Histochemical and biochemical studies on the effect of the prostacyclin derivative iloprost on CCl4-induced lipid peroxidation in rat liver and its significance for hepatoprotection

The mitochondrial translocator protein (TSPO, 18 kDa): A key multifunctional molecule in liver diseases

Translocator protein (TSPO, 18 kDa), previously known as peripheral-type benzodiazepine receptor, is an evolutionarily conserved and tryptophan-rich 169-amino-acid protein located on the outer mitochondrial membrane. TSPO plays a crucial role in various fundamental physiological functions and cellular processes. Its expression is altered in pathological conditions, thus rendering TSPO a potential tool for diagnostic imaging and an appealing therapeutic target. The investigation of synthetic TSPO ligands as both agonists and antagonists has provided valuable insights into the regulatory mechanisms and functional properties of TSPO. Recently, accumulating evidence has highlighted the significance of TSPO in liver diseases. However, a comprehensive summary of TSPO function in the normal liver and diverse liver diseases is lacking. This review aims to provide an overview of recent advances in understanding TSPO function in both normal liver cells and various liver diseases, with a particular emphasis on its involvement in liver fibrosis and inflammation and addresses the existing knowledge gaps in the field that require further investigation.

Carbon tetrachloride-induced hepatic injury through formation of oxidized diacylglycerol and activation of the PKC/NF-κB pathway

Protein kinase C (PKC) participates in signal transduction, and its overactivation is involved in various types of cell injury. PKC depends on diacylglycerol (DAG) for its activation in vivo We have previously reported that DAG peroxides (DAG-O(O)H) activate PKC in vitro more strongly than unoxidized DAG, suggesting that DAG-O(O)H, if generated in vivo under oxidative stress, would act as an aberrant signal transducer. The present study examined whether DAG-O(O)H are formed in carbon tetrachloride (CCl(4))-induced acute rat liver injury in association with activation of the PKC/nuclear factor (NF)-κB pathway. A single subcutaneous injection of CCl(4) resulted in a marked increase in hepatic DAG-O(O)H content. At the molecular level, immunohistochemistry and subcellular fractionation combined with immunoblotting localized PKCα, βI, βII and δ isoforms to cell membranes, while immunoblotting showed phosphorylation of the p65 subunit of NF-κB, and immunoprecipitation using isoform-specific anti-PKC antibodies revealed specific association of PKCα and p65. In addition, expression of tumor necrosis factor α (TNFα) and neutrophil invasion increased in the CCl(4)-treated rats. Furthermore, we demonstrated that Vitamin E, one of the most important natural antioxidants that suppresses peroxidation of membrane lipids, significantly inhibited the CCl(4)-induced increase in hepatic DAG-O(O)H content and TNFα expression as well as phosphorylation of PKCα and p65. These data demonstrate for the first time that DAG-O(O)H are generated in the process of CCl(4)-induced liver injury, resulting in activation of the PKC/NF-κB pathway and TNFα-mediated aggravation of liver injury.

Prostacyclin in liver disease: a potential therapeutic option

Complex molecular and cellular mechanisms are involved in the initiation and progression of hepatic fibrosis. Recent studies have shown that hepatic stellate cells, endothelin, cytokines and prostacyclin play crucial roles in this pathology. Prostacyclin exerts vasorelaxant, antioxidant and antifibrotic properties that prevent the development of fibrosis and cirrhosis in liver diseases. In this editorial, the authors discuss some of the molecular and cellular mechanisms involved in the initiation and progression of liver fibrosis and the role played by prostacyclin in counteracting it. At the moment, however, only limited information is available from clinical studies demonstrating the effectiveness of prostacyclin in liver diseases and this makes it difficult to draw any conclusions; further efforts are necessary to verify whether prostacyclin, alone or in combination with other drugs, may be a valid therapeutic option in liver diseases.

