KS0365, a novel activator of the transient receptor potential vanilloid 3 (TRPV3) channel, accelerates keratinocyte migration.

BACKGROUND AND PURPOSE: Ca2+ signalling mediated by the thermosensitive, non-selective, Ca2+ -permeable transient receptor potential channel TRPV3 is assumed to play a critical role in regulating several aspects of skin functions, such as keratinocyte proliferation, differentiation, skin barrier formation and wound healing. Studying the function of TRPV3 in skin homeostasis, however, is still constrained by a lack of potent and selective pharmacological modulators of TRPV3. EXPERIMENTAL APPROACH: By screening an in-house compound library using fluorometric intracellular Ca2+ assays, we identified two chemically related hits. The more potent and efficient TRPV3 activator 2-(2-chloro-3-isopropylcyclopent-2-en-1-yl)-4-methylphenol (KS0365) was further evaluated in fluo-4-assisted Ca2+ assays, different Ca2+ imaging approaches, electrophysiological studies, cytotoxicity and migration assays. KEY RESULTS: KS0365 activated recombinant and native mouse TRPV3 more potently and with a higher efficacy compared with 2-APB and did not activate TRPV2 or TRPV4 channels. The activation of TRPV3 by KS0365 super-additively accelerated the EGF-induced keratinocyte migration, which was inhibited by the TRP channel blocker ruthenium red or by siRNA-mediated TRPV3 knockdown. Moreover, KS0365 induced strong Ca2+ responses in migrating front cells and in leading edges of keratinocytes. CONCLUSIONS AND IMPLICATIONS: The selective TRPV3 activator KS0365 triggers increases in [Ca2+ ]i with most prominent signals in the leading edge and accelerates migration of keratinocytes. TRPV3 activators may promote re-epithelialization upon skin wounding.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products.

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products.

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

Synthesis of (-)-Mitrephorone A via a Bioinspired Late Stage C-H Oxidation of (-)-Mitrephorone B.

We present a bioinspired late-stage C-H oxidation of the ent-trachylobane natural product mitrephorone B to mitrephorone A. The realization of this unprecedented transformation was accomplished by either an iron-catalyzed or electrochemical oxidation and enabled access to the densely substituted oxetane in one step. Formation of mitrephorone C, which is lacking the central oxetane unit but features a keto-function at C2, was not formed under these conditions.

Distribution of omega-3 fatty acids in tissues of rabbits fed a flaxseed-supplemented diet.

Diets rich in omega-3 polyunsaturated fatty acids are associated with decreased incidences of cardiovascular disease. The extent of incorporation and distribution of these beneficial fats into body tissues is uncertain. Rabbits were fed regular rabbit chow or a diet containing 10% ground flaxseed that is highly enriched with the omega-3 polyunsaturated fatty acid alpha-linolenic acid (ALA). The high-flaxseed diet resulted in an incorporation of ALA in all tissues, but mostly in the heart and liver with little in the brain. Docosahexaenoic and eicosapentaenoic acid levels were also selectively increased in some tissues, and the effects were not as large as ALA. Arachidonic acid and the ratio of omega-6/omega-3 fatty acids were decreased in all tissues obtained from the flax-supplemented group. Consumption of dietary flaxseed appears to be an effective means to increase ALA content in body tissues, but the degree will depend upon the tissues examined.

Differential sensitivities of the NCX1.1 and NCX1.3 isoforms of the Na+-Ca2+ exchanger to alpha-linolenic acid.

