Characterization of the metabolic effects of irisin on skeletal muscle in vitro.

AIMS: This work explored the effects of irisin on metabolism, gene expression and mitochondrial content in cultured myocytes. METHODS: C2C12 myocytes were treated with various concentrations of irisin for various durations. Glycolysis and oxidative metabolism were quantified by measurement of extracellular acidification and oxygen consumption, respectively. Metabolic gene expression was measured by quantitative real-time polymerase chain reaction (qRT-PCR) and mitochondrial content was assessed by flow cytometry and confocal microscopy. RESULTS: Cells treated with irisin exhibited significantly increased oxidative metabolism. Irisin treatment also significantly increased mitochondrial uncoupling at various doses and durations. Lastly, treatment with irisin also significantly elevated metabolic gene expression including peroxisome proliferator-activated receptor γ coactivator-1 alpha (PGC-1α), nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (TFAM), irisin, glucose transporter 4 (GLUT4) and mitochondrial uncoupling protein 3 (UCP3) leading to increased mitochondrial biogenesis. CONCLUSIONS: Our observations are the first to document increased metabolism in myocytes through irisin-mediated induction of mitochondrial biogenesis and uncoupling with corresponding gene expression. These observations support the need for further investigation into the therapeutic and pharmacological effects of irisin, as well as development of irisin-based therapy.

Cardiovascular disease risk factors and diet of Fulani pastoralists of northern Nigeria.

BACKGROUND: The Fulani of northern Nigeria are seminomadic pastoralists who consume a diet rich in saturated fats, do not use tobacco, are lean, and have an active lifestyle. Little is known about their serum lipid profiles and corresponding risk of cardiovascular disease. OBJECTIVE: We measured serum lipid, homocysteine, folate, and vitamin B-12 concentrations in Fulani men and women and assessed the nutrient content of their diet. DESIGN: Blood samples from 42 men (18-64 y old) and 79 women (15-77 y old) living in the Jos Plateau of Nigeria were analyzed for cholesterol (total, HDL, and LDL), triacylglycerol, homocysteine, folate, and vitamin B-12 serum concentrations. Body composition was determined by bioelectrical impedance analysis. Dietary information was obtained with use of a 7-d dietary recall and a food-frequency questionnaire. Results were compared with US referent ranges. RESULTS: The mean energy content of the Fulani diet was relatively low (men, 6980 kJ; women, 6213 kJ) and the mean protein content was high (men, 20% of energy; women, 16% of energy). Nearly one-half of energy was provided by fat, and one-half of that was derived from saturated fatty acids. The diet provided marginal to adequate amounts of vitamins B-12, B-6, and C but only one-third of the US recommended dietary allowance for folate. The mean total cholesterol, HDL-cholesterol, and triacylglycerol concentrations of Fulani adults were within the referent ranges; the mean LDL-cholesterol concentration of Fulani adults below the range; and the mean serum homocysteine concentration of Fulani men above the range. Homocysteine and folate concentrations were inversely correlated for both men and women. CONCLUSIONS: Despite a diet high in saturated fat, Fulani adults have a lipid profile indicative of a low risk of cardiovascular disease. This finding is likely due to their high activity level and their low total energy intake.

Bcl-2 mediates sex-specific differences in recovery of mice from LPS-induced signs of sickness independent of IL-6.

Chronic pulmonary diseases are more common in boys than in girls. Therefore, we investigated the differences in signs of sickness in male and female mice that were exposed to lipopolysaccharide (LPS) by intranasal instillation. Because apoptosis is important in the resolution of inflammation, we tested the hypothesis that reduced levels of Bcl-2, a regulator of apoptosis, may play a role in gender-specific differences in response to inflammation. Bcl-2 wild-type (+/+) female mice recovered from an LPS-induced drop in body temperature and loss in body weight significantly faster than male (+/+) mice. Female heterozygous (+/-) mice showed reduced Bcl-2 levels and exhibited a slower recovery than female (+/+) mice that was similar to the recovery pattern in male (+/+) and (+/-) mice. Interleukin-6 (IL-6) activity levels in the bronchoalveolar lavage fluid were higher in male than in female mice but were not different between (+/+) and (+/-) mice. We conclude that Bcl-2 plays a role in mediating the faster recovery of female (+/+) mice from LPS-induced signs of sickness independent of IL-6. These studies indicate that apoptotic mechanisms may be involved in gender-specific differences in chronic pulmonary diseases.

