Effect of Caffeine Ingestion on Indirect Markers of Exercise-Induced Muscle Damage: A Systematic Review of Human Trials

The effect of caffeine on mitigating exercise-induced muscle damage (EIMD) is still poorly understood, but it was hypothesized that caffeine could contribute to decreasing delayed onset muscle soreness, attenuating temporary loss of strength, and reducing circulating levels of blood markers of muscle damage. However, evidence is not conclusive and beneficial effects of caffeine ingestion on EIMD are not always observed. Factors, such as the type of exercise that induces muscle damage, supplementation protocol, and type of marker analyzed contribute to the differences between the studies. To expand knowledge on the role of caffeine supplementation in EIMD, this systematic review aimed to investigate the effect of caffeine supplementation on different markers of muscle damage. Fourteen studies were included, evaluating the effect of caffeine on indirect muscle damage markers, including blood markers (nine studies), pain perception (six studies), and MVC maximal voluntary contraction force (four studies). It was observed in four studies that repeated administration of caffeine between 24 and 72 h after muscle damage can attenuate the perception of pain in magnitudes ranging from 3.9% to 26%. The use of a single dose of caffeine pre-exercise (five studies) or post-exercise (one study) did not alter the circulating blood levels of creatine kinase (CK). Caffeine supplementation appears to attenuate pain perception, but this does not appear to be related to an attenuation of EIMD, per se. Furthermore, the effect of caffeine supplementation after muscle damage on strength recovery remains inconclusive due to the low number of studies found (four studies) and controversial results for both dynamic and isometric strength tests

ACE as a Mechanosensor to Shear Stress Influences the Control of Its Own Regulation via Phosphorylation of Cytoplasmic Ser1270

Objectives: We tested whether angiotensin converting enzyme (ACE) and phosphorylation of Ser(1270) are involved in shear-stress (SS)-induced downregulation of the enzyme. Methods and Results: Western blotting analysis showed that SS (18 h, 15 dyn/cm(2)) decreases ACE expression and phosphorylation as well as p-JNK inhibition in human primary endothelial cells (EC). CHO cells expressing wild-type ACE (wt-ACE) also displayed SS-induced decrease in ACE and p-JNK. Moreover, SS decreased ACE promoter activity in wt-ACE, but had no effect in wild type CHO or CHO expressing ACE without either the extra-or the intracellular domains, and decreased less in CHO expressing a mutated ACE at Ser(1270) compared to wt-ACE (13 vs. 40%, respectively). The JNK inhibitor (SP600125, 18 h), in absence of SS, also decreased ACE promoter activity in wt-ACE. Finally, SS-induced inhibition of ACE expression and phosphorylation in EC was counteracted by simultaneous exposure to an ACE inhibitor. Conclusions: ACE displays a key role on its own downregulation in response to SS. This response requires both the extra- and the intracellular domains and ACE Ser(1270), consistent with the idea that the extracellular domain behaves as a mechanosensor while the cytoplasmic domain elicits the downstream intracellular signaling by phosphorylation on Ser(1270).Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[01/00009-0]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[03/14115-2]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[06/52053-7]Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)[480120/2007-2

