Cannabinoids in anaesthesia and pain therapy

Quantification and time course of subjective psychotropic and somatic effects of tetrahydrocannabinol - a prospective, single-blind, placebo-controlled exploratory trial in healthy volunteers

BACKGROUND

Cannabis is increasingly used and debates about the legalisation of the recreational use of cannabis are ongoing. In this prospective, placebo-controlled study in healthy volunteers not regularly consuming cannabis, subjective psychotropic and somatic effects after a single dose of intravenous THC were assessed and quantified over 48 h.

METHODS

Twenty-five healthy volunteers received a single IV bolus of THC and 6 received normal saline. Psychotropic and somatic effects of THC were assessed by two questionnaires that were completed at up to 14 timepoints from shortly before drug administration to 48 h later.

RESULTS

Demographic data did not differ between groups. Differences between THC and placebo for all assessed effects, except for euphoria, irritation and headache, were clearly discernible. Subdimensions related to positive mood were less and those related to negative mood were more pronounced in the THC group. Peak plasma concentrations were observed at 1 to 5 min after THC administration while peak effects occurred between 45 and 60 min. Differences between THC and placebo were pronounced and seen for up to 90 to 120 min for most effects, except for "sleepiness" and "deactivation", where the effect of THC was discernible for up to 5 h. At 24 and 48 h, there were no statistically significant difference between THC and placebo group.

CONCLUSIONS

THC triggers a large range of psychotropic and somatic effects with peak effects at 45 to 60 min after IV administration of THC, much later than plasma peak levels. Most effects are short-lasting with a duration of up to 2 h, but some effects like sleepiness and deactivation can be longer-lasting and persist for 5 h or longer in cannabis-naïve or cannabis-abstinent individuals. Since effects of THC demonstrate a time course that differs from the time course of plasma concentrations it might be important to base the judgment of a possible impairment related to THC consumption on clinical or behavioral tests in addition to THC plasma levels.

TRIAL REGISTRATION

www.isrctn.com ; registration number ISRCTN53019164.

Therapeutic applications of cannabinoids

The psychoactive property of cannabinoids is well known and there has been a continuous controversy regarding the usage of these compounds for therapeutic purposes all over the world. Their use for medical and research purposes are restricted in various countries. However, their utility as medications should not be overshadowed by its negative physiological activities. This review article is focused on the therapeutic potential and applications of phytocannabinoids and endocannabinoids. We further highlights their mode of action, overall effects on physiology, various in vitro and in vivo studies that have been done so far and the extent to which these compounds can be useful in different disease conditions such as cancer, Alzheimer's disease, multiple sclerosis, pain, inflammation, glaucoma and many others. Thus, this work is an attempt to make the readers understand the positive implications of these compounds and indicates the significant developments of utilizing cannabinoids as therapeutic agents.

Diabetic Peripheral Neuropathy: Epidemiology, Diagnosis, and Pharmacotherapy

PURPOSE

Diabetic peripheral neuropathy (DPN) is the commonest cause of neuropathy worldwide, and its prevalence increases with the duration of diabetes. It affects approximately half of patients with diabetes. DPN is symmetric and predominantly sensory, starting distally and gradually spreading proximally in a glove-and-stocking distribution. It causes substantial morbidity and is associated with increased mortality. The unrelenting nature of pain in this condition can negatively affect a patient's sleep, mood, and functionality and result in a poor quality of life. The purpose of this review was to critically review the current literature on the diagnosis and treatment of DPN, with a focus on the treatment of neuropathic pain in DPN.

METHODS

A comprehensive literature review was undertaken, incorporating article searches in electronic databases (EMBASE, PubMed, OVID) and reference lists of relevant articles with the authors' expertise in DPN. This review considers seminal and novel research in epidemiology; diagnosis, especially in relation to novel surrogate end points; and the treatment of neuropathic pain in DPN. We also consider potential new pharmacotherapies for painful DPN.

