5-Amino-1-ß-D-Ribofuranosyl-Imidazole-4-Carboxamide (AICAR) Reduces Peripheral Inflammation by Macrophage Phenotype Shift.

The stimulation of the AMP-activated kinase (AMPK) by 5-amino-1-ß-D-ribofuranosyl-imidazole-4-carboxamide (AICAR) has been associated with antihyperalgesia and the inhibition of nociceptive signaling in the spinal cord in models of paw inflammation. The attenuated nociception comes along with a strongly reduced paw edema, indicating that peripheral antiinflammatory mechanisms contribute to antinociception. In this study, we investigated the impact of AICAR on the immune cell composition in inflamed paws, as well as the regulation of inflammatory and resolving markers in macrophages. By using fluorescence-activated cell sorting (FACS) analysis and immunofluorescence, we found a significantly increased fraction of proresolving M2 macrophages and anti-inflammatory interleukin (IL)-10 in inflamed tissue, while M1 macrophages and proinflammatory cytokines such as IL-1 were decreased by AICAR in wild type mice. In AMPKα2 knock-out mice, the M2 polarization of macrophages in the paw was missing. The results were supported by experiments in primary macrophage cultures which also showed a shift to a proresolving phenotype with decreased levels of proinflammatory mediators and increased levels of antiinflammatory mediators. However, in the cell cultures, we did not observe differences between the AMPKα2+/+ and -/- cells, thus indicating that the AICAR-induced effects are at least partially AMPK-independent. In summary, our results indicate that AICAR has potent antiinflammatory and proresolving properties in inflammation which are contributing to a reduction of inflammatory edema and antinociception.

AMPK contributes to aerobic exercise-induced antinociception downstream of endocannabinoids.

Physical exercise has been repeatedly associated with decreased nociceptive responses but the underlying mechanisms have still not been fully clarified. In this study, we investigated exercise-induced effects after a single bout of treadmill running on the mouse model of formalin-induced inflammatory nociception. As potential molecular mediators, we focused on endogenous endocannabinoids as well as AMP-activated protein kinase (AMPK). Our results showed that wild type mice display a reduced nociceptive response in the formalin test after treadmill running, while exercise had no effect on inflammatory nociception in AMPKα2 knockout mice. Levels of the endocannabinoid anandamide (AEA) were increased after physical activity in both wild type and AMPKα2 knockout mice, in association with decreased expression of the AEA-hydrolyzing enzyme FAAH and an increased level of the cannabinoid receptor 1 (CB1). Accordingly, treatment of wild type mice with the CB1 inverse agonist AM251 prior to the treadmill running reversed exercise-induced antinociception. However, if mice received AM251 in combination with the AMPK activator 5-amino-1-ß-d-ribofuranosyl-imidazole-4-carboxamide (AICAR), the positive effect of treadmill running on inflammatory nociception was restored, indicating that AMPK affects exercise-induced antinociception downstream of endocannabinoids. This assumption was further supported by cell culture experiments showing AMPK activation after stimulation of neuronal cells with AEA. In conclusion, our data suggest that AMPK is an intermediate effector in endocannabinoid-mediated exercise-induced antinociception. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Activation of AMPK and its Impact on Exercise Capacity.

Activation of the adenosine monophosphate (AMP)-activated kinase (AMPK) contributes to beneficial effects such as improvement of the hyperglycemic state in diabetes as well as reduction of obesity and inflammatory processes. Furthermore, stimulation of AMPK activity has been associated with increased exercise capacity. A study published in 2008, directly before the Olympic Games in Beijing, showed that the AMPK activator AICAR (5-amino-1-ß-D-ribofuranosyl-imidazole-4-carboxamide) increased the running capacity of mice without any training and thus, prompted the World Anti-Doping Agency (WADA) to include certain AMPK activators in the list of forbidden drugs. This raises the question as to whether all AMPK activators should be considered for registration or whether the increase in exercise performance is only associated with specific AMPK-activating substances. In this review, we intend to shed light on currently published AMPK-activating drugs, their working mechanisms, and their impact on body fitness.

AMP-activated protein kinase is activated by non-steroidal anti-inflammatory drugs.

