Folic acid supplementation delays atherosclerotic lesion development in apoE-deficient mice

Folic acid and plasma lipids: Interactions and effect of folate supplementation

Dyslipidaemia and hyperhomocysteinemia are known risk factors for cardiovascular disease. While it is evident that optimization of plasma lipid is associated with low risk of cardiovascular disease in the general population, it is not yet fully clear whether reduction of homocysteinemia is associated with an improvement in risk in all subjects. The aim of our narrative review is to highlight eventual effects of folate supplementation on LDL-C levels, LDL-C oxidation and atherosclerosis-related complications. A comprehensive literature search was done in electronic database, including PubMed, Web of Science, Cochrane, and Scopus from inception up to January 2024. Based on the available evidence, epidemiological data, pathophysiological observations and meta-analyses of randomized clinical trials suggest that folic acid supplementation may modestly but significantly improve plasma lipid levels, lipid atherogenicity, and atherosclerosis-related early vascular damage, and that folic acid supplementation may significantly reduce the risk of cerebrovascular disease. Considering the low-cost and high safety profile of folic acid, its long-term supplementation could be considered for dyslypidaemic patients in secondary prevention for cardiovascular disease.

The Controversial Role of HCY and Vitamin B Deficiency in Cardiovascular Diseases

Plasma homocysteine (HCY) is an established risk factor for cardiovascular disease CVD and stroke. However, more than two decades of intensive research activities has failed to demonstrate that Hcy lowering through B-vitamin supplementation results in a reduction in CVD risk. Therefore, doubts about a causal involvement of hyperhomocysteinemia (HHcy) and B-vitamin deficiencies in atherosclerosis persist. Existing evidence indicates that HHcy increases oxidative stress, causes endoplasmatic reticulum (ER) stress, alters DNA methylation and, thus, modulates the expression of numerous pathogenic and protective genes. Moreover, Hcy can bind directly to proteins, which can change protein function and impact the intracellular redox state. As most mechanistic evidence is derived from experimental studies with rather artificial settings, the relevance of these results in humans remains a matter of debate. Recently, it has also been proposed that HHcy and B-vitamin deficiencies may promote CVD through accelerated telomere shortening and telomere dysfunction. This review provides a critical overview of the existing literature regarding the role of HHcy and B-vitamin deficiencies in CVD. At present, the CVD risk associated with HHcy and B vitamins is not effectively actionable. Therefore, routine screening for HHcy in CVD patients is of limited value. However, B-vitamin depletion is rather common among the elderly, and in such cases existing deficiencies should be corrected. While Hcy-lowering with high doses of B vitamins has no beneficial effects in secondary CVD prevention, the role of Hcy in primary disease prevention is insufficiently studied. Therefore, more intervention and experimental studies are needed to address existing gaps in knowledge.

Gestational folate deficiency alters embryonic gene expression and cell function

Folic acid is a nutrient essential for embryonic development. Folate deficiency can cause embryonic lethality or neural tube defects and orofacial anomalies. Folate receptor 1 (Folr1) is a folate binding protein that facilitates the cellular uptake of dietary folate. To better understand the biological processes affected by folate deficiency, gene expression profiles of gestational day 9.5 (gd9.5) Folr1^-/- embryos were compared to those of gd9.5 Folr1^+/+ embryos. The expression of 837 genes/ESTs was found to be differentially altered in Folr1^-/- embryos, relative to those observed in wild-type embryos. The 837 differentially expressed genes were subjected to Ingenuity Pathway Analysis. Among the major biological functions affected in Folr1^-/- mice were those related to 'digestive system development/function', 'cardiovascular system development/function', 'tissue development', 'cellular development', and 'cell growth and differentiation', while the major canonical pathways affected were those associated with blood coagulation, embryonic stem cell transcription and cardiomyocyte differentiation (via BMP receptors). Cellular proliferation, apoptosis and migration were all significantly affected in the Folr1^-/- embryos. Cranial neural crest cells (NCCs) and neural tube explants, grown under folate-deficient conditions, exhibited marked reduction in directed migration that can be attributed, in part, to an altered cytoskeleton caused by perturbations in F-actin formation and/or assembly. The present study revealed that several developmentally relevant biological processes were compromised in Folr1^-/- embryos.

