In vivo modulation of brain cholesterol level and learning performance by a novel plant lipid: indications for interactions between hippocampal-cortical cholesterol and learning

Gestational high fat diet protects 3xTg offspring from memory impairments, synaptic dysfunction, and brain pathology

Maternal history for sporadic Alzheimer's disease (AD) predisposes the offspring to the disease later in life. However, the mechanisms behind this phenomenon are still unknown. Lifestyle and nutrition can directly modulate susceptibility to AD. Herein we investigated whether gestational high fat diet influences the offspring susceptibility to AD later in life. Triple transgenic dams were administered high fat diet or regular chow throughout 3 weeks gestation. Offspring were fed regular chow throughout their life and tested for spatial learning and memory, brain amyloidosis, tau pathology, and synaptic function. Gestational high fat diet attenuated memory decline, synaptic dysfunction, amyloid-β and tau neuropathology in the offspring by transcriptional regulation of BACE-1, CDK5, and tau gene expression via the upregulation of FOXP2 repressor. Gestational high fat diet protects offspring against the development of the AD phenotype. In utero dietary intervention could be implemented as preventative strategy against AD.

High fat diet and its effects on cognitive health: alterations of neuronal and vascular components of brain

It has been well recognized that intake of diets rich in saturated fats could result in development of metabolic disorders such as type 2 diabetes mellitus, obesity and cardiovascular diseases. Recent studies have suggested that intake of high fat diet (HFD) is also associated with cognitive dysfunction. Various preclinical studies have demonstrated the impact of short and long term HFD feeding on the biochemical and behavioural alterations. This review summarizes studies and the protocols used to assess the impacts of HFD feeding on cognitive performance in rodents. Further, it discuss the key mechanisms that are altered by HFD feeding, such as, insulin resistance, oxidative stress, neuro-inflammation, transcriptional dysregulation and loss of synaptic plasticity. Along with these, HFD feeding also alters the vascular components of brain such as loss of BBB integrity and reduced cerebral blood flow. It is highly possible that these factors are responsible for the development of cognitive deficits as a result of HFD feeding.

Natural products improve healthspan in aged mice and rats: A systematic review and meta-analysis

Over the last decades a decrease in mortality has paved the way for late onset pathologies such as cardiovascular, metabolic or neurodegenerative diseases. This evidence has led many researchers to shift their focus from researching ways to extend lifespan to finding ways to increase the number of years spent in good health; "healthspan" is indeed the emerging concept of such quest for ageing without chronic or disabling diseases and dysfunctions. Regular consumption of natural products might improve healthspan, although the mechanisms of action are still poorly understood. Since preclinical studies aimed to assess the efficacy and safety of these compounds are growing, we performed a systematic review and meta-analysis on the effects of natural products on healthspan in mouse and rat models of physiological ageing. Results indicate that natural compounds show robust effects improving stress resistance and cognitive abilities. These promising data call for further studies investigating the underlying mechanisms in more depth.

The effects of cholesterol on learning and memory

Cholesterol is vital to normal brain function including learning and memory but that involvement is as complex as the synthesis, metabolism and excretion of cholesterol itself. Dietary cholesterol influences learning tasks from water maze to fear conditioning even though cholesterol does not cross the blood brain barrier. Excess cholesterol has many consequences including peripheral pathology that can signal brain via cholesterol metabolites, pro-inflammatory mediators and antioxidant processes. Manipulations of cholesterol within the central nervous system through genetic, pharmacological, or metabolic means circumvent the blood brain barrier and affect learning and memory but often in animals already otherwise compromised. The human literature is no less complex. Cholesterol reduction using statins improves memory in some cases but not others. There is also controversy over statin use to alleviate memory problems in Alzheimer's disease. Correlations of cholesterol and cognitive function are mixed and association studies find some genetic polymorphisms are related to cognitive function but others are not. In sum, the field is in flux with a number of seemingly contradictory results and many complexities. Nevertheless, understanding cholesterol effects on learning and memory is too important to ignore.

