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

Combined treatment with vitamin C, hydrocortisone and thiamine does not attenuate morbidity and mortality of septic sheep

BACKGROUND

Sepsis is associated with a highest mortality rate in the ICU. Present study tests the efficacy of combined therapy with vitamin C, hydrocortisone and thiamine (combined therapy) in the ovine model of sepsis induced by Pseudomonas aeruginosa. In this study, sepsis was induced in sheep by instillation of Pseudomonas aeruginosa (1 × 1011 CFU) into the lungs via bronchoscope, under anesthesia. Nine hours after injury, intravenous infusion of vitamin C (0.75 g every 6 h), hydrocortisone (25 mg every 6 h), and thiamine (100 mg every 12 h) or saline was given to the treatment and control groups. Cardiopulmonary variables were recorded.

RESULTS

The survival rate was 16.7% in control and 33.3% in treatment groups. In the control group, mean arterial pressure dropped from 93.6 ± 8.6 to 75.5 ± 9.7 mmHg by 9 h, which was not affected by the combined therapy. Pulmonary dysfunction was not attenuated by the combined therapy either. The combined therapy had no effect on increased extravascular lung water content and fluid effusion into thoracic cavity. The bacterial number in the bronchoalveolar lavage fluid was significantly increased in the treatment group than the control group. The blood bacterial number remained comparable between groups.

CONCLUSIONS

Combined vitamin C, hydrocortisone, and thiamine did not attenuate severity of ovine sepsis.

Endothelial cell dysfunction and targeted therapeutic drugs in sepsis

Sepsis is a life-threatening organ dysfunction caused by an abnormal host response to microbial infections. During its pathogenesis, vascular endothelial cells (ECs) play a pivotal role as essential components in maintaining microcirculatory homeostasis. This article aims to comprehensively review the multifaceted physiological functions of vascular ECs, elucidate the alterations in their functionality throughout the course of sepsis, and explore recent advancements in research concerning sepsis-related therapeutic drugs targeting ECs.

Effect of high-dose intravenous ascorbic acid on microcirculation and endothelial glycocalyx during sepsis and septic shock: a double-blind, randomized, placebo-controlled study

Previous studies indicate supplemental vitamin C improves microcirculation and reduces glycocalyx shedding in septic animals. Our randomized, double-blind, placebo-controlled trial aimed to investigate whether a high dose of intravenous ascorbic acid (AA) might improve microcirculation and affect glycocalyx in septic patients. In our study, 23 septic patients were supplemented with a high dose (50 mg/kg every 6 h) of intravenous AA or placebo for 96 h. Sublingual microcirculation was examined using a handheld Cytocam-incident dark field (IDF) video microscope. A sidestream dark field video microscope (SDF), connected to the GlycoCheck software (GlycoCheck ICU®; Maastricht University Medical Center, Maastricht, the Netherlands), was employed to observe glycocalyx. We found a significantly higher proportion of perfused small vessels (PPV) 6 h after the beginning of the trial in the experimental group compared with placebo. As an indicator of glycocalyx thickness, the perfused boundary region was lower in capillaries of the 5-9 μm diameter in the AA group than placebo after the first dose of AA. Our data suggest that high-dose parenteral AA tends to improve microcirculation and glycocalyx in the early period of septic shock. The study was retrospectively registered in the clinicaltrials.gov database on 26/02/2021 (registration number NCT04773717).

Unwinding the potentials of vitamin C in COVID-19 and other diseases: An updated review

Background: The discovery of vitamin C (ascorbic acid) is related to the ancient history of persistent research on the origins of the haemorrhagic disease scurvy. Vitamin C is an important nutrient that aids in a variety of biological and physiological processes. Scientists have been researching the function of vitamin C in the prevention and ailment of sepsis and pneumonia for decades. This has created a potential platform for applying these results to individuals suffering from severe coronavirus infection (COVID-19). Vitamin C's ability to activate and enhance the immune system makes it a promising treatment in the present COVID-19 pandemic. Vitamin C also aids in the activation of vitamin B, the production of certain neurotransmitters, and the transformation of cholesterol into bile acids. Hence, vitamin C is used for the treatment of many diseases. Aim: This review highlights the Vitamin C investigations that are performed by various researchers on patients with COVID 19 infection, the clinical studies and their observations. The authors have additionally updated information on the significance of vitamin C insufficiency, as well as its relevance and involvement in diseases such as cancer, wound healing, iron deficiency anaemia, atherosclerosis and neurodegenerative disorders. Here, we discuss them with the references. Methods: The method used in order to perform literature search was done using SciFinder, PubMed and ScienceDirect. Results: There is a potential role of vitamin C in various diseases including neurodegenerative disorders, COVID-19 and other diseases and the results are highlighted in the review with the help of clinical and preclinical data. Conclusion: More research on vitamin C and the undergoing clinical trials might prove a potential role of vitamin C in protecting the population from current COVID-19 pandemic.

The future of intensive care: the study of the microcirculation will help to guide our therapies

The goal of hemodynamic resuscitation is to optimize the microcirculation of organs to meet their oxygen and metabolic needs. Clinicians are currently blind to what is happening in the microcirculation of organs, which prevents them from achieving an additional degree of individualization of the hemodynamic resuscitation at tissue level. Indeed, clinicians never know whether optimization of the microcirculation and tissue oxygenation is actually achieved after macrovascular hemodynamic optimization. The challenge for the future is to have noninvasive, easy-to-use equipment that allows reliable assessment and immediate quantitative analysis of the microcirculation at the bedside. There are different methods for assessing the microcirculation at the bedside; all have strengths and challenges. The use of automated analysis and the future possibility of introducing artificial intelligence into analysis software could eliminate observer bias and provide guidance on microvascular-targeted treatment options. In addition, to gain caregiver confidence and support for the need to monitor the microcirculation, it is necessary to demonstrate that incorporating microcirculation analysis into the reasoning guiding hemodynamic resuscitation prevents organ dysfunction and improves the outcome of critically ill patients.

Novelties in the evaluation of microcirculation in septic shock

Microvascular alterations were first described in critically ill patients about 20 years ago. These alterations are characterized by a decrease in vascular density and presence of non-perfused capillaries close to well-perfused vessels. In addition, heterogeneity in microvascular perfusion is a key finding in sepsis. In this narrative review, we report our actual understanding of microvascular alterations, their role in the development of organ dysfunction, and the implications for outcome. Herein, we discuss the state of the potential therapeutic interventions and the potential impact of novel therapies. We also discuss how recent technologic development may affect the evaluation of microvascular perfusion.

Early ascorbic acid administration prevents vascular endothelial cell damage in septic mice

Oxidation of BH₄, a cofactor of nitric oxide synthase (NOS), produces reactive oxygen species (ROS) through uncoupling of NOS and affects vascular endothelial dysfunction. Ascorbic acid (AsA) inhibits the oxidation of BH₄ and reduces ROS. However, the kinetic changes of BH₄ in sepsis and its effect on the kinetic changes in AsA administration therapy, as well as the appropriate timing of AsA administration for AsA therapy to be effective, are unclear. Mice with sepsis, induced by cecal ligation and puncture (CLP), were examined for the effect of AsA administration (200 mg/kg) on vascular endothelial cell dysfunction at two administration timings: early group (AsA administered immediately after CLP) and late group (AsA administered 12 h after CLP). Survival rates were compared between the early and late administration groups, and vascular endothelial cell damage, indicated by the dihydrobiopterin/tetrahydrobiopterin ratio, serum syndecan-1, and endothelial nitric oxide synthase, as well as liver damage, were examined. The early group showed significantly improved survival compared to the non-treatment group (p < 0.05), while the late group showed no improved survival compared to the non-treatment group. Compared to the non-treated group, the early AsA group showed less oxidation of BH₄ in sepsis. Syndecan1, a marker of vascular endothelial cell damage, was less elevated and organ damage was reduced in the early AsA-treated group. In septic mice, early AsA administration immediately after CLP may protect vascular endothelial cells by inhibiting BH₄ oxidation, thereby reducing organ dysfunction and improving survival.

