Pathogenesis of schistosomal 'pipestem' fibrosis: a low-protein diet inhibits the development of 'pipestem' fibrosis in mice

Protein undernutrition reduces the efficacy of praziquantel in a murine model of Schistosoma mansoni infection

Background

Undernutrition and schistosomiasis are public health problems and often occur in low and middle-income countries. Protein undernutrition can alter the host-parasite environment system and aggravate the course of schistosomiasis. This study aimed to assess the impact of a low-protein diet on the efficacy of praziquantel.

Methodology/Principal findings

Thirty-day-old mice were fed with a low-protein diet, and 40 days later, they were individually infected with fifty Schistosoma mansoni cercariae. A 28-day-treatment with praziquantel at 100 mg/kg for five consecutive days followed by distilled water begins on the 36^th day post-infection. Mice were sacrificed on the 64^th day post-infection. We determined the parasitological burden, liver and intestine histomorphometry, liver injury, and immunomodulation parameters. Praziquantel treatment of infected mice fed with a standard diet (IN-PZQ) resulted in a significant reduction of worm and egg burdens and a normalization of iron and calcium levels. The therapy also improved schistosomiasis-induced hepatopathy and oxidative stress. The anti-inflammatory and immunomodulatory activities of praziquantel were also significant in these mice. When infected mice receiving the low-protein diet were treated with praziquantel (ILP-PZQ), the body weight loss and hepatomegaly were not alleviated, and the worm and liver egg burdens were significantly higher than those of IN-PZQ mice (P < 0.001). The treatment did not reduce the increased activities of ALT and γ-GGT, the high malondialdehyde concentration, and the liver granuloma volume. The iron and calcium levels were not ameliorated and differed from those of IN-PZQ mice (P < 0.001 and P < 0.05). Moreover, in these mice, praziquantel treatment did not reverse the high level of IL-5 and the low mRNA expression of CCL3/MIP-1α and CXCL-10/IP-10 induced by S. mansoni infection.

Conclusion/Significance

These results demonstrated that a low-protein diet reduced the schistosomicidal, antioxidant, anti-inflammatory, and immunomodulatory activities of praziquantel.

Almost 90% of people requiring schistosomiasis preventive chemotherapy in 2018 lived in sub-Saharan Africa. Besides, 205.3 million children under five years suffer and die of undernutrition in low- and middle-income countries. The physiopathology of schistosomiasis mansoni involves liver damage, oxidative stress, and perturbation of the immune response. These disturbances are intensified by undernutrition. Praziquantel is used to treat schistosomiasis, but its efficacy on the comorbidity of S. mansoni infection and undernutrition has not been investigated. We conducted this study to assess the effectiveness of praziquantel on S. mansoni infection in mice fed with a low-protein diet. We recorded growth retardation, hepatomegaly, and high worm and egg burdens in mice fed with a low-protein diet and treated with PZQ. Moreover, the treatment did not reverse the liver function injury, oxidative stress, high iron level, and low calcium level. The proinflammatory cytokine IL-5 was still high, and the gene expression of some macrophage-associated chemokines was reduced. Therefore, this study demonstrated that in a murine model of a low-protein diet, the efficacy of praziquantel on S. mansoni infection was reduced. It also underlines the importance of targeting protein deficiency and malnutrition in populations living in schistosomiasis endemic areas for efficient disease control.

Could diet composition modulate pathological outcomes in schistosomiasis mansoni? A systematic review of in vivo preclinical evidence

Schistosomiasis and malnutrition are often overlapped in poor communities, resulting in disproportionately high mortality rates. Currently, fragmented data make it difficult to define the relationship between diet and schistosomiasis. Thus, we systematically review the preclinical evidence on the impact of diet in Schistosoma mansoni infection. From a structured search, we recovered 27 original articles. All studies used mice and most of them investigated hypoproteic (70.37%), hyperlipidic (22.22%) or vitamin-deficient (7.41%) diets. Diets based on carbohydrate, zinc or milk supplementation were investigated at a reduced frequency (3.70% each). Hypoproteic diets attenuated parasitic load and granulomatous inflammation, but also reduced host resistance to S. mansoni infection, determining higher mortality rates. By stimulating steatohepatitis, parasitic load and granulomatous inflammation, hyperlipidic diets increase organ damage and mortality in infected animals. Although a high-sugar diet and vitamin restriction potentiate and zinc supplementation attenuates S. mansoni infection, the current evidence for these diets remains inconclusive. Analysis of methodological quality indicated that the current evidence is at high risk of bias due to incomplete characterization of the experimental design, diet composition and treatment protocols. From the bias analysis, we report methodological limitations that should be considered to avoid systematic reproduction of inconsistent and poorly reproducible experimental designs.