Dietary Intake of Homocysteine Metabolism-Related B-Vitamins and the Risk of Stroke: A Dose-Response Meta-Analysis of Prospective Studies

Observational studies regarding the putative associations between dietary intake of homocysteine metabolism-related B-vitamins (vitamin B-6, folate, and vitamin B-12) and stroke risk have yielded inconsistent results. Thus, we conducted a systematic meta-analysis of prospective studies in order to examine the relation between the dietary (from diet and supplements) intake of these B-vitamins and the risk of stroke. PubMed and Web of Science were searched for relevant articles published through to 25 February, 2020, and RR of stroke in relation to dietary intake of vitamin B-6, folate, and vitamin B-12 were pooled using a random-effects model. Eleven publications of 12 prospective studies comprising 389,938 participants and 10,749 cases were included in the final analysis. We found that dietary intake of vitamin B-6 and folate were associated with a reduced risk of stroke, and this inverse association remained significant in studies with >10 y of follow-up periods and among participants without a pre-existing stroke event. A dose-response analysis revealed a linear inverse association between folate and vitamin B-6 intake and the risk of stroke, with a pooled RR of 0.94 (95% CI: 0.90-0.98) and 0.94 (95% CI: 0.89-0.99) for each 100 μg/d increment in folate intake and 0.5 mg/d increment in vitamin B-6 intake, respectively. In contrast, we found no significant association between dietary vitamin B-12 intake and the risk of stroke, with an RR of 1.01 (95% CI: 0.97-1.06) per 3 μg/d increase. In conclusion, our findings suggest that increased intake of vitamin B-6 and folate is associated with a reduced risk of stroke, supporting the notion that increasing habitual folate and vitamin B-6 intake may provide a small but beneficial effect with respect to stroke.

Folic acid delays development of atherosclerosis in low-density lipoprotein receptor-deficient mice

Many studies support the cardioprotective effects of folic acid (FA). We aimed to evaluate the utility of FA supplementation in preventing the development of atherosclerotic in low‐density lipoprotein receptor‐deficient (LDLR−/−) mice and to elucidate the molecular processes underlying this effect. LDLR−/− mice were randomly distributed into four groups: control group, HF group, HF + FA group and the HF + RAPA group. vascular smooth muscle cells (VSMCs) were divided into the following four groups: control group, PDGF group, PDGF + FA group and PDGF + FA + RAPA group. Blood lipid levels, oxidative stress and inflammatory cytokines were measured. Atherosclerosis severity was evaluated with oil red O staining. Haematoxylin and eosin (H&E) staining was used to assess atherosclerosis progression. Immunohistochemical staining was performed with antismooth muscle α‐actin (α‐SMA) antibodies and anti‐osteopontin (OPN) antibodies that demonstrate VSMC dedifferentiation. The protein expression of α‐SMA, OPN and mechanistic target of rapamycin (mTOR)/p70S6K signalling was detected by Western blot analysis. FA and rapamycin reduced serum levels of total cholesterol, triacylglycerol, LDL, inhibiting oxidative stress and the inflammatory response. Oil red O and H&E staining demonstrated that FA and rapamycin inhibited atherosclerosis. FA and rapamycin treatment inhibited VSMC dedifferentiation in vitro and in vivo, and FA and rapamycin attenuated the mTOR/p70S6K signalling pathway. Our findings suggest that FA attenuates atherosclerosis development and inhibits VSMC dedifferentiation in high‐fat‐fed LDLR−/− mice by reduced lipid levels and inhibiting oxidative stress and the inflammatory response through mTOR/p70S6K signalling pathway.

Folic acid prevents cardiac dysfunction and reduces myocardial fibrosis in a mouse model of high-fat diet-induced obesity

Background

Folic acid (FA) is an antioxidant that can reduce reactive oxygen species generation and can blunt cardiac dysfunction during ischemia. We hypothesized that FA supplementation prevents cardiac fibrosis and cardiac dysfunction induced by obesity.

Methods

Six-week-old C57BL6/J mice were fed a high-fat diet (HFD), normal diet (ND), or an HFD supplemented with folic acid (FAD) for 14 weeks. Cardiac function was measured using a transthoracic echocardiographic exam. Phenotypic analysis included measurements of body and heart weight, blood glucose and tissue homocysteine (Hcy) content, and heart oxidative stress status.

Results

HFD consumption elevated fasting blood glucose levels and caused obesity and heart enlargement. FA supplementation in HFD-fed mice resulted in reduced fasting blood glucose, heart weight, and heart tissue Hcy content. We also observed a significant cardiac systolic dysfunction when mice were subjected to HFD feeding as indicated by a reduction in the left ventricular ejection fraction and fractional shortening. However, FAD treatment improved cardiac function. FA supplementation protected against cardiac fibrosis induced by HFD. In addition, HFD increased malondialdehyde concentration of the heart tissue and reduced the levels of antioxidant enzyme, glutathione, and catalase. HFD consumption induced myocardial oxidant stress with amelioration by FA treatment.

