Kazuyuki Narimatsu

Free cholesterol accumulation in hepatic stellate cells: Mechanism of liver fibrosis aggravation in nonalcoholic steatohepatitis in mice

Although nonalcoholic steatohepatitis (NASH) is associated with hypercholesterolemia, the underlying mechanisms of this association have not been clarified. We aimed to elucidate the precise role of cholesterol in the pathophysiology of NASH. C57BL/6 mice were fed a control, high‐cholesterol (HC), methionine‐choline‐deficient (MCD), or MCD+HC diet for 12 weeks or a control, HC, high‐fat (HF), or HF+HC diet for 24 weeks. Increased cholesterol intake accelerated liver fibrosis in both the mouse models without affecting the degree of hepatocellular injury or Kupffer cell activation. The major causes of the accelerated liver fibrosis involved free cholesterol (FC) accumulation in hepatic stellate cells (HSCs), which increased Toll‐like receptor 4 protein (TLR4) levels through suppression of the endosomal‐lysosomal degradation pathway of TLR4, and thereby sensitized the cells to transforming growth factor (TGF)β‐induced activation by down‐regulating the expression of bone morphogenetic protein and activin membrane‐bound inhibitor. Mammalian‐cell cholesterol levels are regulated by way of a feedback mechanism mediated by sterol regulatory element‐binding protein 2 (SREBP2), maintaining cellular cholesterol homeostasis. Nevertheless, HSCs were sensitive to FC accumulation because the high intracellular expression ratio of SREBP cleavage‐activating protein (Scap) to insulin‐induced gene (Insig) disrupted the SREBP2‐mediated feedback regulation of cholesterol homeostasis in these cells. HSC activation subsequently enhanced the disruption of the feedback system by Insig‐1 down‐regulation. In addition, the suppression of peroxisome proliferator‐activated receptor γ signaling accompanying HSC activation enhanced both SREBP2 and microRNA‐33a signaling. Consequently, FC accumulation in HSCs increased and further sensitized these cells to TGFβ‐induced activation in a vicious cycle, leading to exaggerated liver fibrosis in NASH. Conclusion: These characteristic mechanisms of FC accumulation in HSCs are potential targets to treat liver fibrosis in liver diseases including NASH. (Hepatology 2014;58:154–169)

Acyl-CoA:cholesterol acyltransferase 1 mediates liver fibrosis by regulating free cholesterol accumulation in hepatic stellate cells

BACKGROUND & AIMS Acyl-coenzyme A: cholesterol acyltransferase (ACAT) catalyzes the conversion of free cholesterol (FC) to cholesterol ester, which prevents excess accumulation of FC. We recently found that FC accumulation in hepatic stellate cells (HSCs) plays a role in progression of liver fibrosis, but the effect of ACAT1 on liver fibrosis has not been clarified. In this study, we aimed to define the role of ACAT1 in the pathogenesis of liver fibrosis. METHODS ACAT1-deficient and wild-type mice, or Toll-like receptor 4 (TLR4)(-/-)ACAT1(+/+) and TLR4(-/-)ACAT1(-/-) mice were subjected to bile duct ligation (BDL) for 3 weeks or were given carbon tetrachloride (CCl4) for 4 weeks to induce liver fibrosis. RESULTS ACAT1 was the major isozyme in mice and human primary HSCs, and ACAT2 was the major isozyme in mouse primary hepatocytes and Kupffer cells. ACAT1 deficiency significantly exaggerated liver fibrosis in the mouse models of liver fibrosis, without affecting the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation. ACAT1 deficiency significantly increased FC levels in HSCs, augmenting TLR4 protein and downregulating expression of transforming growth factor-β (TGFβ) pseudoreceptor Bambi (bone morphogenetic protein and activin membrane-bound inhibitor), leading to sensitization of HSCs to TGFβ activation. Exacerbation of liver fibrosis by ACAT1 deficiency was dependent on FC accumulation-induced enhancement of TLR4 signaling. CONCLUSIONS ACAT1 deficiency exaggerates liver fibrosis mainly through enhanced FC accumulation in HSCs. Regulation of ACAT1 activities in HSCs could be a target for treatment of liver fibrosis.

