Insulin-like growth factor II promoter expression in cultured rodent osteoblasts and adult rat bone

Skeletal actions of insulin-like growth factors

Insulin-like growth factors (IGFs) promote longitudinal growth and display anabolic effects in adult bone by acting through endocrine and autocrine/paracrine mechanisms. Binding of IGF-I to its specific tyrosine-kinase receptor leads to interaction with the intracellular proteins, insulin receptor substrate-1 and -2, and the activation of distinct intracellular signaling pathways. In cartilage, IGF-I regulates the differentiation of chondrocytes and stimulates the synthesis of components of the extracellular matrix. In bone tissue, IGF-I increases the function of the differentiated osteoblasts and mediates selected anabolic actions of parathyroid hormone. Genetically modified mice, in which selected components of the IGF system were targeted in a tissue-specific fashion, have documented that circulating IGF-I is essential for physiological skeletal growth and adult bone remodeling and that local autocrine/paracrine IGF-I activities are required for optimal trabecular bone mass and mineralization. Studies in humans have indicated a correlation between serum IGF-I levels and bone mineral density. However, there is little information on the use of IGF-I in patients with metabolic bone disease.

L-carnitine and isovaleryl L-carnitine fumarate positively affect human osteoblast proliferation and differentiation in vitro

Age-related bone loss is characterized by decreased osteoblast activity, possibly related to the reduction of energy production. Carnitine promotes energy availability and its concentration declines with age; Therefore, two Carnitine derivatives, L-carnitine fumarate (LC) and isovaleryl L-carnitine fumarate (Iso-V-LC), have been tested on several parameters of human osteoblasts in vitro. Both compounds significantly increased osteoblast activity, but the new compound Iso-V-LC was more efficient than LC at lower concentrations. They both significantly enhanced cell proliferation, [3H]-proline incorporation and the expression of collagen type I (COLLI), and the bone sialoproteins (BSPs) and osteopontin (OPN). The percentage of alkaline phosphatase (ALP)-positive cells and the secretion of osteocalcin were not modified by LC and Iso-V-LC. Both molecules increased the formation of mineralized nodules, but Iso-V-LC reached the maximum effect at a concentration 10-fold lower than that of LC. Furthermore, we showed that insulin-like growth factor (IGF)-I and IGF-II mRNA levels were not modified by the treatment. However, the two compounds induced an increase of insulin-like growth factor binding protein (IGFBP)-3 and a decrease of IGFBP-5 in both osteoblast lysates and the extracellular matrix (ECM). In conclusion these data suggest that carnitine and, in particular, its new derivative, Iso-V-LC supplementation in the elderly may stimulate osteoblast activity and decrease age-related bone loss.

Role of Activated Growth Factors in Lumbar Spinal Fusions

BACKGROUND

The concentration of platelets into an activated growth factor (AGF) gel may stimulate graft consolidation into a fusion mass. Preoperative hemodilution and intraoperative clot activation may also reduce the overall blood loss. Consequently, the need for postoperative transfusions may also be reduced.

OBJECTIVE

The objective of this work was to report our experience with AGF platelet gels in transforaminal lumbar interbody fusion (TLIF) procedures.

METHODS

A consecutive series of patients between 1996 and 1999 undergoing one- and two-level TLIFs with AGF were compared with a consecutive series of TLIF patients who did not receive AGF. Sixty-two control subjects who did not receive AGF and 22 patients who received an AGF platelet gel were compared after 41 and 34 months of follow-up, respectively.

RESULTS

On average, the AGF group required 18 minutes of additional preincision anesthesia (P = 0.0001). No statistical differences in the operative times, estimated blood loss, postoperative drainage, percentage of patients requiring a transfusion, or length of hospitalization were appreciated between the two groups. The 19% decrease in the arthrodesis rate of the AGF group, as compared with the control group, did not reach statistical significance. Platelet counts from the AGF platelet concentrates demonstrated an average 3.5-fold increase compared with preoperative serum levels.

CONCLUSIONS

The theoretical benefits of AGF platelet gel technology were not clinically appreciated. The cost of implementing this technology may therefore outweigh its theoretical benefits.

Inhibition of proliferation in human MNNG/HOS osteosarcoma and SK-ES-1 Ewing sarcoma cell lines in vitro and in vivo by antagonists of growth hormone-releasing hormone: effects on insulin-like growth factor II

BACKGROUND

Antagonists of growth hormone-releasing hormone (GH-RH) can inhibit the proliferation of various tumors either indirectly through the suppression of the pituitary growth hormone/hepatic insulin-like growth factor I (IGF-I) axis and the lowering of serum IGF-I concentration or directly by reducing the levels of IGF-I and IGF-II and their mRNA expression in tumors and blocking the effect of autocrine GH-RH. In this study, the authors investigated the effects of the GH-RH antagonist JV-1-38 on MNNG/HOS human osteosarcoma and SK-ES-1 human Ewing sarcoma cell lines.

