Synergistic effects of S-adenosylhomocysteine and homocysteine on DNA damage in a murine microglial cell line

Nicotinamide N-methyltransferase as a potential therapeutic target for neurodegenerative disorders: Mechanisms, challenges, and future directions

Neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), are characterized by progressive neuronal loss and functional decline, posing significant global health challenges. Emerging evidence highlights nicotinamide N-methyltransferase (NNMT), a cytosolic enzyme regulating nicotinamide (NAM) methylation, as a pivotal player in NDs through its dual impact on epigenetic regulation and metabolic homeostasis. This review synthesizes current knowledge on NNMT's role in disease pathogenesis, focusing on its epigenetic modulation via DNA hypomethylation and histone modifications, alongside its disruption of NAD+ synthesis and homocysteine (Hcy) metabolism. Elevated NNMT activity depletes NAD+, exacerbating mitochondrial dysfunction and impairing energy metabolism, while increased Hcy levels drive oxidative stress, neuroinflammation, and aberrant protein aggregation (e.g., Aβ, tau, α-synuclein). Notably, NNMT overexpression in AD and PD correlates with neuronal hypomethylation and neurotoxicity, as observed in postmortem brain studies and transgenic models. Mechanistically, NNMT consumes S-adenosylmethionine (SAM), limiting methyl donor availability for DNA methyltransferases (DNMTs) and histone methyltransferases (HMTs), thereby altering gene expression patterns critical for neuronal survival. Concurrently, NNMT-mediated NAD+ depletion disrupts sirtuin activity (e.g., SIRT1) and mitochondrial biogenesis, accelerating axonal degeneration. Therapeutic strategies targeting NNMT, such as RNA interference (RNAi), small-molecule inhibitors and exercise therapy, show promise in preclinical models by restoring NAD+ levels and reducing Hcy toxicity. However, challenges persist in achieving cellular specificity, optimizing blood-brain barrier penetration, and mitigating off-target effects. This review underscores NNMT's potential as a multifactorial therapeutic target, bridging metabolic and epigenetic dysregulation in NDs. Future research should prioritize elucidating tissue-specific NNMT interactions, refining inhibitor pharmacokinetics, and validating translational efficacy in clinical trials. Addressing these gaps could pave the way for novel disease-modifying therapies to combat the rising burden of neurodegeneration.

Association between dietary folate and hyperuricemia based on inflammation and cardiovascular disease status

BACKGROUND AND AIMS

The impact of dietary folate intake on serum uric acid is not yet conclusive. This study aims to investigate the association between dietary folate intake and the risk of hyperuricemia according to inflammatory status and comorbidities in Korean adults.

METHODS AND RESULTS

The cross-sectional analysis was conducted on 14,445 subjects aged ≥19 years enrolled in the Korea National Health and Nutrition Examination Survey (KNHNES) from 2016 to 2021. Dietary folate intake was assessed using the 24-h recall method. Dietary folate consumption was positively associated with the intake of beans, vegetables, and fruits, and negatively associated with cereals and meat intake. After adjusting for potential confounders, increased folate intake was found to be associated with a decreased risk of hyperuricemia (odds ratio for the highest tertile compared to the lowest tertile = 0.71 (95 % CI: 0.62-0.82)). The protective effect of folate intake against hyperuricemia was higher in individuals with normal inflammatory status compared to those with low-grade inflammation. Furthermore, the protective effect was greater in individuals without hypertension, dyslipidemia, and cardiovascular disease compared to those with these conditions.

CONCLUSION

These results suggest that dietary intake may help mitigate hyperuricemia, and individuals with inflammatory condition or cardiovascular diseases may require higher intake levels to achieve similar protective effects compared to healthy individuals.

DNA damage-induced senescence is associated with metabolomic reprogramming in breast cancer cells

Senescence due to exogenous and endogenous stresses triggers metabolic reprogramming and is associated with many pathologies, including cancer. In solid tumors, senescence promotes tumorigenesis, facilitates relapse, and changes the outcomes of anti-cancer therapies. Hence, cellular and molecular mechanisms regulating senescent pathways make attractive therapeutic targets. Cancer cells undergo metabolic reprogramming to sustain the growth-arrested state of senescence. In the present study, we aimed to understand the metabolic reprogramming in MCF-7 breast tumor cells in response to two independent inducers of DNA damage-mediated senescence, including ionizing radiation and doxorubicin. Increased DNA double-strand breaks, as demonstrated by γH2AX staining, showed a senescence phenotype, with expression of senescence-associated β-galactosidase accompanied by the upregulation of p21 and p16 in both groups. Further, untargeted analysis of the senescence-related extracellular metabolome profile of MCF-7 cells showed significantly reduced concentrations of carnitine and pantothenic acid and increased levels of S-adenosylhomocysteine in doxorubicin-treated cells, indicating the accumulation of ROS mediated DNA damage and impaired mitochondrial membrane potential. Similarly, a significant decline in the creatine level was observed in radiation-exposed cells, suggesting an increase in oxidative stress-mediated DNA damage. Our study, therefore, provides key effectors of the metabolic changes in doxorubicin and radiation-induced early senescence in MCF-7 breast cancer cells.

