Changes in membrane fatty acids and delta-9 desaturase in senescence accelerated (SAMP8) mouse hippocampus with aging

Effects of Dietary Food Components on Cognitive Functions in Older Adults

Population aging has recently been an important issue as the number of elderly people is growing worldwide every year, and the extension of social security costs is financially costly. The increase in the number of elderly people with cognitive decline is a serious problem related to the aging of populations. Therefore, it is necessary to consider not only physical care but also cognitive patterns in the future care of older adults. Since food contains a variety of bioactive substances, dietary patterns may help improve age-related cognitive decline. However, the relationship between cognitive function and individual food components remains ambiguous as no clear efficacy or mechanism has been confirmed. Against this background, this review summarizes previous reports on the biological process of cognitive decline in the elderly and the relationship between individual compounds in foods and cognitive function, as well as the role of individual components of food in cognitive function, in the following order: lipids, carotenoids, vitamins, phenolic compounds, amino acids, peptides, and proteins. Based on the research presented in this review, a proper diet that preserves cognitive function has the potential to improve age-related cognitive decline, Alzheimer's disease, and Parkinson's disease. Hopefully, this review will help to trigger the development of new foods and technologies that improve aging and cognitive functions and extend the healthy life span.

Neuronal control of lipid metabolism by STR-2 G protein-coupled receptor promotes longevity in Caenorhabditis elegans

The G protein-coupled receptor (GPCR) encoding family of genes constitutes more than 6% of genes in Caenorhabditis elegans genome. GPCRs control behavior, innate immunity, chemotaxis, and food search behavior. Here, we show that C. elegans longevity is regulated by a chemosensory GPCR STR-2, expressed in AWC and ASI amphid sensory neurons. STR-2 function is required at temperatures of 20°C and higher on standard Escherichia coli OP50 diet. Under these conditions, this neuronal receptor also controls health span parameters and lipid droplet (LD) homeostasis in the intestine. We show that STR-2 regulates expression of delta-9 desaturases, fat-5, fat-6 and fat-7, and of diacylglycerol acyltransferase dgat-2. Rescue of the STR-2 function in either AWC and ASI, or ASI sensory neurons alone, restores expression of fat-5, dgat-2 and restores LD stores and longevity. Rescue of stored fat levels of GPCR mutant animals to wild-type levels, with low concentration of glucose, rescues its lifespan phenotype. In all, we show that neuronal STR-2 GPCR facilitates control of neutral lipid levels and longevity in C. elegans.

n-3 Polyunsaturated Fatty Acids and Their Derivates Reduce Neuroinflammation during Aging

: Aging is associated to cognitive decline, which can lead to loss of life quality, personal suffering, and ultimately neurodegenerative diseases. Neuroinflammation is one of the mechanisms explaining the loss of cognitive functions. Indeed, aging is associated to the activation of inflammatory signaling pathways, which can be targeted by specific nutrients with anti-inflammatory effects. Dietary n-3 polyunsaturated fatty acids (PUFAs) are particularly attractive as they are present in the brain, possess immunomodulatory properties, and are precursors of lipid derivates named specialized pro-resolving mediators (SPM). SPMs are crucially involved in the resolution of inflammation that is modified during aging, resulting in chronic inflammation. In this review, we first examine the effect of aging on neuroinflammation and then evaluate the potential beneficial effect of n-3 PUFA as precursors of bioactive derivates, particularly during aging, on the resolution of inflammation. Lastly, we highlight evidence supporting a role of n-3 PUFA during aging.

Higher dietary fat quality is associated with lower anxiety score in women: a cross-sectional study

BACKGROUND

The relationship between anxiety and dietary fat quality (DFQ) has not been well studied. The aim of this study was to investigate the relationship between anxiety disorder and fatty acids' intake in women.

METHODS

This cross-sectional study included 300 women aged 18-49 attending healthcare centers. Dietary exposure was measured by a 168-item semi-quantitative food frequency questionnaire (FFQ). To determine the status of anxiety, the Depression, Anxiety, and Stress Scale (DASS) questionnaire was used. Based on the total score of anxiety, the participants were divided into two groups of without anxiety (< 8) and with anxiety (≥ 8). The relationship between fatty acids intake and odd ratio (OR) for anxiety was analyzed by simple logistic regression.

