Salim A. Kanaan

Endotoxin-induced local inflammation and hyperalgesia in rats and mice: a new model for inflammatory pain

&NA; Lipopolysaccharide, also known as endotoxin (ET), is a major constituent of the outer membrane of the cell wall of most gram negative bacteria. ET is known to cause a number of pathophysiological changes associated with illness including inflammatory pain. The aim of this study is to characterize the peripheral hyperalgesia induced by ET in rats and mice. Different groups of rats and mice received different doses of ET ranging from 0.6 &mgr;g to 40 &mgr;g dissolved in 50 &mgr;l saline and injected in the plantar area of the left hind legs. All animals were subjected to tail immersion (TF), hot plate (HP) and paw pressure (PP) tests, 2–3 days prior to ET injection and during the following 1–2 days. ET injections produced a dose‐dependent decrease in the latencies of the HP and PP tests of the injected leg reaching a maximum decrease of 50–60% of the control with 20–40 &mgr;g ET at 9 h (rats) and 24 h (mice) after the injection. Almost complete recovery was observed after 24 h in rats and 48 h in mice. TF latencies showed a less but a significant decrease while PP of the opposite leg and all tests in saline‐injected animals did not elicit significant variations and served as additional controls. Our results indicate that the use of ET‐produced hyperalgesia is a valid model for local and reversible inflammatory pain, with minimal distress to the animal. This model can also be used to study the efficacy of various anti‐inflammatory and analgesic drugs and the molecular mechanisms of inflammation induced by bacterial invasion.

Interleukin-10 reduces the endotoxin-induced hyperalgesia in mice

In the endotoxin-induced inflammation, interleukin-10 reduced significantly, and in a dose-dependent manner, the inflammatory pain as assessed by mechanical and thermal tests. The levels of Tumour Necrosis Factor (TNF)alpha and NGF were upregulated at 1.5 h whereas those of IL-1beta at 6 h after ET injection. IL-10 downregulated the levels of TNFalpha (from 4974.75 +/- 875.78 to 1008 +/- 350 pg/hind paw), NGF (from 352.9 +/- 46.7 to 33.9 +/- 2.4 pg/hind paw) and IL-1beta (from 2773.88 +/- 423.96 to 1108 +/- 399.56 pg/hind paw). These data suggest that IL-10 inhibits ET-induced hyperalgesia by downregulation of TNFalpha, IL-1beta and NGF production.

Involvement of interleukin‐1β, nerve growth factor and prostaglandin E2 in endotoxin‐induced localized inflammatory hyperalgesia

1 Intraplantar endotoxin (ET) injection (1.25 μg) into the hind paw of rats resulted in a localized inflammatory hyperalgesia, as assessed by paw pressure (PP), paw immersion (PI), tail flick (TF) and hot plate (HP) tests. 2 ET injection resulted in a significant elevation in the levels of interleukin‐1β (IL‐1β) and nerve growth factor (NGF) in the injected foot as compared with the non‐injected foot. This increase was attenuated by intraperitoneal injections of dexamethasone (200 and 400 μg kg−1) and to a lesser extent by indomethacin (2 and 8 mg kg−1). 3 The tripeptide Lys‐D‐Pro‐Val, which is known to antagonize IL‐1β and prostaglandin E2 (PGE2) reversed mechanical hyperalgesia, as assessed by the PP test, and reduced significantly thermal hyperalgesia, as assessed by the HP and TF tests. 4 IL‐1ra reversed both mechanical (PP) and thermal (PI) nociceptive thresholds tested on the injected leg and significantly reduced thermal hyperalgesia, as assessed by the HP and TF tests. 5 A sheep, anti‐mouse NGF antiserum reversed mechanical hyperalgesia (PP test) but had little or no effect on thermal hyperalgesia (PI, HP and TF tests). 6 Our results indicate the importance of IL‐1β, NGF and prostaglandin E2 (PGE2) in the development of ET induced hyperalgesia and the possible existence of different mechanisms underlying thermal and mechanical as well as central and peripheral hyperalgesia.

Magnetic resonance imaging in intradural and extradural spinal echinococcosis

The potential of magnetic resonance imaging (MRI) in the evaluation of spinal hydatidosis has not yet been fully explored. Only a few sporadic case reports have demonstrated interesting capabilities for detection of cystic echinococcal lesions in and around the spine, but to our knowledge none has described the MRI findings in intradural hydatid cysts. We present two cases of hydatid disease of the spine with extradural and intradural involvement illustrating the value of MRI in the preoperative evaluation, operative planning, and immediate postsurgical results.

