BACKGROUND: The distinctive feature of liver fibrosis is the progressive replacement of healthy hepatic cells by the extracellular matrix protein, which is abundant in collagen I and III, with impaired matrix remodeling. The activation of myofibroblastic cells enhances the fibrogenic response of complex interactions of hepatic stellate cells, fibroblasts, and inflammatory cells to produce the excessive deposition of the extracellular protein matrix. This process is activated by multiple fibrogenic mediators and cytokines, such as TNF-α and IL-1β, accompanied with a decrease in the anti-fibrogenic factor NF-κβ. Mesenchymal stem cells (MSCs) represent a promising therapy for liver fibrosis, allowing for a more advanced regenerative influence when cultured with extrinsic or intrinsic proliferative factors, cytokines, antioxidants, growth factors, and hormones such as melatonin (MT). However, previous studies showed conflicting findings concerning the therapeutic effects of adipose (AD) and bone marrow (BM) MSCs; therefore, the present work aimed to conduct a comparative and comprehensive study investigating the impact of MT pre-treatment on the immunomodulatory, anti-inflammatory, and anti-apoptotic effects of AD- and BM-MSCs and to critically analyze whether MT-pre-treated AD-MSCs and BM-MSCs reveal equal or different therapeutic and regenerative potentials in a CCl4-injured liver experimental rat model.
MATERIALS AND METHODS: Six groups of experimental rats were used, with ten rats in each group: group I (control group), group II (CCl4-treated group), group III (CCl4- and BM-MSC-treated group), group IV (CCl4 and MT-pre-treated BM-MSC group), group V (CCl4- and AD-MSC-treated group), and group VI (CCl4 and MT-pre-treated AD-MSC group). Liver function tests and the gene expression of inflammatory, fibrogenic, apoptotic, and proliferative factors were analyzed. Histological and immunohistochemical changes were assessed.
RESULTS: The present study compared the ability of AD- and BM-MSCs, with and without MT pre-treatment, to reduce hepatic fibrosis. Both types of MSCs improved hepatocyte function by reducing the serum levels of ALT, aspartate aminotransferase (AST), alkaline phosphatase (AKP), and total bilirubin (TBIL). In addition, the changes in the hepatocellular architecture, including the hepatocytes, liver sinusoids, central veins, portal veins, biliary ducts, and hepatic arteries, showed a decrease in hepatocyte injury and cholestasis with a reduction in inflammation, apoptosis, and necrosis of the hepatic cells, together with an inhibition of liver tissue fibrosis. These results were augmented by an analysis of the expression of the pro-inflammatory cytokines TNFα and IL-1β, the anti-fibrogenic factor NF-κβ, the apoptotic factor caspase-3, and the proliferative indicators antigen Ki-67 and proliferating cell nuclear antigen (PCNA). These findings were found to be statistically significant, with the restoration of normal parameters in the rats that received AD-MSCs pre-treated with MT, denoting optimal regenerative and therapeutic effects.
CONCLUSIONS: AD-MSCs pre-treated with MT are the preferred choice in improving hepatic fibrosis and promoting the therapeutic and regenerative ability of liver tissue. They represent a very significant tool for future stem cell use in the tissue regeneration strategy for the treatment of liver diseases.