Critically ill septic patients have elevated oxidative stress biomarkers: lack of attenuation by parenteral vitamin C.

Patients with septic shock are under an intense inflammatory burden, which is closely associated with increased oxidative stress and depletion of antioxidants such as vitamin C. We hypothesized that patients with septic shock would present with elevated oxidative stress (assessed as F2-isoprostanes) and that administration of parenteral vitamin C to these patients would attenuate F2-isoprostane concentrations. We recruited 40 critically ill patients with septic shock into a randomized placebo-controlled trial and assessed the effect of short-term (4-day) parenteral vitamin C administration (100 mg/kg/d) on 8-isoprostane F2α concentrations, which were measured using enzyme-linked immunosorbent assays. Sources of sepsis and intensive care unit severity scores were recorded. Smokers (n = 20) and nonsmoking controls (n = 50) were assessed for comparison. The median baseline 8-isoprostane F2α concentration in the septic patients was 3.95 (interquartile range [Q1, Q3] 2.1, 6.63) ng/mg creatinine; this was higher than smokers 1.61 [1.25, 2.82] P = .007 ng/mg creatinine; P = .005) and nonsmoking controls 1.12 [0.76, 1.57] ng/mg creatinine; P < .0001). The 8-isoprostane F2α concentrations in the placebo group did not vary significantly over the duration of the study. Although parenteral vitamin C administration significantly increased the vitamin C status of the patients within 24 hours, this did not affect their 8-isoprostane F2α concentrations. In conclusion, patients with septic shock have elevated 8-isoprostane F2α excretion, which short-term parenteral vitamin C administration is unable to attenuate. If vitamin C is to work by antioxidant mechanisms, then early administration, before the development of shock, may be required. This trial was registered at anzctr.org.au (ACTRN12617001184369).

Intravenous vitamin C administration to patients with septic shock: a pilot randomised controlled trial.

BACKGROUND: Intravenous vitamin C administration in septic shock may have a sparing effect on vasopressor requirements, and vitamin C's enzyme cofactor functions provide a mechanistic rationale. Our study aimed to determine the effect of intravenous vitamin C administration on vasopressor requirements and other outcomes in patients with septic shock. METHODS: This was a double-blind, randomised placebo-controlled trial in 40 patients with septic shock who were randomised (1:1) to receive intravenous vitamin C (at a dose of 25 mg/kg of body weight every 6 h) or placebo (intravenous 5% dextrose) for up to 96 h, or until death or discharge. The primary outcome was intravenous vasopressor requirements (dose and duration), and secondary outcomes included Sequential Organ Failure Assessment (SOFA) scores, intensive care unit (ICU) and hospital length of stay, and mortality. In addition, blood samples were collected to determine vitamin C kinetics and inflammatory marker concentrations. RESULTS: Median plasma vitamin C concentrations were deficient at baseline (9.2 [4.4, 12] µmol/L) and increased to 408 (227, 560) µmol/L following 72 h of intervention. The mean duration of intravenous vasopressor infusion in the vitamin C group was 48 (95% CI 35-62) hours and in the placebo group was 54 (95% CI 41-62) hours (p = 0.52). The dose of vasopressor delivered over time was comparable between the two groups, as were SOFA scores (p > 0.05). The median ICU length of stay in the intervention group was 3.8 (2.2, 9.8) days versus 7.1 (3.1, 20) days in the placebo group (p = 0.12). The median hospital length of stay for the vitamin C group was 18 (11, 35) days versus 22 (10, 52) days for the placebo group (p = 0.65). Mortality was comparable between the two groups (p > 0.05). Of the inflammatory markers, neutrophil counts were elevated in the vitamin C group relative to placebo by 72 h (p = 0.01). C-reactive protein and myeloperoxidase concentrations were elevated at baseline, however, the two groups were comparable over time (p > 0.05). CONCLUSIONS: Our pilot study indicated that intravenous vitamin C did not provide significant decreases in the mean dose or duration of vasopressor infusion. Further research that takes into account the potential impact of intervention timing, dose and duration, and location of trial, may provide more definitive evidence. TRIAL REGISTRATION: ACTRN12617001184369 (11/8/2017).

