Glibenclamide impairs responses of neutrophils against Burkholderia pseudomallei by reduction of intracellular glutathione

Melioidosis in people living with diabetes; clinical presentation, clinical course and implications for patient management

BACKGROUND

Despite the well-established link between diabetes mellitus and melioidosis, the precise impact of diabetes, its complications, and its therapy on the presentation and clinical course of melioidosis is incompletely defined. The influence of glycaemic control on the diverse clinical manifestations and the clinical course of melioidosis in patients with diabetes has also not been examined in detail.

METHODS

We examined all cases of culture-confirmed melioidosis in Far North Queensland, Australia between October 1, 2016, and April 30, 2024. We hoped to define the impact of diabetes, its control and its therapy on the patients' presentation and their clinical course.

RESULTS

There were 321 cases of culture-confirmed melioidosis during the study period; the patients' median (interquartile range (IQR)) age was 57 (46-69) years, 212/321 (66 %) were male, 130/321 (41 %) identified as First Nations Australians. Diabetes was the most common risk factor for melioidosis in the cohort (163/321, 51 %); in 19/163 (12 %) this was a new diagnosis. The median (IQR)) glycosylated haemoglobin prior to presentation was 9.1 % (7.2-11.5) and 96/162 (59 %) with complete data had established macrovascular or microvascular complications. People with diabetes were more likely - than people without diabetes - to have involvement of the liver (odds ratio (OR) 95 % confidence interval (CI): 9.68 (2.21-42.46), p = 0.003), the spleen (OR (95 % CI): 7.32 (1.64-32.80), p = 0.009) or to have disseminated disease (OR (95 % CI): 2.93 (1.26-6.78), p = 0.01). However, people with diabetes were no more likely than people without diabetes to require intensive care unit admission (OR (95 % CI): 0.82 (0.47-1.42), p = 0.48) or to die before hospital discharge (12/163 (7 %) versus 19/158 (12 %), OR (95 % CI): 0.58 (0.27-1.24), p = 0.16). Only 58/163 (36 %) with diabetes had specialist endocrinology review during their hospitalisation and only 22/72 (31 %) with accessible data had good glycaemic control (glycosylated haemoglobin ≤7 %) in the 12 months after discharge, increasing their risk of subsequent diabetic complications. Of the 151 people with diabetes surviving their hospitalisation, 26 (17 %) died, at a median (IQR) of 1.0 (0.40-4.1) years after discharge. Of the individuals with diabetes who had completed five years of follow up, 21/60 (35 %) had died at a median (IQR) age of 67 (51-84) years.

CONCLUSIONS

Individuals with diabetes and melioidosis are more likely to have liver and spleen abscesses and disseminated disease than individuals without diabetes, manifestations that appear to be linked directly to glycaemic control. In Australia's well-resourced health system <10 % of patients with diabetes and melioidosis will die from their infection. However, five-year all-cause mortality in individuals with diabetes who survive their melioidosis is greater than 30 %, emphasising the importance of close, holistic multidisciplinary follow-up to ensure their optimal long-term health outcomes.

Vitamin D3 regulates PM-driven primary human neutrophil inflammatory responses

Recent evidence has demonstrated that both acute and chronic exposure to particulate air pollution are risk factors for respiratory tract infections and increased mortality from sepsis. There is therefore an urgent need to establish the impact of ambient particulate matter (PM) on innate immune cells and to establish potential strategies to mitigate against adverse effects. PM has previously been reported to have potential adverse effects on neutrophil function. In the present study, we investigated the impact of standard urban PM (SRM1648a, NIST) and PM2.5 collected from Chiang Mai, Thailand, on human peripheral blood neutrophil functions, including LPS-induced migration, IL-8 production, and bacterial killing. Both NIST and the PM2.5, being collected in Chiang Mai, Thailand, increased IL-8 production, but reduced CXCR2 expression and migration of human primary neutrophils stimulated with Escherichia coli LPS. Moreover, PM-pretreated neutrophils from vitamin D-insufficient participants showed reduced E. coli-killing activity. Furthermore, in vitro vitamin D3 supplementation attenuated IL-8 production and improved bacterial killing by cells from vitamin D-insufficient participants. Our findings suggest that provision of vitamin D to individuals with insufficiency may attenuate adverse acute neutrophilic responses to ambient PM.