Vitamin C improves microvascular reactivity and peripheral tissue perfusion in septic shock patients

Background

Vitamin C has potential protective effects through antioxidant and anti-inflammatory properties. However, the effect of vitamin C supplementation on microvascular function and peripheral tissue perfusion in human sepsis remains unknown. We aimed to determine vitamin C effect on microvascular endothelial dysfunction and peripheral tissue perfusion in septic shock patients.

Methods

Patients with septic shock were prospectively included after initial resuscitation. Bedside peripheral tissue perfusion and skin microvascular reactivity in response to acetylcholine iontophoresis in the forearm area were measured before and 1 h after intravenous vitamin C supplementation (40 mg/kg). Norepinephrine dose was not modified during the studied period.

Results

We included 30 patients with septic shock. SOFA score was 11 [8–14], SAPS II was 66 [54–79], and in-hospital mortality was 33%. Half of these patients had vitamin C deficiency at inclusion. Vitamin C supplementation strongly improved microvascular reactivity (AUC 2263 [430–4246] vs 5362 [1744–10585] UI, p = 0.0004). In addition, vitamin C supplementation improved mottling score (p = 0.06), finger-tip (p = 0.0003) and knee capillary refill time (3.7 [2.6–5.5] vs 2.9 [1.9–4.7] s, p < 0.0001), as well as and central-to-periphery temperature gradient (6.1 [4.9–7.4] vs 4.6 [3.4–7.0] °C, p < 0.0001). The beneficial effects of vitamin C were observed both in patients with or without vitamin C deficiency.

Conclusion

In septic shock patients being resuscitated, vitamin C supplementation improved peripheral tissue perfusion and microvascular reactivity whatever plasma levels of vitamin C.

ClinicalTrials.gov Identifier: NCT04778605 registered 26 January 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03891-8.

Antioxidants as Therapeutic Agents in Acute Respiratory Distress Syndrome (ARDS) Treatment-From Mice to Men

Acute respiratory distress syndrome (ARDS) is a major cause of patient mortality in intensive care units (ICUs) worldwide. Considering that no causative treatment but only symptomatic care is available, it is obvious that there is a high unmet medical need for a new therapeutic concept. One reason for a missing etiologic therapy strategy is the multifactorial origin of ARDS, which leads to a large heterogeneity of patients. This review summarizes the various kinds of ARDS onset with a special focus on the role of reactive oxygen species (ROS), which are generally linked to ARDS development and progression. Taking a closer look at the data which already have been established in mouse models, this review finally proposes the translation of these results on successful antioxidant use in a personalized approach to the ICU patient as a potential adjuvant to standard ARDS treatment.

Vitamin C for sepsis intervention: from redox biochemistry to clinical medicine

Vitamin C, also known as ascorbic acid or ascorbate, is a water-soluble vitamin synthesized in plants as well as in animals except humans and several other animal species. Humans obtain vitamin C from dietary sources and via vitamin supplementation. Vitamin C possesses important biological functions, including serving as a cofactor for many enzymes, acting as an antioxidant and anti-inflammatory compound, and participating in regulating stem cell biology and epigenetics. The multifunctional nature of vitamin C contributes to its essentialness in maintaining and safeguarding physiological homeostasis, especially regulation of immunity and inflammatory responses. In this context, vitamin C has been investigated for its efficacy in treating diverse inflammatory disorders, including sepsis, one of the major causes of death globally and for which currently there is no cure. Accordingly, this Mini-Review surveys recent major research findings on the effectiveness of vitamin C and the underling molecular mechanisms in sepsis intervention in both experimental animal models and randomized controlled trials. To set a stage for discussing the effects and mechanisms of vitamin C in sepsis intervention, this Mini-Review begins with an overview of vitamin C redox biochemistry and its multifunctional properties.

Targeting Oxidative Stress in Septic Acute Kidney Injury: From Theory to Practice

Sepsis is the leading cause of acute kidney injury (AKI) and leads to increased morbidity and mortality in intensive care units. Current treatments for septic AKI are largely supportive and are not targeted towards its pathophysiology. Sepsis is commonly characterized by systemic inflammation and increased production of reactive oxygen species (ROS), particularly superoxide. Concomitantly released nitric oxide (NO) then reacts with superoxide, leading to the formation of reactive nitrogen species (RNS), predominantly peroxynitrite. Sepsis-induced ROS and RNS can reduce the bioavailability of NO, mediating renal microcirculatory abnormalities, localized tissue hypoxia and mitochondrial dysfunction, thereby initiating a propagating cycle of cellular injury culminating in AKI. In this review, we discuss the various sources of ROS during sepsis and their pathophysiological interactions with the immune system, microcirculation and mitochondria that can lead to the development of AKI. We also discuss the therapeutic utility of N-acetylcysteine and potential reasons for its efficacy in animal models of sepsis, and its inefficacy in ameliorating oxidative stress-induced organ dysfunction in human sepsis. Finally, we review the pre-clinical studies examining the antioxidant and pleiotropic actions of vitamin C that may be of benefit for mitigating septic AKI, including future implications for clinical sepsis.

Common anti-oxidant vitamin C as an anti-infective agent with remedial role on SARS-CoV-2 infection. An update

Coronavirus disease -2019 (COVID-19) has led to a worldwide multifaceted crisis. The medical world agonizes to contend with the problem, but a string of tested medications has been proven unavailing. Vitamin C is well described as a salutary antioxidant and some trials conclude that it may be a potential antiviral drug. In high doses, Vitamin C can alternate crucial steps in the pathogenesis of sepsis and acute respiratory distress syndrome. This dynamic was the driving force behind trials around the world that tried immunonutrition as a weapon against clinical entities. We summarize the mechanisms of action of Vitamin C and its role against infections and the current literature referring to the potential role of Vitamin C in SARS-CoV-2 infection, also as a contingent treatment agent.

Knockout of PKC θ gene attenuates oleic acid-induced acute lung injury via reduction of inflammation and oxidative stress

OBJECTIVES

Acute respiratory distress syndrome resulting from acute lung injury has become a momentous clinical concern because of high morbidity and mortality in discharged patients with pulmonary and nonpulmonary diseases. This study aimed to explore the effect of protein kinase C (PKC) θ gene knockout on acute lung injury.

MATERIALS AND METHODS

Wt and PKC θ gene knockout mice were intravenously injected with oleic acid to induce acute lung injury. Pulmonary capillary permeability was assessed via measuring lung wet/dry weight ratio and level of protein in bronchoalveolar lavage fluid (BALF). Histological changes were used to examine acute lung injury. Malondialdehyde (MDA) level, superoxide dismutase (SOD) activity in serum, together with inflammatory cytokines including interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-α), were determined. Furthermore, the expressions of heme oxygenase (HO)-1, nuclear factor kappa B (NF κB), and inhibitor of NF-κB alpha (IκB α) were detected in the lungs.

RESULTS

PKC θ gene knockout decreased lung wet/dry weight ratio, reduced levels of MDA, IL-6, and TNF-α in serum together with level of protein in BALF. Furthermore, PKC θ gene knockout increased the activities of SOD. Knockout of PKC θ was also observed to increase expression of HO-1 and reduce levels of p-NF κB and p-IKB α in the lungs.

CONCLUSION

These results suggest that PKC θ gene knockout attenuates oleic acid-induced acute lung injury via improving oxidative stress and inflammation.

High-dose vitamin C alleviates pancreatic injury via the NRF2/NQO1/HO-1 pathway in a rat model of severe acute pancreatitis

Background

Oxidative stress plays a pivotal role in the progress of severe acute pancreatitis (SAP). Vitamin C (VC) is the most important antioxidant in plasma. However, the effects of an intravenous administration of high-dose VC and the mechanisms by which it exerts its antioxidant function in an experimental model of SAP have not been determined.

Methods

Sodium taurocholate was used to induce rat pancreatic injury and AR42J cells injury. After the establishment of SAP model, SAP rat and injured AR42J cells were treated with VC. For the injured AR42J cells, small interfering RNA-mediated knockdown of NRF2 was conducted after VC treatment. The histopathological characteristics, the apoptosis of pancreatic acinar cells, oxidative stress markers and levels of enzymes, biochemical indicators, and inflammatory cytokines were examined in vivo and in vitro. Furthermore, the mortality of rats was assessed.

