Concomitant use of enteral nutrition therapy is associated with sustained response to infliximab in patients with Crohn's disease.

BACKGROUND/OBJECTIVES: A significant proportion of Crohn's disease (CD) patients receiving infliximab (IFX) maintenance therapy show loss of responsiveness despite a good initial response. The factors other than immunomodulators that prevent IFX dose escalation have yet to be fully elucidated. This study was performed to identify clinical factors or concomitant therapies associated with sustained response to IFX. SUBJECTS/METHODS: Seventy-four consecutive CD patients who had successful IFX induction therapy between 2002 and 2010 underwent IFX maintenance therapy. Patients showing loss of response to IFX were treated with IFX intensification therapy. Factors involved in the sustained response to IFX were investigated retrospectively. RESULTS: After a median follow-up of 85 weeks, loss of response to IFX was observed in 30 (40.5%) cases. On logistic regression analysis, concomitant use of enteral nutrition (EN) therapy (elemental and/or polymeric formulas) was identified as an independent factor associated with sustained response to IFX. Receiver operating characteristic curve analysis indicated a cutoff value of 600 kcal/day. We divided the patients into the 'EN group' (≥ 600 kcal/day) and 'control group' (<600 kcal/day). The cumulative number of loss of response was significantly lower in the EN group (odds ratio: 0.23, P = 0.0043). Kaplan-Meier analysis confirmed the significantly lower rate of loss of response in the EN group (P = 0.013). Multivariate hazard ratio was 0.37 (P = 0.025). Type of EN formula did not affect the results. CONCLUSIONS: Concomitant use of EN ≥ 600 kcal/day is likely to yield a sustained response to IFX in CD patients.

Molecular basis for selectivity of high affinity peptide antagonists for the gastrin-releasing peptide receptor.

Few gastrointestinal hormones/neurotransmitters have high affinity peptide receptor antagonists, and little is known about the molecular basis of their selectivity or affinity. The receptor mediating the action of the mammalian bombesin (Bn) peptide, gastrin-releasing peptide receptor (GRPR), is an exception, because numerous classes of peptide antagonists are described. To investigate the molecular basis for their high affinity for the GRPR, two classes of peptide antagonists, a statine analogue, JMV594 ([d-Phe(6),Stat(13)]Bn(6-14)), and a pseudopeptide analogue, JMV641 (d-Phe-Gln-Trp-Ala-Val-Gly-His-Leupsi(CHOH-CH(2))-(CH(2))(2)-CH(3)), were studied. Each had high affinity for the GRPR and >3,000-fold selectivity for GRPR over the closely related neuromedin B receptor (NMBR). To investigate the basis for this, we used a chimeric receptor approach to make both GRPR loss of affinity and NMBR gain of affinity chimeras and a site-directed mutagenesis approach. Chimeric or mutated receptors were transiently expressed in Balb/c 3T3. Only substitution of the fourth extracellular (EC) domain of the GRPR by the comparable NMBR domain markedly decreased the affinity for both antagonists. Substituting the fourth EC domain of NMBR into the GRPR resulted in a 300-fold gain in affinity for JMV594 and an 11-fold gain for JMV641. Each of the 11 amino acid differences between the GRPR and NMBR in this domain were exchanged. The substitutions of Thr(297) in GRPR by Pro from the comparable position in NMBR, Phe(302) by Met, and Ser(305) by Thr decreased the affinity of each antagonist. Simultaneous replacement of Thr(297), Phe(302), and Ser(305) in GRPR by the three comparable NMBR amino acids caused a 500-fold decrease in affinity for both antagonists. Replacing the comparable three amino acids in NMBR by those from GRPR caused a gain in affinity for each antagonist. Receptor modeling showed that each of these three amino acids faced inward and was within 5 A of the putative binding pocket. These results demonstrate that differences in the fourth EC domain of the mammalian Bn receptors are responsible for the selectivity of these two peptide antagonists. They demonstrate that Thr(297), Phe(302), and Ser(305) of the fourth EC domain of GRPR are the critical residues for determining GRPR selectivity and suggest that both receptor-ligand cation-pi interactions and hydrogen bonding are important for their high affinity interaction.