Insulin-like Growth factor-I Response Research Articles

Somapacitan in Children Born SGA: 52-week Efficacy, Safety, and IGF-I Response Results from the Phase 2 REAL5 Study.

Somapacitan, a once-weekly reversible albumin-binding GH derivative, is evaluated in short children born small for gestational age (SGA). Evaluate efficacy, safety, tolerability as well as total and bioactive insulin-like growth factor-I (IGF-I) response of once-weekly somapacitan compared to daily GH in children born SGA. REAL5 is a randomized, multi-center, open-label, controlled phase 2 study comprising a 26-week main phase, 26-week extension, and an ongoing 4-year safety extension (NCT03878446). Thirty-eight sites across 12 countries. Sixty-two GH-treatment-naïve, prepubertal short children born SGA were randomized; 61 completed 52-weeks of treatment. Patients randomized (1:1:1:1:1) to somapacitan (0.16, 0.20 or 0.24 mg/kg/week) or daily GH (0.035 or 0.067 mg/kg/day), all administered subcutaneously. Estimated mean height velocity (HV; cm/year) at week 52 was 8.5, 10.4 and 10.7 cm/year for somapacitan 0.16, 0.20 and 0.24 mg/kg/week, respectively, and 9.3 and 11.2 cm/year for daily GH 0.035 and 0.067 mg/kg/day, respectively. Dose-dependent increases in total IGF-I as well as peak IGF-I bioactivity were observed for both treatments and were similar between comparator groups. For somapacitan, exposure-response modelling indicated highest efficacy with 0.24 mg/kg/week after 52 weeks of treatment. Similar safety and tolerability were demonstrated across all groups. A sustained dose-dependent growth response was demonstrated for somapacitan after 52 weeks of treatment. Overall, somapacitan 0.24 mg/kg/week provides similar efficacy, safety, and tolerability, as well as comparable bioactive and total IGF-I response, as daily GH (0.067 mg/kg/day) in children born SGA.

Hormonal and inflammatory responses in prepubertal vs. pubertal male children following an acute free-weight resistance training session.

Examine the acute hormonal and cytokine responses to free-weight resistance training in trained prepubertal and pubertal male children. Prepubertal (n = 21; age 11.4 ± 1.1years; Tanner I-II) and pubertal male children (n = 20; age 15.8 ± 0.7years; Tanner III-V) conducted a moderate-intensity free-weight resistance training program to failure with venous blood sampling before (pre), immediately after (post) and during the recovery phase of the program (post-15,-30min). Growth hormone (GH), insulin-like growth factor-I (IGF-I), cortisol, testosterone, IL-6, and TNF-α were analyzed in serum samples. Biological maturation was assessed according to the stages of the Tanner scale. There was a significant time-by-group interaction in IGF-I response (p = 0.044; η2 = 0.209) and testosterone (p < 0.001; η2 = 0.508), indicating a greater change in the pubertal group compared to the prepubertal group. Both groups significantly increased post-exercise GH levels (p < 0.05). Only the prepuberal group significantly increased levels of IL-6 at all post-exercise time points (p < 0.05). Both groups showed a significant (p < 0.05) increase in TNF-α levels compared to resting levels. These data suggest that acute testosterone and IGF-I response following resistance training differ between trained prepubertal and pubertal male children. Moderate-intensity resistance training performed to failure may thus have different effects in trained prepubertal and pubertal male children, which should be considered when giving training advice. Clinical trials number: NCT05022992.

Investigating the Bioavailability and Insulin-like Growth Factor-I Release of Two Different Strengths of Somapacitan: A Randomised, Double-Blind Crossover Trial.

