Gram-negative bacteria are reported as the predominant microorganisms in the normal human brain. In previous articles, we have discussed the mechanisms that lipopolysaccharide endotoxins (LPS) possess to cause neuroinflammation and its results. However, research has gone a little further, associating these molecules with the clinical appearance of neurodegenerative diseases like Alzheimer's Disease (AD).
AD is a progressive disorder manifested by the gradual loss of memory and the subsequent deterioration of mental and behavioral functions. The main risk factor for AD is advanced age. However, there are other factors involved in its pathogenesis such as diabetes mellitus, hyperlipidemia, obesity, vascular factors and depression. The predominant hypothesis for AD is amyloid, which states that changes in the proteolytic processing of amyloid precursor protein leads to amyloid beta (Aβ) peptide accumulation, triggering an immune response that leads to neuro-inflammation and neurodegeneration. However, in recent years, researchers have been paying special attention to the influence of the intestinal microbiota on the modulation of neuro-immune functions.
Based on these studies, there is evidence that exposure of the LPS of Bacteroides fragilis, an abundant Gram-negative bacterium in the gastrointestinal tract, to human primary brain cells is an exceptionally powerful inducer of the NF-kB pro-inflammatory transcription factor (p50/p65). This is a known complex that triggers the expression of pathogenic pathways involved in neurodegenerative inflammation.
On the other hand, in studies carried out in rats, it was observed that Gram-negative bacteria, such as Escherichia coli, place amyloid-β plaques in the brains of these mammals. Later, in research with samples of human brain tissues commonly involved in AD, such as the gray matter of the superior temporal gyrus and the white matter of the frontal lobe, we found not only the presence of LPS but also that of pili E. coli k99. LPS endotoxins were localized with peptides Ab1-40 / 42 on amyloid plaques and around blood vessels. However, the results remain unclear as to whether these bacterial molecules are a cause or result of injury to the brain with AD.
A major question is how the LPS and other molecules related to Gram+ and Gram- bacteria access the brain, which could be promoted by the damage in the blood-brain barrier produced by Gram-negative bacterial endotoxins. Some studies certify the presence of live bacteria in the brain and support the theory that every organ, including the brain, has its own microbiota.
Understanding these underlying mechanisms may provide new perspectives on novel therapeutic strategies for AD as well as other neurodegenerative pathologies. Research companies like Wako Chemicals, a laboratory reagent distributor, have the latest tools to discover novel knowledge, medicines and clinical procedures. The LAL division of Wako markets the PYROSTAR™ line with high purity reagents, accessories and equipment for the qualitative and quantitative detection of endotoxin bacteria using the LAL (Limulus Amebocyte Lysate) method. Limulus Amebocyte Lysate is an aqueous extract of blood cells (amebocytes) from the horseshoe crab (Limulus polyphemus), composed of a chain of trypsin-like enzymes capable of reacting against small amounts of endotoxins. Among its advantages, we can see its high sensitivity and simplicity, requiring less time and sample volume, and its function as a method of quantification.
The PYROSTAR™ catalog includes kits for LAL reagents such as:
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2) Branton, W. G. (2013). Brain microbial populations in HIV/AIDS: α-proteobacteria predominate independent of host immune status. PloS one, 8(1).
3) Jiang, C., Li, G., Huang, P., Liu, Z., & Zhao, B. (2017). The Gut Microbiota and Alzheimer’s Disease. Journal of Alzheimer's Disease, 58(1), 1-15.
4) Lukiw, W. J. (2016). Bacteroides fragilis Lipopolysaccharide and Inflammatory Signaling in Alzheimer’s Disease. Frontiers in Microbiology, 7, 1544.
5) Zhan, X., Stamova, B., Lee-Way, J., DeCarli, C., Phinney, B., & Sharp, F. R. (Noviembre de 2016). Gram-negative bacterial molecules associate with Alzheimer disease pathology. Neurology, 87, 2324-2332.
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