American journal of physiology. Gastrointestinal and liver physiology最新文献

Human sepsis is characterized by increased protein breakdown and changes in arginine and citrulline metabolism. However, it is unclear whether this is caused by changes in transorgan metabolism. We therefore studied in a Pseudomonas aeruginosa induced pig sepsis model the changes in protein and arginine related metabolism on whole body (Wb) and transorgan level. We studied 22 conscious pigs for 18 hours during sepsis, induced by infusing live bacteria (Pseudomonas aeruginosa) or after placebo infusion (control). We used stable isotope tracers to measure Wb and skeletal muscle protein synthesis and breakdown, as well as Wb, splanchnic, skeletal muscle, hepatic and portal drained viscera (PDV) arginine and citrulline disposal and production rates. During sepsis, arginine Wb production (p=0.0146), skeletal muscle release (p=0.0035) and liver arginine uptake were elevated (p=0.0031). Wb de novo arginine synthesis, citrulline production, and transorgan PDV release of citrulline, glutamine and arginine did not differ between sepsis and controls. However, Wb (p<0.0001) and muscle (p<0.001) protein breakdown were increased, suggesting that the enhanced arginine production is predominantly derived from muscle breakdown in sepsis. In conclusion, live-bacterium sepsis increases muscle arginine release and liver uptake, mirroring previous pig endotoxemia studies. In contrast to observations in humans, acute live-bacterium sepsis in pigs does not change citrulline production or arterial arginine concentration. We therefore conclude that the arginine dysregulation observed in human sepsis is possibly initiated by enhanced protein catabolism and splanchnic arginine catabolism, while decreased arterial arginine concentration and citrulline metabolism may require more time to fully manifest in patients.

The stomach's ability to store, mix, propel, and empty its content requires highly coordinated motor functions. However, current diagnostic tools cannot simultaneously assess these motor processes. This study aimed to use magnetic resonance imaging (MRI) to map multifaceted gastric motor functions, including accommodation, tonic and peristaltic contractions, and emptying, through a single noninvasive experiment for both humans and rats. Ten humans and 10 Sprague-Dawley rats consumed MRI-visible semisolid meals and underwent MRI scans. We used a surface model to analyze MRI data, capturing the deformation of the stomach wall on ingestion or during digestion. We inferred muscle activity, mapped motor processes, parcellated the stomach into functional regions, and revealed cross-species distinctions. In humans, both the fundus and antrum distended postmeal, followed by sustained tonic contractions to regulate intragastric pressure. Peristaltic contractions initiated from the distal fundus, including three concurrent wavefronts oscillating at 3.3 cycles/min and traveling at 1.7 to 2.9 mm/s. These motor functions facilitated linear gastric emptying with a 61-min half-time. In contrast, rats exhibited peristalsis from the midcorpus, showing two wavefronts oscillating at 5.0 cycles/min and traveling at 0.4 to 0.9 mm/s. For both species, motility features allowed functional parcellation of the stomach along a midcorpus division. This study maps region- and species-specific gastric motor functions. We demonstrate the value of MRI with surface modeling in understanding gastric physiology and its potential to become a new standard for clinical and preclinical investigations of gastric disorders at both individual and group levels.NEW & NOTEWORTHY A novel MRI technique can visualize how the stomach accommodates, mixes, and propels food for digestion in humans and animals alike. Digital models of gastric MRI reveal the functional maps, organization, and distinction of the stomach across individuals and species. This technique holds the unique potential to advance basic and clinical studies of functional gastric disorders.

Irritable bowel syndrome with diarrhea (IBS-D) is a common intestinal condition that significantly impacts work efficiency and quality of life. The use of animal models is crucial for delving into the pathophysiology of IBS-D and exploring therapeutic options. However, a wide variety of animal models for IBS-D has been used in previous studies, posing a considerable challenge for researchers in selecting a suitable model. In this review, using the Web of Science database, we searched IBS-D-related research spanning from 2014 to 2023; described the differences in animal strains and modeling methods among various IBS-D features recapitulating models; summarized the frequency of model usage, pathogenesis, and pathological characteristics of these models; and discussed their current applications, limitations, and future perspectives. The objective is to offer theoretical guidance for future researchers, aiding them in choosing suitable animal models based on their experimental designs.

