Lower Respiratory Exchange Ratio Research Articles

Effects of Partial Knockout of Skeletal Muscle Dynamin-Related Protein 1 on Skeletal Muscle Characteristics in Lean and Obese Mice

Dynamin-related protein 1 (Drp1) is a key regulator of mitochondrial fission and plays an essential role in maintaining skeletal muscle homeostasis. Recent studies reported muscle atrophy in mice when skeletal muscle Drp1 content was reduced. However, whether such atrophic phenotype also exists in diet-induced obese mice remains unknown. We recently reported that reducing skeletal muscle Drp1 resulted in improved whole-body glucose homeostasis and insulin sensitivity in diet-induced obese mice, but not lean healthy mice, suggesting Drp1 may exert divergent effects on physiological phenotypes under different conditions. OBJECTIVE: To determine the effects of partial knockout of skeletal muscle-specific heterozygous Drp1 (mDrp1+/−) on body composition, energy expenditure and skeletal muscle physiology in lean and obese mice. HYPOTHESIS: mDrp1+/− exhibits divergent alterations in physiological characteristics between lean healthy and obese mice. Methods: Tamoxifen-inducible mDrp1+/− mouse model was generated. Nine-week-old male and female mDrp1+/− and wildtype (WT) mice (n=6-8/group) were fed with either a high-fat diet (HFD) or low-fat diet (LFD) for four weeks, received tamoxifen injections, and remained on their respective diet for another four to six weeks. A DXA scan was conducted to measure body composition. Mice were housed in Promethion metabolic cages for 48 hours to measure energy expenditure. Isolated soleus (SOL) and extensor digitorum longus (EDL) muscles were used for assessing muscle cross sectional area (CSA) and contractility. Results: HFD-fed mice had significantly higher percentage of body fat ( p = 0.045) and lower respiratory exchange ratio ( p <0.0001) than LFD-fed mice, regardless of genotype. Regarding skeletal muscle characteristics, SOL from mDrp1+/− mice exhibited larger CSA ( p = 0.052) than WT mice, regardless of diet. However, there were no differences in muscle force or fatigue resistance in SOL between groups. In contrast, EDL muscle isolated from mDrp1+/− mice fed with HFD had greater muscle force than WT mice, but interestingly the force was lower in mDrp1+/−/LFD mice than WT/LFD mice (genotype x diet interaction effect, p = 0.001). Consistently, a significant interaction was found in both twitch and tetanic rate of force development and relaxation rates (genotype x diet interaction effect, p = 0.022, p = 0.033, p = 0.040, and p = 0.020, respectively). There was no difference in EDL muscle CSA between groups. CONCLUSION: Our data suggests that partial knockout of Drp1 in skeletal muscle induced divergent effects on CSA, force production and fatigability between diet induced obese and lean healthy mice. This study was supported by the National Institute of Health (R15DK131512). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of three-week intake of Matcha green tea powder on heart rate variability metrics

Introduction: Compared to other green teas, higher intake of multiple phytochemicals is achieved with Matcha green tea consumption. Green tea consumption is known to have metabolic effects but is also consumed for supposed calming effects. The aim of the present study was to examine the effects of encapsulated Matcha green tea on heart rate variability metrics during supine rest, as well as on physiological and metabolic responses during both supine rest and moderate-intensity exercise. Methods: Healthy females (n=8, age: 22±3 yrs, body mass: 68±11 kg, height: 162±5 cm) volunteered. The study employed a placebo-controlled, randomised cross-over design. Time-domain heart rate variability metrics during supine rest (n=5) and physiological and metabolic responses using indirect calorimetry techniques during supine rest and 60-min of moderate-intensity (~ 4-METs) treadmill walking (speed: 4.4±0.5 km·h-1) were measured following 3 weeks of 3 g·day-1 of Matcha green tea or placebo. Results: During supine rest with Matcha green tea, all participants had lower heart rates by 13±7% (P=0.01, d= -1.45), higher mean beat-to-beat RR intervals by 16±9% (P=0.03, d=1.25), higher SDNN by 44±32% (P=0.01, d=0.76) and higher pNN50 by 139±139% (P<0.01, d=1.28). Matcha green tea had no effects on the physiological and metabolic responses during supine rest and moderate-intensity treadmill walking (e.g. respiratory exchange ratio, placebo: 0.78±0.04; Matcha: 0.78±0.03, P=0.87). Fat oxidation during supine rest was correlated (r=0.75, P<0.01) with the moderate-intensity walking induced fat oxidation. Conclusions: In young adult healthy females, Matcha green tea beneficially effects heart rate variability metrics during supine rest indicating an alteration in parasympathetic nervous activity and therefore suggestive of a relaxing effect. Matcha green tea did not change the metabolic responses during supine rest and exercise possibly due to the low respiratory exchange ratio in the female cohort. Future work should address the effectiveness of Matcha green tea during conditions of psychological stress.Keywords: Matcha green tea, heart rate variability, rest, walking, substrate oxidation

Effects of the Timing of Carbohydrate Intake on Metabolism and Performance in Soccer Players.

