Characterization of the Sensitizing Potential of Chemicals by In Vitro Analysis of Dendritic Cell Activation and Skin Penetration

Development of in vitro models to identify sensitizing chemicals receives public interest since animal testing should be avoided whenever possible. In this article we analyze two essential properties of sensitizing chemicals: skin penetration and dendritic cell (DC) activation. Activation of immature DC derived from peripheral blood monocytes was evaluated by flow cytometric analysis of CD86 positive cells and quantitative measurement of interleukin-1beta and aquaporin P3 gene expression. The sensitizer 2,4,6-trinitrobenzenesulfonic acid induced a concentration-dependent response for all parameters, whereas the irritant sodium lauryl sulfate did not. When two related aromatic amines, p-toluylenediamine (PTD) and hydroxyethyl-p-phenylenediamine (HE-PPD) were tested, both induced substantial DC activation indicating their potential sensitizing properties. These findings contrasted with in vivo results: in murine local lymph node assays (LLNA) PTD, but not HE-PPD, was sensitizing using acetone/aqua/olive oil as vehicle. Skin penetration measurement revealed that this was due to bioavailability differences. On retesting HE-PPD in the LLNA using the penetration enhancer dimethylsulfoxide as vehicle, it induced a specific response. We conclude that in vitro analysis of DC activation capability of the two selected chemicals demonstrates that prediction of skin sensitization potential is possible provided that skin penetration data indicate sufficient bioavailability of the test compound.

Chemosensory additivity in trigeminal chemoreception as reflected by detection of mixtures

A series of experiments probed into the degree of chemosensory detection additivity exhibited by mixtures of ethyl propanoate and heptanoate in terms of their trigeminal detectability via nasal pungency (i.e., irritation) and eye irritation. Nasal pungency was tested in subjects lacking a functional sense of smell (i.e., anosmics) to avoid olfactory biases. First, we built concentration-detection functions for each chemical and sensory endpoint. Second, we used the data from the functions to prepare mixtures of the two compounds in complementary proportions, and suitable single-chemical standards, all of which should be equally detectable under a rule of complete additivity, i.e., independence of detection. Third, we compared the experimentally obtained detectability with that expected under such rule. The outcome revealed that, at a low detectability level (but still above chance), the mixtures showed complete additivity for both trigeminal endpoints. At a high detectability level (but below perfect detection), the mixtures showed complete additivity for nasal pungency but less than complete additivity for eye irritation. In the context of previous studies, the results consolidate a picture of higher degree of detection additivity at perithreshold levels in trigeminal than in olfactory chemoreception. The outcome presents another line of evidence suggesting broader chemical tuning in chemesthesis compared to olfaction.

Gene expression in rat skin induced by irritating chemicals

Occupational skin disease is the second most significant cause of occupational disease, after accidents. Irritation from occupational chemicals such as solvents, hydrocarbons, and surfactants are one cause of this disease. Gene expression studies provide useful information about normal processes in the skin and responses of the skin to exogenous chemicals. We exposed rats, cutaneously, to sodium lauryl sulfate (SLS, 1% and 10% aqueous solution), m-xylene (pure liquid), and d-limonene (pure liquid) for 1 h and measured transcriptional responses at the end of the exposure and 3 h later for comparison with untreated skin samples. Total skin RNA was isolated and analyzed using the Affymetrix RatTox U34 array. Using the Affymetrix software, we found that 234 of approximately 850 genes were detected as present in at least 80% of the normal skin samples. The largest number of these genes was related to metabolism, oxidative/cellular stress, and signal transduction. Limonene caused the largest change in mRNA levels with a total of 34 increased transcripts and 4 decreased transcripts. Xylene treatment resulted in 6 increased transcripts and 14 decreased transcripts, while 10% SLS caused 5 transcripts to increase and 17 to decrease. Only two transcripts were observed to change in skin following a 1% SLS exposure. Sodium lauryl sulfate transcript changes increased with dose and were maximum at 4 h. Limonene transcript changes were more numerous at 1 h than at 4 h. The observed differences may reflect different mechanisms of irritation.

