Viktor S. Poór

Serum prohepcidin levels in chronic inflammatory bowel diseases

BACKGROUND AND AIMS One of the major symptoms of chronic inflammatory bowel diseases is anemia. The two most common diseases are Crohns disease and ulcerative colitis. Anemia may develop due to intestinal bleeding, iron absorption disturbances, or high levels of inflammatory cytokines. It is not clear whether or not hepcidin, the only known hormone regulating cellular iron uptake in mammals is involved. The transcription of hepcidin is controlled by the iron status of the body, hypoxia, and/or inflammation. This study was meant to find relationship between serum prohepcidin levels and clinical parameters of iron homeostasis or inflammatory state in patients suffering from Crohns disease or ulcerative colitis. METHODS Serum prohepcidin levels were measured with ELISA in 72 patients diagnosed with ulcerative colitis and 30 patients suffering from Crohns disease. RESULTS In both groups serum iron levels were lower, while levels of C-reactive protein were higher than in the healthy controls. Serum prohepcidin levels showed no significant differences compared to those in the control group. In the affected patients only weak correlations were observed between prohepcidin levels and diagnostic parameters: in Crohns disease prohepcidin levels correlated positively with transferrin levels, total iron-binding capacity, transferrin saturation, activity index, and serum albumin levels, while in ulcerative coltitis prohepcidin levels were related to transferrin levels and transferrin saturation. CONCLUSION It seems obvious that serum prohepcidin level determination in itself is not a satisfactory diagnostic or prognostic measure in anemia of chronic inflammatory bowel diseases.

Prohepcidin binds to the HAMP promoter and autoregulates its own expression.

Hepcidin is the major regulatory peptide hormone of iron metabolism, encoded by the HAMP (hepcidin antimicrobial peptide) gene. Hepcidin is expressed mainly in hepatocytes, but is also found in the blood in both a mature and prohormone form. Although, the function of mature hepcidin and the regulation of the HAMP gene have been extensively studied, the intracellular localization and the fate of prohepcidin remains controversial. In the present study, we propose a novel role for prohepcidin in the regulation of its own transcription. Using indirect immunofluorescence and mCherry tagging, a portion of prohepcidin was detected in the nucleus of hepatocytes. Prohepcidin was found to specifically bind to the STAT3 (signal transducer and activator of transcription 3) site in the promoter of HAMP. Overexpression of prohepcidin in WRL68 cells decreased HAMP promoter activity, whereas decreasing the amount of prohepcidin caused increased promoter activity measured by a luciferase reporter-gene assay. Moreover, overexpression of the known prohepcidin-binding partner, α-1 antitrypsin caused increased HAMP promoter activity, suggesting that only the non-α-1 antitrypsin-bound prohepcidin affects the expression of its own gene. The results of the present study indicate that prohepcidin can bind to and transcriptionally regulate the expression of HAMP, suggesting a novel autoregulatory pathway of hepcidin gene expression in hepatocytes.

α‐1 Antitrypsin binds preprohepcidin intracellularly and prohepcidin in the serum

Recent discoveries have indicated that the hormone hepcidin plays a major role in the control of iron homeostasis. Hepcidin regulates the iron level in the blood through the interaction with ferroportin, an iron exporter molecule, causing its internalization and degradation. As a result, hepcidin increases cellular iron sequestration, and decreases the iron concentration in the plasma. Only mature hepcidin (result of the cleavage of prohepcidin by furin proteases) has biological activity; however, prohepcidin, the prohormone form, is also present in the plasma. In this study, we aimed to identify new protein–protein interactions of preprohepcidin, prohepcidin and hepcidin using the BacterioMatch two‐hybrid system. Screening assays were carried out on a human liver cDNA library. Preprohepcidin screening gave the following results: α‐1 antitrypsin, transthyretin and α‐1‐acid glycoprotein showed strong interactions with preprohepcidin. We further confirmed and examined the α‐1 antitrypsin binding in vitro (glutathione S‐transferase, pull down, coimmunoprecipitation, MALDI‐TOF) and in vivo (ELISA, cross‐linking assay). Our results demonstrated that the serine protease inhibitor α‐1 antitrypsin binds preprohepcidin within the cell during maturation. Furthermore, α‐1 antitrypsin binds prohepcidin significantly in the plasma. This observation may explain the presence of prohormone in the circulation, as well as the post‐translational regulation of the mature hormone level in the blood. In addition, the lack of cleavage protection in patients with α‐1 antitrypsin deficiency may be the reason for the disturbance in their iron homeostasis.

