Regulation of G-protein alpha i2 subunit expression by oxidized low-density lipoprotein

Amelioration of atherosclerotic inflammation and plaques via endothelial adrenoceptor-targeted eNOS gene delivery using redox-sensitive polymer bearing l-arginine

Endothelial dysfunction combined with inflammation leads to atherosclerosis. Endothelium-specific delivery of therapeutic agents at the cellular level-specifically in vivo-is still a difficult task for proper management of atherosclerosis. We designed a redox-sensitive poly(oligo-l-arginine) (rsPOLA) playing dual roles as an endothelium α-2 adrenoceptors(α-2ARs)-targeted gene carrier and as a substrate for endothelial nitric oxide synthase (eNOS). Overexpression of α-2ARs on atherosclerotic endothelial cells was confirmed and the eNOS/rsPOLA nanoplexes following systemic injection demonstrated to 1) enhance eNOS gene delivery into endothelial cells via α-2ARs/l-arginine specific binding, 2) increase intracellular level of nitric oxide, 3) suppress inflammatory response in endothelium and finally 4) reduce atherosclerotic plaque in a Ldlr^-/- atherosclerotic mouse model. Among the tested nanoplexes [eNOS/rsPOLA, eNOS/{poly(oligo-d-arginine), rsPODA} and eNOS/(racemic mixture, rsRM)], eNOS/rsPOLA reduced atherosclerotic inflammation most effectively as we hypothesized. Current treatment strategy provides strong potential for further development of a gene therapeutic system to ameliorate inflammation and progressive atherosclerotic plaques.

Endothelial progenitor cells: Exploring the pleiotropic effects of statins

Statins have become a cornerstone of risk modification for ischaemic heart disease patients. A number of studies have shown that they are effective and safe. However studies have observed an early benefit in terms of a reduction in recurrent infarct and or death after a myocardial infarction, prior to any significant change in lipid profile. Therefore, pleiotropic mechanisms, other than lowering lipid profile alone, must account for this effect. One such proposed pleiotropic mechanism is the ability of statins to augment both number and function of endothelial progenitor cells. The ability to augment repair and maintenance of a functioning endothelium may have profound beneficial effect on vascular repair and potentially a positive impact on clinical outcomes in patients with cardiovascular disease. The following literature review will discuss issues surrounding endothelial progenitor cell (EPC) identification, role in vascular repair, factors affecting EPC numbers, the role of statins in current medical practice and their effects on EPC number.

Malondialdehyde mediates oxidized LDL-induced coronary toxicity through the Akt-FGF2 pathway via DNA methylation

Background

Oxidized LDL (oxLDL) is involved in the development of atherosclerotic heart disease through a mechanism that is not fully understood. In this study, we examined the role of malondialdehyde (MDA), an important oxidative stress epitope of oxLDL, in mediating coronary endothelial cytotoxicity.

Results

Human coronary artery endothelial cells (HCAECs) were treated with oxLDL in the presence or absence of antibody against MDA (anti-MDA) or apoB100 (anti-apoB100). In HCAECs treated with oxLDL (100 μg/ml) alone, DNA synthesis, cell viability, and expression of prosurvival fibroblast growth factor 2 (FGF2) were significantly reduced (P < 0.01 vs phosphate buffered saline–treated cells). These inhibitory effects of oxLDL were significantly attenuated in HCAECs cotreated with anti-MDA (0.15 μg/ml; P < 0.05 vs oxLDL-treated cells), but not in those cotreated with anti-apoB100. When we tested the effects of a panel of signal transduction modifiers on the signal transduction pathways of MDA in oxLDL-treated HCAECs, we found that MDA-induced cytotoxicity was mediated partly through the Akt pathway. Using a reporter gene assay, we identified an oxLDL-response element in the FGF2 promoter that was responsible for the transcriptional repression of FGF2 by oxLDL. The results of bisulfite genomic DNA sequencing showed that in HCAECs treated with oxLDL, the GC-rich promoter of FGF2 was heavily methylated at cytosine residues, whereas cotreatment with anti-MDA markedly reduced oxLDL-induced FGF2 promoter methylation.

Conclusion

OxLDL disrupts the growth and survival of HCAECs through an MDA-dependent pathway involving methylation of the FGF2 promoter and repression of FGF2 transcription. This novel epigenetic mechanism of oxLDL may underlie its atherogenicity in patients with atherosclerotic cardiovascular disease.

A-FABP and oxidative stress underlie the impairment of endothelium-dependent relaxations to serotonin and the intima-medial thickening in the porcine coronary artery with regenerated endothelium

Experiments were designed to determine the cause of the selective dysfunction of G(i) proteins, characterized by a reduced endothelium-dependent relaxation to serotonin (5-hydroxytryptamine), in coronary arteries lined with regenerated endothelial cells. Part of the endothelium of the left anterior descending coronary artery of female pigs was removed in vivo to induce regeneration. The animals were treated chronically with vehicle (control), apocynin (antioxidant), or BMS309403 (A-FABP inhibitor) for 28 days before functional examination and histological analysis of segments of coronary arteries with native or regenerated endothelium of the same hearts. Isometric tension was recorded in organ chambers and cumulative concentration-relaxation curves obtained in response to endothelium-dependent [serotonin (G(i) protein mediated activation of eNOS) and bradykinin (G(q) protein mediated activation of eNOS)] and independent [detaNONOate (cGMP-mediated), isoproterenol (cAMP-mediated)] vasodilators. The two inhibitors tested did not acutely affect relaxations of preparations with either native or regenerated endothelium. In the chronically treated groups, however, both apocynin and BMS309403 abolished the reduction in relaxation to serotonin in segments covered with regenerated endothelium and prevented the intima-medial thickening caused by endothelial regeneration, without affecting responses to bradykinin or endothelium-independent agonists (detaNONOate and isoproterenol). Thus, inhibition of either oxidative stress or A-FABP likely prevents both the selective dysfunction of G(i) protein mediated relaxation to serotonin and the neointimal thickening resulting from endothelial regeneration.

Endothelium-derived hyperpolarizing factor mediated relaxations in pig coronary arteries do not involve Gi/o proteins

AIM

Endothelium-dependent relaxations to certain neurohumoral substances are mediated by pertussis toxin-sensitive Gi/o protein. Our experiments were designed to determine the role, if any, of pertussis toxin-sensitive G-proteins in relaxations attributed to endothelium-derived hyperpolarizing factor (EDHF).

METHODS

Pig coronary arterial rings with endothelia were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution maintained at 37 degrees and continuously aerated with 95%O2 and 5% CO2. Isometric tension was measured during contractions to prostaglandin F2alpha in the presence of indomethacin and N(omega)- nitro-L-arginine methyl ester (L-NAME).

RESULTS

Thrombin, the thrombin receptor- activating peptide SFLLRN, bradykinin, substance P, and calcimycin produced dose-dependent relaxations. These relaxations were not inhibited by prior incubation with pertussis toxin, but were abolished upon the addition of charybdotoxin plus apamin. Relaxations to the alpha2-adrenergic agonist UK14304 and those to serotonin were abolished in the presence of indomethacin and L-NAME.

CONCLUSION

Unlike nitric oxide-mediated relaxations, EDHF-mediated relaxations of pig coronary arteries do not involve pertussis toxin-sensitive pathways and are Gi/o protein independent.

Increased oxidative stress with elevated serum thioredoxin level in patients with coronary spastic angina

BACKGROUND

Increased oxidative stress has been implicated in the pathogenesis of coronary vasospasm. Thioredoxin (TRX) is a redox-active protein that is known to be induced by oxidative stress.

HYPOTHESIS

The serum TRX level may be high in patients with coronary vasospasm.

METHODS

The serum TRX level was determined using an enzyme-linked immunosorbent assay in 21 patients with the active stage of coronary spastic angina (CSA), in 18 patients with the inactive stage of CSA (iCSA), in 24 control subjects without coronary artery disease (Control), and in 20 patients with stable effort angina (SEA).

RESULTS

Serum TRX levels (mean +/- standard deviation ng/ml) were significantly higher in CSA (64 +/- 44) than in iCSA (28 +/- 26), in Control (34 +/- 15), and in SEA (36 +/- 16). In contrast, serum alpha-tocopherol levels (mg/g lipids) were significantly lower in CSA (2.8 +/- 0.7) than in Control (4.0 +/- 1.2) and in SEA (3.2 +/- 0.4). Current smoking was significantly more prevalent in CSA (76%) than in any of the other groups. No significant correlation was found between the serum level of TRX and alpha-tocopherol in the study subjects. In nine patients with CSA, the serum TRX level decreased (93 +/- 41 --> 41 +/- 35 ng/ml) and the alpha-tocopherol level increased (2.7 +/- 0.6 --> 3.2 +/- 0.7 mg/g lipids) significantly under medication with calcium entry blockers after an at least 3-month angina-free period.

