Increased Plasma S-Adenosylhomocysteine–Accelerated Atherosclerosis Is Associated With Epigenetic Regulation of Endoplasmic Reticulum Stress in apoE −/− Mice

Serum S-adenosylhomocysteine levels are associated with first stroke in Chinese adults with hypertension

BACKGROUND

The association between S-adenosylhomocysteine (SAH) and stroke has not been confirmed due to the specialized equipment and time requirements necessary for S-adenosylhomocysteine testing. We aimed to explore the association between SAH and stroke.

METHODS

A nested, case-control study drawn from the China Stroke Primary Prevention Trial of rural adults with hypertension, including 557 first stroke cases and 557 matched controls was conducted. Serum SAH was measured by stable-isotope dilution liquid chromatography-tandem mass spectrometry using 4500MD. Multiple conditional logistic regression models were used to evaluate the association between SAH and first stroke.

RESULTS

In females, SAH levels were significantly higher in the stroke population than in the control group (16.0 ng/mL vs. 14.6 ng/mL). When SAH was assessed as quartiles, the odds of stroke were 1.78 (95 % CI: 1.02-3.09) in Quartile 2, 1.31 (95 % CI: 0.73-2.33) in Quartile 3, and 1.93 (95 % CI: 1.03-3.62) in Quartile 4, compared to Quartile 1. When Quartiles 2-4 were combined, the adjusted odds ratio of first stroke was 1.64 (95 % CI: 1.03-2.62) compared with Quartile 1. In subgroup analysis, a significant SAH-stroke association was observed in the lower vitamin D3 group (OR = 3.35, 95 % CI:1.72-6.53; P interaction, 0.035). In males, higher levels of SAH were associated with an increased risk of stroke in those under age 60. Compared with the reference group, the adjusted odds ratio of total stroke was 2.40 (95 % CI: 1.02-5.91) in the combined group (Quartile 2-4). In contrast, no significant association between SAH and stroke was found in males aged 60 or older.

CONCLUSIONS

This study reveals that SAH is associated with a higher risk of stroke independently of homocysteine, especially in females. SAH may be a second predictor of stroke in the metabolic pathway of methionine, after homocysteine.

Epigenetic modulation of Drp1-mediated mitochondrial fission by inhibition of S-adenosylhomocysteine hydrolase promotes vascular senescence and atherosclerosis

AIMS

Vascular senescence, which is closely related to epigenetic regulation, is an early pathological condition in cardiovascular diseases including atherosclerosis. Inhibition of S-adenosylhomocysteine hydrolase (SAHH) and the consequent increase of S-adenosylhomocysteine (SAH), a potent inhibitor of DNA methyltransferase, has been associated with an elevated risk of cardiovascular diseases. This study aimed to investigate whether the inhibition of SAHH accelerates vascular senescence and the development of atherosclerosis.

METHODS AND RESULTS

The case-control study related to vascular aging showed that increased levels of plasma SAH were positively associated with the risk of vascular aging, with an odds ratio (OR) of 3.90 (95% CI, 1.17-13.02). Elevated pulse wave velocity, impaired endothelium-dependent relaxation response, and increased senescence-associated β-galactosidase staining were observed in the artery of SAHH+/- mice at 32 weeks of age. Additionally, elevated expression of p16, p21, and p53, fission morphology of mitochondria, and over-upregulated expression of Drp1 were observed in vascular endothelial cells with SAHH inhibition in vitro and in vivo. Further downregulation of Drp1 using siRNA or its specific inhibitor, mdivi-1, restored the abnormal mitochondrial morphology and rescued the phenotypes of vascular senescence. Furthermore, inhibition of SAHH in APOE-/- mice promoted vascular senescence and atherosclerosis progression, which was attenuated by mdivi-1 treatment. Mechanistically, hypomethylation over the promoter region of DRP1 and downregulation of DNMT1 were demonstrated with SAHH inhibition in HUVECs.

CONCLUSIONS

SAHH inhibition epigenetically upregulates Drp1 expression through repressing DNA methylation in endothelial cells, leading to vascular senescence and atherosclerosis. These results identify SAHH or SAH as a potential therapeutic target for vascular senescence and cardiovascular diseases.

Does Risk of Hyperhomocysteinemia Depend on Thiol-Disulfide Exchange Reactions of Albumin and Homocysteine?

