Targeting mitochondria-derived reactive oxygen species to reduce epithelial barrier dysfunction and colitis.

Epithelial permeability is often increased in inflammatory bowel diseases. We hypothesized that perturbed mitochondrial function would cause barrier dysfunction and hence epithelial mitochondria could be targeted to treat intestinal inflammation. Mitochondrial dysfunction was induced in human colon-derived epithelial cell lines or colonic biopsy specimens using dinitrophenol, and barrier function was assessed by transepithelial flux of Escherichia coli with or without mitochondria-targeted antioxidant (MTA) cotreatment. The impact of mitochondria-targeted antioxidants on gut permeability and dextran sodium sulfate (DSS)-induced colitis in mice was tested. Mitochondrial superoxide evoked by dinitrophenol elicited significant internalization and translocation of E. coli across epithelia and control colonic biopsy specimens, which was more striking in Crohn's disease biopsy specimens; the mitochondria-targeted antioxidant, MitoTEMPO, inhibited these barrier defects. Increased gut permeability and reduced epithelial mitochondrial voltage-dependent anion channel expression were observed 3 days after DSS. These changes and the severity of DSS-colitis were reduced by MitoTEMPO treatment. In vitro DSS-stimulated IL-8 production by epithelia was reduced by MitoTEMPO. Metabolic stress evokes significant penetration of commensal bacteria across the epithelium, which is mediated by mitochondria-derived superoxide acting as a signaling, not a cytotoxic, molecule. MitoTEMPO inhibited this barrier dysfunction and suppressed colitis in DSS-colitis, likely via enhancing barrier function and inhibiting proinflammatory cytokine production. These novel findings support consideration of MTAs in the maintenance of epithelial barrier function and the management of inflammatory bowel diseases.

Interferon-gamma signals via an ERK1/2-ARF6 pathway to promote bacterial internalization by gut epithelia.

The barrier function of the epithelium lining the intestine is essential for health by preventing the free passage of colonic bacteria into the mucosa. Epithelia treated with interferon (IFN)-γ display increased bacteria transcytosis. Much is known of how IFNγ affects the tight junction and paracellular permeability, yet its role in modifying transcellular traffic of commensal bacteria remains poorly understood. Using immunoblotting, ELISA and immunolocalization, IFNγ was found to activate extracellular regulated kinase (ERK)1/2 in the human colon-like T84 epithelial cell line. Pharmacological inhibition of MEK/ERK1/2 signalling with U0126 significantly inhibited IFNγ-induced increases in the transcytosis of non-invasive Escherichia coli (strain HB101). IFNγ treatment enhanced epithelial internalization of E. coli, some of which subsequently escaped the enterocyte. Molecular analyses revealed that ERK1/2 inhibition prevented activation of the ADP-ribosylation factor (ARF)-6, a protein associated with endocytosis, and that siRNA knock-down of ARF6 expression reduced IFNγ-induced E. coli internalization into T84 cells. None of these interventions affected the drop in transepithelial resistance caused by IFNγ. Thus, increased transcellular passage may be a major component of IFNγ-induced increases in epithelial permeability, and ERK1/2 and ARF6 are presented as important molecules in IFNγ-evoked transcytosis of bacteria across gut epithelia.

Indomethacin-induced translocation of bacteria across enteric epithelia is reactive oxygen species-dependent and reduced by vitamin C.

The enteric epithelium must absorb nutrients and water and act as a barrier to the entry of luminal material into the body; this barrier function is a key component of innate immunity. Nonsteroidal anti-inflammatory drug (NSAID)-induced enteropathy occurs via inhibition of prostaglandin synthesis and perturbed epithelial mitochondrial activity. Here, the direct effect of NSAIDs [indomethacin, piroxicam (cyclooxygenase 1 and 2 inhibitors), and SC-560 (a cyclooxygenase 1 inhibitor)] on the barrier function of human T84 epithelial cell line monolayers was assessed by transepithelial electrical resistance (TER) and internalization and translocation of a commensal Escherichia coli. Exposure to E. coli in the presence and absence of drugs for 16 h reduced TER; however, monolayers cotreated with E. coli and indomethacin, but not piroxicam or SC-560, displayed significant increases in internalization and translocation of the bacteria. This was accompanied by increased reactive oxygen species (ROS) production, which was also increased in epithelia treated with E. coli only. Colocalization revealed upregulation of superoxide synthesis by mitochondria in epithelia treated with E. coli + indomethacin. Addition of antioxidants (vitamin C or a green tea polyphenol, epigallocathechin gallate) quenched the ROS and prevented the increase in E. coli internalization and translocation evoked by indomethacin, but not the drop in TER. Evidence of increased apoptosis was not observed in this model. The data implicate epithelial-derived ROS in indomethacin-induced barrier dysfunction and show that a portion of the bacteria likely cross the epithelium via a transcellular pathway. We speculate that addition of antioxidants as dietary supplements to NSAID treatment regimens would reduce the magnitude of decreased barrier function, specifically the transepithelial passage of bacteria.

Early emergence of ethnic differences in type 2 diabetes precursors in the UK: the Child Heart and Health Study in England (CHASE Study).

