Age-dependent diarrhea induced by a rotaviral nonstructural glycoprotein

Role of Ca2+in the replication and pathogenesis of rotavirus and other viral infections

Ca2+ plays a key role in many pathological processes, including viral infections. Rotavirus, the major etiological agent of viral gastroenteritis in children and young animals, provides a useful model to study a number of Ca2+ dependent virus-cell interactions. Rotavirus entry, activation of transcription, morphogenesis, cell lysis, particle release, and the distant action of viral proteins are Ca2+ dependent processes. In the extracellular medium, Ca2+ stabilizes the structure of the viral capsid. During entry into the cell the low cytoplasmic Ca2+ concentration induced the solubilization of the outer protein layer of the capsid and transcriptase activation. Viral protein synthesis modifies Ca2+ homeostasis which, in turn, favours viral morphogenesis and induces cell death. The generation of diarrhea is a multifactorial process involving Ca2+ dependent secretory processes of mediators and water and electrolytes, as well as the induction of cell death in the different cell types that compose the intestinal epithelium. The discovery of the non-structural viral protein NSP4 as a viral enterotoxin and the possible participation of the enteric nervous system in the pathogenesis of diarrhea represent significant advances in its understanding. Ca2+ also plays a role in the replication cycles and pathogenesis of other viral diseases such as poliovirus, Coxsackie virus, cytomegalovirus, vaccinia and measles virus and HIV.

Rotavirus infection impairs intestinal brush-border membrane Na(+)-solute cotransport activities in young rabbits

The mechanism of rotavirus diarrhea was investigated by infecting young, specific pathogen-free, New Zealand rabbits with a lapine rotavirus, strain La/RR510. With 4-wk-old animals, virus shedding into the intestinal lumen peaked at 72 h postinfection (hpi), and a mild, watery diarrhea appeared at 124 hpi. No intestinal lesions were seen up to 144 hpi, indicating that diarrhea does not follow mucosal damage but can precede it, as if cell dysfunction were the cause, not the consequence, of the histological lesions. Kinetic analyses with brush-border membrane vesicles isolated from infected rabbits revealed strong inhibition of both Na(+)-D-glucose (SGLT1) and Na(+)-L-leucine symport activities. For both symporters, only maximum velocity decreased with time. The density of phlorizin-binding sites and SGLT1 protein antigen in the membrane remained unaffected, indicating that the virus effect on this symporter is direct. Because SGLT1 supports water reabsorption under physiological conditions, the mechanism of rotavirus diarrhea may involve a generalized inhibition of Na(+)-solute symport systems, hence, of water reabsorption. Massive water loss through the intestine may eventually overwhelm the capacity of the organ for water reabsorption, thereby helping the diarrhea to get established.

Influenza virus inhibits amiloride-sensitive Na+ channels in respiratory epithelia

Many pathogens causing diarrhea do so by modulating ion transport in the gut. Respiratory pathogens are similarly associated with disturbances of fluid balance in the respiratory tract, although it is not known whether they too act by altering epithelial ion transport. Here we show that influenza virus A/PR/8/34 inhibits the amiloride-sensitive Na(+) current across mouse tracheal epithelium with a half-time of about 60 min. We further show that the inhibitory effect of the influenza virus is caused by the binding of viral hemagglutinin to a cell-surface receptor, which then activates phospholipase C and protein kinase C. Given the importance of epithelial Na(+) channels in controlling the amount of fluid in the respiratory tract, we suggest that down-regulation of Na(+) channels induced by influenza virus may play a role in the fluid transport abnormalities that are associated with influenza infections.

Racecadotril in the treatment of acute watery diarrhea in children

BACKGROUND

Racecadotril (acetorphan), an enkephalinase inhibitor with antisecretory and antidiarrheal actions, is an effective and safe treatment for acute diarrhea in adults and children. Whether treatment with racecadotril and oral rehydration therapy is more effective than treatment with oral rehydration alone in hospitalized children with acute watery diarrhea is not known.

METHODS

We treated 135 boys 3 to 35 months of age who had watery diarrhea of five days' duration or less with racecadotril (1.5 mg per kilogram of body weight orally every eight hours) or placebo, in addition to oral rehydration solution. The primary end point was the 48-hour stool output (measured in grams); the total stool output, duration of diarrhea, and total intake of oral rehydration solution were also measured.