Higher S-adenosylhomocysteine and lower ratio of S-adenosylmethionine to S-adenosylhomocysteine were more closely associated with increased risk of subclinical atherosclerosis than homocysteine

Aim

To examine the relationship of C1 metabolites of the methionine cycle with the risk of subclinical atherosclerosis (SA) in the Chinese population.

Methods

A total of 2,991 participants aged 45–75 years old were included for data analyses based on the baseline data of the Guangzhou Nutrition and Health Cohort. Three core serum methionine metabolites including serum S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), and homocysteine (Hcy) were measured by UPLC-MS/MS. SA was determined by B-mode ultrasound measured carotid intima-media thickness (CIMT) at the common artery and bifurcation segments. Multivariable logistic and linear regression models were performed to estimate the associations of C1 metabolites of the methionine cycle with SA risk or CIMT.

Results

After controlling for potential cofounders and other C1 metabolites, in comparison with the lowest quartile, participants in the highest quartile had lower risk of SA by 27.6% (OR = 0.724; 95% CI:0.563–0.93, P_trend = 0.007) for SAM and 32.2% (OR = 0.678; 95% CI:0.538–0.855, P_trend < 0.001) for SAM/SAH, while increased SA risk by 27.9% (OR = 1.279; 95% CI: 1.065–1.535, P_trend < 0.001) for SAH. No significant association was observed for Hcy with SA after further adjustment of SAH and SAM. The results of multivariable linear regression showed similar findings. The highest two standardized coefficients were observed for SAH (β = 0.104 for CCA and 0.121 for BIF, P< 0.001) and SAM/SAH (β = −0.071 for CCA and −0.084 for BIF, P< 0.001). Subgroup analyses suggested more evident associations of SAH with SA were observed in participants of higher cardiovascular risk profiles.

Conclusion

Our cross-sectional data showed higher serum SAH, but lower SAM/SAH were independently associated with increased risk of SA among the Chinese middle-aged and elderly population.

Regulated Necrosis Orchestrates Microglial Cell Death in Manganese-Induced Toxicity

Microglia, the brain resident immune cells, play prominent roles in immune surveillance, tissue repair and neural regeneration. Despite these pro-survival actions, the relevance of these cells in the progression of several neuropathologies has been established. In the context of manganese (Mn) overexposure, it has been proposed that microglial activation contributes to enhance the neurotoxicity. However, the occurrence of a direct cytotoxic effect of Mn on microglial cells remains controversial. In the present work, we investigated the potential vulnerability of immortalized mouse microglial cells (BV-2) toward Mn²⁺, focusing on the signaling pathways involved in cell death. Evidence obtained showed that Mn²⁺ induces a decrease in cell viability which is associated with reactive oxygen species (ROS) generation. In this report we demonstrated, for the first time, that Mn²⁺ triggers regulated necrosis (RN) in BV-2 cells involving two central mechanisms: parthanatos and lysosomal disruption. The occurrence of parthanatos is supported by several cellular and molecular events: (i) DNA damage; (ii) AIF translocation from mitochondria to the nucleus; (iii) mitochondrial membrane permeabilization; and (iv) PARP1-dependent cell death. On the other hand, Mn²⁺ induces lysosomal membrane permeabilization (LMP) and cathepsin D (CatD) release into the cytosol supporting the lysosomal disruption. Pre-incubation with CatB and D inhibitors partially prevented the Mn²⁺-induced cell viability decrease. Altogether these events point to lysosomes as players in the execution of RN. In summary, our results suggest that microglial cells could be direct targets of Mn²⁺ damage. In this scenario, Mn²⁺ triggers cell death involving RN pathways.

