Altered macrophage function is associated with severe Burkholderia pseudomallei infection in a murine model of type 2 diabetes

Triple threat: how diabetes results in worsened bacterial infections

Diabetes mellitus, characterized by impaired insulin signaling, is associated with increased incidence and severity of infections. Various diabetes-related complications contribute to exacerbated bacterial infections, including hyperglycemia, innate immune cell dysfunction, and infection with antibiotic-resistant bacterial strains. One defining symptom of diabetes is hyperglycemia, resulting in elevated blood and tissue glucose concentrations. Glucose is the preferred carbon source of several bacterial pathogens, and hyperglycemia escalates bacterial growth and virulence. Hyperglycemia promotes specific mechanisms of bacterial virulence known to contribute to infection chronicity, including tissue adherence and biofilm formation. Foot infections are a significant source of morbidity in individuals with diabetes and consist of biofilm-associated polymicrobial communities. Bacteria perform complex interspecies behaviors conducive to their growth and virulence within biofilms, including metabolic cross-feeding and altered phenotypes more tolerant to antibiotic therapeutics. Moreover, the metabolic dysfunction caused by diabetes compromises immune cell function, resulting in immune suppression. Impaired insulin signaling induces aberrations in phagocytic cells, which are crucial mediators for controlling and resolving bacterial infections. These aberrancies encompass altered cytokine profiles, the migratory and chemotactic mechanisms of neutrophils, and the metabolic reprogramming required for the oxidative burst and subsequent generation of bactericidal free radicals. Furthermore, the immune suppression caused by diabetes and the polymicrobial nature of the diabetic infection microenvironment may promote the emergence of novel strains of multidrug-resistant bacterial pathogens. This review focuses on the "triple threat" linked to worsened bacterial infections in individuals with diabetes: (i) altered nutritional availability in diabetic tissues, (ii) diabetes-associated immune suppression, and (iii) antibiotic treatment failure.

Differential Modulation of 25-hydroxycholecalciferol on Innate Immunity of Broiler Breeder Hens

Simple Summary

No predominant changes between R- vs. Ad-feed intake on leukocyte defense against pathogens were observed in broiler breeder hens despite some differences in inflammatory and respiratory burst responses. Overall, supplemental 25-OH-D₃ had more pronounced effects on the innate immunity of Ad-hens. In vitro studies confirmed the differential effects of 25-OH-D₃ to rescue immune functions altered by glucose and/or palmitic acid exposure.

Abstract

Past immunological studies in broilers focused on juveniles within the rapid pre-slaughter growth period and may not reflect adult immune responses, particularly in breeders managed with chronic feed restriction (R). The study aimed to assess innate immune cell functions in respect to R vs. ad libitum (Ad) feed intake in breeder hens with and without dietary 25-hydroxycholecalciferol (25-OH-D₃) supplementation. Ad-feed intake consistently suppressed IL-1β secretion, respiratory burst, and cell livability in peripheral heterophils and/or monocytes along the feeding trial from the age of 51 to 68 weeks. Supplemental 25-OH-D₃ repressed IL-1β secretion and respiratory burst of both cells mostly in R-hens, but promoted monocyte phagocytosis, chemotaxis, and bacterial killing activity in Ad-hens in accompany with relieved hyperglycemia, hyperlipidemia, and systemic inflammation. Overnight cultures with leukocytes from R-hens confirmed the differential effects of 25-OH-D₃ to rescue immune functions altered by glucose and/or palmitic acid exposure. Studies with specific inhibitors further manifested the operative mechanisms via glucolipotoxicity in a cell type- and function-dependent manner. The results concluded no predominant changes between R- vs. Ad-feed intake on leukocyte defense against pathogens despite some differential differences, but supplemental 25-OH-D₃ exerts more pronounced effects in Ad-hens.

Isolation of non-tuberculous mycobacteria among tuberculosis patients, a study from a tertiary care hospital in Lahore, Pakistan

BACKGROUND

There is scarce knowledge on the prevalence of diseases caused by non-tuberculous mycobacteria (NTM) in Pakistan. In the absence of culture and identification, acid-fast bacilli (AFB) causing NTM disease are liable to be misinterpreted as tuberculosis (TB). Introduction of nucleic acid amplification testing for Mycobacterium tuberculosis complex (MTBC) offers improved diagnostic accuracy, compared with smear microscopy, and also assists in differentiating MTBC from other mycobacteria. This study aimed to investigate the prevalence of NTM among patients investigated for TB and describe NTM disease and treatment outcomes at a tertiary care hospital in Pakistan.

METHODS

This is a retrospective study, data on NTM isolates among culture-positive clinical samples over 4 years (2016-19) was retrieved from laboratory records. Information on clinical specimens processed, AFB smear results, and for the AFB positive isolates, results of species identification for MTBC, and for NTM isolates, results of species characterization and drug susceptibility testing was collected. Additional clinical data including patient characteristics, treatment regimens, and outcomes were collected for patients with NTM disease treated at Gulab Devi Hospital, Lahore.

RESULTS

During the study period, 12,561 clinical specimens were processed for mycobacterial culture and 3673 (29%) were reported positive for AFB. Among these 3482 (95%) were identified as MTBC and 191 (5%) as NTM. Among NTM, 169 (88%) were isolated from pulmonary and 22 (12%) from extrapulmonary specimens. Results of NTM speciation were available for 60 isolates and included 55% (n = 33) M. avium complex and 25% (n = 15) M. abscesses. Among these patients, complete clinical records were retrieved for 12 patients with pulmonary disease including nine infected with M. avium complex and three with M. abscessus. All 12 patients had a history of poor response to standard first-line anti-TB treatment. Ten patients were cured after 18 months of treatment, whereas, one with M. abscessus infection died and another was lost to follow up.