In vivo study of schistosomicidal action of 1-benzyl-4-[(4-fluoro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one

Praziquantel has been the drug most widely used therapy against different forms of schistosomiasis around the world. However, this treatment has shown ineffective in humans and in experimental models of Schistosoma mansoni. New therapeutic alternatives have been tested, including the imidazolidine derivative LPSF/PT-09, which has shown high therapeutic potential in vitro. In this work, we tested the schistosomal activity of this derivative in doses of 250mg/kg and 200mg/kg in mice experimentally infected with a high parasite load of S. mansoni. Parasitological evaluations related to the number of S. mansoni worms and their oviposition were performed during the acute phase of the disease and have demonstrated moderate effectiveness of 30-54,4%. However, LPSF/PT-09 did not influence oviposition of the parasites or the embryonic development of the eggs. The results obtained in this model showed that the imidazolidine derivative LPSF/PT-09 presented significant antischistosomal activity in vivo, posing as a potential candidate for this class of drugs. However, a better understanding of the pharmacokinetics and pharmacodynamics of the imidazolidine derivative LPSF/PT-09 is needed.

Protein deficiency alters impact of intestinal nematode infection on intestinal, visceral and lymphoid organ histopathology in lactating mice

Protein deficiency impairs local and systemic immune responses toHeligmosomoides bakeriinfection but little is known about their individual and interactive impacts on tissue architecture of maternal lymphoid (thymus, spleen) and visceral (small intestine, kidney, liver, pancreas) organs during the demanding period of lactation. Using a 2×2 factorial design, pregnant CD1 mice were fed a 24% protein sufficient (PS) or a 6% protein deficient (PD) isoenergetic diet beginning on day 14 of pregnancy and were infected with 100H. bakerilarvae four times or exposed to four sham infections. On day 20 of lactation, maternal organs were examined histologically and serum analytes were assayed as indicators of organ function. The absence of villus atrophy in response to infection was associated with increased crypt depth and infiltration of mast cells and eosinophils but only in lactating dams fed adequate protein. Infection-induced lobular liver inflammation was reduced in PD dams, however, abnormalities in the kidney caused by protein deficiency were absent in infected dams. Bilirubin and creatinine were highest in PD infected mice. Infection-induced splenomegaly was not due to an increase in the lymphoid compartment of the spleen. During lactation, infection and protein deficiency have interactive effects on extra-intestinal pathologies.

Manson's schistosomiasis in the undernourished mouse: some recent findings

This paper deals with current knowledge of the interrelationships between Schistosoma infection and malnutrition. It emphasizes the relevance of these investigations in the face of dynamic and evolving changes occurring in population diets and changes in the epidemiological patterns of schistosomiasis in endemic countries. The paper further discusses the basis for continuing the studies on this subject and the reasons why it represents a misunderstood association. This review also focuses on the cellular and humoral immune responses in the undernourished mouse model infected with Schistosoma mansoni, with updated information on the immune response in wild-type and iNOS knockout mice concerning soluble egg antigen specific antibodies and kinetics of IFN-gamma, IL-4, IL-10 and IL-13 cytokines, in the chronic phase of Manson's schistosomiasis. There is indication that schistosome-infected undernourished mice are able to develop a humoral immune response, but antibody titres are much lower than in the control animals. Cytokine production (IFN-gamma, IL-4, IL-10) is lower in the undernourished mice, but as infection progresses to the chronic phase its kinetics run an antagonistic course when compared to that of well-nourished animals. Marked variation in the secretion of IL-13 (a fibrogenic cytokine) could explain why undernourished mice do not develop liver "pipe-stem" fibrosis described in previous papers on well-nourished animals.

