Stéphanie Chevalier

Insulin Resistance of Protein Metabolism in Type 2 Diabetes

OBJECTIVE—We previously demonstrated that 1) obesity impairs and 2) sex influences insulin sensitivity of protein metabolism, while 3) poor glycemic control in type 2 diabetes accelerates protein turnover in daily fed-fasted states. We hypothesized that type 2 diabetes alters the insulin sensitivity of protein metabolism and that sex modulates it. RESEARCH DESIGN AND METHODS—Hyperinsulinemic (∼570 pmol/l), euglycemic (5.5 mmol/l), and isoaminoacidemic (kept at postabsorptive concentrations) clamps were performed in 17 hyperglycemic type 2 diabetic subjects and 23 subjects without diabetes matched for age and body composition, after 7 days on a inpatient, protein-controlled, isoenergetic diet. Glucose and leucine kinetics were determined using tracers. RESULTS—In type 2 diabetes, postabsorptive (baseline) glycemia was 8–9 mmol/l, glucose production (Ra) and disposal (Rd) were elevated, and once clamped, endogenous glucose Ra remained greater and Rd was less (P < 0.05) than in control subjects. Baseline leucine kinetics did not differ despite higher insulin levels. The latter was an independent predictor of leucine flux within each sex. With clamp, total flux increased less (P = 0.016) in type 2 diabetic men, although protein breakdown decreased equally (∼20%) in male groups but less in female groups. Whereas protein synthesis increased in male control subjects and in both female groups, it did not in male subjects with type 2 diabetes. In men, homeostasis model assessment of insulin resistance predicted 44%, and, in women, waist-to-hip ratio predicted 40% of the change in synthesis. CONCLUSIONS—During our clamp, men with type 2 diabetes have greater insulin resistance of protein metabolism than that conferred by excess adiposity itself, whereas women do not. These results may have implications for dietary protein requirements.

Elevations of plasma methylarginines in obesity and ageing are related to insulin sensitivity and rates of protein turnover

Aims/hypothesisIncreased circulating methylarginines (MA) have been linked to the metabolic syndrome to explain endothelial dysfunction and cardiovascular disease risk. Proteins that contain MA are regulatory and release them during catabolism. We hypothesised that increased protein turnover in insulin-resistant states contributes to an increase in circulating MA.Matwerials and methodsWe performed hyperinsulinaemic, euglycaemic, and isoaminoacidaemic experiments on 49 lean, obese and elderly subjects, with measurements of the kinetics of glucose and protein metabolism. Plasma MA, i.e. asymmetrical dimethylarginine (ADMA), symmetrical dimethylarginine (SDMA), and N -monomethyl-l-arginine (NMMA), lipids and body composition were measured.ResultsInsulin resistance of glucose and protein metabolism occurred in obese and elderly subjects. ADMA concentrations were 29 to 120% higher in obese and 34% higher in elderly than in lean subjects. SDMA were 34 and 20% higher in obese than in lean and than in elderly subjects, respectively. NMMA were 32% higher in obese than in lean subjects. ADMA differed by sex, being higher in men, namely by 1.75× in obese men and by 1.27× in elderly men. Postabsorptive ADMA (r=0.71), SDMA (r=0.46), and NMMA (r=0.31) correlated (all p<0.05) with rates of protein flux. All three MA correlated negatively with clamp glucose infusion rates and uptake (p<0.001). ADMA and SDMA correlated negatively with net protein synthesis and clamp amino acid infusion rates (p<0.05). All MA also correlated with adiposity indices and fasting insulin and triglycerides (p<0.05).Conclusions/interpretationObesity, sex and ageing affect MA. Elevations of the three MA in obese, and of ADMA in elderly men, are related to increased protein turnover and to lesser insulin sensitivity of protein metabolism. These interrelationships might amplify insulin resistance and endothelial dysfunction.

