Local opioids in a model of periodontal disease in rats

The blockade of kappa opioid receptors exacerbates alveolar bone resorption in rats

OBJECTIVES

Bone resorption associated to chronic diseases, such as arthritis and periodontitis, results from exacerbated immuno-inflammatory host response that leads to tissue breakdown. The significance of opioid pathways as endogenous modulators of inflammatory events has already been described. Thus, the aim of this work is to determine whether some of the main three opioid receptors are endogenously activated to prevent bone loss during experimentally-induced alveolar bone resorption.

DESIGN

This study used an experimental model of alveolar bone resorption induced by ligature in rats. A silk thread was placed around the 2nd maxillary molar of male Wistar rats. In the 3rd, 4th and 5th day after ligation the rats received a local injection of different concentrations of opioid antagonists Cyprodime, Naltrindole, or Nor-binaltorphimine, which specifically block mü, delta and kappa opioid receptors, respectively. In the 7th experimental day, rats were euthanized and their maxillae collected for evaluation of alveolar bone and fiber attachment loss, morphometric counting of osteoclasts and osteoblasts, as well as the levels of cytokines IL-1β, IFN-γ, and IL-6 by ELISA.

RESULTS

Selective antagonism of kappa opioid receptors, but not mü and delta, exacerbated alveolar bone resorption induced by ligature in rats. The increased bone loss associated with higher number of osteoclasts surrounding alveolar bone, although osteoblasts' counting remained unchanged. The concentrations of IL-1β and IL-6 in periodontal tissues were also significantly higher in the rats treated with the kappa antagonist.

CONCLUSION

Inhibiting kappa opioid receptors exacerbates alveolar bone resorption.

Tissue-selective inflammation in the oral cavity of the rat

In the current study, carrageenan (CG; 100-1000 μg/site) was injected intraorally in the cheeks of Holtzman or Wistar rats to evaluate the consequences of administration of a non-immunogenic stimulus in the orofacial region. Subsequent inflammation was measured as oedema (increased thickness of the cheek wall using digital calipers), relative to the other cheek injected with saline. Oedema formation and tissue collection for histopathological studies were assessed at 0.5, 1, 2, 3, 4, 6, 24, 48, 72, 96, 120 and 144 h after injection. In parallel, other groups of rats were injected with CG in the hind paw, to provide a reference response. The inhibitor of prostaglandin biosynthesis, indomethacin, and antagonists of histamine, serotonin and NK1 receptors were injected s.c., 0.5 h before CG. CG induced a dose-related oedema more rapidly from 0 to 2 h which lasted for at least 72 h, showing a biphasic profile (peak at 2 and 24 h), compared with the monophasic oedema induced in rat paws (maximal duration of 24 h). Histopathological analysis of the CG-injected cheek revealed oedema formation with little leukocyte recruitment at 1-3 h, mast cell degranulation at 6 h, and a mixed polymorphonuclear and mononuclear cell infiltrate by 24 h. Histamine and serotonin antagonists and indomethacin, but not the NK1 antagonist, decreased cheek oedema in the first 4 h following carrageenan. Taken together, our data indicated important differences in the pattern of inflammation between the oral cavity and the paw which will determine the therapeutic approach to the treatment of inflammatory conditions in the oral cavity.

Myeloperoxidase content is a marker of systemic inflammation in a chronic condition: the example given by the periodontal disease in rats

The study aimed to evaluate the suitability of myeloperoxidase (MPO) content as a local indicator of chronic inflammation, using the periodontal disease model. Anesthetized adult male Holtzman rats had their second left maxilar molar tied by a thread for 11 days and were then killed. Blood samples and photographic images from histopathological inflamed and noninflamed (contralateral) neighboring gingivomucosal specimens were collected for cell counts and MPO level analysis. Diseased animals were also treated with pharmacological tools such as the anti-inflammatory drug celecoxib or the opioid morphine. Increased blood neutrophils and local cell numbers characterized diseased animals. However, local MPO content was increased in inflamed and noninflamed tissues from diseased animals. Celecoxib and morphine reduced blood neutrophils and bilateral MPO content, but only celecoxib reduced local cell numbers in diseased animals. It is concluded that MPO content is a good indicator of a systemic rather than a local inflammation in a chronic inflammatory condition.

Increased leukotriene concentration in submandibular glands from rats with experimental periodontitis

OBJECTIVE AND DESIGN

In the present study, we investigated the relation between the inflammatory mediators such as nitric oxide, prostaglandins, and cysteinyl-leukotrienes with mucin release and the sympathetic system in submandibular glands from rats with experimental periodontitis.

MATERIALS OR SUBJECTS

Submandibular glands from rats with experimental periodontitis.

TREATMENT

For the first experiment, rats were treated with hydrocortisone sc, 1 mg/kg for 3 days. All other experiments were carried out in isolated submandibular glands from untreated rats. Submandibular glands were treated with cysteinyl-leukotrienes, isoproterenol, NDGA, FPL 55712, L-NMMA, Nio, Nz, AMG, indomethacin, DuP 697 and atenolol.

METHODS

Nitric oxide synthase activity, prostaglandin and cysteinyl-leukotriene productions and mucin secretion were determined. The Newman-Keuls statistical test was applied after analysis of variance.

