Plasma levels of total and active ghrelin in acromegaly and growth hormone deficiency

Ghrelin is an endogenous growth hormone (GH) secretagogue recently isolated from the stomach. Although it possesses a strong GH releasing activity in vitro and in vivo, its physiological significance in endogenous GH secretion remains unclear. The aim of this study was to characterize plasma ghrelin levels in acromegaly and growth hormone deficiency (GHD). We investigated plasma total and active ghrelin in 21 patients with acromegaly, 9 patients with GHD and 24 age-, sex- and BMI-matched controls. In all subjects, we further assessed the concentrations of leptin, soluble leptin receptor, insulin, IGF-I, free IGF-I and IGFBP-1, 2, 3 and 6. Patients with acromegaly and GHD as well as control subjects showed similar levels of total ghrelin (controls 2.004+/-0.18 ng/ml, acromegalics 1.755+/-0.16 ng/ml, p=0.31, GHD patients 1.704+/-0.17 ng/ml, p=0.35) and active ghrelin (controls 0.057+/-0.01 ng/ml, acromegalics 0.047+/-0.01 ng/ml, p=0.29, GHD patients 0.062+/-0.01 ng/ml, p=0.73). In acromegalic patients plasma total ghrelin values correlated negatively with IGF-I (p<0.05), in GHD patients active ghrelin correlated with IGF-I positively (p<0.05). In the control group, total ghrelin correlated positively with IGFBP-2 (p<0.05) and negatively with active ghrelin (p=0.05), BMI (p<0.05), WHR (p<0.05), insulin (p=0.01) and IGF-I (p=0.05). Plasma active ghrelin correlated positively with IGFBP-3 (p=0.005) but negatively with total ghrelin and free IGF-I (p=0.01). In conclusion, all groups of the tested subjects showed similar plasma levels of total and active ghrelin. In acromegaly and growth hormone deficiency plasma ghrelin does not seem to be significantly affected by changes in GH secretion.     

Insulin-like growth factors and insulin-like growth factor binding proteins in adult patients with severe liver disease before and after orthotopic liver transplantation

INTRODUCTION: The liver is the main source of serum insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) and the concentration of these proteins might reflect liver function. METHODS: In a retrospective longitudinal study we examined serum levels of total and free IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-6 in 21 adult patients with end-stage liver disease before and after orthotopic liver transplantation (LTX) by sensitive and specific RIAs. In each patient, the mean value of at least three measurements before and after LTX was calculated. RESULTS: Before LTX, serum levels of total and free IGF-I, IGF-II, IGFBP-3 were low and showed a rapid and significant increase in almost all patients after successful LTX (total IGF-I: 30 +/- 7 vs. 256 +/- 30 ng/ml, p < 0.001; free IGF-I: 1.3 +/- 0.3 vs. 3.5 +/- 0.6 ng/ml, p < 0.01; IGF-II: 177 +/- 28 vs. 618 +/- 30 ng/ml, p < 0.001; IGFBP-3: 1,230 +/- 136 vs. 3,665 +/- 264 ng/ml, p < 0.001). In contrast, IGFBP-1 was found to be high immediately before LTX, and declined to normal levels after LTX (210 +/- 40 vs. 90 +/- 15 ng/ml, p < 0.01), while IGFBP-2 did not show any significant changes (1,154 +/- 296 vs. 1,303 +/- 192 ng/ ml). Positive correlations were found between IGF-I, IGF-II or IGFBP-3, and serum pseudocholinesterase (R = 0.50, 0.72 and 0.61 respectively, p < 0.001). Negative correlations were found between IGF-I, IGF-II or IGFBP-3, and prothrombin time (R = 0.50, 0.59 and 0.51 respectively, p < 0.001). CONCLUSION: Patients with severe liver disease show decreased levels of total and free IGF-I, IGF-II and IGFBP-3, and increased levels of IGFBP-1. These abnormalities are promptly normalized after successful LTX. Thus, serum levels of IGF-I, IGF-II and IGFBP-3 might be useful parameters for the assessment of liver function.     

