An Intact ACTH LC-MS/MS Assay as an Arbiter of Clinically Discordant Immunoassay Results

Liquid chromatography-tandem mass spectrometry in clinical laboratory protein measurement

Proteins are essential components of human cells and tissues, and they are commonly measured in clinical laboratories using immunoassays. However, these assays have certain limitations, such as non-specificity binding, insufficient selectivity, and interference of antibodies. More sensitive, accurate, and efficient technology is required to overcome these limitations. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful analytical tool that provides high sensitivity and specificity, making it superior to traditional methods such as biochemical and immunoassays. While LC-MS/MS has been increasingly used for detecting small molecular analytes and steroid hormones in clinical practice recently, its application for protein or peptide analysis is still in its early stages. Established methods for quantifying proteins and peptides by LC-MS/MS are mainly focused on scientific research, and only a few proteins and peptides can be or have the potential to be detected and applied in clinical practice. Therefore, this article aims to review the clinical applications, advantages, and challenges of analyzing proteins and peptides using LC-MS/MS in clinical laboratories.

A hybrid IA-LC-MS/MS method for adrenocorticotropic hormone(1-24) to support interpretation of low-dose cosyntropin-stimulation test

Adrenocorticotropic hormone 1-24 (ACTH[1-24]) has a similar effect as endogenous ACTH(1-39) to generate cortisol by targeting the MC2R receptor on the adrenal gland. A new investigational ACTH receptor antagonist drug is being developed to treat diseases of ACTH excess (e.g., Cushing's disease) by binding to the MC2R receptor. Administration of ACTH(1-24) was used in a Phase I clinical study to assess the ability of this drug candidate to suppress the cortisol response to ACTH stimulation. A hybrid immunoaffinity-LCMS assay measuring ACTH(1-24) with a concentration range of 10 to 400 pg/ml was developed to support the study. Consistent and acceptable A&P results were achieved. The assay development and qualification will be discussed.

A biomarker panel of secondary hypertension is simultaneously quantified by coupling of magnetic solid-phase extraction and liquid chromatography-tandem mass spectrometry

RATIONALE

Secondary hypertension is often caused by activation of complex multi-organ endocrine systems, while renin activity indicated by angiotensins (Angs), aldosterone (ALD) and cortisol (COR) in such systems are generally accepted as its diagnostic markers. As antibody-based methods cannot offer comparable quantification for these biomarkers, a liquid chromatography (LC)-tandem mass spectrometry (MS/MS)-based approach was developed to quantify them simultaneously and accurately.

METHODS

Five different beads for magnetic solid-phase extraction (MSPE) were evaluated towards their enrichment efficiency for these biomarkers. An LC system with optimized elution gradient and a triple-quadrupole MS with tuned parameters were coupled to quantitatively monitor the extracted analytes. The method performance was further examined such as linearity, precision, stability, recovery rate and matrix effect. Based on the developed method, the abundance of Ang II, ALD and COR in plasma was measured and the quantification was compared with that derived from commercial ELISA kits.

RESULTS

As compared with other MSPEs, Angs, ALD and COR were highly enriched by the HLB magnetic beads with satisfactory recoveries. These analytes were simultaneously quantified by LC/MS/MS and all the method parameters for quantification were well matched with the requirements of clinical testing. Comparison of the quantitative results derived from ELISA and LC/MS/MS exhibited that the two methods offered basically comparable values with Pearson r values at 0.896, 0.895 and 0.835, respectively. The stability test for plasma Angs at room temperature indicated that the abundance of Ang II was relatively stable within 3 h, whereas that of Ang I and Ang 1-7 was time-dependently changed.

CONCLUSIONS

Coupling of HLB beads and LC/MS/MS thus enables simultaneous quantification of a set of biomarkers related to secondary hypertension.

