Characterisation of the relaxant response to raloxifene in porcine coronary arteries

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Relaxant Effects of Piperine and Piperlongumine from Piper longum Fruits on Porcine Coronary Artery

Since ancient times, Piper longum Linn. fruits have been recognized for exhibiting various effects, including the diaphoretic effects linked to enhanced blood flow. Piperine and piperlongumine coexist in Piper longum Linn. fruits, although the cardiovascular effects of both compounds remain elusive. We investigated their action of piperine and piperlongumine in porcine coronary arteries, comparing them to the Ca2+ channel antagonist diltiazem. Piperlongumine, unlike piperine or diltiazem, concentration-dependently inhibited basal contractile tone in endothelium-denuded coronary arteries. All three compounds inhibit tonic contractions induced by high potassium chloride (KCl) concentrations. The order of relaxation potency indexed by the half-maximal effective concentration (EC50) were as follows: diltiazem > piperlongumine > piperine. These effects were not different between endothelium-intact and -denuded preparations. In endothelial-denuded preparations, pretreatment with these compounds not only inhibited KCl-induced tonic contractions attenuated calcium chloride (CaCl2)-induced ones in a Ca2+-free medium. Histamine-induced phasic contractions in a Ca2+-free medium containing intracellular Ca2+ chelator was completely suppressed by selective inositol trisphosphate receptor antagonist and piperlongumine, whereas piperine or diltiazem do not have the same effect. These findings suggest that piperine and piperlongumine similar to diltiazem cause vasorelaxation by inhibiting both KCl- and CaCl2-induced contractions in coronary arteries, possibly through the inhibition of voltage-dependent Ca2+ channels. Piperlongumine inhibits histamine-induced contractions in a Ca2+-free medium, which is associated with the intracellular Ca2+ signaling pathway, suggesting that the relaxant effect of piperlongumine differs from that of piperine.

Therapeutically relevant concentrations of raloxifene dilate pressurized rat resistance arteries via calcium-dependent endothelial nitric oxide synthase activation

OBJECTIVE

Selective estrogen receptor modulators (SERMs) inhibit constriction of mammalian conduit arteries. However, it is unknown whether SERMs at therapeutically achievable concentrations could reduce vascular tone in resistance arteries. The present study aimed to examine roles of Ca(2+) influx in endothelium and endothelial nitric oxide synthase (eNOS) activation in dilatations induced by raloxifene, a second-generation SERM in myogenically active arteries.

METHODS AND RESULTS

Small mesenteric arteries from Sprague-Dawley rats were isolated and mounted in a pressure myograph for measurement of changes in vessel diameter. [Ca(2+)](i) images on native endothelial cells of intact arteries were determined by the fluorescence imaging technique, and phosphorylation of eNOS was assayed by Western blotting. Raloxifene (0.3 to 10 nmol/L) produced dilatations on established steady myogenic constriction. Female rat arteries dilated significantly more in response to raloxifene than male arteries. Raloxifene-induced dilatations of female arteries were blunted by N(G)-nitro-l-arginine methyl ester but unaffected by 1400W, charybdotoxin plus apamin, wortmannin, or LY294002. Raloxifene (3 nmol/L) triggered rises in endothelial cell [Ca(2+)](i) and increased eNOS phosphorylation at Ser1177. Both effects were greater in arteries from female rats than in arteries from male rats. Increases in endothelial cell [Ca(2+)](i) and in eNOS phosphorylation were prevented by removal of extracellular Ca(2+) ions. Finally, ICI 182,780 did not affect the raloxifene-stimulated rise in endothelial cell [Ca(2+)](i), eNOS phosphorylation, and vasodilatations. Chronic raloxifene treatment reduced myogenic constriction in arteries from female but not male rats.

CONCLUSION

Raloxifene at therapeutically relevant concentrations inhibits myogenic constriction by an NO-dependent mechanism that causally involves the elevated [Ca(2+)](i) in endothelial cells and subsequent eNOS activation. Raloxifene dilates resistance arteries more effectively in female rats, indicating its significant gender-related action on endothelial cells in microcirculation.

