Suppressive effect of modified arabinoxylan from rice bran (MGN-3) on D-galactosamine-induced IL-18 expression and hepatitis in rats.

We investigated in this study the effect of modified arabinoxylan from rice bran (MGN-3) and its fractions on D-galactosamine (D-GalN)-induced IL-18 expression and hepatitis in rats. Male Wistar rats were pretreated with MGN-3 or fractions of the MGN-3 hydrolysate, or with saline 1 h before administering D-GalN (400 mg/kg B.W.). The serum transaminase activities, IL-18 mRNA expression level in the liver and IL-18 concentration in the serum were determined 24 h after injecting D-GalN. Both the oral and intraperitoneal administration of MGN-3 (20 mg/kg B.W.) alleviated D-GalN-induced hepatic injury under these experimental conditions. The low-molecular-weight fraction (LMW) of MGN-3 showed the strongest protective effect on D-GalN-induced liver injury, its main sugar component being glucose. Moreover, the D-GalN-induced IL-18 expression was significantly reduced by treating with MGN-3 and LMW. The results suggest that MGN-3 and LMW could provide significant protection against D-GalN liver injury, and that IL-18 might be involved in their protective influence.

Protection by dietary Spirulina platensis against D-galactosamine--and acetaminophen-induced liver injuries.

Increasing attention has been paid to Spirulina for its potential clinical uses. The present study investigated the protection by dietary Spirulina platensis against d-galactosamine (d-GalN)- and acetaminophen (APAP)-induced hepatitis in ICR mice. Mice in each group (n 6) were fed with a standard diet (American Institute of Nutrition (AIN)-93G), a positive control diet containing 0.5 % butylated hydroxytoluene (BHT), or a diet containing 3, 6 or 9 % S. platensis for 1 week. On the last day the mice were treated with d-GalN (300 mg/kg body weight, intraperitoneally) or APAP (150 mg/kg body weight, intraperitoneally) and 24 h later the mice were killed. The doses of both 6 and 9 % S. platensis were found to significantly alleviate the increase of serum glutamate oxaloacetoacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) activities in d-GalN- or APAP-intoxicated mice. The observation was very similar to that of the positive control groups. Two more experiments were carried out to investigate the involvement of thiobarbituric acid-reactive substances (TBARS) and IL-18 in the suppression of 6 % S. platensis on d-GalN- and APAP-induced hepatitis. The significant increase of GOT and GPT activities was found to be accompanied with the elevation of hepatic TBARS level, IL-18 mRNA expression and serum IL-18 concentration, and was significantly alleviated by supplementation with 6 % S. platensis in diets. These results showed that dietary S. platensis could provide a significant protection against d-GalN- and APAP-induced liver injuries, and IL-18 and lipid peroxidation might be involved in the protective influence of S. platensis.

Mechanism of the suppression against D-galactosamine-induced hepatic injury by dietary amino acids in rats.

To elucidate the mechanism by which dietary amino acids suppress the D-galactosamine (D-GalN)-induced hepatitis, we examined the involvement of Kupffer cells, tumor necrosis factor-alpha (TNF-alpha) and apoptosis in the mechanism. In experiment 1, the rats were fed with 10% L-glutamine or 5% glycine diet injected with D-GalN with or without gadolinium chloride (GdCl3)-pretreatment. The results indicated that these amino acids suppressed the D-GalN-induced elevation of serum transaminase activities, irrespective of GdCl3-pretreatment. In experiment 2, rats were fed with 10% of L-glutamine, L-serine, L-alanine or L-glutamic acid diets injected with D-GalN. The results demonstrated that all these amino acids suppressed the D-GalN-induced elevation of serum transaminase activities, but that serum TNF-alpha concentrations and hepatic caspase-3 activities in the rats were not appreciably changed. In conclusion, the suppressive effects of amino acids on D-GalN-induced hepatitis were suggested not to be always mediated by the inhibition of Kupffer cells --> TNF-alpha --> apoptosis pathway.

