Vasodilator signals from perivascular adipose tissue

Nonclinical Safety Biomarkers of Drug-induced Vascular Injury

Better biomarkers are needed to identify, characterize, and/or monitor drug-induced vascular injury (DIVI) in nonclinical species and patients. The Predictive Safety Testing Consortium (PSTC), a precompetitive collaboration of pharmaceutical companies and the U.S. Food and Drug Administration (FDA), formed the Vascular Injury Working Group (VIWG) to develop and qualify translatable biomarkers of DIVI. The VIWG focused its research on acute DIVI because early detection for clinical and nonclinical safety monitoring is desirable. The VIWG developed a strategy based on the premise that biomarkers of DIVI in rat would be translatable to humans due to the morphologic similarity of vascular injury between species regardless of mechanism. The histomorphologic lexicon for DIVI in rat defines degenerative and adaptive findings of the vascular endothelium and smooth muscles, and characterizes inflammatory components. We describe the mechanisms of these changes and their associations with candidate biomarkers for which advanced analytical method validation was completed. Further development is recommended for circulating microRNAs, endothelial microparticles, and imaging techniques. Recommendations for sample collection and processing, analytical methods, and confirmation of target localization using immunohistochemistry and in situ hybridization are described. The methods described are anticipated to aid in the identification and qualification of translational biomarkers for DIVI.

One man's side effect is another man's therapeutic opportunity: targeting Kv7 channels in smooth muscle disorders

Retigabine is a first in class anticonvulsant that has recently undergone clinical trials to test its efficacy in epileptic patients. Retigabine's novel mechanism of action - activating Kv7 channels - suppresses neuronal activity to prevent seizure generation by hyperpolarizing the membrane potential and suppressing depolarizing surges. However, Kv7 channels are not expressed exclusively in neurones and data generated over the last decade have shown that Kv7 channels play a key role in various smooth muscle systems of the body. This review discusses the potential of targeting Kv7 channels in the smooth muscle to treat diseases such as hypertension, bladder instability, constipation and preterm labour.

Regulation of vascular smooth muscle tone by adipose-derived contracting factor

Obesity and arterial hypertension, important risk factors for atherosclerosis and coronary artery disease, are characterized by an increase in vascular tone. While obesity is known to augment vasoconstrictor prostanoid activity in endothelial cells, less is known about factors released from fat tissue surrounding arteries (perivascular adipose). Using lean controls and mice with either monogenic or diet-induced obesity, we set out to determine whether and through which pathways perivascular adipose affects vascular tone. We unexpectedly found that in the aorta of obese mice, perivascular adipose potentiates vascular contractility to serotonin and phenylephrine, indicating activity of a factor generated by perivascular adipose, which we designated “adipose-derived contracting factor” (ADCF). Inhibition of cyclooxygenase (COX) fully prevented ADCF-mediated contractions, whereas COX-1 or COX-2-selective inhibition was only partially effective. By contrast, inhibition of superoxide anions, NO synthase, or endothelin receptors had no effect on ADCF activity. Perivascular adipose as a source of COX-derived ADCF was further confirmed by detecting increased thromboxane A₂ formation from perivascular adipose-replete aortae from obese mice. Taken together, this study identifies perivascular adipose as a novel regulator of arterial vasoconstriction through the release of COX-derived ADCF. Excessive ADCF activity in perivascular fat under obese conditions likely contributes to increased vascular tone by antagonizing vasodilation. ADCF may thus propagate obesity-dependent hypertension and the associated increased risk in coronary artery disease, potentially representing a novel therapeutic target.

