Palmitoylethanolamide relieves pain and preserves pancreatic islet cells in a murine model of diabetes.

We previously demonstrated that the intraperitoneal administration of palmitoylethanolamide (PEA) in mice with chronic constriction injury of the sciatic nerve evoked a relief of both thermal hyperalgesia and mechanical allodynia in neuropathic mice. Since diabetic neuropathy is one of the most common long-term complications of diabetes, we explored the ability of PEA to also relief this kind of chronic pain, employing the well established streptozotocin-induced animal model of type 1 diabetes. Our findings demonstrated that PEA relieves mechanical allodynia, counteracts nerve growth factor deficit, improves insulin level, preserves Langerhans islet morphology reducing the development of insulitis in diabetic mice. These results suggest that PEA could be effective in type 1-diabetic patients not only as pain reliever but also in controlling the development of pathology.

Non-neuronal cell modulation relieves neuropathic pain: efficacy of the endogenous lipid palmitoylethanolamide.

We have previously shown that the endogenous lipid palmitoylethanolamide (PEA) induced relief of neuropathic pain through an action upon receptors located on the nociceptive pathway. Recently, it has been proposed that immune cells, in particular mast cells, and microglia, by releasing algogen mediators interact with neurons to alter pain sensitivity thereby contributing to the development and maintenance of chronic pain states. The aim of this work was to explore whether the anti-nociceptive properties of PEA might be accompanied by modulation of these non-neuronal cells. Mice were subjected to a chronic constriction injury model of neuropathic pain and treated with PEA. The data show that at the earlier (3 days) time-point after nerve injury there was a substantial recruitment of mast cells whose activation was not yet pronounced. In contrast, at the later time point (8 days) there was no further increase in mast cell number, but rather a marked activation of these cells. An up-regulation of activated microglia was found in the spinal cord of neuropathic pain mice. PEA delayed mast cell recruitment, protected mast cells against degranulation and abolished the nerve growth factor increase in sciatic nerve concomitantly preserving the nerve from degeneration, while reducing microglia activation in the spinal cord. These findings support the idea that non-neuronal cells may be a valuable pharmacological target to treat neuropathic pain since the current neuronal-direct drugs are still unsatisfactory. In this context PEA could represent an innovative molecule, combining a dual analgesic activity, both on neurons and on nonneuronal cells.

Rimonabant, a cannabinoid CB1 receptor antagonist, attenuates mechanical allodynia and counteracts oxidative stress and nerve growth factor deficit in diabetic mice.

Diabetes is one of the leading causes of painful neuropathy and to date, besides a tight glycemic control, a viable treatment for this complication is not available. Rimonabant is a selective cannabinoid CB(1) receptor antagonist that produces a significant increase in insulin sensitivity and a reduction of HbA(1c) in diabetic patients. This study aimed to investigate the therapeutic potential of rimonabant in relieving diabetes-induced neuropathic pain. The repeated treatment with rimonabant evoked a significant attenuation of mechanical allodynia in diabetic mice that was dose- and time-dependent. This effect occurred without alteration of hyperglycemia, but it was associated with significant effects on many key players in the pathogenesis of diabetic neuropathy. Metabolic changes induced by hyperglycemia lead to oxidative stress, deregulation of cytokine control and reduced production and transport of nerve growth factor (NGF), and all these factors contribute to neuropathic pain. Rimonabant treatment reduced oxidative stress in peripheral nerve, as revealed by the ability of the compound to counteract the reduced glutathione (GSH) depletion. The same repeated treatment inhibited tumor necrosis factor (TNFalpha) overproduction in the spinal cord and increased the NGF support. This rimonabant-induced improvement might favour the nerve regeneration; accordingly, the histological analysis of sciatic nerves showed a marked degeneration of myelinated fibers in diabetic mice, that was substantially reduced after rimonabant administration. These findings support the hypothesis that CB(1) antagonists would represent a new opportunity for diabetic patients, since currently there are no treatments for painful diabetic neuropathy other than treating the diabetic condition per se.

The dual fatty acid amide hydrolase/TRPV1 blocker, N-arachidonoyl-serotonin, relieves carrageenan-induced inflammation and hyperalgesia in mice.

