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Biomedical subjects

Pablo C Okhuysen

Publications and source records attributed to Pablo C Okhuysen.

14 recordsLinked to original sources
PubMed2024

Bacteroides ovatus alleviates dysbiotic microbiota-induced graft-versus-host disease.

Acute lower gastrointestinal GVHD (aLGI-GVHD) is a serious complication of allogeneic hematopoietic stem cell transplantation. Although the intestinal microbiota is associated with the incidence of aLGI-GVHD, how the intestinal microbiota impacts treatment responses in aLGI-GVHD has not been thoroughly studied. In a cohort of patients with aLGI-GVHD (n = 37), we found that non-response to standard therapy with corticosteroids was associated with prior treatment with carbapenem antibiotics and a disrupted fecal microbiome characterized by reduced abundances of Bacteroides ovatus. In a murine GVHD model aggravated by carbapenem antibiotics, introducing B. ovatus reduced GVHD severity and improved survival. These beneficial effects of Bacteroides ovatus were linked to its ability to metabolize dietary polysaccharides into monosaccharides, which suppressed the mucus-degrading capabilities of colonic mucus degraders such as Bacteroides thetaiotaomicron and Akkermansia muciniphila, thus reducing GVHD-related mortality. Collectively, these findings reveal the importance of microbiota in aLGI-GVHD and therapeutic potential of B. ovatus.

Graft vs Host Disease↗
PubMed2023

Bacteroides ovatus alleviates dysbiotic microbiota-induced intestinal graft-versus-host disease.

Acute gastrointestinal intestinal GVHD (aGI-GVHD) is a serious complication of allogeneic hematopoietic stem cell transplantation, and the intestinal microbiota is known to impact on its severity. However, an association between treatment response of aGI-GVHD and the intestinal microbiota has not been well-studied. In a cohort of patients with aGI-GVHD (n=37), we found that non-response to standard therapy with corticosteroids was associated with prior treatment with carbapenem antibiotics and loss of Bacteroides ovatus from the microbiome. In a mouse model of carbapenem-aggravated GVHD, introducing Bacteroides ovatus reduced severity of GVHD and improved survival. Bacteroides ovatus reduced degradation of colonic mucus by another intestinal commensal, Bacteroides thetaiotaomicron, via its ability to metabolize dietary polysaccharides into monosaccharides, which then inhibit mucus degradation by Bacteroides thetaiotaomicron and reduce GVHD-related mortality.

Bacteroides ovatus↗
PubMed2003

Genetic susceptibility to enteroaggregative Escherichia coli diarrhea: polymorphism in the interleukin-8 promotor region.

Enteroaggregative Escherichia coli (EAEC) infection can be identified in 26% of travelers with diarrhea and is associated with fecal interleukin (IL)-8 production. We hypothesized that single-nucleotide polymorphisms (SNPs) in the IL-8 gene are associated with EAEC-related symptoms. Fecal IL-8 production and IL-8 SNPs at 5 loci were identified in 69 US students who remained in Mexico for 5 weeks; 23 subjects had EAEC-associated diarrhea, 7 were asymptomatic EAEC carriers, 22 had nonspecific diarrhea, and 17 were asymptomatic without an enteropathogen. The chances of having EAEC-associated diarrhea were significantly increased among those with the AA genotype at the -251 position (odds ratio [OR], 208.51; 95% confidence interval [CI], 28.5-1525.36) and among those with AT genotype (OR, 14.3; 95% CI, 1.98-105.74), compared with those with the TT genotype at the -251 position. Among subjects with EAEC-associated diarrhea, the AA genotype at the -251 position produced greater concentrations of fecal IL-8 than those with the AT or TT genotype (P=.0053). In the present study, the AA genotype at the -251 position was associated with the occurrence of EAEC-associated diarrhea and increased levels of fecal IL-8.

Diarrhea↗
PubMed2003

Substance P expression correlates with severity of diarrhea in cryptosporidiosis.

Cryptosporidiosis, caused by Cryptosporidium parvum, is self-limited in immunocompetent hosts but may cause chronic diarrhea in patients with acquired immunodeficiency syndrome (AIDS). Substance P (SP), a neuropeptide belonging to the tachykinin family, is expressed in gastrointestinal tract and can cause electrogenic chloride anion secretion. Therefore, we studied SP mRNA and protein expression in jejunal tissue samples of patients with AIDS with naturally occurring chronic cryptosporidiosis and healthy volunteers with mild cryptosporidiosis or asymptomatic infection after experimental C. parvum challenge. SP mRNA was associated with symptoms in cryptosporidiosis. SP protein levels were greater in symptomatic than asymptomatic volunteers. Similarly, greater expression of SP mRNA and protein were noted in patients with AIDS with chronic cryptosporidiosis versus immunocompetent volunteers with self-limited infection. This study demonstrates a direct correlation between SP levels and disease severity and may imply that SP plays a role in diarrhea mediation.

AIDS-Related Opportunistic Infections↗
PubMed2003

Interleukin-8, tumor necrosis factor-alpha, and lactoferrin in immunocompetent hosts with experimental and Brazilian children with acquired cryptosporidiosis.