Effect of high free fatty acids on the anti-contractile response of perivascular adipose tissue in rat aorta

To determine whether high free fatty acids (FFA) could affect the anti-contractile properties of perivascular adipose tissue (PVAT) in rat aortas. Wistar rats were divided into normal, obesity and fenofibrate groups and fed a normal, high-fat, and high-fat plus fenofibrate diet, respectively. Thoracic aortas with or without PVAT (PVAT+ and PVAT-) were prepared with either intact endothelium (E+) or with endothelium removed (E-). Aortas pre-treated with either 500μmol/L of palmitic acid (PA) or physiological salt solution (PSS), as a control, were used for in vitro study. Concentration-dependent responses of aortas to norepinephrine were measured. The anti-contractile effects of PVAT were attenuated in both obese rats with high FFA levels and in the PA group in the presence of endothelium, but not in the absence of endothelium. The attenuation of the anti-contractile effect was restored by reducing FFA levels in the fenofibrate group (P<0.05). Incubation of aortas (PVAT+ E+) with nitric oxide (NO) synthase inhibitor and tumor necrosis factor-alpha (TNF-α) in the normal group caused attenuation of the anti-contractile effect of PVAT (P<0.05). Incubation of aortas (PVAT+ E+) in the obese and PA groups with a NO donor, anti-TNF-α antibodies or free radical scavengers partially restored the anti-contractile effect of PVAT (P<0.05). Under both acute and chronic conditions, high FFA levels could attenuate the anti-contractile properties of PVAT by an endothelium-dependent rather than an endothelium-independent mechanism, in which inflammation and oxidative stress may play important roles.

Blueberry juice causes potent relaxation of rat aortic rings via the activation of potassium channels and the H₂S pathway

The objective of this study was to investigate the in vitro effects of blueberry juice on healthy rat aortic rings, and to explore the roles of potassium channels and of the hydrogen sulphide (H(2)S) pathway in mediating the effects of blueberry juice. Firstly, the antioxidant capacity of blueberry juice was compared to other popular juice drinks using the Folin-Ciocalteu and the DPPH assays. Blueberry juice had significantly higher total polyphenol content than any of the other drinks studied (p < 0.01). The effect of blueberry juice on noradrenaline-contracted aortic rings was then observed, and the juice caused significant inhibition of noradrenaline-induced contractions (p < 0.01). Voltage-gated potassium channel (Kv) blockers 4-aminopyridine (1 mM) and 3,4-diaminopyridine (1 mM), as well as the cystathionine γ-lysase (CSE) inhibitor d,l-propargylglycine (2 mM) were then utilised to elucidate the role of Kv channels and the CSE/H(2)S pathway. Kv channel blocker 3,4-diaminopyridine caused significant blockade at 1/100 and 1/50 dilutions of juice (p < 0.01), whilst 4-aminopyridine caused significant blockade of the 1/100 dilution of blueberry juice (p < 0.05). In addition, d,l-propargylglycine potently inhibited the effect of 1/100 and 1/50 dilutions of blueberry juice (p < 0.01). This study indicates that blueberry juice has potent vasorelaxing properties, and thus may be a useful dietary agent for the prevention and treatment of hypertension. This study also provides strong evidence that Kv channels and the CSE/H(2)S pathway may be responsible, at least in part, for mediating the effects of blueberry juice.

Control of human vascular tone by prostanoids derived from perivascular adipose tissue

Perivascular adipose tissue (PVAT) surrounds most vessels and has now been recognized as a regulator of vascular functions. This effect of PVAT has been mostly demonstrated in vessels obtained from rats and mice. Thus, the aim of this study was to investigate anti-contractile effect of PVAT surrounding human coronary bypass grafts such as saphenous vein (SV) and internal mammary artery (IMA). Moreover, we aimed to determine the involvement of prostanoids in the anticontractile effect of PVAT. Human SV and IMA preparations were set up in an organ bath. The presence of PVAT in SV and IMA preparations significantly attenuated the contractile response to noradrenaline (NA). Preincubation with indomethacin, a cyclooxygenase inhibitor, increased NA contraction in SV preparations with PVAT. This effect was not observed in IMA preparation with PVAT incubated with indomethacin. The lower measurements of prostaglandin E2 (PGE2) released from PVAT surrounding IMA versus SV supported these effects. In conclusion, our results show that PVAT of SV could attenuate NA-induced contraction by releasing both PGE2 and prostacyclin (PGI2). In contrast to SV, PVAT of IMA exerts its anti-contractile effect independently from prostanoids. These observations suggest that retaining PVAT in human SV and IMA preparations may have potential clinical implications to improve coronary bypass graft patency.