FINDINGS

DPN is often misdiagnosed and inadequately treated. Other than improving glycemic control, there is no licensed pathogenetic treatment for diabetic neuropathy. Management of painful DPN remains challenging due to difficulties in personalizing therapy and ascertaining the best dosing strategy, choice of initial pharmacotherapy, consideration of combination therapy, and deciding on defining treatment for poor analgesic responders. Duloxetine and pregabalin remain first-line therapy for neuropathic pain in DPN in all 5 of the major published guidelines by the American Association of Clinical Endocrinologists, American Academy of Neurology, European Federation of Neurological Societies, National Institute of Clinical Excellence (United Kingdom), and the American Diabetes Association, and their use has been approved by the US Food and Drug Administration.

IMPLICATIONS

Clinical recognition of DPN is imperative for allowing timely symptom management to reduce the morbidity associated with this condition.

Recent advances in the pharmaceutical management of pain

Pain is an unpleasant sensory and emotional experience for patients. Management of pain is the most frequent issue encountered by clinicians and treatment is usually with pharmacological therapy. This review discusses recent pharmaceutical advances in pain management with respect to new modes of analgesic delivery, as well as new analgesic agents and adjuvants that are currently being investigated for their analgesic properties. New modes of administration include transdermal delivery in the form of skin patches, transmucosal delivery, inhalational administration, various patient-controlled devices and extended-release analgesic formulations. Up-to-date research is presented on classical analgesics, such as opioids, anti-inflammatory agents, including cyclo-oxygenase-2 inhibitors and paracetamol (acetaminophen), local anesthetics and ketamine. In addition, newer agents such as antidepressants and antiepileptic drugs as well as medicinal cannabinoids are discussed. As our understanding of the multiple pain pathways involved in the pathogenesis of pain expands, further compounds with analgesic properties will be developed.

Cannabinoid agonist WIN 55,212-2 prevents the development of paclitaxel-induced peripheral neuropathy in rats. Possible involvement of spinal glial cells

Spinal glial activation contributes to the development and maintenance of chronic pain states, including neuropathic pain of diverse etiologies. Cannabinoid compounds have shown antinociceptive properties in a variety of neuropathic pain models and are emerging as a promising class of drugs to treat neuropathic pain. Thus, the effects of repeated treatment with WIN 55,212-2, a synthetic cannabinoid agonist, were examined throughout the development of paclitaxel-induced peripheral neuropathy. Painful neuropathy was induced in male Wistar rats by intraperitoneal (i.p.) administration of paclitaxel (1mg/kg) on four alternate days. Paclitaxel-treated animals received WIN 55,212-2 (1mg/kg, i.p.) or minocycline (15 mg/kg, i.p.), a microglial inhibitor, daily for 14 days, simultaneous with the antineoplastic. The development of hypersensitive behaviors was assessed on days 1, 7, 14, 21 and 28 following the initial administration of drugs. Both the activation of glial cells (microglia and astrocytes) at day 29 and the time course of proinflammatory cytokine release within the spinal cord were also determined. Similar to minocycline, repeated administration of WIN 55,212-2 prevented the development of thermal hyperalgesia and mechanical allodynia in paclitaxel-treated rats. WIN 55,212-2 treatment also prevented spinal microglial and astrocytic activation evoked by paclitaxel at day 29 and attenuated the early production of spinal proinflammatory cytokines (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α). Our results confirm changes in the reactivity of glial cells during the development of peripheral neuropathy induced by paclitaxel and support a preventive effect of WIN 55,212-2, probably via glial cells reactivity inactivation, on the development of this neuropathy.

Role of cannabinoids in the treatment of pain and (painful) spasticity

Both the discovery of the endocannabinoid system (ECS) and its role in the control of pain and habituation to stress, as well as the significant analgesic and antihyperalgesic effects in animal studies, suggest the usefulness of cannabinoids in pain conditions. However, in human experimental or clinical trials, no convincing reduction of acute pain, which may be caused by a pronociceptive, ECS-triggered mechanism on the level of the spinal cord, has been demonstrated. In contrast, in chronic pain and (painful) spasticity, an increasing number of randomized, double-blind, placebo-controlled studies have shown the efficacy of cannabinoids, which is combined with a narrow therapeutic index. Patients with unsatisfactory response to other methods of pain therapy and who were characterized by failed stress adaptation particularly benefited from treatment with cannabinoids. None of the attempts to overcome the disadvantage of the narrow therapeutic index, either by changing the route of application or by formulating balanced cannabinoid preparations, have resulted in a major breakthrough. Therefore, different methods of administration and other types of cannabinoids, such as endocannabinoid modulators, should be tested in future trials.