Significance: Increased plasma concentrations of total homocysteine (tHcy; mild-moderate hyperhomocysteinemia: 15-50 μM tHcy) are considered an independent risk factor for the onset/progression of various diseases, but it is not known about how the increase in tHcy causes pathological conditions. Recent Advances: Reduced homocysteine (HSH ∼1% of tHcy) is presumed to be toxic, unlike homocystine (∼9%) and mixed disulfide between homocysteine and albumin (HSS-ALB; homocysteine [Hcy]-albumin mixed disulfide, ∼90%). This and other notions make it difficult to explain the pathogenicity of Hcy because: (i) lowering tHcy does not improve pathological outcomes; (ii) damage due to HSH usually emerges at supraphysiological doses; and (iii) it is not known why tiny increments in plasma concentrations of HSH can be pathological. Critical Issues: Albumin may have a role in Hcy toxicity, because HSS-ALB could release toxic HSH via thiol-disulfide (SH/SS) exchange reactions in cells. Similarly, thiol-disulfide exchange processes of reduced albumin (albumin with free SH group of Cys34 [HS-ALB]) or N-homocysteinylated albumin are plausible alternatives for initiating Hcy pathological events. Adverse effects of albumin and other data reviewed here suggest the hypothesis of a role of albumin in Hcy toxicity. Future Directions: HSS-ALB might be involved in disruption of the antioxidant/oxidant balance in critical tissues (brain, liver, kidney). Since homocysteine-albumin mixed disulfide is a possible intermediate of thiol-disulfide exchange reactions, we suggest that homocysteinylated albumin could be a new pathological factor, and that studies on the redox role of albumin and mixed disulfide production via thiol-disulfide exchange reactions could offer new therapeutic insights for reducing Hcy toxicity.

DNA methylation changes underlie the long-term association between periodontitis and atherosclerotic cardiovascular disease

Periodontitis, the leading cause of adult tooth loss, has been identified as an independent risk factor for cardiovascular disease (CVD). Studies suggest that periodontitis, like other CVD risk factors, shows the persistence of increased CVD risk even after mitigation. We hypothesized that periodontitis induces epigenetic changes in hematopoietic stem cells in the bone marrow (BM), and such changes persist after the clinical elimination of the disease and underlie the increased CVD risk. We used a BM transplant approach to simulate the clinical elimination of periodontitis and the persistence of the hypothesized epigenetic reprogramming. Using the low-density lipoprotein receptor knockout (LDLR^o ) atherosclerosis mouse model, BM donor mice were fed a high-fat diet to induce atherosclerosis and orally inoculated with Porphyromonas gingivalis (Pg), a keystone periodontal pathogen; the second group was sham-inoculated. Naïve LDLR ^o mice were irradiated and transplanted with BM from one of the two donor groups. Recipients of BM from Pg-inoculated donors developed significantly more atherosclerosis, accompanied by cytokine/chemokines that suggested BM progenitor cell mobilization and were associated with atherosclerosis and/or PD. Using whole-genome bisulfite sequencing, 375 differentially methylated regions (DMRs) and global hypomethylation in recipients of BM from Pg-inoculated donors were observed. Some DMRs pointed to the involvement of enzymes with major roles in DNA methylation and demethylation. In validation assays, we found a significant increase in the activity of ten-eleven translocase-2 and a decrease in the activity of DNA methyltransferases. Plasma S-adenosylhomocysteine levels were significantly higher, and the S-adenosylmethionine to S-adenosylhomocysteine ratio was decreased, both of which have been associated with CVD. These changes may be related to increased oxidative stress as a result of Pg infection. These data suggest a novel and paradigm-shifting mechanism in the long-term association between periodontitis and atherosclerotic CVD.

Effect of folic acid supplementation on the change of plasma S-adenosylhomocysteine level in Chinese hypertensive patients: a randomized, double-blind, controlled clinical trial

The relationship between folic acid and S-adenosylhomocysteine (SAH) is controversial. This study aims to explore the effect of different doses of folic acid supplementation on SAH levels in hypertensive patients and the modification of methylene-tetrahydrofolate reductase (MTHFR) C677T gene polymorphism. A randomized, double-blind, controlled clinical trial was conducted. Hypertensive patients aged 45-75 years without a history of stroke and cardiovascular disease were selected, who were randomly assigned to one of 8 dose groups. This trial has been registered with Trial Number: ChiCTR1800016135. In the total population, folic acid supplementation of 0.4-2.0 mg/day had no effect on SAH level (β = 0.47, 95% CI: -0.86-1.79, p = 0.491), while folic acid supplementation of 2.4 mg/day significantly increased SAH level (β = 1.93, 95% CI: 0.22-3.64, p = 0.027). Stratified analysis found that MTHFR C677T genotype CC supplemented with 2.4 mg/day folic acid had no effect on SAH level (β = 0.30, 95% CI: -2.74-3.34, p = 0.847), while CT and TT genotype supplemented with 2.4 mg/day folic acid showed a significant increase in SAH level (CT: β = 2.98, 95% CI: 0.34-5.62, p = 0.027; TT: β = 3.00, 95% CI: -0.51-6.51, p = 0.095; CT combined with TT: β = 2.99, 95% CI: 0.90-5.09, p = 0.005). In conclusion, supplementation of 2.4 mg/day folic acid can lead to increased SAH levels, especially in MTHFR C677T genotype CT and TT.

Integrated network pharmacology and metabolomics to reveal the mechanism of QiShenYiQi Dripping Pills (T101) against cardiac structural and functional abnormalities

Background: Heart failure (HF), the final stage of cardiovascular diseases, is a clinical syndrome of cardiac structural or functional abnormalities. QiShenYiQi Dripping Pills (T101), short for QSYQ (T101), showed effectiveness and safety in the treatment of HF according to modern pharmacological research and clinical studies, but the mechanism remains unclear. This study aims to clarify the mechanism of QSYQ (T101) in treating heart failure through the analysis to critical biomarkers, targets and pathways.

