Query: sirtuins

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Advanced glycation end product level, diabetes, and accelerated cognitive aging <=SEP=> Objective: Several studies report that diabetes increases risk of cognitive impairment; some have hypothesized that advanced glycation end products (AGEs) underlie this association. AGEs are cross-linked products that result from reactions between glucose and proteins. Little is known about the association between peripheral AGE concentration and cognitive aging. Methods: We prospectively studied 920 elders without dementia, 495 with diabetes and 425 with normal glucose (mean age 74.0 years). Using mixed models, we examined baseline AGE concentration, measured with urine pentosidine and analyzed as tertile, and performance on the Modified Mini-Mental State Examination (3MS) and Digit Symbol Substitution Test (DSST) at baseline and repeatedly over 9 years. Incident cognitive impairment (a decline of >1.0 SD on each test) was analyzed with logistic regression. Results: Older adults with high pentosidine level had worse baseline DSST score (p=0.05) but not different 3MS score (p=0.32). On both tests, there was a more pronounced 9-year decline in those with high and mid pentosidine level compared to those in the lowest tertile (3MS 7.0, 5.4, and 2.5 point decline, p overall <0.001; DSST 5.9, 7.4, and 4.5 point decline, p=0.03). Incident cognitive impairment was higher in those with high or mid pentosidine level than those in the lowest tertile (3MS: 24% vs 17%, odds ratio=1.55; 95% confidence interval 1.07–2.26; DSST: 31% vs 22%, odds ratio=1.62; 95% confidence interval 1.13–2.33). There was no interaction between pentosidine level, diabetes status, and cognitive decline. Multivariate adjustment for age, sex, race, education, hypertension, cardiovascular disease, estimated glomerular filtration rate, and diabetes diminished results somewhat but overall patterns remained similar. Conclusion: High peripheral AGE level is associated with greater cognitive decline in older adults with and without diabetes.

Do Sirtuins Promote Mammalian Longevity?: A Critical Review on Its Relevance to the Longevity Effect Induced by Calorie Restriction <=SEP=> Sirtuins (SIRTs), a family of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases, are emerging as key molecules that regulate aging and age-related diseases including cancers, metabolic disorders, and neurodegenerative diseases. Seven isoforms of SIRT (SIRT1–7) have been identified in mammals. SIRT1 and 6, mainly localized in the nucleus, regulate transcription of genes and DNA repair. SIRT3 in the mitochondria regulates mitochondrial bioenergetics. Initial studies in yeasts, nematodes, and flies indicated a strong connection of SIRT with the life-prolonging effects of calorie restriction (CR), a robust experimental intervention for longevity in a range of organisms. However, subsequent studies reported controversial findings regarding SIRT roles in the effect of CR. This review describes the functional roles of mammalian SIRTs and discusses their relevance to mechanisms underlying the longevity effect of CR.

Dietary Advanced Glycation End Products and Aging <=SEP=> Advanced glycation end products (AGEs) are a heterogeneous, complex group of compounds that are formed when reducing sugar reacts in a non-enzymatic way with amino acids in proteins and other macromolecules. This occurs both exogenously (in food) and endogenously (in humans) with greater concentrations found in older adults. While higher AGEs occur in both healthy older adults and those with chronic diseases, research is progressing to both quantify AGEs in food and in people, and to identify mechanisms that would explain why some human tissues are damaged, and others are not. In the last twenty years, there has been increased evidence that AGEs could be implicated in the development of chronic degenerative diseases of aging, such as cardiovascular disease, Alzheimer’s disease and with complications of diabetes mellitus. Results of several studies in animal models and humans show that the restriction of dietary AGEs has positive effects on wound healing, insulin resistance and cardiovascular diseases. Recently, the effect of restriction in AGEs intake has been reported to increase the lifespan in animal models. This paper will summarize the work that has been published for both food AGEs and in vivo AGEs and their relation with aging, as well as provide suggestions for future research.

