Obstructive sleep apnea is characterized by recurrent episodes of pharyngeal collapse during sleep, resulting in intermittent hypoxia (IH), and is associated with a high incidence of hypertension and accelerated renal failure. In rodents, endothelin (ET)-1 contributes to IH-induced hypertension, and ET-1 levels inversely correlate with glomerular filtration rate in patients with end-stage chronic kidney disease (CKD). Therefore, we hypothesized that a dual ET receptor antagonist, macitentan (Actelion Pharmaceuticals), will attenuate and reverse hypertension and renal dysfunction in a rat model of combined IH and CKD. Male Sprague-Dawley rats received one of three diets (control, 0.2% adenine, and 0.2% adenine + 30 mg·kg−1·day−1macitentan) for 2 wk followed by 2 wk of recovery diet. Rats were then exposed for 4 wk to air or IH (20 short exposures/h to 5% O2-5% CO27 h/day during sleep). Macitentan prevented the increases in mean arterial blood pressure caused by CKD, IH, and the combination of CKD + IH. However, macitentan did not improve kidney function, fibrosis, and inflammation. After CKD was established, rats were exposed to air or IH for 2 wk, and macitentan feeding continued for 2 more wk. Macitentan reversed the hypertension in IH, CKD, and CKD + IH groups without improving renal function. Our data suggest that macitentan could be an effective antihypertensive in patients with CKD and irreversible kidney damage as a way to protect the heart, brain, and eyes from elevated arterial pressure, but it does not reverse toxin-induced tubule atrophy.

Hydrogen sulfide (H 2 S) is a small, gaseous molecule with poor solubility in water that is generated by multiple pathways in many species including humans. It acts as a signaling molecule in many tissues with both beneficial and pathological effects. This article discusses its many actions in the vascular system and the growing evidence of its role to regulate vascular tone, angiogenesis, endothelial barrier function, redox, and inflammation. Alterations in some disease states are also discussed including potential roles in promoting tumor growth and contributions to the development of metabolic disease.

These results suggest that CSE’s protective role in the vasculature is impaired by simulated sleep apnea, which also upregulates CSE in the carotid body. Thus, this enzyme system can exert both pro- and antihypertensive effects and may contribute to elevated SNS outflow in sleep apnea.

Small resistance size arteries are key players in vascular resistance and overall blood pressure control. We previously demonstrated that within endothelial cells (EC), H2S‐mediated vasodilation involves activation of transient receptor potential cation channel subfamily V member 4 (TRPV4)‐dependent Ca2+ influx to activate nearby large‐conductance Ca2+‐activated potassium (BK) channel in resistance‐size arteries. Comparison of vasodilatory responses in large and small (resistance‐size) arteries show that small arteries dilate at lower concentrations of H2S donors vs large arteries. The importance of endogenous H2S in endothelium‐dependent vasodilatory responses in small resistance size arteries highlights a role for H2S in regulating blood pressure and flow. However, little is known of the differences in H2S signaling in large and small arteries and how these differences modulate vasodilation. Based on previous reports that cell membrane cholesterol negatively regulates TRPV4 mobility and BK activity, we hypothesized that H2S‐mediated vasodilation is disrupted by elevated EC membrane cholesterol in large arteries. We first verified EC plasma membrane cholesterol content was higher in large vs small arteries by immunofluorescence using the cholesterol stain, filipin III (20 µg/ml) in EC labeled with the glycocalyx marker tomato lectin (20 µg/ml) and the nuclear stain SYTOX green (large 145.20 ± 13.67, small: 59.85 ± 5.50, p = 0.0004, n = 5 animals/group). Next, we examined the effect of cholesterol depletion using methyl β cyclodextrin (MBCD, 100 μM), on dilatory responses to H2S in large (300‐380 μm) and small (60‐130 μm) mesenteric arteries using the H2S donor, NaHS (1, 10 or 100 μM). In large arteries, MBCD pretreatment significantly enhanced H2S‐mediated vasodilation (10 μM +vehicle: 0.72% ± 2.17, +MBCD: 9.71% ± 2.710, p = 0.026), (100 μM +vehicle: 2.25% ± 5.74, +MBCD: 20.55% ± 7.687, p < 0.0001) n = 5 animals/group. Although NaHS dilated small arteries more than large arteries, there was no effect of cholesterol depletion in small arteries (1 μM +vehicle: 16.25% ± 2.36, +MBCD: 16.29% ± 4.44, NS), (10 μM +vehicle: 33.22% ± 7.10, +MBCD: 39.00% ± 5.85, NS), (100 μM +vehicle: 59.84% ±5.98, +MBCD: 63.18% ± 4.639, NS) n = 3 animals/group. Additionally, immunofluorescence studies of EC TRPV4 expression showed no difference between large and small arteries (large 39.6 ± 12.9, small 41.8 ± 14.1, NS) n =3 animals/group. These studies suggest that membrane cholesterol disrupts H2S‐mediated vasodilation and contributes to the relative differences in sensitivity to H2S‐mediated vasodilation in large and small arteries.

Hydrogen sulfide (H2S), the most recently described endothelium‐derived vasodilator, is predominantly produced in the endothelium by cystathionine γ‐lyase (CSE). We previously demonstrated that within endothelial cells (ECs), H2S‐mediated vasodilation involves activation of transient receptor potential cation channel subfamily V member 4 (TRPV4)‐dependent Ca2+ influx and large conductance Ca2+‐activated potassium (BK) channel. In addition, a single concentration of H2S donor NaHS (1 μM) dilated small mesenteric arteries (<100 μm) but had no effect in large mesenteric arteries (>300 μm). Furthermore, inhibiting CSE generation of H2S with β‐cyanoalanine (BCA, 100 μM) impaired acetylcholine (ACh)‐induced dilation in small mesenteric arteries, but had no effect in large mesenteric arteries. These data suggest that H2S‐induced dilation is prominent and important in small resistance arteries but not in larger arteries. It is possible that decreased availability of TRPV4 and/or BK in larger arteries is responsible for the diminished sensitivity to H2S‐induced vasodilation. Previous reports suggest that membrane cholesterol negatively regulates TRPV4 mobility and BK activity. Our current study tested the hypothesis that H2S‐mediated vasodilation is inhibited by membrane cholesterol. Mesenteric arteries induced vasodilation was assessed in pressurized large rat mesenteric arteries (>300 μm). Isolated pressurized mesenteric arteries (320 μm – 360 μm) were pretreated luminally with vehicle (HEPES) or the cholesterol‐depleting agent, methyl β cyclodextran (MBCD, 100 μM) and exposed to NaHS (100 μM). NaHS‐induced dilation in U46619 pre‐constricted arteries was significantly enhanced by MBCD pretreatment (+vehicle: 6.78% ± 1.6, +MBCD: 17.10% ± 6.8, p < 0.05, n=3–4 animals/group). These studies suggest that membrane cholesterol disrupts H2S‐mediated vasodilation. Ongoing studies in isolated mesenteric arteries of different sizes are investigating endothelial cell membrane cholesterol content and the effect of cholesterol depletion on TRPV4‐dependent Ca2+ influx in large and small mesenteric arteries.Support or Funding InformationFunding provided by the NIH HL12330 & HL7736‐23This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.