Aysun Pabuccuoglu

Different p97/VCP complexes function in retrotranslocation step of mammalian Er-associated degradation (ERAD)

Studies in yeast indicate that three specialized endoplasmic reticulum-associated degradation (ERAD) pathways, namely ERAD-L, -M, or -C, dispose substrates with structural lesions in the lumenal, transmembrane, or cytosolic domains, respectively. The ubiquitin ligase (E3) Hrd1p and its cooperating partners are required for ERAD-L and -M pathways, whereas Doa10p complex is required for the ERAD-C pathway. We investigated these pathways in mammalian cells by assessing the requirements of the mammalian ERAD E3s, gp78 and Hrd1, in degradation of four substrates each with different type of structural lesions: CD3δ, Z-variant α1-antitrypsin, tyrosinase (C89R) and mutant cystic fibrosis transmembrane conductance regulator (CFTRΔF508). We demonstrated that tyrosinase (C89R) is a substrate for Hrd1 while all others are gp78 substrates. Knockdown of Hrd1 diminished gp78 substrate levels, but silencing of gp78 had no effect on Hrd1s substrate, suggesting that the functional interaction between Hrd1 and gp78 is unidirectional. Furthermore, while Ufd1 is dispensable for gp78-mediated ERAD, it is essential for Hrd1-mediated ERAD. Interestingly, Npl4 was found to be a key component for both pathways. These results suggest that the Hrd1-mediated ERAD requires a well-established retrotranslocation machinery, the p97/VCP-Ufd1-Npl4 complex, whereas the gp78 pathway needs only p97/VCP and Npl4. In addition, the three distinct ERAD pathways described in yeast may not be strictly conserved in mammalian cells as gp78 can function on three substrates with different structural lesions.

The in vitro effects of Hypericum species on human leukocyte myeloperoxidase activity

Myeloperoxidase (MPO) is a major component of the antimicrobial system of polymorphonuclear neutrophils. The heme enzyme MPO catalyzes the conversion of hydrogen peroxide and chloride to hypochlorous acid. Hypochlorous acid is the major strong oxidant produced by neutrophils and may contribute to inflammatory tissue damage. It was reported that certain antiinflammatory drugs are capable of inhibiting MPO activity and this inhibition may account for their antiinflammatory effect. Hypericum L. is a genus of about 400 species, widespread throughout the world. Some species of genus exhibit a significant antiinflammatory activity beside their several pharmacological properties such as antidepressant, diuretic, antihelmintic, and antibacterial. In this study, we investigated the in vitro effects of three Hypericum species, which exhibit antiinflammatory activity, on human polymorphonuclear leukocyte MPO activity. We found that each extract of Hypericum species reduced the peroxidative and chlorinating activity of human leukocyte MPO in concentration-dependent manner. The antiinflammatory activity of these species may be related with inhibition of MPO activity.

The Effect of Acetaminophen on Oxidative Modification of Low-Density Lipoproteins in Hypercholesterolemic Rabbits

Oxidative modification of low-density lipoproteins (LDL) contributes to the pathology of atherosclerosis. Antioxidants may protect LDL against oxidative modification. Acetaminophen, a widely used analgesic and antipyretic agent, has significant antioxidant properties. However, there is little evidence to suggest that acetaminophen acts as an antioxidant for LDL oxidation in vivo. In this study, we investigated the in vivo effect of acetaminophen on LDL oxidation in hypercholesterolemic rabbits. The oxidative modification of LDL was identified by conjugated dienes and thiobarbituric acid-reactive substances (TBARS). In the cholesterol group which rabbits were fed a diet contained 1% g cholesterol for 8 weeks, TBARS contents and conjugated diene levels in the plasma and isolated LDL samples significantly increased compared with the control rabbits (p<0.05). However, in the cholesterol + acetaminophen group, the TBARS contents and conjugated diene levels were significantly lower than that of the cholesterol group (p<0.05). The results from in vitro studies also demonstrated that the LDL isolated from serum was oxidized by Cu++ ions and this oxidation reduced in the presence of acetaminophen. The reduced oxidative modification of LDL by acetaminophen may be of therapeutic value in preventing the development and progression of atherosclerosis.

