Acute infusions of cocaine result in time- and dose-dependent effects on lymphocyte responses and corticosterone secretion in rats

In the present study, we investigated the effect of intravenously (i.v.) administered cocaine on mitogen-induced lymphocyte proliferation and NK cytolytic activity in rats implanted with indwelling jugular cannula. To assess whether the effects of cocaine were accompanied by adrenal gland activation, plasma corticosterone concentrations were also determined. It was found that the i.v. infusion of cocaine resulted in both a time- and dose-dependent decrease in both blood and splenic Con-A-stimulated lymphocyte proliferative responses. Within 60 minutes, blood responses were maximally inhibited by more than 60% with 5 mg/kg cocaine. By 4 h, the suppression of blood lymphocyte responses was no longer significant. In contrast to these findings, there were no significant effects observed with splenic lymphocyte responses until 4 h after drug administration. At this time, cocaine at doses of 5 and 10 mg/kg inhibited splenic proliferative responses by 50 and 75%, respectively. These effects appeared to be selective, since no concurrent decreases in NK cell activity were observed with 5 mg/kg at either 2 or 4 h. Within 30 min, plasma corticosterone concentrations were maximally increased by 10-fold with 5 and 10 mg/kg doses of cocaine. At lower doses of cocaine (1 mg/kg), neither changes in lymphocyte proliferative responses, NK cytolytic activity nor plasma corticosterone levels were apparent. This study demonstrates that a single i.v. infusion of cocaine results in a selective dose- and time-dependent immunosuppression which is preceded by transient increases in circulating levels of corticosterone.     

Skin response to epicutaneous application of anticoagulant rodenticide warfarin is characterized by differential time- and dose-dependent changes in cell activity

Context: Skin is the target of both acute and chronic exposure to warfarin, coumarin anticoagulant. Single exposure of rat skin to this agent induces early (24?h following epicutaneous administration) local response which might be part of inflammatory/reparatory homeostatic program or introduction to pathological events in exposed skin.

Objective: To examine time-dependent changes in skin of rats exposed to epicutaneously applied warfarin.

Materials and methods: The effect of low (10?μg) and high (100?μg) doses of warfarin on histologically evident changes of epidermis (epidermal thickness) and dermis (numbers of mesenchymal cells and dermal capillaries), skin cell proliferative activity (Ki67⁺ and PCNA⁺ cells) and apoptotic (TUNEL⁺) and necrotic (ultra structural appearance) cells was examined one, three and seven days after the application.

Results: Both warfarin doses affected the majority of skin cell activity, but with differential time-course of skin epidermal and dermal cells state/activity. The occurrence of necrotic/apoptotic epidermal and dermal cells was noted the first day after the application and the activities which point to tissue reparation/remodeling were observed seven days after skin exposure to this agent.

Discussion: The observed pattern of changes (early evidence of cell/tissue injury which was later followed by signs of cell activity characteristic for tissue reparation/remodeling) implied warfarin-induced toxicity in skin cells as stimulus for subsequent activities relevant for tissue homeostasis.

Conclusion: The data presented provide new and additional information concerning skin responses to warfarin that gains access to this tissue.     

Thermoregulatory responses to environmental toxicants: the interaction of thermal stress and toxicant exposure

Thermal stress can have a profound impact on the physiological responses that are elicited following environmental toxicant exposure. The efficacy by which toxicants enter the body is directly influenced by thermoregulatory effector responses that are evoked in response to high ambient temperatures. In mammals, the thermoregulatory response to heat stress consists of an increase in skin blood flow and moistening of the skin surface to dissipate core heat to the environment. These physiological responses may exacerbate chemical toxicity due to increased permeability of the skin, which facilitates the cutaneous absorption of many environmental toxicants. The core temperature responses that are elicited in response to high ambient temperatures, toxicant exposure or both can also have a profound impact on the ability of an organism to survive the insult. In small rodents, the thermoregulatory response to thermal stress and many environmental toxicants (such as organophosphate compounds) is often biphasic in nature, consisting initially of a regulated reduction in core temperature (i.e., hypothermia) followed by fever. Hypothermia is an important thermoregulatory survival strategy that is used by small rodents to diminish the effect of severe environmental insults on tissue homeostasis. The protective effect of hypothermia is realized by its effects on chemical toxicity as molecular and cellular processes, such as lipid peroxidation and the formation of reactive oxygen species, are minimized at reduced core temperatures. The beneficial effects of fever are unknown under these conditions. Perspective is provided on the applicability of data obtained in rodent models to the human condition.     

