L-arginine reverses the antinatriuretic effect of cyclosporin in renal transplant patients

Cyclosporin A suppresses proliferation of endothelial progenitor cells: involvement of nitric oxide synthase inhibition

OBJECTIVE

To investigate the effects of the potent immunosuppressive agent cyclosporin A (CsA) on the proliferation of human endothelial progenitor cells (EPCs) and endothelial nitric oxide synthase (eNOS) expression in EPCs.

METHODS AND RESULTS

The EPCs were obtained from cultured mononuclear cells, which were isolated from the peripheral blood of healthy adults, and stimulated with CsA (10 microg/mL) in the presence or absence of either vascular endothelial growth factor (VEGF; 50 ng/mL) or L-arginine (1 mM). To explore the effect of different concentrations of CsA alone on EPC proliferation, some cells were treated with CsA in a series of final concentrations ranging from 0 to 10 microg/mL. Cell proliferation and apoptosis were determined, respectively, by the Cell Counting Kit-8 assay and terminal deoxynucleotidyl transferase-mediated nick end labeling staining. The expression of eNOS was assayed by reverse transcription-polymerase chain reaction analysis while nitric oxide (NO) generation was detected using the Griess method. The effects of CsA on EPC proliferation, apoptosis, and eNOS/NO production were dose dependent in the concentration ranging from 0.1 microg/mL to 10 microg/mL. Treatment with VEGF (50 ng/mL) significantly promoted EPC proliferation and eNOS/NO production, which were completely abrogated by pre-incubation with CsA (10 microg/mL). The supplement of L-arginine (1 mM) promoted NO production that enhanced EPC proliferation and attenuated the effect of CsA on EPC proliferation and apoptosis.

CONCLUSION

CsA significantly inhibited proliferation, eNOS mRNA expression and NO production of human EPCs, in a dose-dependent manner.

The role of nitric oxide in renal transplantation

This review discusses the concept that nitric oxide synthase (NOS) may orchestrate both the inflammatory response to the renal allograft and anti-inflammatory defense in the graft itself. NO is produced by endothelial, epithelial, as well as inflammatory cells. In the setting of transplantation, the endothelium is the first lining to be subjected to the early response to injury. In turn, activated endothelial cells facilitate leukocyte recruitment, immune-mediated injury, and angiogenesis. On activation by inflammatory stimuli, endothelial cells up-regulate multiple vasoactive substances, oxygen radicals, cytokines, chemokines, and growth factors. Therefore, endothelial integrity, especially the expression of protecting vasoactive agents, such as NO, may be a key factor in resistance or sensitivity to transplantation-mediated injury. Thus, evaluating the mechanisms by which NO is involved in either protecting or injuring the transplanted allogeneic kidney is important for our understanding of renal allograft rejection. This review focuses on the role of NO in the inflammatory endothelial-leukocyte interactions, which are implicated in acute and chronic rejection of the transplanted kidney.

Cyclosporine nephrotoxicity

After more than 20 years of cyclosporine use its nephrotoxicity remains a significant clinical problem. Cyclosporine-induced renal injury has been described in solid organs recipients and in patients treated for autoimmune diseases. It is manifested in 2 distinct and well characterized forms, acute nephrotoxicity and chronic nephrotoxicity. This communication reviews the current literature analyzing the available data about the pathogenesis and mechanisms of acute and chronic cyclosporine-induced nephrotoxicity. A working hypothesis for the possible mechanisms of chronic cyclosporine nephrotoxicity will be provided.

