Synthesis and degradation of eicosanoids in primary rat hepatocyte cultures

Kupffer cells alter organic anion transport through multidrug resistance protein 2 in the post-cold ischemic rat liver

Although Kupffer cells (KCs) may play a crucial role in post-cold ischemic hepatocellular injury, their role in nonnecrotic graft dysfunction remains unknown. This study examined reveal the role of KC in post-cold ischemic liver grafts. Rat livers treated with or without liposome-encapsulated dichloromethylene diphosphonate, a KC-depleting reagent, were stored in University of Wisconsin (UW) solution at 4 degrees C for 8 to 24 hours and reperfused while monitoring biliary output and constituents. The ability of hepatocytes to excrete bile was assessed through laser-confocal microfluorography in situ. Cold ischemia-reperfused grafts decreased their bile output significantly at 8 hours without any notable cell injury. This event coincided with impaired excretion of glutathione and bilirubin-IXalpha (BR-IXalpha), suggesting delayed transport of these organic anions. We examined whether intracellular relocalization of multidrug resistance protein-2 (Mrp2) occurred. Kinetic analyses for biliary excretion of carboxyfluorescein, a fluoroprobe excreted through this transporter, revealed significant delay of dye excretion from hepatocytes into bile canaliculi. The KC-depleting treatment significantly attenuated this decline in biliary anion transport mediated through Mrp2 in the 8-hour cold ischemic grafts via redistribution of Mrp2 from the cytoplasm to the canalicular membrane. Furthermore, thromboxane A(2) (TXA(2)) synthase in KC appeared involved as blocking this enzyme improved 5-carboxyfluorescein excretion while cytoplasmic internalization of Mrp2 disappeared in the KC-depleting grafts. In conclusion, KC activation is an important determinant of nonnecrotic hepatocellular dysfunction, jeopardizing homeostasis of the detoxification capacity and organic anion metabolism of the post-cold ischemic grafts.

Plasma iPGE2 and i6-keto PGF1 alpha in the course of liver cirrhosis

Plasma iPGE2 and i6-keto PGF1 alpha were measured with an EIA assay in twenty patients with alcohol-related liver cirrhosis (ALC group) and 13 patients with hepatitis B virus as an etiologic factor of liver cirrhosis (HLC group). Significant increase of both prostanoids was observed irrespectively of the etiology of liver cirrhosis. Their levels increased depending on the degree of liver insufficiency with the highest values in patients classified as Child-Pugh C class. A significant, positive correlation with Child-Pugh score was found regarding PGE2 (r = 0.657; p < 0.001) as well as 6-keto PGF1 alpha (r = 0.736; p < 0.001). Correlation (r = 0.789; p < 0.001) was also observed between levels of both prostaglandins. In conclusion we have shown that plasma iPGE2 and i6-keto PGF1 alpha arise simultaneously with the degree of liver insufficiency, that can be a result of activation of non-parenchymal liver cells accompanying hepatic fibrosis.

Reduction of the concentrations of prostaglandins E2 and F2alpha, and thromboxane B2 in cultured rat hepatocytes treated with the peroxisome proliferator ciprofibrate

Several hypolipidemic drugs, plasticizers and other chemicals induce peroxisome proliferation and hepatic tumors in rodents, but the mechanism by which they induce tumors is not fully understood. Their carcinogenic activity may be related to alterations in gene expression, such as induction of peroxisomal beta-oxidation enzymes or of the cytochrome P450 4A family. These enzymes metabolize lipids, including eicosanoids and their precursor fatty acids. Because eicosanoids likely play a role in the carcinogenic process, alterations in their concentration by xenobiotics may be important in their carcinogenic or promoting activities. In this study we used isolated hepatocytes to study if peroxisome proliferators alter the metabolism of prostaglandins (PG) and thromboxanes (Tx). Isolated rate hepatocytes were cultured for 4 days with 2 concentrations of ciprofibrate (CIP): 100 and 400 microM. Fatty acyl CoA oxidase activities of the 100 and 400 microM CIP treatment groups at the end of the experiment were increased 5.3 and 9.6 times, respectively. TxB2 and PGF2alpha concentrations in cultures treated with CIP were significantly lower than the control at days 3 and 4, whereas a lower concentration of PGE2 was seen at day 4 only. These studies show that PG and Tx concentrations in cultured hepatocytes are lowered by the peroxisome proliferator CIP.

