Effects of nitric oxide blockade and cyclosporin A on cardiovascular and renal function in normal man

Endothelial nitric oxide synthase gene variation associated with chronic kidney disease after liver transplant

OBJECTIVE

To identify single nucleotide polymorphisms (SNPs) associated with risk of developing chronic kidney disease (CKD), a prevalent comorbidity, after liver transplant (LT).

PATIENTS AND METHODS

This study consists of a cohort of adult (> or =18 years) primary-LT recipients who had normal renal function before LT and who survived 1 year or more after LT at a high-volume US LT program between January 1, 1990, and December 31, 2000. Patients with adequate renal function (estimated glomerular filtration rate, > or =40 mL/min per 1.73 m(2) during follow-up; n=308) and patients with incident CKD (estimated glomerular filtration rate, <40 mL/min per 1.73 m(2) after LT; n=92) were identified. To investigate the association of 6 candidate genes with post-LT CKD, we selected SNPs that have been associated with renal function in the literature. Hazard ratios were estimated using Cox regression, adjusted for potential confounding variables.

RESULTS

The variant allele (298Asp) of the Glu298Asp SNP in the endothelial nitric oxide synthase gene (NOS3) was significantly associated with CKD after LT (P=.05; adjusted for multiple comparisons). The 5-year incidence of CKD was 70% among patients homozygous for the NOS3 variant allele (298Asp) compared with 42% among those not homozygous for the NOS3 variant allele. Specifically, homozygosity for the NOS3 variant allele conferred a 2.5-fold increased risk of developing CKD after LT (P=.005, adjusted for confounding variables).

CONCLUSION

Homozygosity for the variant allele of NOS3 (298Asp) is associated with CKD after LT and may be useful for identifying recipients at higher risk of post-LT CKD.

Effect of a single cyclosporine dose on the single-dose pharmacokinetics of sitagliptin (MK-0431), a dipeptidyl peptidase-4 inhibitor, in healthy male subjects

Sitagliptin (MK-0431) is an orally active, potent, and selective dipeptidyl peptidase-4 inhibitor used for the treatment of patients with type 2 diabetes mellitus. Sitagliptin has been shown to be a substrate for P-glycoprotein in preclinical studies. Cyclosporine was used as a probe P-glycoprotein inhibitor at a high dose to evaluate the potential effect of potent P-glycoprotein inhibition on single-dose sitagliptin pharmacokinetics in healthy male subjects. Eight healthy young men received a single oral 600-mg dose of cyclosporine with a single 100-mg oral sitagliptin dose and a single oral 100-mg sitagliptin dose alone in an open-label, randomized, 2-period, crossover study. Single doses of sitagliptin with or without single doses of cyclosporine were generally well tolerated. The sitagliptin AUC(0-infinity) geometric mean ratio was 1.29 with a 90% confidence interval of (1.24, 1.34). The sitagliptin Cmax geometric mean ratio was 1.68 with a 90% confidence interval of (1.35, 2.08). Cyclosporine coadministration did not appear to affect apparent sitagliptin renal clearance, t(1/2), or C(24 h), suggesting that effects of these high doses of cyclosporine are more likely due to enhanced absorption of sitagliptin, potentially through inhibition of intestinal P-glycoprotein. These results rationalize the use of a single high-dose cyclosporine as a probe inhibitor of P-glycoprotein for compound candidates whose elimination is less dependent on CYP3A4-mediated metabolism.

Curative isosorbide-5-mononitrate treatment, in opposition to the beneficial preventive one, aggravates the prothrombotic and proconstrictor state in cyclosporine-induced hypertensive rats

