Homocysteine but not neopterin declines in demented patients on B vitamins

Blood levels of circulating methionine components in Alzheimer’s disease and mild cognitive impairment: A systematic review and meta-analysis

Background

Circulating methionine components have been reported to be associated with Alzheimer’s disease (AD) and mild cognitive impairment (MCI), although outcomes are not always consistent.

Materials and methods

Database searching was conducted using PubMed, Embase, Cochrane Library, and Web of Science from inception to 26 December 2021. In this study, two reviewers independently identified eligible articles and extracted the data. We used Joanna Briggs Institute (JBI) Critical Appraisal tools to assess the overall quality of the included studies. STATA software was employed to perform meta-analysis evaluating the standardized mean difference (SMD) with its 95% confidence intervals (CIs) using random-effects models. Evidence quality was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria.

Results

Totally, 30 observational studies were eligible for inclusion. Compared with cognitively normal controls, patients with AD had increased homocysteine (Hcy) levels in the blood [standardized mean difference (SMD) = 0.59, 95% confidence interval [CI]: 0.36–0.82, P = 0.000], plasma (SMD = 0.39, 95% CI: 0.23–0.55, P = 0.000), and serum (SMD = 1.56, 95% CI: 0.59–2.95, P = 0.002). Patients with MCI were not significantly different from controls (SMD = 0.26, 95% CI: –0.07–0.58, P = 0.127). Patients with AD or MCI did not significantly differ from controls of blood vitamin B12 levels, AD (SMD = –0.05, 95% CI: –0.19–0.08, P = 0.440), or MCI (SMD = 0.01, 95% CI: –0.16–0.17, P = 0.94). Some cohort studies have suggested that higher Hcy, methionine, and S-adenosylmethionine levels may accelerate cognitive decline in patients with MCI or AD, and vitamin B12 deficiency is a risk factor for the disease; however, the results of other studies were inconsistent. According to the GRADE system, all these outcomes scored very low to low quality, and no high-quality evidence was found.

Conclusion

Only Hcy levels in the plasma and serum were found to be inversely related to the risk of AD. However, due to the low quality of supporting these results, high-quality studies are needed to verify these findings.

Systematic Review Registration

http://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022308961.

Mechanistic Link between Vitamin B12 and Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia in the elderly population, affecting over 55 million people worldwide. Histopathological hallmarks of this multifactorial disease are an increased plaque burden and tangles in the brains of affected individuals. Several lines of evidence indicate that B12 hypovitaminosis is linked to AD. In this review, the biochemical pathways involved in AD that are affected by vitamin B12, focusing on APP processing, Aβ fibrillization, Aβ-induced oxidative damage as well as tau hyperphosphorylation and tau aggregation, are summarized. Besides the mechanistic link, an overview of clinical studies utilizing vitamin B supplementation are given, and a potential link between diseases and medication resulting in a reduced vitamin B12 level and AD are discussed. Besides the disease-mediated B12 hypovitaminosis, the reduction in vitamin B12 levels caused by an increasing change in dietary preferences has been gaining in relevance. In particular, vegetarian and vegan diets are associated with vitamin B12 deficiency, and therefore might have potential implications for AD. In conclusion, our review emphasizes the important role of vitamin B12 in AD, which is particularly important, as even in industrialized countries a large proportion of the population might not be sufficiently supplied with vitamin B12.

Impact of supplementation with vitamins B6 , B12 , and/or folic acid on the reduction of homocysteine levels in patients with mild cognitive impairment: A systematic review

