Lysophosphatidylcholine potentiates vascular contractile responses by enhancing vasoconstrictor-induced increase in cytosolic free Ca2+ in rat aorta

Butyrate inhibits LPC-induced endothelial dysfunction by regulating nNOS-produced NO and ROS production

Lipids oxidation is a key risk factor for cardiovascular diseases. Lysophosphatidylcholine (LPC), the major component of oxidized LDL, is an important triggering agent for endothelial dysfunction and atherogenesis. Sodium butyrate, a short-chain fatty acid, has demonstrated atheroprotective properties. So, we evaluate the role of butyrate in LPC-induced endothelial dysfunction. Vascular response to phenylephrine (Phe) and acetylcholine (Ach) was performed in aortic rings from male mice (C57BL/6J). The aortic rings were incubated with LPC (10 μM) and butyrate (0.01 or 0.1 Mm), with or without TRIM (an nNOS inhibitor). Endothelial cells (EA.hy296) were incubated with LPC and butyrate to evaluate nitric oxide (NO) and reactive oxygen species (ROS) production, calcium influx, and the expression of total and phosphorylated nNOS and ERK½. We found that butyrate inhibited LPC-induced endothelial dysfunction by improving nNOS activity in aortic rings. In endothelial cells, butyrate reduced ROS production and increased nNOS-related NO release, by improving nNOS activation (phosphorylation at Ser1412). Additionally, butyrate prevented the increase in cytosolic calcium and inhibited ERk½ activation by LPC. In conclusion, butyrate inhibited LPC-induced vascular dysfunction by increasing nNOS-derived NO and reducing ROS production. Butyrate restored nNOS activation, which was associated with calcium handling normalization and reduction of ERK½ activation.

Mechanisms underlying lysophosphatidylcholine-induced potentiation of vascular contractions in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat aorta

BACKGROUND AND PURPOSE

The effect of lysophosphatidylcholine (LPC) on aortic contractions in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetic model, was studied.

EXPERIMENTAL APPROACH

Using OLETF rats and control (Long Evans Tokushima Otsuka (LETO)) rats, the effects of LPC on the contractions induced by high-K(+) (10-40 mM), UK14,304 (10 approximately 100 nM; a selective alpha(2)-adrenoceptor agonist) and sodium orthovanadate (SOV; 10 microM approximately 3 mM) in endothelium-denuded aortae were compared. Aortic ERK activity and the mRNA expression for GPR4 (a putative LPC receptor) were also measured.

KEY RESULTS

OLETF rats exhibited (vs. age-matched LETO rats): (1) greater potentiation of high-K(+)-induced contraction by 10 microM LPC - a potentiation attenuated by 10 microM genistein, protein tyrosine kinase (PTK) inhibitor, (2) greater potentiation of UK14,304 (10 approximately 100 nM)-induced contractions by LPC (1 microM approximately 10 microM) - a potentiation attenuated by 10 microM genistein, 50 microM tyrphostin A23 (PTK inhibitor) or 10 microM PD98059 (MEK 1/2 inhibitor), (3) greater basal and LPC (1 microM)-induced ERK activities, (4) greater basal and 100 nM UK14,304-stimulated ERK2 activities in both the absence and presence of 10 microM LPC, (5) greater SOV (10 microM approximately 3 mM)-induced contractions, (6) greater potentiation of SOV-induced contractions by 10 microM LPC - a potentiation suppressed by 10 microM PD98059 or 10 microM genistein, (7) upregulation of GPR4 mRNA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the LPC-induced potentiation of contractions in the OLETF rat aorta may be attributable to increased PTKs or ERK activity and/or to receptor upregulation.

Effects of dual-action genistein derivatives on relaxation in rat aorta

Protein tyrosine kinases and nitric oxide (NO) play important roles in several cardiovascular diseases. In this study, we examined the actions of two compounds, each has structure of genistein (a tyrosine kinase inhibitor) and an NO donor, on endothelium-independent relaxation responses in the isolated rat aorta. By rational drug design, genistein was modified to acquire an NO donor, and we synthesized two such compounds (G-II, G-VI). These compounds and genistein induced dose-dependent relaxation responses in endothelium-denuded aortic strips, the rank order of potencies being G-VI > G-II > genistein. Incubation of endothelium-denuded strips with 1H-[1,2,4] oxadiazolo[4,3-a]-quinoxalin-1-one (ODQ, 10 microM), a guanylyl cyclase inhibitor, inhibited both the G-II- and G-VI-induced relaxations, but not the genistein-induced relaxation. The residual relaxations induced by these two compounds were similar to the genistein-induced relaxation. Incubation of endothelium-denuded strips with lysophosphatidylcholine (LPC, 20 microM)-which is a major atherogenic lysophospholipid component of oxidized low-density lipoprotein and is known to activate tyrosine kinase-caused a significant rightward shift in the dose-response curve for genistein. LPC also shifted the G-II- and G-VI-induced relaxation curves to the right; however, these relaxations in the presence of LPC were greater than that induced by genistein. The sodium nitroprusside-induced relaxation in endothelium-denuded strips was similar between in the absence and presence of LPC. These results suggest that each of our newly developed G-II and G-VI compounds has a dual action, as an NO donor and a tyrosine kinase inhibitor. These compounds may be useful against certain cardiovascular diseases.

