Prolactin does not cause breast cancer and may prevent it or be therapeutic in some conditions

In vivo evaluation of the potential protective effects of prolactin against damage caused by methylmercury

Non-biodegradable metals such as mercury accumulate in living organisms during life (bioaccumulation) and also within trophic webs (biomagnification) and may reach high concentrations in humans. The contamination of humans by mercury in drinking water and food may be common, in particular in riverside communities that have a diet rich in fish. In vitro studies of human cell lines exposed to the cytotoxic and mutagenic effects of methylmercury have shown that prolactin has potential cytoprotective properties and may act as a co-mitogenic factor and inhibitor of apoptosis. The present in vivo study investigated the protective potential of prolactin against the toxic effects of methylmercury in the mammal Mus musculus. Histological and biochemical analyses, together with biomarker of genotoxicity, were used to verify the protective potential of prolactin in mice exposed to methylmercury. The reduction in kidney and liver tissue damage was not significant. However, results of biochemical and genotoxic analyses were excellent. After prolactin treatment, a significant reduction was observed in biochemical parameters and mutagenic effects of methylmercury. The study results therefore indicated that prolactin has protective effects against the toxicity of methylmercury and allowed us to suggest the continuation of research to propose prolactin in the future, as an alternative to prevent the damage caused by mercury, especially in populations that are more exposed.

Use of antipsychotics and risk of breast cancer: a Danish nationwide case-control study

AIMS

Some antipsychotics increase prolactin levels, which might increase the risk of breast cancer. Existing evidence is conflicting and based on sparse data, especially for the increasingly used second-generation antipsychotics. We conducted a nationwide case-control study of the association between antipsychotic use and incident breast cancer.

METHODS

From the Danish Cancer Registry, we identified women with a first-time diagnosis of breast cancer 2000-2015 (n = 60 360). For each case, we age-matched 10 female population controls. Using conditional logistic regression, we calculated odds ratios (ORs) for breast cancer associated with use of antipsychotics. We stratified antipsychotics by first- and second-generation status and by ability to induce elevation of prolactin.

RESULTS

In total, 4951 cases (8.1%) and 47 643 controls (7.9%) had ever used antipsychotics. Long-term use (≥10 000 mg olanzapine equivalents) was associated with breast cancer, with an adjusted OR of 1.18 [95% confidence interval (CI), 1.06, 1.32]. A weak dose-response pattern was seen, with ORs increasing to 1.27 (95% CI 1.01, 1.59) for ≥50 000 mg olanzapine equivalents. Associations were similar for first- and second-generation antipsychotics (ORs 1.17 vs. 1.11), but also for nonprolactin inducing-antipsychotics (OR 1.17). Stratifying by oestrogen receptor status, positive associations were seen for oestrogen receptor-positive cancers (long-term use: OR 1.29; 95% CI 1.13, 1.47) while no associations were observed for oestrogen receptor-negative cancers.

CONCLUSIONS

Overall, our results do not suggest a clinically important association between antipsychotic use and risk of breast cancer. The importance of drug-induced prolactin elevation is unclear but may lead to a slightly increased risk of oestrogen receptor-positive breast cancer.

Relationship between prolactin, breast cancer risk, and antipsychotics in patients with schizophrenia: a critical review

OBJECTIVE

A recent meta-analysis showed that breast cancer probably is more common in female patients with schizophrenia than in the general population (effect size = 1.25, P < 0.05). Increasing experimental and epidemiological data have alerted researchers to the influence of prolactin (PRL) in mammary carcinogenesis. We therefore investigated the possible relationship between antipsychotic-induced hyperprolactinemia (HPRL) and breast cancer risk in female patients with schizophrenia.

METHOD

A literature search (1950 until January 2015), using the MEDLINE database, was conducted for English-language published clinical trials to identify and synthesize data of the current state of knowledge concerning breast cancer risk (factors) in women with schizophrenia and its (their) relationship between HPRL and antipsychotic medication.

