Dietary potassium and magnesium supplementation in cyclosporine-induced hypertension and nephrotoxicity

Abstract

Cyclosporine A (CsA)-induced hypertension and nephrotoxicity are aggravated by high sodium intake. Accumulating evidence suggests that potassium and magnesium supplementation could protect against the detrimental effects of dietary salt. In the present study, we tested the hypothesis of whether concurrent supplementation with potassium and magnesium could protect against the development of CsA-induced hypertension and nephrotoxicity more effectively than supplementation with one mineral alone. Eight-week-old spontaneously hypertensive rats (SHRs) were divided into four groups (N = 10 in each group): (1) CsA group (5 mg/kg subcutaneously) receiving high-sodium diet (Na 2.6%, K 0.8%, Mg 0.2% wt/wt); (2) CsA group receiving a high-sodium, high-potassium diet (Na 2.6%, K 2.4%, Mg 0.2%); (3) CsA group receiving high-sodium, high-magnesium diet (Na 2.6%, K 0.8%, Mg 0.6%); and (4) CsA group receiving high-sodium, high-potassium, high-magnesium diet (Na 2.6%, K 2.4%, Mg 0.6%). CsA induced severe hypertension and deteriorated renal functions in SHRs on high-sodium diet. Histologically, the kidneys showed severe thickening of the media of the afferent artery with fibrinoid necrosis. Potassium supplementation lowered blood pressure (198 +/- 5 vs. 212 +/- 2 mm Hg, P < 0.05) and partially prevented the development of proteinuria (-25%, P < 0.05). Magnesium supplementation decreased blood pressure to the same extent but improved renal functions more effectively than potassium. The greatest protection against CsA toxicity was achieved when dietary potassium and magnesium supplementations were combined. Urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion, a marker for renal proximal tubular damage, increased progressively in CsA-treated SHRs on the high-sodium diet. Neither potassium nor magnesium influenced urinary NAG excretion. We also estimated the activity of the renal dopaminergic system by measuring 24-hour urinary dopamine excretion rates. CsA suppressed the renal dopaminergic system during high-sodium diet. Magnesium supplementation, alone and in combination with potassium, protected against the development of renal dopaminergic deficiency in CsA-treated SHRs on high-sodium diet. Magnesium supplementation increased plasma-free ionized magnesium (iMg) and bone magnesium by 50 and 16%, respectively. Our findings indicate that both potassium and magnesium supplementations showed beneficial effects against CsA-induced hypertension and nephrotoxicity. The protective effect of magnesium clearly exceeded that of potassium. The greatest protection against CsA toxicity was achieved when potassium and magnesium were combined. We also provide evidence that the development of CsA-induced glomerular, tubular, and vascular lesions are associated with renal dopaminergic deficiency.