Renal Disease, Homocysteine, and Cardiovascular Complications

Vitamin B12 deficiency in dialysis patients: risk factors, diagnosis, complications, and treatment: A comprehensive review

Vitamin B12 deficiency is a significant concern among patients with end-stage renal disease undergoing dialysis. However, there hasn't been extensive research conducted on this particular patient group. The reported incidence rates vary widely, ranging from 20% to 90%, reflecting the complexity of its diagnosis. Dialysis patients often face multiple nutritional deficiencies, including a lack of essential vitamins, due to factors such as dietary restrictions, impaired absorption, and nutrient loss during dialysis. Diagnosing vitamin B12 deficiency in these patients is challenging, and addressing it is crucial to prevent complications and improve their overall quality of life. This review paper delves into the available body of evidence on vitamin B12 deficiency in dialysis patients, examining the contributing risk factors, diagnostic challenges, potential complications, and available treatment options. It provides a well-rounded perspective on the topic, making it a valuable resource for researchers, healthcare practitioners, and policymakers interested in addressing the nutritional needs of dialysis patients.

Plasma Homocysteine Levels and Cardiovascular Events in Patients With End-Stage Renal Disease: A Systematic Review

BACKGROUND

Patients with chronic renal disease or failure are at a heightened risk of mortality due to cardiovascular disease (CVD), which is a predominant cause of death in this population. Hyperhomocysteinemia is prevalent in patients with end-stage renal disease (ESRD), which may increase their susceptibility to CVD.

METHODS

We conducted a comprehensive search of PubMed, Science Direct, and Google Scholar for articles published between 2003 and February 2023, using a combination of keywords such as "plasma homocysteine levels," "hyperhomocysteinemia," "end-stage renal disease," "renal failure," "kidney failure," "cardiovascular events," "cardiovascular disease," "myocardial infarction," "coronary artery disease," and "stroke." Our inclusion criteria were studies that investigated the association between total homocysteine (Hcy) level and CVD or total mortality, as well as the impact of vitamin supplementation on cardiovascular or mortality risk. We restricted our search to English-language studies that included ESRD patients and provided data on plasma Hcy levels and associated CVD events.

RESULTS

This systematic review includes 11 articles published between 2003 and 2023 that enrolled a total of 3,953 subjects, of whom 79.15% were male patients. All studies included in the review were either quantitative randomized trials or non-randomized studies, such as cross-sectional, cohort, or case-control studies. Of the total studies included, 10 reported either cardiovascular mortality or CVD events, including cardiovascular death, myocardial infarction (MI), angina, and stroke. One study reported the CVD risk score of the patients, and most of them had higher total homocysteine (tHcy) levels. Overall, a total of 817 CVD events were reported across the studies.

CONCLUSION

In conclusion, the relationship between Hcy and cardiovascular events in ESRD patients is not straightforward and requires further research. However, our review suggests that Hcy could be a predictor of cardiovascular events in this population, and its nutritional characteristics as well as other associated comorbidities may contribute to its inverse association with outcomes.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Gut Microbiome, Functional Food, Atherosclerosis, and Vascular Calcifications-Is There a Missing Link?

The gut microbiome is represented by the genome of all microorganisms (symbiotic, potential pathogens, or pathogens) residing in the intestine. These ecological communities are involved in almost all metabolic diseases and cardiovascular diseases are not excluded. Atherosclerosis, with a continuously increasing incidence in recent years, is the leading cause of coronary heart disease and stroke by plaque rupture and intraplaque hemorrhage. Vascular calcification, a process very much alike with osteogenesis, is considered to be a marker of advanced atherosclerosis. New evidence, suggesting the role of dietary intake influence on the diversity of the gut microbiome in the development of vascular calcifications, is highly debated. Gut microbiota can metabolize choline, phosphatidylcholine, and L-carnitine and produce vasculotoxic metabolites, such as trimethylamine-N-oxide (TMAO), a proatherogenic metabolite. This review article aims to discuss the latest research about how probiotics and the correction of diet is impacting the gut microbiota and its metabolites in the atherosclerotic process and vascular calcification. Further studies could create the premises for interventions in the microbiome as future primary tools in the prevention of atherosclerotic plaque and vascular calcifications.

