Low Red Blood Cell Vitamin C Concentrations Induce Red Blood Cell Fragility: A Link to Diabetes Via Glucose, Glucose Transporters, and Dehydroascorbic Acid

Altered RBC deformability in diabetes: clinical characteristics and RBC pathophysiology

BACKGROUND

Reduced red blood cell deformability (RBCD) is associated with diabetic vascular complications, but early pathophysiological RBC changes and predictive demographic and clinical factors in populations with diabetes are unclear. An understanding of early diabetes-specific RBC changes associated with impaired RBCD is essential in investigating mechanisms that predispose to diabetic vascular complications.

METHODS

We conducted an outpatient cross-sectional study of participants in a well-controlled diabetes cohort (N81) and nondiabetic controls (N78) at the National Institutes of Health. First, between-group differences in RBCD measures were assessed with shear stress-gradient ektacytometry. Differences in structural RBC parameters were assessed using osmotic gradient ektacytometry and NaCl osmotic fragility. Functional RBC changes were assessed using hemoglobin-oxygen dissociation: p50.

RESULTS

All shear-stress gradient RBCD measures were significantly altered in the diabetes cohort vs. nondiabetic controls, even after adjustment for confounding covariates (p < 0.001). Adjusted for diabetes-status and demographic factors, significant predictors of reduced RBCD included older age, Black race, male gender, hyperglycemia, and vascular complications (all p < 0.05). Reduced RBCD was also associated with aberrant osmotic-gradient parameters, with a left-shift on osmotic gradient profile indicative of dehydrated RBCs in diabetes. A structure-function relationship was observed with reduced RBCD associated with reduced osmotic fragility (P < 0.001) and increased hemoglobin-oxygen dissociation (P < 0.01).

CONCLUSIONS

Findings suggest impaired RBCD incurs similar demographic and clinical risk factors as diabetic vascular disease, with early pathophysiological RBC changes indicative of disordered RBC hydration in diabetes. Findings provide strong evidence for disordered oxygen release as a functional consequence of reduced RBCD.

CLINICAL TRIAL NUMBER

NCT00071526.

Complete absence of GLUT1 does not impair human terminal erythroid differentiation

ABSTRACT

The glucose transporter 1 (GLUT1) is 1 of the most abundant proteins within the erythrocyte membrane and is required for glucose and dehydroascorbic acid (vitamin C precursor) transport. It is widely recognized as a key protein for red cell structure, function, and metabolism. Previous reports highlighted the importance of GLUT1 activity within these uniquely glycolysis-dependent cells, in particular for increasing antioxidant capacity needed to avoid irreversible damage from oxidative stress in humans. However, studies of glucose transporter roles in erythroid cells are complicated by species-specific differences between humans and mice. Here, using CRISPR-mediated gene editing of immortalized erythroblasts and adult CD34+ hematopoietic progenitor cells, we generate committed human erythroid cells completely deficient in expression of GLUT1. We show that absence of GLUT1 does not impede human erythroblast proliferation, differentiation, or enucleation. This work demonstrates, to our knowledge, for the first time, generation of enucleated human reticulocytes lacking GLUT1. The GLUT1-deficient reticulocytes possess no tangible alterations to membrane composition or deformability in reticulocytes. Metabolomic analyses of GLUT1-deficient reticulocytes reveal hallmarks of reduced glucose import, downregulated metabolic processes and upregulated AMP-activated protein kinase signaling, alongside alterations in antioxidant metabolism, resulting in increased osmotic fragility and metabolic shifts indicative of higher oxidant stress. Despite detectable metabolic changes in GLUT1-deficient reticulocytes, the absence of developmental phenotype, detectable proteomic compensation, or impaired deformability comprehensively alters our understanding of the role of GLUT1 in red blood cell structure, function, and metabolism. It also provides cell biological evidence supporting clinical consensus that reduced GLUT1 expression does not cause anemia in GLUT1-deficiency syndrome.

Erythrocyte Oxidative Status in People with Obesity: Relation to Tissue Losses, Glucose Levels, and Weight Reduction

BACKGROUND

This study aimed to investigate the impact of reductions in various body mass components on the erythrocyte oxidative status and glycemic state of people with obesity (PWO).

METHODS

A total of 53 PWO followed a six-month individualized low-calorie diet with exercise, during which anthropometric, biochemical, and oxidative parameters were measured. The participants were divided into groups based on weight (W), visceral fat area (VFA), total body water (TBW), and skeletal muscle mass (SMM) losses, as well as normoglycemia (NG) and hyperglycemia (HG).

RESULTS

Weight reduction normalized glycemia and influenced erythrocyte enzyme activity. Regardless of the tissue type lost (VFA, TBW, or SMM), glutathione peroxidase activity decreased in all groups, accompanied by an increase in glutathione reductase activity. Lipofuscin (LPS) and malondialdehyde (MDA) concentrations decreased regardless of the type of tissue lost. The α-/γ-tocopherol ratio increased in those losing >10% body weight, >15% VFA, and >5% TBW. In the NG group, compared to the HG group, there was a decrease in glutathione peroxidase and an increase in glutathione reductase, with these changes being stronger in the HG group. The LPS and MDA concentrations decreased in both groups. Significant correlations were observed between glucose reduction and changes in catalase, retinol, and α-tocopherol, as well as between VFA reduction and changes in vitamin E, L-LPS, and the activities of L-GR and L-GST.

CONCLUSIONS

This analysis highlights the complex interactions between glucose metabolism, oxidative state, and erythrocyte membrane integrity, crucial for understanding diabetes and its management. This study shows the significant metabolic adaptability of erythrocytes in response to systemic changes induced by obesity and hyperglycemia, suggesting potential therapeutic targets to improve metabolic health in obese individuals.

Changes in Haematological Parameters and Lipid Profiles in Diabetes Mellitus: A Literature Review

Diabetes mellitus is a metabolic disorder characterized by elevated blood glucose that has sequelae on cellular, haematological, and metabolic parameters, including lipid profile disturbed homeostasis, which manifest in alterations in haematological parameters and lipid profiles. These changes in haematological parameters and lipid profiles have been reported by previous research; however, the pattern of these changes and their correlation have not been elucidated. This review aims to assess these changes and investigate the degree of correlation between haematological parameters and lipid profiles in patients with type 2 diabetes mellitus (T2DM). The method adopted was a traditional review approach that included a narrative of concepts and a critical assessment of a few selected articles. Findings highlight that haematological parameters and lipid profiles show varied alterations and correlations in T2DM. For instance, statistical significances at p < 0.05 are reported for WBC count (r = -0.75) showing negative correlations (p < 0.001), where RBC count (r = 0.56) showed correlation with high-density lipoprotein cholesterol (HDLC), whereas anaemia (packed cell volume: r = -0.51) and RBC indices (mean corpuscular volume: r = -0.75; mean corpuscular haemoglobin: r = -089) show negative correlations with total cholesterol (TC). The specific haematological parameters, namely, RBC and WBC with differential and platelet counts, as well as indices, showed varied changes and correlation with lipid profiles, namely, HDLC, low-density lipoprotein cholesterol, TC, and triglyceride, in the six reviewed articles. Diabetes is characterized by changes in haematological parameters and lipid profiles. A better understanding of the negative and positive correlating changes could be utilized in routine evaluation of subjects with prediabetes as well as managing complications in diabetes. Correlation between haematological parameters and lipid profiles over the course of diabetes progression using HbA1c as an index of glucose control is necessary for additional empirical data and updates.