RESULTS

The mean (+/-SE) 48-hour stool output was 92+/-12 g per kilogram in the racecadotril group and 170+/-15 g per kilogram in the placebo group (P<0.001), a 46 percent reduction with racecadotril. The results were similar among the 73 boys with rotavirus infections. The total stool output was 157+/-27 g per kilogram in the racecadotril group and 331+/-39 g per kilogram in the placebo group (P<0.001). The median duration of diarrhea was significantly less (P<0.001) in the racecadotril group (28 hours regardless of rotavirus status) than in the placebo group (72 and 52 hours, respectively, for rotavirus-positive and rotavirus-negative patients). The intake of oral rehydration solution was significantly lower in the racecadotril group than in the placebo group (P<0.001). Racecadotril was well tolerated; only seven patients taking racecadotril had adverse effects, which were all mild and transient.

CONCLUSIONS

In young boys with acute watery diarrhea, racecadotril is an effective and safe treatment.

Infantile convulsions with mild gastroenteritis

The development of sensitive new molecular genetic techniques has led to the detection of rotavirus in cerebrospinal fluid, stools and throat swabs from patients with gastroenteritis with accompanying clinical symptoms similar to infantile benign convulsions. Small round structured virus (SRSV) has also been found in stools of patients with similar clinical symptoms by a new procedure. However, the mechanism by which these viral infections induce benign convulsions remains to be elucidated. The present paper reviews recent virological and clinical studies of seizures probably caused by gastroenteritis viruses including rotavirus, SRSV and other viruses.

Membrane-destabilizing activity of rotavirus NSP4 is mediated by a membrane-proximal amphipathic domain

Expression of the rotavirus non-structural glycoprotein NSP4 in E. coli leads to a decrease in optical density of the culture and release of [(3)H]uridine into the medium, effects attributable to the ability of NSP4 to perturb the bacterial membrane. To identify a domain of NSP4 responsible, different regions of the polypeptide were expressed in E. coli. Membrane destabilization is associated with a region of the protein located within residues 48-91, which includes a potential cationic amphipathic helix. A second region of NSP4 that contains a coiled-coil oligomerization domain and a sequence reported to function as a viral enterotoxin enhances the membrane-destabilizing activity of residues 48-91, but has no direct effect on the membrane stability. These studies suggest that the membrane-destabilizing and enterotoxic properties of NSP4 may be mediated by different regions of the polypeptide and suggest a possible basis for the cytotoxicity of NSP4 in mammalian cells.

Norwalk virus open reading frame 3 encodes a minor structural protein

Norwalk virus (NV) is a causative agent of acute epidemic nonbacterial gastroenteritis in humans. The inability to cultivate NV has required the use of molecular techniques to examine the genome organization and functions of the viral proteins. The function of the NV protein encoded by open reading frame 3 (ORF 3) has been unknown. In this paper, we report the characterization of the NV ORF 3 protein expressed in a cell-free translation system and in insect cells and show its association with recombinant virus-like particles (VLPs) and NV virions. Expression of the ORF 3 coding region in rabbit reticulocyte lysates resulted in the production of a single protein with an apparent molecular weight of 23,000 (23K protein), which is not modified by N-linked glycosylation. The ORF 3 protein was expressed in insect cells by using two different baculovirus recombinants; one recombinant contained the entire 3' end of the genome beginning with the ORF 2 coding sequences (ORFs 2+3), and the second recombinant contained ORF 3 alone. Expression from the construct containing both ORF 2 and ORF 3 resulted in the expression of a single protein (23K protein) detected by Western blot analysis with ORF 3-specific peptide antisera. However, expression from a construct containing only the ORF 3 coding sequences resulted in the production of multiple forms of the ORF 3 protein ranging in size from 23,000 to 35,000. Indirect-immunofluorescence studies using an ORF 3 peptide antiserum showed that the ORF 3 protein is localized to the cytoplasm of infected insect cells. The 23K ORF 3 protein was consistently associated with recombinant VLPs purified from the media of insect cells infected with a baculovirus recombinant containing the entire 3' end of the NV genome. Western blot analysis of NV purified from the stools of NV-infected volunteers revealed the presence of a 35K protein as well as multiple higher-molecular-weight bands specifically recognized by an ORF 3 peptide antiserum. These results indicate that the ORF 3 protein is a minor structural protein of the virion.

Probing the structure of rotavirus NSP4: a short sequence at the extreme C terminus mediates binding to the inner capsid particle

The rotavirus nonstructural glycoprotein NSP4 functions as the receptor for the inner capsid particle (ICP) which buds into the lumen of the endoplasmic reticulum during virus maturation. The structure of the cytoplasmic domain of NSP4 from rotavirus strain SA11 has been investigated by using limited proteolysis and mass spectrometry. Digestion with trypsin and V8 protease reveals a C-terminal protease-sensitive region that is 28 amino acids long. The minimal sequence requirements for receptor function have been defined by constructing fusions with glutathione S-transferase and assessing their ability to bind ICPs. These experiments demonstrate that 17 to 20 amino acids from the extreme C terminus are necessary and sufficient for ICP binding and that this binding is cooperative. These observations are consistent with a model for the structure of the NSP4 cytoplasmic region in which four flexible regions of 28 amino acids are presented by a protease-resistant coiled-coil tetramerization domain, with only the last approximately 20 amino acids of each peptide interacting with the surface binding sites on the ICP.

