Homocysteine thiolactone and human cholinesterases

Mild hyperhomocysteinemia alters oxidative stress profile via Nrf2, inflammation and cholinesterases in cardiovascular system of aged male rats

Homocysteine (Hcy) is an independent cardiovascular disease (CVD) risk factor, whose mechanisms are poorly understood. We aimed to explore mild hyperhomocysteinemia (HHcy) effects on oxidative status, inflammatory, and cholinesterase parameters in aged male Wistar rats (365 days old). Rats received subcutaneous Hcy (0.03 μmol/g body weight) twice daily for 30 days, followed by euthanasia, blood collection and heart dissection 12 h after the last injection. Results revealed increased dichlorofluorescein (DCF) levels in the heart and serum, alongside decreased antioxidant enzyme activities (superoxide dismutase, catalase, glutathione peroxidase), reduced glutathione (GSH) content, and diminished acetylcholinesterase (AChE) activity in the heart. Serum butyrylcholinesterase (BuChE) levels also decreased. Furthermore, nuclear factor erythroid 2-related factor 2 (Nrf2) protein content decreased in both cytosolic and nuclear fractions, while cytosolic nuclear factor kappa B (NFκB) p65 increased in the heart. Additionally, interleukins IL-1β, IL-6 and IL-10 showed elevated expression levels in the heart. These findings could suggest a connection between aging and HHcy in CVD. Reduced Nrf2 protein content and impaired antioxidant defenses, combined with inflammatory factors and altered cholinesterases activity, may contribute to understanding the impact of Hcy on cardiovascular dynamics. This study sheds light on the complex interplay between HHcy, oxidative stress, inflammation, and cholinesterases in CVD, providing valuable insights for future research.

Functionally active cross-linked protein oligomers formed by homocysteine thiolactone

Deposition of high-order protein oligomers is a common hallmark of a large number of human diseases and therefore, has been of immense medical interest. From the past several decades, efforts are being made to characterize protein oligomers and explore how they are linked with the disease pathologies. In general, oligomers are non-functional, rather cytotoxic in nature while the functional (non-cytotoxic) oligomers are quite rare. In the present study, we identified new protein oligomers of Ribonuclease-A and Lysozyme that contain functionally active fractions. These functional oligomers are disulfide cross-linked, native-like, and obtained as a result of the covalent modification of the proteins by the toxic metabolite, homocysteine thiolactone accumulated under hyperhomocysteinemia (a condition responsible for cardiovascular complications including atherosclerosis). These results have been obtained from the extensive analysis of the nature of oligomers, functional status, and structural integrity of the proteins using orthogonal techniques. The study implicates the existence of such oligomers as protein sinks that may sequester toxic homocysteines in humans.

Recent Advances in Understanding of Alzheimer's Disease Progression through Mass Spectrometry-Based Metabolomics

Alzheimer's disease (AD) is the leading cause of dementia in the aging population, but despite extensive research, there is no consensus on the biological cause of AD. While AD research is dominated by protein/peptide-centric research based on the amyloid hypothesis, a theory that designates dysfunction in beta-amyloid production, accumulation, or disposal as the primary cause of AD, many studies focus on metabolomics as a means of understanding the biological processes behind AD progression. In this review, we discuss mass spectrometry (MS)-based AD metabolomics studies, including sample type and preparation, mass spectrometry specifications, and data analysis, as well as biological insights gleaned from these studies, with the hope of informing future AD metabolomic studies.

Hyperhomocysteinemia alters cytokine gene expression, cytochrome c oxidase activity and oxidative stress in striatum and cerebellum of rodents

AIMS

Homocysteine has been linked to neurodegeneration and motor function impairments. In the present study, we evaluate the effect of chronic mild hyperhomocysteinemia on the motor behavior (motor coordination, functional performance, and muscular force) and biochemical parameters (oxidative stress, energy metabolism, gene expression and/or protein abundance of cytokine related to the inflammatory pathways and acetylcholinesterase) in the striatum and cerebellum of Wistar male rats.

