A stomach road or “Magenstrasse” for gastric emptying

Drug dissolution and transit in a heterogenous gastric chyme after fed administration: Semi-mechanistic modeling and simulations for an immediate-release and orodispersible tablets containing a poorly soluble drug

Mathematical models that treat the fed stomach content as a uniform entity emptied with a constant rate may not suffice to explain pharmacokinetic profiles recorded in clinical trials. In reality, phenomena such as the Magenstrasse or chyme areas of different pH and viscosity, play an important role in the intragastric drug dissolution and its transfer to the intestine. In this study, we investigated the data gathered in the bioequivalence trial between an immediate-release tablet (Reference) and an orally dispersible tablet (Test) with a poorly soluble weak base drug administered with or without water after a high-fat high-calorie breakfast. Maximum concentrations (Cmax) were significantly greater after administering the Reference product than the Test tablets, despite similar in vitro dissolution profiles. To explain this difference, we constructed a novel semi-mechanistic IVIVP model including a heterogeneous gastric chyme. The drug dissolution in vivo was modeled from the in vitro experiments in biorelevant media simulating gastric and intestinal fluids in the fed state (FEDGAS and FeSSIF). The key novelty of the model was separating the stomach contents into two compartments: isolated chyme (the viscous food content) that carries the drug slowly, and aq_chyme open for rapid Magenstrasse-like routes of drug transit. Drug distribution between these two compartments was both formulation- and administration-dependent, and recognized the respective drug fractions from the clinical pharmacokinetic data. The model's assumption about the nonuniform mixing of the API with the chyme, influencing differential drug dissolution and transit kinetics, led to simulating plasma concentration profiles that reflected well the variability observed in the clinical trial. The model indicated that, after administration, the Reference product mixes to a greater extent with aq_chyme, where the released drug dissolves better and transfers faster to the intestine. In conclusion, this novel approach underlines that diverse gastric emptying of different oral dosage forms may significantly impact pharmacokinetics and affect the outcomes of bioequivalence trials.

A review of the use of numerical analysis in stomach modeling

Food digestion is important for human health. Advances have been made using in vitro models to study food digestion, but there is considerable potential for numerical approaches in stomach modeling, as they can provide a comprehensive understanding of the complex flow and chemistry in the stomach. The focus of this study is to provide a concise review of the developed numerical stomach models over the past two decades. The gastric physiological parameters that are required for a computational model to represent the human gastric digestion process are discussed, including the stomach geometry, gastric motility, gastric emptying, and gastric secretions. Computational methods used to model gastric digestion are introduced and compared, including different computational fluid dynamics as well as solid mechanics methods. The challenges and limitations of current studies are discussed, as well as the areas for future research that need to be addressed. There has been progress in simulating gastric fluid flow with stomach wall motion, but much work remains to be done. The complex food breakdown mechanisms and a comprehensive chemical digestion process have not been implemented in any developed models. Numerical method that was once computationally expensive will be revolutionized as computing power continues to improve. Ultimately, the advancement of modeling of gastric food digestion will allow for additional hypothesis testing to streamline the development of food products that are beneficial to human health.

Preoperative fasting and the risk of pulmonary aspiration-a narrative review of historical concepts, physiological effects, and new perspectives

In the early days of anaesthesia, the fasting period for liquids was kept short. By the mid-20th century 'nil by mouth after midnight' had become routine as the principles of the management of 'full stomach' emergencies were extended to include elective healthy patients. Back then, no distinction was made between the withholding of liquids and solids. Towards the end of the last century, recommendations of professional anaesthesiology bodies began to reduce the fasting time of clear liquids to 2 h. This reduction in fasting time was based on the understanding that gastric emptying of clear liquids is rapid, exponential, and proportional to the current filling state of the stomach. Furthermore, there was no evidence of a link between drinking clear liquids and the risk of aspiration. Indeed, most instances of aspiration are caused by failure to identify aspiration risk factors and adjust the anaesthetic technique accordingly. In contrast, long periods of liquid withdrawal cause discomfort and may also lead to serious postoperative complications. Despite this, more than two decades after the introduction of the 2 h limit, patients still fast for a median of up to 12 h before anaesthesia, mainly because of organisational issues. Therefore, some hospitals have decided to allow patients to drink clear liquids within 2 h of induction of anaesthesia. Well-designed clinical trials should investigate whether these concepts are safe in patients scheduled for anaesthesia or procedural sedation, focusing on both aspiration risk and complications of prolonged fasting.

The acute effect of a β-glucan-enriched oat bread on gastric emptying, GLP-1 response, and postprandial glycaemia and insulinemia: a randomised crossover trial in healthy adults

BACKGROUND

The cereal fibre β-glucan reduces postprandial glycaemia, however, the underlying mechanisms are not fully understood. Thus, the aim of this study was to investigate the acute effect of a β-glucan-enriched oat bread on gastric emptying half-time (T1/2), gastric emptying lag phase (Tlag), and gastric emptying rate (GER), and the secretion of glucagon-like peptide-1 (GLP-1) as potential means to influence postprandial glycaemia.

METHODS

A randomised crossover trial was conducted in 22 healthy adults (age 24.6 ± 3.1 years, BMI 23.1 ± 2.7 kg/m2) receiving 25 g available carbohydrates from a β-glucan-enriched oat bread or a control whole-wheat bread at two non-consecutive days. T1/2, Tlag, and GER were determined based on ultrasound measures of the cross-sectional gastric antrum area in the fasting state and 15, 30, 45, 60, 90, and 120 min postprandially. Capillary glucose, serum insulin, and plasma GLP-1 concentrations were measured at the same time points.

RESULTS

A biphasic pattern of gastric emptying with a distinct Tlag before the commencement of emptying was observed in most subjects for both bread types. While no differences in GER were evident (p = 0.562), consumption of the oat bread significantly increased T1/2 by 18 min and Tlag by 14 min compared with the whole-wheat bread (p = 0.005 and p = 0.010, respectively). In addition, the oat bread significantly reduced iAUC2h for glucose and insulin responses compared with the whole-wheat bread (p = 0.001 and p < 0.001, respectively). There were no significant differences in GLP-1 response between the two breads (p = 0.892).

CONCLUSION

The increased T1/2 and Tlag could offer a potential mechanism for the observed attenuation of postprandial glycaemia and insulinemia after consumption of the β-glucan-enriched oat bread compared with the whole-wheat bread.

TRIAL REGISTRATION

 The study is registered at clinicaltrails.gov (NCT04571866).

