Early events of liver regeneration in rats: a multiparametric analysis

Unveiling the power of microenvironment in liver regeneration: an in-depth overview

The liver serves as a vital regulatory hub for various physiological processes, including sugar, protein, and fat metabolism, coagulation regulation, immune system maintenance, hormone inactivation, urea metabolism, and water-electrolyte acid-base balance control. These functions rely on coordinated communication among different liver cell types, particularly within the liver's fundamental hepatic lobular structure. In the early stages of liver development, diverse liver cells differentiate from stem cells in a carefully orchestrated manner. Despite its susceptibility to damage, the liver possesses a remarkable regenerative capacity, with the hepatic lobule serving as a secure environment for cell division and proliferation during liver regeneration. This regenerative process depends on a complex microenvironment, involving liver resident cells, circulating cells, secreted cytokines, extracellular matrix, and biological forces. While hepatocytes proliferate under varying injury conditions, their sources may vary. It is well-established that hepatocytes with regenerative potential are distributed throughout the hepatic lobules. However, a comprehensive spatiotemporal model of liver regeneration remains elusive, despite recent advancements in genomics, lineage tracing, and microscopic imaging. This review summarizes the spatial distribution of cell gene expression within the regenerative microenvironment and its impact on liver regeneration patterns. It offers valuable insights into understanding the complex process of liver regeneration.

Transection of the hepatic parenchyma associated or not with the contralateral portal vein branch ligature and its effect in liver regeneration

Objective

To analyze the influence of portal vein ligation in hepatic regeneration by immunohistochemical criteria.

Methods

Ten pigs divided into two groups of five animals underwent hepatectomy in two stages, and the groups were differentiated by ligation or not of the left portal vein tributary, which is responsible for vascularization of the left lateral and medial lobes of the pig liver. Five days after the procedure, the animals underwent liver biopsies for further analysis of histological and immunohistochemical with marker Ki67.

Results

The group submitted to hepatectomy with vascular ligation showed an increase of approximately 4% of hepatocytes in regeneration status, as well as a greater presence of Kupffer and inflammatory cells as compared to control.

Conclusion

As a result of positive cell replication observed through the Ki67 marker, we can suspect that the ligation of a tributary of the portal vein associated with liver resection promoted a greater stimulus of liver regeneration when compared to liver resection alone.

Triple labeling with three thymidine analogs reveals a well-orchestrated regulation of hepatocyte proliferation during liver regeneration

AIM

  After a two-thirds partial hepatectomy (PHx) in rodents, the remaining cells will proliferate and restore the lost liver mass within 7 days. Previous studies have proved that the residual hepatocytes proliferate in a synchronous manner. However, the existing data can not reflect the chronicle of individual hepatocytes proliferation during liver regeneration.

METHODS

  In this study, a combination of pulse and continuous labeling using three thymidine analogs, Bromodeoxyuridine (BrdU), Chlorodeoxyuridine (CldU) and Iododeoxyuridine (IdU), were used to analyze the cell proliferation of rat liver after PHx. This strategy allows us to follow an individual cell for more than one cell cycle and to define how many cells and which cells undergo multiple divisions.

RESULTS

  The residual hepatocytes clustered into three subpopulations to initiate the proliferation sequentially, and the corresponding percentage of each was 32%, 17%, and 36%. Meanwhile, the remaining 15% of hepatocytes never proliferated. In addition, the periportal hepatocytes were the first to respond to PHx stimulation and re-proliferated synchronously at 54 h. Furthermore, at least 11% of residual hepatocytes were identified to divide thrice or more.

CONCLUSION

  Based on the present analysis, we concluded a sequential model of the initial proliferation in residual hepatocytes, and for the first time, quantitatively elucidated the proliferation manner of three subpopulations during liver regeneration.

The influence of estrogen on liver regeneration: an experimental study in rats

PURPOSE

To recognize the regenerative capacity influenced by the administration of estradiol.