This study aims to provide information to improve the performance of athletes comparing the effects of carbohydrate-electrolyte intake before and during exercise on metabolism and performance in soccer players. The study had a single-blind cross-over design. Drust's protocol is a soccer-specific intermittent exercise test. The carbohydrate-electrolyte intake experiments were divided into three timings: first, pre-exercise; second, half-time; and third, mixed. Eight participants were included in the data analysis (age: 21.32 ± 1.19 years; BMI: 22.69 ± 1.91 kg/m2; height: 176.5 ± 7.52 cm; weight: 69.5 ± 9.18 kg; Vmax: 16.75 0.71 km/h). The results of the mixed test showed a significantly lower respiratory exchange ratio than those of the placebo and half-time tests (p < 0.05). The mixed test showed significantly more fat oxidation than the half-time test (p < 0.05). The running times are placebo (422.13 ± 133.44 s) and mixed (677.38 ± 217.75 s), and the distances are placebo (1577.25 ± 517.02 m) and mixed (2530.00 ± 832.71 m) (p < 0.05). The mixed test showed a significantly lower rating of perceived exertion than the placebo test (p < 0.05). Carbohydrate oxidation and heart rate showed no significant differences between the experiments (p > 0.05). The exercise protocol in this study showed the metabolic response of soccer players to intermittent high-intensity exercise and subsequent endurance exercise. In conclusion, it can be seen that the intake of carbohydrate-electrolytes improves the performance of soccer players, and the effect varies depending on the timing of carbohydrate-electrolyte intake.

The impact of natural menstrual cycle and oral contraceptive pill phase on substrate oxidation during rest and acute submaximal aerobic exercise.

Previous research has identified sex differences in substrate oxidation during submaximal aerobic exercise including a lower respiratory exchange ratio (RER) in females compared with males. These differences may be related to differences in sex hormones. Our purpose was to examine the impact of the natural menstrual cycle (NAT) and second- and third-generation oral contraceptive pill (OCP2 and OCP3) cycle phases on substrate oxidation during rest and submaximal aerobic exercise. Fifty female participants (18 NAT, 17 OCP2, and 15 OCP3) performed two experimental trials that coincided with the low (i.e., nonactive pill/early follicular) and the high hormone (i.e., active pill/midluteal) phase of their cycle. RER and carbohydrate and lipid oxidation rates were determined from gas exchange measurements performed during 10 min of supine rest, 5 min of seated rest, and two 8-min bouts of submaximal cycling exercise at ∼40% and ∼65% of peak oxygen uptake (V̇o2peak). For all groups, there were no differences in RER between the low and high hormone phases during supine rest (0.73 ± 0.05 vs. 0.74 ± 0.05), seated rest (0.72 ± 0.04 vs. 0.72 ± 0.04), exercise at 40% (0.77 ± 0.04 vs. 0.78 ± 0.04), and 65% V̇o2peak (0.85 ± 0.04 vs. 0.86 ± 0.03; P > 0.19 for all). Similarly, carbohydrate and lipid oxidation rates remained largely unchanged across phases during both rest and exercise, apart from higher carbohydrate oxidation in NAT vs. OCP2 at 40% V̇o2peak (P = 0.019) and 65% V̇o2peak (P = 0.001). NAT and OCPs do not appear to largely influence substrate oxidation at rest and during acute submaximal aerobic exercise.NEW & NOTEWORTHY This study was the first to examine the influence of NAT and two generations of OCPs on substrate oxidation during rest and acute submaximal aerobic exercise. We reported no differences across cycle phases or groups on RER, and minimal impact on carbohydrate or lipid oxidation apart from an increase in carbohydrate oxidation in NAT compared with OCP2 during exercise. Based on these findings, NAT/OCP phase controls may not be necessary in studies investigating substrate oxidation.

331-OR: Fasting Metabolic Flexibility in Prediabetes

Metabolic flexibility cannot be easily clinically assessed, but the respiratory exchange ratio (RER) measured via indirect calorimetry can indicate substrate utilization. When indirect calorimetry is performed to measure resting metabolic rate, a normal RER should reflect a lipolytic metabolism (close to 0.7). We aimed to describe fasting glucose metabolism in relation to RER in patients seeking a nutritional intervention. In 10175 patients (7,222 (71%) females, median (quartiles) age of 46 (36, 55) years, and BMI of 28.3 (25.0, 32.3) kg/m2) a greater RER was associated with higher fasting values of glucose, insulin and higher insulin resistance (HOMA-IR), controlling for sex, age, and BMI (differences going from a RER of 0.7 to 1 RER for glucose 1.7 (95% CI 0.66, 2.8; p=0.002), for insulin 1.9 (95% CI 1.3, 2.6; p=&amp;lt;0.001), and for HOMA-IR 0.49 (95% CI 0.32, 0.66; p=&amp;lt;0.001)). As an higher RER relates to an altered glucose metabolism, within the whole sample we selected patients with prediabetes with 1 year follow-up. We matched 86 patients having either a RER indicating a lipolytic metabolism (&amp;lt;0.775) or glycolytic metabolism (&amp;gt;0.925). Patients were matched for sex, age, BMI, waist circumference, and arm muscle area. The high RER group had a lower probability of normalizing fasting glucose level within 1 year (log(OR) -0.89 (95% CI -1.8, -0.03; p=0.046)), with higher fasting glucose levels at followup (5.4 (95% CI 0.98, 9.9; p=0.017)). Moreover, while losing similar weight than the low RER group (-0.55 (95% CI -3.7, 2.6; p=0.7)), they lost a lower amount of fat mass (1.2 (95% CI 0.02, 2.4; p=0.047)). Our results suggest than an higher RER relates to a dysfunctional glycolytic metabolism at rest. We also show that prediabetic patients with higher RER are more likely to not respond to a lifestyle intervention, warranting a more intensive treatment for this subgroup. This lower probability of success doesn’t seem related to a lower adherence to the proscription, as weight loss was similar across RER categories, but to a lower weight loss quality. Disclosure A.Foppiani: None. R.De amicis: None. A.Leone: None. S.Bertoli: None. A.Battezzati: None. Funding Italian National Recovery and Resilience Plan Mission 4 Component 2 Investment 1.3 - Call for Proposals (341) of 15 March 2022 of Italian Ministry of University and Research funded by the European Union - NextGenerationEU (PE00000003) Concession Decree (1550) of 11 October 2022 adopted by the Italian Ministry of University and Research (CUP D93C22000890001)

