Glycoprotein metabolism in dimethylnitrosamine induced hepatic fibrosis in rats

Molecular pathogenesis of metabolic dysfunction-associated steatotic liver disease, steatohepatitis, hepatic fibrosis and liver cirrhosis

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by intense deposition of fat globules in the hepatic parenchyma that could potentially progress to liver cirrhosis and hepatocellular carcinoma. Here, we evaluated a rat model to study the molecular pathogenesis of the spectrum of MASLD and to screen therapeutic agents. SHRSP5/Dmcr rats were fed a high-fat and cholesterol (HFC) diet for a period of 12 weeks and evaluated for the development of steatosis (MASLD), steatohepatitis, fibrosis and cirrhosis. A group of animals were sacrificed at the end of the 4th, 6th, 8th and 12th weeks from the beginning of the experiment, along with the control rats that received normal diet. Blood and liver samples were collected for biochemical and histopathological evaluations. Immunohistochemical staining was performed for α-SMA and Collagen Type I. Histopathological examinations demonstrated steatosis at the 4th week, steatohepatitis with progressive fibrosis at the 6th week, advanced fibrosis with bridging at the 8th week and cirrhosis at the 12th week. Biochemical markers and staining for α-SMA and Collagen Type I demonstrated the progression of steatosis to steatohepatitis, hepatic fibrosis and liver cirrhosis in a stepwise manner. Control animals fed a normal diet did not show any biochemical or histopathological alterations. The results of the present study clearly demonstrated that the HFC diet-induced model of steatosis, steatohepatitis, hepatic fibrosis and cirrhosis is a feasible, quick and appropriate animal model to study the molecular pathogenesis of the spectrum of MASLD and to screen potent therapeutic agents.

Therapeutic implication of human placental extract to prevent liver cirrhosis in rats with metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) is always accompanied with hepatic fibrosis that could potentially progress to liver cirrhosis and hepatocellular carcinoma. Employing a rat model, we evaluated the role of human placental extract (HPE) to arrest the progression of hepatic fibrosis to cirrhosis in patients with MASH. SHRSP5/Dmcr rats were fed with a high-fat and high-cholesterol diet for 4 weeks and evaluated for the development of steatosis. The animals were divided into control and treated groups and received either saline or HPE (3.6 ml/kg body weight) subcutaneously thrice a week. A set of animals were killed at the end of 6th, 8th, and 12th weeks from the beginning of the experiment. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), hepatic malondialdehyde (MDA), and glutathione content were measured. Immunohistochemical staining was performed for α-smooth muscle actin (α-SMA), 4-hydroxy-2-nonenal (4-HNE), collagen type I, and type III. Control rats depicted progression of liver fibrosis at 6 weeks, advanced fibrosis and bridging at 8 weeks, and cirrhosis at 12 weeks, which were significantly decreased in HPE-treated animals. Treatment with HPE maintained normal levels of MDA and glutathione in the liver. There was marked decrease in the staining intensity of α-SMA, 4-HNE, and collagen type I and type III in HPE treated rats compared with control animals. The results of the present study indicated that HPE treatment mediates immunotropic, anti-inflammatory, and antioxidant responses and attenuates hepatic fibrosis and early cirrhosis. HPE depicts therapeutic potential to arrest the progression of MASH towards cirrhosis.

Epigallocatechin-3-gallate inhibits osteopontin expression and prevents experimentally induced hepatic fibrosis

Osteopontin (OPN) is a matricellular cytokine and a stress-induced profibrogenic molecule that promotes activation of stellate cells during the pathogenesis of hepatic fibrosis. We studied the protective effects of epigallocatechin-3-gallate (EGCG) to suppress oxidative stress, inhibit OPN expression, and prevent experimentally induced hepatic fibrosis. Liver injury was induced with intraperitoneal injections of N-nitrosodimethylamine (NDMA) in a dose of 1 mg/100 g body weight on 3 consecutive days of a week for 28 days. A group of rats received 0.2 mg EGCG/100 g body weight orally everyday during the study. The animals were sacrificed on day 28th from the beginning of exposure. Serum levels of AST, ALT, OPN, malondialdehyde, collagen type IV, and hyaluronic acid were measured. Immunohistochemistry and/or real-time PCR were performed for α-SMA, 4-HNE, OPN, collagen type I, and type III. Serial administrations of NDMA produced well developed fibrosis and early cirrhosis in rat liver. Treatment with EGCG significantly reduced serum/plasma levels of AST, ALT, OPN, malondialdehyde, collagen type IV, and hyaluronic acid and prevented deposition of collagen fibers in the hepatic tissue. Protein and/or mRNA levels demonstrated marked decrease in the expression of α-SMA, 4-HNE, OPN, collagen type I, and type III. Treatment with EGCG prevented excessive generation of reactive oxygen species, suppressed oxidative stress, significantly reduced serum and hepatic OPN levels, and markedly attenuated hepatic fibrosis. The results indicated that EGCG could be used as a potent therapeutic agent to prevent hepatic fibrogenesis and related adverse events.