Given that the pharmacological or genetic inactivation of fatty acid amide hydrolase (FAAH) counteracts pain and inflammation, and on the basis of the established involvement of transient receptor potential vanilloid type-1 (TRPV1) channels in inflammatory pain, we tested the capability of a dual FAAH/TRPV1 blocker, N-arachidonoyl-serotonin (AA-5-HT), to relieve oedema and pain in a model of acute inflammation, and compared its efficacy with that of a single FAAH inhibitor (URB597) or TRPV1 antagonist (capsazepine). Acute inflammation was induced by intraplantar injection of lambda-carrageenan into mice and the anti-inflammatory and anti-nociceptive actions of AA-5-HT were assessed at different doses, time points and treatment schedule. In addition, endocannabinoid levels were measured in paw skin and spinal cord. Systemic administration of AA-5-HT elicited dose-dependent anti-oedemigen and anti-nociceptive effects, whereas it was devoid of efficacy when given locally. When tested in a therapeutic regimen, the compound retained comparable anti-inflammatory effects. TRPV1 receptor mediated the anti-inflammatory property of AA-5-HT, whereas both CB(1) and TRPV1 receptors were involved in its anti-hyperalgesic activity. These effects were accompanied by an increase of the levels of the endocannabinoid anandamide (AEA) in both inflamed paw and spinal cord. AA-5-HT was more potent than capsazepine as anti-oedemigen and anti-hyperalgesic drug, whereas it shows an anti-oedemigen property similar to URB597, which was, however, devoid of the anti-nociceptive effect. AA-5-HT did not induce unwanted effects on locomotion and body temperature. In conclusion AA-5-HT has both anti-inflammatory and anti-hyperalgesic properties and its employment offers advantages, in terms of efficacy and lack of adverse effects, deriving from its dual activity.

Beneficial effects of a Cannabis sativa extract treatment on diabetes-induced neuropathy and oxidative stress.

Neuropathy is the most common complication of diabetes and it is still considered to be relatively refractory to most of the analgesics. The aim of the present study was to explore the antinociceptive effect of a controlled cannabis extract (eCBD) in attenuating diabetic neuropathic pain. Repeated treatment with cannabis extract significantly relieved mechanical allodynia and restored the physiological thermal pain perception in streptozotocin (STZ)-induced diabetic rats without affecting hyperglycemia. In addition, the results showed that eCBD increased the reduced glutathione (GSH) content in the liver leading to a restoration of the defence mechanism and significantly decreased the liver lipid peroxidation suggesting that eCBD provides protection against oxidative damage in STZ-induced diabetes that also strongly contributes to the development of neuropathy. Finally, the nerve growth factor content in the sciatic nerve of diabetic rats was restored to normal following the repeated treatment with eCBD, suggesting that the extract was able to prevent the nerve damage caused by the reduced support of this neurotrophin. These findings highlighted the beneficial effects of cannabis extract treatment in attenuating diabetic neuropathic pain, possibly through a strong antioxidant activity and a specific action upon nerve growth factor.

Glycolipids and benzylammonium lipids as novel antisepsis agents: synthesis and biological characterization.

New glycolipids and a benzylammonium lipid were rationally designed by varying the chemical structure of a D-glucose-derived hit compound active as lipid A antagonist. We report the synthesis of these compounds, their in vitro activity as lipid A antagonists on HEK cells, and the capacity to inhibit LPS-induced septic shock in vivo. The lack of toxicity and the good in vivo activity suggest the use of some compounds of the panel as hits for antisepsis drug development.

The endogenous fatty acid amide, palmitoylethanolamide, has anti-allodynic and anti-hyperalgesic effects in a murine model of neuropathic pain: involvement of CB(1), TRPV1 and PPARgamma receptors and neurotrophic factors.

