Rate Of Repletion Research Articles

Establishing a Rat Model of Intestinal Heme-iron Absorption

Heme iron, derived from hemoglobin and myoglobin of animal products, is efficiently absorbed and utilized by humans. Despite extensive investigation over the last several decades, the exact mechanism(s) of heme-iron absorption and tissue utilization of absorbed heme are unclear. Mice are frequently used for investigation of iron biology; however, mice do not efficiently utilize dietary iron derived from heme, so development of alternative models is warranted. Rats could more efficiently utilize dietary heme iron, but this has not been rigorously tested. Our initial studies demonstrated that dietary heme (derived from porcine RBCs) could partially correct iron-deficiency anemia (IDA) in rats of one strain (rat strain 1), but not in 2 others. We hypothesized that a heme-iron diet would fully replete strain 1 rats with IDA, at a similar rate to a non-heme iron (NHI) diet. We utilized repletion diets containing 50, 75 or 100 ppm heme iron; a control diet contained 50 ppm NHI. Forty-two, three-week-old, female strain 1 rats were weaned onto a low-iron diet with 3-4 ppm NHI, and then after 2 weeks, rats were repleted with the different diets for 8 days. Rats were housed in overhanging wire bottom stainless steel cages during the low-iron feeding period to prevent coprophagia. Blood was collected from the tail vein at baseline and every 4 days thereafter to track correction of anemia. Outcomes showed that repletion of IDA rats with the 50-ppm heme-iron diet resolved the anemia; however, tissue iron depletion indicated that the rats remained iron deficient. Also, the rate of repletion was slightly slower as compared to rats repleted with the control (50 ppm NHI) diet. With higher dietary heme-iron levels, repletion was as fast, or even faster, than in control rats suggesting that a rat strain was identified that can efficiently assimilate dietary heme iron. Our studies support a role for rats as a genetic model to preferentially mimic human nutritional studies of iron and heme absorption. This investigation was funded by grant DK074867 from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (JFC, PI), and grant DK109717 from NIDDK and the Office of Dietary Supplements (to JFC, PI). 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.

Underdiagnosis of iron deficiency anemia among patients with colorectal cancer: an examination of electronic medical records

BackgroundTimely diagnosis and management of iron deficiency anemia (IDA) in colorectal cancer (CRC) patients improves overall quality of life and survival. This study assessed the proportion of CRC patients who were formally diagnosed with IDA and factors that predict a formal diagnosis of IDA and receiving iron therapy.MethodsWe retrieved electronic medical records (EMRs) of CRC patients from a large comprehensive cancer center in the Northeastern part of the United States (n = 499). We abstracted sociodemographic characteristics, relevant laboratory results, IDA diagnosis, and iron supplementation from the EMRs. We assessed relationships between participant characteristics, a diagnosis of IDA and receiving iron therapy through adjusted logistic regressions.ResultsIDA was formally diagnosed in 26 (5.2%) individuals judged by EMR documentation. Only 153 (30.7%) participants had iron laboratory results available. Among the 153 patients with iron panel data available, 113 (73.9%) had iron deficiency. Seventy-six had absolute iron deficiency as shown by ferritin levels below 100 ng/mL and iron saturation less than 20% and 37 had functional iron deficiency as shown by ferritin levels between 100 and 500 ng/mL and iron saturation less than 20%. 12% of all patients had documentation of iron therapy receipt. A formal diagnosis of IDA was not associated with any of the covariates.ConclusionsIron deficiency anemia is under-diagnosed among CRC patients and most likely under-documented in clinical notes. Rates of iron repletion are low, suggesting that many patients with IDA are untreated. Future research should explore provider-level and other strategies for improving assessment and diagnosis of IDA among CRC patients.

Intramyofibrillar glycogen drives endurance exercise capacity.

