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

MiMYB1R1-like and MiMYB44-like transcription factors interact with MiGalDHpro to modulate ascorbic acid metabolism during ethylene-mediated mango fruit ripening

Mango (Mangifera indica L.), a climacteric fruit, undergoes rapid ripening driven by ethylene signaling, which plays a crucial role in modulating ascorbic acid (AsA) metabolism. AsA biosynthesis is primarily governed by the L-galactose pathway, with GDP-L-galactose phosphorylase (MiGalDH) catalyzing a key step. This study investigates the transcriptional regulation of MiGalDH by MiMYB1R1-like and MiMYB44-like during ethylene-mediated ripening. Ethylene treatment accelerated ripening and significantly reduced GalDH activity, leading to a decline in AsA levels. Notably, dehydroascorbic acid (DHA) content increased toward the end of storage, suggesting enhanced AsA turnover. RNA-seq analysis revealed that ethylene upregulated MiMYB1R1-like while downregulating MiMYB44-like. Functional assays, including Y1H, EMSA and Dual-Luc analyses, confirmed that both transcription factors directly bind to the MiGalDH promoter to regulate its expression. Virus-induced gene silencing of MiMYB1R1-like and MiMYB44-like significantly reduced MiGalDH expression and AsA content but increased GalDH activity, suggesting enhanced AsA turnover to maintain redox balance. Overexpression of MiMYB1R1-like sustained GalDH activity and promoted AsA biosynthesis throughout ripening, whereas MiMYB44-like overexpression exhibited stage-specific effects-enhancing GalDH activity early but repressing it later. Overall, our findings highlight the pivotal role of MiGalDH in AsA metabolism and identify MiMYB1R1-like and MiMYB44-like as key transcription factors. This study provides novel insights into the transcriptional control of ethylene-induced ripening and AsA metabolism, offering potential targets for improving fruit quality and extending shelf life.

Vitamin C in Cardiovascular Disease: From Molecular Mechanisms to Clinical Evidence and Therapeutic Applications

Vitamin C, also known as ascorbic acid, is an essential nutrient that humans cannot synthesize, making its intake crucial for health. Discovered nearly a century ago, vitamin C is widely recognized for its ability to prevent scurvy and has become one of the most commonly used supplements. Beyond its antioxidant activity, vitamin C is pivotal in regulating lipid metabolism, promoting angiogenesis, enhancing collagen synthesis, modulating remodeling, and stabilizing the extracellular matrix. While preclinical studies have shown promising results, clinical trials have yielded inconsistent findings, due to suboptimal study design, results misinterpretation, and misleading conclusions. This review provides a holistic overview of existing evidence on the pleiotropic role of vitamin C in cardiovascular diseases, identifying both the strengths and limitations of current research and highlighting gaps in understandings in vitamin C's underlying mechanisms. By integrating molecular insights with clinical data and evaluating the pleiotropic role of vitamin C in cardiovascular disease management and prevention, this review aims to guide future research toward personalized, evidence-based therapeutic strategies in clinical practice.

The Role of Purine Metabolism and Uric Acid in Postnatal Neurologic Development

This review explores the essential roles of purine metabolism including the catabolic product, uric acid, in the development of dopaminergic neurons of the substantia nigra pars compacta. The high energy requirements of the substantia nigra pars compacta alongside necessary purinergic neurotransmission and the influence of oxidative stress during development makes these neurons uniquely susceptible to changes in purine metabolism. Uric acid's role as a central nervous system antioxidant may help to ameliorate these effects in utero. Understanding the mechanisms by which purines and uric acid influence development of the substantia nigra pars compacta can help further explain neurologic consequences of inborn errors of purine metabolism, such as Lesch-Nyhan disease.

Transport of dehydroascorbic acid by glucose transporters GLUTs

Vitamin C is a crucial water-soluble antioxidant and an essential cofactor for enzymes like proline and lysine hydroxylases, playing a vital role in cellular physiology. While sodium-dependent ascorbate co-transporters (SVCT1 and SVCT2) are pivotal for vitamin C absorption and bioavailability, dehydroascorbic acid transporters within the facilitative glucose transporter (GLUT) family complement these functions and are relevant in various cellular, tissue-specific, or pathological contexts. This review focuses on comparing the structural and functional characteristics of GLUTs involved in glucose, dehydroascorbic acid and other substrate transport. It also presents evidence of the physiological and pathophysiological roles of dehydroascorbic acid transporters. Improved understanding of these transporters has the potential to advance strategies for preventing, diagnosing, and treating prevalent diseases such as cancer.