Observations on the transmission of Dientamoeba fragilis and the cyst life cycle stage

Little is known about the life cycle and mode of transmission of Dientamoeba fragilis. Recently it was suggested that fecal–oral transmission of cysts may play a role in the transmission of D. fragilis. In order to establish an infection, D. fragilis is required to remain viable when exposed to the pH of the stomach. In this study, we investigated the ability of cultured trophozoites to withstand the extremes of pH. We provide evidence that trophozoites of D. fragilis are vulnerable to highly acidic conditions. We also investigated further the ultrastructure of D. fragilis cysts obtained from mice and rats by transmission electron microscopy. These studies of cysts showed a clear cyst wall surrounding an encysted parasite. The cyst wall was double layered with an outer fibrillar layer and an inner layer enclosing the parasite. Hydrogenosomes, endoplasmic reticulum and nuclei were present in the cysts. Pelta-axostyle structures, costa and axonemes were identifiable and internal flagellar axonemes were present. This study therefore provides additional novel details and knowledge of the ultrastructure of the cyst stage of D. fragilis.

Biomimetic Closed-Loop Control of a Novel Soft Gastric Simulator Toward Emulating Antral Contraction Waves

Soft gastric simulators are in vitro biomimetic modules that can reproduce the antral contraction waves (ACWs). Along with providing information concerning stomach contents, stomach simulators enable experts to evaluate the digestion process of foods and drugs. Traditionally, open-loop control approaches were implemented on stomach simulators to produce ACWs. Constructing a closed-loop control system is essential to improve the simulator's ability to imitate ACWs in additional scenarios and avoid constant tuning. Closed-loop control can enhance stomach simulators in accuracy, responding to various food and drug contents, timing, and unknown disturbances. In this article, a new generation of anatomically realistic soft pneumatic gastric simulators is designed and fabricated. The presented simulator represents the antrum, the lower portion of the stomach where ACWs occur. It is equipped with a real-time feedback system to implement diverse closed-loop controllers on demand. All the details of the physical design, fabrication, and assembly process are discussed. Also, the measures taken for the mechatronics design and sensory system are highlighted in this article. Through several implementation algorithms and techniques, three closed-loop controllers, including model-based and model-free schemes are designed and successfully applied on the presented simulator to imitate ACWs. All the experimental outcomes are carefully analyzed and compared against the biological counterparts. It is demonstrated that the presented simulator can serve as a reliable tool and method to scrutinize digestion and promote novel technologies around the human stomach and the digestion process. This research methodology can also be utilized to develop other biomimetic and bioinspired applications.

Determination of Gastric Water Emptying in Fasted and Fed State Conditions Using a Compression-Coated Tablet and Salivary Caffeine Kinetics

Because of the importance of gastric emptying for pharmacokinetics, numerous methods have been developed for its determination. One of the methods is the salivary tracer technique, which utilizes an ice capsule containing caffeine as a salivary tracer. Despite the ice capsule's advantage in labeling ingested fluids with caffeine for subsequent salivary detection, its risk of premature melting before swallowing, and its complicated storage and preparation, limit its application, particularly in special populations (e.g., older people). For this reason, here, a compression-coated tablet was developed and validated against the ice capsule in a cross-over clinical trial. The two dosage forms were administered simultaneously to 12 volunteers in an upright position under fasted and fed state conditions. To distinguish the caffeine concentrations in saliva from each dosage form, regular type of caffeine (12C) was added to the tablet, while for the ice capsule 13C3 labelled caffeine was used. The salivary caffeine concentrations showed no statistically significant differences for the pharmacokinetic parameters tmax and AUC0→60 (p > 0.05). Thus, the new formulation is a useful tool for determining gastric emptying that can also be used in special populations.

Soy Protein Isolate-Chitosan Nanoparticle-Stabilized Pickering Emulsions: Stability and In Vitro Digestion for DHA

The purpose of the study was to investigate the stability and oral delivery of DHA-encapsulated Pickering emulsions stabilized by soy protein isolate-chitosan (SPI-CS) nanoparticles (SPI-CS Pickering emulsions) under various conditions and in the simulated gastrointestinal (GIT) model. The stability of DHA was characterized by the retention rate under storage, ionic strength, and thermal conditions. The oral delivery efficiency was characterized by the retention and release rate of DHA in the GIT model and cell viability and uptake in the Caco-2 model. The results showed that the content of DHA was above 90% in various conditions. The retention rate of DHA in Pickering emulsions containing various nanoparticle concentrations (1.5 and 3.5%) decreased to 80%, while passing through the mouth to the stomach, and DHA was released 26% in 1.5% Pickering emulsions, which was faster than that of 3.5% in the small intestine. After digestion, DHA Pickering emulsions proved to be nontoxic and effectively absorbed by cells. These findings helped to develop a novel delivery system for DHA.

Ultrasonographic Evaluation of Gastric Content and Volume in Pediatric Patients Undergoing Elective Surgery: A Prospective Observational Study

Anesthesia-related complications, such as pulmonary aspiration of gastric contents, occur in approximately 0.02-0.1% of elective pediatric surgeries. Aspiration risk can be reliably assessed by ultrasound examination of the gastric antrum, making it an essential non-invasive bedside tool. In this prospective observational study, since most of our patients are immigrants and have communication problems, we wanted to investigate gastric contents and the occurrence of "high risk stomach" in children undergoing elective surgery for the possibility of pulmonary aspiration, even if the children and/or parents reported their last oral intake time. This risk is defined by ultrasound findings of solid content in the antrum and/or a calculated gastric volume exceeding 1.25 mL/kg. Children aged 2-18 were included in the study. Both supine and right lateral decubitus (RLD) ultrasound examinations were performed on the antrum before surgery. Using a qualitative grading scale from 0 to 2, we evaluated the gastric fluid content. The cross-sectional area (CSA) of the antrum was measured in the RLD position, aiding the calculation of the gastric fluid volume according to an established formula by Perlas. Ultrasound measurements of 97 children were evaluated. The median fasting duration was 4 h for liquids and 9 h for thick liquids and solids. Solid content was absent in all the children. Five children (5.2%) exhibited a grade 2 antrum, implying that fluid content was visible in both the supine and RLD positions. The median antral CSA in the RLD was 2.36 cm2, with a median gastric volume of 0.46 mL/kg. For patients with a grade 0 antrum, a moderate and positive correlation was observed between the antral CSA and BMI, and a strong and positive correlation was evident between the antral CSA and age, similar to a grade 1 antrum. Only a single child (1%) had a potentially elevated risk of aspiration of gastric contents. Hence, the occurrence of a "high risk stomach" was 1% (95% confidence interval: 0.1-4.7%) and is consistent with the literature. As a necessary precaution, we propose the regular use of ultrasound evaluations of gastric contents, given their non-invasive, bedside-friendly, and straightforward implementation, for identifying risks when fasting times are uncertain and for ruling out unknown risk factors in each potential patient.

