Functional effects on glomerular hemodynamics of short-term chronic cyclosporine in male rats

Cyclosporin-induced hypertension is associated with the up-regulation of Na+-K+-2Cl- cotransporter (NKCC2)

BACKGROUND

The use of cyclosporin A (CsA) is hampered by the development of nephrotoxicity including hypertension, which is partially dependent on renal sodium retention. To address this issue, we have investigated in vivo sodium reabsorption in different nephron segments of CsA-treated rats through micropuncture study coupled to expression analyses of sodium transporters. To translate the findings in rats to human, kidney-transplanted patients having CsA treatment were enrolled in the study.

METHODS

Adult male Sprague-Dawley rats were treated with CsA (15 mg/kg/day) for 21 days, followed by micropuncture study and expression analyses of sodium transporters. CsA-treated kidney-transplanted patients with resistant hypertension were challenged with 50 mg furosemide.

RESULTS

CsA-treated rats developed hypertension associated with reduced glomerular filtration rate. In vivo microperfusion study demonstrated a significant decrease in rate of absolute fluid reabsorption in the proximal tubule but enhanced sodium reabsorption in the thick ascending limb of Henle's loop (TAL). Expression analyses of sodium transporters at the same nephron segments further revealed a reduction in Na+-H+ exchanger isoform 3 (NHE3) in the renal cortex, while TAL-specific, furosemide-sensitive Na+-K+-2Cl- cotransporter (NKCC2) and NHE3 were significantly upregulated in the inner stripe of outer medulla. CsA-treated patients had a larger excretion of urinary NKCC2 protein at basal condition, and higher diuretic response to furosemide, showing increased FeNa+, FeCl- and FeCa2+ compared with both healthy controls and FK506-treated transplanted patients.

CONCLUSION

Altogether, these findings suggest that up-regulation of NKCC2 along the TAL facilitates sodium retention and contributes to the development of CsA-induced hypertension.

Effects of SGLT2 inhibitor and dietary NaCl on glomerular hemodynamics assessed by micropuncture in diabetic rats

Inhibitors of the main proximal tubular Na-glucose cotransporter (SGLT2) mitigate diabetic glomerular hyperfiltration and have been approved by the United States Food and Drug Administration for slowing the progression of diabetic kidney disease. It has been proposed that SGLT2 inhibitors improve hard renal outcomes by reducing glomerular capillary pressure (PGC) via a tubuloglomerular feedback (TGF) response to a decrease in proximal reabsorption (Jprox). However, the effect of SGLT2 inhibition on PGC has not been measured. Here, we studied the effects of acute SGLT2 blockade (ertugliflozin) on Jprox and glomerular hemodynamics in two-period micropuncture experiments using streptozotocin-induced diabetic rats fed high- or low-NaCl diets. PGC was measured by direct capillary puncture or computed from tubular stop-flow pressure (PSF). TGF is intact while measuring PGC directly but rendered inoperative when measuring PSF. Acute SGLT2 inhibitor reduced Jprox by ∼30%, reduced PGC by 5-8 mmHg, and reduced glomerular filtration rate (GFR) by ∼25% (all P < 0.0001) but had no effect on PSF. The decrease in PGC was larger with the low-NaCl diet (8 vs. 5 mmHg, P = 0.04) where PGC was higher to begin with (54 vs. 50 mmHg, P = 0.003). Greater decreases in PGC corresponded, unexpectedly, to lesser decreases in GFR (P = 0.04). In conclusion, these results confirm expectations that PGC would decline in response to acute SGLT2 inhibition and that a functioning TGF system is required for this. We infer a contribution of postglomerular vasorelaxation to the TGF responses where decreases in PGC were large and decreases in GFR were small.NEW & NOTEWORTHY It has been theorized that Na-glucose cotransporter (SGLT2) blockade slows progression of diabetic kidney disease by reducing physical strain on the glomerulus. This is the first direct measurement of intraglomerular pressure during SGLT2 blockade. Findings confirmed that SGLT2 blockade does reduce glomerular capillary pressure, that this is mediated through tubuloglomerular feedback, and that the tubuloglomerular feedback response to SGLT2 blockade involves preglomerular vasoconstriction and postglomerular vasorelaxation.

Salt sensitivity of tubuloglomerular feedback in the early remnant kidney

We previously reported internephron heterogeneity in the tubuloglomerular feedback (TGF) response 1 wk after subtotal nephrectomy (STN), with 50% of STN nephrons exhibiting anomalous TGF (Singh P, Deng A, Blantz RC, Thomson SC. Am J Physiol Renal Physiol 296: F1158-F1165, 2009). Presently, we tested the theory that anomalous TGF is an adaptation of the STN kidney to facilitate increased distal delivery when NaCl balance forces the per-nephron NaCl excretion to high levels. To this end, the effect of dietary NaCl on the TGF response was tested by micropuncture in STN and sham-operated Wistar rats. An NaCl-deficient (LS) or high-salt NaCl diet (HS; 1% NaCl in drinking water) was started on day 0 after STN or sham surgery. Micropuncture followed 8 days later with measurements of single-nephron GFR (SNGFR), proximal reabsorption, and tubular stop-flow pressure (PSF) obtained at both extremes of TGF activation, while TGF was manipulated by microperfusing Henle's loop (LOH) from the late proximal tubule. Activating TGF caused SNGFR to decline by similar amounts in Sham-LS, Sham-HS and STN-LS [ΔSNGFR (nl/min) = -16 ± 2, -11 ± 3, -11 ± 2; P = not significant by Tukey]. Activating TGF in STN-HS actually increased SNGFR by 5 ± 2 nl/min (P < 0.0005 vs. each other group by Tukey). HS had no effect on the PSF response to LOH perfusion in sham [ΔPSF (mmHg) = -9.6 ± 1.1 vs. -9.8 ± 1.0] but eliminated the PSF response in STN (+0.3 ± 0.9 vs. -5.7 ± 1.0, P = 0.0002). An HS diet leads to anomalous TGF in the early remnant kidney, which facilitates NaCl and fluid delivery to the distal nephron.

Micropuncturing the nephron

To achieve the role of the kidney in maintaining body homeostasis, the renal vasculature, the glomeruli, and the various segments of the nephron and the collecting duct system have to fulfill very diverse and specific functions. These functions are dependent on a complex renal architecture and are regulated by systemic hemodynamics, hormones, and nerves. As a consequence, to better understand the physiology of the kidney, methods are necessary that allow insights on the function of these diverse structures in the physiological context of the intact kidney. The renal micropuncture technique allows direct access to study superficial nephrons in vivo. In this review, the application of micropuncture techniques on the single nephron level is outlined as an approach to better understand aspects of glomerular filtration, tubular transport, and tubulo-glomerular communication. Studies from the author's lab, including experiments in gene-targeted mice, are briefly presented to illustrate some of the approaches and show how they can further advance our understanding of the molecular mechanisms involved in the regulation of kidney function.

Functional Evaluation of Transplanted Kidneys with Diffusion-weighted and BOLD MR Imaging: Initial Experience

PURPOSE

To prospectively evaluate feasibility and reproducibility of diffusion-weighted (DW) and blood oxygenation level-dependent (BOLD) magnetic resonance (MR) imaging in patients with renal allografts, as compared with these features in healthy volunteers with native kidneys.

MATERIALS AND METHODS

The local ethics committee approved the study protocol; patients provided written informed consent. Fifteen patients with a renal allograft and in stable condition (nine men, six women; age range, 20-67 years) and 15 age- and sex-matched healthy volunteers underwent DW and BOLD MR imaging. Seven patients with renal allografts were examined twice to assess reproducibility of results. DW MR imaging yielded a total apparent diffusion coefficient including diffusion and microperfusion (ADC(tot)), as well as an ADC reflecting predominantly pure diffusion (ADC(D)) and the perfusion fraction. R2* of BOLD MR imaging enabled the estimation of renal oxygenation. Statistical analysis was performed, and analysis of variance was used for repeated measurements. Coefficients of variation between and within subjects were calculated to assess reproducibility.

