Cognitive and Disease-Modifying Effects of 11β-Hydroxysteroid Dehydrogenase Type 1 Inhibition in Male Tg2576 Mice, a Model of Alzheimer's Disease

Abstract

Chronic exposure to elevated levels of glucocorticoids has been linked to age-related cognitive decline and may play a role in Alzheimer's disease. In the brain, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) amplifies intracellular glucocorticoid levels. We show that short-term treatment of aged, cognitively impaired C57BL/6 mice with the potent and selective 11β-HSD1 inhibitor UE2316 improves memory, including after intracerebroventricular drug administration to the central nervous system alone. In the Tg2576 mouse model of Alzheimer's disease, UE2316 treatment of mice aged 14 months for 4 weeks also decreased the number of β-amyloid (Aβ) plaques in the cerebral cortex, associated with a selective increase in local insulin-degrading enzyme (involved in Aβ breakdown and known to be glucocorticoid regulated). Chronic treatment of young Tg2576 mice with UE2316 for up to 13 months prevented cognitive decline but did not prevent Aβ plaque formation. We conclude that reducing glucocorticoid regeneration in the brain improves cognition independently of reduced Aβ plaque pathology and that 11β-HSD1 inhibitors have potential as cognitive enhancers in age-associated memory impairment and Alzheimer's dementia.

Figure 1.

UE2316 Characteristics. A, Structural comparison of UE1961 and UE2316. B, Potency and selectivity of UE2316. C, Male C57BL/6 mice were treated with a single 10-mg/kg oral dose of UE2316 (n = 3 animals per time point) and inhibition by scintillation proximity assay was assessed 1, 4, and 6 hours after dosing and expressed as the percentage inhibition compared with values obtained in vehicle-treated mice (one-way ANOVA, P = .009; Bonferroni's post hoc comparisons). *, P < .05 vs vehicle.

Figure 2.

UE2316 improved spatial and fear-associated memory in aged C57BL/6 mice. Aged 22-month-old C57BL/6 mice were treated with 0 (n = 6), 5 (n = 8), or 15 (n = 8) mg/kg · d UE2316 for 23 days via sc implanted osmotic minipumps. A, Spatial memory was assessed by the Y maze on day 10 of treatment. The initial 1 minute ITI was performed prior to surgery. Treatment with 15 mg/kg · d UE2316 increased the time spent in the novel arm in the 2-hour ITI compared with vehicle-treated animals (*, P < .05 by a Student's t test with Bonferroni correction), and a trend for improvement was seen with the 5-mg/kg · d dose. B, Passive avoidance was analyzed on days 13 and 14 of treatment. Both 5 mg/kg · d (*, P = .02 vs vehicle by Student's t test) and 15 mg/kg · d (*, P = .03 by Student's t test) UE2316 improved latency in the retention trial compared with the vehicle-treated group (by two way repeated measures ANOVA drug interaction with training vs retention, P < .05). C, Similarly aged C57BL/6 mice were treated with an infusion of either vehicle (artificial CSF) (n = 9) or 100 ng/h UE2316 (n = 8) via icv cannulas. Spatial memory was assessed by the Y maze on day 9 of treatment. The initial 1-minute ITI was performed prior to surgery. Treatment with UE2316 increased the time spent exploring the novel arm during the 2-hour ITI compared with the vehicle-treated controls (**, P = .005 by Student's t test).

Figure 3.

UE2316 improved fear-associated behavior in the passive avoidance test in Tg2576 mice. Tg2576 and wild-type mice (n = 10 per group) were treated with vehicle or UE2316 at 10 mg/kg · d by sc Alzet minipump infusion from the age of 14 months for 29 days. A, Tg2576 mice were assessed in the passive avoidance task on days 27 and 28 of drug treatment. The latency to enter the dark compartment was assessed in the training trial (pre) and the retention trial (post). UE2316 increased latency to enter the dark compartment 6 hours after shock (two way repeated measures ANOVA drug effect, P < .04; **, P < .01 by Student's t test) to a greater extent in Tg2576 mice (by an increment of 171.6 ± 28.0 sec compared with 42.6 ± 21.5 sec in vehicle treated mice; **, P = .004 by Student's t test). B, Open field was performed after 23 days of treatment in vehicle- and UE2316-treated wild-type and Tg2576 mice. The percentage of time during the 5-minute trial that was spent in the inner zone of the open field apparatus was measured. There was no significant effect of treatment or genotype. C, Spontaneous alternation was assessed at day 26 of treatment. There was a trend for increased alternation with UE2316 treatment (two way ANOVA; treatment: P = .06).