Mixtures in the real world: the importance of plant self-defense toxicants, mycotoxins, and the human diet

A perusal of research presented at the Annual Society of Toxicology Meetings, or in nearly any toxicology journal, will show that the overwhelming emphasis of toxicology research is on synthetic chemistries. Because of substantial potency and exposure to natural chemicals, the overwhelming focus on synthetic chemistries cannot lead to a realistic understanding of chemical risk to the general population. Natural chemicals, simply because of their abundance and potency, may be as likely to be a public health concern and to be involved in chemical interactions (natural:natural, natural:pharmaceutical; or natural:synthetic) as are environmental levels of synthetic chemicals. All plants have a mix of natural self-defense chemistries and mycotoxins that, when tested in a manner comparable to synthetic pesticides, cause the entire spectrum of toxic effects. As a further complication, plants also escalate much of their self-defense chemistry when attacked by insects and fungi, and damaged crops often have higher mycotoxins levels. Effective crop protection will typically reduce the plant's levels of self-defense toxicants and mycotoxins, but may add residues of synthetic pesticides or add some other risk variable. In addition, cooking may also alter the food chemistry (e.g., acrylamide). The mixtures toxicologist needs to address the real world mixture of natural and synthetic chemicals. Public policy on crop-food safety cannot be sensibly guided without these data and large voids in our understanding of risks from real-world mixtures cannot be in the public interest.     

A single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin produces a time- and dose-dependent alteration in the murine bone marrow B-lymphocyte maturation profile.

The halogenated aromatic hydrocarbon, 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), is a ubiquitous, highly toxic environmental contaminant shown to produce immunotoxic effects in mammals. Although its immunotoxicity has been widely reported, little is known regarding its effect upon the development of immune-system cells, especially the B lymphocyte. The present study's purpose was to assess the effect that a single-dose administration of TCDD has, over time, upon bone marrow B-cell progenitors and pro/pre-B-, immature B-, and mature B-cell subpopulations, and to establish a dose-response relationship for these changes. Results showed that the mature B-lymphocyte subpopulation varied in a time-dependent manner, with a significant increase one day following TCDD treatment (30 microg/kg body weight [bw]), followed by a significant decrease at day 9 and a return to near-vehicle levels by day 31. Developing and less mature subpopulations were significantly decreased at days 6 and 9. The earliest B cell-progenitor subpopulation increased until day 9 and then decreased to vehicle-treated levels. Dose response (30, 15, 9, 6, 3, and 0.3 microg TCDD/kg bw) results at 2 days following treatment showed that only the mature-B subpopulation was affected at these doses, and below 6 microg/kg bw no effect was observed. These data suggest that the primary effect of TCDD is on those cells entering, and/or within, the mature B-lymphocyte subpopulation, and the alteration observed in the earlier maturation stages is a compensatory response to the effect on these mature cells.     

黄芩素在人及不同种属肝微粒体中的UDP-glucuronosyltransferase代谢差异（摘要）

目的：研究黄芩素在不同种属肝微粒体中的UDP-葡萄糖醛酸转移酶（UDP-glucuronosyltransferase, UDPGA）代谢差异特性。方法使用肝微粒体体外代谢孵育法、HPLC-UV分析方法,选用不同种属的肝微粒体进行黄芩素UDPGA体外代谢研究。结果黄芩素在人肝微粒体及不同种属的肝微粒中,加入UDPGA进行37℃恒温孵育,孵育结束后离心,取上清液,经HPLC-UV分离检测得到3个代谢产物,分别是：黄芩素-7-O-β-葡萄糖醛酸结合物、黄芩素-6-O-β-葡萄糖醛酸结合物和黄芩素-6-O-葡萄糖醛酸结合物-7-O-β-葡萄糖醛酸结合物;通过与标准品对照确定黄芩素的三个代谢产物都是葡萄糖醛酸化的代谢产物。同时,不同种属间UGT代谢物的活性表现出较大差异,黄芩素-7-O-β-葡萄糖醛酸结合物在人肝微粒体中的代谢活性最强,Km=1.61,Vmax=0.77（BG在人肝微粒体中的代谢活性是SD雌鼠的25.2倍）;黄芩素-6-O-β-葡萄糖醛酸结合物在比格犬肝微粒体中代谢活性最强,Km=3.05,Vmax=3.51（雄性比格犬肝微粒体的活性是雄性恒河猴肝微粒体的2.6倍）;黄芩素-6-O-葡萄糖醛酸-7-O-β-葡萄糖醛酸结合物在猪肝微粒体中代谢活性最强,Km=5.38, Vmax=0.17（猪肝微粒体的活性是人肝微粒体的13.6倍）,其他依次是犬、恒河猴、鼠和人。结论黄芩素在人及不同种属肝微粒体UGT代谢中均生成上述三种葡萄糖醛酸化代谢产物,但是不同种属间的代谢表现出酶动力学的差异。     

