Immunoglobulin G subclasses and prolactin (PRL) isoforms in macroprolactinemia due to anti-PRL autoantibodies

Impact of anti-squamous cell carcinoma antigen antibodies on serum squamous cell carcinoma antigen levels measured by chemiluminescent immunoassay and chemiluminescent enzyme immunoassay

OBJECTIVE

The serum squamous cell carcinoma antigen (SCCA) level is a well-known tumor marker for squamous cell carcinoma. In this study, we examined the impact of immunoglobulin (Ig)-bound macromolecular SCCA on serum SCCA levels measured by 2 different methods.

METHODS

Seventy-five serum samples with an SCCA level >5.0 ng/mL as determined by a chemiluminescent immunoassay (CLIA) were also analyzed using a chemiluminescent enzyme immunoassay (CLEIA). The levels of IgG- and IgA-type anti-SCCA antibodies, which form immunoglobulins and macromolecules, respectively, were determined using an enzyme-linked immunosorbent assay. An absorption test was performed to confirm the presence of anti-SCCA antibodies.

RESULTS

The correlation coefficient between the values measured by CLEIA and CLIA was 0.768. The ratio of SCCA levels measured by CLEIA to those measured by CLIA in 14 samples with IgG-type anti-SCCA antibodies was significantly lower than that in samples without these antibodies (P < .031). Absorption tests showed that SCCA levels measured by CLIA might be falsely high in samples with IgG-type anti-SCCA antibodies, probably due to reactions with SCCA1.

CONCLUSION

The level of SCCA as measured by CLIA and CLEIA methods correlate well, but the presence of SCCA antibodies can affect the results of the CLIA method.

Macroprolactin in mothers and their babies: what is its origin?

OBJECTIVES

Macroprolactinemia is one of the major causes of hyperprolactinemia. The aim of this study was to clarify the origin of macroprolactin (macro-PRL).

METHODS

We examined macro-PRL in the sera of 826 pregnant women and in those of their babies' umbilical cords at delivery. Macro-PRL was evaluated by precipitation with polyethylene glycol (PEG), gel filtration chromatography (GFC), and absorption with protein G (PG).

RESULTS

We detected macro-PRL in 16 out of the 826 pregnant women (1.94 %) and in 14 of their babies, which may indicate the possibility of hereditary origin of macro-PRL. However, the macro-PRL ratios of the babies correlated positively with those of their mothers (r=0.72 for GFC, p<0.001 and r=0.77 for PG, p<0.001), suggesting that the immunoglobulin (Ig)G-type anti-PRL autoantibodies might be actively transferred to babies via the placenta and form macro-PRL by binding to their babies' PRL or PRL-IgG complexes may possibly pass through the placenta. There were two cases in which only mothers had macro-PRL, indicating that the mothers had autoantibodies that did not pass through the placenta, such as IgA, PRL bound to the other proteins or PRL aggregates. No cases were found in which only the babies had macro-PRL and their mothers did not, suggesting that macro-PRL might not arise by non-hereditary congenital causes.

CONCLUSIONS

Macro-PRL in women of reproductive age might be mostly IgG-type anti-PRL autoantibody-bound PRL. The likely origin of macro-PRL in babies is the transplacental transfer of IgG-type anti-PRL autoantibodies or PRL-IgG complexes from the mothers to their babies.

Hormone Immunoassay Interference: A 2021 Update

Immunoassays are powerful qualitative and quantitative analytical techniques. Since the first description of an immunoassay method in 1959, advances have been made in assay designs and analytical characteristics, opening the door for their widespread implementation in clinical laboratories. Clinical endocrinology is closely linked to laboratory medicine because hormone quantification is important for the diagnosis, treatment, and prognosis of endocrine disorders. Several interferences in immunoassays have been identified through the years; although some are no longer encountered in daily practice, cross-reaction, heterophile antibodies, biotin, and anti-analyte antibodies still cause problems. Newer interferences are also emerging with the development of new therapies. The interfering substance may be exogenous (e.g., a drug or substance absorbed by the patient) or endogenous (e.g., antibodies produced by the patient), and the bias caused by interference can be positive or negative. The consequences of interference can be deleterious when clinicians consider erroneous results to establish a diagnosis, leading to unnecessary explorations or inappropriate treatments. Clinical laboratories and manufacturers continue to investigate methods for the detection, elimination, and prevention of interferences. However, no system is completely devoid of such incidents. In this review, we focus on the analytical interferences encountered in daily practice and possible solutions for their detection or elimination.

