Effects of capsaicin in temporomandibular joint arthritis in rats

Capsaicin and Its Role in Chronic Diseases

A significant number of experimental and clinical studies published in peer-reviewed journals have demonstrated promising pharmacological properties of capsaicin in relieving signs and symptoms of non-communicable diseases (chronic diseases). This chapter provides an overview made from basic and clinical research studies of the potential therapeutic effects of capsaicin, loaded in different application forms, such as solution and cream, on chronic diseases (e.g. arthritis, chronic pain, functional gastrointestinal disorders and cancer). In addition to the anti-inflammatory and analgesic properties of capsaicin largely recognized via, mainly, interaction with the TRPV1, the effects of capsaicin on different cell signalling pathways will be further discussed here. The analgesic, anti-inflammatory or apoptotic effects of capsaicin show promising results in arthritis, neuropathic pain, gastrointestinal disorders or cancer, since evidence demonstrates that the oral or local application of capsaicin reduce inflammation and pain in rheumatoid arthritis, promotes gastric protection against ulcer and induces apoptosis of the tumour cells. Sadly, these results have been paralleled by conflicting studies, which indicate that high concentrations of capsaicin are likely to evoke deleterious effects, thus suggesting that capsaicin activates different pathways at different concentrations in both human and rodent tissues. Thus, to establish effective capsaicin doses for chronic conditions, which can be benefited from capsaicin therapeutic effects, is a real challenge that must be pursued.

Differential expression of connexins in trigeminal ganglion neurons and satellite glial cells in response to chronic or acute joint inflammation

Trigeminal nerve activation in response to inflammatory stimuli has been shown to increase neuron-glia communication via gap junctions in trigeminal ganglion. The goal of this study was to identify changes in the expression of gap junction proteins, connexins (Cxs), in trigeminal ganglia in response to acute or chronic joint inflammation. Although mRNA for Cxs 26, 36, 40 and 43 was detected under basal conditions, protein expression of only Cxs 26, 36 and 40 increased following capsaicin or complete Freund's adjuvant (CFA) injection into the temporomandibular joint (TMJ). While Cx26 plaque formation between neurons and satellite glia was transiently increased following capsaicin injections, Cx26 plaque formation between neurons and satellite glia was sustained in response to CFA. Interestingly, levels of Cx36 and Cx40 were only elevated in neurons following capsaicin or CFA injections, but the temporal response was similar to that observed for Cx26. In contrast, Cx43 expression was not increased in neurons or satellite glial cells in response to CFA or capsaicin. Thus, trigeminal ganglion neurons and satellite glia can differentially regulate Cx expression in response to the type and duration of inflammatory stimuli, which likely facilitates increased neuron-glia communication during acute and chronic inflammation and pain in the TMJ.

Repression of calcitonin gene-related peptide expression in trigeminal neurons by a Theobroma cacao extract

ETHNOPHARMACOLOGICAL RELEVANCE

Cocoa bean preparations were first used by the ancient Maya and Aztec civilizations of South America to treat a variety of medical ailments involving the cardiovascular, gastrointestinal, and nervous systems. Diets rich in foods containing abundant polyphenols, as found in cocoa, underlie the protective effects reported in chronic inflammatory diseases. Release of calcitonin gene-related peptide (CGRP) from trigeminal nerves promotes inflammation in peripheral tissues and nociception.

AIM OF THE STUDY

To determine whether a methanol extract of Theobroma cacao L. (Sterculiaceae) beans enriched for polyphenols could inhibit CGRP expression, both an in vitro and an in vivo approach was taken.

RESULTS

Treatment of rat trigeminal ganglia cultures with depolarizing stimuli caused a significant increase in CGRP release that was repressed by pretreatment with Theobroma cacao extract. Pretreatment with Theobroma cacao was also shown to block the KCl- and capsaicin-stimulated increases in intracellular calcium. Next, the effects of Theobroma cacao on CGRP levels were determined using an in vivo model of temporomandibular joint (TMJ) inflammation. Capsaicin injection into the TMJ capsule caused an ipsilateral decrease in CGRP levels. Theobroma cacao extract injected into the TMJ capsule 24h prior to capsaicin treatment repressed the stimulatory effects of capsaicin.

CONCLUSIONS

Our results demonstrate that Theobroma cacao extract can repress stimulated CGRP release by a mechanism that likely involves blockage of calcium channel activity. Furthermore, our findings suggest that the beneficial effects of diets rich in cocoa may include suppression of sensory trigeminal nerve activation.

Neuron-glia signaling in trigeminal ganglion: implications for migraine pathology

OBJECTIVE

The goal of this study was to investigate neuronal-glial cell signaling in trigeminal ganglia under basal and inflammatory conditions using an in vivo model of trigeminal nerve activation.

