The brown bear (Ursus arctos) hibernates for 5 to 6 months each winter and during this time ingests no food or water and remains anuric and inactive. Despite these extreme conditions, bears do not develop azotemia and preserve their muscle and bone strength. To date most renal studies have been limited to small numbers of bears, often in captive environments. Sixteen free-ranging bears were darted and had blood drawn both during hibernation in winter and summer. Samples were collected for measurement of creatinine and urea, markers of inflammation, the calcium-phosphate axis, and nutritional parameters including amino acids. In winter the bear serum creatinine increased 2.5 fold despite a 2-fold decrease in urea, indicating a remarkable ability to recycle urea nitrogen during hibernation. During hibernation serum calcium remained constant despite a decrease in serum phosphate and a rise in FGF23 levels. Despite prolonged inactivity and reduced renal function, inflammation does not ensue and bears seem to have enhanced antioxidant defense mechanisms during hibernation. Nutrition parameters showed high fat stores, preserved amino acids and mild hyperglycemia during hibernation. While total, essential, non-essential and branched chain amino acids concentrations do not change during hibernation anorexia, changes in individual amino acids ornithine, citrulline and arginine indicate an active, although reduced urea cycle and nitrogen recycling to proteins. Serum uric acid and serum fructose levels were elevated in summer and changes between seasons were positively correlated. Further studies to understand how bears can prevent the development of uremia despite minimal renal function during hibernation could provide new therapeutic avenues for the treatment of human kidney disease.

The work presented here was carried out in collaboration between all authors. KA, BS, and OF defi ned the research subject. ALE and JMA designed and supervised capture and fi eldwork. ALE carried out and supervised sampling of bears shot during hunting. BS carried out blood sample laboratory experiments and UB designed and carried out histologypathology. KA and OF analyzed the data, interpreted the results and wrote the paper. All authors have contributed to, seen and approved the manuscript.Correspondence: Ole Fröbert ( ole.frobert@orebroll.se ) AbstractHibernation is an extreme physiological challenge for the brown bear ( Ursus arctos ) in which metabolism is based mainly on lipids. The study objective was to compare plasma lipids in hibernating and active free-ranging brown bears and relate them to arterial histopathology. Blood was drawn from seven immobilized free-ranging brown bears (three females, 2-3 years old) during hibernation in February and from the same bears while active in June and analyzed by enzymatic and automated hematology methods within 48 hours of sampling. Left anterior descending coronary arteries and aortic arches from 12 bears (six females, 1.5-12 years old) killed in hunting were examined by histopathology. Total plasma cholesterol decreased from hibernation to the active period (11.08 ± 1.04 mmol/L vs. 7.89 ± 1.96 mmol/L, P = 0.0028) as did triglyceride (3.16 ± 0.62 mmol/L vs. 1.44 ± 0.27 mmol/L, P = 0.00012) and LDL cholesterol (4.30 ± 0.71 mmol/L vs. 2.02 ± 1.03 mmol/L, P = 0.0075), whereas HDL cholesterol was unchanged. No atherosclerosis, fatty streaks, foam cell infi ltration, or infl ammation were seen in any arterial samples. Brown bears tolerate elevated cholesterol levels, obesity, physical inactivity, and circulatory slow fl ow during hibernation without signs of atherosclerosis. This species might serve as a reverse translational model for atherosclerosis resistance. Clin Trans Sci 2012; Volume 5: 269-272

