ABSTRACT

Oestradiol-17β hydroxysteroid dehydrogenase (E2DH) is present in normal and malignant breast tissues and also in cultured breast cancer cells. It can act in a reductive direction to convert oestrone to the biologically active oestrogen, oestradiol, or in an oxidative direction to metabolize oestradiol to oestrone and may therefore have a crucial role in regulating breast tissue concentrations of oestradiol. Insulin-like growth factor-type I (IGF-I) and IGF-II are both mitogens for breast cancer cells. In this study we have examined the effect of these growth factors on the reductive and oxidative activities of E2DH in MCF-7 (receptor positive) and MDA-MB-231 (receptor negative) breast cancer cells. Both IGF-I (80 ng/ml) and IGF-II (80 ng/ml) significantly stimulated E2DH reductive activity (up to 138%) in MCF-7 cells but had no effect on oxidative activity. Addition of IGF-II (100 ng/ml) to MDA-MB-231 cells resulted in a small but statistically significant (p<0.05) increase in E2DH reductive activity (18%) but in these cells reductive activity is 25-70 times lower than oxidative activity. If IGF-I and IGF-II act to stimulate E2DH reductive activity in breast tumours then such a mechanism could account for the increased concentrations of oestradiol detected in breast tumours.

The role of the antioxidant defense system during endometrial receptivity, a phenomenon crucial for implantation and decidualization, and the effect of ormeloxifene, a selective estrogen receptor modulator, were investigated in the guinea pig, a laboratory mammalian species with interstitial implantation and a long functional luteal phase during each estrous cycle. A sharp rise in the activity of superoxide dismutase (SOD) in both antimesometrial (AM) and mesometrial segments and peroxidase in the AM segment of the uterus was observed on the day of maximal endometrial receptivity. Pretreatment with ormeloxifene resulted in loss of endometrial responsiveness, as evidenced by inhibition of trauma-induced decidualization and the activity of ornithine decarboxylase, a marker of tissue growth and repair. This was associated with a decrease in SOD and estradiol dehydrogenase activities, with corresponding increases in estrone dehydrogenase activity and stimulation of uterine luminal epithelial cell height and a distension of the uterine and glandular lumen. A decrease in peroxidase activity was observed only in the AM segment of the uterus on the imminent day of maximal endometrial receptivity. No effect on peripheral plasma progesterone concentration or surface ultrastructure was evident. These findings demonstrate that SOD plays an important role, with peroxidase having a supplementary role, in the first line of defense against superoxide anion radicals during the period of maximal endometrial receptivity in the guinea pig. Inhibition of endometrial receptivity and decidualization by ormeloxifene administered during the pre-receptive phase appears to be due to a depressed antioxidant defense system via dysregulation of redox-sensitive signaling, resulting in altered cellular toxicity due to increased superoxide radicals, and might contribute to the contraceptive action of ormeloxifene. This might be related to its estrogen antagonistic activity and/or decreased bioavailability of estradiol at a cellular level due to its increased metabolism to biologically less-active estrone via activation of estradiol-17 beta-hydroxysteroid dehydrogenase and suppression of estrone-17 beta-hydroxysteroid dehydrogenase.

ABSTRACT

This study aimed at determining the relationship of sex steroids, particularly in the perinatal period, to the pubertal insulin-like growth factor-I (IGF-I) surge in male mice. We used hypogonadal (hpg) mice, which have a major deletion in the gonadotrophin-releasing hormone (GnRH) gene, in order to have a model lacking all GnRH-induced gonadotrophin and sex steroid secretion throughout pre- and postnatal life. Cross-sectional data on body weights and weights of testes, seminal vesicles, kidneys, liver and spleen from 9 to 77 days of age were obtained in male hpg, heterozygous (Hz) and homozygous normal (N/N) littermates (n = 75–78/group). These data did not reveal any difference between Hz and N/N mice. Hpg mice had decreased body weights which by 70–77 days of age were approximately 18% less than normal controls. Testes and seminal vesicles of hpg mice did not demonstrate any significant postnatal growth. Relative to body weight, kidney weights were also markedly reduced in hpg mice (P<0·0001), deviating significantly from normal by 28–35 days of age, reflecting the impact of androgen deficiency on a non-reproductive organ. From the cross-sectional data it was concluded that puberty commenced soon after weaning (21 days) in the male and that maturity was achieved within 4–5 weeks. Longitudinal study showed that, compared with normal controls, untreated hpg mice had an exaggerated pubertal IGF-I surge (P<0·005) which peaked in mid-puberty. This, together with their reduced body weights (P<0·05), were normalized by treatment from 21 to 70 days of age with two 1 cm s.c. implants of testosterone (n=6) or dihydrotestosterone (n=7). There was no difference in IGF-I levels or in weights of testes, seminal vesicles, kidney, liver or spleen between testosterone and dihydrotestosterone treatments (P>0·05). Prolonged high levels of androgen also restored testicular and seminal vesicle weights to 40% of phenotypically normal controls, while kidney, liver and spleen weights were also significantly increased. The pubertal IGF-I surge in mice does not, therefore, require androgens in either the pre- or postnatal periods, and it is exaggerated in androgen-deficient male mice and dampened to normal regardless of aromatization.

