Fig. 3: Carnosine and kynurenic acid prevent Aβ42 toxicity in a C. elegans model of AD (GMC).

In vivo screening strategy to identify endogenous metabolites that inhibit Aβ42 aggregation is illustrated in (a). We screened six identified candidate metabolites in a C. elegans model of Alzheimer’s disease. Metabolites (depicted as M) were fed at the L4 stage of GMC worms and their effects were assessed at day 5 of adulthood through a (i) motility assay that determines the overall fitness of the worms, in terms of changes in motility, quantified as body bends per minute (BPM) and (ii) quantification of NIAD-4-stained Aβ42 aggregates (screening data shown in Supplementary Fig. 1). Panels b–g show characterization of kynurenic acid and carnosine to rescue a C. elegans model of AD. Panels (b and c) show the motility of worms, measured in body bends per minute (BPM) on Y-axis vs. days of adulthood on X-axis, treated with increasing concentrations of carnosine (blue) and kynurenic acid (red) compared to untreated worms (black). Increased thrashing frequency was observed across the lifespan of the worm up to 15 µM of carnosine and kynurenic acid (b and c). The motility at day 5 of adulthood, where phenotypic manifestations of Aβ42 are prominent in the GMC worm, is significantly improved by increasing carnosine up to 15 µM and for kynurenic acid at 10 µM (d and e). The radar chart shows the overall fitness of C. elegans as a function of speed, bends per minute (BPM) and the live ratio as is seen on each of its axis (d and e). Aggregate staining was quantified after worms were incubated with the amyloidogenic-specific dye NIAD-4 (f–g) (scale bar, 80 μm). White arrows in the panels (f–g) point to NIAD-4-stained Aβ42 aggregates, which appear orange-red in color. At all concentrations tested, carnosine treatment significantly inhibited Aβ42 aggregation compared to the GMC worms as shown in (f). N2 control worms, which do not express Aβ42, are shown for comparison (scale bar, 80 μm). Similar to carnosine, the aggregation of Aβ42 was inhibited by kynurenic acid treatment as shown in (g). For NIAD-4 screening of aggregates, approximately 15–23 animals were analyzed per condition for GMC (AD) worms and ∼10 animals per control (N2) worms. The beneficial effects of kynurenic acid and carnosine were observed in n = 3 biologically independent experiments. All error bars represent the standard error of the mean (SEM). Statistics were performed using one-way ANOVA, Dunnett’s multiple comparisons against the untreated Aβ42 group using GraphPad Prism, p-values are indicated on the plots.