RESULTS

Although an increasing body of evidence supports the involvement of PRL in breast carcinogenesis, results of human prospective studies are limited, equivocal, and correlative (with risk ratios ranging from 0.70 to 1.9 for premenopausal women and from 0.76 to 2.03 for postmenopausal women). Moreover, these studies equally do not take into account the local production of PRL in breast epithelium, although amplification or overexpression of the local autocrine/paracrine PRL loop may be a more important mechanism in tumorigenesis. Until now, there is also no conclusive evidence that antipsychotic medication can increase the risk of breast malignancy and mortality.

CONCLUSION

Other breast risk factors than PRL, such as nulliparity, obesity, diabetes mellitus, and unhealthy lifestyle behaviours (alcohol dependence, smoking, low physical activity), probably are of greater relevance in individual breast cancer cases within the population of female patients with schizophrenia.

The many faces of prolactin in breast cancer

Prolactin (PRL) is a neuroendocrine polypeptide hormone primarily produced by the lactotrophs in the anterior pituitary gland of all vertebrates. The physiological role of PRL in mammary glands is relatively certain while its role in breast tumor has been a topic of debate for over 20 years. In this review, the author attempts to briefly summarize the data coming from his laboratory in the past years, focusing on G129R, a PRL receptor (PRLR) antagonist developed by introducing a single amino acid substitution mutation into human PRL (hPRL) at position 129, and a variety of G129R derivatives. The author has proposed two novel ideas for potential use of PRL, not anti-PRL agents, as an adjuvant agent for breast cancer, making it a hormone of many faces.

Associations between dietary acrylamide intake and plasma sex hormone levels

BACKGROUND

The rodent carcinogen acrylamide was discovered in 2002 in commonly consumed foods. Epidemiologic studies have observed positive associations between acrylamide intake and endometrial, ovarian, and breast cancer risks, which suggest that acrylamide may have sex-hormonal effects.

METHODS

We cross-sectionally investigated the relationship between acrylamide intake and plasma levels of sex hormones and sex hormone-binding globulin (SHBG) among 687 postmenopausal and 1,300 premenopausal controls from nested case-control studies within the Nurses' Health Studies.

RESULTS

There were no associations between acrylamide and sex hormones or SHBG among premenopausal women overall or among never-smokers. Among normal-weight premenopausal women, acrylamide intake was statistically significantly positively associated with luteal total and free estradiol levels. Among postmenopausal women overall and among never-smokers, acrylamide was borderline statistically significantly associated with lower estrone sulfate levels but not with other estrogens, androgens, prolactin, or SHBG. Among normal-weight women, (borderline) statistically significant inverse associations were noted for estrone, free estradiol, estrone sulfate, DHEA, and prolactin, whereas statistically significant positive associations for testosterone and androstenedione were observed among overweight women.

CONCLUSIONS

Overall, this study did not show conclusive associations between acrylamide intake and sex hormones that would lend unequivocal biologic plausibility to the observed increased risks of endometrial, ovarian, and breast cancer. The association between acrylamide and sex hormones may differ by menopausal and overweight status. We recommend other studies investigate the relationship between acrylamide and sex hormones in women, specifically using acrylamide biomarkers.

IMPACT

The present study showed some interesting associations between acrylamide intake and sex hormones that urgently need confirmation.

