Gastric acid secretion and intragastric acidity: measurement in health and disease

In Situ Generation of Red-to-NIR Emissive Radical Cations in the Stomach for Gastrointestinal Imaging

Red-to-near-infrared (NIR) fluorescent probes, with advantages such as high spatiotemporal resolution and in situ sensing abilities, are highly attractive for diagnosis of gastrointestinal diseases and targeted drug development. However, conventional red-to-NIR fluorophores with electron closed-shell structures require tedious synthetic procedures for preparation, and it is difficult to further decorate them with sensing groups. In this study, a series of easily prepared pyrroles with simple structures that can quickly be transformed into red-to-NIR emissive radical cations in acidic buffer solution and in vivo stomachs is developed. The in-situ-generated red-to-NIR emissive pyrrole radical cations in the stomach have excellent biocompatibility and stability and can be used not only for intravital gastrointestinal imaging with high spatiotemporal resolution, but also for dynamic monitoring of the gastric emptying process and assessment of anti-gastric-acid therapy. The acidity-induced generation of pyrrole radical cations is believed to provide a facile strategy for developing red-to-NIR fluorophores and studying gastrointestinal diseases.

Pharmacokinetic and Pharmacodynamic Modeling Analysis of Intravenous Esomeprazole in Healthy Volunteers

Esomeprazole is one of the most commonly used drugs to treat gastroesophageal reflux disease and peptic ulcers, but the quantitative relationships among the pharmacokinetics (PK), pharmacodynamics (PD), and pharmacogenomics (PG) of the drug are not fully understood in special patient populations. A clinical PK/PD/PG study of intravenous (IV) esomeprazole in 5 dosing regimens was conducted in 20 healthy Chinese volunteers, who were categorized into Helicobacter pylori (HP)-negative and HP-positive subgroups. Plasma esomeprazole concentration and intragastric H(+) concentration were monitored for 24 hours postdosing. Population PK (PopPK) models were tested based on elimination characteristics and other data. For a single-dose IV esomeprazole regimen, a 2-compartment model with nonlinear elimination characteristics fitted the PK data well. The elimination of esomeprazole was found to be significantly linked to CYP2C19 genotype by 11% to 29%. A mechanism-based PD model was first tested to mimic the irreversible inhibition of H(+) /K(+) -ATPase by esomeprazole using a cell-killing mechanism and models of gastric H(+) secretion that included the effects of an asymmetric circadian rhythm and food effects. Results from this PD model showed that the turnover rate of H(+) /K(+) -ATPase was significantly different between HP-negative and HP-positive subgroups. In conclusion, the PopPK model quantitatively identified the effects of the CYP2C19 genotype on esomeprazole elimination in healthy subjects for the first time. In addition, the effects of HP status on drug effect, H(+) /K(+) -ATPase turnover, and circadian rhythm amplitude were preliminarily explored using a mechanism-based PD model.

Systematic review: the use of proton pump inhibitors and increased susceptibility to enteric infection

The use of proton pump inhibitors (PPIs) is increasing worldwide. Suppression of gastric acid alters the susceptibility to enteric bacterial pathogens. AIM  This systematic review was undertaken to examine the relationship between PPI use and susceptibility to enteric infections by a specific pathogen based on published literature and to discuss the potential mechanisms of PPI enhanced pathogenesis of enteric infections. METHODS  PubMed, OVID Medline Databases were searched. Search terms included proton pump inhibitors and mechanisms of, actions of, gastric acid, enteric infections, diarrhoea, Clostridium difficile, Salmonella, Shigella and Campylobacter. RESULTS The use of PPIs increases gastric pH, encourages growth of the gut microflora, increases bacterial translocation and alters various immunomodulatory and anti-inflammatory effects. Enteric pathogens show variable gastric acid pH susceptibility and acid tolerance levels. By multiple mechanisms, PPIs appear to increase susceptibility to the following bacterial enteropathogens: Salmonella, Campylobacter jejuni, invasive strains of Escherichia coli, vegetative cells of Clostridium difficile, Vibrio cholerae and Listeria. We describe the available evidence for enhanced susceptibility to enteric infection caused by Salmonella, Campylobacter and C. difficile by PPI use, with adjusted relative risk ranges of 4.2-8.3 (two studies); 3.5-11.7 (four studies); and 1.2-5.0 (17 of 27 studies) for the three respective organisms. CONCLUSIONS Severe hypochlorhydria generated by PPI use leads to bacterial colonisation and increased susceptibility to enteric bacterial infection. The clinical implication of chronic PPI use among hospitalized patients placed on antibiotics and travellers departing for areas with high incidence of diarrhoea should be considered by their physicians.

The Calcium Carbonate Breath Test, a noninvasive test of stimulated gastric acid secretion: preliminary communication

BACKGROUND

Gastric acid secretion is subject to complex control mechanisms, and varies widely between individuals and populations. Its measurement has previously required intubation of the stomach with ingestion of a test meal or injection of a secretion stimulant.

AIM

We describe a novel method of measuring gastric acid secretion noninvasively - the Calcium Carbonate Breath Test.

