Studies on the mechanisms of tumorigenesis induced by polyetherurethane in rats: production of superoxide, tumor necrosis factor, and interleukin 1 from macrophages cultured on different polyetherurethanes

The inflammatory cell influx and cytokines changes during transition from acute inflammation to fibrous repair around implanted materials

The inflammatory and fibrous responses in a subcutaneous rat model were evaluated around degradable polyurethane urea (PUUR; Artelon), with titanium and tissue culture polystyrene (PS) discs having different surface chemical properties but similar surface topography. Cytokines, viability, cellular response, differentiation of cells and fibrous capsule formation and vascularization was investigated after 1, 7 and 21 days of implantation. The exudates retrieved from the pockets were analysed with respect to the total cell numbers, the proportions of cell types, the differentiation of monocytes/macrophages (ED1, ED2), the DNA content and the viability (LD, Trypan blue). Tumour necrosis factor alpha ((h)TNF-alpha) and interleukin-10 ((h)IL-10) were quantified by ELISA. The number of blood vessels, blood vessel luminal area, blood vessel distribution and the fibrous capsule thickness were analysed. The highest number of cells in the exudates around all implants was detected during the early phase of healing (1-7 days). The proportion of ED2-positive cells in the exudates increased from 2-8% at 1 day to 43-56% at 21 days. The levels of TNF-alpha were low with a decrease at 7 days. After 21 days high amounts of IL-10 in the exudates were detected, in particular around PUUR. This study shows that the transition from inflammation to repair (1-21 days) around PUUR, Ti and PS materials was characterized by a decrease in inflammatory cell influx, an increasing proportion of ED2-expressing macrophages, a biphasic TNF-alpha secretion, an increase of IL-10 and a fibrous capsule formation similar to all materials tested.

Indirect induction of endothelial cell injury by PU- or PTFE-mediated activation of monocytes

Polyurethanes (PUs) and polytetrafluoroethylene (PTFE) are widely used for making cardiovascular devices, but thrombus formation on the surfaces of these devices is inevitable. Since endothelial injury can lead to thrombosis, most of the studies on PUs or PTFE focused on their damage to endothelial cells. However, few studies have attempted to clarify whether the use of foreign objects as biomaterials can cause endothelial injury by activating the innate immune system. In this study, we aimed to investigate the roles of PU- or PTFE-stimulated immune cells in endothelial-cell injury. First, monocytes (THP-1 cells) were stimulated with PU or PTFE for 24 h and, subsequently, human umbilical vein endothelial cells (HUVECs) were treated with the supernatants of the stimulated cells for 24 h. We measured the generation of intracellular reactive oxygen species (ROS) from THP-1 cells treated with PU and PTFE for 24 h, meanwhile hydrogen dioxide (H(2)O(2)), tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the supernatants were also detected. Then, we assessed the apoptosis rate of the HUVECs and determined the expression of NO, inducible nitric oxide synthase (iNOS), and apoptosis-related proteins (p53, Bax, Bcl-2) in the HUVECs. The results showed that large amounts of ROS and low levels of pro-inflammatory cytokines (TNF-α and IL-1β) were produced by the stimulated THP-1 cells. After culturing with the supernatants of the PU- or PTFE-stimulated THP-1 cells, the apoptosis rate, NO production and expression of iNOS, p53 and Bax in the HUVECs were up-regulated, while Bcl-2 expression was down-regulated. In conclusion, the release of ROS by PU- or PTFE-treated THP-1 cells may induce iNOS expression and cause apoptosis in HUVECs via the p53, Bax and Bcl-2 proteins. These data provide the interesting finding that endothelial injury in the process of biomaterial-induced thrombosis can be initiated through the release of soluble mediators by monocytes.

