Harmful Algal Bloom Toxicity in Lithobates catesbeiana Tadpoles

Abstract

Harmful algal blooms (HAB) have become a major health concern worldwide, not just to humans that consume and recreate on contaminated waters, but also to the fauna that inhabit the environments surrounding affected areas. HABs contain heterotrophic bacteria, cyanobacterial lipopolysaccharide, and cyanobacterial toxins such as microcystins, that can cause severe toxicity in many aquatic species as well as bioaccumulation within various organs. Thus, the possibility of trophic transference of this toxin through the food chain has potentially important health implications for other organisms in the related food web. While some species have developed adaptions to attenuate the toxic effects of HAB toxins, there are still numerous species that remain vulnerable, including Lithobates catesbeiana (American bullfrog) tadpoles. In the current study we demonstrate that acute, short-term exposure of tadpoles to HAB toxins containing 1 µg/L (1 nmol/L) of total microcystins for only 7 days results in significant liver and intestinal toxicity within tadpoles. Exposed tadpoles had increased intestinal diameter, decreased intestinal fold heights, and a constant number of intestinal folds, indicating pathological intestinal distension, similar to what is seen in various disease processes, such as toxic megacolon. HAB-toxin-exposed tadpoles also demonstrated hepatocyte hypertrophy with increased hepatocyte binucleation consistent with carcinogenic and oxidative processes within the liver. Both livers and intestines of HAB-toxin-exposed tadpoles demonstrated significant increases in protein carbonylation consistent with oxidative stress and damage. These findings demonstrate that short-term exposure to HAB toxins, including microcystins, can have significant adverse effects in amphibian populations. This acute, short-term toxicity highlights the need to evaluate the influence HAB toxins may have on other vulnerable species within the food web and how those may ultimately also impact human health.

Antioxidant Therapy Significantly Attenuates Hepatotoxicity following Low Dose Exposure to Microcystin-LR in a Murine Model of Diet-Induced Non-Alcoholic Fatty Liver Disease

“…In our study, we performed immunostaining of the liver tissues and observed elevated levels of protein carbonylation in the mice that were exposed to the toxin as compared to Vehicle and these levels were lowered upon treatment with targeted antioxidant therapy. Previously we have reported significant increases in protein carbonyl levels in both liver and intestines of tadpoles exposed to 1 µg/L of MC-LR for just 7 days [ 66 ]. In another interesting study conducted by Hwang et al, the authors have reported that repeated MCLR exposure potentiates Kainic Acid-induced excitotoxicity in the hippocampus by enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC and p-ERK [ 67 ].…”

Complex Organisms Must Deal with Complex Threats: How Does Amphibian Conservation Deal with Biphasic Life Cycles?

“…Hypoxia has been shown to cause serious abnormalities in the central nervous system of bullfrog (Lithobates catesbeianus) larvae, and reduce body mass and length in exposed individuals [95]. Extreme temperatures also increase bacterial blooms in ponds, giving rise to deleterious pathogens, such as heterotrophic bacteria (Cyanobacterial lipopolysaccharide) and cyanobacterial toxins (microcystins) that can affect embryo masses and cause significant liver and intestinal toxicity in larvae [90,96]. Such changes in temperature can also compromise immunity at the larvae stage, leading to increased susceptibility to infections [97,98].…”

As We Drink and Breathe: Adverse Health Effects of Microcystins and Other Harmful Algal Bloom Toxins in the Liver, Gut, Lungs and Beyond

“…MCs’ impact on the gut is not confined to mammalian species. In another study done in Lithobates catesbeiana (American bullfrog) tadpoles, it was observed that acute, short-term exposure of tadpoles to HAB toxins containing 1 μg/L (1 nmol/L) of total microcystins for only 7 days resulted in significant liver and GI toxicity [ 86 ]. MC-LR-exposed tadpoles showed increased intestinal diameter, decreased intestinal fold heights, and a constant number of intestinal folds, indicating pathological intestinal distension, similar to toxic megacolon.…”

“…These findings underscore the need to evaluate the GI-related effects related to HAB toxin exposure, including MCs. This also highlights the need to evaluate the influence HAB toxins may have on other vulnerable species within the food web and how those may ultimately also impact human health [ 86 ].…”