Overproduction of reactive oxygen species under pathophysiological conditions, including dyslipidemia, hypertension, diabetes, and smoking, is integral in the development of cardiovascular diseases (CVD). The reactive oxygen species released from all types of vascular cells regulate various signaling pathways that mediate not only vascular inflammation in atherogenesis but also antioxidative and antiinflammatory responses. One such protective and stress-induced protein is heme oxygenase (HO). HO is the first rate-limiting enzyme in heme breakdown to generate equimolar quantities of carbon monoxide, biliverdin, and free ferrous iron. Accumulating evidence has shown that inducible HO (HO-1) and its products function as adaptive molecules against oxidative insults. The proposed mechanisms by which HO-1 exerts its cytoprotective effects include its abilities to degrade the pro-oxidative heme, to release biliverdin and subsequently convert it bilirubin, both of which have antioxidant properties, and to generate carbon monoxide, which has antiproliferative and antiinflammatory as well as vasodilatory properties. Herein, I highlight the relationship of HO and cardiovascular disease, especially atherosclerosis, gene-targeting approaches in animal models, and the potential for and concern about HO-1 as a novel therapeutic target for cardiovascular diseases.

Background: Chronic kidney disease (CKD) is recognized as a common condition that elevates the risk of atherosclerotic cardiovascular disease (CVD). Evidence suggests that increased oxidative stress is an emerging key mechanism of atherosclerosis in CKD. One recent study reported that indoxyl sulfate (IS), a uremic toxin derived from dietary protein, could cause vascular disorder, however, little is known about the mechanism involved. The present study examined the signaling pathway that is activated by IS to induce monocyte chemoattractant protein-1 (MCP-1), which plays an important role in the development of atherosclerosis, in cultured human umbilical vein endothelial cells (HUVEC). Methods and Results: We show that IS enhanced reactive oxygen species (ROS) production, assessed by dihydroethidium staining, by HUVEC. IS also induced the expression of MCP-1, which was measured by enzyme-linked immunosorbent assay and real-time reverse transcription-polymerase chain reaction. These changes were suppressed by apocynin, a specific inhibitor of NADPH oxidase. Furthermore, IS induced the expression of NADPH oxidase 4 (Nox4) mRNA. IS-induced stimulation of ERK1/2 and p38 phosphorylation, detected by immunoblotting, was inhibited by apocynin. Finally, IS activated NF-κB, which was suppressed by inhibiting ERK1/2 and p38, resulting in reduced MCP-1 expression. These results suggest that IS increases NADPH oxidase-derived ROS, which in turn, activates the MAPK/NF-κB pathway and leads to induction of MCP-1 expression in HUVEC. Conclusions: These findings raise the possibility that IS plays an important pathophysiological role in the development of CVD in individuals with CKD. (Circ J 2010; 74: 2216-2224)

Background: Indoxyl sulfate (IS) is a uremic toxin that causes renal injury, but little is known about its adverse effects on the cardiovascular system. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor that mediates adaptive and toxic responses in cells. Recent studies identified IS as an endogenous agonist for AhR, as well as other tryptophan metabolites. The aim of the study was to investigate whether IS activates AhR, with subsequent inflammatory responses contributing to the development of atherogenesis, in human umbilical vein endothelial cells (HUVECs). Methods and Results: We demonstrated that IS stimulates the expression of AhR target genes, including cytochromes P450 1A1 and 1B1 mRNA, in a time-dependent manner, as well as translocation of AhR into the nucleus from the cytoplasm, indicating AhR activation. IS-stimulated AhR activation was accompanied by an increase in oxidative stress, proven by enhanced NADPH oxidase 4 expression and dihydroethidium staining. Additionally, AhR inhibitors abolished the IS-induced increase in monocyte chemoattractant protein-1 (MCP-1) expression in a dose-dependent manner. Taken together, these results suggest that IS activates AhR as an endogenous agonist and induces MCP-1 expression through reactive oxygen species production in HUVECs. Conclusions: Our findings give a novel understanding of the physiological effect of IS on the cardiovascular system and indicate possibilities for preventing cardiorenal syndrome by regulating serum IS levels. (Circ J 2013; 77: 224–230)

Inflammation and oxidative stress play a pivotal role in the development of atherosclerosis, and they are strongly associated with cardiovascular disease risk,

Inhibiting the onset of arteriosclerotic disease, which has been increasing due to the westernized diet and aging, is a significant social challenge. Curcumin, a type of polyphenol, has anti-oxidative effects and anti-inflammatory action and is expected to treat and to have prophylactic effects on different diseases. In this study, we examined the effects of long-term administration of curcumin on vascular aging and chronic inflammation—the causes of arteriosclerotic disease. Eight-week-old C57BL/6J mice were fed with high fat diet (HFD) or 0.1% curcumin-mixed HFD (HFD + Cu) until 80 weeks old (n = 20 for each group). After the breeding, we examined the expression of antioxidant enzymes, heme oxygenase-1 (HO-1), oxidative stress, vascular aging, and inflammatory changes in the aorta. In the HFD group, oxidative stress increased with decreased sirt1 expression in the aorta followed by increased senescent cells and enhanced inflammation. Whereas in the HFD + Cu group, HO-1 was induced in the aorta with the suppression of oxidative stress. Additionally, it was shown that sirt1 expression in the aorta in the HFD + Cu group remained at a level comparable to that of the 8-week-old mice with suppression of increased senescent cells and enhanced inflammation. Consequently, disorders associated with HFD were resolved. These results suggest that curcumin might be a food with a prophylactic function against arteriosclerotic disease.

Monocyte chemoattractant protein 1 (MCP-1) and the receptor for MCP-1, CCR2, play a pivotal role in the recruitment of monocytes to the subendothelium, which is the initial event in atherosclerosis. Heme oxygenase (HO) is a microsomal enzyme that catalyzes the degradation of heme into biliverdin, which is subsequently reduced to bilirubin, free iron, and carbon monoxide, and induction of HO-1 is potentially associated with cellular protection, especially against oxidative insults. The present study was designed to examine the role of HO-1 in monocytes in angiotensin II (Ang II)-induced chemotactic response. Ang II significantly stimulated superoxide formation in monocytes, as measured by nitro blue tetrazolium reduction assay, as well as the chemotactic response to MCP-1 with the increased expression of CCR2 determined by RT-PCR and western blotting analysis. Hemin-treated monocytes displayed an enhanced HO activity with the increased accumulation of bilirubin determined by immunostaining, when compared with control monocytes. The induction of HO-1 in monocytes suppresses not only Ang II-stimulated superoxide formation, but also Ang II-enhanced chemotactic activity. Exogenously applied bilirubin and carbon monoxide mimicked the inhibitory effect of HO-1 on the chemotactic response. These findings suggest that monocytic HO-1 might be a new therapeutic target for atherosclerosis.