Circadian rhythm of VEGF expression in the liver of hepatectomized-tumor-bearing adult and young mice

We analyzed VEGF expression in regenerating liver (after partial hepatectomy) of tumor-bearing adult and young mice, throughout one complete circadian cycle. The animals were sacrificed every 4 h, from 26 to 46 h post-hepatectomy. Liver samples were processed for immunohistochemistry. The results showed circadian variation of VEGF expression in hepatectomized mice (control group) and hepatectomized-tumor-bearing mice. The maximum value of VEGF expression was found at 16:00/30 h of day/hour post-hepatectomy (HD/HPH) in tumor-bearing young mice, and at 20:00/34 HD/HPH in the controls. In adult mice the maximum values of VEGF expression were at 16:00/30 HD/HPH in tumor-bearing mice, and at 08:00/46 HD/HPH in the controls. Young tumor-bearing mice showed significantly higher mean values than the controls. In conclusion, the presence of the tumor in the animals induces modifications in the intensity and the temporal distribution of the circadian curves of VEGF expression.     

Hyperbaric oxygen preconditioning promotes angiogenesis in rat liver after partial hepatectomy

Hyperbaric oxygen preconditioning (HBO-PC) increases the level of HIF-1alpha (hypoxia inducible factor-1alpha) and its target gene VEGF (vascular endothelial growth factor) which is involved in angiogenesis. Liver regeneration is an angiogenesis-dependent process. We hypothesized that HIF-1alpha and VEGF mediated the angiogenesis effect of HBO-PC on regenerating rat liver. Male Sprague Dawley rats received HBO-PC followed by 70% partial hepatectomy. Proliferation of hepatocytes and endothelial cells was evaluated by BrdU (bromodeoxyuridine) staining. Microvascular density was assessed by immunohistochemistry. mRNA expression of HIF-1alpha was assessed by quantitative RT-PCR and protein levels of HIF-1alpha and VEGF were assessed by western blot. HIF-1alpha DNA-binding activity was determined with an ELISA-based kit. HBO-PC increased the proliferation index of endothelial cells and microvascular density at 48 h after partial hepatectomy. The protein level and DNA-binding activity of HIF-1alpha and the protein level of VEGF were increased by HBO-PC before and after partial hepatectomy. Partial hepatectomy alone also increased proliferation index and the expressions of HIF-1alpha and VEGF. Our results indicated that the angiogenesis effect of HBO-PC on liver after partial hepatectomy could be achieved by increased HIF-1alpha activity and VEGF expression. However, the angiogenic effect of HBO-PC is moderate and HBO-PC failed to produce additional effect on the enhancement of HIF-1alpha and VEGF induced by partial hepatectomy alone.     

A partial hepatectomy results in altered expression of clock-related and cyclic glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes

The liver is among the peripheral organs that display a clear circadian rhythmicity. To investigate whether specific pathological conditions affect circadian rhythms in the liver, we examined the expression profiles of the clock-related and glyceraldehyde 3-phosphate dehydrogenase (GADPH) genes following a partial hepatectomy in the mouse. This surgical procedure causes dynamic proliferation of residual hepatocytes and within one day of the operation the hepatectomized mice demonstrated higher expression of both mPer1 and mPer2 genes in the remaining liver tissue when compared to control mice that had undergone a Sham-operation. In contrast, the mCry1 gene in hepatectomized mice displayed a circadian gene expression profile that was similar to the control group. In addition, GAPDH levels, that demonstrated no oscillations in Sham-hepatectomized mice, underwent daily alterations following a partial hepatectomy. These findings suggest that the regenerative state of the liver affects the expression not only of clock-related genes but also of genes that are constitutively expressed under steady state conditions.     

Expression and role of vascular endothelial growth factor in liver regeneration after partial hepatectomy in rats.