Materials and Methods: In this study, the efficacies of QSYQ (T101) in non-human primates and rodents were evaluated, and the mechanism was demonstrated by integrating network pharmacology and metabolomics analysis. Furthermore, the targets from network pharmacology and the metabolites from targeted metabolomics were jointly analyzed to screen the critical pathways.

Results: In rhesus monkeys with spontaneous chronic heart failure, nasogastric administration of QSYQ (T101) for 12 weeks caused profound improvement of systolic and diastolic function as evidenced by echocardiography detection. Consistently, QSYQ (T101) administration especially with higher dose lowered the blood pressure and improved the ventricular remodeling, collagen deposition and fibrosis markedly in Spontaneous Hypertension Rats (SHR) model. Computational prediction showed that QSYQ (T101) exhibited anti-HF effects possibly through HIF-1 signaling pathway, FoxO signaling pathway, TNF signaling pathway, PI3K-Akt signaling pathway and other enriched paths. Metabolomics analysis obtained 23 significantly altered metabolites, revealing that QSYQ (T101) significantly regulated the abnormal levels of fatty acids, carnitines, organic acids pyridines, nucleosides, which were mostly involved in myocardial energy metabolism related pathways.

Conclusion: Based on serum and myocardium metabolomics and network pharmacology, the present study revealed that the actions of QSYQ (T101) in treating HF depend on multi-components, multi-targets and multi-pathways.

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.

Inhibition of S-adenosylhomocysteine hydrolase induces endothelial senescence via hTERT downregulation

BACKGROUND AND AIMS

It has been established that endothelial senescence plays a critical role in the development of atherosclerosis. Elevated S-adenosylhomocysteine (SAH) level induced by inhibition of S-adenosylhomocysteine hydrolase (SAHH) is one of the risk factors of atherosclerosis; however, the interplay between endothelial senescence and inhibition of SAHH is largely unknown.

METHODS

Human umbilical vein endothelial cells (HUVECs) after serial passage were used. SAHH-specific inhibitor adenosine dialdehyde (ADA) and SAHH siRNA treated HUVECs and SAHH^+/-mice were used to investigate the effect of SAHH inhibition on endothelial senescence.

RESULTS

HUVECs exhibited distinct senescence morphology as HUVECs were passaged, together with a decrease in intracellular SAHH expression and an increase in intracellular SAH levels. SAHH inhibition by ADA or SAHH siRNA elevated SA β-gal activity, arrested proliferation, and increased the expression of p16, p21 and p53 in HUVECs and the aortas of mice. In addition, decreased expression of hTERT and reduced occupancy of H3K4me3 over the hTERT promoter region were observed following SAHH inhibition treatment. To further verify the role of hTERT in the endothelial senescence induced by SAHH inhibition, hTERT was overexpressed with a plasmid vector under CMV promoter. hTERT overexpression rescued the senescence phenotypes in endothelial cells induced by SAHH inhibition.

CONCLUSIONS

SAHH inhibition induces endothelial senescence via downregulation of hTERT expression, which is associated with attenuated histone methylation over the hTERT promoter region.

Epigenetic Upregulation of H19 and AMPK Inhibition Concurrently Contribute to S-Adenosylhomocysteine Hydrolase Deficiency-Promoted Atherosclerotic Calcification

BACKGROUND

S-adenosylhomocysteine (SAH) is a risk factor of cardiovascular disease; inhibition of SAH hydrolase (SAHH) results in SAH accumulation and induces endothelial dysfunction and atherosclerosis. However, the effect and mechanism of SAHH in atherosclerotic calcification is still unclear. We aimed to explore the role and mechanism of SAHH in atherosclerotic calcification.

METHODS

The relationship between SAHH and atherosclerotic calcification was investigated in patients with coronary atherosclerotic calcification. Different in vivo genetic models were used to examine the effect of SAHH deficiency on atherosclerotic calcification. Human aortic and murine vascular smooth muscle cells (VSMCs) were cultured to explore the underlying mechanism of SAHH on osteoblastic differentiation of VSMCs.

RESULTS

The expression and activity of SAHH were decreased in calcified human coronary arteries and inversely associated with coronary atherosclerotic calcification severity, whereas plasma SAH and total homocysteine levels were positively associated with coronary atherosclerotic calcification severity. Heterozygote knockout of SAHH promoted atherosclerotic calcification. Specifically, VSMC-deficient but not endothelial cell-deficient or macrophage-deficient SAHH promoted atherosclerotic calcification. Mechanistically, SAHH deficiency accumulated SAH levels and induced H19-mediated Runx2 (runt-related transcription factor 2)-dependent osteoblastic differentiation of VSMCs by inhibiting DNMT3b (DNA methyltransferase 3 beta) and leading to hypomethylation of the H19 promoter. On the other hand, SAHH deficiency resulted in lower intracellular levels of adenosine and reduced AMPK (AMP-activated protein kinase) activation. Adenosine supplementation activated AMPK and abolished SAHH deficiency-induced expression of H19 and Runx2 and osteoblastic differentiation of VSMCs. Finally, AMPK activation by adenosine inhibited H19 expression by inducing Sirt1-mediated histone H3 hypoacetylation and DNMT3b-mediated hypermethylation of the H19 promoter in SAHH deficiency VSMCs.

