Combined effects of endogenous sex hormone levels and mammographic density on postmenopausal breast cancer risk: results from the Breakthrough Generations Study.

BACKGROUND: Mammographic density and sex hormone levels are strong risk factors for breast cancer, but it is unclear whether they represent the same aetiological entity or are independent risk factors. METHODS: Within the Breakthrough Generations Study cohort, we conducted a case-control study of 265 postmenopausal breast cancer cases and 343 controls with prediagnostic mammograms and blood samples. Plasma was assayed for oestradiol, testosterone and sex hormone-binding globulin (SHBG) concentrations and mammographic density assessed by Cumulus. RESULTS: Oestradiol and testosterone were negatively and SHBG positively associated with percentage density and absolute dense area, but after adjusting for body mass index the associations remained significant only for SHBG. Breast cancer risk was independently and significantly positively associated with percentage density (P=0.002), oestradiol (P=0.002) and testosterone (P=0.007) levels. Women in the highest tertile of both density and sex hormone level were at greatest risk, with an odds ratio of 7.81 (95% confidence interval (CI): 2.89-21.1) for oestradiol and 4.57 (95% CI: 1.75-11.9) for testosterone and high density compared with those who were in the lowest tertiles. The cumulative risk of breast cancer in the highest oestradiol and density tertiles, representing 8% of controls, was estimated as 12.8% at ages 50-69 years and 19.4% at ages 20-79 years, and in the lowest tertiles was 1.7% and 4.3%, respectively. Associations of breast cancer risk with tertiles of mammographic dense area were less strong than for percentage density. CONCLUSIONS: Endogenous sex hormone levels and mammographic density are independent risk factors for postmenopausal breast cancer, which in combination can identify women who might benefit from increased frequency of screening and chemoprophylaxis.

Effect of tamoxifen or anastrozole on steroid sulfatase activity and serum androgen concentrations in postmenopausal women with breast cancer.

BACKGROUND: In postmenopausal women estrogens can be formed by the aromatase pathway, which gives rise to estrone, and the steroid sulfatase (STS) route which can result in the formation of estrogens and androstenediol, a steroid with potent estrogenic properties. Aromatase inhibitors, such as anastrozole, are now in clinical use whereas STS inhibitors, such as STX64, are still undergoing clinical evaluation. STX64 was recently shown to block STS activity and reduce serum androstenediol concentrations in postmenopausal women with breast cancer. In contrast, little is known about the effects of aromatase inhibitors or anti-estrogens on STS activity or serum androgen levels. PATIENTS AND METHODS: Study 1: Blood was collected from ten postmenopausal women with breast cancer before and after two-week treatment with anastrozole and serum concentrations of androstenediol and other androgens and estrogens were assessed. Study 2: Blood samples were collected from 15 breast cancer patients before and after four-week treatment with anastrozole and 10 patients before and after four-week treatment with tamoxifen. Blood was used to assess STS activity in peripheral blood lymphocytes (PBLs) and serum dehydroepiandrosterone sulfate and dehydroepiandrosterone levels. RESULTS: Neither anastrozole nor tamoxifen had any significant effect on STS activity as measured in PBLs. Anastrozole did not affect serum androstenediol concentrations. CONCLUSION: Anastrozole and tamoxifen did not inhibit STS activity and serum androstenediol concentrations were not reduced by aromatase inhibition. As androstenediol has estrogenic properties, it is possible that the combination of an aromatase inhibitor and STS inhibitor may give a therapeutic advantage over the use of either agent alone.

Metabolic syndrome and renal sodium handling in three ethnic groups living in England.

