Malnutrition and hepatic fibrosis in murine schistosomiasis

Dietary glycemic and energy load differentially modulates Schistosoma mansoni-induced granulomatous inflammation and response to antiparasitic chemotherapy

The impact of diet composition and energy content on schistosomiasis evolution and treatment efficacy is still controversial. This study compared the impact of sucrose-rich diet and intermittent fasting on Schistosoma mansoni infection and praziquantel (PZQ)-based chemotherapy response in mice. BALB/c mice were infected with S. mansoni and followed for 15 weeks. The animals were randomized into nine groups receiving high glycemic load (high-sucrose diet - HSD), low caloric load (standard chow alternate-day fasting - ADF), and standard chow ad libitum (AL). Eight weeks after S. mansoni infection, these groups remained untreated or were treated with PZQ (300 mg/kg/day) for 3 days. Our results indicated that parasite load (S. mansoni eggs and parasite DNA levels), granulomatous inflammation (granulomas number and size), and liver microstructural damage (reduction in hepatocytes number, increase in nucleus-cytoplasm ratio, connective stroma expansion and fibrosis) were increased in ADF-treated animals. These animals also showed decreased eggs retention, granulomatous inflammation and collagen accumulation in the small intestine. Conversely, HSD diet and PZQ treatment attenuated all these parameters and stimulated hepatic regenerative response. PZQ also stimulated fibrosis resolution in HSD-treated mice, effect that was limited ADF-exposed mice. Our findings indicate that dietary glycemic and energy load can modulate schistosomiasis progression and the severity of hepatic and intestinal granulomatous inflammation in untreated and PZQ-treated mice. Thus, lower intestinal eggs retention may potentially be linked to worsening liver disease in ADF, while attenuation of hepatic and intestinal granulomatous inflammation is consistent with reduced parasite load in HSD- and PZQ-treated animals.

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.

Undernutrition - thirty years of the Regional Basic Diet: the legacy of Naíde Teodósio in different fields of knowledge

Undernutrition is characterized by an imbalance of essential nutrients with an insufficient nutritional intake, a disorder in which the clinical manifestations in most cases are the result of the economic and social context in which the individual lives. In 1990, the study by the medical and humanitarian Naíde Teodósio (1915-2005) and coworkers, which formulated the Regional Basic Diet (RBD) model for inducing undernutrition, was published. This diet model took its origin from the observation of the dietary habits of families that inhabited impoverished areas from the Pernambuco State. RBD mimics an undernutrition framework that extends not only to the Brazilian population, but to populations in different regions worldwide. The studies based on RBD-induced deficiencies provide a better understanding of the impact of undernutrition on the pathophysiological mechanisms underlying the most diverse prevalent diseases. Indexed papers that are analyzed in this review focus on the importance of using RBD in different areas of knowledge. These papers reflect a new paradigm in translational medicine: they show how the study of pathology using the RBD model in animals over the past 30 years has and still can help scientists today, shedding light on the mechanisms of prevalent diseases that affect impoverished populations.

Host Adaptive Immune Status Regulates Expression of the Schistosome AMP-Activated Protein Kinase

Schistosomes exhibit profound developmental adaptations in response to the immune status of their mammalian host, including significant attenuation of parasite growth, development and reproduction in response to deficits in host adaptive immunity. These observations led us to hypothesize that schistosomes regulate the utilization of energy resources in response to immunological conditions within the host. To test this hypothesis, we identified and characterized the Schistosoma mansoni AMP-activated protein kinase (AMPK), a heterotrimeric enzyme complex that is central to regulating energy metabolism at the cellular and organismal level in eukaryotes. We show that expression of the catalytic α subunit is developmentally regulated during the parasite life cycle, with peak expression occurring in adult worms. However, the protein is present and phosphorylated in all life cycle stages examined, suggesting a need for active regulation of energy resources throughout the life cycle. In contrast, transcription of the AMPK α gene is down-regulated in cercariae and schistosomula, suggesting that the protein in these life cycle stages is pre-synthesized in the sporocyst and that expression must be re-initiated once inside the mammalian host. We also show that schistosome AMPK α activity in adult worms is sensitive to changes in the parasite's environment, suggesting a mechanism by which schistosome metabolism may be responsive to host immune factors. Finally, we show that AMPK α expression is significantly down-regulated in parasites isolated from immunodeficient mice, suggesting that modulation of parasite energy metabolism may contribute to the attenuation of schistosome growth and reproduction in immunodeficient hosts. These findings provide insights into the molecular interactions between schistosomes and their vertebrate hosts and suggest that parasite energy metabolism may represent a novel target for anti-schistosome interventions.

