Mass spectrometry - an alternative in growth hormone measurement

Simultaneous quantification of the 22-kDa isoforms of human growth hormone 1 and 2 in human plasma by multiplexed immunocapture and LC-MS/MS

An LC-MS/MS method is presented for the simultaneous quantification of two structurally closely related protein biomarker isoforms, the 22-kDa isoforms of human growth hormone 1 and human growth hormone 2, in human plasma. It is based on multiplexed immunocapture using two monoclonal antibodies immobilized on magnetic beads, tryptic digestion and quantification of two specific signature peptides plus an additional peptide for estimation of total growth hormone related concentrations. A full validation according to international guidelines was performed across the clinically relevant concentration ranges of 0.5 to 50 ng/mL for growth hormone 1, and 2 to 50 ng/mL for growth hormone 2 and demonstrated satisfactory method performance in terms of accuracy, precision, stability and absence of interference. The method's applicability for routine analysis and its ability to effectively distinguish between GH1 and GH2 was demonstrated by the analysis of plasma samples from pregnant individuals to study the changes in growth hormone levels during pregnancy.

HGH1 and the immune landscape: a novel prognostic marker for immune-desert tumor microenvironment identification and immunotherapy outcome prediction in human cancers

HGH1 homolog, a protein-coding gene, plays a crucial role in human growth and development. However, its role in human cancer remains unclear. For the first time, this study comprehensively evaluated the potential involvement of HGH1 in cancer prognosis and immunological function. To achieve this, data from various databases, including The Cancer Genome Atlas, Genotype Tissue Expression, Cancer Cell Lineage Encyclopedia, Human Protein Atlas, cBioPortal, Tumor Immune Estimation Resource and Immune Cell Abundance Identifier, were collated, as well as from one large clinical study, three immunotherapy cohorts and in vitro experiments. This study aims to elucidate the role of HGH1 expression in cancer prognosis and immune response. Our findings revealed a significant association between increased HGH1 expression and a worse prognosis across various cancer types. Predominantly, copy number variations were identified as the most common genetic mutations. Additionally, HGH1 was observed to not only regulate cell cycle-related functions to promote cell proliferation but also influence autoimmunity-related functions within both the innate and adaptive immune systems, along with other relevant immune-related signaling pathways. Gene set enrichment analysis and gene set variation analysis were used to substantiate these findings. HGH1 overexpression contributed to an immune-deficient (immune-desert) tumor microenvironment, which was characterized by a significant expression of immune-related features such as immune-related gene and pathway expression and the number of immune-infiltrating cells. Furthermore, the correlation between HGH1 expression and tumor mutational burden in four cancers and microsatellite instability in eight cancers was observed. This suggests that HGH1 has potential as an immunotherapeutic target. Immunotherapy data analysis supports this notion, demonstrating that patients with low HGH1 expression treated with immune checkpoint inhibitors exhibit improved survival rates and a higher likelihood of responding to immunotherapy than patients with high HGH1 expression. Collectively, these findings highlight the significant role of HGH1 in human cancers, illuminating its involvement in tumorigenesis and cancer immunity. Elevated HGH1 expression was identified to be indicative of an immune-desert tumor microenvironment. Consequently, the targeting of HGH1, particularly in combination with immune checkpoint inhibitor therapy, holds promise for enhancing therapeutic outcomes in patients with cancer.

Selective quantification of the 22-kDa isoform of human growth hormone 1 in serum and plasma by immunocapture and LC-MS/MS