METHODS

13C-labelled calcium carbonate is ingested by a fasting participant. The carbonate neutralizes gastric acid to produce 13CO2, which is expired in the breath. Measurement of the excess 13CO2 in the breath allows back-calculation of the amount of gastric acid secreted during the test, provided that other variables affecting CO2 production and excretion are minimized or controlled for.

RESULTS

Studies on a single healthy individual have shown reproducible estimations of acid secretion and over 80% suppression of acid secretion after the proton pump inhibitor treatment.

CONCLUSION

The method seems to be promising, but further studies on other individuals need to be carried out. The Calcium Carbonate Breath Test may have wide applications in epidemiological studies, clinical management of acid-related diseases, screening for hypochlorhydria and development of new acid-suppressing treatments.

Analysis of the acidity index and integrated intragastric acidity in 645 patients presenting with gastroesophageal reflux disease symptoms

OBJECTIVE

In a recent study of patients receiving proton-pump inhibitor (PPI) therapy, a new parameter, the acidity index, was described as being less complicated to calculate and of comparable accuracy (r = 0.93) to integrated intragastric acidity (IA) in assessing intragastric pH control. The aim of this study was to correlate AI with IA using a large database of ambulatory 24-h pH-metry studies in untreated patients presenting with gastroesophageal reflux disease (GERD) symptoms.

MATERIAL AND METHODS

We retrospectively analyzed 645 studies obtained from 1995 to 2001. Daytime (0800 h-2200 h), night-time (2200 h-0800 h) and 24-h IA and AI were calculated according to age, gender and the presence or absence of GERD, and correlations between these parameters were assessed using linear regression with F-statistic values, p-values and Akaike's Information Criterion values. GERD was defined as total esophageal pH time <4.0, 5 cm above the lower esophageal sphincter, for > or =4.2% of the day. IA and AI were calculated as follows: IA (mmol x h/l) = summation operator(acid in mmol/l at time "t" + acid in mmol/l at time "t - 1")/2 x ("t"-"t - 1"); AI = (%time pH < 4-%time pH < 3) x 1+(%time pH < 3-%time pH < 2) x 10+(%time pH < 2-%time pH < 1) x 100 + (%time pH < 1-%time pH < 0.8) x 1000.

RESULTS

Overall, the mean 24-h IA value was 882.0+/-820.0 mmol x h/l (daytime 392.0+/-400.0, night-time 490.0+/-486.0). The mean 24-h AI value was 102.0+/-87.0 (daytime 86.0+/-80.0, night-time 120.0+/-114.0, p < 0.001). The mean 24-h IA value was 1057.0+/-829.4 mmol x h/l (daytime 459.8+/-406.0, night-time 597.2+/-500.4, p < 0.001) in GERD patients and 713.0+/-775.0 mmol x h/l (daytime 326.0+/-383.0, night-time 387.0+/-448.5) in non-GERD patients (p < 0.001). The mean 24-h AI value was 122.1+/-88.1 (daytime 101.4+/-82.5, night-time 145.3+/-120.7) in GERD patients and 83.0+/-81.0 (daytime 71.0+/-73.9, night-time 96.4+/-102.6) in non-GERD patients (p < 0.001). Our statistical modeling demonstrated that the correlation between the acidity index and IA becomes progressively poorer with increasing values of acidity.

CONCLUSIONS

We conclude that gastric acid production assessed by both IA and AI is higher during evening hours in comparison with daytime hours and the difference between night-time and daytime values is statistically significant. In addition, gastric acid production assessed by both IA and AI is significantly higher in GERD patients than non-GERD patients. This difference is primarily due to differences in nocturnal acid production. The AI correlates poorly with measured IA, especially at higher levels of gastric acidity. Therefore, AI is not an acceptable surrogate for IA in assessing gastric acid production.

Influence of age and gender on gastric acid secretion as estimated by integrated acidity in patients referred for 24-hour ambulatory pH monitoring

OBJECTIVES

Earlier studies have suggested that gastric acid secretion declines with age. Integrated acidity (IA) calculated from ambulatory 24-h pH studies provides an estimation of gastric acid secretion that is less cumbersome than nasogastric aspiration. The aim of this study was to calculate IA as a function of age and gender.

METHODS

In a retrospective study, 753 ambulatory 24-h pH studies from 1994 to 2001 were analyzed. Subjects were classified according to nine age groups: <35 yr (n = 124), 35-39 yr (n = 90), 40-44 yr (n = 92), 45-49 yr (n = 111), 50-54 yr (n = 96), 55-59 yr (n = 61), 60-64 yr (n = 59), 65-69 yr (n = 42), and > or =70 yr (n = 64). Basal integrated acidity (BIA) was defined as IA between 12 midnight and 8 AM when no meals were consumed. Daytime and nocturnal IA/h was measured from 8 AM to 8 PM and from 8 PM to 8 AM. Postprandial IA (PIA) was measured for 2 h after the largest meal peak in each patient.

