AJP Gastrointestinal and Liver Physiology

Amouzandeh, Mariam; Sundström, Anna; Wahlin, Staffan; Wernerman, Jan; Rooyackers, Olav; Norberg, Åke

doi: 10.1152/ajpgi.00072.2023pmid: 37605837

Synthesis of plasma proteins is an important function of the liver that has sparsely been investigated by modern techniques in patients with advanced chronic liver disease (CLD). Twenty-eight well-characterized patients with CLD under evaluation for liver transplantation were included. Albumin and fibrinogen synthesis rates were measured by the flooding dose technique using stable isotope labelled phenylalanine. Transcapillary escape rate of albumin and plasma volume were assessed by radio-iodinated human serum albumin. The absolute albumin synthesis rates were low (65 mg/kg/day, range 32-203), and associated with impaired liver function, as reflected by the risk-scores Child-Pugh (p = 0.025) and Model for End-stage Liver Disease rs = -0.62, p=0.0005. The fibrinogen synthesis rate (12.8 mg/kg/day, range 2.4-52.9) was also negatively associated with liver function. The synthesis rates of albumin and fibrinogen were positively correlated. Plasma volume was high (51 ± 9 mL/kg body weight), which contributed to an almost normal intravascular albumin mass despite low plasma concentration. Autoimmune inflammatory etiologies to CLD were associated with higher fibrinogen synthesis. De novo synthesis rates of albumin and fibrinogen in advanced chronic liver failure were negatively correlated to prognostic scores of liver disease. Albumin synthesis rate was low and associated with both liver failure and autoimmune inflammation, while fibrinogen synthesis was often normal and positively associated with chronic inflammation. This is different from acute inflammatory states in which both albumin and fibrinogen synthesis rates are high.

Colucci, Silvia; Carvalho Oliveira, Tiago; Muckenthaler, Martina U.; Marques, Oriana

doi: 10.1152/ajpgi.00085.2023pmid: 37667844

The liver plays a crucial role in maintaining systemic iron homeostasis through iron storage, sensing of systemic iron needs, and production of the iron-regulatory hormone hepcidin. While mice are commonly used as models for studying human iron homeostasis, their liver structure differs significantly from humans. Since the mouse liver is structured in 6 separated lobes, often, the analysis of a single defined lobe is preferred due to concerns over data reproducibility between experimental cohorts. In this study, we compared iron-related parameters in distinct liver lobes of C57BL/6 wild-type mice across different ages. We found that the non-heme iron levels, as well as the mRNA and protein expression of iron storage protein Ferritin and the iron importer Transferrin Receptor 1, were similar between liver lobes. Additionally, the mRNA expression of Hepcidin, as well as its regulators, Bmp2 and Bmp6, and iron importers Zip8 and Zip14 were comparable. Minor differences were observed in Ferroportin mRNA levels of 24-weeks old mice; however, this did not correlate with altered iron content. The findings in wild-type mice were reproduced in Hfe knock-out mice - a well-established genetic model of the most prevalent form of hemochromatosis. Overall, our results indicate that C57BL/6 mouse liver lobes can be used interchangeably for assessing iron content and expression of iron-related genes. Understanding if these findings are applicable to other mouse developmental stages, strains or models of (iron-related) disorders will be key to promote reduction of experimental animal numbers and facilitate resource sharing among research groups studying liver iron homeostasis.

Arslan, Alin; Romano, Antonio; Wang, Qiang; Wang, Benny; Brismar, Torkel B.; Nowak, Greg

doi: 10.1152/ajpgi.00040.2023pmid: 37581219

Introduction: It is believed that whole liver grafts adjust their size to fit the body size of the recipient after transplantation, despite lack of evidence. The aim of this study was to test this hypothesis. Methods: This was a retrospective cohort study of 113 liver transplantations performed at Karolinska University Hospital. The cohort was divided based on graft volume-to-standard liver volume ratio (GV/SLV) into quartiles of small, mid and large grafts. Serial volumetric assessment was performed on the day of transplantation and at post-transplant check-ups early (<2 months) and late (9-13 months) after transplantation using computed tomography (CT) volumetry. Change in GV/SLV-ratio over time was analyzed with ANOVA repeated measures. A multiple regression model was used to investigate the influence of intraoperative blood flow, recipient body size, age and relative sickness on graft volume changes. Results: Between the three timepoints, mean GV/SLV-ratio adapted to: 0.55 -0.94 - 1.00 in small grafts (n=29, p<0.001); 0.87 - 1.18 - 1.13 in mid grafts (n=56, p<0.001); 1.11 - 1.51 - 1.18 in large grafts (n=28, p<0.001). Regression analysis showed a positive correlation between post-transplant graft growth and portal flow (β=1.18, p=0.005), arterial flow (β=0.17, p=0.001) and recipient body surface area (β=59.85, p<0.001). A negative correlation was observed for graft weight-to-recipient weight ratio (GRWR) (β=-33.12, p<0.001). Conclusions: Grafts with initial GV/SLV-ratio<0.6 adapt towards the ideal volume for recipient body size one year after transplantation. The disparity between graft size relative to recipient body size, and the portal and arterial perfusion, influence volumetric graft changes.

