Misoprostol hepatoprotection against ischemia-reperfusion-induced liver injury in the rat

Effect of prostaglandin E-1 on Wisconsin University and histidine-tryptophan-ketoglutarate preservation solutions on preservation injury of the perfused liver

BACKGROUND

The aim of this study was to investigate the effects of prostaglandin E-1 (PGE-1) on preservation injury in livers perfused with the University of Wisconsin (UW) or histidine-tryptophan-ketoglutarate (HTK) solutions.

MATERIALS AND METHODS

Five groups each including six rats included. Ringer's lactate RL (group 1), HTK (group 2), HTK + PGE-1 (group 3), UW (group 4), or UW PGE-1 (group 5). Liver tissue and preservation fluid samples were obtained from the perfused lives for pathological and biochemical examinations respectively at 0, 6 and 12 hours.

RESULTS

Upon biochemical examination, aspartate aminotrasnferase and alanine aminotransferase values were highest among the group with RL solution and lowest with PGE-1. Liver structure was found to be damaged immediately after RL solution, whereas it was preserved in the other four groups. Fewer cellular changes were reported at the end of 12 hours in the groups administered PGE-1 compared with the other groups.

CONCLUSIONS

PGE-1 when applied before preservation protected liver functions, decreased pathologic injury, and delayed changes that occur under cold ischemic conditions.

Identification and preliminary validation of novel biomarkers of acute hepatic ischaemia/reperfusion injury using dual-platform proteomic/degradomic approaches

Hepatic ischaemia/reperfusion (I/R), a major cause of liver damage associated with multiple trauma, haemorrhagic and septic shock, and liver transplantation, contributes significantly to multiple organ failure. Development of novel sensitive biomarkers that detect early stages of liver damage is vital for effective management and treatment of ischaemic liver injury. By using high-throughput immunoblotting and cation-anion exchange chromatography/reversed-phase liquid chromatography-tandem mass-spectrometry, we identified several hepatic proteins, including argininosuccinate synthase (ASS) and estrogen sulfotransferase (EST-1), which were degraded in the liver and rapidly released into circulation during I/R injury. ASS accumulated in serum within 10 min, reached a steady state at 30 min, and persisted up until 3 h after reperfusion following 30 min of total hepatic ischaemia. EST-1 appeared rapidly in blood and attained maximum within 1 hour followed by a decline at 3 h of reperfusion. No ASS or EST-1 protein was detected in serum of control or sham operated rats. ASS and EST-1 exhibited greater sensitivity and specificity toward I/R liver injury as compared with alanine aminotransferase (ALT), an established marker of hepatocellular necrosis. In contrast, serum ASS and EST-1 were undetectable in rats with chronic alcoholic liver disease, while the levels of ALT protein were significantly increased. In addition, ASS, but not EST-1 or ALT accumulated in blood only 6 h after treatment with hepatotoxic combination of lipopolysaccharide and D-galactosamine. These data demonstrate the utility of ASS and EST-1 as novel sensitive and specific biomarkers of acute liver ischaemic injury for prospective clinical studies.

Misoprostol therapeutics revisited

Misoprostol, a prostaglandin E1 analog, is a racemate of four stereoisomers. On administration it rapidly de-esterifies to its active form, misoprostolic acid. Misoprostolic acid is 85% albumin bound and has a half-life of approximately 30 minutes. It is excreted in urine as inactive metabolites. No significant drug interactions have been reported. Besides its gastrointestinal protective and uterotonic activities, misoprostol regulates various immunologic cascades. It inhibits platelet-activating factor and leukocyte adherence, and modulates adhesion molecule expression. It protects against gut irradiation injury, experimental gastric cancer, enteropathy, and constipation. It improves nutrient absorption in cystic fibrosis. Misoprostol has utility in acetaminophen and ethanol hepatotoxicity, hepatitis, and fibrosis. It is effective in asthmatics and aspirin-sensitive asthmatic and allergic patients. It lowers cholesterol and severity of peripheral vascular diseases, prolongs survival of cardiac and kidney transplantation, synergizes cyclosporine, and protects against cyclosporine-induced renal damage. It works against drug-induced renal damage, interstitial cystitis, lupus nephritis, and hepatorenal syndrome. It is useful in periodontal disease and dental repair. Misoprostol enhances glycosoaminoglycan synthesis in cartilage after injury. It prevents ultraviolet-induced cataracts and reduces intraocular pressure in glaucoma and ocular hypertension. It synergizes antiinflammatory and analgesic effects of diclofenac or colchicine and has been administered to treat trigeminal neuralgic pain. It reduces chemotherapy-induced hair loss and recovery time from burn injury, and is effective in treating sepsis, multiple sclerosis, and pancreatitis.

