Catalase activity in coronary artery endothelium protects smooth muscle against peroxide damage

Antidiabetic and vasoprotective activity of lithium: Role of glycogen synthase kinase-3

OBJECTIVES

Lithium is a drug of choice in maniac disorder. Lithium inhibits the glycogen synthase kinase-3 (GSK-3), an enzyme involved in the insulin signalling pathway. Elevated levels of GSK-3 were found in diabetic rats and humans. We aimed to determine the effect of lithium chloride in diabetes and associated vascular complications in diabetic rats.

MATERIALS AND METHODS

Type 2 diabetes was induced by high fat diet and low dose of streptozotocin. Diabetic rats were divided into diabetic control and lithium chloride treatment groups. Lithium chloride was used as a GSK-3 inhibitor. The treatment was given for 4 weeks. Various biochemical parameters were measured before initiation and the end of treatment. Systolic blood pressure was measured by the non-invasive tail-cuff method, while various biochemical and tissue parameters were estimated for efficacy. Vasoreactivity was performed by taking the contractile response of H(2)O(2) (10(-6) M to 10(-3)M) and angiotensin II (10(-11) to 10(-7) M) in rat thoracic aortas of different groups. Statistical comparisons between all groups were performed by using two tailed one-way ANOVA followed by the Dunnett test. P-values <0.05 were considered statistically significant.

RESULTS

Treatment with lithium chloride significantly reduced the augmented systolic blood pressure, various biochemical parameters, and antioxidant parameters in diabetic-treated rats. Treatment also showed the decrease in augmented responses of H(2)O(2) and angiotensin II in rat thoracic aortas of treated rats.

CONCLUSIONS

We can conclude that lithium chloride treatment reduces the diabetic state as well as diabetes-induced vascular dysfunction.

Upregulation of arginase by H2O2 impairs endothelium-dependent nitric oxide-mediated dilation of coronary arterioles

OBJECTIVE

Overproduction of reactive oxygen species such as hydrogen peroxide (H2O2) has been implicated in various cardiovascular diseases. However, mechanism(s) underlying coronary vascular dysfunction induced by H2O2 is unclear. We studied the effect of H2O2 on dilation of coronary arterioles to endothelium-dependent and endothelium-independent agonists.

METHODS AND RESULTS

Porcine coronary arterioles were isolated and pressurized without flow for in vitro study. All vessels developed basal tone and dilated dose-dependently to activators of nitric oxide (NO) synthase (adenosine and ionomycin), cyclooxygenase (arachidonic acid), and cytochrome P450 monooxygenase (bradykinin). Intraluminal incubation of vessels with H2O2 (100 micromol/L, 60 minutes) did not alter basal tone but inhibited vasodilations to adenosine and ionomycin in a manner similar as that by NO synthase inhibitor L-NAME. H2O2 affected neither endothelium-dependent responses to arachidonic acid and bradykinin nor endothelium-independent dilation to sodium nitroprusside. The inhibited adenosine response was not reversed by removal of H2O2 but was restored by excess L-arginine. Inhibition of L-arginine consuming enzyme arginase by alpha-difluoromethylornithine or N(omega)-hydroxy-nor-L-arginine also restored vasodilation. Administering deferoxamine, an inhibitor of hydroxyl radical production, prevented the H2O2-induced impairment of vasodilation to adenosine. Western blot and reverse-transcription polymerase chain reaction results indicated that arginase I was upregulated after treating vessels with H2O2.

CONCLUSIONS

H2O2 specifically impairs endothelium-dependent NO-mediated dilation of coronary microvessels by reducing L-arginine availability through upregulation of arginase. The formation of hydroxyl radicals from H2O2 may contribute to this process.

