Specific Immunoassay Reveals Increased Serum Trypsinogen 3 in Acute Pancreatitis

Discovery of varlaxins, new aeruginosin-type inhibitors of human trypsins

Low-molecular weight natural products display vast structural diversity and have played a key role in the development of novel therapeutics. Here we report the discovery of novel members of the aeruginosin family of natural products, which we named varlaxins. The chemical structures of varlaxins 1046A and 1022A were determined using a combination of mass spectrometry, analysis of one- and two-dimensional NMR spectra, and HPLC analysis of Marfey's derivatives. These analyses revealed that varlaxins 1046A and 1022A are composed of the following moieties: 2-O-methylglyceric acid 3-O-sulfate, isoleucine, 2-carboxy-6-hydroxyoctahydroindole (Choi), and a terminal arginine derivative. Varlaxins 1046A and 1022A differ in the cyclization of this arginine moiety. Interestingly, an unusual α-D-glucopyranose moiety derivatized with two 4-hydroxyphenylacetic acid residues was bound to Choi, a structure not previously reported for other members of the aeruginosin family. We sequenced the complete genome of Nostoc sp. UHCC 0870 and identified the putative 36 kb varlaxin biosynthetic gene cluster. Bioinformatics analysis confirmed that varlaxins belong to the aeruginosin family of natural products. Varlaxins 1046A and 1022A strongly inhibited the three human trypsin isoenzymes with IC₅₀ of 0.62-3.6 nM and 97-230 nM, respectively, including a prometastatic trypsin-3, which is a therapeutically relevant target in several types of cancer. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and provide evidence that the aeruginosin family is a source of strong inhibitors of human serine proteases.

Biliary hCGβ Is a Potential Novel Marker for Prediction of Biliary Neoplasia in Primary Sclerosing Cholangitis Patients

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disease, which is associated with an increased risk of cholangiocarcinoma (CCA). Novel markers, to complement or replace CA19-9, are urgently needed for the screening of PSC-associated biliary neoplasia. Previous studies have suggested that serum trypsinogen-2 and human chorionic gonadotropin β-subunit (hCGβ) may serve as such markers. Using highly specific in-house immunoassays, we studied trypsin(ogen)-2 and -3, SPINK1 and hCGβ in bile samples of 214 patients, referred for endoscopic retrograde cholangiography. We found that biliary trypsinogen-2 was decreased (p = 0.027) and hCGβ was elevated (p < 0.001) in PSC patients who were diagnosed 1.6 years (median, range 0.1–8.8 years) later with CCA or in whom biliary dysplasia was observed at least twice in brush cytology (n = 11) as compared to PSC patients without CCA or repeated dysplasia (n = 171). The other studied markers did not show significant differences between these groups. Our results warrant further evaluation of hCGβ as a predictive marker for PSC-associated biliary neoplasia.

Dramatic increase in serum trypsinogens, SPINK1 and hCGβ in aortic surgery patients after hypothermic circulatory arrest

The concentrations of several diagnostic markers have been found to increase dramatically in critically ill patients with a severe disturbance of normal physiological homeostasis, without indication of the diseases they are normally associated with. To prevent false diagnoses and inappropriate treatments of critically ill patients, it is important that the markers aiding the selection of second-line treatments are evaluated in such patients and not only in the healthy population and patients with diseases the markers are associated with. The levels of trypsinogen isoenzymes, the trypsin inhibitor serine peptidase inhibitor Kazal type 1 (SPINK1), hCG and hCGβ, which are used as pancreatitis and cancer markers, were analyzed by immunoassays from serum samples of 17 adult patients who have undergone surgery of the ascending aorta during hypothermic circulatory arrest (HCA) with optional selective cerebral perfusion. Highly elevated levels of trypsinogen-1, -2 and -3, SPINK1 and hCGβ were observed in patients after HCA. This was accompanied by increased concentrations of S100β and NSE. In conclusion, this study highlights the importance of critically evaluating the markers used for aiding selection of second line of treatments in critically ill patients.

