Decreased sensitivity to nitric oxide in the aorta of severely hypercholesterolemic apolipoprotein E-deficient mice

Reactive Oxygen Species in the Aorta and Perivascular Adipose Tissue Precedes Endothelial Dysfunction in the Aorta of Mice with a High-Fat High-Sucrose Diet and Additional Factors

Metabolic syndrome (Mets) is the major contributor to the onset of metabolic complications, such as hypertension, type 2 diabetes mellitus (DM), dyslipidemia, and non-alcoholic fatty liver disease, resulting in cardiovascular diseases. C57BL/6 mice on a high-fat and high-sucrose diet (HFHSD) are a well-established model of Mets but have minor endothelial dysfunction in isolated aortas without perivascular adipose tissue (PVAT). The purpose of this study was to evaluate the effects of additional factors such as DM, dyslipidemia, and steatohepatitis on endothelial dysfunction in aortas without PVAT. Here, we employed eight-week-old male C57BL/6 mice fed with a normal diet (ND), HFHSD, steatohepatitis choline-deficient HFHSD (HFHSD-SH), and HFHSD containing 1% cholesterol and 0.1% deoxycholic acid (HFHSD-Chol) for 16 weeks. At week 20, some HFHSD-fed mice were treated with streptozocin to develop diabetes (HFHSD-DM). In PVAT-free aortas, the endothelial-dependent relaxation (EDR) did not differ between ND and HFHSD (p = 0.25), but in aortas with PVAT, the EDR of HFHSD-fed mice was impaired compared with ND-fed mice (p = 0.005). HFHSD-DM, HFHSD-SH, and HFHSD-Chol impaired the EDR in aortas without PVAT (p < 0.001, p = 0.019, and p = 0.009 vs. ND, respectively). Furthermore, tempol rescued the EDR in those models. In the Mets model, the EDR is compromised by PVAT, but with the addition of DM, dyslipidemia, and SH, the vessels themselves may result in impaired EDR.

Atherosclerosis differentially affects calcium signalling in endothelial cells from aortic arch and thoracic aorta in Apolipoprotein E knockout mice

Apolipoprotein‐E knockout (ApoE^−/−) mice develop hypercholesterolemia and are a useful model of atherosclerosis. Hypercholesterolemia alters intracellular Ca²⁺ signalling in vascular endothelial cells but our understanding of these changes, especially in the early stages of the disease process, is limited. We therefore determined whether carbachol‐mediated endothelial Ca²⁺ signals differ in plaque‐prone aortic arch compared to plaque‐resistant thoracic aorta, of wild‐type and ApoE^−/− mice, and how this is affected by age and the presence of hypercholesterolemia. The extent of plaque development was determined using en‐face staining with Sudan IV. Tissues were obtained from wild‐type and ApoE^−/− mice at 10 weeks (pre‐plaques) and 24 weeks (established plaques). We found that even before development of plaques, significantly increased Ca²⁺ responses were observed in arch endothelial cells. Even with aging and plaque formation, ApoE^−/− thoracic responses were little changed, however a significantly enhanced Ca²⁺ response was observed in arch, both adjacent to and away from lesions. In wild‐type mice of any age, 1–2% of cells had oscillatory Ca²⁺ responses. In young ApoE^−/− and plaque‐free regions of older ApoE^−/−, this is unchanged. However a significant increase in oscillations (~13–15%) occurred in thoracic and arch cells adjacent to lesions in older mice. Our data suggest that Ca²⁺ signals in endothelial cells show specific changes both before and with plaque formation, that these changes are greatest in plaque‐prone aortic arch cells, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

We have investigated aortic endothelial cell calcium signalling changes in the Apolipoprotein E knockout mouse model of atherosclerosis. Our data show that calcium signals in endothelial cells undergo specific changes both before and with plaque formation, that these changes are greater in plaque‐prone aortic arch than in plaque‐resistant thoracic aorta, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

Impaired acetylcholine-induced endothelium-dependent aortic relaxation by caveolin-1 in angiotensin II-infused apolipoprotein-E (ApoE-/-) knockout mice

Objective

The angiotensin II (AngII)-infused apolipoprotein E-deficient (ApoE^−/−) mouse model is widely used to study atherosclerosis and abdominal aortic aneurysm. An increase in blood pressure has been reported in this model however the underlying mechanism has not been fully explored. In this study, we investigated whether vasomotor dysfunction develops in AngII-infused ApoE^−/− mice and the underlying mechanism involved.