Figure 4.

Long-term administration of UE2316 improves cognition in Tg2576 mice. Tg2576 mice were treated with either control diet (RM1, n = 16) or RM1 supplemented with 175 ppm UE2316 for an estimated dose of 30 mg/kg · d (n = 32) from the age of 6–7 months for 57 weeks. A, Passive avoidance was analyzed after 15 weeks of treatment with vehicle (n = 13) or UE2316 (n = 23). Both groups exhibited significantly increased latency to enter the dark compartment in the retention test, indicating preserved cognitive function, but there was no effect of UE2316 (by two way ANOVA training vs the retention effect, P < .001; drug effect, P = .26; by Student's t test; *, P = .03, ***, P = .0007). B, Passive avoidance was retested after 41 weeks of treatment with vehicle (n = 13) or UE2316 (n = 23) in chow. UE2316- but not vehicle-treated mice demonstrated a significant increase in latency to enter the dark compartment in the retention test (by Student's t test; **, P = .004).

Figure 5.

Behavior of Tg2576 mice after long-term administration of UE2316. A, Open field was performed in control (vehicle: n = 5; UE2316: n = 5) and Tg2576 mice (vehicle: n = 13; UE2316: n = 23) after 38 weeks of treatment with either normal chow or diet containing UE2316. The Tg2576 mice spent more time in the inner zone than their wild-type counterparts; however, there was no effect of drug administration (by two way ANOVA, *, P < .05). B, Spontaneous alternation was assessed in Tg2576 mice after 39 weeks of vehicle (n = 13) or UE2316 treatment (n = 23). UE2316-treated mice exhibited a significant increase in percentage alternation compared with control mice (by Student's t test; *, P = .04). C, The spatial Morris water maze test was performed after 52 weeks of treatment. Mice that were able to find the platform in a visible platform test were tested in their ability to find the submerged platform using spatial cues located around the testing room. UE2316-treated mice (n = 9) exhibited significant decreases in latency to find the hidden platform across the testing period compared with the vehicle-treated animals (n = 6) (two way repeated measures ANOVA; drug effect, P = .02, and interaction of drug with time, P < .01; by Student's t tests; *, P < .05 at d 3, 5, and 6).

Figure 6.

Effect of short- and long-term UE2316 administration on amyloid plaque burden in Tg2576 mice. A, Short-term plaque number. The 6E10-positive amyloid plaques were counted in at least five nonsequential sections per mouse treated for 29 days with vehicle or UE2316 (n = 10 per treatment) via sc minipumps using the KS300 imaging program, and the total number of positive plaques was expressed per area of the brain. UE2316 had no effect on plaque number in the hippocampus but decreased 6E10 staining in the cortices (Student's t test, **, P = .002), amygdala (Student's t test, *, P = .05), and whole brain (Student's t test, *, P = .01) in comparison with vehicle. B, Short term plaque area. Total plaque area of short-term (29) treated mice was measured using the KS300 imaging program and was expressed as plaque area divided by the total area of the brain region in question. The total plaque area in the cortex was decreased by UE2316 in comparison with vehicle (Student's t test, ***, P = .0001). C, Long-term plaque number. The 6E10-positive amyloid plaques were counted in at least five nonsequential sections per mouse treated for 44 weeks with vehicle or UE2316 (n = 5 per treatment) in the diet using the KS300 imaging program and the total number of positive plaques was expressed per area of the brain. UE2316 had no statistically significant effect on plaque number in the hippocampus or cortex in comparison with vehicle.

Figure 7.

Effects on brain pathology in Tg2576 mice treated with UE2316. A, Representative brain sections from Tg2576 mouse showing amyloid plaques in brain regions stained with 6E10 antibody. a, cortex, vehicle treated; b, cortex, UE2316 treated; c, amygdala, vehicle treated; d, amygdala, UE2316 treated; e, hippocampus, vehicle treated; f, hippocampus, UE2316 treated. B, Representative Western blot of cortex protein (30 μg/sample) from 29-day treated mice. Quantitation was performed using the Odyssey Infrared imaging system and adjusted for β-tubulin. IDE levels were increased in UE2316-treated cortices compared with vehicle-treated tissues in both wild-type and Tg2576 animals (see Table 1).