Vitamin B6 and oxalic acid in clinical nephrology

Vitamin Supplement Use in Patients With CKD: Worth the Pill Burden?

All vitamins play essential roles in various aspects of body function and systems. Patients with chronic kidney disease (CKD), including those receiving dialysis, may be at increased risk of developing vitamin deficiencies due to anorexia, poor dietary intake, protein energy wasting, restricted diet, dialysis loss, or inadequate sun exposure for vitamin D. However, clinical manifestations of most vitamin deficiencies are usually subtle or undetected in this population. Testing for circulating levels is not undertaken for most vitamins except folate, B12, and 25-hydroxyvitamin D because assays may not be available or may be costly to perform and do not always correlate with body stores. The last systematic review through 2016 was performed for the Kidney Disease Outcome Quality Initiative (KDOQI) 2020 Nutrition Guideline update, so this article summarizes the more recent evidence. We review the use of vitamins supplementation in the CKD population. To date there have been no randomized trials to support the benefits of any vitamin supplementation for kidney, cardiovascular, or patient-centered outcomes. The decision to supplement water-soluble vitamins should be individualized, taking account the patient's dietary intake, nutritional status, risk of vitamins deficiency/insufficiency, CKD stage, comorbid status, and dialysis loss. Nutritional vitamin D deficiency should be corrected, but the supplementation dose and formulation need to be personalized, taking into consideration the degree of 25-hydroxyvitamin D deficiency, parathyroid hormone levels, CKD stage, and local formulation. Routine supplementation of vitamins A and E is not supported due to potential toxicity. Although more trial data are required to elucidate the roles of vitamin supplementation, all patients with CKD should undergo periodic assessment of dietary intake and aim to receive various vitamins through natural food sources and a healthy eating pattern that includes vitamin-dense foods.

Abnormal Porphyrin Metabolism in Autism Spectrum Disorder and Therapeutic Implications

Autism spectrum disorder (ASD) is a mosaic of neurodevelopmental conditions composed of early-onset social interaction and communication deficits, along with repetitive and/or restricted patterns of activities, behavior, and interests. ASD affects around 1% of children worldwide, with a male predominance. Energy, porphyrin, and neurotransmitter homeostasis are the key metabolic pathways affected by heavy metal exposure, potentially implicated in the pathogenesis of ASD. Exposure to heavy metals can lead to an altered porphyrin metabolism due to enzyme inhibition by heavy metals. Heavy metal exposure, inborn genetic susceptibility, and abnormal thiol and selenol metabolism may play a significant role in the urinary porphyrin profile anomalies observed in ASD. Altered porphyrin metabolism in ASD may also be associated with, vitamin B6 deficiency, hyperoxalemia, hyperhomocysteinemia, and hypomagnesemia. The present review considers the abnormal porphyrin metabolism in ASD in relation to the potential pathogenic mechanism and discusses the possible metabolic therapies such as vitamins, minerals, cofactors, and antioxidants that need to be explored in future research. Such targeted therapeutic therapies would bring about favorable outcomes such as improvements in core and co-occurring symptoms.

Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

Chronic kidney disease (CKD) is a significant global public health concern associated with high morbidity and mortality rates. The maintenance of oxalate homeostasis plays a critical role in preserving kidney health, particularly in the context of CKD. Although the relationship between oxalate and kidney stone formation has been extensively investigated, our understanding of oxalate homeostasis in non-stone-forming CKD remains limited. This review aims to present an updated analysis of the existing literature, focusing on the intricate mechanisms involved in oxalate homeostasis in patients with CKD. Furthermore, it explores the key factors that influence oxalate accumulation and discusses the potential role of oxalate in CKD progression and prognosis. The review also emphasizes the significance of the gut-kidney axis in CKD oxalate homeostasis and provides an overview of current therapeutic strategies, as well as potential future approaches. By consolidating important findings and perspectives, this review offers a comprehensive understanding of the present knowledge in this field and identifies promising avenues for further research.

