Neutrophil killing of Staphylococcus aureus in diabetes, obesity and metabolic syndrome: a prospective cellular surveillance study

The role of pathogens in diabetes pathogenesis and the potential of immunoproteomics as a diagnostic and prognostic tool

Diabetes mellitus (DM) is a group of metabolic diseases marked by hyperglycemia, which increases the risk of systemic infections. DM patients are at greater risk of hospitalization and mortality from bacterial, viral, and fungal infections. Poor glycemic control can result in skin, blood, bone, urinary, gastrointestinal, and respiratory tract infections and recurrent infections. Therefore, the evidence that infections play a critical role in DM progression and the hazard ratio for a person with DM dying from any infection is higher. Early diagnosis and better glycemic control can help prevent infections and improve treatment outcomes. Perhaps, half (49.7%) of the people living with DM are undiagnosed, resulting in a higher frequency of infections induced by the hyperglycemic milieu that favors immune dysfunction. Novel diagnostic and therapeutic markers for glycemic control and infection prevention are desirable. High-throughput blood-based immunoassays that screen infections and hyperglycemia are required to guide timely interventions and efficiently monitor treatment responses. The present review aims to collect information on the most common infections associated with DM, their origin, pathogenesis, and the potential of immunoproteomics assays in the early diagnosis of the infections. While infections are common in DM, their role in glycemic control and disease pathogenesis is poorly described. Nevertheless, more research is required to identify novel diagnostic and prognostic markers to understand DM pathogenesis and management of infections. Precise monitoring of diabetic infections by immunoproteomics may provide novel insights into disease pathogenesis and healthy prognosis.

IL-10 Dysregulation Underlies Chemokine Insufficiency, Delayed Macrophage Response, and Impaired Healing in Diabetic Wounds

Persistent inflammation is a major contributor to healing impairment in diabetic chronic wounds. Paradoxically, diabetic wound environment during the acute phase of healing is completely different because it exhibits a reduced macrophage response owing to inadequate expression of CCL2 proinflammatory cytokine. What causes a reduction in CCL2 expression in diabetic wounds early after injury remains unknown. In this study, we report that in contrast to prolonged exposure to high glucose, which makes monocytes proinflammatory, short-term exposure to high glucose causes a rapid monocyte reprogramming, manifested by increased expression and secretion of IL-10, which in an autocrine/paracrine fashion reduces glucose uptake and transforms monocytes into an anti-inflammatory phenotype by dampening signaling through toll-like receptors. We show that IL-10 expression is significantly increased in diabetic wounds during the acute phase of healing, causing significant reductions in toll-like receptor signaling and proinflammatory cytokine production, delaying macrophage and leukocyte responses, and underlying healing impairment in diabetic wounds. Importantly, blocking IL-10 signaling during the acute phase of healing improves toll-like receptor signaling, increases proinflammatory cytokine production, enhances macrophage and leukocyte responses, and stimulates healing in diabetic wounds. We posit that anti-IL-10 strategies have therapeutic potential if added topically after surgical debridement, which resets chronic wounds into acute fresh wounds.

Diet-induced obesity in mice impairs host defense against Klebsiella pneumonia in vivo and glucose transport and bactericidal functions in neutrophils in vitro

