Vitamin C revisited
Critical Care volume 18, Article number: 460 (2014)
This narrative review summarizes the role of vitamin C in mitigating oxidative injury-induced microcirculatory impairment and associated organ failure in ischemia/reperfusion or sepsis. Preclinical studies show that high-dose vitamin C can prevent or restore microcirculatory flow impairment by inhibiting activation of nicotinamide adenine dinucleotide phosphate-oxidase and inducible nitric oxide synthase, augmenting tetrahydrobiopterin, preventing uncoupling of oxidative phosphorylation, and decreasing the formation of superoxide and peroxynitrite, and by directly scavenging superoxide. Vitamin C can additionally restore vascular responsiveness to vasoconstrictors, preserve endothelial barrier by maintaining cyclic guanylate phosphatase and occludin phosphorylation and preventing apoptosis. Finally, high-dose vitamin C can augment antibacterial defense. These protective effects against overwhelming oxidative stress due to ischemia/reperfusion, sepsis or burn seems to mitigate organ injury and dysfunction, and promote recovery after cardiac revascularization and in critically ill patients, in the latter partially in combination with other antioxidants. Of note, several questions remain to be solved, including optimal dose, timing and combination of vitamin C with other antioxidants. The combination obviously offers a synergistic effect and seems reasonable during sustained critical illness. High-dose vitamin C, however, provides a cheap, strong and multifaceted antioxidant, especially robust for resuscitation of the circulation. Vitamin C given as early as possible after the injurious event, or before if feasible, seems most effective. The latter could be considered at the start of cardiac surgery, organ transplant or major gastrointestinal surgery. Preoperative supplementation should consider the inhibiting effect of vitamin C on ischemic preconditioning. In critically ill patients, future research should focus on the use of short-term high-dose intravenous vitamin C as a resuscitation drug, to intervene as early as possible in the oxidant cascade in order to optimize macrocirculation and microcirculation and limit cellular injury.
Critically ill patients suffer from multiple organ dysfunction mostly occurring in the course of ischemia/reperfusion or septic shock. In these conditions, overwhelming amounts of reactive oxygen species (ROS) and reactive nitrogen species are generated. ROS are oxidizing agents produced during mitochondrial respiration and phagocytosis. In addition, ROS cause post-translational modifications of proteins, modifying their action and affecting cellular signaling, gene expression, oxygen sensing and other physiological processes ,. In low concentrations, ROS also enhance the antioxidant response via nuclear factor-erythroid 2-related factor 2 activation, and thereby promote cell survival . While ROS are crucial for body homeostasis and defense, they cause harm if abundant production overwhelms the antioxidant defense. In that case, ROS can induce reversible or irreversible injury to proteins, lipids and nucleic acids, thereby contributing to endothelial dysfunction, cellular injury and multiple organ dysfunction.
Endothelial dysfunction is a uniform, ROS-mediated manifestation of ischemia/reperfusion and sepsis. Furthermore, ROS-induced damage to the glycocalyx, cellular membranes and junctions leads to increased permeability, adhesion of leukocytes and platelets with local activation of inflammation and coagulation, leads to loss of endothelial vasodilatation and attenuates the vascular response to vasoconstrictors -. Subsequent hypotension, vascular leakage and microcirculatory flow impairment at reperfusion augment tissue hypoxia due to increased diffusion distance for oxygen and may thereby enhance cellular damage and organ failure ,. Ascorbate, the redox form of vitamin C, is a physiological antioxidant. We hypothesize that the early administration of a high pharmacological dose of vitamin C to patients with sepsis or after ischemia/reperfusion can reduce oxidative damage to endothelial and other cells, and thereby improve tissue perfusion and oxygenation, and mitigate subsequent organ dysfunction ,.
Vitamin C also has other effects. Vitamin C improves immune function, and facilitates enteral uptake of nonheme iron, reduction of folic acid intermediates and synthesis of collagen (wound healing), cortisol, catecholamines and carnitine -. These effects are beyond the scope of this review.
The aim of this narrative review is to summarize the role of vitamin C in mitigating ROS-induced damage to endothelial and myocardial cells in ischemia/reperfusion or sepsis. By limiting endothelial dysfunction, vitamin C might improve tissue perfusion and reduce tissue hypoxia and subsequent organ dysfunction. Experimental and clinical studies on the use of vitamin C are reported with a focus on cardiovascular effects.
Ischemia/reperfusion-induced and sepsis-induced endothelial dysfunction is initiated by increased amounts of ROS produced by the induction of enzymes such as nicotinamide adenine dinucleotide phosphate-oxidase (NOX) and uncoupling of mitochondrial oxidative phosphorylation and endothelial nitric oxide synthase (eNOS). ROS are additionally produced by xanthine oxidase, lipoxygenase and cyclooxygenase, and during oxidation of catecholamines (Figure 1) ,.
Unopposed ROS oxidize tetrahydrobiopterin (BH4), the cofactor of eNOS, and thereby reduce eNOS activity, the enzyme producing endothelial nitric oxide (eNO). eNO initiates vasodilatation by stimulating soluble guanylcyclase and increasing cyclic guanosine monophosphate in smooth muscle cells . It also inhibits platelet aggregation and adhesion of activated platelets and leukocytes. eNO is therefore crucial for patency of the microcirculation and its depletion hampers organ perfusion and oxygenation. In the absence of BH4, eNOS becomes uncoupled, producing superoxide (O2 –) rather than nitric oxide (NO) . O2 – and NO yield peroxynitrite, the most damaging ROS.
Role of vitamin C: in vitrostudies
The underlying mechanisms for the effect of ascorbate on these pathways have been demonstrated in in vitro studies with cultured endothelial cells. Endothelial cells can accumulate ascorbate to millimolar levels  and represent an appropriate model to study the effects of high-dose vitamin C. In vitro studies are presented focusing on protective effects of vitamin C (ascorbate) in ischemia/reperfusion and sepsis.
Ascorbate decreases oxidative stress in endothelial cells by reducing the production of O2 –, hydrogen peroxide and peroxynitrite. Mechanisms include prevention of NOX activation, decreased inducible nitric oxide synthase (iNOS) expression and increased NO bioavailability (Figure 1) -. NOX is the major source of ROS in endothelial and myocardial cells ,. Activation of NOX leads to the formation of intracellular O2 –. Addition of ascorbate to endothelial cells exposed to oxidative stress prevented activation of NOX by inhibition of subunit p47phox expression (mediated by the Jak2/Stat1/IRF1 signaling pathway) . NOX-derived ROS additionally increase the expression of iNOS , producing excessive NO. Abundant NO in the presence of O2 – generates peroxynitrite. Ascorbate prevented iNOS expression . Ascorbate also scavenges O2 –, but only at high levels ≥10 mmol/l .
