Maternal nutrient metabolism in the liver during pregnancy

The liver plays pivotal roles in nutrient metabolism, and correct hepatic adaptations are required in maternal nutrient metabolism during pregnancy. In this review, hepatic nutrient metabolism, including glucose metabolism, lipid and cholesterol metabolism, and protein and amino acid metabolism, is first addressed. In addition, recent progress on maternal hepatic adaptations in nutrient metabolism during pregnancy is discussed. Finally, the factors that regulate hepatic nutrient metabolism during pregnancy are highlighted, and the factors include follicle-stimulating hormone, estrogen, progesterone, insulin-like growth factor 1, prostaglandins fibroblast growth factor 21, serotonin, growth hormone, adrenocorticotropic hormone, prolactin, thyroid stimulating hormone, melatonin, adrenal hormone, leptin, glucagon-like peptide-1, insulin glucagon and thyroid hormone. Our vision is that more attention should be paid to liver nutrient metabolism during pregnancy, which will be helpful for utilizing nutrient appropriately and efficiently, and avoiding liver diseases during pregnancy.

Bile acids as putative social signals in Mozambique tilapia (Oreochromis mossambicus)

Chemical cues provide potential mates with information about reproductive status and resource-holding potential. In the Mozambique tilapia (Oreochromis mossambicus), males can distinguish female reproductive status through chemical cues, and accessibility of males to females depends on their position in the hierarchy, determined in part by chemical cues. Here, we hypothesized that tilapia faecal cues are attractive to conspecifics once released into the water. C18 solid-phase extracts of faeces from dominant males and pre-ovulatory females evoked stronger olfactory epithelium electrical responses (EOG) than, respectively, subordinate males and post-spawning females. Mass spectrometry of the reverse-phase C18 high-performance liquid chromatography fractions of these extracts with highest EOG, identified by amino acids and bile acids. Faeces from pre-ovulatory females contain significantly higher concentrations of cholic acid (CA) and taurocholic acid (TCH) than both post-spawning females and males. A pool of amino acids had no effect on aggression or attraction in males. However, males were attracted to the scent of pre-ovulatory female faeces, as well as CA and TCH, when applied separately. This attraction was accompanied by increased digging behaviour compared to the odour of post-spawning females. CA and TCH exert their action through separate receptor mechanisms. These findings are consistent with a role for faeces - and bile acids therein - in chemical communication in this species, acting as an attractant for males to reproductive females.

A possible role for ketorolac in the management of increased biliary drain output

Percutaneous transhepatic biliary drainage is used to achieve biliary decompression in jaundiced patients with biliary obstruction. High drain output >2000 mL/day is rare, and can cause dehydration and electrolyte derangements, without effective treatments. We present the first patient, to our knowledge, who reacted to the use of the analgesic ketorolac with progressive reduction in biliary output, in the setting of malignant biliary obstruction from duodenal adenocarcinoma.

Intercellular crosstalk of liver sinusoidal endothelial cells in liver fibrosis, cirrhosis and hepatocellular carcinoma

Intercellular crosstalk among various liver cells plays an important role in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Capillarization of liver sinusoidal endothelial cells (LSECs) precedes fibrosis and accumulating evidence suggests that the crosstalk between LSECs and other liver cells is critical in the development and progression of liver fibrosis. LSECs dysfunction, a key event in the progression from fibrosis to cirrhosis, and subsequently obstruction of hepatic sinuses and increased intrahepatic vascular resistance (IHVR) contribute to development of portal hypertension (PHT) and cirrhosis. More importantly, immunosuppressive tumor microenvironment (TME), which is closely related to the crosstalk between LSECs and immune liver cells like CD8+ T cells, promotes advances tumorigenesis, especially HCC. However, the connections within the crosstalk between LSECs and other liver cells during the progression from liver fibrosis to cirrhosis to HCC have yet to be discussed. In this review, we first summarize the current knowledge of how different crosstalk between LSECs and other liver cells, including hepatocytes, hepatic stellate cells (HSCs), macrophoges, immune cells in liver and extra cellular matrix (ECM) contribute to the physiological function and the progrssion from liver fibrosis to cirrhosis, or even to HCC. Then we examine current treatment strategies for LSECs crosstalk in liver fibrosis, cirrhosis and HCC.