AIM/HYPOTHESIS: Increased proximal renal sodium re-absorption is associated with central adiposity and insulin resistance in white men. Our study examined whether this association also exists in other ethnic groups with different prevalences of insulin resistance and associated metabolic abnormalities. METHODS: We studied the association between fractional renal excretion of endogenous lithium (FELi) and metabolic syndrome in a population study of 1190 randomly selected men and women who where 40 to 59 years of age (426 white, 397 of African and 367 of South Asian origin). Anthropometric values, blood pressure, biochemical values, questionnaire data and timed urine collections were obtained with standardised techniques. Endogenous lithium in serum and urine was measured by absorption spectrophotometry. Metabolic markers were the homeostasis model assessment (HOMA) index, waist circumference, serum triglycerides, serum HDL cholesterol and metabolic syndrome as defined by Adult Treatment Panel III criteria. RESULTS: In white men and women a higher rate of proximal sodium re-absorption was inversely associated with higher waist circumference, serum triglycerides and HOMA index, and with lower serum HDL cholesterol (all p< or =0.001). No associations were found in people of African or South Asian origin. The former had lower FELi than the other groups. White people with the metabolic syndrome had a lower FELi than those without (15.9% vs 19.0%; p=0.003). No difference was found in people of African or South Asian origin. CONCLUSIONS/INTERPRETATION: Increased proximal sodium re-absorption is associated with the metabolic syndrome in white men and women. This relationship is not seen in people of African or South Asian origin, despite a greater degree of insulin resistance.

Effects of the potassium channel blocker barium on sodium and potassium transport in the rat loop of Henle in vivo.

In vitro evidence suggests that the 'recycling' of K(+) ions through luminal K(+) channels in the thick ascending limb of the loop of Henle (TALH) is essential for the normal operation of the luminal Na(+)-K(+)-2Cl(-) co-transporter. In the present study these channels were investigated in vivo by perfusing superficial loops of Henle in anaesthetised rats with and without the K(+) channel blocker barium. Using a standard perfusate, intraluminal barium (5 mmol l(-1)) reduced sodium reabsorption (J(Na)) from 1887 +/- 50 to 1319 +/- 53 pmol min(-1) (P < 0.001). When the experiment was repeated using a low-Na(+) perfusate, designed to inhibit reabsorption in the pars recta (the initial segment of the loop of Henle), a similar reduction in J(Na) was observed (from 698 +/- 47 to 149 +/- 23 pmol min(-1), P < 0.001), strongly suggesting that the effect of barium is localised to the TALH. The magnitude of the reduction in J(Na) during blockade of K(+) channels confirms the importance of K(+) recycling in facilitating Na(+) reabsorption in the TALH in vivo. However, the reduction in J(Na) was not associated with a fall in the K(+) concentration of the fluid collected at the early distal tubule. When bumetanide, an inhibitor of the Na(+)-K(+)-2Cl(-) co-transporter, was included in the low-Na(+) perfusate, net K(+) secretion was observed. Addition of barium to this perfusate reduced, but did not abolish, the secretion, suggesting that bumetanide-induced K(+) secretion results partly from paracellular transport. Experimental Physiology (2001) 86.4, 469-474.

Transepithelial electrochemical gradients in the proximal convoluted tubule during potassium depletion in the rat.

1. In order to examine the electrochemical gradient for potassium reabsorption across the S2 segment of the proximal convoluted tubule, transepithelial potential differences and transepithelial potassium concentrations were measured in anaesthetized potassium-replete and potassium-depleted rats. 2. Potassium-depleted rats were markedly hypokalaemic (plasma potassium, 1.4 +/- 0.1 vs. 4.1 +/- 0.1 mmol l-1 in potassium-replete rats) and had a significantly reduced muscle potassium content. In confirmation of previous reports, glomerular filtration rate was slightly reduced, while fractional reabsorption in the proximal convoluted tubule was enhanced. 3. In potassium-replete animals, the transepithelial potential difference (PD) at the late proximal convoluted tubule was +2.1 +/- 0.3 mV (lumen positive) and the tubular fluid to plasma ultrafiltrate concentration ratio for potassium (TFK/UFK) at the same site was 1. 03 +/- 0.01. In potassium-depleted rats, there was a striking reversal of the transepithelial PD (to -4.0 +/- 0.4 mV), while the TFK/UFK was increased to 1.19 +/- 0.03. 4. The data from both potassium-replete and potassium-depleted animals are consistent with accumulating evidence that potassium reabsorption in the proximal convoluted tubule is passive in nature and depends partly on diffusion down an electrochemical gradient.