Hyperlipidemia is associated with altered levels of insulin-like growth factor-I

Previous studies revealed altered levels of the circulating insulin-like growth factor-I (IGF-I) and of its binding protein-3 (IGFBP-3) in subjects with coronary atherosclerosis, metabolic syndrome and premature atherosclerosis. Hyperlipidemia is a powerful risk factor of atherosclerosis. We expected IGF-I and IGFBP-3 alterations in subjects with moderate/severe hyperlipidemia but without any clinical manifestation of atherosclerosis. Total IGF-I and IGFBP-3 were assessed in 56 patients with mixed hyperlipidemia (MHL; cholesterol >6.0 mmol/l, triglycerides >2.0 mmol/l), in 33 patients with isolated hypercholesterolemia (IHC; cholesterol >6.0 mmol/l, triglycerides <2.0 mmol/l), and in 29 healthy controls (cholesterol<6.0 mmol/l, triglycerides<2.0 mmol/l). The molar ratio of IGF-I/IGFBP-3 was used as a measure of free IGF-I. IHC subjects differed from controls by lower total IGF-I (164+/-60 vs. 209+/-73 ng/ml, p=0.01) and IGF-I /IGFBP-3 ratio (0.14+/-0.05 vs. 0.17+/-0.04, p=0.04). Compared to controls, MHL subjects had lower total IGF-I (153+/-54 ng/ml, p=0.0002) and IGFBP-3 (2.8+/-0.6 mg/ml, p<0.0001), but higher IGF-I/IGFBP-3 ratio (0.25+/-0.06, p<0.0001). Differences remained significant after the adjustment for clinical and biochemical covariates, except for triglycerides. Patients with both IHC and MHL have lower total IGF-I compared to controls. The mechanism is presumably different in IHC and MHL. Because of prominent reduction of IGFBP-3 in patients with MHL, they have reduced total IGF-I despite the actual elevation IGF-I/IGFBP-3 ratio as a surrogate of free IGF-I.     

Are plasma insulin-like growth factor I (IGF-I) and IGF-binding protein 3 (IGFBP-3) useful markers of prostate cancer?

Increased concentrations of insulin-like growth factor I (IGF-I) and decreased insulin-like growth factor binding protein 3 (IGFBP-3) in serum have been proposed as markers of prostate cancer (CaP). The evidence for this, however, is contradictory. We assayed serum for IGF-I, IGFBP-3 and prostate-specific antigen (PSA) in patients with CaP and benign prostatic hyperplasia (BPH) and in healthy controls (HC). The mean +/- SD concentration of IGF-I in CaP (98.3 +/- 39.3 ng/mL; n = 15) was lower than in BPH (119 +/- 31.1 ng/mL; n=24) and HC (119 +/- 36.1 ng/mL; n=46), but the differences between the three groups were not statistically significant (p > 0.05). The mean IGFBP-3 concentrations in CaP (2691 +/- 1105 ng/mL; n = 16; p = 0.029) and BPH (2618 +/- 816 ng/mL; n = 26; p = 0.006) patients were significantly lower than that of the HC (3119 +/- 618 ng/mL; n=59), but the difference between the two groups of patients was not significant (p > 0.05). PSA concentrations in CaP (median = 80.8 ng/mL; n = 25) were significantly higher than those in BPH (median = 8.6 ng/mL; n = 39) (p < 0.001). Ninety-six percent of CaP and 72% of BPH patients had PSA concentrations >4.0 ng/mL; the proportions of patients with concentrations exceeding 20 ng/mL were 76% and 10%, respectively. We conclude that IGF-I and IGFBP-3 are inferior to PSA for CaP detection.     

Overnight responses of the circulating IGF-I system after acute, heavy-resistance exercise.

This study evaluated the individual components of the insulin-like growth factor I (IGF-I) system [i.e., total and free IGF-I, insulin-like growth factor binding protein (IGFBP)-2 and -3, and the acid-labile subunit (ALS)] in 10 young, healthy men (age: 22 +/- 1 yr, height: 177 +/- 2 cm, weight: 79 +/- 3 kg, body fat: 11 +/- 1%) overnight for 13 h after two conditions: a resting control (Con) and an acute, heavy-resistance exercise protocol (Ex). The Ex was a high-volume, multiset exercise protocol that alternated between 10- and 5-repetition maximum sets with 90-s rest periods between sets. The Ex was performed from 1500 to 1700; blood was obtained immediately postexercise and sampled throughout the night (every 10 min for the first hour and every hour thereafter) until 0600 the next morning. For the first hour, significant differences (P < or = 0.05) were only observed for IGFBP-3 (Ex: 3,801 > Con: 3,531 ng/ml). For the overnight responses, no differences were observed for total or free IGF-I or IGFBP-3, whereas IGFBP-2 increased (Ex: 561 > Con: 500 ng/ml) and ALS decreased (Ex: 35 < Con: 39 microg/ml) after exercise. The results from this study suggest that the impact that resistance exercise exerts on the circulating IGF-I system is not in the alteration of the amount of IGF-I but rather of the manner in which IGF-I is partitioned among its family of binding proteins. Thus acute, heavy-resistance exercise can lead to alterations in the IGF-I system that can be detected in the systemic circulation.     

