Role of histamine and platelet-activating factor in allergic rhinitis

Detecting Changes in Mast Cell Numbers Versus Activation in Human Disease: A Roadblock for Current Biomarkers?

The pathophysiology of mast cell (MC)-driven disorders is diverse, ranging from localized reactions to systemic disorders caused by abnormal accumulation and activation in multiorgan systems. Prompt and accurate diagnosis is critically important, both for informing treatment and objective assessment of treatment outcomes. As new therapeutics are being developed to deplete MCs or silence them (eg, by engaging inhibitory receptors that block activation), new biomarkers are needed that can distinguish between MC activation versus burden. Serum tryptase is the gold standard for assessing both MC burden and activation; however, commercial tryptase assays have limitations related to timing of release, lack of discernment between inactive (α) and active (β) forms of tryptase, and interpatient variability of baseline levels. Alternative approaches to measuring MC activation include urinary MC mediators, flow cytometry-based assays or gene expression profiling. Additional markers of MC activation are needed for use in clinical diagnostics, to help selection of treatment of MC diseases, and for assessing outcomes of therapy. We review the spectrum of disorders with known or suspected MC contribution, describe the utility and limitations of current MC markers and assays, and discuss the need for new markers that can differentiate between MC activation and burden.

Severe Type 2 Inflammation Leads to High Platelet-Activating-Factor-Associated Pathology in Chronic Rhinosinusitis with Nasal Polyps-A Hierarchical Cluster Analysis Using Bulk RNA Barcoding and Sequencing

Platelet-activating factor (PAF) is a phospholipid-derived inflammatory mediator that triggers various inflammatory conditions, including eosinophil activation and recruitment. This study aimed to evaluate the expressions of PAF-metabolism-associated genes, namely genes coding the enzymes involved in PAF synthesis (LPCAT1, LPCAT2, LPCAT3, and LPCAT4), PAF degradation (PAFAH1B2, PAFAH1B3, and PAFAH2), and the gene for the PAF receptor (PTAFR) in subtypes of CRSwNP classified by clinical- or hierarchal-analysis-based classifications. Transcriptomic analysis using bulk RNA barcoding and sequencing (BRB-seq) was performed with CRSwNP, including eosinophilic CRS (ECRS) (n = 9), nonECRS (n = 8), ECRS with aspirin-exacerbated respiratory disease (Asp) (n = 3), and controls with a normal uncinate process mucosa (n = 6). PTAFR was only upregulated in ECRS and nonECRS. In the hierarchical cluster analysis with clusters 1 and 2 reflecting patients with low-to-moderate and high levels of type 2 inflammation, respectively, cluster 1 exhibited a significant downregulation of LPCAT2 and an upregulation of PTAFR expression, while cluster 2 showed an upregulation of LPCAT1, PAFAH1B2, and PTAFR and downregulation of PAFAH2 expression. Understanding this strong PAF-associated pathophysiology in the severe type 2 inflammation group could provide valuable insights into the treatment and management of CRSwNP.

Therapeutic effects of intranasal tocotrienol-rich fraction on rhinitis symptoms in platelet-activating factor induced allergic rhinitis

Background

Platelet-activating factor (PAF) has been suggested to be a potent inflammatory mediator in Allergic rhinitis (AR) pathogenesis. Vitamin E, an essential nutrient that comprises tocopherol and tocotrienol, is known as a potential therapeutic agent for airway allergic inflammation. This study aimed to investigate the beneficial effects of intranasal Tocotrienol-rich fraction (TRF) on PAF-induced AR in a rat model.

Methods

Sprague Dawley rats were randomly assigned into 3 groups: Control, PAF-induced AR and PAF-induced AR with TRF treatment. To induce AR, 50 μl of 16 μg/ml PAF was nasally instilled into each nostril. From day 1 to 7 after AR induction, 10 μl of 16 μg/μl TRF was delivered intranasally to the TRF treatment group. Complete upper skulls were collected for histopathological evaluation on day 8.

