Carnitine palmitoyl transferase-I activity in the aging mouse heart

Mitochondrial Dysfunction: A Roadmap for Understanding and Tackling Cardiovascular Aging

Cardiovascular aging is a progressive remodeling process constituting a variety of cellular and molecular alterations that are closely linked to mitochondrial dysfunction. Therefore, gaining a deeper understanding of the changes in mitochondrial function during cardiovascular aging is crucial for preventing cardiovascular diseases. Cardiac aging is accompanied by fibrosis, cardiomyocyte hypertrophy, metabolic changes, and infiltration of immune cells, collectively contributing to the overall remodeling of the heart. Similarly, during vascular aging, there is a profound remodeling of blood vessel structure. These remodeling present damage to endothelial cells, increased vascular stiffness, impaired formation of new blood vessels (angiogenesis), the development of arteriosclerosis, and chronic vascular inflammation. This review underscores the role of mitochondrial dysfunction in cardiac aging, exploring its impact on fibrosis and myocardial alterations, metabolic remodeling, immune response remodeling, as well as in vascular aging in the heart. Additionally, we emphasize the significance of mitochondria-targeted therapies in preventing cardiovascular diseases in the elderly.

Lipid and glucose metabolism in senescence

Senescence is an inevitable biological process. Disturbances in glucose and lipid metabolism are essential features of cellular senescence. Given the important roles of these types of metabolism, we review the evidence for how key metabolic enzymes influence senescence and how senescence-related secretory phenotypes, autophagy, apoptosis, insulin signaling pathways, and environmental factors modulate glucose and lipid homeostasis. We also discuss the metabolic alterations in abnormal senescence diseases and anti-cancer therapies that target senescence through metabolic interventions. Our work offers insights for developing pharmacological strategies to combat senescence and cancer.

Increasing maternal age associates with lower placental CPT1B mRNA expression and acylcarnitines, particularly in overweight women

Older pregnant women have increased risks of complications including gestational diabetes and stillbirth. Carnitine palmitoyl transferase (CPT) expression declines with age in several tissues and is linked with poorer metabolic health. Mitochondrial CPTs catalyze acylcarnitine synthesis, which facilitates fatty acid oxidization as fuel. We hypothesized that the placenta, containing maternally-inherited mitochondria, shows an age-related CPT decline that lowers placental acylcarnitine synthesis, increasing vulnerability to pregnancy complications. We assessed CPT1A, CPT1B, CPT1C and CPT2 mRNA expression by qPCR in 77 placentas and quantified 10 medium and long-chain acylcarnitines by LC-MS/MS in a subset of 50 placentas. Older maternal age associated with lower expression of placental CPT1B, but not CPT1A, CPT1C or CPT2. CPT1B expression positively associated with eight acylcarnitines and CPT1C with three acylcarnitines, CPT1A negatively associated with nine acylcarnitines, while CPT2 did not associate with any acylcarnitine. Older maternal age associated with reductions in five acylcarnitines, only in those with BMI≥ 25 kg/m2, and not after adjusting for CPT1B expression. Our findings suggest that CPT1B is the main transferase for placental long-chain acylcarnitine synthesis, and age-related CPT1B decline may underlie decreased placental metabolic flexibility, potentially contributing to pregnancy complications in older women, particularly if they are overweight.

Initial Liver Copper Status in Finishing Beef Steers Fed Three Dietary Concentrations of Copper Affects Beta Agonist Performance, Carcass Characteristics, Lipolysis Response, and Muscle Inflammation Markers

Simple Summary

Beta agonists are commonly used in the United States beef industry, offering improved performance in the days leading up to harvest by influencing energy metabolism. Copper has been shown to regulate the biological pathway leading to increased lipid mobilization. However, this connection has not been evaluated in cattle. Therefore, the objective of this study was to determine how Cu influences beta agonist-induced performance, energy metabolism and inflammation in feedlot cattle. Supplementation of Cu resulted in increased liver Cu concentrations, while cattle performance, lipolysis, and some markers of inflammation responded to Cu supplementation differently, depending on whether or not cattle were fed a beta agonist. Therefore, strategic supplementation of Cu may help optimize growth of cattle receiving a beta agonist.

