Substance P receptor antagonist reverses intestinal pathophysiological alterations occurring in a novel ex-vivo model of Cryptosporidium parvum infection of intestinal tissues derived from SIV-infected macaques

Substance P—Friend or Foe

Substance P (SP), a neuropeptide and pain transmitter has multiple roles and is involved in various processes in the body [...]

Substance P and the regulation of inflammation in infections and inflammatory bowel disease

Substance P (SP) and its natural analogue hemokinin-1 (HK1) are produced by lymphocytes and macrophages, and at times B cells. These peptides are an important component of the immune response during several infections and in inflammatory bowel disease (IBD). The synthesis of SP and HK1 in leucocytes is subject to immune regulation. IL12 and IL23 stimulate T cells and macrophages to make SP respectively. The cytokines driving HK1 production are not presently defined. These peptides act through a shared receptor called neurokinin-1. T cells, macrophages and probably other immune cell types can express this receptor. Several cytokines IL12, IL18 and TNFα as well as T-cell antigen receptor activation induce neurokinin-1 receptor expression on T cells, while IL10 blocks receptor display. TGFβ delays internalization of the SP/neurokine-1R complex on T cells resulting in stronger receptor signalling. One of the functions of SP and neurokinin-1 receptor is to enhance T cell IFNγ and IL17 production, amplifying the proinflammatory response. Thus, SP and HK1 have overlapping functions and are part of a sophisticated immune regulatory circuit aimed at amplifying inflammation at mucosal surfaces and in other regions of the body as shown in animal models of infection and IBD.

Protozoan infections of the gastrointestinal tract

The review provides current views on human protozoan parasites of the gut. The recognition of the importance of cryptosporidium, cyclospora and microsporidia over the last three decades emphasises the possibility that more pathogenic intestinal protozoa are presently unrecognized. Each of these is a zoonotic infection and the potential for a zoonotic element to the transmission of giardiasis has been recognized. A common theme in increased understanding of the biology and pathological mechanisms involved in causing disease is the application of molecular techniques to the various stages of the parasite life cycle. Molecular methods are increasingly contributing to laboratory diagnosis of these conditions with increased yields of positive results though in the tropics it is likely that fecal microscopy will remain the standard for some time to come. The nitroimidazole compounds are the mainstay of treatment for giardia and amebiasis with no major advance in therapeutics since their role was appreciated. Nitazoxanide was shown to be effective for cryptosporidiosis in the 1990s.

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.