Vascular endothelial growth factor (VEGF) plays a major role in angiogenesis, which is essential for both healing of injured tissue and proliferation of carcinoma cells. In this study we elucidated the expression and role of VEGF in rat liver regeneration after partial hepatectomy. VEGF expression was mainly detected in periportal hepatocytes and reached a maximal level 48-72 hr after partial hepatectomy by both immunohistochemistry and in situ hybridization. Similarly, immunohistochemistry for Ki-67 showed that the proliferative activity of sinusoidal endothelial cells was highest in the periportal area and reached a maximal level 72 hr after partial hepatectomy. Moreover, neutralization of VEGF significantly inhibited proliferative activity of hepatocytes (p<0. 0001), as well as sinusoidal endothelial cells (p<0.001), at 48 and 96 hr after partial hepatectomy. Conversely, injection of VEGF significantly promoted proliferative activity of hepatocytes (p<0. 0001) as well as sinusoidal endothelial cells (p<0.0005) at 48 hr after partial hepatectomy. These results suggest that VEGF promotes proliferation of hepatocytes through reconstruction of liver sinusoids by proliferation of sinusoidal endothelial cells. Furthermore, these data point to a new therapeutic strategy, the use of VEGF and other hepatocyte growth factors in fulminant or severe acute hepatitis.     

Roles of alpha 1- and beta-adrenergic receptors in adrenergic responsiveness of liver cells formed after partial hepatectomy

The adrenergic receptor involved in the action of epinephrine changed dramatically during the process of active proliferation which follows partial hepatectomy. In control or sham-operated animals, the stimulation of glycogenolysis, gluconeogenesis and ureogenesis by epinephrine was mediated through alpha 1-adrenergic receptors. In contrast, in hepatocytes obtained from animals partially hepatectomized 3 days before experimentation, the receptor involved in the stimulation of these metabolic pathways by epinephrine was of the beta-adrenergic type. Interestingly, the adrenergic receptor involved in the metabolic actions of epinephrine, in hepatocytes from rats partially hepatectomized 7 days before experimentation was again of the alpha 1-subtype. Thus, it appears that during the process of liver regeneration which follows partial hepatectomy there is a transition in the type of adrenergic receptor involved in the hepatic actions of catecholamines from beta in the initial stages to later alpha 1. A similar transition seems to occur as the animal ages. Cyclic AMP accumulation in response to beta-adrenergic stimulation was significantly enhanced in hepatocytes obtained from rats partially hepatectomized 3 days before the experiment, as compared to control hepatocytes or cells obtained from animals operated 7 days before experimentation. This enhanced beta-adrenergic sensitivity is probably related to the increased number of beta-adrenergic receptors observed at this stage. However, a clear dissociation between cyclic AMP levels and metabolic effects was evidenced when the different conditions were compared. The number and affinity (for epinephrine or prazosin) of alpha 1-adrenergic receptors did not change at any stage of the process, which indicates that the markedly diminished alpha 1-adrenergic sensitivity observed in hepatocytes obtained from rats partially hepatectomized 3 days before experimentation is probably due to defective generation or intracellular processing of the alpha 1-adrenergic signal, rather than to changes at the receptor level.     

Inhibiting effect of plasma from normal and tumour bearing mice on the mitotic rate of regenerating liver