To examine the importance of intestinal inflammation in the diagnosis and pathogenesis of human cryptosporidiosis, stools of healthy adult volunteers before and after experimental infection were tested for fecal lactoferrin, interleukin-8 (IL-8), and tumor necrosis factor-alpha (TNF-alpha). Stool samples of Brazilian children with well-defined Cryptosporidium infection, with or without diarrhea, were also tested for IL-8 and TNF-alpha. Only one of the 14 volunteers challenged with Cryptosporidium had increased fecal lactoferrin. However, of 17 stool specimens from children with only Cryptosporidium infection from a previous study, 12 had mild to moderately elevated lactoferrin despite negative work-up for inflammatory enteritides. One of 10 adult volunteers who developed diarrhea with experimental cryptosporidiosis and three of 11 children with cryptosporidiosis and diarrhea had detectable fecal IL-8. The level of TNF-alpha was increased only in one of 14 volunteers and in none of the children. Although considered relatively non-inflammatory. cryptosporidiosis is often associated with mild inflammation, especially in children in an endemic area.

Adult↗
PubMed2002

Infectivity of a Cryptosporidium parvum isolate of cervine origin for healthy adults and interferon-gamma knockout mice.

The infectivity of a Cryptosporidium parvum isolate of cervine origin (type 2, Moredun) propagated in calves was investigated simultaneously in healthy adult human volunteers and in interferon-gamma knockout (GKO) mice. After exposure to 100-3000 oocysts, 16 volunteers recorded, for a duration of 6 weeks, the number and form of stools that they passed and any symptoms that they experienced. Oocyst excretion was assessed by enzyme-linked immunosorbent assay and direct immunofluorescence assay. Eleven subjects (69%) became ill, and 8 subjects (50%) shed oocysts in stool. The median duration of illness was 169 h, and the median number of unformed stools passed was 24. The duration and intensity of symptoms were more severe than were those associated with previously studied isolates. The median infectious dose was estimated to be 300 oocysts for humans and 1 oocyst for the GKO mouse model. The Moredun isolate was more pathogenic than the reference GCH-1 isolate. The GKO mouse model of cryptosporidiosis is useful for discerning isolate-specific differences in pathogenicity.

Adult↗
PubMed2002

HIV1 and the gut in the era of highly active antiretroviral therapy.

The gut and its gut-associated lymphoid tissue serve as a preferential site for HIV1 entry, active viral replication, reservoir, and HIV-mediated CD4 cell apoptosis. The widespread use of highly active antiretroviral therapy (HAART) has resulted in a significant decrease in the incidence of opportunistic enteric pathogens as a consequence of immune recovery. Nonetheless, patients with advanced HIV1 disease who were recently diagnosed or have poor response to HAART can still suffer from opportunistic infections with pathogens such as Cryptosporidium, microsporidia, Isospora belli, Cyclospora cayetanensis, Mycobacterium avium complex, and cytomegalovirus, among others. This review describes the impact of HIV1 infection on gut immune function, the salient features of the most common opportunistic enteric pathogens and HIV-associated enteropathy, and the effects of immune reconstitution after introduction of HAART.

AIDS-Related Opportunistic Infections↗
PubMed2002

Molecular cloning and analysis of the Cryptosporidium parvum aminopeptidase N gene.

Cryptosporidium parvum proteases have been associated with release of infective sporozoites from oocysts, and their specific inhibition blocks parasite excystation in vitro. Additionally, proteases have been implicated in the processing of parasite adhesion molecules found on the surface of sporozoites and merozoites. In this study, we cloned and expressed the C. parvum aminopeptidase N gene by screening a large insert, P1 artificial chromosome library with a probe identified from a Cryptosporidium genome survey-sequencing project. Analysis of the predicted protein encoded by the 2.3 kb gene demonstrated a high degree of homology with prokaryotic and eukaryotic aminopeptidases. The 783 amino acid sequence predicted a M(r) of approximately 89,000. The active site sequence was found to be highly conserved when compared with other Apicomplexan aminopeptidases. Motifs commonly found in aminopeptidases of this class and a unique single Arg-Gly-Asp (RGD) tripeptide motif predictive of cell adhesion were identified. The aminopeptidase N mRNA was expressed in infective sporozoites and during the infection of human HCT-8 enterocytes as revealed by reverse transcription PCR.

Amino Acid Sequence↗
PubMed2002

Cryptosporidium virulence determinants--are we there yet?

Exposure to Cryptosporidium parvum in healthy individuals results in transient infection that may be asymptomatic or can result in self-limited diarrhoea. In contrast, acquired immune deficiency syndrome patients with cryptosporidiosis can experience severe manifestations of disease. Volunteer studies have demonstrated that as few as 10 oocysts can cause infection in otherwise healthy adults and that isolates from geographically diverse regions differ in infectivity and, perhaps, virulence. Variability in isolate pathogenicity and infectivity has also been seen in bovine and murine models, respectively. Furthermore, isolate specific differences in protein composition and in host immunoreactivity have been observed. The molecular basis for differences in pathogenicity is not understood. Determining which factors are responsible for host selectivity and for the initiation, establishment, and perpetuation of infection with Cryptosporidium is key to rational drug design and vaccine development. To date, no specific virulence factors have been unequivocally shown to individually cause direct or indirect damage to host tissues nor have mutant strains been produced that could prove that particular deletions result in less virulent strains. Nevertheless, a number of candidate molecules have been identified by immunological and molecular methods. Here, we review the salient characteristics of some of these putative virulence determinants, including molecules that are involved in adhesion, protein degradation and the modulation of the host responses.