Fermentable fibers induce rapid macro- and micronutrient depletion in Toll-like receptor 5-deficient mice

Functional fermentable fibers are considered essential for a healthy diet. Recently, we demonstrated that gut microbiota dysbiotic mice fed an inulin-containing diet (ICD) developed hepatocellular carcinoma (HCC) within 6 mo. In particular, a subset of Toll-like receptor 5-deficient (T5KO) mice prone to HCC exhibited rapid onset of hyperbilirubinemia (HB) and cholemia; these symptoms provide rationale that ICD induces cholestasis. Our objective in the present study was to determine whether inulin-fed T5KO-HB mice exhibit other known consequences of cholestasis, including essential fatty acid and fat-soluble vitamin deficiencies. Here, we measured hepatic fatty acids and serum vitamin A and D levels from wild-type (WT), T5KO low bilirubin (LB) and T5KO-HB mice fed ICD for 4 wk. Additionally, hepatic RNAseq and proteomics were performed to ascertain other metabolic alterations. Compared with WT and T5KO-LB, T5KO-HB mice exhibited steatorrhea, i.e., ~50% increase in fecal lipids. This could contribute to the significant reduction of linoleate in hepatic neutral lipids in T5KO-HB mice. Additionally, serum vitamins A and D were ~50% reduced in T5KO-HB mice, which was associated with metabolic compromises. Overall, our study highlights that fermentable fiber-induced cholestasis is further characterized by depletion of macro-and micronutrients.NEW & NOTEWORTHY Feeding a dietary, fermentable fiber diet to a subset of Toll-like receptor 5 deficient (T5KO) mice induces early onset hyperbilirubinemia and cholemia that later manifests to hepatocellular carcinoma (HCC). Our study highlights that fermentable fiber-induced cholestasis is characterized with modest macro- and micronutrient deficiencies that may further contribute to hepatic biliary disease. Compared with chemical induction, immunization, surgery, or genetic manipulation, these findings provide a novel approach to study the cholestatic subtype of HCC.

Chronic Methylmercury Exposure Induces Production of Prostaglandins: Evidence From A Population Study and A Rat Dosing Experiment

Methylmercury (MeHg) is a well-known environmental neurotoxicant affecting millions worldwide who consume contaminated fishes and other food commodities. Exposure to MeHg has been shown to associate positively with some chronic diseases including cardiovascular diseases, but the mechanism is poorly characterized. MeHg had been shown to affect prostaglandin (PG) regulations in in vitro studies, but neither in vivo nor human studies investigating the effects of MeHg on PG regulations has been reported. Thus, the current study aimed to investigate the association between MeHg exposure and serum PG concentrations in a cross-sectional study among human adults followed by a validation investigation on the cause-effect relationship using a rat model. First, a total of 121 women were recruited from two cities: Wanshan and Leishan in Guizhou, China. Statistical analysis of the human data showed a positive association between blood total mercury (THg) levels and serum concentrations of PGF2α, 15-deoxy-PGJ2, and PGE2 after adjusting for site effects. In the animal study, adult female Sprague-Dawley rats were dosed with 40 μg MeHg/kg body weight/day for 12 weeks. Serum 15-deoxy-PGJ2 and 2,3 d-6-keto-PGF1α concentrations were found to increase significantly after 6 and 10 weeks of MeHg dosing, respectively, while serum PGF2α concentration increased significantly after 12 weeks of MeHg dosing. Combined results of our human and rat studies have shown that chronic MeHg exposure induced dysregulation of PG metabolism. As PGs are a set of mediators with very diverse functions, its abnormal production may serve as the missing mechanistic link between chronic MeHg exposure and various kinds of associated clinical conditions including neurodegeneration and cardiovascular diseases.

Dietary fat and gut microbiota interactions determine diet-induced obesity in mice

Objective

Gut microbiota may promote positive energy balance; however, germfree mice can be either resistant or susceptible to diet-induced obesity (DIO) depending on the type of dietary intervention. We here sought to identify the dietary constituents that determine the susceptibility to body fat accretion in germfree (GF) mice.

Methods

GF and specific pathogen free (SPF) male C57BL/6N mice were fed high-fat diets either based on lard or palm oil for 4 wks. Mice were metabolically characterized at the end of the feeding trial. FT-ICR-MS and UPLC-TOF-MS were used for cecal as well as hepatic metabolite profiling and cecal bile acids quantification, respectively. Hepatic gene expression was examined by qRT-PCR and cecal gut microbiota of SPF mice was analyzed by high-throughput 16S rRNA gene sequencing.

Results

GF mice, but not SPF mice, were completely DIO resistant when fed a cholesterol-rich lard-based high-fat diet, whereas on a cholesterol-free palm oil-based high-fat diet, DIO was independent of gut microbiota. In GF lard-fed mice, DIO resistance was conveyed by increased energy expenditure, preferential carbohydrate oxidation, and increased fecal fat and energy excretion. Cecal metabolite profiling revealed a shift in bile acid and steroid metabolites in these lean mice, with a significant rise in 17β-estradiol, which is known to stimulate energy expenditure and interfere with bile acid metabolism. Decreased cecal bile acid levels were associated with decreased hepatic expression of genes involved in bile acid synthesis. These metabolic adaptations were largely attenuated in GF mice fed the palm-oil based high-fat diet. We propose that an interaction of gut microbiota and cholesterol metabolism is essential for fat accretion in normal SPF mice fed cholesterol-rich lard as the main dietary fat source. This is supported by a positive correlation between bile acid levels and specific bacteria of the order Clostridiales (phylum Firmicutes) as a characteristic feature of normal SPF mice fed lard.

