Dietary monounsaturated fat in early life regulates IGFBP2: implications for fat mass accretion and insulin sensitivity

Nano Chromium Picolinate Improves Gene Expression Associated with Insulin Signaling in Porcine Skeletal Muscle and Adipose Tissue

Simple Summary

Dietary chromium has been shown to reduce fat deposition and improve insulin action whereas dietary fat can increase fat deposition and cause insulin resistance. This study found that dietary nanoparticles of chromium picolinate, an organic form of chromium, caused changes in the genes involved in insulin action in both muscle and fat tissue that indicated improved insulin action. Conversely, a moderate increase in dietary fat caused changes consistent with increased fat deposition and reduced insulin action. In conclusion, nanoparticles of chromium picolinate offer a means of supplementing pigs diets to improve growth performance and carcass composition.

Abstract

The aim of this study was to investigate the interactive effects of dietary nano chromium picolinate (nCrPic) and dietary fat on genes involved in insulin signaling in skeletal muscle and subcutaneous adipose tissue of pigs. Forty-eight gilts were stratified on body weight into four blocks of four pens of three pigs and then within each block each pen was randomly allocated to four treatment groups in a 2 × 2 factorial design. The respective factors were dietary fat (22 or 57 g/kg) and dietary nCrPic (0 or 400 ppb nCrPic) fed for six weeks. Skeletal muscle samples were collected from the Longissimus thoracis and subcutaneous adipose tissue collected from above this muscle. Dietary nCrPic increased adiponectin, uncoupling protein 3 (UCP3) and serine/threonine protein kinase (AKT) mRNA expression, whereas dietary fat decreased adiponectin and increased leptin, tumor necrosis factor-α (TNF-α), peroxisome proliferator-activated receptors γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα) mRNA expression in adipose tissue. In skeletal muscle, dietary nCrPic increased phosphatidylinositol 3 kinase (PI3K), AKT, UCP3 and interleukin-15 (IL-15), as well as decreased suppressor of cytokine signaling 3 (SOCS3) mRNA expression. The improvement in insulin signaling and muscle mass and the reduction in carcass fatness by dietary nCrPic may be via decreased SOCS3 and increased UCP3 and IL-15 in skeletal muscle and increased adiponectin in subcutaneous adipose tissue.

Serum IGFBP-2 levels are associated with reduced insulin sensitivity in obese children

Insulin-like growth factor binding protein 2 (IGFBP-2) may represent a critical link between body composition and insulin sensitivity. We investigated the relationship between circulating IGFBP-2 levels, body composition, insulin sensitivity, energy intake and physical activity in children with obesity. Children were recruited via the Weight Management Service at the Royal Children's Hospital, Melbourne, as part of the Childhood Overweight BioRepository of Australia (COBRA). Comprehensive anthropometric, biochemical and environmental data were collected and compared to serum IGFBP-2 levels (measured by enzyme-linked immunosorbent assay). Multiple regression modelling was used to assess the influence of circulating IGFBP-2 levels on anthropometric and biochemical measures. One hundred and ninety-four children were included in this study (46% male). Circulating IGFBP-2 negatively correlated with age, anthropometric measures, blood pressure and insulin concentration. Positive associations were observed between insulin sensitivity index-homeostasis model assessment (ISI-HOMA) and serum IGFBP-2. In multiple regression modelling, IGFBP-2 significantly contributes to variance in systolic blood pressure (-19%, P < 0.05), circulating triglycerides (-16%, P < 0.05) and ISI-HOMA (18%, P < 0.05). No associations were observed between dietary energy intake or physical activity and IGFBP-2 levels. Circulating IGFBP-2 levels in children with obesity correlate inversely with body mass and markers of metabolic dysfunction, and positively with insulin sensitivity. These findings suggest that reduced levels of IGFBP-2 may play an important role in the pathogenesis of obesity complications in early life.

The Role of the Growth Hormone/Insulin-Like Growth Factor System in Visceral Adiposity

There is substantial evidence that the growth hormone (GH)/insulin-like growth factor (IGF) system is involved in the pathophysiology of obesity. Both GH and IGF-I have direct effects on adipocyte proliferation and differentiation, and this system is involved in the cross-talk between adipose tissue, liver, and pituitary. Transgenic animal models have been of importance in identifying mechanisms underlying these interactions. It emerges that this system has key roles in visceral adiposity, and there is a rationale for targeting this system in the treatment of visceral obesity associated with GH deficiency, metabolic syndrome, and lipodystrophies. This evidence is reviewed, gaps in knowledge are highlighted, and recommendations are made for future research.

Effects of nutritional manipulation on body composition in the developing marsupial, Macropus eugenii

When 60-day-old tammar wallaby pouch young (Macropus eugenii) are fostered to mothers at 120 days of lactation, their growth, developmental rate and maturation of their GH/IGF axes are markedly accelerated. To determine the effect of fostering on energy intake, body composition and fat accretion, we first measured total body fat and lean mass in these young. Next, we mimicked the triglyceride oleic and palmitic acid composition of 120-day milk by supplementing 60 day young with these fatty acids and comparing their growth with that of growth accelerated young. There was no difference in the weight or growth axis maturation of supplemented young but there was significantly more body fat in these and in the growth-accelerated fostered young than in controls. We conclude that the accelerated growth and GH/IGF axis maturation observed previously in fostered young is most likely due to increased milk consumption and earlier access to specific nutrients.