Human coronary artery perivascular adipocytes overexpress genes responsible for regulating vascular morphology, inflammation, and hemostasis

Inflammatory cross talk between perivascular adipose tissue and the blood vessel wall has been proposed to contribute to the pathogenesis of atherosclerosis. We previously reported that human perivascular (PV) adipocytes exhibit a proinflammatory phenotype and less adipogenic differentiation than do subcutaneous (SQ) adipocytes. To gain a global view of the genomic basis of biologic differences between PV and SQ adipocytes, we performed genome-wide expression analyses to identify differentially expressed genes between adipocytes derived from human SQ vs. PV adipose tissues. Although >90% of well-expressed genes were similarly regulated, we identified a signature of 307 differentially expressed genes that were highly enriched for functions associated with the regulation of angiogenesis, vascular morphology, inflammation, and blood clotting. Of the 156 PV upregulated genes, 59 associate with angiogenesis, vascular biology, or inflammation, noteworthy of which include TNFRSF11B (osteoprotegerin), PLAT, TGFB1, THBS2, HIF1A, GATA6, and SERPINE1. Of 166 PV downregulated genes, 21 associated with vascular biology and inflammation, including ANGPT1, ANGPTL1, and VEGFC. Consistent with the emergent hypothesis that PV adipocytes differentially regulate angiogenesis and inflammation, cell culture-derived adipocyte-conditioned media from PV adipocytes strongly enhanced endothelial cell tubulogenesis and monocyte migration compared with media from SQ adipocytes. These findings demonstrate that PV adipocytes have the potential to significantly modulate vascular inflammatory crosstalk in the setting of atherosclerosis by their ability to signal to both endothelial and inflammatory cells.

Perivascular adipose tissue potentiates contraction of coronary vascular smooth muscle: influence of obesity

BACKGROUND

This investigation examined the mechanisms by which coronary perivascular adipose tissue (PVAT)-derived factors influence vasomotor tone and the PVAT proteome in lean versus obese swine.

METHODS AND RESULTS

Coronary arteries from Ossabaw swine were isolated for isometric tension studies. We found that coronary (P=0.03) and mesenteric (P=0.04) but not subcutaneous adipose tissue augmented coronary contractions to KCl (20 mmol/L). Inhibition of CaV1.2 channels with nifedipine (0.1 µmol/L) or diltiazem (10 µmol/L) abolished this effect. Coronary PVAT increased baseline tension and potentiated constriction of isolated arteries to prostaglandin F2α in proportion to the amount of PVAT present (0.1-1.0 g). These effects were elevated in tissues obtained from obese swine and were observed in intact and endothelium denuded arteries. Coronary PVAT also diminished H2O2-mediated vasodilation in lean and, to a lesser extent, in obese arteries. These effects were associated with alterations in the obese coronary PVAT proteome (detected 186 alterations) and elevated voltage-dependent increases in intracellular [Ca(2+)] in obese smooth muscle cells. Further studies revealed that the Rho-kinase inhibitor fasudil (1 µmol/L) significantly blunted artery contractions to KCl and PVAT in lean but not obese swine. Calpastatin (10 μmol/L) also augmented contractions to levels similar to that observed in the presence of PVAT.

CONCLUSIONS

Vascular effects of PVAT vary according to anatomic location and are influenced by an obese phenotype. Augmented contractile effects of obese coronary PVAT are related to alterations in the PVAT proteome (eg, calpastatin), Rho-dependent signaling, and the functional contribution of K(+) and CaV1.2 channels to smooth muscle tone.

Endogenous hydrogen sulfide in perivascular adipose tissue: role in the regulation of vascular tone in physiology and pathology