Whole-body protein anabolic response is resistant to the action of insulin in obese women

BACKGROUND Obesity is associated with insulin resistance of glucose and lipid metabolism. OBJECTIVE We sought to determine the effects of obesity on the insulin sensitivity of protein metabolism. DESIGN Whole-body [(13)C]leucine and [(3)H]glucose kinetics were measured in 9 lean and 10 obese women in the postabsorptive state and during a hyperinsulinemic, euglycemic, isoaminoacidemic clamp. RESULTS In the postabsorptive state, the leucine endogenous rate of appearance (catabolism), normalized for fat-free mass, was 11% greater and the nonoxidative rate of disappearance (synthesis) was 8% greater in the obese than in the lean women, but net balance was 29% more negative (P < 0.05). Clamp amino acid and glucose infusion rates were significantly lower in the obese women than in the lean women (0.65 +/- 0.02 compared with 0.85 +/- 0.04 and 5.7 +/- 0.3 compared with 9.1 +/- 0.5 mg x kg fat-free mass(-1) x min(-1), respectively; P < 0.0001 for both), and their rates correlated positively (r = 0.635, P = 0.005). During hyperinsulinemia, synthesis was stimulated less and net leucine balance was much lower in the obese women than in the lean women (-0.08 +/- 0.06 and 0.30 +/- 0.03 mumol x kg fat-free mass(-1) x min(-1), respectively; P < 0.0001). The percentage change in net leucine balance correlated negatively with all adiposity indexes. Plasma free fatty acids were less suppressed and the respiratory quotient was lower in the obese women than in the lean women. CONCLUSION Obese women show a blunted protein anabolic response to hyperinsulinemia that is consistent with resistance to the action of insulin on protein concurrent with that on glucose and lipid metabolism.

The physical functional capacity of frail elderly persons undergoing ambulatory rehabilitation is related to their nutritional status

Objectives: To estimate the prevalence of malnutrition in frail elders undergoing rehabilitation and the association between their nutritional status and physical function.Design: Observational study of new participants undergoing ambulatory rehabilitation.Setting: Two Geriatric Day Hospitals (GDH) in Montreal, Quebec.Participants: 121 women and 61 men.Intervention: Evaluation of nutritional status, body composition and physical function.Measurements: The nutritional status was assessed with a composite index based on anthropometric measurements and serum albumin, as well as using the Mini Nutritional Assessment (MNA) questionnaire. Patients were classified as well-nourished, having mild/at risk of malnutrition or malnourished. Body composition was estimated by bioimpedance and handgrip strength and gait speed by standard methods.Results: 13% of patients were found to be mildly malnourished, whereas 6% were malnourished. Malnourished patients were older and had worse cognition, lower BMI, and % body fat (all p<0.05). Malnourished patients and those with mild malnutrition had lower weight, triceps skinfold thickness, muscle and fat mass (all, p<0.003). Handgrip strength was different according to the nutritional status (p=0.034) and correlated with muscle mass (r=0.65, p<0.001). MNA classified 53% of patients as being at risk whereas 3% were malnourished and it correlated with gait speed (r=0.26, p=0.001).Conclusion: There is a high prevalence of patients in GDH at risk or with mild malnutrition. Being malnourished was associated with worse physical performance, which suggests that a nutritional intervention may be of benefit in improving their physical function.

Normal protein anabolic response to hyperaminoacidemia in insulin-resistant patients with lung cancer cachexia

BACKGROUND & AIMS Insulin resistance of protein anabolism has been speculated to underlie the skeletal muscle wasting characteristic of cancer cachexia. We tested whether insulin resistance is present in cachectic lung cancer patients and if a sustained, physiological elevation of amino acids with hyperinsulinemia would compensate for it. METHODS Whole-body [(13)C]leucine and [(3)H]glucose kinetics were assessed in 10 male non-small cell lung cancer (NSCLC) patients and 10 healthy matched controls during a euglycemic, hyperinsulinemic clamp under conditions of isoaminoacidemia followed by hyperaminoacidemia. RESULTS Postabsorptive glucose and protein kinetics were comparable between groups. Glucose uptake was significantly lower in NSCLC patients during hyperinsulinemia. During concurrent isoaminoacidemia, protein breakdown was suppressed in both, but rates were elevated in NSCLC; rates of synthesis did not change, resulting in reduced net protein balance (synthesis - breakdown) in response to insulin in NSCLC. With subsequent hyperaminoacidemia, synthesis increased significantly with no further change in breakdown, resulting in similar increase in net balance between groups. CONCLUSIONS NSCLC patients with moderate cachexia showed considerable insulin resistance of glucose and of whole-body protein anabolism. Their anabolic protein response was stimulated normally by hyperaminoacidemia. Thus, ample provision of amino acids is a feasible strategy to overcome the protein anabolic failure of cancer cachexia.

