Advanced glycation end products facilitate bacterial adherence in urinary tract infection in diabetic mice

Insulin receptor signaling engages bladder urothelial defenses that limit urinary tract infection

Urinary tract infections (UTIs) commonly afflict people with diabetes. To better understand the mechanisms that predispose diabetics to UTIs, we employ diabetic mouse models and altered insulin signaling to show that insulin receptor (IR) shapes UTI defenses. Our findings are validated in human biosamples. We report that diabetic mice have suppressed IR expression and are more susceptible to UTIs caused by uropathogenic Escherichia coli (UPEC). Systemic IR inhibition increases UPEC susceptibility, while IR activation reduces UTIs. Localized IR deletion in bladder urothelium promotes UTI by increasing barrier permeability and suppressing antimicrobial peptides. Mechanistically, IR deletion reduces nuclear factor κB (NF-κB)-dependent programming that co-regulates urothelial tight junction integrity and antimicrobial peptides. Exfoliated urothelial cells or urine samples from diabetic youths show suppressed expression of IR, barrier genes, and antimicrobial peptides. These observations demonstrate that urothelial insulin signaling has a role in UTI prevention and link IR to urothelial barrier maintenance and antimicrobial peptide expression.

Association between Moraxella keratitis and advanced glycation end products

Diabetes mellitus is recognized as a major predisposing factor for Moraxella keratitis. However, how diabetes mellitus contributes to Moraxella keratitis remains unclear. In this study, we examined Moraxella keratitis; based on the findings, we investigated the impact of advanced glycation end products (AGEs) deposition in the cornea of individuals with diabetic mellitus on the adhesion of Moraxella isolates to the cornea. A retrospective analysis of 27 culture-proven cases of Moraxella keratitis at Ehime University Hospital (March 2006 to February 2022) was performed. Moraxella isolates were identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Among the patients, 30.4% had diabetes mellitus and 22.2% had the predominant ocular condition of using steroid eye drops. The species identified were Moraxella nonliquefaciens in 59.3% and Moraxella lacunata in 40.7% of patients. To investigate the underlying mechanisms, we assessed the effects of M. nonliquefaciens adherence to simian virus 40-immortalized human corneal epithelial cells (HCECs) with or without AGEs. The results demonstrated the number of M. nonliquefaciens adhering to HCECs was significantly increased by adding AGEs compared with that in controls (p < 0.01). Furthermore, in the corneas of streptozotocin-induced diabetic C57BL/6 mice treated with or without pyridoxamine, an AGE inhibitor, the number of M. nonliquefaciens adhering to the corneas of diabetic mice was significantly reduced by pyridoxamine treatment (p < 0.05). In conclusion, the development of Moraxella keratitis may be significantly influenced by the deposition of AGEs on the corneal epithelium of patients with diabetes mellitus.

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.

Staphylococcus aureus Biofilm Inhibiting Activity of Advanced Glycation Endproduct Crosslink Breaking and Glycation Inhibiting Compounds

Staphylococcus aureus is a Gram-positive bacterium that plays a role in the pathogenesis of skin lesions in diabetes mellitus, atopic dermatitis, and psoriasis, all of which are associated with elevated non-enzymatic glycation biomarkers. The production of biofilm protects resident bacteria from host immune defenses and antibiotic interventions, prolonging pathogen survival, and risking recurrence after treatment. Glycated proteins formed from keratin and glucose induce biofilm formation in S. aureus, promoting dysbiosis and increasing pathogenicity. In this study, several glycation-inhibiting and advanced glycation endproduct (AGE) crosslink-breaking compounds were assayed for their ability to inhibit glycated keratin-induced biofilm formation as preliminary screening for clinical testing candidates. Ascorbic acid, astaxanthin, clove extract, n-phenacylthiazolium bromide, and rosemary extract were examined in an in vitro static biofilm model with S. aureus strain ATCC 12600. Near complete biofilm inhibition was achieved with astaxanthin (ED₅₀ = 0.060 mg/mL), clove extract (ED₅₀ = 0.0087 mg/mL), n-phenacylthiazolium bromide (ED₅₀ = 5.3 mg/mL), and rosemary extract (ED₅₀ = 1.5 mg/mL). The dosage necessary for biofilm inhibition was not significantly correlated with growth inhibition (R² = 0.055. p = 0.49). Anti-glycation and AGE breaking compounds with biofilm inhibitory activity are ideal candidates for treatment of S. aureus dysbiosis and skin infection that is associated with elevated skin glycation.

