Experimental models for the biological detection of N-nitroso compounds formed from amines and nitrite

The secondary and tertiary amines morpholine, aminopyrine and cimetidine as well as their nitroso products were examined for mutagenicity with the Ames Salmonella typhimurium microsome test (strains TA1535 and TA100) and the host-mediated assay. The formation of mutagenic nitroso compounds from morpholine and aminopyrine in the presence of nitrite could be demonstrated in artificial gastric juice and was confirmed in the stomach of mice in vivo. In contrast, the positive response of the chemical nitrosation in vitro with cimetidine did not match with the mammalian host-mediated assay results. To enhance sensitivity the role of modifiers of nitrosation, such as ascorbic acid and thiocyanate as well as the influence of biotransformation were studied.     

Effect of various chemicals on macromolecular binding during oxidative dealkylation of dimethylnitrosamine by hamster liver microsomes

Differential inhibitory effects of various chemicals on both formaldehyde formation and total macromolecular binding have been examined during oxidative demethylation of [¹⁴C]dimethylnitrosamine (DMN) by hamster liver microsomes. One group of chemicals such as diethyldithiocarbamate (DEDTC), aminoacetonitrile (AAN), 2-[(2,4-dichloro-6-phenyl) phenoxy]-ethylamine (DPEA), azide and ethanol inhibits both HCHO formation and total macromolecular binding. A second group of chemicals such as reduced glutathione, semicarbazide and N-(1-naphthyl)thiourea (NTU) inhibits macromolecular binding without appreciably affecting HCHO formation. Possible mechanisms of these differential inhibitory effects by these chemicals are discussed.     

Mutagenicity and antimutagenicity of hispidulin and hortensin, the flavonoids from Millingtonia hortensis L.

Studies of the mutagenicity and antimutagenicity of hispidulin and hortensin, the flavonoids from Millingtonia hortensis L. (Bignoniaceae), were performed using the liquid preincubation method of the Salmonella/microsome test. At the highest dose tested, 100 micrograms/plate, both compounds showed no mutagenicity and no cytotoxicity toward S. typhimurium strains TA98 and TA100 either in the presence or absence of S9 mix. However, these substances were antimutagens toward 2-aminoanthracene, aflatoxin B1 (in TA98), and dimethylnitrosamine (in TA100); but neither substance inhibited the direct mutagenic activity of 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide nor that of sodium azide in strains TA98 and TA100, respectively.     

Regulation of dimethylnitrosamine metabolism by androgenic hormones

Hormonal regulation of dimethylnitrosamine (DMN) metabolism by mouse kidney microsomes was investigated using an in vitro mutagenesis system that detects bioactive metabolites of this procarcinogen by measuring reverse mutation in Salmonella typhimurium his auxotrophs. Induction of microsomal DMN metabolizing enzymes was androgen-specific. Testosterone and medroxyprogesterone acetate were active inducers, d/1 norgestrel was less active, while epitestosterone, estradiol, and progesterone were ineffective. The response to testosterone and medroxyprogesterone acetate was time- and dose-dependent. Eleven strains of inbred mice were screened for their response to exogenous testosterone. DMN metabolism was stimulated in all mouse strains except for RF/J mice. Other androgenic end points were responsive in the latter strain, however. These observations suggest that induction of renal microsomal DMN metabolising enzymes is androgen-specific and probably mediated via the androgen receptor. The insensitivity of RF/J mice may be due to a mutation affecting a key step in the enzymatic activation of DMN.     

Metabolism-mediated cytotoxicity of chemical carcinogens and non-carcinogens

The results presented in this paper clearly demonstrate that a fibroblast suppression test system incorporating viable hepatocytes can be of value in studying the problems of metabolism-mediated cytotoxicity for those compounds and/or metabolites that are sufficiently stable to traverse cell membranes. The possibility that this test system can be used to distinguish carcinogenic and non-carcinogenic chemicals cannot be resolved at this time, however.     

Inhibition of CYP2E1 catalytic activity in vitro by S-adenosyl-L-methionine

The objective of this work was to evaluate the possible in vitro interactions of S-adenosyl-l-methionine (SAM) and its metabolites S-(5'-Adenosyl)-l-homocysteine (SAH), 5'-Deoxy-5'-(methylthio)adenosine (MTA) and methionine with cytochrome P450 enzymes, in particular CYP2E1. SAM (but not SAH, MTA or methionine) produced a type II binding spectrum with liver microsomal cytochrome P450 from rats treated with acetone or isoniazid to induce CYP2E1. Binding was less effective for control microsomes. SAM did not alter the carbon monoxide binding spectrum of P450, nor denature P450 to P420, nor inhibit the activity of NADPH-P450 reductase. However, SAM inhibited the catalytic activity of CYP2E1 with typical substrates such as p-nitrophenol, ethanol, and dimethylnitrosamine, with an IC(50) around 1.5-5mM. SAM was a non-competitive inhibitor of CYP2E1 catalytic activity and its inhibitory actions could not be mimicked by methionine, SAH or MTA. However, SAM did not inhibit the oxidation of ethanol to alpha-hydroxyethyl radical, an assay for hydroxyl radical generation. In microsomes engineered to express individual human P450s, SAM produced a type II binding spectrum with CYP2E1-, but not with CYP3A4-expressing microsomes, and SAM was a weaker inhibitor against the metabolism of a specific CYP3A4 substrate than a specific CYP2E1 substrate. SAM also inhibited CYP2E1 catalytic activity in intact HepG2 cells engineered to express CYP2E1. These results suggest that SAM interacts with cytochrome P450s, especially CYP2E1, and inhibits the catalytic activity of CYP2E1 in a reversible and non competitive manner. However, SAM is a weak inhibitor of CYP2E1. Since the K(i) for SAM inhibition of CYP2E1 activity is relatively high, inhibition of CYP2E1 activity is not likely to play a major role in the ability of SAM to protect against the hepatotoxicity produced by toxins requiring metabolic activation by CYP2E1 such as acetaminophen, ethanol, carbon tetrachloride, thioacetamide and carcinogens.     