Effect of voluntary exercise and food restriction in response to lipopolysaccharide in hamsters.

We tested the hypothesis that voluntary running and moderate food restriction alter the acute phase response (APR), one index of nonspecific immune function. Hamsters were kept sedentary or permitted to run and were fed ad libitum or had food restricted for 20 days and were then injected intraperitoneally with saline or lipopolysaccharide (LPS). Fever and circulating interleukin-6, serum amyloid A (SAA), serum iron, and cortisol were measured by biotelemetry, B-9 cell growth assay, indirect enzyme-linked immunosorbent assay, colorimetric analysis, and radioimmunoassay, respectively. The febrile temperature; hypoferremia; and elevation of circulating interleukin-6, SAA, and cortisol after LPS injection were not altered by exercise. Because baseline temperatures were elevated in the exercised hamsters, the change in temperature in response to LPS was less than it was in the sedentary hamsters. Food restriction significantly decreased SAA and elevated cortisol after LPS injection and depressed the absolute temperature to which the core temperature rose in response to LPS in one trial but not in another. Because food restriction depressed baseline temperatures, it also affected the change in temperature after LPS injection. The hypoferremic response to LPS was inhibited in hamsters that were both food restricted and permitted to run. We conclude that exercise does not enhance the APR to a low dose of LPS, whereas food restriction and the combination of exercise and food restriction depress some portions of the APR in hamsters.

Effect of exercise and food restriction on selected markers of the acute phase response in hamsters.

Acute aerobic exercise has been shown to elicit physiological changes characteristic of the acute phase response (APR), a nonspecific host defense response. Regular evocation of these changes may prime the immune system to improve resistance to disease. Because food deprivation is associated with an impaired APR, food restriction may prevent these beneficial changes. We tested the hypotheses that voluntary exercise elicits an APR and that food restriction modifies this response in four groups of hamsters: ad libitum-fed sedentary, ad libitum-fed exercised, food-restricted sedentary, and food-restricted exercised. Five variables altered during an APR were examined: core temperature, serum iron, serum interleukin-6, serum amyloid A, and serum glucocorticoids measured by biotelemetry, colorimetric analysis, B-9 cell growth assay, indirect enzyme-linked immunosorbent assay, and radioimmunoassay, respectively. Blood was drawn during the hamsters' inactive period after 19-20 days of access to running wheels. Resting core temperature was elevated by exercise and depressed by food restriction (P < 0.01). Iron was depressed by food restriction (P < 0.01). Cortisol, but not corticosterone, was elevated by food restriction (P < 0.001). There were no significant differences among groups in interleukin-6 (P > 0.49) or serum amyloid A (P > 0.29). We conclude that there is little evidence that voluntary exercise or exercise combined with food restriction causes an APR in hamsters.

The adaptive value of fever.

There is overwhelming evidence in favor of fever being an adaptive host response to infection that has persisted throughout the animal kingdom for hundreds of millions of years. As such, it is probable that the use of antipyretic/anti-inflammatory/analgesic drugs, when they lead to suppression of fever, results in increased morbidity and mortality during most infections; this morbidity and mortality may not be apparent to most health care workers because fever is only one of dozens of host defense responses. Furthermore, most infections are not life-threatening and subtle changes in morbidity are not easily detected.

Body temperature, motor activity, and feeding behavior of mice treated with beta-chlornaltrexamine.

The effects of an irreversible long term opioid antagonism on circadian rhythms in body temperature (Tb), locomotor activity (Act) and feeding under normal conditions and following lipopolysaccharide administration (LPS; 2.5 mg/kg) have been investigated in unrestrained mice housed at their thermoneutral zone (30 degrees C). beta-chlornaltrexamine (beta-CNA; 5 mg/kg) given intraperitoneally decreased Tb on the day of injection, depressed Act, and reduced food and water intake for several days. The drug destroyed circadian rhythm in Tb for 4 consecutive days after administration due to prevention of the night time increases in temperature, whereas mean day time Tb of mice treated with beta-CNA remained similar to controls. Between days 5-8 the day-time Tb of beta-CNA-injected mice decreased, and the mice started displaying regular daily variations albeit with smaller amplitude and at lower level than controls. The depressive effect of beta-CNA on circadian variation in activity was more prolonged than its effect on Tb suggesting that these two variables are independently regulated. beta-CNA prevented the febrile response of the mice to LPS and enhanced the hypophagic effect of LPS. We conclude that normal circadian rhythms in Tb and Act, as well as certain symptoms of sickness behavior, have an opioid component.