Prostacyclin prevents nitric oxide-induced megakaryocyte apoptosis

1 We have previously demonstrated that nitric oxide (NO) triggers CD34(+)-derived megakaryocyte apoptosis. We here show that prostacyclin (PGI(2)) inhibits PAPA/NO-induced megakaryocyte death detected by fluorescent microscopy and flow cytometry. 2 The cAMP-specific phosphodiesterase inhibitor, Ro 20-1724, and the permeable analog dibutyryl-cAMP also delayed apoptosis. PGI(2) effect was fully prevented when adenylyl cyclase activity was suppressed by SQ 22536, and partially reversed by the permeable protein kinase A inhibitor PKI 14-22 amide. ELISA showed that while both PGI(2) and NO alone or synergistically raised cAMP, only NO was able to increase intracellular cGMP levels. 3 Treatment of megakaryocytes with PGI(2) abolished both basal and NO-raised cGMP levels. Addition of 8-pCPT-cGMP or activation of soluble guanylyl cyclase by BAY 41-2272 induced cell death in a concentration-dependent manner, and ODQ, an inhibitor of guanylyl cyclase, prevented both PAPA/NO- or BAY 41-2272-induced apoptosis. Specific cGMP phosphodiesterase inhibition by Zaprinast or suppression of adenylyl cyclase by SQ 22536 enhanced the PAPA/NO proapoptotic effect. 4 PGI(2) completely inhibited NO-mediated generation and the increased activity of the cleaved form of caspase-3. 5 In conclusion, our results demonstrate that contrary to their well-known direct and synergistic inhibitory effects on platelets, PGI(2) and NO regulate opposite megakaryocyte survival responses through a delicate balance between intracellular cyclic nucleotide levels and caspase-3 activity control.

Iloprost: an adjunctive approach to chronic viral hepatitis treatment

Chronic viral liver disease may evolve to cirrhosis. The medical treatment to slow down this passage is based on anti-viral and anti-fibrotic properties of interferon. Recently, we evidenced significant increase of portal vein flow velocity and volume after a prostacyclin analog (iloprost) infusion in subjects without and with chronic viral hepatitis. On the basis of these results and considering both the pathophysiology of viral liver disease and the mechanism of action of iloprost in portal microcirculation, we hypothesize that it may be of some efficacy in chronic liver disease ameliorating the portal hemodynamics and producing an anti-oxidant liver effect.

Increased islet viability by addition of beraprost sodium to collagenase solution

The digestion of pancreatic tissue with collagenase is an essential part of the islet isolation procedure. However, the process exposes islets to various types of harmful factors, including collagenase contaminants, enzymes released from the acinar cells, warm ischemia, and mechanical agitation. Nitrogen oxide production and cytokine release may also contribute to islet cell damage. Protection of islets from such damage would improve the islet yield, survival, and function. Beraprost sodium (BPS) is a prostaglandin I2 analogue, is stable in aqueous solution, and has a cytoprotective effect on various types of cells. BPS has been shown to improve the yield and function of cryopreserved and/or cultured islets. These findings prompted us to examine its cytoprotective effect on islets during the islet isolation process. Canine islets were isolated by means of a two-step digestion method and purified on Euro-Ficoll density gradient solutions (the procedure used for human islets). BPS at a concentration of 100 nM was added to the collagenase solution. After purification, the islet yield was 434,561 +/- 35.691 islet number expressed as 150 microm equivalent size (IEQ)/pancreas or 8,799 +/- 345 IEQ/g of pancreas in the BPS group and 349,987 +/- 52,887 IEQ/pancreas or 7,998 +/-1610 IEQ/g of pancreas in the control group (n = 8, each). The percent viability was 88.5 +/- 0.7% in the BPS group and 82.0 +/-0.9% in the control group (P < 0.01). Therefore, the recovery of viable islets (calculated by islet number x % viability) was 384,586 +/- 46,804 IEQ/pancreas (7,743 IEQ/g) in the BPS group and 286,989 +/- 43,367 IEQ/pancreas (6,558 IEQ/g) in the control group (P < 0.02). After culture, significantly higher numbers of islets were also recovered in the BPS group than in the control group. The islet insulin content was significantly higher in the BPS group than controls (237.8 +/- 38.5 versus 92.3 +/- 25.6 microU/IEQ; P < 0.02), although islets of both groups responded with high stimulation indices (>6). These results indicate that the addition of BPS to the collagenase solution increases the recovery of viable islets, and improves beta cell function.