Abstract 592: Marfan Syndrome Mice Fed On High Fat Diet Have An Altered Metabolism

Introduction: Marfan syndrome (MFS) is a genetic disorder, caused by different mutations in the fibrillin-1 gene ( FBN1 ) and affects the connective tissue. Patients suffer from a wide range of clinical symptoms at the cardiovascular, skeletal and ocular level. However, MFS patients are also often characterized as very slender. Body weight gain in these patients can be a challenge, and the reason for this is still not fully understood. Objective: To determine if individuals with MFS have an altered metabolism. Methods: 9-11 weeks old male Fbn1 C1041G/+ (MFS) mice and wild-type littermates were given either a chow, high cholesterol diet (HCD) or a high fat diet (HFD), for 12 weeks. These mice were then housed individually in a metabolic cage for 1 week before euthanasia was performed. Results: HFD resulted in higher body weights compared to chow diet, and the HFD groups became insulin resistant as measured by the intraperitoneal glucose tolerance test. However, body weight gain was not different in this MFS mouse model, as compared to WT mice, regardless of diet. The HFD groups had increased fat weight compared to chow groups. Interestingly, MFS mice had an enhanced heart weight compared to WT mice, independent of the diet. As expected, aortic root diameters were enlarged in MFS compared to WT mice. However, in the ascending aorta there was a significant increase in diameter in the WT HFD as compared to WT chow, indicating that enhanced lipid levels promote aortic growth. Metabolic cage data showed that the HFD groups had a lower respiratory exchange ratio (RER), indicating that HFD groups used fat as a predominant source of fuel and that chow groups used primarily carbohydrates as an energy source. MFS mice had overall lower RER compared to WT mice, revealing that MFS mice use more lipids under any condition, most likely to manage the significantly elevated activity in the MFS mice. Conclusion: Taken together, MFS mice seem metabolically different.

Voluntary wheel running and lithium supplementation promotes fatigue resistance, fat oxidation, and improves insulin tolerance in D2 mdx mice

BACKGROUND: Duchenne muscular dystrophy (DMD) is an X-linked disorder characterized by progressive muscle wasting and premature death. Many DMD patients will also exhibit signs of metabolic dysfunction such as insulin resistance that predisposes them to type 2 diabetes and worsened cardiovascular disease. Most treatments for DMD aim to lower muscle inflammation and improve strength, however, none have addressed the complication of insulin resistance. The current standard of treatment is corticosteroids, which prolongs ambulation, however, chronic use increases susceptibility to obesity, insulin resistance, and type 2 diabetes. It is well-established that regular aerobic exercise enhances insulin sensitivity. Further, we have recently found that inhibiting glycogen synthase kinase 3 with lithium (Li), a known insulin mimetic, improves force production and fatigue resistance in wildtype (WT) mice. Here, we tested whether voluntary wheel running (VWR) and Li supplementation, together, could improve whole-body fatigue, metabolism, and insulin sensitivity in the DBA/2J (D2) mdx mouse model of DMD. METHODS: 5-week old male D2 WT and mdx mice were separated into four groups: WT, mdx sedentary (SED), mdx VWR, and mdx Li+VWR (n=11/group). The mdx VWR and mdx Li+VWR mice had unlimited access to a cagewheel, and mdx Li+VWR mice were given a low dose of Li (50 mg/kg/day) via their drinking water throughout the study. A treadmill time-to-fatigue test was performed to assess whole-body fatigue. Mice were housed for 48-hours in metabolic cages to measure energy expenditure. Glucose handling was measured using glucose and insulin tolerance tests. RESULTS: As expected, WT mice had ~2-fold greater total cage activity compared to all mdx groups. When examining cagewheel distance, we found that mdx Li+VWR mice ran half the total distance in kilometres than mdx VWR mice (39.1 ± 9.6 km vs. 74.8 ± 13.6 km). Despite this, VWR with and without Li improved whole-body fatigue as only mdx SED mice (22.8 ± 0.9 min) had a shorter time to exhaustion than WT mice (32.6 ± 0.9 min). All mdx groups had higher energy expenditure than WT mice, suggestive of a hypermetabolic phenotype. When examining the respiratory exchange ratio (RER) among mdx mice, mdxLi+VWR (0.87) mice had a lower RER than mdx SED mice (0.91), indicative of enhanced fat oxidation. Glucose tolerance was equally impaired among mdx groups compared to WT mice. However, insulin tolerance was notably improved in mdx VWR and mdx Li+VWR mice, with a greater improvement observed in the mdx Li+VWR mice. CONCLUSION: Despite running less than mdx VWR mice, mdx Li+VWR mice had enhanced fatigue resistance, fat utilization, and insulin sensitivity, suggesting Li may be a viable treatment to improve muscle and metabolic function in mdx mice. CIHR CRC (Tier II) to VAF This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Investigating the effects of thermoneutral housing on skeletal and cardiac muscle function in D2 mdx mice

