A high-throughput mammalian cell-based transient transfection assay.

In eukaryotic organisms gene expression is regulated through a variety of upstream transacting factors (transcription factors) whose primary function appears to be the targeting of coregulatory protein complexes, which interact with basal transcription machinery to define the relative rate of transcription for a specific gene. Understanding the regulatory forces mediating transcription factor activity has been the focus of both academic and industrial research efforts over the past 15 yr, and in this time frame a variety of methodologies have been developed for reconstituting and assaying transcription factor activities in mammalian cell environments. Presented here is a high-throughput version of one of these methodologies that can be readily adapted to the screening of a variety of transcription factors. This technology utilizes co-transfection of mammalian expression and luciferase reporter plasmids to reconstitute transcription events in a mammalian host cell. Included is a detailed protocol for the use of a 96-well plate format, along with a variety of cost-effective measures that can be implemented to facilitate the use of the technology in the average low budget academic laboratory.

Assessing the toxicity of polymeric food-contact substances.

The US Food and Drug Administration's Office of Food Additive Safety in the Center for Food Safety and Applied Nutrition conducts safety assessments of food additives, including food-contact substances such as polymeric and oligomeric materials that have the potential to migrate to food. Traditionally, little toxicity testing has been conducted on the low-molecular weight oligomeric fraction (< 1000 Da) of these food-contact substances. At lower exposures (≤ 150 µg/person/day), safety has been assessed based on the use of toxicity data on the monomeric components of these polymers as a sufficiently conservative approach for addressing the concern for genetic toxicity and carcinogenicity of the low-molecular weight oligomers (LMWOs). This paper discusses this assumption relative to the available data on these substances and their monomeric components in the context of exposures of ≤ 150 µg/person/day with emphasis on the evaluation of the potential genetic toxicity of these compounds. In most instances, data are available on either the monomers or the monomers' structural class to conservatively address the potential genetic toxicity of the LMWOs. Caveats to this generalization are also discussed. The assessment of LMWOs is important because they can be one of the primary migrants to food from a polymeric food-contact substance.

The Role of NF-kappaB in PPARalpha-Mediated Hepatocarcinogenesis.

In this review, the role of NF-kappaB in the induction of hepatocarcinogenesis by peroxisome proliferators is examined. The administration of peroxisome proliferators for more than a three-day period leads to the activation of NF-kappaB in the livers of rats and mice. On the other hand, peroxisome proliferator activated receptor-alpha (PPARalpha) activation in non-hepatic tissues can lead to the inhibition of NF-kappaB activation. Several lines of evidence support the hypothesis that the activation of NF-kappaB by peroxisome proliferators in the liver is mediated by oxidative stress. The role of NF-kappaB in peroxisome proliferator-induced hepatocarcinogenesis has been examined using NF-kappaB knockout models. Specifically, the induction of cell proliferation and the promotion of liver carcinogenesis are inhibited in mice lacking the p50 subunit of NF-kappaB. Overall, the activation of NF-kappaB appears to be important in the carcinogenic activity of peroxisome proliferators.

The use of structure-activity relationship analysis in the food contact notification program.

Food contact substances (FCS) include polymers, paper and paperboard, and substances used in their manufacture, that do not impart a technical effect on food. Moreover, FCSs are industrial chemicals generally consumed at dietary concentrations (DC) of less than 1mg/kg food (ppm), and more commonly at less than 0.05 ppm (50 ppb), in the daily diet. As such, many industrial chemicals have been analyzed for toxicological concern, some of which may share structural similarity with FCSs or their constituents, and the majority of these studies are available in the public domain. The DCs of these compounds lend themselves to using structure-activity relationship (SAR) analysis, as the available "expert systems" and use of analogs allows for prediction and management of potential carcinogens. This paper describes the newly implemented food contact notification (FCN) program, the program by which FDA reviews FCSs for safe use, the administrative review of FCSs, the SAR tools available to FDA, and qualitative and quantitative risk assessments using SAR analysis within the regulatory framework of reviewing the safety of FCSs.