Furthermore, ascorbate can increase NO bioavailability by preventing BH4 oxidation and recovering oxidized BH4. Recovery of BH4 by ascorbate prevents uncoupling of eNOS and associated O2 – production and restores eNOS activity and subsequent generation of eNO, which has a pivotal role in endothelial-dependent vasodilatation.
ROS additionally increase endothelial permeability , causing edema and contributing to organ dysfunction. Ascorbate can tighten the endothelial barrier through several pathways.
Constitutive eNO is required to control endothelial permeability and prevent loss of tight junctions between cells . Loading endothelial cells with ascorbate preserved eNO generation through eNOS and decreased endothelial permeability. This effect depended on eNOS and guanylatecyclase, suggesting that tightening of the endothelium involved NO generation by eNOS and subsequent NO-dependent activation of guanylatecyclase .
Exposure of endothelial cells to lipopolysaccharide (LPS) increases endothelial permeability by inducing NOX-dependent protein phosphatase 2A activity and subsequent occludin dephosphorylation. Phosphorylated occludin is crucial to maintain tight junctions. Ascorbate protects against vascular leakage by inhibiting protein phosphatase 2A activation .
Furthermore, oxidants and LPS increase apoptosis, impairing the endothelial barrier. LPS decreases Bcl-2 (which inhibits apoptosis) and increases Bax (which suppresses the ability of Bcl2 to block apoptosis). Ascorbate inhibited apoptosis  and protected endothelial progenitor cells . Simultaneous administration with vitamin E had a synergistic effect on the prevention of apoptosis.
Impairment of microcirculatory flow
Oxidative stress stimulates the expression of tissue factors and cellular adhesion molecules at the surface of platelets and endothelial cells , promoting adhesion of leucocytes to the endothelium and formation of microthrombi and thus impairing microcirculatory flow. In cultured endothelial cells, ascorbate inhibited the tumor necrosis factor alpha-induced expression of intracellular adhesion molecule-1 in a dose-dependent manner , probably by modulating the production of ROS and reactive nitrogen species. By preventing intracellular adhesion molecule expression, ascorbate reduces leukocyte plugging in microvessels and microcirculatory flow impairment.
Myocardial effects of vitamin C in ischemia/reperfusion
Ischemia/reperfusion injures not only the endothelium but also the myocardium, leading to stunning and arrhythmias. Loading isolated cardiomyocytes subjected to hypoxia/reoxygenation with ascorbate improved their resistance to cell death by decreasing ROS generation and inhibiting (proapoptotic) Bax expression, caspase-3 activation, and cytochrome-c translocation into the cytoplasm . Pretreatment with vitamin C or vitamin E of isolated cardiomyocytes exposed to singlet oxygen reduced the number of hypercontracted cardiomyocytes in a concentration-dependent manner. Simultaneous administration of both vitamins acted synergistically .
Immune effects of vitamin C in sepsis
In sepsis, ascorbate also influences macrophage activity and bacterial growth. Macrophages play an important role in sepsis, enhancing cytokine production as well as production of several types of ROS. ROS are necessary to overcome infections, but are only beneficial if their production is controlled. Incubation of macrophages with ascorbate regulated the phagocytic process by reducing adherence, chemotaxis, ingestion and O2 – anion production . Furthermore, ascorbate has profound bacteriostatic activity. Ascorbate (in concentrations from 100 to 1,000 μM) significantly inhibited bacterial replication in dilute fecal samples in vitro.
Role of vitamin C: animal studies
Beneficial effects of ascorbate pretreatment on organ function were observed in ischemia reperfusion injury models of rat heart  and rabbit kidney , and of rat skeletal muscle ,, lung  and liver -. Studies are summarized in Table 1.
In a rat model of cardiac arrest (ventricular fibrillation and electrical shock), intravenous ascorbate at the start of resuscitation alleviated postcardiac arrest myocardial necrosis and mitochondrial damage, reduced lipid peroxidation and improved the resuscitation success rate and 72-hour survival . In a pig model of coronary artery ischemia/reperfusion and preconditioning, intravenous ascorbate started 30 minutes before ischemic preconditioning or ischemia had no effect on infarct size, but abolished the reduction in infarct size by ischemic preconditioning . In a rabbit renal ischemia model, ascorbate ameliorated renal structure and function . Ascorbate also had a positive effect on muscle injury when administered intravenously (i.v.) during ischemia/reperfusion of the leg in rats . Experiments with different intravenous ascorbate doses to rats prior to hepatic ischemia reperfusion found antioxidant effects at low and moderate doses and predominant pro-oxidant effects at extremely high doses (1,000 mg/kg) . In addition, vitamin C administered after ischemic preconditioning but before clamping of the liver blood flow reduced hepatic mitochondrial damage and dysfunction . Thus, in these animal models, ascorbate reduced ischemic organ injury and improved function, but abolished the protective effects of ischemic preconditioning on organ injury.
The most frequently used sepsis animal models are feces injection into the peritoneum (FIP), cecal ligation and puncture (CLP) and intraperitoneal injection of LPS.
Ascorbate plasma concentrations rapidly declined in lymphocytes and macrophages , muscle  and plasma , of septic rodents. Endotoxin also depleted myocardial ascorbate in guinea pig hearts after as early as 4 hours, even after dietary supplementation for 5 weeks .
