Obesity increases the risk of small intestinal bacterial overgrowth (SIBO)

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) has been associated with anatomical and motility-related abnormalities. Specifically, obesity has been postulated to alter small bowel motility, leading to SIBO.

AIMS

(i) Assess the prevalence of SIBO in obesity; (ii) determine the relationship of obesity and SIBO, using small bowel transit time (SBTT) and pH; (iii) profile the gut microbiome in obese and non-obese patients with SIBO.

METHODS

Thirty consecutive participants referred for SIBO underwent lactulose breath tests (LBTs) and wireless motility capsule (WMC) studies. Composition of the intestinal microbiome was assessed by analyzing samples from three different gastrointestinal sites via 16S rRNA gene-sequencing.

KEY RESULTS

SIBO was more frequent among obese patients vs non-obese patients (88.9% vs 42.9%, P < .05). Obesity did not correlate with small bowel transit time (SBTT), gastric pH, and small bowel pH. In patients with normal SBTT, obesity was associated with an 11-fold increase (P = .05) in the risk of SIBO. Whereas in those with prolonged SBTT, there was no correlation between obesity and SIBO. Obese vs non-obese patients exhibited significant differences in microbiome diversity in rectal samples. Obesity was associated with increased odds of developing SIBO (P = .04) in multivariate regression analyses.

CONCLUSIONS AND INFERENCES

While obesity was significantly associated with SIBO, our findings suggest that alterations in gut pH, SBTT, and decline in species richness do not account for the obesity-SIBO relationship.

Toxoplasma gondii-A Gastrointestinal Pathogen Associated with Human Brain Diseases

Serious psychiatric disorders such as schizophrenia, bipolar disorder, and major depression are important causes of mortality and morbidity worldwide. While these are primarily diseases involving altered brain functioning, numerous studies have documented increased rates of gastrointestinal inflammation and dysfunction in many individuals with these disorders. Toxoplasma gondii is an apicomplexan protozoan intracellular parasite with a widespread distribution in both developed and developing countries. Toxoplasma organisms enter the ecosystem through the shedding of oocysts by Toxoplasma-infected felines. In almost all cases of postnatal human infection, Toxoplasma enters its hosts through the intestinal tract either by the ingestion of oocysts or by the consumption of meat from food animals which themselves were infected by Toxoplasma oocysts. It had previously been thought that most cases of Toxoplasma infection in immune competent children and adults were inapparent and asymptomatic. However, recent studies cast doubt on this concept as exposure to Toxoplasma has been associated with a range of acute and chronic symptoms. Of particular note has been the finding of an increased rate of a range of neurological and psychiatric disorders associated with serological evidence of Toxoplasma exposure. A role of Toxoplasma infection in brain diseases is also supported by the consistent finding of altered cognition and behavior in animal models of infections. Much of the attention relating to the role of Toxoplasma infection in neuropsychiatric disorders has focused on the brain, where Toxoplasma tissue cysts can persist for extended periods of time. However, recent discoveries relating to the role of the gastrointestinal tract in cognition and behavior suggest that Toxoplasma may also increase susceptibility to human brain diseases through immune activation, particularly involving the gastrointestinal mucosa. The study of the pathways relating to the pathobiology and immunology of Toxoplasma infection may provide insights into the pathogenesis of a range of human neuropsychiatric disorders as well as into cognitive functioning in otherwise healthy individuals.

