bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Hyperhydration on the Cardiovascular Responses to an LBNP Presyncopal Challenge
Authors: Pawluk Cristyn , Payne Taylor , Gibson Morgan , Davis John E
Published: November 2023

PURPOSE

To determine the effects of hyperhydration on heart rate, blood pressure, leg blood volume and forearm blood flow during a lower body negative challenge to presyncope.

METHODS

Nine subjects (Age = 20.2 ± 1.3 yrs, Weight = 75.3 ± 21.1 kgs) participated in two graded LBNP (Lower Body Negative Pressure) tests to pre‐syncope while forearm blood flow (FBF), heart rate (HR), blood pressure (BP), and leg blood volume were measured. Each subject was tested in a control trial (with no fluid ingestion), and after consumption of a hypervolemia‐inducing beverage (NaCl solution of 4.9g per kg of body weight in 10mL of grape flavored Propel). Treatment order was randomized for all subjects. A cumulative stress index (CSI) was subsequently calculated (minutes completed x box pressure) to assess changes in orthostatic tolerance between the control and fluid ingestion LBNP. For all trials in the LBNP chamber, subjects were tested at LBNP levels of −20 mmHg, −40 mmHg, and −60 mmHg for three minutes at each trial, and then an additional increase of −10 mmHg every three minutes until pre‐syncopal symptoms appeared. Forearm blood flow was measured using venous occlusion plethysmography. Near‐infrared spectroscopy (Portamon, Artinis, Inc.) in the right calf muscle was used to determine lower leg blood volume.

RESULTS

There were no significant differences in CSI between the hyperhydration (619.8 ± 55.2mmHg.min) and control conditions (640.0 ± 70.3 mmHg.min). Furthermore, the change in forearm blood flow, lower leg blood volume, and heart rate during the LBNP hyperhydration trial were not different from the control trial.

CONCLUSION

Ingestion of a hypervolemia‐inducing beverage did not alter orthostatic tolerance or the cardiovascular responses to an orthostatic challenge. This suggests that either a larger volume of fluid or a fluid with a different composition needs to be ingested to improve orthostatic tolerance.
The Impact of Caloric Restriction and Resistance Training on Bone Mineral Density and Bone Strength in Growing Male Rats
Authors: Slater Brady , Lee Kassandra , Folta Haley , Wong Quinton , Gettleman Brandon , Hernandez John , Prakash Anu , Jaque S Victoria , Sumida Ken D
Published: November 2023

The purpose of this study was to examine the impact of caloric restriction and resistance training on bone mineral density (BMD, in g/cm2, measured via DXA) and bone strength (Fmax, in Newtons, measured via 3 pt bending rig) of the tibia in growing male rats. 32 male rats (initially 8 wks old) were randomly divided into: a non‐exercised ad libitum fed Control group (C, n=8) pair fed with a non‐exercised group fed a 20% caloric restrictive diet (D, n=8), and an exercised ad libitum fed group (RT, n=8) pair fed with an exercised group fed a 20% caloric restrictive diet (DT, n=8). The exercise groups were conditioned to climb a 1 meter vertical ladder 4X per session with weights appended to their tail 3 days/wk for 6 wks. All exercised animals initially carried 30% of their body weight (BW) and progressed to 150% BW by week 6. After 6 wks, the body weight was significantly lower for diet fed animals (383.8 ± 6.8 g) compared to ad libitum fed animals (459.9 ± 9.3 g). There were no interaction effects (exercise x diet) for BMD or bone strength. The main effect of exercise on BMD was significantly greater (P = 0.047) for trained groups (RT and DT = 0.215 ± 0.002) compared to non‐exercised groups (C and D = 0.206 ± 0.002) whereas the main effect of diet on BMD was not statistically significant (P = 0.086) for ad libitum fed groups (C and RT = 0.214 ± 0.004) compared to diet fed groups (D and DT = 0.207 ± 0.002). The main effect of exercise on Fmax was significantly greater (P = 0.001) for exercised groups (RT and DT = 139.5 ± 5.1) compared to non‐exercised groups (C and D = 118.7 ± 3.8) and the main effect of diet on Fmax was significantly greater (P = 0.001) for ad libitum fed groups (C and RT = 138.8 ± 5.3) compared to diet fed groups (D and DT = 119.4 ± 3.8). The results indicate that during growth, resistance training elevated BMD and bone strength whereas a 20% caloric restrictive diet lowered bone strength in the absence of a decline in BMD.

Support or Funding Information

Chapman University Faculty Research Grant
Does Local Heating of the Carotid Body Chemoreceptors Modulate Ventilation or Hemodynamics?
Authors: Johnson Blair D , Sackett James R , Sarker Suman , Coleman Gregory L , Chapman Christopher L , Schlader Zachary J
Published: November 2023

Background

Activation of the carotid body chemoreceptors is sympathoexcitatory and causes increases in ventilation, heart rate, and blood pressure. In vitro evidence indicates that heat stressed carotid body chemoreceptors are activated and cause an increase in carotid sinus nerve activity. However, the role that the carotid body chemoreceptors play in the physiological responses to whole body heat stress is not clear. We developed an experimental model to isolate heat stress to the carotid body chemoreceptors. This model will allow us to determine if local heating of the carotid body chemoreceptors influences ventilation and hemodynamics.

Purpose

We tested the hypothesis that local heating of the carotid body chemoreceptors modulates ventilation and hemodynamics.