Metabolism of N-nitrosodimethylamine, methylation of macromolecules, and development of hepatic fibrosis in rodent models

Hepatic fibrosis and cirrhosis are chronic diseases affecting liver and a major health problem throughout the world. The hallmark of fibrosis and cirrhosis is inordinate synthesis and deposition of fibril forming collagens in the extracellular matrix of the liver leading to nodule formation and loss of normal architecture. Hepatic stellate cells play a crucial role in the pathogenesis and progression of liver fibrosis through secretion of several potent fibrogenic factors that trigger hepatocytes, portal fibrocytes, and bone marrow-derived fibroblasts to synthesize and deposit several connective tissue proteins, especially collagens between hepatocytes and space of Disse. Regulation of various events involved in the activation and transformation of hepatic stellate cells seems to be an appropriate strategy for the arrest of hepatic fibrosis and liver cirrhosis. In order to unravel the molecular mechanisms involved in the pathogenesis and progression of hepatic fibrosis, to determine proper and potent targets to arrest fibrosis, and to discover powerful therapeutic agents, a quick and reproducible animal model of hepatic fibrosis and liver cirrhosis that display all decompensating features of human condition is required. This review thoroughly evaluates the biochemical, histological, and pathological features of N-nitrosodimethylamine-induced model of liver injury, hepatic fibrosis, and early cirrhosis in rodents.

Alteration of Trace Elements during Pathogenesis of N-Nitrosodimethylamine Induced Hepatic Fibrosis

The biochemical abnormalities and oxidative stress during pathogenesis of hepatic fibrosis could lead to alteration of trace elements. We studied the alteration of major trace elements during the pathogenesis of N-nitrosodimethylamine (NDMA)-induced hepatic fibrosis in rats. The biochemical and pathological indices of liver functions and hepatic fibrosis were evaluated. Serum and liver levels of copper, iron and zinc were determined using atomic absorption spectrophotometry. Cobalt, manganese, and molybdenum in the serum and liver were estimated by inductively coupled plasma mass spectrometry. Serial administrations of NDMA resulted in decreased serum albumin, biochemical abnormalities, increase of total liver collagen, and well-developed fibrosis and early cirrhosis. Serum and liver zinc content significantly decreased on all the days following NDMA administration. When copper and molybdenum markedly increased in the serum, liver molybdenum decreased dramatically. Both iron and manganese content significantly increased in the liver following NDMA-induced fibrosis. The results of the present study indicate that alteration of trace elements during pathogenesis of hepatic fibrosis is due to metabolic imbalance, biochemical abnormalities, decreased serum albumin, and ascites following NDMA-induced liver injury. The modulation of trace elements during hepatic fibrosis could play a prominent role in progression of the disease.

Molecular mechanisms in the pathogenesis of N-nitrosodimethylamine induced hepatic fibrosis

Hepatic fibrosis is marked by excessive synthesis and deposition of connective tissue proteins, especially interstitial collagens in the extracellular matrix of the liver. It is a result of an abnormal wound healing in response to chronic liver injury from various causes such as ethanol, viruses, toxins, drugs, or cholestasis. The chronic stimuli involved in the initiation of fibrosis leads to oxidative stress and generation of reactive oxygen species that serve as mediators of molecular events involved in the pathogenesis of hepatic fibrosis. These processes lead to cellular injury and initiate inflammatory responses releasing a variety of cytokines and growth factors that trigger activation and transformation of resting hepatic stellate cells into myofibroblast like cells, which in turn start excessive synthesis of connective tissue proteins, especially collagens. Uncontrolled and extensive fibrosis results in distortion of lobular architecture of the liver leading to nodular formation and cirrhosis. The perpetual injury and regeneration process could also results in genomic aberrations and mutations that lead to the development of hepatocellular carcinoma. This review covers most aspects of the molecular mechanisms involved in the pathogenesis of hepatic fibrosis with special emphasize on N-Nitrosodimethylamine (NDMA; Dimethylnitorsmaine, DMN) as the inducing agent.

