Peptidergic innervation and endocrine cells in the human liver

Development of the nervous system in mouse liver

BACKGROUND

The role of the hepatic nervous system in liver development remains unclear. We previously created functional human micro-hepatic tissue in mice by co-culturing human hepatic endodermal cells with endothelial and mesenchymal cells. However, they lacked Glisson’s sheath [the portal tract (PT)]. The PT consists of branches of the hepatic artery (HA), portal vein, and intrahepatic bile duct (IHBD), collectively called the portal triad, together with autonomic nerves.

AIM

To evaluate the development of the mouse hepatic nervous network in the PT using immunohistochemistry.

METHODS

Liver samples from C57BL/6J mice were harvested at different developmental time periods, from embryonic day (E) 10.5 to postnatal day (P) 56. Thin sections of the surface cut through the hepatic hilus were examined using protein gene product 9.5 (PGP9.5) and cytokeratin 19 (CK19) antibodies, markers of nerve fibers (NFs), and biliary epithelial cells (BECs), respectively. The numbers of NFs and IHBDs were separately counted in a PT around the hepatic hilus (center) and the peripheral area (periphery) of the liver, comparing the average values between the center and the periphery at each developmental stage. NF-IHBD and NF-HA contacts in a PT were counted, and their relationship was quantified. SRY-related high mobility group-box gene 9 (SOX9), another BEC marker; hepatocyte nuclear factor 4α (HNF4α), a marker of hepatocytes; and Jagged-1, a Notch ligand, were also immunostained to observe the PT development.

RESULTS

HNF4α was expressed in the nucleus, and Jagged-1 was diffusely positive in the primitive liver at E10.5; however, the PGP9.5 and CK19 were negative in the fetal liver. SOX9-positive cells were scattered in the periportal area in the liver at E12.5. The Jagged-1 was mainly expressed in the periportal tissue, and the number of SOX9-positive cells increased at E16.5. SOX9-positive cells constructed the ductal plate and primitive IHBDs mainly at the center, and SOX-9-positive IHBDs partly acquired CK19 positivity at the same period. PGP9.5-positive bodies were first found at E16.5 and HAs were first found at P0 in the periportal tissue of the center. Therefore, primitive PT structures were first constructed at P0 in the center. Along with remodeling of the periportal tissue, the number of CK19-positive IHBDs and PGP9.5-positive NFs gradually increased, and PTs were also formed in the periphery until P5. The numbers of NFs and IHBDs were significantly higher in the center than in the periphery from E16.5 to P5. The numbers of NFs and IHBDs reached the adult level at P28, with decreased differences between the center and periphery. NFs associated more frequently with HAs than IHBDs in PTs at the early phase after birth, after which the number of NF-IHBD contacts gradually increased.

CONCLUSION

Mouse hepatic NFs first emerge at the center just before birth and extend toward the periphery. The interaction between NFs and IHBDs or HAs plays important roles in the morphogenesis of PT structure.

Hepatic Nervous System in Development, Regeneration, and Disease

The liver is innervated by autonomic and sensory fibers of the sympathetic and parasympathetic nervous systems that regulate liver function, regeneration, and disease. Although the importance of the hepatic nervous system in maintaining and restoring liver homeostasis is increasingly appreciated, much remains unknown about the specific mechanisms by which hepatic nerves both influence and are influenced by liver diseases. While recent work has begun to illuminate the developmental mechanisms underlying recruitment of nerves to the liver, evolutionary differences contributing to species-specific patterns of hepatic innervation remain elusive. In this review, we summarize current knowledge on the development of the hepatic nervous system and its role in liver regeneration and disease. We also highlight areas in which further investigation would greatly enhance our understanding of the evolution and function of liver innervation.

Pathobiology of biliary epithelia

Cholangiocytes are epithelial cells that line the intra- and extrahepatic biliary tree. They serve predominantly to mediate the content of luminal biliary fluid, which is controlled via numerous signaling pathways influenced by endogenous (e.g., bile acids, nucleotides, hormones, neurotransmitters) and exogenous (e.g., microbes/microbial products, drugs etc.) molecules. When injured, cholangiocytes undergo apoptosis/lysis, repair and proliferation. They also become senescent, a form of cell cycle arrest, which may prevent propagation of injury and/or malignant transformation. Senescent cholangiocytes can undergo further transformation to a senescence-associated secretory phenotype (SASP), where they begin secreting pro-inflammatory and pro-fibrotic signals that may contribute to disease initiation and progression. These and other concepts related to cholangiocyte pathobiology will be reviewed herein. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Dietary guidance and ileal enteroendocrine cells in patients with irritable bowel syndrome

The enteroendocrine cells of the ileum are stimulated by the luminal contents to release specific hormones that regulate its functions. The density of ileal enteroendocrine cells is abnormal in patients with irritable bowel syndrome (IBS), and the majority of patients with IBS associate their symptoms to the consumption of certain foodstuffs. The present study investigated the effect of dietary guidance on the enteroendocrine cells of the ileum in 11 patients with IBS. A total of 10 control subjects were also included. Each patient received three sessions of dietary guidance. Colonoscopies were performed on both controls and patients with IBS (at baseline and 3-9 months after the patients had received dietary guidance). Biopsy samples from the ileum were immunostained for all enteroendocrine cells and quantified by computerized image analysis. The densities of serotonin-immunoreactive cells in controls and in patients with IBS prior to and following dietary guidance were 35.5±5.7, 38.7±7.1 and 22.3±2.6 cells/mm², respectively (mean ± standard error of the mean; P=0.046); the corresponding values for PYY-immunoreactive cells were 16.7±2.8, 20.2±5.1 and 21.3±2.7 cells/mm² (P=0.86). These results suggest that changes in enteroendocrine cell densities in the ileum along with changes in enteroendocrine cells throughout the gastrointestinal tract may contribute to the improvement in IBS symptoms following dietary guidance.

Changes in small intestinal chromogranin A-immunoreactive cell densities in patients with irritable bowel syndrome after receiving dietary guidance

Chromogranin A (CgA) is a common marker for enteroendocrine cells in the gut, and CgA-immunoreactive cell densities are abnormal in patients with irritable bowel syndrome (IBS). The majority of patients with IBS report that their symptoms develop after consuming certain foodstuffs. In the present study, we investigated the effects of dietary guidance on the total enteroendocrine cell densities in the small intestine, as detected by CgA. A total of 14 patients with IBS underwent a gastroscopy with duodenal biopsies and 11 of them also underwent a colonoscopy, with biopsy samples obtained from the ileum. Fourteen control subjects were also included. Each patient received 3 sessions of dietary guidance. Gastroscopies and colonoscopies were performed on both the controls and patients with IBS (at baseline and at 3–9 months after receiving guidance). Biopsy samples obtained from the duodenum and ileum were immunostained for CgA using the avidin-biotin complex (ABC) method and were quantified using computerized image analysis. The density of CgA-immunoreactive cells in the duodenum (mean ± SEM values) in the control subjects was 235.9±31.9 cells/mm²; in the patients with IBS, the density was 36.9±9.8 and 103.7±16.9 cells/mm² before and after they received dietary guidance, respectively (P=0.007). The density of CgA-immunoreactive cells in the ileum in the control subjects was 47.4±8.3 cells/mm²; in the patients with IBS, the density was 48.4±8.1 and 17.9±4.4 cells/mm², before and after they received dietary guidance, respectively (P=0.0006). These data indicate that changes in CgA-immunoreactive cell densities in patients with IBS after receiving dietary guidance may reflect a change in the densities of the small intestinal enteroendocrine cells, which may contribute to an improvement in the IBS symptoms.

Role of glycogen phosphorylase in liver glycogen metabolism

Liver glycogen is synthesized after a meal in response to an increase in blood glucose concentration in the portal vein and endocrine and neuroendocrine signals, and is degraded to glucose between meals to maintain blood glucose homeostasis. Glycogen degradation and synthesis during the diurnal cycle are mediated by changes in the activities of phosphorylase and glycogen synthase. Phosphorylase is regulated by phosphorylation of serine-14. Only the phosphorylated form of liver phosphorylase (GPa) is catalytically active. Interconversion between GPa and GPb (unphosphorylated) is dependent on the activities of phosphorylase kinase and of phosphorylase phosphatase. The latter comprises protein phosphatase-1 in conjunction with a glycogen-targeting protein (G-subunit) of the PPP1R3 family. At least two of six G-subunits (GL and PTG) expressed in liver are involved in GPa dephosphorylation. GPa to GPb interconversion is dependent on the conformational state of phosphorylase which can be relaxed (R) or tense (T) depending on the concentrations of allosteric effectors such as glucose, glucose 6-phosphate and adenine nucleotides and on the acetylation state of lysine residues. The G-subunit, GL, encoded by PPP1R3B gene is expressed at high levels in liver and can function as a phosphorylase phosphatase and a synthase phosphatase and has an allosteric binding site for GPa at the C-terminus which inhibits synthase phosphatase activity. GPa to GPb conversion is a major upstream event in the regulation of glycogen synthesis by glucose, its downstream metabolites and extracellular signals such as insulin and neurotransmitters.