Glucose load and renal sodium handling in mild essential hypertension on different sodium intakes.

The aims of the present study were to investigate the effects of changes in sodium intake in patients with untreated mild essential hypertension on the hormonal (plasma renin activity and aldosterone) and renal tubular responses to short-term hyperinsulinemia as achieved by an oral glucose tolerance test (OGTT). Fourteen patients with essential hypertension (mean age, 46 years; average blood pressure (BP), 151/96 mm Hg) were studied. After a 1 week run-in period on their usual diet they entered a randomized double-blind crossover study of a week of low (10 mmol/day) vs a week of high (350 mmol/day) sodium intake. On the last day of each diet they underwent a standard 2-h OGTT. Blood and urines were taken hourly and segmental tubular sodium handling was assessed by the endogenous lithium clearance. The results demonstrate that the plasma insulin and glucose response to a short-term oral glucose load were not influenced significantly by the changes in dietary sodium intake. However, the glucose load was associated with marked renal sodium retention in the absence of any change in systemic BP. The reduction in renal sodium excretion was independent of circulating aldosterone but appeared to be due to an increase in renal distal tubular re-absorption.

The relationship between 17 beta hydroxysteroid dehydrogenase and breast tumour site and size.

The activity of 17 beta hydroxysteroid dehydrogenase (170HSD) was measured in adipose tissue adjacent to benign or malignant breast tumours. 170HSD activity was significantly correlated with tumour size in malignant tumours (r = 0.75) but not with benign tumours (r = 0.28). Enzyme activity was reduced in adipose tissue adjacent to tumours obtained from inferior breast quadrants.

Aromatase activity in uterine leiomyomata.

Of the 24 samples of leiomyoma tissues examined 14 were shown to have aromatase activity in vitro. In contrast only 1 of 12 samples of myometrium had any demonstrable activity. Measurements of tissue oestrogen levels showed no correlation with the amount of aromatase activity although oestradiol levels were consistently higher in the tumour tissues compared with the normal myometrium.

The action of dexamethasone and prolactin on aromatase activity in human adipose tissue.

Using slices of human adipose tissue maintained in medium 199 for 40 h at 37 degrees C, it was observed that in the absence of any other additions, the presence of foetal calf serum (10%) inhibits basal levels of aromatase activity. Including dexamethasone (1 X 10(-7) M) in the medium increases aromatase activity approximately 10-fold in the presence of foetal calf serum but has only a small stimulatory effect in its absence. The combined addition of dexamethasone (1 X 10(-7) M) and human prolactin (0.8 ng/ml) has a marked additional incremental effect in the presence or absence of foetal calf serum. In contrast, the addition of prolactin to the medium without glucocorticoid did not stimulate oestrogen production. The possibility that prolactin could be the substance in foetal calf serum responsible for mediating the stimulatory effect of glucocorticoids on oestrogen production is considered.

17 Beta-hydroxysteroid dehydrogenase and aromatase activity in breast fat from women with benign and malignant breast tumours.

The activity of 17 beta-hydroxysteroid dehydrogenase and aromatase was studied in adipose tissue taken from women aged between 22 and 83 years with benign or malignant breast lesions. The benign and malignant groups showed no significant differences in the mean activities of either of the enzymes studied. Under the experimental conditions used, the rate of conversion of oestrone to oestradiol varied markedly between subjects (6-169 ng oestradiol/mg protein/h), and there was a positive correlation between oestrone reduction and the total body weight of the tissue donor. In contrast, although the apparent Km for oestradiol (0.1-2.6 mumol/l) was lower than that for oestrone (9-14 mumol/l) the maximum velocity for oestrone production was very low (10-50 pmol/mg protein/h), and there was no obvious correlation with the age or body weight of the tissue donor. Aromatase activity in breast fat was at the lower end of the normal range of activity previously reported for abdominal adipose tissue, and there was no correlation between oestrone production and age or body weight.

Aromatization of steroids in peripheral tissues.

