) as well as maximum (C_max) and time-to-maximum (T_max) concentration. Depending on normality, data were expressed as the mean ± standard deviation or median (range), and differences between responses to MgCl₂ or placebo were measured using the paired t-test or Wilcoxon signed-rank test. Following MgCl₂ administration versus placebo administration, we observed significantly greater increases in iMg²⁺ concentrations (AUC = 1.51 ± 0.96 vs. 0.84 ± 0.82 mg/dL•24h; C_max = 1.38 ± 0.13 vs. 1.32 ± 0.07 mg/dL, respectively; both p < 0.05) but not in serum total magnesium (AUC = 27.00 [0, 172.93] vs. 14.55 [0, 91.18] mg/dL•24h; C_max = 2.38 [1.97, 4.01] vs. 2.24 [1.98, 4.31] mg/dL) or in urinary magnesium (AUC = 201.74 ± 161.63 vs. 139.30 ± 92.84 mg•24h; C_max = 26.12 [12.91, 88.63] vs. 24.38 [13.51, 81.51] mg/dL; p > 0.05). Whole blood iMg²⁺ may be a more sensitive measure of acute oral intake of magnesium compared to serum and urinary magnesium and may be preferred for assessing supplement bioavailability.

Circulating Ionized Magnesium: Comparisons with Circulating Total Magnesium and the Response to Magnesium Supplementation in a Randomized Controlled Trial

Ionized Mg (iMg) is considered the biologically active fraction of circulating total Mg (tMg). It is possible that iMg may be a more physiologically relevant marker than tMg. Using data from a double-blind pilot randomized controlled trial, we tested (1) whether oral Mg supplementation will increase iMg concentrations compared with placebo and (2) the relationship between iMg and tMg at baseline. Additionally, we evaluated the agreement between iMg measured in fresh whole blood versus stored samples. A total of fifty-nine participants were randomized 1:1 to oral Mg supplementation (400 mg/day, Mg Oxide) or placebo for 10 weeks. Fasting blood samples were obtained at baseline and follow-up. The analysis used linear regression and an intent-to-treat approach. Participants were generally healthy, the mean age was 62, and 73% were female. The baseline iMg and tMg were modestly and positively associated (r = 0.50). The ratio of baseline iMg to tMg was 64%. The mean supplement effect on iMg was 0.03 mmol/L (95% CI:0.01, 0.05) for Mg supplementation versus placebo. The supplement effect on iMg was not statistically significantly different according to baseline iMg status (above/below median). Compared to fresh blood, iMg was consistently higher in refrigerated and frozen samples by 0.14 and 0.20 mmol/L, respectively. In this relatively healthy adult population, Mg supplementation over 10 weeks resulted in increased iMg concentrations. Whether iMg is a more appropriate measure of Mg status than tMg, and the public health or clinical utility of measuring iMg remains to be determined.

Relationship between anti-erythropoietin receptor autoantibodies and responsiveness to erythropoiesis-stimulating agents in patients on hemodialysis: a multi-center cross-sectional study

BACKGROUND

A decreased response to erythropoiesis-stimulating agents (ESAs) leads to refractory anemia and worse prognosis in patients with chronic kidney disease. We examined the association between autoantibodies to the erythropoietin receptor (EPOR) and responsiveness to ESAs in patients on maintenance hemodialysis.

METHODS

A total of 108 Japanese patients on maintenance hemodialysis at three institutions were enrolled. Sera from these patients were screened for anti-EPOR antibodies using an enzyme-linked immunosorbent assay. An ESA resistance index (ERI) was calculated, and patients in the highest ERI quartile were defined as ESA hyporesponsive.

RESULTS

Anti-EPOR antibodies were detected in 11 patients (10%). Body mass index and hemoglobin, platelet, magnesium, and ferritin levels decreased with higher ERI levels. On the other hand, C-reactive protein (CRP) levels and the prevalence of anti-EPOR antibodies increased with higher ERI levels. In multivariate analysis, the presence of anti-EPOR antibodies together with CRP was a significant risk factor for ESA hyporesponsiveness.

CONCLUSIONS

Anti-EPOR antibodies were detected in patients on maintenance hemodialysis, and these autoantibodies were independent factors for hyporesponsiveness to ESAs in these patients.

Use Profile of Magnesium Sulfate in Anesthesia in Brazil

Objectives: The use of magnesium sulfate in the perioperative period has several benefits, including analgesia, inhibition of the release of catecholamines and prevention of vasospasm. The aim of this survey was to provide an overview of the use of magnesium sulfate in anesthesia. Method: This was a prospective descriptive cross-sectional study. An online questionnaire was sent to 9,869 Brazilian anesthesiologists and trainees. The questionnaire comprised closed questions mainly regarding the frequency, clinical effects, adverse events, and doses of magnesium sulfate used in anesthesia. Results: Of the 954 doctors who responded to the survey, 337 (35.32%) reported using magnesium sulfate in anesthesia. The most commonly cited clinical effects for the use of magnesium sulfate in anesthesia were (n/%): postoperative analgesia (245/72.70%), reduction of anesthetic consumption (240/71.21%) and prevention and treatment of preeclampsia and seizures in eclampsia (220/65.28%). The most frequently reported adverse events were hypotension (187/55.48%), residual neuromuscular blockade (133/39.46%), hypermagnesemia (30/8.90%), and intravenous injection pain (26/7.71%). The intravenous doses of magnesium sulfate used in most general anesthesia inductions were between 30 and 40 mg.kg-1. Conclusions: Magnesium sulfate is an important adjuvant drug in the practice of anesthesia, with several clinical effects and a low incidence of adverse events when used at recommended doses.

