Fascioliasis: role of proline in bile duct hyperplasia

Fasciolosis: pathogenesis, host-parasite interactions, and implication in vaccine development

Fasciola hepatica is distributed worldwide, causing substantial economic losses in the animal husbandry industry. Human fasciolosis is an emerging zoonosis in Andean America, Asia, and Africa. The control of the disease, both in humans and animals, is based on using anthelmintic drugs, which has resulted in increased resistance to the most effective anthelmintics, such as triclabendazole, in many countries. This, together with the concerns about drug residues in food and the environment, has increased the interest in preventive measures such as a vaccine to help control the disease in endemic areas. Despite important efforts over the past two decades and the work carried out with numerous vaccine candidates, none of them has demonstrated consistent and reproducible protection in target species. This is at least in part due to the high immunomodulation capacity of the parasite, making ineffective the host response in susceptible species such as ruminants. It is widely accepted that a deeper knowledge of the host-parasite interactions is needed for a more rational design of vaccine candidates. In recent years, the use of emerging technologies has notably increased the amount of data about these interactions. In the present study, current knowledge of host-parasite interactions and their implication in Fasciola hepatica vaccine development is reviewed.

Pathogenicity and virulence of the liver flukes Fasciola hepatica and Fasciola Gigantica that cause the zoonosis Fasciolosis

Fasciolosis caused by the liver flukes Fasciola hepatica and Fasciola gigantica is one of the most important neglected parasitic diseases of humans and animals. The ability of the parasites to infect and multiply in their intermediate snail hosts, and their adaptation to a wide variety of mammalian definitive hosts contribute to their high transmissibility and distribution. Within the mammalian host, the trauma caused by the immature flukes burrowing through the liver parenchyma is associated with most of the pathogenesis. Similarly, the feeding activity and the physical presence of large flukes in the bile ducts can lead to anemia, inflammation, obstruction and cholangitis. The high frequency of non-synonymous polymorphisms found in Fasciola spp. genes allows for adaptation and invasion of a broad range of hosts. This is also facilitated by parasite’s excretory-secretory (ES) molecules that mediate physiological changes that allows their establishment within the host. ES contains cathepsin peptidases that aid parasite invasion by degrading collagen and fibronectin. In the bile ducts, cathepsin-L is critical to hemoglobin digestion during feeding activities. Other molecules (peroxiredoxin, cathepsin-L and Kunitz-type inhibitor) stimulate a strong immune response polarized toward a Treg/Th2 phenotype that favors fluke’s survival. Helminth defense molecule, fatty acid binding proteins, Fasciola-specific glycans and miRNAs modulate host pro-inflammatory responses, while antioxidant scavenger enzymes work in an orchestrated way to deter host oxidant-mediated damage. Combining these strategies Fasciola spp. survive for decades within their mammalian host, where they reproduce and spread to become one of the most widespread zoonotic worm parasites in the world.

Complementary transcriptomic and proteomic analyses reveal the cellular and molecular processes that drive growth and development of Fasciola hepatica in the host liver

Background

The major pathogenesis associated with Fasciola hepatica infection results from the extensive tissue damage caused by the tunnelling and feeding activity of immature flukes during their migration, growth and development in the liver. This is compounded by the pathology caused by host innate and adaptive immune responses that struggle to simultaneously counter infection and repair tissue damage.

Results

Complementary transcriptomic and proteomic approaches defined the F. hepatica factors associated with their migration in the liver, and the resulting immune-pathogenesis. Immature liver-stage flukes express ~ 8000 transcripts that are enriched for transcription and translation processes reflective of intensive protein production and signal transduction pathways. Key pathways that regulate neoblast/pluripotent cells, including the PI3K-Akt signalling pathway, are particularly dominant and emphasise the importance of neoblast-like cells for the parasite’s rapid development. The liver-stage parasites display different secretome profiles, reflecting their distinct niche within the host, and supports the view that cathepsin peptidases, cathepsin peptidase inhibitors, saposins and leucine aminopeptidases play a central role in the parasite’s destructive migration, and digestion of host tissue and blood. Immature flukes are also primed for countering immune attack by secreting immunomodulating fatty acid binding proteins (FABP) and helminth defence molecules (FhHDM). Combined with published host microarray data, our results suggest that considerable immune cell infiltration and subsequent fibrosis of the liver tissue exacerbates oxidative stress within parenchyma that compels the expression of a range of antioxidant molecules within both host and parasite.

