The role of oxidants and vitamin C on neutrophil apoptosis and clearance

Role of AScorbic acid Infusion in critically ill patients with Transfusion Related Acute Lung Injury (ASTRALI)

INTRODUCTION

In critically ill patients, Transfusion Related Acute Lung Injury (TRALI) remains the leading cause of transfusion-related fatalities in critical care setting and associated with inflammation and oxidative stress state. Recent research raised the potential efficacy of high dose intravenous ascorbic acid in critically ill patients.

OBJECTIVE

The aim of this trial was to investigate the effect of high dose intravenous ascorbic acid (VC) as a targeted therapy for TRALI in terms of serum proinflammatory (interleukin-8, interleukin-1β, C-reactive protein), anti-inflammatory (interleukin-10), oxidative stress (superoxide dismutase, malondialdehyde) markers, and plasma VC levels. Secondary outcomes were oxygenation (PaO₂ /FiO₂ ratio), vasopressor use, duration of mechanical ventilation, ICU length of stay, 7-days mortality and 28-days mortality.

METHODS

Eighty critically ill patients with TRALI (n=80) were randomized to receive 2.5gm/6hr intravenous vitamin C for 96 hours (ASTRALI group) or placebo. Patients were followed-up to measure the outcomes initially (T0) and at the end of treatment (T96).

RESULTS

When compared to control group, ASTRALI group at T96, showed significantly higher median of interleukin-10 (31.6 ± 25.8 Vs. 17.7 ± 12.0 pg/mL, p<0.0001) levels and superoxide dismutase (12876 ± 4627 U/L Vs. 5895 ± 6632 U/L, p<0.0001) activities, lower median C-reactive protein (76 ± 50 Vs. 89 ± 56 mg/L, p=0.033), interleukin-8 (11.8 ± 7.3, 35.5 ± 19.8 pg/mL, p<0.0001), and malondialdehyde (0.197 ± 0.034 Vs. 0.234 ± 0.074 μM/L, p=0.002) levels.

CONCLUSION

High dose ascorbic acid was associated with significantly reduced oxidative stress, reduced pro-inflammatory markers except IL-1β, elevated anti-inflammatory marker, and elevated plasma VC levels.

Defective Neutrophil Function in Patients with Sepsis Is Mostly Restored by ex vivo Ascorbate Incubation

Background

Neutrophil function is essential for effective defence against bacterial infections but is defective in patients with sepsis. Ascorbate or vitamin C, which is low in the plasma of patients with sepsis, is stored inside human neutrophils and is essential for their normal function.

Objective

This study aimed to determine if ascorbate treatment ex vivo improved neutrophil function in patients with sepsis.

Patients and Methods

Human blood neutrophils were isolated from 20 patients with sepsis and 20 healthy age-matched controls. Neutrophils were incubated with or without ascorbate (1, 5, 10, 20 and 40 mM) for periods up to 2h. Chemotaxis was evaluated using a chemotactic chamber in response to the chemoattractant, fMLP. Phagocytosis (uptake of pHrodo red stained S. aureus) and apoptosis (annexin-V/propidium iodide staining) were measured by flow cytometry. Neutrophil extracellular trap (NET) formation was detected and quantified using DAPI, anti-myeloperoxidase and anti-neutrophil elastase immuno-fluorescence staining. Quantifluor detected the amount of dsDNA in NET supernatants, while quantitative PCR identified changes in expression of PADI4 gene.

Results

Chemotactic and phagocytic activities were decreased in patients with sepsis but increased after treatment with the high concentrations of ascorbate. Apoptosis was increased in the sepsis patients but not altered by ascorbate treatment. Spontaneous NET formation was observed in patients with sepsis. A quantity of 1mM ascorbate decreased spontaneous NETosis to that of normal, healthy neutrophils, while high concentrations of ascorbate (>10mM) further promoted NET formation.

Conclusion

Dysregulated neutrophil function was observed in patients with sepsis which could contribute to disease pathology and outcomes. Exposure to ascorbate could reverse some of these changes in function. These novel discoveries raise the possibility that ascorbate treatment could be used as an adjunctive therapy that could result in improved neutrophil function during sepsis.

Prolonged exposure to hypoxia induces an autophagy-like cell survival program in human neutrophils

Neutrophils contribute to low oxygen availability at inflammatory sites through the generation of reactive oxidants. They are also functionally affected by hypoxia, which delays neutrophil apoptosis. However, the eventual fate of neutrophils in hypoxic conditions is unknown and this is important for their effective clearance and the resolution of inflammation. We have monitored the survival and function of normal human neutrophils exposed to hypoxia over a 48 h period. Apoptosis was delayed, and the cells remained intact even at 48 h. However, hypoxia promoted significant changes in neutrophil morphology with the appearance of many new cytoplasmic vesicles, often containing cell material, within 5 hours of exposure to low O₂ . This coincided with an increase in LC3B-II expression, indicative of autophagosome formation and an autophagy-like process. In hypoxic conditions, neutrophils preferentially lost myeloperoxidase, a marker of azurophil granules. Short-term (2 h) hypoxic exposure resulted in sustained potential to generate superoxide when O₂ was restored, but the capacity for oxidant production was lost with longer periods of hypoxia. Phagocytic ability was unchanged by hypoxia, and bacterial killing by neutrophils in both normoxic and hypoxic conditions was substantially diminished after 24 hours. However, pre-exposure to hypoxia resulted in an enhanced ability to kill bacteria by oxidant-independent mechanisms. Our data provide the first evidence for hypoxia as a driver of neutrophil autophagy that can influence the function and ultimate fate of these cells, including their eventual clearance and the resolution of inflammation.