Results

In vivo and in vitro results demonstrated that VC treatment ameliorated apoptosis of pancreatic acinar cells, as evidenced by the increase in Bcl-2, Bcl-XL, and MCL-1 expressions and decrease in Bax and cleaved caspase-3 expression along with decreased TUNEL-positive cells. Also, we found that the elevation of MDA and decrease of SOD, GPx, GSH/GSSG, and T-AOC induced by SAP were reversed by VC treatment in vivo and in vitro, and VC treatment increased expressions of Nrf2, NQO1, and HO-1 in SAP model at protein and gene level, indicating that VC attenuated oxidative stress via the NRF2/NQO1/HO-1 pathway. Meanwhile, it was found that sodium taurocholate significantly induced the release of amylase, lipase, IL-1β, and IL-6 in rat plasma and AR42J cells, which were declined by VC treatment. In vitro results also revealed that these alterations in sodium taurocholate-injured AR42J cells due to VC treatment was attenuated by NRF2 knockdown. In addition, VC at a dose of 500 mg/kg decreased the levels of lactic acid, Cre, NGAL, AST, and ALT in the plasma of SAP rats, suggesting the improvement of renal and pancreatic injury and liver function of SAP rats. Furthermore, the mortality of SAP rats was 50%, which declined to 30% after VC treatment.

Conclusions

The present study suggests that high-dose of VC ameliorate pancreatic injury of SAP via the NRF2/NQO1/HO-1 pathway to inhibit oxidative stress.

Vitamin C in Health and Disease: A Companion Animal Focus

Vitamin C is synthesized in the liver in most species, including dogs and cats, and is widely distributed through body tissues. Vitamin C has an important physiologic role in numerous metabolic functions including tissue growth and maintenance, amelioration of oxidative stress, and immune regulation. It is also a co-factor in the production of important substances such as catecholamines and vasopressin. Decreased vitamin C levels have been documented in a wide variety of diseases, and in critically ill human patients may be associated with increased severity of disease and decreased survival. Intravenous supplementation with vitamin C has been proposed as a potential life-saving treatment in conditions such as septic shock, and results of small some human trials are promising. Data in companion in animals is very limited, but the possible benefits and , seemingly low risk of adverse effects , and the low cost of this treatment make vitamin C therapy a promising area of future investigation in critically ill dogs and cats.

A Cecal Slurry Mouse Model of Sepsis Leads to Acute Consumption of Vitamin C in the Brain

Vitamin C (ascorbate, ASC) is a critical antioxidant in the body with specific roles in the brain. Despite a recent interest in vitamin C therapies for critical care medicine, little is known about vitamin C regulation during acute inflammation and critical illnesses such as sepsis. Using a cecal slurry (CS) model of sepsis in mice, we determined ASC and inflammatory changes in the brain following the initial treatment. ASC levels in the brain were acutely decreased by approximately 10% at 4 and 24 h post CS treatment. Changes were accompanied by a robust increase in liver ASC levels of up to 50%, indicating upregulation of synthesis beginning at 4 h and persisting up to 7 days post CS treatment. Several key cytokines interleukin 6 (IL-6), interleukin 1β (IL-1β), tumor necrosis factor alpha (TNFα), and chemokine (C-X-C motif) ligand 1 (CXCL1, KC/Gro) were also significantly elevated in the cortex at 4 h post CS treatment, although these levels returned to normal by 48 h. These data strongly suggest that ASC reserves are directly challenged throughout illness and recovery from sepsis. Given the timescale of this response, decreases in cortical ASC are likely driven by hyper-acute neuroinflammatory processes. However, future studies are required to confirm this relationship and to investigate how this deficiency may subsequently impact neuroinflammation.

Bench to bedside review: therapeutic modulation of nitric oxide in sepsis-an update

Nitric oxide is a signalling molecule with an extensive range of functions in both health and disease. Discovered in the 1980s through work that earned the Nobel prize, nitric oxide is an essential factor in regulating cardiovascular, immune, neurological and haematological function in normal homeostasis and in response to infection. Early work implicated exaggerated nitric oxide synthesis as a potentially important driver of septic shock; however, attempts to modulate production through global inhibition of nitric oxide synthase were associated with increased mortality. Subsequent work has shown that regulation of nitric oxide production is determined by numerous factors including substrate and co-factor availability and expression of endogenous regulators. In sepsis, nitric oxide synthesis is dysregulated with exaggerated production leading to cardiovascular dysfunction, bioenergetic failure and cellular toxicity whilst at the same time impaired microvascular function may be driven in part by reduced nitric oxide synthesis by the endothelium. This bench to bedside review summarises our current understanding of the ways in which nitric oxide production is regulated on a tissue and cellular level before discussing progress in translating these observations into novel therapeutic strategies for patients with sepsis.

Thinking forward: promising but unproven ideas for future intensive care

Progress toward determining the true worth of ongoing practices or value of recent innovations can be glacially slow when we insist on following the conventional stepwise scientific pathway. Moreover, a widely accepted but flawed conceptual paradigm often proves difficult to challenge, modify or reject. Yet, most experienced clinicians, educators and clinical scientists privately entertain untested ideas about how care could or should be improved, even if the supporting evidence base is currently thin or non-existent. This symposium encouraged experts to share such intriguing but unproven concepts, each based upon what the speaker considered a logical but unproven rationale. Such free interchange invited dialog that pointed toward new or neglected lines of research needed to improve care of the critically ill. In this summary of those presentations, a brief background outlines the rationale for each novel and deliberately provocative unconfirmed idea endorsed by the presenter.

Vitamin C alone does not improve treatment outcomes in mechanically ventilated patients with severe sepsis or septic shock: a retrospective cohort study

Background

Vitamin C has shown several beneficial effects on sepsis in preclinical studies. However, clinical data supporting these reports are scarce. This study aimed to evaluate whether adjunctive intravenous vitamin C therapy could reduce hospital mortality in patients with severe sepsis or septic shock requiring mechanical ventilation.

Methods

For this retrospective cohort study, consecutive medical ICU patients with severe sepsis or septic shock requiring mechanical ventilation were included. The study patients were classified into the vitamin C or control groups depending on the administration of intravenous vitamin C (2 g every 8 hours). The primary outcome was hospital mortality.

Results

Thirty-five patients in the vitamin C group and 40 patients in the control group were included. The two groups were comparable in regards to the baseline characteristics at ICU admission. The hospital mortality was 46% (16 of 35 patients) in the vitamin C group and 40% (16 of 40 patients) in the control group, showing a statistically nonsignificant difference (P=0.62). The mortality at 90 days after ICU admission (60% vs. 48%) did not significantly differ between groups. The median time to shock reversal was 3 days [interquartile range (IQR), 2 to 5 days] in both groups. The changes in the Sepsis-related Organ Failure Assessment (SOFA) scores during the first 4 ICU days were -1.4±3.3 and -1.4±3.0 in the vitamin C and control groups, respectively.

Conclusions

Adjunctive intravenous vitamin C therapy alone did not reduce hospital mortality in mechanically ventilated patients with severe sepsis or septic shock.