MMP-13 deletion decreases profibrogenic molecules and attenuates N-nitrosodimethylamine-induced liver injury and fibrosis in mice

Connective tissue growth factor (CTGF) is involved in inflammation, pathogenesis and progression of liver fibrosis. Matrix metalloproteinase‐13 (MMP‐13) cleaves CTGF and releases several fragments, which are more potent than the parent molecule to induce fibrosis. The current study was aimed to elucidate the significance of MMP‐13 and CTGF and their downstream effects in liver injury and fibrosis. Hepatic fibrosis was induced using intraperitoneal injections of N‐nitrosodimethylamine (NDMA) in doses of 10 μg/g body weight on three consecutive days of each week over a period of 4 weeks in both wild‐type (WT) and MMP‐13 knockout mice. Administration of NDMA resulted in marked elevation of AST, ALT, TGF‐β1 and hyaluronic acid in the serum and activation of stellate cells, massive necrosis, deposition of collagen fibres and increase in total collagen in the liver of WT mice with a significant decrease in MMP‐13 knockout mice. Protein and mRNA levels of CTGF, TGF‐β1, α‐SMA and type I collagen and the levels of MMP‐2, MMP‐9 and cleaved products of CTGF were markedly increased in NDMA‐treated WT mice compared to the MMP‐13 knockout mice. Blocking of MMP‐13 with CL‐82198 in hepatic stellate cell cultures resulted in marked decrease of the staining intensity of CTGF as well as protein levels of full‐length CTGF and its C‐terminal fragments and active TGF‐β1. The data demonstrate that MMP‐13 and CTGF play a crucial role in modulation of fibrogenic mediators and promote hepatic fibrogenesis. Furthermore, the study suggests that blocking of MMP‐13 and CTGF has potential therapeutic implications to arrest liver fibrosis.

Propolis reduces Leishmania amazonensis-induced inflammation in the liver of BALB/c mice

Experimental models of mouse paw infection with L. amazonensis show an induction of a strong inflammatory response in the skin, and parasitic migration may occur to secondary organs with consequent tissue injury. There are few studies focusing on the resolution of damage in secondary organs caused by Leishmania species-related cutaneous leishmaniasis. We investigated the propolis treatment effect on liver inflammation induced by Leishmania amazonensis infection in the mouse paw. BALB/c mice were infected in the hind paw with L. amazonensis (10(7)) promastigote forms. After 15 days, animals were treated daily with propolis (5 mg/kg), Glucantime (10 mg/kg), or with propolis plus Glucantime combined. After 60 days, mice were euthanized and livers were collected for inflammatory process analysis. Liver microscopic analysis showed that propolis reduced the inflammatory process compared to untreated infected control. There was a decrease of liver myeloperoxidase and N-acetyl-β-glucosaminidase activity levels, collagen fiber deposition, pro-inflammatory cytokine production, and plasma aspartate transaminase and alanine transaminase levels. Furthermore, propolis treatment enhanced anti-inflammatory cytokine levels and reversed hepatosplenomegaly. Our data demonstrated that daily low doses of Brazilian propolis reduced the secondary chronic inflammatory process in the liver caused by L. amazonensis subcutaneous infection in a susceptible mice strain.

Role of fibrogenic and inflammatory cytokines in HCV-induced fibrosis

HCV is one of the main causative agents of liver fibrosis and hepatocellular carcinoma. Liver inflammation resulting from HCV infection triggers fibrosis. In HCV-related fibrosis, differentiated hepatic stellate cells (HSCs) known as myofibroblasts participate in the fibrogenic and inflammatory response. TGF-β1 and CTGF, released from these HSCs, have been implicated as master cytokines mediating HCV induced hepatic fibrosis. PDGF is another potent mitogen, which facilitates the progression of liver fibrosis by enhancing the proliferation and migration of HSCs. In addition to these major cytokines, the release of TNF-α, IL-6, IL-1b and IL-10 by immune cells also promotes the effect of HCV induced fibrosis. Targeting these cytokines may offer the potential for treatments to prevent or cure fibrosis.