Homocysteine-Lowering Interventions in Chronic Kidney Disease

The incidence of cardiovascular events and mortality is higher in patients with chronic kidney disease (CKD) compared to the general population. Homocysteine (Hcy) appears to be an independent risk factor for cardiovascular diseases in general populations and patients with CKD. Further, hyperhomocysteinemia can cause endothelial damage and increase the activity and production of coagulation factors, and its prevalence among patients with end-stage renal disease is approximately 85%-100%. Most treatments, which lower Hcy levels and have been considered in previous studies, include folic acid, B vitamins, omega-3 fatty acids, and N-acetylcysteine. However, the effect of therapies that can decrease Hcy levels and thus cardiovascular events in these patients is still unclear. The results are conflicting and require further investigation. To guide treatment decisions and improve patient outcomes, multiple databases were searched, including Web of Science, PubMed, and Medline to summarize the available evidence (i.e., clinical trial and meta-analyses) on Hcy-lowering interventions and cardiovascular events.

Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies

Obesity is a worldwide epidemic responsible for 5% of global mortality. The risks of developing other key metabolic disorders like diabetes, hypertension and cardiovascular diseases (CVDs) are increased by obesity, causing a great public health concern. A series of epidemiological studies and animal models have demonstrated a relationship between the importance of vitamin B12 (B12) and various components of metabolic syndrome. High prevalence of low B12 levels has been shown in European (27%) and South Indian (32%) patients with type 2 diabetes (T2D). A longitudinal prospective study in pregnant women has shown that low B12 status could independently predict the development of T2D five years after delivery. Likewise, children born to mothers with low B12 levels may have excess fat accumulation which in turn can result in higher insulin resistance and risk of T2D and/or CVD in adulthood. However, the independent role of B12 on lipid metabolism, a key risk factor for cardiometabolic disorders, has not been explored to a larger extent. In this review, we provide evidence from pre-clinical and clinical studies on the role of low B12 status on lipid metabolism and insights on the possible epigenetic mechanisms including DNA methylation, micro-RNA and histone modifications. Although, there are only a few association studies of B12 on epigenetic mechanisms, novel approaches to understand the functional changes caused by these epigenetic markers are warranted.

Folic Acid and Vitamin B12 Administration in CKD, Why Not?

Patients affected by chronic kidney disease (CKD) or end-stage renal disease (ESRD) experience a huge cardiovascular risk and cardiovascular events represent the leading causes of death. Since traditional risk factors cannot fully explain such increased cardiovascular risk, interest in non-traditional risk factors, such as hyperhomocysteinemia and folic acid and vitamin B12 metabolism impairment, is growing. Although elevated homocysteine blood levels are often seen in patients with CKD and ESRD, whether hyperhomocysteinemia represents a reliable cardiovascular and mortality risk marker or a therapeutic target in this population is still unclear. In addition, folic acid and vitamin B12 could not only be mere cofactors in the homocysteine metabolism; they may have a direct action in determining tissue damage and cardiovascular risk. The purpose of this review was to highlight homocysteine, folic acid and vitamin B12 metabolism impairment in CKD and ESRD and to summarize available evidences on hyperhomocysteinemia, folic acid and vitamin B12 as cardiovascular risk markers, therapeutic target and risk factors for CKD progression.

Folic Acid and Homocysteine in Chronic Kidney Disease and Cardiovascular Disease Progression: Which Comes First?

Background

Hyperhomocysteinemia (Hhcy) occurs in about 85% of chronic kidney disease (CKD) patients because of impaired renal metabolism and reduced renal excretion. Folic acid (FA), the synthetic form of vitamin B₉, is critical in the conversion of homocysteine (Hcy) to methionine. If there is not enough intake of FA, there is not enough conversion, and Hcy levels are raised.

Summary

Hhcy is regarded as an independent predictor of cardiovascular morbidity and mortality in end-stage renal disease. Hhcy exerts its pathogenic action on the main processes involved in the progression of vascular damage. Research has shown Hhcy suggests enhanced risks for inflammation and endothelial injury which lead to cardiovascular disease (CVD), stroke, and CKD. FA has also been shown to improve endothelial function without lowering Hcy, suggesting an alternative explanation for the effect of FA on endothelial function. Recently, the role of FA and Hhcy in CVD and in CKD progression was renewed in some randomized trials.

Key Messages

In the general population and in CKD patients, it remains a topic of discussion whether any beneficial effects of FA therapy are to be referred to its direct effect or to a reduction of Hhcy. While waiting for the results of confirmatory trials, it is reasonable to consider FA with or without methylcobalamin supplementation as appropriate adjunctive therapy in patients with CKD.