Evaluation of monomeric prolactin level by TRACE method and precipitation with polyethylene glycol

Prolactin exists in various forms including the monomeric biologically active form (23kDa) and a higher molecular weight form, bound most commonly to IgG, known as macroprolactin (>100kDa). Macroprolactin lacks biological activity and is one of the causes of false-positive results. In Russian Federation the most common method for macroprolactin determination is PEG precipitation test. We had conducted a retrospective analysis of 37 samples of patients with hyperprolactinemia (3 of them were males). The mean age was 30 [25;35] years. Prolactin level was measured by the immunoenzyme method with manual PEG precipitation and TRACE. The mean values found by the immunoenzyme method with manual PEG precipitation were 461,6 [375,0;821,2] mU/l, by TRACE - 449,9 [357,2;749,2] mU/l. The number of patients with normal prolactin levels was 30% (11) confirmed by two methods, high prolactin level at 46% (17). The prevalence of clinical symptoms of hyperprolactinemia was not differ depend the groups. The phenomenon of macroprolactinemia was registered in 32% (12) of patients. In 8 persons of this group normal prolactin level was revealed and in 4 patients hyperprolactinemia was found by TRACE. Measurements of prolactin levels by the TRACE method is useful for correct diagnosis in patients with equivocal results received by traditional method with PEG precipitation.

Circulating macroprolactin exhibits molecular heterogeneity and is not exclusively an antibody complex

BACKGROUND

Macroprolactin (macPRL) is considered to be solely a prolactin antibody complex. We examined macPRL heterogeneity in samples from thirteen patients suspected of macroprolactinemia.

METHODS

Polyethylene glycol (PEG) precipitation, gel permeation (GPC), protein-G affinity, and Lectin affinity chromatography were used to investigate the nature of macPRL.

RESULTS

Using PEG, 8, 3, and 2 samples were macPRL positive, negative, and indeterminate respectively. Using GPC, prolactin appeared at high (H) (≥150 kDa), mid (M) (≥30 < 150 kDa), and low (L) (<30 k Da) forms. For macPRL positive samples, 52.3 to 95.0%, 3.6 to 34.1%, and 1.4 to 34.5% appeared at the (H), (M), and (L) regions respectively, compared with samples negative for macPRL with 1.2 to 5.1%, 60.0 to 79.4%, and 15.4 to 38.9% prolactin activity respectively. macPRL positive samples showed 30.4 to 86.5% binding to protein G column compared with negative samples at 1.2 to 5.1%. GPC-separated forms showed macPRL is heterogenous being either antibody bound (protein G studies) or glycosylated aggregates (lectin studies). Samples with identified macPRL forms were analysed using 4 immunoassay analysers.

CONCLUSIONS

Samples with (H) and (M) macPRL forms showed significant positive bias in 2 immunoassays. The study is limited by the small number of samples and a larger scale study is required.

Global Prevalence of Macroprolactinemia among Patients with Hyperprolactinemia: A Systematic Review and Meta-Analysis

Hyperprolactinemia (hPRL) often poses a diagnostic dilemma due to the presence of macroprolactin. Understanding the prevalence of macroprolactinemia (mPRL) has an important implication in managing patients with hPRL. The primary aim of this study was to determine the prevalence of mPRL globally and to explore selected factors influencing the prevalence estimate. Studies with original data related to the prevalence of mPRL among patients with hPRL from inception to March 2020 were identified, and a random effects meta-analysis was performed. Of the 3770 records identified, 67 eligible studies from 27 countries were included. The overall global prevalence estimate was 18.9% (95% CI: 15.8%, 22.1%) with a substantial statistical heterogeneity (I² = 95.7%). The highest random effects pooled prevalence was observed in the African region (30.3%), followed by Region of the Americas (29.1%), European (17.5%), Eastern Mediterranean (13.9%), South-East Asian (12.7%), and Western Pacific Region (12.6%). Lower prevalence was observed in studies involving both sexes as compared to studies involving only female participants (17.1% vs. 25.4%) and in more recent studies (16.4%, 20.4%, and 26.5% in studies conducted after 2009, between 2000 and 2009, and before 2000, respectively). The prevalence estimate does not vary according to the age group of study participants, sample size, and types of polyethylene glycol (PEG) used for detection of macroprolactin (PEG 6000 or PEG 8000). With macroprolactin causing nearly one-fifth of hPRL cases, screening for mPRL should be made a routine before an investigation of other causes of hPRL.

Evaluation of autoantibodies and immunoglobulin G subclasses in women with suspected macroprolactinemia

BACKGROUND

Macroprolactin mostly composed of an immunoglobulin G (IgG) and a monomeric prolactin (PRL) represents the major circulating PRL form in the patients with macroprolactinemia that are usually asymptomatic and may not require treatment. In this study, we aimed to evaluate the prevalence of antithyroid and antinuclear antibodies, as well as the IgG subclass distributions in the patients suspected for macroprolactinemia.

