Insulin-like growth factors and their receptors in normal physiology and pathological states

Effects of Resistance and Endurance Training Alone or Combined on Hormonal Adaptations and Cytokines in Healthy Children and Adolescents: A Systematic Review and Meta-analysis

BACKGROUND

No previous systematic review has quantitatively compared the effects of resistance training, endurance training, or concurrent training on hormonal adaptations in children and adolescents. Objective was to examine the effects of exercise training and training type on hormonal adaptations in children and adolescents.

METHODS

A systematic literature search was conducted in the following databases: PubMed, Web of Science, and EBSCO. Eligibility criteria were: population: healthy youth population sample (mean age < 18 years); intervention: resistance training, endurance training, or concurrent training (> 4 weeks duration); comparison: control group; outcome: pre- and post-levels of hormones and cytokines; and study design: randomized and non-randomized controlled trials. We used a random-effect model for the meta-analysis. The raw mean difference in hormones from baseline to post-intervention was presented alongside 95% confidence intervals (CI). Further, the certainty of evidence quality and the risk of bias were assessed.

RESULTS

A total of 3689 records were identified, of which 14 studies were eligible for inclusion. Most studies examined adolescents with fewer studies on children (age < 12 years, N = 5 studies) and females (N = 2 studies). Nine exercise training programs used endurance training, five studies used resistance training, and no eligible study used concurrent training. The meta-analysis showed no significant effect of exercise training on testosterone (MD = 0.84 nmol/L), cortisol (MD = - 17.4 nmol/L), or SHBG (MD = - 5.58 nmol/L). Subgroup analysis showed that resistance training significantly increased testosterone levels after training (MD = 3.42 nmol/L) which was not observed after endurance training (MD = - 0.01 nmol/L). No other outcome differed between training types. Exercise training resulted in small and non-significant changes in GH (MD = 0.48 ng/mL, p = 0.06) and IGF-I (MD = - 22.90 ng/mL, p = 0.07). GH response to endurance training may be age-dependent and evident in adolescents (MD = 0.59 ng/mL, p = 0.04) but not when children and adolescents are pooled (MD = 0.48 ng/mL, p = 0.06). Limited evidence exists to conclude on IL-6 and TNF-α effects of exercise training. Assessments of GRADE domains (risk of bias, consistency, directness, or precision of the findings) revealed serious weaknesses with most of the included outcomes (hormones and cytokines).

CONCLUSIONS

This systematic review suggests that exercise training has small effects on hormonal concentrations in children and adolescents. Changes in testosterone concentrations with training are evident after resistance training but not endurance training. GH's response to training may be affected by maturation and evident in adolescents but not children. Further high-quality, robust training studies on the effect of resistance training, endurance training, and concurrent training are warranted to compare their training-specific effects.

REGISTRATION

PROSPERO: CRD42021241130.

Aging Regulated Through a Stability Model of Insulin/Insulin Growth Factor Receptor Function

Mutations of the insulin-like receptor in Drosophila extend lifespan. New research suggests this receptor operates in two modes. The first extends lifespan while slowing reproduction and reducing growth. The second strongly extends lifespan without impairing growth or reproduction; it confers longevity assurance. The mutation that confers longevity assurance resides in the kinase insert domain, which contains a potential SH2 binding site for substrate proteins. We apply a recent model for the function of receptor tyrosine kinases to propose how insulin receptor structure can modulate aging. This concept hypothesizes that strong insulin-like ligands promote phosphorylation of high threshold substrate binding sites to robustly induce reproduction, which impairs survival as a consequence of trade-offs. Lower levels of receptor stimulation provide less kinase dimer stability, which reduces reproduction and extends lifespan by avoiding reproductive costs. Environmental conditions that favor diapause alter the expression of insulin ligands to further repress the stability of the interacting kinase domains, block phosphorylation of low threshold substrates and thus induce a unique molecular program that confers longevity assurance. Mutations of the insulin receptor that block low-phosphorylation site interactions, such as within the kinase insert domain, can extend lifespan while maintaining overall dimer stability. These flies are long-lived while maintaining reproduction and growth. The kinase insert domain of Drosophila provides a novel avenue from which to seek signaling of the insulin/insulin-like growth factor system of humans that modulate aging without impacting reproduction and growth, or incurring insulin resistance pathology.