CONCLUSIONS

Patients with coronary spastic angina had a higher serum TRX level associated with a lower serum level of antioxidant vitamin E, with redox equilibrium appearing to be related to the disease activity of coronary vasospasm in these patients. Oxidative stress may be related to the genesis of coronary vasospasm.

Lovastatin enhances clearance of apoptotic cells (efferocytosis) with implications for chronic obstructive pulmonary disease

Statins are potent, cholesterol-lowering agents with newly appreciated, broad anti-inflammatory properties, largely based upon their ability to block the prenylation of Rho GTPases, including RhoA. Because phagocytosis of apoptotic cells (efferocytosis) is a pivotal regulator of inflammation, which is inhibited by RhoA, we sought to determine whether statins enhanced efferocytosis. The effect of lovastatin on efferocytosis was investigated in primary human macrophages, in the murine lung, and in human alveolar macrophages taken from patients with chronic obstructive pulmonary disease. In this study, we show that lovastatin increased efferocytosis in vitro in an 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase-dependent manner. Lovastatin acted by inhibiting both geranylgeranylation and farnesylation, and not by altering expression of key uptake receptors or by increasing binding of apoptotic cells to phagocytes. Lovastatin appeared to exert its positive effect on efferocytosis by inhibiting RhoA, because it 1) decreased membrane localization of RhoA, to a greater extent than Rac-1, and 2) prevented impaired efferocytosis by lysophosphatidic acid, a potent inducer of RhoA. Finally, lovastatin increased efferocytosis in the naive murine lung and ex vivo in chronic obstructive pulmonary disease alveolar macrophages in an HMG-CoA reductase-dependent manner. These findings indicate that statins enhance efferocytosis in vitro and in vivo, and suggest that they may play an important therapeutic role in diseases where efferocytosis is impaired and inflammation is dysregulated.

Physiological and pathophysiological aspects of ceramide

Activation of cells by receptor- and nonreceptor-mediated stimuli not only requires a change in the activity of signaling proteins but also requires a reorganization of the topology of the signalosom in the cell. The cell membrane contains distinct domains, rafts that serve the spatial organization of signaling molecules in the cell. Many receptors or stress stimuli transform rafts by the generation of ceramide. These stimuli activate the acid sphingomyelinase and induce a translocation of this enzyme onto the extracellular leaflet of the cell membrane. Surface acid sphingomyelinase generates ceramide that serves to fuse small rafts and to form large ceramide-enriched membrane platforms. These platforms cluster receptor molecules, recruit intracellular signaling molecules to aggregated receptors, and seem to exclude inhibitory signaling factors. Thus ceramide-enriched membrane platforms do not seem to be part of a specific signaling pathway but may facilitate and amplify the specific signaling elicited by the cognate stimulus. This general function may enable these membrane domains to be critically involved in the induction of apoptosis by death receptors and stress stimuli, bacterial and viral infections of mammalian cells, and the regulation of cardiovascular functions.

Heterologous desensitization of insulin secretion by GIP (glucose-dependent insulinotropic peptide) in INS-1 cells: the significance of Galphai2 and investigations on the mechanism involved

Heterologous desensitization is a term that describes the observation that chronic exposure of a cell to an agonist attenuates its response to other agonists. To characterize the cellular mechanisms that might be responsible for heterologous desensitization in an insulin secretory cell system (INS-1), we investigated the link between G-protein alphai2 level and insulin secretion as the biological effect after prolonged incubation with glucose-dependent insulinotropic polypeptide (GIP). Persistent activation (8 h) of the GIP signalling pathway decreased the GLP (glucagon-like peptide)-1 dependent insulin secretion (specific radioimmunoassay) accompanied by an upregulation of G-protein alphai2 protein level to about 126% whereas G-protein alphai3 and alphas protein levels remained unchanged (assessed by Western blots using specific antibodies). This was accompanied by similar changes in Galphai2 mRNA. By using either the CaM kinase II inhibitor KN-62, the calcineurin inhibitor FK 506 or the protein kinase A (PKA) inhibitor Rp-8-Br-cAMPS, the GIP-mediated Galphai2 mRNA increase was fully reversed. Heterologous desensitization of GLP-1-dependent insulin secretion by pretreatment with GIP, however, was not inhibited by calcium/calmodulin-dependent enzymes (using KN-62 and FK 506), but only by suppressing the cAMP/PKA signalling pathway using Rp-8-Br-cAMPS. The outcome is not disturbed by effects initiated by these compounds per se since an 8-h preincubation of cells did not affect glucose-induced insulin secretion. We, therefore, suggest that heterologous desensitization in INS-1 cells may be mediated by Galphai2 changes but depend on the cAMP/PKA signalling pathway probably distant form the Galphai2 protein.

High remnant lipoprotein levels in patients with variant angina

BACKGROUND

Dyslipidemia with increased oxidative stress but without elevation of low-density lipoprotein cholesterol has been recently implicated in the pathogenesis of coronary vasospasm.

HYPOTHESIS

Disordered triglyceride-rich lipoprotein metabolism may be linked to the genesis of coronary artery spasm.

METHODS

Both serum remnant lipoprotein (RLP) and alpha-tocopherol levels were determined in 18 patients with the active stage of variant angina (VA), in 16 patients with the inactive stage of variant angina (IVA), and in 19 control subjects (CONTROL).

RESULTS

The RLP levels were significantly (p < 0.05) higher in VA (6.4 +/- 2.7 mg/dl) than in IVA (4.4 +/- 1.5 mg/dl). In contrast, alpha-tocopherol levels were significantly lower in VA than that in CONTROL. Serum trigyceride levels were not significantly different among the study groups, although serum high-density lipoprotein cholesterol levels were significantly lower in VA than in CONTROL. Smoking was significantly (p < 0.05) more prevalent in VA (72%) than in IVA (25%) and CONTROL (37%). Serum RLP levels correlated positively with triglyceride levels (R = 0.73) and correlated inversely with alpha-tocopherol levels (R = -0.31) significantly in all study subjects.

CONCLUSIONS

Patients with active stage of variant angina had higher RLP levels than inactive patients with variant angina and lower alpha-tocopherol levels than control subjects. Disordered triglyceride-rich lipoprotein metabolism with increased oxidative stress appears to be linked to the activity of coronary vasospasm, suggesting a possible role in its pathogenesis.

Improvement of endothelium-dependent coronary vasodilation after a single LDL apheresis in patients with hypercholesterolemia

The purpose of this study was to determine whether a single LDL apheresis would improve impaired endothelium-dependent dilation of the coronary artery in patients with hypercholesterolemia. Hypercholesterolemia is associated with impaired endothelial function, and human studies using cholesterol-lowering drugs indicate that endothelial function in the coronary arteries improves with reduction of serum LDL cholesterol over 6 to 12 months. The internal diameter of the left coronary artery and the coronary blood flow were measured by intracoronary Doppler-wire measurement and quantitative angiography before and immediately after a single LDL apheresis in a population of 15 patients with familial hypercholesterolemia. Endothelium-dependent vasodilation was assessed by intracoronary infusion of acetylcholine (1, 10, and 50 microg/min), and endothelium-independent vasodilation was assessed by intracoronary bolus infusion of isosorbide dinitrate (2.5 mg) or papaverine (10 mg). A single 3-hour LDL apheresis reduced serum LDL cholesterol by an average of 86.6 +/- 1.7%. After the LDL apheresis, the changes in the coronary artery diameter and coronary blood flow in response to an infusion of 50 microg/min of acetylcholine increased significantly compared to the pre-apheresis values (from -19.7 +/- 4.8 to -2.9 +/- 3.0% [P < 0.01] and from 80.7 +/- 27.6 to 155.3 +/- 23.5% [P < 0.01], respectively). The LDL apheresis did not significantly change the response of either parameter to infusion with isosorbide dinitrate or papaverine. The endothelial function of the epicardial coronary artery and the coronary microvasculature improved in hypercholesterolemic patients after only a single LDL apheresis, a procedure that markedly reduces the serum level of LDL cholesterol.

Different mechanisms of adhesion molecule expression in human dermal microvascular endothelial cells by xanthoma tissue-mediated and copper-mediated oxidized low density lipoproteins

BACKGROUND

Oxidation of low density lipoprotein (LDL) has been implicated in infiltration of foam cells derived from circulating monocytes. Monocyte adhesion to endothelial cells and migration into dermis are essential steps for infiltration of foam cells.

OBJECTIVE

We investigated the role of adhesion molecules contributing to the process of monocyte adhesion to human dermal microvascular endothelial cells (HDMEC). Special attention was paid to the signal transduction for adhesion molecule expression induced by two distinct types of oxidized LDL.