BACKGROUND

Activation of trigeminal ganglion nerves and release of calcitonin gene-related peptide (CGRP) are implicated in the pathology of migraine. Cell bodies of trigeminal neurons reside in the ganglion in close association with glial cells. Neuron-glia interactions are involved in all stages of inflammation and pain associated with several central nervous system (CNS) diseases. However, the role of neuron-glia interactions within the trigeminal ganglion under normal and inflammatory conditions is not known.

METHODS

Sprague-Dawley rats were utilized to study neuron-glia signaling in the trigeminal ganglion. Initially, True Blue was used as a retrograde tracer to localize neuronal cell bodies in the ganglion by fluorescent microscopy and multiple image alignment. Dye-coupling studies were conducted under basal conditions and in response to capsaicin injection into the TMJ capsule. S100B and p38 expression in neurons and glia were determined by immunohistochemistry following chemical stimulation. CGRP levels in the ganglion were measured by radioimmunoassay in response to capsaicin. In addition, the effect of CGRP on the release of 19 different cytokines from cultured glial cells was investigated by protein microarray analysis.

RESULTS

In unstimulated control animals, True Blue was detected primarily in neuronal cell bodies localized in clusters within the ganglion corresponding to the V3 region (TMJ capsule), V2 region (whisker pad), or V1 region (eyebrow and eye). However, True Blue was detected in both neuronal cell bodies and adjacent glia in the V3 region of the ganglion obtained from animals injected with capsaicin. Dye movement into the surrounding glia correlated with the time after capsaicin injection. Chemical stimulation of V3 trigeminal nerves was found to increase the expression of the inflammatory proteins S100B and p38 in both neurons and glia within the V3 region. Unexpectedly, increased levels of these proteins were also observed in the V2 and V1 regions of the ganglion. CGRP and the vesicle docking protein SNAP-25 were colocalized in many neuronal cell bodies and processes. Decreased CGRP levels in the ganglion were observed 2 hours following capsaicin stimulation. Using protein microarray analysis, CGRP was shown to differentially regulate cytokine secretion from cultured trigeminal ganglion glia.

CONCLUSIONS

We demonstrated that activation of trigeminal neurons leads to changes in adjacent glia that involve communication through gap junctions and paracrine signaling. This is the first evidence, to our knowledge, of neuron-glia signaling via gap junctions within the trigeminal ganglion. Based on our findings, it is likely that neuronal-glial communication via gap junctions and paracrine signaling are involved in the development of peripheral sensitization within the trigeminal ganglion and, thus, are likely to play an important role in the initiation of migraine. Furthermore, we propose that propagation of inflammatory signals within the ganglion may help to explain commonly reported symptoms of comorbid conditions associated with migraine.

Intraarticular induction of interleukin-1beta expression in the adult mouse, with resultant temporomandibular joint pathologic changes, dysfunction, and pain

OBJECTIVE

To examine the effects of intraarticular induction of interleukin-1beta (IL-1beta) expression in adult mice.

METHODS

We used somatic mosaic analysis in a novel transgenic mouse with an inducible IL-1beta transcription unit. Transgene activation was induced by Cre recombinase in the temporomandibular joints (TMJs) of adult transgenic mice (conditional knockin model). The effects of intraarticular IL-1beta induction were subsequently evaluated at the cellular, histopathologic, and behavioral levels.

RESULTS

We developed transgenic mice capable of germline transmission of a dormant transcription unit consisting of the mature form of human IL-1beta as well as the reporter gene beta-galactosidase driven by the rat procollagen 1A1 promoter. Transgene activation by a feline immunodeficiency virus Cre vector resulted in histopathologic changes, including articular surface fibrillations, cartilage remodeling, and chondrocyte cloning. We also demonstrated up-regulation of genes implicated in arthritis (cyclooxygenase 2, IL-6, matrix metalloproteinase 9). There was a lack of inflammatory cells in these joints. Behavioral changes, including increased orofacial grooming and decreased resistance to mouth opening, were used as measures of nociception and joint dysfunction, respectively. The significant increase in expression of the pain-related neurotransmitter calcitonin gene-related peptide (CGRP) in the sensory ganglia as well as the auxiliary protein CGRP receptor component protein of the calcitonin-like receptor in the brainstem further substantiated the induction of pain.

CONCLUSION

Induction of IL-1beta expression in the TMJs of adult mice led to pathologic development, dysfunction, and related pain in the joints. The somatic mosaic model presented herein may prove useful in the preclinical evaluation of existing and new treatments for the management of joint pathologic changes and pain, such as in osteoarthritis.

Statistical correlation between pharyngitis and temporomandibular joint disease

OBJECTIVE

The objective of this study was to evaluate the upper respiratory infection (URI) as an aggravating factor in the established temporomandibular joint (TMJ) disease.