Journal of Endocrinology (1993) 139, 57–65

Thyroid hormone (TH) deficiency results in delayed proliferation and migration of cerebellar granule cells. Although extensive cell loss during the development of the cerebellum under hypothyroid conditions is known, its nature and its mechanism are poorly understood. Bcl-2 family gene expression is known to determine the fate of cells to undergo apoptosis. We evaluated the effect of hypothyroidism on Bcl-2 family gene expression in the developing rat cerebellum. Electrophoresis and Western blotting were used to analyze DNA fragmentation and expression of DNA fragmentation factor (DFF-45), Bcl-2, Bcl-xL and Bax genes respectively. In the hypothyroid condition, extensive DNA fragmentation and enhanced cleavage of DFF-45 were seen throughout development (postnatal day 0 to day 24) and adulthood whereas they were absent in the euthyroid state. The anti-apoptotic genes Bcl-2 and Bcl-xL were down-regulated and the pro-apoptotic gene Bax was expressed at higher levels compared with the euthyroid state. These results suggest that normal levels of TH prevent cerebellar apoptosis to a large extent, whereas hypothyroidism not only increases the extent but also the duration of apoptosis by down-regulating the anti-apoptotic genes and maintaining a high level of the pro-apoptotic gene Bax.

Myometrial inflammation is thought to have a pivotal role in the onset of term and some forms of preterm labour. This is based on the comparison of samples taken from women undergoing term elective CS prior to the onset of labour with those taken from women in established labour. Consequently, it is not clear whether myometrial inflammation is a cause or a consequence of labour. Our objective is to test the hypothesis that myometrial inflammation is a consequence of the onset of labour. To test this hypothesis, we have obtained myometrial samples from women at various stages of pregnancy and spontaneous labour and studied the activation of the AP-1 (c-Jun) and NFκB (p65) systems, cytokine mRNA expression and protein levels and inflammatory cell infiltration and activation. We found that the activation of p65 declined from preterm to term not in labour samples and thereafter increased in early and established labour. Cytokine mRNA expression and protein levels increased in established labour only. Using flow cytometry of myometrial tissue, we found that the number of neutrophils did increase with the onset of labour, but on tissue section, these were seen to be intravascular and not infiltrating into the myometrium. These data suggest that myometrial inflammation is a consequence rather than a cause of term labour.

ABSTRACT

Dietary factors are known to modulate concentrations of sex hormone-binding globulin (SHBG). In the present study we have investigated the possibility that insulin like growth factor-type I (IGF-I) may be an additional regulator of SHBG using cultured human hepatoma cells which secrete SHBG. The inhibitory effect of insulin on SHBG secretion by these cells was confirmed but, in addition, IGF-I was shown to inhibit SHBG secretion by about 40% at a concentration of 100 nmol/l. A similar degree of inhibition was achieved using insulin at a concentration of 10 umol/l. Insulin, but not IGF-I, was also found to inhibit the secretion of a low molecular weight IGF-binding protein (IBP-I), which is also secreted by hepatoma cells. It is concluded that IGF-I is an additional regulator of SHBG secretion by these cells and that it may be involved in regulating SHBG secretion in vivo in response to dietary factors.