Randomised, double-blind, crossover trial to confirm bioequivalence of somapacitan, a long-acting growth hormone (GH), in 5mg/1.5mL and 10mg/1.5mL strengths in equimolar doses. Healthy participants were randomised (1:1:1) to subcutaneous somapacitan treatment in one dosing period with 5mg/1.5mL and two periods with 10mg/1.5mL. Eligibility criteria included age 18-45years and body mass index 18.5-24.9kg/m2. Exclusion criteria included history of GH deficiency, previous GH treatment, weight > 100.0kg and participation in any clinical trial of an investigational medicinal product within 45days or five times the half-life of the previous investigational product before screening. Area under the curve from time 0 until last quantifiable observation (AUC0-t), maximum serum concentration (Cmax), time to Cmax and terminal half-life of somapacitan and safety were assessed. In total, 33 participants were randomised. For AUC0-t, estimated treatment ratio (ETR) (5mg/1.5mL versus 10mg/1.5mL) was 0.95 (90% confidence interval [CI] 0.89-1.01). Point estimate and 90%CIs were within the acceptance range (0.80-1.25). For Cmax, ETR was 0.77 (90%CI 0.68-0.89). Point estimate and 90%CIs were outside the acceptance range (0.80-1.25). Mean insulin-like growth factor-I (IGF-I) and IGF-I standard deviation score concentration-time curves for each strength were almost identical. No new safety issues were identified. Bioequivalence criterion for somapacitan 5mg/1.5mL and 10mg/1.5mL was met for AUC0-t but not for Cmax. The two strengths had equivalent IGF-I responses. ClinicalTrials.gov, NCT03905850 (3 April 2019).

OR21-01 Pre-treatment Blood Transcriptome Predicts First-year Growth And IGF-I Response To Somapacitan Treatment In Children With GH Deficiency

Abstract Disclosure: T. Garner: Grant Recipient; Self; Novo Nordisk. P.E. Clayton: Grant Recipient; Self; Novo Nordisk. M. Hojby: Employee; Self; Novo Nordisk. Stock Owner; Self; Novo Nordisk. P. Murray: Grant Recipient; Self; Novo Nordisk. A. Stevens: Grant Recipient; Self; Novo Nordisk. Background: Growth hormone (GH) replacement therapy often requires daily subcutaneous injections that can be burdensome for patients and their caregivers. Somapacitan is a long-acting, once-weekly GH derivative in development for treating GH deficiency (GHD) in children. Somapacitan reduces treatment burden and shows a similar efficacy and safety profile as daily GH in children with GHD. Here, we investigate the prediction of first-year growth and insulin-like growth factor-I (IGF-I) response based on baseline blood transcriptome in children with GHD treated with somapacitan or daily GH. Methods: 200 treatment-naïve prepubertal children with GHD were enrolled into REAL4, a randomised, multinational, open-labelled, and active-controlled phase 3 trial. 128 consented to a baseline blood transcriptome profile. Children were treated with once-weekly somapacitan (n=81) or daily GH (n=47) for 52 weeks and categorised based on treatment response: the upper quartile of height velocity (HV; cm/year) was defined as good responders, and the lower quartile as poor responders. We split the somapacitan group into training (70%) and testing (30%) sets for prediction validation of HV and the GH response marker: ΔIGF-I standard deviation score (SDS). Gene expression was assessed between the target quartile and the remaining quartiles for both HV and ΔIGF-I SDS to identify the top 100 differentially expressed genes by adjusted p-value. Classes were balanced using a synthetic minority oversampling technique and Boruta, a feature selection algorithm, was used to refine gene lists. We performed random forest and calculated “out of box” (OOB) area under the curve (AUC) and OOB error rate (ER), measures of predictive accuracy and robustness, respectively. Results: HV prediction from the transcriptome was excellent for both treatments (AUC range: 0.95-0.99). It was more robust for identifying good responders (ER: 7.0-7.5%) than poor responders (ER: 13.2-17.5%). Genes previously identified as predictive of growth response for daily GH (Stevens et al., 2021. The Pharmacogenomics J., 21:594-607) were demonstrated to have high predictive value for once-weekly somapacitan and daily GH treatment in this study (AUC range: 0.84-0.97, ER &amp;lt;22%). Using the somapacitan group for validation, HV prediction (AUC range: 0.78-0.81) was stronger than ΔIGF-I SDS prediction (AUC range: 0.63-0.72). Conclusions: We demonstrate pre-treatment blood transcriptome predicts first-year growth response for somapacitan. This represents an independent validation of earlier observations and shows that genes predictive of growth response for daily GH treatment in children with GHD are also predictive for once-weekly somapacitan. Further, we demonstrate that the pre-treatment blood transcriptome predicts growth response better than it predicts IGF-I SDS response. Presentation: Saturday, June 17, 2023

Population Pharmacokinetics and Pharmacodynamics of Once-Daily Growth Hormone Norditropin® in Children and Adults.

