Association between serum ferritin and mortality: findings from the USA, Japan and European Dialysis Outcomes and Practice Patterns Study

Background

The Kidney Disease: Improving Global Outcomes guidelines have cautioned against administering intravenous (IV) iron to hemodialysis patients with high serum ferritin levels due to safety concerns, but prior research has shown that the association between high ferritin and mortality could be attributed to confounding by malnutrition and inflammation. Our goal was to better understand the ferritin-mortality association and relative influence of IV iron and inflammation in the USA, where ferritin levels have recently increased dramatically, and in Europe and Japan, where ferritin levels are lower and anemia management practices differ.

Methods

Data from 18 261 patients in Phases 4 and 5 (2009-15) of the international Dialysis Outcomes and Practice Patterns Study, a prospective cohort study, were analyzed. Using Cox regression, we modeled the association between baseline ferritin and 1-year mortality with restricted cubic splines and assessed the impact of potential confounders.

Results

Median ferritin levels were 718 ng/mL in the USA, 405 in Europe and 83 in Japan. High ferritin levels were associated with elevated mortality (relative to region-specific medians) in all three regions. The strength of this association was attenuated more by adjustment for malnutrition and inflammation than by IV iron and erythropoiesis-stimulating agent dose in each region.

Conclusion

The utility of high ferritin as a biomarker for clinical risk due to excess iron stores may be limited, although caution regarding IV iron dosing to higher upper ferritin targets remains warranted. Research to resolve biomarker criteria for iron dosing, and whether optimal anemia management strategies differ internationally, is still needed.

Behavioral assessment of neuropathic pain, fatigue, and anxiety in experimental autoimmune encephalomyelitis (EAE) and attenuation by interleukin-10 gene therapy

Relapsing-remitting multiple sclerosis is commonly associated with motor impairments, neuropathic pain, fatigue, mood disorders, and decreased life expectancy. However, preclinical pharmacological studies predominantly rely on clinical scoring of motor deficit as the sole behavioral endpoint. Thus, the translational potential of these studies is limited. Here, we have assessed the therapeutic potential of a novel anti-inflammatory interleukin-10 (IL-10) non-viral gene therapy formulation (XT-101-R) in a rat relapsing remitting experimental autoimmune encephalomyelitis (EAE) model. EAE induced motor deficits and neuropathic pain as reflected by induction of low-threshold mechanical allodynia, suppressed voluntary wheel running, decreased social exploration, and was associated with markedly enhanced mortality. We also noted that voluntary wheel running was depressed prior to the onset of motor deficit, and may therefore serve as a predictor of clinical symptoms onset. XT-101-R was intrathecally dosed only once at the onset of motor deficits, and attenuated each of the EAE-induced symptoms and improved survival, relative to vehicle control. This is the first pharmacological assessment of such a broad range of EAE symptoms, and provides support for IL-10 gene therapy as a clinical strategy for the treatment of multiple sclerosis.

Adenosine 2A receptor agonism: A single intrathecal administration attenuates motor paralysis in experimental autoimmune encephalopathy in rats

A single intrathecal dose of adenosine 2A receptor (A2AR) agonist was previously reported to produce a multi-week reversal of allodynia in two different models of neuropathic pain in addition to downregulating glial activation markers in the spinal cord. We aimed to determine whether a single intrathecal administration of an A2AR agonist was able to attenuate motor symptoms induced by experimental autoimmune encephalopathy. Two A2AR agonists (CGS21680 and ATL313) significantly attenuated progression of motor symptoms following a single intrathecal administration at the onset of motor symptoms. OX-42, a marker of microglial activation, was significantly attenuated in the lumbar spinal cord following A2AR administration compared to vehicle. Therefore, A2AR agonists attenuate motor symptoms of EAE by acting on A2AR in the spinal cord.

Systemic administration of an alpha-7 nicotinic acetylcholine agonist reverses neuropathic pain in male Sprague Dawley rats

