SCO-792, an enteropeptidase inhibitor, attenuated renal and hepatic cyst progression in a mouse model of autosomal dominant polycystic kidney disease

Amino acids, especially branched-chain amino acids (BCAAs), are key regulator of the mammalian target of the rapamycin (mTOR). Excessive administration of BCAAs to the PKD-1 knockout mice accelerates kidney and hepatic cyst formation via the mTOR activation, leading to exacerbated renal function. SCO-792, an enteropeptidase inhibitor, decreases amino acid uptake by preventing the enzymatic breakdown of dietary proteins into absorbable amino acids, which has been shown to lower serum BCAA levels and suppress the mTOR cascade in a mouse model of diabetic kidney disease. We hypothesized that SCO-792 could slow the disease progression in autosomal dominant polycystic kidney disease (ADPKD) model mice through suppression of the mTOR signaling.

Pkd1 conditional knockout mice (Pkd1flox/flox Mx-1-Cre mice) were randomly assigned to a standard diet or a diet containing 0.003% (w/w) or 0.01% (w/w) SCO-792 starting on postnatal day 28. Body weight and food intake were measured weekly. All mice were sacrificed at 56 days of age. Renal and liver cystic phenotypes were assessed by kidney or liver to body weight ratios (KW/BW, LW/BW) and cystic index (CI), defined as the percentage of cyst areas in hole tissue. Serum blood urea nitrogen (BUN) and creatinine (Cr) levels were measured. Cyst growth pathways were assessed using immunofluorescence for Ki-67, TUNEL staining, immunohistochemistry (IHC) for ribosomal protein S6 (S6), and Western blot analysis of kidney and liver samples for S6 and AMPK. An oral protein challenge was conducted to evaluate the dose-dependent effects of SCO-792 on amino acid absorption.

There were significant reductions in KW/BW, LW/BW, and CI in the 0.01% group compared to the other group (KW/BW: 3.32±1.08%, 3.23±1.24% and 2.10±0.40%, p<0.05. LW/BW: 5.88±0.97%, 5.66±0.86% and 4.43±0.52%, p<0.05. kidney CI: 57.0±11.7%, 52.3±7.7% and 44.7±7.6%, p<0.05. liver CI: 17.6±5.8%, 16.7±5.4% and 12.8±3.1%, p<0.05). Serum BUN levels did not significantly differ among the three groups, whereas serum Cr levels were lower in the 0.01% group than in the control group (BUN: 82.6±29.7%, 80.5±24.7% and 65.9±14.1%. Cr: 0.28±0.11%, 0.25±0.07% and 0.17±0.11%, p<0.05). The percentage of Ki-67-positive cells in both the kidney and the liver was significantly reduced in the 0.01% group. Additionally, the percentage of TUNEL-positive cells in the kidney was also significantly decreased in the 0.01% group. Western blot analysis revealed a significant downregulation of phosphorylated-S6 (p-S6) protein in the kidneys of the 0.01% group. Consistent with the western blot analysis, IHC demonstrated that p-S6 expression in renal cyst-lining epithelial cells was downregulated in the 0.01% group. Total food intake was comparable among the three groups; however, body weight was significantly reduced in the 0.01% group. Despite the decrease in body weight, no upregulation of p-AMPK was observed on western blot analysis. In the oral protein challenge test, SCO-792 inhibited amino acid absorption in a dose-dependent manner.

SCO-792 ameliorated renal and hepatic cyst growth and preserved kidney function by inhibiting the mTOR pathway activation in Pkd1-deficient mice.