Regulation of alpha(2)-adrenoceptors in human vascular smooth muscle cells

Genetic and functional analysis of Raynaud's syndrome implicates loci in vasculature and immunity

Raynaud's syndrome is a dysautonomia where exposure to cold causes vasoconstriction and hypoxia, particularly in the extremities. We performed meta-analysis in four cohorts and discovered eight loci (ADRA2A, IRX1, NOS3, ACVR2A, TMEM51, PCDH10-DT, HLA, and RAB6C) where ADRA2A, ACVR2A, NOS3, TMEM51, and IRX1 co-localized with expression quantitative trait loci (eQTLs), particularly in distal arteries. CRISPR gene editing further showed that ADRA2A and NOS3 loci modified gene expression and in situ RNAscope clarified the specificity of ADRA2A in small vessels and IRX1 around small capillaries in the skin. A functional contraction assay in the cold showed lower contraction in ADRA2A-deficient and higher contraction in ADRA2A-overexpressing smooth muscle cells. Overall, our study highlights the power of genome-wide association testing with functional follow-up as a method to understand complex diseases. The results indicate temperature-dependent adrenergic signaling through ADRA2A, effects at the microvasculature by IRX1, endothelial signaling by NOS3, and immune mechanisms by the HLA locus in Raynaud's syndrome.

Inhibiting Intracellular α2C-Adrenoceptor Surface Translocation Using Decoy Peptides: Identification of an Essential Role of the C-Terminus in Receptor Trafficking

The G protein-coupled α2-adrenoceptor subtype C (abbreviated α2C-AR) has been implicated in peripheral vascular conditions and diseases such as cold feet-hands, Raynaud's phenomenon, and scleroderma, contributing to morbidity and mortality. Microvascular α2C-adrenoceptors are expressed in specialized smooth muscle cells and mediate constriction under physiological conditions and the occlusion of blood supply involving vasospastic episodes and tissue damage under pathological conditions. A crucial step for receptor biological activity is the cell surface trafficking of intracellular receptors, triggered by cAMP-Epac-Rap1A GTPase signaling, which involves protein-protein association with the actin-binding protein filamin-2, mediated by critical amino acid residues in the last 14 amino acids of the receptor carboxyl (C)-terminus. This study assessed the role of the C-terminus in Rap1A GTPase coupled receptor trafficking by domain-swapping studies using recombinant tagged receptors in transient co-transfections and compared with wild-type receptors using immunofluorescence microscopy. We further tested the biological relevance of the α2C-AR C-terminus, when introduced as competitor peptides, to selectively inhibit intracellular α2C-AR surface translocation in transfected as well as in microvascular smooth muscle cells expressing endogenous receptors. These studies contribute to establishing proof of principle to target intracellular α2C-adrenoceptors to reduce biological activity, which in clinical conditions can be a target for therapy.

GPER Acts Through the cAMP/Epac/JNK/AP-1 Pathway to Induce Transcription of Alpha 2C Adrenoceptor in Human Microvascular Smooth Muscle Cells

ABSTRACT

Raynaud's phenomenon, which results from exaggerated cold-induced vasoconstriction, is more prevalent in females than males. We previously showed that estrogen increases the expression of alpha 2C-adrenoceptors (α 2C -AR), the sole mediator of cold-induced vasoconstriction. This effect of estrogen is reproduced by the cell-impermeable form of the hormone (E 2 :bovine serum albumin [BSA]), suggesting a role of the membrane estrogen receptor, G-protein-coupled estrogen receptor [GPER], in E 2 -induced α 2C -AR expression. We also previously reported that E 2 upregulates α 2C -AR in microvascular smooth muscle cells (VSMCs) via the cAMP/Epac/Rap/JNK/AP-1 pathway, and that E 2 :BSA elevates cAMP levels. We, therefore, hypothesized that E 2 uses GPER to upregulate α 2C -AR through the cAMP/Epac/JNK/AP-1 pathway. Our results show that G15, a selective GPER antagonist, attenuates the E 2 -induced increase in α 2C -AR transcription. G-1, a selective GPER agonist, induced α 2C -AR transcription, which was concomitant with elevated cAMP levels and JNK activation. Pretreatment with ESI09, an Epac inhibitor, abolished G-1-induced α 2C -AR upregulation and JNK activation. Moreover, pretreatment with SP600125, a JNK-specific inhibitor, but not H89, a PKA-specific inhibitor, abolished G-1-induced α 2C -AR upregulation. In addition, transient transfection of an Epac dominant negative mutant (Epac-DN) attenuated G-1-induced activation of the α 2C -AR promoter. This inhibitory effect of Epac-DN on the α 2C -AR promoter was overridden by the cotransfection of constitutively active JNK mutant. Furthermore, mutation of AP-1 site in the α 2C -AR promoter abrogated G1-induced expression. Collectively, these results indicate that GPER upregulates α 2C -AR through the cAMP/EPAC/JNK/AP-1 pathway. These findings unravel GPER as a new mediator of cold-induced vasoconstriction, and present it as a potential target for treating Raynaud's phenomenon in estrogen-replete females.

Fetoplacental vascular effects of maternal adrenergic antihypertensive and cardioprotective medications in pregnancy

Maternal cardiovascular diseases, including hypertension and cardiac conditions, are associated with poor fetal outcomes. A range of adrenergic antihypertensive and cardioprotective medications are often prescribed to pregnant women to reduce major maternal complications during pregnancy. Although these treatments are not considered teratogenic, they may have detrimental effects on fetal growth and development, as they cross the fetoplacental barrier, and may contribute to placental vascular dysregulation. Medication risk assessment sheets do not include specific advice to clinicians and women regarding the safety of these therapies for use in pregnancy and the potential off-target effects of adrenergic medications on fetal growth have not been rigorously conducted. Little is known of their effects on the fetoplacental vasculature. There is also a dearth of knowledge on adrenergic receptor activation and signalling within the endothelium and vascular smooth muscle cells of the human placenta, a vital organ in the maintenance of adequate blood flow to satisfy fetal growth and development. The fetoplacental circulation, absent of sympathetic innervation, and unique in its reliance on endocrine, paracrine and autocrine influence in the regulation of vascular tone, appears vulnerable to dysregulation by adrenergic antihypertensive and cardioprotective medications compared with the adult peripheral circulation. This semi-systematic review focuses on fetoplacental vascular expression of adrenergic receptors, associated cell signalling mechanisms and predictive consequences of receptor activation/deactivation by antihypertensive and cardioprotective medications.

Cooling-induced cutaneous vasodilatation is mediated by small-conductance, calcium-activated potassium channels in tail arteries from male mice

Cooling causes cutaneous dilatation to restrain cold-induced constriction and prevent tissue injury. Cooling increases communication through myoendothelial gap junctions (MEGJs), thereby increasing endothelium-derived hyperpolarization (EDH)-type dilatation. EDH is initiated by calcium-activated potassium channels (KCa ) activated by endothelial stimuli or muscle-derived mediators traversing MEGJs (myoendothelial feedback). The goal of this study was to determine the individual roles of KCa with small (SK3) and intermediate (IK1) conductance in cooling-induced dilatation. Vasomotor responses of mice isolated cutaneous tail arteries were analyzed by pressure myography at 37°C and 28°C. Cooling increased acetylcholine-induced EDH-type dilatation during inhibition of NO and prostacyclin production. IK1 inhibition did not affect dilatations to acetylcholine, whereas SK3 inhibition inhibited dilatation at both temperatures. Cooling uncovered myoendothelial feedback to inhibit constrictions in U46619. IK1 inhibition did not affect U46619 constrictions, whereas SK3 inhibition abolished the inhibitory effect of cooling without affecting U46619 constriction at 37°C. Immunoblots confirmed SK3 expression, which was localized (immunofluorescence) to holes in the internal elastic lamina consistent with myoendothelial projections. Immunoblots and Immunofluorescence did not detect IK1. Studies in non-cutaneous arteries have highlighted the predominant role of IK1 in EDH-type dilatation. Cutaneous arteries are distinctly reliant on SK3, which may enable EDH-type dilation to be amplified by cooling.

