IMMUNOBLOT STUDIES OF THE ACID-LABILE SUBUNIT (ALS) IN BIOLOGICAL-FLUIDS, NORMAL HUMAN SERUM AND IN CHILDREN WITH GH DEFICIENCY AND GH RECEPTOR DEFICIENCY BEFORE AND AFTER LONG-TERM THERAPY WITH GH OR IGF-I RESPECTIVELY
Ji. Labarta et al., IMMUNOBLOT STUDIES OF THE ACID-LABILE SUBUNIT (ALS) IN BIOLOGICAL-FLUIDS, NORMAL HUMAN SERUM AND IN CHILDREN WITH GH DEFICIENCY AND GH RECEPTOR DEFICIENCY BEFORE AND AFTER LONG-TERM THERAPY WITH GH OR IGF-I RESPECTIVELY, Clinical endocrinology, 47(6), 1997, pp. 657-666
OBJECTIVE The aims of this investigation were (a) to study the presenc
e of immunoreactive forms of the acid-labile subunit (ALS) in differen
t human biological fluids, (b) to define the age dependence of serum A
LS in normal children and adults and (c) to compare the regulation of
ALS by GH or IGF-I in children with GH deficiency (GHD) and GH recepto
r deficiency (GHRD) before and after 1 year of therapy with GH or IGF-
I, respectively. DESIGN AND PATIENTS Selected human biological fluids
from different consenting volunteers and serum from 68 normal children
and 5 adults were analysed. Four children diagnosed as GHD and 7 chil
dren diagnosed as GHRD were treated with recombinant human (rh) GH at
a dosage of 0.05 mg/kg/day s.c. or rhIGF-I at a dosage of 120 mu g/kg
twice daily s.c., respectively, for 12 months. MEASUREMENTS Immunoreac
tive forms of ALS were studied by Western immunoblot using a specific
rabbit antiserum derived against synthetic human ALS and quantified by
laser densitometry analysis. Serum from children with GHD or GHRD wer
e sampled before and at 6 and 12 months of therapy; serum from these p
atients had been also assayed at baseline for determination of IGF-I a
nd IGF binding protein (IGFBP)-3 by radioimmunoassay and immunoradiome
tric assay, respectively.RESULTS An immunoreactive 85 kDa doublet of A
LS was detected in serum, plasma, follicular, peritoneal and synovial
fluid, but not in urine, seminal plasma, amniotic or extra-embryonic c
oelomic fluids. Assessment of serum from newborns to adults revealed a
n age dependence; the ALS doublet was low, but detectable, in newborns
, increased during adolescence and remained constant in adulthood. ALS
levels were significantly lower in GHD (P=0.02) and in GHRD children
(P=0.001) than in age-matched controls. Treatment with rhGH in GHD chi
ldren produced a 2.7-fold increase in serum ALS concentrations at 6 mo
nths of therapy (P=0.01), which was maintained after I year of treatme
nt (P=0.006), leading to normalization of ALS concentrations. In contr
ast, administration of rhIGF-I to GHRD children failed to increase and
normalize serum ALS levels either at 6 or 12 months of therapy. CONCL
USIONS Immunoreactive forms of acid-labile subunit are present in seru
m and plasma, as well as in follicular, peritoneal and synovial fluids
, suggesting that acid-labile subunit can either cross the capillary b
arrier or be secreted locally. Acid-labile subunit concentrations are
age-dependent with a sharp increase during adolescence, and are reduce
d in GH deficient and GH receptor deficient children. While treatment
with rhGH is able to increase and normalize acid-labile subunit concen
trations in GH deficient children, therapy with rhIGF-I fails to incre
ase serum acid-labile subunit levels in GH receptor deficient patients
. These data suggest that acid-labile subunit is directly GH-regulated
, and that IGF-I cannot increase acid-labile subunit levels, as assess
ed by Western immunoblot.