Densities of rectal peptide YY and somatostatin cells as biomarkers for the diagnosis of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common chronic disorder. IBS diagnosis is a diagnosis of exclusion since there are no blood tests, radiological or endoscopic examinations for this disorder. Although several attempts have been made to develop a symptoms-based diagnosis, such systems are not widely used in clinics. Several tests and examinations measuring pathological findings in IBS have been considered for the diagnosis of IBS, but none of them has proved useful as a biomarker. Abnormalities in the cell densities of rectal peptide YY (PYY) and somatostatin cells have been reported in IBS patients. The aim of the present study was to determine the utility of these abnormalities as biomarkers for the diagnosis of IBS. Patients with IBS established according to Rome III criteria (n = 101) were included in this study (71 females and 30 males with a mean age of 35 years; range 18-61 years), and 62 healthy subjects (38 females and 24 males with a mean age of 41 years; range 18-65 years) were recruited as controls. Both the patients and controls underwent colonoscopy during which rectal biopsy samples were taken. The tissue samples were immunostained for PYY and somatostatin, and the number of stained cells was quantified relative to both the area of epithelial cells and per microscopic field. The density of PYY cells was significantly lower in IBS patients than in the healthy controls (P < 0.0001); receiver operator characteristic (ROC) analysis revealed an area under the ROC curve (AUC) of 0.99. The somatostatin cell density in IBS patients was higher than in the controls (P < 0.0001); ROC analysis revealed an AUC of 0.86. The densities of the rectal PYY and somatostatin cells appear to be clinically effective biomarkers for IBS. Furthermore, measurement of these parameters is inexpensive, rapid and does not require considerable experience or sophisticated equipment.

Effect of 5-HT7 receptor blockade on liver regeneration after 60-70% partial hepatectomy

Background

Serotonin exhibits a vast repertoire of actions including cell proliferation and differentiation. The effect of serotonin, as an incomplete mitogen, on liver regeneration has recently been unveiled and is mediated through 5-HT₂ receptor. The aim of the present study was to investigate the effect of 5-HT₇ receptor blockade on liver regeneration after partial hepatectomy.

Methods

Male Wistar rats were subjected to 60-70% partial hepatectomy. 5-HT₇ receptor blockade was applied by intraperitoneal administration of SB-269970 hydrochloride two hours prior to and sixteen hours after partial hepatectomy and by intraperitoneal administration of SB-258719 sixteen hours after partial hepatectomy. Animals were sacrificed at different time points until 72 h after partial hepatectomy. Liver regeneration was evaluated by [³H]-thymidine incorporation into hepatic DNA, the mitotic index in hematoxylin-eosin (HE) sections and by immunochemical detection of Ki67 nuclear antigen. Reversion of 5-HT₇ blockade was performed by intraperitoneal administration of AS-19. Serum and liver tissue lipids were also quantified.

Results

Liver regeneration peaked at 24 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and at 32 h (mitotic index in HE sections) in the control group of rats. 5-HT₇ receptor blockade had no effect on liver regeneration when applied 2 h prior to partial hepatectomy. Liver regeneration was greatly attenuated when blockade of 5-HT₇ receptor was applied (by SB-258719 and SB-269970) at 16 h after partial hepatectomy and peaked at 32 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and 40 h (mitotic index in HE sections) after partial hepatectomy. AS-19 administration totally reversed the observed attenuation of liver regeneration.

Conclusions

In conclusion, 5-HT₇ receptor is a novel type of serotonin receptor implicated in hepatocyte proliferation.

Ontogenic development of nerve fibers in human fetal livers: an immunohistochemical study using neural cell adhesion molecule (NCAM) and neuron-specific enolase (NSE)

The aim of the study was to investigate nerve fibers (NF) in human fetal livers. An immunohistochemical study was performed. NF were classified into portal tract innervation (PoI) and parenchymal innervation (PaI). The hilum area showed many Pol NF at 7 GW, and NF increased with gestational week (GW). Direct innervations to biliary epithelium were recognized. In large portal tracts, a few NCAM-positive mesenchymal cells were seen at 8 GW and many mesenchymal cells were noted around 12 GW. Apparent NF emerged around 15 GW, and NF increased with GW. Many NF plexuses were seen in 30-40 GW. In small portal tracts, no NF were seen in 7-10 GW. A few NCAM-positive mesenchymal cells emerged in 11 GW, and they increased thereafter. Apparent NF were seen around 20 GW and NF increased with GW. At term (40 GW), PoI NF were still immature. Ductal plate (DP) was positive for NCAM, NSE, chromogranin and synaptophysin, and direct innervations to DP were seen. The direct innervations to developing bile ducts and peribiliary glands were also seen. PaI NF were first seen at 21 GW and was consistent until 40 GW in which a few NF were seen in PaI. These observations suggest that PoI NF arise from committed portal mesenchyme. PaI NF are very immature at 40 GW. There are direct innervations to bile ducts, peribiliary glands, portal veins, hepatic arteries, and DP.

Abnormal rectal endocrine cells in patients with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder. In a previous study the total number of endocrine cells in the rectum of IBS patients, as detected by chromogranin A, did not differ from that of healthy controls. While the total endocrine cell content of the rectum appears to be unchanged in IBS patients, changes in particular endocrine cells cannot be excluded. This study was undertaken, therefore, to investigate the cell density of different rectal endocrine cell types in (IBS) patients. Fifty patients with IBS (41 females and 9 males) were included in the study. Thirty patients had diarrhoea (IBS-D) and 20 had constipation (IBS-C) as the predominant symptom. Twenty-seven subjects were included as controls (19 females and 8 males). Rectal biopsy specimens were immunostained using the avidin-biotin-complex method for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), and oxyntomodulin and somatostatin cells. The cell densities were quantified by computerised image analysis. The serotonin cell density did not differ significantly, although a type II statistical error cannot be excluded, due to the small size of the sample. The densities of PYY and Oxyntomodulin cells were significantly lower and that of somatostatin were significantly higher in IBS patients than controls. These abnormalities were observed in both IBS-D and IBS-C patients. The abnormalities in the endocrine cells observed in this study in the rectum differed considerably from those seen in the colon of IBS patients. This indicates that caution in using the rectum to represent the large intestine in these patients. These abnormalities could be primary (genetic) or secondary to changes in the gut hormones found in other segments of the gut and/or other pathological processes. Although the-cause-and effect relationship of the abnormalities found in rectal endocrine cells is difficult to elucidate, they might contribute to the symptoms associated with IBS. The densities of PYY and somatostatin cells are potential biomarkers with good sensitivity and specificity for the diagnosis of IBS.

Neuropeptide Y inhibits biliary hyperplasia of cholestatic rats by paracrine and autocrine mechanisms

Neuropeptide Y (NPY) exerts its functions through six subtypes of receptors (Y₁-Y₆). Biliary homeostasis is regulated by several factors through autocrine/paracrine signaling. NPY inhibits cholangiocarcinoma growth; however, no information exists regarding the autocrine/paracrine role of NPY on biliary hyperplasia during cholestasis. The aims of this study were to determine: 1) the expression of NPY and Y₁-Y₅ in cholangiocytes and 2) the paracrine/autocrine effects of NPY on cholangiocyte proliferation. Normal or bile duct ligation (BDL) rats were treated with NPY, neutralizing anti-NPY antibody, or vehicle for 7 days. NPY and NPY receptor (NPYR) expression was assessed in liver sections and isolated cholangiocytes. NPY secretion was assessed in serum and bile from normal and BDL rats, as well as supernatants from normal and BDL cholangiocytes and normal rat cholangiocyte cell line [intrahepatic normal cholangiocyte culture (NRICC)]. We evaluated intrahepatic bile ductal mass (IBDM) in liver sections and proliferation in cholangiocytes. With the use of NRICC, the effects of NPY or anti-NPY antibody on cholangiocyte proliferation were determined. The expression of NPY and all NPYR were increased after BDL. NPY levels were lower in serum and cholangiocyte supernatant from BDL compared with normal rats. NPY secretion from NRICC was detected at both the basolateral and apical domains. Chronic NPY treatment decreased proliferating cellular nuclear antigen (PCNA) expression and IBDM in BDL rats. Administration of anti-NPY antibody to BDL rats increased cholangiocyte proliferation and IBDM. NPY treatment of NRICC decreased PCNA expression and increased the cell cycle arrest, whereas treatment with anti-NPY antibody increased proliferation. Therapies targeting NPY-mediated signaling may prove beneficial for the treatment of cholangiopathies.

High densities of serotonin and peptide YY cells in the colon of patients with lymphocytic colitis

AIM: To investigate colonic endocrine cells in lymphocytic colitis (LC) patients.