Effects of low-protein diet onSchistosoma mansonimorphology visualized by morphometry and confocal laser scanning microscopy

Previous studies have shown that protein deficiencies can hamper both the course of experimental schistosomiasis and normal development of adult worms. To further investigate this relationship, we compared adult male and femaleSchistosoma mansonifrom malnourished and well-fed mice through morphometric and confocal laser scanning microscopy analysis. Swiss mice were fed protein-deficient diets (8%) and infected subcutaneously with approximately 80S.mansonicercariae (BH strain, Brazil). Control mice were fed a standard rodent diet (23% protein). The nutritional status was evaluated by body weight gain and albumin values. Mice were sacrificed 63 days post-infection. Recovered worms were stained with hydrochloric carmine and preserved as whole-mounts for bright-field examination and confocal microscopy. The body weight gain and serum albumin concentrations were significantly lower (P<  0.05) in malnourished mice than in controls. In general, all morphometric values of specimens grown in malnourished mice were lower than those of control mice. Schistosome worms grown in malnourished mice had statistically significant differences (P<  0.05) in the reproductive system and tegument than those grown in mice fed standard diets. In female worms, vitelline glands showed few remaining follicles and ovaries lacked mature oocytes. In male parasites, tubercles were fewer in number on the dorsal surface and testicular lobes presented fewer differentiated germinal cells. In summary, we describe novel data supporting the view that low-protein diets may influence the development of adult worms.

Effects of a protein-free diet on worm recovery, growth, and distribution of Echinostoma caproni in ICR mice

The effects of a protein-free diet on the host–parasite relationship of Echinostoma caproni in ICR mice were studied. The experimental diet was a customized protein-free diet (PFD) in pellet form containing 0% protein. The control diet consisted of a standard laboratory diet containing 23% casein as a source of protein. A total of 24 mice were each infected with 15 metacercarial cysts of E. caproni. Twelve mice were placed on the experimental diet (experimentals) and the remaining mice (controls) were placed on the control diet. Experimental and control mice were necropsied at 2, 3, and 4 weeks postinfection (p.i.). The weight of mice on the PFD was markedly lower than that of mice on the control diet. The length and circumference of the small intestine of infected mice on the PFD were significantly lower than those of the controls at 3 weeks p.i. (Student's t-test; P < 0.05). Worm recoveries from mice on the PFD were significantly lower than those of the controls at 3 weeks p.i. There was a significant decline in worm body area in worms from the mice on the PFD compared with those on the control diet at 2, 3, and 4 weeks p.i. Worm dry weights from mice on the PFD were significantly lower than those on the control diet at 2 weeks p.i. Worms from hosts on the PFD were located more posteriad in the gut than those recovered from mice on the control diet. The findings suggest that the PFD contributes to growth retardation of E. caproni in ICR mice.

Repeated infections with Schistosoma mansoni and liver fibrosis in undernourished mice

The mouse model of schistosomal periportal fibrosis (Symmers' "pipestem" fibrosis), that develops in 30-50% of the infected animals, is not reproduced in undernourished mice. Host nutritional status is likely to be a variable that may influence the outcome and progression of infection, since it interferes with the dynamics of connective tissue changes occurring in chronic hepatic schistosomiasis. Re-infections increase the occurrence of periportal liver fibrosis in well-nourished animals, but it is not known how undernourished mice would behave being repeatedly re-infected. So, 21-day-old male albino Swiss mice were individually exposed to 30 cercariae (percutaneous route) of the BH strain of Schistosoma mansoni, 4 weeks after being on a low-protein diet. Control animals were fed on a commercial balanced chow for mice. The nutritional status was evaluated by body weight gain and measurement of food intake. Mice were divided into four groups: A1 (undernourished, single infected), A2 (well-nourished, single infected), B1 (undernourished, re-infected), B2 (well-nourished, re-infected). The primary infection was performed 4 weeks after ingesting the respective diet. Re-infections started 45 days later, with exposure to 15 cercariae, at 15 day intervals. Mice were sacrificed 18 weeks after the primary exposure. The livers were submitted to morphological (gross and microscopic pathology), morphometric (percentage of fibrosis; granuloma size; volume and numerical densities) by using semi-automatic morphometry, and biochemical (quantification of collagen as hydroxyproline) studies. Worm burdens and hepatic egg counting were also recorded. Values for body weight gains were always lower in undernourished mice, the effects of re-infection being minimal on this regard. Liver and spleen weights were higher in well-nourished mice (either single infected or re-infected) and mainly related to the type of ingested diet. A greater number of re-infected well-nourished mice developed periportal fibrosis, but undernourished re-infected animals did not reproduce this lesion. The percentage of fibrosis and hepatic collagen content were higher in well-nourished mice, but differences between single infected and re-infected groups were not statistically significant.