Methods

ApoE^−/− mice were infused with vehicle (distilled water) or AngII subcutaneously for 14 days. Blood pressure and heart rate were measured using the non-invasive tail cuff method. Aortic vascular reactivity and expression of key proteins (endothelial nitric oxide synthase (eNOS), phospho-eNOS and caveolin-1) were assessed using tension myography and Western blotting respectively. Plasma nitric oxide (NO) level was estimated using a colorimetric assay.

Results

AngII infusion caused a time-dependent increase in blood pressure (P<0.001). Aortas from AngII-infused mice were significantly less responsive to acetylcholine-induced endothelium-dependent relaxation when compared to aortas from mice infused with vehicle control (P<0.05). Contractile responses to phenylephrine (P<0.01) and potassium chloride (P<0.001) were significantly enhanced in aortas from AngII-infused mice. eNOS phosphorylation was significantly decreased in the aorta of AngII-infused mice (P<0.05). Aortic caveolin-1 protein expression was significantly increased in AngII-infused mice (P<0.05). Plasma nitrate/nitrite level was significantly reduced in AngII-infused mice (P<0.05). Pharmacological disruption of caveolae using methyl-β-cyclodextrin (MβCD) in isolated aortas from AngII-infused mice caused a significant leftward shift of the acetylcholine-induced relaxation concentration-response curve when compared to vehicle control (P<0.05).

Conclusion

Upregulation of caveolin-1 protein expression and reduced NO bioavailability contributes to aortic endothelial dysfunction in AngII-infused ApoE^−/− mice.

Vascular function during prolonged progression and regression of atherosclerosis in mice

OBJECTIVE

Endothelial dysfunction is associated with atherosclerosis in mice, but it is difficult to reduce cholesterol levels enough to study regression of atherosclerosis in genetically modified mice. The goal of this study was to examine vascular structure and function before and after reducing elevated plasma lipid levels with a genetic switch in Reversa mice, and identify novel mechanisms contributing to structural and functional improvements in the vasculature after reduction of blood lipids.

METHODS AND RESULTS

After 6 months of hypercholesterolemia, endothelial function (maximum relaxation to acetylcholine) in aorta was impaired and responses to nitric oxide were unaffected. Further impairment in endothelial function was observed after 12 months of hypercholesterolemia and was associated with reductions in sensitivity to nitric oxide. Expression of dihydrofolate reductase was reduced at 6 and 12 months, and addition of the tetrahydrobiopterin precursor sepiapterin significantly improved endothelial function. Reducing cholesterol levels at 6 months normalized dihydrofolate reductase expression and prevented further impairment in endothelial function. Similar functional changes were observed after 12 months of hypercholesterolemia followed by 2 months of lipid lowering.

CONCLUSIONS

Our data suggest that endothelial dysfunction after prolonged hypercholesterolemia is the result of both impairment of sensitivity to nitric oxide and reduced nitric oxide synthase cofactor bioavailability. Both of these changes can be prevented by normalizing blood lipids during moderately severe or advanced atherosclerosis.

Cardiac and vascular phenotypes in the apolipoprotein E-deficient mouse

Cardiovascular death is frequently associated with atherosclerosis, a chronic multifactorial disease and a leading cause of death worldwide. Genetically engineered mouse models have proven useful for the study of the mechanisms underlying cardiovascular diseases. The apolipoprotein E-deficient mouse has been the most widely used animal model of atherosclerosis because it rapidly develops severe hypercholesterolemia and spontaneous atherosclerotic lesions similar to those observed in humans. In this review, we provide an overview of the cardiac and vascular phenotypes and discuss the interplay among nitric oxide, reactive oxygen species, aging and diet in the impairment of cardiovascular function in this mouse model.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

Modulation of vascular sarco/endoplasmic reticulum calcium ATPase in cardiovascular pathophysiology

