Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

Development and single laboratory validation of a targeted liquid chromatography-triple quadrupole mass spectrometry-based method for the determination of insulin like growth factor-1 in different types of milk samples

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Bovine insulin growth factor 1 (IGF-1) was estimated in different cow milk samples.

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In house validation of a LC-MS/MS IGF-1 investigation method in milks obtained by different technological treatments.

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Development of a sample treatment for the extraction of IGF-1 from different types of cow milk.

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IGF-1 level in cow’s milk was not dependent form milk technological processing.

A simple and reliable targeted liquid chromatography-electrospray-tandem mass spectrometry (LC-MS/MS) method was developed and validated through the selection of two biomarker peptides for the identification and determination of bovine insulin like growth factor-1 (IGF-1) in milk samples. Two urea-based sample extraction procedures were tested. The validation results provided detection limits at the 1–5 ng IGF-1/mL level as a function of the milk matrix, precision ranged from 3 to 8% and the method accuracy in the different milk matrices was assured. Finally, IGF-1 was measured in milk samples obtained by treatment with eleven different technological processes: IGF-1 concentrations were spread over a wide range from 11.2 ± 0.3 ng/mL to 346 ± 8 ng/mL with a median of 57.0 ± 0.2 ng/mL. The highest amount of IGF-1 was found in fresh whole milk samples and no significant correlation was found between the total milk protein content and the IGF-1 concentration level.

Effect of growth factors on proliferation of normal, borderline, and malignant breast epithelial cells

Growth factors play an important role in the development and growth regulation of normal breast. They are also known to be autocrine or paracrine stimulators of breast cancer cells. However, their role on cells of proliferative breast disease has not been studied so far. This study was undertaken to quantitate the proliferative effect of various growth factors on "normal," borderline, and malignant breast epithelial cells. For this purpose, epithelial cell lines of histologically normal human breast and histologically proven proliferative breast diseases were established. Cell lines MCF-7 and T47D were used as malignant cells. The growth factors under study include epidermal growth factor, fibroblast growth factors acidic and basic, platelet-derived growth factor, and insulin-like growth factors 1 (IGF-1) and 2 (IGF-2). Their proliferative effect was determined by incubating the cells with growth factors for 24 h after achieving basal conditions in serum-free medium for 72 h, followed by quantitating the S-phase fraction by flow cytometry. All of the growth factors were found to be capable of inducing cellular proliferation on the entire range of mammary epithelia. Epidermal growth factor was consistently found to be a potent mitogen. Fibroblast growth factor acidic had a higher effect compared to fibroblast growth factor basic in inducing the cells to move from G(0)/G(1) to S-phase. Platelet-derived growth factor had a moderate proliferative response. In the family of insulin-like growth factors, IGF-1 was the dominant mitogen for normal cells and IGF-2 was the dominant proliferative stimulus for the cell line MCF-7. In the cell lines of proliferative breast disease and T47D, both were at par as mitogenic agents. These results suggest that the cells of proliferative breast disease develop some of the biological characteristics of malignancy.

Limited proteolysis of the IGF binding protein-2 (IGFBP-2) by a specific serine protease activity in early breast milk

IGF in milk possibly promote maturation of the gastrointestinal tract in newborns. We studied the composition of milk samples derived from 99 healthy women at regular intervals during a period beginning 3 d and ending 6 mo after birth. The concentrations measured by RIA on d 3 were 10.7+/-0.4 ng/mL for IGF-II, 1.9+/-0.1 ng/mL for IGF-I, 100+/-5 ng/mL for IGF binding protein-3 (IGFBP-3), and 2163+/-108 ng/mL for IGFBP-2. All factor concentrations decreased by up to 70% in the course of the 6 mo. The most striking finding was an IGFBP-2-specific protease activity. Protease assays performed by incubation of 125I-IGFBP-2 with milk yielded fragments of 14, 16, 23, and 25 kD. 125I-IGFBP-3 was not cleaved. Proteolysis occurred only in milk from mothers until 4 wk postpartum and could be visualized by immunoblots. Since the affinity of the fragments to 125I-IGF-II was low, they were not demonstrable by ligand blot. Inhibitor studies and pH optimizing classified the IGFBP-2 protease as an Me2(+)-dependent serine protease with a pH optimum of 7 to 8. The proteolytic activity of further milk proteins, known as IGFBP proteases, was analyzed. Epidermal growth factor receptor peptide and prostate-specific antigen did not cleave IGFBP-2, although the protease activity correlated (r = 0.84, p < 0.00003) with the prostate-specific antigen concentration in milk. The y-nerve growth factor cleaved 125I-IGFBP-2, but in a completely different manner than the milk protease. In conclusion, the IGFBP-2 protease in milk is most probably a kallikrein. The specific proteolysis of IGF/IGFBP-2 complexes may increase the biologic availability of IGF in early milk. This mechanism may promote growth of the maternal breast epithelium and maturation of the gastrointestinal tract of newborns.

Dairy products and breast cancer: the IGF-I, estrogen, and bGH hypothesis

Research on the role of dietary factors in breast cancer causation has focused predominantly on fat intake. While some studies have examined associations between breast cancer rates and consumption of whole milk, there has been less attention given to dairy products in general. Dairy products contain both hormones and growth factors, in addition to fat and various chemical contaminants, that have been implicated in the proliferation of human breast cancer cells. This literature review evaluates the epidemiological and mechanistic evidence linking dairy consumption with breast cancer risk.