CONCLUSION

In TB endemic areas, NTM can be misdiagnosed as pulmonary TB leading to repeated failed anti-TB treatment and increased morbidity, emphasizing the need for improved diagnosis.

Identification of defective early immune responses to Burkholderia pseudomallei infection in a diet-induced murine model of type 2 diabetes

Co-occurrence of bacterial infections with type 2 diabetes (T2D) is a global problem. Melioidosis caused by Burkholderia pseudomallei is 10 times more likely to occur in patients with T2D, than in normoglycemic individuals. Using an experimental model of T2D, we observed that greater susceptibility in T2D was due to differences in proportions of infiltrating leucocytes and reduced levels of MCP-1, IFN-γ and IL-12 at sites of infection within 24 h post-infection. However, by 72 h the levels of inflammatory cytokines and bacteria were markedly higher in visceral tissue and blood in T2D mice. In T2D, dysregulated early immune responses are responsible for the greater predisposition to B. pseudomallei infection.

Hand Infections Associated with Systemic Conditions

Systemic conditions are associated with higher rates of hand and upper extremity infections, leading to more severe and atypical presentations. Understanding the unique problems associated with some of the most common systemic conditions, including human immunodeficiency virus, diabetes mellitus, and rheumatoid arthritis, can assist the hand surgeon in diagnosing and treating infection in these patients. This article reviews the most common presentation of hand infections for these patients and summarizes current approaches to the management of hand infections for patients with common immunocompromising conditions.

Comorbid diabetes results in immune dysregulation and enhanced disease severity following MERS-CoV infection

Middle East respiratory syndrome coronavirus (MERS-CoV) emerged in 2012 in Saudi Arabia and has caused over 2400 cases and more than 800 deaths. Epidemiological studies identified diabetes as the primary comorbidity associated with severe or lethal MERS-CoV infection. Understanding how diabetes affects MERS is important because of the global burden of diabetes and pandemic potential of MERS-CoV. We used a model in which mice were made susceptible to MERS-CoV by expressing human DPP4, and type 2 diabetes was induced by administering a high-fat diet. Upon infection with MERS-CoV, diabetic mice had a prolonged phase of severe disease and delayed recovery that was independent of virus titers. Histological analysis revealed that diabetic mice had delayed inflammation, which was then prolonged through 21 days after infection. Diabetic mice had fewer inflammatory monocyte/macrophages and CD4+ T cells, which correlated with lower levels of Ccl2 and Cxcl10 expression. Diabetic mice also had lower levels of Tnfa, Il6, Il12b, and Arg1 expression and higher levels of Il17a expression. These data suggest that the increased disease severity observed in individuals with MERS and comorbid type 2 diabetes is likely due to a dysregulated immune response, which results in more severe and prolonged lung pathology.

Leptin signaling impairs macrophage defenses against Salmonella Typhimurium

In the present study, we identify and describe an important cross-talk between leptin signaling and macrophage functions in the context of Salmonella Typhimurium infection. Genetic ablation of leptin receptor or pharmacological antagonization of leptin augmented lysosomal functions in macrophages, reduced S. Typhimurium burden, and diminished inflammation both in vitro and in vivo. Leptin signaling activates mTORC2/Akt pathway through the down-regulation of Phlpp1 phosphatase, thus impairs lysosome-mediated pathogen clearance.

The dynamic interplay between metabolism and immune responses in health and disease, by which different immune cells impact on metabolic processes, are being increasingly appreciated. However, the potential of master regulators of metabolism to control innate immunity are less understood. Here, we studied the cross-talk between leptin signaling and macrophage function in the context of bacterial infections. We found that upon infection with Gram-negative pathogens, such as Salmonella Typhimurium, leptin receptor (Lepr) expression increased in both mouse and human macrophages. Unexpectedly, both genetic Lepr ablation in macrophages and global pharmacologic leptin antagonization augmented lysosomal functions, reduced S. Typhimurium burden, and diminished inflammation in vitro and in vivo. Mechanistically, we show that leptin induction activates the mTORC2/Akt pathway and subsequently down-regulates Phlpp1 phosphatase, allowing for phosphorylated Akt to impair lysosomal-mediated pathogen clearance. These data highlight a link between leptin signaling, the mTORC2/Phlpp1/Akt axis, and lysosomal activity in macrophages and have important therapeutic implications for modulating innate immunity to combat Gram-negative bacterial infections.

Immune-endocrine interactions related to a high risk of infections in chronic metabolic diseases: The role of PPAR gamma

Diverse disturbances in immune-endocrine circuitries are involved in the development and aggravation of several chronic metabolic diseases (CMDs), including obesity, diabetes, and metabolic syndrome. The chronic inflammatory syndrome observed in CMDs culminates in dysregulated immune responses with low microbial killing efficiency, by means low host innate immune response, and loss of ability to eliminate the pathogens, which results in a high prevalence of infectious diseases, including pneumonia, tuberculosis, and sepsis. Herein, we review evidence pointing out PPARγ as a putative player in immune-endocrine disturbances related to increased risk of infections in CMDs. Cumulated evidence indicates that PPARγ activation modulates host cells to control inflammation during CMDs because of PPARγ agonists have anti-inflammatory and pro-resolutive properties, increasing host ability to eliminate pathogen, modulating hormone production, and restoring glucose and lipid homeostasis. As such, we propose PPARγ as a putative therapeutic adjuvant for patients with CMDs to favor a better infection control.