Results

The average severity scores of AR were significantly higher in the PAF-induced AR rats compared to both control and PAF-induced AR with TRF treatment. The histologic examination of the nasal structures showed moderate degree of inflammation and polymorphonuclear cells infiltration in the lamina propria, mucosa damage and vascular congestion in the PAF-induced AR rats. TRF was able to ameliorate the AR symptoms by restoring the nasal structures back to normal. H&E staining demonstrated a statistically significant benefit upon TRF treatment, where minimal degree of inflammation, and a reduction in the infiltration of polymorphonuclear cells, mucosa damage and vascular congestion were observed.

Conclusion

TRF exhibited symptomatic relief action in AR potentially due to its antioxidant, anti-inflammatory and anti-allergic properties.

Higher efficacy of rupatadine 20 mg and 10 mg versus placebo in patients with perennial allergic rhinitis: a pooled responder analysis

Background

The clinical efficacy of rupatadine in terms of responders has not been previously explored in perennial allergic rhinitis (PAR).

Methods

This pooled analysis included data from 6 randomised, double-blind, placebo-controlled trials conducted in PAR patients treated with rupatadine 10 mg or 20 mg, or placebo. Participants were aged ≥ 18 years, with diagnosis of PAR and a Total 4 Nasal Symptom Score (T4NSS) ≥ 5. We evaluated the T4NSS and Total 5 Symptom Score (T5SS) for 28 days of treatment, the responder proportion (50% and 75% response), and the time to response.

Results

Efficacy data from 1486 patients were analysed: 585 received placebo, 682 rupatadine 10 mg, and 219 rupatadine 20 mg. Compared with placebo, rupatadine promoted greater symptom improvements and higher responder proportions (50% and 75% response) for T4NSS and T5SS over 28 days. Symptom improvements and responder proportions were higher in the rupatadine 20 mg group vs the 10 mg group. The time to response was shorter in the rupatadine 20 mg group vs the 10 mg group for T4NSS (16 and 9 days for the 50% and 75% responses, respectively) and for T5SS (13 and 8 days for the 50% and 75% responses, respectively).

Conclusions

Rupatadine was efficacious in reducing allergic rhinitis symptoms, showing high responder proportions. The faster and stronger effect of rupatadine 20 mg may suggest its use in patients with severe PAR or not responding to the standard dose.

Clinically relevant effect of rupatadine 20 mg and 10 mg in seasonal allergic rhinitis: a pooled responder analysis

Background

Different clinical trials showed the superior efficacy of rupatadine compared to placebo at improving seasonal allergic rhinitis (SAR) symptoms, but no study has assessed if the response promoted is clinically meaningful.

Methods

This study is a pooled analysis of data of seven randomized, double-blind, placebo-controlled SAR studies comparing responder proportions upon treatment with rupatadine (10 or 20 mg) or placebo. We evaluated the following symptom scores at baseline (Visit 1) and over 14 days of treatment: Total 4 Nasal Symptom Score (T4NSS), Total 2 Ocular Symptom Score (T2OSS) and Total 6 Symptom Score (T6SS). The proportion of responders (50% and 75% response) and the time to response were compared between groups on days 7 (Visit 2) and 14 (Visit 3). Responder rates were compared between groups on days 7 and 14 for the complete/near-to-complete response for T4NSS (TN4SS score ≤ 2 and each symptom score ≤ 1) and T6SS (T6SS score ≤ 3 and each symptom score ≤ 1).

Results

Data from 1470 patients were analyzed: 332 treated with placebo, 662 with rupatadine 10 mg and 476 with rupatadine 20 mg. The reduction in T4NSS, T2OSS and T6SS over 14 days of treatment relative to baseline was statistically higher in rupatadine groups vs the placebo group, with greater improvements in the 20 mg group. A statistically higher proportion of patients reached the 50% and 75% response for T4NSS, T2OSS and T6SS in rupatadine groups compared to the placebo group across the visits. Among rupatadine-treated patients, those receiving 20 mg compared favourably for both cut-off responses. The time to achieve a proportion of responders was shorter in the rupatadine 20 mg group than in the rupatadine 10 mg and placebo groups for all the symptom scores. The number of patients who achieved a complete/near-to-complete response for both symptom scores was higher in rupatadine groups than in the placebo group, with higher proportions in the 20 mg group.