Since its discovery, the mdx mouse has been the foundation for research on Duchenne muscular dystrophy (DMD) and its potential therapies. Although, nearly all studies using mdx mice as an experimental model have been conducted under “standard” lab conditions using room (22C) instead of thermoneutral (TN, 30C) temperature housing. Room temperature (RT) is a mild cold stress to mice, causing metabolic adaptations that can confound experimental results, limiting their interpretation and translation to humans. This study investigated the effects of housing temperature on whole-body metabolism and skeletal and cardiac muscle function in the mdx mouse. To this end, 20 D2 mdx mice (age 5 weeks, n = 10 per group) were housed at RT and TN for 10 weeks. Metabolic cage analysis demonstrated that TN housed mdx mice displayed significantly decreased VO2 consumption and reduced food intake that was likely due to lowered daily energy expenditure. TN housed mice also had significantly lower respiratory exchange ratio values, indicative of increased fat metabolism. However, there were no differences in body mass or composition (i.e., % lean and fat mass). Treadmill-to-fatigue experiments revealed no differences in exercise performance. Furthermore, ex vivo muscle contractility analysis displayed no differences in extensor digitorum longus or soleus specific force generation between TN and RT housed mice. Analysis of cardiac structure/function demonstrated that TN housed mdx mice exhibited a reduction in cardiac output, which we attributed to diastolic dysfunction. While ejection fraction and fractional shortening were not different among the two groups, TN housing led to a significant reduction in end diastolic volume (EDV) and left ventricle internal diameter (diastole, LVID;d), as well as increased relative wall thickness (diastole, RWT;d) compared to RT housed mice. Though isovolumic relaxation time was prolonged in TN-housed mice, this did not reach statistical significance. Taken together, our results demonstrate that TN housing had minimal effects on skeletal muscle contractility, but did lead to signs of diastolic dysfunction in young mdx mice. Future studies will examine the effects of TN housing in aged mdx mice, when systolic dysfunction occurs, as well as any influence of TN housing on the efficacy of potential muscle wasting therapeutics. Overall, our results support the growing literature that highlights the importance of selecting the appropriate housing temperature when studying metabolism or muscle wasting conditions in mice. NSERC This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sex-specific effects of CD248 on metabolism and the adipose tissue lipidome.

Cd248 has recently been associated with adipose tissue physiology, demonstrated by reduced weight gain in high fat diet-fed mice with genetic deletion of Cd248 relative to controls. Here we set out to determine the metabolic consequences of loss of Cd248. Strikingly, we find these to be sex specific; By subjecting Cd248-/- and Cd248+/+ mice to a high fat diet and indirect calorimetry study, we identified that only male Cd248-/- mice show reduced weight gain compared to littermate control wildtype mice. In addition, male (but not female) mice showed a lower respiratory exchange ratio on both chow and high fat diets, indicating a predisposition to metabolise lipid. Lipidomic studies on specific fat depots found reduced triglyceride and diglyceride deposition in male Cd248-/- mice, and this was supported by reduced expression of lipogenic and adipogenic genes. Finally, metabolomic analysis of isolated, differentiated preadipocytes found alterations in metabolic pathways associated with lipid deposition in cells isolated from male, but not female, Cd248-/- mice. Overall, our results highlight the importance of sex controls in animal studies and point to a role for Cd248 in sex- and depot-specific regulation of lipid metabolism.

Diagnostic usefulness of spiroergometry and risk factors of long -COVID in patients with normal left ventricular ejection fraction