The effect of prostanoids on hepatic bile flow in dogs with normal liver and bile duct cell hyperplasia

Bile flow rates and composition are subject to a wide variety of neural, endocrine and paracrine influences. The effects of these multiple factors may be different in the diseased liver compared to the response produced in the normal liver. As prostanoids may have a therapeutic role in liver disease it was intended to evaluate the effects of two principal therapeutic prostanoids, prostaglandin E2 and prostacyclin, on bile flow in dogs with a normal liver and in dogs with hepatotoxin-induced liver injury. Initially, in awake animals with chronic biliary and gastric fistulas the bile flow response to prostaglandin E2 and prostacyclin was evaluated and compared to the response produced by bile salt infusion alone and to that produced by the standard choleretic hormones, secretin and glucagon. The animals were then fed alpha-naphthylisothiocyanate (ANIT) and the studies repeated. ANIT is a hepatoxin that produces bile duct cell hyperplasia which was confirmed in dogs by demonstrating that ANIT increased [3H]thymidine incorporation by isolated canine bile duct cells. In normal dogs, the prostanoids, secretin, and glucagon increased hepatic bile flow. 10 days of ANIT feeding produced a hypercholeresis. While secretin was able to stimulate the hyperplastic biliary epithelium and increase bile flow over values produced by the hyperplastic biliary epithelium alone, neither prostaglandin E2, prostacyclin, or glucagon appeared to stimulate the hyperplastic biliary epithelium. As ANIT produced evidence of cholestasis and hepatocellular damage, only secretin would seem to have a potential therapeutic role in increasing bile flow in cholestatic liver disorders associated with bile duct cell hyperplasia.

Early enteral feeding in postsurgical cancer patients. Fish oil structured lipid-based polymeric formula versus a standard polymeric formula

OBJECTIVES

The authors compared the safety, gastrointestinal tolerance, and clinical efficacy of feeding an enteral diet containing a fish oil/medium-chain triglyceride structured lipid (FOSL-HN) versus an isonitrogenous, isocaloric formula (O-HN) in patients undergoing major abdominal surgery for upper gastrointestinal malignancies.

SUMMARY BACKGROUND DATA

Previous studies suggest that feeding with n-3 fatty acids from fish oil can alter eicosanoid and cytokine production, yielding an improved immunocompetence and a reduced inflammatory response to injury. The use of n-3 fatty acids as a structured lipid can improve long-chain fatty acid absorption.

METHODS

This prospective, blinded, randomized trial was conducted in 50 adult patients who were jejunally fed either FOSL-HN or O-HN for 7 days. Serum chemistries, hematology, urinalysis, gastrointestinal complications, liver and renal function, plasma and erythrocyte fatty acid analysis, urinary prostaglandins, and outcome parameters were measured at baseline and on day 7. Comparisons were made in 18 and 17 evaluable patients based a priori on the ability to reach a tube feeding rate of 40 mL/hour.

RESULTS

Patients receiving FOSL-HN experienced no untoward side effects, significant incorporation of eicosapentaenoic acid into plasma and erythrocyte phospholipids, and a 50% decline in the total number of gastrointestinal complications and infections compared with patients given O-HN. The data strongly suggest improved liver and renal function during the postoperative period in the FOSL-HN group.

CONCLUSION

Early enteral feeding with FOSL-HN was safe and well tolerated. Results suggest that the use of such a formula during the postoperative period may reduce the number of infections and gastrointestinal complications per patient, as well as improve renal and liver function through modulation of urinary prostaglandin levels. Additional clinical trials to fully quantify clinical benefits and optimize nutritional support with FOSL-HN should be undertaken.

