Toxicity testing of urinary catheters

Design of Thermoplastic Polyurethanes with Conferred Antibacterial, Mechanical, and Cytotoxic Properties for Catheter Application

Thermoplastic polyurethanes (TPUs) are proposed as suitable solution for the fabrication of biocompatible catheters with appropriate mechanical parameters and confirmed antibacterial and cytocompatible properties. For this purpose, a series of quaternary ammonium salts (QASs) and quaternary phosphonium salts (QPSs) based monomers were prepared followed by the determination of their minimal inhibitory concentrations (MICs) against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa). A combination of the most active ammonium (QAS-C₁₄) and phosphonium (QPS-TOP) salts led to a MIC down to 2.4 μg/mL against S. aureus and 9 μg/mL against P. aeruginosa, corroborating the existence of a synergistic effect. These quaternary onium salt (QOS) units were successfully incorporated along the polymer chain, as part of a two-step synthesis approach. The resulting TPU-QOS materials were subsequently characterized through thermal, mechanical, and surface analyses. TPU-Mix (combining the most active QAS-C₁₄ and QPS-TOP units) showed the highest antibacterial efficiency, confirming the synergistic effect between both QOS groups. Finally, an MTT assay on the SiHa cell line revealed the low cytotoxicity level of these polymeric films, making these materials suitable for biomedical application. To go one step further in the preindustrialization approach, proof of concept regarding the catheter prototype fabrication based on TPU-QAS/QPS was validated by extrusion.

Mechanisms of cell death induced by infusion sets leachables in in vitro experimental settings

Leachable materials that are released from infusion sets during their use can induce local and systemic toxic effects. We studied the mechanisms and kinetics of cell death induced by infusion sets leachates in vitro using L-929 and bEnd. 3 cells. Changes in cell morphology and metabolic activity were determined using light microscopy and the MTT test, respectively. Detailed analysis of the mechanisms of cell death was performed using membrane integrity and caspases 3 and 7 activity tests, annexin V-FITC/7-AAD analysis by FACS, and DAPI nuclear staining followed by confocal microscopy. Infusion sets released toxic leachables and induced toxic effects. Latex flashball was the most toxic part of the studied infusion sets, and it potently induced cell oncosis via increased permeability of the cell membrane. Latex-induced decrease in cells metabolic activity and cell death were not accompanied by activation of caspases 3 and 7, changes in nuclear morphology, or substantial annexin V-FITC cell staining. Leachables from the tube part of the infusion sets were less toxic, and induced some biochemical changes without altering the cells morphology. Further studies are needed to reveal the in vivo toxicity of infusion sets and its correlation with the results of in vitro toxicity studies.

The cytotoxicity assessment of the novel latex urinary catheter with prolonged antimicrobial activity

The purpose of this study was to evaluate the in vitro biocompatibility of the novel Sparfoxacin (SPA)-treated latex catheter with previously performed prolonged antimicrobial activity. Rectangular-shaped test samples of silicone latex catheter were fabricated according to patented procedure permitting the immobilization of SPA on heparin (HP)-coated catheter by means of mixed, covalent and non-covalent bonds. Samples subjected to cytotoxicity assay were divided into four groups: (1) the untreated catheter, (2) HP-coated catheter, (3) HP-coated catheter with SPA immobilized in low SPA concentration solution (SPA-L treated sample), and (4) high SPA concentration solution (SPA-H treated sample). Then the samples were placed directly into green monkey kidney (GMK) cell monolayer for 24 h. After the incubation period, cytotoxicity was determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The degree of cytotoxicity of each sample was evaluated according to the reference value represented by the control cells cultured without catheter sample. Statistical significance was determined by repeated t-test (P < 0.05). The cytotoxic effect of treated and untreated catheters was also estimated by microscopic observations of GMK cells morphological changes. SPA-treated catheters demonstrated high survival rates in MTT assay (>93%) on the contrary to the untreated catheters (6.13%) and HP-coated catheters (80.90%). Moreover, microscopic observation of GMK cells exposed to SPA-treated samples revealed no morphological changes and no cell growth reduction. We suggest that SPA-treated latex catheters are biofilm formation resistant (as we revealed in our previous work), considerably less toxic than untreated ones, and can be undoubtedly used in urological practice.

