The effect of aging on the autophagic and heat shock response in human peripheral blood mononuclear cells.

Autophagy is a lysosome degradation pathway through which damaged organelles and macromolecules are degraded within the cell. A decrease in activity of the autophagic process has been linked to several age-associated pathologies, including triglyceride accumulation, mitochondrial dysfunction, muscle degeneration, and cardiac malfunction. Here, we examined the differences in the autophagic response using autophagy-inducer rapamycin (Rapa) in peripheral blood mononuclear cells (PBMCs) from young (21.8 ± 1.9 years) and old (64.0 ± 3.7 years) individuals. Furthermore, we tested the interplay between the heat shock response and autophagy systems. Our results showed a significant increase in LC3-II protein expression in response to Rapa treatment in young but not in old individuals. This was associated with a decreased response in MAP1LC3B mRNA levels, but not SQSTM1/p62. Furthermore, HSPA1A mRNA was upregulated only in young individuals, despite no differences in HSP70 protein expression. The combined findings suggest a suppressed autophagic response following Rapa treatment in older individuals.

Salivary antimicrobial protein response to prolonged running.

INTRODUCTION: Prolonged exercise may compromise immunity through a reduction of salivary antimicrobial proteins (AMPs). Salivary IgA (IgA) has been extensively studied, but little is known about the effect of acute, prolonged exercise on AMPs including lysozyme (Lys) and lactoferrin (Lac). OBJECTIVE: To determine the effect of a 50-km trail race on salivary cortisol (Cort), IgA, Lys, and Lac. METHODS: 14 subjects: (6 females, 8 males) completed a 50km ultramarathon. Saliva was collected pre, immediately after (post) and 1.5 hrs post race (+1.5). RESULTS: Lac concentration was higher at +1.5 hrs post race compared to post exercise (p < 0.05). Lys was unaffected by the race (p > 0.05). IgA concentration, secretion rate, and IgA/Osm were lower +1.5 hrs post compared to pre race (p < 0.05). Cort concentration was higher at post compared to +1.5 (p < 0.05), but was unaltered from pre race levels. Subjects finished in 7.81±1.2 hrs. Saliva flow rate did not differ between time points. Saliva Osm increased at post (p < 0.05) compared to pre race. CONCLUSIONS: The intensity could have been too low to alter Lys and Lac secretion rates and thus, may not be as sensitive as IgA to changes in response to prolonged running. Results expand our understanding of the mucosal immune system and may have implications for predicting illness after prolonged running.

Effect of heat stress on LPS-induced febrile response in D-galactosamine-sensitized rats.

We have previously reported that heat conditioning augments lipopolysaccharide (LPS)-induced fever in rats, which is accompanied by an accumulation of heat shock protein (HSP) in the liver and the reduction of the plasma level of tumor necrosis factor (TNF-alpha) (Kluger MJ, Rudolph K, Soszynski D, Conn CA, Leon LR, Kozak W, Wallen ES, and Moseley PL. Am J Physiol Regulatory Integrative Comp Physiol 273: R858-R863, 1997). In the present study we have tested whether inhibition of protein synthesis in the liver can reduce the effect of this heat conditioning on the LPS-induced febrile response in the rat. D-galactosamine (D-gal) was used to selectively inhibit liver protein synthesis. D-gal (500 mg/kg) or PBS as control was administered intraperitoneally 1 h before heat stress. LPS (50 microg/kg ip) was injected 24 h post-heat exposure. Treatment with D-gal blunted the febrile response to LPS. Moreover, heat-conditioned rats treated first with D-gal and subsequently with LPS demonstrated a profound fall in core temperature 10--18 h post-LPS. A significant increase of serum TNF-alpha accompanied this effect of D-gal on fever. Heat-conditioned animals receiving D-gal showed an inhibition in inducible HSP-70 in the liver. These data support the role of hepatic function in modulating the febrile response to LPS.

Response of F344 rats to inhalation of subclinical levels of sarin: exploring potential causes of Gulf War illness.

Subclinical, repeated exposures of F344 rats to sarin resulted in brain alterations in densities of chlonergic receptor subtypes that may be associated with memory loss and cognitive dysfunction. The exposures also depressed the immune system. The rat appears to be a good model for studying the effects of subclinical exposure to a nerve gas.

Role of cytochrome P-450 in endogenous antipyresis.

