Sex differences in the metabolism of hexachlorobenzene by rats and the development of porphyria in females

Male and female F 344 rats were dosed every other day for 103 days with 50 μmole of hexachlorobenzene (HCB)/kg. Females developed a hepatic porphyria, the urine and liver levels of porphyrins being 40- and 310-fold high respectively than those of males. Urine was periodically hydrolysed and analysed for the three metabolites pentachlorophenol, 2,3,5,6-tetrachlorobenzene-1,4-diol and pentachlorothiophenol (derived from the mercapturate). The combined urinary excretion of these was greater in females than males, especially during the first 10 weeks. Pentachlorthiophenol was particularly high in female urine. After 103 days this metabolite was slightly less in female faeces than in male's but free hepatic pentachlorothiophenol was 3.6-fold greater. Although total 24 hr excretions of metabolites were higher by females than males and after 7 daily doses of HCB, a difference in this respect was not conclusively proven. However, total pentachlorothiophenol excretion was always significantly greater by females. The male/female ratios for pentachlorophenol and pentachlorothiophenol in bile were identical to those for faeces. Excretion of metabolites by both adult males and females was stimulated by pretreatment with diethylstilboestrol (DES). No sex differences in metabolism were observed with immature rats.     

Studies on sex differences in excretion of sulphur derivatives of hexachlorobenzene and pentachloronitrobenzene by rats

The appearance of sex-related differences in the excretion of sulphur derivatives of hexachlorobenzene (HCB) and pentachloronitrobenzene (PCNB) was studied in vitro and in vivo. Sexually immature rats given HCB showed initially no differences in the excretion of N-acetyl-S-(pentachlorophenyl)cysteine, but 5-8 days after weaning the urinary levels of the sulphur derivative began to increase in females until a 10-fold difference between both sexes was established. The studies in vitro and the analysis of tissues after in vivo administration of PCNB showed that conjugation with glutathione and hydrolysis of the conjugates to yield free pentachlorothiophenol do not present sex-related differences. These data tend to reinforce the view that an active renal secretory mechanism probably induced by estrogens during sexual maturation is responsible for the highly efficient excretion of sulphur derivatives of HCB and PCNB by female rats.     

Biotransformation of trichloroethene: dose-dependent excretion of 2,2,2-trichloro-metabolites and mercapturic acids in rats and humans after inhalation

 Chronic bioassays with trichloroethene (TRI) demonstrated carcinogenicity in mice (hepatocellular carcinomas) and rats (renal tubular cell adenomas and carcinomas). The chronic toxicity and carcinogenicity is due to bioactivation reactions. TRI is metabolized by cytochrome P450 and by conjugation with glutathione. Glutathione conjugation results in S-(dichlorovinyl) glutathione (DCVG) and is presumed to be the initial biotransformation step resulting in the formation of nephrotoxic metabolites. Enzymes of the mercapturic acid pathway cleave DCVG to the corresponding cysteine S-conjugate, which is, after translocation to the kidney, cleaved by renal cysteine S-conjugate β-lyase to the electrophile chlorothioketene. After N-acetylation, cysteine S-conjugates are also excreted as mercapturic acids in urine. The object of this study was the dose-dependent quantification of the two isomers of N-acetyl-S-(dichlorovinyl)-L-cysteine, trichloroethanol and trichloroacetic acid, as markers for the glutathione- and cytochrome P450-mediated metabolism, respectively, in the urine of humans and rats after exposure to TRI. Three male volunteers and four rats were exposed to 40, 80 and 160 ppm TRI for 6 h. A dose-dependent increase in the excretion of trichloroacetic acid, trichloroethanol and N-acetyl-S-(dichlorovinyl)-L-cysteine after exposure to TRI was found both in humans and rats. Amounts of 3100 μmol trichloroacetic acid+trichloroethanol and 0.45 μmol mercapturic acids were excreted in urine of humans over 48 h after exposure to 160 ppm TRI. The ratio of trichloroacetic acid+trichloroethanol/mercapturic acid excretion was comparable in rats and humans. A slow rate of elimination with urine of N-acetyl-S-(dichlorovinyl)-L-cysteine was observed both in humans and in rats. However, the ratio of the two isomers of N-acetyl-S-(dichlorovinyl)-L-cysteine was different in man and rat. The results confirm the finding of the urinary excretion of mercapturic acids in humans after TRI exposure and suggest the formation of reactive intermediates in the metabolism of TRI after bioactivation by glutathione also in humans. Received: 22 June 1995 / Accepted: 5 October 1995     