Cultured differentiated human urothelial cells in the biomaterials field

To review the use of normal cultured differentiated human urothelial cells in the biomaterials field, we checked the literature for human urothelial cells in culture (HUC) both for their use in biocompatibility assessment and as bioartificial devices. The in vitro culture of differentiated human urothelium is now a simple and reliable procedure. These techniques provide new tools for biocompatibility assessment of urinary biomaterials, because for the rational design of a testing procedure, it is preferable that the particular cell culture models selected should be closely related to the end-use application. The emerging use of HUC culture should lead to the development of bioartificial tissue for urinary tract reconstruction. Tissue engineering techniques require urothelial cells and cell delivery matrices. The cytocompatibility of novel artificial delivery matrices should be assessed in vitro before implantation using cultured HUC to find the best material available.

Biocompatibility testing of a new silver-impregnated catheter in vivo

The purpose of this investigation was to compare the local effects of polyurethane (Tecothane) and silicone tubes with or without silver impregnation in rats. Bacterial colonization or infection of the exit site and/or tunnel were documented and interpreted. All tubes were placed subcutaneously or percutaneously in the neck of 41 Sprague-Dawley rats and guided beneath the dorsal muscles into the peritoneal cavity. The incidence of bacterial abscesses along the implanted tubes was evaluated daily. After 90 days, or earlier if sepsis developed, the animals were killed painlessly and various organs and tissues from the entry site and the catheter tunnel examined histologically. In the group where polyurethane tubes were placed percutaneously, there was no difference in the frequency of abscesses between silver-impregnated and non-impregnated tubes (5/6 with and 5/7 without silver). The only difference noted was in the group with percutaneously placed silicone tubes between those with and without silver. Abscesses only occurred in 2/4 animals in the silver group and in 5/5 animals in the control group. Histological examination showed no difference in either group between infectious and foreign body reactions. Silver particles in subcutaneous, muscle and peritoneal tissue could not be demonstrated.

An in vitro biocompatibility evaluation of double-J stents

OBJECTIVES

For several years, studies performed to estimate in vitro biocompatibility of urinary catheters have been carried out using permanent cell lines. However, for a rational design of the testing procedure, the cell culture model should depend on the material application. We assess the biocompatibility of 13 double-J stents using an in vitro model of normal human urothelial cells (HUC). This article aims to mimic in vitro, on HUC monolayers, the close contact existing in vivo between the urothelium and double-J stents and to evaluate the subsequent effect on these cells.

METHODS

Fragments of each stent were deposited into the wells containing confluent HUC, with close contact maintained between the material and the cells. The same procedure with either no material or fragments of latex catheter was undertaken to provide the negative and positive controls, respectively. The contact was maintained for 1, 3, and 8 days. At the end of the incubation period, fragments of stent were removed and cell activity tests were performed (neutral red assay, MTT assay, and cell proliferation).

RESULTS

One of the silicone stents is significantly deleterious on HUC as determined by three tests after 8 days of contact. For two copolymers, a tendency to increase cell proliferation was noted. Concerning polyurethanes, we observed significant decreases in HUC viability and cell metabolic activity for five stents after 8 days of contact. All seven polyurethane stents significantly inhibited cell proliferation.

CONCLUSIONS

The HUC culture model may be of relevance for the screening of materials intended for use as double-J stents.

First use of cultured human urothelial cells for biocompatibility assessment: application to urinary catheters

For several years, studies performed to estimate in vitro biocompatibility of urinary catheters have been carried out using permanent cell lines. But for a rational design of the testing procedure, the cell culture model should relate to the material application. This work presents the results of a probe study designed to obtain an in vitro model of normal human urothelial cells (HUC) and to test the relevance of this system in cytocompatibility experiments of urinary catheters currently used.A comparison is made with continuous cell lines, the use of which is recommended by normalization bodies. We exposed monolayers of HUC (well characterized for their proliferation, qualitative evaluation, and quantitative measurement of cytokeratins) and two continuous human cell lines to liquid extracts (either pure or diluted in the culture medium) of nine available catheters, including positive (latex) and negative controls, for a 24 h incubation. Then colorimetric assays (Neutral Red and MTT) were performed. The extracts of two polyurethanes provoked a significant toxic effect on HUC only, suggesting differences in sensitivity between the models used. This effect could be due to the presence of a great amount of barium (used as a radioopacifier) in extracts, as highlighted by results of absorption emission spectroscopy. A culture model of HUC may be of relevance for the screening of materials intended for urological practice.