Abstract

Ninety-three Angus-crossbred steers (470 ± 35 kg) were assigned to a 3 × 2 factorial to determine the effects of Cu status and beta agonist (BA) on performance, carcass characteristics, lipolytic rate, and muscle inflammation. Factors included Cu supplementation (mg Cu/kg dry matter (DM)) at: 0 (LO), 10 (MED), or 20 (HI) from Cu amino acid complex (Availa Cu; Zinpro) with no BA (NoRAC) or 300 mg·steer⁻¹·day⁻¹ of ractopamine hydrochloride (RAC; Optaflexx; Elanco) for final 28 days of 88-day trial. Linear and quadratic effects of Cu status within BA treatment were tested. Pre-BA gain was not affected by Cu supplementation (p ≥ 0.57), although day 53 liver Cu quadratically increased (p = 0.01). Average daily gain and muscle IL-8 gene expression quadratically increased (p ≤ 0.01), with MED having greatest gain and gene expression. Ribeye area tended to quadratically increase with Cu supplementation within RAC (p = 0.08). In vitro basal lipolytic rate tended to quadratically increase with Cu supplementation within RAC (p = 0.11), while stimulated lipolytic rate tended to linearly increase within NoRAC (p = 0.10). These data suggest lipolysis and the BA response of steers are influenced by dietary and liver Cu concentrations.

Daily Consumption of a Specially Formulated Essential Amino Acid-Based Dietary Supplement Improves Physical Performance in Older Adults With Low Physical Functioning

We have investigated the hypothesis that nutritional supplementation of the diet in low-physical-functioning older individuals with a specially formulated composition based on essential amino acids (EAAs) would improve physical function as compared to supplementation with the same amount of whey protein. A third group of comparable volunteers were given nutrition education but no supplementation of the diet. After 6 weeks of whey protein supplementation (n = 32), there was no effect on the distance walked in 6 minutes, but the distance walked improved significantly from the pre-value after 12 weeks of whey supplementation. EAA consumption (n = 28) significantly improved walking distance at both 6 and 12 weeks. The distance walked at 12 weeks (419.0 ± 25.0 m) was 35.4 m greater than the pre-value of 384.0 ± 23.0 m (p < .001). The increase in distance walked by the EAA group was also significantly greater than that in the whey group at both 6 and 12 weeks (p < .01). In contrast, a decrease in distance walked was observed in the control group (n = 32) (not statistically significant, NS). EAA supplementation also improved grip strength and leg strength, and decreased body weight and fat mass. Plasma low-density lipoprotein concentration was significantly reduced in the EAA group, as well as the concentration of macrophage migration inhibitory factor. There were no adverse responses in any groups, and compliance was greater than 95% in all individuals consuming supplements. We conclude that dietary supplementation with an EAA-based composition may be a beneficial therapy in older individuals with low physical functional capacity. Clinical Trials Registration Number: This study was registered with ClinicalTrials.gov: NCT03424265-"Nutritional interventions in heart failure."

Metabolic shifts during aging and pathology

The heart is a very special organ in the body and has a high requirement for metabolism due to its constant workload. As a consequence, to provide a consistent and sufficient energy a high steady-state demand of metabolism is required by the heart. When delicately balanced mechanisms are changed by physiological or pathophysiological conditions, the whole system's homeostasis will be altered to a new balance, which contributes to the pathologic process. So it is no wonder that almost every heart disease is related to metabolic shift. Furthermore, aging is also found to be related to the reduction in mitochondrial function, insulin resistance, and dysregulated intracellular lipid metabolism. Adenosine monophosphate-activated protein kinase (AMPK) functions as an energy sensor to detect intracellular ATP/AMP ratio and plays a pivotal role in intracellular adaptation to energy stress. During different pathology (like myocardial ischemia and hypertension), the activation of cardiac AMPK appears to be essential for repairing cardiomyocyte's function by accelerating ATP generation, attenuating ATP depletion, and protecting the myocardium against cardiac dysfunction and apoptosis. In this overview, we will talk about the normal heart's metabolism, how metabolic shifts during aging and different pathologies, and how AMPK regulates metabolic changes during these conditions.

Cardiac aging and insulin resistance: could insulin/insulin-like growth factor (IGF) signaling be used as a therapeutic target?

