Insulin-like growth factor I and calcium balance: evolving concepts of an evolutionary process

The effect of subcutaneous Insulin-like Growth Factor-1 (IGF-1) injection on rabbit auricular cartilage autograft viability

Insulin-like Growth Factor-1 (IGF-1) is one of the significant substances affecting the growth and development of cartilage tissue in the body. The aim of this study is to evaluate the possible histopathological effects of local IGF-1 injection on the viability of rabbit auricular cartilage autografts. To this end, the single-piece and sliced cartilage tissues obtained from 20 albino rabbits' auricula were implanted in the subcutaneous pockets created on the back skins of the experimental animals. Every two weeks IGF-1 (10 mg/ml) injections were performed on the autograft implants of one group and normal saline (0.9%) injections were performed on the other group. Experimental animals were sacrificed at the end of the third month. A total of 34 tissue samples obtained after dissection were evaluated and scored histopathologically according to their cartilage viability, environmental reaction, and regenerative activities. The intergroup evaluation carried out for the single-piece and sliced cartilage grafts revealed that there was statistically more cartilage viability and less foreign-body reaction in the IGF-1 group than the normal saline group (p<0.05). While there was a statistically significant difference between the groups for single-piece grafts regarding regenerative activity (p<0.05), there was no significant difference for sliced grafts. The IGF-1 group, however, showed more activity. The results we obtained point out to the fact that IGF-1 increases the tissue viability of the implanted auricular autograft and it suppresses immune modulation effect.

Evaluation of the bone status in high-level cyclists

The purpose of this study was to evaluate the bone status in highly trained professional cyclists subjected to regular training and tough competitions. Bone mineral density (BMD) was measured at different regions of interest by dual-energy X-ray absorptiometry, and main biological parameters related to bone metabolism were obtained in 29 cyclists. Lumbar BMD was 0.94 ± 0.01g/cm(2) (Z-score=-1.28 ± 0.07), and 1 cyclist out of 4 had an abnormally low value (Z-score <-2). The mean Z-score at the total femoral site was -1.22 ± 0.21, and 45% of athletes had an Z-score of <-2. All femoral neck BMD values were within normal boundaries. The lowest BMD Z-score was measured at the midradius or 1/3 proximal site with a mean Z-score of -1.77 ± 0.78, but only 3 cyclists (15%) had Z-scores <-2. Biochemical parameters of bone formation (serum osteocalcin and alkaline phosphatase) were normal. Three cyclists had low 25-hydroxyvitamin D levels. Blood testosterone and thyroid stimulating hormone were in the normal range. Insulin-like growth factor 1 levels were in the normal range; however, a significant inverse correlation was found with lumbar BMD (r=0.495; p=0.003). We confirm that cycling has no positive effect on BMD, BMD being often lower than in normal controls at the lumbar site; femoral BMD is less concerned. The absence of beneficial changes at the spine can be explained by biomechanical conditions related to the cyclists' position, reducing loading strains. It is necessary to pay greater attention to the bone status of high-level athletes to prevent an increased risk of fractures.

Milk consumption and circulating insulin-like growth factor-I level: a systematic literature review

Studies suggest that the circulating insulin-like growth factor I (IGF-I) level is positively associated with the prostate cancer risk. The association of milk consumption and circulating IGF-I level has been examined in epidemiological studies with inconsistent results. We conducted a systematic literature review to summarize and quantify the current evidence for milk or dairy product consumption and the circulating IGF-I level. We searched relevant papers published in English up to March 2009 in various databases. Fifteen cross-sectional studies and eight randomized controlled trials were finally identified. Ten cross-sectional studies showed statistically positive correlation between milk consumption and the circulating IGF-I level. Randomized controlled trials indicated that the circulating IGF-I level was significantly higher in the milk intervention group. After meta-analysis, the weighted mean difference of the circulating IGF-I level was 13.8 ng/ml (95% confidence interval: 6.1-21.5 ng/ml) comparing the intervention group with the control group. The current evidence suggests that milk consumption may increase the circulating IGF-I level.