Arachidonic Acid Metabolites in Cardiovascular and Metabolic Diseases

Lipid and immune pathways are crucial in the pathophysiology of metabolic and cardiovascular disease. Arachidonic acid (AA) and its derivatives link nutrient metabolism to immunity and inflammation, thus holding a key role in the emergence and progression of frequent diseases such as obesity, diabetes, non-alcoholic fatty liver disease, and cardiovascular disease. We herein present a synopsis of AA metabolism in human health, tissue homeostasis, and immunity, and explore the role of the AA metabolome in diverse pathophysiological conditions and diseases.

Quantifying the Effect of Diabetes on Surgical Hand and Forearm Infections

PURPOSE

Diabetes has long been established as a risk factor for hand and forearm infections. The purpose of this study was to review the effect of glycemic factors on outcomes among diabetic patients with surgical upper-extremity infections. We hypothesized that diabetic inpatients may benefit from stronger peri-infection glycemic control.

METHODS

A prospective cohort study enrolled diabetic and nondiabetic surgical hand and forearm infections over 3 years. Glycemic factors included baseline glycosylated hemoglobin, blood glucose (BG) at presentation, and inpatient BG. Poor baseline control was defined as glycosylated hemoglobin of 9.0% or greater and poor inpatient control as average BG of 180 mg/dL or greater. The main outcome of interest was the need for repeat therapeutic drainage. Multivariable logistic regression quantified the association between diabetic factors and this outcome.

RESULTS

The study involved 322 patients: 76 diabetic and 246 nondiabetic. Diabetic infections were more likely than nondiabetic infections to result from idiopathic mechanisms, occur in the forearm, and present as osteomyelitis, septic arthritis, and necrotizing fasciitis. Diabetic microbiology was more likely polymicrobial and fungal. After first drainage, diabetic patients were more likely to require repeat drainage and undergo eventual amputation. Among diabetic patients, poor inpatient control was associated with need for repeat drainage.

CONCLUSIONS

Diabetes exacerbates the burden of surgical upper-extremity infections: specifically, more proximal locations, deeper involved anatomy at presentation, broader pathogenic microbiology, increased need for repeat drainage, and higher risk for amputation. Among diabetic patients, poor inpatient glycemic control is associated with increased need for repeat drainage.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic I.

Isolated cerebral aspergillosis in an immunocompetent woman on treatment for bacterial infected necrotizing pancreatitis: A case report

RATIONALE

Cerebral aspergillosis (CA) is a rare manifestation of invasive aspergillosis. It usually affects seriously immunocompromised hosts. Pancreatic bacterial or/and fungal infection is common in patients with severe acute pancreatitis.

PATIENT CONCERNS

We report the first case of an immunocompetent woman with infected necrotizing pancreatitis due to multidrug resistant Acinetobacter baumannii who, in the course of treatment, developed isolated CA.

DIAGNOSES

Magnetic resonance imaging, rather than computed tomography, revealed latent homolateral sinus disease-the possible source of the Aspergillus infection.

INTERVENTIONS

The pancreatic infection was controlled by open necrosectomy, and the CA was disappeared after neuronavigation-guided drainage and voriconazole antifungal therapy.

OUTCOME

The patient was discharged without complications. Our report revealed that persistent hyperglycemia, sepsisassociated immunoparalysis, and prolonged antibiotic use could impair severe patient's immunocompetence, making them more susceptible to opportunistic cerebral Aspergillus infection; the risk may be especially high in patients with paranasal sinus diseases.

LESSONS

Timely neurosurgical intervention combined with voriconazole antifungal therapy can provide a favorable outcome.

Infection with Burkholderia pseudomallei - immune correlates of survival in acute melioidosis

Melioidosis, caused by Burkholderia pseudomallei, is a potentially lethal infection with no licensed vaccine. There is little understanding of why some exposed individuals have no symptoms, while others rapidly progress to sepsis and death, or why diabetes confers increased susceptibility. We prospectively recruited a cohort of 183 acute melioidosis patients and 21 control subjects from Northeast Thailand and studied immune parameters in the context of survival status and the presence or absence of diabetes. HLA-B*46 (one of the commonest HLA class I alleles in SE Asia) and HLA-C*01 were associated with an increased risk of death (odds ratio 2.8 and 3.1 respectively). Transcriptomic analysis during acute infection in diabetics indicated the importance of interplay between immune pathways including those involved in antigen presentation, chemotaxis, innate and adaptive immunity and their regulation. Survival was associated with enhanced T cell immunity to nine of fifteen immunodominant antigens analysed including AhpC (BPSL2096), BopE (BPSS1525), PilO (BPSS1599), ATP binding protein (BPSS1385) and an uncharacterised protein (BPSL2520). T cell immunity to GroEL (BPSL2697) was specifically impaired in diabetic individuals. This characterization of immunity associated with survival during acute infection offers insights into correlates of protection and a foundation for design of an effective multivalent vaccine.

A Protective Role of Glibenclamide in Inflammation-Associated Injury

Glibenclamide is the most widely used sulfonylurea drug for the treatment of type 2 diabetes mellitus (DM). Recent studies have suggested that glibenclamide reduced adverse neuroinflammation and improved behavioral outcomes following central nervous system (CNS) injury. We reviewed glibenclamide's anti-inflammatory effects: abundant evidences have shown that glibenclamide exerted an anti-inflammatory effect in respiratory, digestive, urological, cardiological, and CNS diseases, as well as in ischemia-reperfusion injury. Glibenclamide might block K_ATP channel, Sur1-Trpm4 channel, and NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome activation, decrease the production of proinflammatory mediators (TNF-α, IL-1β, and reactive oxygen species), and suppress the accumulation of inflammatory cells. Glibenclamide's anti-inflammation warrants further investigation.

