A proposed approach to study the toxicology of complex mixtures of petroleum products: the integrated use of QSAR, lumping analysis and PBPK/PD modeling.

Abstract

Mixture toxicity is a topic that has become a matter of concern during the last two decades. One of the major problems with assessing the toxicity of mixtures and the associated human and environmental risk is the large number of possible mixtures, as well as the fact that the actual mixture effect for a given set of constituents might strongly depend on the actual composition of the mixture, i.e., the ratios of the constituent, as well as their nature. This paper presents a possible approach to describe and thereby better understand the pharmacokinetics and dynamics of complex mixtures by combining quantitative structure-activity relationships to predict needed parameters, lumping to reduce the complexity of the problem, and physiologically based pharmacokinetic/pharmacodynamic modeling to integrate all this information into a complete toxicological description of the mixture. It is our hope that by presenting this conceptual approach we might be able to stimulate some criticisms and discussions in the toxicology community regarding this complex and yet very important area of research.Environ Health Perspect 105(Suppl 1): 179-195 (1997) Key words: QSAR, lumping analysis, PBPK/PD modeling, predictive toxicology, jet fuel, mixture toxicity Introduction Traditionally, both human and environmental toxicologists have studied the toxic effects (both lethal and sublethal, acute and chronic) of single substances. For to dealing with the first problem, that of the existence of too many compounds to test for toxic effects, is the discipline known as predictive toxicology. This is a discipline that tries to predict the biological effects, including but not limited to acute toxicity, of chemicals from considerations of compound structure and knowledge about the target biological systems and subsystems. Two tools predictive toxicology has developed over the years are quantitative structure-activity relationships (QSAR) and physiologically based pharmacokinetic/ pharmacodynamic (PBPK/PD) modeling.QSAR attempts to predict the qualitative structure-activity (SAR) or quantitative QSAR effect of a compound by analogy with a number of similar compounds (9). SARs generally define a common substructure or overall shape similarity between compounds with similar modes of toxic action, using the presence or absence of this substructure in an unknown compound or the similarity of the unknown to the known active compounds to predict the likelihood of the unknown of exhibiting the same toxicity. QSARs attempt to identify quantitative structural parameters that correlate with the actual effect dose or concentration that elicits a common effect level (for example, LD50 or LC50). All three techniques mentioned above will be described in more detail in another section of this paper as will ways in which these techniques might be combined into a comprehensive predictive toxicological approach. These techniques will be illustrated wherever possible by examples using such complex mixtures as JP-5, automotive gasoline, and other petroleum p...

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