Occlusion of dentinal tubules and selective block of pulp innervation prevent the nociceptive behaviour induced in rats by intradental application of irritants

OBJECTIVES

Application of irritants on the exposed dentine of the incisors has been shown to produce aversive behaviour in awake rats. This study aims to demonstrate that the observed aversion is due to the infiltration of irritants through the dentinal tubules and the activation of capsaicin sensitive fibres in the tooth pulp.

METHODS

Different groups of rats were subjected, under anaesthesia, to cutting of the distal 2 mm of their lower incisors and the fixation of an artificial crown that allows the application of 10-15 microl of solution. Several procedures were followed to prevent the action of the irritants including occlusion of the dentinal tubules, local application of lidocaine, selective ablation of the capsaicin sensitive primary afferents (CSPA) or incisor pulpectomy; the reactions to intradental application of either capsaicin (1%) or formalin (2.5%) were tested using a newly designed behavioural score.

RESULTS

Occlusion of dentinal tubules produced significant attenuation of the nociceptive behaviour induced by dentinal application of either capsaicin or formalin. Similar results were observed following either local block with lidocaine (2%), selective ablation of capsaicin sensitive afferents or total denervation by pulpectomy.

CONCLUSIONS

The present results confirm the hypothesis of infiltration of irritants to the incisor pulp through the dentinal tubules and suggest that the reported inflammatory reaction and hyperalgesia are mediated, to a large extent, by capsaicin sensitive primary afferents.

Sensory and associated reactions to mineral dusts: sodium borate, calcium oxide, and calcium sulfate

Occupational exposure limits (OELs) for irritant dusts have had no quantifiable bases. This study (1) charted chemosensory feel, denoted chemesthesis here, to dusts of calcium oxide (1 to 5 mg/m(3)), sodium tetraborate pentahydrate [sodium borate] (5 to 40 mg/m(3)), and calcium sulfate (10 to 40 mg/m(3)); (2) examined correlates of the chemesthetic sensations; and (3) sought to illuminate the basis for potency. Twelve screened men exercised against a light load while they breathed air in a dome fed with controlled levels of dust for 20 min. Measured parameters included nasal resistance, nasal secretion, minute ventilation, heart rate, blood oxygenation, mucociliary transport time, and chemesthetic magnitude, calibrated to pungency of carbon dioxide. Subjects registered time-dependent feel from exposures principally in the nose, secondarily in the throat, and hardly in the eyes. Calcium oxide had the greatest potency, followed by sodium borate, with calcium sulfate a distant third. Of the physiological parameters, amount of secretion showed the best association with chemesthetic potency. That measure, as well as mucociliary transport time and minute ventilation, went into calculation of mass of dust dissolved into mucus. The calculations indicated that the two alkaline dusts increased in equal molar amounts with time. At equal molar concentrations, they had, to a first approximation, equal chemesthetic magnitude. On the basis of mass concentration in air or dissolved into mucus, calcium oxide and sodium borate differed in potency by a factor just above five, equal to the difference in their molecular weights. This relationship could inform the setting of OELs for a critical effect of irritation.

Cholecystokinin-induced gastroprotection: a review of current protective mechanisms

Cholecystokinin (CCK) is a member of a family of gastrointestinal peptides known to physiologically regulate pancreatic protein secretion, gallbladder contractility, and gut motility. In addition, CCK has been found to play important roles in endocrine and neural systems in the periphery as well as in the central nervous system. CCK has been proposed to play a role in satiety, anxiety, and intestinal transit in addition to its well-described effects in coordinating digestion of a meal. We and others have shown that exogenous and endogenous CCK prevent gastric injury from luminal irritants. These data suggest that the release of CCK may represent an important component of the intrinsic gastric mucosal defense system. This review focuses on the ability of CCK to render the stomach more resistant to injury from luminal insults and will summarize recent studies that examine the possible mechanisms involved.