Propionibacterium acnes is a Gram-positive, slow-growing, anaerobic bacillus, predominantly found as a commensal on the skin and mucous membranes of adults. It is, however, also considered an opportunistic pathogen; mostly associated with acne vulgaris, but rarely also with severe infections such as infective endocarditis, prosthetic joint infections, and deep sternal wound infections following cardiothoracic surgery. In addition, P. acnes has recently been found in high frequency in prostate tissue from patients with prostatitis and prostate cancer. The NOD-like receptors (NLR) act as intracellular sensors of microbial components, and a number of various bacteria have been found to induce assembling and activation of NLR-inflammasomes; leading to a pro-inflammatory response. The inflammasome-mediated formation of the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18 involves the auto-proteolytic maturation of caspase-1. This study investigated if P. acnes activates inflammasomes. Propionibacterium acnes isolates (n = 29) with diverse origin were used as stimuli for peripheral leukocytes obtained from blood donors (BDs). The activity of inflammasomes was determined by measuring caspase-1 by flow cytometry and cytokine production by ELISA. A significant amount of caspase-1 was found in neutrophils upon P. acnes stimulation, whereas only a modest activation was seen in monocytes. The activation was mainly produced by components of the bacterial cell and no exo-products, because heat-killed and live bacteria caused high activation of caspase-1 as well as cytokine production, whereas the bacterial supernatant elicited minor effect. The response among different BDs varied significantly, almost fivefold. In addition, P. acnes of various origins showed considerable variation, however, the commensal isolates showed a stronger response compared with the invasive. In conclusion, although regarded as a harmless commensal of the skin, P. acnes strongly activates the inflammasome of human peripheral neutrophils.

BackgroundThe NLRP3 inflammasome has been recognized as one of the key components of the innate immunity by sensing a diversity of insults. Inflammasome activation results in the maturation of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. Increased production of IL-1β is found in patients with gain-of-function polymorphisms in genes encoding the NLRP3 inflammasome. Since approximately 5% of the Swedish population are heterozygote carriers of these combined gene variants, their impact on inflammasome status and a relationship on disease development is therefore highly relevant to study. The present study investigates levels of inflammasome-produced cytokines as a measure of inflammasome activation in healthy individuals carrying Q705K polymorphism in the NLRP3 gene combined with C10X in the CARD8 gene.Materials and MethodsGenotyping of 1006 healthy blood donors was performed for the polymorphisms Q705K in the NLRP3 and C10X in the CARD8 genes. IL-1β, IL-18, IL-33, as well as a number of other pro-inflammatory cytokines, were analyzed by Luminex or ELISA in plasma from individuals carrying the polymorphisms and in age and gender matched non-carrier controls.Results & DiscussionThe prevalence of the polymorphisms was in line with previous studies. Plasma levels of IL-1β and IL-33 were elevated among carriers of combined Q705K+C10X polymorphisms compared to controls, whereas no difference was found for IL-18 and the other cytokines measured. Moreover, carriers of C10X or Q705K per se had similar plasma levels of IL-1β as non-carriers. These data suggest that the combined polymorphisms create inflammasomes with increased basal activation state, which might provide a more favourable innate immune response. In spite of this, it could also represent the mechanisms by which the inflammatory loop is triggered into a long-term inflammatory phenotype.

Background: Hibernation involves periods of severely depressed metabolism (torpor) and decreases in body temperature (Tb). Small arctic mammals (<5kg), in which Tb generally drop drastically, display leukopenia during hibernation. This raised the question of whether the decreased leukocyte counts in mammalian hibernators is due to torpor per se or is secondary to low Tb. The present study examined immune cell counts in brown bears (Ursus arctos), where torpor is only associated with shallow decreases in Tb. The results were compared across hibernator species for which immune and Tb data were available.Methods and Results: The white blood cell counts were determined by flow cytometry in 13 bears captured in the field both during summer and winter over 2 years time. Tb dropped from 39.6±0.8 to 33.5±1.1°C during hibernation. Blood neutrophils and monocytes were lower during hibernation than during the active period (47%, p= 0.001; 43%, p=0.039, respectively), whereas no change in lymphocyte counts was detected (p=0.599). Further, combining our data and those from 10 studies on 9 hibernating species suggested that the decline in Tb explained the decrease in innate immune cells (R2=0.83, p<0.0001).Conclusions: Bears have fewer innate immune cells in circulation during hibernation, which may represent a suppressed innate immune system. Across species comparison suggests that, both in small and large hibernators, Tb is the main driver of immune function regulation during winter dormancy. The lack of a difference in lymphocyte counts in this context requires further investigations.