Intrinsic cardiac aging is an independent risk factor for cardiovascular disease and is associated with structural and functional changes that impede cardiac responses to stress and to cardio-protective mechanisms. Although systemic insulin resistance and the associated risk factors exacerbate cardiac aging, cardiac-specific insulin resistance without confounding systemic alterations, could prevent cardiac aging. Thus, strategies aimed to reduce insulin/insulin-like growth factor (IGF) signaling in the heart prevent cardiac aging in lower organisms and in mammals but the mechanisms underlying this protection are not fully understood. In this review, we describe the impact of aging on the cardiovascular system and discuss the mounting evidence that reduced insulin/IGF signaling in the heart could alleviate age-associated alterations and preserve cardiac performance.

Evidence for association of mitochondrial metabolism alteration with lipid accumulation in aging rats

Adipogenesis and lipid accumulation during aging have a great impact on the aging process and the pathogenesis of chronic, age-related diseases. However, little is known about the age-related molecular changes in lipid accumulation and the mechanisms underlying them. Here, using 5-month- and 25-month-old rats (young and old, respectively), we found that epididymal fat is the only tissue to accumulate during aging. By testing tissues rich with mitochondria in old and young animals, we found that the old animals had elevated levels of triglycerides in their muscle, heart and liver tissues but not in their kidneys, while, the mRNA level of fatty acid synthase remained unchanged among the four tissues. Regarding lipid catabolism, we determined that the activities of mitochondrial ETC. complexes changed in aged rats (muscle: decreased complex I and V activities; heart: decreased complex I activity; liver: increased complex I and III activities; kidney: decreased complex I and increased complex II activities), while changes in mitochondrial content were not observed in the muscle, heart nor in the liver tissue except increased complex IV and V subunits in aged kidneys. Furthermore, decreased mitochondrial fusion marker Mfn2 and decreased PGC-1α level were observed in the aged muscle, heart and liver but remained unchanged in the kidneys. Down-regulation of Mfn2 with siRNA in 293T cells induced significant mitochondrial dysfunction including decreased oxygen consumption, decreased ATP production, and increased ROS production, followed by increased triglyceride content suggesting a contributing role of decreased mitochondrial fusion to lipid deposit. Meanwhile, judging from autophagy marker p62/SQSTM1 and LC3-II, autophagy was suppressed in the aged muscle, heart and liver but remained unchanged in the kidneys. Taken together, these data suggest that reduction in PGC-1α expression and disruption of mitochondrial dynamics and autophagy might contribute to lipid accumulation during aging.

Recent advances in metabolic imaging

Abnormalities in myocardial substrate metabolism play a central role in the manifestations of most forms of cardiac disease such as ischemic heart disease, heart failure, hypertensive heart disease, and the cardiomyopathy due to either obesity or diabetes mellitus. Their importance is exemplified by both the development of numerous imaging tools designed to detect the specific metabolic perturbations or signatures related to these different diseases, and the vigorous efforts in drug discovery/development targeting various aspects of myocardial metabolism. Since the prior review in 2005, we have gained new insights into how perturbations in myocardial metabolism contribute to various forms of cardiac disease. For example, the application of advanced molecular biologic techniques and the development of elegant genetic models have highlighted the pleiotropic actions of cellular metabolism on energy transfer, signal transduction, cardiac growth, gene expression, and viability. In parallel, there have been significant advances in instrumentation, radiopharmaceutical design, and small animal imaging, which now permit a near completion of the translational pathway linking in-vitro measurements of metabolism with the human condition. In this review, most of the key advances in metabolic imaging will be described, their contribution to cardiovascular research highlighted, and potential new clinical applications proposed.

