Lipid peroxidation in regenerating rat liver

Human Placenta Hydrolysate Promotes Liver Regeneration via Activation of the Cytokine/Growth Factor-Mediated Pathway and Anti-oxidative Effect

Liver regeneration is a very complex process and is regulated by several cytokines and growth factors. It is also known that liver transplantation and the regeneration process cause massive oxidative stress, which interferes with liver regeneration. The placenta is known to contain various physiologically active ingredients such as cytokines, growth factors, and amino acids. In particular, human placenta hydrolysate (hPH) has been found to contain many amino acids. Most of the growth factors found in the placenta are known to be closely related to liver regeneration. Therefore, in this study, we investigated whether hPH is effective in promoting liver regeneration in rats undergoing partial hepatectomy. We confirmed that cell proliferation was significantly increased in HepG2 and human primary cells. Hepatocyte proliferation was also promoted in partial hepatectomized rats by hPH treatment. hPH increased liver regeneration rate, double nucleic cell ratio, mitotic cell ratio, proliferating cell nuclear antigen (PCNA), and K_i-67 positive cells in vivo as well as interleukin (IL)-6, tumor necrosis factor alpha (TNF-α), and hepatocyte growth factor (HGF). Moreover, Kupffer cells secreting IL-6 and TNF-α were activated by hPH treatment. In addition, hPH reduced thiobarbituric acid reactive substances (TBARs) and significantly increased glutathione (GSH), glutathione peroxidase (GPx), and superoxide dismutase (SOD). Taken together, these results suggest that hPH promotes liver regeneration by activating cytokines and growth factors associated with liver regeneration and eliminating oxidative stress.

Lipid Peroxidation and Cancer: A Critical Reconsideration

The author reviews the problem of the pattern of lipid peroxidation in cancer cells with special reference to a comparison between normal liver cells and hepatomas both transplanted and induced by diethylnitrosamine. It is stated that the loss of lipid peroxidation is proportional to the degree of dedifferentiation of hepatoma cells. During carcinogenesis, however, the loss is already evident at the stage of preneoplastic nodules. A common feature of all tumors, independently of the extent of the loss of peroxidation in basal conditions, is the lack of further stimulation by ADP/iron or by ascorbate/iron. As regards the reasons for the decline in lipid peroxidation, they are certainly not unique. An important cause is the low activity of the enzymes of the monooxygenase microsomal chain. Another very important one is the change in lipid composition of membranes, with a marked decrease in polyunsaturated fatty acids, which are the main substrate for lipid peroxidation. It has been shown that enrichment of membranes of hepatomas with arachidonic acid results in restoration of stimulation of peroxidation by ascorbate/iron, but not with ADP/iron. The last type of stimulation mostly reflects the behaviour of the monooxygenase chain, whereas ascorbate/ iron-induced stimulation does not require the presence of an efficient cytochrome P450-chain. Another cause for decreased lipid peroxidation in tumors is the increased rigidity of membranes, due to the large increase in cholesterol content: this prevents to some extent the influx of oxygen inside the membranes. Yet another cause is the presence of increased amounts of antioxidants in both cytosol and membranes. The main toxic product of lipid peroxidation, 4-hydroxynonenal, has been found to elicit several actions at extremely low concentrations. In fact, 4-hydroxynonenal stimulates Chemotaxis of polymorphonuclear leukocytes, stimulates plasma membrane adenylate cyclase, stimulates plasma membrane guanylate cyclase, and stimulates phospholipase C. The last three enzymes involve the action of G-proteins. The effect of the aldehyde is present at less than micromolar concentrations, which may occur inside the cells in certain conditions. Morever, at concentrations from 10–6 to 10–7 M, the aldehyde is able to block oncogene c-myc expression in the human erythroleukemic K562 cell line, which at the same time becomes able to express the gamma-globin gene. These facts are discussed with reference to a possible biological meaning of the loss of lipid peroxidation in tumors.

Ischemia-Reperfusion Injury of Sciatic Nerve in Rats: Protective Role of Combination of Vitamin C with E and Tissue Plasminogen Activator

An ischemia/reperfusion injury of rat's sciatic nerve was experimentally developed. In this model, we measured the in vivo production of superoxide radical, as a marker of oxidative stress and the occludin expression as an indicator of blood-nerve barrier function and we examined potential protective innervations against these abnormalities. Right sciatic nerves of the animals underwent 3 h of ischemia followed by 7 days of reperfusion and were divided into three groups: ischemic, pretreated with vitamin C in conjunction with vitamin E and treated with tissue plasminogen activator. Compared to measurements from left sciatic nerves used as sham, the ischemic group showed significantly increased superoxide radical and reduced expression of occludin in western blot and immunohistochemistry. No such differences were detected between sham and nerves in the vitamin or tissue plasminogen activator groups. It is suggested that the experimental ischemia/reperfusion model was suitable for studying the relationship between oxidative state and blood-nerve barrier. The reversion of abnormalities by the applied neuroprotective agents might prove to be a clinically important finding in view of the implication of vascular supply derangement in various neuropathies in humans.

Effects of Urtica dioica on oxidative stress, proliferation and apoptosis after partial hepatectomy in rats

The present study was performed to investigate the effect of Urtica dioica (UD) on liver regeneration after partial hepatectomy (PH) in rats. A total of 24 male Sprague Dawley rats were divided into three groups: sham-operated, PH and PH + UD; each group contains eight animals. The rats in UD-treated groups were given UD oils (2 ml/kg/day) once a day orally for 7 days starting 3 days prior to hepatectomy operation. At day 7 after resection, liver samples were collected. The levels of malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH) were estimated in liver homogenates. Moreover, histopathological examination, mitotic index (MI), proliferating cell nuclear antigen labeling, proliferation index (PI), transferase-mediated deoxyuridine triphosphate nick end-labeling assay, apoptotic index (AI) were evaluated at day 7 after hepatectomy. As a result, UD significantly increased MI and PI, significantly decreased AI and also attenuated hepatic vacuolar degeneration and sinusoidal congestion in PH rats. UD treatment significantly decreased the elevated tissue MDA level and increased the reduced SOD activity and GSH level in the tissues. These results suggest that UD pretreatment was beneficial for rat liver regeneration after partial hepatectomy.

