In vitro activation of brain protein kinase C by the cannabinoids

Real-World Long-Term Experience on Endoxifen in Bipolar Disorder with Psychotic Symptoms

Evidence suggests that inhibition of protein kinase C (PKC) signalling may have a contributing role in the treatment of bipolar affective disorder (BPAD). Endoxifen, an active metabolite of tamoxifen, is a potent direct PKC inhibitor. This report presents a severe case of a BPAD patient with a baseline Young Mania Rating Scale (YMRS) score of 49, associated family history and addiction to psychostimulants, with no improvement by the first and second-generation antipsychotics. Treatment with endoxifen 8 mg once a day showed improvement in manic symptoms with a YMRS score of 4 and a reduction in the use of psychostimulants as well as other antipsychotic concomitant medications. No adverse effects were noted up to 8-month follow-up. Long-term treatment with endoxifen is safe and effective in severe BPAD.

Dynamic Change of Endocannabinoid Signaling in the Medial Prefrontal Cortex Controls the Development of Depression After Neuropathic Pain

Many patients with chronic pain conditions suffer from depression. The mechanisms underlying pain-induced depression are still unclear. There are critical links of medial prefrontal cortex (mPFC) synaptic function to depression, with signaling through the endocannabinoid (eCB) system as an important contributor. We hypothesized that afferent noxious inputs after injury compromise activity-dependent eCB signaling in the mPFC, resulting in depression. Depression-like behaviors were tested in male and female rats with traumatic neuropathy [spared nerve injury (SNI)], and neuronal activity in the mPFC was monitored using the immediate early gene c-fos and in vivo electrophysiological recordings. mPFC eCB Concentrations were determined using mass spectrometry, and behavioral and electrophysiological experiments were used to evaluate the role of alterations in eCB signaling in depression after pain. SNI-induced pain induced the development of depression phenotypes in both male and female rats. Pyramidal neurons in mPFC showed increased excitability followed by reduced excitability in the onset and prolonged phases of pain, respectively. Concentrations of the eCBs, 2-arachidonoylglycerol (2-AG) in the mPFC, were elevated initially after SNI, and our results indicate that this resulted in a loss of CB1R function on GABAergic interneurons in the mPFC. These data suggest that excessive release of 2-AG as a result of noxious stimuli triggers use-dependent loss of function of eCB signaling leading to excessive GABA release in the mPFC, with the final result being behavioral depression.SIGNIFICANCE STATEMENT Pain has both somatosensory and affective components, so the complexity of mechanisms underlying chronic pain is best represented by a biopsychosocial model that includes widespread CNS dysfunction. Many patients with chronic pain conditions develop depression. The mechanism by which pain causes depression is unclear. Although manipulation of the eCB signaling system as an avenue for providing analgesia per se has not shown much promise in previous studies. An important limitation of past research has been inadequate consideration of the dynamic nature of the connection between pain and depression as they develop. Here, we show that activity-dependent synthesis of eCBs during the initial onset of persistent pain is the critical link leading to depression when pain is persistent.

Genetic or pharmacological depletion of cannabinoid CB1 receptor protects against dopaminergic neurotoxicity induced by methamphetamine in mice

Accumulating evidence suggests that cannabinoid ligands play delicate roles in cell survival and apoptosis decisions, and that cannabinoid CB1 receptors (CB1R) modulate dopaminergic function. However, the role of CB1R in methamphetamine (MA)-induced dopaminergic neurotoxicity in vivo remains elusive. Multiple high doses of MA increased phospho-ERK and CB1R mRNA expressions in the striatum of CB1R (+/+) mice. These increases were attenuated by CB1R antagonists (i.e., AM251 and rimonabant), an ERK inhibitor (U0126), or dopamine D2R antagonist (sulpiride). In addition, treatment with MA resulted in dopaminergic impairments, which were attenuated by CB1R knockout or CB1R antagonists (i.e., AM251 and rimonabant). Consistently, MA-induced oxidative stresses (i.e., protein oxidation, lipid peroxidation and reactive oxygen species) and pro-apoptotic changes (i.e., increases in Bax, cleaved PKCδ- and cleaved caspase 3-expression and decrease in Bcl-2 expression) were observed in the striatum of CB1R (+/+) mice. These toxic effects were attenuated by CB1R knockout or CB1R antagonists. Consistently, treatment with four high doses of CB1R agonists (i.e., WIN 55,212-2 36mg/kg and ACEA 16mg/kg) also resulted in significant oxidative stresses, pro-apoptotic changes, and dopaminergic impairments. Since CB1R co-immunoprecipitates PKCδ in the presence of MA or CB1R agonists, we applied PKCδ knockout mice to clarify the role of PKCδ in the neurotoxicity elicited by CB1Rs. CB1R agonist-induced toxic effects were significantly attenuated by CB1R knockout, CB1R antagonists or PKCδ knockout. Therefore, our results suggest that interaction between D2R, ERK and CB1R is critical for MA-induced dopaminergic neurotoxicity and that PKCδ mediates dopaminergic damage induced by high-doses of CB1R agonist.

