Phagocytic activity of neutrophils improves over the course of therapy of diabetic foot infections

Neutrophil (dys)function due to altered immuno-metabolic axis in type 2 diabetes: implications in combating infections

Metabolic and inflammatory pathways are highly interdependent, and both systems are dysregulated in Type 2 diabetes (T2D). T2D is associated with pre-activated inflammatory signaling networks, aberrant cytokine production and increased acute phase reactants which leads to a pro-inflammatory 'feed forward loop'. Nutrient 'excess' conditions in T2D with hyperglycemia, elevated lipids and branched-chain amino acids significantly alter the functions of immune cells including neutrophils. Neutrophils are metabolically active cells and utilizes energy from glycolysis, stored glycogen and β-oxidation while depending on the pentose phosphate pathway for NADPH for performing effector functions such as chemotaxis, phagocytosis and forming extracellular traps. Metabolic changes in T2D result in constitutive activation and impeded acquisition of effector or regulatory activities of neutrophils and render T2D subjects for recurrent infections. Increased flux through the polyol and hexosamine pathways, elevated production of advanced glycation end products (AGEs), and activation of protein kinase C isoforms lead to (a) an enhancement in superoxide generation; (b) the stimulation of inflammatory pathways and subsequently to (c) abnormal host responses. Neutrophil dysfunction diminishes the effectiveness of wound healing, successful tissue regeneration and immune surveillance against offending pathogens. Hence, Metabolic reprogramming in neutrophils determines frequency, severity and duration of infections in T2D. The present review discusses the influence of the altered immuno-metabolic axis on neutrophil dysfunction along with challenges and therapeutic opportunities for clinical management of T2D-associated infections.

Potential Advances of Adjunctive Hyperbaric Oxygen Therapy in Infective Endocarditis

Patients with infective endocarditis (IE) form a heterogeneous group by age, co-morbidities and severity ranging from stable patients to patients with life-threatening complications with need for intensive care. A large proportion need surgical intervention. In-hospital mortality is 15-20%. The concept of using hyperbaric oxygen therapy (HBOT) in other severe bacterial infections has been used for many decades supported by various preclinical and clinical studies. However, the availability and capacity of HBOT may be limited for clinical practice and we still lack well-designed studies documenting clinical efficacy. In the present review we highlight the potential beneficial aspects of adjunctive HBOT in patients with IE. Based on the pathogenesis and pathophysiological conditions of IE, we here summarize some of the important mechanisms and effects by HBOT in relation to infection and inflammation in general. In details, we elaborate on the aspects and impact of HBOT in relation to the host response, tissue hypoxia, biofilm, antibiotics and pathogens. Two preclinical (animal) studies have shown beneficial effect of HBOT in IE, but so far, no clinical study has evaluated the feasibility of HBOT in IE. New therapeutic options in IE are much needed and adjunctive HBOT might be a therapeutic option in certain IE patients to decrease morbidity and mortality and improve the long-term outcome of this severe disease.

Determinants of Diabetic Peripheral Neuropathy and Their Clinical Significance: A Retrospective Cohort Study

BACKGROUND

In this study, we investigated the epidemiological characteristics and predictors of diabetic peripheral neuropathy (DPN) in adult patients with type 2 diabetes mellitus (DM).

METHODS

The study was designed as a retrospective cohort trial at the First Affiliated Hospital of Wenzhou Medical University. From January 2017 to December 2020, a total of 1,262 patients with DM were enrolled to assess the risk factors for DPN. The patients were divided into two groups (DPN group and non-DPN group). The Mann-Whitney U test or t-test, receiver operating characteristic (ROC) analyses, univariate chi-square analyses, and multiple logistic regression analyses were used to analyze the adjusted predictors of DPN.

