Comparative Pharmacology and Toxicology of Pharmaceuticals in the Environment: Diphenhydramine Protection of Diazinon Toxicity in Danio rerio but Not Daphnia magna

Abstract

Abstract. Pharmaceuticals and other contaminants of emerging concern present unique challenges to environmental risk assessment and management. Fortunately, mammalian pharmacology and toxicology safety data are more readily available for pharmaceuticals than other environmental contaminants. Identifying approaches to read-across such pharmaceutical safety information to non-target species represents a major research need to assess environmental hazards. Here, we tested a biological readacross hypothesis from emergency medicine with common aquatic invertebrate and vertebrate models. In mammals, the antihistamine diphenhydramine (DPH) confers protection from poisoning by acetylcholinesterase inhibition because DPH blocks the acetylcholine receptor. We employed standardized toxicity methods to examine individual and mixture toxicity of DPH and the acetylcholinesterase inhibitor diazinon (DZN) in Daphnia magna (an invertebrate) and Danio rerio (zebrafish, a vertebrate). Though the standardized Fish Embryo Toxicity method evaluates early life stage toxicity of zebrafish (0-3 days post fertilization, dpf), we further evaluated DPH, DZN, and their equipotent mixture during three development stages (0-3, 3-6, 7-10 dpf) in zebrafish embryos. Independent action and concentration addition mixture models and fish plasma modeling were used to assist interpretation of mixture toxicity experiments. Though our primary hypothesis was not confirmed in acute studies with Daphnia magna, DPH conferred a protective effect for acute DZN toxicity to zebrafish when DPH plasma levels were expected to be greater than mammalian therapeutic, but lower than acutely lethal, internal doses. We further observed that timing of developmental exposure influenced the magnitude of DZN and DPH toxicity to zebrafish, which suggests that future zebrafish toxicity studies with pharmaceuticals and pesticides should examine exposure during developmental stages.KEY WORDS: alternative toxicity test methods; biological read-across; comparative pharmacology and toxicology; mixture toxicology; pharmaceuticals in the environment.

Age matters: Developmental stage of Danio rerio larvae influences photomotor response thresholds to diazinion or diphenhydramine

“…Such behavior observations were consistent with our initial age-specific and time of day studies reported above. However, unlike our previous observations of increased DZN acute mortality with increasing zebrafish age (Kristofco et al, 2015), age-specific differences for DZN behavioral toxicity was not consistently observed in the present study (Fig. 2), though several treatment levels significantly decreased activity of 7 dpf and 10 dpf zebrafish compared to 4 dpf organisms.…”

“…Tropical 5D wild type zebrafish ( Danio rerio ) were maintained under standard culture conditions at Baylor University as previously described (Kristofco et al, 2015; Usenko et al, 2011). Briefly, zebrafish were raised ≤5–6 adult fish per 1.5 L tank in a filtered (Compact system, Lifeguard Aquatics, Cerritos, CA, USA) recirculating z-mod system (Marine Biotech Systems, Beverly, MA, USA) maintained at 28 °C on a 16 h light/8 h dark photoperiod.…”

“…In our previous research, three larval zebrafish ages over 10 dpf were identified to display differential mortality sensitivities to DPH and DZN (Kristofco et al, 2015). We thus extended these observations to examine whether behavioral responses were more sensitive than endpoints previously examined by the FET approach, and to determine whether behavioral toxicity thresholds differed among developmental ages.…”

“…For all experiments, 5 embryos or larvae were placed in each 100 mL experimental unit (glass beakers with 30 mL of solution) for treatment levels and negative controls; 8 replicate experimental units were included per treatment level. In additional to examining a range of sublethal concentrations, the highest treatment levels of DZN and DPH used in this study were age specific LC 50 values from our recent findings (Kristofco et al, 2015), and were selected to understand the magnitude of sensitivity differences between traditional mortality and alternative behavioral responses of different ages. These nominal treatment levels were 700, 250, and 50 mg/L for DPH, and 15,12, and 5.5 mg/L for DZN for the 1–4, 4–7 and 7–10 dpf experiments, respectively.…”

“…In addition, the magnitude of toxicity differs across fish developmental stages for some molecules. For example, we recently identified a sensitivity gradient over the first 10 days of zebrafish development in which mortality responses to the acetylcholinesterase (AChE) inhibitor diazinon (DZN) and the antihistamine diphenhydramine (DPH) were more pronounced in slightly older organisms than are employed in early life stage studies (Kristofco et al, 2015). Whether such differential sensitivity throughout development extends to behavioral observations is not understood.…”