Systemic circulation, microcirculation and permeability
Ascorbate (76 mg/kg i.v.) restored blood pressure and prevented microvascular dysfunction in skeletal muscle of septic rats . In a mouse model of FIP, ascorbate (10 mg/kg i.v.) inhibited impairment of microvascular perfusion when administered early (0 hours) and reversed septic platelet adhesion and flow impairment with late administration (after 6 hours) . Similarly, ascorbate improved capillary blood flow by an eNOS-dependent mechanism when administered 6 hours after FIP ,. In addition, ascorbate (200 mg/kg i.v.) administration before CLP protected against impaired arteriolar constriction and loss of catecholamine responsiveness and improved 24-hour survival in mice ,. Ascorbate prevented arteriolar vasoconstriction by inhibiting eNOS uncoupling and iNOS-derived and neuronal nitric oxide synthase-derived NO production, when given before but also 3 hours after CLP in mice -. Moreover, ascorbate (200 mg/kg i.v.) prevented vascular leakage in a mouse CLP model by inhibiting excessive production of NO by iNOS and neuronal nitric oxide synthase, and of O2 – by NOX, and by inhibiting the activation of protein phosphatase 2A, thereby preserving occludin phosphorylation . Ascorbate thus restored several seemingly contradictory disorders contributing the heterogeneity of the septic circulation. Ascorbate improved microcirculatory perfusion by NOX inhibition and arteriolar vasodilator responsiveness (neuronal nitric oxide synthase related), restored vasoconstrictor responsiveness by inhibiting iNOS expression and prevented vascular leakage.
Effects on organ injury and function
Vitamin C prevented the increase in endotoxin-induced myocardial uric acid accumulation, a marker of ischemia-induced oxidative stress , and protected against endotoxin-induced oxidative damage to proteins in the guinea pig liver . Ascorbate (100 mg/kg i.v.) reduced hepatic microvascular dysfunction during polymicrobial sepsis when administered immediately after CLP in rats by reducing oxidative stress and lipid peroxidation, and regulating hepatic vasoregulatory gene expression ,. In addition, ascorbate prevented the sepsis-induced decrease in several cytochrome P450 enzyme activities, thereby improving drug-metabolizing function . Ascorbate (200 mg/kg i.v.) also attenuated sepsis-induced acute lung injury in a mouse model of FIP or LPS , and improved 72-hour survival . Finally, oral prefeeding with ascorbate decreased bacterial concentrations and improved survival after intraperitoneal injection of Klebsiella pneumonia in mice .
Role of vitamin C in ischemia/reperfusion and sepsis: human volunteers
In human volunteers, both ischemia/reperfusion injury (20 minutes of forearm ischemia)  and low-dose LPS  reduced plasma vitamin C concentrations and diminished acetylcholine-induced, endothelial-dependent vasodilatation. High-dose (24 mg/minute) intra-arterial vitamin C increased BH4 concentrations , reduced neutrophil oxidative burst and completely restored the response to acetylcholine, but not to glyceryl-trinitrate (endothelium-independent dilatation), supporting its endothelial protective effect. Vitamin C also corrected the LPS-induced decreased responsiveness to norepinephrine and angiotensin II . Both vasopressors act independent of the endothelium, but their effect is blunted by oxidative stress and inflammation. These volunteer studies originate from the same group.
Several preclinical in vitro, animal and volunteer studies thus show that vitamin C in moderate to high doses can reduce ROS-induced microcirculatory flow impairment, microvascular leakage, decreased responsiveness to vasoconstrictors, and myocardial and other organ injury. Contradictory results in ischemia/reperfusion can partially be explained by the timing of administration, because vitamin C abrogates ischemic preconditioning. Furthermore, vitamin C reduces the overwhelming neutrophil response and inhibits bacterial replication.
Plasma concentrations, dose and pharmacokinetics of vitamin C: patients
Vitamin C plasma concentrations depend on absorption, the distribution volume, cellular uptake, consumption and renal reabsorption and excretion. Patients with sepsis, hemorrhage, multiple organ failure, stroke, traumatic brain injury or after cardiac surgery have low vitamin C concentrations in plasma - and leukocytes , probably due to increased consumption in the cell  and high leukocyte turnover. Since intracellular ascorbate concentrations in mononuclear leucocytes and in granulocytes are respectively 80 and 25 times higher than in plasma , a high production and turnover of these cells contributes to depletion. Low plasma concentrations correlate with inflammation (C-reactive protein)  and multiple organ failure , suggesting consumption during oxidative stress.
Recommended doses of vitamins are generally based on preventing deficiency in healthy humans. In healthy volunteers, manifestations of vitamin C deficiency (fatigue and/or irritability) occurred at plasma concentrations below 20 μmol/l. Clear scurvy can develop below 11 μmol/l . With sufficient vitamin C intake (100 to 300 mg/day), plasma concentrations plateau at 70 to 85 μmol/l and do not exceed 220 μmol/l at maximal oral intake (3 g six times daily) . Oral dose is limited by intestinal absorption and high oral intake causes diarrhea . Urinary excretion depends on the plasma concentration and is minimal at low plasma concentrations due to active tubular reabsorption ,. Threshold plasma concentration for excretion may be 55 μmol/l .
Ascorbate is transported into the cell by ascorbate-specific membrane transporters and less so as dehydroascorbic acid via glucose transporters . Within the cell, dehydroascorbic acid can be rapidly reduced to ascorbate, thereby recycling ascorbate . The ascorbate transporter SVCT1 is expressed predominantly in epithelial tissues such as the intestine and kidney, maintaining optimal vitamin C concentrations in the body. The ascorbate transporter SVCT2 delivers ascorbic acid to tissues . Immune and inflammatory cells have intracellular concentrations 10 to 80 times higher than plasma, protecting them against ROS generated by respiratory burst or phagocytosis . Neurons have concentrations as high as 10 mmol/l, sufficient for scavenging O2 –,. Of note, ascorbate does not pass the blood–brain barrier. However, dehydroascorbic acid does so via the glucose transporter GLUT1 and is reduced to ascorbate after uptake in neurons. Intravenous administration of dehydroascorbic acid confers supraphysiologic concentrations of ascorbate in the brain .
Notably, concentrations attained with high oral dosing are sufficient to modulate enzymes such as nicotinamide adenine dinucleotide phosphate but not for scavenging O2 –, which reacts with NO at a rate 105-fold greater than that with ascorbate . A plasma concentration of 10 mmol/l would be required to compete with NO and for complete restoration of NO bioavailability. High plasma concentrations can be obtained with intravenous administration. However, mild dietary supplementation of vitamin C reduced peroxynitrite formation and atrial electrophysiological remodeling induced by rapid pacing in dogs , probably due to higher intracellular vitamin C concentration.