Homocysteine and hydrogen sulfide in epigenetic, metabolic and microbiota related renovascular hypertension

Over the past several years, hydrogen sulfide (H₂S) has been shown to be an important player in a variety of physiological functions, including neuromodulation, vasodilation, oxidant regulation, inflammation, and angiogenesis. H₂S is synthesized primarily through metabolic processes from the amino acid cysteine and homocysteine in various organ systems including neuronal, cardiovascular, gastrointestinal, and kidney. Derangement of cysteine and homocysteine metabolism and clearance, particularly in the renal vasculature, leads to H₂S biosynthesis deregulation causing or contributing to existing high blood pressure. While a variety of environmental influences, such as diet can have an effect on H₂S regulation and function, genetic factors, and more recently epigenetics, also have a vital role in H₂S regulation and function, and therefore disease initiation and progression. In addition, new research into the role of gut microbiota in the development of hypertension has highlighted the need to further explore these microorganisms and how they influence the levels of H₂S throughout the body and possibly exploiting microbiota for use of hypertension treatment. In this review, we summarize recent advances in the field of hypertension research emphasizing renal contribution and how H₂S physiology can be exploited as a possible therapeutic strategy to ameliorate kidney dysfunction as well as to control blood pressure.

Hyperhomocysteinaemia as a potential marker of early renal function decline in middle-aged Asian people without chronic kidney disease

PURPOSE

High levels of serum total homocysteine (tHcy), often observed in chronic kidney disease (CKD) patients, are a risk factor for cardiovascular disease. However, little is known about the relationship between tHcy and renal function in healthy individuals. We examined whether tHcy levels are related to renal function in Asian individuals without CKD.

METHODS

This cross-sectional study examined 2032 subjects, aged 40-64 years. Individuals with kidney diseases or other conditions that could affect tHcy were excluded. Renal function was determined by estimated glomerular filtration rate (eGFR) from levels of serum creatinine (sCr) and cystatin C.

RESULTS

Age, tHcy, sCr, and cystatin C of the subjects were 54.1 ± 6.0 years, 9.5 (8.0-11.4) μmol/L, 0.81 ± 0.1 mg/dL, and 0.82 ± 0.1 mg/L, respectively. In a multiple linear regression analysis, tHcy was a significant independent determinant of sCr and cystatin C in men (β = 0.206 and β = 0.282, respectively) and women (β = 0.247 and β = 0.229, respectively). Highest tHcy levels were independently associated with increased cystatin C (>s1.10 mg/L) with an odds ratio (OR) of 5.00 [95% confidence interval (CI) 2.81-8.09] and decreased eGFR (<90 mL/min/1.73 m(2)) with an OR of 1.69 (95% CI 1.36-2.11) compared to tHcy levels in the 1st-3rd quartiles.

CONCLUSIONS

Higher levels of tHcy are independently associated with sCr and cystatin C elevation. Our study suggests that tHcy levels may be influenced by renal function in Asian populations without CKD. Future studies are needed to define the role of tHcy in renal function.

Homocysteine in renovascular complications: hydrogen sulfide is a modulator and plausible anaerobic ATP generator

Homocysteine (Hcy) is a non-protein amino acid derived from dietary methionine. High levels of Hcy, known as hyperhomocysteinemia (HHcy) is known to cause vascular complications. In the mammalian tissue, Hcy is metabolized by transsulfuration enzymes to produce hydrogen sulfide (H2S). H2S, a pungent smelling gas was previously known for its toxic effects in the central nervous system, recent studies however has revealed protective effects in a variety of diseases including hypertension, diabetes, inflammation, atherosclerosis, and renal disease progression and failure. Interestingly, under stress conditions including hypoxia, H2S can reduce metabolic demand and also act as a substrate for ATP production. This review highlights some of the recent advances in H2S research as a potential therapeutic agent targeting renovascular diseases associated with HHcy.

Low-dose B vitamins supplementation ameliorates cardiovascular risk: a double-blind randomized controlled trial in healthy Chinese elderly

PURPOSE

We investigated whether daily supplementation with low-dose B vitamins in the healthy elderly population improves the Framingham risk score (FRS), a predictor of cardiovascular disease risk.

METHODS

Between 2007 and 2012, a double-blind randomized controlled trial was conducted in a rural area of North China. In all, 390 healthy participants aged 60-74 were randomly allocated to receive daily vitamin C (50 mg; control group) or vitamin C plus B vitamins (400 µg folic acid, 2 mg B6, and 10 µg B12; treatment group) for 12 months. FRSs were calculated for all 390 subjects.