Contrast-Enhanced Multispectral Optoacoustic Tomography for Functional Assessment of the Gastrointestinal Tract

Real-time imaging and functional assessment of the intestinal tract and its transit pose a significant challenge to conventional clinical diagnostic methods. Multispectral optoacoustic tomography (MSOT), a molecular-sensitive imaging technology, offers the potential to visualize endogenous and exogenous chromophores in deep tissue. Herein, a novel approach using the orally administered clinical-approved fluorescent dye indocyanine green (ICG) for bedside, non-ionizing evaluation of gastrointestinal passage is presented. The authors are able to show the detectability and stability of ICG in phantom experiments. Furthermore, ten healthy subjects underwent MSOT imaging at multiple time points over eight hours after ingestion of a standardized meal with and without ICG. ICG signals can be visualized and quantified in different intestinal segments, while its excretion is confirmed by fluorescent imaging of stool samples. These findings indicate that contrast-enhanced MSOT (CE-MSOT) provides a translatable real-time imaging approach for functional assessment of the gastrointestinal tract.

Intragastric Carbon Dioxide Release Prolongs the Gastric Residence Time of Postprandially Administered Caffeine

Sparkling water is said to increase gastric motility by the release of carbon dioxide, thereby potentially affecting the pharmacokinetics of orally administered drugs. The hypothesis of the present work was that the induction of gastric motility by intragastric release of carbon dioxide from effervescent granules could promote the mixing of drugs into the chyme under postprandial conditions, resulting in a prolonged drug absorption. For this purpose, an effervescent and a non-effervescent granule formulation of caffeine as a marker for gastric emptying were developed. In a three-way crossover study with twelve healthy volunteers, the salivary caffeine pharmacokinetics, after administration of the effervescent granules with still water and the administration of the non-effervescent granules with still and sparkling water, were investigated after intake of a standard meal. While the administration of the effervescent granules with 240 mL of still water led to a significantly prolonged gastric residence of the substance compared to the administration of the non-effervescent granules with 240 mL still water, the application of the non-effervescent granules with 240 mL sparkling water did not prolong gastric residence via mixing into caloric chyme. Overall, the mixing of caffeine into the chyme following the administration of the effervescent granules did not seem to be a motility mediated process.

Gastroparesis: An Evidence-Based Review for the Bariatric and Foregut Surgeon

Gastroparesis is a gastric motility disorder characterized by delayed gastric emptying. It is a rare disease and difficult to treat effectively; management is a dilemma for gastroenterologists and surgeons alike. We conducted a systematic review of the literature to evaluate current diagnostic tools as well as treatment options. We describe key elements in the pathophysiology of the disease, in addition to current evidence on treatment alternatives, including nutritional considerations, medical and surgical options, and related outcomes.

Effects of peristaltic amplitude and frequency on gastric emptying and mixing: a simulation study

The amplitude and frequency of peristaltic contractions are two major parameters for assessing gastric motility. However, it is not fully understood how these parameters affect the important functions of the stomach, such as gastric mixing and emptying. This study aimed to quantify the effects of peristaltic amplitude and frequency on gastric mixing and emptying using computational fluid dynamics simulation of gastric flow with an anatomically realistic model of the stomach. Our results suggest that both the increase and decrease in peristaltic amplitude have a significant impact on mixing strength and emptying rate. For example, when the peristaltic amplitude was 1.2 times higher than normal, the emptying rate was 2.7 times faster, whereas when the amplitude was half, the emptying rate was 4.2 times slower. Moreover, the emptying rate increased more than proportionally with the peristaltic frequency. The nearest contraction wave to the pylorus and the subsequent waves promoted gastric emptying. These results suggest the importance of maintaining parameters within normal ranges to achieve healthy gastric function.

Modeling digestion, absorption, and ketogenesis after administration of tricaprilin formulations to humans

At present, tricaprilin is used as a ketogenic source for the management of mild to moderate Alzheimer's disease. After administration of the medium-chain triglyceride, tricaprilin is hydrolyzed to octanoic acid and further metabolized to ketones, acting as an alternative energy substrate for the brain. In this investigation, we developed a physiologically-based biopharmaceutics model simulating in vivo processes following the peroral administration of tricaprilin. The model includes multiple data sources to establish a partially verified framework for the simulation of plasma profiles. The input parameters were identified based on existing literature data and in vitro digestion studies. Model validation was conducted using the data from a phase I clinical trial. A partial parameter sensitivity analysis elucidated various influences on the plasma ketone levels that are mainly responsible for the therapeutic effects of tricaprilin. Based on our findings, we concluded that dispersibility and lipolysis of tricaprilin together with the gastric emptying patterns are limiting ketogenesis, while other steps such as the conversion of octanoic acid to ketone bodies play a minor role only.

Quantifying intrafractional gastric motion using auto-segmentation on MRI: Deformation and respiratory-induced displacement compared

BACKGROUND AND PURPOSE

For accurate pre-operative gastric radiotherapy, intrafractional changes must be taken into account. The aim of this study is to quantify local gastric deformations and compare these deformations with respiratory-induced displacement.

MATERIALS AND METHODS

Coronal 2D MRI scans (15-16 min; 120 repetitions of 25-27 interleaved slices) were obtained for 18 healthy volunteers. A deep-learning network was used to auto-segment the stomach. To separate out respiratory-induced displacements, auto-segmentations were rigidly shifted in superior-inferior (SI) direction to align the centre of mass (CoM) within every slice. From these shifted auto-segmentations, 3D iso-probability surfaces (isosurfaces) were established: a reference surface for P_Occ  = 0.50 and 50 other isosurfaces (from P_Occ  = 0.01 to 0.99), with P_Occ indicating the probability of occupation by the stomach. For each point on the reference surface, distances to all isosurfaces were determined and a cumulative Gaussian was fitted to this probability-distance dataset to obtain a standard deviation (SD_deform ) expressing local deformation. For each volunteer, we determined median and 98^th percentile of SD_deform over the reference surface and compared these with the respiratory-induced displacement SD_resp , that is, the SD of all CoM shifts (paired Wilcoxon signed-rank, α = 0.05).