High intravenous vitamin C doses, up to 3 to 6 g daily, are needed to restore normal plasma concentrations in critically ill patients . To attain plasma concentrations over 10 mmol/l for 3 hours, a short-term infusion of 30 to 100 g would be required ,. High pharmacological doses of vitamin C seem to be well tolerated ,. Prolonged oral intake of high-dose vitamin C increases the risk of oxalate kidney stones . However, this complication has not been reported with short-term high intravenous dosing . Of note, low dose ascorbate can also act as a pro-oxidant . However, after a 1 g vitamin C intravenous infusion, ascorbyl radical concentrations increased much more in healthy controls than in septic patients, who had a lower baseline concentration .
Role of vitamin C in ischemia/reperfusion: clinical studies
Whereas most preclinical studies investigate the role of vitamin C alone, clinical studies often used a combination of antioxidants. Some studies are performed in conditions similar to animal models, reporting the use of vitamin C before the ischemic incident (coronary bypass surgery) or directly at reperfusion (percutaneous coronary interventions) or shock resuscitation (burns). In the critically ill studies, combinations of antioxidants were generally given after the hyperacute phase.
Percutaneous coronary intervention
In patients undergoing elective percutaneous coronary intervention, vitamin C in a dose of 1 g over 1 hour improved microcirculatory reperfusion, and left ventricular and renal function . This improvement was associated with reduced markers of oxidative injury.
Atrial fibrillation is the most common arrhythmia after cardiac surgery, developing in 15 to 50 % of patients depending on several risk factors . Atrial fibrillation increases short-term and long-term morbidity and length of hospital stay ,, and necessitates anticoagulation to prevent stroke. Its pathogenesis is multimodal but accumulating evidence indicates a role of oxidative stress -. Ischemia/reperfusion, atrial stress and angiotensin increase atrial NOX activity, which is associated with postoperative atrial fibrillation -. Oxidative damage initiates breakdown of cell membranes, mitochondrial dysfunction, calcium overload, apoptosis and also inflammation by signaling activation of nuclear factor-kappaB and activator protein-1 transcription factors , thereby initiating electrophysiological remodeling.
After cardiac surgery, a massive depletion of vitamin C has been observed . Several studies suggest a beneficial effect of vitamin C on the occurrence of new atrial fibrillation and some on enhanced recovery, although not all studies are positive (Table 2). In a matched control study, the perioperative use of vitamin C reduced the incidence of new postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting . A subsequent randomized controlled trial found a reduction in postoperative atrial fibrillation when adding vitamin C to a β-blocker . In the largest trial, vitamin C did not reduce atrial fibrillation, but it reduced time on mechanical ventilation . Another clinical trial found a reduction in atrial fibrillation, but its incidence in the control group was extremely high . The most recent randomized controlled trial found a reduction in postoperative atrial fibrillation comparing preoperative ω-3 poly-unsaturated fatty acids with vitamin C and vitamin E supplementation with placebo (see Table 2) . An older Chinese study using a very high dose of intravenous vitamin C (250 mg/kg) found less cardiac injury, better cardiac performance and shorter intensive care and hospital stay .
Studies differ in the timing, route and dose of vitamin C, and in the combination of other antioxidants. Timing may be crucial in cardiac surgery, because preoperative episodes of ischemia and reperfusion protect the myocardium against perioperative ischemic damage and vitamin C may hamper the beneficial effects of ischemic preconditioning on reducing infarct size .
Critically ill patients
Several clinical trials in critically ill patients have reported favorable results of high-dose vitamin C alone ,, or in combination with vitamin E , or with selenium, zinc and vitamin B , (Table 3). The main beneficial outcomes include reduction in pulmonary morbidity and new organ failure, less mechanical ventilation days and shorter length of ICU and/or hospital stay. Some studies measured lower markers of oxidative stress ,. Although ROS can signal host defense in low concentrations, the parallel finding of less oxidant stress and less organ dysfunction suggests a beneficial effect of reducing overwhelming ROS during critical illness. The largest study, however, using a mixture of micronutrients including oral vitamin C, found no effect on 28-day mortality or length of stay. Of note, the control group in Berger and colleagues’ study received 500 mg/day vitamin C .
Combined administration with vitamin E and other micronutrients obscures the role of vitamin C. However, vitamin C regenerates vitamin E, and vitamin E is only consumed after depletion of vitamin C . Two small studies in burn patients studied a very high dose of vitamin C alone (66 mg/kg/hour) for about 24 hours and found a reduction in resuscitation volume, better gas exchange and less days on mechanical ventilation  and increased urinary output , probably indicating less capillary leak. No signs of acidosis or renal insufficiency were found with this high dose. However, although vitamin C reduced morbidity in some studies, a mortality reduction was not found. We hypothesize that the effect of vitamin C can be improved by very early administration of a high intravenous dose as part of the resuscitation bundle in patients with shock.
This narrative review summarizes the role of vitamin C in mitigating ROS-induced microcirculatory impairment and associated organ failure in ischemia/reperfusion or sepsis. Preclinical studies show that high-dose vitamin C can prevent or restore ROS-induced microcirculatory flow impairment, prevent or restore vascular responsiveness to vasoconstrictors, preserve endothelial barrier and augment antibacterial defense. These protective effects against oxidative stress seem to mitigate organ injury and dysfunction, and promote recovery in most but not all clinical studies after cardiac revascularization and in critically ill patients.
Of note, many questions remain to be solved, including the optimal dose, timing, combination of vitamin C with other antioxidants and the inhibiting effect of vitamin C on the protection of ischemic preconditioning. However, high-dose vitamin C provides a cheap, strong and multifaceted antioxidant. Future research should answer the question of whether short-term high-dose intravenous vitamin C can mitigate the overwhelming oxidant cascade and thereby improve resuscitation of the macrocirculation and microcirculation and limit cellular injury in critically ill patients.
- BH4 :
Cecal ligation and puncture
Endothelial nitric oxide
Endothelial nitric oxide synthase
Feces injection into the peritoneum
Inducible nitric oxide synthase
Nicotinamide adenine dinucleotide phosphate-oxidase
- O2 – :
reactive oxygen species
Bedard K, Krause KH: The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology. Physiol Rev. 2007, 87: 245-313.
Kobayashi M, Yamamoto M: Molecular mechanisms activating the Nrf2-Keap1 pathway of antioxidant gene regulation. Antioxid Redox Signal. 2005, 7: 385-394.
