Effects of Pituitary Surgery and High-Dose Cabergoline Therapy on Metabolic Profile in Patients With Prolactinoma Resistant to Conventional Cabergoline Treatment

A Century of Prolactin: Emerging Perspectives as a Metabolic Regulator

Prolactin, a hormone that has been studied for almost a century, has evolved from a reproductive regulator to a key player in metabolic health. Initially identified for its lactogenic role, the impact of prolactin on glucose and lipid metabolism became evident in the 1970s, leading to a paradigm shift in our understanding. Deviations in prolactin levels, including hyperprolactinaemia and hypoprolactinaemia, have been associated with adverse effects on glucose and lipid metabolism. Mechanistically, prolactin regulates metabolic homoeostasis by maintaining islet abundance, regulating the hypothalamic energy regulatory centre, balancing adipose tissue expansion, and regulating hepatic metabolism. Given the widespread use of pharmaceutical agents that affect prolactin levels, it is important to examine prolactin-related metabolic effects. Recently, a profound exploration of the intricate metabolic role of prolactin has been conducted, encompassing its rhythm-dependent regulatory influence on metabolism and its correlation with cognitive impairment associated with metabolic diseases. In this review, we highlight the role of prolactin as a metabolic regulator, summarise its metabolic effects, and discuss topics related to the association between prolactin and metabolic comorbidities.

An Overview of Cardiovascular Risk in Pituitary Disorders

Cardiovascular comorbidities owing to hormonal excess or deficiency are the main cause of mortality in patients with pituitary disorders. In patients with Cushing's Disease, there is an increased prevalence of cardiovascular diseases and/or risk factors including visceral obesity, insulin resistance, atherosclerosis, arterial hypertension, dyslipidaemia, hypercoagulability as well as structural and functional changes in the heart, like cardiac hypertrophy and left ventricle (LV) dysfunction. Notably, these demonstrate limited reversibility even after remission. Furthermore, patients with acromegaly may manifest insulin resistance but also structural and functional heart changes, also known as "acromegalic cardiomyopathy". Patients with prolactinomas demonstrate an aggravation of metabolic parameters, obesity, dysregulation of glucose and lipid metabolism as well as endothelial dysfunction. Hypopituitarism and conventional hormonal replacement therapy may also contribute to an unhealthy metabolic status, which promotes atherosclerosis and may lead to premature mortality. This review discusses the literature on cardiovascular risk in patients with pituitary disorders to increase physician awareness regarding this aspect of management in patients with pituitary disorders.

Quality of life in Prolactinoma: A systematic review

BACKGROUND

Prolactinomas are common tumours that significantly reduce quality-of-life (QOL) due to sellar mass effect, secondary hypogonadism, and the peripheral effects of prolactin. Understanding the factors that influence QOL would provide insights into therapeutic targets to optimise patient outcomes and improve wellbeing in prolactinoma.

METHODS

A systematic review was performed in accordance with the PRISMA statement. Studies that reported patient QoL using validated metrics were included. Bias and methodological rigour were assessed using the MINORS criteria.

RESULTS

A total of 18 studies were identified studies were available for review, comprising 877 patients. Most were small cross-sectional studies at high risk of bias. Prolactinoma exhibit worse QOL than healthy controls, particularly mental and psychosocial wellbeing. QOL is also worse than patients with non-functional adenomas, but better than those with Cushing's disease and acromegaly. QOL correlates with prolactin levels, and approaches population baseline with prolonged biochemical control. Dopamine agonists and surgery both improve overall QOL, however improvements are more rapid with surgery.

CONCLUSION

Poor quality of life in prolactinoma is multifactorial, related to biochemical control, side effects of therapy, and sellar mass effect. Targeting persistent symptoms, reducing healthcare costs, and reducing side-effects of therapy are avenues to improving QOL in patients with prolactinoma.