Conclusions

In conclusion, our study identified dietary cholesterol as a candidate ingredient affecting the crosstalk between gut microbiota and host metabolism.

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Cholesterol-based but not plant sterol-based high-fat diet protects germfree (GF) mice from diet-induced obesity (DIO).

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DIO resistant GF mice show preferential carbohydrate oxidation, higher energy expenditure and energy and fat excretion.

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DIO resistance in GF mice is accompanied by increased steroid hormone levels but decreased bile acid levels in the cecum.

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Substrate oxidation and fat excretion in DIO resistant GF mice is linked to decreased hepatic Cyp7a1 and Nr1h4 expression.

Intestinal microbiota in metabolic diseases: from bacterial community structure and functions to species of pathophysiological relevance

The trillions of bacterial cells that colonize the mammalian digestive tract influence both host physiology and the fate of dietary compounds. Gnotobionts and fecal transplantation have been instrumental in revealing the causal role of intestinal bacteria in energy homeostasis and metabolic dysfunctions such as type-2 diabetes. However, the exact contribution of gut bacterial metabolism to host energy balance is still unclear and knowledge about underlying molecular mechanisms is scant. We have previously characterized cecal bacterial community functions and host responses in diet-induced obese mice using omics approaches. Based on these studies, we here discuss issues on the relevance of mouse models, give evidence that the metabolism of cholesterol-derived compounds by gut bacteria is of particular importance in the context of metabolic disorders and that dominant species of the family Coriobacteriaceae are good models to study these functions.

Bile formation and secretion

Bile is a unique and vital aqueous secretion of the liver that is formed by the hepatocyte and modified down stream by absorptive and secretory properties of the bile duct epithelium. Approximately 5% of bile consists of organic and inorganic solutes of considerable complexity. The bile-secretory unit consists of a canalicular network which is formed by the apical membrane of adjacent hepatocytes and sealed by tight junctions. The bile canaliculi (∼1 μm in diameter) conduct the flow of bile countercurrent to the direction of portal blood flow and connect with the canal of Hering and bile ducts which progressively increase in diameter and complexity prior to the entry of bile into the gallbladder, common bile duct, and intestine. Canalicular bile secretion is determined by both bile salt-dependent and independent transport systems which are localized at the apical membrane of the hepatocyte and largely consist of a series of adenosine triphosphate-binding cassette transport proteins that function as export pumps for bile salts and other organic solutes. These transporters create osmotic gradients within the bile canalicular lumen that provide the driving force for movement of fluid into the lumen via aquaporins. Species vary with respect to the relative amounts of bile salt-dependent and independent canalicular flow and cholangiocyte secretion which is highly regulated by hormones, second messengers, and signal transduction pathways. Most determinants of bile secretion are now characterized at the molecular level in animal models and in man. Genetic mutations serve to illuminate many of their functions.

Improved outcome in neonatal short bowel syndrome using parenteral fish oil in combination with ω-6/9 lipid emulsions

BACKGROUND

Newborn infants with short bowel syndrome (SBS) represent a high-risk group of developing intestinal failure-associated liver disease (IFALD), which may be fatal. However, infants have a great capacity for intestinal growth and adaptation if IFALD can be prevented or reversed. A major contributing factor to IFALD may be the soybean oil-based intravenous lipid emulsions used since the introduction of parenteral nutrition (PN) 40 years ago.

METHODS

This retrospective study compares the outcome in 20 neonates with SBS treated with parenteral fish oil (Omegaven) in combination with ω-6/9 lipid emulsions (ClinOleic) with the outcome in a historical cohort of 18 patients with SBS who received a soybean oil-based intravenous lipid emulsion (Intralipid).

RESULTS

Median gestational age was 26 weeks in the treatment group and 35.5 weeks in the historical group. All patients were started on PN containing Intralipid that was switched to ClinOleic/Omegaven in the treatment group at a median age of 39 gestational weeks. In the treatment group, direct bilirubin levels were reversed in all 14 survivors with cholestasis (direct bilirubin >50 umol/L). Median time to reversal was 2.9 months. Only 2 patients died of liver failure (10%). In the historical cohort, 6 patients (33%) died of liver failure, and only 2 patients showed normalization of bilirubin levels.

CONCLUSIONS

Parenteral fish oil in combination with ω-6/9 lipid emulsions was associated with improved outcome in premature neonates with SBS. When used instead of traditional soybean-based emulsions, this mixed lipid emulsion may facilitate intestinal adaptation by increasing the IFALD-free period.

The role of parenteral lipids in the development of advanced intestinal failure-associated liver disease in infants: a multiple-variable analysis

BACKGROUND

Given the recent interest in the role of ω-6 lipids in the development of intestinal failure-associated liver disease (IFALD), the authors sought to examine the role of parenteral lipids in the development of a serum conjugated bilirubin >100 µmol/L (5.9 mg/dL; CB100) in infants.

METHOD

Between 2003 and 2004, data were collected prospectively on infants undergoing an abdominal surgical procedure. Univariate logistic regression models for the prediction of CB100 by 1 year postoperatively were developed. Predictors significant at the 0.2 level on univariate analysis were entered into a backward stepwise multiple variable logistic regression.

