Free IGF-I Research Articles

The insulin-like growth factor axis: a potential link between glycemic index and cancer

The question of how diet affects cancer risk has been debated for many years. Dietary fiber is thought to decrease the transit time of food in the colon and to dilute carcinogens, thus minimizing the body’s exposure to toxins. The presence of certain compounds that induce the production of beneficial xenobiotic metabolizing enzymes may be important. In addition, high concentrations of antioxidants, which decrease free radical–induced damage, may play a role. At this time, however, the mechanism by which some foods promote and others protect against cancer remains largely unknown. The novel dietary factor glycemic index (GI) has been linked to the risk of several types of cancer, including breast, ovarian, endometrial, pancreatic, and colorectal (1), although the mechanisms involved were not previously examined. The GI reflects the way in which a food (meal or diet) affects postprandial blood glucose and, consequently, insulin concentrations. Foods that are rapidly digested in the gut, including most refined-grain products and potato, have a high GI, whereas nonstarchy vegetables, fruit, and legumes tend to have a low GI (2). In this issue of the Journal, Brand-Miller et al (3) suggest that a high-GI diet may increase cancer risk by modulating the insulin-like growth factor (IGF) axis. Using 10 healthy subjects, the authors compared the effects of a high-GI meal and a low-GI meal on glucose, insulin, and various components of the IGF axis in the serum over 4 h. The meals were well matched for macronutrient composition. As intended, the areas under the curve for glucose and insulin were 40% and 70% lower, respectively, after the low-GI meal than after the high-GI meal. There was no change in either free or total IGF-I. At 4 h, the high-GI meal reduced IGF-binding protein (IGFBP)-1 by 13 ng/mL and reduced IGFBP-3 by 110 ng/mL. The low-GI meal, on the other hand, reduced IGFBP-1 by 55 ng/mL and increased IGFBP-3 by 251 ng/mL. Thus, the low-GI meal produced a greater decrease in IGFBP-1 than did the high-GI meal and produced an increase, rather than a decrease, in IGFBP-3. To understand the significance of these changes, it is important to consider the complexity of IGF-I signaling. IGF-I has powerful effects; it stimulatesanabolicmetabolism,cellproliferation,andcell differentiation and can also inhibit apoptosis. IGF-I in the serum is thought to be derived primarily from the liver and complexed to IGFBPs (4). IGFBP-3 is the major IGFBP in the serum, and most circulatingIGF-I ispresent in ternarycomplexeswith theacid-labile subunit and with either IGFBP-3 or -5. IGF-I in the ternary complex is sequestered in the plasma and hence has a prolonged half-life. Circulating IGF-I is also found in binary complexes of IGF-I and IGFBP-1, -2, -4, or -6, all of which may exit the vasculature more freely. Only a small amount of IGF-I exists freely in the circulation. At the cellular level, IGF-I signals primarily through the IGF-I receptor, a tyrosine kinase, but it can also interact with the insulin receptor and the IGF-II receptor. The interaction of IGF-I with these receptors is also modulated by IGFBPs, which can either promote or attenuate IGF-I activity. Some IGFBPs are known to have effects on cell growth and proliferation that are independent of either IGF-I or its receptor. Furthermore, IGFBP activity is itself regulated by posttranslational modifications such as phosphorylation and by proteolysis. Given the redundancy of the IGF system and its many layers of regulation, it is not surprising that IGFBPs are found to have varied biological effects. For example, IGFBP-1 promotes apoptosis of breast cancer cells under some conditions but not under others (5, 6). IGFBP-3 has been shown to promote apoptosis in most in vitro studies. Nonetheless the fact that transgenic mice overexpressing IGFBP-3 in the involuting mammary gland displayed decreased apoptosis suggests that factors other than the amount of IGFBP-3 determine its actions (7). One finds similar inconsistencies in epidemiologic studies of the role of the IGFBPs in cancer. On the basis of in vitro data, it might be expected that high concentrations of IGFBP-3 would reduce the risk of cancer. Whereas some studies found such an association, a large meta-analysis failed to show any protective effect of serum IGFBP-3 concentrations on the risk of prostate, colorectal, or breast cancer (8). Similarly, IGFBP-1 concentrations have been shown to be both positively and negatively associated with cancer risk (5, 9). Brand-Miller et al were the first, in the study reported in this issue of theJournal, todocument theeffectsofGIon theIGFaxis.Clearly, the magnitude of the changes they found was small: 6% for IGFBP-3. Moreover, there was no corresponding change in either totalor freeIGF-I. It isalsosurprising that IGFBP-1,which isknown to be suppressed by insulin, was reduced to a greater extent after the low-GI challenge. This suggests that the GI may have effects on the IGF system that are independent of insulin.