Methods

Five healthy men (age: 25 ± 2) participated in two local heating protocols. In the CB heat protocol, local heaters (surface area: 7.9 cm2) were adhered to the skin at the bifurcation of the left and right carotid artery and set to 44°C. In the ARM heat protocol, local heaters were adhered to the ventral side of both forearms and set to 44°C. Heat was applied for 45 minutes in both protocols. The protocols were randomized and separated by a minimum of 30 minutes or until skin blood flow returned to baseline values. We measured ventilation (heated pneumotach), heart rate (ECG), blood pressure (Finometer), and forearm skin blood flow (laser Doppler) throughout each protocol. Skin blood flow was also normalized to mean arterial pressure (MAP) and expressed as a percentage of the local heating induced maximal cutaneous vascular conductance (%CVCmax).

Results

Four of the five participants had an increase in ventilation from baseline ranging from 5–16% during CB heat. However, the change in ventilation from baseline was not statistically distinguishable between CB heat (0.5 ± 0.7 L/min) and ARM heat (−0.6 ± 1.2 L/min) (P = 0.14). The change in heart rate from baseline tended to be greater in CB heat vs. ARM heat (4 ± 4 vs. −3 ± 5 bpm; P < 0.08). The change in MAP was not different between protocols (CB heat: 3 ± 4 mmHg vs. ARM heat: 3 ± 3 mmHg; P = 0.45). When compared to baseline, skin blood flow (20 ± 9 vs. 13 ± 3 PU; P < 0.10) and %CVCmax tended to be lower during CB heat (7.2 ± 0.6 vs. 5.2 ± 1.8%; P < 0.07).

Conclusions

These preliminary data indicate that the carotid body chemoreceptors appear to play an independent role in the ventilatory and hemodynamic responses to heat stress.

Support or Funding Information

This project was supported by the University at Buffalo Innovative Micro‐Programs Accelerating Collaboration in Themes (IMPACT) program.
Effects of exercise‐induced increases in body temperatures on local skin thermal sensitivity in Multiple Sclerosis patients
Authors: Filingeri Davide , Chaseling Georgia K , Hoang Phu , Barnett Michael , Davis Scott L , Jay Ollie
Published: November 2023

Exercise and concomitant increases in body temperature reduces local skin thermal sensitivity via hypothesized analgesic‐effects. Abnormal thresholds for thermal sensations and heat‐sensitivity are well‐established symptoms and modulatory factors, respectively, of Multiple Sclerosis. However, it is unknown whether increases in body temperature modulate sensory abnormalities in MS. We therefore investigated the hypothesis that changes in local skin thermal sensitivity are reduced in relapsing‐remitting MS patients during cycling in the heat (30°C; 35%RH). Seven MS patients (age 54±7 y; body mass 76.1±10.9 kg; body surface area 1.9±0.2 m2), with increased warmth thresholds (0.61±0.58°C) compared to 4 age‐, mass‐ and body surface area‐matched healthy controls (CTR) (53±9 y; 75.6±14.0 kg; 1.9±0.2 m2; warmth threshold: 0.38±0.25°C); were asked to perform 30‐min cycling at an intensity of 3.3 W/kg of total body mass. A quantitative thermo‐sensory test, consisting of reporting (visual analogue scale) perceived magnitude of local warm (38°C) and cold (22°C) thermal stimuli (25 cm2‐thermal probe) applied to the dorsum of the hand, was performed before and after every 10 min of cycling. Rectal temperature increased similarly between MS (+0.20±0.17°C) and CTR (+0.15±0.09°C) (p=0.619), whereas changes in mean skin temperature were greater in MS (1.41±0.38°C) than CTR (0.96±0.28°C) (p=0.077). 30 min of cycling reduced CTR thermo‐sensitivity to warm (−10.5±10.0%) and cold (−14.1±8.5%) thermal stimuli. MS patients also experienced exercise‐induced reductions in local thermo‐sensitivity, however these were of smaller magnitude, both for warm (−2.7±16.4%) and cold (−10.4±8.6%) thermal stimuli. In line with previous research, exercise‐induced increases in body temperature reduce skin thermo‐sensitivity providing an analgesic effect in healthy controls. However, MS diminishes the magnitude of such effect.

Support or Funding Information

This study was supported by a MS Research Australia Incubator Grant (Holders: Jay, Barnett, Hoang and Davis) and a University of Sydney International Collaboration research Award (IRCA) (Holders: Davis and Jay). Dr Filingeri was supported by a Government of Australia Endeavour Fellowship
Steady State Skeletal Muscle Temperature during Moderate Intensity Single Leg Dynamic Knee Extension Exercise
Authors: Mangum Joshua Earl , Luttrell Meredith , Ely Matthew , Abdala Pedro , Sieck Dylan , Halliwill John
Published: November 2023

In resting skeletal muscle, there is a temperature gradient with deeper tissue typically having higher temperatures than more superficial tissue. During exercise, skeletal muscle temperature increases with the rise in metabolism. Our lab has previously used a model of dynamic knee extension exercise which consists of single‐leg kicking for 60 minutes at 60% of peak power output. The rate of skeletal muscle temperature rise, maximal temperature attained, and range of intramuscular temperatures with this mode of exercise is unknown. Therefore, the purpose of this study was to examine the changes in skeletal muscle temperature at three different depths during exercise using this model. It was hypothesized that the three depths within skeletal muscle would have different temperatures at rest, and these would rapidly increase, converging at some point during exercise. Five young (ages 21–38) healthy male subjects completed the exercise protocol and intramuscular temperature was measured via a percutaneous intramuscular thermocouple that measured temperature at three different depths within the vastus lateralis. Individual temperatures from each depth were measured and also averaged to express a mean intramuscular temperature. Within 10 minutes of exercise, mean intramuscular temperature increased from 34.59 ± 0.44°C to 37.06 ± 0.10°C (mean ± SE, p < 0.01). By 30 minutes, mean intramuscular temperature reached a plateau of 39.15 ± 0.11°C. The variability of temperature in muscle, expressed as the range of the three different intramuscular temperatures, decreased from 1.40 ± 0.39°C to 0.60 ± 0.21°C by 30 minutes (p = 0.08), and did not further decrease to the end of exercise. These data suggest that skeletal muscle temperature increases rapidly during exercise, and the heterogeneity in temperatures typically associated with depth is reduced. As well, these data suggest that there is a steady intramuscular temperature reached within 30 minutes of steady state exercise at 60% of peak power output.