Physiological Associations between Vitamin B Deficiency and Diabetic Kidney Disease

The number of people living with chronic kidney disease (CKD) is growing as our global population continues to expand. With aging, diabetes, and cardiovascular disease being major harbingers of kidney disease, the number of people diagnosed with diabetic kidney disease (DKD) has grown concurrently. Poor clinical outcomes in DKD could be influenced by an array of factors-inadequate glycemic control, obesity, metabolic acidosis, anemia, cellular senescence, infection and inflammation, cognitive impairment, reduced physical exercise threshold, and, importantly, malnutrition contributing to protein-energy wasting, sarcopenia, and frailty. Amongst the various causes of malnutrition in DKD, the metabolic mechanisms of vitamin B (B1 (Thiamine), B2 (Riboflavin), B3 (Niacin/Nicotinamide), B5 (Pantothenic Acid), B6 (Pyridoxine), B8 (Biotin), B9 (Folate), and B12 (Cobalamin)) deficiency and its clinical impact has garnered greater scientific interest over the past decade. There remains extensive debate on the biochemical intricacies of vitamin B metabolic pathways and how their deficiencies may affect the development of CKD, diabetes, and subsequently DKD, and vice-versa. Our article provides a review of updated evidence on the biochemical and physiological properties of the vitamin B sub-forms in normal states, and how vitamin B deficiency and defects in their metabolic pathways may influence CKD/DKD pathophysiology, and in reverse how CKD/DKD progression may affect vitamin B metabolism. We hope our article increases awareness of vitamin B deficiency in DKD and the complex physiological associations that exist between vitamin B deficiency, diabetes, and CKD. Further research efforts are needed going forward to address the knowledge gaps on this topic.

Hyperhomocysteinemia in acute hepatic porphyria (AHP) and implications for treatment with givosiran

INTRODUCTION

Homocysteine is a sulfur-containing amino acid formed in the intermediary metabolism of methionine. Amino acid metabolism and heme biosynthesis pathways are complexly intertwined. Plasma homocysteine elevation, hyperhomocysteinemia (HHcy), has been reported in patients with acute hepatic porphyria (AHP), a family of rare genetic disorders caused by defects in hepatic heme biosynthesis.

AREAS COVERED

This article summarizes published case series in which givosiran, a subcutaneously administered small interfering RNA approved for AHP treatment, appeared to exacerbate dysregulated homocysteine metabolism in patients with AHP. A comprehensive exploratory analysis of ENVISION trial data demonstrated that on a population level, givosiran increased homocysteine but with wide interpatient variations, and there is no proof of correlations between HHcy and changes in efficacy or safety of givosiran.

EXPERT OPINION

The strong correlation and co-increase of homocysteine and methionine suggest that HHcy associated with givosiran is likely attributable to the impaired trans-sulfuration pathway catalyzed by cystathionine β-synthase, which uses vitamin B6 as a cofactor. Data-based consensus supports monitoring total plasma homocysteine and vitamin B6, B12, and folate levels before and during givosiran treatment; supplementing with pyridoxine/vitamin B6 in patients with homocysteine levels >100 μmol/L; and involving patients with homocysteine levels >30 μmol/L in decisions to supplement.

Hyperhomocysteinemia in patients with acute porphyrias: A potentially dangerous metabolic crossroad?

BACKGROUND

Acute porphyrias (AP) are characterized by heme deficiency and induction of hepatic 5-aminolevulinate synthase (ALAS1). Hyperhomocysteinemia (HHcy) is associated with endothelial damage, neurotoxicity and increased risk for vascular diseases. Interestingly, both heme biosynthesis and sulphur amino acid metabolism require vitamin B6, (Pyridoxal-phosphate, PLP) an important cofactor of ALAS1 and of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL) enzymes that catabolize homocysteine (Hcy). Moreover, heme itself is an important cofactor for CBS.

AIM

to assess plasma Hcy status and HHcy main determinants in patients with AP.

MATERIALS AND METHODS

A total of 46 patients with AP (31 with Acute Intermittent Porphyria,15 with Variegate Porphyria) were assessed for clinical status (symptomatic vs. asymptomatic), serum Hcy, Cysteine (Cys), Vit.B6, Vit.B12, red blood cell folates and urinary delta-aminolevulinic acid (ALA) and porphobilinogen(PBG) levels (mean of six measurements).

RESULTS

Symptomatic AP patients had significantly higher urinary ALA and PBG levels, plasma Hcy, HHcy prevalence and Hcy/Cys ratio when compared to asymptomatic carriers of AP. Even though no significant correlation was observed between ALA/PBG urinary levels and serum Hcy levels, patients with higher levels of ALA and PBG had significantly higher levels of Hcy, a higher prevalence of moderate-to severe HHcy and serum PLP levels below the 25^th percentile of a reference assessment with 300 healthy Italian subjects(<45nmol/L).

