Sources of proteins in human bile

Bile multi-omics analysis classifies lipid species and microbial peptides predictive of carcinoma of gallbladder

BACKGROUND AND AIMS

Histopathological examination is the gold standard for detection of gallstone (GS) or gallbladder carcinoma (CAGB). Bile concentrated in the gallbladder (GB) is expected to recapitulate metagenomics and molecular changes associated with development of CAGB.

APPROACH AND RESULTS

Bile samples were screened for lipidomics and metaproteome (metagenomics) signatures capable of early detection of cancer in GB anomalies. Analysis of the training cohort (n = 87) showed that metastability of bile was reduced in CAGB (p < 0.05). CAGB bile showed significant alteration of lipidome and microbiome as indicated by multivariate partial least squares regression analysis and alpha-diversity and beta-diversity indexes (p < 0.05). Significant reduction of lipid species and increase in bacterial taxa were found to be associated with patients with CAGB, CAGB with GS, and GS (p < 0.05, log fold change >1.5). A multimodular correlation network created using weighted lipid/metaproteomic correlation network analysis showed striking associations between lipid and metaproteomic modules and functionality. CAGB-linked metaproteomic modules/functionality directly correlated with lipid modules, species, clinical parameters, and bile acid profile (p < 0.05). Increased bacterial taxa (Leptospira, Salmonella enterica, Mycoplasma gallisepticum) and their functionality showed a direct correlation with lipid classes such as lysophosphatidylinositol, ceramide 1-phosphate, and lysophosphatidylethanolamine and development of CAGB (r²  > 0.85). Lipid/metaproteomic signature-based probability of detection for CAGB was > 90%, whereas that for GS was > 80% (p < 0.05). Validation of eight lipid species using four machine learning algorithms in two separate cohorts (n = 38; bile [test cohort 1] and paired plasma [test cohort 2]) showed accuracy (99%) and sensitivity/specificity (>98%) for CAGB detection.

CONCLUSIONS

Bile samples of patients with CAGB showed significant reduction in lipid species and increase in bacterial taxa. Our study identifies a core set of bile lipidome and metaproteome signatures which may offer universal utility for early diagnosis of CAGB.

Intraoperative guidance using ICG fluorescence imaging system for safe and precise laparoscopic liver resection

BACKGROUND

Laparoscopic liver resection (LLR) has been spread as minimally invasive surgery for liver disease. Advances in surgical technique and devices enabled us to perform various procedures of LLR. Indocyanine green (ICG) fluorescence imaging has been suggested as useful tool to identify liver tumors, anatomical territory of liver parenchyma, and cholangiography in open liver surgery. Due to recent development, this technology can be applied in LLR. we describe safe and effective using of the ICG fluorescence imaging during LLR.

METHODS

From September 2013 to August 2019, 34 patients were performed LLR using a total of 46 procedures by ICG fluorescence imaging system for purposes including identification of anatomic domain of the liver in 12 LLRs, detection of liver tumors in 30 nodules, or intraoperative cholangiography in 4 LLRs.

RESULTS

During the detection of liver tumors, 25 nodules in 30 malignant to benign tumors were positively detected (83.3%). Although there has been no publication regarding information on ICG fluorescence imaging of low grade malignant or benign tumors, we found positive emission in focal nodular hyperplasia, an angiomyolipoma, and an intraductal papillary neoplasm of the bile duct. The identification of anatomic domain in the liver was successful in all 12 LLRs with negative and positive staining techniques. In the intraoperative cholangiography, all 4 tests were successfully performed. One of 4 patients were found to have biliary leakage which was repaired intraoperatively.

CONCLUSIONS

The ICG fluorescence imaging could be useful in safe and precise performance of LLR.

Near-Infrared Fluorescence Imaging and Photodynamic Therapy for Liver Tumors

Surgery with fluorescence equipment has improved to treat the malignant viscera, including hepatobiliary and pancreatic neoplasms. In both open and minimally invasive surgeries, optical imaging using near-infrared (NIR) fluorescence is used to assess anatomy and function in real time. Here, we review a variety of publications related to clinical applications of NIR fluorescence imaging in liver surgery. We have developed a novel nanoparticle (indocyanine green lactosome) that is biocompatible and can be used for imaging cancer tissues and also as a drug delivery system. To date, stable particles are formed in blood and have an ~10–20 h half-life. Particles labeled with a NIR fluorescent agent have been applied to cancer tissues by the enhanced permeability and retention effect in animals. Furthermore, this article reviews recent developments in photodynamic therapy with NIR fluorescence imaging, which may contribute and accelerate the innovative treatments for liver tumors.

Some more about dogs: Proteomics of neglected biological fluids

We report in this manuscript what is known about the protein makeup of a selection of biological fluids in the domestic dog. The samples we review - amniotic and allantoic fluid, seminal fluid, saliva, bile, synovial fluid, tears - are still very poorly characterized in this species. For some of them we can present results from our own, mainly unpublished experiments. SIGNIFICANCE: The dog is one of the most widespread companion animals, and also of medical relevance as model species for some human diseases. Still, investigation of body fluids other than serum and urine is not so commonly undertaken, although - like in humans - also these sample types may have potential for diagnostic purposes. We compile published data about proteomes of fetal fluids, seminal plasma, saliva, bile, synovial fluid and tears, enriched by some yet unpublished data of our own (proteins of amniotic and allantoic fluid, tears). Closing gaps in our knowledge on dog proteins will further our understanding of (patho)physiological processes.

[Guidelines for application of computer-assisted indocyanine green molecular fluorescence imaging in diagnosis and surgical navigation of liver tumors (2019)]

Computer-assisted combined indocyanine green (ICG) molecular fluorescence imaging technology can be used for preoperative planning and intraoperative detection from three-dimensional (3D) morphological anatomy and level of cellular function to guide the anatomical, functional and radical hepatectomy of liver tumor. This technology has received wide acceptance and has shown important diagnostic and therapeutic value. This guideline is intended to standardize the application of computer-assisted combined ICG molecular fluorescence imaging for accurate diagnosis and treatment of liver tumors in the following aspects: (1) the workflow of 3D visualization technology; (2) the mechanism and application flow of ICG molecular fluorescence imaging; (3) clinical application of 3D visualization technology and virtual reality technology; and (4) clinical application of ICG molecular fluorescence imaging. ICG molecular fluorescence imaging can help to define tumor boundary, determine hepatic segment and hepatic lobectomy tangent at the molecular and cellular level, and detect small lesions or metastases. According to the fluorescence signal characteristics of liver tumors and combined with rapid frozen pathological examination during operation, the differentiation degree of liver space-occupying lesions (such as primary liver cancer) can be preliminarily determined, and residual tumors and biliary leakage on the hepatic section can be detected after hepatectomy. Computer-assisted ICG molecular fluorescence imaging in the diagnosis and surgical navigation of liver tumors provides a new approach to digital diagnosis and treatment of liver tumors. With its development in clinical practice and the technological innovation, this technology will be further improved to allow more accurate diagnosis and treatment of liver tumors.