Hydrogen sulfide (H2S) is synthesized from L-cysteine by cystathionine β-synthase (CBS) or cystathionine γ-lyase (CSE), and is enzymatically metabolized in mitochondria by sulfide:quinone oxidoreductase (SQR). Recent studies have indicated that H2S is synthesized by CSE in perivascular adipose tissue (PVAT), and is responsible for the anticontractile effect of PVAT on adjacent vessels. The lipophilic statin atorvastatin increases PVAT-derived H2S by suppressing its mitochondrial oxidation; the effect that results from statin-induced depletion of ubiquinone. Experimental obesity induced by a highly palatable diet has a time-dependent effect on H2S in PVAT. Adipose tissue hypoxia suppresses H2S oxidation and increases its level in short-term obesity not associated with insulin resistance. In contrast, in long-term obesity, insulin resistance and (or) hyperinsulinemia result in the down-regulation of CSE and H2S deficiency, which is corrected by treatment with the insulin sensitizer rosiglitazone. In addition, cannabinoid CB1 receptor agonist administered for 2 weeks increases H2S by impairing mitochondria biogenesis. This indicates that the rate of mitochondrial H2S oxidation plays an important role in the regulation of H2S level in PVAT. Up-regulation of H2S signaling in short-term obesity and (or) by elevated endocannabinoids may be a compensatory mechanism that maintains vascular tone, despite endothelial dysfunction.

Interplay between adipose tissue and blood vessels in obesity and vascular dysfunction

There is a close anatomical and functional relationship between adipose tissue and blood vessels. The crosstalk between these two organs is vital to both metabolic and vascular homeostasis. On the one hand, adipose tissue is highly vascularized, and maintenance of ample supply of blood flow is essential for both expansion and metabolic functions of adipose tissue. Vascular endothelium also secretes many factors to regulate adipogenesis and adipose tissue remodeling. On the other hand, almost all blood vessels are surrounded by perivascular adipose tissue (PVAT), which regulates vascular function by producing a large number of "vasocrine" molecules. Under the normal conditions, PVAT exerts its anti-contractile effects by release of vasorelaxants (such as adipocyte-derived relaxation factors and adiponectin) that promote both endothelium-dependent and -independent relaxations of blood vessels. However, PVAT in obesity becomes highly inflamed and induces vascular dysfunction by augmented secretion of vasoconstriction factors (such as the major components of renin-angiotensinogen-aldosterone system and superoxide) and pro-inflammatory adipokines (such as TNF-α and adipocyte fatty acid binding protein), the latter of which are important contributors to endothelial activation, vascular inflammation and neointimal formation. Furthermore, several adipocyte-derived adipokines impair vascular function indirectly, by acting in the brain to activate sympathetic nerve system (such as leptin) or by exerting their actions in major metabolic organs to induce vascular insulin resistance, which in turn aggravates endothelial dysfunction. Aberrant secretion of adipokines and other vasoactive factors in adipose tissue is a major contributor to the onset and progression of obesity-related metabolic and vascular complications.

Mechanisms of perivascular adipose tissue dysfunction in obesity

Most blood vessels are surrounded by adipose tissue. Similarly to the adventitia, perivascular adipose tissue (PVAT) was considered only as a passive structural support for the vasculature, and it was routinely removed for isolated blood vessel studies. In 1991, Soltis and Cassis demonstrated for the first time that PVAT reduced contractions to noradrenaline in rat aorta. Since then, an important number of adipocyte-derived factors with physiological and pathophysiological paracrine vasoactive effects have been identified. PVAT undergoes structural and functional changes in obesity. During early diet-induced obesity, an adaptative overproduction of vasodilator factors occurs in PVAT, probably aimed at protecting vascular function. However, in established obesity, PVAT loses its anticontractile properties by an increase of contractile, oxidative, and inflammatory factors, leading to endothelial dysfunction and vascular disease. The aim of this review is to focus on PVAT dysfunction mechanisms in obesity.

Role of KCNQ channels in skeletal muscle arteries and periadventitial vascular dysfunction

