Repeated five-day administration of L-BMAA, microcystin-LR, or as mixture, in adult C57BL/6 mice - lack of adverse cognitive effects

Oddvar Myhre,Synne Kleiven,Tim Hofer,Dag Marcus Eide,Hans Christian Utkilen

doi:10.1038/s41598-018-20327-y

Oddvar Myhre, Synne Kleiven + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-20327-y

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Abstract

The cyanobacterial toxins β-methylamino-L-alanine (L-BMAA) and microcystin-LR (MC-LR; a potent liver toxin) are suspected to cause neurological disorders. Adult male C57BL/6JOlaHsd mice aged approximately 11 months were subcutaneously injected for five consecutive days with L-BMAA and microcystin-LR alone, or as a mixture. A dose-range study determined a tolerable daily dose to be ~31 µg MC-LR/kg BW/day based on survival, serum liver status enzymes, and relative liver and kidney weight. Mice tolerating the first one-two doses also tolerated the subsequent three-four doses indicating adaptation. The LD50 was 43–50 μg MC-LR/kg BW. Long-term effects (up to 10 weeks) on spatial learning and memory performance was investigated using a Barnes maze, were mice were given 30 µg MC-LR/kg BW and/or 30 mg L-BMAA/kg BW either alone or in mixture for five consecutive days. Anxiety, general locomotor activity, willingness to explore, hippocampal and peri-postrhinal cortex dependent memory was investigated after eight weeks using Open field combined with Novel location/Novel object recognition tests. Toxin exposed animals did not perform worse than controls, and MC-LR exposed animals performed somewhat better during the first Barnes maze re-test session. MC-LR exposed mice rapidly lost up to ~5% body weight, but regained weight from day eight.

Highlights

The cyanobacterial toxins β-methylamino-L-alanine (L-BMAA; non-endogenous N-alkylated amino acid) and microcystin-LR (MC-LR; ring-formed polypeptide) are suspected of causing developmental neurotoxicity and neurodegeneration in humans
During World War II, the Guamanians were undernourished and their diet consisted of cycad seed flour containing L-BMAA as well as flying foxes and other animals that consume cycad seeds (L-BMAA is biomagnified in the food chain)[7]
This study investigates the effects of MC-LR on behavior in adult animals, and the combinatorial effect of MC-LR + L-BMAA

Summary

Introduction

The cyanobacterial toxins β-methylamino-L-alanine (L-BMAA; non-endogenous N-alkylated amino acid) and microcystin-LR (MC-LR; ring-formed polypeptide) are suspected of causing developmental neurotoxicity and neurodegeneration in humans. L-BMAA has been thought to mainly affect neurons in motor area regions which is supported by two high-dose long-term administration studies in adult monkeys[15] and rats[16]. MC-LR is reported to be developmental neurotoxic in young rats and both single[25] and long-term (14–56 days) repeated low-dose administration affected spatial learning and memory[26,27,28]. In this study we were interested in if five-day repeated daily administrations of L-BMAA and MC-LR alone, or in combination, in adult 11-month-old (male C57BL/6 become about 26 months) mice would cause long-term behavioral effects. The chosen five-day exposure period is supposedly more suitable than a single dose as mice could die, and could for instance resemble adult exposure from a batch of contaminated food consumed over a few days (e.g. vegetables and/or seafood), a visit to a summerhouse over a few days where the drinking and/or swimming water is contaminated (lake activities and wind can result in aerosol/droplet formation), or consuming a contaminated batch of cyanobacterial food supplements for a few days

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