Effect of intravenous vitamin C on arterial blood gas analyser and Accu-Chek point-of-care glucose monitoring in critically ill patients.

Background: Intravenous vitamin C is known to interfere with some point-of-care blood glucose meters. We aimed to determine the concentrations at which ascorbate interferes with glucose concentrations measured using a point-of-care blood glucose meter. We also compared the point-of-care meter and an arterial blood gas (ABG) analyser in the intensive care unit with laboratory glucose monitoring in septic patients receiving intravenous vitamin C infusions. Methods: Blood samples containing normal, depleted and supplemented glucose and increasing concentrations of ascorbate (0.1-1.0 mmol/L) were tested using an Accu-Chek Inform II (Roche Diagnostics, USA) glucometer. For the in vivo study, 41 individual blood samples were drawn daily from septic patients (n = 16) receiving infusions of 25 mg/kg of vitamin C every 6 hours. The glucose values of matched blood samples were assessed using Accu-Chek, ABG and laboratory glucose methods. Results: For every 1 mmol/L of ascorbate added, the glucose concentration measured by the point-of-care monitor increased by 1.4 mmol/L (95% CI, 1.0-1.8; P < 0.001). Analysis of matched blood samples collected following intravenous vitamin C infusion indicated that 98% of the ABG and 83% of the Accu-Chek values met the International Organization for Standardization (ISO) 15197:2013 accuracy criteria. One patient had severe renal impairment, which contributed to elevated plasma vitamin C concentrations (median, 0.95 mmol/L; range, 0.64-1.10 mmol/L), resulting in elevated Accu-Chek readings and presenting a moderate clinical risk for the highest value. Conclusions: Vitamin C concentrations < 0.8 mmol/L do not interfere with point-of-care glucose monitoring. Intravenous vitamin C infusion of 25 mg/kg every 6 hours does not interfere with point-of-care glucose monitoring unless the patient has renal impairment, in which case laboratory glucose tests should be used.

Circulating protein carbonyls are specifically elevated in critically ill patients with pneumonia relative to other sources of sepsis.

BACKGROUND: Septic shock is a life-threatening dysregulated response to severe infection and is associated with elevated oxidative stress. We aimed to assess protein carbonyls in critically ill patients with different sources of sepsis and determine the effect of vitamin C intervention on protein carbonyl concentrations. METHODS: Critically ill patients with septic shock (n = 40) were recruited, and sources of sepsis and ICU severity scores were recorded. The patients were randomised to receive either intravenous vitamin C (100 mg/kg body weight/day) or placebo infusions. Blood samples were collected at baseline and daily for up to three days for measurement of cell counts, vitamin C concentrations, protein carbonyls, C-reactive protein, and myeloperoxidase concentrations. RESULTS: Protein carbonyl concentrations increased 2.2-fold in the cohort over the duration of the study (from 169 to 369 pmol/mg protein; p = 0.03). There were significant correlations between protein carbonyl concentrations and ICU severity scores (APACHE III r = 0.47 and SOFA r = 0.37; p < 0.05) at baseline. At study admission, the patients with pneumonia had nearly 3-fold higher protein carbonyl concentrations relative to the patients with other sources of sepsis (435 vs 157 pmol/mg protein, p < 0.0001). The septic patients had deficient vitamin C status at baseline (9.8 ± 1.4 µmol/L). This increased to 456 ± 90 µmol/L following three days of intravenous vitamin C intervention. Vitamin C intervention did not attenuate the increase in protein carbonyl concentrations. CONCLUSIONS: Circulating protein carbonyls are specifically elevated in critically ill patients with pneumonia relative to other sources of sepsis. The reasons for this are currently unclear and may indicate a mechanism unique to pulmonary sources of sepsis. Intravenous vitamin C administration did not attenuate the increase in protein carbonyls over time.

