Tumor necrosis factor alpha enhances the sensitivity of rat trigeminal neurons to capsaicin.

Tumor necrosis factor alpha (TNFalpha), a pro-inflammatory cytokine, enhances the development of pain and hyperalgesia, although the molecular mechanisms are not well understood. This study evaluated the hypothesis that TNFalpha increases the sensitivity of rat trigeminal neurons to capsaicin via two different mechanisms triggered by either brief or sustained exposure to the cytokine. A brief (5 min) application of TNFalpha significantly sensitized capsaicin-evoked accumulation of intracellular calcium ([Ca2+]i) (226.4+/-37.7 nM vs. 167.5+/-31.3 nM) and increased capsaicin-evoked nocifensive behavior (78.3+/-9.7 vs. 30.9+/-3.6 s) as compared with vehicle pretreatment (P<0.01 for both). Sustained (30 min to 4 h) exposure of cultured neurons to TNFalpha evoked a twofold increase in mRNA transcript (P<0.05) and protein levels (P<0.01) of transient potential receptor vanilloid type 1 (TRPV1). This long-term up-regulation of TRPV1 expression by TNFalpha correlated with enhancement in capsaicin-induced calcitonin gene-related peptide release (P<0.05). Demonstration of colocalization of TNFalpha receptor subtypes I and II with TRPV1 in almost all (>90%) TRPV1 expressing neurons provides evidence consistent with a direct interaction on the same subpopulation of sensory neurons. In summary, our data demonstrate that TNFalpha directly enhances the sensitivity of rat trigeminal neurons to capsaicin via both rapid, non-genomic mechanisms as well as sustained genomic regulation in TRPV1 expression. Thus, increased sensitization and up-regulation of TRPV1 constitutes a potential mechanism by which TNFalpha mediates inflammatory hyperalgesia and pain.

Trigeminal nociceptors express prostaglandin receptors.

Orofacial inflammation is associated with prostaglandin release and the sensitization of nociceptive receptors such as the transient receptor potential subtype V(1) (TRPV(1)). We hypothesized that certain PGE(2) receptor subtypes (EP1-EP4) are co-expressed with TRPV(1) in trigeminal nociceptors and sensitize responses to a TRPV(1) agonist, capsaicin. Accordingly, combined in situ hybridization was performed with immunohistochemistry on rat trigeminal ganglia. We next evaluated the effects of specific EP2 and EP3 agonists (butaprost and sulprostone) in cultured trigeminal ganglia neurons. The results showed that EP2 and EP3 are expressed in trigeminal neurons (58% and 53% of total neurons, respectively) and are co-expressed in TRPV(1)-positive neurons (64% and 67 % of TRPV(1)-positive neurons, respectively). Moreover, most of the cells expressing EP2 or EP3 mRNA were of small to medium diameter (< 30 microm). The application of butaprost and sulprostone triggered neuropeptide exocytosis, and butaprost sensitized capsaicin responses. Analysis of these data, collectively, supports the hypothesis that prostaglandins regulate trigeminal TRPV(1) nociceptors via activation of the EP2 and EP3 receptors.

Oral Sciences PhD Program Enrollment, Graduates, and Placement: 1994 to 2016.

For decades, dental schools in the United States have endured a significant faculty shortage. Studies have determined that the top 2 sources of dental faculty are advanced education programs and private practice. Those who have completed both DDS and PhD training are considered prime candidates for dental faculty positions. However, there is no national database to track those trainees and no evidence to indicate that they entered academia upon graduation. The objective of this study was to assess outcomes of dental school-affiliated oral sciences PhD program enrollment, graduates, and placement between 1994 and 2016. Using the American Dental Association annual survey of advanced dental education programs not accredited by the Commission on Dental Accreditation and data obtained from 22 oral sciences PhD programs, we assessed student demographics, enrollment, graduation, and placement. Based on the data provided by program directors, the average new enrollment was 33, and graduation was 26 per year. A total of 605 graduated; 39 did not complete; and 168 were still in training. Among those 605 graduates, 211 were faculty in U.S. academic institutions, and 77 were faculty in foreign institutions. Given that vacant budgeted full-time faculty positions averaged 257 per year during this period, graduates from those oral sciences PhD programs who entered academia in the United States would have filled 9 (3.6%) vacant faculty positions per year. Therefore, PhD programs have consistently generated only a small pipeline of dental school faculty. Better mentoring to retain talent in academia is necessary. Stronger support and creative funding plans are essential to sustain the PhD program. Furthermore, the oral sciences PhD program database should be established and maintained by dental professional organizations to allow assessments of training models, trends of enrollment, graduation, and placement outcomes.