METHODS

From January to July in 2018, totally 317 patients with elevated PRL were subjected to the polyethylene glycol (PEG) precipitation assay. The patients with recovery rates of ≤60% were subjected for IgG subclass determination and autoantibody testing including thyroid peroxidase antibody (aTPO), antithyroglobulin antibody (aTG), and antinuclear antibodies (ANA).

RESULTS

The higher the post-PEG PRL recovery rates, the less typical hyperprolactinemia symptoms and the higher prevalence of autoantibodies were observed. The IgG1 and IgG3 were the predominant subclasses in the PRL-IgG complexes according to the immunoprecipitation experiments.

CONCLUSION

The patients with post-PEG PRL recovery rates of <40% and 40%-60% were likely to represent two distinct populations of different clinical presentations. The prevalence of autoantibodies and IgG subclasses distribution suggested their pathogenic significance in the development of macroprolactinemia.

Interpretation of common endocrine laboratory tests: technical pitfalls, their mechanisms and practical considerations

Pitfalls in hormonal assays are commonly seen in clinical practice and may lead to erroneous clinical impressions and treatments. In this article, we address common laboratory pitfalls encountered during evaluation of patients with real or presumed endocrine disorders including high dose hook effect and falsely normal prolactin in cases of macroprolactinomas, macroprolactinemia and falsely elevated prolactin, macrothyrotropinemia and falsely elevated TSH, heterophile antibodies leading to false elevation of hormonal concentration, biotin interference with different hormonal assays, cross-reactivity of steroid hormones immunoassays, and others. We describe the mechanisms of such laboratory pitfalls, review clinical scenarios in which they might occur, and discuss the ways to resolve such conundrums. The aim of this article is to present a learning material for the endocrine trainees and practitioners.

Laboratory and clinical significance of macroprolactinemia in women with hyperprolactinemia

The role of macroprolactinemia in women with hyperprolactinemia is currently controversial and can lead to clinical dilemmas, depending upon the origin of macroprolactin, the presence of hyperprolactinemic symptoms and monomeric prolactin (PRL) levels. Macroprolactinemia is mostly considered an extrapituitary phenomenon of mild and asymptomatic hyperprolactinemia associated with normal concentrations of monomeric PRL and a predominance of macroprolactin confined to the vascular system, which is biologically inactive. Patients can therefore be reassured that macroprolactinemia should be considered a benign clinical condition, resistant to antiprolactinemic drugs, and that no diagnostic investigations or prolonged follow-up should be necessary. However, a significant proportion of macroprolactinemic patients appears to suffer from hyperprolactinemia-related symptoms and radiological pituitary findings commonly associated with true hyperprolactinemia. The symptoms of hyperprolactinemia are correlated to the levels of monomeric PRL excess, which may be explained as coincidental, by dissociation of macroprolactin, or by physiological, pharmacological and pathological causes. The excess of monomeric PRL levels in such cases is of primarily importance and the diagnosis of macroprolactinemia is misleading or inadequate. However, macroprolactinemia of pituitary origin associated with radiological findings of pituitary adenomas may rarely occur with similar hyperprolactinemic manifestations, exclusively due to bioactivity of macroprolactin. Therefore, in such cases with hyperprolactinemic signs and pituitary findings, macroprolactinemia should be considered a pathological biochemical condition of hyperprolactinemia. Accordingly, individualized diagnostic investigations with the introduction of dopamine agonists, or other treatment with prolonged follow-up, should be mandatory. The review analyses the laboratory and clinical significance of macroprolactinemia in hyperprolactinemic women suggesting clinically useful diagnostic and treatment strategies.

Controversial issues in the management of hyperprolactinemia and prolactinomas - An overview by the Neuroendocrinology Department of the Brazilian Society of Endocrinology and Metabolism

Prolactinomas are the most common pituitary adenomas (approximately 40% of cases), and they represent an important cause of hypogonadism and infertility in both sexes. The magnitude of prolactin (PRL) elevation can be useful in determining the etiology of hyperprolactinemia. Indeed, PRL levels > 250 ng/mL are highly suggestive of the presence of a prolactinoma. In contrast, most patients with stalk dysfunction, drug-induced hyperprolactinemia or systemic diseases present with PRL levels < 100 ng/mL. However, exceptions to these rules are not rare. On the other hand, among patients with macroprolactinomas (MACs), artificially low PRL levels may result from the so-called "hook effect". Patients harboring cystic MACs may also present with a mild PRL elevation. The screening for macroprolactin is mostly indicated for asymptomatic patients and those with apparent idiopathic hyperprolactinemia. Dopamine agonists (DAs) are the treatment of choice for prolactinomas, particularly cabergoline, which is more effective and better tolerated than bromocriptine. After 2 years of successful treatment, DA withdrawal should be considered in all cases of microprolactinomas and in selected cases of MACs. In this publication, the goal of the Neuroendocrinology Department of the Brazilian Society of Endocrinology and Metabolism (SBEM) is to provide a review of the diagnosis and treatment of hyperprolactinemia and prolactinomas, emphasizing controversial issues regarding these topics. This review is based on data published in the literature and the authors' experience.

