Advanced glycation and endothelial functions: a link towards vascular complications in diabetes

The formation of advanced glycation end-products (AGEs), also called the Maillard reaction, occurs ubiquitously and irreversibly in patients with diabetes mellitus, and its consequences are especially relevant to vascular dysfunctions. The interaction of AGEs with their receptors (RAGE) has been implicated in the development of vascular complications. This interaction elicits remarkable vascular cell changes analogous to those observed in diabetes mellitus, including angiogenic and thrombogenic responses of endothelial cells, increased oxidative stress, and functional alterations in vascular tone control. This review focuses on AGEs formation, the interaction with their specific receptors and how the triggered intracellular events determine functional alterations of vascular endothelium. Finally, some potential pharmacological approaches undertaken to circumvent the deleterious effects of AGEs are also discussed.     

Tissue inhibitor of metalloproteinases-4 suppresses vascular smooth muscle cell migration and induces cell apoptosis

In a previous study, we have demonstrated that overexpression of the tissue inhibitors of metalloproteinases-4 (TIMP-4) can inhibit the neointima formation in the rat carotid model. To define the functions of tissue inhibitor of metalloproteinases-4 (TIMP-4) in SMCs, we transduced human TIMP-4 cDNA into rat aortic SMCs by using adenoviral vector. Overexpression of TIMP-4 blocked the conversion of pro-MMP-2 to the active form and inhibited basic fibroblast growth factor-induced migration by 56.7% (p < 0.01). Overexpression of TIMP-4 markedly increased apoptotic cell death without changing their proliferation. Importantly, overexpression of human TIMP-4 in the wall of balloon-injured rat carotid artery also increased SMC apoptosis. The percentages of TUNEL-positive cells of total cells increased significantly in AdTIMP-4 infected group compared with AdGFP infected group. These findings demonstrate that TIMP-4 can inhibit SMCs migration and induce apoptosis in vitro and in vivo, which may generate new targets for prevention and treatment of vascular diseases.     

Role of myocardial hypoxia in the remodeling of the embryonic avian cardiac outflow tract

The embryonic cardiac outflow myocardium originates from a secondary heart-forming field to connect the developing ventricles with the aortic sac. The outflow tract (OFT) subsequently undergoes complex remodeling in the transition of the embryo to a dual circulation. In avians, elimination of OFT cardiomyocytes by apoptosis (stages 25-32) precedes coronary vasculogenesis and is necessary for the shortening of the OFT and the posterior rotation of the aorta. We hypothesized that regional myocardial hypoxia triggers OFT remodeling. We used immunohistochemical detection of the nitroimidazole EF5, administered by intravascular infusion in ovo, as an indicator of relative tissue oxygen concentrations. EF5 binding was increased in the OFT myocardium relative to other myocardium during these stages (25-32) of OFT remodeling. The intensity of EF5 binding paralleled the prevalence of apoptosis in the OFT myocardium, which are first detected at stage 25, maximal at stage 30, and diminished by stage 32. Evidence of coincident hypoxia-dependent responses included the expression of the vascular endothelial growth factor (VEGF) receptor 2 by the OFT myocardium, the predominant expression of VEGF122 (diffusible) isoform in the OFT, and the recruitment of QH1-positive pro-endothelial cells to the OFT and vasculogenesis. Exposure of embryos to hyperoxia (95% O(2)/5% CO(2)) during this developmental window reduced the prevalence of cardiomyocyte apoptosis and attenuated the shortening and rotation of the OFT, resulting in double-outlet right ventricle morphology, similar to that observed when apoptosis is directly inhibited. These results suggest that regional myocardial hypoxia triggers cardiomyocyte apoptosis and remodeling of the OFT in the transition to a dual circulation, and that VEGF autocrine/paracrine signaling may regulate these processes.     

Xanthine oxidase activates pro-matrix metalloproteinase-2 in cultured rat vascular smooth muscle cells through non-free radical mechanisms

Reactive oxygen species (ROS) have been implicated in the regulation of matrix metalloproteinases (MMPs). The xanthine/xanthine oxidase (X/XO) reaction has been widely used as a source of exogenous ROS in studying MMPs, but commercial XO has also been known to be contaminated by proteolytic activity, and MMPs are protease sensitive substrate. We have investigated the activation of proMMP-2 by X/XO in cultured vascular smooth muscle cells (SMCs). SMCs were incubated with X/XO (unpurified or purified) or XO alone for 24h. X/XO activated proMMP-2 in a dose-dependent manner. A similar profile was observed using XO. Purified XO produced lower amounts of active MMP-2 compared to unpurified XO. EPR study showed that X/XO, not XO itself, produced superoxide anion, which was completely scavenged by SOD. However, X/XO-induced proMMP-2 activation could not be inhibited by combination of SOD and catalase. Incubation with XO either in cell-free conditioned media or in cells resulted in similar amounts of active MMP-2, suggesting that membrane-type-MMPs were not involved in proMMP-2 activation. This was further confirmed by the lack of inhibitory effect of hydroxamate MMP inhibitor, BB1101. Aprotinin blocked unpurified XO-induced proMMP-2 activation in a dose-dependent manner, demonstrating the proteolytic activity contained in XO is essential. We conclude that proteolytic activity contained in XO, rather the ROS derived from X/XO, is responsible for proMMP-2 activation in cultured SMCs. The results also suggest that caution needs to be taken when interpreting the reported results on activation of MMPs where X/XO had been used as an "authentic" source of superoxide anion.     