Complete absence of GLUT1 does not impair human terminal erythroid differentiation

The Glucose transporter 1 (GLUT1) is one of the most abundant proteins within the erythrocyte membrane and is required for glucose and dehydroascorbic acid (Vitamin C precursor) transport. It is widely recognized as a key protein for red cell structure, function, and metabolism. Previous reports highlighted the importance of GLUT1 activity within these uniquely glycolysis-dependent cells, in particular for increasing antioxidant capacity needed to avoid irreversible damage from oxidative stress in humans. However, studies of glucose transporter roles in erythroid cells are complicated by species-specific differences between humans and mice. Here, using CRISPR-mediated gene editing of immortalized erythroblasts and adult CD34+ hematopoietic progenitor cells, we generate committed human erythroid cells completely deficient in expression of GLUT1. We show that absence of GLUT1 does not impede human erythroblast proliferation, differentiation, or enucleation. This work demonstrates for the first-time generation of enucleated human reticulocytes lacking GLUT1. The GLUT1-deficient reticulocytes possess no tangible alterations to membrane composition or deformability in reticulocytes. Metabolomic analyses of GLUT1-deficient reticulocytes reveal hallmarks of reduced glucose import, downregulated metabolic processes and upregulated AMPK-signalling, alongside alterations in antioxidant metabolism, resulting in increased osmotic fragility and metabolic shifts indicative of higher oxidant stress. Despite detectable metabolic changes in GLUT1 deficient reticulocytes, the absence of developmental phenotype, detectable proteomic compensation or impaired deformability comprehensively alters our understanding of the role of GLUT1 in red blood cell structure, function and metabolism. It also provides cell biological evidence supporting clinical consensus that reduced GLUT1 expression does not cause anaemia in GLUT1 deficiency syndrome.

Vitamin C Urinary Loss and Deficiency in Human Immunodeficiency Virus (HIV): Cross-sectional Study of Vitamin C Renal Leak in Women With HIV

BACKGROUND

Reduced plasma vitamin C (vitC) concentrations in human immunodeficiency virus (HIV) may result from abnormal urinary excretion: a renal leak. VitC renal leak indicates underlying nutritional dysregulation independent of diet. We hypothesized that increased renal leak prevalence in HIV would be associated with deficient vitC concentrations.

METHODS

We conducted an outpatient cross-sectional study of 96 women (40 HIV [PWH] and 56 without HIV [PWOH]) at the National Institutes of Health and Georgetown University. Renal leak was defined as abnormal urinary vitC excretion at fasting plasma concentrations <43.2µM, 2 SDs below vitC renal threshold in healthy women. To determine the primary outcome of renal leak prevalence, matched urine and plasma samples were collected the morning after overnight fast. Secondary outcomes assessed group differences in mean plasma vitC concentrations and prevalence of vitC deficiency. Exploratory outcomes assessed clinical parameters associated with renal leak. VitC was measured by high-performance liquid chromatography with coulometric electrochemical detection.

RESULTS

PWH had significantly higher renal leak prevalence (73%vs14%; OR (odds ratio):16; P<.001), lower mean plasma vitC concentrations (14µMvs50µM; P<.001), and higher prevalence of vitC deficiency (43%vs7%; OR:10; P<.001) compared with PWOH, unchanged by adjustments for confounding factors. Significant predictors of renal leak included antiretroviral therapy (ART), Black race, older age, and metabolic comorbidities but not viral load or CD4 count. When compared with other chronic disease cohorts, PWH had the highest prevalence of renal leak and vitC deficiency (P<.001).

CONCLUSIONS

High prevalence of vitC renal leak in HIV was associated with vitC deficiency, ART use, and race/ethnicity differences.

Red Blood Cell Vitamin C Concentration and Its Effect on Deformability in Pediatric Sickle Cell Disease

Red cell rigidity is common in sickle cell disease (SCD). The contribution of oxidative stress on deformability remains unknown. This study investigated red blood cell (RBC) vitamin C concentrations in pediatric SCD (n=43) compared with healthy controls ( n =23) and developed a protocol to raise RBC vitamin C concentrations to measure the effect on deformability. Sickle cell RBC vitamin C concentrations seem low (20.5 μM, SD: 16.2 vs. 51.7 μM, SD: 15.8; P <0.0001). Vitamin C can be successfully loaded into sickle cell RBCs but seems to have minimal effect on deformability. Future studies are needed to understand the clinical implications of vitamin C deficiency in pediatric SCD.

A comprehensive meta-analysis on the association between vitamin C intake and gestational diabetes mellitus: Insights and novel perspectives

BACKGROUND

Gestational Diabetes Mellitus (GDM) is a significant health concern in pregnant women and their offspring. Although Vitamin C is known to play a role in maintaining normal physiological processes, its relationship with GDM has not been fully elucidated.

METHODS

We conducted a systematic review and meta-analysis following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, analyzing data from 15 studies selected from PubMed, Embase, Web of Science, and the Cochrane Library up to May 16, 2023. These studies were selected based on inclusion criteria such as study design, outcome of interest, exposure factor, and data extractability. Quality assessment was performed using the Newcastle-Ottawa Scale. We assessed the heterogeneity between studies and conducted a sensitivity analysis.

RESULTS

Data from 10,131 subjects, including 1304 diagnosed GDM cases, were analyzed. The meta-analysis showed that women in the low Vitamin C exposure group had higher odds of developing GDM (odds ratio 2.72, 95% CI:1.24-4.19). There was a greater likelihood of increased GDM risk with lower Vitamin C exposure (standardized mean difference: -0.71, 95% CI [-1.07 -0.36]). Subgroup analysis revealed that both internal and external Vitamin C exposure, along with exposure during the second or third trimester of pregnancy, was associated with higher GDM incidence rates under low Vitamin C exposure. Sensitivity analysis confirmed the robustness of the results, and no significant publication bias was detected.

CONCLUSION

Low Vitamin C exposure during pregnancy may increase the risk of GDM. Given these findings, it could be beneficial for pregnant women to increase their intake of Vitamin C-rich foods and to ensure adequate blood Vitamin C levels as a preventive measure against GDM.

Vitamin C Urinary Loss in Fabry Disease: Clinical and Genomic Characteristics of Vitamin C Renal Leak

BACKGROUND

Reduced plasma vitamin C concentrations in chronic diseases may result from abnormal urinary excretion of vitamin C: a renal leak. We hypothesized that vitamin C renal leak may be associated with disease-mediated renal dysregulation, resulting in aberrant vitamin C renal reabsorption and increased urinary loss.

OBJECTIVES

We investigated the prevalence, clinical characteristics, and genomic associations of vitamin C renal leak in Fabry disease, an X-linked lysosomal disease associated with renal tubular dysfunction and low plasma vitamin C concentrations.

METHODS

We conducted a non-randomized cross-sectional cohort study of men aged 24-42 y, with Fabry disease (n = 34) and controls without acute or chronic disease (n = 33). To match anticipated plasma vitamin C concentrations, controls were placed on a low-vitamin C diet 3 wk before inpatient admission. To determine the primary outcome of vitamin C renal leak prevalence, subjects were fasted overnight, and matched urine and fasting plasma vitamin C measurements were obtained the following morning. Vitamin C renal leak was defined as presence of urinary vitamin C at plasma concentrations below 38 μM. Exploratory outcomes assessed the association between renal leak and clinical parameters, and genomic associations with renal leak using single nucleotide polymorphisms (SNPs) in the vitamin C transporter SLC23A1.

RESULTS

Compared with controls, the Fabry cohort had 16-fold higher odds of renal leak (6% vs. 52%; OR: 16; 95% CI: 3.30, 162; P < 0.001). Renal leak was associated with higher protein creatinine ratio (P < 0.01) and lower hemoglobin (P = 0.002), but not estimated glomerular filtration rate (P = 0.54). Renal leak, but not plasma vitamin C, was associated with a nonsynonymous single nucleotide polymorphism in vitamin C transporter SLC23A1 (OR: 15; 95% CI: 1.6, 777; P = 0.01).

CONCLUSIONS

Increased prevalence of renal leak in adult men with Fabry disease may result from dysregulated vitamin C renal physiology and is associated with abnormal clinical outcomes and genomic variation.

Mitochondrial dysfunction and oxidative stress: Role in chronic kidney disease

Chronic kidney disease (CKD) is associated with a variety of distinct disease processes that permanently change the function and structure of the kidney across months or years. CKD is characterized as a glomerular filtration defect or proteinuria that lasts longer than three months. In most instances, CKD leads to end-stage kidney disease (ESKD), necessitating kidney transplantation. Mitochondrial dysfunction is a typical response to damage in CKD patients. Despite the abundance of mitochondria in the kidneys, variations in mitochondrial morphological and functional characteristics have been associated with kidney inflammatory responses and injury during CKD. Despite these variations, CKD is frequently used to define some classic signs of mitochondrial dysfunction, including altered mitochondrial shape and remodeling, increased mitochondrial oxidative stress, and a marked decline in mitochondrial biogenesis and ATP generation. With a focus on the most significant developments and novel understandings of the involvement of mitochondrial remodeling in the course of CKD, this article offers a summary of the most recent advances in the sources of procured mitochondrial dysfunction in the advancement of CKD. Understanding mitochondrial biology and function is crucial for developing viable treatment options for CKD.