Acute postischemic treatment with estrogen receptor-alpha agonist or estrogen receptor-beta agonist improves myocardial recovery

BACKGROUND

After ischemia/reperfusion (I/R) injury, female hearts demonstrate improved functional recovery compared with male, which suggests a protective role for estrogen. Acute postischemic treatment with 17-beta-estradiol (E2) attenuates myocardial dysfunction. However, it is unknown by which estrogen receptor (ER) E2 mediates this acute cardioprotection during I/R. Therefore, we hypothesize that postischemic infusion of the selective ER-alpha agonist (4,4',4''-[4-propyl-(1H)-pyrazole-1,3,5-triyl]tris-phenol [PPT]) or the selective ER-beta agonist (2,3-bis(4-hydroxyphenyl)-propionitrile [DPN]) will improve myocardial function after I/R injury.

METHODS

Isolated, perfused hearts (Langendorff) from adult male rats were subjected to 25 minutes of ischemia followed by 40 minutes of reperfusion. Hearts (n = 4-6 per group) were randomly infused with either perfusate, PPT or DPN at 1, 10, or 100 nmol/L throughout reperfusion. After I/R, heart tissue was analyzed for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, vascular endothelial growth factor (VEGF), and lactate dehydrogenase (LDH).

RESULTS

Postischemic treatment with 10 nmol/L of PPT significantly improved myocardial function. Additionally, 10 or 100 nmol/L of DPN significantly increased myocardial functional recovery after I/R injury, with maximum benefit at the 10 nmol/L dose. A trend toward lower levels of LDH was noted in DPN- and PPT-treated groups after I/R injury. Neither PPT nor DPN affected myocardial production of TNF-alpha or IL-1beta. However, higher levels of myocardial VEGF were noted in the PPT-treated group compared with controls.

CONCLUSION

Both ER-alpha and ER-beta are involved in mediating E2-induced rapid cardioprotection after I/R injury. Advancing our understanding of both ER subtypes may be useful for the development of novel strategies that may benefit both males and females in response to myocardial ischemia.

Breast cancer, estrogen receptor and ligands

This review emphasizes the relationship of breast cancer, estrogen receptor and ligands, especially the centrality of the estrogen receptor, which mediates on one hand the hormone-induced gene transcription and on the other hand the anti-estrogen action against breast cancer. The characterization of the estrogen receptor ligand-binding domain co-crystallized with agonists or antagonists provided a molecular basis to gain an insight into the regulation of estrogen receptor and, thereby, to describe the mechanism of the hormone therapy in treating breast cancer.

Postischemic infusion of 17-beta-estradiol protects myocardial function and viability

BACKGROUND

Females demonstrate improved cardiac recovery after ischemia/reperfusion injury compared with males. Attenuation of myocardial dysfunction with preischemic estradiol suggests that estrogen may be an important mediator of this cardioprotection. However, it remains unclear whether post-injury estradiol may have clinical potential in the treatment of acute myocardial infarction. We hypothesize that postischemic administration of 17beta-estradiol will decrease myocardial ischemia/reperfusion injury and improve left ventricular cardiac function.

MATERIALS AND METHODS

Adult male Sprague Dawley rat hearts (n = 20) (Harlan, Indianapolis, IN) were isolated, perfused with Krebs-Henseleit solution via Langendorff model, and subjected to 15 min of equilibration, 25 min of warm ischemia, and 40 min reperfusion. Experimental hearts received postischemic 17beta-estradiol infusion, 1 nm (n = 4), 10 nm (n = 4), 25 nm (n = 4), or 50 nm (n = 4), throughout reperfusion. Control hearts (n = 4) were infused with perfusate vehicle.

RESULTS

Postischemic recovery of left ventricular developed pressure was significantly greater with 1 nm (51.6% +/- 7.4%) and 10 nm estradiol (47.7% +/- 8.6%) than with vehicle (37.8% +/- 9.7%) at end reperfusion. There was also greater recovery of the end diastolic pressure with 1 nm (47.8 +/- 4.0 mmHg) and 10 nm estradiol (54.0 +/- 4.0) compared with vehicle (75.3 +/- 7.5). Further, 1 nm and 10 nm estrogen preserved coronary flow after ischemia and decreased coronary effluent lactated dehydrogenase compared with controls. Estrogen at 25 nm and 50 nm did not provide additional benefit in terms of functional recovery. Estrogen at all concentrations increased extracellular signal-regulated protein kinase phosphorylation.

