Effects of hypokalemia and hypomagnesemia on zidovudine (AZT) and didanosine (ddI) nephrotoxicity in rats.

BACKGROUND: Zidovudine (AZT) and didanosine (ddI) are antiretroviral drugs widely used in AIDS patients. Hypokalemia and hypomagnesemia are frequently encountered in AIDS patients using AZT and/or ddI. OBJECTIVE: To verify the effects of AZT and ddI on rat renal function submitted to normal diet, low potassium diet and magnesium-free diet. METHODS: Glomerular filtration rate and renal hemodynamic were measured in Wistar rats submitted to a normal or a potassium-depleted diet. The animals were given AZT, ddI for 15 days. Six groups of rats were studied: normal diet, normal diet + AZT, normal diet + ddI, low K diet, low K diet + AZT and low K diet + ddI. Three additional groups of rats submitted to magnesium depletion for 15 days were also studied: magnesium-free diet, magnesium-free diet + AZT and magnesium-free diet + ddI. RESULTS: AZT and didanosine did not modify renal function of rats on a normal diet. However, in hypokalemic rats, both drugs produced a decrease in glomerular filtration rate and in renal blood flow consequent to renal vasoconstriction and associated with alterations in tubular function (characterized by an increased fractional excretion of sodium). Hypomagnesemia induced a decrease in glomerular filtration rate and in renal blood flow only in AZT-treated rats. CONCLUSION: Our data suggest that hypokalemia predisposes to AZT and ddI nephrotoxicity, while hypomagnesemia predisposes only to AZT nephrotoxicity. Thus, chronic AZT and ddI administration may produce acute renal failure in AIDS patients with hypokalemia and/or hypomagnesemia. Serum K and Mg levels should be carefully monitored in these patients.

Effects of sodium artesunate, a new antimalarial drug, on renal function.

BACKGROUND: Sodium artesunate is currently used in malaria treatment. Adverse effects of this drug have not been described, probably because they cannot be differentiated from malaria-related effects. METHODS: The effects on renal function of an acute infusion of sodium artesunate (12 mg/kg body weight) were studied in the rat with clearance techniques. We also evaluate the effect of sodium artesunate on chloride lumen-bath flux (Cl Jlb) in the isolated thick ascending limb of the loop of Henle (TALH) microperfused in vitro. RESULTS: Acute infusion of artesunate to the rat decreased inulin clearance, despite an increase in renal blood flow. These effects were associated with an increase in urinary excretion of sodium, chloride, potassium, and nitric oxide metabolites (NO(2)/NO(3)). In water-loaded animals, artesunate increased sodium and water distal delivery and decreased free water clearance (C(H(2)O)) factored for sodium and water delivery. Following hypertonic NaCl infusion, artesunate decreased free water excretion (Tc(H(2)O)) corrected by clearance of osmolarity (C(Osm)). In vitro, artesunate 10(-6) and 10(-3) mol/L added to bath solution decreased chloride lumen-bath flux in isolated rabbit TALH in a dose-dependent manner, with the threshold effect at 10(-4) mol/L. This effect was completely blocked by N(G)-nitroL-arginine-metilester (L-NAME) 5 mmol/L. Artesunate 10(-4) mol/L added to the perfusion solution did not change Cl Jlb. CONCLUSION: These findings suggest that artesunate decreases glomerular filtration rate and increases renal blood flow and urinary excretion of Na, Cl, and K. These effects were due, at least in part, to the inhibition of Cl transport across cortical and medullary TALH, and were mediated by local production of nitric oxide, since it is associated with an increase in NO(2)/NO(3) urinary excretion and it is blocked by L-NAME in vitro.

Beneficial and harmful effects of L-arginine on renal ischaemia.