Demand for Water-Soluble Vitamins in a Group of Patients with CKD versus Interventions and Supplementation-A Systematic Review

BACKGROUND

Increasingly, chronic kidney disease (CKD) is becoming an inevitable consequence of obesity, metabolic syndrome, and diabetes. As the disease progresses, and through dialysis, the need for and loss of water-soluble vitamins both increase. This review article looks at the benefits and possible risks of supplementing these vitamins with the treatment of CKD.

METHODS

Data in the PubMed and Embase databases were analyzed. The keywords "chronic kidney disease", in various combinations, are associated with thiamin, riboflavin, pyridoxine, pantothenic acid, folates, niacin, cobalamin, and vitamin C. This review focuses on the possible use of water-soluble vitamin supplementation to improve pharmacological responses and the overall clinical condition of patients.

RESULTS

The mechanism of supportive supplementation is based on reducing oxidative stress, covering the increased demand and losses resulting from the treatment method. In the initial period of failure (G2-G3a), it does not require intervention, but later, especially in the case of inadequate nutrition, the inclusion of supplementation with folate and cobalamin may bring benefits. Such supplementation seems to be a necessity in patients with stage G4 or G5 (uremia). Conversely, the inclusion of additional B6 supplementation to reduce CV risk may be considered. At stage 3b and beyond (stages 4-5), the inclusion of niacin at a dose of 400-1000 mg, depending on the patient's tolerance, is required to lower the phosphate level. The inclusion of supplementation with thiamine and other water-soluble vitamins, especially in peritoneal dialysis and hemodialysis patients, is necessary for reducing dialysis losses. Allowing hemodialysis patients to take low doses of oral vitamin C effectively reduces erythropoietin dose requirements and improves anemia in functional iron-deficient patients. However, it should be considered that doses of B vitamins that are several times higher than the recommended dietary allowance of consumption may exacerbate left ventricular diastolic dysfunction in CKD patients.

CONCLUSIONS

Taking into account the research conducted so far, it seems that the use of vitamin supplementation in CKD patients may have a positive impact on the treatment process and maintaining a disease-free condition.

Oxidants and Antioxidants in the Redox Biochemistry of Human Red Blood Cells

Red blood cells (RBCs) are exposed to both external and internal sources of oxidants that challenge their integrity and compromise their physiological function and supply of oxygen to tissues. Autoxidation of oxyhemoglobin is the main source of endogenous RBC oxidant production, yielding superoxide radical and then hydrogen peroxide. In addition, potent oxidants from other blood cells and the surrounding endothelium can reach the RBCs. Abundant and efficient enzymatic systems and low molecular weight antioxidants prevent most of the damage to the RBCs and also position the RBCs as a sink of vascular oxidants that allow the body to maintain a healthy circulatory system. Among the antioxidant enzymes, the thiol-dependent peroxidase peroxiredoxin 2, highly abundant in RBCs, is essential to keep the redox balance. A great part of the RBC antioxidant activity is supported by an active glucose metabolism that provides reducing power in the form of NADPH via the pentose phosphate pathway. There are several RBC defects and situations that generate oxidative stress conditions where the defense mechanisms are overwhelmed, and these include glucose-6-phosphate dehydrogenase deficiencies (favism), hemoglobinopathies like sickle cell disease and thalassemia, as well as packed RBCs for transfusion that suffer from storage lesions. These oxidative stress-associated pathologies of the RBCs underline the relevance of redox balance in these anucleated cells that lack a mechanism of DNA-inducible antioxidant response and rely on a complex and robust network of antioxidant systems.

High-Dose Intravenous Ascorbate in Sepsis, a Pro-Oxidant Enhanced Microbicidal Activity and the Effect on Neutrophil Functions

Vitamin C (ascorbic acid), a water-soluble essential vitamin, is well-known as an antioxidant and an essential substrate for several neutrophil functions. Because of (i) the importance of neutrophils in microbial control and (ii) the relatively low vitamin C level in neutrophils and in plasma during stress, vitamin C has been studied in sepsis (a life-threatening organ dysfunction from severe infection). Surprisingly, the supraphysiologic blood level of vitamin C (higher than 5 mM) after the high-dose intravenous vitamin C (HDIVC) for 4 days possibly induces the pro-oxidant effect in the extracellular space. As such, HDIVC demonstrates beneficial effects in sepsis which might be due to the impacts on an enhanced microbicidal activity through the improved activity indirectly via enhanced neutrophil functions and directly from the extracellular pro-oxidant effect on the organismal membrane. The concentration-related vitamin C properties are also observed in the neutrophil extracellular traps (NETs) formation as ascorbate inhibits NETs at 1 mM (or less) but facilitates NETs at 5 mM (or higher) concentration. The longer duration of HDIVC administration might be harmful in sepsis because NETs and pro-oxidants are partly responsible for sepsis-induced injuries, despite the possible microbicidal benefit. Despite the negative results in several randomized control trials, the short course HDIVC might be interesting to use in some selected groups, such as against anti-biotic resistant organisms. More studies on the proper use of vitamin C, a low-cost and widely available drug, in sepsis are warranted.

Vitamin C deficiency reveals developmental differences between neonatal and adult hematopoiesis

Hematopoiesis, a process that results in the differentiation of all blood lineages, is essential throughout life. The production of 1x10¹² blood cells per day, including 200x10⁹ erythrocytes, is highly dependent on nutrient consumption. Notably though, the relative requirements for micronutrients during the perinatal period, a critical developmental window for immune cell and erythrocyte differentiation, have not been extensively studied. More specifically, the impact of the vitamin C/ascorbate micronutrient on perinatal as compared to adult hematopoiesis has been difficult to assess in animal models. Even though humans cannot synthesize ascorbate, due to a pseudogenization of the L-gulono-γ-lactone oxidase (GULO) gene, its generation from glucose is an ancestral mammalian trait. Taking advantage of a Gulo^-/- mouse model, we show that ascorbic acid deficiency profoundly impacts perinatal hematopoiesis, resulting in a hypocellular bone marrow (BM) with a significant reduction in hematopoietic stem cells, multipotent progenitors, and hematopoietic progenitors. Furthermore, myeloid progenitors exhibited differential sensitivity to vitamin C levels; common myeloid progenitors and megakaryocyte-erythrocyte progenitors were markedly reduced in Gulo^-/- pups following vitamin C depletion in the dams, whereas granulocyte-myeloid progenitors were spared, and their frequency was even augmented. Notably, hematopoietic cell subsets were rescued by vitamin C repletion. Consistent with these data, peripheral myeloid cells were maintained in ascorbate-deficient Gulo^-/- pups while other lineage-committed hematopoietic cells were decreased. A reduction in B cell numbers was associated with a significantly reduced humoral immune response in ascorbate-depleted Gulo^-/- pups but not adult mice. Erythropoiesis was particularly sensitive to vitamin C deprivation during both the perinatal and adult periods, with ascorbate-deficient Gulo^-/- pups as well as adult mice exhibiting compensatory splenic differentiation. Furthermore, in the pathological context of hemolytic anemia, vitamin C-deficient adult Gulo^-/- mice were not able to sufficiently increase their erythropoietic activity, resulting in a sustained anemia. Thus, vitamin C plays a pivotal role in the maintenance and differentiation of hematopoietic progenitors during the neonatal period and is required throughout life to sustain erythroid differentiation under stress conditions.