The human growth hormone GH1 (22 kDa) is a commonly measured biomarker for diagnosis and during treatment of growth disorders, but its quantification by ligand binding assays may be compromised by the occurrence of a number of isoforms. These can interfere in the assays and lead to differences in results between laboratories and potentially even in the treatment of patients. We present an LC-MS/MS method that is able to distinguish the major growth hormone isoform (GH1, 22 kDa) from other isoforms and quantify it without any interference across the clinically relevant concentration range of 0.5 to 50 ng/mL. Analysis involves purification of a 100-µL serum sample by immunocapture using an anti-GH-directed antibody, tryptic digestion, and LC-MS/MS quantification of an isoform-specific signature peptide for GH1 (22 kDa). A tryptic peptide occurring in all GH isoforms is monitored in the same 16-min analytical run as a read-out for total GH. Stable-isotope-labeled forms of these two peptides are included as internal standards. Full validation of the method according to recent guidelines, against a recombinant form of the analyte in rat plasma calibrators, demonstrated intra-assay and inter-assay imprecision below 6% across the calibration range for both signature peptides and recoveries between 94 and 102%. An excellent correlation was found between nominal and measured concentrations of the WHO reference standard for GH1 (22 kDa). Addition of up to 1000 ng/mL biotin or the presence of a 100-fold excess of GH binding protein did not affect the measurement. Equivalent method performance was found for analysis of GH in serum, EDTA, and heparin plasma. Analyte stability was demonstrated during all normal sample storage conditions. Comparison with the IDS-iSYS GH immunoassay showed a good correlation with the LC-MS/MS method for the isoform-specific signature peptide, but a significant positive bias was observed for the LC-MS/MS results of the peptide representing total GH. This seems to confirm the actual occurrence of other GH isoforms in serum. Finally, in serum from pregnant individuals, no quantifiable GH1 (22 kDa) was found, but relatively high concentrations of total GH.

Quantitation of thrombin-activatable fibrinolysis inhibitor in human plasma by isotope dilution mass spectrometry

Measurement of Thrombin-activatable fibrinolysis inhibitor (TAFI) in human plasma is dependent on reproducible assays. To date, standards for measuring TAFI are frequently calibrated relative to pooled normal human plasma and arbitrarily assigned a potency of 100% TAFI, despite variation in TAFI concentrations between plasma pools. Alternatively, TAFI calibrators can be assigned a value in SI units but the approach used for value assignment is not consistent and furthermore, if purified TAFI is used to determine TAFI concentration in plasma, may be adversely affected by matrix effects. A TAFI plasma standard in mass units with traceability to the SI unit of mass is desirable. We report here the establishment of a quantitative mass spectrometry method for TAFI in plasma. Traceability is obtained by reference to calibrators that consist of blank plasma spiked with a defined amount of purified TAFI, value assigned by amino acid analysis. The calibrators are run alongside the samples, using the same preparation steps and conditions; an acetonitrile assisted tryptic digestion and multi-dimensional liquid chromatography (LC) separation followed by SRM-MS analysis. We measured the TAFI quantitatively in human plasma with reproducibility, reliability and precision, and demonstrated the applicability of this approach for value assigning a common reference standard.

Provocative growth hormone testing in children: how did we get here and where do we go now?

OBJECTIVES

Provocative growth hormone (GH) tests are widely used for diagnosing pediatric GH deficiency (GHD). A thorough understanding of the evidence behind commonly used interpretations and the limitations of these tests is important for improving clinical practice.

CONTENT

To place current practice into a historical context, the supporting evidence behind the use of provocative GH tests is presented. By reviewing GH measurement techniques and examining the early data supporting the most common tests and later studies that compared provocative agents to establish reference ranges, the low sensitivity and specificity of these tests become readily apparent. Studies that assess the effects of patient factors, such as obesity and sex steroids, on GH testing further bring the appropriateness of commonly used cutoffs for diagnosing GHD into question.

SUMMARY AND OUTLOOK

Despite the widely recognized poor performance of provocative GH tests in distinguishing GH sufficiency from deficiency, limited progress has been made in improving them. New diagnostic modalities are needed, but until they become available, clinicians can improve the clinical application of provocative GH tests by taking into account the multiple factors that influence their results.