Pharmacokinetics, Safety, and Tolerability of the α2C -Adrenoreceptor Antagonist BAY 1193397 in Healthy Male Subjects

The α_2C -adrenoreceptor antagonist BAY 1193397 is in development for the oral treatment of diabetic foot ulcers. Safety, tolerability, and pharmacokinetics of BAY 1193397 were investigated in 3 randomized, single-center phase 1 studies in healthy male subjects: a first-in-human study (single oral doses of 0.5-50 mg), a relative bioavailability and food effect study (single doses of 1 and 10 mg), and a multiple-dose escalation study (using 2 and 5 mg twice daily and 10 and 20 mg once daily for 9 consecutive days). BAY 1193397 was rapidly absorbed in the fasted state, peak concentrations were reached between 0.6 and 2 hours. The mean terminal half-life was in the range of 17 to 20 hours. Area under the plasma concentration-time curve and maximum concentration appeared to be dose proportional, with a negligible food effect. There were no high-accumulation effects of BAY 1193397 after repeated dosing. BAY 1193397 was safe and well tolerated. At supratherapeutic plasma concentrations, there were slight transient increases in norepinephrine levels, heart rate, and blood pressure that were more pronounced after a single dose compared to steady state and appeared to be maximum concentration dependent. The results of the presented studies support the conduct of subsequent clinical trials with BAY 1193397 in patients with diabetes and compromised microcirculation.

Dexmedetomidine 2 ppm Is Appropriate for the Enhancement Effect of Local Anesthetic Action of Lidocaine in Inferior Alveolar Nerve Block: A Preliminary, Randomized Cross-over Study

OBJECTIVE

Local anesthesia is essential for pain management in dentistry. The duration of anesthetic action of the addition of 5.0 and 7.5 ppm of dexmedetomidine (DEX) was significantly longer than the addition of adrenaline, and the mean duration of anesthetic action of the addition of 2.5 ppm DEX was also longer than the addition of adrenaline. We hypothesized that it is possible to safely achieve an equal local anesthesia effect as with 1:80,000 adrenaline, without using adrenaline or felypressin, by the addition of <2.5 ppm DEX to the local anesthetic solution.

MATERIALS AND METHODS

Nineteen healthy volunteers were randomly assigned by a computer to receive 1.8 mL of 1 of 3 drug combinations (1.8% lidocaine with 1.0 ppm [1.8 μg] DEX, lidocaine with 2.0 ppm [3.6 μg] DEX or lidocaine with 1:80,000 [22.5 μg] adrenaline), to produce inferior alveolar nerve block. Pulp latency and lower lip numbness (for assessing onset and duration of anesthesia) were tested, and sedation level, blood pressure, and heart rate were recorded every 2 minutes for 10 minutes, every 5 minutes from 10 to 20 minutes, and every 10 minutes from 20 to 60 minutes.

RESULTS

Pulp latency increased compared with the baseline, from 4 minutes until 60 minutes; there were no significant intergroup differences at any timepoint. Anesthesia onset did not differ between groups. Anesthesia duration did not differ between groups. Blood pressure and heart rate did not change in any group. Sedation score did not indicate deep sedation in any of the groups.

DISCUSSION

DEX at a concentration of 1.0 to 2.0 ppm enhances the local anesthetic action of lidocaine. DEX at 2.0 ppm produces similar enhancement of local anesthesia effect as the addition of 1:80,000 adrenaline.

Raynaud's phenomenon and related vasospastic disorders

Raynaud's phenomenon, which is characterized by episodic digital pallor, cyanosis and rubor upon exposure to cold environment or to stress, is relatively common, although the prevalence depends on the climate. Still, it is under-diagnosed, under-treated, and often confused with other conditions. Primary Raynaud's phenomenon (i.e., Raynaud disease) must be distinguished from secondary Raynaud's phenomenon (i.e., Raynaud syndrome) as long-term morbidity and outcomes differ vastly between the two conditions. Additionally, the practitioner must differentiate between Raynaud's phenomenon and related vascular disorders, such as acrocyanosis, pernio, and livedo reticularis. In this article, we review differences between the conditions and suggest an approach to diagnosis and treatment strategy for these disorders.

EPAC in Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) are major components of blood vessels. They regulate physiological functions, such as vascular tone and blood flow. Under pathological conditions, VSMCs undergo a remodeling process known as phenotypic switching. During this process, VSMCs lose their contractility and acquire a synthetic phenotype, where they over-proliferate and migrate from the tunica media to the tunica interna, contributing to the occlusion of blood vessels. Since their discovery as effector proteins of cyclic adenosine 3′,5′-monophosphate (cAMP), exchange proteins activated by cAMP (EPACs) have been shown to play vital roles in a plethora of pathways in different cell systems. While extensive research to identify the role of EPAC in the vasculature has been conducted, much remains to be explored to resolve the reported discordance in EPAC’s effects. In this paper, we review the role of EPAC in VSMCs, namely its regulation of the vascular tone and phenotypic switching, with the likely involvement of reactive oxygen species (ROS) in the interplay between EPAC and its targets/effectors.

Cooling-induced dilatation of cutaneous arteries is mediated by increased myoendothelial communication

Cold exposure causes cutaneous vasoconstriction via a reflex increase in sympathetic activity and a local effect to augment adrenergic constriction. Local cooling also initiates cutaneous dilatation, which may function to restrain cold-induced constriction. However, the underlying mechanisms and physiological role of cold-induced dilatation have not been defined. Experiments were performed to assess the role of endothelial-derived mediators in this response. In isolated pressurized cutaneous mouse tail arteries, cooling (28°C) did not affect the magnitude of dilatation to acetylcholine in preconstricted arteries. However, inhibition of nitric oxide (NO) [N^G-nitro-l-arginine methyl ester (l-NAME)] and prostacyclin (PGI₂) (indomethacin) reduced acetylcholine-induced dilatation at 37°C but not at 28°C, suggesting that cooling increased NO/PGI₂-independent dilatation. This NO/PGI₂-independent dilatation was reduced by inhibition of endothelial SK (UCL1684) and IK (TRAM34) Ca²⁺-activated K⁺-channels (K_Ca), consistent with endothelium-derived hyperpolarization (EDH). Cooling also increased dilatation to direct activation of K_Ca channels (SKA31, CyPPA) but did not affect dilatation to exogenous NO (DEA-NONOate). This cooling-induced increase in EDH-type dilatations was associated with divergent effects on potential downstream EDH mechanisms: cooling reduced dilatation to K⁺, which mimics an intercellular K⁺ cloud, but increased direct communication between endothelial and smooth muscle cells (myoendothelial coupling), assessed by cellular transfer of biocytin. Indeed, inhibition of gap junctions (carbenoxolone) abolished the EDH-type component of dilatation to acetylcholine during cooling but did affect NO-dominated dilatation at 37°C. Cooling also inhibited U46619 constriction that was prevented by inhibition of IK and SK K_Ca channels or inhibition of gap junctions. The results suggest that cooling dilates cutaneous arteries by increasing myoendothelial communication and amplifying EDH-type dilatation.NEW & NOTEWORTHY Cold causes cutaneous vasoconstriction to restrict heat loss. Although cold also initiates cutaneous dilatation, the mechanisms and role of this dilatation have not been clearly defined. This study demonstrates that cooling increases myoendothelial coupling between smooth muscle and endothelial cells in cutaneous arteries, which is associated with increased endothelium-derived hyperpolarization (EDH)-type dilatation. Dysfunction in this process may contribute to excessive cold-induced constriction and tissue injury.