The glycemic index of foods influences postprandial insulin-like growth factor–binding protein responses in lean young subjects

Growth in normal and malignant tissues has been linked to hyperinsulinemia and insulin-like growth factors (IGFs). We hypothesized that IGF and IGF-binding protein (IGFBP) responses may be acutely affected by differences in the glycemic index (GI) of foods. We compared the postprandial responses of IGFs and IGFBP to 2 foods of similar macronutrient composition but with greatly different GIs-pearled barley (GI: 25) and instant mashed potato (GI: 85). Ten young lean subjects consumed 50-g carbohydrate portions of the 2 foods or water (extended fast) in random order after an overnight fast. Capillary blood was collected at regular intervals over 4 h for measurement of blood glucose, insulin, and components of the IGF system. Serum IGFBP-1 declined markedly after both meals, but the mean (+/-SEM) change at 4 h was significantly (P < 0.01) more prolonged after the low-GI meal (-55 +/- 20 ng/mL) than after the high-GI meal (-13 +/- 15 ng/mL). Conversely, the change in serum IGFBP-3 concentration at 4 h was significantly (P < 0.05) higher after the low-GI meal (251 +/- 102 ng/mL) than after the high-GI meal (-110 +/- 96 ng/mL); the same pattern was observed at 2 h. Changes in IGFBP-2, free IGF-1, and total IGF-1 responses were minimal and did not differ significantly from those during the 4-h fast. Acute changes in IGFBP-3 after low-GI and high-GI foods may provide a biologic mechanism linking cell multiplication with greater consumption of high-GI carbohydrates.

The IGF-system is not affected by a twofold change in protein intake in patients with type 1 diabetes

Objective In type 1 diabetes the circulating IGF-system is altered with low IGF-I and changes in levels of IGF-binding proteins (IGFBPs) which may be of importance for the development of diabetes complications. Our aim was to study if IGF-I, as supported by experimental data in animals, can be affected by dietary protein intake. Design and methods Twelve patients with type 1 diabetes, age 37.5 ± 10.0 years (mean ± SD), diabetes duration 20.1 ± 9.3 years and HbA1c 6.3 ± 0.6% were allocated to isocaloric diets with either low normal protein content (LNP), (10 E%; 0.9 g protein/kg body weight) or high normal protein content (HNP) (20 E%; 1.8 g protein/kg body weight) in an open randomised cross-over study. Each diet was taken for 10 days with a wash-out period of 11 days in between. Circulating levels of total and free IGF-I and -II, IGFBP-1, -2 and -3 and GH-binding protein (GHBP) as well as ghrelin were measured with validated in-house immunoassays. Results At day 10, urinary urea excretion was 320 ± 75 mmol/24 h during LNP diet compared with 654 ± 159 mmol/24 h during HNP diet ( p < 0.001). There were no changes in body weight or glycaemic control between the diets. Fasting levels of total IGF-I were 121 ± 33 μg/L after LNP and 117 ± 28 μg/L after HNP diet (ns) and the corresponding concentrations of IGFBP-1 were 142(141) and 132(157) μg/L [median (IQR)] (ns). There were no differences in plasma concentrations of total IGF-II, free IGF-I and -II, IGFBP-3, GHBP and ghrelin, whereas a small difference was found for IGFBP-2 (302 ± 97 vs. 263 ± 66 μg/L; LNP vs. HNP; p < 0.04). Conclusions A twofold change of the dietary protein intake does not influence the altered circulating IGF-system in type 1 diabetes. In order to affect the IGF-system other interventions must be used.

Cotreatment of Acromegaly with a Somatostatin Analog and a Growth Hormone Receptor Antagonist

Pegvisomant is a GH receptor antagonist that blocks the peripheral actions of GH in acromegaly. Pegvisomant, in contrast to somatostatin (SMS) analogs, does not suppress the activity of the GH-producing adenoma. We assessed the effects of cotreatment with pegvisomant and SMS in acromegaly on GH secretion, IGF-I levels, and glucose tolerance. Eleven patients with persistent disease despite previous therapy underwent the following fixed treatment algorithm: 1) on SMS therapy, 2) off therapy for 2 months, 3) 6-wk treatment with 10 mg/d pegvisomant, 4) 6-wk treatment with 15 mg/d pegvisomant, and 5) 3-month treatment with 15 mg pegvisomant plus SMS. Blood was sampled in the fasting state and during an oral glucose tolerance test. Total serum IGF-I levels (micrograms per liter) decreased after pegvisomant, but the lowest levels were obtained with cotreatment [458 +/- 67 (SMS), 562 +/- 78 (active), 376 +/- 51 (10 mg), 269 (15 mg), 195 +/- 24 (combined) (P < 0.0001)]. Free and bioactive IGF-I changed in a similar pattern. Steady-state pegvisomant levels (micrograms per liter) were obtained, but SMS cotreatment increased pegvisomant levels by 20% (P = 0.02) [2631 +/- 616 (10 mg), 6536 +/- 1413 (15 mg), 8030 +/- 1914 (combined)]. Pegvisomant increased endogenous GH levels (micrograms per liter), which was countered by SMS cotreatment [5.1 +/- 1.3 (SMS), 8.9 +/- 2.9 (active), 14.6 +/- 4.9 (10 mg), 19.7 +/- 6.5 (15 mg), 11.8 +/- 2.8 (combined) (P < 0.01)]. Plasma glucose levels (millimoles per liter) were highest during SMS and lowest during pegvisomant 15 mg [2-h oral glucose tolerance test: 10.3 +/- 0.7 (SMS), 8.9 +/- 0.7 (active), 7.2 +/- 0.7 (10 mg), 6.5 +/- 0.5 (15 mg), 8.0 +/- 0.8 (combined) (P = 0.02)]. Dual blockade of the GH axis with pegvisomant and a SMS analog is feasible in acromegaly.

