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

OBJECTIVEThe aims of this investigation were (a) to study the presence of immunoreactive forms of the acid‐labile subunit (ALS) in different human biological fluids, (b) to define the age dependence of serum ALS 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 receptor deficiency (GHRD) before and after 1 year of therapy with GH or IGF‐I, respectively.DESIGN AND PATIENTSSelected 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 children 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 μg/kg twice daily s.c., respectively, for 12 months.MEASUREMENTSImmunoreactive 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 were sampled before and at 6 and 12 months of therapy; serum from these patients had been also assayed at baseline for determination of IGF‐I and IGF binding protein (IGFBP)‐3 by radioimmunoassay and immunoradiometric assay, respectively.RESULTSAn immunoreactive 85 kDa doublet of ALS was detected in serum, plasma, follicular, peritoneal and synovial fluid, but not in urine, seminal plasma, amniotic or extra‐embryonic coelomic fluids. Assessment of serum from newborns to adults revealed an 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 children produced a 2.7‐fold increase in serum ALS concentrations at 6 months of therapy (P = 0.01), which was maintained after 1 year of treatment (P = 0.006), leading to normalization of ALS concentrations. In contrast, administration of rhIGF‐I to GHRD children failed to increase and normalize serum ALS levels either at 6 or 12 months of therapy.CONCLUSIONSImmunoreactive forms of acid‐labile subunit are present in serum and plasma, as well as in follicular, peritoneal and synovial fluids, suggesting that acid‐labile subunit can either cross the capillary barrier or be secreted locally. Acid‐labile subunit concentrations are age‐dependent with a sharp increase during adolescence, and are reduced in GH deficient and GH receptor deficient children. While treatment with rhGH is able to increase and normalize acid‐labile subunit concentrations in GH deficient children, therapy with rhIGF‐I fails to increase 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 assessed by Western immunoblot.