Pepsin and pH of Gastric Juice in Patients With Gastrointestinal Reflux Disease and Subgroups.

GOAL: The aim of this study was to investigate the pepsin values and pH results of gastric juice among the subtypes of gastroesophageal reflux disease (GERD) and functional heartburn. BACKGROUND: The major destructive agents of GERD on the esophageal epithelium are gastric acid and pepsin. No precise information about pepsin concentration in gastric juice exists. STUDY: Ninety patients with GERD, 39 erosive reflux disease (ERD) Los Angeles (LA) grade A/B, 13 ERD LA grade C/D, 19 nonerosive reflux disease (NERD), 8 esophageal hypersensitivity, 11 functional heartburn, and 24 healthy controls were included in the study. During endoscopy gastric juices from the patients were aspirated and their pH readings immediately recorded. Gastric juice samples were analyzed using Peptest, a lateral flow device containing 2 unique human monoclonal antibodies to detect any pepsin present in the gastric juice sample. RESULTS: The highest mean gastric pepsin concentration (0.865 mg/mL) and the lowest median gastric pH (1.4) was observed in the LA grade C/D group compared with the lowest mean gastric pepsin concentration (0.576 mg/mL) and the highest median gastric pH (2.5) seen in the NERD group. Comparing pH, the NERD patient group was significantly higher (P=0.0018 to P=0.0233) when compared with all other GERD patient groups. CONCLUSIONS: The basal gastric pepsin level in the healthy control group was comparable to literature values. There was good correlation and a significant linear relationship between the gastric pepsin level and gastric pH within the patient groups. The severity of the GERD disease is related to the lowest pH and the highest pepsin concentration in gastric juice.

A Novel In Vitro Model for Determining the Optimum pH and Dose Volume of New Liquid Alginate for Infant Reflux Suppression.

BACKGROUND: Gastroesophageal reflux frequently occurs in infants from birth to 2 years and is characterised by reflux and regurgitation often occurring during or immediately after feeds. These reflux events can range in both frequency and severity, and as the reflux events increase, they become increasingly distressing for both the infant and the parent. The study aimed to characterise the properties of a new infant liquid alginate product, determining the optimum gastric pH and dose volume for maximum reflux suppressant activity. METHODS: An in vitro infant stomach model was designed and developed that allowed products to be assessed for their reflux suppression activity. The validation of the model was completed by three independent operators comparing a milk control with infant Gaviscon to evaluate the models' robustness, reproducibility, and ease of use. The model was used to establish reflux suppression activity of a new liquid alginate infant formulation in comparison with a milk control. Suppression activity was assessed at varying doses and pH within a physiological range. RESULTS: The validation study demonstrated no significant difference in refluxate volumes for the milk control within each reflux event when comparing across the three individual operators. Similarly, no statistical differences were seen during the infant Gaviscon experiments, confirming the robustness and reproducibility of the model. Significant reflux suppression was seen across the pH range (except at pH 5.75); the pH most advantageous for reflux suppression was pH 5.25. The optimum dose volume for consistently suppressing reflux was shown to be 5 ml. An infant stomach model was designed for evaluating reflux suppression activity of a formulation of liquid alginate. The optimum gastric pH and dose volume for demonstrating significant reflux suppression and the thickening of formula milk by the infant liquid alginate formulation were established. CONCLUSION: This study confirms the mode of action of the alginate formula, demonstrating a superior reduction in the retrograde movement of in vitro gastric contents and volume of regurgitation. The study also demonstrates that optimal performance occurs in conditions that are in line physiologically with the target patient. Both actions compliment and support the efficacy of the alginate formulation as a reflux therapy agent.

Salivary Pepsin as an Intrinsic Marker for Diagnosis of Sub-types of Gastroesophageal Reflux Disease and Gastroesophageal Reflux Disease-related Disorders.

