Published online before print July 1, 2003
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University of South Florida, Department of Medical Microbiology & Immunology, Tampa
1Correspondence: University of South Florida, College of Medicine, MDC Box 10, Department of Medical Microbiology and Immunology, 12901 Bruce Downs Blvd., Tampa, FL 33612. E-mail: tklein{at}hsc.usf.edu
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Key Words: marijuana Th1 cells chemotaxis tumor G protein CB1
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The medicinal uses of marijuana were described centuries ago for diseases such as asthma, migraine, pain, convulsions, and anxiety (reviewed in ref. [9
]). More recently, emphasis has been placed on marijuanas putative, beneficial effects on appetite, glaucoma, spasticity in multiple sclerosis, pain, and inflammation [10
]. Recent experimental evidence supports marijuanas therapeutic potential in some of these maladies [11
]. The active plant ingredients in marijuana belong to the C21-cannabinoid compounds including the primary psychoactive compound,
9-tetrahydrocannabinol (THC). This cannabinoid along with others such as
8-THC, cannabidiol, and cannabinol, as well as chemical analogs, have been extensively studied over the years for their biological and therapeutic properties [8
]. Some of the properties of these agents have included effects on immunity ranging from suppression of resistance to infection to enhancement of IL-1 production by macrophages. These early studies about the immunomodulating effects of these drugs have been the subject of previous overviews [7
, 12
13
14
15
16
17
18
] and will not be reviewed here. Instead, we will briefly summarize the general features of the cannabinoid system and review recent findings on the structure and function of the cannabinoid system components in the immune system. For convenience, we will refer to this as the "immunocannabinoid" system.
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8-THC (HU210), which has a much higher affinity for cannabinoid receptors than THC (ref. [21
];Table 1). In addition to the tricyclic cannabinoids, bicyclic analogs, such as CP55,940 [29
], and aminoalkylindoles, such as R-(+)-WIN55,212 [30
], have also been synthesized with cannabimimetic activity and with affinities higher than THC (Table 1)
. All of these agents have been widely used in examining the biology of the cannabinoid system and as can be seen from Table 1
, these agents are relatively nonselective for cannabinoid receptors in that their Kis are similar for both. More recently, CB2-selective agonists have been synthesized, such as JWH-015, which displays a higher affinity for CB2 than for CB1 (ref. [31
]; Table 1
). |
View this table: [in a new window] |
Table 1. Binding Affinities of Cannabinoid Receptor Ligands
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Figure 1. The endocannabinoid system and cell function. An influx of Ca2+ activates phospholipases (PL), which drive the conversion of membrane arachidonic acid (AA) to endocannabinoids such as anandamide (ANA), 2-arachidonoylglycerol (2-AG), and 2-arachidonylglyceryl ether (2-AGE). The endocannabinoids can be taken up and metabolized by fatty acid amide hydrolase (FAAH) or can bind to CB1 or CB2. These are G protein-coupled receptors (GPCR) capable of signaling through G protein subunits, G , -ß, and - , leading to a modulation of nitric oxide (NO) and adenylyl cyclase (AC). In neurons, this signaling can lead to a change in K+ and Ca2+ currents and secretion of transmitters such as -aminobutyric acid (GABA). In addition, CB1 and CB2 signaling can lead to the activation of many other factors, including PLC, protein kinase C (PKC), nuclear factor- B (NF- B), extracellular signal-regulated protein kinase (ERK), focal adhesion kinase (FAK), steroid receptor coactivator (Src), mitogen-activated protein kinase (MAPK), and MAPK kinase (MEK).
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Cannabinoid receptors
Pharmacological evidence initially supported the existence of cannabinoid receptors of high affinity in brain tissue and with specificity sufficient to distinguish different enantiomers of cannabinoid analogs [20
, 39
]. Subsequent to this, the first receptor, CB1, was cloned from a rat brain cDNA library using a probe derived from the sequence of bovine substance-K receptor [40
]. The translated sequence of the gene yielded a protein of 473 amino acids and the structure of a 7-transmembrane, GPCR. Since then, homologues of CB1 have been cloned from humans [41
] and mice [42
], displaying 9799% amino acid sequence identity from one species to the other. CB1 mRNAs are expressed in brain, especially in the basal ganglia, as well as several tissues in the periphery including immune tissue (see below). Polymorphisms in the human gene have been reported, including a G-to-A silent mutation at position 1359 in the coding exon and an (AAT)n repeat polymorphism outside of the exon [43
]. The significance of these changes in terms of gene function and disease is not clear at this time. The CB1 coding sequence is contained in a single exon, but other cDNA segments have been reported, such as a 5'-untranslated first-exon and a large 3'-untranslated sequence. The second receptor, CB2, was cloned from a cDNA library from the promyelocytic, human cell line, HL60 [44
]. The protein encoded by this gene was reported to contain only 360 amino acids and showed only 44% identity with the human CB1 receptor. The mouse [45
] and rat [46
] CB2 genes also have been cloned and encode proteins of 347 and 410 amino acids, respectively. The variation in length among these proteins occurs in the carboxy end with the rat protein containing an extended carboxy terminus [46
]. Amino acid identity of CB2 from species to species is lower than for CB1, and the mRNAs for CB2 are found in peripheral tissues, such as spleen, but not in brain and tissue, such as heart.