Anti-mycobacterial function of macrophages is impaired in a diet induced model of type 2 diabetes

Type 2 diabetes (T2D) is one of the major risk factors for tuberculosis (TB). In this study, a diet induced murine model of T2D (DIMT2D) was developed and characterized in the context of metabolic, biochemical and histopathological features following diet intervention. Mycobacterial susceptibility was investigated using Mycobacterium fortuitum as a surrogate. Phagocytic capability of alveolar macrophages and resident peritoneal macrophages were determined by in vitro assays using mycolic acid coated beads and M. fortuitum. Results demonstrated that bacillary loads were significantly higher in liver, spleen, and lungs of diabetic mice compared to controls. Higher inflammatory lesions and impaired cytokine kinetics (TNF-α, MCP-1, IL-12, IFN-γ) were also observed in diabetic mice. Macrophages isolated from diabetic mice had lower uptake of mycolic acid coated beads, reduced bacterial internalization and killing and altered cytokine responses (TNF-α, IL-6, MCP-1). This model will be useful to further investigate different facets of host-pathogen interactions in TB-T2D.

Defective production of interleukin-1 beta in patients with type 2 diabetes mellitus: Restoration by proper glycemic control

The underlying immune defect of susceptibility in diabetes mellitus type 2 to infections remains unknown. The qualitative changes in cytokine biosynthesis by circulating mononuclear cells (PBMCs) and its modulation by glycemic control were investigated. PBMCs were isolated from 39 patients and 25 controls. They were stimulated with purified ligands and heat-killed bacteria in the absence/presence of glucose and NLPR3 inflammasome ligands. Experiments were repeated after 3 and 6months. Cytokine production was measured in cell supernatants; pro-interleukin(IL)-1 β was measured in cell lysates. Gene expression of IL-1β and activity of caspase-1 were measured as well. Adequate release of interleukin (IL)-1β was found in 42.9% of patients compared to 90% of controls (p: 0.0001). This was related with down-regulation of the NLRP3 inflammasome since gene expression of IL-1β remained unaltered whereas both the ratio of IL-1β to the intracellular pro-IL-1β and the activity of caspase-1 was lower in patients than controls. Addition of glucose did not modify defective IL-1β production. IL-6 production was increased after stimulation with Pam3Cys, phytohemagglutinin and C. albicans. After proper glycemic control, release of IL-1β was increased and of IL-6 decreased; cells of patients with improved glycemic control responded better to LPS stimulation under increased concentrations of glucose. It is concluded that diabetes type 2 is characterized by defective production of IL-1β from circulating monocytes due to impaired activation of the NLRP3 inflammasome and increased production of the anti-inflammatory IL-6. Defects are restored with proper glycemic control.

Development of a diet-induced murine model of diabetes featuring cardinal metabolic and pathophysiological abnormalities of type 2 diabetes

The persistent rise in global incidence of type 2 diabetes (T2D) continues to have significant public health and economic implications. The availability of relevant animal models of T2D is critical to elucidating the complexity of the pathogenic mechanisms underlying this disease and the implications this has on susceptibility to T2D complications. Whilst many high-fat diet-induced rodent models of obesity and diabetes exist, growing appreciation of the contribution of high glycaemic index diets on the development of hyperglycaemia and insulin resistance highlight the requirement for animal models that more closely represent global dietary patterns reflective of modern society. To that end, we sought to develop and validate a murine model of T2D based on consumption of an energy-dense diet containing moderate levels of fat and a high glycaemic index to better reflect the aetiopathogenesis of T2D. Male C57BL/6 mice were fed an energy-dense (ED) diet and the development of pathological features used in the clinical diagnosis of T2D was assessed over a 30-week period. Compared with control mice, 87% of mice fed an ED diet developed pathognomonic signs of T2D including glucose intolerance, hyperglycaemia, glycosylated haemoglobin (HbA1c) and glycosuria within 30 weeks. Furthermore, dyslipidaemia, chronic inflammation, alterations in circulating leucocytes and renal impairment were also evident in ED diet-fed mice compared with mice receiving standard rodent chow. Longitudinal profiling of metabolic and biochemical parameters provide support of an aetiologically and clinically relevant model of T2D that will serve as a valuable tool for mechanistic and therapeutic studies investigating the pathogenic complications of T2D.

Overrepresentation of Diabetes in Soft Tissue Nontuberculous Mycobacterial Infections

Diabetes predisposes patients to bacterial infections. Although diabetes confers susceptibility to tuberculosis, the association between nontuberculous mycobacterial (NTM) infections and diabetes remains unknown. A retrospective chart analysis of patients in northern Australia during a 20-year period with soft tissue NTM infections revealed that patients with diabetes were three times overrepresented in comparison to the general population (odds ratio = 3.13). There was a statistically significant association between NTM infections and diabetes in this patient cohort (P = 0.0082).

Consensus on the development of vaccines against naturally acquired melioidosis

Several candidates for a vaccine against Burkholderia pseudomallei, the causal bacterium of melioidosis, have been developed, and a rational approach is now needed to select and advance candidates for testing in relevant nonhuman primate models and in human clinical trials. Development of such a vaccine was the topic of a meeting in the United Kingdom in March 2014 attended by international candidate vaccine developers, researchers, and government health officials. The focus of the meeting was advancement of vaccines for prevention of natural infection, rather than for protection from the organism’s known potential for use as a biological weapon. A direct comparison of candidate vaccines in well-characterized mouse models was proposed. Knowledge gaps requiring further research were identified. Recommendations were made to accelerate the development of an effective vaccine against melioidosis.

