Substance P is responsible for physiological alterations such as increased chloride ion secretion and glucose malabsorption in cryptosporidiosis

Immunity to Cryptosporidium: insights into principles of enteric responses to infection

Cryptosporidium parasites replicate within intestinal epithelial cells and are an important cause of diarrhoeal disease in young children and in patients with primary and acquired defects in T cell function. This Review of immune-mediated control of Cryptosporidium highlights advances in understanding how intestinal epithelial cells detect this infection, the induction of innate resistance and the processes required for activation of T cell responses that promote parasite control. The development of a genetic tool set to modify Cryptosporidium combined with tractable mouse models provide new opportunities to understand the principles that govern the interface between intestinal epithelial cells and the immune system that mediate resistance to enteric pathogens.

Advances in therapeutic and vaccine targets for Cryptosporidium: Challenges and possible mitigation strategies

Cryptosporidium is known to be the second most common diarrheal pathogen in children, causing potentially fatal diarrhea and associated with long-term growth stunting and cognitive deficits. The only Food and Drug Administration-approved treatment for cryptosporidiosis is nitazoxanide, but this drug has not shown potentially effective results in susceptible hosts. Therefore, a safe and effective drug for cryptosporidiosis is urgently needed. Cryptosporidium genome sequencing analysis may help develop an effective drug, but both in vitro and in vivo approaches to drug evaluation are not fully standardized. On the other hand, the development of partial immunity after exposure suggests the possibility of a successful and effective vaccine, but protective surrogates are not precise. In this review, we present our current perspectives on novel cryptosporidiosis therapies, vaccine targets and efficacies, as well as potential mitigation plans, recommendations and perceived challenges.

Intestinal epithelial barrier and neuromuscular compartment in health and disease

A number of digestive and extra-digestive disorders, including inflammatory bowel diseases, irritable bowel syndrome, intestinal infections, metabolic syndrome and neuropsychiatric disorders, share a set of clinical features at gastrointestinal level, such as infrequent bowel movements, abdominal distension, constipation and secretory dysfunctions. Several lines of evidence indicate that morphological and molecular changes in intestinal epithelial barrier and enteric neuromuscular compartment contribute to alterations of both bowel motor and secretory functions in digestive and extra-digestive diseases. The present review has been conceived to provide a comprehensive and critical overview of the available knowledge on the morphological and molecular changes occurring in intestinal epithelial barrier and enteric neuromuscular compartment in both digestive and extra-digestive diseases. In addition, our intent was to highlight whether these morphological and molecular alterations could represent a common path (or share some common features) driving the pathophysiology of bowel motor dysfunctions and related symptoms associated with digestive and extra-digestive disorders. This assessment might help to identify novel targets of potential usefulness to develop original pharmacological approaches for the therapeutic management of such disturbances.

Cryptosporidiosis Drug Discovery: Opportunities and Challenges

The apicomplexan parasite Cryptosporidium is the second most important diarrheal pathogen causing life-threatening diarrhea in children, which is also associated with long-term growth faltering and cognitive deficiency. Cryptosporidiosis is a parasitic disease of public health concern caused by Cryptosporidium parvum and Cryptosporidium hominis. Currently, nitazoxanide is the only approved treatment for cryptosporidium infections. Unfortunately, it has limited efficacy in the most vulnerable patients, thus there is an urgent need for a safe and efficacious cryptosporidiosis drug. In this work, we present our current perspectives on the target product profile for novel cryptosporidiosis therapies and the perceived challenges and possible mitigation plans at different stages in the cryptosporidiosis drug discovery process.

Gastrointestinal Parasites and the Neural Control of Gut Functions

Gastrointestinal motility and transport of water and electrolytes play key roles in the pathophysiology of diarrhea upon exposure to enteric parasites. These processes are actively modulated by the enteric nervous system (ENS), which includes efferent, and afferent neurons, as well as interneurons. ENS integrity is essential to the maintenance of homeostatic gut responses. A number of gastrointestinal parasites are known to cause disease by altering the ENS. The mechanisms remain incompletely understood. Cryptosporidium parvum, Giardia duodenalis (syn. Giardia intestinalis, Giardia lamblia), Trypanosoma cruzi, Schistosoma species and others alter gastrointestinal motility, absorption, or secretion at least in part via effects on the ENS. Recent findings also implicate enteric parasites such as C. parvum and G. duodenalis in the development of post-infectious complications such as irritable bowel syndrome, which further underscores their effects on the gut-brain axis. This article critically reviews recent advances and the current state of knowledge on the impact of enteric parasitism on the neural control of gut functions, and provides insights into mechanisms underlying these abnormalities.

