title: Alternative models for low dose-response analysis of biochemical and immunological endpoints for tetrachlorodibenzo-p-dioxin.
abstract: As part of the current reassessment of dioxin, the empirical relationships between administered tetrachlorodibenzo-p-dioxin and selected immune and biochemical endpoints were investigated. A dose-response analysis from the published literature was performed using Linear, Sigmoid-Emax and Power Law functions. The results of this analysis indicate that the use of a wide dose range may bias the interpretation of low-dose phenomenon. The Power Law function was applied exclusively to low-dose subsets enabling estimation of dose response in the low-dose range. Subsequently, high-dose data were fit using Power Law subset analysis. This approach resulted in a change in slope value from low- to high-dose subsets for thymic atrophy, immune suppression, benzo(a)pyrene hydroxylase activity, and ethoxyresorufin-o-deethylase activity. This change suggests that there is a high probability that there is a tissue concentration along the dose-response continuum which results in biological activity from low to high dose. This analysis also demonstrates that the Power Law functional fit to the low-dose data differs quantitatively from the fit to the high-dose data for several noncancer endpoints. Therefore, by using the Power Law function a more accurate and biologically relevant assessment of risk can be produced for non-cancer endpoints.
mesh_terms: D000818:Animals; D001284:Atrophy; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000276:immunology; D008099:Liver / Q000201:enzymology; D008954:Models, Biological; D000072317:Polychlorinated Dibenzodioxins / Q000276:immunology* / Q000378:metabolism / Q000633:toxicity*; D012307:Risk Factors; D013950:Thymus Gland / Q000187:drug effects* / Q000276:immunology / Q000473:pathology
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D003577:Cytochrome P-450 Enzyme System