Function of cannabinoid system
Cannabinoid receptors are GPCR, and very early on, it was recognized that they were linked to inhibition of adenylyl cyclase (ref. [20
]; Fig. 1
). In addition, GPCR are known to be linked to a variety of other second messengers and signaling components [47
48
49
], and ligation of CB1 and CB2 has been shown to not only suppress adenylyl cyclase but also to activate it [50
], suggesting these receptors activate factors other than G
i [51
]. In addition to adenylyl cyclase, cannabinoid receptor ligation has been shown to activate PLC [52
], which in turn, might activate diacylglycerol and inositol triphosphatase, increasing intracellular calcium and PKC. Ligation also has been shown to inhibit Ca2+ currents and activate K currents [53
, 54
] and to increase NO [55
] synthesis (Fig. 1)
. Cannabinoid receptor ligation also has been shown to lead to the activation of transcription factors such as members of the MAPK [56
] and NF-
B [57
, 58
] families. From this and other evidence, it is clear that signaling through cannabinoid receptors and other GPCR involves numerous second messengers and signaling factors and that a variety of cellular and genetic activities are regulated by these kinds of receptors, including neuronal excitability [59
] and IL-12 gene expression [49
].
Cannabinoid receptors and ligands are found in the brain and peripheral tissues, and our current understanding of its function, at least in the brain, is beginning to take shape. The role of endocannabinoids and cannabinoid receptors in modulation of neurotransmitter release recently has been reviewed [59 60 61 ]. Several reports in 2001 showed that CB1 is located on presynaptic nerve terminals, that endocannabinoids are released from depolarized postsynaptic neurons, and that CB1 agonists and antagonists can modulate presynaptic neurotransmitter release [62 63 64 ]. Stimulation of the CB1 receptors was shown to suppress the release of neurotransmitters, such as GABA, thus allowing the cannabinoid system to turn down the activity of the GABA terminal in a retrograde manner back across the synapse. In the case of GABA release in hippocampal cells, the cannabinoid system appears to mediate depolarization-induced suppression of inhibition and may account for the inhibitory effects of cannabinoid ligands on memory and movement [60 ].
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Cannabinoid receptor expression in immune cells
By Northern blotting, the initial report on the cloning of CB1 failed to detect the expression of CB1 mRNA in tissues outside of the brain [40
]. However, the cloning of the human gene demonstrated the message in testis tissue, but again, other tissues, including immune system tissues, were negative [41
]. In 1992, Kaminski et al. [74] reported the demonstration of CB1 mRNA in mouse splenocytes using the more sensitive method of reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of receptors by these cells was also supported by pharmacological studies using cannabinoid agonist effects on in vitro antibody production by the splenocytes. Several agonists, such as THC, CP55,940, and HU210, suppressed antibody production in a dose-dependent manner when added to sheep red blood cell-stimulated splenocyte cultures. However, the affinity and efficacy of these agonists were lower with spleen cells than reported for behavioral studies and studies involving neural tissue, suggesting a lower density of surface receptors and variation from neural tissue in receptor coupling and affinity in immune cells. Also, as immune cells express CB2 receptors in addition to CB1 (see below), it is not clear whether CB1 or CB2 was being stimulated in these studies. Subsequent studies showed that CB1 mRNA levels varied among cell subpopulations. In human peripheral blood cells, message was reported to be most abundant in B cells, and the rank order was B cells > NK cells > polymorphonuclear neutrophils (PMNs) > CD8 cells > monocytes > CD4 cells [75
]. The level of message also varied among different leukocyte cell lines; Jurkat cells were negative, and THP1 cells were highly positive [75
]. CB1 message levels also varied in mouse immune subpopulations, and consistent with human cells, splenic B cells expressed more message than macrophages or T cells [76
77
78
]. In addition to mouse splenocytes, CB1 message has been detected in rat brain microglia cells [79
] and in human peripheral blood cell-derived dendritic cells (DC) [80
]. We also have observed that CB1 and CB2 mRNAs are expressed in bone marrow-derived DC from mice (unpublished results).
