Metabolism of prostaglandins D2 and F2α in primary cultures of rat hepatocytes

Triptolide protects against podocyte injury in diabetic nephropathy by activating the Nrf2/HO-1 pathway and inhibiting the NLRP3 inflammasome pathway

Objectives: Diabetic nephropathy (DN) is the most common microvascular complication of diabetes mellitus. This study investigated the mechanism of triptolide (TP) in podocyte injury in DN.Methods: DN mouse models were established by feeding with a high-fat diet and injecting with streptozocin and MPC5 podocyte injury models were induced by high-glucose (HG), followed by TP treatment. Fasting blood glucose and renal function indicators, such as 24 h urine albumin (UAlb), serum creatinine (SCr), blood urea nitrogen (BUN), and kidney/body weight ratio of mice were examined. H&E and TUNEL staining were performed for evaluating pathological changes and apoptosis in renal tissue. The podocyte markers, reactive oxygen species (ROS), oxidative stress (OS), serum inflammatory cytokines, nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway-related proteins, and pyroptosis were detected by Western blotting and corresponding kits. MPC5 cell viability and pyroptosis were evaluated by MTT and Hoechst 33342/PI double-fluorescence staining. Nrf2 inhibitor ML385 was used to verify the regulation of TP on Nrf2.Results: TP improved renal function and histopathological injury of DN mice, alleviated podocytes injury, reduced OS and ROS by activating the Nrf2/heme oxygenase-1 (HO-1) pathway, and weakened pyroptosis by inhibiting the nod-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome pathway. In vitro experiments further verified the inhibition of TP on OS and pyroptosis by mediating the Nrf2/HO-1 and NLRP3 inflammasome pathways. Inhibition of Nrf2 reversed the protective effect of TP on MPC5 cells.Conclusions: Overall, TP alleviated podocyte injury in DN by inhibiting OS and pyroptosis via Nrf2/ROS/NLRP3 axis.

Peroxisomal L-bifunctional protein (EHHADH) deficiency causes male-specific kidney hypertrophy and proximal tubular injury in mice

BACKGROUND

Proximal tubular (PT) cells are enriched in mitochondria and peroxisomes. Whereas mitochondrial fatty acid oxidation (FAO) plays an important role in kidney function by supporting the high-energy requirements of PT cells, the role of peroxisomal metabolism remains largely unknown. EHHADH, also known as L-bifunctional protein, catalyzes the second and third step of peroxisomal FAO.

METHODS

We studied kidneys of WT and Ehhadh KO mice on a C57BL/6N background using histology, immunohistochemistry, immunofluorescence, immunoblot, RNA-sequencing, and metabolomics. To assess the role of androgens in the kidney phenotype of Ehhadh KO mice, mice underwent orchiectomy.

RESULTS

We observed male-specific kidney hypertrophy and glomerular filtration rate reduction in adult Ehhadh KO mice. Transcriptome analysis unveiled a gene expression signature similar to PT injury in acute kidney injury mouse models. This was further illustrated by the presence of KIM-1 (kidney injury molecule-1), SOX-9, and Ki67-positive cells in the PT of male Ehhadh KO kidneys. Male Ehhadh KO kidneys had metabolite changes consistent with peroxisomal dysfunction as well as an elevation in glycosphingolipid levels. Orchiectomy of Ehhadh KO mice decreased the number of KIM-1 positive cells to WT levels. We revealed a pronounced sexual dimorphism in the expression of peroxisomal FAO proteins in mouse kidney, underlining a role of androgens in the kidney phenotype of Ehhadh KO mice.

CONCLUSIONS

Our data highlight the importance of EHHADH and peroxisomal metabolism in male kidney physiology and reveal peroxisomal FAO as a sexual dimorphic metabolic pathway in mouse kidneys.

