Nitric oxide production in acute gastroenteritis in Indian children

Rotavirus induces intercellular calcium waves through ADP signaling

Rotavirus causes severe diarrheal disease in children by broadly dysregulating intestinal homeostasis. However, the underlying mechanism(s) of rotavirus-induced dysregulation remains unclear. We found that rotavirus-infected cells produce paracrine signals that manifested as intercellular calcium waves (ICWs), observed in cell lines and human intestinal enteroids. Rotavirus ICWs were caused by the release of extracellular adenosine 5'-diphosphate (ADP) that activated P2Y1 purinergic receptors on neighboring cells. ICWs were blocked by P2Y1 antagonists or CRISPR-Cas9 knockout of the P2Y1 receptor. Blocking the ADP signal reduced rotavirus replication, inhibited rotavirus-induced serotonin release and fluid secretion, and reduced diarrhea severity in neonatal mice. Thus, rotavirus exploited paracrine purinergic signaling to generate ICWs that amplified the dysregulation of host cells and altered gastrointestinal physiology to cause diarrhea.

Immune Response Modulation by Caliciviruses

Noroviruses and Sapoviruses, classified in the Caliciviridae family, are small positive-stranded RNA viruses, considered nowadays the leading cause of acute gastroenteritis globally in both children and adults. Although most noroviruses have been associated with gastrointestinal disease in humans, almost 50 years after its discovery, there is still a lack of comprehensive evidence regarding its biology and pathogenesis mainly because they can be neither conveniently grown in cultured cells nor propagated in animal models. However, other members of this family such as Feline calicivirus (FCV), Murine norovirus (MNV), Rabbit hemorrhagic disease virus (RHDV), and Porcine sapovirus (PS), from which there are accessible propagation systems, have been useful to study the calicivirus replication strategies. Using cell cultures and animal models, many of the functions of the viral proteins in the viral replication cycles have been well-characterized. Moreover, evidence of the role of viral proteins from different members of the family in the establishment of infection has been generated and the mechanism of their immunopathogenesis begins to be understood. In this review, we discuss different aspects of how caliciviruses are implicated in membrane rearrangements, apoptosis, and evasion of the immune responses, highlighting some of the pathogenic mechanisms triggered by different members of the Caliciviridae family.

Plasma citrulline, arginine, nitric oxide, and blood ammonia levels in neonatal calves with acute diarrhea

Background

Plasma citrulline (CIT) concentration is considered to be a reliable marker of functional enterocyte mass, primarily in humans. However, information about CIT levels along with related metabolites, arginine (ARG), nitric oxide (NO), and ammonia in neonatal calves are lacking.

Objectives

To compare plasma CIT, ARG, NO, and whole blood ammonia concentrations in neonatal calves with acute diarrhea with those in healthy calves and to assess their possible relationships with diarrhea‐related criteria.

Animals

Seventy neonatal calves (60 with acute diarrhea and 10 healthy).

Methods

Observational case‐control study. Diarrheic calves were classified into subgroups on the basis of etiology, severity of diarrhea, degree of dehydration, and systemic inflammatory response syndrome (SIRS) status. Plasma CIT and ARG concentrations were measured by liquid chromatography/tandem mass spectrometry.

Results

Plasma CIT (median [range]: 67.5 [61.9‐75.4] vs 30.1 [15.0‐56.1] μmol/L) and ARG (170.7 [148.5‐219.5] vs 106.1 [54.4‐190.7] μmol/L) were lower and plasma NO (4.42 [3.29‐5.58] vs 6.78 [5.29‐8.92] μM) and blood ammonia concentrations (28.7 [26.1‐36.9] vs 59.8 [34.6‐99.5] μmol/L) were higher in the neonatal calves with diarrhea (P < .001). Plasma CIT (β = −0.29, P = .02), ARG (β = −0.33, P = .01), NO (β = 0.55, P < .001), and blood ammonia (β = 0.63, P <.001) were affected by SIRS status. Except for ammonia (0.52), the effects sizes for severity of diarrhea and degree of dehydration were small (ηp2 ≤ 0.45) for CIT, ARG, and NO.

Conclusions and Clinical Importance

The changes in these variables might have diagnostic, prognostic, and therapeutic value in diarrheic neonatal calves.

Feline calicivirus- and murine norovirus-induced COX-2/PGE2 signaling pathway has proviral effects

Cyclooxygenases (COXs)/prostaglandin E₂ (PGE₂) signaling pathways are known to modulate a variety of homeostatic processes and are involved in various pathophysiological conditions. COXs/PGE₂ signaling pathways have also been demonstrated to have proviral or antiviral effects, which appeared different even in the same virus family. A porcine sapovirus Cowden strain, a member of genus Sapovirus within the Caliciviridae family, induces strong COX-2/PGE₂ but transient COX-1/PGE₂ signaling to enhance virus replication. However, whether infections of other viruses in the different genera activate COXs/PGE₂ signaling, and thus affect the replication of viruses, remains unknown. In the present study, infections of cells with the feline calicivirus (FCV) F9 strain in the genus Vesivirus and murine norovirus (MNV) CW-1 strain in the genus Norovirus only activated the COX-2/PGE₂ signaling in a time-dependent manner. Treatment with pharmacological inhibitors or transfection of small interfering RNAs (siRNAs) against COX-2 enzyme significantly reduced the production of PGE₂ as well as FCV and MNV replications. The inhibitory effects of these pharmacological inhibitors against COX-2 enzyme on the replication of both viruses were restored by the addition of PGE₂. Silencing of COX-1 via siRNAs and inhibition of COX-1 via an inhibitor also decrease the production of PGE₂ and replication of both viruses, which can be attributed to the inhibition COX-1/PGE₂ signaling pathway. These data indicate that the COX-2/PGE₂ signaling pathway has proviral effects for the replication of FCV and MNV, and pharmacological inhibitors against these enzymes serve as potential therapeutic candidates for treating FCV and MNV infections.

