Homocysteine, Infections, Polyamines, Oxidative Metabolism, and the Pathogenesis of Dementia and Atherosclerosis

High plasma homocysteine levels predict the progression from mild cognitive impairment to dementia

High levels of blood homocysteine (HCy), a well-known cardiovascular risk factor and promoter of oxidative stress, have been associated with the incidence of cognitive impairment and dementia. Nonetheless, contrasting data are still present on its involvement in the progression from Mild Cognitive Impairment (MCI) to overt dementia. In this study we aimed to observe whether blood HCy level are associated with the evolution from MCI, divided into amnestic MCI (aMCI) and non-amnestic MCI (naMCI), to dementia. Blood HCy was measured in 311 MCI subjects (aMCI: 64%, naMCI: 36%) followed-up for a median of 33 months (range 10-155 months). At follow-up, 137 individuals converted to dementia (naMCI, n = 34; aMCI, n = 103). Based on HCy distribution, subjects in the highest tertile had a greater risk to convert to dementia compared to tertile I (Hazard Ratio (95% confidence interval): 2.25 (1.05-4.86); p = 0.04). aMCI subjects did not show increased risk to convert to dementia with increasing HCy concentration, but was significant in naMCI (p = 0.04). We observed a non-significant increase in the risk of progression to dementia from naMCI/low HCy (reference group, HCy cutoff value = 16 μmol/L) to naMCI/high HCy, but it was significant from aMCI/low HCy (HR: 2.73; 95%CI: 1.06-7.0; p:0.03), to aMCI/high HCy (HR: 3.24; 95%CI: 1.17-8.47; p:0.02). Our results suggest that HCy levels are associated with the progression from MCI to dementia. This association seems significant only for the naMCI group, indirectly supporting the notion that hyperhomocysteinemia damages the nervous system through its role as a vascular risk factor.

Exploring the complexities of 1C metabolism: implications in aging and neurodegenerative diseases

The intricate interplay of one-carbon metabolism (OCM) with various cellular processes has garnered substantial attention due to its fundamental implications in several biological processes. OCM serves as a pivotal hub for methyl group donation in vital biochemical reactions, influencing DNA methylation, protein synthesis, and redox balance. In the context of aging, OCM dysregulation can contribute to epigenetic modifications and aberrant redox states, accentuating cellular senescence and age-associated pathologies. Furthermore, OCM's intricate involvement in cancer progression is evident through its capacity to provide essential one-carbon units crucial for nucleotide synthesis and DNA methylation, thereby fueling uncontrolled cell proliferation and tumor development. In neurodegenerative disorders like Alzheimer's and Parkinson's, perturbations in OCM pathways are implicated in the dysregulation of neurotransmitter synthesis and mitochondrial dysfunction, contributing to disease pathophysiology. This review underscores the profound impact of OCM in diverse disease contexts, reinforcing the need for a comprehensive understanding of its molecular complexities to pave the way for targeted therapeutic interventions across inflammation, aging and neurodegenerative disorders.

Homocysteine, Cognitive Functions, and Degenerative Dementias: State of the Art

There is strong evidence that homocysteine is a risk factor not only for cerebrovascular diseases but also for degenerative dementias. A recent consensus statement renewed the importance and the role of high levels of homocysteine in cognitive decline in several forms of degenerative dementia, such as Alzheimer's disease. Although the molecular mechanisms by which homocysteine causes cell dysfunction are known, both the impact of homocysteine on specific cognitive functions and the relationship between homocysteine level and non-Alzheimer dementias have been poorly investigated. Most of the studies addressing the impact of hyperhomocysteinemia on dementias have not examined the profile of performance across different cognitive domains, and have only relied on screening tests, which provide a very general and coarse-grained picture of the cognitive status of the patients. Yet, trying to understand whether hyperhomocysteinemia is associated with the impairment of specific cognitive functions would be crucial, as it would be, in parallel, learning whether some brain circuits are particularly susceptible to the damage caused by hyperhomocysteinemia. These steps would allow one to (i) understand the actual role of homocysteine in the pathogenesis of cognitive decline and (ii) improve the diagnostic accuracy, differential diagnosis and prognostic implications. This review is aimed at exploring and revising the state of the art of these two strictly related domains. Suggestions for future research are provided.

Relationship between carotid artery stiffness and total serum homocysteine in coronary slow flow phenomenon: a high-resolution echo-tracking study

BACKGROUND

Coronary slow flow phenomenon (CSFP) is not uncommon in conventional coronary angiography. A disorder of serum homocysteine (tHcy) metabolism may play a role in the pathogenesis of slow coronary flow. Moreover, elevated tHcy concentration is closely associated with atherosclerosis. We aimed to evaluate the relationship between carotid artery stiffness and serum tHcy levels in patients with CSFP.

METHODS

This was a case-control study. The study population comprised 146 patients with newly diagnosed stable angina, including 73 patients with CSFP and 73 patients with normal coronary flow. All participants underwent conventional coronary angiography, carotid ultrasonography, and biochemical examination.