Plasma from normal mice and from mice bearing the ES2 transplantable malignant tumour was injected intraperitoneally at a dose of 0.01 ml/g body weight in partially hepatectomized mice. Control animals were injected with a solution of sodium citrate in saline. The recipients were killed at the first (14:00 hours/48 h). These times are the time of day and the number of h after partial hepatectomy and second (14:00 hours/72 h) peak times after partial hepatectomy. The number of colchicine metaphases per 1000 nuclei was determined for hepatocytes and litoral cells. A different effect was obtained with plasma from tumour-bearing compared with normal mice. Plasma from both sources when injected 26 h after partial hepatectomy (16:00 hours/26 h) inhibited the mitotic activity of hepatocytes at the next peak of regenerative activity (14:00 hours/48 h). The plasma from tumour-bearing mice also inhibited the peak on the following day (14:00 hours/72 h), whereas plasma from normal mice had no inhibitory effect and, indeed, a compensatory wave was observed at this time. Furthermore, plasma from tumour-bearing mice also showed an inhibitory effect at the first peak (14:00 hours/48 h) when injected at the time of partial hepatectomy (14:00 hours/00 h) or at 22 h before partial hepatectomy (16:00 hours/-22 h) whereas the injection of plasma from normal mice at these times had no inhibitory effect. In the litoral cells the injection of plasma from tumour-bearing mice made 22 h before hepatectomy (16:00 hours/-22 h) led to a stimulation of mitotic activity which was controlled at 14:00 hours/48 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

DNA synthesis in tongue keratinocytes of hepatectomized and tumor-bearing mice

Tongue keratinocytes have high S-phase and mitotic indices with evident circadian variation. Transplanted tumors modify the intensity and temporal structure of the S-phase index in cell populations in tumor-bearing animals; also, partial hepatectomy changes the concentrations of substances involved in cellular proliferation, leading to compensatory liver hyperplasia. The aim of our study was to analyze the interaction between tumor growth and the liver regeneration that follows partial hepatectomy, and the effects of both these processes on lingual keratinocytes. We used 380 adult male mice divided into six groups: tumor-free and tumor-bearing mice without surgery, with sham hepatectomy, and with partial hepatectomy. Each group was divided into six subgroups, which were killed at 4-h intervals until a circadian cycle was completed (from 26 until 50h post-surgery in the operated animals). Each animal was injected with 5-bromodeoxyuridine (50mg/kg) 1h before it was killed, and tongue samples were obtained and processed for histology. The sections were placed on silanized slides and incubated with the primary antibody Bu 20a (1/100 dilution). The reaction was developed using diaminobenzidine and staining was detected visually. SIs were measured as the number of labeled nuclei per thousand cells. The mean+/-S.E. of each group was calculated. Differences among experimental groups were analyzed by ANOVA and the Student-Newman-Keuls Multiple Comparisons Test. The results show that the presence of a tumor alters the normal circadian curve of SI in lingual keratinocytes, irrespective of whether the mice underwent surgery. This finding has to be considered in drug treatments for neoplasms and in experiments related to growth.     

Vascular endothelial growth factor and nitric oxide in rat liver regeneration

In this work we investigated the role of nitric oxide (NO) in the angiogenesis mediated by vascular endothelial growth factor (VEGF) during rat liver regeneration after two-thirds partial hepatectomy. Sham operated (Sh) and partially hepatectomized (PH) male Wistar rats were randomized in three experimental groups: control (treated with vehicle); pre-treated with sodium nitroprusside (SNP: 0.25 mg/kg body weight, i.v. at a rate of 1 ml/h) and pre-treated with the preferential iNOS inhibitor, aminoguanidine (AG, 100 mg/kg body weight, i.p.). Animals were killed at 5, 24 and 72 h after surgery. At 5 h post-surgery, NO production was estimated by EPR (Sh-Control: 37.65+/-10.70; PH-Control: 88.13+/-1.60(); Sh-SNP: 90.35+/-3.11(); PH-SNP: 119.5+/-12.10()(#); Sh-AG: 33.27+/-5.23, PH-AG: 36.80+/-3.40(#)) (p<0.05 vs Sh-Control; (#)p<0.05 vs PH-Control). At 24 h after PH, VEGF levels showed no difference between PH-Control and PH-SNP animals. However, after 72 h, VEGF protein levels in PH-SNP animals were found to be increased (above 300%) with respect to PH-Control. On the other hand, aminoguanidine (AG) pre-treatment blocked the rise of inhibition of NO generation and decreased VEGF expression. Our results demonstrated that NO plays a role in modulating VEGF protein expression after hepatectomy in rats.     

