Expression And Significance Of INOS And VEGF During Rat Dental Pulp Injury And Reparation

ObjectiveInducible nitric oxide synthase (iNOS) is one of the most important limiting factor about the synthesis of nitric oxide (NO) in body, which can make the body to produce higher concentration of NO than physiological[1]. And NO is an important regulator in the process of cell information transmission, which extensively involved in the process of physiological and pathological like a double-edged sword[2].After subject to various incentives, such as injury, root fracture, orthodontic force and reversible pulpitis, some of the pulp cells may secrete a variety of peptide growth factors, which can increase vascular permeability and promote angiogenesis. Angiogenesis is a prerequisite for successfully repair of dentin, and vascular endothelial growth factor (VEGF) is one of an important vascular endothelial growth factors.When subject to various incentives, such as trauma, pulp can produce a series of reaction, including againsting stimulus and carrying out self-repair capacity. But the mechanism of pulp repair is not clear. This study aimed to explore the expression of iNOS and VEGF in rat dental pulp after injury, reveal the relationship between the two, and show the different distribution of iNOS expression after direct pulp capping with different pulp capping agent, in order to understand the role of iNOS in the process of dental pulp injury and repair, and find out the relationship between iNOS and VEGF.Materials and MethdodsPreparation of rat dental pulp mechanical injury model and direct pulp capping model with CH (calcium hydroxide) and MTA (mineral trioxide aggregate). The rats will be executed at immediately, 1d,3d,7d,14d,21d and 28d, heart perfusion fixed with 4% paraformaldehyde, drawn, decalcification, embedded in paraffin, prepare sections, and to observe the pathological changes and the expression of iNOS and VEGF in the group of mechanical injure, and the expression of iNOS in capping groups after immunohistochemistry (SABC). Software for image analysis was used to test the optical density (OD) of each Specimen. The data were analyzed by one-way ANOVA, pearson correlation analysis and paired t-test with SPSS 13.0, P<0.05 was considered statistically significant.Results1,In normal pulp, the stain of iNOS was negative; immediately after pulp injury was low-level expression while 3days was strong positive; after 7 days the stain became less positive gradually till 21 days approach to normal. The expression mainly located in neutrophils, fibroblasts, odontoblasts, and a few endothelial cells. The expression intensity of iNOS was different from normal controls after injury 1d,3d,7d,14d.2,The VEGF stained strongly positive, in vascular endothelial cells, weakly positive or no color in odontoblasts in normal pulp. After pulp injury, the staining of VEGF was markedly increased and then decreased, the strongest expression was at3 days,7days slightly decreased, and reduced to near normal levels at 28day. The expression mainly located in vascular endothelial cells, fibroblasts, neutrophils and some of the odontoblast. The expression intensity of VEGF was different from normal controls after injury 1d,3d,7d,14d.3,Pearson correlation analysis showed that iNOS and VEGF were positive correlation in the dental pulp injury and repair (r=0.817, P<0.05).4,In the two pulp capping groups, iNOS expression was weakly positive at immediately, while 3days was the most strongest positive; after 7 days the stain became less positive gradually till 21-28 days approach to normal. The degree of pulpitis in the group of MTA was lower than the CH, and reparative dentin was more than the CH group. The expression of iNOS in the group of CH was significantly higher than MTA, 3days after direct pulp capping.Conclusions1,In the process of rat dental pulp injury and repair, the expression of iNOS and VEGF expression was increased at first and then decreased, which has some relationship with the early inflammation and late repair degree and the expression of iNOS was correlated with VEGF.2,After direct pulp capping with CH, the degree of pulp inflammation and necrosis was worse than MTA, the expression of iNOS was significantly higher than MTA at 3 days.Maybe MTA can reduce the activity of iNOS in pulp, so that the degree of inflammation lower than the group of CH. The kind of pulp capping agents was impact on the pulp repairation and the expression of iNOS.