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

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

Ovarian fluid proteome variation associates with sperm swimming speed in an externally fertilizing fish.

Sperm velocity is a key trait that predicts the outcome of sperm competition. By promoting or impeding sperm velocity, females can control fertilization via postcopulatory cryptic female choice. In Chinook salmon, ovarian fluid (OF), which surrounds the ova, mediates sperm velocity according to male and female identity, biasing the outcome of sperm competition towards males with faster sperm. Past investigations have revealed proteome variation in OF, but the specific components of OF that differentially mediate sperm velocity have yet to be characterized. Here we use quantitative proteomics to investigate whether OF protein composition explains variation in sperm velocity and fertilization success. We found that OF proteomes from six females robustly clustered into two groups and that these groups are distinguished by the abundance of a restricted set of proteins significantly associated with sperm velocity. Exposure of sperm to OF from females in group I had faster sperm compared to sperm exposed to the OF of group II females. Overall, OF proteins that distinguished between these groups were enriched for vitellogenin and calcium ion interactions. Our findings suggest that these proteins may form the functional basis for cryptic female choice via the biochemical and physiological mediation of sperm velocity.

Circulating myeloperoxidase is elevated in septic shock and is associated with systemic organ failure and mortality in critically ill patients.

BACKGROUND: Neutrophils are elevated in critically ill patients during the systemic inflammatory response to trauma and sepsis. The neutrophil-derived enzyme myeloperoxidase generates reactive oxygen species which can react with host tissue resulting in cell damage and dysfunction. Thus, elevated myeloperoxidase in the circulation may be associated with adverse patient outcomes. METHODS: Circulating myeloperoxidase concentrations were measured in a cohort of 44 critically ill patients, 55% of whom were diagnosed with septic shock, and 44 healthy controls. Intensive care mortality prediction scores (SOFA, SAPS, APACHE) and ICU and hospital mortality were obtained from the patients' clinical notes. Hematological and biochemical assessments included blood cell counts, lactate, alanine transaminase, creatinine, bilirubin, C-reactive protein, and PaO2. Myeloperoxidase was measured using a commercial ELISA kit and cell free DNA was detected using SytoxGreen™ fluorescence staining. RESULTS: Myeloperoxidase concentrations were significantly higher in critically ill patients than control samples (234 ±â€¯30 ng/ml versus 15 ±â€¯4 ng/ml, p < 0.001), and were elevated in septic shock relative to non-septic patients (302 ±â€¯42 ng/ml versus 156 ±â€¯38 ng/ml, p = 0.02), despite neutrophil counts being comparable between the two subgroups (p = 0.6). Myeloperoxidase correlated with SOFA scores in the critically ill patients (r = 0.395, p = 0.02), and with markers of tissue dysfunction and injury such as lactate (r = 0.572, p < 0.001), log10 alanine transferase (r = 0.392, p = 0.016) and log10 cell free DNA (r = 0.371, p = 0.03). The subgroup of patients with higher than mean APACHE III scores (i.e. >78, n = 16) exhibited significantly elevated myeloperoxidase concentrations in the non-survivors compared with survivors (416 ±â€¯59 ng/ml versus 140 ±â€¯33 ng/mL, p = 0.001). Hospital mortality for the whole cohort was 27%; mortality in the high APACHE III subgroup was 38%, and when combined with higher than mean myeloperoxidase (i.e. >234 ng/mL), mortality increased to 71%. CONCLUSIONS: Myeloperoxidase is associated with markers of tissue injury and systemic organ failure, particularly in septic patients. The enzyme is also associated with mortality in patients with higher APACHE III scores, and thus has potential as an additional diagnostic marker to improve mortality prediction.

Hypovitaminosis C and vitamin C deficiency in critically ill patients despite recommended enteral and parenteral intakes.