RESULTS

Of 152 infants who received parenteral nutrition (PN) postoperatively, 22 developed CB100. Predictors that met criteria for consideration in the multiple-variable model were age, weight, small bowel length, presence of a stoma, proportion of enteral feeds postoperatively, septic episodes, days of maximal PN amino acid (>2.5 g/kg/d), days of maximal lipid (>2.5 g/kg/d), and PN duration. The final model included septic episodes (odds ratio, 3.23; 95% confidence interval, 1.8-5.9) and days of lipid >2.5 g/kg/d (1.04; 1.003-1.06). At 60 days of maximal lipid, the odds of advanced IFALD were increased 10-fold.

CONCLUSIONS

This model suggests a key role of parenteral lipids and septic events in the development of CB100 from IFALD. These data may provide targets, such as careful line care, reduction in maximal lipid dose, or alternate lipids such as ω-3 fatty acids, to prevent CB100, an identified marker of subsequent liver failure from IFALD.

Prevention and reversal of intestinal failure-associated liver disease in premature infants with short bowel syndrome using intravenous fish oil in combination with omega-6/9 lipid emulsions

Although premature infants with short bowel syndrome are at the highest risk of developing intestinal failure-associated liver disease (IFALD), they have great capacity for intestinal growth and adaptation if IFALD can be prevented. Conventional soybean oil-based intravenous lipid emulsions have been associated with IFALD. This study presents data on 5 premature neonates with short bowel syndrome treated with a combination of parenteral fish oil- and olive/soybean-based lipid emulsion for periods ranging between 7 and 17 months. Despite an enteral tolerance of less than 50% in 4 of these patients during their first year of life, direct bilirubin levels normalized while on this combination of ClinOleic (Baxter, Maurepas, France)/Omegaven (Fresenius Kabi, Bad Homburg, Germany) at a 1:1 ratio. None of our patients developed irreversible IFALD even though all of them were premature, had undergone multiple major surgical procedures, and had experienced several episodes of sepsis. Thus far, we have not seen any adverse effects of this mixed lipid emulsion in these preterm infants. All 5 patients are growing and developing well and have normal liver function.

Changing the paradigm: omegaven for the treatment of liver failure in pediatric short bowel syndrome

BACKGROUND

Parenteral omega-3 fatty acids, such as Omegaven, may benefit patients with pediatric short bowel syndrome (SBS) who develop parenteral nutrition-associated liver disease (PNALD).

PATIENTS AND METHODS

Retrospective cohort describing the outcome of all 12 children with SBS and advanced PNALD who were treated with Omegaven (target omega-6 to omega-3 fatty acid ratio = 1:1 to 2:1).

RESULTS

The median age was 7.5 (range 3.6-46) months, and median parenteral nutrition duration before starting Omegaven was 28.4 (range 15.3-55.3) weeks. Median initial serum conjugated bilirubin was 137 (range 54-203) micromol/L (8.06 [3.18-11.94] mg/dL). Of the 12 patients, 9 had complete and sustained resolution of hyperbilirubinemia within a median of 24 (range 7-37) weeks, and all are no longer being considered for liver transplantation. Improvements in markers of hepatic inflammation as well as nutritional status also were noted in these patients. Three patients received a liver-intestine transplant while taking Omegaven. There were no complications attributable to Omegaven.

CONCLUSIONS

Omegaven is associated with restoration of liver function in patients with SBS and advanced liver disease. Parenteral omega-3 fatty acids, such as Omegaven, have the potential to fundamentally alter the paradigm of neonatal SBS from one of early death or transplantation from liver failure to a more chronic disease. More children with SBS should achieve full enteral tolerance and those who do not have the capacity for intestinal adaptation should be able to survive and receive an intestinal graft when older.

The rationale for the use of parenteral omega-3 lipids in children with short bowel syndrome and liver disease

Parenteral nutrition associated liver disease (PNALD) is the major source of morbidity and mortality in children with short bowel syndrome (SBS). There is emerging evidence that omega-6 fatty acids (omega6FA) within the parenteral solution play a major role in PNALD and their effects may be reversed or ameliorated by substitution with omega-3 fatty acids (omega3FA). This paper reviews the mechanisms whereby omega3FAs may influence PNALD by improving bile flow, inhibiting steatosis, and having immunomodulatory effects. The early clinical experience with omega3FAs in SBS and PNALD is briefly reviewed and the implications of such, and future directions are considered.