Adaptive cytoprotection induced by pretreatment with ethanol protects against gastric cell damage by NSAIDs

In this study, we examined adaptive cytoprotection against NSAIDs in human gastric carcinoma cells in culture. Pretreatment of cells with low (nontoxic) concentrations of ethanol protected cells from cell death induced by subsequent exposure to NSAIDs. The adaptive cytoprotection against NSAIDs induced by ethanol was not attenuated by pretreatment of cells with inhibitors of protein synthesis or prostaglandin synthesis, thus inferring that neither newly synthesized proteins nor prostaglandins are involved in this process. Furthermore, treatment of cells with the low concentration of ethanol did not affect the synthesis and secretion of mucin. In in vivo experiments on rats, oral preadministration of a low dose of ethanol protected the gastric mucosa from gastric lesions induced by subsequent oral administration of NSAIDs. One possible explanation for this in vivo phenomenon is that the adaptive cytoprotection induced by ethanol protects the gastric mucosa from the direct cytotoxic effect of NSAIDs.

Keratinocyte ATP release assay for testing skin-irritating potentials of structurally diverse chemicals

Irritant dermatitis represents innate inflammatory responses to toxic chemicals. We have reported recently that ATP released from chemically injured keratinocytes may serve as a causative mediator for irritant dermatitis. In this study, we examined whether ATP release from keratinocytes would serve as a reliable readout for predicting skin irritating potentials of structurally diverse compounds. A vast majority (19/20) of the tested compounds, i.e., strong and weak irritant chemicals selected from the literature, induced rapid (<10 min) and significant (P<0.05) ATP release from Pam 212 keratinocytes. Two compounds caused no detectable skin inflammation in our standard mouse model, documenting relatively high sensitivity (false negative rate of 0/18) and specificity (false positive rate of 1/20) of our ATP release assay. Selected compounds, primarily those containing phenol residues or hydrophobic hydrocarbon chains, triggered rapid (<10 min) and robust leakage of a fluorescence probe from liposomes, suggesting that lipid bilayers serve as one, but not the only, target moiety on keratinocytes. Not only do our data support the pathogenic role for keratinocyte-derived ATP in irritant dermatitis, they also form the basis for a formal validation study to evaluate the utility of the keratinocyte-based in vitro assay in screening environmental and industrial chemicals.

The effects of protein kinase C activity on synaptic transmission in two areas of rat hippocampus

The effects of three protein kinase C (PKC) agonists (phorbol ester, ingenol and indolactam-V) and two PKC antagonists (D-erythro-sphingosine and chelerythrine) on input-output (I-O) relations in the Schaffer collateral pathway to CA1 (SC-CA1) and mossy fiber pathway to CA3 (MF-CA3) were determined in rat hippocampus brain slices. In the SC-CA1 pathway, phorbol esters and indolactam-V had only small effects on field excitatory post-synaptic potentials (fEPSP) in slices from 60-day animals, although ingenol, an activator of novel PKC isozymes, caused a significant decrease of the field excitatory post-synaptic potentials amplitude in 60-day animals, but not in 30-day animals. In contrast, in the MF-CA3 pathway, PKC agonists induced a significant increase in the field excitatory post-synaptic potentials. PKC antagonists depressed the field excitatory post-synaptic potentials in the SC-CA1 pathway, but had no significant effect in the MF-CA3 pathway. In the MF-CA3 pathway, paired-pulse facilitation was abolished by PKC agonists and unaffected by antagonists. In SC-CA1, it was depressed by agonists to levels below control, whereas it was significantly increased by chelerythine. We conclude that PKC plays important but different roles in both regions. In the SC-CA1 pathway, PKC is almost maximally active under control circumstances, and PKC antagonists significantly reduce synaptic responses. In contrast, in the MF-CA3 pathway, there is no apparent activation under resting circumstances, but significant potentiation of synaptic transmission is induced when PKC is activated. There are developmental changes in the pattern of PKC isozymes, and both pre- and post-synaptic actions are important.

