Functional expression of sodium-dependent vitamin C transporter 2 in human endothelial cells.

Since oxidative stress plays an important role in dysregulation of the microcirculation as well as the pathogenesis of atherosclerosis, therapeutic intervention with antioxidants has been speculated to prevent cardiovascular diseases. Ascorbic acid (AA) has been reported to improve endothelial function; however, its intracellular metabolic pathway has not been fully determined. Sodium-dependent vitamin C transporter (SVCT) types 1 and 2 were recently cloned. In the present study, we investigated whether SVCT-2 is functionally expressed in vascular endothelial cells and, if so, what factors modulate its activity. The uptake of AA into human umbilical vein endothelial cells (HUVECs) was examined by incubation with radiolabeled AA (14C-AA). AA was transported into HUVECs in a dose- and time-dependent manner. Replacement of sodium chloride with choline chloride in the medium suppressed the uptake of AA. RT-PCR revealed that HUVECs expressed SVCT-2 mRNA, but not SVCT-1. Transfection of HUVECs with the antisense oligonucleotide of SVCT-2 significantly suppressed the uptake of AA. Furthermore, tumor necrosis factor-alpha and interleukin-1beta inhibited the transport activity of AA. Thus, SVCT-2 is functionally expressed in human endothelial cells, and its activity is negatively regulated by inflammatory cytokines. Our findings might provide a new insight into understanding the treatment of cardiovascular diseases with AA.

Expressional changes of the vascular antioxidant system in atherosclerotic coronary arteries.

Oxidative stress induced by reactive oxygen species (ROS) plays an important role in atherogenesis, and the redox state is determined by the balance between antioxidants and the ROS generating system. To defend against enhanced ROS, mammalian cells have a complex network of antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase. To clarify the role of the vascular antioxidant system, we investigated by immunohistochemistry the expressional changes of antioxidative enzymes in coronary arteries obtained from autopsied cases. In nonatherosclerotic coronary arteries, Cu/Zn SOD and Mn SOD were expressed in medial smooth muscle cells (SMC), whereas cytosolic GPx (GPx-1) was expressed mainly in endothelium and weakly in medial SMC. Catalase was expressed in medial SMC and endothelium. Progression of atherosclerosis did not result in an additional increase in the expression of antioxidative enzymes in SMC in the media or endothelium. However, migrating SMC and macrophages in atheromatous plaques expressed these four antioxidative enzymes intensively. Double staining with cell markers confirmed the cell-specific expression of the antioxidative enzymes. Thus, the expressional pattern showed regional heterogeneity. In response to oxidative stress, the vascular antioxidant system was upregulated in atherosclerotic lesions. The imbalance between vascular antioxidant and oxidant systems might play an important role in coronary atherogenesis.

Expression of tissue transglutaminase and elafin in human coronary artery: implication for plaque instability.

BACKGROUND: the extracellular matrix (ECM) is an important determinant of plaque instability. Since tissue transglutaminase (tTG) and elafin act as stabilizing factors, they might play a crucial role in the pathogenesis of acute coronary syndrome. We examined their expression in human coronary arteries and the regulation of tTG expression in cultured vascular smooth muscle cells (SMCs). METHODS AND RESULTS: immunohistochemical studies on autopsy samples of human coronary arteries revealed the expression of tTG and elafin in the endothelium, medial SMCs, and the ECM in non-atherosclerotic coronary arteries. Their expression in SMCs, endothelium, and ECM was enhanced in atherosclerotic coronary arteries. In contrast, they were hardly detectable in accumulating macrophages or at the lipid core. Double staining demonstrated that elafin was co-localized with tTG. Moreover, some tTG-expressing cells were positive for TNF-alpha, suggesting that this cytokine might play an important role in the regulation of tTG. Treatment of cultured rat aortic SMCs with TNF-alpha increased their tTG mRNA, protein expression and enzyme activity. CONCLUSIONS: the expression of tTG and elafin increased in atherosclerotic coronary arteries. The investigation with cultured SMCs suggested that TNF-alpha might mediate the upregulation of tTG. Our findings may provide new insights into the mechanism of plaque instability and the pathogenesis of acute coronary syndrome.