Jerzy Sarosiek

Human esophageal secretion: Mucosal response to luminal acid and pepsin

BACKGROUND/AIMS Although esophageal histology in humans reveals numerous submucosal mucous glands, their secretion has never been explored. Therefore, we have studied the chemical composition and physical characteristics of esophageal secretion under the impact of luminal saline, acid, and acid/pepsin solutions. METHODS The esophageal lumen in 21 healthy volunteers was continuously perfused with saline, HCI, or HCI/pepsin. Perfusates were assayed for mucin, protein, and viscosity. In addition, analysis of amino acid and sugar composition of purified esophageal mucin was performed. RESULTS Esophageal perfusion with saline resulted in luminal release of mucin at the rate of 0.23 +/- 0.03 mg.cm-2 x min-1. Acid/pepsin solution significantly enhanced luminal release of mucin (0.32 +/- 0.03 mg.cm-2 x min-1; P < 0.01). HCI/pepsin solution also significantly increased the luminal output of protein (P < 0.01) and significantly impaired the viscosity of the esophageal perfusate (P < 0.05). Threonine, serine, and proline were the major amino acids within the esophageal mucin, whereas galactose was the predominant carbohydrate. CONCLUSIONS Luminally released esophageal mucin, shown for the first time in humans, contributes significantly to maintaining the high viscosity of esophageal secretions. Significant increase in the luminal release of mucin under the impact of acid and pepsin, with subsequent decline of the perfusate viscosity, may indicate that mucin is the major target for gastric acid and pepsin, absorbing the deleterious impact of the gastroesophageal refluxate.

The Interrelationship Between Salivary Epidermal Growth Factor and the Functional Integrity of the Esophageal Mucosal Barrier in the Rat

The role of salivary epidermal growth factor (sEGF) in the maintenance of the esophageal mucosal mucus coat and its permselective properties was investigated for this study. Eighteen Sprague-Dawley male rats underwent sialoadenectomy (SAD), while 18 others with sham operation served as a control. Nine SAD rats in each group received EGF in a dose of 15 micrograms/kg/d for five consecutive days prior to sacrifice. Esophageal mucosa dissected from the muscle layer was placed in the central port of a specially designed permeability chamber filled on both sides with equimolar solutions of NaCl or HCl (0.155 M). The rate of hydrogen ion diffusion from the mucosal to the serosal side was estimated by continuous recording of pH in the NaCl compartment. In addition, the mucosal mucus coat was evaluated by Alcian blue uptake methodology. SAD led to a 108% increase in the rate of permeability of the esophageal mucosa to hydrogen ion. Simultaneously, an 83% decrease in the mucus content on the surface of the esophageal mucosa was observed. A five-day supplementation of EGF substantially improved the permeability of esophageal mucosa (67%) and the mucous layer of esophagus (41%). sEGF seems to play an important physiological role in the maintenance of the functional integrity of the esophageal mucosa.

Declined human esophageal mucin secretion in patients with severe reflux esophagitis

It has been recently demonstrated that human esophageal submucosal mucous glands exhibit the ability to secrete copious amounts of mucin, well known within the gastrointestinal tract for its protective quality against hydrogen ion and pepsin. Since mucin may also play a protective role within the esophageal compartment, we have studied the rate of secretion of esophageal mucin in patients with RE. Mucin was assessed by periodic acid-Schiff methodology in esophageal secretion collected during continuous perfusion with saline (period I) followed by HCl (period II), HCl/pepsin (period III), and final saline (period IV), mimicking the natural gastroesophageal scenario. The basal rate of the luminal release of mucin in patients with grade II RE was 18% lower as compared with controls. During exposure of the esophageal mucosa to an HCl/pepsin solution, esophageal mucin output in the RE group was 52% lower than in the control group (0.154 ± 0.027 vs 0.320 ± 0.049 mg/cm2/min;P=0.025). Furthermore, the rates of esophageal mucin output in patients with grade III RE during esophageal perfusion with saline and HCl/pepsin were 62% (0.090 ± 0.021 vs 0.239 ± 0.036 mg/cm2/min;P=0.016) and 86% (0.048 ± 0.010 vs 0.320 ± 0.049 mg/cm2/min;P=0.001) lower when compared with corresponding values in controls. After endoscopic healing of RE, the overall impairment in the rate of esophageal mucin secretion in patients with grade II improved from 31% to 17% at the end of therapy, whereas in patients with grade III the impairment in mucin secretion improved only marginally from 71% to 69%. Significant impairment in the rate of esophageal mucin output in patients with severe esophagitis (grade III), prevailing despite healing of endoscopic changes, indicates that a low rate of esophageal mucin secretion may be a potential contributing factor in the development of severe mucosal damage in patients with excessive gastroesophageal reflux.