RESULTS

Gender distribution was similar between groups (chi(2) = 6.42, 3 df, p = 0.093). Mean gastric pH was similar between genders (2.96 +/- 1.36 women; 3.01 +/- 1.42 men; p = 0.71). Women and men had similar BIA (361.1 +/- 384.1 vs 434.6 +/- 436.6 mmol/L/h, p = 0.10), daytime IA (33.5 +/- 33.0 vs 34.1 +/- 33.7 mmol/L, p = 0.90) and nocturnal IA (43.3 +/- 42.1 vs 48.0 +/- 46.6 mmol/L, p = 0.42), and PIA (38.2 +/- 58.7 vs 36.0 +/- 58.5 mmol/L/h, p = 0.47). Mean gastric pH, daytime and nocturnal IA, BIA, and PIA did not differ between age groups (p > 0.1). None of the parameters studied had a linear association with age (mean gastric pH, r = 0.106; BIA, r = -0.124; daytime IA, r = -0.046; nocturnal IA, r = -0.104; PIA, r = -0.117).

CONCLUSIONS

Based on this study, we conclude that IA is unaffected by gender or age.

Effect of nizatidine 300 mg at night and omeprazole 20 mg in the morning on 24-hour intragastric pH and bacterial overgrowth in patients with acute duodenal ulcer

The study investigated the effect of either nocturnal acid suppression by the H2 antagonist nizatidine 300 mg at night or prolonged acid suppression by the proton- pump inhibitor omeprazole 20 mg in the morning, during four weeks, on intragastric pH profile, occurrence of bacterial growth in gastric fluid and biopsies, and healing rate in 23 patients with an acute duodenal ulcer. The endoscopic healing rate did not differ significantly between the two treatment modalities. The 24-hr acid secretion was significantly more reduced by omeprazole than nizatidine (P < 0.002). After treatment by nizatidine and omeprazole, respectively, median 24-hr intragastric pH increased from 1.5 to 1.8 (P < 0.01) and from 1.5 to 6.1 (P < 0.01), respectively. Nighttime acid inhibition did not differ significantly. The difference in gastric bacterial colonization after either omeprazole or nizatidine did not reach significance. However, median 24-hr pH and the fraction of the day with pH < 3 and pH < 4 were significantly correlated to bacterial colonization of the gastric fluid (P < 0.05).

Twenty-four-hour intragastric acidity: 300 mg ranitidine b.d., 20 mg omeprazole o.m., 40 mg omeprazole o.m. vs. placebo

BACKGROUND

There is considerable controversy about the degree of acid suppression that is optimal for the treatment of peptic disorders.

AIM

To compare the effects of three different regimens that are reported to strongly inhibit acid secretion.

METHODS

Intragastric 24-hour pH monitoring was performed in 11 healthy subjects in a randomized, multiple, cross-over, double-blind study. Each subject received four dose regimens, each for 2 weeks, in a random order. The regimens were: 300 mg ranitidine b.d., 20 mg omeprazole o.m., 40 mg omeprazole o.m., and placebo.

RESULTS

The decrease in gastric acidity during the daytime and during the total 24-hour period by all three treatments was significantly greater than after placebo; a significant difference in acid inhibition was found between ranitidine and 40 mg omeprazole, but not between ranitidine and 20 mg omeprazole, nor between the two doses of omeprazole. During the night-time the decrease in gastric acidity by all three treatments was significantly greater than after placebo; no difference was seen between the two doses of omeprazole and ranitidine. For the time of pH greater than 3 we found no statistical difference between the various acid decreasing regimens. The pH remained significantly longer above 4 after ranitidine and the two doses of omeprazole compared with placebo, and also longer above 4 after 40 mg omeprazole compared with ranitidine, but not after 20 mg omeprazole compared with ranitidine, nor after the two different doses of omeprazole.

CONCLUSIONS

Dosing with 300 mg ranitidine b.d., 20 mg omeprazole or 40 mg omeprazole is superior in gastric acid inhibition compared with placebo, when measured using 24-hour pH monitoring.

Problems with the interpretation of gastric pH measurement

The present study examines some of the assumptions underlying the use of intragastric pH-metry for assessing the degree of therapeutic gastric inhibition. Three separate studies were performed to determine the relationship between pH and titratable hydrogen ion concentration in gastric juice and to assess the relationship between the concentration of acid and the rate of gastric secretion. The concentration of acid derived from pH measurements tended to be lower than the titrated hydrogen ion concentration. The difference between the two readings--the "buffered" hydrogen ion concentration--was increased by the presence of food and was reduced during gastric secretory inhibition with ranitidine. The titrated hydrogen ion concentration reflected more accurately the amount of hydrochloric acid added to a container in vitro than pH measurement. However, in vivo even the measurement of titratable acidity was poorly correlated with the volume of secreted gastric juice so that measurement of gastric acid concentration does not permit inferences about the rate of gastric secretion. The results of the present study indicate that measurement of intragastric pH is unsatisfactory for assessing gastric secretion, particularly in response to a food stimulus, so that measurement of gastric acidity alone does not reflect the rate, or changes in the rate, of gastric acid secretion.