Obesity impairs host defense against Klebsiella pneumoniae, but responsible mechanisms are incompletely understood. To determine the impact of diet-induced obesity on pulmonary host defense against K. pneumoniae, we fed 6-wk-old male C57BL/6j mice a normal diet (ND) or high-fat diet (HFD) (13% vs. 60% fat, respectively) for 16 wk. Mice were intratracheally infected with Klebsiella, assayed at 24 or 48 h for bacterial colony-forming units, lung cytokines, and leukocytes from alveolar spaces, lung parenchyma, and gonadal adipose tissue were assessed using flow cytometry. Neutrophils from uninfected mice were cultured with and without 2-deoxy-d-glucose (2-DG) and assessed for phagocytosis, killing, reactive oxygen intermediates (ROI), transport of 2-DG, and glucose transporter (GLUT1-4) transcripts, and protein expression of GLUT1 and GLUT3. HFD mice had higher lung and splenic bacterial burdens. In HFD mice, baseline lung homogenate concentrations of IL-1β, IL-6, IL-17, IFN-γ, CXCL2, and TNF-α were reduced relative to ND mice, but following infection were greater for IL-6, CCL2, CXCL2, and IL-1β (24 h only). Despite equivalent lung homogenate leukocytes, HFD mice had fewer intraalveolar neutrophils. HFD neutrophils exhibited decreased Klebsiella phagocytosis and killing and reduced ROI to heat-killed Klebsiella in vitro. 2-DG transport was lower in HFD neutrophils, with reduced GLUT1 and GLUT3 transcripts and protein (GLUT3 only). Blocking glycolysis with 2-DG impaired bacterial killing and ROI production in neutrophils from mice fed ND but not HFD. Diet-induced obesity impairs pulmonary Klebsiella clearance and augments blood dissemination by reducing neutrophil killing and ROI due to impaired glucose transport.

A Bittersweet Response to Infection in Diabetes; Targeting Neutrophils to Modify Inflammation and Improve Host Immunity

Chronic and recurrent infections occur commonly in both type 1 and type 2 diabetes (T1D, T2D) and increase patient morbidity and mortality. Neutrophils are professional phagocytes of the innate immune system that are critical in pathogen handling. Neutrophil responses to infection are dysregulated in diabetes, predominantly mediated by persistent hyperglycaemia; the chief biochemical abnormality in T1D and T2D. Therapeutically enhancing host immunity in diabetes to improve infection resolution is an expanding area of research. Individuals with diabetes are also at an increased risk of severe coronavirus disease 2019 (COVID-19), highlighting the need for re-invigorated and urgent focus on this field. The aim of this review is to explore the breadth of previous literature investigating neutrophil function in both T1D and T2D, in order to understand the complex neutrophil phenotype present in this disease and also to focus on the development of new therapies to improve aberrant neutrophil function in diabetes. Existing literature illustrates a dual neutrophil dysfunction in diabetes. Key pathogen handling mechanisms of neutrophil recruitment, chemotaxis, phagocytosis and intracellular reactive oxygen species (ROS) production are decreased in diabetes, weakening the immune response to infection. However, pro-inflammatory neutrophil pathways, mainly neutrophil extracellular trap (NET) formation, extracellular ROS generation and pro-inflammatory cytokine generation, are significantly upregulated, causing damage to the host and perpetuating inflammation. Reducing these proinflammatory outputs therapeutically is emerging as a credible strategy to improve infection resolution in diabetes, and also more recently COVID-19. Future research needs to drive forward the exploration of novel treatments to improve infection resolution in T1D and T2D to improve patient morbidity and mortality.

The Antimicrobial Activity of Origanum vulgare L. Correlated with the Gastrointestinal Perturbation in Patients with Metabolic Syndrome

(1) The metabolic syndrome (MS) promotes acute and chronic infections, due to the pro-inflammatory condition given by TNFα and IL6 or by affecting the microbiota. MS is also correlated with insulin resistance, causing inflammation and infections throughout the organism. (2) The purpose of this study was to track the effect of using the essential oil of Origanum vulgare L. (EOO) as an antibacterial treatment, compared to allopathic treatment with antibiotics in MS patients. A group of 106 people with MS was divided into four subgroups: L1-staphylococcal infection group, L2-Escherichia coli infection group, L3-streptococcal infection group with EOO treatment, and CG-control group without infection or treatment. (3) EOO is responsible for the antibacterial effect, and reduced minor uncomplicated infections. After a 10-day treatment, intestinal side effects were absent, improving the phase angle. (4) The results suggest that EOO may exhibit an antibacterial effect, similar to the antibiotic treatment, without promoting MS-specific dysbiosis, and it also improves the phase angle in patients, which is used as an index of health and cellular function.