Comparative pathogenesis of enteric viral infections of swine

At least 11 enteric viruses belonging to 6 distinct families (Adenoviridae, Astroviridae, Caliciviridae, Coronaviridae, Parvoviridae, and Reoviridae) cause diarrhea in swine mainly during the nursing and immediate post-weaning period. Most infect the small intestinal enterocytes, inducing various degrees of villous atrophy and subsequently a malabsorptive, maldigestive diarrhea. In addition rotaviruses possess an enterotoxin (NSP4) which induces a secretory diarrhea in mice. These viruses have distinct predilections for different vertical (villus/crypt) and horizontal (duodenum, jejunum, ileum, colon) replication sites in the intestine and the diarrhea intensity is often related to the extent of viral replication at these sites. In addition concurrent infections with multiple enteric viruses can produce synergistic or additive effects leading to more extensive villous atrophy throughout the intestine and more severe and prolonged diarrhea. Knowledge of enteric viral replication sites and comparative mechanisms of diarrhea induction may lead to new or improved vaccine strategies or therapeutic approaches for the prevention or treatment of these viral diarrheas.

Oral rehydration solution therapy in the management of children with rotavirus diarrhea

Rotavirus infections are the most common cause of gastroenteritis among children younger than 3 years of age and are associated with sporadic outbreaks of diarrhea in elderly and immunocompromised patients. Oral rehydration solutions (ORS) are formulated to correct dehydration and acidosis. Currently, ORS do not promote intestinal healing; however, investigators are examining the role of nutrition in promoting intestinal healing. This article reviews the composition of several ORS in human medicine and summarizes our current knowledge of the nutritional treatment of rotavirus diarrhea and intestinal healing.

Rotavirus infection induces an increase in intracellular calcium concentration in human intestinal epithelial cells: role in microvillar actin alteration

Rotaviruses, which infect mature enterocytes of the small intestine, are recognized as the most important cause of viral gastroenteritis in young children. We have previously reported that rotavirus infection induces microvillar F-actin disassembly in human intestinal epithelial Caco-2 cells (N. Jourdan, J. P. Brunet, C. Sapin, A. Blais, J. Cotte-Laffitte, F. Forestier, A. M. Quero, G. Trugnan, and A. L. Servin, J. Virol. 72:7228-7236, 1998). In this study, to determine the mechanism responsible for rotavirus-induced F-actin alteration, we investigated the effect of infection on intracellular calcium concentration ([Ca(2+)](i)) in Caco-2 cells, since Ca(2+) is known to be a determinant factor for actin cytoskeleton regulation. As measured by quin2 fluorescence, viral replication induced a progressive increase in [Ca(2+)](i) from 7 h postinfection, which was shown to be necessary and sufficient for microvillar F-actin disassembly. During the first hours of infection, the increase in [Ca(2+)](i) was related only to an increase in Ca(2+) permeability of plasmalemma. At a late stage of infection, [Ca(2+)](i) elevation was due to both extracellular Ca(2+) influx and Ca(2+) release from the intracellular organelles, mainly the endoplasmic reticulum (ER). We noted that at this time the [Ca(2+)](i) increase was partially related to a phospholipase C (PLC)-dependent mechanism, which probably explains the Ca(2+) release from the ER. We also demonstrated for the first time that viral proteins or peptides, released into culture supernatants of rotavirus-infected Caco-2 cells, induced a transient increase in [Ca(2+)](i) of uninfected Caco-2 cells, by a PLC-dependent efflux of Ca(2+) from the ER and by extracellular Ca(2+) influx. These supernatants induced a Ca(2+)-dependent microvillar F-actin alteration in uninfected Caco-2 cells, thus participating in rotavirus pathogenesis.

The authentic sequence of rotavirus SA11 nonstructural protein NSP4

Recent studies demonstrate that the rotavirus nonstructural protein NSP4 functions as an enterotoxin and plays an important role in viral pathogenesis. Previous in vitro studies of NSP4 have used a cDNA clone of gene 10 derived from the prototypic rotavirus strain, SA11. We recently compared the sequence of the commonly used NSP4 cDNA with the sequence obtained from several SA11 isolates by direct sequencing of reverse transcription polymerase chain reaction products. One codon difference was identified between the cDNA clone and the SA11 virus isolates, and this resulted in a predicted amino acid substitution at position 47. The cDNA sequence specifies an asparagine at position 47, and the SA11 virus gene 10 encodes a hisitidine. To determine if this amino acid substitution altered the function of NSP4, we analyzed the ability of both NSP4-Asn47 and NSP4-His47 to regulate intracellular calcium levels and exhibit cell cytotoxicity. Our results indicate that the expression of NSP4-His47 from a recombinant baculovirus displays enhanced cytotoxicity and calcium flux.