AMP-activated kinase (AMPK) is a cellular energy sensor, which is activated in stages of increased adenosine triphosphate (ATP) consumption. Its activation has been associated with a number of beneficial effects such as decrease of inflammatory processes and inhibition of disease progression of diabetes and obesity. A recent study suggested that salicylate, the active metabolite of the non-steroidal anti-inflammatory drug (NSAID) acetyl-salicylic acid (aspirin), is able to activate AMPK pharmacologically. This observation raised the question whether or not other NSAIDs might also act as AMPK activators and whether this action might contribute to their cyclooxygenase (COX)-independent anti-inflammatory properties. In this study, we investigated mouse and human neuronal cells and liver tissue of mice after treatment with various NSAIDs. Our results showed that the non-selective acidic NSAIDs ibuprofen and diclofenac induced AMPK activation similar to aspirin while the COX-2 selective drug etoricoxib and the non-opioid analgesic paracetamol, both drugs have no acidic structure, failed to activate AMPK. In conclusion, our results revealed that AMPK can be activated by specific non-steroidal anti-inflammatory drugs such as salicylic acid, ibuprofen or diclofenac possibly depending on the acidic structure of the drugs. AMPK might therefore contribute to their antinociceptive and anti-inflammatory properties.

TANK-binding kinase 1 (TBK1) modulates inflammatory hyperalgesia by regulating MAP kinases and NF-κB dependent genes.

BACKGROUND: TANK-binding kinase (TBK1) is a non-canonical IκB kinase (IKK) involved in the regulation of type I interferons and of NF-κB signal transduction. It is activated by viral infections and inflammatory mediators and has therefore been associated with viral diseases, obesity, and rheumatoid arthritis. Its role in pain has not been investigated so far. Due to the important roles of NF-κB, classical IκB Kinases and the IKK-related kinase, IKKε, in inflammatory nociception, we hypothesized that TBK1, which is suggested to form a complex with IKKε under certain conditions, might also alter the inflammatory nociceptive response. METHODS: We investigated TBK1 expression and regulation in "pain-relevant" tissues of C57BL/6 mice by immunofluorescence, quantitative PCR, and Western blot analysis. Furthermore, nociceptive responses and the underlying signal transduction pathways were assessed using TBK1(-/-) mice in two models of inflammatory nociception. RESULTS: Our data show that TBK1 is expressed and regulated in the spinal cord after peripheral nociceptive stimulation and that a deletion of TBK1 alleviated the inflammatory hyperalgesia in mice while motor function and acute nociception were not altered. TBK1-mediated effects are at least partially mediated by regulation of NF-κB dependent COX-2 induction but also by alteration of expression of c-fos via modulation of MAP kinases as shown in the spinal cord of mice and in cell culture experiments. CONCLUSION: We suggest that TBK1 exerts pronociceptive effects in inflammatory nociception which are due to both modulation of NF-κB dependent genes and regulation of MAPKs and c-fos. Inhibition of TBK1 might therefore constitute a novel effective tool for analgesic therapy.

LPS inhibits caspase 3-dependent apoptosis in RAW264.7 macrophages induced by the AMPK activator AICAR.

AMP-activated kinase is a cellular energy sensor which is activated in stages of increased ATP consumption. Its activation has been associated with a number of beneficial effects such as decreasing inflammatory processes and the disease progress of diabetes and obesity, respectively. Furthermore, AMPK activation has been linked with induction of cell cycle arrest and apoptosis in cancer and vascular cells, indicating that it might have a therapeutic impact for the treatment of cancer and atherosclerosis. However, the impact of AMPK on the proliferation of macrophages, which also play a key role in the formation of atherosclerotic plaques and in inflammatory processes, has not been focused so far. We have assessed the influence of AICAR- and metformin-induced AMPK activation on cell viability of macrophages with and without inflammatory stimulation, respectively. In cells without inflammatory stimulation, we found a strong induction of caspase 3-dependent apoptosis associated with decreased mTOR levels and increased expression of p21. Interestingly, these effects could be inhibited by co-stimulation with bacterial lipopolysaccharide (LPS) but not by other proinflammatory cytokines suggesting that AICAR induces apoptosis via AMPK in a TLR4-pathway dependent manner. In conclusion, our results revealed that AMPK activation is not only associated with positive effects but might also contribute to risk factors by disturbing important features of macrophages. The fact that LPS is able to restore AMPK-associated apoptosis might indicate an important role of TLR4 agonists in preventing unfavorable cell death of immune cells.

Activation of the AMP-activated protein kinase reduces inflammatory nociception.