N-Acetyl-S-(1-carbamoyl-2-hydroxy-ethyl)-L-cysteine (iso-GAMA) a further product of human metabolism of acrylamide: comparison with the simultaneously excreted other mercaptuic acids

The N-acetyl-S-(1-carbamoyl-2-hydroxy-ethyl)-l-cysteine (iso-GAMA) could be identified as a further human metabolite of acrylamide. In this study, we report the excretion of d₃-iso-GAMA in human urine after single oral administration of deuterium labelled acrylamide (d₃-AA). One healthy male volunteer ingested a dose of about 1 mg d₃-AA which is equivalent to a dose of 13 μg/kg bodyweight. Over a period of 46 h the urine was collected and the d₃-iso-GAMA levels analysed by LC-ESI-MS/MS. The excretion of iso-GAMA begins five hours after application. It rises to a maximum concentration (c _max) of 43 μg/l which was quantified in the urine excreted after 22 h (t _max). The excretion pattern is parallel to that of the major oxidative metabolite N-acetyl-S-(2-carbamoyl-2-hydroxy-ethyl)-l-cysteine (GAMA). Total recovery of iso-GAMA was about 1% of the applied dose. Together with N-acetyl-S-(2-carbamoylethyl)-l-cysteine (AAMA) and GAMA, 57% of the applied dose is eliminated as mercapturic acids. The elimination kinetics of the three mercapturic acids of AA are compared. We show that dietary doses of acrylamide (AA) cause an overload of detoxification via AAMA and lead to the formation of carcinogenic glycidamide (GA) in the human body.     

N-acetylcysteine-induced inhibition of gastric emptying: A mechanism affording protection to mice from the hepatotoxicity of concomitantly administered acetaminophen

Swiss Webster male mice, 22 ± 3 g, killed 17–18 h following the concomitant oral administration of acetaminophen (350 mg/kg) and N-acetylcysteine (NAC, 100–500 mg/kg, treated) had statistically significant lower plasma transaminases (GOT and GPT) than control mice (acetaminophen + water). Possible mechanisms underlying this protective effect of NAC were examined. NAC (500 mg/kg) reduced [¹⁴C]acetaminophen-derived radioactivity in the blood and tissues but increased the percentage of the dose in the gastrointestinal tract. Depletion of hepatic sulphydryl compounds below 75% of the control value was prevented by NAC treatment, whereas urinary excretion of mercapturate and sulfate, metabolites derived from sulphydryls, were proportionally increased and excretion of unchanged drug was decreased by NAC. Absorption of acetaminophen from the small intestine was prevented by NAC and this was attributed to an inhibition in gastric emptying. Since all changes observed following NAC treatment could be attributed to inhibition of gastric emptying, it was considered the major mechanism responsible for affording in mice protection from acetaminophen-induced hepatocellular damage following concomitant oral administration.     

Biotransformation of derivatives of the fungicides pentachloronitrobenzene and hexachlorobenzene in mammals

1. Biotransformation of N-acetyl-S-(2, 3, 5, 6-tetrachlorophenyl)cysteme and N-acetyl-S-(pentachlorophenyl)cysteine-S-oxide, of the metabolites of both PCNB and HCB, namely N-acetyl-S-(pentachlorophenyl)cysteine, pentachlorothiophenol, penta-chlorothioanisole, 4-methylthio-tetrachlorothiophenol and tetrachloro-1,4-bis(methyl-thio)benzene, and of the PCNB metabolites, S, S'-(tetrachloro-p-phenyleni')dicysteine, and the isomeric tetrachlorothiophenols, has been studied in rabbits, rats and mice, as well as in vitro.