Effect of Cabergoline on weight and glucose metabolism in patients with acromegaly

PURPOSE

Cabergoline (CAB) has shown to have benefic effects on the metabolism in different clinical settings but its metabolic role in acromegaly disease has not been studied yet. Aim of our study was to evaluate the impact of CAB on glucose metabolism and weight in patients with acromegaly.

METHODS

All patients with acromegaly undergoing continuous treatment with CAB for at least 6 months were retrospectively screened. Exclusion criteria were discontinuation of CAB for more than one month, change of antidiabetic or other therapy for acromegaly, concomitant untreated hormonal deficiency, initiation of pregnancy and/or breastfeeding. All patients were evaluated in terms of biochemical disease control, glucose metabolism and weight at baseline (T0) and after the introduction of CAB therapy at 6 (T6) and 12 months (T12).

RESULTS

Twenty-six patients (15 females and 11 males) were evaluated at T0 and T6 and 19 patients (12 females and 7 males) were also evaluated at T12. Insulin-like growth factor I (IGF-I) and prolactin (PRL) levels were significantly lower at T6 and T12 compared to baseline (p < 0.001 for IGF-I, p < 0.05 for PRL) even if no further differences were observed between T12 and T6. Considering the entire cohort, no differences were appreciated regarding the metabolic parameters but a significant reduction in weight and body mass index (BMI) was observed at both T6 (p = 0.009 for weight, p = 0.021 for BMI) and T12 (p = 0.014 for weight, p = 0.017 for BMI) compared to baseline.

CONCLUSION

Our results confirm the efficacy of CAB in providing a significant improvement in the biochemical disease control but do not demonstrate a marked benefit on glucose metabolism of acromegaly patients. In such patients, CAB appears to have a rapid effect on weight and BMI, with significant changes noticeable as early as 6 months and persisting for at least 12 months.

Metabolic Syndrome Components in Patients with Pituitary Adenoma

Pituitary adenomas are benign tumors of the anterior portion of the pituitary gland (adenohypophysis), representing the 25% of all the tumor alterations. Pituitary adenomas are classified by the type of hormone secreted, cellularity, size, and structural alterations by the hormonal segregation. The diagnosis consists on the histopathological identification of cell types and the image-guided by magnetic resonance or tomography; the treatment can be both pharmacological and surgical. Metabolic Syndrome is the set of clinical conditions that increase the risk of cardiovascular diseases with an estimated prevalence of 25% worldwide. The alterations of metabolic syndrome are obesity, hypertension, dyslipidemia, insulin resistance, and diabetes mellitus type II. Pituitary adenomas and metabolic syndrome have an important relationship, hormone-secreting by pituitary adenomas affects a myriad of signaling pathways, which allows a favorable environment for the appearance of the metabolic syndrome. Moreover, patients with pituitary adenomas are shown to have an improvement in metabolic parameters after the medical/surgical treatment. The objective of this review is to explore the possible mechanisms through which PAs contributes to MetSx.

Approach to the Patient With Prolactinoma

Prolactinomas are the most common pituitary tumor histotype, with microprolactinomas being prevalent in women and macroprolactinomas in men. Hyperprolactinemia is among the most common causes of hypogonadotropic hypogonadism in both sexes, prompting medical advice for hypogonadism (infertility, oligo-amenorrhea, impotence, osteoporosis/osteopenia) in both sexes, and for signs and symptoms of mass effects (hypopituitarism, visual loss, optic chiasm compression, cranial nerve deficits, headaches) predominantly in men. Diagnostic workup involves a single prolactin measurement and pituitary imaging, but some laboratory artifacts (ie, the "hook effect" and macroprolactin) can complicate or delay the diagnosis. The treatment of choice for prolactinomas is represented by dopamine agonists, mainly cabergoline, which are able to induce disease control, restore fertility in both sexes, and definitively cure one-third of patients, thus permitting treatment discontinuation. Pregnancy and menopause may promote spontaneous prolactin decline and anticipate cabergoline discontinuation in women. Surgery and/or radiotherapy are indicated in case of resistance to cabergoline not overcome by the increase in drug dose up to the maximally tolerated or the patient's personal choice of surgery. The evidence of resistance to cabergoline in invasive and proliferative tumors may indicate biological aggressiveness, thus requiring alternative therapeutic approaches mainly based on temozolomide use as monotherapy or combined with radiotherapy. In uncontrolled patients, new medical approaches (alternative hormonal treatments, cytotoxic drugs, peptide receptor radionuclide therapy, mTOR/Akt inhibitors, tyrosine kinase inhibitors, or immunotherapy) may be offered but the experience collected to date is still very scant. This article reviews different facets of prolactinomas and discusses approaches to the condition in more common clinical situations.