KCNQ channels have been identified in arterial smooth muscle. However, their role in vasoregulation and chronic vascular diseases remains elusive. We tested the hypothesis that KCNQ channels contribute to periadventitial vasoregulation in peripheral skeletal muscle arteries by perivascular adipose tissue and that they represent novel targets to rescue periadventitial vascular dysfunction. Two models, spontaneously hypertensive rats and New Zealand obese mice, were studied using quantitative polymerase chain reaction, the patch-clamp technique, membrane potential measurements, myography of isolated vessels, and blood pressure telemetry. In rat Gracilis muscle arteries, anticontractile effects of perivascular fat were inhibited by the KCNQ channel blockers XE991 and linopirdine but not by other selective K(+) channel inhibitors. Accordingly, XE991 and linopirdine blocked noninactivating K(+) currents in freshly isolated Gracilis artery smooth muscle cells. mRNAs of several KCNQ channel subtypes were detected in those arteries, with KCNQ4 channels being dominant. In spontaneously hypertensive rats, the anticontractile effect of perivascular fat in Gracilis muscle arteries was largely reduced compared with Wistar rats. However, the vasodilator effects of KCNQ channel openers and mRNA expression of KCNQ channels were normal. Furthermore, KCNQ channel openers restored the diminished anticontractile effects of perivascular fat in spontaneously hypertensive rats. Moreover, KCNQ channel openers reduced arterial blood pressure in both models of hypertension independent of ganglionic blockade. Thus, our data suggest that KCNQ channels play a pivotal role in periadventitial vasoregulation of peripheral skeletal muscle arteries, and KCNQ channel opening may be an effective mechanism to improve impaired periadventitial vasoregulation and associated hypertension.

Adipose tissue: friend or foe?

The perception of adipose tissue has changed considerably with the dramatic increase in the incidence of obesity and obesity-related comorbidities over the past 3 decades. Excess fat is no longer associated with wealth, but is instead recognized as a risk factor for many diseases. Adipose tissue is increasingly being identified as a vital, complex endocrine organ, and not simply as a fat store. Not all fat is created equal--regional, developmental, structural, and functional variations exist. Epicardial adipose tissue is a metabolically active organ producing a number of factors that modulate cardiac structure and function. The global epidemic of obesity and metabolic syndrome imposes a major disease burden, particularly of cardiovascular disease. In this Review, we describe the various types of adipose tissue--their developmental biology, differentiation, cell heterogeneity, and functional characteristics. We discuss the link between adipose tissue and inflammation, the signaling factors released by adipose tissue, as well as cardiac adiposity and its relevance to cardiovascular diseases. Finally, we review the myocardial regenerative potential of adipose-tissue-derived stem cells. We believe that a thorough understanding of adipose tissue is of great clinical value.

Reduced anti-contractile effect of perivascular adipose tissue on mesenteric small arteries from spontaneously hypertensive rats: role of Kv7 channels

Perivascular adipose tissue (PVAT) has been shown to produce vasoactive substances and regulate vascular tone. This function of PVAT has been reported to be altered in hypertension. However, the underlying mechanisms are not fully understood. In this study we used age-matched normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) as well as Sprague-Dawley rats and tested effects of PVAT on mesenteric small arteries. Vessels were mounted in a Mulvany-Halpern myograph and cumulative concentration-response relations to noradrenaline were determined in the presence or absence of PVAT. We found that PVAT has an anti-contractile effect on mesenteric small vessels, irrespective of strains. A reduced effect of PVAT was observed in SHR compared to WKY rats; the difference between strains was eliminated by 10 μM XE991, a blocker of Kv7 (KCNQ) voltage-dependent potassium channels. The anti-contractile effect of PVAT was not affected by depolarizing smooth muscle cells with high K(+) solution. Sensitivities to exogenous vasodilators acetylcholine or sodium nitroprusside were not potentiated but reduced in vessels with PVAT. Our results suggest that the reduced anti-contractile effect of PVAT in SHR correlates with a deficiency in Kv7 channels. Diffusion hindrance of PVAT is also a factor that should be considered in investigations on rat mesenteric small arteries.

'No-touch' saphenous vein harvesting improves graft performance in patients undergoing coronary artery bypass surgery: a journey from bedside to bench

The saphenous vein is the most commonly used conduit in patients undergoing coronary artery bypass surgery yet its patency is inferior to the internal thoracic artery. Vascular damage inflicted to the vein when using conventional harvesting techniques affects its structure. Endothelial denudation is associated with early vein graft failure while damage of the outermost vessel layers has adverse long-term effects on graft performance. While many in vitro and in vivo experimental studies aimed at improving vein graft patency have been performed to date no significant 'bench to bedside' advances have been made. Among experimental strategies employed is the use of pharmacological agents, gene targeting and external stents. A 'no-touch' technique, where the saphenous vein is removed with minimal trauma and normal architecture preserved, produces a superior graft with long term patency comparable to the internal thoracic artery. Interestingly, many experimental studies are aimed at repairing or replacing those regions of the saphenous vein damaged when harvesting conventionally. 'No-touch' harvesting is superior in coronary artery bypass patients with long-term data published 5years ago. Here we describe a 'bedside to bench' situation where the mechanisms underlying the improved performance of 'no touch' saphenous vein grafts in patients have been studied in the laboratory.

