Influence of oxygen tension on myocardial performance. Evaluation by tissue Doppler imaging

Background

Endothelial function in hypercholesterolemic rabbits is usually evaluated ex vivo on isolated aortic rings. In vivo evaluation requires invasive imaging procedures that cannot be repeated serially.

Aim

We evaluated a non-invasive ultrasound technique to assess early endothelial function in rabbits and compare data with ex vivo measurements.

Methods

Twenty-four rabbits (fed with a cholesterol diet (0.5%) for 2 to 8 weeks) were given progressive infusions of acetylcholine (0.05–0.5 μg/kg/min) and their endothelial function was assessed in vivo by transcutaneous vascular ultrasound of the abdominal aorta. Ex vivo endothelial function was evaluated on isolated aortic rings and compared to in vivo data.

Results

Significant endothelial dysfunction was demonstrated in hypercholesterolemic animals as early as 2 weeks after beginning the cholesterol diet (aortic cross-sectional area variation: -2.9% vs. +4% for controls, p < 0.05). Unexpectedly, response to acetylcholine at 8 weeks was more variable. Endothelial function improved in 5 rabbits while 2 rabbits regained a normal endothelial function. These data corroborated well with ex vivo results.

Conclusion

Endothelial function can be evaluated non-invasively in vivo by transcutaneous vascular ultrasound of the abdominal aorta in the rabbit and results correlate well with ex vivo data.     

Sensitivity of molecular dynamics simulations to the choice of the X-ray structure used to model an enzymatic reaction

A subject of great practical importance that has not received much attention is the question of the sensitivity of molecular dynamics simulations to the initial X-ray structure used to set up the calculation. We have found two cases in which seemingly similar structures lead to quite different results, and in this article we present a detailed analysis of these cases. The first case is acyl-CoA dehydrogenase, and the chief difference of the two structures is attributed to a slight shift in a backbone carbonyl that causes a key residue (the proton-abstracting base) to be in a bad conformation for reaction. The second case is xylose isomerase, and the chief difference of the two structures appears to be the ligand sphere of a Mg2+ metal cofactor that plays an active role in catalysis.     

The structure and specificity of Escherichia coli maltose acetyltransferase give new insight into the LacA family of acyltransferases

The crystallographic three-dimensional structure of the Escherichia coli maa gene product, previously identified as a maltose O-acetyltransferase (MAT) [Brand, B., and Boos, W. (1991) J. Biol. Chem. 266, 14113-14118] has been determined to 2.15 A resolution by the single anomalous dispersion method using data from a crystal cocrystallized with trimethyllead acetate. It is shown here that MAT acetylates glucose exclusively at the C6 position and maltose at the C6 position of the nonreducing end glucosyl moiety. Furthermore, MAT shows higher affinity toward artificial substrates containing an alkyl or hydrophobic chain as well as a glucosyl unit. The presence of a long hydrophobic patch near the acceptor site provides the structural explanation for this preference. The three-dimensional structure reveals the expected trimeric left-handed parallel beta-helix structure found in all other known hexapeptide repeat enzymes. In particular, the structure shows similarities both overall and at the putative active site to the recently determined structure of galactoside acetyltransferase (GAT), the lacA gene product [Wang, X.-G., Olsen, L. R., and Roderick, S. L. (2002) Structure 10, 581-588]. The structure, together with the new biochemical data, suggests that GAT and MAT are more closely related than previously thought and might have similar cellular functions. However, while GAT is specific for acetylation of galactosyl units, MAT is specific for glucosyl units and is able to acetylate maltooligosaccharides, an important property for biotechnological applications. Structural differences at the acceptor site reflect the differences in substrate specificity.     

Supplementation with vitamin E but not with vitamin C lowers lipid peroxidation in vivo in mildly hypercholesterolemic men.