Conclusions

This responder analysis confirms the superior efficacy of rupatadine vs placebo to treat SAR. Rupatadine promoted higher proportions of responders according to stringent response criteria and in a dose-dependent manner, with faster and higher response rates in the 20 mg group.

Platelet-Activating Factor (PAF) in Allergic Rhinitis: Clinical and Therapeutic Implications

Platelet-activating factor (PAF) is a lipid mediator involved in several allergic reactions. It is released from multiple cells of the immune system, such as eosinophils, neutrophils, and mast cells, and also exerts its effect on most of them upon specific binding to its receptor, becoming a pleiotropic mediator. PAF is considered a potential relevant mediator in allergic rhinitis, with a key role in nasal congestion and rhinorrhoea due to its effect on vascular permeability. Interestingly, despite its potential relevance as a therapeutic target, no specific PAF inhibitors have been studied in humans. However, rupatadine, a second-generation antihistamine with dual antihistamine and anti-PAF effects has shown promising results by both blocking nasal symptoms and inhibiting mast cell activation induced by PAF, in comparison to antihistamine receptor drugs. In conclusion, the inhibition of PAF may be an interesting approach in the treatment of allergic rhinitis as part of a global strategy directed at blocking as many relevant inflammatory mediators as possible.

Long-term safety and efficacy of rupatadine in Japanese patients with perennial allergic rhinitis: a 52-week open-label clinical trial

Objective: Long-term safety and efficacy of 10- and 20-mg rupatadine in Japanese patients with perennial allergic rhinitis (PAR) were investigated in a 52-week open-label study (JapicCTI-152952, clinicaltrials.jp).

Methods: The rupatadine dose was fixed to 10 mg once daily for the first 2 weeks. Thereafter, the study investigator was allowed to increase the dosage to 20 mg if the response was insufficient. Safety was evaluated on the basis of treatment-emergent adverse events, laboratory findings, and vital sign measurements. The primary efficacy endpoint was changed from baseline to Week 2 in the total 4 nasal symptom score. Secondary efficacy endpoints included changes over time in ocular symptoms, patient and physician clinical overall impression, and patient quality-of-life.

Results: Seventy-two immunoglobulin E positive patients (mean age = 32.1 years), consisting of 58 adults (age ≥ 18 years) and 14 adolescents (12–17 years), were enrolled. Ninety-four treatment-emergent adverse events were reported in 48 patients (66.7%), including nine adverse drug reactions in nine patients (12.5%). The most frequently reported adverse drug reaction was somnolence (9.7%). The primary and secondary efficacy endpoints demonstrated a statistically significant clinical benefit with rupatadine. The rupatadine dose was increased from 10 to 20 mg in 36 patients (50.0%), which resulted in better symptom management.

Conclusions: Rupatadine 10- and 20-mg once-daily doses were well tolerated in long-term use. Updosing to 20 mg is a reasonable option in PAR patients whose symptoms cannot be controlled effectively by the 10-mg dose.

Efficacy and safety of rupatadine in Japanese patients with seasonal allergic rhinitis: A double-blind, randomized, multicenter, placebo-controlled clinical trial

BACKGROUND

Rupatadine is a novel non-sedating second-generation H₁-antihistamine with antiplatelet-activating factor activity, first marketed in Spain in 2003. It is used for treating allergic rhinitis in more than 80 countries. This study investigated its efficacy and safety in Japanese patients with seasonal allergic rhinitis (SAR).