Novel method of intraoperative liver tumour localisation with indocyanine green and near-infrared imaging

INTRODUCTION

Fluorescence imaging (FI) with indocyanine green (ICG) is increasingly implemented as an intraoperative navigation tool in hepatobiliary surgery to identify hepatic tumours. This is useful in minimally invasive hepatectomy, where gross inspection and palpation are limited. This study aimed to evaluate the feasibility, safety and optimal timing of using ICG for tumour localisation in patients undergoing hepatic resection.

METHODS

From 2015 to 2018, a prospective multicentre study was conducted to evaluate feasibility and safety of ICG in tumour localisation following preoperative administration of ICG either on Day 0-3 or Day 4-7.

RESULTS

Among 32 patients, a total of 46 lesions were resected: 23 were hepatocellular carcinomas (HCCs), 12 were colorectal liver metastases (CRLM) and 11 were benign lesions. ICG FI identified 38 (82.6%) lesions prior to resection. The majority of HCCs were homogeneous fluorescing lesions (56.6%), while CLRM were homogeneous (41.7%) or rim-enhancing (33.3%). The majority (75.0%) of the lesions not detected by ICG FI were in cirrhotic livers. Most (84.1%) of ICG-positive lesions detected were < 1 cm deep, and half of the lesions ≥ 1 cm in depth were not detected. In cirrhotic patients with malignant lesions, those given ICG on preoperative Day 0-3 and Day 4-7 had detection rates of 66.7% and 91.7%, respectively. There were no adverse events.

CONCLUSION

ICG FI is a safe and feasible method to assist tumour localisation in liver surgery. Different tumours appear to display characteristic fluorescent patterns. There may be no disadvantage of administering ICG closer to the operative date if it is more convenient, except in patients with liver cirrhosis.

Biliary tract external drainage improves inflammatory mediators and pathomorphology of the intestine, liver, and lung in septic rats

BACKGROUND

To investigate the effect of biliary tract external drainage (BTED) on inflammatory mediators and pathomorphism of intestine, liver, and lung in septic rats.

METHOD

48 SD rats (n = 8 per group) were randomized into six groups: control, sepsis, sepsis plus BTED, normal bile (obtained from eight healthy rats), and septic bile infusion for 6 hours respectively to test the effects of BTED bile infusion on cytokines' expression and tissue injury in the intestine, liver, and lung of septic/normal rats. Co-cultivation of intestinal epithelial cells (IEC-6) with bile for 12 hours was performed to evaluate the potential cytotoxicity of septic bile. Survival rate for sepsis plus BTED rats was detected compared with sepsis without BTED group (n = 20 per group) at 24, 48, and 72 hours, respectively.

RESULTS

BTED for 6 hours significantly reduced the mRNA expression levels of tumor necrosis factor alpha (TNF-α) and IL-1β (all p < 0.05 vs. sepsis group), whereas mRNA expression of TNF-α and IL-1β in the intestine was increased after 6 hours' septic bile infusion compared with normal bile infusion group (all p < 0.05). TNF-α concentration in septic bile was significantly higher than that in the control group (p < 0.001). Tissue injury was significantly attenuated after 6 hours' BTED.

CONCLUSIONS

BTED can significantly restrain the mRNA expression of TNF-α and IL-1β in the intestine, liver, and lung and attenuate histological damage in septic rats.

Constitutive release of CPS1 in bile and its role as a protective cytokine during acute liver injury

Carbamoyl phosphate synthetase-1 (CPS1) is the major mitochondrial urea cycle enzyme in hepatocytes. It is released into mouse and human blood during acute liver injury, where is has a short half-life. The function of CPS1 in blood and the reason for its short half-life in serum are unknown. We show that CPS1 is released normally into mouse and human bile, and pathologically into blood during acute liver injury. Other cytoplasmic and mitochondrial urea cycle enzymes are also found in normal mouse bile. Serum, bile, and purified CPS1 manifest sedimentation properties that overlap with extracellular vesicles, due to the propensity of CPS1 to aggregate despite being released primarily as a soluble protein. During liver injury, CPS1 in blood is rapidly sequestered by monocytes, leading to monocyte M2-polarization and homing to the liver independent of its enzyme activity. Recombinant CPS1 (rCPS1), but not control r-transferrin, increases hepatic macrophage numbers and phagocytic activity. Notably, rCPS1 does not activate hepatic macrophages directly; rather, it activates bone marrow and circulating monocytes that then home to the liver. rCPS1 administration prevents mouse liver damage induced by Fas ligand or acetaminophen, but this protection is absent in macrophage-deficient mice. Moreover, rCPS1 protects from acetaminophen-induced liver injury even when given therapeutically after injury induction. In summary, CPS1 is normally found in bile but is released by hepatocytes into blood upon liver damage. We demonstrate a nonenzymatic function of CPS1 as an antiinflammatory protective cytokine during acute liver injury.