Mild irritant prevents ethanol-induced gastric mucosal microcirculatory disturbances through actions of calcitonin gene-related peptide and PGI2 in rats

Pretreatment with a mild irritant such as 1 M NaCl prevented ethanol-induced mucosal injury, which was abolished by indomethacin, suggesting involvement of endogenous PGs. With the use of intravital microscopy, we investigated the mechanism in microcirculation whereby a mild irritant prevents ethanol-induced mucosal injury. Microcirculation of the basal part of gastric mucosa in anesthetized rats was observed through a window with transillumination. Diameters of arterioles, collecting venules, and venules were measured with an electric microscaler. One molar NaCl alone caused dilation of arterioles and constrictions of collecting venules and venules, which were inhibited by indomethacin. Ethanol (50%) applied to mucosa constricted collecting venules and venules but dilated arterioles. Constriction of collecting venules resulted in mucosal congestion. Pretreatment with 1 M NaCl inhibited ethanol-induced constrictions of collecting venules and venules, and administration of indomethacin or a calcitonin gene-related peptide (CGRP) antagonist, CGRP-(8-37), abolished elimination of constrictions. Topical application (1 nM-10 microM) of PGE2 or beraprost sodium (a PGI2 analog) to microvasculature markedly and dose-dependently dilated arterioles, whereas that of PGE2, but not beraprost, slightly constricted collecting venules. Pretreatment of microvasculature with a nonvasoactive concentration of PGE2 (100 nM) or beraprost (1 nM) completely inhibited ethanol-induced constriction of collecting venules. The inhibitory effect of beraprost but not of PGE2 was abolished by CGRP-(8-37). Present results suggest that the mechanism whereby 1 M NaCl prevents ethanol-induced injury is elimination of constrictions of collecting venules and venules by CGRP whose release may be enhanced by PGI2 but not by PGE2.

Capsaicin-induced joint inflammation is not blocked by local anesthesia

The purpose of this study was to evaluate the effect of local anesthetic blockade of afferent innervation on the development of capsaicin-induced edema in the rat temporomandibular joint (TMJ) region and on reflex jaw muscle activity. Under halothane anesthesia, 64 male Sprague-Dawley rats were prepared for monitoring of edema development by lateral movement of a needle overlying the left TMJ region and for acute recording of electromyographic activity in ipsilateral digastric and masseter muscles. A double-barrel catheter was inserted into the TMJ region for delivery of saline or 0.5% bupivacaine from 1 needle, followed with the injection of 1% capsaicin, 0.1% capsaicin, or vehicle control from the other needle 5 minutes later. Application of capsaicin into the saline pretreated TMJ region led to dose-dependent edema development and reflex jaw muscle activity; however, only 1% capsaicin solution resulted in significant tissue expansion and muscle activity when compared with the vehicle control. Pretreatment of the rat TMJ region with bupivacaine failed to inhibit capsaicin-induced edema development, although successful blockade of nerve conduction was confirmed with the absence of reflex jaw muscle activity. Capsaicin-induced edema of the rat TMJ region developed independent of axonal conduction, suggesting neurogenic inflammation may arise regardless of functional nerve conduction.

Contact sensitizer nickel sulfate activates the transcription factors NF-kB and AP-1 and increases the expression of nitric oxide synthase in a skin dendritic cell line

Nuclear factor kappa B (NF-kB) and activating protein-1 (AP-1) transcription factors are ubiquitously expressed signaling molecules known to regulate the transcription of a large number of genes involved in immune responses, namely the inducible isoform of nitric oxide synthase (iNOS). In this study, we demonstrate that a fetal skin-derived dendritic cell line (FSDC) produces nitric oxide (NO) in response to the contact sensitizer nickel sulfate (NiSO(4)) and increases the expression of the iNOS protein, as determined by immunofluorescence and Western blot analysis. The sensitizer NiSO(4) increased cytoplasmic iNOS expression by 31.9 +/- 10.3% and nitrite production, as assayed by the Griess reaction, by 27.6 +/- 9.5%. Electrophoretic mobility shift assay (EMSA), showed that 30 min of FSDC exposure to NiSO(4) activates the transcription factor NF-kB by 58.2 +/- 7.0% and 2 h of FSDC exposure to NiSO(4) activates the transcription factor AP-1 by 26.0 +/- 1.4%. Together, these results indicate that NiSO(4) activates the NF-kB and AP-1 pathways and induces iNOS expression in skin dendritic cells.

Irritant potential of some constituents from oleo-gum-resin of Commiphora myrrha

The irritant potentials of essential oil and seven sesquiterpenoids compounds newly isolated from the oleo-gum-resin of Commiphora myrrha were investigated by open mouse ear assay. The essential oil, curzerenone, furanodiene-6-one and furanoeudesma-1,3-diene showed potent and persistent irritant effects while others possess least irritant potentials.