Ascorbate uptake in pig coronary artery endothelial cells

Although smooth muscle and endothelial cells in pig coronary artery are morphologically and functionally distinct, ascorbate uptake has been characterized only in smooth muscle cells. Ascorbate transporters in kidney and intestinal epithelial cells differ from those in smooth muscle. We examined ascorbate transport and mRNA expression of sodium-dependent vitamin C transporters (SVCT) by RT-PCR in the pig coronary artery endothelial cell cultures. When 14C-ascorbate uptake in endothelial cells was examined as 14C or by HPLC, the two values did not differ from each other. 14C-ascorbate uptake was Na(+)-dependent, stereoselective for L-ascorbate and inhibited by sulfinpyrazone. The kinetic characteristics of the uptake were: Km = 27 +/- 3 microM (Hill coefficient = 1) for ascorbate and Km = 73 +/- 14 mM (Hill coefficient = 2) for Na+. Surprisingly, endothelial cells had similar kinetic parameters as smooth muscle cells, except for a slightly lower uptake velocity in endothelial cells. Comparison with the smooth muscle showed that both tissue types expressed mRNA for SVCT2. Endothelial cells differ from epithelial cells which express mainly SVCT1 but resemble smooth muscle cells in this respect.

Effects of peroxynitrite on sarco/endoplasmic reticulum Ca2+ pump isoforms SERCA2b and SERCA3a

Sarco(endo)plasmic reticulum Ca2+ (SERCA) pumps are important for cell signaling. Three different genes, SERCA1, 2, and 3, encode these pumps. Most tissues, including vascular smooth muscle, express a splice variant of SERCA2 (SERCA2b), whereas SERCA3a is widely distributed in tissues such as vascular endothelium, tracheal epithelium, mast cells, and lymphoid cells. SERCA2b protein is readily inactivated by peroxynitrite that may be formed during cardiac ischemia reperfusion or during immune response after infection. Here, we compared the peroxynitrite sensitivity of SERCA2b and SERCA3a by using microsomes prepared from HEK-293T cells overexpressing the pumps. We incubated the microsomes with different concentrations of peroxynitrite and determined Ca2+ uptake, Ca2+-Mg2+-ATPase, Ca2+-dependent formation of acylphosphate intermediate, and protein mobility in Western blots. Ca2+ uptake, Ca2+-Mg2+-ATPase, and Ca2+-dependent formation of acylphosphate intermediate were inactivated for both SERCA2b and SERCA3a, but the latter was more resistant to the inactivation. Western blots showed that SERCA2b and SERCA3a proteins oligomerized after treatment with peroxynitrite, but each with a slightly different pattern. Compared with monomers, the oligomers may be less efficient in forming the acylphosphate intermediate and in conducting the remainder of the steps in the reaction cycle. We conclude that the resistance of SERCA3a to peroxynitrite may aid the cells expressing them in functioning during exposure to oxidative stress.

Endothelium and smooth muscle of pig coronary artery: differences in metabolism

Here, we report that the smooth muscle and endothelium of the pig coronary artery differ in the profiles of energy metabolism nucleotides. ATP levels in the freshly isolated smooth muscle (1490 +/- 93, all the values are in pmol/mg protein) were significantly greater than in the endothelium (418 +/- 68). In contrast, endothelium contained higher levels of NADH (328 +/- 21), NAD+ (1210 -/+ 28), NADPH (87 +/- 2), and NADP+ (77 +/- 4) than smooth muscle (17 +/- 2, 96 +/- 14, 7 +/- 1, and 8 +/- 1, respectively). However, smooth muscle and endothelium do not differ from each other in the ratios of NADH/NAD+ or NADPH/NADP+. Cells cultured from smooth muscle and endothelium contained less ATP (93 +/- 2, 141 +/- 6) and had lower ratios of NADH/ NAD+ than the freshly isolated tissues but the NADPH/NADP+ ratios remained similar. We conclude that (a) freshly isolated smooth muscle and endothelium differ in their profiles of the energy metabolism nucleotides, and (b) culturing the cells alters the profile.