BACKGROUND: The role of nitric oxide (NO) in acute renal failure (ARF) is not yet completely understood. L-Arginine (L-arg) is protective against different ARF models, while L-arg addition in isolated proximal tubules enhances hypoxia/reoxygenation (H/R) injury. The aim of this study was to evaluate the effects of L-arg on renal ischaemia. METHODS: In in vivo studies, Wistar rats were subjected to 60 min renal artery clamping, and renal function was evaluated 2 and 15 days after ischaemia. Four groups were studied: (1) control; (2) acute L-arg (50 mg/kg/bw i.v.); (3) L-nitro-arginine-methyl esther (L-NAME; 0.5 mg/kg/bw i.v.); and (4) chronic L-arg (L-arg 0.25% in drinking water/7 days). For the in vitro studies, proximal tubules (PTs), isolated by collagenase digestion and Percoll gradient, were studied from three groups: (1) untreated; (2) L-arg-treated (L-arg 0.25% in drinking water/7 days); and (3) L-NAME-treated rats (3 mg/kg in drinking water/7 days). PTs were kept oxygenated or subjected to 15 min hypoxia (H-15) and 35 min reoxygenation (R-35). In some experiments, additional doses of L-arg and L-NAME were administered. Cell injury was assessed by lactate dehydrogenase (LDH) release. NO production was evaluated by NO2-/NO3- measurement (Griess reaction) in both urine and isolation medium. RESULTS: After 2 days, L-arg infusion protected against ischaemia compared with control rats (0.4 vs 0.2 ml/min/100 g, P < 0.001), while neither L-NAME nor chronic L-arg supplementation ameliorated renal function. After 15 days, both acute and chronic L-arg groups showed a higher glomerular filtration rate (0.6 and 0.75 ml/min/100 g) compared with control rats (0.3 ml/min/100 g, P < 0.05) and L-NAME-treated rats (0.2 ml/min/100 g, P < 0.05). Despite similar recovery in both L-arg groups, the mortality rate was 25% in the chronic L-arg group. Tubular function was also better preserved in the acute L-arg group. PTs isolated from L-arg-treated rats were more sensitive to isolation injury. L-Arg addition enhanced H/R injury (44.9 vs 51.8%, P < 0.05), whereas L-NAME addition protected (44.9 vs 24%, P < 0.001) in untreated rats. In L-arg-treated rats, addition of L-arg did not enhance H/R injury (49.6 vs 53.5%, NS) and L-NAME was still protective (49.6 vs 32.3%, P < 0.001). In PTs from L-NAME-treated rats, L-arg addition also did not enhance H/R injury (50 vs 54%, NS) whereas L-NAME was protective (50 vs 27%, P < 0.001). NO2-/NO3- production paralleled L-arg and L-NAME supplementation. CONCLUSION: It was demonstrated that acute L-arg infusion was beneficial in in vivo renal ischaemia while it was harmful in isolated H/R tubules. In contrast, chronic L-arg supplementation was deleterious both in in vivo and in vitro renal ischaemia, suggesting that injurious effects had overcome the beneficial effects during excess NO exposure.

Protective effect of L-arginine on hypercholesterolemia-enhanced renal ischemic injury.

The effects of hypercholesterolemia on ischemic renal failure were evaluated in rats subjected to 60 min of left renal artery clamping and contralateral nephrectomy. One group of rats (HC) was kept on a cholesterol-supplemented diet for 3 weeks before renal injury and compared to a group fed a regular diet (ND). Two days after renal ischemia, inulin clearance (C(in), ml/min per 100 g BW) was lower in HC-rats (0.033 +/- 0.011) than in ND-rats (0.227 +/- 0.037; P < 0.01). indicating that hypercholesterolemia potentiated renal ischemic injury. Twenty-one days after renal ischemia the C(in) of HC-rats did not differ from ND-rats, suggesting that hypercholesterolemia did not limit late recovery. Since nitric oxide production is impaired in HC, L-arginine (50 mg/kg BW i.v.) was administered immediately after ischemia. Two days after ischemia, L-arg did not protect ND-rats from ischemia, while the C(in) and renal blood flow were higher in L-arg-treated HC rats than in untreated HC rats (C(in) = 0.125 +/- 0.013 rats vs. 0.033 +/- 0.011; P < 0.001) (RBF = 3.96 +/- 0.64 vs. 2.40 +/- 0.20 ml/min per 100 g BW; P < 0.05), indicating that L-arg protects HC rats from renal ischemia. The administration of D-arginine to ND rats induced a significant decrease of the C(in) and a significant increase of FE H2O, FE Na and FE K compared to the L-arginine and not treated groups. Cultures of inner medullary collecting duct cells from ND rats were resistant to 24-h hypoxia. In contrast, IMCD cell cultures from HC rats showed higher LDH release after 24-h hypoxia than normoxic cells (69.2 +/- 3.4 vs. 30.9 +/- 3.6%, P < 0.001); 1 mM L-arg added to the medium attenuated LDH release (44.3 +/- 2.4%, P < 0.01). These data demonstrate that HC predisposes renal tubular cells to hypoxic injury and L-arg protects cells of HC.