Inhibition of rat brain monoamine oxidase enzymes by fluoxetine and norfluoxetine

Fluoxetine and its primary metabolite, norfluoxetine, are inhibitors of neuronal uptake of 5-hydroxytryptamine. While fluoxetine has also been reported to inhibit monoamine oxidase (MAO) in vitro at concentrations much lower than those measured in brain following chronic fluoxetine treatment, neurochemical profiles are not consistent with substantial MAO inhibition in vivo. In an attempt to explain this inconsistency, we have examined the interactions of fluoxetine and norfluoxetine with rat brain MAO-A and -B by a radiochemical assay method.Fluoxetine and norfluoxetine were competitive inhibitors of MAO-A in vitro, with K_i values of 76.3 M and 90.5 M, respectively. Both compounds were non competitive or uncompetitive inhibitors of MAO-B in vitro. Inhibition of MAO-B was time-dependent and was very slowly reversible by dialysis. IC₅₀ values versus metabolism of 50 M, -phenylethylamine were 17.8 M (fluoxetine) and 18.5 M (norfluoxetine). Analysis of the time-dependence of MAO-B inhibition by fluoxetine revealed that an initial competitive interaction between the enzyme and the inhibitor (K_i 245 M) was followed by tight-binding enzyme inactivation (k_inact 0.071 min^–1).Following administration of fluoxetine (20 mg kg^–1 day^–1]) for 7 days, the cortical concentration of fluoxetine + norfluoxetine was estimated by gas-liquid chromatography to be 700 M. Such drug treatment reduced MAO-A activity by 23% in 1:8 (w/v) cortical homogenates, but not in 1:80 homogenates. Inhibition of MAO-B in 1:8 homogenates was modest (12%) and was not significantly reduced by homogenate dilution. The concentration of 5-hydroxyindole-3-acetic acid, measured by high pressure liquid chromatography, was reduced by 47% in cortices from drug-treated rats, while concentrations of 5-hydroxytryptamine, noradrenaline, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid were unchanged. These results suggest that, following chronic drug administration leading to relatively high tissue concentrations of fluoxetine and norfluoxetine, inhibition of either form of MAO would be restricted by competition for the enzyme with intraneuronal amine substrates.     

The inhibition of UDP-glucuronosyltransferases (UGTs) by tetraiodothyronine (T4) and triiodothyronine (T3)

1.?UDP-glucuronosyltransferases (UGTs) are important drug-metabolizing enzymes (DMEs) catalyzing the glucuronidation elimination of various xenobiotics and endogenous substances. Endogenous substances are important regulators for the activity of various UGT isoforms. Triiodothyronine (T3) and thyroxine (T4) are important thyroid hormones essential for normal cellular differentiation and growth. The present study aims to elucidate the inhibition behavior of T3 and T4 on the activity of UGT isoforms.

2.?In vitro recombinant UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was used to screen the inhibition potential of T3 and T4 on the activity of various UGT isoforms. Initial screening results showed that T4 exerted stronger inhibition potential than T3 on the activity of various UGT isoforms at 100?μM. Inhibition kinetics was determined for the inhibition of T4 on the representative UGT isoforms, including UGT1A1, -1A3, -1A7, -1A8, -1A10 and -2B7. The results showed that T4 competitively inhibited the activity of UGT1A1, -1A3, -1A7, 1A10 and -2B7, and noncompetitively inhibited the activity of UGT1A8. The inhibition kinetic parameters were calculated to be 1.5, 2.4, 11, 9.6, 4.8 and 3.0?μM for UGT1A1, -1A3, -1A7, -1A8, -1A10 and -2B7, respectively. In silico docking method was employed to demonstrate why T4 exerted stronger inhibition than T3 towards UGT1A1. Stronger hydrogen bonds and hydrophobic interaction between T4 and activity cavity of UGT1A1 than T3 contributed to stronger inhibition of T4 towards UGT1A1.