Proprotein convertases regulate insulin-like growth factor 1-induced membrane-type 1 matrix metalloproteinase in VSMCs via endoproteolytic activation of the insulin-like growth factor-1 receptor

The IGF-1 receptor (IGF-1R) and MT1-MMP are synthesized as larger precursor proproteins, which require endoproteolytic activation by the proprotein convertases (PCs) furin/PC5 to gain full biological activity. The aim of this study was to investigate the contribution of PCs to IGF-1R and/or MT1-MMP activation in vascular smooth muscle cells (VSMCs) as well as VSMC proliferation/migration, which are key elements in vascular remodeling. Furin and PC5 mRNAs and proteins were found in VSMCs. Inhibition of furin-like PCs with the specific pharmacological inhibitor dec-CMK inhibited IGF-1R endoproteolytic activation. Inhibition of IGF-1R maturation abrogated IGF-induced IGF-1R autophosphorylation, PI3-kinase and MAPK induction, as well as VSMC proliferation (p<0.05 vs. controls), whereas it had no effect of PDGF-stimulated signaling pathways or cell growth. Both, IGF-1 and PDGF-BB, induced MT1-MMP expression, but only IGF-1-mediated MT1-MMP induction was inhibited by dec-CMK. Induction of MMP-2 by IGF-1 was inhibited by the PI3-kinase inhibitor wortmannin, but not by the MEK-inhibitor PD98059. Dec-CMK inhibited VSMC chemotaxis comparable to the effects of the MMP-inhibitor GM6001 (both p<0.05 vs. controls), supporting that MMPs are involved. In conclusion, this study demonstrates that targeting furin-like PCs and thus inhibiting IGF-1R activation is a novel target to inhibit IGF-1-mediated signaling and cell functions, such as IGF-1-induced MT1-MMP/MMP-2 in VSMCs.     

Expression of adiponectin receptors in human macrophages and regulation by agonists of the nuclear receptors PPARalpha, PPARgamma, and LXR

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors expressed in macrophages where they control cholesterol homeostasis and inflammation. In an attempt to identify new PPARalpha and PPARgamma target genes in macrophages, a DNA array-based global gene expression profiling experiment was performed on human primary macrophages treated with specific PPARalpha and PPARgamma agonists. Surprisingly, AdipoR2, one of the two recently identified receptors for adiponectin, an adipocyte-specific secreted hormone with anti-diabetic and anti-atherogenic activities, was found to be induced by both PPARalpha and PPARgamma. AdipoR2 induction by PPARalpha and PPARgamma in primary and THP-1 macrophages was confirmed by Q-PCR analysis. Interestingly, treatment with a synthetic LXR agonist induced the expression of both AdipoR1 and AdipoR2. Furthermore, co-incubation with a PPARalpha ligand and adiponectin resulted in an additive effect on the reduction of macrophage cholesteryl ester content. Finally, AdipoR1 and AdipoR2 are both present in human atherosclerotic lesions. Moreover, AdipoR1 is more abundant than AdipoR2 in monocytes and its expression decreases upon differentiation into macrophages, whereas AdipoR2 remains constant. In conclusion, AdipoR1 and AdipoR2 are expressed in human atherosclerotic lesions and macrophages and can be modulated by PPAR and LXR ligands, thus identifying a mechanism of crosstalk between adiponectin and these nuclear receptor signaling pathways.     

Viral load in tissues during the early and chronic phase of non-pathogenic SIVagm infection

African green monkeys (AGMs) persistently infected with SIVagm do not develop AIDS, although their plasma viremia levels can reach those reported for pathogenic HIV-1 and SIVmac infections. In contrast, the viral burden in lymph nodes in SIVagm-infected AGMs is generally lower in comparison with HIV/SIVmac pathogenic infections, at least during the chronic phase of SIVagm infection. We searched for the primary targets of viral replication, which might account for the high viremias in SIVagm-infected AGMs. We evaluated for the first time during primary infection SIVagm dissemination in various lymphoid and non-lymphoid tissues. Sixteen distinct organs at a time point corresponding to maximal virus production were analyzed for viral RNA and DNA load. At days 8 and 9 p.i., viral RNA could be detected in a wide range of tissues, such as jejunum, spleen, mesenteric lymph nodes, thymus and lung. Quantification of viral DNA and RNA as well as of productively infected cells revealed that viral replication during this early phase takes place mainly in secondary lymphoid organs and in the gut (5 x 10(4)-5 x 10(8) RNA copies/10(6) cells). By 4 years p.i., RNA copy numbers were below detection level in thymus and lung. Secondary lymphoid organs displayed 6 x 10(2)-2 x 10(6) RNA copies/10(6) cells, while some tissue fragments of ileum and jejunum still showed high viral loads (up to 10(9) copies/10(6) cells). Altogether, these results indicate a rapid dissemination of SIVagm into lymphoid tissues, including the small intestine. The latter, despite showing marked regional variations, most likely contributes significantly to the high levels of viremia observed during SIVagm infection.     

Distribution and biotransformation of arsenic species in chicken cardiac and muscle tissues

This study evaluated the bioaccumulation and biotransformation of arsenic species in chicken heart and meat tissues. The experimental study was carried out using two sets of samples. In the first one, 10-d-old chickens were exposed to sodium arsenate, using spiked drinking water. These chickens grew normally and were killed after 50 d of arsenic exposure. The second set were edible chickens used as blanks for a parallel study. The total arsenic and arsenic species content in the exposed samples were at least twice those in the normal edible chicken. It has been demonstrated that sodium arsenate is biotransformed to arsenite and an unknown species and its distribution varies among the different cardiac and meat tissues. One important aspect is the capability of the auricle to preconcentrate the most toxic species, arsenite, in the exposed chicken. A nonidentified arsenic species from the edible chicken was detected. Arsenobetaine was also detected in several tissues. This article shows that chicken can be used as a representative animal when considering inorganic arsenic exposure in humans.