2. Biotransformation products such as thiophenols, thioanisoles, chlorinated benzenes, phenols and anisoles have been identified by g.l.c.     

Toxicokinetics of acrylamide in rats and humans following single oral administration of low doses

The rodent carcinogen acrylamide (AA) is formed during preparation of starch-containing foods. AA is partly metabolized to the genotoxic epoxide glycidamide (GA). After metabolic processing, the mercapturic acids N-acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA), rac-N-acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) and rac-N-acetyl-S-(1-carbamoyl-moyl-2-hydroxyethyl)-L-cysteine (iso-GAMA) are excreted with urine. In humans, AAMA can be sulfoxidized to AAMA-sulfoxide. The aim of this study was to assess potential species-differences in AA-toxicokinetics in rats and humans after single oral administration of doses similar to the daily human dietary exposure. Male Fischer 344 rats (n = 5/dose group) were administered 20 and 100 μg/kg b.w. ¹³C₃-AA in deionized water via oral gavage. Human subjects (n = 3/gender) were orally administered 0.5 and 20 μg/kg b.w. ¹³C₃-AA with drinking water. Urine samples were collected in intervals for 96 and 94 h, respectively. Urinary concentrations of ¹³C₃-AAMA, ¹³C₃-GAMA and ¹³C₃-AAMA-sulfoxide were monitored by liquid chromatography-tandem mass spectrometry. The recovered urinary metabolites accounted for 66.3% and 70.5% of the 20 and 100 μg/kg b.w. doses in rats and for 71.3% and 70.0% of the 0.5 and 20 μg/kg b.w. doses in humans. In rats, ¹³C₃-AAMA accounted for 33.6% and 38.8% of dose and 32.7% and 31.7% of dose was recovered as ¹³C₃-GAMA; ¹³C₃-AAMA-sulfoxide was not detected in rat urine. In humans, ¹³C₃-AAMA, ¹³C₃-GAMA and ¹³C₃-AAMA-sulfoxide accounted for 51.7% and 49.2%, 6.3% and 6.4% and 13.2% and 14.5% of the applied dose, respectively. The obtained results suggest that the extent of AA bioactivation to GA in humans is lower than in rodents.     

The effects of oestrogen administration on tryptophan metabolism in rats and in menopausal women receiving hormone replacement therapy

The effects of the administration of oestrogens on the activity of hepatic tryptophan oxygenase have been assessed both directly (by measurement of enzyme activity in vitro) and indirectly (by measurement of urinary excretion of tryptophan metabolites) in rats, and indirectly in menopausal women receiving hormone replacement therapy. Intraperitoneal administration of 500 μg of oestradiol or ethinyl oestradiol/kg body wt had no effect on the activity of tryptophan oxygenase in homogenates of liver from mature (13-week-old) female rats. Both adrenalectomy and ovariectomy led to a reduction in the activity of tryptophan oxygenase in homogenates of liver from mature rats; again there was no effect of giving 500 μg of oestradiol/kg body wt by intraperitoneal injection. Intraperitoneal administration of 210 μg of oestrone sulphate/kg body wt for 1 or 2 days before killing, or its incorporation in the diet for up to 8 weeks at an equivalent dose rate, had no effect on the activity of tryptophan oxygenase in homogenates of liver from ovariectomized 6–14-week-old female rats. Intraperitoneal administration of 500 μg oestradiol/kg body wt to intact mature female rats together with 500 mg tryptophan/kg body wt caused a reduction in the urinary excretion of xanthurenic and kynurenic acids, kynurenine and N¹-methyl nicotinamide. When peri- and post-menopausal women were treated with ethinyl oestradiol (20 μg/day) or piperazine oestrone sulphate (3 mg/day) for 3 months, there was an increase in the concn of tryptophan in plasma, with no change in the urinary excretion of xanthurenic and kynurenic acids and kynurenine. This study provides no evidence for the induction of tryptophan oxygenase by oestrogens in rats or human beings.     

