Failure of CD4 T Cell-Deficient Hosts To Control Chronic Nontyphoidal Salmonella Infection Leads to Exacerbated Inflammation, Chronic Anemia, and Altered Myelopoiesis.

Immunocompromised patients are more susceptible to recurrent nontyphoidal Salmonella (NTS) bacteremia. A key manifestation of HIV infection is the loss of CD4 T cells, which are crucial for immunity to Salmonella infection. We characterized the consequences of CD4 T cell depletion in mice where virulent Salmonella establish chronic infection, similar to chronic NTS disease in humans. Salmonella-infected, CD4-depleted 129X1/SvJ mice remained chronically colonized for at least 5 weeks, displaying increased splenomegaly and more severe splenitis than infected mice with CD4 T cells. Mature erythrocytes, immature erythroid cells, and phagocytes accounted for the largest increase in splenic cellularity. Anemia, which is associated with increased mortality in Salmonella-infected humans, was exacerbated by CD4 depletion in infected mice and was accompanied by increased splenic sequestration of erythrocytes and fewer erythropoietic elements in the bone marrow, despite significantly elevated levels of circulating erythropoietin. Splenic sequestration of red blood cells, the appearance of circulating poikilocytes, and elevated proinflammatory cytokines suggest inflammation-induced damage to erythrocytes contributes to anemia and splenic retention of damaged cells in infected animals. Depleting CD4 T cells led to increased myeloid cells in peripheral blood, spleen, and bone marrow, as well as expansion of CD8 T cells, which has been observed in CD4-depleted humans. This work describes a mouse model of Salmonella infection that recapitulates several aspects of human disease and will allow us to investigate the interplay of innate and adaptive immune functions with chronic inflammation, anemia, and susceptibility to Salmonella infection.

Exercise effects on postprandial glucose metabolism in type 1 diabetes: a triple-tracer approach.

To determine the effects of exercise on postprandial glucose metabolism and insulin action in type 1 diabetes (T1D), we applied the triple tracer technique to study 16 T1D subjects on insulin pump therapy before, during, and after 75 min of moderate-intensity exercise (50% V̇o2max) that started 120 min after a mixed meal containing 75 g of labeled glucose. Prandial insulin bolus was administered as per each subject's customary insulin/carbohydrate ratio adjusted for meal time meter glucose and the level of physical activity. Basal insulin infusion rates were not altered. There were no episodes of hypoglycemia during the study. Plasma dopamine and norepinephrine concentrations rose during exercise. During exercise, rates of endogenous glucose production rose rapidly to baseline levels despite high circulating insulin and glucose concentrations. Interestingly, plasma insulin concentrations increased during exercise despite no changes in insulin pump infusion rates, implying increased mobilization of insulin from subcutaneous depots. Glucagon concentrations rose before and during exercise. Therapeutic approaches for T1D management during exercise will need to account for its effects on glucose turnover, insulin mobilization, glucagon, and sympathetic response and possibly other blood-borne feedback and afferent reflex mechanisms to improve both hypoglycemia and hyperglycemia.

Regulation of phenotypic heterogeneity permits Salmonella evasion of the host caspase-1 inflammatory response.

Sensing and adapting to the environment is one strategy by which bacteria attempt to maximize fitness in an unpredictable world; another is the stochastic generation of phenotypically distinct subgroups within a genetically clonal population. In culture, Salmonella Typhimurium populations are bistable for the expression of flagellin. We report that YdiV controls this expression pattern by preventing transcription of the sigma factor that recruits RNA polymerase to the flagellin promoter. Bistability ensues when the sigma factor is repressed in a subpopulation of cells, resulting in two phenotypes: flagellin expressors and flagellin nonexpressors. Although the ability to swim is presumably a critical survival trait, flagellin activates eukaryotic defense pathways, and Salmonella restrict the production of flagellin during systemic infection. Salmonella mutants lacking YdiV are unable to fully repress flagellin at systemic sites, rendering them vulnerable to caspase-1 mediated colonization restriction. Thus, a regulatory mechanism producing bistability also impacts Salmonella virulence.