Serum Biotinidase activity in children with chronic liver disease and its clinical significance

Background Biotinidase is the enzyme responsible for liberating the vitamin biotin from biocytin and dietary protein–bound vitamin. Individuals lacking biotinidase activity become biotin deficient. Because the liver is the major source of plasma biotinidase, chronic liver diseases can lead to decreased serum biotinidase activity and biotin deficiency. The aim of this study is to determine serum biotinidase activity values in children with chronic liver disease and to investigate the relation among enzyme activity, certain liver function tests, and degree of liver damage. Method In this study, using a spectrophotometric method, biotinidase activity was determined in sera from 62 children with chronic liver diseases (median age, 9.73 years; range, 8 months to 18 years) and from 27 healthy controls. Diagnoses of the patient group were as follows: noncirrhotic chronic hepatitis B virus infection (n = 12), metabolic liver diseases (n = 16), autoimmune hepatitis (n = 6), intrahepatic and extrahepatic cholestasis (n = 14), fulminant hepatitis (n = 5), cryptogenic cirrhosis n = 5), prehepatic portal hypertension (n = 4). Meanwhile, serum albumin, total bilirubin, alkaline phosphatase, alanine aminotransferase, and &ggr;-glutamyltransferase concentrations and prothrombine time were determined for each patient and the results were correlated with serum biotinidase activity. Results There was significant difference between mean enzyme activity of the controls (7.6 ± 1.2 nmol · min −1 · mL −1 ) and of all patients with chronic liver disease (6.3 ± 2.5 nmol · min −1 · mL −1 ) (P < 0.05). Serum biotinidase activity in patients with noncirrhotic chronic liver diseases (chronic viral hepatitis, prehepatic portal hypertension, glycogen storage disease, Gaucher disease) was within the normal ranges. However, serum biotinidase activity in patients with cirrhosis and Wilson disease was significantly less than that of the control group (P < 0.05). The lowest enzyme activities were detected in patients with fulminant hepatitis. Conclusion In this study, serum biotinidase activity was significantly lower in patients with cirrhosis, particularly in the patients with decompensated cirrhosis and fulminant hepatitis who exhibited no clinical symptoms related to biotin deficiency. The decreased serum biotinidase activity in chronic liver diseases was associated with severe impairment of hepatocellular function.

Oxidative and Nitrosative Stress Markers in Patients on Hemodialysis and Peritoneal Dialysis

Aim: The aim of this study was to evaluate the effects of hemodialysis (HD) and peritoneal dialysis (PD) treatments on oxidative and nitrosative stress markers comparatively. Methods: Twenty HD and 20 PD patients as well as 20 healthy individuals were included in this study. Plasma advanced oxidation protein products, myeloperoxidase, thiol group and 3-nitrotyrosine (3-NT) levels were measured in all subjects. Results: Plasma advanced oxidation protein products and myeloperoxidase levels were elevated by HD and PD treatments when compared to the control group. Conversely, plasma thiol group levels were decreased in HD and PD patients. 3-NT levels were increased by HD treatment only. Conclusions: The elevated plasma 3-NT levels in pre-HD and post-HD patients suggest that those patients have a considerably increased risk for nitrosative tissue injury. However, similar 3-NT levels of the control and PD groups support the advantage of PD therapy in terms of nitrosative tissue injury.

The report of the 1st Turkey in vitro diagnostic symposium results

Abstract “The 1st Turkish in vitro Diagnostic Symposium” was organized in İzmir between the dates 18–20 February 2016 with cooperation of Turkish Biochemistry Society Izmir Branch and Dokuz Eylul University Institute of Health Sciences. This article presents a collection of the subjects, recommendations and results included in the final report of the symposium. Symposium subjects were analysed under separate titles and evaluated together with results obtained from various reports on medical devices (MD) in the last decade. According to the final report, the subjects to be considered on preferential basis include “configuration of the websites of legal authorities, standardization and accreditation institutions in a way to access work on in vitro Diagnostic (IVD)”, “activation of university-industry cooperation”, “determination of national standards parallel to international standards” and “carrying out the statistics about IVD-MD in Turkey as immediate as possible”. Drawing attention to the fact that there is a requirement for competent man power for every-stage of IVD-MD lifecycle, it is recommended that postgraduate education programmes are founded to serve these fields. Consequently, this symposium enabled to determine the basic problems about the sector by bringing together the stakeholders related to IVD-MD field and to come up with an action plan in accordance with the recommendations.