Basal electrical impedance in relation to sodium lauryl sulphate-induced skin reactions - a comparison of patients with eczema and healthy controls

BACKGROUND

Identification of subjects at risk for contact dermatitis by screening tests is desirable in order to adjust the preventive measures to individual skin susceptibility. The present study aimed to examine the effects of basic physiological features, such as baseline electrical impedance (IMP) and transepidermal water loss (TEWL), on reactivity to sodium lauryl sulphate (SLS).

METHODS

On the basis of two previous studies, we re-evaluated the experimental irritant skin reactions (50 microL of 2% SLS in large Finn Chambers for 24 h) on the volar forearms of 29 patients with eczema and 19 healthy controls.

RESULTS

We found definite differences in the baseline values of IMP, between the patients and the controls. Moreover, patients with eczema showed higher TEWL and lower MIX values on day 3 after exposure to SLS, which may indicate differences in SLS reactivity. After the study, the biophysical parameters of the eczema patients did not return to baseline, which suggests that their skin heals more slowly than that of normal subjects.

CONCLUSIONS

Our findings indicate that the IMP technique may help to 'detect' chemically vulnerable skin. However, more studies are needed to determine the value of the basal electrical impedance parameters in assessing the risk of developing irritant contact dermatitis.

The HET-CAM test combined with histological studies for better evaluation of active ingredient innocuity

In the search for alternative methods to animal testing, the Hen's egg test on chorioallantoic membrane (HET-CAM) plays a central role in evaluating the innocuity of active ingredients. Therefore, in the following studies we combined the HET-CAM test with histological evaluation in order to increase the sensitivity of evaluation. Twenty active ingredients from four different categories of origin (vegetal, marine, biotechnological and chemical synthetic) were subjected to innocuity evaluation at two different concentrations (pure and 10%). We performed the HET-CAM test and histological evaluation after trypan blue and hematoxylin-eosin staining of the chorioallantoic membrane to microscopically evaluate its state of damage after application of each active ingredient. These studies showed that when the active ingredient was diluted (10%), no discrepancy was seen between the classical HET-CAM evaluation and the histological reading of the chorioallantoic membrane. The histological findings corresponded with the visual observation of the CAM. When the active ingredients were tested at pure concentration, 7 out of 20 tested products demonstrated discrepancy between the two tests. In six cases, the histological examination revealed signs of irritation, such as hyperemia, while visual HET-CAM evaluation was negative. In another case, the histological examination revealed a slight hemorrhage whereas the HET-CAM reading showed only hyperemia. Moreover, the results of trypan blue staining corroborated the histological evaluation of the CAM. These results strongly suggest that the combination of histological and visual HET-CAM tests is of interest for a more sensitive evaluation of the innocuity of cosmetic active ingredients. This additional sensitivity may help to prevent some cases of in vivo intolerance reactions.

Characteristics of thermoregulatory and febrile responses in mice deficient in prostaglandin EP1 and EP3 receptors

Previous studies have disagreed about whether prostaglandin EP1 or EP3 receptors are critical for producing febrile responses. We therefore injected lipopolysaccharide (LPS) at a variety doses (1 microg kg(-1)-1 mg kg(-1)) intraperitoneally (i.p.) into wild-type (WT) mice and mice lacking the EP1 or the EP3 receptors and measured changes in core temperature (Tc) by using telemetry. In WT mice, i.p. injection of LPS at 10 microg kg(-1) increased Tc about 1 degrees C, peaking 2 h after injection. At 100 microg kg(-1), LPS increased Tc, peaking 5-8 h after injection. LPS at 1 mg kg(-1) decreased Tc, reaching a nadir at 5-8 h after injection. In EP1 receptor knockout (KO) mice injected with 10 microg kg(-1) LPS, only the initial (< 40 min) increase in Tc was lacking; with 100 microg kg(-1) LPS the mice showed no febrile response. In EP3 receptor KO mice, LPS decreased Tc in a dose- and time-dependent manner. Furthermore, in EP3 receptor KO mice subcutaneous injection of turpentine did not induce fever. Both EP1 and EP3 receptor KO mice showed a normal circadian cycle of Tc and brief hyperthermia following psychological stress (cage-exchange stress and buddy-removal stress). The present study suggests that both the EP1 and the EP3 receptors play a role in fever induced by systemic inflammation but neither EP receptor is involved in the circadian rise in Tc or psychological stress-induced hyperthermia in mice.