Effects of the prostaglandins PGF2alpha and PGE2 on calcium signaling in rat hepatocyte doublets

Coordination of intercellular Ca2+ signals is important for certain hepatic functions including biliary flow and glucose output. Prostaglandins, such as PGF2alpha and PGE2, may modify these hepatocyte functions by inducing Ca2+ increase, but very little is known about the organization of the Ca2+ signals induced by these agonists. We studied Ca2+ signals induced by PGF2alpha and PGE2 in fura-2 AM-loaded hepatocyte doublets. Even though both prostaglandins induced Ca2+ oscillations, neither PGF2alpha nor PGE2 induced coordinated Ca2+ oscillations in hepatocyte doublets. Gap junction permeability (GJP), assessed by fluorescence recovery after photobleaching, showed that this absence of coordination was not related to a defect in GJP. Inositol (1,4,5)trisphosphate [Ins(1,4,5)P3] assays and the increase in Ins(1,4,5)P3 receptor sensitivity to Ins(1,4,5)P3 observed in response to thimerosal suggested that the absence of coordination was a consequence of the very small quantity of Ins(1,4,5)P3 formed by these prostaglandins. Furthermore, when PGE2 and PGF2alpha were added just before norepinephrine, they favored the coordination of Ca2+ signals induced by norepinephrine. However, GJP between hepatocyte doublets was strongly inhibited by prolonged (>or=2 h) treatment with PGF2alpha, thereby preventing the coordination of Ca2+ oscillations induced by norepinephrine in these cells. Thus, depending on the time window, prostaglandins, specially PGF2alpha, may enhance or diminish the propagation of Ca2+ signals. They may therefore contribute to the fine tuning of Ca2+ wave-dependent functions, such as nerve stimulation, hormonal regulation of liver metabolism, or bile secretion, in both normal and pathogenic conditions.

Eicosanoids in cirrhosis and portal hypertension

In the last decade, the knowledge of the pathogenesis of portal hypertension and cirrhosis has increased dramatically. In portal hypertension, almost all the known vasoactive systems/substances are activated or increased and the most recent studies have stressed the importance of the endothelial factors, in particular, prostaglandins. Prostaglandins are formed following the oxygenation of arachidonic acid by the cyclooxygenase (Cox) pathway. An important consideration in portal hypertension and cirrhosis in the periphery is the altered hemodynamic profile and its contributory role in controlling endothelial release of these vasoactive substances. Prostaglandins are released from the endothelium in response to both humoral and mechanical stimuli and can profoundly affect both intrahepatic and peripheral vascular resistance. Within the liver, intrahepatic resistance is altered due to a diminution in sinusoidal responsiveness to vasodilators and an increase in prostanoid vasoconstrictor responsiveness. This review will examine the contributory role of both hormonal and/or hemodynamic force-induced changes in prostaglandin production and signaling in cirrhosis and portal hypertension and the consequence of these changes on the structural and functional response of both the vasculature and the liver.

Increased expression of cyclooxygenase-2 protein during rat hepatocarcinogenesis caused by a choline-deficient, L-amino acid-defined diet and chemopreventive efficacy of a specific inhibitor, nimesulide

Expression of cyclooxygenase (COX)-2 protein during rat hepatocarcinogenesis associated with fatty change, fibrosis, cirrhosis and oxidative DNA damage, caused by a choline-deficient, L-amino acid-defined (CDAA) diet were investigated in F344 male rats, along with the chemopreventive efficacy of the specific COX-2 inhibitor, nimesulide (NIM). Nimesulide, which was administered in the diet at concentrations of 200, 400, 600 and 800 p.p.m. for 12 weeks, decreased the number and size of preneoplastic enzyme-altered liver foci, levels of oxidative DNA damage, and the grade and incidence of fibrosis in a dose-dependent manner. A preliminary long-term study of 65 weeks also revealed that 800 p.p.m. NIM decreased the multiplicity of neoplastic nodules and hepatocellular carcinomas and prevented the development of cirrhosis. Western blot analysis revealed that COX-2 protein was barely expressed in control livers and increased approximately 2.9-fold in the livers of rats fed on a CDAA diet for 12 weeks and approximately 4.5-5.4-fold in tumors, with a diameter larger than 5 mm, at 80 weeks. Immunohistochemically, COX-2 protein was positive in sinusoidal and stromal cells in fibrotic septa, which were identified by immunoelectron microscopy as Kupffer cells, macrophages, either activated Ito cells or fibroblasts, after exposure to the CDAA diet for 12 weeks, whereas it was only occasionally weakly positive in sinusoidal, probably Kupffer, cells in control livers. In neoplastic nodules in rats fed on a CDAA diet for 30 and 80 weeks, sinusoidal cells and cells with relatively large round nuclei and scanty cytoplasm were strongly positive for COX-2 protein, with the neoplastic hepatocytes in the minority of the nodules, but not the cancer cells, being moderately positive. These results clearly indicate that rat hepatocarcinogenesis, along with fatty change, fibrosis and cirrhosis, is associated with increased expression of COX-2 protein, and point to the chemopreventive efficacy of a selective COX-2 inhibitor against, at least, the early stages of hepatocarcinogenesis.

Disturbed bile secretion and cytochrome P450 function during the acute state of experimental colitis in rats

BACKGROUND/AIMS

A variety of hepatobiliary abnormalities has been described in patients with inflammatory bowel diseases. However, the pathophysiological mechanisms leading to these liver alterations are poorly understood. The aim of the present study was to investigate parameters of liver function in a trinitrobenzenesulfonic acid (TNB)-induced rat colitis model.