Production of L-tryptophan-derived catabolites in hepatocytes from streptozotocin-induced diabetic rats.

BACKGROUND: Recently the L-tryptophan (Trp) metabolites such as L-kynurenine(Kyn), L-kinurenic acid, quinolinic acid (QA) and picolinic acid (PA) have been shown physiologically important in central nervous and immune system, and various enzyme activities concerning their production were reported to be affected by insulin-dependent diabetes mellitus. However, the states of these metabolites in diabetes have not been clarified enough yet. AIM OF STUDY: The present study was performed to make clear the states of the productions of L-Kyn, QA, PA and nicotinamide (Nam) in vitro in the hepatocytes prepared from streptozotocin (STZ)-induced diabetic rats using [5-3H]L-Trp. METHODS: The diabetic model rats were made by STZ injection (60 mg/kg) and the hepatocytes isolated from the rats were incubated with [5-3H]L-Trp. The amounts of metabolites derived from L-Trp were determined by the isotope-dilution methods. RESULTS: The alpha-amino-beta-carboxymuconate-epsilon-semiarldehyde decarboxylase (ACMSD) mRNA level in the diabetic group was greatly higher than that in the control group. In the STZ-induced diabetes group, the amount of [5-3H]L-Trp converted to tritiated water, L-Kyn or QA were found to be more than 3 times of that in the control group, respectively. The produced amounts of PA and Nam were not significantly different between the diabetic and the control groups. CONCLUSIONS: It is suggested that STZ-diabetes mellitus causes augmentations of both L-Kyn and QA generations but not those of PA and Nam in liver, indicating the possibility that the immune and neuronal systems of insulin dependent diabetes mellitus would be influenced by the increased amounts of LKyn and QA but not by those of PA and Nam.

L-Gln and L-Ser suppress the D-galactosamine-induced IL-18 expression and hepatitis.

D-Galactosamine (GalN) induces acute hepatitis in experimental animals and this hepatitis has been shown to be suppressed by preceding ingestion of amino acids such as Gly, L-Ser, and L-Gln. However, little is known about the mechanism of its action. The present study shows for the first time that IL-18 reduction is involved in the suppressive actions of L-Gln and L-Ser on GalN-induced hepatitis. Elevation of IL-18 mRNA expression in liver and its concentration in serum in GalN-treated rats were found to be suppressed by preceding ingestion of 10% L-Gln- or 10% L-Ser diets, and resulted in the attenuation of the increase in serum transaminase (ALT and AST) activities, indexes of hepatic injury. These results suggest that suppressive effects of some dietary amino acids on the GalN-induced hepatitis are mediated by IL-18 reduction.

Roles of nuclear receptors in the up-regulation of hepatic cholesterol 7alpha-hydroxylase by cholestyramine in rats.

Nuclear receptors are involved in regulating the expression of cholesterol 7alpha-hydroxylase (CYP7A1), however, their roles in the up-regulation of CYP7A1 by cholestyramine (CSR) are still unclear. In the present study, male Wistar rats were divided into four groups and fed [high sucrose + 10% lard diet] (H), [H + 3% CSR diet] (H + CSR), [H + 0.5% cholesterol + 0.25% sodium cholate diet] (C), or [C + 3% CSR diet] (C + CSR) for 2 weeks. Cholestyramine decreased serum and liver cholesterol levels significantly in rats fed C-based diets, but had no effect on these parameters in rats fed H-based diets. Cholestyramine raised hepatic levels of CYP7A1 mRNA and activity in both groups. The gene expression of hepatic ATP-binding cassettes A1 and G5, regulated by liver X receptor (LXR), were unchanged and down-regulated by cholestyramine, respectively. The mRNA levels of the hepatic ATP-binding cassette B11 and short heterodimer partner (SHP), regulated by farnesoid X receptor (FXR), were not changed by cholestyramine. C-based diets, which contained cholesterol and cholic acid, increased SHP mRNA levels compared to H-based diets. Consequently, in rats fed the C+CSR diet, hepatic FXR was activated by dietary bile acids, but the hepatic CYP7A1 mRNA level was increased 16-fold compared to that in rats fed an H diet. These results suggest that cholestyramine up-regulates the expression of CYP7A1 independently via LXR- or FXR-mediated pathways in rats.