Palmitoylethanolamide (PEA) is an endogenous lipid that is thought to be involved in endogenous protective mechanisms activated as a result of stimulation of inflammatory response. In spite of the well demonstrated anti-inflammatory properties of PEA, its involvement in controlling pain pathways still remains poorly characterized. On this basis, we tested the efficacy of PEA in vivo against a peculiar persistent pain, such as neuropathic one. PEA was administered i.p. to mice with chronic constriction injury of sciatic nerve (CCI) once a day for one week starting the day after the lesion. This therapeutic regimen evoked a relief of both thermal hyperalgesia and mechanical allodynia in neuropathic mice. Various selective receptor antagonists were used in order to clarify the relative contribution of cannabinoid, vanilloid and peroxisome proliferator-activated receptor to PEA-induced effects. The results indicated that CB(1), PPARgamma and TRPV1 receptors mediated the antinociception induced by PEA, suggesting that the most likely mechanism might be the so-called "entourage effect" due to the PEA-induced inhibition of the enzyme catalyzing the endocannabinoid anandamide (AEA) degradation that leads to an enhancement of its tissue levels thus increasing its analgesic action. In addition, the hypothesis that PEA might act through the modulation of local mast cells degranulation is sustained by our findings showing that PEA significantly reduced the production of many mediators such as TNFalpha and neurotrophic factors, like NGF. The findings presented here, in addition to prove the beneficial effects of PEA in chronic pain, identify new potential targets for analgesic medicine.

Glial TLR4 receptor as new target to treat neuropathic pain: efficacy of a new receptor antagonist in a model of peripheral nerve injury in mice.

Neuropathic pain remains a prevalent clinical problem because it is often poorly responsive to the currently used analgesics, thus it is crucial the identification of new potential targets and drugs. Recent evidence indicated that microglial cells in the spinal cord are critically involved in the development and maintenance of neuropathic pain, with a pivotal role of toll-like receptor 4 (TLR4). Binding of an endogenous ligand to TLR4 might be considered an important step in the regulation of microglia activity in pain facilitation, suggesting that a mechanism aimed to inhibit such a binding could be effective against neuropathic pain. We have synthesized new ligands to TLR4 with antagonistic activity. In the present work we evaluated the efficacy of the most potent TLR4 antagonist synthesized by us (FP-1), administered in mice with painful neuropathy. The repeated treatment of neuropathic mice with FP-1 (5-10 mg/kg, i.p.) evoked a relief of both thermal hyperalgesia and mechanical allodynia, whereas the administration of the highest dose to TLR4 knockout neuropathic mice revealed that in the absence of TLR4 receptor, the compound lost its efficacy. As consequence of TLR4 binding, the repeated treatment with FP-1 prevented the activation of the transcription factor NF-kB and the TNFalpha overproduction in the spinal cord. Together, our findings support the previous evidence indicative for a contribution of glial TLR4 to the initiation of neuropathic pain, suggest it as potential innovative target to treat this debilitating disease, and propose FP-1 as lead compound for the development of new effective drugs.

Antihyperalgesic effect of a Cannabis sativa extract in a rat model of neuropathic pain: mechanisms involved.

This study aimed to give a rationale for the employment of phytocannabinoid formulations to treat neuropathic pain. It was found that a controlled cannabis extract, containing multiple cannabinoids, in a defined ratio, and other non-cannabinoid fractions (terpenes and flavonoids) provided better antinociceptive efficacy than the single cannabinoid given alone, when tested in a rat model of neuropathic pain. The results also demonstrated that such an antihyperalgesic effect did not involve the cannabinoid CB1 and CB2 receptors, whereas it was mediated by vanilloid receptors TRPV1. The non-psychoactive compound, cannabidiol, is the only component present at a high level in the extract able to bind to this receptor: thus cannabidiol was the drug responsible for the antinociceptive behaviour observed. In addition, the results showed that after chronic oral treatment with cannabis extract the hepatic total content of cytochrome P450 was strongly inhibited as well as the intestinal P-glycoprotein activity. It is suggested that the inhibition of hepatic metabolism determined an increased bioavailability of cannabidiol resulting in a greater effect. However, in the light of the well known antioxidant and antiinflammatory properties of terpenes and flavonoids which could significantly contribute to the therapeutic effects, it cannot be excluded that the synergism observed might be achieved also in the absence of the cytochrome P450 inhibition.