Folate, Vitamin B6 and Vitamin B12 Intake in Relation to Hyperuricemia

To assess the association between intake of folate, vitamin B6, and vitamin B12 with hyperuricemia (HU) among adults from the United States (US), we extracted relevant data from 24,975 US adults aged 20–85 years from the National Health and Nutrition Examination Survey (NHANES) in 2001–2014. All dietary intake was evaluated by 24-h dietary recalls. Multivariable logistic regression analysis was performed to explore the associations after adjustment for confounders. Compared to the lowest quintile (Q1), for males, adjusted odds ratios (ORs) of HU in Q2 to Q5 of folate (dietary folate equivalent, DFE) intake were 0.84 (95% CI, 0.73–0.96), 0.84 (0.73–0.97), 0.72 (0.62–0.84), and 0.64 (0.53–0.77), respectively (p for trend <0.0001). In females, adjusted ORs in Q2 to Q4 of folate (DFE) intake were 0.84 (95% CI, 0.71–0.99), 0.81 (0.68–0.96), and 0.82 (0.68–0.99), with a p for trend of 0.1475. Our findings indicated the intakes of total folate, folic acid, food folate, folate (DFE), vitamin B12, but not vitamin B6, were inversely related to the risk of HU in males. A lower risk of HU with higher intakes of total folate, food folate, and folate (DFE) was found in females, but with no association between intakes of folic acid, vitamin B6, B12, and the risk of HU for females.

The relationship between S-adenosylhomocysteine and coronary artery lesions: A case control study

The role of homocysteine (Hcy) in the pathogenesis of coronary artery disease (CAD) is controversial, as decreased Hcy levels have not demonstrated consistent clinical benefits. Recent studies propose that S-adenosylhomocysteine (SAH), and not Hcy, plays a role in cardiovascular disease (CVD). We aimed to assess the relationship between plasma SAH and coronary artery lesions. Participants (n=160; aged 40-80years) with chest pain and suspected CAD underwent coronary angiography (CAG) for assessment of coronary artery stenosis, and were assigned to either the atherosclerosis (AS) or CAD group. Plasma SAH and S-adenosylmethionine (SAM) concentrations were measured and the association between coronary artery lesions and SAH was assessed. SAH levels were significantly higher in the CAD group (23.09±2.4nmol/L) than in the AS group (19.2±1.5nmol/L). While the AS group had higher values for SAM/SAH (5.1±0.7 vs. 4.1±1.1), levels of SAM, Hcy, folate, and vitamin B12 were similar in the two groups. Coronary artery lesions were associated with SAH (β=11.8 [95% CI: 5.88, 17.7, P<0.05]. Plasma SAH concentrations are independently associated with coronary artery lesions among patients undergoing coronary angiography. Plasma SAH might be a novel biomarker for the early clinical identification of CVD.

Folic acid therapy reduces serum uric acid in hypertensive patients: a substudy of the China Stroke Primary Prevention Trial (CSPPT)

Background: The effect of folic acid supplementation on uric acid (UA) concentrations is still inconclusive.Objective: We aimed to test the efficacy of folic acid therapy in reducing serum UA in hypertensive patients.Design: A total of 15,364 hypertensive patients were randomly assigned to a double-blind daily treatment with a single tablet that contained 10 mg enalapril and 0.8 mg folic acid (n = 7685) or 10 mg enalapril alone (n = 7679). The main outcome was the change in serum UA, which was defined as UA at the exit visit minus that at baseline. Secondary outcomes were as follows: 1) controlled hyperuricemia (UA concentration <357 μmol/L after treatment) and 2) new-onset hyperuricemia in participants with normal UA concentrations (<357 μmol/L).Results: After a median of 4.4 y of treatment, the mean ± SD UA concentration increased by 34.7 ± 72.5 μmol/L in the enalapril-alone group and by 30.7 ± 71.8 μmol/L in the enalapril-folic acid group, which resulted in a mean group difference of -4.0 μmol/L (95% CI: -6.5, -1.6 μmol/L; P = 0.001). Furthermore, compared with enalapril alone, enalapril-folic acid treatment showed an increase in controlled hyperuricemia (30.3% compared with 25.6%; OR: 1.31; 95% CI: 1.01, 1.70) and a decrease in new-onset hyperuricemia (15.0% compared with 16.3%; OR: 0.89; 95% CI: 0.79, 0.99). A greater beneficial effect was observed in subjects with hyperuricemia (P-interaction = 0.07) or higher concentrations of total homocysteine (tHcy) (P-interaction = 0.02) at baseline. Furthermore, there was a significant inverse relation (P < 0.001) between the reduction of tHcy and the change in UA concentrations.Conclusions: Enalapril-folic acid therapy, compared with enalapril alone, can significantly reduce the magnitude of the increase of UA concentrations in hypertensive adults. This trial was registered at clinicaltrials.gov as NCT00794885.