RESULTS

In patients, ADC(tot), ADC(D), and perfusion fraction were similar in the cortex and medulla. In volunteers, values in the medulla were similar to those in the cortex and medulla of patients; however, values in the cortex were higher than those in the medulla (P < .05). Medullary R2* was higher than cortical R2* in patients (12.9 sec(-1) +/- 2.1 [standard deviation] vs 11.0 sec(-1) +/- 0.6, P < .007) and volunteers (15.3 sec(-1) +/- 1.1 vs 11.5 sec(-1) +/- 0.5, P < .0001). However, medullary R2* was lower in patients than in volunteers (P < .004). Increased medullary R2* was paralleled by decreased diffusion in patients with allografts. A low coefficient of variation in the cortex and medulla within subjects was obtained for ADC(tot), ADC(D), and R2* (<5.2%), while coefficient of variation within subjects was higher for perfusion fraction (medulla, 15.1%; cortex, 8.6%). Diffusion and perfusion indexes correlated significantly with serum creatinine concentrations.

CONCLUSION

DW and BOLD MR imaging are feasible and reproducible in patients with renal allografts.

Pathophysiology of ischaemic acute renal failure

This chapter summarizes the pathophysiology of ischaemic acute renal failure from both the experimental and clinical points of view. Traditionally, the abrupt fall in glomerular filtration rate (GFR) is thought to be due to an interplay of haemodynamic and tubular abnormalities. The intrarenal haemodynamic alterations include renal vasoconstriction, leukocyte-endothelium interactions and loss of blood flow and GFR autoregulation. During recent years it has become evident that pronounced outer medulary ischaemia makes an important contribution. In severe and prolonged ischaemia, the tubular epithelial cells can undergo either sublethal or lethal cell damage. Cell death occurs by necrosis and apoptosis. The different mechanisms of post-ischaemic cell damage are discussed. The post-ischaemic kidney also shows a dramatic capacity for recovery. During this recovery phase some of the damaged cells undergo de-differentiation--which is an important step in regeneration of the tubular epithelium. Recent evidence points to the possibility that infiltration of the kidney with bone-marrow-derived stem cells contributes to the repair process. The molecular mechanisms and the effect of growth factors are summarized.

End-stage renal failure and cardiac mortality after heart transplantation

BACKGROUND

Coronary artery disease (CAD) is the leading cause of mortality after the first year of heart transplantation. End-stage renal failure (ESRF) is more frequent because of long-term survival. Impact of ESRF on cardiac mortality in heart transplant patients is unappreciated. The hypothesis of accelerated CAD in uremic patients has been suggested.

METHODS

In Pitié La Salpêtrière hospital, 1211 heart transplants have been performed between 1982 and 2001. Thirty-three patients have reached ESRF. A case-control study was performed to identify risk factors responsible for ESRF and to appreciate the impact of ESRF on cardiac mortality.

RESULTS

In cases at 6 months, serum creatinine tended to be higher (159 +/- 31 micromol/L vs. 141 +/- 44 micromol/L, p = 0.06) and cyclosporine (CSA) dosage (mg/kg) was significantly lower (5.4 +/- 1.8 mg/kg vs. 7.7 +/- 2.7 mg/ kg, p = 0.002). Mean triglyceride level after transplantation until dialysis was significantly lower in cases (2.18 +/- 0.82 mmol/L vs. 1.48 +/- 0.62 mmol/L, p = 0.002). In cases and controls, cardiac mortality was responsible for 67% (10 of 15) and 38% (three of eight) of all deaths, respectively. High triglyceride level (> or = 2 mmol/L) was associated with cardiac mortality [p < 0.03, hazard ratio (HR) = 3.89]. Kaplan Meier cardiac free survival rates were significantly lower in cases than in controls (p < 0.03).

CONCLUSION

These data suggest that CSA nephrotoxicity could result from individually determined susceptibility and that hypertriglyceridemia may have a negative impact on renal function and cardiac mortality. The risk of cardiac mortality is increased in heart transplant patients with ESRF. The hypothesis of accelerated atherosclerosis in ESRF patients after heart transplantation leading to higher cardiac mortality incidence needs further study.

The effects of nifedipine on cyclosporine nephrotoxicity in rats

We have investigated the effect of nifedipine on cyclosporine nephrotoxicity in the Sprague-Dawley rat employing a repeatable, single-shot, isotopic technique of measuring the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Groups of 10 rats received either cyclosporine 5 mg/kg daily or cremaphor with either nifedipine 0.5 mg/kg daily or its vehicle for 14 days. In the cyclosporine group the GFR (P < 0.001, paired t-test), ERPF and filtration fraction (FF) (P < 0.01) all fell significantly. The cyclosporine plus nifedipine group underwent an increase in the ERPF (P < 0.01), the GFR remained unchanged, and the FF fell significantly (P < 0.0001). In this model, nifedipine completely abolished the renal arteriolar vasospasm produced by cyclosporine. That the FF fell in the cyclosporine plus nifedipine-treated animals indicates that cyclosporine has an effect which is not mediated by arteriolar vasoconstriction. This action may be at the glomerular level and is resistant to calcium channel blockade.

Cyclosporine a slows the progressive renal disease of alport syndrome (X-linked hereditary nephritis): results from a canine model

Alport syndrome refers to a hereditary disorder characterized by progressive renal disease and a multilaminar appearance to the glomerular basement membrane (GBM). In a small group of patients with Alport syndrome, cyclosporine A was reported to decrease proteinuria and maintain stable renal function over 7 to 10 yr of follow-up. The present study examined the effect of cyclosporine A on GBM structure and the progression to renal failure in a canine model of X-linked Alport syndrome. Affected male dogs and normal male dogs treated with cyclosporine A underwent serial renal biopsies. Body weight, serum concentrations of creatinine and albumin, and GFR were sequentially determined. Controls consisted of untreated dogs that developed end-stage renal failure by 8 mo of age. Renal biopsies were assessed for glomerulosclerosis and the percent of multilaminar GBM as measured by image analysis. Significant differences were found between treated and untreated affected dogs for weight, serum creatinine, and GFR. There was a significant delay in the progression of multilaminar change to the GBM, although treated affected dogs at termination had attained approximately 100% split GBM as did untreated affected dogs. A significant difference in the number of sclerotic glomeruli was also noted; treated dogs rarely developed obsolete glomeruli during the period studied. Interstitial fibrosis was not significantly affected by cyclosporine A treatment. These findings indicate that cyclosporine A is beneficial in slowing, but not stopping, the clinical and pathologic progression of Alport syndrome. At least part of this beneficial effect comes from a delayed deterioration of GBM structure, which in turn may be related to glomerular hemodynamics altered by cyclosporine A.

Renal response to a protein load persists during long-term follow-up of children after renal transplantation

BACKGROUND

Kidney donors and transplant recipients may be at risk of complications from glomerular hyperfiltration of the single kidney. It has been assumed that tests of the existence of renal functional reserve [delta glomerular filtration rate (deltaGFR), delta effective renal plasma flow (deltaERPF)] can be used to demonstrate hyperfiltration. It would therefore be of interest to evaluate the response of the kidney graft to a protein load. i.e., testing the renal reserve and to find out whether a reduction in baseline GFR is preceded by a loss of deltaGFR.

METHODS

We repeatedly studied the change in GFR and renal plasma flow (ERPF) after an oral protein load in 30 children after renal transplantation (Tx). Follow-up time was 1.0-8.0 years. Renal function was evaluated with the clearances of inulin and para-aminohippuric acid (PAH). Seven recipient/donor pairs were examined twice (median 0.3 and 4 years, after Tx).

RESULTS

The baseline GFR and ERPF remained stable throughout the follow-up and the increase after stimulation (deltaGFR and deltaERPF) did not change in the whole group of Tx children over the years. However, a reduction in the baseline GFR from the first to the last investigation occurred in 23 of 30 children. In the 23 patients whose baseline GFR decreased, deltaGFR was still preserved. In the recipient/donor pairs, the baseline GFR and ERPF were the same, but on the second investigation, donors showed higher deltaGFR.