METHODS

This was a randomized, placebo-controlled, double-blind study conducted at 4 medical institutions in Japan (JapicCTI-152785). Adolescent and adult SAR outpatients aged 12-64 years entered a 1-week placebo run-in period. After eligibility was confirmed, patients orally received placebo, rupatadine 10 mg, or 20 mg once daily for 2 weeks. The primary endpoint was a change from baseline to second week of treatment in total 4 nasal symptom score (T4NSS).

RESULTS

Nine hundred patients were randomly assigned to placebo, rupatadine 10 mg, or rupatadine 20 mg (302, 298, and 300 patients, respectively). The least squares mean difference in the primary endpoint between rupatadine and placebo was -1.085 for 10 mg, and -1.415 for 20 mg (analysis of covariance, both P < 0.001). The rates of adverse events were 6.6%, 14.1%, and 15.0% for placebo, rupatadine 10 mg, and rupatadine 20 mg, respectively. Somnolence was most frequently reported: 7.0% for rupatadine 10 mg and 7.3% for rupatadine 20 mg. No serious adverse drug reactions were observed, and no adverse events resulted in premature discontinuation.

CONCLUSIONS

Rupatadine 10 and 20 mg were significantly superior to placebo in improving nasal and ocular symptoms of SAR, and were well tolerated.

Inflammation, not Cholesterol, Is a Cause of Chronic Disease

Since the Seven Countries Study, dietary cholesterol and the levels of serum cholesterol in relation to the development of chronic diseases have been somewhat demonised. However, the principles of the Mediterranean diet and relevant data linked to the examples of people living in the five blue zones demonstrate that the key to longevity and the prevention of chronic disease development is not the reduction of dietary or serum cholesterol but the control of systemic inflammation. In this review, we present all the relevant data that supports the view that it is inflammation induced by several factors, such as platelet-activating factor (PAF), that leads to the onset of cardiovascular diseases (CVD) rather than serum cholesterol. The key to reducing the incidence of CVD is to control the activities of PAF and other inflammatory mediators via diet, exercise, and healthy lifestyle choices. The relevant studies and data supporting these views are discussed in this review.

Atorvastatin prevents glomerular extracellular matrix formation by interfering with the PKC signaling pathway

Platelet-activating factor (PAF) promotes glomerular extracellular matrix (ECM) deposition, primarily through activation of the protein kinase C (PKC) pathway. The present study was designed to investigate whether atorvastatin, which mediates a protective effect against glomerular ECM deposition and diabetic neuropathy, may interfere with the PKC‑transforming growth factor‑β1 (TGF‑β1) pathway in a model of human mesangial cells (HMCs) exposed to a high glucose (HG) and lysophosphatidylcholine (LPC) environment. HMCs were divided into three treatment groups: Control, high glucose and lysophosphatidylcholine (HG+LPC), and HG+LPC+atorvastatin. Cells were cultured for 24 h. The levels of the ECM‑associated molecules collagen IV (Col IV) and fibronectin (Fn) in the supernatant were detected using an ELISA kit. PKC‑β1, TGF‑β1 and PAF‑receptor gene expression was detected by reverse transcription‑quantitative polymerase chain reaction. PKC‑β1 and TGF‑β1 protein expression was detected by western blotting, and the subcellular localization of PKC‑β1 was assessed using immunofluorescence. The results indicated that atorvastatin may reduce the secretion of ECM components (Fn and Col IV) in HMCs in a HG and LPC environment, by inhibiting the increase in PAF secretion and the activation of the PKC‑TGF‑β1 signaling pathway.

Neuroprotection by platelet-activating factor acetylhydrolase in a mouse model of transient cerebral ischemia