CONCLUSIONS

Most patients with symptomatic AP present HHcy resulting from alterations in sulphur amino acid metabolism. HHcy may represent an indirect marker of ALAS1 induction and its prevalence may be suggestive of a role of HHcy in the pathogenesis and/or comorbidities of AP.

Nutrients and Porphyria: An Intriguing Crosstalk

Porphyria refers to a group of fascinating diseases from a metabolic and nutritional standpoint as it provides an example of how metabolic manipulation can be used for therapeutic purposes. It is characterized by defects in heme synthesis, particularly in the erythrocytes and liver. Specific enzymes involved in heme biosynthesis directly depend on adequate levels of vitamins and minerals in the tissues. Moreover, micronutrients that are required for producing succinyl CoA and other intermediates in the Krebs (TCA) cycle are indirectly necessary for heme metabolism. This review summarizes articles that describe the nutritional status, supplements intake, and dietary practices of patients affected by porphyria, paying special attention to the therapeutic use of nutrients that may help or hinder this group of diseases.

Low Plasma Hydrogen Sulfide Is Associated with Impaired Renal Function and Cardiac Dysfunction

BACKGROUND

Chronic kidney disease (CKD) has been proposed to associate with decreased hydrogen sulfide (H2S) level. Nevertheless, the role of H2S in the pathogenesis of CKD has not been fully investigated. Our study aimed to investigate the plasma level of endogenous H2S in patients with different stages of CKD, and to identify the role of H2S in the progression of CKD and its relationship with cardiovascular diseases.

METHODS

A total of 157 non-dialysis CKD patients were recruited in our study, with 37 age- and sex-matched healthy individuals as control. Plasma concentration of H2S was measured with spectrophotometry. Sulfhemoglobin, the integration of H2S and hemoglobin, was characterized and measured by dual wavelength spectrophotometry. Serum levels of homocysteine (Hcy), cardiac troponin T (cTnT), and N-terminal pro B type natriuretic peptide were measured using automated analyzers. Conventional transthoracic echocardiography was performed and left ventricular ejection fraction (LVEF) was analyzed as a sensitive parameter of cardiac dysfunction.

RESULTS

The plasma H2S level (μmol/L) in CKD patients was significantly lower than those in healthy controls (7.32 ± 4.02 vs. 14.11 ± 5.24 μmol/L, p < 0.01). Plasma H2S level was positively associated with estimated glomerular filtration rate (eGFR; ρ = 0.577, p < 0.01) and negatively associated with plasma indoxyl sulfate concentration (ρ = -0.554, p < 0.01). The mRNA levels of cystathionine β-synthase and cystathionine γ-lyase, 2 catalytic enzymes of H2S formation, were significantly lower in blood mononuclear cells of CKD patients with respect to controls; however, the mRNA level of 3-mercaptopyruvate sulfurtransferase, as another H2S-producing enzyme, was significantly higher in CKD patients. The serum concentration of Hcy, acting as the substrate of H2S synthetase, was higher in the CKD group (p < 0.01). Specifically, the content of serum Hcy in CKD stages 3-5 patients was significantly higher than that in CKD stages 1-2, indicating an increasing trend of serum Hcy with the decline of renal function. Examination of ultrasonic cardiogram revealed a negative -correlation between plasma H2S level and LVEF (ρ = -0.204, p < 0.05) in CKD patients. The H2S level also correlated negatively with cTnT concentration (ρ = -0.249, p < 0.01).

CONCLUSIONS

Plasma H2S level decreased with the decline of eGFR, which may contribute to the cardiac dysfunction in CKD -patients.

Vitamin B-6, Independent of Homocysteine, Is a Significant Factor in Relation to Inflammatory Responses for Chronic Kidney Disease and Hemodialysis Patients

The purpose of this study was to investigate whether plasma pyridoxal 5′-phosphate (PLP) and homocysteine were dependent on or independent of each other in order to be associated with inflammatory markers in patients with chronic kidney disease (CKD) or those receiving hemodialysis treatment. This was a cross-sectional study. Sixty-eight stage 2–5 CKD patients and 68 hemodialysis patients had one time fasting blood drawn for measurements of plasma PLP, pyridoxal (PL), homocysteine, and several inflammatory markers. Early CKD stage (stages 2-3) patients showed significantly lower plasma PLP levels and homocysteine concentrations than patients in an advanced CKD stage (stages 4-5) and those undergoing hemodialysis. Plasma PLP significantly correlated with CRP levels (partial r_s = −0.21, p < 0.05) and plasma PL significantly correlated with IL-10 levels (partial r_s = −0.24, p < 0.01), while plasma PLP plus PL significantly correlated with both CRP levels (partial r_s = −0.20, p < 0.05) and interleukin-1β (partial r_s = 0.22, p < 0.05) levels after adjusting for plasma homocysteine and other potential confounders. Plasma homocysteine displayed no significant correlations with any inflammatory markers. Vitamin B-6 status, rather than homocysteine, appeared to be a significant factor in relation to inflammatory responses for CKD and hemodialysis patients.