Biocompatibility of various indwelling double-J stents

The biocompatibility of 8 double-J stent brands was evaluated both in vivo, by scanning electron microscopy and histological analysis of pig ureters intubated for 6 weeks, and in vitro, by cell culture methods. In vivo findings showed that superficial epithelial destruction was milder in the ureters intubated with hydrogel-coated stents than in those intubated with other stents. Inflammatory reactive changes were milder in the ureters intubated with silicone stents than in those intubated with other stents, while encrustation was more severe on silicone and Grey stents than the others. In vitro, the 3 stent brands made of "modified polyurethane" were found to be cytotoxic while the others were not. Overall, silicone and hydrogel-coated stents seemed to be more biocompatible than the others, and hydrogel-coated stents to be more suitable than silicone stents for long-term ureteral stenting, being less prone to encrustation. Although they are of an experimental nature, these findings may be of relevance to clinical practice.

Recurrence of urethral stricture and late results after optical urethrotomy: comparison of strictures caused by toxic latex catheters and other causes

During the years 1977-1985, 183 new urethral strictures were diagnosed and treated by optical urethrotomy. A sharp increase in the incidence of iatrogenic strictures was found in 1980-1981 which normalized after simultaneous changing of the resectoscope, lubricant and catheter type. In fact, an "epidemic" of urethral strictures associated with the use of indwelling latex catheters in cardiac operations was observed in Finland in those years. It is suggested that toxic latex catheters exacerbated the local mechanical injury caused by endoscopic surgery. The recurrence rate for our "epidemic" strictures was 54%, whereas in other cases it was 37% (p = 0.02), but there were no differences in the later course. The patients age, stricture site, postoperative period of catheter-drainage, length, diameter or multiplicity had no effect on the recurrence rate after the initial urethrotomy. Stricture recurrences occurred up to 8 years after the initial operation. Because of the chronic nature of the urethral stricture, a follow-up time of at least 10 years is needed before the final results of urethrotomy can be evaluated.

Urethral blood circulation during cardiopulmonary bypass

The haemodynamic changes induced by extracorporeal circulation (ECC) are thought to be important in the induction of urethral strictures in open heart surgery when indwelling latex catheters are used. In the present study, 6 piglets were cannulated and connected to extracorporeal perfusion apparatus. Pump flows correlated with human ECC values with non-haemic prime were used. The mucosal and submucosal blood circulation in the urethra reduced by 66% during ECC (P less than 0.05). The brain and hepatic arterial flows increased. A significant reduction was seen in renal blood circulation. The changes in the urethral blood circulation during ECC correlated with previous findings. The reduced wash out levels of chemicals leaching from the indwelling latex catheters as a result of reduced local blood circulation are the main trigger for the induction of urethral strictures during ECC and in other shock-like circulatory disturbances in the human body.

Comparison of two different cell culture methods in evaluation of biocompatibility of latex urinary catheters

International biocompatibility standards for urinary catheters have not yet been set. The used in vivo animal tests earlier have been shown to be insensitive and expensive. The present study compared the sensitivity and other properties of two in vitro cell culture methods, the reference method of the British Standards Institution (BSI) and the thymidine incorporation method (DNA synthesis inhibition test. The cell culture toxicities of thirty-seven latex catheters were measured and 84.8% of the catheters tested passed the BSI reference test while 94.6% passed the thymidine incorporation test. The overall batch-to-batch correlation was poor (p greater than 0.05), but within brands the correlation was better. This is obviously to be explained by the differences the characteristics of the tests and/or the chemical composition of the catheters. The thymidine incorporation test is easier to perform, requires less manpower, and is therefore less liable to subjective interpretations than the BSI test. The biocompatibility toxicity limits for latex urinary catheters need to be tightened. Our experience in this study indicates that the thymidine incorporation test or tests similar to it, which can be highly automated can be recommended for biocompatibility screening in large series, and BSI reference test can be used additionally in unclear cases.

Activation of complement, kallikrein-kinin, fibrinolysis and coagulation systems by urinary catheters. Effect of time and temperature in biocompatibility studies

Urethral strictures induced by the use of latex catheters and combined silicone/latex catheters following open-heart surgery have been reported. These strictures differ from the post-catheterisation type in affecting a greater length of urethra. Recently it was shown that complement was activated by catheters which cause inflammation, in contrast to clinically silent catheters. The present study was designed to investigate a possible association between catheter-induced inflammation and activation of another mediator of inflammation, the contact system. We also investigated various in vitro conditions to optimise biocompatibility studies. Our data indicate that both the complement and the kallikrein-kinin system are activated by potentially harmful silicone/latex catheters and may be involved in the pathophysiology of catheter-induced urethral strictures. In vitro biocompatibility tests may be performed at both 20 and 37 degrees C. Glass test tubes may be used for in vitro complement but not for kallikrein-kinin investigations.