Formation of GSH-derivatives as a pathway for inactive intermediates in vinylidene chloride-treated rats

The two conjugates, S-[N-(2-hydroxyethyl)carbamoylmethyl]glutathione (GSAAE), and its corresponding mercapturic derivative N-acetyl-S-[N-(2-hydroxyethyl)carbamoylmethyl]cysteine (NCySAAE) were administered to fasted Sprague-Dawley rats as putative metabolites of vinylidene chloride (VDC). Methylthioacetylaminoethanol (MAAE) was identified in the urine of GSAAE- or NCySAAE-treated rats (0.5–2.0 mmol/kg i.p.), as well as in the urine of VDC-treated rats (0.5–2.0 mmol/kg p.o.). The effects of VDC, GSAAE and NCySAAE on the kidney and liver were also examined using aspartate aminotransferase (ASAT), N-acetyl-β-d-glucosaminidase (NAG) and β₂-microglobulin (β₂-m) as urinary parameters of nephrotoxicity, and glutamate dehydrogenase (GLDH), sorbitol dehydrogenase (SDH) and alanine aminotransferase (ALAT) as serum parameters of hepatotoxicity. Unlike treatment with VDC, treatment with both GSAAE and NCySAAE failed to cause kidney and liver toxicity. The results support the hypothesis that MAAE originates from the formation of GSAAE and further metabolization to NCySAAE, and that MAAE excretion does not reveal a pathway of reactive intermediates.     

Porphyrogenic effect of chronic treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin in female rats. Dose-effect relationship following urinary excretion of porphyrins

The porphyrogenic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was evaluated in female rats treated chronically for 45 weeks with 0.01, 0.10, and 1.00 μg/kg TCDD per week. The time course of the urinary porphyrin pattern was followed in order to determine the qualitative and quantitative composition in urine and to test the sensitivity of a parameter such as porphyrins in urine as an indication of exposure to TCDD. The results showed that the dose of 0.01 μg/kg/week resulted in significantly enhanced excretion of coproporphyrin from 6 months onward; with the dose of 0.10 μg/kg/week coproporphyrinuria was observed after 3 months and was associated at 10 months with a significant rise in uroporphyrin. The highest dose (1.00 μg/kg/week) caused enhanced excretion of coproporphyrin from 2 months onward. This effect was associated, at 6 months, with an increase in heptacarboxylic porphyrin and uroporphyrin excretion. A marked porphyric state was established in this group of animals from 8 months onward as indicated by massive enhancement of total urinary porphyrin excretion (about 70 times higher than the control group) with a large prevalence of porphyrins with a high number of carboxyl groups and reversal of the coproporphyrin/uroporphyrin ratio. Accumulation of porphyrins was also observed in liver, spleen, and kidneys of this group of animals. Terminal livers of rats treated with 0.01, 0.10, and 1.00 μg/kg/week contained 1050, 4740, and 30,700 ppt, respectively. Comparison of our data with the literature on the porphyrogenic effect of hexachlorobenzene indicated that TCDD can be considered 1400 times more potent.     