Alpha-7 nicotinic acetylcholine receptor (α7 nAChR) agonists attenuate pain and inflammation in preclinical models. This study tested whether systemic delivery of an α7 nAChR agonist attenuates neuropathic pain and associated immune-mediated pro-inflammation. Hind paw response thresholds to mechanical stimuli in male Sprague Dawley rats were assessed before and after sciatic chronic constriction injury (CCI) or sham surgery. Osmotic mini-pumps containing TC-7020, an α7 nAChR selective agonist, were implanted 10 to 14 days after surgery. TC-7020 (1, 3, and 10 mg/kg/d; s.c.) significantly attenuated CCI-induced allodynia, which lasted through 2 weeks of test compound administration. Spinal cords were collected after 2 weeks and processed for microglial and astrocyte activation markers within the ipsilateral L4-L6 dorsal horn. In addition, ipsilateral L4-5 dorsal root ganglia (DRGs) were processed for neuronal injury and satellite cell activation markers. CCI-induced central glial cell activation markers were not suppressed by TC-7020, even though TC-7020 is mildly blood-brain barrier permeable. However, TC-7020 downregulated the integrated density of activation transcription factor 3 (ATF3) but not the number of ATF positive cells. TC-7020 also downregulated phosphorylated extracellular signal kinase (p-ERK) and satellite cell activation in the CCI-affected DRGs. Therefore, systemic α7 nAChR agonist may be effective in treating neuropathic pain via reducing neuronal injury and immune cells activation occurring in the periphery.

PERSPECTIVE

These studies demonstrated that TC-7020, an alpha7 nicotinic acetylcholine receptor agonist with partial blood-brain barrier permeability, reversed neuropathic pain in rats, likely via attenuation of inflammation in the DRG and/or the site of sciatic injury.

Prior exposure to repeated morphine potentiates mechanical allodynia induced by peripheral inflammation and neuropathy

Opioids, such as morphine, induce potent analgesia and are the gold standard for the treatment of acute pain. However, opioids also activate glia, inducing pro-inflammatory cytokine and chemokine production, which counter-regulates the analgesic properties of classical opioid receptor activation. It is not known how long these adverse pro-inflammatory effects last or whether prior morphine could sensitize the central nervous system (CNS) such that responses to a subsequent injury/inflammation would be exacerbated. Here, multiple models of inflammation or injury were induced two days after morphine (5mg/kg b.i.d., five days , s.c.) to test the generality of morphine sensitization of later pain. Prior repeated morphine potentiated the duration of allodynia from peripheral inflammatory challenges (complete Freund's adjuvant (CFA) into either hind paw skin or masseter muscle) and from peripheral neuropathy (mild chronic constriction injury (CCI) of the sciatic nerve). Spinal cord and trigeminal nucleus caudalis mRNAs were analyzed to identify whether repeated morphine was sufficient to alter CNS expression of pro-inflammatory response genes, measured two days after cessation of treatment. Prior morphine elevated IL-1β mRNA at both sites, MHC-II and TLR4 in the trigeminal nucleus caudalis but not spinal cord, but not glial activation markers at either site. Finally, in order to identify whether morphine sensitized pro-inflammatory cytokine release, spinal cord was isolated two days after morphine dosing for five days , and slices stimulated ex vivo with lipopolysaccharide. The morphine significantly induced TNFα protein release. Therefore, repeated morphine is able to sensitize subsequent CNS responses to immune challenges.

Sex and estradiol influence glial pro-inflammatory responses to lipopolysaccharide in rats

There is a greater prevalence of neuroinflammatory diseases in females than males. Microglia, the major immunocompetent cells of the central nervous system, play a key role in neuroinflammation. We aimed to determine if inherent differences in toll-like receptor 4 mediated pro-inflammatory response in glia could possibly contribute to the skewed female prevalence of neuroinflammatory disorders. In addition, in order to identify if estradiol (E2), the major female sex steroid contributes to a heightened pro-inflammatory response, estradiol was added both in vivo and in vitro. Microglia and astrocytes were isolated from neonatal pups and stimulated with lipopolysaccharide (LPS) in the presence and absence of E2. Hippocampal microglia were isolated from adult male and female rats and stimulated ex vivo with LPS. Male neonatal microglia and astrocytes produced greater IL-1β mRNA than females. However, when co-incubated with varying doses of estradiol (E2), the E2 produced anti-inflammatory effects in the male microglia but a pro-inflammatory effect in female microglia. LPS-induced IL-1β mRNA was attenuated by E2 in female but not male adult hippocampal microglia. However, females supplemented with E2 in vivo produced a potentiated IL-1β mRNA response. TLR4 mRNA was decreased by LPS in both microglia and astrocytes but was not affected by sex or E2. CD14 mRNA was increased by LPS and may be elevated more in females than males in microglia but not astrocytes. Therefore, sexual dimorphic differences do occur in both neonatal and adult microglia though maturity of the microglia at the time of isolation influences the pro-inflammatory response.