Estrogen increases expression of vascular alpha 2C adrenoceptor through the cAMP/Epac/JNK/AP-1 pathway and potentiates cold-induced vasoconstriction

Cutaneous cold-induced vasoconstriction is a normal physiological reaction mediated by alpha 2C-adrenergic receptors (α_2C-ARs) expressed in vascular smooth muscle cells (VSMCs). When this reaction is exaggerated, Raynaud's phenomenon (RP) ensues. RP is more prevalent in females compared to age-matched men. We previously established that 17-β estradiol (estrogen) upregulates α_2C-ARs in human VSMCs via a cAMP/Epac/Rap pathway. We also showed that cAMP acts through JNK to increase α_2C-AR expression. However, whether estrogen employs JNK to regulate α_2C-AR is not investigated. Knowing that the α_2C-AR promoter harbors an activator protein-1 (AP-1) binding site that can be potentially activated by JNK, we hypothesized that estrogen regulates α_2C-AR expression through an Epac/JNK/AP-1 pathway. Our results show that estrogen (10^-10 M) activated JNK in human VSMCs extracted from cutaneous arterioles. Pretreatment with ESI09 (10 μM; an Epac inhibitor), abolished estrogen-induced JNK activation. In addition, pre-treatment with SP600125 (3 μM; a JNK specific inhibitor) abolished estrogen-induced expression of α_2C-AR. Importantly, estrogen-induced activation of α_2C-AR promoter was attenuated with SP600125. Moreover, transient transfection of VSMCs with an Epac dominant negative mutant (Epac-DN) abolished estrogen-induced activation of α_2C-AR promoter. However, co-transfection of constitutively active JNK mutant overrode the inhibitory effect of Epac-DN on α_2C-AR promoter. Moreover, estrogen caused a concentration-dependent increase in the activity of AP-1-driven reporter construct. Mutation of AP-1 site in the α_2C-AR promoter abolished its activation by estrogen. This in vitro estrogen-increased α_2C-AR expression was mirrored by an increase in the ex vivo functional responsiveness of arterioles. Indeed, estrogen potentiated α_2C-AR-mediated cold-induced vasoconstriction, which was abolished by SP600125. Collectively, these results indicate that estrogen upregulates α_2C-AR expression via an EPAC-mediated JNK/AP-1- dependent mechanism. These results provide an insight into the mechanism by which exaggerated cold-induced vasoconstriction occurs in estrogen-replete females and identify Epac and JNK as potential targets for the treatment of RP.

The role of α2-adrenergic receptors in hypertensive preeclampsia: A hypothesis

Preeclampsia, a major disorder of human pregnancy, manifests as persistent hypertension and proteinuria presenting after 20 weeks of pregnancy. Multiple systemic symptoms might be associated with preeclampsia including thrombocytopenia, liver impairment, pulmonary edema, and cerebral disturbances. However, vascular dysfunction remains the core pathological driver of preeclampsia. Defective placental implantation followed by dysfunctional placental spiral artery development promotes a hypoxic environment. Massive endothelial dysfunction characterized by reduced vasodilation, augmented vasoconstriction, and increased vascular permeability and inflammation ensues. Interestingly, the same signaling and inflammatory pathways implicated in preeclampsia appear to be shared with other vascular disorders involving alteration of α₂ -AR function. The role of α₂ -ARs in the regulation of microcirculatory function has long been recognized, thus raising the question of whether they are involved in the pathogenesis of vascular dysfunction in preeclampsia. Here, we review possible interplay between signaling and inflammatory pathways common to preeclampsia and α₂ -AR function/regulation. We speculate on the potential contribution of these receptors to the observed phenotype and the potential role for their pharmacological modulators as therapeutic interventions with preeclampsia.

Human Placenta Expresses α2-Adrenergic Receptors and May Be Implicated in Pathogenesis of Preeclampsia and Fetal Growth Restriction

α₂-Adrenergic receptors (α₂ARs) are G-protein-coupled receptors involved in catecholamine signaling by extracellular regulated protein kinase 1 and 2 (ERK1/2) pathways. We examined placental expression and function of α₂AR subtypes in women with severe preeclampsia (sPE) with and without intrauterine growth restriction (IUGR). Placental biopsies were analyzed from 52 women with i) sPE (n = 8); ii) sPE + IUGR (n = 9); iii) idiopathic IUGR (n = 8); iv) idiopathic preterm birth (n = 16); and v) healthy term controls (n = 11). Expression of α₂AR subtypes (α_2A, α_2B, α_2C) and phospho-ERK1/2 (receptor activation marker) was investigated by immunohistochemistry and/or quantitative real-time RT-PCR. The effects of α_2CAR knockdown on syncytialization (syncytin-1 and -2) and β-human chorionic gonadotropin secretion were examined in BeWo cells stimulated with forskolin. The effects of α₂AR agonist UK 14,304 and specific α_2CAR antagonist were tested, using a trophoblast migration assay. All three α₂ARs were expressed and functionally active in human placenta with site-specific localization. Highest α_2BAR and α_2CAR mRNA expression was identified in sPE + IUGR. α_2CAR knockdown increased expression of syncytin-1 and -2 but decreased secretion of β-human chorionic gonadotropin. UK 14,304 impaired trophoblast migration. The observed α₂AR expression pattern suggests different function for each subtype. α_2CAR modulates trophoblast syncytialization and migration and may carry pathogenic role in sPE + IUGR.

Efficacy of local dexmedetomidine add-on for spermatic cord block anesthesia in patients undergoing intrascrotal surgeries: randomized controlled multicenter clinical trial

Study objective

The objective of this study was to evaluate the effect of adding dexmedetomidine (DEX) to bupivacaine on the quality of spermatic cord block anesthesia and postoperative analgesia.

Design

This is a randomized, double-blind study.

Setting

This study was performed in an educational and research hospital.

Patients

One hundred twenty adult males were scheduled for intrascrotal surgeries.

Interventions

Patients were divided into two groups: group B received 10 mL of bupivacaine 0.25% for spermatic cord block and intravenous 50 µg of DEX and group BD received 10 mL of bupivacaine 0.25% added to 50 µg of DEX (9.5 mL bupivacaine 0. 25% + 0.5 mL [50 µg] DEX) for spermatic cord block, and for masking purposes, the patients received isotonic saline intravenously.

Measurements

Time to first analgesic request, analgesic consumption, and visual analog scale (VAS) pain score in the first 24 hours postoperatively were assessed.

Main results

Time to first rescue analgesic was significantly delayed in group BD in comparison with group B, median (interquartile) range, 7 (6–12) hours versus 6 (5–7) hours, (p=0.000), the mean cumulative morphine consumption (mg) in the first postoperative 24 hours was significantly lower in group BD compared with group B, 8.13±4.45 versus 12.7±3.79, with a mean difference (95% CI) of −4.57 (−6.06 to −3.07) (p=0.000); also, there was a significant reduction of VAS pain score in group BD in comparison with group B at all measured time points, VAS 2 hours (1.28±0.9 vs 1.92±0.8), VAS 6 hours (2.62±1.5 vs 3.93±1.2), VAS 12 hours (2.40±1.1 vs 3.57±0.65), VAS 24 hours (1.90±0.68 vs 2.53±0.62) (p=0.000)

Conclusion

The addition of 50 µg of DEX to bupivacaine 0.25% in spermatic cord block for intrascrotal surgeries resulted in delay of first analgesic supplementation, reduction of postoperative analgesic consumption as well as improvement of the success rate of the block.

