Changes in profiles of circulating insulin-like growth factor components during hormone replacement therapy according to the responsiveness to therapy in postmenopausal women

Differential effects of various progestogens on metabolic risk factors for breast cancer

Biological and epidemiological findings suggest that metabolic factors - insulin, insulin-like growth factor-I (IGF-I) and sex hormone-binding globulin (SHBG) - are involved in the development and promotion of breast cancer. Estrogens, particularly if administered orally, counteract metabolic factors that increase breast cancer risk, i.e. they reduce insulin and IGF-I and increase SHBG. This could contribute toward explaining epidemiological data showing that unopposed oral estrogens do not increase breast cancer risk, or do so only modestly. In contrast to natural progesterone and progesterone-derived progestins, progestins endowed with androgenic (or glucocorticoid) activity negatively influence these metabolic factors, counteracting the favorable effects of estrogens. While most biological and epidemiological findings suggest that natural progesterone does not augment breast cancer risk, available data show an increased risk with synthetic progestins - with the possible exception of progesterone-derived dydrogesterone. Different mechanisms for different progestins could possibly be involved. Differences from progesterone with regard to pharmacokinetics and pharmacodynamics, potency, interaction with the two isoforms of the progesterone receptor, and binding to other steroid receptors could all be relevant. These remain theoretical speculations for the time being, but the possibility that some progestins increase breast cancer risk through their negative influence on metabolic factors cannot be rejected.

The effects of sex steroid replacement therapy on an expanded panel of IGF-related peptides

BACKGROUND

Oral estrogen alone (EA) decreases concentrations of total IGF-I while increasing IGFBP-1, but data on other IGF-related peptides are inconsistent and/or sparse. Combined oral estrogen and progestin (EP) may have differential effects on IGF-related peptides dependent on its progestin-associated androgenic activity. The aim of this study was to clarify these relationships, as circulating IGF-related peptides are potential surrogates of predisposition to common chronic diseases.

DESIGN

Using an open-labelled cross-sectional design within a bowel cancer screening trial (aged 55-64 years), we determined total IGF-I, IGF-II, IGFBP-2 and IGFBP-3 in fasted serum from 210 healthy women and free IGF-I (by ultrafiltration), insulin, IGFBP-1 and IGFBP-1:IGF-I binary complex in a selected subset of 92 women. Unadjusted and adjusted (using generalized linear models) means were compared.

RESULTS

Among EA users, mean concentrations for total IGF-I (adjusted P=0.004) and free IGF-I (P<0.001) were reduced, whereas mean concentrations of IGFBP-1 (P=0.001) and binary complex (P=0.01) were increased compared with non-users. Taken as a whole group, EP use was not associated with differences in concentrations of IGF-related peptides, but on sub-group analyses, mean concentrations associated with the use of progestins with reduced androgenic activity reflected the use of EA. By contrast, mean IGFBP-2 concentrations were significantly reduced among both EA (P=0.008) and EP (P=0.002) users, irrespective of androgenic activity. Neither EA nor EP influenced mean concentrations of IGF-II, insulin and IGFBP-3.

CONCLUSIONS

The uses of oral sex steroid replacements are associated with significant changes in several IGF-related analytes in a preparation-specific manner, suggesting different regulatory mechanisms. However, the directions of these changes do not fit simple correlative models of predisposition to common diseases.

The relationship among serum insulin-like growth factor-I, insulin-like growth factor-I gene polymorphism, and bone mineral density in postmenopausal women in Korea

OBJECTIVE

The objective of this study was to test the hypothesis that the cytosine-adenine polymorphism in the insulin-like growth factor-I gene is associated with serum insulin-like growth factor-I levels and bone mineral density.

STUDY DESIGN

The insulin-like growth factor-I cytosine-adenine polymorphism was analyzed in 300 postmenopausal Korean women. Serum insulin-like growth factor-I, bone alkaline phosphatase, and carboxy-terminal cross-linking telopeptide of type I collagen were measured by immunoradiometric assay and enzyme-linked immunosorbent assay. Bone mineral density at the lumbar spine and proximal femur was determined by dual energy radiograph absorptiometry.

RESULTS

Serum insulin-like growth factor-I and bone mineral density levels in women who were homozygous for a 194-base pair allele were significantly higher than those levels in the 194-base pair heterozygotes or women who did not possess the 194-base pair allele. A significantly decreased prevalence of the 194/194 genotype was observed in the combined group of women with osteopenia and osteoporosis, compared with normal women. No correlation between insulin-like growth factor-I genotypes and bone turnover markers was found.

CONCLUSION

The insulin-like growth factor-I gene cytosine-adenine polymorphism relates with circulating insulin-like growth factor-I levels and bone mineral density at the lumbar spine and proximal femur.