METHODS: Fifty-seven patients with LC were included. These patients were 41 females and 16 males, with an average age of 49 years (range 19-84 years). Twenty-seven subjects that underwent colonoscopy with biopsies were used as controls. These subjects underwent colonoscopy because of gastrointestinal bleeding or health worries, where the source of bleeding was identified as haemorrhoids or angiodysplasia. They were 19 females and 8 males with an average age of 49 years (range 18-67 years). Biopsies from the right and left colon were obtained from both patients and controls during colonoscopy. Biopsies were fixed in 4% buffered paraformaldehyde, embedded in paraffin and cut into 5 μm-thick sections. The sections immunostained by the avidin-biotin-complex method for serotonin, peptide YY (PYY), pancreatic polypeptide (PP) enteroglucagon and somatostatin cells. The cell densities were quantified by computerised image analysis using Olympus software.

RESULTS: The colon of both the patient and the control subjects were macroscopically normal. Histopathological examination of colon biopsies from controls revealed normal histology. All patients fulfilled the diagnosis criteria required for of LC: an increase in intraepithelial lymphocytes (> 20 lymphocytes/100 epithelial cells) and surface epithelial damage with increased lamina propria plasma cells and absent or minimal crypt architectural distribution. In the colon of both patients and control subjects, serotonin-, PYY-, PP-, enteroglucagon- and somatostatin-immunoreactive cells were primarily located in the upper part of the crypts of Lieberkühn. These cells were basket- or flask-shaped. There was no statistically significant difference between the right and left colon in controls with regards to the densities of serotonin- and PYY-immunoreactive cells (P = 0.9 and 0.1, respectively). Serotonin cell density in the right colon in controls was 28.9 ± 1.8 and in LC patients 41.6 ± 2.6 (P = 0.008). In the left colon, the corresponding figures were 28.5 ± 1.9 and 42.4 ± 2.9, respectively (P = 0.009). PYY cell density in the right colon of the controls was 10.1 ± 1 and of LC patients 41 ± 4 (P = 0.00006). In the left colon, PYY cell density in controls was 6.6 ± 1.2 and in LC patients 53.3 ± 4.6 (P = 0.00007).

CONCLUSION: The change in serotonin cells could be caused by an interaction between immune cells and serotonin cells, and that of PYY density might be secondary.

Chromogranin A cell density in the rectum of patients with irritable bowel syndrome

In a previous study, chromogranin A (CgA) cell density in the colon of patients with irritable bowel syndrome (IBS) was found to be reduced. It has been suggested that intestinal CgA cell density may be used as a marker for the diagnosis of IBS. The rectum harbours a larger number of large intestinal endocrine cells and is more accessible for biopsies than the colon. The present study aimed at determining the CgA cell density in the rectum of IBS patients. A total of 47 patients with IBS that fulfilled the Rome Criteria III (39 females and 8 males; average age, 38 years) were included. A total of 28 patients had diarrhea (IBS-D) and 19 had constipation (IBS-C) as the predominant symptom. A total of 27 subjects that underwent colonoscopy with rectal biopsies were used as the controls. These subjects underwent colonoscopy due to gastrointestinal bleeding (the source of which was identified as haemorrhoids or angiodysplasia; 19 females and 8 males; average age, 49 years), or health worries. The rectal biopsies were immunostained for CgA and quantified by computer image analysis. The CgA density in the controls was 206.3±22.2 (mean ± SEM), in all IBS patients 190.2±14.3, in IBS-D patients 188.8±14.7 and in IBS-C patients 195.3±34.1. There was no statistically significant difference between the controls, IBS, IBS-D or IBS-C patients (P=0.5, 0.5 and 0.7, respectively). The present study showed that although the rectum comprises the same endocrine cell types as the colon, attention must be paid when drawing conclusions regarding the whole large intestine from studies carried out on the rectum. This particularly applies when endocrine cells are investigated. As CgA cell density represents the total endocrine cell content of the rectum, changes in specific endocrine cells in IBS patients cannot be excluded.

Low densities of serotonin and peptide YY cells in the colon of patients with irritable bowel syndrome

BACKGROUND

The gut hormones are important in regulating gastrointestinal motility. Disturbances in gastrointestinal motility have been reported in patients with irritable bowel syndrome (IBS). Reduced endocrine cell density, as revealed by chromogranin A, has been reported in the colon of IBS patients.

AIMS

To investigate a possible abnormality in the colonic endocrine cells of IBS patients.

METHODS

A total of 41 patients with IBS according to Rome Criteria III and 20 controls were included in the study. Biopsies from the right and left colon were obtained from both patients and controls during colonoscopy. The biopsies were immunostained for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), entroglucagon, and somatostatin cells. Cell densities were quantified by computerized image analysis.

RESULTS

Serotonin and PYY cell densities were reduced in the colon of IBS patients. PP, entroglucagon, and somatostatin-immunoreactive cells were too few to enable reliable quantification.

CONCLUSION

The cause of these observations could be primary genetic defect(s), secondary to altered serotonin and/or PYY signaling systems and/or subclinical inflammation. Serotonin activates the submucosal sensory branch of the enteric nervous system and controls gastrointestinal motility and chloride secretion via interneurons and motor neurons. PYY stimulates absorption of water and electrolytes, and inhibits prostaglandin (PG) E2, and vasoactive intestinal peptide, which stimulates intestinal fluid secretion and is a major regulator of the "ileal brake". Although the cause and effect relationship of these findings is difficult to elucidate, the abnormalities reported here might contribute to the symptoms associated with IBS.

A novel mechanism for regulating hepatic glycogen synthesis involving serotonin and cyclin-dependent kinase-5

Hepatic autonomic nerves regulate postprandial hepatic glucose uptake, but the signaling pathways remain unknown. We tested the hypothesis that serotonin (5-hydroxytryptamine [5-HT]) exerts stimulatory and inhibitory effects on hepatic glucose disposal. Ligands of diverse 5-HT receptors were used to identify signaling pathway(s) regulating glucose metabolism in hepatocytes. 5-HT had stimulatory and inhibitory effects on glycogen synthesis in hepatocytes mediated by 5-HT1/2A and 5-HT2B receptors, respectively. Agonists of 5-HT1/2A receptors lowered blood glucose and increased hepatic glycogen after oral glucose loading and also stimulated glycogen synthesis in freshly isolated hepatocytes with greater efficacy than 5-HT. This effect was blocked by olanzapine, an antagonist of 5-HT1/2A receptors. It was mediated by activation of phosphorylase phosphatase, inactivation of glycogen phosphorylase, and activation of glycogen synthase. Unlike insulin action, it was not associated with stimulation of glycolysis and was counteracted by cyclin-dependent kinase (cdk) inhibitors. A role for cdk5 was supported by adaptive changes in the coactivator protein p35 and by elevated glycogen synthesis during overexpression of p35/cdk5. These results support a novel mechanism for serotonin stimulation of hepatic glycogenesis involving cdk5. The opposing effects of serotonin, mediated by distinct 5-HT receptors, could explain why drugs targeting serotonin function can cause either diabetes or hypoglycemia in humans.

Neuropeptide Y inhibits cholangiocarcinoma cell growth and invasion

No information exists on the role of neuropeptide Y (NPY) in cholangiocarcinoma growth. Therefore, we evaluated the expression and secretion of NPY and its subsequent effects on cholangiocarcinoma growth and invasion. Cholangiocarcinoma cell lines and nonmalignant cholangiocytes were used to assess NPY mRNA expression and protein secretion. NPY expression was assessed by immunohistochemistry in human liver biopsies. Cell proliferation and migration were evaluated in vitro by MTS assays and matrigel invasion chambers, respectively, after treatment with NPY or a neutralizing NPY antibody. The effect of NPY or NPY depletion on tumor growth was assessed in vivo after treatment with NPY or the neutralizing NPY antibody in a xenograft model of cholangiocarcinoma. NPY secretion was upregulated in cholangiocarcinoma compared with normal cholangiocytes. Administration of exogenous NPY decreased proliferation and cell invasion in all cholangiocarcinoma cell lines studied and reduced tumor cell growth in vivo. In vitro, the effects of NPY on proliferation were blocked by specific inhibitors for NPY receptor Y2, but not Y1 or Y5, and were associated with an increase in intracellular d-myo-inositol 1,4,5-trisphosphate and PKCα activation. Blocking of NPY activity using a neutralizing antibody promoted cholangiocarcinoma growth in vitro and in vivo and increased the invasiveness of cholangiocarcinoma in vitro. Increased NPY immunoreactivity in human tumor tissue occurred predominantly in the center of the tumor, with less expression toward the invasion front of the tumor. We demonstrated that NPY expression is upregulated in cholangiocarcinoma, which exerts local control on tumor cell proliferation and invasion. Modulation of NPY secretion may be important for the management of cholangiocarcinoma.

Abnormal small-intestinal endocrine cells in patients with irritable bowel syndrome

BACKGROUND

General disturbances in gastrointestinal motility have been reported in patients with irritable bowel syndrome (IBS). The gastrointestinal tract hormones play an important role in regulating gastrointestinal motility.

AIMS

To investigate a possible abnormality in the small intestinal endocrine cells of IBS patients.