Involvement of cyclooxygenase-2 in the potentiation of allyl alcohol-induced liver injury by bacterial lipopolysaccharide

Bacterial endotoxin (lipopolysaccharide; LPS) augments the hepatotoxicity of a number of xenobiotics including allyl alcohol. The mechanism for this effect is known to involve the inflammatory response elicited by LPS. Upregulation of cyclooxygenase-2 (COX-2) and production of eicosanoids are important aspects of inflammation, therefore studies were undertaken to investigate the role of COX-2 in LPS-induced enhancement of liver injury from allyl alcohol. Rats were pretreated (iv) with a noninjurious dose of LPS or sterile saline vehicle and 2 h later were treated (ip) with a noninjurious dose of allyl alcohol or saline vehicle. COX-2 mRNA was determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and liver injury was assessed from activities in serum of alanine and aspartate aminotransferases (ALT and AST, respectively) and from histology. Liver injury was observed only in rats cotreated with LPS and allyl alcohol. Serum ALT activity was increased by 4 h after administration of LPS and continued to increase through 8 h. COX-2 mRNA was detectable at low levels in livers from rats receiving only the vehicles at any time up to 8 h. Expression of COX-2 mRNA was increased by 30 min after administration of LPS and remained elevated through 6 h. Allyl alcohol treatment alone caused an increase in COX-2 mRNA at 4 h (2 h after allyl alcohol) that lasted less than 2 h. In livers from rats cotreated with LPS and allyl alcohol, levels of COX-2 mRNA were greater than levels seen with either LPS or allyl alcohol alone. The increased expression of COX-2 mRNA was accompanied by an increase in the concentration of prostaglandin (PG) D(2) in plasma. Plasma PGD(2) concentration was increased to a greater extent in rats treated with LPS plus allyl alcohol compared to allyl alcohol or LPS alone. Pretreatment with the COX-2 selective inhibitor, NS-398, abolished the increase in plasma PGD(2) and reduced the increase in ALT and AST activities observed in rats cotreated with LPS and allyl alcohol. NS-398 did not affect liver injury from allyl alcohol alone administered at a larger, hepatotoxic dose. In addition, ibuprofen, a nonselective inhibitor of cyclooxygenases, did not protect against liver injury from LPS plus allyl alcohol. In isolated hepatocytes PGD(2), but not PGE(2), reduced the concentration of allyl alcohol required to cause half-maximal cytotoxicity. These results suggest that products of COX-2 play a role in the augmentation of allyl alcohol-induced liver injury by LPS.

Identification and measurement of endogenous beta-oxidation metabolites of 8-epi-Prostaglandin F2alpha

F2-isoprostanes are prostaglandin-like compounds derived from nonenzymatic free radical-catalyzed peroxidation of arachidonic acid. 8-epi-Prostaglandin (PG) F2alpha, a major component of the F2-isoprostane family, can be conveniently measured in urine to assess noninvasively lipid peroxidation in vivo. Measurement of major metabolites of endogenous 8-epi-PGF2alpha, in addition to the parent compound, may be useful to better define its formation in vivo. 2,3-Dinor-5,6-dihydro-8-epi-PGF2alpha is the only identified metabolite of 8-epi-PGF2alpha in man, but its endogenous levels are unknown. In addition to this metabolite, we have identified another major endogenous metabolite, 2,3-dinor-8-epi-PGF2alpha, in human and rat urine. The identity of these compounds, present at the pg/ml level in urine, was proven by a number of complementary approaches, based on: (a) immunoaffinity chromatography for selective extraction; (b) gas chromatography-mass spectrometry for structural analysis; (c) in vitro metabolism in isolated rat hepatocytes; and (d) chemical synthesis of the enantiomer of 2,3-dinor-5, 6-dihydro-8-epi-PGF2alpha as a reference standard. In humans, the urinary excretion rate of both dinor metabolites is comparable with that of 8-epi-PGF2alpha. Both metabolites increase in parallel with the parent compound in cigarette smokers, and they are not reduced during cyclooxygenase inhibition. Another beta-oxidation product, 2, 3,4,5-tetranor-8-epi-PGF2alpha, was identified as a major product of rat hepatocyte metabolism. In conclusion, at least two major beta-oxidation products of 8-epi-PGF2alpha are present in urine, which may be considered as additional analytical targets to evaluate 8-epi-PGF2alpha formation and degradation in vivo.