Integrins regulate opioid receptor signaling in trigeminal ganglion neurons.

The binding of integrins to the extracellular matrix results in focal organization of the cytoskeleton and the genesis of intracellular signals that regulate vital neuronal functions. Recent evidence suggests that integrins modulate G-protein-coupled receptor (GPCR) signaling in hippocampal neurons. In this study we evaluated the hypothesis that integrins regulate the mu opioid receptor in rat trigeminal ganglion neurons. For these studies, primary cultures of adult rat trigeminal ganglion neurons were used to demonstrate the colocalization of beta1 and beta3 integrins with mu opioid receptor in caveolin-1-rich membrane fractions, and at focal adhesions sites generated by integrin ligand binding. Furthermore, we show that the mu opioid receptor agonist, DAMGO ([D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin), inhibits cyclic AMP (cAMP) accumulation in response to prostaglandin E2 (PGE(2)) stimulation in bradykinin-primed, but not unprimed, cultured trigeminal ganglia neurons. Application of soluble GRGDS (Gly-Arg-Gly-Asp-Ser) peptides that bind specific integrins (i.e. RGD-binding integrins) completely abolished the DAMGO effect in bradykinin-primed trigeminal ganglia neurons, but did not alter bradykinin-mediated hydrolysis of phosphatidylinositol. Likewise, monospecific anti-beta1 and anti-beta3 integrin subunit antibodies blocked this DAMGO effect in bradykinin-primed trigeminal ganglia neurons. Indeed, application of anti-beta1 integrin subunit actually reversed DAMGO signaling, resulting in increased cAMP accumulation in these cells. This suggests that the relative amounts of specific activated integrins at focal adhesions may govern signaling by the mu opioid receptor, perhaps by altering interactions with G proteins (e.g. Galphai vs. Galphas). Collectively, these data provide the first evidence that specific integrins regulate opioid receptor signaling in sensory neurons.

Neuropeptide Y modulates effects of bradykinin and prostaglandin E2 on trigeminal nociceptors via activation of the Y1 and Y2 receptors.

BACKGROUND AND PURPOSE: Although previous studies have demonstrated that neuropeptide Y (NPY) modulates nociceptors, the relative contributions of the Y1 and Y2 receptors are unknown. Therefore, we evaluated the effect of Y1 and Y2 receptor activation on nociceptors stimulated by bradykinin (BK) and prostaglandin E2 (PGE2). EXPERIMENTAL APPROACH: Combined immunohistochemistry (IHC) with in situ hybridization (ISH) demonstrated that Y1- and Y2-receptors are collocated with bradykinin (2) (B2)-receptors in rat trigeminal ganglia (TG). The relative functions of the Y1 and Y2 receptors in modulating BK/PGE2-evoked CGRP release and increased intracellular calcium levels in cultured TG neurons were evaluated. KEY RESULTS: The Y1 and Y2 receptors are co-expressed with B2 in TG neurons, suggesting the potential for direct NPY modulation of BK responses. Pretreatment with the Y1 agonist [Leu31,Pro34]-NPY, inhibited BK/PGE2-evoked CGRP release. Conversely, pretreatment with PYY(3-36), a Y2 agonist, increased BK/PGE2 evoked CGRP release. Treatment with NPY evoked an overall inhibitory effect, although of lesser magnitude. Similarly, [Leu31,Pro34]-NPY inhibited BK/PGE2-evoked increases in intracellular calcium levels whereas PYY(3-36) increased responses. NPY inhibition of BK/PGE2-evoked release of CGRP was reversed by the Y1 receptor antagonist, BIBO3304, and higher concentrations of BIBO3304 significantly facilitated CGRP release. The Y2 receptor antagonist, BIIE0246, enhanced the inhibitory NPY effects. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that NPY modulation of peptidergic neurons is due to net activation of inhibitory Y1 and excitatory Y2 receptor systems. The relative expression or activity of these opposing receptor systems may mediate dynamic responses to injury and pain.

NGF up-regulates TRPA1: implications for orofacial pain.