Burke-Gaffney A, Evans TW: Lest we forget the endothelial glycocalyx in sepsis. Crit Care. 2012, 16: 121-
van den Berg BM, Nieuwdorp M, Stroes ES, Vink H: Glycocalyx and endothelial (dys)function: from mice to men. Pharmacol Rep. 2006, 58: 75-80.
Rubio-Gayosso I, Platts SH, Duling BR: Reactive oxygen species mediate modification of glycocalyx during ischemia–reperfusion injury. Am J Physiol Heart Circ Physiol. 2006, 290: H2247-H2256.
Wu F, Wilson JX, Tyml K: Ascorbate inhibits iNOS expression and preserves vasoconstrictor responsiveness in skeletal muscle of septic mice. Am J Physiol Regul Integr Comp Physiol. 2003, 285: R50-R56.
De Backer DS, Orbegozo Cortes D, Donadello K, Vincent JL: Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock. Virulence. 2014, 5: 73-79.
Hernandez G, Bruhn A, Ince C: Microcirculation in sepsis: new perspectives. Curr Vasc Pharmacol. 2013, 11: 161-169.
Biesalski HK, McGregor GP: Antioxidant therapy in critical care – is the microcirculation the primary target?. Crit Care Med. 2007, 35: S577-S583.
May JM: How does ascorbic acid prevent endothelial dysfunction?. Free Radic Biol Med. 2000, 28: 1421-1429.
Shaik-Dasthagirisaheb YB, Varvara G, Murmura G, Saggini A, Caraffa A, Antinolfi P, Tete' S, Tripodi D, Conti F, Cianchetti E, Toniato E, Rosati M, Speranza L, Pantalone A, Saggini R, Tei M, Speziali A, Conti P, Theoharides TC, Pandolfi F: Role of vitamins D, E and C in immunity and inflammation. J Biol Regul Homeost Agents. 2013, 27: 291-295.
May JM, Harrison FE: Role of vitamin C in the function of the vascular endothelium. Antioxid Redox Signal. 2013, 19: 2068-2083.
Levine M, Rumsey SC, Daruwala R, Park JB, Wang Y: Criteria and recommendations for vitamin C intake. JAMA. 1999, 281: 1415-1423.
Hellsten Y, Nyberg M, Jensen LG, Mortensen SP: Vasodilator interactions in skeletal muscle blood flow regulation. J Physiol. 2012, 590: 6297-6305.
Werner ER, Blau N, Thony B: Tetrahydrobiopterin: biochemistry and pathophysiology. Biochem J. 2011, 438: 397-414.
Wu F, Tyml K, Wilson JX: Ascorbate inhibits iNOS expression in endotoxin- and IFN gamma-stimulated rat skeletal muscle endothelial cells. FEBS Lett. 2002, 520: 122-126.
Wu F, Tyml K, Wilson JX: iNOS expression requires NADPH oxidase-dependent redox signaling in microvascular endothelial cells. J Cell Physiol. 2008, 217: 207-214.
Mortensen A, Lykkesfeldt J: Does vitamin C enhance nitric oxide bioavailability in a tetrahydrobiopterin-dependent manner? In vitro, in vivo and clinical studies. Nitric Oxide. 2014, 36: 51-57.
Frey RS, Ushio-Fukai M, Malik AB: NADPH oxidase-dependent signaling in endothelial cells: role in physiology and pathophysiology. Antioxid Redox Signal. 2009, 11: 791-810.
Wu F, Schuster DP, Tyml K, Wilson JX: Ascorbate inhibits NADPH oxidase subunit p47phox expression in microvascular endothelial cells. Free Radic Biol Med. 2007, 42: 124-131.
Jackson TS, Xu A, Vita JA, Keaney JF: Ascorbate prevents the interaction of superoxide and nitric oxide only at very high physiological concentrations. Circ Res. 1998, 83: 916-922.
Wilson JX: Mechanism of action of vitamin C in sepsis: ascorbate modulates redox signaling in endothelium. Biofactors. 2009, 35: 5-13.
May JM, Qu ZC: Nitric oxide mediates tightening of the endothelial barrier by ascorbic acid. Biochem Biophys Res Commun. 2011, 404: 701-705.
Han M, Pendem S, Teh SL, Sukumaran DK, Wu F, Wilson JX: Ascorbate protects endothelial barrier function during septic insult: role of protein phosphatase type 2A. Free Radic Biol Med. 2010, 48: 128-135.
Haendeler J, Zeiher AM, Dimmeler S: Vitamin C and E prevent lipopolysaccharide-induced apoptosis in human endothelial cells by modulation of Bcl-2 and Bax. Eur J Pharmacol. 1996, 317: 407-411.
Fiorito C, Rienzo M, Crimi E, Rossiello R, Balestrieri ML, Casamassimi A, Muto F, Grimaldi V, Giovane A, Farzati B, Mancini FP, Napoli C: Antioxidants increase number of progenitor endothelial cells through multiple gene expression pathways. Free Radic Res. 2008, 42: 754-762.
Chen YH, Lin SJ, Chen YL, Liu PL, Chen JW: Anti-inflammatory effects of different drugs/agents with antioxidant property on endothelial expression of adhesion molecules. Cardiovasc Hematol Disord Drug Targets. 2006, 6: 279-304.
Mo SJ, Son EW, Rhee DK, Pyo S: Modulation of TNF-alpha-induced ICAM-1 expression, NO and H2O2 production by alginate, allicin and ascorbic acid in human endothelial cells. Arch Pharm Res. 2003, 26: 244-251.
Guaiquil VH, Golde DW, Beckles DL, Mascareno EJ, Siddiqui MA: Vitamin C inhibits hypoxia-induced damage and apoptotic signaling pathways in cardiomyocytes and ischemic hearts. Free Radic Biol Med. 2004, 37: 1419-1429.
Rinne T, Mutschler E, Wimmer-Greinecker G, Moritz A, Olbrich HG: Vitamins C and E protect isolated cardiomyocytes against oxidative damage. Int J Cardiol. 2000, 75: 275-281.
Victor VV, Guayerbas N, Puerto M, Medina S, De la Fuente M: Ascorbic acid modulates in vitro the function of macrophages from mice with endotoxic shock. Immunopharmacology. 2000, 46: 89-101.
Armour J, Tyml K, Lidington D, Wilson JX: Ascorbate prevents microvascular dysfunction in the skeletal muscle of the septic rat. J Appl Physiol (1985). 2001, 90: 795-803.
