Effects of Obesity on Substrate Utilization during Exercise

Objective: The capacity for lipid and carbohydrate (CHO) oxidation during exercise is important for energy partitioning and storage. This study examined the effects of obesity on lipid and CHO oxidation during exercise. Research Methods and Procedures: Seven obese and seven lean [body mass index (BMI), 33 ± 0.8 and 23.7 ± 1.2 kg/m², respectively] sedentary, middle‐aged men matched for aerobic capacity performed 60 minutes of cycle exercise at similar relative (50% Vo _2max) and absolute exercise intensities. Results: Obese men derived a greater proportion of their energy from fatty‐acid oxidation than lean men (43 ± 5% 31 ± 2%; p = 0.02). Plasma fatty‐acid oxidation determined from recovery of infused [0.15 μmol/kg fat‐free mass (FFM) per minute] [1‐¹³C]‐palmitate in breath CO₂ was similar for obese and lean men (8.4 ± 1.1 and 29 ± 15 μmol/kg FFM per minute). Nonplasma fatty‐acid oxidation, presumably, from intramuscular sources, was 50% higher in obese men than in lean men (10.0 ± 0.6 versus 6.6 ± 0.8 μmol/kg FFM per minute; p < 0.05). Systemic glucose disposal was similar in lean and obese groups (33 ± 8 and 29 ± 15 μmol/kg FFM per minute). However, the estimated rate of glycogen‐oxidation was 50% lower in obese than in lean men (61 ± 12 versus 90 ± 6 μmol/kg FFM per minute; p < 0.05). Discussion: During moderate exercise, obese sedentary men have increased rates of fatty‐acid oxidation from nonplasma sources and reduced rates of CHO oxidation, particularly muscle glycogen, compared with lean sedentary men.     

Measurement of hemoglobin synthesis rate in vivo using a stable isotope method

We developed a method to measure hemoglobin synthesis rate (SynHb) in humans, assuming that free glycine in the red blood cell (RBC) represents free glycine in bone marrow for hemoglobin synthesis. The present rat study examines this assumption of the method and quantifies SynHb in rats. Sprague-Dawley rats (n = 9) were studied, [2-(13)C]glycine was intravenously infused over 24 h (2.5 mg kg(-1) h(-1)), blood was drawn for glycine and heme isolation, and bone marrow was harvested for glycine isolation. Isotopic enrichments of glycine and heme were measured, fractional hemoglobin synthesis rate (fSynHb% day(-1)) was calculated, and from this a value for SynHb (mg g(-1) day(-1)) was derived. Mean body weight was 446 +/- 10 g (mean +/- SE) and hemoglobin concentration was 14 +/- 0.5 g dl(-1). At 24 h, the mean isotopic enrichment, atom percentage excess (APE), of the RBC free glycine (1.56 +/- 0.18 APE) was similar to the bone marrow (1.68 +/- 0.15 APE). The rate of incorporation of (13)C into heme increased over time from 0.0004 APE/h between 6 and 12 h, to 0.0014 APE/h between 12 and 18 h, and 0.0024 APE/h between 18 and 24 h. Consequently, fSynHb (1.19 +/- 0.32, 2.92 +/- 0.66, and 4.22 +/- 0.56% day(-1), respectively) and SynHb (0.11 +/- 0.03, 0.28 +/- 0.05, and 0.42 +/- 0.05 mg g(-1) day(-1), respectively) showed similar patterns over the 24-h study period. We conclude that (1) enrichment of free glycine in the circulating RBC approximates enrichment of bone marrow free glycine for heme formation and (2) this pattern of hemoglobin synthesis rate is reflecting the characteristic release and gradual maturation of reticulocytes in the circulation.     

Rewiring the transcriptional regulatory circuits of cells

The molecular mechanisms that regulate gene expression can evolve either by changing the cis-acting DNA elements in promoters, or by replacing the trans-acting regulatory proteins. New data from yeast species show that both processes can happen.     

Lysosomal enzymes in the macronucleus of Tetrahymena during its apoptosis-like degradation

A key characteristic of apoptosis is its regulated nuclear degradation. Apoptosis-like nuclear degradation also occurs in the ciliated unicellular organism, Tetrahymena thermophila. Chromatin of the macronucleus undergoes massive condensation, a process that can be blocked by caspase inhibitors. The nucleus becomes TUNEL-positive, and its DNA is cleaved into nucleosome-sized fragments. In a matter of hours the macronucleus is completely degraded, and disappears. The condensed nucleus sequesters acridine orange, which means that it might become an acidic compartment. We therefore asked whether lysosomal bodies fuse with the condensed macronucleus to form an autophagosome. We monitored acid phosphatase (AP) activity, which is associated with lysosomal bodies but is not found in normal nuclei. We find that after the macronucleus condenses AP activity is localized in cap-like structures at its cortex. Later, after the degrading macronucleus loses much of its DNA, acid phosphatase deposits appear deeper within the nucleus. We conclude that although macronuclear elimination is initiated by an apoptosis-like mechanism, its final degradation may be achieved through autophagosomy.     