Influence of fish oil on skeletal muscle mitochondrial energetics and lipid metabolites during high-fat diet.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) enhance insulin sensitivity and glucose homeostasis in rodent models of insulin resistance. These beneficial effects have been linked with anti-inflammatory properties, but emerging data suggest that the mechanisms may also converge on mitochondria. We evaluated the influence of dietary n-3 PUFAs on mitochondrial physiology and muscle lipid metabolites in the context of high-fat diet (HFD) in mice. Mice were fed control diets (10% fat), HFD (60% fat), or HFD with fish oil (HFD+FO, 3.4% kcal from n-3 PUFAs) for 10 wk. Body mass and fat mass increased similarly in HFD and HFD+FO, but n-3 PUFAs attenuated the glucose intolerance that developed with HFD and increased expression of genes that regulate glucose metabolism in skeletal muscle. Despite similar muscle triglyceride levels in HFD and HFD+FO, long-chain acyl-CoAs and ceramides were lower in the presence of fish oil. Mitochondrial abundance and oxidative capacity were similarly increased in HFD and HFD+FO compared with controls. Hydrogen peroxide production was similarly elevated in HFD and HFD+FO in isolated mitochondria but not in permeabilized muscle fibers, likely due to increased activity and expression of catalase. These results support a hypothesis that n-3 PUFAs protect glucose tolerance, in part by preventing the accumulation of bioactive lipid mediators that interfere with insulin action. Furthermore, the respiratory function of skeletal muscle mitochondria does not appear to be a major factor in sphingolipid accumulation, glucose intolerance, or the protective effects of n-3 PUFAs.

PPS, a large multidomain protein, functions with sex-lethal to regulate alternative splicing in Drosophila.

Alternative splicing controls the expression of many genes, including the Drosophila sex determination gene Sex-lethal (Sxl). Sxl expression is controlled via a negative regulatory mechanism where inclusion of the translation-terminating male exon is blocked in females. Previous studies have shown that the mechanism leading to exon skipping is autoregulatory and requires the SXL protein to antagonize exon inclusion by interacting with core spliceosomal proteins, including the U1 snRNP protein Sans-fille (SNF). In studies begun by screening for proteins that interact with SNF, we identified PPS, a previously uncharacterized protein, as a novel component of the machinery required for Sxl male exon skipping. PPS encodes a large protein with four signature motifs, PHD, BRK, TFS2M, and SPOC, typically found in proteins involved in transcription. We demonstrate that PPS has a direct role in Sxl male exon skipping by showing first that loss of function mutations have phenotypes indicative of Sxl misregulation and second that the PPS protein forms a complex with SXL and the unspliced Sxl RNA. In addition, we mapped the recruitment of PPS, SXL, and SNF along the Sxl gene using chromatin immunoprecipitation (ChIP), which revealed that, like many other splicing factors, these proteins bind their RNA targets while in close proximity to the DNA. Interestingly, while SNF and SXL are specifically recruited to their predicted binding sites, PPS has a distinct pattern of accumulation along the Sxl gene, associating with a region that includes, but is not limited to, the SxlPm promoter. Together, these data indicate that PPS is different from other splicing factors involved in male-exon skipping and suggest, for the first time, a functional link between transcription and SXL-mediated alternative splicing. Loss of zygotic PPS function, however, is lethal to both sexes, indicating that its role may be of broad significance.

Transpulmonary lactate shuttle.

The shuttling of intermediary metabolites such as lactate through the vasculature contributes to the dynamic energy and biosynthetic needs of tissues. Tracer kinetic studies offer a powerful tool to measure the metabolism of substrates like lactate that are simultaneously taken up from and released into the circulation by organs, but in each circulatory passage, the entire cardiac output traverses the pulmonary parenchyma. To determine whether transpulmonary lactate shuttling affects whole-body lactate kinetics in vivo, we examined the effects of a lactate load (via lactate clamp, LC) and epinephrine (Epi) stimulation on transpulmonary lactate kinetics in an anesthetized rat model using a primed-continuous infusion of [U-(13)C]lactate. Under all conditions studied, control 1.2 (SD 0.7) (Con), LC 1.9 (SD 2.5), and Epi 1.9 (SD 3.5) mg/min net transpulmonary lactate uptake occurred. Compared with Con, a lactate load via LC significantly increased mixed central venous ([v]) [1.9 mM (SD 0.5) vs. 4.7 (SD 0.4)] and arterial ([a]) [1.6 mM (SD 0.4) vs. 4.1 (SD 0.6)] lactate concentrations (P < 0.05). Transpulmonary lactate gradient ([v] - [a]) was highest during the lactate clamp condition [0.6 mM (SD 0.7)] and lowest during Epi [0.2 mM (SD 0.5)] stimulation (P < 0.05). Tracer measured lactate fractional extractions were similar for control, 16.6% (SD 15.3), and lactate clamp, 8.2% (SD 15.3) conditions, but negative during Epi stimulation, -25.3% (SD 45.5) when there occurred a transpulmonary production, the conversion of mixed central venous pyruvate to arterial lactate. Further, isotopic equilibration between L and P occurred following tracer lactate infusion, but depending on compartment (v or a) and physiological stimulus, [L]/[P] concentration and isotopic enrichment ratios ranged widely. We conclude that pulmonary arterial-vein concentration difference measurements across the lungs provide an incomplete, and perhaps misleading picture of parenchymal lactate metabolism, especially during epinephrine stimulation.