ROLE OF THE RENIN-ANGIOTENSIN SYSTEM IN RESISTANCE EXERCISE-INDUCED CARDIAC HYPERTROPHY

Para avaliar a participação do Sistema Renina Angiotensina (SRA) sobre a Hipertrofia Cardíaca de ratos submetidos ao treinamento resistido foram usados 64 Ratos Wistar divididos em: Controle (CO), Treinado (TR), Controle ou Treinado tratados com Losartan (LOS; 20mg/Kg/d) e Controle ou Treinado tratados com NaCl (SAL; 1% água). Os grupos treinados realizaram quatro séries de 12 repetições, 5x/sem/8sem, com 65-75% de 1 Repetição Máxima (1RM). Hipertrofia cardíaca (HC), obtida pelo peso úmido do VE corrigida pelo Peso Corporal (PC) e pelo Ecocardiograma, foi observada no grupo TR com nenhum prejuízo da função ventricular. Tanto a atividade da ECA, sistêmica e local no coração, quanto a atividade da renina não foram alteradas pelo treinamento. Pelo Western blotting, não foi observada alteração na expressão protéica do peptídeo angiotensina II e do receptor de angiotensina II AT2 com o treinamento, mas observou-se aumento de 31,4% na expressão dos receptores de angiotensina II AT1 no grupo TR. A administração do antagonista do receptor AT1 (Losartan) preveniu a HC em resposta ao treinamento. O mesmo não foi observado com a administração do NaCl para inibir a atividade da Renina. Esses resultados sugerem que o receptor AT1 participa da HC induzida pelo treinamento resistido sem a necessidade de aumento na concentração da angiotensina II cardíaca. Um possível mecanismo seria a ativação direta dos receptores AT1 pelo estiramento mecânico dos cardiomiócitos.Besides the well-known effects of Ang II in stimulating pathological pressure-overload cardiac hypertrophy, little information is available regarding the role of Renin-Angiotensin-System (RAS) in the exercise training-induced cardiac hypertrophy. 64 male Wistar rats were divided into 6 groups: Sedentary, Trained, Sedentary or Trained + Losartan (20mg/Kg/d, n=7) and Sedentary or Trained + Salt (NaCl 1%). The exercise protocol was: 4 x 12 bouts, 5x/week during eight weeks, with 65-75% of 1 Repetition Maximum (1RM). Using LV weight/body weight ratio and echocardiography (ECHO) we have observed cardiac hypertrophy in the Trained group without any impairment in ventricular function. Concerning RAS, neither ACE, analyzed by fluorometric assay (systemic and local in the heart), nor Renin, by RIA, activities were altered after resistance training. In addition, using Western blotting analysis, no change was observed in cardiac Ang II and AT2 receptor levels while the AT1 receptor expression was upregulated in Trained groups by 31,4%. Administration of the AT1 receptor antagonist (losartan) prevented left ventricle hypertrophy in response to the resistance training. The administration of salt, to inhibit the renin activity, did not prevent the cardiac hypertrophy. These results suggest that the AT1 receptor participates in resistance-training-induced cardiac hypertrophy without an increase in Ang II concentration in the heart. A possible mechanism is the direct activation of the AT1 receptor by mechanical stretching of cardiomyocytes

ACE and AT1 receptor are involved in mechanotransduction by hemodynamica forces independently of angiotensin II

No sistema cardiovascular, modificações de pressão e shear stress devido ao fluxo sanguíneo influenciam a morfologia e a patofisiologia dos vasos sanguíneos e do coração. Neste trabalho, estudamos o papel de duas moléculas transmembrânicas do Sistema Renina-Angiotensina: a Enzima Conversora de Angiotensina (ECA) e o Receptor de Angiotensina do tipo I (AT1) como mecanosensoras e mecanotransdutoras dessas forças físicas. A ECA foi por muito tempo conhecida somente por sua ação em converter Angiotensina I em Angiotensina II e por inativar a Bradicinina. Recentemente foi demonstrado que a ECA, além dos efeitos enzimáticos já conhecidos, pode ter sua cauda citoplasmática fosforilada e desencadear vias de sinalização intracelular. Observamos que o shear stress, mas não o estiramento, induziu a diminuição da fosforilação da porção citoplasmática da ECA após 5 minutos de estímulo e se mantém até 18 horas. Demonstramos também que a porção extracelular da ECA tem papel fundamental como mecanosensora e que a via intracelular da JNK participa da mecanotransdução em resposta ao shear stress. Além disto, demonstramos que a diminuição da fosforilação da ECA está associada na diminuição da sua expressão pelo shear stress. O receptor AT1 é a principal molécula efetora das ações da angiotensina II. Recentemente foi demonstrado que esse receptor pode também ser ativado por forças físicas, estiramento celular, independentemente da presença da angiotensina II. No presente estudo, observamos que o receptor AT1 é ativado pelo shear stress e que o Candesartan, mas não o Losartan, é capaz de impedir esta resposta. A via intracelular ativada é dependente de proteína-G e da entrada de cálcio do meio extracelular. Interessantemente, a pré-exposicao dos receptores ao shear stress diminuem a responsividade dos receptores ao peptídeo Angiotensina II porém a Angiotensina II não é capaz de inibir a ativação pelo shear stress.. Em conjunto, demonstramos novos mecanismos de ação da ECA e do AT1 que são duas importantes moléculas do sistema renina angiotensina. A modulação destes componentes por estímulos mecânicos traz novas possibilidades de intervenções farmacologicas sobre esse sistema bem como o melhor entendimento da participação dessas moléculas na fisiopatologia cardiovascular.Hemodynamic forces such as pressure and shear stress modulate the patophysiolgy of the cardiovascular system. In this study, we investigated two transmembranic key molecules of the renin-angiotensin system (RAS) as mechanosensors and mechanotransducers of physical forces: Angiotensin Converting Enzyme (ACE) and Angiotensin II type 1 Receptor (AT1). ACE is an enzyme that converts angiotensin I in angiotensin II. Recently, it was demonstrated that ACE cytoplasmic tail can be phosphorylated by ACE inhibitors and elicited intracellular cell signaling. Here, we observed that shear stress, but not stretch, decreased ACE cytoplasmic phosphorylation after 5 minutes and maintained up to 18 hours. ACE extracellular portion act as mechanosensor and JNK pathway participate in the mechanotransduction activation. In addition, we also demonstrate that decrease in ACE phosphorylation is involved in ACE expression downregulation by shear stress. AT1 receptor is the main effector molecule of angiotensin II cellular responses. It has recently been shown that AT1 receptor can directly be activated by mechanical stretch stress through an angiotensin-II-independent mechanism. In the present study, we observed that shear stress also activates AT1 receptor which is blocked by Candesartan, but not by Losartan. The intracellular pathway activated by shear stress involves both G-protein and extracellular calcium. Interestingly, preconditioning of AT1 receptor by shear stress impairs its responsiveness to angiotensin II while the pretreatment with angiotensin II still allow AT1 responsiveness to shear stress. Altogether, we demonstrated that ACE and AT1 receptor activates intracellular signal in response to mechanical force. This new concept for the RAS, the modulation of these molecules by mechanical forces gives new insigh into the discovery for pharmacological interventions to the RA