Cannabinoid receptor 1 induces a biphasic ERK activation via multiprotein signaling complex formation of proximal kinases PKCε, Src, and Fyn in primary neurons

Cannabinoid receptors 1 (CB1Rs) play important roles in the regulation of dendritic branching, synapse density, and synaptic transmission through multiple G-protein-coupled signaling systems, including the activation of the extracellular signal-regulated kinases ERK1/2. The proximal signaling interactions leading to ERK1/2 activation by CB1R in CNS remain, however, unclear. Here, we present evidence that the CB1R agonist methanandamide induced a biphasic and sustained activation of ERK1/2 in primary neurons derived from E7 telencephalon. We show that E7 neurons natively express high levels of CB1R message and protein, the majority of which associates with PKCɛ at basal conditions. We now demonstrate that the first peak of ERK activation by CB1R was mediated by the sequential activation of G(q), PLC, and PKCɛ, selectively, and that the CB1R-activated PKCɛ acutely formed transient signaling modules containing activated Src and Fyn. A second pool of CB1Rs, coupled to PTX-sensitive activation of G(i/o), utilized as effectors additional Src and Fyn molecules to generate a second, additional wave of ERK activation at 15 min. Concurrently to these intermolecular signaling interactions, cytoskeleton-associated proteins MARCKS and p120catenin were drastically modified by phosphorylation of PKC and Src, respectively. These receptor-proximal signaling events correlated well with induction of neuritic outgrowth in the long term. Our data provide evidence for multiprotein signaling complex formation in the coupling of CB1R to activation of ERK in CNS neurons, and may elucidate several of the less understood acute effects of cannabinoid drugs.

Effects of a cannabinoid agonist on spinal nociceptive neurons in a rodent model of neuropathic pain

The effects of the synthetic cannabinoid WIN 55,212-2 on heat-evoked firing of spinal wide dynamic range (WDR) neurons were examined in a rodent model of neuropathic pain. Fifty-eight WDR neurons (1 cell/animal) were recorded from the ipsilateral spinal dorsal horns of rats with chronic constriction injury (CCI) and sham-operated controls. Relative to sham-operated controls, neurons recorded in CCI rats showed elevations in spontaneous firing, noxious heat-evoked responses, and afterdischarge firing as well as increases in receptive field size. WIN 55,212-2 (0.0625, 0.125, and 0.25 mg/kg, intravenous) dose-dependently suppressed heat-evoked activity and decreased the receptive field areas of dorsal horn WDR neurons in both nerve injured and control rats with a greater inhibition in CCI rats. At the dose of 0.125 mg/kg iv, WIN 55,212-2 reversed the hyperalgesia produced by nerve injury. The effect of intravenous administration of WIN 55,212-2 appears to be centrally mediated because administration of the drug directly to the ligated nerve did not suppress the heat-evoked neuronal activity in CCI rats. Pretreatment with the cannabinoid CB(1) receptor antagonists SR141716A or AM251, but not the CB(2) antagonist SR144528, blocked the effects. These results provide a neural basis for reports of potent suppression by cannabinoids of the abnormal sensory responses that result from nerve injury.

