Intracellular magnesium in elderly patients with heart failure: effects of diabetes and renal dysfunction

Erythrocyte intracellular Mg(2+) concentration as an index of recognition and memory

Magnesium (Mg(2+)) plays an important role in the neural system, and yet scarcely any research has quantitatively analyzed the link between endogenous Mg(2+) level and memory. Using our original technique, we measured erythrocyte intracellular ionized Mg(2+) concentration (RBC [Mg(2+)]i), which linearly correlated to recognition and spatial memory in normal aging rats. In the brain, RBC [Mg(2+)]i significantly correlated to hippocampus extracellular fluid Mg(2+) concentration, and further correlated to hippocampal synapse density. Elevation of Mg(2+) intake in aged rats demonstrated an association between RBC [Mg(2+)]i increase and memory recovery. The therapeutic effect of Mg(2+) administration was inversely correlated to individual basal RBC [Mg(2+)]i. In summary, we provide a method to measure RBC [Mg(2+)]i, an ideal indicator of body Mg(2+) level. RBC [Mg(2+)]i represents rodent memory performance in our study, and might further serve as a potential biomarker for clinical differential diagnosis and precise treatment of Mg(2+)-deficiency-associated memory decline during aging.

Intra-erythrocyte magnesium levels and their clinical implications in geriatric outpatients

OBJECTIVES

Magnesium deficiency has been implicated as a factor in numerous chronic diseases and previous studies suggest a greater prevalence of occult magnesium deficiency among older adults. Serum is the choice for the assessment of most analyses used in clinical medicine, although serum magnesium concentrations have been shown to be poor predictors of intracellular magnesium concentration. The aim of this study was to compare intracellular and extracellular magnesium concentrations in geriatric outpatients. Moreover, we examined whether a significant correlation between magnesium parameters and clinical outcome existed.

DESIGN

Cross-sectional study.

SETTING

Geriatric medicine outpatient clinic of a university hospital.

PARTICIPANTS

A total of 246 patients with a mean age of 71.9 ± 5.7 years were involved.

MEASUREMENTS

Intra-erythrocyte magnesium levels were analyzed with atomic absorption spectrophotometry.

RESULTS

Serum magnesium levels were within normal range in all patients, whereas intra-erythrocyte magnesium measurements were low in 57% of the patients. Increase in serum levels were together with just only a slightly increase in intra-erythrocyte measurements and the relationship was very weak. Intra-erythrocyte Mg levels were not significantly correlated with many laboratory or clinical parameters.

CONCLUSION

Our results confirm that intra-erythrocyte Mg does not correlate with serum levels and clinical parameters in geriatric outpatients, but further studies are needed to define the correlation.

Magnesium metabolism in health and disease

Magnesium (Mg) is the main intracellular divalent cation, and under basal conditions the small intestine absorbs 30-50% of its intake. Normal serum Mg ranges between 1.7-2.3 mg/dl (0.75-0.95 mmol/l), at any age. Even though eighty percent of serum Mg is filtered at the glomerulus, only 3% of it is finally excreted in the urine. Altered magnesium balance can be found in diabetes mellitus, chronic renal failure, nephrolithiasis, osteoporosis, aplastic osteopathy, and heart and vascular disease. Three physiopathologic mechanisms can induce Mg deficiency: reduced intestinal absorption, increased urinary losses, or intracellular shift of this cation. Intravenous or oral Mg repletion is the main treatment, and potassium-sparing diuretics may also induce renal Mg saving. Because the kidney has a very large capacity for Mg excretion, hypermagnesemia usually occurs in the setting of renal insufficiency and excessive Mg intake. Body excretion of Mg can be enhanced by use of saline diuresis, furosemide, or dialysis depending on the clinical situation.