BACKGROUND/AIMS: To determine the value of salivary pepsin in discriminating sub-types of gastroesophageal reflux disease (GERD) and GERD-related disorders. METHODS: Overall, 322 patients with different sub-types of GERD and 45 healthy controls (HC) were studied. All patients took Gastroesophageal Reflux Disease Questionnaire (GerdQ) and underwent endoscopy and 24-hour esophageal pH monitoring and manometry. Salivary pepsin concentration (SPC) was detected by using colloidal gold double-antibody immunological sandwich assay. Oral esomeprazole treatment was administrated in the patients with non-erosive reflux disease (NERD) and extra-esophageal symptoms (EES). RESULTS: Compared to HC, patients with erosive esophagitis, NERD, EES, EES plus typical GERD symptoms, or Barrett's esophagus had a higher prevalence of saliva and SPC (all P < 0.001). There was no significant difference in the positive rate for pepsin in patients with functional heartburn or GERD with anxiety and depression, compared to HC. After esomeprazole treatment, the positive rate and SPC were significantly reduced in NERD (both P < 0.001) and in EES ( P = 0.001 and P = 0.002, respectively). Of the 64 NERD patients, 71.9% (n = 46) were positive for salivary pepsin, which was significantly higher than the rate (43.8%, n = 28) of pathological acid reflux as detected by 24-hour esophageal pH monitoring (P = 0.002). CONCLUSIONS: Salivary pepsin has an important significance for the diagnosis of GERD and GERD-related disorders. Salivary pepsin and 24-hour esophageal pH monitoring may complement with each other to improve the diagnostic efficiency.

Validation in China of a non-invasive salivary pepsin biomarker containing two unique human pepsin monoclonal antibodies to diagnose gastroesophageal reflux disease.

OBJECTIVES: Peptest is a new non-invasive reflux diagnostic test based on lateral flow technology that containing two highly specific human pepsin monoclonal antibodies for detecting pepsin, a biomarker for reflux disease. The primary aim of this multicenter clinical study was to validate the efficacy of Peptest in patients diagnosed with gastroesophageal reflux and healthy controls in China. METHODS: Patients with suspected gastroesophageal reflux underwent an endoscopy and were classified into non-erosive reflux disease and erosive esophagitis subgroups. A healthy control group was also recruited. All participants were given a reflux disease questionnaire-patients scoring greater than 12 and controls scoring zero. All participants provided a postprandial saliva sample and most patients gave an additional post-symptom sample for pepsin analysis. RESULTS: Altogether 1032 participants aged between 19 and 78 years were recruited. They consisted of 488 patients with non-erosive reflux disease, 221 with erosive esophagitis and 323 healthy controls. The number of postprandial and post-symptom samples analyzed totaled 1031 and 692, respectively. The results across all centers showed an overall pepsin-positive sensitivity of 85%, a specificity of 60%, a positive predictive value of 82%, a negative predictive value of 65% and a positive likelihood ratio of 2.12. CONCLUSION: The sensitivity of Peptest was high, but the specificity achieved in some centers was low, resulting overall in only a moderate specificity. Further diagnostic investigative studies are warranted.

Pepsin: biomarker, mediator, and therapeutic target for reflux and aspiration.

Extra-esophageal reflux is suspected to cause a wide range of clinical symptoms in the upper airways. Diagnosis and treatment has focused on acid, but realization of the role of nonacid reflux has resulted in research investigating the use of pepsin as a biomarker for gastric reflux and aspiration. Pepsin analysis can complement the use of questionnaires and office-based diagnosis and lessen the dependency on invasive and expensive diagnostic tests. Furthermore, pepsin as a first-line diagnostic biomarker has been shown to improve the accuracy of reflux diagnosis. In addition to its use as a diagnostic biomarker, pepsin has been shown to cause inflammation independent of the pH of the refluxate and thus despite acid suppression therapy. Research is ongoing to develop new therapies for airway reflux that specifically target pepsin.

A comparative study on the raft chemical properties of various alginate antacid raft-forming products.

OBJECTIVE: Research to measure the chemical characterization of alginate rafts for good raft performance and ascertain how formulation can affect chemical parameters. SIGNIFICANCE: A selection of alginate formulations was investigated all claiming to be proficient raft formers with significance between products established and ranked. METHODS: Procedures were selected which demonstrated the chemical characterization allowing rafts to effectively impede the reflux into the esophagus or in severe cases to be refluxed preferentially into the esophagus and exert a demulcent effect, with focus of current research on methods which complement previous studies centered on physical properties. The alginate content was analyzed by a newly developed HPLC method. Methods were used to determine the neutralization profile and the acid neutralization within the raft determined along with how raft structure affects neutralization. RESULTS: Alginate content of Gaviscon Double Action (GDA) within the raft was significantly superior (p < .0001) to all competitor products. The two products with the highest raft acid neutralization capacity were GDA and Rennie Duo, the latter product not being a raft former. Raft structure was key and GDA had the right level of porosity to allow for longer duration of neutralization. CONCLUSION: Alginate formulations require three chemical reactions to take place simultaneously: transformation to alginic acid, sodium carbonate reacting to form carbon dioxide, calcium releasing free calcium ions to bind with alginic acid providing strength to raft formation. GDA was significantly superior (p <.0001) to all other comparators.