Influence of systemic infection and comorbidities on rehabilitation outcomes in severe acquired brain injury

BACKGROUND

Severe infectious complications are a frequent problem in patients with disability due to a severe acquired brain injury. Previous studies reported that the rehabilitation outcome is significantly lower in patients colonized or infected. However, these results could be influenced by comorbidities of those patients admitted in rehabilitation hospital with a lower functional status.

AIM

To explore the influence of systemic infection, in particular concerning multidrug resistant bacteria and analyze the role of comorbidities, as a risk factor for the development of systemic infection, on rehabilitation outcomes in patients with severe brain injury.

DESIGN

This research is a cohort, prospective-observational study, comparing patients with and without systemic infections, in terms of rehabilitation outcomes.

SETTING

An Italian Intensive Care Rehabilitation Department.

POPULATION

A group of 221 patients (mean age: 59 years, range: 16-93 years, 127 males, 94 females) with severe acquired brain injury admitted to rehabilitation hospital.

METHODS

We compared the rehabilitation outcomes between patients with and without a systemic infection (at least a positive blood culture) during the rehabilitation period. A secondary analysis was performed on 70 patients with infection versus 70 patients without infection, matched for functional status at admission. The used clinical scores were: Cumulative Illness Rating Scale for Geriatrics (CIRS-G), Coma Recovery Scale Revised (CRS-R), Glasgow Coma Scale (GCS), Functional Independence Measure (FIM), Glasgow Outcome Scale (GOS), Disability Rating Scale (DRS), Levels of Cognitive Functioning (LCF) administered at admission and discharge. Length of hospitalization and the role of comorbidities were also considered.

RESULTS

The group of patients with systemic infection (in particular due to Gram-negative bacteria) had a significantly lower outcome for 5 out 6 clinical scales and with a more than doubled length of hospitalization (P<0.001). However, these patients with, at least, a positive blood culture resulted having lower functional status at admission. In the secondary analysis, worst outcome was found in patients with positive blood culture in terms of FIM (P=0.033), GOS (P=0.048), and CRS-R (P=0.001).

CONCLUSIONS

Systemic infections during rehabilitation increased the length of hospitalization and reduce the rehabilitative outcomes, even when the analysis was performed on groups matched for the functional status at admission. Moreover, the cardiological and endocrine metabolic comorbidities seem to influence the outcome, without representing a further risk factor for systemic infection.

CLINICAL REHABILITATION IMPACT

The impact of infections during rehabilitation inpatient should be more taken into account, with specific procedures and suitable environments to avoid the diffusions of infections.

Postoperative Complications Associated With Metabolic Syndrome Following Adult Spinal Deformity Surgery

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

The objective of this study was to examine the effect of metabolic syndrome on 30-day postoperative complications following corrective surgery for the adult spinal deformity (ASD).

SUMMARY OF BACKGROUND DATA

Metabolic syndrome has been shown to increase the risk of cardiovascular morbidity and mortality. Few studies have examined the effect of metabolic syndrome on patients with ASD undergoing surgery.

MATERIALS AND METHODS

We performed a retrospective cohort study of patients who underwent spinal fusion for ASD. Patients were divided into 2 groups based on the presence or absence of metabolic syndrome, which was defined as a combination of hypertension, diabetes mellitus, and obesity. Baseline patient characteristics and operative variables were compared between the 2 groups. We also compared the incidence of 30-day postoperative complications between the 2 groups. A multivariable regression analysis was then performed to identify 30-day postoperative complications that were independently associated with metabolic syndrome.