CONCLUSION

Despite fairly low baseline GFR and ERPF values in the Tx children, no change occurs in the capacity to increase GFR and ERPF after a protein load during follow-up, which suggests that they are not maximally hyperfiltrating.

Renal function of children exposed to cyclosporin in utero

BACKGROUND

The use of cyclosporin (CsA) has improved graft survival in transplant (Tx) patients despite its potential nephrotoxicity. Children born to transplanted women may present with intrauterine growth retardation (IUGR). On the basis of potential reduced nephron mass both in IUGR and in newborn experimental animals exposed to CsA in utero, we investigated the renal function of children >1 year of age born to women under maintenance immunosuppression, including CsA.

METHODS

Fourteen children born to 12 Tx women (nine kidney, one pancreas-kidney, one heart, one liver) were investigated using inulin clearance (C(in)), para-aminohippuric acid clearance (C(PAH)), microalbuminuria, and electrolyte reabsorption rate.

RESULTS

Gestational age of the 14 infants was 34+/-3 weeks and birth weight 2018+/-620 g. During pregnancy, CsA trough blood level was 234+/-115 microg/l and plasma creatinine range was 96-136 micromol/l. Two children were excluded from the study because renal investigation led to a diagnosis of hereditary nephritis (one Alport syndrome, one familial dominant focal segmental glomerulosclerosis) that was retrospectively completed in the mother. Renal function tests were finally performed in 12 children at 2.6+/-1.8 years of age: BP 94+/-7/55+/-5 mmHg, C(in) 117+/-28 ml/min/1.73 m(2), C(PAH) 545+/-124 ml/min/1.73 m(2), filtration fraction 0.23+/-0.03, microalbuminuria 4.2+/-3.5 mg/mmol. Electrolyte tubular reabsorption rates and urine concentrating capacity were normal.

CONCLUSION

These results suggest that in children born to transplanted women taking CsA, renal function develops normally despite prolonged exposure in utero.

Conversion to mycophenolate mofetil in conjunction with stepwise withdrawal of cyclosporine in stable renal transplant recipients

BACKGROUND

Mycophenolate mofetil (MMF) is now part of standard immunosuppression in the first phase after renal transplantation. A relevant question is if it can replace drugs such as cyclosporine (CsA) in the maintenance treatment, improving cardiovascular risk profile.

METHODS

In 17 patients with a stable renal function (at least 6 months) posttransplantation, we studied the effect of CsA replacement by MMF. After starting MMF (1 g b.i.d.), CsA dosage was reduced from regular to low (median trough level 130 microg/L, respectively, 45 microg/L), followed by complete withdrawal, while prednisone (7.5 mg daily) was continued. We measured ambulatory blood pressure, glomerular filtration rate, renal plasma flow, renal vascular resistance, and metabolic factors at start and after 8 weeks on regular, low-dose CsA, respectively, no CsA with MMF and prednisone.

RESULTS

Two patients dropped out after the switch to low-dose CsA/MMF, due to diarrhea in one and a steroid responsive rejection in the other. The complete switch from CsA to MMF was successful in all 15 patients and accompanied by a decrease in 24 hr systolic blood pressure (from 152+/-13 to 145+/-13 mmHg; P<0.01), diastolic blood pressure (93+/-9 to 89+/-12 mmHg; P<0.05), RVR (0.29+/-0.06 to 0.25+/-0.09 mmHg.ml/min; P<0.05), and an increase in glomerular filtration rate (46.6+/-8.8 to 58.0+/-10.5 ml/min; P<0.01) and renal plasma flow. Intermediate low density lipoprotein-cholesterol decreased (0.79+/-0.37 to 0.41+/-0.16 mmol/L; P<0.01). High density lipoprotein-cholesterol decreased, but remained in the safe range. After 1 year two patients stopped the MMF; one because of Kaposi's sarcoma and one because of recurrent infections

CONCLUSIONS

The stepwise switch from CsA to MMF was safe and mostly successful, and had beneficial effects on blood pressure, glomerular hemodynamics, and lipid profile. Beneficial trends were already present after partial withdrawal of CsA.

Mechanism of FK 506/520 action on rat renal proximal tubular Na+, K+-ATPase activity

BACKGROUND

The neurotransmitter in renal sympathetic nerves, norepinephrine (NE), regulates the activity of proximal tubule (PT) Na+,K+-ATPase in a bidirectional manner via stimulation of alpha- and beta-adrenoceptors. The stimulatory alpha-adrenergic pathway is mediated by calcineurin, the target molecule for FK 506 and related compounds. We examined whether the FK 506 analogue FK 520, by interrupting the calcineurin-mediated alpha-adrenergic signaling pathway, enhance the inhibitory beta-adrenergic effect of NE on PT Na+,K+-ATPase activity.

METHODS

The effects of three days of treatment with FK 520 were examined on rat renal PT Na+,K+-ATPase activity, measured as ouabain-sensitive ATP hydrolysis in single, microdissected PT segments. Renal function studies, including glomerular filtration rate (GFR) and urinary excretion of N-acetyl-3-D-glucoseaminidase (NAG), were examined using conventional clearance techniques after three days of treatment with FK 506.

RESULTS

FK 520 treatment induced a pronounced and dose-dependent decrease in PT Na+,K+-ATPase activity. This effect was completely reversed by the competitive FK 520 antagonist, L 685 818, indicating that the effect was dependent on inhibition of calcineurin. To test whether the FK 520-induced decrease in Na+, K+-ATPase activity was mediated by enhanced beta-adrenoceptor signaling, the FK 520 effect was examined in rats pretreated with a beta-adrenoceptor antagonist (propranolol) or rats subjected to renal denervation. Both of these procedures prevented the FK 520-induced decrease in Na+,K+-ATPase activity. Thus, during FK 520 treatment, renal sympathetic nerves mediate an inhibitory effect on PT Na+,K+-ATPase activity via beta-adrenoceptors. Propranolol pretreatment also prevented FK 506-induced decreases in GFR and urinary excretion of NAG, an index of PT dysfunction.

CONCLUSIONS

The results support the hypothesis that the net effect of the neurotransmitter NE on Na+,K+-ATPase activity is dependent on the balance between the alpha- and beta-adrenergic signaling pathways and suggest that agents that interfere with these pathways may, by altering the activity of tubular Na+,K+-ATPase, also alter the function of the renal tubular epithelial cell.

Dexamethasone increases eNOS gene expression and prevents renal vasoconstriction induced by cyclosporin

Cyclosporin A (CsA)-induced renal vasoconstriction (RV) is attributed to an imbalance in vasoactive factors release. Dexamethasone (Dex) exerts a renal vasodilatory effect by a mechanism not yet characterized. This study evaluates whether the effect of Dex is mediated by NO and whether it prevents CsA-induced RV. Micropuncture studies were performed in six groups of uninephrectomized rats treated for 7 days with the following: vehicle (Veh); Veh + 4 mg/kg dexamethasone (Veh+Dex); 30 mg/kg CsA; CsA+Dex; vehicle + 10 mg/kg nitro-L-arginine methyl ester (Veh+L-NAME); and Veh+Dex+L-NAME. NO synthase (NOS) isoform mRNA levels were evaluated in renal cortex and medulla by semiquantitative RT-PCR analysis in the first four groups. Dex produced renal vasodilation, which was blocked by concomitant L-NAME administration, and the effect of Dex was associated with higher cortical and medullary endothelial NOS (eNOS) and cortical inducible NOS (iNOS) mRNA levels. In the CsA group, Dex prevented RV, restoring glomerular hemodynamics to control values. These changes were associated with further enhancement of eNOS and restoration of medullary iNOS and neuronal NOS (nNOS) expression. We conclude that Dex prevents CsA-induced RV, and its vasodilator effect could be mediated by increased intrarenal generation of NO, secondary to enhanced expression of eNOS and iNOS.