RESULTS

About 37.7% of individuals reported anxiety. After adjustment for covariates, an increase in the OR for anxiety was observed across the quintuples of saturated fatty acids (SFAs) (OR 3.17; 95% CI 1.43-7.00; p-trend = 0.005). In addition, higher intakes of monounsaturated fatty acids (MUFAs) (OR 0.15; 95% CI 0.05-0.44; p-trend = 0.001), oleic acid (OR 0.25; 95% CI 0.09-0.67; p-trend = 0.002), alpha-linolenic acid (ALA) (OR 0.07; 95% CI 0.02-0.23; p-trend < 0.001), and n-3:n-6 poly unsaturated fatty acids (PUFAs) (OR 0.56; 95% CI 0.24-1.03; p-trend = 0.02) were found to be related with lower OR of anxiety.

CONCLUSION

Intake of SFAs was positively related to anxiety disorder, whereas MUFAs, oleic acid, ALA, and n-3: n-6 PUFAs intake were inversely related to anxiety score. For investigating the association of fat intake and anxiety disorder, DFQ may be a useful measure.

Peptides and aging: Their role in anorexia and memory

The rapid aging of the world's population has led to a need to increase our understanding of the pathophysiology of the factors leading to frailty and cognitive decline. Peptides have been shown to be involved in the pathophysiology of frailty and cognitive decline. Weight loss is a major component of frailty. In this review, we demonstrate a central role for both peripheral peptides (e.g., cholecystokinin and ghrelin) and neuropeptides (e.g., dynorphin and alpha-MSH) in the pathophysiology of the anorexia of aging. Similarly, peripheral peptides (e.g., ghrelin, glucagon-like peptide 1, and cholecystokinin) are modulators of memory. A number of centrally acting neuropeptides have also been shown to modulate cognitive processes. Amyloid-beta peptide in physiological levels is a memory enhancer, while in high (pathological) levels, it plays a key role in the development of Alzheimer's disease.

Saturated fatty acid metabolism is key link between cell division, cancer, and senescence in cellular and whole organism aging

Cellular senescence is an in vivo and in vitro phenomenon, accompanied by physiological changes including cessation of division and disturbances of organelle structure and function. Review of the literature was undertaken to determine whether there is evidence that whole organism aging and cell senescence share a common initiation pathway. In vivo aged cells of different lineages, including aged T lymphocytes, show high expression of the INK4A-p16 gene. In cell culture when telomeres are shortened past a key length or state, the Arf/Ink gene system (p16/p14 humans, p16/p19 mice) switches on and activates p53, which suppresses further cell division. The p53 gene is a key tumor suppressor and its deletion or mutation allows cancerous growth. The switching on of p53 also causes changes in fatty acid metabolism, especially down-regulation of both fatty acid synthase and stearoyl-CoA (delta-9) desaturase. The co-suppression of these genes together with enhanced uptake of extracellular fatty acids, leads to raised levels of cellular palmitate and induction of either apoptosis or senescence. In senescent cells, the fatty acid composition of the cellular membranes alters and leads to changes in both structure and function of organelles, especially mitochondria. Animal models of accelerated aging exhibit repression of stearoyl-CoA desaturase activity while anti-aging calorie restriction stimulates the same enzyme system. It is concluded that aging in cells and whole organisms share a common initiation pathway and that cellular senescence is protective against cancer. Healthy longevity is likely to be most enhanced by factors that actively suppress excessive cell division.

Senescence-accelerated mouse (SAM) with special references to neurodegeneration models, SAMP8 and SAMP10 mice

The SAM strains, a group of related inbred strains consisting of senescence-prone inbred strains (SAMP) and senescence-resistant inbred strains (SAMR), have been successfully developed by selective inbreeding of the AKR/J strain of mice donated by the Jackson laboratory in 1968. The characteristic feature of aging common to the SAMP and SAMR is accelerated senescence and normal aging, respectively. Furthermore, SAMP and SAMR strains of mice manifest various pathobiological phenotypes spontaneously. Among SAMP strains, SAMP8 and SAMP10 mice show age-related behavioral deterioration such as deficits in learning and memory, emotional disorders (reduced anxiety-like behavior and depressive behavior) and altered circadian rhythm associated with certain pathological, biochemical and pharmacological changes. Here, the previous and recent literature on SAM mice are reviewed with an emphasis on SAMP8 and SAMP10 mice. A spontaneous model like SAM with distinct advantages over the gene-modified model is hoped by investigators to be used more widely as a biogerontological resource to explore the etiopathogenesis of accelerated senescence and neurodegenerative disorders.

