Conclusion
Our study demonstrates that the cyanobacterial toxin BMAA can be detected in the olfactory pathway, a window to the brain, and its presence may increase the occurrence of proinflammatory cytokines, reactive glia, and toxicity to axonal processes. Further studies will be needed to evaluate BMAA's toxicity via this route of exposure and factors that increase susceptibility.
Methods
Olfactory bulb (Ob) tissues were collected during autopsies performed between 2014 and 2017 from six South Florida brain donors (ages 47-78) with residences less than 140 m from a freshwater body. A triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) method validated according to peer AOAC International guidelines was used to detect BMAA and two BMAA isomers: 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)glycine (AEG). Quantitative PCR was performed on the contralateral Ob to evaluate the relative expression of genes related to proinflammatory cytokines (IL-6 & IL-18), apoptotic pathways (CASP1 & BCL2), and mitochondrial stress (IRF1 & PINK1). Immunohistochemistry was also performed on the adjacent olfactory tract (Ot) to evaluate co-occurring neuropathology with BMAA tissue concentration.
Results
BMAA was detected in the Ob of all cases at a median concentration of 30.4 ng/g (Range <LLOQ - 488.4 ng/g). Structural isomers were also detected with median concentrations of 28.8 ng/g (AEG) and 103.6 ng/g (2,4-DAB). In addition, we found that cases with BMAA tissue concentrations above the <LLOQ also displayed increased expression of IL-6 (3.3-fold), CASP1 (1.7-fold), and IRF1 (1.6-fold). Reactive microglial, astrogliosis, myelinopathy, and neuronopathy of axonal processes in the Ot were also observed in cases with higher BMAA tissue concentrations.