RESULTS

A total of 6696 patients were included with 8.3% (n=553) having metabolic syndrome. Patients with metabolic syndrome were more likely to have renal comorbidity (P=0.042), bleeding disorder (P=0.011), American Society of Anesthesiology classification ≥3 (P<0.001), and undergo a long fusion (P=0.009). Patients with metabolic syndrome had higher rates of 30-day mortality (P=0.042), superficial surgical site infection (P=0.006), sepsis (P=0.003), cardiac complications (P<0.001), pulmonary complications (P=0.003), pulmonary embolism (P=0.050), prolonged hospitalization (P=0.010), nonhome discharge (P=0.007), and reoperation (P=0.003). Metabolic syndrome was an independent risk factor for cardiac complications [odds ratio (OR)=4.2; 95% confidence interval (CI): 1.7-10.2; P=0.001], superficial surgical site infection (OR=2.8; 95% CI: 1.4-5.7; P=0.004), sepsis (OR=2.2, 95% CI: 1.2-3.9; P=0.009), reoperation (OR=1.7; 95% CI: 1.2-2.5; P=0.006), pulmonary complications (OR=1.7; 95% CI: 1.1-2.5; P=0.017), and prolonged hospitalization (OR=1.4; 95% CI: 1.0-1.9; P=0.039).

CONCLUSIONS

Recognition and awareness of the relationship between metabolic syndrome and postoperative complications following ASD surgery is important for preoperative optimization and perioperative care.

Advanced Glycated End Products Alter Neutrophil Effect on Regulation of CD4+ T Cell Differentiation Through Induction of Myeloperoxidase and Neutrophil Elastase Activities

CD₄⁺ T cell subset imbalance plays an important role in the development of diabetic complications. Neutrophils have recently been known as the regulator of CD₄⁺ T cell differentiation. However, whether neutrophils affect CD₄⁺ T cell population in diabetes is still elusive. In this study, we investigated the effect of neutrophils stimulated with advanced glycated end products (AGEs), the marker of diabetes, on CD₄⁺ T cell differentiation and its underlying mechanism. Our data showed that the cultural medium of healthy adult neutrophils treated with AGEs increased expressions of both Th₁ (IFN-γ) and Th₁₇ (IL-17) phenotypes and the transcription factors of Th₁ (Tbet) and Th₁₇ (RORγt) in naive CD₄⁺T cells and CD₄⁺CD₂₅⁺FoxP₃⁺ (Treg) T cells in vitro. Next, we found that AGEs induced the generations of myeloperoxidase (MPO) and neutrophil elastase (NE) in neutrophils; inhibition of MPO or NE attenuated the effect of AGE-stimulated neutrophils on CD₄⁺ T cell bias. Furthermore, receptor for AGEs (RAGE) inhibitor interrupted AGE-induced MPO and NE expressions, but MPO and NE inhibitions did not change AGE-increased RAGE gene expression. These results suggested that AGEs drive the effect of neutrophils on CD₄⁺ T cell differentiation into pro-inflammatory program through inducing MPO and NE productions in neutrophils, which is mediated by AGE-RAGE interaction.

Staphylococcus aureus drives expansion of low-density neutrophils in diabetic mice

Diabetic individuals are at considerable risk for invasive infection by Staphylococcus aureus, however, the mechanisms underlying this enhanced susceptibility to infection are unclear. We observed increased mortality following i.v. S. aureus infection in diabetic mice compared with nondiabetic controls, correlating with increased numbers of low-density neutrophils (LDNs) and neutrophil extracellular traps (NETs). LDNs have been implicated in the inflammatory pathology of diseases such as lupus, given their release of large amounts of NETs. Our goal was to describe what drives LDN increases during S. aureus infection in the diabetic host and mechanisms that promote increased NET production by LDNs. LDN development is dependent on TGF-β, which we found to be more activated in the diabetic host. Neutralization of TGF-β, or the TGF-β-activating integrin αvβ8, reduced LDN numbers and improved survival during S. aureus infection. Targeting S. aureus directly with MEDI4893*, an α toxin-neutralizing monoclonal antibody, blocked TGF-β activation, reduced LDNs and NETs, and significantly improved survival. A comparison of gene and protein expression in high-density neutrophils and LDNs identified increased GPCRs and elevated phosphatase and tensin homolog (PTEN) in the LDN subset. Inhibition of PTEN improved the survival of infected diabetic mice. Our data identify a population of neutrophils in infected diabetic mice that correlated with decreased survival and increased NET production and describe 3 therapeutic targets, a bacterial target and 2 host proteins, that prevented NET production and improved survival.