Inbred C57BL/6J and DBA/2J mouse strains exhibit constitutive differences in regional brain fatty acid composition

Major behavioral and neurochemical features observed between inbred C57BL/6 and DBA/2 mouse strains can be reproduced within rodent strains following dietary-induced reductions in brain docosahexaenoic acid (DHA, 22:6n-3) composition. It was therefore hypothesized that C57BL/6 and DBA/2 mice exhibit constitutive differences in brain DHA composition that are independent of diet. To test this, adult C57BL/6J and DBA/2J prefrontal cortex, hippocampus, ventral striatum, and midbrain fatty acid composition was determined by gas chromatography. After correction for multiple comparisons, C57BL/6J mice exhibited significantly lower DHA composition in the hippocampus and ventral striatum, but not prefrontal cortex or midbrain, and significantly greater regional arachidonic acid (ARA, 20:4n-6):DHA ratios, relative to DBA/2J mice. C57BL/6J mice also exhibited significantly lower regional adrenic acid (ADA, 22:4n-6) composition, and a significantly smaller ADA:ARA ratio, relative to DBA/2J mice. C57BL/6J mice exhibited significantly smaller oleic acid:stearic acid ratio in the hippocampus and ventral striatum relative to DBA/2J mice. Among all mice, DHA composition was positively correlated with the ADA:ARA ratio and inversely correlated with the oleic acid:stearic acid ratio. These data demonstrate that inbred C57BL/6J and DBA/2J mouse strains exhibit constitutive and region-specific differences in fatty acid composition independent of diet, and suggest that heritable genetic factors are an important determinant of central fatty acid composition.

The aging human orbitofrontal cortex: decreasing polyunsaturated fatty acid composition and associated increases in lipogenic gene expression and stearoyl-CoA desaturase activity

Orbitofrontal cortex (OFC, Brodmann area 10) gray matter volume reductions and selective reductions in docosahexaenoic acid (DHA, 22:6n-3) are observed in adult patients with major depressive disorder (MDD). OFC gray matter volume also decreases with advancing age in healthy subjects. To examine if OFC gray matter DHA composition decreases during normal aging, we determined age-related changes in OFC gray matter fatty acid composition by gas chromatography in subjects aged 29-80 years (n=30). We additionally determined elongase (HELO1), delta-5 desaturase (FASD1), delta-6 desaturase (FASD2), peroxisomal (PEX19), and stearoyl-CoA desaturase (SCD) mRNA expression in the same tissues. Increasing age was associated with a progressive decline in polyunsaturated fatty acid (PUFA) composition, including DHA and arachidonic acid (AA, 20:4n-6), and transient, apparently compensatory, elevations in elongase and desaturase gene expression. The age-related reduction in PUFA composition was inversely correlated with SCD expression and activity resulting in elevations in monounsaturated fatty acid composition. These dynamic age-related changes in OFC gray matter fatty acid composition and biosynthetic gene expression may contribute to the progressive decline in OFC gray matter volume found with advancing age. The implications of age-related reductions in OFC PUFA composition for affective dysregulation in the elderly are discussed.

Lipid metabolism and diet: Possible mechanisms of slow aging

The ability to survive to an extremely old age is a consequence of complex interactions among genes, environment, lifestyle and luck. In the last two centuries, life expectancy in western countries has doubled, increasing from 40 to 81 years (79 for males and 82 for females). The candidate factors to determine such mortality reduction are reduced exposure to infections and the subsequent reduction in inflammatory responses, and to some extent, improvement in diet and nutrition. Among the people born at the beginning of the previous century, a small portion of individuals (1 in 10,000 born) have reached 100 years, surviving approximately 20 years more than the general population. The successful longevity of these individuals shows a familial component, possibly genetic, as underlined by the centenarian sibling's increased chance of reaching 100 years of age compared to the general population. Genetic studies on long living individuals have led to the discovery of potential genetic causes of extreme longevity. These discoveries have highlighted the role of lipid metabolism as a potential key player in the ability to survive to extreme old age. Additional studies on the longevity phenotype have confirmed the role of lipids and lipid-associated cell activities in the predisposition to longevity, from lower eukaryotes to humans. The main focus of this review is the appreciation of demographic survival data and changes in recent diet with the above mentioned genetic and phenotypic biomarkers of longevity, in order to elucidate hypotheses on mechanisms of slow aging and disease resistance.