Acetyl-L-carnitine supplementation reverses the age-related decline in carnitine palmitoyltransferase 1 (CPT1) activity in interfibrillar mitochondria without changing the L-carnitine content in the rat heart

The aging heart displays a loss of bioenergetic reserve capacity partially mediated through lower fatty acid utilization. We investigated whether the age-related impairment of cardiac fatty acid catabolism occurs, at least partially, through diminished levels of L-carnitine, which would adversely affect carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme for fatty acyl-CoA uptake into mitochondria for β-oxidation. Old (24-28 mos) Fischer 344 rats were fed±acetyl-L-carnitine (ALCAR; 1.5% [w/v]) for up to four weeks prior to sacrifice and isolation of cardiac interfibrillar (IFM) and subsarcolemmal (SSM) mitochondria. IFM displayed a 28% (p<0.05) age-related loss of CPT1 activity, which correlated with a decline (41%, p<0.05) in palmitoyl-CoA-driven state 3 respiration. Interestingly, SSM had preserved enzyme function and efficiently utilized palmitate. Analysis of IFM CPT1 kinetics showed both diminished V(max) and K(m) (60% and 49% respectively, p<0.05) when palmitoyl-CoA was the substrate. However, no age-related changes in enzyme kinetics were evident with respect to L-carnitine. ALCAR supplementation restored CPT1 activity in heart IFM, but not apparently through remediation of L-carnitine levels. Rather, ALCAR influenced enzyme activity over time, potentially by modulating conditions in the aging heart that ultimately affect palmitoyl-CoA binding and CPT1 kinetics.

Longitudinal Evaluation of Fatty Acid Metabolism in Normal and Spontaneously Hypertensive Rat Hearts with Dynamic MicroSPECT Imaging

The goal of this project is to develop radionuclide molecular imaging technologies using a clinical pinhole SPECT/CT scanner to quantify changes in cardiac metabolism using the spontaneously hypertensive rat (SHR) as a model of hypertensive-related pathophysiology. This paper quantitatively compares fatty acid metabolism in hearts of SHR and Wistar-Kyoto normal rats as a function of age and thereby tracks physiological changes associated with the onset and progression of heart failure in the SHR model. The fatty acid analog, ¹²³I-labeled BMIPP, was used in longitudinal metabolic pinhole SPECT imaging studies performed every seven months for 21 months. The uniqueness of this project is the development of techniques for estimating the blood input function from projection data acquired by a slowly rotating camera that is imaging fast circulation and the quantification of the kinetics of ¹²³I-BMIPP by fitting compartmental models to the blood and tissue time-activity curves.

Translation of myocardial metabolic imaging concepts into the clinics

Flexibility in myocardial substrate metabolism for energy production is fundamental to cardiac health. This loss in plasticity or flexibility leads to overdependence on the metabolism of an individual category of substrates, with the predominance in fatty acid metabolism characteristic of diabetic heart disease and the accelerated glucose use associated with pressure-overload left ventricular hypertrophy being prime examples. There is a strong demand for accurate noninvasive imaging approaches of myocardial substrate metabolism that can facilitate the crosstalk between the bench and the bedside, leading to improved patient management paradigms. In this article potential future applications of metabolic imaging, particularly radionuclide approaches, for assessment of cardiovascular disease are discussed.

Altered mitochondrial energy metabolism may play a role in vascular aging

Epidemiological studies demonstrated that even in the absence of other risk factors (e.g., diabetes, hypertension, hypercholesterolemia), vascular aging significantly increases cardiovascular morbidity. Previous studies revealed that vascular aging is characterized by an age-dependent decline in endothelial function due to a decreased bioavailability of NO and increased production of reactive oxygen species. Yet, the mechanisms underlying the process of vascular aging are still poorly understood. Many authors consider that aging is a mitochondrial disease. Indeed, there is evidence that aging is associated with an increase in mtDNA damage and a decline in expression/activity of mitochondrial enzymes in various organs. On the basis of recent observations we predict that similar changes in mitochondrial gene expression profile are present in the aged cardiovascular system as well. It is significant, that components of the electron transport chain (including cytochrome c oxidase) seem to be similarly down-regulated with age in many species. Because pharmacological inhibition of mitochondrial energy metabolism significantly impairs endothelium-dependent vascular relaxation and may increase the production of reactive oxygen species, we propose that alterations of mitochondrial energetic phenotype may contribute to endothelial dysfunction in aging.

