Dirk Lange

Associate Professor

Research Interests

Ureteral stents
antifouling coatings
antimicrobial coatings
device complications

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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Evaluating the anti-bacterial and wound healing promoting effects of PVP/PVP-I containing liquid scaffold in vitro and in vivo (2023)

Background: Based on the WHO report in 2018, 11 million burn injuries occur worldwide annually, 180,000 of which are lethal. Many studies over the past few years have demonstrated that infection and delayed wound healing are responsible for 42%–65% mortality in burn victims. Hence, the development and application of an antibacterial nutritional liquid scaffold in large burn injuries could reduce the infection rate, accelerate wound healing, and ultimately, save lives. MeshFill is a nutritional liquid scaffold found to improve wound healing and esthetic outcomes upon application in a split-thickness meshed skin graft (STMSG) in a porcine model. To expand the efficacy of MeshFill and address the prevention of infections due to wound contamination, our group added antimicrobial properties by replacing polyvinyl alcohol (PVA), a component in the MeshFill complex, with Povidone-iodine (PVP-I). Unlike silver and antibiotics, low concentrations of iodine are not toxic to human cells, and there is no potential for bacterial resistance.Experimental approach: We assessed the antibacterial effect of various ratios of PVP-I/PVP scaffoderm on both gram-positive and gram-negative bacteria during the 4- and 24-hour time points. The cytotoxicity of the three best ratios of PVP-I/PVP scaffoderm was assessed in vitro, while the wound healing effects in terms of antibacterial activity were then evaluated in vivo using relevant rat models. Result: In terms of antibacterial activity, 150% and 200% PVP-I/PVP scaffoderm was shown to kill gram-positive and gram-negative species most effectively in comparison with other groups. Moreover, 100% and 150% PVP-I/PVP scaffoderm showed the best healing results in vivo and did not delay the wound healing process. Conclusion: Scaffoderm containing 150% PVP-I/PVP is most efficacious in terms of antibacterial activity in full-thickness wounds and the promotion of wound healing. The incorporation of PVP-I into MeshFill may be an effective method to prevent impaired wound healing caused by bacterial infection.

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How gut microbiome correlates with oxalate, butyrate and kidney stones formation (2023)

Background: Kidney stone disease (KSD) is a worldwide metabolic disorder, that affects about12% of the world population at some stage of life, representing a financial burden for health systems. The prevalence of urolithiasis is increasing in the past decades, despite progress in the surgical procedures to remove the stones, there is a recurrence rate after the intervention, and there is no definitive cure for it. In the past decades, the role of intestinal microbiota regarding KSD pathology has been gradually unravelled. Oxalate-degrading bacteria and short-chain fatty acid (SCFA) producing microorganisms have been shown to have important roles in crystal formation through direct calcium oxalate breakdown or as inducers of immune responses capable of inhibiting crystal formation in the kidneys.Experimental approach: In order to test the properties of prebiotics in stone formation physiology, we used an in vivo mouse model administering four different formulated diets. A control diet, a sodium oxalate diet to stimulate stone formation, an inulin diet to stimulate SCFA-producing microorganisms, and a tributyrin diet to act as a direct source of butyrate, a specific type of SCFA that we have previously shown to be lacking in kidney stone patients.Results: Results indicated that the sodium oxalate diet reduced the overall mice microbial alpha diversity and the variability of bacterial groups responsible for SCFA production. It also increased oxalate concentrations in the urine and caused crystal formation in the kidney. Furthermore, an inulin diet was able to promote the proliferation of SCFA-related microbiota and SCFA concentrations in the gut, which resulted in reduced oxalate amounts in the urine, therefore, contributing to reducing the risk of stone formation. Tributyrin supplementation did not promote any significant effect.Conclusions: This study corroborates previous research indicating that dietary supplements like inulin are potential prebiotic candidates to promote gut homeostasis, oxalate absorption regulation, and modulate SCFA-related microbial population and SCFA production in the intestine.

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Efficacy of novel coating in preventing Proteus mirabilis adherence and assessing the pathogenic mechanisms utilized to potentiate catheter-associated urinary tract infections (2021)