Receptor-independent actions of cannabinoids on cell membranes: Focus on endocannabinoids

Cannabinoids are a structurally diverse group of mostly lipophilic molecules that bind to cannabinoid receptors. In fact, endogenous cannabinoids (endocannabinoids) are a class of signaling lipids consisting of amides and esters of long-chain polyunsaturated fatty acids. They are synthesized from lipid precursors in plasma membranes via Ca(2+) or G-protein-dependent processes and exhibit cannabinoid-like actions by binding to cannabinoid receptors. However, endocannabinoids can produce effects that are not mediated by these receptors. In pharmacologically relevant concentrations, endocannabinoids modulate the functional properties of voltage-gated ion channels including Ca(2+) channels, Na(+) channels, various types of K(+) channels, and ligand-gated ion channels such as serotonin type 3, nicotinic acetylcholine, and glycine receptors. In addition, modulatory effects of endocannabinoids on other ion-transporting membrane proteins such as transient potential receptor-class channels, gap junctions and transporters for neurotransmitters have also been demonstrated. Furthermore, functional properties of G-protein-coupled receptors for different types of neurotransmitters and neuropeptides are altered by direct actions of endocannabinoids. Although the mechanisms of these effects are currently not clear, it is likely that these direct actions of endocannabinoids are due to their lipophilic structures. These findings indicate that additional molecular targets for endocannabinoids exist and that these targets may represent novel sites for cannabinoids to alter either the excitability of the neurons or the response of the neuronal systems. This review focuses on the results of recent studies indicating that beyond their receptor-mediated effects, endocannabinoids alter the functions of ion channels and other integral membrane proteins directly.

Reversal of Δ9-tetrahydrocannabinol-induced tolerance by specific kinase inhibitors

Tolerance develops to the pharmacological effects of Delta9-tetrahydrocannabinoid (THC) following repetitive administration. Adaptations in signaling pathways involved in tolerance to THC-induced behaviors are not understood. The objective of our study was the evaluation of kinase involvement in the expression of tolerance to the above four THC-induced behaviors. Kinase inhibitors that specifically inhibit cyclic AMP-dependent protein kinase (PKA), cyclic GMP-dependent protein kinase (PKG), calmodulin-dependent protein kinase (PKC) and src tyrosine kinase were tested for reversal of tolerance to THC's effects. PKG and PKC inhibitors did not reverse tolerance in any behavioral measure. Src tyrosine kinase inhibition reversed tolerance to only the hypoactive effects of THC. PKA inhibition reversed tolerance to all measures, although the doses of inhibitor and time-course of inhibition varied among behaviors. Thus, our data suggest that PKA activity plays a major role in THC-induced tolerance, and that THC produces its multiple effects through different signaling pathways.

The role of several kinases in mice tolerant to delta 9-tetrahydrocannabinol

It has been suggested that the cannabinoid receptor type 1 (CB1), a G protein-coupled receptor, is internalized after agonist binding and activation of the second messenger pathways. It is proposed that phosphorylation enhances the down-regulation of the CB1 receptor, thus contributing to tolerance. Alterations in phosphorylation of proteins in the signal transduction cascade after CB1receptor activation could also alter tolerance to cannabinoids. We addressed our hypothesis by evaluating the role of several kinases in antinociceptive tolerance to Delta(9)-tetrahydrocannabinol (THC). We evaluated cAMP-dependent protein kinase (PKA) using KT5720, a PKA inhibitor; protein kinase C (PKC) using bisindolylmaleimide I, HCl (bis), a PKC inhibitor; cGMP-dependent protein kinase (PKG) using KT5823, a PKG inhibitor; beta-adrenergic receptor kinase (beta-ARK) using low molecular weight heparin (LMWH), a beta-ARK inhibitor; and phosphatidylinositol-3 kinase (PI3-K) using 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a PI3-K inhibitor and PP1, a Src family tyrosine kinase inhibitor. The cAMP analog used was dibutyryl-cAMP and the cGMP analog used was dibutyryl-cGMP. Our data indicate that selective kinases may be involved in cannabinoid tolerance. Mice and rats were rendered tolerant to Delta(9)-THC. The PKG inhibitor KT5823, the beta-ARK inhibitor LMWH, the PI3-K inhibitor LY294002, and inhibition of PKC by bis had no effect on tolerance. At a higher dose, bis attenuated the antinociceptive effect of delta(9)-THC in nontolerant mice. PP1, the Src family tyrosine kinase inhibitor, and KT5720, the PKA inhibitor, reversed THC-induced tolerance. In addition, inhibition of PKA reversed a decrease in dynorphin release shown to accompany THC tolerance in rats. These data support a role for PKA and Src tyrosine kinase in phosphorylation events in delta(9)-THC-tolerant mice.