Treatment of Cryptosporidium: What We Know, Gaps, and the Way Forward

Cryptosporidiosis is increasingly recognized as an important global health concern. While initially reported in immunocompromised such as AIDS patients, cryptosporidiosis has now been documented as a major cause of childhood diarrhea and an important factor in childhood malnutrition. Currently, nitazoxanide is the only proven anti-parasitic treatment for Cryptosporidium infections. However, it is not effective in severely immunocompromised patients and there is limited data in infants. Immune reconstitution or decreased immunosuppression is critical to therapy in AIDS and transplant patients. This limitation of treatment options presents a major public health challenge given the important burden of disease. Repurposing of drugs developed for other indications and development of inhibitors for novel targets offer hope for improved therapies, but none have advanced to clinical studies.

Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease

The tachykinins, exemplified by substance P, are one of the most intensively studied neuropeptide families. They comprise a series of structurally related peptides that derive from alternate processing of three Tac genes and are expressed throughout the nervous and immune systems. Tachykinins interact with three neurokinin G protein-coupled receptors. The signaling, trafficking, and regulation of neurokinin receptors have also been topics of intense study. Tachykinins participate in important physiological processes in the nervous, immune, gastrointestinal, respiratory, urogenital, and dermal systems, including inflammation, nociception, smooth muscle contractility, epithelial secretion, and proliferation. They contribute to multiple diseases processes, including acute and chronic inflammation and pain, fibrosis, affective and addictive disorders, functional disorders of the intestine and urinary bladder, infection, and cancer. Neurokinin receptor antagonists are selective, potent, and show efficacy in models of disease. In clinical trials there is a singular success: neurokinin 1 receptor antagonists to treat nausea and vomiting. New information about the involvement of tachykinins in infection, fibrosis, and pruritus justifies further trials. A deeper understanding of disease mechanisms is required for the development of more predictive experimental models, and for the design and interpretation of clinical trials. Knowledge of neurokinin receptor structure, and the development of targeting strategies to disrupt disease-relevant subcellular signaling of neurokinin receptors, may refine the next generation of neurokinin receptor antagonists.

Aprepitant for the prevention of nausea and vomiting associated with chemotherapy and postoperative recovery

Chemotherapy-induced nausea and vomiting (CINV) and postoperative nausea and vomiting (PONV) can negatively impact patient quality of life, functional performance and activities of daily living. Although the development of serotonin receptor antagonists has greatly improved the control of acute emesis, delayed CINV remains a significant clinical issue. Aprepitant (Emend(®)) is the first commercially available drug from a new class of agents, the neurokinin-1 receptor antagonists. Elucidation of its mechanism of action has produced a greater understanding of the pathophysiology of nausea and vomiting. Oral aprepitant, in combination with a selective serotonin (5-HT3) receptor antagonist and corticosteroids, is indicated for the prevention of acute and delayed nausea and vomiting associated with highly and moderately emetogenic chemotherapy in adults. Aprepitant alone or in combination only with dexamethasone does not optimally control acute emesis compared with triple combination therapy. By contrast, aprepitant as monotherapy is indicated for the prevention of PONV. Aprepitant represents an emerging class of agents and its addition to standard therapy provides an advanced benefit in the prevention and treatment of CINV and PONV. Investigations of aprepitant for other indications are ongoing.