Association of Gel-Forming Mucins and Aquaporin Gene Expression With Hearing Loss, Effusion Viscosity, and Inflammation in Otitis Media With Effusion.

Importance: Persistent, viscous middle ear effusion in pediatric otitis media (OM) contributes to increased likelihood of anesthesia and surgery, conductive hearing loss, and subsequent developmental delays. Biomarkers of effusion viscosity and hearing loss have not yet been identified despite the potential that such markers hold for targeted therapy and screening. Objective: To investigate the association of gel-forming mucins and aquaporin 5 (AQP5) gene expression with inflammation, effusion viscosity, and hearing loss in pediatric OM with effusion (OME). Design, Setting, and Participants: Case-control study of 31 pediatric patients (aged 6 months to 12 years) with OME undergoing tympanostomy tube placement and control individuals (aged 1 to 10 years) undergoing surgery for cochlear implantation from February 1, 2013, through November 30, 2014. Those with 1 or more episodes of OM in the previous 12 months, immunologic abnormality, anatomical or physiologic ear defect, OM-associated syndrome (ie, Down syndrome, cleft palate), chronic mastoiditis, or history of cholesteatoma were excluded from the study. All patients with OME and 1 control were recruited from Children's Hospital of Wisconsin, Milwaukee. The remainder of the controls were recruited from Sick Kids Hospital in Toronto, Ontario, Canada. Main Outcomes and Measures: Two to 3 middle ear biopsy specimens, effusions, and preoperative audiometric data (obtained <3 weeks before surgery) were collected from patients; only biopsy specimens were collected from controls. Expression of the mucin 2 (MUC2), mucin 5AC (MUC5AC), mucin 5B (MUC5B), and AQP5 genes were assayed in middle ear biopsy specimens by quantitative polymerase chain reaction. One middle ear biopsy specimen was sectioned for histopathologic analysis. Reduced specific viscosity of effusions was assayed using rheometry. Results: Of the 31 study participants, 24 patients had OME (mean [SD] age, 50.4 [31.9] months; 15 [62.5%] male; 16 [66.7%] white) and 7 acted as controls (mean [SD] age, 32.6 [24.4] months; 2 [26.6%] male; 6 [85.7%] white). Mucins and AQP5 gene expression were significantly higher in patients with OME relative to controls (MUC2: ratio, 127.6 [95% CI, 33.7-482.7]; MUC5AC: ratio, 3748.8 [95% CI, 558.1-25 178.4]; MUC5B: ratio, 471.1 [95% CI, 130.7-1697.4]; AQP5: ratio, 2.4 [95% CI, 1.1-5.6]). A 2-fold increase in MUC5B correlated with increased hearing loss (air-bone gap: 7.45 dB [95% CI, 2.65-12.24 dB]; sound field: 6.66 dB [95% CI, 6.63-6.69 dB]), effusion viscosity (2.75 mL/mg; 95% CI, 0.89-4.62 mL/mg), middle ear epithelial thickness (3.5 µm; 95% CI, 1.96-5.13 µm), and neutrophil infiltration (odds ratio, 1.7; 95% CI, 1.07-2.72). A 2-fold increase in AQP5 correlated with increased effusion viscosity (1.94 mL/mg; 95% CI, 0.08-3.80 mL/mg). Conclusions and Relevance: Further exploration of the role of MUC5B in the pathophysiology of OME holds promise for development of novel, targeted therapies to reduce effusion viscosity, facilitation of effusion clearance, and prevention of disease chronicity and hearing loss in patients with OME.

Ivacaftor and symptoms of extra-oesophageal reflux in patients with cystic fibrosis and G551D mutation.

BACKGROUND: Extra-oesophageal reflux (EOR) may lead to microaspiration in patients with cystic fibrosis (CF), a probable cause of deteriorating lung function. Successful clinical trials of ivacaftor highlight opportunities to understand EOR in a real world study. METHODS: Data from 12 patients with CF and the G551D mutation prescribed ivacaftor (150mg bd) was collected at baseline, 6, 26 and 52weeks. The changes in symptoms of EOR were assessed by questionnaire (reflux symptom index (RSI) and Hull airway reflux questionnaire (HARQ)). RESULTS: Six patients presented EOR at baseline (RSI >13; median 13; range 2-29) and 5 presented airway reflux (HARQ >13; median 12; range 3 to 33). Treatment with ivacaftor was associated with a significant reduction of EOR symptoms (P<0∙04 versus baseline) denoted by the reflux symptom index and Hull airway reflux questionnaire. CONCLUSION: Ivacaftor treatment was beneficial for patients with symptoms of EOR, thought to be a precursor to microaspiration.