CONCLUSIONS

We have confirmed a novel correlation between SAHH deficiency and atherosclerotic calcification and clarified a new mechanism that epigenetic upregulation of H19 and AMPK inhibition concurrently contribute to SAHH deficiency-promoted Runx2-dependent atherosclerotic calcification.

The expression of SAH, IL-1β, Hcy, TNF-α and BDNF in coronary heart disease and its relationship with the severity of coronary stenosis

Background

To investigate the expression of serum S-adenosylhomocysteine (SAH), interleukin-1β (IL-1β), serum homocysteine (Hcy), tumor necrosis factor-α (TNF-α) and brain derived neurotrophic factor (BDNF) in coronary heart disease and their relationship with the degree of coronary artery disease.

Methods

A total of 132 patients with coronary heart disease (CHD) from March 2020 to April 2021 were included in this retrospective study. The experimental group was composed of CHD patients, including single-vascular group (46 cases), dual-vascular group (49 cases), and multi-vascular group (37 cases). 145 healthy subjects during the same period for physical examination constituted the control group.

Results

The levels of SAH, IL-1β, Hcy, TNF-α and BDNF in single-vascular group, dual-vascular group and multi-vascular group were higher than that in control group, and the differences were statistically significant (P < 0.05). The serum levels of SAH, IL-1β, Hcy, TNF-α and BDNF in multi-vascular group were higher than those in single-vascular group and dual-vascular group, and the serum levels of SAH, IL-1β, Hcy, TNF-α and BDNF in dual-vascular group were higher than those in single-vascular group, with statistical significance (P < 0.05). Kendall’s tau-b correlation showed that the levels of SAH, IL-1β, Hcy, TNF-α and BDNF were positively correlated with the number of stenosis vessels (r = 0.421, 0.533, 0.301, 0.265, 0.678, P = 0.016, 0.009, 0.023, 0.036, 0.004).

Conclusion

SAH, IL-1β, Hcy, TNF-α and BDNF in serum of patients with CHD can be used as effective biological indicators to monitor the degree of CHD and severity of coronary stenosis.

Betaine Supplementation Attenuates S-Adenosylhomocysteine Hydrolase-Deficiency-Accelerated Atherosclerosis in Apolipoprotein E-Deficient Mice

S-adenosylhomocysteine (SAH) is a risk factor of cardiovascular diseases and atherosclerosis. However, the causal association between SAH and atherosclerosis is still uncertain. In the present study, heterozygous SAH hydrolase (SAHH^+/−) knockout mice were bred with apolipoprotein E-deficient mice to produce ApoE^−/−/SAHH^+/− mice. At 8 weeks of age, these mice were fed on AIN-93G diets added with or without betaine (4 g betaine/100 g diet) for 8 weeks. Compared with ApoE^−/−/SAHH^WT mice, SAHH deficiency caused an accumulation of plasma SAH concentration and a decrease in S-adenosylmethionine (SAM)/SAH ratio as well as plasma homocysteine levels. Betaine supplementation lowered SAH levels and increased SAM/SAH ratio and homocysteine levels in ApoE^−/−/SAHH^+/− mice. Furthermore, SAHH deficiency promoted the development of atherosclerosis, which was reduced by betaine supplementation. The atheroprotective effects of betaine on SAHH-deficiency-promoted atherosclerosis were associated with inhibition of NFκB inflammation signaling pathway and inhibition of proliferation and migration of smooth muscle cells. In conclusion, our results suggest that betaine supplementation lowered plasma SAH levels and protected against SAHH-deficiency-promoted atherosclerosis through repressing inflammation and proliferation and migration of smooth muscle cells.

Association between plasma S-adenosylmethionine and risk of mortality in patients with coronary artery disease: A cohort study

BACKGROUND

S-adenosylmethionine (SAM) as methyl donors participates in methylation and is converted into S-adenosylhomocysteine (SAH), which is a precursor of homocysteine. Increased plasma SAH and homocysteine are associated with increased risk of cardiovascular disease. However, the relation of plasma SAM with cardiovascular risk is still unclear.

OBJECTIVES

To determine the relation between plasma SAM and risk of mortality among patients with coronary artery disease (CAD).

METHODS

Baseline plasma SAM concentrations were measured in 1553 patients with CAD from the Guangdong Coronary Artery Disease Cohort between October 2008 and December 2011. Proportional hazards Cox analyses were performed to ascertain associations between SAM and risk of all-cause and cardiovascular mortality.