Protein Anabolic Responses to a Fed Steady State in Healthy Aging

BACKGROUND Protein anabolism in response to feeding may be impaired with aging. To determine if this could contribute to muscle loss, we studied fed-state metabolic responses in healthy, non-sarcopenic elderly women. METHODS Whole-body [(3)H]glucose and protein ([(13)C]leucine) kinetics were measured, and muscle protein fractional synthesis rate ([(2)H(5)]phenylalanine) and signaling events were assessed from vastus lateralis biopsies in eight elderly (73 ± 3 years) and eight young women (24 ± 1 years), using a simulated fed steady-state clamp. RESULTS Both groups had similar muscle and lean body mass indices and activity level. During insulin, glucose (8 mmol/L), and amino acid (AA; 2× fasting) infusions, serum insulin was lower in the elderly women and C-peptide increased less. Glucose uptake was stimulated, and production suppressed similarly. Suppression of whole-body protein breakdown was less in the elderly women, leading to lower AA infusion rates, oxidation, and net positive protein balance, but differences were not present when adjusted for serum insulin. Whole-body protein synthesis and muscle protein fractional synthesis rate increased similarly. Similar increases in phosphorylated Akt(Ser473), PRAS40(Thr246), FoxO3a(Thr32), and rpS6(Ser240/244) indicated no alterations in insulin/nutrient signaling with aging. CONCLUSIONS Both whole-body and muscle fed-state protein anabolic responses were preserved, as was insulin sensitivity of glucose metabolism, in active, healthy elderly women. This is consistent with other factors such as sedentarity, low protein intake, and concurrent diseases, being responsible for the sarcopenia of aging.

Anthracycline-containing chemotherapy causes long-term impairment of mitochondrial respiration and increased reactive oxygen species release in skeletal muscle.

Anticancer treatments for childhood acute lymphoblastic leukaemia (ALL) are highly effective but are now implicated in causing impaired muscle function in long-term survivors. However, no comprehensive assessment of skeletal muscle mitochondrial functions in long-term survivors has been performed and the presence of persistent chemotherapy-induced skeletal muscle mitochondrial dysfunction remains a strong possibility. Non-tumour-bearing mice were treated with two drugs that have been used frequently in ALL treatment (doxorubicin and dexamethasone) for up to 4 cycles at 3-week intervals and euthanized 3 months after the 4th cycle. Treated animals had impaired growth and lower muscle mass as well as reduced mitochondrial respiration and increased reactive oxygen species production per unit oxygen consumption. Mitochondrial DNA content and protein levels of key mitochondrial membrane proteins and markers of mitochondrial biogenesis were unchanged, but protein levels of Parkin were reduced. This suggests a novel pattern of chemotherapy-induced mitochondrial dysfunction in skeletal muscle that persists because of an acquired defect in mitophagy signaling. The results could explain the observed functional impairments in adult survivors of childhood ALL and may also be relevant to long-term survivors of other cancers treated with similar regimes.

Dietary Omega-3 Fatty Acids May Be Associated with Increased Neuropathic Pain in Nerve-Injured Rats

Certain dietary proteins and oils are capable of decreasing chronic neuropathic pain levels in rats after partial sciatic nerve ligation injury. We tested, for the first time, the role of dietary polyunsaturated fatty acids in suppressing pain in partial sciatic nerve ligation-injured rats. Six groups of male Wistar rats were fed an identical casein-based, fat-free diet for 1 wk preceding partial sciatic nerve ligation injury and for 1 wk thereafter. In addition, rats received, via gavage, 1 mL/day of pure canola, corn, hemp, soy, or sunflower oil, differing significantly in their &ohgr;-3 and &ohgr;-6 polyunsaturated fatty acid content, or 1 mL of plain water. Responses to tactile and noxious heat stimuli were recorded before and after surgery and a difference score was calculated for each group by subtracting the preoperative from the post-partial sciatic nerve ligation values. Heat hyperalgesia, but not tactile allodynia, was significantly different among the dietary groups (P = 0.005). Heat hyperalgesia of rats fed hemp oil, developing the most robust response, was significantly larger compared with rats fed corn oil, developing the least pain model (difference score: 24.3 ± 4.1 s versus 6.1 ± 3.1 s, respectively; P < 0.001). These oils contain similar levels of &ohgr;-6 polyunsaturated fatty acids (hemp, 60%; corn, 58%) but their &ohgr;-3 levels are 28-fold different (20% versus 0.7%, respectively). A significant correlation was found among dietary levels of &ohgr;-3, but not &ohgr;-6 or the &ohgr;-3/&ohgr;-6 ratio, of the six dietary groups and heat hyperalgesia (P = 0.006). We conclude that dietary oil might predict levels of neuropathic pain in rats and that this effect may be associated with dietary &ohgr;-3 levels.

