Theophylline and magnesium inhibit the contraction elicited with ciclosporin and angiotensin II in mesangial cell cultures

Hypomagnesaemia in kidney transplantation

In the era of calcineurin inhibitors, hypomagnesaemia is a very common finding in kidney transplant recipients. Especially the first weeks after transplantation it is the rule rather than the exception. Hypomagnesaemia or low magnesium intake have been associated with a higher mortality or more cardiovascular events in the general population, but this association has never been explored in kidney transplant recipients, despite their increased cardiovascular risk. Kidney transplant recipients with pre- or post-transplant hypomagnesaemia seem to have an aberrant glucose metabolism and develop diabetes mellitus more frequently. Moreover, observations from alternate study populations, animal experiments or in vitro studies suggest a possible role of magnesium deficiency in graft dysfunction, bone metabolism and transplant immunology. Future observational and especially interventional studies should further define whether and to what extent we should make effort to correct this electrolyte disturbance in transplant recipients. Considering the mechanism of renal magnesium wasting, normalizing the serum magnesium concentration by oral supplementation alone might turn out to be cumbersome in kidney transplant recipients.

Magnesium Supplementation Combined with N-Acetylcysteine Protects against Postischemic Acute Renal Failure

Magnesium is a potent vasodilator whose effects have not been evaluated in renal ischemia. The antioxidant properties of N-acetylcysteine (NAC) partially protect animals from ischemic/reperfusion injury. This study was designed to evaluate magnesium supplementation, alone or combined with NAC, on ischemic acute renal failure. Rats were maintained on normal diets, supplemented or not with MgCl(2).6H(2)O (1% in drinking water) for 23 d, and some rats received NAC (440 mg/kg body wt) on days 20 to 23. On day 21, ischemia was induced by clamping both renal arteries for 30 min. Five groups were studied: Normal, ischemia, ischemia+magnesium, ischemia+NAC, and ischemia+magnesium+NAC. GFR (inulin clearance), renal blood flow (RBF), FEH(2)O, and FENa were determined. Serum magnesium was decreased in ischemia-only rats. Magnesium prevented postischemia GFR and RBF decreases but did not protect against tubular damage. However, NAC completely restored the tubular damage induced by ischemia/reperfusion. Semiquantitative immunoblotting showed that NAC prevented the decreased expression of Na-K-2Cl co-transporter and aquaporin 2 after renal ischemia/reperfusion. Untreated rats with acute renal failure demonstrated markedly decreased endothelial nitric oxide synthase expression. Significantly, treatment with NAC, magnesium, or both completely inhibited downregulation of endothelial nitric oxide synthase. The tubular necrosis scores were lower in rats that were treated with NAC alone or with the magnesium-NAC combination. Magnesium prevented postischemia GFR and RBF decreases but did not protect against tubular damage. The NAC protected tubules from ischemia, decreased infiltrating macrophages/lymphocytes, and had a mild protective effect on GFR. In ischemic/reperfusion injury, renal function benefits more from the magnesium-NAC combination than from magnesium alone.

Vasodilator Agents Protect against Indinavir Nephrotoxicity

Indinavir (IDV) is a protease inhibitor widely used in AIDS treatment. A sustained elevation of creatinine was identified in IDV-treated patients. We have previously demonstrated that IDV causes renal vasoconstriction in rats. The objective of this study was to investigate the mechanism of IDV-induced vasoconstriction and the effect that the vasodilator agents L-arginine (LA), nifedipine (NF), as well as magnesium supplementation (Mg), have on IDV-induced nephrotoxicity. Male Wistar rats were kept on fast overnight and given free access to water. IDV (80 mg/kg BW) and NF (3 mg/kg BW) were given by gavage for 15 days. LA (1.5%) and MgCl2.6H2O (1%) were added to drinking water. Six groups were studied: Control ( n=6): normal rats treated with vehicle, a 0.05 M citric acid solution; IDV ( n=7): IDV-treated rats; IDV+LA ( n=6): IDV- and LA-treated rats; IDV+NF ( n=7): IDV- and NF-treated rats; IDV+Mg ( n=7): IDV- and MgCl2-treated rats; IDV+Mg+L-NAME ( n=9): IDV- and MgCl2-treated rats, supplemented with L-NAME (2.5 mg/l in drinking water). Clearance studies and evaluations of urinary nitrite (NO2) excretion were performed on day 16. No changes in blood pressure were observed. NO2 excretion decreased in IDV-treated rats. LA and NF protected against IDV effects, improving GFR (IDV+LA, 1.95 ±0.10; IDV+NF, 1.94 ±0.07 vs IDV, 1.15 ±0.07 ml/min, P<0.001) and RBF (IDV+LA, 7.83 ±0.09; IDV+NF, 7.63 ±0.14 vs IDV, 6.17 ±0.25 ml/min, P<0.001). These results suggest that IDV-induced vasoconstriction is mediated by NO and Ca2+ channels. Magnesium also ameliorated GFR and RBF in IDV-treated rats (GFR IDV+Mg, 1.77 ±0.08 ml/min, P<0.001; RBF IDV+Mg, 7.35 ±0.158 ml/min, P<0.001). Magnesium protection is not NO-mediated since it was not blocked by L-NAME. In conclusion, LA, NF and Mg protect against IDV-induced nephrotoxicity in rats. This study may have potential clinical implications for prevention of IDV-induced nephrotoxicity.