RESULTS

Folate and vitamin B12 plasma concentrations in the treatment group increased by 253 and 80%, respectively, after 6 months, stopped increasing with continued supplementation after 12 months and returned to baseline levels 6 months after supplementation cessation. Compared with the control group, there was no significant effect of B vitamin supplementation on FRSs after 6 months (mean difference -0.38; 95% CI -1.06, 0.31; p = 0.279), whereas a significant effect of supplementation was evident after 12 months (reduced magnitude 7.6%; -0.77; 95% CI -1.47, -0.06; p = 0.033). However, this reduction disappeared 6 months after supplementation stopped (-0.07; 95% CI -0.80, 0.66; p = 0.855). The reduction in FRS 12 months after supplementation was more pronounced in individuals with a folate deficiency (10.4%; -1.30; 95% CI -2.54, -0.07; p = 0.039) than in those without (4.1%; -0.38; 95% CI -1.12, 0.36; p = 0.313). B vitamins increased high-density lipoprotein cholesterol by 3.4% after 6 months (0.04; 95% CI -0.02, 0.10; p = 0.155) and by 9.2% after 12 months (0.11; 95 % CI 0.04, 0.18; p = 0.003). Compared with the control group, this change in magnitude decreased to 3.3% (0.04; 95 % CI -0.02, 0.10; p = 0.194) 6 months after supplementation cessation.

CONCLUSIONS

Daily supplementation with a low-dose of B vitamins for 12 months reduced FRS, particularly in healthy elderly subjects with a folate deficiency. These reduced effects declined after supplementation cessation, indicating a need for persistent supplementation to maintain the associated benefits.

Altered folate receptor 2 expression in uraemic patients on haemodialysis: implications for folate resistance

BACKGROUND

Folate therapy reduces, but does not normalize homocysteine (Hcy) levels, frequently elevated in chronic kidney disease (CKD). The mechanisms of this folate resistance are unknown. Cellular acquisition of folate is mediated by folate receptors (FRs), whose expression is also modulated by folate status, through an Hcy-dependent regulation mechanism involving heterogeneous nuclear ribonucleoprotein-E1 (hnRNP-E1). Our objective was to evaluate whether an alteration of the FR2 (the form present in nucleated blood cells) expression is present in CKD patients on haemodialysis (HD), and its susceptibility to folate treatment.

METHODS

A population of chronic uraemic patients on HD was enrolled, along with a control group, and studies on FR2 receptor expression and related items were performed in plasma and mononuclear cells from peripheral blood. A subgroup of patients was treated with methyltetrahydrofolate for 1 month.

RESULTS

In HD, there was a significant reduction in FR2 protein expression compared with controls, not correlated with Hcy concentrations, while its mRNA levels were significantly increased. After folate treatment, there was a significant mRNA decrease, in the absence of significant changes in receptor protein expression. hnRNP-E1 gene and protein expression levels increased pre-treatment, while decreased post-treatment.

CONCLUSIONS

In HD, FR2 expression is altered in peripheral mononuclear cells, since its levels are decreased and are not responsive to variations in Hcy concentration, while the intracellular machinery (receptor mRNA and hnRNP-E1), possibly triggering its regulation, is conserved. These findings provide insight into the mechanisms of folate resistance in uraemia.

[Cognitive impairment and chronic kidney disease: which links?]

Ageing of the population leads to an increase of cognitive disorders and chronic renal failure incidence. Compared to the general population, prevalence of cognitive impairment is more important in renal failure patients, especially in dialyzed patients. No direct link has been established between renal failure and cognitive impairment. The care of older and older patients and the high frequency of vascular risk factors, in particular hypertension and diabetes, partially explain the prevalence of vascular dementia and Alzheimer disease in this population. Other factors as the anemia, phosphocalcic metabolism disorders facilitate the cognitive impairment. The present work reviews the links existing between chronic renal failure and cognitive impairment.

Homocysteine as a risk factor for cardiovascular disease in patients treated by dialysis: a meta-analysis

BACKGROUND

In the general population, increased homocysteine concentrations are a risk factor for cardiovascular disease and mortality. However, it is not known whether this also applies to patients with end-stage renal disease.

STUDY DESIGN

Meta-analysis of retrospective (11 studies including 1,506 individuals), prospective observational studies (12 studies including 1,975 individuals), and intervention trials (5 studies including 1,642 dialysis patients). Analyses were carried out separately, according to the study design.

SETTING & POPULATION

Studies of patients with end-stage renal disease treated by means of hemodialysis or peritoneal dialysis.

SELECTION CRITERIA FOR STUDIES

Studies investigating the association between total homocysteine level and cardiovascular disease or total mortality or the influence of vitamin supplementation on cardiovascular or mortality risk.