RESULTS

Larger deformations were mostly seen in the antrum and pyloric region. Median SD_deform (range, 2.0-2.9 mm) was smaller than SD_resp (2.7-8.8 mm) for each volunteer (p < 0.00001); 98^th percentile of SD_deform (3.2-7.3 mm) did not significantly differ from SD_resp (p = 0.13).

CONCLUSION

Locally, gastric deformations can be large. Overall, however, these deformations are limited compared to respiratory-induced displacement. Therefore, unless respiratory motion is considerably reduced, the need to separately include these deformation uncertainties in the treatment margins may be limited.

Effect of stomach motility on food hydrolysis and gastric emptying: Insight from computational models

The peristaltic motion of stomach walls combines with the secretion of digestive enzymes to initiate the process that breaks down food. In this study, the mixing, breakdown, and emptying of a liquid meal containing protein is simulated in a model of a human stomach. In this model, pepsin, the gastric enzyme responsible for protein hydrolysis, is secreted from the proximal region of the stomach walls and allowed to react with the contents of the stomach. The velocities of the retropulsive jet induced by the peristaltic motion, the emptying rate, and the extent of hydrolysis are quantified for a control case as well as for three other cases with reduced motility of the stomach, which may result from conditions such as diabetes mellitus. This study quantifies the effect of stomach motility on the rate of food breakdown and its emptying into the duodenum and we correlate these observations with the mixing in the stomach induced by the wall motion.

Simulating human gastrointestinal motility in dynamic in vitro models

The application of dynamic in vitro gastrointestinal (GI) models has grown in popularity to understand the impact of food structure and composition on human health. Given that GI motility is integral to digestion and absorption, a predictive in vitro model should faithfully replicate the motility patterns and motor functions in vivo. In this review, typical characteristics of gastric and small intestinal motility in humans as well as the biomechanical and hydrodynamic events pertinent to gut motility are summarized. The simulation of GI motility in the presently existing dynamic in vitro models is discussed from an engineering perspective and categorized into hydraulic, piston/probe-driven, roller-driven, pneumatic, and other systems. Each system and its representative models are evaluated in terms of their motility patterns, the key hydrodynamic characteristics concerning gut motility, their performance in simulating the key physiological events, and their ability to establish in vitro-in vivo correlations. Practical Application: The review paper provided useful information in the design of dynamic GI models and the simulation of human gastric and small intestinal motility which are important for understanding food and health.

Computational modeling of drug dissolution in the human stomach: Effects of posture and gastroparesis on drug bioavailability

The oral route is the most common choice for drug administration because of several advantages, such as convenience, low cost, and high patient compliance, and the demand and investment in research and development for oral drugs continue to grow. The rate of dissolution and gastric emptying of the dissolved active pharmaceutical ingredient (API) into the duodenum is modulated by gastric motility, physical properties of the pill, and the contents of the stomach, but current in vitro procedures for assessing dissolution of oral drugs are limited in their ability to recapitulate this process. This is particularly relevant for disease conditions, such as gastroparesis, that alter the anatomy and/or physiology of the stomach. In silico models of gastric biomechanics offer the potential for overcoming these limitations of existing methods. In the current study, we employ a biomimetic in silico simulator based on the realistic anatomy and morphology of the stomach (referred to as "StomachSim") to investigate and quantify the effect of body posture and stomach motility on drug bioavailability. The simulations show that changes in posture can potentially have a significant (up to 83%) effect on the emptying rate of the API into the duodenum. Similarly, a reduction in antral contractility associated with gastroparesis can also be found to significantly reduce the dissolution of the pill as well as emptying of the API into the duodenum. The simulations show that for an equivalent motility index, the reduction in gastric emptying due to neuropathic gastroparesis is larger by a factor of about five compared to myopathic gastroparesis.

Bioavailability Evaluation of Venetoclax Lower-Strength Tablets and Oral Powder Formulations to Establish Interchangeability with the 100 mg Tablet

Background and Objective

Venetoclax is an approved BCL-2 inhibitor, currently under evaluation in different hematological malignancies in adult and pediatric populations. Venetoclax is available as 10, 50, and 100 mg tablets. To provide an alternative to patients who find taking the commonly prescribed 100 mg tablet a challenge, the interchangeability of lower-strength tablets with the 100 mg tablet was investigated. Additionally, newly developed oral suspension powder formulations to facilitate dosing in pediatrics were evaluated.

Methods

Pharmacokinetic data from 80 healthy female participants from three phase I studies were utilized to evaluate the bioavailability of (1) 10 and 50 mg tablets relative to a 100 mg tablet; (2) 0.72 and 7.2% (drug to total weight) oral powder formulations relative to the 100 mg tablet; and (3) oral powder formulations administered using different vehicles (apple juice, apple sauce, and yogurt) relative to water under fed conditions.

Results

Bioavailability assessments at a 100 mg dose of venetoclax demonstrated bioequivalence across the 10, 50, and 100 mg tablet strengths. Oral powder formulations met the bioequivalence criteria (0.80–1.25) with respect to area under the concentration–time curve to time of the last measurable concentration (AUC_t) and to infinite time (AUC_∞) but exhibited a slightly lower maximum plasma concentration (C_max). Exposure–response analyses were utilized to demonstrate that the lower C_max observed with the powder formulations is not clinically meaningful. The delivery vehicles tested did not affect the bioavailability of venetoclax oral powder formulations.

Conclusions

The smaller-sized tablets (10 and 50 mg) and the newly developed oral powder formulations of venetoclax can be used interchangeably with the 100 mg tablets to improve the patients’ experience, while maintaining adequate exposure.

Clinical Trials Identifiers

NCT01682616, 11 September 2012; NCT02005471, 9 December 2013; NCT02242942, 17 September 2014; NCT02203773, 30 July 2014; NCT02287233, 10 November 2014; NCT02993523, 15 December 2016; NCT03069352, 3 March 2017.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40261-022-01172-4.