Inhibition of transforming growth factor-beta1 and UV light-induced apoptosis by prostanoids in primary cultures of rat hepatocytes

Treatment of rat hepatocytes cultured in collagen gel with transforming growth factor-beta1 (TGFbeta1) or with UV light strongly increased the frequency of apoptotic nuclei within 24 h; at doses of 0.5 ng/ml TGFbeta1 or 90 J/m2 UV light about 17 and 22% apoptotic nuclei were determined, respectively. DNA of the treated cells showed internucleosomal DNA fragmentation. Already the presence of the cytokine for only 1 h significantly induced apoptosis. The prostanoids PGI2, PGD2, and PGE1 decreased the frequency of apoptotic nuclei in a dose-dependent manner by up to 70 to 80% and suppressed internucleosomal DNA fragmentation. In contrast, PGE2 and PGF2alpha elicited a smaller protective effect and arachidonic acid had none. In the case of PGE1 it was shown that the prostaglandin was most effective when added together with TGFbeta1 or within 2 h before or after treatment with this cytokine. An early increase of the tumor suppressor gene product p53 is thought to play a decisive role in UV light-induced apoptosis. However, this increase in p53 was not affected by the strong cytoprotective prostacyclin PGI2. Our findings show a marked antiapoptotic activity of the prostanoids PGE1, PGI2, and PGD2 and raise the question of whether these prostanoids may influence apoptosis in pathological processes in the liver.

Effects of the stable prostacyclin analogue iloprost on mesenteric blood flow in porcine endotoxic shock

OBJECTIVE

To determine the effects of the stable prostacyclin analog, iloprost, in a porcine model of endotoxin-induced mesenteric ischemia.

DESIGN

Prospective, experimental, randomized, controlled study.

SETTING

Animal research laboratory at a university medical center.

INTERVENTIONS

Pigs were randomized to receive a constant infusion of iloprost (0.18 microg/kg/min) or an equivalent amount of carrier solution (normal saline) 30 mins before being infused with endotoxin (100 microg/kg over 1 hr). The infusion with iloprost or carrier solution was continued for the duration of the experiment.

MEASUREMENTS AND MAIN RESULTS

Twelve pigs (six per group), weighing between 20 and 22 kg, underwent laparotomy during which a magnetic flowprobe was placed around the superior mesenteric artery and an ileal tonometer was inserted. Thirty minutes before they were infused with endotoxin, the animals were randomized to receive intravenous iloprost or normal saline. Endotoxin was infused centrally over a 60-min period. Animals received normal saline at a rate of 1.2 mL/kg/min which was begun at the start of the endotoxin infusion. Data were measured at the end of the endotoxin infusion (E60) and 1 hr later (E120). Mean arterial pressure was not affected by the dosage of iloprost used in this experiment. After resuscitation, the cardiac output returned to baseline in the iloprost-treated group but remained decreased in the control group (2.6 +/- 0.5 vs. 1.6 +/- 0.4 L/min). Superior mesenteric blood flow increased 34% above baseline levels in animals pretreated with iloprost (from 363 +/- 85 to 485 +/- 81 mL/min). The superior mesenteric PCO2 was significantly higher (53 +/- 9 vs. 40 +/- 5 torr; 7.1 +/- 1.2 vs. 5.3 +/- 0.7 kPa) and the ileal intramucosal pH was significantly lower (7.07 +/- .28 vs. 7.44 +/- .23) in the control group than in the iloprost-treated group.

CONCLUSIONS

Pretreatment with intravenous iloprost effectively increased intestinal blood flow in this model of endotoxin-induced mesenteric ischemia. This action of the drug resulted in an attenuation of ileal intracellular acidosis. Since low-dose iloprost had no effect on mean arterial pressure, it may be a useful adjunct in the treatment of sepsis and septic shock.