Fibromyalgia and fatigue: central processing, widespread dysfunction

Biological and psychological bases for the covariation of pain and fatigue in fibromyalgia (FM) are reviewed. FM is characterized as a disorder of central sensitization, with pain and fatigue as the most prominent symptoms. The roles of sleep disturbance and affective dysregulation as both precipitants and consequences of pain and fatigue in FM are discussed. It is argued that a positive affective disturbance may uniquely characterize pain and fatigue symptoms in FM. Finally, pharmacological and nonpharmacological treatments for FM are highlighted, with an emphasis on the efficacy of these treatments in alleviating pain and fatigue symptoms.

Cannabinoids against pain. Efficacy and strategies to reduce psychoactivity: a clinical perspective

The clinical use of cannabinoids is currently a topic of interest not exclusively, but most importantly, concerning different areas of pain therapy. One of the major obstacles in developing clinically acceptable compounds is the cannabimimetic side-effect profile of delta-9-tetrahydrocannabinol (THC) and other cannabinoids. This article gives a brief overview of the endocannabinoid system, its components and functions and explains the current approaches to avoiding cannabimimetic side effects by separating them from the therapeutic effects. One of these approaches is the addition of cannabidiol (CBD) as well as the use of preparations suitable for oromucosal application. Also cannabinoids, which primarily stimulate peripheral cannabinoid-1 (CB1) receptors or selectively cannabinoid-2 (CB2) receptors, can further separate analgesic activity from cannabimimetic activity. Local or topical modes of application are another attempt aiming in the same direction. Modulating the endogenous cannabinoid tone (via the inhibition of endocannabinoid-metabolising enzymes) is another strategy. The combination of THC in low, non-psychoactive doses with opioids has a synergistic effect and reduces opioid tolerance effects. Available data from these approaches are summarised and their more and less promising aspects are discussed.

Antinociceptive effect of the cannabinoid agonist, WIN 55,212-2, in the orofacial and temporomandibular formalin tests

Orofacial pain disorders are frequent in the general population and their pharmacological treatment is not always adequately resolved. Cannabinoids have demonstrated their analgesic effect in several pain conditions, both in animal models and in clinical situations. The aim of the present study was to evaluate the cannabinoid-mediated antinociception in two inflammatory models of orofacial pain (orofacial and temporomandibular joint (TMJ) formalin test) and to compare it with a spinal inflammatory model (paw formalin test). WIN 55,212-2 (0.5, 1mg/kg), a synthetic cannabinoid agonist, was intraperitoneally (i.p.) administered prior to formalin and significantly reduced the nociceptive behavioural responses in these inflammatory tests. To elucidate which subtype of receptor could be involved in such effect, two selective cannabinoid antagonists were administered prior to WIN. SR141716A (1mg/kg i.p.), the CB1 receptor-selective antagonist, was able to prevent the cannabinoid-induced analgesia in all three models, whereas SR144528 (1mg/kg i.p.), the CB2 receptor-selective antagonist, only prevented it in the paw formalin test. A comparison with the antinociceptive effects of morphine (2.5, 5, 10mg/kg, i.p.), indomethacin (2.5, 5mg/kg, i.p.) and ketamine (25, 50mg/kg, i.p.) was also performed. Morphine displayed a dose-dependent reduction of acute and inflammatory pain in all three models, whereas indomethacin and ketamine only attenuated inflammatory pain at the highest tested doses. These results indicate that the cannabinoid-induced antinociception in the orofacial region is mediated by activation of CB1 cannabinoid receptor. Moreover WIN was as effective as morphine and more effective than indomethacin and ketamine, in oral inflammatory pain.

