Bardoxolone Methyl: A Targeted Antioxidant

Abstract

Diabetic nephropathy is a potential consequence of mitochondrial dysfunction and localized tissue oxidative stress. A number of pathways that generate reactive oxygen species (ROS), such as glycolysis, specific defects in the polyol pathway, uncoupling of nitric oxide synthase, xanthine oxidase, NAD(P)H oxidase, and advanced glycation, have been identified as potential major contributors to the pathogenesis of diabetic chronic kidney disease (CKD). 1 Nrf2 is an active transcription factor for the expression of mRNA that codes for synthesis of a host of cytoprotective molecules. These molecules include enzymes that directly destroy ROS, as well as enzymes that synthesize small molecules such as glutathione that scavenges potentially destructive electrophiles. Animal models have suggested the role of genetic deficiency of Nrf2 in pathogenesis and histology of renal disease including glomerulosclerosis. Also, Nrf2 activation is suppressed in animal models of CKD. 2,3 In search for a specific, well-tolerated agent for the therapeutic induction of Nrf2, a new class of compounds—synthetic oleanane triterpenoids (SO), specifically the methyl ester of 2-cyano-3, 12-dioxooleana-1,9(11)-dien-28-oic acid (bardoxolone methyl) as the most potent representative of this group of molecules, is being focused. The cytoprotective effects are believed to be mediated by binding of the SO to the inhibitory protein Keap1, which then releases its partner, Nrf2 transcription factor, that results in the upregulation of several antioxidant genes including NAD(P)H: quinone oxidoreductase 1, thioredoxin, catalase, superoxide dismutase, and heme oxygenase. This results in the reduction of intracellular ROS and proinflammatory activity of the nuclear factor kappa-light-chain-enhancer of activated B cells pathway, thereby restoring redox homeostasis in areas of inflammation. 4 A recent, phase 2a, multicenter, openlabel study in 20 patients with moderate to severe diabetic CKD showed an apparent increase in kidney function following relatively short-term treatment with bardoxolone methyl with no life-threatening adverse events. 5 Apart from diabetes, SO have been used favorably in experimental animal models of kidney injury caused by toxic agents, cystic fibrosis, and emphysema induced by cigarette smoke, disease states characterized by hyperactivity of the immune system, cancer, including prevention and treatment, Parkinson’s disease, Huntington’s disease, and Alzheimer’s disease. 6 To conclude, bardoxolone methyl and other SO could form the basis of therapies halting the progression of CKD and may be even reversing them. Larger studies are needed to confirm beneficial effect of this drug. Internists should be ready to greet this drug with next sunrise.