Serum prolactin revisited: parametric reference intervals and cross platform evaluation of polyethylene glycol precipitation-based methods for discrimination between hyperprolactinemia and macroprolactinemia

BACKGROUND

Hyperprolactinemia diagnosis and treatment is often compromised by the presence of biologically inactive and clinically irrelevant higher-molecular-weight complexes of prolactin, macroprolactin. The objective of this study was to evaluate the performance of two macroprolactin screening regimes across commonly used automated immunoassay platforms.

METHODS

Parametric total and monomeric gender-specific reference intervals were determined for six immunoassay methods using female (n=96) and male sera (n=127) from healthy donors. The reference intervals were validated using 27 hyperprolactinemic and macroprolactinemic sera, whose presence of monomeric and macroforms of prolactin were determined using gel filtration chromatography (GFC).

RESULTS

Normative data for six prolactin assays included the range of values (2.5th-97.5th percentiles). Validation sera (hyperprolactinemic and macroprolactinemic; n=27) showed higher discordant classification [mean=2.8; 95% confidence interval (CI) 1.2-4.4] for the monomer reference interval method compared to the post-polyethylene glycol (PEG) recovery cutoff method (mean=1.8; 95% CI 0.8-2.8). The two monomer/macroprolactin discrimination methods did not differ significantly (p=0.089). Among macroprolactinemic sera evaluated by both discrimination methods, the Cobas and Architect/Kryptor prolactin assays showed the lowest and the highest number of misclassifications, respectively.

CONCLUSIONS

Current automated immunoassays for prolactin testing require macroprolactin screening methods based on PEG precipitation in order to discriminate truly from falsely elevated serum prolactin. While the recovery cutoff and monomeric reference interval macroprolactin screening methods demonstrate similar discriminative ability, the latter method also provides the clinician with an easy interpretable monomeric prolactin concentration along with a monomeric reference interval.

Pituitary response profile following metoclopramide administration in women with different forms of hyperprolactinemia

AIMS

To test the hypothesis that macroprolactinemia is an extra-pituitary phenomenon by showing that the pituitary production of prolactin in patients with hyperprolactinemia due to macroprolactin is comparable to that in normoprolactinemic women and different from that in women with monomeric hyperprolactinemia.

METHODS

Twenty-five women were studied: eight with macroprolactin hyperprolactinemia, eight with monomeric hyperprolactinemia, and nine controls. Prolactin levels were measured before and after precipitation with polyethylene glycol at baseline and at 5, 10,15, 30, and 60 min after metoclopramide administration (10 mg i.v.) in the three groups.

RESULTS

The response profile of total and monomeric prolactin following the administration of metoclopramide was similar in women with monomeric hyperprolactinemia and normoprolactinemia but different in women with macroprolactinemia. The areas under the curve for total and monomeric prolactin were higher in patients with macroprolactinemia than in the other two groups (p < 0·0001). The maximal concentration of monomeric prolactin was reached before that of total prolactin in macroprolactinemic patients but the differences were not significant.

DISCUSSION

Our findings support the hypothesis that prolactin secretion is comparable in women with macroprolactinemia and in normoprolactinemic women. The dynamics of the secretion suggest that the formation of prolactin complexes is an extra-pituitary process.

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS, AMERICAN COLLEGE OF ENDOCRINOLOGY DISEASE STATE CLINICAL REVIEW: CLINICAL RELEVANCE OF MACROPROLACTIN IN THE ABSENCE OR PRESENCE OF TRUE HYPERPROLACTINEMIA

OBJECTIVE

To review the current literature regarding the prevalence of macroprolactin (macroPRL) in hyperprolactinemic patients and determine recommendations for testing.

METHODS

An electronic United States National Library of Medicine PubMed search (through October, 2014) was conducted for search term "macroprolactin." Only English-language articles were considered.

RESULTS

MacroPRL is an under-recognized cause of elevated prolactin (PRL) and is present in approximately 4% to 40% of hyperprolactinemic patients depending on the referral population. Clinical findings which could be due to hyperprolactinemia are the impetus for testing for PRL. Because of this there is significant overlap in the clinical presentation of patients with true hyperprolactinemia and those with macroPRL, differentiation cannot always be made on the basis of symptoms. A lack of recognition of the presence of macroPRL can lead to unnecessary laboratory investigations, imaging, and pharmacologic or surgical treatment.

