Brian R. Barnes

Physiological responses to short-term exercise in the heat after creatine loading

PURPOSE This investigation was designed to examine the influence of creatine (Cr) supplementation on acute cardiovascular, renal, temperature, and fluid-regulatory hormonal responses to exercise for 35 min in the heat. METHODS Twenty healthy men were matched and then randomly assigned to consume 0.3 g.kg(-1) Cr monohydrate (N = 10) or placebo (N = 10) for 7 d in a double-blind fashion. Before and after supplementation, both groups cycled for 30 min at 60-70% VO2(peak) immediately followed by three 10-s sprints in an environmental chamber at 37 degrees C and 80% relative humidity. RESULTS Body mass was significantly increased (0.75 kg) in Cr subjects. Heart rate, blood pressure, and sweat rate responses to exercise were not significantly different between groups. There were no differences in rectal temperature responses in either group. Sodium, potassium, and creatinine excretion rates obtained from 24-h and exercise urine collection periods were not significantly altered in either group. Serum creatinine was elevated in the Cr group but within normal ranges. There were significant exercise-induced increases in cortisol, aldosterone, renin, angiotensin I and II, atrial peptide, and arginine vasopressin. The aldosterone response was slightly greater in the Cr (263%) compared with placebo (224%) group. Peak power was greater in the Cr group during all three 10-s sprints after supplementation and unchanged in the placebo group. There were no reports of adverse symptoms, including muscle cramping during supplementation or exercise. CONCLUSION Cr supplementation augments repeated sprint cycle performance in the heat without altering thermoregulatory responses.

Alterations in mRNA and protein levels of metalloproteinases-2, -9, and -14 and tissue inhibitor of metalloproteinase-2 responses to traumatic skeletal muscle injury

This study characterizes the temporal relationship of membrane type-1 matrix metalloproteinase (MT1-MMP) and tissue inhibitor of metalloproteinase-2 (TIMP-2) expression in skeletal muscle following injury. Tibialis anterior (TA) muscles from 60 mice were exposed and injured by applying a cold steel probe (-79 degrees C) to the muscle for 10 s. Thereafter, TA muscles from uninjured and injured legs were collected at 3, 10, 24, 48, and 72 h postinjury for analysis of local MT1-MMP, TIMP-2, and matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) mRNA and protein content via quantitative RT-PCR, immunoblotting, zymography, and immunofluorescence. All data are expressed as fold change of injured leg vs. uninjured leg. MT1-MMP mRNA levels were decreased significantly at 48 and 72 h postinjury by approximately 9- and 21-fold, respectively (P < 0.01). Both TIMP-2 and MMP-2 mRNA expression significantly decreased in the injured leg by approximately 4- to 10-fold at 10-72 h postinjury (P < 0.01). MMP-9 mRNA expression was significantly increased at 10, 24, and 48 h postinjury by 6- (P < 0.05), 25-, and 12-fold (P < 0.01), respectively. Protein content of latent (63 kDa) MT1-MMP was decreased at 48 and 72 h postinjury by approximately 2-fold (P < 0.01). Content of the soluble (50 kDa) fragment of MT1-MMP was significantly increased by approximately 17-, 25-, and 67-fold at 24 (P < 0.05), 48, and 72 h (P < 0.01) postinjury, respectively. TIMP-2 protein levels diminished from 3 to 48 h postinjury by 1.5-fold to 1.8-fold (P < 0.01), before returning to baseline levels at 72 h postinjury. Zymography revealed visual increases in gelatinase activity in molecular weight regions corresponding to MMP-9 and MMP-2. In conclusion, skeletal muscle injury initiates a sequence of events in the MT1-MMP proteolytic cascade resulting in elevated levels of the soluble (50 kDa) fragment of MT1-MMP, which could enhance pericellular extracellular matrix remodeling.

IGF-I measurement across blood, interstitial fluid, and muscle biocompartments following explosive, high-power exercise

Insulin-like growth factor-I (IGF-I) resides across different biocompartments [blood, interstitial fluid (ISF), and muscle]. Whether circulating IGF-I responses to exercise reflect local events remains uncertain. We measured the IGF-I response to plyometric exercise across blood, ISF, and muscle biopsy from the vastus lateralis. Twenty volunteers (8 men, 12 women, 22 ± 1 yr) performed 10 sets of 10 plyometric jump repetitions at a 40% 1-repetition maximum. Blood, ISF, and muscle samples were taken pre- and postexercise. Circulating IGF-I increased postexercise: total IGF-I (preexercise = 546 ± 42, midexercise = 585 ± 43, postexercise = 597 ± 45, +30 = 557 ± 42, +60 = 536 ± 40, +120 = 567 ± 42 ng/ml; midexercise, postexercise, and +120 greater than preexercise, P < 0.05); Free IGF-I (preexercise = 0.83 ± 0.09, midexercise = 0.78 ± 0.10, postexercise = 0.79 ± 0.11, +30 = 0.93 ± 0.10, +60 = 0.88 ± 0.10, + 120 = 0.91 ± 0.11 ng/ml; +30 greater than all other preceding time points, P < 0.05). No exercise-induced changes were observed for ISF IGF-I (preexercise = 2.35 ± 0.29, postexercise = 2.46 ± 0.35 ng/ml). No changes were observed for skeletal muscle IGF-I protein, although IGF-I mRNA content increased ∼40% postexercise. The increase in circulating total and free IGF-I was not correlated with increases in ISF IGF-I or muscle IGF-I protein content. Our data indicate that exercise-induced increases in circulating IGF-I are not reflective of local IGF-I signaling.

A potential translational approach for bone tissue engineering through endochondral ossification.

Bone defect repair is a significant clinical challenge in orthopedic surgery. Despite tremendous efforts, the majority of the current bone tissue engineering strategies depend on bone formation via intramembranous ossification (IO), which often results in poor vascularization and limited-area bone regeneration. Recently, there has been increasing interest in exploring bone regeneration through a cartilage-mediated process similar to endochondral ossification (EO). This method is advantageous because long bones are originally developed through EO and moreover, vascularization is an inherent step of this process. Therefore, it may be possible to effectively employ the EO method for the repair and regeneration of large and segmental bone defects. Although a number of studies have demonstrated engineered bone formation through EO, there are no approaches aiming for their clinical translation. In this study, we propose a strategy modeled after the U.S. Food and Drug Administration (FDA) aproved Autologus Chondrocyte Implantation (ACI) procedure. In its implementation, we concentrated human bone marrow aspirate via a minimally manipulated process and demonstrated the potential of human bone marrow derived cells for in vitro pre-cartilage template formation and bone regeneration in vivo.

Patient-Derived and Intraoperatively Formed Biomaterial for Tissue Engineering

In this chapter, we introduce a completely intraoperative procedure for obtaining a patient-derived biomaterial in cell therapy and tissue engineering applications. An automated device for processing human peripheral-blood ensures a reproducible method for retrieving the patients cellular-rich as well as cellular-poor plasma. By substituting calcium for animal-derived thrombin, we engineer a completely autologous hydrogel that eliminates the risk of disease transmission and lowers FDA regulation hurdles. Through this chapter, we will discuss a bedside protocol developed to prepare a patient-derived hydrogel. This method can be effectively used to develop a completely intraoperative tissue engineering strategy (CITES) that can be easily translated into the clinic for surgical use.