Protective effects and mechanisms of sirtuins in the nervous system <=SEP=> Silent information regulator two proteins (sirtuins or SIRTs) are a group of histone deacetylases whose activities are dependent on and regulated by nicotinamide adenine dinucleotide (NAD+). They suppress genome-wide transcription, yet upregulate a select set of proteins related to energy metabolism and pro-survival mechanisms, and therefore play a key role in the longevity effects elicited by calorie restriction. Recently, a neuroprotective effect of sirtuins has been reported for both acute and chronic neurological diseases. The focus of this review is to summarize the latest progress regarding the protective effects of sirtuins, with a focus on SIRT1. We first introduce the distribution of sirtuins in the brain and how their expression and activity are regulated. We then highlight their protective effects against common neurological disorders, such as cerebral ischemia, axonal injury, Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and multiple sclerosis. Finally, we analyze the mechanisms underlying sirtuin-mediated neuroprotection, centering on their non-histone substrates such as DNA repair enzymes, protein kinases, transcription factors, and coactivators. Collectively, the information compiled here will serve as a comprehensive reference for the actions of sirtuins in the nervous system to date, and will hopefully help to design further experimental research and expand sirtuins as therapeutic targets in the future.

Longitudinal magnetic resonance imaging studies of older adults: a shrinking brain. <=SEP=> Age-related loss of brain tissue has been inferred from cross-sectional neuroimaging studies, but direct measurements of gray and white matter changes from longitudinal studies are lacking. We quantified longitudinal magnetic resonance imaging (MRI) scans of 92 nondemented older adults (age 59-85 years at baseline) in the Baltimore Longitudinal Study of Aging to determine the rates and regional distribution of gray and white matter tissue loss in older adults. Using images from baseline, 2 year, and 4 year follow-up, we found significant age changes in gray (p < 0.001) and white (p < 0.001) volumes even in a subgroup of 24 very healthy elderly. Annual rates of tissue loss were 5.4 +/- 0.3, 2.4 +/- 0.4, and 3.1 +/- 0.4 cm3 per year for total brain, gray, and white volumes, respectively, and ventricles increased by 1.4 +/- 0.1 cm3 per year (3.7, 1.3, 2.4, and 1.2 cm3, respectively, in very healthy). Frontal and parietal, compared with temporal and occipital, lobar regions showed greater decline. Gray matter loss was most pronounced for orbital and inferior frontal, cingulate, insular, inferior parietal, and to a lesser extent mesial temporal regions, whereas white matter changes were widespread. In this first study of gray and white matter volume changes, we demonstrate significant longitudinal tissue loss for both gray and white matter even in very healthy older adults. These data provide essential information on the rate and regional pattern of age-associated changes against which pathology can be evaluated and suggest slower rates of brain atrophy in individuals who remain medically and cognitively healthy.

Sirtuins in cognitive ageing and Alzheimer's disease. <=SEP=> PURPOSE OF REVIEW: Sirtuins are a family of enzymes highly conserved in evolution and involved in mechanisms known to promote healthy ageing and longevity. This review aims to discuss recent advances in understanding the role of sirtuins, in particular mammalian SIRT1, in promoting longevity and its potential molecular basis for neuroprotection against cognitive ageing and Alzheimer's disease pathology. RECENT FINDINGS: Accumulative increase in oxidative stress during ageing has been shown to decrease SIRT1 activity in catabolic tissue, possibly by direct inactivation by reactive oxygen. SIRT1 overexpression prevents oxidative stress-induced apoptosis and increases resistance to oxidative stress through regulation of the FOXO family of forkhead transcription factors. In addition, resveratrol strongly stimulates SIRT1 deacetylase activity in a dose-dependent manner by increasing its binding affinity to both the acetylated substrate and NAD(+). Recently, SIRT1 has been shown to affect amyloid production through its influence over the ADAM10 gene. Upregulation of SIRT1 can also induce the Notch pathway and inhibit mTOR signalling. SUMMARY: Recent studies have revealed some of the mechanisms and pathways that are associated with the neuroprotective effects of SIRT1.

At the crossroad of lifespan, calorie restriction, chromatin and disease: meeting on sirtuins. <=SEP=> Longevity, lifespan, cancer, cellular transformation, energy, calorie restriction, diabetes--what can tie together such a diversity of hot topics in biomedical research? Emerging findings suggest that the answer lies in understanding the functions of the recently discovered family of proteins known as Sirtuins. Barcelona hosted the first scientific meeting completely focused on these evolutionary conserved protein deacetylases, bringing together experts in the biochemistry to cellular biology, mice models, drug targeting and pathophysiology of these molecules. Their work, summarized here, establishes the Sirtuins as major players in cellular homeostasis and human diseases that act through a whole range of biochemical substrates and physiological processes. Undoubtedly, this is an increasingly expanding field that it is here to stay and growth.