OBJECTIVE: Dietary intake of omega-3 polyunsaturated fatty acids (PUFA) like alpha-linolenic acid (ALA) is antiarrhythmic and cardioprotective. PUFA may also be beneficial in hypertension. Altered Na(+)-Ca(2+) exchanger (NCX) activity has been implicated in arrhythmias, hypertension and heart failure and may be a target for PUFA. Thus, we tested the effects of ALA and other distinct fatty acids on the cardiac (NCX1.1) and vascular (NCX1.3) NCX isoforms. METHODS: HEK293 cells stably expressing NCX isoforms were ramped from +60 to -100 mV (over 1600 ms) in the absence and presence of 25 microM oleic acid (OA, omega-9), linoleic acid (LA, omega-6), ALA (omega-3), or eicosapentaenoic acid (EPA, omega-3). NiCl(2) (5 mM) was used to inhibit and therefore identify the NCX current. The effect of 25 microM ALA on NCX1.1 and NCX1.3 activity was also assessed in adult rat ventricular cardiomyocytes and rabbit aortic vascular smooth muscle cells (VSMC) by measuring [Ca(2+)](i) following substitution of [Na(+)](o) with Li(+). RESULTS: Application of Ni(2+) had no effect in non-transfected cells. ALA and EPA (25 microM) reduced the Ni(2+)-sensitive forward NCX1.1 current (at -100 mV) by 64% and reverse current (at +60 mV) by 57%, and inhibited the Ni(2+)-sensitive NCX1.3 forward and reverse currents by 79% and 76%, respectively. Neither OA nor LA (25 microM) affected the NCX1.1 currents, but both partially inhibited the forward and reverse mode NCX1.3 currents. Inhibition of NCX1.3 by ALA occurred at a much lower IC(50) ( approximately 19 nM) than for NCX1.1 ( approximately 120 nM). In cardiomyocytes and VSMC, ALA significantly reduced the Li(+)-induced rise in intracellular [Ca(2+)]. CONCLUSIONS: NCX1.3 is more sensitive to inhibition by ALA than NCX1.1. In addition, only omega-3 PUFA inhibits NCX1.1, but several classes of fatty acids inhibit NCX1.3. The differential sensitivity of NCX isoforms to fatty acids may have important implications as therapeutic approaches for hypertension, heart failure and arrhythmias.

Expression of protein kinase C isoforms in cardiac hypertrophy and heart failure due to volume overload.

The present study determined whether changes in the activity and isoforms of protein kinase C (PKC) are associated with cardiac hypertrophy and heart failure owing to volume overload induced by aortocaval shunt (AVS) in rats. A significant increase in Ca2+-dependent and Ca2+-independent PKC activities in the homogenate and particulate fractions, unlike the cystolic fraction, of the hypertrophied left ventricle (LV) were evident at 2 and 4 weeks after inducing the AVS. This increase coincided with increases in PKC-alpha and PKC-zeta contents at 2 week and increases in PKC-alpha, PKC-beta1, PKC-beta2, and PKC-zeta contents at 4 weeks in the hypertrophied LV. By 8 and 16 weeks of AVS, PKC activity and content were unchanged in the failing LV. On the other hand, no increase in the PKC activity or isoform content in the hypertrophied right ventricle (RV) was observed during the 16 weeks of AVS. The content of G alpha q was increased in the LV at 2 weeks but then decreased at 16 weeks, whereas G alpha q content was increased in RV at 2 and 4 weeks. Our data suggest that an increase in PKC isoform content neither plays an important role during the development of cardiac hypertrophy nor participates in the phase leading to heart failure owing to volume overload.

Adenovirally delivered shRNA strongly inhibits Na+-Ca2+ exchanger expression but does not prevent contraction of neonatal cardiomyocytes.

The cardiac Na(+)-Ca(2+) exchanger (NCX1) is the main mechanism for Ca(2+) efflux in the heart and is thought to serve an essential role in cardiac excitation-contraction (E-C) coupling. The demonstration that an NCX1 gene knock-out is embryonic lethal provides further support for this essential role. However, a recent report employing the Cre/loxP technique for cardiac specific knock-out of NCX1 has revealed that cardiac function is remarkably preserved in these mice, which survived to adulthood. This controversy highlights the necessity for further investigation of NCX1 function in the heart. In this study, we report on a novel approach for depletion of NCX1 in postnatal rat myocytes that utilizes RNA interference (RNAi), administered with high efficiency via adenoviral transfection. Depletion of NCX1 was confirmed by immunocytochemical detection, Western blots and radioisotopic assays of Na(+)-Ca(2+) exchange activity. Exchanger expression was inhibited by up to approximately 94%. Surprisingly, spontaneous beating of these cardiomyocytes was still maintained, although at a lower frequency. Electrical stimulation could elicit a normal beating rhythm, although NCX depleted cells exhibited a depressed Ca(2+) transient amplitude, a depressed rate of Ca(2+) rise and decline, elevated diastolic [Ca(2+)], and shorter action potentials. We also observed a compensatory increase in sarcolemmal Ca(2+) pump expression. Our data support an important, though non-essential, role for the NCX1 in E-C coupling in these neonatal heart cells. Furthermore, this approach provides a valuable means for assessing the role of NCX1 and could be utilized to examine other cardiac proteins in physiological and pathological studies.