New roles for glutathione: Modulators of bacterial virulence and pathogenesis

Low molecular weight (LMW) thiols contain reducing sulfhydryl groups that are important for maintaining antioxidant defense in the cell. Aside from the traditional roles of LMW thiols as redox regulators in bacteria, glutathione (GSH) has been reported to affect virulence and bacterial pathogenesis. The role of GSH in virulence is diverse, including the activation of virulence gene expression and contributing to optimal biofilm formation. GSH can also be converted to hydrogen sulfide (H₂S) which is important for the pathogenesis of certain bacteria. Besides GSH, some bacteria produce other LMW thiols such as mycothiol and bacillithiol that affect bacterial virulence. We discuss these newer reported functions of LMW thiols modulating bacterial pathogenesis either directly or indirectly and via modulation of the host immune system.

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.

Burkholderia pseudomallei sepsis with osteoarticular melioidosis of the hip in a patient with diabetes mellitus

Melioidosis is caused by the tropical soil pathogen Burkholderia pseudomallei Infection, usually in the form of pneumonia, disproportionately affects people with a risk factor for immune dysregulation and mortality remains high even with treatment. Climate change and increasing rates of diabetes render the populations of endemic areas increasingly vulnerable to the disease, which is emerging as a serious global health threat. We present here a case of a 68-year-old man from northern Australia with sepsis and osteoarticular melioidosis of the hip, and explore the links between diabetes mellitus and melioidosis, particularly with respect to musculoskeletal infection.

Glibenclamide alters interleukin-8 and interleukin-1β of primary human monocytes from diabetes patients against Mycobacterium tuberculosis infection

Type 2 diabetes mellitus (T2DM) is an important risk factor for development of tuberculosis (TB). Our previous study showed glibenclamide, an anti-diabetic drug used to control blood glucose concentration, reduced interleukin (IL)-8 secretion from primary human monocytes challenged with M. tuberculosis (Mtb). In mice infected with Mtb, IL-1β is essential for host resistance through the enhancement of cyclooxygenase that limits excessive Type I interferon (IFN) production and fosters Mtb containment. We hypothesize that glibenclamide may also interfere with monocyte mediated immune responses against Mtb and alter the balance between IL-1β and IFNα-mediated immunity. Purified monocytes from non-diabetic and diabetic individuals were infected with Mtb or M. bovis BCG. We demonstrate that monocytes from diabetes patients who were being treated with glibenclamide showed reduced IL-1β and IL-8 secretion when exposed to Mtb. Additionally, these responses also occurred when monocytes from non-diabetic individuals were pre-treated with glibenclamide in vitro. Moreover, this pre-treatment enhanced IFNa1 expression but was not involved with prostaglandin E2 (PGE2) expression in response to Mtb infection. Taken together, our data show that glibenclamide might exacerbate susceptibility of diabetes patients to Mtb infection by reducing IL-1β and IL-8 production by monocytes.

Human Melioidosis

The causative agent of melioidosis, Burkholderia pseudomallei, a tier 1 select agent, is endemic in Southeast Asia and northern Australia, with increased incidence associated with high levels of rainfall. Increasing reports of this condition have occurred worldwide, with estimates of up to 165,000 cases and 89,000 deaths per year. The ecological niche of the organism has yet to be clearly defined, although the organism is associated with soil and water. The culture of appropriate clinical material remains the mainstay of laboratory diagnosis. Identification is best done by phenotypic methods, although mass spectrometric methods have been described. Serology has a limited diagnostic role. Direct molecular and antigen detection methods have limited availability and sensitivity. Clinical presentations of melioidosis range from acute bacteremic pneumonia to disseminated visceral abscesses and localized infections. Transmission is by direct inoculation, inhalation, or ingestion. Risk factors for melioidosis include male sex, diabetes mellitus, alcohol abuse, and immunosuppression. The organism is well adapted to intracellular survival, with numerous virulence mechanisms. Immunity likely requires innate and adaptive responses. The principles of management of this condition are drainage and debridement of infected material and appropriate antimicrobial therapy. Global mortality rates vary between 9% and 70%. Research into vaccine development is ongoing.