Effects of resistance exercise and growth hormone administration at low doses on lipid metabolism in middle-aged female rats

hGH (human growth hormone) is a key factor for metabolism as well as for growth. Lack of hGH usually increases LDL (low-density lipoprotein) while impairing exercise capacity and cardiac function [Amato G., Carella C., Fazio S., La Montagna G., Cittadini A., Sabatini D., Marciano-Mone C., Sacca L., and Bellastella A., 1993. Body composition, bone metabolism, and heart structure and function in growth hormone (GH)-deficient adults before and after GH replacement therapy at low doses. J. Clin. Endocrinol. Metab. 77, 1671-1676.]. It is still unclear, however, whether the administration of hGH to humans or animals has a synergic effects on body composition and the desired metabolic parameters with endurance resistance exercise. Therefore, the present study seeks to establish whether or not lipid metabolism is altered by both recombinant GH (growth hormone) and X (resistance exercise) in middle-aged female rats. GH administration resulted in greater weight gain compared with control and exercised animals, but the effect was reduced when combined with exercise. The increased body weight was largely due to increased muscle mass. Exercise did not result in any additional effect of GH on muscle mass. In the exercise group, hepatic HDL (high density lipoprotein) increased compared to the C (control group). The GX (growth hormone+exercise) group's serum and X group's kidney IGF-I (Insulin-like growth factor-I) concentration increased compared to the C group. In G and GX groups, serum insulin and leptin concentrations were higher than in the control, suggesting that GH may induce an insulin resistant state. Any gains in muscle mass were minimal and were not synergistic with exercise. These results suggest that hGH may not be useful for increasing performance in athletes and may induce and acquired insulin resistance.

Imaging of myocardial metabolism

There is compelling evidence that alterations in myocardial substrate use play a key role in a variety of normal and abnormal cardiac conditions such as aging, left ventricular hypertrophy, and diabetic heart disease. However, it is unclear whether the metabolic changes are adaptive or maladaptive. Development of transgenic models targeting key aspects of myocardial substrate use, such as uptake, oxidation, and storage, is accelerating our understanding of the metabolic perturbations of cardiac disease. However, whether the metabolic phenotype in these models is relevant to the human condition is frequently unknown. The importance of altered myocardial metabolism in the pathogenesis of cardiac disease is underscored by the current robust development of novel therapeutics that target myocardial substrate use. Currently, magnetic resonance spectroscopy, single photon emission computed tomography, and positron emission tomography are the 3 methods available to image myocardial substrate metabolism. In this review the role of metabolic imaging in the study of specific cardiac disease processes will be discussed. Both the current and future capabilities of metabolic imaging to furthering our understanding of cardiac disease are highlighted.

Impact of aging on substrate metabolism by the human heart

BACKGROUND

Results of studies in experimental animals have shown that, with age, myocardial fatty acid metabolism decreases, and glucose metabolism increases. Whether similar changes occur in humans is unknown.

METHODS

Seventeen healthy younger normal volunteers (six males, 26 +/- 5 years) and 19 healthy older volunteers (nine males, 67 +/- 5 years) underwent positron emission tomography (PET) under resting conditions in the fasted state. Myocardial blood flow (MBF), myocardial oxygen consumption (MVO(2)), myocardial fatty acid utilization (MFAU) and oxidation (MFAO), and myocardial glucose utilization (MGU) were quantified by PET with (15)O-water, (11)C-acetate, (11)C-palmitate, and(11)C-glucose, respectively.

RESULTS

Although MBF was similar between the groups, MVO(2) was higher in the older subjects (5.6 +/- 1.6 micromol/g/min) compared with younger subjects (4.6 +/- 1.0 micromol/g/min, p < 0.04). Rates of MFAU and MFAO (corrected for MVO(2)) were significantly lower in older subjects than in younger subjects (MFAU/MVO(2): 35 +/- 10 vs. 51 +/- 20 nmol free fatty acids (FFA)/nmol O(2) x 10(-3), p < 0.005, and MFAO/MVO(2): 33 +/- 10 vs. 48 +/- 18 nmol FFA/nmol O(2) x 10(-3), p < 0.004). In contrast, the rates of MGU corrected for MVO(2) did not differ between the groups.

CONCLUSIONS

With aging, humans exhibit a decline in MFAU and MFAO. Although absolute rates of MGU do not increase, by virtue of the decline in MFAU there is likely an increase in relative contribution of MGU to substrate metabolism. The clinical significance of this metabolic switch awaits further study.

