Thalidomide failed to inhibit angiogenesis and fibrosis in hepatic schistosomiasis of the mouse

The relationship between angiogenesis and fibrosis has been demonstrated in several pathological conditions, one of them being schistosomiasis. To observe whether suppression of angiogenesis would interfere with fibrosis, Thalidomide, an anti-angiogenesis drug, was administered during 30 consecutive days to mice with experimental schistosomiasis. Computerized morphometric measurements of fibrosis, and the counting of blood vessels from hepatic schistosomal lesions did not significantly differ when treated animals and their controls were compared at the end of the experiments. These rather unexpected results are presented under the understanding that they may be of interest during further studies on the anti-angiogenesis properties of thalidomide, and the relationship between angiogenesis and fibrosis.     

Evaluation of the role of angiogenic factors in the pathogenesis of schistosomiasis

Schistosomiasis is one disease produced by helminths, which affect many people in tropical areas. Granuloma formation is the main mechanism involved in the pathogenesis of this disease. Experimental studies have demonstrated angiogenesis (blood vessels formation from pre-existing vessels) in the initial phase of granuloma formation. In the present work, VEGF (vascular endothelial growth factor) levels were analyzed in sera from people diagnosed with different helminthic infections. Patients with schistosomiasis and filariasis had significantly high VEGF levels in compared with healthy people and patients diagnosed with hookworms. In addition, the effects of angiogenesis inhibition using anti-angiogenic factors (endostatin) were evaluated in a schistosomiasis murine model. A lesion decrease was observed in mice infected with Schistosoma mansoni and treated with endostatin. Finally, mechanisms of angiogenesis induction were studied and observed that cercariae antigens stimulated the angiogenic factors by host alveolar macrophages.     

Angiogenesis and schistosomal granuloma formation

An increasing amount of evidences points to angiogenesis as playing a paramount role in fibrosis development. However granulomas in general, and periovular schistosomal granulomas in particular, are considered avascular structures, although they usually result in dense areas of focal fibrosis. In order to clarify this apparent paradox, the presence of blood vessels was systematically searched in hepatic schistosomal granulomas of mice, during different stages of the infection, and at different stages of granuloma evolution, by means of vascular injections of colored masses, demonstration of laminin in vascular basement membranes and by ultra structural analysis. Vascular proliferation appeared evident at the early stages of granuloma formation, gradually decreasing thereafter, older granulomas becoming almost avascular structures, sometimes delimited at the periphery by a rich vascular network.     

Remodeling of hepatic vascular changes after specific chemotherapy of schistosomal periportal fibrosis

Hepatosplenic schistosomiasis was the first human disease in which the possibility of extensive long standing hepatic fibrosis being degraded and removed has been demonstrated. When such changes occurred, the main signs of portal hypertension (splenomegaly, esophageal varices) progressively disappeared, implying that a profound vascular remodeling was concomitantly occurring. Hepatic vascular alterations associated with advanced schistosomiasis have already been investigated. Obstruction of the intrahepatic portal vein branches, plus marked angiogenesis and compensatory hyperplasia and hypertrophy of the arterial tree are the main changes present. However, there are no data revealing how these vascular changes behave during the process of fibrosis regression. Here the mouse model of pipestem fibrosis was used in an investigation about these vascular alterations during the course of the infection, and also after treatment and cure of the disease. Animals representing the two polar hepatic forms of the infection were included: (1) "isolated granulomas" characterized by isolated periovular granulomas sparsely distributed throughout the hepatica parenchyma; and (2) 'pipestem fibrosis' with periovular granulomas and fibrosis being concentrated within portal spaces, before and after treatment, were studied by means of histological and vascular injection-corrosion techniques. Instances of widespread portal vein obstruction of several types were commonly found in the livers of the untreated animals. These obstructive lesions were soon repaired, and completely disappeared four months following specific treatment of schistosomiasis. Treatment was accomplished by the simultaneous administration of praziquantel and oxamniquine. The most impressive results were revealed by the technique of injection of colored masses into the portal system, followed by corrosion in strong acid. The vascular lesions of non-treated pipestem fibrosis were represented in the plastic casts by considerable diminution of the fine peripheral portal vein radicles, plus dilatation of periportal collaterals. Four months after treatment, this last picture appeared replaced by tufts of newly interwoven vessels formed along the main portal vein branches, disclosing a strong angiomatoid reparative change. Understanding about the cellular elements at play during fibro-vascular repairing changes of hepatic schistosomiasis represents a matter of considerable scientific and conceptual importance. At present time one may only speculate about the participation of some type of natural stem-cell capable of restoring the diseased liver back to normal once the cause of the disorder has been eliminated.     