Childhood obesity: Current and novel approaches

The prevalence of childhood obesity has increased over the last fifty years by approximately 5% per decade, and approximately a quarter of all children are now either overweight or obese. These children have a significantly increased risk of many future health problems including adult obesity, type 2 diabetes and heart disease. Despite this relentless increase, common-sense approaches aimed at prevention and treatment have failed to solve the problem. Current approaches at prevention have faced major challenges with some progress in implementing smaller scale programs and social marketing, but little action on broad public policy approaches which often appears unpalatable to society or individual governments. Meanwhile, treatment approaches have mainly focused on lifestyle change, and novel approaches are urgently needed. Prevention needs to shift to improving maternal health prior to conception, with more research focussed on the impact of early years in programming offspring to future overweight/obesity. Likewise, treatment paradigms need to move from simply thinking that obesity can be solved by readdressing diet and activity levels. Novel approaches are needed which take into consideration the complex physiology which regulates early childhood growth and the development of obesity in susceptible individuals.

IGFBP-2 - taking the lead in growth, metabolism and cancer

The activity of the Insulin-like Growth Factors (IGFs) ligands elicited via their receptors and transduced by various intracellular signal pathways is modulated by the IGF Binding Proteins (IGFBPs). Among all the IGFBPs, IGFBP-2 has been implicated in the regulation of IGF activity in most tissue and organs. Besides binding to IGFs in the circulation these IGF-regulatory activities of IGFBP-2 involve interactions with components of the extracellular matrix, cell surface proteoglycans and integrin receptors. In addition to these local peri-cellular activities, IGFBP-2 exerts other key functions within the nucleus, where IGFBP-2 directly or indirectly promotes transcriptional activation of specific genes. All of these IGFBP-2 activities, intrinsic or dependent on IGFs, contribute to its functional roles in growth/development, metabolism and malignancy as evidenced by studies in IGFBP-2 animal models and also by many in vitro studies. Finally, preclinical studies have demonstrated that IGFBP-2 administration can be beneficial in improving metabolic responses (inhibition of adipogenesis and enhanced insulin sensitivity), while blockade of IGFBP-2 appears to be an effective approach to inhibiting tumour growth and metastasis.

Dietary chromium picolinate of varying particle size improves carcass characteristics and insulin sensitivity in finishing pigs fed low- and high-fat diets

The aim of the present study was to evaluate the effect of the different-sized particles of chromium (Cr) picolinate (CrPic) and dietary fat on growth performance, carcass traits and insulin sensitivity of finishing pigs. Ninety-six Large White × Landrace gilts were stratified on bodyweight, housed in pens of three pigs and then, on a pen basis, randomly allocated to eight treatment groups in a 2 × 4 factorial design for 6 weeks. The respective factors were dietary fat (2.2% or 5.7%) and dietary CrPic (0 mg/kg, 400 mg/kgnormal-size CrPic, 400 mg/kg 1-μm CrPic (μCrPic), or 400 mg/kg 100-nm CrPic (nCrPic)). Over the first 21 days, average daily gain (ADG) was increased by dietary CrPic (0.94 vs 1.01 kg/day, P = 0.021), although there was no difference (P = 0.17) between the CrPic particle sizes. High dietary fat also increased ADG over this period (0.96 vs 1.03 kg/day, P = 0.013). However, the responses to both dietary CrPic and fat diminished over time and so there was no effect of CrPic (P = 0.35) or fat (P = 0.93) on ADG over the full 42 days. Dietary CrPic increased carcass weight and muscle depth and decreased P2 backfat. Furthermore, dietary Cr decreased plasma insulin (7.66 vs 5.09 mU/L, P = 0.018) and the homeostatic model assessment (1.25 vs 0.82, P = 0.009), indicating an improvement in insulin sensitivity. In conclusion, dietary Cr can increase ADG and improve carcass traits and insulin sensitivity in lean pigs. There were few differences among particle sizes, possibly because the response to dietary CrPic may already be maximised at 400 mg/kg.

Leptin enhances insulin sensitivity by direct and sympathetic nervous system regulation of muscle IGFBP-2 expression: evidence from nonrodent models

Leptin is produced from white adipose tissue and acts primarily to regulate energy balance. Obesity is associated with leptin resistance and increased circulating levels of leptin. Leptin has recently been shown to influence levels of IGF binding protein-2 (IGFBP-2), a protein that is reduced in obesity and type 2 diabetes. Overexpression of IGFBP-2 protects against obesity and type 2 diabetes. As such, IGFBP-2 signaling may represent a novel pathway by which leptin regulates insulin sensitivity. We sought to investigate how leptin regulates skeletal muscle IGFBP-2 levels and to assess the impact of this on insulin signaling and glucose uptake. In vitro experiments were undertaken in cultured human skeletal myotubes, whereas in vivo experiments assessed the effect of intracerebroventricular leptin on peripheral skeletal muscle IGFBP-2 expression and insulin sensitivity in sheep. Leptin directly increased IGFBP-2 mRNA and protein in human skeletal muscle through both signal transducer and activator of transcription-3 and phosphatidylinositol 3-kinase signaling, in parallel with enhanced insulin signaling. Silencing IGFBP-2 lowered leptin- and insulin-stimulated protein kinase B phosphorylation and glucose uptake. In in vivo experiments, intracerebroventricular leptin significantly increased hind-limb skeletal muscle IGFBP-2, an effect completely blocked by concurrent peripheral infusion of a β-adrenergic blocking agent. Sheep receiving central leptin showed improvements in glucose tolerance and circulating insulin levels after an iv glucose load. In summary, leptin regulates skeletal muscle IGFBP-2 by both direct peripheral and central (via the sympathetic nervous system) mechanisms, and these likely impact on peripheral insulin sensitivity and glucose metabolism.