Vitamin C supplementation attenuates oxidative stress and improves erythrocyte deformability in cardiac surgery with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) depletes endogenous Vitamin C and generates oxidative stress in cardiac surgery. This study aimed to clarify whether Vitamin C supplementation reduces oxidant production and improves erythrocyte deformability in cardiac surgery with CPB. In a randomized and controlled design, 30 eligible patients undergoing cardiac surgery with hypothermic CPB were equally assigned to the Vitamin C group and control group. Subjects of the Vitamin C group and control group received an intravenous infusion of Vitamin C 20 mg·kg^-1 and a placebo during rewarming period of CPB, respectively. We measured the plasma level of reactive oxygen species (ROS) and phosphorylation levels of non-muscle myosin IIA (NMIIA) in erythrocyte membrane, as an index of erythrocyte deformability, before and after CPB. Vitamin C supplementation attenuated the surge in plasma ROS after CPB, mean 1.661 ± standard deviation 0.801 folds in the Vitamin C group and 2.743 ± 1.802 in the control group. The tyrosine phosphorylation level of NMIIA after CPB was upregulated in the Vitamin C group compared to the control group, 2.159 ± 0.887 folds and 1.384 ± 0.445 (P = 0.0237). In addition, the phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and focal adhesion kinase (FAK) in erythrocytes was concurrently enhanced in the Vitamin C group after CPB. The phosphorylation level of endothelial nitric oxide synthase in erythrocytes was significantly increased in the Vitamin C group (1.734 ± 0.371 folds) compared to control group (1.102 ± 0.249; P = 0.0061). Patients receiving Vitamin C had lower intraoperative blood loss and higher systemic vascular resistance after CPB compared to controls. Vitamin C supplementation attenuates oxidative stress and improves erythrocyte deformability via VASP/FAK signaling pathway in erythrocytes during CPB.

Erythrocyte osmotic fragility is not linked to vitamin C nutriture in adults with well-controlled type 2 diabetes

Erythrocyte fragility is amplified by oxidative stress and linked to diabetes-specific microvascular disease. Vitamin C supplementation improves glycemic indices in adults with type 2 diabetes (T2D) by improving antioxidant status. This cross-sectional study examined the relationships between vitamin C status and erythrocyte osmotic fragility in adults with or without T2D. Participants provided a fasting blood sample for erythrocyte osmotic fragility testing as a function of hypotonic NaCl concentrations. Additionally, plasma was stabilized with metaphosphoric acid prior to vitamin C analysis using isocratic reverse-phase UV-HPLC separation. Participants were grouped as diagnosed T2D (n = 14; 36% female; 55.5 ± 8.2 y; 31.5 ± 9.0 kg/m²; HbA1c: 7.4 ± 1.9%; plasma vitamin C: 36.0 ± 12.2 μM) or no diabetes (n = 16; 69% female; 38.7 ± 13.5 y; 26.8 ± 6.6 kg/m²; HbA1c: 5.4 ± 0.3%; plasma vitamin C: 34.8 ± 10.9 μM). Participant characteristics differed between groups only for age and hemoglobin A1c (HbA1c; p < 0.05). All hemolysis parameters were in normal ranges for the participants with T2D, and no significant differences in hemolysis parameters were noted between those with or without T2D. However, among participants with T2D, the NaCl concentration eliciting 50% hemolysis was higher for those with low (<7%) vs. high (>7%) HbA1c values (p = 0.037) indicating a slightly higher erythrocyte fragility in the former group. Vitamin C status did not impact any of the hemolysis parameters in adults with or without T2D. Thus, erythrocyte fragility was not elevated in T2D, and vitamin C nutriture was not related to erythrocyte fragility in adults with well-controlled T2D.

Topical Reappraisal of Molecular Pharmacological Approaches to Endothelial Dysfunction in Diabetes Mellitus Angiopathy

Diabetes mellitus (DM) is a frequent medical problem, affecting more than 4% of the population in most countries. In the context of diabetes, the vascular endothelium can play a crucial pathophysiological role. If a healthy endothelium—which is a dynamic endocrine organ with autocrine and paracrine activity—regulates vascular tone and permeability and assures a proper balance between coagulation and fibrinolysis, and vasodilation and vasoconstriction, then, in contrast, a dysfunctional endothelium has received increasing attention as a potential contributor to the pathogenesis of vascular disease in diabetes. Hyperglycemia is indicated to be the major causative factor in the development of endothelial dysfunction. Furthermore, many shreds of evidence suggest that the progression of insulin resistance in type 2 diabetes is parallel to the advancement of endothelial dysfunction in atherosclerosis. To present the state-of-the-art data regarding endothelial dysfunction in diabetic micro- and macroangiopathy, we constructed this literature review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We interrogated five medical databases: Elsevier, PubMed, PMC, PEDro, and ISI Web of Science.

Abnormal urinary loss of vitamin C in diabetes: prevalence and clinical characteristics of a vitamin C renal leak

BACKGROUND

Diabetes is associated with low plasma vitamin C concentrations.

OBJECTIVES

We investigated the contribution of dysregulated vitamin C renal physiology, its prevalence, and associated clinical characteristics.

METHODS

An essential prerequisite was determination of normal vitamin C renal threshold, the plasma concentration at which vitamin C first appears in urine. Using data from 17 healthy participants who underwent vitamin C depletion-repletion studies with a vitamin C dose range of 15-1250 mg daily, renal threshold was estimated using physiology-based pharmacokinetics modeling. Applying renal threshold 95% CIs, we estimated the minimal elimination threshold, the plasma concentration below which no vitamin C was expected in urine of healthy people. Renal leak was defined as abnormal presence of vitamin C in urine with plasma concentrations below the minimal elimination threshold. Criteria were tested in a cross-sectional cohort study of individuals with diabetes (82) and nondiabetic controls (80) using matched plasma and urine samples.

RESULTS

Vitamin C renal thresholds in healthy men and women were [mean (SD)] 48.5 (5.2) µM and 58.3 (7.5) µM, respectively. Compared with nondiabetic controls, participants with diabetes had significantly higher prevalence of vitamin C renal leak (9% compared with 33%; OR: 5.07; 95% CI: 1.97, 14.83; P < 0.001) and 30% lower mean plasma vitamin C concentrations (53.1 µM compared with 40.9 µM, P < 0.001). Fasting plasma glucose, glycosylated hemoglobin A1c, BMI, micro/macrovascular complications, and protein/creatinine ratio were predictive of vitamin C renal leak.

CONCLUSIONS

Increased prevalence of vitamin C renal leak in diabetes is associated with reduced plasma vitamin C concentrations. Glycemic control, microvascular complications, obesity, and proteinuria are predictive of renal leak.

Mitochondrial Pathophysiology on Chronic Kidney Disease

In healthy kidneys, interstitial fibroblasts are responsible for the maintenance of renal architecture. Progressive interstitial fibrosis is thought to be a common pathway for chronic kidney diseases (CKD). Diabetes is one of the boosters of CKD. There is no effective treatment to improve kidney function in CKD patients. The kidney is a highly demanding organ, rich in redox reactions occurring in mitochondria, making it particularly vulnerable to oxidative stress (OS). A dysregulation in OS leads to an impairment of the Electron transport chain (ETC). Gene deficiencies in the ETC are closely related to the development of kidney disease, providing evidence that mitochondria integrity is a key player in the early detection of CKD. The development of novel CKD therapies is needed since current methods of treatment are ineffective. Antioxidant targeted therapies and metabolic approaches revealed promising results to delay the progression of some markers associated with kidney disease. Herein, we discuss the role and possible origin of fibroblasts and the possible potentiators of CKD. We will focus on the important features of mitochondria in renal cell function and discuss their role in kidney disease progression. We also discuss the potential of antioxidants and pharmacologic agents to delay kidney disease progression.

Frequent SLC12A3 mutations in Chinese Gitelman syndrome patients: structure and function disorder

PURPOSES

This study was conducted to identify the frequent mutations from reported Chinese Gitelman syndrome (GS) patients, to predict the three-dimensional structure change of human Na-Cl co-transporter (hNCC), and to test the activity of these mutations and some novel mutations in vitro and in vivo.

METHODS

SLC12A3 gene mutations in Chinese GS patients previously reported in the PubMed, China National Knowledge Infrastructure, and Wanfang database were summarized. Predicted configurations of wild type (WT) and mutant proteins were achieved using the I-TASSER workplace. Six missense mutations (T60M, L215F, D486N, N534K, Q617R, and R928C) were generated by site-directed mutagenesis. 22Na+ uptake experiment was carried out in the Xenopus laevisoocyte expression system. In the study, 35 GS patients and 20 healthy volunteers underwent the thiazide test.

