Correlations Among Gastric Juice pH and Ammonia, Helicobacter Pylori Infection and Gastric Mucosal Histology

Article information

Abstract

INTRODUCTION

Helicobacter pylori has remarkably high urease activity^{1, 2)}, which provides a useful means of detecting its presence. The widely used methods of diagnosing a H. pylori infection based upon urease activity are the rapid urease test (RUT) requiring an endoscopy and a ¹³C or ¹⁴C urea breath test (UBT)^3–6). These techniques take 1 to 24 hours and the final result of the RUT is usually not available until the next day at the earliest. Other investigators have tried measuring gastric juice urea and ammonia concentration as new diagnostic tests that may be performed at the time of an endoscopy and rapidly interpreted, so that patients can be treated for a H. pylori infection immediately after an endoscopic examination^{7, 8)}. They found that H. pylori infected patients have significantly lower urea levels, higher ammonia concentrations, and higher gastric urease activities than uninfected control patients. However, they noted that there is significant overlap in gastric juice ammonia concentrations between infected and uninfected patients. Therefore, the diagnostic role of gastric juice ammonia is still controversial. Kearney et al⁹⁾. concluded that the measurement of a gastric juice ammonia concentration is a relatively insensitive and nonspecific means of diagnosis for H. pylori. Other Korean investigators compared gastric juice ammonia determination to a RUT and found that the gastric juice ammonia test has higher true-positive and lower false-positive rates than does the RUT¹⁰⁾.

The effect of a H. pylori infection on acid secretion, and the relationship between gastric pH and a H. pylori infection and gastric mucosal histology have also been investigated^{11, 12)}. Furuta et al. found that a H. pylori infection and gastritis in the corpus suppress acid secretion and increase gastric pH, resulting in hypergastrinemia, and that the eradication of H. pylori normalizes acid secretion and serum gastrin levels¹²⁾. However, the relationship of gastric juice pH and ammonia concentration with the parameters of a H. pylori infection was not investigated.

The pathophysiology of H. pylori gastritis remains incompletely understood. Previous investigators have hypothesized that the type and severity of inflammation in the gastric mucosa may be related to the amount of ammonia produced by H. pylori with urease activity¹³⁾.

We determined the gastric juice pH and ammonia concentration in H. pylori gastritis, and looked for correlations between the two gastric juice parameters, and their relationship to H. pylori status and gastric mucosal histology, such as H. pylori density, gastritis severity, and gastritis activity.

MATERIALS AND METHODS

Subjects and study design

The subjects were 143 patients with dyspepsia scheduled for an elective endoscopy at the Gyeongsang National University Hospital, and who were eligible for inclusion in the study. After receiving informed consents, patients were interviewed, and data collection forms were completed, in which all clinical information was recorded. Patients were excluded from the study if they had taken antibiotics, proton pump inhibitors or bismuth compounds, or had undergone treatment for H. pylori during the preceding 4 weeks. Patients with renal insufficiency or liver cirrhosis were also excluded.

All subjects underwent an upper endoscopy and tests for H. pylori. Patients with endoscopically proven peptic ulcers or erosions with a H. pylori infection were submitted to ulcer treatment and H. pylori eradication. Patients received 20 mg of omeprazole or 10 mg of rabeprazole, 1,000 mg of amoxicillin, and 500 mg of clarithromycin twice daily for a week, and a proton pump inhibitor for an additional 5 or 7 weeks. The endoscopic examination and tests for H. pylori were performed at least 4 weeks after treatment.

The 143 patients enrolled in the study consisted of 74 men and 69 women, with a mean age of 49.9 ± 12.5 (range 19 to 71) years. The endoscopic diagnoses were gastric and/or duodenal ulcer (23 patients), erosive gastritis (12 patients), gastric dysplasia (10 patients), reflux esophagitis (5 patients), hyperplastic polyp (4 patients), submucosal tumor (1 patient), and chronic atrophic gastritis (88 patients). A H. pylori infection was documented in 94 patients (65.7%)(Table 1).

Table 1.

Characteristics of enrolled subjects (n=143).

We compared gastric pH and ammonia concentration according to the status of the H. pylori infection, and examined correlations between the two biochemical parameters and their relationship to H. pylori density, gastritis severity, and gastritis activity.

RESULTS

Ninety-four patients (65.7%) were infected with H. pylori and 49 (34.3%) were not infected (Table 1). Seventy-one patients had all three positive tests, 21 had two positive tests, and two had only one positive test. Gastric juice pH was significantly higher in the H. pylori-infected group than in the uninfected group (3.16 vs. 1.55, p=0.0001) (Table 2, Figure 1A). The ammonia concentration in gastric juice was significantly higher in the H. pylori-infected group (5.58 ± 2.69 μmol/L) than in the uninfected group (2.00 ± 1.49 μmol/L)(p=0.0001) (Table 2, Figure 1B).

