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Human genetic polymorphism of xenobiotic metabolism as a host susceptibility factor to environmental risk toxicity
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Workshop 3. Prediction of Individual Susceptibility to Toxicans THE M2 MUSCARINIC ANTAGONIST METHOCTRAMINE CAN ACT DIRECTLY ON G-PROTEINS
Daeffler Laurent, Van Gelderen Hans, Gies Jean-Pierre *.
Neuroimmunopharmacologie Pulmonaire, INSERM U425, Facultd de Pharmacie, 74 rte du Rhin, 67401 lllkirch, France Acetylcholine released from the vagus nerves onto muscarinic M3 receptors causes contraction of the airway smooth muscle, whereas inhibitory neuronal M2 muscarinic receptors limit acetylcholine release. The M2 receptors are guanine nucleotide-binding proteincoupled receptors which have been shown to exist in two states, a high affinity agonist state and also a low affinity agonist state. The agonist, [3H]Oxotremorine-M (Oxo-M, 2 nM), was used to determine the affinity of compounds for the high affinity state, whereas the antagonist, [3H] N-methylscopolamine (NMS, 0.2 nM), in presence of 100/.tM GppNHp, was used to determine the affinity for the low agonist state. The ratio of affinity constants (NMS/OxoM) for the two assays is a useful index of agonist efficacy. In this study we looked for evidence for correlation between M2-muscarinic ligand-receptor binding affinity and ligand intrinsic activity in pig atrial M2-muscarinic receptor enriched membranes. NMS/Oxo-M ratios varied from 1695 for the full agonist carbachol to 0.9 for the antagonist methoctramine with intermediate values for partial agonists. Intrinsic activity was assessed by measurement of [y32p]GTP hydrolysis and referred to maximal increase by carbachol (100%) which was 30 to 40% above basal GTPasic activity. We obtained values ranging from 100% for carbachol to 0% for the antagonist atropine. But the antagonist methoctramine showed a negative GTPase activity. It inhibits basal GTPase activity by 39.5%. This activity was not antagonized by atropine a neutral muscarinic antagonist, but methoctramine inhibits GTPase activity induced by mastoparan which acts directly on G protein. Indeed close correlation (r = 0.92) was found between the NMS/Oxo-M ratios of the ligands on the one hand, and their ability to activate the M2-receptor coupled Gi-protein pathway on the other hand. We also identified a M2 muscarinic antagonist that can directly inhibits G proteins activity and may be responsible for the loss of inhibitory M2 receptor function.
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DIFFERENCE IN ACUTE AND CHRONIC EFFECT OF CIGARETTE SMOKE ON NONSPECIFIC BRONCHIAL REACTIVITY IN OCCUPATIONAL EXPOSURE TO IRRITANTS
Davor Plavec *, Dijana Kukin. Institute for Medical Research and
Occupational Health, Zagreb, Croatia In 160 healthy subjects (nonsmokers = 71, smokers = 89) and 143 workers occupationally exposed to irritants (nonsmokers = 64, smokers = 79) we measured nonspecific bronchial reactivity (NBR) in relation to occupational exposure and smoking habit. NBR to histamine was measured according to Chai et al. [1]. Results were expressed as a logarithm of the dose-response slope [2]. Number of cigarettes smoked per day, years of smoking and pack-years (3) were determined in each subject. There was no significant difference in the level of NBR between groups and between smokers and nonsmokers in the tested groups. Significant positive correlation (r = 0.366, p < 0.01) was found in both groups of smokers between years of smoking and level of NBR. Significant negative correlation (r = -0.28, p < 0.05) was found only in smokers occupationally exposed to irritants between the number of cigarettes smoked per day and level of NBR. According to our results it seems that there is a difference between acute and chronic effect of cigarette smoke on the bronchial mucosa in subjects occupationally exposed to irritants. Chronic effect was the same in both examined groups of smokers (increased bronchial reactivity). Acute effect was present only in smokers occupationally
exposed to irritants and was the opposite to chronic effect. This could be explained by the influence of cigarette smoke on the nitric oxide metabolism induced by exposure to irritants. [1] Chai, H, et al., J Allergy Clin lmmunol, 56, 323-7. 1975. [2] O'Connor, G, et al., Am Rev Respir Dis, 136, 1412-7, 1987. [3] Chen, Y, et al., Am Rev Respir Dis, 43, 1224-30, 1991.