Metformin-induced suppression of IFN-α via mTORC1 signalling following seasonal vaccination is associated with impaired antibody responses in type 2 diabetes

Diabetes mellitus (DM) patients are at an increased risk of complications following influenza-virus infection, seasonal vaccination (SV) is recommended. However, SV with trivalent influenza vaccine (TIV) can induce antibody and type-I interferon (IFN) responses, and the effect of anti-DM treatment on these responses is incompletely understood. We evaluated the antibody response and IFN-α expression in individuals with and without type 2 DM (T2DM) following SV, and examined the effects on anti-DM treatment. TIV elicited sero-protection in all groups, but antibody persistency was <8 months, except for the antibody response to B-antigens in non-DM. T2DM impaired the IgG avidity index, and T2DM showed a significantly decreased response against H1N1 and H3N2, in addition to delaying and reducing haemagglutination-inhibition persistency against influenza B-antigens in DM groups treated with metformin (Met-DM) or glibenclamide (GB-DM). Following TIV, the Met-DM and GB-DM groups exhibited reduced IFN-α expression upon stimulation with whole- and split-virion influenza vaccines. Suppression of IFN-α expression in the Met-DM group was associated with a reduction in the mechanistic target of rapamycin complex-1 pathway and impaired IgG avidity index. Thus, single-dose TIV each year might not be suitable for T2DM. Our data could aid the development of an efficacious influenza vaccine for T2DM.

Glibenclamide Reduces Primary Human Monocyte Functions Against Tuberculosis Infection by Enhancing M2 Polarization

Tuberculosis (TB) is a global public health problem, which is caused by Mycobacterium tuberculosis (Mtb). Type 2 diabetes mellitus (T2DM) is one of the leading predisposing factors for development of TB after HIV/AIDS. Glibenclamide is a widely used anti-diabetic drug in low and middle-income countries where the incidence of TB is very high. In a human macrophage cell line, glibenclamide, a K⁺ATP-channel blocker, promoted alternative activation of macrophages by enhancing expression of the M2 marker CD206 during M2 polarization. M2 macrophages are considered poorly microbicidal and associated with TB susceptibility. Here, we investigated the effect of glibenclamide on M1 and M2 phenotypes of primary human monocytes and further determined whether specific drug treatment for T2DM individuals influences the antibacterial function of monocytes in response to mycobacterial infection. We found that glibenclamide significantly reduced M1 (HLA-DR⁺ and CD86⁺) surface markers and TNF-α production on primary human monocytes against mycobacterial infection. In contrast, M2 (CD163⁺ and CD206⁺) surface markers and IL-10 production were enhanced by pretreatment with glibenclamide. Additionally, reduction of bactericidal activity also occurred when primary human monocytes from T2DM individuals who were being treated with glibenclamide were infected with Mtb in vitro, consistent with the cytokine responses. We conclude that glibenclamide reduces M1 and promotes M2 polarization leading to impaired bactericidal ability of primary human monocytes of T2DM individuals in response to Mtb and may lead to increased susceptibility of T2DM individuals to TB and other bacterial infectious diseases.

Uric acid disrupts hypochlorous acid production and the bactericidal activity of HL-60 cells

Uric acid is the end product of purine metabolism in humans and is an alternative physiological substrate for myeloperoxidase. Oxidation of uric acid by this enzyme generates uric acid free radical and urate hydroperoxide, a strong oxidant and potentially bactericide agent. In this study, we investigated whether the oxidation of uric acid and production of urate hydroperoxide would affect the killing activity of HL-60 cells differentiated into neutrophil-like cells (dHL-60) against a highly virulent strain (PA14) of the opportunistic pathogen Pseudomonas aeruginosa. While bacterial cell counts decrease due to dHL-60 killing, incubation with uric acid inhibits this activity, also decreasing the release of the inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF- α). In a myeloperoxidase/Cl^-/H₂O₂ cell-free system, uric acid inhibited the production of HOCl and bacterial killing. Fluorescence microscopy showed that uric acid also decreased the levels of HOCl produced by dHL-60 cells, while significantly increased superoxide production. Uric acid did not alter the overall oxidative status of dHL-60 cells as measured by the ratio of reduced (GSH) and oxidized (GSSG) glutathione. Our data show that uric acid impairs the killing activity of dHL-60 cells likely by competing with chloride by myeloperoxidase catalysis, decreasing HOCl production. Despite diminishing HOCl, uric acid probably stimulates the formation of other oxidants, maintaining the overall oxidative status of the cells. Altogether, our results demonstrated that HOCl is, indeed, the main relevant oxidant against bacteria and deviation of myeloperoxidase activity to produce other oxidants hampers dHL-60 killing activity.

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Uric acid decreased microbicide activity and release of cytokines by dHL-60 cells.

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Uric acid decreased HOCl in cells and in the myeloperoxidase/Cl^-/H₂O₂ system.

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Uric acid induces a pro-oxidant redox imbalance.

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HOCl is crucial for Pseudomonas aeruginosa killing by dHL-60.

