Interruption of central neuronal pathway of imidazoline I1 receptor mediates the hypertensive effect of cyclosporine in rats

Brain α2δ-1-Bound NMDA Receptors Drive Calcineurin Inhibitor-Induced Hypertension

BACKGROUND

Calcineurin is highly enriched in immune T cells and the nervous system. Calcineurin inhibitors, including cyclosporine and tacrolimus (FK506), are the cornerstone of immunosuppressive regimens for preserving transplanted organs and tissues. However, these drugs often cause persistent hypertension owing to excess sympathetic outflow, which is maintained by N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory input to the hypothalamic paraventricular nucleus (PVN). It is unclear how calcineurin inhibitors increase NMDAR activity in the PVN to augment sympathetic vasomotor activity. α2δ-1 (encoded by the Cacna2d1 gene), known colloquially as a calcium channel subunit, is a newly discovered NMDAR-interacting protein. In this study, we determined whether α2δ-1 plays a role in calcineurin inhibitor-induced synaptic NMDAR hyperactivity in the PVN and hypertension development.

METHODS

Immunoblotting and coimmunoprecipitation assays were used to quantify synaptic protein levels and the physical interaction between GluN1 (the obligatory NMDAR subunit) and α2δ-1. Whole-cell patch-clamp recordings of retrogradely labeled, spinally projecting PVN were conducted in perfused brain slices to measure presynaptic and postsynaptic NMDAR activity. Radio-telemetry was implanted in rodents to continuously record arterial blood pressure in conscious states.

RESULTS

Prolonged treatment with FK506 in rats significantly increased protein levels of α2δ-1, GluN1, and the α2δ-1-GluN1 complex in PVN synaptosomes. These effects were blocked by inhibiting α2δ-1 with gabapentin or interrupting the α2δ-1-NMDAR interaction with an α2δ-1 C-terminus peptide. Treatment with FK506 potentiated the activity of presynaptic and postsynaptic NMDARs in spinally projecting PVN neurons; such effects were abolished by gabapentin, Cacna2d1 knockout, or α2δ-1 C-terminus peptide. Furthermore, microinjection of α2δ-1 C-terminus peptide into the PVN diminished renal sympathetic nerve discharges and arterial blood pressure that had been increased by FK506 treatment. Remarkably, concurrent administration of gabapentin prevented the development of FK506-induced hypertension in rats. Additionally, FK506 treatment induced sustained hypertension in wild-type mice but not in Cacna2d1 knockout mice.

CONCLUSIONS

α2δ-1 is essential for calcineurin inhibitor-induced increases in synaptic NMDAR activity in PVN presympathetic neurons and sympathetic outflow. Thus, α2δ-1 and α2δ-1-bound NMDARs represent new targets for treating calcineurin inhibitor-induced hypertension. Gabapentinoids (gabapentin and pregabalin) could be repurposed for treating calcineurin inhibitor-induced neurogenic hypertension.

Three new oxygenated yohimbane-type alkaloids from Ophiorrhiza japonica

A series of oxygenated yohimbane alkaloids, including three new compounds, ophiorrhines H-J (1-3), and seven known compounds, were isolated from the aerial parts of Ophiorrhiza japonica. The structures with absolute configurations were elucidated by extensive MS and NMR spectroscopic methods, as well as the single crystal X-ray diffraction and ECD calculations. Ophiorrhines H (1) and I (2) represent key oxygenated intermediates in the formation of aromatic ring E in the demethoxycarbonyl-3,14-dihydrogambirtannine (10). Ophiorrhine J (3) is a highly oxidized yohimbane derivative with the planar superconjugated system. The cytotoxic activities of all alkaloids against five human cancer cell lines were evaluated.

Crosstalk between central pathways of nitric oxide and carbon monoxide in the hypertensive action of cyclosporine

Although the intermediary role of central neurons in the hypertensive and sympathoexcitatory actions of cyclosporine (CSA) has been recognized in previous studies including our own, the underlying mechanism remains obscure. In this study, we tested the hypothesis that central pathways of nitric oxide (NO) and carbon monoxide (CO) modulate the blood pressure (BP) response elicited by CSA in conscious rats. Hemodynamic effects of CSA were evaluated in absence and presence of maneuvers that inhibit or facilitate biosynthesizing enzymes of NO (NOS) or CO (heme oxygenase, HO). CSA (20mg/kg i.v.) produced abrupt increases in BP that peaked in 5min and maintained for at least 45min. The hypertensive effect of CSA disappeared in rats pretreated intracisternally (i.c.) with N(ω)-nitro-l-arginine methyl ester (L-NAME, nonselective NOS inhibitor), N(5)-(1-iminoethyl)-l-ornithine (L-NIO, selective eNOS inhibitor), N(ω)-propyl-l-arginine (NPLA, selective nNOS inhibitor), or 1H-[1,2,4] oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, guanylate cyclase inhibitor), suggesting the importance of central eNOS/nNOS/GC cascade in CSA-induced hypertension. L-NAME also abolished the hypotension caused by the sympatholytic drug moxonidine, indicating a tonic sympathoinhibitory action for NO. The inhibition of HO activity by zinc protoporphyrin IX (ZnPP) abrogated the hypertensive action of CSA. The abolition by L-NAME or ZnPP of CSA hypertension was compromised upon simultaneous i.c. exposure to hemin (HO substrate) and l-arginine (NOS substrate), respectively. Together, the interruption of the mutually facilitated NOS/NO and HO/CO pathways and coupled GC/cGMP in central neuronal pools accounts, at least partly, for the hypertensive and perhaps sympathoexcitatory actions of CSA.

