Cyclosporine A inhibits relaxation but does not induce vasoconstriction in human subcutaneous resistance vessels

Hypertension: The Neglected Complication of Transplantation

Arterial hypertension and transplantation are closely linked, and its association may promote impaired graft and overall survival. Since the introduction of calcineurin inhibitors, it is observed in 50–80% of transplanted patients. However, many pathophysiological mechanisms are involved in its genesis. In this review, we intend to provide an updated overview of these mechanisms, dealing with the causes common to all kinds of transplantation and emphasizing special cases with distinct features, and to give a perspective on the pharmacological approach, in order to help clinicians in the management of this frequent complication.

Pathogenesis of calcineurin inhibitor-induced hypertension

This article reviews the current understanding of the mechanisms of calcineurin inhibitor-induced hypertension. Already early after the introduction of cyclosporine in the 1980s, vasoconstriction, sympathetic excitation and sodium retention by the kidney had been shown to play a role in this form of hypertension. The vasoconstrictive effects of calcineurin inhibitors are related to interference with the balance of vasoactive substances, including endothelin and nitric oxide. Until recently, the renal site of the sodium-retaining effect of calcineurin inhibitors was unknown. We and others have shown that calcineurin inhibitors increase the activity of the thiazide-sensitive sodium chloride cotransporter through an effect on the kinases WNK and SPAK. Here, we review the pertinent literature on the hypertensinogenic effects of calcineurin inhibitors, including neural, vascular and renal effects, and we propose an integrated model of calcineurin inhibitor-induced hypertension.

Astrocyte control of synaptic transmission and neurovascular coupling

From a structural perspective, the predominant glial cell of the central nervous system, the astrocyte, is positioned to regulate synaptic transmission and neurovascular coupling: the processes of one astrocyte contact tens of thousands of synapses, while other processes of the same cell form endfeet on capillaries and arterioles. The application of subcellular imaging of Ca2+ signaling to astrocytes now provides functional data to support this structural notion. Astrocytes express receptors for many neurotransmitters, and their activation leads to oscillations in internal Ca2+. These oscillations induce the accumulation of arachidonic acid and the release of the chemical transmitters glutamate, d-serine, and ATP. Ca2+ oscillations in astrocytic endfeet can control cerebral microcirculation through the arachidonic acid metabolites prostaglandin E2 and epoxyeicosatrienoic acids that induce arteriole dilation, and 20-HETE that induces arteriole constriction. In addition to actions on the vasculature, the release of chemical transmitters from astrocytes regulates neuronal function. Astrocyte-derived glutamate, which preferentially acts on extrasynaptic receptors, can promote neuronal synchrony, enhance neuronal excitability, and modulate synaptic transmission. Astrocyte-derived d-serine, by acting on the glycine-binding site of the N-methyl-d-aspartate receptor, can modulate synaptic plasticity. Astrocyte-derived ATP, which is hydrolyzed to adenosine in the extracellular space, has inhibitory actions and mediates synaptic cross-talk underlying heterosynaptic depression. Now that we appreciate this range of actions of astrocytic signaling, some of the immediate challenges are to determine how the astrocyte regulates neuronal integration and how both excitatory (glutamate) and inhibitory signals (adenosine) provided by the same glial cell act in concert to regulate neuronal function.

Gender differences in myogenic tone in superoxide dismutase knockout mouse: animal model of oxidative stress

Oxidative stress mediated by prooxidants has been implicated in the pathogenesis of vascular disorders. However, the effect of prooxidants on myogenic regulation of vascular function and the differential influence of gender is not known. SOD, an intracellular enzyme, restricts excess prooxidant levels and may limit vascular dysfunction. We therefore tested the effects of Cu,Zn SOD deficiency on vascular tone in both male and female SOD knockout (SOD−/−) mice. We hypothesized that myogenic tone would be enhanced in SOD−/− mice by excess prooxidants compared with wild-type control mice. Indeed, resistance-sized mesenteric arteries from SOD−/− mice exhibited enhanced myogenic tone compared with control mice. Myogenic tone was lower in female than male control mice. Interestingly, this gender effect was absent in SOD−/− mice, such that myogenic tone of mesenteric arteries from females was equated to that of arteries from males. Furthermore, the pathways that modulate myogenic tone were diverse. In both male and female control mice, inhibition of prostaglandin H synthase (PGHS) and nitric oxide synthase (NOS) pathways enhanced myogenic tone. In female SOD−/− mice, inhibition of PGHS and NOS pathways enhanced myogenic tone to a greater extent compared with control mice. Conversely, in male SOD−/− mice, NOS and PGHS inhibition did not alter tone and only inhibition of gap junctions enhanced myogenic tone. In conclusion, this study revealed enhanced myogenic tone in SOD−/− mice compared with control mice. Furthermore, Cu,Zn SOD deficiency particularly enhanced myogenic tone in female mice such that their vascular tone attained the level of male SOD−/− mice, possibly mediated by prooxidants.