Intravenous Vitamin C attenuates hemorrhagic shock-related renal injury through the induction of SIRT1 in rats

To investigate the effect of intravenous Vitamin C (VC) on hemorrhagic shock (HS)-associated rat renal injury and the involved mechanism. Thirty SD rats were randomly assigned to the sham surgery (sham), hemorrhagic shock (HS), HS+100 mg/kg VC (H + VL), HS+500 mg/kg VC (H + VH) and HS+100 mg/kg VC + EX527 (H + VL + E) groups. Tissue and blood samples were collected 6 h after surgery. Kidney pathological changes were scored. Creatinine (CRE), blood urea nitrogen (BUN), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) levels in serum and Vitamin C levels and superoxide dismutase (SOD) activity and the ability to suppress hydroxyl radical (RAFHR) in plasma were measured. The expression of Sirtuin1 (SIRT1), Acetyl-NF-κB (Ace-NF-κB), heme oxygenase-1 (HO-1), TNF-α, and IL-1β in tissues was analyzed by ELISA or western-blot. In the HS group, the kidney pathological score and CRE, BUN, TNF-α, and IL-1β levels in serum were significantly higher than in the Sham group (P < 0.05), while SOD and RAFHR were significantly decreased in the plasma (P < 0.05). SOD activity and SIRT1 expression were remarkably lower in the kidney in the HS group than in the Sham group (P < 0.05), while MDA, TNF-α, and IL-1β concentrations and Acetyl-NF-κB andHO-1 expression in the kidney showed a noteworthy increase compared to the Sham group (P < 0.05). Compared to the HS group, VC treatment led to a remarkable reduction in the kidney pathological score and CRE,BUN,TNF-α, and IL-1β levels (P < 0.05), and a significant increase in Vitamin C, SOD, and RAFHR levels in the plasma (P < 0.05). Additionally, MDA, TNF-α, IL-1β and Acetyl-NF-κB expression levels were decreased in the kidney (P < 0.05), while SOD, SIRT1 and HO-1 levels were notably enhanced. There were no differences between the H + VL and H + VH groups aside from plasma Vitamin C levels. The effect of Vitamin C was decreased after the addition of EX527, which inhibits SIRT1. Intravenous Vitamin C might attenuate HS-related renal injury via the SIRT1 pathway, and it appears that there were no differences in the effects between the high and low doses.

Vitamin C for the critically ill: Is the evidence strong enough?

Vitamin C exhibits interesting properties in the context of critical illness, with benefits described in neurologic, cardiovascular, renal, and hematologic systems, both in in vitro and in animal models. Through direct effects on bacterial replication, immunomodulation, and antioxidant reserve of the organism, vitamin C directly affects the pathophysiological process of sepsis, trauma, burn, and systemic inflammation. Even if several observational trials have linked vitamin C deficiency to worse outcomes, the evidence is not such as to provide us with a distinction between causality effects or simple epiphenomenon, and the current focus is on interventional trials. Pharmacokinetic data suggest that a minimal supplementation of 3 g/d intravenously is required to restore normal serum values in critically ill patients with known deficiency. According to these data, only five trials, including a retrospective analysis, studied pharmacologic dose: three as an antioxidant cocktail and two as monotherapy. The largest trial, conducted in 2002, reported reduced incidence of multiorgan failure and duration of mechanical ventilation. Recently a retrospective analysis reported impressive results after administration of vitamin C, thiamine, and hydrocortisone. The two most recent trials reported improved clinical outcomes, including improved mortality, but contained significant methodological limitations. A recent systematic review did not find clinical benefits with the most-studied low-dose oral supplementation, potentially because of suboptimal or insufficient repletion. Current guidelines do not support the administration of high-dose vitamin C in critically ill patients. Future larger trials are required to support any therapy, but the low cost and safety profile can justify supplementation in the meantime. Metabolomics study will further help understand biological effect.

Vitamin C supplementation in the critically ill: A systematic review and meta-analysis

BACKGROUND

Low plasma levels of vitamin C are associated with adverse outcomes, including increased mortality, in critically ill patients. Several trials have suggested that the administration of intravenous vitamin C in this setting may have beneficial effects, such as reducing the incidence of organ failure and improving survival. However, these studies have generally involved combination therapies consisting of vitamin C along with other antioxidants, confounding the effects of vitamin C alone. The primary objective of this meta-analysis is to investigate the effects of isolated intravenous supplementation of vitamin C in adults with critical illness.

METHODS

A database search was conducted for studies on the use of intravenous vitamin C in adult patients with critical illness. The primary outcome assessed was mortality at the longest follow-up time available. Secondary outcomes were the duration of mechanical ventilation, duration of vasopressor support, fluid requirements, and urine output in the first 24 h of intensive care unit admission.

RESULTS

Five studies (four randomized controlled trials and one retrospective review) enrolling a total of 142 patients were included in this meta-analysis. Compared with controls, the administration of intravenous vitamin C was associated with a decreased need for vasopressor support (standardized mean difference -0.71; 95% confidence interval (-1.16 to -0.26); p = 0.002) and decreased duration of mechanical ventilation (standardized mean difference -0.5; 95% confidence interval (-0.93 to -0.06); p = 0.03), but no difference was found in mortality (odds ratio 0.76; 95% confidence interval (0.27 to 2.16); p = 0.6). Trends were also noted toward decreased fluid requirements and increased urine output. No adverse effects were reported.

CONCLUSION

The administration of intravenous vitamin C may lead to vasopressor sparing effects and a reduced need for mechanical ventilation in the critically ill, without affecting overall mortality. However, these results should be interpreted in light of the limitations of the primary literature and should serve as a preview of upcoming trials in this area.

Seven unconfirmed ideas to improve future ICU practice

With imprecise definitions, inexact measurement tools, and flawed study execution, our clinical science often lags behind bedside experience and simply documents what appear to be the apparent faults or validity of ongoing practices. These impressions are later confirmed, modified, or overturned by the results of the next trial. On the other hand, insights that stem from the intuitions of experienced clinicians, scientists and educators-while often neglected-help place current thinking into proper perspective and occasionally point the way toward formulating novel hypotheses that direct future research. Both streams of information and opinion contribute to progress. In this paper we present a wide-ranging set of unproven 'out of the mainstream' ideas of our FCCM faculty, each with a defensible rationale and holding clear implications for altering bedside management. Each proposition was designed deliberately to be provocative so as to raise awareness, stimulate new thinking and initiate lively dialog.

The Effect of Sepsis on the Erythrocyte

Sepsis induces a wide range of effects on the red blood cell (RBC). Some of the effects including altered metabolism and decreased 2,3-bisphosphoglycerate are preventable with appropriate treatment, whereas others, including decreased erythrocyte deformability and redistribution of membrane phospholipids, appear to be permanent, and factors in RBC clearance. Here, we review the effects of sepsis on the erythrocyte, including changes in RBC volume, metabolism and hemoglobin's affinity for oxygen, morphology, RBC deformability (an early indicator of sepsis), antioxidant status, intracellular Ca²⁺ homeostasis, membrane proteins, membrane phospholipid redistribution, clearance and RBC O₂-dependent adenosine triphosphate efflux (an RBC hypoxia signaling mechanism involved in microvascular autoregulation). We also consider the causes of these effects by host mediated oxidant stress and bacterial virulence factors. Additionally, we consider the altered erythrocyte microenvironment due to sepsis induced microvascular dysregulation and speculate on the possible effects of RBC autoxidation. In future, a better understanding of the mechanisms involved in sepsis induced erythrocyte pathophysiology and clearance may guide improved sepsis treatments. Evidence that small molecule antioxidants protect the erythrocyte from loss of deformability, and more importantly improve septic patient outcome suggest further research in this area is warranted. While not generally considered a critical factor in sepsis, erythrocytes (and especially a smaller subpopulation) appear to be highly susceptible to sepsis induced injury, provide an early warning signal of sepsis and are a factor in the microvascular dysfunction that has been associated with organ dysfunction.

Voluntary running exercise protects against sepsis-induced early inflammatory and pro-coagulant responses in aged mice

Background

Despite many animal studies and clinical trials, mortality in sepsis remains high. This may be due to the fact that most experimental studies of sepsis employ young animals, whereas the majority of septic patients are elderly (60 − 70 years). The objective of the present study was to examine the sepsis-induced inflammatory and pro-coagulant responses in aged mice. Since running exercise protects against a variety of diseases, we also examined the effect of voluntary running on septic responses in aged mice.