Effects of chronic lead intoxication on rat serotoninergic system and anxiety behavior

Chronic lead exposure has been shown to produce behavioral disturbances in human and animal models. These disturbances are associated with alterations in monoaminergic neurotransmission in the central nervous system (CNS), some of which have been attributed to serotonin (5-HT). This study was undertaken to investigate the chronic effects of lead exposure on the serotoninergic system in the dorsal raphe nucleus (DRN) and the consequences of its toxicity on rat behavior. Adult male Wistar rats were chronically exposed for 3 months to 0.5% lead acetate in drinking water. The serotoninergic system was evaluated using immunohistochemistry and the anxiety behavior was assessed by the light/dark box test. The results show that chronic lead exposure induces a significant increase of blood and brain lead levels in treated rats compared with controls. The density of the immunoreactive serotoninergic cell bodies was significantly higher in treated rats in all parts of the DRN. Assessment of animal behavior using the light/dark box test showed that lead-treated rats spent significantly more time in the light chamber compared with controls (P = 0.001). These findings suggest that lead exposure may possibly induce increased anxiety as a consequence of changes in neuronal 5-HT content in the DRN.     

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.     

PFD对二甲基亚硝胺诱导的大鼠肝纤维化治疗疗效和CTGF表达的影响

目的观察不同剂量PFD对二甲基亚硝胺（Dimethylnitrosamine DMN）诱导大鼠肝纤维化的治疗作用和CTGF表达的影响,初步探讨其可能的作用机制。方法健康雄性Wistar大鼠105只随机分为正常组21只,给予生理盐水10 mg/kg体重腹腔内注射,每周前三天连续给药,1次/日,连续注射3周;造模组84只,给予1%DMN溶液10 mg/kg体重腹腔注射,每周前三天连续给药,1次/日,连续注射3周。两周末将造模组随机分为4组,每组21只,分别是：模型组、IFN-α治疗组、PFD 120 mg、PFD 240 mg治疗组。各组大鼠均于造模第3周第一天给予药物治疗,每周七天,1次/日,治疗共4周。各组给药剂量及方法如下：正常组、模型组予以0.5%CMCNa 6 m L/kg灌胃;PFD不同剂量组予以相应剂量PFD灌胃;IFN-α组予以IFN-α10万单位/只,皮下注射。治疗四周后处死所有大鼠,留取肝组织行Masson染色,免疫组织化学法测Ⅰ型胶原,CTGF表达。结果 （1）Masson染色SSS半定量评分,模型组与正常组比较显著升高（P〈0.05）。IFN-α组、PFD组SSS半定量评分较模型组显著降低（P〈0.05）。免疫组化法检测肝组织Ⅰ型胶原的表达,模型组与正常组比较显著升高（P〈0.05）,PFD组与模型组比较显著降低（P〈0.05）,IFN-α组与模型组比较无统计学差异（P〉0.05）,（2）免疫组化法检测肝组织CTGF的表达,模型组与正常组比较显著升高（P〈0.05）。PFD 120 mg、PFD 240 mg各组与模型组比较显著降低（P〈0.05）。结论 （1）PFD具有治疗DMN诱导的大鼠肝纤维化的作用,与α-IFN无明显差别。（2）PFD抗DMN诱导大鼠肝纤维化的作用机制可能与下调CTGF的表达,抑制促纤维化因子有关。     

Elevated noise power in gamma band related to negative symptoms and memory deficit in schizophrenia

Background

There is an increasing consideration for a disorganized cerebral activity in schizophrenia, perhaps relating to a synaptic inhibitory deficit in the illness. Noise power (scalp-recorded electroencephalographic activity unlocked to stimuli) may offer a non-invasive window to assess this possibility.

Methods

29 minimally-treated patients with schizophrenia (of which 17 were first episodes) and 27 healthy controls underwent clinical and cognitive assessments and an electroencephalographic recording during a P300 paradigm to calculate signal-to-noise ratio and noise power magnitudes in the theta and gamma bands.

Results

In comparison to controls, a significantly higher gamma noise power was common to minimally-treated and first episode patients over P3, P4, T5 and Fz electrode sites. Those high values were directly correlated to negative symptom severity and inversely correlated to verbal memory scores in the patients. There were no differences in signal-to-noise ratio magnitudes among the groups. Gamma noise power at Fz discriminated significantly between patients and controls. No significant differences were found in theta noise power or in gamma noise power over the other electrode sites between the groups of patients and controls.

Limitations

We have not assessed phase-locked and non-phase locked power changes, a complementary approach that may yield useful information.

Conclusions

Gamma noise power may represent a useful and non-invasive tool for studying brain dysfunction in psychotic illness. These results suggest an inefficient activation pattern in schizophrenia.