Abstract Background Recent evidence has shown that patients with acute SARS-CoV-2 infection might present symptoms of infection a long time after a recovery. Purpose To investigate the risk factors and assess the utility of spiroergometry parameters in differential diagnosing patients presenting the symptoms (dyspnea, fatique, pain in chest, muscle pain, cognitive impairment, taste and smell disturbances) persisting for a few months after recovery from COVID 19 (symptoms of long COVID). Methods and results The 146 patients (pts) with normal left ventricular ejection fraction and without respiratory diseases, hospitalised in Cardiology Department recovering from COVID-19 at three to six months after confirmed diagnosis were included. The clinical examination, laboratory results, echocardiography using Vivid E95–GE Healthcare, non-invasive body mass analysis using Body Composition Analyzer (Tanita Pro), spiroergometry using The MetaSoft® Studio application were analyzed. The subjects were divided into the two following groups: group demonstrating long COVID symptoms (i.e. suffering from one of the following dyspnea, fatique, pain in chest, muscle pain, cognitive impairment, taste or smell disturbances) [N=44 pts] and the group without long COVID symptoms [N=102 pts]. Pts with long COVID symptoms presented significantly higher age (58 versus [vs] 44 years; p&amp;lt;0.0001), higher metabolic age (53 vs 45 years; p=0.01), higher left atrial diameter (37 vs 35 mm; p=0.04), higher left ventricular mass index (LVMI) (83 vs 74 g/m2, p=0.03), higher E/E' (7.3 vs 6; p&amp;lt;0.001) compared to control group. In CPET long COVID pts presented lower forced vital capacity (FVC) (3.6 vs 4.3 L; p=0.009), lower maximal oxygen consumption measured during incremental exercise indexed per kilogram (VO2max) (21 vs 23 ml/min/kg; p=0.04), lower respiratory exchange ratio (RER) (1.0 vs 1.1; p=0.04); lower forced expiratory volume in one second (FEV1) (2.9 vs 3.25 L; p=0,03); higher ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC) (106 vs 100%; p=0.0002) – Figure 1, there were no significant changes in electrocardiogram between groups. The laboratory results pointed that pts with long COVID symptoms had also lower rate of red blood cells (RBC) (4,4 vs 4,6 mln; p=0.01); higher level of glucose (92 vs 90 mg%; p=0.02); lower glomerular filtration rate (GFR) estimate by Modification of Diet in Renal Disease (MDRD) (88 vs 95; p=0.02); higher level of hypersensitive cardiac Troponin T (hsTnT) (6.1 vs 3.9 ng/L; p=0.03). The parameters significant in univariate analyses were included to the multivariate model. The results of multiple logistic regression were as follows: age (OR 4.6, 95% CI: 1.7–11.5; p=0.001) and LVMI (OR 2.5, 95% CI: 1.0–6.6; p=0.04). Conclusions Persistent symptoms in long COVID can mimic those of cardiovascular disease. Spiroergometric parameters are useful in making a proper diagnosis. Funding Acknowledgement Type of funding sources: Public hospital(s). Main funding source(s): Polish Mother's Memorial Hospital Research Institute

Energy Expenditure and Substrate Utilization with Hands-Free Crutches Compared to Conventional Lower-Extremity Injury Mobility Devices.

A Hands-Free crutch (HFC) is a relatively new device that can be used during the nonweightbearing period to increase mobility. The primary aim of this investigation was to examine aerobic oxygen consumption (V.o2) and substrate utilization with HFC compared to conventional ambulation devices as well as normal ambulation. A secondary purpose was to quantify perceived exertion, pain, and performance during each ambulation condition. Forty participants completed 4 separate 10-minute ambulation conditions around a rectangular course. The order of the ambulation conditions was randomized and consisted of (1) walking, (2) medical knee scooter (MKS), (3) HFC, and (4) axillary crutch (AC). Indirect calorimetry was used to determine V.o2 and the respiratory exchange ratio (RER), an indicator of substrate utilization. Perceived exertion and pain were also assessed using questionnaires. All mobility devices significantly elevated V.o2 (+35%) compared to walking (13.14 ± 1.70 mL/kg/min; P < .001). AC had significantly greater V.o2 requirements (20.26 ± 2.62 mL/kg/min) compared to both the MKS (15.28 ± 2.29 mL/kg/min; P < .001) and HFC (15.88 ± 2.03 mL/kg/min; P < .001). There was no difference in average V.o2 between MKS and HFC (P = .368). Compared to walking (0.78 ± 0.43), RER was significantly elevated in MKS (0.81 ± 0.05, P < .001) and AC (0.84 ± 0.06, P < .001), but not in HFC (0.79 ± 0.04, P = .350). RPE and pain were elevated in all ambulatory conditions (all P values <.001). Pain was significantly greater in AC compared with MKS (P < .001) and HFC (P < .001). HFC and MKS share similar V.o2 requirements over a 10-minute ambulation interval and are below those needed in AC. Substrate utilization in HFC was similar to regular walking with a greater reliance on lipid utilization for energy as evidenced by a lower RER. Exertion and pain scores were the most tolerable in HFC and MKS. Level II, prospective comparative study.

Metabolic Impact of MKP-2 Upregulation in Obesity Promotes Insulin Resistance and Fatty Liver Disease.

