Growth factors in asymptomatic osteoarthritis - insulin, insulin-like growth factor-1, growth hormone

Effects of GH/IGF axis on bone and cartilage

Growth hormone (GH) and its mediator, the insulin-like growth factor-1 (IGF-1) regulate somatic growth, metabolism and many aspects of aging. As such, actions of GH/IGF have been studied in many tissues and organs over decades. GH and IGF-1 are part of the hypothalamic/pituitary somatotrophic axis that consists of many other regulatory hormones, receptors, binding proteins, and proteases. In humans, GH/IGF actions peak during pubertal growth and regulate skeletal acquisition through stimulation of extracellular matrix production and increases in bone mineral density. During aging the activity of these hormones declines, a state called somatopaguss, which associates with deleterious effects on the musculoskeletal system. In this review, we will focus on GH/IGF-1 action in bone and cartilage. We will cover many studies that have utilized congenital ablation or overexpression of members of this axis, as well as cell-specific gene-targeting approaches used to unravel the nature of the GH/IGF-1 actions in the skeleton in vivo.

Role of the Growth Hormone/Insulin-like Growth Factor-1 Paracrine Axis in Rheumatic Diseases

OBJECTIVES

Hypothalamic-pituitary axis abnormalities have been associated with systemic disturbances in several rheumatic diseases. Longitudinal analysis of erythrocyte, serum, urinary and synovial fluid growth hormone (GH), insulin-like growth factor-1 (IGF-1), and somatostatin levels could provide important surrogate measures of disease activity in rheumatic diseases.

METHODS

The authors reviewed the population and longitudinal studies literature on GH, IGF-1, and somatostatin levels in rheumatic disorders using the PubMed and Medlines databases from the National Library of Medicine. In addition to the literature search, primary data were analyzed for basal somatostatin levels in patients with hand, knee, and spine osteoarthritis (OA) as well as primary and secondary hip OA.

RESULTS

A review of the literature supports the view that hypothalamic-pituitary axis dysfunction accompanies clinical symptoms in many rheumatic diseases. In studies from our laboratory, serum GH levels were elevated in patients with OA, rheumatoid arthritis (RA), fibromyalgia, and diffuse idiopathic skeletal hyperostosis but not in patients with gout, pseudogout, or systemic lupus erythematosus. In OA and RA, synovial fluid GH levels exceeded serum GH levels. However, the literature remains controversial regarding the significance of changes in IGF-1 levels in rheumatic disorders. Many studies support an inverse relationship between age and IGF-1. Elevated serum GH levels in various rheumatic diseases were not coupled to changes in serum IGF-1 in diffuse idiopathic skeletal hyperostosis, RA, and fibromyalgia. In particular, serum IGF-1 levels in OA were shown to be lower or no different compared with age-matched normal subjects. Further, in OA, impaired articular chondrocyte response to IGF-1 was attributed, in part, to low synovial fluid IGF-1 that further compromised IGF-1 chondrocyte responses as a result of increased levels of synovial fluid IGF-1 binding proteins. Of note, serum somatostatin levels and "specific" somatostatin receptor levels were often lower in RA and systemic lupus erythematosus, but basal serum somatostatin levels were generally not altered in OA.

CONCLUSIONS

The results of these analyses support the view that some rheumatic diseases such as OA and diffuse idiopathic skeletal hyperostosis, heretofore considered to be purely focal and degenerative, could be reclassified as systemic metabolic disturbances. We propose that serum GH, IGF-1, and somatostatin levels be monitored on a longitudinal basis during the course of medical therapy of rheumatic diseases to determine the extent to which changes in clinical symptoms (exemplified by reduced pain and inflammation and improved range of joint motion) are accompanied by changes in the basal concentration of these hypothalamic/pituitary-related hormones.

Age-related changes in serum growth hormone, insulin-like growth factor-1 and somatostatin in system lupus erythematosus

BACKGROUND

Systemic lupus erythematosus is an age- and gender-associated autoimmune disorder. Previous studies suggested that defects in the hypothalamic/pituitary axis contributed to systemic lupus erythematosus disease progression which could also involve growth hormone, insulin-like growth factor-1 and somatostatin function. This study was designed to compare basal serum growth hormone, insulin-like growth factor-1 and somatostatin levels in female systemic lupus erythematosus patients to a group of normal female subjects.

METHODS

Basal serum growth hormone, insulin-like growth factor-1 and somatostatin levels were measured by standard radioimmunoassay.

RESULTS

Serum growth hormone levels failed to correlate with age (r2 = 3.03) in the entire group of normal subjects (i.e. 20 - 80 years). In contrast, serum insulin-like growth factor-1 levels were inversely correlated with age (adjusted r2 = 0.092). Of note, serum growth hormone was positively correlated with age (adjusted r2 = 0.269) in the 20 - 46 year range which overlapped with the age range of patients in the systemic lupus erythematosus group. In that regard, serum growth hormone levels were not significantly higher compared to either the entire group of normal subjects (20 - 80 yrs) or to normal subjects age-matched to the systemic lupus erythematosus patients. Serum insulin-like growth factor-1 levels were significantly elevated (p < 0.001) in systemic lupus erythematosus patients, but only when compared to the entire group of normal subjects. Serum somatostatin levels differed from normal subjects only in older (i.e. >55 yrs) systemic lupus erythematosus patients.