Pterostilbene inhibits dimethylnitrosamine-induced liver fibrosis in rats

Pterostilbene, found in grapes and berries, exhibits pleiotropic effects, including anti-inflammatory, antioxidant, and anti-proliferative activities. This study was conducted to investigate the effect of pterostilbene on liver fibrosis and the potential underlying mechanism for such effect. Sprague-Dawley rats were intraperitoneally given dimethyl n-nitrosamine (DMN) (10mg/kg) 3 days per week for 4 weeks. Pterostilbene (10 or 20mg/kg) was administered by oral gavage daily. Liver function, morphology, histochemistry, and fibrotic parameters were examined. Pterostilbene supplementation alleviated the DMN-induced changes in the serum levels of alanine transaminase and aspartate transaminase (p<0.05). Fibrotic status and the activation of hepatic stellate cells were improved upon pterostilbene supplementation as evidenced by histopathological examination as well as the expression of α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), and matrix metalloproteinase 2 (MMP2). These data demonstrated that pterostilbene exhibited hepatoprotective effects on experimental fibrosis, potentially by inhibiting the TGF-β1/Smad signaling.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

Molecular pathogenesis of hepatic fibrosis and current therapeutic approaches

The pathogenesis of hepatic fibrosis involves significant deposition of fibrilar collagen and other extracellular matrix proteins. It is a rather dynamic process of wound healing in response to a variety of persistent liver injury caused by factors such as ethanol intake, viral infection, drugs, toxins, cholestasis, and metabolic disorders. Liver fibrosis distorts the hepatic architecture, decreases the number of endothelial cell fenestrations and causes portal hypertension. Key events are the activation and transformation of quiescent hepatic stellate cells into myofibroblast-like cells with the subsequent up-regulation of proteins such as α-smooth muscle actin, interstitial collagens, matrix metalloproteinases, tissue inhibitor of metalloproteinases, and proteoglycans. Oxidative stress is a major contributing factor to the onset of liver fibrosis and it is typically associated with a decrease in the antioxidant defense. Currently, there is no effective therapy for advanced liver fibrosis. In its early stages, liver fibrosis is reversible upon cessation of the causative agent. In this review, we discuss some aspects on the etiology of liver fibrosis, the cells involved, the molecular pathogenesis, and the current therapeutic approaches.

Effect of fluoride exposure on serum glycoprotein pattern and sialic acid level in rabbits

This study describes the effects of fluoride exposure on the protein profile, glycoprotein pattern, and total sialic acid concentration of serum in rabbits. For this aim; 20 healthy New Zealand rabbits were used. The rabbits were divided into two equal groups each with ten animals according to their weighing: control group and experimental group. The rabbits in control group were given drinking tap water containing 0.29 mg/l sodium fluoride and experimental group received the same tap water to which was added 40 mg/l sodium fluoride for 70 days. Blood samples were taken from each rabbit on day 70. Serum fluoride concentrations were measured by a fluoride-specific ion electrode in serum. The fluoride levels in the serum were found as 18.4 (+/-1.58) microg/L in control and 301.3 (+/-52.18) microg/L in fluoride exposed rabbits. The sialic acid levels were found as 69.2 (+/-0.32) mg/dL in control and 43.4 (+/-0.13) mg/dL in fluoride exposed group. The electrophoretic patterns of serum proteins, glycoproteins, and total sialic acid concentration were determined. Fifteen different protein fractions with molecular weights ranging from 22 to 249 kDa were displayed in the serum protein electrophoretic gel of both groups. The raw concentrations of the protein fractions decreased in fluoride exposed rabbits as compared with the control rabbits. The serum glycoprotein pattern revealed seven major protein bands from 47 to 167 kDa in experimental and control groups. The slight decrease of raw concentration of the protein bands in glycoprotein pattern of serum was observed in fluoride toxication comparing to control. The results suggest that serum TSA determination and serum protein electrophoresis can be used to evaluate prognosis of fluoride exposure as a supplementary laboratory test in combination with clinical and other laboratory findings of fluorosis.

