Hepatic regeneration and metabolism after partial hepatectomy in normal rats: effects of insulin therapy

HIF-1alpha is necessary to support gluconeogenesis during liver regeneration

Coordinated recovery of hepatic glucose metabolism is prerequisite for normal liver regeneration. To examine roles of hypoxia inducible factor-1alpha (HIF-1alpha) for hepatic glucose homeostasis during the reparative process, we inactivated the gene in hepatocytes in vivo. Following partial hepatectomy (PH), recovery of residual liver weight was initially retarded in the mutant mice by down-regulation of hepatocyte proliferation, but occurred comparably between the mutant and control mice at 72h after PH. At this time point, the mutant mice showed lowered blood glucose levels with enhanced accumulation of glycogen in the liver. The mutant mice exhibited impairment of hepatic gluconeogenesis as assessed by alanine tolerance test. This appeared to result from reduced expression of PGK-1 and PEPCK since 3-PG, PEP and malate were accumulated to greater extents in the regenerated liver. In conclusion, these findings provide evidence for roles of HIF-1alpha in the regulation of gluconeogenesis under liver regeneration.

Using higher-order crossings to distinguish liver regeneration indices in hepatectomized diabetic and non-diabetic rats

BACKGROUND AND AIMS

Diabetes mellitus is implicated in several liver diseases; hence, its potential affection to liver regenerative capacity is an open research question. So far, only sporadic studies have addressed this issue, mainly using basic statistical techniques. The current study evaluated the ability of a novel technique, namely higher-order crossings (HOC), based on liver DNA biosynthesis and thymidine kinase (TK) enzymatic activity data, to discriminate liver regeneration processes between hepatectomized diabetic and non-diabetic rats.

METHODS

We used 251 adult male rats, divided in two groups; diabetic by Alloxan injection and non-diabetic control, subjected to 70% partial hepatectomy and killed at different time intervals post-partial hepatectomy (PH) (0-240 h). The rate of tritiated thymidine (3HTdR) incorporation into hepatic DNA and the enzymatic activity of liver TK were estimated and, after proper interpolation, were analyzed using HOC sequences. Changes of the latter were captured and used as a means for linear discrimination between the two groups.

RESULTS

Ninth-order HOC estimated for post-PH (24, 28, 40, 44, 72 and 84 h) exhibited linear discrimination for the rate of 3HTdR incorporation, whereas second-order HOC estimated for (44-72 h) post-PH exhibited linear discrimination for the TK enzymatic activity data. Fuzzy logic-based c-means cluster analysis of HOC provided distinct areas of group categorization (100% accuracy) for diagnostic distinctions (P < 0.001). The data grouping pointed out by the HOC-based analysis revealed an onset delay in the liver regeneration process when Alloxan diabetes was present (P < 0.05).

CONCLUSIONS

Our results suggest that HOC have the potential to linearly discriminate between experimentally induced diabetic and non-diabetic liver regeneration post-PH processes, based on two liver regeneration indices, capturing the delay seen in the liver regeneration process due to Alloxan diabetes, fostering their use as an efficient classification tool. In this way, HOC could be used as an advanced, easily implemented and user-friendly method to thoroughly analyze liver regeneration processes.

Hepatocyte growth factor inhibits insulin-stimulated glycogen synthesis in primary cultured hepatocytes

BACKGROUND/AIMS

Hepatocyte growth factor (HGF) plays an important role as a mitogen in liver regeneration. However, little is known about the metabolic effects of HGF in the liver. Studies were performed to examine whether HGF influences carbohydrate metabolism, which is drastically changed in the early course of the regeneration.

METHODS

Primary cultured rat hepatocytes were treated with glucoregulatory hormones such as insulin, glucagon and adrenaline in the presence or absence of HGF. Cellular glycogen deposition and activities of its metabolic enzymes were compared.