Sustained antinociceptive effect of cannabinoid receptor agonist WIN 55,212-2 over time in rat model of neuropathic spinal cord injury pain

A significant complaint associated with spinal cord injury (SCI) is chronic pain, which includes symptoms such as cutaneous hypersensitivity and spontaneous unevoked pain and is difficult to treat with currently available drugs. One complication with current analgesics is tolerance, a decrease in efficacy with repeated treatment over time. One promising class of pharmacological treatment is cannabinoid (CB) receptor agonists. The current study assessed the efficacy of the CB receptor agonist WIN 55,212-2 (WIN) in a rat model of neuropathic SCI pain. Brief spinal compression leads to significant hindpaw hypersensitivity to tactile stimulation. WIN dose-dependently increased withdrawal thresholds and continued to demonstrate efficacy over a twice-daily 7-day treatment regimen. By contrast, the efficacy of morphine in SCI rats decreased over the same treatment period. Similarly, the antinociceptive efficacy of WIN to acute noxious heat in uninjured rats diminished over time. These data suggest that the sustained efficacy of a CB receptor agonist for pain could depend on the pain state. Such agonists may hold promise for long-term use in alleviating chronic SCI pain.

Volatile anesthetics and endogenous cannabinoid anandamide have additive and independent inhibitory effects on alpha(7)-nicotinic acetylcholine receptor-mediated responses in Xenopus oocytes

In earlier studies, the volatile anesthetics and the endogenous cannabinoid anandamide have been shown to inhibit the function of alpha(7)-nicotinic acetylcholine receptors. In the present study, interactions between the effects of volatile anesthetics and anandamide on the function of alpha(7)-nicotinic acetylcholine receptors expressed in Xenopus oocytes were investigated using the two-electrode voltage-clamp technique. Anandamide and volatile anesthetics isoflurane and halothane inhibited currents evoked with acetylcholine (100 microM) in a reversible and concentration-dependent manner. Coapplication of anandamide and volatile anesthetics caused a significantly greater inhibition of alpha(7)-nicotinic acetylcholine receptor function than anandamide or volatile anesthetics alone. Analyses of oocytes by matrix-assisted laser desorption/ionization mass spectroscopy indicated that volatile anesthetics did not alter the lipid profile of oocytes. Results of studies with chimeric alpha(7)-nicotinic acetylcholine-5-HT(3) receptors comprised of the N-terminal domain of the alpha(7)-nicotinic acetylcholine receptor and the transmembrane and carboxyl-terminal domains of 5-HT(3) receptors suggest that while isoflurane inhibition of the alpha(7)-nicotinic acetylcholine receptor is likely to involve the N-terminal region of the receptor, the site of action for anandamide involves transmembrane and carboxyl-terminal domains of the receptors. These data indicate that endocannabinoids and isoflurane have additive inhibitory effects on alpha(7)-nicotinic acetylcholine receptor function through allosteric binding sites located on the distinct regions of the receptor.

Activation of CB1 specifically located on GABAergic interneurons inhibits LTD in the lateral amygdala

Previously, we found that in the lateral amygdala (LA) of the mouse, WIN55,212-2 decreases both glutamatergic and GABAergic synaptic transmission via activation of the cannabinoid receptor type 1 (CB1), yet produces an overall reduction of neuronal excitability. This suggests that the effects on excitatory transmission override those on inhibitory transmission. Here we show that CB1 activation by WIN55,212-2 and Delta(9)-THC inhibits long-term depression (LTD) of basal synaptic transmission in the LA, induced by low-frequency stimulation (LFS; 900 pulses/1 Hz). The CB1 agonist WIN55,212-2 blocked LTD via G(i/o) proteins, activation of inwardly rectifying K+ channels (K(ir)s), inhibition of the adenylate cyclase-protein kinase A (PKA) pathway, and PKA-dependent inhibition of voltage-gated N-type Ca2+ channels (N-type VGCCs). Interestingly, WIN55,212-2 effects on LTD were abolished in CB1 knock-out mice (CB1-KO), and in conditional mutants lacking CB1 expression only in GABAergic interneurons, but were still present in mutants lacking CB1 in principal forebrain neurons. LTD induction per se was unaffected by the CB1 antagonist SR141716A and was normally expressed in CB1-KO as well as in both conditional CB1 mutants. Our data demonstrate that activation of CB1 specifically located on GABAergic interneurons inhibits LTD in the LA. These findings suggest that CB1 expressed on either glutamatergic or GABAergic neurons play a differential role in the control of synaptic transmission and plasticity.