Effect of three plastic catheters on survival and growth of Pseudomonas aeruginosa

The effect of polyvinylchloride (PVC), polyurethane (PU) and siliconized latex (SL) catheters on the survival and growth of six non-mucoid and three mucoid strains of Pseudomonas aeruginosa was evaluated. Pseudomonas aeruginosa (1 x 10(8)) was incubated in PBS alone (control) or with 30 1-cm length segments of each catheter and the number of viable microorganisms was determined after 8 h, 1, 2, 5, 7 and 10 days. The presence of PVC catheters significantly favoured the survival and growth of non-mucoid strains in comparison to the control (P less than 0.05 at 5 days, P less than 0.01 at 7 days and thereafter); a similar result was observed with SL catheters (P less than 0.05 at 2 days, P less than 0.01 at 5 days and thereafter). No differences were observed with PU catheters. The number of mucoid microorganisms decreased with time in all controls and suspensions containing segments of catheter, but non-mucoid revertants appeared and quickly increased in the presence of PVC and SL (but not PU) catheters. Eluates of PBS previously containing PVC or SL segments induced a 100- to 500-fold increase in the growth of a non-mucoid strain in comparison with PBS alone. It is concluded that some plastic catheters can release substance(s) that favour the viability of P. aeruginosa.

Influence of the nervous system on experimentally induced urethral inflammation

We have studied the contribution of the nervous system on experimentally induced urethral inflammation in the rat. Urethral inflammation was induced by inserting latex strips into the urethra. The effects of different experimental procedures was assessed by using a 4-graded inflammation scale based on the histological findings. Attenuation of urethral inflammation was produced by administration of capsaicin at birth. A more complete attenuation was produced by sympathectomy prior to application of the latex strip. Urethral inflammation was also severe in the spontaneous hypertensive rat. Injection of morphine into the third ventricle of the brain significantly reduced the experimentally induced urethral inflammation. These data taken together indicate that the sensory and postganglionic innervation of the urethral mucosa as well as the central nervous system is critically involved in the inflammatory reaction of the urethra following exposure to latex strips.

Intralesional corticosteroid injections in combination with internal urethrotomy in the treatment of urethral strictures

In the treatment of 38 patients with urethral stricture, 21 received intralesional corticosteroid injections, combined in 17 cases with internal urethrotomy. The aetiology of the lesion is discussed, together with a review of the pertaining literature, and the results of the treatment are evaluated.

Histological changes in the urinary bladder secondary to urethral catheterisation

The macroscopic and microscopic features of the urothelial response of the human urinary bladder to urethral catherisation are described. The catheter reaction is characterised by a predominantly eosinophilic inflammatory response producing, macroscopically, a papillary mucosal appearance termed polypoid cystitis. The severity of the epithelial inflammatory response correlates significantly with the duration of catheterisation. Urothelial dysplasia confined to the catheter reaction site was noted in 6% of cases. The possible implications of these findings are discussed.

Biocompatibility of urinary catheters. Effect on complement activation

The ability of 2 brands of urinary catheters to activate the complement system in vitro as a marker of biocompatibility was investigated. Pieces of a silicone/latex catheter and an all-silicone catheter were incubated in human serum. Complement activation was tested in 2 enzyme immunoassays, one evaluating C3 activation and the other the terminal complement complex (TCC) formation. The silicone/latex catheter caused considerably more complement activation in both assays than did the all-silicone one. The findings are in agreement with previous results of tissue toxicity tests. The methods presented may prove valuable for the practical purpose of testing the biocompatibility of urinary catheters.

Urinary catheter structure and testing methods in relation to tissue toxicity

Eluates from 56 latex urinary catheters from seven manufacturers were divided into three categories according to covering material (siliconized, silicone elastomer coated and teflon coated) and tested for tissue toxicity by means of cell cultures based on the inhibition of DNA synthesis. The silicone elastomer coated catheters showed the lowest toxicity. Only 4 of 13 such catheters gave unacceptable toxic values, whereas half of the siliconized catheters were abandoned as toxic. Teflon and elastomer coatings had the best protective properties against toxic substances leaching from the catheter core. The surface contour of the catheters estimated by scanning electron microscopy (SEM) did not correlate with toxicity, whereas the cracks seen on the catheters did correlate with toxicity. The simple in vivo test methods used by the manufactures turned out to be insensitive to tissue toxicity testing of urinary catheters. The method used in this study was the most reliable for assessing the safety of latex urinary catheters. Thus manufacturers using multiple and in vitro cell culture tests had products of better quality than those using only a single test or simple in vivo tests.