Role of the enteric nervous system in the fluid and electrolyte secretion of rotavirus diarrhea

The mechanism underlying the intestinal fluid loss in rotavirus diarrhea, which often afflicts children in developing countries, is not known. One hypothesis is that the rotavirus evokes intestinal fluid and electrolyte secretion by activation of the nervous system in the intestinal wall, the enteric nervous system (ENS). Four different drugs that inhibit ENS functions were used to obtain experimental evidence for this hypothesis in mice in vitro and in vivo. The involvement of the ENS in rotavirus diarrhea indicates potential sites of action for drugs in the treatment of the disease.

Gastrointestinal infections in children

New pathogens that cause gastroenteritis in children are being recognized. Even well-recognized pathogens, such as Clostridium difficile, may require more extensive testing than was previously thought necessary. Several new tests have emerged that allow for faster identification of these pathogens so that same-day results may be possible. Probiotic therapy has emerged as a novel strategy for the treatment of gastroenteritis. New vaccines against both viral and bacterial causes of gastroenteritis are being developed. The most exciting recent advance in vaccine development may be the creation of edible vaccines.

Sequence analysis of the NSP4 gene from human rotavirus strains isolated in the United States

Two major and one minor genotype of the rotavirus NSP4 gene have been described. The sequences of 29 NSP4 genes from rotavirus isolates obtained in the United States during the 1996-1997 rotavirus season (types P[8]G1, P[8]G9, P[4]G2 and P[6]G9) and 10 strains isolated during previous rotavirus seasons (types P[8]G1 and P[4]G2) were determined. All NSP4 genes from strains with short E types (6 P[4]G2, 4 P[6]G9) belonged to genotype NSP4A, whereas all 19 strains with long E types (16 P[8]G1, 3 P[8]G9) had NSP4 genes of genotype NSP4B. Genetic variation within genotypes was low ( < or = 2.3% for both NSP4A and NSP4B), confirming that the NSP4 genes are highly conserved. Nonetheless, at least two distinct sub-lineages could be detected within each genotype: strains isolated in the same year, regardless of geographic location, were more closely related or even identical at the deduced amino acid level; strains isolated in different years were more distinct. Thus, geographic distance did not affect genetic distance. Northern hybridization analysis with NSP4A and NSP4B total gene probes failed to detect any unusual combinations of the VP6 and NSP4 genes in 31 additional isolates from the 1996-1997 rotavirus season.

Oral electrolyte therapy

Diarrhea is a common condition in neonatal calves and can be caused by a wide variety of infections and noxious agents. Oral electrolyte therapy is a simple and economical method of treating diarrheic calves. Oral electrolyte solutions can correct dehydration and acidosis, and they may also have a role in preventing or alleviating mucosal damage. Indications, the principles of administration, and choosing an electrolyte product are discussed with examples.

Concentration-dependent differential induction of necrosis or apoptosis by HIV-1 lytic peptide 1

The mechanism by which human immunodeficiency virus type 1 induces depletion of CD4+ T-lymphocytes remains controversial, but may involve cytotoxic viral proteins. Synthetic peptides (lentivirus lytic peptide type 1) corresponding to the carboxyl terminus of the human immunodeficiency virus type 1 transmembrane glycoprotein induce cytopathology at concentrations of 100 nM and above. At these concentrations lentivirus lytic peptide type 1 disrupts mitochondrial integrity of CD4+ T-lymphoblastoid cells and induces other changes characteristic of necrosis. In contrast, at concentrations of 20 nM, lentivirus lytic peptide type 1 potently induces apoptosis. Thus, the mechanism by which human immunodeficiency virus type 1 mediates cell death, necrosis or apoptosis, may depend, in part, on the tissue concentration of transmembrane glycoprotein.