Contribution of endocannabinoids in the endothelial protection afforded by ischemic preconditioning in the isolated rat heart

The aim of the present study was to assess the contribution of endogenous cannabinoids in the protective effect of ischemic preconditioning on the endothelial function in coronary arteries of the rat. Isolated rat hearts were exposed to a 30-min low flow ischemia (1 ml/min) followed by 20-min reperfusion, after which the response to the endothelium-dependent vasodilator, serotonine (5-HT), was compared with that of the endothelium-independent vasodilator, sodium nitroprusside (SNP). In untreated hearts, ischemia-reperfusion diminished selectively 5-HT-induced vasodilatation, compared with time-matched sham hearts, the vasodilatation to SNP being unaffected. A 5-min zero-flow preconditioning ischemia in untreated hearts preserved the vasodilatation produced by 5-HT. Blockade of either CB(1)-receptors with SR141716A or CB(2)-receptors with SR144528 abolished the protective effect of preconditioning on the 5-HT vasodilatation. Perfusion with either palmitoylethanolamide or 2-arachidonoylglycerol 15 min before and throughout the ischemia mimicked preconditioning inasmuch as it protected the endothelium in a similar fashion. This protection was blocked by SR144528 in both cases, whereas SR141716A only blocked the effect of PEA. The presence of CB(1) and CB(2)-receptors in isolated rat hearts was confirmed by Western blots. In conclusion, the data suggest that endogenous cannabinoids contribute to the endothelial protective effect of ischemic preconditioning in rat coronary arteries.

Stimulation of cannabinoid receptors reduces levodopa-induced dyskinesia in the MPTP-lesioned nonhuman primate model of Parkinson's disease

Long-term treatment with levodopa in Parkinson's disease results in the development of motor fluctuations, including reduced duration of antiparkinsonian action and involuntary movements, i.e., levodopa-induced dyskinesia. Cannabinoid receptors are concentrated in the basal ganglia, and stimulation of cannabinoid receptors can increase gamma-aminobutyric acid transmission in the lateral segment of globus pallidus and reduce glutamate release in the striatum. We thus tested the hypothesis that the cannabinoid receptor agonist nabilone (0.01, 0.03, and 0.10 mg/kg) would alleviate levodopa-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) -lesioned marmoset model of Parkinson's disease. Coadministration of nabilone (0.1 mg/kg) with levodopa was associated with significantly less total dyskinesia (dyskinesia score, 12; range, 6-17; primate dyskinesia rating scale) than levodopa alone (22; range, 14-23; P < 0.05). This effect was more marked during the onset period (0-20 minutes post levodopa). There was no reduction in the antiparkinsonian action of levodopa. Furthermore, the intermediate dose of nabilone used (0.03 mg/kg) increased the duration of antiparkinsonian action of levodopa by 76%. Thus, cannabinoid receptor agonists may be useful in the treatment of motor complications in Parkinson's disease.

Delta(9)-tetrahydrocannabinol increases endogenous extracellular glutamate levels in primary cultures of rat cerebral cortex neurons: involvement of CB(1) receptors

The effects of the principal psychoactive component of marijuana, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), on endogenous extracellular glutamate levels in primary cultures of rat cerebral cortex neurons were investigated. Locally applied Delta(9)-THC (0.03, 3, 300, and 1,000 nM) concentration-dependently increased basal extracellular glutamate levels (+18% +/- 11%, +54% +/- 10%, +90% +/- 14%, +149% +/- 33% vs. basal). The facilitatory effects of Delta(9)-THC (3 and 300 nM) on cortical glutamate were fully counteracted in the presence of the selective CB(1) receptor antagonist SR141716A (10 nM) and by replacement of the normal Krebs-Ringer bicarbonate buffer with a low-Ca(2+) (0.2 mM) medium. Delta(9)-THC application also induced an enhancement in K(+)-evoked glutamate levels. These findings suggest that an increase in cortical glutamatergic transmission mediated by local CB(1) receptor activation may underlie some of the psychoactive and behavioral effects of acute marijuana consumption.

