Autoimmune Thyroiditis Mitigates the Effect of Metformin on Plasma Prolactin Concentration in Men with Drug-Induced Hyperprolactinemia

Metformin inhibits the secretory function of overactive anterior pituitary cells, including lactotropes. In women of childbearing age, this effect was absent if they had coexisting autoimmune (Hashimoto) thyroiditis. The current study was aimed at investigating whether autoimmune thyroiditis modulates the impact of metformin on the plasma prolactin concentration in men. This prospective cohort study included two groups of middle-aged or elderly men with drug-induced hyperprolactinemia, namely subjects with concomitant Hashimoto thyroiditis (group A) and subjects with normal thyroid function (group B), who were matched for baseline prolactin concentration and insulin sensitivity. Titers of thyroid peroxidase and thyroglobulin antibodies, levels of C-reactive protein, markers of glucose homeostasis, concentrations of pituitary hormones (prolactin, thyrotropin, gonadotropins, and adrenocorticotropic hormone), free thyroxine, free triiodothyronine, testosterone, and insulin growth factor-1 were measured before and six months after treatment with metformin. Both study groups differed in titers of both antibodies and concentrations of C-reactive protein. The drug reduced the total and monomeric prolactin concentration only in group B, and the impact on prolactin correlated with the improvement in insulin sensitivity and systemic inflammation. There were no differences between the follow-up and baseline levels of the remaining hormones. The results allow us to conclude that autoimmune thyroiditis mitigates the impact of metformin on prolactin secretion in men.

Impaired Prolactin-Lowering Effects of Metformin in Women with Polycystic Ovary Syndrome

The effect of metformin on prolactin concentration seems to be sex-dependent. The aim of this study was to determine whether the androgen status modulates the impact of metformin on plasma prolactin levels in women. This study included two matched groups of prediabetic women with hyperprolactinemia: 25 with PCOS and 25 control subjects with androgen levels within the reference range and with normal ovarian morphology. Glucose homeostasis markers, prolactin, the remaining anterior pituitary hormones, sex hormones, SHBG and IGF-1 were determined before and after six months of metformin treatment. At baseline, both groups differed in LH, LH/FSH ratio, testosterone, FAI, DHEA-S, androstenedione and estradiol. Although metformin improved insulin sensitivity and increased SHBG in both study groups, these effects were more pronounced in control subjects than in women with PCOS. In control subjects, the drug decreased total and monomeric prolactin and increased LH. In women with PCOS, metformin reduced LH, LH/FSH ratio, testosterone and FAI. In the control group, the impact on total and monomeric prolactin positively correlated with their baseline levels and with the degree of improvement in insulin sensitivity, as well as negatively correlated with testosterone and FAI. In women with PCOS, treatment-induced changes in testosterone and FAI positively correlated with the changes in LH and LH/FSH ratio. The obtained results suggest that the prolactin-lowering properties of metformin are less pronounced in women with coexisting PCOS than in women with elevated prolactin levels, probably owing to the increased production of endogenous testosterone.

Pituitary effects of metformin in men with early-onset androgenic alopecia

Males with early-onset androgenic alopecia are characterized by elevated androgen levels. The aim of the present study was to investigate whether the presence of this condition modulates the impact of metformin on pituitary hormone production. This study compared two groups of young men with prediabetes, matched for age, blood pressure and insulin sensitivity: 23 subjects with early-onset male-pattern baldness (group 1) and 25 individuals with normal hair growth (group 2). Throughout the study, both groups were treated with metformin for six months. Circulating levels of glucose, insulin, glycated hemoglobin, gonadotropins, thyrotropin, prolactin, ACTH, insulin-like growth factor-1 and androgens were determined at the beginning of the study and six months later. At entry, LH, the LH/FSH ratio, total testosterone, bioavailable testosterone, ACTH and DHEA-S were higher in group 1 than in group 2. The effect of metformin on fasting glucose, insulin sensitivity and glycated hemoglobin was more pronounced in group 2 than in group 1. Only in group 1, metformin reduced LH levels and the LH/FSH ratio. Metformin did not affect plasma levels of the remaining hormones. In untreated men with androgenic alopecia (group 3, n = 22), glucose homeostasis markers and hormone levels remained at a similar level throughout the study period. The obtained results suggest that the impact of metformin on gonadotroph secretory function is stronger in men with early-onset androgenic alopecia than in men with normal hair growth. Metformin treatment may protect men with early-onset androgenic alopecia against the development of gonadotroph hyperplasia and/or of focal testicular changes. This article is protected by copyright. All rights reserved.