METHODS

HDMEC were incubated with xanthoma tissue-modified LDL (x-LDL), a model of extravasated LDL oxidized in xanthoma lesions, or Cu(2+)-treated LDL (Cu-LDL), a model of oxidized LDL. Adhesion of U937 cells, a human monocytic leukemia cell line, to HDMEC and expression of endothelial cell adhesion molecules on HDMEC were examined. Signal transduction pathways for the adhesion molecule expression were evaluated by employing specific inhibitors.

RESULTS

x-LDL induced adhesion of U937 cells to HDMEC through vascular cell adhesion molecule-1 (VCAM-1) and E-selectin by activating tyrosine kinase pathway. Cu-LDL up-regulated the adhesion through not only VCAM-1 and E-selectin but also intercellular cell adhesion molecule-1 (ICAM-1) by activating G(i) protein pathway.

CONCLUSION

Extravasated and oxidized LDL in xanthoma lesions contributes to foam cell recruitment by activating tyrosine kinase pathway and inducing adhesion of monocytes to HDMEC through VCAM-1 and E-selectin. Cu-LDL, on the other hand, activates G(i) protein pathway and induces the adhesion through ICAM-1, VCAM-1 and E-selectin.

Low density lipoprotein particles are small in patients with coronary vasospasm

Increased lipid oxidative stress has been recently implicated in the pathogenesis of coronary artery spasm. Small, dense LDL with high susceptibility to oxidation may be linked to the genesis of coronary vasospasm. The relative migratory distance of the predominant densitometric peak of LDL from that of VLDL to that of HDL in a 3% polyacrylamide gel electrophoresis was determined as a measure of LDL particle size in 49 patients with coronary spastic angina (CSA), in 56 patients with stable effort angina and a significant coronary artery stenosis (SEA) and also in 40 control subjects without coronary artery disease (Control). The incidence of detection of small, dense LDL (particle diameter <25.5 nm) or a relative migratory distance above 0.36 was significantly higher in CSA (57%) and also in SEA (39%) than in Control (20%). In SEA, a significantly higher serum level of triglyceride was noted in the subgroup with the small, dense LDL as compared with the subgroup without. In contrast, in CSA, the serum level of triglyceride was not significantly different between the subgroups with and without the small, dense LDL, although significantly lower serum levels of both HDL-cholesterol and alpha-tocopherol were noted in the former. In 16 patients of CSA, the detection of the small, dense LDL was significantly decreased after a >6-month angina-free period (69-->31%). We conclude that patients with coronary spastic angina had smaller LDL particles, associated not with hypertriglyceridemia but low serum levels of both HDL-cholesterol and vitamin E. Dyslipidemia with small, dense LDL may be related to the genesis of coronary vasospasm.

Nitric oxide, atherosclerosis and the clinical relevance of endothelial dysfunction

The endothelium plays a key role in vascular homeostasis through the release of a variety of autocrine and paracrine substances, the best characterized being nitric oxide. A healthy endothelium acts to prevent atherosclerosis development and its complications through a complex and favorable effect on vasomotion, platelet and leukocyte adhesion and plaque stabilization. The assessment of endothelial function in humans has generally involved the description of vasomotor responses, but more widely includes physiological, biochemical and genetic markers that characterize the interaction of the endothelium with platelets, leukocytes and the coagulation system. Stable markers of inflammation such as high sensitivity C-reactive protein are indirect and potentially useful measures of endothelial function for example. Attenuation of the effect of nitric oxide accounts for the majority of what is described as endothelial dysfunction. This occurs in response to atherosclerosis or its risk factors. Much remains to be learned about the molecular and genetic pathophysiological mechanisms of endothelial cell abnormalities. However, pharmacological intervention with a growing list of medications can favorably modify endothelial function, paralleling beneficial effects on cardiovascular morbidity and mortality. In addition, several small studies have provided tantalizing evidence that measures of endothelial health might provide prognostic information about an individual patient's risk of subsequent events. As such, the sum of this evidence makes the clinical assessment of endothelial function an attractive surrogate marker of atherosclerosis disease activity. The review will focus on the role of nitric oxide in atherosclerosis and the clinical relevance of these findings.

Endothelial function. From vascular biology to clinical applications

The endothelium, by releasing nitric oxide (NO), promotes vasodilation and inhibits inflammation, thrombosis, and vascular smooth muscle cell proliferation. These biological actions of NO make it an important component in the endogenous defense against atherosclerosis and its overt clinical complications. Loss of the functional integrity of the endothelium, as seen commonly in the milieu of cardiovascular risk factors, plays an integral role in all stages of atherosclerosis from lesion initiation to plaque rupture. A number of established techniques can assess endothelial function in human vascular beds. The outcome of endothelial testing has profound prognostic implications and is an independent predictor of atherosclerosis disease progression and cardiovascular event rates. The large clinical benefit of statins and angiotensin-converting enzyme inhibitors in patients with atherosclerosis involves favorable effects of endothelial function. Studies of endothelial function represent a prime example of a successful application of insights derived from vascular biology at the bedside.

Exposure to oxidized low-density lipoprotein reduces activable Ras protein in vascular endothelial cells

Oxidized low-density lipoprotein (ox-LDL) has been shown to alter the migratory and proliferative activities of the vascular endothelial cells (EC) in response to serum and growth factors. The mechanism underlying the antiproliferative effect of ox-LDL on vascular EC has not been fully elucidated. In this report, we show that exposure of vascular EC to ox-LDL results in a marked reduction of the membrane-associated Ras protein. Further study shows that in ox-LDL-treated EC, reduction of the membrane-associated Ras protein is correlated with a reduced amount of active Ras (Ras-guanosine triphosphate), indicating that the Ras signaling pathway is attenuated. The attenuation of the Ras signaling pathway in ox-LDL-treated EC may thus be responsible for the retarded response to the mitogenic stimulation of serum and growth factors.

Obesity, atherosclerosis and the vascular endothelium: mechanisms of reduced nitric oxide bioavailability in obese humans

It is now well established that obesity is an independent risk factor for the development of coronary artery atherosclerosis. The maintenance of vascular homeostasis is critically dependent on the continued integrity of vascular endothelial cell function. A key early event in the development of atherosclerosis is thought to be endothelial cell dysfunction. A primary feature of endothelial cell dysfunction is the reduced bioavailability of the signalling molecule nitric oxide (NO), which has important anti atherogenic properties. Recent studies have produced persuasive evidence showing the presence of endothelial dysfunction in obese humans NO bioavailability is dependent on the balance between its production by a family of enzymes, the nitric oxide synthases, and its reaction with reactive oxygen species. The endothelial isoform (eNOS) is responsible for a significant amount of the NO produced in the vascular wall. NO production can be modulated in both physiological and pathophysiological settings, by regulation of the activity of eNOS at a transcriptional and post-transcriptional level, by substrate and co-factor provision and through calcium dependent and independent signalling pathways. The present review discusses general mechanisms of reduced NO bioavailability including factors determining production of both NO and reactive oxygen species. We then focus on the potential factors responsible for endothelial dysfunction in obesity and possible therapeutic interventions targetted at these abnormalities.

Mechanisms underlying attenuated contractile response of aortic rings to noradrenaline in fructose-fed mice

We hypothesized that an impairment of endothelial dysfunction and an increased response to alpha-adrenoceptor agonists may occur in fructose-fed, insulin-resistant mice. The aim of the present study was to assess the relationship between endothelial dysfunction and agonist-induced contractile responses in such mice. The acetylcholine-induced relaxation was significantly attenuated in streptozotocin-diabetic and fructose-fed mice. The contractile response to noradrenaline was significantly weaker than the control in fructose-fed but not in streptozotocin-diabetic mice; treatment with N(G)-nitro-L-arginine effectively restored this response. Incubating aortic rings with noradrenaline increased the NO(x) [nitrite (NO(2)(-)) and nitrate (NO(3)(-))] level and this level was significantly higher in fructose-fed mice than in control mice. Clonidine induced a dose-dependent relaxation in aortic rings pre-contracted with prostaglandin F(2alpha) that was completely abolished by N(G)-nitro-L-arginine; this relaxation was markedly enhanced in fructose-fed mice. In both control and fructose-fed mice, the clonidine-induced relaxation was significantly attenuated and the noradrenaline-induced contraction augmented by pertussis toxin. These results suggest that endothelial function is attenuated in both fructose-fed and streptozotocin-diabetic mice. It is suggested that the decreased noradrenaline contractile response in fructose-fed mice (compared to both controls and streptozotocin-diabetic mice) may be due to an increase in nitric oxide formation mediated by endothelial GTP-binding-coupled alpha(2)-adrenoceptors.