Dual infection of gnotobiotic calves with bovine strains of group A and porcine-like group C rotaviruses influences pathogenesis of the group C rotavirus

There is serological evidence that bovine group C rotaviruses exist in the United States, but there are no reports of their isolation. Ninety fecal samples from calves with diarrhea, 81 samples from adult cows with diarrhea (winter dysentery), and 20 fecal samples from healthy adult cows were tested for group C rotaviruses by polyacrylamide gel electrophoresis, immune electron microscopy, and reverse transcription-PCR (RT-PCR). Three samples from adult cow diarrhea cases were positive only by RT-PCR, and a group C rotavirus was isolated from a positive sample in monkey kidney (MA104) cells (WD534tc/C). Genetically and serologically, the WD534tc/C strain was more closely related to the Cowden porcine group C strain than to the Shintoku bovine strain. Because the original cow feces also contained a group A rotavirus (detected after passage in cell culture), we hypothesized that such dual-rotavirus infections might play a role in the pathogenesis and host adaptation of rotaviruses. Thus, we examined the pathogenesis of WD534tc/C alone or combined with virulent (IND/A) or attenuated (NCDV/A) bovine group A rotaviruses in gnotobiotic calves. WD534tc/C alone induced diarrhea without (or with limited) virus shedding in inoculated calves (n = 3). In contrast, all calves coinfected with WD534tc/C and IND/A (n = 2) developed diarrhea and shed both viruses, whereas calves coinfected with WD534tc/C and NCDV/A (n = 3) developed diarrhea but did not shed either virus. Infection with WD534tc/C or NCDV/A alone caused only mild villous atrophy (jejunum and/or ileum), whereas dual infection with both viruses induced lesions throughout the small intestine. Although IND/A alone caused villous atrophy, more-widespread small intestinal lesions occurred in calves coinfected with WD534tc/C and IND/A. In conclusion, coinfection of calves with group A rotaviruses enhanced fecal shedding of a bovine group C rotavirus and the extent of histopathological lesions in the small intestines. Thus, our findings suggest a potential novel hypothesis involving dual infections for the adaptation of heterologous rotaviruses to new host species.

The Epithelial Cell Response to Rotavirus Infection

Rotavirus is the most important worldwide cause of severe gastroenteritis in infants and young children. Intestinal epithelial cells are the principal targets of rotavirus infection, but the response of enterocytes to rotavirus infection is largely unknown. We determined that rotavirus infection of HT-29 intestinal epithelial cells results in prompt activation of NF-κB (&lt;2 h), STAT1, and ISG F3 (3 h). Genetically inactivated rotavirus and virus-like particles assembled from baculovirus-expressed viral proteins also activated NF-κB. Rotavirus infection of HT-29 cells induced mRNA for several C-C and C-X-C chemokines as well as IFNs and GM-CSF. Mice infected with simian rotavirus or murine rotavirus responded similarly with the enhanced expression of a profile of C-C and C-X-C chemokines. The rotavirus-stimulated increase in chemokine mRNA was undiminished in mice lacking mast cells or lymphocytes. Rotavirus induced chemokines only in mice &lt;15 days of age despite documented infection in older mice. Macrophage inflammatory protein-1β and IFN-stimulated protein 10 mRNA responses occurred, but were reduced in p50−/− mice. Macrophage inflammatory protein-1β expression during rotavirus infection localized to the intestinal epithelial cell in murine intestine. These results show that the intestinal epithelial cell is an active component of the host response to rotavirus infection.

Viral gastroenteritis

A large number of viruses can be found in the human intestine. Some (bacteriophages) infect the bacteria present as normal flora and others use the gut as a portal of entry. This review examines the virology, pathogenesis, immunology, epidemiology, clinical features, treatment and prevention of the viral enteropathogens. Rotavirus is undoubtedly the most important, causing an estimated 800,000 deaths each year, especially in developing countries. Recently, an oral live quadrivalent rhesus rotavirus vaccine has been licensed for use in the USA. It has great potential but there are a number of hurdles to be overcome before it can be given to infants in developing countries. Molecular techniques are revolutionizing our understanding of rotavirus pathogenesis, and the tremendous diversity of Caliciviridae and Astroviridae, as well as producing new diagnostic techniques and vaccines.

Diarrhea induction by rotavirus NSP4 in the homologous mouse model system

Comparison of the NSP4 amino acid sequences from 31 strains of mammalian rotaviruses revealed the presence of four distinct NSP4 alleles; i.e., the Wa, KUN, AU-1, and EW alleles. The EW allele consists only of NSP4s from murine rotavirus strains and is divergent from other NSP4 alleles from the evolutionary perspective. There have been conflicting reports regarding the enterotoxigenic activity of NSP4 in the mouse model system; heterologous simian and porcine rotavirus NSP4s function as an enterotoxin in mice, while a homologous EC NSP4 does not play a dominant role as an enterotoxin in the cystic fibrosis conductance regulator knockout mice. To further examine the enterotoxigenic activity of NSP4, we expressed in Escherichia coli a recombinant protein consisting of glutathione S-transferase and amino acid residues 86-175 of the EW NSP4. We found that this fusion protein caused diarrhea in the majority (8/14) of 5- to 6-day-old CD1 mice. This study confirmed and extended that group A rotavirus NSP4s were able to induce diarrhea in neonatal mice and had an enterotoxigenic activity.