Endothelial dysfunction associated with decreased nitric oxide (NO) bioactivity is a major feature of vascular diseases such as atherosclerosis or diabetes. Sodium nitroprusside (SNP)-induced relaxation is entirely dependent on cyclic guanosine monophosphate (cGMP) and preserved in atherosclerosis, suggesting that smooth muscle response to NO donor is intact. However, NO gas activates both cGMP-dependent and -independent signal pathways in vascular smooth muscle cells, and oxidative stress associated with vascular diseases selectively impairs cGMP-independent relaxation to NO. Sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA), which regulates intracellular Ca(2+) levels by pumping Ca(2+) into store, is a major cGMP-independent target for NO. Physiological levels of reactive nitrogen species (RNS) S-glutathiolate SERCA at Cys674 to increase its activity, and the augmentation of RNS in vascular diseases irreversibly oxidizes Cys674 or nitrates tyrosine residues at Tyr296-Tyr297, which are associated with loss of function. S-glutathiolation of various proteins by NO can explain redox-sensitive cGMP-independent actions, and oxidative inactivation of target proteins for NO can be associated with the pathogenesis of cardiovascular diseases. Oxidative inactivation of SERCA is also implicated with dysregulation of smooth muscle migration, promotion of platelet aggregation, and impairment of cardiac function, which can be implicated with restenosis, pathological angiogenesis, thrombosis, as well as heart failure. Analysis of posttranslational oxidative modifications of SERCA and the preservation of SERCA function can be novel strategies against cardiovascular diseases associated with oxidative stress.

PCB-induced endothelial cell dysfunction: role of poly(ADP-ribose) polymerase

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants implicated in the development of pro-inflammatory events critical in the pathology of atherosclerosis and cardiovascular disease. PCB exposure of endothelial cells results in increased cellular oxidative stress, activation of stress and inflammatory pathways leading to increased expression of cytokines and adhesion molecules and ultimately cell death, all of which can lead to development of atherosclerosis. To date no studies have been performed to examine the direct effects of PCB exposure on the vasculature relaxant response which if impaired may predispose individuals to hypertension, an additional risk factor for atherosclerosis. Overactivation of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) following oxidative/nitrosative stress in endothelial cells and subsequent depletion of NADPH has been identified as a central mediator of cellular dysfunction. The aim therefore was to investigate whether 2,2',4,6,6'-pentachlorobiphenyl (PCB 104) directly causes endothelial cell dysfunction via increased oxidative stress and subsequent overactivation of PARP. Exposure of ex vivo rat aortic rings to PCB 104 impaired the acetylcholine-mediated relaxant response, an effect that was dependent on both concentration and exposure time. In vitro exposure of mouse endothelial cells to PCB 104 resulted in increased cellular oxidative stress through activation of the cytochrome p450 enzyme CYP1A1 with subsequent overactivation of PARP and NADPH depletion. Pharmacological inhibition of CYP1A1 or PARP protected against the PCB 104-mediated endothelial cell dysfunction. In conclusion, the environmental contaminants, PCBs, can activate PARP directly impairing endothelial cell function that may predispose exposed individuals to development of hypertension and cardiovascular disease.

Altered TP receptor function in isolated, perfused kidneys of nondiabetic and diabetic ApoE-deficient mice

Early manifestations of kidney disease occur in atherosclerosis and activation of TP (thromboxane A2) receptors is implicated in atherosclerotic, diabetes, and renal diseases. The purpose of the present study was to analyze, in isolated, perfused mouse kidneys, the participation of TP receptors in renal vasoconstrictions and vasodilatations. In kidneys, taken from wild-type C57BL6, apolipoprotein E-deficient (ApoE-KO) and diabetic ApoE-KO mice, changes in perfusion pressure were recorded. Constrictions to TP receptor ligands U 46619, arachidonic acid, PGH2, and 8-iso-PGF2α, but not those to angiotensin II, endothelin, or norepinephrine, were inhibited by the selective TP receptor antagonist Triplion (S 18886; 10 nM). Acetylcholine and prostacyclin evoked biphasic responses during methoxamine constrictions; the constrictor part was blocked by Triplion. In ApoE-KO mouse kidneys, compared with C57BL6, a specific decrease in norepinephrine response and no modification in dilator responses were observed. In diabetic ApoE-KO mouse kidneys, constrictions to U 46619 and those to 8-iso-PGF2α were significantly and selectively augmented, without modification in the expression of the TP receptor, and again without any significant change in vasodilator activity. Thus TP receptors are functional, and their activation is not involved in norepinephrine, endothelin, and angiotensin II vasoconstrictions but is implicated in the unusual vasoconstrictions to acetylcholine and prostacyclin. Increased responsiveness of TP receptors occurs in diabetic ApoE-KO mouse kidneys. Thus early changes in TP receptor-mediated vasoconstrictor activity may participate in the development of kidney disease in atherosclerosis and diabetes.