Although the use of vitamin E supplements has been associated with a reduction in coronary events, assumed to be due to lowered lipid peroxidation, there are no previous long-term clinical trials into the effects of vitamin C or E supplementation on lipid peroxidation in vivo. Here, we have studied the long-term effects of vitamins C and E on plasma F2-isoprostanes, a widely used marker of lipid peroxidation in vivo. As a study cohort, a subset of the "Antioxidant Supplementation in Atherosclerosis Prevention" (ASAP) study was used. ASAP is a double-masked placebo-controlled randomized clinical trial to study the long-term effect of vitamin C (500 mg of slow release ascorbate daily), vitamin E (200 mg of D-alpha-tocopheryl acetate daily), both vitamins (CellaVie), or placebo on lipid peroxidation, atherosclerotic progression, blood pressure and myocardial infarction (n = 520 at baseline). Lipid peroxidation measurements were carried out in 100 consecutive men at entry and repeated at 12 months. The plasma F2-isoprostane concentration was lowered by 17.3% (95% CI 3.9-30.8%) in the vitamin E group (p = 0.006 for the change, as compared with the placebo group). On the contrary, vitamin C had no significant effect on plasma F2-isoprostanes as compared with the placebo group. There was also no interaction in the effect between these vitamins. In conclusion, long-term oral supplementation of clinically healthy, but hypercholesterolemic men, who have normal vitamin C and E levels with a reasonable dose of vitamin E lowers lipid peroxidation in vivo, but a relatively high dose of vitamin C does not. This observation may provide a mechanism for the observed ability of vitamin E supplements to prevent atherosclerosis.     

Expressed sequence tags from roots and nodule primordia of Lotus japonicus infected with Mesorhizobium loti

Messenger RNA from young Lotus japonicus roots carrying root nodule primordia appearing after inoculation with Mesorhizobium loti bacteria were used to construct a cDNA expression library. Single-pass sequencing employing colony-polymerase chain reaction (PCR) and analysis of PCR products established a total of 2,397 new expressed sequence tags (ESTs). We have putatively identified 1,236 known and 484 hypothetical proteins coded by the corresponding mRNAs. The remaining cDNAs are unknown (316) or redundant overlapping cDNAs (361). We hope that this batch of ESTs will assist in the recognition of plant genes involved during development of nitrogen-fixing root nodules.     

Determination of first order rate constants by natural logarithm of the slope plot exemplified by analysis of Aspergillus niger in batch culture

Finding rate constants from experimental data is often difficult because of offset and noise. A computer program was developed to average experimental data points, reducing the effect of noise, and to produce a log_e of slope plot – a plot of the natural logarithm of the slope of a curve – eliminating the effect of any offset. If y-values depend exponentially on x-values the log_e of slope plot is rectilinear and the slope is equal to the first order rate constant. Therefore the log_e of slope plot provides easy identification of exponential sections of any experimental or calculated data, corresponding rate constants, and small changes in the rate constant as exemplified by analysis of titrant added to a batch culture of Aspergillus niger. The log_e of slope plot was easily applicable and superior to conventional methods of analysis of exponential decreasing or increasing data.     

Distinct pathways of mannan-binding lectin (MBL)- and C1-complex autoactivation revealed by reconstitution of MBL with recombinant MBL-associated serine protease-2

Mannan-binding lectin (MBL) plays a pivotal role in innate immunity by activating complement after binding carbohydrate moieties on pathogenic bacteria and viruses. Structural similarities shared by MBL and C1 complexes and by the MBL- and C1q-associated serine proteases, MBL-associated serine protease (MASP)-1 and MASP-2, and C1r and C1s, respectively, have led to the expectation that the pathways of complement activation by MBL and C1 complexes are likely to be very similar. We have expressed rMASP-2 and show that, whereas C1 complex autoactivation proceeds via a two-step mechanism requiring proteolytic activation of both C1r and C1s, reconstitution with MASP-2 alone is sufficient for complement activation by MBL. The results suggest that the catalytic activities of MASP-2 split between the two proteases of the C1 complex during the course of vertebrate complement evolution.     

A simple system for monitoring biodiversity in protected areas of a developing country

The achievements of initiatives to strengthen biodiversity conservation in developing countries may be difficult to assess, since most countries have no system for monitoring biodiversity. This paper describes a simple and cost-effective, field-based biodiversity monitoring system developed specifically for areas where specialist staff is lacking. We discuss the preliminary lessons learned from protected areas in the Philippines. Whilst the monitoring system aims to identify trends in biodiversity and its uses so as to guide management action, it also promotes the participation of local people in the management, stimulates discussions about conservation amongst stakeholders and builds the capacity of park staff and communities in management skills. In addition, it seeks to provide people with direction regarding the aims of protected areas, and reinforces the consolidation of existing livelihoods through strengthening community-based resource management systems. The field methods are: (1) standardised recording of routine observations, (2) fixed point photographing, (3) line transect survey, and (4) focus group discussion. Both bio-physical and socio-economic data are used and given equal importance. The system can be sustained using locally available resources. The approach is useful in countries embarking on shared management of park resources with local communities, where rural people depend on use of natural ecosystems, and where the economic resources for park management are limited. We hope this paper will encourage other countries to develop their own biodiversity monitoring system, letting its development become a means for capacity building whilst at the same time supporting the creation of ownership.