The association between serum magnesium levels and community-acquired pneumonia 30-day mortality

Background

Community acquired pneumonia (CAP) is a common illness affecting hundreds of millions worldwide. Few studies have investigated the relationship between serum magnesium levels and outcomes of these patients. We aimed to study the association between serum magnesium levels and 30-day mortality among patients with CAP.

Methods

Retrospective overview of patients hospitalized with CAP between January 1, 2010 and December 31, 2016. Participants were analyzed retrospectively in order to identify the risk factors for a primary endpoint of 30-day mortality. Normal levels of magnesium levels in our laboratory varies between 1.35 and 2.4 mg/dl.

Results

3851 patients were included in our cohort. Age > 75 years, blood urea nitrogen (BUN) > 20 mg/dl, hypoalbuminemia, and abnormal levels of magnesium were all associated with increased risk of 30-day mortality. Normal magnesium levels were associated with the lowest mortality rate (14.7%). Notably, within the normal levels, high normal magnesium levels (2–2.4 mg/dl) were correlated with higher mortality rates (30.3%) as compared to levels that ranged between 1.35–2 mg/dl (12.9%). Hypomagnesemia and hypermagnesemia were both associated with excess of 30-day mortality, 18.4 and 50%, respectively.

Conclusion

Hypomagnesemia and hypermagnesemia on admission were associated with an increased rate of 30-day mortality among adult patients hospitalized with CAP. Interestingly, magnesium levels within the upper normal limits were associated with higher mortality.

Major and trace elements in Boletus aereus and Clitopilus prunulus growing on volcanic and sedimentary soils of Sicily (Italy)

The aim of this study was to determine and compare the content of 28 elements (Ag, Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sb, Se, Sr, Tl, U, V and Zn) in fruiting bodies of Boletus aereus Bull. and Clitopilus prunulus P. Kumm collected from eleven unpolluted sites of Sicily (Italy) and, also to relate the abundance of chemical elements in soil with their concentration in mushrooms. Median concentrations of the most abundant elements in Boletus aereus ranged from 31,290 μg/g (K) to 107 μg/g (Zn) in caps and from 24,009 μg/g (K) to 57 μg/g (Zn) in stalks with the following abundance order: K > Na > Ca > Mg > Fe > Al > Rb > Zn. The same elements, in the whole fruiting body of Clitopilus prunulus samples, varied in the range 54,073-92 μg/g following the abundance order: K > Na > Mg > Ca > Fe > Al > Rb > Zn. Metal contents in Boletus aereus and in the whole fruiting body of Clitopilus prunulus, collected from the same sampling sites, showed statistically significant differences for most elements. In particular, Clitopilus prunulus contained around two to four times more Co, Cr, Fe, Mg, Mo, Pb, U and V than caps and stalks of Boletus aereus species which, in turn, was from two to four times more enriched in Cu, Se and Tl. Thus, the elemental content of Boletus aereus and Clitopilus prunulus appeared to be species-dependent. The distribution of chemical elements in Boletus aereus was not uniform throughout the whole fruiting body as most elements were significantly bioconcentrated in caps. Furthermore, the fruit bodies of Boletus aereus from the volcanic soil differed both in major and minor elements concentrations from those collected from sedimentary soils. Cadmium and lead concentrations were below the threshold limits for wild mushrooms proposed by EU Directives (2008 and 2015). The elemental content was not significantly influenced by soil pH.

Serum magnesium but not calcium was associated with hemorrhagic transformation in stroke overall and stroke subtypes: a case-control study in China

Association between serum calcium and magnesium versus hemorrhagic transformation (HT) remains to be identified. A total of 1212 non-thrombolysis patients with serum calcium and magnesium collected within 24 h from stroke onset were enrolled. Backward stepwise multivariate logistic regression analysis was conducted to investigate association between calcium and magnesium versus HT. Calcium and magnesium were entered into logistic regression analysis in two models, separately: model 1, as continuous variable (per 1-mmol/L increase), and model 2, as four-categorized variable (being collapsed into quartiles). HT occurred in 140 patients (11.6%). Serum calcium was slightly lower in patients with HT than in patient without HT (P = 0.273). But serum magnesium was significantly lower in patients with HT than in patients without HT (P = 0.007). In logistic regression analysis, calcium displayed no association with HT. Magnesium, as either continuous or four-categorized variable, was independently and inversely associated with HT in stroke overall and stroke of large-artery atherosclerosis (LAA). The results demonstrated that serum calcium had no association with HT in patients without thrombolysis after acute ischemic stroke. Serum magnesium in low level was independently associated with increasing HT in stroke overall and particularly in stroke of LAA.

Zinc, Magnesium, Selenium and Depression: A Review of the Evidence, Potential Mechanisms and Implications

Micronutrient deficiency and depression are major global health problems. Here, we first review recent empirical evidence of the association between several micronutrients—zinc, magnesium, selenium—and depression. We then present potential mechanisms of action and discuss the clinical implications for each micronutrient. Collectively, empirical evidence most strongly supports a positive association between zinc deficiency and the risk of depression and an inverse association between zinc supplementation and depressive symptoms. Less evidence is available regarding the relationship between magnesium and selenium deficiency and depression, and studies have been inconclusive. Potential mechanisms of action involve the HPA axis, glutamate homeostasis and inflammatory pathways. Findings support the importance of adequate consumption of micronutrients in the promotion of mental health, and the most common dietary sources for zinc and other micronutrients are provided. Future research is needed to prospectively investigate the association between micronutrient levels and depression as well as the safety and efficacy of micronutrient supplementation as an adjunct treatment for depression.