Dietary l-carnitine stimulates carnitine acyltransferases in the liver of aged rats

Aging affects oxidative metabolism in liver and other tissues. Carnitine acyltransferases are key enzymes of this process in mitochondria. As previously shown, the rate of transcription and activity of carnitine palmitoyltransferase CPT1 are also related to carnitine levels. In this study we compared the effect of dietary l-carnitine (100 mg l-carnitine/kg body weight/day over 3 months) on liver enzymes of aged rats (months 21-24) to adult animals (months 6-9) and age-related controls for both groups. The transcription rate of CPT1, CPT2, and carnitine acetyltransferase (CRAT) was determined by quantitative reverse transcription real-time PCR (RTQPCR) and compared to the activity of the CPT1A enzyme. The results showed that the transcription rates of CPT1, CPT2, and CRAT were similar in aged and adult control animals. Carnitine-fed old rats had a significant (p<0.05) 8-12-fold higher mean transcription rate of CPT1 and CRAT compared to aged controls, adult carnitine-fed animals, and adult controls, whereas the transcription rate of CPT2 was stimulated 2-3-fold in carnitine-fed animals of both age groups. With regard to the enzymatic activity of CPT1 there was a 1.5-fold increase in the old carnitine group compared to all other groups. RNA in situ hybridization also indicated an enhanced expression of CPT1A in hepatocytes from l-carnitine-supplemented animals. These results suggest that l-carnitine stimulates transcription of CPT1, CPT2, and CRAT as well as the enzyme activity of CPT1 in the livers of aged rats.

Aging skeletal muscle mitochondria in the rat: decreased uncoupling protein-3 content

The goal of the present study was to discern the cellular mechanism(s) that contributes to the age-associated decrease in skeletal muscle aerobic capacity. Skeletal muscle mitochondrial content, a parameter of oxidative capacity, was significantly lower (25 and 20% calculated on the basis of citrate synthase and succinate dehydrogenase activities, respectively) in 24-mo-old Fischer 344 rats compared with 6-mo-old adult rats. Mitochondria isolated from skeletal muscle of both age groups had identical state 3 (ADP-stimulated) and ADP-stimulated maximal respiratory rates and phosphorylation potential (ADP-to-O ratios) with both nonlipid and lipid substrates. In contrast, mitochondria from 24-mo-old rats displayed significantly lower state 4 (ADP-limited) respiratory rates and, consequently, higher respiratory control ratios. Consistent with the tighter coupling, there was a 68% reduction in uncoupling protein-3 (UCP-3) abundance in mitochondria from elderly compared with adult rats. Congruent with the respiratory studies, there was no age-associated decrease in carnitine palmitoyltransferase I and carnitine palmitoyltransferase II activities in isolated skeletal muscle mitochondria. However, there was a small, significant decrease in tissue total carnitine content. It is concluded that the in vivo observed decrease in skeletal muscle aerobic capacity with advanced age is a consequence of the decreased mitochondrial density. On the basis of the dramatic reduction of UCP-3 content associated with decreased state 4 respiration of skeletal muscle mitochondria from elderly rats, we propose that an increased free radical production might contribute to the metabolic compromise in aging.

Impact of cardiac transplantation on molecular pathology of ET-1, VEGF-C, and mitochondrial metabolism and morphology in dilated versus ischemic cardiomyopathic patients

Little is known about the long-term impact of cardiac transplantation on activity and modifications of endothelin (ET)-1 system, vascular endothelial growth factor (VEGF), and mitochondrial metabolism and morphology in patients with ischemic cardiomyopathy (ICM) versus dilated cardiomyopathy (DCM). Messenger RNA (mRNA) expression levels of ET-1, endothelin converting enzyme (ECE)-1, VEGF-C, carnitine palmitoyltransferase (CPT)-1, and carnitine acetyltransferase (CARAT), as well as the number of normal, edematous, and degenerated mitochondria were assessed in left ventricular biopsies of 21 patients with DCM and 20 with ICM (New York Heart Association class III-IV) before and up to 3 months after cardiac transplantation. Cardiac samples of donated, nonfailing hearts served as controls (n=10). In cardiac biopsies of both ICM and DCM patients, ET-1, VEGF-C, CPT-1, and CARAT mRNA were up-regulated, whereas ECE-1 mRNA was down-regulated (P<0.05). Degenerated mitochondria had the highest number in both groups, followed by normal and edematous mitochondria. After cardiac transplantation, in ICM patients impaired gene expression levels decreased to, or below, normal levels, and the number of normal mitochondria increased (P<0.05). In implanted hearts of DCM patients, however, up-regulated ET-1 transcript levels persisted and the number of normal mitochondria decreased, whereas the number of degenerated mitochondria increased (P<0.05), and edematous mitochondria remained unchanged in number. These results show that cardiac transplantation corrects the impaired hemodynamic and echocardiographic parameters in both groups, whereas in DCM, the molecular pathology of ET-1 system and mitochondria persists. Therefore, it is more likely that these changes are the cause rather than a consequence of DCM.

