Postfracture survival in a population-based study of adults aged ≥66 yr: a call to action at hospital discharge.

Postfracture survival rates provide prognostic information but are rarely reported along with other mortality outcomes in adults aged ≥50 yr. The timing of survival change following a fracture also needs to be further elucidated. This population-based, matched-cohort, retrospective database study examined 98 474 patients (73% women) aged ≥66 yr with an index fracture occurring at an osteoporotic site (hip, clinical vertebral, proximal non-hip non-vertebral [pNHNV], and distal non-hip non-vertebral [dNHNV]) from 2011 to 2015, who were matched (1:1) to nonfracture individuals based on sex, age, and comorbidities. All-cause 1- and 5-yr overall survival and relative survival ratios (RSRs) were assessed, and time trends in survival changes were characterized starting immediately after a fracture. In both sexes, overall survival was markedly decreased over 6 yr of follow-up after hip, vertebral, and pNHNV fractures, and as expected, worse survival rates were observed in older patients and males. The lowest 5-yr RSRs were observed after hip fractures in males (66-85 yr, 51.9%-63.9%; ≥86 yr, 34.5%), followed by vertebral fractures in males (66-85 yr, 53.2%-69.4%; ≥86 yr, 35.5%), and hip fractures in females (66-85 yr, 69.8%-79.0%; ≥86 yr, 52.8%). Although RSRs did not decrease as markedly after dNHNV fractures in younger patients, relatively low 5-yr RSRs were observed in females (75.9%) and males (69.5%) aged ≥86 yr. The greatest reduction in survival occurred within the initial month after hip, vertebral, and pNHNV fractures, indicating a high relative impact of short-term factors, with survival-reduction effects persisting over time. Therefore, the most critical period for implementing interventions aimed at improving post-fracture prognosis appears to be immediately after a fracture; however, considering the immediate need for introducing such interventions, primary fracture prevention is also crucial to prevent the occurrence of the initial fracture in high-risk patients.

Impact of Tesamorelin, a Growth Hormone-Releasing Factor (GRF) Analogue, on the Pharmacokinetics of Simvastatin and Ritonavir in Healthy Volunteers.

The potential impact of tesamorelin on CYP3A activity was investigated by examining its effect on the pharmacokinetics of simvastatin and ritonavir. In two randomized, two-way crossover studies, subjects were administered 2 mg tesamorelin on Days 1-7 with 80 mg simvastatin or 100 mg ritonavir co-administered on Day 6 (Treatment A), and a single dose of simvastatin or ritonavir alone on Day 6 (Treatment B). Pharmacokinetic samples were collected on Day 6 to measure simvastatin, ritonavir and tesamorelin plasma concentrations. For simvastatin, A/B ratios of least squares geometric means and corresponding 90% confidence intervals (CIs) for AUC0-t , AUC0-inf and Cmax were contained within the usual no effect range of 80-125%. For ritonavir, ratios and 90% CIs for AUCs were within this acceptance range, but the lower CI for Cmax was 74.8%, suggesting a decreased rate of exposure. However, since the A/B ratios for AUCs and Cmax parameters were approximately 90%, these were minor decreases and no dose adjustment of ritonavir is required in the presence of tesamorelin. These studies showed that the impact of tesamorelin on CYP3A activity appears to be minimal, if any. Either medication may be co-administered with tesamorelin in patients without changing their original dosing regimen.

Differential modulation of citrate synthesis and release by fatty acids in perfused working rat hearts.

The objective of this study was to test the effect of increasing fatty acid concentrations on substrate fluxes through pathways leading to citrate synthesis and release in the heart. This was accomplished using semirecirculating work-performing rat hearts perfused with substrate mixtures mimicking the in situ milieu (5.5 mM glucose, 8 nM insulin, 1 mM lactate, 0.2 mM pyruvate, and 0.4 mM oleate-albumin) and 13C methods. Raising the fatty acid concentration from 0.4 to 1 mM with long-chain oleate or medium-chain octanoate resulted in a lowering ( approximately 20%) of cardiac output and efficiency with unaltered O2 consumption. At the metabolic level, beyond the expected effects of high fatty acid levels on the contribution of pyruvate decarboxylation (reduced >3-fold) and beta-oxidation (enhanced approximately 3-fold) to citrate synthesis, there was also a 2.4-fold lowering of anaplerotic pyruvate carboxylation. Despite the dual inhibitory effect of high fatty acids on pyruvate decarboxylation and carboxylation, tissue citrate levels were twofold higher, but citrate release rates remained unchanged at 11-14 nmol/min, representing <0.5% of citric acid cycle flux. A similar trend was observed for most metabolic parameters after oleate or octanoate addition. Together, these results emphasize a differential modulation of anaplerotic pyruvate carboxylation and citrate release in the heart by fatty acids. We interpret the lack of effects of high fatty acid concentrations on citrate release rates as suggesting that, under physiological conditions, this process is maximal, probably limited by the activity of its mitochondrial or plasma membrane transporter. Limited citrate release at high fatty acid concentrations may have important consequences for the heart's fuel metabolism and function.

Metabolic phenotyping of the diseased rat heart using 13C-substrates and ex vivo perfusion in the working mode.

