Mononuclear blood cell magnesium in older subjects: evaluation of its use in clinical practice

Magnesium in joint health and osteoarthritis

Osteoarthritis (OA) is a prevalent debilitating age-related skeletal disease. The hallmark of OA is the degradation of articular cartilage that cushions the joint during movement. It is characterized by chronic pain and disability. Magnesium, a critical trace element in the human body, plays a pivotal role in metabolism homeostasis and the energy balance. Humans obtain magnesium mainly from the diet. However, inadequate magnesium intake is not uncommon. Moreover, the magnesium status deteriorates with ageing. There has been a growing body of clinical studies pointing to an intimate relationship between dietary magnesium and OA although the conclusion remains controversial. As reported, the magnesium ion concentration is essential to determine cell fate. Firstly, the low-concentration magnesium ions induced human fibroblasts senescence. Magnesium supplementation was also able to mitigate chondrocyte apoptosis, and to facilitate chondrocyte proliferation and differentiation. In this literature review, we will outline the existing evidence in animals and humans. We will also discuss the controversies on plasma or intracellular level of magnesium as the indicator of magnesium status. In addition, we put forward the interplay between dietary magnesium intake and intestinal microbiome to modulate the inflammatory milieu in the conjecture of OA pathogenesis. This leads to an emerging hypothesis that the synergistic effect of magnesium and probiotics may open a new avenue for the prevention and treatment of OA.

Hypomagnesaemia and pregnancy

Hypomagnesaemia is common in pregnancy, particularly in developing countries and low-income communities. Despite the frequent therapeutic use of magnesium in pregnancy, and the evidence regarding the association of hypomagnesaemia with adverse pregnancy outcomes in animal studies, it remains unclear whether hypomagnesaemia is associated with complications in human pregnancy. Three case reports of pregnancies complicated by moderate-severe hypomagnesaemia are presented and magnesium physiology in pregnancy is discussed. The evidence as to whether hypomagnesaemia may represent a direct cause, a consequence of other disease processes or an epiphenomenon in adverse pregnancies outcomes is reviewed.

Magnesium basics

As a cofactor in numerous enzymatic reactions, magnesium fulfils various intracellular physiological functions. Thus, imbalance in magnesium status-primarily hypomagnesaemia as it is seen more often than hypermagnesaemia-might result in unwanted neuromuscular, cardiac or nervous disorders. Measuring total serum magnesium is a feasible and affordable way to monitor changes in magnesium status, although it does not necessarily reflect total body magnesium content. The following review focuses on the natural occurrence of magnesium and its physiological function. The absorption and excretion of magnesium as well as hypo- and hypermagnesaemia will be addressed.

Precision of the magnesium determination in mononuclear blood cells and erythrocytes

OBJECTIVE

Establishing the analytical variation and reproducibility of the intracellular magnesium (Mg) assay in mononuclear blood cells (MBC) and erythrocytes (RBC).

DESIGN AND METHODS

We assessed the analytical variation of the several determination steps, and the reproducibility for the complete intracellular Mg-assay (combination of preanalytical, analytical, and biological variation). The influence of platelets was determined by comparing Mg concentrations obtained from heparinized blood and defibrinated blood.

RESULTS

Coefficients of variation of the several determination steps used in the MBC- and RBC-assay were < or = 5.4%. The overall analytical variation was 5.0-6.8%, and reproducibility of the complete Mg-assay 11.6-14.0%. Mg measurements in MBC (expressed as fmol/cell) obtained from heparinized blood showed significantly higher values than those obtained from defibrinated blood.

CONCLUSION

This is the first study to describe in detail reproducibility data for the individual steps in the overall procedure to measure intracellular magnesium. It is shown that results obtained in daily practice should be interpreted with care. Moreover, the removal of platelets is essential in the determination of Mg in MBC.

Noninvasive measurement of tissue magnesium and correlation with cardiac levels

BACKGROUND

Intracellular magnesium ([Mg]i) plays an important role in the regulation of myocardial metabolism, contractility, and the maintenance of transsarcolemmal and intracellular ionic gradients. An understanding of the role of magnesium in the clinical setting, however, is hampered by the lack of an assay of intracellular tissue magnesium levels.