Table 2.

Gastric juice pH and ammonia concentration in H. pylori-infected and uninfected groups.

Figure 1.

(A) Gastric pH was higher in the infected group than in the uninfected group (3.16 vs. 1.55, p=0.0001). (B) Gastric ammonia concentration was higher in the infected group than in the uninfected group (5.58 ± 2.69 vs. 2.00 ± 1.49 μmoL/L, p=0.0001).

Among the patients with a peptic ulcer or erosive gastritis, 28 patients infected with H. pylori and who wanted eradication underwent eradication therapy. Treatment was successful in 19 patients (67.9%), and their gastric pH levels and ammonia concentrations were significantly lower than those of the nine patients who experienced eradication failure (1.60 vs. 2.33, p=0.007; 1.77 ± 1.28 vs. 4.02 ± 1.20 μmol/L, p=0.0001) (Table 3, Figure 2). The Gastric juice pH levels and ammonia concentrations were significantly decreased after the eradication of H. pylori, when compared to pre-eradication treatment levels in the 19 patients who experienced successful eradication (1.60 vs. 2.33, p=0.002; 1.77 ± 1.28 vs. 5.32 ± 2.58 μmol/L, p=0.047) (Table 4, Figure 3).

Table 3.

Differences in gastric juice pH and ammonia concentration between H. pylori eradicated and H. pylori non-eradicated groups.

Figure 2.

Among 28 patients who underwent H. pylori eradication therapy, 19 (67.9%) had a successful outcome. A) Their gastric pH levels were significantly lower than those in 9 patients who experienced eradication failure (1.60 vs. 2.33, p=0.007). B) Their gastric ammonia concentrations were significantly lower than those in 9 patients who experienced eradication failure (1.77 ± 1.28 vs. 4.02 ± 1.20, p=0.0001).

Table 4.

Differences in gastric juice pH and ammonia concentration between the before and after eradication of H. pylori in 19 patients who experienced a successful eradication.

Figure 3.

(A) Gastric juice pH levels were decreased after H. pylori eradication therapy, when compared to pre-eradication treatment levels in the 19 patients, who experienced, successful eradication (1.60 vs. 2.33, p=0.002). B) Gastric ammonia concentrations were also decreased after H. pylori eradication therapy, when compared to pre-eradication treatment levels in the 19 patients who experienced successful eradication (1.77 ± 1.28 vs. 5.32 ± 2.58, p=0.047).

Gastric pH was significantly correlated with the intragastric ammonia level (rs=0.495, p<0.01), H. pylori density (rs=0.467, p<0.01), gastritis severity (rs=0.343, p<0.01), and gastritis activity (rs=0.418, p<0.01) (Figure 4). The gastric juice ammonia level was also significantly correlated with H. pylori density (rs=0.735, p<0.01), gastritis severity (rs=0.478, p<0.01), and gastritis activity (rs=0.579, p<0.01) (Figure 5). Multiple linear regression analysis was carried out for the variables such as age, sex, gastritis severity, gastritis activity, and gastric juice ammonia concentration. H. pylori density was excluded for analysis because the correlation coefficient between gastric juice ammonia concentration and H. pylori density was very high (multiple colinearity). Gastric juice pH was significantly associated with gastric juice ammonia concentration (p=0.025) and gastritis activity (p=0.018), but not with gastritis severity (p=0.386), sex (p=0.072), and age (p=0.366) (Table 5).

Figure 4.

Gastric pH was significantly correlated with the intragastric ammonia level (A, rs=0.495, p<0.01), H. pylori density (B, rs=0.467, p<0.01), gastritis severity (C, rs=0.343, p<0.01), and gastritis activity (D, rs=0.418, p<0.01).

Figure 5.

The gastric ammonia level was also significantly correlated with H. pylori density (rs=0.735, p<0.01), gastritis severity (rs=0.478, p<0.01), and gastritis activity (rs=0.579, p<0.01).

Table 5.

Multiple linear regression analysis of the variables influencing gastric juice pH.

