Prabhakaran Balagopal

Effects of aging on in vivo synthesis of skeletal muscle myosin heavy-chain and sarcoplasmic protein in humans

A decline in muscle mass and contractile function are prominent features of the sarcopenia of old age. Because myosin heavy chain is an important contractile protein, it was hypothesized that synthesis of this protein decreases in sarcopenia. The fractional synthesis rate of myosin heavy chain was measured simultaneously with rates of mixed muscle and sarcoplasmic proteins from the increment of [13C]leucine in these proteins purified from serial needle biopsy samples taken from 24 subjects (age: from 20 to 92 yr) during a primed continuous infusion of L-[1-(13)C]leucine. A decline in synthesis rate of mixed muscle protein (P < 0.01) and whole body protein (P < 0.01) was observed from young to middle age with no further change with advancing age. An age-related decline of myosin heavy-chain synthesis rate was also observed (P < 0.01), with progressive decline occurring from young, through middle, to old age. However, sarcoplasmic protein synthesis did not decline with age. Myosin heavy-chain synthesis rate was correlated with measures of muscle strength (P < 0.05), circulating insulin-like growth factor I (P < 0.01), and dehydroepiandrosterone sulfate (P < 0.05) in men and women and free testosterone levels in men (P < 0.01). A decline in the synthesis rate of myosin heavy chain implies a decreased ability to remodel this important muscle contractile protein and likely contributes to the declining muscle mass and contractile function in the elderly.A decline in muscle mass and contractile function are prominent features of the sarcopenia of old age. Because myosin heavy chain is an important contractile protein, it was hypothesized that synthesis of this protein decreases in sarcopenia. The fractional synthesis rate of myosin heavy chain was measured simultaneously with rates of mixed muscle and sarcoplasmic proteins from the increment of [13C]leucine in these proteins purified from serial needle biopsy samples taken from 24 subjects (age: from 20 to 92 yr) during a primed continuous infusion ofl-[1-13C]leucine. A decline in synthesis rate of mixed muscle protein ( P < 0.01) and whole body protein ( P < 0.01) was observed from young to middle age with no further change with advancing age. An age-related decline of myosin heavy-chain synthesis rate was also observed ( P < 0.01), with progressive decline occurring from young, through middle, to old age. However, sarcoplasmic protein synthesis did not decline with age. Myosin heavy-chain synthesis rate was correlated with measures of muscle strength ( P < 0.05), circulating insulin-like growth factor I ( P < 0.01), and dehydroepiandrosterone sulfate ( P < 0.05) in men and women and free testosterone levels in men ( P < 0.01). A decline in the synthesis rate of myosin heavy chain implies a decreased ability to remodel this important muscle contractile protein and likely contributes to the declining muscle mass and contractile function in the elderly.

Nontraditional Risk Factors and Biomarkers for Cardiovascular Disease: Mechanistic, Research, and Clinical Considerations for Youth A Scientific Statement From the American Heart Association

The rapid increase in the prevalence and severity of obesity in children is likely to lower the age of onset and increase the incidence of cardiovascular disease worldwide. Understanding the pathophysiology and improving the clinical management of cardiovascular disease involve a knowledge of novel risk factors and biomarkers. The clinical and mechanistic roles of these novel biological factors during childhood are currently being investigated. The goals of this scientific statement are to present the existing knowledge and theoretical framework of nontraditional risk factors for cardiovascular disease as they relate to children and adolescents, to describe the relevance and weight of available experimental and clinical evidence and the therapeutic implications pertaining to nontraditional risk factors in the pediatric population, and to stimulate further research with a goal of developing valid and reliable approaches to identify and validate novel risk factors that will aid in the clinical evaluation and perhaps prediction of cardiovascular disease in the pediatric population. Although several biomarkers are promising, substantial research is required before nontraditional risk factors can be used to identify and reduce cardiovascular disease risk in children and adolescents.