Conclusions

The migration of immature F. hepatica parasites within the liver is associated with an increase in protein production, expression of signalling pathways and neoblast proliferation that drive their rapid growth and development. The secretion of a defined set of molecules, particularly cathepsin L peptidases, peptidase-inhibitors, saponins, immune-regulators and antioxidants allow the parasite to negotiate the liver micro-environment, immune attack and increasing levels of oxidative stress. This data contributes to the growing F. hepatica -omics information that can be exploited to understand parasite development more fully and for the design of novel control strategies to prevent host liver tissue destruction and pathology.

Controversial aspects of the life cycle of Fasciola hepatica

Fasciola hepatica is a well-known helminth parasite, with significant economic and public health importance all over the world. It has been known since more than 630 years ago and a considerable research work has been carried out on the life cycle of this important parasite. In the hepatic phase of the life cycle of F. hepatica, it is assumed that the young flukes, after about 6-7 weeks of migration in the liver parenchyma, enter into the bile ducts of the definitive hosts and become sexually mature. Even though the secretion of cysteine peptidases including cathepsin L and B proteases by F. hepatica may justify this opinion, because of several scientific reasons and based on the experimental studies conducted in different animals (reviewed in this article), the entry of parasites into the bile ducts, after their migration in the liver parenchyma seems to be doubtful. However, considering all the facts relating to the hepatic and biliary phases of the life cycle of F. hepatica, two alternative ideas are suggested: 1) some of the migrating juvenile flukes may enter into the bile ducts immediately after reaching the liver parenchyma while they are still very small, or 2) when newly excysted juvenile flukes are penetrating into the intestinal wall to reach the liver through the abdominal cavity, a number of these flukes may enter into the choleduct and reach the hepatic bile ducts, where they mature. According to the previously performed natural and experimental studies in different animals and human beings, the supporting and opposing evidences for the current opinion as well as the evidences that might justify the two new ideas are reviewed and discussed briefly. In conclusion, our present knowledge about the time and quality of the entry of F. hepaticas into the bile ducts, seems to be insufficient, therefore, there are still some dark corners and unknown aspects in this field that should be clarified.

Parasitic liver disease in travelers

Liver disease is an important source of morbidity among ill returning travelers. Jaundice is one of the most common and obvious symptoms of liver disease, the differential diagnosis of which is extensive, especially in travelers. Jaundice in travelers can arise from both infectious and noninfectious causes. We herein summarize the most common parasitic etiologies that may lead to jaundice in the returned traveler, visitors of friends and relatives, or new immigrants, and describe the etiology, epidemiology, and pathogenesis of clinical features of each.

Hepatic fibrosis and Fasciola hepatica infection in cattle

This study focuses on the development of fibrosis of the liver of cattle with Fasciola hepatica infection, correlating with the intensity of infection. Animals with an established diagnosis of chronic F. hepatica infection were identified in a slaughterhouse in Lima, Perú. The study included 24 fresh cattle livers from infected animals and two uninfected controls. Tissues were stored at 4°C for approximately 8 h after which they were brought to a necropsy room and examined. Between 9 and 12 biopsies were randomly obtained from each liver. Histological staining of formalin-fixed liver sections with haematoxylin and eosin (H & E) and Masson's trichrome were performed. Liver samples were examined using a pathology protocol that included 30 items. Histopathologically, 16 out of 30 liver specimens (67.6%) showed diffuse fibrotic lesions (cirrhosis) with a mean number of Fasciola of 116 ± 30 (range 4–435). Pathological data were matched to number of adult parasites and presence of cirrhosis after being reviewed by two independent pathologists. There was concordance between the two pathologists (K = 0.72). The group with cirrhosis showed an average of 116 ± 30 adult parasites whereas the group not showing cirrhosis contained 56 ± 28 flukes (P = 0.2). To measure how number of flukes and diagnosis of cirrhosis are related we used Kendall's tau-b coefficient; the correlation was +0.296 (P = 0.04). Receiver Operating Characteristic (ROC) curve results showed that the best point was 38 parasite adults, which had 93.8% sensitivity and 75% specificity. We conclude that as the number of F. hepatica adult forms increases, the likelihood of developing liver fibrosis will also increase in cattle.

Ursodeoxycholate further increases bile-duct cell proliferative response induced by partial bile-duct ligation in rats

BACKGROUND

Bile salts (BSs) stimulate cholangiocyte proliferation in vitro and in vivo in normal rats. In this study, we evaluated the effects of BS-enriched diets on cholangiocyte proliferative activity already triggered by partial bile-duct ligation (pBDL), a surgical model that induces mild cholestatic conditions, focusing our attention on ursodeoxycholate (UDC).

METHODS

Animals (n=45) were fed either a standard diet, or a 0.2% deoxycholate- or 0.2% UDC-enriched diet for 4 weeks. Then, in each group, ten animals underwent pBDL and five underwent sham operation. Serum and biliary BS levels, serum cholestasis and cytolysis indexes, as well as liver conventional histology, apoptosis and proliferative activity were evaluated 48 h after the operation.