Introduction: Proteus mirabilis is a gram-negative, urease-positive bacterium that infects the urinary tract and is linked with catheter-associated urinary tract infections (CAUTIs). CAUTIs are painful, and both physically and financially burdensome infections that are associated with the presence of a urinary catheter that drains urine from the bladder. The insertion of a catheter allows for entry and scaffolding of bacteria, such as P. mirabilis to adhere to and propagate infection in the urinary tract.Methods: In vitro experiments assessed the ability of a novel anti-fouling catheter coating to prevent P. mirabilis adhesion. Coated and uncoated catheters were exposed to bacteria and adherence was quantified via colony-forming units (CFU) counts. In vivo studies utilized a mouse model implanted with coated or uncoated catheters and inoculated with P. mirabilis. Furthermore, adherence of wildtype and mutant P. mirabilis strains to catheters were conducted by co-incubating samples in artificial urine and bacteria; adherence was quantified via CFU counts. Cellular adhesion and invasion assays were utilized to observe wildtype, mutant, and complemented P. mirabilis associations with uroepithelial cells. Briefly, cells were exposed to different strains of P. mirabilis and co-cultured; for adhesion assays, cells were washed, lysed, and plated for CFU counts. For invasion assays: cells were treated with antibiotics to eliminate extracellular bacteria, then washed, lysed, and plated for CFU counts. In vivo experiments assessed bladders, urine, and catheters in mice infected with different P. mirabilis strains.Results: In vitro and in vivo results indicated increased adherence and invasion abilities in wildtype P. mirabilis, compared to mutant strains. Specifically, wildtype was the only strain able to invade uroepithelial cells at 24 hours post-infection. Furthermore, our novel anti-adhering coating significantly reduced bacterial attachment to catheters both in vitro and in vivo.Conclusion: We have shown our novel coating to be highly effective in preventing bacterial adherence both in vitro and in vivo. Moreover, we have observed wildtype P. mirabilis to be capable of invading and adhering to uroepithelial cells at an increased capacity, compared to mutant strains. Through gaining greater insight into the pathogenic mechanisms utilized, we can target and diminish P. mirabilis CAUTIs.

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Novel one-step approach to a universal anti-adhesion coating to prevent P. mirabilis induced catheter-associated urinary tract infection (2020)

Introduction: Catheter-associated urinary tract infections (CAUTIs) account for a vast number of hospital-acquired infections and are a significant burden to healthcare systems. In the USA and Canada, more than 33 million catheters are inserted each year. Urinary catheters provide ideal surfaces for bacterial attachment and biofilm formation. Several attempts to change catheter biomaterial design to prevent biofilm formation have met with poor success. We have developed a two-component coating that is highly biocompatible and effective in preventing bacterial biofilm formation. Here, we present data showing the efficacy of the coating against a difficult to treat uropathogen, Proteus mirabilis and show decreased biofilm formation and encrustation in vitro and in a murine model of CAUTI .Materials and methods: A novel binary coating composed of polydopamine (PDA) and poly (N,N-dimethylacrylamide)(PDMA) was developed and applied via a simple dip coating mechanism. The antifouling activity was determined in vitro following incubation of coated and uncoated catheter material to P. mirabilis at 4, 8, 12, and 24 hours post-exposure. Adherent bacteria were quantified via colony forming units (CFU) counts. The in vivo efficacy of our coating was determined using a murine model of CAUTI. Briefly, 4 mm (24G) catheters (coated and uncoated) were introduced into the mouse bladder percutaneously with ultrasound guidance followed by inoculation of 105 P. mirabilis. Adherent bacteria and struvite formation were quantified following 3-days post-infection. Results: The in vitro study showed that our novel coating decreased P. mirabilis adhesion to polyurethane (PU) surfaces by 99% reduction compared to uncoated surfaces. Furthermore, in vivo studies showed an 87.9% reduction in P. mirabilis adhesion on coated compared to uncoated catheters. In both in vitro and in vivo models, the accumulation of struvite and calcium oxalate encrustations on the coated surfaces were significantly reduced. Conclusions: Using relevant in vitro and in vivo models, we have shown our novel binary coating to be highly efficacious at decreasing P. mirabilis attachment and subsequent biofilm formation and inorganic crystal accumulation on urinary materials. Further testing of this novel coating in validating the results in a porcine infection model will be important

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Erythropoietin promotes functional recovery via anti-apoptotic mechanisms in mice unilateral ureteral obstruction (2018)

The ureter transfers urine from the kidney through sequential contractions, called peristalsis. When obstructed, accumulated urine builds up high pressure which leads to dysfunction in the urological tracts. Our laboratory showed that, in mice, ureteral peristalsis is not recovered for 10 days after removing a 24-hour obstruction. Delayed ureteral recovery affects the kidney negatively as the ureter cannot transport urine properly. Studies have shown that erythropoietin (EPO), a hematopoietic hormone, protects different organs against various injuries mainly by suppressing apoptosis, via EPO receptor (EPOR) and β-common receptor (βCR) heterodimers. Our laboratory showed that prophylactic EPO treatment of obstructed mice accelerated recovery of the ureter and the kidney following the reversal of ureteral obstruction. We hypothesized that EPO treatment promotes functional recovery of the ureter and the kidney via anti-apoptotic mechanisms. The objective of this study was to investigate EPO-induced mechanisms in accelerating recovery from ureteral obstruction in 2 mice strains.Unilateral ureteral obstruction was created for 24, 48, 72 hours using non-traumatic micro-clip (n=10). EPO was administered daily for 4 days either prophylactically or concomitantly with ureteral obstruction. TUNEL assay and immunohistochemistry with phospho-NF-κB p65 and phospho-STAT5 antibodies on ureteral tissues and qRT-PCR with primers specific to EPO, EPOR, βCR, STAT5A, BCL-2, BCL-XL, BAX and NF-κB on ureteral and renal tissues were performed. Our study showed that ureteral obstruction decreased ureteral peristalsis and increased apoptosis in 72-hour obstructed ureters. Ureteral obstruction decreased anti-apoptotic EPOR-βCR signaling and increased phospho-NF-κB p65. EPO treatment on ureteral obstruction improved ureteral function and suppressed apoptosis in obstructed ureters, by suppressing NF-κB and decreasing apoptotic BAX. EPO treatment did not induce erythropoiesis in our study, which supports that EPO’s protective effect is a separate mechanism from increased blood circulation by hematopoiesis. Also, EPO treatment without obstruction did not change EPOR-βCR signaling.In conclusion, ureteral obstruction increased apoptosis in ureteral tissues and decreased anti-apoptotic EPOR signaling with increased phospho-NF-κB p65, along with obstruction induced ureteral dysfunction. EPO treatment improved ureteral peristalsis and suppressed ureteral apoptosis, via suppression of NF-κB activation and decreased expression of BAX that compensated for the decreased expression of BCL-2 and BCL-XL by obstruction.

