Inhibition of uridine uptake in cultured cells: A rapid, sublethal cytotoxicity test

In Vitro Alternatives for Ocular Safety Testing: An Outline of Assays and Possible Future Developments

An increasing number of in vitro tests are being proposed as alternatives for animals in ocular safety testing. These in vitro systems use a variety of approaches and measure a broad range of endpoints, including cellular cytotoxicity and metabolism. We will briefly review the development and validation of these model systems. Several tests appear promising, and may prove useful as adjuncts in our current ocular safety assessment schemes. We will also discuss how these tests can most rapidly be brought to use in ocular safety assessment, and where efforts should be directed to develop more-highly predictive in vitro model systems for the future.

Acrylonitrile-induced reversible inhibition of uridine uptake by isolated rat intestinal epithelial cells

Isolated rat intestinal epithelial cells (IEC) were used to investigate the mechanism(s) of acrylonitrile (VCN)-induced gastro-intestinal damage. The isolated cells were 93% structurally intact for 60 min, as indicated by trypan blue exclusion. Uridine uptake by isolated IEC was linear from 6-20 min, after which a steady state was reached for up to 40 min. Exposure of isolated IEC to various concentrations of VCN reduced the ability of the cells to take up uridine in a concentration-dependent manner. A concentration of 82 mum VCN inhibited the [(3)H]uridine uptake of the cells by 50% (IU(50)). A time-course study indicated that the maximal inhibition of uridine uptake occurred at 15 min after exposure to VCN. The VCN-induced inhibition of uridine uptake was found to be reversible. IEC exposed to two sublethal doses of VCN (41 and 82 mum) for 15 min regained normal uridine uptake activity within 50 min after removal of VCN. The present study provides a sensitive approach for the detection and evaluation of cytotoxic risk of sublethal doses of the gastro-intestinal toxin VCN using IEC as target cells. The observed in vitro cytotoxicity of sublethal doses of VCN will be used to investigate further the mechanism of VCN-induced gastro-intestinal damage.

IRAG working group 4. Cell cytotoxicity assays. Interagency Regulatory Alternatives Group

Twenty-seven data sets from 12 cellular cytotoxicity assays, intended to predict ocular irritation, were submitted to the Interagency Regulatory Alternatives Group (IRAG) for review. These data consisted of paired in vivo (Draize) and in vitro responses to individual chemicals and formulations. In vivo data consisted of individual tissue scores so that the predictive value of the in vitro assay could be assessed for each tissue response normally measured in the standard Draize assay. Data were compiled and evaluated according to the IRAG Guidelines Document. The Pearson's linear correlation coefficient was used as the first step in assessing the relationship between the in vitro and in vivo responses. The majority of the data sets represented the study of surfactant-based materials. In many cases, there was good correlation between the in vitro scores and the in vivo tissue responses. Most pronounced were the particularly good correlations between the in vitro scores and conjunctival redness scores across most of the assays. Based on the data submitted, a number of the cell cytotoxicity assays show considerable promise as screens for ocular irritancy. None of the submitters recommended that their cell cytotoxicity assay be used as a sole replacement for in vivo assessment. For almost all of these assays, the materials being tested should be water-soluble/miscible. The toxicity of products with reserve acidity or alkalinity or with high reactivity may be underestimated. A given user may prefer certain assays depending on the types of materials to be tested, the expected range of toxicities and the resources available. The cell cytotoxicity assays can serve as a valuable component of a tiered or battery testing program. As with any assay, a sufficient number of replicate values, concurrent positive and negative controls, and a strict adherence to assay acceptance criteria are essential to produce credible data.

The comparative study of cardiovascular toxins utilizing a sensitive indicator of sublethal toxic injury

This study measures the inhibition of [3H]uridine uptake by smooth muscle cells to determine sublethal toxic injury by the cardiovascular toxins, allylamine, isoproterenol, and beta-aminopropionitrile. The exposure period or the concentration of toxin which inhibited 30% of [3H]uridine uptake by smooth muscle cells could be utilized as an endpoint for ranking toxicity. Cytotoxicity of the three toxins to smooth muscle cells were ranked as: allylamine greater than isoproterenol greater than beta-aminopropionitrile. Recovery of cells utilizing [3H]uridine uptake inhibition as a method for assessing comparative cytotoxicity and for screening of agents potentially injurious to vascular cells.