Asif R. Pathan

Stretch-Activation of Angiotensin II Type 1a Receptors Contributes to the Myogenic Response of Mouse Mesenteric and Renal Arteries

Rationale: Vascular wall stretch is the major stimulus for the myogenic response of small arteries to pressure. The molecular mechanisms are elusive, but recent findings suggest that G protein–coupled receptors can elicit a stretch response. Objective: To determine whether angiotensin II type 1 receptors (AT1R) in vascular smooth muscle cells exert mechanosensitivity and identify the downstream ion channel mediators of myogenic vasoconstriction. Methods and Results: We used mice deficient in AT1R signaling molecules and putative ion channel targets, namely AT1R, angiotensinogen, transient receptor potential channel 6 (TRPC6) channels, or several subtypes of the voltage-gated K+ (Kv7) gene family (KCNQ3, 4, or 5). We identified a mechanosensing mechanism in isolated mesenteric arteries and in the renal circulation that relies on coupling of the AT1R subtype a to a Gq/11 protein as a critical event to accomplish the myogenic response. Arterial mechanoactivation occurs after pharmacological block of AT1R and in the absence of angiotensinogen or TRPC6 channels. Activation of AT1R subtype a by osmotically induced membrane stretch suppresses an XE991-sensitive Kv channel current in patch-clamped vascular smooth muscle cells, and similar concentrations of XE991 enhance mesenteric and renal myogenic tone. Although XE991-sensitive KCNQ3, 4, and 5 channels are expressed in vascular smooth muscle cells, XE991-sensitive K+ current and myogenic contractions persist in arteries deficient in these channels. Conclusions: Our results provide definitive evidence that myogenic responses of mouse mesenteric and renal arteries rely on ligand-independent, mechanoactivation of AT1R subtype a. The AT1R subtype a signal relies on an ion channel distinct from TRPC6 or KCNQ3, 4, or 5 to enact vascular smooth muscle cell activation and elevated vascular resistance.

Impact of Cell Therapy on Myocardial Perfusion and Cardiovascular Outcomes in Patients With Angina Refractory to Medical Therapy A Systematic Review and Meta-Analysis

RATIONALE The effect of stem/progenitor cells on myocardial perfusion and clinical outcomes in patients with refractory angina remains unclear because studies published to date have been small phase I-II trials. OBJECTIVE We performed a meta-analysis of randomized controlled trials to evaluate the effect of cell-based therapy in patients with refractory angina who were ineligible for coronary revascularization. METHODS AND RESULTS Several data sources were searched from inception to September 2015, which yielded 6 studies. The outcomes pooled were indices of angina (anginal episodes, Canadian Cardiovascular Society angina class, exercise tolerance, and antianginal medications), myocardial perfusion, and clinical end points. We combined the reported clinical outcomes (myocardial infarction, cardiac-related hospitalization, and mortality) into a composite end point (major adverse cardiac events). Mean difference (MD), standardized mean differences, or odds ratio were calculated to assess relevant outcomes. Our analysis shows an improvement in anginal episodes (MD, -7.81; 95% confidence interval [CI], -15.22 to -0.41), use of antianginal medications (standardized MD, -0.59; 95% CI, -1.03 to -0.14), Canadian Cardiovascular Society class (MD, -0.58; 95% CI, -1.00 to -0.16), exercise tolerance (standardized MD, 0.331; 95% CI, 0.08 to 0.55), and myocardial perfusion (standardized MD, -0.49; 95% CI, -0.76 to -0.21) and a decreased risk of major adverse cardiac events (odds ratio, 0.49; 95% CI, 0.25 to 0.98) and arrhythmias (odds ratio, 0.25; 95% CI, 0.06 to 0.98) in cell-treated patients when compared with patients on maximal medical therapy. CONCLUSIONS The present meta-analysis indicates that cell-based therapies are not only safe but also lead to an improvement in indices of angina, relevant clinical outcomes, and myocardial perfusion in patients with refractory angina. These encouraging results suggest that larger, phase III randomized controlled trials are in order to conclusively determine the effect of stem/progenitor cells in refractory angina.