RESULTS

Animals that underwent pBDL showed sustained proliferative response compared with sham-operated rats. BS-enriched diets did not influence cholangiocyte proliferation in sham-operated rats. However, significantly increased proliferation was observed in pBDL rats fed a UDC-enriched diet. The evaluation of humoral and histological parameters excluded the possibility that the increased proliferation induced by UDC-enriched diet could be related to concomitant liver cell damage.

CONCLUSION

A UDC-enriched diet is able to amplify the magnitude of the cholangiocyte hyperplastic process, which occurs by a stimulatory mechanism after partial bile-duct ligation.

Hepatobiliary fascioliasis: clinical and radiologic features and endoscopic management

Fasciola hepatica is a zoonotic liver fluke that can cause disease in humans. Fascioliasis is an uncommon disease. We retrospectively analyzed 9 cases of fascioliasis and reviewed the relevant literature. A high index of suspicion and specific ultrasonographic findings are very helpful in the diagnosis of the disease. However, serological studies and endoscopic retrograde cholangiopancreatography confirm the diagnosis. The disease has 2 stages: hepatic stage and biliary stage. While several drugs are used during the hepatic stage, endoscopic retrograde cholangiopancreatography is particularly effective in the biliary stage.

Morphological Characterization of Ductular Reactions in Canine Liver Disease

Intrahepatic bile duct proliferation (ductular reaction) was examined histologically, immunohistochemically and ultrastructurally in four cases of canine liver disease, diagnosed as chronic hepatitis, liver fibrosis, cirrhosis and cholangiocellular carcinoma. Ductular reaction was a common finding in all cases. Most of the proliferated bile ducts were similar to normal bile ducts. In addition, duct-like structures occurred, consisting of hepatocytes and of intermediate cells that had phenotypic characteristics of both cholangiocytes and hepatocytes. The proliferated bile ducts were immunohistochemically negative for proliferating cell nuclear antigen (PCNA) and stem cell factor (SCF). The proliferated bile ducts in these four cases of canine liver disease thus showed both typical ductular reactions, such as elongation and tortuosity of the existing bile ducts, and atypical ductular reactions resulting from metaplasia of hepatocytes.

Expression of tenascin in bile duct cancer of hamster liver by combined treatment of dimethylnitrosamine with Opisthorchis viverrini infections

Tenascin is an extracellular matrix glycoprotein known to be an essential factor for the modulation of reciprocal interactions between the epithelium and mesenchyme during embryogenesis and tumourigenesis. The interactions between the expression of tenascin in the liver of Syrian golden hamster and the development of bile duct cancer in an Opisthorchis viverrini-associated cholangiocarcinoma model were investigated. The tenascin was expressed in connective tissues surrounding the dilated ducts, ductal rims and the stroma of cancers, and strongly in the stroma flame of necrotic cancer nodules. The mRNA signal for tenascin was also recognized in the stroma cells. The potential roles of tenascin as prognostic tumour markers are discussed.

Blood eicosanoids and immune indices during fasciolosis in water buffaloes

The effects of trickle infections of water buffaloes with Fasciola hepatica (60 metacercariae daily during a period of 20 days) on the blood plasma levels of prostaglandin E(2) (PGE2), 6-keto-prostaglandin F(1alpha) (6-keto-PG F(1alpha)) and thromboxane B(2) (TXB2) were assessed. F. hepatica specific IgG and T- and B-lymphocyte ratios were evaluated as indicators of the immune response. Although the applied mode of infection did not result in clinical disease, changes in the plasma eicosanoid pattern were observed. Plasma PGE2 values were significantly elevated in the infected water buffaloes 11 weeks post-infection (w.p.i.). In contrast, transiently but significantly lower TXB2 values than in the uninfected controls were recorded in the phase of chronic fasciolosis. Plasma 6-keto-PGF(1alpha) values were not considerably altered by the infection throughout the study period. F. hepatica-specific IgG were detected from 4 to 21 w.p.i. The proportion of peripheral T- and B-lymphocytes shifted towards B-cells from 2 to 12 w.p.i., gradually returning to control values afterwards. Although the water buffaloes appeared to be rather resistant to trickle infection with F. hepatica, moderate changes in plasma eicosanoid patterns were observed, indicating tissue damage and/or inflammation. Induction of the immune response could be monitored by an increase of F. hepatica-specific IgG, which was paralleled by a relative increase of the B-lymphocyte population.