Hexadecane enhances non-biliary,intestinal excretion of stored hexachlorobenzene by rats

[¹⁴C] Hexachlorobenzene (100 mg/kg) was orally administered to 4 groups of rats. Ten days later the effects of hexadecane (3 × 5 ml/kg by gavage) and/or bile duct ligation on urinary and fecal excretion and tissue levels of hexachlorobenzene, were examined. Hexadecane did not affect urinary excretion of hexachlorobenzene, whereas bile duct ligation tripled it. Each of the 3 treatments (n-hexadecane, bile duct ligation and the combination of the two) resulted in a significant increase in fecal excretion of hexachlorobenzene. Moreover, the combination of hexadecane and bile duct ligation produced a greater increase in fecal excretion of hexachlorobenzene in blood, fat and kidney were not affected by any of the treatments, but liver concentrations were reduced significantly by bile duct ligation. Concentrations of hexachlorobenzene in intestinal contents indicate that intestinal-wall passage is the primary route of elimination from the body and that enhancement of elimination occurs mostly distal to the jejunum.     

A-80426, a potent and selective α2-adrenoceptor antagonist with serotonin uptake-blocking activity and putative antidepressant-like effects: II. Pharmacology profile

A-80426 N-[2-(benzofuran-6-yl)ethyl]-N-[(R)?( + (-5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl methyl]-N-methylamine) is a compound that combines in vitro selective inhibition of serotonin synaptosomal uptake and α₂-adrenoceptor antagonism. In the present studies, A-80426 was evaluated in vivo for its ability to block serotonin uptake and α₂-adrenoceptors. The antidepressant potential of the compound was also assessed. In rats, A-80426 significantly reduced p-chloroamphetamine (PCA)-induced hyperactivity, a measure of the in vivo blockade of serotonin uptake, after acute (ED₅₀ = 13 μmoles/kg, po) and chronic (14 day) (ED₅₀ = 4.1 μmoles/kg, po) dosing. At doses of 6.7 and 22 μmoles/kg, po, A-80426 was effective in this test procedure for at least 12 h following administration. Doses of 6.7 to 224 μmoles/kg, ip, of A-80426, however, failed to block hypothermia and hypoactivity produced by the α₂-adrenoceptor agonist clonidine, and doses of 100 and 300 μmoles/kg, po, were required to blocked clonidine-induced mydriasis. Thus, the in vitro α₂ receptor binding and blocking effects observed with A-80426 did not translate into the in vivo situation. A-80426 was able to reverse the step-down passive avoidance deficit seen in olfactory bulbectomized rats (ED₇₀ = 7.1 μmoles/kg, po), a finding suggesting that the compound has antidepressant potential. The compound was, however, inactive in the tail suspension and forced swim tests of antidepressant activity in mice at doses up to 72 μmoles/kg, ip. In contrast, fluoxetine was active in all three paradigms. Despite its favorable in vitro profile, A-80426 is not an effective α₂ blocker in vivo and is inactive in the behavioral dispair models of depression. It is unlikely that A-80426 would have antidepressant activity equivalent to existing selective serotonin reuptake inhibitors. α₂ blockade as a potential approach to eliciting antidepressant activity is discussed. © 1995 Wiley-Liss, Inc.     

Sex differences in excretion of zenarestat in rat

1. Rat shows a marked sex difference in the excretion of ¹⁴C-zenarestat: only 1% of the dose was excreted in the urine of males, about 45% of the dose was excreted in the urine of females. ¹⁴C in the urine of female rats was almost entirely unchanged drug.

2. Plasma protein binding was similar in both sexes: 99.3–99.5% in males and 99.4–99.6% in females.

3. The type and ratio of metabolites in the faeces and bile were not significantly different between males and females.

4. Renal clearance experiments, and inhibition of urinary excretion by probenecid, indicated that female rats may possess an active secretory mechanism which is lacking or relatively inactive in male rats.     

Factors Affecting the Metabolism of Phenacetin I. Influence of Dose,Chronic Dosage,Route of Administration and Species on the Metabolism of [1-14C-Acetyl]Phenacetin

1. Metabolism and excretion of [acetyl-1-¹⁴C]phenacetin have been studied in relation to dose, chronic dosage, route of administration and species.

