Antihyperalgesic and antiallodynic effect of sirolimus in rat model of adjuvant arthritis.

Sirolimus is an immunosupressive drug that specifically inhibit the activation of T-lymphocytes. This study was undertaken to investigate whether treatment with sirolimus exert analgesic effect in rat adjuvant-induced arthritis, an animal model of rheumatoid arthritis. Arthritis was induced by a single subcutaneous injection of Freund's complete adjuvant to male Wistar rats that were divided into four groups; control (saline), vehicle (ethanol), sirolimus 0.75 and sirolimus 1.5. Sirolimus (0.75 and 1.5mg/kg/day) was administered intraperitoneally using Monday-Wednesday-Friday dosing schedule for 29 days, this dosing regimen revealed acceptable trough blood concentrations in arthritic rats. Adjuvant inoculation resulted in paw inflammation, hyperalgesia and allodynia as assessed by pletismometer, analgesymeter and dynamic plantar aesthesiometer respectively. Light microscopic evaluation of the arthritic metacarpophalangeal joints revealed synovial hypertrophy with inflammatory cellular infiltration, cartilage destruction and partial subchondral bone resorption. ELISA tests of serum TNF-α, IL-1ß or IL-6 did not show any change in arthritic rats, while Western blotting analysis revealed a significant increase in TNF-α (P<0.001), but not IL-1ß or IL-6, protein expression in the lumbar spinal cord of arthritic rats. Treatment with sirolimus significantly decreased the arthritic lesions (P<0.001) and paw swelling (P<0.05), alleviated the histological features in the metacarpophalangeal joint, resulted in antihyperalgesic and antiallodynic effects without affecting the locomotor activity and prevented the increased spinal cord TNF-α level (P<0.05). It seems that prevention of the increased TNF-α expression in the spinal cord may partially contribute to the antihyperalgesic effect of sirolimus in adjuvant arthritic rats and sirolimus could be a promising immunosupressive agent in the treatment of arthritic pain.

Antihyperalgesic and antiallodynic effect of sirolimus in neuropathic pain and the role of cytokines in this effect.

Recent studies have revealed that T lymphocytes play a role in neuropathic pain following nerve injury in rats through releasing several cytokines. Sirolimus is an immunosuppressive antibiotic inhibiting T cell activation. This study aimed to determine the effect of sirolimus on hyperalgesia and allodynia and on serum and spinal cord TNF-alpha, IL-1beta and IL-6 levels in rat neuropathic pain. Neuropathic pain was induced by loose ligation of the sciatic nerve and evaluated by tests measuring the mechanical hyperalgesia and allodynia. Sirolimus (0.75 and 1.5 mg/kg) was administered intraperitoneally once every 3 days for 2 weeks (7 doses totally). This dosing regimen revealed acceptable blood concentrations in neuropathic rats. Chronic constriction injury of the sciatic nerve resulted in hyperalgesia and allodynia. Serum levels of cytokines remained unchanged in neuropathic rats. However, TNF-alpha, but not IL-1beta or IL-6, protein level was increased in the spinal cord tissue as evaluated by Western blotting analysis. Treatment with sirolimus resulted in antihyperalgesic and antiallodynic effects and prevented the increased spinal cord TNF-alpha level. It seems that sirolimus could be a promising immunosuppressive agent in the treatment of neuropathic pain.

Effects of repeated administered ghrelin on chronic constriction injury of the sciatic nerve in rats.

Chronic constriction injury (CCI) is a peripheral mononeuropathic pain model that is caused by an injury to the peripheral nervous system and refractory to available conventional treatment. Mechanisms involved in neuropathic pain are still unclear. Previous studies reveal that proinflammatory cytokines contribute to CCI-induced peripheral nerve pathology. Ghrelin, a novel identified gastric peptide, has been shown to have antinociceptive activity and also anti-inflammatory properties by decreasing proinflammatory cytokines. Therefore, the aim of the present study was to investigate the effects of ghrelin on the CCI and its relationship with proinflammatory cytokines in rats. Wistar rats underwent sciatic nerve ligation to induce CCI fallowed by repeated ghrelin administrations (50 and 100microg/kg i.p., once daily) for a period of 14 days. Mechanical hyperalgesia was assessed before surgery and at day 14 after CCI. TNF-alpha, IL-1beta and IL-6 were measured in blood and spinal cord. The changes of sciatic nerve was assessed histologically by both light and electron microscopy. Ghrelin attenuated mechanical hyperalgesia, reduced spinal TNF-alpha and IL-1beta levels and enhanced sciatic nerve injury with correlated morphometric recovery. These results indicate that the protective effect by ghrelin in the spinal cord is mediated through the suppression of TNF-alpha and IL-1beta. Thus ghrelin may be a promising peptide in the management of neuropathic pain.

Apocynin restores endothelial dysfunction in streptozotocin diabetic rats through regulation of nitric oxide synthase and NADPH oxidase expressions.

AIM: Increased production of reactive oxygen species (ROS) in the diabetic vasculature results in the impairment of nitric oxide (NO)-mediated relaxations leading to impaired endothelium-dependent vasodilation. An important source of ROS is nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and the inhibition of this enzyme is an active area of interest. This study aimed to investigate the effects of apocynin, an NADPH oxidase inhibitor, on endothelial dysfunction and on the expression of NO synthase (NOS) and NADPH oxidase in thoracic aorta of diabetic rats. METHOD: Streptozotocin (STZ)-diabetic rats received apocynin (16 mg/kg per day) for 4 weeks. Endothelium-dependent and -independent relaxations were determined in thoracic aortic rings. Western blotting and RT-PCR analysis were performed for NOSs and NADPH oxidase in the aortic tissue. RESULTS: Acetylcholine-induced relaxations and l-NAME-induced contractions were decreased in diabetic aorta. The decrease in acetylcholine and l-NAME responses were prevented by apocynin treatment without a significant change in plasma glucose levels. Endothelial NOS (eNOS) protein and mRNA expression exhibited significant decrease in diabetes, while protein and/or mRNA expressions of inducible NOS (iNOS) as well as p22(phox) and gp91(phox) subunits of NADPH oxidase were increased, and these alterations were markedly prevented by apocynin treatment. CONCLUSION: NADPH oxidase expression is increased in diabetic rat aorta. NADPH oxidase-mediated oxidative stress is accompanied by the decreased eNOS and increased iNOS expressions, contributing to endothelial dysfunction. Apocynin effectively prevents the increased NADPH oxidase expression in diabetic aorta and restores the alterations in NOS expression, blocking the vicious cycle leading to diabetes-associated endothelial dysfunction.