Inositol 1,4,5-Trisphosphate (IP3) Receptor Up-regulation in Hypertension Is Associated with Sensitization of Ca2+ Release and Vascular Smooth Muscle Contractility

Background: The role of the vascular IP3 receptor (IP3R) in hypertension is unknown. Results: IP3R are up-regulated in vascular smooth muscle (VSM) in hypertension through the calcineurin-NFAT pathway. Conclusion: Up-regulated IP3R in VSM sensitize Ca2+ release and enhance contraction. Significance: Up-regulated vascular IP3R may contribute to vascular resistance in hypertension. Resistance arteries show accentuated responsiveness to vasoconstrictor agonists in hypertension, and this abnormality relies partly on enhanced Ca2+ signaling in vascular smooth muscle (VSM). Although inositol 1,4,5-triphosphate receptors (IP3Rs) are abundant in VSM, their role in the molecular remodeling of the Ca2+ signaling machinery during hypertension has not been addressed. Therefore, we compared IP3R expression and function between mesenteric arteries of normotensive and hypertensive animals. Levels of IP3R transcript and protein were significantly increased in mesenteric arteries of hypertensive animals, and pharmacological inhibition of the IP3R revealed a higher contribution of IP3-dependent Ca2+ release to vascular contraction in these arteries. Subsequently, we established cultured aortic VSM A7r5 cells as a cellular model that replicates IP3R up-regulation during hypertension by depolarizing the VSM cell membrane. IP3R up-regulation requires Ca2+ influx through L-type Ca2+ channels, followed by activation of the calcineurin-NFAT axis, resulting in IP3R transcription. Functionally, IP3R up-regulation in VSM is associated with enhancement and sensitization of IP3-dependent Ca2+ release, resulting in increased VSM contraction in response to agonist stimulation.

Postsynaptic density-95 scaffolding of Shaker-type K⁺ channels in smooth muscle cells regulates the diameter of cerebral arteries.

Non‐Technical Summary  Shaker‐type potassium channels are found on the smooth muscle cells of blood vessels in the brain and are important in keeping the blood vessels open or dilated. We show that a protein called PSD95, previously found in nerve cells, interacts with these potassium channels. PSD95 may act as a scaffold to ensure that the potassium channels are expressed in adequate numbers and in the right location on the smooth muscle cells. When we reduced the number of PSD95 proteins, we saw that the potassium channels were also reduced and the blood vessels were not as dilated compared to blood vessels with normal amounts of PSD95. This research may help us understand how abnormal constriction of blood vessels in the brain occurs in diseases such as high blood pressure and stroke.

Oral bioavailability, efficacy and gastric tolerability of P2026, a novel nitric oxide-releasing diclofenac in rat.

The present study was designed to evaluate, P2026 [(2-((2-(nitrooxy)ethyl)disulfanyl)ethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate)], a novel NO (nitric oxide) donor prodrug of diclofenac for its ability to release NO and diclofenac, and whether P2026 provides advantage of improved activity/gastric tolerability over diclofenac. Oral bioavailability of P2026 was estimated from plasma concentration of diclofenac and nitrate/nitrite (NOx). Anti-inflammatory activity was evaluated in three different models of inflammation: acute (carrageenan-induced paw oedema), chronic (adjuvant-induced arthritis), and systemic (lipopolysaccharide-induced endotoxic shock). Gastric tolerability was evaluated from compound’s propensity to cause gastric ulcers. P2026 exhibited dose-dependent diclofenac and NOx release. Similar to diclofenac, P2026 showed potent anti-inflammatory activity in acute and chronic model, whereas it improved activity in systemic model. Both diclofenac and P2026 inhibited gastric prostaglandin, but only diclofenac produced dose-dependent haemorrhagic ulcers. Thus, the results suggest that coupling of NO and diclofenac contribute to improved gastric tolerability while retaining the anti-inflammatory properties of diclofenac.