Does Intravenous Magnesium Benefit Patients of Cardiac Arrest? a Meta-Analysis

Objective

Evidence shows that magnesium has anti-arrhythmic roles. However, clinical trials suggest that there are conflicting outcomes of cardiac arrest patients given magnesium. The study aimed to examine the effects of magnesium sulfate therapy on cardiac arrest patients using a meta-analysis.

Methods

We searched the MEDLINE (1966-July 2011), OVID (1980-July 2011), EMBASE (1980-July 2011), Chinese bio-medical literature & retrieval system (1978-July 2011), Chinese medical current contents (1995-July 2011), and Chinese medical academic conference (1994-July 2011). Studies were included if (1) the study design was a randomised controlled trial (RCT); (2) the study population included cardiac arrest patients who received cardiopulmonary resuscitation and either intravenous magnesium or placebo (0.9% normal saline); (3) the study provided data on return of spontaneous circulation (ROSC) and survival to hospital discharge. Relative risk (RR) and 95% confidence interval (CI) were used to pool the effect.

Results

The study included six RCTs with a total of 531 participants from cardiac arrest. The pooled data demonstrated that ROSC and hospital discharge rates in patients treated with magnesium were 35.5% (95% CI=29.7%-41.3%) and 10.4% (95% CI=6.7%-14.1%) compared with placebo (ROSC rate: 31.3%, 95% CI=25.8%-36.8%; hospital discharge rate: 8.5%, 95% CI=5.2%-11.8%). Administration of intravenous magnesium sulfate could not significantly increase ROSC (RR=1.14, 95% CI=0.91-1.43, P=0.26) and survival to hospital discharge (RR=1.22, 95% CI=0.74-2.02, P=0.43) compared with placebo.

Conclusions

Administration of magnesium sulfate does not improve ROSC and survival to hospital discharge in patients of cardiac arrest.

Factors Associated With Changes in Magnesium Levels in Asymptomatic Neonates: A Longitudinal Analysis

Background:

Neonates and infants with hypomagnesemia present with seizures and psychomotor delay.

Objectives:

The present study evaluated the changes in magnesium (Mg) levels and factors associated with these in the first three days of life.

Materials and Methods:

We monitored 50 clinically asymptomatic neonates; they were not given any magnesium supplements even if they had hypomagnesemia at baseline. The variables analysed were: serum Mg; gestational age; birth weight; length; and the ponderal index. We used random effects (RE) models for longitudinal analysis of these data.

Results:

The mean standard deviation (SD) gestational age was 36.3 (3.6) weeks and the mean (SD) weight was 2604.2 (754.4) grams. About 31% of the neonates had hypomagnesemia (< 1.6 mg/dL) on day one; however, all had normal magnesium levels by day three of life (P < 0.001). At birth, after adjusting for intrauterine growth retardation status (IUGR), serum Mg levels were lower by 0.0097 mg/dL (95% CI: -0.019 to -0.0003) per 100 grams increase in weight of the neonate. After adjusting for IUGR status, the mean increase in the serum Mg levels was 0.14 mg/dL (95% confidence intervals [CI]: 0.10 to 0.18) per day. The per-day increase in magnesium levels was significantly higher in low birth weight babies (0.10, 95% CI: 0.01 to 0.18) compared with normal birth weight babies.

Conclusions:

Asymptomatic neonates may have a high prevalence of hypomagnesemia; however, the levels become normal without any magnesium supplementation. Even though regular monitoring of magnesium levels is useful, no supplements are required - particularly in clinically asymptomatic neonates.

The Importance of Magnesium in the Human Body: A Systematic Literature Review

Magnesium, the second and fourth most abundant cation in the intracellular compartment and whole body, respectively, is of great physiologic importance. Magnesium exists as bound and free ionized forms depending on temperature, pH, ionic strength, and competing ions. Free magnesium participates in many biochemical processes and is most commonly measured by ion-selective electrode. This analytical approach is problematic because complete selectivity is not possible due to competition with other ions, i.e., calcium, and pH interference. Unfortunately, many studies have focused on measurement of total magnesium rather than its free bioactive form making it difficult to correlate to disease states. This systematic literature review presents current analytical challenges in obtaining accurate and reproducible test results for magnesium.

Metabolic responses differentiate between interictal, ictal and persistent epileptiform activity in intact, immature hippocampus in vitro

Interictal spikes, ictal responses, and status epilepticus are characteristic of abnormal neuronal activity in epilepsy. Since these events may involve different energy requirements, we evaluated metabolic function (assessed by simultaneous NADH and FAD+ imaging and tissue O2 recordings) in the immature, intact mouse hippocampus (P5-P7, in vitro) during spontaneous interictal spikes and ictal-like events (ILEs), induced by increased neuronal network excitability with either low Mg2+ media or decreased inhibition with bicuculline. In low Mg2+ medium NADH fluorescence showed a small decrease both during the interictal build-up leading to an ictal event and before ILE occurrences, but a large positive response during and after ILEs (up to 10% net change). Tissue O2 recordings (pO2) showed an oxygen dip (indicating oxygen consumption) coincident with each ILE at P5 and P7, closely matching an NADH fluorescence increase, indicating a large surge in oxidative metabolism. The ILE O2 dip was significantly larger at P7 as compared to P5 suggesting a higher metabolic response at P7. After several ILEs at P7, continuous, low voltage activity (late recurrent discharges: LRDs) occurred. During LRDs, whilst the epileptiform activity was relatively small (low voltage synchronous activity) oxygen levels remained low and NADH fluorescence elevated, indicating persistent oxygen utilization and maintained high metabolic demand. In bicuculline, NADH fluorescence levels decreased prior to the onset of epileptiform activity, followed by a slow positive phase, which persisted during interictal responses. Metabolic responses can thus differentiate between interictal, ictal-like and persistent epileptiform activity resembling status epilepticus, and confirm that spreading depression did not occur. These results demonstrate clear translational value to the understanding of metabolic requirements during epileptic conditions.

