The Anti-fatigue Effects of the Low-Molecular-Weight Fraction of Bonito Extract in Mice

Abstract

Bonito extract (BE), a hot-water extract of bonito muscle, has traditionally been considered as a folk remedy for fatigue. In this study we investigated the effects of BE on physical fatigue. BE was divided into, high, mid, and low-molecular-weight fractions (LMF), to explore the effectiveness of BE compounds. The swimming times to exhaustion of mice administered 0.86 g/kg BE and those administered 0.86 g/kg LMF were significantly longer than those of the vehicle-treated mice in a forced swimming model, indicating that BE possesses an anti-fatigue effect and that the LMF contributes to this effect. The LMF was also confirmed to aid the recovery of locomotor activity after physical fatigue in a forced walking model. We also examined respiratory gas levels and found that oxygen consumption and lipid oxidation were significantly greater in the group administered LMF than in the vehicle group, indicating that LMF promotes the utilization of fatty acids as an energy source. To elucidate why the mice administered LMF showed an anti-fatigue effect, we evaluated metabolic variables during exercise. The concentrations of nonesterified fatty acids and ketone bodies were higher, whereas serum and muscle lactic acid levels were lower in the mice administered LMF than in those in the vehicle group after the start of swimming. When the results were taken as a group they indicated that the effect of BE administration on improving endurance capacity was mediated, at least partly, by an increased utilization of lipids as a source of energy during exercise.Key words bonito extract; fatigue; endurance capacity; locomotor activity; respiratory gas Biol. Pharm. Bull. 32(3) 468-474 (2009) © 2009 Pharmaceutical Society of Japan * To whom correspondence should be addressed. e-mail: yoshizu_nozawa@ajinomoto.com (LMF), using an NTU-3250 membrane filter (Nitto Denko Co., Osaka, Japan) and a Prep/Scale TFF Cartridge PLC (Millipore Co., MA, U.S.A.). The HMF was prepared by fractionation from BE using a membrane with a molecular pore size of 6000. LMF and MMF were obtained by separation of BE after the HMF had been removed using a membrane with a molecular pore size of 1000. The HMF was dried and the amount of HMF in the BE was calculated. As the drying of MMF and LMF was difficult, the amount of LMF was calculated from the ratio of free amino acid content in the LMF to that in BE. The amount of the MMF was calculated by subtracting the total amount of LMF and HMF from BE. Because all free amino acids in BE was almost concentrated into the LMF after the fractionation. The amounts of the HMF, MMF, and LMF in BE were 10.4%, 25.9%, and 63.7%, respectively. After the three fractions were prepared, we confirmed that the HMF and MMF fractions had almost no free amino acids, organic acids, minerals, or nucleic acids.Forced Swimming Model (Experiment 1) We used an adjustable-current water pool to evaluate the effect of BE and fractionated BE on physical fatigue. The details of this apparatus were described previously.10,11) Briefly, we used an ...

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