Behavioral thermoregulation in mice inoculated with influenza virus.

Mice housed at 30 degrees C and inoculated with a mouse-adapted influenza virus show a fall in body temperature (Tb) and a decrease in food intake to almost 0 grams per day. This study tested whether the fall in Tb could be accounted for by the decreased food intake and whether the fall in Tb was due to a decrease of thermoregulatory set point or to an inability to maintain Tb at set point level. The fall in Tb of influenza-infected mice was greater than that of food-deprived mice. When food deprived, mice given access to a thermal gradient increased their preference for warmer areas in the gradient and, as a result, Tb did not fall as much as Tb of starved mice not given access to a thermal gradient. When infected with influenza virus, mice given a thermal gradient decreased Tb less and at a slower rate than mice not given a gradient. However, this fall in Tb of influenza-infected mice was greater than that of food-deprived mice given a thermal gradient. Mice given a thermal gradient increased their preference for the warmer temperatures after inoculation; this returned to preinoculation preference for cooler temperatures during the later days of infection despite a continuous fall in Tb. Influenza-infected mice given a thermal gradient survived significantly fewer days than infected mice not given a thermal gradient. We conclude that the influenza-induced fall of Tb in mice cannot be explained solely by the decrease in food intake, and is partially due to a decrease in thermoregulatory set point.

Body temperature rhythm and response to pyrogen in exercising and sedentary hamsters.

In this study, we tested the hypothesis that daily voluntary exercise results in a chronic elevation in core temperature in the female golden hamster. Temperature and activity were measured by biotelemetry. Hamsters ran 6-7 km per night (12:12 L:D) when permitted access to wheels. No running occurred during the light periods. During the 3rd wk of running, temperatures of exercising hamsters were significantly elevated by 0.5 degree C (P less than 0.001) during the dark period and by 0.3 degree C (P less than 0.003) during the light period compared with sedentary hamsters. Cessation of running removed the difference between groups, and resumption of running restored it. Both the injection of endotoxin and the psychological stress of cage switch resulted in similar peak temperatures in exercising and sedentary hamsters despite higher pre-treatment temperatures in the exercise group. We interpret these results to support the hypothesis that regular exercise may cause an upward resetting of the set-point for body temperature.

Food restriction postpones, not prevents, exercise-induced growth in hamsters.

Voluntary exercise during ad libitum feeding accelerates growth in mature female hamsters. If food is restricted during the exercise period, growth is suppressed, but ad libitum access to food at the cessation of exercise permits rapid catch-up growth in length and weight during retirement. To see whether the exercise-induced stimulus to grow persists when food-restriction is continued during retirement, female golden hamsters were matched by weight and assigned to exercise (EX) and sedentary (SED) groups fed ad libitum and to corresponding activity groups (REST-EX, REST-SED) food-restricted to 80% of starting weight. At the end of each week for 3 weeks following retirement, one REST-EX and one REST-SED group were fed ad libitum. At 21-35 days post-refeeding, mean gains in length and weight of each exercise group were greater (p < 0.05) than the gains of the corresponding sedentary group. Thus, exercise under food restriction remained an effective stimulus for acceleration of growth throughout three weeks of continued food restriction beyond termination of exercise, and ad libitum feeding permitted the delayed expression of exercise-induced catch-up growth in hamsters.

Animal models of pulmonary infection in the compromised host: potential usefulness for studying health effects of inhaled particles.