The metabolic role of prolactin: systematic review, meta-analysis and preclinical considerations

INTRODUCTION

Hyperprolactinemia has been proven to induce hypogonadism and metabolic derangements in both genders, while the consequences of prolactin (PRL) deficiency have been poorly investigated.

AREAS COVERED

To systematically review and analyze data from clinical studies focusing on the metabolic consequences of abnormally high prolactin levels (HPRL) and low prolactin levels (LPRL). In addition, data from preclinical studies about underlying pathophysiological mechanisms were summarized and discussed.

EXPERT OPINION

PRL contributes to providing the correct amount of energy to support the mother and the fetus/offspring during pregnancy and lactation, but it also has a homeostatic role. Pathological PRL elevation beyond these physiological conditions, but also its reduction, impairs metabolism and body composition in both genders, increasing the risk of diabetes and cardiovascular events. Hence, hypoprolactinemia should be avoided as much as possible during treatment with dopamine agonists for prolactinomas. Patients with hypoprolactinemia, because of endogenous or iatrogenic conditions, deserve, as those with hyperprolactinemia, careful metabolic assessment.

Ectopic Cavernous Sinus Microprolactinoma Treated Medically

Ectopic prolactin-secreting microadenomas are rare and management is often surgical in contrast to intrasellar pituitary prolactin-secreting microadenomas. We present a case of ectopic dopamine-resistant microprolactinoma treated with cabergoline which led to symptom resolution, hormonal remission, and cystic degeneration of the tumor. A 30-year-old active duty male presented with a chief complaint of inability to maintain an erection for 6 months. Initial workup revealed suppressed serum testosterone of 128.60 ng/ml with an elevated prolactin level at 275.10 ng/ml. Pituitary magnetic resonance imaging showed a small mass measuring 9 mm in the left cavernous sinus. Medical management was initiated with cabergoline, which was titrated over the course of a year from 0.5 mg a week to 3.5 mg a week at its peak before being weaned off completely at 54 months. After treatment, the patient's symptoms resolved, his prolactin decreased to 29.5 ng/ml, near-normal, and his tumor had decreased size with cystic degeneration. Management for any prolactinoma has three primary goals: remittance of symptoms, decrease in prolactin levels, and decrease in tumor size. These are achieved through primarily medical management or surgery. Even though ectopic microprolactinomas are still frequently addressed surgically, this case shows that medical therapy can successfully treat ectopic prolactin-secreting pituitary microadenomas even in cases of dopamine resistance.

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.

Metabolic effects of prolactin and the role of dopamine agonists: A review

Prolactin is a polypeptide hormone that is well known for its role in reproductive physiology. Recent studies highlight its role in neurohormonal appetite regulation and metabolism. Elevated prolactin levels are widely associated with worsening metabolic disease, but it appears that low prolactin levels could also be metabolically unfavorable. This review discusses the pathophysiology of prolactin related metabolic changes, and the less commonly recognized effects of prolactin on adipose tissue, pancreas, liver, and small bowel. Furthermore, the effect of dopamine agonists on the metabolic profiles of patients with hyperprolactinemia are discussed as well.