Tsai MS, Huang CH, Tsai CY, Chen HW, Lee HC, Cheng HJ, Hsu CY, Wang TD, Chang WT, Chen WJ: Ascorbic acid mitigates the myocardial injury after cardiac arrest and electrical shock. Intensive Care Med. 2011, 37: 2033-2040.
Lloberas N, Torras J, Herrero-Fresneda I, Cruzado JM, Riera M, Hurtado I, Grinyo JM: Postischemic renal oxidative stress induces inflammatory response through PAF and oxidized phospholipids. Prevention by antioxidant treatment. FASEB J. 2002, 16: 908-910.
Kearns SR, Moneley D, Murray P, Kelly C, Daly AF: Oral vitamin C attenuates acute ischaemia–reperfusion injury in skeletal muscle. J Bone Joint Surg Br. 2001, 83: 1202-1206.
Ulug BT, Aksungar FB, Mete O, Tekeli F, Mutlu N, Calik B: The effect of vitamin C on ischemia reperfusion injury because of prolonged tourniquet application with reperfusion intervals. Ann Plast Surg. 2009, 62: 194-199.
Baltalarli A, Ozcan V, Bir F, Aybek H, Sacar M, Onem G, Goksin I, Demir S, Teke Z: Ascorbic acid (vitamin C) and iloprost attenuate the lung injury caused by ischemia/reperfusion of the lower extremities of rats. Ann Vasc Surg. 2006, 20: 49-55.
Seo MY, Lee SM: Protective effect of low dose of ascorbic acid on hepatobiliary function in hepatic ischemia/reperfusion in rats. J Hepatol. 2002, 36: 72-77.
Hsu CC, Wang JJ: L-ascorbic acid and alpha-tocopherol attenuates liver ischemia–reperfusion induced of cardiac function impairment. Transplant Proc. 2012, 44: 933-936.
Wang NT, Lin HI, Yeh DY, Chou TY, Chen CF, Leu FC, Wang D, Hu RT: Effects of the antioxidants lycium barbarum and ascorbic acid on reperfusion liver injury in rats. Transplant Proc. 2009, 41: 4110-4113.
Lee WY, Lee JS, Lee SM: Protective effects of combined ischemic preconditioning and ascorbic acid on mitochondrial injury in hepatic ischemia/reperfusion. J Surg Res. 2007, 142: 45-52.
Skyschally A, Schulz R, Gres P, Korth HG, Heusch G: Attenuation of ischemic preconditioning in pigs by scavenging of free oxyradicals with ascorbic acid. Am J Physiol Heart Circ Physiol. 2003, 284: H698-H703.
Victor VM, Guayerbas N, Puerto M, De la Fuente M: Changes in the ascorbic acid levels of peritoneal lymphocytes and macrophages of mice with endotoxin-induced oxidative stress. Free Radic Res. 2001, 35: 907-916.
Tyml K, Li F, Wilson JX: Delayed ascorbate bolus protects against maldistribution of microvascular blood flow in septic rat skeletal muscle. Crit Care Med. 2005, 33: 1823-1828.
Rojas C, Cadenas S, Herrero A, Mendez J, Barja G: Endotoxin depletes ascorbate in the guinea pig heart. Protective effects of vitamins C and E against oxidative stress. Life Sci. 1996, 59: 649-657.
Secor D, Li F, Ellis CG, Sharpe MD, Gross PL, Wilson JX, Tyml K: Impaired microvascular perfusion in sepsis requires activated coagulation and P-selectin-mediated platelet adhesion in capillaries. Intensive Care Med. 2010, 36: 1928-1934.
Tyml K, Li F, Wilson JX: Septic impairment of capillary blood flow requires nicotinamide adenine dinucleotide phosphate oxidase but not nitric oxide synthase and is rapidly reversed by ascorbate through an endothelial nitric oxide synthase-dependent mechanism. Crit Care Med. 2008, 36: 2355-2362.
McKinnon RL, Lidington D, Tyml K: Ascorbate inhibits reduced arteriolar conducted vasoconstriction in septic mouse cremaster muscle. Microcirculation. 2007, 14: 697-707.
Wu F, Wilson JX, Tyml K: Ascorbate protects against impaired arteriolar constriction in sepsis by inhibiting inducible nitric oxide synthase expression. Free Radic Biol Med. 2004, 37: 1282-1289.
Zhou G, Kamenos G, Pendem S, Wilson JX, Wu F: Ascorbate protects against vascular leakage in cecal ligation and puncture-induced septic peritonitis. Am J Physiol Regul Integr Comp Physiol. 2012, 302: R409-R416.
Cadenas S, Rojas C, Barja G: Endotoxin increases oxidative injury to proteins in guinea pig liver: protection by dietary vitamin C. Pharmacol Toxicol. 1998, 82: 11-18.
Kim JY, Lee SM: Effect of ascorbic acid on hepatic vasoregulatory gene expression during polymicrobial sepsis. Life Sci. 2004, 75: 2015-2026.
Kim JY, Lee SM: Vitamins C and E protect hepatic cytochrome P450 dysfunction induced by polymicrobial sepsis. Eur J Pharmacol. 2006, 534: 202-209.
Fisher BJ, Seropian IM, Kraskauskas D, Thakkar JN, Voelkel NF, Fowler AA, Natarajan R: Ascorbic acid attenuates lipopolysaccharide-induced acute lung injury. Crit Care Med. 2011, 39: 1454-1460.
Fisher BJ, Kraskauskas D, Martin EJ, Farkas D, Wegelin JA, Brophy D, Ward KR, Voelkel NF, Fowler AA, Natarajan R: Mechanisms of attenuation of abdominal sepsis induced acute lung injury by ascorbic acid. Am J Physiol Lung Cell Mol Physiol. 2012, 303: L20-L32.
Gaut JP, Belaaouaj A, Byun J, Roberts LJ, Maeda N, Frei B, Heinecke JW: Vitamin C fails to protect amino acids and lipids from oxidation during acute inflammation. Free Radic Biol Med. 2006, 40: 1494-1501.
Pleiner J, Schaller G, Mittermayer F, Marsik C, MacAllister RJ, Kapiotis S, Ziegler S, Ferlitsch A, Wolzt M: Intra-arterial vitamin C prevents endothelial dysfunction caused by ischemia–reperfusion. Atherosclerosis. 2008, 197: 383-391.