Protein losing enteropathy: comprehensive review of the mechanistic association with clinical and subclinical disease states

Protein losing enteropathy (PLE) has been associated with more than 60 different conditions, including nearly all gastrointestinal diseases (Crohn’s disease, celiac, Whipple’s, intestinal infections, and so on) and a large number of non-gut conditions (cardiac and liver disease, lupus, sarcoidosis, and so on). This review presents the first attempt to quantitatively understand the magnitude of the PLE in relation to the associated pathology for three different disease categories: 1) increased lymphatic pressure (e.g., lymphangiectasis); 2) diseases with mucosal erosions (e.g., Crohn’s disease); and 3) diseases without mucosal erosions (e.g., celiac disease). The PLE with lymphangiectasis results from rupture of the mucosal lymphatics, with retrograde drainage of systemic lymph into the intestinal lumen with the resultant loss of CD4 T cells, which is diagnostic. Mucosal erosion PLE results from macroscopic breakdown of the mucosal barrier, with the epithelial capillaries becoming the rate-limiting factor in albumin loss. The equation derived to describe the relationship between the reduction in serum albumin (C_P) and PLE indicates that gastrointestinal albumin clearance must increase by at least 17 times normal to reduce the C_P by half. The strengths and limitations of the two quantitative measures of PLE (⁵¹Cr-albumin or α₁-antitrypsin [αAT] clearance) are reviewed. αAT provides a simple quantitative diagnostic test that is probably underused clinically. The strong, unexplained correlation between minor decreases in C_P and subsequent mortality in seemingly healthy individuals raises the question of whether subclinical PLE could account for the decreased C_P and, if so, could the mechanism responsible for PLE play a role in the increased mortality? A large-scale study correlating αAT clearance with serum albumin concentrations will be required in order to determine the role of PLE in the regulation of the serum albumin concentration of seemingly healthy subjects.

Clinical application of indocyanine green-fluorescence imaging during hepatectomy

In hepatobiliary surgery, the fluorescence and bile excretion of indocyanine green (ICG) can be used for real-time visualization of biological structure. Fluorescence cholangiography is used to obtain fluorescence images of the bile ducts following intrabiliary injection of 0.025-0.5 mg/mL ICG or intravenous injection of 2.5 mg ICG. Recently, the latter technique has been used in laparoscopic/robotic cholecystectomy. Intraoperative fluorescence imaging can be used to identify subcapsular hepatic tumors. Primary and secondary hepatic malignancy can be identified by intraoperative fluorescence imaging using preoperative intravenous injection of ICG through biliary excretion disorders that exist in cancerous tissues of hepatocellular carcinoma (HCC) and in non-cancerous hepatic parenchyma around adenocarcinoma foci. Intraoperative fluorescence imaging may help detect tumors to be removed, especially during laparoscopic hepatectomy, in which visual inspection and palpation are limited, compared with open surgery. Fluorescence imaging can also be used to identify hepatic segments. Boundaries of hepatic segments can be visualized following injection of 0.25-2.5 mg/mL ICG into the portal veins or by intravenous injection of 2.5 mg ICG following closure of the proximal portal pedicle toward hepatic regions to be removed. These techniques enable identification of hepatic segments before hepatectomy and during parenchymal transection for anatomic resection. Advances in imaging systems will increase the use of fluorescence imaging as an intraoperative navigation tool that can enhance the safety and accuracy of open and laparoscopic/robotic hepatobiliary surgery.

Evaluation of fluorescence imaging with indocyanine green in hepatocellular carcinoma

Background

We hypothesized that indocyanine green (ICG) fluorescence patterns using Clairvivo OPT in resected liver specimens could confirm hepatocellular carcinoma (HCC) better than earlier commercial imaging systems. This preclinical trial evaluated the effectiveness of fluorescence imaging as an intraoperative cancer navigation tool.

Methods

ICG fluorescence images of resected specimens from 190 patients with HCC were classified into two groups according to whether high fluorescence was seen in the HCC (high cancerous [HC] group) or in the surrounding liver tissue (high surrounding [HS] group). The HC and HS groups were sub-classified into whole and partial types and whole and ring types, respectively.

Results

The HC group had significantly higher prevalence of esophageal or gastric varices, and worse liver function than patients in the HS group. The HC group also had a higher percentage of limited resection cases than did the HS group. Cirrhotic liver histology was significantly more common in the HC group than in the HS group. Multivariate analysis revealed that the HC group was a predictive factor for cirrhosis in HCC patients. Among the HC patients, a higher percentage of well-differentiated HCC cases were seen in the partial-type subgroup than in the whole-type subgroup (23/48 (48 %) vs. 7/68 (10 %)). In the HS group, the ring-type subgroup had a higher percentage of poorly differentiated HCC cases than did the whole-type subgroup (6/37 (16 %) vs. 0/37 (0 %)).

Conclusion

Tumor differentiation and fibrosis in the non-cancerous liver parenchyma could affect ICG fluorescence imaging in HCC. ICG fluorescence imaging may be a good indication for fibrosis stage. In future, we will try to evaluate fluorescence imaging with ICG for intraoperative cancer navigation in HCC, using a portable near-infrared fluorescence imaging system.

Bile proteome in health and disease

The study of bile proteins could improve the understanding of physiological processes involved in the regulation of the hepato-biliary system. Researchers have tried for years to investigate the bile proteome but, until recently, only a few tens of proteins were known. The advent of proteomics, availing of large-scale analytical devices paired with potent bioinformatic resources, lately allowed the identification of thousands of proteins in bile. Nevertheless, the knowledge of their role in the hepato-biliary system still represents almost a "blank page in the book of physiology." In this review, we first guide the reader through the historical phases of the analysis of bile protein content, emphasizing the recent progresses achieved through the use of proteomic techniques. Thereafter, we deeply explore the involvement of bile proteins in health and disease, with a particular focus on the discovery of biomarkers for biliary tract malignancies.

Rituximab as therapy for the recurrence of bile salt export pump deficiency after liver transplantation

Progressive familial intrahepatic cholestasis type 2 (PFIC2) results from recessive mutations in the adenosine triphosphate-binding cassette B11 gene, which encodes for bile salt export pump (BSEP). Liver transplantation (LT) is offered to PFIC2 patients with end-stage liver disease. Reports have described recurrent cholestasis in PFIC2 patients after transplantation, and this has been associated with immunoglobulin G antibodies to BSEP. High-titer anti-BSEP antibodies appear to correlate with episodes of cholestatic graft dysfunction. There is no established paradigm for treating antibody-mediated posttransplant BSEP disease. It appears to be refractory to changes in immunosuppressant medications that would typically be effective in treating allograft rejection. Taking what is known about its pathophysiology, we designed a treatment consisting of rituximab, a chimeric monoclonal anti-CD20 antibody, in combination with intravenous immunoglobulin and plasmapheresis. Using this approach, we report the successful management of 2 patients with antibody-mediated recurrence of PFIC2 after LT.