(+)-naloxone, an opioid-inactive toll-like receptor 4 signaling inhibitor, reverses multiple models of chronic neuropathic pain in rats

Previous work demonstrated that both the opioid antagonist (-)-naloxone and the non-opioid (+)-naloxone inhibit toll-like receptor 4 (TLR4) signaling and reverse neuropathic pain expressed shortly after chronic constriction injury. The present studies reveal that the TLR4 contributes to neuropathic pain in another major model (spinal nerve ligation) and to long established (2-4 months) neuropathic pain, not just to pain shortly after nerve damage. Additionally, analyses of plasma levels of (+)-naloxone after subcutaneous administration indicate that (+)-naloxone has comparable pharmacokinetics to (-)-naloxone with a relatively short half-life. This finding accounts for the rapid onset and short duration of allodynia reversal produced by subcutaneous (+)-naloxone. Given that toll-like receptor 2 (TLR2) has also recently been implicated in neuropathic pain, cell lines transfected with either TLR4 or TLR2, necessary co-signaling molecules, and a reporter gene were used to define whether (+)-naloxone effects could be accounted for by actions at TLR2 in addition to TLR4. (+)-Naloxone inhibited signaling by TLR4 but not TLR2. These studies provide evidence for broad involvement of TLR4 in neuropathic pain, both early after nerve damage and months later. Additional, they provide further support for the TLR4 inhibitor (+)-naloxone as a novel candidate for the treatment of neuropathic pain.

PERSPECTIVE

These studies demonstrated that (+)-naloxone, a systemically available, blood-brain barrier permeable, small molecule TLR4 inhibitor can reverse neuropathic pain in rats, even months after nerve injury. These findings suggest that (+)-naloxone, or similar compounds, be considered as a candidate novel, first-in-class treatment for neuropathic pain.

Toll-like receptors in chronic pain

Proinflammatory central immune signaling contributes significantly to the initiation and maintenance of heightened pain states. Recent discoveries have implicated the innate immune system, pattern recognition Toll-like receptors in triggering these proinflammatory central immune signaling events. These exciting developments have been complemented by the discovery of neuronal expression of Toll-like receptors, suggesting pain pathways can be activated directly by the detection of pathogen associated molecular patterns or danger associated molecular patterns. This review will examine the evidence to date implicating Toll-like receptors and their associated signaling components in heightened pain states. In addition, insights into the impact Toll-like receptors have on priming central immune signaling systems for heightened pain states will be discussed. The influence possible sex differences in Toll-like receptor signaling have for female pain and the recognition of small molecule xenobiotics by Toll-like receptors will also be reviewed.

Prior laparotomy or corticosterone potentiates lipopolysaccharide-induced fever and sickness behaviors

Stimulating sensitized immune cells with a subsequent immune challenge results in potentiated pro-inflammatory responses translating into exacerbated sickness responses (i.e. fever, pain and lethargy). Both corticosterone (CORT) and laparotomy cause sensitization, leading to enhanced sickness-induced neuroinflammation or pain (respectively). However, it is unknown whether this sensitization affects all sickness behaviors and immune cell responses equally. We show that prior CORT and prior laparotomy potentiated LPS-induced fever but not lethargy. Prior CORT, like prior laparotomy, was able to potentiate sickness-induced pain. Release of nitric oxide (NO) from peritoneal macrophages stimulated ex vivo demonstrates that laparotomy, but not CORT sensitizes these cells.

Pain intensity and duration can be enhanced by prior challenge: initial evidence suggestive of a role of microglial priming

Activation of spinal microglia and consequent release of proinflammatory mediators facilitate pain. Under certain conditions, responses of activated microglia can become enhanced. Enhanced microglial production of proinflammatory products may result from priming (sensitization), similar to macrophage priming. We hypothesized that if spinal microglia were primed by an initial inflammatory challenge, subsequent challenges may create enhanced pain. Here, we used a "two-hit" paradigm using 2 successive challenges, which affect overlapping populations of spinal microglia, presented 2 weeks apart. Mechanical allodynia and/or activation of spinal glia were assessed. Initially, laparotomy preceded systemic lipopolysaccharide (LPS). Prior laparotomy caused prolonged microglial (not astrocyte) activation plus enhanced LPS-induced allodynia. In this "two-hit" paradigm, minocycline, a microglial activation inhibitor, significantly reduced later exaggerated pain induced by prior surgery when minocycline was administered intrathecally for 5 days starting either at the time of surgery or 5 days before LPS administration. To test generality of the priming effect, subcutaneous formalin preceded intrathecal HIV-1 gp120, which activates spinal microglia and causes robust allodynia. Prior formalin enhanced intrathecal gp120-induced allodynia, suggesting that microglial priming is not limited to laparotomy and again supporting a spinal site of action. Therefore, spinal microglial priming may increase vulnerability to pain enhancement.

