Significance of chymase-dependent angiotensin II formation in the progression of human liver fibrosis

Chymase as a Possible Therapeutic Target for Amelioration of Non-Alcoholic Steatohepatitis

The development and progression of non-alcoholic steatohepatitis (NASH) are linked to oxidative stress, inflammation, and fibrosis of the liver. Chymase, a chymotrypsin-like enzyme produced in mast cells, has various enzymatic actions. These actions include activation of angiotensin II, matrix metalloproteinase (MMP)-9, and transforming growth factor (TGF)-β, which are associated with oxidative stress, inflammation, and fibrosis, respectively. Augmentation of chymase activity in the liver has been reported in various NASH models. Generation of hepatic angiotensin II and related oxidative stress is upregulated in NASH but attenuated by treatment with a chymase inhibitor. Additionally, increases in MMP-9 and accumulation of inflammatory cells are observed in NASH but are decreased by chymase inhibitor administration. TGF-β and collagen I upregulation in NASH is also attenuated by chymase inhibition. These results in experimental NASH models demonstrate that a chymase inhibitor can effectively ameliorate NASH via the reduction of oxidative stress, inflammation, and fibrosis. Thus, chymase may be a therapeutic target for amelioration of NASH.

Mast Cells in Liver Fibrogenesis

Mast cells (MCs) are immune cells of the myeloid lineage that are present in the connective tissue throughout the body and in mucosa tissue. They originate from hematopoietic stem cells in the bone marrow and circulate as MC progenitors in the blood. After migration to various tissues, they differentiate into their mature form, which is characterized by a phenotype containing large granules enriched in a variety of bioactive compounds, including histamine and heparin. These cells can be activated in a receptor-dependent and -independent manner. Particularly, the activation of the high-affinity immunoglobulin E (IgE) receptor, also known as FcεRI, that is expressed on the surface of MCs provoke specific signaling cascades that leads to intracellular calcium influx, activation of different transcription factors, degranulation, and cytokine production. Therefore, MCs modulate many aspects in physiological and pathological conditions, including wound healing, defense against pathogens, immune tolerance, allergy, anaphylaxis, autoimmune defects, inflammation, and infectious and other disorders. In the liver, MCs are mainly associated with connective tissue located in the surrounding of the hepatic arteries, veins, and bile ducts. Recent work has demonstrated a significant increase in MC number during hepatic injury, suggesting an important role of these cells in liver disease and progression. In the present review, we summarize aspects of MC function and mediators in experimental liver injury, their interaction with other hepatic cell types, and their contribution to the pathogenesis of fibrosis.

High Fib4 index in patients with suspected NASH is associated with elevation of chymase-dependent angiotensin II-forming activity in circulating mononuclear leucocytes

Fatal hepatic disease is closely related to non-alcoholic fatty liver disease, especially non-alcoholic steatohepatitis (NASH). NASH is associated with cardiovascular events because it develops on the background of lifestyle-related diseases. Chymase-dependent angiotensin II-forming activity (dAIIFA) in circulating mononuclear leucocytes (CML) is a marker of local angiotensin II production and inflammation. This study investigated the association between CML chymase dAIIFA and NASH. Cardiovascular outpatients were recruited and the Fib4 index (F4I) was calculated. Patients with an F4I > 2.67 were classified into the high F4I group and these patients were strongly suspected to have NASH, while patients with an F4I < 1.30 were classified into the low F4I group. Patient background factors were compared between these groups. CML chymase dAIIFA was measured by ELISA using Nma/Dnp-modified angiotensin I. Among 499 patients, 16% were classified into the high F4I group. Compared with the low F4I group, the high F4I group had a significantly higher age, pancytopenia, more frequent diabetes mellitus, lower diastolic blood pressure, lower estimated glomerular filtration rate, higher brain natriuretic peptide, lower plasma aldosterone concentration, higher total AIIFA, higher CML chymase dAIIFA, and higher pulse wave velocity. Contrary to expectations, the body mass index, triglycerides, and low-density lipoprotein cholesterol were relatively low in the high F4I group. Many cardiovascular outpatients have a high F4I and can probably be categorized as NASH. The high F4I patients had few features of metabolic syndrome and were suspected to have elevated tissue chymase dAIIFA contributing to inflammation in the liver as well as in cardiovascular organs.