In the mid-20th century, Bergström et al. (1967) showed the world that cyclists could exercise three times as long after a high carbohydrate diet as after a low carbohydrate diet, with intermediate performance time after a mixed diet. Exercise time to exhaustion highly correlated with initial glycogen levels in the lateral portion of the quadriceps femoris. Previously, Bergström & Hultman (1966) had demonstrated using one-legged cycling that glycogen supercompensation occurred after exhausting cycling in the exercised leg but not in the leg that had rested during the exercise. Together, these studies spawned a legacy of inquiry regarding diet, glycogen and exercise which has been well-introduced and discussed by Jensen et al. (2020) in this issue of The Journal of Physiology. Given the heterogeneity of intracellular localization of glycogen in skeletal muscle fibres, key questions that arose were whether glycogen repletion after exercise would differ among the intracellular glycogen pools. Marchand et al. (2007) approached the first question by assessing glycogen repletion in vastus lateralis fibres after exhaustive cycling. Subsarcolemmal glycogen volume exceeded total myofibrillar glycogen at all time points (0–48 h) after exercise, but its rate of repletion trailed that of total myofibrillar glycogen. The intramyofibrillar pool recovered at the greatest relative rate. The authors speculated that the low initial glycogen level in the intramyofibrillar pool meant that the exercise had preferentially depleted this depot. A subsequent electron microscopy study compared depot- and fibre-type-specific glycogen use and repletion during and after a 20 km cross-country skiing time trial (Nielsen et al. 2011). Among the intermyofibrillar, intramyofibrillar and subsarcolemmal glycogen fractions, the intramyofibrillar pool suffered the greatest relative depletion during the skiing trial in type I and II fibres of triceps brachii and type I fibres of vastus lateralis. Subsarcolemmal and intermyofibrillar glycogen stores fully recovered to pre-exercise levels by 22 h after exercise independently of carbohydrate ingestion during the first 4 h after exercise. In contrast, repletion of the intramyofibrillar fraction lagged recovery of the other pools and further slackened in the absence of carbohydrate intake in the first 4 h after exercise. To address a remaining gap in the field, Jensen et al. (2020) hypothesized that intramyofibrillar glycogen would be relatively preferentially used and then repleted during and after prolonged aerobic exercise, respectively, and that exercise time-to-exhaustion would be most closely correlated to pre-exercise levels of intramyofibrillar glycogen. In homage to the pioneers of skeletal muscle glycogen research, Jensen et al. (2020) followed the diet and exercise protocol of Bergström et al. (1967). They performed fibre-typing and glycogen volume measures for vastus lateralis fibres by electron microscopy following a protocol similar to that of Nielsen et al. (2011). Intramyofibrillar glycogen volume of type I fibres before exercise and after 1 h of exercise correlated best with time to exhaustion despite having the smallest volume among the subcellular pools (Fig. 1). The subsarcolemmal glycogen fraction responded most to loading by the high carbohydrate diet. Further, the data suggest that large subsarcolemmal glycogen pools mediate sparing of intramyofibrillar glycogen in the initial hour of exercise. Standing on the shoulders of their predecessors (e.g. Bergström & Hultman, 1966; Bergström et al. 1967; Marchand et al. 2007; Nielsen et al. 2011; and others), Jensen et al. (2020) have painted an intriguing picture of depot-specific glycogen depletion and re-loading and set the stage for future discovery. Thus, they continue down the exciting trail of inquiry into diet, glycogen and exercise performance initially blazed by Bergström et al. (Bergström & Hultman, 1966; Bergström et al. 1967). None. Sole author. None.

Randomized, Double-Blind, Pharmacokinetic Equivalence Trial Comparing DRL-Rituximab With MabThera in Patients With Diffuse Large B-Cell Lymphoma

PURPOSEWe sought to compare the pharmacokinetics (PKs) of DRL-rituximab (DRL_RI; potential biosimilar) and innovator rituximab MabThera (Roche, Grenzach-Wyhlen, Germany; reference medicinal product [RMP]) in patients with diffuse large B-cell lymphoma (DLBCL). Efficacy, pharmacodynamics (PDs), safety, and immunogenicity were also compared.PATIENTS AND METHODSWe conducted a double-blind, parallel-group study in patients with untreated DLBCL who were eligible to receive cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) therapy. Patients were randomly assigned at a one-to-one ratio to receive DRL_RI or RMP for six 21-day cycles of rituximab plus CHOP, with 18 months of follow-up after day 1, cycle 6 (C6). Primary end point was C1 PKs, measured as area under the plasma concentration–time curve from day 0 to 21 (AUC0-21 days) and maximum plasma concentration (Cmax). Equivalence was defined as 90% CIs for the DRL_RI/RMP geometric mean ratios (GMRs) within 80% and 125%. Secondary end points included efficacy noninferiority measured by objective response rate (ORR) at C6 and event-free survival and overall survival at 87 weeks, PK equivalence at C6 and PD equivalence (rate of B-cell depletion and repletion), safety, and immunogenicity. The trial was stopped after sufficient patients for primary end point evaluation were enrolled. Secondary end points are reported as observed.RESULTSA total of 151 patients were randomly assigned (DRL_RI, n = 76; RMP, n = 75). DRL_RI/RMP GMRs for AUC0-21 days and Cmax in C1 were 99.77 (90% CI, 87.60 to 113.63) and 96.19 (90% CI, 88.65 to 104.38), respectively. ORR at C6 for DRL_RI and RMP were 82.0% and 84.8%, respectively. Rates of B-cell depletion/repletion, immunogenicity, and adverse events were comparable in both groups.CONCLUSIONDRL_RI and RMP had equivalent PKs, with comparable efficacy, PDs, safety, and immunogenicity.

Response of saliva Na/K ratio to changing Na supply of lactating cows under tropical conditions.