Practical Anemia Bundle for Sustained Blood Recovery (PABST-BR) in critical illness: a protocol for a randomised controlled trial.

INTRODUCTION: Anaemia is highly prevalent in critical illness and is associated with impaired outcomes during and after hospitalisation. However, the impact of interventions designed to attenuate or treat anaemia during critical illness on post-hospitalisation haemoglobin recovery and functional outcomes is unclear. METHODS AND ANALYSIS: The Practical Anemia Bundle for Sustained Blood Recovery (PABST-BR) clinical trial is a pragmatic, open-label, parallel group, single-centre, randomised clinical trial assessing the impact of a multifaceted anaemia prevention and treatment strategy versus standard care for improvement of haemoglobin concentrations and functional outcomes after critical illness. The intervention, which will be delivered early in critical illness for those with moderate-to-severe anaemia (ie, haemoglobin <100 g/L), includes three components: (1) optimised phlebotomy, (2) clinical decision support and (3) pharmacological anaemia treatment directed at the underlying aetiology of anaemia. In-person assessments will occur at 1 and 3 months post-hospitalisation for laboratory evaluations and multidimensional functional outcome assessments. The primary outcome is differences in haemoglobin concentrations between groups, with secondary endpoints of anaemia-related fatigue, physical function, cognition, mental health, quality of life, phlebotomy volumes and frequency, transfusions, readmissions and mortality through 1-year post-hospitalisation. ETHICS AND DISSEMINATION: The study has been approved by the Institutional Review Board of the Mayo Clinic in Minnesota, USA. A Data Safety Monitoring Plan has been created in accordance with the policies of the Institutional Review Board and the study funder, the National Heart, Lung and Blood Institute of the National Institutes of Health (NIH). The study will comply with NIH data sharing and dissemination policies. Results will be presented at national and international meetings and published in peer-reviewed journals. Designing and testing strategies to optimise haemoglobin recovery and improve functional outcomes after critical illness remain important research gaps. The PABST-BR trial will inform the development of a larger multicentre clinical trial. TRIAL REGISTRATION NUMBER: NCT05167734.

Transpulmonary pyruvate kinetics.

Shuttling of intermediary metabolites, such as pyruvate, contributes to the dynamic energy and biosynthetic needs of tissues. Tracer kinetic studies offer a powerful tool to measure the metabolism of substrates like pyruvate that are simultaneously taken up from and released into the circulation by organs. However, we understood that during each circulatory passage, the entire cardiac output transits the pulmonary circulation. Therefore, we examined the transpulmonary pyruvate kinetics in an anesthetized rat model during an unstimulated (Con), lactate clamp (LC), and epinephrine infusion (Epi) conditions using a primed-continuous infusion of [U-¹³C]pyruvate. Compared with Con and Epi stimulation, LC significantly increased mixed central venous ([v]) and arterial ([a]) pyruvate concentrations (P < 0.05). We hypothesized that the lungs, specifically the pulmonary capillary beds are sites of simultaneous production and removal of pyruvate and contributes significantly to whole body carbohydrate intermediary metabolism. Transpulmonary net pyruvate balances were positive during all three conditions, indicating net pyruvate uptake. Net balance was significantly greater during epinephrine stimulation compared with the unstimulated control (P < 0.05). Tracer-measured pyruvate fractional extraction averaged 42.8 ± 5.8% for all three conditions and was significantly higher during epinephrine stimulation (P < 0.05) than during either Con or LC conditions, that did not differ from each other. Pyruvate total release (tracer measured uptake - net balance) was significantly higher during epinephrine stimulation (400 ± 100 µg/min) vs. Con (30 ± 20 µg/min) (P < 0.05). These data are interpreted to mean that significant pyruvate extraction occurs during circulatory transport across lung parenchyma. The extent of pulmonary parenchymal pyruvate extraction predicts high expression of monocarboxylate (lactate/pyruvate) transporters (MCTs) in the tissue. Western blot analysis of whole lung homogenates detected three isoforms, MCT1, MCT2, and MCT4. We conclude that a major site of circulating pyruvate extraction resides with the lungs and that during times of elevated circulating lactate, pyruvate, or epinephrine stimulation, pyruvate extraction is increased.