Epigallocatechin-3-gallate exhibits anti-fibrotic effect by attenuating bleomycin-induced glycoconjugates, lysosomal hydrolases and ultrastructural changes in rat model pulmonary fibrosis

Pulmonary fibrosis is characterized by excessive deposition of extracellular matrix components in the alveolar space, which hampers normal respiration process. Pathophysiological enzymes, glycoprotein moieties and matrix degrading lysosomal hydrolases are key markers and play a crucial role in the progression of fibrosis. Bleomycin is an anti-neoplastic drug, used for the treatment of various types of cancers and induces pulmonary fibrosis due its deleterious side effect. Tea catechin epigallocatechin-3-gallate (EGCG) is known for its wide array of beneficial effects. The present study was intended to evaluate the beneficial efficacy of EGCG against bleomycin-induced glycoconjugates, lysosomal hydrolases and ultrastructural changes in the lungs of Wistar rats. Intratracheal instillation of bleomycin (6.5 U/kg body weight) to rats increased the activities of pathophysiological enzymes such as aspartate transaminase, alanine transaminase, lactate dehydrogenase and alkaline phosphatase, which were attenuated upon EGCG treatment. The increased level of hydroxyproline and histopathological parameters in bleomycin-induced rats were decreased upon EGCG treatment. Bleomycin-induced increase in the level of glycoconjugates was restored closer to normal levels on EGCG treatment. Furthermore, the increased activities of matrix degrading lysosomal enzymes in bleomycin-induced rats were reduced upon EGCG supplementation. Treatment with EGCG also attenuated bleomycin-induced ultrastructural changes as observed from transmission electron microscopy studies. The results of the present study put-forward EGCG as a potential anti-fibrotic agent due to its attenuating effect on potential fibrotic markers.

Operculina turpethum attenuates N-nitrosodimethylamine induced toxic liver injury and clastogenicity in rats

The root extract of Operculina turpethum (OTE) has been used as an anti-inflammatory, purgative, and hepato-protective agent. N-Nitrosodimethylamine (NDMA) is a potent hepatotoxin that induces fibrosis of the liver. In the present study, we examined the therapeutic effects of OTE root extract against NDMA-induced hepatotoxicity and clastogenicity in rats. Hepatic fibrosis was induced in adult male albino rats through serial intraperitoneal administrations of NDMA at a concentration of 10mg/kg body weight on three consecutive days of each week over a period of three weeks. A group of rats received OTE orally in doses of 75, 150 and 200mg/kg body weight at 5h after the administration of NDMA. The controls and treated animals were sacrificed on days-7, 14 and 21 after the start of the administration of NDMA. The progression of hepatic fibrosis as well as the amelioration effect of OTE was evaluated through histopathologically as well as by immunohistochemical staining for the activation of hepatic stellate cells. Alterations in serum and liver biochemical parameters and LDH isoenzymes were also studied. Serial administration of NDMA resulted in well formed fibrosis in the liver and induction of micronuclei in the bone marrow cells. Staining of alpha-SMA demonstrated activated stellate cells from day-7 onwards which was dramatically increased on day-21. An elevation of micronuclei count, liver function enzymes, serum hydroxyproline levels and LDH isoenzymes 4 and 5 were also observed. All these changes were remarkably reduced in OTE administered animals and fibrogenesis was completely absent. Our results suggest that OTE has hepatoprotective and anti-clastogenic effects against NDMA-induced hepatic fibrosis. Therefore OTE may be used as a hepatoprotective agent against various liver diseases including toxic liver injury.

Elevated serum β-glucuronidase reflects hepatic lysosomal fragility following toxic liver injury in rats

The level of serum β-glucuronidase increases in various pathological conditions, including liver disorders. The aim of this investigation was to study the changes in liver lysosomal membrane stability during experimentally induced hepatic fibrosis that may result in the elevation of serum β-glucuronidase. Liver injury was induced by intraperitoneal injections of N-nitrosodimethylamine (NDMA) in adult male albino rats over 3 weeks. The progression of fibrosis was evaluated histopathologically as well as by monitoring liver collagen content. Lipid peroxides and β-glucuronidase levels were measured in the liver homogenate and subcellular fractions on days 0, 7, 14, and 21 after the start of NDMA administration. Serum β-glucuronidase levels were also determined. A significant increase was observed in β-glucuronidase levels in the serum, liver homogenate, and subcellular fractions, but not in the nuclear fraction on days 7, 14, and 21 after the start of NDMA administration. Lipid peroxides also increased in the liver homogenate and the lysosomal fraction. The measurement of lysosomal membrane stability revealed a maximum lysosomal fragility on day 21 during NDMA-induced fibrosis. In vitro studies showed that NDMA has no significant effect on liver lysosomal membrane permeability. The results of this investigation demonstrated that lysosomal fragility increases during NDMA-induced hepatic fibrosis, which could be attributed to increased lipid peroxidation of lysosomal membrane. In this study, we also elucidated the mechanism of increased β-glucuronidase and other lysosomal glycohydrolases in the serum during hepatic fibrosis.