Antibodies to CB1 have been produced and used to examine the expression of CB1 protein on immune cells. Rabbit polyclonal antiserum to a CB1glutathione-S-transferase (GST) fusion protein demonstrated several immunoreactive proteins in membrane preparations from Jurkat and a CB1-positive neuroblastoma cell line. Proteins of 45, 60, 70, and 87 kDa were consistent with CB1 expression [81 ]. Similarly, a 58-kDa protein was demonstrated in membranes from rat microglia cells using an antiserum to CB1GST fusion proteins [79 ], and proteins of 64 and 83 kDa were demonstrated in human DC [80 ]. We have prepared polyclonal rabbit antiserum to the 14 terminal amino acids of CB1 conjugated to keyhole limpet hemocyanin (KLH) and used this to analyze cell membrane proteins from mouse splenocyte immune cell subpopulations. Figure 2 shows the antiserum detected a major band at 80 kDa in splenocyte subpopulations with B cells and macrophages showing more protein than T/NK cells. In addition, the neuroblastoma cell line, N18TG2, showed several bands, and the predominant one was at 67 kDa, suggesting a variation in immunoreactive protein size between brain cells and immune cells. We also tested several commercial polyclonal antisera prepared to CB1 peptides. Figure 3A and 3B , shows these antibodies demonstrate major bands at 65 kDa (Company A) and 75 kDa (Company B) and that these bands are also the major ones demonstrated in the neuroblastoma cell line. Curiously, all three antisera (Fig. 3A 3B 3C) demonstrate analogous protein bands in spleen cell preparations from CB1 homozygous knockout mice provided by Dr. Andreas Zimmer and co-workers [82 ]. This could result from several factors. The first is that other proteins expressed in mouse immune and neural tissue share epitopes with the CB1 protein. A search of the mouse genome using the website <http://www.ensembl.org/> and the 14 amino acids of the amino terminal end of the mouse CB1 protein shows scores of identical matches of five amino acids or less in the translated portion of the genome, suggesting that these CB1 epitopes are shared by many proteins of the mouse. A second possibility stems from the fact that in the knockout mice, the CB1 gene is disrupted with the neor cassette in the middle of the single-coding exon, leaving short 5' and 3' portions of this exon intact [82 ]. In fact, mRNA containing the 5' end of the coding exon up to position 93 (accession #U22948) can be detected by RT-PCR in splenocytes from these mice at a higher level than in wild-type mice (unpublished results). It is possible, therefore, that fusion proteins containing amino and carboxy fragments of CB1 plus the neor insert are expressed in these mice and are being detected by the antisera. We are currently testing antiserum to epitopes coded by the deleted portion of the CB1 gene to see whether it can detect proteins of comparable size in immune tissue from knockout and wild-type mice and N18 cells. It is possible that this antiserum will detect comparable bands in only wild-type and N18 cells, suggesting the possibility of expression of CB1 fusion proteins in knockout mice. At this time, the specificity of available anti-CB1 antibodies remains in question.
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Figure 2. Western blotting of membrane proteins from splenocytes using anti-CB1 antibody. Affinity-purified, polyclonal antiserum to CB1 peptide (MKSILDGLADTTFR-C) was used (160 ng/ml) to probe membrane proteins from splenocyte subpopulations and N18TG2 neuroblastoma cells. Lane 1, N18 cells; lane 2, whole splenocytes; lane 3, nonadherent splenocytes; lane 4, adherent splenocytes; lane 5, T cells; lane 6, B cells.
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Figure 3. Analysis of CB1 by Western blotting of splenocyte membrane proteins from wild-type and knockout mice. (A) Membrane proteins probed with anti-CB1 antibody from Company A: lane 1, N18TG2 neuroblastoma cells; lane 2, wild-type splenocytes; lane 3, wild-type splenocytes; lane 4, homozygous knockout splenocytes. (B) Membrane proteins probed with anti-CB1 antibody from Company B: lane 1, N18 cells; lane 2, wild-type splenocytes; lane 3, wild-type splenocytes; lane 4, homozygous knockout splenocytes. (C) Membrane proteins probed with antibody prepared as in Figure 2
: lane 1, N18 cells; lane 2, homozygous knockout splenocytes; lane 3, heterozygous knockout splenocytes; and lane 4, wild-type splenocytes. USF, University of South Florida.