CONCLUSION

Until there is a commercially available PRL assay that is not subject to interference by macroPRL, clinicians should consider the possibility of macroPRL, especially if the clinical presentation, imaging findings, and/or response to therapy reveal inconsistencies.

Serum macroprolactin levels in pregnancy and association with thyroid autoimmunity

BACGROUND

To assess the contribution of macroprolactin to high serum prolactin levels and their association with thyroid status and thyroid autoimmunity during pregnancy.

METHODS

138 pregnant women who suspected of having thyroid dysfunction were studied and divided into three groups according to the thyroid status; group 1; euthyroidism (n 40), group 2; hypothyroidism (n 54), and group 3; hyperthyroid (n 44). Polyethylene glycol (PEG) precipitation method was used for detection of macroprolactin. A percentage recovery of 40 % or less is considered as macroprolactinemia. If macroprolactin was negative, the percentage of monomeric prolactin recovery (monoPRL %) after PEG precipitation was used for comparison between the groups.

RESULTS

Macroprolactinemia was found in two patients (1.4 %) one from hypothyroid and other from euthyroid group. Basal prolactin levels in these patients were 400 and 403 ng/mL respectively. Referring to all patients, there was no correlation between PRL, macroPRL or monoPRL % with thyroid hormone status and also with the serum levels of thyroid antibodies (p > 0.05). A positive correlation was observed between the serum levels of PRL with TSH (p = 0.014 and r = 0.219), while a negative correlation was found with FT4 (p = 0.011 and r = -0.227).

CONCLUSIONS

Despite the fact that serum prolactin levels were found to be high during pregnancy, the contribution of macroprolactin was found to be insignificant in our study. Unlike other auto immune diseases, we could not find any relationship between thyroid autoimmunity and PRL, macroPRL or monoPRL %. These results confirmed that measured prolactin was quite homogeneous during pregnancy.

Proteomics of the human pituitary tissue: bioanalytical methods and applications

The pituitary is the central endocrine gland that plays complex regulatory roles in growth, reproduction and metabolism of the body. The human pituitary tissue proteome has been the target of a number of investigations that applied various combinations of advanced separation techniques, mass spectrometry, and bioinformatics tools. This review describes the main features of the bioanalytical workflows used in pituitary proteomics, and summarizes major applications in pituitary proteome mapping, differential protein expression profiling in health and disease, and discovery of post-translational modifications in pituitary proteins.

Determination of prolactin: the macroprolactin problem

Serum prolactin is frequently measured when investigating patients with reproductive disorders and elevated concentrations are found in up to 17% of such cases. Clinical laboratories rely predominantly on automated analysers to quantify prolactin levels using sandwich immunometric methodologies. Though generally robust and reliable, such immunoassays are susceptible to interference from a high molecular mass prolactin/IgG autoantibody complex termed macroprolactin. While macroprolactin remains reactive to varying degrees in all prolactin immunoassays, it exhibits little if any biological activity in vivo and consequently its presence is considered clinically irrelevant. Macroprolactinaemia, defined as hyperprolactinaemia due to excess macroprolactin with normal concentrations of bioactive monomeric prolactin, may lead to misdiagnosis and mismanagement of hyperprolactinemic patients if not recognised. Current best practice recommends that all sera with elevated total prolactin concentrations are sub-fractionated using polyethylene glycol precipitation to provide a more meaningful clinical measurement of the bioactive monomeric prolactin content. Manufacturers of prolactin assays should strive to minimise interference from macroprolactin in their assays. Clinical laboratories should introduce screening procedures to exclude macroprolactinaemia in all patients identified as having hyperprolactinaemia. Clinicians should be aware of this potential diagnostic pit fall and insist on PEG screening of all hyperprolactinaemic sera.

Macroprolactinemia in a patient with invasive macroprolactinoma: a case report and minireview

Background. Macroprolactin, the high-molecular prolactin isoform, is considered to be an inactive in vivo product with extrapituitary origin. Patients with macroprolactinemia are usually asymptomatic, with negative pituitary imaging. Based on these data, most authors do not recommend treatment and long-term followup in subjects with macroprolactinemia. However, there is evidence for overlapping clinical features among subjects with hyperprolactinemia due to monomeric or “big big” PRL isoform. Case Presentation. We present a 35-year-old female patient with secondary amenorrhea, mild obesity, hirsutism, headache and blurred vision. Hormonal evaluation revealed an extreme hyperprolactinemia (PRL = 10 610 mIU/L) almost exclusively due to macroprolactin isoform (MPRL = 10 107 mIU/L; recovery after PEG precipitation 4.7%) and hypogonadotropic hypogonadism. An invasive pituitary macroadenoma was visualized on MRI, and cabergoline therapy was initiated. Disappearance of clinical signs and symptoms, normalization of gonadotropin levels, and restoration of regular ovulatory menstrual cycles after 1 year of treatment are arguments in favor of preserved-macroprolactin bioactivity in this case. The significant decrease in MPRL levels and tumor volume in response to dopamine agonist therapy is suggestive for the tumoral origin of this isoform. Conclusions. Although macroprolactinemia is considered to be a benign condition, pituitary imaging, dopamine agonist treatment, and prolonged followup should be recommended in some particular cases.