Melioidosis

Burkholderia pseudomallei is a Gram-negative environmental bacterium and the aetiological agent of melioidosis, a life-threatening infection that is estimated to account for ∼89,000 deaths per year worldwide. Diabetes mellitus is a major risk factor for melioidosis, and the global diabetes pandemic could increase the number of fatalities caused by melioidosis. Melioidosis is endemic across tropical areas, especially in southeast Asia and northern Australia. Disease manifestations can range from acute septicaemia to chronic infection, as the facultative intracellular lifestyle and virulence factors of B. pseudomallei promote survival and persistence of the pathogen within a broad range of cells, and the bacteria can manipulate the host's immune responses and signalling pathways to escape surveillance. The majority of patients present with sepsis, but specific clinical presentations and their severity vary depending on the route of bacterial entry (skin penetration, inhalation or ingestion), host immune function and bacterial strain and load. Diagnosis is based on clinical and epidemiological features as well as bacterial culture. Treatment requires long-term intravenous and oral antibiotic courses. Delays in treatment due to difficulties in clinical recognition and laboratory diagnosis often lead to poor outcomes and mortality can exceed 40% in some regions. Research into B. pseudomallei is increasing, owing to the biothreat potential of this pathogen and increasing awareness of the disease and its burden; however, better diagnostic tests are needed to improve early confirmation of diagnosis, which would enable better therapeutic efficacy and survival.

The antioxidant glutathione protects against enteric neuron death in situ, but its depletion is protective during colitis

Enteric glia play an important neuroprotective role in the enteric nervous system (ENS) by producing neuroprotective compounds such as the antioxidant reduced glutathione (GSH). The specific cellular pathways that regulate glial production of GSH and how these pathways are altered during, or contribute to, neuroinflammation in situ and in vivo are not fully understood. We investigated this issue using immunohistochemistry to localize GSH synthesis enzymes within the myenteric plexus and tested how the inhibition of GSH synthesis with the selective inhibitor l-buthionine sulfoximine impacts neuronal survival and inflammation. Both enteric glia and neurons express the cellular machinery necessary for GSH synthesis. Furthermore, glial GSH synthesis is necessary for neuronal survival in isolated preparations of myenteric plexus. In vivo depletion of GSH does not induce colitis but alters myenteric plexus neuronal phenotype and survival. Importantly, global depletion of glutathione is protective against some macroscopic and microscopic measures of colonic inflammation. Together, our data highlight the heterogeneous roles of GSH in the myenteric plexus of the ENS and during gastrointestinal inflammation. NEW & NOTEWORTHY Our results show that both enteric glia and neurons express the cellular machinery necessary for glutathione (GSH) synthesis and that glial GSH synthesis is necessary for neuronal survival in isolated enteric nervous system (ENS) preparations. In vivo depletion of GSH with the selective inhibitor l-buthionine sulfoximine is not sufficient to induce inflammation but does alter neuronal neurochemical composition and survival. Together, our data highlight novel heterogeneous roles for GSH in the ENS and during gastrointestinal inflammation.

Effect of paricalcitol on pancreatic oxidative stress, inflammatory markers, and glycemic status in diabetic rats

OBJECTIVES

This study is designed to explore the effect of paricalcitol (vitamin D receptor agonist) on pancreatic oxidative stress, inflammatory markers, and adiponectin and glycemic status in diabetic rats.

MATERIALS AND METHODS

Forty Sprague-Dawley male rats aged 10-12 weeks (150-250 g) were used in this study. Type 2 diabetes was developed by providing 4 weeks of high-fat-diet feeding before one shot of streptozotocin injection (40 mg/kg i.p.). Four study groups were designed as normal control rats, diabetic control vehicle-treated, diabetic paricalcitol-treated (0.8 μg/kg), and diabetic glibenclamide-treated (0.6 mg/kg) groups with 10 animals in each. After treatment of diabetic rats for 3 months, pancreatic inflammatory and oxidative stress markers, plasma adiponectin, glycemic status parameters, and histopathological pancreatic islet changes were evaluated.

RESULTS

Paricalcitol and glibenclamide treatment significantly (P < 0.05) decreased plasma glucose, insulin resistance, and pancreatic malondialdehyde and tumor necrosis factor-α levels. Moreover, they significantly (P < 0.05) increased plasma fasting insulin, C-peptide, adiponectin, pancreatic IL-2, catalase, superoxide dismutase, glutathione peroxidase, and reduced glutathione when contrasted with diabetic control rats. Furthermore, they prevented extensive histopathological damage in the pancreas of diabetic rats.

CONCLUSIONS

Paricalcitol reduced pancreatic oxidative stress and inflammatory markers, and improved glycemic status in diabetic rats.