The mechanisms connecting obesity with type 2 diabetes, insulin resistance, nonalcoholic fatty liver disease, and cardiovascular diseases remain incompletely understood. The function of MAPK phosphatase-2 (MKP-2), a type 1 dual-specific phosphatase (DUSP) in whole-body metabolism, and how this contributes to the development of diet-induced obesity, type 2 diabetes (T2D), and insulin resistance is largely unknown. We investigated the physiological contribution of MKP-2 in whole-body metabolism and whether MKP-2 is altered in obesity and human fatty liver disease using MKP-2 knockout mice models and human liver tissue derived from fatty liver disease patients. We demonstrate that, for the first time, MKP-2 expression was upregulated in liver tissue in humans with obesity and fatty liver disease and in insulin-responsive tissues in mice with obesity. MKP-2-deficient mice have enhanced p38 MAPK, JNK, and ERK activities in insulin-responsive tissues compared with wild-type mice. MKP-2 deficiency in mice protects against diet-induced obesity and hepatic steatosis and was accompanied by improved glucose homeostasis and insulin sensitivity. Mkp-2−/− mice are resistant to diet-induced obesity owing to reduced food intake and associated lower respiratory exchange ratio. This was associated with enhanced circulating insulin-like growth factor-1 (IGF-1) and stromal cell-derived factor 1 (SDF-1) levels in Mkp-2−/− mice. PTEN, a negative regulator of Akt, was downregulated in livers of Mkp-2−/− mice, resulting in enhanced Akt activity consistent with increased insulin sensitivity. These studies identify a novel role for MKP-2 in the regulation of systemic metabolism and pathophysiology of obesity-induced insulin resistance and fatty liver disease.

Silk Hydrogel-Mediated Delivery of Bone Morphogenetic Protein 7 Directly to Subcutaneous White Adipose Tissue Increases Browning and Energy Expenditure.

Objective: Increasing the mass and/or activity of brown adipose tissue (BAT) is one promising avenue for treating obesity and related metabolic conditions, given that BAT has a high potential for energy expenditure and is capable of improving glucose and lipid homeostasis. BAT occurs either in discrete “classical” depots, or interspersed in white adipose tissue (WAT), termed “inducible/recruitable” BAT, or ‘beige/brite’ adipocytes. We and others have demonstrated that bone morphogenetic protein 7 (BMP7) induces brown adipogenesis in committed and uncommitted progenitor cells, resulting in increased energy expenditure and reduced weight gain in mice. BMP7 is therefore a reliable growth factor to induce browning of WAT. Methods: In this study, we sought to deliver BMP7 specifically to subcutaneous (sc)WAT in order to induce tissue-resident progenitor cells to differentiate into energy-expending recruitable brown adipocytes, without off-target effects like bone formation, which can occur when BMPs are in the presence of bone progenitor cells (outside of WAT). BMP7 delivery directly to WAT may also promote tissue innervation, or directly activate mitochondrial activity in brown adipocytes, as we have demonstrated previously. We utilized silk protein in the form of an injectable hydrogel carrying BMP7. Silk scaffolds are useful for in vivo delivery of substances due to favorable material properties, including controlled release of therapeutic proteins in an active form, biocompatibility with minimal immunogenic response, and prior FDA approval for some medical materials. For this study, the silk was engineered to meet desirable release kinetics for BMP7 in order to mimic our prior in vitro brown adipocyte differentiation studies. Fluorescently-labeled silk hydrogel loaded with BMP7 was directly injected into WAT through the skin and monitored by non-invasive in vivo whole body imaging, including in UCP1-luciferase reporter mice, thereby enabling an approach that is translatable to humans. Results: Injection of the BMP7-loaded silk hydrogels into the subcutaneous WAT of mice resulted in “browning”, including the development of multilocular, uncoupling protein 1 (UCP1)-positive brown adipocytes, and an increase in whole-body energy expenditure and skin temperature. In diet-induced obese mice, BMP7-loaded silk delivery to subcutaneous WAT resulted in less weight gain, reduced circulating glucose and lower respiratory exchange ratio (RER). Conclusions: In summary, BMP7 delivery via silk scaffolds directly into scWAT is a novel translational approach to increase browning and energy expenditure, and represents a potential therapeutic avenue for delivering substances directly to adipose depots in pursuit of metabolic treatments.

Chronic High Phosphate Intake in Mice Affects Macronutrient Utilization and Body Composition.

In the last decades, dietary phosphate intake has increased due to a higher consumption of ultraprocessed food. This higher intake has an impact on body composition and health state. Recently, this study finds that a high chronic phosphate diet leads to no major renal alterations, but negatively affects parameters of bone health probably due to the chronic acid load. Here the effect of high phosphate consumption on parameters of energy metabolism is assessed. Healthy mature adult mice are fed for 1 year or 4 months with either a standard (0.6 % w/w) or a high phosphate (1.2 % w/w) diet. Males and females of two different genetic backgrounds are investigated. Mice feed the high phosphate diet show an attenuated body-weight gain, lower respiratory exchange ratio, decreased body fat mass, and increased lean-to-fat mass ratio. Moreover, the high phosphate diet leads to fasting hypoglycemia with no differences in the glucose response to an oral glucose tolerance test. Triglycerides and cholesterol in blood are similar independently of dietary phosphate content. However, 1-methylhistidine is lower in animals feed a chronic high phosphate intake. High phosphate diet attenuates body weight gain, but induces hypoglycemia and may alter muscle homeostasis.

Surya Namaskar: As an Alternative for Aerobic Fitness.