Support or Funding Information

Support provided by NIH grant HL115027
A Lower Heat Activated Sweat Gland Density in Larger Individuals Does Not Impair Local Sweat Rates During Hot and Humid Heat Stress
Authors: Ravanelli Nicholas , Imbeault Pascal , Jay Ollie
Published: November 2023

While the absolute number of sweat glands is primarily determined in utero, a larger body surface area (BSA) will naturally reduce the density of sweat glands per surface area which may compromise sweat rate per unit BSA, and consequently the maximal skin surface sweat coverage (i.e. skin wettedness: ωmax) during exercise in a hot/humid environment. The purpose of the present study was to compare the heat activated sweat gland density (HASGD), sweat gland output (SGO), local sweat rate (LSR) and ωmax between groups differing greatly in BSA during hot and humid active heat stress. Twelve participants separated into two groups based on body size (Small (SM): n=6, 65±6 kg, 1.8±0.1 m2; Large (LG): n=6, 102±13 kg, 2.3±0.1 m2) exercised on an upright cycle ergometer at an evaporative heat balance requirement (Ereq) of 240 W/m2 and 290 W/m2 for up to 75 min at 36°C, 70% RH. LSR of the upper back was measured throughout and expressed relative to surface area (mg/cm2/min). HASGD in number of sweat glands per cm2 (glands/cm2) was measured medially to LSR using the starch iodine technique every 15 minutes and averaged throughout the trial. Mean SGO was derived from the division of LSR and mean HASGD, and expressed as μg/gland/min. On a separate occasion ωmax was measured using a humidity‐ramp protocol (increase of 0.3 kPa from 2.3 kPa every 7.5‐min) during exercise at a fixed external workload of 100W at 36°C until an inflection of esophageal temperature was observed. LSR was similar at 240 W/m2 (SM: 1.24±0.24; LG: 1.40±0.47 mg/cm2/min, P=0.25) and 290 W/m2 (SM: 1.36±0.18; LG: 1.36±0.36 mg/cm2/min, P=0.48). HASGD was greater in SM compared to LG group at 240 W/m2 (SM: 67±12; LG: 55±6 glands/cm2, P=0.03) and 290 W/m2 (SM: 73±9; LG: 57±11 glands/cm2, P<0.01). SGO was trending to be greater in the LG group at 240 W/m2 (SM: 18.6±5.0; LG: 25.2±10.2 μg/gland/min, P=0.10) while significantly greater in the LG group at 290 W/m2 (SM: 17.3±1.6; LG: 21.2±5.7 μg/gland/min, P=0.03). On the other hand, ωmax was not different between groups (SM: 0.82±0.16; LG: 0.72±0.07, P=0.13). In conclusion, a lower HASGD in people with a greater BSA is compensated by a greater SGO to yield a similar LSR up to an Ereq of 290 W/m2 and a similar ωmax. Future research should attempt to assess how even greater reductions in HASGD due to disproportionally larger differences in BSA (ie morbid obesity) compromise LSR, ωmax, and therefore the level of heat stress that can be physiologically compensated.

Support or Funding Information

Supported by a NSERC Discovery Grant (P. Imbeault & O. Jay)
Does Body Surface Area Independently Alter Whole‐body Sweat Loss during Exercise at a Fixed Absolute Evaporative Requirement for Heat Balance?
Authors: Cramer Matthew N , Coombs Geoffrey B , Ravanelli Nicholas M , Jay Ollie
Published: November 2023

The absolute evaporative requirement for heat balance (Ereq) is the principal determinant of whole‐body sweat loss (WBSL) during fixed‐duration exercise in ambient conditions that permit complete sweat evaporation, regardless of body size. However, exercise at a fixed absolute Ereq in hot/humid conditions may lead to disproportionately greater WBSL among individuals of smaller body surface area (BSA) due to a lower absolute maximum evaporative capacity and thus higher skin wettedness required for heat balance (ωreq) and lower sweating efficiency (Seff). To test this hypothesis, young adult males of small (SM: 1.81±0.07 m2; n=4) or large (LG: 2.28±0.15 m2; n=3) BSA cycled for 70 min at 34±0.3°C, 71.8±1.3% RH at an exercise intensity set to elicit a fixed VO2 of 1.5 L/min, and therefore a metabolic heat production of ~450 W and an Ereq of ~430 W (indirect calorimetry). Body mass was measured at 0, 45, and 70 min to estimate WBSL during non‐steady‐state (0–45 min) and steady‐state (45–70 min) exercise. Seff was calculated as the quotient of the WBSL required to attain Ereq with complete evaporation and the observed WBSL during the steady‐state period, and expressed as a percentage. The attainment of a steady state (i.e., the actual rate of evaporation equaled the required rate of evaporation) from 45 to 70 min was confirmed by stable esophageal and skin temperatures (±0.1°C throughout steady state). During non‐steady‐state exercise, ωreq was not different between groups (SM: 0.81±0.05 g; LG: 0.73±0.08 g; P=0.17), and no between‐group difference in WBSL was observed (SM: 522±81 g; LG: 476±115 g; P=0.56). In contrast, steady‐state ωreq was greater in SM (SM: 0.81±0.03; LG: 0.71±0.04; P=0.02), leading to significantly higher WBSL (SM: 361±49 g; LG: 260±54 g; P<0.05) and diminished Seff (SM: 74.1±12.7%; LG: 96.3±6.4%; P=0.04) in the SM group. In summary, our preliminary data suggest that in hot/humid ambient conditions, a large between‐group difference in BSA may lead to disproportionately greater steady‐state WBSL in smaller individuals despite exercising at the same absolute Ereq due to an independent effect of BSA on Seff.