Differential effects of cystathionine-γ-lyase-dependent vasodilatory H2S in periadventitial vasoregulation of rat and mouse aortas

Background

Hydrogen sulfide (H₂S) is a potent vasodilator. However, the complex mechanisms of vasoregulation by H₂S are not fully understood. We tested the hypotheses that (1) H₂S exerts vasodilatory effects by opening KCNQ-type voltage-dependent (K_v) K⁺ channels and (2) that H₂S-producing cystathionine-γ-lyase (CSE) in perivascular adipose tissue plays a major role in this pathway.

Methodology/Principal Findings

Wire myography of rat and mouse aortas was used. NaHS and 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADTOH) were used as H₂S donors. KCNQ-type K_v channels were blocked by XE991. 4-Propargylglycine (PPG) and ß-cyano-l-alanine (BCA), or 2-(aminooxy)-acetic acid (AOAA) were used as inhibitors of CSE or cystathionine-ß-synthase (CBS), respectively. NaHS and ADTOH produced strong vasorelaxation in rat and mouse aortas, which were abolished by KCNQ channel inhibition with XE991. Perivascular adipose tissue (PVAT) exerted an anticontractile effect in these arteries. CSE inhibition by PPG and BCA reduced this effect in aortas from rats but not from mice. CBS inhibition with AOAA did not inhibit the anticontractile effects of PVAT. XE991, however, almost completely suppressed the anticontractile effects of PVAT in both species. Exogenous l-cysteine, substrate for the endogenous production of H₂S, induced vasorelaxation only at concentrations >5 mmol/l, an effect unchanged by CSE inhibition.

Conclusions/Signficance

Our results demonstrate potent vasorelaxant effects of H₂S donors in large arteries of both rats and mice, in which XE991-sensitive KCNQ-type channel opening play a pivotal role. CSE-H₂S seems to modulate the effect of adipocyte-derived relaxing factor in rat but not in mouse aorta. The present study provides novel insight into the interaction of CSE-H₂S and perivascular adipose tissue. Furthermore, with additional technical advances, a future clinical approach targeting vascular H₂S/KCNQ pathways to influence states of vascular dysfunction may be possible.

Anticontractile Effect of Perivascular Adipose Tissue and Leptin are Reduced in Hypertension

Leptin causes vasodilatation both by endothelium-dependent and -independent mechanisms. Leptin is synthesized by perivascular adipose tissue (PVAT). The hypothesis of this study is that a decrease of leptin production in PVAT of spontaneously hypertensive rats (SHR) might contribute to a diminished paracrine anticontractile effect of the hormone. We have determined in aorta from Wistar-Kyoto (WKY) and SHR (i) leptin mRNA and protein levels in PVAT, (ii) the effect of leptin and PVAT on contractile responses, and (iii) leptin-induced relaxation and nitric oxide (NO) production. Leptin mRNA and protein expression were significantly lower in PVAT from SHR. Concentration-response curves to angiotensin II were significantly blunted in presence of PVAT as well as by exogenous leptin (10⁻⁹ M) only in WKY. This anticontractile effect was endothelium-dependent. Vasodilatation induced by leptin was smaller in SHR than in WKY, and was also endothelium-dependent. Moreover, release of endothelial NO in response to acute leptin was higher in WKY compared to SHR, but completely abolished in the absence of endothelium. In conclusion, the reduced anticontractile effect of PVAT in SHR might be attributed to a reduced PVAT-derived leptin and to an abrogated effect of leptin on endothelial NO release probably due to an impaired activation of endothelial NO synthase.