1. The aim of the present study was to evaluate the effect of preventive and curative isosorbide-5-mononitrate (Is-5-Mn) treatment on the development of hypertension, cGMP content, thromboxane (TX) A(2)/prostaglandin (PG) I2 balance, the peripheral serotonergic system, platelet activation, lipid peroxidation and plasma lipids in cyclosporine A (CsA)-induced hypertensive rats. 2. Control, CsA (5 mg/kg per day) and Is-5-Mn (150 mg/kg per day, b.i.d.) rat groups were treated orally over a period of 7 weeks. The preventive Is-5-Mn group (Is-5-Mn + CsA) was first treated for 2 weeks with Is-5-Mn, followed by 7 weeks with both drugs; the curative Is-5-Mn group (CsA + Is-5-Mn) was treated for a period of 7 weeks with CsA and with both drugs for an additional 5 weeks. The control group received oral vehicle. 3. Whereas in the group undergoing preventive treatment the CsA-induced increase in blood pressure (BP), compared with the control group, was avoided, in the group undergoing curative treatment, the increase in BP was even higher. The decreased arterial cGMP content in the CsA group was prevented and reverted when Is-Mn was administered either preventatively or curatively with CsA. Platelet TXA2 production, although unaffected in the Is-5-Mn + CsA group, was significantly higher in the CsA + Is-5-Mn group compared with the group receiving CsA alone. Furthermore, plasma TXA2 was reduced following preventive Is-5-Mn treatment, but was worsened in the group undergoing curative therapy. Aortic PGI2 synthesis was identical in all groups. Consequently, the TXA2/PGI2 ratio was only altered in the CsA + Is-5-Mn group, demonstrating a markedly higher value. In both groups treated simultaneously with CsA and Is-5-Mn, a higher platelet 5-hydroxytryptamine (5-HT) content was obtained compared with CsA treatment alone, but only preventive treatment with Is-5-Mn resulted in a significant reduction in plasma 5-HT. Changes in ADP and collagen-induced platelet aggregation paralleled those of plasma 5-HT and TXA2: the hyperaggregation profile of the CsA group, although partially prevented, was not reverted by simultaneous treatment with Is-5-Mn and CsA. Lipid peroxidation and lipid profile values also worsened in the CsA + Is-5-Mn group compared with the group administered CsA alone. 4. In conclusion, the beneficial effects of concomitant Is-5-Mn and CsA treatment were demonstrated when Is-5-Mn was administered preventatively because not only was arterial hypertension prevented, but platelet aggregation and plasma TXA2 and 5-HT levels were also reduced. In contrast, following curative treatment, the BP, platelet/vascular vasoconstrictor balance, lipid peroxidation and plasma lipids were aggravated, recommending a judicious evaluation of the impact of nitrate therapy throughout the period of its administration.

Central and peripheral haemodynamic effects of L-NAME infusion in healthy volunteers

AIMS

To evaluate the effects of the intravenous administration of the nitric oxide synthesis inhibitor N(g)nitro-L-arginine methyl ester (L-NAME) in healthy volunteers.

METHODS

L-NAME (0.25, 0.5 and 0.75 mg/kg over 8 min) was infused in 13 healthy male volunteers. Finally, subjects were infused with either L- or D-arginine.

RESULTS

L-NAME resulted in dose-dependent falls in heart rate 60 bpm (55-64 bpm) to 49 bpm (46-52 bpm) (P<0.01) and increased mean arterial pressure 77.0 mmHg (73.2-80.8 mmHg) to 90.0 mmHg (87.1-92.8 mmHg) (P<0.01). The cardiac output was significantly reduced after each L-NAME infusion, and systemic vascular resistance increased linearly over the dosage range. Cardiac stroke volume was significantly reduced only following 0.75 mg/kg/min L-NAME: from 100 ml (91.3-108.7 ml) to 83 ml (74.7-91.4 ml); P<0.01. Forearm blood flow was unchanged at any dosage. L-arginine but not D-arginine infusion reversed the haemodynamic effects of L-NAME.

CONCLUSIONS

Contrasting with the profound dose-dependent effects of L-NAME had significant effects on central haemodynamics but no discernible effects on peripheral blood flow.

Isosorbide-5-mononitrate treatment prevents cyclosporin A-induced platelet hyperactivation and the underlying nitric oxide-cyclic guanosine-3',5'-monophosphate disturbances

INTRODUCTION

The clinical use of cyclosporin A (CsA) is commonly associated with the development of hypertension and increased risk of thromboembolic events. Decreased endothelium-dependent relaxation and increased platelet activation seems to be involved on those side effects, but the underlying mechanisms are not yet elucidated. The present study aimed to evaluate the CsA effect on the platelet NO-cyclic guanosine-3',5'-monophosphate (cGMP) pathway and the putative benefits of concomitant isosorbide-5-mononitrate (IS-5-MN) administration on CsA-induced hypertension and on platelet hyperactivation.

MATERIALS AND METHODS

Blood pressures, platelet NO synthase activity and cGMP content, intracellular free calcium concentration ([Ca2+]i) and whole blood platelet aggregation were assessed in three rat groups orally treated, during 7 weeks, with the following diets: orange juice (control group), 5 mg/kg/day of CsA (CsA group) and 150 mg/kg/day, b.i.d., of IS-5-MN for 2 weeks and IS-5-MN plus 5 mg/kg/day of CsA for 7 weeks (IS-5-MN+CsA group).

RESULTS

IS-5-MN treatment has prevented hypertension development obtained in the solely CsA-treated rats. CsA treatment has inhibited NOS activity, which was reverted by the concomitant IS-5-MN and CsA administration. On the contrary, platelets from CsA-treated rats had cGMP content increased when compared with the control rats. The variation obtained when ISMN was present was less predominant. Therefore, the organic nitrate treatment has prevented platelet hyperactivation, namely, by decreasing thrombin-evoked [Ca2+]i and collagen-evoked platelet aggregation, when compared with the solely CsA-treated group. The preventive effect of IS-5-MN was reinforced by electron microscopy studies of platelet activation.