Do Salivary Organic Components Play a Protective Role in Health and Disease of the Esophageal Mucosa

Aggressive factors operating within the esophageal lumen during gastroesophageal reflux are balanced by adequately mobilized protective mechanisms. Esophageal mucosal protection operates at three different although complementary dimensions: (1) preepithelial, (2) epithelial and (3) postepithelial. Since aggressive factors predominantly operate within the esophageal lumen, preepithelial defense is pivotal in mucosal protection. The preepithelial barrier is significantly enhanced by the quantity and the quality of salivary organic components such as salivary mucin, nonmucin protein, salivary epidermal growth factor (EGF) and salivary prostaglandin E2. The rate of secretion of salivary mucin, nonmucin protein and EGF under the impact of intraesophageal mechanical (bolus) and chemical (HCl/pepsin) stimulation, mimicking the natural gastroesophageal reflux scenario, is significantly impaired in patients with RE, whereas the rate of salivary PGE2 output remains essentially unchanged. Salivary secretory response to esophageal mechanical and chemical stimuli in terms of organic components, mediated by the esophagosalivary reflex pathway, exhibits a significant impairment in patients with reflux esophagitis.

The effect of esophageal mechanical and chemical stimuli on salivary mucin secretion in healthy individuals.

Because of a newly developed model of esophageal perfusion in humans, the authors could study the role of esophago—salivary reflex in salivary neutral and acidic mucin output. The basal rate of neutral mucin output was 0.24 ± 0.06 mg per minute. Placement of intraesophageal tubing and inflation of balloons resulted in a highly significant increase in salivary mucin output (2.10 ± 0.22 mg per minute; p < 0.00001). However, implementation of esophageal perfusion with saline resulted in a significant decline of salivary mucin output (1.28 ± 0.10 mg/mL NaCl4 versus 2.08 ± 0.24 mg/mL NaCl1; p < 0.001). Esophageal perfusion with hydrochloric acid prevented the decline of salivary mucin output observed during perfusion with saline, whereas infusion of hydrochloric acid/pepsin resulted in a significant enhancement of salivary mucin output (2.89 ± 0.31 mg per minute; p < 0.01). Therefore, mechanical and chemical stimulations resulted in an overall 9-fold and 12-fold increase in the rate of salivary mucin output over the basal value, respectively. The basal rate of acidic mucin secretion was 0.26 ± 0.06 mg per minute. After placement of intraesophageal tubing, inflation of balloons, perfusion hydrochloric acid, or hydrochloric acid—pepsin solution, a significant enhancement in the rate of salivary acidic mucin output, similar to that observed during measurement of neutral mucin, was observed. Therefore, during mechanical and chemical stimulation, the rate of salivary acidic mucin output increased 7.3-fold and 11.1-fold over the basal value, respectively. A significant increase of salivary mucin output, especially under the impact of esophageal stimulation with acid and pepsin, indicates that mucin may play an important role in esophageal preepithelial defense mechanisms.

What Role Do Salivary Inorganic Components Play in Health and Disease of the Esophageal Mucosa

The integrity of the esophageal mucosa depends upon an equilibrium between aggressive factors and protective mechanisms. Esophageal mucosal protective mechanisms operate at three overlapping levels: (1) preepithelial, (2) epithelial and (3) postepithelial. Since aggressive factors always operate on the luminal side of the esophagus, preepithelial defense remains as the first line in mucosal barrier protection. Salivary secretion quantitatively and qualitatively contributes to the protective potential of the preepithelial barrier. Salivary volume and its buffering capacity are elaborated by lowering intraluminal pH within the esophagus, and are key factors in restoration of physiologic pH within the esophagus. Salivary secretory response to esophageal mechanical (bolus) and chemical (intraluminal pH) stimuli, mediated by the esophagosalivary reflex pathway, is impaired in patients with reflux esophagitis.

What is the secretory potential of submucosal mucous glands within the human gullet in health and disease

Histology of the human esophageal mucosa reveals numerous submucosal mucous glands, scattered along the esophagus and especially accumulated below the upper and above the lower esophageal sphincters. Mucin remains a major organic component of human esophageal secretion, collected using our newly developed esophageal perfusion catheter. Esophageal mucin is accompanied by nonmucin proteins, epidermal growth factor (EGF) and prostaglandin E2 (PGE2). Bicarbonate is the major inorganic component of esophageal secretion in humans. Mucosal exposure to an HC1/pepsin solution, mimicking the natural gastroesophageal scenario, significantly changed the secretory profile of all esophageal secretion components. The rate of secretion of esophageal mucin, EGF and PGE2 under the impact of HC1/pepsin in patients with reflux esophagitis appeared to be significantly impaired, although the basal rate of esophageal PGE2 output remained higher than in controls. These data indicate that a significant impairment in esophageal components of the preepithelial mucosal barrier, paralleling the severity of mucosal inflammation, may have a detrimental impact on the protective potential of the esophageal mucosal barrier, facilitating the development of reflux esophagitis.