Immunopathological study on the development of swine serum-induced bile duct lesions in BALB/c and DBA/2 mice

To compare the difference in the development of swine serum (SS)-induced bile duct lesion (BDL) between high responder BALB/c and low responder DBA/2 mice, the mice of both strains injected with SS twice a week for up to 4 weeks were killed and examined immunopathologically after the 2nd, 4th, 6th and 8th SS-injection, respectively. In BALB/c mice, BDL developed rapidly following the SS-injections, and a slight enlargement of common bile ducts accompanied with infiltration of T helper cells and eosinophils was detected after the 2nd SS-injection. From the 4th injection on, BDL was characterized by proliferation of mucous glands, hyperplasia and hypertrophy of biliary and glandular epithelial cells, periductal fibrosis, infiltration of eosinophils, plasma cells and T helper cells, and increase of mast cells, resulting in more apparent enlargement of common bile ducts. Several hypertrophied biliary and glandular epithelial cells were positive for mouse immunoglobulins and SS. BDL subsided after cessation of the SS-treatment. On the other hand, in DBA/2 mice, immune response and inflammatory reaction were very weak, and only slight BDL were detected.

Eicosanoid production by adult Fasciola hepatica and plasma eicosanoid patterns during fasciolosis in sheep

Fasciola hepatica infection in sheep is known to cause anaemia, fever and elevated levels of liver enzymes. It was hypothesised that eicosanoids play a role in these pathophysiological changes, so the pattern of plasma eicosanoids during the course of acute and chronic fasciolosis was studied in sheep infected with a single dose of 800 F. hepatica metacercariae. Blood plasma was collected weekly until week 17 p.i. from infected sheep, and from uninfected controls. Adult F. hepatica were then recovered from bile ducts and incubated for production of ES products. Eicosanoids were determined by enzyme immuno-assay in blood plasma, fluke homogenates and ES products after chromatographic purification of the samples. Fever and anaemia were seen from 3 to 12 weeks p.i. and from 8 to 17 weeks p.i., respectively. Onset of fever was accompanied by elevated liver enzyme activities (aspartate amino transferase and gamma glutamyl transferase) in the plasma. In general, the plasma levels of prostaglandin E2 (PGE2), prostaglandin I2 (PGI2) and leukotriene B4 (LTB4) were reduced during the acute and chronic stages of the infection, whereas thromboxane B2 (TXB2) was reduced only at 8 weeks p.i. The TXB2/PGI2 ratio was increased in favour of TXB2 at 3 and 11 weeks p.i. Additionally, TXB2, PGI2, PGE2 and LTB4 were detected both in ES products and in homogenates of F. hepatica. It was concluded that eicosanoid depletion in the plasma is caused by parasite-induced liver damage. The changes in eicosanoid levels are highly correlated to the clinical signs of the disease. Changes in the pattern of host plasma eicosanoids during fasciolosis, as well as parasite-derived eicosanoids, may reflect or contribute to the pathology of the disease.

The effect of prostanoids on hepatic bile flow in dogs with normal liver and bile duct cell hyperplasia

Bile flow rates and composition are subject to a wide variety of neural, endocrine and paracrine influences. The effects of these multiple factors may be different in the diseased liver compared to the response produced in the normal liver. As prostanoids may have a therapeutic role in liver disease it was intended to evaluate the effects of two principal therapeutic prostanoids, prostaglandin E2 and prostacyclin, on bile flow in dogs with a normal liver and in dogs with hepatotoxin-induced liver injury. Initially, in awake animals with chronic biliary and gastric fistulas the bile flow response to prostaglandin E2 and prostacyclin was evaluated and compared to the response produced by bile salt infusion alone and to that produced by the standard choleretic hormones, secretin and glucagon. The animals were then fed alpha-naphthylisothiocyanate (ANIT) and the studies repeated. ANIT is a hepatoxin that produces bile duct cell hyperplasia which was confirmed in dogs by demonstrating that ANIT increased [3H]thymidine incorporation by isolated canine bile duct cells. In normal dogs, the prostanoids, secretin, and glucagon increased hepatic bile flow. 10 days of ANIT feeding produced a hypercholeresis. While secretin was able to stimulate the hyperplastic biliary epithelium and increase bile flow over values produced by the hyperplastic biliary epithelium alone, neither prostaglandin E2, prostacyclin, or glucagon appeared to stimulate the hyperplastic biliary epithelium. As ANIT produced evidence of cholestasis and hepatocellular damage, only secretin would seem to have a potential therapeutic role in increasing bile flow in cholestatic liver disorders associated with bile duct cell hyperplasia.