The IGF-Trap: Novel Inhibitor of Carcinoma Growth and Metastasis

The IGFI receptor promotes malignant progression and has been recognized as a target for cancer therapy. Clinical trials with anti-IGFIR antibodies provided evidence of therapeutic efficacy but exposed limitations due in part to effects on, and the compensatory function of, the insulin receptor system. Here, we report on the production, characterization, and biologic activity of a novel, IGF-targeting protein (the IGF-Trap) comprising a soluble form of hIGFIR and the Fc portion of hIgG1. The IGF-Trap has a high affinity for hIGFI and hIGFII but low affinity for insulin, as revealed by surface plasmon resonance. It efficiently blocked IGFIR signaling in several carcinoma cell types and inhibited tumor cell proliferation, migration, and invasion in vitro. In vivo, the IGF-Trap showed favorable pharmacokinetic properties and could suppress the growth of established breast carcinoma tumors when administered therapeutically into tumor-bearing mice, improving disease-free survival. Moreover, IGF-Trap treatment markedly reduced experimental liver metastasis of colon and lung carcinoma cells, increasing tumor cell apoptosis and reducing angiogenesis. Finally, when compared with an anti-IGFIR antibody or IGF-binding protein-1 that were used at similar or higher concentrations, the IGF-Trap showed superior therapeutic efficacy to both inhibitors. Taken together, we have developed a targeted therapeutic molecule with highly potent anticancer effects that could address limitations of current IGFIR-targeting agents.

Crosstalk between IGF1R and estrogen receptor signaling in breast cancer

After the discovery that depriving certain breast tumors of estrogen promoted tumor regression, therapeutic strategies aimed at depriving tumors of this hormone were developed. The tumorigenic properties of estrogen are regulated through the estrogen receptor-alpha (ER), making understanding the mechanisms that activate this receptor highly relevant. In addition to estrogen activating the ER, other growth factor pathways, such as the insulin-like growth factors (IGFs), can activate the ER. This review will examine the interaction between these two pathways. Estrogen can activate the growth stimulatory properties of the IGF pathway via ER's genomic and non-genomic functions. Further, blockade of ER function can inhibit IGF-mediated mitogenesis and blocking IGF action can inhibit estrogen stimulation of breast cancer cells. Collectively, these observations suggest that the two growth regulatory pathways are tightly linked and a more thorough understanding of the mechanism of this crosstalk could lead to improved therapeutic strategies in breast cancer.

Endogenous anabolic hormone responses to endurance versus resistance exercise and training in women

Research in exercise endocrinology has flourished over the past few decades. In general, research examining short- and long-term hormone responses to endurance exercise preceded studies on resistance exercise, and research on women lagged behind research on men. Sufficient data are now available to allow a comparison of endogenous anabolic hormone responses to endurance versus resistance exercise and training in women. Circulating levels of testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulphate, estradiol, growth hormone and cortisol have been shown to increase in response to an acute bout of endurance exercise in women. However, only growth hormone, estradiol and cortisol have been reported to increase following resistance exercise. Hormone changes following training, either endurance or resistance, have been variable, probably because of differences in experimental design and major differences in the length, intensity and volume of training programmes. With the notable exception of growth hormone, the anabolic hormones reviewed here appear to decline with endurance training. Resistance training has little effect on resting hormone levels, except insulin-like growth factor-I, which has been shown to increase following a training programme. These hormone changes potentially have both metabolic and hypertrophic implications, and future research needs to focus on the biological significance of these adaptations.

Serum Insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3) in growing preterm infants on enteral nutrition

We analyzed the range of serum concentrations of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) and their inter-relationships with age and some parameters of nutritional and hormonal status in 46 growing preterm infants on enteral nutrition. 72 nutritional balances were performed, with a cross-sectional study design, at a mean age of 35.3 +/- 17.2 days, equivalent to a mean corrected age (gestational + postnatal age) of 36 +/- 2.3 weeks. Serum concentrations of IGF-I (mean 64 +/- 36 ng/ml) and IGFBP-3 (mean 1.15 +/- 0.53 mg/l) correlated significantly with each other (r = 0.46) and both correlated with body weight (r = 0.43 and 0.34), body length (r = 0.44 and 0.36) and serum concentrations of prealbumin, apolipoprotein A and cholesterol. IGF-I also correlated with urinary excretion of C-peptide (r = 0.32). There was a weak correlation between IGFBP-3 and postnatal age (r = 0.36) but no correlation between IGF-I and IGFBP-3 and correlated age or urinary excretion of growth hormone. In growing preterm infants, at least until 40 weeks of corrected age, serum concentrations of IGF-I and IGFBP-3 seem to be related principally to body weight, body length and nutritional factors, but not to growth hormone.