Laboratory production of human prolactin from CHO cells adapted to serum-free suspension culture

Human prolactin (hPRL) is a polypeptide with 199 amino acids and a molecular mass of 23 kDa. Previously, a eukaryotic hPRL expression vector was used to transfect Chinese hamster ovary (CHO) cells: this work describes a fast and practical laboratory adaptation of these transfected cells, in ~40 days, to grow in suspension in serum-free medium. High cell densities of up to 4.0 × 10(6) cell/ml were obtained from spinner flask cultures and a stable and continuous production process was developed for at least 30 days. Two harvesting strategies were set up, 50 or 100 % of the total conditioned medium being collected daily and replaced by fresh culture medium. The volumetric productivity was 5-7 μg hPRL/ml, as determined directly in the collected medium via reversed-phase HPLC (RP-HPLC). A two-step process based on a cationic exchanger followed by size exclusion chromatography was applied to obtain purified hPRL from conditioned medium. Two hPRL isoforms, non-glycosylated and glycosylated, could also be separated by high-performance size-exclusion chromatography (HPSEC) and, when analyzed by RP-HPLC, HPSEC, Western blotting, and bioassay, were found to be comparable to the World Health Organization International Reference Reagent of hPRL. These results are useful for the practical scale-up to the pilot and industrial scale of a bioprocess based on CHO cell culture.

Breast carcinomas with hyperprolactinemia at the time of diagnosis-clinico-biological association

AIM

To analyse association between preoperative hyperprolactinemia serum levels and clinical and biological features of breast tumors.

METHODS

Serum levels of prolactin were measured in 253 women with invasive breast cancer. Clinical and biological parameters analysed were age, size, lymph node involvement, distant metastasis and immunohistochemical expression of estrogen receptor, progesterone receptor, androgen receptor, bcl-2, p53 and Ki67.

RESULTS

In ductal carcinomas hyperprolactinemia were associated with high age (p = 0.017), and with bcl-2 + + + expression (p = 0.017). Furthermore, serum prolactin values were significantly higher in bcl-2 +++ cases vs negative (p = 0.029); the same happened when we considered the positivity threshold of 25 ng/mL (p = 0.015).

CONCLUSION

Is possible to detect in 6% of infiltrating ductal breast carcinomas hyperprolactinemia (>25 ng/mL), being associated only with increasing age, but not with other clinical or biological factors; and 2) the most surprising data was the association between prolactinemia (qualitative (>25 ng/mL) and quantitative) and intense bcl-2 tissue expression, which suggests that, probably, this (prolactinemia) is not a sign of worse prognosis and evolution.

Hypothesis: prolactin is tumorigenic to human breast: dispelling the myth that prolactin-induced mammary tumors are rodent-specific

The commonly held assumption that rodent mammary tumors resulting from elevated prolactin are species-specific, or not biologically relevant to humans, is incorrect. Substantial epidemiological, clinical, and biological evidence now exists confirming the role of prolactin in human breast cancer. This evidence is evaluated and the argument presented that the tumorigenic risk from prolactin is therefore not species-specific to rodents but directly applies to humans. Further, as the mechanisms of prolactin-induced mammary tumor promotion and development appear analogous between rodents and humans, mammary tumorigenic findings in rodent carcinogenicity bioassays are both predictive and biologically relevant to the human response. Toxicologists and regulators need to consider this in carcinogenicity risk assessments.

A 12-month moderate-intensity exercise intervention does not alter serum prolactin concentrations

INTRODUCTION

Many studies have investigated the immediate impact of physical activity on prolactin concentrations; however, it is currently unclear what impact exercise may have on prolactin concentrations in the long-term, particularly among women. Understanding the role of exercise on prolactin is important because epidemiologic studies have reported increased risks of breast cancer in association with high prolactin concentrations. We investigated whether exercise alters serum prolactin concentrations at two time points within a one-year exercise intervention.

METHODS

Out of 96 women aged 40-75 years, 47 were randomized to a 12-month regimen of moderate-intensity physical activity and 49 were randomized to the control group. Participants in the exercise group (exercisers) took part in exercise at gym facilities 3 times per week and 3 times per week on their own. Serum prolactin was collected from participants at baseline, 3 and 12 months. Using generalized linear models, we compared the percent change in prolactin concentrations from baseline to the two follow-up time points in the exercisers versus the control group.

RESULTS

While we observed the suggestion of differences in the change in serum prolactin concentrations in some subgroups, overall there was no difference in the change in prolactin concentrations between exercisers and controls at 3 months (p=0.57) or 12 months (p=0.42).