"Surya Namaskar" (SN) may be used as a need-based short-duration aerobic activity in a confined space to establish as a substitute of an equivalent routine physical training in challenging stressful conditions. Noninvasive oxygen-kinetics metabolic responses between SN and endurance work on bicycle ergometry (BE) were compared across different phases of maximal oxygen uptake percentage (%VO2 max). SN, comprising three complete rounds per min (36 beats/min of a metronome; SN consists of 12 poses per round), was performed rhythmically and continuously for 5 min to simulate an incremental BE test (25 watts/2 min at 60 rpm). SN results in a significant (P < 0.05) greater increase of arteriovenous oxygen difference at 71%-80% VO2 max while keeping a low respiratory exchange ratio (P < 0.01 and 0.001) at 41%-80% VO2 max exercising state. SN could be an ideal form of aerobic exercise instead of BE.

Chemerin regulates formation and function of brown adipose tissue: Ablation results in increased insulin resistance with high fat challenge and aging.

Apart from its role in inflammation and immunity, chemerin is also involved in white adipocyte biology. To study the role of chemerin in adipocyte metabolism, we examined the function of chemerin in brown adipose tissue. Brown and white adipocyte precursors were differentiated into adipocytes in the presence of Chemerin siRNA. Chemerin-deficient (Chem-/- ) mice were compared to wild-type mice when fed a high-fat diet. Chemerin is expressed during brown adipocyte differentiation and knock down of chemerin mRNA results in decreased brown adipocyte differentiation with reduced fatty acid uptake in brown adipocytes. Chem-/- mice are leaner than wild-type mice but gain more weight when challenged with high-fat diet feeding, resulting in a larger increase in fat deposition. Chem-/- mice develop insulin resistance when on a high-fat diet or due to age. Brown adipose depots in Chem-/- mice weigh more than in wild-type mice, but with decreased mitochondrial content and function. Compared to wild-type mice, male Chem-/- mice have decreased oxygen consumption, CO2 production, energy expenditure, and a lower respiratory exchange ratio. Additionally, body temperature of Chem-/- mice is lower than that of wild-type mice. These results revealed that chemerin is expressed during brown adipocyte differentiation and has a pivotal role in energy metabolism through brown adipose tissue thermogenesis.

High-Fat Diet Accelerates Pathological Progression and Intestinal Inflammation in a Type 2 Diabetes Rodent Model

Insulin signaling lowers postprandial glucose by stimulating cell surface translocation of the insulin sensitive glucose transporter 4 (GLUT4). In order to better understand how insulin resistance contributes to the pathophysiological progression of type 2 diabetes, we generated human GLUT4 promoter-driven insulin receptor knockout (GIRKO) mice and characterized their metabolic features relative to control mice. Although the role of insulin resistance in diabetes is beyond dispute, our previous studies showed that GIRKO mice fed normal chow diet (NCD) had an unexpectedly low rate of frank diabetes despite severe insulin resistance in muscle, fat, and brain.In the current study, we first sought to determine whether GIRKO mice would respond to high-fat diet (HFD) challenge with worsened glycemic outcome compared to control mice on HFD. Secondly, we sought to determine whether HFD-induced pathologies in GIRKO mice were caused by adaptations in the gastrointestinal (GI) tract and microbiome. We discovered that after beginning the HFD-feeding regimen, GIRKO mice rapidly developed hyperinsulinemia and hyperglycemia without excessive adiposity gain. Furthermore, GIRKO mice displayed dyslipidemia via increased hepatic lipid accumulation and serum lipid content. We used indirect calorimetry to characterize the metabolic features of single-housed mice. HFD-fed GIRKO mice had comparatively lower respiratory exchange ratio (RER), indicating relatively greater lipid metabolism compared to control mice on HFD. Despite having increased circulating incretins, GIRKO mice had impaired oral glucose tolerance and limited glucose-lowering benefit from Exendin-4 (Ex-4) injections. Since HFD promotes inflammation in the gastrointestinal (GI) tract, we performed gene expression analysis and pathway analysis of duodenal mRNAs to investigate whether inflammatory response, glucose transport, and lipid transport were altered in HFD-fed GIRKO mice. Among the top pathways discovered in pathway analysis were those involved with inflammatory signaling, carbohydrate transport, and xenobiotic metabolism, which supports that HFD-fed GIRKO mice have increased GI tract inflammation which may promote impaired glucose homeostasis.In conclusion, our studies suggest that HFD increased intestinal inflammation and exacerbated insulin resistance, which catalyzed the pathological progression of diabetes. Future studies are necessary to identify the molecular and cellular signaling pathways which culminate in frank diabetes, which may lead to therapeutic targets for regulating glucose homeostasis in the context of insulin resistance.