T-Cell Responses Are Associated with Survival in Acute Melioidosis Patients

Background

Melioidosis is an increasingly recognised cause of sepsis and death across South East Asia and Northern Australia, caused by the bacterium Burkholderia pseudomallei. Risk factors include diabetes, alcoholism and renal disease, and a vaccine targeting at-risk populations is urgently required. A better understanding of the protective immune response in naturally infected patients is essential for vaccine design.

Methods

We conducted a longitudinal clinical and immunological study of 200 patients with melioidosis on admission, 12 weeks (n = 113) and 52 weeks (n = 65) later. Responses to whole killed B. pseudomallei were measured in peripheral blood mononuclear cells (PBMC) by interferon-gamma (IFN-γ) ELIspot assay and flow cytometry and compared to those of control subjects in the region with diabetes (n = 45) and without diabetes (n = 43).

Results

We demonstrated strong CD4+ and CD8+ responses to B. pseudomallei during acute disease, 12 weeks and 52 weeks later. 28-day mortality was 26% for melioidosis patients, and B. pseudomallei-specific cellular responses in fatal cases (mean 98 IFN-γ cells per million PBMC) were significantly lower than those in the survivors (mean 142 IFN-γ cells per million PBMC) in a multivariable logistic regression model (P = 0.01). A J-shaped curve association between circulating neutrophil count and mortality was seen with an optimal count of 4000 to 8000 neutrophils/μl.

Melioidosis patients with known diabetes had poor diabetic control (median glycated haemoglobin HbA_1c 10.2%, interquartile range 9.2–13.1) and showed a stunted B. pseudomallei-specific cellular response during acute illness compared to those without diabetes.

Conclusions

The results demonstrate the role of both CD4+ and CD8+ T-cells in protection against melioidosis, and an interaction between diabetes and cellular responses. This supports development of vaccine strategies that induce strong T-cell responses for the control of intracellular pathogens such as B. pseudomallei.

Melioidosis is a key cause of death in South East Asia and Northern Australia. It is caused by the soil-dwelling bacteria Burkholderia pseudomallei, and presents as a range of clinical illnesses including pneumonia and bloodstream infections. About two-thirds of patients with melioidosis in Thailand have diabetes, but the immune responses associated with death and diabetes are unknown. This study examined the relationship between immune responses to the bacteria and death by studying the bacteria-specific lymphocyte responses in 200 patients admitted to hospital with acute melioidosis and following the patients for up to one year where possible. 26% of patients died within 28 days despite receiving antibiotics and supportive care. We showed people with melioidosis make bacteria-specific lymphocyte responses, with lower levels seen in fatal cases compared to survivors. People with diabetes make lower responses than people without diabetes, and higher levels of circulating neutrophils on admission to hospital were associated with lower lymphocyte responses both during illness and three months later in survivors. This highlighting of lymphocyte responses to melioidosis is important for the design of vaccines to target at risk groups.

Immunological mechanisms contributing to the double burden of diabetes and intracellular bacterial infections

Diabetes has been recognized as an important risk factor for a variety of intracellular bacterial infections, but research into the dysregulated immune mechanisms contributing to the impaired host-pathogen interactions is in its infancy. Diabetes is characterized by a chronic state of low-grade inflammation due to activation of pro-inflammatory mediators and increased formation of advanced glycation end products. Increased oxidative stress also exacerbates the chronic inflammatory processes observed in diabetes. The reduced phagocytic and antibacterial activity of neutrophils and macrophages provides an intracellular niche for the pathogen to replicate. Phagocytic and antibacterial dysfunction may be mediated directly through altered glucose metabolism and oxidative stress. Furthermore, impaired activation of natural killer cells contributes to decreased levels of interferon-γ, required for promoting macrophage antibacterial mechanisms. Together with impaired dendritic cell function, this impedes timely activation of adaptive immune responses. Increased intracellular oxidation of antigen-presenting cells in individuals with diabetes alters the cytokine profile generated and the subsequent balance of T-cell immunity. The establishment of acute intracellular bacterial infections in the diabetic host is associated with impaired T-cell-mediated immune responses. Concomitant to the greater intracellular bacterial burden and potential cumulative effect of chronic inflammatory processes, late hyper-inflammatory cytokine responses are often observed in individuals with diabetes, contributing to systemic pathology. The convergence of intracellular bacterial infections and diabetes poses new challenges for immunologists, providing the impetus for multidisciplinary research.

Plasmacytoid dendritic cell bactericidal activity against Burkholderia pseudomallei

Melioidosis sepsis, caused by Burkholderia pseudomallei, is associated with high mortality due to an overwhelming inflammatory response. Plasmacytoid dendritic cells (pDC) are potent producers of type I interferons (IFN). This study investigated whether pDC and type I IFN play a role during the early stages of B. pseudomallei infection. Human and murine pDC internalised and killed B. pseudomallei as efficiently as murine conventional DC (cDC). pDC derived from B. pseudomallei-susceptible (BALB/c) mice demonstrated poor intracellular killing and increased IFN-alpha compared to pDC derived from B. pseudomallei-resistant (C57BL/6) mice. This is the first evidence of pDC bactericidal activity against B. pseudomallei infection.