Pattern of bile acid regurgitation and metabolism during perfusion of the bile duct obstructed rat liver

Bile acid processing in the long-term, bile duct obstructed rat liver was studied ex vivo. Twenty four and 72 h, respectively, after bile duct obstruction the isolated liver was perfused with taurodeoxycholate (16 nmol/min per g liver) the bile duct still being closed. Uptake, metabolism and regurgitation profile were traced by bolus injection of tritium-labeled bile acid; in addition, concurrent histological changes were examined by light- and electron microscopy. Ligation caused dilatation of the intrahepatic ductular branches and increased the serum bile acid concentration to 740 +/- 75 microM (controls: 16 +/- 2.12), reaching its maximum within 24 h. At 16 nmol/min per g liver uptake rate was > 96% in controls and in bile duct obstructed rats. Maximal uptake rates (assessed separately) differed between controls and bile duct obstructed rats (700 nmol/min per g liver vs. 460). Controls excreted more than 80% of labeled bile acid in bile within 10 min after bolus injection. Biliary recovery of label was virtually completed after 30 min. In bile duct obstructed rats excretion of label back to the perfusate effluent (regurgitation) started quantitatively 5 min after bolus application and peaked between 10 and 40 min; after 80 min, effluent recovery was incomplete (about 60% of bolus injected). Biliary bile acids of controls consisted of about 20% taurodeoxycholate-metabolites; bile acids in the perfusate effluent of bile duct obstructed rats of about 55%. The major metabolite in all animal groups was taurocholate; minor metabolites were tauroursocholate, tauro-3 alpha,7 = 0,12 alpha-cholanoic acid and 3-sulfo-taurodeoxycholate. Histologically, inflammation and periportal edema were present after 1 day of bile duct obstruction. After 3 days, marked proliferation of bile ductules was the dominant histological feature. It is concluded that during initial bile duct obstruction, bile acid processing is not altered, although ultrastructural alterations occur early.

Strong promoting effect of Opisthorchis viverrini infection on dimethylnitrosamine-initiated hamster liver

Continuous administration of dimethylnitrosamine (DMN) to Syrian hamsters infected with the liver fluke, Opisthorchis viverrini (OV) results in a 100% incidence of cholangiocellular carcinomas. In a two-stage experiment, however, dosing with liver flukes caused only a few lesions to develop (Flavel, D.J. and Lucus, S.B. (1983) Carcinogenesis, 4, 927]. To clarify this anomaly, Syrian hamsters were initiated with 20 mg/kg DMN injected i.p. 19 days prior to 80 OV metacercaria infection. At 45 weeks, the animals receiving both DMN and the parasite demonstrated a 44% incidence of cholangiocarcinomas, a 93% incidence of cholangiofibrosis, a 35% incidence of mucous cystadenomas and a 98% incidence of hepatocellular nodules with an average number of 9.1 +/- 4.1 per animal. Animals receiving DMN alone developed 85% hepatocellular nodules with an average number of only 3.0 +/- 2.7 and no bile duct lesions. In the parasite alone group, only cholangiofibrosis was detected in a few animals and no lesions were encountered in untreated controls. These results thus demonstrate that the post-initiation influence of Opisthorchiasis is indeed effective in promoting the development of both cholangiolar and hepatocellular lesions initiated by DMN.

Lack of promoting effect of proline on bile duct cancer development in dimethylnitrosamine-initiated hamster livers

Bile duct hyperplasia caused by proline is believed to represent a chemical effect of the liver fluke, Fasciola hepatica, and the resultant cell division might be expected to play a role as a tumor promoter. To investigate the potential promoting effect of proline on bile duct cancer development, Syrian hamsters were therefore divided into 8 treatment groups: dimethylnitrosamine (DMN) + proline intraperitoneally (i.p.); DMN + proline s.c.; DMN + saline i.p.; DMN + saline s.c.; proline i.p.; proline s.c.; saline i.p.; and saline s.c. DMN was injected i.p. at 20 mg/kg to the animals 2 weeks prior to commencement of proline treatment, whereby 1 ml of a 2 M solution was given by i.p. or s.c. injection 3 times a week for 20 weeks. At the end of week 42, assessment of preneoplastic lesion development did not reveal any significant modulating influence of proline on DMN-initiated lesion development nor did it itself cause persistent bile duct hyperplasia.