Community built environment factors and mobility around senior wellness centers: the concept of "safe senior zones".

The authors investigated built environment (BE) factors in urban neighborhoods in DeKalb County, Georgia. Each volunteering, consenting senior was placed into one of two groups: walking tours outside, then discussions (n=37); and focus group discussions indoors about photographs of BE conditions potentially influencing mobility (n=43). The authors sought to identify BE factors-both real and perceived by participating seniors-related to their ability to walk around senior wellness centers in a healthy and safe manner. The authors focused specifically on available literature and pilot study data for their concept of "safe senior zones" around senior wellness centers serving urban communities in this article. They also characterized their study population regarding sociodemographic variables and doctor-diagnosed chronic diseases, and types of walking aids reported used to help prevent falls. Their results can inform future applied practice and research on traffic-related exposures and BE factors concerning seniors, and support policy and planning to benefit community environmental public health.

Higher unacylated ghrelin and insulin sensitivity following dietary restriction and weight loss in obese humans.

BACKGROUND & AIMS: Unacylated ghrelin (UnAG) modulates insulin sensitivity. Low plasma UnAG occurs in obesity and potentially contributes to obesity-associated insulin resistance. We hypothesized that improvements in insulin sensitivity in obese people induced by moderate caloric restriction (CR) may be paralleled and at least in part explained by concurrent increases in UnAG levels. METHODS: 20 general community obese people were randomly assigned to 16-week CR (n = 11) or control diet (n = 9). We investigated the impact of CR on the interaction between insulin sensitivity changes [area under the curve (AUCg) of glucose infusion to maintain euglycemia during hyperinsulinemic-euglycemic clamp] and plasma total (TotalG), acylated (AG) and Unacylated ghrelin (UnAG). Plasma pro-inflammatory tumor necrosis factor alpha (TNFα) and anti-inflammatory interleukin-10 (IL-10) were also measured since changes in inflammation may contribute to UnAG activities. RESULTS: CR reduced BMI and increased insulin sensitivity (p < 0.05). TotalG and UnAG but not AG increased in CR but not in Control (p < 0.05). Il-10 and IL-10/TNFα ratio also increased in CR (p < 0.05). Changes in UnAG were positively associated with changes in AUCg in all subjects (n = 20; p < 0.01) also after adjustment for treatment and changes in BMI and cytokines. CONCLUSIONS: Caloric restriction modifies circulating ghrelin profile with selective increase in unacylated hormone in obese individuals. The current study supports the hypothesis that higher unacylated ghrelin contributes to improvements in insulin sensitivity following diet-induced weight loss in human obesity.

Training improves the response in glucose flux to exercise in postmenopausal women.

