Mechanisms of the killing of cultured hepatocytes by hydrogen peroxide

Mechanisms of H2O2-induced cell injury were explored in primary cultures of rat hepatocytes. Cells prepared from male rats and cultured for 1 day prior to treatment were killed by H2O2 either added directly to the medium at 0.25-2 mM or generated in situ by glucose oxidase (0.25-2 U/ml) or xanthine oxidase (20-120 mM/ml) and 2 mM xanthine. Catalase protected the cells in each case. Lipid peroxidation as measured by the accumulation of malondialdehyde (MDA) preceded the cell death due to H2O2 added directly to the cultures or generated in the medium. The antioxidants N,N'-diphenyl-p-phenylenediamine (DPPD) and promethazine prevented the accumulation of MDA in both cases and protected the cells treated with H2O2 directly. DPPD and promethazine did not react directly with H2O2. Other antioxidants including butylated hydroxytoluene, vitamin E, and N-propylgallate had varied protective activity against the addition of H2O2 in proportion to their ability to reduce MDA accumulation. In glucose oxidase-treated cultures, DPPD and promethazine prevented the cell killing during the first hour but failed to protect between 1 and 3 h despite prevention of lipid peroxidation. The cell killing between 1 and 3 h in the presence of DPPD was prevented by catalase indicating its dependence upon continued generation of H2O2. Further addition of H2O2 in the presence of DPPD also increased the number of dead cells without lipid peroxidation. The data are consistent with at least two mechanisms of hepatocyte killing by H2O2. The first pathway is prevented by the antioxidants DPPD and promethazine and is very likely related to the peroxidation of membrane phospholipids. The second is independent of lipid peroxidation yet dependent upon the continued presence of H2O2.     

The evolution of alpha/beta barrel enzymes

Of the enzymes whose structure is known, roughly one out of ten has an eight-stranded alpha/beta barrel domain. Structural and chemical evidence suggests that all of these domains may have diverged from a common ancestor.     

Problems of resistance of the causative agent of melioidosis to antibiotics]

It was shown that the pathogen causing melioidosis was highly resistant to antibiotics including beta-lactams. Antibiotic sensitive mutants of P. pseudomallei were isolated after mutagenesis induced by nitrosoguanidine. Permeability for 3H-tetracycline and tetracycline sensitivity of the mutant cells was respectively 3 and 20 times as high as those of the initial parent strain. Gas liquid chromatography revealed quantitative and qualitative changes in separate sugars of the lipopolysaccharide structure in antibiotic sensitive mutants as compared to the initial strain.     

Differential recruitment of expiratory muscles during opossum development

Relationships between time-averaged electromyogram (EMG) discharge in abdominal (ABD) and lateralintercostal (IC) muscles (interspaces 1-10) were evaluated when Inactin-anesthetized supine opossums between 20 and 100 days of age were challenged by positive-pressure breathing (PPB) (3, 6, and 8 cmH2O). Expiratory activity upon initiation of PPB was observed in ABD muscles after the 30th postnatal day; recruitment of IC muscles requires further maturation. For example, at a PPB level of 6 cmH2O, animals up to 50-55 days of age recruited IC muscles from the lowest three interspaces on 44% of the occasions where ABD muscles were activated; in older animals the incidence of IC recruitment increased to 87%. Additionally, the occurrence of IC relative to ABD recruitment increased with increasing levels of PPB; IC muscles of highest interspaces (1-3) were activated less often at all pressures. At the onset of PPB, ABD muscles were usually recruited before IC muscles; this effect was more prominent in the younger animals. During the 5th min of PPB, ABD muscles were recruited earlier in expiration than IC muscles in the majority of animals at all ages. Since IC and ABD motor groups are activated from similar levels of the spinal cord, the delayed maturation of IC muscle responses to PPB may reflect developmental processes involving reflexes from the chest or abdomen, and/or may be a function of nonrespiratory utilization (i.e., postural) of ABD and IC muscles.     

HYPERTENSIVE-ISCHEMIC LEG ULCERS

Ischemic ulcers of the leg having characteristics different from those of ordinary leg ulcers have been observed in a small number of hypertensive patients, mostly women, during the past few years.Such ulcers are usually located above the ankle. They begin with a small area of purplish discoloration at the site of slight trauma, and progress to acutely tender ulceration.In studies of tissue removed from the margin and the base of an ulcer of this kind, obliterative arteriolar sclerotic changes, ischemic-appearing connective tissue and inflammatory changes were noted.Two additional cases are reported.