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 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.

Effects of hypoxia on the oxygen-dependent metabolism of prostaglandins and adenosine in liver cells

In this study, the capacity of hepatocytes to degrade prostaglandins diminished if the partial oxygen pressure dropped below 5%. This decrease was accompanied by an increased lactate/pyruvate ratio, a decrease in fatty acid oxidation and a drop in the ATP level. The degradation of exogenous adenosine increased with decreasing oxygen tension. At a partial oxygen pressure below 10%, the conversion of uric acid to allantoin, the final catabolite of adenosine in the rat, was strongly inhibited, resulting in the accumulation of uric acid in the medium. A good correlation was observed between the partial oxygen pressure, the oxidation of uric acid to allantoin and the degradation of prostaglandins D2 and E2, suggesting a peroxisomal pathway of hepatic prostaglandin oxidation. Subcellular fractionation of liver homogenates revealed peroxisomes as the site of degradation of prostaglandins D2 and E2 augmented by cytosolic components. The similarity of the degradation products found in the cell-free system, in hepatocytes and in the perfused liver further supports a peroxisomal degradation of prostaglandins in vivo. Stimulated liver macrophages (Kupffer cells) produced the same amount and pattern of eicosanoids at 1% and 21% O2. Even the formation of superoxide remained unaffected down to a partial pressure of 1%. At partial O2 pressures below 1%, the production of prostaglandins and superoxide became strongly inhibited. These results indicate that essential oxygenation reactions in activated Kupffer cells, including prostaglandin synthesis, possess high affinities to oxygen, while the peroxisomal pathway of prostaglandin oxidation in hepatocytes is sensitive to an O2 tension as low as 5%.

Stimulation of glycogen degradation by prostaglandin E2 in primary cultured rat hepatocytes

Hepatocytes isolated from rats by the collagenase perfusion method were cultured as monolayers at concentrations of 0.4-1.1 x 10(6) attached cells/dish (9 cm2) for 1-3 days and the effect of prostaglandins on their glycogenolysis was studied. By use of [14C]glycogen-labeled cells, prostaglandin E2 (PGE2) was found to have a stimulatory effect on glycogen degradation at high cell density (more than 0.8 x 10(6) cells/dish) in 1-day cultures. PGE2 was maximally effective at 10(-7) M, increasing [14C]release from cellular [14C]glycogen to 2-3 times the basal level after 1 h incubation, and to plateau level within 2 h. PGE1, 16,16-dimethyl PGE2 and PGF2 alpha had similar effects, but PGD2 and dinor-PGE1 (a metabolite of PGE1 and PGE2 in hepatocytes) had no effect. This prostaglandin-induced glycogen degradation was observed in 1-day cultures, with a maximum between 20-30 h, but not in 2-day and later cultures. Treatment of hepatocytes with pertussis toxin potentiated PGE2-stimulated glycogen degradation, indicating that the effect involves a different pathway from that for inhibition of glucagon- and epinephrine-stimulated glycogenolysis by E series prostaglandins reported previously.

Stimulation of glucose incorporation into glycogen by E-series prostaglandins in cultured rat hepatocytes

In primary cultures of rat hepatocytes, 16,16-dimethylprostaglandin E2 (16,16-dimethyl PGE2), a biologically active analogue of prostaglandin E2 (PGE2), stimulated the basal rate of [14C]glucose incorporation into glycogen. 16,16-Dimethyl PGE2 caused concentration-dependent stimulation (ED50: 10(-8) M) with a maximum 2-3 h after its addition. Prostaglandin E1 (PGE1), PGE2 and prostaglandin F2 alpha (PGF2 alpha) stimulated also the incorporation, but less effectively than 16,16-dimethyl PGE2. However, prostaglandin D2 (PGD2) did not show such effect. Cellular glycogen analysis revealed that PGE2 and 16,16-dimethyl PGE2 increased a net glycogen accumulation time-dependently. Pretreatment of the cultured hepatocytes with pertussis toxin blocked the effects of PGE2 and 16,16-dimethyl PGE2 completely and concentration-dependently. These findings indicate that E-series prostaglandins have significant effects on hepatic glycogenesis via pertussis-toxin-sensitive G protein, in addition to their inhibitory effects on hormone-stimulated glycogenolysis reported previously (Okumura, T., Sago, T. and Saito, K. (1988) Prostaglandins 36, 463-475).