We examined the effects of endurance training on parameters of glucose flux during rest and exercise in postmenopausal women. Ten sedentary, but healthy women (55 +/- 1 yr) completed 12 wk of endurance exercise training on a cycle ergometer [5 days/wk, 1 h/day, 65% peak oxygen consumption (Vo(2peak))]. Flux rates were determined by primed continuous infusion of [6,6-(2)H]glucose (D(2)-glucose) during 90 min of rest and 60 min of cycle ergometer exercise during one pretraining exercise trial [65% Vo(2peak) (PRE)] and two posttraining exercise trials [the power output that elicited 65% pretraining Vo(2peak) (ABT) and 65% posttraining Vo(2peak) (RLT)]. Training increased Vo(2peak) by 16.3 +/- 3.9% (P < 0.05). Epinephrine and glucagon were lower during ABT and lactate was lower during ABT and RLT (P < 0.05), but the apparent insulin response was unchanged. Whole body glucose rate of appearance decreased posttraining during exercise at a given power output (4.58 +/- 0.39 mg.kg(-1).min(-1) during ABT compared with 5.21 +/- 0.48 mg.kg(-1).min(-1) PRE, P < 0.05), but not at the same relative workload (5.85 +/- 0.36 mg.kg(-1).min(-1)). Training resulted in a 35% increase in glucose MCR during exercise at the same relative intensity (7.16 +/- 0.42 ml.kg(-1).min(-1) during RLT compared with 5.28 +/- 0.42 ml.kg(-1).min(-1) PRE, P < 0.05). Changes in parameters of glucose kinetics during exercise were accomplished without changes in dietary composition, body weight, or body composition. We conclude that despite changes in the hormonal milieu that occur at menopause, endurance training results in a similar magnitude in training-induced alterations of glucose flux as seen previously in younger women.

TFAM Enhances Fat Oxidation and Attenuates High-Fat Diet-Induced Insulin Resistance in Skeletal Muscle.

Diet-induced insulin resistance (IR) adversely affects human health and life span. We show that muscle-specific overexpression of human mitochondrial transcription factor A (TFAM) attenuates high-fat diet (HFD)-induced fat gain and IR in mice in conjunction with increased energy expenditure and reduced oxidative stress. These TFAM effects on muscle are shown to be exerted by molecular changes that are beyond its direct effect on mitochondrial DNA replication and transcription. TFAM augmented the muscle tricarboxylic acid cycle and citrate synthase facilitating energy expenditure. TFAM enhanced muscle glucose uptake despite increased fatty acid (FA) oxidation in concert with higher ß-oxidation capacity to reduce the accumulation of IR-related carnitines and ceramides. TFAM also increased pAMPK expression, explaining enhanced PGC1α and PPARß, and reversing HFD-induced GLUT4 and pAKT reductions. TFAM-induced mild uncoupling is shown to protect mitochondrial membrane potential against FA-induced uncontrolled depolarization. These coordinated changes conferred protection to TFAM mice against HFD-induced obesity and IR while reducing oxidative stress with potential translational opportunities.

Enhanced Protein Translation Underlies Improved Metabolic and Physical Adaptations to Different Exercise Training Modes in Young and Old Humans.

The molecular transducers of benefits from different exercise modalities remain incompletely defined. Here we report that 12 weeks of high-intensity aerobic interval (HIIT), resistance (RT), and combined exercise training enhanced insulin sensitivity and lean mass, but only HIIT and combined training improved aerobic capacity and skeletal muscle mitochondrial respiration. HIIT revealed a more robust increase in gene transcripts than other exercise modalities, particularly in older adults, although little overlap with corresponding individual protein abundance was noted. HIIT reversed many age-related differences in the proteome, particularly of mitochondrial proteins in concert with increased mitochondrial protein synthesis. Both RT and HIIT enhanced proteins involved in translational machinery irrespective of age. Only small changes of methylation of DNA promoter regions were observed. We provide evidence for predominant exercise regulation at the translational level, enhancing translational capacity and proteome abundance to explain phenotypic gains in muscle mitochondrial function and hypertrophy in all ages.

Mechanism by Which Caloric Restriction Improves Insulin Sensitivity in Sedentary Obese Adults.

Caloric restriction (CR) improves insulin sensitivity and reduces the incidence of diabetes in obese individuals. The underlying mechanisms whereby CR improves insulin sensitivity are not clear. We evaluated the effect of 16 weeks of CR on whole-body insulin sensitivity by pancreatic clamp before and after CR in 11 obese participants (BMI = 35 kg/m(2)) compared with 9 matched control subjects (BMI = 34 kg/m(2)). Compared with the control subjects, CR increased the glucose infusion rate needed to maintain euglycemia during hyperinsulinemia, indicating enhancement of peripheral insulin sensitivity. This improvement in insulin sensitivity was not accompanied by changes in skeletal muscle mitochondrial oxidative capacity or oxidant emissions, nor were there changes in skeletal muscle ceramide, diacylglycerol, or amino acid metabolite levels. However, CR lowered insulin-stimulated thioredoxin-interacting protein (TXNIP) levels and enhanced nonoxidative glucose disposal. These results support a role for TXNIP in mediating the improvement in peripheral insulin sensitivity after CR.

