Amine oxidase copper-containing 3 (AOC3) inhibition: a potential novel target for the management of diabetic retinopathy.

BACKGROUND: Diabetic retinopathy (DR), a microvascular complication of diabetes, is the leading cause of visual impairment in people aged 20-65 years and can go undetected until vision is irreversibly lost. There is a need for treatments for non-proliferative diabetic retinopathy (NPDR) which, in comparison with current intravitreal (IVT) injections, offer an improved risk-benefit ratio and are suitable for the treatment of early stages of disease, during which there is no major visual impairment. Efficacious systemic therapy for NPDR, including oral treatment, would be an important and convenient therapeutic approach for patients and physicians and would reduce treatment burden. In this article, we review the rationale for the investigation of amine oxidase copper-containing 3 (AOC3), also known as semicarbazide-sensitive amine oxidase and vascular adhesion protein 1 (VAP1), as a novel target for the early treatment of moderate to severe NPDR. AOC3 is a membrane-bound adhesion protein that facilitates the binding of leukocytes to the retinal endothelium. Adherent leukocytes reduce blood flow and in turn rupture blood vessels, leading to ischemia and edema. AOC3 inhibition reduces leukocyte recruitment and is predicted to decrease the production of reactive oxygen species, thereby correcting the underlying hypoxia, ischemia, and edema seen in DR, as well as improving vascular function. CONCLUSION: There is substantial unmet need for convenient, non-invasive treatments targeting moderately severe and severe NPDR to reduce progression and preserve vision. The existing pharmacotherapies (IVT corticosteroids and IVT anti-vascular endothelial growth factor-A) target inflammation and angiogenesis, respectively. Unlike these treatments, AOC3 inhibition is predicted to address the underlying hypoxia and ischemia seen in DR. AOC3 inhibitors represent a promising therapeutic strategy for treating patients with DR and could offer greater choice and reduce treatment burden, with the potential to improve patient compliance.

Characterization of the properties of a selective, orally bioavailable autotaxin inhibitor in preclinical models of advanced stages of liver fibrosis.

BACKGROUND AND PURPOSE: Autotaxin (ATX) is a secreted phospholipase which hydrolyses lysophosphatidylcholine to generate lysophosphatidic acid (LPA). The extracellular signalling molecule LPA exerts its biological actions through activation of six GPCRs expressed in various cell types including fibroblasts. Multiple preclinical studies using knockout animals, LPA receptor antagonists or ATX inhibitors have provided evidence for a potential role of the ATX/LPA axis in tissue fibrosis. Despite growing evidence for a correlation between ATX levels and the degree of fibrosis in chronic liver diseases, including viral hepatitis and hepatocellular carcinoma, the role of ATX in non-alcoholic steatohepatitis (NASH) remains unclear. EXPERIMENTAL APPROACH: The relevance of ATX in the pathogenesis of liver fibrosis was investigated by oral administration of Ex_31, a selective ATX inhibitor, in a 10 week model of carbon tetrachloride-induced liver injury and in a 14 week model of choline-deficient amino acid-defined diet-induced liver injury in rats. KEY RESULTS: Oral administration of Ex_31, a selective ATX inhibitor, at 15 mg·kg-1 twice daily in therapeutic intervention mode resulted in efficient ATX inhibition and more than 95% reduction in plasma LPA levels in both studies. Treatment with Ex_31 had no effect on biomarkers of liver function, inflammation, or fibrosis and did not result in histological improvements in diseased animals. CONCLUSIONS AND IMPLICATIONS: Our findings question the role of ATX in the pathogenesis of hepatic fibrosis and the potential of small molecule ATX inhibitors for the treatment of patients with NASH and advanced stages of liver fibrosis.

Improved lipid profile through liver-specific knockdown of liver X receptor alpha in KKAy diabetic mice.

Nuclear hormone receptors liver X receptor (LXRalpha and LXRbeta) ligands are attractive approaches for the treatment of dyslipidemia and atherosclerosis. To further elucidate the function of LXRalpha in liver lipid metabolism in a disease-relevant animal model, the KKAy mouse, we used adenoviral vectors to selectively knock down LXRalpha gene expression. Out of five different short hairpin RNAs (shRNAs) that were tested in vitro, one construct was selected for detailed analysis of LXRalpha knockdown in vivo. Reduction of LXRalpha transcript levels to 48 +/- 13% compared with control virus transduction resulted in a significant downregulation of the LXRalpha-regulated lipogenic genes sterol-regulatory element binding protein-1c (SREBP1c) and stearoyl CoA desaturase 1 in vivo. Interestingly, ABCA1 and phoshoenolpyruvate carboxykinase 1 expression was not affected, whereas lipoprotein lipase (LPL) expression was found to be increased. In addition, 8 days after virus transduction, both plasma and liver triglycerides (TGs) were reduced by about 50%. Changes in TG levels were not due to reduced food intake in virus-treated animals, because pair-fed mice showed unchanged TG levels. Taken together, liver-specific knockdown of LXRalpha in vivo by shRNA reduced expression of lipogenic master genes, like SREBP1c, and improved the lipid profile of hypertriglyceridemic KKAy mice.

Normalization of prandial blood glucose and improvement of glucose tolerance by liver-specific inhibition of SH2 domain containing inositol phosphatase 2 (SHIP2) in diabetic KKAy mice: SHIP2 inhibition causes insulin-mimetic effects on glycogen metabolism, gluconeogenesis, and glycolysis.

Type 2 diabetes is characterized by a progressive resistance of peripheral tissues to insulin. Recent data have established the lipid phosphatase SH2 domain-containing inositol phosphatase 2 (SHIP2) as a critical negative regulator of insulin signal transduction. Mutations in the SHIP2 gene are associated with type 2 diabetes. Here, we used hyperglycemic and hyperinsulinemic KKA(y) mice to gain insight into the signaling events and metabolic changes triggered by SHIP2 inhibition in vivo. Liver-specific expression of a dominant-negative SHIP2 mutant in KKA(y) mice increased basal and insulin-stimulated Akt phosphorylation. Protein levels of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase were significantly reduced, and consequently the liver produced less glucose through gluconeogenesis. Furthermore, SHIP2 inhibition improved hepatic glycogen metabolism by modulating the phosphorylation states of glycogen phosphorylase and glycogen synthase, which ultimately increased hepatic glycogen content. Enhanced glucokinase and reduced pyruvate dehydrogenase kinase 4 expression, together with increased plasma triglycerides, indicate improved glycolysis. As a consequence of the insulin-mimetic effects on glycogen metabolism, gluconeogenesis, and glycolysis, the liver-specific inhibition of SHIP2 improved glucose tolerance and markedly reduced prandial blood glucose levels in KKA(y) mice. These results support the attractiveness of a specific inhibition of SHIP2 for the prevention and/or treatment of type 2 diabetes.