Rh/IGF-I/rhIGFBP-3 administration to patients with type 2 diabetes mellitus reduces insulin requirements while also lowering fasting glucose

Administration of insulin-like growth factor-I to patients with diabetes enhances insulin action and reduces the degree of hyperglycemia but it is associated with a high rate of adverse events. Infusion of the combination of rhIGFBP-3 (the principal binding protein for IGF-I in plasma) with rhIGF-I to patients with type I diabetes improved insulin sensitivity and was associated with a low incidence in side effects. In this study, 52 patients with insulin-treated type 2 diabetes received recombinant human IGF-I plus rhIGFBP-3 in one of four dosage regimens for 14 days. The four groups were: (1) continuous subcutaneous infusion of 2 mg/kg/day; (2) the same 2 mg/kg dose infused subcutaneously over 6 h between 2000 and 0200 h; (3) 1 mg/kg twice a day by bolus subcutaneous injection; (4) a single bedtime subcutaneous injection of 1 mg/kg. Across these four groups rhIGF-I/rhIGFBP-3 decreased insulin requirements between 54% and 82%. Fasting glucose decreased by 32–37%. Mean daily blood glucose (4 determinations per day) declined in all 4 groups (range 9–23% decrease). Frequent sampling for total IGF-I, free IGF-I and IGFBP-3 was performed on days 0, 1, 7, 14 and 15. The peak total IGF-I values were increased to 4.0–4.8-fold at 16–24 h. For free IGF-I the increase varied between 7.1 and 8.2-fold and peak values were attained at 16–20 h after administration. Both the time to maximum concentration (Tmax) and the maximum free IGF-I levels (Cmax) on day 1 for all groups were substantially less than previously published studies, wherein lower doses of rhIGF-I were given without IGFBP-3. The improvement in glucose values and the degree of reduction in insulin requirement were the greatest in groups 2 and 3 and the patients in those groups had the highest free IGF-I levels. The frequency of side effects such as edema, jaw pain and arthralgias was 4% which is less than that has been reported in previous studies wherein IGF-I was administered without IGFBP-3. We conclude that rhIGF-I/rhIGFBP-3 significantly lowers insulin requirements yet improves glucose values and these changes may reflect improvement in insulin sensitivity. Coadministration of IGFBP-3 with IGF-I produces lower free IGF-I (Tmax and Cmax) levels compared to administration of IGF-I alone and is associated with relatively low incidence of side effects during 2 weeks of administration.

The somatostatin analogue SOM230, compared with octreotide, induces differential effects in several metabolic pathways in acromegalic patients

Recently, our first clinical study with the novel multiligand somatostatin (SRIF) analogue SOM230 in acromegalic patients showed that SOM230, due to its beneficial inhibitory effects on GH levels compared with octreotide (OCT), might increase the number of patients that can be biochemically controlled. Since SRIF analogues are also known to interact with other metabolic pathways, IGF-I, IGFBP-1, glucose and insulin concentrations on the control day (CD) and on treatment days following a single s.c. injection SOM230 100 and 250 microg, were compared to those following OCT 100 microg. Randomized, cross-over, double-blinded proof-of-concept trial in 12 patients with active acromegaly. Free IGF-I levels were suppressed after 24 h by OCT, SOM230 250 and 100 microg, whereas at 48 h only both SOM230 dosages still induced these inhibitory effects. Circulating IGFBP-1 levels (AUC; 0830-1430 h) compared with CD, increased sharply after OCT (from 48 to 237 microg/l/h; P < 0.001 vs. CD), while SOM230 250 and 100 microg elicited a lower and dose-dependent effect (163 and 90 microg/l/h, respectively, P < 0.05 vs. CD and OCT). Neither insulin nor GH levels showed statistically significant correlation with IGFBP-1 levels either after SOM230 or OCT. An early rise in glucose levels 1 h postinjection with SOM230 250 microg compared with OCT and CD was observed 8.3 +/- 0.8, 4.4 +/- 0.5 and 4.9 +/- 0.4 mmol/l, respectively: P < 0.05). SOM230 250 microg (19 +/- 4 vs. 46 +/- 3 mU/l on CD: P < 0.05), although clearly less potent than OCT (5.4 +/- 0.4 mU/l: P < 0.01 vs. CD), inhibited insulin release. Since these corresponding absolute insulin levels cannot entirely explain this hyperglycaemic effect of SOM230, other mechanisms seem involved in this glucose rise. If SOM230 would influence glucose homeostasis in peripheral target tissues of insulin action, expression of SS-receptors (sst) seems a logical necessity. In normal human liver tissues, analysed by quantitative polymerase chain reaction (PCR), the average sst1 mRNA expression level appeared significantly higher compared with sst2 (n = 6, relative copy number 161 +/- 46 vs. 57 +/- 6; P < 0.05). Fat tissue expressed both sst1 and sst2 mRNA, whereas in muscle only sst2 mRNA was found. Both dosages of SOM230 inhibit free IGF-I in a more sustained fashion compared to OCT, implying longer duration of action. The superior action of OCT compared with SOM230 in stimulating IGFBP-1 levels, suggests direct regulation of IGFBP-1 by SRIF analogues via sst2. Finally, expression of only sst1 and sst2 in target tissues of insulin action, might point towards additional modulatory effects by SOM230 on glucose homeostasis.