Antioxidative, antiapoptotic, and proliferative effect of curcumin on liver regeneration after partial hepatectomy in rats

The aim of the present study was to assess the influence of curcumin on liver regeneration after partial hepatectomy (PH) in rats. A total of 24 male Sprague Dawley rats were divided into three groups: sham-operated (SH), PH, and PH + curcumin; each group contains eight animals. The rats in curcumin-treated groups were given curcumin (in a dose of 100 mg/kg body weight) once a day orally for 7 days, starting 3 days prior to hepatectomy operation. At 7 days after resection, liver samples were collected. The malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) levels were estimated in liver homogenates. Moreover, histopathological examination, mitotic index (MI), proliferating cell nuclear antigen labeling, proliferation index (PI), transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick end-labeling assay, and apoptotic index (AI) were evaluated at 7 days after hepatectomy. As a result, curcumin significantly increased MI and PI and significantly decreased AI in PH rats. Additionally, curcumin remarkably inhibited MDA elevation, restored impaired antioxidant SOD activity and GSH level and also attenuated hepatic vacuolar degeneration and sinusoidal congestion. These results suggested that curcumin treatment had a beneficial effect on liver regenerative capacity of the remnant liver tissue after hepatectomy, probably due to its antioxidative, antiapoptotic, and proliferative properties.

Effects of bicyclol on liver regeneration after partial hepatectomy in rats

Bicyclol is a synthetic antihepatitis drug with antioxidative property. The present study was performed to investigate the effect of bicyclol on liver regeneration after partial hepatectomy in rats. Bicyclol (300 mg/kg) was given to rats subjected to 70% hepatectomy three times before operation. At 6, 24, and 48 h after resection, samples were collected for the measurement of serum alanine aminotransferase (ALT), total bilirubin (TBil), hepatic glycogen, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH). Moreover, liver regeneration rate, proliferating cell nuclear antigen (PCNA) labeling, proliferation index, and histopathological examination were evaluated at 48 h after hepatectomy. As a result, bicyclol significantly increased regeneration rate, mitotic index (MI), PCNA labeling index, and proliferation index in PH rats. Additionally, bicyclol remarkably inhibited the elevation of serum ALT and TBil levels, alleviated the formation of liver MDA, restored impaired antioxidant SOD and GSH, increased hepatic glycogen content, and also attenuated hepatic vacuolar degeneration. These results suggested that bicyclol had a beneficial effect on liver regenerative capacity of the remnant liver tissue after hepatectomy, probably due to its antioxidative property.

Proteomic analysis of differential protein expression in early process of pancreatic regeneration in pancreatectomized rats

AIM

A broad-range proteomic approach was applied to investigate the complexity of the mechanisms involved in pancreatic regeneration for identification of new targets of diabetes treatment and potential markers of pancreatic stem cells.

METHODS

A regeneration pancreatic model was induced by 90% partial pancreatectomy (Px) in rats. Changes in the protein expression in regenerating rat pancreas on the third day after Px, as compared with rats that received sham surgery, were analyzed by using 2-D gel electrophoresis (2-DE), mass spectrometry (MS), and mass fingerprinting.

RESULTS

2-DE revealed 91 spots with at least 1.5-fold increases in expression at 3 d after pancreatectomy and 53 differentially expressed proteins that were identified by peptide mass fingerprinting (PMF). These included cell growth-related, lipid and energy metabolism-related, protein and amino acid metabolism-related proteins, and signal transduction proteins. Vimentin, CK8, L-plastin, hnRNP A2/B1, and AGAT are associated with embryogenesis and cell differentiation, and may be new potential pancreatic stem cells markers.

CONCLUSION

The proteome profiling technique provided a broad-based and effective approach for the rapid assimilation and identification of adaptive protein changes during pancreas regeneration induced by pancreatectomy. Our data clarify the global proteome during the pancreatic proliferation and differentiation processes, which is important for better understanding of pancreatic regeneration and for discovering of protein biomarkers for pancreatic stem cells.

Chemotherapy-associated oxidative stress: impact on chemotherapeutic effectiveness

Antineoplastic agents induce oxidative stress in biological systems. During cancer chemotherapy, oxidative stress-induced lipid peroxidation generates numerous electrophilic aldehydes that can attack many cellular targets. These products of oxidative stress can slow cell cycle progression of cancer cells and cause cell cycle checkpoint arrest, effects that may interfere with the ability of anticancer drugs to kill cancer cells. The aldehydes may also inhibit drug-induced apoptosis (programmed cell death) by inactivating death receptors and inhibiting caspase activity. These effects would also diminish the efficacy of the treatment. The use of anti-oxidants during chemotherapy may enhance therapy by reducing the generation of oxidative stress-induced aldehydes.

Oxidative state in intestine and liver after partial hepatectomy in rats. Effect of bombesin and neurotensin

OBJECTIVES

Extended liver resection is a situation with major implication of the gut-liver axis. In the present study, we aimed to investigate intestinal and liver oxidative stress after partial hepatectomy and explore the influence of exogenous administration of gut regulatory peptides bombesin (BBS) and neurotensin (NT).

DESIGN AND METHODS

Ninety male Wistar rats were randomly divided into five groups: control, sham operated, partially hepatectomized (70%), and partially hepatectomized treated with either BBS or NT. Forty-eight hours after surgery, lipid peroxidation, protein oxidation, reduced and oxidized glutathione were measured on intestinal and liver homogenates. Endotoxin levels were determined in portal and aortic blood.

