The role of exercise and hypoxia on glucose transport and regulation.

Muscle glucose transport activity increases with an acute bout of exercise, a process that is accomplished by the translocation of glucose transporters to the plasma membrane. This process remains intact in the skeletal muscle of individuals with insulin resistance and type 2 diabetes mellitus (T2DM). Exercise training is, therefore, an important cornerstone in the management of individuals with T2DM. However, the acute systemic glucose responses to carbohydrate ingestion are often augmented during the early recovery period from exercise, despite increased glucose uptake into skeletal muscle. Accordingly, the first aim of this review is to summarize the knowledge associated with insulin action and glucose uptake in skeletal muscle and apply these to explain the disparate responses between systemic and localized glucose responses post-exercise. Herein, the importance of muscle glycogen depletion and the key glucoregulatory hormones will be discussed. Glucose uptake can also be stimulated independently by hypoxia; therefore, hypoxic training presents as an emerging method for enhancing the effects of exercise on glucose regulation. Thus, the second aim of this review is to discuss the potential for systemic hypoxia to enhance the effects of exercise on glucose regulation.

Effects of graded hypoxia during exhaustive intermittent cycling on subsequent exercise performance and neuromuscular responses.

PURPOSE: This study examined the effect of graded hypoxia during exhaustive intermittent cycling on subsequent exercise performance and neuromuscular fatigue characteristics in normoxia. METHODS: Fifteen well-trained cyclists performed an exhaustive intermittent cycling exercise (EICE 1; 15 s at 30% of anaerobic power reserve interspersed with 45 s of passive recovery) at sea level (SL; FiO2 ~ 0.21), moderate (MH; FiO2 ~ 0.16) and severe hypoxia (SH; FiO2 ~ 0.12). This was followed, after 30 min of passive recovery in normoxia, by an identical exercise bout in normoxia (EICE 2). Neuromuscular function of the knee extensors was assessed at baseline, after EICE 1 (post-EICE 1), and EICE 2 (post-EICE 2). RESULTS: The number of efforts completed decreased with increasing hypoxic severity during EICE 1 (SL: 39 ± 30, MH: 22 ± 13, SH: 13 ± 6; p ≤ 0.02), whereas there was no difference between conditions during EICE 2 (SL: 16 ± 9, MH: 20 ± 14, SH: 24 ± 17; p ≥ 0.09). Maximal torque (p = 0.007), peripheral (p = 0.02) and cortical voluntary activation (p < 0.001), and twitch torque (p < 0.001) decreased from baseline to post-EICE 1. Overall, there were no significant difference in any neuromuscular parameters from post-EICE 1 to post-EICE 2 (p ≥ 0.08). CONCLUSION: Increasing hypoxia severity during exhaustive intermittent cycling hampered exercise capacity, but did not influence performance and associated neuromuscular responses during a subsequent bout of exercise in normoxia performed after 30 min of rest.

Changing Behaviour towards Aerobic and Strength Exercise (BASE): Design of a randomised, phase I study determining the safety, feasibility and consumer-evaluation of a remotely-delivered exercise programme in persons with multiple sclerosis.

BACKGROUND: Multiple sclerosis is a chronic progressive neurological disease. Evidence attests to the benefits of exercise, guidelines for exercise in multiple sclerosis are available. Remote-delivery of exercise adherence programmes based on the exercise guidelines require urgent testing. AIMS: The design, and outcomes of Behaviour towards Aerobic and Strength Exercise in MS (BASE-MS), a remotely-delivered exercise training study based principles of behaviour change, will further evaluate the remote-delivery of the current exercise guidelines. METHODS: BASE is a 4-month clinically relevant randomised controlled trial to explore the delivery of a remotely supervised, guidelines-based exercise programme for persons with multiple sclerosis, underpinned by principles of health behaviour change. Initially, 72 persons with mild to moderate multiple sclerosis will be randomised in a 1:1:1 allocation to receive the BASE programme, or act as controls continuing usual care. On programme completion, exercise participants will be further randomised to an optimised adherence treatment or usual adherence. Our online survey assesses the primary outcome of exercise participation, and secondary outcomes of symptoms, and correlates of behaviour change at baseline, month four, month five and month eleven. Online surveys will capture coach and participant feedback to identify the contexts, mechanisms and outcomes of BASE implementation. CONCLUSIONS: The research and clinical landscape for MS management must remain in-step with public health and health communication. BASE tests the remote-delivery of the current exercise guidelines for exercise in persons with MS. Safety, feasibility and evaluative outcomes will provide rich data for future remote-delivery of exercise in neurological conditions.