Comprehensive proteomic analysis of human bile

Bile serves diverse functions from metabolism to transport. In addition to acids and salts, bile is composed of proteins secreted or shed by the hepatobiliary system. Although there have been previous efforts to catalog biliary proteins, an in-depth analysis of the bile proteome has not yet been reported. We carried out fractionation of non-cancerous bile samples using a multipronged approach (SDS-PAGE, SCX and OFFGEL) followed by MS analysis on an LTQ-Orbitrap Velos mass spectrometer using high resolution at both MS and MS/MS levels. We identified 2552 proteins - the largest number of proteins reported in human bile till date. To our knowledge, there are no previous studies employing high-resolution MS reporting a more detailed catalog of any body fluid proteome in a single study. We propose that extensive fractionation coupled to high-resolution MS can be used as a standard methodology for in-depth characterization of any body fluid. This catalog should serve as a baseline for the future studies aimed at discovering biomarkers from bile in gallbladder, hepatic, and biliary cancers.

Intraoperative indocyanine green fluorescent imaging for prevention of bile leakage after hepatic resection

BACKGROUND

Bile leakage is a common complication of hepatectomy, and is associated with an increase in sepsis and liver failure. There are no standard preventive methods against bile leakage after hepatic surgery. The aim of the present randomized clinical trial was to evaluate the application of indocyanine green (ICG) fluorescent cholangiography for preventing postoperative bile leakage.

METHODS

102 patients who underwent hepatic resection without biliary reconstruction were divided into 2 groups. The control group (n = 50) underwent a leak test with ICG dye alone, and the experimental group underwent a leak test with ICG dye, followed by ICG fluorescent cholangiography using the Photodynamic Eye (PDE group, n = 52).

RESULTS

Among 42 patients with fluorescence in the PDE group, 25 patients had insufficient closure of bile ducts on the cut surface of the liver, which were closed by suture or ligation. There were 5 patients who developed postoperative bile leakage in the control group versus no bile leakage in the PDE group (10% vs 0%, P = .019).

CONCLUSION

ICG fluorescent cholangiography could detect insufficiently closed bile ducts that could not be identified by a standard bile leak test. ICG fluorescent cholangiography may have useful potential for prevention of bile leakage after hepatic resection.

Proteomic analysis of human bile and potential applications for cancer diagnosis

Bile is a body fluid produced by the liver and drained by biliary ducts into the duodenum. It has two major functions: first, it contains bile acids, which are critical for the digestion of fats, and second, it is an excretory pathway for many endogenous and exogenous compounds. Proteomic analysis of bile is particularly difficult since this fluid contains high concentrations of various substances that strongly interfere with protein separation and identification techniques. Furthermore, owing to its deep location in the body, bile must be collected by surgical or endoscopic procedures. However, as was speculated for other body fluids, bile appears to be a promising sample for the discovery of disease biomarkers leaking from proximal tissues: the liver, pancreas or biliary tree. The interest in clinical proteomics was demonstrated by two studies that identified in bile potential biomarkers for two deadly and difficult to diagnose neoplasms, pancreatic cancer and cholangiocarcinoma.

Contribution of solid-phase hexapeptide ligand libraries to the repertoire of human bile proteins

Proteins in bile may have important physiological functions and serve as disease biomarkers. Here, the protein composition of human gallbladder bile was analyzed using a recently described chromatography-like technology capable to enhance the signal of low-abundance species. First, proteins present in bile fluid were treated with immobilized peptide ligand libraries to concentrate dilute and very dilute species while concomitantly diluting the high-abundance proteins. The analysis of resulting protein mixture was then performed using LC-MS/MS after having classically separated proteins by a mini preparative gel electrophoresis. Overall 222 gene products were found; 143 of them were not reported before in proteomics studies. Ligand libraries by themselves contributed to find 81 new gene products distributed throughout different categories. The described chromatographic approach provides a significant contribution to the bile protein repertoire and opens new perspectives for the discovery of markers for specific biliary tract diseases.

Large-scale identification of human biliary proteins from a cholesterol stone patient using a proteomic approach

Gallbladder bile, one of the most important body fluids, is composed of water, inorganic ions, conjugated bile salts, phospholipids, cholesterol, bilirubin, mucin and proteins. The separation and identification of bile proteins remain difficult due to the complexity of this matrix. In the present study, human gallbladder bile was obtained from a cholesterol stone patient, and the proteins were isolated and purified by dialysis, precipitation and delipidation procedures. The resulting proteins were divided into several aliquots. One aliquot was subjected to two-dimensional gel electrophoresis (2DE). The protein spots were then in-gel digested and analyzed by liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). Another aliquot was directly digested and analyzed by a combination of strong cation-exchange (SCX) and reversed-phase (RP) chromatography prior to tandem mass spectrometry (2D-LC/MS/MS). Eventually, 48 and 218 unique proteins were identified from 2DE/MS and 2D-LC/MS/MS, respectively, resulting in a total of 222 unique identified proteins. Of the 218 proteins identified by 2D-LC/MS/MS, 92 were identified based on more than one unique tryptic peptide, and, of the total 222 proteins, 98 were identified based on more than one unique tryptic peptide.

Bile mediates intestinal pathology in endotoxemia in rats

Intestinal pathology frequently accompanies experimental endotoxic shock and is mediated by proinflammatory cytokines. Our hypotheses are that hepatobiliary factors operating from the luminal side of the gut make a major contribution to this damage and that tumor necrosis factor alpha (TNF-alpha) is involved in the pathology. We treated rats with lipopolysaccharide (LPS) intravenously and found that external drainage of bile totally protected the gastrointestinal tract, macroscopically and microscopically, 4 h after LPS administration and dramatically improved survival of the animals for 48 h after LPS administration. The concentration of TNF-alpha in bile increased markedly after LPS administration and was over 30 times higher in bile than in serum. Tissue damage and the biliary TNF-alpha response were abrogated when animals were pretreated with gadolinium chloride to eliminate Kupffer cells. TNF-alpha infusion into the duodenal lumen caused intestinal damage similar to that elicited by intravenous LPS. In rats treated with LPS, survival was significantly increased during the first 36 h in animals given an infusion of anti-TNF-alpha antibody into the duodenum. These results demonstrate that in endotoxemia, intestinal damage is mediated by factors derived from the bile. The findings indicate that luminally acting TNF-alpha contributes to the intestinal damage.