RESULTS

T60M, T163M, D486N, R913Q, R928C, and R959frameshift were frequent SLC12A3 gene mutations (mutated frequency >3%) in 310 Chinese GS families. The protein's three-dimensional structure was predicted to be altered in all mutations. Compared with WT hNCC, the thiazide-sensitive 22Na+ uptake was significantly diminished for all six mutations: T60M 22 ± 9.2%, R928C 29 ± 12%, L215F 38 ± 14%, N534K 41 ± 15.5%, Q617R 63 ± 22.1%, and D486N 77 ± 20.4%. In thiazide test, the net increase in chloride fractional excretion in 20 healthy controls was significantly higher than GS patients with or without T60M or D486N mutations.

CONCLUSIONS

Frequent mutations (T60M, D486N, and R928C) and novel mutations (L215F, N534K, and Q617R) lead to protein structure alternation and protein dysfunction verified by 22Na+ uptake experiment in vitro and thiazide test on the patients.

Redox Properties of Human Erythrocytes Are Adapted for Vitamin C Recycling

Ascorbic acid (AA; or vitamin C) is an important physiological antioxidant and radical scavenger. Some mammalian species, including homo sapiens, have lost the ability to synthetize AA and depend on its nutritional uptake. Erythrocytes from AA-auxotroph mammals express high amounts of the glucose transporter GLUT1. This isoform enables rapid uptake of glucose as well as dehydroascorbate (DHA), the fully oxidized form of AA. Here, we explored the effects of DHA uptake on the redox metabolism of human erythrocytes. DHA uptake enhanced plasma membrane electron transport (PMET) activity. This process is mediated by DCytb, a membrane bound cytochrome catalyzing extracellular reduction of Fe³⁺ and ascorbate free radical (AFR), the first oxidized form of AA. DHA uptake also decreased cellular radical oxygen species (ROS) levels. Both effects were massively enhanced in the presence of physiological glucose concentrations. Reduction of DHA to AA largely depleted intracellular glutathione (GSH) and induced the efflux of its oxidized form, GSSG. GSSG efflux could be inhibited by MK-571 (IC₅₀ = 5 μM), indicating involvement of multidrug resistance associated protein (MRP1/4). DHA-dependent GSH depletion and GSSG efflux were completely rescued in the presence of 5 mM glucose and, partially, by 2-deoxy-glucose (2-DG), respectively. These findings indicate that human erythrocytes are physiologically adapted to recycle AA both intracellularly via GLUT1-mediated DHA uptake and reduction and extracellularly via DCytb-mediated AFR reduction. We discuss the possibility that this improved erythrocyte-mediated AA recycling was a prerequisite for the emergence of AA auxotrophy which independently occurred at least twice during mammalian evolution.

Neutrophils Isolated from Septic Patients Exhibit Elevated Uptake of Vitamin C and Normal Intracellular Concentrations despite a Low Vitamin C Milieu

Vitamin C (ascorbate) plays an important role in neutrophil function and is accumulated by the cells either directly via vitamin C transporters (SVCT) or indirectly following oxidation to dehydroascorbic acid. Septic patients are known to have significantly depleted plasma ascorbate status, but little is known about the ascorbate content of their circulating cells. Therefore, we assessed the ascorbate concentrations of plasma, leukocytes and erythrocytes from septic patients and compared these to healthy controls. Non-fasting blood samples were collected from healthy volunteers (n = 20) and critically ill patients with sepsis (n = 18). The ascorbate content of the plasma and isolated neutrophils and erythrocytes was measured using HPLC and plasma myeloperoxidase concentrations were determined using ELISA. Ex vivo uptake of ascorbate and dehydroascorbic acid by neutrophils from septic patients was also assessed. Neutrophils isolated from septic patients had comparable intracellular ascorbate content to healthy volunteers (0.33 vs. 0.35 nmol/10⁶ cells, p > 0.05), despite significantly lower plasma concentrations than the healthy controls (14 vs. 88 µmol/L, p < 0.001). In contrast, erythrocytes from septic patients had significantly lower intracellular ascorbate content than healthy controls (30 vs. 69 µmol/L, p = 0.002), although this was 2.2-fold higher than the matched plasma concentrations in the patients (p = 0.008). Higher concentrations of myeloperoxidase, a source of reactive oxygen species, were observed in the septic patients relative to healthy controls (194 vs. 14 mg/mL, p < 0.0001). In contrast to neutrophils from healthy volunteers, the neutrophils from septic patients demonstrated elevated uptake of extracellular ascorbate. Overall, neutrophils from septic patients exhibited comparable intracellular ascorbate content to those from healthy controls, despite the patients presenting with hypovitaminosis C. The mechanisms involved are currently uncertain, but could include increased generation of dehydroascorbic acid in septic patients, enhanced basal activation of their neutrophils or upregulation of their vitamin C transporters.

Using redox potential as a feasible marker for banked blood quality and the state of oxidative stress in stored red blood cells

BACKGROUND

Stored red blood cells (RBCs) may undergo oxidative stress over time, with functional changes affecting oxygen delivery. Central to these changes are oxidation-reduction (redox) reactions and redox potential (RP) that must be maintained for cell function. RP imbalance can lead to oxidative stress that may contribute to storage lesions. This study's purpose was to identify changes in RP over time in banked RBCs, and among RBCs of similar age.

METHODS

Multiple random RBC segments from RBC units were tested (n = 32), ranging in age from 5 to 40 days, at 5-day intervals. RP was recorded by measuring open circuit potential of RBCs using nanoporous gold electrodes with Ag/AgCl reference. RP measures were also performed on peripheral venous blood from 10 healthy volunteers. RP measures were compared between RBC groups, and with volunteer blood.

RESULTS

Stored RBCs show time-dependent RP increases. There were significant differences in Day 5 RP compared to all other groups (p ≤ 0.005), Day 10-15 vs. ages ≥ Day 20 (p ≤ 0.025), Day 20-25 vs. Day 40 (p = 0.039), and all groups compared to healthy volunteers. RP became more positive over time suggesting ongoing oxidation as RBCs age; however, storage time alone was not predictive of RP measured in a particular unit/segment.

CONCLUSIONS

There are significant differences in RP between freshly stored RBCs and all others, with RP becoming more positive over time. However, storage time alone does not predict RP, indicating RP screening may be an important measure of RBC oxidative stress and serve as an RBC quality marker.

A Properly Balanced Reduction Diet and/or Supplementation Solve the Problem with the Deficiency of These Vitamins Soluble in Water in Patients with PCOS

Polycystic ovary syndrome (PCOS) is an increasingly common problem for women in the reproductive age throughout the entire world. A reduction diet with a low glycaemic index (GI) has proved to support the treatment of PCOS. The aim of the study was to analyse the influence of the diet on the level of vitamins soluble in water. The study included 55 women, 40 of which suffered from PCOS (identified by means of the Rotterdam Criteria) and 15 healthy women of the Caucasian race. The level of vitamins before and after the dietary intervention was measured. The diet was a reduction diet with a reduced glycaemic index (GI). Biochemical analyses were made on the basis of liquid chromatography-Infinity 1260 Binary liquid chromatography (LC) Agilent Technology. The level of vitamins in the serum was analysed together with the consumption before and after the dietary intervention. A higher level of vitamin C in the plasma was observed before and after the dietary intervention in the PCOS group in comparison to the control group despite the lower intake of this vitamin in the PCOS group. The remaining vitamins were at a comparable or lower level (B1, B3, B5, B6 and B12). After the dietary intervention, only B1 and B9 were at a clearly lower level (a trend of p = 0.093 and p = 0.085). A properly balanced reduction diet with reduced GI improves the supply of vitamins in women with PCOS. An additional recommendation should be the additional supplementation of B1, niacinamide and the combination of folates with inositol. The level of vitamin C in the plasma may not be a good marker of its supply in the PCOS group.