Pulmonary infection leading to pneumonia is a significant cause of morbidity and mortality worldwide. Airborne particles have been associated with pneumonia through epidemiological research, but the mechanisms by which particles affect the incidence of pneumonia are not well established. The purpose of this review is to examine the potential of animal models to improve our understanding of the mechanisms by which inhaled particles might affect the incidence and resolution of pulmonary infection. The pathogenesis of pneumonia in most animal models differs from that in humans because humans frequently have underlying diseases that predispose them to infection with relatively low doses of pathogens. Normal, healthy animals lack the underlying pathology often found in humans and clear bacteria and viruses rapidly from their lungs. To overcome this, animals are administered large inocula of pathogens, are treated with agents that cause mucosal lesions, or are treated with immunosuppressive drugs. Alternatively, pathogenic bacteria are protected from phagocytosis by encasing them in agar. No one animal model will replicate a human disease in its entirety, and the choice of model depends upon how well the animal infection mimics the particular human response being examined. The advantages and disadvantages of animal models in current use for bacterial and viral infections important in the etiology of human pneumonia are reviewed in detail. Considerable data indicate that prior exposure to particles compromises the ability of experimental animals to resolve a subsequent infection. In addition, information is available on the effects of particle exposure on various portions of respiratory defense including phagocytic function, ciliary movement, inflammation, and antibody response in the absence of infection. In contrast, little research to date has examined the consequences of particle exposure on the host defense mechanisms of animals already infected or on their ability to resolve their infection.

Experimental cachexia: effects of MCA sarcoma in the Fischer rat.

Temporal patterns of the cachectic effects of tumor growth and their relation to systemic levels of tumor necrosis factor (TNF) and IL-6 (interleukin-6) were examined in a rat model of experimental cancer cachexia employing the methylcholanthrene (MCA) sarcoma. Fischer 344 rats, implanted with biotelemeters for measuring temperature and activity, were implanted subdermally with tumor tissue fragments. Ad libitum-fed and pair-fed controls were sham incised. Bioassays for TNF and IL-6 were performed on serial plasma samples, obtained via jugular vein at 3- to 6-day intervals throughout the experimental period. Tumor growth induced significant anorexia, weight loss, and a decline in motor activity corresponding to an increase in mean plasma IL-6 levels, independent of reduced food intake or weight loss alone as shown in pair-fed controls. A significant lowering of body temperature then developed, followed by a two- to threefold increase in water consumption. The patterns of weight loss and temperature reduction differed in rate and degree from those seen with pair feeding.

Fever, tumor necrosis factor, and interleukin-6 in young, mature, and aged Fischer 344 rats.

The purpose of this study was to compare the febrile responses of Fischer 344 rats of different ages [young (3-5 mo), mature (12-15 mo), and aged (24-27 mo; n = 8)] to two psychological stress paradigms, cage switch and exposure to an open field, as well as to injection of lipopolysaccharide (LPS). In addition, the cytokines tumor necrosis factor-alpha (TNF) and interleukin-6 were also measured in the plasma of these rats at 90 min postinjection with LPS. There was no significant difference among groups in febrile responses to switching their cages. Exposure to an open field for 30 min resulted in a smaller rise in temperature in the aged rats (0.62 degree C) than in the young rats (1.26 degrees C). This difference disappeared if rats were exposed to an open field for 60 min. Injection of LPS led to fevers that developed at a slower rate in aged rats than in the mature groups. The peak fevers, however, were not different. The activity of interleukin-6 90 min after injection of LPS was higher in aged rats (297,858 U/ml) than in young (17,462 U/ml) and mature rats (28,819 U/ml). TNF levels were also higher in aged rats (16,380 U/ml) compared with young (574 U/ml) and mature rats (36 U/ml). We conclude that although the magnitude of the febrile response is not different among rats of different ages, the rise in body temperature occurs slower in aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipopolysaccharide induces fever and depresses locomotor activity in unrestrained mice.

The purpose of this study was to characterize the basic biology of fever to lipopolysaccharide (LPS) in unrestrained mice. Although LPS has been shown to induce fevers in many laboratory animals (e.g., rats, guinea pigs, rabbits), there is some question of whether LPS causes a fall or rise in body temperature (Tb) in mice. Tb was measured by biotelemetry in unrestrained mice maintained at an ambient temperature of 30 degrees C. Intraperitoneal injections of LPS at doses of 1.0, 2.5, and 3.0 mg/kg induced dose-independent prompt decreases of Tb for 5.7 h. After this postinjection reduction, Tb increased and reached a peak at approximately 24 h postinjection. The peak rises in Tb were dose dependent. Changes in Tb due to LPS were accompanied by suppression of locomotor activity. Indomethacin, at a dose that did not affect normal Tb, enhanced the temperature-lowering effect of LPS as well as inhibited the febrile rise of Tb after LPS. Indomethacin did not modify the reduction in activity caused by the injections of LPS. Food intake of the mice was decreased by LPS in a dose-dependent manner, and tolerance developed to a second injection of LPS. We conclude that freely moving mice can develop pronounced and reproducible fevers in response to LPS, which is different in time course, dose-dependent profile, induction of pyrogenic tolerance profile, and mode of inhibition by indomethacin from those responses that have been observed in other species studied so far.