Role of cyclooxygenase in the vascular responses to extremity cooling in Caucasian and African males

NEW FINDINGS

What is the central question of this study? Compared with Caucasians, African individuals are more susceptible to non-freezing cold injury and experience greater cutaneous vasoconstriction and cooler finger skin temperatures upon hand cooling. We investigated whether the enzyme cyclooxygenase is, in part, responsible for the exaggerated response to local cooling. What is the main finding and its importance? During local hand cooling, individuals of African descent experienced significantly lower finger skin blood flow and skin temperature compared with Caucasians irrespective of cyclooxygenase inhibition. These data suggest that in young African males the cyclooxygenase pathway appears not to be the primary reason for the increased susceptibility to non-freezing cold injury. Individuals of African descent (AFD) are more susceptible to non-freezing cold injury (NFCI) and experience an exaggerated cutaneous vasoconstrictor response to hand cooling compared with Caucasians (CAU). Using a placebo-controlled, cross-over design, this study tested the hypothesis that cyclooxygenase (COX) may, in part, be responsible for the exaggerated vasoconstrictor response to local cooling in AFD. Twelve AFD and 12 CAU young healthy men completed foot cooling and hand cooling (separately, in 8°C water for 30 min) with spontaneous rewarming in 30°C air after placebo or aspirin (COX inhibition) treatment. Skin blood flow, expressed as cutaneous vascular conductance (as flux per millimetre of mercury), and skin temperature were measured throughout. Irrespective of COX inhibition, the responses to foot cooling, but not hand cooling, were similar between ethnicities. Specifically, during hand cooling after placebo, AFD experienced a lower minimal skin blood flow [mean (SD): 0.5 (0.1) versus 0.8 (0.2) flux mmHg^-1 , P < 0.001] and a lower minimal finger skin temperature [9.5 (1.4) versus 10.7 (1.3)°C, P = 0.039] compared with CAU. During spontaneous rewarming, average skin blood flow was also lower in AFD than in CAU [2.8 (1.6) versus 4.3 (1.0) flux mmHg^-1 , P < 0.001]. These data provide further support that AFD experience an exaggerated response to hand cooling on reflection this appears to overstate findings; however, the results demonstrate that the COX pathway is not the primary reason for the exaggerated responses in AFD and increased susceptibility to NFCI.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

Dexmedetomidine Dose Dependently Enhances the Local Anesthetic Action of Lidocaine in Inferior Alveolar Nerve Block: A Randomized Double-Blind Study

BACKGROUND AND OBJECTIVES

Dexmedetomidine (DEX) dose dependently enhances the local anesthetic action of lidocaine in rats. We hypothesized that the effect might also be dose dependent in humans. We evaluated the effect of various concentrations of DEX with a local anesthetic in humans.

METHODS

Eighteen healthy volunteers were randomly assigned by a computer to receive 1.8 mL of 1 of 4 drug combinations: (1) 1% lidocaine with 2.5 ppm (parts per million) (4.5 μg) DEX, (2) lidocaine with 5.0 ppm (9.0 μg) DEX, (3) lidocaine with 7.5 ppm (13.5μg) DEX, or (4) lidocaine with 1:80,000 (22.5 μg) adrenaline (AD), to produce inferior alveolar nerve block. Pulp latency and lower lip numbness (for assessing onset and duration of anesthesia) were tested, and sedation level, blood pressure, and heart rate were recorded every 5 minutes for 20 minutes, and every 10 minutes from 20 to 60 minutes.

RESULTS

Pulp latency of each tooth increased compared with baseline, from 5 to 15 minutes until 60 minutes. There were no significant intergroup differences at any time point. Anesthesia onset was not different between groups. Anesthesia duration was different between groups (that with DEX 7.5 ppm was significantly longer than that with DEX 2.5 ppm and AD; there was no difference between DEX 2.5 ppm and AD). Blood pressure decreased from baseline in the 5.0 and 7.5 ppm DEX groups at 30 to 60 minutes, although there was no hypotension; moreover, heart rate did not change in any group. Sedation score did not indicate deep sedation in any of the groups.

CONCLUSIONS

Dexmedetomidine dose dependently enhances the local anesthetic action of lidocaine in humans. Dexmedetomidine at 2.5 ppm produces similar enhancement of local anesthesia effect as addition of 1:80,000 AD.

Raynaud's Phenomenon: A Brief Review of the Underlying Mechanisms

Raynaud’s phenomenon (RP) is characterized by exaggerated cold-induced vasoconstriction. This augmented vasoconstriction occurs by virtue of a reflex response to cooling via the sympathetic nervous system as well as by local activation of α_2C adrenoceptors (α_2C-AR). In a cold-initiated, mitochondrion-mediated mechanism involving reactive oxygen species and the Rho/ROCK pathway, cytoskeletal rearrangement in vascular smooth muscle cells orchestrates the translocation of α_2C-AR to the cell membrane, where this receptor readily interacts with its ligand. Different parameters are involved in this spatial and functional rescue of α_2C-AR. Of notable relevance is the female hormone, 17β-estradiol, or estrogen. This is consistent with the high prevalence of RP in premenopausal women compared to age-matched males. In addition to dissecting the role of these various players, the contribution of pollution as well as genetic background to the onset and prevalence of RP are also discussed. Different therapeutic approaches employed as treatment modalities for this disease are also highlighted and analyzed. The lack of an appropriate animal model for RP mandates that more efforts be undertaken in order to better understand and eventually treat this disease. Although several lines of treatment are utilized, it is important to note that precaution is often effective in reducing severity or frequency of RP attacks.

α2-Adrenoreceptor Constraint of Catecholamine Release and Blood Pressure Is Enhanced in Female Spontaneously Hypertensive Rats

α2-adrenoceptors (α2AR) lower central sympathetic output and peripheral catecholamine release, and may therefore prevent sympathetic hyperactivity and hypertension. The α2AR are dysfunctional in male spontaneously hypertensive rats (SHR). Premenopausal females are less hypertensive than males. The purpose of this study was to test if this difference could be explained by functional α2AR in the female SHR. A 15-min tyramine-infusion was used to stimulate norepinephrine release through the re-uptake transporter, consequently preventing re-uptake. Presynaptic control of vesicular release will therefore be reflected as differences in overflow to plasma. The surgical trauma activates secretion of epinephrine, also subjected to α2AR auto-inhibition. Blood pressure was monitored through a femoral artery catheter and cardiac output by ascending aorta flow in 12-14 weeks-old (early hypertension) SHR and normotensive rats (WKY). Total peripheral vascular resistance (TPR) was calculated. Female SHR, unlike male, were close to normotensive. Pre-treatment with none-selective (clonidine) or non-A-selective (ST-91) α2AR agonist reduced, and none-selective α2AR antagonist (L-659,066) increased tyramine-induced norepinephrine overflow in female WKY and SHR. L-659,066 also increased secretion of epinephrine. The L-659,066-induced increase in catecholamine release was further enhanced by additional pre-treatment with ST-91 or angiotensin AT1 receptor antagonist (losartan) in SHR only. L-659,066 eliminated the tyramine-induced rise in TPR in both strains in female rats.

CONCLUSION

α2AR-mediated control of catecholamine release and vascular tension was therefore functional in female SHR, unlike that previously observed in male SHR. Functional α2AR is likely to have a protective function and may explain the lack of hypertension in the young female SHR.

Cold Stress Effects on Exposure Tolerance and Exercise Performance

Cold weather can have deleterious effects on health, tolerance, and performance. This paper will review the physiological responses and external factors that impact cold tolerance and physical performance. Tolerance is defined as the ability to withstand cold stress with minimal changes in physiological strain. Physiological and pathophysiological responses to short-term (cold shock) and long-term cold water and air exposure are presented. Factors (habituation, anthropometry, sex, race, and fitness) that influence cold tolerance are also reviewed. The impact of cold exposure on physical performance, especially aerobic performance, has not been thoroughly studied. The few studies that have been done suggest that aerobic performance is degraded in cold environments. Potential physiological mechanisms (decreases in deep body and muscle temperature, cardiovascular, and metabolism) are discussed. Likewise, strength and power are also degraded during cold exposure, primarily through a decline in muscle temperature. The review also discusses the concept of thermoregulatory fatigue, a reduction in the thermal effector responses of shivering and vasoconstriction, as a result of multistressor factors, including exhaustive exercise.