RESULTS

In hepatectomized rats, all parameters of oxidative stress in remnant liver were decreased. In the intestine, oxidative protein damage was increased, while lipid peroxidation and glutathione oxidation were reduced. BBS and NT reduced protein and glutathione oxidation in both tissues and prevented lipid peroxidation in the intestine. Furthermore, portal and aortic endotoxemia were decreased in peptides-treated rats.

CONCLUSIONS

After partial hepatectomy, liver regeneration takes place under low oxidative stress, while increased oxidative damage to proteins occurs in the intestine. Gut regulatory peptides BBS and NT exert an antioxidant effect in both organs and prevent endotoxemia.

Role of nitric oxide increase on induced programmed cell death during early stages of rat liver regeneration

We analysed the possible cellular mechanism involved in the NO action in the balance between apoptosis and cell proliferation in liver regeneration process. We determined p53, proapoptotic protein Bax, antiapoptotic Bcl-xL, proliferating cell nuclear antigen (PCNA) and apoptotic index at the early stages of regenerative process after NO increase by lipopolysaccharide-induction (LPS) of inducible-type nitric oxide synthase (iNOS) and by direct NO donor (sodium nitroprusside, SNP). Male Wistar rats were randomised in four experimental groups: sham operated control (Sh), partial hepatectomised control (PH-C), partial hepatectomised pretreated with LPS (2 mg/kg body weight, i.p.) (PH-LPS), and partial hepatectomised pretreated with SNP (2.5 mg/kg body weight, i.v. at a rate of 1 ml/h) (PH-SNP). Animals were killed 5 h post-surgery. Hepatic cytosolic iNOS showed an increase of 34% in PH-C animals with respect to Sh, and LPS-treatment increased iNOS protein levels 30% compared with PH-C. Bax and p53 protein levels showed significant increases in LPS- and SNP-treated hepatectomised rats with respect to PH-C. The apoptotic indexes were increased 75% in both, PH-LPS and PH-SNP rats versus PH-C. The increase of NO did not show any change in the proliferation process. These results suggest that NO is involved in apoptosis via p53 and Bax proteins after PH, showing a tightly regulated growth process in liver regeneration.

4-hydroxynonenal and regulation of cell cycle: effects on the pRb/E2F pathway

The hypothesis that 4-hydroxynonenal (HNE), a product of lipid peroxidation, might negatively affect cell proliferation, arose from the observation that lipid peroxidation is very low in tumors. In leukemic cells HNE inhibited cell growth and reduced c-myc and c-myb expression. HNE also induced differentiation in different leukemic cell lines. In HL-60 human leukemic cells, HNE induced the accumulation of cells in the G(0)/G(1) phase of the cell cycle accompanied by a decrease of cyclins D1, D2, and A. Moreover, HNE caused an increase in p21 expression. As cyclin D/CDK2 and cyclin A/CDK2 phosphorylate pRB, these findings suggested that pRb phosphorylation could be affected by HNE. Hypophosphorylated pRb binds and inactivates the E2F transcription factors. HNE induced the dephosphorylation of pRb and the increase in pRb/E2F1 complexes, whereas pRb/E2F4 complexes were reduced, because HNE downregulated E2F4 protein expression. The analysis of E2F binding to the P2 c-myc promoter revealed that HNE caused a decrease in "free" E2F, as well as an increase in pRb (and pRB family members) bound to E2F, with consequent repression of the transcription. In conclusion, HNE reduces E2F transcriptional activity by modifying a number of genes involved in regulation of the pRb/E2F pathway.

Inhibitory effect of vitamin e administration on the progression of liver regeneration induced by partial hepatectomy in rats

We have proposed that controlled peroxidative modifications of membranes could be playing a role in the early steps of liver regeneration. Hence, lipid peroxidation (LP) was modified in vivo by treatment with vitamin E in rats subjected to partial hepatectomy (PH), and its influence on liver regeneration was evaluated. Our results, using several methods to monitor LP, indicate that vitamin E administration promoted a decreased LP rate in liver subcellular membranes. Vitamin E drastically diminished cytosolic LP, shifting earlier increased LP in plasma membranes, and promoted a higher increase of nuclear LP in animals subjected to PH. Pretreatment with vitamin E induced a striking reduction of liver mass recovery and nuclear bromodeoxyuridine labeling (clearly shown at 24 hours after surgery), as well as promoted a decreased expression of cyclin D1 and of the proliferating cell nuclear antigen after PH. These effects seem to lead to a decreased mitotic index at 48 hours after PH. Vitamin E pretreatment also diminished PH-induced hypoglycemia but elevated serum bilirubin level, which was not observed in PH animals without vitamin treatment. In conclusion, an enhanced but controlled LP seems to play a critical role during the early phases of liver regeneration. Decreasing magnitude or time course of the PH-promoted enhanced LP (at early post-PH stages) by in vivo treatment with vitamin E could promote an early termination of preparative cell events, which lead to the replicative phase, during PH-promoted liver proliferation. The latter could have a significant implication in the antitumorigenic effect ascribed to the treatment with vitamin E.

Lipid peroxidation, DNA damage, and cellular morphology of R1 Rhabdomyosarcoma cell line irradiated in vitro by gamma-rays with different dose rates

The study examines the relationship between lipid peroxidation, DNA damage, and cell morphology after the exposure of R1 Rhabdomyosarcoma cells to two different dose-rates of gamma rays. Exponential cultures of R1 cells were irradiated with single dose of 5 Gy at high dose rate (0.833 Gy/min) and low dose rate (0.0707 Gy/min). The concentration of two aldehydes, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), were determined. DNA damage induction and repair were measured by using the alkaline version of the comet assay. Cellular alteration was also estimated microscopically as was the frequency of cells with micronuclei and proportion of apoptosis and necrosis. These parameters were evaluated immediately (time 0) and after different times up to 48 h of incubation in 37 degrees C, after irradiation. Results indicate that a low dose rate in comparison to high dose rate caused a significantly higher increase of aldehydes concentration observed at 12 h, followed by obviously higher DNA damage at 48 h and altered cellular morphology. The inverse dose-rate effect estimated for the gamma rays Co-60 source was found to be related to the measured biochemical and morphological parameters.