Protein malnutrition impairs the immune control of Trichinella spiralis infection

OBJECTIVES

We aimed to analyze the effect of a protein-deficient diet on mucosal and systemic immunity during a Trichinella spiralis infection.

METHODS

Two groups of weaning Wistar rats received a protein-deficient diet (6.5% casein) and the other two groups received a control diet (20% casein). After 10 d, one group of each diet was infected (PD_I and C_I) with muscle larvae (infecting stage). Food intake and body weight were assessed over time. Blood eosinophils counts, antibodies in serum, and tissue extracts were assessed at different days postinfection. Histologic studies were done in the lungs and intestines, and adult worm (AW) fecundity index score and muscle parasite burden were determined.

RESULTS

Food and protein intake were lower in PD_I than in C_I. Body weight was lower in PD_I than in a non-infected protein-deficient diet. Eosinophils counts were lower in PD_I than in C_I. Total and specific antibodies were lower in PD_I than C_I. PD_I had a reduced number of mast and goblet cells in the lungs and intestines compared with C_I. The persistence of AW in the intestines and migrant larvae at the lungs was longer in PD_I than in C_I.. The AW fecundity index score was higher in PD_I than in C_I. Finally, PD_I evidenced a higher muscular parasite burden than C_I.

CONCLUSIONS

Protein deficiency affects the mucosal and systemic immune response to Trichinella spiralis and delays the expulsion and increases the fecundity index score of AW, which leads to a higher parasite burden in the muscles.

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.

Low transformation growth factor-β1 production and collagen synthesis correlate with the lack of hepatic periportal fibrosis development in undernourished mice infected with Schistosoma mansoni

Undernourished mice infected (UI) submitted to low and long-lasting infections by Schistosoma mansoni are unable to develop the hepatic periportal fibrosis that is equivalent to Symmers’ fibrosis in humans. In this report, the effects of the host’s nutritional status on parasite (worm load, egg viability and maturation) and host (growth curves, biology, collagen synthesis and characteristics of the immunological response) were studied and these are considered as interdependent factors influencing the amount and distribution of fibrous tissue in hepatic periovular granulomas and portal spaces. The nutritional status of the host influenced the low body weight and low parasite burden detected in UI mice as well as the number, viability and maturation of released eggs. The reduced oviposition and increased number of degenerated or dead eggs were associated with low protein synthesis detected in deficient hosts, which likely induced the observed decrease in transformation growth factor (TGF)-β1 and liver collagen. Despite the reduced number of mature eggs in UI mice, the activation of TGF-β1 and hepatic stellate cells occurred regardless of the unviability of most miracidia, due to stimulation by fibrogenic proteins and eggshell glycoproteins. However, changes in the repair mechanisms influenced by the nutritional status in deficient animals may account for the decreased liver collagen detected in the present study.

Renal parenchyma developmental plasticity in mice infected with Schistosoma mansoni, whose mothers were malnourished during lactation

Effects of maternal malnutrition during lactation on the kidneys in mice infected with Schistosoma mansoni. Kidneys from programmed infected mice and their respective controls fed a normal diet (23% protein), a protein-restricted group (PR) (8% protein) and a caloric-restricted group (CR) (according to the PR group intake) evaluated by biometry, morphometry and histopathology. Both PR and CR groups showed a reduction in the number of glomeruli when compared with the control group (CR: -29% vs C; PR: -41% vs C; p<0.05) as well as infected mice (ICR: -32% vs IC; IPR: -47% vs IC; p<0.05). Among infected mice, ICR group showed higher kidney weights (+18% vs IC and +12% vs IPR; p<0.01). The ICR and IPR groups showed largest perimeter and area when compared to the corresponding uninfected group (ICR vs CR: +26%; IPR vs PR: +21%, p<0.05) and area (ICR vs CR: +95%; IPR vs PR: +50%, p<0.05). The ICR group showed an increase of within Bowman (CR vs ICR: +56%, p<0.05), whereas Bowman's space was reduced (PR vs IPR, -61%; p<0.05). Conclude that malnutrition during lactation programmed the metabolic state of the host, resulting in the evolution of the histology of the renal parenchyma.