In previous reports, we (15, 18) and others (29) demonstrated data showing that various inhibitors of cytochrome P-450/epoxygenase augment fever in rats and mice, indicating that the enzyme may be involved in endogenous antipyresis. The aim of this study was to further test the hypothesis that the P-450-dependent epoxygenase pathway of arachidonic acid is part of the homeostatic system to control the height of fever. Sprague-Dawley rats were implanted with biotelemeters to monitor body temperature. Fever was induced by intraperitoneal injection of lipopolysaccharide (LPS; 80 microg/kg). We demonstrate that intraperitoneal administration of P-450 inducers (bezafibrate and dehydroepiandrosterone, 10 and 100 mg/kg) before LPS reduced fever in rats in a dose-dependent manner. In complementary experiments, rats were implanted with brain cannulas in addition to the biotelemeters. Various isomers of epoxyeicosanoids were administered into the lateral ventricle at doses of 0.01 to 10 microg/rat to test their influence on LPS-induced fever in rats. Four of five isomers were antipyretic in a dose-dependent manner. The most potent antipyretic isomers were 11, 12-epoxyeicosatrienoic acid (EET) followed by 14,15-EET, 8,9-EET, and 12(R) hydroxyeicosatetraenoic acid. These data support the hypothesis that the cytochrome P-450/epoxygenase pathway of arachidonate metabolism is part of the endogenous antipyretic system.

Endotoxaemia does not limit heat tolerance in rats: the role of plasma lipoproteins.

Severe hyperthermia disrupts the intestinal barrier, allowing bacterial lipopolysaccharides (LPS) to enter the bloodstream. Since the symptoms of heat stroke resemble those of endotoxic shock, there is a common belief that endotoxaemia induces heat stroke. Therefore, we studied the effects of different doses, from moderate to sublethal, of Escherichia coli LPS and an antipyretic (indomethacin) upon the temperature equilibrium of the brain and body of rats exposed to a constant ambient temperature of 38 degrees C. The animals were then heated until they developed heat stroke, which was identified using a critical thermal maximum (CTM) behavioural test. In separate experiments on defence against endotoxaemia, we compared plasma lipid composition in rats exposed to a sublethal dose of LPS, hyperthermia and heat stroke. Neither LPS nor indomethacin, injected into rats while they were in a hyperthermic steady-state condition of 40-41 degrees C, influenced their thermal equilibrium. Unexpectedly, moderate doses of LPS significantly elevated the thermal tolerance of rats, such that the mean (SEM) CTM value of body temperature was raised from 42.7 (0.3) degrees C to 43.1 (0.1) degrees C (P < 0.05). Indomethacin and huge doses of LPS failed to induce any change in this parameter. The sublethal dose of LPS did not induce mortality in rats subjected to heat stroke. Hyperthermic steady-state conditions and heat stroke alone significantly decreased plasma concentrations of cholesterol, triglyceride and high-density lipoproteins, while the concentrations of low-density lipoproteins increased. A similar pattern of changes was recorded in normothermic rats injected with a sublethal dose of LPS. In conclusion, endotoxaemia in heat-stressed rats induces neither a secondary increase in their core temperature nor a decrease in their ultimate thermal tolerance. Low-density lipoproteins are likely to protect heat-stressed animals against endotoxin-induced death.

Molecular mechanisms of fever and endogenous antipyresis.

This review summarizes recent studies on endogenous antipyretic mechanisms. Fever is the result of a balance between pyrogenic and cryogenic cytokines and hormones. Although there is considerable evidence that fever evolved as a host defense response, it is important that the rise in body temperature not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified during the last 25 years. These include alpha-MSH, arginine vasopressin, glucocorticoids, TNF (under certain circumstances), and IL-10. Most recently, evidence has accumulated that cytochrome P-450 (P-450), part of the alternative pathway for arachidonic acid metabolism, plays an important role in reduction of fever and inflammation. Supporting a role for P-450 in endogenous antipyresis and antiinflammation includes evidence that (1) inducers of P-450 reduce fever, (2) inhibitors of P-450 cause a larger fever, (3) and P-450 arachidonic acid metabolites reduce fever.

Behavioral approach to the study of the upper limit of temperature tolerance in rats.

A simple test of critical thermal maximum (CTM) to assess a break-down of heat-escape behavior in rats is described. Experiments were performed on 18 unrestrained adult Wistar rats of both sexes. Hypothalamic and intraperitoneal (i.p.) temperatures as well as motor activity were simultaneously and continuously recorded in the rats exposed to heat. When animals were growing restless, as evidenced by an increase in their motor activity, which was usually recorded at hypothalamic temperatures well above 41 degrees C, we started testing CTM. To assess heat-escape behavior we used a precooled cooling bar (a part of a camp-cooler) which was placed at intervals in a climatic chamber. The hyperthermic rats, given the bar for 30 s, mounted it vigorously until they failed at particular levels of brain and body temperatures which were recognized as respective CTM values. Rapid external cooling of rats prevented lethal effects of the heat exposure. We were able to show effects of timing of heat exposure on heat tolerance. We also managed to detect small but significant differences in heat tolerance of warm-reared (an increase), cold-reared (a decrease), and bacterial-endotoxin-treated (an increase) rats. The heat-escape behavior was less heat-resistant than selective brain cooling response which was still present at CTM point. In conclusion, our CTM test is a safe and reliable way to study heat tolerance in rats.