Alteration of plasma trace elements in patients undergoing open heart surgery

Trace elements may contribute to myocardial dysfunction and susceptibility of the phospholipid cell membrane to free-radical damage and oxidative changes. We studied the concentration of trace elements copper, zinc, and magnesium in cardiac surgery. Fifty-four consecutive patients for elective coronary artery bypass grafting (n = 30) and valve replacement (n = 24) were studied. Blood samples were collected every 30 min (T1-T5) during cardiopulmonary bypass and postoperatively (T6-T9). Plasma concentrations of copper, zinc, and magnesium were measured with flame atomic absorption spectrophotometry. The concentrations of copper, zinc, and magnesium were significantly different during and after cardiopulmonary bypass (p < 0.01). The zinc concentration at T7 and T8 (p < 0.01) and the copper concentration at T1, T9 (p < 0.05) were significantly different between two groups. However, the magnesium concentration had no significant differences between the two groups (p > 0.05). In patients undergoing valve replacement or coronary artery bypass grafting, the concentrations of copper and zinc decreased significantly during cardiopulmonary bypass. Our study suggests that the current cardiopulmonary bypass protocol is adequate in the maintenance of c magnesium. However, the low copper and zinc concentrations found in the present study may suggest that in the future, supplementation particularly of copper and zinc may become a necessary procedure in cardiac surgery with cardiopulmonary bypass.

Relation between zinc, copper, and magnesium concentrations following cardiopulmonary bypass and postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting

Atrial fibrillation is the most frequently encountered arrhythmia following cardiac surgery. Since the essential trace elements zinc, copper, and magnesium are suspected to have an effect on postoperative atrial fibrillation, the concentrations of these elements were determined by flame atomic absorption spectrophotometry in the plasma of 60 patients undergoing elective coronary artery bypass grafting. Blood samples were collected every 30 min during cardiopulmonary bypass and postoperatively. Plasma concentrations of copper, zinc, and magnesium were measured with flame atomic absorption spectrophotometry. All patients were monitored by continuous electrocardiography until they became outpatients or immediately after atrial fibrillation had taken place. Atrial fibrillation occurred in 13 of the 60 patients, corresponding to 21.7%. The zinc and copper concentrations at postoperative days 1 and 3 were significantly different (P < 0.05) between patients with and without atrial fibrillation. The concentrations of zinc following cardiopulmonary bypass recovered more slowly in patients with postoperative atrial fibrillation than in patients without it. Whether or not supplemental zinc could lower the incidence of postoperative atrial fibrillation should be evaluated in future prospective randomized clinical trials.

Do the Micronutrients Zinc and Magnesium Play a Role in Adult Depression?

Depression is a widespread disorder that affects more than 120 million people worldwide. The unsatisfactory clinical efficacy and adverse effects of antidepressant medication have prompted the search for novel treatments. Micronutrient deficiencies may play a role in the development of depression, and recent research studies have explored the use of micronutrient supplementation as an adjunct to the pharmacotherapy of this psychiatric illness. This article provides a review of the empirical evidence linking zinc and magnesium deficiency and depression, discusses possible mechanisms of action in the psychopathology and therapy of depression, and explores the nursing and registered dietitian implications of these findings.

A peculiar form of epilepsy induced by crying in infancy

We describe a peculiar form of epilepsy following prolonged and vigorous bouts of crying in infancy which was misdiagnosed as breath holding spells. Three patients with crying-induced epilepsy had the following characteristics. The patients were born after uncomplicated pregnancy, labor, and delivery. The seizures presented between the ages of 10 and 18 months, the patients had normal development and cranial MRIs, no past or family histories of epilepsy or cardiac disease, and developed generalized tonic clonic seizures only following crying after a sudden, unexpected and mildly unpleasant stimulus. The seizures usually lasted no longer than 1 min and their EEG showed focal spikes in interictal states and generalized spikes in ictal states. The seizures were well controlled with valproate sodium. This peculiar form of epilepsy may be a benign age-dependent reflex epilepsy in infancy.