RESULTS

The overall prevalence of DPN in DM patients was 72.7% (n = 793/1,091). Multivariate analysis revealed that age > 66 years (odds ratio [OR], 2.647; 95% confidence interval [CI] 1.469-4.770; p = 0.002), history of hypertension (OR, 1.829; 95% CI 1.146-2.920; p = 0.011), neutrophil (NE) levels exceeding 4.0 × 10⁹/L (OR 0.256; 95% CI 0.162-0.405; p = 0.001), lymphocyte (LY) levels over 3.0 × 10⁹/L (OR 7.173; 95% CI 4.258-12.086; p = 0.000), HbA1c > 7.7% (OR 3.151; 95% CI 1.959-5.068; p = 0.000), and FT3 > 4.4 pmol/L (OR 0.417; 95% CI 0.263-0.662; p = 0.000) were six significant predictive factors for the prevalence of DPN.

CONCLUSIONS

High levels of LY, HbA1c, history of hypertension, and > 66 years of age increase the risk of DPN in adult patients with DM, while high levels of NE and FT3 were protective factors of DPN. Thus, the prediction of DPN can significantly be improved by identifying older patients over the age of 66 and history of hypertension, as well as establishing the biochemical cutoff values of NE, LY, HbA1c, and FT3.

Diabetic Wound-Healing Science

Diabetes mellitus is an increasingly prevalent chronic metabolic disease characterized by prolonged hyperglycemia that leads to long-term health consequences. It is estimated that impaired healing of diabetic wounds affects approximately 25% of all patients with diabetes mellitus, often resulting in lower limb amputation, with subsequent high economic and psychosocial costs. The hyperglycemic environment promotes the formation of biofilms and makes diabetic wounds difficult to treat. In this review, we present updates regarding recent advances in our understanding of the pathophysiology of diabetic wounds focusing on impaired angiogenesis, neuropathy, sub-optimal chronic inflammatory response, barrier disruption, and subsequent polymicrobial infection, followed by current and future treatment strategies designed to tackle the various pathologies associated with diabetic wounds. Given the alarming increase in the prevalence of diabetes, and subsequently diabetic wounds, it is imperative that future treatment strategies target multiple causes of impaired healing in diabetic wounds.

The Effects of Hyperbaric Oxygenation on Oxidative Stress, Inflammation and Angiogenesis

Hyperbaric oxygen therapy (HBOT) is commonly used as treatment in several diseases, such as non-healing chronic wounds, late radiation injuries and carbon monoxide poisoning. Ongoing research into HBOT has shown that preconditioning for surgery is a potential new treatment application, which may reduce complication rates and hospital stay. In this review, the effect of HBOT on oxidative stress, inflammation and angiogenesis is investigated to better understand the potential mechanisms underlying preconditioning for surgery using HBOT. A systematic search was conducted to retrieve studies measuring markers of oxidative stress, inflammation, or angiogenesis in humans. Analysis of the included studies showed that HBOT-induced oxidative stress reduces the concentrations of pro-inflammatory acute phase proteins, interleukins and cytokines and increases growth factors and other pro-angiogenesis cytokines. Several articles only noted this surge after the first HBOT session or for a short duration after each session. The anti-inflammatory status following HBOT may be mediated by hyperoxia interfering with NF-κB and IκBα. Further research into the effect of HBOT on inflammation and angiogenesis is needed to determine the implications of these findings for clinical practice.

The role of neutrophils in mediating stroke injury in the diabetic db/db mouse brain following hypoxia-ischemia

Diabetic mice exhibit increased mortality and morbidity following stroke. Recent studies from our laboratory have indicated that increased morbidity in diabetic db/db mice relative to their non-diabetic db/+ littermates is associated with increased levels of MMP-9 protease activity, increased blood-brain barrier (BBB) permeability, and greater neutrophil infiltration following hypoxic/ischemic (H/I) insult. Neutrophils are a major source of proteases and reactive oxygen species and studies have reported neutrophil depletion/inhibition is protective in certain models of experimental stroke. The objective of the current study is to determine the role of neutrophils in the increased morbidity seen in db/db mice following acute ischemic stroke. In this study, we found a significant increase in circulating neutrophils in the db/db mice at 4 h post H/I, which bound to endothelial cells in the ipsilateral hemisphere and infiltrated into brain tissue by 24 h of recovery. Depletion of circulating neutrophils resulted in reduced neutrophil concentrations in blood and in the ipsilateral hemispheres of the brain of both db/+ and db/db mice and decreased the levels of MMP-9 within the infarcted area. This resulted in smaller infarct size in the db/db mice compared to non-treated controls but did not affect stroke outcome in db/+ mice. While there was a significant correlation between neutrophil number and the levels of MMP-9 in the ipsilateral hemisphere of control and diabetic mice, surprisingly, neutrophil depletion had no effect on BBB permeability in either group. Thus, the current study suggests that neutrophil depletion reduces MMP-9 protease levels and improves stroke outcome in db/db mice but not in their db/+ counterparts.