CONCLUSION

Our study does not support the hypothesis that long-term exercise influences serum prolactin concentrations.

The risk for breast cancer is not evidently increased in women with hyperprolactinemia

The question has been raised whether hyperprolactinemia in humans is associated with an excess risk for breast cancer. We aimed to assess the risk of breast cancer in a previously defined large cohort of patients treated for idiopathic hyperprolactinemia or prolactinomas. Based on the pattern of drug prescriptions we identified 11,314 subjects in the PHARMO network with at least one dispensing of dopamine agonists between 1996 and 2006. Of these, 1,607 subjects were considered to have dopamine agonist-treated hyperprolactinemia based on the prescribing pattern. For the present analysis, we included only women (n = 1,342). Patients with breast cancer were identified by hospital discharge codes. Data on breast cancer incidence in the Netherlands were derived from the Dutch cancer registry. Standardized mortality ratio (SMR) was the measure of outcome to assess the association between hyperprolactinemia and breast cancer. The 1,342 patients accounted for a total of 6,576 person years. Eight patients with breast cancer during follow-up were identified. Indirect standardization with incidence proportions from the general Dutch population revealed a 7.47 expected cases. The calculated SMR for breast cancer risk in patients treated hyperprolactinemia was 1.07 (95% confidence interval 0.50-2.03). In conclusion, there is no clear evidence for increased breast cancer risk in female patients treated for either idiopathic hyperprolactinemia or prolactinomas. The uncertainty about the exact risk that is due to the relatively low number of breast cancer cases, should be overcome by pooling results in a future meta-analysis.

Enhancement of human prolactin synthesis by sodium butyrate addition to serum-free CHO cell culture

Sodium butyrate (NaBu) has been used as a productivity enhancer for the synthesis of recombinant proteins in Chinese hamster ovary (CHO) cells. Thus, the influence of NaBu on the production of recombinant human prolactin (hPRL) from CHO cells was investigated for the first time. CHO cell cultures were submitted to a treatment with different concentrations of NaBu (0.25 to 4 mM). Quantitative and qualitative analyses by reverse-phase high-performance liquid chromatography (RP-HPLC) and Western blot or SDS-PAGE, carried out directly on CHO-conditioned medium, showed that the highest hPRL expression was obtained with 1 mM NaBu. In vitro biological assays based on noble rat lymphoma (Nb2) and mouse pro-B lymphoma (Ba/F3-LLP) cells were carried out on purified hPRL. Its bioactivity in the presence of NaBu was not apparently different from that of the First International Reference Reagent of recombinant hPRL (WHO 97/714). Our results show that NaBu increased the synthesis of recombinant hPRL in CHO cells, apparently without compromising either its structure or function.

Distinct effects of calorie restriction and exercise on mammary gland gene expression in C57BL/6 mice

Energy balance, including diet, weight, adiposity, and physical activity, is associated with carcinogenesis. Epidemiologic studies indicate that obesity and sedentary and/or active behavior are risk factors for breast cancer in postmenopausal women and survival in both premenopausal and postmenopausal breast cancer patients. Thus, understanding the influence of energy balance modulation on changes in gene expression patterns in the normal mammary gland is important for understanding mechanisms linking energy balance and breast cancer. In a 6-week-long study, female C57BL/6 mice (9-week-old) were randomized into four groups: (a) food consumed ad libitum (AL), (b) AL with access to running wheels (AL+EX), (c) 30% calorie restricted (CR), and (d) 30% CR with access to running wheels (CR+EX). CR mice received 70% of calories but 100% of all other nutrients compared with AL mice. Diet and exercise treatments, individually and combined, had significant effects on body composition and physical activity. Affymetrix oligomicroarrays were used to explore changes in gene expression patterns in total RNA samples from excised whole mammary glands. Contrasting AL versus CR resulted in 425 statistically significant expression changes, whereas AL versus AL+EX resulted in 45 changes, with only 3 changes included among the same genes, indicating that CR and EX differentially influence expression patterns in noncancerous mammary tissue. Differential expression was observed in genes related to breast cancer stem cells, the epithelial-mesenchymal transition, and the growth and survival of breast cancer cells. Thus, CR and EX seem to exert their effects on mammary carcinogenesis through distinct pathways.