Effect of the prostacyclin analogue, iloprost, on infarct size after permanent focal cerebral ischemia

This investigation was undertaken to study the effect of iloprost, a stable analogue of prostacyclin, on infarct size after permanent focal cerebral ischemia in the rabbit. Forty-two adult rabbits were subjected to left middle cerebral artery occlusion via the transorbital route. Fourteen rabbits received an intravenous (i.v.) infusion of 30 micrograms/kg iloprost, 7 rabbits received an i.v. infusion of 10 micrograms/ kg, and 9 rabbits received an i.v. infusion of 20 micrograms/kg iloprost. Twelve rabbits received an intravenous infusion of saline. Treatment with iloprost started immediately after middle cerebral artery occlusion and continued for 1 h. After killing the animals, brains were removed and five coronal slices were incubated in a 2,3,5-triphenyltetrazolium chloride solution to determine the infarct size. Treatment with 30 micrograms/kg iloprost significantly reduced the infarct size compared with treatment with saline (3.49 +/- 2.79% vs. 9.03 +/- 4.26%, P < 0.001), but the lower doses of iloprost did not have a beneficial effect on the size of the infarct. These results suggest that intravenous iloprost treatment after occlusion has a highly protective effect without any side effects such as hypotension.

Effects of OP 2507, a stable analogue of prostaglandin I2, on carbon tetrachloride-induced liver damage in starved rats

It has been reported that vasodilatory prostaglandins have cytoprotective effects against various types of liver damage. We investigated the effects OP 2507, a stable analogue of prostaglandin I2, on carbon tetrachloride-induced liver damage in starved rats. Intraperitoneal administration of OP 2507 at 1,500 micrograms/kg lessened both an increase in serum alanine aminotransferase activity and an inhibition of starvation ketosis, both of which were induced by carbon tetrachloride. At lower doses, however, OP 2507 not only failed to ameliorate the carbon tetrachloride-induced changes, but it actually exaggerated them. Although the deterioration of carbon tetrachloride-induced liver damage by lower doses of OP 2507 was not statistically significant, it seems possible that OP 2507 has dual effects on carbon tetrachloride-induced liver damage. While none of the three agents cimetidine, reduced glutathione and deferoxamine, prevented increase in serum alanine aminotransferase activity induced with lower dose OP 2507, allopurinol had a tendency to prevent the increase, indicating that lower doses of OP 2507 may promote a reaction catalyzed by xanthine oxidase. We propose that both the co-administration of prostaglandins and other potentially hepatotoxic drugs, and the administration of prostaglandins to patients with drug-induced liver damage should be done carefully.

Expression of clusterin (testosterone-repressed prostate message-2) mRNA during growth and regeneration of rat liver

Clusterin has been used as a marker for apoptosis (often denoted "active" "or programmed" cell death) in the prostate, mammary gland and other solid organs. The protein is thought to be involved in membrane remodelling during separation of apoptotic cells from their vital neighbours and fragmentation into apoptotic bodies. In the present study, we have looked at the expression of clusterin during the growth and regression of rat liver induced by short term administration of the hepatomitogen, cyproterone acetate. The steady state level of clusterin mRNA, as measured by Northern and slot blot analysis, is low in control hepatocytes. Following administration of cyproterone acetate, the clusterin mRNA level is increased during both liver growth and regression. In situ hybridization reveals that clusterin is expressed in all hepatocytes, indicating that it is not confined to cell death by apoptosis. These results suggest that the gene product may be involved in maintaining membrane integrity, which is necessary during both mitosis and apoptosis. To determine whether clusterin mRNA is induced by membrane remodelling independent of either mitosis or apoptosis, we examined the expression of clusterin mRNA in the liver after a necrogenic dose of carbon tetrachloride. During the first 24-48 h of this time period, necrosis is the predominant form of cell death and liver regeneration starts after approximately 24 h. Elevated levels of clusterin mRNA are found as early as 12 h after carbon tetrachloride administration and persist for at least 72 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoid production in experimental alcoholic liver disease is related to vitamin E levels and lipid peroxidation

We investigated the association between vitamin E, lipid peroxidation and eicosanoid production in experimental alcoholic liver injury. We used the intragastric feeding rat model in which animals were fed corn oil and ethanol (CO+E) and corn oil and dextrose (CO+D) for 2 and 4 week periods. At sacrifice, we measured plasma levels of alpha-tocopherol, 8-isoprostane, thromboxane B2 (TXB2) and 6-ketoprostaglandin F1 alpha (6-KetoPGF1 alpha). Animals fed CO+E had significantly lower concentrations of alpha-tocopherol and higher concentrations of 8 isoprostane at both 2 and 4 weeks. a significant inverse correlation was seen between alpha-tocopherol concentrations and the TXB2: PGF1 alpha ratio (r = 0.72, p < 0.01). A positive correlation was seen between the TXB2: PGF1 alpha ratio and 8 isoprostane levels (r = 0.84, p < 0.001). These results suggest that vitamin E depletion and enhanced lipid peroxidation may affect eicosanoid metabolism in experimental alcoholic liver disease in such a way so as to increase the thromboxane to prostacyclin ration.

