Estimation of Somatomedin-C Levels in Normals and Patients with Pituitary Disease by Radioimmunoassay

Furlanetto, Richard W.; Underwood, Louis E.; Wyk, Judson J. Van; D’Ercole, A. Joseph

doi:10.1172/jci108816

Cited by 909 publications

(320 citation statements)

References 22 publications

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“…For assay purposes, hrIGF-I (Bachem Inc., Torrance, Calif., USA) was used as standard and tracer. The hormone was iodinated with 125 I by means of the chloramine-T method [21] at a specific activity of 400-450 µCi/µg and purified on a Sephadex G-50 column [22]. The rabbit polyclonal antibody (UBK487), employed at 1 : 10 000 dilution, was a generous gift from Dr. L. E. Underwood (Division of Pediatric Endocrinology, University of North Carolina at Chapel Hill, USA).…”

Section: Igf-i Assaymentioning

confidence: 99%

Relationship between non-enzymatic glycosylation and changes in serum insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 levels in patients with type 2 diabetes mellitus

et al. 1998

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The possible occurrence of increased non-enzymatic glycosylation of serum insulin-like growth factor binding protein-3 (IGFBP-3) in vivo and the changes that would simultaneously occur in serum levels of IGFBP-3 and insulin-like growth factor-1 (IGF-I) were investigated. We measured levels of IGF-I and IGFBP-3 and the degree of glycation of total serum protein and IGFBP-3, in serum samples obtained from patients with poorly controlled noninsulin-dependent diabetes (type 2) and from age-matched non-diabetic controls. Type 2 diabetic patients had significantly higher glycated serum protein (GlyP) levels. GlyP significantly correlated with age in the control (r = 0.315, P < 0.05) but not in the type 2 diabetes group. Control and diabetic subjects had comparable serum IGF-I levels and in both groups IGF-I levels tended to decrease with age (r = -0.567, P < 0.001 and r = -0.465, P < 0.05 for control and type 2 diabetic subjects, respectively). In the type 2 diabetes group, IGF-I levels showed a negative correlation with serum GlyP values (r = -0.476, P < 0.05). Type 2 diabetic and control patients had comparable serum IGFBP-3 levels, which were significantly higher in diabetic patients in the older age subgroups. A negative correlation was found between IGFBP-3 levels and age in the control (r = -0.705, P < 0.001) and in the type 2 diabetes groups (r = -0.463, P < 0.05). A significant negative correlation was found between IGFBP-3 levels and GlyP in control (r = -0.449, P < 0.002) but not in type 2 diabetic subjects. The mean glycated IGFBP-3 (GlyIGFBP-3) levels were higher in the oldest type 2 diabetic patients. In these patients, GlyIGFBP-3 was negatively associated with IGF-I levels (r = -0.447, P < 0.05). The IGF-I/IGFBP-3 molar ratio was significantly reduced in the 46-60-year-old type 2 diabetic group, whereas the IGF-I/IGFBP-3 ratio was positively and significantly correlated with GlyP levels only in the control group (r = 0.489, P < 0.01). Our results show that: a) increased non-enzymatic glycosylation of IGFBP-3 occurs in vivo; and b) this effect is accompanied by an increase in IGFBP-3 levels. These results suggest that the IGF-I/IGFBP-3 system is another target for the metabolic derangements of type 2 diabetes. Its alterations might play a role in diabetic complications.

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Section: Igf-i Assaymentioning

confidence: 99%

Relationship between non-enzymatic glycosylation and changes in serum insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 levels in patients with type 2 diabetes mellitus

et al. 1998

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“…In 1977, the first RIA for insulin-like growth factor 1 (IGF1) was described by Furlanetto et al (1). Since then, IGF1 immunoassays have been used to screen patients for the presence of GH deficiency (GHD) or acromegaly.…”

Section: Introductionmentioning

confidence: 99%

Heterophilic antibodies may be a cause of falsely low total IGF1 levels

Brugts

Luermans

Lentjes

et al. 2009

European Journal of Endocrinology

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Background: A low serum total IGF1 is considered as a diagnostic indicator of GH deficiency (GHD) in the presence of hypopituitarism. Introduction of IRMA and chemiluminescent immunometric assay (CLIA) IGF1 immunoassays has introduced endogenous antibodies as a new source of interference. In general, this goes unnoticed and might lead to unnecessary diagnostic and therapeutic interventions. Case: A 56-year-old man was referred with a decline in physical performance, unexplained osteopenia, and weight loss of 3 kg over the past 8 months. Although clinical signs and symptoms were unremarkable, laboratory results pointed to secondary hypothyroidism and secondary hypogonadism. In addition, the serum total IGF1 level (CLIA; Siemens Medical Solutions Diagnostics) was in the low normal range. Two GH stimulation tests were performed, but these tests did not support the diagnosis GHD. Moreover, IGF1 bioactivity measured by the kinase receptor activation assay was normal. Interference of heterophilic antibodies was considered. After pretreatment with specific heterophilic blocking tubes that contain blocking reagents to eliminate heterophilic antibodies, serum-free thyroxine, testosterone, and IGF1 levels turned out to be normal. Conclusion: To the best of our knowledge, we here describe the first case in the literature of a patient with low serum total IGF1 levels due to interference from heterophilic antibodies in the used IGF1 immunoassay. When confronted with low-IGF1 levels that do not fit the clinical picture, interference of heterophilic antibodies should be considered in the differential diagnosis.

