THE MEASUREMENT OF GASTRIC ACID

An indolium-based near-infrared fluorescent probe for non-invasive real-time monitoring of gastric pH in vitro and in vivo

Abnormal gastric acidity is closely linked to severe gastrointestinal diseases, making the real-time monitoring of gastric pH critical for investigating stomach-related physiological and pathological processes, diagnosing related diseases, and evaluating drug efficacy. In this study, we developed a near-infrared (NIR) fluorescent probe, named Hcy-pH, by conjugating a p-dimethylaminophenyl moiety with an indolium fluorophore via extended double bonds. The probe displayed significant NIR fluorescence at 820 nm in a PBS buffer, with a large Stokes shift of 240 nm. The fluorescence intensity of the probe decreased progressively as the pH decreased from 4.0 to 2.5, with a calculated pKa of 2.98. Hcy-pH exhibited excellent biocompatibility and enabled the visualization of pH fluctuations in vitro by living HeLa cells. Moreover, the non-invasive monitoring of gastric pH in vivo was achieved in live mice, underscoring its great potential for studying stomach-related diseases and evaluating related pharmaceuticals.

Colorimetric pH-sensing of artificial gastric fluid using naphthalimide-based CH acids

In this study, we introduce novel colorimetric pH-sensing probes based on naphthalimide malonate derivatives. These probes were synthesized by reacting 4-bromo-1,8-naphthalimide with various malonates, including malononitrile, ethyl cyanoacetate, and diethyl malonate. Each derivative exhibited distinct pH-sensing characteristics due to their differing CH acidities. The malononitrile-based probe, NPI-N2, demonstrated pronounced chromogenic pH-signaling behavior, transitioning from colorless to red-violet, accompanied by a decrease in fluorescence intensity. Notably, NPI-N2 retained its pH-sensing capability in the presence of common metal ions, anions, and pepsin, a key component of gastric fluid. The pKa of NPI-N2 was determined to be 3.08 through pH-dependent absorbance curve fitting. To modulate the pH-sensing range, ester-nitrile (NPI-EN) and diethyl ester (NPI-E2) subunits were incorporated into the naphthalimide framework, resulting in increased pKa values of 6.73 and 10.76, respectively. The pH-signaling mechanism of NPI-N2 was elucidated by 1H and 13C NMR spectroscopy, revealing deprotonation of the malononitrile moiety and subsequent resonance extension through the naphthalimide structure. To facilitate practical pH determination, NPI-N2 was integrated into a paper-based test strip, enabling convenient and reliable pH measurement of artificial gastric fluid.

In Situ Gastric pH Imaging with Hydrogel Capsule Isolated Paramagnetic Metallo-albumin Complexes

Abnormal gastric pH (pH > 3) has instructive significance for early diagnosis of various diseases, including cancer. However, for low patient compliance, limited penetration depth, high dependence on physiological function or unsafety issue, in situ noninvasive monitoring gastric pH is challenged. Herein, we developed a hydrogel capsule isolated human serum albumin-manganese complex (HSA-Mn) for in situ magnetic resonance imaging (MRI) gastric pH monitoring for the first time. In this strategy, the rotation motion restriction of Mn²⁺ after binding to HSA significantly increased the R₁ (longitudinal relaxation rate) signal, and its high correlation with protonation imparted the HSA-Mn system sensitive responsiveness to varying pH (R₁(pH 7)/R₁(pH 1) = 8.2). Moreover, a screw jointed hydrogel capsule with signal confinement and internal standard abilities was designed. Such a nanoporous hydrogel capsule with size selectivity to surrounding molecules enabled a stable and sensitive response to different pH simulated gastric fluid within 0.5 h. In addition, with the unique structural outline and stable MRI characteristics, the capsule could also work as an internal standard, which facilitates the collection of signals and trace of the capsule in vivo. Through validating in a rabbit model, the precise abnormal gastric pH recognition capacity of the HSA-Mn hydrogel capsule was amply confirmed. Hence, the hydrogel capsule isolated HSA-Mn system strategy with great biocompatibility could be expected to be a potent tool for in situ anti-disturbance MRI of gastric pH in future clinical application.