RESULTS

After a median follow-up of 9.2 (IQR: 8.5-10.2) y, of 1553 participants, 321 had died, including 227 deaths from cardiovascular diseases. Patients in the lowest quartile of SAM concentrations had a higher risk of all-cause death (HR, 1.59; 95% CI: 1.14, 2.21) and cardiovascular death (HR, 2.14; 95% CI: 1.41, 3.27) than those in the highest quartile in multivariable adjusted analysis. Each 1-SD decrease in the SAM concentration remained associated with a 42% greater risk of total death (HR, 1.42; 95% CI: 1.23, 1.64) and a 66% higher risk of cardiovascular death (HR, 1.66; 95% CI: 1.37, 2.01) after fully adjusting for other cardiovascular risk factors. Furthermore, each 1-SD decrease in plasma SAM/SAH ratio, as the methylation index, was also inversely associated with the risk of all-cause (HR, 1.80; 95% CI: 1.42, 2.29) and cardiovascular mortality (HR, 1.68; 95% CI: 1.29, 2.19) in fully adjusted analyses.

CONCLUSIONS

Our data show a significant inverse relation between plasma SAM and risk of mortality in patients with CAD after adjustment for homocysteine, SAH, and other cardiovascular disease risk factors.

Epigenetic regulation of TXNIP-mediated oxidative stress and NLRP3 inflammasome activation contributes to SAHH inhibition-aggravated diabetic nephropathy

S-adenosylhomocysteine (SAH) is hydrolyzed by SAH hydrolase (SAHH) to homocysteine and adenosine. Increased plasma SAH levels were associated with disturbed renal function in patients with diabetes. However, the role and mechanism of SAHH in diabetic nephropathy is still unknown. In the present study, we found that inhibition of SAHH by using its inhibitor adenosine dialdehyde (ADA) accumulates intracellular or plasma SAH levels and increases high glucose-induced podocyte injury and aggravates STZ-induced diabetic nephropathy, which is associated with Nod-like receptor protein 3 (NLRP3) inflammasome activation. Inhibition or knockout of NLRP3 attenuates SAHH inhibition-aggravated podocyte injury and diabetic nephropathy. Additionally, SAHH inhibition increases thioredoxin-interacting protein (TXNIP)-mediated oxidative stress and NLRP3 inflammasome activation, but these effects were not observed in TXNIP knockout mice. Mechanistically, SAHH inhibition increased TXNIP by inhibiting histone methyltransferase enhancer of zeste homolog 2 (EZH2) and reduced trimethylation of histone H3 lysine 27 and its enrichment at promoter of early growth response 1 (EGR1). Moreover, EGR1 is activated and enriched at promoters of TXNIP by SAHH inhibition and is essential for SAHH inhibition-induced TXNIP expression. Inhibition of EGR1 protected against SAHH inhibition-induced NLRP3 inflammasome activation and oxidative stress and diabetic nephropathy. Finally, the harmful effects of SAHH inhibition on inflammation and oxidative stress and diabetic nephropathy were also observed in heterozygote SAHH knockout mice. These findings suggest that EZH2/EGR1/TXNIP/NLRP3 signaling cascade contributes to SAHH inhibition-aggravated diabetic nephropathy. Our study firstly provides a novel insight into the role and mechanism of SAHH inhibition in diabetic nephropathy.

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SAHH inhibition accumulates SAH levels and aggravates podocyte injury and diabetic nephropathy.

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SAHH inhibition induces TXNIP-mediated oxidative stress and NLRP3 inflammasome activation.

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SAHH inhibition increases TXNIP by inhibiting EZH2 and reducing H3K27me3 and its enrichment at promoter of EGR1.

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EGR1 is required for SAHH inhibition-induced TXNIP and NLRP3 inflammasome activation and diabetic nephropathy.

No Effect of Diet-Induced Mild Hyperhomocysteinemia on Vascular Methylating Capacity, Atherosclerosis Progression, and Specific Histone Methylation

Hyperhomocysteinemia (HHcy) is a risk factor for atherosclerosis through mechanisms which are still incompletely defined. One possible mechanism involves the hypomethylation of the nuclear histone proteins to favor the progression of atherosclerosis. In previous cell studies, hypomethylating stress decreased a specific epigenetic tag (the trimethylation of lysine 27 on histone H3, H3K27me3) to promote endothelial dysfunction and activation, i.e., an atherogenic phenotype. Here, we conducted a pilot study to investigate the impact of mild HHcy on vascular methylating index, atherosclerosis progression and H3K27me3 aortic content in apolipoprotein E-deficient (ApoE ^-/-) mice. In two different sets of experiments, male mice were fed high-fat, low in methyl donors (HFLM), or control (HF) diets for 16 (Study A) or 12 (Study B) weeks. At multiple time points, plasma was collected for (1) quantification of total homocysteine (tHcy) by high-performance liquid chromatography; or (2) the methylation index of S-adenosylmethionine to S-adenosylhomocysteine (SAM:SAH ratio) by liquid chromatography tandem-mass spectrometry; or (3) a panel of inflammatory cytokines previously implicated in atherosclerosis by a multiplex assay. At the end point, aortas were collected and used to assess (1) the methylating index (SAM:SAH ratio); (2) the volume of aortic atherosclerotic plaque assessed by high field magnetic resonance imaging; and (3) the vascular content of H3K27me3 by immunohistochemistry. The results showed that, in both studies, HFLM-fed mice, but not those mice fed control diets, accumulated mildly elevated tHcy plasmatic concentrations. However, the pattern of changes in the inflammatory cytokines did not support a major difference in systemic inflammation between these groups. Accordingly, in both studies, no significant differences were detected for the aortic methylating index, plaque burden, and H3K27me3 vascular content between HF and HFLM-fed mice. Surprisingly however, a decreased plasma SAM: SAH was also observed, suggesting that the plasma compartment does not always reflect the vascular concentrations of these two metabolites, at least in this model. Mild HHcy in vivo was not be sufficient to induce vascular hypomethylating stress or the progression of atherosclerosis, suggesting that only higher accumulations of plasma tHcy will exhibit vascular toxicity and promote specific epigenetic dysregulation.