Hyperhomocysteinemia is an independent predictor of the risk for cognitive decline and may be a result of low levels of vitamins B₁₂ , B₆ , and folate. Previous findings suggest that adequate intake of these vitamins may reduce homocysteine levels. This review aimed to assess the effects of treatment with vitamins B_6, B₁₂ , and/or folic acid in the homocysteine levels in patients with mild cognitive impairment (MCI). A systematic literature review was conducted in EMBASE, MEDLINE®, PsycINFO, and Cochrane Central Register of Controlled Trials. The research question was formulated using the Population, Intervention, Comparison, and Outcome (PICO) framework: in patients with MCI (P); what is the efficacy of vitamins B₆ , B₁₂ , and/or folic acid intake (I); compared with baseline values, and/or compared with controls (C); in reducing homocysteine levels from baseline (O). A total of eight primary studies with a total of 1,140 participants were included in the review. Four were randomized controlled trials, one was a quasi-controlled trial, and three were observational studies. All studies included folic acid in their intervention, seven vitamin B₁₂ , and four vitamin B₆ . Mean (SD) length of the intervention period was 18.8 (19.3) months, ranging from 1 to 60 months. All studies showed a statistically significant decrease in homocysteine levels in groups treated with vitamins B_6, B₁₂ , and/or folic acid compared to controls, with a mean decline of homocysteine concentration of 31.9% in the intervention arms whereas it increased by 0.7% in the control arm. This review identified evidence of a reduction of plasma homocysteine levels in MCI patients taking vitamins B_6, B₁₂ , and/or folic acid supplements, with statistically significant declines being observed after 1 month of supplementation. Findings support that supplementation with these vitamins might be an option to reduce homocysteine levels in people with MCI and elevated plasma homocysteine.

The Immunopathogenesis of Alzheimer's Disease Is Related to the Composition of Gut Microbiota

The microbiota-gut-brain axis plays an important role in the development of neurodegenerative diseases. Commensal and pathogenic enteric bacteria can influence brain and immune system function by the production of lipopolysaccharides and amyloid. Dysbiosis of the intestinal microbiome induces local and consecutively systemic immune-mediated inflammation. Proinflammatory cytokines then trigger neuroinflammation and finally neurodegeneration. Immune-mediated oxidative stress can lead to a deficiency of vitamins and essential micronutrients. Furthermore, the wrong composition of gut microbiota might impair the intake and metabolization of nutrients. In patients with Alzheimer's disease (AD) significant alterations of the gut microbiota have been demonstrated. Standard Western diet, infections, decreased physical activity and chronic stress impact the composition and diversity of gut microbiota. A higher abundancy of "pro-inflammatory" gut microbiota goes along with enhanced systemic inflammation and neuroinflammatory processes. Thus, AD beginning in the gut is closely related to the imbalance of gut microbiota. Modulation of gut microbiota by Mediterranean diet, probiotics and curcumin can slow down cognitive decline and alter the gut microbiome significantly. A multi-domain intervention approach addressing underlying causes of AD (inflammation, infections, metabolic alterations like insulin resistance and nutrient deficiency, stress) appears very promising to reduce or even reverse cognitive decline by exerting positive effects on the gut microbiota.

Neopterin as an Effect Modifier of the Cardiovascular Risk Predicted by Total Homocysteine: A Prospective 2-Cohort Study

BACKGROUND

Plasma total homocysteine (tHcy) is related to plasma neopterin, an indicator of interferon-γ-mediated immune activation, and both biomarkers positively predict cardiovascular risk. We examined whether the association between tHcy and subsequent risk of acute myocardial infarction (AMI) was modified by systemic concentrations of neopterin and C-reactive protein among patients with coronary heart disease.

METHODS AND RESULTS

By Cox modeling, we explored the association between tHcy and risk of AMI in 4164 patients with suspected stable angina pectoris. Subgroup analyses were performed according to median levels of neopterin and C-reactive protein. A replication study was performed among 3749 patients with AMI at baseline. Median follow-up was 7.3 and 8.3 years among patients with stable angina pectoris and AMI, respectively. tHcy and neopterin correlated in both cohorts (r_s=0.34 and r_s=0.30 among stable angina pectoris and AMI patients, respectively, both P<0.001). tHcy predicted AMI in both cohorts, independent of B-vitamin treatment. However, significant risk associations were confined to patients with plasma neopterin above the median (hazard ratios [95% confidence interval] per 1-SD increment of log-transformed tHcy 1.38 [1.26-1.50] and 1.18 [1.10-1.26] among stable angina pectoris and AMI patients, respectively) (P_int<0.005 in both cohorts). Further, adding information on the interaction between tHcy and neopterin improved model discrimination and reclassification. tHcy and C-reactive protein were weakly related, and no effect modification was found by C-reactive protein.