The transient receptor potential ankyrin repeat 1 (TRPA1) channel is believed to be involved in many forms of acute and chronic hyperalgesia. Nerve Growth Factor (NGF) regulates chronic inflammatory hyperalgesia by controlling gene expression in sensory neurons, including genes involved in inflammatory hyperalgesia in the dental pulp. We hypothesized that NGF increases functional activities of the TRPA1 channel in trigeminal ganglion neurons. Here, we show that NGF induced a concentration- and time-dependent up-regulation of TRPA1 mRNA in trigeminal ganglia neurons, as detected by real-time RT-PCR and in situ hybridization. In addition, NGF evoked a time-dependent increase of mustard oil (MO)-evoked TRPA1 activation in trigeminal ganglia neurons. Collectively, these findings demonstrate that NGF participates in the functional up-regulation of TRPA1 in trigeminal ganglia neurons. These enhanced activities of TRPA1 could play an important role in the development of hyperalgesia following nerve injury and inflammation in the orofacial region.

The RNA binding and transport proteins staufen and fragile X mental retardation protein are expressed by rat primary afferent neurons and localize to peripheral and central axons.

Neuronal proteins have been traditionally viewed as being derived solely from the soma; however, accumulating evidence indicates that dendritic and axonal sites are capable of a more autonomous role in terms of new protein synthesis. Such extra-somal translation allows for more rapid, on-demand regulation of neuronal structure and function than would otherwise be possible. While mechanisms of dendritic RNA transport have been elucidated, it remains unclear how RNA is trafficked into the axon for this purpose. Primary afferent neurons of the dorsal root (DRG) and trigeminal (TG) ganglia have among the longest axons in the neuraxis and such axonal protein synthesis would be advantageous, given the greater time involved for protein trafficking to occur via axonal transport. Therefore, we hypothesized that these primary sensory neurons might express proteins involved in RNA transport. Rat DRG and TG neurons expressed staufen (stau) 1 and 2 (detected at the mRNA level) and stau2 and fragile x mental retardation protein (FMRP; detected at the protein level). Stau2 mRNA was also detected in human TG neurons. Stau2 and FMRP protein were localized to the sciatic nerve and dorsal roots by immunohistochemistry and to dorsal roots by Western blot. Stau2 and FMRP immunoreactivities colocalized with transient receptor potential channel type 1 immunoreactivity in sensory axons of the sciatic nerve and dorsal root, suggesting that these proteins are being transported into the peripheral and central terminals of nociceptive sensory axons. Based on these findings, we propose that stau2 and FMRP proteins are attractive candidates to subserve RNA transport in sensory neurons, linking somal transcriptional events to axonal translation.

Trigeminal nociceptors express TLR-4 and CD14: a mechanism for pain due to infection.

Although certain bacterial species appear to be risk factors for pain due to odontogenic infections, comparatively little is known about the potential mechanisms mediating this effect. In this study, we tested the hypothesis that trigeminal nociceptive neurons express the TLR4 or CD14 receptors, thus enabling sensory neurons to detect and respond to tissue levels of bacterial substances such as lipopolysaccharide (LPS). Immunohistochemical analyses of human and rat trigeminal neurons demonstrated that a capsaicin-sensitive subclass of nociceptors (defined by expression of TRPV1, a capsaicin receptor) expresses both TLR4 and CD14. Moreover, human dental pulp collected from patients with caries lesions demonstrated co-localization of TLR4 and CD14, with markers of peripheral sensory neurons. Collectively, these studies indicate that the capsaicin-sensitive subclass of trigeminal nociceptors expresses TLR4 and CD14. These results indicate that pain due to bacterial infections may result, in part, from direct activation of nociceptors by bacterial products such as LPS.

Tissue pH and temperature regulate pulpal nociceptors.

The TRPV1 receptor acts as a sensor for environmental changes in pH and temperature. Since many nociceptors express TRPV1, it is possible that local tissue-cooling may inhibit nociceptor activity via reduction of TRPV1 activation. The present study used isolated superfused rat dental pulp to test the hypothesis that capsaicin receptors are activated in inflamed tissue, as measured by alterations in neuropeptide release. We tested the hypothesis that alterations in the tissue temperature and pH of isolated superfused rat dental pulp regulate capsaicin-induced release of calcitonin gene-related peptide (CGRP). Application of capsaicin with increased proton concentration (i.e., lowered pH) produced a nearly two-fold increase in peak immunoreactive CGRP release, as compared with capsaicin applied at a pH of 7.4. Reduction in tissue temperature from 37 degrees C to 26 degrees C completely blocked the capsaicin effect. The study indicates that environmental stimuli regulate the activity of capsaicin-sensitive neurons innervating dental pulp, and these factors may be significant clinically in the development and amelioration of dental pain.