Mucin gene expression in reflux laryngeal mucosa: histological and in situ hybridization observations.

Objectives/Hypothesis. To determine if laryngopharyngeal reflux alters mucin gene expression in laryngeal mucosa. Methods. In situ hybridization was employed to study the expression of the 8 well-characterised mucin genes MUC1-4, 5AC, 5B, 6, and 7 in reflux laryngeal mucosa from laryngeal ventricles, posterior commissures, and vocal folds compared to control/normal laryngeal mucosa. Results. MUC1-5 genes are expressed in normal and reflux laryngeal mucosa. MUC1, 3 and 4 are expressed in respiratory and squamous mucosa whereas MUC2 and 5AC are expressed in respiratory mucosa only. MUC3, 4 and 5AC are downregulated in reflux mucosa. MUC5AC expression is significantly reduced in the 3 mucosal sites and when mucosal type was taken into account, this remains significant in combined laryngeal and ventricular mucosa only. Conclusions. MUC3, 4 and 5AC expression is downregulated in laryngopharyngeal reflux. This may be due to laryngeal mucosal metaplasia and/or alteration of mucin gene expression in the preexisting mucosa. Altered mucin gene expression might predispose laryngeal mucosa to the damaging effect of reflux.

The modulation of pancreatic lipase activity by alginates.

Alginates are comprised of mannuronic (M) and guluronic acid (G) and have been shown to inhibit enzyme activity. Pancreatic lipase is important in dietary triacylglycerol breakdown; reducing pancreatic lipase activity would reduce triacylglycerol breakdown resulting in lower amounts being absorbed by the body. Lipase activity in the presence of biopolymers was assessed by enzymatic assay using natural and synthetic substrates. Alginate inhibited pancreatic lipase by a maximum of 72.2% (±4.1) with synthetic substrate (DGGR) and 58.0% (±9.7) with natural substrate. High-G alginates from Laminaria hyperborea seaweed inhibited pancreatic lipase to a significantly higher degree than High-M alginates from Lessonia nigrescens, showing that inhibition was related to alginate structure. High-G alginates are effective inhibitors of pancreatic lipase and are used in the food industry at low levels. They could be included at higher levels in foods without altering organoleptic qualities, potentially reduce the uptake of dietary triacylglycerol aiding in weight management.

Laryngopharyngeal reflux and GERD.

In patients with laryngopharygeal reflux (LPR), gastric contents exhibit retrograde flow into the upper aero-digestive tract, causing extraesophageal symptoms including chronic cough, hoarseness, indigestion, difficulty swallowing, globus pharyngis, and asthma. The following on laryngopharyngeal reflux includes commentaries on the use of patient-completed questionaires and anti-human pepsin antibodies and other non-invasive tests in diagnosis; the role of pepsin and acid in the etiologies of laryngeal cancers; and the application of proton pump inhibitor (PPI) therapy for the treatment of LPR.

Assessment of the Safety and Efficacy of a Raft-Forming Alginate Reflux Suppressant (Liquid Gaviscon) for the Treatment of Heartburn during Pregnancy.

Gastro-oesophageal reflux (GER) and the symptoms of heartburn and regurgitation are common in pregnancy. These symptoms are transient and mostly resolve postpartum but have a negative impact on quality of life. Here, we present a prospective clinical evaluation of the safety and efficacy of an alginate raft-forming oral suspension that is licensed for use in pregnancy. The study was a multicentre, prospective, open-label, and baseline-controlled study of Liquid Gaviscon (LG) in the treatment of heartburn in pregnant women with current symptoms of heartburn and/or reflux requiring treatment (recruited 144). The efficacy of the study medication was rated by the investigator (primary endpoint) and patient. Treatment was deemed to be a success in 91% of patients as judged by the investigator (95% CI 85.0-95.3) and 90% (95% CI 84.1-94.8) when assessed by the patient themselves. Very few adverse events or serious adverse events were reported that were considered to be related to the study medication, and these were consistent with the normal population incidences. Serum sodium levels remained unchanged. This prospective open-label study in a large number of pregnant women has shown that LG is both safe and highly efficacious in the treatment of heartburn and GER symptoms in pregnancy.