Support or Funding Information

Supported by an NSERC Discovery Grant (O. Jay)
Leucine Modulates mTORC1 Signaling by Acting Specifically to Alter the Phosphorylation Status of Sestrin2
Authors: Kimball Scot R , Gordon Bradley S , Moyer Jenna E , Dennis Michael D , Jefferson Leonard S
Published: November 2023

Studies performed more than 35 years ago showed that the branched‐chain amino acids, and in particular leucine, were as effective as a complete mixture of amino acids in stimulating protein synthesis in skeletal muscle, heart, and diaphragm. Subsequent studies showed that the leucine‐induced stimulation of protein synthesis occurred through activation of the initiation phase of mRNA translation, and that in turn was due to activation of the protein kinase referred to as the mechanistic target of rapamycin in complex 1 (mTORC1). Over the past decade studies performed primarily using cells in culture exposed to either complete amino acid depletion or repletion conditions have yielded the identification of a molecular pathway through which amino acids signal to mTORC1. However, despite these advances in our knowledge, we still do not know how leucine acts selectively to activate mTORC1 or how its availability is recognized. In the present study, we assessed the role of Sestrin2 in mediating the leucine‐specific activation of mTORC1. We found that in cells in culture exposed to medium lacking leucine, Sestrin2 phosphorylation was enhanced, and that leucine repletion rapidly (within 10 min) reversed the phosphorylation. Moreover, leucine‐induced dephosphorylation occurred over physiological concentrations of the amino acid, and was inversely proportional to changes in phosphorylation of the mTORC1 substrate, p70S6K1. The effect was specific for leucine, as neither glutamine nor arginine had any effect on Sestrin2 phosphorylation, even though arginine was as potent as leucine in activating mTORC1. Interestingly, phosphorylation of Sestrin2 correlated with enhanced interaction with the GATOR2 complex, a key upstream regulator of mTORC1 activity. Finally, three Sestrin2 phosphorylation sites were identified by mass spectrometry, and site‐directed mutagenesis is currently being used to assess their role in mediating leucine‐specific modulation of mTORC1 activity. Overall, the results support a model in which leucine selectively promotes dephosphorylation of Sestrin2, causing it to dissociate from GATOR2 to allow activation of mTORC1.

Support or Funding Information

Supported by NIH grant DK15658
Contractile Properties of the Rat Extensor Digitorum Longus Muscle in Relation to Regional Variation in Fibre Type Composition
Authors: Kissane Roger , Egginton Stuart , Askew Graham N
Published: November 2023

Muscle contractile characteristics are commonly investigated in relation to global phenotype. The extensor digitorum longus (EDL) muscle has frequently been used in physiological studies as an example of a typical fast muscle. However, the fibre type composition is not homogeneous. In the rat, the EDL contains a mixture of oxidative and glycolytic fibres, heterogeneously distributed across the muscle cross section to produce a gradient of aerobic capacity. The aim of this study was to characterize the contractile characteristics of this mixed muscle in relation to the regional variation in fibre type composition. It was hypothesized that isometric twitch characteristics and optimal frequency for power generation would not differ regionally, while the fatigability will correlate with aerobic capacity.

The EDL muscle from male Wistar rats comprises four segments which insert on to phalanges 2–5; we used the medial and lateral segments, which insert on to phalanges 2 and 5, respectively. The contractile characteristics of each segment were determined under isometric conditions, in order to quantify twitch kinetics and tetanic stress. Power output of the muscle was measured at a range of cycle frequencies during cyclical contractions, using the work loop technique. The ability to sustain power was quantified using a series of repeated cyclical contractions. A range of monoclonal antibodies was used to determine fibre type composition.

The two muscle segments had significantly different fibre type composition; the medial segment containing 41% Type IIb, 49% Type IIa and 10% Type I while the lateral segment contained 95% Type IIb and 5% Type IIa. The medial segment had slower twitch kinetics than the lateral segment, consistent with the presence of Type 1 fibres and lower proportion of Type 2 fibres. Isometric stress was lower in the medial segment producing 155.3 kN m−2 compared to 194.6 kN m−2 in the lateral segment; this may be related to the higher proportion of non‐contractile elements such as mitochondria in the medial segment, i.e. a lower proportion of myofibrils, compared with the lateral segment. Peak net power output and the frequency at which this was attained were similar between both muscle segments.