Background and ObjectiveOnce-daily injectable recombinant human growth hormone (GH) formulations (e.g. Norditropin®; Novo Nordisk A/S) are used to treat GH deficiency in children and adults, with much of the therapeutic effect mediated via the insulin-like growth factor-I (IGF-I) response. Despite a long history of use, there are few data on the pharmacokinetics and pharmacodynamics (serum IGF-I response) of this therapy, or of potential differences in the relationship of GH pharmacokinetic/pharmacodynamic (PK/PD) effects between children and adults. This study aimed to characterise the GH pharmacokinetics and IGF-I profile following daily subcutaneous GH in adults and children with GH deficiency.MethodsA model was developed based on a population PK/PD modelling meta-analysis of data from three phase I clinical trials (two using Norditropin® as a comparator with somapacitan, and one as a comparator with a pegylated GH product). Sequential model building was performed, first developing a model that could describe GH pharmacokinetics. A PD model of IGF-I data was then developed using PK and PD data, and where all PK parameters were kept fixed to those estimated in the PK model.ResultsThe model developed accurately describes and predicts GH pharmacokinetics and IGF-I response. Body weight was shown to have an important inversely correlated influence on GH exposure (and IGF-I standard deviation score), and this largely explained differences between adults and children.ConclusionsThe pharmacokinetics/pharmacodynamics developed here can inform expectations about the PD effects of different doses of GH in patients with GH deficiency of different body weights, regardless of their age.Clinical Trial RegistrationPooled modelling analysis of data from ClinicalTrials.gov identifiers NCT01973244, NCT00936403 and NCT01706783.Dates of registrationNCT01973244: 22 October, 2013; NCT00936403: 9 July, 2009; NCT01706783: 11 October, 2012.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40262-021-01011-3.

Relationship between plasma concentrations of IGF-I and clinical endometritis, and response to progesterone synchrony in dairy cows during early lactation

The first aim of this study was to evaluate the relationship between the concentrations of plasma insulin-like growth factor-I (IGF-I) in the transition period and the incidence of clinical endometritis postpartum. The second aim was to evaluate the relationship between the concentration of plasma IGF-I in the transition period and the estrous synchrony response and pregnancy rate to a controlled internal drug release (CIDR) protocol. A total of 402 dairy cows, 250 multiparous and 152 primiparous, were enrolled. A blood sample was taken from all cows 2 and 1 wk precalving and wk 1, 3, 4, and 5 postcalving for subsequent analysis of IGF-I. Vaginal discharge score as a measurement of uterine health was recorded in wk 3, 4, and 5 postcalving. Estrous cycles of all cows were synchronized on ≥37 d in milk (mean = 59; range 37-93) using an 8-d CIDR protocol. All cows were scanned at 32 to 35 d after insemination to confirm pregnancy. Data were analyzed using Proc Mixed and Proc Logistic models in SAS (version 9.3; SAS Institute Inc., Cary, NC). Plasma IGF-I concentrations were significantly greater in the primiparous cows than in the multiparous cows, both before and after calving, and were therefore analyzed separately. In multiparous cows plasma IGF-I concentrations postcalving were significantly lower among cows with uterine infection than in those without infection, and multiparous cows with a plasma IGF-I concentration less than 40 ng/mL 1 wk after calving were 3 times more likely to suffer from a uterine infection 4 to 5 weeks postcalving (odds ratio 2.8; 95% confidence interval 1.0-7.6). Plasma IGF-I concentrations were significantly greater after calving in the 121 primiparous cows that exhibited estrus post-CIDR protocol (mean 125 ng/mL) than in the 25 primiparous cows that did not respond (mean 95 ng/mL). Multiparous cows with greater plasma IGF-I concentrations postcalving had a significantly greater chance of conceiving (mean plasma IGF-I concentration of conceiving cows = 86 ng/mL; nonconceiving = 70 ng/mL). These results show an association between greater concentrations of plasma IGF-I postcalving and response to CIDR protocol in primiparous animals (mean plasma IGF-I concentration of responders = 116 ng/mL; nonresponders = 95 ng/mL). In contrast no association was detected between concentrations of plasma IGF-I in relation to the response to the CIDR protocol in multiparous cows. In conclusion, changes in circulating concentrations of plasma IGF-I early postpartum may help predict reproductive status of dairy cows.

