Endothelial dysfunction as predictor of mortality in sepsis*:

Does hyperglycemia affect arginine metabolites in critically ill patients? A prospective cohort and in vitro study

BACKGROUND

Changes in the arginine metabolites asymmetric dimethyl-L-arginine (ADMA) and L-homoarginine and acute blood glucose concentrations have been shown to cause endothelial dysfunction and be independently associated with mortality in Intensive Care Unit (ICU) patients. The aim of this study was to investigate whether hyperglycemia potentially modulates these arginine metabolite concentrations to provide a mechanism that may link hyperglycemia and mortality in this patient group.

METHODS

A clinical and in vitro study were undertaken. Glucose, glycosylated hemoglobin-A1c (HbA1c) and the stress hyperglycemia ratio (SHR) (to quantify absolute, chronic and relative hyperglycemia respectively) were measured in 1155 acutely unwell adult patients admitted to a mixed medical-surgical ICU. SHR was calculated by dividing the admission glucose by the estimated average glucose over the last 3 months, which was derived from HbA1c. ADMA and L-homoarginine were measured in a plasma sample collected at admission to ICU by liquid chromatography tandem mass spectrometry. The activity of dimethylarginine-dimethylaminohydrolase 1 (DDAH1), the main enzyme regulating ADMA concentrations, was assessed at varying glucose concentrations in vitro by quantifying the conversion of ADMA to citrulline in HEK293 cells that overexpress DDAH1.

RESULTS

In the clinical study, plasma ADMA was not significantly associated with any measure of hyperglycemia. L-homoarginine was positively associated with glucose (β = 0.067, p = 0.018) and SHR (β = 0.107, p < 0.001) after correction for glomerular filtration rate. However, as L-homoarginine is a negative predictor of mortality, the direction of these associations are the opposite of those expected if hyperglycemia was affecting mortality via changes in L-homoarginine. In vitro DDAH1 activity was not significantly influenced by glucose concentrations (p = 0.506).

CONCLUSION

In critically ill patients the association between relative hyperglycemia and mortality is not mediated by changes in ADMA or L-homoarginine. Trial registration ANZCTR Trial ID ACTRN12615001164583.

Endothelial Dysfunction and Impaired Neurovascular Coupling Responses Precede Cognitive Impairment in a Mouse Model of Geriatric Sepsis

Sepsis is a life-threatening condition, the incidence of which is significantly increased in elderly patients. One of the long-lasting effects of sepsis is cognitive impairment defined as a new deficit or exacerbation of preexisting deficits in global cognition or executive function. Normal brain function is dependent on moment-to-moment adjustment of cerebral blood flow to match the increased demands of active brain regions. This homeostatic mechanism, termed neurovascular coupling (NVC, also known as functional hyperemia), is critically dependent on the production of vasodilator NO by microvascular endothelial cells in response to mediators released from activated astrocytes. The goal of this study was to test the hypothesis that sepsis in aging leads to impairment of NVC responses early after treatment and that this neurovascular dysfunction associates with impairments in cognitive performance and vascular endothelial dysfunction. To test this hypothesis, we used a commonly studied bacterial pathogen, Listeria monocytogenes, to induce sepsis in experimental animals (males, 24 months of age) and subjected experimental animals to a standard clinical protocol of 3 doses of ampicillin i.p. and 14 days of amoxicillin added to the drinking water. NVC responses, endothelial function and cognitive performance were measured in septic and age-matched control groups within 14 days after the final antibiotic treatment. Our data demonstrate that sepsis in aging significantly impairs NVC responses measured in somatosensory cortex during whisker stimulation, significantly impairs endothelial function in isolated and pressure cannulated aorta rings in response to acetylcholine stimulation. No significant impairment of cognitive function in post-sepsis aged animals has been observed when measured using the PhenoTyper homecage based system. Our findings suggest that sepsis-associated endothelial dysfunction and impairment of NVC responses may contribute to long-term cognitive deficits in older sepsis survivors.