Converting enzyme inhibition and the glomerular hemodynamic response to glycine in diabetic rats

GFR normally increases during glycine infusion. This response is absent in humans and rats with established diabetes mellitus. In diabetic patients, angiotensin-converting enzyme inhibition (ACEI) restores the effect of glycine on GFR. To ascertain the glomerular hemodynamic basis for this effect of ACEI, micropuncture studies were performed in male Wistar-Froemter rats after 5 to 6 wk of insulin-treated streptozotocin diabetes. The determinants of single-nephron GFR (SNGFR) were assessed in each rat before and during glycine infusion. Studies were performed in diabetics, diabetics after 5 d of ACEI (enalapril in the drinking water), and weight-matched controls. Diabetic rats manifest renal hypertrophy and glomerular hyperfiltration but not glomerular capillary hypertension. ACEI reduced glomerular capillary pressure, increased glomerular ultrafiltration coefficient, and did not mitigate hyperfiltration. In controls, glycine increased SNGFR by 30% due to increased nephron plasma flow. In diabetics, glycine had no effect on any determinant of SNGFR. In ACEI-treated diabetics, the SNGFR response to glycine was indistinguishable from nondiabetics, but the effect of glycine was mediated by greater ultrafiltration pressure rather than by greater plasma flow. These findings demonstrate that: (1) The absent response to glycine in established diabetes does not indicate that renal functional reserve is exhausted by hyperfiltration; and (2) ACEI restores the GFR response to glycine in established diabetes, but this response is mediated by increased ultrafiltration pressure rather than by increased nephron plasma flow.

Beneficial effects of calcium channel blockade on acute glomerular hemodynamic changes induced by cyclosporine

Experimental and human studies have documented that cyclosporine (CsA) acutely reduces glomerular filtration rate (GFR). It has been reported that this effect can be partially prevented by calcium (Ca) channel blockade; however, the mechanisms by which this combination exerts its beneficial effects are unknown. We evaluated glomerular ultrafiltration determinants during acute CsA administration in the rat. First, we determined that maximal whole-kidney functional changes occur between 120 and 150 minutes after CsA administration and confirmed that pretreatment of MWF rats with the Ca channel blocker lacidipine effectively prevents a reduction in GFR. Micropuncture measurements in CsA-treated animals showed that a reduction in GFR (0.49 +/- 0.24 v 0.88 +/- 0.26 mL/min; P < 0.05; CsA-treated v untreated rats) is associated with a significant increase in glomerular capillary pressure (Pgc; 63.1 +/- 2.1 v 52.8 +/- 2.8 mm Hg; P < 0.01) and efferent arteriolar resistance, whereas single-nephron (SN) GFR and ultrafiltration coefficient (Kf) are both importantly reduced (34.0 +/- 11.7 v 68.9 +/- 23.8 nL/min; P < 0.05 and 1.04 +/- 0.33 v 4.40 +/- 2.36 nL/min/mm Hg; P < 0.01, respectively). Lacidipine partially prevented SNGFR (43.1 +/- 14.3 nL/min) and Kf decline (2.08 +/- 1.10 nl/min/mm Hg) despite the presence of elevated Pgc. This study further documents that Ca channel blockade has favorable effects on CsA-induced acute renal dysfunction. The mechanism of protection includes the prevention of glomerular hemodynamic changes induced by CsA, mainly GFR decline and reduction in glomerular Kf.

Cyclosporine increases local glomerular synthesis of reactive oxygen species in rats: effect of vitamin E on cyclosporine nephrotoxicity

BACKGROUND

We report an investigation of the effects of cyclosporine (CsA) on kidney function, the glomerular synthesis of reactive oxygen species, the peroxidation of lipids, and the levels of thromboxane B2 (TXB2). The effect of the simultaneous administration of the antioxidant vitamin E (Vit E) and CsA in rats was also evaluated.

METHODS

Adult male Wistar rats were treated for 30 days with CsA (30 mg/kg/day), with Vit E (0.05 mg/ml), with CsA plus Vit E, or with the vehicle used for administration of CsA, namely 12.6% ethanol.

RESULTS

CsA induced kidney failure and increased the glomerular synthesis of superoxide anion, H2O2, malonyldialdehyde, and TXB2. Vit E minimized the adverse effects of CsA on kidney function and the glomerular synthesis of these compounds.

CONCLUSIONS

Our results suggest that the acute decrease in glomerular filtration rate induced by CsA might be mediated by the synthesis of reactive oxygen species and subsequent peroxidation of lipids, which increases the levels of TXB2. Treatment with Vit E prevented these effects, suggesting a possible role for antioxidants in the prevention of CsA nephrotoxicity.

Acute reversal of cyclosporine nephrotoxicity by neutral endopeptidase inhibition in stable renal transplant recipients

BACKGROUND

Atrial natriuretic peptide and cyclosporine have opposing effects on renal hemodynamics and excretory function.

METHODS

Twelve male stable cyclosporine-treated renal transplant recipients received a single 100-mg i.v. dose of the neutral endopeptidase EC 24.11 inhibitor candoxatrilat in a double-blind, placebo-controlled cross-over study. Each study day consisted of 2 hr of baseline and 7 hr of postdose evaluation.

RESULTS

After administration of candoxatrilat, plasma atrial natriuretic factor rose from 12.8+/-1.6 (mean +/- SEM) to 44.1+/-6.8 pmol/L (P<0.001) in association with a threefold increase in urine cGMP excretion (573+/-195 pmol/min baseline to 1823+/-545 pmol/ min; P<0.001), marked natriuresis (207+/-34 micromol/min baseline to 416+/-62 micromol/min; P<0.001), fractional sodium excretion (3.3+/-0.5% baseline to 5.6+/-0.7%; P<0.01), and diuresis (3.4+/-0.5 ml/min baseline to 7.4+/-1 ml/min; P<0.001). All parameters remained elevated above baseline for the remaining 7-hr study period. In response to candoxatrilat, the glomerular filtration rate rose by 19% (P=0.01), renal plasma flow by 7% (P=0.04), renal blood flow by 13% (P=0.03) in association with an increase in filtration fraction from 24+/-2% to 28+/-2% (P=0.002) and small fall in renal vascular resistance from 0.38+/-0.04 to 0.30+/-0.04 mmHg x min x 1.73 m2 x ml(-1) (P=0.02). There was a fall in plasma angiotensin II without a change in plasma renin concentration or plasma aldosterone. Median urinary albumin excretion increased after candoxatrilat administration from 48 (3-131) to 114 (32-641) microg/min (P<0.01).

CONCLUSIONS

Acute neutral endopeptidase inhibition with candoxatrilat appears to reverse the adverse renal hemodynamic and renal excretory effects of cyclosporine in stable renal transplant recipients.

Effects of a selective adenosine A1 receptor antagonist on the development of cyclosporin nephrotoxicity

1. The clinical application of cyclosporin as an immunosuppressive agent is limited by its nephrotoxicity. 2. The effect of FK453, a selective A1-receptor antagonist, administered twice daily to rats at a dose of 100 mg kg-1 was assessed on the development of nephrotoxicity induced by cyclosporin (10 mg kg-1 i.p. daily) administered for 14 days. The effects of nifedipine administered twice daily (0.3 mg kg-1 s.c.) for 14 days, on cyclosporin nephrotoxicity were also studied. 3. Cyclosporin induced a 46.58% and 35.78% decline in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) respectively and a reduction of 16.69% in filtration fraction (FF). Co-administration of FK453 resulted in falls of 30.5%, 18.59% and 14.7% in GFR, ERPF and FF respectively, the former two significantly less than the falls seen with cyclosporin (CyA) alone (P < 0.05 vs CyA, ANOVA). 4. Nifedipine appeared to have a more pronounced protective effect resulting in a decline of only 20.91% in GFR, with no significant change in ERPF (increase of 0.93%) when co-administered with CyA. 5. These observations indicate adenosine plays a minor role in the pathophysiology of CyA nephrotoxicity.