Nitric oxide release and enhancement of lipid peroxidation in regenerating rat liver

BACKGROUND/AIMS

Clarification of the role of lipid peroxidation in the onset of liver proliferation has been hampered by the fact that both higher and lower lipid peroxidation have been reported after two-thirds partial hepatectomy. Recently, it has been shown that nitric oxide might be involved in the control of early responses after partial hepatectomy. We analysed the possible involvement of nitric oxide production in lipid peroxidation levels during liver regeneration.

METHODS

Sham-operated, hepatectomised and sham and hepatectomised rats pretreated with two inhibitors of oxide nitric synthesis (aminoguanidine or N(G)-monomethyl-L-arginine) were used throughout. Animals were killed at 1, 3, 5 and 15 h after surgery. Cytosolic superoxide dismutase and microsomal-lysosomal catalase activities were measured. Lipid peroxidation levels were measured as thiobarbituric acid-reactive substances and conjugated dienes. Cytosolic nitrate (a stable metabolic product of nitric oxide) was enzymatically determined. Inducible-type nitric oxide synthase (iNOS) was analysed in hepatic cytosol by immunoblotting. DNA synthesis 24 and 48 h after surgery was assessed by [3H]thymidine incorporation.

RESULTS

Increased lipid peroxidation was found in total homogenate, cytosol and microsomes. The hepatic cytosolic content of nitrates increased, reaching the highest values at 5 h posthepatectomy. Aminoguanidine or N(G)-monomethyl-L-arginine pretreatment blocked the rise of nitric oxide production and lipid peroxidation levels and decreased the DNA synthesis. The increase in hepatic iNOS protein expression at 5 h after partial hepatectomy disappeared with aminoguanidine pretreatment.

CONCLUSIONS

Our experiments suggest that nitric oxide plays a role in the proliferation mechanism, although it is responsible, at least in part, for the enhanced lipid peroxidation.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Preoperative internal biliary drainage is superior to external biliary drainage in liver regeneration and function after hepatectomy in obstructive jaundiced rats

OBJECTIVE

To examine the differences in regeneration rates and functions of the liver at the time of and after hepatectomy in obstructive jaundiced rats with preoperative external and internal biliary drainage.

SUMMARY BACKGROUND DATA

The significance of biliary drainage before surgery is controversial in patients with obstructive jaundice.

METHODS

After biliary obstruction for 7 days, rats were randomly divided into three groups: obstructive jaundice and hepatectomy (OJ-Hx), external biliary drainage and hepatectomy (ED-Hx), and internal biliary drainage and hepatectomy (ID-Hx). The OJ-Hx group underwent hepatectomy without biliary drainage; the other two groups underwent hepatectomy after biliary drainage for 7 days. At the time of hepatectomy, all rats were provided with internal biliary drainage. On days 0, 1, 2, 3, and 7 after hepatectomy, the DNA synthesis rate and the concentrations of adenine nucleotides and malondialdehyde in the liver were determined as markers of the hepatic regeneration rate, energy status, and lipoperoxide concentration, respectively. Portal endotoxin concentrations were measured and serum hyaluronic acid concentrations were determined as an indicator of hepatic endothelial function.

RESULTS

The relative liver weight was significantly higher in the ID-Hx group than in the OJ-Hx group on days 1, 3, and 7 after hepatectomy and than in the ED-Hx group on days 1 and 2. The rate of hepatic DNA synthesis was significantly higher in the ID-Hx group than in the OJ-Hx and ED-Hx groups on day 1. The rate was similar in the ED-Hx and ID-Hx groups on day 2 but was significantly higher than in the OJ-Hx group. The hepatic malondialdehyde concentration was significantly higher on day 1 in the ED-Hx group than in the other two groups. It was lowest in the ID-Hx group throughout the study. Both biliary drainage procedures lowered the portal endotoxin concentration and serum hyaluronic acid concentration at the time of hepatectomy. The serum hyaluronic acid concentration was lowest in the ID Hx group. Hepatic adenine triphosphate concentrations and energy charge levels were similar among the three groups.

CONCLUSION

Although both external and internal biliary drainage before hepatectomy improved serum liver function tests, portal endotoxin concentration, and serum hyaluronic acid concentration at the time of surgery, preoperative internal biliary drainage was superior to external drainage, as evidenced by the better liver regeneration and function after hepatectomy.

The effect of dietary fat on malondialdehyde concentrations in Fischer 344 rats

The effects of dietary fat and age on the level of malondialdehyde (MDA), a product of lipid peroxidation, were investigated in cerebellum, kidney, and liver tissues of female Fischer 344 rats. Groups of rats were fed diets containing various levels of corn oil (3, 5, 10, 15, or 20%), starting at 57 days of age, for a duration of 2, 10, or 20 weeks. High fat diets are thought to promote tumor formation, diabetes, and cardiovascular diseases via induction of oxidation stress, and this can begin early in the lifespan. However, it was observed that rats chronically consuming 3 and 5% corn oil diets yielded significantly higher levels of MDA, as analyzed by high-performance liquid chromatography, compared with those fed higher fat diets. After 20 weeks of feeding, the concentration of MDA in each of the three organs studied showed no significant differences among rats consuming diets containing 10, 15, or 20% corn oil. The levels of MDA were highest in the cerebellum, followed by kidney, and lowest in liver. Over the 20-week feeding period, a decrease in MDA level in both cerebellum and liver was observed.

