Abstract
This study tested the hypothesis that combined therapy with melatonin (Mel) and exendin-4 (Ex4) would be superior to either therapy alone for preventing the deterioration of renal function in cardiorenal syndrome (CRS). Male adult Sprague Dawley rats (n = 48) were randomly and equally divided into sham-control (SC), chronic kidney disease (CKD; induced by 5/6 nephrectomy), CRS (CKD + dilated cardiomyopathy, DCM; induced by doxorubicin 7 mg/kg i.p. every 5 days, 4 doses), CRS-Mel (20 mg/kg/day), CRS-Ex4 (10 µg/kg/day) and CRS-Mel-Ex4. They were euthanized by day 60 after CRS induction. By day 60, plasma creatinine level, urine protein/creatinine ratio and kidney injury histopathology score were highest in CRS, lowest in SC, and progressively decreased from CKD, CRS-Mel, CRS-Ex4 to CRS-Mel-Ex4 (all P<0.0001). The kidney protein expressions of inflammation (TNF-α/NF-κB/MMP-9/iNOS/RANTES), oxidative stress (NOX-1/NOX-2/NOX-4/oxidized protein), apoptosis (cleaved caspase-3/cleaved PARP/Bax), DNA-damaged marker (γ-H2AX) and fibrosis (p-mad3/TFG-β) showed identical patterns of creatinine level, whereas kidney protein expressions of GLP-1R showed a progressive increase from SC to CRS-Mel-Ex4 (all P<0.0001). Cellular expressions of inflammatory (CD14/CD68), DNA/kidney-damaged (γ-H2AX/KIM-1) and podocyte/renal tubule dysfunction signaling (β-catenin/Wnt1/Wnt4) biomarkers in kidney tissue exhibited an identical pattern of creatinine level (all P<0.0001). Podocyte components (podocin/dystroglycan/p-cadherin/synatopodin) were highest in SC, lowest in CRS, and significantly progressively increased from CKD to CRS-Mel-Ex4 (all P<0.0001). In conclusion, combined Mel-Ex4 therapy was superior to either one alone in preserving renal-function and kidney architectural integrity in the setting of CRS.