Regional differences in vasculotoxic effects of cyclosporin in rats

Studies on cyclosporin-induced vasculotoxicity often yielded discrepant results, possibly as a result of differences in study protocols. The aim of the present study was to analyse cyclosporin-induced vasculotoxicity in arteries of different size and origin. Therefore, rats were treated with cyclosporin, 20 mg.kg-1.day-1, by gastric gavage for 10 days. In our previous studies, this treatment schedule induced renal functional impairment in vivo and an impaired relaxation response of thoracic aortic rings in vitro. Relaxation of various arteries (thoracic and abdominal aorta and carotid, renal, and interlobar arteries) from cyclosporin-treated and control rats in response to endothelium-dependent and -independent vasodilators was analysed. The thoracic aorta showed diminished endothelium-dependent and -independent relaxations; in the abdominal aorta no impairment was observed. Moreover, the dysfunction of the thoracic aorta seemed to be homogeneous along its length and showed an abrupt termination at the level of the diaphragm. In all other segments studied, no impairment of the relaxation responses was found. A similar pattern of vascular damage was found in rats treated with a very toxic cyclosporin treatment (50 mg.Kg-1.day-1 s.c. x 7 days). The results indicate regional differences in cyclosporin-induced vasculotoxicity. The thoracic aorta, and in view of the fall of the renal blood flow, most likely also the renal resistance vessels, could be more susceptible than other vessels to cyclosporin-induced vascular dysfunction.

FK 506: effects on glomerular hemodynamics and on mesangial cells in culture

FK 506 is a new immunosuppressive drug that, like cyclosporine A (CsA), presents nephrotoxicity. Glomerular hemodynamic studies showed that acute FK 506 infusion (N = 9, 3 mg/kg body wt, i.v. in bolus) caused a 57% reduction in glomerular filtration rate (GFR) (0.74 +/- 0.03 to 0.32 +/- 0.02 ml/min, P < 0.05) and a 40% reduction in single nephron glomerular filtration rate (SNGFR; 43.0 +/- 5.2 to 26.0 +/- 2.5 nl/min, P < 0.05) due to a 25% reduction in glomerular plasma flow rate (QA) (133.4 +/- 19.8 to 99.8 +/- 12.0 nl/min) and a 22% reduction in glomerular ultrafiltration coefficient (Kf; 0.1009 +/- 0.0203 to 0.0790 +/- 0.0130 nl/sec. mm Hg). After 10 days of FK treatment (N = 8, 0.6 mg/kg body wt, i.p.), we observed a reduction of 23% in GFR (0.97 +/- 0.02 to 0.75 +/- 0.04 ml/min, P < 0.05) and of 23% in SNGFR (37.9 +/- 3.0 to 29.1 +/- 1.9 nl/min, P < 0.05) due to a 42% reduction in Kf (0.1486 +/- 0.0101 to 0.0870 +/- 0.0110 nl/sec.mm Hg, P < 0.05) and a 38% reduction in QA (117.6 +/- 10.2 to 73.5 +/- 6.1 nl/min, P < 0.05). The latter was consequent to the increment of 72% in total arteriolar resistance (RT) (3.1 +/- 0.2 to 5.2 +/- 0.5 +/- 0.5 10(10).dyn.sec.cm-5, P < 0.05). Thus, the pattern of FK 506 effect on glomerular hemodynamics was similar in both acute and chronic treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

A possible role for nitric oxide in modulating the functional cyclosporine toxicity by arginine

The renal damage consequent to cyclosporine A (CsA) administration ranges from hemodynamic alterations to irreversible chronic lesions. The initial vasoconstriction depends upon the imbalance between the various modulators of the renal vascular tone, among which the most powerful are endothelins and nitric oxide (NO). CsA could play a crucial role by inhibiting the Ca++/calmodulin-mediated activation of the constitutive NO synthase (NOS) isoform, which converts L-arginine (L-Arg) into NO and citrulline, with a 1:1 stoichiometry. To investigate the possibility of modulating CsA nephrotoxicity with L-Arg we studied six groups (G) of Lewis rats treated with daily gavage up to eight weeks: G1, CsA 40 mg/kg; G2, G1 plus L-Arg 300 mg/kg; G3, G2 plus the competitive inhibitor of NOS, NG-nitro-L-Arg (L-NNA); G4, L-Arg alone; G5, L-NNA alone; and G6, controls receiving vehicle alone. After eight weeks L-Arg treated rats were protected against the toxic effects of CsA [creatinine (Cr) values, G2, 0.62 +/- 0.05 mg/dl vs. G1, 0.99 +/- 0.16 mg/dl, P < 0.001; proteinuria (P), G2, 7.2 +/- 1.02 mg/day vs. G1, 15.1 +/- 1.9 mg/day, P < 0.01]. The administration of L-NNA abolished the protective effect of L-Arg (G3, Cr 1.23 +/- 0.16 mg/dl; P 16.9 = 2.3; P < 0.02 and P < 0.005, respectively vs. G2). The levels of Cr in G2 rats were superimposable to control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Effect of renal denervation on elevation of blood pressure in cold-exposed rats

The objective of this experiment was to determine whether bilateral renal denervation (RD) prevents the elevation of blood pressure and cardiac hypertrophy characteristically induced by chronic exposure to cold. Four groups (nine male rats each) were used. The kidneys of two groups were bilaterally denervated, while the remaining two groups were sham operated. Systolic blood pressures of the four groups, measured indirectly from the tail, did not differ significantly during the control period and following RD. At this time, 1 RD and 1 sham-operated group was exposed to cold (5 degrees C, 41 degrees F). The remaining RD and sham-operated groups were kept at 25 degrees C. Blood pressure of the cold-exposed, sham-operated group increased significantly during the 1st week of cold exposure (125 +/- 2 mmHg; 1 mmHg = 133.3 Pa), and rose to 139 +/- 4 mmHg by the 5th week, whereas the blood pressure of the RD group exposed to cold remained at the control level (116 +/- 2 mmHg). Both RD and sham-operated cold-exposed groups developed cardiac hypertrophy with significantly increased resting heart rates compared with controls kept at 25 degrees C. Plasma renin activities and renal norepinephrine content of kidneys of both RD groups at 7 weeks after RD were significantly less than those of sham-operated controls, confirming that renal nerves had been severed. Thus, RD prevented the elevation of blood pressure induced by chronic exposure to cold but had no significant effect on cardiac hypertrophy.

Increased platelet-derived growth factor in the kidneys of cyclosporin-treated rats

We have examined the histological changes and the distribution of immunoreactive platelet-derived growth factor (PDGF) in the kidneys of Sprague-Dawley rats injected with cyclosporin A (CsA, 25 mg/kg/day). Control rats were injected with the olive oil vehicle alone. Groups of rats were killed after 1, 2, 3, 4 weeks of injection and 8 weeks after a 4 week period of injection. Additional controls included groups of rats injected with different doses of CsA and a group of rats subjected to chronic renal ischemia by partial of the aorta. CsA-treated rats gained weight more slowly than olive oil-treated controls (45%, P < 0.05). In rats injected with CsA, a significant increase in serum creatinine concentration (64 +/- 2 mumol/liter vs. 39 +/- 1 mumol/liter, P < 0.01) and a reduction in creatinine clearance rates (0.23 +/- 0.07 ml/min/100 g body wt vs. 0.43 +/- 0.07 ml/min/100 g body wt, P < 0.01) occurred after 3 weeks. After 1 week of CsA treatment, segments of the walls of some afferent and intralobular arterioles were thickened and stained strongly by the periodic acid Schiff (PAS) procedure. Immunostainable PDGF-BB and PDGF-AB were detected within short segments of the afferent and intralobular arterioles of the kidneys of CsA-treated rats and in the kidneys subjected to renal ischemia but not in tissue from other control animals. No PAS staining or immunostaining was evident in CsA treated kidneys eight weeks after the discontinuation of treatment. We conclude that CsA-induced ischemia results in increased accumulation of PDGF in the walls of renal arterioles.