Finite-Time Contraction Control of a Ring-Shaped Soft Pneumatic Actuator Mimicking Gastric Pathologic Motility Conditions

Soft gastric simulators are the latest gastric models designed to imitate gastrointestinal (GI) functions in actual physiological conditions. They are used in in vitro tests for examining the drug and food behaviors in the GI tract. As the main motility function of the GI tract, the peristalsis can be altered in some gastric disorders, for example, by being delayed or accelerated. To simulate the stomach motility, a GI simulator must achieve a prescribed healthy or pathological peristalsis. This requires the simulator to be controlled in a closed loop. Unlike conventional controllers that stabilize a controlled plant asymptotically, a finite-time controller regulates state variables to their equilibrium points in a predetermined time interval. This article presents the design and implementation of a finite-time, model-based state feedback controller (based on the differential Riccati equation) on a soft robotic gastric simulator's actuators for the first time. We propose a mass-spring-damper model of a ring-shaped soft pneumatic actuator (RiSPA). RiSPA is a bellows-driven, elastomer-based actuator developed to reproduce motility functions of the lower part of the stomach (pyloric antrum). The proposed model is augmented by a new approach for modeling the soft tissues, where the moments of inertia of the system constituents are considered as time-varying functions. The finite-time controller is successfully applied on the RiSPA in numerical simulation and experimental implementation, and the results were thoroughly analyzed and discussed. Its accuracy and the ability to control in a predetermined time are highlighted in the tracking of peristalsis trajectory and contractive regulations.

A fully resolved multiphysics model of gastric peristalsis and bolus emptying in the upper gastrointestinal tract

Over the past few decades, in silico modeling of organ systems has significantly furthered our understanding of their physiology and biomechanical function. In spite of the relative importance of the digestive system in normal functioning of the human body, there is a scarcity of high-fidelity models for the upper gastrointestinal tract including the esophagus and the stomach. In this work, we present a detailed numerical model of the upper gastrointestinal tract that not only accounts for the fiber architecture of the muscle walls, but also the multiphasic components they help transport during normal digestive function. Construction details for 3D models of representative stomach geometry are presented along with a simple strategy for assigning circular and longitudinal muscle fiber orientations for each layer. We developed a fully resolved model of the stomach to simulate gastric peristalsis by systematically activating muscle fibers embedded in the stomach. Following this, for the first time, we simulate gravity-driven bolus emptying into the stomach due to density differences between ingested contents and fluid contents of the stomach. Finally, we present a case of retrograde flow of fluid from the stomach into the esophagus, resembling the phenomenon of acid reflux. This detailed computational model of the upper gastrointestinal tract provides a foundation for future models to investigate the biomechanics of acid reflux and probe various strategies for gastric bypass surgeries to address the growing problem of obesity.

Importance of Gastric Secretion and the Rapid Gastric Emptying of Ingested Water along the Lesser Curvature ("Magenstraße") in Predicting the In Vivo Performance of Liquid Oral Dosage Forms in the Fed State Using a Modeling and Simulation

The objective of the present study was to develop an in silico model of the stomach for predicting oral drug absorption in fed humans. We focused on a model capable of simulating dynamic fluid volume changes and included a simulated Magenstraße "stomach road," a route along the lesser curvature that often carries fluids rapidly to assess the gastric emptying of drugs. Two types of model liquid drug formulations, liquid-filled soft gelatin capsules (enzalutamide, cyclosporine, and nifedipine) and oral solutions (levofloxacin and fenfluramine), were used. An in silico model was assembled, and simulations were performed using Stella Professional software. The secretion rate of the gastric juice induced by food ingestion was assessed along with the gastric emptying of the ingested water via the Magenstraße in the fed state. The model for the fed state successfully described the in vivo performance of the model drug formulations. These results clearly indicate the importance of including gastric secretion and the kinetics of Magenstraße when predicting the in vivo performance of dosage forms using an in silico modeling and simulation of fed humans. This simulation model should be further optimized to allow for the different physiological mechanisms following the ingestion of different types of meals, as well as modifications for interindividual and intraindividual variabilities in gastrointestinal physiology in the fed state in the future.

Lilly Absorption Modeling Platform: A Tool for Early Absorption Assessment

Oral drug absorption modeling has developed at a rapid pace in the 40 years or so since the first ideas for mathematical approaches to oral absorption were introduced. The success of compartmental approaches accelerated the uptake of absorption modeling, and over the last 20 years, work on absorption modeling has shifted almost exclusively to the compartmental framework. This report describes a new noncompartmental absorption modeling framework, the Lilly Absorption Modeling Platform (LAMP). LAMP connects a well-mixed stomach to a continuous tube model of the small intestine with plug flow. Within the continuous tube framework, the model includes intestinal mixing and a novel highly tunable precipitation model that can describe a combination of rapid nucleation and slow growth. The framework is designed to balance speed, consistency, and ease of use with a minimum of model complexity to capture the essential features of gastrointestinal (GI) physiology and critical elements of the oral absorption process. The model was validated based on predictions of the fraction absorbed and the maximum absorbable dose for a set of Eli Lilly and Company clinical compounds.

In vitro models to evaluate ingestible devices: Present status and current trends

Orally ingestible medical devices offer significant opportunity in the diagnosis and treatment of gastrointestinal conditions. Their development necessitates the use of models that simulate the gastrointestinal environment on both a macro and micro scale. An evolution in scientific technology has enabled a wide range of in vitro, ex vivo and in vivo models to be developed that replicate the gastrointestinal tract. This review describes the landscape of the existing range of in vitro tools that are available to characterize ingestible devices. Models are presented with details on their benefits and limitations with regards to the evaluation of ingestible devices and examples of their use in the evaluation of such devices is presented where available. The multitude of models available provides a suite of tools that can be used in the evaluation of ingestible devices that should be selected on the functionality of the device and the mechanism of its function.

A literature review on large intestinal hyperelastic constitutive modeling

Impacts, traumas and strokes are spontaneously life-threatening, but chronic symptoms strangle patient every day. Colorectal tissue mechanics in such chronic situations not only regulates the physio-psychological well-being of the patient, but also confirms the level of comfort and post-operative clinical outcomes. Numerous uniaxial and multiaxial tensile experiments on healthy and affected samples have evidenced significant differences in tissue mechanical behavior and strong colorectal anisotropy across each layer in thickness direction and along the length. Furthermore, this study reviewed various forms of passive constitutive models for the highly fibrous colorectal tissue ranging from the simplest linearly elastic and the conventional isotropic hyperelastic to the most sophisticated second harmonic generation image based anisotropic mathematical formulation. Under large deformation, the isotropic description of tissue mechanics is unequivocally ineffective which demands a microstructural based tissue definition. Therefore, the information collected in this review paper would present the current state-of-the-art in colorectal biomechanics and profoundly serve as updated computational resources to develop a sophisticated characterization of colorectal tissues.