Two-Pore Domain K+ Channels: Evidence for TWIK-2 in Blood Pressure Regulation

See related article, pp 672–678 The dynamic regulation of blood pressure relies on the ability of small arteries and arterioles to finely adjust their diameters to maintain peripheral vascular resistance and cardiovascular homeostasis. At the level of the vascular smooth muscle cell (VSMC), contraction is mediated by elevations in cytosolic Ca2+ concentration enabled by Ca2+-conducting channels located intracellularly or in the plasma membrane. The l-type Ca2+ channel opened by membrane depolarization is one key source of activator Ca2+ in VSMCs, and an upregulation of these channels may contribute to hypertension.1 In contrast, K+ channels in the plasma membrane mediate hyperpolarizing K+ efflux to set the resting membrane potential (Em) of VSMCs. A myriad of K+ channels, each showing unique properties and modulated by different neuroendocrine and mechanical factors, act in concert. The hyperpolarizing K+ current closes l-type Ca2+ channels to favor arterial dilation and counteracts pressor influences that could inordinately elevate blood pressure. Different gene families of K+ channels, including the voltage-gated K+ channels, Ca2+-activated K+ channels, inwardly rectifying K+ channels, and ATP-sensitive K+ channels, have been shown to dampen vascular excitability under various conditions. However, some of their properties, including voltage and Ca2+-dependent activation or metabolic dependence, are not well suited for stabilizing the resting Em. On the other hand, “leak” K+ channels, also referred to as “background” or “baseline” K+ channels, were postulated to lack voltage- or time-dependent inactivation and thereby represent ideal candidates for setting the resting Em …

Impact of Cell Therapy on Myocardial Perfusion and Cardiovascular Outcomes in Patients With Angina Refractory to Medical TherapyNovelty and Significance: A Systematic Review and Meta-Analysis

RATIONALE The effect of stem/progenitor cells on myocardial perfusion and clinical outcomes in patients with refractory angina remains unclear because studies published to date have been small phase I-II trials. OBJECTIVE We performed a meta-analysis of randomized controlled trials to evaluate the effect of cell-based therapy in patients with refractory angina who were ineligible for coronary revascularization. METHODS AND RESULTS Several data sources were searched from inception to September 2015, which yielded 6 studies. The outcomes pooled were indices of angina (anginal episodes, Canadian Cardiovascular Society angina class, exercise tolerance, and antianginal medications), myocardial perfusion, and clinical end points. We combined the reported clinical outcomes (myocardial infarction, cardiac-related hospitalization, and mortality) into a composite end point (major adverse cardiac events). Mean difference (MD), standardized mean differences, or odds ratio were calculated to assess relevant outcomes. Our analysis shows an improvement in anginal episodes (MD, -7.81; 95% confidence interval [CI], -15.22 to -0.41), use of antianginal medications (standardized MD, -0.59; 95% CI, -1.03 to -0.14), Canadian Cardiovascular Society class (MD, -0.58; 95% CI, -1.00 to -0.16), exercise tolerance (standardized MD, 0.331; 95% CI, 0.08 to 0.55), and myocardial perfusion (standardized MD, -0.49; 95% CI, -0.76 to -0.21) and a decreased risk of major adverse cardiac events (odds ratio, 0.49; 95% CI, 0.25 to 0.98) and arrhythmias (odds ratio, 0.25; 95% CI, 0.06 to 0.98) in cell-treated patients when compared with patients on maximal medical therapy. CONCLUSIONS The present meta-analysis indicates that cell-based therapies are not only safe but also lead to an improvement in indices of angina, relevant clinical outcomes, and myocardial perfusion in patients with refractory angina. These encouraging results suggest that larger, phase III randomized controlled trials are in order to conclusively determine the effect of stem/progenitor cells in refractory angina.