Impairment of endothelium-dependent relaxation of aortas and pulmonary arteries from spontaneously hyperlipidemic mice (Apodemus sylvaticus)

We evaluated the endothelial function of thoracic aortas and pulmonary arteries in a population of European wood mice (Apodemus sylvaticus), which exhibit hypercholesterolemia. According to the plasma cholesterol level, mice were divided into two groups: hypercholesterolemic (AHL, total plasma cholesterol 200-300 mg/dl) and normocholesterolemic (ANL, total plasma cholesterol <200 mg/dl). Acetylcholine (ACh) caused endothelium-dependent relaxation of precontracted aortas and pulmonary arteries. Relaxation of the pulmonary artery is completely dependent on nitric oxide. This relaxation was inhibited in AHL pulmonary arteries. On the other hand, part of the ACh-induced relaxation of the thoracic aorta was resistant to N(omega)-nitro-L-arginine (L-NNA). L-NNA-sensitive and -resistant relaxation to ACh were also inhibited in AHL aortas. Inhibition of endothelium-dependent relaxation of the aortas was correlated with total plasma cholesterol level. Endothelium-independent relaxation to sodium nitroprusside (SNP) was similar in AHL and ANL pulmonary arteries, but in the thoracic aorta of AHL mice, the sensitivity to SNP was slightly decreased, without a change in maximal response to SNP. No morphological change was observed in the aortas and the pulmonary arteries from AHL and ANL mice. Thus, AHL mice are valuable as a new experimental model to study the relation of hyperlipidemia to vascular disease since the endothelial function is impaired in these mild hyperlipidemic animals.

Cerebral vascular dysfunction during hypercholesterolemia

BACKGROUND AND PURPOSE

Studies of peripheral arteries in hypercholesterolemic animals suggest that increased generation of superoxide contributes to endothelial dysfunction, especially in the presence of atherosclerotic lesions. We tested the hypothesis that vasomotor function is impaired in cerebral arterioles during hypercholesterolemia through a mechanism that involves oxidative stress.

METHODS

Apolipoprotein E-deficient (apoE(-/-)) mice were fed a normal or a high-fat diet for >6 months. ApoE(+/-) mice fed a normal diet were used as normocholesterolemic controls. Responses of cerebral arterioles were examined in open cranial windows in vivo in anesthetized mice.

RESULTS

In apoE(-/-) mice, intimal area was increased only in the proximal aorta on the normal diet and also markedly increased in the distal aorta on the high-fat diet. There were no increases in intimal area in the aortas of control mice or in the cerebral arterioles in any group. The dilator response of cerebral arterioles to ACh (10 micromol/L) in control mice (26+/-4% increase in diameter) was reduced in apoE(-/-) mice on either the normal (13+/-2%) or the high-fat (13+/-3%) diet (P<0.05 vs control). NADPH (10 micromol/L), a substrate for NADPH oxidase, produced dilator responses in control mice (8+/-4%) that were significantly increased in apoE(-/-) mice on the high-fat diet (16+/-2%, P<0.05 vs control). Tempol, a superoxide scavenger, and apocynin, an inhibitor of NADPH oxidase, significantly increased vasodilator responses to ACh and decreased vasodilation to NADPH in apoE(-/-) mice on the high-fat diet. Nitroprusside produced a similar dilatation in the cerebral arterioles of all groups.

CONCLUSIONS

Hypercholesterolemia is associated with oxidative stress and endothelial dysfunction in cerebral arterioles, despite the absence of atherosclerotic lesions.

Increased vascular biosynthesis of tetrahydrobiopterin in apolipoprotein E-deficient mice

Previous studies suggested that loss of tetrahydrobiopterin (BH(4)) may play an important role in the pathogenesis of vascular endothelial dysfunction induced by diabetes and hypertension. In contrast, controversial results have been reported regarding BH(4) metabolism in experimental models of atherosclerosis. Therefore, the present study was designed to characterize the expression and activity of GTP-cyclohydrolase I, a rate-limiting enzyme in biosynthesis of BH(4), during atherogenesis. BH(4) levels were significantly increased in atherosclerotic aortas of apolipoprotein E (apoE)-deficient mice as compared with wild-type mice after 5 mo of Western diet treatment. This increase was further significantly enhanced in apoE-deficient mice fed for 9 and 14 mo. Removal of the endothelium almost eliminated BH(4) in wild-type mice but not in apoE-deficient mice, suggesting that a major component of increased BH(4) synthesis is localized in the vascular media of apoE-deficient mice. Oxidative products of BH(4) were low and did not differ between wild-type and apoE-deficient mice over the course of this study. Increased protein expression and enzymatic activity of GTP-cyclohydrolase I were detected in aortas of apoE-deficient mice (P < 0.05), providing molecular mechanisms responsible for elevation of vascular BH(4). In contrast to aortas, we did not detect any change in levels of BH(4) and in GTP-cyclohydrolase I expression in the brain. Our results demonstrate selective increase of intracellular BH(4) levels via elevation of GTP-cyclohydrolase I activity in vascular tissue of apoE-deficient mice.