Effect of increased physical activity on fructose-induced glycemic response in healthy individuals.

BACKGROUND/OBJECTIVES: The purpose of the current study was to determine whether increased physical activity (PA) altered glycemic control while ingesting an energy-balanced high-fructose diet. SUBJECTS/METHODS: Twenty-two normal-weight men and women (age: 21.2±0.6 years; body mass index: 22.6 ±0.6 kg/m(2)) participated in a randomized, cross-over design study in which they ingested an additional 75 g of fructose for 14 days while either maintaining low PA (FR+inactive) (<4500 steps/day) or high PA (FR+active) (>12,000 steps/day). Before and following the 2-week loading period, a fructose-rich meal challenge was administered and blood was sampled at baseline and for 6 h after the meal and analyzed for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), c-peptide, glucose and insulin concentrations. RESULTS: Plasma insulin, glucose, c-peptide, GIP and GLP-1 concentrations significantly increased in response to the test meal on all test visits (P<0.05). C-peptide incremental area under the curve (AUC) decreased by 10,208 ±120 pmol/l × min for 6 h from pre to post Fr+active intervention (P=0.02) leading to a decrease in plasma insulin total AUC (pre: 58,470.2±6261.0 pmol/l; post: 49,444.3±3883.0 pmol/l; P=0.04) resulting in a decrease Δpeak[Insulin] (P=0.009). Following the FR+active intervention, GIP total AUC significantly decreased (P=0.005) yet only males had a lower total GLP-1 AUC after both interventions (P=0.049). There were no sex differences in GIP levels. CONCLUSIONS: Increased PA attenuates the deleterious effects on glycemic control caused by a high-fructose diet. These changes in glycemic control with PA are associated with decreases in insulin and GIP concentrations.

High-intensity intermittent exercise attenuates ad-libitum energy intake.

OBJECTIVE: To examine the acute effects of high-intensity intermittent exercise (HIIE) on energy intake, perceptions of appetite and appetite-related hormones in sedentary, overweight men. DESIGN: Seventeen overweight men (body mass index: 27.7±1.6 kg m(-2); body mass: 89.8±10.1 kg; body fat: 30.0±4.3%; VO(2peak): 39.2±4.8 ml kg(-1) min(-1)) completed four 30-min experimental conditions using a randomised counterbalanced design. CON: resting control, MC: continuous moderate-intensity exercise (60% VO(2peak)), HI: high-intensity intermittent exercise (alternating 60 s at 100% VO(2peak) and 240 s at 50% VO(2peak)), VHI: very-high-intensity intermittent exercise (alternating 15 s at 170% VO(2peak) and 60 s at 32% VO(2peak)). Participants consumed a standard caloric meal following exercise/CON and an ad-libitum meal 70 min later. Capillary blood was sampled and perceived appetite assessed at regular time intervals throughout the session. Free-living energy intake and physical activity levels for the experimental day and the day after were also assessed. RESULTS: Ad-libitum energy intake was lower after HI and VHI compared with CON (P=0.038 and P=0.004, respectively), and VHI was also lower than MC (P=0.028). Free-living energy intake in the subsequent 38 h remained less after VHI compared with CON and MC (P≤0.050). These observations were associated with lower active ghrelin (P≤0.050), higher blood lactate (P≤0.014) and higher blood glucose (P≤0.020) after VHI compared with all other trials. Despite higher heart rate and ratings of perceived exertion (RPE) during HI and VHI compared with MC (P≤0.004), ratings of physical activity enjoyment were similar between all the exercise trials (P=0.593). No differences were found in perceived appetite between trials. CONCLUSIONS: High-intensity intermittent exercise suppresses subsequent ad-libitum energy intake in overweight inactive men. This format of exercise was found to be well tolerated in an overweight population.

Short-term aerobic exercise training increases postprandial pancreatic polypeptide but not peptide YY concentrations in obese individuals.