The role of the Brambell receptor (FcRB) in liver: protection of endocytosed immunoglobulin G (IgG) from catabolism in hepatocytes rather than transport of IgG to bile

The Brambell receptor (FcRB) mediates functions of both immunoglobulin G (IgG) transport, transmitting immunity from mother to young, and IgG protection, making IgG the longest surviving of all plasma proteins. Reflecting its role as transport receptor (termed FcRn, for neonatal rat intestine, the tissue from which it was first cloned), FcRB is expressed antenatally in the rabbit, mouse and rat fetal yolk sac and in human placental syncytiotrophoblasts, and neonatally in the intestinal epithelium of mice and rats. Reflecting its role as protection receptor (FcRp), FcRB is expressed in the vascular endothelium throughout life, where it protects IgG from the on-going catabolic activities of this tissue. FcRB detected in hepatocytes was hypothesized to mediate transport of IgG from serum to bile, thus potentially extending the transport expression (FcRn) of this receptor beyond the perinatal period. Our results show serum-to-bile transport of IgG to be unaffected in mice functionally deleted for FcRB. Accordingly, the hypothesis is rejected that FcRB functions as transport receptor (FcRn) in liver. The default conclusion is that FcRB in hepatocytes functions as FcRp, serving to protect IgG from catabolism in hepatocytes that accompanies the endocytic activity of these cells. We conclude that there remains to date no evidence of an FcRn-like transport function of the Brambell receptor beyond the perinatal period, after which the FcRp function of the receptor predominates, paralleling the endocytic activities of the associated tissues.

Hepatic bile versus gallbladder bile: a comparison of protein and lipid concentration and composition in cholesterol gallstone patients

Many studies have demonstrated that gallbladder bile (but not hepatic bile) of animals or patients with cholesterol gallstones contains higher protein concentrations than does gallbladder bile of control patients without stones or with pigment stones. The underlying defect has not been elucidated. To establish whether there is net production or net absorption/degradation of protein by gallbladder epithelium for different classes of protein, paired samples of hepatic and gallbladder bile were obtained from fourteen patients with cholesterol gallstones during elective cholecystectomy. In these paired samples, lipid and protein composition were determined. To obtain the concentration ratio (CR) of protein and lipid, its concentration in the gallbladder was divided by the concentration determined in the paired hepatic bile sample. The CR of bile salts was used as a parameter for water absorption in the gallbladder. Of the biliary proteins that were determined only mucin, albumin, immunoglobulin (Ig) G, and aminopeptidase N appeared to increase in the gallbladder from another cause than water absorption. A strong correlation was found between mucin, albumin, and IgG. Haptoglobin, alpha1-acid glycoprotein, IgM, and IgA appeared to be absorbed by gallbladder epithelium in the majority of patients. In cholesterol gallstone patients, total protein concentration in gallbladder bile of cholesterol gallstone patients is increased when compared with hepatic bile. The increase in protein concentration cannot be explained for all bile samples solely by water absorption. In this study we show that the defect is largely caused by a selective increase in albumin, mucin, and IgG. All other proteins which were investigated are taken up by the gallbladder.

Plasma clearance of rat bikunin: evidence for receptor-mediated uptake

Bikunin is a chondroitin sulphate-containing protease inhibitor with a molecular mass of 25 kDa. It is secreted into the blood by hepatocytes, and recent observations indicate that it may have an extravascular function. Here we have studied the plasma clearance of bikunin in rats and mice. On intravenous injection, radiolabelled bikunin was found to have a half-life of 10 min; in rats with ligated renal arteries, the clearance time was twice as long, implying that the kidneys account for half the uptake. As judged by gel filtration, the size of bikunin is similar to that of albumin. Autoradiographic analysis of kidneys removed 2 min after the injection of radiolabelled bikunin indicated that, despite its size, bikunin is cleared by glomerular filtration. On ligation of the renal arteries, the plasma concentration of bikunin increased linearly to at least four times normal. This finding shows that the non-renal uptake system is saturated and therefore presumably receptor-mediated. Most of the non-renal uptake of injected bikunin was found to occur in non-visceral tissues such as the skin. Analysis of skin samples by autoradiography after injection of radiolabelled bikunin suggested that bikunin had been transferred from the plasma to the interstitial space.

A major histocompatibility complex class I-related Fc receptor for IgG on rat hepatocytes

Intestinal epithelial cells of the neonatal rat and mouse have been shown to express a major histocompatibility complex (MHC) class I-like Fc receptor, or FcRn, which transports IgG in an apical to basolateral direction. Previous studies have suggested the possible expression of this receptor beyond the neonatal period within the liver. Since bile contains high levels of IgG, we sought to determine whether the FcRn was functionally expressed by adult rat hepatocytes. Using primers specific for FcRn, which did not cross hybridize with MHC class I transcripts, FcRn DNA was amplified by reverse transcriptase polymerase chain reaction from RNA of adult rat hepatocytes. This RNA contained functional FcRn transcripts as it encoded a beta 2-microglobulin-associated cell surface protein as determined by immunoprecipitation of biotinylated cell surface proteins with a polyclonal anti-FcRn specific antiserum. Western blotting of hepatocyte canalicular (apical) and sinusoidal (basolateral) plasma membranes with an FcRn-specific monoclonal antibody further confirmed the protein expression and suggested that FcRn was enriched on the canalicular surface membranes. FcRn, on the surface of hepatocytes, was biologically functional as it bound Fc fragments of IgG at pH 6.0 but not 8.0, which is the same pH dependence observed for FcRn in rat neonatal enterocytes. Thus, FcRn is functionally expressed outside of the neonatal period on the canalicular cell surface of adult hepatocytes. This suggests that hepatocyte FcRn may bind luminal IgG, providing a potential functional communication between parenchymal immune cells and bile.

Cholinergic modulation of immunoglobulin secretion from avian plasma cells: the role of calcium

The existence of a functional connection between the nervous and immune systems has long been argued. To determine if such a link exists in the secretory immune system, we have examined the avian lacrimal gland (Harderian gland) which contains large numbers of plasma cells. We have shown that these plasma cells bind an antibody to muscarinic acetylcholine receptor and that carbachol, an acetylcholine agonist, increases the secretion rate of IgG by these cells above a constitutive baseline level. This neurotransmitter-dependent increase of immunoglobulin secretion requires an influx of Ca2+, whereas the constitutive baseline secretion is apparently less dependent on such a flux. Furthermore, the Ca2+ flux appears to be mediated by voltage-dependent calcium channels. These data support the hypothesis that plasma cells can respond to neurotransmitters and, in the case of acetylcholine, increase immunoglobulin secretion.

