Dirk Lange

Associate Professor

Research Interests

Ureteral stents
antifouling coatings
antimicrobial coatings
device complications

Relevant Degree Programs

Affiliations to Research Centres, Institutes & Clusters

 
 

Recruitment

Master's students
Doctoral students
Postdoctoral Fellows
2021

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Graduate Student Supervision

Master's Student Supervision (2010 - 2018)
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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