METHODS

Glucose output, bile acid secretion, bile acid uptake, and the cytochrome P-450 metabolic capacity during TNB-colitis were studied in the perfused liver model. Furthermore, hepatic bile acid- and glycogen content was measured. To evaluate the inflammatory response in the colon and liver, NF-kappaB/Rel was quantified by electrophoretic mobility shift assays. As an NF-kappaB/Rel regulated gene the inducible NO-synthase (NOS2) was evaluated by Western blot analysis. As possible mediators released from the inflamed colon into the portal vein, endotoxin and the stable metabolite of prostaglandin I2 (6-keto-prostaglandin-F1alpha) were determined.

RESULTS

Glucose output, bile acid secretion, bile acid uptake, and cytochrome P-450 metabolic capacity decreased on the first and second day of TNB-colitis. Hepatic bile acid content increased at day 14 of colitis. Glycogen content was reduced, most likely due to an inadequate chow intake of these animals. A low level of portal endotoxin was detectable during the first 2 days of colitis. In addition, 6-keto-prostaglandin-F1alpha was clearly increased in portal blood. NF-kappaB/Rel binding activity and inducible NOS2 were strongly positive in the colon during colitis. Although low levels of portal endotoxin were measured during the first 2 days of colitis, no significant NF-kappaB/Rel activity and NOS2 induction were detected in the liver.

CONCLUSION

Our results indicate that during the acute state of the TNB-colitis, bile acid secretion and cytochrome P-450 function are disturbed in the absence of distinct inflammatory changes in the liver.

Intravenous fish oil emulsion attenuates total parenteral nutrition-induced cholestasis in newborn piglets

Total parenteral nutrition (TPN) causes intrahepatic cholestasis and membrane phospholipid changes. Fatty acid (FA) composition of bile and hepatocyte phospholipid is influenced by dietary FA composition. We hypothesized that altering FA composition of i.v. lipid emulsions modifies 1) severity of TPN-induced cholestasis; 2) hepatocyte membrane composition and function; 3) bile flow and composition. Newborn piglets received either sow's milk, TPN with i.v. soybean oil or TPN with i.v. fish oil (FO). After 3 wk, basal and stimulated bile flow were measured after bolus injections of 20, 50, and 100 micromol/kg of taurocholate (TCA). Bile was analyzed for bile acids, cholesterol, phospholipids, and phospholipid-FA. Sinusoidal and canalicular membrane PL-FA, fluidity, and Na+/K+-ATPase were measured. Although the soybean oil-fed animals developed cholestasis, the FO and milk group had similar liver and serum bilirubin. Basal and stimulated bile flow rates were impaired in the soybean oil but not in the FO group. Hepatocyte membrane FA composition reflected dietary FA. Changes in sinusoidal and canalicular membrane fluidity and sinusoidal Na+/K+-ATPase activity did not explain the effect of FO on TPN-induced cholestasis. Intravenous FO reduces TPN-induced cholestasis by unknown mechanisms.

cDNA cloning, expression, and mutagenesis study of liver-type prostaglandin F synthase

Prostaglandin (PG) F synthase catalyzes the reduction of PGD2 to 9alpha,11beta-PGF2 and that of PGH2 to PGF2alpha on the same molecule. PGF synthase has at least two isoforms, the lung-type enzyme (Km value of 120 microM for PGD2 (Watanabe, K., Yoshida, R., Shimizu, T., and Hayaishi, O. (1985) J. Biol. Chem. 260, 7035-7041) and the liver-type one (Km value of 10 microM for PGD2 (Chen, L. -Y., Watanabe, K., and Hayaishi, O. (1992) Arch. Biochem. Biophys. 296, 17-26)). The liver-type enzyme was presently found to consist of a 969-base pair open reading frame coding for a 323-amino acid polypeptide with a Mr of 36,742. Sequence analysis indicated that the bovine liver PGF synthase had 87, 79, 77, and 76% identity with the bovine lung PGF synthase and human liver dihydrodiol dehydrogenase (DD) isozymes DD1, DD2, and DD4, respectively. Moreover, the amino acid sequence of the liver-type PGF synthase was identical with that of bovine liver DD3. The liver-type PGF synthase was expressed in COS-7 cells, and its recombinant enzyme had almost the same properties as the native enzyme. Furthermore, to investigate the nature of catalysis and/or substrate binding of PGF synthase, we constructed and characterized various mutant enzymes as follows: R27E, R91Q, H170C, R223L, K225S, S301R, and N306Y. Although the reductase activities toward PGH2 and phenanthrenequinone (PQ) of almost all mutants were not inactivated, the Km values of R27E, R91Q, H170C, R223L, and N306Y for PGD2 were increased from 15 to 110, 145, 75, 180, and 100 microM, respectively, indicating that Arg27, Arg91, His170, Arg223, and Asn306 are essential to give a low Km value for PGD2 of the liver-type PGF synthase and that these amino acid residues serve in the binding of PGD2. Moreover, the R223L mutant among these seven mutants especially has a profound effect on kcat for PGD2 reduction. The Km values of R223L, K225S, and S301R for PQ were about 2-10-fold lower than the wild-type value, indicating that the amino acid residues at 223, 225 and 301 serve in the binding of PQ to the enzyme. On the other hand, the Km value of H170C for PGH2 was 8-fold lower than that of the wild type, indicating that the amino acid residue at 170 is related to the binding of PGH2 to the enzyme and that Cys170 confer high affinity for PGH2. Additionally, the 5-fold increase in kcat/Km value of the N306Y mutant for PGH2 compared with the wild-type value suggests that the amino acid at 306 plays an important role in catalytic efficiency for PGH2.

