GENEVA, Switzerland—"Knock, knock. Who's there? Nox1." Sobegins an editorial in support of a new study authored by researchers from the Baker IDI Heart &Diabetes Research Institute in Melbourne, Australia, and Maastricht Universityin the Netherlands, as they describe their discovery of how oxidative stressand proinflammatory markers cause atherosclerosis in diabetic mice.
In diabetes mellitus, vascular complications such as atherosclerosisare a major cause of death. Although the key underlying pathomechanisms areunclear, hyperglycemic oxidative stress appears to play a role with NADPHoxidase (Nox), the only known dedicated enzyme to generate reactive oxygenspecies.
"NADPH oxidases are enzymes that are entirely devoted togenerate reactive oxygen species (ROS). We have shown that these enzymes areupregulated in diabetes, and thus, the increased formation of ROS results inincreased oxidative stress in the vasculature. In the kidney, Nox4 has beenidentified to play an important role in mediating diabetes associated kidneydisease, but the most relevant isoform in the vasculature had not beenidentified so far," explains Prof. Karin Jandeleit-Dahm, head of DiabeticComplications Research at the Baker IDI Heart & Diabetes Institute, and alead author on the study. "Nox1 is expressed at very low levels in normalstates, but is upregulated in disease states, making an attractive target totreat or prevent in diabetes associated atherosclerosis."
Several Nox isoforms are present in the vasculature: Nox1,Nox2, Nox4 and Nox5. These isoforms have been proposed to play an importantrole in vascular pathobiology, inducing both inflammation and fibrosis. Invascular cells, Nox1 mRNA expression is low under physiological conditions, butinduced in the presence of factors elevated in diabetes mellitus, such asplatelet derived growth factor and angiotensin II (AngII), and otherpathological conditions such as atherosclerosis and hypertension.
In this study, published May 7 in the American HeartAssociation journal Circulation, theresearchers identify the Nox1 isoform as playing a key and pharmacologicallytargetable role in the accelerated development of diabetic atherosclerosis. Theresearchers began with a human in-vitromodel of diabetes mellitus–associated oxidative stress using human aorticendothelial cells (HAEC) cultured under high-glucose conditions. Production ofreactive oxygen species—as well as proinflammatory and profibrotic markers—wereassessed under high-glucose conditions and after siRNA silencing as well asafter treatment with GKT137831, a NOX1 and NOX4 inhibitor that has beendeveloped by Genkyotex, a company based in Geneva, Switzerland.
The in-vivorelevance of these findings was then examined in genetic mouse models ofatherosclerosis 10 weeks after induction of diabetes mellitus withstreptozotocin in mice with and without deletion of various Nox isoforms orGKT137831 treatment. Deletion of Nox1, but not Nox4, had a profound antiatheroscleroticeffect correlating with reduced reactive oxygen species formation, attenuationof chemokine expression, vascular adhesion of leukocytes, macrophageinfiltration and reduced expression of proinflammatory and profibrotic markers.Similarly, treatment of diabetic apolipoprotein E–deficient mice with GKT137831attenuated atherosclerosis development.
"Initially, the focus was on Nox4, as Nox4 has beensuggested to play an important role in kidney disease including in diabeticnephropathy. We were surprised but to see that Nox1 appeared to be the mostimportant Nox isoform in the vasculature, whereas Nox4 appeared to be importantin the kidney," says Jandeleit-Dahm.
According to the researchers, now that positive results havebeen demonstrated in Phase I studies, further studies with GKT137831 arewarranted. Genkyotex plans to conduct Phase II clinical studies with GKT137831in patients with diabetic nephropathy, another important complication of thedisease, says Jandeleit-Dahm.
"The next steps in our research will be to investigatelonger duration and even more advanced plaque formation, as well as a delayedintervention approach which is clinically more relevant," says Jandeleit-Dahm. "Diabetesleads to a range of micro-and macrovascular complications, including kidneydisease, often requiring dialysis, and macrovacsular disease leading to heart attacksstrokes and amputations. Cardiovascular risk is significantly increased indiabetes and most patients with diabetes will suffer a cardiovascular event atsome stage. Our current treatment strategies fail to prevent the developmentand progression of diabetic complications. Thus, novel and more effectivetreatments are urgently needed."