Hypochlorite-modified low density lipoprotein inhibits nitric oxide synthesis in endothelial cells via an intracellular dislocalization of endothelial nitric-oxide synthase

Hypochlorous acid/hypochlorite, generated by the myeloperoxidase/H(2)O(2)/halide system of activated phagocytes, has been shown to oxidize/modify low density lipoprotein (LDL) in vitro and may be involved in the formation of atherogenic lipoproteins in vivo. Accordingly, hypochlorite-modified (lipo)proteins have been detected in human atherosclerotic lesions where they colocalize with macrophages and endothelial cells. The present study investigates the influence of hypochlorite-modified LDL on endothelial synthesis of nitric oxide (NO) measured as formation of citrulline (coproduct of NO) and cGMP (product of the NO-activated soluble guanylate cyclase) upon cell stimulation with thrombin or ionomycin. Pretreatment of human umbilical vein endothelial cells with hypochlorite-modified LDL led to a time- and concentration-dependent inhibition of agonist-induced citrulline and cGMP synthesis compared with preincubation of cells with native LDL. This inhibition was neither due to a decreased expression of endothelial NO synthase (eNOS) nor to a deficiency of its cofactor tetrahydrobiopterin. Likewise, the uptake of l-arginine, the substrate of eNOS, into the cells was not affected. Hypochlorite-modified LDL caused remarkable changes of intracellular eNOS distribution including translocation from the plasma membrane and disintegration of the Golgi location without altering myristoylation or palmitoylation of the enzyme. In contrast, cyclodextrin known to deplete plasma membrane of cholesterol and to disrupt caveolae induced only a disappearance of eNOS from the plasma membrane that was not associated with decreased agonist-induced citrulline and cGMP formation. The present findings suggest that mislocalization of NOS accounts for the reduced NO formation in human umbilical vein endothelial cells treated with hypochlorite-modified LDL and point to an important role of Golgi-located NOS in these processes. We conclude that inhibition of NO synthesis by hypochlorite-modified LDL may be an important mechanism in the development of endothelial dysfunction and early pathogenesis of atherosclerosis.

Atherogenic lipids and endothelial dysfunction: mechanisms in the genesis of ischemic syndromes

Atherogenic lipids, particularly oxidized low-density lipoprotein, are responsible for a wide range of cellular dysfunctions within the vessel wall. The effects on endothelial cells disrupt normal control of vasomotion, with a reduction of effective nitric oxide activity, the development of a procoagulant surface, chronic low-grade inflammation, and abnormal cell growth. These changes are central not only in the development of atherosclerosis but also in the evolution of both stable and unstable ischemic syndromes. There is growing evidence that these abnormal changes in cell function respond rapidly to changes in the atherogenic lipids. Certain cell functions can improve within hours or days of cholesterol lowering.

Coronary microcirculation: physiology and pharmacology

Coronary microvessels play a pivotal role in determining the supply of oxygen and nutrients to the myocardium by regulating the coronary flow conductance and substance transport. Direct approaches analyzing the coronary microvessels have provided a large body of knowledge concerning the physiological and pharmacological characteristics of the coronary circulation, as has the rapid accumulation of biochemical findings about the substances that mediate vascular functions. Myogenic and flow-induced intrinsic vascular controls that determine basal tone have been observed in coronary microvessels in vitro. Coronary microvascular responses during metabolic stimulation, autoregulation, and reactive hyperemia have been analyzed in vivo, and are known to be largely mediated by metabolic factors, although the involvement of other factors should also be taken into account. The importance of ATP-sensitive K(+) channels in the metabolic control has been increasingly recognized. Furthermore, many neurohumoral mediators significantly affect coronary microvascular control in endothelium-dependent and -independent manners. The striking size-dependent heterogeneity of microvascular responses to all of these intrinsic, metabolic, and neurohumoral factors is orchestrated for optimal perfusion of the myocardium by synergistic and competitive interactions. The regulation of coronary microvascular permeability is another important factor for the nutrient supply and for edema formation. Analyses of collateral microvessels and subendocardial microvessels are important for understanding the pathophysiology of ischemic hearts and hypertrophied hearts. Studies of the microvascular responses to drugs and of the impairment of coronary microvessels in diseased conditions provide useful information for treating microvascular dysfunctions. In this article, the endogenous regulatory system and pharmacological responses of the coronary circulation are reviewed from the microvascular point of view.

Vascular superoxide production by NAD(P)H oxidase: association with endothelial dysfunction and clinical risk factors

Superoxide anion plays important roles in vascular disease states. Increased superoxide production contributes to reduced nitric oxide (NO) bioactivity and endothelial dysfunction in experimental models of vascular disease. We measured superoxide production by NAD(P)H oxidase in human blood vessels and examined the relationships between NAD(P)H oxidase activity, NO-mediated endothelial function, and clinical risk factors for atherosclerosis. Endothelium-dependent vasorelaxations and direct measurements of vascular superoxide production were determined in human saphenous veins obtained from 133 patients with coronary artery disease and identified risk factors. The predominant source of vascular superoxide production was an NAD(P)H-dependent oxidase. Increased vascular NAD(P)H oxidase activity was associated with reduced NO-mediated vasorelaxation. Furthermore, reduced endothelial vasorelaxations and increased vascular NAD(P)H oxidase activity were both associated with increased clinical risk factors for atherosclerosis. Diabetes and hypercholesterolemia were independently associated with increased NADH-dependent superoxide production. The association of increased vascular NAD(P)H oxidase activity with endothelial dysfunction and with clinical risk factors suggests an important role for NAD(P)H oxidase-mediated superoxide production in human atherosclerosis. The full text of this article is available at http://www.circresaha.org.

Impaired endothelial function in arterial hypertension and hypercholesterolemia: potential mechanisms and differences

This review focuses on the role of impaired endothelial function for the development of atherosclerosis in human arterial hypertension and hypercholesterolemia in vivo. Potential mechanisms underlying impaired endothelial function and decreased bioavailability of nitric oxide under these clinical conditions are discussed and potential differences in these mechanisms between arterial hypertension and hypercholesterolemia are outlined. It further addresses therapeutic strategies aiming to improve the bioavailability of nitric oxide in these patients. The overall conclusion is that the bioavailability of nitric oxide is probably impaired not by a single defect, but by various mechanisms affecting nitric oxide synthesis as well as nitric oxide breakdown. In both diseases, increased superoxide anion production and oxidative stress represents a major mechanism. However, potential differences in the underlying mechanisms of superoxide production or nitric oxide synthesis are evident between arterial hypertension and hypercholesterolemia. Decreased bioavailability of nitric oxide does not only impair endothelium-dependent vasodilation, but also activates other mechanisms that play an important role in the pathogenesis of atherosclerosis. Thus, therapeutic strategies should aim to restore bioavailability of nitric oxide, which has been demonstrated for lipid-lowering therapy in hypercholesterolemia. The mechanisms by which nitric oxide bioavailability can be improved by any drug therapy remain to be elucidated and may provide further insights into the mechanisms that are involved in impaired endothelial function and atherogenesis.

Oxidized-low density lipoprotein inhibits cyclic AMP production by porcine luteal cells

Oxidized(OX)-low density lipoprotein (LDL) inhibits steroidogenesis by luteal cells (LC) from regressing porcine CL. The present study was designed to investigate the mechanism of inhibition by determining whether OX-LDL inhibits basal and agonist-stimulated cAMP production in regressing LC. Collagenase-dispersed porcine LC (n = 7 animals, estrous cycle Day 12-15) were cultured (2.5 x 10(5) cells/0.5 ml) in serum-free DMEM/Hams F-12 in duplicate wells at 37 degrees C. Approximately 18 hr after plating, media were replaced and LC were immediately treated with human LDL (0, 25, or 100 microg/ml) or OX-LDL (25 or 100 microg/ml). LC were incubated for 2 hr before addition of isobutylmethylxanthine (IBMX) to inhibit phosphodiesterase activity, immediately followed by hCG (100 ng/ml), cholera toxin (CT; 0.1 microM), forskolin (FS; 50 microM), or no further treatment (controls). LC were incubated for an additional 90 min. After removal of culture media, cells were extracted with 0.1 N HCl. Cell extracts were assayed for cAMP by enzyme immunoassay (EIA). HCG, CT, and FS increased (P < 0.05) cAMP production approximately four-, 10-, and 25-fold, respectively, relative to controls. OX-LDL (25 and 100 microg/ml) inhibited (P < 0.05) cAMP production by unstimulated, hCG-, and CT-stimulated LC, but not that by FS-stimulated LC. The highest concentration of OX-LDL (100 microg/ml) reduced cAMP formation by 39.8 +/- 6.6%, 44.7 +/- 10.5%, and 67.7 +/- 4.5% in unstimulated, hCG-, and CT-stimulated LC, respectively. In contrast, unmodified LDL (25 and 100 microg/ml) did not alter cAMP production. We conclude that OX-LDL can interfere with the cAMP signaling pathway in regressing luteal cells by acting at sites proximal to adenylate cyclase activation.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Stimulation of phospholipase D activity by oxidized LDL in mouse peritoneal macrophages