Effects of peroxynitrite on sarcoplasmic reticulum Ca2+ pump in pig coronary artery smooth muscle

Peroxynitrite generated in arteries from superoxide and NO may damage Ca(2+) pumps. Here, we report the effects of peroxynitrite on ATP-dependent azide-insensitive uptake of Ca(2+) into pig coronary artery vesicular membrane fractions F2 [enriched in plasma membrane (PM)] and F3 [enriched in sarcoplasmic reticulum (SR)]. Membranes were pretreated with peroxynitrite and then with DTT to quench this agent. This pretreatment inhibited Ca(2+) uptake in a peroxynitrite concentration-dependent manner, but the effect was more severe in F3 than in F2. The inhibition was thus not overcome by excess DTT used to quench peroxynitrite and was not affected if catalase, SOD, or mannitol was added along with peroxynitrite. Such damage to the pump protein would be difficult to repair if produced during ischemia-reperfusion. The acylphosphates formed with ATP in F3 corresponded mainly to the SR Ca(2+) pump (110 kDa), but in F2 both PM (140 kDa) and 110-kDa bands were observed. Peroxynitrite treatment of F2 inhibited only the 110-kDa band. Inhibition of Ca(2+) uptake and acylphosphate formation from ATP correlated well in peroxynitrite-treated F3 samples. However, inhibition of acylphosphates from orthophosphate (reverse reaction of the pump) was slightly poorer. Peroxynitrite treatment also covalently cross-linked the pump protein, yielding no dimers but only larger oligomers. In contrast, cross-linking of the SR Ca(2+) pump in skeletal and cardiac muscles gives dimers as the first oligomers. Therefore, we speculate that SERCA2 has a different quaternary structure in the coronary artery smooth muscle.

Effects of free radicals on coronary artery

Coronary arteries supply blood to the heart and hence the control of coronary tone is pivotal to human survival. Reactive oxygen species (ROS) in specified amounts play an important role in normal metabolic and signalling processes. However, excess ROS can cause severe cardiovascular damage. For example, NO is produced by endothelium as a signal for relaxation. However, in an inflammatory response, NO from endothelium or macrophages can combine with superoxide to produce more deleterious peroxynitrite. Excess ROS have been associated with loss of coronary artery pliability--loss of contraction in some instances and relaxation in others. Atherosclerosis may also be considered an inflammatory response that leads to artery blockage, coronary disease and ischaemia-reperfusion. ROS produce various types of damage to ion channels and pumps and this damage is associated with vascular diseases such as atherosclerosis and hypertension. Endothelium and smooth muscle in the coronary artery are also affected differently by individual ROS. In fact, endothelium may act to protect the underlying smooth muscle against ROS. This review will give an overview of this field.

Effects of hydrogen peroxide on pig coronary artery endothelium

Peroxides and other reactive oxygen species damage arteries during ischemia-reperfusion. Here, we report on the effects of H(2)O(2) on contractility of pig coronary artery. We either treated 3-mm coronary artery rings with 0 to 0.5 mM H(2)O(2) in organ baths or we perfused the arteries with H(2)O(2) and then cut them into rings. In each instance, we monitored the force of contraction of 3-mm rings in H(2)O(2)-free solution with 30 mM KCl and then we determined the A23187 induced endothelium dependent relaxation as a percent of this contraction. Treatment with H(2)O(2) in the organ bath caused a decrease in the contraction but it did not affect the percent relaxation. Treating arteries with H(2)O(2) by luminal perfusion did not affect the contraction but it decreased the percent relaxation. Perfusion alone decreased the amount of endothelium remaining in the arteries and perfusing with H(2)O(2) decreased it further. The percent relaxation with A23187 correlated well with the endothelium remaining in the arteries. We propose that H(2)O(2) and shear stress can cause a loss of endothelium and that endothelium can also protect the underlying smooth muscle against luminal H(2)O(2).