Effect of 17 beta-estradiol on PAF and prostaglandin levels in oophorectomized rat uterus

The effects of 17 beta-estradiol on the levels of platelet-activating factor (PAF) and prostaglandins and their precursor phospholipid in the uterus of oophorectomized rats were studied. Oophorectomy results in the decrease in the uterine PAF level to one-third of that in natural estrus. This level was recovered by subcutaneous administration of 17 beta-estradiol. The level of uterine phospholipids, which are rich in arachidonic acid, was significantly decreased by estradiol treatment. More arachidonate-PC was depleted than arachidonate-PE. The molecular structure was confirmed by gas chromatography-mass spectrometry. The amount of PGF2 alpha in the oophorectomized uterine tissue was 10-times that of PAF, but like the latter, increased 3-4 times on estradiol treatment. The chemical structures of PAF and PGF2 alpha formed on estradiol treatment were confirmed by mass spectrometry. The present data strongly suggest a correlation between the formations of PAF and PGF2 alpha, and indicate that estradiol may regulate the physiological formations of PAF and PGs in non-pregnant rat uterus.

Synthesis and degradation of eicosanoids in primary rat hepatocyte cultures

Arachidonic acid metabolites may play an important role in liver physiology, yet hepatocyte prostaglandin synthesis has not been characterized extensively. We used RIA to study production and clearance of several eicosanoids in confluent primary cultures of rat hepatocytes in serum-free, hormonally-defined medium. Under basal, unstimulated conditions 6-keto-PGF1 alpha (spontaneous breakdown product of prostacyclin) and 13,14-dihydro-15-keto-PGE (DHK-PGE, a metabolite of PGE) accumulated in the culture medium. Hepatocytes cleared 6-keto-PGF1 alpha, thromboxane B2, and DHK-PGE from the medium. Production of eicosanoids by primary cultures appeared resistant to indomethacin and several other cyclooxygenase inhibitors. This apparent resistance to indomethacin was not caused by rapid metabolism of indomethacin, by failure of the drug to enter hepatocytes, or by insensitivity of hepatocyte cyclooxygenase to the drug. Metabolism of PGE to DHK-PGE may be saturated under in vitro conditions. Hepatocytes can synthesize significant amounts of eicosanoids, although they are probably less active in this regard than are non-parenchymal cells.

Kupffer cell-hepatocyte interactions and the changes in 1-14C-arachidonate incorporation in response to endotoxin in vitro

The present experiments were undertaken to elucidate the effect of either the hepatocyte (HC) or hepatocyte supernatant on prelabeled endotoxin (LPS)-stimulated Kupffer cell (KC) arachidonic acid utilization. HC, KC, or their coculture were incubated for 18 hours with labeled 1-14C- arachidonic acid followed by a 24 hour incubation with 10 micrograms/ml LPS. LPS had no effect on the percent distribution of labeled arachidonate into the HC phospholipid or neutral lipid. KC showed a decreased percent neutral lipid labeled arachidonic acid distribution with generally no effect on the phospholipid. However, KC:HC cocultures or the addition of HC supernatant to KC exposed to LPS dramatically reversed the labeled arachidonate distribution into the KC with an increased incorporation into neutral lipid. Labeled PGE2 and PGD2 were increased in the KC following incubation with HC supernatant while only labeled PGE2 levels were elevated in the cocultures. The changes in the distribution of cell's labeled arachidonate required the addition of LPS. These results suggest that the HC can promote changes in the lipid fraction during sepsis by elaborating a substance that can modulate labeled arachidonate distribution in the KC lipids as well as stimulate prostaglandin production.

