Processing-independent analysis (PIA): a method for quantitation of the total peptide-gene expression

Cholecystokinin - portrayal of an unfolding peptide messenger system

This review describes how the classic gut hormone, cholecystokinin (CCK), should be comprehended in 2025. In the early physiological tradition of studying gastrointestinal hormones, the hormones were named after the function that lead to their discovery. Hence, in 1928, the hormonal factor in the upper gut that regulated gallbladder contraction was called cholecystokinin. In 1968, Viktor Mutt and Erik Jorpes identified the porcine structure of this factor as an O-sulfated and carboxyamidated peptide of 33 amino acid residues (CCK-33). Its C-terminal bioactive heptapeptide amide turned out to be homologous to that of the antral hormone, gastrin. The structure allowed in vitro synthesis of peptide fragments for physiological studies and for production of CCK-antibodies for immunoassays and immunohistochemistry. Today, these tools have revealed CCK to be highly complex: CCK is a heterogenous, multifunctional peptide messenger system, widely expressed both in and outside the gut. Thus, the CCK gene encodes six different bioactive peptides (CCK-83, -58, -33, -22, -8, and -5) that are expressed in a cell-specific manner in O-sulfated and non-sulfated forms. Moreover, CCK peptides are not only hormones. They are also potent neurotransmitters, paracrine growth and satiety factors, anti-inflammatory cytokines, incretins, potential fertility factors and useful tumor-markers. Moreover, CCK has a phylogenetic history of nearly 600 million years. Particular interest has been given to the neuroscience of CCK, because CCK is the predominant peptide transmitter in the brain, expressed in amounts that surpass any other neuropeptide. Vice versa, the brain is the main production site of CCK in mammals.

The cckOMA syndrome and its relation to the Zollinger-Ellison syndrome: a diagnostic challenge

OBJECTIVE

Among patients with enteropancreatic neuroendocrine tumor syndromes only one case with a cholecystokinin (CCK) secreting tumor has been reported. She had significant hyperCCKemia leading to a specific syndrome of severe diarrheas, weight loss, repeated duodenal ulcers and a permanently contracted gallbladder with gallstones. There are, however, reasons to believe that further CCKomas exist, for instance among Zollinger-Ellison patients with normal plasma gastrin concentrations. The present review is a call to gastroenterologists for awareness of such CCKoma patients.

METHOD

After a short case report, the normal endocrine and oncological biology of CCK is described. Subsequently, the CCKoma symptoms are discussed with particular reference to the partly overlapping symptoms of the Zollinger-Ellison syndrome. In this context, the diagnostic use of truly specific CCK and gastrin assays are emphasized. The discussion also entails the problem of access to accurate CCK measurements.

CONCLUSION

Obviously, the clinical awareness about the CCKoma syndrome is limited. Moreover, it is also likely that the knowledge about the necessary specificity demands of diagnostic gastrin and CCK assays have obscured proper diagnosis of the CCKoma syndromes in man.

Gastrointestinal hormones: History, biology, and measurement

This chapter attempts to provide an all-round picture of a dynamic and major branch of modern endocrinology, i.e. the gastrointestinal endocrinology. The advances during the last half century in our understanding of the dimensions and diversity of gut hormone biology - inside as well as outside the digestive tract - are astounding. Among major milestones are the dual brain-gut relationship, i.e. the comprehensive expression of gastrointestinal hormones as potent transmitters in central and peripheral neurons; the hormonal signaling from the enteroendocrine cells to the brain and other extraintestinal targets; the role of gut hormones as growth and fertility factors; and the new era of gut hormone-derived drugs. Accordingly, gastrointestinal hormones have pathogenetic roles in major metabolic disorders (diabetes mellitus and obesity); in tumor development (common cancers, sarcomas, and neuroendocrine tumors); and in cerebral diseases (anxiety, panic attacks, and probably eating disorders). Such clinical aspects require accurate pathogenetic and diagnostic measurements of gastrointestinal hormones - an obvious responsibility for clinical chemistry/biochemistry. In order to obtain a necessary insight into today's gastrointestinal endocrinology, the chapter will first describe the advances in gastrointestinal endocrinology in a historical context. The history provides a background for the subsequent description of the present biology of gastrointestinal hormones, and its biomedical consequences - not least for clinical chemistry/biochemistry with its specific responsibility for selection of appropriate assays and reliable measurements.