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As with CB1, antibodies also have been used to examine the expression of CB2 protein on immune cells. Polyclonal antiserum to a C-terminal peptide of CB2 was used for immunofluorescence studies in human tonsillar tissue [83
]. Immunoreactive tissue was highest in germinal centers, suggesting B cells or antigen-presenting cells (APCs) were expressing the receptor. Polyclonal antiserum produced to amino acids 320336 of the mouse protein conjugated to KLH was used to examine CB2 protein expression in homogenates of cultured rat peritoneal macrophages and brain microglia [85
]. The main immunoreactive protein in peritoneal macrophages was
40 kDa, and in microglia preparations, the protein was 27 kDa. The reason for the relatively small size of the microglia protein was not clear but was suggested to be a result of a degradation product of the predicted 40-kDa protein or a variant form unique to microglia [85
]. In addition to these studies, commercial antibodies were used to analyze CB2 protein in rat spleen and human blood-derived DC [80
]. In these samples, immunoreactive bands of 39, 47, and 59 kDa were observed, although the reason for the multiple bands was not clear. As with anti-CB1 antibodies, the specificity and reliability still remain in question.
Modulation of cannabinoid receptor expression by cell activation
Immune cells frequently express new gene products when stimulated with antigens and other bioactive substances. This also appears to be the case with cannabinoid receptors. The initial suggestion of this came with the cloning of CB2, wherein it was shown that CB2 mRNA was increased in HL60 cells by treatment with agents such as phorbol myristate acetate (PMA) [44
]. At basal levels, HL60 cells were negative for CB2 mRNA by Northern blotting but became positive by 24 h following 12-O-tetradecanoylphorbol 13-acetate treatment. Since this report, stimuli, ranging from lipopolysaccharide (LPS) to anti-CD40 antibodies (Fig. 4
), have been shown to increase CB2 expression. For example, the level of CB2 mRNA and protein in human tonsillar B cells [86
] and mRNA in mouse splenocytes [84
] was increased following activation by anti-CD40 antibody, and CB2 expression was increased by IFN-
in mouse macrophages and microglia [85
]. In addition, we recently showed that chronic marijuana smoking increased the CB2 mRNA in PBMC [71
], suggesting that drug exposure may cause a change in receptor expression in humans as has been reported with CB1 in animal models [87
]. Stimulation of immune cells also leads to a suppression of CB2 expression (Fig. 4)
. For example, the differentiation of B cells in tonsils was accompanied by decreased expression of CB2 mRNA and protein in centroblasts as opposed to virgin B cells [86
], and the stimulation by LPS of mouse splenocytes, macrophages, rat microglia, and human DC resulted in decreased expression of CB2 message [80
, 84
, 85
]. In addition, TGF-ß treatment of cultured human peripheral blood lymphocytes led to a decrease in CB2 protein with increasing concentration of the cytokine [88
].
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Figure 4. CB1 and CB2 expression is increased or decreased following cell activation. Stimuli reported to increase CB1 are LPS, anti-CD40 antibody, PHA, and marijuana use, and agents suppressing CB1 are LPS, PMA/ionomycin (Io), and anti-CD3 antibody. Stimuli reported to increase CB2 are PMA, anti-CD40 antibody, interferon- (IFN- ), and marijuana use, and agents suppressing CB2 are LPS, differentiation, and transforming growth factor-ß (TGF-ß). PHA, Phytohemagglutinin.
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Cannabinoid receptor signaling in immune cells
A number of studies have defined various signaling events associated with CB1 and CB2 (see Function of cannabinoid system section). Many of these results were obtained in receptor-transfected cell systems or primary cells other than immune cells. However, a few reports have examined signaling events in immune cells in response to cannabinoid treatment. For example, intracellular calcium mobilization was studied in concanavalin A (Con A)-treated mouse thymocytes using fluorescent indicators and drug treatment with THC [90
]. Cytosolic-free calcium was increased by Con A treatment, and this effect was suppressed by treatment with THC. The suppression of cytosolic calcium mobilization was a result of a drug-induced inhibition of extracellular influx as well as inhibition of calcium release from intracellular stores [90
]. THC was also shown to suppress forskolin-stimulated adenylyl cyclase activity in mouse spleen cells [91
] and purified splenic T cells [77
]. The suppression of adenylyl cyclase by THC and CP55,940 was shown to be attenuated by treatment with pertussis toxin, suggesting that the cannabinoids were acting through Gi proteins [92
]. Members of the NF-
B family of proteins also have been shown to be modulated in immune cells. The NK-like cell line, NKB61A2 [93
], when treated with THC, was shown to increase the transcription of the IL-2R
gene and increase the nuclear level of NF-
B protein [58
]. However, in the macrophage cell line, RAW 264.7, THC was shown to inhibit NF-
B activity in response to treatment with LPS [57
], suggesting that the type of cannabinoid effect on this family of proteins may be cell type- and stimulus-dependent. Several other immune cell lines have been tested for signaling modulation following cannabinoid treatment. The HL60 cell line was treated with CP55,940 and was shown to express higher levels of MAPK and Krox-24 gene activation [56
], suggesting these signaling properties were increased by the drugs. In addition, EL4.IL2 mouse lymphoma cells treated with cannabinol or THC showed a decrease in PKA activity, activated protein-1, and NF-activated T cells binding [94
, 95
]; furthermore, treatment of splenocytes with cannabinol decreased ERKMAPK activity [96
]. From these results, it appears that cannabinoid treatment of immune cells leads to modulation of various cannabinoid receptor-signaling pathways. This fact, coupled with immune modulation effects of these agents, suggests that cannabinoids may modulate immune cell function through CB1 and CB2 signaling mechanisms.