The thromboxane A2 receptor antagonist S18886 prevents enhanced atherogenesis caused by diabetes mellitus

BACKGROUND

S18886 is an orally active thromboxane A2 (TXA2) receptor (TP) antagonist in clinical development for use in secondary prevention of thrombotic events in cardiovascular disease. We previously showed that S18886 inhibits atherosclerosis in apolipoprotein E-deficient (apoE(-/-)) mice by a mechanism independent of platelet-derived TXA2. Atherosclerosis is accelerated by diabetes and is associated with increased TXA(2) and other eicosanoids that stimulate TP. The purpose of this study was to determine whether S18886 lessens the enhanced atherogenesis in diabetic apoE(-/-) mice.

METHODS AND RESULTS

Diabetes mellitus was induced in apoE(-/-) mice with streptozotocin and was treated or not with S18886 (5 mg.kg(-1).d(-1)). After 6 weeks, aortic lesion area was increased >4-fold by diabetes in apoE(-/-) mice, associated with similar increases in serum glucose and cholesterol. S18886 largely prevented the diabetes-related increase in lesion area without affecting the hyperglycemia or hypercholesterolemia. S18886 prevented deterioration of endothelial function and endothelial nitric oxide synthase expression, as well as increases in intimal markers of inflammation associated with diabetes. In human aortic endothelial cells in culture, S18886 also prevented the induction of vascular cell adhesion molecule-1 and prevented the decrease in endothelial nitric oxide synthase expression caused by high glucose.

CONCLUSIONS

The TP antagonist inhibits inflammation and accelerated atherogenesis caused by diabetes, most likely by counteracting effects on endothelial function and adhesion molecule expression of eicosanoids stimulated by the diabetic milieu.

Persistence of the nitric oxide pathway in the aorta of hypercholesterolemic apolipoprotein-E-deficient mice

The markers of the bioavailability of NO (endothelium-dependent relaxation to acetylcholine and cyclic GMP content) in the thoracic aorta of apolipoprotein-E-deficient (ApoE KO) mice, 20 weeks old with enriched cholesterol diet or 35 weeks old on regular chow, are not decreased, in contrast with other models of atherosclerosis. However, severe hypercholesterolemia, the presence of atherosclerotic lesions and increased NADPH oxidase activity have been reported as early as at 20 weeks of age. The present experiments were designed to test if an increased capacity of NO production in these mice explains this paradox. The expressions of the 3 isoforms of NO synthase (NOS) were compared in ApoE KO and C57Bl/6J mice using Western blot and localized by immunohistochemistry. No adaptive increase in the expression of NOS was detected in ApoE KO mice. NO bioavailability could also be preserved by upregulation of enzymes involved in redox status such as CuZn or Mn superoxide dismutase and catalase. However, these enzymes were less expressed in ApoE KO mice than in control mice. These results highlight that ApoE KO mice represent an atypical model of atherosclerosis.

Fluvastatin prevents renal dysfunction and vascular NO deficit in apolipoprotein E-deficient mice

OBJECTIVE

The objective of this study was to investigate the effects of fluvastatin on atherosclerosis, systemic and regional hemodynamics, and vascular reactivity in apolipoprotein E-deficient (ApoE(-/-)) mice.

METHODS AND RESULTS

Hemodynamics (fluospheres) and vasomotor responses of thoracic aorta and carotid artery were evaluated in male wild-type (WT) and untreated (ApoE(-/-) Control) or fluvastatin-treated (50 mg/kg per day for 20 weeks) ApoE(-/-) mice, all fed a Western-type diet. Plasma cholesterol and aortic root atherosclerotic lesions (ALs) were greater in ApoE(-/-) Control mice (19+/-1 mmol/L and 63,0176+/-38,785 micro m(2), respectively) than in WT mice (2+/-1 mmol/L and 1+/-1 micro m(2), respectively, P<0.01). Fluvastatin significantly decreased plasma cholesterol (-53%) but failed to limit ALs. Renal blood flow was significantly reduced in ApoE(-/-) Control versus WT (-25%, P<0.05) mice. This reduction was prevented by fluvastatin. Aortic and carotid endothelium-dependent relaxations to acetylcholine were not altered in ApoE(-/-) Control versus WT mice. In carotid arteries from WT mice, these responses were abolished after nitro-L-arginine (L-NA), whereas those from ApoE(-/-) Control were only partially inhibited after L-NA but fully abolished after L-NA+diclofenac. Thus, in carotid arteries from ApoE(-/-) mice, vasodilating prostanoids compensate the deficit in NO availability. Fluvastatin prevented this carotid NO deficit.