OBJECTIVE: Short-term exercise training improves glycemic control, but the effect of short-term training on postprandial satiety peptide responses or perceived satiety remains unknown. We tested the hypothesis that short-term aerobic exercise training (15 days) would alter postprandial pancreatic and gut peptide (pancreatic polypeptide (PP) and peptide YY (PYY)) responses and perceived appetite and satiety in obese individuals. SUBJECTS: Thirteen healthy obese men and women (age: 42±2 years; body mass index: 30-45 kg m(-2)). MEASUREMENTS: Subjects were studied before and after 15 days of training (walking 1 h at 70-75% VO(2peak)). On the study day, subjects consumed 1500 kcal as six meals (250 kcal: 9 g protein, 40 g carbohydrate, 6 g fat), while blood samples and satiety measurements were taken at baseline and every 20 min for 12 h. Blood was analyzed for PP, PYY, glucose and insulin levels. Appetite and satiety was assessed with a visual analog scale throughout the day. RESULTS: Incremental area under the curve (iAUC) for PP increased significantly with training (pre: 2788±753; post: 3845±830 pg ml(-1)·per min for 12 h; P<0.001), but there was no difference in the PP response to each meal. The initial PP response to the first meal increased (ΔPP(min 20-0): pre 86±25; post 140±36 pg ml(-1); P<0.05) with training. PYY iAUC showed no significant changes with training but showed a significant main effect of time across meals, with the largest response being to the first meal (P<0.005). There were no changes in satiety, glucose or insulin levels with training. CONCLUSION: Short-term exercise training increases postprandial PP concentrations in obese individuals; however, PYY levels and glycemic control remain unaffected. Both PP and PYY show meal-induced increases at all meals, but PYY has a greater response at the first meal with reduced responses at subsequent meals.

Satiety, but not total PYY, Is increased with continuous and intermittent exercise.

OBJECTIVE: This study determined the hormonal and subjective appetite responses to exercise (1-h continuous versus intermittent exercise throughout the day) in obese individuals. DESIGN AND METHODS: Eleven obese subjects (>30 kg/m(2) ) underwent three 12-h study days: control condition [sedentary behavior (SED)], continuous exercise condition [(EX) 1-h exercise], and intermittent exercise condition [(INT) 12 hourly, 5-min bouts]. Blood samples (every 10 min) were measured for serum insulin and total peptide YY (PYY) concentrations, with ratings of appetite (visual analog scale [VAS): every 20 min]. Both total area under the curve (AUC), and subjective appetite ratings were calculated. RESULTS: No differences were observed in total PYY AUC between conditions, but hunger was reduced with INT (INT < EX; P < 0.05), and satiety was increased with both SED and INT conditions (INT > EX and SED > EX; P < 0.05). A correlation existed between the change in total PYY and insulin levels (r = -0.81; P < 0.05), and total PYY and satiety (r = 0.80; P < 0.05) with the EX condition, not the SED and INT conditions. CONCLUSIONS: The total PYY response to meals is not altered over the course of a 12-h day with either intermittent or continuous exercise; however, intermittent exercise increased satiety and reduced hunger to a greater extent than continuous exercise in obese individuals.

Assessment of endothelial function and blood metabolite status following acute ingestion of a fructose-containing beverage.

AIM: Fructose intake has increased concurrent with sugar intake and this increase has been implicated in contributing to the development of metabolic syndrome risk factors. Recent evidence suggests a role for uric acid (UA) as a potential mediator via suppression of nitric oxide (NO) bioavailability. The aim of this study was to explore this hypothesis by measuring changes in UA concentration and systemic NO bioavailability as well as endothelial function in response to acute ingestion of a glucose-fructose beverage. METHODS: Ten young (26.80 +/- 4.80 years), non-obese (body mass index: 25.1 +/- 2.55 kg m(-2); percent body fat: 13.5 +/- 6.9%) male subjects ingested either a glucose (100 g dextrose in 300 mL) or isocaloric glucose-fructose (glucose : fructose; 45 : 55 g in 300 mL) beverage. Blood was sampled pre- and every 15-min post-ingestion per 90 min and assayed for glucose, lactate, fructose, total nitrate/nitrate, UA and blood lipids. Forearm blood flow and pulse-wave velocity were recorded prior to and at 30 and 45 min time intervals post-ingestion, respectively, while heart rate, systolic and diastolic blood pressure were recorded every 15 min. RESULTS: The glucose-fructose ingestion was associated with a significant (P < 0.05) increase in plasma lactate concentration and altered free fatty acid levels when compared with glucose-only ingestion. However, UA was not significantly different (P = 0.08) between conditions (AUC: -1018 +/- 1675 vs. 2171 +/- 1270 micromol L(-1) per 90 min for glucose and glucose-fructose conditions respectively). Consequently, no significant (P < 0.05) difference in endothelial function or systemic NO bioavailability was observed. CONCLUSION: Acute consumption of a fructose-containing beverage was not associated with significantly altered UA concentration, endothelial function or systemic NO bioavailability.