ABSTRACT

The interleukin-6 soluble receptor (IL-6sR) may regulate the ability of IL-6 to stimulate oestrogen synthesis in breast cancer cells and breast tumours. Significant aromatase activity was detectable in IL-6 stimulated fibroblasts derived from subcutaneous adipose tissue, but the combination of IL-6sR plus IL-6 resulted in a marked 21-fold stimulation of aromatase activity. To examine the control of IL-6sR release, the effects of oestradiol, 4-hydroxytamoxifen (4-OHT), dexamethasone, TPA, TNFα or IL-6 on this process was examined using MCF-7 breast cancer cells. Oestradiol, TNFα and dexamethasone all markedly increased IL-6sR release. While 4-OHT had a small stimulatory effect on IL-6sR release, it blocked the ability of oestradiol to increase IL-6sR release. Significant concentrations of IL-6sR were also detected in conditioned medium collected from lymphocytes and macrophages and in cytosols prepared from normal and malignant breast tissues. These results indicate that IL-6sR may have an important role in potentiating the effect of IL-6 on oestrogen synthesis in breast cancer cells. The abilities of oestradiol or tamoxifen to potentiate or inhibit the IL-6 stimulation of oestrogen synthesis in breast cancer cells may result from their effects on IL-6sR release.

Micronutrients influence hormone action and host metabolism. Dietary minerals, trace elements, and vitamins can alter blood glucose and cellular glucose metabolism, and several micronutrients are associated with the risk and progression of type 2 diabetes. Dietary components, microbes, and host immune, endocrine, and metabolic responses all interact in the intestine. There has been a focus on macronutrients modifying the host-microbe relationship in metabolic disease. Micronutrients are positioned to alter host-microbe symbiosis that participates in host endocrine control of glucose metabolism. Minerals and trace elements can alter the composition of the intestinal microbiota, gut barrier function, compartmentalized metabolic inflammation, cellular glucose transport, and endocrine control of glucose metabolism, including insulin and thyroid hormones. Dietary vitamins also influence the composition of the intestinal microbiota and vitamins can be biotransformed by gut microbes. Host-microbe regulation of vitamins can alter immunity, lipid and glucose metabolism, and cell fate and function of pancreatic beta cells. Causal effects of micronutrients in host-microbe metabolism are still emerging, and the mechanisms linking dietary excess or deficiency of specific micronutrients to changes in gut microbes directly linked to metabolic disease risk are not yet clear. Dietary fiber, fat, protein, and carbohydrates are key dietary factors that impact how microbes participate in host glucose metabolism. It is possible that micronutrient and microbiota-derived factors also participate in host-microbe responses that tip the balance in the endocrine control of host glucose metabolism. Dietary micronutrients should be considered, tested, and controlled in pre-clinical and clinical studies investigating host-microbe factors in metabolic diseases.

SLC30A8 encodes the zinc transporter ZnT8. SLC30A8 haploinsufficiency protects against type 2 diabetes (T2D), suggesting that ZnT8 inhibitors may prevent T2D. We show here that, while adult chow fed Slc30a8 haploinsufficient and knockout (KO) mice have normal glucose tolerance, they are protected against diet-induced obesity (DIO), resulting in improved glucose tolerance. We hypothesize that this protection against DIO may represent one mechanism whereby SLC30A8 haploinsufficiency protects against T2D in humans and that, while SLC30A8 is predominantly expressed in pancreatic islet beta cells, this may involve a role for ZnT8 in extra-pancreatic tissues. Consistent with this latter concept we show in humans, using electronic health record-derived phenotype analyses, that the ‘C’ allele of the non-synonymous rs13266634 SNP, which confers a gain of ZnT8 function, is associated not only with increased T2D risk and blood glucose, but also with increased risk for hemolytic anemia and decreased mean corpuscular hemoglobin (MCH). In Slc30a8 KO mice, MCH was unchanged but reticulocytes, platelets and lymphocytes were elevated. Both young and adult Slc30a8 KO mice exhibit a delayed rise in insulin after glucose injection, but only the former exhibit increased basal insulin clearance and impaired glucose tolerance. Young Slc30a8 KO mice also exhibit elevated pancreatic G6pc2 gene expression, potentially mediated by decreased islet zinc levels. These data indicate that the absence of ZnT8 results in a transient impairment in some aspects of metabolism during development. These observations in humans and mice suggest the potential for negative effects associated with T2D prevention using ZnT8 inhibitors.