INTERVENTION

In intervention studies, vitamin preparations with folic acid alone or in combination with other vitamins, such as vitamin B(12) and B(6), were used.

OUTCOMES

In retrospective studies, cases are patients with cardiovascular diseases. Outcomes for prospective observational and intervention studies are cardiovascular events and total mortality.

RESULTS

In retrospective studies, there was no significant overall difference in homocysteine concentrations between cases and controls (weighted mean difference in homocysteine, 2.82 micromol/L; 95% confidence interval [CI], -2.22 to 7.86; P = 0.3). The pooled overall risk estimate for prospective observational studies suggests no association between homocysteine level (5-micromol/L increase) and total mortality (hazard ratio [HR], 1.02; 95% CI, 0.93 to 1.12; P = 0.7), but there was an association with cardiovascular events (HR, 1.09; 95% CI, 1.03 to 1.14; P = 0.001). In subgroup analysis of patients not receiving vitamins, an increase in homocysteine level was associated with increased mortality (HR, 1.07; 95% CI, 1.02 to 1.13; P = 0.01). For intervention trials with B vitamins, there was a significant risk reduction for cardiovascular disease (relative risk, 0.73; 95% CI, 0.56 to 0.94; P = 0.02), but no risk reduction for total mortality or the composite end point including total mortality (relative risk, 1.01; 95% CI, 0.88 to 1.15; P = 0.9).

LIMITATIONS

Many studies are small, which may lead to the observed heterogeneity. Some intervention trials are neither placebo controlled nor randomized. Separate analyses for specific end points and patients treated by means of hemodialysis or peritoneal dialysis were not possible.

CONCLUSION

Total homocysteine level may be a risk factor for cardiovascular events and total mortality in patients with end-stage renal disease not receiving vitamin supplementation or folic acid food fortification. There may be a potential for reducing cardiovascular disease in this population by folic acid supplementation.

Chronic Renal Dysfunction as an Independent Risk Factor for the Development of Cardiovascular Disease

Cardiac disease is the leading cause of death in patients having end-stage renal disease (ESRD). Patients with ESRD have a higher risk for developing coronary artery disease (CAD) than one would estimate from the presence of traditional risk factors such as hypertension, diabetes, hyperlipidemia, and cigarette smoking. Patients with milder forms of renal dysfunction who do not require dialysis also appear to have an increased risk for CAD. ESRD is associated with anemia, hyperhomocystinemia, increased calcium-phosphate product, hypoalbuminemia, increased troponin, increased markers of inflammation, increased oxidant stress, and decreased nitric oxide activity, factors that could contribute to increased CAD risk. Patients with ESRD require aggressive management of traditional risk factors for CAD, which include hypertension, hyperlipidemia, hyperhomocystinemia, and hypercoagulability. Milder forms of renal dysfunction could also be predictors of occult CAD and should be screened for in assessing cardiac risk in asymptomatic individuals.

Elevated plasma homocysteine is positively associated with age independent of C677T mutation of the methylenetetrahydrofolate reductase gene in selected Egyptian subjects

This study aimed to evaluate the plasma homocysteine (tHcy) and folate levels as well as the methylenetetrahydrofolate reductase (MTHFR) C677T mutation in Egyptian subjects. Fasting total homocysteine (tHcy) and the (MTHFR) C677T mutation were evaluated in 50 healthy young control males (age 35-50 years, Gp1), 50 elderly males age ranged between 50-75 years without any cardiovascular diseases (Gp2) and 50 age matched elderly male patients (Gp3) with myocardial infarction. There was a significant elevation of plasma tHcy in the patients group and Gp2 compared to the young control group (Gp1). The total plasma homocysteine (tHcy) in the control group, Gp2 and the patients group were 17.99 +/- 9.76, 39.9 +/- 20.06 and 43.8 +/- 13.13 mumol/L respectively. The frequency of the TT genotype was 12% in the patient group compared with 8 % in the young healthy controls and elderly subjects (Gp2). The CT genotype constituted 36%, 48% and 44% in the control group, Gp2 and the patients group respectively. There was no significant difference in the occurrence of the TT genotype between the studied groups. Plasma tHcy correlated positively with age, total cholesterol, urea, creatinine, glucose levels and carotid intimal thickness (CIT). Conclusion: The MTHFR mutation does not seem to be associated with either high tHcy or the occurrence of cardiovascular diseases in the studied patients. However, elevated plasma tHcy level positively correlates with age in the studied subjects.