Variation in the physiological properties of the lateral and medial segments of the rat EDL are consistent with the decrease in oxidative capacity and a decrease in the proportion of fast‐twitch fibres from medial to lateral sides. This suggests that there may be regional variation in mechanical function, with a shift from the medial segment providing work for ankle flexion at relatively low speeds, to the lateral segment increasingly fulfilling the role at higher speeds.
Energy production in patients with chronic obstructive pulmonary disease: Evidence of mitochondrial and not O2 supply limitation
Authors: Layec Gwenael , Hart Corey , Trinity Joel , Haseler Luke , Le Fur Yann , Jeong Eun‐Kee , Richardson Russell
Published: November 2023

It is well documented that chronic obstructive pulmonary disease (COPD) is associated with both muscular and vascular dysfunctions. Interestingly, although both peripheral oxygen (O2) transport and muscle O2 utilization capacity appear to be impaired in patients with COPD, it is still unclear which peripheral component of the O2 cascade actually limits overall muscle aerobic capacity. Therefore, purpose of the present study was to determine whether mitochondrial function in vivo is limited by convective O2 delivery or the intrinsic capacity of mitochondria to synthesize ATP in patients with COPD. To this aim, we combined phosphorus magnetic resonance spectroscopy (31P‐MRS), near‐infrared spectroscopy (NIRS), and Doppler ultrasound, to examine the effect of superimposing reactive hyperaemia (RH), induced by a period of brief ischemia during the last min of exercise, on O2 delivery and mitochondrial function in the calf muscle of 16 patients with moderate to severe COPD in comparison to free‐flow conditions (FF). Limb blood flow [area under the curve (AUC), FF: 2.5 ± 1.2 L; RH: 3.3 ± 1.0 L, P<0.05] and convective O2 delivery (AUC, FF: 0.46 ± 0.23 L; RH: 0.61 ± 0.21 L, P=0.08) were increased in RH in comparison to FF. RH was also associated with significantly higher capillary blood flow (AUC, FF: 26 ± 14 L; RH: 37 ± 25 L, P<0.05). However, despite an increased muscle perfusion and O2 delivery, the peak rate of mitochondrial ATP synthesis did not differ significantly between conditions (FF: 28 ± 14 mM.min−1; RH: 27 ± 9 mM.min−1, P=0.83). Taken together, these results indicate that an increase in convective O2 delivery does not improve mitochondrial function in the plantar flexor muscles of the patients with COPD, thereby revealing that the peak rate of mitochondrial ATP synthesis of these patients appears to be limited by the intrinsic mitochondrial capacity and not O2 availability.

Support or Funding Information

This work was funded in part by grants from the Flight Attendant Medical Research Institute (FAMRI), NIH National Heart, Lung, and Blood Institute (K99HL125756, PO1 HL 091830) and VA Merit grant E6910R.
Adipose‐Derived Exosomes From Severely Obese Individuals Regulate Skeletal Muscle Metabolism
Authors: Park Sanghee , Zheng Donghai , Barberio Matt , Hubal Monica , Houmard Joseph
Published: November 2023

Accumulation of subcutaneous and visceral fat mass with severe obesity (BMI > 40 kg/m2) is closely associated with various metabolic derangements, including insulin resistance, type 2 diabetes and cardiovascular disease. The mechanism in which expanded visceral tissue promotes insulin resistance in peripheral tissues (i.e. skeletal muscle) is unclear. Exosomes, extracellular nano‐vesicles secreted from almost all types of organs in the body, are known to regulate cellular signaling through endocrine mechanism suggesting that exosomes released from visceral fat can be one of important mediators to communicate with skeletal muscle. In addition, a previous study has shown that certain mature miRNAs from visceral exosomes, which target many confirmed or putative mRNAs, are differentially expressed in adipose‐derived exosomes from obese vs. lean individuals, indicating that adipose‐derived exosomal miRNAs in obesity may play an important role in developing metabolic dysfunction in human skeletal muscle. We, therefore, hypothesize that adipose‐derived exosomes may induce insulin resistance in skeletal muscle. Exosomes were isolated from visceral adipose tissues from severely obese individuals (BMI > 40kg/m2) using ExoQuick‐TC (System Biosciences). Skeletal muscle cells were obtained from lean and several obese individuals (N=8: BMI < 25kg/m2 and BMI > 40kg/m2, respectively). Following proliferation and differentiation, fully mature myotubes were incubated with adipose‐derived exosomes (0.3ug/ml) for 24 hours and stimulated by insulin (100nM) for the last10 minutes. Then, cells were harvested to measure protein expressions in glucose metabolism using immunoblotting techniques. To measure the functional importance of exosome treatment, we examined insulin‐stimulated glycogen synthesis and glucose oxidation. While adipose‐derived exosomes significantly suppressed phosphorylation of AktSer 473 in skeletal muscle cells from both lean and obese individuals, we could not observe any changes in insulin‐stimulated glycogen synthesis and glucose oxidation. The main finding from this study is that adipose‐derived exosomes significantly suppressed Akt phosphorylation; however, there were no changes in glucose metabolism. This would suggest that, though it impairs intracellular signaling, exosomes may not be responsible for impaired glucose metabolism with severe obesity.

Support or Funding Information

This study was supported by the National Institute of Health (DK 56112).
Metformin Limits Loss of Mitochondrial Respiration Seen With Doxorubicin Treatment Without Affecting Muscle Function
Authors: Murphy Tyler Steadman , Crandall Amy Dee , Louw Makensie Joann , Bernhisel Drew , Reynolds Merrick , Hancock Chad R
Published: November 2023