Factorial determination of the sodium (Na) requirement of heat-stressed lactating cows is hindered by accurate estimates of the Na losses through sweat. Direct studies, therefore, may be needed requiring information on the time course of healthy animals to become Na depleted and the subsequent rate of repletion. The rate of Na depletion and subsequent rate of Na repletion with two levels of dietary Na to lactating dairy cows housed under tropical conditions were investigated using the salivary Na/K. The 12 lactating cows (salivary Na/K ratio 14.6) rapidly developed clinical signs of Na deficiency, including pica, polyuria and polydipsia, reduced body weight and reduced milk yield when fed a low-Na ration (0.33 g kg-1 dry matter (DM)) for 3 weeks. Deficiency symptoms were associated with a rapid decrease in salivary Na/K ratio to <4.3 from 7 to 21 days. Subsequent repletion of the cows with NaCl to a ration concentration of 1.1 or 1.6 g Na kg-1 DM for 5 weeks did not restore salivary Na/K ratio to values of >6. A daily Na intake of heat-stressed lactating cows to a ration intake of 1.6 g Na kg-1 DM was insufficient to restore Na deficiency. One week was sufficient to deplete heat-stressed lactating cows of Na, allowing for rapid dose-response studies utilizing the salivary Na/K ratio as a parameter for Na status of cows under tropical conditions. © 2016 Society of Chemical Industry.

Safety, Tolerability, Pharmacokinetic and Pharmacodynamic Properties of SBI-087, a CD20-Directed B-cell Depleting Agent: Phase 1 Dose Escalating Studies in Patients With Either Mild Rheumatoid Arthritis or Systemic Lupus

PurposeSBI-087 is a Small Modular Immunopharmaceutical Protein™(SMIP™) drug that binds to CD20 and has been reported to deplete B cells in murine/primate studies. The safety, tolerability and pharmacokinetic/pharmacodynamic properties of SBI-087 were evaluated in patients with rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE). MethodsSingle-dose SBI-087 was evaluated in 2 Phase I, open-label, escalating-dose studies in patients with RA or SLE. The studies included 6 IV/4 SC escalating doses (RA) and 1 IV/4 SC escalating doses (SLE). Escalation was determined by tolerability/rate of B-cell depletion. Serum was collected for analyses of pharmacokinetic and pharmacodynamic (CD19+ B cells) properties and immunogenicity. Patients were followed until B-cell counts were normalized or stabilized. Safety, tolerability was evaluated from adverse events, physical examinations, vital sign measurements, ECG, and clinical laboratory results. FindingsSixty patients with RA (IV, 28; SC, 32) and 30 patients with SLE (6 per cohort) were enrolled. Mild to moderate infusion reactions occurred in several patients at the top doses in the RA study despite a pretreatment regimen of IV doses. Unanticipated reactions after SC administration of SBI-087 included fever, chills, and malaise, seen on the day of dosing in the lowest-dose cohorts in both studies. These events were abrogated in subsequent cohorts by a pre/postdose treatment regimen consisting of oral corticosteroids, acetaminophen, and an antihistamine. SBI-087 clearance (IV) ranged from 22 to 229 mL/h; volume of distribution at steady state ranged from 5 to 12 L. Apparent clearance (SC) ranged from 44.7 to 105 mL/h; volume of distribution ranged from 14.3 to 32.1 L. Overall, PK properties were similar at equivalent doses between IV/SC administrations in patients with RA/SLE. Mean t½ (IV) ranged from 2.1 to 10.7 days (less at lower doses). SBI-087 concentration and B-cell depletion were generally dose proportional across IV and SC cohorts. However, the extent of B-cell depletion was less, and rate of repletion was faster, in patients with SLE versus RA. In both studies, B-cell repletion to baseline did not occur in the majority of patients by the end of the observation period. Overall, the prevalence and type of adverse events were similar to those seen with other anti-CD20–depleting agents. ImplicationsIn patients with mild RA/SLE, SBI-087 was well tolerated when administered intravenously or subcutaneously with pre- and posttreatment regimens. B-cell depletion is long lasting, and the duration and extent of depletion may be greater in RA compared with SLE. SBI-087 exhibited slow elimination and low distribution in both populations. Clinicaltrials.gov identifiers: NCT00641225 (RA) and NCT00714116 (SLE).

Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation

Vitamin D insufficiency is prevalent in chronic kidney disease (CKD) and associated with secondary hyperparathyroidism (SHPT) and increased risk of bone and vascular disease. Unfortunately, supplementation of stage 3 or 4 CKD patients with currently recommended vitamin D2 or D3 regimens does not reliably restore serum total 25-hydroxyvitamin D to adequacy (≥30ng/mL) or effectively control SHPT. Preclinical and clinical studies were conducted to evaluate whether the effectiveness of vitamin D repletion depends, at least in part, on the rate of repletion. A modified-release (MR) oral formulation of calcifediol (25-hydroxyvitamin D3) was developed which raised serum 25-hydroxyvitamin D3 and calcitriol levels gradually. Single doses of either bolus intravenous (IV) or oral MR calcifediol were administered to vitamin D deficient rats. Bolus IV calcifediol produced rapid increases in serum 25-hydroxyvitamin D3, calcitriol and FGF23, along with significant induction of CYP24A1 in both kidney and parathyroid gland. In contrast, oral MR calcifediol produced gradual increases in serum 25-hydroxyvitamin D3 and calcitriol and achieved similar hormonal exposure, yet neither CYP24A1 nor FGF23 were induced. A 10-fold greater exposure to bolus IV than oral MR calcifediol was required to similarly lower intact parathyroid hormone (iPTH). Single doses of oral MR (450 or 900μg) or bolus IV (450μg) calcifediol were administered to patients with stage 3 or 4 CKD, SHPT and vitamin D insufficiency. Changes in serum 25-hydroxyvitamin D3 and calcitriol and in plasma iPTH were determined at multiple time-points over the following 42 days. IV calcifediol produced abrupt and pronounced increases in serum 25-hydroxyvitamin D3 and calcitriol, but little change in plasma iPTH. As in animals, these surges triggered increased vitamin D catabolism, as evidenced by elevated production of 24,25-dihydroxyvitamin D3. In contrast, MR calcifediol raised serum 25-hydroxyvitamin D3 and calcitriol gradually, and meaningfully lowered plasma iPTH levels. Taken together, these studies indicate that rapid increases in 25-hydroxyvitamin D3 trigger CYP24A1 and FGF23 induction, limiting effective exposure to calcitriol and iPTH reduction in SHPT. They also support further investigation of gradual vitamin D repletion for improved clinical effectiveness.This article is part of a Special Issue entitled "17th Vitamin D Workshop".

Vitamin D deficiency is associated with mortality and adverse vascular access outcomes in patients with end-stage renal disease

Plasma 25 hydroxycholecalciferol (vitamin D) deficiency has been associated with adverse cardiovascular outcomes in epidemiologic studies. Chronic kidney disease is associated with loss of 1α-hydroxylase and consequently vitamin D deficiency. We hypothesized that vitamin D deficiency was associated with increased mortality and increased vascular access failure in patients undergoing permanent vascular access for end-stage renal disease. This retrospective cohort study analyzed 128 patients undergoing permanent vascular access surgery between 2003 and 2012 for whom concurrent plasma vitamin D levels were also available. Levels were considered deficient at<20ng/mL. Multivariable analysis was used to determine the association between vitamin D and mortality and vascular access outcomes. The mean age was 66.7years, 96.8% were male, 32.0% were African American, and 60.9% had diabetes mellitus. In the entire cohort, 55.5% were vitamin D-deficient, despite similar rates of repletion among the vitamin D-deficient and nondeficient groups. During a median follow-up of 2.73years, there were 40 deaths (31%). Vitamin D-deficient patients tended to be younger (P= .01) and to have higher total cholesterol (P= .001) and lower albumin (P= .017) and calcium (P= .007) levels. Despite their younger age, mortality was significantly higher (P= .026) and vascular access failure was increased (P= .008) in the vitamin D-deficient group. Multivariate logistic regression analysis found vitamin D deficiency (odds ratio [OR], 3.64; 95% confidence interval [CI], 1.12-11.79; P= .031), hemodialysis through a central catheter (OR, 3.08; 95% CI, 1.04-9.12; P= .042), coronary artery disease (OR, 3.08; 95% CI, 1.06-8.94; P= .039), increased age (OR, 1.09; 95% CI, 1.03-1.15; P= .001), and albumin (OR, 0.27; 95% CI, 0.09-0.83; P= .023) remained independent predictors of mortality. Vitamin D deficiency (hazard ratio [HR], 2.34; 95% CI, 1.17-4.71; P= .02), a synthetic graft (HR, 3.50; 95% CI, 1.38-8.89; P= .009), and hyperlipidemia (HR, 0.42; 95% CI, 0.22-0.81; P= .01) were independent predictors of vascular access failure in a Cox proportional hazard model. Vitamin D deficiency is highly prevalent in patients undergoing vascular access procedures. Patients who are deficient in vitamin D have worse survival and worse vascular access outcomes. Further study is warranted to assess whether aggressive vitamin D repletion will improve outcomes in this population.

Plasticity of Mouse Brain Docosahexaenoic Acid: Modulation by Diet and Age

Decreases in brain docosahexaenoic acid (DHA) have been associated with losses in brain function leading to an interest in the conditions which lead to such brain decreases, and such variables as age. Also of relevance would be the rate of repletion of DHA when the n-3 dietary deficiency is reversed. This experiment describes dietary deficiency in n-3 fatty acids induced in weanling (3week) and young adult (7week) mice. There was an immediate and continuous loss of brain DHA with similar rates in the two age groups. Serum DHA declined more rapidly in younger animals with respect to similarly treated adults. Brain and serum docosapentaenoic acid (DPAn-6) increased more rapidly and to higher levels in the younger animals. A second experiment determined the rates of normalization of brain fatty acid profiles when alpha-linolenic acid was added to the diets of n-3 deficient mice. Brain DHA recovery occurred at a faster rate (half-time, T 1/2=1.4weeks) when begun at weaning relative to young adult mice (T 1/2=3.5weeks). Correspondingly, brain DPAn-6 recovered faster in the younger animals; the adult group had a half-time of more than twice that of the 3-week old group. This study therefore demonstrates that the young adult mouse brain DHA is somewhat plastic and can be partially depleted via a low n-3 fatty acid diet and subsequently restored when dietary n-3 fatty acids are repleted. Relevance of these findings for human nutrition is discussed.