Methods

Male C57BL/6 mice were housed in our institute from 2–3 to 22 months (an age mimicking that of the elderly). Mice were prevented from becoming obese by food restriction (given 70–90% of ad libitum consumption amount). Between 20 and 22 months, a subgroup of mice ran voluntarily on wheels, alternating 1–3 days of running with 1–2 days of rest. At 22 months, mice were intraperitoneally injected with sterile saline (control) or 3.75 g/kg fecal slurry (septic). At 7 h post injection, we examined (1) neutrophil influx in the lung and liver by measuring myeloperoxidase and/or neutrophil elastase in the tissue homogenates by spectrophotometry, (2) interleukin 6 (IL6) and KC in the lung lavage by ELISA, (3) pulmonary surfactant function by measuring percentage of large aggregates, (4) capillary plugging (pro-coagulant response) in skeletal muscle by intravital microscopy, (5) endothelial nitric oxide synthase (eNOS) protein in skeletal muscle (eNOS-derived NO is putative inhibitor of capillary plugging) by immunoblotting, and (6) systemic blood platelet counts by hemocytometry.

Results

Sepsis caused high levels of pulmonary myeloperoxidase, elastase, IL6, KC, liver myeloperoxidase, and capillary plugging. Sepsis also caused low levels of surfactant function and platelet counts. Running exercise increased eNOS protein and attenuated the septic responses.

Conclusions

Voluntary running protects against exacerbated sepsis-induced inflammatory and pro-coagulant responses in aged mice. Protection against pro-coagulant responses may involve eNOS upregulation. The present discovery in aged mice calls for clinical investigation into potential beneficial effects of exercise on septic outcomes in the elderly.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1783-1) contains supplementary material, which is available to authorized users.

Vitamin C and Microvascular Dysfunction in Systemic Inflammation

Sepsis, life-threatening organ dysfunction caused by a dysfunctional host response to infection, is associated with high mortality. A promising strategy to improve the outcome is to inject patients intravenously with ascorbate (vitamin C). In animal models of sepsis, this injection improves survival and, among others, the microvascular function. This review examines our recent work addressing ascorbate's ability to inhibit arteriolar dysfunction and capillary plugging in sepsis. Arteriolar dysfunction includes impaired vasoconstriction/dilation (previously reviewed) and impaired conduction of vasoconstriction/dilation along the arteriole. We showed that ascorbate injected into septic mice prevents impaired conducted vasoconstriction by inhibiting neuronal nitric oxide synthase-derived NO, leading to restored inter-endothelial electrical coupling through connexin 37-containing gap junctions. Hypoxia/reoxygenation (confounding factor in sepsis) also impairs electrical coupling by protein kinase A (PKA)-dependent connexin 40 dephosphorylation; ascorbate restores PKA activation required for this coupling. Both effects of ascorbate could explain its ability to protect against hypotension in sepsis. Capillary plugging in sepsis involves P-selectin mediated platelet-endothelial adhesion and microthrombi formation. Early injection of ascorbate prevents capillary plugging by inhibiting platelet-endothelial adhesion and endothelial surface P-selectin expression. Ascorbate also prevents thrombin-induced platelet aggregation and platelet surface P-selectin expression, thus preventing microthrombi formation. Delayed ascorbate injection reverses capillary plugging and platelet-endothelial adhesion; it also attenuates sepsis-induced drop in platelet count in systemic blood. Thrombin-induced release of plasminogen-activator-inhibitor-1 from platelets (anti-fibrinolytic event in sepsis) is inhibited by ascorbate pH-dependently. Thus, under acidotic conditions in sepsis, ascorbate promotes dissolving of microthrombi in capillaries. We propose that protected/restored arteriolar conduction and capillary bed perfusion by ascorbate contributes to reduced organ injury and improved survival in sepsis.

Ascorbate inhibits platelet-endothelial adhesion in an in-vitro model of sepsis via reduced endothelial surface P-selectin expression

Plugging of the capillary bed can lead to organ failure and mortality in sepsis. We have reported that intravenous ascorbate injection reduces platelet adhesion to the capillary wall and capillary plugging in septic mice. Both platelet adhesion and capillary plugging require P-selectin, a key adhesion molecule. To elucidate the beneficial effect of ascorbate, we hypothesized that ascorbate reduces platelet-endothelial adhesion by reducing P-selectin surface expression in endothelial cells. We used mouse platelets, and monolayers of cultured microvascular endothelial cells (mouse skeletal muscle origin) stimulated with lipopolysaccharide, to examine platelet-endothelial adhesion. P-selectin mRNA expression in endothelial cells was determined by real-time PCR and P-selectin protein expression at the surface of these cells by immunofluorescence. Secretion of von Willebrand factor from cells into the supernatant (a measure of P-selectin-containing granule exocytosis) was determined by ELISA. Lipopolysaccharide (10 μg/ml, 1 h) increased platelet-endothelial adhesion. P-selectin-blocking antibody inhibited this adhesion. Lipopolysaccharide also increased P-selectin mRNA in endothelial cells, P-selectin expression at the endothelial surface, and von Willebrand factor secretion. Ascorbate pretreatment (100 μmol/l, 4 h) inhibited the increased platelet adhesion, surface expression of P-selectin, and von Willebrand factor secretion, but not the increase in P-selectin mRNA. The lipopolysaccharide-induced increase in platelet-endothelial adhesion requires P-selectin presence at the endothelial surface. Ascorbate's ability to reduce this presence could be important in reducing both platelet adhesion to the capillary wall and capillary plugging in sepsis.

Renal perfusion in sepsis: from macro- to microcirculation

The pathogenesis of sepsis-associated acute kidney injury is complex and likely involves perfusion alterations, a dysregulated inflammatory response, and bioenergetic derangements. Although global renal hypoperfusion has been the main target of therapeutic interventions, its role in the development of renal dysfunction in sepsis is controversial. The implications of renal hypoperfusion during sepsis probably extend beyond a simple decrease in glomerular filtration pressure, and targeting microvascular perfusion deficits to maintain tubular epithelial integrity and function may be equally important. In this review, we provide an overview of macro- and microcirculatory dysfunction in experimental and clinical sepsis and discuss relationships with kidney oxygenation, metabolism, inflammation, and function.

Microcirculatory dysfunction in sepsis: pathophysiology, clinical monitoring, and potential therapies

Abnormal microvascular perfusion, including decreased functional capillary density and increased blood flow heterogeneity, is observed in early stages of the systemic inflammatory response to infection and appears to have prognostic significance in human sepsis. It is known that improvements in systemic hemodynamics are weakly correlated with the correction of microcirculatory parameters, despite an appropriate treatment of macrohemodynamic abnormalities. Furthermore, conventional hemodynamic monitoring systems available in clinical practice fail to detect microcirculatory parameter changes and responses to treatments, as they do not evaluate intrinsic events that occur in the microcirculation. Fortunately, some bedside diagnostic methods and therapeutic options are specifically directed to the assessment and treatment of microcirculatory changes. In the present review we discuss fundamental aspects of septic microcirculatory abnormalities, including pathophysiology, clinical monitoring, and potential therapies.

Effect of ascorbate on plasminogen activator inhibitor-1 expression and release from platelets and endothelial cells in an in-vitro model of sepsis

The microcirculation during sepsis fails due to capillary plugging involving microthrombosis. We demonstrated that intravenous injection of ascorbate reduces this plugging, but the mechanism of this beneficial effect remains unclear. We hypothesize that ascorbate inhibits the release of the antifibrinolytic plasminogen activator inhibitor-1 (PAI-1) from endothelial cells and platelets during sepsis. Microvascular endothelial cells and platelets were isolated from mice. Cells were cultured and stimulated with lipopolysaccharide (LPS), tumor necrosis factor alpha (TNFα), or thrombin (agents of sepsis), with/without ascorbate for 1-24 h. PAI-1 mRNA was determined by quantitative PCR. PAI-1 protein release into the culture medium was measured by ELISA. In platelets, PAI-1 release was measured after LPS, TNFα, or thrombin stimulation, with/without ascorbate. In endothelial cells, LPS and TNFα increased PAI-1 mRNA after 6-24 h, but no increase in PAI-1 release was observed; ascorbate did not affect these responses. In platelets, thrombin, but not LPS or TNFα, increased PAI-1 release; ascorbate inhibited this increase at low extracellular pH. In unstimulated endothelial cells and platelets, PAI-1 is released into the extracellular space. Thrombin increases this release from platelets; ascorbate inhibits it pH-dependently. The data suggest that ascorbate promotes fibrinolysis in the microvasculature under acidotic conditions in sepsis.