Effects of Dietary Carbohydrate Restriction with High Protein Intake on Protein Metabolism and the Somatotropic Axis

Alterations in dietary macronutrient intake can influence protein turnover. The purpose of this study was to assess the influence of a low-carbohydrate/high-protein diet (LC/HP) on skeletal muscle protein synthesis and whole-body proteolysis, without the confounding influence of a negative energy balance. Nine-day dietary intervention was applied. Subjects remained in the General Clinical Research Center throughout the 9-d study. Eight young, healthy volunteers participated. Subjects ate a typical Western diet (60% carbohydrate, 30% fat, 10% protein) for 2 d, followed immediately by 7 d of an isocaloric LC/HP (5% carbohydrate, 60% fat, 35% protein). Skeletal muscle fractional synthetic rate and whole-body proteolysis [leucine rate of appearance in plasma (Ra)] were measured after an overnight fast before and after 2 and 7 d of LC/HP. We also measured plasma concentrations of insulin, GH, and IGF-I. Leucine Ra was increased (P = 0.03) after 2 and 7 d of LC/HP, and muscle fractional synthetic rate was approximately 2-fold higher (P < 0.01) after 7 d of LC/HP. Fat free mass was not altered by LC/HP. Average 24-h plasma insulin concentration was 50% lower (P < 0.001) after 2 and 7 d of LC/HP, whereas GH secretion and total plasma IGF-I concentrations were unchanged with LC/HP. However, plasma free IGF-I decreased by approximately 30% after 7 d of LC/HP (P = 0.002), whereas muscle IGF-I mRNA increased about 2-fold (P = 0.05). Increasing dietary protein content during a 7-d carbohydrate restricted diet stimulated muscle protein synthesis and whole-body proteolysis without a measurable change in fat free mass.

Insulin and insulin-like growth factors inhibit and luteinizing hormone augments ovarian theca-interstitial cell apoptosis

Theca-interstitial (T-I) cells play a fundamental role in the control of ovarian function. Steroidogenic activity and growth of the T-I cells are regulated by many paracrine and endocrine factors. However, little is known about the mechanisms controlling T-I death. In an in vitro model of apoptosis, purified rat T-I cells were cultured for 24 h with serum and subsequently for up to an additional 24 h with serum or in serum-free medium with or without insulin, insulin-like growth factors (IGF-I and IGF-II) and LH or 8-bromo-cyclic AMP (8Br-cAMP). Apoptosis was identified by histological assessment of nuclear morphology and by detection of internucleosomal cleavage and quantified by determination of [alpha32P]-dideoxy-ATP 3'-end labeling of low molecular weight DNA. Serum withdrawal resulted in nuclear condensation and fragmentation into apoptotic bodies of T-I cells and led to pronounced DNA cleavage. Insulin (10 nM) protected T-I cells from apoptosis, reducing DNA fragmentation by 39 +/- 8% compared to serum-free controls. IGF-I (10 nM) and IGF-II (10 nM) had comparable antiapoptotic effects, decreasing DNA fragmentation by 55 +/- 9% and 37 +/- 14%, respectively. In contrast, LH (100 ng/ml) and 8Br-cAMP (1 mM) augmented the pro-apoptotic effect of serum withdrawal, increasing DNA fragmentation by 85 +/- 55% and 72 +/- 42%, respectively. The antiapoptotic effects of insulin and IGFs and the pro-apoptotic effect of LH, acting via the cAMP system, may be important in the maintenance of T-I homeostasis. Moreover, excessive levels of insulin and free IGFs may lead to T-I cell hyperplasia characteristic of conditions such as polycystic ovary syndrome.