Role of Oxidized Lipids and TRP Channels in Orofacial Pain and Inflammation.

Acute or chronic inflammation comprises a highly prevalent type of orofacial pain and is mediated by the generation of endogenous agonists that activate numerous receptors expressed on terminals of trigeminal (TG) nociceptive afferent neurons. One such studied receptor is transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is a ligand-gated cation channel that is expressed on a major subclass of nociceptors and is found in many orofacial tissues, including dental pulp. Antagonists to TRPV1 reveal an important role for this channel in mediating hypersensitivity in preclinical models of inflammatory or neuropathic pain. Recent studies have demonstrated that endogenous TRPV1 agonists are generated by oxidation of omega-6 polyunsaturated fatty acids, including both linoleic acid and arachidonic acid. A major mechanism triggering the release of oxidative linoleic acid metabolites (OLAMs) and oxidative arachidonic acid metabolites (OAAMs) is the action of oxidative enzymes. Oxidative enzymes such as cytochrome P450 isozymes are rapidly upregulated in TG neurons after orofacial inflammation and increase the capacity of TG neurons to generate OLAMs. Cytochrome P450 isozymes are also increased in immune cells in irreversibly inflamed human dental pulp, and extracts of this tissue have significantly increased capacity to generate OLAMs. Together, these studies point to a novel pain mechanism involving the enzymatic generation of endogenous OLAM and OAAM agonists of TRPV1. This finding provides a rationale for an entirely new class of analgesics by inhibition of oxidative enzyme activity.

Phosphatidylethanolamine methyltransferase: evidence for influence of diet fat on selectivity of substrate for methylation in rat brain synaptic plasma membranes.

Male weanling rats were fed diets containing 20% (w/w) fat differing in fatty acid composition for 24 days. Synaptic plasma membranes were isolated from the brain and the fatty acid composition of phosphatidylethanolamine and phosphatidylcholine was determined. In vitro assays of phosphatidylethanolamine methyl-transferase activity were performed on fresh membrane samples to assess effect of dietary fat on the rate of phosphatidylethanolamine methylation for phosphatidylcholine synthesis via the phosphatidylethanolamine methyltransferase pathway. Dietary level of n-6 and ratio of n-6 to n-3 fatty acids influenced membrane phospholipid fatty acid composition and activity of the lipid-dependent phosphatidylethanolamine methyltransferase pathway. Rats fed a diet rich in n-6 fatty acids produced a high ratio of n-6/n-3 fatty acids in synaptosomal membrane phosphatidylethanolamine, and elevated rates of methylation of phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine methyltransferases, suggesting that the pathway exhibits substrate selectivity for individual species of phosphatidylethanolamine containing long-chain homologues of dietary n-6 and n-3 fatty acids (20:4(n-6), 22:4(n-6), 22:5(n-6) and 22:6(n-3). It may be concluded that diet alters the membrane content of n-6, n-3 and monounsaturated fatty acids, and that change in phosphatidylethanolamine species available for methylation to phosphatidylcholine alters the rate of product synthesis in vivo by the phosphatidylethanolamine methyltransferase pathway.

Dietary control of diacylphosphatidylethanolamine species in brain.

The content and composition of the brain diacylphosphatidylethanolamine species was examined in response to dietary fat intake. Synaptic plasma membrane and microsomal membrane subcellular fractions contain phosphatidylethanolamine species profiles that respond differently to modulation by diet fat. The microsomal content of individual phosphatidylethanolamine species was most responsive to diet treatment and to addition of cholesterol to the diet. Feeding fish oil or linseed oil diets resulted in an increased membrane content of phosphatidylethanolamine species containing six double bonds for both microsomal and synaptic plasma membranes, compared with soya-bean oil- or sunflower oil-fed animals. The 22:5(n - 6) content present in phosphatidylethanolamine species of linseed oil and fish oil-fed animals was also reduced. For microsomal membranes, increase in dietary 18:3(n - 3) resulted in an increased content of phosphatidylethanolamine species containing one double bond. Addition of cholesterol to linseed oil or fish oil diets decreased the microsomal membrane content of phosphatidylethanolamine species containing six double bonds and increased the membrane content of species containing one double bond. For synaptic plasma membrane, addition of cholesterol to linseed oil and fish oil diets increased membrane content of species containing six double bonds. Fish oil-fed animals exhibited a decreased content of species containing a single double bond. The implications of the diet-induced changes in phospholipid species content and composition are discussed.

