Monoclonal antibodies directed to human insulin-like growth factor I (IGF I). Use for radioimmunoassay and immunopurification of IGF

Production of monoclonal antibodies recognising different epitopes present on insulin-like growth factor 1

Monoclonal antibodies (MAbs) were generated against recombinant human insulin-like growth factor 1 (IGF-1) by fusion of NS-1 myeloma cells with spleen cells from BALB/c X DBA mice immunised with recombinant IGF-1 and synthetic peptide sequences derived from the published amino acid sequence of IGF-1. MAbs were produced that recognised four distinct epitopes including two defined segments of the C and D domains. All MAbs were IgM mouse immunoglobulins. These results indicate the feasibility of producing MAbs to highly conserved proteins.

A mutant of human insulin-like growth factor II (IGF II) with the processing sites of proinsulin. Expression and binding studies of processed IGF II

A mutant of human insulin-like growth factor II (IGF II) was constructed by site-directed mutagenesis: the nucleotides coding for Ser33 and Ser39 were changed to yield Arg and Lys, respectively, thus creating two pairs of basic residues, Arg-Arg and Lys-Arg, as flanking sequences of the remaining C domain. [Arg33, Lys39]IGF II was expressed in NIH-3T3 cells as a processed two-chain peptide with a deletion of amino acid residues 37-40 and crosslinked by three disulfide bonds. This des(37-40)[Arg33]IGF II showed 3.6-fold and 7.4-fold reduced affinities to the type 1 and type 2 IGF receptor overexpressing cells, respectively, whereas the thymidine incorporation potency was the same as that of wild-type IGF II. We speculate that the discrepancy between the reduced binding to the type 1 IGF receptor and the full thymidine incorporation potency is due to the 6.1-fold reduced affinity of the expressed mutant to the co-expressed IGF binding protein 3 (IGFBP-3). The results suggest that des(37-40)[Arg33]IGF II assumes a conformation very similar to IGF II, and that the entire length of the C domain is not essential for biological activity.

Effect of growth hormone administration on human ovarian function and steroidogenic gene expression in granulosa-luteal cells

OBJECTIVE

To study the effect of growth hormone (GH) in combination with an ultrashort-term gonadotropin-releasing hormone analogue/human menopausal gonadotropin (hMG)/human chorionic gonadotropin (hCG) regimen in ovarian hyperstimulation for in vitro fertilization (IVF).

DESIGN

Prospective randomized placebo-controlled study.

SETTING

University-based IVF program.

PATIENTS

Fifty-four normally cycling women (27 control and 27 GH-treated) participated in this study.

INTERVENTIONS

Human recombinant GH (24 IU)/placebo was given intramuscularly on alternate days starting on cycle day 4 until the day of last hMG injection.

RESULTS

Serum estradiol (E2) and progesterone (P) concentrations were slightly lower in the GH group than in the placebo group on the day of hCG injection and 1 day thereafter (P < 0.01 to 0.001). Serum luteinizing hormone, follicle-stimulating hormone, prolactin, testosterone (T), and sex hormone-binding globulin did not differ between the groups. The follicular fluid (FF) concentration of T was higher in the GH group than in the placebo group (15.9 +/- 6.0 nmol/L versus 10.2 +/- 4.9 nmol/L, P < 0.005), and no differences were observed in the FF concentrations of E2, P, and insulin-like growth factor I between the groups. In granulosa cells isolated from patients who received GH treatment, the levels of 3 beta-hydroxysteroid dehydrogenase and aromatase messenger ribonucleic acid were significantly higher than in the patients receiving placebo. The number of hMG ampules needed for follicular development and the number of follicles and oocytes recovered were similar in both groups.

CONCLUSIONS

These results indicate that GH administration modifies ovarian steroidogenic response to gonadotropins in IVF patients, suggesting a role for GH in the regulation of human ovarian function.

