[Show abstract][Hide abstract] ABSTRACT: Thiol oxidative stress leads to macrophage dysfunction and cell injury, and has been implicated in the development of atherosclerotic lesions. We investigated if strengthening the glutathione-dependent antioxidant system in macrophages by overexpressing glutathione reductase (GR) decreases the severity of atherosclerosis.
Bone marrow cells infected with retroviral vectors expressing either enhanced green fluorescent protein (EGFP) or an EGFP-fusion protein of cytosolic GR (GR(cyto)-EGFP) or mitochondrial GR (GR(mito)-EGFP) were transplanted into low-density lipoprotein receptor-deficient mice. Five weeks after bone marrow transplantation, animals were challenged with a Western diet for 10 weeks. No differences in either plasma cholesterol and triglyceride levels or peritoneal macrophage content were observed. However, mice reconstituted with either GR(cyto)-EGFP or GR(mito)-EGFP-expressing bone marrow had lesion areas (P<0.009) that were 32% smaller than recipients of EGFP-expressing bone marrow. In cultured macrophages, adenovirus-mediated overexpression of GR(cyto)-EGFP or GR(mito)-EGFP protected cells from mitochondrial hyperpolarization induced by oxidized low-density lipoprotein.
This study provides direct evidence that the glutathione-dependent antioxidant system in macrophages plays a critical role in atherogenesis, and suggests that thiol oxidative stress-induced mitochondrial dysfunction contributes to macrophage injury in atherosclerotic lesions.
[Show abstract][Hide abstract] ABSTRACT: Dietary free fatty acids have been reported to have various effects on the endothelium including the generation of nitric oxide. The goal of the current study was to determine the mechanism whereby free fatty acid causes an increase in nitric oxide synthesis. The specific hypothesis tested was that free fatty acid association with CD36, a class B scavenger receptor, induces the activation of endothelial nitric-oxide synthase (eNOS). A human microvascular endothelial cell line and a transfected Chinese hamster ovary cell system were used to determine which free fatty acids stimulate eNOS. Surprisingly, only myristic acid, and to a lesser extent palmitic acid, stimulated eNOS. The stimulation of eNOS was dose- and time-dependent. Competition experiments with other free fatty acids and with a CD36-blocking antibody demonstrated that the effects of myristic acid on eNOS required association with CD36. Further mechanistic studies demonstrated that the effects of myristic acid on eNOS function were not dependent on PI 3-kinase, Akt kinase, or calcium. Pharmacological studies and dominant negative constructs were used to demonstrate that myristic acid/CD36 stimulation of eNOS activity was dependent on the activation of AMP kinase. These data demonstrate an unexpected link among myristic acid, CD36, AMP kinase, and eNOS activity.
Journal of Biological Chemistry 09/2005; 280(33):29543-50. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The controversy surrounding hormone replacement therapy has induced fear in patients and left many researchers with the impression that estrogen produces negative effects on cardiovascular function. The aim of this review is to summarize recent findings illustrating that estrogen also has positive effects even if estrogen replacement therapy is not a cure-all.
Studies have unveiled new aspects of estrogen action in the cardiovascular system; however, clinical trials have not demonstrated a protective effect of the most widely used modalities of hormone replacement therapy against cardiovascular disease. New information has emerged showing that estrogen has both beneficial and detrimental effects. Further mechanistic studies and use of well defined forms of estrogens and selective estrogen receptor modulators will continue to provide novel mechanistic information that will likely lead to the development of new avenues for therapeutic interventions.
Estrogens, like other steroid hormones, are potent actors in the cardiovascular system. Since half the population have high levels of estrogen most of their lives it is plain that estrogen has a variety of beneficial physiologic functions. Clinical studies, however, have demonstrated that a specific formulation of a combination of potent estrogens and metabolites is not a magic bullet, but induces both positive and negative impacts on different organ systems. More research into the mechanistic actions of estrogens in specific pathways in individual cell types is necessary to determine appropriate therapeutic interventions to replace the loss of positive effects of estrogens while minimizing the negative effects in postmenopausal women.
