Gut inflammation associated with age and Alzheimer's disease pathology: a human cohort study.

Age-related disease may be mediated by low levels of chronic inflammation ("inflammaging"). Recent work suggests that gut microbes can contribute to inflammation via degradation of the intestinal barrier. While aging and age-related diseases including Alzheimer's disease (AD) are linked to altered microbiome composition and higher levels of gut microbial components in systemic circulation, the role of intestinal inflammation remains unclear. To investigate whether greater gut inflammation is associated with advanced age and AD pathology, we assessed fecal samples from older adults to measure calprotectin, an established marker of intestinal inflammation which is elevated in diseases of gut barrier integrity. Multiple regression with maximum likelihood estimation and Satorra-Bentler corrections were used to test relationships between fecal calprotectin and clinical diagnosis, participant age, cerebrospinal fluid biomarkers of AD pathology, amyloid burden measured using 11C-Pittsburgh compound B positron emission tomography (PiB PET) imaging, and performance on cognitive tests measuring executive function and verbal learning and recall. Calprotectin levels were elevated in advanced age and were higher in participants diagnosed with amyloid-confirmed AD dementia. Additionally, among individuals with AD dementia, higher calprotectin was associated with greater amyloid burden as measured with PiB PET. Exploratory analyses indicated that calprotectin levels were also associated with cerebrospinal fluid markers of AD, and with lower verbal memory function even among cognitively unimpaired participants. Taken together, these findings suggest that intestinal inflammation is linked with brain pathology even in the earliest disease stages. Moreover, intestinal inflammation may exacerbate the progression toward AD.

Association of Amyloid Pathology With Myelin Alteration in Preclinical Alzheimer Disease.

IMPORTANCE: The accumulation of aggregated ß-amyloid and tau proteins into plaques and tangles is a central feature of Alzheimer disease (AD). While plaque and tangle accumulation likely contributes to neuron and synapse loss, disease-related changes to oligodendrocytes and myelin are also suspected of playing a role in development of AD dementia. Still, to our knowledge, little is known about AD-related myelin changes, and even when present, they are often regarded as secondary to concomitant arteriosclerosis or related to aging. OBJECTIVE: To assess associations between hallmark AD pathology and novel quantitative neuroimaging markers while being sensitive to white matter myelin content. DESIGN, SETTING, AND PARTICIPANTS: Magnetic resonance imaging was performed at an academic research neuroimaging center on a cohort of 71 cognitively asymptomatic adults enriched for AD risk. Lumbar punctures were performed and assayed for cerebrospinal fluid (CSF) biomarkers of AD pathology, including ß-amyloid 42, total tau protein, phosphorylated tau 181, and soluble amyloid precursor protein. We measured whole-brain longitudinal and transverse relaxation rates as well as the myelin water fraction from each of these individuals. MAIN OUTCOMES AND MEASURES: Automated brain mapping algorithms and statistical models were used to evaluate the relationships between age, CSF biomarkers of AD pathology, and quantitative magnetic resonance imaging relaxometry measures, including the longitudinal and transverse relaxation rates and the myelin water fraction. RESULTS: The mean (SD) age for the 19 male participants and 52 female participants in the study was 61.6 (6.4) years. Widespread age-related changes to myelin were observed across the brain, particularly in late myelinating brain regions such as frontal white matter and the genu of the corpus callosum. Quantitative relaxometry measures were negatively associated with levels of CSF biomarkers across brain white matter and in areas preferentially affected in AD. Furthermore, significant age-by-biomarker interactions were observed between myelin water fraction and phosphorylated tau 181/ß-amyloid 42, suggesting that phosphorylated tau 181/ß-amyloid 42 levels modulate age-related changes in myelin water fraction. CONCLUSIONS AND RELEVANCE: These findings suggest amyloid pathologies significantly influence white matter and that these abnormalities may signify an early feature of the disease process. We expect that clarifying the nature of myelin damage in preclinical AD may be informative on the disease's course and lead to new markers of efficacy for prevention and treatment trials.

Insulin Resistance is Associated with Higher Cerebrospinal Fluid Tau Levels in Asymptomatic APOEɛ4 Carriers.

BACKGROUND: Insulin resistance (IR) is linked with the occurrence of pathological features observed in Alzheimer's disease (AD), including neurofibrillary tangles and amyloid plaques. However, the extent to which IR is associated with AD pathology in the cognitively asymptomatic stages of preclinical AD remains unclear. OBJECTIVE: To determine the extent to which IR is linked with amyloid and tau pathology in late-middle-age. METHOD: Cerebrospinal fluid (CSF) samples collected from 113 participants enrolled in the Wisconsin Registry for Alzheimer's Prevention study (mean age = 60.6 years), were assayed for AD-related markers of interest: Aß42, P-Tau181, and T-Tau. IR was determined using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Linear regression was used to test the effect of IR, and APOEɛ4, on tau and amyloid pathology. We hypothesized that greater IR would be associated with higher CSF P-Tau181 and T-Tau, and lower CSF Aß42. RESULTS: No significant main effects of HOMA-IR on P-Tau181, T-Tau, or Aß42 were observed; however, significant interactions were observed between HOMA-IR and APOEɛ4 on CSF markers related to tau. Among APOEɛ4 carriers, higher HOMA-IR was associated with higher P-Tau181 and T-Tau. Among APOEɛ4 non-carriers, HOMA-IR was negatively associated with P-Tau181 and T-Tau. We found no effects of IR on Aß42 levels in CSF. CONCLUSION: IR among asymptomatic APOEɛ4 carriers was associated with higher P-Tau181 and T-Tau in late-middle age. The results suggest that IR may contribute to tau-related neurodegeneration in preclinical AD. The findings may have implications for developing prevention strategies aimed at modifying IR in mid-life.