Neuronal damage after transient cerebral ischemia is exacerbated by signaling pathways involving activated platelet-activating factor (PAF) and ameliorated by PAF-acetylhydrolase (PAF-AH); but whether cerebral neurons can be rescued by human recombinant PAF-AH (rPAF-AH) remains unknown. Adult male mice underwent a 60 min middle cerebral artery occlusion (MCAO) and reperfusion for 24h. Then, the mice received intravenous tail injections with different drugs. Neurological behavioral function was evaluated by Bederson's test, and cerebral infarction volume was assessed with tetrazolium chloride (TTC) staining. mRNA and protein expression levels of matrix metalloproteinase-2 (MMP-2, collagenase-1), MMP-9 (gelatinase-B), and vascular endothelial growth factor (VEGF) were determined by quantitative real-time PCR (RT-PCR) and western blot analysis, respectively. Compared with the vehicle group, rPAF-AH significantly improved sensorimotor function (42%, P=0.0001). The volume of non-infarcted brain tissue was increased by the rPAF-AH treatment (16.3±4.6% vs. 46.0±10.3%, respectively). rPAF-AH significantly reduced mRNA and protein levels of MMP-2 and MMP-9, but increased the mRNA (P<0.001) and protein levels (P<0.01) of VEGF. These results demonstrate that rPAF-AH provides neuroprotection against ischemic injury. Neuroprotection might be induced not only by decrease in MMP-2 and MMP-9 expression, but also by increased VEGF expression.

A direct comparison of efficacy between desloratadine and rupatadine in seasonal allergic rhinoconjunctivitis: a randomized, double-blind, placebo-controlled study

Background

H1-antihistamines are recommended as the first-line symptomatic treatment of allergic rhinitis. The objective of this study was to evaluate the effects of rupatadine (RUP) versus desloratadine (DES) in subjects with seasonal allergic rhinitis (SAR).

Method

To assess the efficacy and safety of RUP in SAR in comparison with placebo (PL) and DES. A randomized, double-blind, multicenter, international, and PL-controlled study was carried out. The main selection criteria included SAR patients over 12 years old with a positive prick test to a relevant seasonal allergen for the geographic area. Symptomatic patients at screening with a nasal symptom sum score of ≥6 points (nasal discharge, nasal obstruction, sneezing, and nasal pruritus), a non-nasal score of ≥3 points (ocular pruritus, ocular redness, and tearing eyes), and a rhinorrhea score of ≥2 points with laboratory test results and electrocardiography within acceptable limits were included in the study. Change from baseline in the total symptom-score (T7SS) over the 4-week treatment period (reflective evaluation) was considered the primary efficacy variable. Secondary efficacy measures included total nasal symptom score (T4NSS) and conjunctival symptom score (T3NNSS), both of which are reflective and instantaneous evaluations. Furthermore questions related to quality of life (eg, sleep disturbances or impairment of daily activities) have also been evaluated. Safety was assessed according to adverse events reported, as well as laboratory and electrocardiography controls.

Results

A total of 379 patients were randomized, of which 356 were included and allocated to PL (n = 122), RUP (n = 117), or DES (n = 117). Mean change of T7SS over the 4-week treatment period was significantly reduced in the RUP (–46.1%, P = 0.03) and DES (–48.9%, P = 0.01) groups, compared with PL. Similarly, RUP and DES were comparable and significantly superior to PL for all secondary endpoints, including nasal and conjunctival symptoms and patients’ and investigator’s overall clinical opinions. Symptom score evaluation (both reflective and instantaneous evaluations) throughout the treatment period showed a progressive and maintained significant improvement with both treatments at day 7 (P = 0.01), day 14 (P = 0.007), and day 21 (P = 0.01) in comparison with PL. Adverse events were scarce and were similar in both treatment groups. Electrocardiography (QTc) and lab test results did not show any relevant findings

Conclusion

RUP is a very good choice for SAR due to its contribution to the improvement of nasal (including obstruction) and non-nasal symptoms to a similar degree as DES.

Systemic up-regulation of TLR4 causes lipopolysaccharide-induced augmentation of nasal cytokine release in allergic rhinitis

BACKGROUND

Allergic rhinitis is a systemic disorder, and it is clinically well recognized that it can be aggravated by infection. Activation of the innate immune system constitutes a critical element in the process. Toll-like receptors (TLRs) comprise a part of the innate immune system, and lipopolysaccharide (LPS)-induced activation of TLR4 represents bacterial-induced interactions in various model systems. The present study examines how TLR2 and TLR4 expression is affected by symptomatic allergic rhinitis, and if LPS added upon allergen affects nasal cytokine release.

