Inhibition of hepatic drug metabolism and carbon tetrachloride toxicity in Fischer-344 rats by exercise

Skeletal Muscle Interleukin-6 Regulates Hepatic Cytochrome P450 Expression: Effects of 16-Week High-Fat Diet and Exercise

High-fat diet (HFD) induces several changes to the pathways regulating energy homeostasis and changes the expression of the hepatic cytochrome p450 (Cyp) enzyme-system. Despite these pervious findings, it is still unclear how the effects of HFD and especially HFD in combination with treadmill running affect hepatic Cyp expression. In this study, we investigated the mRNA and protein expression of selected Cyp's in mice subjected to 16 weeks of HFD and treadmill running. To understand the regulatory mechanisms behind the exercise-induced reversion of the HFD-induced changes in Cyp expression, we used a model in which the exercise-induced myokine and known regulator of hepatic Cyp's, interleukin-6 (IL-6), were knocked out specifically in skeletal muscle. We found that HFD increased the mRNA expression of Cyp1a1 and Cyp4a10, and decreased the expression of Cyp2a4, Cyp2b10, Cyp2e1, and Cyp3a11. HFD in combination with treadmill running reversed the HFD increase in Cyp4a10 mRNA expression. In addition, we observed increased Cyp1a and Cyp3a protein expression as an effect of exercise, whereas Cyp2b expression was lowered as an effect of HFD. IL-6 effected the response in Cyp3a11 and Cyp1a expression. We observed no changes in the content of the aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, or peroxisome proliferation activator receptor alpha. In conclusion, we show that both HFD and exercise in HFD-fed animals can regulate hepatic Cyp expression and that changes in Cyp3a in response to HFD and exercise are dependent on skeletal muscular IL-6.

Physical activity and cancer prevention : pathways and targets for intervention

The prevalence of obesity, an established epidemiological risk factor for many cancers, has risen steadily for the past several decades in the US and many other countries. Particularly alarming are the increasing rates of obesity among children, portending continuing increases in the rates of obesity and obesity-related cancers for many years to come. Modulation of energy balance, via increased physical activity, has been shown in numerous comprehensive epidemiological reviews to reduce cancer risk. Unfortunately, the effects and mechanistic targets of physical activity interventions on the carcinogenesis process have not been thoroughly characterized. Studies to date suggest that exercise can exert its cancer-preventive effects at many stages during the process of carcinogenesis, including both tumour initiation and progression. As discussed in this review, exercise may be altering tumour initiation events by modifying carcinogen activation, specifically by enhancing the cytochrome P450 system and by enhancing selective enzymes in the carcinogen detoxification pathway, including, but not limited to, glutathione-S-transferases. Furthermore, exercise may reduce oxidative damage by increasing a variety of anti-oxidant enzymes, enhancing DNA repair systems and improving intracellular protein repair systems. In addition to altering processes related to tumour initiation, exercise may also exert a cancer-preventive effect by dampening the processes involved in the promotion and progression stages of carcinogenesis, including scavenging reactive oxygen species (ROS); altering cell proliferation, apoptosis and differentiation; decreasing inflammation; enhancing immune function; and suppressing angiogenesis. A paucity of data exists as to whether exercise may be working as an anti-promotion strategy via altering ROS in initiated or preneoplastic models; therefore, no conclusions can be made about this possible mechanism. The studies directly examining cell proliferation and apoptosis have shown that exercise can enhance both processes, which is difficult to interpret in the context of carcinogenesis. Studies examining the relationship between exercise and chronic inflammation suggest that exercise may reduce pro-inflammatory mediators and reduce the state of low-grade, chronic inflammation. Additionally, exercise has been shown to enhance components of the innate immune response (i.e. macrophage and natural killer cell function). Finally, only a limited number of studies have explored the relationship between exercise and angiogenesis; therefore, no conclusions can be made currently about the role of exercise in the angiogenesis process as it relates to tumour progression. In summary, exercise can alter biological processes that contribute to both anti-initiation and anti-progression events in the carcinogenesis process. However, more sophisticated, detailed studies are needed to examine each of the potential mechanisms contributing to an exercise-induced decrease in carcinogenesis in order to determine the minimum dose, duration and frequency of exercise needed to yield significant cancer-preventive effects, and whether exercise can be used prescriptively to reverse the obesity-induced physiological changes that increase cancer risk.

