Triterpenoid CDDO-methylamide improves memory and decreases amyloid plaques in a transgenic mouse model of Alzheimer's disease

Abstract

Oxidative stress is one of the earliest events in the pathogenesis of Alzheimer's disease (AD) and can markedly exacerbate amyloid pathology. Modulation of antioxidant and anti-inflammatory pathways represents an important approach for AD therapy. Synthetic triterpenoids have been found to facilitate antioxidant response and reduce inflammation in several models. We investigated the effect of the triterpenoid, 2-Cyano-3,12-Dioxooleana-1,9-Dien-28-Oic acid-MethylAmide (CDDO-MA) in Tg19959 mice, which carry the human amyloid precursor protein with two mutations. These mice develop memory impairments and amyloid plaques as early as 2-3 months of age. CDDO-MA was provided with chow (800 mg/kg) from 1 to 4 months of age. CDDO-MA significantly improved spatial memory retention and reduced plaque burden, Abeta42 levels, microgliosis, and oxidative stress in Tg19959 mice.

Fig. 1

Cyano-3,12-dioxooleana-1,9-dien-2-8-oic acid methylamide (CDDO-MA) improved spatial memory retention in Tg19959 mice in the Morris water maze. (a) Scheme of strategies to search for the target quadrant during the probe trial. (b) Percent of the first 15 s spent in each quadrant. (c) Percent of the first 15 s spent in the NW (target) quadrant. (d) Differences between the percent time spent in the NW and NE quadrants during the first 15 s (means ± SE). Tg19959 mice fed CDDO-MA preferred the NW (target) quadrant, whereas Tg19959 mice fed with control chow did not (c and d; *p < 0.05). CON, control; NW, northwest; SW, southwest; NE, northeast; SE, southeast; Wt, wild type.

Fig. 2

Cyano-3,12-dioxooleana-1,9-dien-28-oic acid methylamide (CDDO-MA) decreased plaque burden and microglia in the hippocampus of Tg19959 mice. (a) Representative photograph of plaques detected by Aβ42 antibody, AB5078P. (b) Plaque count and (c) percent area occupied by plaque in Tg19959 mice fed CDDO-MA or control (CON) chow (means ± SE). In hippocampus, CDDO-MA reduced significantly the plaque count (b; n = 6 per group; *p = 0.0211) and the percent area occupied by plaque (c; n = 6 per group; *p = 0.0072). (d) Representative photographs of microglial staining detected by CD40 antibody with high magnification views in the insets. (e) Area covered by microglia (means ± SE). In hippocampus, CDDO-MA reduced the area covered by microglia (n = 6 per group; *p = 0.0437). ns, not significant.

Fig. 3

Cyano-3,12-dioxooleana-1,9-dien-28-oic acid methylamide (CDDO-MA) decreased levels of sodium dodecyl sulfate-soluble Aβ42 but did not affect amyloid precursor protein (APP) processing. Levels of Aβ42 (a) and Aβ40 (b) by ELISA. Administration of CDDO-MA reduced significantly levels of Aβ42 in Tg19959 mice (a; *p = 0.0453). Levels of full length APP (c), α-CTFs (d), β-CTFs (e), neprilysin (f) and insulin degrading enzyme (g) in Tg19959 mice were measured by western blots. Data were expressed as ratios to tubulin (means ± SE). No differences were found between Tg19959 mice fed CDDO-MA and Tg19959 mice fed control (CON) chow. ns, not significant; CTF, carboxyterminal fragment of APP.

Fig. 4

Effects of cyano-3,12-dioxooleana-1,9-dien-28-oic acid methylamide (CDDO-MA) on Aβ oligomers in Tg19959 mice. (a) Representative photograph of immunoreactivity detected by anti-oligomer antibody A11. (b,c) Count of A11-immunoreactive patches and area occupied by A11-immunoreactivity in Tg19959 mice fed CDDO-MA or control (CON) chow (means ± SE). No significant differences were found between Tg19959 mice fed control versus CDDO-MA chow (n = 5 per group). (d) Aβ oligomers by western blot with 6E10. Densitometric ratios of trimers (~12 kDa; the 14 kDa represents β-CTFs, as confirmed by 369 antibody) to tubulin (means ± SE). No differences in Aβ trimers were found after 3-month administration of CDDO-MA. CTF, carboxyterminal fragment of APP; ns, not significant.

Fig. 5

Cyano-3,12-dioxooleana-1,9-dien-2-8-oic acid methylamide (CDDO-MA) decreased oxidative stress in Tg19959 mice. (a) Protein carbonyls by western blot. (b) Ponceau S staining for protein levels. (c) Densitometric ratios of protein carbonyls to tubulin. Tg19959 mice had increased protein carbonyl levels compared with wild-type (Wt) mice (*p < 0.05). CDDO-MA administration for 3 months reduced protein carbonyl levels in Tg19959 mice (*p < 0.05). (d) Heme oxygenase-1 (HO-1) protein levels by western blot normalized to tubulin in Wt mice, Tg19959 mice fed control (CON) chow (Tg), and Tg19959 mice fed CDDO-MA (TgCDDO). Tg19959 mice fed CDDO-MA had increased HO-1 compared with Tg19959 fed CON chow (*p < 0.05). (e) Protein carbonyls by western blots of bovine serum albumin oxidized in the presence of 0, 20, 40, or 100 nM CDDO-MA. ns, not significant.