Is there an increased cardiovascular risk in patients with prolactinoma? A challenging question

Cardiometabolic effects of hypoprolactinemia

The fall of PRL levels below the lower limit of the normal range configures the condition of hypoprolactinemia. Unlike PRL excess, whose clinical features and treatments are well established, hypoprolactinemia has been only recently described as a morbid entity requiring prompt identification and proper therapeutic approach. Particularly, hypoprolactinemia has been reported to be associated with the development of metabolic syndrome and impaired cardiometabolic health, as visceral obesity, insulin-resistance, diabetes mellitus, dyslipidaemia, chronic inflammation, and sexual dysfunction have been found more prevalent in patients with hypoprolactinemia as compared to those with normoprolactinemia. This evidence has been collected mainly in patients on chronic treatment with dopamine agonists for PRL excess due to a PRL-secreting pituitary tumour, and less frequently in those receiving the atypical antipsychotic aripiprazole. Nowadays, hypoprolactinemia appears to represent a novel and unexpected risk factor for cardiovascular diseases, as is the case for hyperprolactinemia. Nevertheless, current knowledge still lacks an accurate biochemical definition of hypoprolactinemia, since no clear PRL threshold has been established to rule in the diagnosis of PRL deficiency enabling early identification of those individual subjects with increased cardiovascular risk directly ascribable to the hormonal imbalance. The current review article focuses on the effects of hypoprolactinemia on the modulation of body weight, gluco-insulinemic and lipid profile, and provides latest knowledge about potential cardiovascular outcomes of hypoprolactinemia.

Serum Prolactin Levels and Mortality in Adults Without Prolactinoma: A Meta-Analysis

CONTEXT

Prolactin (PRL) is a highly versatile, multifunctional hormone synthesized and secreted by lactotroph cells of the anterior pituitary. Its metabolic role has been extensively studied even in normoprolactinemic populations. Recently, a wealth of observational data have outlined the potential prognostic value of PRL in various clinical settings.

OBJECTIVE

This systematic review aims to systematically evaluate and quantitatively synthesize the association between serum PRL levels and risk of mortality in adults without prolactinoma.

METHODS

A systematic literature search was conducted up to June 10, 2023, to identify studies reporting the association of serum PRL levels with clinical outcomes of adults without prolactinoma. A random-effects meta-analysis was conducted to quantify the adjusted hazard ratios [(a)HRs] for all-cause and cardiovascular death (CVD) during follow-up.

RESULTS

Twenty-eight studies were deemed eligible reporting the outcomes of adults without prolactinoma, in whom serum PRL levels were measured for risk-stratification. Fourteen studies reported appropriate data for meta-analysis encompassing a total of 23 596 individuals. Each unit of PRL increase was independently associated with increased risk of all-cause (pooled aHR = 1.17 [1.08-1.27]; I2 = 48%) and CV mortality (pooled aHR = 1.54 [1.14-2.09]; I2 = 89%). Individuals belonging to the highest PRL category had significantly higher risk for all-cause (pooled aHR = 1.81 [1.43-2.30]; I2 = 65%) and CV (pooled aHR = 1.59 [1.04-2.42]; I2 = 82%) mortality compared to their lowest-PRL category counterparts. The association between PRL levels and in-hospital death did not reach statistical significance.

CONCLUSION

PRL levels seem to be an independent predictor for mortality. Further validation is warranted before its role as a risk-stratification tool can be delineated in clinical practice.

Association of prolactin with all-cause and cardiovascular mortality among patients with type 2 diabetes: a real-world study

AIMS

The association between prolactin and mortality has been less studied, and findings were inconsistent among different populations. We aimed to investigate the association between serum prolactin (PRL) and mortality among patients with type 2 diabetes.