The objective of the present study was to compare energy substrate fluxes through metabolic pathways leading to mitochondrial citrate synthesis and release in normal and diseased rat hearts using 13C-substrates and mass isotopomer analysis by gas chromatography-mass spectrometry (GCMS). This study was prompted by our previous finding of a modulated citrate release by perfused rat hearts and by the possibility that a dysregulated myocardial citrate release represents a specific chronic alteration of energy metabolism in cardiac patients. The 15-week-old spontaneously hypertensive rat (SHR) was chosen as our animal model of disease and the Wistar-Kyoto (WKY) rat as its matched control. Ex vivo work-performing hearts were perfused with a semi-recirculating buffer containing physiological concentrations of unlabeled (glucose) and 13C-labeled ([U-13C3](lactate + pyruvate) and/or [1-(13)C]oleate) substrates. In parallel to the continuous monitoring of indices of the heart's functional and physiological status, the following metabolic parameters were documented: (i) citrate release rates and citric acid cycle intermediate tissue levels, (ii) the contribution of fatty acids as well as pyruvate decarboxylation and carboxylation to citrate synthesis, and (iii) lactate and pyruvate uptake and efflux rates. Working hearts from both rat species showed a similar percent contribution of carbohydrates for citrate synthesis through decarboxylation (70%) and carboxylation (10%). SHR hearts showed the following metabolic alterations: a higher citrate release rate, which was associated with a parallel increase in its tissue level, a lower contribution of oleate beta-oxidation to citrate synthesis, and an accelerated efflux rate of unlabeled lactate from glycolysis. These metabolic changes were not explained by differences in myocardial oxygen consumption, cardiac performance or efficiency, nor correlated with indices of tissue necrosis or ischemia. This study demonstrates how the alliance between ex vivo semi-recirculating working perfused rat hearts with 13C-substrates and mass isotopomer analysis by GCMS, can provide an unprecedented insight into the metabolic phenotype of normal and diseased rat hearts. The clinical relevance of metabolic alterations herein documented in the SHR heart is suggested by its resemblance to those reported in cardiac patients. Taken altogether, our results raise the possibility that the increased citrate release of diseased hearts results from an imbalance between citrate synthesis and utilization rates, which becomes more apparent underconditions of substrate abundance.

Reverse flux through cardiac NADP(+)-isocitrate dehydrogenase under normoxia and ischemia.

Little is known about the role of mitochondrial NADP(+)-isocitrate dehydrogenase (NADP(+)-ICDH) in the heart, where this enzyme shows its highest expression and activity. We tested the hypothesis that in the heart, NADP(+)-ICDH operates in the reverse direction of the citric acid cycle (CAC) and thereby may contribute to the fine regulation of CAC activity (Sazanov and Jackson, FEBS Lett 344: 109-116, 1994). We documented a reverse flux through this enzyme in rat hearts perfused with the medium-chain fatty acid octanoate using [U-(13)C(5)]glutamate and mass isotopomer analysis of tissue citrate (Comte et al., J Biol Chem 272: 26117-26124, 1997). In this study, we assessed the significance of our previous finding by perfusing hearts with long-chain fatty acids and tested the effects of changes in O(2) supply. We showed that under all of these conditions citrate was enriched in an isotopomer containing five (13)C atoms. This isotopomer can only be explained by substrate flux through reversal of the NADP(+)-ICDH reaction, which is evaluated at 3-7% of flux through citrate synthase. Small variations in reversal fluxes induced by low-flow ischemia that mimicked hibernation occurred despite major changes in contractile function and O(2) consumption of the heart as well as citrate and succinate release rates and tissue levels. Our data show a reverse flux through NADP(+)-ICDH and support its hypothesized role in the fine regulation of CAC activity in the normoxic and O(2)-deprived heart.

Probing the link between citrate and malonyl-CoA in perfused rat hearts.

Little is known about the sources of cytosolic acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of fatty acid oxidation in the heart. We tested the hypothesis that citrate provides acetyl-CoA for malonyl-CoA synthesis after its mitochondrial efflux and cleavage by cytosolic ATP-citrate lyase. We expanded on a previous study where we characterized citrate release from perfused rat hearts (Vincent G, Comte B, Poirier M, and Des Rosiers C. Citrate release by perfused rat hearts: a window on mitochondrial cataplerosis. Am J Physiol Endocrinol Metab 278: E846-E856, 2000). In the present study, we show that citrate release rates, ranging from 6 to 22 nmol/min, can support a net increase in malonyl-CoA concentrations induced by changes in substrate supply, at most 0.7 nmol/min. In experiments with [U-(13)C](lactate + pyruvate) and [1-(13)C]oleate, we show that the acetyl moiety of malonyl-CoA is derived from both pyruvate and long-chain fatty acids. This (13)C-labeling of malonyl-CoA occurred without any changes in its concentration. Hydroxycitrate, an inhibitor of ATP-citrate lyase, prevents increases in malonyl-CoA concentrations and decreases its labeling from [U-(13)C](lactate + pyruvate). Our data support at least a partial role of citrate in the transfer from the mitochondria to cytosol of acetyl units for malonyl-CoA synthesis. In addition, they provide a dynamic picture of malonyl-CoA metabolism: even when the malonyl-CoA concentration remains constant, there appears to be a constant need to supply acetyl-CoA from various carbon sources, both carbohydrates and lipids, for malonyl-CoA synthesis.