MAIN METHODS

Rodents were submitted to one injection of homocysteine (0.03 μmol Hcy/g of body weight) between 30th and 60th postnatal days twice a day. After hyperhomocysteinemia induction, rats were submitted to horizontal ladder walking, beam balance, suspension, and vertical pole tests and/or euthanized to brain dissection for biochemical and molecular assays.

KEY FINDINGS

Chronic mild hyperhomocysteinemia did not alter motor function, but induced oxidative stress and impaired mitochondrial complex IV activity in both structures. In the striatum, hyperhomocysteinemia decreased TNF-α gene expression and increased IL-1β gene expression and acetylcholinesterase activity. In the cerebellum, hyperhomocysteinemia increased gene expression of TNF-α, IL-1β, IL-10, and TGF-β, while the acetylcholinesterase activity was decreased. In both structures, hyperhomocysteinemia decreased acetylcholinesterase protein abundance without altering total p-NF-κB, NF-κB, Nrf-2, and cleaved caspase-3.

SIGNIFICANCE

Chronic mild hyperhomocysteinemia compromises several biochemical/molecular parameters, signaling pathways, oxidative stress, and chronic inflammation in the striatum and cerebellum of rats without impairing motor function. These alterations may be related to the mechanisms in which hyperhomocysteinemia has been linked to movement disorders later in life and neurodegeneration.

Homocysteine and Real-Space Navigation Performance among Non-Demented Older Adults

BACKGROUND

High plasma homocysteine (Hcy) level is related to higher risk of Alzheimer's disease (AD) and lower cognitive performance in older adults.

OBJECTIVE

To assess the association between plasma Hcy level and real-space navigation performance and the role of vascular risk and protective factors, APOE status, and white matter lesions (WML) on this association.

METHODS

Ninety-two non-demented older adults (29 with amnestic mild cognitive impairment, 46 with subjective cognitive decline, and 17 cognitively normal older adults) underwent spatial navigation testing of egocentric, allocentric, and mixed navigation in a real-space analogue of the Morris water maze, neuropsychological examination, blood collection, and MRI brain scan with evaluation of WML.

RESULTS

In the regression analyses controlling for age, gender, education, and depressive symptoms, higher plasma Hcy level was related to worse mixed and egocentric (β= 0.31; p = 0.003 and β= 0.23; p = 0.017) but not allocentric (p > 0.05) navigation performance. Additional controlling for vascular risk and protective factors, WML, and APOE status did not modify the results. High total cholesterol and low vitamin B12 and folate levels increased the adverse effect of Hcy on egocentric and mixed navigation. WML did not explain the association between plasma Hcy level and navigation performance.

CONCLUSION

Elevated plasma Hcy level may affect real-space navigation performance above and beyond vascular brain changes. This association may be magnified in the presence of high total cholesterol and low folate or vitamin B12 levels. Attention to the level of plasma Hcy may be a viable intervention strategy to prevent decline in spatial navigation in non-demented older adults.

Lipid, Oxidative and Inflammatory Profile and Alterations in the Enzymes Paraoxonase and Butyrylcholinesterase in Plasma of Patients with Homocystinuria Due CBS Deficiency: The Vitamin B12 and Folic Acid Importance