Liver and muscle glycogen repletion using13C magnetic resonance spectroscopy following ingestion of maltodextrin, galactose, protein and amino acids

The present study evaluated whether the inclusion of protein (PRO) and amino acids (AA) within a maltodextrin (MD) and galactose (GAL) recovery drink enhanced post-exercise liver and muscle glycogen repletion. A total of seven trained male cyclists completed two trials, separated by 7 d. Each trial involved 2 h of standardised intermittent cycling, followed by 4 h recovery. During recovery, one of two isoenergetic formulations, MD-GAL (0.9 g MD/kg body mass (BM) per h and 0.3 g GAL/kg BM per h) or MD-GAL-PRO+AA (0.5 g MD/kg BM per h, 0.3 g GAL/kg BM per h, 0.4 g whey PRO hydrolysate plus l-leucine and l-phenylalanine/kg BM per h) was ingested at every 30 min. Liver and muscle glycogen were measured after depletion exercise and at the end of recovery using 1H-13C-magnetic resonance spectroscopy. Despite higher postprandial insulin concentations for MD-GAL-PRO+AA compared with MD-GAL (61.3 (se 6.2) v. 29.6 (se 3.0) mU/l, (425.8 (se 43.1) v. 205.6 (se 20.8) pmol/l) P= 0.03), there were no significant differences in post-recovery liver (195.3 (se 2.6) v. 213.8 (se 18.0) mmol/l) or muscle glycogen concentrations (49.7 (se 4.0) v. 51.1 (se 7.9) mmol/l). The rate of muscle glycogen repletion was significantly higher for MD-GAL compared with MD-GAL-PRO+AA (5.8 (se 0.7) v. 3.7 (se 0.6) mmol/l per h, P= 0.04), while there were no significant differences in the rate of liver glycogen repletion (15.0 (se 2.5) v. 13.0 (se 2.7) mmol/l per h). PRO and AA within a MD-GAL recovery drink, compared with an isoenergetic mix of MD-GAL, did not enhance but matched liver and muscle glycogen recovery. This suggests that the increased postprandial insulinaemia only compensated for the lower MD content in the MD-GAL-PRO+AA treatment.

INCAP Studies of Hematologic and Gastrointestinal Function in Healthy Individuals and those with Protein–Energy Malnutrition and Infection

Anemia is highly prevalent, especially in poorly nourished populations living in unsanitary conditions. Studies of the Central American population showed that iron was the predominant deficient hematopoietic micronutrient and that correction of nutrient deficiencies led to hematological normality as defined by WHO. The bioavailability of diverse iron compounds added to the mostly vegetable diets of such populations showed the superior absorption of chelated iron (NaFeEDTA) and its strong effectiveness in correcting iron deficiency when added to sugar. The consequences on development and mental behavioral functions as well as on work capacity of iron deficiency and anemia in infants, children and adults, and the positive effects of their correction was demonstrated. In protein-energy malnourished (PEM) children, the deficit in active tissue mass (basal oxygen consumption) and in total hemoglobin content were closely related. This relationship persisted as the rates of active tissue mass repletion was modified by levels of protein intake. This demonstrated the strong adaptive nature of hemoglobin content in response to oxygen needs in PEM and during recovery. Gastrointestinal functions in PEM and in populations demonstrated the bacterial invasion of the upper GI tract and how this resulted in secondary bile acids that are toxic to the intestinal mucosal cells impairing their absorptive functions. Environmental hygiene in populations reversed gut bacterial migration and improved GI function.

A Role for the Transcriptional Coactivator PGC-1α in Muscle Refueling

The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) has been identified as an inducible regulator of mitochondrial function. Skeletal muscle PGC-1alpha expression is induced post-exercise. Therefore, we sought to determine its role in the regulation of muscle fuel metabolism. Studies were performed using conditional, muscle-specific, PGC-1alpha gain-of-function and constitutive, generalized, loss-of-function mice. Forced expression of PGC-1alpha increased muscle glucose uptake concomitant with augmentation of glycogen stores, a metabolic response similar to post-exercise recovery. Induction of muscle PGC-1alpha expression prevented muscle glycogen depletion during exercise. Conversely, PGC-1alpha-deficient animals exhibited reduced rates of muscle glycogen repletion post-exercise. PGC-1alpha was shown to increase muscle glycogen stores via several mechanisms including stimulation of glucose import, suppression of glycolytic flux, and by down-regulation of the expression of glycogen phosphorylase and its activating kinase, phosphorylase kinase alpha. These findings identify PGC-1alpha as a critical regulator of skeletal muscle fuel stores.

