Bioassay Using the DR-EcoScreen System to Measure Dioxin-Related Compounds in Serum Samples from Individuals Exposed to Dioxins Originating from Agent Orange in Vietnam

Abstract

A bioassay for dioxin analysis of human samples has the advantages of cost effectiveness and requiring only a small sample volume. Using a DR-EcoScreen bioassay, we measured the biological equivalency (BEQ) levels in serum samples from 32 men exposed to dioxins in Bien Hoa and 32 unexposed men in Hanoi, Vietnam. For the Bien Hoa men, the World Health Organization toxic equivalent (WHO-TEQ) levels of dioxins had already been measured by instrumental analysis. The difference in fat-based BEQ levels between exposed and unexposed men was greater than for crude BEQ levels, with a strong correlation between fat-based BEQ and WHO-TEQ levels. The fat-based BEQ levels in Bien Hoa men with longer residency but lower WHO-TEQ levels were significantly higher than those in unexposed men and Bien Hoa men with shorter residency but higher WHO-TEQs, suggesting that fat-based BEQ may be an effective marker of dioxin-like activity. Additionally, comparisons of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and TEQs between shorter- and longer-residency groups indicated that higher levels of polychlorinated dibenzo-p-dioxins (PCDDs), particularly TCDD, contribute to increased BEQ levels. Taken together, the DR-EcoScreen bioassay may be useful to analyze dioxin-like activity associated with WHO-TEQs of men in a dioxin contamination hotspot originating from Agent Orange in Vietnam.

Keywords: Vietnamese men; bioassay; biological equivalency; dioxins; serum samples; the World Health Organization toxic equivalent.

Figure 1

Summary of luciferase reporter gene assay using DR-EcoScreen cells ((A): scheme of luciferase induction; (B): a rapid and simple procedure).

Figure 2

Analytical sensitivity (a), recovery (b) and reproducibility of inter/intra assay (c). (a): The limit of quantification and detection, (b): the recovery rate performed by spiking the samples with 40 pg/mL of 2,3,7,8-TCDD. (c): Coefficients of variation (C.V.) for intra and inter-assay variability when high and low controls and NIST standard sample were measured.

Figure 3

Scatter plots between TEQ−PCDD/Fs/dl−PCBs levels by instrumental analysis and fat-based (A) and crude (B) BEQ levels. log10: logarithm base 10, *: p < 0.05, **: p < 0.01, ρ: Spearman’s correlation coefficients, β: standardized regression coefficients after adjusting for age, serum cholesterol, and smoking (yes, no).