Microcystin-LR Does Not Alter Cell Survival and Intracellular Signaling in Human Bronchial Epithelial Cells

Abstract

Changes in ecological and environmental factors lead to an increased occurrence of cyanobacterial water blooms, while secondary metabolites-producing cyanobacteria pose a threat to both environmental and human health. Apart from oral and dermal exposure, humans may be exposed via inhalation and/or swallowing of contaminated water and aerosols. Although many studies deal with liver toxicity, less information about the effects in the respiratory system is available. We investigated the effects of a prevalent cyanotoxin, microcystin-LR (MC-LR), using respiratory system-relevant human bronchial epithelial (HBE) cells. The expression of specific organic-anion-transporting polypeptides was evaluated, and the western blot analysis revealed the formation and accumulation of MC-LR protein adducts in exposed cells. However, MC-LR up to 20 µM neither caused significant cytotoxic effects according to multiple viability endpoints after 48-h exposure, nor reduced impedance (cell layer integrity) over 96 h. Time-dependent increase of putative MC-LR adducts with protein phosphatases was not associated with activation of mitogen-activated protein kinases ERK1/2 and p38 during 48-h exposure in HBE cells. Future studies addressing human health risks associated with inhalation of toxic cyanobacteria and cyanotoxins should focus on complex environmental samples of cyanobacterial blooms and alterations of additional non-cytotoxic endpoints while adopting more advanced in vitro models.Keywords: microcystin-LR; human bronchial epithelial cells; in vitro; HBE1; 16HBE14o-, mitogen-activated protein kinase; cytotoxicity; OATP Key Contribution:The study demonstrated the uptake of microcystin-LR into human bronchial epithelial cells HBE1 and 16HBE14o-. No significant changes in the cell viability, impedance (cell layer integrity) or activation of MAPKs ERK1/2 and p38 were detected in multiple exposure and concentration scenarios.

Microcystin Toxicokinetics, Molecular Toxicology, and Pathophysiology in Preclinical Rodent Models and Humans

“…Using in vitro expression systems, it was shown that the organic anion transporting polypeptides, specifically, OATP1B1, OATP1B3, OATP1A2, and Oatp1b2 are responsible for the uptake of microcystins and multidrug resistance-associated protein 2 (MRP2) is responsible for its efflux [ 58 , 59 , 60 ]. Interestingly, several cell lines that do not express these OATP variants have also exhibited microcystin uptake, suggesting that there are other microcystin uptake transporters that have not been identified [ 61 , 62 ]. The following section summarizes what is known regarding microcystin toxicokinetics and important gaps that remain to be addressed ( Figure 2 ).…”

Identification of Novel Molecular Targets of Four Microcystin Variants by High-Throughput Virtual Screening

“…Microcystins (MCs), one of the most common cyanotoxins, are produced by different genera of cyanobacteria and are considered to be a potent hepatotoxin with a wide range of effects [5,6]. They are cyclic heptapeptides, and most of them are hydrophilic due to carboxylic acids at positions 3 and 6, and to arginine, which is frequently found at positions 2 and 4 [5].…”

“…However, structural modifications due to amino acid combinations can change the polarity of a peptide. MCs are a diverse group of toxins since variations in functional groups by methylation/demethylation, hydroxylation, and epimerization generate a wide variety of congeners; to date, more than 270 variants have been described [5][6][7].…”

Ameliorative effects of jamun seed and orange peel extracts on microcystin LR induced alterations in calcitonin cells and parathyroid gland of rats

“…These cyanobacteria produce and release a large variety of biologically active secondary metabolites, cyanotoxins (Carmichael, 2001; Zhou, Tu, & Xu, 2015). Microcystins are an environmentally abundant large group of cyclic heptapeptide hepatotoxins (Brózman, Kubickova, & Pavel Babica Petra, 2020; Spoof et al, 2020). there are about 250 microcystin congeners varying primarily in amino acid constitution and degree of methylation (Spoof & Catherine, 2017) among which microcystin LR is widely studied variant (Brózman et al, 2020).…”

“…Microcystins are an environmentally abundant large group of cyclic heptapeptide hepatotoxins (Brózman, Kubickova, & Pavel Babica Petra, 2020; Spoof et al, 2020). there are about 250 microcystin congeners varying primarily in amino acid constitution and degree of methylation (Spoof & Catherine, 2017) among which microcystin LR is widely studied variant (Brózman et al, 2020). Microcystin LR has been reported to accumulate in various organisms (Amorim & Vasconcelos, 1999; Greer, Meneely, & Elliott, 2018; Papadimitriou, Kagalou, Stalikas, Pilidis, & Leonardos, 2012; Prepas, Kotak, Campell, Evans, & Hrudey, 1997; Williams, Dawe, Kent, Andersen, & Craig, 1997; Xie, Xie, Guo, Miyabara, & Park, 2005) and produce a variety of effects, for example, hepatic damage (Kim et al, 2006; Srivastava & Srivastav, 2017), kidney (Dias et al, 2009; Shahi, Monalisa, Mallika, Sarmaa, & Dasa, 2012; Wang et al, 2019; Xiping et al, 2019), heart (Shahi et al, 2012), germ cell apoptosis (Zhao, Liu, Wang, Xu, & Xie, 2018) and human respiratory system (Brózman et al, 2020).…”