ACE mutants used to dissect the SS-induced response in CHO cells.

<p>(A) Schematic diagram of wt-ACE, Cyt-del-ACE, Extra-del-ACE, and S¹²⁷⁰A-ACE. (B) Analysis of ACE constructs expression in the cell lineages by PCR using specific primers to extracellular (Primer 1) and intracellular (Primer 2) domain of ACE. (C) Representative western blots using antibody against ACE Ser¹²⁷⁰ phosphorylation or total ACE expression (by Dr Sergei M Danilov). 10 ug of protein was loaded in the gel for each sample. (D). Representative western blots to demonstrate S¹²⁷⁰A-ACE mutant localized on cell membrane fraction (C for cytoplasmic fraction and M for membrane bound fractions).</p

SS-induced decrease in ACE and phosphorylation on Ser¹²⁷⁰ is counteracted by ACE inhibitor treatment.

<p>(A) ACE phosphorylation on Ser¹²⁷⁰, (B) ACE protein expression downregulation, and (C) Representative western blots. Saphenous vein endothelial cells were concomitant submitted to laminar shear stress (15 dyne/cm²; SS 18 h) and treated with ACE inhibitor enelapril (Ena, 1 µM). Each bar represents mean ± SEM of 3 to 4 separate experiments. *p<0.05 vs control (CTRL).</p

CHO cells expressing ACE recapitulate the behavior of endothelial cells.

<p>ACE phosphorylation on Ser¹²⁷⁰ and p-JNK is diminuished in CHO cells expressing wild-type ACE (wt-ACE) submitted do laminar shear stress. (A) ACE phosphorylation on Ser¹²⁷⁰ in response to laminar shear stress in wt-ACE cells. (B) p-JNK in CHO, wt-ACE and S¹²⁷⁰A-ACE cells in response to laminar shear stress. Cells were exposed to 18 h of laminar shear stress (15 dyne/cm²; SS 18 h). Each bar represents mean ± SEM of 4 to 6 separate experiments. *p<0.05 vs static control (CTRL).</p

ACE extracellular and intracellular domains are necessary for SS-induced downregulation of ACE promoter activity.

<p>ACE promoter activity assessed in (A) Extra-del-ACE cells, (B) Cyto-del-ACE and (C) S¹²⁷⁰A-ACE cells submitted to shear stress (15 dyne/cm²; SS 18 h). Effects of shear-conditioned medium (Conditioning for 18 h) and treatment of wt-ACE cell with Enalapril or Captopril (1 µM, 18 h) were also assessed in Extra-del-ACE cells. The results are represented as relative luciferase activity of static control cells. Each bar is mean ± SEM of 5 to 7 separate experiments. *p<0.05 vs static control (CTRL).</p

Shear stress diminishes ACE expression and signaling in Human Safenous Vein Endothelial Cells (SVEC).

<p>(A) ACE protein expression downregulation, (B) ACE phosphorylation on Ser¹²⁷⁰, and (C) p-JNK in response to laminar shear stress. SVEC were exposed to 18 h of laminar shear stress (15 dyne/cm²; SS 18 h). Each bar represents mean ± SEM of 5 separate experiments. *p<0.05 vs static control (CTRL).</p