Adenosine A(2A) agonists as therapy for glomerulonephritis

Acute rejection after kidney transplantation promotes graft fibrosis with elevated adenosine level in rat

Aims

Chronic allograft nephropathy is a worldwide issue with the major feature of progressive allograft fibrosis, eventually ending with graft loss. Adenosine has been demonstrated to play an important role in process of fibrosis. Our study aimed to investigate the relationship between adenosine and fibrosis in renal allograft acute rejection in rat.

Materials and methods

Wistar rats and SD rats were selected as experimental animals. Our study designed two groups. In the allograft transplantation group, kidneys of Wistar rats were orthotopically transplanted into SD rat recipients, the same species but not genetically identical, to induce acute rejection. Kidney transplantations of SD rats to SD rats which were genetically identical were served as the control. We established rat models and detected a series of indicators. All data were analyzed statistically. P<0.05 was considered statistically significant.

Results

Compared with the control group, levels of adenosine increased significantly in the allograft transplantation group, in which acute rejection was induced (P<0.05). Progressive allograft fibrosis as well as collagen deposition were observed.

Conclusions

These findings suggested that level of adenosine was upregulated in acute rejection after kidney allograft transplantation in rat. Acute rejection may promote renal allograft fibrosis via the adenosine signaling pathways.

Adenosine kinase inhibition protects the kidney against streptozotocin-induced diabetes through anti-inflammatory and anti-oxidant mechanisms

Adenosine provides anti-inflammatory effects in cardiovascular disease via the activation of adenosine A2A receptors; however, the physiological effect of adenosine could be limited due to its phosphorylation by adenosine kinase. We hypothesized that inhibition of adenosine kinase exacerbates extracellular adenosine levels to reduce renal inflammation and injury in streptozotocin-induced diabetes. Diabetes was induced in male C57BL/6 mice by daily injection of streptozotocin (50mg/kg/day, i.p. for 5 days). Control and diabetic mice were then treated with the adenosine kinase inhibitor ABT702 (1.5mg/kg, i.p. two times a week for 8 weeks, n=7-8/group) or the vehicle (5% DMSO). ABT702 treatment reduced blood glucose level in diabetic mice (∼20%; P<0.05). ABT702 also reduced albuminuria and markers of glomerular injury, nephrinuria and podocalyxin excretion levels, in diabetic mice. Renal NADPH oxidase activity and urinary thiobarbituric acid reactive substances (TBARS) excretion, indices of oxidative stress, were also elevated in diabetic mice and ABT702 significantly reduced these changes. ABT702 increased renal endothelial nitric oxide synthase expression (eNOS) and nitrate/nitrite excretion levels in diabetic mice. In addition, the diabetic mice displayed an increase in renal macrophage infiltration, in association with increased renal NFκB activation. Importantly, treatment with ABT702 significantly reduced all these inflammatory parameters (P<0.05). Furthermore, ABT702 decreased glomerular permeability and inflammation and restored the decrease in glomerular occludin expression in vitro in high glucose treated human glomerular endothelial cells. Collectively, the results suggest that the reno-protective effects of ABT702 could be attributed to the reduction in renal inflammation and oxidative stress in diabetic mice.

Purinergic signalling in the kidney in health and disease

The involvement of purinergic signalling in kidney physiology and pathophysiology is rapidly gaining recognition and this is a comprehensive review of early and recent publications in the field. Purinergic signalling involvement is described in several important intrarenal regulatory mechanisms, including tuboglomerular feedback, the autoregulatory response of the glomerular and extraglomerular microcirculation and the control of renin release. Furthermore, purinergic signalling influences water and electrolyte transport in all segments of the renal tubule. Reports about purine- and pyrimidine-mediated actions in diseases of the kidney, including polycystic kidney disease, nephritis, diabetes, hypertension and nephrotoxicant injury are covered and possible purinergic therapeutic strategies discussed.

Adenosine A2A receptor: a target for regulating renal interstitial fibrosis in obstructive nephropathy

Renal interstitial fibrosis (RIF) is the common pathological process of chronic kidney diseases leading inevitably to renal function deterioration. RIF and its preceding epithelial-mesenchymal transition (EMT) are commonly triggered by an early occurring renal inflammation. However, an effective approach to prevent EMT and RIF is still lacking and of urgent need. Recently, the adenosine A_2A receptor (A_2AR) emerges as a novel inflammation regulator, therefore manipulation of A_2AR may suppress the EMT process and as such protect against RIF. To test this hypothesis we applied a unilateral ureteral obstruction (UUO) model of RIF on A_2AR knockout mice and their wild-type littermates, combined with the intervention of a selective A_2AR agonist, CGS 21680. On days 3, 7 and 14 post-UUO we evaluated the effects of A_2AR manipulation on the molecular pathological progresses of RIF, including the cellular component of interstitial infiltration, expression of profibrotic factors, cellular biomarkers of EMT, and collagen deposition of extracellular matrix. Our data demonstrated that activation of A_2AR significantly suppressed the deposition of collagen types I and III, reduced the infiltration of CD4+ T lymphocytes, and attenuated the expression of TGF-β1 and ROCK1, which in turn inhibited and postponed the EMT progress. Conversely, genetic inactivation of A_2AR exacerbated the aforementioned pathological processes of UUO-induced RIF. Together, activation of A_2AR effectively alleviated EMT and RIF in mice, suggesting A_2AR as a potential therapeutic target for the treatment of RIF.