The impact of metformin on hypothalamic-pituitary-thyroid axis activity in postmenopausal women with untreated non-autoimmune subclinical hypothyroidism

Metformin was found to reduce elevated thyrotropin levels in subjects with hypothyroidism. The impact on thyrotropin levels was stronger in women receiving oral contraceptive pills than in women not using any contraception. The aim of the present study was to determine whether physiological levels of oestradiol determine the effect of metformin on hypothalamic-pituitary-thyroid axis activity. The study population included 40 postmenopausal women with prediabetes and untreated non-autoimmune subclinical hypothyroidism, using (group A; n = 18) or not using (group B; n = 22) oestradiol replacement therapy. Over the entire study periods, all subjects were treated with metformin (2.55-3.00 g daily). Plasma levels of glucose, lipids, insulin, thyrotropin, free thyroxine, free triiodothyronine, prolactin, gonadotropins and oestradiol were measured, while the structure parameters of thyroid homeostasis and the degree of insulin sensitivity were calculated at the beginning of the study and 6 months later. At entry, both groups differed in gonadotropin and oestrogen levels. Despite improving insulin sensitivity, thyrotropin levels and Jostel's thyrotropin index in both study groups, these effects were stronger in group A than group B. Only in group A, metformin increased SPINA-GT, while only in group B the drug decreased FSH levels. Levels of the other variables remained at a similar level throughout the study. The effect of treatment on thyrotropin levels correlated with its baseline values, as well as with the improvement of insulin sensitivity. The results obtained suggest that the impact of metformin on hypothalamic-pituitary-thyroid axis activity depends on the oestrogen status of patients.

Metformin and primary bone cancer risk in Taiwanese patients with type 2 diabetes mellitus

BACKGROUND

The effect of metformin on primary bone cancer risk has not been researched. This retrospective cohort study investigated the risk of primary bone cancer between metformin initiators and non-metformin initiators in patients with type 2 diabetes mellitus.

METHODS

A total of 673,532 patients with newly diagnosed type 2 diabetes mellitus and had been prescribed antidiabetic drugs for 2 or more times during 1999-2009 were enrolled from Taiwan's National Health Insurance. Metformin initiators and non-metformin initiators were defined according to the prescriptions of antidiabetic drugs within the initial 12 months. The patients were then followed up until December 31, 2011 for the incidence of primary bone cancer. Cox regression incorporated with the inverse probability of treatment-weighting using propensity scores was used to estimate hazard ratios in intention-to-treat and per-protocol analyses.

RESULTS

In the intention-to-treat analysis, the respective incidence rates were 10.56 and 12.90 per 100,000 person-years in 453,532 metformin initiators and 220,000 non-metformin initiators and the hazard ratio for initiators versus non-initiators was 0.830 (95% confidence interval 0.686-1.004, P-value = 0.0551). In the per-protocol analysis, the incidence rates were 7.58 and 11.77 per 100,000 person-years, respectively, and the hazard ratio was 0.615 (95% confidence interval 0.468-0.808, P-value = 0.0005). Subgroup analyses with regards to sex and age (<60 and ≥60 years) showed that the significantly lower risk associated with metformin use was only observed in men aged ≥60 years in the per-protocol analysis.

CONCLUSIONS

A significantly lower risk of primary bone cancer can be observed in patients with type 2 diabetes mellitus who adhere to metformin treatment. This benefit can only be observed in men aged ≥60 years.

Hypothalamic-pituitary-gonadal axis and sexual functioning in metformin-treated men after discontinuation of testosterone replacement therapy: A pilot study

WHAT IS KNOWN AND OBJECTIVE

Metformin was found to reduce elevated gonadotropin levels. The aim of the present study was to determine whether metformin modulates the impact of discontinuation of testosterone therapy on hypothalamic-pituitary-gonadal axis activity and sexual function in men with low testosterone levels.

METHODS

The study included 28 men with late-onset hypogonadism (defined according to the criteria of the European Male Aging Study group) receiving testosterone undecanoate (120 mg in three equal doses), 12 of whom had been treated with oral metformin (1.7-3 g daily). Both testosterone and metformin had been administered for at least six months before enrolment. In all patients, testosterone replacement required to be discontinued. The control group included 16 testosterone- and metformin-treated men with late-onset hypogonadism who during the entire study period continued their treatment. Glucose homeostasis markers, as well as plasma levels of insulin, gonadotropins, testosterone, calculated bioavailable testosterone, dehydroepiandrosterone-sulphate, oestradiol, thyrotropin, free thyroxine, prolactin, insulin-growth factor-1 and cortisol were measured at the beginning of the study and four months later. Moreover, at the beginning and the end of the study, all enrolled patients completed a questionnaire assessing their sexual functioning (IIEF-15).