Immunoassay interferences: laboratory pitfall in the diagnosis of adrenocortical carcinoma

A woman in her late 50s with recent onset of hypertension, diabetes, lumbar pain and unintentional weight loss was diagnosed with a cortisol and androgen-producing adrenal mass. Despite this, serum adrenocorticotropic hormone (ACTH) concentration was inappropriately elevated, which was investigated thoroughly. Investigations included a brain magnetic resonance imaging to exclude concomitant pituitary adenoma, a corticotropin-releasing hormone stimulation test and a gallium-68 DOTATATE and 18F-FDOPA PET scan, both excluding ectopic ACTH production. Considering the disparity between clinical presentation and biochemical results, the ACTH was reanalysed using the Cobas immunoassay (Roche, Switzerland), ultimately unveiling the cause for ACTH elevation. ACTH levels had previously been measured with ACTH Immulite (Siemens, Germany), a two-site immunoassay which is prone to interferences causing falsely elevated ACTH concentrations. Inaccurate laboratory levels can lead to diagnosis delay and unnecessary diagnostic procedures and a close communication between the physicians and laboratorians is of utmost importance.

Recognition of Nonneoplastic Hypercortisolism in the Evaluation of Patients With Cushing Syndrome

The evaluation of suspected hypercortisolism is one of the most challenging problems in medicine. The signs and symptoms described by Dr Harvey Cushing are common and often create diagnostic confusion to even experienced endocrinologists. Cushing syndrome is classically defined as neoplastic hypercortisolism resulting from an ACTH-secreting tumor or from autonomous secretion of excess cortisol associated with benign or malignant adrenal neoplasia. The increasing recognition of the negative cardiometabolic effects of mild cortisol excess without overt physical signs of Cushing syndrome has led to more screening for endogenous hypercortisolism in patients with adrenal nodular disease, osteoporosis, and the metabolic syndrome. However, sustained or intermittent activation of the dynamic hypothalamic-pituitary-adrenal axis caused by chemical (alcohol), inflammatory (chronic kidney disease), psychologic (major depression), and physical (starvation/chronic intense exercise) stimuli can result in clinical and/or biochemical features indistinguishable from neoplastic hypercortisolism. Nonneoplastic hypercortisolism (formerly known as pseudo-Cushing syndrome) has been recognized for more than 50 years and often causes diagnostic uncertainty. This expert consultation describes two patients with features of Cushing syndrome who were referred for inferior petrosal sinus sampling for the differential diagnosis of ACTH-dependent hypercortisolism. Both patients were discovered to have nonneoplastic hypercortisolism: one from a covert alcohol use disorder and the other to chronic kidney disease. This consultation emphasizes the value of a good history and physical examination, appropriate laboratory testing, and the desmopressin acetate stimulation test to aid in distinguishing neoplastic from nonneoplastic hypercortisolism.

An antibody-free LC-MS/MS method for the quantification of sex hormone binding globulin in human serum and plasma

OBJECTIVES

Sex hormone binding globulin (SHBG) is a hormone binding protein which plays an important role in regulating the transport and availability of biologically active androgens and estradiol to target cells and used to calculate free testosterone concentrations.

METHODS

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed, featuring an albumin removal step followed by a tryptic digestion. After a reduction step with dithiothreitol and alkylation with iodoacetamide three signature peptides were used for the quantification of SHBG.

RESULTS

The method enables the quantification of serum and plasma SHBG over the clinically relevant range of 200-20,000 ng/mL and was validated according to the most recent guidelines. The LC-MS/MS method correlates well with the Abbott Alinity immunoassay (R2>0.95), but the LC-MS/MS results are on average 16-17% lower than the immunoassay results, which is consistent for all three signature peptides.

CONCLUSIONS

The LC-MS/MS method which includes an albumin depletion step allows quantification of SHBG in serum and plasma without an immunocapture step at clinically relevant SHBG levels, thus contributing to better lab-to-lab consistency of results.

Clinical Study and Systematic Review of Pituitary Microadenomas vs. Macroadenomas in Cushing's Disease: Does Size Matter?

