The effects of retinoic acid on the insulin-like growth factor axis in primary tissue culture from hyperparathyroidism

Role of growth factors on human parathyroid adenoma cell proliferation

INTRODUCTION

Primary hyperparathyroidism (pHPT) is caused by a single monoclonal adenoma in more than 80% of patients. Biomolecular mechanisms causing pHPT are still not completely known, even if a great amount of studies have been developed recently, mainly regarding angiogenesis and growth factors. Among the latter, insulin-like growth factor 1 (IGF-1), basic fibroblastic growth factor (bFGF), vascular endothelial growth factor (VEGF), and transforming growth factor beta 1 (TGF-beta1) and their effects have been extensively evaluated in different kinds of endocrine disease.

METHODS

Parathyroid cell cultures were prepared from six human adenomatous parathyroid glands that were surgically removed. After 7 days of culture, the cells were refed with DMEM supplemented with 2% FCS alone (control group), or containing hrTGFbeta1, or hrIGF-I, or hrbFGF, or hrVEGF. Then, after 48-hour incubation, cell count was performed by a particle count and size analyzer, and prevalence of cell cycle was analyzed by using a flow cytometer.

RESULTS

Cell count (x10000) in the control group was 3.73 +/- 0.32. Low-dose TGF-beta1 stimulation resulted in 5.25 +/- 0.38 cells, and high-dose TGF-beta1 stimulation resulted in 2.35 +/- 0.37 cells. IGF-1 stimulation resulted in 5.4 +/- 0.65 cells, bFGF stimulation in 5.68 +/- 0.86 cells, and VEGF stimulation resulted in 6.03 +/- 1.03 cells. Statistical analysis revealed significant differences in the control group compared with the growth factor-stimulated groups. Cytometry showed different results in the percentage of cells in S-phase, in particular 22.65 +/- 4.98% of IGF-1-stimulated cells were found in S-phase compared with 7.55 +/- 3.2% of control group cells (p < 0.0001).

CONCLUSIONS

Growth factors seem to play an important role in parathyroid adenoma cell proliferation; IGF-1, bFGF, VEGF, and low-dose TGF-beta1 promote cell proliferation, whereas high-dose TGF-beta1 inhibits these phenomena.

Opposite effects of glucagon and insulin on compensation for spectacle lenses in chicks

PURPOSE

Chick eyes compensate for the defocus imposed by positive or negative spectacle lenses. Glucagon may signal the sign of defocus. Do insulin (or IGF-1) and glucagon act oppositely in controlling eye growth, as they do in metabolic pathways and in control of retinal neurogenesis?

METHODS

Chicks, wearing lenses or diffusers or neither over both eyes, were injected with glucagon, a glucagon antagonist, insulin, or IGF-1 in one eye (saline in the other eye). Alternatively, chicks without lenses received insulin plus glucagon in one eye, and either glucagon or insulin in the fellow eye. Ocular dimensions, refractive errors, and glycosaminoglycan synthesis were measured over 2 to 4 days.

RESULTS

Glucagon attenuated the myopic response to negative lenses or diffusers by slowing ocular elongation and thickening the choroid; in contrast, with positive lenses, it increased ocular elongation to normal levels and reduced choroidal thickening, as did a glucagon antagonist. Insulin prevented the hyperopic response to positive lenses by speeding ocular elongation and thinning the choroid. In eyes without lenses, both insulin and IGF-1 speeded, and glucagon slowed, ocular elongation, but glucagon and insulin each increased the rate of thickening of the crystalline lens. When injected together, insulin blocked choroidal thickening by glucagon, at a dose that did not, by itself, thin the choroid.

CONCLUSIONS

Glucagon and insulin (or IGF-1) cause generally opposite modulations of eye growth, with glucagon mostly increasing choroidal thickness and insulin mostly increasing ocular elongation. These effects are mutually inhibitory and depend on the visual input.