Predictors of age-associated decline in maximal aerobic capacity: a comparison of four statistical models

Studiesassessing changes in maximal aerobic capacity(O_{2 max}) associatedwith aging have traditionally employed the ratio ofO_{2 max} to bodyweight. Log-linear, ordinary least-squares, and weighted least-squaresmodels may avoid some of the inherent weaknesses associated with theuse of ratios. In this study we used four different methods to examinethe age-associated decline inO_{2 max} in across-sectional sample of 276 healthy men, aged 45-80 yr.Sixty-one of the men were aerobically trained athletes, and theremainder were sedentary. The model that accounted for the largestproportion of variance was a weighted least-squares model that includedage, fat-free mass, and an indicator variable denoting exercisetraining status. The model accounted for 66% of the variance inO_{2 max} and satisfiedall the important general linear model assumptions. The otherapproaches failed to satisfy one or more of these assumptions. Theresults indicated thatO_{2 max} declines atthe same rate in athletic and sedentary men (0.24 l/min or 9%/decade)and that 35% of this decline (0.08 l · min¹ · decade¹) is due to theage-associated loss of fat-free mass.

     

Expanded blood volumes contribute to the increased cardiovascular performance of endurance-trained older men

To determine whether expanded intravascular volumes contributeto the older athlete's higher exercise stroke volume and maximal oxygen consumption(O_{2 max}),we measured peak upright cycle ergometry cardiac volumes(^99mTc ventriculography) andplasma (¹²⁵I-labeled albumin) andred cell (NaCr⁵¹) volumes in 7 endurance-trained and 12 age-matched lean sedentary men. The athleteshad ~40% higherO_{2 max} values thandid the sedentary men and larger relative plasma (46 vs. 38 ml/kg), red cell (30 vs. 26 ml/kg), and total blood volumes (76 vs. 64 ml/kg) (allP < 0.05). Athletes hadlarger peak cycle ergometer exercise stroke volume indexes (75 vs. 57 ml/m²,P < 0.05) and 17% largerend-diastolic volume indexes. In the total group,O_{2 max}correlated with plasma, red cell, and total blood volumes(r = 0.61-0.70,P < 0.01). Peakexercise stroke volume was correlated directly with the blood volumevariables (r = 0.59-0.67,P < 0.01). Multiple regressionanalyses showed that fat-free mass and plasma or total blood volume,but not red cell volume, were independent determinants ofO_{2 max} andpeak exercise stroke volume. Plasma and total blood volumes correlated with the stroke volume and end-diastolic volume changes from rest topeak exercise. This suggests that expanded intravascular volumes, particularly plasma and total blood volumes, contribute to the higherpeak exercise left ventricular end-diastolic volume, stroke volume, andcardiac output and hence the higherO_{2 max} in master athletes by eliciting both chronic volume overload and increased utilization of the Frank-Starling effect during exercise.

     

Enzyme variation among clones of Trypanosoma cruzi

The genetic relationships within and between stocks of Trypanosoma cruzi were studied by the in vitro isolation of clones and sub-clones and by the comparison of their isoenzyme patterns in thin-layer starch-gel electrophoresis. Altogether 13 clones and 36 sub-clones were isolated from stocks CL89 and Y207 of T. cruzi. Employing the enzymes L-alanine aminotransferase (ALAT), L-aspartate aminotransferase (ASAT), glucose phosphate isomerase (GPI), malic enzyme (ME), malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), and phosphoglucomutase (PGM), two zymodemes, B and C, emerged among the clones with distinct banding patterns. These zymodemes were consistently distinguished by ALAT, ASAT, GPI, G6PD, 6PGD, and PGM and the differences in enzyme profiles were simultaneously reflected in all six enzyme systems. That the enzymic characters as genetic determinants are stable was demonstrated after recloning and successive replica-platings, i.e., the distinct enzyme patterns remained consistent and homogeneous, the siblings retained the enzyme profiles of their parental clones, and no segregation of the enzyme patterns was observed. Our data from clone and sub-clone examinations show that the isoenzymes act as labels to characterize T. cruzi stocks. Furthermore, enzyme variation was demonstrated among clones isolated from stock CL89.     

