Risk factors for exercise-related acute cardiac events. A case-control study.

BACKGROUND: In spite of the benefits of physical activity, exercise may provoke acute cardiac events in susceptible individuals. Understanding risk factors of exercise-related acute cardiac events may identify opportunities for prevention. METHODS: A case-control study was conducted to examine determinants of acute cardiac events in athletes. The cases were athletes who suffered an acute cardiac event during or shortly after vigorous exercise. Athletes who visited a hospital because of a minor sports injury were selected as controls. Information on cardiovascular disease, family history of cardiovascular disease, cardiovascular symptoms and other potential risk factors was collected through questionnaires. RESULTS: 57 cases (mean age 41.8 years, range 11-73) and 57 controls (mean age 40.9 years, range 13-68) were included in the study. Athletes with a history of cardiovascular disease were at a markedly increased risk for cardiac events during exercise (OR = 32; 95% CI 7.4 to 143). Smoking (OR 5.9; 95% CI 1.9 to 18), fatigue (OR = 12; 95% CI 1.2 to 118) and flu-like symptoms (OR 13; 95% CI 1.4 to 131) in the month preceding the event were related to acute cardiac events in athletes. CONCLUSIONS: Prior cardiovascular disease, smoking, and a recent episode of fatigue or flu-like symptoms are associated with an increased risk of exercise-related acute cardiac events. Athletes and physicians should pay careful attention when these factors exist or occur.

[Establishment of a national registry for sudden cardiac arrest in athletes]. / Oproep landelijke registratie plotse hartstilstand bij sporters.

Physical activity is healthy but can also trigger sudden cardiac arrest in vulnerable subjects. A Dutch national registry of sudden cardiac arrest in athletes has been established under the name of SPORTCOR. The aim of the registry is to obtain a better understanding of the incidence and causes of sudden cardiac arrest in athletes. Medical doctors and family members can register cases of sudden cardiac arrest in athletes at the website www.sportcor.nl. The website also provides background information for those who are interested.

GroEL binds a late folding intermediate of phage P22 coat protein.

GroEL recognizes proteins that are folding improperly or that have aggregation-prone intermediates. Here we have used as substrates for GroEL, wildtype (WT) coat protein of phage P22 and 3 coat proteins that carry single amino acid substitutions leading to a temperature-sensitive folding (tsf) phenotype. In vivo, WT coat protein does not require GroEL for proper folding, whereas GroEL is necessary for the folding of the tsf coat proteins; thus, the single amino acid substitutions cause coat protein to become a substrate for GroEL. The conformation of WT and tsf coat proteins when in a binary complex with GroEL was investigated using tryptophan fluorescence, quenching of fluorescence, and accessibility of the coat proteins to proteolysis. WT coat protein and the tsf coat protein mutants were each found to be in a different conformation when bound to GroEL. As an additional measure of the changes in the bound conformation, the affinity of binding of WT and tsf coat proteins to GroEL was determined using a fluorescence binding assay. The tsf coat proteins were bound more tightly by GroEL than WT coat protein. Therefore, even though the proteins are identical except for a single amino acid substitution, GroEL did not bind these substrate polypeptides in the same conformation within its central cavity. Therefore, GroEL is likely to bind coat protein in a conformation consistent with a late folding intermediate, with substantial secondary and tertiary structure formed.

Purification, characterization, and structural analysis of a plant low-temperature-induced protein.

We have purified to near homogeneity a recombinant form of the protein BN28 (rBN28), expressed in response to low temperature in Brassica napus plants, and we have determined its solution structure. Antibodies raised against rBN28 were used to characterize the recombinant and native proteins. Similar to many other low-temperature-induced proteins, BN28 is extremely hydrophilic, such that it remains soluble following boiling. Immunoblot analysis of subcellular fractions indicated that BN28 was not strongly associated with cellular membranes and was localized exclusively within the soluble fraction of the cell. Contrary to predicted secondary structure that suggested significant helical content, circular dichroism analysis revealed that rBN28 existed in aqueous solution largely as a random coil. However, the helical propensity of the protein could be demonstrated in the presence of trifluoroethanol. Nuclear magnetic resonance analysis further showed that rBN28 was in fact completely unstructured (100% coil) in aqueous solution. Although it had earlier been speculated that BN28-like proteins from Arabidopsis thaliana might possess antifreeze protein activity (S. Kurkela and M. Franck [1990] Plant Mol Biol 15: 137-144), no such activity could be detected in ice recrystallization assays with rBN28.

Expression of a Low-Temperature-Induced Protein in Brassica napus.

BN28 is a low-temperature-induced, boiling-soluble protein in Brassica napus. We used antibodies raised against a recombinant BN28 to examine the expression of this protein in cold-acclimating plants and to investigate its relationship to plant freezing tolerance. Changes in the steady-state levels of BN28 protein appear to lag several days behind those of the mRNA. BN28 is first detected on immunoblots after approximately 8 d of exposure to low temperature, and thereafter levels remain stable while plants are maintained at 4[deg]C. Radiolabeling studies indicate that BN28 is synthesized at a relatively low rate. A decline in protein levels is observed soon after returning plants to control temperatures, and little or no protein can be detected after 7 d of deacclimation. The disappearance of the protein precedes a loss in freezing tolerance, suggesting that BN28 is not involved in maintaining plasma membrane integrity. Expression of BN28 is observed primarily in leaves and appears to be low-temperature specific. Quantitative analysis indicated that BN28 accumulates to approximately 82.7 pmol mg-1 total protein in cold-acclimated leaves. This concentration is similar to that reported for two group 2 late-embryogenesis-abundant-like proteins.

Superoxide dismutase enhances tolerance of freezing stress in transgenic alfalfa (Medicago sativa L.).

Activated oxygen or oxygen free radicals have been implicated in a number of physiological disorders in plants including freezing injury. Superoxide dismutase (SOD) catalyzes the dismutation of superoxide into O2 and H2O2 and thereby reduces the titer of activated oxygen molecules in the cell. To further examine the relationship between oxidative and freezing stresses, the expression of SOD was modified in transgenic alfalfa (Medicago sativa L.). The Mn-SOD cDNA from Nicotiana plumbaginifolia under the control of the cauliflower mosaic virus 35S promoter was introduced into alfalfa using Agrobacterium tumefaciens-mediated transformation. Two plasmid vectors, pMitSOD and pChlSOD, contained a chimeric Mn-SOD construct with a transit peptide for targeting to the mitochondria or one for targeting to the chloroplast, respectively. The putatively transgenic plants were selected for resistance to kanamycin and screened for neomycin phosphotransferase activity and the presence of an additional Mn-SOD isozyme. Detailed analysis of a set of four selected transformants indicated that some had enhanced SOD activity, increased tolerance to the diphenyl ether herbicide, acifluorfen, and increased regrowth after freezing stress. The F1 progeny of one line, RA3-ChlSOD-30, were analyzed by SOD isozyme activity, by polymerase chain reaction for the Mn-SOD gene, and by polymerase chain reaction for the neo gene. RA3-ChlSOD-30 had three sites of insertion of pChlSOD, but only one gave a functional Mn-SOD isozyme; the other two were apparently partial insertions. The progeny with a functional Mn-SOD transgene had more rapid regrowth following freezing stress than those progeny lacking the functional Mn-SOD transgene, suggesting that Mn-SOD serves a protective role by minimizing oxygen free radical production after freezing stress.