Vitamin C-Dependent Uptake of Non-Heme Iron by Enterocytes, Its Impact on Erythropoiesis and Redox Capacity of Human Erythrocytes

In the small intestine, nutrients from ingested food are absorbed and broken down by enterocytes, which constitute over 95% of the intestinal epithelium. Enterocytes demonstrate diet- and segment-dependent metabolic flexibility, enabling them to take up large amounts of glutamine and glucose to meet their energy needs and transfer these nutrients into the bloodstream. During glycolysis, ATP, lactate, and H+ ions are produced within the enterocytes. Based on extensive but incomplete glutamine oxidation large amounts of alanine or lactate are produced. Lactate, in turn, promotes hypoxia-inducible factor-1α (Hif-1α) activation and Hif-1α-dependent transcription of various proton channels and exchangers, which extrude cytoplasmic H+-ions into the intestinal lumen. In parallel, the vitamin C-dependent and duodenal cytochrome b-mediated conversion of ferric iron into ferrous iron progresses. Finally, the generated electrochemical gradient is utilized by the divalent metal transporter 1 for H+-coupled uptake of non-heme Fe2+-ions. Iron efflux from enterocytes, subsequent binding to the plasma protein transferrin, and systemic distribution supply a wide range of cells with iron, including erythroid precursors essential for erythropoiesis. In this review, we discuss the impact of vitamin C on the redox capacity of human erythrocytes and connect enterocyte function with iron metabolism, highlighting its effects on erythropoiesis.

Endogenous and exogenous protection from surgically induced reactive oxygen and nitrogen species

Surgical intervention creates reactive oxygen species through diverse molecular mechanisms, including direct stimulation of immune-mediated inflammation necessary for wound healing. However, dysregulation of redox homeostasis in surgical patients overwhelms the endogenous defense system, slowing the healing process and damaging organs. We broadly surveyed reactive oxygen species that result from surgical interventions and the endogenous and/or exogenous antioxidants that control them. This study assimilates current reports on surgical sources of reactive oxygen and nitrogen species along with literature reports on the effects of endogenous and exogenous antioxidants in human, animal, and clinical settings. Although exogenous antioxidants are generally beneficial, endogenous antioxidant systems account for over 80% of total activity, varying based on patient age, sex, and health or co-morbidity status, especially in smokers, the diabetic, and the obese. Supplementation of exogenous compounds for support in surgical patients is thus theoretically beneficial, but a lack of persuasive clinical evidence has left this potential patient support strategy without clear guidelines. A more thorough understanding of the mechanisms of exogenous antioxidants in patients with compromised health statuses and pharmacokinetic profiling may increase the utility of such support in both the operating and recovery rooms.

Scurvy presenting as difficulty in walking in a child

Scurvy, a disease caused by ascorbic acid (vitamin C) deficiency, is a rare disease in the modern world. We report a case of a boy in middle childhood, with a background of autism, presenting bed-bound due to progressive bilateral lower limb pain, with concomitant rashes, bleeding gums and worsening lethargy. Detailed dietary history revealed a severely restricted diet. Physical examination showed bilateral lower limb ecchymoses, perifollicular hemorrhages, perifollicular hyperkeratosis and cockscrew hairs which are pathognomonic features of scurvy. A low serum ascorbic acid level confirmed the diagnosis. Therapy with oral vitamin C supplement and rehabilitation with multidisciplinary care was successful, with complete resolution of symptoms. This case emphasises the importance of thorough dietary evaluation in children with autism and food selectivity presenting with non-specific symptoms. Physician awareness of nutritional deficiencies avoids unnecessary extensive investigations and sub-specialty referrals and translates to savings in medical expenses.

Lessons learned from "the great mimicker disease": A retrospective study of 18 patients with scurvy

Purpose

Scurvy is an uncommon medical condition that affects children and is caused by an inadequate intake of vitamin C. This study presents the characteristics of patients with scurvy to raise awareness of the diagnostic process in developing countries where laboratory testing for vitamin C levels is often not available.

Methods

A retrospective study was performed from period of 2018 to 2023. Data extraction includes patient age, sex, body mass index, constitutional symptoms, musculoskeletal, mucosal, cutaneous symptoms, other accompanying disorders, anemia, erythrocyte sedimentation rate, C-reactive protein, radiographic examination, vitamin C dose, and duration of treatment. Descriptive statistical analysis was performed in this study.

Results

Eighteen cases (17 males, 1 female) of scurvy were referred to our institution. Thirteen of 18 patients were misdiagnosed before referral. The median age at presentation was 4.5 (range, 2-11) years. The average body mass index was 13.93 ± 0.63 kg/m2. Half of patients had healthy weight. All patients presented with lower limb pain and 17 of 18 with refusal to walk. The median onset of diagnosis was 11 (range 4-48) weeks. White line of Frankel was described in all patients. Seven had anemia and 6 of 18 had increase in erythrocyte sedimentation rate and/or C-reactive protein levels. Only one patient had ascorbic acid levels evaluation before treatment since it was not readily available in our country. Treatment length varied from 2 weeks to 6 months.

