Administration of bovine casein-derived peptide prevents cognitive decline in Alzheimer disease model mice

There is a growing interest in identifying natural food ingredients that may serve to prevent dementia such as that due to Alzheimer disease (AD). Peptides derived from food proteins have been demonstrated to have various physiological activities such as a hypotensive action. Recent findings have indicated possible associations of hypertension with AD progression, and suggest that angiotensin converting enzyme (ACE) inhibitors with potential to pass through the blood brain barrier (BBB) may reduce the risk of AD. In this study, we investigated the effect of milk peptide (CH-3) on cognitive function in AD model mice. CH-3 contains a tripeptide (methionine-lysine-proline, MKP) that has been found to have a strong ACE inhibitory effect and the potential to pass through the BBB. Adult male ddY mice were used in this study, and an animal model of AD was induced by intracerebroventricular (ICV) injection of Aβ1–42. CH-3 (250 mg/kg/day) or MKP (0.5 mg/kg/day) was orally administered every day starting 2 days before ICV injection. At 3 weeks after ICV injection, cognitive function was evaluated by the Morris water maze test. Brain samples were obtained after behavioral testing, and expression of inflammatory cytokines and NADPH oxidase subunits was measured by real-time quantitative RT-PCR. ICV injection of Aβ1–42 significantly impaired cognitive function compared with that in PBS-injected mice. Daily administration of CH-3 markedly attenuated this Aβ1-42-induced cognitive decline. Aβ1–42 injection significantly enhanced the expression of tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and p22phox in the mouse hippocampus compared with PBS injection, and showed a tendency to increase the expression of monocyte chemoattractant protein-1 (MCP-1), p47phox and gp91phox, whereas CH-3 treatment markedly reduced Aβ1-42-induced TNF-α, MCP-1, iNOS, p47phox and gp91phox expression. Finally, administration of MKP also attenuated Aβ1-42-induced cognitive impairment with an increase in cerebral blood flow. The present study demonstrated that repeated oral administration of CH-3 to AD model mice not only improved cognitive function but also suppressed the expression of inflammatory cytokines and production of oxidative stress, and suggests its therapeutic potential for preventing cognitive impairment in AD.

当前，学界对筛选可预防阿尔茨海默病（Alzheimer disease, AD）型痴呆的天然食品成分的兴趣与日俱增。从食品蛋白中提取的肽类已被证实具有多种生理活性，例如降压作用。近期研究发现，高血压与AD进展可能存在关联，并提示能够穿过血脑屏障（blood brain barrier, BBB）的血管紧张素转换酶（angiotensin converting enzyme, ACE）抑制剂或可降低AD发病风险。本研究探讨了乳源肽CH-3对AD模型小鼠认知功能的影响。CH-3含有一种三肽——甲硫氨酸-赖氨酸-脯氨酸（methionine-lysine-proline, MKP），该肽已被证实具有强效ACE抑制活性且具备穿过血脑屏障的潜力。本研究选用成年雄性ddY小鼠，通过脑室内（intracerebroventricular, ICV）注射Aβ₁–₄₂构建AD动物模型。于脑室内注射前2日起，每日经口给予CH-3（250 mg/kg/日）或MKP（0.5 mg/kg/日）。脑室内注射后3周，采用莫里斯水迷宫（Morris water maze）试验评估小鼠认知功能。行为学测试结束后采集脑组织样本，通过实时定量逆转录聚合酶链反应（real-time quantitative RT-PCR）检测炎性细胞因子及NADPH氧化酶亚基的表达水平。与磷酸盐缓冲液（phosphate buffered saline, PBS）注射组小鼠相比，脑室内注射Aβ₁–₄₂可显著损伤认知功能。每日给予CH-3可显著缓解Aβ₁–₄₂诱导的认知衰退。与PBS注射组相比，Aβ₁–₄₂注射可显著增强小鼠海马组织中肿瘤坏死因子-α（tumor necrosis factor-α, TNF-α）、诱导型一氧化氮合酶（inducible nitric oxide synthase, iNOS）及p22phox的表达，并呈现出升高单核细胞趋化蛋白-1（monocyte chemoattractant protein-1, MCP-1）、p47phox及gp91phox表达的趋势；而CH-3处理可显著降低Aβ₁–₄₂诱导的TNF-α、MCP-1、iNOS、p47phox及gp91phox表达上调。此外，给予MKP同样可改善Aβ₁–₄₂诱导的认知损伤，并提升脑血流量。本研究证实，对AD模型小鼠反复经口给予CH-3，不仅可改善认知功能，还可抑制炎性细胞因子表达与氧化应激产物生成，提示其在预防AD认知损伤方面具有治疗潜力。