Current Opinion in Lipidology 11/2004; 15(5):589-93. · 5.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The endothelium is a dynamic organ that secretes several biologically active substances and plays a major functional role in the health of an organism in both physiological and pathological conditions. For instance, the endothelium is involved in control of the exchange of plasma and tissue biomolecules, regulation of vessel tone, inflammation, lipid metabolism, vessel growth and remodeling, and modulation of coagulation and fibrinolysis. The endothelium generates nitric oxide, which is a key regulator of vasodilation and plays important roles in preventing, or in some cases promoting, numerous cardiovascular diseases. Several recent studies have examined the interplay between lipids and nitric oxide generation, especially in relation to atherosclerosis. The endothelium is continuously exposed to circulating lipids in the form of lipoproteins and protein carriers that may have a direct impact on nitric oxide synthesis and function. The purpose of this review is to illustrate some of the recent findings that link lipids (plasma and cellular) to nitric oxide generation (see Fig. 1).
AJP Endocrinology and Metabolism 10/2004; 287(3):E386-9. · 4.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cardiovascular diseases remain the leading cause of death in the United States. Two factors associated with a decreased risk of developing cardiovascular disease are elevated HDL levels and sex - specifically, a decreased risk is found in premenopausal women. HDL and estrogen stimulate eNOS and the production of nitric oxide, which has numerous protective effects in the vascular system including vasodilation, antiadhesion, and anti-inflammatory effects. We tested the hypothesis that HDL binds to its receptor, scavenger receptor class B type I (SR-BI), and delivers estrogen to eNOS, thereby stimulating the enzyme. HDL isolated from women stimulated eNOS, whereas HDL isolated from men had minimal activity. Studies with ovariectomized and ovariectomized/estrogen replacement mouse models demonstrated that HDL-associated estradiol stimulation of eNOS is SR-BI dependent. Furthermore, female HDL, but not male HDL, promoted the relaxation of muscle strips isolated from C57BL/6 mice but not SR-BI null mice. Finally, HDL isolated from premenopausal women or postmenopausal women receiving estradiol replacement therapy stimulated eNOS, whereas HDL isolated from postmenopausal women did not stimulate eNOS. We conclude that HDL-associated estrodial is capable of the stimulating eNOS. These studies establish a new paradigm for examining the cardiovascular effects of HDL and estrogen.
Journal of Clinical Investigation 06/2003; 111(10):1579-87. · 12.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Estradiol has numerous physiological and pathophysiological effects on the cardiovascular system, and the ongoing controversy surrounding estrogen replacement therapy clearly illustrates the importance of understanding the molecular mechanisms of estrogen action. Many recent mechanistic studies have focused on the ability of estradiol to stimulate endothelial nitric oxide synthase (eNOS) and the subsequent generation of nitric oxide (NO). NO is centrally involved in many processes such as mitogenesis, cell adhesion, thrombosis, atherosclerosis and hypertension. Consequently, elucidating the mechanisms whereby estradiol influences NO production will directly impact on our understanding of the advantages and disadvantages of estrogen replacement therapy. An exciting aspect of this emerging area of study is that the estrogen, NO and caveolae research fields have merged to identify a novel and clinically relevant molecular process. The goal of this review is to highlight the recent findings in this area and to point out areas of controversy and areas where more studies are needed.
Trends in Endocrinology and Metabolism 05/2003; 14(3):114-7. · 8.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Protease inhibitors decrease the viral load in HIV patients, however the patients develop hypertriglyceridemia, hypercholesterolemia, and atherosclerosis. It has been assumed that protease inhibitor-dependent increases in atherosclerosis are secondary to the dyslipidemia. Incubation of THP-1 cells or human PBMCs with protease inhibitors caused upregulation of CD36 and the accumulation of cholesteryl esters. The use of CD36-blocking antibodies, a CD36 morpholino, and monocytes isolated from CD36 null mice demonstrated that protease inhibitor-induced increases in cholesteryl esters were dependent on CD36 upregulation. These data led to the hypothesis that protease inhibitors induce foam cell formation and consequently atherosclerosis by upregulating CD36 and cholesteryl ester accumulation independent of dyslipidemia. Studies with LDL receptor null mice demonstrated that low doses of protease inhibitors induce an increase in the level of CD36 and cholesteryl ester in peritoneal macrophages and the development of atherosclerosis without altering plasma lipids. Furthermore, the lack of CD36 protected the animals from protease inhibitor-induced atherosclerosis. Finally, ritonavir increased PPAR-gamma and CD36 mRNA levels in a PKC- and PPAR-gamma-dependent manner. We conclude that protease inhibitors contribute to the formation of atherosclerosis by promoting the upregulation of CD36 and the subsequent accumulation of sterol in macrophages.
Journal of Clinical Investigation 03/2003; 111(3):389-97. · 12.81 Impact Factor