METHODS

42 female Wistar rats were used, divided into two groups, the control and the experiment group. A resection of approximately 70% of the liver was made in the liver of these animals. The control group received an intramuscular injection of one ml of peanut oil. The experiment group were given estradiol hexahydrobenzoate (50 microg) diluted in one ml of peanut oil. Calibrations were done after 36 hours and 7 days, using three methods: the formula of Kwon et al.21, to recognize gain in volume, counting of the mitosis figures in five fields and the percentage of positive PCNA nuclei.

RESULTS

Gain in volume (mass) was similar in both groups after 36 hours (p=0.1873) and higher in the experiment groups after seven days (p=0.0447). Microscopy showed a similar number of mitosis figures after 36 hours (p=0.3528) and a tendency to be higher in the experiment group after 7 days (p=0.0883). The average of positive PCNA nuclei was higher in the experiment group both after 36 hours (p=0.0009) and 7 days (p=0.0000).

CONCLUSION

The estradiol hexahydrobenzoate improved liver regeneration in rats submitted to a 70% hepatectomy.

Effect of aging on liver regeneration in rats

PURPOSE: Regeneration and/or healing of tissues is believed to be more difficult in elderly people. The liver is one of the most complex organs in the human body, and is involved in a variety of functions. Liver regeneration is the body's protection mechanism against loss of functional liver tissue. The aim of this study is to identify the regenerative capacity of the liver in older animals and to compare it with that of young adult animals. METHODS: Thirty-four Wistar rats were used, of which 17 were 90 days old (young animals) and 17 were 460 days old (old animals). Approximately 70% of the liver was surgically removed. Examinations were carried out after 24 hours and on day 7, using 3 methods: KWON et al.'s formula to identify increase in volume; mitotic figure count in 5 fields; and the percentage of PCNA-positive nuclei in 5 fields. RESULTS: The increase in volume of the remaining liver was greater in the young animals after both 24 hours (p=0.0006) and on day 7 (p=0.0000). Histological cuts showed a greater mitotic figure count in young animals evaluated after 24 hours (p=0.0000). Upon evaluation on day 7, recovery was observed in the old animals. This recovery was similar to that of the young ones (p=0.2851). The PCNA-positive nucleus count was greater in the young animals' liver cuts after 24 hours (p=0.0310), and, while it had decreased in young animals by day 7, recovery was observed in the older animals (p=0.0298). CONCLUSION: The data confirm that age is related to delay in liver regeneration in rats.

Biliary tract malformations

The biliary tree extends from the canals of Hering at the margin of the most peripheral portal tracts to the ampulla of Vater. Malformations occur at every level of this structure. Phenotypic features dominate present understanding of these malformations and of the disorders with which they are associated. Classifications of disease will likely shift from a phenotypic basis to a genotypic basis as genes implicated in biliary tree development and function are identified. Involvement of such genes in biliary tree disorders now considered inflammatory, such as extrahepatic biliary atresia, awaits study. The concept of "feeble cholangiocytes" postnatally susceptible to the effects of "toxic bile" is presented.

Mitogenic properties of endogenous and pharmacological doses of macrophage inflammatory protein-2 after 70% hepatectomy in the mouse

Recent studies show CXC chemokine elevations after hepatic resection; blockade of epithelial neutrophil-activating protein (ENA-78), a CXC chemokine, retards hepatic regeneration after resection. Additional studies demonstrate that exogenous macrophage inflammatory protein (MIP)-2, another CXC chemokine, is therapeutic in a murine acetaminophen toxicity model when other therapies fail. The current investigations study MIP-2's effects on the cellular mechanisms involved in liver regeneration in mice after 70% hepatectomy. Administration of exogenous MIP-2 after 70% hepatectomy dramatically increased hepatocyte proliferation as measured by 5-bromo-2'-deoxyuridine staining. Signal transducer and activator of transcription-3 (stat-3) was also detected in greater abundance and persisted in hepatic nuclear extracts from MIP-2-treated mice compared with control mice after hepatic resection. Further, inhibition of the MIP-2 receptor, CXCR2, decreased baseline hepatocyte proliferation and stat-3 expression in the setting of partial hepatectomy. These data show that MIP-2 is important for hepatocyte proliferation after partial hepatectomy and that pharmacological MIP-2 doses after hepatic injury accelerate hepatic regeneration.