Cystathionine-β-synthase (CBS) deficiency is the main cause of homocystinuria. Homocysteine (Hcy), methionine, and other metabolites of Hcy accumulate in the body of affected patients. Despite the fact that thromboembolism represents the major cause of morbidity in CBS-deficient patients, the mechanisms of cardiovascular alterations found in homocystinuria remain unclear. In this work, we evaluated the lipid and inflammatory profile, oxidative protein damage, and the activities of the enzymes paraoxonase (PON1) and butyrylcholinesterase (BuChE) in plasma of CBS-deficient patients at diagnosis and during the treatment (protein-restricted diet supplemented with pyridoxine, folic acid, betaine, and vitamin B12). We also investigated the effect of folic acid and vitamin B12 on these parameters. We found a significant decrease in HDL cholesterol and apolipoprotein A1 (ApoA-1) levels, as well as in PON1 activity in both untreated and treated CBS-deficient patients when compared to controls. BuChE activity and IL-6 levels were significantly increased in not treated patients. Furthermore, significant positive correlations between PON1 activity and sulphydryl groups and between IL-6 levels and carbonyl content were verified. Moreover, vitamin B12 was positively correlated with PON1 and ApoA-1 levels, while folic acid was inversely correlated with total Hcy concentration, demonstrating the importance of this treatment. Our results also demonstrated that CBS-deficient patients presented important alterations in biochemical parameters, possibly caused by the metabolites of Hcy, as well as by oxidative stress, and that the adequate adherence to the treatment is essential to revert or prevent these alterations.

Hyperhomocysteinemia induced by methionine dietary nutritional overload modulates acetylcholinesterase activity in the rat brain

Methionine is the only endogenous precursor of homocysteine, sulfur-containing amino acid and well known as risk factor for various brain disorders. Acetylcholinesterase is a serine protease that rapidly hydrolyzes neurotransmitter acetylcholine. It is widely distributed in different brain regions. The aim of this study was to elucidate the effects of methionine nutritional overload on acetylcholinesterase activity in the rat brain. Males of Wistar rats were randomly divided into control and experimental group, fed from 30th to 60th postnatal day with standard or methionine-enriched diet (double content comparing to standard, 7.7 g/kg), respectively. On the 61st postnatal day, total homocysteine concentration was determined and showed that animals fed with methionine-enriched diet had significantly higher serum total homocysteine concentrations comparing to control rats (p < 0.01). Acetylcholinesterase activity has been determined spectrophotometrically in homogenates of the cerebral cortex, hippocampus, thalamus, and nc. caudatus. Acetylcholinesterase activity showed tendency to decrease in all examined brain structures in experimental comparing to control rats, while statistical significance of this reduction was achieved in the cerebral cortex (p < 0.05). Brain slices were stained with haematoxylin and eosin (H&E) and observed under light microscopy. Histological analysis of H&E-stained brain slices showed that there were no changes in the brain tissue of rats which were on methionine-enriched diet compared to control rats. Results of this study showed selective vulnerability of different brain regions on reduction of acetylcholinesterase activity induced by methionine-enriched diet and consecutive hyperhomocysteinemia.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Limitations of conventional inhibitor classifications

Enzyme inhibitors are usually classified as competitive, non-competitive or mixed non-competitive. Each of these designations has a serious limitation in that it only describes an extreme of inhibitory behaviour. The non-competitive inhibition equation only considers an approach to complete inhibition of the catalytic turnover rate, while the competitive inhibition equation predicts an infinite increase in the Michaelis-Menten constant (decrease in enzyme affinity for substrate), resulting from increased inhibitor concentration. Both of these models exclude the possibility of a finite inhibitor-induced change in the kinetic parameters of the enzyme they are affecting. They also exclude the possibility of an inhibitor affecting both the substrate affinity and the catalytic turnover at the same time. Mixed non-competitive inhibition describes a hybrid form of inhibition displaying some characteristics of both competitive and non-competitive inhibition. It also suffers from an inability to describe finite changes in activity and to describe concomitant changes in substrate affinity and catalytic turnover. Two inhibitor binding constants are invoked in this equation, suggesting that such inhibitors interact with the enzyme in two completely independent manners. From these considerations, it is suggested here that conventional equations do not adequately describe observed kinetic data due to a lack of distinction between the mass action binding term describing inhibitor-enzyme association and the terms representing the actual effect of the inhibitor on the enzyme. Herein we describe an alternate approach for representing enzyme activity modulation based on a re-examination of conventional inhibition equations. The arguments presented are illustrated using the known competitive inhibition of Kallikrein with benzamidine.