Identification of a 130-kilodalton human biliary concanavalin A binding protein as aminopeptidase N

BACKGROUND/AIMS

Human gallbladder bile contains a group of nonmucin glycoproteins that binds to the lectin concanavalin A (con A) and has been reported to promote cholesterol monohydrate crystal nucleation, an event preceding the formation of gallstones. Several of these proteins, including a 130-kilodalton protein, have been isolated and shown to promote nucleation in vitro. The aim of this study was to identify this and other major biliary con A binding glycoproteins.

METHODS

Gallbladder bile was chromatographed on con A agarose, and the eluted proteins were electrophoresed, blotted, and subjected to amino-terminal sequence analysis.

RESULTS

The major con A binding proteins were identified as aminopeptidase N (a 130-kilodalton protein), alpha 2 macroglobulin, hemopexin, immunoglobulin heavy chains, and the beta chain of haptoglobin. After further purification, aminopeptidase N was found to be enzymatically active and to promote cholesterol crystallization at its approximate physiological concentration in bile.

CONCLUSIONS

It is likely that aminopeptidase N is the previously characterized 130-kilodalton biliary crystallization promoting protein. Aminopeptidase N is probably released from the biliary canalicular membrane by the detergent activity of bile salts and may be one factor that promotes cholesterol crystallization in the gallbladder.

Bikunin in rat plasma, lymph and bile

Bikunin is a protease inhibitor consisting of a 16 kDa polypeptide and an 8 kDa chondroitin sulphate chain which has an apparent molecular mass of 60-70 kDa upon gel filtration. It is synthesized by hepatocytes and occurs in plasma, both in free form, and in complex with other polypeptides--mainly as the 180 kDa protein inter-alpha-inhibitor. Bikunin binds to proteases less avidly than other plasma inhibitors, making its role in the blood unclear. However, some observations indicate that bikunin has important functions outside the blood system. To assess its capacity to reach extravascular spaces, we have determined the total concentration of bikunin in plasma (0.17 mg/ml), lymph (31 micrograms/ml) and bile (0.2 microgram/ml). Quantitation after removal of complexed bikunin (inter-alpha-inhibitor) by acid precipitation showed that the concentration of free bikunin in those fluids was 3, 1.4 and 0.05 micrograms/ml, respectively. These values yield a lymph/plasma ratio of free bikunin of 0.5, which is higher than expected for a protein of the hydrodynamic size and charge of bikunin. The bile/plasma ratio (0.02), however, is similar to that of other proteins of comparable size. The corresponding values for inter-alpha-inhibitor, 0.16 and 0.001, respectively, indicate that its capacity to pass through the vascular endothelium is relatively high whereas transfer to bile is restricted. Furthermore, we have found that in a perfusate of an isolated rat liver, the ratio of free to complexed bikunin was 30-40 times higher than in plasma, consistent with previous observations showing that free bikunin is cleared from the blood stream much more rapidly than inter-alpha-inhibitor.

Differential colchicine effects on the transport of membrane and secretory proteins in rat hepatocytes in vivo: bipolar secretion of albumin

We carried out a comparative investigation on the effects of colchicine (25 mumoles/100 gm body wt) on the intracellular transport, processing and discharge by secretion or proteolytic processing of a membrane protein (i.e., the polymeric IgA receptor) and a secretory protein (i.e., albumin) in rat hepatocytes. The results obtained indicated the following: (a) the transport and processing of polymeric IgA receptor is strongly inhibited and delayed, but the appearance of secretory component in the bile is not arrested; (b) polymeric IgA receptor reaches the sinusoidal plasmalemma in colchicine-treated specimens, as it does in controls; (c) albumin discharge into the plasma is strongly inhibited and markedly delayed in colchicine-treated as compared with control animals; (d) the reverse applies for albumin secretion in the bile, which is increased by a large factor; (e) newly synthesized albumin secreted directly from hepatocytes in control and in colchicine-treated animals is the major source of bile albumin; and (f) colchicine affects in different ways the polymeric IgA receptor and albumin arrival at the sinusoidal front and especially at the biliary front of the hepatocyte.

Mechanisms of metal transport across liver cell plasma membranes

The liver's pivotal role in the homeostasis of essential trace metals and detoxification of exogenous metals is attributed to its ability to efficiently extract metals from plasma, metabolize, store, and redistribute them in various forms either into bile or back into the bloodstream. Bidirectional transport across the sinusoidal plasma membrane allows the liver to control plasma concentrations and therefore availability to other tissues. In contrast, transport across the canalicular membrane is largely, but not exclusively, unidirectional and is a major excretory pathway. Although each metal has relatively distinct hepatic transport characteristics, some generalizations can be made. First, movement of metals from plasma to bile follows primarily a transcellular route. The roles of the paracellular pathway and of ductular secretion appear minimal. Second, intracellular binding proteins and in particular metallothionein play only indirect roles in transmembrane flux. The amounts of metallothionein normally secreted into plasma and bile are quite small and cannot account for total metal efflux. Third, metals traverse liver cell plasma membranes largely by facilitated diffusion, and by fluid-phase, adsorptive, and receptor-mediated endocytosis/exocytosis. There is currently no evidence for primary active transport. Because of the high rate of hepatocellular membrane turnover, metal transport via endocytic vesicles probably makes a larger contribution than previously recognized. Finally, there is significant overlap in substrate specificity on the putative membrane carriers for the essential trace metals. For example, zinc and copper share many transport characteristics and apparently compete for at least one common transport pathway. Similarly, canalicular transport of five of the metals discussed in this overview (Cu, Zn, Cd, Hg, and Pb) is linked to biliary GSH excretion. These metals may be transported as GSH complexes by the canalicular glutathione transport system(s). Unfortunately, none of the putative membrane carrier proteins have been studied at the subcellular or molecular level. Our knowledge of their biochemical properties is rudimentary and rests almost entirely on indirect evidence obtained in vivo or in intact cell systems. The challenge for the future is to isolate and characterize these putative metal carriers, and to determine how they are functionally regulated.