Modulation of T helper (Th) cells
Th cells are powerful regulators of cell-mediated (Th1) and humoral (Th2) adaptive immunity. Regulation of the development of these cells and the link between innate and adaptive immunity are areas of intense investigation [97
] to better understand how infectious agents and other environmental factors affect the processes fundamental to activating host immunity. It is now clear that in addition to microbial products, drugs and endogenous factors regulate the development of Th1 and Th2 cells (Fig. 5
). For example, prostaglandins increase Th2 activity and decrease Th1 activity [2
]. In addition, glucocorticoids [98
], morphine [99
], and certain chemokines [49
] are reported to suppress Th1 immunity, and adrenergic agents such as norepinephrine increase Th1 immunity [100
].
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Figure 5. Drugs and endogenous factors regulate the development of Th cells. Naïve CD4 Th (Th0) receive immune signals and in addition, receive signals from drugs and endogenous factors in the selective differentiation to Th1 or Th2 cells. Th1 development is decreased ( ) by prostaglandins, glucocorticoids, morphine, chemokines, and cannabinoids and is increased ( ) by norepinephrine. In contrast, Th2 development is decreased ( ) by norepinephrine and increased ( ) by prostaglandins, glucocorticoids, morphine, chemokines, and cannabinoids.
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and IL-12 as well as the expression of IL-12 receptors, and in addition, drug treatment increased the expression of the Th2-promoting cytokine, IL-4 [102
]. It was also demonstrated, using CB1 and CB2 antagonists, that both receptors were involved in this THC-induced Th cell biasing. Other laboratories have reported Th biasing effects of cannabinoids (Fig. 5)
. Splenocytes taken from THC-injected mice and stimulated in vitro with Con A were shown to produce reduced amounts of IL-2 and IFN-
[103
] and Propionibacterium acnes-primed mice injected with LPS showed a decreased production of IL-12 and increase of IL-10 when pretreated with HU210 and other cannabinoids [104
]. Biasing toward Th2 immunity was also reported in a murine tumor model [105
]. Mice injected with tumor cells and THC showed enhanced tumor growth, depressed cell-mediated immunity, and increased Th2 activity such as production of IL-10 and TGF-ß, and these effects were attenuated by treatment with the CB2 antagonist, SR144528. A similar shift to Th2 cytokines was demonstrated in response to THC in activated peripheral blood T cell cultures [106
]. In drug-treated cultures, proliferation was inhibited along with Th1 cytokines; Th2 cytokines were increased, and the CB2 antagonist inhibited the effects [106
]. There is now ample evidence that cannabinoids and other GPCR agonists can modulate the development of Th (Fig. 5)
. In the case of cannabinoids, it is possible that CB1 and CB2 may be differentially expressed on different subpopulations of APCs and Th cells. This selective expression could lead to an increase in Th2 development and a decrease in the development of Th1 cells, resulting in decreased cell-mediated immunity and increased antibody immunity. Continued research on the distribution and function of cannabinoid receptors as well as the production of endocannabinoids by different immune cells will provide greater insight into these mechanisms.