Role of S-adenosylhomocysteine in cardiovascular disease and its potential epigenetic mechanism

Transmethylation reactions utilize S-adenosylmethionine (SAM) as a methyl donor and are central to the regulation of many biological processes: more than fifty SAM-dependent methyltransferases methylate a broad spectrum of cellular compounds including DNA, histones, phospholipids and other small molecules. Common to all SAM-dependent transmethylation reactions is the release of the potent inhibitor S-adenosylhomocysteine (SAH) as a by-product. SAH is reversibly hydrolyzed to adenosine and homocysteine by SAH hydrolase. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. However, a major unanswered question is if homocysteine is causally involved in disease pathogenesis or simply a passive and indirect indicator of a more complex mechanism. A chronic elevation in homocysteine levels results in a parallel increase in intracellular or plasma SAH, which is a more sensitive biomarker of cardiovascular disease than homocysteine and suggests that SAH is a critical pathological factor in homocysteine-associated disorders. Previous reports indicate that supplementation with folate and B vitamins efficiently lowers homocysteine levels but not plasma SAH levels, which possibly explains the failure of homocysteine-lowering vitamins to reduce vascular events in several recent clinical intervention studies. Furthermore, more studies are focusing on the role and mechanisms of SAH in different chronic diseases related to hyperhomocysteinemia, such as cardiovascular disease, kidney disease, diabetes, and obesity. This review summarizes the current role of SAH in cardiovascular disease and its effect on several related risk factors. It also explores possible the mechanisms, such as epigenetics and oxidative stress, of SAH. This article is part of a Directed Issue entitled: Epigenetic dynamics in development and disease.

Plasma S-adenosylhomocysteine is associated with the risk of cardiovascular events in patients undergoing coronary angiography: a cohort study

BACKGROUND

Although cross-sectional studies have shown that plasma S-adenosylhomocysteine (SAH), the metabolic precursor of homocysteine, is associated with cardiovascular disease, the prospective relation between plasma SAH and cardiovascular disease risk is unknown.

OBJECTIVE

The aim of this study was to prospectively evaluate the association between plasma SAH and cardiovascular disease risk in coronary angiography patients.

DESIGN

Baseline plasma SAH and homocysteine concentrations were measured in 1003 patients aged between 21 and 87 y who underwent coronary angiography. Cox proportional hazards models were used to analyze the association between SAH and homocysteine and the risk of cardiovascular events, including fatal cardiovascular diseases, nonfatal myocardial infarction, and stroke.

RESULTS

During the median follow-up period of 3.0 y, 93 participants developed cardiovascular events (32.7/1000 person-years). The age- and sex-adjusted hazard ratio of cardiovascular events was 3.38 (95% CI: 2.12, 5.39) for each 1-SD increase in the natural log-transformed SAH concentration. The age- and sex-adjusted hazard ratios of cardiovascular events across quartiles of SAH concentrations were 1.0, 2.25, 2.72, and 3.40 (P-trend = 0.007). Further adjustment for other cardiovascular disease risk factors and plasma homocysteine affected the results only slightly. This positive association between SAH and cardiovascular disease risk did not change when participants were stratified by age group, sex, and other baseline covariates. The results among a subset of participants with significant coronary stenosis were similar.

CONCLUSION

Higher concentrations of plasma SAH are independently associated with an increased risk of cardiovascular events among patients undergoing coronary angiography. This trial was registered at www.chictr.org as ChiCTR-RNRC-08000270.

Endogenous elevation of homocysteine induces retinal neuron death in the cystathionine-beta-synthase mutant mouse

PURPOSE

To determine the effects of endogenous elevation of homocysteine on the retina using the cystathionine beta-synthase (cbs) mutant mouse.

METHODS

Retinal homocysteine in cbs mutant mice was measured by high-performance liquid chromatography (HPLC). Retinal cryosections from cbs(-/-) mice and cbs(+/-) mice were examined for histologic changes by light and electron microscopy. Morphometric analysis was performed on retinas of cbs(+/-) mice maintained on a high-methionine diet (cbs(+/-) HM). Changes in retinal gene expression were screened by microarray.

RESULTS

HPLC analysis revealed an approximate twofold elevation in retinal homocysteine in cbs(+/-) mice and an approximate sevenfold elevation in cbs(-/-) mice. Distinct alterations in the ganglion, inner plexiform, inner nuclear, and epithelial layers were observed in retinas of cbs(-/-) and 1-year-old cbs(+/-) mice. Retinas of cbs(+/-) HM mice demonstrated an approximate 20% decrease in cells of the ganglion cell layer (GCL), which occurred as early as 5-weeks after onset of the HM diet. Microarray analysis revealed alterations in expression of several genes, including increased expression of Aven, Egr1, and Bat3 in retinas of cbs(+/-) HM mice.