Inhibition of D1, D2, and A-cyclin expression in HL-60 cells by the lipid peroxydation product 4-hydroxynonenal

4-Hydroxynonenal (HNE), a product of lipid peroxidation, is an highly reactive aldehyde that, at concentration similar to those found in normal cells, blocks proliferation and induces a granulocytic-like differentiation in HL-60 cells. These effects are accompained by a marked increase in the proportion G0/G1 cells. The mechanisms of HNE action were investigated by analyzing the expression of the cyclins and cyclin-dependent protein kinases (CDKs), controlling the cell cycle progression. Data obtained by exposing cells to dimethyl sulfoxide (DMSO) were used for comparison. 4-Hydroxynonenal downregulated both mRNA and protein contents of cyclins D1, D2, and A until 24 h from the treatments, whereas DMSO inhibited cyclin D1 and D2 expression until the end of experiment (2 days) and induces an increase of cyclin A until 1 day. Cyclins B and E, and protein kinase CDK2 and CDK4 expressions were not affected by HNE, whereas DMSO induced an increase of cyclin E, B, and CDK2 from 8 h to 1 day. These data are in agreement with previous results indicating a different time-course of accumulation in G0/G1 phases of cells treated with HNE and DMSO and suggest that the HNE inhibitory effect on proliferation and cell cycle progression may depend by the downregulation of D1, D2, and A cyclin expression.

Liver cancer is induced by a subnecrogenic dose of DENA when associated with fasting/refeeding: role of glutathione-transferase and lipid peroxidation

In previous studies, we reported that fasting/refeeding has a role in sustaining the initiation of liver cancer by a subnecrogenic (noninitiating) dose of diethylnitrosamine (DENA). This research investigated whether the metabolic alterations imposed by fasting/refeeding provide an imbalance between the generation of carcinogenic molecules and the scavenger defense mechanisms in rat liver. Metabolism of DENA, levels of reduced glutathione (GSH) and GSH transferase (GST) activity, as well as basal and stimulated malondialdehyde (MDA) production, were examined. Rats fasted for 4 days showed a decrease in the liver levels of GSH, GST activity, monounsaturated fatty acids and % of labeled nuclei. After 1 day of refeeding, at which point DENA was administered, the levels of GSH recovered, GST activity remained below control values, basal and stimulated MDA production and content of total polyunsaturated fatty acids in liver phospholipids decreased. One day after DENA treatment, MDA production further decreased, although the % of labeled nuclei increased. No significant changes in the content of arachidonic acid, the main target of peroxidation, were observed at any time. The results indicated that the induction of the hepatocellular carcinoma was associated with a depression of GST activity and lipid peroxidation when rats were given 20 mg/kg of DENA after 1 day of refeeding after 4-day fasting.

Mitochondrial oxidative alterations following partial hepatectomy

Mitochondria, isolated from rat livers during the early phase of liver regeneration (7-24 h after partial hepatectomy), show: (i) decrease in the rate of ATP synthesis; (ii) increase of malondialdehyde and of oxidized protein production; (iii) decrease of the content of intramitochondrial glutathione and of protein thiols on mitochondrial proteins; (iv) increase of the glutathione bound to mitochondrial proteins by disulfide bonds. These observations suggest an increase of production of oxygen radicals in liver mitochondria, following partial hepatectomy, which can alter the function of the enzymes involved in the oxidative phosphorylation. Blue-native gel electrophoresis of rat liver mitochondria, isolated after partial hepatectomy, shows, during the early phase of liver regeneration (0-24 h after partial hepatectomy), a progressive decrease of the content of F0F1-ATP synthase complex. The amount of glutathione bound to the F0F1-ATP synthase, electroeluted from the blue-native gels, progressively increased during the early phase of liver regeneration. It is concluded that partial hepatectomy causes mitochondrial oxidative stress that, in turn, modifies proteins (such as F0F1-ATP synthase) involved in the mitochondrial oxidative phosphorylation.

Lipid peroxidation and antioxidant activities in regenerating liver after partial hepatectomy in splenectomized rats

Lipid peroxidation, antioxidant activities, and total fatty acids were investigated in the regenerating liver after partial hepatectomy in splenectomized male Wistar rats. The lipoperoxide levels were significantly lower in the splenectomized rats than in the non-splenectomized rats. The hepatic superoxide dismutase (SOD) activity was significantly higher in the splenectomized rats than in the controls, whereas the alpha-tocopherol content, and the activities of glutathione (GSH) peroxidase and catalase did not differ so widely between splenectomized and nonsplenectomized rats. In both groups, the fatty acid composition of the total lipids was not so different in the early stages of hepatic regeneration after partial hepatectomy, but it was noted that in the later stages of hepatic regeneration, polyunsaturated fatty acids tended to increase in the splenectomized rats. These results suggest that splenectomy attenuates lipid peroxidation, and tends to increase in polyunsaturated fatty acids in the remnant liver after partial hepatectomy, which may be attributable to high SOD activity, the maintenance of alpha-tocopherol, and the remaining activities of GSH peroxidase and catalase.

Selective enhancement of lipid peroxidation in plasma membrane in two experimental models of liver regeneration: partial hepatectomy and acute CC14 administration

It has been proposed that lipid peroxidation (LP) might be a modulator of cell division, influencing initiation and cessation of mitosis in regenerating liver. However, the understanding of the participating role of this event in the onset of liver proliferation has been hampered by the fact that both higher or lower LP have been reported after two-thirds partial hepatectomy (PH). Therefore, the present study deals with the extent of LP in the main subcellular fractions from rat liver at early stages of regeneration, induced by either PH of 70% or acute CCl4 administration. Our results, using several methods to monitor LP, indicate a differential effect in the peroxidative pattern of specific subcellular fractions from regenerating liver after 24 hours of PH: a decrease in microsomes and an increase confined to plasma membrane and cytosolic fractions, peaking after 24 hours of PH. In CCl4-treated rats, higher LP was also noted in plasma membrane and cytosol, being maximal at the replicative stage in this experimental model (48 hours). In addition, increased LP was found in microsomal and nuclear fractions, declining before the 48 hours. In hepatectomized rats, changes in LP seem to be an organ-specific event and related to only PHs capable of triggering a synchronized proliferative response, namely above 40%. These results show that LP, promoted by PH and CCl4 administration, is qualitatively distinct among subcellular fractions and may indeed be a normal cell event of physiological importance in the regenerating liver.