Short and Long-Term Effects of Growth Hormone in Children and Adolescents With GH Deficiency

The syndrome of impaired GH secretion (GH deficiency) in childhood and adolescence had been identified at the end of the 19^th century. Its non-acquired variant (naGHD) is, at childhood onset, a rare syndrome of multiple etiologies, predominantly characterized by severe and permanent growth failure culminating in short stature. It is still difficult to diagnose GHD and, in particular, to ascertain impaired GH secretion in comparison to levels in normally-growing children. The debate on what constitutes an optimal diagnostic process continues. Treatment of the GH deficit via replacement with cadaveric pituitary human GH (pit-hGH) had first been demonstrated in 1958, and opened an era of therapeutic possibilities, albeit for a limited number of patients. In 1985, the era of recombinant hGH (r-hGH) began: unlimited supply meant that substantial long-term experience could be gained, with greater focus on efficacy, safety and costs. However, even today, the results of current treatment regimes indicate that there is still a substantial fraction of children who do not achieve adult height within the normal range. Renewed evaluation of height outcomes in childhood-onset naGHD is required for a better understanding of the underlying causes, whereby the role of various factors - diagnostics, treatment modalities, mode of treatment evaluation - during the important phases of child growth - infancy, childhood and puberty - are further explored.

Growth hormone - past, present and future

Growth hormone (GH) research and its clinical application for the treatment of growth disorders span more than a century. During the first half of the 20th century, clinical observations and anatomical and biochemical studies formed the basis of the understanding of the structure of GH and its various metabolic effects in animals. The following period (1958-1985), during which pituitary-derived human GH was used, generated a wealth of information on the regulation and physiological role of GH - in conjunction with insulin-like growth factors (IGFs) - and its use in children with GH deficiency (GHD). The following era (1985 to present) of molecular genetics, recombinant technology and the generation of genetically modified biological systems has expanded our understanding of the regulation and role of the GH-IGF axis. Today, recombinant human GH is used for the treatment of GHD and various conditions of non-GHD short stature and catabolic states; however, safety concerns still accompany this therapeutic approach. In the future, new therapeutics based on various components of the GH-IGF axis might be developed to further improve the treatment of such disorders. In this Review, we describe the history of GH research and clinical use with a particular focus on disorders in childhood.

Discordance between mass spectrometry and immunometric IGF-1 assay in pituitary disease: a prospective study

PURPOSE

Measuring IGF-1, a biomarker for GH activity, is critical to evaluating disordered hypothalamic-pituitary GH axis. Inconsistent IGF-1 measurements among different immunoassays are well documented. We switched from Immulite 2000 immunoassay to narrow-mass-extraction, high-resolution liquid chromatography mass-spectrometry (LC-MS) compliant with recent consensus recommendations on assay standardization. Comparability of these two assays in patients with pituitary disease in a clinical practice setting is not known. We sought to compare IGF-1 levels on Immulite 2000 and LC-MS in samples from naïve and treated patients with secretory and non-secretory pituitary masses.

METHODS

We prospectively collected serum samples from 101 patients treated at the Cedars-Sinai Pituitary Center between February 2012 and March 2014. We intentionally recruited more patients with acromegaly or GH deficiency to ensure a clinically representative cohort. Samples were classified as in or out of the respective reference ranges. Bland-Altman analysis was used to assess agreement between assays.

RESULTS

Twenty-four percent of samples were classified differently as below, in, or above range. Agreement between the assays was poor overall, with a significant bias for immunoassay reporting higher values than LC-MS. This pattern was also observed in patients with acromegaly and those with ≥ 2 pituitary hormone deficiencies.

CONCLUSIONS

IGF-1 results may differ after switching from an older immunoassay to a consensus-compliant assay such as LC-MS. Clinicians should consider the potential impact of assay switching before altering treatment due to discrepant results, particularly in patients monitored over time, such as those with acromegaly and GH deficiency.

Immunoaffinity techniques coupled to mass spectrometry for the analysis of human peptide hormones: advances and applications

INTRODUCTION

The accurate and comprehensive determination of peptide hormones from biological fluids has represented a considerable challenge to analytical chemists for decades. Besides long-established bioanalytical ligand binding assays (or ELISA, RIA, etc.), more and more mass spectrometry-based methods have been developed recently for purposes commonly referred to as targeted proteomics. Eventually the combination of both, analyte extraction by immunoaffinity and subsequent detection by mass spectrometry, has shown to synergistically enhance the test methods' performance characteristics. Areas covered: The review provides an overview about the actual state of existing methods and applications concerning the analysis of endogenous peptide hormones. Here, special focus is on recent developments considering the extraction procedures with immobilized antibodies, the subsequent separation of target analytes, and their detection by mass spectrometry. Expert commentary: Key aspects of procedures aiming at the detection and/or quantification of peptidic analytes in biological matrices have experienced considerable improvements in the last decade, particularly in terms of the assays' sensitivity, the option of multiplexing target compounds, automatization, and high throughput operation. Despite these advances and progress as expected to be seen in the near future, immunoaffinity purification coupled to mass spectrometry is not yet a standard procedure in routine analysis compared to ELISA/RIA.

Diagnosis of growth hormone deficiency in the paediatric and transitional age

Growth hormone deficiency is a rare cause of childhood short stature, but one for which treatment exists in the form of recombinant human growth hormone. A diagnosis of growth hormone deficiency is made based on auxology, biochemistry and imaging. Although no diagnostic gold standard exists, growth hormone provocation tests are considered the mainstay of diagnostic investigations. However, these must be interpreted with caution in view of issues with variability and reproducibility, as well as the limited evidence-base for cut-off values used to distinguish growth hormone deficient and non-growth hormone deficient subjects. In addition, nutritional and pubertal status can affect results, with no consensus on the role of priming with sex steroid hormones. Difficulties with assays exist both for growth hormone as well as insulin-like growth factor-1. Pituitary magnetic resonance imaging is a useful diagnostic, and possibly prognostic, aid. Although genetic testing is not routine, the discovery of more relevant mutations makes it an increasingly important investigation. Children with growth hormone deficiency are retested biochemically on completion of growth, to assess whether they remain so into adulthood.

Personalized Proteomics: The Future of Precision Medicine

Medical diagnostics and treatment has advanced from a one size fits all science to treatment of the patient as a unique individual. Currently, this is limited solely to genetic analysis. However, epigenetic, transcriptional, proteomic, posttranslational modifications, metabolic, and environmental factors influence a patient’s response to disease and treatment. As more analytical and diagnostic techniques are incorporated into medical practice, the personalized medicine initiative transitions to precision medicine giving a holistic view of the patient’s condition. The high accuracy and sensitivity of mass spectrometric analysis of proteomes is well suited for the incorporation of proteomics into precision medicine. This review begins with an overview of the advance to precision medicine and the current state of the art in technology and instrumentation for mass spectrometry analysis. Thereafter, it focuses on the benefits and potential uses for personalized proteomic analysis in the diagnostic and treatment of individual patients. In conclusion, it calls for a synthesis between basic science and clinical researchers with practicing clinicians to design proteomic studies to generate meaningful and applicable translational medicine. As clinical proteomics is just beginning to come out of its infancy, this overview is provided for the new initiate.

Controversies in the diagnosis and management of growth hormone deficiency in childhood and adolescence

Growth hormone deficiency (GHD) is a rare but important cause of short stature in childhood with a prevalence of 1 in 4000. The diagnosis is currently based on an assessment of auxology along with supporting evidence from biochemical and neuroradiological studies. There are significant controversies in the diagnosis and management of GHD. Growth hormone (GH) stimulation tests continue to play a key role in GHD diagnosis but the measured GH concentration can vary significantly with stimulation test and GH assay used, creating difficulties for diagnostic accuracy. Such issues along with the use of adjunct biochemical markers such as IGF-I and IGFBP-3 for the diagnosis of GHD, will be discussed in this review. Additionally, the treatment of GHD remains a source of much debate; there is no consensus on the best mechanism for determining the starting dose of GH in patients with GHD. Weight and prediction based models will be discussed along with different mechanisms for dose adjustment during treatment (auxology or IGF-I targeting approaches). At the end of growth and childhood treatment, many subjects diagnosed with isolated GHD re-test normal. It is not clear if this represents a form of transient GHD or a false positive diagnosis during childhood. Given the difficulties inherent in the diagnosis of GHD, an early reassessment of the diagnosis in those who respond poorly to GH is to be recommended.