Dietary flaxseed protects against ventricular fibrillation induced by ischemia-reperfusion in normal and hypercholesterolemic Rabbits.

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the (n-3) PUFA found in fish oils, exert antiarrhythmic effects during ischemia. Flaxseed is the richest plant source of another (n-3) PUFA, alpha-linolenic acid (ALA), yet its effects remain largely unknown. Our objective was to determine whether a flaxseed-rich diet is antiarrhythmic in normal and hypercholesterolemic rabbits. Male New Zealand White (NZW) rabbits (n = 14-16) were fed as follows: regular diet (REG group); diet containing 10% flaxseed (FLX group); 0.5% cholesterol (CHL group); or 0.5% cholesterol + 10% flaxseed (CHL/FLX group) for up to 16 wk. Plasma cholesterol was significantly elevated in the CHL and CHL/FLX groups. Plasma triglycerides were unchanged. ALA levels increased significantly in plasma and hearts of the FLX and CHL/FLX groups. After the feeding period, rabbit hearts were isolated and subjected to global ischemia (30 min) and reperfusion (45 min). Ventricular fibrillation (VF) occurred during ischemia in 33% of REG but in none of FLX hearts, and 28% of CHL but only 6% of CHL/FLX hearts. VF incidence during reperfusion was 28% and 26% in REG and FLX hearts, respectively. The incidence significantly increased to 64% in CHL hearts, and was significantly attenuated (18%) in CHL/FLX hearts. CHL markedly prolonged the QT interval, whereas FLX significantly shortened the QT interval and reduced arrhythmias in the FLX and CHL/FLX hearts. In vitro application of (n-3) PUFA shortened the action potential duration, an effect consistent with the QT data. This study demonstrates that dietary flaxseed exerts antiarrhythmic effects during ischemia-reperfusion in rabbit hearts, possibly through shortening of the action potential.

Role of oxidative stress in ischemia-reperfusion-induced changes in Na+,K(+)-ATPase isoform expression in rat heart.

The aim of this study was to assess whether depression of cardiac Na+,K(+)-ATPase activity during ischemia/reperfusion (I/R) is associated with alterations in Na+,K(+)-ATPase isoforms, and if oxidative stress participates in these I/R-induced changes. Na+,K(+)-ATPase alpha1, alpha2, alpha3, beta1, beta2, and beta3 isoform contents were measured in isolated rat hearts subjected to I/R (30 min of global ischemia followed by 60 min of reperfusion) in the presence or absence of superoxide dismutase plus catalase (SOD+CAT). Effects of oxidative stress on Na+,K(+)-ATPase isoforms were also examined by perfusing the hearts for 20 min with 300 microM hydrogen peroxide or 2 mM xanthine plus 0.03 U/ml xanthine oxidase (XXO). I/R significantly reduced the protein levels of all alpha and beta isoforms. Treatment of I/R hearts with SOD+CAT preserved the levels of alpha2, alpha3, beta1, beta2, and beta3 isoforms, but not that of the alpha1 isoform. Perfusion of hearts with hydrogen peroxide and XXO depressed all Na+,K(+)-ATPase alpha and beta isoforms, except for alpha1. These results indicate that the I/R-induced decrease in Na+,K(+)-ATPase may be due to changes in Na+,K(+)-ATPase isoform expression and that oxidative stress plays a role in this alteration. Antioxidant treatment attenuated the I/R-induced changes in expression of all isoforms except alpha1, which appears to be more resistant to oxidative stress.