Macroprolactinemia: diagnostic, clinical, and pathogenic significance

Macroprolactinemia is characterized by a large molecular mass of PRL (macroprolactin) as the main molecular form of PRL in sera, the frequent elevation of serum PRL (hyperprolactinemia), and the lack of symptoms. Macroprolactin is largely a complex of PRL with immunoglobulin G (IgG), especially anti-PRL autoantibodies. The prevalence of macroprolactinemia is 10–25% in patients with hyperprolactinemia and 3.7% in general population. There is no gender difference and a long-term followup demonstrates that macroprolactinemia develops before middle age and is likely a chronic condition. Polyethylene-glycol- (PEG-) precipitation method is widely used for screening macroprolactinemia, and gel filtration chromatography, protein A/G column, and I125-PRL binding studies are performed to confirm and clarify its nature. The cross-reactivity of macroprolactin varies widely according to the immunoassay systems. The epitope on PRL molecule recognized by the autoantibodies is located close to the binding site for PRL receptors, which may explain that macroprolactin has a lower biological activity. Hyperprolactinemia frequently seen in macroprolactinemic patients is due to the delayed clearance of autoantibody-bound PRL. When rats are immunized with rat pituitary PRL, anti-PRL autoantibodies are produced and hyperprolactinemia develops, mimicking macroprolactinemia in humans. Screening of macroprolactinemia is important for the differential diagnosis of hyperprolactinemia to avoid unnecessary examinations and treatments.

Macroprolactinemia: new insights in hyperprolactinemia

Hypersecretion of prolactin by lactotroph cells of the anterior pituitary may lead to hyperprolactinemia in physiological, pathological and idiopathic conditions. Most patients with idiopathic hyperprolactinemia may have radiologically undetected microprolactinomas, but some may present other causes of hyperprolactinemia described as macroprolactinemia. This condition corresponds to the predominance of higher molecular mass prolactin forms (big-big prolactin, MW > 150 kDa), that have been postulated to represent prolactin monomer complexed with anti-prolactin immunoglobulins or autoantibodies. The prevalence of macroprolactinemia in hyperprolactinemic populations between 15–46% has been reported. In the pathophysiology of macroprolactinemia it seems that pituitary prolactin has antigenicity, leading to the production of anti-prolactin autoantibodies, and these antibodies reduce prolactin bioactivity and delay prolactin clearance. Antibody-bound prolactin is big enough to be confined to vascular spaces, and therefore macroprolactinemia develops due to the delayed clearance of prolactin rather than increased production. Although the clinical symptoms are less frequent in macroprolactinemic patients, they could not be diff erentiated from true hyperprolactinemic patients, on the basis of clinical features alone. Although gel filtration chromatography (GFC) is known to be the gold standard for detecting macroprolactin, the polyethylene glycol precipitation (PEG) method has off ered a simple, cheap, and highly suitable alternative. In conclusion, macroprolactinemia can be considered a benign condition with low incidence of clinical symptoms and therefore hormonal and imaging investigations as well as medical or surgical treatment and prolonged follow-up are not necessary.

Detection of Macroprolactinemia and Molecular Characterization of Prolactin Isoforms in Blood Samples of Hyperprolactinemic Women

Prolactin (PRL) circulates in the blood in the form of monomeric prolactin, dimeric prolactin and macroprolactin. Macroprolactin is a common cause of hyperprolactinemia. The objective of this study was to assess the prevalence of macroprolactinemia in hyperprolactinemic women and to undertake the biochemical characterization of macroprolactin. A retrospective cross-sectional study was conducted on one hundred hyperprolactinemic patients. All the sera were subjected to polyethylene glycol (PEG) precipitation and were divided into true hyperprolactinemics (PRL recovery >60%), probable macroprolactinemics (PRL recovery between 40 and 60%) and macroprolactinemics (PRL recovery < 40%). The prevalence of macroprolactinemia was found to be 34%. Sera from each group were further analyzed for isoforms of prolactin by gel filtration chromatography (GFC). The clinical spectrum of presenting complaints in the hyperprolactinemic cohort included oligomenorrhea, galactorrhea and infertility, but the presentation did not differ between macroprolactinemic and truly hyperprolactinemic patients. GFC showed three major PRL isoforms, viz., 23.5 kDa (monomeric), 47 kDa (dimeric) and 150-174.6 kDa (PRL-IgG complexes) along with the medium and heavy weight aggregates of prolactin. The results of the study showed that macroprolactinemia is one of the causes of hyperprolactinemia with high prevalence. It is recommended that all hyperprolactinemic patients be screened for macroprolactinemia.