Effect of parasitic infection on dopamine biosynthesis in dopaminergic cells

Infection by the neurotropic agent Toxoplasma gondii alters rodent behavior and can result in neuropsychiatric symptoms in humans. Little is understood regarding the effects of infection on host neural processes but alterations to dopaminergic neurotransmission are implicated. We have previously reported elevated levels of dopamine (DA) in infected dopaminergic cells however the involvement of the host enzymes and fate of the produced DA were not defined. In order to clarify the effects of infection on host DA biosynthetic enzymes and DA packaging we examined enzyme levels and activity and DA accumulation and release in T. gondii-infected neurosecretory cells. Although the levels of the host tyrosine hydroxylase (TH) and DOPA decarboxylase and AADC (DDC) did not change significantly in infected cultures, DDC was found within the parasitophorous vacuole (PV), the vacuolar compartment where the parasites reside, as well as in the host cytosol in infected dopaminergic cells. Strikingly, DDC was found within the intracellular parasite cysts in infected brain tissue. This finding could provide some explanation for observations of DA within tissue cysts in infected brain as a parasite-encoded enzyme with TH activity was also localized within tissue cysts. In contrast, cellular DA packaging appeared unchanged in single-cell microamperometry experiments and only a fraction of the increased DA was accessible to high potassium-induced release. This study provides some understanding of how this parasite produces elevated DA within dopaminergic cells without the toxic ramifications of free cytosolic DA. The mechanism for synthesis and packaging of DA by T. gondii-infected dopaminergic cells may have important implications for the effects of chronic T. gondii infection on humans and animals.

MicroRNA-132 dysregulation in Toxoplasma gondii infection has implications for dopamine signaling pathway

Congenital toxoplasmosis and toxoplasmic encephalitis can be associated with severe neuropsychiatric symptoms. However, which host cell processes are regulated and how Toxoplasma gondii affects these changes remain unclear. MicroRNAs (miRNAs) are small noncoding RNA sequences critical to neurodevelopment and adult neuronal processes by coordinating the activity of multiple genes within biological networks. We examined the expression of over 1000 miRNAs in human neuroepithelioma cells in response to infection with Toxoplasma. MiR-132, a cyclic AMP-responsive element binding (CREB)-regulated miRNA, was the only miRNA that was substantially upregulated by all three prototype Toxoplasma strains. The increased expression of miR-132 was also documented in mice following infection with Toxoplasma. To identify cellular pathways regulated by miR-132, we performed target prediction followed by pathway enrichment analysis in the transcriptome of Toxoplasma-infected mice. This led us to identify 20 genes and dopamine receptor signaling was their strongest associated pathway. We then examined myriad aspects of the dopamine pathway in the striatum of Toxoplasma-infected mice 5days after infection. Here we report decreased expression of D1-like dopamine receptors (DRD1, DRD5), metabolizing enzyme (MAOA) and intracellular proteins associated with the transduction of dopamine-mediated signaling (DARPP-32 phosphorylation at Thr34 and Ser97). Increased concentrations of dopamine and its metabolites, serotonin (5-HT) and 5-hydroxyindoleacetic acid were documented by HPLC analysis; however, the metabolism of dopamine was decreased and 5-HT metabolism was unchanged. Our data show that miR-132 is upregulated following infection with Toxoplasma and is associated with changes in dopamine receptor signaling. Our findings provide a possible mechanism for how the parasite contributes to the neuropathology of infection.

Neurological sequalae and toxoplasma infection: Possible mechanisms to explain associations with schizophrenia

Latent infection with the common intracellular protozoan parasite Toxoplasma gondii has been shown to result in altered behaviour of its host. This behaviour manipulation has been proposed to increase predation of the intermediate host (e.g. rodents and birds) enhancing parasite transmission. Other psychologicalsequalae have also been associated with latent toxoplasmosis including human affective disorders, as human are accidental hosts for Toxoplasma. During cyst stages of the life cycle found in the brain and other tissues, there is a complex interaction between the parasite and the host. Our research is concerned with the possibility that the parasite-induced behavioural changes are mediated by neurotransmitters. Potential factors in neurotransmitter levels include the location of the cyst, the host immune response, and direct parasite products. The cyst is found in many brain regions but elevated numbers have been reported in the hippocampus, amygdala, and nucleus accumbens. The host response involves interferon gamma suppressing growth through tryptophan degradation that could decrease serotonin levels. The parasite could directly manipulate the host brain through altering dopamine levels. We have found a change in dopamine associated with infection. Indeed, the parasite itself encodes the rate-limiting enzyme in dopamine synthesis, tyrosine hydroxylase. Dopamine's role is also supported by finding haloperidol, a dopamine antagonist, blocks manipulation of rodents by Toxoplasma. Our current investigations of alterations in neurotransmitter levels during chronic infection and association with brain cysts will be presented. Our data presents an interesting interplay with the ‘dopamine hypothesis’ that has postulated a link between elevated dopamine and schizophrenia.