17beta-estradiol regulation of human growth hormone (hGH), insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) axis in hypoestrogenic, hypergonadotropic women

OBJECTIVE: Ovarian hormonal function may be as important contributing factor to hGH-IGF-I-IGFBP-3 axis as age. AIM: To examine plasma hGH, IGF-1 and IGFBP-3 levels in women with premature ovarian failure compared to healthy normal controls and postmenopausal ones. PATIENTS: Group A-15 women with premature ovarian failure (POF) (mean: age 38.9+/-5.2 years, FSH 101.4+/-29.0 IU/l; 17beta-estradiol 22.5+/-14.6 ng/l). Group B consisted of 15 menopausal women (mean: age 54.7+/-2.7 years; FSH 81.9+/-32.1 IU/l; 17beta-estradiol 17.1+/- 8.0 ng/l). Group C - controls - 15 normally menstruating women (mean: age 37.1+/-9.0 years; FSH 6.2+/-1.0 IU/l; 17beta-estradiol 144.8+/-117.1 ng/l). METHODS: Body mass and BMI were measured. Basic fasting plasma hGH, IGF-I, IGFBP-3, insulin, testosterone and LH as well as prolactin (PRL), FSH and estradiol were assessed by RIA kits. Statistical analysis. Shapiro-Wilk test, Mann-Whitney u-test, Spearman rang correlation coefficient, stepwise multiple regression. RESULTS: Mean serum IGF-I level was the lowest (p<0.005) in group B (172.0+/-54.6 microg/l) and the highest in group C (273.6+/-109.0 microg/l). The mean plasma IGF-I level in group A was similar (NS) (208.3+/-66.5 microg/l) to that found in group B and lower (p<0.02) compared with that in group C. The lowest (p<0.005) serum IGFBP-3 level was found in group B (3.1+/-0.7 microg/l) compared to group C (4.4+/-0.3 microg/l). The mean plasma IGFBP-3 level (3.1+/-1.0 microg/l) in group A was lower than in group C (p<0.005) but identical as in group B. No statistically significant differences between groups were observed in mean hGH levels. Women in group A and C were younger (p<0.001) than those in group B. The lowest mean estradiol level was found in groups A and B. The highest was in group C (p<0.001). Mean plasma LH and FSH levels were higher (p<0.001) in groups A and B vs group C. In group C there were links between IGF-I and age (r=-0.60; p=0.014) The IGF-I/age relation disappeared in the groups A and B (rA=-0.26; rB=0.10; NS). The same regards IGFBP-3/ age link (rA=-0.44, NS; rB=0,31;NS). Estradiol level was related to hGH levels in group C (r=-0.54; p<0.05). In none of groups hGH/IGF-1 as well as IGFBP-3/hGH relations were found. Prolactin accounted for 69% of the variance in IGF-I level in the group B (p=0.003) and for 24% in group A (NS). Testosterone accounted for 88% (p=0.004) of the variance in IGF-I level in group B and IGFBP-3 was responsible for 86% (p=0.038) of the variance in IGF-I level in group C. Again IGFBP-3 was responsible for 47% (p=0.023) in group A and for 49% (p=0.04) in group B of the hGH variance. CONCLUSIONS: 17b-estradiol may be as important contributor to insulin-like growth factor-I (IGF-I) plasma level as age in hypoestrogenic, hypogonadotropic women.     

Energy flux, more so than energy balance, protein intake, or fitness level, influences insulin-like growth factor-I system responses during 7 days of increased physical activity.

