The MTHFR 677T allele may influence the severity and biochemical risk factors of Alzheimer's disease in an Egyptian population

The methylenetetrahydrofolate reductase C677T and A1298C genetic polymorphisms and plasma homocysteine in Alzheimer's disease in an Algerian population

BACKGROUND

The etiology of Alzheimer's disease (AD) is multifactorial. The most important challenge of research is the identification of potential biomarkers associated with AD pathogenesis that may significantly contribute to early diagnosis of the disease. We aim to explore an eventual association of the C677T and A1298C genetic polymorphisms in the MTHFR gene with AD risk in an Algerian population.

METHODS

This case-control study involved comparing a group of 106 patients that had developed AD to another group of 104 non-demented individuals. The MTHFR genotypes were determined using PCR-RFLP method. Additionally, the homocysteine level was evaluated.

RESULTS

Genotypes analysis did not show an association for both MTHFR677CT and 677TT variants with AD risk (OR = 1.12; p = 0.66; OR = 1.76; p = 0.09) respectively. As expected, the 677CC wild type genotype showed a protective role against AD (OR = 0.52; p = 0.03). For 1298AC MTHFR variant, the distribution of different genotypes did not show a statistical significant difference between the two cohorts. However the silmutaneous carrier, CT/AC presented association with AD (OR = 5.96; p = 0.05). On the other hand, carrier-state of MTHFR T allele showed a relationship with AD (OR = 1.98; p = 0.02). Additionally, hyperhomocysteinemia seems to be a risk factor for AD (OR = 1.08; p = 0.02).

CONCLUSION

Our exploration reveals that the silmutaneous carrier, CT/AC, carrier-state of MTHFR T allele, and hyperhomocysteinemia seem to be risk factors for AD.

Blood and CSF Homocysteine Levels in Alzheimer's Disease: A Meta-Analysis and Meta-Regression of Case-Control Studies

OBJECTIVE

Hyperhomocysteinemia (HHcy), as an important risk factor for Alzheimer's disease (AD), would aggravate cognitive dysfunction. This study aimed to investigate whether and to what degree the homocysteine (Hcy) levels in blood and cerebrospinal fluid (CSF) were elevated in AD patients compared with healthy controls and to explore the factors related to the elevated Hcy levels in AD patients.

METHODS

PubMed and Embase databases were searched to identify eligible studies, and study quality was evaluated using the Newcastle-Ottawa Quality Assessment Scale. Ratio of mean (RoM) Hcy concentrations was used as a measure of fold-change between AD patients and healthy control subjects.

RESULTS

We identified 35 eligible studies, consisting a total of 2172 patients with AD and 2289 healthy controls. The pooled results showed that patients with AD had a significantly higher blood level of Hcy (RoM, 1.32; 95% CI, 1.25-1.40; p<0.001) than controls did, with large heterogeneity across studies (I²=81.4%, p<0.001). Hcy level in CSF did not differ significantly between patients with AD than controls (RoM, 1.12; 95% CI, 0.90-1.39, p=0.293; I²=69.4%, p=0.02). A random effects meta-regression analysis revealed that there was an inverse correlation between the blood levels of Hcy and folate (p=0.006). There was no link found between the blood levels of vitamin B_12, or the Mini-Mental Status Examination scores reflecting the degree of cognitive impairment, and blood levels of Hcy.

CONCLUSION

Regardless of dementia severity, there is an approximate one-third increase in blood Hcy in AD patients, which is robustly associated with a decreased level of blood folate in AD, but not with that of blood vitamin B₁₂ nor the degree of dementia. Future investigation on the cause-and-effect link between Hcy and folate is warranted to clarify this issue.