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“…Natural IGF-I (lot 16SPII) was kindly provided by R. E. Humbel (7). Antiserum to human SM-C was obtained from the Hormone Distribution Program, National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases (23). Both natural IGF-I and synthetic IGF-I were labeled with "2I by a modification of the lactoperoxidase method (24) to a specific activity of 150-250 ,uCi/,ug (1 Ci = 3.7 X 1010 Bq).…”

mentioning

confidence: 99%

Total synthesis of insulin-like growth factor I (somatomedin C).

Li¹,

Yamashiro²,

Gospodarowicz³

et al. 1983

Proc. Natl. Acad. Sci. U.S.A.

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Human insulin-like growth factor I (somatomedin C) with 70 amino acid residues and three disulfide bridges has been synthesized by the solid-phase method. The synthetic product behaves as a pure polypeptide in paper electrophoresis, isoelectric focusing, and high-performance liquid chromatography. Its elution behavior in Sephadex G-50, isoelectric point, amino acid composition, and growth-stimulating activity in bovine adrenal cortical cells or granulosa cells are comparable to those reported for the natural product. In radioimmunoassay, the synthetic product is indistinguishable from the natural hormone when either synthetic or natural product is used as the labeled ligand.Production of somatomedins (SMs) and insulin-like growth factors (IGFs) is known to be stimulated by growth hormone (somatotropin) in animals (1, 2) and human subjects (3, 4). SM-C (5) and IGFs (6) have been purified to homogeneity from human plasma. Complete amino acid sequences for IGF-I (7) and IGF-II (8) have been proposed, but only limited sequence data for SM-C are known (5). Various bioassay and radioimmunoassay (RIA) data indicate that IGF-I and SM-C are identical (5, 9, 10). IGF-I consists of 70 amino acid residues with three disulfide bridges, and its structure is homologous to that of proinsulin (7, 11). Fig. 1 presents the primary structure of IGF-I as proposed by Rinderknecht and Humbel (7). Because chemical synthesis of any known growth factor has not been reported, this communication describes the total synthesis of IGF-I (SM-C). MATERIALS AND METHODSProtected IGF-I Resin. 4-(Boc-alanyloxymethyl)-phenylacetamidomethyl-resin (1.60 g, 0.60 mmol) prepared as described (12) was placed in a Beckman model 990 peptide synthesizer and carried through procedures of solid-phase synthesis (13) consisting of (i) 15-min deprotection with 50% (vol/vol) trifluoroacetic acid/CH2Cl2, (ii) neutralization with 5% (vol/vol) diisopropylethylamine (DIEA)/CH2Cl2 (two times). Coupling was effected with preformed symmetrical anhydrides (1.8 mmol, 3 eq) of for 20 min in CH2Cl2 except for Boc-Met(O)-OH, Boc-Arg(Tos)-OH, and Boc-Gln-OH, for which 40-min coupling was allowed and sufficient N,N-dimethylformamide was employed to give concentrations of 20, 15, and 20%, respectively. Boc-Asn-OH was coupled with dicyclohexylcarbodiimide and 1-hydroxybenzotriazole (15). In all cases a second coupling stage was performed (20 min): (i) for residues 69 through 59 and all subsequent couplings in which dimethylformamide was used 1 eq of DIEA was added (16); (ii) for all other residues 1 eq of N-methylmorpholine and sufficient trifluoroethanol to give a concentration of 20% were added (16). The following side-chain blocking groups were used: Asp, cyclopentyl (17); Thr, Ser, and Glu, benzyl; Cys, 3,4-dimethylbenzyl (18); Met, sulfoxide (19); Tyr and Lys, 2-bromobenzyloxycarbonyl; Arg, tosyl. The yield of protected peptide resin was 7.92 g (weight gain was 87% of theory).IGF-I. Protected IGF-I resin (1.336 g, 0.101 mmol) was treated with 50% trifluoroacetic ac...

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Estimation of Somatomedin-C Levels in Normals and Patients with Pituitary Disease by Radioimmunoassay

Cited by 909 publications

References 22 publications

Relationship between non-enzymatic glycosylation and changes in serum insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 levels in patients with type 2 diabetes mellitus

Relationship between non-enzymatic glycosylation and changes in serum insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 levels in patients with type 2 diabetes mellitus

Heterophilic antibodies may be a cause of falsely low total IGF1 levels

Total synthesis of insulin-like growth factor I (somatomedin C).

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