Insulin-like growth factors in milk and mammary gland

Milk contains insulin-like growth factor I and II (IGF-I and IGF-II) and four IGF binding proteins (IGFBP). Their concentrations are highest prepartum and early postpartum, coinciding with maximal proliferation of mammary cells and the time when the infant gut is the least developed. This has lead to the suggestion that IGFs may be important for the growth and development of the mammary gland and that IGFs in milk play a role in promoting development of the gastrointestinal tract of the newborn. IGF-I and, to a lesser extent, IGF-II can stimulate milk yield and blood flow in goats when infused directly into the mammary gland, suggesting they may also be important in supporting established lactation. Thus IGFs may have a dual function in the mammary gland, establishing and maintaining the maternal mammary system and, once secreted into milk, supporting gastrointestinal development in the newborn.

The ontogeny of serum insulin-like growth factor-I concentration in foals: effects of dam parity, diet, and age at weaning

The effects of dam parity, age at weaning, and preweaning diet were examined in the ontogeny of serum insulin-like growth factor-I (IGF-I) concentrations in foals. Foals born to 13 primiparous and 19 multiparous draft-cross mares were weighed and bled near birth. About one-half of the foals in each group were weaned early (about 13 wk old); the remaining foals were weaned late (about 16 wk of age). Pooled values for serum IGF-I concentrations between birth and 17 wk of age were higher (P < 0.065) for foals born to multiparous (386 ng/ml) than to primiparous mares (237.5 ng/ml). Colts (378 ng/ml) had higher (P < 0.05) serum IGF-I concentrations than fillies (254.5 ng/ml), regardless of dam parity. Colts (173.5 kg) also tended (P = 0.12) to be heavier than fillies (159.2 kg). Weaning, whether at 13 or 16 wk of age, reduced (P < 0.05) growth rates and serum IGF-I concentrations. Serum IGF-I values recovered to preweaning values within 1-3 wk postweaning concurrent to an improved weight gain. Fifteen 1-d-old foals in a second study were fed milk replacer for 7 wk and were compared with five foals that nursed their mares for 8 wk. During the first 2 wk, replacer-fed foals (0.46 kg/d) did not gain as rapidly (P < 0.03) as mare-nursed foals (1.73 kg/d). The associated serum IGF-I values for replacer foals (139.4 ng/ml) were lower (P < 0.0001) than values for mare-nursed foals (317.4 ng/ml). Despite similarity in gains for both groups there-after, serum IGF-I concentrations of replacer-fed foals were only 36 and 60% of values obtained for mare-nursed foals at 8 (weaning) and 18 wk of age, respectively. The intrinsic differences between mare-nursed and milk-replacer foals in serum IGF-I concentrations persisted to 1 yr of age despite similarities in dietary management and body weight of the foals. At 1 yr of age, the serum IGF-I concentration of mare-nursed foals (1,203 ng/ml) was 48% higher than that of replacer-fed foals (815 ng/ml). These data indicate that dam parity, sex of foal, and preweaning nutrition affect the ontogeny of serum IGF-I concentration in the foal. The chronic, persistent difference in serum IGF-I values created by the early nutritional management of growing animals has implications in the interpretation of longitudinal serum IGF-I studies in all species.

A comparison of hormone levels in follicle-lutein-cysts and in normal bovine ovarian follicles

Insulin-like growth factors 1 and 2 (IGF-1 and 2), oxytocin, progesterone, estradiol and ubiquitin were measured in bovine follicle-lutein-cysts and in follicular fluid after the classification of ovarian follicles by size (Class I = <4 mm; Class II = 5-8 mm; Class III = 9-12 mm; Class IV = preovulatory; Class V = cystic). It was found that IGF-1 concentrations increased during growth from 280 ng/ml in small follicles to 489 ng/ml in preovulatory follicles; IGF-2 appeared to remain constant in follicular fluid and in cysts (275 ng/ml). Oxytocin values were low in Class I, II and III follicles (30 pg/ml) but increased in preovulatory and cystic follicles (75 pg/ml). Estradiol increased significantly only in preovulatory follicles. Ubiquitin, a protein reflecting cellular replicative activity, could be found in bovine follicular fluid in high concentrations: 1.6 mug/ml in Class I,II and III follicles with the highest amounts in preovulatory follicles (2.3 mug/ml). In contrast with normal follicles, cysts were found to have a minimal concentration of ubiquitin (0.3 mug/ml). Progesterone levels were 5 times higher in cysts (325 ng/ml) and IGF-1 concentrations were markedly higher in cystic follicles (881 ng/ml) than in the other follicles. Simultaneously, maximum gene expression for IGF-1 was found in granulosa/lutein cells of cystic follicles (Class V), suggesting de novo synthesis of IGF-1. Between the different follicle classes progesterone, oxytocin and IGF-1 concentrations correlated positively (r=0.82). Hormonal levels in follicle-lutein-cysts indicated an arrested stage of insufficient luteinization as a possible result from the premature release of LH or from the release of amounts of LH inadequate to cause ovulation.