Inhibition of MicroRNA 195 Prevents Apoptosis and Multiple-Organ Injury in Mouse Models of Sepsis

BACKGROUND

MicroRNAs (miRs) are a class of short RNA molecules, which negatively regulate gene expression. The levels of circulating miR-15 family members are elevated in septic patients and may be associated with septic death. This study investigated whether inhibition of miR-195, a member of the miR-15 family, provided beneficial effects in sepsis.

METHODS AND RESULTS

Sepsis was induced by injection of feces into the peritoneum in mice. miR-195 was upregulated in the lung and liver of septic mice. Silencing of miR-195 increased the protein levels of BCL-2, Sirt1, and Pim-1; prevented apoptosis; reduced liver and lung injury; and improved the survival in septic mice. Silencing of miR-195 provided similar protection in lipopolysaccharide-induced endotoxemic mice. In endothelial cells, upregulation of miR-195 induced apoptosis, and inhibition of miR-195 prevented lipopolysaccharide-induced apoptosis. miR-195 repressed expression of its protein targets, BCL-2, Sirt1, and Pim-1. Furthermore, overexpression of Pim-1 prevented apoptosis induced by lipopolysaccharide and miR-195 mimic. Inhibition of Pim-1 attenuated the protective effects of miR-195 silencing in septic mice.

CONCLUSIONS

Silencing of miR-195 reduced multiple-organ injury and improved the survival in sepsis, and the protective effects of miR-195 inhibition were associated with upregulation of Bcl-2, Sirt1, and Pim-1. Thus, inhibition of miR-195 may represent a new therapeutic approach for sepsis.

Effect of ascorbate on fibrinolytic factors in septic mouse skeletal muscle

Plugging of the capillary bed in tissues correlates with organ failure during sepsis. In septic mouse skeletal muscle, we showed that blood in capillaries becomes hypercoagulable and that ascorbate injection inhibits capillary plugging. In the present study, we hypothesized that ascorbate promotes fibrinolysis, reversing this plugging. Sepsis in mice was induced by fecal injection into peritoneum. Mice were injected intravenously with a bolus of streptokinase (fibrinolytic agent) or ascorbate at 5-6 h. Both agents reversed capillary plugging in muscle at 7 h. Sepsis increased mRNA expression of urokinase plasminogen activator (u-PA) (profibrinolytic) and plasminogen activator inhibitor 1 (PAI-1) (antifibrinolytic) in muscle and liver homogenates at 7 h. Ascorbate did not affect u-PA mRNA in either tissue, but it inhibited PAI-1 mRNA in muscle, suggesting enhanced fibrinolysis in this tissue. However, ascorbate did not affect increased PAI-1 mRNA in the liver (dominant source of soluble PAI-1 in systemic blood). Consistently, ascorbate affected neither elevated PAI-1 protein/enzymatic activity in septic liver nor lowered plasmin antiplasmin level in septic blood. Furthermore, hypocoagulability of septic blood revealed by thrombelastography and thrombin-induced PAI-1 release from isolated platelets (ex-vivo model of sepsis) were not affected by ascorbate. Based on the PAI-1 protein data, the present study does not support the hypothesis that ascorbate promotes fibrinolysis in sepsis.

Novel relationships between oxidative stress and angiogenesis-related factors in sepsis: New biomarkers and therapies

Sepsis is a systemic uncontrolled inflammatory response in the presence of an infection. It remains a major cause of morbidity and mortality in hospitalized patients. According to its severity, sepsis can progress to three different states: severe sepsis, septic shock, and multiple organ dysfunction syndrome, related to organ dysfunction and/or tissue hypoperfusion. Different processes underlie its pathophysiology; among them are oxidative stress, endothelial and mitochondrial dysfunction, and angiogenesis-related factors. However, no studies have integrated these elements in sepsis. The main difficulty in sepsis is its diagnosis. Currently, the potential of inflammatory biomarkers in septic patients remains weak. In this context, the research into new biomarkers is essential to aid with sepsis diagnosis and prognostication. Furthermore, even though the current management of severe forms of sepsis has been effective, morbimortality remains elevated. Therefore, it is essential to explore alternative approaches to therapy development. The aim of this review is to present an update of evidence supporting the role of oxidative stress and angiogenesis-related factors in the pathophysiology of the different forms of sepsis. It proposes a novel convergence between both elements in their role in the disease, and it will cover their utility as new diagnostic tools, predictors of outcome, and as novel therapeutic targets.

Ascorbic acid reduces HMGB1 secretion in lipopolysaccharide-activated RAW 264.7 cells and improves survival rate in septic mice by activation of Nrf2/HO-1 signals

High mobility group box 1 (HMGB1) is now recognized as a late mediator of sepsis. We tested hypothesis that ascorbic acid (AscA) induces heme oxygenase (HO)-1 which inhibits HMGB1 release in lipopolysaccharide (LPS)-stimulated cells and increases survival of septic mice. AscA increased HO-1 protein expression in a concentration- and time-dependent manner via Nrf2 activation in RAW 264.7 cells. HO-1 induction by AscA was significantly reduced by Nrf2 siRNA-transfected cells. Mutation of cysteine to serine of keap-1 proteins (C151S, C273S, and C288S) lost the ability of HO-1 induction by AscA, due to failure of translocation of Nrf-2 to nucleus. The PI3 kinase inhibitor, LY294002, inhibited HO-1 induction by AscA. Oxyhemoglobin (HbO2), LY294002, and ZnPPIX (HO-1 enzyme inhibitor) reversed effect of AscA on HMGB1 release. Most importantly, administration of AscA (200mg/kg, i.p.) significantly increased survival in LPS-induced endotoxemic mice. In cecal ligation and puncture (CLP)-induced septic mice, AscA reduced hepatic injury and serum HMGB1 and plasminogen activator inhibitor (PAI)-1 in a ZnPPIX-sensitive manner. In addition, AscA failed to increase survival in Nrf2 knockout mice by LPS. Thus, we concluded that high dose of AscA may be useful in the treatment of sepsis, at least, by activation of Nrf2/HO-1 signals.

Vitamin C revisited

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.

Intravenous ascorbic acid as an adjuvant to interleukin-2 immunotherapy

Interleukin-2 (IL-2) therapy has been demonstrated to induce responses in 10-20% of advanced melanoma and renal cell carcinoma patients, which translates into durable remissions in up to half of the responsers. Unfortunately the use of IL-2 has been associated with severe toxicity and death. It has been previously observed and reported that IL-2 therapy causes a major drop in circulating levels of ascorbic acid (AA). The IL-2 induced toxicity shares many features with sepsis such as capillary leakage, systemic complement activation, and a relatively non-specific rise in inflammatory mediators such as TNF-alpha, C-reactive protein, and in advanced cases organ failure. Animal models and clinical studies have shown rapid depletion of AA in conditions of sepsis and amelioration associated with administration of AA (JTM 9:1-7, 2011). In contrast to other approaches to dealing with IL-2 toxicity, which may also interfere with therapeutic effects, AA possesses the added advantage of having direct antitumor activity through cytotoxic mechanisms and suppression of angiogenesis. Here we present a scientific rationale to support the assessment of intravenous AA as an adjuvant to decrease IL-2 mediated toxicity and possibly increase treatment efficacy.

Ascorbate reduces mouse platelet aggregation and surface P-selectin expression in an ex vivo model of sepsis

OBJECTIVE

Compromised perfusion of the capillary bed can lead to organ failure and mortality in sepsis. We have reported that intravenous injection of ascorbate inhibits platelet adhesion and plugging in septic capillaries. In this study, we hypothesized that ascorbate reduces aggregation of platelets and their surface expression of P-selectin (a key adhesion molecule) in mice.

METHODS

Platelets were isolated from control mice and subjected to agents known to be released into the bloodstream during sepsis (thrombin, ADP or U46619, thromboxane A2 analog). Platelet aggregation was analyzed by aggregometry and P-selectin expression by flow cytometry.