Rotavirus infections: guidelines for treatment and prevention

The classification of rotaviruses as well as the pathogenesis and the diagnosis of rotavirus infections are briefly reviewed. Treatment of rotavirus disease consists mainly of oral or intravenous rehydration, using World Health Organization-recommended oral rehydration solutions or lactated Ringer's solutions, respectively. Specific antivirals have been tried in animal models but are not used for human treatment at present. The epidemiology of rotaviruses is complex as at any one time and in any geographical area different types co-circulate. The development of rotavirus candidate vaccines is reviewed, one of which, the tetravalent, rhesus rotavirus-based human reassortant vaccine, was licensed for universal use in the US in 1998. Its implementation requires careful surveillance of co-circulating rotavirus types (molecular epidemiology) as well as of any potential adverse effects not previously detected.

Comparisons of nucleotide and deduced amino acid sequences of NSP4 genes of virulent and attenuated pairs of group A and C rotaviruses

The NSP4 protein of rotavirus is a nonstructural glycoprotein and has a crucial function in virus morphogenesis during infection of host cells. It was recently reported that NSP4 may also function as a viral enterotoxin in the induction of rotavirus diarrhea by causing Ca++ influx in the cytoplasm of the infected cells. We sequenced and analyzed two (Wa and M strains) pairs of NSP4 genes of virulent (v) and attenuated (a) (after 30 to 40 passages in cell culture) human group A rotaviruses and a pair of NSP4 genes of virulent and attenuated porcine group C rotavirus (Cowden strain). These strains were previously identified as virulent (induce diarrhea) or attenuated (no diarrhea) in a gnotobiotic pig model of rotavirus infection [Bohl et al. (4), Saif et al. (13), Ward et al. (17)]. The NSP4 genes of the Wa, M and Cowden strains were amplified with RT-PCR using a proof reading polymerase (Tli) and the RT-PCR product was sequenced directly. Analysis of the NSP4 deduced amino acid sequences showed that only 3 (Wa) and 2 (M and Cowden) amino acids differed between the virulent and attenuated strains. For the Wa strain, the changes from the virulent to attenuated strain were in amino acids 13 (V to A), 16 (L to S) and 34 (P to L); in the M strain, the difference was in amino acids 53 (T to I) and 104 (K to E), and in the Cowden strains, amino acids 50 (L to F) and 97 (D to N) differed between virulent and attenuated strains. To our knowledge, this is the first sequence comparison between NSP4 of a virulent and attenuated pair of group C rotaviruses. The potential impact of these few amino acid changes on the pathogenesis of the NSP4 protein for piglets is unclear, relative to previous findings in mice (1), but requires further study using purified recombinant NSP4 proteins or peptides.

NSP4 elicits age-dependent diarrhea and Ca(2+)mediated I(-) influx into intestinal crypts of CF mice

Homologous disruption of the murine gene encoding the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) leads to the loss of cAMP-mediated ion transport. Mice carrying this gene defect exhibit meconium ileus at birth and gastrointestinal plugging during the neonatal period, both contributing to high rates of mortality. We investigated whether infectious mammalian rotavirus, the recently characterized rotaviral enterotoxin protein NSP4, or its active NSP4(114-135) peptide, can overcome these gastrointestinal complications in CF (CFTR(m3Bay) null mutation) mice. All three agents elicited diarrhea when administered to wild-type (CFTR(+/+)), heterozygous (CFTR(+/-)), or homozygous (CFTR(-/-)) 7- to 14-day-old mouse pups but were ineffective when given to older mice. The diarrheal response was accompanied by non-age-dependent intracellular Ca(2+) mobilization within both small and large intestinal crypt epithelia. Significantly, NSP4 elicited cellular I(-) influx into intestinal epithelial cells from all three genotypes, whereas both carbachol and the cAMP-mobilizing agonist forskolin failed to evoke influx in the CFTR(-/-) background. This unique plasma membrane halide permeability pathway was age dependent, being observed only in mouse pup crypts, and was abolished by either the removal of bath Ca(2+) or the transport inhibitor DIDS. These findings indicate that NSP4 or its active peptide may induce diarrhea in neonatal mice through the activation of an age- and Ca(2+)-dependent plasma membrane anion permeability distinct from CFTR. Furthermore, these results highlight the potential for developing synthetic analogs of NSP4(114-135) to counteract chronic constipation/obstructive bowel syndrome in CF patients.

Effect of rotavirus infection on small gut pathophysiology in a mouse model

AIM

To study the effect of rotavirus infection on amino acid uptake in the small intestine in an experimental mouse model.