Diabetes downregulates the antimicrobial peptide psoriasin and increases E. coli burden in the urinary bladder

Diabetes is known to increase susceptibility to infections, partly due to impaired granulocyte function and changes in the innate immunity. Here, we investigate the effect of diabetes, and high glucose on the expression of the antimicrobial peptide, psoriasin and the putative consequences for E. coli urinary tract infection. Blood, urine, and urine exfoliated cells from patients are studied. The influence of glucose and insulin is examined during hyperglycemic clamps in individuals with prediabetes and in euglycemic hyperinsulinemic clamped patients with type 1 diabetes. Important findings are confirmed in vivo in type 2 diabetic mice and verified in human uroepithelial cell lines. High glucose concentrations induce lower psoriasin levels and impair epithelial barrier function together with altering cell membrane proteins and cytoskeletal elements, resulting in increasing bacterial burden. Estradiol treatment restores the cellular function with increasing psoriasin and bacterial killing in uroepithelial cells, confirming its importance during urinary tract infection in hyperglycemia. In conclusion, our findings present the effects and underlying mechanisms of high glucose compromising innate immunity.

Glycosuria Alters Uropathogenic Escherichia coli Global Gene Expression and Virulence

Uropathogenic Escherichia coli (UPEC) is the principal etiology of more than half of urinary tract infections (UTI) in humans with diabetes mellitus. Epidemiological data and studies in mouse model of ascending UTI have elucidated various host factors responsible for increasing the susceptibility of diabetic hosts to UPEC-UTI. In contrast, diabetic urinary microenvironment-mediated alterations in UPEC physiology and its contributions to shaping UPEC-UTI pathogenesis in diabetes have not been examined. To address our central hypothesis that glycosuria directly induces urinary virulence of UPEC, we compared virulence characteristics and gene expression in human UPEC strains UTI89 (cystitis) and CFT073 (pyelonephritis), exposed for 2 h in vitro to urine from either male or female donors that was either plain or supplemented with glucose to mimic glycosuria. Compared to control UPEC exposed to nutrient-rich culture medium, lysogeny broth, glycosuria-exposed UPEC exhibited significant increase in biofilm formation and reduction in the hemagglutination of Guinea pig erythrocytes (a measure of type 1 piliation). In addition, the analysis of UTI89 transcriptome by RNA sequencing revealed that 2-h-long, in vitro exposure to glycosuria also significantly alters expression of virulence and metabolic genes central to urinary virulence of UPEC. Addition of galactose as an alternative carbon source affected biofilm formation and gene expression profile of UPEC to an extent similar to that observed with glucose exposure. In summary, our results provide novel insights into how glycosuria-mediated rapid changes in UPEC fitness may facilitate UTI pathogenesis in the diabetic urinary microenvironment.

IMPORTANCE Uropathogenic Escherichia coli (UPEC) is an important causative agent of urinary tract infections in diabetic humans. We examined the effects of in vitro exposure to glycosuria (presence of glucose in urine) on the virulence and gene expression by UPEC. Our results show that glycosuria rapidly (in 2 h) alters UPEC gene expression, induces biofilm formation, and suppresses type 1 piliation. These results offer novel insights into the pathogenesis of UPEC in the urinary tract.

Systematic Review of Literature Examining Bacterial Urinary Tract Infections in Diabetes

This systematic review addresses the central research question, "what is known from the published, peer-reviewed literature about the impact of diabetes on the risk of bacterial urinary tract infections (UTI)?" We examine the results from laboratory studies where researchers have successfully adapted mouse models of diabetes to study the pathophysiology of ascending UTI. These studies have identified molecular and cellular effectors shaping immune defenses against infection of the diabetic urinary tract. In addition, we present evidence from clinical studies that in addition to diabetes, female gender, increased age, and diabetes-associated hyperglycemia, glycosuria, and immune impairment are important risk factors which further increase the risk of UTI in diabetic individuals. Clinical studies also show that the uropathogenic genera causing UTI are largely similar between diabetic and nondiabetic individuals, although diabetes significantly increases risk of UTI by drug-resistant uropathogenic bacteria.