Background: Reports on clinical and biochemical differences between adrenocorticotropic hormone (ACTH)-secreting pituitary microadenomas and macroadenomas are limited and inconsistent. Objective: Compare clinical and biochemical characteristics of patients with corticotroph microadenomas and macroadenomas and assess predictive factors for biochemical response to dynamic testing for Cushing’s disease (CD) in a clinical trial and a systematic review. A second aim was to evaluate differences between macroadenomas with and without cavernous and sphenoid sinus invasion. Methods: Retrospective charts review of patients with CD, treated at Rabin Medical Center between 2000 and 2020 or at Maccabi Healthcare Services in Israel between 2005 and 2017. Clinical and biochemical factors were compared between patients with corticotroph microadenomas and macroadenomas. We have also performed a systematic review of all studies (PRISMA guidelines) comparing corticotroph microadenomas with macroadenomas up to 31 November 2021. Results: The cohort included 105 patients (82 women, 78%; mean age, 41.5 ± 14.5 years), including 80 microadenomas (mean size, 5.2 ± 2.2 mm) and 25 macroadenomas (mean size, 18.0 ± 7.7 mm). Other baseline characteristics were similar between groups. Most common presentation suggestive for hypercortisolemia among patients with both micro- and macroadenomas were weight gain (46.3% vs. 48.0%, p = NS) and Cushingoid features (27.5% vs. 20.0%, p = NS). Mean 24 h urinary free cortisol (5.2 ± 5.4 × ULN vs. 7.8 ± 8.7 × ULN) and serum cortisol following low-dose dexamethasone (372.0 ± 324.5 vs. 487.6 ± 329.8 nmol/L), though higher for macroadenomas, were not significant. Levels of ACTH were greater for macroadenomas (1.9 ± 1.2 × ULN vs. 1.3 ± 0.8 × ULN, respectively, p = 0.01). Rates of recurrent/persistent disease were similar, as were rates of post-operative adrenal insufficiency and duration of post-operative glucocorticoid replacement. Macroadenomas with sphenoid or cavernous sinus invasion were associated with higher ACTH, 24 h free urinary cortisol, and serum cortisol following low-dose dexamethasone, compared with suprasellar or intrasellar macroadenomas. Conclusions: While ACTH-secreting macroadenomas exhibit higher plasma ACTH than microadenomas, there was no association between tumor size with cortisol hypersecretion or clinical features of hypercortisolemia. Though overall rare, increased awareness is needed for patients with CD with tumor extension in the cavernous or sphenoid sinus, which displays increased biochemical burden, highlighting that extent/location of the adenoma may be more important than size per se. Our systematic review, the first on this topic, highlights differences and similarities with our study.

An automated magnetic bead extraction method for measuring plasma metanephrines and 3-methoxytyramine using liquid chromatography tandem mass spectrometry

Liquid chromatography tandem mass spectrometry (LC-MS/MS) is used routinely in clinical diagnostics; however, automating the sample pretreatment is challenging. We established and evaluated an automated method based on the magnetic bead extraction principle (MBE) to measure normetanephrine (NMN), metanephrine (MN), and 3-methoxytyramine (3-MT). The target analytes were extracted, purified, and concentrated using different solvents and chemical bond-modified magnetic beads transferred via a magnetic bar. The linearity, recovery, matrix effect, and precision of MBE were evaluated thoroughly, and compared with traditional solid-phase extraction (SPE) using 131 plasma samples. The chromatography peaks of metanephrines and 3-MT, extracted via MBE, are symmetrical, without interfering peaks. The linearity was excellent with correlation coefficient (r) > 0.99. The MBE exhibited good reproducibility with within-run coefficient variations (CVs) of 1.96-2.00%, 4.06-5.75%, and 3.89-4.90% for MN, NMN, and 3-MT, respectively. The total CVs for MN, NMN, and 3-MT were 1.96-2.80%, 5.12-5.75%, and 5.44-6.27%, respectively. The relative recoveries for MN, NMN, and 3-MT varied between 93.5 and 107.4%, whereas their biases were all within 10%. The results for MN, NMN, and 3-MT extracted via MBE compared with SPE exhibited excellent correlation, with r > 0.99; the mean bias% for MN, NMN, and 3-MT were small (-2.9%, -3.2%, and -3.2%, respectively). In conclusion, the automated MBE method for measuring plasma metanephrines and 3-MT can be applied in future routine clinical diagnostics, and the MBE principle may indicate a new era for LC-MS/MS in clinical application.