Microvascular changes in liver after ischemia-reperfusion injury. Protection with misoprostol

Morphological changes in the hepatic microvasculature were studied in experimentally induced ischemia-reperfusion injury in the rat using a vascular casting technique. Partial hepatic ischemia was induced for 90 min followed by 24 hr reperfusion. Microvascular casting was performed after 24 hr reperfusion by either intraarterial or intravenous infusion of acrylic resin (Mercox). After corrosion of the tissue, the cast was examined by scanning electron microscopy. Casts of normal livers showed good patency with no evidence of unfilled areas. The mean diameter of sinusoids was 14 +/- 3 microns with those in zone 1 slightly smaller than those in zone 3. Liver casts from rats subjected to ischemia and reperfusion resulted in gross disruption of normal architecture. The common characteristics seen in both prograde and retrograde casts were clusters of closed sinusoids around zones 2 and 3 of the liver acini, which resulted in cavities of various sizes. Varicosities were observed in some areas. The mean diameter of sinusoids in areas of patent microvascular structure (10 +/- 2 microns) was significantly smaller compared to those in normal livers (P < 0.001). Misoprostol given at 1 min before reperfusion markedly reduced the microvascular injury. The hepatic microvascular was generally intact with mild focal unfilled areas. The majority of the sinusoids were of normal size and no clusters of blind ending sinusoids were detected. The present study shows that hepatic ischemia-reperfusion results in extensive microvascular injury in the liver. The protective effects of misoprostol against this injury may occur at the vascular level.

Prostaglandin cytoprotection of galactosamine-incubated hepatocytes isolated from young and old rats

The aim of the study was to investigate the effect of aging on cytoprotective properties of prostaglandins. Hepatocytes were obtained by collagenase perfusion of livers of young (4-6 mo) and old (24-28 mo) male Wistar rats. Cells were incubated for 1.5 h in Krebs-Ringer-bicarbonate buffer containing glucose and 3H-leucine in the presence of galactosamine (2.5-100 mM), PGE1, or two prostacyclin analogues: 9 beta-methylcarbacyclin and TRK-100. Cell damage was assessed by decrease in the rate of protein synthesis measured as 3H-leucine incorporation into acid precipitable material, and by increase in lactate dehydrogenase release into the medium. Hepatocytes from old rats were more susceptible to suppression of protein synthesis by GalN than cells of young ones. Preincubation of cells for 15 min with 9MC (41-560 nM) or PGE1 (10-100 nM), but not with TRK-100, before adding 10 mM GalN, led to a partial recovery of protein synthesis in both age groups. GalN increased LDH release and decreased ATP/ADP ratio to a similar extent in hepatocytes of young and old rats; both parameters were not altered by preincubation of cells with PGs. PGE1 and 9MC, but not TRK-100, elevated cyclic AMP content in hepatocytes of young but not old rats. Glucagon and forskolin similarly increased cyclic AMP content in cells of both young and old animals. These in vitro results suggest that PGE1 and some prostacyclin analogues might protect hepatocytes of both young and old rats from chemical damage, and stress the necessity for further research on cyto- and hepato-protection in the elderly.