Present status of hepatoprotectants

Perpetual exposure of liver to xenobiotics and therapeutic agents leads to toxic manifestations of a complex and diverse nature. Not a single curative therapeutic agent has been found so far which could provide lasting remedy to patients suffering from hepatic disorders. In fact, the remedies available in the modern system of medicine provide only symptomatic relief without any significant changes on the disease process. Moreover, their use is associated with severe side effects and chances of relapses. Except some natural products claimed to be effective, no safe synthetic product is yet available for the management of hepatic disorders. Lack of effective, least toxic and curative hepatoprotectants made the task difficult to discover newer drugs. This review is an attempt to provide an overall view of the development of synthetic and natural products as hepatoprotective agents.

The mechanism of hepatic graft protection against reperfusion injury by prostaglandin E1

The purpose of this study was to evaluate the effect of prostaglandin E1 (PGE1) on protecting against hepatic endothelial cell damage and increasing graft viability after cold preservation and reperfusion, using an isolated perfused rat liver (IPRL) model. The grafts were divided into three groups, according to the cold preservation time and PGE1 administration, namely: 4h preservation (group 1, n = 9), 6h preservation (group 2, n = 9), and 6h preservation followed by PGE1 infusion (group 3, n = 9). After cold storage, the grafts were put on the recirculating IPRL system, then reperfused for 120 min at 37 degrees C with oxygenated Krebs-Henseleit buffer containing hyaluronic acid (HA). To examine the function of the sinusoidal endothelial cells and hepatocytes, serial measurements of HA, tumor necrosis factor-alpha (TNFalpha), thromboxane B2 (TXB2), acid phosphatase, and conventional parameters in the perfusate were made. After perfusion, the trypan blue exclusion test was performed to assess the presence of any microscopic sinusoidal lining cell damage. In group 3, the bile output and HA clearance were significantly greater, while glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, TNFalpha, TXB2, and acid phosphatase in the perfusate were significantly lower than in group 2. Histologically, less endothelial cell damage and hepatocyte damage than in group 2 was also confirmed. These results therefore suggest that the improvement of hepatic graft viability by PGE1 administration is mainly due to sinusoidal endothelial cell protection.

Protective effect of prostaglandin E1 against ischemia/reperfusion-induced liver injury: results of a prospective, randomized study in cirrhotic patients undergoing subsegmentectomy

BACKGROUND/AIMS

The cytoprotective effects of prostaglandin E1 on livers suffering from ischemia/reperfusion injury in the clinical setting are unproved. These effects were examined, focusing on inflammatory cytokine and nitric oxide metabolism.

METHODS

Twenty-four cirrhotic patients with hepatocellular carcinoma undergoing subsegmentectomy under ischemia induced only by Pringle's maneuver were divided into two groups (patients given prostaglandin E1 by injection and untreated controls) and postoperative results were compared. Peripheral blood was taken perioperatively and the plasma aminotransferase, cytokines and nitrate/nitrite levels of the two groups were compared. Two liver specimens were taken from each patient, one before ischemia and the other after hepatectomy, and the levels of inducible nitric oxide synthase and cytokine mRNAs and proteins were analyzed.

RESULTS

Although no apparent differences were recognized in postoperative complications or duration of postoperative hospital stay between the groups, the perioperative plasma aminotransferase level was significantly lower in the prostaglandin E1 group. Significant differences were also seen in interleukin-6 and nitrate plasma levels during the observation period and the interleukin-6 protein levels in the liver supernatants after hepatectomy in the two groups. In contrast, no significant differences were apparent between the interleukin-1 beta and tumor necrosis factor-alpha plasma levels of the two groups. The corrected fluorescence activities of interleukin-6 and inducible nitric oxide synthase mRNAs in the liver after hepatectomy correlated significantly. No interleukin-1 beta or tumor necrosis factor-alpha mRNAs or proteins were detected.

