| Heme oxygenase(HO) is an rate-limiting enzyme that catalyzes the degradation of heme to yield the linear tetrapyrrole biliverdin, and one atom each of iron and carbon monoxide(CO).According to recent study, there has been a special interest in the potential physiological and pathological roles that may be played by these breakdown products. The HO enzyme exists in three isoforms: HO-1(inducible HO), HO-2 (constitutive HO) and HO-3(low catalytic activity). Heme oxygenase enzyme has been detected in almost all species and in almost all tissues and it mainly stays in mitochondrial and cytosolic.The HO-1 and HO-2 can play many roles in physiological and pathological process as we know, but the mechanism of these roles has not been made clearly. However, people have realized that the potential physiological and pathological roles of HO may be played by these breakdown products, as CO, iron and biliverdin, especially by CO. A new kind of gaseous molecule, exogenous carbon monoxide(CO) recently emerges and shares some of the chemical and biological properties ofnitric oxide(NO). It can play an biology effect in many process, like relaxation of blood vessels, controlling the proliferation of smooth muscle cell(SMC), cellular protection, anti-inflammation and anti-tumor,etc,by cGMP-dependent path and/or no-cGMP-dependent path.The blood flow in the dental pulp , which is a highly vascularized tissue, is regulated by a variety of endogenous mediators. Many authors have studied the hemodynamics of the dental pulp by many different means. Recently, people have realized that gaseous molecule may play an important role in the regulation of dental vascular homeostasis and have done many studies about it. These studies mainly focus on the involvement of the L-arginine/nitric oxide pathway in the regulatory mechanism. However, there are scarcely any data regarding the involvement of the HO/CO pathway in the regulatory mechanism. Another characteristic of dental pulp tissue is that it has the function of reparative regeneration in response to environmental stimuli in a certain extent. Reactionary dentin is secreted by surviving odontoblasts in response to stimuli, leading to an increase in metabolic activities of the cells. Accoding to recent study, dental pulp cells can differentiate to become odontoblasts, osteoblasts, chondroblasts and fibroblasts in different transplanted environment. The complicated process of cellular differentiation needs the cooperation of many kinds of growth-factors, ground substance and cellular characteristics and the preciselymechanism of this process has not been illuminated yet, although many kinds of hypothesis has been posed.Since the last stage of 19th, many studies have showed that nitric oxide synthase(NOS) express in human dental pulp tissue widely and nitric oxide (NO) can regulate the pulp blood flow and pulp pressure and even play a part in the process of dentinification and cellular differentiation. In view of CO, as a new kind of gaseous molecule, has many egregious resemblances with NO and has so many important biological roles in organism, we presume that the HO-CO system is likely to take part in the physiological and pathological process of dental tissue. In 2006, people found the expression of HO in human dental pulp tissue and realized the cellular protection role of HO during the early phase of pulp inflammation through a study performed by Kyung-San Min. However, little is known about the precisely role of HO-CO system in physiological and pathological process of dental pulp. Furthermore, there is no other study concerning the distribution of HO in human dental pulp tissue. So we want to investigate the distribution and expression of HO-1, HO-2 in human healthy dental pulp tissue by morphological researching means and initially approach the role of the HO-CO system in dental pulp tissue; we also hope to perform some preparative works for thoroughly studying of the relationship between gaseous molecule and the physiological and pathological process of dental pulp.The purpose of present studies were that the distribution and expression of HO-1, HO-2 in human healthy dental pulp tissue was investigated by immunohistochemical method and the role of the HOCO system in dental pulp tissue was initially approached . By this study, we want to perform some preparative works for thoroughly studying of the relationship between gaseous molecule and the physiological and pathological process of dental pulp ; we also want to do some groping work for studying further about the specific mechanisms of many complicated physiological and pathological process of dental pulp.Material and Methods30 pulp tissue were obtained from clinically extracted human healthy premolars and third molars. The expression and distribution of HO-1,HO-2 in human dental pulp tissue were detected by means of SABC immunohistochemical technology.Result1. HO-1, HO-2 immunoreactivity were both observed in pulp vascular endothelial cell. The endothelial cells of arteriole and venule showed HO-1 positive strongly, but HO-2 positive weakly; the endothelial cells of blood capillary showed HO-1 positive weakly or no HO-1 immunoreactivity, but HO-2 positive strongly.2. HO-1, HO-2 immunoreactivity were both observed in odontoblasts , that was especially expressed distinct near the predentin.3. HO-1, HO-2 immunoreactivity were both observed in some fibroblasts and maybe some undifferentiated mesenchymal cells around the blood vessel.4. HO-1, HO-2 immunoreactivity were both observed in some nerve fibers in pulp, but weakly.Conclusion1. The positive expression of HO-1, HO-2 in vascular endothelial cells suggests that HO-CO system may play an important role in human dental pulp flow regulation.2. The expression of HO-1, HO-2 in odontoblasts suggests that they may take part in dentin production and its calcifying.3. The expression of HO-1 in fibroblasts around the blood vessel suggests that it may have some relationship with dental pulp cells metabolism, differentiation and tissue reparative regeneration.
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