PERSPECTIVE

Spinal microglia may become "primed" (sensitized) following their activation by disparate forms of peripheral trauma/inflammation. As a result, such primed microglia may overrespond to subsequent challenges, thereby enhancing pain intensity and duration.

Differences in the relative involvement of peripherally released interleukin (IL)-6, brain IL-1β and prostanoids in mediating lipopolysaccharide-induced fever and sickness behavior

Although peripherally released interleukin (IL)-6 is critical for fever, its role in sickness behaviors, in particular anorexia and lethargy, induced by lipopolysaccharide (LPS) administration appears to be less important. Using quantifiable measures of fever, anorexia and lethargy, that is, body temperature, food intake and voluntary wheel-running, we investigated whether the less-than-essential role for IL-6 in mediating sickness behaviors compared to fever implies important roles for other inflammatory mediators, particularly IL-1β and prostanoids, in these responses. Male Sprague-Dawley rats were randomly assigned to receive one of the following three injections before receiving a subcutaneous (SC) injection of LPS (250 μg/kg) or saline: (1) intraperitoneal injection of pre-immune serum or antiserum to IL-6 (IL-6AS), to reduce the biological activity of peripherally released IL-6; (2) intracerebroventricular injection of vehicle or a caspase-1 inhibitor, to inhibit the production of mature IL-1β; or (3) intraperitoneal injection of vehicle or one of the two doses (1 or 10 mg/kg) of diclofenac, a nonselective cyclooxygenase inhibitor shown to block the formation of prostanoids. LPS administration induced fever, anorexia and lethargy with an accompanying increase in IL-6 and IL-1β concentrations in the circulation and IL-1β in the brain. Rats pre-treated with: (1) IL-6AS had reduced plasma levels of bioactive IL-6, no fever and attenuated sickness behaviors; (2) the caspase-1 inhibitor had reduced concentrations of IL-1β in the pre-frontal cortex, hypothalamus and hippocampus, and attenuated fever and sickness behaviors; (3) diclofenac had a dose-dependent attenuation in fever and sickness behaviors. Doses of diclofenac which completely abolished fever however had lesser effects on anorexia and lethargy. Our results confirm a difference in the sensitivity of sickness responses to IL-6 antagonism and identify that it may be related to different levels of sensitivity or responsiveness in brain regions and/or mechanisms, to prostanoids, IL-1β, or IL-6 itself.

Intrathecal injection of an alpha seven nicotinic acetylcholine receptor agonist attenuates gp120-induced mechanical allodynia and spinal pro-inflammatory cytokine profiles in rats

Nicotinic acetylcholine receptors (nAchRs) are not only key receptors in the autonomic nervous system, but also are present on immune cells. The alpha seven subunit of nAchR (alpha7nAchR) suppresses pro-inflammation in peripheral monocytes by decreasing pro-inflammatory cytokine production. In spinal cord, alpha7nAchRs are found on microglia, which are known to induce and maintain pain. We predicted that alpha7nAchR agonists might attenuate intrathecal HIV-1 gp120-induced, pro-inflammatory cytokine- and microglia-dependent mechanical allodynia. Choline, a precursor for acetylcholine and selective agonist for alpha7nAchR, was administered intrathecally either with, or 30 min after, intrathecal gp120. Choline significantly blocked and reversed gp120-induced mechanical allodynia for at least 4 h after drug administration. In addition, intrathecal choline, delivered either with or 30 min after gp120, reduced gp120-induced IL-1beta protein and pro-inflammatory cytokine mRNAs within the lumbar spinal cord. A second alpha7nAchR agonist, GTS-21, also significantly reversed gp120-induced mechanical allodynia and lumbar spinal cord levels of pro-inflammatory cytokine mRNAs and IL-1beta protein. A role of microglia is suggested by the observation that intrathecal choline suppressed the gp120-induced expression of, cd11b, a macrophage/microglial activation marker. Taken together, the data support that alpha7nAchR may be a novel target for treating pain where microglia maintain the pro-inflammatory state within the spinal cord.