Cannabinoids and chemotaxis
Chemokine receptors, as noted above, are GPCR. It appears that other receptors of this group such as those for opioids and cannabinoids also are linked to cell-migration gene programs. For example, opioids are chemotactic when added to cultures of human blood monocytes and neutrophils, and these drugs can cross-desensitize cells to chemotaxis in combination with chemokines such as CCL5 [107
]. These and other results provided evidence that the process of heterologous desensitization was occurring among chemotactic receptors that have varying affinities for different ligands such as chemokines and opioids. Cannabinoids also appear to have chemotactic activity for various cell types. HL60 cells expressing CB2 receptors were shown to migrate in response to CP55,940, and the migration could be demonstrated in experiments measuring chemotaxis and chemokinesis [108
]. Drug treatment was also shown to increase the production of various cytokines and chemokines. Other cell types of immune lineage have been shown to migrate in response to cannabinoids. Myeloid leukemia cells expressing CB2 receptors displayed chemotaxis and chemokinesis in response to 2-AG but not in response to a variety of other cannabimimetic agents, and the migration was enhanced in the presence of IL-3 or granulocyte macrophage-colony stimulating factor [109
]. 2-AG was also chemotactic for mouse spleen cells, and it was concluded that a major function for the CB2 receptor on these cells was the regulation of migration [109
]. Mouse microglia cells also were shown to migrate in response to 2-AG through a CB2-mediated mechanism, and this effect was antagonized by the nonpsychotropic cannabinoids, cannabinol and cannabidiol [110
]. Finally, in contrast to these immune cell studies, nonimmune cell migration is suppressed in response to cannabinoids. Human umbilical vein endothelial cells, when precultured with cannabinoids for 18 h, showed reduced chemotaxis in response to lysophosphatidic acid [111
]. The CB2 antagonist inhibited this effect, and cannabinoid treatment was shown to suppress other functions involved in angiogenesis. From these studies, it appears that cannabinoids are similar to opioids in modulating cell migration and suggest that at least one function of the immunocannabinoid system is to regulate migration of immune cells.
Cannabinoids and tumor suppression
Marijuana smoking has been related to an increased incidence of head and neck cancer (see Cellular effects section); however, paradoxically, cannabinoids have been shown to suppress tumor development. Anandamide and other cannabinoids induce apoptosis in human PBMC, and this was suggested to account for the drug-induced suppression of lymphocyte proliferation [112
]. These drugs were also shown to induce apoptosis and decrease Bcl-2 in macrophages and splenocytes, and this was suggested to contribute to increased processing and release of IL-1 [113
]. Anti-tumor effects also have been linked to cannabinoid induction of apoptosis. Established gliomas in rats regressed in response to intra-tumor injection of THC and WIN55,212 [114
]. Treatment of C6 glioma cells in culture with cannabinoids induced apoptosis by a pathway involving cannabinoid receptors and discrete signaling pathways involving ceramide and ERK activation. Similar experiments were performed using the CB2-selective agonist, JWH-133 [115
]. Again, regression of established C6 tumors was observed following intra-tumor injection. In addition, a CB2 antagonist inhibited the effects, and cultures of C6 cells were induced to apoptosis in response to treatment with cannabinoids [115
]. In other studies, proliferation of C6 glioma cells was suppressed by cannabinoids, an effect mediated by cannabinoid and vanilloid receptors [116
]; furthermore, a variety of human and mouse malignant immune cell lines were induced to apoptosis by cannabinoid treatment, were suppressed in vivo by cannabinoids, and were inhibited through CB2-mediated mechanisms [117
]. From these studies, it appears that cannabinoids can induce apoptosis and the inhibition of tumors through CB1 and CB2 mechanisms, suggesting their potential as anti-cancer drugs.
In addition to effects mediated by apoptosis, cannabinoids appear to suppress tumor cell growth by several other mechanisms. One of these involves the suppression of prolactin receptors. Endocannabinoids and synthetic cannabinoids were observed to inhibit the proliferation of human breast cancer cells [118 ]. The effect was CB1-dependent and resulted from the down-regulation of the long form of the prolactin receptor. Subsequent studies showed that endocannabinoids such as anandamide suppress the receptor by inhibiting adenylyl cyclase and MAPK and also can inhibit nerve growth factor receptor by CB1- but not CB2-mediated mechanisms [119 , 120 ]. From this, it appears that in some tumor suppression systems, both cannabinoid receptors are not involved, as in the case of apoptosis, suggesting cannabinoids affect tumor growth by mechanisms other than programmed cell death. Finally, cannabinoids have been reported to suppress tumor growth in several other ways, such as inducing the accumulation of lipid droplets in the tumor cells [121 ] and the suppression of angiogenesis [111 ], again suggesting that these drugs have the potential to affect tumor growth in a variety of ways. In contrast, the CB2 receptor has been reported to have oncogenic activity by inhibiting neutrophil differentiation through MEK/ERK and phosphatidylinositol-3 kinase signaling pathways [109 ]. It appears that the effect of marijuana and cannabinoids on tumor growth and development is exceedingly complex, showing enhancing and suppressive effects. This would suggest that the application of these agents to tumor therapy should proceed slowly and with consideration of all possible outcomes.