Dietary cholesterol impairs memory and memory increases brain cholesterol and sulfatide levels

Cholesterol and sulfatides play many important roles in learning and memory. To date, our observations about the effects of cholesterol on learning have been assessed during response acquisition; that is, the learning of a new memory. Here, we report for the first time to our knowledge, on the effect of a cholesterol diet on a previously formed memory. Rabbits were given trace conditioning of the nictitating membrane response for 10 days, then fed a 2% cholesterol diet for 8 weeks, and then assessed for memory recall of the initially learned task. We show that dietary cholesterol had an adverse effect on memory recall. Second, we investigated whether dietary cholesterol caused an increase in brain cholesterol and sulfatide levels in four major brain structures (hippocampus, frontal lobe, brainstem, and cerebellum) using a technique for analyzing myelin and myelin-free fractions separately. Although our data confirm previous findings that dietary cholesterol does not directly affect cholesterol and establish that it does not affect sulfatide levels in the brain, these levels did increase rather significantly in the hippocampus and frontal lobe as a function of learning and memory.

Functional relationships between serum total cholesterol levels, executive control, and sustained attention

This study investigated the potential relationship between serum total cholesterol (TC) and two specific aspects of cognition (executive control and sustained attention) in a non-elderly sample, after controlling for life stress and several sociodemographic and health variables. For each participant (n = 46), measurements of TC, physical health, and life stress were obtained, and executive control and sustained attention were assessed using the Tower of London and the Digit Vigilance Test. The outcomes of these cognitive assessments were correlated with TC, and a covariate-adjusted analysis was performed. After controlling for several co-variates, TC was found to be significantly negatively associated with components of executive control and sustained attention. Because these cognitive functions are crucial in the moment-to-moment regulation of behavior, elevated TC may have negative behavioral consequences in everyday life situations.

High dietary cholesterol facilitates classical conditioning of the rabbit's nictitating membrane response

Studies have shown that modifying dietary cholesterol may improve learning and that serum cholesterol levels can be positively correlated with cognitive performance. Rabbits fed a 0, 0.5, 1 or 2% cholesterol diet for eight weeks and 0.12 ppm copper added to their drinking water received trace and then delay classical conditioning pairing tone with corneal air puff during which movement of the nictitating membrane (NM) across the eye was monitored. We found that the level of classical conditioning and conditioning-specific reflex modification (CRM) as well as the number of beta amyloid-labeled neurons in the cortex and hippocampus were a function of the concentration of cholesterol in the diet. The data provide support for the idea that dietary cholesterol may facilitate learning and memory.

Cholesterol-enriched diet affects spatial learning and synaptic function in hippocampal synapses

The aim of the present study was to determine the effect of a cholesterol-rich diet on learning performance and monitor possible related changes in synaptic function. To this purpose, we compared controls with rats fed with a cholesterol-enriched diet (CD). By using a Morris water-maze paradigm, we found that CD rats learned a water-maze task more quickly than rats fed with a regular diet (RD). A longer period of this diet tended to alter the retention of memory without affecting the improvement in the acquisition of the task. Because of the importance of the hippocampus in spatial learning, we hypothesized that these behavioral effects of cholesterol would involve synaptic changes at the hippocampal level. We used whole-cell patch-clamp recording in the CA1 area of a hippocampal rat slice preparation to test the influence of the CD on pre- and postsynaptic function. CD rats displayed an increase in paired-pulse ratio in both glutamatergic synapses (+48 +/- 9%) and GABAergic synapses (+41 +/- 8%), suggesting that the CD induces long-lasting changes in presynaptic function. Furthermore, by recording NMDA-receptor-mediated currents (I(NMDA)) and AMPA-receptor-mediated currents (I(AMPA)) in the same set of cells we found that CD rats display a lower I(NMDA)/I(AMPA) ratio (I(NMDA)/I(AMPA) = 0.75 +/- 0.32 in RD versus 0.10 +/- 0.03 in CD), demonstrating that cholesterol regulates also postsynaptic function. We conclude that a cholesterol-rich diet affects learning speed and performance, and that these behavioral changes occur together with robust, long-lasting, synaptic changes at both the pre- and postsynaptic level.