Untangling huge literature to disinter genetic underpinnings of Alzheimer's Disease: A systematic review and meta-analysis

Drug discovery for Alzheimer's Disease (AD) is channeled towards unravelling key disease specific drug targets/genes to predict promising therapeutic candidates. Though enormous literature on AD genetics is available, there exists dearth in data pertinent to drug targets and crucial pathological pathways intertwined in disease progression. Further, the research findings revealing genetic associations failed to demonstrate consistency across different studies. This scenario prompted us to initiate a systematic review and meta-analysis with an aim of unearthing significant genetic hallmarks of AD. Initially, a Boolean search strategy was developed to retrieve case-control studies from PubMed, Cochrane, ProQuest, Europe PMC, grey literature and HuGE navigator. Subsequently, certain inclusion and exclusion criteria were framed to shortlist the relevant studies. These studies were later critically appraised using New Castle Ottawa Scale and Q-Genie followed by data extraction. Later, meta-analysis was performed only for those Single Nucleotide Polymorphisms (SNPs) which were evaluated in at least two different ethnicities from two different reports. Among, 204,351 studies retrieved, 820 met our eligibility criteria and 117 were processed for systematic review after critical appraisal. Ultimately, meta-analysis was performed for 23 SNPs associated with 15 genes which revealed significant associations of rs3865444 (CD33), rs7561528 (BIN1) and rs1801133 (MTHFR) with AD risk.

Homocysteine and Folic Acid: Risk Factors for Alzheimer's Disease-An Updated Meta-Analysis

Background: Recent studies have reported that homocysteine (Hcy) may play a vital role in the pathogenesis of vascular dementia (VaD) and Alzheimer's disease (AD). Our study explored the relationship between the plasma Hcy and folate levels and the risk of dementia.

Methods: We searched Embase, PubMed, and Web of Science for published literature, including case-control studies and prospective cohort studies, and performed a systematic analysis.

Results: The results of our meta-analysis, consisting of case-control studies, showed higher levels of Hcy and lower levels of folate in dementia, AD, and VaD patients than those in non-demented controls (for dementia: SMD = 0.812, 95% CI [0.689, 0.936], p = 0.000 for Hcy; SMD = −0.677, 95% CI [−0.828, −0.525], p = 0.000 for folate). AD patients showed significantly lower plasma Hcy levels compared to VaD patients (SMD = −0.278, 95% CI [−0.466, −0.09], p = 0.000). Subgroup analysis revealed that ethnicity, average age, and dementia type had no significant effect on this association. Furthermore, from the analysis of prospective cohort studies, we identified that elevated plasma Hcy levels were associated with an increased risk of dementia, AD, and VaD (RR_dementia = 1.22, 95% CI [1.08, 1.36]; RR_AD = 1.07, 95% CI [1.04, 1.11]; RR_VaD = 1.13, 95% CI [1.04, 1.23]). In addition, every 5 μmol/L increase in the plasma Hcy level was associated with a 9% increased risk of dementia and a 12% increased risk of AD.

Conclusion: Hcy and folic acid are potential predictors of the occurrence and development of AD. A better understanding of their function in dementia could provide evidence for clinicians to rationalize clinical intervention strategies.

Genetic Variants Associated With Alzheimer Disease in the 22 Arab Countries: A Systematic Review

BACKGROUND AND AIMS

Alzheimer disease (AD) is a progressive and complex neurodegenerative disease. Approximately 70% of AD risk is attributed to genetic risk factors, including variants in amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) genes. Several studies have revealed a considerable number of candidate loci and genes for AD among different ethnic populations. However, the outcomes of these studies have been inconsistent. In this study, we aimed to investigate the spectrum of variants that are associated with the onset and development of AD among 22 Arab countries.

METHODOLOGY

We systematically searched 4 literature databases (Science Direct, Scopus, PubMed, and Web of Science) from the date of inception until July 2020 using various search terms to obtain all the reported genetic data on Arab AD cases.

RESULTS

In total, 18 studies were included, comprising a total of 2173 individuals, of whom 888 were clinically diagnosed AD patients and were genetically tested for genes and variants associated with AD. A total of 27 variants in 8 genes were found to be associated with AD. Of these variants, 17 were unique to the Arab population and 10 were shared with other ethnic groups.

CONCLUSIONS

There is a dearth of studies on the genetics of AD in the Arab world. There seems to be distinctive genetic and clinical susceptibility profiles for Arab patients with AD.