METHODS AND RESULTS

We performed a retrospective cohort study of 10 907 patients with at least 2 prolactin measurements within 2 years since their first inpatient diagnosis of type 2 diabetes. Baseline and mean values of serum PRL were used as exposures. A multivariable-adjusted Cox proportional hazards model was used to estimate the association between PRL and mortality. During a mean follow-up of 5.34 years, 863 patients died, of whom 274 were due to cardiovascular events. Multivariable-adjusted hazard ratios (aHRs) based on different levels of baseline PRL (<100, 100-199, 200-299, and ≥300 mIU/L) were 1.00, 1.10 [95% confidence interval (CI), 0.90-1.36], 1.35 (95% CI 1.11-1.67), and 1.49 (95% CI 1.18-1.84) for all-cause mortality and 1.00, 1.24 (95% CI 0.86-1.81), 1.71 (95% CI 1.14-2.62), and 2.42 (95% CI 1.55-3.78) for cardiovascular mortality, respectively. Positive associations were also found when we used the mean values of PRL as the exposure. These associations were consistent among patients of different baseline characteristics. Further sensitivity analyses excluding patients with subclinical or clinical hypothyroidism at baseline and who died within the first 6 months since baseline demonstrated similar results.

CONCLUSIONS

A positive association between baseline PRL and mortality was observed among patients with type 2 diabetes. Prolactin may be considered a potential biomarker of mortality among patients with type 2 diabetes.

Metabolic effects of prolactin

Over the last years, the metabolic role of PRL has emerged. PRL excess is known to promote weight gain, obesity, metabolic syndrome, and impairment in gluco-insulinemic and lipid profiles, likely due to the suppression of physiologic dopaminergic tone. Prolactin receptors and dopamine receptors type 2 have been demonstrated to be expressed on both human pancreatic β- cell and adipocytes, supporting a key role of prolactin and dopamine in peripheral metabolic regulation. Medical treatment with the dopamine agonists bromocriptine and cabergoline has been demonstrated to decrease the prevalence of metabolic syndrome and obesity, and significantly improve gluco-insulinemic and lipid profiles. In hyperprolactinemic men with concomitant hypogonadism, correction of hyperprolactinaemia and testosterone replacement has been proven to restore metabolic impairment. In turn, low prolactin levels have also been demonstrated to exert a detrimental effect on weight gain, glucose and lipid metabolism, thus leading to an increased prevalence of metabolic syndrome. Therefore, PRL values ranging from 25 to 100 mg/L, in absence of other recognizable pathological causes, have been proposed to represent a physiological response to the request for an increase in metabolic activity, and nowadays classify the so-called HomeoFIT- PRL as a promoter of metabolic homeostasis. The current review focuses mainly on the effects of hyperprolactinemia and its control by medical treatment with DAs on the modulation of food intake, body weight, gluco-insulinemic and lipid profile. Furthermore, it provides the latest knowledge about the metabolic impact of hypoprolactinemia.

The interplay between prolactin and cardiovascular disease

Hyperprolactinemia can be caused by several conditions and its effects on the hypothalamic-pituitary-gonadal axis are understood in more detail. Nevertheless, in recent decades, other metabolic effects have been studied and data pointed to a potential increased cardiovascular disease (CVD) risk. A recent study showed a decrease in total and LDL- cholesterol only in men with prolactinoma treated with dopamine agonists (DA) supporting the previous results of a population study with increased CVD risk in men harboring prolactinoma. However, other population studies did not find a correlation between prolactin (PRL) levels and CVD risk or mortality. There is also data pointing to an increase in high-density lipoprotein levels, and decreases in triglycerides, carotid-intima-media thickness, C-reactive protein, and homocysteine levels in patients with prolactinoma on DA treatment. PRL was also implicated in endothelial dysfunction in pre and postmenopausal women. Withdrawal of DA resulted in negative changes in vascular parameters and an increase in plasma fibrinogen. It has been shown that PRL levels were positively correlated with blood pressure and inversely correlated with dilatation of the brachial artery and insulin sensitivity, increased homocysteine levels, and elevated D-dimer levels. Regarding possible mechanisms for the association between hyperprolactinemia and CVD risk, they include a possible direct effect of PRL, hypogonadism, and even effects of DA treatment, independently of changes in PRL levels. In conclusion, hyperprolactinemia seems to be associated with impaired endothelial function and DA treatment could improve CVD risk. More studies evaluating CVD risk in hyperprolactinemic patients are important to define a potential indication of treatment beyond hypogonadism.