CONCLUSIONS

Prostaglandin E1 exerted hepatoprotective effects on livers suffering from ischemia/reperfusion injury, and interleukin-6 might play an important role in these effects.

Attenuation of ischemic liver injury by prostaglandin E1 analogue, misoprostol, and prostaglandin I2 analogue, OP-41483

BACKGROUND

Prostaglandin has been reported to have protective effects against liver injury. Use of this agent in clinical settings, however, is limited because of drug-related side effects. This study investigated whether misoprostol, prostaglandin E1 analogue, and OP-41483, prostaglandin I2 analogue, which have fewer adverse effects with a longer half-life, attenuate ischemic liver damage.

STUDY DESIGN

Thirty beagle dogs underwent 2 hours of hepatic vascular exclusion using venovenous bypass. Misoprostol was administered intravenously for 30 minutes before ischemia and for 3 hours after reperfusion. OP-41483 was administered intraportally for 30 minutes before ischemia (2 microg/kg/min) and for 3 hours after reperfusion (0.5 microg/kg/min). Animals were divided into five groups: untreated control group (n=10); high-dose misoprostol (total 100 microg/kg) group (MP-H, n=5); middle-dose misoprostol (50 microg/kg) group (MP-M, n=5); low-dose misoprostol (25 microg/kg) group (MP-L, n=5); and OP-41483 group (OP, n=5). Animal survival, hepatic tissue blood flow (HTBF), liver function, and histology were analyzed.

RESULTS

Two-week animal survival rates were 30% in control, 60% in MP-H, 100% in MP-M, 80% in MP-L, and 100% in OP. The treatments with prostaglandin analogues improved HTBF, and attenuated liver enzyme release, adenine nucleotrides degradation, and histologic abnormalities. In contrast to the MP-H animals that exhibited unstable cardiovascular systems, the MP-M, MP-L, and OP animals experienced only transient hypotension.

CONCLUSIONS

These results indicate that misoprostol and OP-41483 prevent ischemic liver damage, although careful dose adjustment of misoprostol is required to obtain the best protection with minimal side effects.

Fish oil-supplemented feeding does not attenuate warm liver ischemia and reperfusion injury in the rat

Liver ischemia and reperfusion injury is mediated by oxygen free radicals, cytokines, and prostanoids produced by Kupffer cells and infiltrating neutrophils. Fish oil-supplemented diets alter membrane phospholipid composition and modify prostanoids and cytokine production in response to ischemia and reperfusion. This study tested the hypothesis that a fish oil-supplemented diet would attenuate warm liver ischemia and reperfusion injury in the rat. Male Sprague-Dawley rats were fed Vital HN supplemented with either fish oil (FO) or corn oil (CO) by the continuous duodenal infusion for 5 days. Total dietary fat (26% of total calories), caloric intake (70 cal/day), and volume (60 ml/day) were identical between two groups. Plasma eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels increased significantly in rats fed fish oil (0 to 16.3% for EPA and 2 to 12% for DHA). Liver histology was similar in both groups before ischemia. On Day 6, rats were subjected to 60 min of reversible hepatic ischemia. Plasma TNF levels, 1 and 24 hr after reperfusion, were not different between FO and CO rats. Liver injury assessed by bile flow, histology, plasma ALT, and bile glutathione efflux did not differ between groups. We conclude that our fish oil-supplemented enteral diet does not attenuate warm liver ischemia and reperfusion injury in rats.