Mutants of human insulin-like growth factor II (IGF II). Expression and characterization of truncated IGF II and of two naturally occurring variants

Insulin-like growth factor II (IGF II) and four structural analogs, constructed by site-directed mutagenesis, were expressed as protein A fusion proteins in Escherichia coli BL21pLysS cells, cleaved with cyanogen bromide and purified by affinity chromatography and HPLC. Two mutants (Ser29 substituted by Arg-Leu-Pro-Gly, and Ser33 substituted by Cys-Gly-Asp) represent two naturally occurring variants of IGF II. The other two mutants, (7-67)IGF II and (9-67)IGF II, are truncated at the amino-terminus in analogy to the naturally occurring des(1-3)IGF I ('truncated IGF I'). These mutants were tested for their binding affinities to type-1 and type-2 IGF receptors, to IGF binding protein-3 (IGFBP-3) and for their stimulation of thymidine incorporation into DNA. The affinities of the Ser29 and Ser33 mutants to the type-1 IGF receptor were 85% and 39%, respectively, compared to wild-type IGF II, those of (7-67)IGF II and (9-67)IGF II 96% and 15%, respectively. The potencies of the Ser33 and the (9-67) mutant to stimulate thymidine incorporation into DNA correlated closely with the affinities to the type-1 IGF receptor, whereas the bioavailability of the Ser29 mutant was lower and that of the (7-67) mutant higher than the type-1 receptor binding, possibly due to interferences with endogenously secreted IGFBPs. The affinities of the Ser29 and Ser33 mutants to the type-2 IGF receptor were 110% and 71%, respectively, those of the two truncated mutants 25% and 23%, respectively. The affinity of the Ser29 mutant to IGFBP-3 was increased to 171%, whereas those of the Ser33 mutant and the two truncated mutants were reduced (34%, 10% and 19%, respectively).

Cotreatment with growth hormone, after pituitary suppression, for ovarian stimulation in in vitro fertilization: a randomized, double-blind, placebo-control trial

OBJECTIVE

To explore the effect of cotreatment with growth hormone (GH) for ovarian stimulation after pituitary suppression.

DESIGN

A randomized, double-blind, placebo-controlled study.

SETTING

Specialist Reproductive Endocrine and In Vitro Fertilization (IVF) Unit.

PATIENTS, PARTICIPANTS

Twenty-five IVF patients who had responded suboptimally in a previous treatment cycle. A subgroup of 18 patients were found to have ultrasound (US) findings of polycystic ovaries (PCO).

MAIN OUTCOME MEASURE

The amount of gonadotropin used, development of follicles greater than or equal to 14 mm, number of oocytes collected, fertilized, cleaved and replaced, serum and follicular fluid (FF) insulin-like growth factor I (IGF-I) concentrations.

RESULTS

Cotreatment with GH was associated with a significant reduction in gonadotropins requirement (P less than 0.05). In patients with US-diagnosed PCO more follicles developed (P less than 0.05), more oocytes were collected (P less than 0.03), fertilized (P less than 0.004), and cleaved (P less than 0.02). A significantly higher FF IGF-I concentrations were found in patients receiving cotreatment with GH compared with those who received placebo (P less than 0.04).

CONCLUSION

We believe that there may be a place for GH treatment in selected IVF cycles after pituitary suppression but what the role of IGF-I should further be investigated.

Serum and follicular fluid insulin like growth factors I and II during growth hormone co-treatment for in-vitro fertilization and embryo transfer

OBJECTIVE

We wished to assess the changes in serum IGF-I and IGF-II concentrations during gonadotrophin treatment alone or with additional GH treatment and to compare follicular fluid IGF-I and IGF-II concentrations in the two treatment groups.

DESIGN

We performed an open study of co-treatment with GH and subsequently a randomized double blind comparison of addition of placebo or GH to clomiphene citrate and gonadotrophins.

PATIENTS

We studied previously poor responders to superovulation regimens for in-vitro fertilization and embryo transfer, six women in an open study, four of whom had ultrasound diagnosed polycystic ovaries, and 17 women in a double blind study, 12 of whom had polycystic ovaries.

MEASUREMENTS

We measured serum IGF-I and IGF-II concentrations throughout treatment cycles. Follicular fluid concentrations were measured at the time of oocyte recovery.