CONCLUSIONS

Among patients with coronary heart disease, tHcy predicted risk of AMI only in subjects with concomitantly elevated plasma neopterin. Our results motivate further research on the relationship between homocysteine metabolism, cellular immune activation, and atherothrombosis.

Association between Plasma Homocysteine Levels and Neuronal Injury in HIV Infection

Objective

To investigate the role of homocysteine in neuronal injury in HIV infection.

Methods

Using a cross-sectional design and archived samples, we compared concentrations of plasma homocysteine and cerebrospinal fluid (CSF) neurofilament light protein (NFL), a sensitive marker of neuronal injury, in 83 HIV-1-infected subjects without antiretroviral treatment. We also analyzed plasma vitamin B₁₂, serum folate, CSF, and plasma HIV RNA, the immune activation marker neopterin in CSF and serum, and albumin ratio as a marker of blood-brain barrier integrity. Twenty-two subjects provided a second sample median of 12.5 months after antiretroviral treatment initiation.

Results

A significant correlation was found between plasma homocysteine and CSF NFL concentrations in untreated individuals (r = 0.52, p < 0.0001). As expected, there was a significant inverse correlation between homocysteine and B₁₂ (r = –0.41, p < 0.001) and folate (r = –0.40, p = < 0.001) levels. In a multiple linear regression analysis homocysteine stood out as an independent predictor of CSF NFL in HIV-1-infected individuals. The correlation of plasma homocysteine and CSF NFL was also present in the group receiving antiretroviral therapy (r = 0.51, p = 0.016).

Conclusion

A correlation between plasma homocysteine and axonal injury, as measured by CSF NFL, was found in both untreated and treated HIV. While this study is not able to prove a causal link, homocysteine and functional B₁₂/folate deficiency appear to play a role in neural injury in HIV-infected individuals.

Lowered Levels of Carbonyl Proteins after Vitamin B Supplementation in Patients with Mild Cognitive Impairment and Alzheimer's Disease

BACKGROUND

The critical role of neuro-inflammation and oxidative stress in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD) has become evident.

OBJECTIVE

The aim of this study is to assess the influence of vitamin supplementation on parameters of oxidative stress, inflammation as well as on cognition in patients with AD and mild cognitive impairment.

METHODS

In our study, patients with cognitive impairment and healthy controls were enrolled. All patients were intended to receive vitamin supplementation (vitamin B1, B6, B12 and folic acid) for 3 months. Mini Mental State Examination (MMSE) and laboratory markers [carbonyl proteins (CPs), malondialdehyde, tryptophan (Trp), kynurenine (Kyn), neopterin, folic acid, vitamin B12 level] were assessed for patients and controls at baseline and after 3 months. After half of the patients had been treated for 3 months, analyses were performed resulting in 3 subgroups: healthy controls without supplementation (15 subjects, 11 females), patients with vitamin supplementation (17 subjects, 10 females) and patients without vitamin supplementation (16 subjects, 9 females; baseline values prior to supplementation).

RESULTS

Age was significantly higher for the supplemented group (76.4 ± 6.7 years) compared to vitamin-naïve patients (63.3 ± 13.7 years; p < 0.01). The MMSE score was higher in the supplemented group (23.1 ± 4.8 vs. 20.3 ± 9.5) but did not reach significance. Levels of CPs were significantly higher in the vitamin-naïve patients (p < 0.05). Levels of Kyn and the Kyn/Trp ratio were significantly lower in vitamin-naïve patients compared to the supplemented group (p < 0.05). No significant difference was seen for the other markers.