Anticontractile Effect of Perivascular Adipose Tissue and Leptin are Reduced in Hypertension

Leptin causes vasodilatation both by endothelium-dependent and -independent mechanisms. Leptin is synthesized by perivascular adipose tissue (PVAT). The hypothesis of this study is that a decrease of leptin production in PVAT of spontaneously hypertensive rats (SHR) might contribute to a diminished paracrine anticontractile effect of the hormone. We have determined in aorta from Wistar-Kyoto (WKY) and SHR (i) leptin mRNA and protein levels in PVAT, (ii) the effect of leptin and PVAT on contractile responses, and (iii) leptin-induced relaxation and nitric oxide (NO) production. Leptin mRNA and protein expression were significantly lower in PVAT from SHR. Concentration-response curves to angiotensin II were significantly blunted in presence of PVAT as well as by exogenous leptin (10(-9) M) only in WKY. This anticontractile effect was endothelium-dependent. Vasodilatation induced by leptin was smaller in SHR than in WKY, and was also endothelium-dependent. Moreover, release of endothelial NO in response to acute leptin was higher in WKY compared to SHR, but completely abolished in the absence of endothelium. In conclusion, the reduced anticontractile effect of PVAT in SHR might be attributed to a reduced PVAT-derived leptin and to an abrogated effect of leptin on endothelial NO release probably due to an impaired activation of endothelial NO synthase.

Perivascular adipose tissue-derived relaxing factors: release by peptide agonists via proteinase-activated receptor-2 (PAR2) and non-PAR2 mechanisms

BACKGROUND AND PURPOSE

We hypothesized that proteinase-activated receptor-2 (PAR2)-mediated vasorelaxation in murine aorta tissue can be due in part to the release of adipocyte-derived relaxing factors (ADRFs).

EXPERIMENTAL APPROACH

Aortic rings from obese TallyHo and C57Bl6 intact or PAR2-null mice either without or with perivascular adipose tissue (PVAT) were contracted with phenylephrine and relaxation responses to PAR2-selective activating peptides (PAR2-APs: SLIGRL-NH(2) and 2-furoyl-LIGRLO-NH(2) ), trypsin and to PAR2-inactive peptides (LRGILS-NH(2) , 2-furoyl-OLRGIL-NH(2) and LSIGRL-NH(2) ) were measured. Relaxation was monitored in the absence or presence of inhibitors that either alone or in combination were previously shown to inhibit ADRF-mediated responses: L-NAME (NOS), indomethacin (COX), ODQ (guanylate cyclase), catalase (H(2) O(2) ) and the K(+) channel-targeted reagents, apamin, charybdotoxin, 4-aminopyridine and glibenclamide.

KEY RESULTS

Endothelium-intact PVAT-free preparations did not respond to PAR2-inactive peptides (LRGILS-NH(2) , LSIGRL-NH(2) , 2-furoyl-OLRGIL-NH(2) ), whereas active PAR2-APs (SLIGRL-NH(2) ; 2-furoyl-LIGRLO-NH(2) ) caused an L-NAME-inhibited relaxation. However, in PVAT-containing preparations treated with L-NAME/ODQ/indomethacin together, both PAR2-APs and trypsin caused relaxant responses in PAR2-intact, but not PAR2-null-derived tissues. The PAR2-induced PVAT-dependent relaxation (SLIGRL-NH(2) ) persisted in the presence of apamin plus charybdotoxin, 4-aminopyridine and glibenclamide, but was blocked by catalase, implicating a role for H(2) O(2) . Surprisingly, the PAR2-inactive peptides, LRGILS-NH(2) and 2-furoyl-OLRGIL-NH(2) (but not LSIGRL-NH(2) ), caused relaxation in PVAT-containing preparations from both PAR2-null and PAR2-intact (C57Bl, TallyHo) mice. The LRGILS-NH(2) -induced relaxation was distinct from the PAR2 response, being blocked by 4-aminopyridine, but not catalase.

CONCLUSIONS

Distinct ADRFs that may modulate vascular tone in pathophysiological settings can be released from murine PVAT by both PAR2-dependent and PAR2-independent mechanisms.