Localization of the prostaglandin F2 alpha receptor in rat tissues

The localization of the prostaglandin F2alpha (FP) receptor was examined in rat tissues by immunohistochemistry and in situ hybridization. Immunohistochemistry on paraffin sections was performed with a rabbit polyclonal antiserum raised against a synthetic peptide derived from the rat FP receptor sequence. In situ hybridization on cryosections was done with 35S-labelled rat FP receptor antisense and sense riboprobes. The most intense FP receptor-like immunoreactivity was observed in granulosa luteal cells, muscle and epithelial cells, e.g. cardiac, skeletal and smooth muscle, and hepatocytes. Weaker immunoreactivity was found in connective tissue fibroblasts. In the eye, intense immunostaining was associated with the corneal and conjunctival epithelium and moderate staining with the ciliary body, retina, iris and connective tissues. In situ hybridization generally confirmed the results. The riboprobe hybridized weakly with the heart, skeletal muscle, uterus, liver, lung and corpus luteum. Thus, the prostaglandin FP receptor was found to be widely distributed in rat tissues.

Effects of nitric oxide on leukotriene D4 decreased bile secretion in the perfused rat liver

Nitric oxide (NO) and leukotrienes are potent vasoactive agents that are involved in the control of portal blood flow. The present study investigated the role of leukotriene D4 and NO in a non-recirculating constant pressure rat liver perfusion model to analyse their interchanges on portal flow and bile secretion. The addition of leukotriene D4 (20 nM) to the perfusate for 5 minutes resulted in a decrease in portal blood flow (-55.3%), in bile flow (-24.4%) as well as bile acid release (-35.2%). In parallel, leukotriene D4 increased glucose output. The administration of a lower dose of leukotriene D4 (5 nM) reduced the respective parameters to a lesser degree, indicating dose-dependence. The addition of NO via the infusion of sodium nitroprusside (0.05 mM, 1 mM) reduced the effect of leukotriene D4 on portal flow, bile flow and bile acid secretion whereas the leukotriene D4 effects on hepatic glucose output remained unaffected. Correlation coefficient between decrease in portal flow and reduction of bile flow by infusing leukotriene D4 was R = 0.91, while in the presence of sodium nitroprusside R = 0.85. These results suggest that the leukotriene D4-induced cholestasis is dependent on portal flow. In contrast, hepatic vasoconstriction does not contribute to glycogenolysis stimulated by leukotriene D4 in the perfused liver.

Effects of selective phosphodiesterase 3 inhibition in the perfused liver of the rat after endotoxin treatment

1. This study was designed to investigate the role of rat phosphodiesterase 3 (RPDE3) in regulation of liver metabolism in sepsis. We studied the effects of the phosphodiesterase 3 inhibitor (PDI), enoximone, alone and in combination with regulating factors of hepatic carbohydrate metabolism and bile secretion in the perfused liver of rats treated 4 h earlier with endotoxin. In addition, cyclic AMP and cyclic GMP levels were determined in the effluate and bile by radio immunoassay methods. 2. After endotoxin treatment, infusion of enoximone at three concentrations (1 microM, 10 microM) resulted in an increased glucose output from -1.4 +/- 0.9 to 7.8 +/- 2.5 mumol l-1 20 min-1. Bile acid-independent bile flow increased also, in a dose-dependent manner. 3. In untreated livers, cyclic AMP release increased in the effluate from 1000 +/- 73 fmol g-1 min-1 to 1710 +/- 143 fmol g-1 min-1 when enoximone (10 microM) was administered. In bile from untreated livers, the level of cyclic AMP was also significantly increased by enoximone. After endotoxin treatment, the enoximone (10 microM) effect on cyclic AMP levels in effluate and bile was greatly reduced. Levels of cyclic GMP in the effluate and bile appeared unchanged in the presence of enoximone. 4. During co-infusion of glucagon (1 nM) and enoximone (10 microM), cyclic nucleotide levels in the effluate and bile of livers after endotoxin treatment were determined. In the effluate, cyclic AMP release increased from 827 +/- 144 fmol g-1 min-1 to 17802 +/- 2821 fmol g-1 min-1 when glucagon was administered. The presence of enoximone enhanced cyclic AMP further to 41696 +/- 920 fmol g-1 min-1. The same changes in cyclic AMP release were found in bile. Levels of cyclic GMP in the effluate and bile were not significantly affected by the administration of glucagon and the PDI. 5. Glucose release was determined during glucagon, sympathetic nerves stimulation and phenylephrine administration in the presence and absence of enoximone. The addition of enoximone to glucagon increased glucose release by 8.2 +/- 2.8 mumol g-1 20 min-1, without alteration of lactate balance. The PDI enhanced the glycogenolytic effects of nerve stimulation and of phenylephrine, accompanied by a reduction in lactate production. 6. Enoximone significantly enhanced the bile acid independent bile flow after glucagon, nerves stimulation and after administration of phenylephrine. Bile acid secretion was unaffected by the PDI. The vasoconstrictor effect of nerve stimulation was reduced by the PDI. 7. We conclude that endotoxin treatment reduces the ability of the PDI, enoximone, to increase cyclic AMP release in the perfused liver. The significant increase in cyclic AMP release after stimulation with glucagon and enoximone favours the view that RPDE3 is involved in the degradation of cyclic AMP in the liver after exposure to endotoxin. Additionally, the inhibition of the RPDE3 results in glucose release, vasodilatation and choleresis in endotoxin pretreated livers.

