Luteolin inhibits microglia and alters hippocampal-dependent spatial working memory in aged mice

Abstract

A dysregulated overexpression of inflammatory mediators by microglia may facilitate cognitive aging and neurodegeneration. Considerable evidence suggests the flavonoid luteolin has antiinflammatory effects, but its ability to inhibit microglia, reduce inflammatory mediators, and improve hippocampal-dependent learning and memory in aged mice is unknown. In initial studies, pretreatment of BV-2 microglia with luteolin inhibited the induction of inflammatory genes and the release of inflammatory mediators after lipopolysaccharide (LPS) stimulation. Supernatants from LPS-stimulated microglia caused discernible death in Neuro.2a cells. However, treating microglia with luteolin prior to LPS reduced neuronal cell death caused by conditioned supernatants, indicating luteolin was neuroprotective. In subsequent studies, adult (3-6 mo) and aged (22-24 mo) mice were fed control or luteolin (20 mg/d)-supplemented diet for 4 wk and spatial working memory was assessed as were several inflammatory markers in the hippocampus. Aged mice fed control diet exhibited deficits in spatial working memory and expression of inflammatory markers in the hippocampus indicative of increased microglial cell activity. Luteolin consumption improved spatial working memory and restored expression of inflammatory markers in the hippocampus compared with that of young adults. Luteolin did not affect either spatial working memory or inflammatory markers in young adults. Taken together, the current findings suggest dietary luteolin enhanced spatial working memory by mitigating microglial-associated inflammation in the hippocampus. Therefore, luteolin consumption may be beneficial in preventing or treating conditions involving increased microglial cell activity and inflammation.

FIGURE 1

Luteolin inhibited LPS-induced IL-1β production (A) and mRNA expression (B) in BV-2 cells. Bars represent means ± SEM, n = 3. Means without a common letter differ, P < 0.05.

FIGURE 2

Treatment of microglia with luteolin prior to LPS stimulation inhibited neuronal cell death caused by microglial supernatants. Bars represent means ± SEM, n = 3. Means without a common letter differ, P < 0.05.

FIGURE 3

Effects of luteolin on performance of adult and aged mice during the 6-d acquisition phase of the Morris water maze. The distance swam to locate the static platform was measured. Values are means ± SEM, n = 12–14. Repeated-measures ANOVA: day, P < 0.001; diet, P < 0.001.

FIGURE 4

Effects of luteolin on performance of adult and aged mice in a reversal test of spatial working memory. The distance swam to find the relocated platform was measured. Two-way ANOVA: age × diet, P < 0.05. Bars represent means ± SEM, n = 12–14. Means without a common letter differ, P < 0.05.

FIGURE 5

IL-1β mRNA in the hippocampus of adult and aged mice fed control or luteolin diet. Two-way ANOVA of IL-1β mRNA: age, P < 0.001; diet, P < 0.03; and age × diet , P = 0.13. Bars represent means ± SEM, n = 6–7. Means without a common letter differ, P < 0.05.