Physicochemical analysis of phasic menstrual cycle effects on acid-base balance

In accordance with Stewart's physicochemical approach, the three independent determinants of plasma hydrogen ion concentration ([H(+)]) were measured at rest and during exercise in the follicular (FP) and luteal phase (LP) of the human menstrual cycle. Healthy, physically active women with similar physical characteristics were tested during either the FP (n = 14) or LP (n = 14). Arterialized blood samples were obtained at rest and after 5 min of upright cycling at both 70 and 110% of the ventilatory threshold (T(Vent)). Measurements included plasma [H(+)], arterial carbon dioxide tension (Pa(CO(2))), total weak acid ([A(Tot)]) as reflected by total protein, and the strong-ion difference ([SID]). The transition from rest to exercise in both groups resulted in a significant increase in [H(+)] at 70% T(Vent) versus rest and at 110% T(Vent) versus both rest and 70% T(Vent). No significant between-group differences were observed for [H(+)] at rest or in response to exercise. At rest in the LP, [A(Tot)] and Pa(CO(2)) were significantly lower (acts to decrease [H(+)]) compared with the FP. This effect was offset by a reduction in [SID] (acts to increase [H(+)]). After the transition from rest to exercise, significantly lower [A(Tot)] during the LP was again observed. Although the [SID] and Pa(CO(2)) were not significantly different between groups, trends for changes in these two variables were similar to changes in the resting state. In conclusion, mechanisms regulating [H(+)] exhibit phase-related differences to ensure [H(+)] is relatively constant regardless of progesterone-mediated ventilatory changes during the LP.     

Oxaloacetate synthesis in the methanarchaeon Methanosarcina barkeri: pyruvate carboxylase genes and a putative Escherichia coli-type bifunctional biotin protein ligase gene (bpl/birA) exhibit a unique organization

Evidence is presented that, in Methanosarcina barkeri oxaloacetate synthesis, an essential and major CO(2) fixation reaction is catalyzed by an apparent alpha(4)beta(4)-type acetyl coenzyme A-independent pyruvate carboxylase (PYC), composed of 64.2-kDa biotinylated and 52.9-kDa ATP-binding subunits. The purified enzyme was most active at 70 degrees C, insensitive to aspartate and glutamate, mildly inhibited by alpha-ketoglutarate, and severely inhibited by ATP, ADP, and excess Mg(2+). It showed negative cooperativity towards bicarbonate at 70 degrees C but not at 37 degrees C. The organism expressed holo-PYC without an external supply of biotin and, thus, synthesized biotin. pycA, pycB, and a putative bpl gene formed a novel operon-like arrangement. Unlike other archaeal homologs, the putative biotin protein ligases (BPLs) of M. barkeri and the closely related euryarchaeon Archaeoglobus fulgidus appeared to be of the Escherichia coli-type (bifunctional, with two activities: BirA or a repressor of the biotin operon and BPL). We found the element Tyr(Phe)ProX(5)Phe(Tyr) to be fully conserved in biotin-dependent enzymes; it might function as the hinge for their "swinging arms."     

Plasmid vaccination with insulin B chain prevents autoimmune diabetes in nonobese diabetic mice

The insulin B (InsB) chain bears major type 1 diabetes-associated epitopes of significance for disease in humans and nonobese diabetic (NOD) mice. Somatic expression of InsB chain initiated early in life by plasmid inoculation resulted in substantial protection of female NOD mice against disease. This was associated with a T2 shift in spleen, expansion of IL-4-producing and, to a lesser extent, of IFN-gamma-secreting T cells in pancreatic lymph nodes, as well as intermolecular Th2 epitope spreading to glutamic acid decarboxylase determinants. A critical role of IL-4 for the Ag-specific protective effect triggered by plasmid administration was revealed in female IL-4(-/-) NOD mice that developed diabetes and higher Th1 responses. Coadministration of IL-4-expressing plasmid or extension of the vaccination schedule corrected the unfavorable response of male NOD mice to DNA vaccination with InsB chain. Thus, plasmid-mediated expression of the InsB chain early in diabetes-prone mice has the potential to prevent transition to full-blown disease depending on the presence of IL-4.