DISCUSSION

We found that H. pylori-infected patients had significantly higher gastric juice pH levels and ammonia concentrations as compared to uninfected subjects. In addition, high gastric juice pHs and ammonia concentrations were decreased after the eradication of H. pylori to significantly lower levels compared to uninfected groups. Other investigators have also found such encouraging results^{7, 8)}. However, they noted that there is a significant overlap in gastric juice ammonia concentrations between infected and uninfected patients^{7, 8)}, yielding a sensitivity for elevated gastric juice ammonia of 60%, specificity of 100%, positive predictive value of 100%, and a negative predictive value of 63% (using a cutoff value of 4.26 mM)⁷⁾. Furthermore, findings in conflict with the previous encouraging results have recently been reported. Kearney et al.⁹⁾ found that gastric juice ammonia concentration and the detection of ammonia using a rapid test device have inferior test characteristics as compared to previously published studies using currently available techniques. These findings suggest that the gastric ammonia level alone has limitations in the diagnosis of a H. pylori infection. Another study on the effect of a H. pylori infection on gastric juice pH observed that gastric juice pH is significantly higher in peptic ulcer patients (especially in gastric ulcer patients) than in control patients, and that gastric juice pH and serum gastrin levels in ulcer patients are significantly decreased compared to control levels after H. pylori eradication¹²⁾. Most in vitro studies have also shown that H. pylori inhibits acid secretion. Several substances, including N^α methyl histamine produced by H. pylori¹⁵⁾ and interleukin-1β (IL-1β) and tissue necrotic factor-α(TNF-α) induced by a H. pylori infection^{16, 17)}, are thought to inhibit acid secretion^{18, 19)}. In particular, IL-1β is known as a potent inhibitor of acid secretion; the peripheral and central administration of IL-1β potently inhibits gastric acid secretion in experimental animals^19–23). IL-1β also directly inhibits acid secretion by cultured rabbit parietal cells, and impairs the function of enterochromaffin-like cells in vitro, which may be followed by a markedly decreased acid output²⁴⁾. Gastric acid secretion is decreased and serum gastrin levels are increased in Mongolian gerbils infected with H. pylori, and acid output and serum gastrin levels return to control levels after a recombinant human IL-1 receptor antagonist injection²⁵⁾. Cytokines and serum gastrin levels were not determined in our study, but our data on gastric juice pH agree with previous findings¹²⁾. Furthermore, the median gastric juice pH in the H. pylori negative group in our study was 1.55, which is almost the same as in other studies^{12, 26)}. Previous studies and our findings suggest that gastric juice pH and ammonia concentrations are good indications of the status of a H. pylori infection, and they may be useful as compensatory tools in the diagnosis and eradication of a H. pylori infection.

We also analyzed the effect of gastric juice ammonia on gastric juice pH with sex, age, severity and the activity of gastritis by multiple regression analysis, and assessed the relationships between gastric pH and ammonia concentrations, between gastric pH and histology such as H. pylori density, severity and the activity of gastritis, and between gastric ammonia levels and histology. Gastric juice pH was significantly associated with gastric juice ammonia concentration (p=0.025) and gastritis activity (p=0.018). Furthermore, gastric juice pH and ammonia concentration correlated well with each other. Those levels also correlated well with H. pylori density, severity and the activity of gastritis. Bercik et al.²⁷⁾ have recently observed a higher gastric pH in H. pylori-positive subjects than in H. pylori-negative subjects during the administration of omeprazole, and concluded that a higher pH is predominantly attributable to neutralization by H. pylori-derived ammonia. Their conclusion agrees with ours. We did not performed a quantitative analysis of the relationship between ammonia production and gastric acidity, so we do not point to gastric ammonia as a major factor influencing gastric pH. However, according to our data, gastric juice ammonia produced by H. pylori appeared to contribute to the increase of gastric juice pH in active H. pylori gastritis. Urease of H. pylori protects the bacteria from gastric acid by the production of ammonia, which increases the pH in the microenvironment around the organism²⁸⁾. Direct injury to gastric epithelial cells occurs in vitro from ammonia²⁸⁾. Kearney et al.⁹⁾ also reported on the relationship between gastric ammonia concentration and the severity of gastritis. It has been hypothesized that the ammonia produced by bacterial urease activity may play a role in the pathogenesis of gastritis^{13, 14)}. There are many evidences to support a role for ammonia in the pathogenesis of gastritis. There is a significant correlation between gastric juice ammonia concentration and the number of polymorphonuclear cells among patients with chronic renal failure with a high blood urea nitrogen concentration, upon gastric histological examination²⁹⁾. Oral administration of an ammonia solution to rats has also been shown to result in gastric mucosal injury³⁰⁾, and there is evidence to suggest that ammonia may impair the host immune response by decreasing the phagocytic activity of polymorphonuclear leukocytes in vivo³¹⁾. Our study supports the notion that the severity and activity of gastritis may be correlated to an increased gastric ammonia concentration produced by a greater colonization of H. pylori, and gastric ammonia may play a partial role in the increased gastric pH in H. pylori gastritis.

Further studies are warranted to clarify the role of ammonia on gastric pH and the pathogenic role of ammonia in H. pylori gastritis.

Article information Continued