Pleiner J, Mittermayer F, Schaller G, MacAllister RJ, Wolzt M: High doses of vitamin C reverse Escherichia coli endotoxin-induced hyporeactivity to acetylcholine in the human forearm. Circulation. 2002, 106: 1460-1464.
Mittermayer F, Pleiner J, Schaller G, Zorn S, Namiranian K, Kapiotis S, Bartel G, Wolfrum M, Brugel M, Thiery J, Macallister RJ, Wolzt M: Tetrahydrobiopterin corrects Escherichia coli endotoxin-induced endothelial dysfunction. Am J Physiol Heart Circ Physiol. 2005, 289: H1752-H1757.
Pleiner J, Mittermayer F, Schaller G, Marsik C, MacAllister RJ, Wolzt M: Inflammation-induced vasoconstrictor hyporeactivity is caused by oxidative stress. J Am Coll Cardiol. 2003, 42: 1656-1662.
Borrelli E, Roux-Lombard P, Grau GE, Girardin E, Ricou B, Dayer J, Suter PM: Plasma concentrations of cytokines, their soluble receptors, and antioxidant vitamins can predict the development of multiple organ failure in patients at risk. Crit Care Med. 1996, 24: 392-397.
Ballmer PE, Reinhart WH, Jordan P, Buhler E, Moser UK, Gey KF: Depletion of plasma vitamin C but not of vitamin E in response to cardiac operations. J Thorac Cardiovasc Surg. 1994, 108: 311-320.
Metnitz PG, Bartens C, Fischer M, Fridrich P, Steltzer H, Druml W: Antioxidant status in patients with acute respiratory distress syndrome. Intensive Care Med. 1999, 25: 180-185.
Schorah CJ, Downing C, Piripitsi A, Gallivan L, Al-Hazaa AH, Sanderson MJ, Bodenham A: Total vitamin C, ascorbic acid, and dehydroascorbic acid concentrations in plasma of critically ill patients. Am J Clin Nutr. 1996, 63: 760-765.
Blee TH, Cogbill TH, Lambert PJ: Hemorrhage associated with vitamin C deficiency in surgical patients. Surgery. 2002, 131: 408-412.
Lassnigg A, Punz A, Barker R, Keznickl P, Manhart N, Roth E, Hiesmayr M: Influence of intravenous vitamin E supplementation in cardiac surgery on oxidative stress: a double-blinded, randomized, controlled study. Br J Anaesth. 2003, 90: 148-154.
Polidori MC, Mecocci P, Frei B: Plasma vitamin C levels are decreased and correlated with brain damage in patients with intracranial hemorrhage or head trauma. Stroke. 2001, 32: 898-902.
Doise JM, Aho LS, Quenot JP, Guilland JC, Zeller M, Vergely C, Aube H, Blettery B, Rochette L: Plasma antioxidant status in septic critically ill patients: a decrease over time. Fundam Clin Pharmacol. 2008, 22: 203-209.
Hume R, Weyers E, Rowan T, Reid DS, Hillis WS: Leucocyte ascorbic acid levels after acute myocardial infarction. Br Heart J. 1972, 34: 238-243.
Rumelin A, Jaehde U, Kerz T, Roth W, Kramer M, Fauth U: Early postoperative substitution procedure of the antioxidant ascorbic acid. J Nutr Biochem. 2005, 16: 104-108.
Evans RM, Currie L, Campbell A: The distribution of ascorbic acid between various cellular components of blood, in normal individuals, and its relation to the plasma concentration. Br J Nutr. 1982, 47: 473-482.
Levine M, Padayatty SJ, Espey MG: Vitamin C: a concentration–function approach yields pharmacology and therapeutic discoveries. Adv Nutr. 2011, 2: 78-88.
Padayatty SJ, Sun H, Wang Y, Riordan HD, Hewitt SM, Katz A, Wesley RA, Levine M: Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med. 2004, 140: 533-537.
Duconge J, Miranda-Massari JR, Gonzalez MJ, Jackson JA, Warnock W, Riordan NH: Pharmacokinetics of vitamin C: insights into the oral and intravenous administration of ascorbate. P R Health Sci J. 2008, 27: 7-19.
Rumelin A, Humbert T, Luhker O, Drescher A, Fauth U: Metabolic clearance of the antioxidant ascorbic acid in surgical patients. J Surg Res. 2005, 129: 46-51.
Deutsch JC: Dehydroascorbic acid. J Chromatogr A. 2000, 881: 299-307.
Kuo SM, Tan CH, Dragan M, Wilson JX: Endotoxin increases ascorbate recycling and concentration in mouse liver. J Nutr. 2005, 135: 2411-2416.
Burzle M, Suzuki Y, Ackermann D, Miyazaki H, Maeda N, Clemencon B, Burrier R, Hediger MA: The sodium-dependent ascorbic acid transporter family SLC23. Mol Aspects Med. 2013, 34: 436-454.
Harrison FE, May JM: Vitamin C function in the brain: vital role of the ascorbate transporter SVCT2. Free Radic Biol Med. 2009, 46: 719-730.
May JM: Vitamin C transport and its role in the central nervous system. Subcell Biochem. 2012, 56: 85-103.
Huang J, Agus DB, Winfree CJ, Kiss S, Mack WJ, McTaggart RA, Choudhri TF, Kim LJ, Mocco J, Pinsky DJ, Fox WD, Israel RJ, Boyd TA, Golde DW, Connolly ES: Dehydroascorbic acid, a blood–brain barrier transportable form of vitamin C, mediates potent cerebroprotection in experimental stroke. Proc Natl Acad Sci U S A. 2001, 98: 11720-11724.
Carnes CA, Chung MK, Nakayama T, Nakayama H, Baliga RS, Piao S, Kanderian A, Pavia S, Hamlin RL, McCarthy PM, Bauer JA, Van Wagoner DR: Ascorbate attenuates atrial pacing-induced peroxynitrite formation and electrical remodeling and decreases the incidence of postoperative atrial fibrillation. Circ Res. 2001, 89: E32-E38.
Long CL, Maull KI, Krishnan RS, Laws HL, Geiger JW, Borghesi L, Franks W, Lawson TC, Sauberlich HE: Ascorbic acid dynamics in the seriously ill and injured. J Surg Res. 2003, 109: 144-148.