Cryptic parasite revealed improved prospects for treatment and control of human cryptosporidiosis through advanced technologies

Cryptosporidium is an important genus of parasitic protozoa of humans and other vertebrates and is a major cause of intestinal disease globally. Unlike many common causes of infectious enteritis, there are no widely available, effective vaccine or drug-based intervention strategies for Cryptosporidium, and control is focused mainly on prevention. This approach is particularly deficient for infections of severely immunocompromised and/or suppressed, the elderly or malnourished people. However, cryptosporidiosis also presents a significant burden on immunocompetent individuals, and can, for example have lasting effects on the physical and mental development of children infected at an early age. In the last few decades, our understanding of Cryptosporidium has expanded significantly in numerous areas, including the parasite life-cycle, the processes of excystation, cellular invasion and reproduction, and the interplay between parasite and host. Nonetheless, despite extensive research, many aspects of the biology of Cryptosporidium remain unknown, and treatment and control are challenging. Here, we review the current state of knowledge of Cryptosporidium, with a focus on major advances arising from the recently completed genome sequences of the two species of greatest relevance in humans, namely Cryptosporidium hominis and Cryptosporidium parvum. In addition, we discuss the potential of next-generation sequencing technologies, new advances in in silico analyses and progress in in vitro culturing systems to bridge these gaps and to lead toward effective treatment and control of cryptosporidiosis.

Cryptosporidiosis-an overview

Apicomplexan protozoan parasites of the genus Cryptosporidium infect the gastrointestinal tract and lungs of a wide variety of animals, including humans. The majority of human infections are due to either Cryptosporidium hominis (C. hominis) and/or Cryptosporidium parvum (C. parvum). The parasite has a complex life cycle that includes both asexual and sexual stages. While there are invasive free living stages, proliferation and differentiation take place within a unique parasitrophorous vacuole under the host cell brush border but outside the host cell cytoplasm. Infection is spread by environmentally resistant spores that primarily contaminate drinking water and occasionally food sources, which may cause significant outbreaks of diarrhea that generally lasts less than 2 w in immunocompetent individuals. In immunodeficient or immunosuppressed individuals, diarrhea may be copious and can result in significant morbidity and mortality, particularly in AIDS patients. Although diagnosis is relatively simple, effective drug treatment, particulary for infections in immunodeficient patients, has not been uniformly successful. This overview summarizes the species known to infect humans, aspects of the parasite life cycle, sources of infection, the pathophysiology of cryptosporidiosis, the immune response to infection, diagnosis, treatment and some aspects of cryptosporidiosis in China.

Challenges in understanding the immunopathogenesis of Cryptosporidium infections in humans

Water and foodborne enteric cryptosporidiosis is a globally emerging public health issue. Although the clinical manifestations of enteric cryptosporidiosis are generally limited to intestinal infection and subsequent diarrhoea, extra-intestinal invasion has also been diagnosed in immunocompromised individuals, particularly in those infected with human immunodeficiency virus (HIV) or AIDS. Due to an inadequate understanding of Cryptosporidium immunopathogenesis in humans, the development of vaccines or therapeutic agents and their application in diseases management is difficult. Current therapeutic measures are not fully effective in the treatment of the disease. Therefore, the implementation of strategies designed to control the chain of cryptosporidiosis transmission (environment ↔ human ↔ food/water ↔ animal) is a critical but challenging issue to public health authorities across the world. Several excellent studies have been done on innate, acquired and mucosal immunity against Cryptosporidium infections using animal models, in vitro human cell lines and human volunteers. However, there are still multiple challenges in understanding the intestinal immune response (immunopathogenesis) to Cryptosporidium infection in humans. This paper reviews recent updates on immunopathogenesis and immune responses to Cryptosporidium infection in humans, while also discussing the current limitations that exist regarding a precise understanding of the immunopathological mechanisms.

Cryptosporidium parvum isolate-dependent postinfectious jejunal hypersensitivity and mast cell accumulation in an immunocompetent rat model

Cryptosporidium spp. are a cause of self-limited diarrhea in immunocompetent hosts. In immunocompetent rats, Cryptosporidium parvum infection induced digestive hypersensitivity, a key pathophysiological factor in functional digestive disorders such as irritable bowel syndrome (IBS). In such a rat model, we sought to document whether jejunal hypersensitivity depends on C. parvum isolate and is associated with a mast cell accumulation. Five-day-old rats were orally administered 10(5) oocysts of either Nouzilly (NoI) or Iowa (IoI) C. parvum isolate. NoI-infected rats exhibited the lowest food intake on days 7 and 14 postinfection (p.i.). On day 7 p.i., small intestine villus atrophy, crypt hyperplasia, and inflammatory cell infiltration were prominent in NoI-infected rats, with higher numbers of Cryptosporidium forms than in IoI-infected rats. Compared to uninfected control rats, jejunal intraepithelial lymphocytes (IELs) were increased only in NoI-infected rats on day 14 p.i. On day 50 p.i., jejunal hypersensitivity to distension was found only in NoI-infected rats; this hypersensitivity is associated with activated mast cell accumulation. The number of mast cells in the jejunal lamina propria was increased from day 36 p.i. in NoI-infected rats and only at day 120 p.i. in IoI-infected rats. Our data suggest that both the severity of infection (weight loss, reduced food intake, villus atrophy, and IEL accumulation) and the onset of a jejunal hypersensitivity after infection in association with an activated mast cell accumulation are isolate dependent and related to NoI infection. This cryptosporidiosis rat model is a relevant model for the study of underlying mechanisms of postinfectious IBS-like symptoms.