Metabolic Pathways Fueling the Endothelial Cell Drive

Endothelial cell (EC) metabolism is important for health and disease. Metabolic pathways, such as glycolysis, fatty acid oxidation, and amino acid metabolism, determine vasculature formation. These metabolic pathways have different roles in securing the production of energy and biomass and the maintenance of redox homeostasis in vascular migratory tip cells, proliferating stalk cells, and quiescent phalanx cells, respectively. Emerging evidence demonstrates that perturbation of EC metabolism results in EC dysfunction and vascular pathologies. Here, we summarize recent insights into EC metabolic pathways and their deregulation in vascular diseases. We further discuss the therapeutic implications of targeting EC metabolism in various pathologies.

Inhibition of S-Adenosylhomocysteine Hydrolase Induces Endothelial Dysfunction via Epigenetic Regulation of p66shc-Mediated Oxidative Stress Pathway

BACKGROUND

Elevated levels of S-adenosylhomocysteine (SAH), the precursor of homocysteine, are positively associated with the risk of cardiovascular disease and with the development and progression of atherosclerosis. However, the role of SAH in endothelial dysfunction is unclear.

METHODS

Apolipoprotein E-deficient ( apoE^-/-) mice received dietary supplementation with the SAH hydrolase (SAHH) inhibitor adenosine dialdehyde or were intravenously injected with a retrovirus expressing SAHH shRNA. These 2 approaches, along with the heterozygous SAHH gene knockout ( SAHH^+/-) mouse model, were used to elevate plasma SAH levels and to examine the role of SAH in aortic endothelial dysfunction. The relationship between plasma SAH levels and endothelial dysfunction was also investigated in human patients with coronary artery disease and healthy control subjects.

RESULTS

Plasma SAH levels were increased in SAHH^+/- mice and in apoE^-/- mice after dietary administration of adenosine dialdehyde or intravenous injection with SAHH shRNA. SAHH^+/- mice or apoE^-/- mice with SAHH inhibition showed impaired endothelium-dependent vascular relaxation and decreased nitric oxide bioavailability after treatment with acetylcholine; this was completely abolished by the administration of the endothelial nitric oxide synthase inhibitor N^G-nitro-l-arginine methyl ester. Furthermore, SAHH inhibition induced production of reactive oxygen species and p66shc expression in the mouse aorta and human aortic endothelial cells. Antioxidants and p66shc siRNA prevented SAHH inhibition-induced generation of reactive oxygen species and attenuated the impaired endothelial vasomotor responses in high-SAH mice. Moreover, inhibition of SAHH induced hypomethylation in the p66shc gene promoter and inhibited expression of DNA methyltransferase 1. Overexpression of DNA methyltransferase 1, induced by transduction of an adenovirus, was sufficient to abrogate SAHH inhibition-induced upregulation of p66shc expression. Finally, plasma SAH levels were inversely associated with flow-mediated dilation and hypomethylation of the p66shc gene promoter and positively associated with oxidative stress levels in patients with coronary artery disease and healthy control subjects.

CONCLUSIONS

Our findings indicate that inhibition of SAHH results in elevated plasma SAH levels and induces endothelial dysfunction via epigenetic upregulation of the p66shc-mediated oxidative stress pathway. Our study provides novel molecular insight into mechanisms of SAH-associated endothelial injury that may contribute to the development of atherosclerosis.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov . Unique identifier: NCT03345927.

Endoplasmic reticulum stress and NLRP3 inflammasome: Crosstalk in cardiovascular and metabolic disorders

When endoplasmic reticulum (ER) homeostasis is disrupted, known as ER stress (ERS), the ER generates an adaptive signaling pathway called the unfolded protein response to maintain the homeostasis of this organelle. However, if homeostasis is not restored, the ER initiates death signaling pathways, which contribute to the pathogenesis of various disorders. The activation of inflammatory mechanisms is also emerging as a crucial component of cardiovascular and metabolic disorders. Furthermore, the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has attracted more attention than others and is the best-characterized member of the NLR family of inflammasomes to date. ERS intersects with many different inflammatory pathways, particularly the NLRP3 inflammasome. In this review, we focus on the interactions between ERS and the NLRP3 inflammasome. The pharmacologic and nonpharmaceutical manipulation of these two processes may offer novel opportunities for the treatment of cardiovascular and metabolic disorders.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

The immunomodulatory mechanism of brain injury induced by hyperhomocysteinemia in spontaneously hypertensive rats

BACKGROUND

Elevated plasma homocysteine (Hcy) concentration is considered as the diagnostic criteria of Hyperhomocysteinemia (HHcy), which is associated with the inflammatory response and blood-brain barrier disruption. Previous studies have proposed that HHcy with hypertension was associated with the brain injury by enhancing the cerebrovascular permeability, however, the immune mechanism remains obscure. The purpose of the study is to explore the immunomodulatory mechanism of brain injury in spontaneously hypertensive rats (SHRs) induced by HHcy.

