A reaction route graph analysis of the electrochemical hydrogen oxidation and evolution reactions

The reaction route (RR) graph approach recently developed by us for complex, non-linear kinetic mechanisms is applied to the hydrogen oxidation and evolution reactions. A corresponding RR graph is constructed and translated into an equivalent electrical circuit network by associating each elementary step with a characteristic resistance for the steady-state case and considering the overall reaction as a power source. It is further shown that the steady-state kinetics of the reaction can be investigated employing the conventional methods of the electrical network theory. Using a set of rate constants for the hydrogen evolution reaction (her) in alkaline solutions from the literature, the dominant RRs are identified and simplified mechanisms and kinetics derived.     

Differential Effects of Immunosuppressive Drugs on T-Cell Motility

The best-characterized mechanism of the action of immunosuppressive drugs is to prevent T-cell clonal expansion, thus containing the magnitude of the ensuing immune response. As T-cell recruitment to the inflammatory site is another key step in the development of T-cell-mediated inflammation, we analyzed and compared the effects of two commonly used immunosuppressants, cyclosporin A (CsA) and the rapamycin-related compound SDZ-RAD, on the motility of human CD4+ T cells. We show that CsA, but not SDZ-RAD, inhibits T-cell transendothelial migration in vitro. CsA selectively impaired chemokine-induced T-cell chemotaxis while integrin-mediated migration was unaffected. The inhibition of T-cell chemotaxis correlated with reduced AKT/PKB but not ERK activation following exposure to the chemokine CXCL-12/SDF-1. In addition, CsA, but not SDZ-RAD, prevents some T-cell receptor-mediated effects on T-cell motility. Finally, we show that CsA, but not SDZ-RAD inhibits tissue infiltration by T cells in vivo. Our data suggest a prominent antiinflammatory role for CsA in T-cell-mediated tissue damage, by inhibiting T-cell trafficking into tissues in addition to containing clonal expansion.     

Osteoclastic inhibition: an action of nitric oxide not mediated by cyclic GMP.

The osteoclast is unique in its ability to resorb bone, and excessive osteoclastic activity has been implicated in osteoporosis, Paget disease of bone, rheumatoid arthritis, and the growth of metastases in bone. The activity of this cell is controlled by the main circulating inhibitor, calcitonin, in association with locally produced modulators. We show that nitric oxide (NO) may be an important member of the latter group. NO is produced by the vascular endothelium and nervous system and is involved in both neurotransmission and the regulation of blood pressure. However, our results show that the autocoid is also a potent inhibitor of osteoclast function. NO (30 microM) produced a decrease to approximately 50% of the original osteoclast spread area. Similar effects were also produced by 3-morpholinosydnonimine or sodium nitroprusside, reagents that spontaneously release NO. These shape changes were associated with a reduction of bone resorption after a 24-hr incubation of isolated osteoclasts on devitalized bone slices. NO is thought to act by stimulating guanylate cyclase, with a consequent increase in cyclic GMP, but a different mode of action is likely in the osteoclast since dibutyryl or 8-bromo cyclic GMP have no effect. It should be noted that calcitonin can produce similar changes in shape and activity but is associated with an increase in osteoclast intracellular calcium and cessation of membrane movement; neither of these is produced by NO, suggesting that its mode of action is different. The abundance of NO-producing endothelial cells in bone marrow and their proximity to osteoclasts suggests that marrow endothelial cells may play a physiological role in the regulation of osteoclastic activity.     

Surgical treatment of paravalvular abscess: long-term results.

OBJECTIVE: To examine the outcomes of surgery for active infective endocarditis with paravalvular abscess. METHODS: Paravalvular abscess was defined as infective necrosis of the valve annulus that required patch reconstruction before implanting a new valve. Of 383 patients with active infective endocarditis who underwent surgical treatment, 135 (35%) had paravalvular abscess. Patients' mean age was 51+/-16 years and 68% were men. The infected valve was native in 69 patients and prosthetic in 66. The abscess involved the aortic annulus in 73 patients, the mitral annulus in 27, the aortic and mitral annuluses in 33, and the aortic and tricuspid and/or pulmonary annuluses in 2. Surgery consisted of radical resection of the abscess, reconstruction of the annulus with patches and valve replacement. Mean follow-up was 6.2+/-5.2 years and complete. RESULTS: There were 21 (15.5%) operative deaths. Preoperative shock and abscess in the aortic and mitral annuluses were independent predictors of operative death. There were 34 (25%) late deaths. Survival at 15 years was 43+/-6% for all patients, 50+/-8% for native valve endocarditis and 35+/-9% for prosthetic (p=0.41). Age by increments of 5 years and recurrent endocarditis were independent predictors of late death. There were 16 episodes of recurrent endocarditis in 15 patients, and the freedom from recurrent endocarditis was 82+/-4% at 15 years. Fifteen reoperations were performed in 14 patients. Freedom from reoperation was 72+/-9% at 15 years. CONCLUSIONS: Surgery for active endocarditis with paravalvular abscess was associated with high operative mortality, particularly in patients in shock and abscess of both mitral and aortic annuluses. Long-term survival was adversely affected by age and recurrent bouts of endocarditis.