Improvement in mitral regurgitation after aortic valve replacement

This study sought to determine whether there is a quantitative improvement in mitral regurgitation (MR) after aortic valve replacement (AVR) for aortic stenosis (AS) and, if so, the mechanisms for this change. MR frequently accompanies AS. The addition of mitral valve replacement to AVR significantly increases the risk of surgery. Although previous studies have suggested a qualitative improvement in MR severity after AVR, semiquantitative analysis of this improvement has not been documented nor have the underlying mechanisms been examined. We evaluated 28 patients who had undergone 2-dimensional echo and color flow Doppler imaging an average of 1.5 +/- 2.5 months before and 2.5 +/- 4.2 months after AVR. Maximum MR area, MR percentage (MR area/left atrial area), mitral annular area, left atrial area, aortic gradient, and parameters of left ventricular geometry were measured to evaluate MR severity and to assess functional mechanisms for improvement in MR. There was a significant decrease in MR area (5.5 +/- 2.8 cm2 vs 2.5 +/- 1.9 cm2, p < or =0.0001) and MR percentage (25 +/- 11% vs 12 +/- 10% after operation, p < or =0.0001) between preoperative and postoperative studies. There was a significant reduction in aortic gradient, mitral annular area, left atrial area, and left ventricular length postoperatively. In univariate analysis, MR improvement was related to the lower preoperative left ventricular fractional area change (p = 0.027) and to the changes in fractional area change (p = 0.001) and left ventricular systolic area (p = 0.001). Thus, improvement in MR after AVR is related to changes in left ventricular function postoperatively. These data suggest that reduction in MR is due not only to decreased intraventricular pressure, but also to changes in ventricular morphology.     

Lack of effect of spaceflight on bone mass and bone formation in group-housed rats

As part of an experiment to study the role of corticosteroids in bone changes during spaceflight, male Sprague-Dawley rats (6 wk old, 165 g body weight) were placed in orbit for 17 days, in groups of six, in animal-enclosure modules (AEMs) aboard the space shuttle Columbia (STS-78). Control rats were group housed in a similar manner in ground-based AEMs or standard vivarium cages. Adrenal hypertrophy occurred in flight rats, but bone histomorphometric analyses revealed a lack of significant changes in bone mass and bone formation in these animals. Cancellous bone volume and osteoblast surface in the proximal tibial metaphysis were nearly the same in flight and ground-based rats. Normal levels of cancellous bone mass and bone formation were also detected in the lumbar vertebrae and femoral necks of flight rats. In the tibial diaphysis, periosteal bone formation rate was found to be identical in flight and ground-based rats. The results indicate that, under conditions of group housing in AEMs, spaceflight has minimal effects on bone mass and bone formation in rapidly growing rats. These findings emphasize the need to investigate the importance of rat age, strain, and especially housing conditions for studies of the skeletal effects of spaceflight.     

Early transition to oral antibiotic therapy for community-acquired pneumonia: duration of therapy, clinical outcomes, and cost analysis

Our objective was to compare therapeutic outcome and analyse cost-benefit of a 'conventional' (7-day course of i.v. antibiotic therapy) vs. an abbreviated (2-day i.v. antibiotic course followed by 'switch' to oral antibiotics) therapy for in-patients with community-acquired pneumonia (CAP). We used a multicenter prospective, randomized, parallel group with a 28 day follow-up, at the University-based teaching hospitals: The Medical Center of Louisiana in New Orleans, LA and hospitals listed in the acknowledgement. Ninety-five patients were randomized to receive either a 'conventional' course of intravenous antibiotic therapy with cefamandole 1 g i.v. every 6 h for 7 days (n = 37), or an abbreviated course of intravenous therapy with cefamandole (1 g i.v. every 6 h for 2 days) followed by oral therapy with cefaclor (500 mg every 8 h for 5 days). No difference was found in the clinical courses, cure rates, survival or the resolution of the chest radiograph abnormalities among the two groups. The mean duration of therapy (6.88 days for the conventional group compared to 7-30 days for the early oral therapy group) and the frequencies of overall symptomatic improvement (97% vs. 95%, respectively) were similar in both groups. Patients who received early oral therapy had shorter hospital stays (7.3 vs. 9.71 days, P = 0.01), and a lower total cost of care ($2953 vs. $5002, P < 0.05). It was concluded that early transition to an oral antibiotic after an abbreviated course of intravenous therapy in CAP is substantially less expensive and has comparable efficacy to conventional intravenous therapy. Altering physicians' customary management of hospitalized patients with CAP can reduce costs with no appreciable additional risk of adverse patient outcome.     

Thiols as mechanistic probes for catalysis by the free radical enzyme galactose oxidase

Galactose oxidase, a mononuclear copper enzyme, oxidizes primary alcohols to aldehydes using molecular oxygen. A unique type of cross-link between tyrosine 272, an active-site copper ligand, and cysteine 228 provides a modified tyrosine radical site believed to act as a one-electron redox center. Substrate analogs incorporating a primary thiol group in place of the primary alcohol group in normal substrates (RCH2OH) have been studied as active-site mechanistic probes. Thiol sulfur coordinates to the active-site copper, leading to enzyme inactivation in a time- and concentration-dependent manner. The mechanism of inactivation involves redox chemistry related to the active-site redox centers, though inactivation does not proceed through the rate-determining hydrogen atom abstraction step that occurs in alcohol oxidation. Thiols are therefore classified as active-site-directed redox inactivators. The thiol analog of galactose, 6-Thio-Me-Gal, is also turned over by the enzyme, albeit at a much reduced rate, indicating that the energetics of turnover is changed significantly. Thiols constitute a particularly good model of the ground state enzyme-substrate complex. The Michaelis complex for thiol substrate analogs is stabilized at least 200-fold compared to the analogous alcohol substrates, whereas the transition state of H atom abstraction is destabilized, presumably due to a slight increase in distances of reacting atoms and weakening of hydrogen-bonding interactions due to the larger atomic radius of sulfur compared to that of oxygen.     

Interaction of the second binding region of troponin I with the regulatory domain of skeletal muscle troponin C as determined by NMR spectroscopy

Two dimensional 1H,15N-heteronuclear single quantum correlation NMR was used to monitor the resonance frequency changes of the backbone amide groups belonging to the 15N-labeled regulatory domain of calcium saturated troponin C (N-TnC) upon addition of synthetic skeletal N-acetyl-troponin I 115-131-amide peptide (TnI115-131). Utilizing the change in amide chemical shifts, the dissociation constant for 1:1 binding of TnI115-131 to N-TnC in low salt and 100 mM KCl samples was determined to be 28 +/- 4 and 24 +/- 4 microM, respectively. The off rate of TnI115-131 was determined to be 300 s-1 from observed N-TnC backbone amide 1H,15N-heteronuclear single quantum correlation cross-peak line widths, which is on the order of the calcium off rates (Li, M. X., Gagné, S. M., Tsuda, S., Kay, C. M., Smillie, L. B., and Sykes, B. D. (1995) Biochemistry 34, 8330-8340), and agrees with kinetic expectations for biological regulation of muscle contraction. The TnI115-131 binding site on N-TnC was determined by mapping of chemical shift changes onto the N-TnC NMR structure and was demonstrated to be in the "hydrophobic pocket" (Gagné, S. M., Tsuda, S., Li, M. X., Smillie, L. B., and Sykes, B. D. (1995) Nat. Struct. Biol. 2, 784-789).