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Received March 10, 2003; revised April 5, 2003; accepted April 7, 2003.
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9-tetrahydrocannabinol is mediated through the inhibition of nuclear factor-
B/Rel activation Mol. Pharmacol. 50,334-341[Abstract]
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9-tetrahydrocannabinol is mediated by nuclear factor
B and CB1 cannabinoid receptor DNA Cell Biol. 16,301-309[Medline]
9-tetrahydrocannabinol, cytokines and immunity to Legionella pneumophila Proc. Soc. Exp. Biol. Med. 209,205-212[Abstract]
9-Tetrahydrocannabinol suppresses concanavalin A induced increase in cytoplasmic free calcium in mouse thymocytes Life Sci. 51,151-160[CrossRef][Medline]
9-Tetrahydrocannabinol treatment suppresses immunity and early IFN-
, IL-12, and IL-12 receptor ß2 responses to Legionella pneumophila infection J. Immunol. 164,6461-6466
-9-Tetrahydrocannabinol inhibits antitumor immunity by a CB2 receptor-mediated, cytokine-dependent pathway J. Immunol. 165,373-380
9-Tetrahydrocannabinol regulates Th1/Th2 cytokine balance in activated human T cells J. Neuroimmunol. 133,124-131[CrossRef][Medline]
9-Tetrahydrocannabinol induces apoptosis in macrophages and lymphocytes: involvement of Bcl-2 and caspase-1 J. Pharmacol. Exp. Ther. 286,1103-1109This article has been cited by other articles:
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F. Fezza, S. Oddi, M. Di Tommaso, C. De Simone, C. Rapino, N. Pasquariello, E. Dainese, A. Finazzi-Agro, and M. Maccarrone Characterization of biotin-anandamide, a novel tool for the visualization of anandamide accumulation J. Lipid Res., June 1, 2008; 49(6): 1216 - 1223. [Abstract] [Full Text] [PDF] |
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P. Pacher and B. Gao Endocannabinoids and Liver Disease. III. Endocannabinoid effects on immune cells: implications for inflammatory liver diseases Am J Physiol Gastrointest Liver Physiol, April 1, 2008; 294(4): G850 - G854. [Abstract] [Full Text] [PDF] |
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M. L. Gillison, G. D'Souza, W. Westra, E. Sugar, W. Xiao, S. Begum, and R. Viscidi Distinct Risk Factor Profiles for Human Papillomavirus Type 16-Positive and Human Papillomavirus Type 16-Negative Head and Neck Cancers J Natl Cancer Inst, March 19, 2008; 100(6): 407 - 420. [Abstract] [Full Text] [PDF] |
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F. Montecucco, F. Burger, F. Mach, and S. Steffens CB2 cannabinoid receptor agonist JWH-015 modulates human monocyte migration through defined intracellular signaling pathways Am J Physiol Heart Circ Physiol, March 1, 2008; 294(3): H1145 - H1155. [Abstract] [Full Text] [PDF] |
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P. Pacher and Z. Ungvari Pleiotropic effects of the CB2 cannabinoid receptor activation on human monocyte migration: implications for atherosclerosis and inflammatory diseases Am J Physiol Heart Circ Physiol, March 1, 2008; 294(3): H1133 - H1134. [Full Text] [PDF] |
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H. Xu, C. L. Cheng, M. Chen, A. Manivannan, L. Cabay, R. G. Pertwee, A. Coutts, and J. V. Forrester Anti-inflammatory property of the cannabinoid receptor-2-selective agonist JWH-133 in a rodent model of autoimmune uveoretinitis J. Leukoc. Biol., September 1, 2007; 82(3): 532 - 541. [Abstract] [Full Text] [PDF] |
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L. McCollum, A. C. Howlett, and S. Mukhopadhyay Anandamide-Mediated CB1/CB2 Cannabinoid Receptor-Independent Nitric Oxide Production in Rabbit Aortic Endothelial Cells J. Pharmacol. Exp. Ther., June 1, 2007; 321(3): 930 - 937. [Abstract] [Full Text] [PDF] |
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M. Bifulco, C. Grimaldi, P. Gazzerro, S. Pisanti, and A. Santoro Rimonabant: Just an Antiobesity Drug? Current Evidence on Its Pleiotropic Effects Mol. Pharmacol., June 1, 2007; 71(6): 1445 - 1456. [Abstract] [Full Text] [PDF] |