Anti-prolactin (PRL) autoantibodies suppress PRL bioactivity in patients with macroprolactinaemia

OBJECTIVE

Macroprolactinaemia, mainly caused by anti-prolactin (PRL) autoantibodies, is frequently found in patients with hyperprolactinaemia. Characteristically, these patients lack clinical symptoms of hyperprolactinaemia, but the serum bioactive PRL concentrations in vitro measured by the Nb2 bioassay are usually high. In this study, we investigated the causes of the discrepancy and the true biological features of macroprolactin.

SUBJECTS AND METHODS

Sixteen patients with macroprolactinaemia due to anti-PRL autoantibodies were studied. PRL bioactivity was determined by the phosphorylation of signal transducer and activator of transcription (Stat)5 in T47D human breast cancer cells and the proliferation of Nb2 rat lymphoma cells.

RESULTS

PRL bioactivity by the T47D bioassay, expressed as the density of the band of phosphorylated Stat5/immunoreactive PRL, was significantly lower in sera containing anti-PRL autoantibodies (2.4 +/- 1.1) than in control sera (7.2 +/- 3.1). Dissociation of PRL from the autoantibodies by acidification resulted in an increase in phosphorylated Stat5. PRL bioactivity by the Nb2 bioassay was not significantly different between sera with and without anti-PRL autoantibodies, and free PRL in the medium gradually increased during the incubation in a time-dependent manner in sera containing anti-PRL autoantibodies.

CONCLUSIONS

We conclude that the level of bioactivity of macroprolactin in the Nb2 bioassay is normal due to dissociation of PRL from the autoantibodies as a result of the longer incubation and more dilute assay conditions than in the T47D bioassay. The bioactivity of macroprolactin is low in vivo due to anti-PRL autoantibodies, but monomeric PRL dissociated from the autoantibodies retains full biological activity in patients with macroprolactinaemia.

Development of anti-PRL (prolactin) autoantibodies by homologous PRL in rats: a model for macroprolactinemia

Macroprolactinemia is hyperprolactinemia in humans mainly due to anti-PRL (prolactin) autoantibodies and is a pitfall for the differential diagnosis of hyperprolactinemia. Despite its high prevalence, the pathogenesis remains unclear. In this study, we examined whether anti-PRL autoantibodies develop via immunization with homologous rat pituitary PRL in rats to elucidate what mechanisms are involved and whether they cause hyperprolactinemia with low PRL bioactivity, as seen in human macroprolactinemia. Anti-PRL antibodies were developed in 19 of 20 rats immunized with homologous rat pituitary PRL and 29 of 30 rats with heterogeneous bovine or porcine pituitary PRL but did not develop in 25 control rats. In rats with anti-PRL antibodies, the basal serum PRL levels were elevated, and a provocative test for PRL secretion using dopamine D2 receptor antagonist (metoclopramide) showed a normal rising response with a slower clearance of PRL because of the accumulation of macroprolactin in blood. Antibodies developed by porcine or rat pituitary PRL reduced the bioactivity of rat serum PRL, and gonadal functions in these rats were normal despite hyperprolactinemia. Anti-PRL antibodies were stable and persisted for at least 5 wk after the final injection of PRL. These findings suggest that pituitary PRL, even if homologous, has antigenicity, leading to the development of anti-PRL autoantibodies. We successfully produced an animal model of human macroprolactinemia, with which we can explain the mechanisms of its clinical characteristics, i.e. asymptomatic hyperprolactinemia.