Homocysteine level is positively and independently associated with serum creatinine and urea nitrogen levels in old male patients with hypertension

A cross-sectional study to show whether and how serum fasting homocysteine levels are associated with renal function changes in patients with hypertension. Homocysteine levels were associated with serum creatinine and blood urea nitrogen (BUN) levels with coefficients of 2.04 and 0.07, respectively, only in males and independent of confounders. In addition, low density lipoprotein cholesterol (LDL-C) levels were positively and left ventricular ejection fraction (LVEF) was negatively associated with serum creatinine level in males; age was positively associated with serum creatinine levels in females. Age was a common risk factor positively associated with BUN levels in both sexes, while total cholesterol (TC) levels and glycemic control were independent risk factors that were positively associated with BUN levels only in males. LDL-C levels and LVEF were negatively associated with BUN levels in females. Body mass index (BMI) was positively associated and hemoglobin A1c (HbA1c) levels, high density lipoprotein cholesterol (HDL-C) levels and the presence of stroke were negatively associated with serum uric acid levels in male patients. In contrast, only LVEF was positively associated with uric acid levels in females. In conclusion, homocysteine level is an independent risk factor associated with serum creatinine and BUN levels in male patients with hypertension.

Autophagy activation is required for homocysteine-induced apoptosis in bovine aorta endothelial cells

An elevated level of homocysteine (Hcy) in plasma is an independent risk factor for cardiovascular disease and central nervous system disease. Endothelial dysfunction as a result of apoptosis in endothelial cells is involved in the development and progression of these diseases. In this study, we aimed to investigate the effect of autophagy activation by amino acid starvation on Hcy-induced cytotoxicity in bovine aorta endothelial cells (BAECs). Hcy-induced lactate dehydrogenase (LDH) release was promoted by amino acid starvation. In addition, Hcy increased cleaved caspase-3 level, an indicator of apoptosis, by amino acid starvation. We revealed that oxidative stress is not involved in the Hcy-induced cytotoxicity promoted by amino acid starvation. Salazosulfapyridine (SASP), an SLC7A11 inhibitor, protected against the Hcy-induced LDH release promoted by amino acid starvation. SASP decreased the Hcy-induced cleaved caspase-3 level by amino acid starvation. We demonstrate for the first time that autophagy activation by amino acid starvation promotes Hcy-induced apoptosis in BAECs. Moreover, SLC7A11 inhibitor SASP, which is an amino acid transporter, protects against Hcy-induced apoptosis due to autophagy.

The C677T Polymorphism of the Methylenetetrahydrofolate Reductase Gene and Susceptibility to Late-onset Alzheimer's Disease

Folate metabolism makes a crucial contribution towards late-onset Alzheimer's disease (LOAD). Moreover, methylenetetrahydrofolate reductase (MTHFR) constitutes the primary enzyme of the folate pathway. We hypothesize that there is an association of C677T polymorphism in the MTHFR gene with the susceptibility to LOAD. Previous published research has investigated the link between the MTHFR C677T polymorphisms and LOAD susceptibility; nevertheless, the findings have continued to be not only controversial, but also indecisive. Accordingly, we carried out the present meta-analysis for the assessment of the potential link that exists between the MTHFR C677T polymorphism and the susceptibility to LOAD. Furthermore, we carried out a literature search of the PubMed, EMBASE, Cochrane Library, and WanFang database up to August 10, 2018. The odds ratios (ORs) with the respective 95% confidence interval (95%CI) were put to use for the evaluation of the robustness of the link of the MTHFR C677T polymorphism with the vulnerability to LOAD. All statistical analyses were carried out using STATA 15.0. An aggregate of 14 case-control research works was retrieved, involving 2,467 LOAD patients as well as 2,877 controls. We found that a substantial link exists between C677T polymorphism and LOAD risk in a codominant framework (TC vs. CC: OR=1.22, 95%CI=1.00-1.49, P=0.049). In addition to the stratified analysis based on ethnicity, which suggested that C677T polymorphism was likely linked only to an augmented threat of LOAD in Asians, it did not exist among Caucasians. Furthermore, in the subgroup analysis carried out using APOE ɛ4 status, a substantial increase in the susceptibility to LOAD was detected in APOE ɛ4 carriers as well as non-APOE ɛ4 carriers. In sum, the current meta-analysis revealed that MTHFR C677T polymorphism was associated with susceptibility to LOAD. Further extensive case-control studies are required.