Doxorubicin (DOX) is a commonly‐used chemotherapeutic drug with a well characterized side effect of skeletal muscle wasting and weakness. It has been shown that DOX contributes to skeletal muscle damage through increasing oxidative stress. It has been suggested that this is due to DOX reacting with free cellular iron which then catalyzes the production of reactive oxygen species (ROS). ROS contribute to cell damage and dysfunction, and thus may play a role in the skeletal muscle wasting seen with DOX treatment. Recent work has shown that Metformin (MET) may protect against this oxidative environment by increasing iron storage capacity, thus preventing skeletal muscle wasting. We hypothesized that mice treated with DOX would see decreased muscle function and decreased respiratory capacity, and that pretreatment with MET would ameliorate these negative side effects. Male C57BL/6 mice were randomly placed into three groups: control, DOX or MET+DOX. Control mice received five doses of saline orally for five days before sacrifice, and one dose of saline intraperitoneally three days before sacrifice. DOX mice received one dose of DOX at 15 mg/kg three days before sacrifice. MET+DOX mice were given MET at 500 mg/kg two days before DOX treatment at 15 mg/kg. They were given this same dosage of MET every day until they were sacrificed three days after DOX treatment. Muscle function was measured in the gastrocnemius, plantaris and soleus muscle complex in situ, with mice under anesthesia (100 msec tetanic contractions at 0.5 Hz for 6 min). Mitochondrial respiratory function was measured in permeabilized fiber bundles from red gastrocnemius muscle using high‐resolution respirometry (OROBOROS Oxygraph‐2k). Treatment with DOX resulted in a 16.0–20.2% reduction in overall body weight in both the DOX and MET+DOX groups as compared to control (p‐value < 0.001). The weight difference between DOX and MET+DOX groups was not significant. Compared to control, DOX treatment caused a reduction in complex I stimulated, complex II stimulated, and uncoupled respiration (20–60% with p‐value < 0.001). MET significantly prevented these reductions (i.e. max uncoupled respiration was 81% of control with p‐value 0.08). Surprisingly we saw no significant differences in absolute force, twitch force, half relaxation time, or muscle fatigue between any of the three groups. These findings show that pretreatment with MET prevents decreases in mitochondrial respiration caused by DOX, but may not prevent muscle wasting. More research is needed in this area to find treatment options for DOX‐induced skeletal muscle dysfunction.

Support or Funding Information

Brigham Young University
Overexpression of PGC‐1α Increases Peroxisomal Biogenesis and Mitochondrial Lipid Oxidation in Human Primary Myotubes
Authors: Huang Tai‐Yu , Zheng Donghai , Houmard Joseph A , Brault Jeffrey J , Hickner Robert C , Cortright Ronald N
Published: November 2023

The conventional view of peroxisomal biogenesis has assumed that it is under the transcriptional regulation by PPAR. However, recent studies in hepatic cells have shown that the transcriptional co‐activator, PGC‐1α, can induce peroxisomal gene expression and abundance in a PPAR‐independent fashion. Also, metabolic linkage between mitochondria and peroxisomes may converge in terms of lipid metabolism. It is unknown whether the regulatory mechanism of peroxisomal biogenesis is through the same node as mitochondrial biogenesis in human skeletal muscle and whether fatty acid metabolism is affected. Therefore, we hypothesized that PGC‐1α acts as a biological “driver” for both peroxisomal and mitochondrial biogenesis in human skeletal muscle, leading to metabolic interactions in terms of fatty acid oxidation. Human skeletal muscle cells from vastus lateralis biopsies of lean donors (BMI= 23.6 ± 1.5 kg/m2, age=26.7 ± 3.5 years, n=3) were exposed to adenovirus encoding PGC‐1α or GFP at day 4 post differentiation and harvested at day 7. Peroxisomal biogenesis proteins (peroxins) and genes (PEXs) responsible for proliferation and function were assessed by western blot and quantitative real time‐PCR. 1‐14C lignoceric acid, necessarily oxidized first by peroxisomes, was used to assess mitochondrial oxidation of peroxisomal derived fatty acid metabolites.

Results

Following overexpression of PGC‐1α (protein increased 9.7 fold) 1) peroxisomal exclusive PMP70 and mitochondrial citrate synthase protein content were elevated 3 and 2.8 fold respectively (P<0.05) and PEX19 protein increased by 43% compared to the ad‐GFP controls 2) PGC‐1α, PMP70, PEX19 and a peroxisomal β‐oxidation enzyme, peroxisomal acyl‐coenzyme A oxidase 1, mRNA content were increased by 34.7, 4, 1.3, and 1.5 fold respectively (P<0.05) and 3) A concomitant 2.5‐fold increase in peroxisomal derived lignoceric acid metabolite oxidation by mitochondria was observed.

Conclusion

In addition to the proliferative power on mitochondria, PGC‐1α is responsible (at least in part) for regulating peroxisomal biogenesis accompanied by elevations in the functional interactions of peroxisomes with mitochondrial lipid disposal in human skeletal muscle.

Support or Funding Information

Supported in part by a seed grant from the Diabetes Obesity Institute, East Carolina University (RNC), NIH DK 056112(JAH), NIH 1R15HL113854‐01A1 (RCH)
Estrogen Treatment Restores Muscle Mitochondrial Function and Redox Homeostasis, reversing the Pro‐Diabetogenic State induced by Ovariectomy
Authors: Torres Maria Jose , Reese Lauren , Smith Cheryl , Pennington Edward , Ryan Terence , Shaikh Raza , Neufer Peter Darrell
Published: November 2023