Development of a neurotoxic equivalence scheme of relative potency for assessing the risk of PCB mixtures

PCBs produce adverse effects in humans and animals by several modes of action. The first mode of action is binding of coplanar or mono-ortho-PCBs to the aryl hydrocarbon (Ah) receptor leading to effects associated with the activation of this receptor. The remaining PCB congeners do not activate this receptor and have different modes of action underlying their toxic effects. One mode of action that has been shown for di-ortho-substituted non-coplanar PCBs (PCB congeners with two or more chlorines in the ortho-positions) is the interference with intracellular signaling pathways dependent on Ca(2+) homeostasis and the resulting cellular, organ-level and organismal effects. The ortho-substituted non-coplanar congeners produce other cellular or organ-level effects including changes in protein kinase C translocation, changes in cellular dopamine (DA) uptake, formation of reactive oxygen species, and thyroid effects. Here, we propose a scheme for developing relative potency estimates (REP) for the PCB congeners not considered in the TEF scheme used to assess the toxicity of coplanar and mono-ortho-PCBs and chlorinated dioxins and furans. Because a number of the modes of action listed here for the ortho-substituted non-coplanar PCB congeners have been implicated in the neurotoxic effects of these PCBs congeners, this relative potency scheme is referred to here as the Neurotoxic Equivalent (NEQ) scheme for estimating toxicity of PCB mixtures. The Neurotoxic Equivalent (NEQ) values are developed in a way similar in concept to the derivation of the well-known TEF congener values. Although this scheme is in its infancy and the set of NEQ values are limited by the current data, there are several compelling reasons for proposing such a scheme now. First, it should open discussions as to how different modes of action can be utilized to predict congener potency differences for the effects they produce. Second, consideration and evaluation of the ability of the proposed NEQ scheme to predict the toxicity of PCB mixtures will assist in the identification of the specific modes of action relevant to the effects produced by non-coplanar PCBs. If other modes of action are suggested and subsequently identified, then other schemes of relative potency could be developed specifically for those modes of action, distinct from either the TEF scheme or the NEQ scheme. Knowing these other modes of action and the relative toxicity of the various congeners would advance our understanding of PCB toxicology and thereby ultimately improve our ability to estimate the toxic potency of PCB mixtures for each identified mode of action. Third, a quantitative scheme for assessing the toxicity of the non-coplanar PCB congeners present in a mixture has the potential to improve significantly future risk assessments of PCB mixtures.

Resolving the Two "Bony" Faces of PPAR-gamma

Bone loss with aging results from attenuated and unbalanced bone turnover that has been associated with a decreased number of bone forming osteoblasts, an increased number of bone resorbing osteoclasts, and an increased number of adipocytes (fat cells) in the bone marrow. Osteoblasts and adipocytes are derived from marrow mesenchymal stroma/stem cells (MSC). The milieu of intracellular and extracellular signals that controls MSC lineage allocation is diverse. The adipocyte-specific transcription factor peroxisome proliferator-activated receptor-gamma (PPAR-gamma) acts as a critical positive regulator of marrow adipocyte formation and as a negative regulator of osteoblast development. In vivo, increased PPAR-gamma activity leads to bone loss, similar to the bone loss observed with aging, whereas decreased PPAR-gamma activity results in increased bone mass. Emerging evidence suggests that the pro-adipocytic and the anti-osteoblastic properties of PPAR-gamma are ligand-selective, suggesting the existence of multiple mechanisms by which PPAR-gamma controls bone mass and fat mass in bone.

What's new with PTH in osteoporosis: where are we and where are we headed?

A new era in osteoporosis management began with the recent approval of parathyroid hormone (PTH) for postmenopausal and idiopathic osteoporosis treatment. Intermittent PTH dramatically increases spine bone mineral density and significantly reduces fragility fractures. However, the skeletal response to PTH varies greatly and there are few large scale, randomized, placebo-controlled trials in conditions such as glucocorticoid-induced osteoporosis. Moreover, the mechanisms of PTH action are complex, involving multiple pathways linked to common signaling peptides regulating osteoblast gene transcription. In addition, important interactions between osteoclasts and osteoblasts are activated by PTH. This review presents recent findings on PTH signaling in bone and discusses how they could be used to design randomized trials and establish clinical practice guidelines for this novel anabolic peptide.