Effect of glycogen concentration and form on the response to electrical stimulation and rate of post-mortem glycolysis in ovine muscle

The associations between the muscle glycogen concentration and form and the rate of post-mortem glycolysis in ovine muscle were investigated. Twenty-two merino wethers (18–24 months) were allocated to either roughage or concentrate pelleted diets for 34 days prior to slaughter. An exercise depletion/repletion model was applied four days prior to slaughter to generate differences in muscle glycogen levels at slaughter. Muscle biopsies were taken from the m. semimembranosus (SM) and m. semitendinosus (ST) prior to and immediately after exercise for muscle glycogen determination. At slaughter, one side was electrically stimulated and both sides were conventionally chilled for 24 h. The pH response to electrical stimulation (ΔpH) and the rate of pH decline adjusted to a constant temperature of 38 °C over the initial 6 h post-mortem period was determined in three muscles ( m. longissimus thoracis et lumborum LTL, SM and ST). In addition, the concentrations of glycogen, proglycogen (PG), macroglycogen (MG) and lactate in the three muscles immediately after slaughter were determined. The glycogen loss due to exercise was influenced by diet ( P < 0.01; concentrate 63% and roughage 73%) but did not differ between muscles. The rates of repletion significantly varied between muscles (SM > ST) and diet (concentrate > roughage). The available glycogen (glycogen A) and MG concentrations at slaughter varied significantly depending on the diet ( P < 0.01) and muscle ( P < 0.001). The percentage of MG relative to MG + PG varied between muscles (46%, 50% and 57% for the ST, LTL and SM). The concentration and form of available glycogen at slaughter did not influence the response to electrical stimulation after adjusting for pre-stimulation pH ( P < 0.01). The ΔpH varied significantly between muscles (0.39 ± 0.03, 0.26 ± 0.02 and 0.20 ± 0.03 for the ST, LTL and SM) after adjusting for pre-stimulation pH. Differences in the temperature adjusted rate of pH decline were observed between the muscles (LTL > SM > ST). Importantly, a positive linear association ( P = 0.05) was found between muscle glycogen A concentration at slaughter and the rate of pH decline (temperature adjusted).

Addition of glutamine to essential amino acids and carbohydrate does not enhance anabolism in young human males following exercise

We examined the effect of a post-exercise oral carbohydrate (CHO, 1 g.kg(-1).h(-1)) and essential amino acid (EAA, 9.25 g) solution containing glutamine (0.3 g/kg BW; GLN trial) versus an isoenergetic CHO-EAA solution without glutamine (control, CON trial) on muscle glycogen resynthesis and whole-body protein turnover following 90 min of cycling at 65% VO2 peak. Over the course of 3 h of recovery, muscle biopsies were taken to measure glycogen resynthesis and mixed muscle protein synthesis (MPS), by incorporation of [ring-2H5] phenylalanine. Infusion of [1-13C] leucine was used to measure whole-body protein turnover. Exercise resulted in a significant decrease in muscle glycogen (p < 0.05) with similar declines in each trial. Glycogen resynthesis following 3 h of recovery indicated no difference in total accumulation or rate of repletion. Leucine oxidation increased 2.5 fold (p < 0.05) during exercise, returned to resting levels immediately post-exercise,and was again elevated at 3 h post-exercise (p < 0.05). Leucine flux, an index of whole-body protein breakdown rate, was reduced during exercise, but increased to resting levels immediately post-exercise, and was further increased at 3 h post-exercise (p < 0.05), but only during the CON trial. Exercise resulted in a marked suppression of whole-body protein synthesis (50% of rest; p < 0.05), which was restored post-exercise; however, the addition of glutamine did not affect whole-body protein synthesis post-exercise. The rate of MPS was not different between trials. The addition of glutamine to a CHO + EAA beverage had no effect on post-exercise muscle glycogen resynthesis or muscle protein synthesis, but may suppress a rise in whole-body proteolysis during the later stages of recovery.

Effect of impaired glucose uptake on postexercise glycogen repletion in skeletal muscles of insulin-treated streptozotocin-diabetic fasted rats

During recovery from intense exercise performed while fasting, the replenishment of muscle glycogen stores from glucose requires the activation of glucose transport. This study examines if insulin-treated streptozotocin (STZ) diabetes in rats impairs the rate of muscle glucose utilization and glycogen repletion when no food is ingested during recovery from high-intensity exercise. Rats fasted for 24 hours were injected with high doses of STZ (150 mg/kg) to cause severe diabetes, and their glycemia was normalized for 10 days with twice-daily insulin injections. High-intensity exercise in these rats resulted in a marked increase in plasma glucose, which remained higher than preexercise levels thereafter, whereas in control animals, the rise in glycemia was only of a short duration. During recovery, the rates of 2-deoxy-[ 3H]glucose utilization in muscles rich in fast twitch red fibers (red and mixed gastrocnemius muscles) were much lower in STZ-diabetic than in control rats, but were not affected by diabetes in muscles comprised mainly of fast twitch white fibers (white gastrocnemius muscle). Despite these effects on glucose utilization, STZ diabetes had no inhibitory effect on the rate and extent of glycogen deposition and fractional velocities of glycogen synthase across all muscles. In conclusion, although insulin-treated STZ diabetes in fasted rats inhibits glucose transport rates in fast twitch red muscle fibers post–intense exercise, this has no effect on muscle glycogen repletion either because glucose transport does not control the rate of glycogen synthesis or because of a compensatory increase in the activity of lactate glyconeogenesis in these muscles.