Follicular fluid concentrations of free insulin-like growth factor (IGF)-I during follicular development in mares

The objective of the present study was to evaluate changes in concentrations of free insulin-like growth factor (IGF)-I in follicular fluid (FFL) during follicle development in the mare. Mares ( n = 14) were classified as either in the follicular phase ( n = 8) or luteal phase ( n = 6). Follicles ( n = 92) were categorized as small (6–15 mm; n = 54), medium (16–25 mm; n = 23) or large (>25 mm; n = 15) and FFL was collected. Free IGF-I levels in FFL in large follicles of follicular phase mares were greater ( P < 0.05) than in large follicles of luteal phase mares and small or medium follicles of luteal and follicular phase mares. Free IGF-I concentrations were greater ( P < 0.05) in large follicles of luteal phase mares than small but not medium follicles of luteal phase mares. FFL ratio of estradiol:progesterone paralleled changes in free IGF-I. Free IGF-I concentrations were negatively correlated ( P < 0.05) with insulin-like growth factor binding protein (IGFBP)-2, -4 and -5 but not IGFBP-3 levels. In addition, free IGF-I concentrations in FFL were positively correlated ( P < 0.01) with FFL estradiol, progesterone, androstenedione, estradiol:progesterone ratio, total IGF-I and total IGF-II. We conclude that increases in intrafollicular levels of bioavailable (free) IGF-I are associated with increased steroidogenesis in developing mare follicles.

Ovarian and IGF-I axis control of mammary development in prepubertal heifers

Although much is known about the endocrine control of bovine mammary development, most heifer work has focused on periods near the time of puberty or during gestation. However, we have found that ovariectomy in the prepubertal period also markedly impacts mammary development well before the onset of estrus would have normally occurred. Interactions between the pituitary and ovary to control udder development are mediated at least in part via alteration in concentrations of local IGF-I axis molecules within the developing mammary gland. For example, in heifers treated with growth hormone or estrogen, expression of IGF-I binding proteins (IGFBP-3) protein was reduced, thus effecting an increase in free IGF-I. Ovariectomized heifers had reduced rates of epithelial cell proliferation, fewer IGF-I receptors, and less local IGF-I. Mammary tissue expression of fibronectin was increased in ovariectomized heifers, but laminin expression was higher in controls. Thus, alterations in specific extracellular matrix proteins likely impact heifer mammary development. As a result, we have initiated calfhood studies. At 30 days of age, it is difficult to detect parenchymal tissue in the udder. Only a thin cord of parenchymal tissue (150 mg per gland) is discernible. By 75 days of age, a rounded, walnut-like mass of mammary parenchymal tissue becomes very evident and at 90 days of age, this mass of tissue has grown to approximately 10 g, a ∼60-fold increase. At 2 months of age, most proliferating epithelial cells (>92%) are confined to a population of light and intermediate-staining parenchymal cells. Between 2 and 5 months of age, a dark-staining cell population markedly emerges, but these dark cells were rarely labeled with bromodeoxyuridine (BrdU) and are likely to represent a more differentiated or committed cell lineage. The coordinated change in the proportions of each cell type suggests a progression from light-, to intermediate-, to dark-staining cell phenotypes. We are currently focusing on the importance of the ovary and mammary tissue synthesis of estrogens on emergence of specific populations of putative mammary stem cells.

Ethinylestradiol and testosterone have divergent effects on circulating IGF system components in adolescents with constitutional tall stature

Pharmacological doses of estrogens or testosterone are used to limit the final height of girls or boys with constitutional tall stature but the mechanism behind this growth inhibition is still debated. We therefore studied the changes in the circulating components of the insulin-like growth factor (IGF) system during high dose sex steroid therapy. Twenty three girls and twenty boys with constitutional tall stature were treated with 100 microg ethinylestradiol per day or 250 mg testosterone ester every 14 days respectively. In 19 girls and 18 boys, the levels of IGF-I, free IGF-I, IGF-II, acid-labile subunit (ALS) and IGF binding proteins (IGFBP)-2 to -6 were measured before and 3-6 months after the start of therapy (group 1). In 18 girls and 11 boys, samples were collected at the end of therapy and 3 to 6 months afterwards (group 2). Fourteen girls and nine boys belonged to both groups. All parameters were measured by radioimmunoassay or ELISA. Levels of IGF-I were decreased significantly by estrogen treatment but remained unchanged during testosterone treatment. Free IGF-I decreased during estrogen treatment but increased during testosterone therapy. Estrogens increased IGF-II and testosterone reduced it. The important reduction of IGFBP-2 during estrogen therapy is not reproduced by androgen therapy, neither is the stimulation by estrogens of IGFBP-4. IGFBP-3 is not modulated by either sex steroid. We found that IGFBP-6 is up-regulated by testosterone but not by estrogens; the reverse is true for ALS, which increased during estrogen treatment but remained unchanged during testosterone treatment. Our findings demonstrate that androgens and estrogens exert differential effects on the circulating levels of several IGF components.