Splenectomy-reduced hepatic injury induced by ischemia/reperfusion in the rat

In the present study, we investigated the role of the spleen in experimental hepatic ischemia/reperfusion in the rat. After a 90-min period of ischemia in the left and middle hepatic lobes, the ischemia was released and the liver was reperfused for up to 24 h. Plasma alanine aminotransferase reached a peak 3 h after the onset of reperfusion, and gradually decreased thereafter. A histological examination revealed evidence of hepatocellular necrosis and degeneration, especially 24 h after the onset of reperfusion. In addition, there was a noticeable accumulation of polymorphonuclear cells in the liver following ischemia/reperfusion. A splenectomy performed just prior to ischemia/reperfusion reduced both biochemical and histological hepatocellular injury. The number of polymorphonuclear cells in the liver following ischemia/reperfusion was significantly reduced in rats subjected to splenectomy, suggesting that the increase in polymorphonuclear cells may contribute to liver injury. The number of mononuclear cells also increased in the marginal zones of the spleen following ischemia/reperfusion, and appeared to be derived from the splenic monocyte/macrophage population, based on immunohistochemical studies. The spleen plays an important role in the pathogenesis of hepatic ischemia/reperfusion injury and the splenic monocyte/ macrophage population contributes to liver damage.

The influence of prostaglandin E1 on platelet adherence and injury in preserved rat liver allografts

We have previously shown that part of the injury sustained by cold-preserved livers on reperfusion is the consequence of platelet adhesion to sinusoidal endothelium. The purpose of the present study was to determine whether prostaglandin E1 (PGE1) can reduce the injury and if so, how to maximize this beneficial effect. Rat livers were cold-preserved in University of Wisconsin solution for 30 hours then subjected to 1-hour warm ischemia after which they were reperfused at 37 degrees C with oxygenated Krebs-Henseleit solution with or without isolated platelets. PGE1 was used to treat the donor liver during harvesting, cold preservation, and reperfusion. In some studies, PGE1 was used to pretreat platelets before exposing them to the liver, and in other studies, both liver and platelets were treated. Pretreatment of platelets with paraformaldehyde, which inactivates them, or ADP, which activates them, was also studied. Treatment of livers with PGE1 significantly decreased preservation injury when livers were reperfused in the absence of platelets. However, when platelets were added to the perfusate, prior treatment of the liver with PGE1 had relatively minor beneficial effects. Pretreatment of platelets alone with PGE1 was also beneficial, but again the effect was small. However, when both liver and platelets were treated with PGE1 there was a highly significant decrease in the extent of liver injury and platelet adhesion. Perfusate transaminase levels were lower, bile flow was improved, and histologically, livers appeared less injured. Pretreatment of platelets with paraformaldehyde produced similar results to pretreatment with PGE1. When platelets were preactivated with adenosine diphosphate, extensive hepatic injury occurred upon reperfusion despite PGE1 treatment of the liver. PGE1 can lessen preservation-reperfusion injury impressively when administered to both liver and platelets but has little effect when platelets have been preactivated.

Hepatic ischemia-reperfusion injury modification during liver surgery in rats: pretreatment with nifedipine or misoprostol

The aim of the study was to determine if pretreatment with misoprostol (a prostaglandin analogue) or nifedipine (a calcium antagonist), know protectants of the whole liver, would ameliorate the ischemia-reperfusion injury (IRI) of resected liver associated with vascular occlusion. Male Wistar rats were allocated to 5 groups (n = 20 each group): sham-operated, liver resection only, liver resection plus pretreatment with 0.1 mg/kg misoprostol, 10 mg/kg, or 2 mg/kg nifedipine during the 3 days before IRI with liver resection. Fifteen percent of the liver was made ischemic by 30-minute continuous vascular occlusion, and the remaining 85% nonischemic liver was resected. The model was designed to have survival of the rats so that liver function could be studied over 3 weeks. Seventeen of 20 control resection rats survived indicating a suitable model for study. The bilirubin level was reduced by 25% on postoperative days 3 through 23 with misoprostol. The serum alanine aminotransferase (ALT) peak was significantly lower on day 1 with misoprostol and high-dose nifedipine (both reduced to half the control resection value). There was a modest but significant reduction of serum alkaline phosphatase (SAP) for low-dose nifedipine on days 1, 2, and 23. Prothrombin had a lower peak and lower values on days 1 through 4 with misoprostol. Liver histological changes were minor, being cytoplasmic vacuolization only, and was slightly more marked in the nifedipine groups. Preoperative misoprostol 0.1 mg/kg and nifedipine 10 mg/kg each ameliorate the IRI associated with liver resection, as measured by liver function tests. Different aspects of liver function were altered by the different agents. These results justify initiating a trial for human liver resections.

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.

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)