PATIENTS AND METHODS

Four hundred seventeen patients suffering from temporomandibular disorder (TMD) were selected and investigated by means of questionnaires and clinical examinations. After excluding the patients with only muscle disorders, 283 patients were included for the association study between TMJ disease and infectious conditions. The screened infectious conditions were otitis media, maxillary sinusitis/rhinitis, and pharyngitis/tonsillitis. The chi-square test was used to determine the association between variables and stepwise logistical regression was then used.

RESULTS

The prevalence of maxillary sinusitis/rhinitis in TMD patients was 7.0%. The patients who had mouth-opening limitation were 9.93 times more likely to have maxillary sinusitis/rhinitis than those without ( P = .0004). The prevalence of tonsillitis/pharyngitis in TMD patients was 9.1%. The patients who had mouth-opening limitation were 3.50 times more likely to have tonsillitis/pharyngitis than those without it ( P = .0028). The patients who had TMJ capsulitis were 3.91 times more likely to have tonsillitis/pharyngitis than those without it ( P = .0028).

CONCLUSION

The conclusion is made that pharyngitis/sinusitis is significantly associated with some clinical symptoms of TMD. The infection of closely related anatomical structures with TMJ may have an influence on TMJ symptoms. Thus, pharyngitis/sinusitis in the established TMD patients can be a significant warning sign for TMJ symptoms to appear shortly thereafter.

Hematogenous infection of the human temporomandibular joint

Objective This study was designed to discover the relationship between bacteremia and the presence of specific bacterial species in the synovial fluid of the human temporomandibular joint (TMJ). Study design Sixteen volunteers (female to male, 1:2.2; average age, 30.00 +/- 9.93 years) who received operations via intraoral incision participated in this study. Samples from the blood and TMJ synovial fluid of the patients were taken preoperatively and postoperatively and analyzed by PCR assays with specific primers for the clinically important bacteria Staphylococcus aureus , Streptococcus mitis , and beta-hemolytic Streptococcus . Results PCR-based assays revealed the occurrence of S aureus in 68.8% and 50% of the total blood and synovial fluid samples collected immediately after the operations, which statistically differed from the preoperative samples ( P < .05). However, the frequency of the other bacteria, S mitis and beta-hemolytic Streptococcus , in pre- and postoperative blood samples had no such a difference ( P > .05). The chi-square test showed a significant association between the presence of S aureus in the blood and in TMJ synovial fluid (chi 2 = 6.409, P < .05), and the probability of hematogenous infection of the TMJ was estimated as 55.5%. Conclusion Hence, the data obtained provided evidence that the invasion of S aureus into TMJ synovial fluid was due to the presence of these bacteria in the blood. To our knowledge, this is the first report of the bacteremia-related mechanism of S aureus invasion in the human TMJ.

The presence of bacteria in the synovial fluid of the temporomandibular joint and clinical significance: preliminary study

PURPOSE

The objective of this study was to find any relation between the presence of specific bacterial species in the synovial fluid of the temporomandibular joint (TMJ) and clinical parameters.

PATIENTS AND METHODS

We studied 43 patients (male-to-female ratio, 1:1.69; average age, 34.37 +/- 14.55 years). Thirty-three patients had a displaced disc in the TMJ (DD group), and 10 patients did not have a displaced disc of the TMJ or any symptom related to TMJ disorders (NDD group). Clinical examinations were made to determine maximum mouth opening, joint sounds, previous trauma history, systemic disease, and TMJ pain. Six bacterial species that were reported in other studies were chosen to evaluate the presence of bacteria in the TMJ for this study.

RESULTS

Mycoplasma genitalium was most frequently detected in synovial fluid (86.0%). Staphylococcus aureus, Mycoplasma fermentans/orale, Actinobacillus actinomycetemcomitans, and Streptococcus mitis were detected in 51.2%, 37.2%, 25.6%, and 7.0% of samples, respectively. beta-Hemolytic Streptococcus was not detected. The prevalence of S aureus was significantly higher in the DD group than in the NDD group (P <.05). The patients who had M. fermentans/orale were 5.40 times more likely to be younger than 30 years than were those without M. fermentans/orale (P <.05). Those with M. genitalium were 5.81 times more likely to be female than were those without M. genitalium (P <.05).

CONCLUSION

The presence of S. aureus in TMJ synovial fluid was related to TMJ disorder symptoms and clinical parameters seemed to be influenced by bacterial presence in TMJ synovial fluid.

NGF modulates CGRP synthesis in human B-lymphocytes: a possible anti-inflammatory action of NGF?