Conclusion

FA supplementation significantly lowers blood glucose levels and heart tissue Hcy content and reverses cardiac dysfunction induced by HFD in mice. These functional improvements of the heart may be mediated by the alleviation of oxidative stress and myocardial fibrosis.

Folic acid attenuates homocysteine and enhances antioxidative capacity in atherosclerotic rats

Atherosclerosis is a chronic disease that can seriously endanger human life. Folic acid supplementation modulates several disorders, including atherosclerosis, via its antiapoptotic and antioxidative properties. This study investigated whether folic acid alleviates atherogenesis by restoring homocysteine levels and antioxidative capacity in atherosclerosis Wistar rats. To this end, 28 Wistar rats were randomly divided into 4 groups (7 rats/group) as follows: (i) wild-type group, fed only the AIN-93 semi-purified rodent diet (folic acid: 2.1 mg/kg); (ii) high-fat + folic acid-deficient group (HF+DEF) (folic acid: 0.2 mg/kg); (iii) high-fat + normal folic acid group (folic acid: 2.1 mg/kg); and (iv) high-fat + folic acid-supplemented group (folic acid: 4.2 mg/kg). After 12 weeks, histopathological changes in the atherosclerotic lesions of the aortic arch were determined. In addition, serum folate levels, plasma homocysteine levels, plasma S-adenosyl-homocysteine levels, antioxidant status, oxidant status, and lipid profiles were evaluated. The results show aggravated atherosclerotic lesions in the HF+DEF group. Folic acid supplementation increased concentrations of serum folate. Further, folic acid supplementation increased high-density lipoprotein-cholesterol, decreased plasma homocysteine levels, and improved antioxidant capacity in atherogenic rats. These findings are consistent with the hypothesis that folic acid alleviates atherogenesis by reducing plasma homocysteine levels and improving antioxidant capacity in rats fed a high-fat diet.

Antioxidants in Cardiovascular Therapy: Panacea or False Hope?

Oxidative stress is a key feature of the atherothrombotic process involved in the etiology of heart attacks, ischemic strokes, and peripheral arterial disease. It stands to reason that antioxidants represent a credible therapeutic option to prevent disease progression and thereby improve outcome, but despite positive findings from in vitro studies, clinical trials have failed to consistently show benefit. The aim of this review is to re-appraise the concept of antioxidants in the prevention and management of cardiovascular disease. In particular, the review will explore the reasons behind failed antioxidant strategies with vitamin supplements and will evaluate how flavonoids might improve cardiovascular function despite bioavailability that is not sufficiently high to directly influence antioxidant capacity. As well as reaching conclusions relating to those antioxidant strategies that might hold merit, the major myths, limitations, and pitfalls associated with this research field are explored.

Novel insights on interactions between folate and lipid metabolism

Folate is an essential B vitamin required for the maintenance of AdoMet-dependent methylation. The liver is responsible for many methylation reactions that are used for post-translational modification of proteins, methylation of DNA, and the synthesis of hormones, creatine, carnitine, and phosphatidylcholine. Conditions where methylation capacity is compromised, including folate deficiency, are associated with impaired phosphatidylcholine synthesis resulting in non-alcoholic fatty liver disease and steatohepatitis. In addition, folate intake and folate status have been associated with changes in the expression of genes involved in lipid metabolism, obesity, and metabolic syndrome. In this review, we provide insight on the relationship between folate and lipid metabolism, and an outlook for the future of lipid-related folate research.

Folate and risk of coronary heart disease: a meta-analysis of prospective studies

BACKGROUND AND AIMS

Epidemiologic studies are inconsistent regarding the association between folate and coronary heart disease (CHD) risk. The aim was to perform a meta-analysis to determine whether an association exists between folate and total CHD endpoints in prospective studies.

METHODS AND RESULTS

We searched the PUBMED and EMBASE databases for studies conducted from 1966 through August 2010. Data were independently abstracted by 2 investigators using a standardized protocol. Study-specific risk estimates were combined by using a random effects model. A total of 14 studies were included in the meta-analysis: 7 studies on dietary folate intake and 8 studies on blood folate levels. For dietary intake, the summary relative risk (RR) indicated a significant association between the highest folate intake and reduced risk of CHD (summary RR: 0.69; 95% CI: 0.60, 0.80). Furthermore, an increase in folate intake of 200 ug/day was associated with a 12% decrease in the risk of developing CHD (summary RR: 0.88; 95% CI: 0.82, 0.94). For blood folate levels, we also found a borderline inverse association of highest blood folate levels on CHD risk (summary RR: 0.74; 95% CI: 0.53, 1.02); our dose-response analysis indicated that an increment in blood folate levels of 5 mmol/l was associated with an 8% decrease in the risk of developing CHD (summary RR: 0.92; 95% CI: 0.84, 1.00).

