Predicting Drug-Induced Hepatotoxicity Using QSAR and Toxicogenomics Approaches

Quantitative Structure-Activity Relationship (QSAR) modeling and toxicogenomics are used independently as predictive tools in toxicology. In this study, we evaluated the power of several statistical models for predicting drug hepatotoxicity in rats using different descriptors of drug molecules, namely their chemical descriptors and toxicogenomic profiles. The records were taken from the Toxicogenomics Project rat liver microarray database containing information on 127 drugs (http://toxico.nibio.go.jp/datalist.html). The model endpoint was hepatotoxicity in the rat following 28 days of exposure, established by liver histopathology and serum chemistry. First, we developed multiple conventional QSAR classification models using a comprehensive set of chemical descriptors and several classification methods (k nearest neighbor, support vector machines, random forests, and distance weighted discrimination). With chemical descriptors alone, external predictivity (Correct Classification Rate, CCR) from 5-fold external cross-validation was 61%. Next, the same classification methods were employed to build models using only toxicogenomic data (24h after a single exposure) treated as biological descriptors. The optimized models used only 85 selected toxicogenomic descriptors and had CCR as high as 76%. Finally, hybrid models combining both chemical descriptors and transcripts were developed; their CCRs were between 68 and 77%. Although the accuracy of hybrid models did not exceed that of the models based on toxicogenomic data alone, the use of both chemical and biological descriptors enriched the interpretation of the models. In addition to finding 85 transcripts that were predictive and highly relevant to the mechanisms of drug-induced liver injury, chemical structural alerts for hepatotoxicity were also identified. These results suggest that concurrent exploration of the chemical features and acute treatment-induced changes in transcript levels will both enrich the mechanistic understanding of sub-chronic liver injury and afford models capable of accurate prediction of hepatotoxicity from chemical structure and short-term assay results

Correlation between Ca2+ oscillation and cell proliferation via CCKB/gastrin receptor

AbstractGastrin stimulates cell proliferation through the CCKB receptor coupled to Gq-protein, whereas the m3 muscarinic receptor, which also couples to Gq, has no trophic effects. In order to elucidate the cause of the difference, we stably transfected CHO cells with human CCKB and m3 receptors. Stimulation of the CCKB, but not the m3 receptor increased cell growth. Activation of MAP kinase via the m3 receptor was to the same extent as that via CCKB, indicating that there is an initial signaling common to both receptors. Stimulation of either receptor induced a transient increase in [Ca2+]i followed by a sustained plateau phase. After 2 h of stimulation, the [Ca2+]i response to the m3 receptor disappeared, whereas that to the CCKB receptor remained as a [Ca2+]i oscillation. Removal of extracellular Ca2+, which abolished [Ca2+]i oscillation, completely inhibited DNA synthesis via CCKB. When the C-terminal part of the CCKB receptor was truncated, the trophic effect as well as the [Ca2+]i response after 2 h of stimulation disappeared, whereas the chimeric CCKB receptor with the C-terminal region of the m3 receptor preserved its ability to elicit both DNA synthesis and [Ca2+]i oscillation. These results suggest that desensitization might be a principal determinant of cell proliferation, and the persistence of the [Ca2+]i response as [Ca2+]i oscillation could be essential for this type of signal transduction

Feedback Response to Selective Depletion of Endogenous Carbon Monoxide in the Blood

The physiological roles of endogenous carbon monoxide (CO) have not been fully understood because of the difficulty in preparing a loss-of-function phenotype of this molecule. Here, we have utilized in vivo CO receptors, hemoCDs, which are the supramolecular 1:1 inclusion complexes of <i>meso</i>-tetrakis­(4-sulfonatophenyl)­porphinatoiron­(II) with per-<i>O</i>-methylated β-cyclodextrin dimers. Three types of hemoCDs (hemoCD1, hemoCD2, and hemoCD3) that exhibit different CO-affinities have been tested as CO-depleting agents in vivo. Intraperitoneally administered hemoCD bound endogenous CO within the murine circulation, and was excreted in the urine along with CO in an affinity-dependent manner. The sufficient administration of hemoCD that has higher CO-affinity than hemoglobin (Hb) produced a pseudoknockdown state of CO in the mouse in which heme oxygenase-1 (HO-1) was markedly induced in the liver, causing the acceleration of endogenous CO production to maintain constant CO-Hb levels in the blood. The contents of free hemin and bilirubin in the blood plasma of the treated mice significantly increased upon removal of endogenous CO by hemoCD. Thus, a homeostatic feedback model for the CO/HO-1 system was proposed as follows: HemoCD primarily removes CO from cell-free CO-Hb. The resulting oxy-Hb is quickly oxidized to met-Hb by oxidant(s) such as hydrogen peroxide in the blood plasma. The met-Hb readily releases free hemin that directly induces HO-1 in the liver, which metabolizes the hemin into iron, biliverdin, and CO. The newly produced CO binds to ferrous Hb to form CO-Hb as an oxidation-resistant state. Overall, the present system revealed the regulatory role of CO for maintaining the ferrous/ferric balance of Hb in the blood