METHODS

Included in the study were 41 patients with irritable bowel syndrome according to Rome Criteria III and 42 healthy controls. Duodenal biopsies were obtained from both patients and controls during gastroscopy. The biopsies were immunostained by avidin-biotin-complex method for secretin, CCK, GIP, somatostatin, and serotonin cells. The cell densities were quantified by computerized image analysis.

RESULTS

The density of secretin- and CCK-immunoreactive cells in patients with IBS was significantly reduced. The reduction in secretin and CCK cells occurred only in IBS-diarrhea patients, but not in IBS-constipation subtype. Both GIP and somatostatin cell densities were reduced in the duodenum of IBS patients. There was no statistical difference between the subtypes of IBS patients, regarding secretin, CCK, GIP, or somatostatin cell densities. Serotonin cell density was not affected in patients with IBS.

CONCLUSIONS

The low densities of secretin and CCK cells in IBS-diarrhea patients may cause a functional pancreatic insufficiency as well as inadequate gall emptying, as these hormones stimulate pancreatic bicarbonate and enzyme secretion and CCK stimulates as well gall bladder contraction. Low densities of secretin, GIP, and somatostatin cells in IBS patients might result in a high secretion of gastric acid, as secretin, GIP, and somatostatin inhibit gastric acid secretion.

Chromogranin A as a possible tool in the diagnosis of irritable bowel syndrome

OBJECTIVE

Serum chromogranin A (CgA) levels have been reported to be normal, reduced or elevated in irritable bowel syndrome (IBS) patients. The aim of the present study was to establish a possible abnormality in CgA plasma level and in intestinal CgA cell density in IBS patients and to evaluate the outcome for the diagnosis of IBS.

MATERIAL AND METHODS

Forty-one patients with irritable bowel syndrome according to Rome Criteria III (39 females and 2 males; average age 35 years) and 59 healthy controls (37 females and 22 males; average age 45.5 years) were included in the study. Duodenal and colonic biopsies were obtained from all IBS patients. Forty-two of these healthy subjects underwent gastroscopy with duodenal biopsies. The remaining 17 subjects underwent colonoscopy with biopsies. The biopsies were immunostained with avidin-biotin-complex method for CgA cells. The cell densities were quantified by computerized image analysis. CgA plasma level was determined with ELISA technique.

RESULTS

The density of CgA cells in both the duodenum and colon was reduced in patients with IBS. CgA cell density in the left colon was, however, unaffected in patients with IBS-constipation. There was no difference in the plasma level of CgA between patients with IBS and controls.

CONCLUSION

The reduced density of intestinal CgA cells should be considered as a reduction in the total amount of intestinal endocrine cells. Which endocrine cell type is affected remains to investigate. This reduction may offer a histopathological test for the diagnosis of IBS. It is doubtful that the blood level of CgA has any clinical impact in IBS.

Biogenic amines serotonin and dopamine regulate cholangiocyte hyperplastic and neoplastic growth

Biogenic amines, such as serotonin and dopamine, regulate a multitude of cellular responses. A great deal of effort has been invested into understanding the effects of these molecules and their corresponding receptor systems on cholangiocyte and cholangiocarcinoma secretion, apoptosis and growth. This review summarizes the results of these efforts and highlights the importance of these regulatory molecules on the physiology and pathophysiology of cholangiocytes. Specifically we have focused on the recent findings into the effects of serotonin and dopamine on cholangiocyte hyperplasia and neoplastic growth.

Distribution and possible origin of neuropeptide-containing nerve elements in the mammalian liver

The intrahepatic distribution of nerve fibres is highly species dependent, therefore we searched for a species where the innervation pattern is similar to that of the human liver. Livers of rats, cats, guinea pigs and humans were used. The different nerve elements were identified by ABC immunohistochemistry and analysed semiquantitatively. Large numbers of neuropeptide Y (NPY) and dopamine-beta-hydroxylase immunoreactive (IR) nerve fibres were observed in the human and guinea pig liver, and they were in close contact with portal triads, central veins and ran parallel with liver sinuses. A few substance P, somatostatin and vasoactive intestinal polypeptide IR nerve fibres were also detected intralobularly, while galanin nerve fibres were only observed around portal triads. In the rat liver only a few NPY-positive nerve fibres were found, exclusively in portal tracts. Some nerve cell bodies (IR for NPY and somatostatin) were also found in the liver of guinea pigs, young cats and humans, therefore some of the nerve terminals might originate from these intrinsic ganglia. It can be concluded that the innervation pattern of the guinea pig liver shows the highest similarity to that of the human liver.

The role of the autonomic nervous liver innervation in the control of energy metabolism

Despite a longstanding research interest ever since the early work by Claude Bernard, the functional significance of autonomic liver innervation, either sympathetic or parasympathetic, is still ill defined. This scarcity of information not only holds for the brain control of hepatic metabolism, but also for the metabolic sensing function of the liver and the way in which this metabolic information from the liver affects the brain. Clinical information from the bedside suggests that successful human liver transplantation (implying a complete autonomic liver denervation) causes no life threatening metabolic derangements, at least in the absence of severe metabolic challenges such as hypoglycemia. However, from the benchside, data are accumulating that interference with the neuronal brain-liver connection does cause pronounced changes in liver metabolism. This review provides an extensive overview on how metabolic information is sensed by the liver, and how this information is processed via neuronal pathways to the brain. With this information the brain controls liver metabolism and that of other organs and tissues. We will pay special attention to the hypothalamic pathways involved in these liver-brain-liver circuits. At this stage, we still do not know the final destination and processing of the metabolic information that is transferred from the liver to the brain. On the other hand, in recent years, there has been a considerable increase in the understanding which brain areas are involved in the control of liver metabolism via its autonomic innervation. However, in view of the ever rising prevalence of type 2 diabetes, this potentially highly relevant knowledge is still by far too limited. Thus the autonomic innervation of the liver and its role in the control of metabolism needs our continued and devoted attention.

Prospective evaluation of aminopeptidase activities in plasma and peripheral organs of streptozotocin-induced diabetic rats

The cleavage of peptides by aminopeptidase enzyme types could be among the mechanisms related to certain disruptions on mediator and modulatory functions in diabetes mellitus. In order to examine this hypothesis, we measured representative aminopeptidase activities in tissues of peripheral organs of control and streptozotocin-diabetic rats. None of the examined aminopeptidase activities differed between diabetics and controls in plasma, ileum, stomach or lung. Soluble and membrane-associated alanyl, and membrane-associated cystyl aminopeptidase activities were higher in the kidney of diabetics. Decreased activity was observed in soluble and membrane-associated aspartyl and soluble dipeptidyl-peptidase IV, while increased activity was observed in soluble alanyl, arginyl, and cystyl aminopeptidases in the pancreas of diabetics. In the jejunum, soluble cystyl aminopeptidase increased in diabetics. Soluble arginyl and type-1-pyroglutamyl aminopeptidase and membrane-associated dipeptidyl-peptidase IV activities increased in the liver of diabetics. Membrane-associated dipeptidyl-peptidase IV and alanyl aminopeptidase activities in the spleen were higher in diabetics than in controls. Membrane-associated alanyl aminopeptidase activity also increased in the heart of diabetics. All these changes in streptozotocin-treated rats were avoided by the administration of insulin. Our comparative analysis of a diverse array of aminopeptidase activities supported the proposal that the regulation of peptide cleavage by these enzyme types is associated with the effects of streptozotocin-diabetes mellitus on peripheral organs.

The function of serotonin within the liver

Serotonin or 5-hydroxytryptamine (5-HT) is known to regulate several key aspects of liver biology and these functions include hepatic blood flow, innervation and wound healing. Given the importance of these functions it is surprising that relatively little time has been dedicated to studying the precise function and mechanisms of serotonin within the liver. Here we describe what is known about serotonin and the liver and those receptor types that mediate the observed effects with an aim to stimulating new interest in the field of serotonin and liver biology.

Ontogeny of human intrahepatic innervation

Intrahepatic nerves serve important metabolic, sensory and motor functions. Their ontogeny in human liver has not been elucidated. We aimed to characterise the ontogeny of human intrahepatic innervation, to assess its relationship with biliary structures and to examine the distribution and nature of peptidergic nerves during development. We used immunohistochemistry on archival normal human liver tissue from 63 fetuses [8-40 gestational weeks (gw)] and 10 adults with antibodies to pan-neural markers and neuropeptides. Few nerve fibers appeared in portal tracts at 8 gw. Their density increased gradually from 12 gw and reached adult levels at 32-33 gw. Rare intra-acinar nerves, restricted to periportal areas, appeared at 40 gw. Galanin-, somatostatin- and calcitonin-gene-related peptide-positive nerve fibers were noted only in portal tracts from 22, 26 and 32 gw, respectively. In human adult liver, dense portal and intra-acinar neural supply was observed. Human fetal liver contains a neural network distributed mainly in portal tracts with a density that increases progressively towards term. Intra-acinar innervation appears at term, suggesting that is not required for normal liver function during development, while peptidergic nerves are important for intrauterine liver functions. Developmentally regulated expression of galanin and somatostatin may play a role in liver morphogenesis.