Effects of various kinds of edible seaweeds in diets on the development of D-galactosamine-induced hepatopathy in rats.

In the present study we investigated the effects of 11 kinds of edible seaweeds (6 brown and 5 red algae) which contain characteristic seaweed dietary fibers on the induction of D-GalN (D-galactosamine)-hepatopathy in rats (Exps. 1 and 2). Then, the efficacy of various components prepared from Gelidium sp., which was found to alleviate the hepatopathy in Exps. 1 and 2, was examined (Exp. 3). The rats were fed the diets containing various kinds of seaweeds (Exps. 1 and 2), or several components of Gelidium sp. such as total dietary fiber (TDF), soluble dietary fiber (SDF), insoluble dietary fiber (IDF) and dietary fiber-free components (DFFC) (Exp. 3), for 8 d. The rats in all experiments were injected with D-GalN (800 mg/kg body weight) intraperitoneally at the 7th day to induce liver injury and were sacrificed 24 h after the injection of D-GalN. The serum transaminase activities (ALT and AST) and lactate dehydrogenase (LDH) were determined to evaluate the levels of hepatopathy. In Exp. 3, the total GSH concentration in the liver, plasma and cecal contents and organic acid concentration in cecal contents were also evaluated. In Exps. 1 and 2, repressive effects against D-GalN-hepatopathy were shown by four seaweeds Laminaria sp., Gelidium sp., Sargassum fulvellum and Eisenia bicyclis. In Exp. 3, it was found that protective activity in Gelidium sp. against D-GalN-hepatopathy existed not only in the SDF but also in the DFFC fraction. The results in Exp. 3 also indicated that the total GSH but not organic acid concentration in the cecal contents were significantly correlated with serum AST activity, suggesting that the protective effect of Gelidium sp. on D-GalN-hepatopathy in rats is related to GSH metabolism in the intestine.

Effect of dietary fiber in edible seaweeds on the development of D-galactosamine-induced hepatopathy in rats.

Previous studies in our laboratory demonstrated the repressive effect of seaweeds (Laminaria sp., Sargassum fulvellum, Eisenia bicyclis and Gelidium sp.) against D-galactosamine (D-GalN)-induced hepatopathy. However, the mechanism by which these four seaweeds attenuate the D-GalN-hepatopathy has not been completely clarified. This study was carried out to determine the constituents of these seaweeds that protect rats against the D-GalN-hepatopathy. Male Wistar rats were fed for 8 d diets containing 5% seaweeds with or without the antibiotic neomycin (NEO) in experiment 1, and typical seaweed dietary fibers (laminaran, fucoidan, alginate, agar and kappa-carrageenan) of these seaweeds in experiment 2. On the 7th day, the rats were treated with D-GalN (1,900 mg in experiment 1 and 800 mg/kg in experiment 2) and then sacrificed 24 h after the injection of D-GalN. Their serum transaminase (aspartate and alanine aminotransferases: AST and ALT) activities were then determined. In experiment 1, the serum AST and ALT levels in the rats fed the four kinds of seaweeds without NEO were significantly low in comparison to that of the control group, but those with NEO were not significantly different among the groups. In experiment 2, the serum AST and ALT levels in the rats fed fucoidan were significantly low in comparison to those of the other groups fed the dietary fibers and the control. These results suggest that the protective effect of the three kinds of brown seaweeds Laminaria sp., Sargassum fulvellum and Eisenia bicyclis against D-GalN-hepatopathy was caused at least in part by fucoidan.

Dietary protein level and dietary interaction affect quinolinic acid concentration in rats.

