Acute cyclosporine nephrotoxicity—Prototype for a renal membrane signalling disorder

Continuous cyclosporine a infusion in patients with severe Kawasaki disease

BACKGROUND

The efficacy and safety of continuous intravenous infusion of cyclosporine A (CICsA) in patients with intravenous immunoglobulin-resistant Kawasaki disease are unclear.

METHODS

Between 2010 and 2020, 83 patients with Kawasaki disease that was not responsive to intravenous immunoglobulin (total dose ≥ 4 g/kg) were enrolled. All patients were started on CICsA (3 mg/kg/day) and switched to oral cyclosporine A (CsA) (4-6 mg/kg/day). Treatment efficacy, occurrence of coronary artery lesions (CALs), and laboratory parameters were evaluated. Patients were divided into two groups according to CICsA response: the responder group (afebrile ≤24 h after CICsA without additional treatment) and the weak responder group (afebrile >24 h after CICsA requiring additional treatment).

RESULTS

Fifty-five patients became afebrile within 24 and 74 h became afebrile in less than 72 h. Adverse events included hypertension in four and hyperkalemia in two patients. Thirty-nine patients were defined as responders and 44 patients as weak responders. There were no significant differences in CAL between the two groups. In weak responders, white blood cells, neutrophils, and C-reactive protein levels were higher, and albumin, immunoglobulin G, and CsA concentration were lower than in responders, indicating that weak responders had more severe inflammatory findings. However, there were no significant differences in CAL. Logistic regression analysis revealed that the response to treatment for CICsA was associated with immunoglobulin G levels at baseline and CsA concentrations the day after CICsA.

CONCLUSION

Although CICsA required additional treatments in about half of the cases, a favorable clinical course was observed by using this strategy, especially for reducing CAL.

Renal protective effects of leukotriene receptor blockers in an experimental model of cyclosporine nephrotoxicity

BACKGROUND

Chronic cyclosporine (CsA) nephrotoxicity is associated with renal fibrosis and hyaline arteriolopathy. Fibrogenic cytokines, such as transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF), play a pivotal role in CsA nephrotoxicity. Previous studies have demonstrated the possible role of leukotrienes (LT) in chronic CsA nephrotoxicity. The aim of this study was to examine the possible beneficial effects of LT blockers in attenuating the morphological and histochemical effects induced by CsA in a rat model of CsA nephrotoxicity.

MATERIALS AND METHODS

Twenty-four male Wistar rats were divided into 3 groups (n = 8). The first group (G1) was treated with vehicle intraperitoneally (IP) for 60 days. The second group (G2) was treated with 15 mg/kg CsA IP for 60 days. The third group (G3) was treated with the same dose of CsA plus 4 mg/kg montelukast administered by oral gavage for 60 days.

RESULTS

There was a statistically significant decrease in glomerular filtration rate (GFR) among G2 compared with G1 animals: 0.41 +/- 0.03 vs 1.63 +/- 0.12 mL/min (P < .001), or G3 hosts: 0.41 +/- 0.03 vs 0.95 +/- 0.05 mL/min (P < .005), respectively. The percentage of hyaline arteriolopathic changes was higher in G2 than G1 or G3: 81.66% +/- 8.2% vs 11.83% +/- 0.87% (P < .01) or 37.0% +/- 8.8% (P < .01), respectively. Fibrosis score was higher in G2 compared with G1 or G3: 1.5 +/- 0.04 vs 0.16 +/- 0.02 (P < .001) and 1.0 +/- 0.05 (P < .05), respectively. TGF-beta and VEGF immunoexpression were significantly increased in G2 compared with G1 (P < .05) or G3 (P < .05).

CONCLUSIONS

Our study suggested that LT may play a critical role in the pathogenesis of chronic CsA nephrotoxicity; the administration of montelukast, a LT receptor blocker, may prevent CsA-induced nephrotoxicity.

Engineering polysaccharide-based polymeric micelles to enhance permeability of cyclosporin A across Caco-2 cells

PURPOSE

To assess and compare the effectiveness of two types of polysaccharide-based micelles as delivery vehicles for poorly water soluble drugs by monitoring their permeability across Caco-2 cell monolayers.

METHODS

Dextran (DEX) and hydroxypropylcellulose (HPC) were hydrophobically modified (HM) by grafting polyoxyethylene cetyl ether (POE-C16, 15 mol% and 5.4 mol%, respectively). The onset of micellization and mean diameter of polymeric micelles formed by HM-DEX and HM-HPC were determined by fluorescence spectroscopy and dynamic light scattering, respectively. Cyclosporin A (CsA)-loaded polymeric micelles were prepared by a dialysis procedure, and the amount of incorporated CsA was assayed by high performance liquid chromatography (HPLC). The stability of micelles in simulated gastric and intestinal fluids was studied as a function of contact time, and their cytotoxicity toward Caco-2 cells was evaluated using the MTT colorimetric assay. The bidirectional transport across Caco-2 cell monolayers of CsA entrapped in HM-DEX and HM-HPC micelles and of the polymers themselves was evaluated in the presence and absence of P-glycoprotein inhibitor.

RESULTS

The amount of CsA incorporated in HM-HPC and HM-DEX micelles reached 5.5 and 8.5% w/w, respectively (entrapment efficiency of 22% or more). The polymeric micelles exhibited high stability in gastric and intestinal fluids and no significant cytotoxicity toward Caco-2 cells. The apical to basal permeability of CsA across Caco-2 cells increased significantly when loaded in polymeric micelles compared to free CsA.

CONCLUSIONS

Polysaccharide-based polymeric micelles are promising carriers for the oral delivery of poorly water soluble drugs. In vitro tests indicate that, overall, HM-HPC micelles are more effective compared to HM-DEX micelles.

Renal transplantation: basic concepts and evolution of therapy

Within the last 5 years, dramatic changes in the area of renal transplantation have occurred. There have been shifts in the dominant types of rejection, and in the types and utilization of immunosuppressants. Hyperacute rejection is now rarely seen, and acute cellular rejection within the first 6 to 12 months has been reduced to about 10%. However, humoral/antibody-mediated rejection has become a more prevalent problem. In the area of immunosuppressants, the ability to reduce acute cellular rejection to about 10% has been achieved through more judicious use of calcineurin inhibitors (cyclosporine and tacrolimus), increased use of mycophenolate mofetil, and the recent introduction of sirolimus (rapamycin). The polyclonal antibody (antithymocyte globulin), as well as monoclonal antibodies directed against the alpha chain of CD25 (daclizumab and basilixamab), have added substantially to the improved success of renal allografts. Because of numerous serious toxicities from glucocorticoids and calcineurin inhibitors, particularly cyclosporine, new studies are utilizing calcineurin-free and/or glucocorticoid avoidance or rapid elimination protocols often in combination with a monoclonal antibody and sirolimus. New immunosuppressants such as FTY720 and Campath-1 are also under study. In addition to its use in treating patients with low-level donor-specific antibody before transplantation in order to avoid hyperacute rejection, apheresis is utilized in various combination protocols after transplantation in the management of humoral/antibody-mediated rejection, in the treatment of hemolytic uremia syndrome that sometimes occurs with calcineurin inhibitors and sirolimus, as well as in the treatment of focal segmental glomerulosclerosis that has a major risk of recurrence in renal transplants.