Chymase Inhibitor as a Novel Therapeutic Agent for Non-alcoholic Steatohepatitis

Non-alcoholic steatohepatitis (NASH) is characterized by inflammation and fibrosis, in addition to steatosis, of the liver, but no therapeutic agents have yet been established. The mast cell protease chymase can generate angiotensin II, matrix metalloproteinase-9 and transforming growth factor-β, all of which are associated with liver inflammation or fibrosis. In animal models of NASH, augmented chymase has been observed in the liver. In histological analysis, chymase inhibitor prevented hepatic steatosis, inflammation, and fibrosis. Chymase inhibitor also attenuated the augmentation of angiotensin II, matrix metalloproteinase-9, and transforming growth factor-β observed in the liver of NASH. Oxidative stress, inflammatory markers, and collagen were attenuated by chymase inhibition. Moreover, chymase inhibitor showed a mitigating effect on established NASH, and survival rates were significantly increased by treatment with chymase inhibitor. In this review, we propose that chymase inhibitor has potential as a novel therapy for NASH.

A novel hamster nonalcoholic steatohepatitis model induced by a high-fat and high-cholesterol diet

Nonalcoholic steatohepatitis (NASH), in which there is steatosis and fibrosis in the liver, is linked to metabolic syndrome and progresses to hepatic cirrhosis. In this study, a novel hamster NASH model derived from metabolic syndrome was made using hamsters. Hamsters were fed a normal or a high-fat and high-cholesterol (HFC) diet for 12 weeks. Body weight and the ratio of liver weight to body weight were significantly greater in HFC diet-fed hamsters than in normal diet-fed hamsters. Triglyceride, low-density lipoprotein cholesterol, and glucose levels in blood were significantly increased in HFC diet-fed hamsters, and blood pressure also tended to be high, suggesting that the HFC diet-fed hamsters developed metabolic syndrome. Hepatic steatosis and fibrosis were observed in liver sections of HFC diet-fed hamsters, as in patients with NASH, but they were not seen in normal diet-fed hamsters. Chymase generates angiotensin II and transforming growth factor (TGF)-β, both of which are related to hepatic steatosis and fibrosis, and a significant augmentation of chymase activity was observed in livers from HFC diet-fed hamsters. Both angiotensin II and TGF-β were also significantly increased in livers of HFC diet-fed hamsters. Thus, HFC diet-fed hamsters might develop metabolic syndrome-derived NASH that clinically resembles that in NASH patients.

Chymase inhibitor prevents the development and progression of non-alcoholic steatohepatitis in rats fed a high-fat and high-cholesterol diet

The effect of the chymase inhibitor TY-51469 on the development and progression of non-alcoholic steatohepatitis (NASH) was evaluated in rats fed a high-fat and high-cholesterol (HFC) diet. To evaluate the preventive effect of TY-51469 on the development of NASH, stroke-prone spontaneously hypertensive rat 5 (SHRSP5)/Dmcr rats were fed either a normal or HFC diet for 8 weeks, and concurrently administered either placebo or TY-51469 (1 mg/kg per day). To evaluate the effect of TY-51469 on the survival rate, TY-51469 was administered either concurrently with HFC diet (pretreated group) or 8 weeks after HFC diet at which point NASH had developed (posttreated group). Eight weeks after HFC diet, significant increases of steatosis, fibrosis and chymase-positive cells were observed in liver from the placebo-treated rats. Significant increases of myeloperoxidase, transforming growth factor-β, matrix metalloproteinase-9, and collagen I mRNA levels were also observed. However, all parameters were significantly attenuated in the TY-51469-treated group. A survival rate of the placebo-treated group fed the HFC diet was 0% at 14 weeks. In comparison, the rates of TY-51469-pretreated and TY-51469-posttreated groups were 100% and 50% at 14 weeks, respectively. Chymase inhibitor may be applicable to preventing the development and progression of NASH.

Role of Chymase in the Development of Liver Cirrhosis and Its Complications: Experimental and Human Data

Background

Tissue Angiotensin II (Ang-II), produced through local non ACE-dependent pathways, stimulates liver fibrogenesis, renal vasoconstriction and sodium retention.

Aim

To highlight chymase-dependent pathway of Ang-II production in liver and kidney during cirrhosis development.