Evidence that tricyclic small molecules may possess toll-like receptor and myeloid differentiation protein 2 activity

Opioids have been discovered to have Toll-like receptor (TLR) activity, beyond actions at classical opioid receptors. This raises the question whether other pharmacotherapies for pain control may also possess TLR activity, contributing to or opposing their clinical effects. We document that tricyclics can alter TLR4 and TLR2 signaling. In silico simulations revealed that several tricyclics docked to the same binding pocket on the TLR accessory protein, myeloid differentiation protein 2 (MD-2), as do opioids. Eight tricyclics were tested for effects on TLR4 signaling in HEK293 cells over-expressing human TLR4. Six exhibited mild (desipramine), moderate (mianserin, cyclobenzaprine, imiprimine, ketotifen) or strong (amitriptyline) TLR4 inhibition, and no TLR4 activation. In contrast, carbamazepine and oxcarbazepine exhibited mild and strong TLR4 activation, respectively, and no TLR4 inhibition. Amitriptyline but not carbamazepine also significantly inhibited TLR2 signaling in a comparable cell line. Live imaging of TLR4 activation in RAW264.7 cells and TLR4-dependent interleukin-1 release from BV-2 microglia revealed that amitriptyline blocked TLR4 signaling. Lastly, tricyclics with no (carbamazepine), moderate (cyclobenzeprine), and strong (amitriptyline) TLR4 inhibition were tested intrathecally (rats) and amitriptyline tested systemically in wildtype and knockout mice (TLR4 or MyD88). While tricyclics had no effect on basal pain responsivity, they potentiated morphine analgesia in rank-order with their potency as TLR4 inhibitors. This occurred in a TLR4/MyD88-dependent manner as no potentiation of morphine analgesia by amitriptyline occurred in these knockout mice. This suggests that TLR2 and TLR4 inhibition, possibly by interactions with MD2, contributes to effects of tricyclics in vivo. These studies provide converging lines of evidence that several tricyclics or their active metabolites may exert their biological actions, in part, via modulation of TLR4 and TLR2 signaling and suggest that inhibition of TLR4 and TLR2 signaling may potentially contribute to the efficacy of tricyclics in treating chronic pain and enhancing the analgesic efficacy of opioids.

Selection, Preparation, and Evaluation of Small- Molecule Inhibitors of Toll-Like Receptor 4

Toll-like receptor 4 (TLR4), a membrane spanning receptor protein that functions in complex with its accessory protein MD-2, is an intriguing target for therapeutic development. Herein we report the identification of a series of novel TLR4 inhibitors and the development of a robust, enantioselective synthesis using an unprecedented Mannich-type reaction to functionalize a pyrazole ring. In silico and cellular assay results demonstrated that compound 1 and its analogues selectively block TLR4 activation in live cells. Animal model tests showed that 1 and its derivatives could potentiate morphine-induced analgesia in vivo, presumably by attenuating the opioid-induced TLR4 activation.

Release of plasmid DNA-encoding IL-10 from PLGA microparticles facilitates long-term reversal of neuropathic pain following a single intrathecal administration

PURPOSE

Interleukin-10 (IL-10) is an anti-inflammatory molecule that has achieved interest as a therapeutic for neuropathic pain. In this work, the potential of plasmid DNA-encoding IL-10 (pDNA-IL-10) slowly released from biodegradable microparticles to provide long-term pain relief in an animal model of neuropathic pain was investigated.

METHODS

PLGA microparticles encapsulating pDNA-IL-10 were developed and assessed both in vitro and in vivo.

RESULTS

In vitro, pDNA containing microparticles activated macrophages, enhanced the production of nitric oxide, and increased the production of IL-10 protein relative to levels achieved with unencapsulated pDNA-IL-10. In vivo, intrathecally administered microparticles embedded in meningeal tissue, induced phagocytic cell recruitment to the cerebrospinal fluid, and relieved neuropathic pain for greater than 74 days following a single intrathecal administration, a feat not achieved with unencapsulated pDNA. Therapeutic effects of microparticle-delivered pDNA-IL-10 were blocked in the presence of IL-10-neutralizing antibody, and elevated levels of plasmid-derived IL-10 were detected in tissues for a prolonged time period post-injection (>28 days), demonstrating that therapeutic effects are dependent on IL-10 protein production.

CONCLUSIONS

These studies demonstrate that microparticle encapsulation significantly enhances the potency of intrathecally administered pDNA, which may be extended to treat other disorders that require intrathecal gene therapy.