BACKGROUND: Adults of South Asian origin living in the United Kingdom have high risks of type 2 diabetes and central obesity; raised circulating insulin, triglyceride, and C-reactive protein concentrations; and low HDL-cholesterol when compared with white Europeans. Adults of African-Caribbean origin living in the UK have smaller increases in type 2 diabetes risk, raised circulating insulin and HDL-cholesterol, and low triglyceride and C-reactive protein concentrations. We examined whether corresponding ethnic differences were apparent in childhood. METHODS AND FINDINGS: We performed a cross-sectional survey of 4,796 children aged 9-10 y in three UK cities who had anthropometric measurements (68% response) and provided blood samples (58% response); ethnicity was based on parental definition. In age-adjusted comparisons with white Europeans (n = 1,153), South Asian children (n = 1,306) had higher glycated haemoglobin (HbA1c) (% difference: 2.1, 95% CI 1.6 to 2.7), fasting insulin (% difference 30.0, 95% CI 23.4 to 36.9), triglyceride (% difference 12.9, 95% CI 9.4 to 16.5), and C-reactive protein (% difference 43.3, 95% CI 28.6 to 59.7), and lower HDL-cholesterol (% difference -2.9, 95% CI -4.5 to -1.3). Higher adiposity levels among South Asians (based on skinfolds and bioimpedance) did not account for these patterns. Black African-Caribbean children (n = 1,215) had higher levels of HbA1c, insulin, and C-reactive protein than white Europeans, though the ethnic differences were not as marked as in South Asians. Black African-Caribbean children had higher HDL-cholesterol and lower triglyceride levels than white Europeans; adiposity markers were not increased. CONCLUSIONS: Ethnic differences in type 2 diabetes precursors, mostly following adult patterns, are apparent in UK children in the first decade. Some key determinants operate before adult life and may provide scope for early prevention.

Muscarinic regulation of ether-a-go-go-related gene K+ currents in interstitial cells of Cajal.

The interstitial cells of Cajal (ICC) of the myenteric plexus generate a set of currents that evoke a pacemaker potential that sets the initial conditions for the contraction frequency and duration of the electrically coupled intestinal musculature. The synapse-like contacts between ICC and myenteric motor nerves highlight the potential role of the enteric nervous system in regulating the pacemaking currents in ICC. The objective of the present study was to investigate muscarinic regulation of the ether-a-go-go-related gene (ERG) K(+) current. Immunoreactivity of the M(3) receptor (M(3)R) but not the M(2) receptor was detected on murine jejunal ICC-Auerbach's plexus (ICC-AP). The muscarinic agonist bethanechol reduced hyperpolarization-evoked peak ERG currents at -100 mV by 23 +/- 1% and increased both fast and slow time constants of deactivation, resulting in increased steady-state currents between -55 and -35 mV. Bethanechol also increased depolarization-evoked steady-state currents by 59 +/- 10% at -40 mV, whereas currents were decreased at potentials positive to 0 mV. The half-maximal voltage of activation was shifted 11.9 mV leftward. Interestingly, the time constant of activation increased only at -40 mV. Atropine prevented and 2 muM E4031 [1-[2-(6-methyl-2-pyridyl)-ethyl-4-(methylsulfonylaminobenzoyl)piperidine] inhibited bethanechol-affected currents. The effect of bethanechol was mimicked by protein kinase C (PKC) activation and diminished by PKC inhibition. Our results indicate that the ERG K(+) channel in ICC is affected by stimulation of muscarinic receptors, probably the M(3)R, via a PKC-dependent mechanism. Modulation of the ERG K(+) current in ICC-AP will affect the kinetics of pacemaking in the intestinal musculature.

Volume-activated chloride currents in interstitial cells of Cajal.

Interstitial cells of Cajal (ICC) undergo marked morphological changes on contraction of the musculature, making it essential to understand properties of mechanosensitive ion channels. The whole cell patch-clamp technique was used to identify and to characterize volume-activated Cl- currents in ICC cultured through the explant technique. Hypotonic solutions (approximately 210 mosM) activated an outwardly rectifying current, which reversed near the equilibrium potential for Cl-. Time-dependent inactivation occurred only at pulse potentials of +80 mV, with a time constant of 478 +/- 182 ms. The degree of outward rectification was calculated using a rectification index, the ratio between the slope conductances of +65 and -55 mV, which was 13.9 +/- 1.5 at 76 mM initial extracellular Cl- concentration. The sequence of relative anion permeability of the outwardly rectifying Cl- channel was I- > Cl- > aspartate-. The chloride channel blockers, DIDS and 5-nitro-2-(3-phenlypropl-amino)benzoic acid, caused a voltage-dependent block of the outwardly rectifying Cl- current, inhibition occurring primarily at depolarized potentials. On exposure to hypotonic solution, the slope conductance significantly increased at the resting membrane potential (-70 mV) from 1.2 +/- 0.2 to 2.0 +/- 0.4 nS and at the slow-wave plateau potential (-35 mV) from 2.1 +/- 0.3 to 5.0 +/- 1.0 nS. The current was constitutively active in ICC and contributed to the resting membrane potential and excitability at the slow-wave plateau. In conclusion, swelling or volume change will depolarize ICC through activation of outwardly rectifying chloride channels, thereby increasing cell excitability.