Keywords: smoking; respiratory irritants; nonspecific bronchial reactivity; histamine
W3. Prediction of Individual Susceptibility to Toxicans ~ - ]
PHYSIOLOGICAL FACTORS PREDISPOSING TO TOXICITY
David E. Ray. Medical Research Council Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, United Kingdom Many factors determine individual susceptibility to toxic agents in addition to their primary interaction with the target site. Absorption, delivery to target tissues, bio-activation, bio-inactivation, elimination, and adaptive or protective responses all play important parts in determining the overall response of the individual. In addition changes in the physiological significance of the function which is disrupted may be critically important. Pulmonary absorption can be limited by ventilation or perfusion, both of which increase with work rate. Tissue uptake can be limited by local blood flow, which is strongly influenced by local functional activity. In areas with a blood-tissue barrier, such as brain and testis, tissue uptake can be strongly influenced by developmental state, protein binding or vascular damage. Metabolic transformation can show marked inter-individual variations at both hepatic and extrahepatic sites, due to genetic or nutritional influences. The capacity for adaptation to toxicological insult can also vary markedly, depending on functional reserve capacity as well as on inherent plasticity. Examples used to illustrate these factors will include: the influence of motor activity on the toxicity of carbon monoxide; of noise on the ototoxicity of aminoglycoside antibiotics; of brain activity on the neurotoxicity of dinitrobenzene [1]; of acid-base balance on the toxicity of nicotine; and of developmental stage on the neurotoxicity of haloperidol. In addition disease states can influence sensitivity. Thus anaemia sensitises to manganese; protein deficiency to heavy metals; nerve trauma to hexane; systemic lupus erythematosus to ultraviolet light, and Wilson's disease to copper overload. [1] Ray, D.E., Holton, J.L., Lister, T. & Nolan, C.C. Arch. Tox.Suppl. 18: 140148.
Keywords: sensitivity; atypical reaction; dinitrobenzene; aminoglycoside; DDT
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HUMAN GENETIC POLYMORPHISM OF XENOBIOTIC METABOLISM AS A HOST SUSCEPTIBILITY FACTOR TO ENVIRONMENTAL RISK TOXICITY
Margarita Ladona. Barcelona, Spain Abstract not availabe at time of publication.
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Workshop 3. Prediction of Individual Susceptibility to Toxicans THE M2 MUSCARINIC ANTAGONIST METHOCTRAMINE CAN ACT DIRECTLY ON G-PROTEINS
Daeffler Laurent, Van Gelderen Hans, Gies Jean-Pierre *.
Neuroimmunopharmacologie Pulmonaire, INSERM U425, Facultd de Pharmacie, 74 rte du Rhin, 67401 lllkirch, France Acetylcholine released from the vagus nerves onto muscarinic M3 receptors causes contraction of the airway smooth muscle, whereas inhibitory neuronal M2 muscarinic receptors limit acetylcholine release. The M2 receptors are guanine nucleotide-binding proteincoupled receptors which have been shown to exist in two states, a high affinity agonist state and also a low affinity agonist state. The agonist, [3H]Oxotremorine-M (Oxo-M, 2 nM), was used to determine the affinity of compounds for the high affinity state, whereas the antagonist, [3H] N-methylscopolamine (NMS, 0.2 nM), in presence of 100/.tM GppNHp, was used to determine the affinity for the low agonist state. The ratio of affinity constants (NMS/OxoM) for the two assays is a useful index of agonist efficacy. In this study we looked for evidence for correlation between M2-muscarinic ligand-receptor binding affinity and ligand intrinsic activity in pig atrial M2-muscarinic receptor enriched membranes. NMS/Oxo-M ratios varied from 1695 for the full agonist carbachol to 0.9 for the antagonist methoctramine with intermediate values for partial agonists. Intrinsic activity was assessed by measurement of [y32p]GTP hydrolysis and referred to maximal increase by carbachol (100%) which was 30 to 40% above basal GTPasic activity. We obtained values ranging from 100% for carbachol to 0% for the antagonist atropine. But the antagonist methoctramine showed a negative GTPase activity. It inhibits basal GTPase activity by 39.5%. This activity was not antagonized by atropine a neutral muscarinic antagonist, but methoctramine inhibits GTPase activity induced by mastoparan which acts directly on G protein. Indeed close correlation (r = 0.92) was found between the NMS/Oxo-M ratios of the ligands on the one hand, and their ability to activate the M2-receptor coupled Gi-protein pathway on the other hand. We also identified a M2 muscarinic antagonist that can directly inhibits G proteins activity and may be responsible for the loss of inhibitory M2 receptor function.