Cyclosporine A amplifies Ca2+ signaling pathway in LLC-PK1 cells through the inhibition of plasma membrane Ca2+ pump

Cyclosporine A (CsA), a neutral, highly hydrophobic cyclic peptide with 11 amino acids, is currently the most widely used immunosuppressive drug for preventing graft rejection and autoimmune diseases. Despite its efficacy, the use of CsA is limited by severe side effects, mainly nephrotoxicity and arterial hypertension. Single cell microfluorimetry was used to evaluate the role of CsA on Ca(2+) signaling pathway in intact cells of the porcine proximal tubule-like cell line LLC-PK1; the assay of the in vitro activity of the plasma membrane Ca(2+) pump (PMCA) was carried out through the preparation and isolation of membranes. The addition of CsA to incubation medium at doses ranging from 0.1 to 2 microM did not change the basal level of intracellular calcium ([Ca(2+)](i)), whereas it affected the [Ca(2+)](i) response to thapsigargin (TG), a powerful inhibitor of microsomal Ca(2+) pump. In control studies, 5 microM TG produced a biphasic response: [Ca(2+)](i) peaked with a 60-s lag, and it then declined to a plateau of elevated [Ca(2+)](i), which remains above basal. However, it became evident that CsA strengthened the Ca(2+) response to TG because the addition of 5 microM TG to cells exposed to 400 nM CsA did not affect the peak response to TG, but it markedly affected the subsequent sustained phase ([Ca(2+)](i) = 156 +/- 4.84 versus 130 +/- 3.28 nmol, mean +/- SEM, n = 6, P < 0.001). In membrane preparations, 200 nM CsA brought about, in the presence of 10 microM calmodulin (CaM), a significant decrease of plasma membrane Ca(2+) pump (PMCA) activity (46.96 +/- 0.26 versus 53.48 +/- 1.96 nmol x mg of protein(-1) x min(-1), n = 6, P < 0.02), a value similar to that obtained in the presence of equimolar amounts of cyclosporine H (CsH), a non-immunosuppressive analogue of CsA. These findings suggest that in this cell line CsA affects the Ca(2+) export pathway through the reduction of the PMCA activity with consequent amplification and strengthening of [Ca(2+)](i) response after exposure to agents that trigger intracellular Ca(2+) release. The increased cell sensitivity during Ca(2+) signaling events ensuing from the impairment of this "defense system" may be regarded as one of the basic mechanisms involved in the development of the side effects induced by CsA.

Effect of cyclosporine a on hepatic compensatory growth: role of calcium status

Cyclosporine A (CsA) has been reported to positively influence hepatic compensatory growth (HCG) in normal animals. The role of calcium in the CsA-mediated influence on HCG was studied in normal and in chronically hypocalcemic rats, a model in which HCG is perturbed. CsA (3.33 mg/kg/day for 10 days) was administered before 2/3 partial hepatectomy (PHx). CsA did not influence serum Ca(2+) but significantly increased concentrations of the vitamin D hormone calcitriol. After PHx in normal animals, CsA accelerated DNA synthesis without influencing liver weight restitution, suggesting that its main effect was to mediate an accelerated progression through the cell cycle G(0) to G(1)/S phase(s). In hypocalcemic rats, CsA did not influence DNA synthesis, but normalization of circulating calcium alone accelerated DNA synthesis but abrogated the stimulatory effect of CsA, indicating that CsA could not superimpose its stimulatory effect on the calcium effect. In vitro investigation on the CsA mechanisms of action revealed a dose-dependent increase in hepatocyte basal resting cytoplasmic Ca(2+) and an increase in inositol-1,4,5-trisphosphate-sensitive Ca(2+) pool, which was dependent on the presence of normal extracellular Ca(2+) during CsA exposure. CsA also mediated a significant increase in cellular Ca(2+) mobilization by phenylephrine, vasopressin, and epidermal growth factor (EGF) in the presence of extracellular Ca(2+) concentration. Our data, therefore, demonstrate that CsA accelerates HCG after PHx by, in part, increasing the cellular Ca(2+) pools and the response to EGF and Ca(2+)-mobilizing hormones known to be comitogens for hepatocytes.

Effect of long-term cyclosporine administration on muscle flap hemodynamics

Long-term use of cyclosporine A (CsA) is associated with deleterious effects such as nephrotoxicity and hypertension as a result of its toxicity on microvasculature. These effects raise the possibility that long-term CsA use harms the microvasculature of the skeletal muscle tissue. An experimental study was conducted to investigate the effect of chronic systemic cyclosporine administration on the microvasculature of the cremaster flap model in the rat. Thirty male Sprague-Dawley rats were divided into five groups of 6 animals each. The control group received no treatment. The four CsA treatment groups received a daily subcutaneous injection of 2 mg per kilogram, 4 mg per kilogram, 8 mg per kilogram, and 16 mg per kilogram of cyclosporine for 6 weeks before surgery. The effect of long-term CsA administration on cremaster flap microcirculation was evaluated in vivo using an intravital microscopy system. Hemodynamic parameters of the cremaster muscle flap such as vessel diameter, red blood cell velocity, capillary density, leukocyte-endothelial interaction, and microvascular permeability were measured. There was no significant (p > 0.05) difference in vessel diameter in all groups. There was a significant increase in the number of adherent leukocytes in the 8-mg and 16-mg CsA group compared with the control (12 +/- 4.8 leukocytes per 100 microm and 12 +/- 4.5 leukocytes per 100 microm vs. 6 +/- 4.3 leukocytes per 100 microm; p < 0.05). Microvascular permeability indices increased significantly at 0 and 30 minutes after fluorescent isothiocyanate-albumin injection in the 8-mg and 16-mg CsA groups compared with the control (0 minutes: 0.6 +/- 0.2% and 0.5 +/- 0.1% vs. 0.4 +/- 0.05%; 30 minutes: 0.8 +/- 0.2% and 0.7 +/- 0.1% vs. 0.5 +/- 0.04%; p < 0.05). Histologically, the cremaster muscle flaps in all cyclosporine groups showed evidence of interstitial inflammation and venous vasculitis. In the 8-mg and 16-mg CsA groups there was also focal muscle injury. The toxic effect of CsA on the microvascular tree of a muscle flap was demonstrated by the increased permeability index in vivo, and the moderate venulitis and focal muscle injury histologically. Systemic CsA administration seems to have minimal impact on the viability of the muscle flaps, which was confirmed by preserved capillary function and muscle flap perfusion. These data suggest that there is a minimal risk in undertaking a pedicled muscle flap transfer procedure using a CsA immunosuppressive protocol.