3.?In conclusion, more clinical monitoring should be given for the patients with the elevation of T4 level due to stronger inhibition of UGT isoforms-catalyzed metabolism of drugs or endogenous substances by T4.     

Cultivation and modelling of encapsulated Saccharomyces cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes

The cultivation of encapsulated S. cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes was studied. The results showed that the encapsulated microorganisms had the same growth trends as in its free cell culture and, thus, NaCS-PDMDAAC microcapsules were suitable for the encapsulation of these biological substances. The encapsulated S. cerevisiae cells were fermented sequentially for 16 batches. The highest cell density in the capsules reached 2.64 #50 10 10 cells mL -1 and the ethanol concentration was 47.0 g L -1 . A model of the cultivation of the encapsulated S. cerevisiae was developed.     

In vitro effects of rosmarinic acid on glutathione reductase and glucose 6-phosphate dehydrogenase

Context: Glutathione reductase (GR, NADPH:oxidized glutathione oxidoreductase, E.C 1.6.4.2) is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG). GR is a crucial enzyme in the antioxidant system by maintaining reduced glutathione (GSH). Glucose 6-phosphate dehydrogenase (G6PD, glucose 6-phosphate (G6P):NADP⁺ oxidoreductase, EC 1.1.1.49) is the key regulatory enzyme of the pentose phosphate pathway and maintains NADPH for reductive reactions.

Objective: Rosmarinic acid (RA; α-O-caffeoyl-3,4-dihydroxyphenyl lactic acid) is an ester of caffeic acid (CA) and 3,4-dihydroxyphenyllactic acid. It has a number of interesting biological activities. The inhibiting activities of the RA on GR and G6PD are investigated here for the first time.

Materials and methods: GR and G6PD were purified from tissues, then the effects of RA are investigated.

Results: This study reports that RA, which was isolated from Echium vulgare L. (Boraginaceae), inhibits purified GR and G6PD in a concentration-dependent manner. Kinetic characterizations and inhibition constants are investigated.

Discussion and conclusion: Because of their importance in the antioxidative defense system, investigation of the inhibitors of these enzymes is important for drug development.     

From simple toxicological models to prediction of toxic effects in time

The ability to predict the effects of toxicants in organisms with reasonable accuracy depends to a great extent on the toxico-kinetic models used to describe such effects. Toxic effects of organic chemicals and heavy metals have been described adequately using a hyperbolic model that considers the concentration of the toxicant and the time of exposure only. Such a model relies on the median time to effect (ET₅₀) of a chemical to estimate effects at any exposure time, but cannot make predictions for concentrations other than those tested experimentally. A complementary log-to-log model can calculate all ET₅₀ values for a toxicant, thus enabling the hyperbolic model to predict any level of effect for any combination of concentrations and times of exposure. The parameter values used in both models are obtained from experimental bioassays where the time-to-effect of a toxicant is recorded regularly in addition to standard acute or chronic toxicity data. These models will facilitate the risk assessment of chemicals by (1) predicting effects under any combination of time and concentrations, and (2) reducing to a minimum the experimental efforts required to obtain comprehensive ecotoxicity data.     

Inhibition of Cytochrome P450 Enzymes by Drugs—Molecular Basis and Practical Applications

Drug-drug interactions are a major cause of hospitalization and deaths related to drug use. A large fraction of these is due to inhibition of enzymes involved in drug metabolism and transport, particularly cytochrome P450 (P450) enzymes. Understanding basic mechanisms of enzyme inhibition is important, particularly in terms of reversibility and the use of the appropriate parameters. In addition to drug-drug interactions, issues have involved interactions of drugs with foods and natural products related to P450 enzymes. Predicting drug-drug interactions is a major effort in drug development in the pharmaceutical industry and regulatory agencies. With appropriate in vitro experiments, it is possible to stratify clinical drug-drug interaction studies. A better understanding of drug interactions and training of physicians and pharmacists has developed. Finally, some P450s have been the targets of drugs in some cancers and other disease states.     

