, Byounggwan Leea , Heejin Kimb , Mikyung Kima 
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Fatigue refers to the feeling of tiredness and a lack of energy [1]. Many studies have reported that the majority of people suffer from health problems related to fatigue [2,3]. Fatigue after exhaustive exercise can be divided into two types: peripheral muscle fatigue (local fatigue of the muscles involved in the exercise) and central fatigue (the central nervous system fails to compensate for physiological disturbances) [4,5]. Peripheral muscle fatigue caused by physical activity is primarily caused by the accumulation of lactate when anaerobic glycolysis occurs in the muscle [6]. Lactate is one of the major products from the oxidation of pyruvate by lactate dehydrogenase during glycolysis and lactate circulation is promoted by the proton-linked monocarboxylate transporter (MCT) [7,8]. The MCT family has 14 members all of whom are located in the cell membrane and function to transport monocarboxylate via single transport in and out of the cell. MCT1 is mainly present in the oxidative muscles and carries substances into the cells. MCT4 is mainly present in the fast glycolytic muscle and transports the produced substance to the outside of the cell [9].
Ginseng root is one of the traditional medical treatment used in many Asian countries to promote health and treat diseases [10]. Red ginseng, a product produced by the processing of ginseng plants, has been studied with a focus on various physiological functions, including anti-fatigue and anti-inflammatory effects [11,12]. The mechanism of the anti-fatigue properties of red ginseng remainsunclear, although many studies have reported the anti-fatigue properties of these compounds. Thus, this study investigated the anti-fatigue effect of red ginseng after exhausting exercise. We measured physical exercise capacity, such as locomotor activity, motor balance, and swimming and confirmed the reduction in the fatigue of treated animalsby measuring lactate accumulation after exhausting exercise and measuring the level of expression of mRNA and protein related to MCT1 and MCT4.
Six-year-old red ginseng powder (RGP) (ginsenoside Rg1＋Rb1＋Rg3 6 mg/g) was obtained from Jeonggwanjang (Seoul, Korea), dissolved in distilled water (DW) (22±2 ℃) and administered orally to experimental mice. This administration was performed 30 min before any evaluations and continued for 5 days.
Male 6-week-old ICR mice (29-34 g) were obtained from Hanlim Laboratory Animals Company. Animals were group housed in an animal room with controlled conditions (light on at 7 am with a 12-hour contrast cycle, a temperature of 22±2 ℃, and humidity at 55±5%). Food and water were freely available and after a 1-week adaptation period, the animals were treated with DW, 100, and 200 mg/kg RGP for 5 days via oral administration. Animal treatment and maintenance were carried out in accordance with the Principles of Laboratory Animal Care (National Institutes of Health publication no. 85-23, revised 1985) and the Animal Care and Use Guidelines of Sahmyook University (Seoul, Korea SYUIACUC2020-003).
Changes in locomotor activity were measured using the open field tests (OFT) and the EthoVision system (ver. 3.1, Noldus Information Technology, Netherlands). Each animal was treated with DW or RGP 100, or 200 mg/kg for 5 days and then placed in the observation equipment, a black Plexiglas box (42×42×42 cm). The total distance moved (cm) and movement duration (s) were monitored over a 10 min after 2 min of habituation.
Experimental mice were placed to run forward on a horizontal bar rotating at a speed of 36 rpm (47650, UgoBasile, Italy). The latency time to the first fall and the falling frequency for 10 min were measured manually. The experimental mice were habituated to the equipment once a day for 2 days before the experiment for 3 min.
The hanging wire test evaluates grip retention and serves as an indicator for fatigue and neuromuscular damage [13]. After placing the experimental mice to hold the horizontal wire (diameter 5 mm, length 150 cm, 80 cm above the floor) using their front paws, hind paws, and tail, the latency time to the first fall and falling frequency were measured for 10 min. The experimental mice were habituated to hang from the wire for 3 min the day before the start of the experiments.