Oxidative stress induces transient O-GlcNAc elevation and tau dephosphorylation in SH-SY5Y cells.

O‐linked β‐N‐acetlyglucosamine or O‐GlcNAc modification is a dynamic post‐translational modification occurring on the Ser/Thr residues of many intracellular proteins. The chronic imbalance between phosphorylation and O‐GlcNAc on tau protein is considered as one of the main hallmarks of Alzheimers disease. In recent years, many studies also showed that O‐GlcNAc levels can elevate upon acute stress and suggested that this might facilitate cell survival. However, many consider chronic stress, including oxidative damage as a major risk factor in the development of the disease. In this study, using the neuronal cell line SH‐SY5Y we investigated the dynamic nature of O‐GlcNAc after treatment with 0.5 mM H2O2 for 30 min. to induce oxidative stress. We found that overall O‐GlcNAc quickly increased and reached peak level at around 2 hrs post‐stress, then returned to baseline levels after about 24 hrs. Interestingly, we also found that tau protein phosphorylation at site S262 showed parallel, whereas at S199 and PHF1 sites showed inverse dynamic to O‐Glycosylation. In conclusion, our results show that temporary elevation in O‐GlcNAc modification after H2O2‐induced oxidative stress is detectable in cells of neuronal origin. Furthermore, oxidative stress changes the dynamic balance between O‐GlcNAc and phosphorylation on tau proteins.

PCR-based identification of drowning: four case reports

Proper diagnosis in drowning victims is often difficult due to the lack of signs specific to drowning. The diatom test is a widely used procedure for the diagnosis. Some types of water contain only minimal amounts of diatom cells which may provide false-negative results, while a negative diatom test result does not exclude drowning. In proving drowning, we used a polymerase chain reaction (PCR)-based biological method in addition to the conventional methods. DNA was extracted from postmortem spleen tissues and water of the drowning site. Samples were tested with algae (diatoms and small green algae)- and cyanobacteria (blue-green algae)-specific primers. We present here multiple drowning cases in which diatom tests of the postmortem tissue samples and the water were negative. In each case, the presence of phytoplanktonic DNA strengthened the autopsy diagnosis of drowning even in the absence of visible diatoms. In the future, the PCR method may be of consideration as a possible supplement of the diatom test in the examination of presumed drowning cases.

Hepcidin and its potential clinical utility

A number of pathophysiological conditions are related to iron metabolism disturbances. Some of them are well known, others are newly discovered or special. Hepcidin is a newly identified iron metabolism regulating hormone, which could be a promising biomarker for many disorders. In this review, we provide background information about mammalian iron metabolism, cellular iron trafficking, and the regulation of expression of hepcidin. Beside these molecular biological processes, we summarize the methods that have been used to determine blood and urine hepcidin levels and present those pathological conditions (cancer, inflammation, neurological disorders) when hepcidin measurement may have clinical relevance.

Lithium Induces ER Stress and N-Glycan Modification in Galactose-Grown Jurkat Cells

We previously reported that lithium had a significant impact on Ca2+ regulation and induced unfolded protein response (UPR) in yeast cells grown on galactose due to inhibition of phosphoglucomutase (PGM), however the exact mechanism has not been established yet. In this study, we analysed lithiums effect in galactose-fed cells to clarify whether these ER-related changes are the result of a relative hypoglycemic state. Furthermore, we investigated whether the alterations in galactose metabolism impact protein post-translational modifications. Thus, Jurkat cells were incubated in glucose or galactose containing media with or without lithium treatment. We found that galactose-fed and lithium treated cells showed better survivability than fasting cells. We also found higher UDP-Hexose and glycogen levels in these cells compared to fasting cells. On the other hand, the UPR (X-box binding protein 1 mRNA levels) of galactose-fed and lithium treated cells was even greater than in fasting cells. We also found increased amount of proteins that contained N-linked N-acetyl-glucosamine, similar to what was reported in fasting cells by a recent study. Our results demonstrate that lithium treatment of galactose-fed cells can induce stress responses similar to hypoglycemia, however cell survival is still secured by alternative pathways. We propose that clarifying this process might be an important addition toward the better understanding of the molecular mechanisms that regulate ER-associated stress response.