Hypercalcemia in a renal transplant recipient suffering with Pneumocystis carinii pneumonia

Hypercalcemia occurs frequently after renal transplantation. Preexisting hyperparathyroidism is the most common cause of post-transplantation hypercalcemia. We describe a renal transplant recipient infected with Pneumocystis carinii pneumonia (PCP) who developed hypercalcemia, elevated 1,25-dihydroxyvitamin D, and suppressed parathyroid hormone levels. This phenomenon mimics the extrarenal production of 1,25-dihydroxyvitamin D by activated alveolar macrophages in granulomatous diseases with hypercalcemia. To the best of our knowledge, this is the first report of 1,25-dihydroxyvitamin D-mediated hypercalcemia caused by PCP in a renal transplant recipient. This entity should be included in the differential diagnosis for renal transplant recipients with hypercalcemia, especially in patients who develop lung infections.

Effect of cyclosporin A on nitric oxide production in cultured LLC-PK1 cells

The effect of Cyclosporin A on nitric oxide production was studied in cultured LLC- PK1 cells. For this purpose the cells were incubated with vehicle (olive oil, 10 microg/ml in DMSO), Cyclosporin A (CsA, 10 microg/ml), tumor necrosis factor (TNF-alpha, 150 U/ml) + interferon (IFN-gamma, 500 U/ml) to upregulate NOS synthesis, and therefore NO production (used as a positive control), or CsA + TNF-alpha + IFN-gamma. After 72 hours the culture medium was collected and nitrite was determined by the Griess method. The results were normalized to the protein harvested from these cells as measured by the Lowry method. Viability was determined by the exclusion of the fluorescent dyes (acridine orange and ethidium bromide). Intracellular calcium was measured spectrophotometrically using the fluorescent calcium indicator fura-2 AM. In CsA treated cells, the nitrite (pmoles/mg of protein) was decreased when compared to control (12.8 +/- 0.5 vs. 18.3 +/- 0.6; p < 0.05; both n = 8). TNF-alpha + IFN-gamma increased the nitrite synthesis (52.0 +/- 0.2; p < 0.05 vs. control; n = 6). This effect was decreased significantly by the simultaneous treatment with CsA (38.8 +/- 0.3; p < 0.05; n = 6). Cell viability in CsA group was decreased when compared to the control (84.7 +/- 0.2% vs. 93.6 +/- 0.1%; p < 0.05; both n = 10). TNF-alpha + IFN-gamma had no effect on viability (93.0 +/- 0.3%; n = 10). However, when combined with CsA, viability was decreased relative to the control (85.0 +/- 0.2%; p < 0.05; n = 10). Acute (1 h) or chronic (72 h) treatment of LLC- PK1 cells with CsA had no effect on basal calcium levels. Our results demonstrate a reduced level of nitric oxide production in LLC-PK1 cells treated with CsA. There was no effect of the drug on intracellular calcium levels, however CsA treatment did reduce cellular viability. We suggest that, in part, the decreased levels of NO production are a secondary consequence of direct cell damage. However, CsA may also be exerting direct effects on NO synthesis through its interactions with both iNOS and cNOS. These results also provide a dual mechanism of action for CsA induced nephrotoxicity, that is, direct cell damage and interference with the NO system within the nephron.

Nifedipine prevents changes in nitric oxide synthase mRNA levels induced by cyclosporine

Cyclosporine toxicity mainly affects kidney and liver function. We have previously shown that cyclosporine nephrotoxicity alters kidney nitric oxide synthase mRNA pattern of expression. To determine if nitric oxide synthase expression changes are mediated directly by cyclosporine or by secondary hemodynamic alterations induced by cyclosporine, we evaluated if these effects are tissue specific and if nifedipine-induced vasodilation prevents these alterations. Uninephrectomized Wistar rats treated for 7 days with olive oil, cyclosporine (30 mg/kg), nifedipine (3 mg/kg), and nifedipine+cyclosporine were studied. In vehicle and cyclosporine groups, the gene expression of the neuronal, inducible, and endothelial nitric oxide synthases in cerebellum, heart, intestine, liver, renal cortex, and medulla was evaluated. The administration of cyclosporine was associated with nephrotoxicity and hepatotoxicity, increased endothelial nitric oxide synthase mRNA levels in renal cortex and liver, and a decrease in inducible nitric oxide synthase and neuronal nitric oxide synthase in renal medulla. The mRNA levels of the 3 nitric oxide synthase isoforms were not affected in any other tissue. Nifedipine did not alter nitric oxide synthase expression in the control group but prevented changes associated with cyclosporine. These results suggest that cyclosporine-induced changes in the pattern of expression of the nitric oxide synthases may be secondary to its hemodynamic effects.

Cyclosporine A up-regulates angiotensin II receptors and calcium responses in human vascular smooth muscle cells

BACKGROUND

The most widely used immunosuppressive drug for preventing graft rejection and treating autoimmune diseases is currently cyclosporine A (CsA). However, CsA also causes vasoconstriction, which is considered to be at the origin of CsA-induced nephrotoxicity and hypertension. To evaluate the cellular basis for these side effects, we studied the influence of CsA on the regulation of the free cytosolic Ca2+ concentration ([Ca2+]c) in cultured human vascular smooth muscle cells (SMCs).

METHODS

SMCs were isolated from the medial layer of human aorta. [Ca2+]c regulation was studied by fluorimetry with fura 2 and by measuring 45Ca2+ effluxes. Angiotensin II (Ang II) receptors were detected by [125I]Ang II binding.

RESULTS

Pretreatment of human SMCs for 24 hours with CsA in its therapeutic concentration range (0. 1 to 10.0 microM) had no effect on basal [Ca2+]c, but increased the [Ca2+]c elevation and 45Ca2+ efflux when cells were stimulated with Ang II. Half-maximal effects occurred at approximately 1 microM CsA. The CsA effects on [Ca2+]c were accompanied by a nearly twofold increase in Ang II receptor number, whereas no change in affinity to Ang II was observed. CsA did not alter endothelin-1- or thapsigargin-induced 45Ca2+ efflux. Increases in both Ca2+ responses and [125I]Ang II binding were attenuated by the transcriptional inhibitor actinomycin D. The effects of CsA did not appear to be mediated by calcineurin inhibition because cyclosporine H, which is not immunosuppressive, also increased the Ang II-induced 45Ca2+ efflux.