METHODS

Male nude mice bearing subcutaneous xenografts of MNNG/HOS or SK-ES-1 tumors were treated subcutaneously with JV-1-38 at a dose of 20 microg twice daily for 4 weeks. The concentrations of IGF-I and IGF-II in serum and in tumor tissue were measured by radioimmunoassay. Tumor and liver levels of mRNA for IGF-I and IGF-II were determined by reverse transcriptase-polymerase chain reaction analysis. The effects of JV-1-38, IGF-I, and IGF-II on cell proliferation in vitro were evaluated.

RESULTS

GH-RH antagonist significantly (P < 0.05) inhibited the tumor volume and tumor weight of MNNG/HOS and SK-ES-1 tumors by > 50% after 4 weeks and increased tumor doubling time. JV-1-38 lowered the serum IGF-I level, decreased the expression of mRNA for IGF-I in the liver, and significantly (P < 0.05-0.01) reduced the concentration of IGF-II and mRNA levels for IGF-II in both sarcomas. The concentration of IGF-I was lowered only in SK-ES-1 tumors. In vitro, the proliferation of SK-ES-1 and MNNG/HOS cells was inhibited by JV-1-38 and by antisera to IGF-I and IGF-II.

CONCLUSIONS

The inhibition of MNNG/HOS osteosarcoma and SK-ES-1 Ewing sarcoma by GH-RH antagonists was linked to a suppression of IGF-II production in tumors. However, in SK-ES-1 tumors, the effects on IGF-I also may be involved.

Osteoinductive molecules in orthopaedics: basic science and preclinical studies

Osteoinductive molecules are characterized by their ability to promote the formation of bone. Most osteoinductive molecules are cytokines, which are extracellular proteins or peptides that mediate cell to cell signaling. Examples of osteoinductive cytokines are certain bone morphogenetic proteins and some growth and differentiation factors. Some osteoinductive molecules are not secreted molecules. LIM mineralization protein-1 is an example of an intracellular osteoinductive molecule. Significant advances have been made in characterizing the molecular composition and mechanism of action of these osteoinductive molecules. Preclinical studies with these molecules have provided better understanding of the doses, formulation, and delivery mechanism necessary for effective bone formation in model systems of spinal fusion and other orthopaedic problems. The current authors will review the most important basic science and preclinical studies involving these osteoinductive molecules.

Transcriptional regulation of connective tissue growth factor by cortisol in osteoblasts

Glucocorticoids have important effects on osteoblastic function. Connective tissue growth factor (CTGF)/insulin-like growth factor binding protein-related protein 2 (IGFBP-rP2) plays a role in cell adhesion and function. We examined the regulation of CTGF/IGFBP-rP2 synthesis in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). Cortisol caused a time- and dose-dependent increase in CTGF/IGFBP-rP2 mRNA levels in Ob cells. Cycloheximide did not preclude the effect, indicating that it was not protein synthesis dependent. Cortisol increased the rate of CTGF/IGFBP-rP2 transcription and, in transcriptionally arrested Ob cells, did not modify the decay of the transcript. Parathyroid hormone decreased, whereas transforming growth factor-beta and, to a lesser extent, bone morphogenetic protein 2 increased CTGF/IGFBP-rP2 mRNA levels, but other hormones and growth factors had no effect. In conclusion, cortisol stimulates CTGF/IGFBP-rP2 transcription in Ob cells. Because CTGF/IGFBP-rP2 binds IGFs, its increased expression could be relevant to the actions of cortisol in bone.

Cortisol inhibits hepatocyte growth factor/scatter factor expression and induces c-met transcripts in osteoblasts

Hepatocyte growth factor/scatter factor (HGF/SF) is expressed by osteoblasts and has important effects on repair and bone remodeling. Because glucocorticoids regulate these two functions, we tested the effects of cortisol on the expression of HGF/SF and c-met, the protooncogene encoding the HGF/SF receptor, in cultures of osteoblast-enriched cells from 22-day fetal rat calvariae (Ob cells). Cortisol decreased HGF/SF mRNA levels and diminished the induction of HGF/SF transcripts by fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor BB (PDGF BB). Cortisol also decreased FGF-2 and PDGF BB-induced HGF/SF mRNA and polypeptide levels in MC3T3 cells. In contrast, cortisol enhanced the expression of c-met transcripts in Ob cells. Cortisol did not modify the half-life of HGF/SF or of c-met mRNA in transcriptionally arrested cells, and it increased the rate of transcription of c-met. In conclusion, cortisol decreases HGF/SF transcripts in Ob cells and enhances c-met expression transcriptionally. The effects of cortisol on HGF/SF could be relevant to its inhibitory actions on bone formation and repair.