siRNA-mediated knockdown of connective tissue growth factor prevents N-nitrosodimethylamine-induced hepatic fibrosis in rats

Hepatic fibrosis is a dynamic process that involves the interplay of different cell types in the hepatic tissue. Connective tissue growth factor (CTGF) is a highly profibrogenic molecule and plays a crucial role in the pathogenesis of hepatic fibrosis. The aim of the present investigation was three-fold. First, we studied the expression of CTGF in the cultured hepatic stellate cells using immunohistochemical technique. Second, we induced hepatic fibrosis in rats through serial intraperitoneal injections of N-nitrosodimethylamine (NDMA; dimethylnitrosamine, DMN) and studied the upregulation of CTGF and TGF-beta1 during hepatic fibrogenesis. Third, we downregulated CTGF expression using CTGF siRNA and examined the role of CTGF siRNA to prevent the progression of NDMA-induced hepatic fibrosis. The results depicted strong staining of CTGF in the transformed hepatic stellate cells in culture. Serial administrations of NDMA resulted in activation of hepatic stellate cells, upregulation of CTGF and TGF-beta1 both at mRNA and protein levels and well-developed fibrosis in the liver. Immunostaining, Western blot analysis, semiquantitative and real-time RT-PCR studies showed downregulation of CTGF and TGF-beta1 after treatment with CTGF siRNA. The results of the present study demonstrated that CTGF gene silencing through siRNA reduces activation of hepatic stellate cells, prevents the upregulation of CTGF and TGF-beta1 gene expression and inhibits accumulation of connective tissue proteins in the liver. The data further suggest that knockdown of CTGF upregulation using siRNA has potential therapeutic application to prevent hepatic fibrogenesis.

Mineral metabolism in dimethylnitrosamine-induced hepatic fibrosis

OBJECTIVES

Complications such as ascites during the pathogenesis of hepatic fibrosis and cirrhosis may lead to several abnormalities in mineral metabolism. In the present investigation, we have monitored serum and liver concentrations of calcium, magnesium, sodium and potassium during experimentally induced hepatic fibrosis in rats.

DESIGN AND METHODS

The liver injury was induced by intraperitoneal injections of dimethylnitrosamine (DMN; N-nitrosodimethylamine, NDMA) in doses 1 mg/100 g body weight on 3 consecutive days of each week over a period of 21 days. Calcium, magnesium, sodium and potassium were measured by atomic absorption spectrophotometry in the serum and liver on days 7, 14 and 21 after the start of DMN administration.

RESULTS

Negative correlations were observed between liver function tests and serum mineral levels, except with albumin. Calcium, magnesium, potassium and sodium concentrations in the serum were decreased after the induction of liver injury. The liver calcium content was increased after DMN treatment. No change occurred in liver sodium content. However, magnesium and potassium content was significantly reduced in the hepatic tissue.

CONCLUSIONS

The results suggest that DMN-induced hepatic fibrosis plays certain role in the alteration of essential elements. The low levels of albumin and the related ascites may be one of the major causes of the imbalance of mineral metabolism in hepatic fibrosis and further aggravation of the disease.

Serum hyaluronan and hyaluronidase: very early markers of toxic liver injury

BACKGROUND

Dimethylnitrosamine (DMN), a potent hepatotoxin, administered to rats, provides a convenient model for toxic liver injury. Indicators of early liver injury are important clinically, for surveillance, for screening new drugs that are potentially hepatotoxic and for identifying drugs that protect against liver injury. Both cirrhosis and wound healing culminate in deposition of fibrous connective tissue and scarring. Increased hyaluronan (HA) occurs in the earliest stage of wound healing. Hyaluronidase, the enzyme that degrades hyaluronan, is also elevated whenever rapid turnover of hyaluronan occurs. We test the hypothesis that elevated levels of circulating hyaluronan and hyaluronidase could provide indicators of very early liver damage.

METHODS

Dimethylnitrosamine was administered to adult male albino rats by intraperitoneal injections for 7 consecutive days.