Impact of Cell Therapy on Myocardial Perfusion and Cardiovascular Outcomes in Patients With Angina Refractory to Medical TherapyNovelty and Significance

RATIONALE The effect of stem/progenitor cells on myocardial perfusion and clinical outcomes in patients with refractory angina remains unclear because studies published to date have been small phase I-II trials. OBJECTIVE We performed a meta-analysis of randomized controlled trials to evaluate the effect of cell-based therapy in patients with refractory angina who were ineligible for coronary revascularization. METHODS AND RESULTS Several data sources were searched from inception to September 2015, which yielded 6 studies. The outcomes pooled were indices of angina (anginal episodes, Canadian Cardiovascular Society angina class, exercise tolerance, and antianginal medications), myocardial perfusion, and clinical end points. We combined the reported clinical outcomes (myocardial infarction, cardiac-related hospitalization, and mortality) into a composite end point (major adverse cardiac events). Mean difference (MD), standardized mean differences, or odds ratio were calculated to assess relevant outcomes. Our analysis shows an improvement in anginal episodes (MD, -7.81; 95% confidence interval [CI], -15.22 to -0.41), use of antianginal medications (standardized MD, -0.59; 95% CI, -1.03 to -0.14), Canadian Cardiovascular Society class (MD, -0.58; 95% CI, -1.00 to -0.16), exercise tolerance (standardized MD, 0.331; 95% CI, 0.08 to 0.55), and myocardial perfusion (standardized MD, -0.49; 95% CI, -0.76 to -0.21) and a decreased risk of major adverse cardiac events (odds ratio, 0.49; 95% CI, 0.25 to 0.98) and arrhythmias (odds ratio, 0.25; 95% CI, 0.06 to 0.98) in cell-treated patients when compared with patients on maximal medical therapy. CONCLUSIONS The present meta-analysis indicates that cell-based therapies are not only safe but also lead to an improvement in indices of angina, relevant clinical outcomes, and myocardial perfusion in patients with refractory angina. These encouraging results suggest that larger, phase III randomized controlled trials are in order to conclusively determine the effect of stem/progenitor cells in refractory angina.

Chapter 84 – Potassium, Sodium, and Chloride Channels in Smooth Muscle Cells

The opening of potassium (K + ) channels mediates hyperpolarization and vasodilation of small arteries and arterioles, thereby modulating blood flow to critical organs and regulating blood pressure. Many gene families of K + channels with unique properties act in concert to determine the level of vascular tone, and also to mediate specialized dilator responses to endothelial factors, metabolic stimuli or mechanical stress. This chapter will emphasize several types of K + channels in vascular smooth muscle cells (SMCs) that provide a critical dilator influence in different vascular beds. Subsequently, we will focus on two of the lesser studied ion channels in SMCs, the voltage-gated Na + channels and the Cl - channel families, which may participate in the regulation of vascular SMC excitability. Our discussion of each ion channel also will briefly broaden to include the non-vascular SMCs of the respiratory and gastrointestinal tracts. Ultimately, the ion channel families expressed in SMCs will collectively modulate cell excitability so that SMC-containing organs can optimally perform their physiological functions.

Chapter 44 – Smooth Muscle Excitability

The resting membrane potential and excitability profiles of smooth muscle cells (SMCs) determine the patterns of contraction and relaxation in SMC-containing organs including the vasculature, the gastrointestinal tract and the respiratory system. The populations of ion channels are organ and site-specific and thereby uniquely situated to support the distinctly different physiological functions of each organ. This chapter has taken the liberty of focusing on the contribution of K + and Ca 2+ -conducting channels to SMC excitation–contraction coupling using vascular smooth muscle as an initial model. Subsequent sections emphasize that the SMCs of different organ systems express unique blueprints of ion channels, which are subjected to modulation by external stimuli including neurotransmitters, autocoids and other specialized input to determine the final level of smooth muscle tone.