We investigated whether the sensory neuropeptide, calcitonin gene-related peptide (CGRP), could be synthesised by human lymphocytes. Our results indicate that in activated B-cells, there is a strong expression of CGRP gene transcripts, which is almost absent in resting cells. Since B-cells autocrinally produce NGF, the neutralisation of endogenous NGF by anti-NGF antibodies resulted in a marked reduction in CGRP expression in both resting and activated B-cells. Thus, NGF appears to directly affect the synthesis of CGRP in B-cells as in sensory neurons. By regulating CGRP synthesis in lymphocytes and neuronal cells, NGF can influence the intensity and duration of the immune response.

Modulation of the inflammatory response in the rat TMJ with increasing doses of complete Freund's adjuvant

OBJECTIVES

Acute inflammation stresses the physiological system, which must respond in order to reestablish homeostasis. The purpose of this study was to determine whether bilateral temporomandibular joint (TMJ) injections of different doses of Complete Freund's Adjuvant (CFA) produced dose-dependent changes in biologic markers of acute inflammation. The ability to establish an animal model with varying degrees of joint inflammation would allow evaluation of agents or conditions that could modulate the severity of the disease.

DESIGN

The TMJs of three groups of male Sprague-Dawley rats were injected with CFA containing varying doses of Mycobacterium tuberculosis (MT). A group of non-injected and a group of saline injected rats were used as controls. Food intake, body weights, swelling and chromodacryorrhea were recorded daily. Interleukin-1 beta (IL-1 beta) and corticosterone levels were assayed and condylar cartilage thickness was measured 48 h after injections.

RESULTS

Twenty-four hours post-injection, bilateral TMJ swelling and chromodacryorrhea were significantly (P< 0.05) increased following 10 microg of MT and further increased with elevated MT dose. In the CFA groups food intake was attenuated (P< 0.01) 24 and 48 h post-injection and negatively correlated with dose at 24 h. Body weight was also negatively correlated with dose. TMJ retrodiscal tissues IL-1 beta was increased (P< 0.05) in a dose-dependent manner. CFA increased corticosterone (P< 0.05), but this elevation was not dose dependent. Condylar cartilage thickness was decreased in a dose-dependent manner.

CONCLUSIONS

These data suggest that an intermediate dose of CFA can be used to effect submaximal levels of TMJ inflammation that will allow experimental modulation in future studies.

Meal pattern analysis in response to temporomandibular joint inflammation in the rat

Inflammation of the temporomandibular joint (TMJ) can alter behavioral responses such as food intake and mobilize stress hormones. The hypothesis of this study was that food intake and diurnal corticosterone analysis can be used as indicators of adjuvant-induced TMJ inflammation. Groups of rats received adjuvant or no injections at the beginning of the resting (AM) or activity (PM) phase. Forty-eight hours (early) or 6 weeks (late) after adjuvant injection, plasma corticosterone was assayed and food intake was recorded. Food intake was suppressed up to 4 days post-injection. As expected, the non-injected group showed low AM and high PM corticosterone. AM corticosterone was elevated, but PM corticosterone was attenuated in both early- and late-stage-injected rats. A computerized pair-fed experiment showed that adjuvant-induced hypophagia did not alter corticosterone levels. Meal pattern analysis revealed decreased food intake due to a decrease in the number of meals taken. Notably, meal size remained the same but meal duration increased. This model demonstrated that food intake and stress hormone analysis could be used as indicators for sequelae of adjuvant-induced TMJ inflammation.

Calcitonin gene-related peptide and substance P immunoreactivity in rat trigeminal ganglia and brainstem following adjuvant-induced inflammation of the temporomandibular joint

The immunoreactivity of two inflammatory mediators, calcitonin gene-related peptide (CGRP) and substance P, was measured in the trigeminal ganglia and brainstem to characterize an adjuvant-induced inflammation within the rat temporomandibular joint at various acute (6, 24 and 48 h) and intermediate (10 day) time intervals. Concentrations of adjuvant-related neuropeptides were compared to those in both contralateral vehicle-related tissues and non-injected controls. By 6 h, CGRP immunoreactivity in the trigeminal ganglia was significantly above that in contralateral vehicle-injected tissue. The CGRP had decreased at each of the following time-points, but remained significantly elevated at 10 days. Substance P in the ganglion on the injected side was significantly increased for all four time periods. In brainstem subnucleus caudalis, CGRP was significantly increased for all four time periods. Substance P immunoreactivity in the subnucleus caudalis was significantly increased for the initial three time periods, but by day 10 had been reduced to that of the control. These data show that the pattern of changes in neuropeptides following the induction of inflammation is different between substance P and CGRP. Moreover, the pattern of change varies between the brainstem and the trigeminal ganglion. This suggests that the two neuropeptides may have different roles in the inflammatory process, and that this process may be modulated by different mechanisms at the brainstem and ganglion.