Effects of dietary restriction on age-related changes in the phospholipid fatty acid composition of various rat tissues

BACKGROUND AND AIMS

Polyunsaturated fatty acids (PUFAs) are essential components of the cell lipid bilayer and are involved in membrane fluidity and normal functioning, but they are vulnerable to free radical attack. Given the role of oxidative stress in the aging process, age-related changes in phospholipid fatty acid (PLFA) composition in rat liver, kidney and heart were assessed in 3-, 12- and 24-month-old rats fed either ad libitum but only every other day, or daily but only 60% of the quantity normally consumed by age-matched controls.

METHODS

Lipids were extracted and phospholipids (PLs) were separated using the solid phase extraction technique, then transesterified and assayed by gas-liquid chromatography.

RESULTS

Saturated fatty acids (FAs) did not change significantly with age; mono- and bi-unsaturated FAs decreased in the liver and heart, and the ratio of the former to the latter increased in the liver, kidney and heart. PUFAs increased in the liver and heart. As regards individual FAs, 20:1(n-9) decreased in all organs, 14:1 and 18:1(n-7) increased in the kidney and heart, 18:1(n-9) increased in the kidney, 20:2(n-6), 18:2(n-6) and 22:5(n-3) decreased in the liver and heart, 20:3(n-6) decreased in the kidney and increased in the heart. The most abundant PUFAs, 20:4(n-6) and 22:6(n-3), either remained the same or increased with age. The N-9 family increased in the kidney, the N-7 family increased in the kidney and heart, the N-6 family decreased in all three organs, and the N-3 family increased in the liver and kidney. Dietary restriction (DR) significantly counteracted most of these changes, but changes in some FAs [20:2(n-6) in the heart] were magnified by DR and may not be age-related.

CONCLUSIONS

Most age-related changes (that occurred in the rat liver, kidney and heart and were counteracted by the two different types of DR) may be involved in the mechanism of aging.

Effects of dietary omega-3 polyunsaturated fatty acids on brain gene expression

Polyunsaturated fatty acids (PUFA) are essential structural components of the central nervous system. Their role in controlling learning and memory has been well documented. A nutrigenomic approach with high-density microarrays was used to reveal brain gene-expression changes in response to different PUFA-enriched diets in rats. In aged rats fed throughout life with PUFA-enriched diets, genes with altered expressions included transthyretin, alpha-synuclein, and calmodulins, which play important roles in synaptic plasticity and learning. The effect of perinatal omega-3 PUFA supply on gene expression later in life also was studied. Several genes showed similar changes in expression in rats fed omega-3-deficient diets in the perinatal period, regardless of whether they or their mothers were fed omega-3 PUFA-sufficient diets after giving birth. In this experiment, among the down-regulated genes were a kainate glutamate receptor and a DEAD-box polypeptide. Among the up-regulated genes were a chemokine-like factor, a tumor necrosis factor receptor, and cytochrome c. The possible involvement of the genes with altered expression attributable to different diets in different brain regions in young and aged rats and the possible mode of regulatory action of PUFA also are discussed. We conclude that PUFA-enriched diets lead to significant changes in expression of several genes in the central nervous tissue, and these effects appear to be mainly independent of their effects on membrane composition. The direct effects of PUFA on transcriptional modulators, the downstream developmentally and tissue-specifically activated elements might be one of the clues to understanding the beneficial effects of the omega-3 PUFA on the nervous system.

Stearoyl-CoA desaturase, a short-lived protein of endoplasmic reticulum with multiple control mechanisms

Stearoyl-CoA desaturase (SCD) is a short-lived, polytopic membrane-bound non-heme iron enzyme localized primarily in the endoplasmic reticulum. SCD is required for the biosynthesis of monounsaturated fatty acids, and plays a key role in hepatic synthesis of triglycerides and very-low-density lipoproteins. The intracellular concentration of SCD fluctuates in a wide range in response to complex and often competing hormonal and dietary factors. A combination of transcriptional regulation and rapid protein degradation produces transient elevations of SCD enzyme activity in response to physiologic demands. Dysregulation of SCD has been implicated in non-alcoholic fatty liver disease, hyperlipidemia, and obesity.

