Acute effect of a single dose of N-acetylcysteine (NAC) on prooxidant/antioxidant balance, intestinal barrier permeability and markers of skeletal muscle damage in physically active men.

This study is controlled, double-blind, parallel intervention trial in healthy men (amateur long distance runners). The purpose of this intervention is to evaluate the effect of a single dose (600 mg) of N-acetylcysteine (NAC) on prooxidant/antioxidant balance, intestinal barrier permeability and markers of skeletal muscle damage. The study will be carried out in four stages: Stage I In the first stage, blood will be drawn in all subjects at rest to assess blood coagulation indices. An echocardiogram will also be performed to assess acquired and/or congenital heart defects. If symptoms suggestive of blood clotting abnormalities and/or heart defects are confirmed by the physician caring for the subjects, such subjects will be excluded from the study. The process and results will be assessed by a medical doctor and nurse. Subjects who meet the inclusion criteria will undergo an assessment of anthropometric indices using the InBody Data Management System and will be subjected to a nutritional analysis using food diaries and the Diet 6 computer software. The process and results will be assessed by a nutritionist. Subsequently, the subjects will perform a running test with gradually increasing load on a moving treadmill (Cosmed, Germany) to assess aerobic capacity. During the test, the running speed will be increased by 2km/h every 3 min until a running speed of 14 km/h is reached, and then the angle of the treadmill to the ground will be increased by 2.5º until the body's maximum muscle workload is reached individually. During the run, continuous measurement of oxygen uptake will be carried out using a gas analyser (Oxycon, Jaeger, Germany), heart rate will be measured using a Polar-3500PE sports-tester (Finland). Blood lactate concentration will be measured by enzyme-amperometry using an analyser from EKF Biosen C-Line. The process and results will be assessed by a medical doctor and nurse. The interval between the first and second stage will be at least 7 days. The approximate time taken for stage 1 is 1,5h for each subject. Stage II The subjects will perform a 60-minute running test on a treadmill with an incline angle of -10º (this type of exercise induces eccentric muscle contractions and causes muscle microtrauma and fatigue) at 60% of their individually determined VO2max. Blood for the study will be collected before the start of the exercise test, 3 min post-exercise, at 1 h and 24 h post-exercise restitution. The total blood volume will be: approximately 21 ml. The process and results will be assessed by a medical doctor and nurse. The approximate time taken for stage 2 is 2h for each subject. Stage III At least 3 weeks rest period. Stage IV In the fourth stage, the subjects will be randomly allocated to two groups: consuming NAC or placebo. One hour after taking a dose of NAC or placebo, they will perform a 60-minute running test on a -10º treadmill at 60% of their VO2max. Blood for biochemical testing will be collected 4 times i.e. before the start of the exercise test, 3-5 min after the end of the test, at 1 h post-exercise restitution and 24 h post-exercise. The total blood volume will be 21 ml. NAC will be administered by oral tablet by nurse. To assess compliance with the intervention, NAC or placebo will be administered to subjects one hour before the exercise test. Subjects will consume NAC or placebo in the presence of a nurse. The process and results will be assessed by a medical doctor and nurse. The approximate time taken for stage 4 is 4h for each subject.