Migration of dendritic cells facilitates systemic dissemination of Burkholderia pseudomallei

Burkholderia pseudomallei, the etiological agent for melioidosis, is an important cause of community-acquired sepsis in northern Australia and northeast Thailand. Due to the rapid dissemination of disease in acute melioidosis, we hypothesized that dendritic cells (DC) could act as a vehicle for dissemination of B. pseudomallei. Therefore, this study investigated the effect of B. pseudomallei infection on DC migration capacity and whether migration of DC enabled transportation of B. pseudomallei from the site of infection. B. pseudomallei stimulated significantly increased migration of bone marrow-derived DC (BMDC), both in vitro and in vivo, compared to uninfected BMDC. Furthermore, migration of BMDC enabled significantly increased in vitro trafficking of B. pseudomallei and in vivo dissemination of B. pseudomallei to secondary lymphoid organs and lungs of C57BL/6 mice. DC within the footpad infection site of C57BL/6 mice also internalized B. pseudomallei and facilitated dissemination. Although DC have previously been shown to kill intracellular B. pseudomallei in vitro, the findings of this study demonstrate that B. pseudomallei-infected DC facilitate the systemic spread of this pathogen.

Phagocytosis via complement or Fc-gamma receptors is compromised in monocytes from type 2 diabetes patients with chronic hyperglycemia

Type 2 diabetes patients (DM2) have a higher risk of tuberculosis (TB) that may be attributed to functional defects in their mononuclear phagocytes given the critical role of these cells in Mycobacterium tuberculosis containment. Our previous findings suggest that monocytes from DM2 have reduced association with serum-opsonized M. tuberculosis. To determine if this alteration is due to defects in phagocytosis via complement or Fc-gamma receptors (FcγRs), in this study we evaluated the uptake of sheep red blood cells coated with IgG or complement, respectively, by monocytes from individuals with and without DM2. We found that chronic hyperglycemia was significantly associated with reduced phagocytosis via either receptor by univariable and multivariable analyses. This defect was independent of host serum opsonins and flow cytometry data indicated this was not attributed to reduced expression of these phagocytic receptors on DM2 monocytes. The positive correlation between both pathways (R = 0.64; p = 0.003) indicate that monocytes from individuals with chronic hyperglycemia have a defect in the two predominant phagocytic pathways of these cells. Given that phagocytosis is linked to activation of effector mechanisms for bacterial killing, it is likely that this defect is one factor contributing to the higher susceptibility of DM2 patients to pathogens like M. tuberculosis.

Resolvins, specialized proresolving lipid mediators, and their potential roles in metabolic diseases

Inflammation is associated with the development of diseases characterized by altered nutrient metabolism. Although an acute inflammatory response is host-protective and normally self-limited, chronic low-grade inflammation associated with metabolic diseases is sustained and detrimental. The resolution of inflammation involves the termination of neutrophil recruitment, counterregulation of proinflammatory mediators, stimulation of macrophage-mediated clearance, and tissue remodeling. Specialized proresolving lipid mediators (SPMs)-resolvins, protectins, and maresins-are novel autacoids that resolve inflammation, protect organs, and stimulate tissue regeneration. Here, we review evidence that the failure of resolution programs contributes to metabolic diseases and that SPMs may play pivotal roles in their resolution.

Glyburide reduces bacterial dissemination in a mouse model of melioidosis

Background

Burkholderia pseudomallei infection (melioidosis) is an important cause of community-acquired Gram-negative sepsis in Northeast Thailand, where it is associated with a ∼40% mortality rate despite antimicrobial chemotherapy. We showed in a previous cohort study that patients taking glyburide ( = glibenclamide) prior to admission have lower mortality and attenuated inflammatory responses compared to patients not taking glyburide. We sought to define the mechanism underlying this observation in a murine model of melioidosis.

Methods

Mice (C57BL/6) with streptozocin-induced diabetes were inoculated with ∼6×10² cfu B. pseudomallei intranasally, then treated with therapeutic ceftazidime (600 mg/kg intraperitoneally twice daily starting 24 h after inoculation) in order to mimic the clinical scenario. Glyburide (50 mg/kg) or vehicle was started 7 d before inoculation and continued until sacrifice. The minimum inhibitory concentration of glyburide for B. pseudomallei was determined by broth microdilution. We also examined the effect of glyburide on interleukin (IL) 1β by bone-marrow-derived macrophages (BMDM).

Results

Diabetic mice had increased susceptibility to melioidosis, with increased bacterial dissemination but no effect was seen of diabetes on inflammation compared to non-diabetic controls. Glyburide treatment did not affect glucose levels but was associated with reduced pulmonary cellular influx, reduced bacterial dissemination to both liver and spleen and reduced IL1β production when compared to untreated controls. Other cytokines were not different in glyburide-treated animals. There was no direct effect of glyburide on B. pseudomallei growth in vitro or in vivo. Glyburide directly reduced the secretion of IL1β by BMDMs in a dose-dependent fashion.

Conclusions

Diabetes increases the susceptibility to melioidosis. We further show, for the first time in any model of sepsis, that glyburide acts as an anti-inflammatory agent by reducing IL1β secretion accompanied by diminished cellular influx and reduced bacterial dissemination to distant organs. We found no evidence for a direct effect of glyburide on the bacterium.