The alpha2-adrenergic receptor agonist UK 14,304 inhibits secretin-stimulated ductal secretion by downregulation of the cAMP system in bile duct-ligated rats

Secretin stimulates ductal secretion by activation of cAMP --> PKA --> CFTR --> Cl(-)/HCO(3)(-) exchanger in cholangiocytes. We evaluated the expression of alpha(2A)-, alpha(2B)-, and alpha(2C)-adrenergic receptors in cholangiocytes and the effects of the selective alpha(2)-adrenergic agonist UK 14,304, on basal and secretin-stimulated ductal secretion. In normal rats, we evaluated the effect of UK 14,304 on bile and bicarbonate secretion. In bile duct-ligated (BDL) rats, we evaluated the effect of UK 14,304 on basal and secretin-stimulated 1) bile and bicarbonate secretion; 2) duct secretion in intrahepatic bile duct units (IBDU) in the absence or presence of 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na(+)/H(+) exchanger isoform NHE3; and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in purified cholangiocytes. alpha(2)-Adrenergic receptors were expressed by all cholangiocytes in normal and BDL liver sections. UK 14,304 did not change bile and bicarbonate secretion of normal rats. In BDL rats, UK 14,304 inhibited secretin-stimulated 1) bile and bicarbonate secretion, 2) expansion of IBDU luminal spaces, and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in cholangiocytes. There was decreased lumen size after removal of secretin in IBDU pretreated with UK 14,304. In IBDU pretreated with EIPA, there was no significant decrease in luminal space after removal of secretin in either the absence or presence of UK 14,304. The inhibitory effect of UK 14,304 on ductal secretion is not mediated by the apical cholangiocyte NHE3. alpha(2)-Adrenergic receptors play a role in counterregulating enhanced ductal secretion associated with cholangiocyte proliferation in chronic cholestatic liver diseases.

Proliferating cholangiocytes: a neuroendocrine compartment in the diseased liver

In the last 15 years, the intrahepatic biliary tree has become the object of extensive studies, which highlighted the extraordinary biologic properties of cholangiocytes involved in bile formation, proliferation, injury repair, fibrosis, angiogenesis, and regulation of blood flow. Proliferation is a "typical" property of cholangiocytes and is key as a mechanism of repair responsible for maintaining the integrity of the biliary tree. Cholangiocyte proliferation occurs virtually in all pathologic conditions of liver injury where it is associated with inflammation, regeneration, and repair, thus conditioning the evolution of liver damage. Interestingly, proliferating cholangiocytes acquire the phenotype of neuroendocrine cells, and secrete different cytokines, growth factors, neuropeptides, and hormones, which represent potential mechanisms for cross talk with other liver cells. Many studies suggest the generation of a neuroendocrine compartment in the injured liver, mostly constituted by cells with cholangiocyte features, which functionally conditions the progression of liver disease. These insights on cholangiocyte pathophysiology will provide new potential strategies for the management of chronic liver diseases. The purpose of this review is to summarize the recent findings on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte biology.

Heterogeneity of the intrahepatic biliary epithelium

The objectives of this review are to outline the recent findings related to the morphological heterogeneity of the biliary epithelium and the heterogeneous pathophysiological responses of different sized bile ducts to liver gastrointestinal hormones and peptides and liver injury/toxins with changes in apoptotic, proliferative and secretory activities. The knowledge of biliary function is rapidly increasing because of the recognition that biliary epithelial cells (cholangiocytes) are the targets of human cholangiopathies, which are characterized by proliferation/damage of bile ducts within a small range of sizes. The unique anatomy, morphology, innervation and vascularization of the biliary epithelium are consistent with function of cholangiocytes within different regions of the biliary tree. The in vivo models [e.g., bile duct ligation (BDL), partial hepatectomy, feeding of bile acids, carbon tetrachloride (CCl₄) or α-naphthylisothiocyanate (ANIT)] and the in vivo experimental tools [e.g., freshly isolated small and large cholangiocytes or intrahepatic bile duct units (IBDU) and primary cultures of small and large murine cholangiocytes] have allowed us to demonstrate the morphological and functional heterogeneity of the intrahepatic biliary epithelium. These models demonstrated the differential secretory activities and the heterogeneous apoptotic and proliferative responses of different sized ducts. Similar to animal models of cholangiocyte proliferation/injury restricted to specific sized ducts, in human liver diseases bile duct damage predominates specific sized bile ducts. Future studies related to the functional heterogeneity of the intrahepatic biliary epithelium may disclose new pathophysiological treatments for patients with cholangiopathies.

Central thyrotropin-releasing hormone increases hepatic cyclic AMP through vagal-cholinergic and prostaglandin-dependent pathways in rats

Central neuropeptides play roles in many physiologic regulations through the autonomic nervous system. We have demonstrated that central thyrotropin-releasing hormone (TRH), one of neuropeptides, induces a stimulation of hepatic proliferation through vagal-cholinergic pathways. Since cAMP is known to play an important role in the hepatic proliferation, effect of central TRH on hepatic cAMP was investigated. Rats were intracisternally injected with either a TRH analog, RX-77368 (1-100 ng), or saline. The liver was removed 2-72 h after the TRH analog and hepatic cAMP content was determined by radioimmunoassay. In some experiments, pretreatment with hepatic vagotomy, atropine methyl nitrate, or 6-hydroxydopamine (6-OHDA) was performed. Hepatic cAMP was dose-dependently increased by intracisternal TRH analog (5-100 ng) with a peak response occurring 12 h postinjection. The central TRH-induced increase in hepatic cAMP was abolished by vagotomy, atropine and indomethacin, but not by 6-OHDA. Intravenous injection of the TRH analog (10 ng) did not affect hepatic cAMP. These results demonstrate that TRH acts in the brain to increase hepatic cAMP through vagal-cholinergic and prostaglandin-dependent pathways, suggesting that central TRH modulates hepatic functions through cAMP-mediated signaling pathways.

Innervation of the sinusoidal wall: regulation of the sinusoidal diameter

In the livers of humans, cats, guinea pigs, and tupaia, nerve endings are distributed all over the hepatic lobules. Nerve endings in the intralobular spaces are localized mainly in the Disse spaces and are oriented toward the hepatic stellate cells (HSCs), sinusoidal endothelial cells, and hepatocytes. They are especially closely related to HSCs. Various neurotransmitters such as substance P exist in the nerve endings. In addition, HSCs possess endothelin (ET) and adrenergic receptors and contract in response to the corresponding agonists. In contrast, nitric oxide (NO) inhibits the contraction of HSCs. HSCs thus appear to be involved in the regulation of hepatic sinusoidal microcirculation by contraction and relaxation. In the cirrhotic liver, intralobular innervation is decreased, but ET, ET receptors, and NO are overexpressed in the HSCs. These findings indicate that HSCs in cirrhotic liver may play an important role in the sinusoidal microcirculation through agents such as ET or NO rather than through intralobular innervation.

Studies on unfolded β2-microglobulin at C-terminal in dialysis-related amyloidosis

BACKGROUND

In 1997, Stoppini et al reported that monoclonal antibody specific to the C-terminal 92-99 of beta(2)-microglobulin (beta(2)m) had been capable of inhibiting fibrillogenesis of beta(2)m in vitro. Meanwhile, recent studies have indicated that an acidifying procedure can unfold conformation of the precursor protein, leading to fibril formation of beta(2)m as well as a transthyretin.

METHODS

We thus prepared monoclonal antibody specific to the C-terminal 92-99 (mAb 92-99), and investigated its reactivity in plasma ultrafiltrate and amyloid tissues from 18 hemodialysis patients with dialysis-related amyloidosis (DRA).

RESULTS

beta(2)m extracted from ultrafiltrate showed no reaction for mAb 92-99, whereas acidified beta(2)m from ultrafiltrate showed a reaction for mAb 92-99. Similarly, a homogenate of carpal amyloid tissues showed a strong reaction for mAb 92-99 on immunoblotting. Immunohistochemical study showed also a distinct staining for mAb 92-99 in 7 Congophilic specimens from DRA patients. More interestingly, staining for mAb 92-99 could be found in most, though not all, non-Congophilic tissues.

CONCLUSION

This study demonstrates that the monoclonal antibody specific to the C-terminal 92-99 of beta(2)m can detect the conformational intermediate in amyloidogenesis of beta(2)m ex vivo, and demonstrates that an unfolded beta(2)m at C-terminal could be found not only in Congophilic area but even in non-Congophilic area as well.