Transcriptional adaptations of lipid metabolism in tibialis anterior muscle of endurance-trained athletes

It was hypothesized that transcriptional reprogramming is involved in the structural and functional adaptations of lipid metabolism in human tibialis anterior muscle (TA) from endurance-trained male subjects. RT-PCR experiments demonstrated a significant upregulation of the mRNA level of key enzymes involved in 1) lipolytic mobilization of fatty acids (FA) from intramyocellular lipid (IMCL) stores via hormone-sensitive lipase (LIPE), 2) intramyocellular FA transport via muscle fatty acid binding protein (FABP3), and 3) oxidative phosphorylation (cytochrome c oxidase I, COI), in TA of endurance-trained vs. untrained subjects. In contrast, mRNAs for factors involved in glycolysis (muscle 6-phosphofructokinase, PFKM), intramyocellular storage of FA (diacylglycerol O-acyltransferase 1, DGAT), and beta-oxidation (long-chain acyl-coenzyme A dehydrogenase, ACADL) were invariant between TA of trained and untrained subjects. Correlation analysis identified an association of LIPE with FABP3 and LPL (lipoprotein lipase) mRNA levels and indicated coregulation of the transcript level for LIPE, FABP3, and COI with the level of mRNA encoding peroxisome proliferator-activated receptor-alpha (PPAR-alpha), the master regulator of lipid metabolism. Moreover, a significant correlation existed between LPL mRNA and the absolute rate of IMCL repletion determined by magnetic resonance spectroscopy after exhaustive exercise. Additionally, the LIPE mRNA level correlated with ultrastructurally determined IMCL content and mitochondrial volume density. The present data point to a training-induced, selective increase in mRNA levels of enzymes which are involved in metabolization of intramuscular FA, and these data confirm the well-established phenomenon of enhanced lipid utilization during exercise at moderate intensity in muscles of endurance-trained subjects.

Oral iron therapy in inflammatory bowel disease: usage, tolerance, and efficacy.

Iron deficiency is common in inflammatory bowel disease (IBD). Anecdotal evidence suggests that oral iron is poorly tolerated and may exacerbate disease activity in patients with IBD. AIM The aim of this study was to retrospectively compare usage, tolerance, and efficacy of oral iron therapy in patients with IBD and noninflammatory causes of iron deficiency. Case records of 277 patients with IBD and 24 non-IBD iron-deficient control patients covering a 4-year period were retrospectively analyzed. Fifty-three of 277 (19%) of the patients with IBD studied had received oral iron. In only 40% of the patients who had IBD and 63% of the patients who did not (p = not significant) was iron deficiency formally confirmed before treatment. Intolerance to iron was reported in only 25% of the patients who had IBD and 17% of the patients who did not (p = not significant). In only two of eight adequately monitored iron-intolerant patients with IBD was iron therapy associated with an increase in inflammatory markers. When formally checked, iron repletion was successfully achieved as frequently in patients who had IBD (59%) as in patients who did not (45%). Iron therapy is often used without a formal diagnosis of iron deficiency having been made, at least in part because of the difficulty in making this diagnosis using ferritin, an acute-phase protein. Patients with IBD are no more intolerant of oral iron than other patients and have similar rates of repletion.

Effect of Copper Source and Level on the Rate and Extent of Copper Repletion in Holstein Heifers

