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.
Highlights
Cyanobacteria, the most diverse group of Gram-negative prokaryotes and Earth’s oldest known oxygen photoautotrophs, are an important part of both terrestrial and aquatic ecosystems [1,2,3].Cyanobacteria are experiencing a boom in recent years along with the increasing eutrophication of the environment, decreased diversity of phytoplankton, rising CO2 levels, and global increase of temperature [4,5,6,7]
The results show no major changes in the activation of ERK1/2 and p38 caused by 1 μM MC-LR in HBE1 and 16HBE14o-cells, suggesting that MC-LR does not significantly interfere with intracellular signaling in these cells
Results of densitometric evaluation show mitogen-activated protein kinases (MAPKs) activation activation in Results of densitometric evaluation show activation by MC-LR treatment expressed as fold changes over the solvent control (SC) with normalization to treatment expressed as changes fold changes over the solventsignal-regulated control (SC) with the negative control by (NC; horizontal dotted line): fold in (a,b) extracellular normalization to the negative control (NC; horizontal dotted fold changes in (a,b)
Summary
Cyanobacteria, the most diverse group of Gram-negative prokaryotes and Earth’s oldest known oxygen photoautotrophs, are an important part of both terrestrial and aquatic ecosystems [1,2,3].Cyanobacteria are experiencing a boom in recent years along with the increasing eutrophication of the environment, decreased diversity of phytoplankton, rising CO2 levels, and global increase of temperature [4,5,6,7]. Humans can be exposed to cyanobacterial toxins via drinking of water, consumption of contaminated food, or during recreational activities when contaminated water is swallowed or inhaled [2,4,8]. Whilst oral and dermal exposures are considered the main routes of cyanotoxins entering the human body, the inhalation exposure has gained attention relatively recently [10], along with the fact that aerosolized cyanobacteria have been detected in the human upper respiratory tract and central airways [11] and several toxin-producing cyanobacteria including Microcystis sp. Cyanobacteria and associated toxins may enter the human body through inhalation of aerosolized particles from wave breaking [12,13] or inhalation/swallowing of contaminated water during swimming and other recreational activities, such as paddling or surfing [4,14]
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