Background Dietary fibers are metabolized by gastrointestinal (GI) bacteria into short-chain fatty acids (SCFAs). We investigated the potential role of these SCFAs in β-amyloid (Aß) mediated pathological processes that play key roles in Alzheimer’s disease (AD) pathogenesis. Research design and methods Multiple complementary assays were used to investigate individual SCFAs for their dose-responsive effects in interfering with the assembly of Aß1-40 and Aß1-42 peptides into soluble neurotoxic Aß aggregates. Results We found that several select SCFAs are capable of potently inhibiting Aß aggregations, in vitro. Conclusion Our studies support the hypothesis that intestinal microbiota may help protect against AD, in part, by supporting the generation of select SCFAs, which interfere with the formation of toxic soluble Aß aggregates.

Amyloid β‐protein (Aβ) molecules tend to aggregate and subsequently form low MW (LMW) oligomers, high MW (HMW) aggregates such as protofibrils, and ultimately fibrils. These Aβ species can generally form amyloid plaques implicated in the neurodegeneration of Alzheimer disease (AD), but therapies designed to reduce plaque load have not demonstrated clinical efficacy. Recent evidence implicates amyloid oligomers in AD neuropathology, but the precise mechanisms are uncertain. We examined the mechanisms of neuronal dysfunction from HMW‐Aβ1‐42 exposure by measuring membrane integrity, reactive oxygen species (ROS) generation, membrane lipid peroxidation, membrane fluidity, intracellular calcium regulation, passive membrane electrophysiological properties, and long‐term potentiation (LTP). HMW‐Aβ1‐42 disturbed membrane integrity by inducing ROS generation and lipid peroxidation, resulting in decreased membrane fluidity, intracellular calcium dysregulation, depolarization, and impaired LTP. The damaging effects of HMW‐Aβ1‐42 were significantly greater than those of LMW‐Aβ1‐42 Therapeutic reduction of HMW‐Aβ1‐42 may prevent AD progression by ameliorating direct neuronal membrane damage.—Yasumoto, T., Takamura, Y., Tsuji, M., Watanabe‐Nakayama, T., Imamura, K., Inoue, H., Nakamura, S., Inoue, T., Kimura, A., Yano, S., Nishijo, H., Kiuchi, Y., Teplow, D. B., Ono, K. High molecular weight amyloid β1‐42 oligomers induce neurotoxicity via plasma membrane damage. FASEB J. 33, 9220–9234 (2019). http://www.fasebj.org

The intestinal microbiota actively converts dietary flavanols into phenolic acids, some of which are bioavailable in vivo and may promote resilience to select neurological disorders by interfering with key pathologic mechanisms. Since every person harbors a unique set of gut bacteria, we investigated the influence of the gut microbiota's interpersonal heterogeneity on the production and bioavailability of flavonoid metabolites that may interfere with the misfolding of alpha (α)synuclein, a process that plays a central role in Parkinson's disease and other α-synucleinopathies. We generated two experimental groups of humanized gnotobiotic mice with compositionally diverse gut bacteria and orally treated the mice with a flavanol-rich preparation (FRP). The two gnotobiotic mouse groups exhibited distinct differences in the generation and bioavailability of FRP-derived microbial phenolic acid metabolites that have bioactivity towards interfering with αsynuclein misfolding or inflammation. We also demonstrated that these bioactive phenolic acids are effective in modulating the development and progression of motor dysfunction in a Drosophila model of α-synucleinopathy. Lastly, through in vitro bacterial fermentation studies, we identified select bacteria that are capable of supporting the generation of these bioavailable and bioactive phenolic acids. Outcomes from our studies provide a better understanding of how interpersonal heterogeneity in the gut microbiota differentially modulates the efficacy of dietary flavanols to protect against select pathologic mechanisms. Collectively, our findings provide the basis for future developments of probiotic, prebiotic, or synbiotic approaches for modulating the onset and/or progression of α-synucleinopathies and other neurological disorders involving protein misfolding and/or inflammation. Keywordsmicrobiome; humanized gnotobiotic mice; polyphenol metabolism; phenolic acids; αsynucleinopathy; Drosophila MATERIALS AND METHODS Chemicals, solvents, peptides and proteinsChemicals were obtained from Sigma-Aldrich (St Louis, MO, USA) and, unless otherwise stated, were of the highest purity available. Solvents were high-performance liquid chromatography (HPLC) grade and were obtained from Fisher Scientific. Water was doubledistilled and deionized using a Milli-Q system (Millipore Corp., Bedford, MA). Monomeric α-synuclein peptide was purchased from rPeptide (Watkinsville, GA). Glutathione Stransferase (GST) was purchased from Sigma-Aldrich.

Worldwide, Alzheimer’s disease (AD) is the most common age-related neurodegenerative disease and is characterized by unique pathological hallmarks in the brain, including plaques composed of amyloid β-protein (Aβ) and neurofibrillary tangles of tau protein. Genetic studies, biochemical data, and animal models have suggested that Aβ is responsible for the pathogenesis of AD (i.e., the amyloid hypothesis). Indeed, Aβ molecules tend to aggregate, forming oligomers, protofibrils, and mature fibrils. However, while these Aβ species form amyloid plaques of the type implicated in AD neurodegeneration, recent clinical trials designed to reduce the production of Aβ and/or the plaque burden have not demonstrated clinical efficacy. In addition, recent studies using synthetic Aβ peptides, cell culture models, Arctic transgenic mice, and human samples of AD brain tissues have suggested that the pre-fibrillar forms of Aβ, particularly Aβ protofibrils, may be the most critical species, compared with extracellular fibrillar forms. We recently reported that protofibrils of Aβ1-42 disturbed membrane integrity by inducing reactive oxygen species generation and lipid peroxidation, resulting in decreased membrane fluidity, intracellular calcium dysregulation, depolarization, and synaptic toxicity. Therefore, the therapeutic reduction of protofibrils may prevent the progression of AD by ameliorating neuronal damage and cognitive dysfunction through multiple mechanisms.

Lymphoma-associated hemophagocytic syndrome (LAHS), which is the major subtype of adult-onset secondary hemophagocytic lymphohistiocytosis (HLH), has a poor outcome. Although the early diagnosis and treatment of LAHS contributes to a better outcome, the lack of mass formation and the absence of distinct lymph node enlargement often delay the diagnosis of underlying lymphoma. A recent study, which statistically analyzed HLH cases in the literature, showed that the serum soluble interleukin-2 receptor (sIL-2R)/ferritin ratio could be used as a marker to diagnosis of LAHS. To verify this finding, we retrospectively analyzed the laboratory findings of 21 patients with HLH (10 benign disease-associated HLH and 11 LAHS). No significant differences were observed in the levels of LDH or CRP levels. The mean sIL-2R levels (units per milliliter) were significantly higher in the LAHS group (4,176 vs. 13,451, p = 0.0031), and ferritin levels (nanogram per milliliter) were higher in the benign disease-associated HLH group (20,462 vs. 2,561, p = 0.0031). Consequently, the mean serum sIL-2R/ferritin ratio of patients with LAHS was markedly higher than that of patients with benign disease-associated HLH (0.66 vs. 8.56, p = 0.0004). Thus, the results of this study demonstrated that the serum sIL-2R/ferritin ratio is a very useful marker for diagnosing of LAHS, which was further supported by clinical case analysis. Further studies to clarify the pathophysiology of secondary HLH caused by various triggers are needed.