Ischemia-reperfusion injury (IRI) is an intrinsic risk associated with liver transplantation. Ex vivo hepatic machine perfusion (MP) is an emerging organ preservation technique that can mitigate IRI, especially in livers subjected to prolonged warm ischemia time (WIT). However, a method to quantify the biological response to WIT during MP has not been established. Previous studies used physiologically based pharmacokinetic (PBPK) modeling to demonstrate that a decrease in hepatic transport and biliary excretion of the tracer molecule sodium fluorescein (SF) could correlate with increasing WIT in situ. Furthermore, these studies proposed intracellular sequestration of the hepatocyte canalicular membrane transporter multidrug resistance-associated protein 2 (MRP2) leading to decreased MRP2 activity (maximal transport velocity; V_max) as the potential mechanism for decreased biliary SF excretion. We adapted an extant PBPK model to account for ex vivo hepatic MP and fit a six-parameter version of this model to control time-course measurements of SF in MP perfusate and bile. We then identified parameters whose values were likely insensitive to changes in WIT and fixed them to generate a reduced model with only three unknown parameters. Finally, we fit the reduced model to each individual biological replicate SF time course with differing WIT, found the mean estimated value for each parameter, and compared them using a one-way ANOVA. We demonstrated that there was a significant decrease in the estimated value of V_max for MRP2 at the 30-min WIT. These studies provide the foundation for future studies investigating real-time assessment of liver viability during ex vivo MP.NEW & NOTEWORTHY We developed a computational model of sodium fluorescein (SF) biliary excretion in ex vivo machine perfusion and used this model to assess changes in model parameters associated with the activity of MRP2, a hepatocyte membrane transporter, in response to increasing warm ischemia time. We found a significant decrease in the parameter value describing MRP2 activity, consistent with a role of decreased MRP2 function in ischemia-reperfusion injury leading to decreased secretion of SF into bile.

Our prior study reveals that the distension-contraction profiles using high-resolution manometry impedance recordings can distinguish patients with dysphagia symptom but normal esophageal function testing ("functional dysphagia") from control subjects. The aim of this study was to determine the diagnostic value of the recording protocol used in our prior studies (10-mL swallows with subjects in the Trendelenburg position) against the standard clinical protocol (5-mL swallows with subjects in the supine position). We used advanced machine learning techniques and robust metrics for classification purposes. Studies were performed on 30 healthy subjects and 30 patients with functional dysphagia. A custom-built software was used to extract the relevant distension-contraction features of esophageal peristalsis. Ensemble methods, i.e., gradient boost, support vector machines (SVMs), and logit boost, were used as the primary machine learning algorithms. Although the individual contraction features were marginally different between the two groups, the distension features of peristalsis were significantly different. The receiver operating characteristic (ROC) curve values for the standard recording protocol and the distension features ranged from 0.74 to 0.82; they were significantly better for the protocol used in our prior studies, ranging from 0.81 to 0.91. The ROC curve values using three machine learning algorithms were far superior for the distension than the contraction features of esophageal peristalsis, revealing a value of 0.95 for the SVM algorithm. Current patient classification for esophageal motility disorders, based on the contraction phase of peristalsis, ignores a large number of patients who have an abnormality in the distension phase of peristalsis. Distension-contraction plots should be the standard for assessing esophageal peristalsis in clinical practice.NEW & NOTEWORTHY Our findings underscore the superiority of distension features over contraction metrics in diagnosing esophageal dysfunctions. By leveraging state-of-the-art machine learning techniques, our study highlights the diagnostic potential of distension-contraction plots of peristalsis. Implementation of these plots could significantly enhance the accuracy of identifying patients with esophageal motor disorders, advocating for their adoption as the standard in clinical practice.