The action of glucocorticoids on aromatase activity in human adipose tissue has been investigated. Oestrogen production was increased in tissue maintained in the presence of dexamethasone and cortisol. Dexamethasone was effective at concentrations as low as 1 nmol/l. In contrast, over the 40 h incubation period, cortisol was only effective at concentrations in excess of 500 nmol/l, although after conditions of prolonged incubation, induction of aromatase activity was measurable using cortisol concentrations as low as 28 nmol/l. There were apparent variations in both basal levels of aromatic activity and in response to glucocorticoids in adipose tissue taken from various sites within the body.

Failure of FSH to influence aromatization in human adipose tissue.

Since gonadotrophins are known to influence aromatase activity in gonadal tissue, an attempt was made to correlate serum gonadotrophin concentrations with the activity of aromatase enzyme in adipose tissue. No relationship between in-vitro measurements of adipose tissue aromatase activity and FSH or LH levels in serum was found. Four of five women studied with premature ovarian failure had low levels of aromatase activity despite having postmenopausal levels of serum gonadotrophins. In addition, FSH receptors could not be demonstrated on while adipose tissue, isolated fat cells or stromal vascular tissue.

Studies on the activity of 17 beta-hydroxysteroid dehydrogenase in human adipose tissue.

The activity of 17 beta-hydroxysteroid dehydrogenase has been investigated in human subcutaneous adipose tissue. Using oestrone as substrate, oestradiol formation was linear with time and the concentration of protein in the tissue homogenate. The optimum pH was 8.0 and the Km for oestrone was 2.5 x 10(-6) M. With NADH, the production of oestradiol was about 30% of that with NADPH. Oestradiol was also a substrate for the enzyme although under the experimental conditions used reduction of oestrone appeared to be favoured in adipose tissue. In the presence of progesterone (31.8 x 10(-6) M) the Km for oestrone was increased fivefold.

Oestrogen production in adipose tissue from normal women and women with endometrial cancer in vitro.

The in vitro conversion of androstenedione to oestrone and oestrone to oestradiol was investigated in human adipose tissue. Higher rates of oestrone (range 1.2-44.0 pg/mg protein/3h) and oestradiol (range 0.6-15.2 ng/mg protein/h) production were observed in tissue samples obtained from women aged 40-50 years compared with the rates measured using adipose tissue from younger women (range 0.7-7.7 pg oestrone/mg protein/3 h and 0.4-1.8 ng oestradiol/mg protein/h). Five subjects studied with endometrial cancer did not show a market increase in conversion of androstenedione to oestrone or oestrone to oestradiol in subcutaneous adipose tissue compared with normal women of similar age and weight. A sample of omental adipose tissue from one subject with endometrial cancer did show a high conversion rate of androstenedione to oestrone (104.0 pg oestrone/mg protein/3 h), although the rate of conversion of oestrone to oestradiol was lower than that observed in subcutaneous adipose tissue, indicating that steroid metabolism is not uniform in adipose tissue throughout the body.

The relationship between the binding ability and the rate of activation of the complement component C1.

The strength of the bond between C1 and C1 binders (as measured by C1q binding) has been correlated with the ability of the binders to activate C1. The rate of activation of C1 has been studied by following the extent of hydrolysis of the C1r and C1s subcomponents, using a purified preparation of C1 labelled with 125I. The rate of activation of C1 was not correlated with the binding strength between C1q and the C1 binders. Immune complexes were found to activate C1 rapidly, whereas glutaraldehyde-aggregated IgG failed to activate faster than the spontaneous activation seen on incubation of C1 alone; the strength of the bond between C1q and the binders was similar in the two cases. It is suggested that an interaction other than the binding between C1q and C1 binders is necessary for activation of C1. C1 bound to immune complexes was not activated in the presence of C1 inhibitor, indicating that the inhibitor can prevent the hydrolysis of C1r under the test conditions.

A simple method for the detection and assay of C1.

A simple method is described for the production of human serum deficient in the complement component C1. This C1-deficient serum can be used for the assay of C1. If the amount of C1 is expressed in terms of its subcomponent C1q, the method can detect C1 when the C1q subcomponent content is only 10 pg.