BACKGROUND: Vitamin C is an essential water-soluble nutrient which cannot be synthesised or stored by humans. It is a potent antioxidant with anti-inflammatory and immune-supportive roles. Previous research has indicated that vitamin C levels are depleted in critically ill patients. In this study we have assessed plasma vitamin C concentrations in critically ill patients relative to infection status (septic shock or non-septic) and level of inflammation (C-reactive protein concentrations). Vitamin C status was also assessed relative to daily enteral and parenteral intakes to determine if standard intensive care unit (ICU) nutritional support is adequate to meet the vitamin C needs of critically ill patients. METHODS: Forty-four critically ill patients (24 with septic shock, 17 non-septic, 3 uncategorised) were recruited from the Christchurch Hospital Intensive Care Unit. We measured concentrations of plasma vitamin C and a pro-inflammatory biomarker (C-reactive protein) daily over 4 days and calculated patients' daily vitamin C intake from the enteral or total parenteral nutrition they received. We compared plasma vitamin C and C-reactive protein concentrations between septic shock and non-septic patients over 4 days using a mixed effects statistical model, and we compared the vitamin C status of the critically ill patients with known vitamin C bioavailability data using a four-parameter log-logistic response model. RESULTS: Overall, the critically ill patients exhibited hypovitaminosis C (i.e., < 23 µmol/L), with a mean plasma vitamin C concentration of 17.8 ± 8.7 µmol/L; of these, one-third had vitamin C deficiency (i.e., < 11 µmol/L). Patients with hypovitaminosis C had elevated inflammation (C-reactive protein levels; P < 0.05). The patients with septic shock had lower vitamin C concentrations and higher C-reactive protein concentrations than the non-septic patients (P < 0.05). Nearly 40% of the septic shock patients were deficient in vitamin C, compared with 25% of the non-septic patients. These low vitamin C levels were apparent despite receiving recommended intakes via enteral and/or parenteral nutritional therapy (mean 125 mg/d). CONCLUSIONS: Critically ill patients have low vitamin C concentrations despite receiving standard ICU nutrition. Septic shock patients have significantly depleted vitamin C levels compared with non-septic patients, likely resulting from increased metabolism due to the enhanced inflammatory response observed in septic shock.

Sperm competition risk drives rapid ejaculate adjustments mediated by seminal fluid.

In many species, males can make rapid adjustments to ejaculate performance in response to sperm competition risk; however, the mechanisms behind these changes are not understood. Here, we manipulate male social status in an externally fertilising fish, chinook salmon (Oncorhynchus tshawytscha), and find that in less than 48 hr, males can upregulate sperm velocity when faced with an increased risk of sperm competition. Using a series of in vitro sperm manipulation and competition experiments, we show that rapid changes in sperm velocity are mediated by seminal fluid and the effect of seminal fluid on sperm velocity directly impacts paternity share and therefore reproductive success. These combined findings, completely consistent with sperm competition theory, provide unequivocal evidence that sperm competition risk drives plastic adjustment of ejaculate quality, that seminal fluid harbours the mechanism for the rapid adjustment of sperm velocity and that fitness benefits accrue to males from such adjustment.

Cryptic female choice enhances fertilization success and embryo survival in chinook salmon.

In this study, we investigated two potentially important intersexual postcopulatory gametic interactions in a population of chinook salmon (Oncorhynchus tshawytscha): (i) the effect of female ovarian fluid (OF) on the behaviour of spermatozoa during fertilization and (ii) the effects of multilocus heterozygosity (MLH) (as an index of male quality) and female-male genetic relatedness on sperm behaviour and male fertilization success when there is sperm competition in the presence of that OF. To do this, we conducted a series of in vitro competitive fertilization experiments and found that, when ejaculates from two males are competing for access to a single female's unfertilized eggs, fertilization success was significantly biased towards the male whose sperm swam fastest in the female's OF. Embryo survival--a measure of fitness--was also positively correlated with both sperm swimming speed in OF and male MLH, providing novel evidence that cryptic female choice is adaptive for the female, enhancing the early survival of her offspring and potentially influencing her fitness.