RESULTS

Platelet-activating agents increased aggregation and P-selectin expression. Ascorbate inhibited these increases. This inhibitory effect was NOS-independent (LNAME had no effect). In contrast to the platelet-activating agents, direct stimuli lipopolysaccharide, TNFα, or plasma from septic mice did not increase aggregation/expression, a finding consistent with the literature. The results suggest a complex mechanism of platelet aggregation and P-selectin expression in sepsis, where generation of platelet-activating stimuli is required first, before platelet aggregation and adhesion in capillaries occur.

CONCLUSION

The ability of ascorbate to reduce platelet aggregation and P-selectin expression could be an important mechanism by which ascorbate inhibits capillary plugging in sepsis.

The effect of vitamin C on plasma volume in the early stage of sepsis in the rat

Background

Previous experimental studies have shown that vitamin C has several beneficial effects in sepsis and burns, such as decreased tissue oedema, improved endothelial barrier function and decreased transcapillary leakage of plasma markers. It has still not been investigated, though, if vitamin C has any impact specifically on plasma volume. The present study aims at testing the hypothesis that vitamin C decreases plasma volume loss in sepsis.

Methods

Anaesthetized male adult Sprague-Dawley rats were used in this prospective randomized study. All experiments were carried out at a university hospital laboratory. Sepsis was induced by caecal ligation and incision. After 3 h, vitamin C was given either as a bolus dose (66 mg/kg) followed by a continuous infusion (33 mg/kg/h) (n = 9), or as a single bolus dose (200 mg/kg) (n = 9). A sham group (n = 9) underwent the same surgical procedure, but no vitamin C was given. Plasma volume was measured (¹²⁵I-dilution technique) at baseline, at 3 h after end of initiation of sepsis and at the end of the experiment 3 h later. Arterial blood samples for analyses of electrolytes, blood gases, haematocrit and lactate were taken at the same time points.

Results

There were no significant differences in plasma volumes or the physiological parameters analysed between any of the three groups at any time point. There was a significantly larger urine production in the single bolus dose group (200 mg/kg) compared to the sham group.

Conclusions

Vitamin C treatment did not decrease the loss of plasma volume in the septic rat. The diuretic effect of vitamin C was in accordance with previous studies.

Evaluation of vitamin C for adjuvant sepsis therapy

SIGNIFICANCE

Evidence is emerging that parenteral administration of high-dose vitamin C may warrant development as an adjuvant therapy for patients with sepsis.

RECENT ADVANCES

Sepsis increases risk of death and disability, but its treatment consists only of supportive therapies because no specific therapy is available. The characteristics of severe sepsis include ascorbate (reduced vitamin C) depletion, excessive protein nitration in microvascular endothelial cells, and microvascular dysfunction composed of refractive vasodilation, endothelial barrier dysfunction, and disseminated intravascular coagulation. Parenteral administration of ascorbate prevents or even reverses these pathological changes and thereby decreases hypotension, edema, multiorgan failure, and death in animal models of sepsis.

CRITICAL ISSUES

Dehydroascorbic acid appears to be as effective as ascorbate for protection against microvascular dysfunction, organ failure, and death when injected in sepsis models, but information about pharmacodynamics and safety in human subjects is only available for ascorbate. Although the plasma ascorbate concentration in critically ill and septic patients is normalized by repletion protocols that use high doses of parenteral ascorbate, and such doses are tolerated well by most healthy subjects, whether such large amounts of the vitamin trigger adverse effects in patients is uncertain.

FUTURE DIRECTIONS

Further study of sepsis models may determine if high concentrations of ascorbate in interstitial fluid have pro-oxidant and bacteriostatic actions that also modify disease progression. However, the ascorbate depletion observed in septic patients receiving standard care and the therapeutic mechanisms established in models are sufficient evidence to support clinical trials of parenteral ascorbate as an adjuvant therapy for sepsis.

Vasoplegia in septic shock: do we really fight the right enemy?

Vasoplegia is a key factor for the death of patients with septic shock in intensive care unit owing to persistent and irreversible hypotension. Impairment of vascular reactivity has been attributed to a combination of endothelial injury, arginine-vasopressin system dysfunction, release of other vasodilatory inflammatory mediators, and muscle hyperpolarizaton. Nitric oxide induced by a Ca(+2) independent isoform of nitric oxide synthase has been suggested to play an important role in sepsis-induced vasoplegia. However, inhibition of nitric oxide synthase only partially restores the endotoxin-induced vascular hyporeactivity. The aim of this review is to discuss in detail the recent suggested alternative mechanisms of vasoplegia and to briefly outline the current therapeutic strategies and the novel therapeutic options based on those mechanisms.

Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the various mechanisms that are potentially involved in their development and the implications of these alterations. Endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability are the main mechanisms involved in the development of these alterations. Microcirculatory alterations increase the diffusion distance for oxygen and, due to the heterogeneity of microcirculatory perfusion in sepsis, may promote development of areas of tissue hypoxia in close vicinity to well-oxygenated zones. The severity of microvascular alterations is associated with organ dysfunction and mortality. At this stage, therapies to specifically target the microcirculation are still being investigated.

Hydroxysafflor yellow A suppresses oleic acid-induced acute lung injury via protein kinase A

Inflammation response and oxidative stress play important roles in acute lung injury (ALI). Activation of the cAMP/protein kinase A (PKA) signaling pathway may attenuate ALI by suppressing immune responses and inhibiting the generation of reactive oxygen species (ROS). Hydroxysafflor yellow A (HSYA) is a natural flavonoid compound that reduces oxidative stress and inflammatory cytokine-mediated damage. In this study, we examined whether HSYA could protect the lungs from oleic acid (OA)-induced injury, which was used to mimic ALI, and determined the role of the cAMP/PKA signaling pathway in this process. Arterial oxygen tension (PaO2), carbon dioxide tension, pH, and the PaO2/fraction of inspired oxygen ratio in the blood were detected using a blood gas analyzer. We measured wet/dry lung weight ratio and evaluated tissue morphology. The protein and inflammatory cytokine levels in the bronchoalveolar lavage fluid and serum were determined using enzyme-linked immunoassay. The activities of superoxide dismutase, glutathione peroxidase, PKA, and nicotinamide adenine dinucleotide phosphate oxidase, and the concentrations of cAMP and malondialdehyde in the lung tissue were detected using assay kits. Bcl-2, Bax, caspase 3, and p22(phox) levels in the lung tissue were analyzed using Western blotting. OA increased the inflammatory cytokine and ROS levels and caused lung dysfunction by decreasing cAMP synthesis, inhibiting PKA activity, stimulating caspase 3, and reducing the Bcl-2/Bax ratio. H-89 increased these effects. HSYA significantly increased the activities of antioxidant enzymes, inhibited the inflammatory response via cAMP/PKA pathway activation, and attenuated OA-induced lung injury. Our results show that the cAMP/PKA signaling pathway is required for the protective effect of HSYA against ALI.

Administration of tetrahydrobiopterin improves the microcirculation and outcome in an ovine model of septic shock

OBJECTIVE

Supplementation with tetrahydrobiopterin, a nitric oxide synthase cofactor, may reduce microvascular endothelial dysfunction in severe sepsis. We studied whether tetrahydrobiopterin administration exerts beneficial effects in an ovine septic shock model.

DESIGN

Randomized animal study.

SETTING

University hospital animal research laboratory.

SUBJECTS

Fourteen adult female sheep.

INTERVENTIONS

Fecal peritonitis was induced, and the sheep were randomized to receive tetrahydrobiopterin (n=7), given intravenously as 20 mg/kg boluses at 4 and 12 hrs after sepsis induction, or placebo (n=7). All animals were fluid resuscitated. The experiment was continued until death or for a maximum of 30 hrs.