The objective of this study was to evaluate the rate and extent of Cu repletion in Holstein heifers using two Cu sources (organic and inorganic) at two levels (15 and 30mg/kg). An additional repletion treatment included a Cu oxide bolus. Heifers (n = 50) were individually fed a total mixed ration fortified with S and Mo at 0.40%, and 15mg/kg of dry matter of the total diet, respectively. After 111 d of depletion, heifers were stratified by liver Cu concentration and randomly allotted to one of five repletion treatments. Four treatments consisted of feed sources of Cu (feed-Cu), 1) CuSO4 at 15mg/kg; 2) CuSO4 at 30mg/kg; 3) Availa-Cu at 15mg/kg; and 4) Availa-Cu at 30mg/kg. Availa-Cu is an organic Cu source that produces a Cu-amino acid complex. A fifth treatment, consisting of an intraruminal bolus (IB), provided a single dose of 25g of CuO needles. Repletion treatments were delivered in the same total mixed ration without supplemental S and Mo. Copper status was assessed in blood and liver samples collected on 14-d intervals for 70 d. Irrespective of treatment, all heifers increased in body weight during the repletion period. Liver Cu increased in each feed-Cu treatment over time. Heifers treated with an IB reached a peak in liver Cu concentration (165.5mg/kg) on d 28. Mean liver Cu concentrations were higher in heifers receiving 30mg/kg of Cu compared with heifers receiving 15mg/kg of Cu. Red blood cell superoxide dismutase (SOD) activity was higher (P<0.001) in heifers receiving CuSO4 than Availa-Cu (0.98 vs 0.87 U). Also, SOD activity was higher when heifers were supplemented with 30 vs 15mg/kg Cu (0.98 vs 0.87 U). Heifers receiving the Cu IB had higher SOD activity than heifers receiving feed-Cu sources (1.03 vs 0.92 U). Plasma ceruloplasmin concentration was higher (P<0.001) in IB-treated heifers vs. other treatments. No differences in plasma ceruloplasmin were detected for feed-Cu source or level. These results indicate that all Cu sources evaluated in this study elevated Cu status of depleted heifers, particularly when provided at higher dietary levels.

The influence of cow genetic merit for milk production on response to level of concentrate supplementation in a grass-based system

AbstractThe objective of this study was to investigate if there is a genotype ✕ feeding system interaction for milk production in Holstein-Friesian dairy cows. For this purpose, 48 high genetic merit (HM) and 48 medium genetic merit (MM) dairy cows, were used in a two (genotypes) ✕ three (levels of concentrate feeding) randomized-block design experiment in three consecutive years. In year 1, all animals were in their first lactation, while in year 2 and year 3, 18 and 12 first lactation cows replaced animals culled at the end of the previous lactation. A total of 66 cows remained in the study in the same feeding system for the 3-year duration of the study. Concentrate feeding levels were 376, 810 and 1540 kg per cow per lactation; these were identified as the LC, MC and HC feeding systems respectively. There was a separate farmlet for each feeding system; farmlets were managed so that pre-grazing and post-grazing herbage height were similar for all three feeding systems. When compared on treatment means there was a significant genotype ✕ feeding system interaction for fat yield, while for mean solid-corrected milk yield the interaction was close to statistical significance (P = 0·07). However, regression coefficients of both milk and protein yield on pedigree index for milk and protein yield were significantly different between the LC and the HC. The interaction between feeding system and the regression of both on pre-experimental milk and protein yield were close to statistical significance (P = 0·08 and P = 0·09 respectively). Outputs of milk, fat, protein and lactose were greater for the HM than the MM cows. Feeding system had a significant effect on milk, fat, protein and lactose yields. There was a significant genotype ✕ feeding system interaction for body condition score (BCS) at the end of lactation; the MM cows had a higher rate of body tissue repletion than the HM cows especially in the HC system. The results suggest that there is a genotype ✕ concentrate feeding level interaction and that feeding systems developed in the past for animals of lower genetic merit may require adaptation if they are to be optimal for higher genetic merit animals.

Gamma-Glutamyl transpeptidase and glutathione biosynthesis in non-tumorigenic and tumorigenic rat liver oval cell lines.

Glutathione synthesis and growth properties were studied in the gamma-glutamyl transpeptidase(GGT)-negative, non-tumorigenic rat liver oval cell line OC/CDE22, and in its GGT-positive, tumorigenic counterpart line M22. gamma-Glutamylcysteine synthetase (GGCS) activities were comparable. Growth rates of M22 cells exceeded those of OC/CDE22 cells at non-limiting and limiting exogenous cysteine concentrations. A monoclonal antibody (Ab 5F10) that inhibits the transpeptidatic but not the hydrolytic activity of GGT did not affect the growth rates of OC/CDE22, and decreased those of M22 to the OC/CDE22 level. In GSH-depleted M22, but not in OC/CDE22 cells, the rate and extent of GSH repletion with exogenous cysteine and glutamine exceeded those obtained with exogenous cysteine and glutamate. With Ab 5F10, repletion with cysteine/glutamine was similar to that obtained with cysteine/glutamate. Repletion with exogenous GSH occurred only in M22 cells, and was abolished by the GGT inhibitor acivicin. Repletion with gamma-glutamylcysteine (GGC) in OC/CDE22 was resistant to acivicin whereas that in M22 was inhibited by acivicin. Repletion with exogenous GSH or cysteinylglycine (CG) required aminopeptidase activity and was lower than that obtained with cysteine. Unless reduced, CG disulfide did not support GSH repletion. The findings are compatible with the notions that (i) GGT-catalyzed transpeptidation was largely responsible for the growth advantage of M22 cells at limiting cysteine concentration, and for their high GSH content via the formation of GGC from a gamma-glutamyl donor (glutamine) and cyst(e)ine, and (ii) aminopeptidase/dipeptidase activity is rate-limiting in GSH repletion when GSH or CG serve as cysteine sources.