Lysophosphatidylcholine activates extracellular-signal-regulated protein kinase and potentiates vascular contractile responses in rat aorta

We previously reported that in the endothelium-denuded rat aorta, lysophosphatidylcholine (LPC) potentiates the contractile responses induced by high-K(+), UK14,304 (a selective alpha(2)-adrenoceptor agonist), and phorbol ester with an associated tyrosine-phosphorylation of proteins. To further investigate this phenomenon, we examined the effects of extracellular-signal-regulated protein kinase (ERK)-kinase (MEK) inhibitors on the LPC-induced potentiation of the contractile responses to high-K(+) and UK14,304 in this tissue. Although PD98059 (3 x 10(-)(5) M) did not affect the high-K(+)-induced contractile response itself, it selectively inhibited the potentiating effect of LPC on the contraction and strongly inhibited the LPC-induced augmentation of the associated increase in [Ca(2+)](i). PD98059 also attenuated the LPC-induced augmentations of the increases in [Ca(2+)](i) and contractile tension induced by UK14,304. U0126 (5 x 10(-)(5) M), another MEK inhibitor, also attenuated the potentiating effect of LPC on high-K(+)-induced contractions. Western blot analysis revealed that LPC produced an increase in ERK-phosphorylation, and that this was inhibited by PD98059. Nicardipine inhibited the contractile response to 15 mM K(+) in the LPC-treated aorta, but not the increase in ERK-phosphorylation induced by LPC. These results suggest that the LPC-induced augmentation of contractile responses in the rat aorta is due to activation of ERK, which in turn regulates Ca(2+) influx.

Lysophosphatidylcholine potentiates vascular contractile responses in rat aorta via activation of tyrosine kinase

We previously reported that while lysophosphatidylcholine (LPC) does not itself produce contraction, it significantly potentiates the contractile responses induced by high-K(+), UK14,304 (a selective alpha(2)-adrenoceptor agonist) and phorbol ester in the endothelium-denuded rat aorta. To further investigate this phenomenon, we examined the effects of genistein and tyrphostin B42 (both tyrosine kinase inhibitors) on the LPC-induced potentiation of the contractile responses to high-K(+) and UK14,304 in the endothelium-denuded rat aorta. Although genistein (3 x 10(-6) M, 10(-5) M) did not affect the high-K(+)-induced contractile response, it selectively inhibited the potentiating effect of LPC on the contraction and it strongly inhibited the LPC-induced augmentation of the associated increases in [Ca(2+)](i). Genistein also attenuated the LPC-induced augmentation effects on both the increase in [Ca(2+)](i) and contractile response induced by the UK14,304. In contrast, daidzein (10(-5) M) did not inhibit the potentiating effect of LPC. Tyrphostin B42 (3 x 10(-5) M) attenuated the potentiating effect of LPC on high K(+)-induced contractions. Western blot analysis showed that LPC increased the tyrosine phosphorylation of a number of proteins, including 42 and 44 kDa proteins and 53 - 64 kDa proteins. These protein phosphorylations were inhibited by genistein. Sodium orthovanadate (10(-4) M), a tyrosine phosphatase inhibitor, also markedly enhanced the high-K(+)-induced contractile responses. This enhancing effect was attenuated by genistein. These results suggest that the LPC-induced augmentation of contractile responses in the rat aorta is due to activation of tyrosine kinase, which in turn regulates Ca(2+) influx.