CONCLUSIONS

In ApoE(-/-) mice, chronic fluvastatin treatment preserved renal perfusion and vascular NO availability independently from atherosclerotic lesion prevention.

Reduced sarco/endoplasmic reticulum Ca(2+) uptake activity can account for the reduced response to NO, but not sodium nitroprusside, in hypercholesterolemic rabbit aorta

BACKGROUND

Hypercholesterolemia (HC) impairs acetylcholine-induced relaxation but has little effect on that caused by the NO donor sodium nitroprusside (SNP), suggesting that acetylcholine releases less NO from the endothelium in HC. The relaxation to authentic NO gas, however, is also impaired in HC aortic smooth muscle, indicating an abnormal smooth muscle response. NO relaxes arteries by both cGMP-dependent and -independent mechanisms, and the response involves calcium (Ca(2+)) store refilling via the sarco/endoplasmic reticulum calcium ATPase (SERCA). We studied the involvement of cGMP and SERCA in the smooth muscle response to NO and SNP in HC rabbit aorta.

METHODS AND RESULTS

A selective guanylyl cyclase inhibitor, 1H-[1,2,4]-oxadiazole-[4,3-a]quinoxalin-1-one, eliminated SNP-induced relaxation but only partially blocked NO-induced relaxation in both normal and HC aorta. The residual relaxation to NO was still less in HC and, in both normal and HC aorta, was abolished by concomitant administration of the SERCA inhibitor cyclopiazonic acid (CPA). In contrast, CPA did not affect SNP-induced relaxation in either normal or HC aorta. SERCA activity measured by (45)Ca(2+) uptake was markedly decreased in HC, although SERCA2 protein expression did not change significantly.

CONCLUSIONS

These data suggest that NO-induced relaxation but not that to SNP is partially mediated by cGMP-independent Ca(2+) uptake into sarco/endoplasmic reticulum and that reduced sarco/endoplasmic reticulum Ca(2+) pump function can account for the impaired response to NO in HC.

Mechanism of endothelial dysfunction in apolipoprotein E-deficient mice

Endothelium-dependent relaxations mediated by NO are impaired in a mouse model of human atherosclerosis. Our objective was to characterize the mechanisms underlying endothelial dysfunction in aortas of apolipoprotein E (apoE)-deficient mice, treated for 26 to 29 weeks with a lipid-rich Western-type diet. Aortic rings from apoE-deficient mice showed impaired endothelium-dependent relaxations to acetylcholine (10(-)(9) to 10(-)(5) mol/L) and Ca(2+) ionophore (10(-)(9) to 10(-)(6) mol/L) and endothelium-independent relaxations to diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate, 10(-)(10) to 10(-)(5) mol/L) compared with aortic rings from C57BL/6J mice (P<0.05). By use of confocal microscopy of an oxidative fluorescent probe (dihydroethidium), increased superoxide anion (O(2)(-)) production was demonstrated throughout the aortic wall but mainly in smooth muscle cells of apoE-deficient mice. CuZn-superoxide dismutase (SOD) and Mn-SOD protein expressions were unaltered in the aorta exposed to hypercholesterolemia. A cell-permeable SOD mimetic, Mn(III) tetra(4-benzoic acid) porphyrin chloride (10(-)(5) mol/L), reduced O(2)(-) production and partially normalized relaxations to acetylcholine and DEA-NONOate in apoE-deficient mice (P<0.05). [(14)C]L-Citrulline assay showed a decrease of Ca(2+)-dependent NOS activity in aortas from apoE-deficient mice compared with C57BL/6J mice (P<0.05), whereas NO synthase protein expression was unchanged. In addition, cGMP levels were significantly reduced in the aortas of apoE-deficient mice (P<0.05). Our results demonstrate that in apoE-deficient mice on a Western-type fat diet, impairment of endothelial function is caused by increased production of O(2)(-) and reduced endothelial NO synthase enzyme activity. Thus, chemical inactivation of NO with O(2)(-) and reduced biosynthesis of NO are key mechanisms responsible for endothelial dysfunction in aortas of atherosclerotic apoE-deficient mice.