Misoprostol protection against acetaminophen-induced hepatotoxicity in the rat

The hepatoprotective effects of misoprostol on acetaminophen (APAP)-induced toxicity were studied in the rat. Liver injury was evaluated at 36 hr after APAP administration by measuring serum ornithine carbamoyltransferase (OCT) and alanine aminotransferase (ALT) levels, by using tetranitroblue tetrazolium (TNBT) staining and by histological analysis. After APAP administration, peak serum levels of the drug were detected at 15 min. Liver GSH was depleted from control levels of 448 +/- 48 micrograms/g to 82 +/- 2 micrograms/g (P < 0.01) within 3 hr. Serum ALT levels increased significantly after 16 hr and H&E staining revealed significant hepatic necrosis after 12 hr. Rats treated with misoprostol before and after APAP administration showed reduced OCT and ALT levels at 36 hr of overdose (454 +/- 446 IU/liter and 2571 +/- 2944 IU/liter, respectively) compared to those without misoprostol treatment (1348 +/- 480 IU/liter and 6077 +/- 3025 IU/liter, respectively, P < 0.01). TNBT staining showed a reduced area of damage from 28.6 +/- 22.3% to 7.3 +/- 8.9% (P < 0.01), and H&E staining also showed less extensive hepatic necrosis in rats treated with misoprostol before and after the overdose. In a time sequence study, misoprostol treatment starting within 10 hr of overdose showed the same protective effect as when it was given before and after APAP ingestion. No protection was detected when the treatment was started during the development of hepatic injury. However, misoprostol given when injury was established seemed to be protective. Our results show that misoprostol protects the liver against APAP-induced injury if given within 10 hr of overdose.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of hepatic fibrogenesis: a review of pharmacologic candidates

Therapeutic attempts with anti-fibrotic drugs are still at an experimental stage. The clinical efficacies of most agents listed in Table II have not been proved. Some potential agents, such as colchicine, analogues of PGE, gamma-interferon, inhibitors of prolyl hydroxylase, malotilate, and PUL, must be further evaluated in controlled clinical trials. In addition, almost all anti-fibrotic agents, except HOE 077, are neither liver-nor fibrosis-specific. Some site-directed (targeted) drug delivery systems, drug-loaded vesicle carrier systems, like liposomes and erythrocyte ghosts, which selectively affect the extracellular matrix-producing cells, may improve efficacy and reduce adverse effects if they can be carriers for anti-fibrotic agents. Developments in biochemistry, immunohistochemistry, and molecular biology have considerably advanced our understanding of pathogenic mechanisms of hepatic fibrosis. With the development of available pathologic and serologic markers for ongoing fibrogenesis, experimental and clinical anti-fibrotic trials have become more active. Some therapeutic strategies have chosen targets for interference in collagen metabolism. In vivo inhibition of Ito cell activation has been a focus for the anti-fibrotic studies (70). In the present review an update of pharmacologic intervention in the process of metabolic pathways of collagen, the main extracellular matrices in both interstitium and basement membrane, has been summarized. Several drugs or biochemical agents that act on different steps of collagen synthesis, crosslinking, and breakdown are listed and discussed briefly. Moreover, agents that inhibit other matrix components are also involved in the review.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased prostacyclin production by liver non-parenchymal cells precedes liver injury in experimental alcoholic liver disease

We used the intragastric feeding rat model for alcoholic liver disease to investigate the relationship between prostacyclin and liver injury. Rats were fed the following diets for periods ranging from 1 to 8 weeks: corn oil plus ethanol (CO+E), corn oil plus dextrose (CO+D), saturated fat plus ethanol (SF+E) and saturated fat plus dextrose (SF+D). Prostacyclin production (assessed by 6-ketoprostaglandin F1 alpha) by liver non-parenchymal cells decreased steadily over the 8 week period in animals fed CO+E (liver injury present) whereas in animals fed SF+E (no liver injury) there was no change in prostacyclin production. Plasma levels of 6-ketoprostaglandin F1 alpha were also significantly lower in the CO+E group compared to the other groups studied. We propose that decreased prostacyclin production by liver non-parenchymal cells may contribute to the hepatotoxic effect of ethanol.

Role of eicosanoids in experimental alcoholic liver disease

Based on our previous observations that linoleic acid is an important dietary requirement for the development of liver injury in the intragastric feeding rat model for alcoholic liver disease, we postulated that the conversion of linoleic acid to arachidonic acid and various eicosanoids could be important in the pathogenesis of liver injury. We showed that liver nonparenchymal cell production of thromboxane B2 and leukotriene B4 was higher in rats fed corn oil and ethanol (liver injury model) than in animals fed saturated fat and ethanol (no liver injury). In contrast, prostaglandin E2 levels were lower in the former group. The best correlate of pathologic changes was the plasma level of thromboxane B2. The importance of thromboxanes in alcoholic liver injury is further suggested by the fact that inhibition of thromboxane production is accompanied by amelioration of liver injury.