Impact of Helicobacter pylori colonization on immunoreactive epidermal growth factor and transforming growth factor-alpha in gastric juice. Its potential pathogenetic implications.

Epidermal growth factor (EGF), pivotal in mucosal protection, is partly degraded proteolytically at low pH in the gastric milieu; gastric acid secretion, on the other hand, remains influenced byH. pylori colonization. The aim of this study, therefore, was to evaluate the impact of low pH andH. pylori colonization status on immunoreactive EGF and the other member of EGF-family, immunoreactive transforming growth factor-α (TGF-α). Eighteen patients with nonulcer dyspepsia (NUD) colonized byH. pylori and 55 NUD patients withoutH. pylori colonization were investigated. Gastric juice samples were aspirated at the beginning of the endoscopy procedure and immediately placed on ice, and their pH was recorded. The measurement of immunoreactive EGF and TGF-α was performed using commercially available radioimmunoassays (RIAs) after adjustment of pH to neutral using an assay buffer. Statistical analysis was performed using Σ-Stat for Windows. The concentration of immunoreactive EGF in patients with NUD colonized byH. pylori was 80% lower (P < 0.02) than in those withoutH. pylori and in both groups immunoreactive EGF was significantly lower when the pH of gastric juice was below 4.0. The concentration of immunoreactive EGF inH. pylori(+) andH. pylori(−) patients was similar when the pH of aspirated gastric juice was above 4.0. However, with gastric juice pH<4.0, the EGF concentration was 64% lower inH. pylori(+) patients thanH. pylori(−) patients (P<0.05). In general, the concentration of immunoreactive TGF-α in gastric juice was unaffected byH. pylori colonization or pH of gastric juice. It is concluded that: (1) significantly lower immunoreactive EGF concentrations in patients with pH below 4.0 indicate that immunoreactive EGF but not immunoreactive TGF-α is affected by an acidic gastric milieu; (2) the further reduction of gastric juice immunoreactive EGF at pH below 4.0 in patients colonized byH. pylori suggests that this microorganism may elaborate factors that accelerate its proteolytic degradation or inhibit its rate of synthesis and/or secretion; and (3) this diminished content of immunoreactive EGF at low pH, especially in patients colonized byH. pylori, may facilitate the development and/or progression of mucosal damage.

Augmented salivary protective potential: Is it one explanation to the lower prevalence of reflux esophagitis and complications in African-Americans?

It is well known that African-Americans (AA) are less likely to develop reflux esophagitis (RE) and its complications than Caucasians (C). Since salivary protective components play a key role in the maintenance of the integrity of the esophageal mucosa, we hypothesized that AA may benefit from their higher protective quality of saliva. Aims: 1. To assess content of salivary glycoconjugate (mucin), protein, bicarbonate, non-bicarbonate, TGFa, and PGE 2 in AA. 2. To compare these results with corresponding values in a C population, comparable in terms of age and gender. Subjects & Methods: The study was approved by IRB and conducted in 27 AA (12F and 15M, mean age of 41, range 29-52) and in 39 C (16F and 23M, mean age of 39, range 26-56) asymptomatic volunteers. Salivary secretions were collected under basal conditions, during mastication, and during intraesophageal mechanical and chemical stimulation, mimicking the gastroesophageal reflux scenario by using an esophageal perfusion catheter (Wilson-Cook Med. Inc., NC). Salivary glycoconjugate (mucin) and protein in salivary secretion were quantitated using PAS and Lowry methods, respectively. Salivary bicarbonate and non-bicarbonate were measured using Titra-Lab (Radiometer America, IL), whereas TGFa, and PGE 2 by RIA (Amersham, IL) and analyzed statistically by E-Stat (Jandel Sci. CA). Results: African-Americans secreted significantly more of salivary glycoconjugate (P < 0.01), protein (P < 0.05), and non-bicarbonate buffers (P < 0.01) in basal conditions; glycoconjugate (P < 0.05), protein (P < 0.05), and non-bicarbonate (P < 0.05) during mastication; glycoconjugate (P < 0.05), protein (P < 0.01), bicarbonate (0.05), non-bicarbonate (P < 0.01), and TGFa (P < 0.001) during intraesophageal mechanical stimulation; protein (P < 0.0001), bicarbonate (P < 0.05), non-bicarbonate (P < 0.05), and TGFa (P < 0.001) during intraesophageal chemical stimulation than Caucasians. Conc_!usion: • These data indicate that a significantly enhanced secretion of salivary protective factors in AA may prevent the development of esophageal mucosal pathology and subsequent complications during episodes of GER.