Effect of antioxidant supplementation on skeletal muscle and metabolic profile in aging mice.

Aging induces drastic changes in muscle mass and function (sarcopenia); however, the detailed mechanisms underlying sarcopenia remain poorly understood. Recent studies suggested that age-related increases in oxidative stress induce muscle atrophy. In this study, we investigated the effect of 6-month supplementation of antioxidants, specifically piceatannol (PIC) and enzymatically modified isoquercitrin (EMIQ), on age-related physiological changes, including skeletal muscle weight and quality, in 25-month-old (OLD) mice, compared to in 4-month-old (young, YNG) C57BL/6J mice. Muscle weight corrected by body weight significantly declined in OLD mice, compared to in YNG mice. The control OLD mice also showed changes in the expression of genes related to muscle fiber type, reduced locomotor activity, and increased oxidative stress markers in blood. Consistent with the muscle weight and quality changes, whole-body fat oxidation during sedentary conditions and exercise periods in control OLD mice was significantly lower than that in YNG mice. Interestingly, compared to the control OLD mice, the PIC- or EMIQ-fed OLD mice showed higher fat oxidation. Furthermore, EMIQ, but not PIC, increased locomotor activity, the expression of genes encoding antioxidant enzymes, and suppressed the carbonylated protein in the skeletal muscle of OLD mice. These results suggested that chronic antioxidant intake could alleviate aging-related muscle function changes.

Assessing palatability of long-chain fatty acids from the licking behavior of BALB/c mice.

Dietary oils such as corn oil, olive oil, and canola oil, which primarily contain triacylglycerol and small quantities of fatty acids, are highly palatable to animals. In a previous study, we examined the short-term (60 s) licking behavior of mice and observed that they exhibited a high licking response to a low concentration of fatty acid (linoleic acid), which is comparable to that observed for pure corn oil. This finding suggests that fatty acids contribute to the palatability of dietary oils. In order to supplement our knowledge of the fundamental features of fatty acid palatability in the oral cavity, we assessed the licking behavior of BALB/c mice to investigate the palatability of various types of long-chain fatty acids. The mice showed high licking responses to 1% unsaturated 16- and 18-carbon fatty acids (palmitoleic acid, 16:1; oleic acid, 18:1; linoleic acid, 18:2; and linolenic acid, 18:3), low licking responses to 16- and 20-carbon fatty acids (palmitic acid, 16:0 and arachidonic acid, 20:4), and no significant response to saturated fatty acids (stearic acid, 18:0 and arachidic acid, 20:0) or fatty acid derivatives (methyl linoleate and linole alcohol). Additionally, there were differences in the palatability of 18-carbon unsaturated fatty acids at very low concentrations. At fatty acid concentrations of 0.04% and 0.0625%, the mice showed significant preference for linoleic acid and linolenic acid, but not oleic acid, when compared with mineral oil. These results suggest that mice show high licking responses to 16- and 18-carbon unsaturated long-chain fatty acids at low concentrations. Further, we suggest that sensitivity to fatty acids is affected by the saturated state of the fatty acid, carbon chain length, and terminal carboxyl group.

Preference for dietary fat induced by release of beta-endorphin in rats.

AIMS: To determine whether beta-endorphin contributes to the ingestion of and preference for dietary oil, we examined the relationship between the dynamics of beta-endorphin, before and after the ingestion of corn oil, and the intake volume of corn oil. MAIN METHODS: Rats were offered 5% corn oil for 20 min for 5 consecutive days so they could acquire a preference for corn oil. On day 6, seven groups of rats were presented with the oil for defined time periods, and we measured the beta-endorphin levels in the serum and cerebrospinal fluid (CSF) before and after the presentation of corn oil as well as the consumed volume of corn oil at defined time points. KEY FINDINGS: Beta-endorphin levels in serum and CSF were significantly increased 15 min after the ingestion of corn oil, followed by a rapid decrease and maintenance at the basal level throughout the rest of the experimental period. The intake of corn oil was the lowest in the time period of 15-30 min, when the beta-endorphin level reached a peak value. The intake volume of corn oil might be inversely correlated with beta-endorphin levels in serum and CSF. The pretreatment of naloxone, an antagonist of the opioid receptor, decreased the initial licking rate for corn oil and increased the latency for corn oil in the licking test. SIGNIFICANCE: The beta-endorphin was rapidly released after oil ingestion, which contributed to the hedonic preference and ingestive behavior for fat.

Contribution of gustation to the palatability of linoleic acid.

We investigated the palatability of a low concentration of linoleic acid (LA) in short-term two-bottle choice tests and licking tests. To examine the contribution of gustation, mice were rendered anosmic with olfactory nerve transection surgery and test solutions were prepared using mineral oil (saturated long-chain hydrocarbon) to minimize textural effects. In the two-bottle choice tests between various pairs of different concentrations of corn oil and LA, both anosmic and the sham-operated mice constantly preferred a higher concentration of corn oil and LA. In the licking tests, the initial licking rate for 1% LA was higher than that for mineral oil in anosmic mice. In accordance with the results of the two-bottle choice test, the initial licking rate for corn oil and LA increased in a concentration-dependent manner in both anosmic and sham-operated mice in the licking test, and reached its peak at 100% corn oil and 1% LA. A preference comparison between 1% LA and 100% corn oil showed that anosmic mice preferred 1% LA over 100% corn oil. These results suggest that mice could recognize dietary fat and fatty acid solutions in the oral cavity without any olfactory or textural cues and the fatty acid recognition on their tongues might provide a pivotal cue to how dietary fat is recognized in the oral cavity.