Immune response against polyester implants is influenced by the coating substances

The aim of this study was to evaluate the influence of the coating of polymer implants upon the individual humoral immune response to the polymer matrix. Intramuscular implantation and explantation of samples from three different polyester vascular prostheses coated with collagen, gelatin, or human serum albumin was performed in LEW.1A rats and subsequently compared to sham operated control animals. Antibodies in serum samples were detected by means of enzyme immunoassays employing particles of pure polyester and the respective prosthesis, or solid phase bound coating substances as targets. In contrast to the controls, all animals with implants demonstrated a high antipolyester antibody response with a broad individual variability graduated according to the prosthesis coatings: gelatin > albumin > collagen. This was further significantly increased after the second implantation/first explantation and declined following the last explantation. Only animals with albumin-coated implants revealed specific antibodies to the coating as well as the strongest overall immunological reaction against the prosthesis already on day 8. Specificity of polymer antibodies was demonstrated by competitive inhibition of median antibody binding. Our results showed a specific immune reaction as a result of the applied polymer, which varied due to the surface-coating and individual factors.

Understanding the biodegradation of polyurethanes: from classical implants to tissue engineering materials

After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity has been sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility, and more recently their biodegradation character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings containing PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegradation and the desire to further understand the biological mechanisms for in vivo biodegradation. The advent of molecular biology into mainstream biomedical engineering permitted the probing of molecular pathways leading to the biodegradation of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but has also been translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of physical properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degradation in vivo and the subsequent studies that have led to the field's further understanding of the biological processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug + polymer) products and tissue regeneration applications will then be presented.

Cytokine secretion from mononuclear cells culturedin vitro with starch-based polymers and poly-L-lactide

The cytokine network is one of the major controlling systems of the inflammatory process, driving the magnitude and duration of the host response against invading microorganisms, foreign materials, or altered internal stimuli. Pro- and antiinflammatory cytokines were quantified after in vitro culture of a mixed population of monocytes/macrophages and lymphocytes with biodegradable polymers. Different blends of starch-based polymers and their composites filled with hydroxyapatite were studied and compared with poly-L-lactide. Interleukin (IL)-1beta, IL-6, and tumour necrosis factor-alpha were investigated as the markers of immunological reactivity because they are known to act at the early stages of injury/invasion. Interferon-gamma, recognized as a proinflammatory cytokine, although not present during early responses was also investigated. Contrarily, IL-4 derived from T lymphocytes, was investigated because it is an immunoregulator that counteracts some aspects of inflammation. T lymphocyte activation was also determined by quantifying IL-2. The results support the hypothesis that different biodegradable polymers can affect mononuclear cell activation and the production of several cytokines associated with the inflammatory process. No IL-2 or interferon-gamma was found in the culture supernatants after 3, 7, and 14 days in the presence of any of the materials. IL-6 was detected in the highest amounts, for all the conditions, followed by tumour necrosis factor-alpha. IL-1beta was produced in very low amounts, being undetectable with some of the starch-based materials. IL-4 was the only cytokine that did not demonstrate any significant difference within this group of materials. Starch-based polymers and composites induced lower production of proinflammatory cytokines in comparison to poly-L-lactide.

Biomaterial surface chemistry dictates adherent monocyte/macrophage cytokine expression in vitro

An in vitro human monocyte culture system was used to determine whether adherent monocyte/macrophage cytokine production was influenced by material surface chemistry. A polyethylene terephthalate (PET) base surface was modified by photograft copolymerization to yield hydrophobic, hydrophilic, anionic and cationic surfaces. Freshly isolated human monocytes were cultured onto the surfaces for periods up to 10 days in the presence or absence of interleukin-4 (IL-4). Semi-quantitative RT-PCR analysis on days 3, 7 and 10 of cell culture revealed that interleukin-10 (IL-10) expression significantly increased in cells adherent to the hydrophilic and anionic surfaces but significantly decreased in the cationic surface adherent monocytes/macrophages. Conversely, interleukin-8 (IL-8) expression was significantly decreased in cells adherent to the hydrophilic and anionic surfaces. Further analysis revealed that the hydrophilic and anionic surfaces inhibited monocyte adhesion and IL-4-mediated macrophage fusion into foreign body giant cells (FBGCs). Therefore, hydrophilic and anionic surfaces promote an anti-inflammatory type of response by dictating selective cytokine production by biomaterial adherent monocytes and macrophages. These studies contribute information necessary to enhance our understanding of biocompatibility to be used to improve the in vivo lifetime of implanted medical devices and prostheses.