Idiopathic short stature and growth hormone sensitivity in prepubertal children.

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range. Forty-six prepubertal children (~7.1years) born at term were studied: ISS (n=23; 74% boys) and NS (n=23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5. Children with idiopathic short stature were 1.90 SDS lighter (P<0.0001) but had 4.5% more body fat (P=0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentageIGF-I response to rhGH stimulation in univariable (r=0.45; P=0.002) and multivariable models (β=24.6; P=0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P<0.0001). GHBP levels (P=0.002) were suppressed in ISS children (-19%; P=0.029) but increased among NS children (+18%; P=0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P=0.006). A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

A Concerted Action Of Estradiol And Insulin Like Growth Factor I Underlies Sex Differences In Mood Regulation By Exercise

Mood homeostasis present sexually dimorphic traits which may explain sex differences in the incidence of mood disorders. We explored whether diverse behavioral-setting components of mood may be differentially regulated in males and females by exercise, a known modulator of mood. We found that exercise decreases anxiety only in males. Conversely, exercise enhanced resilience to stress and physical arousal, two other important components of mood, only in females. Because exercise increases brain input of circulating insulin-like growth factor I (IGF-I), a potent modulator of mood, we explored whether sex-specific actions of exercise on mood homeostasis relate to changes in brain IGF-I input. We found that exercise increased hippocampal IGF-I levels only in cycling females. Underlying mechanism involved activation of estrogen (E2) receptors in brain vessels that led to increased uptake of serum IGF-I as E2 was found to stimulate IGF-I uptake in brain endothelial cells. Indeed, modulatory effects of exercise on mood were absent in female mice with low serum IGF-I levels or after either ovariectomy or administration of an E2 receptor antagonist. These results suggest that sex-specific brain IGF-I responses to physiological stimuli such as exercise contribute to dimorphic mood homeostasis that may explain sex differences in affective disorders.

Direct influence of rooibos-derived compound on rabbit ovarian functions and their response to gonadotropins

AbstractRooibos is widely used in folk medicine, but its influence on reproductive processes has been studied insufficiently. The aim of present study was to examine possible involvement of rooibos on the release of progesterone (P4), testosterone (T) and insulin-like growth factor I (IGF-I), as well as its response to gonadotropin - follicle-stimulating and luteinizing hormone (FSH+LH), the most known hormonal regulators for reproduction. Rabbit ovarian fragments were cultured in the presence of rooibos (1, 10 and 100 μg/mL medium), FSH+LH (0.01, 0.1 and 1 IU/mL medium) and rooibos (10 μg/mL medium) in combination with FSH+LH (0.01, 0.1 and 1 IU/mL medium). The release of hormones was evaluated by using radioimmunoassay. It was observed that rooibos addition to culture medium stimulated P4 and inhibited T release. IGF-I release was significantly stimulated by rooibos at all doses added. FSH+LH when given alone promoted IGF-I, but not P4 or T release. The addition of rooibos induced the suppressive effect of FSH+LH on P4 release, the stimulatory action of FSH+LH on T output and reduced the response of IGF-I to FSH+LH treatment. These data suggest that rooibos is able to directly affect the release of steroid (P4 and T) and peptide (IGF-I) hormones by rabbit ovarian cells and to modulate their response to gonadotropins.

Growth Hormone Bioavailability, Insulin-Like Growth Factor-I and IGFBinding-Protein-3 Release in Japanese and Caucasian Subjects

Context: The pharmacokinetics (PK) of the recombinant human GH (rhGH) is poorly documented for the Japanese adult population, and a study comparing the PK, insulin-like growth factor-I (IGF-I) and IGF-bindingprotein- 3 (IGFBP-3) release between Japanese and Caucasian subjects after rhGH administration has previously not been reported. Objective: To compare the profiles of serum GH concentrations and the IGF-I and IGFBP-3 responses after administration of identical doses of rhGH to healthy Japanese and Caucasian subjects. Design and Setting: A randomised, double-blind, placebo-controlled, parallel-group study. Participants and Intervention: A total of 80 healthy male subjects (40 Japanese and 40 Caucasians) completed the study. A single dose of rhGH or placebo was administered subcutaneously, and blood samples were drawn up to 24 hours post-administration. Main Outcome Measures: Standard PK parameters, including the area under the GH concentration–time curve from 0 to 24 hours (AUC[0-24h]) and maximum GH concentration from 0 to 24 hours (Cmax). The IGF-I and IGFBP-3 levels were measured at various timepoints during the sampling period. Results: The bioavailabilities for Japanese and Caucasian subjects in terms of AUC(0–24 h) and Cmax were considered equivalent. The time to maximum GH concentration from 0–24 hours (tmax) was not statistically different for Japanese and Caucasian subjects. No differences in IGF-I or IGFBP-3 levels were observed. Conclusion: The bioavailabilities of rhGH for Japanese and Caucasian subjects are considered equivalent. Basal circulating IGF-I and IGFBP-3 levels and the release of IGF‑I and IGFBP-3 after administration of rhGH were similar between the two ethnic populations.

