Establishment of an oral burn model in streptozotocin-induced diabetic rats

Abstract

Background: Oral ulcers are painful mucosal lesions prone to infection and inflammation. To evaluate the effectiveness of treatments, a suitable experimental animal model with an appropriate healing period is required. The aim of this study was to develop an animal model for oral ulcer research by comparing oral burn wounds of different sizes and locations in diabetic rats.

Methods: Forty-four male Sprague-Dawley rats with induced diabetes were divided into six groups based on burn wound location and size: T5 (n = 10, tongue 5 mm), T3 (n = 10, tongue 3 mm), P5 (n = 10, palate 5 mm), P3 (n = 10, palate 3 mm), CT (n = 2, control tongue), and CP (n = 2, control palate). The burn wounds were induced by applying a heated device (100-120 °C) for 3 s. At 1- and 2-weeks post-surgery, macroscopic examination, histological staining, immunohistochemistry, and Western blot analysis were performed to compare the healing progress.

Results: Healing progressed more rapidly in the second week than in the first for all groups, with burns on the tongue (Groups T5 and T3) showing more advanced healing compared to burns on the palate (Groups P5 and P3). By the second week, Group T3 was almost completely healed, while Group T5 had some remaining wounds. In contrast, Groups P5 and P3 showed minimal healing. This faster healing on the tongue was further supported by significantly lower expression levels of TNF-α and IL-1β and a reduction in ulcer size, particularly on the tongue compared to the palate.

Conclusion: A 3 mm or 5 mm burn wound on the tongue of diabetic rats can serve as a useful animal model for evaluating new treatments for wound healing, particularly up to the first week. However, for studies extending to the second week, the 5 mm burn wound model on the tongue might be more advantageous.

Keywords: Burns; Diabetes mellitus; Oral ulcer; Rat; Wound healing.

Fig. 1

Schematic diagram of the study design and animal grouping

Fig. 2

a Device used for inducing burn wounds. b Application of the device to the tongue. c Application of the device to the palate

Fig. 3

a Healing progression of burn wounds over time in each group. Group T3 exhibited the fastest healing, with almost complete wound closure by the second week. Group T5 also demonstrated advanced healing, although some wounds remained by the second week. Groups P3 and P5 showed significantly slower healing, with minimal improvement by the second week. b Percentage of Healing at 1 Week Post-Injury in Diabetic Rats. Healing was observed in all groups, with the groups T3 and T5 showing higher healing percentages compared to the groups P3 and P5. c Percentage of Healing at 2 Week Post-Injury in Diabetic Rats. At 2 weeks, healing progressed, with Group T3 showing nearly complete healing. Group T5 also exhibited substantial healing, whereas the groups P3 and P5 showed slower progression

Fig. 4

a Epithelial continuity changes and TNF-α, IL-1β immunostaining in T5 and T3 groups over 2 weeks. Epithelial continuity gradually improved in Group T5 but was not fully restored by the second week, whereas Group T3 showed complete epithelial restoration within the same timeframe. Immunohistochemical analysis revealed elevated TNF-α and IL-1β expression in both groups at week 1, with Group T5 maintaining slightly higher levels at week 2, while Group T3's expression levels returned to near-control values. b Immunostaining results for the control group (Group CT) are shown for comparison

Fig. 5

a Epithelial continuity changes and TNF-α, IL-1β immunostaining in P5 and P3 groups over 2 weeks. Group P5 exhibited persistent disruption in epithelial continuity by the second week, with no significant healing progress, while Group P3 showed partial recovery. TNF-α and IL-1β expression remained elevated in both groups throughout the 2-week period, with little change from the initial levels observed at week 1. b Immunostaining results for the control group (Group CP) are presented for comparison

Fig. 6

a Western blot analysis of TNF-α and IL-1β expression. b TNF-α expression levels in different groups over time. T5 and T3 exhibited significantly higher TNF-α levels at 1 week compared to the control (CT), with a slight decrease by week 2. Group T3 showed a statistically significant reduction in TNF-α expression by the second week, whereas Group T5 maintained relatively high levels. Groups P5 and P3 maintained consistently high TNF-α levels across both time points, with no significant changes. c IL-1β expression levels in different groups over time. A marked increase in IL-1β expression was seen in Group T5 at 1 week, which significantly decreased by the second week. Group T3 also demonstrated a reduction in IL-1β levels by week 2, approaching the control group (CT) levels. Groups P5 and P3 showed persistently high IL-1β expression with no significant reduction over time