Development of mutant human immunoreactive trypsinogen 1 (IRT1) and mutant human immunoreactive trypsinogen 2 (IRT2) for use in immunoassays

Immunoreactive Trypsinogen (IRT) is a protein-based pancreatic proenzyme that has an important role in protein digestion in humans. In human body, once IRT present in the small intestine, the proteolytic cleavage activates trypsinogen into trypsin. When IRT is in the active form, it is capable to cleave antibodies, other proteins and even itself while it is desired to use in immunoassays. According to the literature, there are three important IRT isoforms called Immunoreactive Trypsinogen 1 (IRT1), Immunoreactive Trypsinogen 2 (IRT2), and Immunoreactive Trypsinogen 3 (IRT3). However, trypsinogen 1 (cationic trypsinogen, IRT1) and trypsinogen 2 (anionic trypsinogen, IRT2) are the major isoforms in human pancreatic juice and used in the diagnosis of cystic fibrosis (CF). In this study, it is aimed to restrain its proteolytic activity with K23D mutation, which changes lysine (K) residue at the 23rd position to aspartic acid (D). Because we wanted to produce a hassle-free human recombinant immune reactive trypsinogen proenzyme which has similar antigenic properties with the native form. It is also aimed that the mutant IRTs do not exhibit proteolytic activity for the development of durable detection kits with a longer shelf life for both two isoforms. The innovation was actualized in order to use IRTs as a standard antigen in Immunoassays such as ELISA kits. The gene was synthesized as mutated and expressed in P. pastoris X-33 strain. The loss of proteolytic activity has been proven with the BAEE test. Antigenic properties of K23D IRTs and the effect of proteolytic inactivation on their performance in immunoassays were assessed with ELISA and Western Blot. In ELISA results K23D mutated IRTs showed higher signals than Wild-Type forms.

Specificity profiling of human trypsin-isoenzymes

In humans, three different trypsin-isoenzymes have been described. Of these, trypsin-3 appears to be functionally different from the others. In order to systematically study the specificity of the trypsin-isoenzymes, we utilized proteome-derived peptide libraries and quantitative proteomics. We found similar specificity profiles dominated by the well-characterized preference for cleavage after lysine and arginine. Especially, trypsin-1 slightly favored lysine over arginine in this position, while trypsin-3 did not discriminate between them. In the P1' position, which is the residue C-terminal to the cleavage site, we noticed a subtle enrichment of alanine and glycine for all three trypsins and for trypsin-3 there were additional minor P1' and P2' preferences for threonine and aspartic acid, respectively. These findings were confirmed by FRET peptide substrates showing different susceptibility to cleavage by different trypsins. The preference of trypsin-3 for aspartic acid in P2' is explained by salt bridge formation with the unique Arg193. This salt bridge enables and stabilizes a canonical oxyanion conformation by the amides of Ser195 and Arg193, thus manifesting a selective substrate-assisted catalysis. As trypsin-3 has been proposed to be a therapeutic target and marker for cancers, our results may aid the development of specific inhibitors for cancer therapy and diagnostic probes.

Serum Serine Peptidase Inhibitor Kazal-Type 1, Trypsinogens 1 to 3, and Complex of Trypsin 2 and α1-Antitrypsin in the Diagnosis of Severe Acute Pancreatitis

OBJECTIVES

We explored prediction of severe acute pancreatitis (AP) and development of organ dysfunction (OD).

METHODS

Serum concentrations of serine peptidase inhibitor Kazal type 1 (SPINK1), trypsinogen 1, trypsinogen 2, and trypsinogen 3, complex between trypsin 2 and α1-antitrypsin, serum C-reactive protein, creatinine, and pancreatic amylase were measured in 239 AP patients with disease onset within 72 hours.