Role of adenosine A2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100μg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.

Pioglitazone abrogates cyclosporine-evoked hypertension via rectifying abnormalities in vascular endothelial function

In addition to insulin sensitization, the thiazolidenedione drug pioglitazone exhibits favorable circulatory effects. Here, we hypothesized that pioglitazone protects against the hypertension and related vascular derangements caused by the immunosuppressant drug cyclosporine (CSA). Compared with vehicle (olive oil)-treated rats, chronic treatment with CSA (20mg/kg/day s.c., for 14 days) increased blood pressure (BP), reduced the aortic protein expression of phosphorylated eNOS (p-eNOS), and impaired responsiveness of isolated aortas to endothelium-dependent vasorelaxations induced by carbachol. The effects of CSA on BP, aortic p-eNOS, and carbachol relaxations were abolished upon concurrent administration of pioglitazone (2.5mg/kg/day). Serum levels of adiponectin, an adipose tissue-derived adipokine, were not altered by CSA but showed significant elevations in rats treated with pioglitazone or pioglitazone plus CSA. The possibility that alterations in the antioxidant and/or lipid profile contributed to the CSA-pioglitazone BP interaction was investigated. Pioglitazone abrogated the oxidative (aortic superoxide dismutase), lipid peroxidation (aortic malondialdyde), and dyslipidemic (serum LDL levels and LDL/HDL ratio) effects of CSA. Histologically, CSA caused focal disruption in the endothelial lining of the aorta and this effect disappeared in rats co-treated with pioglitazone. Collectively, pioglitazone abrogates the hypertensive effect of CSA via ameliorating detrimental changes in vascular endothelial NOS/NO pathway and oxidative and lipid profiles caused by CSA.

Facilitation of central imidazoline I(1)-site/extracellular signal-regulated kinase/p38 mitogen-activated protein kinase signalling mediates the hypotensive effect of ethanol in rats with acute renal failure

BACKGROUND AND PURPOSE

This study investigated the role of central sympathetic activity and related mitogen-activated protein kinase (MAPK) signalling in the cardiovascular effects of ethanol in a model of acute renal failure (ARF).

EXPERIMENTAL APPROACH

The effects of pharmacological interventions that inhibit peripheral or central sympathetic activity or MAPK on the cardiovascular actions of ethanol in rats with ARF induced by glycerol were evaluated.

KEY RESULTS

Glycerol (50%, 10 mL.kg(-1), i.m.) caused progressive increases and decreases in blood pressure (BP) and heart rate (HR) respectively. Subsequent i.v. ethanol (0.25 or 1 g.kg(-1)) elicited dose-related changes in BP (decreases) and HR (increases). These effects were replicated after intracisternal (i.c.) administration of ethanol. Blockade of nicotinic cholinoceptors (nAChR, hexamethonium, 20 mg.kg(-1)) or alpha(1)-adrenoceptors (prazosin, 1 mg.kg(-1)) attenuated cardiovascular effects of ethanol. Ethanol hypotension was also attenuated after the centrally acting sympatholytic drug moxonidine (selective I(1)-site agonist, 100 microg.kg(-1) i.v.), but not guanabenz (selective alpha(2)-receptor agonist, 30 microg.kg(-1), i.v.), suggesting involvement of central circuits of I(1) sites in ethanol-evoked hypotension. Selective blockade I(1) sites (efaroxan) but not alpha(2) (yohimbine) adrenoceptors abolished the hypotensive response to ethanol. Intracisternal administration of PD98059 or SB203580, inhibitors of extracellular signal-regulated kinase (ERK 1/2) and p38 MAPK, respectively, reduced the hypotensive action of moxonidine or ethanol. When used simultaneously, the two MAPK inhibitors produced additive attenuation of ethanol hypotension.

CONCLUSIONS AND IMPLICATIONS

Sympathoinhibitory pathways of central I(1)-sites and downstream ERK/p38 MAPK signalling were involved in the hypotensive action of ethanol in ARF.