Glucocorticoids alter fever and IL-6 responses to psychological stress and to lipopolysaccharide.

The purpose of this study was to determine whether glucocorticoids exert inhibitory feedback on lipopolysaccharide (LPS)-induced fever, stress-induced fever (exposure to an open field), and plasma concentrations of interleukin-6 (IL-6)-like and tumor necrosis factor-alpha (TNF)-like activity in biotelemetered rats. Injections of LPS (50 micrograms/kg) or exposure to an open field (30 min) led to significantly higher fevers in adrenalectomized (ADX) rats than in sham-ADX rats. To test the hypothesis that higher fevers were specifically the result of an absence of glucocorticoids, the glucocorticoid antagonist RU 38486 (20 mg/kg) was administered orally to rats with intact adrenal glands. The RU 38486-treated rats had higher plasma concentrations of IL-6-like activity and developed significantly higher fevers than did vehicle-treated rats. Rats injected intracerebroventricularly with 10 ng RU 38486 also developed higher fevers. Other ADX animals were implanted subcutaneously with replacement corticosterone pellets before exposure to an open field or injection with LPS. In response to an open field or injection with LPS, ADX animals implanted with replacement pellets that mimic plasma concentrations of corticosterone observed in stressed animals (100-mg pellets) developed fevers that were significantly lower than those observed in ADX rats given placebo pellets, but that were not different from fevers in sham-ADX rats given placebo pellets. ADX animals implanted with replacement pellets that mimic plasma concentrations of corticosterone observed in unstressed animals (25-mg pellets) developed fevers that were significantly higher than those observed in sham-ADX rats given placebo pellets, but that were not different from fevers in ADX rats given placebo pellets.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of systemic and intrahypothalamic IL-6 and tumor necrosis factor during endotoxin fever in guinea pigs.

The time course of activity of interleukin-6 (IL-6) and tumor necrosis factor (TNF) was measured in blood plasma and hypothalamic push-pull perfusates during the febrile response to intramuscular injection of bacterial endotoxin (Escherichia coli, 20 micrograms/kg) in 24 guinea pigs. Injection of endotoxin caused a dramatic increase of IL-6 activity in plasma. The logarithmic values of plasma IL-6 activities showed a linear correlation to the febrile change in body temperature (r = 0.898) during the whole time course of fever. IL-6 activity in hypothalamic perfusates increased 12-fold in the first hour after pyrogen application and declined slowly despite the further increase in body temperature. Hypothalamic IL-6 activity did not correlate with the febrile increase in body temperature (r = -0.048). TNF activity in plasma, not detectable before pyrogen application, had its peak in the first hour after endotoxin injection and rapidly declined to 15-20% of the peak activity within the next 2 h and to an undetectable value 5 h after injection. In the hypothalamus TNF was not detectable before endotoxin injection, but it could be monitored in most animals after pyrogen application without a clear correlation to the fever response. These results taken together indicate that endotoxin fever represents a physiological situation in which production and release of cytokines in the peripheral immune system and in the hypothalamus are regulated and stimulated in independent patterns.

Group housing accelerates growth and induces obesity in adult hamsters.

To determine whether variable body heat loss may influence control of growth and regulation of body fat content in hamsters, mature female hamsters were housed for 7-14 wk in one of three conditions: individually in metal cages (n = 6), individually in plastic boxes with bedding (n = 6), or communally (6 per box) in plastic boxes with bedding. Their resting metabolic rate (RMR) was measured individually or in pairs of two between days 65 and 75. When thermal properties of shelter varied alone, singly housed hamsters regulated energy balance fairly accurately by compensatory changes in food intake, and their rate of growth was unaffected. In contrast, group housing induced acceleration of growth and obesity without hyperphagia, was associated with an acute inhibition of RMR in hamsters tested in pairs, and was associated with a chronic inhibition of RMR in hamsters tested individually. We conclude that conspecific body contact in mature group-housed hamsters accelerates somatic growth and increases fat deposition. Energy for this anabolism is derived, in part, from reduced RMR and, in part, from a slight increase in food consumption.