Clinical Spectrum of Adrenal Cushing's Syndrome and the Caution for Interpretation of Adrenocorticotrophic Hormone: A Single-Center Experience

To describe the differences in presentation, biochemistry, and radiological evaluation of various etiologies of adrenal Cushing's syndrome (CS) from a single center. To emphasize caution for interpretation of plasma adrenocorticotropic hormone (ACTH), as a spuriously unsuppressed ACTH level by immunometric assay may lead to therapeutic misadventures in adrenal CS.

DESIGN

 Retrospective, single-center, observational study.

METHODS

  Fifty-eight adrenal CS patients [Adrenocortical carcinoma (ACC), n=30; Adenoma (ACA), n=15; Primary pigmented nodular adrenocortical disease (PPNAD), n=10; ACTH independent macronodular adrenal hyperplasia (AIMAH), n=3) evaluated at a tertiary care center in western India between January 2006 to March 2020 were included. Data on demography, clinical evaluation, biochemistry, imaging, management, histopathology, and outcome were recorded in a standard format and analyzed.

RESULTS

  Cortisol secreting ACC presented at 38(1-50) years with abdominal mass in 26/30 (86.7%) and 16/30 (53.3%) had metastases at presentation. ACA with autonomous cortisol excess presented at 25(4.9-40) years with discriminating features of CS in 14/15 (93.3%), sex steroid production in 2/15, unenhanced HU <10 in only one, and relative washout >40% in 8/11 (72.7%). One ACA and eight ACC patients had plasma ACTH (by Siemens Immulite assay) > 20 pg/ml, despite hypercortisolemic state.

CONCLUSIONS

  Cortisol-secreting ACC and ACA most often present with mass effects and florid CS, respectively. Baseline HU has low sensitivity to differentiate cortisol-secreting ACA from ACC. Plasma ACTH measured by Seimens Immulite is often unsuppressed, especially in ACC patients, which can be addressed by measuring ACTH by more accurate assays.

Proteoforms and their expanding role in laboratory medicine

The term “proteoforms” describes the range of different structures of a protein product of a single gene, including variations in amino acid sequence and post-translational modifications. This diversity in protein structure contributes to the biological complexity observed in living organisms. As the concentration of a particular proteoform may increase or decrease in abnormal physiological states, proteoforms have long been used in medicine as biomarkers of health and disease. Notably, the analytical approaches used to analyze proteoforms have evolved considerably over the years. While ligand binding methods continue to play a large role in proteoform measurement in the clinical laboratory, unanticipated or unknown post-translational modifications and sequence variants can upend even extensively tested and vetted assays that have successfully made it through the medical regulatory process. As an alternate approach, mass spectrometry—with its high molecular selectivity—has become an essential tool in detection, characterization, and quantification of proteoforms in biological fluids and tissues. This review explores the analytical techniques used for proteoform detection and quantification, with an emphasis on mass spectrometry and its various applications in clinical research and patient care including, revealing new biomarker targets, helping improve the design of contemporary ligand binding in vitro diagnostics, and as mass spectrometric laboratory developed tests used in routine patient care.

Aptamer-based enrichment of TDP-43 from human cells and tissues with quantification by HPLC-MS/MS

BACKGROUND

There is great interest in detecting, characterizing and quantifying transactive response DNA binding protein of 43 kDa (TDP-43), and its post-translational modifications, due to its association with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis. Unfortunately, detailed analysis of TDP-43 in human biological matrices by immunometric methods has been hindered by the relatively low abundance of TDP-43 and poor antibody reagent specificity.

NEW METHOD

With the goal of developing a selective and multiplex method for characterizing TDP-43, we previously developed a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) assay for relative quantification of TDP-43 in human brain tissue and cells. To improve analytical sensitivity and to perform absolute quantification, we coupled a novel RNA-based aptamer enrichment workflow (and inclusion of a stable isotope-labeled standard) to HPLC-MS/MS.

RESULTS

The TDP-43 aptamer-enrichment-HPLC-MS/MS assay was linear from 0.37 to 2.55nmol/L, a range suitable for analysis of both human cells and brain tissue homogenates, and had a total CV of 14.8%. Quantitative TDP-43 peptide profiles were developed for cases of FTD with TDP-43 pathology and cases with no neurodegenerative pathology.

