Is the hemochromatosis gene a modifier locus for cystic fibrosis?
Rohlfs EM, Shaheen NJ, Silverman LM
Department of Pathology & Laboratory Medicine, University of North
Carolina, Chapel Hill 27599, USA.
The variable clinical manifestations of cystic fibrosis (CF) suggest
the influence of modifier genes. For example, meconium ileus is
present in approximately 10-15% of neonates with cystic fibrosis;
however, the genetic and, or environmental factors that determine
whether an individual will develop this complication have not been
determined. We propose the HFE gene as a candidate modifier locus for
CF based on (1) the suggestion of an association between the HLA loci
and CF phenotypes; (2) the location of the HFE gene near the HLA loci
and; (3) the similarity between the gastrointestinal manifestations of
hereditary hemochromatosis and CF. We have determined the frequency of
the C282Y and H63D mutations in a group of 89 CF patients who were
homozygous for delta F508 and for whom meconium ileus status was
known. The carrier frequency of C282Y among the CF patients with
meconium ileus was significantly different from that of our unaffected
control group (19.4% versus 7.7%). However, the difference between the
meconium ileus and the nonmeconium ileus groups was not significant
(19.4% versus 10.3%). There was no difference in the frequency of the
H63D among the three groups that were studied. These data are
suggestive of a relationship between the development of meconium ileus
or other gastrointestinal diseases in CF and the HFE gene. Further
study of a larger group of patients is warranted.
Division of Pulmonary and Critical Care Medicine, University of Kansas
School of Medicine, Kansas City, USA.
PURPOSE: Extracellular free iron, or iron bound to ferritin, may
promote oxidative injury and bacterial growth in airways of patients
with chronic airway inflammation due to cystic fibrosis (CF) or
chronic bronchitis (CB). In this study, we assessed sputum content of
total iron, ferritin, and transferrin in patients with CF or CB as
well as sputum from normal subjects with acute airway inflammation
caused by viral upper respiratory tract infections (URTIs). METHODS:
Spontaneously produced sputum was obtained from 33 subjects, including
10 subjects with CF, 18 subjects with CB (10 acute exacerbations, 8
with stable CB), and 5 subjects with URTIs (control subjects). After
lysing and dilution, total iron concentrations were determined by
controlled coulometry, ferritin was measured by radioimmunoassay, and
transferrin was measured by enzyme-linked immunosorbent assay.
RESULTS: Iron was not present in detectable amounts in control
sputums, but ferritin was present (6+/-2 ng/mg protein, mean+/-SE), as
was transferrin (2.37+/-0.44 microg/mg). Compared with control
subjects, concentrations of iron in sputum were increased in patient
groups with higher amounts in CF patients (242+/-47 ng/mg, p<0.01)
than CB patients with acute exacerbations or patients with stable CB
(98+/-50 and 42+/-12 ng/mg, p<0.05 for both). Ferritin content of
sputum was also increased in each group, with CF patients (113+/-22
ng/mg, p<0.001) higher than CB patients (acute, 45+/-10 ng/mg; stable,
87+/-24 ng/mg; p<0.01 for both). Compared with control subjects,
sputum transferrin was decreased in CF patients (1.09+/-0.40
microg/mg, p<0.05), but not CB patients. CONCLUSIONS: These findings
indicate there are increased airway concentrations of total iron and
ferritin-bound iron in patients with CB and, to a greater extent, in
patients with CF. Particularly in CF patients who also demonstrated
decreased airway concentrations of transferrin, ferritin-bound iron in
airways may promote oxidative injury and enhance bacterial growth.
Ability of Pseudomonas pseudomallei malleobactin to acquire transferrin-bound,
lactoferrin-bound, and cell-derived iron.
Yang H, Kooi CD, Sokol PA
Department of Microbiology and Infectious Diseases, University of
Calgary Health Sciences Centre, Alberta, Canada.
The ability of malleobactin to mobilize iron from transferrin and
lactoferrin was examined in an equilibrium dialysis assay in the
absence of bacteria. Malleobactin was capable of removing iron from
both transferrin and lactoferrin at pH values of 7.4, 6.0, and 5.0.
However, the levels of iron mobilization were greater for transferrin
than for lactoferrin at all the pH values used in the assay. The
ability of Pseudomonas pseudomallei to acquire iron from 30%
iron-saturated transferrin and K562 human erythroleukemic cells was
compared in parallel cultures as described previously (J. H. Brock, P.
H. Williams, J. Liceaga, and K. G. Woldridge, Infect. Immun.
59:3185-3190, 1991). P. pseudomallei U7 tended to acquire iron from
transferrin. In contrast, P. aeruginosa PAO and P. cepacia Pc275C
acquired iron from both sources. P. cepacia H1721, which does not
produce detectable siderophores, but can utilize malleobactin,
pyochelin, and azurechelin as iron sources, was used in a similar
experiment. Addition of malleobactin resulted in iron uptake only from
transferrin, whereas pyochelin and azurechelin promoted iron uptake
from both sources. When the siderophores were incubated with K562
cells alone, malleobactin was less efficient at removing iron from
cells than pyochelin and azurechelin. It was also determined that
malleobactin was less effective in binding to or entering cells than
pyochelin and azurechelin. These results suggest that malleobactin can
acquire iron more effectively from host proteins than from cellular
sources. Pyochelin and azurechelin can acquire cell-derived iron in
addition to iron bound to host proteins.
