<p> The fibrinolytic system has an important role in maintaining vascular patency by restricting fibrin clot formation to prevent occlusion of the blood vessel. Plasminogen activation is the central event in fibrinolysis and is tightly regulated by activators and inhibitors. Histidine-rich glycoprotein (HRG) is an abundant plasma protein that has been proposed to have a regulatory role in many biological processes, including fibrinolysis. Approximately 50% ofplasminogen in the blood circulates in complex with HRG. Conflicting reports dispute the role of HRG in fibrinolysis, specifically whether it promotes or inhibits plasminogen activation. To elucidate the role of HRG in fibrinolysis, we isolated HRG from human plasma and analyzed its effect on plasminogen activation by tissue-type plasminogen activator in a kinetic assay. HRG had no significant effect on plasminogen activation by tissue-type plasminogen activator once contaminating plasminogen was eliminated from our HRG preparations. Based on these results, the focus of our research was redirected to analyzing the effect of HRG on additional plasminogen activators, namely urinary-type plasminogen activator and factor (F) Xlla. HRG inhibited plasminogen activation by both activators. HRG had the greatest inhibitory effect on FXIIa activity. This novel finding led us to explore the relationship between HRG and FX.IIa by measuring the affinity of HRG for FXIIa by surface plasmon resonance, and by analyzing the effect of HRG on FXIIa activity in various contact pathway reactions. ZnCh was also included in these reactions because it plays an important role in enhancing both HRG-and FXII-mediated interactions and is released by activated platelets. In the presence of 12.5 μM ZnCl2, FXIIa bound to the histidine-rich region of HRG with very high affinity (Kd = 56 ± 8.9 pM). Interestingly, HRG does not bind to FXII. Functional analysis of HRG revealed that it significantly inhibits a number of contact pathway reactions, including FXII autoactivation, kallikreinmediated FXII activation, and FXIIa-mediated FXI activation. Conversely, HRG enhanced FXIIa-mediated prekallikrein activation. Based on these findings, we hypothesize that HRG binds to an exosite on FXIIa, which is not expressed by the zymogen FXII, and alters FXIIa activity. The mechanism of HRG-mediated FXIIa inhibition is not fully understood and needs to be further analyzed by both binding and functional assays. These observations raise the possibility that the main function of HRG is to modulate FXIIa activity, rather than plasminogen activation. Because of its abundance, HRG may function as a modulator of haemostasis through its effect on coagulation and fibrinolysis. </p> / Thesis / Master of Science (MSc)

This study was aimed at investigating adverse and beneficial long-term effects of jejunoileal bypass (JIB) sugery in obese patients. The JIB was the first widly used surgical procedure for treatment of morbid obesity. The weight loss was remarkable, but the procedure was declared not appropiate for obesity surgery in the late 1970's. Serious late adverse effects such as liver cirrhosis and malignancies, have been postulated. Unexpectedly few studies have adressed these problems. In the long-term follow-up of 87 uniformly operated patients, several persisting beneficial effects were found. The mean Body Mass Index was 41.5 kg/m2 at the time of operation and 29.7 kg/m2 sixteen years after the operation. Diabetes type II and hyperlipidemia, common in an obese population, was not found in this group. Reversals were performed in 3% of the patients in contrast to 20-30% in many earlier studies. Revisions performed in 8% of the patients due to excessive weight loss could have contributed to the good long-term outcome. Percutaneous liver biopsies from 44 patients taken 14-20 (mean 17) years after JIB revealed normal or fatty liver, a lower degree of histological abnormalities than in 11 biopsies taken at the time of operations 1-14 (mean 6) years postoperatively. Liver cirrhosis seen early in one patient could not be found in the late biopsies. Reduced activity of the fibrinolytic system has been shown to be a new cardiovacular risk factor. In 45 patients studied 14-20 years after JIB, the levels of both plasminogen activator inhibitor type 1 (PAI-1) and tissue plasminogen activator (tPA) were significantly lower than in a control group of 10 morbidly obese patients ( PAI-1: 8.4 vs 32 U/mL, tPA: 7.2 vs 12 pg/L). Bile acids are regarded as cofactors in the carcinogenesis in the colon and experimentally an increased frequency of malignant tumors has been demonstated after JIB in carcinogen-induced rats. In 30 of the operated patients, colonoscopy with biopsy was performed 11-17 yeras after the operation. No evidence for malignant transformation was found as reflected by an abscense of polyp formation, histologic dysplasia or aneuploidia in flow cytometric DNA analysis. Eight hundred and thirty patients from 10 hospitals subjected to JIB were compared to 1660 controls with respect to malignant diagnosis over a 20 years period. No significantly increased risk for colorectal carcinoma could be demonstrated. However the overall risk for malignant disease was increased in the operated patients. The frequency of endometrial carcinoma was significantly elevated up to five years after the operation but was normal after that time. In conclusion the postulated progress of serious adverse effects of JIB such as liver cirrhosis and malignant disease has not been possible to demonstrate. Several beneficial effects such as weight loss and reduction of cardiovascular risk factors have been found a long time after the operation. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1995, härtill 5 uppsatser.</p> / digitalisering@umu