Follicular helper T cells recruit eosinophils into host liver by producing CXCL12 during Schistosoma japonicum infection

Schistosomiasis affects at least 200 million people in tropical and subtropical areas. The major pathology of schistosomiasis is egg‐induced liver granuloma characterized by an eosinophil‐rich inflammatory infiltration around the eggs, which subsequently leads to hepatic fibrosis and circulatory impairment in host. However, the mechanisms how eosinophils are recruited into the liver, which are crucial for the better understanding of the mechanisms underlying granuloma formation and control of schistosomiasis, remain unclear. In this study, we showed that follicular helper T (Tfh) cells participate in recruitment of eosinophils into liver partially by producing CXCL12 during schistosome infection. Our findings uncovered a previously unappreciated role of Tfh cells in promotion of the development of liver granuloma in schistosomiasis, making Tfh‐CXCL12‐eosinophil axis a potential target for intervention of schistosomiasis.     

Vascular endothelial growth factor (VEGF) - part 1: in physiology and pathophysiology

Angiogenesis is an important component of many physiological processes, such as the female sexual cycle, placenta formation, the processes of growth and differentiation of tissues, and reparative processes including wound healing, fracture repair, and liver regeneration. The formation of new blood vessels during angiogenesis and vasculogenesis allows the growth and functioning of multicellular organisms. Pathological angiogenesis most commonly occurs in ischaemic, inflammatory and neoplastic diseases. Conditions in the pathogenesis of which angiogenesis plays an important role are sometimes labelled angiogenic diseases. To date, a number of pro-and anti-angiogenic factors have been defined. VEGF is the only specific mitogen for endothelial cells. It stimulates their growth and inhibits apoptosis, increases vascular permeability in many tissues, promotes vasculogenesis and angiogenesis. VEGF signalling activity in relation to the cell is dependent on having its specific membrane receptors (Flt-1, KDR, Flt-4). Angiogenesis plays a protective role in ischaemic heart disease and myocardial infarction. Angiogenesis extends life for patients after a stroke. Most of the facts about physiological angiogenesis are derived from studies into liver regeneration as a result of an acute injury or partial hepatectomy. Pathological hepatic angiogenesis occurs in the course of inflammation, fibrosis, hypoxia, and during tumourogenesis. There is interesting data relating to liver steatosis and obesity.     

Fibroblast stimulation in schistosomiasis. V. Egg granuloma macrophages spontaneously secrete a fibroblast-stimulating factor