COMPARISON WITH EXISTING METHODS

Compared to immunoenrichment, aptamer-enrichment yielded cleaner recoveries of TDP-43. The aptamer-enrichment-HPLC-MS/MS method, compared to our previous method without enrichment, increased analytical sensitivity by 8.7-fold and 11.8-fold for endogenous TDP-43 in human cells and brain tissue, respectively. Critically, inclusion of the aptamer enrichment step improved sequence resolution and enabled identification of TDP-43 C-terminal fragments.

CONCLUSIONS

The aptamer-enrichment-HPLC-MS/MS method enabled highly selective quantification, enhanced sequence coverage and structural characterization of endogenous TDP-43.

Identifying Glucocorticoid Insufficiency in Silent Corticotroph Adenoma with Elevated Adrenocorticotropic Hormone

Silent corticotroph adenoma (SCA) is as an aggressive pituitary tumor. A 48 year old man developed hypogonadotrophic hypogonadism. The basal morning adrenocorticotropic hormone (ACTH) was elevated, but the basal morning and peak after ACTH (1-24) stimulation cortisol were normal. A 3.7 cm sellar mass with evidence of internal hemorrhage, encasement of the right internal carotid artery, and invasion of the right cavernous sinus were identified, resected, and stained positive for ACTH. Over the next 5 years, the basal morning ACTH and cortisol were normal, and imaging revealed the presence of a small residual tumor. One year later, the patient became fatigued and nauseated, with elevated ACTH. An overnight metyrapone stimulation test (OMST) revealed glucocorticoid insufficiency, without further increase in ACTH. Symptoms resolved with hydrocortisone treatment. This case study suggests that SCA can secrete an ACTH precursor that is detected by clinical assays but is not active biologically. Postoperative OMST reveals glucocorticoid insufficiency in this context.

Investigation of the Hypothalamo-pituitary-adrenal (HPA) axis: a contemporary synthesis

The hypothalamo-pituitary-adrenal (HPA) axis is one of the main components of the stress system. Maintenance of normal physiological events, which include stress responses to internal or external stimuli in the body, depends on appropriate HPA axis function. In the case of severe cortisol deficiency, especially when there is a triggering factor, the patient may develop a life-threatening adrenal crisis which may result in death unless early diagnosis and adequate treatment are carried out. The maintenance of normal physiology and survival depend upon a sufficient level of cortisol in the circulation. Life-long glucocorticoid replacement therapy, in most cases meeting but not exceeding the need of the patient, is essential for normal life expectancy and maintenance of the quality of life. To enable this, the initial step should be the correct diagnosis of adrenal insufficiency (AI) which requires careful evaluation of the HPA axis, a highly dynamic endocrine system. The diagnosis of AI in patients with frank manifestations is not challenging. These patients do not need dynamic tests, and basal cortisol is usually enough to give a correct diagnosis. However, most cases of secondary adrenal insufficiency (SAI) take place in a gray zone when clinical manifestations are mild. In this situation, more complicated methods that can simulate the response of the HPA axis to a major stress are required. Numerous studies in the assessment of HPA axis have been published in the world literature. In this review, the tests used in the diagnosis of secondary AI or in the investigation of suspected HPA axis insufficiency are discussed in detail, and in the light of this, various recommendations are made.

Consideration triggered by the choice of heterophilic antibody interference detection tests in measuring ACTH for a teenager boy with a rare adrenal disease

BACKGROUND

Plasma ACTH is an important marker for Cushing syndrome; inaccurate measurement of ACTH concentrations due to the serum heterophile antibody may mislead diagnosis by physicians. We describe the case of a teenage boy with a rare adrenal disease who presented falsely increased ACTH concentrations (20.3 pg/ml; Siemens Immulite).

METHODS

Low dose dexamethasone inhibition test showed no inhibition of serum cortisol. While biochemical evidence suggested ACTH-dependent Cushing, the imaging tests suggested otherwise. Hence, further tests for interference identification, including test platform replacement, sample dilution, PEG precipitation, and use of blocking antibodies, were conducted.

RESULTS

The measurements of the same patient sample on three different analytical platforms suggested ACTH concentrations below 5 pg/ml. Serial dilutions of serum samples revealed nonlinearity, PEG recovery resulted in ACTH concentrations dropping to < 5 pg/ml, and interferences in plasma were blocked by a heterophilic blocking reagent (21.2 vs < 5 pg/ml), suggesting that assay interference performed on Siemens Immulite led to false-positive ACTH. Finally, the boy was diagnosed with a rare type of ACTH-independent Cushing syndrome.