Role of nitric oxide in renal hemodynamic abnormalities of cyclosporin nephrotoxicity

To evaluate the participation of nitric oxide (NO) in chronic cyclosporin A (CsA) nephrotoxicity, the glomerular hemodynamic response to NO inhibition with N-nitro-L-arginine-methyl-ester (NAME) and stimulation of NO production with L-arginine was studied in uninephrectomized rats. Chronic CsA administration produced renal vasoconstriction, characterized by increased afferent (AR) and efferent (ER) resistances, decrease of glomerular plasma flow (QA) and ultrafiltration coefficient (Kf) that resulted in a 53% fall of single-nephron glomerular filtration rate (SNGFR). NAME infusion in vehicle group (V) elevated mean arterial pressure (MAP), AR and ER, reduced qA and Kf, and increased glomerular capillary pressure (PGC), resulting in a 28.9% fall of SNGFR. In the CsA group, NAME also increased MAP, but renal vasoconstriction was more intense; a greater rise of AR lowered PGC (P < 0.05 vs. V) further decreasing SNGFR by 38.9%. In control rats, L-arginine infusion induced a vasodilatory response of AR and ER, and elevation of QA and Kf, which resulted in a 72.6% increase in SNGFR. In the CsA group, greater vasodilation was observed and SNGFR rose by 114.9%. NO2-/NO3- urinary excretion was similar in CsA and V groups, and it was not modified by NAME in either group, but it increased five- to sixfold during L-arginine infusion in both groups. In conclusion, in CsA nephrotoxicity NO production seems to be normal and the ability of the renal endothelium to produce NO is maintained. Therefore renal vasoconstriction associated with CsA is not mediated by NO deficiency, although NO appears to attenuate it.

Effect of cyclosporin A on glomerular filtration rate in children with minimal change nephrotic syndrome

Cyclosporin A (CyA) is now commonly used in the management of children with steroid-dependent nephrotic syndrome. In order to assess nephrotoxicity related to CyA therapy, we measured glomerular filtration rate (GFR) on 123 occasions in 24 children with minimal change nephrotic syndrome receiving CyA. GFR was estimated from the plasma clearance of 51chromium-EDTA every 3 months during CyA therapy of up to 27 months duration. There was a significant reduction in GFR after 3 months of CyA therapy [118 +/- 33 (SD) to 93 +/- 24 ml/min per 1.73 m2] but no further fall thereafter, although the reduction in GFR was sustained for the duration of CyA therapy. This reduction in GFR appeared to be reversible upon cessation of CyA, but careful monitoring of renal function is necessary in such patients to prevent the development of longer term nephrotoxic sequelae.

Renal functional reserve in cyclosporin-treated recipients of kidney transplant

The aims of this study were to determine whether renal functional reserve (RFR) is still present in cyclosporin-treated renal transplant recipients, and to examine the relationship between RFR and proximal reabsorption. A serial study was carried out in 12 renal allograft recipients (R) with good renal graft function at 20 +/- 2.5 days (S1) and at 7.6 +/- 0.4 months (S2) post-transplantation, and the results were compared to those in eight subjects who had undergone unine-phrectomy (one-kidney controls: UNx.C) and in 12 healthy volunteers (two-kidney controls: 2K.C). R and C were in similar sodium and protein balance and with similar plasma renin and aldosterone levels. R had normal serum creatinine level on moderate doses of cyclosporin (whole blood cyclosporin concentration: 212 +/- 20 and 125 +/- 20 ng/ml at S1 and S2, respectively). Eight one-hour clearance periods were performed prior to, during and following a three-hour i.v. infusion of a mixture of 20 l-amino acids (Azonutril 25, 4.5 mg amino acids/kg/min). Baseline glomerular filtration rate (GFR) was lower in recipients at S1 and S2 (55 +/- 5 and 54 +/- 4 ml/min/1.73 m2, respectively) than in UNx.C and 2K.C (72 +/- 4 and 113 +/- 4 ml/min/1.73 m2, respectively, P < 0.05 and 0.001). Amino acid infusion elicited significant GFR increases in controls as well as in recipients in spite of higher renal vascular resistances (RVR). The greater measured increase in GFR, which represented RFR, was 18 +/- 3 and 28 +/- 2 ml/min/1.73 m2 in UNx.C and 2K.C, respectively (P < 0.001), and 17 +/- 3 ml/min/1.73 m2 in R at both S1 and S2 (P < 0.001). Contrary to both UNx and 2K controls, the acute hyperfiltration in R at S1 and S2 occurred with a significant increase in effective renal plasma flow, no alteration in filtration fraction and a large decrease (approximately 20 and 17%) in RVR while no correlation could be detected between the RFR and baseline GFR. Baseline lithium clearance, used as a marker of overall proximal fluid delivery (CLi), was significantly lower, whereas baseline fractional excretion of lithium (FELi) was significantly higher in R at S1 and S2 and in UNx.C (41 +/- 4, 40 +/- 3 and 38 +/- 3%, respectively) than in 2K.C (31 +/- 2%, P < 0.05). Consistent and significant increase in CLi, FELi and absolute proximal reabsorption occurred both in R at S1 and S2 and in UNx and 2K controls during elicitation of RFR.(ABSTRACT TRUNCATED AT 400 WORDS)

Dosing time-dependent nephrotoxicity of cyclosporin A during 21-day administration to Wistar rats

The incidence of cyclosporine A (CsA) nephrotoxicity with reference to the temporal stage of administration was studied during a chronic 21-day treatment in male Wistar rats. Oral administration (20 mg/kg/day) was given at four different times: 1, 7, 13, or 19 hours after light onset (HALO). Plasma creatinine and blood urea nitrogen (BUN) levels were determined at regular intervals over the 24 h: before treatment (day 0); 7, 14, and 21 days after the beginning of treatment (days 7, 14, and 21); and 7 and 14 days after CsA withdrawal (days 28 and 35). At the same times, creatinine clearance and g-glutamyl transferase urinary excretion were determined in the groups of animals treated at 7 and 19 HALO. Residual concentrations of CsA in the renal tissue were measured at the end of the treatment period (day 21) in all groups. Nephrotoxicity of CsA was dependent on the temporal stage of administration. The renal vasoconstriction showed by the increase in plasma creatinine and BUN levels and the decrease in creatinine clearance was maximal when the CsA was given at 7 and 19 HALO and was correlated to the tissue concentrations of CsA. Tubular injury seems to occur earlier and the return to normal function less rapidly in animals treated at 19 HALO compared with animals treated at 7 HALO.

Acute tubular necrosis in kidney transplant patients treated with enalapril

We report two cases of acute renal failure in renal transplant patients using cyclosporine-A (CsA) after the introduction of angiotensin-converting enzyme inhibitor (ACEI) to control arterial hypertension. They had no renal artery stenosis or acute rejection. Both patients presented severe acute tubular necrosis (ATN), which subsided after discontinuation of the ACEI. Synergistic toxic effect of ACEI and CsA on the renal tubules might explain ATN in these two cases.

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.

Effects of growth hormone and IGF-I on glomerular ultrafiltration in growth hormone-deficient rats

In growth hormone deficient states glomerular filtration rate (GFR) and renal plasma flow rate (RPF) are both reduced. Studies were performed in growth hormone deficient rats to delineate the physiologic mechanisms by which growth hormone and IGF-I contribute to the regulation of glomerular function. Growth hormone deficient dw/dw rats received, for one week, subcutaneous infusions of vehicle, des(1-3)IGF-I or were injected i.m. with recombinant human growth hormone. Subsequent renal micropuncture and clearance studies revealed a low GFR and single nephron GFR (SNGFR) in vehicle treated growth hormone deficient animals. Glomerular function became normal with growth hormone or IGF-I treatment, respectively. Both treatments raised SNGFR by reducing arteriolar resistance and increasing the glomerular ultrafiltration coefficient. Furthermore, the two treatments also increased the glomerular tuft volume and the kidney weight which may contribute to the rise in SNGFR and GFR. It is concluded that, (1) in growth hormone deficiency glomerular function is reduced secondary to a high renal arteriolar resistance and a low ultrafiltration coefficient. Both result from a lack in IGF-I rather than the growth hormone deficiency state per se. (2) The growth hormone-IGF-I axis may contribute to the maintenance and physiologic regulation of GFR.