Evidence that intrathecal morphine-3-glucuronide may cause pain enhancement via toll-like receptor 4/MD-2 and interleukin-1beta

Morphine-3-glucoronide (M3G) is a major morphine metabolite detected in cerebrospinal fluid of humans receiving systemic morphine. M3G has little-to-no affinity for opioid receptors and induces pain by unknown mechanisms. The pain-enhancing effects of M3G have been proposed to significantly and progressively oppose morphine analgesia as metabolism ensues. We have recently documented that morphine activates toll-like receptor 4 (TLR4), beyond its classical actions on mu-opioid receptors. This suggests that M3G may similarly activate TLR4. This activation could provide a novel mechanism for M3G-mediated pain enhancement, as (a) TLR4 is predominantly expressed by microglia in spinal cord and (b) TLR4 activation releases pain-enhancing substances, including interleukin-1 (IL-1). We present in vitro evidence that M3G activates TLR4, an effect blocked by TLR4 inhibitors, and that M3G activates microglia to produce IL-1. In vivo, intrathecal M3G (0.75 microg) induced potent allodynia and hyperalgesia, blocked or reversed by interleukin-1 receptor antagonist, minocycline (microglial inhibitor), and (+)-and (-)-naloxone. This latter study extends our prior demonstrations that TLR4 signaling is inhibited by naloxone nonstereoselectively. These results with (+)-and (-)-naloxone also demonstrate that the effects cannot be accounted for by actions at classical, stereoselective opioid receptors. Hyperalgesia (allodynia was not tested) and in vitro M3G-induced TLR4 signaling were both blocked by 17-DMAG, an inhibitor of heat shock protein 90 (HSP90) that can contribute to TLR4 signaling. Providing further evidence of proinflammatory activation, M3G upregulated TLR4 and CD11b (microglial/macrophage activation marker) mRNAs in dorsal spinal cord as well as IL-1 protein in the lumbosacral cerebrospinal fluid. Finally, in silico and in vivo data support that the glucuronic acid moiety is capable of inducing TLR4/MD-2 activation and enhanced pain. These data provide the first evidence for a TLR4 and IL-1 mediated component to M3G-induced effects, likely of at least microglial origin.

Minocycline suppresses morphine-induced respiratory depression, suppresses morphine-induced reward, and enhances systemic morphine-induced analgesia

Recent data suggest that opioids can activate immune-like cells of the central nervous system (glia). This opioid-induced glial activation is associated with decreased analgesia, owing to the release of proinflammatory mediators. Here, we examine in rats whether the putative microglial inhibitor, minocycline, may affect morphine-induced respiratory depression and/or morphine-induced reward (conditioned place preference). Systemic co-administration of minocycline significantly attenuated morphine-induced reductions in tidal volume, minute volume, inspiratory force, and expiratory force, but did not affect morphine-induced reductions in respiratory rate. Minocycline attenuation of respiratory depression was also paralleled with significant attenuation by minocycline of morphine-induced reductions in blood oxygen saturation. Minocycline also attenuated morphine conditioned place preference. Minocycline did not simply reduce all actions of morphine, as morphine analgesia was significantly potentiated by minocycline co-administration. Lastly, morphine dose-dependently increased cyclooxygenase-1 gene expression in a rat microglial cell line, an effect that was dose-dependently blocked by minocycline. Together, these data support that morphine can directly activate microglia in a minocycline-suppressible manner and suggest a pivotal role for minocycline-sensitive processes in the mechanisms of morphine-induced respiration depression, reward, and pain modulation.

Neutralisation of muscle tumour necrosis factor alpha does not attenuate exercise-induced muscle pain but does improve muscle strength in healthy male volunteers

OBJECTIVE

Inflammatory mediators, such as tumour necrosis factor alpha (TNFalpha), may contribute to delayed-onset muscle soreness. The effect of neutralising TNFalpha with etanercept, a soluble TNFalpha receptor, on delayed-onset muscle soreness (DOMS) induced in the quadriceps muscle was analysed.

DESIGN

On two separate occasions at least 6 weeks apart, etanercept 25 mg or vehicle was given subcutaneously 1 hour before unaccustomed exercise to 12 healthy men in a randomised double-blind cross-over format. To induce DOMS, subjects completed 4 sets of 15 repetitions at 80% of their one-repetition maximum (1RM), using a 45 degrees inclined leg press. Muscle soreness was assessed using a 100-mm visual analogue scale (VAS), and pressure pain threshold (PPT) on the thigh before and 24, 48 and 72 hours after exercise. Changes in the subject's muscle strength were detected by reassessing the subject's 1RM 24, 48 and 72 hours after exercise.