In vivo effects of pregnancy-associated plasma protein-A, activin-A and vascular endothelial growth factor on other follicular-fluid factors during follicle deviation in mares

During a follicular wave in mares, the two largest follicles (F1 and F2) begin to deviate in diameter when F1 is a mean of 22.5 mm. The intrafollicular effects of pregnancy-associated plasma protein-A (PAPP-A), IGF-I, activin-A and vascular endothelial growth factor (VEGF) on other follicular-fluid factors during deviation were studied. In four treated groups (n = 7/group), a single dose of one of the four factors was injected into F2 when F1 was > or = 20.0 mm (expected beginning of deviation). In a control group (n = 7), F2 was injected with vehicle. One day after treatment, a sample of follicular fluid was taken from F1 and F2 of the control group and from F2 of the treated groups and was assayed for free IGF-I, oestradiol, androstenedione, activin-A, inhibin-A, follistatin and VEGF. In the control group, the means for all end points were significantly greater in F1 than in F2, except that concentrations of androstenedione were lower in F1 than in F2. The treatment effects for F2 were significant as follows: PAPP-A increased the concentrations of free IGF-I, inhibin-A, follistatin and VEGF and decreased the concentrations of androstenedione; IGF-I increased the concentration of inhibin-A and decreased the concentration of androstenedione; activin-A decreased the concentrations of follistatin and androstenedione and increased the diameter of F2; and VEGF increased the concentration of IGF-I and decreased the concentration of androstenedione. These results support the hypotheses that during deviation in mares PAPP-A increases the follicular-fluid concentrations of free IGF-I, follistatin responds to changes in follicular-fluid concentrations of activin-A, and VEGF affects the concentrations of other follicular-fluid factors.

A Twin Study for Serum Leptin, Soluble Leptin Receptor, and Free Insulin-Like Growth Factor-I in Pubertal Females

Leptin and IGF-I are two peripheral metabolic signals linking body energy status to hypothalamus GnRH generator and involved in the pubertal development and metabolic disorders. The changes of their biological activity through puberty and the genetic basis are not clear. To determine the genetic and environmental influences to the variations of basal leptin, soluble leptin receptor (SOB-R), free leptin index (FLI), and free IGF-I levels in pubertal females. A twin study was performed in 2003. Participants were recruited from the Qingdao Twin Registry, a school-based registry. A total of 360 twin girls aged 6-18 yr were enrolled, consisting of 132 pairs of monozygotic and 48 pairs of dizygotic twins. Anthropometric and sexual characteristics were examined. Serum total leptin and free IGF-I were measured by immunoradiometric assay, and SOB-R was measured by ELISA. Estimates of genetic and environmental components of variance were based on the theory of normal maximum likelihood in Mx package, a computer program specifically designed for the analysis of twin and family data. Serum leptin concentrations increased persistently throughout puberty, especially from Tanner stage III to Tanner stage IV (P < 0.05), which in consistent with the increase of percentage of body fat. However, SOB-R decreased significantly from Tanner stage I to Tanner stage II (P < 0.05), which results in a continuous rise of FLI (ratio of leptin to SOB-R), especially from Tanner stage I to Tanner stage II (P < 0.05). Serum free IGF-I increased dramatically from Tanner stage I to II and declined since then. Results of correlation analysis suggest that FLI predicts the pubertal growth and sexual maturation more effectively, whereas leptin sensitively reflects the fat mass of body composition. Quantitative genetic model fittings showed that SOB-R and free IGF-I have higher heritability (0.62-0.77, 0.54-0.66) and leptin and FLI have lower heritability (0.38-0.48, 0.44-0.55). Fast increase of FLI and free IGF-I from Tanner stage I to II might be involved in the onset of puberty and the onset of thelarche. The peak of free IGF-I in Tanner stage II might be presumed as an indicator of the peak of pubertal growth spurt in females, and the significant rise of leptin along with percentage of body fat from Tanner stage III to IV might be as a predictor of the forthcoming menarche. Our results stress the importance of research into the genetic regulation on the endocrine regulators involved in the pubertal development and metabolic disorders, including pubertal obesity and diabetes.