Hydrosoluble vitamins

The hydrosoluble vitamins are a group of organic substances that are required by humans in small amounts to prevent disorders of metabolism. Significant progress has been made in our understanding of the biochemical, physiologic and nutritional aspects of the water-soluble vitamins. Deficiency of these particular vitamins, most commonly due to inadequate nutrition, can result in disorders of the nervous system. Many of these disorders have been successfully prevented in developed countries; however, they are still common in developing countries. Of the hydrosoluble vitamins, the nervous system depends the most on vitamins B and C (ascorbic acid) for proper functioning. The B group vitamins include thiamin (vitamin B1), riboflavin (vitamin B2), niacin or niacinamide (vitamin B3), pantothenic acid (vitamin B5), pyridoxine or pyridoxal (vitamin B6) and cobalamin (vitamin B12). Clinical findings depend upon the deficiency of the underlying vitamin; generally, deficiency symptoms are seen from a combination rather than an isolated vitamin deficiency. True hereditary metabolic disorders and serious deficiency-associated diseases are rare and in general limited to particular geographic regions and high-risk groups. Their recognition is truly important as that determines the appropriate therapeutic management. The general availability of vitamins to practically everyone and several national health programs have saved many lives and prevented complications. However, there has been some apprehension for several decades about how harmless generous dosages of these vitamins are. Overt overdosages can cause vitamin toxicity affecting various body systems including the nervous system. Systemically, vitamin toxicity is associated with nonspecific symptoms, such as nausea, vomiting, diarrhea, and skin rash which are common with any acute or chronic vitamin overdose. At a national level, recommended daily allowances for vitamins become policy statements. Nutrition policy has far reaching implications in the food industry, in agriculture, and in food provision programs. Overall, water-soluble vitamins are complex molecular structures and even today, many areas of vitamin biochemistry still need to be explored. Many readers might be of the opinion that the classic forms of nutritional deficiency diseases have faded into the background of interesting history. This has caused their diverse symptoms to be neglected by most modern physicians since vitamin enrichment of many foods automatically erases them from their consideration in differential diagnosis. Vitamin B12 and folic acid deficiencies are discussed in other chapters.

A metabolomic study of low estimated GFR in non-proteinuric type 2 diabetes mellitus

AIMS/HYPOTHESIS

We carried out a urinary metabolomic study to gain insight into low estimated GFR (eGFR) in patients with non-proteinuric type 2 diabetes.

METHODS

Patients were identified as being non-proteinuric using multiple urinalyses. Cases (n = 44) with low eGFR and controls (n = 46) had eGFR values <60 and ≥60 ml min(-1) 1.73 m(-2), respectively, as calculated using the Modification of Diet in Renal Disease formula. Urine samples were analysed by liquid chromatography/mass spectrometry (LC/MS) and GC/MS. False discovery rates were used to adjust for multiple hypotheses testing, and selection of metabolites that best predicted low eGFR status was achieved using least absolute shrinkage and selection operator logistic regression.

RESULTS

Eleven GC/MS metabolites were strongly associated with low eGFR after correction for multiple hypotheses testing (smallest adjusted p value = 2.62 × 10(-14), largest adjusted p value = 3.84 × 10(-2)). In regression analysis, octanol, oxalic acid, phosphoric acid, benzamide, creatinine, 3,5-dimethoxymandelic amide and N-acetylglutamine were selected as the best subset for prediction and allowed excellent classification of low eGFR (AUC = 0.996). In LC/MS, 19 metabolites remained significant after multiple hypotheses testing had been taken into account (smallest adjusted p value = 2.04 × 10(-4), largest adjusted p value = 4.48 × 10(-2)), and several metabolites showed stronger evidence of association relative to the uraemic toxin, indoxyl sulphate (adjusted p value = 3.03 × 10(-2)). The potential effect of confounding on the association between metabolites was excluded.

CONCLUSIONS/INTERPRETATION

Our study has yielded substantial new insight into low eGFR and provided a collection of potential urinary biomarkers for its detection.