The purpose of this study was to determine the impact of dietary factors and exercise-associated factors on the response of IGF-I and its binding proteins (IGFBPs) during a period of increased physical activity. Twenty-nine men completed a 4-day (days 1-4) baseline period of a controlled energy balanced diet while maintaining their normal physical activity level followed by 7 days (days 5-11) of a 1,000 kcal/day increase in physical activity above their normal activity levels. Two subject groups, one sedentary (Sed, mean Vo(2peak): 39 mlxkg(-1)xmin(-1), n = 7) and one fit (FIT1, mean Vo(2peak): 56 ml.kg(-1)xmin(-1), n = 8) increased energy intake to maintain energy balance throughout the 7-day intervention. In two other fit subject groups (FIT2, n = 7 and FIT3, n = 7), energy intake remained at baseline resulting in a 1,000 kcal/day exercise-induced energy deficit. Of these, FIT2 received an adequate protein diet (0.9 g/kg), and FIT3 received a high-protein diet (1.8 g/kg). For all four groups, IGF-I, IGFBP-3, and the acid labile subunit (ALS) were significantly decreased by day 11 (27 +/- 4%, 10 +/- 2%, and 19 +/- 4%, respectively) and IGFBP-2 significantly increased by 49 +/- 21% following day 3. IGFBP-1 significantly increased only in the two negative energy balance groups, FIT2 (38 +/- 6%) and FIT3 (46 +/- 8%). Differences in initial fitness level and dietary protein intake did not alter the IGF-I system response to an acute increase in physical activity. Decreases in IGF-I were observed during a moderate increase in physical activity despite maintaining energy balance, suggesting that currently unexplained exercise-associated mechanisms, such as increased energy flux, regulate IGF-I independent of energy deficit.     

Zinc supplementation increases the level of serum insulin-like growth factor-I but does not promote growth in infants with nonorganic failure to thrive

We investigated in a randomized double-blind placebo-controlled study the effects of zinc supplementation (2 mg/kg/day) for 12 weeks on growth, serum insulin-like growth factor-I (IGF-I) and insulin-like factor binding protein-3 (IGFBP-3) on 3- to 9-month-old infants with nonorganic failure to thrive (NOFTT). 25 infants completed the study, 14 received zinc supplementation (group A), and 11 received placebo (group B). The control group for baseline measurements was composed of 10 age-matched normal growing infants. There were no significant changes in weight for age, length for age, or weight for length during the entire study period in either group A or B. Serum IGF-I levels at baseline were similar in all the groups. After 12 weeks of therapy, serum IFG-I levels increased significantly only in the zinc-supplemented group, from 40.3 +/- 7 ng/ml at baseline to 65 +/- 8 ng/ml (p < 0.05). There was a marked difference in serum IGF-I levels between the zinc-supplemented group and the placebo group after 12 weeks: 65 +/- 8 vs. 49.4 +/- 5 ng/ml (p = 0.058, 95% CI of difference 9.88-21.31). No change was demonstrated in serum IGFBP-3 levels in either study group. We conclude that although zinc supplementation increased serum IGF-I levels, it did not improve the growth parameters of infants with NOFTT.     

IGF-I, IGFBP-2 and -3 but not GH concentrations are different in normal and poor growing piglets.

In this study we investigated the somatotropic axis in piglets with evident growth delay. Female Suffolk crossbred piglets (30 days old; N = 12) were divided into normal weight (10 +/- 0.9 kg) and poor growing subjects (7 +/- 0.5 kg) and bled for growth hormone (GH), Insulin-like growth factor-I (IGF-I), Insulin-like growth factor binding protein 2 and 3 (IGFBP-2 and -3) determination. Basal and induced-GH levels were not different in the groups. Plasma IGF-I concentrations were significantly different (p < 0.001): 101.8 +/- 9.8 ng x mL(-1) (normal weight group) and 39.5 +/- 4.0 ng x mL(-1) (poor growing group). IGFBP-2 and -3 concentrations were significantly (p < 0.001) lower in poor growing than in normal piglets. Piglet weight was positively correlated (r = 0.98, p < 0.001) with IGF-I and IGFBP-2 or -3 concentrations. Our data indicate that growth rate was not correlated to basal or secretagogue-induced GH secretion.     

Systemic levels contribute significantly to increased intraocular IGF-I, IGF-II and IGF-BP3 [correction of IFG-BP3] in proliferative diabetic retinopathy.

Increased intraocular levels of angiogenic growth factors such as insulin-like growth factor I (IGF-I) have been demonstrated in proliferative diabetic retinopathy (PDR). It is unclear whether increased leakage of the blood retina barrier or local synthesis primarily determine intraocular levels of IGFs in man, which is of special interest regarding possible therapeutic options with somatostatin analogues in PDR. This is the first study investigating parallelly serum and vitreous levels of IGF-I/II, IGF-BP3 and the liver-derived permeability marker albumin to determine in vivo the amount of circulation-derived intraocular IGFs. A control group without retinal proliferation and patients with PDR were compared. Levels of IGF-I/II, IGF-BP3 and albumin were determined by immunological methods. Vitreous levels of albumin were 2.2-fold elevated in patients with PDR (254.1 +/- 37.2mg/dl; n = 27; p = 0.0027) compared to controls (115.7 +/- 36.2mg/dl; n =10), whereas serum levels were slightly decreased in diabetes patients (5049 +/- 196 mg/dl vs. 4330 +/- 186 mg/dl; p = 0.0283). This was comparable to an increase of IGF-I/11 and IGF-BP3 in vitreous from PDR patients (IGF-I: 2.3 +/- 1.1 ng/ml p = 0.005. IGF-II: 37.9 +/- 4.9 ng/ml; p = 0.0003. IGF-BP3: 97.9 +/- 26.9 ng/ml; p = 0.0001; n = 34) compared to controls (IGF-I: 0.7 +/- 0.1 ng/ml. IGF-II: 21.3 +/- 4.2 ng/ml. IGF-BP3: 31.3 +/- 4.9 ng/ml: n = 19). Serum levels did not differ significantly among the groups regarding IGF-I, II and IGF-BP3. Intraocular albumin and IGF-I levels calculated as percentage of the respective serum levels correlated significantly (r = 0.42; p = 0.012). This study demonstrates that influx of IGF-I, II and IGF-BP3 in PDR quantitatively parallels influx of the liver derived serum protein albumin suggesting that leakage of the blood retina barrier and serum levels of IGF primarily determine intravitreal IGF levels rather than local synthesis. Suppression of systemic IGF levels by new, highly effective somatostatin-analogues therefore provides a promising approach to prevent PDR.     

Effect of single wrist exercise on fibroblast growth factor-2, insulin-like growth factor, and growth hormone

Anabolic effects of exercise are mediated, in part, by fibroblast growth factor-2 (FGF-2), insulin-like growth factor-I (IGF-I), and growth hormone (GH). To identify local vs. systemic modification of these mediators, 10 male subjects performed 10 min of unilateral wrist-flexion exercise. Blood was sampled from catheters placed in basilic veins of both arms. Lactate was significantly increased only in the exercising arm. FGF-2 decreased dramatically (P < 0.01) in both the resting (from 1.49 +/- 0.32 to nadir at 0.11 +/- 0.11 pg/ml) and exercising arm (1.80 +/- 0.60 to 0.29 +/- 0.14 pg/ml). Small but significant increases were found in both the resting and exercising arm for IGF-I and IGF binding protein-3 (IGFBP-3). GH was elevated in blood sampled from both the resting (from 1.04 +/- 0.68 to a peak of 2.57 +/- 0.53 ng/ml) and exercising arm (1.04 +/- 0.66 to 2.43 +/- 0.42 ng/ml, P < 0.05). Unilateral wrist exercise was not sufficiently intense to increase circulating lactate or heart rate, but it led to systemic changes in GH, IGF-I, IGFBP-3, and FGF-2. Low-intensity exercise involving small muscle groups can influence the circulating levels of growth factors.     

IGF-I- and IGFBP-3-expression in cultured human preadipocytes and adipocytes.

The expression and secretion of IGF-I and IGFBP-3 were investigated in cultured human preadipocytes and in in vitro differentiated adipocytes derived from human subcutaneous adipose tissue under chemically defined culture conditions. Human preadipocytes expressed mRNAs for IGF-I and IGFBP-3 and secreted the corresponding proteins into the culture medium as measured by sensitive radioimmunoassays. In human adipocytes; specific mRNA-expression was comparable to that found in preadipocytes, but IGF-I secretion was increased 10-fold (3.87 +/- 0.69 vs. 0.41 +/- 0.11 ng/ml/10(6) cells/48 hrs, p < 0.05) and IGFBP-3 secretion 2.5-fold (7.34+/-1.15 vs. 3.27+/-0.38 ng/ml/10(6) cells/48 hrs, p<0.05) in the presence of adipogenic medium probably resulting in an increase of unbound IGF-I. Under serum-free, chemically defined conditions human growth hormone (hGH) and insulin were found to be positive regulators and cortisol was found to be a negative regulator of IGF-I and IGFBP-3 secretion in preadipocytes. In cultured human adipocytes, hGH showed no effect on IGF-I and IGFBP-3 secretion, whereas insulin stimulated and cortisol inhibited the secretion of both proteins. We conclude that IGF-I and IGFBP-3 may not only exert their actions in human adipose tissue via circulation, but also in an auto/paracrine way.     

Influence of energy deficiency on the insulin-like growth factor I axis in a military training program.

The aim of this study was to determine wether continuous heavy physical activities as well as lack of food and sleep during military training (three weeks of conditioning followed by a five-day combat course) alter serum concentrations of IGF-I and/or its binding proteins, evaluating the relationship to metabolic changes. Before and after training, we measured serum levels of both total and free IGF-I, IGFBP-1 and IGFBP-3 as well as plasma levels of branched-chain amino acids (valine, leucine and isoleucine) and glucose from 26 cadets (21 +/- 2 yr). Total and free IGF-I levels were decreased after training from 228 +/- 12 to 160 +/- 7 ng/ml and from 0.80 +/- 0.08 to 0.52 +/- 0.06 ng/ml, p < 0.001 respectively) as well as IGFBP-3 (p < 0.001), while IGFBP-1 levels were increased (p < 0.001). BCAA levels were decreased from 245.4 +/- 7.5 to 215.9 +/- 5.1 micromol/l, p < 0.001, while those of glucose remained unchanged. There were correlations between changes in total IGF-I and IGFBP-3 (p < 0.05) and between free IGF-I and IGFBP-1 (p < 0.01). Several correlations appeared between changes in all the components of the IGF-I axis and branched-chain amino acids. We concluded that responses of the IGF-I system during an intense training could represent an adaptative response to the encountered energy deficiency, resulting a diversion of substrate from growth to acute metabolic needs.     

Insulin-like growth factors and binding proteins in early milk from mothers of preterm and term infants

Breast-fed preterm infants often show a better outcome, partly ascribed to the benefit of insulin-like growth factors (IGFs) and their binding proteins (IGFBP). We compared IGF-I, IGF-II, IGFBP-2 and IGFBP-3 levels, measured by radioimmunoassays in milk samples from 30 mothers of preterm (<31 weeks) and from 19 mothers of term (>37 weeks) infants at days 7 and 21 postpartum. Proteolysis of IGFBP-2 within mother's milk and digestion of (125)I-IGF-II and (125)I-IGFBP-2 by gastric juice from neonates were assessed by electrophoretic techniques. Mean concentrations did not differ between preterm and term milk: IGF-I (2.8 +/- 0.2 vs. 2.3 +/- 0.1 ng/ml), IGF-II (12.0 +/- 0.4 vs. 12.2 +/- 0.5 ng/ml), IGFBP-3 (100.0 +/- 5.1 vs. 80.0 +/- 5.8 ng/ml), but did so for IGFBP-2 (3,144 +/- 172 vs. 2,428 +/- 188 ng/ml, p < 0.02). Immunoblots revealed 42% (p < 0.05) more IGFBP-2 fragments of 14 and 25 kDa in preterm milk. Incubation with gastric juice caused cleavage of (125)I-IGFBP-2 and partial cleavage of (125)I-IGF-II. Mutual complexation protected IGF-II and IGFBP-2 from cleavage, suggesting that both are likely to arrive in the bowel in an intact form to exert promotive effects. The results provide further evidence that IGFBP-2 and IGF-II in breast milk are relevant factors for the early development of preterm infants.     

Insulin resistance (HOMA) in relation to plasma cortisol,IGF-I and IGFBP-3. A study in normal short-statured and GH-deficient children

OBJECTIVE: To investigate the possible contribution of plasma cortisol and growth hormone (GH) as reflected by insulin-like growth factor-I (IGF-I)/insulin-like growth factor-binding protein-3 (IGFBP-3) on insulin action in short-statured children. METHODS: In this study, insulin resistance (HOMA) was determined in 34 normal short-statured (age 9.4 +/- 3.5 years) and in 19 GH-deficient children (age 10.4 +/- 2.2 years). HOMA was examined in relation to fasting plasma cortisol, IGF-I, IGFBP-3 and in addition to birthweight and body mass index (BMI). RESULTS: Birthweight was not correlated to insulin resistance. In GH-deficient children, BMI was significantly augmented and was associated with HOMA (p < 0.02). In both groups of patients, fasting plasma cortisol was related to HOMA (normal: r = 0.295, p < 0.05, GH-deficient: r = 0.495, p < 0.02). Only in normal short-statured children IGF-I (r = 0.338, p < 0.03) and IGFBP-3 (r = 0.493, p < 0.002) were associated with insulin resistance. CONCLUSION: The results indicated that at a young age cortisol contributed to insulin resistance in short-statured children. In normal short-statured children HOMA was associated with IGF-I and IGFBP-3. Possibly GH, a known cause of insulin resistance, contributed to HOMA as IGF-I and IGFBP-3 do not mediate insulin resistance but reflect growth hormone secretion. The results in GH-deficient children supported this conclusion as in the absence of GH insulin resistance was not associated with IGF-I/IGFBP-3.     

Effects of sc administration of recombinant human insulin-like growth factor I (IGF-I) on normal human subjects

Recombinant human insulin-like growth factor I (IGF-I) was administered subcutaneously to each of 5 normal human subjects at doses of 0 mg/kg (control), 0.06 mg/kg, or 0.12 mg/kg successively at one week intervals. After 0.06 mg/kg or 0.12 mg/kg IGF-I injections, plasma IGF-I levels increased from 185 +/- 17 ng/ml (mean +/- SEM) to maximal levels of 396 +/- 21 ng/ml at 3 hours and from 169 +/- 14 ng/ml to 480 +/- 27 ng/ml at 4 hours, respectively. These two peak values were statistically different (p less than 0.05). After 0.06 mg/kg and 0.12 mg/kg IGF-I administration, blood glucose levels decreased from 85 +/- 2 mg/dl to minimal levels of 73 +/- 3 mg/dl at 3 hours and from 83 +/- 1 mg/dl to 50 +/- 4 mg/dl at 2 hours, respectively. These two minimal values were statistically different (p less than 0.001). Serum insulin and C-peptide levels were decreased in a dose dependent manner after IGF-I administration. There were no changes between blood urea nitrogen levels before and 4 hours after IGF-I administration. The urinary GH concentration decreased after 0.06 mg/kg IGF-I administration, but increased and maintained normal values after 0.12 mg/kg IGF-I administration.     

Differential regulation of insulin-like growth factor-(IGF) I and IGF-binding protein (IGFBP) secretion by human peripheral blood mononuclear cells

BACKGROUND: Recent studies have shown that immunocompetent cells synthesize and express growth hormone (GH), growth hormone receptors (GH-R), insulin-like growth factor I (IGF-I), IGF-I receptors (IGF-I-R) and different insulin-like growth factor binding proteins (IGFBPs). The aim of the current study was to evaluate the regulation of IGFBP and IGF-I secretion from immunocompetent cells by different mitogens. METHODS/RESULTS: We studied the in vitro secretion pattern of IGFBPs and IGF-I from human peripheral blood mononuclear cells (PBMC), derived from 10 normal adults and 8 GH-deficient patients with adult onset. In serum-free conditioned medium of unstimulated PBMC, derived from normal adults, Western ligand blotting (1D-WLB) revealed a 24-kD, a 34-kD and a 39/43-kD doublet band to be most prominent. According to their molecular weight and two-dimensional Western ligand blot analysis (2D-WLB), these bands are deglycosylated IGFBP-4, IGFBP-2 and IGFBP-3, respectively. When the cells were treated with the T-cell mitogen phytohemagglutinin (PHA) (10 microg/ml), a differential stimulation of IGFBPs was found with a 2.57 +/- 0.48-fold increase of IGFBP-4 (p < 0.01), a 1.55 +/- 0.13-fold increase of IGFBP-2 (p < 0.01), and a 1.35 +/- 0.19-fold increase of IGFBP-3 (n.s.). In contrast, treatment with the B-cell mitogen pokeweed mitogen (PWM) (10 microg/ml) caused only a modest 1.40 +/- 0.07-fold increase of IGFBP-4 (p < 0.01). Treatment with rhGH (100 ng/ml) or rhIGF-I (200 ng/ml) caused no significant induction of any specific band, respectively. In contrast to the secretion pattern of IGFBPs, IGF-I secretion of the PBMC was not stimulated by either PHA or PWM, but showed a significant increase after GH incubation (p < 0.01). A similar differentiated secretion pattern of IGFBPs and IGF-I was also observed in the conditioned medium of PBMC, derived from GH-deficient patients. CONCLUSION: In summary, at least three different IGFBPs are secreted by human PBMC. Secretion of IGFBPs by PBMC is differentially regulated by different lymphocyte mitogens. Secretion of IGFBPs by PBMC is independent of GH or IGF-I, whereas the secretion of IGF-I is stimulated by GH. PBMC derived from normal adults and GH-deficient patients show similar patterns of IGF-I and IGFBPs secretion, thus indicating that the paracrine/autocrine IGF-I-IGFBPs interactions of the PBMC are not altered by pituitary GH deficiency.     