Prostacyclin (PGI2) protects rat cortical neurons in culture against hypoxia/reoxygenation and glutamate-induced injury

Arachidonic acid and its metabolites are released in brain extracellular fluids as a result of ischemia and may participate in either damaging or protecting neural tissues. This study investigates the neuroprotective effect of prostacyclin (PGI2) on hypoxia (5 h)/reoxygenation (3 h) and on the excitotoxic neurotransmitter, glutamate (10 microM), in rat cortical neuron cultures. At microM concentrations, PGI2 inhibits lactate dehydrogenase release, a cell-injury marker. These results, showing a direct cytoprotective effect of PGI2 on brain cells, reinforce its beneficial properties on vessels and circulating cells in cerebral ischemia.

Transforming growth factor-beta 1 as a signal for induction of cell death by apoptosis

Cell death by apoptosis is a major determinant of growth of normal tissues and tumours. The present study aimed to elucidate signal factors involved in its regulation. Epithelial cells in control liver, during regression of cyproterone acetate induced liver hyperplasia, in liver (pre)neoplasia and in uterus undergoing apoptosis in vivo show immunostaining for transforming growth factor beta 1 (TGF-beta 1) as detected by anti-pre(266-278) TGF-beta 1 antibodies. Positive immunostaining is also seen in a few intact cells of hyperplastic, regressing liver apparently preparing for apoptosis, but is virtually not found in hepatocytes of normal or growing liver nor in cells undergoing death by necrosis. Recombinant latency associated protein (rLAP, dimer of the pro-region non-covalently associated with the mature region) complex and mature TGF-beta 1 induce apoptosis in isolated hepatocytes cultured in vitro. These findings suggest an involvement of TGF-beta 1 in the induction of apoptosis in certain epithelia in vivo.

Paracetamol toxicity and its prevention by cytoprotection with iloprost

In a well-established two phase model of paracetamol toxicity in hamster hepatocytes cell death was accompanied, but not preceded, by a rise in cytosolic free calcium [Ca2+]i. Cell death appears to involve reversible oxidative damage, possibly to the cytoskeleton or mitochondria. In this model low concentrations (10(-8) to 10(-14) M) of iloprost, a stable analogue of prostacyclin, offered protection against the toxic effects of paracetamol. In preliminary studies with a rat liver epithelial cell line transduced with murine P4501A2 the toxicity of paracetamol was attenuated by iloprost. Inhibition of protein synthesis with cycloheximide had no effect on paracetamol toxicity but abolished the cytoprotective effect of iloprost.

Cytoprotection by iloprost against paracetamol-induced toxicity in hamster isolated hepatocytes

1 The ability of iloprost (ZK36374) to protect hamster isolated hepatocytes from the toxic effects of paracetamol and its reactive metabolite N-acetyl-p-benzoquinoneimine (NABQI) was investigated. The cytoprotection provided by iloprost was compared with that of N-acetyl-L-cysteine. 2 Treatment of hepatocytes with either NABQI (0.4 mM) or paracetamol (2 mM) alone resulted in a considerable loss of cell viability, as assessed by trypan blue exclusion or leakage of lactate dehydrogenase, accompanied by an increase in the percentage of viable cells that were blebbed. N-acetyl-L-cysteine (1.25 mM) pretreatment diminished the loss of cell viability and the percentage of blebbed cells resulting from exposure to NABQI or paracetamol, whereas iloprost (10(-16) M to 10(-10) M) pretreatment reduced only the loss of cell viability, not the percentage of viable cells exhibiting blebbing. Pretreatment with N-acetyl-L-cysteine significantly attenuated the depletion by paracetamol of glutathione and decreased the covalent binding of [14C]-paracetamol to cellular proteins, whereas iloprost was without any such effects. 3 The effects of iloprost and N-acetyl-L-cysteine were also investigated by use of a model of paracetamol toxicity in which it is possible to study the biochemical events leading to cell injury separate from the generation of toxic metabolites. Hamster hepatocytes were incubated with paracetamol (4 mM) for 90 min at 37 degrees C during which metabolism of paracetamol occurs with minimal loss of cell viability. Following washing of cells, to remove paracetamol and its metabolites, there was a progressive loss of viability and increase in the percentage of cells exhibiting blebbing when incubated in buffer alone. Addition of either N-acetyl-L-cysteine (1.25 mM) or iloprost (10 14M to 10 -M), following washing, significantly reduced the expected loss of cell viability. Iloprost at concentrations outside this range was without effect.4. Paracetamol toxicity to isolated hepatocytes could be prevented or delayed by treatment with either N-acetyl-L-cysteine or iloprost, but whereas the former prevented or even reversed plasma membrane blebbing with a resultant reduction in the percentage of viable cells that were blebbed, the prostanoid appeared only to delay the progression from plasma membrane blebbing to loss of viability. Hence, the percentage of viable cells that were ultimately blebbed following exposure to paracetamol was not significantly reduced by addition of iloprost.5. Aspirin or ibuprofen exacerbated the loss of viability induced by prior incubation with paracetamol. Thus, there may be a role for endogenous prostaglandins in protecting hepatocytes from paracetamol toxicity.6. Iloprost is cytoprotective without any effect upon toxin metabolism or detoxication. The mechanism of action of iloprost probably does not involve induction of prostaglandin synthesis or activation of the previously-characterized prostacyclin receptor.