Vitamin C Transporters and Their Implications in Carcinogenesis

Vitamin C is implicated in various bodily functions due to its unique properties in redox homeostasis. Moreover, vitamin C also plays a great role in restoring the activity of 2-oxoglutarate and Fe²⁺ dependent dioxygenases (2-OGDD), which are involved in active DNA demethylation (TET proteins), the demethylation of histones, and hypoxia processes. Therefore, vitamin C may be engaged in the regulation of gene expression or in a hypoxic state. Hence, vitamin C has acquired great interest for its plausible effects on cancer treatment. Since its conceptualization, the role of vitamin C in cancer therapy has been a controversial and disputed issue. Vitamin C is transferred to the cells with sodium dependent transporters (SVCTs) and glucose transporters (GLUT). However, it is unknown whether the impaired function of these transporters may lead to carcinogenesis and tumor progression. Notably, previous studies have identified SVCTs’ polymorphisms or their altered expression in some types of cancer. This review discusses the potential effects of vitamin C and the impaired SVCT function in cancers. The variations in vitamin C transporter genes may regulate the active transport of vitamin C, and therefore have an impact on cancer risk, but further studies are needed to thoroughly elucidate their involvement in cancer biology.

Ascorbate and Tumor Cell Iron Metabolism: The Evolving Story and Its Link to Pathology

Significance: Vitamin C or ascorbate (Asc) is a water-soluble vitamin and an antioxidant that is involved in many crucial biological functions. Asc's ability to reduce metals makes it an essential enzyme cofactor. Recent Advances: The ability of Asc to act as a reductant also plays an important part in its overall role in iron metabolism, where Asc induces both nontransferrin-bound iron and transferrin-bound iron uptake at physiological concentrations (∼50 μM). Moreover, Asc has emerged to play an important role in multiple diseases and its effects at pharmacological doses could be important for their treatment. Critical Issues: Asc's role as a regulator of cellular iron metabolism, along with its cytotoxic effects and different roles at pharmacological concentrations, makes it a candidate as an anticancer agent. Ever since the controversy regarding the studies from the Mayo Clinic was finally explained, there has been a renewed interest in using Asc as a therapeutic approach toward cancer due to its minimal side effects. Numerous studies have been able to demonstrate the anticancer activity of Asc through selective oxidative stress toward cancer cells via H₂O₂ generation at pharmacological concentrations. Studies have demonstrated that Asc's cytotoxic mechanism at concentrations (>1 mM) has been associated with decreased cellular iron uptake. Future Directions: Recent studies have also suggested other mechanisms, such as Asc's effects on autophagy, polyamine metabolism, and the cell cycle. Clearly, more has yet to be discovered about Asc's mechanism of action to facilitate safe and effective treatment options for cancer and other diseases.

Vitamin C Deficiency and the Risk of Osteoporosis in Patients with an Inflammatory Bowel Disease

Recent research studies have shown that vitamin C (ascorbic acid) may affect bone mineral density and that a deficiency of ascorbic acid leads to the development of osteoporosis. Patients suffering from an inflammatory bowel disease are at a risk of low bone mineral density. It is vital to notice that patients with Crohn’s disease and ulcerative colitis also are at risk of vitamin C deficiency which is due to factors such as reduced consumption of fresh vegetables and fruits, i.e., the main sources of ascorbic acid. Additionally, some patients follow diets which may provide an insufficient amount of vitamin C. Moreover, serum vitamin C level also is dependent on genetic factors, such as SLC23A1 and SLC23A2 genes, encoding sodium-dependent vitamin C transporters and GSTM1, GSTP1 and GSTT1 genes which encode glutathione S-transferases. Furthermore, ascorbic acid may modify the composition of gut microbiota which plays a role in the pathogenesis of an inflammatory bowel disease.

Comprehensive and quantitative stability study of ascorbic acid using capillary zone electrophoresis with ultraviolet detection and high-resolution tandem mass spectrometry

Ascorbic acid is a powerful antioxidant compound involved in many biological functions, and a chronic deficiency is at the origin of scurvy disease. A simple, rapid, and cost-effective capillary electrophoresis method was developed for the separation and simultaneous quantification of ascorbic acid and the major degradation products: dehydroascorbic acid, furfural, and furoic acid. Systematic optimization of the conditions was performed that enabled baseline separation of the compounds in less than 10 min. In addition to simultaneous quantification of ascorbic acid alongside to the degradation products, stability studies demonstrated the possibility using capillary electrophoresis to separate and identify the major degradation products. Thus, high-resolution tandem mass spectrometry experiments were conducted in order to identify an unknown degradation product separated by capillary electrophoresis and significantly present in degraded samples. Comparison of mass spectrometry data and capillary electrophoresis electropherograms allowed to identify unambiguously trihydroxy-keto-valeraldehyde. Finally, capillary electrophoresis was successfully applied to evaluate the composition of different pharmaceutical preparation of ascorbic acid. Results showed the excellent performance of the capillary electrophoresis method due to the separation of excipients from the compounds of interest, which demonstrated the relevance of using an electrophoretic separation in order to perform comprehensive stability studies of ascorbic acid.

Glucose transporters in adipose tissue, liver, and skeletal muscle in metabolic health and disease

A family of facilitative glucose transporters (GLUTs) is involved in regulating tissue-specific glucose uptake and metabolism in the liver, skeletal muscle, and adipose tissue to ensure homeostatic control of blood glucose levels. Reduced glucose transport activity results in aberrant use of energy substrates and is associated with insulin resistance and type 2 diabetes. It is well established that GLUT2, the main regulator of hepatic hexose flux, and GLUT4, the workhorse in insulin- and contraction-stimulated glucose uptake in skeletal muscle, are critical contributors in the control of whole-body glycemia. However, the molecular mechanism how insulin controls glucose transport across membranes and its relation to impaired glycemic control in type 2 diabetes remains not sufficiently understood. An array of circulating metabolites and hormone-like molecules and potential supplementary glucose transporters play roles in fine-tuning glucose flux between the different organs in response to an altered energy demand.

Erythroid glucose transport in health and disease

Glucose transport is intimately linked to red blood cell physiology. Glucose is the unique energy source for these cells, and defects in glucose metabolism or transport activity are associated with impaired red blood cell morphology and deformability leading to reduced lifespan. In vertebrate erythrocytes, glucose transport is mediated by GLUT1 (in humans) or GLUT4 transporters. These proteins also account for dehydroascorbic acid (DHA) transport through erythrocyte membrane. The peculiarities of glucose transporters and the red blood cell pathologies involving GLUT1 are summarized in the present review.

The implications of vitamin content in the plasma in reference to the parameters of carbohydrate metabolism and hormone and lipid profiles in PCOS

So far, there have been no analyses of correlations between the level of water-soluble vitamins in women with polycystic ovary syndrome (PCOS) and hormone and lipid profiles as well as carbohydrate metabolism. The unpopular concept that PCOS may also be conditioned by a chronic infection leads to a suspicion that water-soluble vitamins may be involved in the struggle against PCOS. This is why the aim of this research was to determine whether there are any indications that could confirm this hypothesis. The study included 64 women of Caucasian race: 50 patients aged 29.52 ± 7.01 years with PCOS, diagnosed according to the Rotterdam criteria. The control group consisted of 14 women aged 30.23 ± 6.3 years with correct BMI. HPLC Infinity1260 Binary LC (Agilent Technologies, Waldbronn, Germany) was used to analyze nine vitamins. The vitamins were separated using the gradient method, a buffer of 25 mM HK2PO4 with pH equal to 7.0, and 100 % methanol buffer. The acquired results were compared using Statistica 12.0 (Statsoft, Tulsa, Oklahoma, USA). Non-parametric tests were used: Mann-Whitney tests for comparisons between groups (PCOS and control group, CG), in which p < 0.05 was considered statistically significant. Subsequently, we performed a correlation matrix of the biochemical parameters of blood with vitamins at p ≤ 0.05. Higher concentrations of ascorbic acid were observed in PCOS. The content of the remaining vitamins was higher in the control group, and the statistical differences were significant in reference to thiamine, riboflavin, pyridoxine and folic acid in comparison to the control group. A significant positive correlation was observed between vitamin C and testosterone/insulin, another between riboflavin and androstenedione/testosterone, next between biotin and thyrotropic hormone (TSH), between pantothenic acid and dehydroepiandrosteron (DHEA-SO4), and finally between pyridoxine and androstenedione. A negative correlation was observed in the case of niacin with sex hormone binding protein (SHBG) and high density lipoprotein (HDL). Water-soluble vitamins play an important role in the therapy of women with PCOS through the reduction of antioxidative stress and low-intensity inflammation caused by various factors, including chronic infection.