METHODS

In patients with pollen-induced allergic rhinitis and healthy non-allergic volunteers, nasal lavage (NAL), peripheral blood and bone marrow were sampled before and during the pollen season. TLR2 and TLR4 expression was determined flow cytometrically. Changes in the TLR receptor expression pattern were evaluated by a nasal challenge with allergen followed by LPS, or vice versa. Symptoms along with cells and cytokines in NAL were analyzed.

RESULTS

TLR4 expression increased in leukocytes in NAL, peripheral blood and bone marrow during symptomatic allergic rhinitis. A similar increase was seen for TLR2 in neutrophils in blood. Nasal challenge with allergen followed by LPS augmented the release of IL-4, IL-5, IL-10, IL-13, IFN-γ and TNF-α.

CONCLUSION

A systemic up-regulation of TLR4 in symptomatic allergic rhinitis may explain why LPS preceded by allergen increases nasal cytokine release.

In Vitro and In Vivo Effects of Statins on Platelet-Activating Factor and Its Metabolism

Platelet activating factor (PAF) is implicated in cardiovascular disease (CVD). Statins are widely used in these situations. Therefore, we assessed their effect on the biological activities and metabolism of PAF. Several statins, including simvastatin, exhibited an inhibitory effect against PAF, comparable with that of PAF-inhibitors. Simvastatin also suppressed in vivo PAF-biosynthesis via the de novo pathway, in leukocytes of 6 simvastatin-treated volunteers. Total cholesterol and low-density lipoprotein cholesterol were also significantly decreased, whereas high-density lipoprotein cholesterol, triacylglycerol, EC50, and lag time were unaffected in these participants. Simvastatin with an intact lactone ring also inhibited PAF-activities, while incubation of human mesangial cells with it also resulted in decreased de novo PAF-biosynthesis. This suggests that these simvastatin-dependent effects are independent of its lactone ring. These new actions of statins should be further studied in PAF-implicated pathological conditions such as CVD, cancer, and renal disease.

Rupatadine and its effects on symptom control, stimulation time, and temperature thresholds in patients with acquired cold urticaria

BACKGROUND

Patients with acquired cold urticaria (ACU) show itchy wheals during cold exposure. This disturbing condition involves histamine and platelet-activating factor in its pathogenesis. Rupatadine is a dual antagonist of both histamine and platelet-activating factor.

OBJECTIVE

To assess rupatadine efficacy in preventing reactions to cold challenge in patients with ACU.

METHODS

A crossover, randomized, double-blind, placebo-controlled study in which 21 patients with ACU received rupatadine, 20 mg/d, or placebo for 1 week each is presented. The main outcome was the critical stimulation time threshold (CSTT) determined by ice cube challenge. Secondary outcomes included CSTT and the critical temperature threshold assessed by a cold provocation device (TempTest 3.0), as well as scores for wheal reactions, pruritus, burning sensations, and subjective complaints after cold challenge.

RESULTS

After rupatadine treatment, 11 (52%) of 21 patients exhibited a complete response (ie, no urticaria lesions after ice cube provocation). A significant improvement in CSTT compared with placebo was observed after ice cube and TempTest 3.0 challenge (P = .03 and P = .004, respectively). A significant reduction of critical temperature threshold (P < .001) and reduced scores for cold provocation-induced wheal reactions (P = .01), pruritus (P = .005), burning sensation (P = .03), and subjective complaints (P = .03) after rupatadine treatment were also found. Mild fatigue (n = 4), somnolence (n = 1), and moderate headache (n = 1) were reported during active treatment.

CONCLUSION

Rupatadine, 20 mg/d, shows high efficacy and is well tolerated in the treatment of ACU symptoms.

Anti-platelet-activating factor effects of highly active antiretroviral therapy (HAART): a new insight in the drug therapy of HIV infection?

