Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs

The mechanisms by which amorphous silica dissolves have proven elusive because noncrystalline materials lack the structural order that allows them to be studied by the classical terrace, ledge, kink-based models applied to crystals. This would seem to imply amorphous phases have surfaces that are disordered at an atomic scale so that the transfer of SiO(4) tetrahedra to solution always leaves the surface free energy of the solid unchanged. As a consequence, dissolution rates of amorphous phases should simply scale linearly with increasing driving force (undersaturation) through the higher probability of detaching silica tetrahedra. By examining rate measurements for two amorphous SiO(2) glasses we find, instead, a paradox. In electrolyte solutions, these silicas show the same exponential dependence on driving force as their crystalline counterpart, quartz. We analyze this enigma by considering that amorphous silicas present two predominant types of surface-coordinated silica tetrahedra to solution. Electrolytes overcome the energy barrier to nucleated detachment of higher coordinated species to create a periphery of reactive, lesser coordinated groups that increase surface energy. The result is a plausible mechanism-based model that is formally identical with the classical polynuclear theory developed for crystal growth. The model also accounts for reported demineralization rates of natural biogenic and synthetic colloidal silicas. In principle, these insights should be applicable to materials with a wide variety of compositions and structural order when the reacting units are defined by the energies of their constituent species.     

Binding of heme by glutathione S-transferase: a possible role of the erythrocyte enzyme

Human erythrocyte glutathione S-transferase activity is inhibited, probably competitively, by hemin with a Ki of 10(-7) M. It is postulated that glutathione S-transferase functions physiologically as a hemin-binding and/or transport protein in developing erythroid cells.     

Interpretation of liver chemistries in adult donors after living donor liver transplantation

OBJECTIVES: The safety of donors is paramount in adult living donor liver transplantation. Our goal is to compare the pattern of recovery of hepatic synthetic function and aminotransferases in healthy adult donors with and without complications. METHODS: We reviewed 47 consecutive patients undergoing right donor hepatectomy at our center. Laboratory data were collected through the first 2 postoperative weeks and results from donors with and without complications were compared. RESULTS: Donor morbidity was 25% and there were no donor deaths. Total bilirubin peaked on postoperative day 3, whereas aminotransferases and international normalized ratio peaked on postoperative day 1. Peak total bilirubin was higher in patients with fluid collections (n = 7) compared with those without fluid collections (n = 40), 4.6 mg/dL and 2.3 mg/dL, respectively, P = 0.02. On postoperative day 3 the peak total bilirubin was greater than 3.0 mg/dL in 86% of donors with fluid collections and 15% of donors without fluid collections, (P = 0.0005) whereas aminotransferases and alkaline phosphatase were not significantly different between these 2 groups. CONCLUSIONS: After right donor hepatectomy a total bilirubin greater than 3.0 mg/dL on postoperative day 3 should prompt an evaluation for a fluid collection, even if other liver tests are normal or declining.     

乐胃煎逆转胃癌前病变AgNOR及细胞图像分析

目的研究乐胃煎逆转胃癌前病变不完全结肠型肠化和／或中度异型增生的疗效．方法胃镜病理证实为不完全结肠型肠化和／或中度异型增生４６例．治疗组３０例用乐胃煎，对照组１６例用德诺（Ｄｅ＿Ｎｏｌ）．治疗前后胃镜活检胃窦固定部位粘膜标本作ＡｇＮＯＲ染色及细胞图像分析．结果乐胃煎对不完全结肠型肠化及中度异型增生总有效率均高于Ｄｅ＿Ｎｏｌ，分别为７２％比２５％（Ｐ＜００５）和８９５％比４４４％（Ｐ＜００５）．乐胃煎治疗前后，ＡｇＮＯＲ计数分别为７３０±１１６和４８１±１５０（Ｐ＜００１），Ｄｅ＿Ｎｏｌ组为７７３±０９２和７０５±１０２（Ｐ＜００１）．两组治疗前后ＡｇＮＯＲ计数差值均数相比，统计学上也有显著性差异，分别为２５２±１５４和０６９±０４８（Ｐ＜００１）．乐胃煎组中２０例作细胞图像分析，治疗后各参数（长轴、短轴、核浆比、结构异型指数等）均有不同程度的降低，有显著性差异．结论乐胃煎确有较好地逆转胃癌前病变的功效．     

Woven Endobridge device for treatment of dissection-related PICA aneurysm

Ruptured vertebrobasilar dissecting aneurysms require urgent, often challenging treatment as they have with a high re-hemorrhage rate within the first 24 hours. The patient is a 57-year-old woman who presented with severe-sudden onset headache. Further work up showed a ruptured dissecting aneurysm of the caudal loop of the posterior inferior cerebellar artery (PICA) with associated narrowing distally, in the ascending limb. The aneurysm was immediately occluded with a Woven Endobridge (WEB) device (MicroVention, Tustin, CA, USA) while flow diversion treatment of the diseased ascending limb was postponed. Follow-up angiography three months later showed complete occlusion of the aneurysm, as well as healing of the diseased distal vessel, obviating the need for further intervention. WEB embolization of a ruptured dissecting posterior circulation aneurysm provided an excellent outcome for this patient.     