Regulation of chemokine production in response to pro-inflammatory cytokines in first trimester decidual cells.

OBJECTIVE: Chemokines initiate the immune response by controlling leukocyte migration and lymphocyte development. Macrophage infiltration of the decidua has been implicated in the genesis of recurrent miscarriage and preeclampsia. Therefore, we determined whether cultured human decidual cells produce monocyte/macrophage-recruiting chemokines in response to a potent pro-inflammatory cytokine, interleukin-1beta (IL-1beta), and whether decidual cell-conditioned medium contains monocyte- and macrophage-chemoattractant activity. METHODS: Leukocyte-free first trimester decidual cells were treated for 6h with estradiol (E(2)) and medroxyprogesterone acetate (MPA) to mimic the steroidal milieu of pregnancy, or E(2) and MPA and IL-1beta (1 ng/ml) to mimic inflamed decidua. Total RNA was used for cDNA synthesis. Biotinylated cRNAs were generated and chemically fragmented for hybridization on Affymetrix HG_U133 Plus 2.0 chips followed by fluorescence labeling and optical scanning. Raw data generated from Affymetrix GCOS 1.2 (GeneChip Operating Software) were analyzed by GeneSpring 7.2 software. Subsequently microarray results were validated by real time RT-PCR and Western blotting. A functional study of monocyte migration was carried out also using conditioned media from culture. RESULTS: Five chemokines responsible for monocyte/macrophage chemoattraction and activation, including C-C motif ligand 2 (CCL2), CCL5, C-X-C motif ligand 2 (CXCL2), CXCL3 and CXCL8, were markedly elevated from 29- to 975-fold after exposure to IL-1beta in cultured first trimester decidual cells. The results of real-time RT-PCR (up-regulation from 43- to 3069-fold) and Western blotting (up-regulation from 15- to 300-fold) confirmed the microarray findings. Monocyte migration was significantly induced by the conditioned medium from IL-1beta-treated decidual cells. CONCLUSIONS: Treatment of first trimester decidual cells with IL-1beta induces secretion of monocyte/macrophage recruiting-chemokines and promotes monocyte migration. Extrapolation of these in vitro results to the milieu of implantation site suggests a mechanism whereby IL-1beta could mediate excessive macrophage infiltration of the decidua.

Glycogen resynthesis in the absence of food ingestion during recovery from moderate or high intensity physical activity: novel insights from rat and human studies.

The finding that during recovery from high intensity exercise, rats have the capacity to replenish their muscle glycogen stores even in the absence of food intake has provided us with an experimental model of choice to explore further this process. Our objective here is to share those questions arising from research carried out by others and ourselves on rats and humans that are likely to be of interest to comparative biochemists/physiologists. On the basis of our findings and those of others, it is proposed that across vertebrate species: (1). the capacity of muscles to replenish their glycogen stores from endogenous carbon sources is dependent on the type of physical activity and animal species; (2). lactate and amino acids are the major endogenous carbon sources mobilized for the resynthesis of muscle glycogen during recovery from exercise, their relative contributions depending on the duration of recovery and type of exercise; (3). the relative contributions of lactate glyconeogenesis and hepatic/renal gluconeogenesis to muscle glycogen synthesis is species- and muscle fiber-dependent; and (4). glycogen synthase and phosphorylase play an important role in the control of the rate of glycogen synthesis post-exercise, with the role of glucose transport being species-dependent.

Acidic hydrolysis as a mechanism for the cleavage of the Glu(298)-->Asp variant of human endothelial nitric-oxide synthase.