Rapid salivary pepsin test: blinded assessment of test performance in gastroesophageal reflux disease.

OBJECTIVE/HYPOTHESIS: Pepsin lateral flow device (LFD) is a rapid noninvasive test to detect salivary pepsin as a surrogate marker for gastroesophageal reflux disease (GERD). We aimed to establish the test sensitivity, specificity, positive and negative predictive values (PPV, NPV) in patients with symptomatic and objective evidence of GERD compared to healthy controls. STUDY DESIGN: Prospective, blinded, controlled cohort study. METHODS: A total of 230 samples were analyzed. In vitro bench testing was conducted on 52 gastric juice and 54 sterile water samples to assess test sensitivity and specificity. Saliva was collected from 58 patients with GERD and 51 controls. All patients with GERD underwent esophagogastroduodenoscopy (EGD) and wireless 48-hour pH monitoring off acid suppressive therapy. PPV and NPV were calculated based on disease definition of esophagitis and/or abnormal pH monitoring. RESULTS: Receiver operating characteristics analysis of in vitro samples found assay sensitivity and a specificity of 87%. There were 6/51 (12%) control subjects and 13/58 (22%) patients with GERD who tested positive for salivary pepsin (P = .25). There was a step-wise increase in the prevalence of positive salivary pepsin: esophagitis (55%), abnormal pH monitoring (43%), GERD symptoms only (24%) (P < .001). Salivary pepsin test showed a PPV of 81% and NPV of 78% for those with objective evidence of GERD (abnormal pH and/or esophagitis). CONCLUSIONS: Rapid LFD for salivary pepsin has acceptable test characteristics in patients with GERD. A positive salivary pepsin test in this group may obviate the need for more expensive diagnostic testing by EGD or pH monitoring.

Reflux revisited: advancing the role of pepsin.

Gastroesophageal reflux disease is mediated principally by acid. Today, we recognise reflux reaches beyond the esophagus, where pepsin, not acid, causes damage. Extraesophageal reflux occurs both as liquid and probably aerosol, the latter with a further reach. Pepsin is stable up to pH 7 and regains activity after reacidification. The enzyme adheres to laryngeal cells, depletes its defences, and causes further damage internally after its endocytosis. Extraesophageal reflux can today be detected by recognising pharyngeal acidification using a miniaturised pH probe and by the identification of pepsin in saliva and in exhaled breath condensate by a rapid, sensitive, and specific immunoassay. Proton pump inhibitors do not help the majority with extraesophageal reflux but specifically formulated alginates, which sieve pepsin, give benefit. These new insights may lead to the development of novel drugs that dramatically reduce pepsinogen secretion, block the effects of adherent pepsin, and give corresponding clinical benefit."For now we see through a glass, darkly."-First epistle, Chapter 13, Corinthians.

Evaluation of an Innovative Over-the-Counter Treatment for Symptoms of Reflux Disease: Quick-Dissolving Alginate Granules.

Traditional antacids and alginate-based reflux suppressants are OTC products commonly used to treat reflux symptoms. There has been a lack of innovation of new formulations in this therapy area despite consumers finding established products unpalatable. Here we evaluate a novel product formulation which takes the form of quick-dissolving alginate granules in single-dose sachets (Gaviscon Direct Powder (GDP)). Market research and taste evaluation confirmed that reflux sufferers considered GDP to have good flavour and taste, no chalky aftertaste and dissolved rapidly in the mouth with 68% noting so within 10 seconds. GDP was considered convenient and easy to use. The consumer-driven product development was also shown to form a strong alginate raft in standardised in vitro conditions that met the specifications of the BP monograph (raft strength > 7.5 g). Gastric retention of GDP and a test meal was investigated in healthy volunteers using gamma scintigraphy in comparison to Liquid Gaviscon. Both products formed an alginate raft in the stomach above the test meal and emptied after the meal. The gastric retention of the GDP product was found to be noninferior to Liquid Gaviscon. In conclusion, the innovative GDP product formed an effective raft and was well liked by consumers.

Gastroesophageal reflux and idiopathic pulmonary fibrosis: a prospective study.