Substance P receptor antagonism for treatment of cryptosporidiosis in immunosuppressed mice

Cryptosporidiosis, caused by the protozoan parasite Cryptosporidium parvum, causes self-limited diarrhea in normal hosts but can cause life-threatening diarrhea for immunosuppressed patients. There is an urgent need for new drugs to treat this chronic disease. Cryptosporidium parvum infection is associated with intestinal structural and pathophysiologic changes, including villi blunting and glucose malabsorption. Substance P (SP), a neuropeptide and pain transmitter, is associated with the gastrointestinal tract and is elevated in humans and macaques after experimental C. parvum challenge. To examine the relevance of SP in the pathogenesis of cryptosporidiosis, and to determine if SP receptor antagonism can be employed for treatment of cryptosporidiosis in immunosuppressed hosts, we used an immunosuppressed murine model (dexamethasone-immunosuppressed mice) that is frequently utilized for examining chemotherapeutic potential of drugs. Quantitative ELISA was used to measure intestinal SP levels in immunosuppressed mice with, and without, C. parvum infection. Intestinal physiological alterations, as studied by the Ussing chamber technique, plus weight change, fecal oocyst shedding, and villi measurements, were compared in infected mice with, and without, SP receptor antagonist (aprepitant) treatment. Immunosuppressed mice infected with C. parvum demonstrated increased SP levels as well as physiological alterations (glucose malabsorption), weight loss, fecal oocyst shedding, and structural alterations (increased intestinal villi blunting) compared to uninfected mice. Each of these defects was significantly inhibited by aprepitant treatment. These studies demonstrate the potential of SP receptor antagonism for treatment of pathogenesis of cryptosporidiosis in immunosuppressed hosts.

Lymphoproliferative and cytokine responses to Cryptosporidium parvum in patients coinfected with C. parvum and human immunodeficiency virus

We compared the lymphoproliferative and cytokine responses to Cryptosporidium parvum in human immunodeficiency virus (HIV)-seropositive and -seronegative patients. The lymphoproliferative and cytokine responses (interleukin-2 [IL-2], IL-4, IL-5, IL-10, gamma interferon, and tumor necrosis factor alpha) were assessed for 11 HIV-seropositive, Cryptosporidium-positive (group I) patients; 20 HIV-seropositive, Cryptosporidium-negative (group II) patients; 10 HIV-seronegative, Cryptosporidium-positive (group III) patients, including four post-renal transplant (group IIIa) and 6 presumably immunocompetent (group IIIb) patients; and 20 HIV-seronegative, Cryptosporidium-negative healthy individuals (group IV). No significant difference was observed in the number of patients showing positive lymphoproliferative responses in group I compared to group III (post-renal transplant [group IIIa] or immunocompetent [group IIIb]) patients, while a comparison of the median stimulation indices shows that responses were significantly lower in Cryptosporidium-infected, immunosuppressed (group I and IIIa) patients than in immunocompetent (group IIIb) patients. The number of patients showing positive responses and median stimulation indices was significantly higher for Cryptosporidium-infected (HIV-seropositive and -seronegative) individuals than for uninfected individuals, suggesting that Cryptosporidium induces significant in vitro lymphoproliferative responses in infected individuals. Cytokine levels, except for that of IL-5, were significantly higher in Cryptosporidium-infected (groups I and III) individuals than in uninfected (groups II and IV) individuals. There was no significant difference between the group I and III patients and between Cryptosporidium-infected immunosuppressed (group I or IIIa) and immunocompetent (group IIIb) patients.