Effect of acute sleep deprivation and recovery on Insulin-like Growth Factor-I responses and inflammatory gene expression in healthy men.

Acute sleep deprivation in humans has been found to increase inflammatory markers and signaling pathways in the periphery through a possible Toll-like receptor 4 (TLR-4). In addition, short duration sleep has been associated with low circulating total Insulin-like Growth Factor-I (IGF-I) concentrations. We aimed to determine whether a total sleep deprivation (TSD) protocol with recovery altered whole-blood gene expression of the proinflammatory cytokines TNF-α and IL-6, as well as TLR-4 expression, and to examine the relationship with circulating concentrations of the IGF-I system. Twelve healthy men participated in a five-day TSD (two control nights followed by one night of sleep deprivation and one night of recovery). Blood was sampled at 0800, before and after sleep deprivation (D2 and D4), and after recovery (D5). It is shown that 25 h of sleep deprivation (D4) induced significant increases in mRNA levels of TNF-α and its soluble receptor R1 (P<0.01 respectively), as well as TLR-4 (P<0.05), while IL-6 mRNA levels remained unchanged. Circulating concentrations of free IGF-I were decreased at D4 (P<0.001). One night of recovery was sufficient to restore basal expression levels for TNF-α, sTNF-R1, TLR-4 and circulating IGF-I. Changes in TLR-4 mRNA levels during the protocol correlated positively with those of TNF-α and sTNF-R1 (r=0.393 and r=0.490 respectively), and negatively with circulating free IGF-I (r=-0.494). In conclusion, 25 h of sleep deprivation in healthy subjects is sufficient to induce transient and reversible genomic expression of the pro-inflammatory cytokine TNF-α and its R1 receptor, and its mediator TLR-4, with a possible link to IGF-I axis inhibition.

Critical role of a survivin/TGF-β/mTORC1 axis in IGF-I-mediated growth of prostate epithelial cells.

Survivin is a unique member of the inhibitor of apoptosis (IAP) proteins that is overexpressed in numerous cancers through poorly defined mechanisms. One such mechanism may be through constitutive activation of the insulin-like growth factor-I (IGF-I) signaling pathway, implicated in the development and progression of prostate cancer. Using the pre-neoplastic NRP-152 rat prostate cell line as a model, we showed that IGF-I induces Survivin expression, and that silencing Survivin by lentiviral-mediated small hairpin RNA (shRNA) represses IGF-I-stimulated cell growth, implicating Survivin as a mediator of this growth response. Moreover, our data support that the induction of Survivin by IGF-I occurs through a transcriptional mechanism that is mediated in part by the PI3K/Akt/mTORC1 pathway. Use of various Survivin promoter-luciferase constructs revealed that the CDE and CHR response elements in the proximal region of the Survivin promoter are involved in this IGF-I response. Transforming growth factor (TGF-β) signaling antagonists similarly activated the Surivin promoter and rendered cells refractory to further promoter activation by IGF-I. IGF-I suppressed levels of phospho-Smads 2 and 3 with kinetics similar to that of Survivin induction. Suppression of TGF-β signaling, either by TGF-β receptor kinase inhibitors or by silencing Smads 2 and 3, induced Survivin expression and promoted cell growth similar to that induced by IGF-I. TGF-β receptor antagonists also rescued cells from down-regulation of Survivin expression and growth suppression by pharmacological inhibitors of PI3K, Akt, MEK and mTOR. Sh-RNA gene silencing studies suggest that mTORC1 induces while mTORC2 represses the expression of Survivin by IGF-I. Taken together, these results suggest that IGF-I signaling through a PI3K/Akt/mTORC1 mechanism elevates expression of Survivin and promotes growth of prostate epithelial cells by suppressing Smad-dependent autocrine TGF-β signaling.