COPD: magnesium in the plasma and polymorphonuclear cells of patients during a stable phase

Magnesium is one of the most important factors for regulation of inflammatory response as well as muscle function, and COPD is a multicomponent disease characterized by abnormal inflammatory response of the lungs with systemic muscle dysfunction. Because polymorphonuclear (PMN) cells are significantly represented in the pathogenesis of COPD, concentrations of total (tMg) and ionised magnesium (iMg) were determined in plasma and isolated PMN cells in 46 patients in stable phase of COPD (past smokers, current smokers, and non-smokers), 24 healthy smokers and 37 healthy non-smokers. In the same samples concentrations of total (tCa) and ionised calcium (iCa) were determined, due to the antagonism of magnesium towards calcium. We found decreased biological active iMg in PMN compared to the group of healthy non-smokers (5.42, 1.98-17.31 micromol/10(9) cells vs. 7.50, 3.27-15.15 micromol/10(9) cells, p < 0.05). In the plasma and isolated PMN of the patients the ratio of total calcium/total magnesium (tCa/tMg) was significantly increased (2.89, 2.15-3.86 and 1.19, 0.07-9.87) compared to the group of healthy non-smokers (2.65, 2.19-3.44 and 0.67, 0.14-2.40, p < 0.05) and to the group of healthy smokers (2.58, 2.26-3.24 and 0.66, 0.14-2.85, p < 0.05). In the group of patients the concentration of tCa was significantly increased in all samples compared to the healthy group of non-smokers and healthy smokers. The results of univariant logistic regression analysis for smoking, concentration of tCa and ratio of tCa/tMg in PMN showed high odds ratio for COPD status. These results raise a possibility that intracellular polymorphonuclear value of magnesium could be a distinctive marker for COPD risk disclosure among smokers.

Hypomagnesemia after Major Abdominal Operations in Cancer Patients: Clinical Implications

BACKGROUND

Serum magnesium levels are rarely measured in routine chemistry panels. The extent and impact of postoperative serum magnesium changes remain unclear.

METHODS

One hundred seventy-one cancer patients who had undergone celiotomy procedures during a 38-month period were evaluated retrospectively for postoperative electrolyte alterations, with special emphasis on serum magnesium. Clinicopathologic predictors and early postoperative outcome correlations were examined.

RESULTS

There were 151 major procedures and 20 minor operations. All postoperative electrolyte and hematocrit values were significantly different from preoperative values, except for serum phosphate. Preoperative total serum magnesium (normal range: 1.7-2.5 mg/dL {0.7-1.03 mmol/L}), obtained prior to any bowel cleansing, differed from postoperative levels (means +/- standard deviation: 2.0 +/- 0.46 vs. 1.53 +/- 0.33 mg/dL; p < 0.0001). A lowered postoperative serum magnesium was observed in those patients who had either undergone an operation with curative intent (p = 0.0035), a major resection (vs. no resection, p = 0.0259), or preoperative bowel cleansing with sodium phosphate (p = 0.024). Other laboratory serum parameters that correlated with the postoperative magnesium level included postoperative levels of phosphate (p = 0.009), potassium (p = 0.01), and total calcium (p = 0.012), as well as preoperative calcium (p = 0.017). The complication rate was 20%, with five postoperative deaths (2.9%). Postoperative morbidity was predicted by preoperative potassium (p = 0.004) and albumin levels (p = 0.016); deaths were predicted by postoperative infections (p = 0.0007) and correlated to postoperative hypokalemia (p = 0.03).

CONCLUSIONS

Major abdominal cancer operations lead to significant electrolyte alterations. The severity of these changes correlates with the resection extent, especially in procedures with curative intent. In addition, bowel cleansing with sodium phosphate may participate in lowering serum magnesium as well as other electrolytes. In light of our postoperative magnesium replacement policy, no untoward events could be linked to postoperative hypomagnesemia in this series. To evaluate the impact of postoperative hypomagnesemia or magnesium replacement on postoperative outcomes requires a prospective randomized trial.

Studies on cerebrospinal fluid ionized calcium and magnesium concentrations in convulsive children

BACKGROUND

The concentrations of ionized calcium (iCa) and ionized magnesium (iMg) were measured in the cerebrospinal fluid (CSF) of convulsive and non-convulsive children, to investigate the relationship between seizure manifestation and CSF iCa and iMg concentrations. Standard concentrations of CSF iCa and iMg were also established.

METHODS

CSF samples from 23 patients, ages 0-15 years, with various forms of seizures and 26 age-matched non-convulsive children were collected by lumbar puncture. CSF was obtained anaerobically and the concentrations of CSF iCa and iMg were measured with an electolyte analyzer (Stat Profile Ultra M1, NOVA, USA) immediately after the lumbar puncture.

RESULTS

The concentrations of CSF iCa were significantly higher in non-convulsive children younger than 11 months old compared with children older than 12 months. The concentrations of CSF iMg in non-convulsive children did not differ significantly with aging. The concentrations of CSF iCa in convulsive children did not differ significantly from the concentrations of non-convulsive children. The concentrations of CSF iMg in convulsive children were significantly lower than in non-convulsive children.

CONCLUSION

These results suggest that seizure manifestation is related to age-dependent changes in iCa and decreased iMg in the developing brain.

Magnesium and experimental vasospasm

Object. Interest has developed in the use of magnesium (Mg++) as a neuroprotectant and antivasospastic agent. Magnesium may increase cerebral blood flow (CBF) and reduce the contraction of cerebral arteries caused by various stimuli. In this study the authors tested the hypothesis that a continuous intravenous infusion of Mg++ reduces cerebral vasospasm after experimental subarachnoid hemorrhage (SAH).

