Review for 10.1186/1471-230X-10-107 (2010)

Reviewer's report
Title:Lubiprostone ameliorates the cystic fibrosis mouse intestinal phenotype
Version: 1Date:30 March 2010
Reviewer: Hugo De Jonge
Reviewer's report:
In this study the authors have exploited previously developed and published
methods to test a potential improvement of the intestinal phenotype of cystic
fibrosis (CF) mice (Cftr-/-) by in vivo treatment with the putative ClC-2 activator
and anti-constipation drug lubiprostone (once daily gavage of 0.1 ml emulsion in
Peptamen; 10 µg/kg/day for 2 weeks). It is concluded that lubiprostone treatment
has beneficial effects on some CF-relevant parameters (decreased bacterial
overgrowth in the small intestine; reduced activation of mast cell genes in CF
mice) but not on others (body weight gain, crypt width, mucus accumulation,
small intestinal transit). Unexpectedly, lubiprostone promoted bacterial
overgrowth in WT mice, and slightly enhanced rather than reduced mucus
accumulation in the intestinal crypts of Cftr-/- mice, suggesting a
Cftr-independent, stimulatory effect on mucus secretion in CF intestine.
Major Compulsory Revisions:
1. All Cftr-/- mice in this study are maintained on a liquid diet (Peptamen) rather
than solid diet. Unfortunately, this choice did not allow the authors to investigate
potential beneficial effects of lubiprostone on intestinal obstruction and survival,
i.e. the most prominent intestinal phenotype of CF mice. If lubiprostone would be
able to activate intestinal chloride and fluid secretion through a non-CFTR
mediated pathway, possibly involving ClC2, one would expect to see a reduced
obstruction and increased survival in lubiprostone-treated CF mice.
2. A very recent study performed too in Cftr-/- mice (Harmon GS et al 2010
Nature Med 16: 313-318) shows that PPAR-# signaling is defective in CF colon
and that PPAR-# agonists (e.g. rosiglitazone) can induce bicarbonate secretion,
reduce mucus retention, and promote survival of CF mice in a Cftr-independent
fashion. In the present manuscript, stimulation of bicarbonate and mucus
solubility and secretion rather than chloride secretion by lubiprostone, possibly
triggered through EP4 receptors, is suggested as the most plausible mechanism
by which lubiprostone may exert its anti-inflammatory and multiple other actions
in the CF intestine. Both studies together raise the question whether
lubiprostone, similar to 15-keto-PGE2, might additionally act as a PPAR-#
agonist and could partially rescue the intestinal CF phenotype through this
pathway. This possibility should be explored, or at least discussed in the
manuscript.
3. Even if lubiprostone targets CFTR rather than apical ClC2 channels in the
enterocyte (if they exist), it remains possible that the compound promotes luminal
hydration in Cftr-/- mice through an EP4/cAMP/PKA signaling pathway that is
known to result in inhibition of NHE3 and NaCl/fluid absorption. Such a potential
anti-absorptive action is ignored in the present manuscript.
4. Most experiments were apparently performed using total mouse intestine,
despite the fact that intestinal functions may vary considerably along the length of
the intestine. For example, the bacterial overgrowth and mucus retention from
goblet cells is expected to be more prominent in the ileum as compared with
jejunum. Were the measurements of crypt width (as an estimate of mucus
accumulation) performed in ileum, jejunum, or in both segments? Idem for the
microarrays?
Minor Essential Revisions:
1. p. 14, l. 10: The finding that lubiprostone can activate PGE2 receptors in the
intestine is confirmed in ref. 10, showing inhibition of lubiprostone-induced anion
secretion by a specific EP4 antagonist. Therefore this reference should be
mentioned in addition to ref. 23.
2. p. 17, l. 13-14: A crucial finding reported in ref. 10 is that lubiprostone not only
failed to induce intestinal chloride secretion in Cftr-/- mice but also in the ileal and
rectal epithelium from human CF patients. This finding should be quoted in the
Discussion.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests.