Ethnicity affects IGFBP-3 and IGF-II in normal healthy young adult subjects

OBJECTIVE

While the effects of age on the growth hormone/insulin-like growth factor (IGF) axis are well documented, the influence of ethnic background is unknown. The differences in IGF and IGF binding proteins (IGFBPs) were investigated in two ethnic groups.

DESIGN

A cross-sectional study of an age-selected cohort of healthy, normoglycaemic, non-obese Caucasian (C) and Asian (A) subjects.

PATIENTS

Fifty-three (27 C, 26 A) subjects with a mean age (+/- SD) of 20.6 +/- 0.8 years were studied.

MEASUREMENTS

Fasting measurements of glucose, insulin, IGF-I, IGF-II, IGFBP-1 and IGFBP-3. Western ligand blotting and immunoblotting with IGFBP-2 and IGFBP-3 of serum samples.

RESULTS

There were no significant differences in IGF-I levels between Caucasian and Asian subjects (C 218 +/- 55 vs A 229 +/- 40 micrograms/l; P = 0.44). IGF-II (C 707 +/- 110 vs A 583 +/- 75 micrograms/l; P < 0.0001) and IGFBP-3 (C 5.9 +/- 1.2 vs A 5.12 +/- 1.17 mg/l; P = 0.01) levels were significantly higher in Caucasian subjects. Immunoblotting of ligand blots revealed no protease activity on either IGFBP-3 or IGFBP-2 to account for these ethnic differences.

CONCLUSIONS

Ethnic differences in IGFBP-3 and associated IGF-II levels may affect the inter-relationships of IGFs and their binding proteins and need to be considered when interpreting IGF data on growth and metabolism.

Critical illness is associated with low circulating concentrations of insulin-like growth factors-I and -II, alterations in insulin-like growth factor binding proteins, and induction of an insulin-like growth factor binding protein 3 protease

OBJECTIVES

To describe the sequential changes in the circulating concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding proteins in critically ill patients. To determine whether critical illness is associated with induction of a specific protease directed against insulin-like growth factor binding protein 3 and to relate these changes to outcome.

DESIGN

Prospective, descriptive study.

SETTING

Intensive care unit (ICU) of a university hospital.

PATIENTS

Eighteen heterogeneous critically ill patients, requiring ventilatory support.

INTERVENTIONS

Serial daily blood samples were collected until death or discharge from the ICU. In five patients, samples were also obtained on the ward before discharge from the hospital.

MEASUREMENTS AND MAIN RESULTS

Serum concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding proteins 1, 2, and 3 were measured by radioimmunoassay. After 5 days, insulin-like growth factor binding protein 3 concentrations were measured on alternate days. Alterations in binding of insulin-like growth factor-I to insulin-like growth factor binding protein 3 and the presence of protease activity directed against insulin-like growth factor binding protein 3 were investigated by Western ligand blotting. Circulating concentrations of insulin-like growth factor-I and insulin-like growth factor-II were low and remained low throughout the 7-day study period. Insulin-like growth factor binding protein 1 concentrations were initially increased to within the fasting range, but subsequently decreased. There was considerable variability in insulin-like growth factor binding protein 2 concentrations, but generally, concentrations were at the upper end of the normal range throughout. Insulin-like growth factor binding protein 3 concentrations were consistently low and Western ligand blotting at the nadir of the insulin-like growth factor-I concentration demonstrated the presence of a protease directed against insulin-like growth factor binding protein 3. The last recorded concentrations of insulin-like growth factor-I and insulin-like growth factor binding protein 3 were higher in survivors than in nonsurvivors (p < .05). Two patients were also studied for a prolonged period. In one patient, a survivor, insulin-like growth factor-I and insulin-like growth factor binding protein 3 were low initially, but later increased in association with recovery and cessation of protease activity over a period of 33 days. In another patient, a nonsurvivor, insulin-like growth factor-I and insulin-like growth factor binding protein 3 remained low and protease activity persisted until the patient died 38 days after admission to the ICU.

CONCLUSIONS

Critical illness is associated with low circulating concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding protein 3 and these low values are associated with induction of protease activity specifically directed against insulin-like growth factor binding protein 3. In survivors, recovery is associated with increasing insulin-like growth factor-I and insulin-like growth factor binding protein 3 concentrations and cessation of protease activity. The therapeutic effects of exogenous growth factors are likely to be influenced by these changes.

Influence of treatment with tamoxifen and change in tumor burden on the IGF-system in breast cancer patients

Plasma levels of IGF-I, IGFBP-I and IGFBP-3 were measured before and during treatment with tamoxifen up to 19+ months in 34 post-menopausal patients with advanced breast cancer. In 28 patients, pro-IGF-IIE (IGF-IIE) levels were determined and IGFBP-3 was evaluated by immunoblot in 27 patients. Tamoxifen suppressed plasma levels of IGF-I by a mean value of 25.5%-37.7% at different times. This effect was fully developed after 1-2 months of treatment. IGF-IIE was decreased by a mean value of 7.7-23.2% at different time intervals during treatment with tamoxifen, but this effect was significant after long-term treatment (19 months +) only. Plasma IGFBP-I increased by a mean value varying between 48.6% and 190.1%. Tamoxifen had no significant effect on total IGFBP-3 levels. However, patients responding to treatment had a 28% reduction in fragmentation of IGFBP-3, while patients with progressive disease had a 36% increase in fragmentation. The difference between responders and non-responders was highly significant. These findings confirm and extend previous observations regarding the effects of treatment with tamoxifen on IGF-I and IGFBP-I. The finding that patients responding to tamoxifen achieve a reduction in the ratio of fragmented to intact IGFBP-3, while patients progressing on therapy experience an increase in the IGFBP-3 fragmentation ratio, suggest that the tumor burden influences IGFBP-3 protease activity in breast- cancer patients.

Serum insulin-like growth factor II levels in normal adolescents and those with insulin dependent diabetes mellitus

OBJECTIVE

Unlike IGF-I and its principal binding proteins, data regarding IGF-II levels have not been well defined in normal subjects and those with insulin-dependent diabetes mellitus (IDDM). We have therefore measured IGF-II, as well as IGF-I, and IGFBP-3, levels in a large cohort of subjects with IDDM and in age/sex matched controls.

PATIENTS

One hundred and fourteen patients with IDDM (57 males, 57 females) and 89 control subjects (49 males, 40 females).

MEASUREMENTS

Random blood samples were obtained from each subject for the measurement of IGF-II, IGF-I and IGFBP-3 levels.

RESULTS

Mean values of IGF-II (+/- SEM) were 630 (+/- 27.8) micrograms/l and 646 (+/- 32.3) micrograms/l in female and male controls, compared to 569 (+/- 23.3) micrograms/l and 623.3 (+/- 28.1) micrograms/l in female and male diabetics respectively. IGF-II levels did not differ significantly between the sexes or show any change with transition through puberty in either control or diabetic groups. In contrast, IGF-I levels increased through puberty peaking at stages 3-5 in controls (P < 0.001) and G4-5 (P = 0.002) in diabetic males but not females. IGF-I levels in all diabetics were generally lower than in controls, differences reaching significance at G4-5 in males (P = 0.002) and B5 in females (P = 0.002). IGFBP-3 levels did not show any variation with puberty stage in diabetics, in contrast to controls where levels increased, peaking at G4-5 in males (P = 0.001) and B3 in females. IGFBP-3 levels were lower in diabetics of both sexes and at all stages compared to controls (P range 0.047 to < 0.001). Multiple regression analysis revealed significant correlations between IGF-II and IGFBP-3 (F = 20.1, P = < 0.001) and reaffirmed previously observed associations for IGF-I and IGFBP-3. The sum of IGF-I and IGF-II (expressed as nmol/l) correlated with IGFBP-3; r = 0.47 in controls and 0.60 in diabetics.

CONCLUSIONS

Insulin-dependent diabetes mellitus is not associated with any significant changes in IGF-II levels during puberty. The binding of IGFBP-3 for both IGF-I and IGF-II is unaltered by insulin-dependent diabetes mellitus.

The role of IGFBP-3 in the regulation of IGFBP-4 proteolysis

The biological effects of insulin-like growth factors (IGFs) are mediated by cell surface receptors but their bioavailability is regulated by IGF binding proteins (IGFBPs) which bind IGF with higher affinity than the receptor. Proteolytic cleavage of the binding proteins reduces their affinity for IGF making the IGF more available to the cell receptor. In the current study we have examined the regulation of IGFBP-4 protease produced by cultured human dermal fibroblasts. IGF-I and the analogs of IGF-I (LR3 and Des[1-3]) induced a dose dependent increase in both proliferation and IGFBP-3 production. Low concentrations of IGF-I induced a marked loss of IGFBP-4 by Western ligand blotting (WLB). This effect was confirmed by the ability of media collected from cells exposed to increasing concentrations of IGF-I to fragment recombinant IGFBP-4, an effect blocked by EDTA. IGFBP-4 proteolysis was observed when cells were exposed to Des[1-3] (albeit at higher concentrations) but not with LR3. Both analogs bind to the IGF receptor but do not bind to IGFBP-4 and have reduced (Des[1-3]) or no (LR3) affinity for IGFBP-3. This demonstrated that neither receptor activation nor ligand binding directly to IGFBP-4 was necessary for IGF induced proteolysis. Protease activity correlated with affinity for IGFBP-3 suggesting a role for IGFBP-3 in the regulation of IGFBP-4 proteolysis. This was confirmed by the ability of excess recombinant IGFBP-3 to inhibit the IGF-I and Des[1-3] induced proteolysis of IGFBP-4. Addition of IGF-I to media from cells unexposed to IGF induced IGFBP-4 proteolysis but this was not seen with LR3 which does not bind to IGFBP-3. Fragmentation occured at higher concentrations of Des[1-3] consistent with its reduced affinity for IGFBP-3. This data suggests that IGFBP-4 proteolysis is regulated in a novel manner by IGFBP-3 which is dependent on the relative proportions of the different binding proteins and the levels of IGFs.

Effects of treatment with megestrol acetate, aminoglutethimide, or formestane on insulin-like growth factor (IGF) I and II, IGF-binding proteins (IGFBPs), and IGFBP-3 protease status in patients with advanced breast cancer

The effects of treatment with the aromatase inhibitors aminoglutethimide (AG) and formestane or the synthetic progestin megestrol acetate (MA) on plasma levels of insulin-like growth factor I (IGF-1), IGF-II, IGF-binding proteins (IGFBPs), and IGFBP-3 protease status were investigated in 39 patients suffering from advanced breast cancer. Treatment with AG and MA elevated plasma levels of IGF-I by mean values of 27% (n = 15; P < 0.025) and 81% (n = 7; P < 0.025), respectively, whereas treatment with formestane had no effect (n = 13). Treatment with AG increased plasma levels of IGFBP-2, as evaluated by Western blotting (P < 0.01). MA caused a significant reduction in IGFBP-3 protease activity (mean reduction, 69%; P < 0.05). These alterations in plasma IGF-I and IGFBP-3 protease activity were reversed 4 weeks after terminating MA therapy (n = 8; P < 0.025). Taken together, 13 of 15 patients had reduced IGFBP-3 protease activity during treatment with MA compared to the control situation (P < 0.0025). Total levels of IGFBP-3 as measured by RIA were moderately elevated by treatment with MA (mean increase, 19%; P < 0.05), and Western immunoblotting revealed an increase in the amount of intact IGFBP-3 and reduced amounts of IGFBP-3 in the modified form. None of the treatment modalities had any influence on plasma levels of IGF-II. The increase in the plasma IGF-I concentration seen during treatment with MA may be secondary to an increased level of intact IGFBP-3. This could reflect an alteration in IGF availability that contributes to the antitumor effect of MA.

Altered insulin-like growth factor-II (IGF-II) level and IGF-binding protein-3 (IGFBP-3) protease activity in interstitial fluid taken from the skin lesion of psoriasis

In the present study, we have investigated insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in serum and artificially raised blister fluid from uninvolved and involved areas of nine patients with psoriasis. Both levels of IGFs and IGFBP-3, and profiles of IGFBP in serum and fluid from the uninvolved areas of these patients were comparable to those seen in normal subjects. In fluid from the involved areas, the IGF-II but not IGF-I level was significantly elevated. Among five molecular forms of IGFBP, the density of 41.5- and 38.5-kDa forms of IGFBP-3 were apparently increased in fluid from the involved areas, shown by Western ligand blotting. Radioimmunoassay further showed that the IGFBP-3 concentration in the involved areas was significantly raised. Immunoblotting revealed that the predominant form of IGFBP-3 in fluid from the uninvolved areas was a 29-kDa proteolytically modified product. In contrast, intact doublet IGFBP-3 was the main form of IGFBP-3 in fluid from the involved areas. Fluid from the involved areas but not the matched serum concentration-dependently inhibited the degradation of 125I-labeled nonglycosylated IGFBP-3 (ngIGFBP-3) caused by fluid from the uninvolved areas, suggesting the presence of an IGFBP-3 protease inhibitor(s) in psoriatic skin lesion. These findings suggest that the alterations in IGF/IGFBP system may contribute to the pathogenesis of psoriasis.

Insulin-like growth factor (IGF) I and II, IGF-binding proteins, and IGF-binding protein proteases are produced by theca and stroma of normal and polycystic human ovaries

There is increasing evidence for an important regulatory role for the insulin-like growth factor (IGF) system in the human ovary. IGF-I and -II and IGF-binding proteins (IGFBPs)-1 to -4 have been identified by analysis of follicular fluid and granulosa cell-conditioned medium and by in situ hybridization and Northern and dot blot analyses of ovarian tissues. It has been suggested that abnormalities of intraovarian IGF-I or IGFBPs may play a part in the pathogenesis of polycystic ovary syndrome. The aim of this study was to identify production of IGF-I and -II and IGFBP-1 to -4 by unstimulated normal and polycystic ovaries. IGF-I and -II were measured by RIA after acid-gel exclusion chromatography in medium conditioned by incubation for 48 h with granulosa cells or explants of theca or stroma. Both IGF-I and -II were present in the low nanograms per mL range in theca- and stroma-conditioned medium (T+SCM). IGFBPs in T+SCM were initially analyzed by Western ligand blotting, which revealed that low mol wt IGFBPs were predominant, especially IGFBP-2 (35 kDa). There was a band corresponding to 26 kDa with smaller amounts of a 31-kDa band, but only a trace of IGFBP-3 (44 and 40 kDa, confirmed by immunoblot). We found no consistent differences between normal and polycystic ovary syndrome ovaries, and although there was a trend toward increased IGFBP accumulation in response to LH, this was not consistent. We were unable to detect IGFs or IGFBPs by Western ligand blotting in granulosa cell-conditioned medium. In further studies we attempted to measure IGFBP-3 by RIA using two different antisera (alpha-BP-3gl and 1287-2-14) that detect different epitopes of IGFBP-3 and allow the presence of proteolytic activity to be demonstrated. Results obtained using alpha-BP-3gl were lower than those using 1287-2-14, suggesting proteolysis of IGFBP-3 in the medium. There was no evidence of proteolysis of serum IGFBP-3 after incubation with conditioned medium, but in contrast, radiolabeled [125I]IGFBP-3 was cleaved after incubation with T+SCM. Immunoblotting revealed intact IGFBP-2 (35 kDa) and bands of various sizes between 16-33 kDa. Immunoreactive fragments of IGFBP-3 between 13-40 kDa were seen. In conclusion, T+SCM contained IGF-I and -II. IGFBP-2 and -4 were the predominant species of IGFBP in T+SCM. T+SCM also contained significant protease activity directed toward IGFBP-2 and -3. Proteolytic activity may be an important mechanism by which bioactive IGFs are made available to these tissues.

The differential regulation of the circulating levels of the insulin-like growth factors and their binding proteins (IGFBP) 1, 2 and 3 after elective abdominal surgery

OBJECTIVES

Patients undergoing abdominal surgery often suffer from morbidity associated with increased protein catabolism. Therapeutic recombinant human insulin-like growth factor (rhIGF)-I has been proposed as a means of reversing this process. As IGFBPs modulate the bioavailability of the IGFs, we have studied the changes in the circulating levels of these peptides during surgery.

DESIGN

Patients undergoing elective intestinal surgery were recruited prospectively. Blood samples were taken before, during and after surgery. Standard anaesthetic techniques were used.

METHODS

Twelve adults (aged 30-70 years; 9 female, 3 male) undergoing surgery were studied. Serum was taken before premedication (preop), end of surgery (end surg), 2 h, 6 h post surgery, on days 1-4, 7, 10 and 14, and on recovery at 6 weeks.

MEASUREMENTS

Serum IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3, insulin and C-peptide were measured by radioimmunoassay. IGFBP profiles were also assessed by Western ligand blot (WLB). Samples taken preop and at 2 days were separated by fast-phase liquid chromatography (FPLC) using a Superose 12 column under neutral conditions (pH 7.4), and the fractions were analysed subsequently by WLB and immunoblot using a specific IGFBP-3 antiserum.

RESULTS

IGF-I fell rapidly during surgery from 170 +/- 21 (preop) to 133 +/- 14 micrograms/l (end surg) (P < 0.05). The magnitude of this fall could not be explained by haemodilution. IGF-I levels then fell further to a nadir of 103 +/- 10 micrograms/l at day 4 (P < 0.05). IGF-II fell from 580 +/- 46 (preop) to 397 +/- 38 micrograms/l (day 2). Both IGF-I and IGF-II recovered to preop levels at 6 weeks (205 +/- 14 micrograms/l and 623 +/- 30 micrograms/l respectively). IGFBP-3 levels fell similarly from 4.46 +/- 0.45 to 3.2 +/- 0.3 mg/l (end surg) and to a nadir of 2.66 +/- 0.19 mg/l at day 2. There was a close correlation between IGFBP-3 levels and the sum of IGF-I and IGF-II levels before surgery (r = 0.9, P < 0.01) and this was maintained throughout the post-operative period (mean correlation coefficient of 0.86 +/- 0.02, P < 0.05). On days 2 and 3 there was a small but significant increase in the ratio between serum IGF-I and IGFBP-3 levels compared with the preop ratio (P < 0.05 and < 0.005, respectively). WLB demonstrated almost complete absence of IGFBP-3 by day 2. This discrepancy between RIA and WLB analysis of IGFBP-3 suggested the presence of IGFBP-3 protease activity between days 1 and 4. This was confirmed by WLB and immunoblot analyses of samples taken 2 days after surgery. The decrease in IGFBP-3 on WLB was shown to be associated with an increase in the proteolytically cleaved fragments of IGFBP-3. These fragments following FPLC were detected in the high molecular weight fractions, suggesting that the fragments were still able to form the high molecular weight IGFBP-3/ALS complex which is thought to form only when IGF is bound by IGFBP-3. IGFBP-1 levels rose during surgery (mean duration of surgery was 125 minute) from 18 +/- 3 (preop) to 51 +/- 12 micrograms/l (end surg) (P < 0.05). This rise in IGFBP-1 paralleled increases in insulin from 7.3 +/- 1.0 to 20.8 +/- 7.5 mU/l and glucose from 4.6 +/- 0.3 to 8.7 +/- 1.2 mmol/l. IGFBP-1 levels then fell to basal values by 6 hours. IGFBP-2, in contrast, fell slightly during surgery from 636 +/- 14 to 599 +/- 96 mg/l and then returned to basal levels by 6 hours.

CONCLUSION

After major surgery there are complex and diverse changes in the IGFs and IGFBPs. The effect of these changes on IGF bioavailability may significantly affect the therapeutic potential of IGF-I in this setting.

The insulin-like growth factor system in criticalillness: pathophysiology and therapeutic potential

Insulin-like growth factor-I (IGF-I) mediates at least some of the anabolic actions of growth hormone (GH). Most IGF-I in the circulation is held in a 150 kD complex with IGF binding protein-3 (IGFBP-3). In critical illness there is GH resistance which results in low serum levels of IGF-I, although its bioavailability may initially be maintained by serum proteases which modify the IGFBP-3 and reduce its affinity for IGF-I. Attempts to treat the protein catabolism associated with critical illness by hyperalimentation have had only limited success. The use of recombinant human GH combined with nutritional support increases protein synthesis, but the GH resistance necessitates high doses and GH has adverse direct metabolic effects including insulin resistance and impaired glucose tolerance. Treatment with recombinant human IGF-I inhibits proteolysis but may cause hypoglycaemia if administered intravenously. Its effects are often transient and show tachyphylaxis. A combination of GH and IGF-I with nutritional support may be the most effective treatment to counter the catabolism associated with critical illness. The costs of such therapy could be offset by shorter hospital stays. Further controlled studies are necessary to establish the clinical effectiveness of growth factor treatment.

Could abnormalities in insulin-like growth factors and their binding proteins during pregnancy result in gestational diabetes?

A number of dramatic changes have been documented in the insulin-like growth factors (IGFs-I and -II) and their binding proteins (IGFBPs) during pregnancy. In this study we have tested the hypothesis that a failure of the normal proteolytic modification of IGFBP-3 is responsible for gestational diabetes by examining serum samples taken in the third trimester from 29 women with uncomplicated pregnancies, 21 women with established Type 1 diabetes and 20 women with gestational diabetes. Analysis of IGFBP-3 by Western immunoblotting revealed that it was present in a modified form, migrating at around 29 kDa, in the circulation of all of the women investigated. Semiquantification of the activity of the protease which modifies the IGFBP-3 demonstrated considerable variation between individuals in their ability to fragment radiolabelled IGFBP-3 following a 45-min co-incubation. Surprisingly, in one individual (with gestational diabetes) there was no detectable protease activity even though her endogenous IGFBP-3 had been modified. However, overall there was no clear-cut difference in protease activity between the different groups. Radioimmunometric analysis of IGF-I revealed significantly higher levels in women with gestational diabetes than either of the other two groups (P < 0.05). Similarly IGFBP-3 levels were also increased in these same women (P < 0.05). In contrast, IGF-II levels did not alter between the three groups. In conclusion, our hypothesis was not supported by these data and gestational diabetes was found not to be associated with any reduction in the activity of the circulating IGFBP-3 protease which could have decreased the availability of the IGF nor with any alteration in IGFs which could explain the onset of diabetes in these women.

