Increased Levels of 27-Hydroxycholesterol Induced by Dietary Cholesterol in Brain Contribute to Learning and Memory Impairment in Rats.

SCOPE: Dietary cholesterol has been shown to play a role in the development of Alzheimer's disease (AD). It is proposed that oxysterol especially 27-hydroxycholesterol (27-OHC) may play a potential role in ß-amyloid peptides (Aß) production and accumulation during AD progression. METHODS AND RESULTS: To investigate the mechanisms of dietary cholesterol and 27-OHC on learning and memory impairment, male Sprague-Dawley rats are fed with cholesterol diet with or without 27-OHC synthetase inhibitor (anastrozole) injection. The levels of cholesterol, 27-OHC, 24-hydroxycholesterol (24S-OHC), 7α-hydroxycholesterol, and 7ß-hydroxycholesterol in plasma are determined; apolipoprotein A (ApoA), apolipoprotein B (ApoB), HDL-cholesterol (HDL-C), and LDL-cholesterol (LDL-C) in plasma or brain; CYP27A1 and CYP7A1 in liver and CYP46A1 and CYP7B1 in brain; cathepsin B, cathepsin D, and acid phosphatase in lysosome; and Aß1-40 and Aß1-42 in brain. Results show increased levels of 27-OHC (p < 0.01), LDL-C (p < 0.01), and ApoB (p < 0.01), and decreased level of HDL-C (p < 0.05) in plasma, upregulated CYP27A1 (p < 0.01) and CYP7A1 (p < 0.01) expression in liver, altered lysosomal function, and increased level of Aß in brain (p < 0.05). CONCLUSIONS: This study indicates that the mechanisms of dietary cholesterol on learning and memory impairment may be involved in cholesterol metabolism and lysosome function with the increase of plasma 27-OHC, thus resulting in Aß formation and accumulation.

High­cholesterol diet results in elevated amyloid­ß and oxysterols in rats.

The aim of the present study was to investigate the effects of diet cholesterol on oxysterol levels and amyloid­ß (Aß) production in the peripheral blood and the brains of Sprague­Dawley (SD) rats. SD rats were randomly divided into five groups and fed 0.015, 0.05, 0.2, 0.5 and 1.6% cholesterol­containing diets for 8 weeks. The effect of the different diets on the levels of cholesterol, oxysterols [including 27­hydroxycholesterol (OHC), 24S­OHC, 7α­OHC and 7ß­OHC], and the Aß1­40 and Aß1­42 peptides were examined in the plasma and the brain of the rats. The results demonstrated that diet cholesterol increased the levels of plasma cholesterol in a dose­dependent manner. The plasma levels of 27­OHC, 7α­OHC and 7ß­OHC significantly increased in the 0.5 and 1.6% cholesterol diet groups and the brain levels of 27­OHC significantly increased in the 1.6% cholesterol diet group. Increased concentration of cholesterol in the diet had no significant influence on plasma and brain levels of 24S­OHC in the rats. In addition, Aß1­40 and Aß1­42 levels in plasma and brain were significantly elevated following administration of 0.5 and 1.6% diet cholesterol. The present study revealed that high diet cholesterol contributed to increased level of oxysterols, especially 27­OHC, in the peripheral blood and the brain, which may be the link between increased peripheral cholesterol and brain Aß production.

27-Hydroxycholesterol regulates cholesterol synthesis and transport in C6 glioma cells.

The oxysterol 27-Hydroxycholesterol (27-OHC) is a major cholesterol metabolite that can cross the blood brain barrier (BBB) from peripheral circulation to the brain. Currently, the role of 27-OHC on cholesterol homeostasis in astrocytes and the underlying mechanisms are not defined. Since all brain cholesterol is essentially synthesized in brain itself and astrocytes as net producers of cholesterol are essential for normal brain function, here we investigated the effects of 27-OHC on cholesterol synthesis and transport in C6 glioma cells. C6 cells were treated with 5, 10 and 20µM 27-OHC for 24h and the cell viability and apoptosis, the cholesterol levels and metabolism-related mediators, genes and proteins were subsequently assessed using cell-counting kit (CCK)-8, Amplex red, ELISA, real-time PCR and Western blot, respectively. We found that 27-OHC decreased cholesterol levels by down-regulating the expression of sterol-regulated element binding protein-1 (SREBP-1a), 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CR) and low density lipoprotein receptor (LDLR) and promoted cholesterol transport by up-regulating the expression of peroxisome proliferator-activated receptors-γ (PPAR-γ), liver X receptor-α (LXR-α), ATP-binding cassette transporter protein family member A1 (ABCA1) and apolipoprotein E (ApoE)genes. Our results suggested that 27-OHC may represent a sensitive modulator of cholesterol metabolism disorder by suppressing cholesterol synthesis and stimulating cholesterol transport in astrocytes.