The occurrence and sources of natural antibody in human bile and serum against the O antigens of two Escherichia coli serotypes

Paired serum and bile samples from normal subjects as well as patients with biliary disease were tested for natural antibody to two individual Escherichia coli O antigens by ELISA. Serum antibody was most commonly of IgM and IgG class. Antibody was less frequently detected in bile and was more commonly IgM than IgA, with IgG activity detected infrequently. Little relation was apparent between antibody in paired samples; activity could be present in both serum and bile or in either fluid alone. Titres in paired samples also did not correspond when 'normalized' with respect to the concentrations of relevant isotypes; bile was frequently enriched for natural antibody as a proportion of total immunoglobulin compared with serum. Secretory component-bound antibody was detectable in some biles that contained IgA and/or IgM activity and in the serum of 33% of subjects with biliary disorders but not in normal sera. A series of paired samples taken from three individuals was also examined for antibody against each subject's own intestinal commensal E. coli. Serum IgM and IgG activity was present in all samples, but antibody in bile was less frequent and was of IgM or IgA class. These results suggest that natural antibody in human bile occurs independently of antibody in serum and that it is substantially derived from local sources.

Isolation of a potent cholesterol nucleation-promoting activity from human gallbladder bile: role in the pathogenesis of gallstone disease

Gallbladder bile contains nucleation-promoting activity that binds to concanavalin A. The activity was found in gallbladder bile from cholesterol gallstone patients but also in gallbladder bile from patients without stones and patients with pigment stones. Bile from patients with multiple cholesterol gallstones contained high concanavalin A-binding nucleation-promoting activity. The activity was much lower in bile samples from pigment stone patients, patients without stones and patients with a solitary cholesterol stone. Serum contained very little activity and no concanavalin A-binding nucleation-promoting activity could be demonstrated in gallbladder mucosa. This suggests that concanavalin A-binding nucleation promoter is produced in the liver or bile duct epithelium. The activity was fully resistant to digestion with pronase but was heat labile and could be destroyed by prolonged incubation with a mixed glycosidase preparation indicating that sugar residues are important for this activity. On a Superose 12 gel permeation column, promoting activity eluted in two major peaks at apparent molecular weights of 150 +/- 30 kD (n = 5) and less than 5 kD respectively. The mobility on the column was not influenced by pronase digestion. The factor with the higher molecular weight could be isolated further by polyacrylamide gel electrophoresis under nondenaturing conditions. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the apparent molecular weight of the glycoprotein was 130 kD. In conclusion, gallbladder bile contains nucleation-promoting activity that binds to concanavalin A. The activity is increased in bile from patients with multiple cholesterol gallstones and could therefore play an important role in the pathogenesis of gallstone disease.

The polymeric immunoglobulin A receptor is present on hepatocytes in human liver

A monoclonal antibody raised against human colostrum secretory component produced even staining of hepatocyte plasma membranes, as well as bile duct lining cells, in all sections examined from eight normal and three abnormal human livers. Human bile samples incubated with free secretory component degraded it to varying extents, probably proteolytically; true levels of free secretory component will therefore often be higher than those reported. It seems likely that human liver resembles that of other mammals in transferring polymeric IgA through hepatocytes to the bile by means of the polymeric IgA receptor.

An appraisal of the role of biliary phospholipases in the pathogenesis of gallstone disease

Human bile contains proteins that influence nucleation of cholesterol. Recently, it has been suggested that activity of phospholipases in bile may play a role in this process. To study the influence of phospholipase on nucleation we have determined the effect of phospholipases A2, C and D on the nucleation time of model bile. Phospholipase C decreased the nucleation time, whereas phospholipase A2 inhibited nucleation. The phospholipases were effective only at relatively high concentrations. Phospholipase D was strongly inhibited in model bile and probably only influenced the nucleation time by an aspecific protein effect. The cleavage products of the different phospholipases were determined in native bile samples of 14 cholesterol gallstone patients, 6 patients without stones and 4 patients with pigment stones. In all samples, choline, phosphorylcholine and free fatty acids (FFA) could be detected. However, there was no significant difference between the three groups of patients. The rate of production of choline, phosphorylcholine and FFA was measured in bile incubated at 37 degrees C. Again, there was no significant difference between the three groups of patients. We conclude that phospholipase activity in bile does not play an important role in the pathogenesis of gallstone disease.

Appearance of IgG and IgA antibodies in human bile after tetanus toxoid immunization

Humans immunized intramuscularly with one dose of tetanus toxoid exhibited IgG, and in some cases IgA antibody, in their bile as well as serum. Both isotypes appeared in bile transiently with titres declining after about day 10 for both classes. These kinetics resembled those of the serum IgA response but were markedly different to those for IgG antibody in serum. Measured IgG titres in bile were between 0.07 and 4.2% of those in paired sera, and IgA titres were between 6.8 and 124% of sera. Peak responses in bile, while generally of smaller size, exceeded those of paired sera when expressed as antibody/mg of IgG or IgA present. This calculation showed that during the peak response bile was up to nineteen-fold more abundant in IgG antibody than was serum taken at the same time, and up to forty-five-fold more for IgA. Enrichment of antibody in bile is not consistent with the Ig of bile being solely conferred by plasma, and may mean the involvement of local synthesis too. This study indicates that tetanus toxoid immunization of humans results in biliary antibody and raises the possibility of intra-hepatic antibody production for export to the intestinal tract in man.

Total protein output during rapid reduction of bile salt secretion rates in man

An investigation was undertaken to study the effect of bile salt secretion on total biliary protein secretion in man. Bile was collected in eight patients from a tube in the bile duct. Collection was started after a meal and continued for six hours, in order to obtain bile salt secretion rates over the entire physiological range. Total protein secretion rates did not vary with change in bile salt secretion or bile flow. The protein pattern assessed by SDS-PAGE did not vary with bile salt secretion. The results indicate that bile salt secretion has little influence on biliary protein secretion under these conditions in man. Changes in bile salt secretion were associated with linear change in bile flow, but there was no relationship between bile flow and protein secretion rates. This argues against convective sieving of plasma proteins into bile.