Trans fatty acids exacerbate dextran sodium sulphate-induced colitis by promoting the up-regulation of macrophage-derived proinflammatory cytokines involved in T helper 17 cell polarization

Numerous reports have shown that a diet containing large amounts of trans fatty acids (TFAs) is a major risk factor for metabolic disorders. Although recent studies have shown that TFAs promote intestinal inflammation, the underlying mechanisms are unknown. In this study, we examined the effects of dietary fat containing TFAs on dextran sodium sulphate (DSS)‐induced colitis. C57 BL/6 mice were fed a diet containing 1·3% TFAs (mainly C16:1, C18:1, C18:2, C20:1, C20:2 and C22:1), and then colitis was induced with 1·5% DSS. Colonic damage was assessed, and the mRNA levels of proinflammatory cytokines and major regulators of T cell differentiation were measured. The TFA diet reduced survival and exacerbated histological damage in mice administered DSS compared with those fed a TFA‐free diet. The TFA diet significantly elevated interleukin (IL)‐6, IL‐12p40, IL‐23p19 and retinoic acid‐related orphan receptor (ROR)γt mRNA levels in the colons of DSS‐treated animals. Moreover, IL‐17A mRNA levels were elevated significantly by the TFA diet, with or without DSS treatment. We also examined the expression of proinflammatory cytokines in lipopolysaccharide (LPS)‐stimulated RAW264.7 cells and peritoneal macrophages. These cells were exposed to TFAs (linoelaidic acid or elaidic acid) with or without LPS and the mRNA levels of various cytokines were measured. IL‐23p19 mRNA levels were increased significantly by TFAs in the absence of LPS. Cytokine expression was also higher in LPS‐stimulated cells exposed to TFAs than in unexposed LPS‐stimulated cells. Collectively, our results suggest that TFAs exacerbate colonic inflammation by promoting Th17 polarization and by up‐regulating the expression of proinflammatory cytokines in the inflamed colonic mucosa.

Involvement of autotaxin/lysophospholipase D expression in intestinal vessels in aggravation of intestinal damage through lymphocyte migration

Lysophosphatidic acid (LPA) has a critical role in lymphocyte migration to secondary lymphoid organs. Autotaxin (ATX)/lysophospholipase D, in the vascular endothelium, is the main enzyme involved in LPA production. Whether ATX is involved in pathological lymphocyte migration to the inflamed mucosa has not been studied. We investigated the involvement of ATX in inflammatory bowel disease patients and two murine models of colitis. Tissue samples were obtained by intestinal biopsies from patients with Crohn’s disease and those with ulcerative colitis with informed consent. ATX immunoreactivity was colocalized with MAdCAM-1-positive high-endothelial-like vessels, close to sites of lymphocyte infiltration. Enhanced expression of ATX mRNA was observed in the inflamed mucosa from Crohn’s disease and ulcerative colitis patients. ATX mRNA expression level was remarkably higher in the actively inflamed mucosa than in the quiescent mucosa in the same patient. In the T-cell-transferred mouse model, ATX mRNA expression level gradually increased as colitis developed. In the dextran sodium sulfate mouse model, the expression level was considerably higher in colonic mucosa of chronically developed colitis than in colonic mucosa of acute colitis. Administration of an ATX inhibitor, bithionol, remarkably decreased lymphocyte migration to the intestine and ameliorated both dextran sodium sulfate-induced colitis and CD4-induced ileocolitis. In transwell assays, administration of bithionol or 1-bromo-3(s)-hydroxy-4-(palmitoyloxy) butylphosphonate (BrP-LPA) significantly decreased transmigration of splenocytes through high-endothelial-like vessels induced by TNF-α. We conclude that enhanced expression of ATX in the active mucosa has been implicated in the pathophysiology of inflammatory bowel disease through enhancing aberrant lymphocyte migration to the inflamed mucosa.