Co-ordinate control of CDP-choline and phosphatidylethanolamine methyltransferase pathways for phosphatidylcholine biosynthesis occurs in response to change in diet fat.

Brain microsomal and synaptic plasma membrane phosphatidylcholine composition and biosynthetic activity were examined in relation to the composition of diet fat fed. Phosphocholinetransferase and methyltransferase activities are shown to be modulated by the diet, and by changes in the membrane phospholipid content of long-chain polyunsaturated fatty acids. This physiological modulation is co-ordinated such that the rate of phosphatidylcholine synthesis via one route is inversely regulated with activity of the alternate pathway.

Epinephrine suppresses stress-induced increases in plasma immunoreactive beta-endorphin in humans.

The present study evaluated the hypothesis that increased plasma levels of epinephrine (EPI) stimulate immunoreactive beta-endorphin (i beta END) secretion in humans experiencing a mild stress. The stressor consisted of intraoral injections of a local anesthetic solution (with or without EPI) just before the surgical extraction of impacted third molars in 26 awake unsedated patients. The EPI group experienced a 30-fold increase in plasma EPI levels by 2 min after injection; these concentrations were physiologically active, as evidenced by increased pulse rate and systolic blood pressure. However, compared to a no EPI control group the EPI group had a significantly reduced i beta END response to the stressor, as evaluated by comparison of plasma levels at individual time points, maximal increases in plasma i beta END levels, and areas under the time-response curve. Whereas there was no association between plasma levels of EPI and i beta END in the EPI group (r = 0.119; P = NS), EPI and i beta END levels were strongly related in the no EPI group (r = 0.82; P less than 0.001). These results do not support the hypothesis of a stimulatory effect for EPI on i beta END release and, instead, suggest that an inhibitory relationship may exist in humans experiencing stress. The association between EPI and i beta END responses observed in the control group during this form of stress appears to be due to activation of a common central neural element.

Glucocorticoids suppress levels of immunoreactive bradykinin in inflamed tissue as evaluated by microdialysis probes.

Although circulating bradykinin increases during surgery, concentrations remain unknown in the biologically relevant compartment, the inflamed tissue. We have developed a new method, using microdialysis probes, for collecting tissue samples of immunoreactive bradykinin in both postoperative patients and rats injected with carrageenan. In vitro studies determined optimal flow rate, that dialysate levels of immunoreactive bradykinin were linearly related to external concentrations, and that the probes do not activate bradykinin synthesis. In oral surgery patients, tissue levels of immunoreactive bradykinin peaked approximately 3 hours after surgery. Preoperative administration of methylprednisolone (125 mg) reduced immunoreactive bradykinin levels by 62% (p less than 0.001) compared with placebo. Comparison of bradykinin levels to concurrent pain revealed a counterclockwise hysteresis, suggesting a delay between peak levels of bradykinin in the effect compartment and pain. In rats, dexamethasone suppressed tissue levels of immunoreactive bradykinin. The glucocorticoid suppression was dependent on de novo protein synthesis. Microdialysis appears to be a novel and useful method for measuring the peripheral release of bradykinin and, possibly, other inflammatory mediators.

Ibuprofen elevates immunoreactive beta-endorphin levels in humans during surgical stress.

Release of beta-endorphin is modulated by physiologic stress and a variety of hormonal and pharmacologic factors. Prostaglandin E2 inhibits release of beta-endorphin and corticotropin from pituitary corticotroph cells, suggesting that suppression of prostaglandin levels should increase beta-endorphin release. This hypothesis was tested by administration of 600 mg ibuprofen before surgical stress in humans in comparison to placebo and methylprednisolone. Plasma samples were analyzed for immunoreactive beta-endorphin with concurrent measurement of pain and apprehension. Levels of immunoreactive beta-endorphin increased during surgery in the placebo group but were significantly greater in the group of patients pretreated with ibuprofen. Methylprednisolone suppressed intraoperative immunoreactive beta-endorphin, compared with both placebo and ibuprofen. Parallel in vivo and in vitro studies indicate that nonsteroidal anti-inflammatory drug potentiation of endorphin release is mediated at the level of the pituitary corticotroph cell. These results show that ibuprofen enhances pituitary release of beta-endorphin by corticotroph cells in response to stress.