Arginine feeding modifies cyclosporine nephrotoxicity in rats

Glycine (G) infusion causes renal vasodilation mediated by nitric oxide (NO). Cyclosporine A (CsA) nephrotoxicity is characterized by preglomerular vasoconstriction and decreased efferent arteriolar tone probably related to reduced NO and angiotensin II, respectively. L-Arginine (ARG) is a precursor to NO. To test the hypothesis that chronic CsA decreases renal NO activity, we compared the glomerular hemodynamic response to glycine infusion in rats after 8 d of CsA (30 mg/kg per d s.c.), CsA and ARG (1.6 g/kg per d p.o.) (A/CsA), and in two groups of pair-fed controls (CON, A/CON). Single nephron GFR (SNGFR), single nephron plasma flow (SNPF), glomerular capillary hydrostatic pressure gradient (delta P), proximal tubular reabsorption (APR), and kidney tissue angiotensin II (AIIk) were measured before and during G. CsA was associated with baseline decrements in SNGFR, SNPF, delta P, and AIIk, and with a blunted hemodynamic response to G. In CON, ARG did not affect baseline hemodynamics or modify the response to G. In CsA, ARG decreased baseline preglomerular resistance and restored the glomerular hemodynamic response to G. G was associated with a significant increase in AIIk in both CON and CsA. These findings suggest that (a) CsA is associated with decreased AIIk, and (b) CsA may diminish NO activity within the kidney, and that this capacity may be partially restored by arginine feeding.

Cyclosporine- and FK506-induced sympathetic activation correlates with calcineurin-mediated inhibition of T-cell signaling

Cyclosporine A (CsA)-induced hypertension appears to be caused in part by neurogenic vasoconstriction, but the mechanism by which CsA activates the sympathetic nervous system is unknown. In T lymphocytes, the cellular target of CsA and the macrolide immunosuppressant FK506 (as complexes with their endogenous cytoplasmic receptors, or immunophilins) is the Ca(2+)-calmodulin-dependent phosphatase calcineurin. The presence of calcineurin and its colocalization with immunophilin in the brain led us to hypothesize that the phosphatase also mediates CsA-induced sympathetic activation. We now report that sympathetic activity and arterial pressure in rats are increased not only by CsA but also by FK506, which is structurally unrelated to CsA but inhibits the same calcineurin-sensitive T-cell signaling pathway. In contrast, sympathetic activity and blood pressure are not increased by rapamycin, which forms an immunophilin complex that does not bind calcineurin. Furthermore, CsA- and FK506-induced sympathetic activation is attenuated for drug analogues possessing modest changes in molecular structure in a way that closely parallels the ability of each analogue to inhibit calcineurin-mediated T-cell signaling. These results implicate an important role for extralymphoid (ie, neuronal) calcineurin in mediating immunosuppressive drug toxicity.

Effect of CsA on the expression of renin and angiotensin type 1 receptor genes in the rat kidney

To determine whether Cyclosporine A (CsA) alters the intrarenal expression of the renin and type 1 angiotensin II receptor genes, male adult Sprague-Dawley rats were given 25 mg/kg/day CsA s.c. for three weeks (CsA, N = 20) and were compared to pair-fed vehicle treated rats (Con, N = 20). The intrarenal distribution of renin and its mRNA was assessed by immunocytochemistry and in situ hybridization. In addition, kidney renin and type 1 angiotensin II (AT1) receptor mRNA levels were determined by Northern blot analysis. The percentage of juxtaglomerular apparatuses containing renin was higher in the CsA (84 +/- 5.5%) than in the Con (61 +/- 6.7%) group, (P < 0.05). The length of renin immunostaining along afferent arterioles was higher in the CsA (74 +/- 4.5 microns) than in the Con (37 +/- 5.1 microns) group, (P < 0.05). In contrast, neither renin mRNA levels nor its intrarenal distribution were altered by chronic CsA administration. Kidney AT1 receptor mRNA levels were lower in the CsA group than in the Con group. We conclude that chronic CsA: (1) induces recruitment of renin containing cells along the afferent arteriole, (2) causes no changes in intrarenal renin mRNA levels or distribution, suggesting that post-transcriptional events may be responsible for the persistence and/or uptake of renin by the preglomerular vasculature, (3) promotes a downregulation of AT1 receptor gene in the kidney, suggesting that local angiotensin II may control AT1 receptor gene expression by a negative feedback.

Interaction between alpha 2-adrenergic and angiotensin II systems in the control of glomerular hemodynamics as assessed by renal micropuncture in the rat

The hypothesis that renal alpha 2 adrenoceptors influence nephron filtration rate (SNGFR) via interaction with angiotensin II (AII) was tested by renal micropuncture. The physical determinants of SNGFR were assessed in adult male Munich Wistar rats 5-7 d after ipsilateral surgical renal denervation (DNX). DNX was performed to isolate inhibitory central and presynaptic alpha 2 adrenoceptors from end-organ receptors within the kidney. Two experimental protocols were employed: one to test whether prior AII receptor blockade with saralasin would alter the glomerular hemodynamic response to alpha 2 adrenoceptor stimulation with the selective agonist B-HT 933 under euvolemic conditions, and the other to test whether B-HT 933 would alter the response to exogenous AII under conditions of plasma volume expansion. In euvolemic rats, B-HT 933 caused SNGFR to decline as the result of a decrease in glomerular ultrafiltration coefficient (LpA), an effect that was blocked by saralasin. After plasma volume expansion, B-HT 933 showed no primary effect on LpA but heightened the response of arterial blood pressure, glomerular transcapillary pressure gradient, and LpA to AII. The parallel results of these converse experiments suggest a complementary interaction between renal alpha 2-adrenergic and AII systems in the control of LpA.

Risk factors for cyclosporine-induced nephropathy in patients with autoimmune diseases. International Kidney Biopsy Registry of Cyclosporine in Autoimmune Diseases

BACKGROUND

Cyclosporine is an immunosuppressive drug that is used to treat patients with autoimmune disease as well as patients who have received allografts. The drug can cause renal damage, but the incidence of and risk factors for nephropathy in patients treated with cyclosporine for autoimmune or inflammatory diseases are not known.

METHODS

We analyzed data from renal biopsies performed in 192 patients (129 adults and 63 children) who had been treated with cyclosporine for insulin-dependent diabetes mellitus of recent onset, uveitis, psoriasis, Sjögren's syndrome, or polychondritis. The mean (+/- SD) initial dose of cyclosporine was 8.2 +/- 2.8 mg per kilogram of body weight per day, and the duration of treatment was 4 to 39 months (median, 13).

RESULTS

Forty-one patients (37 adults and 4 children) had cyclosporine-induced nephropathy, defined as at least moderate focal interstitial fibrosis with tubular atrophy, arteriolar alterations, or both. As compared with patients in whom nephropathy did not develop, these patients received a larger initial dose of cyclosporine (9.3 +/- 2.8 vs. 8.0 +/- 2.8 mg per kilogram per day), had a larger maximal increase in the serum creatinine concentration above base-line values (101 +/- 77 percent vs. 50 +/- 33 percent), and were older (31 +/- 13 vs. 23 +/- 12 years). These three variables were shown by multivariate logistic-regression analysis to be significant risk factors. The duration of the elevation in the serum creatinine concentration and the occurrence of elevated blood pressure were not additional risk factors.

CONCLUSIONS

Nephropathy is an important potential effect of cyclosporine therapy. The risk of its development in patients with autoimmune diseases who are treated with cyclosporine can be minimized by allowing a dose no higher than 5 mg per kilogram per day and avoiding increases in serum creatinine of more than 30 percent above the patient's base-line value.

Cyclosporin reduces proteinuria in rats with aminonucleoside nephrosis

The effect of cyclosporin (CS) was assessed in Sprague-Dawley rats with puromycin aminonucleoside (PA) nephrosis induced by a single intraperitoneal injection of PA. Three groups of rats were injected intraperitoneally with CS (10 mg/kg body weight) daily, beginning 1 day before PA administration, or 5 or 10 days after PA administration, for 10 days. CS significantly reduced proteinuria in rats with PA nephrosis in comparison with untreated nephrotic controls. After discontinuation of the CS treatment, proteinuria gradually increased, reaching values similar to those in control nephrotic rats. CS pretreatment did not prevent the induction of PA-induced nephrotic syndrome. Light microscopy and assessment of anionic sites in the glomerular basement membrane revealed no differences between normal rats, nephrotic controls, and CS-treated rats. These results show that CS can reduce proteinuria in PA nephrosis, but cannot ameliorate the glomerular changes.