Homocysteine and Alzheimer's Disease: Evidence for a Causal Link from Mendelian Randomization

BACKGROUND/OBJECTIVE

The relationship between plasma homocysteine (Hcy) levels and Alzheimer's disease (AD) has been studied for many years, but remains controversial. While a recent meta-analysis of epidemiological studies, which included observational studies, indicated that homocysteine may be a risk factor for AD, there remains a need to further demonstrate this link due to the large degree of heterogeneity between studies. Epidemiological studies have certain limitations, as their results can be affected by confounding factors and reverse causation. In this study, we evaluated the relationship between plasma homocysteine and AD by using a Mendelian randomization method to avoid problems of confounding bias and reverse causality.

METHODS

We searched the PubMed and EMBASE databases for reports regarding the MTHFR C677T polymorphism (rs1801133) from the time of their inception to September 2015. These reports were combined with related observational studies, and used to evaluate the effect of MTHFR C677T (rs1801133) on the risk for AD. A recent meta-analysis of genome-wide association studies had previously suggested a relationship between homocysteine and MTHFR C677T (rs 1801133).

RESULTS

Our met-analysis included 34 studies with 9397 subjects, and demonstrated a significant relationship between plasma total homocysteine levels and the risk for AD (OR = 3.37; 95% CI = 1.90-5.95; p = 2.9×10-5).

CONCLUSION

Our meta-analysis demonstrated a causal link between plasma total homocysteine and the risk for AD, and provides a new insight into the etiology and prevention of AD.

Impact of Mediterranean diet on metabolic syndrome, cancer and longevity

Obesity symbolizes a major public health problem. Overweight and obesity are associated to the occurrence of the metabolic syndrome and to adipose tissue dysfunction. The adipose tissue is metabolically active and an endocrine organ, whose dysregulation causes a low-grade inflammatory state and ectopic fat depositions. The Mediterranean Diet represents a possible therapy for metabolic syndrome, preventing adiposopathy or "sick fat" formation.The Mediterranean Diet exerts protective effects in elderly subjects with and without baseline of chronic diseases. Recent studies have demonstrated a relationship between cancer and obesity. In the US, diet represents amount 30-35% of death causes related to cancer. Currently, the cancer is the second cause of death after cardiovascular diseases worldwide. Furthermore, populations living in the Mediterranean area have a decreased incidence of cancer compared with populations living in Northern Europe or the US, likely due to healthier dietary habits. The bioactive food components have a potential preventive action on cancer. The aims of this review are to evaluate the impact of Mediterranean Diet on onset, progression and regression of metabolic syndrome, cancer and on longevity.

MTHFR (C677T) CT genotype and CT-apoE3/3 genotypic combination predisposes the risk of ischemic stroke

The predisposition to ischemic stroke (IS) might involve interactions of several genes and environmental factors. The present study was aimed to evaluate the influence of polymorphisms in methylenetetrahydrofolate reductase (MTHFR-C677T) and apolipoprotein-E (apo-E) as risk factors for IS patients in south Indian population. 200 IS patients and 193 age and sex matched controls were genotyped for MTHFR-C677T and apoE by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method. Statistically significant association was observed for MTHFR CT genotype (IS-Pooled: OR=4.29; p=5.01×10(-5); IS-Males: OR=4.13; p=0.001; IS-Females: OR=8.62; p=0.027; IS-Large Vessel Disease (LVD)- Pooled: OR=4.14; p=0.0002) and T allele (IS-Pooled: OR=4.82; p=1.49×10(-5); IS-Males: OR=4.33; p=0.0002; IS-Females: OR=7.99; p=0.031; IS-LVD-Pooled: OR=4.13; p=0.0001). Further, reduced frequencies of CC genotype (IS-Pooled: OR=0.20; p=9.80×10(-6); IS-Males: OR=0.25; p=0.001; IS-Females: OR=0.12; p=0.027; IS-LVD-Pooled: OR=0.23; p=0.0001) and C allele (IS-Pooled: OR=0.21; p=1.49×10(-5); IS-Males: OR=0.23; p=0.0002; IS-Females: OR=0.13; p=0.031; IS-LVD-Pooled: OR=0.24; p=0.0001) were observed in IS patients than the controls. No association was observed for apoE genotypes/alleles in IS/LVD cases. Our study demonstrated the presence of risk for MTHFR CT genotype/T allele and 'CT-3/3' (n=33 vs. 5; OR=7.42; p=0.001) genotypic combination in the development of IS in south India. Further, follow-up study of these stroke cases i.e., in later stages of the disease whether they are developing the neurological disorders such as Alzheimer's Disease (AD) and vascular dementia (VaD) is needed to draw a fruitful conclusion in connection between neurological disorders and with these two polymorphisms, before translating it into clinical practice.