A sex difference in the effect of prostaglandins on hormone-stimulated glycogenolysis in primary cultures of rat hepatocytes

E series prostaglandins and their biologically active analogue, 16,16-dimethylprostaglandin E2 (dimethylprostaglandin E2), have inhibited hormone-stimulated glycogenolysis in hepatocytes cultured from male rats (Okumura, T., Sago, T. and Saito, K. (1988) Biochim. Biophys. Acta 958, 179-187). However, in the case of female rat hepatocytes, it is evident that dimethylprostaglandin E2 did not inhibit the glycogenolysis stimulated by glucagon, isoproterenol (beta-adrenergic response) or epinephrine (with propranolol, alpha 1-adrenergic response) in cultures on day 1. Dimethylprostaglandin E2 inhibited such hormone-stimulated glycogenolysis in cultures on day 2 and 3, but to a lesser extent than in the male-derived cells. The concentration for 50% inhibition was approx. 10(-8) M; inhibition was completely blocked by a pertussis toxin. Prostaglandin E2 had the same effect as dimethylprostaglandin E2; prostaglandins D2 and F2 alpha had no effect. Additions of sex hormones, 17 beta-estradiol and testosterone, and palmitic acid (diminishing the prostaglandin catabolism) to the culture medium did not change the effect of dimethylprostaglandin E2. These data indicate that a sex difference exists in the inhibition of hepatic glycogenolysis by prostaglandin E2 and its analogue in rat cultured hepatocytes, although the factor causing such a difference is a present unknown.

Changes of prostacyclin and thromboxane synthesis in the course of mouse liver perfusion. Stimulated thromboxane A2 synthesis of freshly prepared isolated mouse hepatocytes

The formation of prostacyclin and thromboxane A2 (measured as 6-keto PGF1 alpha and TXB2 by radioimmunoassay) was investigated during a 30 min perfusion of mouse liver in a recirculation system. After cannulation of the portal vein an immediate increase of de novo synthesis and secretion of PGI2 occurred followed by a sharp decrease. Increased PGI2 synthesis was also followed by a continuous increase of TXA2 synthesis and secretion reaching a maximum at the end of the 30 min perfusion. Elevated TXA2 synthesis was also shown in freshly isolated hepatocytes investigated in the course of a 20 min incubation period immediately after the perfusion. However, the elevated TXA2 formation was not observed when it was measured after a 120 min preincubation of the cells. Both PGI2 and TXA2 production could be provoked to a similar extent by the addition of arachidonate and A 23187 immediately after the perfusion or after a 120 min preincubation.

Modulation of prostaglandin E2 catabolism and action by fuel substrates in rat hepatocytes

The hepatic level of prostaglandins will reflect the balance between synthesis of prostaglandins and their rapid catabolism via beta-oxidation by hepatocytes. In the present study we examined the effect of physiological fuel substrates on the breakdown and action of prostaglandin E2 (PGE2) in isolated rat hepatocytes. Palmitic acid (0.32 mM), a long-chain fatty acid, inhibited the rate of PGE2 breakdown (10(-7) M) by approx. 80%. As the palmitic acid concentration was increased from 0 to 0.8 mM, the percentage of PGE2 remaining in the incubation 5 min following prostaglandin addition was raised from approx. 10% to over 98%. Octanoic acid (0.8 mM) also inhibited PGE2 catabolism, while butyric acid (0.8 mM) and pyruvic acid (2.5 mM) were without effect. The inhibition of glucagon-stimulated glycogenolysis by PGE2 was increased in the presence of 0.6 mM palmitic acid, consistent with decreased PGE2 catabolism. These studies demonstrate that changes within the range of free fatty acid concentrations seen physiologically in vivo may dramatically alter PGE2 catabolism and, therefore, the effect of PGE2 to modulate hormonal action in the liver.

cAMP dependent inhibition of thromboxane A2, prostacyclin and PGF2 alpha synthesis in mouse hepatocytes