Abstract 4079: Control of survivin expression by IGF-I in prostate epithelial cells.

Abstract Survivin, a unique member of the inhibitor of apoptosis (IAP) proteins, is overexpressed in numerous cancers through poorly defined mechanisms. We show that insulin-like growth factor-I (IGF-I), which is implicated in the etiology of prostate cancer, induces the expression of Survivin in a variety of pre-neoplastic and malignant prostate cell lines. Using the pre-neoplastic NRP-152 rat prostate cell line as a model, we showed that silencing Survivin by lentiviral-mediated shRNA represses IGF-I-stimulated cell growth, suggesting that the induction of Survivin is critical to this growth response. Moreover, we show that IGF-I induces the expression of Survivin through a transcriptional mechanism that is mediated in part by the PI3K/Akt/mTORC1 pathway. The CDE and CHR response elements in the proximal region of the Survivin promoter are decisive for this IGF-I response. TGF-β signaling antagonists similarly induced this promoter activity and rendered cells refractory to further promoter activation by IGF-I. Suppression of TGF-β signaling, either by TGF-β receptor kinase inhibitors or by silencing Smads 2 and 3, induced Survivin expression and promoted cell growth similar to that induced by IGF-I. TGF-β receptor antagonists also rescued cells from down-regulation of Survivin expression and growth suppression by pharmacological inhibitors of PI3K, Akt, MEK and mTORC1. Sh-RNA gene silencing studies suggest that mTORC1 induces while mTORC2 represses the expression of Survivin. We conclude that IGF-I signaling through a PI3K/Akt/mTORC1-dependent mechanism elevates expression of Survivin and promotes growth of prostate epithelial cells by suppressing Smad-dependent autocrine TGF-β signaling. Citation Format: David Danielpour, Kyung Song, Eswar Shankar, Jiayi Yang, Kara L. Bane. Control of survivin expression by IGF-I in prostate epithelial cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4079. doi:10.1158/1538-7445.AM2013-4079

Pharmacogenomics of insulin-like growth factor-I generation during GH treatment in children with GH deficiency or Turner syndrome

Individual responses to growth hormone (GH) treatment are variable. Short-term generation of insulin-like growth factor-I (IGF-I) is recognized as a potential marker of sensitivity to GH treatment. This prospective, phase IV study used an integrated genomic analysis to identify markers associated with 1-month change in IGF-I (ΔIGF-I) following initiation of recombinant human (r-h)GH therapy in treatment-naïve children with GH deficiency (GHD) (n=166) or Turner syndrome (TS) (n=147). In both GHD and TS, polymorphisms in the cell-cycle regulator CDK4 were associated with 1-month ΔIGF-I (P<0.05). Baseline gene expression was also correlated with 1-month ΔIGF-I in both GHD and TS (r=0.3; P<0.01). In patients with low IGF-I responses, carriage of specific CDK4 alleles was associated with MAPK and glucocorticoid receptor signaling in GHD, and with p53 and Wnt signaling pathways in TS. Understanding the relationship between genomic markers and early changes in IGF-I may allow development of strategies to rapidly individualize r-hGH dose.

IGF-I measurement across blood, interstitial fluid, and muscle biocompartments following explosive, high-power exercise

Insulin-like growth factor-I (IGF-I) resides across different biocompartments [blood, interstitial fluid (ISF), and muscle]. Whether circulating IGF-I responses to exercise reflect local events remains uncertain. We measured the IGF-I response to plyometric exercise across blood, ISF, and muscle biopsy from the vastus lateralis. Twenty volunteers (8 men, 12 women, 22 ± 1 yr) performed 10 sets of 10 plyometric jump repetitions at a 40% 1-repetition maximum. Blood, ISF, and muscle samples were taken pre- and postexercise. Circulating IGF-I increased postexercise: total IGF-I (preexercise = 546 ± 42, midexercise = 585 ± 43, postexercise = 597 ± 45, +30 = 557 ± 42, +60 = 536 ± 40, +120 = 567 ± 42 ng/ml; midexercise, postexercise, and +120 greater than preexercise, P < 0.05); Free IGF-I (preexercise = 0.83 ± 0.09, midexercise = 0.78 ± 0.10, postexercise = 0.79 ± 0.11, +30 = 0.93 ± 0.10, +60 = 0.88 ± 0.10, + 120 = 0.91 ± 0.11 ng/ml; +30 greater than all other preceding time points, P < 0.05). No exercise-induced changes were observed for ISF IGF-I (preexercise = 2.35 ± 0.29, postexercise = 2.46 ± 0.35 ng/ml). No changes were observed for skeletal muscle IGF-I protein, although IGF-I mRNA content increased ∼40% postexercise. The increase in circulating total and free IGF-I was not correlated with increases in ISF IGF-I or muscle IGF-I protein content. Our data indicate that exercise-induced increases in circulating IGF-I are not reflective of local IGF-I signaling.