Proteomic analysis of chinook salmon (Oncorhynchus tshawytscha) ovarian fluid.

The ovarian, or coelomic, fluid that is released with the egg mass of many fishes is increasingly found to play an important role in several biological processes crucial for reproductive success. These include maintenance of oocyte fertility and developmental competence, prolonging of sperm motility, and enhancing sperm swimming speed. Here we examined if and how the proteome of chinook salmon (Oncorhynchus tshawytscha) ovarian fluid varied among females and then sought to examine the composition of this fluid. Ovarian fluid in chinook salmon was analyzed using 1D SDS PAGE and LC-MS/MS tryptic digest screened against Mascot and Sequest databases. We found marked differences in the number and concentrations of proteins in salmon ovarian fluid across different females. A total of 174 proteins were identified in ovarian fluid, 47 of which were represented by six or more peptides, belonging to one of six Gene Ontology pathways. The response to chemical stimulus and response to hypoxia pathways were best represented, accounting for 26 of the 174 proteins. The current data set provides a resource that furthers our understanding of those factors that influence successful egg production and fertilisation in salmonids and other species.

Delineating the roles of males and females in sperm competition.

Disentangling the relative roles of males, females and their interactive effects on competitive fertilization success remains a challenge in sperm competition. In this study, we apply a novel experimental framework to an ideally suited externally fertilizing model system in order to delineate these roles. We focus on the chinook salmon, Oncorhynchus tshawytscha, a species in which ovarian fluid (OF) has been implicated as a potential arbiter of cryptic female choice for genetically compatible mates. We evaluated this predicted sexually selected function of OF using a series of factorial competitive fertilization trials. Our design involved a series of 10 factorial crosses, each involving two 'focal' rival males whose sperm competed against those from a single 'standardized' (non-focal) rival for a genetically uniform set of eggs in the presence of OF from two focal females. This design enabled us to attribute variation in competitive fertilization success among focal males, females (OF) and their interacting effects, while controlling for variation attributable to differences in the sperm competitive ability of rival males, and male-by-female genotypic interactions. Using this experimental framework, we found that variation in sperm competitiveness could be attributed exclusively to differences in the sperm competitive ability of focal males, a conclusion supported by subsequent analyses revealing that variation in sperm swimming velocity predicts paternity success. Together, these findings provide evidence that variation in paternity success can be attributed to intrinsic differences in the sperm competitive ability of rival males, and reveal that sperm swimming velocity is a key target of sexual selection.

Chemical composition of seminal and ovarian fluids of chinook salmon (Oncorhynchus tshawytscha) and their effects on sperm motility traits.

The relationships between the compositions of ovarian, seminal fluids and sperm function are not well known in teleostean fish species. The objective of the present study was to determine the concentration of the major inorganic ions (Na(+), K(+), Ca(2+), Mg, Cl(-)), osmolality, and pH of ovarian and seminal fluid of sexually mature chinook salmon (Oncorhynchus tshawytscha), and to determine if the composition of these fluids influences sperm motility traits (swimming speed, duration of forward mobility, swimming path trajectory, and percent motility). Cation concentrations and osmolality were significantly different in the two fluids. The ionic composition of ovarian fluid differed among individual females, and also among samples collected at different times through the spawning season. Carbonate and bicarbonate were the principal buffer ions in ovarian fluid, and its viscosity was considerably greater than that of water and was shear-dependent. The duration of forward motility (longevity) of spermatozoa, swimming speed, percent motility, and path trajectory were measured using milt from 10 males activated in the ovarian fluid from 7 females whose ion concentrations were known. No significant correlations were observed between the composition of the seminal fluid and sperm traits. However, in ovarian fluid, sperm longevity was negatively correlated with variation in [Ca(2+)] and [Mg(2+)], while percent motility increased with increasing [Mg(2+)]. These observations provide a possible chemical basis for cryptic female mate choice whereby female ovarian fluid differentially influences the behaviour of sperm from different males, and thus their fertilization success.