Adult↗
PubMed2002

Cryptosporidiosis.

PURPOSE OF REVIEW: Cryptosporidiosis is a self-limited diarrheal disease that occurs in the community setting but can be chronic and potentially serious in immunocompromised patients. Community outbreaks are often associated with water-borne transmission. Cryptosporidium research has increased dramatically since the human disease was first recognized in 1976. The present review summarizes recent work in three of the several areas of active Cryptosporidium investigation. RECENT FINDINGS: Molecular techniques have revealed that current taxonomic designations need re-evaluation and that humans are host to several Cryptosporidium spp. that were once believed to be limited to the veterinary realm. These findings have important public health implications for water quality standards in the USA and other developed countries. Second, techniques for detecting the parasite in infected individuals (or environmental samples) have progressed from acid-fast staining of fecal smears to the currently used antibody-based systems (enzyme immunoassays and immunofluorescent assays). New molecular methodologies, based on polymerase chain reaction amplification of gene loci, are being developed to improve the sensitivity and specificity for diagnostic and epidemiologic purposes. Third, curative therapy is attained only by an effective immune response or the reconstitution of a failing immune system in the compromised host. However, several drugs are in development, and compounds such as nitazoxanide appear to hold some promise. SUMMARY: Cryptosporidiosis continues to be a serious problem in immunocompromised patients and on a worldwide scale in undernourished infants and children. The lack of an effective treatment, and the propensity of the parasite to survive in and be transmitted through source waters make this an important public health threat.

Animals↗
PubMed2002

Cryptosporidium dose response studies: variation between isolates.

The infectivity of three different isolates of the waterborne protozoan parasite Cryptosporidium parvum has been tested in human feeding studies. These three isolates (Iowa, TAMU, and UCP) have different ID50s, indicating substantial variation in their infectivity for humans. This finding is of great importance for quantitative risk assessment as it provides strong evidence for heterogeneity in infectivity among isolates of the same species.

Animals↗
PubMed2002

Cryptosporidium dose-response studies: variation between hosts.

The issue of variation is highly important in dose-response analysis: variation among genetically related pathogens infecting the same host, but also variation among hosts, in susceptibility to infection by the same pathogen. This latter issue is addressed here for the protozoan parasite Cryptosporidium parvum, the causative agent for many outbreaks of water-borne gastrointestinal illness. In human feeding studies, infectivity has been shown to be low in subjects with high preexisting anti-Cryptosporidium IgG-levels. Here we adapt the hit theory model of microbial infection to incorporate covariables, characterizing the immune status of the susceptible host. The probability of any single oocyst in the inoculum to cause infection appears to depend on preexisting IgG-levels. This does not necessarily imply direct protection by the humoral immune system; high IgG-levels may reflect a recent episode of infection/illness, and be an epi-phenomenon associated with other protective responses. The IgG-dependence of the dose-response relation can be easily applied in quantitative risk analysis. The distribution of anti-Cryptosporidium IgG levels in the general population is accessible by analyzing serum banks, which are maintained in many Western countries. Using such an approach provides first insights into the variation of susceptibility to infection in the general population.

Animals↗
PubMed2002

Characterization of aminopeptidase activity from three species of microsporidia: Encephalitozoon cuniculi, Encephalitozoon hellem, and Vittaforma corneae.

Microsporidia are obligate intracellular parasites of the phylum Microspora. To date, more than 1,200 species within 144 genera have been described, with 14 infecting humans. Currently, no effective treatment exists for human microsporidiosis. In this study, the biochemical properties of the aminopeptidases were investigated within several species of microsporidia. Aminopeptidase activity was detected in 3 species of microsporidia, Encephalitozoon cuniculi, E. hellem, and Vittaforma corneae, using a fluorometric substrate assay. Each species exhibited distinct aminopeptidase properties. The cytosolic neutral aminopeptidase activities of the Encephalitozoon spp. were characterized as preferentially cleaving leucine, whereas those of V. corneae cleaved arginine. Native polyacrylamide gel electrophoresis estimated the molecular mass of E. cuniculi, E. hellem, and V. corneae as 74, 72, and 79 kDa, respectively. Enzymatic activity was inhibited by bestatin and it's analogue, nitrobestatin, indicating that the enzyme was an aminopeptidase for all species. Inhibition with the chelating agents ethylenediaminetetraacetic acid and 1,10phenanthroline characterized the enzymes as metalloaminopeptidases. Subcellular fractionation of the 3 microsporidial species suggested that the enzyme activity was localized in the cytosolic fraction. Optimal enzyme activity was observed at pH 7.2 for all species. This is the first report of enzyme characterization from these 3 species of microsporidia.

Aminopeptidases↗