The plasma kallikrein-kinin system as a modulator in liver injury/remodeling

Abstract

Background: Liver injury is an apparent condition of the body system owing to the numerous functions of the liver. Most of the etiologies are due to the actions of many drugs, toxins, hepatotropic viruses, and idiosyncratic factors. Moreover, the occurrence and persistence of hepatic injury lead to its remodeling; hence, acute, and chronic liver disease results due to apoptosis, necrosis, and inflammation. Besides, the compromise in the liver architecture during other organs or tissue’s dysfunction could become a challenge. The plasma kallikrein-kinin system (PKKS) plays diverse roles in coagulation, vascular injury, tissue inflammation, and wound-healing. In liver injury, the protease-activated receptors 1 and 2 play significant roles in the whole process while plasma kallikrein (PK), the main effector of the system role’s is unknown. Yet, reports have shown the increase in PK’s synthesis in acute liver injury. In terms of PK’s significance in other diseases, a cohort study of type 1 diabetic patients observed the significant increase in the activity of PK compared to control. However, PK’s role in liver injury and other disease-state liver like type 1 diabetes is still unclear. Aims: In this study, the objective is to characterize the role of the PKSS in both acute and chronic liver injury models of non-diabetic and diabetic mice; and assess how it modulates its downstream targets in liver injury. Methods: Acute liver injury was induced in 10-12 weeks old C57BL/6J male mice after a single injection of 0.6 mL/kg carbon tetrachloride (CCl4), intraperitoneally. Chronic liver injury was induced after the injection of 0.6 mL/kg CCl4, twice a week, for 2.5, 4, 6 or 7 weeks. In some group of mice, 0.05 mL/g streptozotocin (STZ) was injected daily for three to five days, to induce diabetes. Following the confirmation of the diabetic state, two weeks post STZ-injections by measuring the plasma glucose levels, the mice were injected with CCl4 or its vehicle, mineral oil, either once for the acute liver injury or for 2.5 weeks for the chronic liver injury. In the liver, necrosis was observed by hematoxylin and eosin staining. Fibrosis was examined by assessing collagen fibers using picro sirius red staining and immunohistochemistry was performed for plasma pre-kallikrein. Quantitative polymerase chain reaction was used to assess the expression of hepatic genes such as the plasma kallikrein-kinin system, inflammation, and fibrosis. By Spearman correlation analysis, the PKKS genes were correlated to necrotic area, inflammatory and fibrotic markers, and fibrotic area. In vitro studies were conducted via hepG2 cells to investigate cell-death and PK-related signaling pathways. Results: A single injection of CCl4 induced necrosis was negatively and weakly associated to the PKKS genes except for the Kng1 gene (Klkb1, F2r, Kng1; r = -0.25, -0.20, -0.50 respectively; p > 0.05 except for Kng1 gene). However, they were positively associated with cell-death ligand gene, Hmgb1 (Klkb1, F2r, Kng1; r = -0.75, -0.44, -0.79 respectively; p < 0.05 except for Kng1 gene). Analysis by immunohistochemistry showed the PPK around the necrotic areas at day 2 and 3 of CCl4 induction, and significantly increased the F2R and IL1B genes while it decreased the CCN2 gene expression in PK-induced hepG2 cells. Likewise, PK increased the proliferation of CCl4-induced hepG2 cells by 140%. Varying time-points of liver fibrosis showed an increase in the mRNA levels of F2r (thrombin receptor), F2rl1, Bdkrb1 and Bdkrb2. Spearman correlation showed a strong positive correlation to profibrotic factors, Lgal3 and Ccn2 genes, and fibrotic area; p < 0.05. In diabetes mice, we observed the upregulation of hepatic PKKS genes in response to chronic administration of CCl4. Conclusion: The PKKS play diverse role in liver injury, fibrosis, and resolution. Although PAR-1 and PAR-2 are implicated in liver fibrosis progression, they interact with diverse agonists. PK, which is an agonist, could be a purposed therapeutic agent in the regeneration of injured hepatocytes. However, additional investigations are needed to decipher the mechanism of interaction of PK in liver injury or fibrosis. Likewise, more research is also needed to understand the role of the bradykinin receptors in liver fibrosis.