RESULTS

Increased serum hyaluronan levels observed on day 2 reached a maximum on day 4. Hyaluronidase was elevated on the first day and reached a maximum on day 2 that was 30-times control levels. Hyaluronan-specific staining in liver sections was maximal on day 7, occurring predominantly in portal triads and in sinusoidal spaces. Individual hepatocytes were slightly enlarged and contained intracellular hyaluronan, which was not evident in control sections. Though circulating hyaluronan levels had decreased after day 4, continued hyaluronan staining persisted in liver sections through day 21. Conventional indicators of liver injury, such as serum aminotransferase enzymes, did not reach a peak until day 7. Conventional gross and histopathological changes, including severe centrilobular congestion and hemorrhagic necrosis, were observed only after day 7. Both hyaluronan and hyaluronidase are indicators of very early liver damage in the dimethylnitrosamine-treated rat, occurring well before conventional indicators appear, or before overt histopathologic changes of liver damage can be seen. However, levels are increased only transiently, indicating that serial assays are necessary.

CONCLUSIONS

Measures of circulating hyaluronidase activity may be used to assess liver damage.

Expression of hyaluronic acid in N-nitrosodimethylamine induced hepatic fibrosis in rats

Hyaluronic acid (HA) plays prominent role in the pathogenesis of liver fibrosis. The mechanism of increased serum and liver HA during hepatic fibrosis was studied in rats. Liver injury was induced by intraperitoneal injections of N-nitrosodimethylamine (NDMA) for 7 consecutive days. A group of animals were sacrificed on everyday during injection and also on days 14 and 21 after the start of NDMA administration. The alpha-smooth muscle actin (alpha-SMA) was stained as a marker for activated stellate cells. Liver HA was studied by histochemical methods and serum HA was monitored by HA binding protein assay. CD44 was stained immunohistochemically. After the start of NDMA administration, necrosis was initiated on day 3 and massive necrosis was observed on days 5 and 7. Fibrosis was developed on day 14 and early cirrhosis was present on day 21. Staining of alpha-SMA demonstrated activated stellate cells from day 3 onwards. Serum HA peaked on day 7 and reduced afterwards. Serial liver sections stained for HA revealed excessive accumulation of HA during NDMA administration. On days 14 and 21, alpha-SMA and HA staining was remarkable in fibrotic and cirrhotic areas. CD44 staining was negative except during necrosis. It is concluded that the early elevation of serum HA is due to the increased synthesis and simultaneous release from the necrotic liver. In latter stages the increase of both serum and liver HA is contributed by the increased synthesis by the activated stellate cells and reduced clearance by the impaired sinusoidal endothelial cells.

Ascorbic acid concentrations in dimethylnitrosamine-induced hepatic fibrosis in rats

BACKGROUND

Ascorbic acid is a potent antioxidant and is involved in many metabolic activities including collagen biosynthesis. In the present investigation, ascorbic acid and lipid peroxides were monitored in the blood and liver samples during the progression of experimentally induced hepatic fibrosis.

METHODS

Liver injury was induced by intraperitoneal injections of dimethylnitrosamine (DMN) on three consecutive days of every week over a period of 21 days. The progression of fibrosis was assessed by histopathological examination and by monitoring of the collagen content of the liver tissue. Ascorbic acid and lipid peroxides were monitored in both blood and liver samples on days 0, 7, 14, and 21 after the start of DMN administration. The liver total protein was also measured during the investigation.

RESULTS

Histopathological examination demonstrated centrilobular necrosis, fibrosis, and early cirrhosis during DMN treatment. The collagen content increased four-fold on the 21st day of investigation. Lipid peroxides were elevated significantly in both blood and liver specimens on days 7, 14, and 21. A drastic decrease was observed in the ascorbic acid concentrations in both liver and blood samples on all days after the start of DMN administration. Liver total protein concentrations were significantly reduced during DMN administration.

CONCLUSIONS

The exact mechanism of the decrease of ascorbic acid during DMN-induced hepatic fibrosis is not clear. The most probable reason for the decreased blood and liver ascorbic acid during DMN-induced hepatic fibrosis is the increased utilization of ascorbic acid for free radical scavenging in order to reduce the highly elevated oxidative stress.