Circulating Levels of Insulin-like Growth Factors, their Binding Proteins, and Breast Cancer Risk

Earlier data support the hypothesis that the relation between circulating insulin-like growth factor-I (IGF-I) levels and breast cancer risk differs by menopausal status. The strong association of IGF-I with height in childhood and weak or no association between adult levels and adult height also suggest that IGF levels in young women may better reflect an exposure time period of importance to breast cancer. Few studies have assessed IGF binding protein-1 (IGFBP-1) or free IGF and breast cancer risk. We conducted a large case-control study nested within the prospective Nurses' Health Study. Plasma concentrations of IGF-I, free IGF, IGFBP-3, and IGFBP-1 were measured in blood samples collected in 1989 to 1990. Eight hundred women were identified who had a diagnosis of invasive or in situ breast cancer after blood collection, up to 1998, 27% of whom were premenopausal at blood collection. To those 800 women, one to two controls were age-matched for a total of 1,129 controls. We used logistic regression models to estimate the relative risk (RR) of breast cancer associated with IGF levels. Among postmenopausal women, neither IGF-I, IGFBP-3, IGFBP-1, nor free IGF was associated with breast cancer risk [RRs, top versus bottom quintile: IGF-I, 1.0; 95% confidence interval (95% CI), 0.7-1.4; IGFBP-3, 0.8; 95% CI, 0.6-1.1; IGFBP-1, 0.9; 95% CI, 0.6-1.5; and free IGF, 1.0; 95% CI, 0.6-1.4]. Among premenopausal women, IGFBP-3, IGFBP-1, and free IGF similarly were not associated with breast cancer risk (RRs, top versus bottom quintile: IGFBP-3, 1.2; 95% CI, 0.8-2.3; IGFBP-1, 1.5; 95% CI, 0.8-3.0; and free IGF, 1.1; 95% CI, 0.7-2.1). Higher IGF-I plasma levels, however, were associated with a modestly elevated breast cancer risk (RR, 1.6; 95% CI, 1.0-2.6) among the premenopausal women, with a stronger association among premenopausal women ages < or =50 (RR, 2.5; 95% CI, 1.4-4.3); further adjustment for IGFBP-3 did not greatly change these estimates. Circulating IGF-I levels seem to be modestly associated with breast cancer risk among premenopausal women, but not among postmenopausal women. IGFBP-3, IGFBP-1, and free IGF are not associated with breast cancer risk in either premenopausal or postmenopausal women in this cohort.

Testosterone and Estradiol Regulate Free Insulin-Like Growth Factor I (IGF-I), IGF Binding Protein 1 (IGFBP-1), and Dimeric IGF-I/IGFBP-1 Concentrations

The present study tests the clinical postulate that elevated testosterone (Te) and estradiol (E2) concentrations modulate the effects of constant iv infusion of saline vs. recombinant human IGF-I on free IGF-I, IGF binding protein (IGFBP)-1, and dimeric IGF-I/IGFBP-1 concentrations in healthy aging adults. To this end, comparisons were made after administration of placebo (Pl) vs. Te in eight older men (aged 61 +/- 4 yr) and after Pl vs. E2 in eight postmenopausal women (62 +/- 3 yr). In the saline session, E2 lowered and Te increased total IGF-I; E2 specifically elevated IGFBP-1 by 1.5-fold and suppressed free IGF-I by 34%; and E2 increased binary IGF-I/IGFBP-1 by 5-fold more than Te. During IGF-I infusion, the following were found: 1) total and free IGF-I rose 1.4- to 2.0-fold (Pl) and 2.1-2.5-fold (Te) more rapidly in men than women; 2) binary IGF-I/IGFBP-1 increased 3.4-fold more rapidly in men (Te) than women (E2); and 3) end-infusion free IGF-I was 1.6-fold higher in men than women. In summary, E2, compared with Te supplementation, lowers concentrations of total and ultrafiltratably free IGF-I and elevates those of IGFBP-1 and binary IGF-I/IGFBP-1, thus putatively limiting IGF-I bioavailability. If free IGF-I mediates certain biological actions, then exogenous Te and E2 may modulate the tissue effects of total IGF-I concentrations unequally.

The ‘bio-assay’ quality of life might be a better marker of disease activity in acromegalic patients than serum total IGF-I concentrations

To investigate the quality of life (QoL) in acromegalic patients in relation to biochemical parameters. Single-center, open label study in 14 acromegalic patients (eight woman and six men, age 33-77 years), with normal serum IGF-I levels during long-term treatment with monthly injections of 20 mg of long-acting octreotide. We investigated which biochemical parameter might reflect optimal QoL, using the SF-36 questionnaire. We observed that six patients had a low QoL score at baseline in the same range as observed in cancer patients. The other eight patients had a normal QoL. GH, IGF-I nor free IGF-I could discriminate these two subgroups at baseline. After skipping one monthly injection, all six subjects with the low QoL escaped in their free IGF-I concentrations. Also total IGF-I concentrations escaped in four of these six. In the subjects with normal QoL, free IGF-I levels remained normal in all, while total IGF-I levels only escaped in one. This study tells us that the currently used biochemical criteria for disease control in acromegaly might be sufficient in assessing long-term mortality and morbidity, but they are insufficient in addressing the most important parameter from the patient's perspective--QoL.