BACKGROUND AND OBJECTIVE: Idiopathic pulmonary fibrosis (IPF) is the most common of the idiopathic interstitial pneumonias. There is evidence of the increased prevalence of gastroesophageal reflux disease in patients with IPF. The aim of this prospective study was to evaluate reflux in patients with IPF by analyzing the scores of the reflux cough questionnaire, measurement of pepsin in exhaled breath condensate (EBC) to detect extraesophageal reflux, and Helicobacter pylori serology to evaluate the prevalence of this stomach bacterium in patients with IPF. MATERIAL AND METHODS: The Hull airway reflux questionnaire (HARQ) was completed by 40 patients with IPF and 50 controls in order to evaluate reflux symptoms. EBC was collected from 23 patients (17 patients with IPF and 6 controls) for measurement of pepsin by the lateral flow technique. A prospective study of 57 subjects (34 patents with IPF and 23 controls) for H. pylori antibody detection by ELISA was preformed. RESULTS: Significantly higher HARQ scores (maximum score, 70) were recorded in patients with IPF compared with controls (19.6 [SD, 12.4] vs. 3 [SD, 2.9], P<0.001). There was no significant difference in EBC pepsin positivity between patients with IPF and controls (2 of the 17 patients vs. none of the 6 controls, P=0.38). There was no significant difference in H. pylori serology between patients with IPF and controls (17 of the 34 patients vs. 14 of the 23 controls, P=0.42). CONCLUSION: Patients with IPF had significantly increased scores of airway reflux symptoms. However, no objective evidence of extraesophageal reflux or H. pylori infection in patients with IPF was obtained in this study. The role of gastroesophageal and extraesophageal reflux in pathogenesis of IPF should be evaluated in a larger prospective study.

Physiological parameters governing the action of pancreatic lipase.

The most widely used pharmacological therapies for obesity and weight management are based on inhibition of gastrointestinal lipases, resulting in a reduced energy yield of ingested foods by reducing dietary lipid absorption. Colipase-dependent pancreatic lipase is believed to be the major gastrointestinal enzyme involved in catalysis of lipid ester bonds. There is scant literature on the action of pancreatic lipase under the range of physiological conditions that occur within the human small intestine, and the literature that does exist is often contradictory. Due to the importance of pancreatic lipase activity to nutrition and weight management, the present review aims to assess the current body of knowledge with regards to the physiology behind the action of this unique gastrointestinal enzyme system. Existing data would suggest that pancreatic lipase activity is affected by intestinal pH, the presence of colipase and bile salts, but not by the physiological range of Ca ion concentration (as is commonly assumed). The control of secretion of pancreatic lipase and its associated factors appears to be driven by gastrointestinal luminal content, particularly the presence of acid or digested proteins and fats in the duodenal lumen. Secretion of colipase, bile acids and pancreatic lipase is driven by cholecystokinin and secretin release.

Laryngeal mucosa: its susceptibility to damage by acid and pepsin.

OBJECTIVES/HYPOTHESIS: Exposure of pig laryngeal mucosa to pepsin and acid will have a differential damaging effect depending on the anatomical site, mirroring the effects seen in the human larynx in laryngopharyngeal reflux (LPR). This study aims to quantitate damage caused to laryngeal tissue by acid alone, and acid and pepsin, and also to determine if the extent of this damage depends on the tissue site. STUDY DESIGN: Prospective translational research study. METHODS: An excised porcine laryngeal damage model in a small Ussing chamber was used to measure the effect of pepsin and acid on five sites (ventricles, vocal folds, posterior commissure, supraglottic, and subglottic mucosa). The tissue samples were incubated on the lumenal side for 1 hour with pH 2 and 4 HCl, pH 2 plus 1 mg/mL pepsin, and pH 4 plus 1 mg/mL pepsin. Damage was assessed by changes in absorbance of the bathing solution at optical density (OD) 260 nm and OD 280 nm and by measurement of released DNA compared to tissues bathed in pH 7.4 buffer. Damage was also assessed histologically. RESULTS: Based on histology, all the tissues were resistant to pH 4.0 except the subglottic mucosa. Only the posterior commissure was not damaged by pH 2.0 plus pepsin. Similar patterns were observed with absorbance changes and DNA release. CONCLUSIONS: The subglottic mucosa was the most susceptible to damage and the posterior commissure the least. Laryngeal tissues are essentially resistant to damage at pH 4.0, but are damaged when pepsin is present. This suggests that in LPR, pH 4.0 or above refluxate would only be damaging if it contains pepsin.