Retinal photocoagulation does not influence intraocular levels of IGF-I, IGF-II and IGF-BP3 in proliferative diabetic retinopathy-evidence for combined treatment of PDR with somatostatin analogues and retinal photocoagulation?

Retinal photocoagulation reduces the incidence of severe visual loss in proliferative diabetic retinopathy (PDR). Reduced levels of VEGF/VPF might result in an improved function of the blood-retina barrier and cause a decrease of blood derived intraocular growth factors such as IGF-I. This study investigates whether retinal photocoagulation is able to normalize the concentrations of IGF-I, IGF-II and IGF-BP3 in the vitreous humor of patients undergoing vitrectomy. Levels of IGFs and the permeability marker, albumin, were measured in serum and vitreous of 52 patients. Three groups were compared: controls without proliferating eye disease (n = 19) and patients with PDR with (PDR+; n = 25) and without (PDR-; n = 8) previous retinal photocoagulation. IGF-I, IGF-II, IGF-BP3 and albumin were determined by immunological methods and were confirmed to be increased in patients with PDR compared to controls. Retinal photocoagulation influenced neither the intraocular concentration of the permeability marker albumin (PDR+: 253.2 +/- 46 mg/dl; PDR-: 256.4 +/- 66.5 mg/dl) nor the levels of IGFs (PDR+: IGF-I: 1.2 +/- 0.1 ng/ml; p = 0.38; IGF-II: 34.8 +/- 2.2 ng/ml; p = 0.1; IGF-BP3: 75.7 +/- 9.7 ng/ml; p = 0.27; PDR-: IGF-I: 1.1 +/- 0.2ng/ml; IGF-II: 29.3 +/- 5.2 ng/ml; IGF-BP3: 61.5 +/- 18.3 ng/ml). Systemic levels of albumin and IGFs were not changed significantly by retinal photocoagulation. These results demonstrate that previous retinal photocoagulation in patients undergoing vitrectomy does not functionally reestablish the blood-retina barrier despite decreases in VEGF/VPF. The lack of influence on intraocular concentrations of the serum-derived growth factors, IGF-I, IGF-II and IGF-BP3, might in part explain the failure of previous photocoagulation in the investigated patients. These results suggest that a combined treatment with retinal photocoagulation and growth hormone-lowering drugs, such as somatostatin analogues, could be a useful treatment, which may prevent further loss of visual acuity in patients with PDR.     

Up-regulation of IGF-I receptors on IM-9 cells by IGF-II peptides

To examine a possible role for IGF-II in the regulation of IGF-I receptors we measured 125I-IGF-I binding on IM-9 cells following pre-incubation with IGF-II/IGF-I mixtures, purified MSA (a rat IGF-II-like peptide), pure IGF-I, or insulin. Whereas all preparations tested induced down-regulation of IGF-I binding after 20 hours, distinct differences were noted after six hour pre-incubation: IGF-I (100 ng/ml) and insulin (1 microgram/ml) both induced down-regulation of IGF-I binding (15 +/- 2% and 19 +/- 2% respectively). However, a mixture of IGF-II and IGF-I (100 ng/ml each) induced consistent up-regulation of IGF-I binding (16 +/- 2%) (mean +/- SE, n = 14), and a preparation enriched in IGF-II (250 ng/ml IGF-II and 75 ng/ml IGF-I) induced 20 +/- 5% (n = 3) up-regulation at six hours. Purified MSA (200 ng/ml) induced 15% up-regulation of IGF-I binding at six hours. Scatchard analysis of displacement curves showed that increased binding was due to loss of low affinity binding, with enhancement of high affinity sites. The up-regulation of IGF-I binding was unaffected by treatment with 0.1 mM cycloheximide, but was blunted by 5 microM colchicine. It is concluded that 1. IGF-II induces up-regulation of IGF-I receptors on IM-9 cells following 6 hour pre-incubation; 2. This phenomenon is not mimicked by the structurally-related peptides IGF-I or insulin; The up-regulation is due to enhanced high affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)