Role of hypomagnesemia in chronic cyclosporine nephropathy

BACKGROUND

Hypomagnesemia is a common finding of cyclosporine (CsA)-treated patients and has been proposed as both a cause and a consequence of CsA-induced nephrotoxicity. This experiment was conducted to elucidate the role of hypomagnesemia in the pathogenesis of chronic CsA nephropathy.

METHODS

CsA (15 mg/kg/day subcutaneously) was administered to rats maintained on a low-sodium diet for 1, 2, and 4 weeks, and the effects of magnesium (Mg) supplementation on renal function, renal histology, and renal gene expression profile of fibrogenic molecules and vasoconstrictors was examined.

RESULTS

CsA elicited hypomagnesemia and induced a progressive decline in glomerular filtration. At 28 day, renal tubular atrophy and cortical striped interstitial fibrosis were evident with CsA treatment. Dietary supplementation of Mg ameliorated CsA-induced hypomagnesemia and almost completely abolished CsA-induced chronic fibrotic lesions. Neither CsA nor Mg supplementation affected blood pressure. Renal cortical mRNA of transforming growth factor beta, plasminogen activator inhibitor (PAI)-1, and extracellular matrix started to increase at 14 days and elevated further at 28 days. In contrast, the increase in mRNA of tissue inhibitor of matrix metalloproteinase-1 and renin was evident early at 7 days and reached peak at 14 days. These mRNA increases, except that of renin, were almost abolished when hypomagnesemia was corrected. Magnesium supplementation also improved glomerular dysfunction, at least in part, through inhibition of up-regulated mRNA of endothelin-1.

CONCLUSION

CsA-induced hypomagnesemia contributes to chronic renal fibrotic lesions seen during CsA treatment through up-regulation of fibrogenic molecules, most notably early activation of tissue inhibitor of matrix metalloproteinase-1 expression.

Inhibition of cyclosporin-induced in vitro glomerular contraction by theophylline

Cyclosporin A (CsA) induces in vivo severe nephrotoxicity characterized by a large decrease in renal haemodynamics. The aim of this study is to show the ability of theophylline, a xanthic derivative, to diminish the CsA-induced vasoconstrictive effects by using two in vitro rat glomerular models, for example isolated glomeruli and cultured mesangial cells. Isolated glomeruli are obtained from the superficial renal cortex of male Sprague-Dawley rats by a sieving method. Mesangial cells are cultured in RPMI 1640 medium with 15% foetal calf serum (FCS). The area of either isolated glomeruli or mesangial cells is assessed by an image analyser with a video camera. Each glomerulus or mesangial cell serves as its own control by photographing them before any drug incubation and after incubation for 10, 20 and 30 min either in control solution or control solution with CsA or CsA and theophylline. CsA (10(-6)m) induces an important time-dependent decrease in the glomerular area (about 13.4% after 30 min). When theophylline is added only a slight decrease is noticed (about 3.4% after 30 min). The same results are obtained with mesangial cells. In conclusion, a direct vasoconstrictive effect of CsA in isolated glomeruli and mesangial cells can be confirmed. In addition, this effect can be partially prevented by theophylline.

Interleukin 1beta and tumour necrosis factor alpha induce a macrophage-type of nitric oxide synthase in rat renal mesangial cells

Treatment of mesangial cells with interleukin 1 beta (IL-1 beta) or tumour necrosis factor alpha (TNF alpha) has been shown to increase cGMP formation, most probably due to induction of nitric oxide synthase. Here we report that maximum stimulation of cGMP formation over a 24-h period required the presence of IL-1 beta or TNF alpha during the first 18 h of induction. N4-monomethyl-L-arginine (L-NMMA) was a potent inhibitor of cytokine-induced cGMP formation while N4-nitro-L-arginine (L-NNA) was less active. Formation of nitric oxide was detected in the cytosol of cytokine-treated mesangial cells by activation of purified soluble guanylate cyclase and was stimulated by tetrahydrobiopterin, but not by calcium calmodulin. Treatment of cells with IL-1 beta or TNF alpha markedly attenuated the contractile response to a subsequent challenge with angiotensin II. Furthermore, conditioned medium from IL-1 beta-treated cells increased cGMP in untreated control cells.