Influence of physical exercise on 5-HT1A receptor- and anxiety-related behaviours

Treadmill exercise (1 h at 20 m/min) has been shown to increase brain serotonin (5-HT) synthesis/metabolism in 4-day trained rats. This work has analysed whether these changes are associated with (5-HT-dependent or -independent) alterations in pre- and postsynaptic 5-HT1A receptor-mediated behaviours; in addition, the controversial hypothesis that exercised rats are less anxious than sedentary rats was tested in the elevated plus-maze and the social interaction models. Acute administration of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.125-0.5 mg/kg) triggered hyperphagia, forepaw treading, and flat body posture, the amplitude of which were not affected by training or acute exercise. In the elevated plus-maze, training, but not acute exercise, reduced the number of total arm entries. In the social interaction test, trained and acutely exercised rats displayed increased locomotion and decreased defecation, compared to resting rats, but social interaction and rearings were not affected. It is suggested that the aforementioned effects of acute exercise upon 5-HT synthesis/metabolism in short-term trained rats are not associated with changes in 5-HT1A receptor- and anxiety-related behaviours.

Chronic physical activity: hepatic hypertrophy and increased total biotransformation enzyme activity

Does chronic voluntary physical activity alter hepatic or intestinal capacities for xenobiotic biotransformation? This question was investigated by comparing biotransformation enzyme activities in liver and small intestine of active and sedentary rats. Male rats allowed unlimited access to a running wheel and fed ad lib. for 6 weeks were weight-matched to sedentary controls; the active rats ate 22% more food than the sedentary rats (P less than 0.05). Active rats ran 2.8 +/- 0.6 miles/day. Liver weights were higher in the active rats (11.2 +/- 0.2 vs 9.8 +/- 0.2 g; P less than 0.05), as were total liver protein, and liver microsomal and cytosolic protein (P less than 0.05). As a result of liver hypertrophy, the active rats showed higher total liver activity of several biotransformation enzymes, including 2-naphthol sulfotransferase, styrene oxide hydrolase, benzphetamine N-demethylase, ethacrynic acid glutathione S-transferase and morphine UDP-glucuronosyltransferase (P less than 0.05). In contrast, there was no detectable difference in total liver N-acetyltransferase activity toward p-aminobenzoic acid, 2-naphthylamine, and 2-amino-fluorene as well as, relative hepatic enzyme activity (expressed per g liver or per mg protein) and total and relative intestinal enzyme activity. We conclude that chronic voluntary physical activity, accompanied by an increased food intake, results in liver hypertrophy and potentially increases total hepatic capacity to biotransform certain xenobiotic chemicals.

Differential effects of swimming and running on microsomal metabolism in middle-aged and aged Fischer 344 rats

Cytochrome P-450 (P-450) content as well as p-nitroanisole (pNA) O-demethylase and UDP-glucuronyltransferase (UDPGT) activities were determined in livers of middle-aged (MA; 12 or 18 months) and aged (24-26 months) rats exercised by either treadmill running or swimming. In addition, aniline hydroxylase activity was measured in MA runners and aged swimmers and compared to respective sham and non-handled controls. Treadmill exercise consisted of running aged and MA rats on a motorized treadmill for 16 and 20 m/min respectively, 60 min/day and 4 times per week, for 8 weeks. Sham rats were placed on the treadmill twice per week for 5 min at 8 m/min. No differences were found in any parameter comparing sham rats to non-handled controls. Running did not affect body weight or hepatic microsomal protein during the 8-week study. A 33-35% decline in microsomal P-450 content in treadmill exercised MA and aged rats was found. PNA O-demethylase activity was decreased 30% in MA and 45% in aged runners and aniline metabolism was inhibited 21% in MA rats. UDPGT activity was not affected by running in MA or aged rats. Swimming exercise was accomplished by placing the rats in a tank of water (32-33 degrees C) filled to a depth of 2 ft. Swim time was 60 min twice daily, 5 times per week. The aged and MA rats were trained for 6 months and 1 year, respectively. Two control groups, non-swimming sedentary (dry control) and 1 min swim/day sham (wet control), were utilized. MA and aged wet controls and swimmers weighted 8% and 15% less respectively, than MA and aged sedentary rats. Microsomal protein was significantly increased in MA swimmers compared to sedentary (20%) and wet control (35%) but no change was found with swimming in the aged rats. The results of the enzymatic studies were variable in the MA rats. Increases in P-450 content were found in wet controls (16%) and swimmers (27%) of the MA group, but only the swimming change was significant. No significant change was determined for pNA metabolism between swimmers and wet (22%) or dry (17%) controls. Aged swimmers and wet controls were more consistent, with no change in any of the parameters except aniline metabolism which was significantly increased in wet controls (25%) and swimmers (28%) as compared to dry controls. No significant change in UDPGT activity was measured in either age group of swimmers.(ABSTRACT TRUNCATED AT 400 WORDS)