'-W-'~
DIFFERENCE IN ACUTE AND CHRONIC EFFECT OF CIGARETTE SMOKE ON NONSPECIFIC BRONCHIAL REACTIVITY IN OCCUPATIONAL EXPOSURE TO IRRITANTS
Davor Plavec *, Dijana Kukin. Institute for Medical Research and
Occupational Health, Zagreb, Croatia In 160 healthy subjects (nonsmokers = 71, smokers = 89) and 143 workers occupationally exposed to irritants (nonsmokers = 64, smokers = 79) we measured nonspecific bronchial reactivity (NBR) in relation to occupational exposure and smoking habit. NBR to histamine was measured according to Chai et al. [1]. Results were expressed as a logarithm of the dose-response slope [2]. Number of cigarettes smoked per day, years of smoking and pack-years (3) were determined in each subject. There was no significant difference in the level of NBR between groups and between smokers and nonsmokers in the tested groups. Significant positive correlation (r = 0.366, p < 0.01) was found in both groups of smokers between years of smoking and level of NBR. Significant negative correlation (r = -0.28, p < 0.05) was found only in smokers occupationally exposed to irritants between the number of cigarettes smoked per day and level of NBR. According to our results it seems that there is a difference between acute and chronic effect of cigarette smoke on the bronchial mucosa in subjects occupationally exposed to irritants. Chronic effect was the same in both examined groups of smokers (increased bronchial reactivity). Acute effect was present only in smokers occupationally
exposed to irritants and was the opposite to chronic effect. This could be explained by the influence of cigarette smoke on the nitric oxide metabolism induced by exposure to irritants. [1] Chai, H, et al., J Allergy Clin lmmunol, 56, 323-7. 1975. [2] O'Connor, G, et al., Am Rev Respir Dis, 136, 1412-7, 1987. [3] Chen, Y, et al., Am Rev Respir Dis, 43, 1224-30, 1991.
Keywords: smoking; respiratory irritants; nonspecific bronchial reactivity; histamine
W3. Prediction of Individual Susceptibility to Toxicans ~ - ]
PHYSIOLOGICAL FACTORS PREDISPOSING TO TOXICITY
David E. Ray. Medical Research Council Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, United Kingdom Many factors determine individual susceptibility to toxic agents in addition to their primary interaction with the target site. Absorption, delivery to target tissues, bio-activation, bio-inactivation, elimination, and adaptive or protective responses all play important parts in determining the overall response of the individual. In addition changes in the physiological significance of the function which is disrupted may be critically important. Pulmonary absorption can be limited by ventilation or perfusion, both of which increase with work rate. Tissue uptake can be limited by local blood flow, which is strongly influenced by local functional activity. In areas with a blood-tissue barrier, such as brain and testis, tissue uptake can be strongly influenced by developmental state, protein binding or vascular damage. Metabolic transformation can show marked inter-individual variations at both hepatic and extrahepatic sites, due to genetic or nutritional influences. The capacity for adaptation to toxicological insult can also vary markedly, depending on functional reserve capacity as well as on inherent plasticity. Examples used to illustrate these factors will include: the influence of motor activity on the toxicity of carbon monoxide; of noise on the ototoxicity of aminoglycoside antibiotics; of brain activity on the neurotoxicity of dinitrobenzene [1]; of acid-base balance on the toxicity of nicotine; and of developmental stage on the neurotoxicity of haloperidol. In addition disease states can influence sensitivity. Thus anaemia sensitises to manganese; protein deficiency to heavy metals; nerve trauma to hexane; systemic lupus erythematosus to ultraviolet light, and Wilson's disease to copper overload. [1] Ray, D.E., Holton, J.L., Lister, T. & Nolan, C.C. Arch. Tox.Suppl. 18: 140148.
Keywords: sensitivity; atypical reaction; dinitrobenzene; aminoglycoside; DDT
[--~~
HUMAN GENETIC POLYMORPHISM OF XENOBIOTIC METABOLISM AS A HOST SUSCEPTIBILITY FACTOR TO ENVIRONMENTAL RISK TOXICITY
Margarita Ladona. Barcelona, Spain Abstract not availabe at time of publication.