The 'dawn phenomenon' in adolescents with insulin dependent diabetes mellitus: possible contribution of insulin-like growth factor binding protein-1

OBJECTIVE

Insulin resistance increases during adolescence, and is exaggerated in patients with insulin dependent diabetes mellitus (IDDM). A relative deficiency of insulin-like growth factor-I (IGF-I) may contribute to this increased insulin requirement. Two mechanisms have been proposed: (a) increased GH secretion, caused by failure of IGF feedback control, leading to increased insulin resistance and (b) lack of insulin-like action of the IGFs which is reinforced by high plasma levels of IGFBP-1, an inhibitor of IGF action. The contribution of these two mechanisms to the 'dawn phenomenon' is assessed.

DESIGN

The two possible mechanisms were studied during the dawn rise of glucose in pubertal adolescent patients with IDDM. Two overnight studies were performed in each subject. Patients remained on the same insulin regimen throughout.

SUBJECTS

Twenty-two diabetic adolescent subjects, aged (mean +/- SEM) 14.0 +/- 0.4 years, duration of IDDM 7.9 +/- 0.8 years, were recruited. Pubertal status was: group 1 (breast stage 1-2; testicular volume < 4-8 ml) 3 male and 4 female, group 2 (breast stage 3; testicular volume 10-12 ml) 0 male 4 female, group 3 (breast stage 4-5; testicular volume 15-25 ml) 4 male and 7 female. Height standard deviation score (mean +/- SD) (-0.02 +/- 0.99) and daily insulin dose (50.4 +/- 3.1 U/day) did not change between studies. There were no differences in HbA1 (study A 11.26 +/- 0.45%, study B 11.09 +/- 0.42%).

METHODS

The subjects were admitted for the two studies 0.3 +/- 0.03 years apart. Blood samples were taken via an indwelling cannula every 20 minutes between 1900 and 0700 h.

MEASUREMENTS

GH was assayed every 20 minutes, IGFBP-1, glucose and free insulin every hour and IGF-I at 0700 h. GH, IGFBP-1, IGF-I and free insulin were measured by radioimmunoassay. IGFBPs were also analysed by Western ligand blotting techniques. GH profiles were analysed by Pulsar and results compared by paired Student's t-test. The relations between the dawn rise in glucose and the changes in IGFBP-1, GH and free insulin were examined by multiple linear regression analysis.

RESULTS

Serum IGFBP-1 levels rose overnight in the two studies (study A, from 9 +/- 1 at 2200 to 59 +/- 9 micrograms/l at 0700 h; study B, from 10 +/- 1 at 2100 to 64 +/- 14 micrograms/l at 0700 h) whilst insulin levels fell from 47 +/- 5 at 2200 to 16 +/- 2 mU/l at 0700 h (study A) and from 45 +/- 5 at 2000 to 14 +/- 2 mU/l at 0700 h (study B). Glucose levels fell from 16.0 +/- 1.0 to 9.3 +/- 0.9 mmol/l at 0400 h, and then rose to 11.9 +/- 1.1 mmol/l at 0700 h during study A, and from 13.4 +/- 1.3 to 10.1 +/- 1.1 mmol/l at 0400 h and then rose to 13.5 +/- 1.0 mmol/l at 0700 h during study B. There were no differences in GH secretion between studies (mean GH levels (mean +/- SD) (study A, 15.7 +/- 6.6 mU/l; study B, 16.2 +/- 7.1 mU/l; correlation within subjects between studies r = 0.77, P < 0.001), sum of GH peaks (study A, 189.9 +/- 90.3 mU/l; study B, 185.8 +/- 100.2 mU/l; r = 0.57, P = 0.006)). Mean GH levels varied with pubertal stage (group 1, 12.1 +/- 1.5 mU/l; group 2, 23.3 +/- 2.1 mU/l; group 3, 15.3 +/- 1.2 mU/l). Serum IGF-I levels were not different (study A, 203 +/- 12 micrograms/l; study B, 218 +/- 13 micrograms/l). REGRESSION ANALYSIS: The change in plasma glucose between 0200 and 0700 h in both studies related to free insulin, IGFBP-1 and the sum of the GH levels over the preceding hour (log glucose = 7.87 + 5.32 log IGFBP-1 (P = 0.0001) - 5.05 log free insulin (P = 0.0001) - 1.44 log GH (P = 0.004); R2 = 72%). Mean overnight GH levels did not predict the morning rise in plasma glucose.

CONCLUSION

The morning rise of IGFBP-1 and plasma glucose appear to be related in this group of subjects with IDDM and this was a consistent finding in the two studies. This relation was additive to the effect of insulin deficiency.

The effects of repeated daily recombinant human insulin-like growth factor I administration in adolescents with type 1 diabetes