Ageing-related tissue-specific alterations in mitochondrial composition and function are modulated by dietary fat type in the rat

This study investigated the way in which feeding rats with two fat sources (olive or sunflower oils) affected electron-transport components and function of mitotic (liver) and postmitotic (heart and skeletal muscle) tissues during ageing. Rats adapted the mitochondrial-membrane-lipid profile to dietary fat throughout the study, suggesting that the benefits to eat either of the two fats might be maintained lifelong. Liver was more resistant to dietary changes and ageing than heart and skeletal muscle, which showed higher levels of coenzyme Q, cytochrome b, and cytochrome a + a3 with ageing and lower cytochrome c oxidase and complex IV turnover. Dietary fat differentially modulated the response of tissues during ageing, with sunflower oil leading to the highest levels of coenzyme Q and cytochromes b and a + a3. Since high levels of cytochrome b have been related to increased age, it could be hypothesized that olive oil could lead to less aged mitochondria.

Energy restriction reduces long-chain saturated fatty acids associated with plasma lipids in aging male rats

Energy restriction is associated with decreased plasma insulin and glucose concentrations, whereas long-chain saturated fatty acids (LCSFA) are strongly associated with insulin resistance. Our hypothesis is that energy restriction reduces LCSFA associated with plasma lipids in adult aging rats. Plasma LCSFA associated with triglycerides (TG), nonesterified fatty acids and phospholipids, as well as glucose, insulin, free fatty acids, TG and adipocyte glucose transport and insulin-sensitive glucose transporter (GLUT4) content were determined in aging, energy restricted [ER; 60% of ad libitum (AL) intake] and AL rats. In ER rats, plasma glucose concentrations were lower than in AL rats at each age. In contrast, body weight and plasma TG concentrations increased with age in both groups, but especially in the AL rats. In AL rats, combined LCSFA associated with plasma lipids was greater than in ER rats (P < 0.0001). Adipocyte insulin-stimulated glucose transport decreased in both groups with age but was most severe in AL rats, whereas GLUT4 was reduced only in AL rats. In ER rats it is possible that decreased plasma LCSFA contribute to reduced blood glucose concentrations as well as increased adipocyte GLUT4 compared with AL rats.

Antibody to amyloid beta protein alleviates impaired acquisition, retention, and memory processing in SAMP8 mice

SAMP8 (senescence-accelerated mouse, P8 strain) mice overproduce amyloid precursor protein and beta-amyloid and have learning and memory deficits. Preliminary data have indicated that overproduction of beta-amyloid plays a role in the pathogenesis of acquisition and retention deficits in SAMP8 mice. In the studies reported here, the authors examined the effects of polyclonal and monoclonal antibodies to beta-amyloid on acquisition and retention in an aversive T-maze testing paradigm when injected intracerebroventricularly (ICV) into 12-month SAMP8/TaJF mice. Both the polyclonal and monoclonal antibodies improved acquisition and retention when injected ICV 1 to 14 days prior to acquisition testing. Injection of all three antibodies intrahippocampally immediately following training improved retention on the T-maze when mice were tested 7 days later. The authors next studied the effect of monoclonal beta-amyloid antibody injected 48 h prior to training on the effect on retention in the T-maze of drugs modulating classical neurotransmitters. Arecoline and glutamate were injected directly into the hippocampus, and ketanserin, methiothepen, bicuculline, and OH-saclofen were injected into the septum. Previously, the authors have found that the doses of these drugs required to improve retention are markedly altered in 12-month SAMP8/TkJF mice compared to 4-month P8 mice. In these studies, it was demonstrated that antibody to beta-amyloid resulted in these drugs improving retention at doses that improved memory in 4-month SAMP8/TaJF mice. Based on these findings, we conclude that beta-amyloid overproduction is at least in part responsible for the acquisition and memory deficits in 12-month-old SAMP8/TaJF mice. Antibody to beta-amyloid restores the retention response to neurotransmitter manipulation to that seen in 4-month-old mice. beta-amyloid appears to play a key role in the loss of acquisition and retention seen in SAMP8/TaJF mice.