Methods

Liver histology, portal pressure, liver and kidney function, and hormonal status were investigated in rat liver cirrhosis induced through 13 weeks of CCl₄, with or without chymase inhibitor SF2809E, administered between 4^th and 13^th CCl₄ weeks; liver and kidney chymase immunolocation and Ang-II content were assessed. Chymase immunohistochemistry was also assessed in normal and cirrhotic human liver, and chymase mRNA transcripts were measured in human HepG2 cells and activated hepatic stellate cells (HSC/MFs) in vitro.

Results

Rats receiving both CCl₄ and SF2809E showed liver fibrotic septa focally linking portal tracts but no cirrhosis, as compared to ascitic cirrhotic rats receiving CCl₄. SF2809E reduced portal pressure, plasma bilirubin, tissue content of Ang-II, plasma renin activity, norepinephrine and vasopressin, and increased glomerular filtration rate, water clearance, urinary sodium excretion. Chymase tissue content was increased and detected in α-SMA-positive liver myofibroblasts and in kidney tubular cells of cirrhotic rats. In human cirrhosis, chymase was located in hepatocytes of regenerative nodules. Human HepG2 cells and HSC/MFs responded to TGF-β1 by up-regulating chymase mRNA transcription.

Conclusions

Chymase, through synthesis of Ang-II and other mediators, plays a role in the derangement of liver and kidney function in chronic liver diseases. In human cirrhosis, chymase is well-represented and apt to become a future target of pharmacological treatment.

Expression of recombinant human mast cell chymase with Asn-linked glycans in glycoengineered Pichia pastoris

Recombinant human mast cell chymase (rhChymase) was expressed in secreted form as an active enzyme in the SuperMan5 strain of GlycoSwitch® Pichia pastoris, which is engineered to produce proteins with (Man)5(GlcNAc)2 Asn-linked glycans. Cation exchange and heparin affinity chromatography yielded 5mg of active rhChymase per liter of fermentation medium. Purified rhChymase migrated on SDS-PAGE as a single band of 30 kDa and treatment with peptide N-glycosidase F decreased this to 25 kDa, consistent with the established properties of native human chymase (hChymase). Polyclonal antibodies against hChymase detected rhChymase by Western blot. Active site titration with Eglin C, a potent chymase inhibitor, quantified the concentration of purified active enzyme. Kinetic analyses with succinyl-Ala-Ala-Pro-Phe (suc-AAPF) p-nitroanilide and thiobenzyl ester synthetic substrates showed that heparin significantly reduced KM, whereas heparin effects on kcat were minor. Pure rhChymase with Asn-linked glycans closely resembles hChymase. This bioengineering approach avoided hyperglycosylation and provides a source of active rhChymase for other studies as well as a foundation for production of recombinant enzyme with human glycosylation patterns.

Chymase inhibitor ameliorates hepatic steatosis and fibrosis on established non-alcoholic steatohepatitis in hamsters fed a methionine- and choline-deficient diet

AIM

Chymase plays a role in the augmentation of angiotensin II formation, which is involved in liver fibrosis. The therapeutic effects of a chymase inhibitor, TY-51469, on established hepatic steatosis and fibrosis were investigated in a model of developed non-alcoholic steatohepatitis.

METHODS

Hamsters were fed a normal diet or methionine- and choline-deficient (MCD) diet for 12 weeks. Then, treatment with TY-51469 (1 mg/kg per day) or placebo was initiated, and the treatment was continued concurrently with the MCD diet for an additional 12 weeks.

RESULTS

At 12 weeks after initiating the MCD diet, marked hepatic steatosis and fibrosis were observed in MCD diet-fed hamsters. Malondialdehyde and gene expression levels of collagen I, collagen III, α-smooth muscle actin (α-SMA) and Rac-1 in liver extracts were also increased in the MCD-diet-fed hamsters at 12 weeks. At 24 weeks, hepatic steatosis and fibrosis were more prominent in the placebo-treated hamsters that were fed the MCD-diet for 24 weeks versus 12 weeks. Hamsters treated with TY-51469 for 12 weeks after being on a 12-week MCD diet had significant ameliorations in both hepatic steatosis and fibrosis, and there were no significant differences compared to normal diet-fed hamsters. There were significant augmentations in angiotensin II and malondialdehyde, and gene expressions of collagen I, collagen III, α-SMA and Rac-1 in the placebo-treated hamsters at 24 weeks; however, these levels were reduced to normal levels in the TY-51469-treated hamsters.