Menopause comes with a significant decline in 17β‐estradiol (E2) levels, increased adiposity and a higher risk for type‐2 diabetes, but hormone therapy can help revert these effects. However, we still lack a comprehensive understanding of the mechanism(s) by which E2 modulates insulin sensitivity. Herein, 10 week‐old C57BL‐NJ mice were studied after 2 weeks of ovariectomy to avoid the development of obesity (OVX‐2w), and following 2 weeks of E2 replacement (OVX+E2, 1μg/day) administered via a subcutaneous miniosmotic pump. Control groups included normally cycling females (NC) in the Proestrus stage (high physiological E2 levels) and an OVX group implanted with a saline control pump (OVX‐ctl). E2 treatment effectively reversed fasting hyperglycemia developed in the OVX‐2w and OVX‐ctl groups (+25%, p<0.05), decreased fat mass by 48% relative to OVX‐ctl (p<0.05), and restored ex‐vivo insulin‐stimulated muscle glucose uptake. Accompanying these effects, we demonstrate that soon after ovarian E2 withdrawal a decrease in mitochondrial function and an oxidative shift in the cellular redox environment occur; both conditions associated with the etiology of insulin resistance. Furthermore, spectrophotometric assessment of specific activities of the electron transport complexes in isolated skeletal mitochondria revealed a ~40% decrease in Complex I (p<0.005) and Complex III (p<0.05) activities in OVX mice. While Complex II activity was not altered, transfer of electrons between Complex I and III, as well as between II and III was reduced by 50% in OVX‐2w (p<0.05), and 35% in OVX‐ctl (p<0.05), but completely restored in OVX+E2. Concomitant with a decrease in mitochondrial membrane fluidity (~‐50%, p<0.05), OVX‐2w mice also showed reduced electron transport supercomplex formation (p<0.05), but all changes were fully rescued in OVX+E2. Overall, we show that E2 protects mitochondrial function and redox homeostasis via non‐genomic pathways; by increasing Complex I and Complex IIII activities, enhancing electron transfer supercomplex assembly, promoting electron transfer efficiency within the Q‐pool, preventing mitochondrial free radical leak, and increasing fluidity of mitochondrial membranes. Our findings offer new insights into the mechanism(s) by which menopause sets, and E2 therapy reverses a pro‐diabetogenic state. A deeper understanding of E2 mechanisms of action in metabolism is of paramount importance to advance in the development of alternative non‐hormonal therapies; that can optimize the metabolic benefits, without the reproductive, oncogenic, and cardiovascular risks associated with HRT, for natural or surgically‐induced menopausal women.

Support or Funding Information

NIH DK096907
Triclosan is Excluded from Fetal Brain When Administered to the Pregnant Ewe
Authors: Quevedo Darla , Bryan Daphne , Zarate Miguel , Wood Charles E.
Published: November 2023

Triclosan (TCS: 5‐chloro‐2‐(2,4‐dichlorophenoxy)‐phenol) is a synthetic antibacterial compound that is commonly added to personal care products. TCS acts as an antibacterial because it interrupts fatty acid synthesis by inhibiting enoyl reductase in bacteria. Because of its action on a bacterial enzyme that is not expressed in the human being, it is thought to be safe for use in humans. We have previously found that TCS administration to the late‐gestation pregnant ewe stimulates a genomic response in the fetal hypothalamus that is consistent with disturbance in lipid biosynthesis and metabolism. We performed the present experiment to test whether the action of TCS on the fetal brain is direct or indirect. Late‐gestation pregnant ewes and their fetuses were chronically catheterized, allowed to recover from surgery, then infused with TCS (0.1 mg/kg/day, iv) for 2 days. TCS concentrations were measured in plasma and after extraction from tissues using an ELISA (Abraxis Corp). The infusion increased maternal plasma TCS concentration to 3.0±0.5 ng/mL compared to 0.2±0.5 ng/mL in saline‐infused ewes. TCS was detected in relatively high concentrations in placenta (0.73±0.18 ng/g, n=4, compared to 0.07±0.05 ng/g, n=4, in untreated fetuses), but not in fetal cerebral cortex (0.24±0.04 ng/g, n=8, compared to 0.27±0.12 ng/g in untreated fetuses, n=8). Interestingly, TCS was measured in plasma and tissue of some untreated animals, perhaps resulting from environmental TCS exposure. This was confirmed by measurement of low levels of TCS in the drinking water in this facility (0.13±0.01 ng/mL, n=3). We conclude that there is a functional barrier that prevents TCS infused into the pregnant ewe from entering the fetal brain. We speculate, therefore, that fetal brain genomic responses to maternal infusions of TCS are an indirect response.

Support or Funding Information

This work was supported by NIH grants R01 HD033053, R01 HD057561, and R25 HL103181.
The Effect of Perinatal Blockade of Androgen Receptors on the Expression of Hypothalamic Estrogen Receptor‐a and Sexual Motivation in Male Rats
Authors: Gopalan Chaya , Shah Binita , Khan Talha , Taylor George
Published: November 2023

Male sexual differentiation of the brain occurs during the perinatal period and is dependent on testosterone (T), which is subsequently metabolized to estrogen (E) or dihydrotestosterone (DHT). E released from T results in the masculinization of the male brain by binding to hypothalamic estrogen receptor‐a (ER‐a). Whether DHT plays a role in this process is unclear. Flutamide, an anti‐androgen agent, blocks androgen receptors (AR). Whether this blockade of AR modulates the concentrations of ER‐a in mediating the effects of T through E was tested. Additionally, sexual activation of young adult male rat depends on increased levels of T but it is unknown whether its effects are dependent on ER or AR. Male Long Evans rats were administered Flutamide (20mg/kg; SC) or vehicle during the critical period of sexual dimorphism (perinatal period: prenatal day 4 to postnatal day 4). Subsequently, the rats were divided into three treatment groups, finasteride (20mg/kg, SC), a 5‐alpha reductase blocker; letrozole (2mg/kg, SC), an aromatase inhibitor; or vehicle during adulthood (postnatal day 65). Each male rat had a choice of approaching a cage containing a gonadally‐intact female or an ovariectomized (OVX) rat for 20 minutes. The movement of the male rat was video‐tracked by Any‐Maze. Animals were sacrificed after 7 weeks of drug treatment, blood sample was collected for serum estrogen measurement using ELISA and the hypothalamus was isolated to measure ER‐a concentrations using chemiluminescent western blots. Flutamide‐treated groups exhibited no preference for the gonadally‐intact or the OVX female, and their hypothalamic ER‐a and serum estrogen levels were significantly increased. These results suggest that the blockade of AR during the perinatal period causes a permanent increase in E and ER‐a expression within the hypothalamus and any further manipulation during activation period is ineffective.
Characterization of Calcium Signaling in TαT1 Thyrotrophs
Authors: Tomic Melanija , Bargi‐Souza Paula , Leiva‐Salcedo Elias , Nunes Maria Teresa , Stojilkovic Stanko S
Published: November 2023