UNLABELLED: The activation of the adenosine monophosphate (AMP)-activated kinase (AMPK) has been associated with beneficial effects such as improvement of hyperglycemic states in diabetes as well as reduction of obesity and inflammatory processes. Recent studies provide evidence for a further role of AMPK in models of acute and neuropathic pain. In this study, we investigated the impact of AMPK on inflammatory nociception. Using 5-amino-1-ß-d-ribofuranosyl-imidazole-4-carboxamide (AICAR) and metformin as AMPK activators, we observed anti-inflammatory and antinociceptive effects in 2 models of inflammatory nociception. The effects were similar to those observed with the standard analgesic ibuprofen. The mechanism appears to be based on regulation of the AMPKα2 subunit of the kinase because AMPKα2 knockout mice showed increased nociceptive responses that could not be reversed by the AMPK activators. On the molecular level, antinociceptive effects are at least partially mediated by reduced activation of different MAP-kinases in the spinal cord and a subsequent decrease in pain-relevant induction of c-fos, which constitutes a reliable marker of elevated activity in spinal cord neurons following peripheral noxious stimulation. In summary, our results indicate that activation of AMPKα2 might represent a novel therapeutic option for the treatment of inflammation-associated pain, providing analgesia with fewer unwanted side effects. PERSPECTIVE: AMPK activation is associated with beneficial effects on diabetes and obesity. In addition, we have shown analgesic properties of pharmacologic AMPK activation in inflammatory nociception, indicating that AMPK might serve as a novel therapeutic target in pain with fewer unwanted side effects.

Novel findings in pain processing pathways: implications for miRNAs as future therapeutic targets.

miRNAs are small noncoding RNAs that are important players in development, as well as in a number of physiological and pathophysiological processes. Due to their regulatory role in protein expression, it has been assumed that they are associated with peripheral and central sensitization mechanisms in the nervous system after nociceptive insults. However, the study of miRNAs in pain has emerged only recently. First reports mostly focused on miRNA regulations in different pain states while studies examining the functional role of individual miRNAs are only now arising. In this review, the authors summarize the current knowledge and progress in miRNA research in pain and discuss their potential role as therapeutic antinociceptive targets.

Modulation of central nervous system-specific microRNA-124a alters the inflammatory response in the formalin test in mice.

microRNAs (miRNAs) are small noncoding RNAs that have been linked to a number of disease-related signal transduction pathways. Several studies indicate that they are also involved in nociception. It is not clear, however, which miRNAs are important and which genes are modulated by miRNA-associated mechanisms. This study focuses on the regulation and function of the central nervous system (CNS)-specific miRNA-124a in the spinal cord of mice in a formalin model of inflammatory nociception. miRNA-124a is constitutively expressed in the spinal cord of mice, particularly in neurons of the dorsal horn. Peripheral noxious stimulation with formalin led to significant down-regulation of its expression. Knock-down of miRNA-124a by intravenous administration of a specific miRNA-124a inhibitor further increased the nociceptive behavior associated with an upregulation of the pain-relevant miRNA-124a target MeCP2 and proinflammatory marker genes. In contrast, administration of a miRNA-124a mimic counteracted these effects and decreased nociception by down-regulation of the target gene. In conclusion, our results indicate that miRNA-124a is involved in inflammatory nociception by regulation of relevant target proteins and might therefore constitute a novel target for anti-inflammatory therapy.

Altered gene expression in the prefrontal cortex of young rats induced by the ADHD drug atomoxetine.

Atomoxetine (ATX), a selective norepinephrine reuptake inhibitor, is a non-stimulant approved for the treatment of attention deficit/hyperactivity disorder (ADHD). Little is known about the molecular basis for its therapeutic effect. The objective of this animal study was to determine alterations in gene expression patterns in the prefrontal cortex after long-term administration of atomoxetine. Rats were treated for 21 days during childhood and early adolescent stages of development with a once-daily oral application of 0.05 g/kg atomoxetine, which resulted in plasma levels similar to those described in children. A whole genome RNA-microarray of rat prefrontal cortical gene expression after administration of atomoxetine versus sterile water revealed an mRNA increase in 114 genes (≥2-fold) while 11 genes were down-regulated (≤0.5-fold). By applying quantitative real-time PCR (qRT-PCR) and Western Blot we confirmed a significant increase in the expression of GABA A receptor subunits as well as ubiquinol-cytochrome c reductase complex core protein 2 (Uqcrc2). SNAP-25 (synaptosomal-associated protein of 25 kDa), which is an ADHD candidate gene and an important vesicle protein involved in axonal growth, synaptic plasticity and regulation of neurotransmitter release was also significantly upregulated on RNA- and protein level after atomoxetine treatment. In summary, we could show that long-term treatment with the ADHD drug atomoxetine induces the regulation of several genes in the prefrontal cortex of young rats. Especially the increased expression of SNAP-25 and GABA-A receptor subunits may indicate additional active therapeutic mechanisms for atomoxetine.