RESULTS

Neither serum IGF-I nor IGF-II concentrations were altered by gonadotrophin treatment alone. However, co-treatment with GH led to a significant rise in serum IGF-I concentrations in women with ultrasound diagnosed polycystic ovaries. Concentrations of IGF-I and IGF-II in follicular fluid were lower than in serum, although follicular fluid IGF-I concentrations were higher in women receiving GH than in those receiving placebo.

CONCLUSIONS

Poor responders to superovulation regimens may have an abnormality of growth factor response. GH co-treatment leads to an increase in circulating IGF-I concentrations in women with polycystic ovaries but our results do not support the hypothesis that GH stimulates IGF-I production in the human ovary.

Expression of a human insulin-like growth factor II cDNA in NIH-3T3 cells

Recombinant human insulin-like growth factor II (IGF-II) was produced in NIH-3T3 cells transfected with a plasmid containing a construct encoding the signal peptide and the sequence of mature human IGF II. Successfully transfected clones secreted correctly processed recombinant human IGF II at rates of about 100ng per 24 hours per 10(6) cells. The biological activity of the purified recombinant human IGF II exhibited similar potencies as standard human IGF II isolated from serum in radio-receptorassays as well as in thymidine incorporation assays.

A comparative study of single-dose growth hormone therapy as an adjuvant to gonadotrophin treatment for ovulation induction

One intramuscular injection of biosynthetic human growth hormone (24 IU), administered on the first day of gonadotrophin treatment for ovulation induction, significantly augmented the ovarian response to gonadotrophic stimulation in seven patients. Compared with a protocol involving six injections of 24 IU of GH given on alternate days to the same patients, the smaller dose had an intermediate but highly significant effect in reducing the amount, duration of treatment and daily effective dose of hMG needed to induce ovulation. The difference between the effect of the one-dose and six-dose protocols was small. The action of growth hormone on the human ovary, probably mediated by insulin-like growth factor-1 (IGF-1), appears effective in enhancing the response to gonadotrophin therapy even when given in a single dose.

Cotreatment with human growth hormone and gonadotropins for induction of ovulation: a controlled clinical trial

A randomized, double-blind, placebo-controlled trial of cotreatment with biosynthetic, human sequence, growth hormone (GH), and human menopausal gonadotropins (hMG) for induction of ovulation was performed in 16 women with amenorrhea and anovulatory infertility. Patients were randomly allocated to treatment with hMG + GH (24 IU on alternate days, total dose 144 IU) or hMG + placebo. Those who received placebo were given GH in a subsequent course of treatment. On cotreatment with GH compared with placebo, there was a significant reduction in the required dose of hMG, duration of treatment, and the daily effective dose of gonadotropins. Serum insulin-like growth factor-I (IGF-I) rose during treatment with GH but not with placebo. We conclude that growth hormone augments the response of the human ovary to stimulation by gonadotropins. These results suggest a role for the use of GH in induction of ovulation.

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).

Insulin-like growth factor II in human adrenal pheochromocytomas and Wilms tumors: expression at the mRNA and protein level

Two forms of insulin-like growth factor (IGF) II with molecular masses of 10 and 7.5 kDa, respectively, were found in tumor tissue from human adrenal pheochromocytomas. The tumors contained 5.3-7.1 micrograms of immunoreactive IGF-II per g of tissue, which is about 20 times more than in adrenal medulla. The total bioactive IGF in the pheochromocytomas exceeded that in normal liver or kidney, which contained only the 7.5-kDa IGF-II species, by a factor of approximately equal to 100. By contrast, the amount of IGF-I was just measurable and did not vary significantly between tumor and normal tissue. The high amounts of IGF-II in the pheochromocytomas were not reflected, however, by a corresponding increase of mRNA. The opposite situation was found in Wilms tumors, where IGF-II content was in the same range as in nontumor tissues despite increased expression of IGF-II mRNA.