Non-invasive method for the assessment of gastric acid secretion

Methods for the measure of gastric acid secretion include invasive and non-invasive tests. The gold-standard to measure the acid output is the collection of gastric after in basal condition (Basal Acid Output, B.A.O.) and after an i.m. injection of pentagastrin (Maximal Acid Output, M.A.O.). However, direct measurement of gastric acid production is out of order in clinical practice, but many GI symptoms are claimed to be related with acid disorders and empirically cured. Hypochlorhydria is associated with precancerous conditions such as chronic atrophic gastritis (CAG). Acid measurement with non-invasive methods (pepsinogens) is supported by international guidelines.

Functional Photoacoustic Imaging of Gastric Acid Secretion Using pH-Responsive Polyaniline Nanoprobes

A stomach functional imaging technique based on photoacoustics achieves noninvasive gastric acid secretory assessment utilizing pH-responsive polyaniline nanoprobes. A testing protocol mimicking clinical practice is established using a mouse model. After imaging, the nanoprobes are excreted outside the body without inducing systematic toxicity. Further optimization and translation of this technology can help alleviate patients' suffering and side effects.

Effects of potassium diformate on the gastric function of weaning piglets

Potassium diformate (KDF), as an acidifier, has been shown to improve growth performance in pigs, but it is not yet known whether KDF regulates gastric function. Thus, the objective of the present study was to investigate the effects of dietary KDF on gastric function in weaning piglets. One hundred and eighty Landrace × Large White piglets (bodyweight = 5.80 ± 0.15 kg) were weaned at 28 days old and randomly allocated into two groups, with six pens in each group and 15 piglets in each pen. Piglets in the control group were fed the basal diet, whereas the KDF-treated group was fed the basal diet supplemented with 10 g/kg KDF. After 35 days of feeding, the KDF treatment improved the bodyweight (P = 0.034) and reduced the relative weight of stomach (P = 0.050), decreased the hydrochloric acid concentration (P = 0.016) in the gastric digesta and the pepsin activity in the gastric oxyntic mucosa (P = 0.001) and increased the lactic acid concentration (P = 0.001) in the gastric digesta. Furthermore, KDF treatment increased the level of somatostatin (SS) (P = 0.009), but did not change the concentration of gastrin (P = 0.497) and the activity of H+-K+-ATPase (P = 0.575) in the gastric oxyntic mucosa. However, KDF treatment downregulated the expression of SS mRNA in the gastric oxyntic mucosa (P = 0.031) and upregulated the mRNA expression of gastrin (P < 0.001) and H+-K+-ATPase (P < 0.001) in the gastric oxyntic mucosa. These results suggest that the effects of KDF on weaning piglets may be related to the regulation of gastric function gene expression.

Measuring the interaction of meal and gastric secretion: a combined quantitative magnetic resonance imaging and pharmacokinetic modeling approach

BACKGROUND

The stimulation and intragastric accumulation of gastric secretion has been recognized as an important factor in gastroesophageal reflux disease. However, the interaction of gastric secretion and meal emptying has not been fully understood. Current methods to assess gastric secretion are either invasive or unable to provide information on its volume, distribution and dynamics. The aim of this study was to quantify the interaction between meal emptying and meal induced gastric secretion by using quantitative magnetic resonance imaging (MRI) and pharmacokinetic analysis.

METHODS

A chocolate test meal was developed which is secretion stimulating and MRI compatible. Meal emptying and gastric secretion were assessed in fourteen healthy volunteers using a validated quantitative MRI technique. A population based pharmacokinetic model was developed and applied to the extracted volume data, assessing the meal emptying rate, rate of secretion and their interaction.

KEY RESULTS

The test meal continuously induced gastric secretion in all subjects, which partly accumulated at the meal-air interface, forming a 'secretion layer' in the proximal stomach. Traditional fitting detected a significant correlation between meal emptying rate and rate of secretion. The pharmacokinetic model quantified this interaction and estimated a 2.3 ± 1 fold higher effect of meal on secretion than vice versa. The efficacy of the emptied meal to produce gastric secretion was 61%.