CONCLUSIONS

Postischemic infusion of 17beta-estradiol protects myocardial function and viability. The attractive potential for the clinical application of postischemic estrogen therapy warrants further study to elucidate the mechanistic pathways and differences between males and females.

Characterization of the relaxant response to N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine in porcine coronary arteries

N,N'-Dialkyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines show structural analogy with estrogens and selective estrogen receptor modulators. Because the vasodilator properties of these compounds are unknown, we investigated their potential to relax porcine coronary arteries and determined the mechanism(s) of relaxation. Isolated porcine coronary arterial rings were suspended in organ chambers, precontracted with KCl (30 mM), and the relaxant response was determined by measurement of changes in isometric force. Dependent on the chemical structure, the drugs induced concentration-dependent relaxation in rings with and without endothelium. N,N'-Dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine (8) was most potent and showed a 12- to 15-fold higher vasodilatory effect than 17beta-estradiol (E2). The vasorelaxation was independent of endothelium. Calcium concentration-dependent contractions in high-potassium depolarizing medium were insurmountably inhibited by 8. The effect of the L-type Ca2+ channel activator (S)-(-)-Bay K 8644 [(S)-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine-carboxylic acid methyl ester], which induced a leftward shift of Ca2+ contraction, was blocked by 8. The relaxant response to 8 was unaffected by the estrogen receptor antagonist ICI 182,780 (7alpha-[9-[(4,4,5,5,5-pentafluoropentyl]-sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17beta-diol) and K+ channel blockers, i.e., TEA, glibenclamide, and 4-aminopyridine. Furthermore, the vasodilatory effect of 8 was unaffected by the adenylyl cyclase inhibitor SQ 22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine], the guanylyl cyclase inhibitor ODQ [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one], the protein kinase A inhibitor KT 5720 [(9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid hexyl ester], the protein kinase G inhibitor KT 5823 [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester], and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB 203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole]. Western blot analysis demonstrated that 8, unlike E2, raloxifene, and tamoxifen, failed to stimulate p38 MAPK. It is concluded that N,N'-dipropyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine induces endothelium-independent relaxation of coronary arteries; the mechanism apparently involves inhibition of L-type Ca2+ channels. The drug may be protective against cardiovascular diseases.

Raloxifene inhibits transient outward and ultra-rapid delayed rectifier potassium currents in human atrial myocytes

The selective estrogen receptor modulator raloxifene is widely used in the treatment of postmenopausal osteoporosis, and has cardioprotective properties. However, effects of raloxifene on cardiac ion channels are unclear. The present study was designed to investigate the effects of raloxifene and beta-estradiol on transient outward and ultra-rapid delayed rectifier potassium currents (Ito1 and IKur) in human atrial myocytes with a whole cell patch-clamp technique. Ito1 was inhibited by raloxifene in a concentration-dependent manner with an IC50 of 0.9 microM. Raloxifene at 1 microM decreased Ito1 by 40.2+/-1.9% (at +50 mV, n=14, P<0.01 vs control). Time-dependent recovery from inactivation was slowed, and time to peak and time-dependent inactivation of Ito1 were significantly accelerated, while steady-state voltage dependent activation and inactivation of Ito1 were not affected by raloxifene. In addition, raloxifene remarkably suppressed IKur (IC50=0.7 microM). Raloxifene at 1 microM decreased IKur by 57.3+/-3.3% (at +50 mV, n=10, P<0.01 vs control). However, beta-estradiol inhibited Ito1 (IC50=10.3 microM) without affecting IKur. The inhibitory effects of raloxifene and beta-estradiol on Ito1 and/or IKur were unaffected by the estrogen receptor antagonist ICI 182,780. Our results indicate that raloxifene directly inhibits the human atrial repolarization potassium currents Ito1 and IKur. Whether raloxifene is beneficial for supraventricular arrhythmias remains to be studied.