Modeling responses of Daphnia magna to pesticide pulse exposure under varying food conditions: intrinsic versus apparent sensitivity

Recent studies showed that limiting food conditions resulted in either increased or decreased sensitivity of Daphnia magna to toxicants. It remained unclear whether these contrasting food-dependent alterations in toxicity resulted from differences in intrinsic sensitivity of the daphnids or from changes in toxicokinetics and resource allocation. It is hypothesized here that, if food level only affects accumulation kinetics and resource allocation, then the intrinsic sensitivity to this toxicant should be the same for all food regimes. This hypothesis was investigated using the DEBtox model, which is based on the theory of Dynamic Energy Budgets. We examined results of two recently conducted life-cycle studies on the combined effects of food level and a pulsed exposure to the pyrethroid insecticide fenvalerate (FV) on D. magna. The model described the effects of the time-varying exposure well, and indicated that when the animals did not die from exposure to FV, full reversibility of toxic effects was possible, allowing a complete recovery. Results revealed furthermore that the data from both studies could be described by the same NECs for survival and assimilation, killing rate and tolerance concentration (132 (49.2-228) x 10(-6) microg/L, 0 (0-1.18 x 10(-5)) microg/L, 74.4 (55.6-96.4) L (microg d)(-1) and 5.39 (2.72-18.5) x 10(-3) microg/L, respectively). It is therefore concluded that food-dependent FV toxicity can be explained by altered toxicokinetics and resource allocation, but not by changes in the intrinsic sensitivity of the daphnids. This study implies that the effect of pesticide application in the field depends on the trophic state of the receiving water body, but also that full recovery of survivors is possible after FV application.     

普罗帕酮和心肌快钠通道结合及解离过程的动力学

<正> 普罗帕酮(propafenone,Pro)又称心律平,是I_c类抗心律失常药。我室对国产Pro的研究表明,它对心肌快钠通道和慢钙通道都有阻滞作用。作为I类抗心律失常药物,其抗心律失常和致心律失常作用强度和其与心肌快钠通道结合,解离速率有关。本文对国产Pro进行动力学研究,并与国外报道进行比较,为临床用药提供参考。     

Characteristics of indirect pharmacodynamic models and applications to clinical drug responses

This review describes four basic physiologic indirect pharmacodynamic response (IDR) models which have been proposed to characterize the pharmacodynamics of drugs that act by indirect mechanisms such as inhibition or stimulation of the production or dissipation of factors controlling the measured effect. The principles underlying IDR models and their response patterns are described. The applicability of these basic IDR models to characterize pharmacodynamic responses of diverse drugs such as inhibition of gastric acid secretion by nizatidine and stimulation of MX protein synthesis by interferon α-2a is demonstrated. A list of other uses of these models is provided. These models can be readily extended to accommodate additional complexities such as nonstationary or circadian baselines, equilibration delay, depletion or accumulation of a precursor pool, sigmoidicity, or other mechanisms. Indirect response models which have a logical mechanistic basis account for time-delays in many responses and are widely applicable in clinical pharmacology.     

HCV screening to enable early treatment of hepatitis C: a mathematical model to analyse costs and outcomes in two populations

Early treatment of acute hepatitis C virus (HCV) infections reflects a new clinical paradigm and a significant option to reduce the socioeconomic burden of HCV. Therefore, this approach seems suitable as a new strategy to face HCV and prevent end stage liver diseases and premature deaths due to progressed chronic HCV-infections. The main limitation of this approach is that the majority of acute infections show an asymptomatic course and do thus not present to the health-care settings. Screening for HCV has already been extensively studied in the literature. This paper offers further insights in screening for HCV using cost effectiveness analysis for the impact of screening in two cohorts: Injecting Drug Users (IDUs) and Individuals With Surgery (IWSs). The setting of the cost effectiveness simulation is the Veneto Region in the North-east of Italy. Using a Markov model of the natural history of HCV infection we derive costs, quality-adjusted life years (QALYs) and incremental cost-effectiveness related to screening vs. no-screening strategies. In the IDUs cohort, the screening strategy can result in a substantial difference in premature deaths and dominates (less costs better outcomes) the no-screening one. The overall outcomes of the screening strategy are mostly affected by the prevalence of HCV and of genotypes that are more relatively more difficult to treat (above 10% of prevalence for its cost effectiveness). The number of premature deaths prevented in the IWSs cohort is lower and there seems to be an unacceptable incremental cost per QALY gained, which may be unsustainable for society.