Burkholderia pseudomallei infection (also called melioidosis) is a common cause of bacterial infection in Northeast Thailand, where the mortality rate is 43% despite appropriate antibiotic treatment. We showed previously that patients taking glyburide ( = glibenclamide) prior to admission have lower mortality rates and lower levels of inflammation in the blood. In this study, we used a mouse model to better understand the mechanism underlying this observation. In this study, we used a mouse model of diabetes and infected the mice with B. pseudomallei. Half the mice were treated with glyburide and half were not. We also performed in vitro experiments to find the minimum concentration of glyburide that would inhibit the growth of B. pseudomallei. We found that glyburide treatment was associated with reduced inflammation (as measured by the flow of cells into the lungs and by interleukin-1β production) and reduced spread of the bacterium to liver and spleen when compared to untreated controls. There was no direct effect of glyburide on B. pseudomallei growth in vitro or in vivo. Because the effect of glyburide is on the host and not on the bacterium, it is possible that this effect will be seen in other causes of sepsis, not just melioidosis.

Dietary composition of carbohydrates contributes to the development of experimental type 2 diabetes

Evidence has emerged supporting a link between high glycaemic index (GI) diets and type 2 diabetes (T2D). The aim of this study was to determine if dietary GI influences the development of hyperglycaemia in C57BL/6 mice to more closely reflect T2D. Male C57BL/6 mice (n=30) were randomly divided into 3 dietary groups consisting of either standard rodent chow (4.8 % fat, 20 % protein), or a high fat (HF) diet (21-23 % fat, 19 % protein) with low GI (15.4 % starch; HF-LG) or high GI (50.5 % dextrose; HF-HG) ad libitum for 10 weeks. Body weight, blood glucose, glucose tolerance, and circulating cholesterol and triglyceride levels were measured for the duration of the study. We found that increasing the GI of a moderately HF diet induces severe hyperglycaemia and insulin resistance in C57BL/6 mice, reflective of criteria for diagnosis of T2D, whilst littermates consuming an equivalent low GI diet maintain glucose homeostasis. This study demonstrates the significant contribution of both dietary carbohydrate and fat composition in the aetiopathogenesis of T2D.

Development of Burkholderia mallei and pseudomallei vaccines

Burkholderia mallei and Burkholderia pseudomallei are Gram-negative bacteria that cause glanders and melioidosis, respectively. Inhalational infection with either organism can result in severe and rapidly fatal pneumonia. Inoculation by the oral and cutaneous routes can also produce infection. Chronic infection may develop after recovery from acute infection with both agents, and control of infection with antibiotics requires prolonged treatment. Symptoms for both meliodosis and glanders are non-specific, making diagnosis difficult. B. pseudomallei can be located in the environment, but in the host, B. mallei and B. psedomallei are intracellular organisms, and infection results in similar immune responses to both agents. Effective early innate immune responses are critical to controlling the early phase of the infection. Innate immune signaling molecules such as TLR, NOD, MyD88, and pro-inflammatory cytokines such as IFN-γ and TNF-α play key roles in regulating control of infection. Neutrophils and monocytes are critical cells in the early infection for both microorganisms. Both monocytes and macrophages are necessary for limiting dissemination of B. pseudomallei. In contrast, the role of adaptive immune responses in controlling Burkholderia infection is less well understood. However, T cell responses are critical for vaccine protection from Burkholderia infection. At present, effective vaccines for prevention of glanders or meliodosis have not been developed, although recently development of Burkholderia vaccines has received renewed attention. This review will summarize current and past approaches to develop B. mallei and B. pseudomalllei vaccines, with emphasis on immune mechanisms of protection and the challenges facing the field. At present, immunization with live attenuated bacteria provides the most effective and durable immunity, and it is important therefore to understand the immune correlates of protection induced by live attenuated vaccines. Subunit vaccines have typically provided less robust immunity, but are safer to administer to a wider variety of people, including immune compromised individuals because they do not reactivate or cause disease. The challenges facing B. mallei and B. pseudomalllei vaccine development include identification of broadly protective antigens, design of efficient vaccine delivery and adjuvant systems, and a better understanding of the correlates of protection from both acute and chronic infection.

Impaired early cytokine responses at the site of infection in a murine model of type 2 diabetes and melioidosis comorbidity

Bacterial infections are a common and serious complication of type 2 diabetes (T2D). The prevalence of melioidosis, an emerging tropical infection caused by the Gram-negative bacterium Burkholderia pseudomallei, is increased in people with T2D. This is the first study to compare murine models of T2D and melioidosis. Susceptibility and disease progression following infection with B. pseudomallei were compared in our diet-induced polygenic mouse model and a leptin receptor-deficient monogenic model of T2D. The metabolic profile of mice with diet-induced diabetes, including body weight, blood glucose, cholesterol, triglycerides, insulin resistance, and baseline levels of inflammation, closely resembled that of clinical T2D. Following subcutaneous infection with B. pseudomallei, bacterial loads at 24 and 72 h postinfection in the blood, spleen, liver, lungs, and subcutaneous adipose tissue (SAT) at the site of infection were compared in parallel with the expression of inflammatory cytokines and tissue histology. As early as 24 h postinfection, the expression of inflammatory (interleukin-1β [IL-1β], tumor necrosis factor alpha [TNF-α], and IL-6) and T(H)1 (IL-12 and gamma interferon [IFN-γ]) cytokines was impaired in diabetic mice compared to nondiabetic littermates. Early differences in cytokine expression were associated with excessive infiltration of polymorphonuclear neutrophils (PMN) in diabetic mice compared to nondiabetic littermates. This was accompanied by bacteremia, hematogenous dissemination of bacteria to the lungs, and uncontrolled bacterial growth in the spleens of diabetic mice by 72 h postinfection. The findings from our novel model of T2D and melioidosis comorbidity support the role of impaired early immune pathways in the increased susceptibility of individuals with T2D to bacterial infections.