Glycation of gut proteins initiates microbial dysbiosis and can promote establishment of diabetes in experimental animals

Diabetes and obesity is associated with change in the gut microbiota, however, the reason for such transition is still unknown. The secondary complications in diabetes mainly stem from protein glycation, oxidative stress and inflammatory response. It is intended to study the correlation between gut proteins glycation and microbial dysbiosis and thereby progression to diabetes. The study was carried out through feeding high fructose to male Wistar rats and evaluating their gut microbiota. The rate of gut flora excretion via faecal matter was found to decrease on fructose feed for 7 days. Intestinal flora was drastically reduced and pathogenic succession observed. Intestinal fluorescence studies confirmed that there is heavy glycation of gut proteins. Microbes obtained from fructose fed animals could grow on glycated BSA. There was significant increase in level of TNF-α and IFN-γ providing evidence of inflammation. Though microbial dysbiosis was observed in diabetes, the cause for this remained elusive. In the present study we prove that high fructose feed and glycation of the gut proteins probably prevent adherence/survival of the gut microflora in control animals and promotes transition to a changed microflora which is capable of adhering/utilizing glycated proteins as well as high fructose. The changed microbiota, enhanced protein glycation and inflammation help in establishing insulin resistance.

Repurposing pyridoxamine for therapeutic intervention of intravascular cell-cell interactions in mouse models of sickle cell disease

Adherent neutrophils on vascular endothelium positively contribute to cell-cell aggregation and vaso-occlusion in sickle cell disease. In the present study, we demonstrated that pyridoxamine, a derivative of vitamin B6, might be a therapeutic agent to alleviate intravascular cell-cell aggregation in sickle cell disease. Using real-time intravital microscopy, we found that one oral administration of pyridoxamine dose-dependently increased the rolling influx of neutrophils and reduced neutrophil adhesion to endothelial cells in cremaster microvessels of sickle cell disease mice challenged with hypoxia-reoxygenation. Short-term treatment also mitigated neutrophil-endothelial cell and neutrophil-platelet interactions in the microvessels and improved the survival of sickle cell disease mice challenged with tumor necrosis factor-α. The inhibitory effects of pyridoxamine on intravascular cell-cell interactions were potentiated by co-treatment with hydroxyurea. We observed that long-term (5.5 months) oral treatment with pyridoxamine significantly diminished the adhesive function of neutrophils and platelets and down-regulated the expression of E-selectin and intercellular adhesion molecule-1 on the vascular endothelium in tumor necrosis factor-α-challenged sickle cell disease mice. Ex vivo studies revealed that the surface amount of αMβ2 integrin was significantly decreased in stimulated neutrophils isolated from sickle cell disease mice treated with pyridoxamine-containing water. Studies using platelets and neutrophils from sickle cell disease mice and patients suggested that treatment with pyridoxamine reduced the activation state of platelets and neutrophils. These results suggest that pyridoxamine may be a novel therapeutic and a supplement to hydroxyurea to prevent and treat vaco-occlusion events in sickle cell disease.

Exposure to Moderate Glycosuria Induces Virulence of Group B Streptococcus

To explore whether glycosuria induces virulence of uropathogens, in turn facilitating urinary tract infection (UTI), we exposed group B Streptococcus (GBS) strain 10/84 to human urine plain or with 300 mg/dL glucose (mimicking moderate glycosuria). Exposure to moderate glycosuria significantly augmented bacterial growth, kidney bacterial burden in a mouse model of ascending UTI, and virulence characteristics and expression of corresponding genes. Exposure to glycosuria increased GBS adherence to human bladder epithelial cell line and expression of corresponding PI2a fimbrial gene, antimicrobial peptide LL-37 resistance and bacterial surface charge modulating dltA, and GBS hemolytic ability and expression of genes encoding pore-forming toxins.