Reduced insulin-like growth factor bioactivity has been linked to poor metabolic control and growth hormone hypersecretion in adolescents with Type 1 diabetes. The safety and efficacy of recombinant human insulin-like growth factor I administered subcutaneously in a dose of 40 micrograms kg-1 for 28 days was studied in a group of 6 adolescent male subjects with Type 1 diabetes (aged 13.6-19.4 years, puberty stage 3-5). After a 4-week run-in period (week -4 day 0) recombinant human insulin-like growth factor I was administered for 4 weeks (day 0 to week +4) before a run-out of a further 4 weeks duration (week +4 to +8). HbA1c levels were measured throughout the study and overnight profiles were undertaken to study levels of insulin-like growth factor 1, insulin-like growth factor binding protein-3, and growth hormone concentrations (week -1, day 0, and week +4). The injections were well tolerated and hypoglycaemia was not problematic at any stage of the study. Recombinant insulin-like growth factor I administration appeared to lead to a sustained increase in insulin-like growth factor I levels (week -1; 198 +/- 16 ng ml-1, week +4; 422 +/- 18 ng ml-1, mean +/- SEM; p = 0.03). Insulin-like growth factor binding protein-3 concentrations (n = 6) increased in 5 subjects (week -1; 4.5 +/- 0.3 micrograms ml-1, week +4; 5.1 +/- 0.4 micrograms ml-1) and mean overnight growth hormone decreased (week -1; 14.0 +/- 3.1 mUI-1, week +4; 7.6 +/- 1.7 mUI-1) during the period of study but these differences were not statistically significant. HbA1c levels fell significantly at the time of rhIGF-I administration (day 0; 10.4 +/- 1.9% vs week +4; 9.4 +/- 1.9%; p = 0.03) despite a reduction in subcutaneous isophane insulin dose from 0.50 +/- 0.02 U kg-1 to 0.41 +/- 0.02 U kg-1 (p = 0.03). There was no significant change in biochemical and haematological indices, glomerular filtration rate or urinary albumin excretion. The restoration of IGF-I levels in adolescents with Type 1 diabetes may have a beneficial impact on glycaemic control.

Insulin-like growth factors (IGFs) and IGF-binding proteins in human skin interstitial fluid

Despite extensive investigation of the insulin-like growth factor (IGF)/IGF-binding protein (IGFBP) system in the circulation and body fluids, there is no information on this in interstitial fluid. We have compared the IGF/IGFBP system in the circulation with that in fluid obtained from blisters artificially raised by negative pressure in 10 healthy volunteers. IGFBP-1, -2, -3, and -4 were all found in blister fluid, but in concentrations much lower than those in matched serum. The IGF-I, IGF-II, and IGFBP-3 levels measured by RIA were 18%, 14%, and 16% of those in serum, respectively. Fast protein liquid chromoatography showed that both IGF-I and IGFBP-3 in 150- and 50-kilodalton complexes were approximately 13% and 37%, respectively, of the corresponding peaks found in matched serum. Compared to that in serum, the IGFBP-3 in the blister fluid was predominantly in a modified 29-kilodalton form, and there was increased activity of an IGFBP-3 protease. Therefore, although IGF concentrations are much lower in interstitial fluid than in the circulation, a greater proportion of this IGF is in forms more readily available for interaction with tissue receptors. The blister fluid appears to represent physiological interstitial fluid and may provide a model for studying the physiology and pathophysiology of growth factors in the interstitial environment.

Choice of treatment affects plasma levels of insulin-like growth factor-binding protein-1 in noninsulin-dependent diabetes mellitus

Insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) modulates the metabolic and mitogenic effects of IGFs. Although IGFBP-1 levels are abnormally high in insulin-dependent diabetes (IDDM), relatively little is known in NIDDM; conflicting data have suggested both high and low levels. We investigated whether treatment modifies IGFBP-1 levels in two groups of NIDDM patients. Study 1 examined fasting concentrations in groups of patients with NIDDM, comparable except for treatment type (sulfonylurea, n = 23; once daily insulin, n = 15; sulfonylurea plus once daily insulin, n = 14; multiple insulin injections, n = 9) and 25 nondiabetic subjects. In sulfonylurea-treated patients there were markedly reduced plasma IGFBP-1 concentrations (median, interquartile range in parentheses): control, 61.0 (36-96) micrograms/L; sulfonylureas alone, 31.5 (21-61) micrograms/L (P < 0.01); and sulfonylureas plus insulin, 31.5 (9-53) micrograms/L (P < 0.01). Once daily insulin was associated with values similar to those in the control group [62.0 (27-103) micrograms/L; P = NS], whereas IGFBP-1 levels were higher with multiple insulin injection therapy [156.0 (71-184) micrograms/L; P < 0.05]. Proinsulin levels were higher in sulfonylurea-treated patients, but there was no significant correlation between IGFBP-1 and proinsulin within any individual group. Study 2 examined the effects of treatment on the dynamics of IGFBP-1 levels between 0800-1900 h. In control subjects (n = 8), levels fell from 0800 h (mean +/- SEM, 22.4 +/- 5.2 micrograms/L) to 1000 h (14 +/- 5.2 micrograms/L), followed by a rise, more rapid after food, to a peak at 1240 h (20.6 +/- 3.7 micrograms/L). Levels then declined until 1500 h (10.7 +/- 2.9 micrograms/L), with a further postprandial peak at 1840 h (23.1 +/- 3.2 micrograms/L). Sulfonylurea therapy (n = 6) resulted in a complete loss of this pattern, with a marked fall in IGFBP-1 from 0800 h (22 +/- 2.7 micrograms/L) to less than 7 micrograms/L for the remainder of the study (area under the curve, 1150-1400 h, P < 0.001 vs. control). By contrast, in metformin-treated patients (n = 7), neither IGFBP-1 levels nor postprandial peaks were significantly different from those in the control group. Our findings suggest that in patients with NIDDM, the regulation of IGFBP-1 is markedly influenced by the choice of treatment.

