Preventive effects of 5-fluorouridine and uridine on d-galactosamine-induced liver injury

Gut microbiota dysbiosis links chronic apical periodontitis to liver fibrosis in nonalcoholic fatty liver disease: Insights from a mouse model

AIM

In this study, we investigated the systemic implications of chronic apical periodontitis (CAP). CAP may contribute to the nonalcoholic fatty liver disease (NAFLD) progression through the gut microbiota and its metabolites, which are related to the degree of fibrosis.

METHODOLOGY

Sixteen 7-week-old male apolipoprotein E knockout (apoE-/-) mice were randomly divided into two groups: the CAP and Con groups. A CAP model was established by sealing the first- and second-maxillary molars with bacterium-containing cotton balls. Apical lesions were evaluated by micro-CT. Histological evaluations of NAFLD were performed using second harmonic generation/two-photon excitation fluorescence (SHG/TPEF) assays. Additionally, we comprehensively analyzed the gut microbiota using 16S rRNA gene sequencing and explored metabolic profiles by liquid chromatography-mass spectrometry (LC-MS). Immunofluorescence analysis was used to examine the impact of CAP on tight junction proteins and mucin expression. Transcriptome assays have elucidated gene expression alterations in liver tissues.

RESULTS

Micro-CT scans revealed an evident periapical bone loss in the CAP group, and the total collagen percentage was increased (Con, 0.0361 ± 0.00510%, CAP, 0.0589 ± 0.00731%, p < .05). 16S rRNA sequencing revealed reduced diversity and distinct taxonomic enrichment in the CAP group. Metabolomic assessments revealed that differentially enriched metabolites, including D-galactosamine, were enriched and that 16-hydroxyhexadecanoic acid and 3-methylindole were depleted in the CAP group. Immunofluorescence analyses revealed disruptions in tight junction proteins and mucin production, indicating intestinal barrier integrity disruption. Liver transcriptome analysis revealed upregulation of Lpin-1 expression in the CAP group.

CONCLUSION

This study provides comprehensive evidence of the systemic effects of CAP on liver fibrosis in NAFLD patients by elucidating alterations in the gut microbiota composition and metabolism.

Intraperitoneal injection ofd-galactosamine provides a potent cell proliferation stimulus for the detection of initiation activities of chemicals in rat liver

In an in vivo 5-week initiation assay model, chemical hepatectomy by hepato-toxicant administration was utilized as a cell proliferation stimulus as an alternative to the two-thirds partial hepatectomy. The study investigated the effect of an intraperitoneal (i.p.) injection of D-galactosamine (D-gal) for this purpose in a medium-term liver bioassay, with a further focus on cell proliferation kinetics and cytochrome P450 (CYP) expression. In experiment I, cell proliferation in rat liver after a single administration of D-gal (700 mg kg(-1), i.p.) was analysed by the bromodeoxyuridine (BrdU) labeling method, and CYP isozymes were quantified by immunoblotting. In experiment II, the induction of glutathione S-transferase placental form (GST-P) positive foci by 1,2-dimethylhydrazine (DMH) was evaluated in a modified in vivo 5-week initiation assay model. At 84 hours after single administration of d-gal (i.p.) the BrdU index was markedly elevated (27.5% +/- 9.5%). Although CYP 2E1 and 1A2 apoprotein contents decreased transiently to less than 20% of the control level, subsequently they recovered to 60% and 40% of the control level, respectively, at 84 hours. Induction of GST-P positive foci in the group given DMH at 84 hours after a single administration of d-gal was significantly greater than in the control group, correlating with the kinetics of cell proliferation. In conclusion, the sensitivity of the present initiation assay using D-gal i.p. is high, so that D-gal i.p. can be considered an effective cell proliferation stimulus.