Tetrahydrocannabinol (THC) alters synthesis and release of surfactant-related material in isolated fetal rabbit type II cells

Over the years, there has been a great deal of interest in the biological consequences of marijuana use. While evidence indicates that cannabinoids may have therapeutic uses in alleviating certain disease discomfort, there is little recent information on potential health risks, particularly related to the developing fetus. The present study was undertaken to determine the effects of delta 9-tetrahydrocannabinol (THC), the major psychoactive component in marijuana on fetal lung development specifically related to surfactant production. The rationale for the choice of this model lies in the importance of adequate lung development and surfactant production for the successful transition of the fetus to an air-breathing environment. Lung type II cells, the source of pulmonary surfactant, were isolated from fetal rabbit lungs on the 24th gestational day and incubated concurrently with various concentrations of THC and [3H]choline to label disaturated phosphatidylcholine (DSPC) the major surface-active phospholipid of surfactant. Under these conditions THC significantly reduced radiolabelling of DSPC and at the highest concentration (10(-4) M) induced release of DSPC. Pulse-chase studies were also conducted. Cells were prelabelled with [3H]choline, removed to fresh medium with THC (10(-4) M) and incubated for various time periods. Aqueous- and organic-soluble intermediates of DSPC formation were isolated. THC induced a significant increase in radiolabelling of CDPcholine, the rate-limiting conversion in DSPC synthesis. Radiolabelling of total phosphatidylcholine and DSPC was also significantly increased. Assay of CTP: cholinephosphate cytidylyltransferase which enzymatically converts cholinephosphate to CDPcholine showed that THC and phosphatidylglycerol (PG) both induced activation of the enzyme in fetal lung cytosol but not in the membranes. This effect of THC and PG was not additive. THC activated the enzyme only in fetal and not adult rabbit lung. The ability of THC to induce release of surfactant related material was also examined. In cells prelabelled with [3H]choline, THC induced release of [3H]DSPC in both cultured and freshly isolated fetal type II cells. These results suggest THC reduces formation of surfactant DSPC, probably through alterations in membrane dynamics. However, intracellular THC may actually increase formation of DSPC through an effect on the rate-limiting enzyme. THC also increases release of previously formed surfactant-related material.

Endocannabinoids and cannabinoid receptor genetics

This review presents the remarkable advances that have been achieved in marijuana (cannabinoid) research, with the discovery of specific receptors and the existence of naturally occurring cannabis-like substances in the human body and brain. The last decade has seen more rapid progress in marijuana research than any time in the thousands of years that marijuana has been used by humans, particularly in cannabinoid genomics. The cDNA and genomic sequences encoding G protein-coupled cannabinoid receptors (Cnrs) from several species have now been cloned. Endogenous cannabinoids (endocannabinoids), synthetic and hydrolyzing enzymes and transporters that define neurochemically-specific cannabinoid brain pathways have been identified. Endocannabinoid lipid signaling molecules alter activity at G protein-coupled receptors (GPCR) and possibly at anandamide-gated ion channels, such as vanilloid receptors. Availability of increasingly-specific CB1 and CB2 Cnr antagonists and of CB1 and CB2 Cnr knockout mice have increased our understanding of these cannabinoid systems and provides tantalizing evidence for even more G protein-coupled Cnrs. Initial studies of the Cnr gene structure, regulation and polymorphisms whet our appetite for more information about these interesting genes, their variants and roles in vulnerabilities to addictions and other neuropsychiatric disorders. Behavioral studies of cannabinoids document the complex interactions between rewarding and aversive effects of these drugs. Pursuing cannabinoid-related molecular, pharmacological and behavioral leads will add greatly to our understanding of endogenous brain neuromodulator systems, abused substances and potential therapeutics. This review of CB1 and CB2 Cnr genes in human and animal brain and their neurobiological effects provide a basis for many of these studies. Therefore, understanding the physiological cannabinoid control system in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