Octreotide regulates CC but not CXC LPS-induced chemokine secretion in rat Kupffer cells

Kupffer cells (KC) and lipopolysaccharide (LPS) interaction is the initial event leading to hepatic inflammation and fibrosis in many types of liver injury. We studied chemokine secretion by KC activated with LPS and the possible effect of the somatostatin analogue octreotide, in the regulation of this process. KC isolated from Sprague-Dawley rats were cultured in the presence of LPS added alone or with different concentrations of octreotide for 24 and 48 h, and chemokine production was assessed in culture supernatants by ELISA. CC chemokine mRNA expression was assessed by semiquantitative RT-PCR. Vehicle-stimulated KC produced a basal amount of CC and CXC chemokines. LPS-stimulated KC secreted significantly increased amounts of IL-8 (GRO/CINC-1) (P<0.001), MIP-2 (P<0.001), MCP-1 (P<0.001), and RANTES (P<0.01). Octreotide inhibited LPS-induced secretion of the CC chemokines MCP-1 (P<0.05) and RANTES (P<0.05), but not the CXC chemokines IL-8 (GRO/CINC-1) and MIP-2, in a concentration-dependent manner. Downregulation of basal and LPS-induced mRNA expression of the CC chemokines was also observed in the presence of octreotide. Pretreatment with phosphatidylinositol 3 (PI3)-kinase inhibitors reduced chemokine production by LPS-treated KC in both the mRNA and protein level. Furthermore, it prevented the octreotide inhibitory effect on LPS-induced chemokine secretion, indicating a possible involvement of the PI3-kinase pathway. In conclusion, these data demonstrate that chemokine secretion by KC can be differentially regulated by octreotide, and suggest that this somatostatin analogue may have immunoregulatory effects on resident liver macrophages. British Journal of Pharmacology (2004) 141, 477-487. doi:10.1038/sj.bjp.0705633

Neural connections between the hypothalamus and the liver

After receiving information from afferent nerves, the hypothalamus sends signals to peripheral organs, including the liver, to keep homeostasis. There are two ways for the hypothalamus to signal to the peripheral organs: by stimulating the autonomic nerves and by releasing hormones from the pituitary gland. In order to reveal the involvement of the autonomic nervous system in liver function, we focus in this study on autonomic nerves and neuroendocrine connections between the hypothalamus and the liver. The hypothalamus consists of three major areas: lateral, medial, and periventricular. Each area has some nuclei. There are two important nuclei and one area in the hypothalamus that send out the neural autonomic information to the peripheral organs: the ventromedial hypothalamic nucleus (VMH) in the medial area, the lateral hypothalamic area (LHA), and the periventricular hypothalamic nucleus (PVN) in the periventricular area. VMH sends sympathetic signals to the liver via the celiac ganglia, the LHA sends parasympathetic signals to the liver via the vagal nerve, and the PVN integrates information from other areas of the hypothalamus and sends both autonomic signals to the liver. As for the afferent nerves, there are two pathways: a vagal afferent and a dorsal afferent nerve pathway. Vagal afferent nerves are thought to play a role as sensors in the peripheral organs and to send signals to the brain, including the hypothalamus, via nodosa ganglia of the vagal nerve. On the other hand, dorsal afferent nerves are primary sensory nerves that send signals to the brain via lower thoracic dorsal root ganglia. In the liver, many nerves contain classical neurotransmitters (noradrenaline and acetylcholine) and neuropeptides (substance P, calcitonin gene-related peptide, neuropeptide Y, vasoactive intestinal polypeptide, somatostatin, glucagon, glucagon-like peptide, neurotensin, serotonin, and galanin). Their distribution in the liver is species-dependent. Some of these nerves are thought to be involved in the regulation of hepatic function as well as of hemodynamics. In addition to direct neural connections, the hypothalamus can affect metabolic functions by neuroendocrine connections: the hypothalamus-pancreas axis, the hypothalamus-adrenal axis, and the hypothalamus-pituitary axis. In the hypothalamus-pancreas axis, autonomic nerves release glucagon and insulin, which directly enter the liver and affect liver metabolism. In the hypothalamus-adrenal axis, autonomic nerves release catecholamines such as adrenaline and noradrenaline from the adrenal medulla, which also affects liver metabolism. In the hypothalamus-pituitary axis, release of glucocorticoids and thyroid hormones is stimulated by pituitary hormones. Both groups of hormones modulate hepatic metabolism. Taken together, the hypothalamus controls liver functions by neural and neuroendocrine connections.

Anatomy of efferent hepatic nerves

The role of neural elements in regulating blood flow through the hepatic sinusoids, solute exchange, and parenchymal function is incompletely understood. This is due in part to limited investigation in only a few species whose hepatic innervation may differ significantly from humans. For example, most experimental studies have used rats and mice having livers with little or no intralobular innervation. In contrast, most other mammals, including humans, have aminergic and peptidergic nerves extending from perivascular plexus in the portal space into the lobule, where they course in Disse's space in close relationship to stellate cells (fat storing cells of Ito) and hepatic parenchymal cells. While these fibers extend throughout the lobule, they predominate in the periportal region. Cholinergic innervation, however, appears to be restricted to structures in the portal space and immediately adjacent hepatic parenchymal cells. Neuropeptides have been colocalized with neurotransmitters in both adrenergic and cholinergic nerves. Neuropeptide Y (NPY) has been colocalized in aminergic nerves supplying all segments of the hepatic-portal venous and the hepatic arterial and biliary systems. Nerve fibers immunoreactive for substance P and somatostatin follow a similar distribution. Intralobular distribution of all of these nerve fibers is species-dependent and similar to that reported for aminergic fibers. Vasoactive intestinal peptide and calcitonin gene-related peptide (CGRP) are reported to coexist in cholinergic and sensory afferent nerves innervating portal veins and hepatic arteries and their branches, but not the other vascular segments or the bile ducts. Nitrergic nerves immunoreactive for neuronal nitric oxide (nNOS) are located in the portal tract where nNOS colocalizes with both NPY- and CGRP-containing fibers. In summary, the liver is innervated by aminergic, cholinergic, peptidergic, and nitrergic nerves. While innervation of structures in the portal tract is relatively similar between species, the extent and distribution of intralobular innervation are highly variable as well as species-dependent and may be inversely related to the density of gap junctions between contiguous hepatic parenchymal cells.

Protective effect of central thyrotropin-releasing hormone on carbon tetrachloride-induced acute hepatocellular necrosis in rats

BACKGROUND/AIMS

Thyrotropin-releasing hormone (TRH) acts in the brain to stimulate hepatic proliferation and blood flow through vagal-muscarinic and prostaglandin-mediated pathways. Hepatic blood flow and prostaglandins are well recognized as cytoprotective factors for liver damage, and central TRH is known to play a role in gastric cytoprotection. The effect of central TRH on carbon tetrachloride (CCl(4))-induced acute hepatocellular necrosis was investigated in rats.

METHODS

Male fasted rats were injected with either TRH analog, RX 77368 (1-10 ng), or vehicle intracisternally, and CCl(4) (2.0 ml/kg) was injected subcutaneously 60 min later. Acute hepatocellular necrosis was assessed by serum hepatic enzymes and histological changes 24 h after CCl(4).

RESULTS

Intracisternal TRH dose-dependently inhibited elevation of serum alanine aminotransferase level induced by CCl(4). Intracisternal TRH reduced CCl(4)-induced hepatic histological changes. The cytoprotective effect of central TRH on CCl(4)-induced acute hepatocellular necrosis was abolished by hepatic branch vagotomy, atropine, indomethacin and N(G)-nitro-L-arginine methyl ester, but not by 6-hydroxydopamine. Intravenous TRH did not influence CCl(4)-induced acute hepatocellular necrosis.

CONCLUSIONS

These results suggest that the cytoprotective effect of central TRH on acute hepatocellular necrosis is mediated through vagal-muscarinic, and prostaglandin- and nitric oxide-dependent pathways.

Triple therapy with octreotide, galanin, and serotonin reduces the size and blood vessel density and increases apoptosis of a rat colon carcinoma

A rat colonic adenocarcinoma was implanted subcutaneously in female nude (C57BL/6JBom-nu) mice. After 7 days, the animals were divided into different groups. One group received triple therapy with octreotide, galanin, and serotonin, 10 microg/kg body weight of each, twice daily. The second group served as controls and received only saline solution. Three groups received 10 microg/kg body weight twice daily of octreotide, galanin, or serotonin. The last group consisted of controls that received only saline solution. The treatment lasted for 5 days. The tumour volume, wet weight, and relative volume density of blood vessels were significantly decreased after the triple treatment, as compared to controls. Apoptotic index was significantly increased, but the proliferation index was not affected in the group of mice that received triple therapy. There was no significant difference between controls and mice treated with octreotide, galanin, or serotonin regarding tumour volume or weight. The relative volume density of blood vessels was decreased in tumours treated with galanin, but not with octreotide or serotonin. There was no statistical difference in the proliferation index between controls and animals treated with octreotide, galanin, or serotonin, as compared with controls. Tumour necrosis and increased apoptosis may be responsible for the reduction in the volume and weight of the tumour after triple therapy. Tumour necrosis may be caused by the induction of tumour ischemia due to a reduction in tumour blood flow, which is caused by decreased incidence of tumour-feeding blood vessels, and by constriction of tumour-feeding arterioles. These results are promising and may offer treatment for colon cancer.