METHODS AND RESULTS

We used energy-dispersive x-ray analysis to measure [Mg]i in sublingual epithelial cells and to correlate the level with those in atrial biopsy specimens from the same patients during cardiopulmonary bypass. Levels were also measured in acute myocardial infarction (AMI) patients before and after intravenous magnesium sulfate administration and compared with those from intensive care unit (ICU) patients and healthy individuals. A strong correlation between sublingual epithelial cell (mean, 32.1 +/- 0.3 mEq/L) and atrial tissue (mean, 32.1 +/- 0.3 mEq/L) [Mg]i was present in 18 cardiac surgery patients (r = .68, P < .002). Epithelial and atrial [Mg]i levels were lower than in healthy individuals (33.7 +/- 0.5 mEq/L, P < .01) studied at that time and correlated poorly with serum magnesium. Mean [Mg]i in 22 AMI patients was 30.7 +/- 0.4 mEq/L, which was significantly lower than in 21 ICU patients and 15 healthy individuals (35.0 +/- 0.5 mEq/L and 34.5 +/- 0.7 mEq/L, respectively, P < .001). Intravenous magnesium sulfate was administered to most of the AMI patients (mean dose, 36 +/- 6 mmol). [Mg]i rose significantly in the AMI patients over the first 24 hours, and the magnitude of the increase was greater in those who received higher doses of intravenous magnesium sulfate.

CONCLUSIONS

Sublingual epithelial cell [Mg]i correlates well with atrial [Mg]i but not with serum magnesium. [Mg]i levels are low in patients undergoing cardiac surgery and those with AMI. Intravenous magnesium sulfate corrects low [Mg]i levels in AMI patients. Energy-dispersive x-ray analysis determination of sublingual cell [Mg]i may expedite the investigation of the role of magnesium deficiency in heart disease.

Biological variation of serum and urinary magnesium in apparently healthy males

The biological variations of serum (S-) magnesium and urinary (U-) magnesium concentrations and excretions have been investigated. Serum samples, 24-h and fasting urinary samples were collected from each of 60 supposedly healthy male volunteers. In addition, 12 volunteers collected additional samples 7 and 112 days after the initial sample. The reference interval for S-magnesium was 0.765-0.997 mmol l-1. The biological variation for S-magnesium was 3.2% within subjects and 7.4% between subjects. This indicated an index of indivduality of 0.5, which means that significant changes in S-magnesium can occur within the limits of the reference interval, and that serial determinations of S-magnesium might prove useful as an indicator of changes in whole body magnesium status. It is, on the other hand, unlikely that a single determination of S-magnesium can be used in assessing whole-body magnesium status in the individual. The reference interval for the 24-h U-magnesium excretion, corrected for surface area, was 1.306-4.762 mumol min-1 1.73 m-2. The 24-h U-magnesium excretion exhibited a biological within-subject variation of 36% and a between-subject variation of 26%. The 24-h U-magnesium excretion did not correlate with S-magnesium, and only slightly (r = 0.58) with the fasting U-magnesium/creatinine concentration. This, and the very large coefficients of variation, make it unlikely that the renal magnesium excretion can be used as a measure of whole body magnesium status, or that changes in the renal magnesium excretion can be used as a measure of changes in whole body magnesium status.

Magnesium deficiency in critically ill patients

A study was performed to assess the value of estimation of intracellular magnesium in peripheral blood cells (red and mononuclear blood cells) in critically ill patients as an index of tissue magnesium content. A magnesium loading test was used to diagnose magnesium depletion in 16 critically ill patients. Patients were divided into magnesium depleted and non-depleted groups according to their response to the loading test. Pre-infusion plasma and intracellular (blood cell) magnesium levels were measured. There were no significant difference between the magnesium depleted (mean plasma magnesium 0.81 mmol.l-1, red blood cell magnesium 2.34 mmol.l-1, mononuclear blood cell magnesium 25.16 mmol.kg-1 dry weight) and non-depleted groups (mean plasma magnesium 0.90 mmol.l-1, red blood cell magnesium 2.18 mmol.l-1, mononuclear blood cell magnesium 18.1 mmol.kg-1 dry weight). We conclude that the diagnosis of magnesium depletion cannot be excluded in the face of normal plasma, red blood cell or mononuclear blood cell concentrations of magnesium.