L-arginine-induced vasodilation of the renal vasculature is not altered in hypertensive patients with type 2 diabetes

OBJECTIVE

Diabetes, arterial hypertension, hypercholesterolemia, and aging are associated with endothelial dysfunction in various vasculatures. Endothelium-dependent vasodilation of the renal vasculature cannot be easily assessed, but infusion of L-arginine, the substrate of endothelial nitric oxide synthase, leads to an increase in renal plasma flow (RPF) in humans. We have examined the effect of L-arginine infusion on renal hemodynamics in hypertensive patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty-three elderly patients with type 2 diabetes (age, 65 +/- 6 years; HbA(1c), 7.8 +/- 1.6%) with coexisting arterial hypertension (158 +/- 19/83 +/- 11 mmHg) and elevated cholesterol levels (total cholesterol, 215 +/- 33 mg/dl) were examined. These patients were compared with a young and healthy reference group (n = 20; age, 26 +/- 2 years). The effect of L-arginine infusion (100 mg/kg over 30 min) on RPF and glomerular filtration rate were measured using the constant input clearance technique with p-aminohippurate and inulin, respectively.

RESULTS

L-arginine infusion similarly influenced renal hemodynamics in patients and reference subjects: RPF increased by 7 +/- 11 and 7 +/- 11% in diabetic and reference subjects, respectively (P = NS). Other parameters of renal hemodynamics such as glomerular filtration rate (5 +/- 5 vs. 4 +/- 4%) and filtration fraction (-1 +/- 8 vs. -1 +/- 9%) were not significantly different between diabetic and reference subjects, too.

CONCLUSIONS

L-arginine-induced vasodilation of the renal vasculature is not different between a group of hypertensive diabetic patients and a young, healthy reference group. These data were obtained using low-dose L-arginine infusion.

Acute renal failure: is nitric oxide the bad guy?

Nephrotoxicity is a major side effect in clinical practice, frequently leading to acute renal failure (ARF). Many physiological mechanisms have been implicated in drug-induced renal injury. Currently, nitric oxide (NO) is considered to be an important regulator of renal vascular tone and a modulator of glomerular function under both basal and physiopathological conditions. Historically, NO has been implicated in ARF and, after its discovery, several publications have suggested that changes in NO production could play an important role in the hemodynamic alterations observed in ARF. In this review, we evaluate the participation of NO in ARF and summarize many of the findings in this research area in an attempt to elucidate the role of NO in ARF.

Assessment of endothelial function of the renal vasculature in human subjects

BACKGROUND

L-Arginine, the substrate of nitric oxide (NO) synthase, and N(G)-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of endothelial NO synthase, are used to analyze endothelial function of the renal vasculature. However, little is known about the appropriate dose of L-arginine to be used and the duration of action of L-arginine and L-NMMA.

METHODS

Twenty-nine healthy male subjects (age, 27+/-1 years) were examined. In protocol 1 (N = 17), L-arginine at low (100 mg/kg) and high dose (250 mg/kg), and high-dose L-arginine combined either with L-NMMA (total dose, 4.25 mg/kg; N = 9) or placebo (N = 8) were given. In protocol 2 (N = 12), L-NMMA was given before L-arginine infusion (100 mg/kg). Glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured at rest and at the end of each infusion step.

RESULTS

In protocol 1, L-arginine dose dependently increased RPF and GFR (RPF: 599+/-19 v 630+/-18 v 690+/-24 mL/min, P <.05; GFR: 111+/-3 v 115+/-3 v 121+/-3 mL/min, P <.01; for baseline, L-arginine 100 mg/kg and 250 mg/kg, respectively). However, these changes could not be antagonized by coinfusion of L-NMMA to L-arginine 250 mg/kg: RPF and GFR remained unchanged in both the placebo and the L-NMMA group. In protocol 2, L-NMMA decreased RPF (492+/-18 v 567+/-27 mL/min, P <.01) and increased GFR (122+/-4 v 118+/-3 mL/min, P <.05). These changes could only be partially reversed by subsequent infusion of L-arginine (RPF: 533+/-15 mL/min; GFR: 121+/-4 mL/min; both parameters P = NS v L-NMMA and v baseline).

CONCLUSIONS

L-arginine at a dose of 100 mg/kg is sufficient to analyze endothelial function of the renal vasculature. The prolonged effect of L-NMMA and L-arginine must be taken into account in study protocols using both substances. Thus, stimulation and blockade of NO synthase cannot be examined in the same protocol.