Tanaka H, Matsuda T, Miyagantani Y, Yukioka T, Matsuda H, Shimazaki S: Reduction of resuscitation fluid volumes in severely burned patients using ascorbic acid administration: a randomized, prospective study. Arch Surg. 2000, 135: 326-331.
Kahn SA, Beers RJ, Lentz CW: Resuscitation after severe burn injury using high-dose ascorbic acid: a retrospective review. J Burn Care Res. 2011, 32: 110-117.
Taylor EN, Stampfer MJ, Curhan GC: Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol. 2004, 15: 3225-3232.
Auer BL, Auer D, Rodgers AL: Relative hyperoxaluria, crystalluria and haematuria after megadose ingestion of vitamin C. Eur J Clin Invest. 1998, 28: 695-700.
Galley HF, Davies MJ, Webster NR: Ascorbyl radical formation in patients with sepsis: effect of ascorbate loading. Free Radic Biol Med. 1996, 20: 139-143.
Basili S, Tanzilli G, Mangieri E, Raparelli V, Di SS, Pignatelli P, Violi F: Intravenous ascorbic acid infusion improves myocardial perfusion grade during elective percutaneous coronary intervention: relationship with oxidative stress markers. JACC Cardiovasc Interv. 2010, 3: 221-229.
Mathew ST, Patel J, Joseph S: Atrial fibrillation: mechanistic insights and treatment options. Eur J Intern Med. 2009, 20: 672-681.
Attaran S, Shaw M, Bond L, Pullan MD, Fabri BM: A comparison of outcome in patients with preoperative atrial fibrillation and patients in sinus rhythm. Ann Thorac Surg. 2011, 92: 1391-1395.
Neuman RB, Bloom HL, Shukrullah I, Darrow LA, Kleinbaum D, Jones DP, Dudley SC: Oxidative stress markers are associated with persistent atrial fibrillation. Clin Chem. 2007, 53: 1652-1657.
Negi S, Sovari AA, Dudley SC: Atrial fibrillation: the emerging role of inflammation and oxidative stress. Cardiovasc Hematol Disord Drug Targets. 2010, 10: 262-268.
Youn JY, Zhang J, Zhang Y, Chen H, Liu D, Ping P, Weiss JN, Cai H: Oxidative stress in atrial fibrillation: an emerging role of NADPH oxidase. J Mol Cell Cardiol. 2013, 62: 72-79.
Rodrigo R, Prieto JC, Castillo R: Cardioprotection against ischaemia/reperfusion by vitamins C and E plus n-3 fatty acids: molecular mechanisms and potential clinical applications. Clin Sci (Lond). 2013, 124: 1-15.
Rodrigo R: Prevention of postoperative atrial fibrillation: novel and safe strategy based on the modulation of the antioxidant system. Front Physiol. 2012, 3: 93-
Bowie AG, O'Neill LA: Vitamin C inhibits NF-kappa B activation by TNF via the activation of p38 mitogen-activated protein kinase. J Immunol. 2000, 165: 7180-7188.
Eslami M, Badkoubeh RS, Mousavi M, Radmehr H, Salehi M, Tavakoli N, Avadi MR: Oral ascorbic acid in combination with beta-blockers is more effective than beta-blockers alone in the prevention of atrial fibrillation after coronary artery bypass grafting. Tex Heart Inst J. 2007, 34: 268-274.
Bjordahl PM, Helmer SD, Gosnell DJ, Wemmer GE, O'Hara WW, Milfeld DJ: Perioperative supplementation with ascorbic acid does not prevent atrial fibrillation in coronary artery bypass graft patients. Am J Surg. 2012, 204: 862-867.
Papoulidis P, Ananiadou O, Chalvatzoulis E, Ampatzidou F, Koutsogiannidis C, Karaiskos T, Madesis A, Drossos G: The role of ascorbic acid in the prevention of atrial fibrillation after elective on-pump myocardial revascularization surgery: a single-center experience – a pilot study. Interact Cardiovasc Thorac Surg. 2011, 12: 121-124.
Dingchao H, Zhiduan Q, Liye H, Xiaodong F: The protective effects of high-dose ascorbic acid on myocardium against reperfusion injury during and after cardiopulmonary bypass. Thorac Cardiovasc Surg. 1994, 42: 276-278.
Tsovolas K, Iliodromitis EK, Andreadou I, Zoga A, Demopoulou M, Iliodromitis KE, Manolaki T, Markantonis SL, Kremastinos DT: Acute administration of vitamin C abrogates protection from ischemic preconditioning in rabbits. Pharmacol Res. 2008, 57: 283-289.
Collier BR, Giladi A, Dossett LA, Dyer L, Fleming SB, Cotton BA: Impact of high-dose antioxidants on outcomes in acutely injured patients. JPEN J Parenter Enteral Nutr. 2008, 32: 384-388.
Nathens AB, Neff MJ, Jurkovich GJ, Klotz P, Farver K, Ruzinski JT, Radella F, Garcia I, Maier RV: Randomized, prospective trial of antioxidant supplementation in critically ill surgical patients. Ann Surg. 2002, 236: 814-822.
Berger MM, Soguel L, Shenkin A, Revelly JP, Pinget C, Baines M, Chiolero RL: Influence of early antioxidant supplements on clinical evolution and organ function in critically ill cardiac surgery, major trauma, and subarachnoid hemorrhage patients. Crit Care. 2008, 12: R101-
Heyland D, Muscedere J, Wischmeyer PE, Cook D, Jones G, Albert M, Elke G, Berger MM, Day AG: A randomized trial of glutamine and antioxidants in critically ill patients. N Engl J Med. 2013, 368: 1489-1497.
Crimi E, Liguori A, Condorelli M, Cioffi M, Astuto M, Bontempo P, Pignalosa O, Vietri MT, Molinari AM, Sica V, Della CF, Napoli C: The beneficial effects of antioxidant supplementation in enteral feeding in critically ill patients: a prospective, randomized, double-blind, placebo-controlled trial. Anesth Analg. 2004, 99: 857-863.
Niki E: Role of vitamin E as a lipid-soluble peroxyl radical scavenger: in vitro and in vivo evidence. Free Radic Biol Med. 2014, 66: 2-12.
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Oudemans-van Straaten, H.M., Man, A.M.Sd. & de Waard, M.C. Vitamin C revisited. Crit Care 18, 460 (2014). https://doi.org/10.1186/s13054-014-0460-x