CONCLUSIONS & INFERENCES

The combined quantitative MRI and pharmacokinetic model approach allows for the quantification of gastric secretion volume and its interaction on meal emptying. The observed secretion layer might explain previous findings postulating the presence of an intragastric 'acid pocket'.

Review article: methods of measuring gastric acid secretion

BACKGROUND

Gastric acid has an important pathophysiological role in human beings. Numerous methods have been evaluated over the years in an attempt to measure gastric acid and stomach acidity, to study the role of gastric acid in gastrointestinal diseases in humans and to evaluate the effects of acid suppressing drugs.

AIM

To review methods that have been used to measure gastric acid and gastric acidity.

METHODS

Searches of the electronic databases PUBMED, MEDLINE and EMBASE, were performed with articles restricted to English language and human subjects. References were also identified from the bibliographies of selected articles.

RESULTS

Methods for measuring gastric acid include both invasive and non-invasive techniques. Invasive tests include the conventional gastric acid aspiration tests, gastric pH measurement techniques and endoscopic methods. Non-invasive methods use urinary analysis, breath analysis, serum pepsinogens assay, scintigraphic techniques, impedence tomography and alkaline tide for measurement of gastric acid.

CONCLUSIONS

Several methods of measuring gastric acid exist. Invasive tube tests are uncomfortable and time consuming, whereas most of the non-invasive methods are at best semiquantitative and useful in detecting low or absent acid secretion. Further attempts to explore new methods for measuring gastric acid are therefore warranted.

Gastric acid secretion and gastric emptying of liquids in 99 male duodenal ulcer patients

Gastric acid hypersecretion and accelerated gastric emptying are commonly considered as possible determinants of duodenal ulcer, but the relative frequencies of these gastric dysfunctions have never been evaluated in a homogeneous group of patients. We studied basal and pentagastrin-stimulated gastric acid secretion and gastric emptying of a radiolabeled caloric liquid meal in 99 consecutive male patients with endoscopically proven, active, uncomplicated duodenal ulcers. Compared to matched healthy subjects, ulcer patients presented increased basal and stimulated acid secretion (P less than 0.001). Sixty-nine patients had peak acid output values above the 95% confidence limits of the control population (14.2-30.6 meq/hr). Cigarette smoking was correlated with gastric acid hypersecretion. No significant difference was found between duodenal ulcer patients and controls in mean gastric emptying times. Ulcer patients showed a greater variance of gastric acid secretion and emptying values than healthy subjects. This reflects varied gastrointestinal function among ulcer patients. No significant correlation was found between gastric acid output and gastric emptying times. These findings suggest that gastric acid hypersecretion, but not accelerated gastric emptying of liquids, play a relevant role in the pathogenesis of duodenal ulcer.

Correlation of salivary and gastric acid secretions in duodenal ulcer patients in tropics

Salivary flow rates on mechanical stimulation by forced spitting method and by chemical stimulation with 10% citric acid and gastric acidity using an augmented histamine test were determined in 20 adult patients suffering from duodenal ulcer and in 20 adult control subjects matched with respect to age, sex, and body weight. Salivary flow rates were found to be much higher in response to chemical than to mechanical stimulus in both the groups. Duodenal ulcer patients exhibited an unexplained exaggerated response to chemical stimulation. Salivary pH, amylase, sodium, and potassium levels showed no significant differences between the two groups. The flow rates by either method generally showed a positive correlation with body weight in both the groups. Histamine stimulated gastric acid secretion was higher in duodenal ulcer patients than in controls. Acid secretion did not appear to be related to weight and also showed no consistent correlation with the salivary flow rates. It was concluded that (1) the salivary flow was dependent on body weight in duodenal ulcer patients as well as in controls, and (2) although salivary gland hyperplasia could be postulated in duodenal ulcer patients on the basis of increased salivary flow, the latter was poorly related to maximal acid secretion and therefore, if a combination of parietal cell and salivary gland hyperplasia did exist, it should be considered as incidental.