Relationship between oxysterols and mild cognitive impairment in the elderly: a case-control study.

BACKGROUND: To investigate the relationship between oxysterols and mild cognitive impairment (MCI) in a matched case-control study. METHODS: The plasma levels of four oxysterols, 27-hydroxycholesterol (27-OHC), 24S-hydroxycholesterol (24S-OHC), 7α-hydroxycholesterol (7α-OHC) and 7ß-hydroxycholesterol (7ß-OHC), were analyzed by High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) and compared between 70 MCI patients and 140 matched controls with normal cognition. The odds ratio (OR) was calculated using logistic analyses to assess the association between oxysterols and MCI. RESULTS: Compared with controls with normal cognition, plasma level of 27-OHC was significantly higher in MCI patients. Logistic analyses suggested high plasma level of 27-OHC was significantly associated with MCI even after multivariate adjustment (OR = 2.86, 95 % CI: 1.52 ~ 5.37). CONCLUSIONS: Our findings suggested that the increased plasma level of 27-OHC was associated with MCI, suggesting high plasma levels of 27-OHC may pay an important role in the development of MCI.

Association between Exposure to the Chinese Famine in Different Stages of Early Life and Decline in Cognitive Functioning in Adulthood.

OBJECTIVE: To investigate whether exposure to the Chinese Famine in different life stages of early life is associated with cognitive functioning decline in adulthood. METHODS: We recruited 1366 adults born between 1950 and 1964 and divided them into fetal-exposed, early childhood-exposed (1-3 years old during the famine), mid childhood-exposed (4-6 years old during the famine), late childhood-exposed (7-9 years old during the famine), and non-exposed groups. A selection of cognitive tests was administered to assess their cognitive performance. Association between malnutrition in different famine exposure periods and adult cognitive performance was estimated by multivariate logistic and multiple linear regression analyses. RESULTS: There were significant differences in cognitive performance between subjects exposed to famine during different life stages. For the general cognitive tests, fetal-exposed period was associated with decreased scores of the Mini-Mental State Examination (MMSE), and late childhood-exposed with decreased scores of the Montreal Cognitive Assessment (MoCA). We also found exposure to famine during mid and late childhood was associated with worse performance on the Stroop color and word test. CONCLUSION: Famine exposure in utero and during childhood is associated with overall and specific cognitive decline, affecting selective attention and response inhibition particularly.

The oxysterol 27-hydroxycholesterol increases oxidative stress and regulate Nrf2 signaling pathway in astrocyte cells.

The disturbance in cholesterol metabolism has been considered as a cause of alzheimer's disease (AD), which dues to the oxidative damage and cell apoptosis in the brain. We aimed to investigate the toxicity and mechanism of AD-like pathology caused by cholesterol oxidation metabolite 27-hydroxycholesterol (27-OHC) in astrocyte cells. C6 cells were treated with 0, 5, 10, 20 µM 27-OHC for 24 h (h). The cell viability was monitored by using methyl thiazolyl tetrazolium test, generation of reactive oxygen species (ROS) was measured by using 2', 7'-dichlorodihydrofluorescein diacetate fluorescent probe under flow cytometry. The concentrations of 8-hydroxyl deoxyguanosine, the anti-oxidative enzymes such as total superoxide dismutase (tSOD), reduced glutathione (rGSH) and glutathione peroxidase (GSH-Px) were tested by using enzyme-linked immunosorbent assay and enzymic method, respectively. The gene and protein expression of nuclear factor E2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NAD(P)H dehydrogenase quinone 1 (NQO1) and γ-glutamylcysteine synthetase (γ-GCS) in C6 cells were detected by quantitative western blot analysis and real-time PCR analysis. Moreover, the Nrf2 expressions in both of the cytoplasm and nucleus were detected with western blot analysis, and the localization of Nrf2 was performed by immunocytochemistry and confocal microscopy. 27-OHC increased the levels of ROS and decreased the levels of tSOD, rGSH, GSH-Px in C6 cells dose-dependently. In addition, 27-OHC down regulated the expressions of Nrf2, HO-1, NQO1 and γ-GCS at both of gene and protein levels, while Nrf2 expression in the cytoplasm showed decreased trend after incubated for 24 h with 27-OHC. The cholesterol metabolite 27-OHC is toxic to C6 cells and contributed to oxidative damage via regulating the Nrf2 signaling pathway. Our results suggest that 27-OHC may represent a common pathogenic factor in AD.