Dimethylnitrosamine-induced liver injury in rats: the early deposition of collagen

Dimethylnitrosamine (DMN) is a potent hepatotoxin that can cause fibrosis of the liver. It's ability to provide a suitable rapid experimental murine model for early human cirrhosis was examined. The drug was administered to adult male albino rats in order to document sequential pathological and biochemical alterations. Injury was produced by intraperitoneal injections of DMN on three consecutive days of each week over a 3-week period. A rapid increase in collagen content was documented, with linear increases occurring from days 7 to 21. Livers were examined for histopathological changes on days 7, 14 and 21 following the beginning of exposure. Severe centrilobular congestion and haemorrhagic necrosis could be observed on day 7. Centrilobular necrosis and intense neutrophilic infiltration were observed on day 14. By day 21, collagen fiber deposition could be observed, together with severe centrilobular necrosis, with focal fatty changes, bile duct proliferation, bridging necrosis and fibrosis surrounding the central veins. A decrease in total protein and increase in DNA were also documented. DMN-induced liver injury in rats appears to be a potential animal model for early human cirrhosis and the rapid deposition of collagen, and may serve as a convenient procedure for screening antifibrotic agents.

Biochemical abnormalities during the progression of hepatic fibrosis induced by dimethylnitrosamine

OBJECTIVES

The pathogenesis of hepatic fibrosis is accompanied with several biochemical and metabolic abnormalities. To obtain more information about the alteration of biochemical and metabolic parameters during alcoholic liver fibrosis, we have monitored the changes of certain important biochemical compounds in experimentally induced hepatic fibrosis.

DESIGN AND METHODS

The liver injury was induced in adult male albino rats by using dimethylnitrosamine (DMN) in doses of 1 mg/100 g body weight. Total collagen, total protein, cholesterol, lipid peroxides, glucose, urea, and inorganic phosphorus were monitored in liver and blood/serum samples on Days 0, 7, 14, and 21 after the start of DMN administration. Serum insulin levels were assayed by radioimmunoassay. The serum and urinary levels of hydroxyproline, uric acid, and creatinine were also monitored.

RESULTS

The total collagen content in the liver was increased about 4-fold by Day 21 after the start of DMN administration. A significant increase was observed in lipid peroxide levels in both liver and blood samples. Although inorganic phosphorus level decreased in both serum and liver tissue, cholesterol was lowered only in the serum. Increased serum insulin level with impaired glucose tolerance was observed after 21 days. Serum hydroxyproline level increased throughout after the start of DMN administration. The urinary excretion of hydroxyproline was also significantly increased with a striking elevation on Day 7. Elevated uric acid levels were recorded in serum and urine samples during the latter periods of DMN treatment. No alteration was observed in blood urea and creatinine levels.

CONCLUSIONS

The results of the present investigation demonstrated important alterations in metabolic parameters and biochemical abnormalities during experimentally induced liver damage. All alterations are compatible with the deterioration of liver functions during the pathogenesis of hepatic fibrosis.

A canine model of multiple portosystemic shunting

The objective of this study was to develop and describe an experimental canine model of multiple acquired portosystemic shunts (PSS) similar in nature to spontaneously occurring PSS. Sixteen dogs were used and were divided into a control (n = 6) and a diseased group (n = 10). Dogs of the diseased group were administered dimethylnitrosamine (2 mg/kg of body weight, po) twice weekly, and clinicopathologic, ultrasonographic, and hepatic scintigraphic findings were recorded during the development of hepatic disease and PSS. Surgery was then performed to permit visual verification of multiple shunts, catheter placement for portography examination, and biopsy of the liver. All diseased dogs developed severe hepatic disease and multiple PSS as documented visually at surgery and on portography. Based on this study, dimethylnitrosamine-induced portosystemic shunting appears to be an appropriate model for spontaneously occurring multiple PSS secondary to portal hypertension.

Glycoprotein composition in cyclophosphamide-induced lung fibrosis

The present study investigated the glycosylation state of proteins in lung tissue of a cyclophosphamide-induced model of pulmonary fibrosis in rats. In fibrotic lung, the carbohydrate constituents (total hexose, fucose, sialic acid and hexosamine) of salt-soluble, collagenase, elastase and papain digested glycoproteins were significantly higher compared to normal lungs. Interestingly, fibrotic lung tissues had higher activities of mannosyl, glucosyl, galactosyl, sialyl and fucosyl transferases than normal lung tissues. Similarly, mannosyl, glucosyl, galactosyl, sialyl and fucosyl transferases were higher in serum from rats with fibrosis than in that from normals. These data indicate that glycoprotein metabolism is significantly altered from normal in animals with interstitial lung fibrosis.