Keratin intermediate filaments form dynamic filamentous networks, which provide mechanical stability, scaffolding, and protection against stress to epithelial cells. Keratins and other intermediate filaments have been increasingly linked to the regulation of mitochondrial function and homeostasis in different tissues and cell types. While deletion of keratin 8 (K8^-/-) in mouse colon elicits a colitis-like phenotype, epithelial hyperproliferation, and blunted mitochondrial ketogenesis, the role of K8 in colonocyte mitochondrial function and energy metabolism is unknown. We used two K8 knockout mouse models and CRISPR/Cas9 K8^-/- colorectal adenocarcinoma Caco-2 cells to answer this question. The results show that K8^-/- colonocyte mitochondria in vivo are smaller and rounder and that mitochondrial motility is increased in K8^-/- Caco-2 cells. Furthermore, K8^-/- Caco-2 cells displayed diminished mitochondrial respiration and decreased mitochondrial membrane potential compared with controls, whereas glycolysis was not affected. The levels of mitochondrial respiratory chain complex proteins and mitochondrial regulatory proteins mitofusin-2 and prohibitin were decreased both in vitro in K8^-/- Caco-2 cells and in vivo in K8^-/- mouse colonocytes, and reexpression of K8 into K8^-/- Caco-2 cells normalizes the mitofusin-2 levels. Mitochondrial Ca²⁺ is an important regulator of mitochondrial energy metabolism and homeostasis, and Caco-2 cells lacking K8 displayed decreased levels and altered dynamics of mitochondrial matrix and cytoplasmic Ca²⁺. In summary, these novel findings attribute an important role for colonocyte K8 in stabilizing mitochondrial shape and movement and maintaining mitochondrial respiration and Ca²⁺ signaling. Further, how these metabolically compromised colonocytes are capable of hyperproliferating presents an intriguing question for future studies.NEW & NOTEWORTHY In this study, we show that colonocyte intermediate filament protein keratin 8 is important for stabilizing mitochondria and maintaining mitochondrial energy metabolism, as keratin 8-deficient colonocytes display smaller, rounder, and more motile mitochondria, diminished mitochondrial respiration, and altered Ca²⁺ dynamics. Changes in fusion-regulating proteins are rescued with reexpression of keratin 8. These alterations in colonocyte mitochondrial homeostasis contribute to keratin 8-associated colitis pathophysiology.

The internal anal sphincter (IAS) functions to maintain continence. Previous studies utilizing mice with cell-specific expression of GCaMP6f revealed two distinct subtypes of intramuscular interstitial cells of Cajal (ICC-IM) with differing Ca²⁺ activities in the IAS. The present study further examined Ca²⁺ activity in ICC-IM and its modulation by inhibitory neurotransmission. The spatiotemporal properties of Ca²⁺ transients in Type II ICC-IM mimicked those of smooth muscle cells (SMCs), indicating their joint participation in the "SIP" syncytium. Electrical field stimulation (EFS; atropine present) abolished localized and whole cell Ca²⁺ transients in Type I and II ICC-IM. The purinergic antagonist MRS2500 did not abolish EFS responses in either cell type, whereas the nitric oxide synthase (NOS) inhibitor N^G-nitro-l-arginine (l-NNA) abolished responses in Type I but not Type II ICC-IM. Combined antagonists abolished EFS responses in Type II ICC-IM. In both ICC-IM subtypes, the ability of EFS to inhibit Ca²⁺ release was abolished by l-NNA but not MRS2500, suggesting that the nitrergic pathway directly inhibits ICC-IM by blocking Ca²⁺ release from intracellular stores. Since inositol (1,4,5)-trisphosphate receptor-associated cGMP kinase substrate I (IRAG1) is expressed in ICC-IM, it is possible that it participates in the inhibition of Ca²⁺ release by nitric oxide. Platelet-derived growth factor receptor α (PDGFRα)⁺ cells but not ICC-IM expressed P2Y₁ receptors (P2Y₁R) and small-conductance Ca²⁺-activated K⁺ channels (SK3), suggesting that the purinergic pathway indirectly blocks whole cell Ca²⁺ transients in Type II ICC-IM via PDGFRα⁺ cells. This study provides the first direct evidence for functional coupling between inhibitory motor neurons and ICC-IM subtypes in the IAS, with contractile inhibition ultimately dependent upon electrical coupling between SMCs, ICC, and PDGFRα⁺ cells via the SIP syncytium.NEW & NOTEWORTHY Two intramuscular interstitial cells of Cajal (ICC-IM) subtypes exist within the internal anal sphincter (IAS). This study provides the first evidence for direct coupling between nitrergic motor neurons and both ICC-IM subtypes as well as indirect coupling between purinergic inputs and Type II ICC-IM. The spatiotemporal properties of whole cell Ca²⁺ transients in Type II ICC-IM mimic those of smooth muscle cells (SMCs), suggesting that ICC-IM modulate the activity of SMCs via their joint participation in a SIP syncytium (SMCs, ICC, and PDGFRα⁺ cells).