Hyperglucagonemia Mitigates the Effect of Metformin on Glucose Production in Prediabetes.

The therapeutic mechanism of metformin action remains incompletely understood. Whether metformin inhibits glucagon-stimulated endogenous glucose production (EGP), as in preclinical studies, is unclear in humans. To test this hypothesis, we studied nine prediabetic individuals using a randomized, placebo-controlled, double-blinded, crossover study design. Metformin increased glucose tolerance, insulin sensitivity, and plasma glucagon. Metformin did not alter average basal EGP, although individual variability in EGP correlated with plasma glucagon. Metformin increased basal EGP in individuals with severe hyperglucagonemia (>150 pg/ml). Decreased fasting glucose after metformin treatment appears to increase glucagon to stimulate EGP and prevent further declines in glucose. Similarly, intravenous glucagon infusion elevated plasma glucagon (>150 pg/ml) and stimulated a greater increase in EGP during metformin therapy. Metformin also counteracted the protein-catabolic effect of glucagon. Collectively, these data indicate that metformin does not inhibit glucagon-stimulated EGP, but hyperglucagonemia may decrease the ability of the metformin to lower EGP in prediabetic individuals.

Predictors of Whole-Body Insulin Sensitivity Across Ages and Adiposity in Adult Humans.

CONTEXT: Numerous factors are purported to influence insulin sensitivity including age, adiposity, mitochondrial function, and physical fitness. Univariate associations cannot address the complexity of insulin resistance or the interrelationship among potential determinants. OBJECTIVE: The objective of the study was to identify significant independent predictors of insulin sensitivity across a range of age and adiposity in humans. DESIGN, SETTING, AND PARTICIPANTS: Peripheral and hepatic insulin sensitivity were measured by two stage hyperinsulinemic-euglycemic clamps in 116 men and women (aged 19-78 y). Insulin-stimulated glucose disposal, the suppression of endogenous glucose production during hyperinsulinemia, and homeostatic model assessment of insulin resistance were tested for associations with 11 potential predictors. Abdominal subcutaneous fat, visceral fat (AFVISC), intrahepatic lipid, and intramyocellular lipid (IMCL) were quantified by magnetic resonance imaging and spectroscopy. Skeletal muscle mitochondrial respiratory capacity (state 3), coupling efficiency, and reactive oxygen species production were evaluated from muscle biopsies. Aerobic fitness was measured from whole-body maximum oxygen uptake (VO2 peak), and metabolic flexibility was determined using indirect calorimetry. RESULTS: Multiple regression analysis revealed that AFVISC (P < .0001) and intrahepatic lipid (P = .002) were independent negative predictors of peripheral insulin sensitivity, whereas VO2 peak (P = .0007) and IMCL (P = .023) were positive predictors. Mitochondrial capacity and efficiency were not independent determinants of peripheral insulin sensitivity. The suppression of endogenous glucose production during hyperinsulinemia model of hepatic insulin sensitivity revealed percentage fat (P < .0001) and AFVISC (P = .001) as significant negative predictors. Modeling homeostatic model assessment of insulin resistance identified AFVISC (P < .0001), VO2 peak (P = .001), and IMCL (P = .01) as independent predictors. CONCLUSION: The reduction in insulin sensitivity observed with aging is driven primarily by age-related changes in the content and distribution of adipose tissue and is independent of muscle mitochondrial function or chronological age.

Effects of Dietary n-3 Fatty Acids on Hepatic and Peripheral Insulin Sensitivity in Insulin-Resistant Humans.