Body weight and maximal acid output

Dose-response curves were obtained from forty male control subjects and forty male patients with duodenal ulcer from India on the subcutaneous histamine test.

The body weight and maximal acid output (MAO) showed a positive correlation just significant at the 5% level in control subjects (P=0·05) but not in patients with duodenal ulcer.

The values of MAO on dose-response curves are comparable in control subjects but are appreciably lower in patients with duodenal ulcer from India compared with those from Britain and North America. However, the values expressed as μEq/kg body weight are considerably higher in both groups of subjects from India compared with those from western populations.

Massive Resection of Small Bowel

This is a report of the management and gastro-intestinal function of a pensioner, aged 81 years, living comfortably after resection of all but 30 cm. of small bowel as the result of a mesenteric artery occlusion.

The aurate assessment of aximal gastric secretion in control subjects and patients with duodenal ulcer

Maximal gastric secretion was studied in 34 control subjects and 29 patients with duodenal ulcer using the histamine-infusion test with the addition of an inert marker, phenol red, to correct for pyloric losses of gastric secretion.

In the control group, statistically significant correlations were found between maximal gastric secretion and almost all the indices of body stature. Correction for pyloric loss improved all the correlations and raised those correlation coefficients which were not significant to levels of confidence of 95 percent or more.

The validity of calculation of lean body mass from height and weight was checked by the estimation of total body potassium in 26 subjects.

When lean body mass was taken into account it was confirmed that maximal gastric secretion decreased with age, but the sex difference in maximal gastric secretion was no longer statistically significant.

In the duodenal ulcer group, maximal gastric secretion was also significantly correlated with stature, though not with age. It is, therefore, proposed that stature should be taken into account when defining hypersecretion.

As expected, patients with duodenal ulcer produced as a group significantly higher levels of maximal gastric secretion than did control subjects, but the effect appeared to be due to a minority of patients with hypersecretion.

Patients with a history of less than 4 years secreted proportionately less gastric juice than those with a longer history. This finding raises the possibility that gastric hypersecretion is a result of duodenal ulceration rather than a cause.

Observations on gastric acid output by a three-hour histamine infusion test using maximal doses on patients with duodenal ulcer and in normal controls

The results of a series of histamine infusion tests extended over a period of three hours in 100 patients with duodenal ulcer and in 30 normal controls showed that while in the former group acid secretion continued to rise hourly both quantitatively and qualitatively throughout each of the three-hour periods of the tests, this did not occur in the normal controls in whom acid secretion levelled off during the second hour. Assay of 30-minute aspirates in the duodenal ulcer group showed that the 90-120 minute specimen (doubled) gave a close approximation to the values obtained during the third hour and represents maximal acid secretion of the gastric mucosa.

Factors affecting maximal acid secretion

The mechanisms by which different factors affect the maximal acid secretion of the stomach are discussed with particular reference to nationality, sex, age, body weight or lean body mass, procedural details, mode of calculation, the nature, dose and route of administration of a stimulus, the synergistic action of another stimulus, drugs, hormones, electrolyte levels, anaemia or deficiency of the iron-dependent enzyme system, vagal continuity and parietal cell mass.

Gastric acid secretion in chronic uraemia and after renal transplantation

In 45 patients with chronic uraemia the basal acid output was the same as in 22 controls. Maximal acid output in uraemic patients was less than in the controls but not significantly so. In uraemia the maximal acid output was directly related to the duration of uraemia and inversely related to both haemoglobin level and age; it was not related to the height of the blood urea. Neutralization of gastric acid by ammonia probably occurred in the basal juice, but not when acid secretion was maximally stimulated. The presence of secondary hyperparathyroidism was associated with a 50% increase in the maximal acid output, but the increase may have been due to the younger age of this group.Successful renal transplantation was followed in two out of seven patients by a considerable increase in acid output and both patients showed evidence of peptic ulceration.