Methylenetetrahydrofolate Reductase (MTHFR) C677T Polymorphism and Alzheimer Disease Risk: a Meta-Analysis

Methylenetetrahydrofolate reductase (MTHFR) is key enzyme of folate/homocysteine pathway. Case control association studies on MTHFR C677T polymorphism and Alzheimer's disease (AD) have been repeatedly performed over the last two decades, but the results are inconclusive. The aim of the present study was to assess the risk of MTHFR C677T polymorphism for AD. Forty-one studies were identified by a search of PubMed, Google Scholar, Elsevier, and Springer Link databases, up to January 2015. Odds ratios (ORs) with corresponding 95 % confidence interval (CI) were calculated using fixed effect model or random effect model. The subgroup analyses based on ethnicity were performed. MTHFR C677T polymorphism had a significant association with susceptibility to AD in all genetic models (for T vs C OR = 1.29, 95 % CI = 1.07-1.56, p = 0.003; for TT + CT vs CC OR = 1.29, 95 % CI = 1.19-1.40, p = 0.0004; for TT vs CC OR = 1.31, 95 % CI = 1.16-1.48, p = 0.001; for CT vs CC OR = 1.24, 95 % CI = 1.13-1.35, p < 0.004; and for TT vs CT + CC OR = 1.13, 95 % CI = 1.00-1.28, p = 0.02). Results of present meta-analysis supported that the MTHFR C677T polymorphism was associated with an increased risk of AD.

Homocysteine-Induced Endothelial Dysfunction

This review discussed and in particular emphasis the potential cellular pathways and the biological processes involved that lead to homocysteine-induced endothelial dysfunction, in particular in the impaired endothelial dependent dilatation aspect. Hyperhomocysteinemia is an independent cardiovascular risk factor that has been associated with atherosclerotic vascular diseases and ischemic heart attacks. The potential mechanisms by which elevated plasma homocysteine level leads to reduction in nitric oxide bioavailability include the disruptive uncoupling of nitric oxide synthase activity and quenching of nitric oxide by oxidative stress, the enzymatic inhibition by asymmetric dimethylarginine, endoplasmic reticulum stress with eventual endothelial cell apoptosis, and chronic inflammation/prothrombotic conditions. Homocysteine-induced endothelial dysfunction presumably affecting the bioavailability of the potent vasodilator ‘nitric oxide', and such dysfunction can easily be monitor by flow-mediated dilation method using ultrasound. Understanding the mechanisms by which plasma homocysteine alter endothelial nitric oxide production is therefore essential in the comprehension of homocysteine-induced impairment of endothelial dependent dilatation, and its association of cardiovascular risk and its pathophysiology.

Nutritional supplementation for Alzheimer's disease?

PURPOSE OF REVIEW

Evidence for the benefit of nutrition in Alzheimer's disease continues to accumulate. Many studies with individual vitamins or supplements show marginal, if any, benefit. However, new findings with combinatorial formulations demonstrate improvement in cognitive performance and behavioral difficulties that accompany Alzheimer's disease. Herein, we review some of the most recent clinical advances and summarize supportive preclinical studies.

RECENT FINDINGS

We present novel positive effects on Alzheimer's disease derived from diet, trace elements, vitamins and supplements. We discuss the inherent difficulty in conducting nutritional studies because of the variance in participants' nutritional history, versus pharmacological interventions in which participants are naive to the intervention. We examine the evidence that epigenetics play a role in Alzheimer's disease and how nutritional intervention can modify the key epigenetic events to maintain or improve cognitive performance.