The ileal FGF15/19 to hepatic FGFR4 axis regulates liver regeneration after partial hepatectomy in mice

Fibroblast growth factor (FGF) has been considered to modulate liver regeneration (LR) after partial hepatectomy (PH) at the tissue level. Previous studies have demonstrated that FGF15 and FGF19 induce the activation of its receptor, FGF receptor 4 (FGFR4), which can promote hepatocellular carcinoma progression and regulate liver lipid metabolism. In this study, we aimed to explore the role of the ileal FGF15/19- hepatic FGFR4 axis in the LR after PH. Male C57BL/6 mice aged 8–12 weeks were partially hepatectomized and assessed for expression of ileal FGF15/19 to hepatic FGFR4 signaling. We used recombinant human FGF19 protein and a small interfering RNA (siRNA) of FGFR4 to regulate expression of the FGF15/19-FGFR4 axis in vitro and in vivo. The proliferation and cell cycle of hepatocytes, the expression levels of FGF15/19-FGFR4 downstream molecules, liver recovery, and lipid metabolism were assessed. We found that both ileal and serum FGF15 expression were upregulated and hepatic FGFR4 was activated after PH in mice. FGF15/19 promoted cell cycle progression, enhanced proliferation, and reduced hepatic lipid accumulation of hepatocytes both in vitro and in vivo. Furthermore, the proliferative effect and lipid regulatory properties of FGF15/19 were dependent on FGFR4 in hepatocytes. In addition, ileal FGF15/19-hepatic FGFR4 transduction during hepatocyte proliferation was regulated by extracellular regulated protein kinase (ERK) 1/2. In conclusion, the ileal FGF15/19 to hepatic FGFR4 axis is activated and promotes LR after PH in mice, supporting the potential of ileal FGF15/19 to hepatic FGFR4 axis-targeted therapy to enhance LR after PH.     

Chronobiology of the proliferative events related to angiogenesis in mice liver regeneration after partial hepatectomy

In liver regeneration the formation of new capillary blood vessels is a fundamental requirement for cellular proliferation. Vascular endothelial growth factor (VEGF) is involved in the events of angiogenesis, the mRNA of which is expressed in both hepatocytes and non-parenchymal cells. In this experimental design we try to establish if during liver regeneration in mouse, the expression of VEGF is produced before or after the hepatocytes proliferation. C3H/S adult male mice were divided in three groups in order to study: VEGF expression; S-phase index (SI); and mitotic activity (MA) of hepatocytes. The results that were analyzed by ANOVA, show that VEGF expression starts to increase 26 h after PH with a peak at 28 h. Furthermore, the DNA synthesis (DNAs) reaches maximal level 42 h after pH, meanwhile the MA of the hepatocytes shows an increase 8h after the DNAs peak. In conclusion, it could be argued that the chronobiology of the events related to liver regeneration in mice started with a release of VEGF by the hepatocytes, followed by its DNAs and mitosis.     

Change in the resistance of partially hepatectomized mice to transplanted tumors in the period of liver regeneration completion]

There were two inhibition periods of the growth of ascitic hepatoma 22a when its cells were transplanted intraperitoneally to partially hepatectomized A/he mice 1 to 12 days after the operation. The first inhibition took place when the transplantation was performed one day, and the second--3 to 10 days, after partial hepatectomy. The animals which were most resistant to this tumour (5 to 8 days after the operation) proved to be resistant, although to a lesser extent, to the intraperitoneal transplantation of sarcoma 37 and Ehrlich's adenocarcinoma.     

Effect of thyroid status on microsomal enzymes during liver regeneration in the rat

The effects of thyroid status upon cyt. P 450 concentration and ethoxycoumarin deethylase, benzopyrene hydroxylase and UDP-glucuronosyltransferase activities in the liver microsome fraction were far more important in partially hepatectomized rats than in control animals. The partial hepatectomy simultaneously lowered the MFO enzymes activities in the hepatic microsome fraction and made them more sensitive to thyroid hormones effects.     

