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Lewis L Smith Syngenta

The role of cell transport systems in medicating the toxic effects of drugs and chemicals. Mechanisms of paraquat poisoning. Lewis L Smith Syngenta. Toxicology. Identification of Hazard Characterisation of Hazard Relevance to MAN RISK Assessment RISK Management. Descriptive. Research.

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Lewis L Smith Syngenta

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  1. The role of cell transport systems in medicating the toxic effects of drugs and chemicals. Mechanisms of paraquat poisoning. Lewis L Smith Syngenta

  2. Toxicology • Identification of Hazard • Characterisation of Hazard • Relevance to MAN • RISK Assessment • RISK Management Descriptive Research

  3. Mechanisms of Toxicity Relevant to Man? Similar to Man? Qualitatively or quantitatively similar to Man?

  4. Inhibition of putrescine (1µM) accumulation into rat lung slices by selected amino acids and their decarboxylated derivatives Slices of rat lung were incubated in KRP (pH 7.4) containing 1 µM [14C)-putrescine in the presence of various concentrations of the compounds indicated. I50 values were determined by the method of Ross and Krieger, each animal acting as its own control. Results are expressed as the mean ± SEM, at least 3 animals being employed per compound studied.

  5. The inhibitory potencies of various triamines against putrescine (1µM) accumulation by rat lung slices Slices of rat lung were incubated in KRP medium containing putrescine (1µM) in the presence of the triamine indicated. I50 values expressed as the mean ± SEM (n>3) derived by the method of Ross and Krieger.

  6. The inhibitory potencies of methylglyoxal-bis (guanylhydrazone) against the accumulation of putrescine (1 (µM) by rat lung slices

  7. . Eadie-Hofstee plot for the derivation of Km and Vmax of the accumulation process for MGBG into rat lung slices 100- 90- 80- 70- 60- 50- 40- 30- 20- 10- 0- . . . . 0 10 20 V (nmoles/g.wet wt.lung/hr) S (medium substrate conc. (µM) Rat lung slices were incubated at 37o in the presence of various concentrations of [14C]-MGBG. Accumulation of [14C]-MGBG(V) was determined after 30,15 and 5 min for substrate medium concentrations <1µM and after 60,30 and 15 min for substrate medium concentrations >1µM. Triplicates were determined at each time point and all slices taken from the same rat. Rates of accumulation were determined by linear regression analysis. The results shown are from a single experiment typical of 3 and by linear regression analysis the estimated kinetic parameters from this experiment were: Km=4.6µM. Vmax=83.5nmols/g wet wt. Lung/hr (correlation coefficient r= -0.93).

  8. Compounds Structure I50 (µM) 139.9 (±50.1) Ethidium 17.9±3.8 Pentamidine Primaquine 51.8 (±23.9) Chloroquine 20.1 (±11.3)

  9. Hanes – Woolf Plot of Cystamine Uptake . 180 VMAX = 1/Slope KM = Y-Intercept x VMAX 150 . . 120 s/v . KM = 503uM 90 . . 60 . KM = 12uM 30 0 0 100 200 300 400 500 (S) (uM)

  10. + + H3N(CH2)2S-S(CH2)2NH3 CH2 CH S N S CH2 CH2 + + + H3N-(CH2)2-SO3 H3N(CH2)2SH H3N-(CH2)2-SO2 + H3N-CH2-CH2-S-SH Possible Routes of Cystamine Metabolism 2 GSH Cystamine Cystaldimine 3 1 4 GSSCys Cysteamine Thiocysteamine 5 6 Hypotaurine Taurine - - NAD+ NADH 1 Postulated thiol-disulphide exchange 2 Amine:oxygen oxidoreductase (deaminating) 3 Spontaneous 4 Uncharacterised 5 Cysteamine dioxygenase 6 Hypotaurine dehydrogenase

  11. State of 14C-Label after 30’ Incubation

  12. Aims of Current Studies • Holistic identification of molecular pathways involved in PQ-induced lung fibrosis using Toxicogenomics • Develop testable hypotheses for therapeutic intervention

  13. 165 genes had no annotation Overview of molecular functions and pathways associated with PQ-responsive genes 543 Paraquat-responsive genes Gene Ontology terms (biological functions)

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