Characterization of complementary deoxyribonucleic acids encoding preprogalanin and its alternative splice variants in the goldfish

This paper reports the identification of five preprogalanin complementary deoxyribonucleic acids encoding preprogalanin peptides in the goldfish. Preprogalanin 1A, 1B and 1C are encoded in galanin gene 1 and 2A and 2B are encoded in gene 2. Preprogalanin 1B and 2B have a 24 amino acids insert in the mature peptide region and form 1C has a deletion of 23 amino acids in the middle of the galanin message associated peptide region. The mature peptides from the preprogalanin 1A and 1C are 29 amino acids. However, the mature peptide is 31 amino acids from preprogalanin 2A, 53 amino acids from 1B and 55 amino acids from 2B. The physiological significance of multiple forms of galanin peptide is unknown. Organization of galanin gene 1, which is similar to the mammalian galanin gene has been identified. Expression of preprogalanin messenger ribonucleic acids was widely detected in goldfish brain and several peripheral tissues.

Lafutidine increases hepatic blood flow via potentiating the action of central thyrotropin-releasing hormone in rats

BACKGROUND

Lafutidine, (+/-)-2-(furfurylsulfinyl)-N-[4-[4-(piperidinomethyl)-2-pyridyl]oxy-(Z)-2 butenyl]acetamide, is a newly synthesized histamine H2 receptor antagonist and possesses a cytoprotective efficacy, which comprises mucin biosynthesis and stimulation of gastric blood flow mediated through capsaicin-sensitive sensory neurons and endogenous calcitonin gene-related peptide (CGRP). In the present study, an effect of lafutidine on hepatic blood flow was investigated in rats that received an intracisternal injection of a subthreshold dose of thyrotropin-releasing hormone (TRH) analog, RX 77368.

METHODS

Change in hepatic blood flow was determined by laser Doppler flowmetry. Male Wistar rats were anesthetized with urethane (1.5 g/kg, i.p.), and positioned on a stereotaxic apparatus. An abdominal incision was made, and a probe of laser Doppler flowmeter was placed on the surface of the liver. After a 60-min stabilization, basal hepatic blood flow was measured for 30 min, and lafutidine (0.5, 1, 3, 5 or 10 mg/kg) or vehicle was injected into the portal vein and a subthreshold dose (1.5 ng) of RX 77368 was injected intracisternally. Hepatic blood flow was monitored for 120 min postinjection. To investigate a role of capsaicin-sensitive sensory neurons and endogenous CGRP, systemic capsaicin treatment (125 mg/kg, s.c., 10-14 days before) and intravenous infusion of a CGRP receptor antagonist, human CGRP-(8-37) (15 micro g/kg as a bolus, followed by infusion at 3 micro g/kg/h) were performed, respectively.

RESULTS

Intracisternal injection of RX 77368 (1.5 ng) or intraportal lafutidine (10 mg/kg) by itself did not affect hepatic blood flow, but co-injection of intracisternal RX 77368 (1.5 ng) and intraportal lafutidine (5 mg/kg) increased it with peak response at 30 min postinjection. The effect of lafutidine on hepatic blood flow in rats given RX 77368 was dose-related over the range 1-5 mg/kg. By contrast, intracisternal injection of RX 77368 (1.5 ng) did not change hepatic blood flow in rats injected with another histamine H2 receptor antagonist, famotidine (5 mg/kg), intraportally. The stimulatory effect of co-injection of TRH analog and lafutidine was abolished by systemic capsaicin-treatment and CGRP antagonist.

CONCLUSION

These data suggest that lafutidine increases hepatic blood flow by sensitizing the liver to the action of central TRH via both capsaicin-sensitive sensory neurons and endogenous CGRP in urethane-anesthetized rats.

The nitrergic autonomic innervation of the liver

Using immunohistochemical approaches, the nitrergic innervation of the liver has been studied in mammals and in fish. The morphofunctional relationships described here indicate a high degree of evolutionary conservation of the hepatic nitrergic transmission and its possible involvement in the neural control of the hepatic function in health and disease.

Triple therapy with octreotide, galanin and serotonin induces necrosis and increases apoptosis of a rat colon carcinoma

A rat colonic adenocarcinoma was implanted subcutaneously (s.c.) in nude mice. After 7 days, the animals were divided into different groups. Two groups received subcutaneous injections twice daily with 3 or 6 micro g/kg body weight octreotide, galanin and serotonin. Three groups were respectively treated with 20, 30, and 40 micro g/kg body weight of the previously mentioned bioactive substances. Control group received only saline solution in the same fashion as treated animals. The treatment lasted for 5 days. The tumour volume and weight, the relative density of blood vessels, of tumour necrotic tissue, of apoptotic nuclei and of proliferating nuclei were measured. Apoptosis was detected by in situ labelling of nuclear DNA fragmentation according to TUNEL method, and proliferation by immunocytochemistry. Morphometry was done with the classical stereological point-counting method. Food consumption, animal weight, faeces weight and its water content were measured for 3 days before and after treatment. Triple therapy with 3 and 6 micro g/kg body weight had no effect on any of the parameters measured, except in reducing the relative volume density of tumour blood vessels. Treatment with 20, 30 and 40 micro g/kg body weight of the previously mentioned bioactive substances reduced the tumour volume, the relative volume density of blood vessels and increased the relative volume density of necrotic tissue and of apoptotic nuclei (in the 20 micro g group). However, there was no difference between treated mice and controls regarding the relative volume density of proliferating nuclei. There was no statistical difference between treated animals regarding food consumption, body weight, faeces weight and its water content before and during treatment. The present study confirms that triple therapy with octreotide, galanin and serotonin causes regression of a rat colon carcinoma. It further showed that optimum treatment dose is 20 micro g/kg body weight of each bioactive substance. Moreover, this therapy regime does not show apparent side effects in the experiments carried out on mice.

Gastrointestinal transit in an animal model of human diabetes type 2: relationship to gut neuroendocrine peptide contents

Gastrointestinal transit (GIT) was determined in obese diabetic mice (ob/ob, Umeå/Bom). Blood glucose level, and insulin concentration in the serum and pancreas extracts as well as neuroendocrine peptide contents were measured in several segments of the gut. GIT was significantly slower in the obese diabetic mice, but was not correlated with the blood glucose level, serum insulin, or pancreatic insulin content. GIT was correlated with duodenal secretin content and colonic vasoactive intestinal peptide (VIP) content, but not with the content of other neuroendocrine peptides in different segments investigated. The antral gastrin content in obese diabetic mice was significantly higher than in controls. The concentration of secretin in obese diabetic mice was higher than in controls. Whereas the contents of peptide YY (PYY) and somatostatin were higher in obese diabetic mice, the contents of substance P and VIP were lower. The increased content of duodenal secretin and decreased content of colonic VIP may be among the factors that cause slow GIT in obese diabetic mice. The changes in the colonic contents of PYY, VIP and somatostatin may cause low intestinal secretion and, together with slow GIT, give rise to constipation, which is a common symptom in diabetes.

Gastrointestinal transit in relation to gut endocrine cells in animal models of human diabetes

Gastrointestinal transit was measured in non-obese diabetic (NOD) mice, as an animal model of human diabetes type 1, and in obese diabetic mice, as an animal model of human diabetes type 2. The endocrine cells known to correlate to gastrointestinal transit, namely secretin, serotonin, Peptide YY (PYY) and enteroglucagon cells, were identified by immunocytochemistry and quantified by computer image analysis in different segments of the gut. Gastrointestinal transit was significantly accelerated in NOD mice and slower in obese diabetic mice than in controls. The density of duodenal secretin and serotonin as well as colonic PYY and enteroglucagon cells in NOD mice was significantly higher than that of control mice. On the other hand, the density of duodenal secretin and serotonin cells was significantly lower in obese diabetic mice than in controls. It was concluded that changes in duodenal secretin and colonic serotonin, PYY and enteroglucagon cells may play a role in accelerated gastrointestinal transit in NOD mice and delayed gastrointestinal transit in obese diabetic mice.

Centrally applied atrial natriuretic factor diminishes bile secretion in the rat

Little is known about the role of centrally applied peptides in the regulation of bile secretion. We previously reported that the intravenous injection of atrial natriuretic factor (ANF) reduces bile acid dependent flow without affecting portal venous pressure in the rat. In the present work, we studied the effects of centrally applied ANF on bile secretion and the possible pathways involved. Rats were cannulated in the brain lateral ventricle for the administration of 1, 10 and 100 ng/microl ANF. After 1 week, the common bile duct was cannulated and bile samples were collected every 15 min for 60 min after the administration of ANF. The excretion rate of various biliary components was assessed. Bile secretion experiments were also performed after bilateral truncal vagotomy or atropine administration to evaluate the participation of a vagal pathway. In addition, the role of the sympathetic system was addressed by combined administration of propranolol and phentolamine. Centrally applied ANF did not modify blood pressure but diminished bile flow and bile acid output. It also reduced sodium and potassium secretion but did not modify protein or phospholipid excretion. Neither bilateral truncal vagotomy nor atropine administration abolished ANF response. Furthermore, combined administration of adrenergic antagonists did not alter ANF inhibitory effect on bile flow. In conclusion, centrally applied ANF reduced bile acid dependent flow not through a vagal or adrenergic pathway in the rat, suggesting the involvement of a peptidergic pathway.