METHODS

Infant mice (7-8 days of age) were orally infected with the EB serotype 3 strain of rotavirus and animals (both infected and control) were killed on days 0, 1, 3, 5, 7 and 10 post inoculation (PI) after recording their bodyweights. Gamma-glutamyltranspeptidase (GGT), leucine amino peptidase (LAP), glutathione (GSH) and leucine amino acid uptake in the jejunum and ileum were assessed.

RESULTS

Infected animals showed significant reduction in their bodyweights and intestinal lengths on the third day PI compared with controls. Leucine amino peptidase, GGT, GSH and leucine uptake were significantly reduced in the ileum on the third and fifth day PI compared with controls while uptake in the jejunum was only reduced on third day PI. The LAP, GGTP, GSH and leucine uptake attained normal levels on the seventh day when diarrhoea stopped. Histology showed damage to the villi in the jejunum and prominent cytoplasmic vacuolation in the ileum of infected animals on the third and fifth day PI.

CONCLUSION

Rotavirus affects amino acid uptake in the small intestine at the time of peak infection.

Passive immunity against rotavirus in infants

Passive immunity against a variety of gastrointestinal infections, using orally administered human antibodies, has been tried in a number of clinical trials. Recently, antibodies from other species such as cows and chickens, which have shown efficacy in experimental animal systems, have also been tried in humans. This review summarizes published data on the use of immunoglobulin-containing preparations for prophylaxis and therapy against rotavirus infections in infants and children, and directions for their future use are suggested.

The regulation of epithelial cell cAMP- and calcium-dependent chloride channels

This chapter has focused on two types of chloride conductance found in epithelial cells. The leap from the Ussing chamber to patch-clamp studies has identified yet other conductances present which have also been electrophysiologically characterized. In the case of the swelling activated wholecell chloride current, a physiological function is apparent and a single-channel basis found, but its genetic identity remains unknown (see reviews by Frizzell and Morris, 1994; and Strange et al., 1996). The outwardly rectified chloride channel has been the subject of considerable electrophysiological interest over the past 10 years and is well characterized at the single-channel level, but its physiological function remains controversial (reviewed by Frizzell and Morris, 1994; Devidas and Guggino, 1997). Yet other conductances related to the CLC gene family also appear to be present in epithelial cells of the kidney (reviewed by Jentsch, 1996; Jentsch and Gunter, 1997) where physiological functions for some isoforms are emerging. Clearly, there remain many unknowns. Chief among these is the molecular basis of GCa2+Cl and many of other the conductances. As sequences become available it is expected that the wealth of information gained by investigation into CFTR function will provide a conceptual blueprint for similar studies in these later channel clones.

Solid state NMR studies of hydrogen bonding in a citrate synthase inhibitor complex

The ionization state and hydrogen bonding environment of the transition state analogue (TSA) inhibitor, carboxymethyldethia coenzyme A (CMX), bound to citrate synthase have been investigated using solid state NMR. This enzyme-inhibitor complex has been studied in connection with the postulated contribution of short hydrogen bonds to binding energies and enzyme catalysis: the X-ray crystal structure of this complex revealed an unusually short hydrogen bond between the carboxylate group of the inhibitor and an aspartic acid side chain [Usher et al. (1994) Biochemistry 33, 7753-7759]. To further investigate the nature of this short hydrogen bond, low spinning speed 13C NMR spectra of the CMX-citrate synthase complex were obtained under a variety of sample conditions. Tensor values describing the chemical shift anisotropy of the carboxyl groups of the inhibitor were obtained by simulating MAS spectra (233 +/- 4, 206 +/- 5, and 105 +/- 2 ppm vs TMS). Comparison of these values with our previously reported database and ab initio calculations of carbon shift tensor values clearly indicates that the carboxyl is deprotonated. New data from model compounds suggest that hydrogen bonds in a syn arrangement with respect to the carboxylate group have a pronounced effect upon the shift tensors for the carboxylate, while anti hydrogen bonds, regardless of their length, apparently do not perturb the shift tensors of the carboxyl group. Thus the tensor values for the enzyme-inhibitor complex could be consistent with either a very long syn hydrogen bond or an anti hydrogen bond; the latter would agree very well with previous crystallographic results. Two-dimensional 1H-13C heteronuclear correlation spectra of the enzyme-inhibitor complex were obtained. Strong cross-peaks were observed from the carboxyl carbon to proton(s) with chemical shift(s) of 22 +/- 5 ppm. Both the proton chemical shift and the intensity of the cross-peak indicate a very short hydrogen bond to the carboxyl group of the inhibitor, the C.H distance based upon the cross-peak intensity being 2.0 +/- 0.4 A. This proton resonance is assigned to Hdelta2 of Asp 375, on the basis of comparison with crystal structures and the fact that this cross-peak was absent in the heteronuclear correlation spectrum of the inhibitor-D375G mutant enzyme complex. In summary, our NMR studies support the suggestion that a very short hydrogen bond is formed between the TSA and the Asp carboxylate.