Renin-angiotensin blockade attenuates cardiac myofibrillar remodelling in chronic diabetes.

Previous studies have shown that the renin-angiotensin system (RAS) is activated in diabetes and this may contribute to the subcellular remodelling and heart dysfunction in this disease. Therefore, we examined the effects of RAS blockade by enalapril, an angiotensin-converting enzyme inhibitor, and losartan, an angiotensin receptor AT1 antagonist, on cardiac function, myofibrillar and myosin ATPase activity as well as myosin heavy chain (MHC) isozyme expression in diabetic hearts. Diabetes was induced in rats by a single injection of streptozotocin (65 mg/kg; i.v.) and these animals were treated with and without enalapril (10 mg/kg/day; oral) or losartan (20 mg/kg/day; oral) for 8 weeks. Enalapril or losartan prevented the depressions in left ventricular rate of pressure development, rate of pressure decay and ventricular weight seen in diabetic animals. Both drugs also attenuated the decrease in myofibrillar Ca2+-ATPase, Mg2+-ATPase and myosin ATPase activity seen in diabetic rats. The diabetes-induced increase in beta-MHC content and gene expression as well as the decrease in alpha-MHC content and mRNA levels were also prevented by enalapril and losartan. These results suggest the occurrence of myofibrillar remodelling in diabetic cardiomyopathy and provide evidence that the beneficial effects of RAS blockade in diabetes may be associated with attenuation of myofibrillar remodelling in the heart.

Ischemia-reperfusion alters gene expression of Na+-K+ ATPase isoforms in rat heart.

The present study investigated whether oxidative stress plays a role in ischemia-reperfusion-induced changes in cardiac gene expression of Na(+)-K(+) ATPase isoforms. The levels of mRNA for Na(+)-K(+) ATPase isoforms were assessed in the isolated rat heart subjected to global ischemia (30 min) followed by reperfusion (60 min) in the presence or absence of superoxide dismutase (5 x 10(4)U/L) plus catalase (7.5 x 10(4)U/L), an antioxidant mixture. The levels of mRNA for the alpha(2), alpha(3), and beta(1) isoforms of Na(+)-K(+) ATPase were significantly reduced in the ischemia-reperfusion hearts, unlike the alpha(1) isoform. Pretreatment with superoxide dismutase+catalase preserved the ischemia-reperfusion-induced changes in alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, whereas the alpha(1) mRNA levels were unaffected. In order to test if oxidative stress produced effects similar to those seen with ischemia-reperfusion, hearts were perfused with an oxidant, H(2)O(2) (300 microM), or a free radical generator, xanthine (2mM) plus xanthine oxidase (0.03 U/ml) for 20 min. Perfusion of hearts with H(2)O(2) or xanthine/xanthine oxidase depressed the alpha(2), alpha(3), and beta(1) isoform mRNA levels of the Na(+)-K(+) ATPase, but had lesser effects on alpha(1) mRNA levels. These results indicate that Na(+)-K(+) ATPase isoform gene expression is altered differentially in the ischemia-reperfusion hearts and that antioxidant treatment appears to attenuate these changes. It is suggested that alterations in Na(+)-K(+) ATPase isoform gene expression by ischemia-reperfusion may be mediated by oxidative stress.

Preconditioning attenuates ischemia-reperfusion-induced remodeling of Na+-K+-ATPase in hearts.