Secretions of the biliary mucosa in experimental clonorchiasis

The histological change of the biliary mucosa in clonorchiasis is characterized as adenomatous hyperplasia, and cross-sectioned mucosa looks like intestinal mucosa. In addition to the glandular hyperplasia, the metaplasia of mucin secreting cells is also known. The present study investigated the presence of intestinal secretion from the biliary mucosal cells of rabbits and rats with Clonorchis sinensis infection. The rabbit was infected with 300 and the rat was infected with 100 metacercariae of C. sinensis. A part of the animals were followed up after praziquantel treatment. The rabbit livers were prepared for histochemistry to observe any endocrine secretion and the bile duct mucosa of the mice was processed for the activity of brush border membrane (BBM)-bound enzymes of the small intestine. Immunohistochemistry with the polyclonal antibodies and biotin-streptavidin-peroxidase staining kit showed no positive cells for gastrin and secretin, but a few cells were positive for serotonin. The proliferated biliary mucosa of the mice revealed no activity of disaccharidases and aminopeptidase. Only alkaline phosphatase activity was found both in the control and the infected. The hyperplastic biliary mucosal cells showed no gastrointestinal secretory functions. The serotonin secreting cells may be one of the inflammatory cells.

Morphology of the bile ducts of the brook lamprey, Lampetra lamottenii (Le Sueur) before and during infection with the nematode, Truttaedacnitis stelmioides (Vessichelli, 1910) (Nematoda: Cucullanidae)

Routine light microscopy and transmission and scanning electron microscopy were used to describe and compare the biliary tree of larval Lampetra lamottenii before and during infestation of the bile ducts with the nematode, Truttaedacnitis stelmioides. The most prominent changes to the biliary tree following infection by the parasite are the dilation of the bile ducts, alterations to their epithelial cells, and an increase in periductal fibrous tissue. In recently infected animals, the simple epithelium of dilated bile ducts often contains many mitotic figures. In long-term infestations, the epithelium is stratified or pseudostratified. Changes to the fine structure of the biliary epithelial cells include increase and/or dilation of the RER and SER, and increases in microfilaments, intermediate filaments, and microtubules. The abundance of dense bodies may reflect enhance reabsorption of biliary constituents, and their accumulation may ultimately result in cytolysis. There are increased mucous granules in the apical cytoplasm of biliary epithelial cells and an abundance of mucinous material within the bile duct lumen, and the basal lamina appears thickened. The changes to the liver of L. lamottenii following infection are discussed and compared to those reported in small mammals following bile duct ligation, in patients with extrahepatic biliary obstruction, and in parasitic infection of the biliary tree.

Schistosoma mansoni: higher free proline levels in the livers of infected mice

The concentration of L-hydroxyproline in the liver of ICR female mice increased rapidly during the 8th to 11th weeks of Schistosoma mansoni infection. Free L-proline concentration began to increase about the 7th week and reached its maximum at the 8th to 9th weeks of the infection, when the granulomatous response to the schistosome eggs in the liver was most prominent, as indicated by the increase in liver wet weight and its deoxyribonucleic acid concentration. A significant increment in the total activity of ornithine-delta-transaminase (EC 2.6.1.13) and the decrease in the specific activity of proline oxidase (EC 1.4.3.2) became detectable in the liver homogenate of infected mice on the 8th week. However, changes in these enzymatic activities were not parallel to that of the hepatic free L-proline content. Intraperitoneal administration of S. mansoni egg granulomas or 15,000g x 30 min supernatant fluid of their extracts into uninfected, normal mice significantly increased the hepatic free L-proline content without any appreciable effect on the enzymatic activities of proline oxidase and ornithine-delta-transaminase. These findings suggest that S. mansoni egg granulomas contain a factor(s) which may be responsible for the elevation of free L-proline content in the fibrotic liver caused by experimental schistosomiasis mansoni.

Amino acid metabolism in helminths

Amino acids are major constituents of biological material. Chemically they are extremely stable and combine a relatively simple molecular structure with a wide range of properties and functions. In general, amino acid metabolism in helminths has been relatively neglected and the information available is often uneven and of uncertain quality. However, the search for new target sites for anthelmintic development has led to a renewed interest in this area. The amino acid composition of helminths is similar to that of other invertebrates and no unique amino acids have been reported. With the possible addition of tyrosine, helminths seem to require the same 10 essential amino acids as mammals and, where studied in detail, the pathways of amino acid synthesis in helminths are similar to those of mammals. Although amino acids are not a significant energy source in parasites, helminths are able to catabolize amino acids by pathways which, again, appear identical to those found in mammals. Helminths have also been shown to carry out a number of oxidative reactions associated with amino acid metabolism, including cysteine dioxygenase, proline hydroxylase and tryptophan hydroxylase. There are, however, differences in detail between the pathways of amino acid metabolism in helminths and mammals, particularly in the metabolism of the sulphur amino acids and arginine and proline. These differences may be exploitable in anthelmintic design and proline analogues and proline biosynthesis inhibitors show some potential as fasciolicides (Sheers et al., 1982). Differences in metabolism between parasites and their hosts may be the result of parasitic adaptation or they may merely reflect general features of the invertebrate phyla as a whole. Thus a comparison of amino acid metabolism in parasitic helminths with that of their free-living relatives may give some insight into the biochemical basis of parasitism.