Albumin synthesis and catabolism following partial hepatectomy in the rat. The effects of amino acids and adrenocortical steroids on albumin synthesis after partial hepatectomy.

Plasma albumin levels were measured in partially hepatectomized, sham operated and control rats. The levels fell in both the partially hepatectomized and sham operated groups; while the latter group returned to normal within a few days, the low plasma albumin in the partially hepatectomized animals was sustained. Albumin synthesis rates in the isolated perfused rat liver were measured in the three groups of animals at varying intervals after partial hepatectomy. There was a significant depression of albumin synthesis rate in terms of both liver and whole animal weights when compared to the sham operated and control animals. This depression was almost completely reversed by the addition of arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine added together to 10 times their normal plasma concentrations. The addition of hydrocortisone had no effect on the albumin synthesis rate after partial hepatectomy. Studies in vivo in the three groups of animals (partially hepatectomized, sham operated and control animals) revealed a fall in the albumin catabolic rate after partial hepatectomy coinciding with the fall in the albumin synthesis rate. An hypothesis whereby the amino acids may have their stimulatory effect is proposed.     

Effect of chemical carcinogens and partial hepatectomy on "in vivo" (35S)methionine interaction with rat liver tRNA

The effect of carcinogens given by a single or multiple injections on the extent of (35S)methionine interaction with hepatic tRNA was studied in normal and partially hepatectomized rats. Either partial hepatectomy or administration of ethionine (100 or 330 mg/kg body weight) and dimethylnitrosamine (120 mg/kg body weight) by multiple i.p. injections inhibited the (35S)methionine-tRNA interaction, while administration of hepatocarcinogenic chemicals plus PH resulted rather in a stimulation. Methylnitrosourea enhanced the extent of interaction when administered in a single dose (100 mg per kg body weight) 18 h after partial hepatectomy.     

Dehydroepiandrosterone (DHEA) facilitates liver regeneration after partial hepatectomy in rats

In this study we investigated whether or not liver regeneration is facilitated by dehydroepiandrosterone (DHEA) after partial (70%) hepatectomy in rats. Treatment with DHEA (300 mg/kg body weight) did not cause any significant increase in the expression ratio of proliferating cell nuclear antigen (PCNA) in sham-operated controls; however, in partially hepatectomized rats it caused a significant increase in the ratio in hepatocytes 24 and 36 hr after hepatectomy. In partially hepatectomized rats, DHEA treatment significantly accelerated the restoration of liver 48, 60, and 72 hr after partial hepatectomy. The restoration rate in DHEA-treated hepatectomized rats at 72 hr was 1.3-fold greater than in partially hepatectomized controls. Treatment with androstenedione (300 mg/kg body weight), the first metabolite of DHEA, did not cause any significant increase in the expression of PCNA in either sham-operated controls or partially hepatectomized rats. These results indicate that DHEA itself promotes the liver regenerative process after partial hepatectomy in rats.     

The Circadian Optimal Time for Hepatectomy in the Study of Liver Regeneration

Standardized (light from 0600 to 1800) C3HS mice, hepatectomized at different circadian stages, were killed at 1400 (the peak time of mitotic activity in intact mice). The higher values of mitotic index were those of mice operated at 1400, 48 hr before. The curve of mitotic activity of the regenerating liver of mice operated at 1400 and that of mice operated at 0200 (an opposite time in the circadian stage) are, both, grossly in phase with the curves of mitotic index in young and adult mice liver. The amplitude of the first peak of mitotic activity in mice operated at 0200 was dramatically lower than that of animals operated at 1400. The same applies to hepatocytes as well as to the sinusoid litoral population of cells. It is concluded that 1400 hr, as contrast to 0200 hr, is an optimal time for hepatectomy if one wants to obtain the highest mitotic index first peak during regeneration in a normal phase position (the position of the mitotic index peak in the liver of normal young and adult mice).     