The use of 3-hydroxy-2-naphthoic acid hydrazide and Fast Blue B for the histochemical detection of lipid peroxidation in animal tissues--a microphotometric study

The possibility of detecting lipid peroxidation histochemically by means of the 3-hydroxy-2-naphthoic acid/Fast Blue B (NAH-FBB) reaction was evaluated microspectrophotometrically. The procedure was modified in order to prevent exposure of tissue sections to lipid solvents. In fresh rat or mouse liver cryostat sections exposed in vitro to various prooxidant conditions (NADPH-Fe2+, NADPH-ADP/Fe3+, BrCCl3-NADPH), a close correlation was found between the intensity of the NAH-FBB (blue-violet) stain and the amount of malondialdehyde - taken as biochemical index of lipid peroxidation - released in the incubation medium. Stain intensities obtained with NAH-FBB reaction were several fold higher than those obtainable with direct Schiff reaction - a previously used procedure - and better parallelled in time the appearance of lipid peroxidation in tissue. In particular, by means of selective delipidation it was observed that NAH-FBB reaction is remarkably more efficient than Schiff reaction in detecting protein and phospholipid-associated lipid peroxidation-derived carbonyl functions. The ability of the NAH-FBB reaction to reveal lipid peroxidation occurring in tissues in vivo was verified with animals intoxicated with prooxidant toxins, i.e. the haloalkanes bromotrichloromethane and carbon tetrachloride, and the glutathione-depleting agent bromobenzene. In livers from haloalkane-treated rats, NAH-FBB positivity provided with the specific absorption spectrum was observed in centrolobular regions. In bromobenzene-poisoned mice, NAH-FBB positivity with specific absorption was found - besides the liver - also in kidney (tubular epithelium) and lung (bronchiolar epithelium). The use of the NAH-FBB reaction is therefore suggested for the discrimination of cell types undergoing lipid peroxidation in vivo.

Modification of the inhibitory effects of CCl4 on phospholipid and protein biosynthesis by prostacyclin

CCl4 induced cellular injury and its modification by prostacyclin (PGI2) was studied in cultured rat hepatocytes. Biosynthesis of both intracellular and serum proteins and that of phospholipids decreased upon CCl4 treatments (IC50 7.0, 2.5 and 3.2 mM, respectively). After 1 hr exposure of the cells to CCl4, the reductions in the biosynthesis increased further with time. PGI2 treatments (10(-5)-10(-9) M) of the hepatocytes subsequent to CCl4 poisoning resulted in partial recovery from the cell injury evaluated at the fifth hour of the experiment. Optimal effects of PGI2 were found at a concentration of 10(-7)-10(-8) M, while higher and lower concentrations offered less protection. Upon the addition of CCl4 a higher catabolic rate of PIP2 and an increased formation of inositol phosphates were observed. This alteration was shown to precede the defects in the labelling of the major phospholipid components. Furthermore, these changes were circumvented in the presence of PGI2. Thus, PIP2 metabolism appears to be a critical process in the mechanism of this type of cellular injury and its protection by PGI2.