Activation of COX-2/PGE2 Promotes Sapovirus Replication via the Inhibition of Nitric Oxide Production

Enteric caliciviruses in the genera Norovirus and Sapovirus are important pathogens that cause severe acute gastroenteritis in both humans and animals. Cyclooxygenases (COXs) and their final product, prostaglandin E₂ (PGE₂), are known to play important roles in the modulation of both the host response to infection and the replicative cycles of several viruses. However, the precise mechanism(s) by which the COX/PGE₂ pathway regulates sapovirus replication remains largely unknown. In this study, infection with porcine sapovirus (PSaV) strain Cowden, the only cultivable virus within the genus Sapovirus, markedly increased COX-2 mRNA and protein levels at 24 and 36 h postinfection (hpi), with only a transient increase in COX-1 levels seen at 24 hpi. The treatment of cells with pharmacological inhibitors, such as nonsteroidal anti-inflammatory drugs or small interfering RNAs (siRNAs) against COX-1 and COX-2, significantly reduced PGE₂ production, as well as PSaV replication. Expression of the viral proteins VPg and ProPol was associated with activation of the COX/PGE₂ pathway. We observed that pharmacological inhibition of COX-2 dramatically increased NO production, causing a reduction in PSaV replication that could be restored by inhibition of nitric oxide synthase via the inhibitor N-nitro-l-methyl-arginine ester. This study identified a pivotal role for the COX/PGE₂ pathway in the regulation of NO production during the sapovirus life cycle, providing new insights into the life cycle of this poorly characterized family of viruses. Our findings also reveal potential new targets for treatment of sapovirus infection.

IMPORTANCE

Sapoviruses are among the major etiological agents of acute gastroenteritis in both humans and animals, but little is known about sapovirus host factor requirements. Here, using only cultivable porcine sapovirus (PSaV) strain Cowden, we demonstrate that PSaV induced the vitalization of the cyclooxygenase (COX) and prostaglandin E₂ (PGE₂) pathway. Targeting of COX-1/2 using nonsteroidal anti-inflammatory drugs (NSAIDs) such as the COX-1/2 inhibitor indomethacin and the COX-2-specific inhibitors NS-398 and celecoxib or siRNAs targeting COXs, inhibited PSaV replication. Expression of the viral proteins VPg and ProPol was associated with activation of the COX/PGE₂ pathway. We further demonstrate that the production of PGE₂ provides a protective effect against the antiviral effector mechanism of nitric oxide. Our findings uncover a new mechanism by which PSaV manipulates the host cell to provide an environment suitable for efficient viral growth, which in turn can be a new target for treatment of sapovirus infection.

Towards a human rotavirus disease model

While the clinical importance of human rotavirus (RV) disease is well recognized and potent vaccines have been developed, our understanding of how human RV causes diarrhoea, vomiting and death remains unresolved. The fact that oral rehydration corrects electrolyte and water loss, indicates that enterocytes in the small intestine have a functional sodium-glucose co-transporter. Moreover, RV infection delays gastric emptying and loperamide appears to attenuate RV diarrhoea, thereby suggesting activation of the enteric nervous system. Serotonin (5-HT) receptor antagonists attenuate vomiting in young children with gastroenteritis while zinc and enkephalinase inhibitors attenuate RV-induced diarrhoea. In this review we discuss clinical symptoms, pathology, histology and treatment practices for human RV infections and compile the data into a simplified disease model.

Noroviruses as a cause of diarrhea in travelers to Guatemala, India, and Mexico

Noroviruses (NoVs) are increasingly being recognized as an important enteric pathogen of gastroenteritis worldwide. The prevalence of NoVs as a cause of diarrhea acquired by travelers in developing countries is not well known. We examined the prevalence and importance of NoV infection in three international traveler cohorts with diarrhea acquired in three developing regions of the world, Mexico, Guatemala, and India. We also characterized the demographics and symptoms associated with NoV diarrhea in these travelers. Stool samples from 571 international travelers with diarrhea were evaluated for traditional enteropathogens. NoVs were identified using reverse transcription-PCR and probe hybridization. NoVs were identified in 10.2% of cases of travelers' diarrhea and, overall, was the second most common pathogen, following diarrheagenic Escherichia coli. The detection of NoV diarrhea significantly varied over the three study time periods in Guadalajara, Mexico, ranging from 3 of 98 (3.0%) diarrheal stools to 12 of 100 (12.0%) fecal specimens (P=0.03). The frequency of NoV diarrhea was also dependent upon the geographic region, with 17 of 100 (17.0%) travelers to Guatemala, 23 of 194 (11.9%) travelers to India, and 3 of 79 (3.8%) travelers to Mexico testing positive for NoVs from 2002 to 2003 (P=0.02). NoVs are important pathogens of travelers' diarrhea in multiple regions of the world. Significant variation in the prevalence of NoV diarrhea and in the predominant genogroup infecting travelers was demonstrated, dependent upon the specific geographic location and over time.