Erythrocyte Ascorbate Is a Potential Indicator of Steady-State Plasma Ascorbate Concentrations in Healthy Non-Fasting Individuals

Plasma vitamin C concentrations fluctuate in response to recent dietary intake; therefore levels are typically determined in the fasting state. Erythrocyte ascorbate concentrations have been shown to be similar to plasma levels, but little is known about the kinetics of ascorbate accumulation in these cells. In this study, we investigated ascorbate uptake into erythrocytes after dietary supplementation with vitamin C and compared it to changes in plasma ascorbate concentrations. Seven individuals with baseline fasting plasma vitamin C concentrations ≥ 50 µmol/L were depleted of vitamin C-containing foods and drinks for one week, and then supplemented with 250 mg vitamin C/day in addition to resuming their normal diet. Fasting or steady-state plasma ascorbate concentrations declined to almost half of their baseline concentration over the week of vitamin C depletion, and then returned to saturation within two days of beginning supplementation. Erythrocyte ascorbate concentrations exhibited a very similar profile to plasma levels, with values ~76% of plasma, and a strong linear correlation (r = 0.89, p < 0.0001). Using a pharmacokinetic study design in six individuals with baseline fasting plasma vitamin C concentrations ≥50 µmol/L, we also showed that, unlike plasma, which peaked between 2 and 4 h following ingestion of 200 mg of vitamin C, erythrocyte ascorbate concentrations did not change in the six hours after supplementation. The data from these two intervention studies indicate that erythrocyte ascorbate concentration provides a stable measure of steady-state plasma ascorbate status and could be used to monitor ascorbate status in healthy non-fasting individuals.

Vitamin E sequestration by liver fat in humans

BACKGROUNDWe hypothesized that obesity-associated hepatosteatosis is a pathophysiological chemical depot for fat-soluble vitamins and altered normal physiology. Using α-tocopherol (vitamin E) as a model vitamin, pharmacokinetics and kinetics principles were used to determine whether excess liver fat sequestered α-tocopherol in women with obesity-associated hepatosteatosis versus healthy controls.METHODSCustom-synthesized deuterated α-tocopherols (d3- and d6-α-tocopherols) were administered to hospitalized healthy women and women with hepatosteatosis under investigational new drug guidelines. Fluorescently labeled α-tocopherol was custom-synthesized for cell studies.RESULTSIn healthy subjects, 85% of intravenous d6-α-tocopherol disappeared from the circulation within 20 minutes but reappeared within minutes and peaked at 3-4 hours; d3- and d6-α-tocopherols localized to lipoproteins. Lipoprotein redistribution occurred only in vivo within 1 hour, indicating a key role of the liver in uptake and re-release. Compared with healthy subjects who received 2 mg, subjects with hepatosteatosis had similar d6-α-tocopherol entry rates into liver but reduced initial release rates (P < 0.001). Similarly, pharmacokinetics parameters were reduced in hepatosteatosis subjects, indicating reduced hepatic d6-α-tocopherol output. Reductions in kinetics and pharmacokinetics parameters in hepatosteatosis subjects who received 2 mg were echoed by similar reductions in healthy subjects when comparing 5- and 2-mg doses. In vitro, fluorescent-labeled α-tocopherol localized to lipid in fat-loaded hepatocytes, indicating sequestration.CONCLUSIONSThe unique role of the liver in vitamin E physiology is dysregulated by excess liver fat. Obesity-associated hepatosteatosis may produce unrecognized hepatic vitamin E sequestration, which might subsequently drive liver disease. Our findings raise the possibility that hepatosteatosis may similarly alter hepatic physiology of other fat-soluble vitamins.TRIAL REGISTRATIONClinicalTrials.gov, NCT00862433.FUNDINGNational Institute of Diabetes and Digestive and Kidney Diseases and NIH grants DK053213-13, DK067494, and DK081761.

Combination Therapy with Vitamin C Could Eradicate Cancer Stem Cells

Cancer remains one of the most feared and dreaded diseases in this era of modern medicine, claiming the lives of many, and affecting the quality of life of several others around the globe despite major advances in the diagnosis, treatment, palliative care and the immense resources invested into cancer research. While research in cancer has largely focused on the neoplasm/tumor and the cancerous cells that make up the tumor, more recently, the existence, proliferation, differentiation, migration and invasion of cancer stem cells (CSCs) and the role that CSCs play in tumor initiation, progression, metastasis, drug resistance and relapse/recurrence of the disease has gained widespread interest in cancer research. Although the conventional therapeutic approaches such as surgery, chemotherapy and radiation therapy are effective cancer treatments, very often these treatment modalities fail to target the CSCs, which then later become the source of disease recurrence. A majority of the anti-cancer agents target rapidly dividing cancer cells and normal cells and hence, have side effects that are not expected. Targeting CSCs remains a challenge due to their deviant nature with a low proliferation rate and increased drug resistance mechanism. Ascorbic acid/Vitamin C (Vit.C), a potent antioxidant, is a cofactor for several biosynthetic and gene regulatory enzymes and a vital contributor to immune defense of the body, and was found to be deficient in patients with advanced stages of cancer. Vit.C has gained importance in the treatment of cancer due to its ability to modulate the redox status of the cell and influence epigenetic modifications and significant roles in HIF1α signaling. Studies have reported that intravenous administration of Vit.C at pharmacological doses selectively kills tumor cells and targets CSCs when administered along with chemotherapeutic drugs. In the current article, we provide an in-depth review of how Vit.C plays an important role in targeting CSCs and its possible use as an adjuvant, neoadjuvant or co-treatment in the treatment of cancers.

Glut-1 explains the evolutionary advantage of the loss of endogenous vitamin C-synthesis: The electron transfer hypothesis

Introduction

During evolution, some species including humans, monkeys and fruit bats lost the ability for ascorbic acid (AA) biosynthesis due to inactivation of the enzyme l-gulono-lactone oxidase (GLO) and subsequently became dependent on dietary vitamin C. There are four current hypotheses in relation to the benefit of vitamin C dependence in the context of adaptation and reproduction. Here we advance and test a new ‘electron transfer hypothesis’, which focusses on the role of the expression of glucose transporter 1 (Glut-1) in red blood cells (RBCs) in recycling vitamin C, thereby increasing the efficiency of micronutrient uptake.

Methods

To evaluate the benefit of Glut-1 expression, we determined vitamin C uptake into RBCs and potential release from two different species, humans with l-Gulono-lactone-oxidase (GLO-loss) and pigs with functional GLO.

Results

The oxidized form of vitamin C (dehydroascorbate, DHA) was transported into human RBCs via Glut-1. There was no transport of either the reduced (AA) or the oxidized vitamin in pig erythrocytes.

Conclusion

We propose that the transport of vitamin C increases an intracellular electron pool, which transfers electrons from intracellular ascorbate to extracellular substances like ascorbyl free radical or DHA, resulting in 100-fold smaller daily requirement of this essential redox sensitive micronutrient. This would be an advantage during seasonal changes of the availability from food and may be the key for the survival of individuals without vitamin C biosynthesis.

Lay Summary

40 million years ago some individuals lost the ability to synthesize vitamin C. Why did they survive such as humans until now? Individuals with a specific glucose transporter Glut-1 on their erythrocytes which transports vitamin C need less and are protected from scarcity due to seasons and food competitors.