Normal opioid tone and hypothalamic–pituitary–adrenal axis function in chronic fatigue syndrome despite marked functional impairment

To determine whether the functional impairment seen in chronic fatigue syndrome (CFS) is associated with reduced levels of central opioids and/or deficiency of the hypothalamic-pituitary-adrenal (HPA) axis. Single-blinded case-control study measuring functional and psychological status, basal hormonal parameters and ACTH/cortisol response to naloxone and ovine corticotrophin-releasing hormone (oCRH) vs. placebo in people with CFS and healthy controls. Twelve people with CFS and 11 age-matched controls. Hormonal parameters: basal levels of 09:00 h plasma cortisol, dehydroepiandrosterone sulfate (DHEAS) and IGF-1. 24-h urinary free cortisol. Plasma ACTH and cortisol response to naloxone 125 microg/kg, oCRH 1 microg/kg and placebo (normal saline). Psychological parameters: SF-36, Hamilton Depression Score, Hospital Anxiety and Depression Scale and Fatigue Scale. There were highly significant differences between the CFS subjects and the controls with respect to the measures of fatigue and physical functioning. However, there were no differences in basal levels of 09:00 h cortisol (367 +/- 37 vs. 331 +/- 39 nmol/l, P = 0.51), DHEAS (4.2 +/- 0.6 vs. 4.0 +/- 0.5 micromol/l, P = 0.81), 24-h urinary free cortisol (182 +/- 27 vs. 178 +/- 21 nmol/24 h, P = 0.91) or IGF-1 (145 +/- 19 vs. 130 +/- 11 microg/l, P = 0.52) between the CFS group and controls, respectively. There was also no difference between the groups with respect to the ACTH and cortisol response to either oCRH or naloxone. Our data do not support an aetiological role for deficiency in central opioids or the HPA axis in the symptoms of CFS.

Effects of tamoxifen and octreotide LAR on the IGF-system compared with tamoxifen monotherapy

The insulin-like growth factor (IGF)-system was evaluated in 150 breast cancer patients participating in a randomised phase III trial comparing octreotide pamoate and tamoxifen with tamoxifen + placebo. Alterations in the IGF-system in the two treatment arms and individual changes with respect to outcome were compared. Serum IGF-I and -II, free IGF-I, and insulin-like growth factor binding protein 1–3 (IGFBP1-3) were measured by radioimmmunoassay (RIA)/immunoradiometric assay (IRMA) and IGFBPs by Western ligand blots (WLB) before and during treatment. Combined treatment caused a higher increase in IGFBP-1 and larger suppression of total and free IGF-I, IGF-II, and IGFBP-3 ( P < 0.01 for all), but less suppression of IGFBP-2 ( P < 0.05) compared with tamoxifen monotherapy. An increase in IGFBP-2 ⩾25% was associated with decreased progression-free survival (PFS) in the total patient population and combined treatment group. Similar response rates and time to progression in the treatment arms suggests moderate suppression of circulating IGF-I has no influence on clinical outcome.

Reversible Weight Gain and Prolactin Levels - Long-term Follow-up in Childhood

In adult patients weight gain is a frequent complaint of hyperprolactinaemia and it has been associated with a high prevalence of obesity. Normalization of prolactin (PRL) levels result in weight loss. The nature of this link is poorly defined. In this report we describe a 14 year-old female with primary amenorrhea and persistent progressive weight gain. The patient's height, weight and BMI were 152 cm, 70 kg, and 30.3 kg/m2, respectively. Basal hormonal investigation showed normal free thyroxin, TSH, IGF-I, cortisol and ACTH values. Serum PRL level was very high (16,278 mIU/l; normal range 63-426 mIU/l). Magnetic resonance imaging scan showed the presence of a pituitary microadenoma. Treatment with the non-selective dopamine agonist pergolide caused a significant reduction of serum PRL concentration with a remarkable decrease of body weight. During follow-up, repeat MRI scan revealed disappearance of the microadenoma. The reduction of the daily dose of pergolide was associated with an increase of serum PRL with significant weight gain. A further reduction of body weight was subsequently observed with an increase of pergolide dosage. Serum PRL measurement may be useful as part of the endocrine work-up of obese children with a history of unexplained recent weight gain, especially if associated with pituitary-gonadal axis dysfunction. The relationship between PRL secretion and weight change needs to be examined in prospective larger studies.

Non islet cell tumor hypoglycaemia in a metastatic Leydig cell tumor

Non islet cell tumour hypoglycaemia (NICTH) is a rare cause of hypoglycaemia associated with malignancy and can be considered as a paraneoplastic syndrome. The hormonal factor associated with this condition is big IGF II, which exerts negative feedback effect and decreases the production of growth hormone and insulin. Due to low growth hormone levels, hepatic production of IGFBP 3 (the main binding protein of IGF II) is impaired. Excess free big IGF II is thus available for binding with insulin receptors to cause hypoglycaemia. Treatment options are either surgical removal of the tumour, administration of growth hormone, glucocorticoids or combination of treatments. A case of metastatic Leydig cell tumour causing NICTH has been discussed and the mechanism of NICTH hypoglycaemia and the treatment is outlined.