The peripheral immune response in hyperglycemic stroke

OBJECTIVES

Hyperglycemia is common in acute ischemic stroke patients and is associated with poor clinical outcome. However, aggressive reduction of post-stroke hyperglycemia did not improve clinical outcome, suggesting that other mechanisms are playing a detrimental role in hyperglycemic stroke. We hypothesize that the acute post-stroke immune response is altered in the hyperglycemic state leading to higher mortality and morbidity. The objective of this study was to characterize temporal changes in circulating immune cells after stroke and their association with clinical outcomes in hyperglycemic compared to euglycemic patients.

PATIENTS AND METHODS

This retrospective study included 97 (58 % euglycemic, 42 % hyperglycemic) patients presenting within 12 h of symptom onset of stroke. Blood neutrophil, monocyte and lymphocyte concentrations were measured sequentially for 96 h post stroke. Primary clinical outcome was the difference in the NIH stroke scale at admission compared to discharge. Secondary outcome measures included discharge disposition and the modified Rankin Scale (mRS) at 90 days.

RESULTS

Circulating neutrophils were significantly higher in hyperglycemic than in euglycemic patients within the first 48 h post stroke, while lymphocyte counts trended to be lower. Hyperglycemic patients had higher mortality rates, less favorable discharge disposition and worse neurological function at 90 days. In both groups, the neutrophil to lymphocytes ratio ((NLR) remained strongly associated with neurological function at discharge within the first 24 h (p < 0.001), and remained significant in hyperglycemic patients up to 48 h (p < 0.001). Multivariate regression analysis showed no confounding by other factors and a significant correlation with differences in NIHSS score (CI; - 9.287 to -1.46, p = 0.0077**) and NLR (CL; 0.6058-6.901, p = 0.0203*) in hyperglycemic patients.

CONCLUSIONS

Our data suggests that circulating immune cells play an important role in mediating poor clinical outcome in hyperglycemic patients following stroke. The NLR is a strong predictor of neurological outcomes in hyperglycemic patients. Thus, the modulation of immune cells may be a viable therapeutic approach to improve outcomes for this high risk group.

The significance of neutrophil-lymphocyte ratio, platelet-lymphocyte ratio and lymphocyte-monocyte ratio in predicting peripheral arterial disease, peripheral neuropathy, osteomyelitis and amputation in diabetic foot infection

AIMS

The aim of the study was to evaluate the value of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR) and lymphocyte to monocyte ratio (LMR) in predicting peripheral arterial disease, peripheral neuropathy, osteomyelitis and need for amputation in diabetic foot infection (DFI).

METHODS

A total of 280 patients were analyzed retrospectively. The NLR, PLR and LMR were evaluated statistically in DFI.

RESULTS

A total of 280 patients were enrolled in the study. PLR was significantly higher in osteomyelitis and NLR was found higher in peripheral arterial disease in DFI (p = 0.008, p = 0.007). A PLR of >187.3 was calculated as the cut off value with 67.9% sensitivity and 59.1% specificity in predicting osteomyelitis. A NLR of >6.5 was calculated as the cut off with 53.3% sensitivity and 63% specificity in predicting peripheral arterial disease. NLR, PLR and LMR had a predictive value in predicting amputation in DFI (p < 0.001, p < 0.001, p = 0.006). NLR and PLR were higher in patients who required amputation than in patients who required debridement/drainage (p < 0.001, p = 0.002). NLR was significant in determining amputation levels (minor or major) (p = 0.013).

CONCLUSIONS

NLR can predict peripheral arterial disease and elevated PLR can predict osteomyelitis in DFI. NLR, PLR and LMR are predictive of the need for amputation in DFI.