Alzheimer's disease through the eye of a mouse. Acceptance lecture for the 2001 Gayle A. Olson and Richard D. Olson prize

There is now ample evidence that beta-amyloid proteins decrease memory. The SAMP8 mouse (P8) develops an early decline in the ability to learn and to retain new information. The studies reviewed here suggest that this is due to overproduction of beta-amyloid. Both antibodies to beta-amyloid and specific antisense to the amyloid precursor protein reverse these deficits in the P8 mouse. This antisense can cross the blood brain barrier. It is hypothesized that the overproduction of beta-amyloid leads to a decline in Delta(9) desaturase activity with an alteration in membrane fatty acids. This results in altered membrane mobility leading to a decline in neurotransmitter activity and a decreased release of acetylcholine. This decreased cholinergic activity results in a decreased ability of the P8 mouse to learn and retain new information.

Nutrition in the elderly

It is now well accepted that older persons experience a physiologic anorexia, the anorexia of aging, which is caused by alterations in hedonic qualities of food, fundal compliance, and increased leptin levels. Depression is the most common pathologic cause of weight loss in older persons. Older persons fail to recognize thirst and as such have an increased risk of dehydration. Alterations in brain membrane fatty acids can lead to cognitive impairment in older persons.

Nutritional factors and Alzheimer's disease

Nutritional factors are integrally linked with Alzheimer's disease (AD). Although AD patients have no changes in energy metabolism, fluctuations in weight are fairly common. The potential role of vitamin B(12) and folate, with the production of hyperhomocysteinemia, in the pathophysiology of AD is explored. The role of free-radical damage in AD is discussed. It is stressed that alterations in dietary lipids may play an important role in cognitive defects in AD secondary to their effects on neuronal membrane lipids. More research is needed on the role of nutrition in the ongoing development of cognitive changes in AD.

Isolation and characterization of the human stearoyl-CoA desaturase gene promoter: requirement of a conserved CCAAT cis-element

Stearoyl-CoA desaturase is the rate-limiting enzyme in the production of mono-unsaturated fatty acids. We have recently cloned and characterized the human Scd cDNA and SCD (the stearoyl-CoA desaturase structural gene) on chromosome 10, as well as the non-transcribed pseudogene on chromosome 17. In order to further define SCD regulation and function, we have isolated and characterized the promoter of the structural gene. Screening of chromosome-10-specific libraries resulted in the isolation of 4.1 kb of SCD sequence upstream of the translation start site. Binding sites for transcription factors critical for mouse Scd1 and Scd2 promoter activity, such as sterol-regulated-element-binding protein and nuclear factor Y, were present in the human SCD promoter (Scd is the mouse stearoyl-CoA desaturase gene). Deletion analysis in HaCaT keratinocytes identified a critical region for promoter activity between nts 496-609 upstream of the translation start site. Site-directed mutagenesis of binding sites in this region identified the CCAAT box as the critical cis-element for SCD promoter activity. An electrophoretic mobility-shift assay confirmed that this element binds nuclear proteins from HaCaT keratinocytes. The polyunsaturated-fatty-acid (PUFA) response element, previously identified in the promoters of mouse Scd1 and Scd2, was found to be conserved in the human SCD promoter, and contained the critical CCAAT cis-element. A minimal promoter construct including this region was responsive to fatty acids, with oleate and linoleate decreasing transcription and stearate increasing it. These studies indicate that CCAAT-box-binding proteins activate SCD transcription in cultured keratinocytes and that fatty acids modulate transcription, most likely through the conserved PUFA response element.

Identification of age-dependent changes in expression of senescence-accelerated mouse (SAMP8) hippocampal proteins by expression array analysis

Aging is associated with extensive cognitive impairments, although the biochemical and physiological basis of these deficits are unknown. As the hippocampus plays a vital role in cognitive functions, we have selected this tissue to analyze changes in gene expression at two different ages. Array technology is utilized to explore how gene expression in hippocampus is affected by accelerated cognitive impairment in Senescence-Accelerated Mouse (SAM P8) strain. We show that the expression of genes associated with stress response and xenobiotic metabolism are strongly affected at a time when cognitive impairment occurs. Affected genes include those involved both in signaling and chaperone function. The effector and regulator family of chaperones, which play an important role in protein folding, and also the xenobiotic metabolizing enzymes that play crucial role in antioxidant systems, show significant changes in gene expression between 4 and 12 months.