The animals were pressured to swim in cold water maintained at 15±1 °C. The experimental setup included a rectangular water tank (width 22.5 cm, 40 cm, height 18 cm) made of plastic, filled with 11 cm of water. Mice were forced to swim until they were exhausted and drowned. Time to swim in the cold water was manually recorded using a stopwatch. After the experiment, the mice were wiped dry with a paper towel.
High-intensity training was conducted using an inclined treadmill [14]. Animals were treated with DW, RGP 100, or 200 mg/kg once a day for 5 days before exercise. On the day of exercise, DW or RGP was administered 30 min prior to exercise and the exercises moved from low to high intensity over a 34 min period. To create a high-intensityexercise environment, the slope of the treadmill was set at 13°. Treadmill adaptation was performed at 0/3/15/20/25 m/min for 5/2/2/2/3 min on the day of exercise, and no electric shock was applied at this stage. After this exercise was conducted, the animals received an additional electric shock (3 mV-4 mV) at 30/35/40 and 45m/min for, 5/5/5, and 5 min. After exercise, the lactate levels in each animal were measured using Accutrend Plus (05050472, Roche Diagnostics, Germany). Additionally, the lactate levels of the drug-naïve and no-exercise groups (CON) were measured to confirm the background lactate level in these animals.
The expression levels of
The amount of MCT1 and MCT4 were measured by western blot. MCT1 and MCT4 are transporters that transport lactate which is measured as a biomarker for fatigue. After the treadmill experiment, the gastrocnemius muscles of the mice were isolated, and stored at －80 ℃. Samples were homogenized in cold homogenization buffer (RIPA buffer, Biosesang, South Korea) containing phosphatase inhibitor and protease inhibitors and the homogenates were centrifuged for 20 min at 16,000 RCF at 4 ℃ and the supernatant was used. Proteins were separated on a 10% SDS/PAGE gel in the sequence of 80 volts for 15 min and 120 volts for 60 min. The separated proteins were transferred to nitrocellulose membranes and blocked with blocking buffer (5% bovine serum albumin dissolved in TBST buffer) for 60 min. Membranes were incubated with primary antibodies [anti-MCT1 polyclonal Ab (MBS8308108), anti-MCT4 monoclonal Ab (MBS9702456), and anti-beta-actin (β-Actin) mouse monoclonal Ab (A5441)] overnight at 4 ℃, then washed three times in TBST for 5 min to remove the remaining primary antibody and incubated with anti-rabbit (1:3000) or anti-mouse secondary antibodies (1:5000) for 60 min at room temperature. Each protein was detected using the ChemiDoc Imaging System (Image Lab software version 6.0, Bio-Rad, USA) after three final washes with TBST and exposure to an enhanced chemiluminescence (Clarity Western ECL) reagent. Values were normalized against β-actin and protein expression was compared to that of the control group.
All data are expressed as the mean±standard error of the mean (SEM). Statistical analysis was performed using one-way analysis of variance (ANOVA) followed by a Bonferroni's post-hoc test when significant group differences were observed. p<0.05 was considered statistically significant.
Figure. 1 compares the locomotor activity between the various treatment groups. One-way ANOVA found asignificant difference in the distance moved in each group [F(2, 24)=3.62, p<0.05; Figure. 1A]. Bonferroni's
There were no significant difference in the level of mobility duration [F(2, 25)=0.95, p=0.399; Figure. 1C] between any of the groups, but there was a general trend for increasing mobility time in the RGP groups, which was similar to the locomotor activity results.
No significant differences were observed in latency time [F(2, 22)=1.86, p=0.178; Figure. 2A] or falling frequency [F(2, 24)=1.15, p=0.331; Figure. 2B] in the rota-rod motor balance and coordination tests. However, there was a trend toward increased latency time and decreased falling frequency in the animals treated with RGP. Thus, we went on to conduct the wire tests to further evaluate the effect of RGP treatment on motor balance and coordination. The hanging wire test is used to measure both limb strength and balance after treatment of materials [15]. We found significant differences between the DW and RGP groups [F(2, 23)=5.74, p<0.01; Figure. 2C]. The post-hoc test showed that the latency time of mice treated with RGP200 increased significantly (p<0.01) when compared to DW treatment, and there was a trend of decreased falling frequency in the RGP groups, which also demonstrated some degree of dose dependence [F(2, 26)=0.80, p=0.459; Figure. 2D].