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.

The contribution of hepatocytes to prostaglandin synthesis in rat liver

The contribution of hepatocytes to liver prostaglandin (PG) synthesis Is not clear. We compared prostaglandin synthesis in homogenates of whole liver, freshly isolated hepatocytes, and mixed non-parenchymal cells from the same rat livers, and optimized the assay. Whole liver homogenates made 27.2 +/- 7.1 mg PGE2/mg protein/5 min (+/- SEM, n = 4 livers). Hepatocyte homogenates made 39 +/- 9% as much PGE2/mg protein as did the matched whole livers. Non-parenchymal cell homogenates made slightly more PGE2 than whole liver, but much more PGD2. Subsequent studies showed that fresh hepatocyte suspensions contain significant contamination with non-parenchymal cells. Homogenates from ricin-purified hepatocyte monolayers made at least half as much PGE2 as did conventional monolayers. However, taking cellular purity into account, hepatocytes must contain much less than a third of liver cyclooxygenase activity.

Stimulation of hepatocyte DNA synthesis by prostaglandin E2 and prostaglandin F2 alpha: additivity with the effect of norepinephrine, and synergism with epidermal growth factor

Previous data obtained in vivo and in vitro suggest that both prostaglandins (PGs) and catecholamines may have a role in promoting hepatocyte proliferation, and PGE2 and PGF2 alpha have also been implicated as mediators of the mitogenic actions of epidermal growth factor (EGF) (and transforming growth factor alpha [TGF alpha]). We have studied the effects of PGs and norepinephrine on DNA synthesis in serum-free primary cultures of rat hepatocytes, and compared the PG effects with those of norepinephrine. PGE2, PGF2 alpha, PGD2, and the synthetic analog dimethyl-PGE2 markedly enhanced the DNA synthesis. A more quantitative analysis of the effects of PGE2 and PGF2 alpha on the DNA synthesis, in the presence and absence of EGF, indicated that these PGs interacted in an essentially multiplicative manner with the effect of EGF. The effects of PGE2 and PGF2 alpha showed almost complete additivity with the stimulation of DNA synthesis produced by maximally effective concentrations of norepinephrine. The data suggest a) that PGE2 and PGF2 alpha facilitate and synergize with, rather than mediate, the actions of EGF in hepatocytes, and b) that this effect of the PGs occurs by mechanisms that are at least partly distinct from those of norepinephrine.

Eicosanoids released following inhibition of the endoplasmic reticulum Ca2+ pump stimulate Ca2+ efflux in the perfused rat liver

In the isolated perfused rat liver 2,5-di(tert-butyl)hydroquinone (tBuHQ), a selective inhibitor of the endoplasmic reticulum Ca2+ pump, induces a prolonged glucose output and stimulates Ca2+ efflux. The present study shows that tBuHQ depleted the hormone-sensitive Ca2+ pool in the perfused liver, abolishing the vasopressin- or phenylephrine-induced Ca2+ efflux. The effects of tBuHQ were reversible, since the response to these agonists gradually returned within 1 hr of perfusion, and protein synthesis was not required for this recovery. Since tBuHQ does not cause Ca2+ efflux from isolated hepatocytes, we examined the mechanism responsible for the tBuHQ-induced Ca2+ efflux observed in the intact liver. The cyclooxygenase inhibitor indomethacin prevented the Ca2+ extrusion stimulated by tBuHQ, but not that induced by vasopressin. During infusion of tBuHQ there was a 9-fold increase in the concentration of thromboxane B2 in the perfusate. The Ca2+ efflux response to tBuHQ was inhibited by the thromboxane/prostaglandin endoperoxide receptor antagonist, L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) in the absence of any effect on thromboxane B2 release. Thus, the inhibition of the endoplasmic reticulum Ca2+ pump by tBuHQ results in a rise in the cytosolic Ca2+ concentration in non-parenchymal cells, leading to the formation of cyclooxygenase products. The released eicosanoids, in turn, stimulate Ca2+ efflux from hepatocytes.