Fish oil, lipid peroxidation and mammary tumor growth

There is evidence that the level and especially the type of dietary fat can be an important determinant of mammary tumor development and growth. Diets containing high levels of fish oil have been shown to inhibit or suppress mammary tumor growth. Various mechanisms have been proposed to explain this modulatory activity of dietary fish oil or fats in general on tumor growth; of special interest is lipid peroxidation. The oxidation of long chain polyunsaturated fatty acids present in fish oil, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can produce an array of secondary products of lipid oxidation that may possess a cytostatic or cytolytic capacity.

Adjuvant therapy with essential fatty acids (EFAs) for primary liver tumors: some hypotheses

Hepatocarcinoma is responsible for approximately 1 million deaths annually. It is usually discovered at an advanced stage and, if inoperable, has a poor prognosis. New therapies combining chemotherapy, hyperthermia, radiotherapy and immunomodulators have been recently attempted with various levels of success. Once the tumor is detected at an early stage, some possibilities of cure seem to emerge either by intratumoral percutaneous injection (PEI) of alcohol or by chemoembolization and interstitial hyperthermia. When the tumor volume is more than 5 cm, these therapies are less successful and radiotherapy can be used. All the techniques described have some limits; PEI, for instance, does not achieve a complete eradication of lesions > 3 cm and a non-homogenous alcohol distribution within the tumor leads to areas of necrosis. Radiotherapy, even if effective, is limited by dose-related radiation hepatitis. Another important limiting factor is the incomplete response to therapy and tumor recurrence. Essential fatty acids, especially gamma linolenic acid (GLA) and eicosapentaenoic acid (EPA) are discussed here for their ability to control primary tumor proliferation and increase response to chemotherapy, radiotherapy and hyperthermic treatment, thanks to their effects on cellular membranes (increased lipoperoxidation and modification of tumor stroma).

Developmental changes in the peroxidation potential of rat brain homogenate and mitochondria

Lipid peroxidation, one of the most common expressions of oxidative stress, may be altered during normal physiological states including development. We have examined the changes in lipid peroxidation in rat brain, a tissue highly susceptible to oxidative damage, during this physiological state. In vivo lipid peroxidation was moderate in the foetal and neonatal period and increased during the postnatal development. Lipid peroxidation potential in brain homogenate and mitochondria, in Tris-HCl buffer or with exogenous cofactors, such as ascorbate-Fe2+, NADPH ADP-Fe3+ and cumene hydroperoxide, showed significant changes during pre- and postnatal development. In general, brain as well as liver (used as a standard tissue for comparison) seem to have low peroxidation potential in the foetal and neonatal period which then increases at different rates during development to reach adult values at different days. The low peroxidation potential corresponds to the rapid phase of cell proliferation. These results taken together with similar earlier finding in other systems may indicate a possible occurrence of a 'permissible period' during which the low levels of lipid peroxidation may be able to yield only low amounts of cytostatic aldehydes and peroxides as byproducts, thereby allowing rapid proliferation of cells.

Lipid peroxidation in microsomes of murine bone marrow after low-dose gamma-irradiation

The principal aim of the study was to investigate the effect of low-dose gamma-irradiation on lipid peroxidation (LPO) in murine bone marrow. To this end, the degree of LPO in suspensions of microsomes of murine bone marrow cells (BMC) was determined in terms of malondialdehyde (MDA) formation after whole-body or in vitro exposure to various doses of gamma-radiation. These effects were compared to some extent with similar effects in liver and spleen preparations. As to the effect of gamma-irradiation on LPO in BMC, the response depends on the dose level and on whether whole-body or in vitro exposures are involved. Whole-body irradiation did not result in an increase in LPO in BMC microsomes, even at such high doses as 15 Gy, although hepatic microsomes showed a marked increase. In contrast, in vitro irradiation of BMC microsomes with 0.1, 10 and 50 Gy brought about an increase in LPO. This increase was already significant (P < 0.05) at 0.1 Gy following a post-irradiation incubation and substantial at 50 Gy, even without subsequent incubation. The results show that low doses of gamma-irradiation are able to induce an elevation of LPO in murine BMC microsomes, but only after in vitro irradiation. In the case of whole-body irradiation cellular radical scavengers and other metabolic reactions may prevent a measurable increase in LPO. This is partly illustrated by the case of vitamin-E deficiency, where a substantial increase in LPO in BMC microsomes is observed even without gamma-irradiation in comparison with euvitaminotic mice because normally occurring radicals are not scavenged sufficiently.

Control of neoplastic cell proliferation and differentiation by restoration of 4-hydroxynonenal physiological concentrations

Several studies point to the existence of an inverse correlation between cellular lipid peroxidation and both cell proliferation and neoplastic transformation. In anaplastic cell lines products of membrane lipid peroxidation are very low or undetectable. Furthermore numerous results demonstrate effect of lipid peroxidation products on central biochemical pathways and intracellular signalling at physiological concentrations. 4-hydroxynonenal (HNE) is one of the most active products of lipid peroxidation. The restoration of HNE physiological concentrations in neoplastic cells may inhibit cell proliferation and modulate cell re-differentiation. This review try to summarize and critically discuss the effects of physiological concentrations of HNE on normal and neoplastic cell line.