MATERIALS AND METHODS

Sixty SHRs were randomly assigned to three groups: SHR-C (control group), SHR-M (methionine group) and SHR-T (treatment group). Physical examination of body weight, systolic blood pressure (SBP) and plasma Hcy content was measured every 4 weeks. Besides, T-helper cell 17 and regulatory T cells (Treg)-related inflammatory cytokines (interleukin [IL]-6, IL-17, IL-10, and transforming growth factor beta [TGF-β]) and genes (RORγt and FoxP3) were detected by enzyme-linked immunosorbent assay, quantitative polymerase chain reaction , Western blot, and immunohistochemistry.

RESULTS

High methionine diet could cause weight loss, SBP rising, and plasma Hcy content significantly elevated. IL-16 and IL-17A levels in peripheral blood and in brain tissue both lifted, while IL-10 and TGF-β levels dropped; RORγt expression raised in brain, nevertheless, FoxP3 levels were the opposite. After the intervention with vitamin B6, B12, and folic acid in SHR-T group, these trends would be eased or completely changed. Furthermore, brain tissue slices showed that IL-17-positive cells tended to decrease, and IL-10-positive cells increased in SHR-T group, which was reversed in SHR-M group.

CONCLUSIONS

HHcy may promote inflammation that can lead to brain lesions and down-regulate immune response to protect the brain.

Cell‑specific histone modifications in atherosclerosis (Review)

Histone modifications are the key epigenetic mechanisms that have been identified to regulate gene expression in many human diseases. However, in the early developmental stages, such as in utero and the postnatal stages, histone modifications are essential for gene regulation and cell growth. Atherosclerosis represents a classical example of the involvement of different cell types, and their cumulative effects in the development of atheroma and the progression of the disease. Post translational modifications on proteins either induces their functional activity or renders them inactive. Post translational modifications such as methylation or acetylation on histones have been well characterized, and their role in enhancing or inhibiting specific gene expression was clearly elucidated. In the present review article, the critical roles of different histone modifications that occur in atherosclerosis have been summarized. Different histone proteins have been identified to serve a critical role in the development of atherosclerosis. Specifically, histone methylation and histone acetylation in monocytes, macrophages, vascular smooth muscle cells and in endothelial cells during the progression of atherosclerosis, have been well reported. In recent years, different target molecules and genes that regulate histone modifications have been examined for their effects in the treatment of atherosclerosis in animal models and in clinical trials. An increasing body of evidence suggests that these epigenetic changes resulting from DNA methylation and non-coding RNA may also be associated with histone modifications, thereby indicating that novel therapeutic strategies can be developed by targeting these post translational modifications, which may in turn aid in the treatment of atherosclerosis.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

A coupled photometric assay for characterization of S-adenosyl-l-homocysteine hydrolases in the physiological hydrolytic direction

S-Adenosyl-l-homocysteine hydrolases (SAHases) are important metabolic enzymes and their dysregulation is associated with some severe diseases. In vivo they catalyze the hydrolysis of S-adenosyl-l-homocysteine (SAH), the by-product of methylation reactions in various organisms. SAH is a potent inhibitor of methyltransferases, thus its removal from the equilibrium is an important requirement for methylation reactions. SAH hydrolysis is also the first step in the cellular regeneration process of the methyl donor S-adenosyl-l-methionine (SAM). However, in vitro the equilibrium lies towards the synthetic direction. To enable characterization of SAHases in the physiologically relevant direction, we have developed a coupled photometric assay that shifts the equilibrium towards hydrolysis by removing the product adenosine, using a high affinity adenosine kinase (AK). This converts adenosine to AMP and thereby forms equimolar amounts of ADP, which is phosphorylated by a pyruvate kinase (PK), in turn releasing pyruvate. The readout of the assay is the consumption of NADH during the lactate dehydrogenase (LDH) catalyzed reduction of pyruvate to lactic acid. The applicability of the assay is showcased for the determination of the kinetic constants of an SAHase from Bradyrhizobium elkanii (K_M,SAH 41±5μM, v_max,SAH 25±1μM/min with 0.13mg/mL enzyme). This assay is a valuable tool for in vitro characterization of SAHases with biotechnological potential, and for monitoring SAHase activity in diagnostics.

Involvement of histone methylation in macrophage apoptosis and unstable plaque formation in methionine-induced hyperhomocysteinemic ApoE-/- mice

AIMS

Hyperhomocysteinemia (Hhcy) is an independent risk factor of atherosclerosis and promotes unstable plaque formation. Epigenetic mechanisms play an important role in the pathogenesis of atherosclerosis induced by Hhcy. However, the exact mechanism is still undefined. Lesional apoptotic cells and necrotic core formation contribute greatly to the progression of plaque. The present study sought to determine whether modification of histone methylation is involved in macrophage apoptosis and unstable plaque formation in the condition of Hhcy.