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The gut microbiome and metabolic pathways of recurrent kidney stone patients and their non-stone-forming live-in partners (2018)

Background: Metabolism-associated kidney stones such as oxalate, uric acid and cystine stonesare caused by over-accumulation or under-excretion of their associated metabolites in thehuman body. Although the kidney is the primary excretion site for these metabolites, theintestine is an important alternative site of excretion. Intestinal bacterial community memberscontribute to the breakdown, transport and assimilation of stone-associated metabolites includingoxalate, uric acid, cystine and butyrate. To better diagnose and prevent the formation ofmetabolic kidney stones, the intestinal microbiome should be examined at the level of bacterial communities and interconnected metabolic pathways.Experimental approach: This study examines the differences in bacterial communities andmetabolic pathways between the intestinal microbiomes of recurrent kidney stone patients andnon-stone-forming controls. Fecal samples were collected from 17 recurrent kidney stonepatients and 17 controls with no stone-forming history. Bacterial DNA was then extracted fromthe fecal samples. To examine bacterial taxonomy, specific variable regions of the 16S rRNAgene were sequenced from the DNA and aligned to a bacterial gene database to identify andquantify the bacteria present. To examine metabolic pathways, metagenomic DNA libraries weresequenced, assembled and aligned to a metabolic gene database to identify and quantify themetabolic genes present.Results: Bacterial populations in patient microbiomes appear to be less diverse than those incontrol microbiomes. At the bacterial species level, we found that patient microbiomes had lowerabundance of Oxalobacter formigenes, a well-known oxalate-degrading bacterium. At themetabolic pathway level, patient microbiomes were found to contain a lower abundance of genesimportant for the production of butyrate, a fatty acid that promotes overall intestinal integrity andhas been found to upregulate the expression of oxalate transporters in the gut.Conclusions: This study verifies previous findings that a majority of recurrent kidney stoneformers lack O. formigenes in their intestinal microbiomes. Additionally, analysis intometabolic genes in the gut uncovered an additional deficiency in the butyrate metabolismpathway that could influence overall gut homeostasis. Reduced bacterial diversity in recurrentstone formers also suggest patient microbiomes may be dysbiotic, a state common to manyintestinal diseases.

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Novel Antimicrobial Peptide Coating to Prevent Catheter-Associated Urinary Tract Infections (2016)

Introduction: Urinary catheters provide ideal surfaces for bacterial biofilm formation, being a major factor for hospital-acquired infections. With increased antibiotic resistance, there is a push for non-antibiotic-based measures to prevent catheter-associated urinary tract infections (CAUTI). I pursue the use of polymer-linked, broad-spectrum, host-defense-based antimicrobial peptides (AMPs) as novel catheter coatings. Here, I present the efficacy of tethered AMPs against common uropathogens both in vitro and in vivo.Materials and Methods: Peptides E6, Tet20, Tet26, and Kai13 were linked to surfaces using polymer brushes PDMA, PMPC, and PMPDSAH. All peptides were chosen based on their antimicrobial activity and biocompatibility as suggested by previously published papers. Antimicrobial activity of each coating was determined in vitro via colony counts 6 hours post-exposure to uropathogens. The in vivo efficacy of AMP coatings was also tested using a clinically relevant CAUTI mouse model; bladders of mice were catheterized percutaneously under ultrasound guidance, and 50 μL of 5E+5 CFU/mL P. aeruginosa was instilled. Indwelling polyurethane catheters and urine were collected after 7 days for examination of bacterial adherence and growth.Results: The most effective peptide-brush combination was E6-PDMA, decreasing bacterial adhesion and planktonic growth by up to 94.1% and 63.8%, respectively based on in vitro data. In vivo results look even more promising; the coating decreased bacterial adhesion by up to 99.9958% and planktonic growth by 99.8660% in comparison to untreated mice. Conclusions: Based on our in vitro and in vivo data, E6-PDMA coatings may effectively prevent CAUTI. Further testing of these novel coatings against more common uropathogens as well as tests to confirm the safety of such coatings will be important.

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