Pregnancy and lactation after breast cancer elevate plasma prolactin, do not shorten and may prolong survival

The affliction of breast cancer is doubled for young patients wishing to have a child. Because estrogens can cause breast cancer and its elevation during pregnancy, clinical advice historically restricted pregnancy to at least 5 years post-diagnosis. Opposing evidence gradually relaxed this. Furthermore, in the last decade it was clarified that overall, post-treatment pregnancy and breast-feeding do not shorten survival. Despite this evidence and patients such as S.B. (deceased) and remarkable L.H. (five children, starting immediately after treatment for node-positive breast cancer), much opposition and restrictive advice remain: additional therapy preferred over pregnancy. In healthy women, pregnancy reduces (cause unknown) the risk of breast cancer and lactation may reduce it. These are accompanied by highly elevated plasma prolactin (PRL) over many months (pregnancy, 15-25 x daily mean 10 ng/ml; lactation, up to 30 x daily mean). PRL concentration too increases in other natural and non-biological conditions, also apparently without increasing breast cancer incidence. Nevertheless, firm and implied support for early pregnancy (and lactation) post-diagnosis and treatment may face a new issue. Over a decade, some studies have claimed epidemiological evidence that a relatively minute PRL elevation (from zero to 0.6-0.8 ng/ml) over mean level increases the risk of breast cancer (i.e. it is a carcinogen) and that this supports (and is supported by) a similar view from some laboratory research. This two-pronged mutuality could create further anxiety and unjustified advice dashing the wish for a child. Is this justified? Epidemiology on PRL and breast cancer risk in the eighties/nineties was contradictory and inconclusive; in the last decade, it was also biologically implausible. 'Positive' laboratory results targeting a 'tamoxifen for PRL' have over-shadowed confounding, negative (often called 'inconsistent') laboratory evidence. Increasingly evident complexity of conflicting biochemical, hormonal, cellular and tissue interactions, confused further by failure of molecular genetics to confirm PRL as a carcinogen, make this target more a mirage than an oasis. While recognizing the value of laboratory research primarily for facts, future progress will be most sound and rapid from observation starting with the human entity, not with its parts. Molecular genetics makes this possible and will be the epicentre of breast cancer research. Meanwhile, young breast cancer patients after initial treatment and eager for a child can today reasonably benefit from advice based on phenomena evolved over eons: pregnancy, lactation and accompanying highly-elevated PRL will not increase risk of recurrence and will in some cases prolong survival.

Breast-feeding after breast cancer: if you wish, madam

Breast cancer is the most common malignant tumor-affecting women during the child bearing period. With the rising trend in delaying pregnancy later in life, the issue of subsequent pregnancy and lactation following breast cancer diagnosis has been more frequently encountered. In this context, data is scarce particularly those addressing the issue of lactation. In this review, we discussed different endocrinal, clinical and biological aspects dealing with breast-feeding after breast cancer in an attempt to determine how safe and feasible this approach is.

The contribution of growth hormone to mammary neoplasia

While the effects of growth hormone (GH) on longitudinal growth are well established, the observation that GH contributes to neoplastic progression is more recent. Accumulating literature implicates GH-mediated signal transduction in the development and progression of a wide range malignancies including breast cancer. Recently autocrine human GH been demonstrated to be an orthotopically expressed oncogene for the human mammary gland. This review will highlight recent evidence linking GH and mammary carcinoma and discuss GH-antagonism as a potential therapeutic approach for treatment of breast cancer.