Genetic variation in alpha2-adrenoreceptors and heart rate recovery after exercise

Heart rate recovery (HRR) after exercise is an independent predictor of adverse cardiovascular outcomes. HRR is mediated by both parasympathetic reactivation and sympathetic withdrawal and is highly heritable. We examined whether common genetic variants in adrenergic and cholinergic receptors and transporters affect HRR. In our study 126 healthy subjects (66 Caucasians, 56 African Americans) performed an 8 min step-wise bicycle exercise test with continuous computerized ECG recordings. We fitted an exponential curve to the postexercise R-R intervals for each subject to calculate the recovery constant (kr) as primary outcome. Secondary outcome was the root mean square residuals averaged over 1 min (RMS1min), a marker of parasympathetic tone. We used multiple linear regressions to determine the effect of functional candidate genetic variants in autonomic pathways (6 ADRA2A, 1 ADRA2B, 4 ADRA2C, 2 ADRB1, 3 ADRB2, 2 NET, 2 CHT, and 1 GRK5) on the outcomes before and after adjustment for potential confounders. Recovery constant was lower (indicating slower HRR) in ADRA2B 301-303 deletion carriers (n = 54, P = 0.01), explaining 3.6% of the interindividual variability in HRR. ADRA2A Asn251Lys, ADRA2C rs13118771, and ADRB1 Ser49Gly genotypes were associated with RMS1min. Genetic variability in adrenergic receptors may be associated with HRR after exercise. However, most of the interindividual variability in HRR remained unexplained by the variants examined. Noncandidate gene-driven approaches to study genetic contributions to HRR in larger cohorts will be of interest.

Vascular responses of the extremities to transdermal application of vasoactive agents in Caucasian and African descent individuals

PURPOSE

Individuals of African descent (AFD) are more susceptible to non-freezing cold injury than Caucasians (CAU) which may be due, in part, to differences in the control of skin blood flow. We investigated the skin blood flow responses to transdermal application of vasoactive agents.

METHODS

Twenty-four young males (12 CAU and 12 AFD) undertook three tests in which iontophoresis was used to apply acetylcholine (ACh 1 w/v %), sodium nitroprusside (SNP 0.01 w/v %) and noradrenaline (NA 0.5 mM) to the skin. The skin sites tested were: volar forearm, non-glabrous finger and toe, and glabrous finger (pad) and toe (pad).

RESULTS

In response to SNP on the forearm, AFD had less vasodilatation for a given current application than CAU (P = 0.027-0.004). ACh evoked less vasodilatation in AFD for a given application current in the non-glabrous finger and toe compared with CAU (P = 0.043-0.014) with a lower maximum vasodilatation in the non-glabrous finger (median [interquartile], AFD n = 11, 41[234] %, CAU n = 12, 351[451] %, P = 0.011) and non-glabrous toe (median [interquartile], AFD n = 9, 116[318] %, CAU n = 12, 484[720] %, P = 0.018). ACh and SNP did not elicit vasodilatation in the glabrous skin sites of either group. There were no ethnic differences in response to NA.

CONCLUSION

AFD have an attenuated endothelium-dependent vasodilatation in non-glabrous sites of the fingers and toes compared with CAU. This may contribute to lower skin temperature following cold exposure and the increased risk of cold injuries experienced by AFD.

GABAB receptors are expressed in human aortic smooth muscle cells and regulate the intracellular Ca(2+) concentration

The aim of this study was to investigate the expression of GABAB receptors, a subclass of receptors to the inhibitory neurotransmitter gamma-aminobutyric acid (GABAB), in human aortic smooth muscle cells (HASMCs), and to explore if altering receptor activation modified intracellular Ca(2+) concentration ([Ca(2+)]i) of HASMCs. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABABR1 and GABABR2 in cultured HASMCs. Immunohistochemistry was used to localize the two subunits in human left anterior descending artery (LAD). The effects of the GABAB receptor agonist baclofen on [Ca(2+)]i in cultured HASMCs were demonstrated using fluo-3. Both GABABR1 and GABABR2 mRNA and protein were identified in cultured HASMCs and antibody staining was also localized to smooth muscle cells of human LAD. 100 μM baclofen caused a transient increase of [Ca(2+)]i in cultured HASMCs regardless of whether Ca(2+) was added to the medium, and the effects were inhibited by pre-treatment with CGP46381 (selective GABAB receptor antagonist), pertussis toxin (a Gi/o protein inhibitor), and U73122 (a phospholipase C blocker). GABAB receptors are expressed in HASMCs and regulate the [Ca(2+)]i via a Gi/o-coupled receptor pathway and a phospholipase C activation pathway.

Effect of skin temperature on cutaneous vasodilator response to the β-adrenergic agonist isoproterenol

The vascular response to local skin cooling is dependent in part on a cold-induced translocation of α2C-receptors and an increased α-adrenoreceptor function. To discover whether β-adrenergic function might contribute, we examined whether β-receptor sensitivity to the β-agonist isoproterenol was affected by local skin temperature. In seven healthy volunteers, skin blood flow was measured from the forearm by laser-Doppler flowmetry and blood pressure was measured by finger photoplethysmography. Data were expressed as cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial blood pressure). Pharmacological agents were administered via intradermal microdialysis. We prepared four skin sites: one site was maintained at a thermoneutral temperature of 34°C (32 ± 10%CVCmax) one site was heated to 39°C (38 ± 11%CVCmax); and two sites were cooled, one to 29°C (22 ± 7%CVCmax) and the other 24°C (16 ± 4%CVCmax). After 20 min at these temperatures to allow stabilization of skin blood flow, isoproterenol was perfused in concentrations of 10, 30, 100, and 300 μM. Each concentration was perfused for 15 min. Relative to the CVC responses to isoproterenol at the thermoneutral skin temperature (34°C) (+21 ± 10%max), low skin temperatures reduced (at 29°C) (+17 ± 6%max) or abolished (at 24°C) (+1 ± 5%max) the vasodilator response, and warm (39°C) skin temperatures enhanced the vasodilator response (+40 ± 9%max) to isoproterenol. These data indicate that β-adrenergic function was influenced by local skin temperature. This finding raises the possibility that a part of the vasoconstrictor response to direct skin cooling could include reduced background β-receptor mediated vasodilation.

A vascular mechanistic approach to understanding Raynaud phenomenon

During exposure to cold, our bodies attempt to maintain normal core temperature by restricting heat loss through cutaneous vasoconstriction, and by increasing heat production through shivering and nonshivering thermogenesis. In selected areas of human skin (including on the fingers and toes), the vascular system has specialized structural and functional features that enable it to contribute to thermoregulation. These features include arteriovenous anastomoses, which directly connect the arterial and venous systems and bypass the nutritional capillaries supplying blood to the skin tissue. Of note, Raynaud phenomenon predominantly affects the arterial territories supplying these specialized areas of skin. Indeed, Raynaud phenomenon can be considered a disorder of vascular thermoregulatory control. This Review presents an understanding of Raynaud phenomenon in the context of vascular and thermoregulatory control mechanisms, including the role of unique thermosensitive vascular structural and functional specialization, and describes the potential role of thermogenesis in this disorder. This new approach provides remarkable insight into the disease process and builds a framework to critically appraise the existing knowledge base. This paradigm also explains the deficiencies in some current therapeutic approaches, and highlights new areas of potential relevance to the pathogenesis and treatment of Raynaud phenomenon that should be expanded and explored.

In silico modeling of human α2C-adrenoreceptor interaction with filamin-2

Vascular smooth muscle α2C-adrenoceptors (α2C-ARs) mediate vasoconstriction of small blood vessels, especially arterioles. Studies of endogenous receptors in human arteriolar smooth muscle cells (referred to as microVSM) and transiently transfected receptors in heterologous HEK293 cells show that the α2C-ARs are perinuclear receptors that translocate to the cell surface under cellular stress and elicit a biological response. Recent studies in microVSM unraveled a crucial role of Rap1A-Rho-ROCK-F-actin pathways in receptor translocation, and identified protein-protein interaction of α2C-ARs with the actin binding protein filamin-2 as an essential step in the process. To better understand the molecular nature and specificity of this interaction, in this study, we constructed comparative models of human α2C-AR and human filamin-2 proteins. Finally, we performed in silico protein-protein docking to provide a structural platform for the investigation of human α2C-AR and filamin-2 interactions. We found that electrostatic interactions seem to play a key role in this complex formation which manifests in interactions between the C-terminal arginines of α2C-ARs (particularly R454 and R456) and negatively charged residues from filamin-2 region between residues 1979 and 2206. Phylogenetic and sequence analysis showed that these interactions have evolved in warm-blooded animals.