Microvascular filtration is increased in postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) is related to defective peripheral vasoconstriction of dependent extremities with redistributive hypovolemia.

METHODS AND RESULTS

To test whether enhanced microvascular filtration produces leg enlargement, we studied 12 patients 13 to 19 years of age with POTS and defective leg vasoconstriction and 13 age-matched healthy control subjects, with strain-gauge plethysmography used to measure venous pressure (Pv), forearm and calf blood flow, vascular capacitance, and the microvascular filtration coefficient (Kf). Measurements were made while the patient was supine and at steady state during upright tilt to 35 degrees. Supine Pv was not different in POTS, but upright leg Pv tended to be increased above control. Arm and leg peripheral arterial resistance was decreased in the supine and upright positions in patients with POTS compared with control subjects (P=0.01, upright legs). Supine Kf was not significantly increased in the forearm in patients with POTS but was increased in the calf (9.3+/-2.2 versus 5.7+/-2.4 [10(-3)] mL/100 mL per minute per mm Hg, P=0.04), correlating with calf blood flow (rs=0.84, P=0.002). Kf was invariant with orthostasis. The hydraulic contribution to upright filtered flow at 35 degrees tilt, the product of Kf and Pv, was approximately twice that of control (0.41+/-0.09 versus 0.19+/-0.04 mL/100 mL per minute, P=0.04).

CONCLUSIONS

Increased microvascular filtration accounts for enhanced leg swelling in patients with POTS with increased arterial blood flow.

Testosterone depletion contributes to cyclosporine-induced chronic impairment of acetylcholine renovascular relaxations

The immunosuppressant drug cyclosporine causes nephrotoxicity mainly via alterations of renovascular reactivity. This study investigated whether this effect of cyclosporine is modulated by the male gonadal hormone testosterone. The endothelium-dependent and -independent relaxations evoked by acetylcholine and sodium nitroprusside, respectively, were evaluated in phenylephrine-preconstricted isolated perfused kidneys obtained from sham-operated, castrated, and testosterone-replaced castrated (CAS+T) male rats in the absence and presence of cyclosporine. Compared with sham-operated values, short-term (10 days) castration or cyclosporine treatment caused significant and equivalent reductions in plasma testosterone levels and vasorelaxant responses to acetylcholine. Treatment of castrated rats with cyclosporine caused no further attenuation of acetylcholine relaxations. Testosterone replacement of castrated (CAS+T) or cyclosporine-treated castrated (CAS+CyA+T) rats restored plasma testosterone and acetylcholine relaxations to near-sham-operated levels. On the other hand, castration caused significant increases in nitroprusside relaxations versus no effect for cyclosporine. The relaxant responses to nitroprusside in castrated rats were restored to sham-operated levels after testosterone replacement. Plasma urea and creatinine were not affected by castration but were significantly increased by cyclosporine. These findings suggest that testosterone exerts directionally opposite modulatory effects on endothelium-dependent and -independent renal relaxations. Further, the results demonstrate that testosterone depletion may contribute, at least partly, to the inhibitory effect of cyclosporine on renovascular endothelial function. These data are clinically important because endothelial dysfunction contributes to vascular abnormalities associating cyclosporine therapy.

Depressed renal and vascular nitric oxide synthase expression in cyclosporine-induced hypertension

BACKGROUND

Introduction of cyclosporine (CsA) for clinical use has greatly enhanced the outcome of organ transplantation. However, CsA can cause nephrotoxicity and hypertension (HTN). This study was designed to test the hypothesis that CsA-induced HTN is related to depressed nitric oxide (NO) production.

METHODS

Urinary excretion of NO metabolites (NOx) and endothelial and inducible NO synthase (eNOS and iNOS) proteins were determined in thoracic aortas and kidneys of CsA-treated (given CsA 18 mg/kg/day for 3 weeks) and placebo-treated rats. In addition, renal tissue eNOS and iNOS mRNA and aorta iNOS activity were measured.

RESULTS

CsA administration resulted ina significant rise in arterial blood pressure (BP) coupled with a steady decline in urinary NOx excretion, suggesting depressed NO production. This was accompanied by a significant reduction in iNOS protein abundance in the kidney and thoracic aorta but no change in eNOS protein abundance. The fall in renal iNOS protein in CsA-treated rats was accompanied by a parallel decline in iNOS mRNA abundance and enzymatic activity.

