Gene expression profiling as an initial approach for mechanistic studies of toxicity and tumorigenicity of herbal plants and herbal dietary supplements

Abstract

Dietary supplements are consumed by more than 300 million people worldwide, and herbal dietary supplements represent the most rapidly growing portion of this industry. Even though adverse health effects of many herbal dietary supplements have been reported, safety assurances are not being addressed adequately. Toxicological data on the identification of genotoxic and tumorigenic ingredients in many raw herbs are also lacking. Currently, more than 30 herbal dietary supplements and active ingredients have been selected by the National Toxicology Program (NTP) for toxicity and tumorigenicity studies. Due to the complexity of the chemical components present in plant extracts, there are no established methodologies for determining the mechanisms of toxicity (particularly tumorigenicity) induced by herbs, such as Gingko biloba leaf extract (GBE) and other herbal plant extracts. Consequently, the understanding of toxicity of herbal dietary supplements remains limited. We have proposed that application of DNA microarrays could be a highly practical initial approach for revealing biological pathways and networks associated with toxicity induced by herbal dietary supplements and the generation of hypotheses to address likely mechanisms. The changes in expression of subsets of genes of interest, such as the modulation of drug metabolizing genes, can be analyzed after treatment with an herbal dietary supplement. Although levels of gene expression do not represent fully the levels of protein activities, we propose that subsequent biochemical and genomic experiments based on these initial observations will enable elucidation of the mechanisms leading to toxicity, including tumorigenicity. This review summarizes the current practices of microarray analysis of gene expressions in animals treated with herbal dietary supplements and discusses perspectives for the proposed strategy.

Figure 1

Numbers of drug metabolizing genes altered by 0.5, 1.0 and 2.0 g/kg kava treatments in male rat liver. A gene was identified as differentially expressed if the fold-change was greater than 1.5 (up or down) and the P -value was less than 0.05 in comparison to the control group. The color in gray refers to the number of genes overlapped in three treatments. The data were from Guo et al. (31).

Figure 2

Gene expression of the common cytochrome P450 drug metabolizing genes altered by three kava treatments (0.5, 1.0, and 2.0 g/kg) in male rat livers.

Figure 3

Gene expression changes validated by TaqMan assays in liver of mice treated with three Ginkgo biloba extract treatments (200, 600, and 2000 mg/kg). (A), up-regulated genes; (B), the genes with down-regulation. The data were from Guo et al. (32).

Figure 4

Alteration of NRF2 (nuclear factor erythroid-related factor 2)-mediated oxidative stress response in the liver of male mice treated with Ginkgo biloba extract. The data were from Guo et al. (32).

Figure 5

The first network (cell cycle, cellular movement, and cancer) containing 34 differentially expressed genes in the mice treated with Ginkgo biloba extract. Green indicates down-regulation and red indicates up-regulation. Solid lines indicate direct interactions and dashed lines indicate indirect interactions between two molecules. The data were from Guo et al. (32).