Induction of adipose differentiation related protein and neutral lipid droplet accumulation in keratinocytes by skin irritants

Keratinocytes play an important role in skin irritation. In an attempt to investigate mechanistic bases of human skin irritation response, we recently identified the upregulation by skin irritants of adipose differentiation related protein (ADRP) in reconstituted human epidermis. ADRP is a lipid-storage-droplet-associated protein, governing deposition and release of lipids from droplets. The purpose of this study was to characterize, in a human keratinocyte cell line (NCTC 2544), sodium-dodecyl-sulfate-induced ADRP expression, to identify the biochemical events that lead to ADRP expression, and to understand its function in sodium dodecyl sulfate cytotoxicity. Sodium dodecyl sulfate induced a concentration- and time-related production of ADRP that was associated with lipid droplet accumulation. Lipid accumulation following sodium dodecyl sulfate treatment was due to intracellular redistribution rather than lipid neosynthesis, as indicated by equivalent 14C-oleate and 14C-acetate incorporations. Other skin irritants, namely benzalkonium chloride, tributyltin, and 12-O-tetradecanoylphorbol 13-acetate, also induce lipid droplet accumulation. Sodium-dodecyl-sulfate-induced ADRP expression and lipid droplet accumulation were modulated by the calcium chelator BAPTA, indicating a role of calcium in ADRP induction. Decrease of sodium-dodecyl-sulfate-induced ADRP expression by specific ADRP antisense oligonucleotide resulted in increased cytotoxicity, indicating a protective role of ADRP and lipid accumulation in the process of cell damage induced by skin irritants. ADRP expression was also induced in vivo following treatment with sodium dodecyl sulfate in an experimental model of skin irritation, indicating that the in vitro model represents irritation.

PLUNC (palate, lung and nasal epithelial clone) proteins in human nasal lavage fluid

PLUNC (palate, lung and nasal epithelial clone) is a newly discovered gene that is expressed in the upper respiratory tract and is suggested to be of importance in host defence against bacteria. We have identified two forms of the PLUNC protein in human nasal lavage fluid (NLF) using two-dimensional gel electrophoresis (2-DE) and MS. The apparent molecular masses and isoelectric points of these forms are 24.8 kDa/pI 5.4 and 25.1 kDa/pI 5.5. Notably, the 24.8 kDa/pI 5.4 form of PLUNC is an abundant protein in the 2-DE protein patterns of NLF from healthy subjects. Decreased levels of PLUNC were found in NLF from smokers and workers exposed to reactive epoxy chemicals, indicating that long-term exposure to airway irritants impairs the production of PLUNC in the upper respiratory tract. We have also investigated the presence of lipopolysaccharide (LPS)-binding proteins in NLF. Five proteins were found to adsorb to a LPS-coated surface; two of these proteins correspond to the two PLUNC forms, as judged by 2-DE pattern matching. For comparison, human saliva was found to contain a set of LPS-binding proteins with similar 2-DE spot positions (the same pIs but somewhat lower apparent molecular masses of approximately 20 kDa). These results indicate that PLUNC may be a new marker of airway inflammation and may play a part in the innate immune response, and that human saliva contains yet other members of the family of LPS-binding proteins.

Mouse soluble CD14 truncated at amino acid 71 in transgenic mice: preventive effect on endotoxin-mediated toxic shock