Alpha-adrenoceptor agonists produce Ca2+ oscillations in isolated rat aorta: role of protein kinase C

We investigated the relationship between tension development and the cytosolic free Ca2+ level ([Ca2+]i) in responses to norepinephrine (NE) and selective alpha2-adrenoceptor agonist, UK14,304 of the endothelium-denuded rat aorta loaded with fura PE-3. NE (3 x 10(-8) M) evoked a rapid increase in [Ca2+]i followed by slight decreasing to a steady state level and produced a contraction. After the NE-induced increase in [Ca2+]i had reached a maximum, the [Ca2+]i showed persistent oscillations. The Ca2+ oscillations were superimposed on the sustained increase in [Ca2+]i. UK14,304 (3 x 10(-6) M) also evoked an increase in [Ca2+]i and produced a contraction. However, the UK14,304-induced effect on [Ca2+]i was characterized by pronounced oscillations, and the amplitude of the sustained increase in [Ca2+]i was less than that seen with NE. Protein kinase C inhibitor, Ro31-8220 (3 x 10(-6) M) and verapamil (10(-5) M) abolished both NE and UK14,304-evoked Ca2+ oscillations. UK14,304-induced contractions were also strongly inhibited by Ro31-8220 and verapamil. However, NE induced contractions were partly inhibited by these inhibitors. The sustained increases in [Ca2+]i evoked NE and UK14,304 were not significantly inhibited by Ro31-8220 and verapamil. These results suggest that NE and UK14,304 produce Ca2+ oscillations during sustained contractions in rat aorta. The alpha2 adrenoceptor agonist, UK14,304-induced sustained contraction and Ca2+ oscillations may be due to PKC activation and opening of voltage-dependent L type Ca2+ channels.

The enhancing effect of soybean-derived sterylglucoside and beta-sitosterol beta-D-glucoside on nasal absorption in rabbits

The aim of this study was to elucidate the efficiency of soybean-derived sterylglucoside (SG) and its main component beta-sitosterol beta-D-glucoside (Sit-G), as nasal absorption enhancers. Nasal administration of verapamil with SG and Sit-G showed the higher bioavailabilities (60.4 and 90.7%, respectively) than that with lactose (39.8%). It was clear that SG and Sit-G promoted the absorption of verapamil through nasal mucosa. To elucidate the mechanism, we measured the calcein leakage from liposomes by incubation with SG, Sit-G, oleic acid, soybean-derived sterol, and beta-sitosterol to investigate transcellular absorption and measured the changes in intracellular Ca2+ concentrations ([Ca2+]i) by Sit-G to analyze paracellular absorption. The large amount of calcein leakage induced by enhancers was consistent with an enhancement of bioavailability of verapamil and insulin following nasal administration (oleic acid < SG < Sit-G). Moreover, Sit-G increased [Ca2+]i in the medium containing Ca2+, but not in Ca2+ free medium. This result suggested that Sit-G increases the fluidity of the mucosal membrane and facilitates Ca2+ influx from extracellular sources. In conclusion, a possible explanation for SG and Sit-G to promote drug absorption, is that they may affect both paracellular pathway and transcellular pathways caused by pertubation of lipid.

Marked dissociation between intracellular Ca2+ level and contraction on exposure of rat aorta to lysophosphatidylcholine

We investigated the relationship between tension development and the cytosolic free Ca2+ level ([Ca2+]i) on exposure of the endothelium-denuded isolated rat aorta to palmitoyl-L-alpha-lysophosphatidylcholine. Lysophosphatidylcholine concentration-dependently induced a gradual increase in [Ca2+]i. Application of 10(-4) M lysophosphatidylcholine induced a large and sustained tonic increase in [Ca2+]i (the peak [Ca2+]i was 125.2 +/- 11.5% of the 80 mM K+-induced response) but only a small contraction (4.0 +/- 1.4% of the 80 mM K+ induced contraction). The sustained increase in [Ca2+]i was attenuated when extracellular Ca2+ was removed but it was unaffected by verapamil or 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H-7). Digitonin also produced a gradual increase in [Ca2+]i but with a pronounced contraction. Triton X-100 (0.1%) produced a marked elevation in [Ca2+]i with no detectable contraction. Triton X-100, however, caused a rapid leakage of fura PE-3. Treatment with 10(-4) M lysophosphatidylcholine for 1 or 2 h did not affect the contractile response induced by 80 mM K+ and this treatment did not release lactate dehydrogenase from the rat aorta. Treatment with lysophosphatidylcholine did not affect either the cyclic AMP level or the cyclic GMP level in endothelium-denuded aortic tissues. These results show that in the rat aorta lysophosphatidylcholine produces a large increase in [Ca2+]i (possibly in a non-contractile compartment) which does not induce contraction. Thus, the increase in [Ca2+]i induced by lysophosphatidylcholine (i) requires external Ca2+ but is not due to an increased Ca2+ influx through voltage-dependent L-type Ca2+ channels, (ii) is not primarily due to protein kinase C activation and (iii) is probably not due to a detergent action (like those of digitonin and triton X-100). The relative lack of a contractile response to lysophosphatidylcholine is not due to formation of cyclic AMP or cyclic GMP.