CONCLUSION

Vitamin supplementation leads to reduced levels of CPs in patients. Pearson's correlation coefficient shows a negative relation (r = -0.69) between CPs and MMSE. Future trials should assess whether CPs might be suitable markers for monitoring of demented patients.

Disturbed Amino Acid Metabolism in HIV: Association with Neuropsychiatric Symptoms

Blood levels of the amino acid phenylalanine, as well as of the tryptophan breakdown product kynurenine, are found to be elevated in human immunodeficiency virus type 1 (HIV-1)-infected patients. Both essential amino acids, tryptophan and phenylalanine, are important precursor molecules for neurotransmitter biosynthesis. Thus, dysregulated amino acid metabolism may be related to disease-associated neuropsychiatric symptoms, such as development of depression, fatigue, and cognitive impairment. Increased phenylalanine/tyrosine and kynurenine/tryptophan ratios are associated with immune activation in patients with HIV-1 infection and decrease upon effective antiretroviral therapy. Recent large-scale metabolic studies have confirmed the crucial involvement of tryptophan and phenylalanine metabolism in HIV-associated disease. Herein, we summarize the current status of the role of tryptophan and phenylalanine metabolism in HIV disease and discuss how inflammatory stress-associated dysregulation of amino acid metabolism may be part of the pathophysiology of common HIV-associated neuropsychiatric conditions.

Plasma neopterin level as a marker of peripheral immune activation in amnestic mild cognitive impairment and Alzheimer's disease

OBJECTIVE

Alterations of the immune system play important roles in Alzheimer's disease (AD). The primary purpose of this study was to compare the plasma levels of neopterin, a marker of cellular immune activity, in amnestic mild cognitive impairment (aMCI), early (mild to moderate) AD, and cognitively normal controls. In addition, the correlation of plasma neopterin with interferon-gamma (IFN-γ) and interleukin-6 (IL-6) was also examined.

METHODS

Plasma samples from patients with mild-to-moderate AD (N = 34), aMCI (N = 27), and cognitively normal controls (N = 30) were obtained from the Johns Hopkins Alzheimer's Disease Research Center. Plasma neopterin, IFN-γ, and IL-6 levels were measured using commercially available ELISAs. Multiple linear regression was performed to study differences in the baseline neopterin levels between normal, aMCI, and AD patients. Pearson correlation coefficients were estimated for neopterin and IFN-γ and IL-6 levels. All analyses were conducted using SAS (SAS Institute, Inc., Cary, NC) and GraphPad Prism version 5.00 for Window (GraphPad Software, San Diego, CA, USA).

RESULTS

AD subjects had significantly higher neopterin values compared with aMCI (β = 0.202, p = 0.004) and normal (β = 0.263, p = 0.0004) subjects. There was no statistically significant difference between normal and aMCI subjects. Significant associations between neopterin and IFN-γ (r = 0.41, p < 0.0001) and IL-6 (r = 0.35, p = 0.0006) levels were found.

CONCLUSIONS

Our study demonstrates that peripheral immune response may be stronger in later stages of AD pathophysiology, when dementia has developed.

Early increase of plasma homocysteine in sepsis patients with poor outcome

Moderate hyperhomocysteinemia is a well-established coronary risk factor that develops when dietary supply with folate and/or vitamin B(12) is inadequate. Recently, stimulated peripheral blood mononuclear cells were shown to produce homocysteine. Thus, the stimulated immune system may contribute to moderate hyperhomocysteinemia during certain diseases. Because multiple trauma and sepsis are accompanied by often strong inflammatory responses, we investigated whether hyperhomocysteinemia may develop in patients. Total homocysteine and cysteine concentrations were measured in 83 plasma specimens from 18 patients (14 men, 4 women; 15 posttrauma with sepsis and 3 with sepsis alone) every third day of follow-up. Finally results were compared with concentrations of cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-6, the immune activation marker neopterin and the extent of tryptophan degradation as indicated by the kynurenine-to-tryptophan ratio (kyn/trp). Compared with baseline, average total homocysteine (P < 0.05, d 4-d 10) and cysteine (P < 0.05, d 7-d 13) concentrations increased during follow-up of patients. However, only the increase of homocysteine was related to the survival status: total homocysteine was significantly higher in nonsurvivors (P < 0.05, d 4 and d 10) than in survivors, whereas cysteine concentrations increased in both subgroups. Homocysteine correlated with kyn/trp but not with neopterin concentrations. Increase of total homocysteine is common in patients after trauma with unfavorable outcome. Because all patients received standardized enteral nutrition after the end of hypodynamic shock, inconsistent vitamin supply is unlikely to be the reason for hyperhomocysteinemia in some of the patients; rather, it is associated with a stronger proinflammatory response. Certainly, the number of patients in our study is still small and results can only be regarded as preliminary.