Vitamin C and immune cell function in inflammation and cancer

Vitamin C (ascorbate) is maintained at high levels in most immune cells and can affect many aspects of the immune response. Intracellular levels generally respond to variations in plasma ascorbate availability, and a combination of inadequate intake and increased turnover during severe stress can result in low plasma ascorbate status. Intracellular ascorbate supports essential functions and, in particular, acts as an enzyme cofactor for Fe- or Cu-containing oxygenases. Newly discovered enzymes in this family regulate cell metabolism and epigenetics, and dysregulation of their activity can affect cell phenotype, growth and survival pathways, and stem cell phenotype. This brief overview details some of the recent advances in our understanding of how ascorbate availability can affect the hydroxylases controlling the hypoxic response and the DNA and histone demethylases. These processes play important roles in the regulation of the immune system, altering cell survival pathways, metabolism and functions.

A short overview of vitamin C and selected cells of the immune system

Vitamin C (ascorbic acid) is an essential water-soluble nutrient that primarily exerts its effect on a host defense mechanisms and immune homeostasis and is the most important physiological antioxidant. Stable intake of vitamin C is essential for life in humans because the body does not synthesize it. Even the numerous studies have demonstrated that vitamin C supplementation stimulates the immune system, prevents DNA damage and significantly decreases the risk of a wide range of pathologies; the potential protective mechanisms are still largely unknown. This review summarizes the recently known facts about the role of vitamin C on the selected cells of the immune system and potential molecular mechanisms involved. Further, in this review, many new data about the positive effects of vitamin C on the immune system, potential toxicological effects, vitamin C supplementation in disease development, as well as some proposed mechanisms of vitamin C activity, are discussed.

Effect of vitamin C administration on neutrophil apoptosis in septic patients after abdominal surgery

OBJECTIVE

To investigate the effect of parenteral administration of vitamin C on neutrophil apoptosis by determining Fas receptor expression and caspase-3, poly (ADP-ribose) polymerase (PARP), and Bcl-2 levels in neutrophils from septic abdominal surgery patients.

STUDY DESIGN

Twenty septic abdominal surgery patients were studied in a prospective, randomized, double-blinded clinical trial. A group of healthy volunteers (n = 10) constituted a reference group for baseline parameter values. The patients were randomly assigned to a vitamin C-treated (n = 10) or placebo-treated (n = 10) group. For a 6-d period from 12 h post-surgery, the vitamin C group received 450 mg/d of the vitamin in 3 doses and the placebo group an identical administration of 5% dextrose. Early-morning peripheral blood samples were obtained daily from 24 h after vitamin C administration until d 6 post-surgery (T1d-T6d).

RESULTS

Vitamin C group showed a nonsignificant reduction in Fas (CD95) expression on CD15-positive peripheral blood neutrophils, significantly decreased caspase-3, and PARP levels (caspase-3: T4d: P < 0.05, T5d: P < 0.05, T6d P < 0.01; and PARP: T3d: P < 0.05, T4d: P < 0.05, T6d: P < 0.05), and significantly increased Bcl-2 levels (T3d: P = 0.001) versus placebo group.

CONCLUSIONS

Postoperative vitamin C treatment of septic abdominal surgery patients exerts an antiapoptotic effect on peripheral blood neutrophils, reducing caspase-3 and PARP levels, and increasing Bcl-2 levels. However, these antiapoptotic effects are not maintained at all time points.

Ascorbate does not protect macrophages against apoptosis induced by oxidised low density lipoprotein

Apoptosis of macrophages and smooth muscle cells is observed in atherosclerotic lesions and may play an important role in the disease progression. Oxidised low density lipoprotein (LDL) is cytotoxic and induces apoptosis in a variety of cell types. We reported previously that ascorbate protects arterial smooth muscle cells from apoptosis induced by oxidised LDL containing the peak levels of lipid hydroperoxides. We now demonstrate that macrophages undergo apoptosis when treated with this species of oxidised LDL, as detected by increased annexin V binding and DNA fragmentation. Ascorbate treatment of macrophages did not protect against the cytotoxicity of oxidised LDL, and modestly increased the levels of annexin V binding and DNA fragmentation. Oxidised LDL treatment also increased the expression of the antioxidant stress protein heme oxygenase-1 in macrophages; however, this increase was markedly attenuated by ascorbate pretreatment. Although apoptosis induced by oxidised LDL was modestly promoted by ascorbate, ascorbate apparently decreased the levels of oxidative stress in macrophages, suggesting that this pro-apoptotic effect was not mediated by a pro-oxidant mechanism, but may instead have been due to intracellular protection of the apoptotic machinery by ascorbate.

The roles of vitamin C in Helicobacter pylori associated gastric carcinogenesis

Ascorbic acid, as one of the important water-soluble vitamins, is essential for a range of physiological functions, including the syntheses of collagen, carnitine and neurotransmitters. It is also an important dietary antioxidant against oxidative stress. Current information suggests that vitamin C might be protective against the development of gastric cancer. Chronic infection with Helicobacter pylori is recognized to be a significant cause of gastric adenocarcinoma. Inflammation induced by H. pylori infection in the stomach not only causes significantly enhanced consumption of vitamin C, but also reduces secretion of the vitamin into the gastric lumen. Most of the evidence relating to vitamin C and H. pylori infection derives from clinical studies and experiments directly examining the effect of vitamin C on H. pylori-associated gastric carcinogenesis and remains limited. Furthermore, results from recent studies suggest that vitamin C might also increase the risk of cancer through its pro-oxidant activity and protect against oxidative stress in cancer cells through its antioxidant action. In this article we review recent publications on vitamin C research and assess the potential roles of vitamin C in H. pylori associated gastric carcinogenesis. The possible adverse effects of the vitamin C are also discussed.