Use of Physiologically Based Pharmacokinetic Modeling for Predicting Drug-Food Interactions: Recommendations for Improving Predictive Performance of Low Confidence Food Effect Models

Food can alter drug absorption and impact safety and efficacy. Besides conducting clinical studies, in vitro approaches such as biorelevant solubility and dissolution testing and in vivo dog studies are typical approaches to estimate a drug's food effect. The use of physiologically based pharmacokinetic models has gained importance and is nowadays a standard tool for food effect predictions at preclinical and clinical stages in the pharmaceutical industry. This manuscript is part of a broader publication from the IQ Consortium's food effect physiologically based pharmacokinetic model (PBPK) modeling working group and complements previous publications by focusing on cases where the food effect was predicted with low confidence. Pazopanib-HCl, trospium-Cl, and ziprasidone-HCl served as model compounds to provide insights into why several food effect predictions failed in the first instance. Furthermore, the manuscript depicts approaches whereby PBPK-based food effect predictions may be improved. These improvements should focus on the PBPK model functionality, especially better reflecting fasted- and fed-state gastric solubility, gastric re-acidification, and complex mechanisms related to gastric emptying of drugs. For improvement of in vitro methodologies, the focus should be on the development of more predictive solubility, supersaturation, and precipitation assays. With regards to the general PBPK modeling methodology, modelers should account for the full solubility profile when modeling ionizable compounds, including common ion effects, and apply a straightforward strategy to account for drug precipitation.

Protein acidification and hydrolysis by pepsin ensure efficient trypsin-catalyzed hydrolysis

Enzyme-catalysed hydrolysis is important in protein digestion. Protein hydrolysis is initiated by pepsin at low pH in the stomach. However, pepsin action and acidification happen simultaneously to gastric emptying, especially for liquid meals. Therefore, different extents of exposure to the gastric environment change the composition of the chyme that is emptied from the stomach into the small intestine over time. We assessed the susceptibility of a protein to trypsin-catalysed hydrolysis in the small intestine, depending on its pH and hydrolysis history, simulating chyme at different times after the onset of gastric emptying. Isothermal titration calorimetry was used to study the kinetics of pepsin and trypsin-catalysed hydrolysis. Bovine serum albumin (BSA) that was acidified and hydrolysed with pepsin, showed the highest extent and most efficient hydrolysis by trypsin. BSA in the chyme that would be first emptied from the stomach, virtually bypassing gastric acidity and peptic action, reduced trypsin-catalysed hydrolysis by up to 58% compared to the acidified, intact protein, and 77% less than the acidified, pepsin-hydrolysate. The least efficient substrate for trypsin-catalysed hydrolysis was the acidified, intact protein with a specificity constant (k_cat/K_m) nearly five times lower than that of the acidified, pepsin-hydrolysate. Our results illustrate the synergy between pepsin and trypsin hydrolysis, and indicate that gastric hydrolysis increases the efficiency of the subsequent trypsin-catalysed hydrolysis of a model protein in the small intestine.

Strategies to Refine Gastric Stimulation and Pacing Protocols: Experimental and Modeling Approaches

Gastric pacing and stimulation strategies were first proposed in the 1960s to treat motility disorders. However, there has been relatively limited clinical translation of these techniques. Experimental investigations have been critical in advancing our understanding of the control mechanisms that innervate gut function. In this review, we will discuss the use of pacing to modulate the rhythmic slow wave conduction patterns generated by interstitial cells of Cajal in the gastric musculature. In addition, the use of gastric high-frequency stimulation methods that target nerves in the stomach to either inhibit or enhance stomach function will be discussed. Pacing and stimulation protocols to modulate gastric activity, effective parameters and limitations in the existing studies are summarized. Mathematical models are useful to understand complex and dynamic systems. A review of existing mathematical models and techniques that aim to help refine pacing and stimulation protocols are provided. Finally, some future directions and challenges that should be investigated are discussed.

Leveraging Oral Drug Development to a Next Level: Impact of the IMI-Funded OrBiTo Project on Patient Healthcare

A thorough understanding of the behavior of drug formulations in the human gastrointestinal (GI) tract is essential when working in the field of oral drug development in a pharmaceutical company. For orally administered drug products, various GI processes, including disintegration of the drug formulation, drugrelease, dissolution, precipitation, degradation, dosage form transit and permeation, dictate absorption into the systemic circulation. These processes are not always fully captured in predictive in vitro and in silico tools, as commonly applied in the pre-clinical stage of formulation drug development. A collaborative initiative focused on the science of oral biopharmaceutics was established in 2012 between academic institutions and industrial companies to innovate, optimize and validate these in vitro and in silico biopharmaceutical tools. From that perspective, the predictive power of these models can be revised and, if necessary, optimized to improve the accuracy toward predictions of the in vivo performance of orally administered drug products in patients. The IMI/EFPIA-funded "Oral Bioavailability Tools (OrBiTo)" project aimed to improve our fundamental understanding of the GI absorption process. The gathered information was integrated into the development of new (or already existing) laboratory tests and computer-based methods in order to deliver more accurate predictions of drug product behavior in a real-life setting. These methods were validated with the use of industrial data. Crucially, the ultimate goal of the project was to set up a scientific framework (i.e., decision trees) to guide the use of these new tools in drug development. The project aimed to facilitate and accelerate the formulation development process and to significantly reduce the need for animal experiments in this area as well as for human clinical studies in the future. With respect to the positive outcome for patients, high-quality oral medicines will be developed where the required dose is well-calculated and consistently provides an optimal clinical effect. In a first step, this manuscript summarizes the setup of the project and how data were collected across the different work packages. In a second step, case studies of how this project contributed to improved knowledge of oral drug delivery which can be used to develop improved products for patients will be illustrated.

Mixing and emptying of gastric contents in human-stomach: A numerical study

Stomach is one of the most important organs in human gastro-track. To better understand the operation of human-stomach, the process of mixing and emptying of gastric contents is simulated using a numerical method. The numerical results confirm that a fast pathway is located close to the lesser curvature of the stomach when water is emptied. However, this fast pathway doesn't exist when the gastric contents are composed of water and food boluses with different properties. The muscle contractions enhance the mixing of light food boluses and water, while they have limited effects on heavy food boluses. As a result, the foods are distributed in layers; heavy food boluses are located in the bottom layer. Besides the gastric motility and high viscosity of foods, the food matrix made of heavy food particles is also important to the formation of the Magenstrasse (stomach road). The food matrix and the zone of wrinkles behave like a porous medium which has higher flow resistance to the light food particles than to the water, leading to faster emptying of water. The water is emptied along the stomach wall since the flow resistance in the stomach wrinkles is smaller than the one in the food matrix. This mechanism is supported by the numerical results, while it might interpret the phenomena observed in the experiments.