Magnetic resonance enterocolonography in detecting erosion and redness in intestinal mucosa of patients with Crohn's disease

In Crohns disease (CD), assessment of disease activity and extension is important for clinical management. Endoscopy is the most reliable tool for evaluating disease activity in these patients and it distinguishes between lesions based on ulcer, erosion, and redness. Magnetic resonance imaging (MRI) is less invasive than endoscopy; however, the sensitivity of MRI in detecting lesions is believed to be lower, and whether MRI can detect milder lesions has not been studied. The aim of this study was to compare the detection ability of magnetic resonance enterocolonography (MREC) with ileocolonic endoscopy in patients with CD.

Dietary lipids and sweeteners regulate glucagon-like peptide-2 secretion

Glucagon-like peptide-2 (GLP-2) is a potent intestinal growth factor derived from enteroendocrine L cells. Although food intake is known to increase GLP-2 secretion, its regulatory mechanisms are largely unknown as a result of its very short half-life in venules. The aims of this study were to compare the effects of luminal nutrients on the stimulation of GLP-2 secretion in vivo using lymph samples and to clarify the involvement of the sweet taste receptor in this process in vitro. Lymph samples were collected from the thoracic duct after bolus administration of dietary lipids or sweetening agents into the duodenum of rats. Human enteroendocrine NCI-H716 cells were also used to compare the effects of various nutrients on GLP-2 secretion. GLP-2 concentrations were measured by ELISA in vivo and in vitro. GLP-2 secretion was enhanced by polyunsaturated fatty acid- and monounsaturated fatty acid-rich dietary oils, dietary carbohydrates, and some kinds of sweeteners in rats; this effect was reproduced in NCI-H716 cells using α-linolenic acid (αLA), glucose, and sweeteners. GLP-2 secretion induced by sweetening agents was inhibited by lactisole, a sweetness-antagonizing inhibitor of T1R3. In contrast, lactisole was unable to inhibit GLP-2 secretion induced by αLA alone. Our results suggested that fatty acid- and sweetener-induced GLP-2 secretion may be mediated by two different pathways, with the sweet taste receptor involved in the regulation of the latter.

1,4-Dihydroxy-2-naphthoic acid from Propionibacterium freudenreichii reduces inflammation in interleukin-10-deficient mice with colitis by suppressing macrophage-derived proinflammatory cytokines

The anti‐inflammatory mechanism of prebiotics has recently been shown to have an impact on the host immune system. DHNA from Propionibacterium freudenreichii is known to promote the proliferation of Bifidobacterium and can ameliorate colitis, although its mode of action remains unknown. In this study, we investigated whether DHNA attenuates inflammation in piroxicam‐treated IL‐10−/− mice, particularly focusing on the changes of the host immune mechanism. DHNA was administered to IL‐10−/− mice with colitis, and the expression of adhesion molecules and mRNA levels of proinflammatory cytokines were determined. DHNA pretreatment attenuated the piroxicam‐induced histological changes. The increased F4/80‐positive cell infiltration and VCAM‐1 expression were decreased by DHNA administration. The increased mRNA levels of proinflammatory cytokines were also suppressed by DHNA. In in vitro experiments, increased mRNA levels of proinflammatory cytokines after endotoxin exposure were decreased significantly by DHNA pretreatment in RAW264.7, a macrophage cell line, and IL‐10−/− mice BMMs, whereas the expression of VCAM‐1 in bEnd.3 cells, a endothelial cell line, was not affected. Taken together, these findings suggest that administration of DHNA is useful for the treatment of colitis in piroxicam‐treated IL‐10−/− mice and that attenuation of colitis by DHNA may partly be a result of its direct action on intestinal macrophages to inhibit proinflammatory cytokine production.