Genetic associations of autopsy-confirmed vascular dementia subtypes

BACKGROUND/AIMS

Genetic risk factors have not been clearly established for vascular dementias (VaD) related to stroke and cerebrovascular disease.

METHODS

Samples were genotyped for APOE, MTHFR and ICAM. Aβ levels and choline acetyltransferase (ChAT) activities were assayed in controls and individuals with VaD.

RESULTS

Associations were found between the APOE-ε4 allele and mixed dementia, infarct/stroke dementia and subcortical ischemic vascular dementia (SIVD), and higher Aβ1-42 levels and decreased ChAT activity. MTHFR was more associated with SIVD, mixed dementia, and lower ChAT activity.

CONCLUSIONS

The study demonstrates important differences in the genetic associations of VaD and begins to clarify the genetic basis of key pathological substrates.

Differential effects of short- and long-term hyperhomocysteinaemia on cholinergic neurons, spatial memory and microbleedings in vivo in rats

Hyperhomocysteinaemia (HHcy) has been identified as a cardiovascular risk factor for neurodegenerative brain diseases. The aim of the present study was to investigate the effects of short (5 months) or long (15 months) HHcy in Sprague–Dawley rats in vivo. Short- and long-term HHcy differentially affected spatial memory as tested in a partially baited eight-arm radial maze. HHcy significantly reduced the number of choline acetyltransferase (ChAT)-positive neurons in the basal nucleus of Meynert and ChAT-positive axons in the cortex only after short-term but not long-term treatment, while acetylcholine levels in the cortex were decreased at both time points. Nerve growth factor (NGF) was significantly enhanced in the cortex only after 15 months of HHcy. HHcy did not affect cortical levels of amyloid precursor protein, beta-amyloid(1-42), tau and phospho-tau181 and several inflammatory markers, as well as vascular RECA-1 and laminin density. However, HHcy induced cortical microbleedings, as illustrated by intensive anti-rat IgG-positive spots in the cortex. In order to study the regulation of the key enzyme ChAT, organotypic rat brain slices were incubated with homocysteine, which induced a decline of ChAT that was counteracted by NGF treatment. In conclusion, our data demonstrate that chronic short- and long-term HHcy differentially caused memory impairment, cholinergic dysfunction, NGF expression and vascular microbleedings.

Midlife homocysteine and late-life dementia in women. A prospective population study

Elevated serum total homocysteine (tHcy) is an established risk factor for cardiovascular disease. Its role in dementia is still controversial, and no study has examined the role of midlife tHcy, or reports longer than 8 years of follow-up. We examined the relation between midlife tHcy and late-life dementia in women followed for 35 years. The Prospective Population Study of Women in Gothenburg began in 1968-1969, comprising a representative population of women aged 38-60 years. Four extensive follow-ups were conducted by 2003. Serum samples from 1968 to 1969 were analysed for tHcy in 1368 women. In total, 151 women developed dementia. The highest tHcy tertile was related to a hazard ratio of 1.7 (95% CI 1.1-2.6) for developing any dementia, 2.1 (95% CI 1.2-3.7, n=100) for AD and 2.4 (95% CI 1.3-4.7, n=68) for AD without cerebrovascular disease. Kaplan-Meier plots showed divergence with respect to dementia after 22 years of follow-up. In conclusion, high homocysteine in midlife is an independent risk factor for the development of late-life Alzheimer dementia in women.

Rivastigmine versus placebo in hyperhomocysteinemic Parkinson's disease dementia patients