Tissue IGFBP-3 proteolysis: contrasting pathophysiology to that in the circulation

Endogenous IGFBP-3 has been examined in the circulation and in four different extravascular fluids in normal healthy adults and in patients with psoriasis or arthritis. In all of these cases there was no apparent increase of IGFBP-3 protease activity in the circulation. In contrast, endogenous IGFBP-3 from normal skin interstititial fluid and synovial fluid from healthy adults was found to be predominantly in the 29 kDa proteolytically modified form. This indicated that in these extravascular fluids in normal healthy adults a protease was active which was similar, if not identical, to that found in the circulation in pregnancy and other conditions. This was confirmed by the fragmentation of recombinant IGFBP-3 when incubated with these fluids. When the skin interstitial fluid or synovial fluid were taken from abnormal tissues (psoriasis in the former and osteoarthritis or rheumatoid arthritis in the latter) there was a considerable reduction in the amount of endogenous IGFBP-3 in the 'clipped' form and a reduction in the protease activity. In psoriatic lesions, this reduction in IGFBP-3 protease activity was shown to be due to the presence of an inhibitor in the interstitial fluid but not in the circulation. In both peritoneal and follicular fluid, the ratio of intact to fragmented IGFBP-3 appeared to relate to the oestrogen status. In peritoneal fluid there was a decrease in intact IGFBP-3 during the late proliferative/early secretory phase of the endometrial cycle. In the ovary there was an increase in the amount of fragmented IGFBP-3 in the follicular fluid from the dominant follicle in comparison with atretic follicles from the same ovary. There is normally little proteo-lysis of IGFBP-3 in the circulation but this increases in many conditions where there is increased metabolic activity. The same enzyme(s) appear to be active in many extravascular fluids but under very different regulation. The activity in these extravascular fluids is normally high but can be decreased with local tissue inflammation; this decrease appears to be mediated by the induction of a local inhibitor.

Changes in circulating insulin-like growth factor-binding protein-1 (IGFBP-1) during prolonged exercise: effect of carbohydrate feeding

Plasma levels of glucose, insulin, the insulin-like growth factor (IGF-I and -II) and IGFBP-1 were determined in four young healthy males performing cycle exercise to fatigue while being fed either placebo (trial C) or glucose polymer solution (trial G). There was a significant decline in glucose and insulin from rest to fatigue in C (P < 0.01 and P < 0.05, respectively), but not in G. IGF-I or IGF-II levels did not change significantly in either of the trials. IGFBP-1 levels increased 12-fold in C (11.4 +/- 1.6 ng/ml at rest to 136.5 +/- 19.7 ng/ml at fatigue P < 0.01), and 5.6-fold in G (11.0 +/- 2.3 ng/ml to 62.2 +/- 15 ng/ml, P < 0.05). In C a significant negative correlation was found between IGFBP-1 and glucose (r = 0.69, P < 0.01) and IGFBP-1 and insulin (r = -0.612, P < 0.05) in C, but not in G. These results suggest that during prolonged exercise factors other than insulin or glucose may regulate IGFBP-1 and that IGFBP-1 may serve a role other than to prevent the hypoglycaemic action of the IGFs.

Loss of the normal relationships between growth hormone, growth hormone-binding protein and insulin-like growth factor-I in adolescents with insulin-dependent diabetes mellitus

OBJECTIVE

It has been proposed that the dissociation between growth hormone secretion and insulin-like growth factor-I (IGF-I) concentrations in insulin-dependent diabetes mellitus arises because of partial resistance at the GH receptor. In order to explore this hypothesis further we have examined the relations between IGF-I, GH-binding protein (GHBP), and GH secretion in normal subjects and patients with diabetes during puberty.

DESIGN AND SUBJECTS

Blood samples for the estimation of IGF-I and GHBP levels were obtained from 104 patients with diabetes and 89 puberty matched controls. Thirty-four of the controls and 42 of the patients with diabetes also underwent an overnight GH secretory profile with measurements of GH every 15-20 minutes between 2000 and 0800 h.

RESULTS

In multivariate analysis using sex, puberty stage, and presence or absence of diabetes as dependent variables, diabetes was associated with increased GH levels (F = 23.04, P < 0.001), reduced IGF-I (F = 10.89, P < 0.001), and reduced GHBP levels (F = 31.36, P < 0.001). A negative relation between GH and GHBP levels (r = -0.44, P < 0.01) was found in normal subjects but this was absent in those with diabetes. Both GHBP and IGF-I levels in the diabetic subjects were correlated with total insulin dose (r = 0.4, P < 0.001, and r = 0.46, P < 0.001, respectively). Yet there was no direct correlation between GHBP and IGF-I concentrations. The variation in IGF-I levels was also related to glycosylated haemoglobin levels in the diabetics (r = -0.27, P = 0.01). In a stepwise multiple regression analysis insulin dose contributed 23%, HbA1 4.4% and C-peptide levels 3.7% to the variation in IGF-I levels.

CONCLUSIONS

In adolescents with insulin dependent diabetes mellitus, the elevated GH concentrations are associated with low circulating IGF-I and GHBP concentrations and the normal reciprocal relation between GHBP and GH is no longer evident. Although IGF-I and GHBP are both related to insulin dose, there is no direct correlation between these variables. This may indicate that GHBP reflects GH receptor numbers but not necessarily post receptor events, and the weak positive correlation between GH and IGF-I indicates that increased growth hormone secretion may compensate for reduced receptor numbers.

Insulin-like growth factor binding protein 1 response to acute insulin induced hypoglycaemia in type 1 diabetes

OBJECTIVES

Insulin is believed to be the prime regulator of insulin-like growth factor binding protein 1 (IGFBP-1) secretion, and in normal subjects acute insulin induced hypoglycaemia exerts a rapid effect on concentrations of IGFBP-1, and may also influence insulin-like growth factor I (IGF-I) concentrations. The rise in IGFBP-1 concentrations in normal subjects following hypoglycaemia has been suggested to be due to suppression of endogenous insulin secretion. We have examined this further by studying diabetics with no endogenous insulin secretion.

DESIGN

We have compared the IGFBP-1 response to acute insulin induced hypoglycaemia in normal subjects and patients with Type 1 (insulin dependent) diabetes mellitus.