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.

Reduction of bile secretion by prostaglandins in the rat in vivo

Bile secretion has been reported to be regulated by circulating hormones and by autonomic liver nerves. In the in situ perfused rat liver, prostaglandins reduce bile flow and bile acid secretion. The aim of this study was to investigate the regulation of bile secretion by prostaglandins in the in vivo situation. The bile duct and portal vein of anaesthetised Wistar rats were cannulated by polyethylene tubes. Bile flow was determined gravimetrically. Bile acids were quantified by the 3-alpha-hydroxy-steroid-dehydrogenase method and by high-pressure-liquid-chromatography (HPLC) separation. Administration of 1 microM prostaglandin F2 alpha into the portal vein over 5 minutes reduced bile flow from 1.57 microliter/min.g liver to 0.95 microliter/min.g liver and bile acids secretion from 148 to 81 nmol/100g/min. The administration of different doses (0.1 microM, 1 microM, 10 microM) of prostaglandin F2 alpha reduced hepatic bile secretion in a dose-dependent manner. Similar effects were observed after infusion of prostaglandin D2. However, the ratio of the bile acids (alpha-tauromuricholic acid), beta-tauromuricholic acid, taurocholic acid, taurochenodeoxycholic acid, and taurodeoxycholic acid) was unchanged by prostaglandin F2 alpha. In conclusion, infusion of prostaglandin F2 alpha into the portal vein results in a reduction of bile flow and bile acid secretion in a dose-dependent manner. These results suggest that the effect is linked to canicular bile secretion.

The role of nitric oxide in hemodynamic and metabolic alterations induced by prostaglandin F2 alpha in the perfused rat liver

In the liver prostaglandins have been shown to be potent regulators of portal blood flow, carbohydrate metabolism and bile secretion. It is not known whether these effects represent a direct action of prostaglandins, and it has been suggested that nitric oxide (NO) might be a critical mediator for prostaglandin induced hepatic events. We have studied whether nitric oxide formation or inhibition alters the action of prostaglandin F2 alpha (PG F2 alpha) in a single-pass liver perfusion model. The liver of untreated rats (constitutive NO-synthase) or after pretreatment with endotoxin (inducible form of NO-synthase) was perfused at a constant pressure via the portal vein. Effluate were collected in 1-min intervals and bile in 5-min intervals. In both groups the addition of PG F2 alpha (10 microM) to the perfusate for 5 min resulted in a significant increase of glucose and lactate production, and in a significant decrease in portal blood flow (-0.56 +/- 0.04 ml/g per min), in bile flow (-60.7%) and in bile acid release (-60.6%). Inhibition of NO synthase by adding NG-monomethyl-L-arginine (L-NMMA, 100 microM) to the perfusate did not affect any of the alterations induced by PG F2 alpha. Substitution of the endogenous substrate for the NO synthase L-arginine (500 microM) in the perfusate completely prevented the hemodynamic alterations induced by PG F2 alpha in endotoxin pretreated livers and limited the flow reduction (0.15 +/- 0.04 ml/g per min) in the untreated group. The substitution of L-arginine in the perfusate of endotoxin pretreated livers raised nitrite (from 1.5 +/- 0.3 to 3.6 +/- 0.7 nmol/g per min) and urea release (from 65 +/- 25 to 294 +/- 68 nmol/g per min), but had no effect on any of the other metabolic parameters and bile secretion. We conclude that PG F2 alpha increases glucose and lactate production in the perfused rat liver and decreases portal flow bile secretion. The metabolic effects induced by PG F2 alpha appear to be independent of NO mediation and hemodynamic alterations. Portal flow alone can be influenced by endogenous NO formation.