Influence of age on hypoxia/reoxygenation-induced DNA fragmentation and bcl-2, bcl-xl, bax and fas in the rat heart and brain

To test the hypothesis that the aging mammalian heart and brain might have increased vulnerability to acute stress, DNA fragmentation was studied after hypoxia-reoygenation in young adult (6 months) and old (22-24 months) F344 rats. Heart and brain tissue were examined at the following time points: 30, 60, or 90 min of hypoxia (H, 5% O2, 95% N2) plus 2 h of reoxygenation (R, room air, 21% O2). With increasing duration of hypoxia preceding the reoxygenation, the extent of DNA fragmentation (in situ terminal dUTP nick end labeling, TUNEL, positive cells) was progressively higher in both age groups, greater in the old compared to that of the young adult rat. The levels of the anti-apoptotic proteins bcl-2 and bcl-xL, were similar in young and old at baseline and tended to increase in both age groups after hypoxia/reoxygenation. The pro-apoptotic protein, bax, was higher at baseline in the old; it rose after hypoxia/reoxygenation in the young adult heart and brain, but was unchanged in the old heart and was decreased in the old brain. The ratios of bcl-2/bax and of bcl-xL/bax were higher in the old heart and brain compared to that in the young adult after hypoxia/reoxygenation. Thus, compared to that of the young adult, the heart and brain of the old rat have lower thresholds and are more vulnerable to injury induced by hypoxia/reoxygenation, despite rapid and heightened expression of the anti-apoptotic proteins bcl-2 and bcl-xl. This could be due partly to the age-associated increase in the basal expression of the pro-apoptotic protein bax, as well as possibly other factors.

Resistance of the aged myocardium to exercise-induced chronic changes in glucose transport related protein content

The effects of acute exercise on myocardial content of glut-1 and glut-4 transporters, insulin and IGF-1 receptors were assessed in control and chronically exercised 24-month-old C57B1/6 mice. Myocardial glut-1, glut-4, insulin receptor (Ins R) and insulin like growth factor-1 receptor (IGF-1 R) protein levels were unaffected by 36 weeks of chronic exercise. However, myocardial protein content of glut-1, but not glut-4, was increased 12 h following an acute exercise bout in control (46%) and chronically exercised (83%) aged animals. This increased glut-1 response following acute exercise occurred despite the finding that the chronic exercise failed to increase cardiac or skeletal muscle oxidative capacity as indicated by no change in citrate synthase activity. Myocardial IGF-1 R content was unaffected by acute exercise whereas Ins R protein content was decreased 12 h following the acute exercise bout in the chronically exercised (-52%) and control (-28%) animals. The effect of acute exercise on the protein content of glut-1 and Ins R was 80 and 84% greater respectively, in the chronically exercised animals. This suggests that the amplitude of the expression of these two proteins may be increased by chronic exercise, thus constituting a form of adaptation.

Age-associated alterations in cardiac and skeletal muscle glucose transporters, insulin and IGF-1 receptors, and PI3-kinase protein contents in the C57BL/6 mouse