Hypercholesterolemia aggravates radiocontrast nephrotoxicity: protective role of L-arginine.

It is well known that the radiocontrast-induced ARF depends on risk factors often associated with compromised renal circulation. Since studies have shown that endothelium-dependent vasodilation is impaired in hypercholesterolemia (HC), we studied the effect of radiocontrast (RC) administration (6 ml/kg body wt, via femoral artery) in salt-depleted rats that were kept on a normal cholesterol (NC) or HC diet (4% cholesterol and 1% cholic acid). Inulin clearance (CIn, ml/min/100 g body wt), renal blood flow (RBF; electromagnetic flowmeter, ml/min/100 g body wt), and fractional excretions of sodium, potassium and water (FENa, FEK and FEH2O, respectively), cholesterol (mg/dl), and albumin (g/dl) were measured 24 hours after radiocontrast administration. The administration of RC to HC rats (RCHC) resulted in lower values of CIn compared with NC rats (RCNC) and control rats: 0.36 +/- 0.085 versus 0.76 +/- 0.13 (RCNC; P < 0.01), versus 0.84 +/- 0.03 (control HC; P < 0.01), versus 0.87 +/- 0.06 (control NC; P < 0.01). Hypercholesterolemia per se did not alter renal function, and control HC versus control NC was not significant. Renal blood flow was significantly lower in the RCHC when compared to RCNC (4.3 +/- 0.3 vs. 6.1 +/- 0.3; P < 0.001) and to control animals (control HC 8.2 +/- 0.3; P < 0.001), and control NC 7.5 +/- 0.33 (P < 0.001). To study the role of nitric oxide (NO), HC rats were treated with an infusion of L-arginine or D-arginine (150 mg via femoral artery) in a 50 mg bolus before RC administration and the remaining dose continuously for a period of one hour. The administration of L-arginine to RCHC rats resulted in significantly higher CIn (0.86 +/- 0.1; P < 0.001) when compared to the untreated rats (RCHC). D-arginine did not show a significant difference in CIn (0.49 +/- 0.08). There was a considerable difference between D-arginine RCHC and L-arginine RCHC (P < 0.05). The RBF fall was prevented by L-arginine in RCHC (8.4 +/- 0.23 vs. 4.3 +/- 0.3; P < 0.001), but it was not prevented by D-arginine (5.1 +/- 0.57; P < 0.001). Our data suggest that hypercholesterolemia aggravates nephrotoxicity, which is attenuated by L-arginine but not by D-arginine administration, suggesting that nitric oxide plays a significant role in this model of acute renal failure.

Nephrotoxicity of amphotericin B is attenuated by solubilizing with lipid emulsion.

Nephrotoxicity is the major adverse effect of conventional amphotericin B (AMB/D), often limiting administration of full dosage. The new liposomal amphotericin B seems to be less toxic. The new liposomal amphotericin B seems to be less toxic. In this study, it is proposed that solubilizing the standard AMB/D preparation with 10% lipid emulsion will attenuate nephrotoxicity. Rats were injected with either AMB/D (Fungizone), AMB, AMB/D plus lipid emulsion (AMB/D/LE), or sodium deoxycholate (D). Renal function studies were performed on day 5. To assess a direct tubular toxic effect, isolated rat proximal tubule suspensions and inner medullary collecting duct cells in culture were exposed to AMB/D, AMB, AMB/D/LE, liposomal amphotericin B, and D for 60 min in normoxia. Lactate dehydrogenase (LDH) release was assessed as an index of cell injury. Creatinine clearance (ml/min per 100 g) averaged 0.79 +/- 0.04 in control rats, 0.29 +/- 0.09 in AMB rats (P < 0.001 versus control), 0.38 +/- 0.04 in AMB/D rats, 0.46 +/- 0.05 in D rats, and 0.78 +/- 0.03 in AMB/LE rats. Renal blood flow (ml/min per 100 g) was 3.45 +/- 0.31 in control, 1.29 +/- 0.28 in AMB, 1.42 +/- 0.23 in AMB/D, 3.03 +/- 0.39 in D, and 2.71 +/- 0.21 in AMB/D/LE rats. The fractional excretion of potassium (%) was 27.3 +/- 1.18 in control rats, 61.6 +/- 7.00 in AMB/D rats, 58.4 +/- 15.32 in AMB rats, and 37.9 +/- 2.06 in AMB/D/LE rats. LDH release (%) in proximal tubules incubated with AMB/D and D was 43.6 +/- 3.39 and 58.6 +/- 4.20, respectively. Addition of lipid emulsion decreased LDH release: 21.6 +/- 1.22 for AMB/D/LE and 26.4 +/- 3.03 for deoxycholate plus lipid emulsion. AMB did not demonstrate any toxic effect in proximal tubule suspensions. D was not toxic to inner medullary collecting duct cells at 0.16 mg/ml, whereas D at a higher dose and AMB induced a significant LDH release. Addition of lipid emulsion did not affect the antifungal activity as assessed by the Etest method. In conclusion, an alternative way of administering standard AMB with reduced nephrotoxicity is proposed.