TαT1 cells are mouse pituitary thyrotroph cell line used in studies on thyroid‐stimulating hormone beta subunit gene (Tshb) expression and other cellular functions. Here we studied activation of calcium mobilization and influx pathways in single isolated TαT1 cells in response to application of thyrotropin‐releasing hormone (TRH), a native hypothalamic agonist for thyrotrophs, and extracellular ATP, an intrapituitary agonist for two classes of receptors: G protein‐coupled P2Y receptors and ATP‐gated P2X channels. We also examined contribution of voltage‐gated and voltage‐independent calcium influx pathway to calcium signaling, and the role of triiodothyronine (T3) in cellular calcium homeostasis. Our investigations indicate that TαT1 cells are excitable and fire action potentials spontaneously. The spontaneous electrical activity is coupled to small amplitude fluctuations in intracellular calcium ion concentration. Calcium influx is to a large extent mediated by voltage‐gated calcium channels, as demonstrated by the effects of Bay K 8644, an L‐type voltage‐gated calcium channel agonist. TRH stimulates both calcium mobilization from intracellular pools and calcium influx. Non‐receptor‐mediated depletion of intracellular pool also leads to a prominent facilitation of calcium influx. Both receptor and non‐receptor stimulated calcium influx is substantially attenuated but not completely abolished by inhibition of voltage‐gated calcium channels, suggesting that depletion of intracellular calcium pool in these cells provides a signal for both voltage‐dependent and ‐independent calcium influx. We also found that TαT1 cells express P2Y1 receptors and their activation by extracellular ATP mimics TRH action on calcium mobilization and influx. The thyroid hormone T3 prolongs duration of TRH‐induced calcium spikes during 30‐min exposure. In conclusion, the expression of functional TRH and P2Y1 receptors in TαT1 cells indicates that embryonic thyrotrophs are equipped to respond to feed‐forward action of hypothalamic TRH and intrapituitary effects of released ATP with a rapid calcium mobilization and sustained calcium influx. Moreover, TRH‐induced calcium mobilization in TαT1 cells is amplified by T3, an action consistent with the positive feedback effect of this hormone on calcium‐secretion coupling, presumably through a non‐transcriptional mechanism, in contrast to the transcriptional and post‐transcriptional negative effects of T3 on Tshb expression.

Support or Funding Information

This work was supported by the Intramural Research Program of the Eunice Kennedy Shiver National Institute of Child Health and Human Development (ZIA DH000195‐22).
mTOR signaling coordinates glucose and lipid metabolisms in liver
Authors: Li Ziru
Published: November 2023

Objective

Although aberrant mTOR activity has been linked to the development of obesity and diabetes, its role in hepatic glucose and lipid metabolisms remains largely unknown. We aimed to explore the effects of hepatic mTOR activity on the glucose and lipid homeostatsis.

Methods

TSC1flox/flox mice and mTORflox/flox mice were injected with Cre adenovirus to activate or inhibit mTOR signaling respectively. By breeding albumin‐Cre mice with TSC1flox/flox mice (AT) or mTORflox/flox mice (Am), liver‐specific mTOR signaling was activated or suppressed. OGTT and glucose metabolism related genes were evaluated. Oil‐red O staining and lipid metabolism related genes were assessed as well.

Results

TSC1flox/flox mice with tail vein injection of Ad‐Cre demonstrated an improvement in glucose tolerance relative to wildtype littermates. Levels of genes related to gluconeogenesis, such as PEP carboxykinase (pepck) and pyruvate carboxylase (pc) were significantly decreased. Oil‐red staining demonstrated a significant decrease of hepatic lipid accumulation. Hepatic lipogenesis related genes such as pparγ2, srebp1c, acaca, gpat and dgat were markedly decreased. Interestingly, levels of chREBP mRNA were significantly decreased. This alteration was associated with a decrement in L‐type pyruvate kinase (lpk) and fatty acid synthase (fasn) mRNAs. Inversely, mTORflox/flox mice with tail vein injection of Ad‐Cre showed deteriorated glucose tolerance compared with wildtype littermates. Genes related to gluconeogenesis were significantly increased. Lipids deposition and lipogenesis related genes were increased as well. Similar results were observed in animal models with genetic interference of mTOR signaling including hepatic deletion of TSC1 (AT) and mTOR (Am ). Activation of mTOR signaling in AT mice demonstrated a decrease in hepatic lipid deposit and triglyceride contents. On the other hand, suppression of hepatic mTOR activity in Am mice increased lipid contents in liver.

Conclusion

Our studies indicated that hepatic mTOR signaling plays an important role in glucose and lipid metabolisms. Targeting hepatic mTOR signaling may provide a promising therapeutic approach for hepatic steatosis.

Support or Funding Information

This research was supported by grants from American Diabetes Association grant #1‐13‐BS‐225.