The structural and functional changes of blood cells and molecular components in diabetes mellitus

It is known fact that diabetes mellitus (DM) affects blood cells. Changes in the erythrocyte membrane, disorder in hemoglobin oxygen-binding and modification in mechanical characteristics, are effects of hyperglycemia on red blood cells. Altered susceptibility infection of patients with diabetes has been ascribed to a depression in the function of polymorphonuclear leukocytes. Neutrophil function in patients with diabetes with good glucose control is slightly different than in healthy ones. DM causes significant changes in lymphocytes metabolism and their functions. Patients with diabetes, presenting with acute coronary syndrome, are at higher risk of cardiovascular complications and recurrent ischemic events in comparison to non-diabetic counterparts. Various mechanisms, including endothelial dysfunction, platelet hyperactivity, and abnormalities in coagulation and fibrynolysis have been implicated for this increased atherothrombotic risk. There are many other alterations of blood cells due to DM. In the present review we focused on modifications of blood cells due to DM. Then, as a second point, we explored how the changes affect functions of red blood cells, white blood cells and platelets.

Hyperbaric oxygen therapy and osteonecrosis

Osteonecrosis of the jaw may be caused by radiation, medication, or infection. Optimal therapy requires a multimodal approach that combines surgery with adjuvant treatments. This review focuses on the use of adjunctive hyperbaric oxygen therapy for this condition. In addition to evidence regarding the basic and clinical science behind hyperbaric oxygen therapy, controversies in the field and economic implications are discussed.

Inpatient management of diabetic foot disorders: a clinical guide

The implementation of an inpatient diabetic foot service should be the goal of all institutions that care for patients with diabetes. The objectives of this team are to prevent problems in patients while hospitalized, provide curative measures for patients admitted with diabetic foot disorders, and optimize the transition from inpatient to outpatient care. Essential skills that are required for an inpatient team include the ability to stage a foot wound, assess for peripheral vascular disease, neuropathy, wound infection, and the need for debridement; appropriately culture a wound and select antibiotic therapy; provide, directly or indirectly, for optimal metabolic control; and implement effective discharge planning to prevent a recurrence. Diabetic foot ulcers may be present in patients who are admitted for nonfoot problems, and these ulcers should be evaluated by the diabetic foot team during the hospitalization. Pathways should be in place for urgent or emergent treatment of diabetic foot infections and neuropathic fractures/dislocations. Surgeons involved with these patients should have knowledge and interest in limb preservation techniques. Prevention of iatrogenic foot complications, such as pressure sores of the heel, should be a priority in patients with diabetes who are admitted for any reason: all hospitalized diabetic patients require a clinical foot exam on admission to identify risk factors such as loss of sensation or ischemia. Appropriate posthospitalization monitoring to reduce the risk of reulceration and infection should be available, which should include optimal glycemic control and correction of any fluid and electrolyte disturbances.

Effects of hyperbaric oxygen treatment on antimicrobial function and apoptosis of differentiated HL-60 (neutrophil-like) cells

AIMS

Neutrophil apoptosis is important in the resolution of inflammation in chronic wounds. Hyperbaric oxygen (HBO) therapy, an intermittent inhalation of 100% oxygen at greater than atmospheric pressure, appears to be an effective treatment for chronic wounds. The aim was to use HL-60 cells differentiated using all-trans retinoic acid (ATRA) (neutrophil-like cells) to test the hypothesis that an HBO-induced increase in antimicrobial activity might lead to an increase in apoptosis, thereby contributing to neutrophil clearance from chronic wounds.

MAIN METHODS

ATRA differentiated HL-60 cells, an in vitro neutrophil model, were used to test the effects of normoxia, hypoxia (5% O2), hyperoxia (95% O2), hyperbaric normoxia (pressure) (8.8% O2 at 2.4 ATA) and HBO (97.9% O2 at 2.4 ATA) on antimicrobial function [NBT staining, superoxide and H2O2 production, and phagocytosis activity] and apoptosis (caspase 3/7 activity and morphological changes observed using SYBR Safe staining).