CONCLUSION

These data suggest that CsA preferentially up-regulates the transcription of Ang II receptors, which very likely leads to vasoconstriction in vivo and could be at the origin of CsA-induced hypertension and nephrotoxicity in humans.

Effect of misoprostol on myocardial contractility in rats treated with cyclosporin A

The nephrotoxic side effects of the immunosuppressant cyclosporin A in animals and humans are well known. Misoprostol, a prostaglandin E analog, is used clinically in organ-transplant recipients taking cyclosporin A to protect against these side effects. We reported previously that long-term treatment of rats with cyclosporin A causes a diminution in myocardial peak contractile stress. There is an associated spontaneous sarcomere activity and rest depression of force in the absence of a change in myofilaments sensitivity to intracellular Ca2+. Here we investigated the potential protective effects of misoprostol on the myocardium of cyclosporin A-treated rats. Rats were treated with either cyclosporin A, misoprostol, or their combination. Force-[Ca2+]o and -[Sr2+]o, and force-interval relations as well as the sarcomere length were studied in trabeculae isolated from the right ventricles. At suboptimal [Ca2+]o, cyclosporin A shifted the force-[Ca2+]o relation to the left but reduced peak contractile stress by approximately 35% at the highest (optimal) [Ca2+]o. Co-treatment with misoprostol prevented the leftward shift, and treatment with misoprostol alone did not cause a leftward shift. The diminution of peak stress, however, did not recover with misoprostol treatment, and stress was further reduced. Treatment with only misoprostol also reduced stress generated by the muscles more than that by cyclosporin A alone. Intriguingly, activation of the myofilaments by Sr2+ failed to recover peak stress to control levels in any group treated with misoprostol. Unlike cyclosporin A, however, rest potentiation of force was more pronounced, and spontaneous sarcomere activity was absent with misoprostol. No histopathologic changes were observed with cyclosporin A or misoprostol treatment. Misoprostol modifies the cyclosporin A-induced changes in the Ca2+ handling, but further decreases the stress generated by the muscles.

Contribution of endothelin receptors in renal microvessels in acute cyclosporine-mediated vasoconstriction in rats

Cyclosporine A (CsA), a widely used immunosuppressive agent, causes renal vasoconstriction and systemic hypertension. Recent data suggest that the renal effect of CsA is possibly mediated by endothelin (ET). We investigated the effects of CsA on renal microvessels and the efficacy of ETA or ETA/ETB receptor antagonists in ameliorating CsA effects in the hydronephrotic rat kidney. Infusion of CsA (30 mg.kg-1) induced a transient increase (20%) in mean arterial pressure (MAP) and a sustained reduction (85%) in glomerular blood flow (GBF) due to preferential constriction of the arcuate artery (39%) and the proximal segment of the interlobular artery (23%). Under basal conditions the ETA receptor antagonist BQ-123 had marginal effects consisting of reduction in MAP, rise in GBF and dilation of preglomerular vessels. The non-selective ETA/ETB receptor antagonist PD 145065 also reduced MAP, but tended to decrease GBF and constrict large preglomerular vessels. The difference in effects of the two antagonists indicated that under basal conditions ETB blockade constricts large preglomerular vessels and reduces GBF. After BQ-123 or PD 145065, the constriction of large preglomerular vessels and reduction in GBF induced by CsA was attenuated by about 50%, but the rise in MAP was not influenced. Our data indicate that a sizable part of renal vasoconstriction due to CsA is mediated via ET production in large preglomerular arteries and can be avoided by the blockade of ETA receptors. Additional blockade of ETB receptors does not attenuate the CsA effects further, possibly because ETB receptors mediate both vasoconstriction and dilation.

Pentoxifylline reduces nephrotoxicity associated with cyclosporine in the rat by its rheological properties

BACKGROUND

The goals of this study were to evaluate whether administration of pentoxifylline (POF) reduces the nephrotoxicity associated with cyclosporine (CsA) in the rat, and whether the effect of POF is related to its rheological properties.

METHODS

Mean arterial pressure was measured by an intraarterial catheter. Glomerular filtration rate and renal plasma flow were determined by measuring inulin and para-aminohippurate clearances, after double-blind coadministration for 10 days of CsA (25 mg/kg/day) with either vehicle or POF (45 mg/kg every 12 hr). These results were compared with those obtained in control rats. Blood viscosity and erythrocyte deformability were also evaluated after treatment using a cone plate viscometer and a filtration method, respectively.

RESULTS

No changes were observed in mean arterial pressure in both groups compared with controls. Glomerular filtration rate was significantly lower in CsA-treated rats (0.3+/-0.1 ml/min/100 g) than in control animals (0.6+/-0.1 ml/min/100 g, P<0.02). The coadministration of CsA with POF normalized the glomerular filtration rate (0.6+/-0.1 ml/min/100 g). A parallel decrease in renal plasma flow was observed in CsA-treated rats compared with controls (CsA+vehicle: 1.5+/-0.2 vs. control: 2.2+/-0.1 ml/min/100 g, P<0.02), this effect completely reversed by cotreatment with POF (3.1+/-0.2 ml/min/100 g). Blood viscosity was significantly higher in CsA-treated rats than in the control group (CsA+vehicle: 5.6+/-0.7 vs. control: 5.0+/-0.4 m x Pa x s, P<0.05). This effect was associated with a lower erythrocyte deformability (CsA+vehicle: 1.2+/-0.2 vs. control: 1.5+/-0.3 ml/min, P<0.05). These rheological abnormalities were normalized by coadministration with POF (blood viscosity: 4.9+/-0.7 m x Pa x s and erythrocyte deformability: 1.9+/-0.4 ml/min, P<0.05).

CONCLUSIONS

Our results show that administration of POF prevents the nephrotoxicity associated with CsA. This beneficial effect could be related to its rheological properties.

MAP kinase activation by cyclosporine A

Short treatment of HeLa cells with cyclosporine A led to the activation in the crude cell extracts of a MAP kinase-like activity. Fractionation by chromatography on a Mono Q column allowed the separation of two activities co-eluting with the MAP kinases ERK1 and ERK2. The activation of these two MAP kinases was demonstrated in Western Blotting by the appearance, after CsA treatment, of two new slowly migrating forms on SDS electrophoretic gels. A similar activation was also obtained in renal epithelial BSC-1 cells and 3T3 fibroblasts. MAP kinase activation might result from a perturbation of calcium homeostasis induced by CsA treatment.