Growth and IGF-I response of juvenile Nile tilapia (Oreochromis niloticus) to changes in water temperature and dietary protein level

Water temperature and dietary protein level play an important role in influencing the growth and insulin-like growth factor I (IGF-I) in Nile tilapia juveniles. The combined effect of temperature (20–34°C) and dietary protein level (25–50%) on the specific growth rate (SGR), feed efficiency (FE), serum IGF-I level and hepatic IGF-I mRNA level was examined under laboratory conditions by employing central composite design and response surface method. Results showed that the linear effects of temperature and dietary protein level on the SGR, FE, serum IGF-I and hepatic IGF-I mRNA level were significant (P<0.05); the quadratic effects of temperature and dietary protein level on the FE and serum IGF-I were significant (P<0.05). The interaction of temperature and dietary protein level on the FE, serum IGF-I and hepatic IGF-I mRNA level all proved significant (P<0.05). The optimal temperature/dietary protein level combination was determined, i.e., 29.9°C/40.3%, at which the greatest SGR (2.748%/d) and FE (0.775) were simultaneously arrived. Both SGR and FE were linearly correlated with serum IGF-I or hepatic IGF-I mRNA level. These results suggested that optimum combination of temperature and dietary protein level would enhance tilapia growth efficiency and IGF-I would regulate growth and FE.

Measurement of free GH and bioactive IGF-I in non-diabetic haemodialysis patients treated with GH for 7 days

End-stage renal failure (ESRF) patients demonstrate augmented growth hormone (GH) secretion, but normal insulin-like growth factor-I (IGF-I) concentrations, indicating a state of GH resistance. To test this hypothesis, we compared the IGF-I response with exogenous GH in haemodialysis patients and healthy controls, with special focus on free GH and bioactive IGF-I. Ultrafiltered free GH and total GH were measured in serum collected hourly for 24 h at baseline and after 7 days of recombinant human (rh) GH (50 µg/kg/day) treatment in 11 non-diabetic haemodialysis patients and 10 matched controls. Serum levels of bioactive IGF-I (determined by cell-based IGF-I receptor activation assay), total IGF-I and the GH-binding protein (GHBP) were assayed twice daily. At baseline, patients showed elevated total GH (24 ± 5 versus 9 ± 1 µg/L × h, P < 0.02), free GH (21 ± 5 versus 7 ± 1 µg/L × h, P < 0.02), reduced GHBP (1.5 ± 0.3 versus 2.5 ± 0.2 nmol/L, P < 0.01), high-normal total IGF-I (173 ± 18 versus 135 ± 14 µg/L, P = 0.12) and subnormal bioactive IGF-I (2.1 ± 0.3 versus 2.8 ± 0.2 µg/L, P < 0.05) when compared with controls. After 7 days of rhGH treatment, there was a greater GH increase in the non-diabetic haemodialysis patients than in controls (total GH: 293 ± 33 versus 166 ± 13 µg/L × h, P < 0.001; free GH: 284 ± 40 versus 126 ± 15 µg/L × h, P < 0.001). GHB remained unaffected and total IGF-I increased to the same extent in patients and controls (701 ± 87 versus 572 ± 33 µg/L, P = 0.17), whereas bioactive IGF-I tended to be lower in patients (5.37 ± 0.55 versus 6.63 ± 0.25 µg/L, P < 0.10). When adjusting for the actual increments in plasma GH, the ability of exogenous GH to stimulate bioactive IGF-I levels was reduced by ~50% in ESRF (P < 0.02), whereas the response of total IGF-I remained normal (74%; P= 0.18) The study demonstrates that ESRF is associated with markedly elevated serum levels of free GH. Furthermore changes in bioactive, but not immunoreactive, IGF-I indicated that the hepatic sensitivity to GH was reduced by 50% in ESRF patients. Clearly, the physiological importance of our observations awaits further studies, but they suggest that changes in total IGF-I may not necessarily reflect changes in the endogenous activity of IGF-I in ESRF patients on GH treatment.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: A preliminary study

