Publications

Intact alveolar barrier function is associated with better outcomes in acute lung injury patients; however, the regulation of alveolar epithelial paracellular transport during lung injury has not been extensively investigated. This study was undertaken to determine whether changes in tight junction claudin expression affect alveolar epithelial barrier properties and to determine the mechanisms of altered expression. In anesthetized mice exposed to ventilator-induced lung injury, claudin-4 was specifically induced among tight junction structural proteins. Real-time PCR showed an eightfold increase in claudin-4 expression in the lung injury model. To examine the role of this protein in barrier regulation, claudin-4 function was inhibited with small interfering RNA (siRNA) and a blocking peptide derived from the binding domain of Clostridium perfringens enterotoxin (CPE(BD)). Inhibition of claudin-4 decreased transepithelial electrical resistance but did not alter macromolecule permeability in primary rat and human epithelial cells. In mice, CPE(BD) decreased air space fluid clearance >33% and resulted in pulmonary edema during moderate tidal volume ventilation that did not induce edema in control peptide-treated mice. In vitro phorbol ester induced a ninefold increase in claudin-4 expression that was dependent on PKC activation and the JNK MAPK pathway. These data establish that changes in alveolar epithelial claudin expression influence paracellular transport, alveolar fluid clearance rates, and susceptibility to pulmonary edema. We hypothesize that increased claudin-4 expression early in acute lung injury represents a mechanism to limit pulmonary edema and that the regulation of alveolar epithelial claudin expression may be a novel target for acute lung injury therapy.

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARalpha and beta/delta, RXRalpha, beta, and gamma, thyroid hormone receptor alpha and beta, and estrogen related receptor alpha (ERRalpha) and their coactivators PGC-1alpha, PGC-1beta, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARalpha deficient mice, baseline CPT-1beta and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARalpha signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis.

BACKGROUND & AIMS

The management of inflammatory bowel disease (IBD) has become increasingly complicated, and it is unknown whether poor outcomes (prolonged steroid use, hospitalizations, and surgery) have declined in the general population.

METHODS

This multilevel study used computerized clinical data. The study comprised 2892 adults with Crohn's disease (CD) and 5895 with ulcerative colitis (UC) who received care at 16 medical centers within an integrated care organization in Northern California between 1998 and 2005.

RESULTS

Time trends included (1) a shift in gastroenterology-related visits from the gastroenterology division to primary care; (2) increased use of IBD-related drugs, except for a 7% decline in use of 5-aminosalicylate in CD and no change in steroid use for CD; (3) for the prevalence of prolonged steroid exposure (120 days of continuous use), a 36% decline for CD with a 27% increase for UC; (4) declines in the hospitalization rates of 33% for CD and 29% for UC; and (5) for the surgery rate, no significant change for CD with a 50% decline for UC.

CONCLUSIONS

Declines in prolonged steroid exposure and the hospitalization rate for CD and in the hospitalization and surgery rate for UC are encouraging; however, the increase in prolonged steroid exposure for UC merits concern and further investigation. The variability in care patterns observed in this study suggests lack of standardization of care and the opportunity to identify targets for quality improvement. These findings should stimulate research to quantify the effect of current trends in IBD management.