MEASUREMENTS AND MAIN RESULTS

In addition to standard hemodynamic assessment, the sublingual microcirculation was evaluated using sidestream dark-field videomicroscopy. The first bolus of tetrahydrobiopterin blunted the increase in heart rate and cardiac index seen in the control group without affecting mean arterial pressure, and the second bolus of tetrahydrobiopterin prevented the decreases in cardiac index and mean arterial pressure. The reduction in mixed venous blood oxygen saturation and the increase in blood lactate seen in the control group were also delayed. Tetrahydrobiopterin significantly attenuated the deterioration in perfused small vessel proportion and density, microvascular flow index, and the increase in microvascular heterogeneity observed in the control group. Tetrahydrobiopterin was associated with better preserved lung compliance and PaO2/FIO2 ratio, which were associated with a lower lung wet/dry weight ratio at the end of the study. Median survival time was significantly prolonged in the tetrahydrobiopterin group (25.0 vs. 17.8 hrs, p<.01).

CONCLUSION

In this clinically relevant model of sepsis, tetrahydrobiopterin supplementation attenuated the impairment in sublingual microvascular perfusion and permeability, which was accompanied by better preserved gas exchange, renal flow and urine output, and prolonged survival.

Ascorbate stimulates endothelial nitric oxide synthase enzyme activity by rapid modulation of its phosphorylation status

Long-term exposure to ascorbate is known to enhance endothelial nitric oxide synthase (eNOS) activity by stabilizing the eNOS cofactor tetrahydrobiopterin (BH4). We investigated acute effects of ascorbate on eNOS function in primary (HUVEC) and immortalized human endothelial cells (EA.hy926), aiming to provide a molecular explanation for the rapid vasodilatation seen in vivo upon administration of ascorbate. Enzymatic activity of eNOS and intracellular BH4 levels were assessed by means of an arginine-citrulline conversion assay and HPLC analysis, respectively. Over a period of 4h, ascorbate steadily increased eNOS activity, although endothelial BH4 levels remained unchanged compared to untreated control cells. Immunoblot analyses revealed that as early as 5 min after treatment ascorbate dose-dependently increased phosphorylation at eNOS-Ser1177 and concomitantly decreased phosphorylation at eNOS-Thr495, a phosphorylation pattern indicative of increased eNOS activity. By employing pharmacological inhibitors, siRNA-mediated knockdown approaches, and overexpression of the catalytic subunit of protein phosphatase 2A (PP2A), we show that this effect was at least partly owing to reduction of PP2A activity and subsequent activation of AMP-activated kinase. In this report, we unravel a novel mechanism for how ascorbate rapidly activates eNOS independent of its effects on BH4 stabilization.

Mechanisms of attenuation of abdominal sepsis induced acute lung injury by ascorbic acid

Bacterial infections of the lungs and abdomen are among the most common causes of sepsis. Abdominal peritonitis often results in acute lung injury (ALI). Recent reports demonstrate a potential benefit of parenteral vitamin C [ascorbic acid (AscA)] in the pathogenesis of sepsis. Therefore we examined the mechanisms of vitamin C supplementation in the setting of abdominal peritonitis-mediated ALI. We hypothesized that vitamin C supplementation would protect lungs by restoring alveolar epithelial barrier integrity and preventing sepsis-associated coagulopathy. Male C57BL/6 mice were intraperitoneally injected with a fecal stem solution to induce abdominal peritonitis (FIP) 30 min prior to receiving either AscA (200 mg/kg) or dehydroascorbic acid (200 mg/kg). Variables examined included survival, extent of ALI, pulmonary inflammatory markers (myeloperoxidase, chemokines), bronchoalveolar epithelial permeability, alveolar fluid clearance, epithelial ion channel, and pump expression (aquaporin 5, cystic fibrosis transmembrane conductance regulator, epithelial sodium channel, and Na(+)-K(+)-ATPase), tight junction protein expression (claudins, occludins, zona occludens), cytoskeletal rearrangements (F-actin polymerization), and coagulation parameters (thromboelastography, pro- and anticoagulants, fibrinolysis mediators) of septic blood. FIP-mediated ALI was characterized by compromised lung epithelial permeability, reduced alveolar fluid clearance, pulmonary inflammation and neutrophil sequestration, coagulation abnormalities, and increased mortality. Parenteral vitamin C infusion protected mice from the deleterious consequences of sepsis by multiple mechanisms, including attenuation of the proinflammatory response, enhancement of epithelial barrier function, increasing alveolar fluid clearance, and prevention of sepsis-associated coagulation abnormalities. Parenteral vitamin C may potentially have a role in the management of sepsis and ALI associated with sepsis.

Erythropoietin improves skeletal muscle microcirculation through the activation of eNOS in a mouse sepsis model

BACKGROUND

Sepsis and septic shock remain the major causes of morbidity and mortality in intensive care units. One mechanism that leads to organ failure is microcirculatory dysfunction. Erythropoietin (EPO) is a glycoprotein produced by the kidney that primarily regulates erythropoiesis, but it also can exert hemodynamic, anti-inflammatory, and tissue protective effects. We previously reported that administration of EPO to septic mice improves mouse skeletal muscle capillary perfusion and tissue bioenergetics. The objective of this study was to explore the potential mechanism(s) involved.

METHODS

Sepsis was induced by intraperitoneal (i.p.) injection of a fecal suspension (12.5 g in 0.5 saline/mouse) in mice. At 18 hours after sepsis induction, a single dose of rHuEPO (400 U/kg) was given to the mice. Mouse capillary perfusion density and nicotinamide adenine dinucleotide (NADH) fluorescence in skeletal muscle were observed using intravital microscopy. Endothelial cells derived from the skeletal muscle were treated with rHuEPO (5 U/mL) and endothelial nitric oxide synthase (eNOS) activation and activity were assessed.

RESULTS

Septic mice had decreased capillary perfusion density and increased tissue NADH fluorescence indicating impaired tissue bioenergetics, whereas animals treated with rHuEPO demonstrated an improvement in capillary perfusion density and decreased skeletal muscle NADH fluorescence. The beneficial effect of rHuEPO did not occur in septic mice treated with l-NAME (an NOS inhibitor, 20 mg/kg) or mice genetically deficient in eNOS. Treatment of endothelial cells with rHuEPO resulted in activation of eNOS as indicated by increased eNOS phosphorylation and NO production.

CONCLUSIONS

Our results suggest that eNOS plays an important role in mediating the beneficial effect of rHuEPO on microcirculation in this septic mouse model.

Ascorbic acid attenuates lipopolysaccharide-induced acute lung injury

OBJECTIVE

Sepsis-induced lung injury is a persisting clinical problem with no direct therapy. Recent work suggests that intravenously infused ascorbic acid improves the circulatory dysfunction of sepsis. We used a model of endotoxin-induced acute lung injury to determine whether parenteral ascorbic acid modulates the dysregulated proinflammatory, procoagulant state that leads to lung injury.

DESIGN

C57BL/6 mice were exposed to lethal lipopolysaccharide doses (10 μg/g of body weight) to induce acute lung injury.

SETTING

Laboratory investigation.

SUBJECTS

Wild-type C57BL/6 mice.

INTERVENTIONS

Ascorbic acid or its oxidized form (dehydroascorbic acid) was administered intraperitoneally at 200 mg/kg 30 mins after the lethal lipopolysaccharide dose.

MEASUREMENTS AND MAIN RESULTS

We quantified survival, lung capillary leak, proinflammatory chemokine expression, and lung microvascular thrombosis. Lipopolysaccharide induced 100% lethality in mice within 28 hrs of exposure and in lung we observed intense neutrophil sequestration, loss of capillary barrier function, exuberant pulmonary inflammation, and extensive microthrombus formation. A time-delayed infusion protocol of both ascorbic acid and dehydroascorbic acid significantly prolonged survival. Both ascorbic acid and dehydroascorbic acid preserved lung architecture and barrier function while attenuating proinflammatory chemokine expression and microvascular thrombosis. Ascorbic acid and dehydroascorbic acid attenuated nuclear factor kappa B activation and normalized coagulation parameters.

CONCLUSIONS

Ascorbic acid administered in an interventional manner following lipopolysaccharide infusion attenuates proinflammatory, procoagulant states that induce lung vascular injury in an animal model of sepsis.