Toll-like receptor (TLR) 2 agonists ameliorate indomethacin-induced murine ileitis by suppressing the TLR4 signaling.

Few drugs have been found satisfactory in the treatment of nonsteroidal anti‐inflammatory drugs (NSAIDs)‐induced enteropathy. Toll‐like receptor (TLR) 4 and aberrant leukocyte migration to the intestinal mucosa are reported to be involved in the pathology of intestinal enteropathy and TLR2 agonists have been found to evoke hyposensitivity to TLR4 stimulation in vitro. In this study, we investigated whether and how lipoarabinomannan (LAM) or lipoteichoic acid (LTA), TLR2 agonists, attenuated indomethacin (IND)‐induced intestinal damage.

Phlebosclerotic colitis that was difficult to distinguish from collagenous colitis

Phlebosclerotic colitis is a rare and recently known disease entity and its etiology is still to be elucidated. Some phlebosclerotic colitis cases are difficult to distinguish from collagenous colitis because of the similarity of pathological findings. In all Japanese case reports of phlebosclerotic colitis in which an association with the use of Chinese herbal medicine is suspected, sansisi (gardenia fruit) was included, suggesting pathogenesis of this disease. We report a case of phlebosclerotic colitis that wasdifficult to be distinguished from collagenous colitis, and an association with the use of Chinese herbal medicine was suspected as the cause of the disease.

FFA2 activation combined with ulcerogenic COX inhibition induces duodenal mucosal injury via the 5-HT pathway in rats

Serotonin (5-HT), predominantly synthesized and released by enterochromaffin cells, is implicated in gastrointestinal symptoms such as emesis, abdominal pain, and diarrhea. Because luminal short-chain fatty acids (SCFAs) release 5-HT from enterochromaffin cells, which express the SCFA receptor free fatty acid receptor 2 (FFA2) in rat duodenum, we examined the effects of the selective FFA2 agonist phenylacetamide-1 (PA1) on duodenal 5-HT release with consequent bicarbonate secretion [duodenal bicarbonate secretion (DBS)] and on indomethacin (IND)-induced enteropathy. Intestinal injury was induced by IND (10 mg/kg sc) with or without PA1. We measured DBS in vivo in a duodenal loop perfused with PA1 while measuring 5-HT released in the portal vein. Duodenal blood flow was measured by laser-Doppler flowmetry. IND induced small intestinal ulcers with duodenal sparing. PA1 given with IND (IND + PA1) dose dependently induced duodenal erosions. IND + PA1-induced duodenal lesions were inhibited by the FFA2 antagonist GLPG-0974, ondansetron, or omeprazole but not by RS-23597 or atropine. Luminal perfusion of PA1 augmented DBS accompanied by increased portal blood 5-HT concentrations with approximately eight times more release at 0.1 mM than at 1 µM, with the effects inhibited by coperfusion of GLPG-0974. Luminal PA1 at 1 µM increased, but at 0.1 mM diminished, duodenal blood flow. Cosuperfusion of PA1 (0.1 mM) decreased acid-induced hyperemia, further reduced by IND pretreatment but restored by ondansetron. These results suggest that, although FFA2 activation enhances duodenal mucosal defenses, FFA2 overactivation during ulcerogenic cyclooxygenase inhibition may increase the vulnerability of the duodenal mucosa to gastric acid via excessive 5-HT release and 5-HT3 receptor activation, implicated in foregut-related symptoms such as emesis and epigastralgia.NEW & NOTEWORTHY Luminal free fatty acid receptor 2 agonists stimulate enterochromaffin cells and release serotonin, which enhances mucosal defenses in rat duodenum. However, overdriving serotonin release with high luminal concentrations of free fatty acid 2 ligands such as short-chain fatty acids injures the mucosa by decreasing mucosal blood flow. These results are likely implicated in serotonin-related dyspeptic symptom generation because of small intestinal bacterial overgrowth, which is hypothesized to generate excess SCFAs in the foregut, overdriving serotonin release from enterochromaffin cells.