The enhancing action of d-galactosamine on lipopolysaccharide-induced nitric oxide production in RAW 264.7 macrophage cells

The effect of D-galactosamine (D-GalN) on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells was examined. D-GalN augmented the production of NO, but not tumor necrosis factor (TNF)-alpha in LPS-stimulated RAW 264.7 cells. Pretreatment of D-GalN augmented the NO production whereas its post-treatment did not. D-GalN augmented the NO production in RAW 264.7 cells stimulated with either TNF-alpha and interferon-gamma. The augmentation of LPS-induced NO production by D-GalN was due to enhanced expressions of an inducible type of NO synthase mRNA and proteins. Intracellular reactive oxygen species (ROS) were exclusively generated in RAW 264.7 cells stimulated with D-GalN and LPS. Scavenging of intracellular ROS abrogated the augmentation of NO production. It was therefore suggested that D-GalN might augment LPS-induced NO production through the generation of intracellular ROS.

Dietary nucleotide supplementation reduces thioacetamide-induced liver fibrosis in rats

Dietary nucleotides reportedly promote functionality and repair in fibrotic liver. Liver fibrosis is characterized by an excessive accumulation of extracellular matrix components, which lead to the impairment of the hepatic function. The aim of this work was to evaluate the influence of dietary nucleotides on liver fibrosis induced by thioacetamide and to elucidate the mechanism by which nucleotides exert their protective effects. Rats consumed ad libitum 300 mg/L thioacetamide in drinking water and were pair-fed diets with (group TN) or without nucleotides (group TS) for 4 mo. Liver histology and extracellular matrix components, liver collagenase and prolyl 4-hydroxylase activities, and tissue inhibitor of metalloproteinases-1 were assessed. The degree of fibrosis was lower in group TN than in group TS. Group TN had lower hepatic concentration of hydroxyproline (P < 0.05), collagen type I (P = 0.12) and type III (P = 0.20), fibronectin (P = 0.05), laminin (P = 0.11) and desmin (P = 0.07), higher collagenolytic activity (P < 0.05), lower prolyl 4-hydroxylase activity (P < 0.05) and lower prolyl 4-hydroxylase (P = 0.10) and tissue inhibitor of metalloproteinase-1 (P = 0.06) expression than group TS. Moreover, expression of tissue inhibitor of the metalloproteinases-1 gene was lower in group TN than in group TS (P < 0.05). These data indicate that the reduction of liver fibrosis in nucleotide-supplemented rats may rely on the enhancement of collagenase activity and the reduction of collagen content and maturation.

Role of the hepatic function in the development of the pyrogenic tolerance to muramyl dipeptide

We have demonstrated that the hepatic function may have an important role in the development of tolerance to the pyrogenic effect induced by endotoxin. To further investigate if the role of the hepatic function in the development of tolerance also extends to that induced by other pyrogenic stimuli, we investigated the effect of galactosamine, a specific inhibitor of the hepatic protein synthesis, on the development of tolerance to the pyrogenic effect induced by muramyl dipeptide (MDP) in rats. Pyrogenic tolerance was observed after the second intravenous or intraperitoneal injection of MDP (500 microgram/kg), 24 h after the first injection, similar to what was observed with endotoxin. Pyrogenic tolerance was abolished when galactosamine (300 mg/kg ip) was injected simultaneously with MDP (500 microgram/kg iv) on the first day. When uridine (600 mg/kg ip) was administered simultaneously with galactosamine (300 mg/kg ip) and the first injection of MDP (500 microgram/kg ip), pyrogenic tolerance was again observed after the second injection of the peptidoglycan. In conclusion, the hepatic function may not be important only for the development of tolerance to endotoxin, but also to a totally different pyrogenic stimulus such as MDP.