2. The drug is largely metabolized in the rat, rabbit, guinea-pig, ferret and man by oxidative de-ethylation and deacetylation as well as by minor pathways of aromatic hydroxylation and cysteine conjugation.

3. Species differences exist in the extent to which the various reactions occur; deacetylation is highest in the rat and ferret (21 and 13% of dose respectively); aromatic hydroxylation of phenacetin to 2-hydroxyphenacetin is highest in the ferret (6% of dose) but low (0·1%) in the other species; the formation of the 3-cysteine conjugate of N-acetyl-p-aminophenol is highest in the rabbit (8%) and least in the guinea-pig (0·3%); the pattern of conjugation of N-acetyl-p-aminophenol varies with species, glucuronide conjugation being dominant in the rabbit, guinea-pig and ferret, whereas sulphate conjugation is the main pathway in the rat.

4. The pattern of elimination in the rat of a large oral dose (2000?mg/kg) of [acetyl-¹⁴C]phenacetin differs from that of a smaller dose (125?mg/kg), with (a) slower overall excretion at the higher dose (b) a marked relative increase in the proportion of the drug undergoing deacetylation and (c) a change in the pattern of conjugation of the N-acetyl-p-aminophenol at the higher dose in favour of glucuronic acid conjugation.

5. The pattern of excretion of [acetyl-¹⁴C]phenacetin in the rat is the same when the drug is given orally or by intraperitoneal injection. However, the elimination of radioactivity is slower in rats treated chronically for 14 days with the drug.

6. The findings are discussed in relation to some of the biological properties of phenacetin.     

Biotransformation of 2,3,3,3-tetrafluoropropene (HFO-1234yf) in male, pregnant and non-pregnant female rabbits after single high dose inhalation exposure

2,3,3,3-Tetrafluoropropene (HFO-1234yf) is a novel refrigerant intended for use in mobile air conditioning. It showed a low potential for toxicity in rodents studies with most NOAELs well above 10,000 ppm in guideline compliant toxicity studies. However, a developmental toxicity study in rabbits showed mortality at exposure levels of 5,500 ppm and above. No lethality was observed at exposure levels of 2,500 and 4,000 ppm. Nevertheless, increased subacute inflammatory heart lesions were observed in rabbits at all exposure levels. Since the lethality in pregnant animals may be due to altered biotransformation of HFO-1234yf and to evaluate the potential risk to pregnant women facing a car crash, this study compared the acute toxicity and biotransformation of HFO-1234yf in male, female and pregnant female rabbits. Animals were exposed to 50,000 ppm and 100,000 ppm for 1 h. For metabolite identification by ¹⁹F NMR and LC/MS-MS, urine was collected for 48 h after inhalation exposure. In all samples, the predominant metabolites were S-(3,3,3-trifluoro-2-hydroxypropanyl)-mercaptolactic acid and N-acetyl-S-(3,3,3-trifluoro-2-hydroxypropanyl)-L-cysteine. Since no major differences in urinary metabolite pattern were observed between the groups, only N-acetyl-S-(3,3,3-trifluoro-2-hydroxypropanyl)-L-cysteine excretion was quantified. No significant differences in recovery between non-pregnant (43.10 ± 22.35 μmol) and pregnant female (50.47 ± 19.72 μmol) rabbits were observed, male rabbits exposed to 100,000 ppm for one hour excreted 86.40 ± 38.87 μmol. Lethality and clinical signs of toxicity were not observed in any group. The results suggest that the lethality of HFO-1234yf in pregnant rabbits unlikely is due to changes in biotransformation patterns or capacity in pregnant rabbits.     