RESULTS

In rats with periodontitis hydrocortisone-induced a 36.6% (P < 0.05) decrease in mucin release. Only cysteinyl-leukotriene production was increased in rats with ligature (79.2%, P < 0.001). Either the inhibition of cysteinyl-leukotriene production or the block of leukotriene receptor abolished the increase in mucin secretion by 25.6% (P < 0.05) and 37% (P < 0.01), respectively, in glands from rats with ligature. On the other hand, the presence of cysteinyl-leukotrienes in the incubation medium induced mucin release from submandibular glands. Atenolol diminished by 24% (P < 0.05), the increase in cysteinyl-leukotrienes observed in rats with periodontitis. Besides, isoproterenol induced cysteinyl-leukotriene production in both groups.

CONCLUSION

In submandibular glands from rats with periodontitis, the increment in mucin release and cysteinyl-leukotrienes production are related events and both are associated with the sympathetic system.

Role of systemic and local administration of selective inhibitors of cyclo-oxygenase 1 and 2 in an experimental model of periodontal disease in rats

BACKGROUND AND OBJECTIVE

Periodontal disease is an inflammatory condition of tooth-supporting tissues. Arachidonic acid metabolites have been implicated in development of periodontal disease, especially those derived from the cyclo-oxygenase (COX) pathway. This study investigated the role of inhibitors of cyclo-oxygenases (COX-1 and COX-2) in a model of periodontal disease in rats.

MATERIAL AND METHODS

A ligature was placed around the molar of rats. Losses of fiber attachment and of alveolar bone were measured morphometrically in histologically prepared sections. Infiltration of cells into gingival tissue surrounding the ligated tooth was also determined.

RESULTS

Systemic and local administration of non-selective and selective COX-2 inhibitors, preventively, resulted in significant reduction of the losses of fiber attachment and alveolar bone, as well as decreased leukocyte numbers in gingival tissue. Preventive selective inhibition of COX-1 was as effective as COX-2 inhibition in reducing local fiber attachment loss and cell migration, but did not prevent alveolar bone loss.

CONCLUSION

Our results provide evidence for participation of COX-1 and COX-2 in early stages of periodontal disease in rats. Furthermore, local administration of COX inhibitors reduced the signs of periodontal disease to the same extent as systemic treatment. Therapeutic approaches incorporating locally delivered anti-inflammatory drugs could be of benefit for patients suffering from periodontal disease.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Crucial role of peripheral kappa-opioid receptors in a model of periodontal disease in rats

BACKGROUND AND OBJECTIVE

Periodontal disease is a chronic inflammatory condition of the tooth supporting tissues, the periodontium. Opioids have been shown to account for the relief of various chronic and acute inflammatory conditions. The aim of the present study was to investigate the participation of peripheral opioid receptors in development of periodontal disease.

MATERIAL AND METHODS

Morphine and selective agonists and antagonists of opioid receptors were used in an experimental model of ligature-induced periodontal disease in rats. To evaluate the development of disease, the loss of fiber attachment, alveolar bone and number of cells in periodontal tissues were assessed. Measurements of these indicators were obtained by morphometric analysis of histological sections of periodontal-diseased tissues stained with hematoxylin and eosin.

RESULTS

Local administration of either morphine or a selective kappa-opioid agonist for three consecutive days from the onset of periodontal disease reduced the loss of periodontal tissues, without changing the number of leukocytes in inflamed periodontium. Nor-binaltorphimine, a selective kappa-antagonist, reversed the beneficial effects of both morphine and the compound U-50,488 in this model. The use of either an agonist or an antagonist of delta-opioid receptors, however, did not affect disease progression.

CONCLUSION

Our results showed that the beneficial effect of opioids in periodontal disease depended mainly on the activation of specific kappa-opioid receptors located in the periphery. Activation of such receptors could be considered in the management of periodontal disease, since it would not present the classical central side-effects associated with opioid use.

Sodium hyaluronate accelerates the healing process in tooth sockets of rats

OBJECTIVE

In this study we evaluated the effects of sodium hyaluronate (HY) in the healing process of tooth sockets of rats.

DESIGN

Immediately after the extraction of the upper first molars of male Holtzman rats, right sockets were treated with 1% HY gel (approximately 0.1 ml), while left sockets were used as control (blood clot). The animals were sacrificed at 2, 7, and 21 days after tooth extraction and upper maxillaries processed for histological and morphometric analysis of the apical and medium thirds of the sockets. Carbopol, an inert gel, was used to evaluate the mechanical effect of gel injection into sockets. Expression of bone morphogenetic protein-2 (BMP-2) and osteopontin (OPN) was determined by immunohistochemistry at 1, 2, 3, 4, 5, and 7 days after tooth extraction.

RESULTS

Histological analysis showed that HY treatment induced earlier trabecular bone deposition resulting in a bone matrix more organized at 7 and 21 days after tooth extraction. Also, HY elicited significant increase in the amount of bone trabeculaes at 7 and 21 days after tooth extraction (percentage of trabecular bone area at 7 days: 13.21+/-4.66% vs. 2.58+/-1.36% in the apical third of control sockets) and in the vessels counting at 7 days. Conversely, the number of cell nuclei was decreased in HY-treated sockets. Additionally, expression of BMP-2 and OPN was enhanced in HY-treated sockets compared with control sockets.

CONCLUSIONS

These findings suggest that HY accelerates the healing process in tooth sockets of rats stimulating the expression of osteogenic proteins.