RESULTS

SPINK1 distinguished most accurately patients who later developed severe AP. The area under the receiver operating characteristic curve for SPINK1 was 0.742, followed by trypsinogen 2 (0.726), complex between trypsin 2 and α1-antitrypsin (0.657), creatinine (0.656), trypsinogen 1 (0.652), trypsinogen 3 (0.557), and C-reactive protein (0.499). With a cutoff of 166 μg/L, SPINK1 had a specificity of 93%, a sensitivity of 48%, and diagnostic odds ratio of 11.52. In multivariate logistic regression analysis, only SPINK1 was an independent predictor of severe AP among patients presenting without OD on admission (P < 0.001).

CONCLUSIONS

Plasma levels of the biomarkers and creatinine correlated with the severity of AP and development of OD. In patients presenting without OD at admission, SPINK1 was an independent marker for later development of severe AP.

Biomarker development, from bench to bedside

This review describes studies performed by our group and other laboratories in the field aimed at development of biomarkers not only for cancer but also for other diseases. The markers covered include tumor-associated trypsin inhibitor (TATI), tumor-associated trypsin (TAT), human chorionic gonadotropin (hCG), prostate-specific antigen (PSA) and their various molecular forms, their biology and diagnostic use. The discovery of TATI was the result of a hypothesis-driven project aimed at finding new biomarkers for ovarian cancer among urinary peptides. TATI has since proved to be a useful prognostic marker for several cancers. Recently, it has been named Serine Peptidase Inhibitor Kazal Type 1 (SPINK1) after being rediscovered by several groups as a tumor-associated peptide by gene expression profiling and proteomic techniques and shown to promote tumor development by stimulating the EGF receptor. To explain why a trypsin inhibitor is strongly expressed in some cancers, research focused on the protease that it inhibited led to the finding of tumor-associated trypsin (TAT). Elevated serum concentrations of TAT-2 were found in some cancer types, but fairly high background levels of pancreatic trypsinogen-2 limited the use of TAT-2 for cancer diagnostics. However, trypsinogen-2 and its complex with α1-protease inhibitor proved to be very sensitive and specific markers for pancreatitis. Studies on hCG were initiated by the need to develop more rapid and sensitive pregnancy tests. These studies showed that serum from men and non-pregnant women contains measurable concentrations of hCG derived from the pituitary. Subsequent development of assays for the subunits of hCG showed that the β subunit of hCG (hCGβ) is expressed at low concentrations by most cancers and that it is a strong prognostic marker. These studies led to the formation of a working group for standardization of hCG determinations and the development of new reference reagents for several molecular forms of hCG. The preparation of intact hCG has been adopted as the fifth international standard by WHO. Availability of several well-defined forms of hCG made it possible to characterize the epitopes of nearly 100 monoclonal antibodies. This will facilitate design of immunoassays with pre-defined specificity. Finally, the discovery of different forms of immunoreactive PSA in serum from a prostate cancer patient led to identification of the complex between PSA and α1-antichymotrypsin, and the use of assays for free and total PSA in serum for improved diagnosis of prostate cancer. Epitope mapping of PSA antibodies and establishment of PSA standards has facilitated establishment well-standardized assays for the various forms of PSA.

High serum trypsin levels and the -409 T/T genotype of PRSS1 gene are susceptible to neonatal sepsis

Neonatal sepsis remains an important and common cause of morbidity and mortality among newborn infants, especially in developing countries. The aim of the present study was to determine whether serum trypsin levels and genotypes of cationic trypsinogen (PRSS1) gene could be served as markers for predicting neonatal sepsis. The serum trypsin levels and genotypes of PRSS1 were examined in both 50 infants with infection during neonatal period and 56 healthy neonates as controls. The infected infants were further subdivided into infants with sepsis group (n=18) and infected infants without sepsis (n=32). The genotype of PRSS1 was analyzed by direct sequencing, and the serum trypsin level was measured by immunoassay. It showed that the median value of serum trypsin was significantly higher in infected infants (31.90 ng/mL) than in controls (12.85 ng/mL; P=0.030). More importantly, sepsis subgroup (50.95 ng/mL) had significantly higher median serum trypsin than infected infants without sepsis subgroup (19.10 ng/mL) and controls (12.85 ng/mL) (P=0.015 and P=0.002, respectively). Additionally, the median serum trypsin levels were found significantly higher in infants who had T/T (37.90 ng/mL) genotype of PRSS1 compared with those who had C/T genotype (12.80 ng/mL; P=0.005). This study suggested that serum trypsin and rs10273639 C/T of PRSS1 were revealed to be novel markers for predicting neonatal sepsis.