Age-Related Sarcopenia in Humans Is Associated with Reduced Synthetic Rates of Specific Muscle Proteins

Sarcopenia of aging is not explained entirely on the basis of age-associated reduced physical activity. Progressive neuromuscular changes and diminishing anabolic hormone levels are thought to contribute to the pathogenesis of sarcopenia. Decline in muscle mass indicates a decline in muscle protein content. Recent studies demonstrated an age-related decline in synthesis rate of mixed muscle proteins, myosin heavy chain and mitochondrial protein. Reductions in myosin heavy chain and mitochondrial protein synthesis rates have been correlated with age-associated decrements in muscle strength and aerobic exercise tolerance, respectively. These changes have been reported as early as 50 y of age and are related to the decline in insulin-like growth factor (IGF)-I, testosterone and dehydroepiandrosterone (DHEA)-sulfate. The declining ability to remodel these important muscle proteins may therefore play a role in the development of muscle wasting, metabolic abnormalities and impaired physical functioning seen in old age.

Obesity without Established Comorbidities of the Metabolic Syndrome Is Associated with a Proinflammatory and Prothrombotic State, Even before the Onset of Puberty in Children

BACKGROUND Metabolic syndrome (MS)-related comorbidities in obesity, such as hypertension, dyslipidemia, and glucose intolerance, are increasingly recognized in children, predisposing them to early cardiovascular disease. OBJECTIVE The objective of the study was to investigate whether markers of inflammation and prothrombosis are abnormal in obese children without established MS comorbidities across puberty, as compared with lean, age-matched controls. SUBJECTS AND METHODS Obese children (body mass index >95%) with normal fasting glucose, blood pressure, cholesterol and triglycerides were recruited; lean controls (body mass index 10-75%) had no first-degree relatives with MS. High-sensitivity C-reactive protein (hsCRP), IL-6, plasminogen activator inhibitor 1, and fibrinogen concentrations were measured. Body composition was assessed by waist circumference and dual-energy x-ray absorptiometry. RESULTS Of 623 children screened, 203 enrolled (106 males, 97 females), aged 7-18 yr, 115 obese, 88 lean (balanced for age and gender), 99 prepubertal, and 104 pubertal. Many screen failures were due to silent comorbidities. Obese subjects with insulin resistance but without MS comorbidities had about 10 times higher hsCRP concentrations than controls and higher fibrinogen, IL-6, and plasminogen activator inhibitor-1 (P < 0.01 all). Differences were significant, even in the prepubertal cohort. hsCRP and fibrinogen correlated with waist circumference (r = 0.73 and 0.40, respectively) and percent fat mass (r = 0.76 and 0.47) (P < 0.0001). CONCLUSION Childhood obesity per se is associated with a proinflammatory and prothrombotic state before other comorbidities of the MS are present and even before the onset of puberty. Whether biomarkers like hsCRP and fibrinogen are useful in assessing cardiovascular risk and whether these abnormalities are reversible with earlier therapeutic interventions in very young obese children requires further study.

Changes in Circulating Satiety Hormones in Obese Children: A Randomized Controlled Physical Activity-Based Intervention Study

The aims of this study are to examine in children: (i) obesity‐related alterations in satiety factors such as leptin, ghrelin, and obestatin; (ii) the link between satiety factors and cardiometabolic risk factors; and (iii) the impact of a physical activity‐based lifestyle intervention on the levels of these satiety factors in the obese. We studied a total of 21 adolescents (BMI percentile, 99.0 ± 0.6 for 15 obese and 56.2 ± 1.1 for 6 lean). The obese subjects underwent a 3‐month randomized controlled physical activity‐based lifestyle intervention. Leptin, soluble leptin receptor (sOB‐R), ghrelin, and obestatin levels were determined as the primary outcome measures. Other markers of cardiometabolic disease such as inflammation and insulin resistance were also determined. Body composition was measured by dual‐energy X‐ray absorptiometry. The concentrations of ghrelin, obestatin, and sOB‐R were significantly lower in the obese children compared to the lean controls, whereas that of leptin was higher (all P < 0.05). Although intervention led to a net increase in obestatin (P < 0.01) and no change in ghrelin levels, the balance between ghrelin and obestatin (ratio of ghrelin to obestatin, G/O) decreased (P < 0.02). Intervention reduced leptin and increased sOB‐R (P < 0.01 for both). Significant associations between satiety factors and other cardiometabolic risk factors were also observed. Taken together, alterations in the levels of satiety factors are evident early in the clinical course of obesity, but physical activity‐based lifestyle intervention either prevented their continued increase or normalized their levels. These beneficial effects appear to aid in the maintenance of body weight and reduction in cardiovascular risk.