There were significant differences in the lactate levels [F(3, 34)=8.52, p<0.001; Figure. 3A] between the groups. Post-hoc tests showed that the animals treated with DW produced increased levels of lactate after exhausting exercise on the treadmill when compared to the CON group that did not exercise (p<0.001) while the animals treated with RGP200 did not significantly increase the lactate level after exercise (p<0.11).
Each group displayed significantly different levels of both
There was no significant difference in MCT1 expression [F(3, 18)=0.76, p=0.5308 Figure. 5A] between the groups. For MCT4 expression levels, one-way ANOVA found significant differences between groups [F(3, 18)=6.64, p<0.001; Figure. 5B]. Bonferroni post-tests indicated that MCT4 expression levels in RGP100 (p<0.05) and RGP200 (p<0.01) increased after exhaustive exercise compared to DW. In addition, their expression levels exhibited a trend of increase compared to the CON after exercise, although there were no significant differences in DW compared to CON (p>0.99).
The goal of this study was to investigate the effect of RGP on fatigue in mice using behavioral tests and molecular experiments. This study found that RGP has various anti-fatigue properties, as evidenced by increased exercise capacity in behavioral tests such as OFT, rota-rod tests, and hanging wire tests, as well as decreased blood lactate levels. The anti-fatigue properties of RGP are probably mediated through increased MCT4 activity in the gastrocnemius muscles of mice.
Previous studies have reported that anti-fatigue activity can be interpreted as an increase in exercise capacity [16,17]. For example, decreased locomotor activity in the OFT was interpreted as a sign of increased fatigue [18]. Hsiao et al. reported that micetreated with herbal mixtures including ginseng exhibited increased swimming time in swimming tests and anti-fatigue properties [19]. Mice treated with ginseng polysaccharide fraction or metabolized fractions demonstrated increases in swimming duration and riding time in the swimming and rota-rod tests, respectively. This suggests that RGP supplementation has a positive effect on fatigue as demonstrated by improvements in exercise capacity.
Lactate can be used as a biochemical indicator of muscle fatigue following exercise [6,20,21]. Lactate removal from tissues reduces peripheral nerve muscle fatigue and plays an important role in preserving muscle function [22]. Recovery after high-intensity exercise is affected by the rate of blood lactate reduction [23]. Our results reveal a significant decrease in lactate levels following treatment with RGP. MCT is a family of transporters that transport lactate [7,8]. Increased expression of MCT1 and MCT4 induces an increase in the rate of lactate transport and circulation [24,25]. MCT1 aids in the cellular adsorption of lactate while MCT4 releases lactate into the blood vessels [9]. The amount of MCT1 and MCT4 differs depending on the muscle type, and the type may be easily changed by different stimulation [9,26]. It has been suggested that MCT4 is mainly expressed in white muscles [25,27] and hypoxia may increase its expression [28]. Supramaximal experiments produce glycolysis [29]. Taken together, low-oxygen high-intensity training may be associated with the energy consumption of white muscles.
In conclusion, this study found that RGP has anti-fatigue properties, as evidenced by an increase in exercise capacity, lower blood lactate levels, and an increase in
The authors confirm that they do not have any conflicts of interest.
This study was supported by the National Research Foundation (NRF) funded by the Korea government (NRF-2019R1A6A3A01095209).
Fig. 1. Effect of RGP on locomotor activity and mobility time
Fig. 2. Effects of RGP on motor balance and coordination
Fig. 3. Effects of RGP on lactate levels after exhausting exercise
Fig. 4. Effects of RGP on the mRNA levels of 
Fig. 5. Effects of RGP on the MCT1 and MCT4 protein levels after exhausting exercise
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Funding Information National Research Foundation of Korea