During tryptophan-niacin conversion, hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) [EC4.1.1.45] plays a key role in regulating NAD biosynthesis. ACMSD activity is greatly affected by many factors such as nutritional status and disease. The tryptophan catabolite quinolinic acid has been reported to be associated with the pathogenesis of various disorders and is a potential endogenous toxin. However the effects of dietary protein levels or dietary interaction between protein levels and fatty acid type to this process have not been investigated and are still unknown. In this study, we examined whether dietary protein level, fatty acid type, namely saturated fatty acid and polyunsaturated fatty acid, and their interaction affect serum quinolinic acid concentration in rats. Male Sprague-Dawley rats (4-weeks old) were fed with 20% casein + 10% stearic acid diet (20C10S), 20% casein + 10% linoleic acid diet (20C10L), 40% casein + 10% stearic acid diet (40C10S), or 40% casein + 10% linoleic acid diet (40C10L) for 8 days, and serum quinolinic acid concentration and ACMSD activity were determined. Serum quinolinic acid concentration was significantly increased in the 40C10L group compared with other three groups. There was also the negative correlation between the sum of liver and kidney ACMSD activities, and serum quinolinic acid concentration per tryptophan intake (r = 0.8209, p < 0.01). Increased serum QA concentrations are probably due to a decreased ACMSD activity.

Effect of docosahexaenoic acid intake on lipid peroxidation in diabetic rat retina under oxidative stress.

Docosahexaenoic acid (DHA) plays an important role in visual function but has a highly oxidation-prone chemical structure. Therefore, we investigated how dietary DHA affects the generation of lipid peroxides in rat retina under oxidative stress in diabetes with/without vitamin E (VE) deficiency. Streptozotocin-induced (50 mg i.p./kg B.W.) diabetic Sprague-Dawley (SD) rats were assigned to four groups: (i) control/VE(+), (ii) DHA/VE(+), (iii) control/VE( - ) and (iv) DHA/VE( - ), and raised for 28 days. We then measured lipid peroxide levels in the retina, serum and liver. With a normal intake of VE, dietary DHA increased only the retinal level of thiobarbituric acid-reactive substances (TBARS) slightly. In contrast, in rats with VE deficiency, dietary DHA increased serum and liver lipid peroxide levels but not in the retina. These results suggest that dietary DHA does not necessarily promote lipid peroxidation in the retina even under high oxidative stress.

Effects of dietary corn bran hemicellulose and neomycin on hepatic caspase-3 activity and glycoprotein concentration in rats treated with or without D-galactosamine.

The effects of dietary corn bran hemicellulose (CBH) and neomycin (Neo) on hepatic caspase-3 activity and glycoprotein concentration were investigated to explore the possible mechanism of the alleviative action of dietary CBH and Neo on the development of D-galactosamine (GalN)-hepatitis. Rats were fed a diet containing 5% CBH with or without neomycin (Neo) for 7 or 14 d. On the last day of feeding, the rats were treated with GalN (400 mg/kg body weight, i.p.), and their plasma transaminase activities, hepatic glycoprotein concentrations and hepatic caspase-3 activities were determined 6 or 24 h later. Although the elevations of plasma transaminase activities were suppressed by CBH or Neo 24 h after GalN-treatment, the activities were not affected by CBH or Neo at an early stage (6 h) of GalN action. At 6 h, hepatic caspase-3 activity was elevated by CBH diet alone as high as that of the GalN-injected control-diet group, and the activity was not elevated further by GalN. At the same time, both GalN-treatment and CBH feeding reduced the hepatic glycoprotein (Mw. 64,000-74,000) concentration, but Neo did not affect the caspase activity or the glycoprotein concentration. These results suggest that dietary CBH elevates hepatic caspase-3 activity and reduces hepatic glycoprotein concentration, and may imply that CBH would suppress GalN-hepatitis not at the early- or middle-step of apoptosis but at the late-step of apoptosis or necrosis, although the relation between these phenomena and the alleviative effects of CBH and Neo on GalN-induced hepatitis is yet to be clarified.

Tryptophan-niacin metabolism in rat with puromycin aminonucleoside-induced nephrosis.