Origin, pattern, and mechanism of bile duct proliferation following biliary obstruction in the rat

Proliferation of bile duct-like structures is a hepatic cellular reaction observed in most forms of human liver disease and in a variety of experimental conditions associated with liver injury. Yet the origin, means of initiation, and significance of this hyperplasia are unknown. To clarify these issues we induced bile duct proliferation in rats by ligating the common bile duct and studied (a) hepatic incorporation of [3H]thymidine by histoautoradiography, (b) hepatic morphometry, (c) biliary tree volume using [3H]taurocholate as a marker of biliary transit time, (d) immunohistochemical expression of cytokeratin no. 19, (e) the effect of indomethacin, and (f) the role of increased biliary pressure, in the absence of physiological and biochemical evidence of cholestasis, on [3H]thymidine incorporation by the bile-duct cells. The results have demonstrated that (a) the proliferating bile duct-like cells are products of the extant biliary epithelium and retain its characteristics; (b) bile duct cells divide irrespective of the size of the duct in which they are located and form a system with a lumen continuous with the preexisting one; (c) bile duct proliferation results mainly in elongation, not in circumferential enlargement or sprouting of side branches; (d) portal macrophage infiltration does not play a role in the hyperplastic reaction, and (e) increased biliary pressure is the initiating factor in bile duct cell division. Our results provide evidence that under the present conditions, ductular metaplasia of hepatocytes does not occur and there is no functioning stem cell for biliary epithelial growth segregated in any particular duct size or within the portal connective tissue.

Intrahepatic bile duct changes in human hepatosplenic schistosomiasis mansoni

Wedge liver biopsies of 132 patients with hepatosplenic mansonian schistosomiasis were studied and divided in two groups according to the presence (Group I - 69 cases) or absence (Group II - 63 cases) of markers of the actual presence of the parasite in the liver tissue. Histological variables indicating bile duct injury were analysed in each case: periductal fibrosis, hyperplasia of the bile duct epithelium, bile duct degeneration, and marginal ductular proliferation. The presence of one or more of these variables defined two sub-groups: A - bile duct lesions present (73 cases), and B - bile duct lesions absent (59 cases). The variables "bile duct degeneration" and "ductular proliferation" were related to the actual presence of the parasite in the host. In 55.3% of all cases of human mansonian schistosomiasis a spectrum of injuries to the bile ducts was present. Epithelial hyperplasia alone or associated with patterns of mucopolysaccharide production was observed in 87.6% cases of the Sub-group A. The bile ducts changes in mansonian schistosomiasis are close to those described in liver fluke infestations such as clonorchiasis, fascioliasis and opistorchiasis. Statistical analysis revealed that high mucopolysaccharide production was associated with epithelial hyperplasia. The pathogenesis of the bile duct changes in human mansonian schistosomiasis and its relation to the parasitic infestations and their antigens is discussed.

The influence of various amino acids on the extrahepatic bile ducts in newborn mice--an experimental study

Excess proline in adult animals is associated with extrahepatic biliary hyperplasia. Possible therapeutic application of this amino acid in biliary atresia was postulated. In order to test whether excess proline had an influence on the development of the extrahepatic bile ducts, pregnant mice were injected daily with various amino acids. One day and 1 week after delivery, the extrahepatic bile ducts of the newborn mice were studied and the number of epithelial cells per cross section was determined. Neither proline nor any other amino acid had an influence on the proliferation of extrahepatic bile ducts.

An extrahepatic bile duct growth factor: in vivo effect and preliminary characterization

Rabbit sera injected intraperitoneally into BALB/c mice were noted to produce a considerable and selective enlargement of extrahepatic bile ducts. The gallbladder, intrahepatic ducts, liver and other organs showed no stimulation of growth. Duct enlargement leading to widening of its outer diameter which, on average, was 3.6 times that of normal, was due entirely to an increased number of epithelial cells with prominent proliferation of intramural glandular components. There was no evidence of inflammatory bile duct injury, fibrosis or obstruction. All of the above changes were reversible and regressed slowly after discontinuation of injections. The bile duct growth-promoting factor was detected in sera of many animal species including humans and birds. Host response to this factor was determined by the number of injections and appeared to be strain-related since it was not observed in C57BL or C3H mice. The sex and age of the donor or recipient were not of any relevance to the growth response. In order to isolate and characterize the bile duct growth factor, rabbit serum was separated into various fractions, and the effect of each fraction was tested in the animal model. Proteins in the 33 to 65% ammonium sulfate precipitate of whole rabbit sera had activity equal to that of native sera. Activity was abolished by treating this serum fraction with 1% sodium dodecyl sulfate plus proteinase K, suggesting that the bile duct growth factor is a protein. Lipids extracted from whole sera using chloroform: methanol or ultracentrifugation were devoid of activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell cultures of bile duct epithelium and the pathogenesis of biliary atresia