Derivation of monoclonal antibodies to human somatomedin C/insulin-like growth factor I

Somatomedin C, also called insulin-like growth factor I (Sm-C/IGF-I), is a highly conserved polypeptide required for the proliferation of many cell types. Since several attempts in our laboratory to recover monoclonal antibody-secreting hybrids to this peptide by the direct fusion of hyperimmunized splenocytes with myeloma cells had been unsuccessful, we modified our approach by coculturing hyperimmunized BALB/c splenocytes and a small amount of the antigen for 5 days prior to fusion with the P3X63Ag.8.653 myeloma cell line. Of 88 microcultures at risk, specific antibody was detected in 24. Two clones were expanded in ascites fluid and characterized as to isotype, affinity, and specificity. Both were IgG1,kappa and bound human Sm-C/IGF-I with affinity constants of 1.09 and 1.01 X 10(10) liter/mol, respectively. Both clones were quite specific for Sm-C/IGF-I with inconsequential binding to insulin-like growth factor II, multiplication-stimulating activity, any of the chymotryptic fragments of Sm-C/IGF-I, insulin preparations, hGH, hTSH, mEGF, or mouse albumin. In vitro boosting after primary in vivo immunization appears to provide monoclones of an IgG isotype in contrast to primary in vitro immunization, which reportedly favors an IgM isotype. The antibodies produced in this study have proved to be extraordinarily useful in defining the physiologic role of Sm-I/IGF-I with immunoneutralization techniques and in the purification of human Sm-C/IGF-I by affinity chromatography.

Comparative binding of bovine, human and rat insulin-like growth factors to membrane receptors and to antibodies against human insulin-like growth factor-1

The immunological properties of human, bovine and rat insulin-like growth factors (IGF) and insulin were compared in competitive binding studies with Tr10 and NPA polyclonal antisera raised in rabbits against human IGF-1. Bovine IGF-1 was 11-19% as effective as human IGF-1 in competing for binding with 125I-labelled human IGF-1, whereas IGF-2 reacted poorly and insulin did not compete. Similar competitive binding curves were obtained with the mouse monoclonal anti-(human IGF-1) antibody 3D1, except that bovine IGF-1 showed a severalfold greater affinity for the monoclonal antibody than for either polyclonal antiserum. Membranes isolated from human placenta, sheep placenta and foetal-human liver were used as sources of cellular receptors. In human placental membranes, most of the binding of IGF-1 tracers could be attributed to a type-1 receptor, because insulin inhibited up to 65% of tracer binding. The other two tissues apparently contain only type-2 receptors, as evidenced by the very low potency of bovine or human IGF-1 in competing for binding with IGF-2 tracers and the absence of any competition by insulin. In competition for binding with labelled bovine or human IGF-1 to human placental membranes, bovine IGF-1 had a similar potency to human IGF-1, whereas bovine IGF-1 was more potent in binding studies with tissues rich in type-2 receptors. Rat IGF-2 was considerably less effective than human IGF-2 in competition for receptors on any of the membrane preparations.

Activity in fetal bovine serum that stimulates erythroid colony formation in fetal mouse livers is insulinlike growth factor I

In the present study, the erythropoietic activity of fetal serum was characterized. Using fetal bovine serum (FBS) as a source of the erythropoietic activity and serum-free cultures of fetal mouse livers (FMLC assay) as a detection system, we found that FBS stimulated colony formation from late erythroid progenitor cells (CFU-E) in a dose-dependent fashion. The slope of the dose-response curve, however, was significantly different from that for erythropoietin (Ep), the best-characterized erythropoietic activity so far. The erythropoietic activity of FBS was found in the 120-160- and 40-70-kD range at neutral pH. In the presence of 1 M acetic acid, however, the erythropoietic activity had an apparent molecular mass between 3 and 13 kD. From ion exchange experiments with DEAE-cellulose, the isoionic point of the activity was estimated to about pH 5. Furthermore, the erythropoietic activity of FBS was found to be co-eluted on Sephadex G-150 with the binding proteins of insulinlike growth factors (IGF). The IGF I concentration determined by radioimmunoassay was 70 ng IGF I/ml. The Ep activity of FBS was less than 5 mU/ml when determined with the posthypoxic polycythemic mouse assay for Ep. These results suggest that the erythropoietic activity of FBS is related to IGF and not to Ep. The erythropoietic activity of FBS was abolished by an antiserum against IGF I. Furthermore, IGF I was a factor of approximately 40 more potent than IGF II in stimulating erythroid colony formation. All of these findings suggest that the erythropoietic activity of FBS is IGF I.