The 894G-->T polymorphism within exon 7 of the human endothelial nitric-oxide synthase (eNOS) gene codes for glutamate or aspartate, respectively, at residue 298 and has been associated with several diseases of cardiovascular origin. A recent report indicates that Asp(298)-eNOS (E298D) is cleaved intracellularly to 100- and 35-kDa fragments, suggesting a mechanism for reduced endothelial function. Here we have documented the precise cleavage site of the E298D variant as a unique aspartyl-prolyl (Asp(298)--Pro(299)) bond not seen in wild-type eNOS (Glu(298)). We show that E298D-eNOS, as isolated from cells and in vitro, is susceptible to acidic hydrolysis, and the 100-kDa fragment can be generated ex vivo by increasing temperature at low pH. Importantly, cleavage of E298D was eliminated using a sample buffer system designed to limit acidic hydrolysis of Asp--Pro bonds. These results argue against intracellular processing of E298D-eNOS and suggest that previously described fragmentation of E298D could be a product of sample preparation. We also found that eNOS turnover, NO production, and the susceptibility to cellular stress were not different in cells expressing WT versus E298D-eNOS. Finally, enzyme activities were identical for the respective recombinant enzymes. Thus, intracellular cleavage mechanisms are unlikely to account for associations between the exon 7 polymorphism and cardiovascular diseases.

Cloning and expression profile of human inorganic pyrophosphatase.

We have cloned a 1.23 kb cDNA from a human heart library which encodes a 32 kDa protein that is 94% identical to bovine inorganic pyrophosphatase. The protein contains an aspartate-rich signature sequence that was previously identified in yeast and prokaryotic pyrophosphatases. Our clone detects a single band on Northern blots and is expressed at modest levels in all tissues examined. The cDNA shows linkage to markers on the long arm of chromosome 10.

The Fas/Fas-ligand system: a mechanism for immune evasion in human breast carcinomas.

Breast tumors are frequently associated with a predominantly lymphocytic infiltrate, which constitutes an immune response against the tumor. In spite of this massive infiltrate, the immune response appears to be inefficient and the tumor is able to evade it. We propose that in breast cancer, tumor escape from immunological surveillance results from the induction of apoptosis of Fas-bearing activated lymphocytes by FasL-bearing breast cancer cells. To test this proposal we studied the expression of FasL by human breast carcinomas and the MCF-7 breast cancer cell line by RT-PCR, immunohistochemistry, and Western Blot. Moreover, we describe the presence of apoptosis and Fas expression in the lymphocytic population surrounding the tumor. Strong membranous and cytoplasmic staining was detected in ductal carcinomas and hyperplastic breast tissue, but it was absent from normal breast tissue. No staining was found in normal glands in the non-tumor quadrants; however, the normal appearing ducts surrounding the carcinoma (tumor quadrant) showed intense immunoreactivity. Apoptosis was found predominantly among the lymphocytic population, as well as in the blood vessels and fibro-fatty tissue close to the tumor. Further characterization of apoptotic cells demonstrated that they were CD3+ cells. Our results suggest the breast tumors may elude immunological surveillance by inducing, via the Fas/FasL system, the apoptosis of activated lymphocytes. Recent data have demonstrated FasL RNA in other tumor types. Upregulation of FasL expression in hyperplastic and normal breast ducts close to the tumor also suggests a possible role in early neoplastic transformation and proliferation.

Microinjection of mitochondria into zygotes creates a model for studying the inheritance of mitochondrial DNA during preimplantation development.

OBJECTIVE: To determine the effect of mutant mitochondria on preimplantation embryo development and of preimplantation embryo development on the survival of mutant mitochondrial DNA. DESIGN: Laboratory research. SETTING: Academic research laboratory. PATIENT(S): None. INTERVENTION(S): Mutant and wild-type mitochondria, fractionated from tissue obtained from a patient with MELAS syndrome, a mitochondrial disease, were microinjected into mouse zygotes. Control zygotes received either no injection or sham injection. MAIN OUTCOME MEASURE(S): Preimplantation embryo development and survival of mutant mitochondrial DNA as determined by polymerase chain reaction analysis. RESULT(S): After microinjection into zygotes, the MELAS mutation could be identified by polymerase chain reaction until the hatched blastocyst stage of embryo development. The survival of MELAS-injected zygotes, observed for 4 days after injection, did not differ from the survival of zygotes injected with wild-type mitochondria or from the survival of uninjected or sham-injected controls. CONCLUSION(S): It appears that preimplantation embryo development does not screen out mitochondrial DNA mutations introduced into fertilized oocytes, and low levels of mutant mitochondrial DNA do not disrupt early embryo development.

Mitochondrial deoxyribonucleic acid deletions in oocytes and reproductive aging in women.

