Evaluation of Chick Embryo Neural Retina Cell Culture as a Screen for Developmental Toxicants

Abstract

This paper describes a study to evaluate the concordance with in vivo results of an in vitro screen for developmental toxicants. The screen is a primary culture of chick embryo neural retina cells (CERC) which undergo processes of cell-cell recognition and interaction, growth, and differentiation over a 7-day culture period. Each of these developmentally significant events is measured separately as formation of multicellular aggregates, protein content, and glutamine synthetase activity, respectively. A total of 45 chemicals, 24 of which have been shown to be teratogenic at some dosage to mammalian embryos in utero, 7 of which are embryotoxic (but not teratogenic) in utero at high dosage, and 14 of which have not produced developmental toxicity in vivo, were evaluated in this assay by investigators who were blinded to the identity of the chemicals. Chemicals were tested up to concentrations that were frankly cytolethal, or up to a maximum of 5 mg/ml. Chemicals were present only during the first 24 hr of culture. The chemicals were selected to be representative of a variety of chemical classes (e.g., solvents, metals, food additives, anticonvulsants, antineoplastics). In several cases, pairs of structurally similar compounds with different developmental toxic potencies (e.g., valproate and 2-en-valproate, formamide, and N,N-dimethylformamide) were tested. Of the 31 developmental toxicants, 25 affected at least one endpoint in the assay at concentrations which are achievable in vivo (i.e., below the systemic concentration at a lethal dose), yielding a false-negative rate of 19%. Two of the nondevelopmental toxicants, saccharin, and penicillin G, had adverse effects at concentrations below those that may be biologically achievable in vivo, giving a false-positive rate of 14%. Overall concordance with in vivo results by these criteria was 82%. Quantitative comparisons were also made between the lowest observed effect concentration (LOEC) in the assay and (i) lowest developmentally toxic dosage (mostly ip) reported in rats or mice in vivo and (ii) LOEC in rodent whole embryo culture. In the first instance, 77% of the LOECs (LOELs) were within an order of magnitude and 93% were within a factor of 30. In the second instance 81% of the LOECs were within an order of magnitude. Potency ranking of four alkoxy acids was comparable in CERC and the in vivo rodent embryo. These results indicate that the CERC assay is concordant with developmental toxic potential and potency for the diverse group of compounds selected, and that it could serve as a preliminary screen for developmental toxicity.