Copyright 2011 Yeon Suk Jung et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Currently, nonanimal methods of skin sensitization testing for various chemicals, biodegradable polymers, and biomaterials are being developed in the hope of eliminating the use of animals. The human cell line activation test (h-CLAT) is a skin sensitization assessment that mimics the functions of dendritic cells (DCs). DCs are specialized antigen-presenting cells, and they interact with T cells and B cells to initiate immune responses. Phenotypic changes in DCs, such as the production of CD86 and CD54 and internalization of MHC class II molecules, have become focal points of the skin sensitization test. In this study, we used h-CLAT to assess the effects of biodegradable polymers. The results showed that several biodegradable polymers increased the expression of CD54, and the relative skin sensitizing abilities of biodegradable polymers were PLLG (75 : 25) < PLLC (40 : 60) < PLGA (50 : 50) < PCG (50 : 50). These results may contribute to the creation of new guidelines for the use of biodegradable polymers in scaffolds or allergenic hazards.
1. Introduction
Until recently, studies of skin sensitization have used the guinea pig maximization test (GPMT) [1–3]. Currently, the local lymph node assay (LLNA) [4, 5] is often used as an alternative to GPMT. The advantages of LLNA are the ability to make dose-dependent evaluations, a decrease in animal usage, shorter experimental time periods, and lower costs [6, 7]. In addition, a movement to prohibit the use of animals for safety testing of new materials is spreading throughout the world [8]. Recently, Ashikage et al. (2006) [9], Sakaguchi et al. (2006) [10] and several laboratories have reported the use of a new alternative to animal experiments, the human cell line activation test (h-CLAT) [11, 12].
Dendritic cells (DCs) are in contact with the skin and inner lining of the nose, lungs, stomach, and intestines [13]. They can also be found in an immature state in the blood. Antigens from viruses and microbes not only induce an adaptive immune response in DCs but also induce innate immunity to activate the immune system [14–16]. When skin sensitization develops, DCs immigrate to the secondary lymphoid organs to present naïve T cells [17]. Then, immature DCs mature and intercellular adhesion molecules, costimulatory molecules, and major histocompatibility complex II (MHC II) antigens (CD54, CD86, HLA-DR antigens) [18–21]. The immune reaction of DCs remains weak without costimulatory molecules. Therefore, skin sensitization in in vitro experiments is judged by expressions of CD54 and CD86.
THP-1 cells, a human monocyte cell line, are used in place of DCs in h-CLAT. We can evaluate phenotypical alterations on these THP-1 cells. In the present studies, we assessed skin sensitization to biodegradable polymers by in vitro measures.
2. Materials and Methods
2.1. Cell Cultivation
THP-1 cells purchased from American Type Culture Collection (Manassas, Va, USA) were cultured with RPMI Medium 1640 (GIBCO, Grand Island, NY, USA) supplemented with 10% fetal bovine serum (FBS, Intergen, Purchase, NY, USA), 0.05 mM 2-mercaptoethanol (GIBCO), and 1% streptomycin (GIBCO). The cells used in testing were between 2 weeks to 2 months old.
2.2. Biodegradable Polymers and Their Treatment
Biodegradable polymers P1 to P6 (Table 1) were obtained from Taki Chemical Co., Ltd. (Hyogo, Japan). We made 6 initial stock solutions by dissolving the biodegradable polymers in dimethyl sulfoxide (DMSO, Sigma, Ayrshire, UK). The biodegradable polymers P1, P2, P3, P4, P5, and P6 were dissolved separately in DMSO. 2,4-Dinitrochlorobenzene (DNCB, Sigma-Aldrich, St. Louis, Mo, USA) was also dissolved in DMSO and used as a positive control for the skin sensitization test. We made 6 substock solutions of each polymer using two-times dilution series. These sub-stock solutions were diluted 20 times with RPMI medium 1640. Finally, the working solutions were added to the cells at 100 times dilution.
Table 1: Condition and composition of biodegradable polymers.