We investigated potential age-related changes in cardiac and skeletal muscle protein contents of glut-4 and glut-1 transporters, insulin and insulin-like growth factor-1 (IGF-1) receptors, and phosphatidylinositol 3-kinase (PI3-kinase) in the C57B1/6 mouse. Myocardial glut-4 content increased four- to five-fold between mid- to late-adulthood with no further age-related changes. Increases in myocardial glut-1 preceded the increase in glut-4 and was of a much smaller magnitude (25-40%). Skeletal muscle glut-4 was also increased (38-49%) and no further changes were noted between adulthood and old age. Cardiac insulin receptor and the p85 alpha subunit of PI3-kinase both declined by about 40%, whereas the skeletal muscle content of these two proteins were unaffected by aging. Cardiac (-23 to -24%) and skeletal muscle (-40 to -62%) IGF-1 receptor levels were decreased in adult and old animals with senescence being associated with a further decrease in cardiac IGF-1 receptor levels to 20% of controls. A two- to three-fold increase in both basal and maximal in vitro autophosphorylation of the cardiac insulin and IGF-1 receptors by their respective ligands was observed with senescence. It appears that cardiac and skeletal muscle demonstrate differential responses in terms of the magnitude and temporal responses of age-associated alterations in glucose transport related protein contents in the C57B1/6 mouse.

Oxidative activity in mitochondria isolated from rat liver at different stages of development

The purpose of this study was to evaluate the oxidative capacities in hepatic mitochondria isolated from prepubertal, young adult and adult rats (40, 90 and 180 days of age, respectively). In these rats, mitochondrial respiratory rates using FAD- and NAD-linked substrates as well as mitochondrial protein mass were measured. The results show that only the oxidative capacity of FAD-linked pathways significantly declined in mitochondria from 180-day-old rats compared with those from younger animals. When we consider FAD-linked respiration expressed per g liver, no significant difference was found among rats of different ages because of an increased mitochondrial protein mass found in 180-day-old rats. However, when FAD-linked and lipid-dependent respiratory rates were expressed per 100 g body weight, significant decreases occurred in 180-day-old rats. Therefore, the decrease in liver weight expressed per 100 g body weight rather than an impaired hepatic cellular activity may be the cause of body energy deficit in 180-day-old rats.

Cardiac morphology and function in senescent rats: gender-related differences

OBJECTIVES

We sought to better understand the effects of aging and gender on left ventricular (LV) structure and function.

BACKGROUND

Cardiovascular disease in older persons is associated with increased mortality and morbidity. The influence of gender on age-related cardiac changes is incompletely characterized.

METHODS

We studied 34 senescent, male and female, normotensive Fischer rats with transthoracic Doppler echocardiography and morphometric and histopathologic analyses.

RESULTS

Male rats were larger (396 +/- 31 g vs. 282 +/- 35 g), and LV mass in males was greater (1.04 +/- 0.22 g vs. 0.67 +/- 0.13 g). However, wall and chamber dimensions normalized to body weight revealed proportionately thicker anterior and posterior walls in females. Relative wall thickness ratio (2 [Diastolic posterior wall thickness]/Diastolic LV internal chamber diameter) was greater in females, but abnormal fractional shortening and diastolic filling (E/A ratio) patterns were more common in males. Significant mitral regurgitation (MR) was sevenfold more common among males (88% vs. 12%, p < 0.001). Histopathologic analysis showed that the cardiac myocytes were larger, and there was greater LV fibrosis in males (both p < 0.001).

CONCLUSIONS

Gender-related morphologic and functional differences are important to consider in cardiovascular assessment. Very old rats show significant gender differences in LV size and function. Male rat hearts are larger, thinner and more fibrotic and have indexes of diminished performance. The high prevalence of MR in male rats may play a crucial role in these gender differences.

Correlation between age and DNA damage detected by FADU in human peripheral blood lymphocytes

Fluorometric analysis of DNA unwinding (FADU) is a fast and reliable method for detecting single strand DNA breaks as an index of DNA damage induced by clastogenic agents. A study of damage detected by FADU was conducted on DNA extracted from peripheral blood lymphocytes of 128 healthy nonsmoking regular donors (ranging in age from 19 to 67 years) and from 5 umbilical cord blood samples. DNA damage was measured as percentage of unwound DNA after alkalinization. Statistical analyses, both parametric (Pearson r correlation coefficient, b regression coefficient, ANOVA) and nonparametric (Kruskal-Wallis H test, Spearman rs rank correlation coefficient), support a significant correlation between age of donors and amount of DNA damage. The same results are found when adult donors are divided in four age classes and the ANOVA test performed among the mean percentages of unwound DNA of each class. Furthermore, donors of the same age belonging to different blood groups (A, B, AB and O) do not show any difference in DNA damage detected by FADU.