RESULTS

The carotid artery stiffness parameters of β index (β), pressure-strain elastic modulus (Ep), and local pulse wave velocity (PWV) in the CSFP group were significantly higher than those in the control group (β: 10.75±2.16 vs. 9.02±2.11, P=0.007; Ep: 147.41±41.22 vs. 116.21±39.21, P=0.004; PWV: 7.45±1.23 vs. 6.16±1.20, P=0.003), However, arterial compliance (AC) was lower in the CSFP group than the control group (0.52±0.11 vs. 0.69±0.24, P=0.008). The mean thrombolysis in myocardial infarction (TIMI) frame count and the tHcy concentration in the CSFP group were significantly higher than those in the control group (48.60±1.30 vs. 24.50±3.80, P=0.001; 19.95±4.00 vs. 9.12±2.72, P=0.009). The tHcy concentration was positively correlated with β (R value =0.494, P<0.0001), Ep (R value =0.469, P<0.0001), and PWV (R value =0.436, P<0.0001), but negatively correlated with AC (R value =-0.230, P=0.022). The predictors of CSFP were tHcy concentration, left PWV, right PWV, left β index, and right β index. Among them, the left β index and right β index were the best indictors for predicting CSFP. The cutoff values of left β index, right β index, left PWV, and right PWV were 9.3, 9.3, 6.7, and 6.6, respectively.

CONCLUSIONS

Our data showed that serum tHcy levels were elevated in patients with CSFP compared with the control group. Carotid artery stiffness parameters were correlated with tHcy. The best predictors of CSFP were left β index and right β index. These findings may contribute to a better understanding of systemic vascular disorders in patients with coronary slow flow, rather than simply attributing such disorders to a single and isolated lesion of the epicardial coronary artery.

Homocysteine Associated With Low Cognitive Function Independent of Asymptomatic Intracranial and Carotid Arteries Stenoses in Chinese Elderly Patients: An Outpatient-Based Cross-Sectional Study

INTRODUCTION

A high homocysteine (Hcy) concentration is correlated with cognitive impairment; however, the exact underlying mechanism is still not fully elucidated. The present study aimed to investigate whether asymptomatic intracranial and carotid arteries stenoses are involved in Hcy-related low cognitive function.

METHODS

This was a cross-sectional study in outpatient clinics. Residents aged ≥60 years, who came to the Stroke and Rehabilitation Clinic of Shandong Provincial Third Hospital in Jinan, Shandong Province from December 2019 to May 2020 to seek consultation due to abnormal transcranial Doppler reports (eg., increased cerebral blood flow velocity) were eligible. Information including demographics, medical history, lifestyle habits were collected. Fasting blood was used to detect total serum homocysteine level (tHcy). Cerebrovascular magnetic resonance angiography and neck vascular ultrasound examination were used to confirm the diagnosis of intracranial and carotid artery stenoses. The Mini-Mental State Examination was used to assess the cognitive function of each participant. Logistic regression was used to evaluate the relationship between tHcy levels and cognitive function.

RESULTS

This study included 236 participants (mean age: 64.0 (SD, 7.5) years, female: 58.1%). Multivariable analyses adjusted for several potential confounders, including creatinine and cardiovascular risk factors, showed that tHcy was associated with carotid artery stenosis (CAS). After adjusting for CAS, ICAS and several potential confounders, the association between tHcy level and low cognitive function remained significant (odds ratio: 1.09, 95% confidence interval: (1.03, 1.16), P = 0.032) .

CONCLUSION

Increased serum tHcy level was associated with low cognitive function independent of asymptomatic intracranial and carotid arteries stenoses.

Behavioral profile of vitamin B12 deficiency: A reflection of impaired brain development, neuronal stress and altered neuroplasticity

Our understanding of brain biology and function is one of the least characterized and therefore, there are no effective treatments for most of neurological disorders. The influence of vitamins, and particularly vitamin B₁₂, in neurodegenerative disease is demonstrated but largely unresolved. Behaviors are often quantified to attest brain dysfunction alone or in parallel with neuro-imaging to identify regions involved. Nevertheless, attention should be paid to extending observations made in animal models to humans, since, first, behavioral tests have to be adjusted in each model to address the initial question and second, because brain analysis should not be conducted for a whole organ but rather to specific sub-structures to better define function. Indeed, cognitive functions such as psychiatric disorders and learning and memory are often cited as the most impacted by a vitamin B₁₂ deficiency. In addition, differential dysfunctions and mechanisms could be defined according sub-populations and ages. Vitamin B₁₂ enters the cell bound to Transcobalamin, through the Transcobalamin Receptor and serves in two cell compartments, the lipid metabolism in the mitochondrion and the one-carbon metabolism involved in methylation reactions. Dysfunctions in these mechanisms can lead to two majors outcomes; axons demyelinisation and upregulation of cellular stress involving mislocalization of RNA binding proteins such as the ELAVL1/HuR or the dysregulation of pro- or anti-oxidant NUDT15, TXNRD1, VPO1 and ROC genes. Finally, it appears that apart from developmental problems that have to be identified and treated as early as possible, other therapeutic approaches for behavioral dysfunctions should investigate cellular methylation, oxidative and endoplasmic reticulum stress and mitochondrial function.