Mercaptoacetate inhibition of fatty acid beta-oxidation attenuates the oral acceptance of fat in BALB/c mice.

We investigated the effect of beta-oxidation inhibition on the fat ingestive behavior of BALB/c mice. Intraperitoneal administration to mice of mercaptoacetate, an inhibitor of fatty acid oxidation, significantly suppressed intake of corn oil but not intake of sucrose solution or laboratory chow. To further examine the effect of mercaptoacetate on the acceptability of corn oil in the oral cavity, we examined short-term licking behavior. Mercaptoacetate significantly and specifically decreased the number of licks of corn oil within a 60-s period but did not affect those of a sucrose solution, a monosodium glutamate solution, or mineral oil. In contrast, the administration of 2-deoxyglucose, an inhibitor of glucose metabolism, did not affect the intake or short-term licking counts of any of the tasted solutions. These findings suggest that fat metabolism is involved in the mechanism underlying the oral acceptance of fat as an energy source.

Reinforcing effect for corn oil stimulus was concentration dependent in an operant task in mice.

Corn oil is reported to elicit a conditioned place preference (CPP) in a CPP test in mice. To further investigate a reinforcing effect of corn oil, we studied whether the corn oil acts as a reinforcer under a progressive ratio (PR) schedule in the operant task. BALB/c mice were trained to lever press for sucrose and corn oil. After reaching a stable break-point for 100% corn oil, the PR test was conducted for various concentrations of corn oil (0%-100%). The reinforcing effect of corn oil was increased in a concentration-dependent manner under the PR schedule. A mineral oil and 0.3% xanthan gum as vehicles did not show any reinforcing effect in the PR test, suggesting that oily and viscous texture was not related to the reinforcing property of corn oil. The break-point for corn oil was attenuated by pretreatment with (-)-sulpiride, a D(2) antagonist, in the PR test. On the other hand, SCH23390, a D(1) antagonist, did not influence the break-point. Furthermore, the pretreatment with (-)-sulpiride or SCH23390 did not influence the intake of corn oil in a one-bottle test for 30 min, suggesting that the dopaminergic system is involved in the reinforcing effect but not the consumption of corn oil in mice. In conclusion, operant response to corn oil is concentration-dependently enhanced under the PR schedule. This reinforcing effect of corn oil is at least partly mediated through the dopaminergic systems via D(2) receptors.

The palatability of corn oil and linoleic acid to mice as measured by short-term two-bottle choice and licking tests.

Free fatty acids (FFAs) were reported to be recognized in the oral cavity and possibly involved in fatty foods recognition. To understand the importance of oil recognition in the oral cavity, we investigated the effect of various concentrations of a fatty acid or corn oil on fluid intake as well as mice's preferences in a two-bottle choice test and a licking test. Linoleic acid (LA), which is a main component of corn oil, was used as a representative FFA. In the two-bottle choice test between a pair of different concentrations of corn oil, the mice consistently adopted the higher concentration of corn oil. In the licking test for corn oil, the licking rates for the serial concentration of corn oils (0, 1, 5, 10 and 100%) were increased in a concentration-dependent manner. On the other hand, in the two-bottle test for a pair of different concentrations of LA (0, 0.125, 0.25 and 1%), 0.25% and 1% LA were preferred to mineral oil, but 0.25% and 1% LA were preferred equally in mice. In the licking test for LA, the mice showed the largest number of initial lickings for the 1% LA, while the licking rates for the high concentration of LA decreased. These results suggest that mice could discriminate the concentration of corn oil and LA in the oral cavity. We also suggest that pure corn oil is a highly preferable solution, while an optimal concentration of LA according to the preferences of mice is a low-range concentration (0.25-1%).

Sake yeast suppresses acute alcohol-induced liver injury in mice.

Brewer's and baker's yeasts appear to have components that protect from liver injury. Whether sake yeast, Saccharomyces cerevisiae Kyokai no. 9, also has a hepatoprotective effect has not been examined. Here we show that sake yeast suppresses acute alcoholic liver injury in mice. Male C57BL/6 mice that had been fed a diet containing 1% sake yeast for two weeks received three doses of ethanol (5 g/kg BW). In the mice fed sake yeast, ethanol-induced increases in triglyceride (TG) and glutamate pyruvate transaminase (GPT) were significantly attenuated and hepatic steatosis was improved. In addition, sake yeast-fed mice showed a smaller decrease in hepatic S-adenosylmethionine (SAM) level and a smaller increase in plasma homocysteine (Hcy) level after ethanol treatment than the control mice, suggesting that a disorder of methionine metabolism in the liver caused by ethanol was relieved by sake yeast. These results indicate that sake yeast protects against alcoholic liver injury through maintenance of methionine metabolism in the liver.