Influence of lectin inhibitors on Leishmania major growth and morphology

Gut lectins of the insect vectors play important roles in the transmission of pathogens. Galactosamine, a sandfly midgut lectin inhibitor, was previously demonstrated to increase the intensity of Leishmania infection in sandflies; it was suggested that this was due to the inhibition of sandfly midgut lectin. However, galactosamine might also enhance Leishmania growth in the sandfly. Therefore, the aim of this work was to study the effect of galactosamine and other carbohydrates on Leishmania in vitro. At 50 mM concentration, galactosamine inhibits growth of promastigotes, at 10 mM it induces morphological changes similar to that seen in infected sandflies. Glucosamine effect is less pronounced, galactose has no effect. This suggests that the effect of galactosamine on Leishmania differs in vivo and in vitro. Thus, galactosamine does not enhance Leishmania development in sandflies directly, but rather interferes with some aspect of sandfly physiology (e.g. proteinase and/or lectin activity).

Glycine and uridine prevent D-galactosamine hepatotoxicity in the rat: role of Kupffer cells

Extrahepatic factors, such as increased gut permeability and bacteria from the gut, have been shown to play a role in D-galactosamine toxicity in rats. Because bacterial endotoxin activates Kupffer cells, the purpose of this study was to clarify the role of Kupffer cells in the mechanism of D-galactosamine hepatotoxicity in rats and determine whether uridine, a compound that rescues animals from D-galactosamine toxicity, affects Kupffer cells. Rats were fed control or glycine (5%) containing diets to prevent Kupffer cell activation or treated with gadolinium chloride (GdCl3, 20 mg/kg) to destroy Kupffer cells selectively before injection of D-galactosamine (500 mg/kg, intraperitoneally). D-galactosamine caused panlobular focal hepatocellular necrosis, polymorphonuclear cell infiltration, and increased serum transaminases significantly at 24 hours. Dietary glycine or pretreatment with GdCl3 prevented these effects. D-galactosamine caused a transient increase in circulating endotoxin that was maximal at 1 hour and was blunted significantly by dietary glycine. Additionally, antisera to tumor necrosis factor-alpha (TNF-alpha) prevented hepatotoxicity caused by D-galactosamine. Moreover, apoptosis in hepatocytes caused by D-galactosamine occurred before necrosis (6 hours) and was prevented by glycine, GdCl3, TNF-alpha antiserum, and uridine. Thus, it was hypothesized that TNF-alpha from Kupffer cells causes apoptosis after D-galactosamine administration in the rat. Indeed, increases in TNF-alpha messenger RNA (mRNA) were detected as early as 2.5 hours after D-galactosamine treatment. Previous work proposed that uridine blocks D-galactosamine toxicity by preventing inhibition of mRNA synthesis. In view of these results, the possibility that uridine might affect Kupffer cells was investigated. Uridine significantly blunted the increase in [Ca2+]i and release of TNF-alpha caused by endotoxin in isolated Kupffer cells and prevented apoptosis caused by D-galactosamine treatment in vivo. These data support the hypothesis that uridine prevents D-galactosamine hepatotoxicity not only by rescuing the hepatocyte in the late phases of the injury but also preventing TNF-alpha release from Kupffer cells thereby blocking apoptosis that occurs early after D-galactosamine treatment. Taken together, these data strongly support the role of Kupffer cell activation by endotoxin early after D-galactosamine treatment as an important event in the mechanism of hepatotoxicity in the rat.

Biochemical pharmacology and analysis of fluoropyrimidines alone and in combination with modulators