Mouse soluble CD14 truncated at amino acid 71 (N71) contains the lipopolysaccharide (LPS)-binding sequence. Transgenic mice carrying alpha1-antitrypsin (AT) promoter-N71 fusion genes, designated AT363-1 and AT363-2, were produced. These mice constitutively produced elevated levels of N71. The concentration of LPS in sera after intraperitoneal LPS injection was lower in AT363-1 mice than in nontransgenic mice. The expression of N71 mRNA was enhanced by subcutaneous turpentine oil injection. The levels of serum LPS and tumor necrosis factor-alpha (TNF-alpha) after intraperitoneal LPS injections were lower in AT363-1 mice than in nontransgenic mice. Cell surface TNF-alpha and CD14 expression in exudate peritoneal macrophages prepared by intraperitoneal injection of proteose peptone and then LPS were higher in AT363-1 mice than in nontransgenic mice. Neutrophil infiltration in the liver after induction of the generalized Shwartzman reaction was lower in AT363-1 mice than in nontransgenic mice. Lethality of the Shwartzman reaction was significantly lower in AT363-1 than in nontransgenic mice. These findings suggest that the endotoxin-binding protein (N71) from CD14 prevents endotoxin-mediated toxic shock.

Elevated levels of secretoneurin in the rabbit aqueous humor in response to formaldehyde irritation

BACKGROUND

Secretoneurin, a 33-amino-acid neuropeptide, is generated by proteolytic processing of secretogranin II, which belongs to the chromogranin family. This study aimed to investigate whether secretoneurin is present in the uninflamed rabbit aqueous humor and whether it is released in response to treatment with topical formaldehyde, an agent known to release sensory peptides originating from the trigeminal ganglion.

METHODS

Blood samples and aqueous humor of eyes pretreated with neutral formaldehyde and untreated controls were analyzed for secretoneurin immunoreactivity by a highly sensitive radioimmunoassay. Furthermore, the molecular form of the secretoneurin immunoreactivity was characterized by gel filtration high-performance liquid chromatography (HPLC).

RESULTS

In the blood, secretoneurin levels were found to be below the detection limit of 2 fmol/100 microl. In the aqueous humor, secretoneurin-immunoreactivity was detected in moderate but significant amounts. The mean concentration of secretoneurin was 8.1 (+/-0.34) fmol/100 microl in controls and 7.8 (+/-0.1) fmol/100 microl 15 min after formaldehyde application. Thirty minutes after treatment, the secretoneurin levels were significantly elevated by 63%. Gel filtration HPLC revealed that the main molecular form corresponded to the free peptide secretoneurin.

CONCLUSIONS

The neuropeptide secretoneurin has been detected in the anterior segment of the eye for the first time. The elevation of secretoneurin in formaldehyde-treated eyes may be induced by an enhanced release from the iris/ciliary body complex, as formaldehyde is known to provoke neurogenic inflammation in the anterior segment via release of sensory peptides originating from the trigeminal ganglion. This is why our results indicate a sensory origin of secretoneurin in the eye.

Unaltered pain-related behavior in mice lacking NMDA receptor GluRepsilon 1 subunit

Noxious afferent input following tissue damage and inflammation triggers a state of neuronal hyperexcitability-a phenomenon of central sensitization-which manifests behaviorally as allodynia and hyperalgesia. At the molecular level, maintenance of central sensitization is largely dependent on the N-methyl-D-aspartate receptor (NMDAR) activation. NMDARs are composed of GluRzeta1 (NR1) and one of four GluRepsilon (NR2) subunits, which determine the functional properties of native NMDARs. Although there is accumulating evidence to implicate GluRepsilon 2-containing NMDARs in pain mechanisms, the functional significance of GluRepsilon 1-containing NMDARs in this setting has not been examined in detail. Here, we used hind paw injection of formalin, complete Freund's adjuvant and a nerve injury model to investigate the effects of GluRepsilon 1 subunit gene deletion on pain-related behavior in mice. In all of the models tested, GluRepsilon 1-deficient mice exhibited responses similar to wild-type controls. These results suggest that GluRepsilon 1 disruption does not result in altered nociceptive behavior in mice. Although the contribution of other nociceptive pathways cannot be ruled out, we speculate that the preserved function of GluRepsilon 2-containing NMDARs could explain unaltered nociceptive behavior in mutant mice.