Host Cathelicidin Exacerbates Group B Streptococcus Urinary Tract Infection

Group B Streptococcus (GBS) causes frequent urinary tract infection (UTI) in susceptible populations, including individuals with type 2 diabetes and pregnant women; however, specific host factors responsible for increased GBS susceptibility in these populations are not well characterized. Here, we investigate cathelicidin, a cationic antimicrobial peptide, known to be critical for defense during UTI with uropathogenic Escherichia coli (UPEC). We observed a loss of antimicrobial activity of human and mouse cathelicidins against GBS and UPEC in synthetic urine and no evidence for increased cathelicidin resistance in GBS urinary isolates. Furthermore, we found that GBS degrades cathelicidin in a protease-dependent manner. Surprisingly, in a UTI model, cathelicidin-deficient (Camp-/-) mice showed decreased GBS burdens and mast cell recruitment in the bladder compared to levels in wild-type (WT) mice. Pharmacologic inhibition of mast cells reduced GBS burdens and histamine release in WT but not Camp-/- mice. Streptozotocin-induced diabetic mice had increased bladder cathelicidin production and mast cell recruitment at 24 h postinfection with GBS compared to levels in nondiabetic controls. We propose that cathelicidin is an important immune regulator but ineffective antimicrobial peptide against GBS in urine. Combined, our findings may in part explain the increased frequency of GBS UTI in diabetic and pregnant individuals.IMPORTANCE Certain populations such as diabetic individuals are at increased risk for developing urinary tract infections (UTI), although the underlying reasons for this susceptibility are not fully known. Additionally, diabetics are more likely to become infected with certain types of bacteria, such as group B Streptococcus (GBS). In this study, we find that an antimicrobial peptide called cathelicidin, which is thought to protect the bladder from infection, is ineffective in controlling GBS and alters the type of immune cells that migrate to the bladder during infection. Using a mouse model of diabetes, we observe that diabetic mice are more susceptible to GBS infection even though they also have more infiltrating immune cells and increased production of cathelicidin. Taken together, our findings identify this antimicrobial peptide as a potential contributor to increased susceptibility of diabetic individuals to GBS UTI.

Molecular Paths Linking Metabolic Diseases, Gut Microbiota Dysbiosis and Enterobacteria Infections

Alterations of both ecology and functions of gut microbiota are conspicuous traits of several inflammatory pathologies, notably metabolic diseases such as obesity and type 2 diabetes. Moreover, the proliferation of enterobacteria, subdominant members of the intestinal microbial ecosystem, has been shown to be favored by Western diet, the strongest inducer of both metabolic diseases and gut microbiota dysbiosis. The inner interdependence between the host and the gut microbiota is based on a plethora of molecular mechanisms by which host and intestinal microbes modify each other. Among these mechanisms are as follows: (i) the well-known metabolic impact of short chain fatty acids, produced by microbial fermentation of complex carbohydrates from plants; (ii) a mutual modulation of miRNAs expression, both on the eukaryotic (host) and prokaryotic (gut microbes) side; (iii) the production by enterobacteria of virulence factors such as the genotoxin colibactin, shown to alter the integrity of host genome and induce a senescence-like phenotype in vitro; (iv) the microbial excretion of outer-membrane vesicles, which, in addition to other functions, may act as a carrier for multiple molecules such as toxins to be delivered to target cells. In this review, I describe the major molecular mechanisms by which gut microbes exert their metabolic impact at a multi-organ level (the gut barrier being in the front line) and support the emerging triad of metabolic diseases, gut microbiota dysbiosis and enterobacteria infections.

Inflammation-Induced Adhesin-Receptor Interaction Provides a Fitness Advantage to Uropathogenic E. coli during Chronic Infection

Uropathogenic E. coli (UPEC) is the dominant cause of urinary tract infections, clinically described as cystitis. UPEC express CUP pili, which are extracellular fibers tipped with adhesins that bind mucosal surfaces of the urinary tract. Here we identify the role of the F9/Yde/Fml pilus for UPEC persistence in the inflamed urothelium. The Fml adhesin FmlH binds galactose β1-3 N-acetylgalactosamine found in core-1 and -2 O-glycans. Deletion of fmlH had no effect on UPEC virulence in an acute mouse model of cystitis. However, FmlH provided a fitness advantage during chronic cystitis, which is manifested as persistent bacteriuria, high bladder bacterial burdens, and chronic inflammation. In situ binding confirmed that FmlH bound avidly to the inflamed, but not the naive bladder. In accordance with its pathogenic profile, vaccination with FmlH significantly protected mice from chronic cystitis. Thus, UPEC employ separate CUP pili to adapt to the rapidly changing niche during bladder infection.