Oxidation of LDL is an important factor in the development of atherosclerosis. However, the mechanisms by which oxidized LDL exerts its atherogenic actions are poorly understood. In the present work, we show that oxidized LDL stimulates phospholipase D (PLD) activity in mouse peritoneal macrophages and that this effect increases with the degree of LDL oxidation. Oxidative modification of LDL results in the production of lipid peroxides and the conversion of phosphatidylcholine to lysophosphatidylcholine. Although we found that lysophosphatidylcholine alone activates PLD, the stimulation of this enzyme activity by oxidized LDL is independent of lysophosphatidylcholine formation. Also, 7-ketocholesterol, the major oxysterol in oxidized LDL, failed to stimulate PLD activity. To determine the mechanism(s) whereby oxidized LDL activates PLD, the possible involvements of protein kinase C and tyrosine phosphorylation were investigated. Pretreatment of macrophages with the protein kinase C inhibitor Ro-32-0432 or downregulation of protein kinase C activity by prolonged incubation with 100 nmol/L 4beta-phorbol 12-myristate 13-acetate did not alter the stimulatory effect of oxidized LDL on PLD activation. However, oxidized LDL stimulated tyrosine phosphorylation of several macrophage proteins, and preincubation of the macrophages with genistein, a tyrosine kinase inhibitor, blocked the activation of PLD by oxidized LDL. In addition, pretreatment with orthovanadate, which inhibits tyrosine phosphatases, enhanced basal and oxidized LDL-stimulated PLD activity. Pretreatment of macrophages with pertussis toxin decreased the stimulatory effect of oxidized LDL, indicating that GTP-binding proteins may also be involved in the activation of PLD by oxidized LDL. We also found that the platelet-activating factor receptor antagonists WEB 2086 and L-659,989 inhibit the oxidized LDL stimulation of PLD, suggesting a role for platelet-activating factor receptor in this process. The stimulation of the PLD pathway by oxidized LDL may be of importance in atherogenesis, because PLD activation leads to generation of important second messengers such as phosphatidate, lysophosphatidate, and diacylglycerol, which are known to regulate many cellular functions.

Pulmonary vascular endothelial responses are differentially modulated after cardiopulmonary bypass

The aim of this study was to characterize the mechanisms underlying pulmonary vascular dysfunction after cardiopulmonary bypass (CPB) by examining responses of isolated pulmonary arteries to selective endothelium-dependent and -independent activators in control and post-CPB dogs. Adult male mongrel dogs were placed on closed-chest, hypothermic CPB for 2.5 h, and then allowed to recover. Anatomically matched pulmonary arterial rings were isolated and suspended for isometric tension recording. Contractile responses to the alpha1-adrenergic agonist phenylephrine were similar in endothelium-containing arteries from control and CPB animals. Endothelium denudation increased contractions to phenylephrine to a similar extent in both groups. Endothelium-dependent relaxation to acetylcholine was decreased 4 days after CPB compared with controls. In contrast to acetylcholine, endothelium-dependent relaxation to bradykinin or to A23187 were not impaired 4 days after CPB. Inhibition of nitric oxide synthase (NOS) with L-NAME depressed the response to acetylcholine in control vessels, confirming that a component of the response to acetylcholine was nitric oxide (NO) dependent. At lower concentrations of acetylcholine, this component of the response was abolished after CPB. The residual relaxation evoked by acetylcholine in the presence of L-NAME also was impaired in CPB compared with control arteries. This suggests that the CPB-induced impairment of acetylcholine-evoked relaxation may not involve both an NO-mediated and an NO-independent component. L-NAME depressed the response to bradykinin to a similar degree in control and CPB arteries. Vascular smooth-muscle dilatation to the NO donor, SIN-1, or to the K+ATP-channel opener, cromakalim, were similar in endothelium-denuded arteries from CPB and control animals. These results suggest that CPB causes a selective impairment in endothelial dilator function without changing the vascular smooth-muscle response to vasodilator or vasoconstrictor stimuli.

Galpha(i2)-mRNA and -protein regulation as a mechanism for heterologous sensitization and desensitization of insulin secretion

Prolonged exposure of cells to an agonist of a G-protein-coupled receptor usually results in an attenuation of the cellular response. To elucidate the cellular mechanisms of sensitization or desensitization in an insulin secretory cell system (INS-1 cells), we investigated a regulatory link between G-protein alpha(s)- and alpha(i2)-subunits mRNA, their protein levels and insulin secretion as the biological effect using various compounds. Incubation with epinephrine (50 microM) for 8 h decreased alpha(s)- and alpha(i2)-mRNA levels to 58% and 72%, respectively, which is reversed after a longer incubation. From results using isoprenaline and the alpha2-agonist UK 14,304 epinephrine is shown to mediate its actions via alpha2- but not beta-adrenoceptors. The insulin inhibitory neuropeptide galanin (50 nM) caused a decrease of alpha(s)- and alpha(i2)-mRNA levels, whereas insulinotropic compounds (incretin hormones) such as GIP or GLP-1 (both 10 nM) led to an increase of alpha(s)- and alpha(i2)-mRNA levels. By using the Ca2+ channel blocker verapamil (50 microM) alpha(i2)-mRNA changes clearly depend on Ca2+ influx. The effects on alpha(i2)-mRNA were accompanied by a parallel, albeit weaker effect on the protein level (only GIP and UK 14,304 were investigated). The changes in alpha(i2)-mRNA levels by either compound were paralleled by inverse changes in insulin secretion: preincubation with UK 14,304 for 8 h led to an increased insulin secretion when challenged by either GLP-1, GIP or glucose (8.3 mM). This was similar for galanin, another potent inhibitor of insulin release. On the other hand, exposure to the incretins GIP or GLP-1 for 8 h induced a smaller insulin release when challenged afterwards by either UK 14,304, galanin, GIP, GLP-1, or glucose. Thus the influence on insulin secretion of various compounds is reciprocal to the regulation of alpha(i2)-mRNA levels but not alpha(s)-mRNA levels. There is, therefore, evidence from all the manoeuvres used that alpha(i2)-mRNA regulation may play a role in heterologous sensitization and desensitization of insulin secretion.

Atherogenic lipoproteins and tyrosine kinase mitogenic signaling in mesangial cells

BACKGROUND

Mesangial hypercellularity is a critical early histopathological finding seen in human and experimental glomerular diseases. Hyperlipidemia and the glomerular deposition of atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and its oxidized variants, minimally oxidized/modified LDL (mm-LDL)] are commonly associated with mesangial hypercellularity and the development of glomerular disease. This article reviews signal transduction pathways involved in cell proliferation and provides evidence for the participation of atherogenic lipoproteins in intracellular signaling pathways for mesangial cell proliferation. The mitogenic intracellular signaling pathways are regulated by the activation of a series of transmembrane and cytoplasmic protein tyrosine kinases that converge into the activation of Ras and downstream mitogen-activated protein (MAP) kinase. Activated MAP kinase, through translocating into the nucleus and the activation of various transcription factors and proto-oncogenes, regulates cellular proliferation.

METHODS

Murine mesangial cells were stimulated with LDL and mm-LDL and were analyzed for the tyrosine kinase activity, phosphorylation of membrane proteins, activation of Ras and MAP kinase, and cell proliferation.

RESULTS

The results indicated that the stimulation of mesangial cells with LDL and, with greater activity, mm-LDL induced the phosphorylation of membrane platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptors, activated Ras, and resulted in sustained (up to 24 hr) activation of MAP kinase. LDL/mm-LDL-mediated mesangial cell proliferation and MAP kinase activation were dependent on the activation of tyrosine kinases.

CONCLUSIONS

We suggest that the accumulation of LDL and more potently its oxidized forms within the glomerulus, through the activation of membrane receptor tyrosine kinases, activate the Ras and MAP kinase signaling cascade leading to DNA synthesis and subsequent cell proliferation.

Oxidized low-density lipoprotein stimulates monocyte adhesion to glomerular endothelial cells

BACKGROUND

Abnormalities in lipid and lipoprotein metabolism have been implicated in the pathogenesis of glomerulosclerosis. Atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and oxidized LDL (ox-LDL)] have been shown to stimulate glomerular monocyte chemoattractants involved in monocyte infiltration. However, the role of LDL and ox-LDL in the early monocyte adhesion to glomerular endothelial cells (ECs) and associated intracellular signaling mechanisms are not clearly understood.