RESULTS

Muscle strength decreased 24 and 48 hours after exercise regardless of agent administered (analysis of variance, p<0.001). At 72 hours after exercise, muscle strength was significantly greater (p<0.01) after etanercept than after placebo. The exercise protocol induced significant DOMS for up to 72 hours, as reflected by reduced PPT and increased VAS scores (p<0.001). Etanercept had no effect on PPT or VAS.

CONCLUSION

TNFalpha does not affect muscle soreness associated with unaccustomed exercise, but may improve the recovery of muscle function.

Behavioural, histological and cytokine responses during hyperalgesia induced by carrageenan injection in the rat tail

We produced experimental inflammatory hyperalgesia by injecting carrageenan into the tail of Sprague-Dawley rats. We compared the rats' voluntary running wheel activity following carrageenan injection into the tail to that after carrageenan injection into the hind paw, the conventional site of inflammation, to identify whether the site of inflammatory-induced hyperalgesia altered voluntary activity. We also measured voluntary running before and after injection of carrageenan or saline into the tail or hind paw, and in separate groups of rats we measured the nociceptive response and the associated pro-inflammatory cytokine profiles following a carrageenan injection into the tail. Female rats were injected intradermally with either 2 mg carrageenan or saline into the dorsal surface of the tail. Withdrawal responses to noxious heat (49 degrees C water), and punctate mechanical (electronic anaesthesiometer) challenges were recorded in 12 rats for 3 days before and 1 h to 48 h after injection. In a separate group of rats, interleukin (IL)-1beta, IL-6, tumour necrosis factor-alpha (TNF-alpha) and cytokine-induced neutrophil chemoattractant (CINC-1) concentrations were measured in plasma and tail tissue samples taken at the site of injection, 3 h, 6 h and 24 h after injections. Voluntary wheel running was reduced significantly following carrageenan injection into the hind paw compared to that after saline injection into the hind paw. Carrageenan injection into the tail did not result in significant reduction in wheel running compared to that after saline injection into the tail. Both thermal and mechanical hyperalgesia were present after carrageenan injection into the tail (P<0.01, ANOVA). The hyperalgesia at the site coincided with significant increases in TNF-alpha, IL-1beta, IL-6 and CINC-1 tissue concentrations, peaking 6 h after carrageenan injection (P<0.01, ANOVA). We conclude that carrageenan injection into the tail produces inflammatory hyperalgesia with underlying pro-inflammatory cytokine release, but does not affect voluntary running wheel activity in rats.

The time course of inflammatory cytokine secretion in a rat model of postoperative pain does not coincide with the onset of mechanical hyperalgesia

We characterized the time course of inflammatory cytokine release at the site of injury and in plasma after surgery on the rat tail. Anesthetized Sprague–Dawley rats had a 20 mm long incision made through the skin and fascia of their tails. Control rats were anesthetized, but no incision was made. Blood and tissue samples were taken 2 h and 1, 2, 4, and 8 days after surgery and analysed by ELISA for interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and cytokine-induced neutrophil chemoattractant-1 (CINC-1). In another group of rats, daily behavioral measurements were made of the rats’ responses to a blunt noxious mechanical stimulus (4 Newtons) applied to their tails. Primary hyperalgesia developed within 2 h of surgery and lasted for 6 days. The tissue concentrations of IL-1β, IL-6, and CINC-1 increased within 24 h of surgery, and TNF-α concentration increased within 48 h of surgery. Thereafter, cytokine concentrations remained elevated for 4 (IL-1β and IL-6) to 8 days (CINC-1, TNF-α) after surgery. Control animals did not develop hyperalgesia and no changes in cytokines concentrations were detected. Thus, in our model of postoperative pain, secretion of inflammatory cytokines IL-1β, IL-6, TNF-α, and CINC-1 was not essential for the initiation of postoperative hyperalgesia.