Differences in the degree of cerulein-induced chronic pancreatitis in C57BL/6 mouse substrains lead to new insights in identification of potential risk factors in the development of chronic pancreatitis

A frequently used experimental model of chronic pancreatitis (CP) recapitulating human disease is repeated injection of cerulein into mice. C57BL/6 is the most commonly used inbred mouse strain for biomedical research, but widespread demand has led to generation of several substrains with subtly different phenotypes. In this study, two common substrains, C57BL/6J and C57BL/6NHsd, exhibited different degrees of CP, with C57BL/6J being more susceptible to repetitive cerulein-induced CP as assessed by pancreatic atrophy, pancreatic morphological changes, and fibrosis. We hypothesized that the deficiency of nicotinamide nucleotide transhydrogenase (NNT) protein in C57BL/6J is responsible for the more severe C57BL/6J phenotype but the parameters of CP in NNT-expressing transgenic mice generated on a C57BL6/J background do not differ with those of wild-type C57BL/6J. The highly similar genetic backgrounds but different CP phenotypes of these two substrains presents a unique opportunity to discover genes important in pathogenesis of CP. We therefore performed whole mouse genome Affymetrix microarray analysis of pancreatic gene expression of C57BL/6J and C57BL/6NHsd before and after induction of CP. Genes with differentially regulated expression between the two substrains that might be candidates in CP progression included Mmp7, Pcolce2, Itih4, Wdfy1, and Vtn. We also identified several genes associated with development of CP in both substrains, including RIKEN cDNA 1810009J06 gene (trypsinogen 5), Ccl8, and Ccl6.

Laboratory diagnosis of acute pancreatitis: in search of the Holy Grail

Acute pancreatitis is an acute inflammatory condition of the pancreas, which might extend to local and distant extrapancreatic tissues. The global incidence varies between 17.5 and 73.4 cases per 100,000 and the pathogenesis recognizes alcohol exposure and biliary tract disease as the leading causes, ahead of post-endoscopic retrograde cholangiopancreatography, drugs and abdominal trauma. The diagnosis of acute pancreatitis is substantially based on a combination of clinical signs and symptoms, imaging techniques and laboratory investigations. Contrast-enhanced computed tomography is the reference standard for the diagnosis, as well as for establishing disease severity. The assessment of pancreatic enzymes, early released from necrotic tissue, is the cornerstone of laboratory diagnosis in this clinical setting. Although there is no single test that shows optimal diagnostic accuracy, most current guidelines and recommendations indicate that lipase should be preferred over total and pancreatic amylase. Although a definitive diagnostic threshold cannot be identified, cut-offs comprised between ≥ 2 and ≥ 4 times the upper limit of the reference interval are preferable. The combination of amylase and lipase has been discouraged as although it marginally improves the diagnostic efficiency of either marker alone, it increases the cost of investigation. Some interesting biomarkers have been also suggested (e.g., serum and urinary trypsinogen-1, -2 and -3, phospholipase A2, pancreatic elastase, procalcitonin, trypsinogen activated protein, activation peptide of carboxypeptidase B, trypsin-2-alpha1 antitrypsin complex and circulating DNA), but none of them has found widespread application for a variety of reasons, including the inferior diagnostic accuracy when compared with the traditional enzymes, the use of cumbersome techniques, or their recent discovery. The promising results of recent proteomics studies showed that this innovative technique might allow the identification of changes characterizing pancreatic tissue injury, thus highlighting new potential biomarkers of acute pancreatitis.