Isolated intact egg granulomas from the liver of Schistosoma mansoni-infected mice have been previously shown to elaborate factors in vitro that can stimulate fibroblasts for biological functions that are of potential importance in the pathogenesis of hepatic fibrosis in schistosomiasis. We report here that cell cultures obtained from monodispersed granuloma cell suspensions, and specifically enriched for macrophages (95% to 100%) spontaneously elaborated fibroblast proliferation-stimulating activity in vitro. These cells possessed functional and phenotyptic characteristics of activated macrophages. In contrast, control peritoneal macrophages from uninfected mice lacked such phenotypic characteristics, and did not spontaneously elaborate fibrogenic activity in vitro. The granuloma macrophage activity was present, pre-formed within the isolated cells, and was continuously elaborated during 72 hr of incubation. By gel infiltration chromatography (Sephacryl S-200 sf), fibroblast-stimulating activity was identified in two pooled fractions, one with estimated molecular radius (Mr) of 46 kd to 57 kd and the other with Mr of 10 kd to 16 kd. Preparative isoelectric focusing in granular gel of crude macrophage culture supernatants identified peak activity in fractions with pI approximately 5. Two different serine esterase inhibitors had no effect on the ability of crude granuloma macrophage supernatants to stimulate fibroblast proliferation. Whereas crude and chromatographed fractions of granuloma macrophage supernatant were active for fibroblasts, they had minimal or no interleukin 1 (IL 1) activity when tested in a thymocyte proliferation assay. In contrast, resident peritoneal macrophages from the same infected mice spontaneously secreted substantial IL 1 and fibroblast-stimulating activity in vitro. We conclude that egg granuloma macrophages are activated in vivo to secrete fibrogenic molecules functionally distinct from IL 1, which might contribute to the pathogenesis of hepatic fibrosis in schistosomiasis.     

GdCl3 Attenuates Schistosomiasis japonicum Egg-Induced Granulomatosis Accompanied by Decreased Macrophage Infiltration in Murine Liver

Early-stage hepatic granuloma and advanced-stage fibrosis are important characteristics of schistosomiasis. The direct consequences of gadolinium chloride (GdCl₃) in egg-induced granuloma formation have not been reported, although GdCl₃ is known to block the macrophages. In present study, mice were infected with 15 Schistosoma japonicum (S. japonicum) cercariae and treated with GdCl₃ (10 mg/kg body weight) twice weekly from day 21 to day 42 post-infection during the onset of egg-laying towards early granuloma formation. Histochemical staining showed that repeated injection of GdCl₃ decreased macrophages infiltration in liver of mice infected with S. japonicum. Macrophage depletion by GdCl₃ during the initial phase attenuated liver pathological injury characterized by smaller granuloma size and decreased immune inflammation as well as less fibrogenesis. In addition, IL-13Rα2 expression was reduced by GdCl₃ in liver of mice infected with S. japonicum. The results suggest that GdCl₃ depleted macrophages, which attenuated helminth infected immune responses involving with IL-13Rα2 signal. These findings would highlight a therapeutic potential via manipulating IL-13Rα2+ macrophage in schistosomiasis.     

Differential immunoregulation of granulomatous inflammation, portal hypertension, and hepatic fibrosis in murine schistosomiasis mansoni

The present study investigates the immunoregulation of hepatic fibrosis in experimental murine schistosomiasis. Disease parameters measured were portal pressure, hepatic granuloma area, hepatic interstitial collagen, and glycosaminoglycans. C57BL/6 mice were infected with 25 Schistosoma mansoni cercariae and administered splenocytes or serum derived from uninfected mice or chronically infect syngeneic mice at 6 and 7 wk of infection. Immunologically mediated modulation was noted in animals receiving splenocytes derived from chronically infected mice. Both a reduction in portal pressure and hepatic granuloma areas were noted. Hepatic collagen content but not glycosaminoglycan content was reduced by the administration of either lymphoid cells or serum from chronically infected mice. The isotypic profile of hepatic interstitial collagens was modulated by both the administration of serum or lymphoid cells. Augmented levels of type III collagen was noted on administration of serum derived from chronically infected mice, whereas type I collagen levels were relatively elevated on administration of splenocytes. The data indicate that immunomodulation of inflammation and hepatic fibrosis can occur in murine schistosomiasis but that fibrotic events and inflammatory processes are independently modulated.     

The angiogenesis inhibitor endostatin impairs blood vessel maturation during wound healing.