Serum cholesterol concentrations are associated with visuomotor speed in men: findings from the third National Health and Nutrition Examination Survey, 1988-1994

BACKGROUND

Current international recommendations advise aggressive treatment of relative hypercholesterolemia despite an incomplete understanding of any neurobehavioral effects of low or lowered serum cholesterol.

OBJECTIVE

The objective was to examine the relation between serum cholesterol concentrations and performance in immediate memory, visuomotor speed, and coding speed tests.

DESIGN

The participants were 4110 adults aged 20-59 y who completed a set of neurobehavioral tests and had blood specimens collected as a part of the third National Health and Nutrition Examination Survey, 1988-1994.

RESULTS

After adjustment for sociodemographic variables, serum trace elements and vitamins, dietary energy intake, and risk factors for cardiovascular disease, we found inverse linear associations of serum total cholesterol and non-HDL cholesterol with visuomotor speed in men. The least-squares mean (+/- SE) visuomotor speeds were 231.6 +/- 2.6, 224.0 +/- 2.2, and 218.9 +/- 2.5 ms, respectively, for men with serum total cholesterol concentrations below the 25th, between the 25th and the 75th, and at or above the 75th percentile (P for trend < 0.001) and were 231.7 +/- 2.7, 225.8 +/- 2.4, and 214.1 +/- 2.3 ms, respectively, for men with a non-HDL-cholesterol concentration below the 25th, between the 25th and the 75th, and at or above the 75th percentile (P for trend < 0.001). No significant associations were observed between memory or coding speed and the selected serum cholesterol measures in men, and the scores of the 3 neurobehavioral tests were unrelated to serum cholesterol in women.

CONCLUSION

Low serum total cholesterol and non-HDL cholesterol are associated with slow visuomotor speed in young and middle-aged men.

Cholesterol modifies classical conditioning of the rabbit (Oryctolagus cuniculus) nictitating membrane response

Cholesterol plays an important role in synapse formation, receptor function, and synaptic plasticity, and animal studies show that modifying cholesterol may improve learning and memory. Other data show that feeding animals cholesterol can induce beta amyloid accumulation. Rabbits (Oryctolagus cuniculus) fed 2% cholesterol for 8 weeks were given trace conditioning of the nictitating membrane response using a 100-ms tone, a 700-ms trace, and periorbital electrical stimulation or airpuff. Rabbits fed cholesterol showed significant facilitation of trace conditioning to airpuff and conditioning-specific reflex modification to periorbital electrical stimulation and airpuff. The cholesterol-fed rabbits had beta amyloid accumulation in the cortex, but little in the hippocampus. The data suggest cholesterol had facilitative effects that outweighed potential amnesic effects of cortical beta amyloid.

Effects of lovastatin on cognitive function and psychological well-being

PURPOSE

Animal research and cross-sectional studies suggest that serum lipid concentrations may influence cognitive function, mood, and behavior, but few clinical trials have studied these effects.

SUBJECTS AND METHODS

In this double-blind investigation, 209 generally healthy adults with a serum low-density-lipoprotein (LDL) cholesterol level of 160 mg/dL or higher were randomly assigned to 6-month treatment with lovastatin (20 mg) or placebo. Assessments of neuropsychological performance, depression, hostility, and quality of life were conducted at baseline and at the end of the treatment period. Summary effect sizes were estimated as z scores on a standard deviation (SD) scale.

RESULTS

Placebo-treated subjects improved between baseline and posttreatment periods on neuropsychological tests in all five performance domains, consistent with the effects of practice on test performance (all P <0.04), whereas those treated with lovastatin improved only on tests of memory recall (P = 0.03). Comparisons of the changes in performance between placebo- and lovastatin-treated subjects revealed small, but statistically significant, differences for tests of attention (z score = 0.18; 95% confidence interval (CI), 0.06 to 0.31; P = 0.005) and psychomotor speed (z score = 0.17; 95% CI, 0.05 to 0.28; P = 0. 004) that were consistent with greater improvement in the placebo group. Psychological well-being, as measured several ways, was not affected by lovastatin.