Absence of mitochondrial enhancement in the remnant liver after partial hepatectomy in cirrhotic rats

Changes in energy metabolism after 70% partial hepatectomy were investigated in normal and carbon-tetrachloride-(CCl4)-induced-cirrhotic rats by evaluating hepatic mitochondrial ATP synthesizing activity as well as liver tissue levels of adenine nucleotides and lipid peroxide. Preoperative concentrations of ATP and total adenine nucleotides (TAN: ATP + ADP + AMP) in mumol/g dry weight (dw) and the energy charge potential (ECP) in the cirrhotic livers were 8.53 SEM 0.25, 14.73 SEM 0.54, and 0.74 SEM 0.01, respectively, and were significantly lower than those of normal livers (12.04 SEM 0.34, 15.75 SEM 0.12, and 0.86 SEM 0.01, P less than 0.01 in TAN). There was no difference in the preoperative mitochondrial phosphorylation rate (PR = x 10(-10) mol ATP/sec per mg mitochondrial protein) between normal and cirrhotic livers (21.01 SEM 0.95 and 21.55 SEM 1.03, respectively). After hepatectomy, in the normal livers these values decreased slightly after 12 h, remained low until 48 h, and returned to the preoperative value at 72 h. PR was remarkably enhanced and reached the maximum level of 32.54 SEM 2.07 at 24 h (P less than 0.001, compared to the sham-operated rats) and gradually returned to the preoperative value at 72 h. In the cirrhotic livers, ATP and ECP levels were drastically decreased at 12 h and recovered to the preoperative levels within 24 h, while TAN level remained unchanged. Enhancement of PR was not observed in any of the cirrhotic livers during the experiment. Lipid peroxidation was transiently increased postoperatively with no difference between normal and cirrhotic livers both in the sham-operated and the hepatectomized rats. These findings suggest that the energy status was more depressed in the cirrhotic livers than in normal livers both before and after hepatectomy. This depressed energy status might be attributed to the low preoperative tissue levels of adenine nucleotides and ECP level in the cirrhotic livers as well as to the absence of the enhancement of PR in the remnant livers.

Lipid peroxidation and tumor growth: an inverse relationship

Lipid peroxidation may play a very important role in cell proliferation especially those of tumors. Secondary products of lipid peroxidation may interact in an inhibitory manner with various cell processes and/or cycle phases that are essential for cell division resulting in a decreased tumor growth rate by killing actively dividing cells of the growth fraction and probably increasing cell loss. The inhibitory or static action of diets containing elevated levels of fish oil on tumor growth may be via lipid peroxidation control over cell proliferation.

Aldehyde dehydrogenases and their role in carcinogenesis

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs--1, 2, and 3--have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism. Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression. This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms. The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may an important determinant of the effectiveness of certain chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of exposure of various oxidants on rat liver and intestinal microsomes--a comparative study

Rat liver and intestinal microsomes were exposed to various free radical generating systems and their effect were assessed by studying different parameters such as formation of malonaldehyde (MDA) and conjugated diene, arachidonic acid depletion and alteration in protein thiol groups and tocopherol levels. These studies revealed that liver being highly vulnerable tissue showed all the effects of free radical attack whereas intestinal microsomes were resistant to most oxidants except iron independent generation of free radicals using 2-2'-azobis (2-amidinopropane) dihydrochloride (ABAP). Intestinal microsomes were found to contain considerable amount of non-esterified fatty acids in total lipid fraction as compared to liver microsomes and iron-fatty acid complex may be incapable of participating in peroxidation. In vitro measurement of hydroxyl radical generation showed that intestinal microsomes were incapable of generating these active species. These results suggest that iron dependent free radical mediated lipid peroxidation might not occur in intestinal epithelial cells.

An immunohistochemical study of copper, zinc-containing superoxide dismutase detected by a monoclonal antibody gastric mucosa and gastric cancer

The immunohistochemical localization of copper, zinc-superoxide dismutase (Cu,Zn-SOD) in human gastric mucosa and gastric cancer was studied using a monoclonal antibody. In gastric mucosa, parietal cells, pyloric glandular cells and foci of intestinal metaplasia showed positive staining in the cytoplasm and/or nucleus. The wide distribution of Cu, Zn-SOD in the gastric mucosa suggests cell function may be vulnerable to active oxygen species. In gastric cancer, 34 of 70 cases showed a positive reaction for Cu, Zn-SOD. There was a relationship between the grade of Cu,Zn-SOD immunoreactivity and the histological type of gastric cancer, well-differentiated types of gastric cancer being more frequently positive. The positive cases of poorly-differentiated adenocarcinoma were characterized by a pattern of diffusely infiltrative invasion. These results suggest that some types of gastric cancer are resistant to active oxygen species.

Effect of the peroxisome proliferator ciprofibrate on hepatic DNA synthesis and hepatic composition following partial hepatectomy in rats

The peroxisome proliferator ciprofibrate was examined for its ability to alter liver regrowth following partial hepatectomy in rats. Ciprofibrate was fed to female Sprague-Dawley rats at concentrations of 0, 0.01% and 0.025% in the diet for 2 weeks. All rats were then subjected to partial hepatectomy and were killed at 0, 12, 24, 36, 48, 72, and 168 h afterwards. The increase in liver weight after partial hepatectomy occurred at a similar rate in control and ciprofibrate-fed rats, although liver weights were always higher in ciprofibrate-fed rats. The marked increase in DNA synthesis normally seen after partial hepatectomy, however, was partially inhibited in rats fed 0.025% ciprofibrate, as compared to control rats or rats fed 0.01% ciprofibrate. An increase in the ratio of protein to DNA in the liver was observed in rats fed either level of ciprofibrate. The marked increase in total lipid content normally seen after partial hepatectomy was inhibited by ciprofibrate treatment. Vitamin E levels were also reduced in ciprofibrate-fed rats. The activity of the peroxisomal enzyme fatty acyl CoA oxidase was increased in rats fed ciprofibrate at all time points, verifying the induction of peroxisomes by ciprofibrate. This study shows that the administration of 0.025% ciprofibrate before partial hepatectomy inhibits the peak of DNA synthesis normally seen shortly after partial hepatectomy but does not affect the regrowth of the liver. The regrowth of the liver in rats fed 0.025% ciprofibrate may be caused by cellular hypertrophy, as evidenced by the enhanced protein content of the liver.