The calcium ionophore A23187 increases the tight-junctional permeability in rat liver

The effect of an increase in intracellular Ca2+ concentration on tight-junctional permeability in rat liver was studied by using the calcium ionophore A23187. Infusion of 100 microliters of dimethyl sulphoxide containing various amounts of A23187 over 30 min into isolated perfused livers was followed by a pulse of horseradish peroxidase (HRP) under single-pass conditions. The first biliary HRP peak, a measure of junctional permeability, was increased 4-fold with 100 micrograms of A23187. There were, however, no significant effects on bile flow or on aspartate aminotransferase leakage as compared with the control at this dosage, and thus the increase in junctional permeability was occurring without evidence of appreciable cholestatic or hepatocellular damage. Higher dosages of A23187, however, caused not only an increase in HRP peak height but also changes in bile flow and increases in aminotransferase leakage, indicating more extensive effects at these higher dosages. A second peak of HRP secretion, occurring 20-25 min after the HRP pulse, was also elevated approx. 3.5-fold; this may indicate that pinocytosis and transcellular movement of HRP are also increased under these conditions.

Sodium valproate inhibits the movement of secretory vesicles in rat hepatocytes

Sodium valproate (VPA), a simple 8-carbon branched chain fatty acid, is an effective anti-epileptic drug with an occasional serious side effect of liver damage, including the accumulation of triacylglycerols within hepatocytes, and reductions in serum protein concentrations. By investigating the effects of VPA, using biliary fistula rats and isolated perfused rat livers, we have shown that secretion of triacylglycerols and rat serum albumin at the sinusoidal pole of hepatocytes, and of phospholipids, lysosomal contents, and IgA at their biliary pole, are all reduced, to somewhat different extents, by acute VPA administration. In addition, the vesicular transcytosis of exogenous protein (i.e. bovine serum albumin) from the perfusion fluid into bile is also decreased by VPA administration. To determine whether the phenomena were specific to VPA, a control series of experiments was also performed using octanoate (a straight-chain analogue of VPA). With the biliary fistula rats, octanoate did not show inhibition of secretion as compared with the saline controls; with the isolated perfused livers, however, octanoate did show such an inhibition. These phenomena suggest that VPA inhibition of secretion may be a factor in its hepatotoxicity, as the effects are apparent in both the whole animal and the isolated perfused liver, whereas octanoate is not hepatotoxic in the whole animal. Since when octanoate is administered to the isolated liver it causes an inhibition in secretion similar to that caused by VPA, it may be that the large dose of this compound reaching the liver affects a key step in liver metabolism or vesicle transport under these circumstances. Since octanoate does not normally reach the liver in such amounts, as it will normally be metabolized by other tissues, it is not hepatotoxic in the whole animal as is VPA.

Bile immunoglobulin of the duck (Anas platyrhynchos). II. Antibody response in influenza A virus infections

The capacity of the IgM-like bile immunoglobulin (IgX) of the duck (Anas platyrhynchos) to express antibody activity to H3N2 influenza A viruses, and the dependence of this activity on the co-existence of serum IgM antibodies were investigated. Ducklings infected orally and intranasally at 15-29 days of age with viruses isolated from different host species were examined for haemagglutination-inhibiting (HI) antibodies in biles and sera 16-29 days after infection (p.i.). All biles had antibodies associated with IgX; all sera had antibodies associated only with the 7.8S IgG. Following oral infection of birds 42-days-old with influenza A/duck/HK/7/75 virus, serum HI antibodies were an initial IgM response occurring from 5-12 days p.i., followed by the appearance of 7.8S IgG antibodies. Virus-neutralizing (VN) antibodies in serum were also biphasic; isotype classification was not attempted. Bile IgX developed HI and VN activity. HI antibodies reached peak titres 12 days p.i. and fell to low levels by 24 days p.i. VN antibodies also reached peak titres 12 days p.i., but thereafter persisted at quite high levels throughout the experiment. Development of high titres of antibody in bile coincided with the termination of virus excretion in faeces. These experiments confirm that bile IgX of the duck can function as antibody in response to influenza A viruses, and that its activity appears to be independent of serum IgM. Its possible relevance in determining survival of virus in the intestine is discussed.

Studies on the origin and composition of IgA in rat tears

Experiments were carried out to quantify the proportion of IgA in rat tears that arrives from the circulating IgA pool in the blood, as opposed to that supplied by local synthesis in the lacrymal gland. Rats were injected subcutaneously with an IgA-secreting rat hybridoma cell line (91c), which was allowed to grow in vivo, in order to raise the levels of plasma IgA of known antibody specificity. In rats where serum 91c IgA concentrations had built up to 0.3 mg/ml or more, unstimulated tears contained 91c antibody activity of a molecular weight range that corresponded to that of the polymeric sizes of IgA, and was associated with secretory component. The concentrations of IgA in tear samples were about 0.3% of those in matched serum samples. Thus, a plasma contribution is made to the IgA in tears, but greater than 99% of the tear IgA is synthesized locally in the lachrymal gland.

1-Naphthylisothiocyanate-induced permeability of hepatic tight junctions to proteins

We have studied the early action of 1-naphthylisothiocyanate (ANIT) in relation to its effect on the permeability barrier formed by hepatic tight junctions. Materials having different Mr values [inulin (5000), horseradish peroxidase (HRP) (40,000), ovalbumin (also 40,000) and pig gamma-globulin (IgG) (160,000)] were individually pulsed, within 1 min, into perfused rat livers operating under single-pass conditions. In untreated rats, a small peak of HRP and ovalbumin and a comparatively larger peak of inulin were observed in the bile at 7 min. In rats treated with ANIT, with increasing duration of ANIT treatment the inulin peak increased proportionally, whereas the HRP and ovalbumin peaks remained unchanged until after 10 h of ANIT exposure; gamma-globulin was not detected in the 7 min bile sample until after 14 h of ANIT treatment. Bile flow in all rats remained approximately the same until after 14 h of ANIT pretreatment, when substantial bile-flow reduction was observed. Phenobarbitone pretreatment increased the effect of ANIT and massively elevated the first HRP peak; it also shortened the time (to 4 h) at which the increase in permeability to this protein was observed. In contrast, the first HRP peak was virtually abolished in rats that had received the mixed-function-oxidase inhibitor SKF 525A. These experiments suggest that (i) ANIT progressively increased the permeability of the junctional barrier before the reduction in bile flow, (ii) the ANIT-increased permeability change seems to be inversely dependent upon the Mr of the infused proteins, and (iii) metabolites of ANIT were involved in the development of the junctional permeability change.