Hyperhomocysteinemia, Suppressed Immunity, and Altered Oxidative Metabolism Caused by Pathogenic Microbes in Atherosclerosis and Dementia

Many pathogenic microorganisms have been demonstrated in atherosclerotic plaques and in cerebral plaques in dementia. Hyperhomocysteinemia, which is a risk factor for atherosclerosis and dementia, is caused by dysregulation of methionine metabolism secondary to deficiency of the allosteric regulator, adenosyl methionine. Deficiency of adenosyl methionine results from increased polyamine biosynthesis by infected host cells, causing increased activity of ornithine decarboxylase, decreased nitric oxide and peroxynitrate formation and impaired immune reactions. The down-regulation of oxidative phosphorylation that is observed in aging and dementia is attributed to deficiency of thioretinaco ozonide oxygen complexed with nicotinamide adenine dinucleotide and phosphate, which catalyzes oxidative phosphorylation. Adenosyl methionine biosynthesis is dependent upon thioretinaco ozonide and adenosine triphosphate (ATP), and the deficiency of adenosyl methionine and impaired immune function in aging are attributed to depletion of thioretinaco ozonide from mitochondrial membranes. Allyl sulfides and furanonaphthoquinones protect against oxidative stress and apoptosis by increasing the endogenous production of hydrogen sulfide and by inhibiting electron transfer to the active site of oxidative phosphorylation. Diallyl trisulfide and napabucasin inhibit the signaling by the signal transducer and activator of transcription 3 (Stat3), potentially enhancing immune function by effects on T helper lymphocytes and promotion of apoptosis. Homocysteine promotes endothelial dysfunction and apoptosis by the unfolded protein response and endoplasmic reticulum stress through activation of the N-methyl D-aspartate (NMDA) receptor, causing oxidative stress, calcium influx, apoptosis and endothelial dysfunction. The prevention of atherosclerosis and dementia may be accomplished by a proposed nutritional metabolic homocysteine-lowering protocol which enhances immunity and corrects the altered oxidative metabolism in atherosclerosis and dementia.

Sleep mediates the association between homocysteine and oxidative status in mild cognitive impairment

Tremendous progress has been made over the last few years in understanding how sleep and amyloid-β (Aβ) cooperate to speed up the progression of Alzheimer's disease (AD). However, it remains unknown whether sleep deficits also interact with other risk factors that exacerbate the pathological cascade of AD. Based on evidence showing that higher levels of homocysteine (HCY) and sleep loss increase oxidative damage, we here investigate whether the relationship between HCY and total antioxidant capacity (TAC) is mediated by changes in objective sleep in healthy older (HO, N = 21) and mild cognitive impairment (MCI, N = 21) subjects. Results revealed that reduced TAC levels in MCI was significantly correlated with increased HCY, shorter sleep duration, lower sleep efficiency, and reduced volume of temporal regions. However, only the HCY-TAC association showed diagnostic value, and this relationship was mediated by poorer sleep quality in MCI patients. We further showed that HCY-related cerebral volume loss in MCI depended on the serial relationship between poorer sleep quality and lower TAC levels. These findings provide novel insights into how impaired sleep may contribute to maintain the relationship between HCY and oxidative stress in prodromal AD, and offer empirical foundations to design therapeutic interventions aimed to weaken this link.

Modulation of N-methyl-d-aspartate receptors in isolated rat heart

Considering the limited data on the role of NMDA-Rs in the cardiovascular system, the aim of the present study was to examine the effects of NMDA and DL-Hcy TLHC, alone and in combination with glycine, memantine, and ifenprodil, in the isolated rat heart. The hearts of Wistar albino rats were retrogradely perfused according to the Langendorff technique at a constant perfusion pressure. The experimental protocol for all experimental groups included the stabilization period, application of estimated substance for 5 min, followed by a washout period of 10 min. Using a sensor placed in the left ventricle, we registered the following parameters of myocardial function: dp/dt_max, dp/dt_min, SLVP, DVLP, HR; CF was measured using flowmetry). We estimated the following oxidative stress biomarkers in the coronary venous effluent using spectrophotometry: TBARS, NO₂^-, O₂^-, and H₂O₂. NMDA alone did not induce any change in any of the observed parameters, while DL-Hcy TLHC alone, as well as a combined application of NMDA and DL-Hcy TLHC with glycine, induced a reduction of most cardiodynamic parameters. Memantine and ifenprodil induced a reduction of cardiodynamic parameters and CF, as well as some oxidative stress biomarkers.