Neuronal nitric oxide synthase immunoreactivity in the guinea-pig liver: distribution and colocalization with neuropeptide Y and calcitonin gene-related peptide

AIMS/BACKGROUND

The innervation pattern of the guinea-pig liver is similar to that of the human liver. However, many aspects of the distribution of the neuronal isoform of the enzyme nitric oxide synthase (nNOS) in the guinea-pig liver and its colocalization with neuropeptides remain to be elucidated.

METHODS

The distribution of nNOS was studied in fixed guinea-pig liver by light microscopic immunohistochemistry. Confocal analysis was used to determine its colocalization with neuropeptide Y (NPY) or calcitonin gene-related peptide (CGRP).

RESULTS

nNOS-immunoreactive (nNOS-IR) nerves were observed in relation to hilar and interlobar vessels and in Glisson's capsule. A few nNOS-IR ganglia were observed in the extrahepatic bile duct and close to the interlobar portal triads. In addition, nNOS-IR fibers were located in the interlobular portal triads and pervading the parenchyma. Moreover, nNOS-IR nerves were demonstrated for the first time in the larger central veins and in the hepatic vein. nNOS-NPY and nNOS-CGRP colocalizations were detected in the fibromuscular layer of the bile duct and periductal plexus, respectively.

CONCLUSIONS

These results support the phylogenetic conservation of the nNOS-IR hepatic innervation and its possible contribution to the regulation of hepatic blood flow and certain hepatic functions.

Structural examination of tryptase-, and VIP-positive mast cells in the common bile duct of patients with lithiasis

The morphology of tryptase-, and vasoactive intestinal polypeptide (VIP)-positive mast cells was examined immunohistochemically in 38 common bile ducts collected from patients with secondary chronic cholangitis and varying degrees of inflammatory activity. Mast cells numbers in chronic exacerbated and chronic sclerotic cholangitis were significantly higher as compared with those in controls (72.4 cells/mm2 and 25.2 cells/mm2 vs. 5.9 cells/mm2; p < 0.0001, Student's t test). The increased number of tryptase-positive mast cells in chronic exacerbated cholangitis correlated with the severeness of inflammatory infiltration. In cases of chronic exacerbated cholangitis, the increased number of mast cells was detected in conjunction with active fibroplasia. In chronic sclerotic cholangitis mast cells were lower in number as compared with exacerbated cholangitis and were observed in relation with inactive fibrosis. Numerous VIP-positive mast cells were found in all patients with cholangitis. Ultrastructural immunocytochemistry showed tryptase positivity to be localized over either electron-dense or particulate granules with a mean diameter of 0.261+/-0.073 microm or 0.171+/-0.053 microm, respectively. VIP positivity was formed as a finely or coarsely granular pattern over larger electron-dense granules of 0.475+/-0.14 microm in diameter. Tryptase-positive mast cells were located mainly in and around surface and glandular epithelium. The involvement of tryptase- and VIP-positive mast cells in inflammation, fibrosis and epithelial reactions in the common bile duct is discussed.

Gastrointestinal transit in nonobese diabetic mouse: an animal model of human diabetes type 1

Gastrointestinal transit (GI) in the nonobese diabetic (NOD) mouse, an animal model of human diabetes type 1, was examined in animals with short- (duration 1-5 days) and long-term (duration 28-35 days) diabetes. Blood glucose level, serum insulin concentration, and gut neuroendocrine peptide content were also measured. GI was significantly rapid in NOD mice with long-term diabetes (LTD), but was not correlated with blood glucose level, serum insulin concentration, or pancreatic insulin content. GI was correlated with duodenal secretin content, but not with the content of other neuroendocrine peptides in the different segments investigated. Whereas antral vasoactive intestinal peptide (VIP) content in NOD mice with LTD was significantly higher, colonic VIP was lower in NOD mice with short-term diabetes (STD). In the duodenum, whereas the concentration of secretin in NOD mice with both STD and LTD was lower, the gastrin content was higher. Duodenal somatostatin content in NOD mice with LTD was lower. In colon, the content of galanin in NOD mice with LTD was higher than in controls. The decreased content of secretin may be among the factors that cause rapid GI in NOD mice with LTD. Changes in the antral content of VIP, duodenal somatostatin, and colonic galanin in NOD mice with LTD may cause low intestinal secretion and, together with rapid GI, give rise to diarrhoea, which is a common symptom in diabetes.

Immunocytochemical study on the liver innervation in patients with cirrhosis

In the liver, the autonomic nervous system plays an important role in degenerative and inflammatory changes. The aim of the present study was to investigate the distribution of neuronal fibres containing neuropeptides in livers of 5 patients with cirrhosis by immunocytochemical localization at the light and electron microscopical level of substance P (SP), neuropeptide Y (NPY), somatostatin (SOM), and calcitonin gene-related peptide (CGRP). In patients with alcoholic cirrhosis, a decreased number of neuronal fibres was found in the portal tract and fibrous septa as well as in the sinusoids of regenerative nodules. NPY- and SP-immunoreactive neuronal fibres were more numerous than CGRP-containing fibres. They were located mainly in portal tracts. These findings led to the conclusion that peptidergic innervation plays a role in inflammatory and fibrotic changes in cirrhotic liver.

Liver transplantation restores endocrine cells in patients with familial amyloidotic polyneuropathy

BACKGROUND

The aim of this study was to investigate familial amyloidotic polyneuropathy, Portuguese type patients' endocrine cell content in the stomach and duodenum before and after liver transplantation, and to relate the findings to the patients' gastrointestinal disturbances.

METHODS

Ten liver-transplanted familial amyloidotic polyneuropathy, Portuguese type patients and 10 healthy controls were seen. Endocrine cells were identified by immunohistochemistry and quantified with computerized image analysis. The activity of the cells was appraised by measurements of the cell secretory index and nuclear area. Clinical symptoms were obtained from the patients' medical records.

RESULTS

After transplantation, a significant increase of several endocrine cell types were noted, and the pretransplant depletion of several types of endocrine cells disappeared. For no type of endocrine cell was any difference compared with controls noted after transplantation. There was no significant decrease of the amount of amyloid in the biopsies after liver transplantation. The patients' symptoms remained generally unchanged after transplantation, although a substantial time lapse between pretransplant evaluation and transplantation was present.

CONCLUSIONS

Liver transplantation restores the endocrine cells in the upper part of the gastrointestinal tract. The restoration was not correlated with an improvement of the patients' symptoms. No decrease of the amyloid deposits was noted.

Neuroendocrine changes in colon of mice with a disrupted IL-2 gene

Neuroendocrine peptides have a variety of physiological functions in the gastrointestinal tract. This study was carried out to investigate the impact of IL-2 deficiency on the neuroendocrine system in normal colon, and the neuroendocrine changes during colonic inflammation. Mice with homozygous disrupted IL-2 gene (IL-2-/-) spontaneously developed a bowel disease with similarities to human ulcerative colitis. Different types of colonic endocrine cells and myenteric nerves were analysed in the IL-2-/- mice using immunomorphometry. The neuropeptide contents in the colonic tissues were determined by radioimmunoassay. Age-matched healthy IL-2+/- and IL-2+/+ mice served as controls and the colonic IL-2 levels were compared between these two groups of mice by ELISA. Our data showed that less than half the amount of IL-2 was synthesized in the colon of IL-2+/- mice compared with the IL-2+/+ wild-type mice. Two major differences in the neuroendocrine colon were found between the mice with an intact and disrupted IL-2 gene. One was age-related. The frequencies of various endocrine cells and myenteric nerves increased with age in the IL-2+/+ mice. However, no such increases were seen in the mice with a disrupted IL-2 gene. Instead, the volume densities of enteroglucagon, serotonin cells and substance P (SP), vasoactive intestinal polypeptide (VIP) and total myenteric nerves were lower in the older IL-2+/- and IL-2-/- mice compared with the wild type. The other was disease-related. Polypeptide YY (PYY) cells and tissue levels of PYY, SP and VIP were significantly decreased in the IL-2-/- mice during the course of bowel inflammation compared with the healthy IL-2+/- and IL-2+/+ controls. These findings indicate that colonic neuroendocrine alterations did occur in the mice with a disrupted IL-2 gene and diminished local IL-2 level, suggesting a role of IL-2 in the regulation of the neuroendocrine system and a prevalent interaction between the immune and neuroendocrine systems in normal colon. On the other hand, there were some changes that seemed to correlate with the bowel inflammatory process. They might be associated with the impaired function in inflamed gut and contribute to the development and/or prolongation of disease.