CONCLUSIONS

This study provides the first analysis of morphologic and molecular effects of endogenous elevations of retinal homocysteine in an in vivo model. Increased retinal homocysteine alters inner and outer retinal layers in cbs homozygous mice and older cbs heterozygous mice, and it primarily affects the cells of the GCL in younger heterozygous mice. Elevated retinal homocysteine alters expression of genes involved in endoplasmic reticular stress, N-methyl-d-aspartate (NMDA) receptor activation, cell cycle, and apoptosis.

Effects of S-adenosylmethionine on liver methionine metabolism and steatosis with ethanol-induced liver injury in rats

Background

Hyperhomocysteinemia is implicated in the pathogenesis of various liver diseases. In this study, the effects of S-adenosylmethionine (SAM) on hyperhomocysteinemia and steatosis with ethanol-induced liver injury in rats were examined and their mechanisms were explored.

Methods

Forty-eight female Sprague–Dawley rats were randomly divided into four groups as control, model, low-dose, and high-dose SAM groups. Except the control group, all rats were fed high-fat-containing diet plus ethanol and fish oil gavaged for 8 weeks. SAM was administered by intraperitoneal injection after the 4 weeks’ exposure of ethanol. Serum homocysteine (Hcy), alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol (TC), triglyceride (TG), tumor necrosis factor α (TNF-α), and transforming growth factor β1 (TGF-β1) levels were determined. The contents of liver malondialdehyde (MDA) and glutathione (GSH) were assayed. Liver histology was also examined. The expressions of TNF-α and TGF-β1 mRNAs in the liver were detected by the reverse transcriptase-polymerase chain reaction assay.

Results

Compared with the control group, the model group rats developed marked liver damage, accompanied by an increase in Hcy, ALT, AST, TC, TG, TNF-α, TGF-β1, and MDA levels. However, the levels of GSH were decreased. These responses were associated with the increased expression of TNF-α and TGF-β1 mRNAs in the livers, as well as the existence of hepatocellular necrosis and neutrophil infiltration in the livers. In treatment groups, SAM provided significant protection from the liver injury induced by alcohol, resulting in a decrease in serum TNF-α, TGF-β1 levels, lipid peroxidation, and the expressions of TNF-α and TGF-β1 mRNAs in the livers, as well as an increase in GSH levels. However, no statistical difference was observed in these parameters between the two different dose treatment groups. In the study, SAM did not affect plasma total homocysteine (tHcy) levels significantly.

Conclusion

SAM prevents alcohol-induced liver injury in rats by reducing liver lipid peroxidation, anti-inflammation, and antihyperplasia. In addition, it does not affect the plasma tHcy levels.

Synergistic effects of homocysteine, S-adenosylhomocysteine and adenosine on apoptosis in BV-2 murine microglial cells

Homocysteine (Hcy), S-adenosylhomocysteine (SAH) and adenosine (Ado) are methionine metabolism intermediates that may act synergistically in certain disease. In this study, we examined whether HCy, SAH and Ado may synergistically induce neuronal apoptosis of BV-2 microglial cells. We found that an incubation of BV-2 cells with 1 mM Hcy, 1 muM SAH and 100 muM Ado (SAH + Hcy + Ado) led to marked apoptosis of BV-2 cells, as evidenced by several markers of apoptosis. A synergistic effect of SAH + Hcy + Ado on apoptosis (2.55-fold, P < 0.05) was obtained, as calculated using the data of Annexin V-positive cells. This combination markedly induced intracellular levels of reactive oxygen species (ROS) starting at 6 h and significantly decreased the mitochondrial potential starting at 12 h. The combination significantly elevated caspase-9 and caspase-3 activities at 24 and 48 h. The combination also induced hypomethylation (at 24 and 48 h), as indicated by significantly decreased 5-methyldeoxycytidine levels and SAM/SAH ratios. Pre-incubation of cells with alpha-tocopherol (30 muM) reduced the increase of ROS (at 6 h) and significantly restored cell viability (at 24 and 48~h) in the SAH + Hcy + Ado group. Overall, the present study demonstrates that SAH, Hcy and Ado synergistically induce BV-2 apoptosis, possibly by generation of ROS and induction of intracellular hypomethylation.