L-Arginine and allopurinol protect against cyclosporine nephrotoxicity

The role of nitric oxide (NO) and oxygen free radicals in cyclosporine (CsA) nephrotoxicity was investigated using L-arginine, an NO substrate, and allopurinol, a xanthine oxidase inhibitor (involved in the formation of oxygen radicals) in an experimental model with Wistar rats. CsA, administered at 15 mg/kg/body weight (BW) subcutaneously for 10 days, caused a decrease in glomerular filtration rate, with inulin clearance of 0.33+/-0.04 vs. 1.11+/-0.06 ml/min/100 g BW (P<0.01 vs. control). L-Arginine, 1.5% in drinking water 5 days before and during CsA administration, partially protected the animals against this fall in glomerular filtration rate, with inulin clearance of 0.68+/-0.03 ml/min/100 g BW (P<0.01 vs. CsA). Allopurinol, at 10 mg/kg/BW by gavage, also had a protective action, with inulin clearance of 0.54+/-0.04 ml/min/100 g (P<0.01 vs. CsA). CsA caused an elevation in NO production, as assessed by urinary excretion of its metabolites, nitrite and nitrate (NO2 and NO3; 0.836+/-0.358 vs. 0.107+/-0.019 nmol/microg creatinine). NO production was as much as threefold higher in the L-arginine group (1.853+/-0.206 nmol/g creatinine). This CsA effect is probably related to its vasoconstrictive stimulus. Supplementation with L-arginine, which provides more substrate for NO formation, may enhance vasodilatation and consequently reduce the impairment of renal function. The protection provided by allopurinol may be related to the reduced formation of oxygen radicals, preventing the deleterious effects of lipid peroxidation.

Cyclosporin A increases nitric oxide activity in vivo

The use of cyclosporine is complicated by its vaso-constrictive actions. In vitro cyclosporine has been associated with both decreased endothelium-dependent vasodilatation and increased nitric oxide activity. We studied the interaction between cyclosporine and endothelium-derived nitric oxide in seven healthy volunteers. Using venous-occlusion plethysmography, we measured forearm blood flow during intra-arterial infusion of serotonin, which in the concentrations used is a selective agonist of endothelial nitric oxide release, or NG-monomethyl-L-arginine, a specific inhibitor of nitric oxide synthase, during coinfusion of saline or cyclosporine (75 micrograms/min), respectively. During coinfusion of cyclosporine, forearm blood flow increased on maximal serotonin infusion from 2.9 (SE, 0.2) to 8.1 (0.9) mL/100 mL per minute in forearm tissue, which was significantly higher than the increase during saline coinfusion (3.0[0.3] to 6.0 [0.5]; P < .05). Cyclosporine infusion during a "free" nitric oxide system had no effect on basal forearm blood flow, but in significantly decreased forearm blood flow (21.7[2.8]%; P < .05) during fixed nitric oxide activity. These data suggest that acute administration of cyclosporine enhances both basal and receptor-stimulated nitric oxide activity. The mechanism is not clear but may include cyclosporine-induced shear stress as well as direct effects of cyclosporine. The latter was supported by our observation that gene expression of the enzyme nitric oxide synthase III was enhanced by approximately 50% after coincubation with cyclosporine. In conclusion, the present observation demonstrates that nitric oxide constitutes an important regulating mechanism that protects against cyclosporine-associated vasoconstriction in vivo.

Management of acute renal failure in the elderly. Treatment options

Renal changes that occur with aging mainly consist of impairment in the ability to concentrate urine and to conserve sodium and water. These physiological changes increase the risk of volume depletion and the prerenal type of acute renal failure (ARF) in elderly people. Bladder outlet obstruction caused by benign prostatic hypertrophy is a common cause of ARF in elderly men. Another frequent cause of ARF in the elderly is drug-induced nephropathy. Nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics are most often implicated in the development of ARF in the elderly. However, considering the high usage of these drugs, the incidence of drug-induced nephropathy is relatively small. NSAIDs are more likely to cause ARF in patients with congestive heart failure, chronic renal disease (including diabetic nephropathy) or chronic liver disease than in otherwise healthy individuals. NSAID-induced ARF is often of the prerenal type, but may be caused by acute interstitial nephritis (AIN). The presence of heavy proteinuria or nephrotic syndrome differentiates NSAID-induced AIN from AIN caused by other drugs. Antibiotics, especially semisynthetic penicillins, more commonly give rise to AIN associated with peripheral blood eosinophilia and eosinophiluria than NSAIDs. Ciprofloxacin is increasingly reported to cause AIN. Fever commonly accompanies AIN, especially when induced by antibiotics. Aminoglycosides produce ARF by inducing acute tubular necrosis (ATN), which results from the excessive accumulation of myeloid bodies in the tubules. In all cases of ARF it is essential to obtain a good history, to perform a through physical examination, with particular attention to skin turgor, and to measure blood pressure, pulse rate (supine and upright), urinary electrolyte and creatinine levels. Fractional excretion of sodium and the urine:plasma creatinine ratio are reliable indices that distinguish prerenal ARF from ATN. A prompt response to fluid challenge, with an increase in urine output and urinary sodium excretion, and a rapid decrease in blood urea nitrogen, constitutes strong evidence for prerenal ARF. However, these indices are unreliable when prerenal ARF has progressed to ATN or when ARF has an obstructive pattern to begin with. In all cases of ARF, especially in elderly men, urinary tract obstruction should be suspected unless the history is otherwise clear cut. Ultrasound of the kidneys and bladder is a simple, non-invasive and meaningful test that can be used to rule out obstructive causes of ARF. If obstruction is the cause of ARF, ultrasound will be positive; in contrast, urinary obstruction is very unlikely if ultrasound findings are normal in a patient who has been oliguric or anuric for 48 hours or more. Similarly, acute glomerulonephritis, including rapidly progressive glomerulonephritis, should be suspected when ARF is associated with heavy proteinuria. In such instances, percutaneous renal biopsy is essential to document the diagnosis. It is of utmost importance to establish whether ARF is of prerenal or postrenal type, both of which are potentially fully reversible. In contrast, patients with ATN or rapidly progressive glomerulonephritis may not recover, or may only partially recover, their renal function. Haemodialysis and nutritional support are common measures for patients with severe ATN and a highly catabolic state. Corticosteroids and immunosuppressive therapy should be instituted for rapidly progressive glomerulonephritis, in addition to haemodialysis. haemodiafiltration instead of haemodialysis is recommended for patients who are haemodynamically unstable [i.e., with a persistently low blood pressure (systolic < or = 100 mm Hg)]. Haemodiafiltration has been shown to improve acid-base balance and uraemia better than standard haemodialysis. However, despite dialysis, mortality in patients with ARF associated with ischaemic ATN remains high.