SUMMARY

Overall consideration of the most recent collective evidence suggests that the optimal approach for Alzheimer's disease would seem to combine early, multicomponent nutritional approaches (a Mediterranean-style diet, multivitamins and key combinatorial supplements), along with lifestyle modifications such as social activity and mental and physical exercise, with ultimate addition of pharmacological agents when warranted.

Cancer based pharmacogenomics network supported with scientific evidences: from the view of drug repurposing

BACKGROUND

Pharmacogenomics (PGx) as an emerging field, is poised to change the way we practice medicine and deliver health care by customizing drug therapies on the basis of each patient's genetic makeup. A large volume of PGx data including information among drugs, genes, and single nucleotide polymorphisms (SNPs) has been accumulated. Normalized and integrated PGx information could facilitate revelation of hidden relationships among drug treatments, genomic variations, and phenotype traits to better support drug discovery and next generation of treatment.

METHODS

In this study, we generated a normalized and scientific evidence supported cancer based PGx network (CPN) by integrating cancer related PGx information from multiple well-known PGx resources including the Pharmacogenomics Knowledge Base (PharmGKB), the FDA PGx Biomarkers in Drug Labeling, and the Catalog of Published Genome-Wide Association Studies (GWAS). We successfully demonstrated the capability of the CPN for drug repurposing by conducting two case studies.

CONCLUSIONS

The CPN established in this study offers comprehensive cancer based PGx information to support cancer orientated research, especially for drug repurposing.

The MTHFR C677T polymorphism contributes to increased risk of Alzheimer's disease: evidence based on 40 case-control studies

The association between methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and Alzheimer's Disease (AD) risk has been widely reported with inconsistent results. We performed an updated meta-analysis of all available studies to clarify this situation. We conducted a comprehensive literature search in PubMed Alzgene, Embase, and Chinese Biomedical Literature database (CBM) for the period up to June 2014. Finally, a total of 40 case-control studies with 4503 AD cases and 5767 controls were included. Overall, significant increased AD risk was found, when all studies were pooled into the meta-analysis. In subgroup analyses stratified by ethnicity, age of onset, and APOE ϵ4 status, significant increased AD risk was found in Asians, late-onset AD, and APOE ϵ4 carriers, but not in Caucasians, early-onset AD, and non-APOE ϵ4 carriers. The present meta-analysis suggested that the MTHFR is a candidate gene for AD susceptibility. The MTHFR C677T polymorphism may be a risk factor for AD in Asians, APOE ϵ4 carriers, and late-onset AD. Further, investigations taking the potential gene-gene and gene-environmental interactions into consideration for the MTHFR C677T polymorphism should be conducted.

Lifetime requirement of the methionine cycle for neuronal development and maintenance

PURPOSE OF REVIEW

Nutrition exerts a pervasive impact on normal and pathological conditions of the nervous system. One critical pathway is the methionine cycle, in which folate and B12 convert homocysteine to methionine, which is in turn converted to S-adenosyl methionine (SAM; the major methyl donor). As a consequence of methylation, however, SAM is converted to the neurotoxin homocysteine and must be excreted or drawn back into the methionine cycle, which requires additional folate and B12. Dietary or genetic folate deficiency impairs this cycle, leading to developmental disorders, including those of the nervous system.

RECENT FINDINGS

Folate and SAM exert profound epigenetic effects via DNA and histone methylation. Maternal supplementation during pregnancy has fostered an increase in individuals harboring genetic polymorphisms that compromise folate usage. Such individuals harbor a lifetime requirement for additional dietary folate, often not met beyond peri/postnatal periods. Herein, we consider the potential link of failure to meet this additional requirement to early and age-related cognitive compromise.

SUMMARY

Compromises in the methionine cycle can manifest as a spectrum of disorders throughout life. These considerations underscore how prenatal nutritional supplementation can alleviate developmental disorders by inadvertently establishing latent conditions that, in the absence of continued supplementation, may lead to age-related cognitive decline.