Theoretical modeling of the resistance to gastric emptying and duodenogastric reflux due to pyloric motility alone, presuming antral and duodenal quiescence

A theoretical model of the pyloric channel, approximated as a two-dimensional tube with sinusoidal corrugation, is developed to estimate the degree of resistance offered by the pylorus to transpyloric flow (gastric emptying and duodenogastric reflux) in the viscous regime. Study indicates that the resistance of the channel depends on pressure gradient, flow behavior index and channel diameter. Flow is majorly determined by the extent of luminal opening; since they scale to fourth power of the diameter for Newtonian flow, with the exponent being higher for pseudoplastic and lesser in case of dilatants relative to Newtonian fluid. At zero pressure difference, across the channel, the closing pylorus drives the aborad propulsion of the contents at the intestinal end, and at the gastric end the flow is driven along the orad direction. While no transfer of contents occur at the centre of pylorus due to zero pressure gradients, it is essential to have a non-zero pressure difference to drive the flow through the channel. The extent of pressure difference is found to linearly relate to the transpyloric flow rate. The resistive function of the pyloric channel is observed at a higher occlusion where there is a development of higher pressure barrier that is sensitive to the flow behavior index, frequency, occlusion, and contraction length.

Fate of Methicillin-resistant Staphylococcus aureus (MRSA) under simulated acidic conditions of the human stomach

A known amount (107 cfu/ml) of animal origin Methicillin-resistant Staphylococcus aureus (MRSA) ST398/t011/V and of human origin MRSA ST1/t127/IVa strains were individually inoculated into ricotta cheese and hamburger samples. The pH of each food matrix was gradually decreased from 6.0 down to 2.0 during a period of about 2 hr, under conditions simulating the mechanical digestion of the human stomach. Afterward, the MRSA strains were recovered by using a MRSA-specific plating medium. Although both strains showed a certain acidic resistance, they showed different responses at low pH values during the experiment: ST398 survived unharmed during the course of the experiments to the last stage at pH 2 where counts of 6.4 cfu/g for the hamburger and 7.5 log cfu/g for ricotta cheese assays were obtained. In contrast, the ST1 population was no longer detectable at pH 3 in the hamburger and at pH 2 in the ricotta cheese assays. To the best of our knowledge, this is the first study that investigates the ability of MRSA to overcome the acidic conditions of the human stomach and that adds new evidence that might contribute to expand the scientific knowledge on the significance of MRSA in the food safety debate.

Volume and position change of the stomach during gastric accommodation and emptying: A detailed three-dimensional morphological analysis based on MRI

BACKGROUND

The proximal and distal regions of the stomach are thought to have different roles during gastric accommodation and emptying; however, regional changes in gastric structure and function during and after a meal have not been described in detail. This study applied non-invasive imaging to study changes in regional gastric volume and morphology during accommodation and emptying of a liquid nutrient meal.

METHOD

MRI studies were performed on 16 healthy volunteers. Three-dimensional (3D) gastric morphology was reconstructed by validated image processing technology. The 3D models were segmented into seven regions. The relative contribution of each region to gastric accommodation and emptying was assessed. Changes in morphology were documented by tracking movements of four distinct gastric landmarks.

KEY RESULTS

The initial 100 mL liquid nutrient increases distal stomach volume more than that of other gastric regions (∆V7 = 28 ± 6% ∆TGV; P ≤ .05). Subsequent volume is accommodated mainly in the proximal stomach (∆V1 = 42 ± 10% ∆TGV; P ≤ .05). Early-phase emptying occurs from distal stomach with proximal stomach volume remaining stable. Subsequently, distal stomach volume remains stable while proximal stomach volume decreases progressively. During gastric filling, the stomach elongates and expands anteriorly and inferiorly (15.2 ± 7.4 mm and 32.3 ± 8.4 mm, respectively, for the incisural midpoint) with torsion indicated by ~70° difference in the movements of proximal and distal gastric landmarks.

CONCLUSIONS AND INFERENCES

Non-invasive MRI describes volume change and distribution of a liquid meal within proximal and distal stomach during gastric accommodation and emptying. Additionally, novel observations of changes to 3D gastric morphology within the abdomen are documented.

Stomach 'tastes' the food and adjusts its emptying: A neurophysiological hypothesis (Review)

The presence of taste receptors and their secondary messengers in stomach raised the possibility that the stomach might play a role in food 'tasting' and consequently, it might initiate specific adaptations of its secretory and motor function. Furthermore, activated taste receptors release a variety of chemical mediators able to modulate the activity of the enteric nervous system (ENS), and also to influence both secretory and motor functions of the stomach. Based on the physiological fundamental structure of a reflex arch, the stimulation of the gastric taste receptors activates sensory neurons of the gastric wall, continues with motor neurons which initiate the contraction of the local smooth muscle fibers. Beyond this, compounds which act on different taste receptors initiate different responses, stimulatory or inhibitory. These interactions may be translated in the gastric ability to selectively evacuate different nutritive compounds into the duodenum. Consequently, sugars could be favored to the detriment of other compounds.

Food material properties as determining factors in nutrient release during human gastric digestion: a review

The fundamental mechanisms of nutrient release from solid foods during gastric digestion consists of multiple elementary processes. These include the diffusion of gastric juice into the food matrix and its simultaneous enzymatic degradation and mechanical breakdown by the peristaltic activity of the stomach. Understanding the relative role of these key processes, in association with the composition and structure of foods, is of paramount importance for the design and manufacture of novel foods possessing specific target behavior within the body. This review covers the past and current literature with respect to the in-stomach processes leading to physical and biochemical disintegration of solid foods and release of nutrients. The review outlines recent progress in experimental and modeling methods used for studying food disintegration mechanisms and concludes with a discussion on potential future research directions in this field. Information from pharmaceutical science-based modeling approaches describing nutrient release kinetics as a result of food disintegration in the gastric environment is also reviewed. Future research aimed at understanding gastric digestion is important not only for setting design principles for novel food design but also for understanding mechanisms underpinning dietary guidelines to consume wholesome foods.

Models of the Gut for Analyzing the Impact of Food and Drugs

Models of the human gastrointestinal tract (GIT) can be powerful tools for examining the biological interactions of food products and pharmaceuticals. This can be done under normal healthy conditions or using models of disease-many of which have no curative therapy. This report outlines the field of gastrointestinal modeling, with a particular focus on the intestine. Traditional in vivo animal models are compared to a range of in vitro models. In vitro systems are elaborated over time, recently culminating with microfluidic intestines-on-chips (IsOC) and 3D bioengineered models. Macroscale models are also reviewed for their important contribution in the microbiota studies. Lastly, it is discussed how in silico approaches may have utility in predicting and interpreting experimental data. The various advantages and limitations of the different systems are contrasted. It is posited that only through complementary use of these models will salient research questions be able to be addressed.