Methods. A dose-finding study was conducted in five monkeys (Macaca fascicularis) to determine what doses of intravenous MgSO4 elevate the cerebrospinal fluid (CSF) concentrations of Mg++ to vasoactive levels and to determine what effects these doses have on the diameters of cerebral arteries, as shown angiographically. After a standard dose of MgSO4 had been selected it was then administered in a randomized, controlled, blinded study to 10 monkeys (five animals/group) with SAH, beginning on Day 0 and continuing for 7 days, at which time angiography was repeated. A 0.086-g/kg bolus of MgSO4 followed by an infusion of 0.028 g/kg/day MgSO4 significantly elevated serum and CSF levels of Mg++ (five monkeys). Magnesium sulfate significantly elevated the serum level of total Mg++ from a control value of 0.83 ± 0.04 mmol/L to 2.42 ± 1.01 mmol/L on Day 7 and raised the CSF level from 1.3 ± 0.04 mmol/L to 1.76 ± 0.14 mmol/L. There was no angiographic evidence of any effect of MgSO4 on normal cerebral arteries. After SAH, the vasospasm in the middle cerebral artery was not significantly reduced (46 ± 8% in the MgSO4-treated group compared with 35 ± 6% in the placebo [vehicle]-treated group, p > 0.05, unpaired t-test).

Conclusions. Magnesium sulfate did not significantly reduce cerebral vasospasm after SAH in the doses tested. An investigation of SAH is warranted mainly to test whether a benefit can be achieved by neuroprotection or by augmentation of CBF by dilation of small vessels and/or collateral pathways.

Does high plant feed magnesium and potassium protect healthy ruminants from atherosclerosis? A review

The literature data were surveyed to clarify the role of magnesium and potassium in the development of atherosclerosis (AS) in cows and the findings were compared with human data. Special attention was paid to the eastern Finland where AS is very common in humans and absent in the cattle. A hypothesis is proposed that high magnesium and potassium intakes at plant feeding protect from severe AS processes at least in cows in the absence of chronic infections. In about 1500 necropsies in calves and cows on plant feeding, neither antemortem clinical AS symptoms nor postmortal macroscopical AS were detected in the endocardium or in aorta. Also, abattoiries in endemic selenium- and vitamin E-deficient areas report that no macroscopic AS have been found in the inspected more than 400000 slaughtered cattle. In vitamin D(3) poisoned cows AS is readily detected. The milk-fed calves in magnesium deficiency experiments regularly show AS after 3 months of age. Adult ruminating cattle get daily 150-300 g potassium while the need is 35 g. During the indoor feeding period the cows suffered in eastern Finland often from carotene, vitamin E and selenium deficiencies as well as also of energy, protein, phosphorus and zinc deficiencies before grass ensiling feeding started. Endemic goiter prevalence was about 30%. Still such cows did not have AS under such unfavorable conditions. The findings support the hypothesis that the high magnesium and potassium intakes protect cows from AS.

Development of ionized hypomagnesemia is associated with higher mortality rates

OBJECTIVE

Previous studies have shown a wide variation in the prevalence of total serum hypomagnesemia in intensive are unit (ICU) patients and in associated mortality rates. As the ionized part of magnesium is the active portion, we sought to define the prevalence of ionized hypomagnesemia in critically ill patients and to evaluate its relationship with organ dysfunction, length of stay, and mortality.

DESIGN

Prospective observational study.

SETTING

A 31-bed, medical-surgical, university hospital ICU.

PATIENTS

A total of 446 consecutive patients admitted to the ICU over a 3-month period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The ionized magnesium level (normal value, 0.42-0.59 mmol/L) was measured at admission and then every day until discharge from the ICU. At admission, 18% of patients had ionized hypomagnesemia, 68% had normal ionized magnesium levels, and 14% had ionized hypermagnesemia. There was no significant difference in the length of stay or in the mortality rate between these three groups of patients. Hypomagnesemic patients more frequently had total and ionized hypocalcemia, hypokalemia, and hypoproteinemia. A total of 23 patients developed ionized hypomagnesemia during their ICU stay; these patients had higher Acute Physiology And Chronic Health Evaluation II (14.9 +/- 5.4 vs. 11.0 +/- 6.2) and Sequential Organ Failure Assessment (SOFA; 7.1 +/- 5.4 vs. 3.9 +/- 2.8) scores at admission (p <.01 for both), a higher maximum SOFA score during their ICU stay (10.0 +/- 5.6 vs. 4.4 +/- 3.2, p <.01), a higher prevalence of severe sepsis and septic shock (57 vs. 11%, p <.01), a longer ICU stay (15.4 +/- 15.5 vs. 2.8 +/- 4.7 days, p <.01), and a higher mortality rate (35% vs. 12%, p <.01) than the other patients. The major risk factors for developing hypomagnesemia during the ICU stay were a prolonged ICU stay, treatment with diuretics, and sepsis.

CONCLUSION

Development of ionized hypomagnesemia during an ICU stay is associated with a worse prognosis. It is often associated with the use of diuretics and the development of sepsis. Monitoring of ionized magnesium levels may have prognostic, and perhaps therapeutic, implications.

Magnesium potentiates neuromuscular blockade with cisatracurium during cardiac surgery

PURPOSE

Magnesium potentiates the effect of nondepolarizing neuromuscular blocking agents. It is used in cardiac anesthesia to prevent hypertension and arrhythmias. This study was performed to measure the interaction between magnesium and cisatracurium in cardiac surgery.

METHODS

Twenty patients scheduled for elective cardiac surgery were randomly assigned to receive magnesium sulfate (70 mg x kg(-1) at induction followed by 30 mg x kg(-1) x hr(-1)) or placebo. The ulnar nerve was stimulated and the electromyographic response of the adductor pollicis was measured. Cisatracurium 0.1 mg x kg(-1) was given at induction, followed by 0.05 mg x kg(-1) when the first twitch in the train-of-four reached 25%.