Association between common genetic variants of α2A-, α2B- and α2C-adrenoceptors and the risk of silent brain infarction

Silent brain infarction (SBI) is an asymptomatic cerebrovascular disorder. The aim of the present study was to investigate the association between adrenoceptor-α2 (ADRA2) gene polymorphisms and SBI. A total of 361 patients with SBI and 467 healthy control subjects were examined. The polymerase chain reaction was performed to genotype the ADRA2A 1780G>A, ADRA2B 301-303 insertion/deletion (I/D) and ADRA2C 322-325I/D polymorphisms. The frequency of the ADRA2C 322-325I/D polymorphism was significantly different between patients with SBI and control subjects. When interaction analyses were performed for vascular risk factors, the ADRA2C 322-325ID genotype increased the risk for SBI in the presence of hypertension and elevated plasma homocysteine levels. The ADRA2C 322-325ID genotype and plasma homocysteine levels showed a significant synergistic effect for SBI. In addition, the ADRA2A 1780AA genotype was associated with elevated plasma homocysteine levels. Although further analysis of the association between ADRA2 polymorphisms and clinical risk factors of SBI is required, the present study of a limited set of SBI risk factors with ADRA2 polymorphisms provides the first evidence of the involvement of ADRA2 gene family members in the development of SBI. Further studies using larger and more heterogeneous populations are required to validate the association of ADRA2 polymorphisms with SBI.

Dexmedetomidine dose-dependently enhances local anesthetic action of lidocaine

PURPOSE

The combination of α2-adrenoceptor agonists, such as dexmedetomidine (DEX) and clonidine, with local anesthetics has been found to extend the duration of peripheral nerve blocks, probably owing to the resultant local vasoconstriction in the peripheral nerves. However, because the clear elucidation of the effect of DEX requires examination of the local anesthetic effect with DEX alone and the combination of various concentrations of DEX with local anesthetics, we evaluated the local anesthetic effect of various concentrations of DEX alone and with a local anesthetic.

MATERIALS AND METHODS

The present study assessed the tail-flick (TF) latencies after injection of the appropriate drug in male Sprague-Dawley rats, using an epidural model that allowed constant pain stimulation intensity, dispersion of the anesthetic, and a precise injection site and dose. Lidocaine alone, lidocaine with 2.5-ppm DEX, lidocaine with 5.0-ppm DEX, lidocaine with 7.5-ppm DEX, and DEX alone were administered at the predetermined dose. The TF latency changes over time were compared using repeated measures analysis of variance (ANOVA). Comparisons among the groups were analyzed using ANOVA followed by a post hoc Dunnett's multiple comparison test or Tukey's multiple comparison test.

RESULTS

The addition of DEX to lidocaine increased the TF latency and dose-dependently prolonged its duration as follows: 0-ppm DEX, 20 minutes; 2.5-ppm, 40 minutes; 5.0-ppm, 40 minutes; and 7.5-ppm, 50 minutes. DEX alone did not change the TF latency.

CONCLUSIONS

Our results have demonstrated that DEX dose-dependently enhances the local anesthetic action of lidocaine in a rat TF model.

Cyclic AMP-Rap1A signaling mediates cell surface translocation of microvascular smooth muscle α2C-adrenoceptors through the actin-binding protein filamin-2

The second messenger cyclic AMP (cAMP) plays a vital role in vascular physiology, including vasodilation of large blood vessels. We recently demonstrated cAMP activation of Epac-Rap1A and RhoA-Rho-associated kinase (ROCK)-F-actin signaling in arteriolar-derived smooth muscle cells increases expression and cell surface translocation of functional α2C-adrenoceptors (α2C-ARs) that mediate vasoconstriction in small blood vessels (arterioles). The Ras-related small GTPAse Rap1A increased expression of α2C-ARs and also increased translocation of perinuclear α2C-ARs to intracellular F-actin and to the plasma membrane. This study examined the mechanism of translocation to better understand the role of these newly discovered mediators of blood flow control, potentially activated in peripheral vascular disorders. We utilized a yeast two-hybrid screen with human microvascular smooth muscle cells (microVSM) cDNA library and the α2C-AR COOH terminus to identify a novel interaction with the actin cross-linker filamin-2. Yeast α-galactosidase assays, site-directed mutagenesis, and coimmunoprecipitation experiments in heterologous human embryonic kidney (HEK) 293 cells and in human microVSM demonstrated that α2C-ARs, but not α2A-AR subtype, interacted with filamin. In Rap1-stimulated human microVSM, α2C-ARs colocalized with filamin on intracellular filaments and at the plasma membrane. Small interfering RNA-mediated knockdown of filamin-2 inhibited Rap1-induced redistribution of α2C-ARs to the cell surface and inhibited receptor function. The studies suggest that cAMP-Rap1-Rho-ROCK signaling facilitates receptor translocation and function via phosphorylation of filamin-2 Ser(2113). Together, these studies extend our previous findings to show that functional rescue of α2C-ARs is mediated through Rap1-filamin signaling. Perturbation of this signaling pathway may lead to alterations in α2C-AR trafficking and physiological function.

Angiotensin AT1 - α2C-Adrenoceptor Interaction Disturbs α2A-auto-Inhibition of Catecholamine Release in Hypertensive Rats

α₂-Adrenoceptors lower central sympathetic output and peripheral catecholamine release, and thus may prevent sympathetic hyperactivity and hypertension. α₂AR also influence vascular tension. These α₂AR are malfunctioning in spontaneously hypertensive rats (SHR). Here I tested if an interaction between α₂AR subtypes and the angiotensin AT1 receptor (AT₁R) precipitated these disorders. Blood pressure was monitored through a femoral artery catheter and cardiac output by ascending aorta flow in anesthetized rats. Catecholamine concentrations were determined in plasma collected at the end of a 15-min tyramine-infusion. Tyramine stimulates norepinephrine release through the re-uptake transporter, thus preventing re-uptake. Presynaptic control of vesicular release is therefore reflected as differences in overflow to plasma. Previous experiments showed surgical stress to activate some secretion of epinephrine, also subjected to α₂AR-auto-inhibition. Normotensive rats (WKY) and SHR were pre-treated with (1) vehicle or α₂AR-antagonist (L-659,066), followed by fadolmidine (α_2C>B>A + α₁AR-agonist), ST-91 (α_2non-A-selective agonist), or m-nitrobiphenyline (α_2CAR-agonist + α_2A+B-antagonist), or (2) AT1R-antagonist losartan, losartan + L-659,066, or losartan + clonidine. In WKY, L-659,066 alone, L-659,066 + agonist or losartan + L-659,066 increased catecholamine overflow to plasma after tyramine and eliminated the norepinephrine-induced rise in total peripheral vascular resistance (TPR). In SHR, L-659,066 + fadolmidine/ST-91/m-nitrobiphenyline and losartan + L-659,066 greatly increased, and losartan + clonidine reduced, catecholamine concentrations, and L-659,066 + ST-91, losartan + L-659,066 and losartan + clonidine eliminated the tyramine-induced rise in TPR. Separately, these drugs had no effect in SHR. In conclusion, peripheral α_2CAR-stimulation or AT₁R-inhibition restored failing α_2AAR-mediated auto-inhibition of norepinephrine and epinephrine release and control of TPR in SHR.

