Hydroxyurea therapy associated with declining serum levels of magnesium in children with sickle cell anemia

Magnesium homeostasis in deoxygenated sickle erythrocytes is modulated by endothelin-1 via Na+ /Mg2+ exchange

Painful crises in sickle cell disease (SCD) are associated with increased plasma cytokines levels, including endothelin-1 (ET-1). Reduced red cell magnesium content, mediated in part by increased Na⁺ /Mg²⁺ exchanger (NME) activity, contributes to erythrocyte K⁺ loss, dehydration and sickling in SCD. However, the relationship between ET-1 and the NME in SCD has remained unexamined. We observed increased NME activity in sickle red cells incubated in the presence of 500 nM ET-1. Deoxygenation of sickle red cells, in contrast, led to decreased red cell NME activity and cellular dehydration that was reversed by the NME inhibitor, imipramine. Increased NME activity in sickle red cells was significantly blocked by pre-incubation with 100 nM BQ788, a selective blocker of ET-1 type B receptors. These results suggest an important role for ET-1 and for cellular magnesium homeostasis in SCD. Consistent with these results, we observed increased NME activity in sickle red cells of three mouse models of sickle cell disease greater than that in red cells of C57BL/J6 mice. In vivo treatment of BERK sickle transgenic mice with ET-1 receptor antagonists reduced red cell NME activity. Our results suggest that ET-1 receptor blockade may be a promising therapeutic approach to control erythrocyte volume and magnesium homeostasis in SCD and may thus attenuate or retard the associated chronic inflammatory and vascular complications of SCD.

Total Serum Magnesium Levels and Calcium-To-Magnesium Ratio in Sickle Cell Disease

Background and objectives: Imbalance of calcium/magnesium ratio could lead to clinical complications in sickle cell disease (SCD). Low levels of magnesium have been associated with sickling, increased polymerization and vaso-occlusion (VOC) in sickle cell due to cell dehydration. The K-Cl cotransport plays a very important role in sickle cell dehydration and is inhibited by significantly increasing levels of magnesium. The study evaluated total serum magnesium levels and computed calcium/magnesium ratio in SCD patients and "healthy" controls. Materials and methods: The study was a case-control cross-sectional one, involving 120 SCD patients (79 Haemoglobin SS (HbSS)and 41 Haemoglobin SC (HbSC)) at the steady state and 48 "healthy" controls. Sera were prepared from whole blood samples (n = 168) and total magnesium and calcium measured using a Flame Atomic Absorption Spectrometer (Variant 240FS manufactured by VARIAN Australia Pty Ltd., Melbourne, VIC, Australia). Calcium/magnesium ratios were calculated in patients and the controls. Results: The prevalence of hypomagnesemia and hypocalcaemia among the SCD patients was observed to be 39.17% and 52.50% respectively, higher than the controls (4.17% and 22.92%, for hypomagnesemia and hypocalcaemia, respectively). Level of magnesium was significantly lower in the SCD patients compared to their healthy counterparts (p = 0.002). The magnesium level was further reduced in the HbSS patients but not significantly different from the HbSC patients (p = 0.584). calcium/magnesium ratio was significantly higher in the SCD patients (p = 0.031). Although calcium/magnesium ratio was higher in the HbSC patients compared to those with the HbSS genotype, the difference was not significant (p = 0.101). Conclusion: The study shows that magnesium homeostasis are altered in SCD patients, and their levels are lower in HbSS patients. Although calcium/magnesium ratio is significantly higher in SCD patients compared with controls, there is no significant difference between patients with HbSS and HbSC genotypes. Magnesium supplementation may be required in sickle cell patients.

Serum ionized magnesium levels and ionized calcium-to-magnesium ratios in adult patients with sickle cell anemia

Low levels of total magnesium in sickle cell erythrocytes have been linked to increased sickling due to cell dehydration. We tested the null hypothesis that adult sickle cell anemia (SCA) patients have the same serum level of ionized Mg (Mg(2+)) and Ca(2+)/Mg(2+) ratio as healthy African Americans (AA) and healthy Caucasians (CAUC). We measured serum Mg(2+) and ionized calcium (Ca(2+)) with ion-selective electrodes and calculated the serum Ca(2+)/Mg(2+) ratios in patients with SCA and control groups (AA and CAUC). Seventy-four SCA patients and 61 controls were compared. SCA patients had significantly (P < 0.001) lower levels of serum Mg(2+) (0.52 +/- 0.05) compared to healthy AA (0.57 +/- 0.04) and CAUC (0.62 +/- 0.03). Eighty-six percent of the adult SCA patients had serum Mg(2+) levels below the mean for the AA group, and 96% of SCA patients were above the AA group's mean serum Ca(2+)/Mg(2+). Of the SCA patients studied, 25.6% (95% CI, 16.2-37.2%) had serum Mg(2+) levels below the racially adjusted lower limit of normal and 50% (95% CI, 38.1-61.9%) were above the upper limit of serum Ca(2+)/Mg(2+) for AA controls. By measuring serum Mg(2+) and Ca(2+), we were able to define a subset of SCA patients with hypomagnesemia and elevated Ca(2+)/Mg(2+) ratios, who may benefit from magnesium supplementation.