RESULTS

Ionized magnesium was 1.32 +/- 0.24 mmol x L(-1) in the treatment group vs 0.47 +/- 0.4 mmol x L(-1) in the control group. Duration of action of the intubating dose was longer in the magnesium group (74 +/- 20 min) than in the placebo group (42 +/- 6 min, P = 0.0001). Duration of the first maintenance dose was 69 +/- 16 min in the magnesium group vs 35 +/- 7 min in the placebo group (P = 0.0001). Total dose of cisatracurium administered throughout surgery was 0.19 +/- 0.07 mg x kg(-1) in the magnesium group compared with 0.29 +/- 0.01 mg x kg(-1) in the placebo group (P = 0.017). Hemodynamic variables and temperature were similar in both groups.

CONCLUSION

In patients undergoing cardiac surgery, administration of magnesium sulfate, resulting in ionized levels of 1.3 mmol x L(-1), results in a 30-35 min prolongation of the neuromuscular blockade induced with intubating and maintenance doses of cisatracurium and does not alter hemodynamic stability.

Correction of ionized plasma magnesium during cardiopulmonary bypass reduces the risk of postoperative cardiac arrhythmia

We conducted this randomized controlled trial to determine whether the intraoperative measurement and correction of ionized plasma magnesium can reduce the risk of cardiac arrhythmia after cardiopulmonary bypass. Eighty-five patients presenting for coronary artery bypass grafting were randomly assigned either to the magnesium-corrected group, which received magnesium sulfate on the basis of measured levels of ionized plasma magnesium (n = 43), or to the control group, in which magnesium levels were identified but not corrected (n = 42). Ionized magnesium was determined with an ion-selective electrode with minimal delay, and further samples were taken for laboratory analysis of total plasma magnesium. All patients had Holter electrocardiogram monitoring for 72 h after surgery. Total hypomagnesemia (45 patients; 53% of all patients) was more common than ionized hypomagnesemia (11 patients; 13%) before cardiopulmonary bypass. Both total and ionized magnesium levels declined further during the course of cardiopulmonary bypass in the control group. The incidence of ventricular tachycardia in the first 24 h was less frequent in the magnesium-corrected group (3 patients; 7%) than the control group (12 patients, 30%; P < 0.01). Patients in the magnesium-corrected group were more likely to display continuous sinus rhythm (Lown Grade 0) in the first 24 h (14 patients; 34%) than patients in the control group (2 patients, 5%; P < 0.001). Our results suggest that the intraoperative correction of ionized magnesium is associated with a reduction in postoperative ventricular arrhythmia in cardiac surgical patients.

IMPLICATIONS

In this study the correction of ionized plasma magnesium during cardiopulmonary bypass was guided by measurements from an ion-selective electrode. This intervention resulted in a reduction in the incidence of postoperative ventricular tachycardia and an increased frequency of continuous sinus rhythm. Ion-selective electrodes constitute a convenient near-patient test, providing a basis for the targeted replacement of ionized plasma magnesium.

Variability within individuals of plasma ionic magnesium concentrations

BACKGROUND

With the invention of the ion-selective electrode (ISE), ionic magnesium (iMg) is a common blood assay. This could be advantageous, as iMg is the biologically active form of Mg. There is some evidence that iMg has considerable within subject variability.

RESULTS

Individual ranges averaged.08 mmol/L (range.05 to.14). Coefficients of variation (CV) ranged from 3% to 7% (mean 4%) while analytical variation was determined to be 2.3%. Biological variability thus accounts for almost half of the variability, which is clinically significant, as 9 of the 13 subjects recorded at least one value below a reference range of.46 -.60 mmol/L. A significant within-day variation (p <.001) was noted, with differences between 7:00 and 10:00 as well as 10:00 and 22:00. Between day variations were not significant (p =.56).

CONCLUSIONS

A plausible explanation of this data is that iMg has a circadian rhythm. Thus, cautious interpretation of single iMg values is warranted until future research determines the nature of iMg variability.

Intravenous magnesium sulfate does not increase ventricular CSF ionized magnesium concentration of patients with intracranial hypertension

Magnesium sulfate has attracted interest as a potential neuroprotectant but passage of magnesium ion into the central nervous system has not been well documented. For this study, we quantified plasma and cerebrospinal fluid (CSF) ionized magnesium concentration after systemic magnesium sulfate infusion in patients with intracranial hypertension. Patients ( N = 9) received an intravenous infusion of 5 g/20 mmol magnesium sulfate (125 mL of a 4% wt/vol solution) over 30 minutes. Before and after dosing, CSF (from an indwelling ventricular catheter) and blood samples were collected at hourly intervals. Ionized magnesium concentration in all samples was determined using an electrolyte analyzer. Baseline plasma and CSF ionized magnesium concentrations were 0.58 +/- 0.05 and 0.82 +/- 0.06 mmol/L, respectively. Intravenous magnesium sulfate infusion significantly increased plasma ionized magnesium concentration (peak, 0.89 +/- 0.11 mmol/L), but CSF magnesium levels did not change during the 4-hour study. Systemic administration of magnesium sulfate failed to increase CSF ionized magnesium concentration in patients with intracranial hypertension despite increasing plasma magnesium levels by >50%.