After more than three decades since their introduction, fluoropyrimidines, especially FUra, are still a mainstay in the treatment of various solid malignancies. The antitumor effects of fluoropyrimidines are dependent upon metabolic activation. FdUMP, FUTP and FdUTP were identified as the key cytotoxic metabolites that interfere with the proper function of thymidylate synthase and nucleic acids. The relevance of these metabolites is cell-type specific. Recently, fluorouridine diphospho sugars have been detected, but the precise function of this class of metabolites is currently unknown. In mammalian systems fluoropyrimidines and their natural counterparts share the same metabolic pathways since the substrate properties in enzyme-catalyzed reactions are frequently comparable. Ongoing studies indicate that the metabolism and action of fluoropyrimidines exhibit circadian rhythms, which appear to be due to variations in the activity of metabolizing enzymes. Essential for the expanding knowledge of the pathways and effects of fluoropyrimidines has been the constant improvement of analytical methods. These include ligand binding techniques, numerous dedicated HPLC systems and 19F-NMR. Because the overall response rates achieved with fluoropyrimidines are modest, strategies based on biochemical modulation have been devised to enhance their therapeutic index. Biochemical modulators include a wide range of various compounds with different modes of action. In recently completed clinical trials, combinations of FUra with leucovorin, a precursor for 5,10-methylene tetrahydrofolate, or with levamisole, an anthelminthic with immunomodulatory activity, appeared to be superior to FUra alone. At the preclinical level combinations of fluoropyrimidines with, e.g. interferons or L-histidinol were demonstrated to be interesting candidates for further testing. The future therapeutic utility of fluoropyrimidines will depend on both the improvement of combination regimens currently used in the treatment of cancer patients and the judicious clinical implementation of promising experimental modulation strategies. Moreover, novel fluoropyrimidines with superior pharmacological properties may become important as part of or instead of modulation approaches.

[Effect of D-galactosamine on nucleotides in the rat heart. Effects of cytidine and uridine administration]

The treatment of rats by galactosamine (2 mmol/kg i.p.), which dramatically alters the metabolism of pyrimidine nucleotides in the liver, has been used to investigate the dynamics of pyrimidine nucleotides in the rat heart. Six hours after administration of the drug, the UTP and UDPG myocardial contents were decreased by respectively 40 and 52% while the sum of uracil nucleotides was increased by 66% and that of cytosine nucleotides by 15%. When administered 5 h after galactosamine treatment, cytidine (750 nmol/rat i.v.) induced a further increase in cytosine nucleotides (46% above control value 1 h later) without however effect on uracil nucleotides. On the other hand, the administration of uridine (250 nmol/rat, i.v. 5 h after galactosamine), while restoring UTP, UDPG and the pool of uracil nucleotides, provoked a decrease in cytosine nucleotide level (-17%). In the absence of galactosamine treatment, the administration of uridine and cytidine did not induce changes in nucleotide levels despite a rise in blood cytidine concentration. All these observations support the hypothesis that: 1. the pathway for cytosine nucleotide synthesis predominant in the heart is that utilizing preformed exogenous cytidine and 2. this pathway is mainly controlled by the intracellular concentration of UTP rather than that of CTP.

45Calcium uptake during the transition from reversible to irreversible liver injury induced by D-galactosamine in vivo

The hepatic uptake of 45calcium (45Ca) was studied in rats after administration of D-galactosamine (3 mmoles per kg, i.v.). In contrast to measurements of the hepatic calcium content, 45Ca uptake served as a dynamic rather than a static indicator of calcium homeostasis during the transition from reversible to irreversible liver injury which occurs between 3 and 4 hr after injection of the hepatotoxin. 45Ca uptake during a 1 hr-labeling period increased from 25 to 100% above control between 3 and 4 hr and subsequently remained at this level. The rise in 45Ca uptake and in hepatic calcium content occurred 2 to 3 hr after the D-galactosamine-induced depletion of UTP, UDP-galactose, UDP-glucose and UDP-glucuronate. The level of UDP-glucuronate was the earliest to recover. The enhanced 45Ca uptake was associated with hepatic glycogen breakdown and with an increased SGPT activity in plasma. Inhibition of RNA polymerase II by alpha-amanitin (0.5 mg per kg, i.p.) and of dolichol-dependent protein glycosylation as well as ganglioside synthesis by tunicamycin (2 mg per kg, i.p.) were used to imitate two of the early actions of D-galactosamine and indicated that an interference with either process can lead to an enhanced uptake of 45Ca into the liver in vivo. Uridine, at a dose replenishing uracil nucleotide pools after their depletion by D-galactosamine, prevented or reversed the rise in 45Ca uptake. The antiinflammatory steroid dexamethasone, injected prior to or simultaneously with D-galactosamine also protected against the loss of calcium homeostasis and the development of liver injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Substrate properties of 5-fluorouridine diphospho sugars detected in hepatoma cells

