Site-directed mutagenesis: effect of an extracistronic mutation on the in vitro propagation of bacteriophage Qbeta RNA.

It has been proposed that the nucleotide sequences of the 3' terminal extracistronic regions of phage RNA plus and minus strands have been strictly conserved during evolution because they are stringently required for recognition by the viral replicase. We have devised a method to generate point mutations at selected sites in the genome of phage Qbeta. The in vitro synthesis of Qbeta RAN with G leads to A transition in the 16th position from the 3' end, i.e., in the terminal extracistronic region of the genome, is outlined. When a mixture of about 60% wild-type and 40% mutant RNA was repeatedly replicated, the mutant RNA was enriched to 80%, showing that at least this point mutation in the terminal sequence of Qbeta RNA does not impair its in vitro replication, but in fact slightly accelerates it.     

Target cell specificity of two species of human interferon-alpha produced in Escherichia coli and of hybrid molecules derived from them.

Plasmids containing cDNAs for human interferon (IfN) alpha-1, IFN alpha-2, and several hybrids of the two cDNAs, all joined identically to an Escherichia coli lac promoter fragment gave rise, in E. coli, to fused interferons (fIFNs) that had very different target-cell specificities. fIFN alpha-1 had a lower specific activity on human WISH cells than on bovine MDBK cells, while fIFN alpha-2 showed the opposite behavior. fIFN hybrids with the NH2-proximal half of fIFN alpha-2 behaved qualitatively like fIFN alpha-1, and those with the NH2-proximal half of fIFN alpha-2, behaved like fIFN alpha-2. On mouse L929 cells, fIFN alpha-2 was almost inactive, while fIFN alpha-1 showed relatively high activity. In this case, the fIFN hybrids with the COOH-proximal half of IFN alpha-1 showed activity on mouse cells, while the reciprocal hybrid did not. In many cases, the activity spectrum of the hybrids was very different from that of either parent. We propose that the IFN molecule has either two binding sites or two regions constituting the binding site, one in the COOH- and the other in the NH2-proximal half. The experimental findings can be accounted for if the fits of the two sites to their receptor counterparts on different cell lines are independent of one another.     

Antioxidant vitamin C improves endothelial function in obstructive sleep apnea

RATIONALE: Obstructive sleep apnea (OSA) is associated with oxidative stress, endothelial dysfunction, and increased cardiovascular morbidity and mortality. OBJECTIVE: We tested the hypothesis that endothelial dysfunction in patients with OSA is linked to oxidative stress. METHODS: In the present study, we measured flow-mediated dilation (FMD) of the brachial artery by ultrasound in 10 otherwise healthy, untreated patients with OSA and 10 age-and sex-matched control subjects without sleep-disordered breathing before and after intravenous injection of the antioxidant vitamin C. The investigator performing the FMD measurements was blinded to the status of the patients. RESULTS: When compared with control subjects, baseline FMD was significantly reduced in the patients with OSA. After intravenous injection of 0.5 g vitamin C, vasoreactivity remained unchanged in the control subjects. In the patients with OSA, ascorbate led to an increase in FMD to a level comparable to that observed in the control group. CONCLUSION: The reduced endothelial-dependent vasodilation in untreated patients with OSA acutely improves by the free radical scavenger vitamin C. These results are in favor of oxidative stress being responsible for the endothelial dysfunction in OSA. Antioxidant strategies should be explored for the treatment of OSA-related cardiovascular disease.     

Oxygen sensors in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an essential mechanism adapting lung perfusion to regional ventilation. Perturbations to HPV, such as those occurring in pneumonia, acute respiratory distress syndrome and liver failure, can result in arterial hypoxemia. Under conditions of general hypoxia, HPV increases pulmonary vascular resistance and thus causes acute pulmonary hypertension. Despite intensive research, the underlying mechanisms of HPV have not been fully elucidated. Deciphering signalling pathways that result in HPV could suggest novel approaches to address a failure of HPV, as well as for the treatment of pulmonary hypertension associated with HPV. Within this context, this review focuses on current concepts in the oxygen sensing mechanisms that underlie HPV.     

Granules are necessary for death of neutrophils after phagocytosis of crystalline monosodium urate

Crystalline monosodium urate (MSU) produces inflammation in vivo and kills phagocytes in vitro. A plausible hypothesis to account for crystal-induced cell death is that ingested crystals perforate the phagocytic vacuole into which lysosomes have degranulated: lysis from within. However, it has also been contended that degranulation is not required for crystal-induced cell death. To resolve this controversy, we have prepared neutrophil-derived cytoplasts (neutroplasts) which are devoid of most cellular organelles, including lysosomal granules. Both intact neutrophils and neutroplasts ingested MSU crystals, but inhibition of phagocytosis by cytochalasin B reduced crystal-induced death of neutrophils (release of lactate dehydrogenase) from 42% to 16% without altering lysis of neutroplasts (27% with MSU alone and 26% with MSU and cytochalasin B). Moreover, addition of serum, which prevents direct interaction of crystals with the outer plasma membrane, reduced lysis of neutrophils, reducing cell death from 42% to 25%. After 60 min incubation, serum was totally ineffective in reducing neutrophil death but continued to reduce lysis of neutroplasts from 61% to 13%. Thus, the MSU lysed neutroplasts under conditions in which it ruptured membranes of nonphagocytic structures (erythrocytes, liposomes), i.e., in the absence of serum: lysis from without. These data suggested that death of neutrophils after internalization of MSU requires a component that is lacking in neutroplasts. Granules (lysosomes) are the best candidates for this component, supporting the general validity of the lysis from within hypothesis.Preliminary results of these studies were presented at the Annual Meeting of the American Rheumatism Association, Texas, June 1983.