CONCLUSION

This meta-analysis suggests that dietary folate intake and blood folate level are inversely associated with CHD risk.

Nutritional B vitamin deficiency disrupts lipid metabolism causing accumulation of proatherogenic lipoproteins in the aorta adventitia of ApoE null mice

SCOPE

Cardiovascular disease is the major cause of death in the world. Low dietary folate, elevated homocysteine, and high circulating cholesterol are risk factors.

METHODS AND RESULTS

We investigated whether folate and/or B vitamin deficiency would change lipoprotein and fatty acid metabolism and lipid accumulation in the aorta adventitia of ApoE null mice. Mice (n = 10 per group) were fed a control (C; 4%) or high saturated fat (HF; 21%), and high cholesterol (0.15%) diet for 16 weeks. Folate (F-) or folate, B6 and B12 deficiency (F-B-) were imposed on these diets. Feeding a HF diet increased plasma and liver total cholesterol and HDL cholesterol (two- to threefold; p < 0.05). Total cholesterol increased (twofold; p < 0.05) in aorta adventitial lipid in response to HF. Feeding a diet depleted of folate and B vitamins (F-B-) significantly increased cholesterol accumulation in both liver and aorta adventitial lipid (approximately 50-70%; p < 0.05). Moreover, the proportions of fatty acids in hepatic and adventitial lipid was significantly changed by B vitamin depletion, measured as an increase in saturated fatty acids (approximately 15%) and a decrease (approximately 11%) in monounsaturated fatty acids (p < 0.05).

CONCLUSION

B vitamin deficiency perturbs lipid metabolism in ApoE null mice, causing accumulation of proatherogenic cholesterol and fatty acids in the aorta adventitia.

The homocysteine controversy

Mild to moderate hyperhomocysteinemia has been identified as a strong predictor of cardiovascular disease, independent from classical atherothrombotic risk factors. In the last decade, a number of large intervention trials using B vitamins have been performed and have shown no benefit of homocysteine-lowering therapy in high-risk patients. In addition, Mendelian randomization studies failed to convincingly demonstrate that a genetic polymorphism commonly associated with higher homocysteine levels (methylenetetrahydrofolate reductase 677 C>T) is a risk factor for cardiovascular disease. Together, these findings have cast doubt on the role of homocysteine in cardiovascular disease pathogenesis, and the homocysteine hypothesis has turned into a homocysteine controversy. In this review, we attempt to find solutions to this controversy. First, we explain that the Mendelian randomization analyses have limitations that preclude final conclusions. Second, several characteristics of intervention trials limit interpretation and generalizability of their results. Finally, the possibility that homocysteine lowering is in itself beneficial but is offset by adverse side effects of B vitamins on atherosclerosis deserves serious attention. As we explain, such side effects may relate to direct adverse effects of the B-vitamin regimen (in particular, the use of high-dose folic acid) or to proinflammatory and proproliferative effects of B vitamins on advanced atherosclerotic lesions.

Dietary blueberries attenuate atherosclerosis in apolipoprotein E-deficient mice by upregulating antioxidant enzyme expression

Protective effects of blueberries (BB) against atherosclerosis and potential underlying mechanisms in reducing oxidative stress were examined in apoE-deficient (apoE(-/-)) mice. ApoE(-/-) mice were fed an AIN-93G diet (CD) or CD formulated to contain 1% freeze-dried whole BB for 20 wk. The mean lesion area for apoE(-/-) mice fed BB was reduced by 39% (P < 0.001) in the aorta sinus and 58% (P < 0.001) in the descending aorta compared with CD-fed mice. These atheroprotective effects were independent of the serum lipid profile or total antioxidant capacity (as measured by oxygen radical absorbance capacity). The concentration of a biomarker of lipid peroxidation, F(2)-isoprostane, was lower in liver of BB-fed mice (P < 0.05). Genes analyzed by RT-PCR array showed that 4 major antioxidant enzymes in aorta [superoxide dismutase (SOD) 1, SOD2, glutathione reductase (GSR), and thioredoxin reductase 1] were upregulated in BB-fed mice. Enzyme activities of SOD and GSR were greater (P < 0.05) in liver and/or serum of BB-fed mice than those of CD-fed mice. In addition, serum paraoxonase 1 activity in serum of BB-fed mice was also greater than that of CD-fed mice (P < 0.05) at the end of the study. These results suggest a protective effectiveness of BB against atherosclerosis in this apoE(-/-) mouse model. The potential mechanisms may involve reduction in oxidative stress by both inhibition of lipid peroxidation and enhancement of antioxidant defense.