Metformin use in children with obesity and normal glucose tolerance – effects on cardiovascular markers and intrahepatic fat

Abstract Objective: To determine if metformin improves markers of inflammation, thrombosis, and intrahepatic fat contents in children with uncomplicated obesity. Methods: Obese children with normal glucose tolerance but elevated highly sensitive C-reactive protein (hsCRP) and/or fibrinogen concentrations (>2 standard deviations) were randomized to structured diet/exercise or diet/exercise and metformin for 6 months. Blood samples, dual energy X-ray absorptiometry data, and liver magnetic resonance images were obtained. Results: Forty-two of 66 recruited children (7–18 years) completed 6 months. Weight loss was modest but more pronounced in the metformin group (–4.9±1.0 kg) than in the diet/exercise group (–1.7±1.1 kg, p<0.03), whereas hsCRP and fibrinogen decreased more in the diet/exercise pubertal group. Baseline intrahepatic fat was high but decreased only in the diet/exercise (not metformin) pubertal group. Conclusions: Six months of metformin therapy improved weight loss and reduced abdominal adiposity, but did not enhance the beneficial effect of diet and exercise on markers related to inflammation, thrombosis, or hepatic fat in obese children with normal glucose tolerance.

Sarcopenia and hormonal changes

Sarcopenia is a major determinant to age-related disabilities and is characterized by a decline in muscle mass, muscle weakness, and increased fatigability (1). These changes, in combination with the declining endurance capacity of aging, results in the substantial physical disability of the elderly. The functional capacity of muscle depends upon both the quality and quantity of muscle protein, which accounts for approximately one-fifth of muscle weight. Besides the declining muscle mass, the decline in muscle quality is evident from the reduced muscle performance disproportionate to the loss of muscle mass (2). The quality and quantity of muscle depends on the integrity of a continuous remodeling process that includes breakdown of old proteins and synthesis of new ones. The maintenance of muscle is determined by a delicate balance between these two processes, implying that a decline in muscle mass occurs when protein breakdown exceeds synthesis. Muscle strength depends not only on muscle mass but also on the ability of the tissue to generate adenosine triphosphate (ATP) from nutrient metabolism and the ability to hydrolyze ATP and make this chemical energy available for muscle contraction. The process also can be affected by abnormalities of the remodeling process of proteins (mostly enzymes) responsible for ATP production and hydrolysis. The pathophysiology of sarcopenia of aging is not known, but parallel decline of synthesis rates of muscle proteins and levels of various hormones with sarcopenia of aging and their interactions provide an alluring hypothesis.

Response of fractional synthesis rate (FSR) of fibrinogen, concentration of D-dimer and fibrinolytic balance to physical activity-based intervention in obese children