Cyclic AMP-Rap1A signaling activates RhoA to induce α(2c)-adrenoceptor translocation to the cell surface of microvascular smooth muscle cells

Intracellular signaling by the second messenger cyclic AMP (cAMP) activates the Ras-related small GTPase Rap1 through the guanine exchange factor Epac. This activation leads to effector protein interactions, activation, and biological responses in the vasculature, including vasorelaxation. In vascular smooth muscle cells derived from human dermal arterioles (microVSM), Rap1 selectively regulates expression of G protein-coupled α(2C)-adrenoceptors (α(2C)-ARs) through JNK-c-jun nuclear signaling. The α(2C)-ARs are generally retained in the trans-Golgi compartment and mobilize to the cell surface and elicit vasoconstriction in response to cellular stress. The present study used human microVSM to examine the role of Rap1 in receptor localization. Complementary approaches included murine microVSM derived from tail arteries of C57BL6 mice that express functional α(2C)-ARs and mice deficient in Rap1A (Rap1A-null). In human microVSM, increasing intracellular cAMP by direct activation of adenylyl cyclase by forskolin (10 μM) or selectively activating Epac-Rap signaling by the cAMP analog 8-pCPT-2'-O-Me-cAMP (100 μM) activated RhoA, increased α(2C)-AR expression, and reorganized the actin cytoskeleton, increasing F-actin. The α(2C)-ARs mobilized from the perinuclear region to intracellular filamentous structures and to the plasma membrane. Similar results were obtained in murine wild-type microVSM, coupling Rap1-Rho-actin dynamics to receptor relocalization. This signaling was impaired in Rap1A-null murine microVSM and was rescued by delivery of constitutively active (CA) mutant of Rap1A. When tested in heterologous HEK293 cells, Rap1A-CA or Rho-kinase (ROCK-CA) caused translocation of functional α(2C)-ARs to the cell surface (~4- to 6-fold increase, respectively). Together, these studies support vascular bed-specific physiological role of Rap1 and suggest a role in vasoconstriction in microVSM.

α2C-adrenoceptor modulators: a patent review

INTRODUCTION

α2-Adrenoceptors (α2-ARs) are membrane proteins belonging to the superfamily of GPCRs. Detailed studies have shown three different subtypes, namely α2A, α2B and α2C. Although numerous α2-AR ligands exist, only a small set of compounds have shown even a degree of selectivity among the three α2-AR subtypes. Moreover, these compounds suffer from binding to receptor sites outside the α2-AR subfamily. Efforts made to understand the biological significance of each α2-AR subtype have greatly been assisted by genetically engineered mice. The main results obtained suggest that α2C-AR stimulation may represent a therapeutic strategy to get an analgesic response with reduced sedative effects and undesirable changes in blood pressure due to α2A-AR activation.

AREAS COVERED

This review summarizes the patent literature about the development of α2C-AR modulators from 2000 to early 2010 and their therapeutic effects evoked by the interaction with this receptor subtype.

EXPERT OPINION

Over 90 patents have been deposited in the last 10 years regarding different methods of α2C-AR modulation (use of agonists or antagonists, nucleic acids and polypeptides) for diagnosis, prognosis and treatment of disorders involving this receptor. Nevertheless, despite the numerous published patents, ligands highly selective for the α2C-AR subtype, which continues to be enigmatic, are lacking.

Human skeletal muscle feed arteries studied in vitro: the effect of temperature on α(1)-adrenergic responsiveness

Heat and cold exposure can decrease and increase total peripheral resistance, respectively, in humans. With unique access to human skeletal muscle feed arteries, we sought both to characterize these vessels and to determine the interaction between temperature and α(1)-adrenergic receptor responsiveness. We hypothesized that α(1)-mediated vasocontraction of human feed arteries would be attenuated in response to 39 or 35°C. Skeletal muscle feed arteries were harvested from thirty-two human volunteers and studied using isometric techniques. Vessel function was assessed using KCl, sodium nitroprusside (SNP), phenylephrine (PE) and ACh dose-response curves to characterize non-receptor- and receptor-mediated vasocontraction and vasorelaxation. Single doses of PE (1 mm) and KCl (100 mm) were administered at 37°C and then, in a balanced design, repeated at both 35 and 39°C. The KCl and PE dose-response curves elicited significant vasocontraction (2009 ± 407 and 1974 ± 508 mg developed tension, respectively), whereas SNP and ACh induced the expected vasorelaxation (102 ± 6 and 73 ± 10% relaxation, respectively). Altering the temperature had no effect on inherent smooth muscle function (KCl response), but both a reduction (35°C) and an increase in temperature (39°C) decreased the vasocontractile response to 1 mm PE (37°C, 1478 ± 338 mg; 35°C, 546 ± 104 mg; and 39°C, 896 ± 202 mg; P < 0.05) or across PE dose (P < 0.05, 35 and 39 versus 37°C). Despite clear heterogeneity between both the human volunteers and the feed arteries themselves, this novel approach to the procurement of human vessels revealed a robust 'inverted U' response to altered temperature, such that α(1)-mediated vasocontraction was attenuated with either warming or cooling.

Intracellular α(2C)-adrenoceptors: storage depot, stunted development or signaling domain?

G-protein coupled receptors (GPCRs) are generally considered to function as cell surface signaling structures that respond to extracellular mediators, many of which do not readily access the cell's interior. Indeed, most GPCRs are preferentially targeted to the plasma membrane. However, some receptors, including α(2C)-Adrenoceptors, challenge conventional concepts of GPCR activity by being preferentially retained and localized within intracellular organelles. This review will address the issues associated with this unusual GPCR localization and discuss whether it represents a novel sub-cellular niche for GPCR signaling, whether these receptors are being stored for rapid deployment to the cell surface, or whether they represent immature or incomplete receptor systems.

Rho kinase activation and ROS production contributes to the cooling enhanced contraction in cutaneous equine digital veins

A decrease in environmental temperature can directly affect the contractility of cutaneous vasculature, mediated in part by α2-adrenoceptors. Most of the cellular mechanisms underlying the cooling-enhanced contractility to α2-adrenoceptor agonists have been reported in cutaneous arteries but little information is available on cutaneous veins. To investigate the cellular mechanisms associated with the cooling-enhanced contraction to UK-14304 (α2-adrenoceptor agonist), isolated equine digital veins (EDVs) were studied at 30°C and 22°C. The effects of inhibitors were studied on the contractile response to UK-14304 (0.1 μM). The cooling-enhanced responses were inhibited by Rho kinase inhibitors [maximum response to UK-14304 95.2 ± 8% of response to depolarizing Krebs solution (DKS) in control vessels cooled to 22°C, compared with 31.4 ± 6% in the presence of fasudil 1 μM and 75.8 ± 6% with Y-27632 0.1 μM] and the effects of these inhibitors were considerably less at 30°C (control response 56.4 ± 5% of DKS; 34.9 ± 6% with fasudil 1 μM and 50.6 ± 9% with Y-27632 0.1 μM). Furthermore, Western blotting showed that one of the downstream targets for Rho kinase activity, ezrin/radixin/moesin, was phosphorylated after cooling and reduced by fasudil (1 μM) only at 22°C. The activation of protein kinase C contributed to the contractile response, but predominantly at 30°C (maximum response 82.3 ± 9% of DKS for control; 57.7 ± 10% in the presence of chelerythrine 10 μM) with no significant effect at 22°C. The reduction of the response at 22°C by antioxidants, rotenone (14% reduction), and tempol (21% reduction) suggested the contribution of reactive oxygen species (ROS). No evidence was obtained to support the participation of tyrosine kinase. These data demonstrate that Rho kinase activation and the production of ROS contributes to the cooling-enhanced contraction in these cutaneous digital veins.

Desensitization of vascular response in vivo: contribution of genetic variation in the [alpha]2B-adrenergic receptor subtype

OBJECTIVES

Vascular alpha2B-adrenergic receptors (alpha2B-ARs) mediate vasoconstriction and contribute to peripheral regulation of vascular tone. In vitro, a common 301-303 deletion in the alpha2B-AR gene, ADRA2B, results in loss of alpha2B-AR desensitization. We examined the hypothesis that ADRA2B del301-303 or other common ADRA2B variants alter vascular desensitization in vivo.