METHODS

In this study, we examined the effect of LDL and ox-LDL on intracellular signaling mechanisms associated with monocyte adhesion to glomerular ECs and intercellular adhesion molecule-1 (ICAM-1) expression.

RESULTS

Ox-LDL, but not LDL, stimulated EC ICAM-1 expression and monocyte adhesion. Ox-LDL elevated protein tyrosine kinase (PTK) activity, and the preincubation of ECs with specific PTK inhibitors blocked ox-LDL-induced ICAM-1 message and monocyte adhesion. Whereas experimental maneuvers that inhibit either protein kinase C activation (by PKC depletion or with inhibitors) or Gi-protein-mediated pathways (pertussis toxin sensitive) had no effect on ox-LDL-induced monocyte adhesion and ICAM-1 expression. cAMP-elevating compounds did not induce ICAM-1 or monocyte adhesion.

CONCLUSIONS

The data indicate that ox-LDL, by stimulating monocyte adhesion to the glomerular endothelium, may regulate monocyte infiltration within the glomerulus, supporting an early pathobiological role for atherogenic lipoproteins in glomerular injury. The results suggest that the activation of specific PTK and associated signaling may, at least in part, play a critical role in ox-LDL-mediated endothelial-monocyte interaction-related events. The data suggest that the interventions aimed at modifying associated intracellular signaling events within the glomerulus may provide potential therapeutic modalities in monocyte/macrophage-mediated glomerular disease.

Hypercholesterolemia decreases nitric oxide production by promoting the interaction of caveolin and endothelial nitric oxide synthase

Hypercholesterolemia is a central pathogenic factor of endothelial dysfunction caused in part by an impairment of endothelial nitric oxide (NO) production through mechanisms that remain poorly characterized. The activity of the endothelial isoform of NO synthase (eNOS) was recently shown to be modulated by its reciprocal interactions with the stimulatory Ca2+-calmodulin complex and the inhibitory protein caveolin. We examined whether hypercholesterolemia may reduce NO production through alteration of this regulatory equilibrium. Bovine aortic endothelial cells were cultured in the presence of serum obtained from normocholesterolemic (NC) or hypercholesterolemic (HC) human volunteers. Exposure of endothelial cells to the HC serum upregulated caveolin abundance without any measurable effect on eNOS protein levels. This effect of HC serum was associated with an impairment of basal NO release paralleled by an increase in inhibitory caveolin-eNOS complex formation. Similar treatment with HC serum significantly attenuated the NO production stimulated by the calcium ionophore A23187. Accordingly, higher calmodulin levels were required to disrupt the enhanced caveolin-eNOS heterocomplex from HC serum-treated cells. Finally, cell exposure to the low-density lipoprotein (LDL) fraction alone dose-dependently reproduced the inhibition of basal and stimulated NO release, as well as the upregulation of caveolin expression and its heterocomplex formation with eNOS, which were unaffected by cotreatment with antioxidants. Together, our data establish a new mechanism for the cholesterol-induced impairment of NO production through the modulation of caveolin abundance in endothelial cells, a mechanism that may participate in the pathogenesis of endothelial dysfunction and the proatherogenic effects of hypercholesterolemia.

Effects of vitamin C and of a cell permeable superoxide dismutase mimetic on acute lipoprotein induced endothelial dysfunction in rabbit aortic rings

Low density lipoprotein (LDL) inhibits endothelium-dependent relaxation. The mechanism is uncertain, but increased production of superoxide anion O2- with inactivation of endothelium-derived NO and formation of toxic free radical species have been implicated. We investigated effects of the cell permeable superoxide dismutase mimetic manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTMPyP), the free radical scavenger vitamin C and arginine (which may reduce O2- formation) on acute LDL-induced endothelial dysfunction in rabbit aortic rings, using LDL prepared by ultracentrifugation of plasma from healthy men and aortic rings from New Zealand white rabbits. LDL (150 microg protein ml(-1) for 20 min) markedly inhibited relaxation of aortic rings (in Krebs' solution at 37 degrees C and pre-constricted to 80% maximum tension with noradrenaline) to acetylcholine 82+/-10% (mean percentage difference between sum of relaxations after each concentration of acetylcholine in the presence and absence of LDL, +/-s.e.mean, n=26, P<0.001) but not to the endothelium-independent agonist nitroprusside. MnTMPyP (10 microM) reduced inhibitory effects of LDL from 124+/-27 to 56+/-17% (n=6, P<0.05). Vitamin C (1 mM) reduced inhibitory effects of LDL from 59+/-8 to 22+/-5% (n=6, P<0.05). Inhibitory effects of LDL were similar in the absence or presence of arginine (84+/-12 vs 79+/-16%, n=14, P=0.55). Effects of L-arginine (10 mM) did not differ significantly from those of D-arginine (10 mM). Acute (20 min) exposure of aortic rings to LDL impairs endothelium-dependent relaxation which can be partially restored by MnTMPyP and vitamin C. This is consistent with LDL causing increased O2- generation.

Superoxide production, risk factors, and endothelium-dependent relaxations in human internal mammary arteries

BACKGROUND

In a variety of disease states, endothelium-dependent vasodilation is abnormal. Reduced nitric oxide (NO) production, increased destruction of NO by superoxide, diminished cellular levels of L-arginine or tetrahydrobiopterin, and alterations in membrane signaling have been implicated. We examined these potential mechanisms in human vessels.

METHODS AND RESULTS

Relaxations to acetylcholine, the calcium ionophore A23187, and nitroglycerin, as well as superoxide production and NO synthase expression, were examined in vascular segments from patients with identified cardiovascular risk factors. Endothelium-dependent relaxations were also studied after incubation with L-arginine, L-sepiapterin, and liposome-entrapped superoxide dismutase (SOD) and after organoid culture with cis-vaccenic acid. Relaxations to acetylcholine and to a lesser extent the calcium ionophore A23187 were highly variable and correlated with the number of risk factors present among the subjects studied. Treatment of vessels with L-arginine, L-sepiapterin, liposome-entrapped SOD, or cis-vaccenic acid did not augment endothelium-dependent relaxations. Hypercholesterolemia was the only risk factor associated with high levels of superoxide; however, there was no correlation between superoxide production and the response to either endothelium-dependent vasodilator used.

CONCLUSIONS

In human internal mammary arteries, depressed endothelium-dependent relaxations could not be attributed to increases in vascular superoxide production, deficiencies in either L-arginine or tetrahydrobiopterin, or reduced membrane fluidity. Variability in signaling mechanisms may contribute to the differences in responses to acetylcholine and the calcium ionophore A23187.

High-affinity arginine transport of bovine aortic endothelial cells is impaired by lysophosphatidylcholine

The mechanisms of endothelial dysfunction characterized by the impaired nitric oxide (NO) release have not yet been clarified. Because the phenomenon is mimicked in vitro by the application of oxidized LDL and its major lipid constituent, lysophosphatidylcholine (LPC), we analyzed their effects on the arginine-NO system, especially on the arginine transport system. LPC inhibited NO release induced by ADP in cultured bovine aortic endothelial cells. The inhibition was attenuated by the excess amount of extracellular arginine. LPC was found to inhibit the arginine transport in bovine aortic endothelial cells, which is mediated by high- and low-affinity components. LPC predominantly impaired the high-affinity component. In the presence of a high concentration of arginine, LPC showed apparently no inhibition of arginine transport, because the low-affinity transporter compensated for the activity. Taken together, the impairment of the high-affinity transport system might account for the inhibition of NO release by LPC. LPC also inhibited arginine transport in the intima of intact bovine aorta. Furthermore, LPC inhibited the activity of the high-affinity arginine transporter in endothelial cells, in the cationic amino acid transporter-1 expressed in COS-7 cells. The activity of cationic amino acid transporter-1 might be important for the prevention of endothelial dysfunction.

Dyslipoproteinaemia and hyperoxidative stress in the pathogenesis of endothelial dysfunction in non-insulin dependent diabetes mellitus: an hypothesis

Endothelial dysfunction in non-insulin dependent (Type 2) diabetes mellitus (NIDDM) has implications for the pathogenesis of the two major complications, macrovascular disease and microangiopathy. Endothelial dysfunction is a consequence of a disturbance in the L-arginine/nitric oxide pathway. Its occurrence in NIDDM is well supported by both in vitro and in vivo studies. NIDDM results in diverse abnormalities in lipoprotein metabolism, the most significant being hypertriglyceridaemia which is associated with increased plasma concentrations of small dense LDL and low levels of HDL. Dysglycaemia results in hyperoxidative stress and increased formation of advanced-glycosylation endproducts, both of which enhance the oxidative modification of lipoprotein particles. Based on extensive in vitro studies and on human data, we generate the hypothesis that the development of endothelial dysfunction in NIDDM is a consequence of the effect of dyslipoproteinaemia, in particular increased circulatory concentrations of modified small dense LDL and of hyperoxidative stress on the formation, action and disposal of nitric oxide, by diverse molecular mechanisms; HDL is proposed to have a protective effect on these processes through its enzymic antioxidant properties. The hypothesis proposed is simple, testable and consistent with wide sources of evidence. The practical implications of the hypothesis and the existing opportunities for the prevention and reversal of endothelial dysfunction in NIDDM are also reviewed and discussed.