Scanning electron microscopic detection of nuclear structures involved in DNA replication

In order to evaluate at the ultrastructural level the three dimensional chromatin arrangement during interphase and particularly during the S phase, the immunogold detection of Bromodeoxyuridine (BrdU), as a marker of DNA synthesis, was performed in human HeLa, HL60, and in murine Friend leukemia cells (FLC). Field emission in lens scanning electron microscopy analysis of ultrathin cryosections revealed the presence of a regular three-dimensional network of fibers in dispersed chromatin. This spatial architecture was apparently constituted mainly of 10 nm filaments organized in loops of about 80-100 nm. Nodal points and the overlapping of such coils appeared as thicker structures of about 30 nm in diameter. Thin filaments of about 5 nm did not show a regular distribution. This three-dimensional fiber organization seemed quite constant in the dispersed chromatin of all the cell lines analyzed. The DNase treatment of the samples selectively removed the 10 nm class fibers, whereas the BrdU labeling confirmed the presence of newly synthesized DNA organized into chromatin units with a regular arrangement. These data suggest that the 10 nm chromatin fiber likely represents the DNA condensation order at which DNA duplication starts and the main weft of a three dimensional network within the interphase nucleus.

Comparison of liver progenitor cells in human atypical ductular reactions with those seen in experimental models of liver injury

The ultrastructural characteristics of liver progenitor cell types of human atypical ductular reactions seen in chronic cholestasis, in regenerating human liver after submassive necrosis, in alcoholic liver disease, and in focal nodular hyperplasia are compared with liver progenitor cell types seen during experimental cholangiocarcinogenesis in hamsters; during hepatocarcinogenesis in rats; and in response to periportal liver injury induced by allyl alcohol in rats. Three types of progenitor cells have been identified in human atypical ductular reactions: type I: primitive, has an oval shape, marginal chromatin, few cellular organelles, rare tonofilaments, and forms desmosomal junctions with adjacent liver cells; type II: bile duct-like, is located within ducts, has few organelles, and forms lateral membrane interdigitations with other duct-like cells; and type III: hepatocyte-like, is located in hepatic cords, forms a bile canaliculus, has tight junctions with other hepatocyte-like cells, prominent mitochondria and rough endoplasmic reticulum, and some have lysosomes and a poorly developed Golgi apparatus. Each type is seen during cholangiocarcinogenesis in hamsters, but the most prominent cell type is type II, duct-like. A more primitive cell type ("type 0 cell"), as well as type I cells, are seen in the intraportal zone of the liver within 1 to 2 days after carcinogen exposure or periportal injury in the rat, but both type II and type III are seen later as the progenitor cells expand into the liver lobule. After allyl alcohol injury, type 0 cells precede the appearance of type I and type III cells, but most of the cells that span the periportal necrotic zone are type III hepatocyte-like cells showing different degrees of hepatocytic differentiation. Some type II cells are also seen, but these are essentially limited to ducts. It is concluded that there is a primitive stem cell type in the liver (type 0) that may differentiate directly into type I and then into type II, duct-like or or type III hepatocyte-like cells. The terms oval cell, transitional hepatocyte, biliary hepatocyte, hepatocyte-like cell, atypical ductular cell, neocholangiole, etc., are used to describe these cells. Although these terms are useful as general descriptive terms for liver precursor cells at the light microscopic level, the cells included in these descriptive categories may be very different from one another biologically and ultrastructurally.