Even mealtime distribution of protein intake is associated with greater muscle strength, but not with 3-y physical function decline, in free-living older adults: the Quebec longitudinal study on Nutrition as a Determinant of Successful Aging (NuAge study)

Background: Functional status declines with aging, thus impeding autonomy. Recently, a more even mealtime distribution of dietary protein was positively associated with muscle mass, but the relation of this distribution to physical performance remains unknown.Objective: We examined the relation between mealtime protein-intake distribution and physical performance and its 3-y decline in community-dwelling older adults.Design: Three-year follow-up data from 827 men and 914 women (67-84 y) in the longitudinal study on nutrition and aging [Quebec longitudinal study on Nutrition as a Determinant of Successful Aging (NuAge study); Quebec, Canada] were analyzed. Physical performance, which was measured yearly, was grouped into the following 2 functional composite scores: muscle strength (handgrip, arm, and leg) and mobility (timed-up-and-go, chair stand, and walking speed). Dietary data were collected in 2 sets of three 24-h food recalls at baseline and year 2. The individual mealtime protein distribution was calculated as the CV (i.e., SD divided by the mean) of grams of protein per meal. A mixed model analysis was used to examine trajectories of muscle strength and mobility across time by sex as conditioned by the protein distribution and adjusted for potential covariates.Results: Physical performance deteriorated over 3 y with muscle strength declining more than the mobility score in men (-1.51 ± 1.68 compared with -0.66 ± 2.81) and women (-1.35 ± 1.77 compared with -0.78 ± 2.63) (means ± SD, P < 0.001). More-evenly distributed protein intake, independent of the total quantity, was associated with a higher muscle-strength score in both sexes throughout follow-up. It was also associated with a greater mobility score, but only in men and only before adjustment for covariates. Strength and mobility rates of decline were not affected by protein-intake distribution in either sex.Conclusions: In addition to the previously observed association with lean mass, an even distribution of daily protein intake across meals is independently associated with greater muscle strength, but not with the mobility score, in older adults. A longer-term investigation of the role of protein intake and its distribution on physical performance is warranted, as are intervention studies, to support future recommendations.

Fed-state clamp stimulates cellular mechanisms of muscle protein anabolism and modulates glucose disposal in normal men

Since maximum anabolism occurs postprandially, we developed a simulated fed state with clamped hyperinsulinemia, physiological hyperglycemia, and hyperaminoacidemia (Hyper-3) and explored muscle cellular mechanisms. Whole body [1-(13)C]leucine and [3-(3)H]glucose kinetics in healthy men were compared between hyperinsulinemic, euglycemic, isoaminoacidemic (Hyper-1, n = 10) and Hyper-3 (n = 9) clamps. In Hyper-3 vs. Hyper-1, nonoxidative leucine R(d) [rate of disappearance (synthesis)] was stimulated more (45 +/- 4 vs. 24 +/- 4 micromol/min, P < 0.01) and endogenous R(a) [rate of appearance (breakdown)] was inhibited similarly; hence net balance increased more (86 +/- 6 vs. 49 +/- 2 micromol/min, P < 0.001). Glucose R(d) was similar; thus Hyper-3 metabolic clearance rate (331 +/- 23 vs. 557 +/- 41 ml/min, P < 0.0005) and R(d)/insulin (M, 0.65 +/- 0.10 vs. 1.25 +/- 0.10 mg.min(-1).pmol(-1).l, P < 0.001) were less, despite higher insulin (798 +/- 74 vs. 450 +/- 24 pmol/l, P < 0.005). In vastus lateralis muscle biopsies, phosphorylation of Akt (P = 0.025), mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70(S6K1); P = 0.008), S6 (P = 0.049), and 4E-binding protein 1 (4E-BP1; P = 0.001) increased. With decreased eukaryotic initiation factor-4E (eIF4E).4E-BP1 complex (P = 0.01), these are consistent with increased mTOR complex 1 (mTORC1) signaling and translation initiation of protein synthesis. Although mRNA expression of ubiquitin, MAFbx 1, and MuRF-1 was unchanged, total ubiquitinated proteins decreased 20% (P < 0.01), consistent with proteolysis suppression. The Hyper-3 clamp increases whole body protein synthesis, net anabolism, and muscle protein translation initiation pathways and decreases protein ubiquitination. The main contribution of hyperaminoacidemia is stimulation of synthesis rather than inhibition of proteolysis, and it attenuates the expected increment of glucose disposal.