Smyth, Jessica S.; Truong, Jennifer K.; Rao, Anuradha; Lin, Ruxian; Foulke-Abel, Jennifer; Adorini, Luciano; Donowitz, Mark; Dawson, Paul A.; Keely, Stephen J.

doi: 10.1152/ajpgi.00099.2023pmid: 37697930

Background: Intestinal inflammation and diarrhea are often associated with SARS-CoV-2 infection. The ACE2 receptor plays a key role in SARS-COV-2 pathogenesis, facilitating entry of the virus into epithelial cells, while also regulating mucosal inflammatory responses. Here, we investigated roles for the nuclear bile acid receptor, farnesoid x receptor (FXR), in regulating ACE2 expression and virally-mediated inflammatory responses in intestinal epithelia. Methods: Human colonic or ileal enteroids and cultured T84 and Caco-2 monolayers were treated with the FXR agonists, obeticholic acid (OCA) or GW4064, or infected with live SARS-CoV-2 (2019-nCoV/USA_WA1/2020). Changes in mRNA, protein or secreted cytokines were measured by qPCR, western blotting, and ELISA. Results: Treatment of undifferentiated colonic or ileal enteroids with OCA increased ACE2 mRNA by 2.1 ± 0.4 (n = 3; p = 0.08) and 2.3 ± 0.2 (n = 3; p < 0.05) fold, respectively. In contrast, ACE2 expression in differentiated enteroids was unaltered. FXR activation in cultured epithelial monolayers also upregulated ACE2 mRNA, accompanied by increases in ACE2 expression and secretion. Further experiments revealed FXR activation to inhibit IL-6 release both from Caco-2 cells infected with SARS-CoV-2 and T84 cells treated with the viral mimic, polyinosinic-polycytidylic acid by 46 ± 12% (n = 3, p < 0.05) and 35 ± 6% (n = 8; p < 0.01), respectively. Conclusion: By virtue of its ability to modulate epithelial ACE2 expression and inhibit virus-mediated pro-inflammatory cytokine release, FXR represents a promising target for development of new approaches to prevent intestinal manifestations of SARS-CoV-2.

Jeong, Jain; Tanaka, Masatake; Yang, Yilin; Arefyev, Nikolai; DiRito, Jenna; Tietjen, Gregory; Zhang, Xuchen; McConnell, Matthew J.; Utsumi, Teruo; Iwakiri, Yasuko

doi: 10.1152/ajpgi.00139.2023pmid: 37605828

The liver lymphatic system is essential for maintaining tissue fluid balance and immune function. The detailed structure of lymphatic vessels (LVs) in the liver remains to be fully demonstrated. The aim of this study is to reveal LV structures in normal and diseased livers by developing a tissue-clearing and co-immunolabeling protocol optimized for the tissue size and the processing time for 3D visualization and quantification of LVs in the liver. We showed that our optimized protocol enables in-depth exploration of lymphatic networks in the liver, consisting of LVs along the portal tract (deep lymphatic system) and within the collagenous Glisson's capsule (superficial lymphatic system) in different species. With this protocol, we have shown 3D LVs configurations in relation to blood vessels and bile ducts in cholestatic mouse livers, in which LVs were highly dilated and predominantly found around highly proliferating bile ducts and peribiliary vascular plexuses in the portal tract. We also established a quantification method using a 3D volume rendering approach. We observed a 1.6-fold (p<0.05) increase in average diameter of LVs and a 2.4-fold increase (p<0.05) in the average branch number of LVs in cholestatic/fibrotic livers compared to control livers. Furthermore, cholestatic/fibrotic livers showed a 4.3-fold increase (p<0.05) in total volume of LVs compared to control livers. Our optimized protocol and quantification method demonstrate an efficient and simple liver tissue-clearing procedures that allow the comprehensive analysis of liver lymphatic system.