Serum concentration of an inflammatory glycotoxin, methylglyoxal, is associated with increased cognitive decline in elderly individuals <=SEP=> Background Advanced glycations end products increase oxidant stress, inflammation, and neurotoxicity. Serum levels are increased in diabetes and aging. We examined the relationship between serum methylglyoxal derivatives (sMG), and cognitive decline, in 267 non-demented elderly. Methods Tobit mixed regression models assessed the association of baseline sMG with cognitive decline in the Mini Mental State Exam (MMSE) over time, controlling for sociodemographic factors (age, sex, and years of education), cardiovascular risk factors (diabetes and presence of an APOE4 allele), and kidney function. sMG was assessed by ELISA. Results The fully adjusted model showed an annual decline of 0.26 MMSE points per unit increase in baseline sMG (p=0.03). Significance was unchanged as additional risk factors were added to the model. The interactions of sMG with diabetes, sex, age, kidney function, and APOE4 genotype were not significant. Conclusions Higher levels of baseline sMG were associated with a faster rate of cognitive decline, after adjusting for several sociodemographic and clinical characteristics. This relationship did not differ by sex, APOE4 genotype, or diabetes status suggesting its generality. Since subjects were cognitively normal at the beginning of the study, elevated sMG may be indicative of brain cell injury initiated before clinically evident cognitive compromise.

Brain volume changes on longitudinal magnetic resonance imaging in normal older people. <=SEP=> BACKGROUND AND PURPOSE: The purpose of this study is to investigate the longitudinal age-related changes in human brain volume using stereological methods. METHODS: Sixty-six older participants (34 men, 32 women, age [mean +/- SD] 78.9 +/- 3.3 years, range 74-87 years) with normal baseline and follow-up examinations underwent 2 MRIs (magnetic resonance imaging) of the brain on average 4.4 years apart. The volumes of the cerebrum (defined as cortex, basal ganglia, thalamus, and white matter), lateral ventricles, and cerebellum were estimated on the 2 MRIs using an unbiased stereological method (Cavalieri principle). RESULTS: The annual decrease (mean +/- SD) of the cerebral volume was 2.1% +/- 1.6% (P < .001). The average volume of the lateral ventricles on the second MRI was increased by 5.6% +/- 3.6% per year (P < .001). The average volume of the cerebellum on the second MRI was decreased by 1.2% +/- 2.2% per year (P < .001). Even though the average cerebral volume was significantly different between men and women on initial MRI and second MRI, the percentage change of the age-related cerebral volume decrease in male and female brains between initial MRI and second MRI were identical. CONCLUSIONS: The findings showed that there was age-related atrophy of cerebrum and cerebellum and age-related disproportional enlargement of lateral ventricles in normal older men and women.

SIRT1 Decrease Parallels the Accumulation of tau in Alzheimer Disease <=SEP=> Aging and metabolism-related disorders are risk factors for Alzheimer disease (AD). Since sirtuins may increase the lifespan through regulation of cellular metabolism, we compared the concentration of sirtuin 1 (SIRT1) in the brains of AD patients (n = 19) and controls (n = 22) using Western immunoblots and in situ hybridization. We report a significant reduction of SIRT1 (mRNA: −29%; protein: −45%) in the parietal cortex of AD patients, but not in the cerebellum. Further analyses in a second cohort of 36 subjects confirmed that cortical SIRT1 was decreased in the cortex of AD patients but not in individuals with mild cognitive impairment. SIRT1 mRNA and its translated protein correlated negatively with the duration of symptoms (mRNA: r2 = −0.367; protein: r2 = −0.326) and the accumulation of paired helical filament tau (mRNA: r2 = −0.230; protein: r2 = −0.119), but weakly with insoluble amyloid-β(Aβ42 (mRNA: r2 = −0.090; protein: r2 = −0.072). A significant relationship between SIRT1 levels and global cognition scores proximate to death was also found (r2 = +0.09; p = 0.049). In contrast, cortical SIRT1 levels remained unchanged in a triple-transgenic animal model of AD. Collectively, our results indicate that loss of SIRT1 is closely associated with the accumulation of Aβ and tau in the cerebral cortex of patients with AD.