The pathogenesis of biliary atresia is unknown. The authors describe a technique for culturing extrahepatic bile duct epithelial cells of human and bovine origin in monolayer cell cultures. Light-, electron microscopy and immunohistological studies prove the epithelial nature of the cultured cells. Inoculation of the cells with reovirus 3 showed no destruction; adenovirus 6, herpes simplex and polio virus 1 and 2 destroyed the cells within 24 h. The cells produce a growth factor maintaining the integrity of the cells, even in the absence of serum.

Fasciola hepatica: collagen deposition and other histopathology in the rat host's bile duct caused by the parasite and by proline infusion

Bile ducts were examined histochemically to compare the effects of proline infusion with Fasciola hepatica implantation in rats. After 3 weeks of infusion or implantation, both proline and F. hepatica produced increases in the luminal perimeter and collagen content of the bile duct. However, the effect of the parasite was significantly greater than that of proline, and the parasite produced significant increases in the bile duct wall. These results corroborate earlier biochemical and histological studies indicating the important role of proline in the enlargement of the bile duct in fascioliasis.

Levels of type I and type III collagen in the bile duct of rats infected with Fasciola hepatica

Collagen types and their levels were compared between bile ducts from Fasciola infected rats and bile ducts from uninfected animals. Both collagen types I and III were shown to be increased in infected animals but, levels of type I increased less than type III. These results indicate that fascioliasis produces changes in the collagen composition of the bile duct that are similar to those produced in cirrhosis of the liver and other pathologic conditions including wound healing. Such observations suggest that a study of the chronology of collagen deposition in fascioliasis might provide information on the sequence of molecular events which result in bile duct hyperplasia.

Hepatic proline after bile duct ligation in rats

Since biliary hyperplasia of fascioliasis correlated with hepatic proline level, we examined the occurrence of a similar chemical stimulus during bile obstruction. Uptake of tritiated proline and glycine rose in both hepatocytes and a bile duct enriched cell fraction, following duct ligation in rats. The increased hepatic content of proline but not glycine suggests that proline has a role in post-obstructive biliary proliferation.

A study of the initiation of biliary hyperplasia in rats infected with Fasciola hepatica

Following infection of rats with Fasciola hepatica, an increase in the number of epithelial cells in the common bile duct, labelled with [3H]thymidine, was detected autoradiographically as early as 5 days post-infection (p.i.). This initial mitogenic effect of the infection was limited to that region of the bile duct lying adjacent to the liver, while the region lying next to the duodenum failed to show any increase in labelling until 41 days p.i. Mechanical contact between the parasite and the biliary epithelium did not occur until 41 days p.i. and the initial hyperplasia was evidently not a result of mechanical irritation. The study serves to emphasize the chemical aetiology of the precocious biliary hyperplasia and to more accurately identify its onset.

Bile duct enlargement by infusion of L-proline: potential significance in biliary atresia

The normal signals of control of bile duct morphogenesis and growth are unknown. Consequently, aberrant development is poorly understood, as for example in those infants with biliary atresia or hypoplasia. A previous report by Isseroff et al., showed that a possible mechanism for the common bile duct enlargement by the parasite Fasciola hepatica was excess L-proline secreted by this parasite. This suggested to us that L-proline might be a specific growth factor for bile duct epithelium, and therefore possibly useful in the understanding and treatment of biliary maldevelopment. We now report an experimental study demonstrating the effect of L-proline on the normal biliary tree of the mouse. We also present a summary to date of an ongoing clinical restrospective study. These experimental findings suggest: (1) there may be a specific requirement for L-proline during the rapid growth of the biliary tract during neonatal life; (2) bile duct hypoplasia and atresia may result from a defect in proline metabolism; (3) proline administration during the early phase of biliary atresia may possibly be therapeutic.

Fasciola hepatica human infection. Histopathological study of sixteen cases

Sixteen human cases of Fasciola hepatica infection are described. The liver was involved in 13 cases, the gall bladder in 9 cases and the stomach in 2 cases. Lesions containing parasitic remnants or fluke eggs were rarely seen. Surface scarring of the liver, scar tracks and granulomas within organs were the most characteristic changes seen and were the most useful for the histopathological diagnosis of the disease. The associated liver, bile and gastric lesions are briefly discussed.