Morphological signs of cirrhosis regression

Regression of hepatic cirrhosis is a controversial issue. Recently, a list of histopathological features, observed in human material, was suggested as a hallmark of cirrhosis in the process of regression. An investigation for the presence of these morphologic features was performed at monthly intervals in rats with proved carbon tetrachloride (CCl4)-induced cirrhosis over a period of 9 months following discontinuation of treatment, using sequential liver biopsies. Within the first 4 months, features of the "hepatic repair complex" were identified, together with the enlargement of the hepatic nodules and thinning of the fibrous septa. Subsequent to the 4 months, the histological picture, composed of large and inconspicuous nodules and delimited by thin and frequently incomplete fibrous septa "incomplete septal cirrhosis", appeared to be stabilized. These fibrous septa, when injected with India ink from the portal trunk, presented blood vessels that were seen to drain directly into the sinusoids. These findings suggested that when the cause of cirrhosis is removed, the liver may adapt itself to a new and permanent structure, probably compatible with normal or near-normal function, which may render hepatic cirrhosis clinically, although not morphologically, reversible.

Malnutrition and hepatic fibrosis in murine schistosomiasis

In this paper, four different approaches attempting to reproduce the schistosomal liver fibrosis in undernourished mice are reported: shifting from a deficient to a balanced diet and vice-versa, repeated infections, influence of the genetic background, and immunological response. Infections were performed with 30 cercariae of Schistosoma mansoni and lasted at least four months. Undernourished mice were unable to reproduce the picture of "pipestem" fibrosis, except the C57 BL/10 inbred strain, four out of 21 mice developing the liver lesion. A link of this histological finding to the type of parasite strain can not be discarded at the moment. Repeated infections increased collagen deposition mainly in well nourished animals (seven out of 16 Swiss mice developed "pipestem"-like fibrosis). In undernourished infected Swiss mice the serum levels of soluble egg antigen specific antibodies IgG1, IgG2a, IgG2b, and IgG3 were two to four times lower than those detected for well nourished controls. The decreased humoral immune response coupled to the morphological, morphometric, and biochemical results reinforce the influence of the host nutritional status on the connective tissue changes of hepatic schistosomiasis.

Host nutritional status as a contributory factor to the remodeling of schistosomal hepatic fibrosis

Weaning Swiss mice were percutaneously infected with 30 cercariae of Schistosoma mansoni and submitted to a shifting either from a deficient to a balanced diet or vice-versa, for 24 weeks. The nutritional status was weekly evaluated by measurements of growth curves and food intake. Hepatic fibrosis and periovular granulomas were studied by histological, morphometric and biochemical methods. All mice fed on a deficient diet failed to develop periportal "pipestem" fibrosis after chronic infection. An unexpected finding was the absence of pipestem fibrosis in mice on normal diet, probably related to the sample size. The lower values for nutritional parameters were mainly due to the deficient diet, rather than to infection. Liver/body weight ratio was higher in "early undernutrition" group, after shifting to the balanced diet. Volume density and numerical density of egg granulomas reached lowest values in undernourished animals. The amount of collagen was reduced in undernourished mice, attaining higher concentrations in well-fed controls and in "late undernutrition" (balanced diet shifted to a deficient one), where collagen deposition appeared increased in granulomas. That finding suggested interference with collagen degradation and resorption in "late" undernourished animals. Thus, host nutritional status plays a role in connective tissue changes of hepatic schistosomiasis in mice.

The influence of periportal (pipestem) fibrosis on long term results of surgical treatment for schistosomotic portal hypertension

AIM

To evaluate the degree of influence that periportal fibrosis has on clinical development and the long term results of surgical treatment on patients with hepatic-splenic schistosomiasis with previous gastrointestinal hemorrhages.

