Comparison of the toxic effects of organic and inorganic arsenic in Caenorhabditis elegans using a multigenerational approach

Abstract

Although arsenic (As) is a persistent contaminant in the environment, few studies have assessed its effects over generations, as it requires an animal model with a short lifespan and rapid development, such as the nematode Caenorhabditis elegans. Furthermore, few studies have evaluated the effects of As metabolites such as dimethylarsinic acid (DMA^V), and several authors have considered DMA as a moderately toxic intermediate of As, although recent studies have shown that this chemical form can be more toxic than inorganic arsenic (iAs) even at low concentrations. In the present study, we compared the toxic effects of arsenate (As^V) and DMA^V in C. elegans over 5 subsequent generations. We evaluated biochemical parameters such as reactive oxygen species (ROS) concentration, the activity of antioxidant defense system (ADS) enzymes such as catalase (CAT) and glutathione-S-transferase (GST), and nonenzymatic components of ADS such as reduced glutathione (GSH) and protein-sulfhydryl groups (P-SH). Exposure to 50 μg L^-1 of As^V led to an increase in ROS generation and GSH levels together with a decrease in GST activity, while exposure to DMA^V led to an increase in ROS levels, with an increase in lipid peroxidation, CAT activity, and a decrease in GSH levels. In addition, both treatments reduced animal growth from the third generation onward and caused disturbances in their reproduction throughout all 5 generations. This study shows that the accumulated effects of DMA need to be considered; it highlights the importance of this type of multigenerational approach for evaluating the effects of organic contaminants considered low or nontoxic.

Keywords: antioxidant responses; ecotoxicological effects; growth; oxidative stress; reproduction.

Graphical Abstract

Fig. 1

ROS levels (relative area) measured over 5 generations: first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). Data are expressed as mean + 1 standard error (n = 9). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 2

ACAP—Total antioxidant capacity against peroxyl radicals (relative area): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). Data are expressed as mean + 1 standard error (n = 12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 3

GSH—Reduced glutathione (μmol of GSH/mg of protein): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). And covariance analysis (f). Data are expressed as mean + 1 standard error (n = 12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 4

P-SH—Protein-bound sulfhydryl groups (μmol of P-SH/mg of protein): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). Data are expressed as mean + 1 standard error (n = 12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 5

GST—Glutathione-S-transferase activity (nmol of CDNB conjugated/min/mg of protein): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). And covariance analysis (f). Data are expressed as mean + 1 standard error (=12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 6

CAT—Catalase activity (μmol of H₂O₂/min/mg of protein): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). And covariance analysis (f). Data are expressed as mean + 1 standard error (n = 12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 7

TBARS—Thiobarbituric acid reactive substances (nmol of MDA/mg of protein): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). And covariance analysis (f). Data are expressed as mean + 1 standard error (n = 12). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 8

Growth (length in mm): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). Data are expressed as mean + 1 standard error (n = 40). Different letters represent significant statistical differences from treatments (P < 0.05).

Fig. 9

Reproduction (number of offspring per adult): first generation (a); second generation (b); third generation (c); fourth generation (d); and fifth generation (e). Data are expressed as mean + 1 standard error (n = 9). Different letters represent significant statistical differences from treatments (P < 0.05).