CONCLUSION

TY-51469 not only prevented the progression of hepatic steatosis and fibrosis, but also ameliorated hepatic steatosis and fibrosis.

An assessment of mast cells and myofibroblasts in denture-induced fibrous hyperplasia

OBJECTIVES

The pathogenesis of denture-induced fibrous hyperplasias has not been examined in detail to explain how tissue injury results in fibrous hyperplasia of the oral mucosa.

PATIENTS AND METHODS

We examined the presence of mast cells and myofibroblasts in 33 denture-induced fibrous hyperplasias (DIFH) compared with 10 healthy gingival tissues. The parameters examined included mast cell numbers, tissue distribution, degranulation, and cell subtypes using immunohistochemistry. The presence of myofibroblasts and their likely origin was also examined by double immunofluorescense staining. Furthermore, we investigated the synthesis of osteopontin and TGF-β, considered to be involved in the transformation of a fibroblast to a myofibroblast.

RESULTS

The results demonstrated that the mast cell numbers are significantly increased in the DIFH compared with non-disease controls. The mast cell localization in lesions was higher in the superficial areas with inflammatory cell infiltration compared with the deep fibrotic area (P < 0.01). The number of tryptase-positive mast cells was significantly higher compared with chymase-positive ones. The TGF-β- or osteopontin-positive cell infiltration into the lesion was found in high numbers. The presence of myofibroblasts was identified in 14 of 33 cases (42%), and some of these cells showed apoptosis when assessed by the TUNEL assay. On the survey of the origin of myofibroblasts, results showed αSMA and vimentin positivity indicating these transformed from fibroblasts.

CONCLUSION

These results are the first to show that mast cells and myofibroblasts can be detected in DIFH, indicating important roles of these cells in the pathogenesis of this lesion.

Expression of angiotensinogen during hepatic fibrogenesis and its effect on hepatic stellate cells

BACKGROUND

The liver renin-angiotensin system (RAS) plays an important role in promoting the development of hepatic fibrogenesis. Angiotensinogen (AGT) is an important precursor in tissue RAS. This study aimed to investigate the expression and cellular source of AGT in hepatic fibrogenesis and its effect on proliferation and collagen metabolism of hepatic stellate cells.

MATERIAL/METHODS

In a rat carbon tetrachloride (CCl4)-induced liver fibrosis model the mRNA expression of AGT was determined by real-time PCR and the cellular source of AGT was determined by immunohistochemical staining. In vitro HSC-T6 cells were transfected with AGT, and the expression plasmid, AGT shRNA plasmid and negative shRNA plasmid were constructed. Real-time PCR and ELISA were applied to determine the mRNA expressions and contents of TIMP-1, TGF-β1, type I collagen and type III collagen of the cells or in the supernatants.

RESULTS

Compared to normal liver, the AGT and α-SMA mRNA expressions increased at the early stage of hepatic fibrosis and decreased in hepatic cirrhosis. The expressions of AGT and α-SMA mRNA were correlated with the hepatic fibrosis (r=0.915, P=0.03). Immunohistochemistry demonstrated the activated HSCs were the main source of AGT due to colocalization of AGT and α-SMA expressions. The mRNA and protein of TGF-β1, TIMP-1, type I collagen and type III collagen were markedly up-regulated.

CONCLUSIONS

ACEI and angiotensin II type 1 receptor antagonist (AT1RA) could attenuate the progression of hepatic fibrosis in the early stage. Direct inhibition of AGT from aHSCs may become an effective antifibrotic anti-liver fibrosis strategy.