CONCLUSION

Administration of CsA for three weeks resulted in a significant rise in BP together with marked reductions in urinary NOx excretion, and renal and vascular iNOS expression. These observations suggest that CsA-induced HTN may be, in part, related to impaired NO production. If true, strategies designed to restore NO availability may mitigate HTN and other vascular complications of CsA therapy.

Selective impairment of endothelium-mediated vasodilation in liver transplant recipients with cyclosporin A-induced hypertension

Arterial hypertension is commonly observed in orthotopic liver transplantation (OLT) recipients receiving cyclosporin A (CsA), but the precise pathogenetic mechanisms remain partially unknown. The aim of this study was to investigate endothelium-dependent and -independent dilation and adrenergic constriction of resistance vessels of OLT recipients treated with CsA. Vascular reactivity was examined in 22 OLT patients, 10 with and 12 without arterial hypertension, and in 10 control subjects by assessing the forearm blood flow response to the brachial artery infusion of increasing concentrations of methacholine chloride, sodium nitroprusside, and phenylephrine. In 10 OLT patients, the response to methacholine was also examined after acetylsalicylate. The ratio of serum nitrite and nitrate to serum creatinine was lower (P < .05) in OLT patients with hypertension than in nonhypertensive patients and controls. Basal forearm flow was similar in the three groups. Methacholine vasodilation was impaired in the hypertensive patients as shown by a lower maximum forearm vasodilator response and a shift in the dose response curve to methacholine to the right compared with the nonhypertensive OLT patients and the controls. The response to methacholine was not modified after salicylate. Forearm flow response to nitroprusside was similar in the three groups. No differences between the patients and the controls were found in the maximum forearm flow contraction in response to phenylephrine. An impairment in endothelium-dependent vasodilation could mediate arterial hypertension in OLT patients immunosuppressed with CsA.

Cyclosporine impairs vasodilation without increased sympathetic activity in humans

Hypertension and nephrotoxicity frequently complicate treatment with cyclosporine; two suggested mechanisms are increased sympathetic activity and altered vascular reactivity. It is difficult to assess these mechanisms in patients receiving cyclosporine after transplantation because of the accompanying major physiological alterations. Therefore, we studied 12 patients with rheumatoid arthritis twice--while they were taking and not taking cyclosporine. We measured vascular response in the dorsal hand vein using the linear variable differential transformer technique. Cyclosporine treatment significantly attenuated vasodilation induced by 60 ng/min isoproterenol (no cyclosporine, 19.8 +/- 3.5% versus cyclosporine, 7.9 +/- 2.2%; P = .02) and prostaglandin E1 at 1000 pg/min (no cyclosporine, 72.6 +/- 10.2% versus cyclosporine 45.6 +/- 9.0%) and 2000 pg/min (no cyclosporine, 100.8 +/- 14.7% versus cyclosporine, 68.6 +/- 8.0%; F = 5.47, P = .047). However, neither vascular response to phenylephrine or nitroglycerin nor sympathetic activity assessed by measurement of norepinephrine spillover with a radioisotope dilution technique was affected by cyclosporine (no cyclosporine, 516.1 +/- 47.9 ng/min versus cyclosporine, 476.6 +/- 51.8 ng/min; P = .42). Cyclosporine impaired venodilation in response to two agonists that act through adenylate cyclase without altering alpha-agonist-induced venoconstriction or sympathetic activity. Therefore, in humans impaired vasodilation rather than sympathetic activation or enhanced vasoconstriction may be an important mechanism for the alterations of vascular tone that occur after long-term cyclosporine administration.

Cyclosporine impairs release of endothelium-derived relaxing factors in epicardial and resistance coronary arteries

BACKGROUND

Cyclosporin A is reported to impair endothelium-mediated vasorelaxation and induce endothelin release in some noncoronary vascular beds. We wished to determine whether acute cyclosporine administration induces endothelial dysfunction in coronary conductance or resistance arteries.