Alzheimer’s disease, oxidative stress and B-vitamin depletion

There is an association between cognitive function and vitamin B12 and folate status. Both vitamins participate in recycling the potentially toxic amino acid homocysteine to methionine and, ultimately, to the methyl donor S-adenosylmethionine (SAM). Consequently, B12 and folate indirectly influence glutathione synthesis – a major intracellular antioxidant. Neuroinflammation and oxidative stress are early features of Alzheimer’s disease (AD). Such stress impairs homocysteine recycling, degrades folate and decreases its cellular retention, resulting in limited SAM availability and increased homocysteine levels. Oxidized homocysteine derivatives, such as homocysteic acid, can initiate a vicious cycle by promoting free-radical formation. Decreased SAM also fosters development of characteristic AD neuropathologies – neurofibrillary tangles and amyloid plaques. The latter generate additional free radicals in a further feed-forward cascade. Future therapies should simultaneously halt neuroinflammation, restore redox homeostasis and replace depleted intracellular B vitamins. Developing early markers for these harmful processes will allow targeting of such therapy before irreversible cellular damage ensues.

Homocysteine-lowering therapy does not affect inflammatory markers of atherosclerosis in patients with stable coronary artery disease

OBJECTIVES

A high level of total homocysteine (tHcy) is a risk marker for cardiovascular disease (CVD), and is related to inflammation. We wanted to test the effect of homocysteine-lowering B-vitamin therapy, as used in the Western Norway B-vitamin Intervention Trial (WENBIT), on inflammatory markers associated with atherosclerosis.

DESIGN

Single centre, prospective double-blind clinical interventional study, randomised in a 2 x 2 factorial design.

SUBJECTS AND METHODS

Ninety patients (21 female) with suspected coronary artery disease (CAD), aged 38-80 years, were blindly randomised into one of four groups of daily oral treatment with (A) folic acid (0.8 mg)/vitamin B12 (0.4 mg)/vitamin B6 (40 mg), (B) folic acid/vitamin B12, (C) vitamin B6 alone or (D) placebo. Blood samples were collected before and after 6 months of treatment.

RESULTS

Before intervention, median levels of the analytes were: tHcy 11.0 micromol L(-1), neopterin 8.1 nmol L(-1), soluble CD40 ligand (sCD40L) 3.9 ng mL(-1), interleukin (IL)-6 1.9 pg mL(-1), C-reactive protein (CRP) 1.9 mg L(-1) and low-density lipoprotein (LDL) cholesterol 3.3 mmol L(-1). tHcy was significantly associated with neopterin (r = 0.49, P < 0.001) and with IL-6 (r = 0.29, P = 0.01), but not with CRP or sCD40L. Neither treatment with folic acid/B12 nor with B6 induced significant changes in any of these inflammatory biomarkers (P >or= 0.14). In patients receiving folic acid/B12 (groups A and B), tHcy was reduced with 33% (P < 0.001).

CONCLUSIONS

In patients with stable CAD, homocysteine-lowering therapy with B-vitamins does not affect levels of inflammatory markers associated with atherogenesis. Failure to reverse inflammatory processes, may partly explain the negative results in clinical secondary B-vitamin intervention trials.