Glucagon-like peptide-1 stimulates acute secretion of pro-atrial natriuretic peptide from the isolated, perfused pig lung exposed to warm ischemia

Glucagon-like peptide-1 (GLP-1) has proven to be protective in animal models of lung disease but the underlying mechanisms are unclear. Atrial natriuretic peptide (ANP) is mainly produced in the heart. As ANP possesses potent vaso- and bronchodilatory effects in pulmonary disease, we hypothesised that the protective functions of GLP-1 could involve potentiation of local ANP secretion from the lung. We examined whether the GLP-1 receptor agonist liraglutide was able to improve oxygenation in lungs exposed to 2 h of warm ischemia and if liraglutide stimulated ANP secretion from the lungs in the porcine ex vivo lung perfusion (EVLP) model. Pigs were given a bolus of 40 µg/kg liraglutide or saline 1 h prior to sacrifice. The lungs were then left in vivo for 2 h, removed en bloc and placed in the EVLP machinery. Lungs from the liraglutide treated group were further exposed to liraglutide in the perfusion buffer (1.125 mg). Main endpoints were oxygenation capacity, and plasma and perfusate concentrations of proANP and inflammatory markers. Lung oxygenation capacity, plasma concentrations of proANP or concentrations of inflammatory markers were not different between groups. ProANP secretion from the isolated perfused lungs were markedly higher in the liraglutide treated group (area under curve for the first 30 min in the liraglutide group: 635 ± 237 vs. 38 ± 38 pmol/L x min in the saline group) (p < 0.05). From these results, we concluded that liraglutide potentiated local ANP secretion from the lungs.

A novel method to detect hPG80 (human circulating progastrin) in the blood

hPG₈₀ (human circulating progastrin) is produced and released by cancer cells. We recently reported that hPG₈₀ is detected in the blood of patients with cancers from different origins, suggesting its potential utility for cancer detection. To accurately measure hPG₈₀ in the blood of patients, we developed the DxPG₈₀ test, a sandwich Enzyme-Linked Immunosorbent Assay (ELISA). This test quantifies hPG₈₀ in EDTA plasma samples. The analytical performances of the DxPG₈₀ test were evaluated using standard procedures and guidelines specific to ELISA technology. We showed high specificity for hPG₈₀ with no cross-reactivity with human glycine-extended gastrin (hG17-Gly), human carboxy-amidated gastrin (hG17-NH₂) or the CTFP (C-Terminus Flanking Peptide) and no interference with various endogenous or exogenous compounds. The test is linear between 0 and 50 pM hPG₈₀ (native or recombinant). We demonstrated a trueness of measurement, an accuracy and a variability of hPG₈₀ quantification with the DxPG₈₀ test below the 20% relative errors as recommended in the guidelines. The limit of detection of hPG₈₀ and the limit of quantification were calculated as 1 pM and 3.3 pM respectively. In conclusion, these results show the strong analytical performance of the DxPG₈₀ test to measure hPG₈₀ in blood samples.

On premises and principles for measurement of gastrointestinal peptide hormones

Gastrointestinal hormones are peptides, and the gastrointestinal tract is the largest endocrine organ in the body for production of peptide hormones. As a premise for accurate measurement of gastrointestinal hormones, the present review provides first an overview over the complex biology of the hormones: The structures and structural homologies; biogenetic aspects; phenotype variabilities; and cellular expression in- and outside the digestive tract. Second, the different methodological principles for measurement are discussed: Bioassay, radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), mass-spectrometry (LC-MS/MS) and processing-independent analysis (PIA). Third, the variability of secretion patterns for some of the gut hormones is illustrated. Finally, the diagnostic value of gut hormone measurement is discussed. The review concludes that measurement of gastrointestinal peptide hormones is relevant not only for examination of digestive functions and diseases, but also for extra-intestinal functions. Moreover, it concludes that, so far, immunoassay technologies (RIA and ELISA) in modernized forms are still the most feasible for accurate measurements of gastrointestinal hormones in biological fluids. Mass-spectrometry technologies are promising, but still too insensitive and expensive.