CONCLUSIONS

These results indicated that systemic lupus erythematosus was not characterized by a modulation of the growth hormone/insulin-like growth factor-1 paracrine axis when serum samples from systemic lupus erythematosus patients were compared to age- matched normal female subjects. These results in systemic lupus erythematosus differ from those previously reported in other musculoskeletal disorders such as rheumatoid arthritis, osteoarthritis, fibromyalgia, diffuse idiopathic skeletal hyperostosis and hypermobility syndrome where significantly higher serum growth hormone levels were found. Somatostatin levels in elderly systemic lupus erythematosus patients may provide a clinical marker of disease activity in these patients.

Serum growth hormone and insulin but not insulin-like growth factor-1 levels are elevated in patients with fibromyalgia syndrome

Standard radioimmunoassay (RIA) was employed to quantify basal serum growth hormone (GH), insulin-like growth factor-I (IGF-1), and insulin levels in 32 normoglycemic patients with clinically active fibromyalgia and in 29 normoglycemic control subjects. The GH concentration was significantly higher (P < 0.001) in female fibromyalgia patients than age-matched, normal female subjects. In contrast, basal serum IGF-1 concentrations did not differ between these groups. A scatter plot generated from two-stage, least-squares analysis showed that serum GH lacked correlation with the serum IGF-1 concentrations of normal female subjects (P = 0.73) and female fibromyalgia patients (P = 0.19). In addition to the results from serum GH and IGF-1 RIA, we also found significantly higher fasting serum insulin levels (P = 0.03) in male fibromyalgia patients and a trend toward elevated fasting serum insulin levels in the female fibromyalgia population ( P = 0.07), with the mean fasting level in the male fibromyalgia group (35.7 microU/ml(-1)) exceeding the upper limit of normal serum insulin levels (i.e., 27 microU/ml(-1)). Based on these results, basal serum GH and fasting serum insulin levels appear to be valuable surrogate markers in clinically active, normoglycemic fibromyalgia patients.

Growth factors, insulin-like growth factor-1 and growth hormone, in synovial fluid and serum of patients with rheumatic disorders

OBJECTIVE

Synovial fluid (SF) plays an important role in joint function. We evaluated the growth factors, insulin-like growth factor-1 (IGF-1) and growth hormone (GH) in SF and serum from patients with osteoarthritis (OA), rheumatoid arthritis (RA), gout, pseudogout and diffuse idiopathic skeletal hyperostosis (DISH).

DESIGN

Standard radioimmunoassay techniques were used to measure concurrent levels of IGF-1 and GH. SF samples and serum samples were obtained concomitantly from 27 patients with OA, 22 patients with RA, nine men with gout, 14 patients with pseudogout and eight men with DISH.

RESULTS

In the case of IGF-1, a comparison of serum and SF levels shows that SF levels of IGF-1 are lower than serum levels in all groups. Men and women gave similar values. In contrast, in the case of GH, all groups, except males with RA, had higher GH values in SF when compared with serum values. Individual patients with other forms of arthritis demonstrated similar relationships.

CONCLUSION

The finding that IGF-1 is present in levels about one-half as great in SF as compared with serum suggests that IGF-1 may be produced in lesser amounts or is utilized by the patient in customary joint function. The finding that GH is present in SF at values twice as high, or more, of serum levels in inflammatory arthritides suggests that GH may play a role in the pathophysiology of arthritic disorders.

Local disruption of the insulin-like growth factor system in the arthritic joint

OBJECTIVE

To identify differences in levels of insulin-like growth factor (IGF) and IGF binding proteins (IG-FBPs) between 30 patients with arthritis (14 with rheumatoid arthritis [RA], 16 with osteoarthritis [OA]) and 11 normal control subjects. IGF and IGFBP levels were correlated to the disease activity marker C-reactive protein (CRP) to determine whether they were disease related. We also examined the degree of proteolytic modification of the IGFBPs.

METHODS

Radioimmunoassays were used for measuring IGF and IGFBP-3 levels; CRP was measured by enzyme-linked immunosorbent assay. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western blotting, chemiluminescence, and autoradiography were used for visualizing binding proteins.

RESULTS

There was a significant increase in synovial fluid levels of both IGF-1 and IGFBP-3 in both RA and OA. This resulted in an elevated IGFBP-3 to IGF molar ratio of 1.49 in the OA group and 1.47 in the RA group, compared with 0.86 in the normal control group (P = 0.0002 for both). A significantly lower degree of IGFBP-3 proteolysis was also seen in the synovial fluids from the patients compared with the controls. There were significant correlations between the CRP level and levels of IGF-1, IGF-2, and IGFBP-3 in the RA patients (r = 0.62-0.898, P = 0.04-0.0007).

CONCLUSION

There was significant local disruption of the IGF system in patients with arthritis. This may result in a lower amount of IGF that is able to bind to IGF receptors in the arthritic joint. Levels of IGF-1 IGF-2, and IGFBP-3 all correlated with the CRP level in patients with RA, which indicates the possibility that the IGF system is involved in the disease process.