We investigated the change of tryptophan-niacin metabolism in rats with puromycin aminonucleoside PAN-induced nephrosis, the mechanisms responsible for their change of urinary excretion of nicotinamide and its metabolites, and the role of the kidney in tryptophan-niacin conversion. PAN-treated rats were intraperitoneally injected once with a 1.0% (w/v) solution of PAN at a dose of 100 mg/kg body weight. The collection of 24-hour urine was conducted 8 days after PAN injection. Daily urinary excretion of nicotinamide and its metabolites, liver and blood NAD, and key enzyme activities of tryptophan-niacin metabolism were determined. In PAN-treated rats, the sum of urinary excretion of nicotinamide and its metabolites was significantly lower compared with controls. The kidney alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) activity in the PAN-treated group was significantly decreased by 50%, compared with the control group. Although kidney ACMSD activity was reduced, the conversion of tryptophan to niacin tended to be lower in the PAN-treated rats. A decrease in urinary excretion of niacin and the conversion of tryptophan to niacin in nephrotic rats may contribute to a low level of blood tryptophan. The role of kidney ACMSD activity may be minimal concerning tryptophan-niacin conversion under this experimental condition.

Differential effects of pyrazinamide and clofibrate on gene expression of rat hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase, a key enzyme of the tryptophan-NAD pathway.

Hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) [EC4.1.1.45] plays a key role in regulating NAD biosynthesis from tryptophan. The aim of this study was to evaluate the ACMSD mRNA expression after pyrazinamide or peroxisome proliferators ingestion. When rats were fed a control (pyrazinamide- and clofibrate-free) diet, 1% pyrazinamide- or 0.24% clofibrate-containing diets for 8 days, hepatic ACMSD activity and mRNA in rats consuming the clofibrate-containing diet was strongly suppressed, as compared with those fed the control and pyrazinamide diet. Pyrazinamide suppressed liver and kidney ACMSD activities, but did not affect ACMSD mRNA. Blood NAD was increased in the clofibrate and pyrazinamide groups. Shifting from the control diet to a clofibrate diet suppressed ACMSD mRNA strongly at day 1 and continued through day 4. However ACMSD activity decreased gradually. In rats fed with several kinds of peroxisome-proliferator-containing diets such as phthalate ester, bezafibrate, Wy-14,643, 2-(-4-chlorophenoxy) propionic acid, or dehydroisoandrosterone for 8 days, hepatic ACMSD mRNA was drastically decreased by all the peroxisome proliferators. These results suggest that the transcription level of hepatic ACMSD is modulated by peroxisome proliferators, and the fluctuation of the hepatic ACMSD mRNA expression was followed by that of the ACMSD activity. However, pyrazinamide does not affect the transcription level of hepatic ACMSD.

Differential effects of dietary fatty acids on rat liver alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase activity and gene expression.

Hepatic alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD; formerly termed picolinic carboxylase) [EC4.1.1.45] plays a key role in regulating NAD biosynthesis and the generation of quinolinate (quinolinic acid) from tryptophan. Quinolinate is a potent endogenous excitotoxin of neuronal cells. We previously reported that ingestion of fatty acids by rats leads to a decrease in their hepatic ACMSD activity. However, the mechanism of this phenomenon is not clarified. We previously purified ACMSD and cloned cDNA encoding rat ACMSD. Therefore, in this study, we examined the differential effect of fatty acids on ACMSD mRNA expression by Northern blot. Moreover, we measured quinolinic acid concentration in rats fed on fatty acid. When diets containing 2% level of fatty acid were given to male Sprague-Dawley rats (4 weeks old) for 8 days, long-chain saturated fatty acids and oleic acid did not affect ACMSD mRNA expression in the liver. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) strongly suppressed the liver ACMSD mRNA expression. In rats fed with high linoleic acid diet for 8 days, serum quinolinic acid was significantly increased as compared with the rats fed on a fatty acid-free diet under the condition of the approximately same calorie ingestion. These results suggest that the transcription level of ACMSD is modulated by polyunsaturated fatty acids, and suppressive potency of ACMSD mRNA is n-3 fatty acid family>linoleic acid (n-6 fatty acid)>saturated fatty acid. Moreover, this study provides the information that a high polyunsaturated fatty acid diet affects the production of quinolinic acid in serum by suppressing the ACMSD activity.