Effects of acyclovir on renal function.

The renal effects of acyclovir (100 mg/kg body weight i.p. for 7 days) were studied in rats. All animals became polyuric and presented an increase in blood urea nitrogen and fractional excretion of sodium and potassium. During hypotonic saline infusion, the acyclovir-treated rats showed higher distal fractional delivery compared to normal rats (27.8 +/- 4.7 vs. 11.3 +/- 0.9%, p less than 0.01) and a lower ratio of free-water clearance to distal sodium delivery (33.5 +/- 7.8 vs. 57.2 +/- 3.9%, p less than 0.02). Following hypertonic saline infusion, the ratio of osmolar to inulin clearance was higher in acyclovir rats (47.8 +/- 7.4%) than in normal rats (27.0 +/- 4.8%), whereas the ratio of free-water reabsorption to osmolar clearance was lower in the acyclovir rats (13.6 +/- 4.6 vs. 38.2 +/- 3.2%, p less than 0.01). These findings suggest an effect of acyclovir on the proximal tubule, thick ascending limb and/or inner medullary collecting duct (IMCD). In vitro measurements of 3H2O permeability of perfused IMCD of normal rats showed that vasopressin (50 microU/ml) added to the bath increased the diffusional water permeability (43.4 +/- 4.8 vs. 105.6 +/- 9.1 x 10(-5) cm/s), while in acyclovir rats, the control value (58.8 +/- 9.1 x 10(-5) cm/s) did not increase significantly in the presence of vasopressin (71.3 +/- 13.6 x 10(-5) cm/s). These results suggest that high doses of acyclovir produce azotemia and an abnormal function of the proximal tubule and thick ascending limb associated with resistance to vasopressin of the IMCD.

The effect of protein restriction on the severity and recovery from ischemic renal failure.

The effects of chronic dietary protein restriction on ischemic renal failure were evaluated in rats subjected to 90 min of bilateral renal clamping. The rats were kept on either 20% casein (regular) diet or casein-free (protein-free) diet 10 days before and 21 days after renal injury. Rats on regular protein diet showed higher levels of BUN and serum creatinine and had a lower inulin clearance (microliter/min/100 g BW) than animals on protein-free diet (289 +/- 34 vs 582 +/- 103, p less than 0.05) 2 days after ischemia. However, the inulin clearance measured 21 days following ischemia was significantly higher in rats on regular diet (1468 +/- 181) than those maintained on protein-free diet after ischemia (560 +/- 167). When unilateral 90 min ischemia was performed in rats on regular diet, the postischemic kidneys showed an incomplete recovery of the inulin clearance (226 +/- 35) compared to the contralateral kidney (900 +/- 116), 21 days after ischemia; whereas in rats on a protein-free diet the inulin clearance averaged 106 +/- 17 in the postischemic kidney and 345 +/- 41 in the right kidney. When left renal ischemia and contralateral nephrectomy were performed, the inulin clearance was 1149 +/- 74 in rats on regular diet and 534 +/- 60 in rats on protein-free diet, 21 days following renal insult. These results suggest that protein restriction can play a protective role against renal ischemia in an initial phase, but it limits the late recovery from ischemia. The presence of a normal contralateral kidney inhibits the functional recovery of the postischemic kidney and a contralateral nephrectomy produces a compensatory functional hypertrophy of the postischemic kidney, even in rats on a protein-free diet.