Dose-dependent stimulation/inhibition effects of cyclosporin A on lysosomal cathepsin activities in cultured proximal tubule cells

The effects of cyclosporin A on the activities of lysosomal cysteine proteinases (cathepsin B, H, L+B) in LLC-Pk1 cells were investigated to elucidate their potential role in cyclosporin A-induced nephrotoxicity. Cyclosporin A at lower doses (0.1--1,000 ng/ml) stimulated cathepsin B, H, L+B. In contrast, at a higher dose (10,000 ng/ml), it inhibited these proteinase activities associated with a reduction in protein degradation. In line with the altered proteinase activities, cellular protein content was decreased at the lower dose (10 ng/ml) and increased at the higher dose. The higher dose of cyclosporin A also enhanced cellular lipid peroxide content after an exposure of 4 and 10 h. Co-incubation with superoxide dismutase (40 U/ml) did not ameliorate the inhibition of cathepsin B activity induced by the high dose of cyclosporin A. On the contrary, the calcium channel blocker verapamil (10(-6) M) prevented this inhibition. In conclusion, cyclosporin A exerts a dose-dependent biphasic effect on lysosomal cysteine proteinase activities. A rise in cytosolic Ca2+ concentration, but not an enhanced lipid peroxidation, may be involved in the suppression of cathepsin B activity induced by the higher dose of cyclosporin A. These studies raise the possibility that alterations of tubular proteinase activity may play a role in the cyclosporin A-induced nephrotoxicity.

Transmembrane signaling in kidney health and disease

Transmembrane signal transduction is the process whereby a ligand binds to the external surface of the cell membrane and elicits a physiological response specific for that ligand and cell type. It is now appreciated that numerous disease states represent disturbances in normal transmembrane signaling mechanisms. In the current paper, we focus our attention on the mesangial cell of the glomerular microcirculation as a prototypical model system for understanding normal and abnormal transmembrane signaling processes. Among the major receptor and effector mechanisms for transmembrane signal transduction in the mesangial cell, this paper emphasizes the phospholipase effector response to growth factors and vasoactive hormones. The post-translational and transcriptional pathways for regulation of phospholipase C and phospholipase A2 are described, including consideration of perturbations in these systems that characterize two disease models, namely: acute cyclosporine nephrotoxicity and early diabetic glomerulopathy.

An experimental study of altered nitric oxide metabolism as a mechanism of cyclosporin-induced renal vasoconstriction

Nephrotoxicity caused by cyclosporin A (CSA) is the result of vasoconstriction of the renal microcirculation. The endothelium-derived relaxing factor nitric oxide (NO) regulates microvascular blood flow in various tissues, and mediates the microcirculatory response during hypertension and sepsis. This study investigated the role of NO in CSA-induced renal vasoconstriction. Hydronephrotic kidneys in rats were suspended in an environmentally controlled tissue bath, and interlobular, afferent and efferent arteriolar diameters and blood flow were measured by in vivo videomicroscopy. CSA was administered alone, with the nitric oxide synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) or with exogenous NOS substrate L-arginine. CSA significantly constricted the whole of the renal microvasculature whereas L-NAME alone preferentially constricted the preglomerular vessels. L-Arginine reversed the vasoconstriction induced by CSA whereas L-NAME had no further effect. Preglomerular basal vascular tone is dependent on continuous production of NO and alterations in the L-arginine-NO pathway contribute to CSA-induced renal vasoconstriction.

Dietary fatty acids and the glomerular hemodynamic response to cyclosporine in borderline hypertensive rats

We have recently reported that cyclosporine A (CsA) decreases glomerular filtration rate in the borderline hypertensive rat (BHR), but that the glomerular filtration rate is normal when the rats are maintained on a diet supplemented with evening primrose (EP) oil. The current studies were designed to determine the glomerular hemodynamic changes responsible for this effect. A first group (PLAC-SAFF) received a diet supplemented with safflower oil (SAFF) (10% of calories) and placebo (PLAC). A second group (CsA-SAFF) received a diet supplemented with SAFF and CsA (10 mg/kg/day). A third group (CsA-EP) also received CsA, but the diet was supplemented with EP oil (10% of calories). Routine micropuncture studies were performed after five to nine weeks of treatment. Single nephron glomerular filtration rate (SNGFR) was lower in CsA-SAFF than in PLAC-SAFF (36 +/- 2 vs. 46 +/- 1 nl/min, p < 0.05). Maintenance of SNGFR in CsA-EP compared to CsA-SAFF (48 +/- 2 nl/min vs. 36 +/- 2 nl/min, P < 0.05) was due to higher values for single nephron plasma flow rate (156 +/- 16 vs. 118 +/- 9off/min, P < 0.05), and higher values for the glomerular capillary ultrafiltration coefficient (0.091 +/- 0.013 vs. 0.054 +/- 0.010 nl/s/mm Hg, P < 0.05). Since dietary fatty acids can affect prostaglandin (PG) production, we measured PGE production in isolated glomeruli. Mean values for basal production rates of PGE were greater in rats maintained on EP than in rats maintained on SAFF (3958 +/- 105 vs. 3378 +/- 146 pg PGE/mg glomerular protein, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine produces endothelial dysfunction by increased production of superoxide

Vasoconstriction and hypertension are major side effects of cyclosporine therapy. The mechanism or mechanisms responsible for the vascular effects of cyclosporine are unclear. The vascular effects of cyclosporine may arise as a consequence of endothelial dysfunction induced by the agent. To test this possibility, we compared in vessels prepared in myographs endothelium-mediated relaxations of mesenteric resistance arteries of Wistar-Kyoto rats treated for 21 to 28 days with subcutaneous injections of cyclosporine (25 mg/kg per day), or vehicle. Endothelium-dependent relaxations in response to acetylcholine were impaired in arteries from cyclosporine-treated rats; the concentrations of acetylcholine required to produce 50% relaxation of norepinephrine activation (pD2) were 31.6 +/- 0.1 versus 5 +/- 0.1 nmol/L in control arteries (P < .05). Nitro-L-arginine produced comparable 10-fold decreases in sensitivity to acetylcholine in arteries from both rat groups, indicating that the relaxations were mediated by endothelium-derived nitric oxide. Acetylcholine-induced relaxations in cyclosporine-treated arteries were normalized by pretreatment of the arteries with superoxide dismutase (150 IU/mL; pD2, 3.6 +/- 0.1; P < .05); superoxide dismutase had no effect on relaxations in control arteries. SQ 29,548, an inhibitor of prostaglandin H2/thromboxane A2 receptors; H-7, an inhibitor of protein kinase C; and indomethacin did not alter relaxations in response to acetylcholine in either group of arteries. Cyclosporine-treated arteries were more sensitive than control arteries to nitroprusside, an agent that induces relaxation via nitric oxide (pD2, 1.3 and 6.2 mumol/L, respectively; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal biopsy specimens from patients with rheumatoid arthritis and apparently normal renal function after therapy with cyclosporine. Canadian Multicentre Rheumatology Group