A Study of the Granulomatous Responses Induced by Different Strains of Schistosoma mansoni

The increased pathogenesis of the Schistosoma mansoni BH strain compared with the SJ strain has been attributed to the number of granulomas formed in experimental infections, which increase the mortality in definitive hosts. The aim of the present study was to investigate the development of granulomas around the eggs of the S. mansoni BH and SJ strains and to determine whether this host reaction was strain specific. Four experimental groups were analyzed. Two groups contained mice inoculated in the caudal vein with eggs from the S. mansoni BH or SJ strains and the other two contained mice that were infected with cercariae of the BH strain prior to being inoculated with eggs. The number of granulomas per tissue area in the lungs and liver, as well as the size of the granulomas, was analyzed to characterize the response to schistosome infection. The largest granulomatous responses were observed around eggs of the BH strain. Granulomas covered a larger area in the lungs of mice that were previously infected with cercariae and subsequently inoculated with eggs of the BH strain. These results indicated that specific granulomatous responses occurred following an infection with the BH and SJ strains of S. mansoni.

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.

[Liver function abnormalities in undernourished and Schistosoma mansoni-infected mice]

There are few studies on liver function abnormalities in mice with schistosomiasis associated with malnutrition. In this study, animals were divided into four groups, according to their diet (normal or low protein) and whether they were infected with Schistosoma mansoni or not. All the groups grew slower than the control did (p < 0.0001). Mortality among the animals occurred because of the infection. High levels of aminotransferases in well-fed animals with infection suggested that there was an intensive inflammatory process (p < 0.0001). All the groups presented high levels of alkaline phosphatase. There were increases in aspartate transferase and alkaline phosphatase in infected well-fed animals. The diets modified the albumin levels (p > 0.001) and the serum proteins. Compared with the controls, the groups showed low levels of glucose (p < 0.001). This study found that both infection and malnutrition interfered with the biochemical indicator levels, but the most important liver function abnormalities occurred during the intense inflammation caused by schistosomiasis.

Expression of transforming growth factor-β1 and Smads in hepatic fibrosis induced by Schistosoma Japonica in mice

AIM: To investigate the expression of transforming growth factor-β1 (TGF-β1), Smad2/3, Smad4 and Smad7 in Schistosoma japonicum-fibrotic liver tissues and to explore the fibrogenic molecular mechanism.

METHODS: Eighty healthy ICR mice were randomly divided into model group and normal control group. The model mice were infected with cercaria of Schistosoma japonica. The mice in both groups were killed at the end of the 4^th, 6^th, 8^th and 12^th wk respectively, and their livers, spleens, and bodies were weighed. Liver tissues were taken for HE and scarlet staining. Tissue microarray was prepared and immunohistochemical staining was used to detect the expression of TGF-β1, Smad2/3, Smad4 and Smad7.

RESULTS: In comparison with those in the normal control group, the livers and spleens of model mice were heavier and liver/body ratio was higher (liver, 12 wk: 2.99 ± 0.28 g vs 1.83 ± 0.13 g; spleen, 12 wk: 0.87 ± 0.15 g vs 0.14 ± 0.02 g; liver/body ratio, 12 wk: 0.09 ± 0.01 vs 0.04 ± 0.00; all P < 0.01); the expression of TGF-β1 and Smad2/3 was significantly stronger in livers of the model mice (TGF-β1, 12 wk: 0.105 ± 0.008 vs 0.024 ± 0.002; Smad2/3, 12 wk: 0.094 ± 0.009 vs 0.003 ± 0.001, all P < 0.01), and the above indexes were positively correlated with the degrees of hepatic fibrosis (r = 0.635, 0.482, 0.646, 0.347, and 0.662, respectively; all P < 0.05). Smad4 was found increased in livers of the model mice, but its expression decreased with the development of hepatic fibrosis (4 wk: 0.075 ± 0.011 vs 0.023 ± 0.006, 6 wk: 0.043 ± 0.008 vs 0.010 ± 0.002, 8 wk: 0.038 ± 0.009 vs 0.003 ± 0.002, 12 wk: 0.028 ± 0.004 vs 0.013 ± 0.006, all P < 0.01). Smad7 expression heightened only at the 8^th wk.

CONCLUSION: TGF-β1 and Smad2/3 might play important roles in liver fibrogenesis and Smad4's effect might occur at early and middle stage of hepatic fibrosis.

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.

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