Mechanisms and amelioration of acute renal allograft failure in the cyclosporine era

The fairly wide-ranging spectrum of tactics under investigation for ameliorating acute renal allograft dysfunction caused by harvest/preservation-related ischemia, acute CsA nephrotoxicity, and acute immunologic crises reflect the fact that no single approach has emerged as universally useful for mitigating the vasomotor nephropathy produced by the combined effects of each of these vectors of vasomotor renal allograft injury. Given the clinical heterogeneity of patients and allografts, it is the author's bias that, in addition to careful donor and recipient hemodynamic management, induction immunosuppressive regimens should be individualized on the basis of allograft function in the immediate postreperfusion period (judged by rate of diuresis, intraoperative parenchymal tone, renal scan profiles, and rate of decline of serum creatinine concentration) as well as patient-specific immunologic and general medical risk factors. Promising laboratory and clinical investigations of such agents as calcium channel blockers, substances promoting intrarenal vasodilator vs. vasoconstrictor prostaglandin formation, and atriopeptins have the potential to provide clinically helpful options with regard to adjunctive therapy for ameliorating acute renal allograft dysfunction associated with INF and ACR.

Cyclosporine causes sympathetically mediated elevations in arterial pressure in rats

Cyclosporine-induced immunosuppression has emerged as a new cause of hypertension, but the underlying mechanisms are poorly understood. In patients, this hypertension is accompanied by sympathetic neural activation. We therefore hypothesized that increased sympathetic nerve discharge is an important mechanism by which cyclosporine raises blood pressure. To test this hypothesis, we examined effects of acute administration of cyclosporine (5 mg/kg i.v.) or vehicle on renal and lumbar sympathetic nerve activity, renal and femoral blood flow velocity (pulsed Doppler flowmetry), and arterial pressure in chloralose-anesthetized rats. Vehicle had no effect on sympathetic nerve activity, whereas cyclosporine caused renal and lumbar sympathetic nerve activity to increase progressively over 60 minutes to levels that were 362 +/- 46% and 388 +/- 70%, respectively, of the baseline values (p less than 0.05). These increases in sympathetic nerve activity were accompanied by proportional increases in renal and femoral vascular resistance and sustained increases in mean arterial pressure (+19 +/- 3 mm Hg, p less than 0.05 versus baseline). The cyclosporine-induced increases in regional vascular resistance and arterial pressure were greatly attenuated, or abolished, by ganglionic blockade or by clonidine (central sympatholysis) but were unaffected by angiotensin converting enzyme inhibition. These findings demonstrate that in an anesthetized animal preparation, the vasoconstrictor and blood pressure-raising effects of cyclosporine are caused by sympathetic neural activation.

Renal changes associated with cyclosporine in recent type I diabetes mellitus

The effects of cyclosporine A treatment on arterial pressure and renal function were assessed in 11 young patients with type I diabetes of short duration. Cyclosporine was started at 7.5 mg/kg/day, progressively decreased to 6.3 mg/kg/day at 6 months, and then continued at a lower dose (4.1 mg/kg/day) for an additional 3 months in patients in whom remission of insulin dependency was obtained (n = 6). After 3 months of cyclosporine, a slight but significant increase in arterial pressure (+5.2 +/- 1.5 mm Hg), a rise in renal vascular resistance (approximately 20%), a decrease in glomerular filtration rate (approximately 25%), and a fall in filtration fraction were observed. Such changes were sustained after 6 and eventually 9 months of therapy. The decrease in glomerular filtration rate observed during cyclosporine treatment contrasted with the lack of change in simultaneously estimated creatinine clearance; in fact, the creatinine clearance/glomerular filtration ratio increased from 1.07 +/- 0.05% to 1.33 +/- 0.09% within 3 months of cyclosporine therapy, thus suggesting an enhanced tubular secretion of creatinine. Plasma renin activity and urinary excretion of kallikrein decreased significantly (approximately 50%), whereas plasma aldosterone concentration remained unaltered and plasma concentration of potassium increased during cyclosporine therapy. These changes were observed in the presence of a constant urinary excretion of sodium and potassium and a constant body weight. All parameters returned to pretreatment values within 3 months after cessation of cyclosporine. These results indicate that cyclosporine given for 6-9 months at a moderate dose causes a deleterious but reversible effect on arterial pressure and renal function in young diabetic patients.

Nature and extent of glomerular injury induced by cyclosporine in heart transplant patients

We sought to clarify whether low-dose cyclosporine (5.0 +/- 2.2 mg/kg/day) given for more than two years to prevent cardiac graft rejection induced glomerular injury and to quantify the extent of the lesions. After renal hemodynamic studies, renal biopsy specimens were obtained from 10 patients on cyclosporine and analyzed by a novel morphometric technique consisting of a tridimensional reconstruction of the glomerular tuft. Autopsy kidney specimens from three patients with no clinical history of renal disease, and from four patients who died with dilatative cardiomyopathy served as controls. The glomerular filtration rate and renal plasma flow were significantly depressed below normal values in transplant recipients given cyclosporine, averaging 35 +/- 8 and 325 +/- 94 ml/min/1.73 m2, respectively. Conventional light microscopy of specimens from controls and from patients who died with dilatative cardiomyopathy did not reveal renal structural abnormalities. By contrast kidney specimens from cyclosporine-treated patients had obliterative arteriolopathy and ischemic-type changes, with thickening and wrinkling of glomerular capillary wall. Morphometrical analysis of 28 control glomeruli and 40 glomeruli from patients with dilatative cardiomyopathy showed glomerular capillary tuft volumes (VCT) ranging between 1.2 and 2.3 microns 3 x 10(-6), whereas of 102 glomeruli from cyclosporine-treated patients 42.1% had VCT lower than 1.2 microns 3 x 10(-6) and 24.4% VCT higher than 2.3 microns 3 x 10(-6).(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine-induced sympathetic activation and hypertension after heart transplantation

BACKGROUND

Hypertension is a frequent complication of cyclosporine-induced immunosuppression, but the underlying mechanism is unknown. In anesthetized animals, the administration of cyclosporine increases sympathetic-nerve discharge, which may contribute to hypertension.

METHODS

To determine whether cyclosporine-induced hypertension is accompanied by sustained sympathetic neural activation in patients, we recorded sympathetic action potentials using intraneural microelectrodes (in the peroneal nerve) in heart-transplant recipients receiving azathioprine and prednisone alone (n = 5) or in combination with cyclosporine (n = 14). We performed the same studies in eight patients with myasthenia gravis who were receiving cyclosporine and eight who were not, in five patients with essential hypertension, and in nine normal controls.

RESULTS

Heart-transplant recipients receiving cyclosporine had higher mean arterial blood pressure (+/- SE) than those not receiving cyclosporine (112 +/- 3 vs. 96 +/- 4 mm Hg; P less than 0.05) and a 2.7-fold higher rate of sympathetic-nerve firing (80 +/- 3 vs. 30 +/- 4 bursts per minute; P less than 0.05). For patients with myasthenia gravis, similar doses of cyclosporine were associated with smaller elevations in mean arterial blood pressure (100 +/- 2 mm Hg, as compared with 91 +/- 4 mm Hg in those not receiving cyclosporine; P less than 0.05) and in the rate of sympathetic-nerve firing (46 +/- 3 bursts per minute, as compared with 25 +/- 4 bursts per minute; P less than 0.05). Sympathetic activity in patients with heart transplants or myasthenia gravis who were not being treated with cyclosporine was no different from that in patients with essential hypertension or in normal controls.

CONCLUSIONS

Cyclosporine-induced hypertension is associated with sympathetic neural activation, which may be accentuated by the cardiac denervation that results from heart transplantation.