Cytokine profiles during carrageenan-induced inflammatory hyperalgesia in rat muscle and hind paw

It is not known if a cytokine cascade develops during muscle inflammation and whether cytokines contribute to muscle inflammatory pain. We measured plasma and tissue cytokine concentrations, and behavioral responses to noxious mechanical stimuli, after inducing inflammation in the gastrocnemius muscle and the hind paw of rats. Tissue and plasma samples were taken 3, 6, or 24 h after carrageenan or saline injection into one of the 2 sites. Tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, and cytokine-induced neutrophil chemoattractant 1 (CINC-1) concentrations were measured. Hyperalgesia was present 3 h after carrageenan injection into the hind paw and muscle. The TNF-alpha was elevated significantly in the inflamed hind paw tissue (P < .001) but not in inflamed muscle tissue. IL-1beta was elevated 6 h after carrageenan injection in the hind paw tissue but only 24 h in the muscle tissue (P < .001). The IL-6 was elevated 3 h after injection in the hind paw tissue but only after 6 h in the muscle tissue (P < .01). The CINC-1 in plasma, muscle, and hind paw was elevated from 3 h to 24 h after carrageenan injection (P < .01). The release of IL-1beta and IL-6, known to mediate hyperalgesia elsewhere, is delayed in muscle inflammation compared with cutaneous inflammation, whereas TNF-alpha is not elevated during muscle inflammation.

PERSPECTIVE

The quality and mechanisms of muscle pain are different from that of cutaneous pain. So too is the pattern of cytokine release during inflammation. Inhibiting TNF-alpha is unlikely to be effective in managing inflammatory muscle pain, but other cytokines, notably IL-1beta and CINC-1, may prove useful therapeutic targets.

Rofecoxib and tramadol do not attenuate delayed-onset muscle soreness or ischaemic pain in human volunteers

We assessed the effect of rofecoxib, a cyclo-oxygenase-2 inhibitor, and tramadol, a centrally acting analgesic, on both delayed-onset muscle soreness (DOMS) and experimentally induced ischaemic pain. We induced DOMS in 10 male and 5 female healthy volunteers by downhill running for 30 min at a 12% decline and a speed of 9 km·h–1. We also induced ischaemic pain by finger movements with an arterial tourniquet around the arm. In a randomized, double-blind crossover format, we administered rofecoxib (50 mg, daily), tramadol (50 mg, 3 times per day), and a placebo (orally for 3 days), starting immediately after exercise. A 100 mm visual analogue scale (VAS) and McGill pain questionnaire were used to describe muscle soreness and ischaemic forearm pain 24 h after the exercise. The pressure pain threshold (PPT) in the thigh and ischaemic pain tolerance in the forearm were measured before exercise and 24 and 72 h after exercise. PPT decreased 24 h after exercise, compared with pre-exercise values (ANOVA, p < 0.05), but neither drug had any significant effect on the PPT. Neither rofecoxib nor tramadol had any effect on time of ischaemia tolerated or amount of finger activity during ischaemia. The VAS and pain-rating index, for both muscle soreness and experimental ischaemic pain, were not affected significantly by either drug. Both DOMS and ischaemic pain share peripheral and central mechanisms, yet neither are attenuated by rofecoxib or tramadol.

Determinants of ball release speed in schoolboy fast-medium bowlers in cricket

AIM

Studies investigating determinants of ball release speed have examined the technique and anthropometry of fast bowlers with little work being done on muscular strength. The aim of our study was to determine whether knee biomechanics during bowling and strength of the shoulder and knee could predict ball release speed.

METHODS

Twelve cricketers, aged 16.6+/-0.7) years, from schools in Johannesburg, South Africa, volunteered for the study. Subjects were fast-medium bowlers (mean ball release speed of 29.2+/-1.8 m.s(-1)) and had been bowling for at least 5 years. Three accurate deliveries were filmed on an outdoor cricket pitch, in the sagittal plane with a high-speed digital camera recording at 250 frames per second. The mean ball release speed, knee angle at ball release and knee angle at front foot strike were determined using simple two-dimensional kinematics. On a separate day, peak concentric isokinetic muscle torque was measured for both knees and the dominant shoulder.

RESULTS

Ball release speed was positively correlated to a straight knee at front foot strike (r=0.72, P=0.009) and at ball release (r=0.71, P=0.011). No significant correlation was found between ball release speed and any of the peak torque values (knee extension peak torque, r=-0.11, knee flexion peak torque, r=-0.08, shoulder internal rotation peak torque, r=0.21 and shoulder external rotation, r=0.29, P>0.05). A multiple regression model using knee angle at front foot strike and at ball release, and the angle at which peak torque is generated during shoulder internal and external rotation, predicted ball release speed (adjusted r2=0.85, P<0.002).

CONCLUSIONS

We have confirmed that the angle of the front knee at the beginning and end of a delivery is an important correlate of ball release speed in schoolboy fast-medium bowlers. In addition we have also demonstrated that a multiple regression model based on knee kinematics and shoulder peak torque angles can be used to predict ball release speed.