Platelet-activating factor (PAF) is a potent inflammatory mediator, which seems to play a role in the pathogenesis of several AIDS manifestations such as AIDS dementia complex, Kaposi's sarcoma, and HIV-related nephropathy. PAF antagonists have been studied in these conditions with promising results. In order to examine the possible interactions between PAF and antiretroviral therapy, we studied the effect of nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, and protease inhibitors against PAF biological activities and its basic biosynthetic enzymes dithiothreitol-insensitive PAF-cholinephosphotransferase (PAF-CPT) and lyso-PAF-acetyltransferase (Lyso-PAF-AT), as well as its main degradative enzyme PAF-acetylhydrolase, of human mesangial cell line (HMC). We also studied the effect of several backbones and highly active antiretroviral therapy (HAART) regimens against PAF activity. Among the drugs tested, several inhibited PAF-induced platelet aggregation in a concentration-depended manner, with tenofovir, efavirenz, and ritonavir exhibiting the higher inhibitory effect. In addition, when these drugs were combined in backbones and HAART regimens based on American antiretroviral therapy proposals, they also synergistically exhibited an inhibitory effect against PAF-induced platelet aggregation. Several of these drugs have also inhibited in vitro microsomal PAF-CPT activity, and concentrations of lopinavir-r or tenofovir-DF (similar to their IC(50) against PAF-induced platelet aggregation) exhibited the same effect against PAF-CPT and Lyso-PAF-AT when added in the cell medium of cultured HMC. In addition, in naïve patients treated with one of the most potent anti-PAF HAART regimens (efavirenz/emtricitabine/tenofovir-DF) for a period of 1 month, a significant reduction of the specific activity of PAF-CPT of washed human leukocytes of these patients was also observed, compared with its levels before the HAART treatment. These promising results need to be further studied and confirmed by additional in vivo tests in order to optimize HAART efficacy.

Platelet-activating factor in the enteric nervous system of the guinea pig small intestine

Platelet-activating factor (PAF) is a proinflammatory mediator that may influence neuronal activity in the enteric nervous system (ENS). Electrophysiology, immunofluorescence, Western blot analysis, and RT-PCR were used to study the action of PAF and the expression of PAF receptor (PAFR) in the ENS. PAFR immunoreactivity (IR) was expressed by 6.9% of the neurons in the myenteric plexus and 14.5% of the neurons in the submucosal plexus in all segments of the guinea pig intestinal tract as determined by double staining with anti-human neuronal protein antibody. PAFR IR was found in 6.1% of the neurons with IR for calbindin, 35.8% of the neurons with IR for neuropeptide Y (NPY), 30.6% of the neurons with IR for choline acetyltransferase (ChAT), and 1.96% of the neurons with IR for vasoactive intestinal peptide (VIP) in the submucosal plexus. PAFR IR was also found in 1.5% of the neurons with IR for calbindin, 51.1% of the neurons with IR for NPY, and 32.9% of the neurons with IR for ChAT in the myenteric plexus. In the submucosal plexus, exposure to PAF (200-600 nM) evoked depolarizing responses (8.2 +/- 3.8 mV) in 12.4% of the neurons with S-type electrophysiological behavior and uniaxonal morphology and in 12.5% of the neurons with AH-type electrophysiological behavior and Dogiel II morphology, whereas in the myenteric preparations, depolarizing responses were elicited by a similar concentration of PAF in 9.5% of the neurons with S-type electrophysiological behavior and uniaxonal morphology and in 12.0% of the neurons with AH-type electrophysiological behavior and Dogiel II morphology. The results suggest that subgroups of secreto- and musculomotor neurons in the submucosal and myenteric plexuses express PAFR. Coexpression of PAFR IR with ChAT IR in the myenteric plexus and ChAT IR and VIP IR in the submucosal plexus suggests that PAF, after release in the inflamed bowel, might act to elevate the excitability of submucosal secretomotor and myenteric musculomotor neurons. Enhanced excitability of motor neurons might lead to a state of neurogenic secretory diarrhea.