RESULTS

HGF inhibited insulin-stimulated glycogen deposition, but had no effect on glycogen degradation stimulated by glucagon and adrenaline. HGF decreased glycogen synthase activity and increased glycogen phosphorylase activity in insulin-stimulated hepatocytes, resulting in the inhibition of glycogen synthesis. Experiments with immunoprecipitation revealed that HGF had no effect on the upstream of insulin signaling including an activation of its receptor and association of insulin receptor substrate with phosphatidylinositol 3-kinase, indicating that HGF presumably affects further downstream of these events.

CONCLUSIONS

These results demonstrate that HGF interacts with insulin on glucose metabolism in hepatocytes. HGF may be involved in glucose regulation, and contribute to cell growth and maturation in addition to its mitogenic action during liver regeneration.

Nutritional modulation of liver regeneration by carbohydrates, lipids, and amino acids: a review

The survival of patients after a life-threatening hepatic injury of varying etiology depends on the ability of the remaining hepatocytes to regenerate. Thus, the stimulation of hepatic regeneration can have tremendous therapeutic relevance. Experimental studies--performed mostly on a model of regenerating rat liver after partial hepatectomy--indicate that glucose administration inhibits, whereas infusion of a lipid emulsion can enhance, the rate of liver regeneration. However, the inhibitory effect of glucose on liver regeneration is not observed when glucose is administered together with other nutrients. The results further indicate that administration of a standard amino acid mixture without energy substrate has an inhibitory effect and that development of liver regeneration can be favorably influenced by branched-chain amino acids (valine, leucine, and isoleucine) and glutamine.

Gene therapy for diabetes mellitus in rats by hepatic expression of insulin

Type 1 diabetes mellitus is caused by severe insulin deficiency secondary to the autoimmune destruction of pancreatic beta cells. Patients need to be controlled by periodic insulin injections to prevent the development of ketoacidosis, which can be fatal. Sustained, low-level expression of the rat insulin 1 gene from the liver of severely diabetic rats was achieved by in vivo administration of a recombinant retroviral vector. Ketoacidosis was prevented and the treated animals exhibited normoglycemia during a 24-hr fast, with no evidence of hypoglycemia. Histopathological examination of the liver in the treated animals showed no apparent abnormalities. Thus, the liver is an excellent target organ for ectopic expression of the insulin gene as a potential treatment modality for type 1 diabetes mellitus by gene therapy.

Liver regeneration in rats after complete and partial occlusion of the portal blood influx

The role of portal blood influx in liver regeneration was studied in rats. Partial hepatectomy with removal of 45% of the liver mass was performed after end-to-side portacaval shunt (PCS) leading to complete diversion of portal blood from the liver, or after side-to-side PCS causing partial portal blood deprivation. Liver resection was limited to 45% to avoid the high mortality rate in rats with vascular anastomoses and 70% hepatectomy, but it did not change the pattern of liver regeneration. The total RNA and DNA content, the rate of DNA synthesis and the number of hepatocyte mitoses in regenerating liver were measured in comparison to sham-operated controls. Complete occlusion of the portal blood influx did not block hepatoproliferative response, but caused a significant decrease and delay of regeneration. Partial preservation of portal flow in rats with side-to-side PCS markedly improved liver regeneration in comparison to end-to-side PCS, but the process was slower than in the control group.

Availability of energy substrates during liver regeneration in malnourished rats

A retarded liver regeneration rate during malnutrition has previously been reported. To explore the mechanisms, some energy substrates were studied during liver regeneration and malnutrition. Forty-one rats were allocated to one of three groups (G): GI were normally nourished rats, which were partially hepatectomized; GII were semistarved rats, which were partially hepatectomized; and GIII were normally nourished rats, which were sham-operated. Biopsy specimens were taken from the liver at the time of partial hepatectomy and when they were killed after 48 h of regeneration. The samples were analysed for adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), glycogen, lactate, and pyruvate, and energy charge potential (ECP) was calculated. ATP, ECP, and glycogen levels were decreased in the malnourished group before the resection. After 48 h of regeneration all values were unchanged in the normally nourished group, whereas ATP, ADP, and ECP were increased in the malnourished group compared with the initial values. The lactate/pyruvate quotient was increased in malnourished rats compared with normal rats. The results suggest that the energy supply is not a limiting factor for the reduced regeneration rate seen in malnourished animals.