Chymase-dependent generation of angiotensin II from angiotensin-(1-12) in human atrial tissue

Since angiotensin-(1-12) [Ang-(1-12)] is a non-renin dependent alternate precursor for the generation of cardiac Ang peptides in rat tissue, we investigated the metabolism of Ang-(1-12) by plasma membranes (PM) isolated from human atrial appendage tissue from nine patients undergoing cardiac surgery for primary control of atrial fibrillation (MAZE surgical procedure). PM was incubated with highly purified ¹²⁵I-Ang-(1-12) at 37°C for 1 h with or without renin-angiotensin system (RAS) inhibitors [lisinopril for angiotensin converting enzyme (ACE), SCH39370 for neprilysin (NEP), MLN-4760 for ACE2 and chymostatin for chymase; 50 µM each]. ¹²⁵I-Ang peptide fractions were identified by HPLC coupled to an inline γ-detector. In the absence of all RAS inhibitor, ¹²⁵I-Ang-(1-12) was converted into Ang I (2±2%), Ang II (69±21%), Ang-(1-7) (5±2%), and Ang-(1-4) (2±1%). In the absence of all RAS inhibitor, only 22±10% of ¹²⁵I-Ang-(1-12) was unmetabolized, whereas, in the presence of the all RAS inhibitors, 98±7% of ¹²⁵I-Ang-(1-12) remained intact. The relative contribution of selective inhibition of ACE and chymase enzyme showed that ¹²⁵I-Ang-(1-12) was primarily converted into Ang II (65±18%) by chymase while its hydrolysis into Ang II by ACE was significantly lower or undetectable. The activity of individual enzyme was calculated based on the amount of Ang II formation. These results showed very high chymase-mediated Ang II formation (28±3.1 fmol × min⁻¹ × mg⁻¹, n = 9) from ¹²⁵I-Ang-(1-12) and very low or undetectable Ang II formation by ACE (1.1±0.2 fmol×min⁻¹ × mg⁻¹). Paralleling these findings, these tissues showed significant content of chymase protein that by immunocytochemistry were primarily localized in atrial cardiac myocytes. In conclusion, we demonstrate for the first time in human cardiac tissue a dominant role of cardiac chymase in the formation of Ang II from Ang-(1-12).

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

A review of mast cells and liver disease: What have we learned?

BACKGROUND

Mast cells are recognized as diverse and highly complicated cells. Aside from their notorious role in allergic inflammatory reactions, mast cells are being implicated in numerous disease processes from heart disease to cancer. Mast cells have been implicated in liver pathogenesis including hepatitis and host allograft rejection after liver transplantation.

AIMS

The aim of this review is to discuss the traditional function of mast cells, their location and anatomy with regards to hepatic vasculature and the role of mast cells in hepatic diseases including liver regeneration and rejection. Finally, we will touch on the role of mast cells in liver cancer. In conclusion, we hope that the reader comes away with a better understanding of the diverse and potential role(s) that mast cells may play in liver pathologies.

Chymase inhibition attenuates tetrachloride-induced liver fibrosis in hamsters

AIM

Chymase converts angiotensin I to angiotensin II, which may promote the development of liver fibrosis. In this study, whether a chymase inhibitor TY-51469 attenuated tetrachloride (CCl(4))-induced liver fibrosis was examined.

METHODS

Liver fibrosis was induced by the s.c. injection of 1 mL/kg of CCl(4) twice weekly for 8 weeks, and each hamster was given TY-51469 (1 mg/kg per day) or placebo. Untreated hamsters were used as a control group.

RESULTS

Significant increases of serum alanine aminotransferase, total bilirubin and hyaluronic acid levels were observed in the placebo-treated group compared with the control group, but these levels were significantly attenuated in the TY-51469-treated group. Liver chymase activity was significantly higher in the placebo-treated group than in the control group, whereas the activity in the TY51469-treated group was not. Total angiotensin II-forming activity in the liver was also significantly higher in the placebo-treatedgroup than in the control group or the TY-51469-treated group. The ratio of the fibrotic area to the total area in the liver was significantly higher in the placebo-treated group than in the control group, but the ratio was significantly lower in the TY-51469-treated group than in the placebo-treated group. A significant decrease in the number of alpha-smooth muscle actin (SMA)-positive cells was seen in the TY-51469-treated group compared to the placebo-treated group.

CONCLUSION

Significant correlations between the number of chymase-positive cells and the degree of fibrosis and between the numbers of chymase-positive cells and alpha-SMA-positive cells were observed. Thus, chymase inhibition may be a useful strategy for preventing liver fibrosis.