Post-transcriptional regulation of endothelial nitric oxide synthase mRNA stability by Rho GTPase

The mechanism by which 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors increase endothelial nitric oxide synthase (eNOS) expression is unknown. To determine whether changes in isoprenoid synthesis affects eNOS expression, human endothelial cells were treated with the HMG-CoA reductase inhibitor, mevastatin (1-10 microM), in the presence of L-mevalonate (200 microM), geranylgeranylpyrophosphate (GGPP, 1-10 microM), farnesylpyrophosphate (FPP, 5-10 microM), or low density lipoprotein (LDL, 1 mg/ml). Mevastatin increased eNOS mRNA and protein levels by 305 +/- 15% and 180 +/- 11%, respectively. Co-treatment with L-mevalonate or GGPP, but not FPP or LDL, reversed mevastatin's effects. Because Rho GTPases undergo geranylgeranyl modification, we investigated whether Rho regulates eNOS expression. Immunoblot analyses and [35S]GTPgammaS-binding assays revealed that mevastatin inhibited Rho membrane translocation and GTP binding activity by 60 +/- 5% and 78 +/- 6%, both of which were reversed by co-treatment with GGPP but not FPP. Furthermore, inhibition of Rho by Clostridium botulinum C3 transferase (50 microg/ml) or by overexpression of a dominant-negative N19RhoA mutant increased eNOS expression. In contrast, activation of Rho by Escherichia coli cytotoxic necrotizing factor-1 (200 ng/ml) decreased eNOS expression. These findings indicate that Rho negatively regulates eNOS expression and that HMG-CoA reductase inhibitors up-regulate eNOS expression by blocking Rho geranylgeranylation, which is necessary for its membrane-associated activity.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Remnants of chylomicron and very low density lipoprotein impair endothelium-dependent vasorelaxation

Remnants of chylomicron and very low density lipoprotein (VLDL) have been implicated as potentially atherogenic. Since endothelial dysfunction is an early event in atherosclerosis, we examined effects of the remnants on endothelium-dependent vasorelaxation. The remnant lipoproteins were isolated from postprandial plasma in hyperlipidemic subjects using the immunoaffinity gel mixture of anti apo A-1 and anti apo B-100 monoclonal antibodies and ultracentrifugation. Rabbit aortic strips suspended in the organ chambers were incubated for 2 h with the preparations of lipoproteins and lipids. After incubation, the strips were tested with vasodilators after precontraction with phenylephrine (1 microM). The remnant lipoproteins (750-1500 microg triglyceride/ml) but not VLDL fraction (up to 1500 microg triglyceride/ml) impaired vasorelaxation in responses to acetylcholine, substance P and A23187. Carbamylated or methylated remnant lipoproteins, chemically modified remnant lipoproteins, had comparable impairment of the vasorelaxation as unmodified remnant lipoproteins. Incubation with lipid extracts from the remnant lipoproteins also exerted an inhibitory effect on the vasorelaxation. Relaxation to sodium nitroprusside was fully preserved in all aortas exposed to the lipoprotein preparations. Thus, the remnant lipoproteins impair endothelium-dependent arterial relaxation at the concentrations observed in the plasma in patients with coronary artery disease (500-2000 microg triglyceride of remnant lipoprotein/ml). The impairment may be in apoprotein receptor-independent manner, and the lipids in the remnants seem to contribute to the inhibitory effect. The endothelial dysfunction caused by the remnant lipoproteins may play a role in the high prevalence of atherosclerotic coronary artery disease in postprandial hyperlipidemic patients.

G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 1. Reduced membrane-associated G-protein content due to diminished isoprenylation of G-gamma subunits and p21ras

Mechanisms contributing to altered heterotrimeric G-protein expression and subsequent signaling events during cholesterol accretion have been unexplored. The influence of cholesterol enrichment on G-protein expression was examined in cultured smooth muscle cells that resemble human atherosclerotic cells by exposure to cationized LDL (cLDL). cLDL, which increases cellular free and esterified cholesterol 2-fold and 10-fold, respectively, reduced the cell membrane content of Galphai-1, Galphai-2, Galphai-3, Gq/11, and Galphas. The following evidence supports the premise that the mechanism by which this occurs is due to reduced isoprenylation of the Ggamma-subunit. First, the inhibitory effect of cholesterol enrichment on the membrane content of Galphai subunits was found to be post-transcriptional, since the mRNA steady-state levels of Galphai(1-3) were unchanged following cholesterol enrichment. Second, the membrane expression of alpha and beta subunits was mimicked by cholesterol and 17-ketocholesterol, both of which inhibit HMG-CoA reductase. Third, inhibition of Galphai and Gbeta expression in cholesterol-enriched cells was overcome by mevalonate, the immediate product of HMG-CoA reductase. Fourth, pulse-chase experiments revealed that cholesterol enrichment did not reduce the degradation rate of membrane-associated Galphai subunits. Fifth, cholesterol enrichment also reduced membrane expression of Ggamma-5, Ggamma-7upper; these gamma subunits are responsible for trafficking of the heterotrimeric G-protein complex to the cell membrane as a result of HMG-CoA reductase-dependent post-translational lipid modification (geranylgeranylation) and subsequent membrane association. Cholesterol enrichment did not alter expression of G-gamma-5 mRNA, as assessed by reverse transcriptase polymerase chain reaction, supporting a post-transcriptional defect in Ggamma subunit expression. Fifth, cholesterol enrichment also reduced the membrane content of p21ras (a low molecular weight G-protein requiring farnesylation for membrane targeting) but did not alter the membrane content of the two proteins that do not require isoprenylation for membrane association&sbd;PDGF-receptor or p60-src. Reduced G-protein content in cholesterol-laden cells was reflected by reduced G-protein-mediated signaling events, including ATP-induced GTPase activity, thrombin-induced inhibition of cyclic AMP accumulation, and MAP kinase activity. Collectively, these results demonstrate that cholesterol enrichment reduces G-protein expression and signaling by inhibiting isoprenylation and subsequent membrane targeting. These results provide a molecular basis for altered G-protein-mediated cell signaling processes in cholesterol-enriched cells.

Spontaneous transfer of monoacyl amphiphiles between lipid and protein surfaces

The kinetics of transfer of natural and fluorescent nonesterified fatty acids (NEFA) and lysolecithins (lysoPC) from phospholipid and protein surfaces were measured. The kinetics of transfer of 12-(1-pyrenyl)dodecanoic acid, from liquid crystalline and gel phase single unilamellar phospholipid vesicles, very low, low, and high density lipoproteins, human serum albumin, and rat liver fatty acid-binding protein, were first-order and characterized by similar rate constants. The halftimes (t1/2) of NEFA transfer from lipids and proteins were dependent on the acyl chain structure according to log t1/2 = -0.62n + 0.59m + 12.0, where n and m, respectively, are the numbers of carbon atoms and double bonds. The structure of the donor surface had a measurable but smaller effect on transfer rates. The kinetics of NEFA and lysoPC transfer are slow relative to the lipolytic processes that liberate them. Therefore, one would predict a transient accumulation of NEFA and lysoPC during lipolysis and an attendant modulation of many metabolic processes within living cells and within the plasma compartment of blood. These data will be useful in the refinement of current models of membrane and lipoprotein function and in the selection of fluorescent NEFA analogs for studying transport in living cells.

Cell dysfunction in atherosclerosis and the ischemic manifestations of coronary artery disease

Many of the cellular mechanisms and dysfunctions that underlie atherosclerotic plaque formation have been identified, including adverse interactions between atherogenic lipids and the arterial endothelium, loss of endothelium-dependent dilation, accumulation of inflammatory cells and mediators of inflammation in the intima of the arteries, and a decline in anticoagulant defenses. Several studies have shown that these mechanisms, which appear to be active throughout the pathogenesis and progression of atherosclerosis, are reversible within days, weeks, or months with effective lipid-lowering therapy. In addition, the findings of large-scale trials of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors suggest that the rapid improvement observed in trial participants is attributable to a reversal of endothelial and vascular wall dysfunctions rather than to a reduction in plaque size. The accumulated evidence indicates that improved endothelial function can benefit patients who have angina pectoris and/or are at risk for myocardial infarction. Current understanding of the cellular mechanisms of atherogenesis also suggests avenues of future research to refine treatment approaches and further improve outcomes for patients with coronary artery disease.