ObjectiveStress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49). DesignFemale soldiers (n=62, 18.8±0.6yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1–6, BAP, calcium, CTx, IL1β, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05). ResultsThe SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58±0.58ng/mL; postBT 0.39±0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53±0.37ng/mL; postBT: 0.63±0.45; p≤0.05). ConclusionsOur study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.

Insulin and IGF-I response to a glucose load in European sea bass ( Dicentrarchus labrax) juveniles

A glucose tolerance test was performed in European sea bass juveniles to evaluate the effect of a glucose load on plasma insulin and insulin-like growth factor-I (IGF-I) levels. Interaction between these hormones, plasma triacylglycerides and liver glycogen was also determined. After being fasted for 48 h, fish were intraperitoneally injected with either 1 g of glucose per kg body weight or a saline solution. Plasma glucose levels peaked at 23–25 mmol l − 1 , 2–6 h after the glucose injection and fish exhibited hyperglycemia until 12 h, when plasma glucose recovered to basal levels. Plasma insulin levels did not change significantly between sampling points, but insulin level was higher in the glucose group than in the control 4–6 h and 24 h after injection. Though plasma IGF-I levels remained constant for a long time (except at time 12 h) in the glucose injected fish, at times 6–9 h, 24 h and 48 h IGF-I levels were higher in the glucose group than in the control. Glucose administration led to lower plasma triacylglyceride levels than saline solution at times 9–12 h. Although liver glycogen content was not affected by the glucose injection (except at times 4 h and 48 h), comparative to saline solution injection, there was a significant increase of liver glycogen at 6 h and 9 h. Results of this study indicate that under these experimental conditions glucose is probably not the most important stimulator of insulin release. Insulin may have contributed to the increase of IGF-I levels and to the enhancement of glucose uptake by the liver in glucose injected fish.

Insulin-like growth factor binding protein-3 levels during early and late follow-up after surgery in acromegalic patients.

Disease activity in acromegaly is accurately reflected by growth hormone (GH) concentration during oral glucose tolerance test (OGTT) and insulin-like growth factor-I (IGF-I) levels, representing an integrated index of GH activity. This prospective study was performed to evaluate whether plasma IGF binding protein 3 (IGFBP-3) might also reflect the hormonal disease activity in pituitary acromegaly after operative treatment during early and late follow-up. Twenty-two acromegalic patients were studied. Data were obtained pre-, intra- and post-operatively in 13 cases. In 9 patients the acromegalic activity was studied only after treatment. The hormonal assessment included repeated blood samples for estimation of IGF-I, IGFBP-3 and repeated OGTTs. In each case 100 sigma g octreotide (Sandostatin lambda, Sandoz, Basel) was injected to test the acute response of GH, IGF-I and IGFBP-3. Intraoperatively, GH levels were estimated to examine acutely the influence of tumour reduction on GH levels. Patients were considered cured when GH levels (GH60min) were less than 2 ng/ml during OGTT 4 weeks after surgery. The data outlined that in patients with normalized GH60min levels, normalized IGFBP-3 levels were noticed 4 weeks and 12 months post-operatively. In non-cured patients normalized IGFBP-3 concentrations were found in 11 out of 15 cases in the late post-treatment phase. In contrast only 1 of 7 cured patients had persistently elevated IGF-I levels within the first month post-operatively, whereas no case of the non-cured patients had IGF-I values in the normal range. Despite these observations a strong correlation of IGF-I and IGFBP-3 did not exist before one year post-operatively -- either in the cured or in the non-cured patients. Serum IGFBP-3 in patients with pituitary acromegaly does not provide a predictive value of appreciable magnitude concerning cure or non-cure from the disease- whether examined early or late in the post-operative period. Absolute levels of IGFBP-3 may thus cause misinterpretation concerning cure of acromegalics after surgery.