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Physical activity may reduce the risk of developing breast cancer via its effect on the insulin/insulin-like growth factor (IGF) signaling system. A systematic review searched for randomized controlled trials (RCT), Mendelian randomization and prospective cohort studies that examined the effects of physical activity on insulin/IGF signaling [IGFs, their binding proteins (IGFBP), and markers of insulin resistance] in adult women. Meta-analyses were performed to generate effect estimates. Risk of bias was assessed, and the Grading of Recommendations Assessment, Development, and Evaluation system used to determine the overall quality of the evidence. Fifty-eight RCTs met our inclusion criteria, no observational or Mendelian randomization studies met the criteria for inclusion. Meta-analyses indicated that physical activity interventions (vs. control) reduced fasting insulin, the Homeostatic Model Assessment for Insulin Resistance and fasting glucose. Physical activity increased IGF-1, but there was no clear effect on IGFBP-3 or the ratio of IGF-1:IGFBP-3. Strong evidence was only established for fasting insulin and insulin resistance. Further research is needed to examine the effect of physical activity on C-peptide and HBA1c in women. Reductions in fasting insulin and insulin resistance following exercise suggest some biological plausibility of the first part of the physical activity-insulin/IGF signaling-breast cancer pathway. See related article by Drummond et al., p. 2116.

Brown bears conserve muscle and bone mass during 6 mo of inactive hibernation. The molecular mechanisms underlying hibernation physiology may have translational relevance for human therapeutics. We hypothesize that protective mechanisms involve increased tissue availability of insulin-like growth factors (IGFs). In subadult Scandinavian brown bears, we observed that mean plasma IGF-1 and IGF-2 levels during hibernation were reduced to 36 ± 10% and 56 ± 15%, respectively, compared with the active state (n = 12). Western ligand blotting identified IGF-binding protein (IGFBP)-3 as the major IGFBP in the active state, whereas IGFBP-2 was codominant during hibernation. Acid labile subunit (ALS) levels in hibernation were reduced to 41±16% compared with the active state (n = 6). Analysis of available grizzly bear RNA sequencing data revealed unaltered liver mRNA IGF-1, IGFBP- 2, and IGFBP-3 levels, whereas ALS levels were significantly reduced during hibernation (n = 6). Reduced ALS synthesis and circulating levels during hibernation should prompt a shift from ternary IGF/IGFBP/ALS to smaller binary IGF/IGFBP complexes, thereby increasing IGF tissue availability. Indeed, size-exclusion chromatography of bear plasma demonstrated a shift to lower molecular weight IGF-containing complexes in the hibernating versus the active state. Furthermore, we note that the major IGF-2 mRNA isoform expressed in livers in both Scandinavian brown bears and grizzly bears was an alternative splice variant in which Ser29 is replaced with a tetrapeptide possessing a positively charged Arg residue. Homology modeling of the bear IGF-2/ IGFBP-2 complex showed the tetrapeptide in proximity to the heparin-binding domain involved in bone-specific targeting of this complex. In conclusion, this study provides data which suggest that increased IGF tissue availability combined with tissue-specific targeting contribute to tissue preservation in hibernating bears.

Physical activity may reduce the risk of developing breast cancer via its effect on the insulin/insulin-like growth factor (IGF) signaling system. A systematic review searched for randomized controlled trials (RCT), Mendelian randomization and prospective cohort studies that examined the effects of physical activity on insulin/IGF signaling [IGFs, their binding proteins (IGFBP), and markers of insulin resistance] in adult women. Meta-analyses were performed to generate effect estimates. Risk of bias was assessed, and the Grading of Recommendations Assessment, Development, and Evaluation system used to determine the overall quality of the evidence. Fifty-eight RCTs met our inclusion criteria, no observational or Mendelian randomization studies met the criteria for inclusion. Meta-analyses indicated that physical activity interventions (vs. control) reduced fasting insulin, the Homeostatic Model Assessment for Insulin Resistance and fasting glucose. Physical activity increased IGF-1, but there was no clear effect on IGFBP-3 or the ratio of IGF-1:IGFBP-3. Strong evidence was only established for fasting insulin and insulin resistance. Further research is needed to examine the effect of physical activity on C-peptide and HBA1c in women. Reductions in fasting insulin and insulin resistance following exercise suggest some biological plausibility of the first part of the physical activity–insulin/IGF signaling–breast cancer pathway. See related article by Drummond et al., p. 2116

ObjectiveChanges observed during adult GH deficiency (GHD) are most often reversed with the administration of recombinant human GH (rhGH). To avoid daily injections, a long-acting GH molecule has been obtained by covalent binding of polyethylene glycol (PEG) with rhGH (PEG–GH), allowing weekly s.c. injections. This study was designed to assess its efficacy and safety, in adult GHD subjects.Design and methodsThis was a randomized, double-blind, placebo-controlled, multiple-dose, parallel group study. Subjects were recruited from 34 centers. A total of 105 subjects with GHD were assigned a treatment. They received 6 weekly injections of either PEG–GH or placebo. Subjects were randomized into one out of four treatment groups (Groups A–D) or placebo (Group E). Groups A, B, and C received 1, 3, and 4 mg PEG–GH respectively, for the first 3 weeks followed by 2, 6, and 8 mg PEG–GH respectively, for the remaining 3 weeks. Group D received 4 mg PEG–GH for 6 weeks. Group E received placebo. The study was suspended because of the development of lipoatrophy in certain subjects and restarted with an injection rotation plan, before being terminated due to further subjects developing lipoatrophy.ResultsA total of 13 cases of injection-site lipoatrophy were reported, of which ten were in females and three occurred after the first injection; all cases were independent of PEG–GH dose or IGF1 levels, either basal or under treatment.ConclusionThe unpredictable occurrence of injection-site lipoatrophy with weekly long-acting pegylated GH molecules may be a limiting factor for their development.

Most children born small for gestational age (SGA) normalize their size through spontaneous catch-up growth within the first 2 yr after birth. Some SGA children fail to do so and maintain an abnormally short stature throughout childhood. We have previously reported that high dose GH treatment (66 or 100 microg/kg x day s.c. over 2 yr; age at start, 2-8 yr; n = 38) induces pronounced catch-up growth in short children born SGA, thereby normalizing their height and weight in childhood. Here, we report on the further prepubertal growth course of these children over the first 4 yr after withdrawal of early, high dose GH treatment. Of the 38 treated children, none developed precocious puberty, and 22 remained prepubertal. Mean age of the latter at start of GH was 4.4 yr, height was -3.7 SD score, and height after adjustment for midparental height was -2.9 SD score. Height increased by an average of 2.5 SD during the 2 yr of GH treatment and decreased by 0.4 and 0.3 SD, respectively, during the first and second year after GH withdrawal. Subsequently, when stature was not extremely short at the start (mean adjusted height SD score, -2.7; n = 13), no further GH treatment was given, and the adjusted height was stabilized around -1.0 SD score; when stature was very short at the start (mean adjusted height, -3.3 SD score; n = 9), a second course of GH treatment (66 microg/kg x day s.c.) was initiated either 2 yr (n = 5) or 3 yr (n = 4) after initial GH withdrawal. This second course was associated with renewed catch-up growth and also resulted in a mean adjusted height of -1.0 SD score. In each subgroup, the pattern of the weight course paralleled that of the height course; GH treatment was well tolerated. In conclusion, early, discontinuous, high dose GH treatment appears to be a safe and efficient option to normalize prepubertal height and weight in the majority of short SGA children. It remains to be examined whether the normalized stature will be maintained during pubertal development, either with or without further GH treatment.