Stilbene epoxidation and detoxification in a Photorhabdus luminescens-nematode symbiosis.

Members of the gammaproteobacterial Photorhabdus genus share mutualistic relationships with Heterorhabditis nematodes, and the pairs infect a wide swath of insect larvae. Photorhabdus species produce a family of stilbenes, with two major components being 3,5-dihydroxy-4-isopropyl-trans-stilbene (compound 1) and its stilbene epoxide (compound 2). This family of molecules harbors antimicrobial and immunosuppressive activities, and its pathway is responsible for producing a nematode "food signal" involved in nematode development. However, stilbene epoxidation biosynthesis and its biological roles remain unknown. Here, we identified an orphan protein (Plu2236) from Photorhabdus luminescens that catalyzes stilbene epoxidation. Structural, mutational, and biochemical analyses confirmed the enzyme adopts a fold common to FAD-dependent monooxygenases, contains a tightly bound FAD prosthetic group, and is required for the stereoselective epoxidation of compounds 1 and 2. The epoxidase gene was dispensable in a nematode-infective juvenile recovery assay, indicating the oxidized compound is not required for the food signal. The epoxide exhibited reduced cytotoxicity toward its producer, suggesting this may be a natural route for intracellular detoxification. In an insect infection model, we also observed two stilbene-derived metabolites that were dependent on the epoxidase. NMR, computational, and chemical degradation studies established their structures as new stilbene-l-proline conjugates, prolbenes A (compound 3) and B (compound 4). The prolbenes lacked immunosuppressive and antimicrobial activities compared with their stilbene substrates, suggesting a metabolite attenuation mechanism in the animal model. Collectively, our studies provide a structural view for stereoselective stilbene epoxidation and functionalization in an invertebrate animal infection model and provide new insights into stilbene cellular detoxification.

Vascular and degenerative processes differentially affect regional interhemispheric connections in normal aging, mild cognitive impairment, and Alzheimer disease.

BACKGROUND AND PURPOSE: Despite the critical importance of the corpus callosum (CC) to the connection between brain hemispheres, little is known about the independent contribution of degenerative and vascular processes to regional changes in the microstructural integrity of the CC. Here, we examine these changes in subjects with mild cognitive impairment, with Alzheimer disease, and in cognitively normal elderly adults. METHODS: We used 3-dimensional brain MRI with diffusion tensor imaging in 47 Alzheimer disease, 77 mild cognitive impairment, and 107 cognitively normal subjects, and we calculated mean fractional anisotropy (FA) values for 4 CC regions corresponding to 4 homologous regions of cortical gray matter (GM). To assess vascular and degenerative processes, we also measured cortical GM and white matter hyperintensity (WMH) volume in corresponding regions and evaluated their vascular risk. RESULTS: We found that GM volumes in anterior and posterior regions were significantly related to FA values in the corresponding regions of the CC for all 3 diagnostic groups. Independent of GM volume, frontal WMH volume was also associated with FA values in the corresponding CC regions, but posterior WMH volume was not. Vascular risk was associated with FA of most CC regions, whereas diagnosis of cognitive state was associated only with FA of the anterior and posterior CC regions. CONCLUSIONS: We found differential region-specific associations between degenerative and vascular processes and the structural integrity of the CC across the spectrum of cognitive ability. Based on these results, we propose a model to explain regional disruption in the interhemispheric connection.

Gait Abnormalities and the Risk of Falls in CKD.

BACKGROUND AND OBJECTIVES: Older adults with CKD are at high risk of falls and disability. It is not known whether gait abnormalities contribute to this risk. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Quantitative and clinical gait assessments were performed in 330 nondisabled community-dwelling adults aged ≥65 years. CKD was defined as an eGFR <60 ml/min per 1.73 m2. Cox proportional hazards models were created to examine fall risk. RESULTS: A total of 41% (n=134) of participants had CKD. In addition to slower gait speed, participants with CKD had gait cycle abnormalities including shorter stride length and greater time in the stance and double-support phases. Among people with CKD, lower eGFR was independently associated with the severity of gait cycle abnormalities (per 10 ml/min per 1.73 m2 lower eGFR: 3.6 cm [95% confidence interval (95% CI), 1.4 to 5.8] shorter stride length; 0.7% [95% CI, 0.3 to 1.0] less time in swing phase; 1.1% [95% CI, 0.5 to 1.7] greater time in double-support phase); these abnormalities mediated the association of lower eGFR with slower gait speed. On clinical gait exam, consistent with the quantitative abnormalities, short steps and marked swaying or loss of balance were more common among participants with CKD, yet most had no identifiable gait phenotype. A gait phenotype defined by any of these abnormal signs was associated with higher risk of falls among participants with CKD: compared with people without CKD and without the gait phenotype, the adjusted hazard ratio was 1.72 (95% CI, 1.06 to 2.81) for those with CKD and the phenotype; in comparison, the adjusted hazard ratio was 0.71 (95% CI, 0.40 to 1.25) for people with CKD but without the phenotype (P value for interaction of CKD status and gait phenotype =0.01). CONCLUSIONS: CKD in older adults is associated with quantitative gait abnormalities, which clinically manifest in a gait phenotype that is associated with fall risk.