Diabetes and infection: is there a link?--A mini-review

Diabetes mellitus is one of the most prevalent conditions in the elderly and is associated with considerable morbidity and mortality, mainly from cardiovascular and renal complications. Furthermore, common perception associates diabetes with a generally increased susceptibility to infectious diseases, although epidemiologic data that would prove this are surprisingly scarce. However, it seems to be confirmed that diabetes predisposes to certain types of infection and death thereof, but it is less well understood if metabolic disturbances in diabetes itself, associated hyperglycemia and hyperinsulinemia or diabetes-associated comorbidities provide the link between diabetes and susceptibility to infections. In this review, I will summarize published reports on the incidence and risk for infectious diseases in diabetic people and give a comprehensive overview of the molecular mechanisms that have been suggested to explain the potentially altered immune response to pathogens in patients with diabetes.

Central nervous system aspergillosis: a series of 14 cases from a general hospital and review of 123 cases from the literature

Central nervous system (CNS) aspergillosis is a highly fatal infection. We review the clinical presentation, diagnosis, and outcome of this infection and present a case series of 14 consecutive patients with CNS aspergillosis admitted to Massachusetts General Hospital (MGH) from 2000 to 2011. We also review 123 cases reported in the literature during that time. We included only proven CNS aspergillosis cases conforming to the European Organization for Research and Treatment of Cancer/Mycoses Study Group (EORTC/MSG) definitions of invasive fungal infections. In the MGH case series, neutropenia, hematologic malignancies, autoimmune diseases requiring steroid treatment, and solid organ transplantation were the predominant comorbid conditions. Notably, all MGH patients were immunosuppressed, and more than half (n = 8) had a history of previous brain injury, unrelated to their index hospitalization. For most MGH patients (11 of 14), the lung was the primary focus of aspergillosis, while 2 had paranasal sinus involvement, and 1 had primary Aspergillus discitis. Among reported cases, paranasal sinuses (27.6%) and the lung (26.8%) were the primary foci of infection, whereas 22% of those cases had no obvious primary organ involvement. Although a selection bias should be considered, especially among published cases, our findings suggest that patients who underwent neurosurgery had improved survival, with MGH and literature patients having 25% and 28.6% mortality, respectively, compared to 100% and 60.4%, respectively, among patients who received only medical treatment. Although this was not the case among MGH patients, CNS aspergillosis can affect patients without significant immune suppression, as indicated by the high number of reported immunocompetent cases. In conclusion, mortality among CNS aspergillosis patients remains high, and the infection may be more common among patients with previous brain pathology. When indicated, neurosurgical procedures may improve prognosis.

Burkholderia pseudomallei kills Caenorhabditis elegans through virulence mechanisms distinct from intestinal lumen colonization

The nematode Caenorhabditis elegans is hypersusceptible to Burkholderia pseudomallei infection. However, the virulence mechanisms underlying rapid lethality of C. elegans upon B. pseudomallei infection remain poorly defined. To probe the host-pathogen interaction, we constructed GFP-tagged B. pseudomallei and followed bacterial accumulation within the C. elegans intestinal lumen. Contrary to slow-killing by most bacterial pathogens, B. pseudomallei caused fairly limited intestinal lumen colonization throughout the period of observation. Using grinder-defective mutant worms that allow the entry of intact bacteria also did not result in full intestinal lumen colonization. In addition, we observed a significant decline in C. elegans defecation and pharyngeal pumping rates upon B. pseudomallei infection. The decline in defecation rates ruled out the contribution of defecation to the limited B. pseudomallei colonization. We also demonstrated that the limited intestinal lumen colonization was not attributed to slowed host feeding as bacterial loads did not change significantly when feeding was stimulated by exogenous serotonin. Both these observations confirm that B. pseudomallei is a poor colonizer of the C. elegans intestine. To explore the possibility of toxin-mediated killing, we examined the transcription of the C. elegans ABC transporter gene, pgp-5, upon B. pseudomallei infection of the ppgp-5::gfp reporter strain. Expression of pgp-5 was highly induced, notably in the pharynx and intestine, compared with Escherichia coli-fed worms, suggesting that the host actively thwarted the pathogenic assaults during infection. Collectively, our findings propose that B. pseudomallei specifically and continuously secretes toxins to overcome C. elegans immune responses.

Glutathione deficiency in type 2 diabetes impairs cytokine responses and control of intracellular bacteria

Individuals with type 2 diabetes are at increased risk of acquiring melioidosis, a disease caused by Burkholderia pseudomallei infection. Although up to half of melioidosis patients have underlying diabetes, the mechanisms involved in this increased susceptibility are unknown. We found that B. pseudomallei-infected PBMCs from diabetic patients were impaired in IL-12p70 production, which resulted in decreased IFN-γ induction and poor bacterial killing. The defect was specific to the IL-12-IFN-γ axis. Defective IL-12 production was also observed during Mycobacterium tuberculosis infection, in which diabetes is likewise known to be a strong risk factor. In contrast, IL-12 production in diabetic cells was not affected upon Salmonella enterica infection or in response to TLR2, -3, -4, and -5 ligands. Poor IL-12 production correlated with a deficiency in intracellular reduced glutathione (GSH) concentrations in diabetic patients. Addition of GSH or N-acetylcysteine to PBMCs selectively restored IL-12 and IFN-γ production and improved bacterial killing. Furthermore, the depletion of GSH in mice led to increased susceptibility to melioidosis, reduced production of IL-12p70, and poorer disease outcome. Our data thus establish a link between GSH deficiency in diabetes and increased susceptibility to melioidosis that may open up new therapeutic avenues to protect diabetic patients against some intracellular bacterial pathogens.