The antioxidant action of tamoxifen and its metabolites. Inhibition of lipid peroxidation

The anti-oestrogen drug tamoxifen is an inhibitor of lipid peroxidation in rat liver microsomes and in phospholipid liposomes. Its cis isomer and N-desmethyl form are weaker inhibitors, but 4-hydroxytamoxifen is much more powerful. It is possible that the antioxidant property of tamoxifen might contribute to its biological actions.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Application of deuterated alpha-tocopherols to the biokinetics and bioavailability of vitamin E

alpha-Tocopherol, a superior chain-breaking, peroxyl radical-trapping antioxidant and the most active component of vitamin E, is elevated in liver tumor cells, contributing to their greater resistance towards lipid peroxidation compared to cells from normal tissues. Also, in regenerating rat liver the level of vitamin E has been found to fluctuate in phase with the rate of cell division. In order to study the biokinetics and mechanisms of the distribution of vitamin E in organs and within tissues of animals, deuterated forms of alpha-tocopherol have been synthesized and their uptake into blood and tissues has been measured by gas chromatography-mass spectrometry. Measurement of the competitive uptake from a mixture of the RRR- and SRR-alpha-tocopherol stereoisomers labelled with different amounts of deuterium shows that the liver exerts a strong preference for secretion of the natural (RRR) stereoisomer into the plasma. It is suggested that a tocopherol-binding protein plays a key role in this process.

Lipid peroxidation in liver and Ehrlich ascites cell mitochondria

Ehrlich ascites cell mitochondria are highly resistant to lipid peroxidation as compared to liver mitochondria from host animals. Succinate protects mitochondria from peroxidative damage, proteins from cross-links, enzymes from inactivation of the enzymes and membranes from permeability changes. The sensitivity of Ehrlich ascites cell mitochondrial membranes to lipid peroxidation is significantly increased in submitochondrial particles. Lipid peroxidation in tumour mitochondrial membranes can not be diminished by succinate as effectively as in liver mitochondria. Ascites cell mitochondria seems to be protected very efficiently from peroxidative damage by a glutathione-dependent mechanism.

Studies on lipid peroxidation in normal and tumour tissues. The Yoshida rat liver tumour

Reduced rates of lipid peroxidation have been observed in Yoshida hepatoma cells and microsomes when compared with appropriate control tissue (normal rat liver) under the same pro-oxidant conditions. The pro-oxidant conditions used were incubation with NADPH+ADP+iron or ascorbate+iron or exposure to gamma-irradiation. As previously shown with the Novikoff hepatoma, the relative concentrations of alpha-tocopherol and polyunsaturated fatty acids are important in conferring resistance to lipid peroxidation in the Yoshida hepatoma. Furthermore, NADPH-cytochrome c reductase and the NADPH-cytochrome P-450 electron transport chain, which are involved in the initiation and propagation of certain types of lipid peroxidation, are found at very much reduced levels in the Yoshida hepatoma. The relative importance of these aberrations are discussed.

Lipid peroxidation in tumour cells

Several studies point to the existence of a disturbance in the metabolism of the reactive species of oxygen in cancer cells. Based on this evidence, and in particular on a characteristic behaviour of tumour membrane lipids, namely their growth-related resistance to oxy-radical-induced peroxidation, a sequence of events is outlined that could hypothetically drive the transformed cell to an uncontrolled proliferation. The proposed scheme is also conceived as a framework for further in vivo investigations of the complex biological phenomena of tumour cell growth and invasion in more integrated and kinetically controlled cellular systems.

Vitamin E remains the major lipid-soluble, chain-breaking antioxidant in human plasma even in individuals suffering severe vitamin E deficiency

The chain-breaking (peroxyl radical-trapping) antioxidant activity of plasma obtained from several patients with a very severe vitamin E deficiency has been measured. The total chain-breaking antioxidant activity in lipid extracts has been shown to be approximately equal to the concentration of vitamin E. For whole plasma there is no significant difference in the concentrations of water-soluble, chain-breaking antioxidants between the E-deficient patients and healthy adults. It is concluded that even in cases of very severe vitamin E deficiency the requirement for this vitamin is not met by some other exogenous or endogenous antioxidant.

Vitamin E protects proteins against free radical damage in lipid environments

The fragmentation of the membrane protein monoamine oxidase in submitochondrial particles was induced by defined free radicals during radiolysis and by a system dependent on hydrogen peroxide and a transition metal. By injection of alpha-tocopherol in vivo, the levels of this physiological antioxidant in the mitochondrial preparations could be elevated more than ten-fold. In both radical-generating systems the presence of high levels of alpha-tocopherol in the membrane substantially retarded the protein fragmentation, in parallel with lipid peroxidation. It is suggested that membrane-bound proteins are damaged during lipid peroxidation and that alpha-tocopherol protects cells against both types of damage.

Carbon tetrachloride toxicity as a model for studying free-radical mediated liver injury

A single dose of CCl4 when administered to a rat produces centrilobular necrosis and fatty degeneration of the liver. These hepatotoxic effects of CCl4 are dependent upon its metabolic activation in the liver endoplasmic reticulum to reactive intermediates, including the trichloromethyl free radical. Positive identification of the formation of this free radical in vivo, in isolated liver cells and in microsomal suspensions in vitro has been achieved by e.s.r. spin-trapping techniques. The trichloromethyl radical has been found to be relatively unreactive in comparison with the secondarily derived peroxy radical CCl3O2., although each free radical species contributes significantly to the biological disturbances that occur. Major early perturbations produced to liver endoplasmic reticulum by exposure in vivo or in vitro to CCl4 include covalent binding and lipid peroxidation; studies of these processes occurring during CCl4 intoxication have uncovered a number of concepts of general relevance to free-radical mediated tissue injury. Lipid peroxidation produces a variety of substances that have high biological activities, including effects on cell division; many liver tumours have a much reduced rate of lipid peroxidation compared with normal liver. A discussion of this rather general feature of liver tumours is given in relation to the liver cell division that follows partial hepatectomy.