Early Prediction of Persistent Organ Failure by Circulating Endothelial Progenitor Cells in Patients With Acute Pancreatitis

INTRODUCTION

Increased circulating endothelial progenitor cells (cEPC) have been observed in patients with vascular injury associated with sepsis and acute lung injury. However, a role for cEPC in severe acute pancreatitis (SAP) remains unclear. We therefore conducted a prospective study to study whether the quantities of cEPC can predict persistent organ failure (POF) in patients with predicted SAP.

METHODS

A total of 42 predicted SAP patients who were admitted within 24 h after symptom onset and 10 healthy control subjects were enrolled in our study. The proportions of cEPC were analyzed based on flow cytometry simultaneously. Vascular endothelial growth factor (VEGF) levels were measured by enzyme-linked immunosorbent assay.

RESULTS

The percentage of cEPC was significantly higher in patients with predicted SAP compared with healthy controls. Similarly, the levels of VEGF in peripheral blood were also significantly higher in predicted SAP patients than in the controls. Notably, patients with POF had lower proportion of cEPC compared with patients with transient organ failure (TOF). In contrast, patients with POF had a significantly higher level of VEGF compared with TOF. Of note, the percentages of cEPC were significantly inversely correlated with disease severity scores. More importantly, cEPC showed an excellent discriminative power for predicting POF among predicted SAP patients, whereas plasma VEGF and disease severity scores showed moderate accuracy in predicting future POF.

CONCLUSIONS

Peripheral EPC as a novel biomarker is elevated and may aid to predict the development of POF in patients with predicted SAP.

Vascular Dysfunction in Horses with Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) is a vascular condition of the equine hoof resulting in severe lameness with both welfare and economic implications. EL occurs in association with equine metabolic syndrome and equine Cushing’s disease. Vascular dysfunction, most commonly due to endothelial dysfunction, is associated with cardiovascular risk in people with metabolic syndrome and Cushing’s syndrome. We tested the hypothesis that horses with EL have vascular, specifically endothelial, dysfunction. Healthy horses (n = 6) and horses with EL (n = 6) destined for euthanasia were recruited. We studied vessels from the hooves (laminar artery, laminar vein) and the facial skin (facial skin arteries) by small vessel wire myography. The response to vasoconstrictors phenylephrine (10⁻⁹–10^-5M) and 5-hydroxytryptamine (5HT; 10⁻⁹–10^-5M) and the vasodilator acetylcholine (10⁻⁹–10^-5M) was determined. In comparison with healthy controls, acetylcholine-induced relaxation was dramatically reduced in all intact vessels from horses with EL (% relaxation of healthy laminar arteries 323.5 ± 94.1% v EL 90.8 ± 4.4%, P = 0.01, laminar veins 129.4 ± 14.8% v EL 71.2 ± 4.1%, P = 0.005 and facial skin arteries 182.0 ± 40.7% v EL 91.4 ± 4.5%, P = 0.01). In addition, contractile responses to phenylephrine and 5HT were increased in intact laminar veins from horses with EL compared with healthy horses; these differences were endothelium-independent. Sensitivity to phenylephrine was reduced in intact laminar arteries (P = 0.006) and veins (P = 0.009) from horses with EL. Horses with EL exhibit significant vascular dysfunction in laminar vessels and in facial skin arteries. The systemic nature of the abnormalities suggest this dysfunction is associated with the underlying endocrinopathy and not local changes to the hoof.

Endothelial dysfunction is a potential contributor to multiple organ failure and mortality in aged mice subjected to septic shock: preclinical studies in a murine model of cecal ligation and puncture

INTRODUCTION

The goal of the current study was to investigate the effect of aging on the development of endothelial dysfunction in a murine model of sepsis, and to compare it with the effect of genetic deficiency of the endothelial isoform of nitric oxide synthase (eNOS).

METHODS

Cecal ligation and puncture (CLP) was used to induce sepsis in mice. Survival rates were monitored and plasma indices of organ function were measured. Ex vivo studies included the measurement of vascular function in thoracic aortic rings, assessment of oxidative stress/cellular injury in various organs and the measurement of mitochondrial function in isolated liver mitochondria.