Effects of GSTM1/GSTT1 gene polymorphism and fruit & vegetable consumption on antioxidant biomarkers and cognitive function in the elderly: a community based cross-sectional study.

BACKGROUND: It was reported that Glutathione S-transferase (GST) gene polymorphism and fruit and vegetable (FV) intake were associated with body antioxidant capacity. The oxidative/anti-oxidative imbalance played an important role in the pathogenesis of AD. However, the association of GST genotype, dietary FV consumption with body antioxidant biomarkers and cognitive function in the elderly is not clear. OBJECTIVE: The aim of the present study was to determine the association of GST genotype, and dietary FV intake, with antioxidant biomarkers and cognitive function in the elderly. METHODS: Food frequency questionnaire was used to collect data of dietary FV intakes in 504 community dwelling elderly aged from 55 to 75 years old. GSTM1 and GSTT1 genotypes were determined by using multiple-PCR method. Plasma and erythrocyte antioxidant biomarkers were measured. Cognitive function was measured by using Montreal Cognitive Assessment. Statistical analysis was applied for exploring the association of GST genotype and FV intake with antioxidant biomarkers level and cognitive function in the elderly. RESULTS: Individual GSTM1 or GSTT1 gene deletion affects body antioxidant biomarkers levels, including erythrocyte GST activity, plasma total antioxidant capacity, and glutathione levels. GSTM1and/or GSTT1 gene deletion have no effects on cognitive function in the surveyed participants. The effect of GST genotype on antioxidant biomarkers are FV intake dependent. There is interaction of FV intake and GST genotype on cognitive function in the elderly. CONCLUSION: GST genotype or daily FV consumption impact body antioxidant biomarkers, but not cognitive function in the elderly. There were combined effects of GST genotype and FV consumption on cognitive function in the elderly population. Large scale perspective population study is required to explore the association of GST genetic polymorphism, FV consumption and antioxidant biomarkers and cognitive function in the elderly.

Synaptic responses evoked by tactile stimuli in Purkinje cells in mouse cerebellar cortex Crus II in vivo.

BACKGROUND: Sensory stimuli evoke responses in cerebellar Purkinje cells (PCs) via the mossy fiber-granule cell pathway. However, the properties of synaptic responses evoked by tactile stimulation in cerebellar PCs are unknown. The present study investigated the synaptic responses of PCs in response to an air-puff stimulation on the ipsilateral whisker pad in urethane-anesthetized mice. METHODS AND MAIN RESULTS: Thirty-three PCs were recorded from 48 urethane-anesthetized adult (6-8-week-old) HA/ICR mice by somatic or dendritic patch-clamp recording and pharmacological methods. Tactile stimulation to the ipsilateral whisker pad was delivered by an air-puff through a 12-gauge stainless steel tube connected with a pressurized injection system. Under current-clamp conditions (I = 0), the air-puff stimulation evoked strong inhibitory postsynaptic potentials (IPSPs) in the somata of PCs. Application of SR95531, a specific GABA(A) receptor antagonist, blocked IPSPs and revealed stimulation-evoked simple spike firing. Under voltage-clamp conditions, tactile stimulation evoked a sequence of transient inward currents followed by strong outward currents in the somata and dendrites in PCs. Application of SR95531 blocked outward currents and revealed excitatory postsynaptic currents (EPSCs) in somata and a temporal summation of parallel fiber EPSCs in PC dendrites. We also demonstrated that PCs respond to both the onset and offset of the air-puff stimulation. CONCLUSIONS: These findings indicated that tactile stimulation induced asynchronous parallel fiber excitatory inputs onto the dendrites of PCs, and failed to evoke strong EPSCs and spike firing in PCs, but induced the rapid activation of strong GABA(A) receptor-mediated inhibitory postsynaptic currents in the somata and dendrites of PCs in the cerebellar cortex Crus II in urethane-anesthetized mice.