METHODS

During the period of 1992-1998, 111 patients underwent surgical treatment for the treatment of hepatic-splenic schistosomiasis with previous gastrointestinal hemorrhages. The degree of fibrosis was classified as: degree I - the portal spaces show a rich increase of young connective cells, a slight collagen production and a varying presence of inflammatory infiltrate. The periportal blade unchangeable (29/111); degree II - there is an expansion of the connective tissue with the emission of radial collagen septa, producing a star shaped aspect (38/111); degree III - the connective septa form bridges with other portal spaces or with the vein, with evident angiomatoid neo-formation (44/111).

CONCLUSION

The patients with periportal fibrosis degree I present recurrent hemorrhages statistically less than patients with periportal fibrosis degrees II and III, and that the intensity of the periportal fibrosis is not the only pathophysiological factor of the esophageal varices, gastric varices, prevalence of post-operative portal vein thrombosis and hematological and biochemical alterations of the patients with pure mansoni schistosomiasis.

Morphometric study of Schistosoma mansoni adult worms recovered from Undernourished infected mice

Some unfavourable effects of malnutrition of the host on Schistosoma mansoni worm biology and structure have been reported based upon brigthfield microscopy. This paper aims to study by morphometric techniques, some morphological parameters in male and female adult worms recovered from undernourished albino mice in comparison with parasites recovered from well-fed infected mice. Undernourished animals were fed a multideficient and essentially low protein diet (RBD diet) and compared to well-fed control mice fed with the commercial diet NUVILAB. Seventy-five days post-infection with 80 cercarie (BL strain) animals were sacrificed. All adult worms were fixed in 10% formalin and stained with carmine chloride. One hundred male and 60 female specimens from each group (undernourished and control) were examined using an image system analysis Leica Quantimet 500C and the Sigma Scan Measurement System. The following morphometrical parameters were studied: body length and width, oral and ventral suckers, number and area of testicular lobes, length and width of ovary and uterine egg. For statistical analysis, the Student's t test for unpaired samples was applied. Significant differences (p < 0.05) were detected in body length and width, in parameters of suckers, uterine egg width, ovary length and area of testicular lobes, with lower values for specimens from undernourished mice. The nutritional status of the host has negative influence on S. mansoni adult worms, probably through unavailability of essential nutrients to the parasites.

Parasitological characteristics of Schistosoma mansoni infection in swiss mice with underlying malnutrition

The effects of a protein-restricted diet (8% protein, 81% carbohydrate and 11% lipids) on Schistosoma mansoni infectivity, fecal egg excretion and intestinal egg distribution in Swiss (SW) mice were studied. Pregnant mice received a deficient diet from the middle of gestation until delivery. Seven-days-old mice were exposed to 50 cercariae (BH strain, Brazil). Offspring mice had a free access to the deficient diet since lactation until adulthood. The controls were fed with a commercial mice diet. A parasitological examination was performed between six and eight weeks post-infection while both groups were necropsied one week later. Mice on the experimental diet showed a significant loss in body weight. There was no significant difference (p > 0.05) in pre-patent period, kinetics of egg excretion and worm recovery from mice on either diet. Significant differences (p < 0.05) were found concerning to the percentage of deposited eggs in the distal segment of the small intestine from hosts on the experimental diet. Our data suggest that experimental malnutrition induced for a long term has no detrimental effect on the acute schistosomiais infection in SW mice.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Histomorphometry of hepatic portal fibrosis in patients with surgical schistosomiasis mansoni