OBJECTIVE: Dietary n-3 polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), prevent insulin resistance and stimulate mitochondrial biogenesis in rodents, but the findings of translational studies in humans are thus far ambiguous. The aim of this study was to evaluate the influence of EPA and DHA on insulin sensitivity, insulin secretion, and muscle mitochondrial function in insulin-resistant, nondiabetic humans using a robust study design and gold-standard measurements. RESEARCH DESIGN AND METHODS: Thirty-one insulin-resistant adults received 3.9 g/day EPA+DHA or placebo for 6 months in a randomized double-blind study. Hyperinsulinemic-euglycemic clamp with somatostatin was used to assess hepatic and peripheral insulin sensitivity. Postprandial glucose disposal and insulin secretion were measured after a meal. Measurements were performed at baseline and after 6 months of treatment. Abdominal fat distribution was evaluated by MRI. Muscle oxidative capacity was measured in isolated mitochondria using high-resolution respirometry and noninvasively by magnetic resonance spectroscopy. RESULTS: Compared with placebo, EPA+DHA did not alter peripheral insulin sensitivity, postprandial glucose disposal, or insulin secretion. Hepatic insulin sensitivity, determined from the suppression of endogenous glucose production by insulin, exhibited a small but significant improvement with EPA+DHA compared with placebo. Muscle mitochondrial function was unchanged by EPA+DHA or placebo. CONCLUSIONS: This study demonstrates that dietary EPA+DHA does not improve peripheral glucose disposal, insulin secretion, or skeletal muscle mitochondrial function in insulin-resistant nondiabetic humans. There was a modest improvement in hepatic insulin sensitivity with EPA+DHA, but this was not associated with any improvements in clinically meaningful outcomes.

Eicosapentaenoic acid but not docosahexaenoic acid restores skeletal muscle mitochondrial oxidative capacity in old mice.

Mitochondrial dysfunction is often observed in aging skeletal muscle and is implicated in age-related declines in physical function. Early evidence suggests that dietary omega-3 polyunsaturated fatty acids (n-3 PUFAs) improve mitochondrial function. Here, we show that 10 weeks of dietary eicosapentaenoic acid (EPA) supplementation partially attenuated the age-related decline in mitochondrial function in mice, but this effect was not observed with docosahexaenoic acid (DHA). The improvement in mitochondrial function with EPA occurred in the absence of any changes in mitochondrial abundance or biogenesis, which was evaluated from RNA sequencing, large-scale proteomics, and direct measurements of muscle mitochondrial protein synthesis rates. We find that EPA improves muscle protein quality, specifically by decreasing mitochondrial protein carbamylation, a post-translational modification that is driven by inflammation. These results demonstrate that EPA attenuated the age-related loss of mitochondrial function and improved mitochondrial protein quality through a mechanism that is likely linked with anti-inflammatory properties of n-3 PUFAs. Furthermore, we demonstrate that EPA and DHA exert some common biological effects (anticoagulation, anti-inflammatory, reduced FXR/RXR activation), but also exhibit many distinct biological effects, a finding that underscores the importance of evaluating the therapeutic potential of individual n-3 PUFAs.

Endogenous Nutritive Support after Traumatic Brain Injury: Peripheral Lactate Production for Glucose Supply via Gluconeogenesis.

We evaluated the hypothesis that nutritive needs of injured brains are supported by large and coordinated increases in lactate shuttling throughout the body. To that end, we used dual isotope tracer ([6,6-(2)H2]glucose, i.e., D2-glucose, and [3-(13)C]lactate) techniques involving central venous tracer infusion along with cerebral (arterial [art] and jugular bulb [JB]) blood sampling. Patients with traumatic brain injury (TBI) who had nonpenetrating head injuries (n=12, all male) were entered into the study after consent of patients' legal representatives. Written and informed consent was obtained from healthy controls (n=6, including one female). As in previous investigations, the cerebral metabolic rate (CMR) for glucose was suppressed after TBI. Near normal arterial glucose and lactate levels in patients studied 5.7±2.2 days (range of days 2-10) post-injury, however, belied a 71% increase in systemic lactate production, compared with control, that was largely cleared by greater (hepatic+renal) glucose production. After TBI, gluconeogenesis from lactate clearance accounted for 67.1% of glucose rate of appearance (Ra), which was compared with 15.2% in healthy controls. We conclude that elevations in blood glucose concentration after TBI result from a massive mobilization of lactate from corporeal glycogen reserves. This previously unrecognized mobilization of lactate subserves hepatic and renal gluconeogenesis. As such, a lactate shuttle mechanism indirectly makes substrate available for the body and its essential organs, including the brain, after trauma. In addition, when elevations in arterial lactate concentration occur after TBI, lactate shuttling may provide substrate directly to vital organs of the body, including the injured brain.