KEY FINDINGS

A single 90min HBO exposure caused an increase in the respiratory burst activity of neutrophil-like cells post exposure. Phagocytosis of Staphylococcus aureus was also increased. HBO pre-treatment had a pro-apoptotic effect, increasing caspase 3/7 activity and causing morphological changes associated with apoptosis.

SIGNIFICANCE

The potential detrimental effect of enhanced antimicrobial activity induced by HBO may be offset by enhanced apoptosis. Both hyperoxia and pressure alone seemed to contribute to the HBO-induced increases in antimicrobial activity and apoptosis, although there was no consistent pattern. These data contribute to explaining the effectiveness of HBO in the treatment of chronic wounds.

Association of complement C3 and interleukin-1 with foot infections in diabetic patients

The study of the bacteriological profile, the association of complement C3, interleukin-1beta, and zinc therapy of diabetic foot ulcers (type two) was investigated. Twenty diabetics without foot ulcers (group I), 50 diabetics with foot ulcers (group II), and 10 matched normal controls (group III) were enrolled in this study. Diabetic foot ulcers were mostly of grade 2. The most frequent organisms were Clostridium spp., Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, respectively. Vancomycin, Imipenem, and Meropenem were the most effective against Gram-positive and Gram-negative aerobes, while Imipenem, Meropenem and Chloramphenicol for Gram-positive anaerobes. Group II had abnormal levels of C3 (72%). A significant higher concentration of C3 was found in group II. Group II had abnormal levels of IL-1β (60%). A significant higher concentration of IL-1β was found in group II. Zinc therapy (25 mg/day/oral) induced a highly significant decrease in the frequency of Gram-positive anaerobes and levels of IL-1β. Significantly increases all mineral concentrations in serum level except Mn(+2). The study highlights the prevalence of antibiotic multi-drug resistant bacteria causing foot infections in diabetics which require combined antimicrobial therapy. Altered levels of serum complement C3 and IL-1β might be responsible for depressed immune response which might be causes for delayed wound healing and repeated infections. Zinc supplementation may help in healing the wounds by enhancing the immune response.

Seminar Review: A Review of the Basis of Surgical Treatment of Diabetic Foot Infections

Infection is an extremely challenging complication of foot ulcers in patients with diabetes. Surgery as part of a multidisciplinary approach is key in the management of many types of diabetic foot infections (DFIs). Unfortunately, the surgical treatment of DFIs is based more on clinical judgment and less on structured evidence, which leaves unresolved doubts. The clinical presentation of DFIs is varied. This review examines the basis of nonvascular surgical treatment of DFIs, emphasizing the importance of the anatomic concepts of the foot, the variety of its clinical presentations, and the concepts of timing surgery. Recent evidence and case reports based on the author’s experience are presented in 2 parts. The first part examines clinical presentation of infections, whereas the second part deals with imaging, foot anatomy, and some case reports.

Dendritic cell modification of neutrophil responses to infection after burn injury

Burn patients are highly susceptible to infections due to increased exposure through wounds and impairments in a number of immune functions. Dendritic cells (DCs) are important in activation of numerous immune responses that are essential for the clearance of infections. We have found that prophylactic treatment of burn-injured mice with the DC growth factor FLT3 ligand (FL) significantly increases resistance to burn wound infections in a DC-dependent manner that is correlated closely with enhanced bacterial clearance. However, as DCs are not typically microbicidal, the mechanisms by which DC modulation enhances bacterial clearance are not known. Due to the rapid response of neutrophils to cutaneous wounds, and the reported interactions between DCs and neutrophils, we investigated the role of neutrophils in FL-mediated resistance to burn wound infection. This was examined both in vivo and in vitro through neutrophil depletion, supplementation of neutrophils, and assessment of neutrophil chemotaxis following FL treatment. To test the involvement of DCs, CD11c-diphtheria toxin receptor transgenic mice were used to deplete DCs during FL treatment. Studies revealed that neutrophils do play a critical role in FL-mediated resistance to a burn wound infection. Additionally, treatment with FL after a burn injury enhances neutrophil-mediated control of bacterial spread, neutrophil migratory capacity, and myeloperoxidase production in a DC-dependent manner. The results of this study provide new insight into immunological mechanisms that can offer protection against infection after burn injury.