OBJECTIVE: To determine whether oocytes from women harbor deletions in mitochondrial DNA (mtDNA) and whether deleted mtDNA is more common in oocytes from older women than oocytes from younger women. DESIGN: A polymerase chain reaction (PCR)-based strategy, which depends on deletions approximating otherwise widely separated primers to demonstrate mtDNA deletions in individual oocytes, was used. SETTING: Yale In Vitro Fertilization Clinic and Laboratory at Yale University School of Medicine. MAIN OUTCOME MEASURES: Primers flanked a region of the mitochondrial genome in which long direct repeated sequence predispose to deletions. The primers identified the 0.5-kb "common" deletion. Deleted mtDNA was represented by a 0.5-kb band when primers separated by 5 kb were used. Control reactions used primers that amplify mtDNA outside the deletion hotspot. Positive controls included brain and/or muscle from aged individuals, and negative controls included fetal tissue and DNA-free blanks. Nested primers confirmed the specificity of the deleted product. RESULTS: Unfertilized oocytes, muscle, and brain tissue contained PCR products consistent with deleted mtDNA. Fetal tissue lacked the mtDNA deletion product. Deleted mtDNA was detected in single oocytes. Oocytes from older women were more likely to contain deleted mtDNA than oocytes from younger women. CONCLUSION: Deleted mtDNA in unfertilized oocytes may serve as a marker of oocyte senescence.

A proposed nonpathogenic biological indicator for thermal inactivation of Listeria monocytogenes.

Listeria innocua M1 was developed as a thermal processing indicator organism for L. monocytogenes by selection of a rifampin- and streptomycin-resistant mutant. zetaD values were 5.6 and 5.8 degrees C, and D (68 degrees C) values were 3.8 and 4.9 s for L. monocytogenes and L. innocua, respectively, in skim milk. The advantages of easy selection, similar heat resistance, and nonpathogenicity make L. innocua M1 appropriate for challenge studies designed to evaluate process lethality with respect to L. monocytogenes.

Ineffective staff, ineffective supervision, or ineffective administration? Why some nursing homes fail to provide adequate care.

This study involved 530 nursing staff working in 25 for-profit and nonprofit nursing homes, two of which failed to meet resident care standards required for state recertification. Staff members' job attitudes, opinions regarding elderly residents, and perceptions of the organization climate varied between the successful for-profit and non-profit homes. The organization climate in the failed homes was significantly different from the climate in either the successful for-profit or successful nonprofit homes.

Outcome following femur fracture and subsequent cecal ligation and puncture in endotoxin-sensitive (C3H/HeN) and endotoxin-resistant (C3H/HeJ) mice.

This study examined the effect of sepsis following trauma in a reproducible model of sepsis--cecal ligation and puncture (CLP)--in endotoxin-sensitive (C3H/HeN) and endotoxin-resistant (CeH/HeJ) mice. Studies used CLP with a 25-gauge needle at different time intervals following injury, as induced by femur fracture (FF), to determine the effects of sublethal sepsis on survival after trauma. There was a 3% mortality for FF alone in both groups. Mortality in C3H/HeJ mice was not significantly increased over FF alone except when CLP followed FF by 3 days (45%, P less than 0.02, Chi-square). In contrast, C3H/HeN mice had significantly increased mortality rates (75 to 90%, P less than 0.001) versus FF alone at all intervals between FF and CLP. Mortality for FF plus CLP was significantly greater for C3H/HeN compared to C3H/HeJ (P less than 0.001) for all time intervals between FF and CLP. In conclusion, animals exposed to a septic episode following FF had significantly greater mortality than FF animals without a septic challenge. Endotoxin-sensitive mice had significantly higher mortality after CLP and significantly increased mortality when CLP followed FF (regardless of timing) compared to endotoxin-resistant mice.

Recombinant murine interferon-gamma inhibits the fusion of mouse alveolar macrophages in vitro but stimulates the formation of osteoclastlike cells on implanted syngeneic bone particles in mice in vivo.

Osteoclasts are multinucleated cells that originate from the fusion of mononuclear precursors and are responsible for bone resorption. Indirect evidence from in vitro studies suggests that IFN-gamma and TNF-alpha inhibit and stimulate bone resorption, respectively, but contradictory results have emerged from the literature regarding the effects of IFN-gamma on macrophage multinucleation. Using highly sensitive model systems, the present work demonstrates that, in mice, rMuIFN-gamma inhibits the fusion of alveolar macrophages in vitro but augments the number of osteoclastlike cells on implanted syngeneic bone particles in vivo. Although rMuTNF-alpha fails to stimulate macrophage multinucleation in either system, treatment of implanted animals with rMuIFN-gamma appears to limit the inflammatory reaction and favor tissue repair.