High dietary manganese lowers heart magnesium in pigs fed a low-magnesium diet

Young pigs were fed a diet moderately high or low in manganese (Mn) (0.95 +/- 0.10 mmol Mn/kg, n = 8 or 0.040 +/- 0.003 mmol Mn/kg, n = 6) and deficient in magnesium (Mg) (4.1 mmol Mg/kg) for 5 wk. All eight pigs consuming the high Mn diet died following convulsive seizures, whereas only two of six died in the group fed low Mn. In an attempt to determine the cause of death, a subsequent study examined the interactive effect of deficient dietary Mg and Mn on the tissue distribution of Mg and Mn. Pigs were individually fed, for 5 wk, diets that contained: 4.1 mmol Mg/kg and 36.0 micromol Mn/kg, 4.1 mmol Mg/kg and 0.91 mmol Mn/kg, 4.1 mmol Mg/kg and 0.91 mmol Mn/kg with added ultratrace minerals, or 41.1 mmol Mg/kg and 0. 91 mmol Mn/kg, and ultratrace minerals. Liver and skeletal muscle Mn concentrations were significantly elevated by increased dietary Mn. Increased dietary Mn did not affect heart Mn, but heart Mg concentrations were significantly depressed by high, as compared to low, dietary Mn (38.7 +/- 3.3 vs. 32.7 +/- 2.6 mmol Mg/kg). These data suggest high dietary Mn may exacerbate Mg deficiency in heart muscle and thus may be a complicating factor in the deaths observed in Mg-deficient pigs.

Effects of magnesium supplementation in hypertensive patients: assessment by office, home, and ambulatory blood pressures

An increase in magnesium intake has been suggested to lower blood pressure (BP). However, the results of clinical studies are inconsistent. We studied the effects of magnesium supplementation on office, home, and ambulatory BPs in patients with essential hypertension. Sixty untreated or treated patients (34 men and 26 women, aged 33 to 74 years) with office BP >140/90 mm Hg were assigned to an 8-week magnesium supplementation period or an 8-week control period in a randomized crossover design. The subjects were given 20 mmol/d magnesium in the form of magnesium oxide during the intervention period. In the control period, office, home, and average 24-hour BPs (mean+/-SE) were 148.6+/-1.6/90.0+/-0.9, 136.4+/-1.3/86.8+/-0.9, and 133.7+/-1.3/81.0+/-0.8 mmHg, respectively. All of these BPs were significantly lower in the magnesium supplementation period than in the control period, although the differences were small (office, 3.7+/-1.3/1.7+/-0.7 mmHg; home, 2.0+/-0.8/1.4+/-0.6 mmHg; 24-hour, 2.5+/-1.0/1.4+/-0.6 mm Hg). Serum concentration and urinary excretion of magnesium increased significantly with magnesium supplementation. Changes in 24-hour systolic and diastolic BPs were correlated negatively with baseline BP or changes in serum magnesium concentration. These results indicate that magnesium supplementation lowers BP in hypertensive subjects and this effect is greater in subjects with higher BP. Our study supports the usefulness of increasing magnesium intake as a lifestyle modification in the management of hypertension, although its antihypertensive effect may be small.

The determination of magnesium in human blood plasma by 31P magnetic resonance spectroscopy using a macrocyclic reporter ligand

The ligand 1,4,7-triazacyclononane-1,4,7-tris(methylene methylphosphinic acid), NOTMP, was used to measure free MgII levels in blood plasma by 31P MRS. Separate resonances were observed for the free ligand and the MgII complex and the ratio of their resonance areas was used to evaluate the free, ionized MgII concentration, [Mg]free. The CaII and the ZnII complexes gave rise to separate resonances in the 31P spectrum in an aqueous sample. In human blood plasma samples, however, these resonances were never observed thus excluding the interference of these metal ions. Heparin, up to 150 units/ml, had no influence on the Mg-NOTMP equilibrium. The 31P MRS methodology was applied to twenty human blood plasma samples. Total MgII ([Mg]total), as measured by atomic absorption spectroscopy, averaged 0.85 +/- 0.12 mM while free ionized MgII ([Mg]free) measured by 31P MRS was 0.66 +/- 0.09 mM. The 31P MRS method gave inherently larger values for free ionized MgII than that reported by ion-selective electrodes (ISE). This was traced to a redistribution of existing plasma MgII species after the addition of about 2 mM of NOTMP. Calculations using existing thermodynamic data show that the ionized MgII concentration (iMg) and the concentration of MgII weakly complexed to small anions (Mg(comp)) both drop after the addition of NOTMP, with Mg(comp) dropping to negligible levels. Thus, the 31P MRS method appears to be less sensitive to variations in the concentration of weakly binding anions (bicarbonate, carbonate, chloride, lactate, phosphate, etc.) than the ISE method. Our data indicates that the difference between Mg(total), as measured by atomic absorption spectroscopy, and Mg(free), as measured by 31P MRS, provides an direct estimate of the protein bound MgII fraction.

Mg2+ inhibition of ATP-activated current in rat nodose ganglion neurons: evidence that Mg2+ decreases the agonist affinity of the receptor

The effect of Mg2+ on ATP-activated current in rat nodose ganglion neurons was investigated with the use of the whole cell patch-clamp technique. Mg2+ decreased the amplitude of ATP-activated current in a concentration-dependent manner over the concentration range of 0.25-8 mM, with a 50% inhibitory concentration value of 1.5 mM for current activated by 10 microM ATP. Mg2+ shifted the ATP concentration-response curve to the right in a parallel manner, increasing the 50% effective concentration value for ATP from 9.2 microM in the absence of added Mg2+ to 25 microM in the presence of 1 mM Mg2+. Mg2+ increased the deactivation rate of ATP-activated current without changing its activation rate. The observations are consistent with an action of Mg2+ to inhibit ATP-gated ion channel function by decreasing the affinity of the agonist binding site on these receptors.