Erythropoietin production in a primary culture of human renal carcinoma cells maintained in nude mice

The present studies report erythropoietin (Ep) production in primary cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted to BALB/c nude mice. The levels of erythropoietin in the culture media were estimated using the exhypoxic polycythemic mouse assay (EHPCMA), fetal mouse liver erythroid colony- forming technique (FMLC), and a radioimmunoassay (RIA). The spent culture media of the exponentially growing cells contained less than 10 mU/ml of Ep measured by RIA. However, after the cells became confluent, Ep levels (RIA) in the spent media showed a marked increase to approximately 300 mU/ml. Ep levels estimated using the FMLC and EHPCMA were approximately 2/3 and 1/10, respectively, of those measured by RIA. Rabbit antiserum to highly purified human urinary Ep (70,400 U/mg protein) was utilized for immunocytochemical (peroxidase-antiperoxidase method) localization of Ep in the cultured cells. Very few of the cells in exponential growth exhibited Ep-like immunoreactivity, whereas intense Ep-like immunoreactivity was observed in the cytoplasm of the cells maintained in culture for a prolonged period after reaching confluency. The most intense staining was observed in some of the cells forming domes. The domes developed after the cells reached confluency, and their numbers increased with increasing time in confluent culture, in parallel with the increase in Ep levels in the spent media. This primary cell culture system of a renal cell carcinoma maintained in nude mice, which produces immunologically and biologically active Ep, may provide a useful model for studies of the mechanism of Ep production.     

Immunoglobulin G from patients with heparin-induced thrombocytopenia binds to a complex of heparin and platelet factor 4

Heparin-induced thrombocytopenia (HIT) is an important complication of heparin therapy. Although there is general agreement that platelet activation in vitro by the HIT IgG is mediated by the platelet Fc receptor, the interaction among the antibody, heparin, and platelet membrane components is uncertain and debated. In this report, we describe studies designed to address these interactions. We found, as others have noted, that a variety of other sulfated polysaccharides could substitute for heparin in the reaction. Using polysaccharides selected for both size and charge, we found that reactivity depended on two independent factors: a certain minimum degree of sulfation per saccharide unit and a certain minimum size. Hence, highly sulfated but small (< 1,000 daltons) polysaccharides were not reactive nor were large but poorly sulfated polysaccharides. The ability of HIT IgG to recognize heparin by itself was tested by Ouchterlony gel diffusion, ammonium sulfate and polyethylene glycol precipitation, and equilibrium dialysis. No technique demonstrated reactivity. However, when platelet releasate was added to heparin and HIT IgG, a 50-fold increase in binding of radio-labeled heparin to HIT IgG was observed. The releasate was then depleted of proteins capable of binding to heparin by immunoaffinity chromatography. Only platelet factor 4-immunodepleted releasate lost its reactivity with HIT IgG and heparin. Finally, to determine whether the reaction occurred on the surface of platelets or in the fluid phase, washed platelets were incubated with HIT IgG or heparin and after a wash step, heparin or HIT IgG was added, respectively. Reactivity was only noted when platelets were preincubated with heparin. Consistent with these observations was the demonstration of the presence of PF4 on platelets using flow cytometry. These studies indicate that heparin and other large, highly sulfated polysaccharides bind to PF4 to form a reactive antigen on the platelet surface. HIT IgG then binds to this complex with activation of platelets through the platelet Fc receptors.     

Three cases of autoimmune hepatitis in HIV-infected patients

Autoimmune hepatitis (AIH) is an uncommon liver disease that has previously been reported only 4 times in HIV-infected patients. Our report describes 3 new cases of AIH, 2 probable, and 1 definite. Two of these cases developed while the patient was virologically suppressed on antiretroviral therapy. Liver biopsy findings were critical in establishing the diagnosis of AIH. Because abnormal liver function tests in HIV-positive patients are often ascribed to antiretroviral medications and/or comorbid conditions, AIH may be underdiagnosed in this population. These cases underscore the value of liver biopsy in evaluating hepatitis of unclear etiology in HIV-positive patients. The clinical course of these cases also suggests that standard immunosuppressive therapy for AIH remains the optimal treatment regimen, even in HIV-positive patients.