The role of cAMP dependent regulation in thromboxane A2, prostacyclin and PGF2 alpha synthesis (measured by radioimmunoassay) was investigated in isolated mouse hepatocytes and in microsomal membranes prepared from these cells. In isolated hepatocytes N6,O2-dibutyryl cAMP inhibited the formation of all the three derivatives, while calcium ionophore A 23187 stimulated their synthesis. Addition of the dissociated catalytic subunit of cAMP dependent protein kinase and ATP to microsomal membranes inhibited the production of TXA2, PGI2 and PGF2 alpha by about 50% and this inhibition was counteracted by the combined addition of heat stable inhibitor protein of cAMP dependent protein kinase. It is concluded that in parenchymal liver cells cAMP dependent phosphorylation is directly involved in the inhibition of prostanoid synthesis.

Hepatocyte heterogeneity in response to icosanoids. The perivenous scavenger cell hypothesis

1. The metabolic and hemodynamic effects of prostaglandin F2 alpha, leukotriene C4 and the thromboxane A2 analogue U-46619 were studied during physiologically antegrade (portal to hepatic vein) and retrograde (hepatic to portal vein) perfusion and in a system of two rat livers perfused in sequence. 2. The stimulatory effects of prostaglandin F2 alpha (3 microM) on hepatic glucose release, perfusion pressure and net Ca2+ release were diminished by 77%, 95% and 64%, respectively, during retrograde perfusion when compared to the antegrade direction, whereas the stimulation of 14CO2 production from [1-14C]glutamate by prostaglandin F2 alpha (which largely reflects the metabolism of perivenous hepatocytes) was lowered by only 20%. Ca2+ mobilization and glucose release from the liver comparable to that seen during antegrade perfusion could also be observed in retrograde perfusions; however, higher concentrations of the prostaglandin were required. 3. The glucose, Ca2+ and pressure response to leukotriene C4 (20 nM) or the thromboxane A2 analogue U-46619 (200 nM) of livers perfused in the antegrade direction were diminished by about 90% during retrograde perfusion. Sodium nitroprusside (20 microM) decreased the pressure response to leukotriene C4 (20 nM) and U-46619 (200 nM) by about 40% and 20% in antegrade perfusions, respectively, but did not affect the maximal increase of glucose output. 4. When two livers were perfused antegradely in series, such that the perfusate leaving the first liver (liver I) entered a second liver (liver II), infusion of U-46619 at concentrations below 200 nM to the influent perfusate of liver I increased the portal pressure of liver I, but not of liver II. At higher concentrations of U-46619 there was also an increase of the portal pressure of liver II and with concentrations above 800 nM the pressure responses of both livers were near-maximal [19.6 +/- 0.8 (n = 7) cm H2O and 16.5 +/- 1.1 (n = 8) cm H2O for livers I and II, respectively]. There was a similar behaviour of glucose release from livers I and II in response to U-46619 infusion. When liver I was perfused in the retrograde direction, a significant pressure or glucose response of liver II (antegrade perfusion) could not be observed even with U-46619 concentrations up to 1000 nM. 5. Similarly, the perfusion pressure increase and glucose release induced by leukotriene C4 (10 nM) observed with liver II was only about 20% of that seen with liver I.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prostaglandins and their analogues on hormone-stimulated glycogenolysis in primary cultures of rat hepatocytes

Hepatocytes were isolated by collagenase perfusion method from adult male rats, cultured and then prelabeled with [14C]glucose. The [14C]glycogen-labeled cells were used in experiments for effect of prostaglandins on hormone-stimulated glycogenolysis. Prostaglandin E1, prostaglandin E2 and 16,16-dimethylprostaglandin E2, but not prostaglandin D2 or prostaglandin F2 alpha, inhibited glycogenolysis stimulated by glucagon, epinephrine, isoproterenol (beta-adrenergic agonist) or epinephrine in the presence of propranolol (beta-antagonist) in primary cultured hepatocytes. The inhibitory effects on day 2 of cultures were approx. twice those on day 1. Dimethylprostaglandin E2 (10(-6)M) caused 60-70% inhibitions of the stimulations by these substances. In the case of the stimulation by glucagon, the inhibition further increased by 80-100% on day 3 of culture. Prostaglandin E1 and prostaglandin E2 caused less inhibition than dimethylprostaglandin E2 of all these stimulations. Dinorprostaglandin E1 (9 alpha,13-dihydroxy-7-ketodinorprost-11-enoic acid), which is a hepatocyte-metabolite of prostaglandin E1 and prostaglandin E2, and arachidonic acid did not have any inhibitory effects. These data indicate that the E series of prostaglandins may function as the regulation of hepatic glycogenolysis stimulated by epinephrine and glucagon, and that their rapid degradation system may contribute to the modulation of the action in liver.