The effect of estrogen on phosphorylation of prolactin in the mouse pituitary gland

Several studies have indicated that prolactin (PRL) assumes oligomeric, proteolytically cleaved, phosphorylated and glycosylated forms. Phosphorylated PRL (PPRL) is considered to be the most important posttranslationally modified form in the rat. In the present study, we examined whether or not PRL is present in the mouse pituitary gland in the phosphorylated form. Mouse pituitary PRL was digested with acid phosphatase, resolved by two-dimensional gel electrophoresis, stained with Coomassie brilliant blue, and then immunoblotted against the anti-PRL, anti-phosphoserine and anti-phosphothreonine antibodies. We also examined whether PRL is phosphorylated by protein kinases and semi-quantified the ratios of PPRL to PRL in the pituitary gland. The results indicated that three types of PRL are present in the pituitary glands of both male and female mice. One was non-phosphorylated (isoform 1), and the other two were immunoreactive to anti-phosphoserine (isoform 2) and/or anti-phosphothreonine (isoform 3) antibodies. The ratio between isoforms 2 and 1 of the 30-day-old female mice was higher than that of the 20-day-old female mice. However, the ratios among the three isoforms in the male pituitary glands did not differ with age. The ratio of PPRL to isoform 1 was obviously reduced after ovariectomy (OVX), and it recovered with estrogen replacement. These results suggest that estrogen influences PRL phosphorylation in female mice.

Diagnosis, misdiagnosis and management of hyperprolactinemia

Hyperprolactinemia is a commonly encountered disorder that suppresses both male and female gonadal function. The etiology includes pituitary tumors, hypothalamic or pituitary stalk lesions, drugs and hypothyroidism. In women, the hyperprolactinemic syndrome is characterized by menstrual disorders with or without galactorrhea, while men present with hypogonadism and related symptoms. Occasionally, a pituitary macroadenoma may be associated with pressure symptoms and/or hypopituitarism. Clinically, the most important cause of hyperprolactinemia is a prolactin-secreting pituitary adenoma. The majority of patients with prolactinomas are successfully managed medically with dopamine agonists such as cabergoline or bromocriptine. Misdiagnosis of hyperprolactinemia owing to immunoassay interference by a biologically minimally active form of prolactin termed macroprolactin is common in laboratory medicine . Alhough the etiology of macroprolactinemia is unclear, the condition is commonly associated with the presence of circulating antiprolactin antibodies. In the absence of specific testing, macroprolactin represents a diagnostic pitfall resulting in misdiagnosis and mismanagement of patients. This review examines the investigation and treatment of hyperprolactinemia in the broadened context of screening for macroprolactin and the consequences of failure to identify its presence.

Macroprolactinemia: clinical significance and characterization of the condition

The purpose of this study was to characterize the clinical picture of macroprolactinemic patients and to further assess whether macroprolactinemia was part of an auto-immune syndrome. Eighty-two hyperprolactinemic (serum PRL > 1000 mU/l) patients were investigated and the PEG precipitation test identified 14 patients with macroprolactinemia (bb PRL). They were submitted to a hormonal and autoimmune screening and an IV TRH test. Bioactivity of their serum prolactin was evaluated, using an Nb2 assay. The biochemical nature of bb-PRL was investigated by immunoprecipitation with anti-IgG antibodies. Seventy-nine percent of the studied patients presented with infertility, amenorrhoea, galactorrhoea, mastodynia, gynaecomastia or erectile dysfunction. In most cases, however, these symptoms could be explained by the presence of other non hyperprolactinemia-related pathology. Despite the finding of in vitro biological activity in all macroprolactinemic sera tested, our results suggest a variable in vivo bioactivity of bb-PRL, probably related to a reduced capacity to cross vascular endothelium. In this study, we demonstrated that in 12 out of 13 samples (85%), bb-PRL consisted of PRL-IgG complexes. There was no clinical or laboratory evidence of auto-immunity.

Hyperprolactinaemia and the regular menstrual cycle in asymptomatic women: should it be treated during therapy for infertility?

It is known that hyperprolactinaemia can cause galactorrhoea and irregular cycles or even amenorrhoea. High serum prolactin (PRL) can disturb follicular maturation and corpus luteum function. Treatment of hyperprolactinaemia in patients with resulting bleeding anomalies is established, but the question is how to manage normal cyclic hyperprolactinaemic women? Studies have shown that in a subgroup of asymptomatic patients the serum contains mainly high molecular weight form (big big PRL), which has a low bioactivity, called macroprolactinaemia. It is evident that macroprolactin does not affect the control of pituitary PRL secretion via the short loop feedback mechanism or the secretion of gonadotrophins as does monomeric PRL. Identification of macroprolactinaemia is therefore clinically important to prevent unnecessary examinations and inappropriate treatment. Prolactinoma can be associated with macroprolactinaemia. Performance of pituitary imaging in asymptomatic patients with hyperprolactinaemia may therefore be justified, but further studies are needed to evaluate the relation of costs and benefit. An unsolved problem is the differentiation between inactive and PRL-secreting tumours. Caution should be exercised concerning medical treatment in unstimulated patients and also in patients during ovarian stimulation alone or in combination with intrauterine insemination or in-vitro fertilization. The potential clinical significance of hyperprolactinaemia/macroprolactinaemia in asymptomatic women must be further evaluated.