Endostatin is a cleavage product of collagen XVIII that strongly inhibits tumor angiogenesis. To determine if endostatin affects other angiogenic processes, we generated full-thickness excisional wounds on the back of mice that were systemically treated with recombinant murine endostatin. No macroscopic abnormalities of the wound healing process were observed. Histological analysis revealed normal wound contraction and re-epithelialization, but a slight reduction in granulation tissue formation and reduced matrix deposition at the wound edge. The blood vessel density in the wounds of endostatin-treated mice was not affected. However, ultrastructural analysis demonstrated severe abnormalities in blood vessel maturation. The wound vessels in the endostatin-treated mice were narrowed or closed with an irregular luminal surface, resulting in a severe reduction in the number of functional vessels and extravasation of erythrocytes. Endostatin treatment did not affect the expression level and localization of collagen XVIII mRNA and protein. Furthermore, the angiogenesis regulators vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2 were normally expressed in the wounds of endostatin-treated mice. However, expression of the major wound matrix proteins fibronectin and collagens I and III was significantly reduced. This reduction is likely to explain the reduced density of the wound matrix. Our results demonstrate that endostatin treatment reduces the number of functional blood vessels and the matrix density in the granulation tissue, but does not significantly affect the overall wound healing process.     

IL-10R Blockade during Chronic Schistosomiasis Mansoni Results in the Loss of B Cells from the Liver and the Development of Severe Pulmonary Disease

In schistosomiasis patients, parasite eggs trapped in hepatic sinusoids become foci for CD4⁺ T cell-orchestrated granulomatous cellular infiltrates. Since the immune response is unable to clear the infection, the liver is subjected to ongoing cycles of focal inflammation and healing that lead to vascular obstruction and tissue fibrosis. This is mitigated by regulatory mechanisms that develop over time and which minimize the inflammatory response to newly deposited eggs. Exploring changes in the hepatic inflammatory infiltrate over time in infected mice, we found an accumulation of schistosome egg antigen-specific IgG1-secreting plasma cells during chronic infection. This population was significantly diminished by blockade of the receptor for IL-10, a cytokine implicated in plasma cell development. Strikingly, IL-10R blockade precipitated the development of portal hypertension and the accumulation of parasite eggs in the lungs and heart. This did not reflect more aggressive Th2 cell responsiveness, increased hepatic fibrosis, or the emergence of Th1 or Th17 responses. Rather, a role for antibody in the prevention of severe disease was suggested by the finding that pulmonary involvement was also apparent in mice unable to secrete class switched antibody. A major effect of anti-IL-10R treatment was the loss of a myeloid population that stained positively for surface IgG1, and which exhibited characteristics of regulatory/anti-inflammatory macrophages. This finding suggests that antibody may promote protective effects within the liver through local interactions with macrophages. In summary, our data describe a role for IL-10-dependent B cell responses in the regulation of tissue damage during a chronic helminth infection.     

Schistosome eggs stimulate reactive oxygen species production to enhance M2 macrophage differentiation and promote hepatic pathology in schistosomiasis

Schistosomiasis is a neglected tropical disease of public health concern. The most devastating pathology in schistosomiasis japonica and mansoni is mainly attributed to the egg-induced granulomatous response and secondary fibrosis in host liver, which may lead to portal hypertension or even death of the host. Schistosome eggs induce M2 macrophages-rich granulomas and these M2 macrophages play critical roles in the maintenance of granuloma and subsequent fibrosis. Reactive oxygen species (ROS), which are highly produced by stimulated macrophages during infection and necessary for the differentiation of M2 macrophages, are massively distributed around deposited eggs in the liver. However, whether ROS are induced by schistosome eggs to subsequently promote M2 macrophage differentiation, and the possible underlying mechanisms as well, remain to be clarified during S. japonicum infection. Herein, we observed that extensive expression of ROS in the liver of S. japonicum-infected mice. Injection of ROS inhibitor in infected mice resulted in reduced hepatic granulomatous responses and fibrosis. Further investigations revealed that inhibition of ROS production in S. japonicum-infected mice reduces the differentiation of M2, accompanied by increased M1 macrophage differentiation. Finally, we proved that S. japonicum egg antigens (SEA) induce a high level of ROS production via both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) and mitochondria in macrophages. Our study may help to better understand the mechanism of schistosomiasis japonica-induced hepatic pathology and contribute to the development of potential therapeutic strategies by interfering with ROS production.     