Excretion of 2,3-dihydroxy-propionamide (OH-PA), the hydrolysis product of glycidamide,in human urine after single oral dose of deuterium-labeled acrylamide

A dose of 0.99 mg d₃-acrylamide (d₃-AA) (13.2 μg/kg body weight) was ingested by a healthy male volunteer. Urine samples were collected over a period of 46 h after the intake and analyzed for the hydrolysis product of glycidamide (GA), 2,3-dihydroxy-propionamide (OH-PA), a metabolite of the toxicologically relevant oxidative AA metabolism pathway; 5.4% of the administered d₃-AA dose was eliminated as OH-PA within 46 h after ingestion. Therefore, OH-PA represents a major metabolite of the oxidative metabolism pathway. Elimination kinetics of OH-PA is similar to the oxidative metabolites N-acetyl-S-(2-carbamoyl-2-hydroxyethyl)-cysteine (GAMA) and N-acetyl-S-(1-carbamoyl-2-hydroxyethyl)-cysteine (iso-GAMA). The major excretion of d₃-OH-PA took place between 8 and 22 h with the highest urinary d₃-OH-PA concentration (c _max) of 69.3 μg/L urine, 18 h (t _max) postdose. OH-PA (5.4%), together with the other known urinary metabolites of the oxidative pathway GAMA (4.6%) and iso-GAMA (0.8%), represents 10.8% of the total AA dose. The share of the oxidative pathway metabolites is much smaller than the share of the reductive pathway metabolite N-acetyl-S-(2-carbamoylethyl)-cysteine (AAMA) that represents 51.7% of the ingested d₃-AA dose. However, this new quantitative human data on OH-PA together with the previous data on the other oxidative pathway metabolites are of special importance when evaluating the carcinogenic potential of AA and when comparing human data with data from animal studies.     

N-乙酰半胱氨酸预防亚硒酸钠诱导大鼠白内障的研究

目的 对亚硒酸钠诱导白内障大鼠采用N-乙酰半胱氨酸进行预防性治疗,探讨N-乙酰半胱氨酸对白内障大鼠模型氧化损伤和晶状体浑浊程度的影响。方法 30只SD乳鼠随机分为3组,模型组ip 3.46 mg/kg亚硒酸钠溶液造模后,ip 0.1 mL/10 g生理盐水;实验组ip N-乙酰半胱氨酸10 mg/g,30 min ip亚硒酸钠溶液造模;对照组ip 0.1 mL/10 g生理盐水。所有动物均为隔日注射,连续6次。比较大鼠晶状体浑浊程度和SOD活性、NOS活性和MDA水平。结果 在晶状体核区、后囊区、前囊区+后囊区、前囊区+皮质区+核区+后囊区中,实验组与模型组比较得分差异具有统计学意义（P<0.05）;实验组SOD活性和MDA活性与模型组比较差异均具有统计学意义（P<0.05）。结论 N-乙酰半胱氨酸能够预防后囊和核区白内障的发生,其作用是通过减少MDA水平、提高SOD活性、改善氧化应激实现的。     

Impact of Mrp2 on the Biliary Excretion and Intestinal Absorption of Furosemide,Probenecid, and Methotrexate Using Eisai Hyperbilirubinemic Rats

Purpose. This study assesses the impact of rat multidrug resistance-associated protein 2 (Mrp2) on the biliary excretion and oral absorption of furosemide, probenecid, and methotrexate using Eisai hyperbilirubinemic rats (EHBR). Methods. To assess Mrp2-mediated biliary excretion, rats received a 2-h intravenous infusion of furosemide, probenecid, or methotrexate. Blood and bile samples were collected at specified intervals. To assess Mrp2's impact on oral absorption, rats received furosemide, probenecid, or methotrexate orally at 5 mg/kg. Jugular and portal blood samples were obtained at timed intervals. All samples were analyzed by LC-MS/MS. Pharmacokinetic parameters were estimated using WinNonlin and standard pharmacokinetic equations. Results. Thirty seven- and 39-fold reductions in biliary clearance were observed in EHBR as compared to control rats for probenecid and methotrexate, respectively. Biliary clearance was comparable between EHBR and control rats for furosemide. In all cases, no significant difference in absorption was observed between EHBR and control rats. Conclusions. This study provides the first evidence that Mrp2 mediates the biliary excretion of probenecid but not furosemide. Additionally, Mrp2 apparently has a less profound impact on intestinal absorption than biliary excretion of its substrates. Furthermore, alteration in systemic clearance in EHBR indicates that a potential compensatory mechanism may occur in EHBR.     

