Nitric Oxide Synthase in Healthy and Inflamed Human Dental Pulp

Abstract

Nitric oxide synthase (NOS) plays a significant role in the pathogenesis of pulpitis. In this study, we hypothesized the existence of endothelial (eNOS) and inducible (iNOS) enzyme isoforms in human dental pulp. Extracted third molar pulps were divided into groups based on clinical diagnosis: healthy, hyperemic, and irreversible pulpitis. We have localized the eNOS and iNOS by immunohistochemistry and have tested their mRNA expression by RT-PCR and protein levels by Western blots. eNOS is present in the endothelial cells and odontoblasts of the healthy pulp, but an elevation of eNOS mRNA and protein levels with a concomitant dilation of vessels was characteristic under pathological conditions. Healthy pulp tissue failed to exhibit any iNOS; however, acute inflammation enhanced the mRNA and protein levels of iNOS, mainly in the leukocytes. There are differences in localization and expression between eNOS and iNOS in healthy and inflamed dental pulp.

Nitric Oxide-Induced Apoptosis of Human Dental Pulp Cells Is Mediated by the Mitochondria-Dependent Pathway

“…eNOS is localized in endothelial cells and odontoblasts of the human dental pulp cells [11], indicating that NO synthesized by eNOS is responsible for regulation of the microcirculation within the pulp chamber and may control proliferation and differentiation of odontoblasts [12]. iNOS is expressed in the inflamed dental pulp cells and is mainly involved in inflammatory process and immune reaction [13-15]. The dental pulp cells abundantly express three NOS isoforms such as eNOS, nNOS and iNOS, which are known to play a pivotal role in physiologic and pathologic processes [11-13].…”

Production and physiological role of NO in the oral cavity

“…In addition to odontoblasts, eNOS was also found to be expressed in vascular endothelial cells and fibroblasts (Fig. 1) [14], [15], [16]. NO produced by eNOS in vascular endothelial cells was suggested to be involved in vascular dilation, which is similar to that in many other tissues [16], [17], [18].…”

“…Regarding NOS in human dental pulp, nNOS and eNOS are known to be expressed in odontoblasts, whereas iNOS is not under normal conditions [14], [15], [16]. The function of NO produced by nNOS and eNOS expressed in odontoblasts was examined, and its involvement in the transmission of pain stimulation has been suggested [14].…”

“…Although absent in healthy dental pulp, RT-PCR and Western blotting revealed the expression of iNOS at the mRNA and protein levels with acute inflammation in dental pulp [15]. This iNOS is considered to be derived from white blood cells that migrate from blood vessels in response to pulpitis [15].…”

“…This iNOS is considered to be derived from white blood cells that migrate from blood vessels in response to pulpitis [15]. Fan et al [20] exposed dental pulp in order to induce chronic tooth inflammation in rats, examined the role of NOS in the trigeminal ganglion and trigeminal nucleus caudalis, and found that NO and NOS were crucially involved in both peripheral and central nociceptive information.…”