The Molecular Anatomy of Oral Wound Healing

Overview

Background: * Two important properties distinguish the healing process of skin wounds from that of wounds of the mucous membranes of the mouth (oral mucosa). Although the skin and the oral mucosa tissues are similar in nature, oral mucosa have more rapid healing and a lack of scar tissue formation. However, oral wound healing in general has been poorly studied, and more information is needed to determine how specific aspects of the oral environment affect the healing process. * Researchers are interested in identifying various factors that contribute to oral wound healing. Studying this process would help researchers explore procedures to accelerate the healing of critically-sized oral lesions formed by trauma, surgery, radiation therapy, infection, and other damage to the mouth. In addition, research into scar-free healing could be applied to other mucosal sites to promote healing and minimize unsightly scars that may compromise the tissue. Objectives: \- To identify the specific factors that enable rapid and nearly scar-free healing of oral mucosa. Eligibility: * Healthy male volunteers between 18 and 40 years of age. * Regular cigarette, cigar, and pipe smokers; occasional smokers who smoke more than 1 day a week or have smoked in the prior month; users of chewing tobacco or betel nut; and heavy drinkers (three or more alcoholic drinks per day) will be excluded. Design: * Participants will have a medical history and examination, and will provide blood samples at the start of the study. * Participants will provide oral mucosa samples from the inside of the cheek, taken using a dermal punch. At the same time, participants will provide skin biopsy samples of approximately the same size. After the skin and oral mucosa samples are taken, participants will be divided into three groups for follow-up procedures. * Group 1: No further samples will be collected. This group will help document the normal healing process. * Group 2: A second, slightly larger biopsy, which will include the area of the first biopsy, will be taken on day 3. Both skin and oral mucosa biopsies will be taken. * Group 3: A second, slightly larger biopsy will be taken on day 6, in a similar way as described for Group 2. Both skin and oral mucosa biopsies will be taken. * Wounds will be photographed with a digital camera on days 3, 6, 9, 13, and 15; and the healing will be monitored at the scheduled clinic visits.

BACKGROUND: Two important properties distinguish the process of healing of oral mucosa wounds from those of the skin: more rapid healing and the absence of scar tissue formation. This is remarkable given the apparent similarities of the two tissues. There are, however, prominent differences in the healing environment, such as hydration, growth factor availability, inflammatory response, and microbial exposure. Knowledge as to the causal contribution of each of these factors to the differential healing response of the two epithelia is mostly anecdotal, and oral wound healing has generally been poorly studied. This study seeks to provide a global molecular definition of oral wound healing in comparison to that of the skin. The overall aim will be to identify the specific factors that enable rapid and nearly scar-free healing of oral mucosa. Identification of these physiological and molecular determinants will have widespread implications for human oral health. Among others, it would provide venues for the targeted exploration of procedures to accelerate the healing of critically-sized oral lesions formed by trauma, surgery, radiation therapy, infection, and other oral pathologies, which, if untreated, lead to permanent disability and dysfunction. Moreover, pathways and/or molecules identified in these studies which may facilitate rapid, scar-less healing could be considered for application to non-oral mucosal sites to promote healing and minimize unsightly scars, which may also compromise the functional integrity of the tissue. Hypotheses: * There are significant differences in gene and protein expression between wound healing in skin and oral mucosa. * The recruitment of inflammatory cells associated with a large up-regulation of inflammation-associated genes, including cytokines and chemokines, in the epithelial cells of skin wounds may account for these differences. * There are specific gene programs that can explain the presence of significant scarring in skin tissues but not in oral mucosa. OBJECTIVES: The overall objective of this pilot study proposal is to establish the gene and protein expression profiles during the early stages (1-6 days) of normal oral wound repair. By comparing these profiles with those of cutaneous wound healing, we may be able to identify molecules exclusive to oral wound repair that could represent biomarkers of the healing process or serve as new therapeutic targets in pathological wound healing and cancer. One specific hypothesis to be tested is that the level of expression of pro-inflammatory gene networks by wound-infiltrating keratinocytes constitutes the most significant difference between the human oral and cutaneous wound transcriptomes. The specific hypothesis has been developed from data obtained from our recent complementary oral and skin wound healing studies in animals. ELIGIBILITY: Healthy male volunteers age 18 to 40 will be enrolled in this study. DESIGN: Oral mucosa samples: A sterile 3-mm dermal punch will be used to create uniform, full-thickness biopsy in the mucosa of the cheek just above the occlusal plane. Circular pieces of tissue of approximately 2 mm in depth will be removed on the day of biopsy (day 1). These subjects will be subsequently be randomly grouped as follows: Group 1: no further samples will be collected; pictures will be taken on days 3, 6, 9, 13, and 15 (see Timetable). This group will help document the normal healing process under the conditions of the present study, including the lack of scaring in the area selected for the initial wound in the oral mucosa as compared with the skin. Group 2: a second biopsy will be taken on day 3, which will include the area of the first biopsy with sterile 5 mm punch, following the same procedure as described for day 0; pictures will be taken according to the schedule set in the Timetable. This second biopsy will enabled sampling the healing area induced by the first biopsy. By selecting a punch size two millimeters wider and taking a sample concentric to the first one, we can assure complete removal of the area of interest. Group 3: a second biopsy will be taken on day 6, respectively, in a similar way as described for Group 2; pictures will be taken according to the Timetable. Skin samples: In parallel to the oral biopsies, skin biopsies of similar size and depth as the oral biopsy from the same subjects will be obtained from the axillary region following the same schedule and procedure, including a second biopsy for groups 2 and 3. Wounds will be photographed with a digital camera and the healing monitored at clinic visits per schedule above. The excised tissues in each case will be immediately bisected on ice; half of the sample will be fixed in 4% formaldehyde/PBS and embedded in paraffin for standard histology and immunohistochemistry, and the remaining half will be placed in OCT-filled plastic base molds, flash frozen in liquid nitrogen, and stored at 80 (Infinite)C until processed for genomic and proteomic analysis.