Cannabinol enhancement of interleukin-2 (IL-2) expression by T cells is associated with an increase in IL-2 distal nuclear factor of activated T cell activity

It has been demonstrated previously that cannabinol (CBN) differentially modulates interleukin-2 (IL-2) protein secretion by T cells with a corresponding change in extracellular signal-regulated kinase activity. The objective of the present studies was to further investigate the molecular mechanism by which CBN enhances IL-2 gene expression using the EL4 T cell line. We demonstrate here that steady-state IL-2 mRNA expression was significantly enhanced by CBN in a concentration-dependent manner in EL4 cells activated with suboptimal concentrations of phorbol-12-myristate-13-acetate (2-10 nM). Concordantly, a marked increase was observed in nuclear factor of activated T cells (NF-AT) DNA binding activity to the IL-2 distal NF-AT site, but not to nuclear factor for immunoglobulin kappa chain in B cells or activator protein 1 motifs. Transient transfection of EL4 cells with a reporter gene under the control of multiple IL-2 distal NF-AT motifs exhibited increased transcriptional activity by CBN in suboptimally activated cells. In addition, the CBN-mediated enhancement of IL-2 protein secretion and the transcriptional activity of the IL-2 distal NF-AT reporter gene was abrogated by the calcium/calmodulin-dependent protein kinase inhibitor KN93, but not by the CB2 receptor antagonist SR144528. Enhancement of IL-2 was also demonstrated with CP55940, Delta(9)-tetrahydrocannabinol, and cannabidiol, thus suggesting that the phenomenon is not unique to CBN. Collectively, these results suggest that increased IL-2 secretion by CBN is mediated through the enhancement of IL-2 gene transcription by activation of NF-AT in a CB1/CB2-independent manner.

Receptor-independent effects of natural cannabinoids in rat peritoneal mast cells in vitro

Cannabinoids can activate CB(1) and CB(2) receptors. Since a CB(2) mRNA has been described in rat peritoneal mast cells (RPMC), we investigated a series of cannabinoids and derivatives for their capacity to stimulate RPMC. Effects of natural cannabinoids Delta(9)-tetrahydrocannabinol (Delta(9)-THC), Delta(8)-THC, endocannabinoids (anandamide, palmitoylethanolamide) and related compounds (N-decanoyl-, N-lauroyl-, N-myristoyl-, N-stearoyl- and N-oleoyl-ethanolamines; N-palmitoyl derivatives (-butylamine, -cyclohexylamine, -isopropylamine); and N-palmitoyl, O-palmitoylethanolamine), and synthetic cannabinoids including WIN 55,212-2, SR141716A and SR144528 were assessed for their capacity to induce histamine release or prime RPMC stimulated by compound 48/80. Only Delta(9)-THC and Delta(8)-THC could induce non-lytic, energy- and concentration-dependent histamine releases from RPMC (respective EC(50) values: 23.5+/-1.2; 53.4+/-20.6 microM, and maxima: 71.2+/-5.5; 55.7+/-2.7% of the total RPMC histamine content). These were not blocked by CB(1) (SR141716A) or CB(2) (SR144528) antagonists, but reduced by pertussis toxin (100 ng/ml). Endocannabinoids and analogues did neither induce histamine secretion, nor prime secretion induced by compound 48/80 (0.2 microg/ml). Delta(9)-THC and Delta(8)-THC induced in vitro histamine secretion from RPMC through CB receptor-independent interactions, partly involving G(i/o) protein activation.

Cannabinoid WIN 55,212-2 inhibits the activity-dependent facilitation of spinal nociceptive responses

Cannabinoids suppress nociceptive processing of acute stimuli, but little is known about their effects on processes that lead to hyperexcitability of nociceptive neurons following prolonged noxious stimulation. Wind-up, the increasingly strong response of spinal nociceptive neurons to repetitive noxious electrical stimuli, results from a fast-rising cumulative depolarization and increase in intracellular calcium concentration. These processes produce central sensitization, the increased excitability of spinal nociceptive neurons that contributes to the hyperalgesia and allodynia associated with chronic pain. Intravenous injection of the potent, synthetic cannabinoid agonist WIN 55, 212-2, but not the inactive enantiomer, WIN 55,212-3, dose-dependently decreased the wind-up of spinal wide dynamic range and nociceptive-specific neurons independent of acute responses to activation of low- and high-threshold primary afferents. This is the first direct evidence that cannabinoids inhibit the activity-dependent facilitation of spinal nociceptive responses.