Biliary excretion and enterohepatic circulation of 2,4-dinitrotoluene metabolites in Fischer-344 rats

Technical grade dinitrotoluene (DNT) is hepatocarcinogenic when fed to rats. DNT is oxidatively metabolized by hepatic enzymes and reductively metabolized by rat intestinal microflora in vitro. The objectives of the present studies were to determine the importance of bile as a route of excretion for DNT metabolites and to investigate the role of enterohepatic circulation in the metabolism of DNT. The common bile ducts of male and female F-344 rats were cannulated with an uninterrupted cannula at the hepatic and ileal ends. After 24 hr, male rats were given a po dose of 35, 63, or 100 mg 2,4-[¹⁴C]DNT/kg; female rats received 35 mg 2,4-[¹⁴C]DNT/kg. Immediately prior to dosing, the cannula was snipped and bile was allowed to collect in a glass reservoir, surgically implanted in the peritoneal cavity, which could be sampled externally. In males, excretion of ¹⁴C in bile was linearly related to dose. From 9.2 to 29.2 μmol eq of [¹⁴C]DNT (approximately 25% of the dose) appeared in bile within 24 hr. Females dosed with 35 mg/kg excreted only 18% of the dose in the bile. Over 90% of the radioactivity in the bile was the glucuronide conjugate of 2,4-dinitrobenzyl alcohol (DNBAlc-G). In comparison to control rats, in which bile flow to the small intestine was uninterrupted, collection of bile decreased the amount of ¹⁴C excreted in urine. In both males and females most of the 2,4-DNT dose excreted in the urine was in the form of the oxidized metabolites DNBAlc-G and 2,4-dinitrobenzoic acid. These results indicate that bile is an important route of excretion for 2,4-DNT metabolites and that metabolites excreted in the bile can be reabsorbed from the gut.     

Gender effect on the pharmacokinetics of thymoquinone: Preclinical investigation and in silico modeling in male and female rats

Thymoquinone is the most biologically active constituent of Nigella sativa (black seed). A monoterpene compound chemically known as 2-methyl-5-isopropyl-1, 4-quinone. In this study, the gender-dependent pharmacokinetic behavior of thymoquinone in rats was investigated. Thymoquinone was administered orally (20 mg/kg) and intravenously (5 mg/kg) to male and female rats and blood samples were collected at specific time points. Plasma concentration-time curves were plotted and pharmacokinetic parameters were determined using the non-compartmental analysis. In addition, simulations of steady state concentrations of thymoquinone in male and female rats were performed using GastroPlus PK software. After oral administration, the maximum plasma concentration (C_max) of thymoquinone was 4.52 ± 0.092 μg/ml in male rats and 5.22 ± 0.154 μg/ml in female rats (p = 0.002). Similarly, after intravenous administration, the C_max was 8.36 ± 0.132 μg/ml in males and 9.51 ± 0.158 μg/ml in females (p = 0.550). The area under the plasma concentration-time curve (AUC)_0-∞ following oral dosing was 47.38 ± 0.821 μg/ml·h in females and 43.63 ± 0.953 μg/ml·h in males (p = 0.014). Pharmacokinetics and plasma concentration vs. time profiles for multiple oral doses of thymoquinone in rats were predicted using a simulation model to compare the simulation results with the experimental plasma pharmacokinetic data. The differences observed in thymoquinone pharmacokinetics between male and female rats after a single dose were not evident for the simulated steady-state parameters. The findings suggest that the gender difference does not seem to play a significant role in thymoquinone disposition at steady state.