Summary.  Background: Physical activity‐induced reduction in obesity‐related hyperfibrinogenemia in children has been reported. The underlying mechanisms remain elusive. Further, the effect of such interventions on fibrinolysis in children is scarce. Objectives: To investigate in obese children, before and after a physical activity‐based intervention: (i) the mechanistic role of fractional synthesis rate (FSR) of fibrinogen in the reduction of hyperfibrinogenemia; and (ii) the changes in fibrinolytic factors. Methods: Subjects included 21 (age > 14 < 18 years; Tanner stage, IV–V) children (15 obese, BMI >95%tile for age and sex and six lean, BMI <85%tile). After baseline measurements of FSR of fibrinogen, and concentrations of fibrinogen, D‐dimer, PAI‐1 and t‐PA in all children, studies were repeated after a 3‐month randomized controlled physical activity‐based lifestyle intervention in obese children only. Results: FSR of fibrinogen was higher (P = 0.002) in the obese (vs. lean) group, which was reduced (P = 0.001) after intervention. This almost completely accounted for the reduction in obesity‐related hyperfibrinogenemia. High levels of D‐dimer decreased (P = 0.001) after intervention, whereas fibrinolysis was not enhanced. Conclusions: The direct reduction in the FSR of fibrinogen and the remarkable correlation between the magnitudes of reduction in fibrinogen FSR and concentration signify a mechanistic role for FSR in the regulation of physical activity‐induced reversal of hyperfibrinogenemia in obese children. The congruent reductions in the FSR of fibrinogen and the concentrations of fibrinogen and D‐dimer in response to intervention despite depressed fibrinolysis suggest an overall improvement in the hypercoagulable state in obese children with physical activity‐based lifestyle intervention.

Insulin Resistance and Adiposity in Relation to Serum β-Carotene Levels

OBJECTIVE To determine the effects of placebo vs an encapsulated supplement of fruit and vegetable juice concentrate (FVJC) on serum β-carotene levels, insulin resistance, adiposity, and subclinical inflammation in boys. STUDY DESIGN Thirty age-matched prepubertal boys (9 lean and 21 overweight (OW); age range, 6-10 years) were studied. All participants received nutrition counseling and were randomized to receive FVJC or placebo capsules for 6 months. Total cholesterol, triglycerides, lipid corrected β-carotene, serum retinol, glucose, insulin, retinol binding protein-4, leptin, adiponectin, leptin-to-adiponectin ratio, high-sensitivity C-reactive protein, and interleukin-6 were measured before and after the 6-month intervention. Homeostasis model assessment-insulin resistance (HOMA-IR), acute insulin response to intravenous glucose, along with abdominal fat mass (dual-energy x-ray absorptiometry) were also determined. RESULTS Baseline β-carotene concentrations correlated inversely with HOMA-IR, leptin-to-adiponectin ratio, and abdominal fat mass (P ≤ .01). FVJC intake increased β-carotene concentrations (P ≤ .001) but did not influence retinol or retinol binding protein-4. Retinol insufficiency <1.047 μM was present in 18% of the entire cohort at baseline and in 37% at 6 months. HOMA-IR decreased after supplementation in the OW cohort, when adjusted for percent weight change (P = .014). The percent change in abdominal fat mass increased in the placebo group and decreased in the FVJC group (P = .029). CONCLUSIONS A 6-month supplementation with FVJC in the presence of nutritional counseling was associated with an increase in serum β-carotene concentrations and a reduction in adiposity in conjunction with an improvement in insulin resistance in OW boys.

Skeletal Muscle Myosin Heavy Chain Synthesis in Type 1 Diabetes

Although insulins anticatabolic effect on protein metabolism in type 1 diabetes has been clearly shown to be related to the inhibition of protein breakdown, insulins effect on muscle protein synthesis remains controversial. Cross-limb studies and measurements of synthesis rates of mixed muscle protein have yielded conflicting results. These measurements represent the mean synthesis of several muscle proteins and may miss changes in the synthesis rates of individual muscle proteins. We measured the fractional synthesis rates of myosin heavy chain (MHC), the principal muscle contractile protein, and mixed muscle protein (MMP) in six type 1 diabetic patients during insulin deprivation and insulin treatment. Comparisons were made with six healthy control subjects. Muscle biopsies were taken at 2 h and 8 h during a primed continuous infusion of l-[1- 13C]leucine. MHC was purified by a preparative continuous elution gel electrophoresis, and fractional synthesis rates were calculated. We found that in type 1 diabetic subjects, the fractional synthesis rates of MHC and MMP during insulin treatment are similar to those of control subjects. Acute insulin deprivation did not affect either the synthesis rate or the ratio of MHC to MMP in type 1 diabetic subjects. In the postabsorptive state, acute insulin deprivation has no effect on MHC or MMP synthesis in type 1 diabetic patients.