The usual histology report of hepatic fibrosis in patients with hepatosplenic schistosomiasis mansoni presents no association with hemodynamic and clinical liver parameters. Histomorphometry is adding a new tool of investigation for measuring density of portal fibrosis in these patients. This investigation was set up for assessing a possible agreement between the well-accepted international classification and the fibrosis density grades measured by histomorphometry. Thirty-five children and equal number of adults were included in this study. All patients underwent splenectomy and ligature of the left gastric vein. Histology findings were assessed in surgical liver biopsy stained with Masson trichrome. The official histology report was used as reference. The histomorphometric studies were done by semi-automatic morphometry. The mean percentage (X) of portal fibrosis plus or minus one standard deviation (SD) was classified as grade II (7.06% up to 34.72%); grade I was up to 7.06%; and grade III above 34.72%. Although, not reaching statistical significance, there is a tendency of the fibrosis to be more intense in children than adults (X±SD - 22.02±13.46% versus 20.63%±15.33% "t" = 0.379 p>0.05). Seven out of nine (77.8%) patients classified as grade I, by morphometry, had the same result on the official report, however, two (22.2%) were described as grade III. Sixteen out of forty-four (36.4%) classified as grade II on morphometry had the same classification as the histology grade, but, twenty seven (61.4%) were classified as grade III and one (2.3%) as grade I. Fifteen (21.4%) out of 70 patients had grade III on both classifications, but, two (11.8%) out of seventeen G III on morphometry were grade II. The kappa (k) measurement of agreement between both classification was k = 0.319, showing a fair strength of association. The histomorphometric measurements of Symmers fibrosis in surgical patients with mansonic schistosomiasis partially support the report from The Department of Pathology - University Hospital, Federal University of Pernambuco - Brazil. However, there is a discrepancy in grade III. While in the official classification, the majority (62.8%) accounts for this grade, on morphometry only 38.6% represent the same grade. On the contrary, on morphometry, similar majority (62.8%) is grade II.

Morphological aspects of Schistosoma mansoni adult worms isolated from nourished and undernourished mice: a comparative analysis by confocal laser scanning microscopy

Malnutrition hampers the course of schistosomiasis mansoni infection just as normal growth of adult worms. A comparative morphometric study on adult specimens (male and female) recovered from undernourished (fed with a low protein diet - regional basic diet) and nourished (rodent commercial laboratory food, NUVILAB) white mice was performed. Tomographic images and morphometric analysis of the oral and ventral suckers, reproductive system and tegument were obtained by means of confocal laser scanning microscopy. Undernourished male specimens presented smaller morphometric values (length and width) of the reproductive system (first, third and last testicular lobes) and thickness of the tegument than controls. Besides that, it was demonstrated that the dorsal surface of the male worms bears large tubercles unevenly distributed, but kept grouped and flat. At the subtegumental region, vacuolated areas were detected. It was concluded that the inadequate nutritional status of the vertebrate host has a negative influence mainly in the reproductive system and topographical somatic development of male adult Schistosoma mansoni, inducing some alterations on the structure of the parasite.

Significance of schistosomal granuloma modulation

Hepatic Schistosoma mansoni periovular granulomas undergo changes in size, cellular composition and appearance with time. This phenomenon, known as "immunological modulation", has been thought to reflect host immunological status. However, as modulation has not been observed outside the liver, participation of local factors, hitherto little considered, seems crucial. Components of the extracellular matrix of periovular granulomas of the mouse were particularly studied in three different organs (liver, lung and intestine) and during three periods of infection time (acute, intermediate and chronic) by means of histological, biochemical and immunofluorescence techniques, while quantitative data were evaluated by computerized morphometry, in order to investigate participation of local factors in granuloma modulation. Results confirmed modulation as a exclusively hepatic phenomenon, since pulmonary and intestinal granulomas, formed around mature eggs, did not change size and appearance with time. The matricial components which were investigated (Type I, III and IV collagens, fibronectin, laminin, proteoglycans and elastin) were found in all granulomas and in all organs examined. However, their presence was much more prominent in the liver. Elastin was only found in hepatic granulomas of chronic infection. The large amount of extracellular matrix components found in hepatic granulomas was the main change responsible for the morphological aspects of modulation. Therefore, the peculiar environment of the liver ultimately determines the changes identified in schistosomal granuloma as "modulation".

[Reinfections and the development of schistosomal periportal fibrosis in the murine model]

Experimental pipestem fibrosis of the liver developed more frequently (69.2%) in mice submitted to repeated infections with Schistosoma mansoni, than with single infection (11.1%). The counting of eggs in the liver revealed no significant differences between the two experimental groups. Although the reason why multiple infections favor the development of pipestem fibrosis has not been elucidated, the data obtained represent an experimental support to clinico-epidemiological claims that repeated infections play a role in pathogenesis of hepatosplenic schistosomiasis