New approaches to blockade of the renin-angiotensin-aldosterone system: chymase as an important target to prevent organ damage

Chymase plays a crucial role in angiotensin II formation in various tissues. Angiotensin II induces gene expression of transforming growth factor (TGF)-beta and matrix metalloproteinase (MMP)-9 precursors, and chymase can convert precursors of TGF-beta and MMP-9 to their active forms. In cultured fibroblasts, significant increases in cell growth and TGF-beta levels were observed after chymase injection; these increases were inhibited by a chymase inhibitor, but not by an angiotensin II-receptor blocker. In apolipoprotein E-deficient mice, abdominal aortic aneurysm (AAA) development depends on an increase in MMP-9 activities induced by angiotensin II infusion, but the inhibition of MMP-9 activation by a chymase inhibitor resulted in attenuation of the angiotensin II-induced AAA development. The upregulation of MMP-9 and TGF-beta levels is involved in damage to various organs, but these gene expressions are not completely induced by angiotensin II alone. Therefore, chymase inhibition may be useful for attenuating MMP-9 and TGF-beta levels, in addition to reducing angiotensin II formation, and this function may provide powerful organ protection. In this review, we propose the possible use of chymase inhibitors as agents to prevent organ damage.

Chymase inhibitor prevents the nonalcoholic steatohepatitis in hamsters fed a methionine- and choline-deficient diet

AIM

Mast cells may be involved in the pathogenesis of nonalcoholic steatohepatitis (NASH). The mast cell protease chymase contributes to the formation of angiotensin II and matrix metalloproteinase (MMP)-9, both of which are intimately involved in liver fibrosis. Therefore, we hypothesized that chymase plays an important role in the development of NASH.

METHODS

Hamsters were fed a methionine- and choline-deficient (MCD) diet for 8 weeks. These animals were divided into two groups and received either TY-51469 (1 mg/kg per day) or placebo. A third group was fed a normal diet as a control.

RESULTS

Total plasma bilirubin, triglycerides, and hyaluronic acid levels were significantly higher in the MCD diet-fed hamsters than in the normal diet-fed hamsters, but the levels were significantly lower in chymase inhibitor-treated MCD diet-fed hamsters than in placebo-treated MCD diet-fed hamsters. Using histological analysis, marked steatosis and fibrosis were observed in MCD diet-fed hamsters, but these changes were significantly attenuated by treatment with the chymase inhibitor. Increases in mast cells and chymase-positive cells were observed in the liver after the MCD diet, but the increases disappeared in the chymase inhibitor-treated group. The significant increase observed in chymase activity in liver tissue extract from the MCD diet-fed group was also reduced by treatment with the chymase inhibitor. Chymase inhibition significantly reduced not only angiotensin II expression but also matrix metallopeptidase 9 activity in MCD diet-fed hamsters.

CONCLUSION

These findings demonstrate that the mast cell protease chymase may play a crucial role in the development of NASH in hamsters.

TGF-beta and mesenchymal hepatic involvement after visceral leishmaniasis

The liver involvement in the human visceral leishmaniasis (VL) has been related to parasitism and activated Kupffer cells with further occasional fibrotic alterations, especially after long-term disease without treatment. However, fibrotic alterations have been reported after therapy, whose clinical finding is the persistence of hepatomegaly. Fibrotic involvement of the liver after therapy was never well understood, and the aim of this study was to evaluate this finding through ultrastructural and morphometric analysis. A case-control study was performed with 20 patients (15 cases and five controls). Cases included patients with persistent hepatomegaly (residual) after treatment of VL submitted to liver biopsy to exclude other causes of liver enlargement, including serum tests of viral hepatitis. The material was evaluated by electron microscopy allowing ultrastructural with morphometric analysis of medium portion of hepatic lobule. Narrow sinusoidal lumen and prominent Kupffer cells were found with insignificant alterations of hepatocytes, pit, and endothelial cells. On ultrastructural analysis, the enlargement of the space of Disse was due to fibrous collagen, increase of number of Ito cells, and nonfibrous extracellular matrix that were associated with Kupffer cells enlargement. Immunohistochemistry showed an intense expression of TGF-beta in patients with VL. These findings suggest a production of TGF-beta by Kupffer cells that resulted in the characteristic fibrotic involvement of the liver. Residual hepatomegaly in visceral leishmaniasis could result from sustained Kupffer cell activation with perihepatocytic fibrosis.

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.