CONCLUSIONS

By increasing [Ca2+]i and aggregation, CsA induces platelet hyperactivation and simultaneously increases cGMP content, which might represent a compensatory inhibitory mechanism. The concomitant IS-5-MN treatment prevents the above-mentioned platelet hyperreactivity and tends to normalize the NO-cGMP pathway as well as the development of hypertension.

Vasopressors and the kidney

The changes in renal perfusion induced by vasopressors depend on their effects on systemic hemodynamics and renal vascular resistance. Both effects are largely influenced by the patient's underlying condition such as myocardial contractility and vascular responsiveness. A beneficial effect can be expected if mean arterial pressure increases without decreasing cardiac output and if the effect on renal vascular resistance is less pronounced than on systemic vascular resistance. Acute renal failure is associated with loss of renal autoregulation and sepsis is associated with blood pressures below the autoregulatory threshold. Both conditions might therefore benefit from the administration of vasopressors. Many experimental and clinical data indeed suggest a beneficial effect of norepinephrine on the urine output in sepsis. A beneficial effect on renal function (glomerular filtration) is a less consistent finding suggesting that pressure diuresis might be partially responsible for the pressor-induced diuresis. Administration of vasopressors to patients with oliguria should be considered in fluid-resuscitated patients with distributive shock. Whether other vasopressors offer advantages over norepinephrine requires further investigation.

Impairment of vascular and platelet levels of nitric oxide and cyclic guanosine-3',5'-monophosphate in cyclosporin A-induced hypertensive rats

The therapeutic use of the immunosuppressive agent cyclosporin A (CsA) is associated with arterial hypertension and increased risk of thromboembolism. Impaired endothelium-mediated relaxation is one of the main hypotheses explaining the CsA-induced vascular hyper-reactivity. Since nitric oxide (NO) modulates both vascular and platelet activity, we studied the effects of CsA on the levels of arterial and platelet NO as well as 3',5'-cyclic guanosine monophosphate (cGMP) levels which are influenced by NO. An animal model of CsA-induced hypertension was used. Wistar rats were treated with a clinically relevant, oral dose of 5 mg/kg CsA, daily, for 4 weeks. CsA increased both systolic and diastolic blood pressures compared to non-treated rats (P < 0.01). Nitrite, a NO metabolite, decreased in the entire aorta wall (30%, P < 0.05) and in the aorta wall without the endothelial layer (70 %, P < 0.05) in CsA-treated vs. control groups. cGMP content was also decreased in the CsA-treated group (67%, P < 0.01) vs. control. Taken together, these results suggest a defect on the endothelial NO generation, acceleration of breakdown and/or consumption of NO, as well as marked alterations directly on cGMP metabolism. Conversely, platelet nitrite and cGMP content significantly increased in the CsA-treated rats, which was also observed in in vitro studies of platelet nitrite release following CsA treatment. This suggests a platelet self-regulation mechanism against CsA-induced platelet hyper-reactivity, which, in turn, could compensate vascular impairment.

Production of nitric oxide, but not prostacyclin, is reduced in klotho mice

A novel murine model of aging (kl/kl mice) has been developed by in vivo mutagenesis. We analyzed endothelial function in this strain. Ring preparations of the thoracic aorta were obtained from 6- to 9-week old wild-type (+/+) and heterozygous (kl/+) klotho mice. The aortas of kl/+ mice showed an exaggerated contractile response to norepinephrine and attenuated vasodilator responses to acetylcholine and lecithinized superoxide dismutase (SOD) compared to +/+ mice. The response to sodium nitroprusside was unaltered in kl/+ mice. The contraction in response to norepinephrine was augmented by treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) to a greater extent in +/+ mice than in kl/+ mice. Treatment with L-NAME abolished the vasodilator responses to both acetylcholine and lecithinized SOD. NO metabolites (NO2- and NO3-) and cGMP concentrations in the urine were significantly reduced in kl/+ mice compared to +/+ mice. However, the urinary excretion of 6-keto-prostaglandin F1alpha was unaltered. There was little immunostaining for NO synthase and vascular endothelial growth factor (VEGF) in the aorta of kl/+ mice. No immunostaining for NO synthase was noted in the aorta of kl/kl mice. The expression of the klotho gene product may have a role in the regulation of VEGF expression and is tightly linked to endothelial release of NO.

Cardiovascular effects of an immunosuppressive agent cyclosporin A

Cyclosporin A (CsA) is now routinely used for transplantation of all solid organs, bone marrow transplantation, and for an increasing number of immunological diseases. However, treatment with CsA is an important iatrogenic cause of post-transplant hypertension, hyperlipidemia, and diabetes, which may contribute to the high cardiovascular morbidity in transplant recipients. Recently, the calcineurin inhibitor CsA has been employed in vivo and in vitro to examine the role of calcineurin in the signal transduction leading to cardiac hypertrophy. A cell culture study demonstrated the inhibitory effect of CsA on cytokine production by cardiac myxoma cells, the most common primary tumor of the heart. This review discusses recent data on the cardiovascular effects of CsA.