Effect of partial hepatectomy on the invertor mechanism of regulation of the Na+,K+-ATPase activity in hepatocytes of rats of various ages]

Age peculiarities of partial hepatectomy effect on the hepatocytes plasma membrane Na+, K(+)-ATPase activity and its insulin-induced stimulation has been studied. It has been shown that partial hepatectomy does not change basal Na+, K(+)-ATPase activity in adult rats. In old partial hepatectomised rats Na+, K(+)-ATPase activity is slightly higher than in control old rats, although this increase is not statistically significant. At the same time, partial hepatectomy acts differently on the insulin-induced Na+, K(+)-ATPase activation in adult and old rats. Insulin activates Na+, K(+)-ATPase at the same extent both in control and partial hepatectomized adult animals. In old hepatectomized rats, but not in old control animals, insulin stimulates Na+, K(+)-ATPase activity as well as. Thus hepatectomy "rejuvenates" old hepatocytes and results in recovery of invertor mechanism of Na+, K(+)-ATPase activation.     

Enhancement of aflatoxin B1-induced hepatocarcinogenesis in rats by partial hepatectomy

The effect of enhanced cell replication induced by partial hepatectomy (PH) in aflatoxin B1 (AFB1)-induced hepatocarcinogenesis has been studied in rats of the inbred As2 strain. Animals were given 0.25 mg/kg body weight of AFB1 as a single intraperitoneal dose 24 h after PH. Non-hepatectomized animals given the same dose of AFB1 served as controls. Neoplastic nodules and hepatocellular carcinoma (HCC) were detected respectively in 100% and 90% of hepatectomized animals sacrificed between 55 and 65 weeks after AFB1 administration. None of the ten non-hepatectomized rats sacrificed at this time interval showed HCC or neoplastic nodules. On histochemical staining the tumour population was found to be heterogeneous. Thus PH resulted in enhancement of AFB1-induced hepatocarcinogenesis in rats of the AS2 strain.     

Roles of alpha1- and beta-adrenergic receptors in adrenergic responsiveness of liver cells formed after partial hepatectomy

The adrenergic receptor involved in the action of epinephrine changed dramatically during the process of active proliferation which follows partial hepatectomy. In control or sham-operated animals, the stimulation of glycogenolysis, gluconeogenesis and ureogenesis by epinephrine was mediated through alpha₁-adrenergic receptors. In contrast, in hepatocytes obtained from animals partially hepatectomized 3 days before experimentation, the receptor involved in the stimulation of these metabolic pathways by epinephrine was of the beta-adrenergic type. Interestingly, the adrenergic receptor involved in the metabolic actions of epinephrine, in hepatocytes from rats partially hepatectomized 7 days before experimentation was again of the α₁-subtype. Thus, it appears that during the process of liver regeneration which follows partial hepatectomy there is a transition in the type of adrenergic receptor involved in the hepatic actions of catecholamines from β in the initial stages to later α₁. A similar transition seems to occur as the animal ages. Cyclic AMP accumulation in response to β-adrenergic stimulation was significantly enhanced in hepatocytes obtained from rats partially hepatectomized 3 days before the experiment, as compared to control hepatocytes or cells obtained from animals operated 7 days before experimentation. This enhanced β-adrenergic sensitivity is probably related to the increased number of β-adrenergic receptors observed at this stage. However, a clear dissociation between cyclic AMP levels and metabolic effects was evidenced when the different conditions were compared. The number and affinity (for epinephrine or prazosin) of α₁-adrenergic receptors did not change at any stage of the process, which indicates that the markedly diminished α₁-adrenergic sensitivity observed in hepatocytes obtained from rats partially hepatectomized 3 days before experimentation is probably due to defective generation or intracellular processing of the α₁-adrenergic signal, rather than to changes at the receptor level.     

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.