Gülden Michael, Seibert Hasso
Institut für Experimentelle Toxikologie, Universitätsklinikum Schleswig-Holstein, Weimarer Str. 8, Haus 3, D-24106 Kiel, Germany.
Toxicology. 2003 Aug 1;189(3):211-22. doi: 10.1016/s0300-483x(03)00146-x.
In the present study an extrapolation model for estimating serum concentrations of chemicals equivalent to in vitro effective concentrations is developed and applied to median cytotoxic concentrations (EC(50)) determined in vitro. Nominal concentrations of a chemical in serum and in vitro are regarded as equivalent, if they result in the same aqueous concentration of the unbound form. The algorithm used is based on equilibrium distribution and requires albumin binding data, the octanol-water partition coefficient (K(ow)), and the albumin concentrations and lipid volume fractions in vitro and in serum. The chemicals studied cover wide ranges of cytotoxic potency (EC(50): 2.5-530,000 microM) and lipophilicity (logK(ow): -5 to 7). Their albumin binding characteristics have been determined by means of an in vitro cytotoxicity test as described previously. The equivalent serum concentrations of 19 of the 33 compounds investigated, having high protein binding and/or lipophilicity, were substantially higher than the EC(50)-values, by factors of 2.5-58. Prominent deviations between the equivalent nominal concentrations in serum and in vitro were largely restricted to chemicals with higher cytotoxic potency (EC(50)< or =1000 microM). The results suggest that estimates of equivalent serum concentrations based on in vitro data are robust for chemicals with low lipophilicity (logK(ow)< or =2) and low potency (EC(50)>1000 microM). With more potent chemicals or those with higher lipophilicity partitioning into lipids and/or binding to serum proteins have to be taken into account when estimating in vivo serum concentrations equivalent to in vitro effective concentrations.
在本研究中，开发了一种用于估算与体外有效浓度相当的化学物质血清浓度的外推模型，并将其应用于体外测定的中位细胞毒性浓度（EC(50)）。如果血清和体外化学物质的标称浓度导致未结合形式的水溶液浓度相同，则认为它们是等效的。所使用的算法基于平衡分布，需要白蛋白结合数据、正辛醇-水分配系数（K(ow)）以及体外和血清中的白蛋白浓度和脂质体积分数。所研究的化学物质涵盖了广泛的细胞毒性效力范围（EC(50)：2.5 - 530,000 microM）和亲脂性范围（logK(ow)：-5至7）。如前所述，它们的白蛋白结合特性已通过体外细胞毒性试验确定。所研究的33种化合物中有19种具有高蛋白结合和/或亲脂性，其等效血清浓度显著高于EC(50)值，倍数为2.5 - 58。血清和体外等效标称浓度之间的显著偏差主要限于细胞毒性效力较高的化学物质（EC(50)≤1000 microM）。结果表明，对于亲脂性低（logK(ow)≤2）和效力低（EC(50)>1000 microM）的化学物质，基于体外数据估算等效血清浓度是可靠的。对于效力更高的化学物质或亲脂性更高的化学物质，在估算与体外有效浓度相当的体内血清浓度时，必须考虑它们在脂质中的分配和/或与血清蛋白的结合。