Amino acid sequence of a variant pro-form of insulin-like growth factor II

Human serum contains, in addition to the "classical" 7.5-kDa insulin-like growth factors (IGFs) I and II, small amounts of larger IGF-II. A 10-kDa IGF-II was isolated by gel filtration, immunoaffinity chromatography, and reversed-phase HPLC. Upon amino acid sequence determination, a substitution of Cys-Gly-Asp for Ser-33 was found as well as a COOH-terminal extension of 21 residues (E peptide). These sequence differences suggest that 10-kDa IGF-II is a precursor of a variant IGF-II. Since the substitution is not located at a known intron/exon hinge region, the finding of this variant IGF-II is evidence for the presence of more than one gene for IGF-II.

Insulin-like growth factor II (IGF II) in human brain: regional distribution of IGF II and of higher molecular mass forms

Twenty-four distinct areas of human brain were analyzed for the presence of insulin-like growth factor (IGF). As reported for cerebrospinal fluid, only IGF II-like immunoreactivity, but no significant amounts of IGF I-like immunoreactivity, could be found. Upon gel permeation chromatography, two to five distinct size classes were separated on the basis of their immunoreactivity. The smallest component had an apparent molecular mass of 7.5 kDa, identical to the one of purified IGF II from human serum. Radioimmunoassays and a bioassay also gave results indistinguishable from those of serum IGF II. The highest amounts of IGF II-like immunoreactivity occur in the anterior pituitary--namely, 20-25 pmol equivalents/g of wet weight. This is up to 100 times more than in most other brain regions analyzed. The higher molecular mass immunoreactive species were partially characterized. After immunoaffinity purification, the 38- and 26-kDa species are active in a bioassay. Specific IGF-binding protein activity could be shown after purification of the 38- and 26-kDa species on an IGF-affinity column. The 13-kDa species released significant amounts of 7.5-kDa material. The results are interpreted as evidence for the presence of IGF II synthesized locally in human brain. The structure of the larger forms of IGF II-like immunoreactive material as well as the function of IGF II in brain are not yet known.

Efficient purification of somatomedin-C/insulin-like growth factor I using immunoaffinity chromatography

Somatomedin-C/insulin-like growth factor I was purified from human plasma using a monoclonal antibody affinity column. Combining immunoaffinity chromatography with standard protein purification methods resulted in an overall recovery of 18%. The 35 micrograms of somatomedin-C/insulin-like growth factor I purified from 500 ml of plasma appeared as a single band when analyzed by polyacrylamide gel electrophoresis and could be used in radioimmunoassay and receptor binding studies.

Isolation of insulin-like growth Factors I and II from human plasma

Insulin-like growth factors I and II have been isolated from Cohn fraction IV-1 of human plasma using gel permeation chromatography, ion exchange chromatography, reversed phase chromatography, isoelectric focusing (IEF) and high performance liquid chromatography(HPLC). IGF I of specific activity 89 U/g, as measured by the isolated rat adipocyte assay, and IGF II, of specific activity 78 U/g, were obtained in yields of 16 micrograms and 34 micrograms respectively per 100g of Cohn fraction. Although this process yields IGF I which is contaminated with IGF II (due to the relatively large amount of the latter present in the original plasma), the IGF II preparations appear to be relatively free from IGF I. This separation was mainly achieved with IEF since the two factors elute close together on HPLC. Nevertheless, HPLC is important for their subsequent purification. The process is thus especially suitable for the preparation of IGF II and appears to give better yields than those obtained by earlier methods which used acid-ethanol extraction, gel permeation chromatography and polyacrylamide gel electrophoresis.