Renal biopsies were performed in 14 patients with severe rheumatoid arthritis who had no evidence of compromised renal function after completion of treatment with low-dose cyclosporine (< or = 5 mg/kg/d). Mean serum creatinine at the time of biopsy was 0.84 mg/dL (range, 0.59 to 1.23 mg/dL). In the 13 patients who had received 6 months of cyclosporine therapy, mild glomerular expansion was noted in two biopsy specimens, obsolescent glomeruli (range, 5% to 20%) in five, and glomerular amyloid deposits in one. Five biopsy specimens had mild and three had mild to moderate interstitial fibrosis. Moderate interstitial fibrosis with a striped pattern was attributed to cyclosporine in the 14th patient. The results of a second biopsy performed in one patient after a further 18 months of therapy were unchanged. Although the renal biopsy changes were minimal in 13 patients and pathologic features characteristic of cyclosporine nephropathy were absent from all but one biopsy, a greater frequency of adverse effects due to cyclosporine could not be excluded. In the absence of clinical data, long-term cyclosporine therapy must be administered with caution to patients with rheumatoid arthritis, who commonly have underlying renal damage, and the value of renal biopsies in predicting and preventing end-stage renal failure remains to be determined.

Interleukin-1-induced cyclooxygenase 2 expression is suppressed by cyclosporin A in rat mesangial cells

The immunosuppressive drug cyclosporin A (CsA) has considerable nephrotoxic side effects which seem to be related to its interference with the synthesis of vasoactive prostanoids. Therefore, the molecular mechanism of the effect of CsA on the synthesis of prostaglandin E2 (PGE2) was investigated in rat renal mesangial cells (RMC). CsA effectively inhibited the PGE2 synthesis induced by inflammatory cytokines such as interleukin 1 (IL-1) or tumor necrosis alpha (TNF alpha). The induction by IL-1 and the inhibition by CsA were reflected in the enzyme activity of the cyclooxygenase. The changes in activity could be correlated with the expression of the inducible cyclooxygenase isoform (COX2), which is characterized by its 4.4 kb mRNA: the expression of this enzyme was enhanced by IL-1 and suppressed by CsA on the mRNA and protein level as determined by Northern and Western blot analyses. Suppression of COX2 mRNA was also observed when the message was induced by LPS or ionophore A23187. The expression of the basal cyclooxygenase isoform (COX1), which was constitutively expressed in proliferating mesangial cells, was not affected by IL-1 or CsA. Interferon gamma, which did not induce prostaglandin synthesis or influence COX mRNA expression, augmented the expression of MHC antigens in RMC. This induction was insensitive to CsA treatment. We could thus show that the inducible cyclooxygenase isoform in mesangial cells is a molecular target for CsA providing a possible mechanism for the interference of the drug with the balance of vasoactive prostanoids.

Interaction of dietary fatty acids and cyclosporine A in the borderline hypertensive rat: tissue fatty acids

In this study we examined (i) the effects of cyclosporine A (CS) on tissue lipid composition and (ii) the effect of changes in dietary n-6 fatty acids on tissue responses to CS. Fatty acid composition of liver, kidney, heart and brain were determined after 4 wk of treatment with CS (10 mg/kg.d p.o.) in male borderline hypertensive rats (BHR, n = 4/group), whose diet was supplemented with either safflower oil or evening primrose oil (EPO). Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine/phosphatidylinositol, triglyceride and cholesteryl ester fatty acids were measured in kidney, heart, brain and liver. The same parameters were also measured in safflower-fed BHR (n = 4) receiving placebo. The effects of CS on liver microsomal delta 9, delta 6 and delta 5 desaturases in vitro were also followed. CS affected the fatty acid composition of all tissues examined, with the greatest changes seen in the renal phosphatidylcholine and phosphatidylserine/phosphatidylinositol fractions. All CS-induced changes that occurred in the liver, brain and renal fatty acids were reversed by EPO. CS elevated delta 9 desaturase but had no effect on delta 6 and delta 5 desaturase. In light of (i) the observation that EPO normalizes renal function and blood pressure in CS-treated BHR, and (ii) the importance of the kidney in blood pressure regulation, the data suggest that the beneficial effects of EPO on CS toxicity may involve changes in renal phospholipid fatty acid profiles.

Cyclosporin derivatives inhibit interleukin 1 beta induction of nitric oxide synthase in renal mesangial cells

Treatment of mesangial cells with recombinant human interleukin 1 beta dose dependently increased nitrite formation due to the induction of a macrophage-type of nitric oxide (NO) synthase. Addition of cyclosporin A, cyclosporin G or cyclosporin H dose dependently inhibited interleukin 1 beta-induced nitrite generation. Half-maximal inhibition was observed at concentrations of 0.9 microM, 2.0 microM and 3.8 microM of cyclosporin A, cyclosporin G and cyclosporin H, respectively. Time-course studies indicated that cyclosporin A could be added up to 6 h after the interleukin 1 beta stimulus and still caused maximal inhibition of nitrite production. Furthermore, interleukin 1 beta increased NO synthase mRNA levels in mesangial cells and this effect was potently suppressed by all three cyclosporin derivatives. As cyclosporin H has no immunosuppressive activity, these data indicate that the inhibitory effect of the cyclosporin derivatives on NO synthase expression is not related to the immunosuppressive action of the drugs. This suggestion is further substantiated by the observation that the potent immunosuppressants rapamycin and FK506 did not alter interleukin 1 beta-induced NO synthase mRNA levels or nitrite generation in mesangial cells. In summary, these data demonstrate that cyclosporin derivatives potently modulate the L-arginine-NO pathway in renal mesangial cells.

The effect of prostaglandin E1 analog misoprostol on chronic cyclosporin nephrotoxicity

Cyclosporin A has markedly improved graft survival in transplant patients but its side effects, such as renal toxicity and hypertension, pose management problems in transplant recipients. This toxicity has been attributed to prostaglandin inhibition. Concurrent administration of misoprostol (a prostaglandin E1 analog) prevents chronic cyclosporin A-induced nephrotoxicity but not hypertension in rats.