Naloxone, fentanyl, and diazepam modify plasma beta-endorphin levels during surgery.

Forty-eight patients received either naloxone (10 mg), fentanyl (0.1 mg), diazepam (0.3 mg/kg), or saline solution placebo, and then underwent surgical removal of impacted third molars under local anesthesia. Placebo resulted in significantly elevated levels of immunoreactive beta-endorphin (i beta-END), norepinephrine, and anxiety during surgery. Patients receiving naloxone had significantly greater intraoperative i beta-END and pain as compared with those receiving placebo. The naloxone effect on intraoperative pain was a result of a difference in perceived unpleasantness. Both the fentanyl and diazepam groups had significantly lower intraoperative i beta-END and anxiety levels as compared with the placebo group. Norepinephrine levels increased significantly in response to surgical stress in all groups except the diazepam group. Postoperative circulating levels of i beta-END and norepinephrine and pain increased significantly from the 1 to 3-hour postoperative period for all groups, with the exception of stable norepinephrine levels observed in patients receiving diazepam. Results indicate that opiate antagonists stimulate and agonists suppress the release of i beta-END, possibly by affecting the patient's perceived level of pain and anxiety. In addition, the association of intraoperative hyperalgesia with naloxone predosing suggests that endogenous opioid peptides inhibit the perception of intraoperative pain even in the presence of concurrent local anesthesia.

Dexamethasone alters plasma levels of beta-endorphin and postoperative pain.

Secretion of pituitary immunoreactive beta-endorphin is hypothesized to modulate the perception of pain. The present study examined this question by evaluating the effects of intravenous placebo or dexamethasone (0.1, 0.32, or 1.0 mg) on suppression of immunoreactive beta-endorphin secretion and development of postoperative pain after the surgical removal of impacted third molars in 48 patients. Compared with placebo, all doses of dexamethasone suppressed the postoperative increase in circulating levels of immunoreactive beta-endorphin. Patients administered 0.1 mg dexamethasone reported greater levels of pain, compared with those given placebo, from 60 through 120 minutes after surgery. Postoperative pain for the 0.32 and 1.0 mg doses did not differ from that for the placebo group. The increased pain after suppression of beta-endorphin release by the low dose of dexamethasone suggests that pituitary secretion of immunoreactive beta-endorphin alleviates postoperative pain under these conditions.

Proglumide potentiates morphine analgesia for acute postsurgical pain.

Proglumide, an antagonist of cholecystokinin, has been shown to potentiate morphine analgesia in animal and human experimental pain models. This study was undertaken to determine whether proglumide enhances morphine analgesia for patients experiencing postoperative pain. At onset of pain after the removal of impacted third molars, patients (n = 60) received intravenously either 4 mg morphine, 8 mg morphine, or 4 mg morphine plus proglumide (0.05, 0.5, or 5 mg). The administration of 8 mg morphine significantly reduced pain, in comparison with baseline and 4 mg morphine, for the first 30 minutes. The addition of 0.05 mg proglumide resulted in a significant increase in the magnitude and duration of the analgesic activity of 4 mg morphine; 0.5 and 5.0 mg proglumide did not produce this effect. No difference was seen in respiratory rate or in the frequency of side effects among the various forms of treatment. These data indicate that a low dose of proglumide potentiates both the magnitude and the duration of morphine analgesia in a clinical model of acute pain, without any detectable increase in side effects.

Bradykinin is increased during acute and chronic inflammation: therapeutic implications.

Bradykinin is a potent pain-producing substance, yet little is known about its role in inflammation. The present study measured circulating levels of immunoreactive bradykinin in a clinical model of acute inflammation (oral surgery) and chronic inflammation (rheumatoid arthritis) and in the rat carrageenan model of inflammation. The effects of a kallikrein inhibitor (soybean trypsin inhibitor) on blocking bradykinin synthesis in vitro and its analgesic actions in the rat model were also evaluated. Levels of immunoreactive bradykinin increased threefold to fourfold during oral surgery. Levels were twofold to threefold greater in patients with rheumatoid arthritis compared with control subjects. Levels of immunoreactive bradykinin increased twofold in rats during carrageenan inflammation. Soybean trypsin inhibitor blocked synthesis of bradykinin in vitro and possessed analgesic activity in rats. The results indicate that the bradykinin system is activated during inflammation. Kallikrein inhibitors may represent a new class of analgesic/antiinflammatory drugs.