Quantification of gastric emptying caused by impaired coordination of pyloric closure with antral contraction: a simulation study

Proper coordination of gastric motor functions is required for healthy gastric emptying. However, pyloric function may be impaired by functional disorders or surgical procedures. Here, we show how coordination between pyloric closure and antral contraction affects the emptying of liquid contents. We numerically simulated fluid dynamics using an anatomically realistic gastrointestinal geometry. Peristaltic contractions in the proximal stomach resulted in gastric emptying at a rate of 3-8 ml min-1. When the pylorus was unable to close, the emptying rate increased to 10-30 ml min-1, and instantaneous retrograde flow from the duodenum to the antrum occurred during antral relaxation. Rapid emptying occurred if the pylorus began to open during the terminal antral contraction, and the emptying rate was negative if the pylorus only opened during the antral relaxation phase. Our results showed that impaired coordination between antral contraction and pyloric closure can result in delayed gastric emptying, rapid gastric emptying and bile reflux.

Development of a Gastric Simulation Model (GSM) incorporating gastric geometry and peristalsis for food digestion study

There has been growing interest in developing in vitro gastrointestinal models as alternatives to in vivo tests, which is challenging ethically and financially. An in vitro Gastric Simulation Model (GSM) was developed to reproduce the geometry and motility of human stomach. The peristalsis was generated by a series of syringes squeezing a latex chamber pneumatically. In particular, the distribution, amplitude and frequency of contractions demonstrated similar patterns as in human gastric conditions. The breakdown kinetics and size distribution of sausage particles during the digestion were investigated in GSM to demonstrate the effect of the contraction force. Furthermore, the gastric emptying of water-soluble nutrient (methylene blue) and nondigestible solids (amberlite beads) was investigated. The results indicated that the viscosity of the gastric digesta significantly affected the local flow and emptying behavior of nutrients and solids. This study illustrated the capability of GSM to recreate the transient physiological conditions and dynamic flow of gastric contents due to its specificity of geometry and contraction patterns. The new model can be used to investigate the influence of food matrix and physiological conditions, including gastric secretion and contraction forces on transit and digestion of foods in the stomach.

Toward the establishment of a standardized pre-clinical porcine model to predict food effects - Case studies on fenofibrate and paracetamol

A preclinical porcine model that reliably predicts human food effect of fenofibrate was developed. Fenofibrate was administered to pigs as model compound with a positive food effect. Two different types of fed conditions were explored: a FDA style breakfast and a standard pig pellet feed. In order to assess if complete stomach emptying had been achieved under the employed fasting protocol, the amount of gastric and intestinal content was evaluated post-mortem. In addition, the protocol was designed to evaluate gastric emptying in the pre- and postprandial state using paracetamol as a marker. The study confirmed that micronized fenofibrate displayed a positive food effect with a similar fold difference to humans in FDA style fed state. Post-mortem assessment of stomach and intestinal content confirmed significantly lower content in the fasted compared to the pig pellet fed state. In the case of paracetamol, a delayed gastric emptying in the fed state was not observed, which may suggest that the Magenstrasse phenomena reported in humans, may also occur in landrace pigs. The study demonstrated the utility of a food effect protocol in landrace pigs as a pre-clinical approach to predict human food effects and provided new insights into gastric emptying in pigs.

The mechanisms of pharmacokinetic food-drug interactions - A perspective from the UNGAP group

The simultaneous intake of food and drugs can have a strong impact on drug release, absorption, distribution, metabolism and/or elimination and consequently, on the efficacy and safety of pharmacotherapy. As such, food-drug interactions are one of the main challenges in oral drug administration. Whereas pharmacokinetic (PK) food-drug interactions can have a variety of causes, pharmacodynamic (PD) food-drug interactions occur due to specific pharmacological interactions between a drug and particular drinks or food. In recent years, extensive efforts were made to elucidate the mechanisms that drive pharmacokinetic food-drug interactions. Their occurrence depends mainly on the properties of the drug substance, the formulation and a multitude of physiological factors. Every intake of food or drink changes the physiological conditions in the human gastrointestinal tract. Therefore, a precise understanding of how different foods and drinks affect the processes of drug absorption, distribution, metabolism and/or elimination as well as formulation performance is important in order to be able to predict and avoid such interactions. Furthermore, it must be considered that beverages such as milk, grapefruit juice and alcohol can also lead to specific food-drug interactions. In this regard, the growing use of food supplements and functional food requires urgent attention in oral pharmacotherapy. Recently, a new consortium in Understanding Gastrointestinal Absorption-related Processes (UNGAP) was established through COST, a funding organisation of the European Union supporting translational research across Europe. In this review of the UNGAP Working group "Food-Drug Interface", the different mechanisms that can lead to pharmacokinetic food-drug interactions are discussed and summarised from different expert perspectives.

Advances in the physiology of gastric emptying

There have been many recent advances in the understanding of various aspects of the physiology of gastric motility and gastric emptying. Earlier studies had discovered the remarkable ability of the stomach to regulate the timing and rate of emptying of ingested food constituents and the underlying motor activity. Recent studies have shown that two parallel neural circuits, the gastric inhibitory vagal motor circuit (GIVMC) and the gastric excitatory vagal motor circuit (GEVMC), mediate gastric inhibition and excitation and therefore the rate of gastric emptying. The GIVMC includes preganglionic cholinergic neurons in the DMV and the postganglionic inhibitory neurons in the myenteric plexus that act by releasing nitric oxide, ATP, and peptide VIP. The GEVMC includes distinct gastric excitatory preganglionic cholinergic neurons in the DMV and postganglionic excitatory cholinergic neurons in the myenteric plexus. Smooth muscle is the final target of these circuits. The role of the intramuscular interstitial cells of Cajal in neuromuscular transmission remains debatable. The two motor circuits are differentially regulated by different sets of neurons in the NTS and vagal afferents. In the digestive period, many hormones including cholecystokinin and GLP-1 inhibit gastric emptying via the GIVMC, and in the inter-digestive period, hormones ghrelin and motilin hasten gastric emptying by stimulating the GEVMC. The GIVMC and GEVMC are also connected to anorexigenic and orexigenic neural pathways, respectively. Identification of the control circuits of gastric emptying may provide better delineation of the pathophysiology of abnormal gastric emptying and its relationship to satiety signals and food intake.