Bhebhe, Charity N.; Higham, James P.; Gupta, Rohit A.; Raine, Tim; Bulmer, David C.

doi: 10.1152/ajpgi.00141.2023pmid: 37667839

In numerous subtypes of central and peripheral neurons, small and intermediate conductance Ca2+-activated K+ (SK and IK, respectively) channels are important regulators of neuronal excitability. Transcripts encoding SK channel subunits, as well as the closely related IK subunit, are co-expressed in the soma of colonic afferent neurons with receptors for the algogenic mediators adenosine triphosphate (ATP) and bradykinin, P2X3 and B2, highlighting the potential utility of these channels as drug targets for the treatment of abdominal pain in gastrointestinal diseases such as irritable bowel syndrome. Despite this, pre-treatment with the dual SK/IK channel opener SKA-31 had no effect on the colonic afferent response to ATP, bradykinin or noxious ramp distention of the colon. Inhibition of SK or IK channels with apamin or TRAM-34, respectively, yielded no change in spontaneous baseline afferent activity, indicating these channels are not tonically active. In contrast to its lack of effect in electrophysiological experiments, comparable concentrations of SKA-31 abolished ongoing peristaltic activity in the colon ex vivo. Treatment with the KV7 channel opener retigabine blunted the colonic afferent response to all applied stimuli. Our data therefore highlight the potential utility of KV7, but not SK/IK, channel openers as analgesic agents for the treatment of abdominal pain.

Arunachalam, Athis R.; Samuel, Sanju S.; Mani, Arunmani; Maynard, Janielle P.; Stayer, Kelsey M.; Dybbro, Eric; Narayanan, Subapradha; Biswas, Aalekhya; Pathan, Saliha; Soni, Krishnakant; Kamal, Abu Hena Mostafa; Ambati, Chandra Shekar R.; Putluri, Nagireddy; Desai, Moreshwar S.; Thevananther, Sundararajah

Gao, Jie; Bao, Miaoye; Xing, Yuanming; Ding, Yiming; Han, Tuo; Wen, Ergang; Liu, Jun; Yue, Shaoyun; Wang, Rong; Wang, Ling; Liu, Junhui; Zhao, Sihai; Huang, Jiansheng; Liu, Enqi; Bai, Liang

doi: 10.1152/ajpgi.00076.2023pmid: 37668531

Mediator subunit MED1 mediates ligand-dependent binding of the Mediator coactivator complex to various nuclear receptors and plays critical role in embryonic development, lipid and glucose metabolism, liver regeneration and tumorigenesis. However, the precise role of MED1 in the development of liver fibrosis has been unclear. Here, we showed that MED1 expression was increased in livers from nonalcoholic steatohepatitis (NASH) patients and mice, and positively correlated with TGF-β signaling and pro-fibrotic factors. Upon with CCl4 treatment, hepatic fibrosis was much lesser in liver specific MED1 deletion (MED1ΔLiv) mice than in MED1fl/fl littermates. TGF-β/Smad2/3 signaling pathway was inhibited, and gene expression of fibrotic markers, including α-smooth muscle actin (α-SMA), collagen type 1 alpha 1 (Col1a1), matrix metalloproteinase-2 (Mmp2), and metallopeptidase inhibitor 1 (Timp1) were decreased in livers of MED1ΔLiv mice with CCl4 injection. Transcriptomic analysis revealed that the differentially expressed genes in livers of CCl4-adminstered MED1ΔLiv mice were enriched in pathway of oxidoreductase activity, following with robustly reduced oxidoreductase activity related genes, such as Gm4756, Txnrd3, and Etfbkmt. More importantly, we found that reduction of reactive oxygen species (ROS) in MED1 knockdown hepatocytes blocked the activation of TGF-β/Smad2/3 pathway and the expression of fibrotic genes in LX2 cells. These results indicate that MED1 is a positive regulator for hepatic fibrogenesis and MED1 may be considered as a potential therapeutic target for the regression of liver fibrosis.

de Guilhem de Lataillade, Adrien; Pellegrini, Carolina; Neunlist, Michel; Rolli-Derkinderen, Malvyne; Derkinderen, Pascal

doi: 10.1152/ajpgi.00162.2023pmid: 37643021

Gut-brain axis and inflammation are two hot topics in Parkinson's disease. In this setting, the Leucine-rich repeat kinase 2 (LRRK2) gene, which encodes the eponym protein has attracted much attention. LRRK2 is not only the gene most commonly associated with Parkinson's disease but also a susceptibility gene for Crohn's disease, thereby suggesting that it may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. In contrast to the accumulated data on LRRK2 in the CNS, research on LRRK2 in the digestive tract is still in its infancy and the scope of the present review article is therefore to review existing studies on LRRK2 in the gastrointestinal tract in both physiological and pathological conditions. In the light of current data on LRRK2 in the gastrointestinal tract, we discuss if LRRK2 could be or not regarded as a molecular link between gut inflammation, PD and CD and we suggest directions for future research.

Parkman, Henry P.; Wilson, Laura A.; Silver, Paul; Maurer, Alan H.; Sarosiek, Irene; Bulat, Robert S.; Kuo, Braden; Grover, Madhusudan; Farrugia, Gianrico; Chumpitazi, Bruno P.; Shulman, Robert J.; Malik, Zubair; Miriel, Laura A.; Tonascia, James; Hamilton, Frank; Abell, Thomas L.; Pasricha, Pankaj J.; McCallum, Richard W.;