Malnutrition modifies pig small intestinal inflammatory responses to rotavirus

Infectious diarrheal diseases and malnutrition are major causes of child morbidity and mortality. In this study, malnutrition was superimposed on rotavirus infection in neonatal piglets to simulate the combined intestinal stress of viral enteritis in malnourished infants. Two-day-old piglets were assigned to three treatment groups as follows: 1) noninfected, fully nourished; 2) infected, fully nourished; and 3) infected, malnourished. Intestinal indices of inflammation were monitored over the subsequent 2-wk period. Intestinal damage and diarrhea were observed within 2 d of rotavirus infection and began to subside in nourished piglets by d 9 but persisted through d 16 postinfection in malnourished piglets. Rotavirus upregulated small intestinal expression of major histocompatibility complex (MHC) class I and class II genes; malnutrition intensified MHC class I gene expression and suppressed MHC class II expression. Jejunal CD4(+) and CD8(+) T-lymphocyte numbers were elevated for infected, nourished piglets on d 2, 9 and 16 postinfection. Malnutrition did not significantly affect the local expansion of T cell subsets in response to rotavirus. Intestinal prostaglandin E2 (PGE2) concentrations were elevated early after rotavirus infection independent of nutritional state. By d 9, PGE2 concentrations returned to baseline in infected, nourished piglets but remained elevated in malnourished piglets, corresponding to diarrhea observations. Together, the results identify intestinal indices of inflammation that are modulated by malnutrition and prompt reconsideration of current models of rotavirus pathophysiology.

Fever without apparent source on clinical examination, lower respiratory infections in children, and other infectious diseases

This section focuses on issues in infectious disease that are commonly encountered in pediatric office practice. Paul McCarthy discusses recent literature regarding the evaluation and management of acute fevers without apparent source on clinical examination in infants and children and the evaluation of children with prolonged fevers of unknown origin. Jean Klig reviews recent literature about lower respiratory tract infection in children. Finally, Jeffrey Kahn discusses recent developments concerning rotavirus vaccine.

Rotavirus infection among children with diarrhoea in Italy

Despite the absence of a nationwide surveillance system for rotavirus infection, relevant information concerning the epidemiology of this pathogen in Italy can be obtained from hospital-based studies carried out since the early 1980s on patients with acute diarrhoea. A review of more than 50 papers and congress proceedings published in both international and national literature indicates that rotavirus is the most important cause of diarrhoea in Italy among young children requiring hospitalization, with a prevalence ranging from approximately 20% to 40% in different studies. Infection is predominant among children aged 6-24 months, although cases are also common in younger children and in children 2-3 y of age. Despite differences among studies in geographical area, years and age group under investigation, an increase in rotavirus cases is consistently reported in the winter months, with a peak in February through April. Although a few studies have been conducted in non-hospitalized patients, rotavirus infection is significantly less frequent among outpatients with enteritis than among inpatients. Most circulating rotavirus strains typed from 1981 to 1992 belong to serotype 1 and, to a lesser extent, 4. However, untypable rotavirus strains have been found in these years, with prevalences up to 27%, suggesting a possible spread of non-serotype 1 through 4 strains.

Seasonality and diversity of Group A rotaviruses in Europe

Group A rotaviruses are a major cause of severe gastroenteritis in children under 4 y of age worldwide. Group A rotaviruses have been identified in many animal and bird species, they are antigenically complex, and multiple serotypes infect humans. Re-assortant rotavirus vaccines are now available which confer protection against severe illness due to rotavirus serotypes G1-4. Before vaccines are introduced it is necessary to establish the diversity of rotavirus in the target population to ensure efficacy and to establish a baseline for future surveillance strategies. The purpose of this review is to describe our current knowledge of the diversity of rotaviruses across Europe. Since multinational studies with standardized methodology have not been performed, this review is based on the available published studies. In Europe, more than 90% of Group A rotavirus strains that have been typed are of serotypes G1-4, with an average 8% of non-G1-4 strains in published studies. The percentage of non-typeable strains may fluctuate from one year to another, and has been as high as 18% in one study in Great Britain, indicating the need for a more systematic study. Group A rotavirus infection typically occurs as a winter peak in the European countries studied. Comparison of seasonality data from national laboratory surveillance systems showed seasonal differences, with the annual rotavirus peak occurring first in Spain, usually in December, followed by France in February, and ending in Northern Europe in England and Wales in February or March, and the Netherlands and Finland in March.