Suppressive effect of corn bran hemicellulose on liver injury induced by D-galactosamine in rats.

OBJECTIVE: It is well known that the indigestible oligo- and polysaccharides including dietary fiber are important food components and that they have many physiologic functions. This study examined the effect of water-soluble corn bran hemicellulose (CBH) on the development of D-galactosamine (GalN) hepatitis in rats to obtain some knowledge about new functions of dietary fiber. METHODS: Male Wistar rats were fed diets containing 5% CBH for various days (1 to 14 d). On the final day of feeding rats were treated with GalN (400 mg/kg), and their plasma transaminase (aspartate and alanine aminotransferases) activity (6 or 24 h later) and liver glutathione concentration (6 h later) were determined. RESULTS: Ingested CBH suppressed the increase in plasma aspartate and alanine aminotransferase activities 24 h after GalN treatment. Such suppressive effect was observed only 7 d after CBH ingestion and not after 1 or 3 d. In the early phase of the liver injury, at 6 h after GalN treatment, the liver glutathione concentration in the CBH group was significantly higher than that in the control group, and the concentration in the CBH group after GalN injection was almost the same as that in the control group without GalN treatment. CONCLUSION: Results suggest that dietary CBH suppresses the development of hepatic injury by GalN in rats and that this phenomenon is partly attributable to the increase in hepatic glutathione concentration by CBH.

Phenolic antioxidants richly contained in corn bran are slightly bioavailable in rats.

Phenolic acids (PAs) have been shown to be beneficial to human health and are found most abundantly in corn bran ( approximately 4%, w/w), one of the main dietary fibers. This study therefore evaluated the bioavailabilities of phenolic antioxidants ferulic acid (FA) and p-coumaric acid (PCA) in refined corn bran (RCB) by determining their recovery in the plasma, urine, and feces of rats fed a single meal of a RCB diet containing 5% RCB or adapted to the RCB diet for 10 days. In both studies, 0.4-0.5% of ingested FA and 1.2-2.3% of ingested PCA were recovered in rat urine. By contrast, approximately 81% of FA and approximately 64% of PCA ingested with the single meal were excreted through the rat feces within 3 days after the ingestion. On the other hand, after rats were fed the RCB diet, total FA (all forms of FA) was recovered in plasma at a concentration of 35.0 +/- 2.0 microg/L, total FA and total PCA were excreted through urine at levels of 155.4 +/- 5.8 and 50.9 +/- 6.6 microg/day, respectively. These parameters showed no significant change (P = 0.93, 0.09, and 0.66, respectively) after rats were fed the RCB diet continuously for up to 10 days. These results suggest that the PAs in RCB are bioavailable in rats. Their bioavailabilities, however, are relatively low compared with their high content in RCB and not improved by the adaptation for 10 days to the enriched RCB diet. Additionally, comparison with the results of other studies revealed that high contents of FA and, especially, diferulic acids in cereal bran, which act as cross-links between bran cell wall polysaccharides, may not improve but, rather, limit the bioavailabilities of PAs in vivo.

Digestion and absorption of ferulic acid sugar esters in rat gastrointestinal tract.

We estimated the absorption site and absorptivity of ferulic acid (FA) and its sugar esters, namely 5-O-feruloyl-l-arabinofuranose (FAA) and feruloyl-arabinoxylan (FAXn), in rats on the basis of their recovery in intestinal content and feces by comparing the values with those of a nonabsorbable marker, poly R-478. The results indicated that free FA was absorbed almost completely before reaching cecum. About 40% of dietary FAA was absorbed in rat foregut and 57% disappeared in the cecum. In contrast, about 67% of the FA moiety in FAXn was released and then disappeared predominantly in the hindgut. These results suggested that the existing form of FA in diets affects its absorptivity, its absorption site, and its ensuing fate in the gastrointestinal tract. Those ingested FAs esterified with saccharides; especially, polysaccharides have to transit the hindgut where FA might be released and then absorbed and/or degraded by microflora in lumen. Such microbial degradation may be an important factor affecting the bioavailability of dietary FA.

