oa Protective role of 4-phenylbutyrate against palmitate-induced endoplasmic reticulum stress and renal cell injury

Background and Objectives: Obesity is recognized as a significant risk factor for the development of chronic kidney disease (CKD). Emerging studies indicate that endoplasmic reticulum (ER) stress play a major role in obesity-induced renal damage and the development of CKD in obese patients. Therapeutic interventions to ameliorate ER stress using 4-phenylbutyrate (4-PBA), a chemical chaperone, have been shown to prevent obesity-induced organ damage in the liver and pancreas. Thus, the goal of this study was to investigate the protective role of 4-phenylbutyrate (4-PBA) against palmitic acid (PA)-induced ER stress and renal cell injury using normal rat kidney (NRK-52E) cells. Methods: NRK-52E cells were divided into four groups: Control, PA-treated, 4-PBA-treated, and 4-PBA+PA co-treated. Cells were exposed to 250 µM PA with or without 5 mM 4-PBA for 24 hours, and compared against the control. Western blotting was performed to determine the expression of ER stress markers - glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) in NRK-52E cells. The cytoprotective effect of 4-PBA on PA-induced NRK-52E cell injury was assessed by cell viability measurements and caspase-3/7 activity assay. Results: PA treatment in NRK-52E cells significantly reduced the cell viability (85% to that of the control; P-value < 0.05), increased caspase-3/7 activity (2-fold increase to that of control; P-value < 0.05), and caused profound ER stress - evidenced by induction of GRP78 and CHOP (1.6 and 2 folds of control respectively; P-value < 0.05). Treatment with 4-PBA significantly protected the cells from PA-induced cell death (93.4% vs. 81.3% cell viability in PA treated group; P-value < 0.05), and normalized the activity of caspase-3/7 and the expression of ER stress markers - GRP78 and CHOP. Conclusion: 4-PBA inhibits ER stress and protects renal cells against PA-induced apoptotic cell injury. Further studies are required to ascertain the clinical utility of 4-PBA to prevent renal injury and the development of CKD in obese patients.