Stimulation of prostaglandin release by Ca2+-mobilizing agents from the perfused rat liver. A comparative study on the action of ATP, UTP, phenylephrine, vasopressin and nerve stimulation

Several Ca2+-mobilizing agents were tested for their potential to elicit the net release of prostaglandins from the isolated perfused rat liver. Among these ATP and UTP only led to an efficient stimulation of PGD2 and PGE2 synthesis. 20 microM ATP or 20 microM UTP increased the release of PGD2 8-fold and that of PGE2 2 to 3-fold. In total, at least 40 times more PGD2 than PGE2 left the liver after stimulation. The time course of prostaglandin release was similar for both nucleotides. Vasopressin had almost no effect on the release of both prostaglandins and on portal vein pressure. But phenylephrine and nerve stimulation while raising the PGD2 efflux only slightly caused an elevation of PGE2 outflow and portal pressure.

Studies on synthesis and degradation of eicosanoids by rat hepatocytes in primary culture

The potential of hepatocytes in primary cultures to degrade the prostanoids produced by Kupffer cells and to synthesize eicosanoids, especially leukotriene B4, after treatment with D-galactosamine was studied. Hepatocytes in primary cultures showed a substantial capability to degrade all the prostanoids produced by stimulated Kupffer cells. The rate of degradation, approx. 2 pmol/min per 10(6) hepatocytes, was nearly the same for the prostaglandins D2, E2 and F2a. Lower rates were determined for thromboxane B2 (0.4 pmol/min per 10(6) cells) and for 6-ketoprostaglandin F1a (0.2 pmol/min per 10(6) cells). The degradation products of these prostanoids lacked biological activity, e.g., reactivity with specific antibodies and the ability to contract segments of rabbit femoral artery. In the presence of 30 microM arachidonic acid, hepatocytes produced only very small amounts of prostaglandins and thromboxane, ranging from less than or equal to 22 to 50 fmol/30 min per 10(6) cells. Neither untreated nor D-galactosamine-treated hepatocytes released significant amounts of leukotriene B4. Hepatocytes appear to be the site of degradation rather than synthesis of eicosanoids in the liver.

Prostanoid synthesis in isolated parenchymal and nonparenchymal mouse liver cells in the presence of arachidonic acid

Prostanoid synthesis was investigated in suspensions of isolated mouse hepatocytes and nonparenchymal liver cells. A stable metabolite of thromboxane A2 (TXB2) of prostacyclin (6-keto PGF1 alpha) and one of the prostaglandins (PGF2 alpha) was detected by radio-immuno-assay (RIA). Hepatocytes synthesized mainly TXB2, while smaller amounts of 6-keto PGF1 alpha and PGF2 alpha were detected during 60 min incubation. Homogenization of hepatocytes caused a slight increase of TXB2 production and provoked the synthesis of PGF2 alpha and 6-keto PGF1 alpha. The addition of arachidonate to hepatocytes did not influence prostanoid production at concentrations below 10-5M. Higher concentrations further increased TXB2 production and also increased the synthesis of 6-keto PGF1 alpha and PGF2 alpha. Nonparenchymal cells synthesized all the three types of prostanoids and homogenization of these cells did not result in a marked change. The addition of 10(-7)-10(-5)M arachidonate increased the TXB2, 6-keto PGF1 alpha and PGF2 alpha synthesis in nonparenchymal cells. No further increase was found at higher concentrations.