Cyclosporin A inhibits apical secretory K+ channels in rabbit cortical collecting tubule principal cells

We used the cell-attached patch clamp configuration to examine the effect of basolateral cyclosporin A (CsA) exposure on low conductance K+ channels found in the principal cell apical membrane of rabbit cortical collecting tubule (CCT) primary cultures. Baseline K+ channel activity, measured as mean NPo (number of channels x open probability), was 2.7 +/- 1.1 (N = 29). NPo fell by 69% (0.84 +/- 0.32; N = 32) in cultures pretreated with 500 ng/ml CsA for 30 minutes prior to patching. Chelation of intracellular [Ca2+]i (10 mM BAPTA/AM; N = 8) or removal of extracellular Ca2+ (N = 9), but not prevention of [Ca2+]i store release (10 microM TMB-8; N = 7), abolished CsA-induced inhibition. This suggested that CsA effects were mediated by an initial rise in [Ca2+]i via Ca2+ influx. Either 25 nM AVP (N = 10) or 0.25 microM thapsigargin (N = 8) (causing IP3-dependent and -independent release of [Ca2+]i stores, respectively) augmented, while 25 pM (N = 6) or 250 pM AVP (N = 8) reversed CSA-induced channel inhibition. Apical membrane protein kinase C (PKC) activation with 0.1 microM phorbol ester, PMA (N = 8) or 10 microM synthetic diacylglycerol, OAG (N = 7), mimicked (mean NPo = 0.99 +/- 0.40) the inhibitory effect of CsA. Apical PKC inhibition by prolonged apical exposure to PMA (N = 10) or 100 microM D-sphingosine (N = 6) blocked CsA's effect. Cyclic AMP increasing maneuvers, 10 microM forskolin (N = 5) or 0.5 mM db-cAMP (N = 8), stimulated basal K+ channel activity in the absence of CsA.

IN CONCLUSION

(1) basolateral exposure to CsA inhibits the activity of apical membrane 13 pS channels responsible for physiologic K+ secretion in rabbit CCT principal cells. (2) The inhibition is mediated by changes in intracellular Ca2+ and activation of apical PKC. (3) Pharmacologic AVP (nM) augments CsA-induced inhibition by releasing intracellular Ca2+ stores; more physiologic AVP (pM) attenuates channel inhibition, probably through cAMP generation. (4) Inhibition of apical secretory K+ channels by CsA likely contributes to decreased kaliuresis and clinical hyperkalemia observed in patients on CsA therapy.

Calcium antagonists and the kidney: future therapeutic perspectives

During the past decade, attention has focused on the effects of calcium antagonists on renal function. Recent studies using diverse videomicroscopic techniques including the isolated perfused hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, have demonstrated that calcium antagonists acutely antagonize preglomerular vasoconstriction. In contrast, most studies suggest that the efferent arteriole appears to be refractory to the vasodilatory effects of these agents. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics, including transplant-associated acute renal insufficiency and, possibly, cyclosporine nephrotoxicity. Evidence has accrued to suggest that calcium antagonists also may be protective against acute radiocontrast-induced nephrotoxicity. Finally, the renal hemodynamic and natriuretic effects of calcium antagonists commend their use as antihypertensive agents in the management of essential hypertension and transplant-associated hypertension.

Isolated rat glomerular cells demonstrate L-type Ca(2+)-channel activity

The presence of L-type calcium (Ca2+)-channels and the effects of Ca(2+)-channel antagonists on cells of rat glomeruli were investigated. Glomeruli were isolated by graded sieving and after preincubation (10 min) in zero Ca2+, the uptake of 45Ca2+ by glomerular cells was measured. Depolarization with KCl (50 mM) or the dihydropyridine agonist Bay K 8644 (10 microM) stimulated 45Ca2+ uptake by 13% and 24%, respectively, above control (100%), which was inhibited by nifedipine (Nif, 10 microM), P < 0.05, and by both S and R isomers of verapamil (Ver, 10 microM), P < 0.001. In a separate experimental preparation, isolated glomeruli were preloaded (45 min) with 45Ca2+. Following a 45 min perifusion (37 degrees C, CaCl2 1.26 mM, in the absence of 45Ca2+), both KCl (50 mM) and Bay K 8644 (10 microM) induced cellular 45Ca2+ efflux with peak values above control of 11% and 15%, respectively, (P < 0.05). Exposure to Bay K 8644 preceded by depolarization with KCl resulted in enhanced 45Ca2+ efflux identifying the presence of voltage-dependent Ca(2+)-channel activity. Cultured rat mesangial cells grown to confluence on coverslips were preloaded with Fura-2 and cytosolic Ca2+ was measured by microfluorometry. KCl (50 mM), gramicidin (2 microM) and/or Bay K 8644 (6 microM) stimulated Ca2+ influx which was inhibited by Ver (10 microM). Ver did not alter endothelin-stimulated Ca2+ signalling. We conclude that L-type Ca2+ channels are present on both rat glomerular (endothelial and/or mesangial) cells in vivo and on cultured mesangial cells, and their activation may be hormone specific.

Cellular signaling by cyclosporine A in contractile cells: interactions with atrial natriuretic peptide

Immunosuppressive therapy with cyclosporine A (CyA) may be associated with severe side effects such as nephrotoxicity and arterial hypertension. The partial reversibility of these effects suggests that they are at least in part functional. The present study examined the effects of CyA on cellular signaling in vascular smooth muscle cells and in glomerular mesangial cells and the interactions with the endogenous vasodilator atrial natriuretic peptide (ANP). Intracellular free calcium concentrations ([Ca2+]i) were measured using Fura-2. 45Ca2+ was used to measure Ca2+ efflux and cellular Ca2+ influx. In the presence of cyclosporine (10 micrograms/ml), the Ca(2+)-mobilizing effects of angiotensin II (10(-8)M) in smooth muscle cells and of arginine vasopressin (AVP) in mesangial cells were significantly enhanced. CyA significantly stimulated cellular Ca2+ uptake in both cell types. ANP blocked the Ca2+ mobilization by angiotensin II and AVP and also completely inhibited the potentiating effect of CyA on angiotensin II- and AVP-induced Ca2+ mobilization. ANP also completely blocked the CyA-stimulated Ca2+ uptake. These findings suggest that CyA stimulates transmembrane Ca2+ influx, thereby increasing vasopressor-sensitive intracellular Ca2+ stores and augmenting vasopressor-induced Ca2+ mobilization. This cellular effect of CyA in vitro was markedly diminished by ANP. The effects of CyA on intracellular signaling may directly enhance the contractile response of smooth muscle and the glomerular mesangium to vasopressor stimuli and may also contribute to other disturbances of cell metabolism associated with CyA.