METHODS

We measured sensitivity to a highly selective alpha2-AR agonist, dexmedetomidine, (0.01-1000 ng/min) in the dorsal hand vein in 41 healthy individuals. To induce desensitization a dose of dexmedetomidine that resulted in submaximal constriction was infused for 180 min and dorsal hand vein responses measured. Desensitization was defined as the ratio between the area-under-the-effect curve for each individual's response and the hypothetical area-under-the-effect curve assuming that the initial response had been maintained for 180 min (ratio below 1 reflecting desensitization). The relationship between six ADRA2B variants (one promoter, three coding, and two in the 3' untranslated region ) with an allele frequency of more than 5% and desensitization was determined.

RESULTS

Forty-one individuals (22 men, 21 whites, age 18-45 years) were studied. The ADRA2B 301-303 deletion allele (ins/del and del/del, n = 18) was associated with resistance to desensitization [1.01 (interquartile range 0.90-1.06)] as compared with ins/ins homozygous individuals (n = 23) [0.91 (interquartile range 0.73-0.99)], P = 0.026. In addition, the -98 GG, 1182 CC, and 1776 CC genotypes were associated with significantly less desensitization than GC or CC, and CA or AA genotypes, respectively.

CONCLUSION

Common ADRA2B variants contribute to the interindividual variability in vascular desensitization to an alpha2-AR agonist in vivo.

Genetic variants in the alpha2C-adrenoceptor and G-protein contribute to ethnic differences in cardiovascular stress responses

OBJECTIVES

Cardiovascular responses to stressors are regulated by sympathetic activity, increased in black Americans, and associated with future cardiovascular morbidity. Our aim was to determine whether two functional variants in genes regulating sympathetic activity, a deletion in the alpha2C-adrenergic receptor (ADRA2C del322-325) and a G-protein beta3-subunit variant (GNB3 G825T), affect cardiovascular responses to physiologic stressors and contribute to their ethnic differences.

METHODS

We measured heart rate and blood pressure responses to a cold pressor test (CPT) in 79 healthy participants (40 blacks, 39 whites), aged 25.7+/-5.3 years, and determined genotypes for the ADRA2C and GNB3 variants. We examined the response variables (increase in heart rate and blood pressure) in multiple linear regression analyses adjusting first for baseline measures, ethnicity, and other covariates, and then additionally for genotypes.

RESULTS

Black participants had a greater heart rate response to CPT than whites [mean difference, 9.9 bpm; 95% confidence interval (CI), 4.1 to 15.6; P=0.001]. Both the ADRA2C del/del (15.8 bpm; 95% CI, 8.0-23.7; P<0.001) and GNB3 T/T genotypes (6.8 bpm; 95% CI, 0.9-12.7; P=0.026) were associated with greater heart rate response. After adjusting for genotypes, the ethnic difference was abrogated (1.3 bpm; 95% CI, -5.4-8.0; P=0.70), suggesting that the genetic variants contributed substantially to ethnic differences.

CONCLUSION

Variation in genes that regulate sympathetic activity affects hemodynamic stress responses and contributes to their ethnic differences. This study elucidates how genetic factors may in part explain ethnic differences in cardiovascular regulation.

Marked sympathetic component in the perivascular innervation of the dorsal paratendinous tissue of the patellar tendon in arthroscopically treated tendinosis patients

During the recent years, a few studies have shed new light on the innervation patterns of the human patellar tendon, but the area of the loose paratendinous connective tissue dorsal to the proximal tendon proper has yet not been investigated. That is a drawback, since this is the area targeted in promising treatment regimens of chronic painful patellar tendinosis, namely sclerosing Polidocanol injection therapy, and a new surgical method conforming to ultrasound and color Doppler guided arthroscopic shaving, directed at neovessels found in the region. The present study thus aimed at investigating the paratendinous area dorsal to the proximal patellar tendon proper in seven patients being operated for tendinosis. Biopsies were collected through the new arthroscopic technique, approaching the tendon from the dorsal side. Samples were investigated using immunohistochemistry with antibodies delineating general (PGP 9.5), sensory (SP/CGRP), and sympathetic (TH/NPY) nerve patterns, and also antibodies against alpha1- and alpha2A-adrenoreceptors. Both small and large blood vessels had a marked perivascular innervation (PGP 9.5). Surprisingly, this perivascular innervation was found only to a very limited extent to correspond to sensory nerves, while there were marked immunoreactions for sympathetic markers. Adrenoreceptor immunoreactions frequently occurred in blood vessel walls. In conclusion, this study demonstrates, for the first time, the innervation patterns of the area dorsal to the patellar tendon in man. It shows that the area investigated is under marked influence by the sympathetic nervous system. Thus, sympathetic effects are likely to occur for blood vessels of the area, which is interesting since color Doppler has revealed that vessels of this area ("neovessels") display a pathologically high blood flow in tendinosis. The findings are discussed in relation to aspects of vascular regulation, and to pain symptoms of tendinosis.

Cyclic AMP acts through Rap1 and JNK signaling to increase expression of cutaneous smooth muscle alpha2C-adrenoceptors

Cold increases cutaneous vasoconstriction by unmasking the contractile activity of alpha(2C)-adrenoceptors (alpha(2C)-ARs) in vascular smooth muscle cells (VSMCs), which is mediated by the cold-induced mobilization of alpha(2C)-ARs from the transGolgi to the cell surface. The expression of alpha(2C)-ARs in human cutaneous VSMCs is under dual regulation by cyclic AMP: gene transcription is inhibited by cyclic AMP acting through protein kinase A but is increased by cyclic AMP acting through the exchange protein directly activated by cyclic AMP (EPAC) and the GTP-binding protein Rap1. Experiments were performed to further characterize the Rap1 signaling pathway. Forskolin (10 muM), the selective EPAC activator, 8-pCPT-2'-O-Me-cyclic AMP (CMC; 100 microM), or a constitutively active mutant of Rap1 (Rap1CA) increased the activity of c-Jun NH(2)-terminal kinase (JNK) in human cutaneous VSMCs. This was associated with the increased phosphorylation of c-Jun and activation of an activator protein (AP)-1 reporter construct, which were inhibited by the JNK inhibitor SP600125 (3 microM). Rap1CA increased the activity of an alpha(2C)-AR promoter-reporter construct, which was inhibited by SP600125 (3 microM) or by the mutation of an AP-1 binding site in the alpha(2C)-AR promoter. Furthermore, forskolin (10 microM) or CMC (100 microM) increased the expression of the alpha(2C)-AR protein, and these effects were inhibited by SP600125 (3 microM). Therefore, cyclic AMP increases the expression of alpha(2C)-ARs in cutaneous VSMCs by activating a novel Rap1 signaling pathway, mediated by the activation of JNK, AP-1, and the subsequent transcriptional activation of the alpha(2C)-AR gene. By increasing the expression of cold-responsive alpha(2C)-ARs, this pathway may contribute to enhanced cold-induced vasoconstriction in the cutaneous circulation, including Raynaud's phenomenon.

Regulation of vascular reactivity in scleroderma: new insights into Raynaud's phenomenon

Because of the role of the RhoA/Rho kinase (ROCK) pathway in regulating numerous pathologic processes including vasoconstriction, vascular remodeling, and fibrosis, ROCK inhibitors may be especially beneficial in treating Raynaud's phenomenon and scleroderma.

[Primary and secondary Raynaud's phenomenon]

The term Raynaud's phenomenon describes an abnormal vasospastic response to cold or emotional stress. It is a common condition with a prevalence of 3-5% of the population. Clinically, Raynaud's phenomenon manifests as sharply demarcated colour changes of the skin of the digits that is often accompanied by paraesthesia. Raynaud's phenomenon can be subdivided into primary, or idiopathic, and secondary forms, in the latter of which associated diseases or causes can be identified. The pathogenesis of the disease is incompletely understood. Pathologic changes have been observed primarily in vascular smooth muscle cells, endothelial cells and perineuronal microvasculature. Current therapeutic strategies include supportive treatments, topical therapeutic approaches and systemic medication. Drug therapies with proven efficacy include calcium channel blockers, prostacyclin analogues, fluoxetine, losartan and sildenafil.