Lrg1 is a Driver of Brown Adipose Tissue Dysfunction in Obesity

Background Energy is stored as lipid within white adipose tissue (WAT) however, over-nutrition can lead to excess WAT, obesity and metabolic disease. Brown adipose tissue (BAT) has a primary role in energy expenditure through futile cycling of the electron transport chain (ETC) to generate heat. BATs heat producing capacity may be a novel approach to treating obesity. Adult humans possess metabolically active BAT, but the onset of obesity can reduce BAT thermogenic activity and mass. Obesity can bring about morphological changes to BAT, causing BAT to resemble WAT in a process termed “whitening”. WAT is a well-known endocrine organ. Specific endocrine signals from WAT could be responsible for reduced BAT activity in obesity. Leucine-rich-α2-glycoprotein 1 (LRG1) is an adipose-associated secretory protein and potential adipokine, with plasma levels positively correlated to body mass index in humans. Hypothesis It is hypothesized that LRG1 is an adipokine which negatively regulates thermogenesis in BAT and contributes to obesity related loss of BAT. Methods Male Lrg1 global knockout (KO) mice or wild type (WT) controls were fed standard chow (STD) or high fat diet (HFD) for 10 weeks. At 18 weeks of age systemic and BAT metabolic characteristics were determined by whole body indirect calorimetry, high-resolution tissue respirometry, quantitative PCR and immunoblots. Results After 10 weeks of HFD feeding Lrg1 KO mice fed STD and HFD had significantly higher percentage of body mass comprised of BAT than WT controls (Figure 1A). Lrg1 KO mice fed HFD had a lower respiratory exchange ratio (RER), indicating a greater use of fat oxidation compared to WT controls (Figure 1B). Mitochondrial respiration was used to measure changes in cellular energy. In response to HFD WT mice exhibit a decrease in mitochondrial respiration through complex 1 of the electron transport chain (ETC) (Figure 2A). The mitochondrial function of Lrg1 KO mice BAT is protected from HFD-induced dysfunction at Complex 1 of the ETC (Figure 2A). Uncoupling protein 1 (UCP1), a key protein involved in thermogenesis, Ucp1 mRNA is significantly increased in the BAT of Lrg1 KO STD and HFD fed mice compared to WT (Figure 2B). Ucp1 mRNA expression increase in Lrg1 KO mice was confirmed by measuring UCP1 protein with an immunoblot (Figure 2C). Conclusion Loss of Lrg1 protects BAT from dysfunction in diet-induced obesity.

Sex Differences in Response to Metformin in a Longitudinal Study in Mice

Sexual dimorphisms have been recognized in most aspects of human health and disease, and there is now clear evidence for more pronounced differences in response to pharmacological interventions of aging. Here, male and female C57BL/6J mice at six months of age were administered 0.5% metformin in their diet every-other-week (EOW) for the remainder of their lives. The intervention was well tolerated and did not result in lifespan extension. Male mice treated with metformin EOW lost weight and augmented lean-to-fat ratio. In contrast, EOW females were refractory to changes in body weight and body composition compared to controls. The intervention did not influence non-fasted plasma glucose levels, while causing an increase in lactate in mice of both sexes. Indirect calorimetry was performed to measure energy expenditure in EOW mice that were either ON or OFF metformin during testing. Focusing on the respiratory exchange ratio (RER), males, but not females, preferentially utilized carbohydrates (RER ~0.9-1.0) when OFF metformin, switching to lipids (RER ~0.8-0.9) when ON metformin. This resulted in significant differences compared to controls in both periods (OFF and ON). RER of EOW females was different from controls during OFF metformin (RER ~0.8-0.9), while exhibiting significantly lower RER when ON metformin (RER ~0.7-0.8). These results clearly point at a strong dimorphism in the action of metformin in mice, including its role in metabolic homeostasis and overall health span. A better understanding of how sex influences the health and prolongevity benefits of metformin will benefit our understanding of the longterm clinical implications.

Daily and Not Every-Other-Day Intake of Anthocyanin-Rich New Zealand Blackcurrant Extract Alters Substrate Oxidation during Moderate-Intensity Walking in Adult Males

Daily intake of anthocyanin-rich New Zealand blackcurrant (NZBC) extract can enhance exercise-induced fat oxidation. It is not known whether habitual dietary anthocyanin intake and body composition affects blackcurrant-induced fat oxidation or even if daily intake is required. We examined effects of daily and every-other-day intake of NZBC extract on metabolic and physiological responses during moderate-intensity walking. Sixteen physically active males (age: 24 ± 6 yr, body mass: 78 ± 16 kg, BMI: 24.7 ± 4.2 kg·m −2, body fat: 15.2 ± 5.0%) volunteered. A randomized, cross-over design with a control condition was used and habitual dietary anthocyanin intake quantified. For intake conditions, participants consumed two capsules of NZBC extract (i.e. 210 mg of anthocyanins, CurraNZ™) with breakfast daily or every-other-day for 14 days (14-D and 14-EOD) with 14-days washout. Final two capsules were taken 2-hr before the walk (speed: 5.7 ± 0.7 km·hr−1). There was a trend for lower respiratory exchange ratio and carbohydrate oxidation with changes only for 14-D. Fat oxidation was increased only for 14-D (p < 0.05) with 50% of the participants more than a 10% change. In 14-D, there was a positive correlation for BMI and body fat % with the absolute change in fat oxidation but not with habitual dietary anthocyanin intake. Daily intake of NZBC extract is required to enhance exercise-induced fat oxidation. Enhanced exercise-induced fat oxidation by daily intake of NZBC extract is related to body composition but not to habitual dietary anthocyanin intake in physically active males. Daily anthocyanin intake seems to be required to allow the gradual build-up and maintenance of anthocyanin-derived metabolites that are required to alter mechanisms for exercise-induced substrate oxidation.