RESULTS AND DISCUSSION

Discontinuation of testosterone therapy resulted in a decrease in total testosterone and bioavailable testosterone (by 42% and 45% in metformin-treated patients, and by 52% and 54% in metformin-naïve patients), as well as impaired all aspects of male sexual function. Changes in bioavailable testosterone, as well as in erectile function, orgasmic function and sexual desire were less pronounced if subjects received metformin. Only in metformin-naïve men, follow-up FSH and LH levels were higher than at baseline (by 75% and 62%). Moreover, discontinuation of testosterone therapy in metformin-naïve men increased glycated haemoglobin, as well as worsened insulin sensitivity. There were no differences between baseline and follow-up levels of the remaining hormones. In metformin-naïve subjects, the increase in gonadotropin levels correlated with the changes in testosterone levels and insulin sensitivity. No effect on glucose homeostasis markers, hormone levels and sexual functioning was observed in the control group.

WHAT IS NEW AND CONCLUSION

The obtained results suggest that metformin treatment mitigates the unfavourable effect of discontinuation of testosterone treatment on hypothalamic-pituitary-testicular axis activity and sexual function in men with late-onset hypogonadism.

The impact of metformin on prolactin levels in postmenopausal women

WHAT IS KNOWN AND OBJECTIVE

Metformin-induced reduction in prolactin levels is more pronounced in users of hormonal contraception than in non-users. The current study was aimed at investigating whether physiological concentrations of estradiol determine the impact of metformin on lactotrope secretory function.

METHODS

We studied two matched groups of postmenopausal women with elevated prolactin levels. Twenty-three women were on hormone replacement therapy (group 1), while the remaining ones (group 2, n = 23) did not use sex hormones. Because of coexistent prediabetes, all individuals received metformin (2.55-3 g daily) for the following six months. Circulating levels of total prolactin, monomeric prolactin, thyrotropin, gonadotropins, free thyroid hormones and estradiol were determined at the beginning and at the end of the study.

RESULTS AND DISCUSSION

Compared with group 1, group 2 was characterized by higher gonadotropin levels and lower estrogen levels. Although metformin reduced monomeric prolactin levels in both study groups, this effect was more pronounced in group 1 than in group 2. Only in group 1, metformin decreased total prolactin levels, while only in group 2 the drug reduced FSH levels. Metformin treatment did not affect circulating levels of the remaining hormones. The impact of metformin on total and monomeric prolactin levels correlated with baseline prolactin levels and with the degree of improvement in insulin sensitivity.

WHAT IS NEW AND CONCLUSION

The obtained results indicate that the impact of metformin on lactotrope secretory function is partially determined by the estrogen status of patients.

Vitamin D status determines the impact of metformin on circulating prolactin levels in premenopausal women

WHAT IS KNOWN AND OBJECTIVE

Metformin was found to normalize secretory function of overactive pituitary cells. Its effect on circulating thyrotropin levels was more pronounced in women receiving exogenous vitamin D. The aim of the current study was to investigate whether vitamin D status determines the impact of metformin on prolactin levels in premenopausal women with hyperprolactinaemia.

METHODS

The study population consisted of three groups of women with prediabetes and elevated prolactin levels: vitamin D-naïve women with vitamin D insufficiency (group 1; n = 19), women receiving vitamin D preparations because of vitamin D deficiency (group 2 n = 20), as well as vitamin D-naïve women with normal vitamin D status (group 3 n = 23). All participants were then treated with metformin (2.55-3 g daily). Circulating levels of glucose, insulin, prolactin, thyrotropin, free thyroid hormones, gonadotropins, estradiol, calcium and 25-hydroxyvitamin were determined at baseline and six months later.

RESULTS AND DISCUSSION

At baseline, prolactin levels were higher in group 1 than in the remaining groups of patients. Although metformin decreased glucose levels and improved insulin sensitivity in all treatment groups, this effect was more pronounced in groups 2 and 3. Only in subjects with 25-hydroxyvitamin D levels within the reference range, metformin reduced prolactin levels. The impact on prolactin levels correlated with 25-hydroxyvitamin D levels and with the improvement in insulin sensitivity. The drug produced a neutral effect on circulating levels of thyrotropin, free thyroid hormones, gonadotropins, estradiol, calcium and 25-hydroxyvitamin D.

WHAT IS NEW AND THE CONCLUSION

The results of the current study suggest that the impact of metformin on secretory function of overactive lactotropes depends on the vitamin D status of patients.