RESULTS

eNOS deficiency and aging both exacerbated the mortality of sepsis. Both eNOS-deficient and aged mice exhibited a higher degree of sepsis-associated multiple organ dysfunction syndrome (MODS), infiltration of tissues with mononuclear cells and oxidative stress. A high degree of sepsis-induced vascular oxidative damage and endothelial dysfunction (evidenced by functional assays and multiple plasma markers of endothelial dysfunction) was detected in aortae isolated from both eNOS(-/-) and aged mice. There was a significant worsening of sepsis-induced mitochondrial dysfunction, both in eNOS-deficient mice and in aged mice. Comparison of the surviving and non-surviving groups of animals indicated that the severity of endothelial dysfunction may be a predictor of mortality of mice subjected to CLP-induced sepsis.

CONCLUSIONS

Based on the studies in eNOS mice, we conclude that the lack of endothelial nitric oxide production, on its own, may be sufficient to markedly exacerbate the severity of septic shock. Aging markedly worsens the degree of endothelial dysfunction in sepsis, yielding a significant worsening of the overall outcome. Thus, endothelial dysfunction may constitute an early predictor and independent contributor to sepsis-associated MODS and mortality in aged mice.

Effect of systemic high dose vitamin C therapy on forearm blood flow reactivity during endotoxemia in healthy human subjects

OBJECTIVE

Acute inflammation induced by administration of Escherichia coli lipopolysaccharide endotoxin (LPS) reduces plasma concentrations of vitamin C and impairs vascular endothelium-derived nitric oxide (NO) bioactivity. We tested the hypothesis that systemically administered high dose vitamin C restores the endogenous anti-oxidant potential and improves NO-dependent vasodilatation in the forearm vasculature.

DESIGN & SETTING

36 male subjects were enrolled in this balanced, placebo controlled cross-over study. Forearm blood flow (FBF) reactivity to acetylcholine (ACh) and glyceryl-trinitrate (GTN), a sensitive test for endothelial function, was assessed at baseline and 4h after LPS-administration (20 IU/kg i.v). The effect of two different doses of intravenous vitamin C (Vitamin C-Injektopas®), 320 mg/kg and 480 mg/kg over 2h, or placebo on forearm vascular function was studied after LPS.

MAIN RESULTS

LPS caused transient flu-like symptoms, decreased plasma vitamin C concentrations and reduced the ACh-dependent increase in FBF by up to 76%. Vitamin C at a mean plasma concentration of 3.2 or 4.9 mmol/L restored the response to ACh compared to baseline.

CONCLUSION

High dose systemic vitamin C recovers LPS-induced endothelium-dependent vasodilation in the forearm resistance vasculature. This provides a rationale for a further clinical study of the systemic vitamin C effect under inflammatory conditions.

Aging exacerbates microvascular endothelial damage induced by circulating factors present in the serum of septic patients

The elderly patients show a significantly elevated mortality rate during sepsis than younger patients, due to their higher propensity to microvascular dysfunction and consequential multiorgan failure. We tested whether aging renders vascular endothelial cells more susceptible to damage induced by inflammatory factors present in the circulation during sepsis. Primary microvascular endothelial cells derived from young (3 months) and aged (24 months) Fischer 344 × Brown Norway rats were treated with sera obtained from sepsis patients and healthy controls. Oxidative stress (MitoSox fluorescence), death receptor activation (caspase 8 activity), and apoptotic cell death (caspase 3 activity) induced by treatment with septic sera were exacerbated in aged endothelial cells as compared with responses obtained in young cells. Induction of heme oxygenase-1 and thrombomodulin in response to treatment with septic sera was impaired in aged endothelial cells. Treatment with septic sera elicited greater increases in tumor necrosis factor-α expression in aged endothelial cells, as compared with young cells, whereas induction of inducible nitric oxide synthase, intercellular adhesion molecule-1, and vascular cell adhesion molecule did not differ between the two groups. Collectively, aging increases sensitivity of microvascular endothelial cells (MVECs) to oxidative stress and cellular damage induced by inflammatory factors present in the circulation during septicemia. We hypothesize that these responses may contribute to the increased vulnerability of elderly patients to multiorgan failure associated with sepsis.