Involvement of Interleukin-1β, Nerve Growth Factor, and Prostaglandin-E2in the Hyperalgesia Induced by Intraplantar Injections of Low Doses of Thymulin

The effect of various doses of intraplantar thymulin injection, on nociceptive thresholds, in the hind paw of rats was assessed using different pain tests. As little as 0.5 ng thymulin resulted in localized mechanical hyperalgesia as assessed by the paw pressure test and thermal hyperalgesia as assessed by the paw immersion, hot plate, and tail flick tests. The highest dose of thymulin (10 ng) reduced both paw pressure and paw immersion latencies in the noninjected paw also. Thymulin (5 ng) also resulted in significant elevation in the levels of interleukin-1 beta (IL-1 beta) and nerve growth factor (NGF) levels in the injected paw. Both dexamethasone and indomethacin reversed thymulin-induced hyperalgesia. Also interleukin-1 receptor antagonist (IL-1ra) and a polyclonal anti-NGF antiserum significantly reduced thymulin-induced hyperalgesia. On the other hand, the tripeptide lys-D-pro-val (known to antagonize IL-1 beta and PGE2 induced hyperalgesia) reversed the hyperalgesia due to thymulin. In conclusion, thymulin induces localized hyperalgesia which is mediated by PGE2-dependent mechanisms and this pathway could be either partially dependent on or totally independent of IL-1 beta mechanisms.

The role of cytokines and prostaglandin-E2 in thymulin induced hyperalgesia

We have recently reported that intraperitoneal (i.p.) injection of thymulin at low doses (50 ng) resulted in thermal and mechanical hyperalgesia and upregulation of the level of interleukin-1beta in the liver. In this study, we demonstrate that such injections of thymulin result in a significant elevation in the levels of TNF-alpha (P<0.01), NGF (P<0.01) and PGE(2) (P<0.01) in the liver of the treated rats, in addition to the increase in the levels of IL-1beta. Pretreatment with specific antagonists to each of these factors (polyclonal anti-TNF-alpha, anti-NGF antiserum and IL-1 receptor antagonist) did not result in the abolition of the hyperalgesia as assessed by the paw pressure, hot plate, paw immersion and tail flick tests. However, pretreatment with a combination of the above antagonist and antisera almost completely prevented thymulin-induced hyperalgesia. The cyclooxygenase inhibitor, meloxicam, reversed in a dose dependent manner (0.2, 0.4 and 2 mg/kg) thymulin effects as assessed by the different pain tests. It also abolished the thymulin-induced increase in the level of cytokines and NGF in the liver. Our results indicate that PGE(2) could be the key mediator of the hyperalgesic action of thymulin and the observed upregulation of proinflammatory cytokines and NGF.

Zinc Reduces the Hyperalgesia and Upregulation of NGF and IL-1β Produced by Peripheral Inflammation in the Rat

The effect of systemic zinc administration on the inflammatory hyperalgesia induced by intraplantar injections of either complete Freunds adjuvant (CFA) or bacterial endotoxin/lipopolysaccharide (LPS) in a hindpaw of adult rats was investigated. CFA injection resulted in mechanical and thermal hyperalgesia and an elevation in the levels of interleukin-1 beta (IL-1 beta) and nerve growth factor (NGF) in the ipsilateral hindpaw. Zinc treatment (20 nmole) significantly reduced sensitivity in the early phase of the inflammation and diminished the increase in the levels of IL-1 beta and NGF without affecting paw swelling. Intraplantar LPS injection also produced mechanical hyperalgesia and this too was reduced by zinc administration in a dose-dependent fashion (0.1-20 nmoles). Our results indicate that zinc has an analgesic action during early inflammation and that this may be the consequence of reducing levels of the inflammatory cytokine IL-beta and the growth factor NGF.

Hyperalgesia and upregulation of cytokines and nerve growth factor by cutaneous leishmaniasis in mice.

&NA; Classical description of syndromes produced by cutaneous leishmaniasis (CL) does not include sensory manifestations such as pain and/or itching, despite the evident upregulation of proinflammatory cytokines. Using a murine model of CL we report on evident hyperalgesia, as assessed by acute pain tests, and sustained upregulation of interleukin (IL‐1&bgr;) and nerve growth factor (NGF). This upregulation, especially that of NGF, may explain the observed hyperalgesia, in the light of recent evidence on the role of cytokines in the sensitization of nerve afferents and the subsequent hyperalgesia.

Effects of Various Analgesic and Anti-Inflammatory Drugs on Endotoxin-lnduced Hyperalgesia in Rats and Mice

A new model of endotoxin (ET)-induced hyperalgesia has been used to test the effects of four classes of drugs in rats and mice. Hyperalgesia was assessed by paw pressure (PP), hot plate (HP) and tail flick (TF) tests. Each drug was injected intraperitoneally 24 and 12 h before ET injection and just before each pain test at 3, 6, 9 and 24 h after ET injection. At the dosages used, acetaminophen and dexamethasone were the most effective in reducing PP hyperalgesia and least effective on TF hyperalgesia, while indometacin and morphine produced their main effect on TF hyperalgesia. The four drugs were about equally effective in reversing HP hyperalgesia. We conclude that ET hyperalgesia is mediated by both prostaglandin-sensitive and prostaglandin-independent mechanisms.

Thymulin reduces hyperalgesia induced by peripheral endotoxin injection in rats and mice

In a new model of peripheral localized inflammation, induced by intraplantar endotoxin (1.25 micrograms) injection in the hind paw of rats and mice, thymulin, a hormone of the thymus gland involved in immunomodulation, reduced inflammatory pain. High doses of thymulin reduced significantly, and in a dose-dependent manner, mechanical hyperalgesia as assessed by the paw pressure test and thermal hyperalgesia as assessed by the hot plate test and tail immersion test.