The stimulation of ketogenesis by cannabinoids in cultured astrocytes defines carnitine palmitoyltransferase I as a new ceramide-activated enzyme

The effects of cannabinoids on ketogenesis in primary cultures of rat astrocytes were studied. Delta9-Tetrahydrocannabinol (THC), the major active component of marijuana, produced a malonyl-CoA-independent stimulation of carnitine palmitoyltransferase I (CPT-I) and ketogenesis from [14C]palmitate. The THC-induced stimulation of ketogenesis was mimicked by the synthetic cannabinoid HU-210 and was prevented by pertussis toxin and the CB1 cannabinoid receptor antagonist SR141716. Experiments performed with different cellular modulators indicated that the THC-induced stimulation of ketogenesis was independent of cyclic AMP, Ca2+, protein kinase C, and mitogen-activated protein kinase (MAPK). The possible involvement of ceramide in the activation of ketogenesis by cannabinoids was subsequently studied. THC produced a CB1 receptor-dependent stimulation of sphingomyelin breakdown that was concomitant to an elevation of intracellular ceramide levels. Addition of exogenous sphingomyelinase to the astrocyte culture medium led to a MAPK-independent activation of ketogenesis that was quantitatively similar and not additive to that exerted by THC. Furthermore, ceramide activated CPT-I in astrocyte mitochondria. Results thus indicate that cannabinoids stimulate ketogenesis in astrocytes by a mechanism that may rely on CB1 receptor activation, sphingomyelin hydrolysis, and ceramide-mediated activation of CPT-I.

Activation of the cannabinoid receptor by delta 9-tetrahydrocannabinol reduces gamma-aminobutyric acid uptake in the globus pallidus

The interaction between GABA (gamma-aminobutyric acid) and cannabinoids in the globus pallidus was investigated by evaluating the effects of delta 9-tetrahydrocannabinol on [3H]GABA uptake into slices of rat globus pallidus. delta 9-Tetrahydrocannabinol caused a concentration-dependent decrease in GABA uptake (51% decrease at 100 microM delta 9-tetrahydrocannabinol, IC50 = 18.95 microM). This effect was reversed in a concentration-dependent manner (IC50 = 11.9 microM) by the cannabinoid receptor antagonist SR 141716A (N-(piperidin-1-yl-)5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1 H-pyrazole-3-arboxiamidehydrochloride. SR 141716A alone did not affect GABA uptake. These results show that cannabinoid receptor activation reduces GABA uptake in the globus pallidus.

Effects of anandamide on hepatic fatty acid metabolism

Incubation of rat hepatocytes with anandamide (arachidonoylethanolamide) inhibited acetyl-CoA carboxylase activity and fatty acid synthesis de novo without affecting fatty acid synthase. This was concomitant to a decrease in the intracellular levels of malonyl-CoA. Likewise, anandamide depressed both cholesterol synthesis de novo and the incorporation of exogenous palmitate into triacylglycerols and phospholipids. On the other hand, anandamide stimulated in parallel both carnitine palmitoyltransferase I activity and ketogenesis from palmitate, though ketogenesis from octanoate was unaffected. The effects of anandamide on hepatic fatty acid synthesis and oxidation were: (a) mimicked by arachidonic acid, a product of anandamide breakdown by anandamide amidase; (b) prevented by phenylmethylsulfonyl fluoride, an inhibitor of anandamide amidase; and (c) not affected by bisindolylmaleimide, a specific inhibitor of protein kinase C. Furthermore, delta 9-tetrahydrocannabinol had no effect on any of the parameters determined, ruling out the possibility that the effects of anandamide on hepatic fatty acid metabolism are mediated by the peripheral cannabinoid receptor. The results thus indicate that anandamide might function as a carrier of arachidonic acid in the modulation of hepatic fatty metabolism.