Folic acid mitigated cardiac dysfunction by normalizing the levels of tissue inhibitor of metalloproteinase and homocysteine-metabolizing enzymes postmyocardial infarction in mice

Myocardial infarction (MI) results in significant metabolic derangement, causing accumulation of metabolic by product, such as homocysteine (Hcy). Hcy is a nonprotein amino acid generated during nucleic acid methylation and demethylation of methionine. Folic acid (FA) decreases Hcy levels by remethylating the Hcy to methionine, by 5-methylene tetrahydrofolate reductase (5-MTHFR). Although clinical trials were inconclusive regarding the role of Hcy in MI, in animal models, the levels of 5-MTHFR were decreased, and FA mitigated the MI injury. We hypothesized that FA mitigated MI-induced injury, in part, by mitigating cardiac remodeling during chronic heart failure. Thus, MI was induced in 12-wk-old male C57BL/J mice by ligating the left anterior descending artery, and FA (0.03 g/l in drinking water) was administered for 4 wk after the surgery. Cardiac function was assessed by echocardiography and by a Millar pressure-volume catheter. The levels of Hcy-metabolizing enzymes, cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and 5-MTHFR, were estimated by Western blot analyses. The results suggest that FA administered post-MI significantly improved cardiac ejection fraction and induced tissue inhibitor of metalloproteinase, CBS, CSE, and 5-MTHFR. We showed that FA supplementation resulted in significant improvement of myocardial function after MI. The study eluted the importance of homocysteine (Hcy) metabolism and FA supplementation in cardiovascular disease.

Consumption of hydrogen water prevents atherosclerosis in apolipoprotein E knockout mice

Oxidative stress is implicated in atherogenesis; however most clinical trials with dietary antioxidants failed to show marked success in preventing atherosclerotic diseases. We have found that hydrogen (dihydrogen; H(2)) acts as an effective antioxidant to reduce oxidative stress [I. Ohsawa, M. Ishikawa, K. Takahashi, M. Watanabe, K. Nishimaki, K. Yamagata, K. Katsura, Y. Katayama, S, Asoh, S. Ohta, Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals, Nat. Med. 13 (2007) 688-694]. Here, we investigated whether drinking H(2)-dissolved water at a saturated level (H(2)-water) ad libitum prevents arteriosclerosis using an apolipoprotein E knockout mouse (apoE(-/-)), a model of the spontaneous development of atherosclerosis. ApoE(-/-) mice drank H(2)-water ad libitum from 2 to 6 month old throughout the whole period. Atherosclerotic lesions were significantly reduced by ad libitum drinking of H(2)-water (p=0.0069) as judged by Oil-Red-O staining series of sections of aorta. The oxidative stress level of aorta was decreased. Accumulation of macrophages in atherosclerotic lesions was confirmed. Thus, consumption of H(2)-dissolved water has the potential to prevent arteriosclerosis.

Mechanisms and potential therapeutic targets for folic acid in cardiovascular disease

Folic acid (FA) is a member of the B-vitamin family with cardiovascular roles in homocysteine regulation and endothelial nitric oxide synthase (eNOS) activity. Its interaction with eNOS is thought to be due to the enhancement of tetrahydrobiopterin bioavailability, helping maintain eNOS in its coupled state to favor the generation of nitric oxide rather than oxygen free radicals. FA also plays a role in the prevention of several cardiac and noncardiac malformations, has potent direct antioxidant and antithrombotic effects, and can interfere with the production of the endothelial-derived hyperpolarizing factor. These multiple mechanisms of action have led to studies regarding the therapeutic potential of FA in cardiovascular disease. To date, studies have demonstrated that FA ameliorates endothelial dysfunction and nitrate tolerance and can improve pathological features of atherosclerosis. These effects appear to be homocysteine independent but rather related to their role in eNOS function. Given the growing evidence that nitric oxide synthase uncoupling plays a major role in many cardiovascular disorders, the potential of exogenous FA as an inexpensive and safe oral therapy is intriguing and is stimulating ongoing investigations.