METHODS AND RESULTS

We examined the effect of intracoronary acetylcholine, N omega-nitro-L-arginine methyl ester (L-NAME), L-arginine, nitroglycerin, and adenosine before and after acute cyclosporine administration (3 mg/kg IV over 30 minutes) in anesthetized dogs. Flow velocity was measured with a 0.014-in Doppler wire to assess resistance vessel responses, and epicardial coronary lumen area was simultaneously measured with a 4.3F, 30-MHz imaging catheter inserted over the Doppler wire. In 6 dogs, acetylcholine-induced increase in flow velocity was attenuated by cyclosporine in vehicle (137% to 55% at 10(-5) mol/L, P < .001), as was acetylcholine-induced epicardial vasodilation (14.1% to 6.7% at 10(-5) mol/L, P < .001). Vasodilation in response to intracoronary nitroglycerin (200 micrograms) and adenosine (6 mg) were unchanged by cyclosporine. Epicardial vasoconstriction with L-NAME (10(-4) mol/L) was reduced by cyclosporine (Pre, 7.4 +/- 0.9%; Post, 2.6 +/- 1.2%; P = .04), but L-arginine (10(-4) mol/L) had no effect after cyclosporine. In another 5 dogs, pure cyclosporine impaired acetylcholine-induced vasodilatation to the same degree as cyclosporine in vehicle (Cremophor); vehicle infusion did not impair endothelial function. In 5 more dogs, cyclosporine did not increase either arterial or coronary sinus concentrations of endothelin-1.

CONCLUSIONS

The present study shows that cyclosporine acutely impairs release of endothelium-derived relaxing factor in canine conductance and resistance coronary arteries and provides evidence for decreased epicardial nitric oxide release after cyclosporine. The potential contribution of acute cyclosporine-induced coronary endothelial dysfunction to posttransplant vasculopathy needs further study.

Vascular mechanisms of cyclosporin-induced hypertension in the rat

Numerous studies have explored the pathogenesis of cyclosporin A (CysA)-induced hypertension; however, none has assessed the impact of CysA treatment on resistance arteries in the setting of elevated blood pressure. Therefore, we studied the chronic effect of CysA on rat mesenteric artery resistance vessels (ex vivo). CysA (25 mg/kg per d for 7 d), but not vehicle, significantly raised systolic blood pressure (13.4 +/- 2.2 mmHg, P < 0.003, n = 9 per group). The resistance vessels from CysA-treated rats showed a small but significant decrease in norepinephrine sensitivity (P < 0.03) and a pronounced decrease in endothelium-dependent and -independent relaxation (P < 0.001) compared to controls. Endothelin-1 sensitivity tended to be diminished (P = 0.07). The direct (in vitro) effect of CysA was subsequently evaluated in resistance vessels from nontreated animals (n = 8) and exposed to CysA (2 micrograms/ml) for 24 h. As observed in vivo, CysA significantly decreased endothelium-dependent and -independent relaxations (P < 0.05) and attenuated norepinephrine sensitivity (P = 0.06). Methylene blue, a nitric oxide quencher, significantly inhibited the acetylcholine-induced relaxation in control, but not in CysA vessels, suggesting a selective action of CysA on the nitric oxide pathway. We conclude that CysA-induced hypertension is the consequence of a primary effect on resistance vessel relaxation, not increased vasoconstriction, as previously suggested.

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.

Effects of the immunosuppressant cyclosporine on the circulation of heart transplant recipients

The effect of cyclosporine on the systemic circulation and on heart rate is unknown for heart transplant recipients. Thirty-four heart transplant recipients were studied by right-sided cardiac catheterization after endomyocardial biopsy. A direct linear relation was found between systemic and pulmonary vascular resistance and cyclosporine trough blood levels, which were negatively related to heart rate. The effect of cyclosporine on pulmonary vascular resistance, however, was not statistically significant by multivariate analysis when patient age was considered. In contrast, renal function appeared unrelated to systemic vascular resistance or heart rate. It appears that cyclosporine trough blood levels may have a direct effect on systemic vascular resistance as well as an unexplained negative chronotropic effect on heart rate.

The pathophysiology of Sandimmune (cyclosporine) in man and animals

Part I: The side-effects of Sandimmune that have been of most significance clinically are renal dysfunction, renal vascular damage and arterial hypertension. To examine the nature and the origin of such effects, the actions of Sandimmune on the renal tubule, the renal vessels and systemic vessels have been analyzed. To evaluate whether common vasoconstrictory systems may be involved, changes in the renin-angiotensin-aldosterone system and prostaglandin-thromboxane system have been assessed. Comparison between animal and human data obtained in vivo and in vitro shows the actions of Sandimmune on the renal tubule to be modest and involve only a few specific effects. The major action of Sandimmune is on the vessels, vasoconstriction being the major cause of renal dysfunction and also the cause of arterial hypertension. Neither the circulating renin-angiotension-aldosterone system nor the prostaglandin-thromboxane system is clearly responsible for vasoconstriction. Although not itself a vasoconstrictor, Sandimmune seems to modulate the constrictory and dilatory response to other agents in several vascular beds.