MATERIALS AND METHODS

The unstable plaque formation, lesional apoptotic cells and status of histone methylation were monitored in the aortas of Hhcy ApoE^-/- mice induced by a high-methionine (HM) diet for 20weeks. Involvement of histone methylation in macrophage apoptosis and foam cell formation were assessed in macrophage Raw 264.7 cells after being challenged with homocysteine alone or in combination with the histone methylation inhibitor BIX 01294.

KEY FINDINGS

The unstable plaque formation and lesion apoptotic cells are increased in ApoE^-/- mice supplemented with high-methionine (HM), accompanied with a decreased expression of histone H3 lysine 9 dimethylation. Hhcy increases the apoptosis of macrophages and inhibits the histone H3 lysine 9 dimethylation, as well as the expression of histone methyltransferase G9a in vitro. Inhibition of histone methylation by BIX01294 enhances macrophage apoptosis and foam cell formation in vitro.

SIGNIFICANCE

Our data suggest that Hhcy promotes the progression of atherosclerosis via macrophage apoptosis. Histone methylation might be involved in macrophage apoptosis and unstable plaque formation in methionine induced hyperhomocysteinemic ApoE^-/- mice.

Rational Design of a Profluorescent Substrate for S-adenosylhomocysteine Hydrolase and its Applications in Bioimaging and Inhibitor Screening

S-Adenosylhomocysteine hydrolase (SAHase) is a cellular enzyme that plays a key role in the methylation process, and a potential drug target in the discovery of antiviral and anticancer agents. There is increasing interest in determining its activity in the biological and clinical fields with chemosensors but with limited success so far. Herein, we designed and developed for the first time an off/on-type of fluorogenic substrate (NADE) that is directly responsive to SAHase activity. NADE used 1,8-naphthalimide as the signal reporter and adenosine (Ade) as the reaction center; removal of the Ade moiety enhanced the fluorescence by >10-fold. Kinetic study showed that NADE followed a non-Michaelis-Menten pattern that corresponded to the allosteric behavior of SAHase. NADE showed excellent selectivity and functioned efficiently in cells, allowing the microscopic imaging of SAHase activity. NADE can also be used to identify and measure the effectiveness of inhibitors in a markedly superior way. In a word, NADE would be broadly useful in clinical applications and academic studies.

Plasma S-adenosylhomocysteine: A potential risk marker for cerebral venous thrombosis

BACKGROUND

Despite a plethora of studies suggesting that hyperhomocysteinemia is associated with an increased risk for arterial and venous thrombosis, there is paucity of data on the role of the S-adenosylhomocysteine (SAH), the metabolic precursor of homocysteine (Hcy) as a risk predictor for cerebral venous thrombosis (CVT).

METHOD

We estimated fasting plasma concentrations of total homocysteine (tHcy), SAH and S-adenosylmethionine (SAM), in 185 CVT patients and 248 healthy controls, by reverse-phase high performance liquid chromatography coupled with coulometric electrochemical detection.

RESULTS

Fasting tHcy, SAH and SAM were significantly higher in patients compared with controls. Increased tHcy and SAH concentrations were associated with 4.54-fold (95% CI, 2.74-7.53) and 35.77-fold (95% CI, 19.45-65.79) increase in risk for CVT, respectively. Receiver operating characteristic (ROC) curve analysis showed that the area under curve, sensitivity and specificity was higher for SAH compared to tHcy. Further, discriminant analysis to distinguish between tHcy and SAH showed that SAH had a significantly higher percentage classification, with lower Wilk's lambda and higher χ(2), compared to tHcy.

CONCLUSION

Increased plasma SAH may be a more sensitive risk marker for CVT than plasma tHcy.

S-adenosylhomocysteine induces inflammation through NFkB: A possible role for EZH2 in endothelial cell activation

S-adenosylhomocysteine (SAH) can induce endothelial dysfunction and activation, contributing to atherogenesis; however, its role in the activation of the inflammatory mediator NFkB has not been explored. Our aim was to determine the role of NFkB in SAH-induced activation of endothelial cells. Furthermore, we examined whether SAH, as a potent inhibitor of S-adenosylmethionine-dependent methyltransferases, suppresses the function of EZH2 methyltransferase to contribute to SAH-induced endothelial cell activation. We found that excess SAH increases the expression of adhesion molecules and cytokines in human coronary artery endothelial cells. Importantly, this up-regulation was suppressed in cells expressing a dominant negative form of the NFkB inhibitor, IkB. Moreover, SAH accumulation triggers the activation of both the canonical and non-canonical NFkB pathways, decreases EZH2, and reduces histone 3 lysine 27 trimethylation. EZH2 knockdown recapitulated the effects of excess SAH on endothelial activation, i.e., it induced NFkB activation and the subsequent up-regulation of adhesion molecules and cytokines. Our findings suggest that suppression of the epigenetic regulator EZH2 by excess SAH may contribute to NFkB activation and the consequent vascular inflammatory response. These studies unveil new targets of SAH regulation, demonstrating that EZH2 suppression and NFkB activation mediated by SAH accumulation may contribute to its adverse effects in the vasculature.

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.