Incorporation of 18O2 into thymidine 5'-aldehyde in neocarzinostatin chromophore-damaged DNA

Strand scission of DNA by the chromophore of neocarzinostatin converts the 5'-hydroxyl of deoxyribose to a 5'-aldehyde. The origin of the aldehydic oxygen has now been elucidated by mass spectrometry. DNA-associated thymidine 5'-aldehyde produced by treatment of DNA with neocarzinostatin chromophore in 2H218O/16O2 or in 2H216O/18O2 was reduced, liberated by nuclease treatment, permethylated, and analyzed by gas chromatography-mass spectrometry. The data clearly show that molecular oxygen is the only source of the 5'-aldehydic oxygen. The addition of molecular oxygen at C-5', possibly via a reactive form of neocarzinostatin chromophore, must be involved; a carbonium ion intermediate at C-5' is ruled out.     

Buffer induced modification of 6-sulfated disaccharide in chondroitin lyase digestions

High-performance liquid chromatographic analyses of chondroitin lyase AC or ABC hydrolysates revealed unexpected high content of material coeluting with the nonsulfated disaccharide 2-acetamido-2-deoxy-3-O-(β-d-gluco-4-enepyranosyl uronic acid)-d-galactose. Incubation of a commercial preparation of the 6-sulfated disaccharide, 2-acetamido-2-deoxy-3-O-(β-d-gluco-4-enepyranosyl uronic acid)-6-O-sulfo-d-galactose with “enriched Tris buffer” generated material coeluting with nonsulfated disaccharide. The amount of material exhibiting this anomalous chromatographic behavior was proportional to the amount of 6-sulfated disaccharide added to the incubation mixture. This suggested a precursor/product relationship between the 6-sulfated disaccharide and the anomalous peak. The result was specific for the 6-sulfated disaccharide: incubation of the 4-sulfated disaccharide, 2-acetamido-2-deoxy-3-O-(β-d-gluco-4-enepyranosyl uronic acid)-4-O-sulfo-d-galactose, with enriched Tris buffer did not generate material with anomalous chromatographic properties. When [³⁵S]sulfate labeled cartilage glycosaminoglycans were hydrolyzed with chondroitin lyases, some of the radioactivity coeluted with the nonsulfated disaccharide. Thus, buffer-induced modification of 6-sulfated disaccharide was not caused by hydrolysis of ester sulfate. Although the proportion of the 6-sulfated disaccharide which was recovered in the anomalous peak was constant for incubations done simultaneously, incubations done at different times gave variable results. Thus, control incubations of 6-sulfated disaccharide with chondroitinase buffer must be included with each reaction series to allow correction for the proportion of the material eluting with nonsulfated disaccharide which is actually 6-sulfated.     

Characterization of newly synthesized proteoglycans from rabbit menisci in organ culture.

Rabbit menisci were incubated with Na2 35SO4 in short-term organ culture to label newly synthesized proteoglycans. The radioactive products present in both tissue and culture medium were characterized separately with respect to distribution after ultracentrifugation in CsCl isopycnic density gradients, hydrodynamic size, interaction with hyaluronic acid, and glycosaminoglycan composition (types, size and content). Analysis of proteoglycan size by gel-filtration chromatography of the most-dense CsCl fractions (A1) on Sephacryl S-500 (associative conditions) resolved three species. A peak with Kav. approx. 0.7 was present in each chromatogram, and constituted the principal component in tissue extracts. Two other peaks with Kav. values of approx. 0.2 and 0.45 were also found. When the A1 fraction from tissue was subjected to CsCl-density-gradient ultracentrifugation under dissociative conditions, 71% of the recovered radioactivity was present in the most dense (A1D1) fraction. Incubation with hyaluronic acid of either A1 or A1D1 fraction from associative extract did not alter the apparent size of the labelled product, indicating a lack of aggregate formation. Meniscal proteoglycans showed an unusual and marked tendency to adsorb irreversibly to agarose and agarose-containing gel-filtration-chromatography media. High-pressure liquid-chromatographic analyses indicated that the sulphated glycosaminoglycans consisted of chondroitin 6-sulphate (72%), chondroitin 4-sulphate (19%) and dermatan sulphate (5%). Endo-beta-galactosidase (keratanase) digestion of the material failed to detect the presence of keratan sulphate. Of the labelled glycosaminoglycans, 95% was eluted from Sephacryl S-400 as a single symmetrical peak with a Kav. of 0.5. The results of studies with tissue extracts and culture medium were similar.     

Energy requirement for degradation of tumor-associated protein p53.