Sequential changes in alanine metabolism following partial hepatectomy in the rat

After partial hepatectomy, the liver undergoes an array of metabolic changes until regeneration is complete. Since carbons derived from alanine can be incorporated into most metabolic pools, we studied the metabolism of (14)C-labeled alanine during the early phase of regeneration. Sham operated (controls) and partially hepatectomized rats weighing about 200 g each were injected intraperitoneally with 1-[U-(14)C]alanine at 9, 18, and 36 hours after surgery. The animals were killed 2 hours after injection. Compared to the controls, alanine oxidation was markedly depressed (P < 0.05) in the 9- and 18-hour groups, but was restored in the 36-hour group. The specific activity of plasma glucose and hepatic glycogen was elevated 9 and 18 hours after partial hepatectomy. There was a corresponding increase in the activities of fructose-1,6-diphosphatase and phosphoenolpyruvate carboxykinase. Hepatic protein specific activity increased by 30, 74, and 120%, respectively 9, 18, and 36 hours after partial hepatectomy. Hepatic fatty acids followed a similar pattern. In a separate set of experiments, the distribution of radioactivity in glutamic acid was measured. The results showed that alanine carbons enter the citric acid cycle primarily via the acetyl CoA pathway in the controls, but via the oxaloacetate pathway in partially hepatectomized rats. The results demonstrate significant changes in the activities of metabolic pathways of alanine in the early phase of hepatic regeneration.

Increase in liver glucose transporter mRNA levels during rat liver regeneration

Gene expression of liver facilitated glucose transporter was rapidly induced during the liver regenerating process in rats. It reached maximum of 2.7 times at 8 hr of the regenerating course and returned to normal by 48 hr. The protein synthesis inhibitor, cycloheximide, did not interfere with the increased gene expression of liver facilitated glucose transporter. By contrast, erythrocyte/brain-type glucose transporter mRNA could not be detected in the livers of partially hepatectomized rats and sham-operated rats. The plasma glucose levels were transiently increased within 2 hr of the regenerative course and then decreased to a nadir at 4 hr. These results suggest that the increased gene expression of liver facilitated glucose transporter contributes to the decrease in plasma glucose levels.

Hepatic regeneration and metabolism after partial hepatectomy in diabetic rats: effects of insulin therapy

The effect of insulin deficiency on liver regeneration has been assessed in untreated v. insulin-treated streptozotocin (65 mg kg-1) diabetic rats, 12, 24 and 48 h after partial hepatectomy. Dry weight of regenerating liver increased from 12 to 48 h after partial hepatectomy and insulin treatment caused a further minor increase at 24 h. [6-3H]Thymidine uptake in untreated rats peaked at 24 h (12.5 +/- 3.4% of total cells labelled). Insulin therapy produced a delayed 168% rise in uptake at 48 h. Insulin deficiency alone in sham-operated animals caused a 33% decrease in hepatic [ATP], while [ADP] rose by 43% and [AMP] by 86% at 12 h. Partial hepatectomy produced only minor further abnormalities in untreated animals. Insulin therapy increased hepatic [ATP] and decreased [ADP] and [AMP] 12 h after partial hepatectomy, but [ATP] remained decreased (15%) and [ADP] and [AMP] increased (45% and 73% respectively) compared with insulin-treated sham-operated controls. Metabolite changes observed after partial hepatectomy in untreated animals, including a decrease in hepatic [glycogen] and increases in [triglyceride] and the ratios of [lactate]:[pyruvate] and [3-hydroxybutyrate]:[acetoacetate], were partially reversed by insulin treatment. Insulin deficiency thus impairs regeneration after partial hepatectomy and magnifies the decline in hepatic intracellular energy state and the metabolite changes associated with liver regrowth.