Atherogenic lipids, vascular dysfunction, and clinical signs of ischemic heart disease

LDL is oxidized in vascular endothelial cells to a highly injurious product that results in characteristic cell dysfunction(s) in large arteries and resistance vessels. The characteristic dysfunctions (ie, loss of dilation, constriction, thrombosis, and inflammation) operate before and throughout the development of atherosclerosis and particularly during plaque rupture. Although oxidized LDL appears to induce these cell/vessel wall dysfunctions in a time- and concentration-dependent manner, Tamai and colleagues have shown that this interaction can be dynamic in that a reduction in lipids restores endothelium-dependent vasomotor function almost immediately. The same intervention (ie, lipid lowering) also appears to stabilize atheroma in the long term, improves endothelium-dependent vasomotion over months, and results in a reduction in clinical signs of risk in coronary heart disease (ie, ischemia and the need for revascularization). The above leads us to some important but unanswered questions. Can we rely on clinical measures of arterial vasomotor dysfunction to represent the other important cell dysfunctions (eg, inflammation, abnormal growth) while monitoring the response to therapeutic interventions? How can we effectively inhibit oxidation of LDL in the arterial wall, and is this useful in reversing the many cell dysfunctions and clinical sequelae of coronary atherosclerosis? What is the time course for restoration of endothelial dysfunction in the atherosclerotic epicardial coronary arteries in patients with effective lipid-lowering therapy? The intracellular responses to oxidized LDL are so numerous (loss of vasodilation, loss of anticoagulant mechanisms, abnormal inflammation, and growth) that targeting therapies to specific pathways may prove difficult. Parallel efforts in basic physiological and clinical research have resulted in remarkable progress that has improved outcomes in patients with coronary heart disease. We expect that many of the characteristic cell/vessel wall dysfunctions that result from adverse interactions with risk factors are dynamic and can be manipulated in a relatively short time frame. Treatment of atherogenic lipids with other risk factors must be further refined and may well become the cornerstone for effective management of angina, unstable syndromes, and ischemia in addition to the control of important outcomes such as myocardial infarction and coronary death.

Oxidized phosphatidylcholines that modify proteins. Analysis by monoclonal antibody against oxidized low density lipoprotein

Oxidatively modified low density lipoprotein (OxLDL) is known to be involved in atherogenesis. We have previously developed a murine monoclonal antibody, FOH1a/DLH3, which recognized oxidatively modified lipoproteins as well as foam cells in human atherosclerotic lesions (Itabe, H., Takeshima, E., Iwasaki, H., Kimura, J., Yoshida, Y., Imanaka, T., and Takano, T. (1994) J. Biol. Chem. 269, 15274-15279). The antigen of this monoclonal antibody was formed by peroxidation of phosphatidylcholine (PC), and the antigenic oxidized PC (OxPC) derivatives are thought to form complexes with polypeptides including apolipoproteins. OxLDL was measured by a sensitive sandwich enzyme-linked immunosorbent assay using the monoclonal antibody and anti-human apolipoprotein B antibody, in which antigenic OxPC competed with OxLDL. When antigenic activities of PC analogs were tested by the competition assay, 1-palmitoyl-2-(9-oxononanoyl) PC (9-CHO PC) and the hydroperoxide of egg PC potently inhibited the detection of OxLDL. 1-Palmitoyl-2-linoleoyl PC was oxidized with ferrous ion and ascorbic acid, and the antigenic products were purified from the OxPC extracts on high pressure liquid chromatography columns and subsequently analyzed by laser desorption mass spectrometry. Molecular weight determination and retention times of high pressure liquid chromatography suggest that one of these products was 9-CHO PC. Other products are thought to be 8-carbon aldehyde, dihydroxy, and ketohydroxy derivatives of PC. When a C-terminal 16-mer synthetic peptide of the 70-kDa peroxisomal membrane protein was simply incubated with 9-CHO PC, it was found to be reactive in a sandwich enzyme-linked immunosorbent assay using FOH1a/DLH3 and an anti-peptide antiserum. These results suggest that the anti-OxLDL monoclonal antibody FOH1a/DLH3 reacts with several oxidized products of PC including aldehyde derivatives of PC, which covalently modify polypeptides.

Induction of vascular cell adhesion molecule-1 by low-density lipoprotein

Low-density lipoprotein (LDL) is a well-established risk factor for atherosclerosis. When endothelial cells are incubated with this lipoprotein in pathophysiologic amounts, the cells are activated. Among the documented cellular responses to LDL is increased recruitment of monocytes, which are believed to play a major role in promoting intimal plaque formation. The findings presented here link an atheogenic lipoprotein, LDL, with the induction of an adhesion molecule important in atherogenesis Human LDL induces the vascular cell adhesion molecule-1 (VCAM-1) transcriptionally with an increase in mRNA levels through activation of the VCAM promoter. This effect is blocked by anti-VCAM antibodies. After a 2-day incubation in LDL, the binding of NF-kappa B, which is believed to be a key oxidative-stress sensor for VCAM regulation, remains at basal level. In contrast, the binding activities of AP-1 and GATA, on the other hand, are increased by LDL. Thus, a component of LDL-enhanced endothelial recruitment of monocytes is attributed to VCAM-1 expression, which appears to be mediated through AP-1 and GATA. These data identify LDL as a VCAM-inducer possibly distinct from cytokines and endotoxin.

alpha-Thrombin upregulates G alpha i3 in human vascular endothelial cells

BACKGROUND AND PURPOSE

During thrombosis, alpha-thrombin becomes sequestered by fibrin and the subendothelial basement membrane, and it is available to interact with the vasculature over prolonged periods. In this study, we investigated the long-term effect of alpha-thrombin on G alpha i3 and G alpha s levels in human vascular endothelial cells (EC). Because obesity is associated with changes in receptor signaling in many animal models, we also explored the influence of this clinical risk factor.

METHODS

Primary cultures of human EC were exposed to alpha-thrombin for 16 hours, and immunologically detectable G alpha i3 and G alpha s levels were measured.

RESULTS

alpha-Thrombin (100 nmol/L) increased G alpha i3 levels in EC derived from the cerebral microvasculature and superficial temporal artery (4.2 +/- 1.2-fold and 2.8 +/- 0.32-fold, respectively) but had no significant effect on EC derived from omental artery (P > .6) or from the superficial temporal artery of obese (body mass index > or = 28 kg/m2) patients (P > .4). The expression of G alpha s was unchanged in all cell types (P > or = .1). Two other circulating peptides, vasoactive intestinal peptide and endothelin-1, failed to alter the expression of either G protein in EC from the cerebral microvasculature, further demonstrating the specificity of the alpha-thrombin effect. However, thrombin receptor activating protein-14 mimicked the alpha-thrombin response and increased G alpha i3 in EC derived from the cerebral microvasculature and superficial temporal artery.

CONCLUSIONS

We conclude that alpha-thrombin increases G alpha i3 expression in some EC through activation of its tethered liganded receptor. Obesity appears to suppress this action of alpha-thrombin.

Characterization of G proteins in obstructed kidneys

BACKGROUND

Urinary tract obstruction has a marked effect on renal function. Activation of phospholipases which results in incremental production of vasoactive eicosanoids may contribute to the hemodynamic changes characteristic of an obstructed kidney. G proteins play an important role in transmembrane signal transduction, which control phospholipase activities and eicosanoid production. The present study was designed to determine the presence of G proteins in obstructed kidneys in rats, and to characterize the differences between unilateral ureteral obstruction (UUO) and bilateral ureteral obstruction (BUO).

METHODS

Several G-protein alpha subunits (G alpha s, G alpha i1,2, and G alpha i3) and the beta subunit (G beta) were determined by immunoblotting and immunocytochemical techniques using specific antibodies against these G proteins.

RESULTS

Immunoblots demonstrated a decreased G alpha i3 content in the outer medullary tubules and a significantly lower G beta level in the glomeruli of UUO. In BUO, there was an increased level of G beta in the cortical tubules, and the G alpha s level was markedly reduced in the inner medullary tubules. Immunocytochemical studies revealed that these G proteins were predominantly localized in the brush border side of the cortical tubules. However, we could not demonstrate staining differences between UUO and BUO.

CONCLUSIONS

These results indicate that a modulation of G-protein-coupled transmembrane signal transduction may contribute to the renal functional changes in an obstructed kidney. A different level of expression of G-protein subunits between UUO and BUO may be a factor in the differences of hemodynamics and renal tubular damage between UUO and BUO.