CONCLUSION

Treatment of hypercholesterolemia with lovastatin did not cause psychological distress or substantially alter cognitive function. Treatment did result in small performance decrements on neuropsychological tests of attention and psychomotor speed, the clinical importance of which is uncertain.

Effect of long-term feeding with acetyl-L-carnitine on the age-related changes in rat brain lipid composition: a study by 31P NMR spectroscopy

Changes in brain lipid composition have been determined in 24 months-old Fischer rats with respect to 6 months-old ones. The cerebral levels of sphingomyelin and cholesterol were found to be significantly increased in aged rats, whereas the amount of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidic acid appear to be unaffected by aging. Long-term feeding with acetyl-L-carnitine was able to reduce the age-dependent increase of both sphingomyelin and cholesterol cerebral levels with no effect on the other measured phospholipids. These findings shown that changes in membrane lipid metabolism and/or composition represent one of the alterations occurring in rat brain with aging, and that long-term feeding with acetyl-L-carnitine can be useful in normalizing these age-dependent disturbances.

Learning and memory in the SAMP8 mouse

The SAMP8 (P8) mouse strain develops deficits in learning and memory relatively early in its lifespan. This review provides an overview of the age-related changes that occur in P8 mice. Behavioral studies with P8 mice show impaired acquisition and retention as early as 4 months of age. Deficits in acquisition and retention occur with both aversive and appetitive training tasks. Anatomical studies have detected a number of age-related changes that occur in the central nervous system of P8 mice. The age-related increase in amyloid beta protein is well correlated with the age-related decline in learning and memory. Antibody to amyloid beta protein injected prior to training alleviated impaired acquisition and retention, whereas post-training injections alleviated retention deficits in older P8 mice. Biochemical studies have detected numerous age-related changes with reduced NMDA receptor activity most closely related to impaired learning and memory in P8 mice. Pharmacological studies have found age-related functional changes in the ability of drugs to improve memory processing in P8 mice in the septum and the hippocampus. The specific pattern of pharmacological changes and the inferred change in neurotransmitter activity suggest that age-related impairment in memory processing may be due to impaired septohippocampal interactions. The proposal that P8 mice may be a useful model for studying the early phases of age-related dementia of the Alzheimer type, while still requiring considerable study, seems reasonable.

The effect of manganese-induced hypercholesterolemia on learning in rats

Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated cholesterol in rats exposed daily to 357 and 714 micrograms Mn/kg for 39 d. Significant Mn accumulation was accompanied by increased cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed rats. The rats receiving 357 and 714 micrograms Mn/kg reached the food in 104.5 +/- 13.8 and 113.3 +/- 25.7 s, respectively, on d 30, whereas their untreated counterparts reached the food in 28.7 +/- 11.4 s. This delay was completely corrected to 29.3 +/- 7.8 and 30.7 +/- 6.0 s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 micrograms/kg of Mn. The correction of impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability.

Reversibility of manganese-induced learning defect in rats

In this study the mechanism by which manganese (Mn) induces learning defect and its reversibility has been investigated in rats. Female albino rats were dosed orally with 357 micrograms Mn/kg body weight for 15 or 30 days. Attempts were made to correct the Mn-induced learning defect by (1) co-administration of mevinolin and Mn for 30 days; (2) administration of mevinolin for 15 days after 15 days of dosing with Mn, and (3) by withdrawal of Mn treatment (15 days dosing with Mn followed by 15 days without Mn). Mevinolin was given orally at 235.7 micrograms/kg body weight. Significant increases in the Mn and cholesterol levels in the hippocampus were accompanied by an obvious slowness in learning of rats exposed to Mn. After one training period (day 29) the time required to reach the exit of a T-maze was 104.5 +/- 13.8 sec for rats dosed with Mn for 30 days, whereas that of the controls was 28.7 +/- 11.4 sec on day 30. This delay was completely corrected (to 30.7 +/- 6.0 sec) in rats co-administered mevinolin (an inhibitor of cholesterol biosynthesis) with Mn. Withdrawal of Mn, with or without inhibiting the cholesterol biosynthesis, also corrected the Mn-induced learning defect. These results suggest that Mn toxicity produces learning disability by increasing cholesterol biosynthesis and this reversible disability in learning can be corrected by withdrawal of Mn exposure.