The protein kinase IKKε is a potential target for the treatment of inflammatory hyperalgesia.

Inhibitor-κB kinase ε (IKKε) was only recently identified as an enzyme with high homology to the classical I-κB kinase subunits, IKKα and IKKß. Despite this similarity, it is mainly discussed as a repressor of viral infections by modulating type I IFNs. However, in vitro studies also showed that IKKε plays a role in the regulation of NF-κB activity, but the distinct mechanisms of IKKε-mediated NF-κB activation are not clear. Given the paramount role of NF-κB in inflammation, we investigated the regulation and function of IKKε in models of inflammatory hyperalgesia in mice. We found that IKKε was abundantly expressed in nociceptive neurons in the spinal cord and in dorsal root ganglia. IKKε mRNA and protein levels rapidly increased in spinal cord and dorsal root ganglia during hind paw inflammation evoked by injection of zymosan or formalin. IKKε knockout mice showed normal nociceptive responses to acute heat or mechanical stimulation. However, in inflammatory pain models, IKKε-deficient mice exhibited a significantly reduced nociceptive behavior in comparison with wild type mice, indicating that IKKε contributed to the development of inflammatory hyperalgesia. Antinociceptive effects were associated with reduced activation of NF-κB and attenuated NF-κB-dependent induction of cyclooxygenase-2, inducible NO synthase, and metalloproteinase-9. In contrast, IRF-3, which is an important IKKε target in viral infections, was not regulated after inflammatory nociceptive stimulation. Therefore, we concluded that IKKε modulates inflammatory nociceptive sensitivity by activation of NF-κB-dependent gene transcription and may be useful as a therapeutic target in the treatment of inflammatory pain.

Two-stage revision of infected total knee arthroplasty using a distraction spacer.

BACKGROUND: The infection of a total knee arthroplasty (TKA) has remained as one of the most devastating potential complications. In this context we developed a new technique that keeps the spacer in distraction during the cementation process to achieve better weight-bearing stability. METHODS: We present a case of a 75-year-old male patient, who was treated in our hospital with an infected total knee replacement (TKR) using the distraction spacer. The operative technique includes the removal of the infected prosthesis after radical debridement. Then two carbon rods were inserted overlapping 2-3 cm in the medulla of the tibia and femur. Afterwards an external fixateur with distraction module is attached with two Schanz screws into the distal femur and the proximal tibia. The cementation process was performed under distraction. After hardening of the cement the external fixateur and the Schanz screws are then removed. RESULTS: Postoperatively the patient was mobilized with full weight-bearing using an extension splint. The antibiotic therapy was continued for five weeks. After sterile puncture, the reimplantation was performed using a Zimmer-Rotating-Hinge-Knee without any complications. CONCLUSIONS: This method allows cement hardening without micromovements and early mobilization with partial full weight bearing and prevents the contraction of the capsule and the ligaments during the prosthesis-free period, preparing the knee for a secondary TKA or an intramedullary arthrodesis with a titanium stem.

Surgical treatment of talus fractures: a retrospective study of 80 cases followed for 1-15 years.

We retrospectively reviewed 79 patients (80 talar fractures) operated on between 1994 and 1997. The average follow-up was 6 (1-15) years. 15 patients had a Marti/Weber fracture type I, 14 patients a type II, 32 patients a type III, and 19 patients a type IV fracture. 46 patients suffered a fracture of the talar neck, Hawkins type I in 10 patients, type II in 18, type III in 17 and type IV in 1 patient. 18/23 patients directly placed in our department were operated on within 6 hours of admission. Primary arthrodesis of both the ankle and subtalar joint was performed twice. Secondary arthrodesis of the ankle joint was done in only 3 patients. Combined secondary arthrodesis of the ankle and subtalar joint was performed in 5 and arthrodesis of the talonavicular joint in 1 patient. According to the Hawkins score, 35/80 feet achieved good/very good function versus 43 with the Mazur score. Radiographs showed ankle or subtalar arthrosis in two thirds of the patients. A normal range of motion was achieved in 18 ankle and 19 subtalar joints. The overall rate of talar necrosis was 9/80 fractures.