Effects of oral administration of common antioxidant supplements on the energy metabolism of red blood cells. Attenuation of oxidative stress-induced changes in Rett syndrome erythrocytes by CoQ10

Nutritional supplements are traditionally employed for overall health and for managing some health conditions, although controversies are found concerning the role of antioxidants-mediated benefits in vivo. Consistently with its critical role in systemic redox buffering, red blood cell (RBC) is recognized as a biologically relevant target to investigate the effects of oxidative stress. In RBC, reduction of the ATP levels and adenylate energy charge brings to disturbance in intracellular redox status. In the present work, several popular antioxidant supplements were orally administrated to healthy adults and examined for their ability to induce changes on the energy metabolism and oxidative status in RBC. Fifteen volunteers (3 per group) were treated for 30 days per os with epigallocatechin gallate (EGCG) (1 g green tea extract containing 50% EGCG), resveratrol (325 mg), coenzyme Q10 (CoQ10) (300 mg), vitamin C (1 g), and vitamin E (400 U.I.). Changes in the cellular levels of high-energy compounds (i.e., ATP and its catabolites, NAD and GTP), GSH, GSSG, and malondialdehyde (MDA) were simultaneously analyzed by ion-pairing HPLC. Response to oxidative stress was further investigated through the oxygen radical absorptive capacity (ORAC) assay. According to our experimental approach, (i) CoQ10 appeared to be the most effective antioxidant inducing a high increase in ATP/ADP, ATP/AMP, GSH/GSSG ratio and ORAC value and, in turn, a reduction of NAD concentration, (ii) EGCG modestly modulated the intracellular energy charge potential, while (iii) Vitamin E, vitamin C, and resveratrol exhibited very weak effects. Given that, the antioxidant potential of CoQ10 was additionally assessed in a pilot study which considered individuals suffering from Rett syndrome (RTT), a severe X-linked neuro-developmental disorder in which RBC oxidative damages provide biological markers for redox imbalance and chronic hypoxemia. RTT patients (n = 11), with the typical clinical form, were supplemented for 12 months with CoQ10 (300 mg, once daily). Level of lipid peroxidation (MDA production) and energy state of RBCs were analyzed at 2 and 12 months. Our data suggest that CoQ10 may significantly attenuate the oxidative stress-induced damage in RTT erythrocytes.

The Pharmacokinetics of Vitamin C

The pharmacokinetics of vitamin C (vitC) is indeed complex. Regulated primarily by a family of saturable sodium dependent vitC transporters (SVCTs), the absorption and elimination are highly dose-dependent. Moreover, the tissue specific expression levels and subtypes of these SVCTs result in a compartmentalized distribution pattern with a diverse range of organ concentrations of vitC at homeostasis ranging from about 0.2 mM in the muscle and heart, and up to 10 mM in the brain and adrenal gland. The homeostasis of vitC is influenced by several factors, including genetic polymorphisms and environmental and lifestyle factors such as smoking and diet, as well as diseases. Going from physiological to pharmacological doses, vitC pharmacokinetics change from zero to first order, rendering the precise calculation of dosing regimens in, for example, cancer and sepsis treatment possible. Unfortunately, the complex pharmacokinetics of vitC has often been overlooked in the design of intervention studies, giving rise to misinterpretations and erroneous conclusions. The present review outlines the diverse aspects of vitC pharmacokinetics and examines how they affect vitC homeostasis under a variety of conditions.

Determination of cellular vitamin C dynamics by HPLC-DAD

A redox-sensitive inter-conversion between ascorbic acid (ASC) and its oxidized form dehydroascorbic acid (DHA) in the intracellular environment has been of exceptional interest to recent metabolomics and pharmaceutical research. We developed a chromatographic protocol to instantly determine these vitamers with each identity from cellular extracts, without any labeling and pretreatments. Owing to its simplicity, one can readily continue the assay for hours, an otherwise difficult to cover timescale at which the intracellular DHA-ASC conversion comes into play. The method was validated for the analysis of pancreatic cancer cells, to our knowledge the first-ever study on a nucleated cell type, to trace in detail their kinetics of glucose transporter-dependent DHA uptake and, simultaneously, that for the intracellular ASC conversion. The simplest of all the relevant techniques and yet with the unique ability to provide each vitamer identity on a high-throughput basis, this method should offer the most practical option for VC-involved physiological and pharmaceutical studies including high-dose VC cancer therapy.

Hemolytic jaundice induced by pharmacological dose ascorbic acid in glucose-6-phosphate dehydrogenase deficiency: A case report

RATIONALE

Hemolysis induced by high dose ascorbic acid (AA) in patients with G6PD deficiency has been reported, but is rare. To our knowledge, this is the first reported case of a male with G6PD deficiency, coexpressed with cholecystolithiasis and cholecystitis, who developed extreme hemolysis and hyperbilirubinemia after receiving pharmacological doses ascorbic acid infusion.

PATIENT CONCERNS

A 27-year-old man history with glucose-6-phosphate dehydrogenase deficiency was admitted to our hospital because of cholecystolithiasis and cholecystitis. He appeared with scleral jaundice and very deep colored urine after receiving pharmacological doses ascorbic acid infusion.

DIAGNOSES

Clinical findings when combined with his medical history and various laboratory results confirmed the diagnosis as hemolysis and hyperbilirubinemia induced by ascorbic acid.

INTERVENTIONS

The patient was treated with steroids, hepatoprotective drugs, and folic acid in addition avoidance of agents with known hemolysis risk (such as vitamin C).

OUTCOMES

As a result, the patient's symptoms from hemolytic jaundice improved, hemoglobin remained stable, and the patient was discharged 11 days later.

LESSONS

Clinicians should bear in mind the possibility that vitamin C exposure may result in hemolysis in patients with G6PD deficiency, especially in those with known severe disease.

Ascorbic Acid in Cancer Treatment: Let the Phoenix Fly

Vitamin C (ascorbic acid, ascorbate), despite controversy, has re-emerged as a promising anti-cancer agent. Recent knowledge of intravenous ascorbate pharmacokinetics and discovery of unexpected mechanisms of ascorbate action have spawned many investigations. Two mechanisms of anti-cancer activity with ascorbate have gained prominence: hydrogen peroxide-induced oxidative stress and DNA demethylation mediated by ten-eleven translocation enzyme activation. Here, we highlight salient aspects of the evolution of ascorbate in cancer treatment, provide insights into the pharmacokinetics of ascorbate, describe mechanisms of its anti-cancer activity in relation to the pharmacokinetics, outline promising preclinical and clinical evidence, and recommend future directions.

Impaired brain energy gain upon a glucose load in obesity

BACKGROUND

There is evidence that the brain's energy status is lowered in obesity despite of chronic hypercaloric nutrition. The underlying mechanisms are unknown. We hypothesized that the brain of obese people does not appropriately generate energy in response to a hypercaloric supply.

METHODS

Glucose was intravenously infused in 17 normal weights and 13 obese participants until blood glucose concentrations reached the postprandial levels of 7 mmol/L and 10 mmol/L. Changes in cerebral adenosine triphosphate (ATP) and phosphocreatine (PCr) content were measured by ³¹phosphorus magnetic resonance spectroscopy and stress hormonal measures regulating glucose homeostasis were monitored. Because vitamin C is crucial for a proper neuronal energy synthesis we determined circulating concentrations during the experimental testing.

RESULTS

Cerebral high-energy phosphates were increased at blood glucose levels of 7 mmol/L in normal weights, which was completely missing in the obese. Brain energy content moderately raised only at blood glucose levels of 10 mmol/L in obese participants. Vitamin C concentrations generally correlated with the brain energy content at blood glucose concentrations of 7 mmol/L.

CONCLUSIONS

Our data demonstrate an inefficient cerebral energy gain upon a glucose load in obese men, which may result from a dysfunctional glucose transport across the blood-brain barrier or a downregulated energy synthesis in mitochondrial oxidation processes. Our finding offers an explanation for the chronic neuroenergetic deficiency and respectively missing satiety perception in obesity.

Imaging glutathione depletion in the rat brain using ascorbate-derived hyperpolarized MR and PET probes

Oxidative stress is a critical feature of several common neurologic disorders. The brain is well adapted to neutralize oxidative injury by maintaining a high steady-state concentration of small-molecule intracellular antioxidants including glutathione in astrocytes and ascorbic acid in neurons. Ascorbate-derived imaging probes for hyperpolarized ¹³C magnetic resonance spectroscopy and positron emission tomography have been used to study redox changes (antioxidant depletion and reactive oxygen species accumulation) in vivo. In this study, we applied these imaging probes to the normal rat brain and a rat model of glutathione depletion. We first studied hyperpolarized [1-¹³C]dehydroascorbate in the normal rat brain, demonstrating its robust conversion to [1-¹³C]vitamin C, consistent with rapid transport of the oxidized form across the blood-brain barrier. We next showed that the kinetic rate of this conversion decreased by nearly 50% after glutathione depletion by diethyl maleate treatment. Finally, we showed that dehydroascorbate labeled for positron emission tomography, namely [1-¹¹C]dehydroascorbate, showed no change in brain signal accumulation after diethyl maleate treatment. These results suggest that hyperpolarized [1-¹³C]dehydroascorbate may be used to non-invasively detect oxidative stress in common disorders of the brain.