Conclusion

The diagnosis of scurvy is frequently delayed due to its extreme rarity in modern society and its ability to mimic numerous other conditions. In children presenting with limb pain and/or reluctance to walk and pathognomonic radiological findings, physicians must prioritize scurvy as a differential diagnosis. In scurvy, vitamin C supplementation is curative.

Vitamin C: From nutrition to oxygen sensing and epigenetics

Vitamin C is unbeatable - at least when it comes to sales. Of all the vitamin preparations, those containing vitamin C sell best. This is surprising because vitamin C deficiency is extremely rare. Nevertheless, there is still controversy about whether the additional intake of vitamin C supplements is essential for our health. In this context, the possible additional benefit is in most cases merely reduced to the known effect as an antioxidant. However, new findings in recent years on the mechanisms of oxygen-sensing and epigenetic control underpin the multifaceted role of vitamin C in a biological context and have therefore renewed interest in it. In the present article, therefore, known facts are linked to these new key data. In addition, available clinical data on vitamin C use of cancer therapy are summarized.

The Role of Vitamins in the Pathogenesis of Asthma

Vitamins play a crucial role in the proper functioning of organisms. Disturbances of their levels, seen as deficiency or excess, enhance the development of various diseases, including those of the cardiovascular, immune, or respiratory systems. The present paper aims to summarize the role of vitamins in one of the most common diseases of the respiratory system, asthma. This narrative review describes the influence of vitamins on asthma and its main symptoms such as bronchial hyperreactivity, airway inflammation, oxidative stress, and airway remodeling, as well as the correlation between vitamin intake and levels and the risk of asthma in both pre- and postnatal life.

The Biochemistry and Effectiveness of Antioxidants in Food, Fruits, and Marine Algae

It is more effective to maintain good health than to regain it after losing it. This work focuses on the biochemical defense mechanisms against free radicals and their role in building and maintaining antioxidant shields, aiming to show how to balance, as much as possible, the situations in which we are exposed to free radicals. To achieve this aim, foods, fruits, and marine algae with a high antioxidant content should constitute the basis of nutritional elements, since natural products are known to have significantly greater assimilation efficiency. This review also gives the perspective in which the use of antioxidants can extend the life of food products, by protecting them from damage caused by oxidation as well as their use as food additives.

Identification of Structural Determinants of the Transport of the Dehydroascorbic Acid Mediated by Glucose Transport GLUT1

GLUT1 is a facilitative glucose transporter that can transport oxidized vitamin C (i.e., dehydroascorbic acid) and complements the action of reduced vitamin C transporters. To identify the residues involved in human GLUT1's transport of dehydroascorbic acid, we performed docking studies in the 5 Å grid of the glucose-binding cavity of GLUT1. The interactions of the bicyclic hemiacetal form of dehydroascorbic acid with GLUT1 through hydrogen bonds with the -OH group of C3 and C5 were less favorable than the interactions with the sugars transported by GLUT1. The eight most relevant residues in such interactions (i.e., F26, Q161, I164, Q282, Y292, and W412) were mutated to alanine to perform functional studies for dehydroascorbic acid and the glucose analog, 2-deoxiglucose, in Xenopus laevis oocytes. All the mutants decreased the uptake of both substrates to less than 50%. The partial effect of the N317A mutant in transporting dehydroascorbic acid was associated with a 30% decrease in the V_max compared to the wildtype GLUT1. The results show that both substrates share the eight residues studied in GLUT1, albeit with a differential contribution of N317. Our work, combining docking with functional studies, marks the first to identify structural determinants of oxidized vitamin C's transport via GLUT1.

Gait Disturbance … of Red Herrings, Oranges, and Lemons - A Case of Missed Vitamin C Deficiency and Lessons Learnt

Vitamin C deficiency resulting in scurvy, is considered to be a rare nutritional disorder in developed countries, thus leading to underdiagnosis with exposure to unnecessary investigations and delay in appropriate treatment. The wide myriad of clinical signs and symptoms with which vitamin C deficiency can present (including haematological, musculoskeletal and vague constitutional symptoms that overlap with other common medical conditions), also contributes to this diagnostic challenge. Despite scurvy being habitually thought to be present in children with neurodevelopmental conditions such as autism spectrum disorder, other important at-risk groups that frequently tend to be forgotten include children with persistent fussy eating behaviour, and children with abnormal vitamin C metabolism. We hereunder present a case of a 10-year-old boy who presented to an acute general hospital for further investigation with gait disturbance. The lack of detailed nutritional assessment on presentation in the first instance led to a missed diagnosis of vitamin C deficiency, thus exposing the child to a wide array of unnecessary investigations and treatments. The added perplexity to the case resulting from false positive results of investigations performed as part of this child's workup, is also discussed.