The aim of this study was to determine whether changes in protein content and/or gene expression of Na+-K+-ATPase subunits underlie its decreased enzyme activity during ischemia and reperfusion. We measured protein and mRNA subunit levels in isolated rat hearts subjected to 30 min of ischemia and 30 min of reperfusion (I/R). The effect of ischemic preconditioning (IP), induced by three cycles of ischemia and reperfusion (10 min each), was also assessed on the molecular changes in Na+-K+-ATPase subunit composition due to I/R. I/R reduced the protein levels of the alpha2-, alpha3-, beta1-, and beta2-isoforms by 71%, 85%, 27%, and 65%, respectively, whereas the alpha1-isoform was decreased by <15%. A similar reduction in mRNA levels also occurred for the isoforms of Na+-K+-ATPase. IP attenuated the reduction in protein levels of Na+-K+-ATPase alpha2-, alpha3-, and beta2-isoforms induced by I/R, without affecting the alpha1- and beta1-isoforms. Furthermore, IP prevented the reduction in mRNA levels of Na+-K+-ATPase alpha2-, alpha3-, and beta1-isoforms following I/R. Similar alterations in protein contents and mRNA levels for the Na+/Ca2+ exchanger were seen due to I/R as well as IP. These findings indicate that remodeling of Na+-K+-ATPase may occur because of I/R injury, and this may partly explain the reduction in enzyme activity in ischemic heart disease. Furthermore, IP may produce beneficial effects by attenuating the remodeling of Na+-K+-ATPase and changes in Na+/Ca2+ exchanger in hearts after I/R.

Ischemia-induced dephosphorylation of cardiomyocyte connexin-43 is reduced by okadaic acid and calyculin A but not fostriecin.

The gap junction protein connexin-43 (Cx43) exists mainly in the phosphorylated state in the normal heart, while ischemia induces dephosphorylation. Phosphatase(s) involved in cardiac Cx43 dephosphorylation have not as yet been identified. We examined the acute effects of ischemia on the dephosphorylation of the gap junction protein connexin-43 in isolated adult cardiomyocytes and isolated perfused hearts. In addition we tested the effectiveness of protein phosphatase 1 and 2A (PP1/2A) inhibitors in preventing Cx43 dephosphorylation. In both models, significant accumulation of the 41 kDa non-phosphorylated Cx43, accompanied by decreased relative levels of the 43-46 kDa phosphorylated Cx43, was observed at 30 min of ischemia. Okadaic acid decreased ischemia-induced Cx43 dephosphorylation; it also decreased the accumulation of non-phosphorylated Cx43 at the intercalated discs of myocytes in the whole heart. Calyculin A, but not fostriecin, also decreased ischemia-induced Cx43 dephosphorylation in isolated cardiomyocytes. It is concluded that isolated adult myocytes respond to ischemia in a manner similar to whole hearts and that ischemia-induced dephosphorylation of Cx43 is mediated, at least in part, by PP1-like phosphatase(s).

Differential effects of etomoxir treatment on cardiac Na+-K+ ATPase subunits in diabetic rats.

Etomoxir, an inhibitor of mitochondrial carnitine palmitoyltransferase-1, is known to attenuate the changes in myosin isoforms and sarcoplasmic reticular function that occur in diabetic rat hearts. In the present study, we tested the hypothesis that etomoxir also prevents the diabetes-induced depression of sarcolemmal (SL) Na+-K+ATPase activity by differentially affecting its alpha and beta-subunit levels. Streptozotocin-induced diabetes was associated with a decreased in alpha2-, alpha3-subunit levels, whereas the alpha1-and beta1-subunits were unchanged. Treatment of diabetic rats for 4 weeks with etomoxir (8 mg/kg/day) increased the alpha1-subunit levels, but failed to prevent the decrease in alpha2- and alpha3-subunit levels. In euglycemic control rats, etomoxir increased the alpha1-subunit protein level per g heart weight, but did not alter the alpha2-, alpha3- and beta1-subunit levels. The large decrease in Na+-K+ ATPase activity per g heart weight in diabetic rats was prevented by etomoxir, which suggests that the increased alpha1-subunit levels seen with this drug compensated for the decreased alpha2- and alpha3-subunit levels. The SL yield was also increased by etomoxir in euglycemic rats in proportion to the higher alpha1-subunit level, which resulted in an unchanged alpha1-content when expressed per mg SL protein; however, the alpha2- and beta1-subunit levels were reduced (p < 0.05). The depressed alpha2- and beta3 subunit levels of diabetic rats were associated with reduced mRNA abundance. However, no increase in alpha1-subunit mRNA abundance was seen in the etomoxir treated rats, which suggests that possibly post-transcriptional mechanisms are occurring in these hearts.