A 53,000-dalton protein (p53) present in large amounts in several types of tumorigenic cells was rapidly degraded in nontumorigenic BALB/c 3T3 fibroblasts (t 1/2, approximately 0.5 h) but not in tumorigenic methylcholanthrene-induced mouse sarcoma cells (t 1/2, greater than 2 h). In 3T3 cells, dinitrophenol and 2-deoxyglucose, agents which reduce ATP production, inhibited the rapid degradation of p53 and the slower breakdown of total cell protein. After removal of these agents, the degradation of both p53 and total cell proteins resumed at their normal rates. Inhibitors of intralysosomal proteolysis (Ep475 and chloroquine) did not reduce the rate of degradation of p53. Thus, in 3T3 cells, p53 appears to be degraded by a nonlysosomal, ATP-dependent proteolytic system similar to that previously shown to degrade short- and long-lived proteins in growing fibroblasts. The immunoreactive p53 which remained in ATP-depleted cells had the same molecular weight as the p53 in the control cells. No intermediate products of p53 degradation were detected by immunoprecipitation in either ATP-depleted or control cells. Hence, ATP seems to be required for an initial step in the degradation of p53. Although the amount of labeled p53 was increased in simian virus 40-transformed and methylcholanthrene-induced mouse sarcoma cells, the amount of p53 labeled during a 3-h pulse in Moloney virus- and Rous sarcoma virus-transformed cells and untransformed 3T3 cells was similar. Thus, an increased net rate of p53 accumulation is not a common feature of transformed tumorigenic cells.     

Ca lectin gene insertion has the structural features of a transposable element

The single gene Le1, coding for soybean seed lectin, was compared to le1, a naturally occurring mutant allele containing a 3.4 kb insertion within its coding region. Le1 is devoid of introns and produces a 1.0 kb mRNA. It codes for a signal sequence of 32 amino acids and a mature protein of 253 amino acids. With the exception of six single-base substitutions, the coding and flanking sequences in le1 are identical with those in the uninterrupted gene. The insertion termini are imperfect inverted repeats flanked by a 3 bp duplication of lectin target DNA. Inverted repeats within the lectin gene are located symmetrically with respect to the insertion site and are homologous to a region of the insertion termini. These molecular traits conform with the structural aspects of transposable elements in other organisms and imply some degree of site specificity.     

Differential patterns of incorporation and remodeling among various types of bone grafts

The early (3 months) and later (6 months) patterns of incorporation and bone formation have been evaluated histomorphometrically for different types of bone grafts; that is, vascularized and nonvascularized autografts with and without ciclosporin, and vascularized and nonvascularized dog leukocyte antigen (DLA)-mismatched allografts with and without ciclosporin. The vascularized bones were superior to the nonvascularized ones in healing and remodeling their grafted segments. In the autograft bones, ciclosporin did not alter the incorporation process 3 months after transplantation but delayed and increased the remodeling activities in the long run (6 months). Nonvascularized allografts underwent vigorous resorption, and were markedly porotic. Ciclosporin administration significantly reduced resorption and enhanced remodeling in nonvascularized allografts. The remodeling of allografts was similar to that of autografts in the presence of ciclosporin, but stopped soon after the administration of ciclosporin ceased.     

1H-NMR conformational analysis of a high-affinity antigenic 11-residue peptide from the tryptophan synthase beta 2 subunit.

Two synthetic peptides from the beta 2 subunit of tryptophan synthase have been studied by 1H-NMR spectroscopy at 300 MHz. One peptide, His-Gly-Arg-Val-Gly-Ile-Tyr-Phe-Gly-Met-Lys (peptide 11; Ile, isoleucine) is antigenic and binds with a high affinity to a monoclonal antibody that recognizes the native beta 2 subunit. The second peptide, His-Gly-Arg-Val-Gly-Ile-Tyr-Phe (peptide 8) reacts very weakly with the antibody. The 1H-NMR spectra of the two peptides have been assigned from two-dimensional techniques in H2O, 2H2O and (2H6) dimethyl sulfoxide [(2H6)Me2SO]. The structure has been evaluated through analysis of nuclear Overhauser effects, coupling constants, amide-proton exchange rates and their temperature coefficients, and chemical shifts. In aqueous solvent, the C-terminal part of peptide 11 presents some structure centered around residues Phe-Gly-Met. The relationship between the structure found in peptide 11 and its antigenic nature is discussed.