The effects of rivastigmine versus placebo in Parkinson's disease dementia (PDD) patients with elevated or normal/low plasma homocysteine were determined. In this prospective analysis of a 24-week, randomly assigned, placebo-controlled study of rivastigmine in PDD, subpopulations comprised patients with plasma homocysteine >or=14 micromol/L (elevated) or <14 micromol/L (normal/low). Coprimary outcomes were the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and Alzheimer Disease Cooperative Society-Clinical Global Impression of Change (ADCS-CGIC). Secondary outcomes included additional measures of cognition, including attention and executive function, daily function, and neuropsychiatric symptoms. Adverse events (AEs) were monitored. In total, 342 of 541 patients provided samples for analysis, from which 72% had elevated plasma homocysteine. Hyperhomocysteinemic patients showed treatment differences (rivastigmine vs. placebo) of 4.0 on ADAS-cog and 0.7 on ADCS-CGIC (both P < 0.01), and significant treatment differences on secondary outcomes. Rivastigmine- and placebo-treated hyperhomocysteinemic patients (16.5% and 14.6%) discontinued the study because of AEs. Patients with normal/low homocysteine showed no treatment differences on primary or secondary outcomes (1.4 on the ADAS-cog and 0.1 on ADCS-CGIC, both P = ns); 16.7% and 10.3% rivastigmine- and placebo-treated patients discontinued because of AEs. Elevated homocysteine was associated with greater rivastigmine treatment differences than normal/low homocysteine.

Hyperhomocysteinemia and Alzheimer's disease: A systematic review

Hyperhomocysteinemia (HHcy) is supposed to be one of the modifiable risk factors that, if treated, may delay the onset of Alzheimer's disease (AD). The relation between serum homocysteine (Hcy) and vitamin levels during AD and its preclinical phase was systematically reviewed. Searches through large literature and trial databases were conducted. Data were extracted from studies and, after quality assessment, analyzed using a meta-analysis software package. Nine qualitatively good case-control studies were identified. The pooled standardized mean difference (PSMD) of Hcy levels (631 patients, 703 controls) was 1.04 (0.44-1.63), indicating higher Hcy levels in AD patients. Levels of folate (PSMD=0.65) (0.34-0.95) (387 patients, 312 controls) and vitamin B(12) (PSMD=0.50) (-0.05-1.06) (387 patients, 312 controls) were lower in AD patients. Vitamin B(6) levels were evaluated in 1 case-control study and were not significantly lower in AD patients. Analysis of prospective cohort studies (2569 subjects) revealed a pooled relative risk for AD in HHcy of 2.5 (1.38-4.56, p<0.01). No specific randomized controlled trials (RCTs) concerning Hcy-lowering therapy and AD-risk were identified. Prospective studies on the relation between folate, vitamins B(6) and B(12) levels and the risk of developing AD are warranted, preferably in the form of RCTs.

A versatile equation to describe reversible enzyme inhibition and activation kinetics: Modeling β-galactosidase and butyrylcholinesterase

Current treatments for Alzheimer's disease involve inhibiting cholinesterases. Conversely, cholinesterase stimulation may be deleterious. Homocysteine is a known risk factor for Alzheimer's and vascular diseases and its active metabolite, homocysteine thiolactone, stimulates butyrylcholinesterase. Considering the opposing effects on butyrylcholinesterase of homocysteine thiolactone and cholinesterase inhibitors, understanding how these molecules alter this enzyme may provide new insights in the management of dementia. Butyrylcholinesterase does not strictly adhere to Michaelis-Menten parameters since, at higher substrate concentrations, enzyme activation occurs. The substrate activation equation for butyrylcholinesterase does not describe the effects of inhibitors or non-substrate activators. To address this, global data fitting was used to generate a flexible equation based on Michaelis-Menten principles. This methodology was first tested to model complexities encountered in inhibition by imidazole of beta-galactosidase, an enzyme that obeys Michaelis-Menten kinetics. The resulting equation was sufficiently flexible to permit expansion for modeling activation or inhibition of butyrylcholinesterase, while accounting for substrate activation of this enzyme. This versatile equation suggests that both the inhibitor and non-substrate activator examined here have little effect on the substrate-activated form of butyrylcholinesterase. Given that butyrylcholinesterase inhibition can antagonize stimulation of this enzyme by homocysteine thiolactone, cholinesterase inhibition may have a role in treating Alzheimer and vascular diseases related to hyperhomocysteinemia.