Schistosoma mansoni: angiotensin converting enzyme activity in mice under the influence of praziquantel and/or captopril.

Murine schistosomiasis is usually associated with hepatic granulomatous lesions together with high serum and granuloma angiotensin converting enzyme (ACE) activity. Praziquantel (PRZ) which is known to reduce granuloma size was studied to show whether this effect is related to changes in ACE activity. Furthermore, captopril was studied to show whether by inhibiting ACE activity, the drug could also affect granuloma size. PRZ, captopril, and their combination led to significant reduction in liver granuloma. However, in normal mice, captopril was shown to increase rather than decrease serum ACE. The decrease in ACE activity by PRZ was correlated with its curative effect in infected mice. However, in experimentally induced pulmonary granulomata, the drug reduced granuloma size without affecting ACE activity of either serum or granuloma. It may be concluded that reduction in ACE activity may be beneficial as far as diminution of granuloma size is concerned and irrespective of whether there is an active infection or not. The possible use of Captopril as an antihypertensive in bilharzial infections associated with hypertension would probably not adversely affect the granulomatous lesions.     

Intestinal fibrovascular nodules caused by Schistosoma mansoni infection in Calomys callosus Rengger, 1830 (Rodentia: Cricetidae): a model of concomitant fibrosis and angiogenesis

Human schistosomiasis develops extensive and dense fibrosis in portal space, together with congested new blood vessels. This study demonstrates that Calomys callosus infected with Schistosoma mansoni also develops fibrovascular lesions, which are found in intestinal subserosa. Animals were percutaneously infected with 70 cercariae and necropsied at 42, 45, 55, 80, 90 and 160 days after infection. Intestinal sections were stained for brightfield, polarization microscopy, confocal laser scanning, transmission and scanning electron microscopies. Immunohistological analysis was also performed and some nodules were aseptically collected for cell culture. Numerous intestinal nodules, appearing from 55 up to 160 days after infection, were localized at the interface between external muscular layer and intestinal serosa, consisting of fibrovascular tissue forming a shell about central granuloma(s). Intranodular new vessels were derived from the vasculature of the external vascular layer and were positive for laminin, chondroitin-sulfate, smooth muscle alpha-actin and FVIII-RA. Fibroblastic cells and extracellular matrix components (collagens I, III and VI, fibronectin and tenascin) comprised the stroma. Intermixed with the fibroblasts and vessels there were variable number of eosinophils, macrophages and haemorrhagic foci. In conclusion, the nodules constitute an excellent and accessible model to study fibrogenesis and angiogenesis, dependent on S. mansoni eggs. The fibrogenic activity is fibroblastic and not myofibroblastic-dependent. The angiogenesis is so prominent that causes haemorrhagic ascites.     