Nucleotide sugars derived from 5-fluorouridine were studied in cultured AS-30D hepatoma cells as well as in kinetic enzyme assays in vitro in comparison with the physiologic uridine diphospho sugars. Hepatoma cells converted 5-fluoro [14C]uridine to 5-fluorouridine diphospho (FUDP) glucose, FUDP-galactose, FUDP-N-acetylglucosamine, FUDP-N-acetylgalactosamine, and trace amounts of FUDP-glucuronate, as analyzed by different systems of high-performance liquid chromatography. 5-Fluoro[14C]uridine and [14C]uridine, at concentrations of 5 microM in the culture medium, were phosphorylated by the cells during 60 min to similar amounts of FUTP and UTP, respectively, while the synthesis of [14]FUDP-sugars was reduced to 14% as compared to that of [14C]UDP-sugars. FUDP-sugars, synthesized by chemical and enzymatic procedures, were assayed in vitro as substrates for enzymes of UDP-sugar metabolism. Km and V values in a range comparable to that of the respective UDP-sugars were determined for FUDP-sugars in the reactions catalyzed by UDP-glucose pyrophosphorylase, galactose-1-phosphate uridylyltransferase, UDP-glucose 4-epimerase, UDP-N-acetylglucosamine 2-epimerase, glycogen synthase, and UDP-glucose dehydrogenase. Our experiments in hepatoma cells and with enzymes in vitro have revealed additional reactions of FUDP-sugar metabolism demonstrating a metabolite pattern analogous to that of UDP-sugars. The amounts of FUDP-sugars formed relative to UDP-sugars in intact cells were smaller than suggested on the basis of their kinetic comparison in vitro.

Depletion of blood plasma cytidine due to increased hepatocellular salvage in D-galactosamine-treated rats

Pyrimidine nucleosides in blood plasma of rats were identified by different procedures, including chemical peak shift methods, before their quantification by reversed-phase high-performance liquid chromatography. The concentrations of uridine, cytidine, and deoxycytidine were 1.0 +/- 0.2, 10.6 +/- 1.9, and 33.4 +/- 5.4 mumol/l, respectively. Six hours after the administration of D-galactosamine, the level of circulating cytidine was severely depressed to 25% of control values; uridine decreased to 54% while deoxycytidine remained unchanged. 24 h after the dose of the amino sugar, the levels of cytidine and uridine returned to control values in blood plasma. Total acid-soluble uridine, cytidine, guanosine, and adenosine was determined by reversed-phase HPLC after treatment of the neutralized acid-soluble supernatant of freeze-clamped rat livers with phosphodiesterase and alkaline phosphatase. Six hours after its administration, D-galactosamine induced a 2.2-fold and a 1.6-fold rise in total acid-soluble uridine and cytidine, respectively. Co-administration of N-(phosphonoacetyl)-L-aspartate, an inhibitor of de novo pyrimidine synthesis, suppressed the increase in total acid-soluble uridine observed after D-galactosamine alone, but was without effect on the enhancement of total cytidine. Three hours after D-galactosamine and 15 min after [2-14C] cytidine, there was a rapid fall of the labeled nucleoside in blood plasma to 49% of control animals accompanied by a 2.8-fold rise in the total radioactivity of rat liver homogenates. From these results it can be concluded that the hepatocellular rise in total acid-soluble cytidine after D-galactosamine, in contrast to the increase in total acid-soluble uridine, originates from the phosphorylation of blood plasma cytidine via the salvage pathway. The depletion of circulating cytidine in the presence of hepatocellular UTP deficiency points to the importance of the liver and the hepatic UTP level for the clearance of blood plasma cytidine.