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.

A Narrative Review on Pediatric Scurvy: The Last Twenty Years

Scurvy is a well-known clinical condition caused by vitamin C deficiency. Although considered a rare disease in high-income countries, it has been recently increasingly reported in children, especially in those with abnormal dietary habits, mental or physical disabilities. We performed an extensive review of the literature analyzing studies published in the last 20 years focusing on clinical features, differential diagnosis and diagnostic delay. Fifteen articles were selected, collectively reporting a total of 166 children. Because of the wide clinical spectrum (musculoskeletal complaints and/or mucocutaneous lesions or systemic symptoms), scurvy can mimic several conditions, including autoimmune diseases, infections, and neoplasia. In addition, frequent findings such as normal nutritional status, anemia or elevated inflammatory markers may guide clinicians towards the abovementioned misdiagnoses. Scurvy should be considered in patients presenting with musculoskeletal complaints, not only in those with risk factors but also in healthy children. A focused dietary history and a careful physical examination, assessing other signs of vitamin C deficiency, are mandatory in these patients. When suspected, the dosage of serum vitamin C is the diagnostic gold standard; furthermore, imaging studies, performed by an expert radiologist, can reveal the typical features of scurvy. Only early diagnosis can avoid unnecessary investigations and potentially fatal complications of the disease.

When the limp has a dietary cause: A retrospective study on scurvy in a tertiary Italian pediatric hospital

The limping child frequently represents a diagnostic challenge. The differential diagnosis is broad and should include vitamin C deficiency. Scurvy, resulting from vitamin C deficiency, is the oldest-known nutritional disorder. Despite its rarity in developed countries, scurvy has been increasingly reported in recent years in pediatric patients, particularly those with autism or neurological disabilities. In the present retrospective study, we describe the clinical, laboratory, and radiological features of 8 patients diagnosed with scurvy in the Pediatrics Unit of Meyer Children's University Hospital, between January 2016 and December 2021. The majority (87%) were males, and the median age was 3.7 years. Half of the patients had comorbidities known to be risk factors for scurvy, while the remaining patients were previously healthy. All the children were admitted for musculoskeletal symptoms, ranging from lower limb pain (87%) to overt limping (87%). Mucocutaneous involvement was observed in 75% cases. Microcytic anemia and elevated inflammatory markers were common laboratory findings. Bone radiographs, performed on all patients, were often interpreted as normal at first, with osteopenia (62%) as the most frequent finding; notably, after re-examination, they were reported as consistent with scurvy in four patients. The most common magnetic resonance imaging findings were multifocal symmetrical increased signal on STIR sequence within metaphysis, with varying degrees of bone marrow enhancement, adjacent periosteal elevation and soft tissue swelling. Differential diagnosis was challenging and frequently required invasive diagnostic procedures like bone marrow biopsy, performed in the first three patients of our series. The median time frame between clinical onset and the final diagnosis was 35 days. Notably, the interval times between admission and diagnosis become progressively shorter during the study period, ranging from 44 to 2 days. Treatment with oral vitamin C led to improvement/resolution of symptoms in all cases. In conclusion, scurvy should be considered in the differential diagnosis in a limping child, performing a detailed dietary history and careful physical examination, looking for mucocutaneous lesions. A quick and correct diagnostic path avoids invasive diagnostic procedures and reduces the risk of long-term complications.

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.

Scurvy: A Neglected Cause of Muscle Pain and Weakness in a Child With Picky Eating Behavior

Ascorbic acid (vitamin C) is an essential micronutrient that the human's body cannot synthesize endogenously. Scurvy, a disease of ascorbic acid deficiency, can manifest in a myriad of presentations. Due to its rarity in the modern world, scurvy is considered as a disease of the past. We present a paediatric case of scurvy with musculoskeletal manifestations as a result of picky eating behavior. 

We report a previously healthy nine-year-old boy who presented with unexplained progressive bilateral lower limb generalized weakness and pain for two months. All initial biochemical and radiological investigations were unremarkable. Upon further history taking, he had severe picky eating behavior which raised the suspicion of scurvy. The diagnosis was confirmed with a serum ascorbic acid test. After ascorbic acid supplementation, his symptoms resolved immediately. Further food behavioral modification counselling to his family members helped to change his diet in a lasting way. As a result, he had no recurrence of symptoms.

This case highlights the importance of having a high index of suspicion for an uncommon disease and emphasizes the need for a detailed dietary history upon patient’s presentation.