Do low cholesterol levels slow mental processing?

The plasma cholesterol levels of 279 students were measured and related to decision and movement times in choice reaction time tasks with one, two, four, and eight lamps. In female subjects, low plasma cholesterol levels were associated with slower movement times and, when responding to one or two lamps, slower decision times. In male subjects, there was a nonlinear relationship between cholesterol level and decision times. Because these data are correlational in nature, it is not possible to assume a causal relationship between cholesterol levels and speed of mental processing. The literature, however, supports the suggestion that further work should consider the possibility of a causal relationship.

Cholesterol treatment facilitates spatial learning performance in DBA/2Ibg mice

DBA/2Ibg mice were treated with cholesterol pellets for 11 days. On the seventh day after treatment, animals began 5 consecutive days of training on the spatial form of Morris water task, followed on the third and fourth days by a probe trial, and random platform training on the fifth day. DBA mice with cholesterol pellets exhibited enhanced performance compared to DBA mice that underwent a sham surgery. Our results suggest that subchronic treatment with the steroid hormone precursor, cholesterol, enhances spatial learning performance in DBA mice.

Lowering cholesterol concentrations and mortality: a quantitative review of primary prevention trials

OBJECTIVE

To determine the effects of lowering cholesterol concentrations on total and cause specific mortality in randomised primary prevention trials.

DESIGN

Qualitative (meta-analytic) evaluation of total mortality from coronary heart disease, cancer, and causes not related to illness in six primary prevention trials of cholesterol reduction (mean duration of treatment 4.8 years).

PATIENTS

24,847 Male participants; mean age 47.5 years.

MAIN OUTCOME MEASURES

Total and cause specific mortalities.

RESULTS

Follow up periods totalled 119,000 person years, during which 1147 deaths occurred. Mortality from coronary heart disease tended to be lower in men receiving interventions to reduce cholesterol concentrations compared with mortality in control subjects (p = 0.06), although total mortality was not affected by treatment. No consistent relation was found between reduction of cholesterol concentrations and mortality from cancer, but there was a significant increase in deaths not related to illness (deaths from accidents, suicide, or violence) in groups receiving treatment to lower cholesterol concentrations relative to controls (p = 0.004). When drug trials were analysed separately the treatment was found to reduce mortality from coronary heart disease significantly (p = 0.04).

CONCLUSIONS

The association between reduction of cholesterol concentrations and deaths not related to illness warrants further investigation. Additionally, the failure of cholesterol lowering to affect overall survival justifies a more cautious appraisal of the probable benefits of reducing cholesterol concentrations in the general population.

AL721, a novel membrane fluidizer

AL721, which is a novel lipid mixture extracted from egg yolks, is believed to be a therapeutic pharmacologic agent. AL721 interacts with membranes of various types of cells with a common mode of action. AL721 modifies cellular membrane composition and fluidity through passive extraction and/or exchange of cholesterol. Physiologically diminished cell function due to rigidification of its membrane is reversible both in vitro and in vivo by AL721. Fluidization of aged membranes with AL721 has been shown to restore brain serotonin receptor function both in vitro and in vivo. AL721 can also successfully restore deficient immune responsiveness of lymphocytes to mitogen stimulation in aged subjects. Drug tolerance to morphine and ethanol develops upon elevation of the viscosity of neuronal cell membranes in order to counteract the fluidization effect of the drug. Treatment of rigidified cellular membranes with AL721 in vivo can markedly reduce withdrawal symptoms. The virucidal effect of AL721 on the human immunodeficiency virus is believed to operate by lowering of viral membrane cholesterol thus interfering with the binding of the viral antigen to the host cell. Non-toxicity of AL721 is clearly demonstrated in animal and human safety studies.