CONCLUSIONS

The inaccurate evaluation of ACTH misled the physicians, increasing treatment time and diagnostic testing. Thus, an anti-interference workflow should be established between physicians and laboratories to avoid such cases in the future.

Improving Science by Overcoming Laboratory Pitfalls With Hormone Measurements

Despite all the effort taken, there is often surprisingly little attention paid to the hormone analyses involved in research studies. Thinking carefully about the quality of the hormone measurements in these studies is, however, of major importance, as this attention to methods may prevent false conclusions and inappropriate follow-up studies. We discuss issues regarding hormone measurements that one should consider, ideally prior to starting, or otherwise, as they arise during a scientific study: quality of the technique, expertise, matrices, timing and storage conditions, freeze-thaw cycles, lot-to-lot and day-to-day variation, analyses per batch or sample-wise, singlicate or duplicate measurements, combining methods, and standardization. This article and the examples mentioned herein aim to clarify the need to pay attention to the hormone analyses, and to help in making decisions. In addition, these examples help editors and reviewers of scientific journals to pay attention to the methods section in the submitted manuscripts and ask the right critical questions when needed.

ADRENOCORTICOTROPIC HORMONE IMMUNOASSAY INTERFERENCE IN A PATIENT WITH SUBCLINICAL HYPERCORTISOLISM

Context

Immunoassays are vulnerable to occasional analytical errors despite their sensitivity and specificity. Adrenocorticotropic hormone (ACTH) is among hormones which are vulnerable to assay interference.

Objective

In this case report, we aimed to present a case of ACTH interference in a patient with subclinical hypercortisolism.

Case report

We present a case of subclinical hypercortisolism with unexpectedly elevated levels of ACTH in whom interference was shown by different biochemical methods.It is important for the clinician to keep in mind the possibility of interference when clinical and laboratory results are discordant. The communication between the clinician and laboratory staff is important while interpreting results. This case report shows that ACTH interference should be considered in patients with subclinical hypercortisolism who have unexpectedly high levels of adrenocorticotropic hormone.

Proteomic applications in pathology and laboratory medicine: Present state and future prospects

Clinical mass spectrometry applications have traditionally focused on small molecules, particularly in the areas of therapeutic drug monitoring, toxicology, and measurement of endogenous and exogenous steroids. More recently, the use of matrix assisted laser desorption/ionization time of flight mass spectrometry for the identification of microbial pathogens has been widely implemented. Following this evolution, there has been an expanding role for the measurement of peptides and proteins in pathology and laboratory medicine. This review explores the current state of protein measurement by clinical mass spectrometry and the analytical strategies employed, as well as emerging applications in clinical chemistry, clinical microbiology and anatomical pathology.

Bioelectronic sensor mimicking the human neuroendocrine system for the detection of hypothalamic-pituitary-adrenal axis hormones in human blood

In the neuroendocrine system, corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) play important roles in the regulation of the hypothalamic-pituitary-adrenal (HPA) system. Disorders of the HPA system lead to physiological problems, such as Addison's disease and Cushing's syndrome. Therefore, detection of CRH and ACTH is essential for diagnosing disorders related to the HPA system. Herein, receptors of the HPA axis were used to construct a bioelectronic sensor system for the detection of CRH and ACTH. The CRH receptor, corticotropin-releasing hormone receptor 1 (CRHR1), and the ACTH receptor, melanocortin 2 receptor (MC2R), were produced using an Escherichia coli expression system, and were reconstituted using nanodisc (ND) technology. The receptor-embedded NDs were immobilized on a floating electrode of a carbon nanotube field-effect transistor (CNT-FET). The constructed sensors sensitively detected CRH and ACTH to a concentration of 1 fM with high selectivity in real time. Furthermore, the reliable detection of CRH and ACTH in human plasma by the developed sensors demonstrated their potential in clinical and practical applications. These results indicate that CRHR1 and MC2R-based bioelectronic sensors can be applied for rapid and efficient detection of CRH and ACTH.