Targeting secreted cytokine BMP9 gates the attenuation of hepatic fibrosis

Liver fibrosis is overly exuberant wound healing that leads to portal hypertension or liver cirrhosis. Recent studies have demonstrated the functions of bone morphogenetic protein 9 (BMP9) in liver fibrosis, and thus, targeting liver-specific BMP9 abnormalities will become an attractive approach for developing therapeutics to treat liver fibrosis. Here, we reveal that BMP9 serves as a valuable serum diagnostic indicator and efficient therapeutic target to attenuate liver fibrogenesis. Our analysis of biopsies from liver fibrotic patients revealed that higher BMP9 levels accompanied advanced stages of liver fibrosis. In mouse models, recombinant Bmp9 overexpression accelerated liver fibrosis, and adenovirus-mediated Bmp9 knockdown attenuated liver fibrogenesis. Intriguingly, BMP9 directly stimulated hepatic stellate cell activation via the SMAD signaling pathway to enhance hepatic fibrosis. Moreover, an inhibitory monoclonal antibody targeting Bmp9 was efficacious in treatment of mice with liver fibrosis. These observations delineate a novel model in which BMP9 directly drives SMAD/ID1 signaling in hepatic stellate cells, which modulates liver fibrogenesis development. Moreover, the findings unveil a promising surrogate biomarker for the diagnosis of hepatic fibrosis, thereby representing an efficient “BMP9 neutralization” approach in alleviating hepatic fibrosis.     

Vascular development in early human embryos and in teratomas derived from human embryonic stem cells

During early human embryonic development, blood vessels are stimulated to grow, branch, and invade developing tissues and organs. Pluripotent human embryonic stem cells (hESCs) are endowed with the capacity to differentiate into cells of blood and lymphatic vessels. The present study aimed to follow vasculogenesis during the early stages of developing human vasculature and to examine whether human neovasculogenesis within teratomas generated in SCID mice from hESCs follows a similar course and can be used as a model for the development of human vasculature. Markers and gene profiling of smooth muscle cells and endothelial cells of blood and lymphatic vessels were used to follow neovasculogenesis and lymphangiogenesis in early developing human embryos (4-8 weeks) and in teratomas generated from hESCs. The involvement of vascular smooth muscle cells in the early stages of developing human embryonic blood vessels is demonstrated, as well as the remodeling kinetics of the developing human embryonic blood and lymphatic vasculature. In teratomas, human vascular cells were demonstrated to be associated with developing blood vessels. Processes of intensive remodeling of blood vessels during the early stages of human development are indicated by the upregulation of angiogenic factors and specific structural proteins. At the same time, evidence for lymphatic sprouting and moderate activation of lymphangiogenesis is demonstrated during these developmental stages. In the teratomas induced by hESCs, human angiogenesis and lymphangiogenesis are relatively insignificant. The main source of blood vessels developing within the teratomas is provided by the murine host. We conclude that the teratoma model has only limited value as a model to study human neovasculogenesis and that other in vitro methods for spontaneous and guided differentiation of hESCs may prove more useful.     

IL‐7 suppresses macrophage autophagy and promotes liver pathology in Schistosoma japonicum‐infected mice

In schistosomiasis japonica and mansoni, parasite eggs trapped in host liver elicit severe liver granulomatous inflammation that subsequently leads to periportal fibrosis, portal hypertension, haemorrhage or even death. Macrophages are critical for granuloma formation and the development of liver fibrosis during schistosomiasis. However, whether the aberrant regulation of macrophage autophagy has an effect on the development of liver immunopathology in schistosomiasis remains to be elucidated. In this study, we showed that Schistosoma japonicum (S. japonicum) egg antigen (SEA)‐triggered macrophage autophagy limited the development of pathology in host liver. However, engagement of IL‐7 receptor (IL‐7R/CD127) on macrophages by S. japonicum infection‐induced IL‐7 significantly suppressed SEA‐triggered macrophage autophagy, which led to an enhanced liver pathology. In addition, anti‐IL‐7 neutralizing antibody or anti‐CD127 blocking antibody treatment increased macrophage autophagy and suppressed liver pathology. Finally, we demonstrated that IL‐7 protects macrophage against SEA‐induced autophagy through activation of AMP‐activated protein kinase (AMPK). Our study reveals a novel role for IL‐7 in macrophage autophagy and identifies AMPK as a novel downstream mediator of IL‐7‐IL‐7R signalling and suggests that manipulation of macrophage autophagy by targeting IL‐7‐IL‐7R signalling may have the potential to lead to improved treatment options for liver pathogenesis in schistosomiasis.