Identification and expression of alpha cDNA encoding human 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD): a key enzyme for the tryptophan-niacine pathway and quinolinate hypothesis.

Quinolinate (quinolinic acid) is a potent endogenous excitotoxin of neuronal cells. Elevation of quinolinate levels in the brain has been implicated in the pathogenesis of various neurodegenerative disorders, the so-called "quinolinate hypothesis." Quinolinate is non-enzymatically derived from 2-amino-3-carboxymuconate-6-semialdehyde (ACMS). 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD) is the only known enzyme which can process ACMS to a benign catabolite and thus prevent the accumulation of quinolinate from ACMS. ACMSD seems to be regulated by nutritional and hormonal signals, but its molecular mechanism has, to date, been largely unknown. Utilizing partial amino acid sequences obtained from highly purified porcine kidney ACMSD, a cDNA encoding human ACMSD was cloned and characterized. The cDNA encodes a unique open reading frame of 336 amino acids and displays little homology to any known enzymes or motifs in mammalian databases, suggesting that ACMSD may contain a new kind of protein fold. Real-time PCR-based quantification of ACMSD revealed very low but significant levels of the expression in the brain. Brain ACMSD messages was down- and up-regulated in response to low protein diet and streptozocin-induced diabetes, respectively. Expression of QPRT, another enzyme which catabolizes quinolinate, was also found in the brain. This suggests that a pathway does exist by which the levels of quinolinate in the brain are regulated. In this report, we address the molecular basis underlying quinolinate metabolism and the regulation of ACMSD expression.

Dietary linoleic acid suppresses gene expression of rat liver alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD) and increases quinolinic acid in serum.

Hepatic ACMSD [EC4.1.1.45] plays a key role in regulating NAD biosynthesis from tryptophan. We previously reported that ingestion of polyunsaturated fatty acids by rats leads to a decrease in their hepatic ACMSD activity. We purified ACMSD and cloned cDNA encoding rat ACMSD. Therefore, in this study, we examined whether dietary linoleic acid altered ACMSD gene expression and its protein level. Moreover we measured the tryptophan catabolite quinolinic acid level in rats. In the rats fed with linoleic acid, ACMSD mRNA and its protein levels in the liver were strongly suppressed and serum quinolinic acid was significantly increased as compared with the rats fed on a fat-free diet. These results suggest that the transcription level of ACMSD is modulated by linoleic acids or their metabolites and probably there is an inverse relationship between ACMSD activity and the production of quinolinic acid converted from tryptophan.

Identification of a hepatoprotective peptide in wheat gluten hydrolysate against D-galactosamine-induced acute hepatitis in rats.

A hepatoprotective peptide, pyroglutamyl leucine (pyroGlu-Leu), was identified in wheat gluten hydrolysate through an in vivo activity-guided fractionation approach based on D-galactosamine-induced acute hepatitis in rats and fractionation of peptides with large-scale preparative ampholine-free isoelectric focusing. The active acidic fraction predominantly consisted of pyroglutamyl peptides and free pyroglutamic acid. Pyroglutamyl peptides were derivatized with phenyl isothiocyanate after removal of a pyroglutamyl residue by pyroglutamate aminopeptidase. The derivatives were purified by reversed-phase HPLC and subjected to sequence analysis. The active fraction contained pyroGlu-Ile, pyroGlu-Leu, pyroGlu-Gln, pyroGlu-Gln-Gln, and free pyroGlu. Ingestion of pyroGlu-Leu at 20 mg/kg body weight significantly decreased serum aspartate and alanine aminotransferases to approximately 30% and 20% of those values of the vehicle group, respectively, which were near the normal levels. Thirty minutes after ingestion of pyroGlu-Leu at 20 mg/kg, the concentration of pyroGlu-Leu in portal blood plasma increased to approximately 2 µM.