Vasoactive substances in renal transplantation

During and after transplantation the kidney experiences a variety of insults that result in functional impairment and structural damage. These changes are mediated or influenced by hormones, cytokines, enzymes and growth factors, which are excreted by endothelial, graft parenchymal as well as by graft infiltrating cells. This review evaluates the pathophysiological role of vasoactive substances (for example, the vasoconstrictors angiotensin II and endothelin, as well as vasodilators such as nitric oxide, adrenomedullin and atrial natriuretic peptide) in kidney transplantation and summarizes recent reports that indicate that targeting vasoactive substances may represent effective therapeutic strategies for the achievement of long-term allograft survival.

Calcium Antagonists and Renal Protection from Cyclosporine Nephrotoxicity: Long-term Trial in Renal Transplantation Patients

Cyclosporine (CsA) treatment in solid organ transplantation has represented one of the greatest advances in the past 20 years, reducing acute rejection and increasing long-term survival. However, CsA has an important side effect, producing renal vasoconstriction and systemic hypertension. The main histological findings in the kidney are vascular lesions in the endothelium and smooth muscle cells. On proximal tubule cells, severe atrophy, vacuolization and thickening of the basal membrane can be found. The main mechanisms of vasoconstriction are secondary to endothelium disorders, increasing vasoconstrictor substances like endothelin, thromboxane, free radicals, etc., and reducing vasodilator substances like nitric oxide and prostaglandins. CsA acute nephrotoxicity produces haemodynamic changes with minor histological lesions, which will disappear when the medication is discontinued. Long-term CsA nephrotoxicity has been widely discussed in the literature. For some authors, a limited number of patients can develop end-state renal failure but others did not suffer these complications. Nevertheless, it seems clear that high doses of CsA can produce renal lesion and renal insufficiency, being difficult to evaluate in renal transplant patients because of the frequent association with chronic rejection lesions. Several types of drugs have been used to treat CsA nephrotoxicity in renal transplant patients but calcium antagonists and angiotensin converting enzyme-inhibitors are the most frequently used, especially the former due to their effect on the afferent arteriole vasodilatation, their natriuretic properties and their reducing intracellular calcium. The greatest experience has been with nifedipine, but other drugs like verapamil, diltiazem, amlodipine, felodipine, isradipine, etc., have also been used. Lacidipine, a 1,4-dihydropiridine, has demonstrated a beneficial effect during the short term after renal transplantation, and a multicentre, multinational, double-bind, placebo-controlled clinical trial for the long term currently ongoing.

Renal hemodynamic effects of L-arginine and sodium nitroprusside in heart transplant recipients

BACKGROUND

Long-term treatment with cyclosporine A (CsA) induces vasoconstriction in the kidney and causes renal impairment. An altered L-arginine (L-Arg)/nitric oxide (NO) pathway may play a key role in CsA nephrotoxicity.

METHODS

We studied the effect of L-Arg (dosage, 17 mg/kg/min over 30 min), the precursor of NO synthesis, and sodium nitroprusside (SNP; dosage, 1.0 microgram/kg/min over 30 min) on renal hemodynamics in a double-blind, placebo-controlled, randomized, three-way cross-over study comprising 12 stable cardiac transplant recipients on long-term CsA treatment, 10 patients with chronic nephropathy not receiving CsA, and 13 healthy controls. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured by paraaminohippurate (PAH) and the inulin clearance method, respectively.

RESULTS

In healthy subjects, L-Arg induced an increase in RPF (P = 0.009) and GFR (P = 0.001). By contrast, L-Arg did not induce renal hemodynamic effects in heart transplant patients or patients with chronic nephropathy. SNP reduced RPF (P = 0.050) and GFR (P = 0.005) in patients with chronic nephropathy but did not affect renal hemodynamics in heart transplant recipients or in healthy subjects.

CONCLUSIONS

These data indicate that L-Arg cannot be used to reverse CsA-induced renal vasoconstriction in heart transplant recipients under long-term CsA treatment, although these patients have a normal renal response to SNP.