METHODS

Insulin tolerance tests were performed using a bolus of insulin (0.15 U/kg), in six control subjects and six patients with Type 1 diabetes.

MEASUREMENTS

Serum levels of IGFBP-1, insulin, glucose, and IGF-I were measured at regular intervals during the insulin tolerance test.

RESULTS

Blood glucose fell to a nadir which coincided with the onset of the acute autonomic reaction 'R' in both groups. The basal concentration of IGF-I was significantly lower in the diabetic group at 0.4 +/- 0.1 kU/l, compared to 0.9 +/- 0.1 kU/l in the control group, but there was no significant change in IGF-I concentrations in response to hypoglycaemia in either group. Hypoglycaemia provoked a fall in IGFBP-1 in patients with Type 1 diabetes, from 38 +/- 9 micrograms/l basally to 17 +/- 3 micrograms/l at R + 120 minutes, with a return to basal values of 45 +/- 11 micrograms/l at R + 180 minutes. In the control subjects there was no fall in IGFBP-1, but a significant increase to 71 +/- 14 micrograms/l at R + 180 minutes.

CONCLUSION

This difference in the IGFBP-1 response in the presence of a similar glucose response suggests that in Type 1 diabetes there may be different sensitivities to the actions of exogenous insulin on IGFBP-1 regulation.

The effects of recombinant human insulin-like growth factor-I (IGF-I) administration on the levels of IGF-I, IGF-II and IGF-binding proteins in adolescents with insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) during puberty is associated with a reduction in circulating concentrations of insulin-like growth factor-I (IGF-I) and low IGF bioactivity. Altered levels of the IGF-binding proteins (IGFBPs), including low IGFBP-3 and elevated IGFBP-1, have also been described. These abnormalities have been linked to poor growth and deteriorating blood glucose control. We have therefore examined the effects of recombinant human IGF-I (rhIGF-I) administration on the levels of IGF-I, IGF-II, IGFBP-1, IGFBP-3 and IGF bioactivity in a group of 9 late-pubertal adolescents with IDDM. This was a double-blind placebo controlled study with each individual admitted on two occasions when either rhIGF-I (40 micrograms/kg) or placebo was administered by subcutaneous injection in the thigh at 1800 h. Blood samples were then taken for the subsequent 22 h. The half-life of administered rhIGF-I (12.1-22.2 h) was similar to that previously described in normal subjects. There was a small increase in IGFBP-3 concentrations overnight following rhIGF-I administration when compared to placebo, whereas the levels of IGF-II decreased. Under strict euglycaemic conditions, the relationship between insulin and IGFBP-I did not appear to be affected by rhIGF-I administration although the levels of IGFBP-1 tended to be higher overnight. IGF bioactivity was low during the placebo study, and although within the normal adult range following administration of IGF-I, was still relatively low for adolescents in late puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Menstrual irregularities are more common in adolescents with type 1 diabetes: association with poor glycaemic control and weight gain

Ovarian function in post-menarchal girls with Type 1 diabetes was evaluated. Menstrual histories from 24 adolescents with Type 1 diabetes were compared with those from 24 age and sex matched controls. A fasting blood sample was obtained from subjects with Type 1 diabetes for the measurement of ovarian and adrenal sex hormones, LH and FSH, glucose and insulin, insulin-like growth factor-I (IGF-I), and insulin-like growth factor binding protein-1 (IGFBP-1); and an ovarian ultrasound scan was performed. Menstrual irregularity was more prevalent in patients with Type 1 diabetes than controls (54% vs 21%, p < 0.01) and their mean body mass index (BMI) was greater (22.3 +/- 0.5 (+/- SEM) vs 20.7 +/- 0.6 kg m-2, p < 0.05). Subjects with Type 1 diabetes with irregular menses (when compared with diabetic subjects with a regular cycle) had a significantly higher HbA1 (12.8 +/- 0.4 vs 10.5 +/- 0.5%, p < 0.01) and BMI (23.2 +/- 0.6 vs 21.4 +/- 0.6 kg m-2, p < 0.05) associated with a lower sex hormone binding globulin (SHBG) (37.2 +/- 4.0 vs 52.6 +/- 4.0 nmol l-1, p < 0.025) and IGF-I (1.4 +/- 0.2 vs 2.2 +/- 0.2 mUI-1, p < 0.025) and a higher LH:FSH ratio (2.6 +/- 0.5 vs 1.4 +/- 0.2, p < 0.05). Polycystic ovarian changes were identified in 10/13 (77%) of these patients with an irregular cycle. Menstrual irregularity is common in post-menarchal girls with Type 1 diabetes and is associated with poor glycaemic control and weight gain. The apparent high incidence of polycystic ovarian change requires further investigation.

Insulin preincubation enhances insulin-like growth factor-II (IGF-II) action on steroidogenesis in human granulosa cells

Although abundant mRNA for IGF-II has been detected in the human ovary, a role for IGF-II in steroidogenesis has not yet been established. In rat adipocytes, incubation with insulin greatly increases cell-surface IGF-II receptor (5-fold) and the receptor is rapidly internalised in the absence of insulin. We have therefore investigated the effects of insulin preincubation on the response of granulosa cells from unstimulated ovaries to a range of doses of IGF-II. In the absence of insulin, IGF-II stimulated steroidogenesis in only one of three experiments. After incubation with 10 ng/ml insulin, there was a dose-dependent response to IGF-II in all experiments. Cells incubated with insulin produced 5-10 fold more estradiol in response to IGF-II than those incubated without. In contrast, insulin produced only a small increase of estradiol in response to IGF-I. These results demonstrate a synergistic interaction of insulin with IGF-II in human granulosa cells and suggest that there is an important role for IGF-II in human ovarian steroidogenesis.