TRPV1 activation and induction of nociceptive response by a non-pungent capsaicin-like compound, capsiate

Capsiate is a capsaicin-like ingredient of a non-pungent cultivar of red pepper, CH-19 sweet. To elucidate the mechanisms underlying the non-pungency of capsiate, we investigated whether capsiate activates the cloned capsaicin receptor, TRPV1 (VR1). In patch-clamp experiments, capsiate was found to activate TRPV1 expressed transiently in HEK293 cells with a similar potency as capsaicin. Capsiate induced nociceptive responses in mice when injected subcutaneously into their hindpaws with a similar dose dependency as capsaicin. These data indicate that the non-pungent capsiate is an agonist for TRPV1 and could excite peripheral nociceptors. In contrast to this, capsiate did not induce any significant responses when applied to the skin surface, eye or oral cavity of mice, suggesting that capsiate requires direct access to nerve endings to exhibit its effects. Capsiate was proved to have high lipophilicity and to be easily broken down in normal aqueous conditions, leading to less accessibility to nociceptors. Another highly lipophilic capsaicin analogue, olvanil, was similar to capsiate in that it did not produce irritant responses when applied to the skin surface, although it could activate TRPV1. Taken together, high lipophilicity and instability might be critical determinants for pungency and so help in understanding the effects of capsaicin-related compounds.

CD156 transgenic mice. Different responses between inflammatory types

CD156 (ADAM8) is part of the ADAM family of proteins with the catalytic site consensus sequence of metalloprotease and disintegrins. To examine the role of CD156 in vivo, we generated mutant CD156 (eCD156) transgenic mice expressing the ectodomain of CD156 under the control of the alpha1-antitrypsin (AT) promoter. One of the transgenic mice designated ATMS2-TG18 expressed a 1.84 kb mRNA which was predicted to be a truncated CD156. The expression of the transgenic CD156 mRNA in ATMS2-TG18 mice was abundant in the liver and slight in kidney. Turpentine oil (TO) and lipopolysaccharide (LPS) markedly upregulated the expression. Soluble CD156 (sCD156) was produced constitutively, and increased after the treatment with TO. Casein-induced peritoneal leukocyte infiltration was significantly less extensive in ATMS2-TG18 than non-transgenic mice. The expression of L-selectin in neutrophils (PMN) from peripheral blood leukocytes (PBL) was more strongly downregulated in ATMS2-TG18 than non-transgenic mice, suggesting that L-selectin in PMN from ATMS2-TG18 mice was shed by sCD156. In contrast, oxazolone (Ox)-induced contact hypersensitivity reactions (CHR) were more marked in ATMS2-TG18 than non-transgenic mice. The expression of E-selectin mRNA was detected in inflammatory skin sites from ATMS2-TG18, but not non-transgenic mice, suggesting that sCD156 may activate the endothelial cells and lead to the upregulation of E-selectin. These results suggest that CD156 regulates leukocyte infiltration directly or indirectly.

Activation of neurons in trigeminal caudalis by noxious oral acidic or salt stimuli is not reduced by amiloride

We investigated the possible role of amiloride-sensitive ion channels of the ENaC/DEGenerin superfamily in the activation of trigeminal nociceptive neurons elicited by noxious chemical stimulation of the oral mucosa using two methodologies, single-unit recording and c-fos immunohistochemistry. In pentobarbital-anesthetized rats, single-unit recordings were made from neurons in superficial laminae of dorsomedial trigeminal subnucleus caudalis (Vc) that responded to noxious thermal and chemical stimuli applied to the dorsal tongue. Successive application of each of three chemicals (250 mM pentanoic acid, n=6 units; 250 mM citric acid, n=8; 5 M NaCl, n=6) evoked responses that were not affected following topical application of amiloride (1 mM). In separate experiments, pentobarbital-anesthetized rats received one of the following stimuli delivered to the dorsal tongue: 250 mM pentanoic acid (n=6); 1 mM amiloride followed by 250 mM pentanoic (N=6); 5 M NaCl (n=5); or 1 mM amiloride followed by 5 M NaCl (n=5). Two hours later they were perfused with 4% paraformaldehyde and the brain stems processed for c-fos immunoreactivity. Both pentanoic acid and 5 M NaCl evoked similar numbers and patterns of fos-like immunoreactivity (FLI) in dorsomedial Vc and other brain stem regions, with no significant difference in counts of FLI in animals pretreated with amiloride. These results suggest that amiloride-sensitive Na(+) channels are not essential in mediating the activation of intraoral trigeminal nociceptors.