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S. Oka, J. Wakui, S. Ikeda, S. Yanagimoto, S. Kishimoto, M. Gokoh, M. Nasui, and T. Sugiura Involvement of the Cannabinoid CB2 Receptor and Its Endogenous Ligand 2-Arachidonoylglycerol in Oxazolone-Induced Contact Dermatitis in Mice J. Immunol., December 15, 2006; 177(12): 8796 - 8805. [Abstract] [Full Text] [PDF] |
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M. Bari, P. Spagnuolo, F. Fezza, S. Oddi, N. Pasquariello, A. Finazzi-Agro, and M. Maccarrone Effect of Lipid Rafts on Cb2 Receptor Signaling and 2-Arachidonoyl-Glycerol Metabolism in Human Immune Cells J. Immunol., October 15, 2006; 177(8): 4971 - 4980. [Abstract] [Full Text] [PDF] |
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D. Roosterman, T. Goerge, S. W. Schneider, N. W. Bunnett, and M. Steinhoff Neuronal control of skin function: the skin as a neuroimmunoendocrine organ. Physiol Rev, October 1, 2006; 86(4): 1309 - 1379. [Abstract] [Full Text] [PDF] |
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P. Pacher, S. Batkai, and G. Kunos The Endocannabinoid System as an Emerging Target of Pharmacotherapy Pharmacol. Rev., September 1, 2006; 58(3): 389 - 462. [Abstract] [Full Text] [PDF] |
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E. S. Kimball, C. R. Schneider, N. H. Wallace, and P. J. Hornby Agonists of cannabinoid receptor 1 and 2 inhibit experimental colitis induced by oil of mustard and by dextran sulfate sodium Am J Physiol Gastrointest Liver Physiol, August 1, 2006; 291(2): G364 - G371. [Abstract] [Full Text] [PDF] |
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S. Raduner, A. Majewska, J.-Z. Chen, X.-Q. Xie, J. Hamon, B. Faller, K.-H. Altmann, and J. Gertsch Alkylamides from Echinacea Are a New Class of Cannabinomimetics: CANNABINOID TYPE 2 RECEPTOR-DEPENDENT AND -INDEPENDENT IMMUNOMODULATORY EFFECTS J. Biol. Chem., May 19, 2006; 281(20): 14192 - 14206. [Abstract] [Full Text] [PDF] |
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E. J. Carrier, J. A. Auchampach, and C. J. Hillard Inhibition of an equilibrative nucleoside transporter by cannabidiol: A mechanism of cannabinoid immunosuppression PNAS, May 16, 2006; 103(20): 7895 - 7900. [Abstract] [Full Text] [PDF] |
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R. Kurihara, Y. Tohyama, S. Matsusaka, H. Naruse, E. Kinoshita, T. Tsujioka, Y. Katsumata, and H. Yamamura Effects of Peripheral Cannabinoid Receptor Ligands on Motility and Polarization in Neutrophil-like HL60 Cells and Human Neutrophils J. Biol. Chem., May 5, 2006; 281(18): 12908 - 12918. [Abstract] [Full Text] [PDF] |
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G. K. Rao and N. E. Kaminski Cannabinoid-Mediated Elevation of Intracellular Calcium: A Structure-Activity Relationship J. Pharmacol. Exp. Ther., May 1, 2006; 317(2): 820 - 829. [Abstract] [Full Text] [PDF] |
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U. Pagotto, G. Marsicano, D. Cota, B. Lutz, and R. Pasquali The Emerging Role of the Endocannabinoid System in Endocrine Regulation and Energy Balance Endocr. Rev., February 1, 2006; 27(1): 73 - 100. [Abstract] [Full Text] [PDF] |
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B. Kraft and H. G. Kress Indirect CB2 Receptor and Mediator-Dependent Stimulation of Human Whole-Blood Neutrophils by Exogenous and Endogenous Cannabinoids J. Pharmacol. Exp. Ther., November 1, 2005; 315(2): 641 - 647. [Abstract] [Full Text] [PDF] |
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M. D. Van Sickle, M. Duncan, P. J. Kingsley, A. Mouihate, P. Urbani, K. Mackie, N. Stella, A. Makriyannis, D. Piomelli, J. S. Davison, et al. Identification and Functional Characterization of Brainstem Cannabinoid CB2 Receptors Science, October 14, 2005; 310(5746): 329 - 332. [Abstract] [Full Text] [PDF] |
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S. Engeli, J. Bohnke, M. Feldpausch, K. Gorzelniak, J. Janke, S. Batkai, P. Pacher, J. Harvey-White, F. C. Luft, A. M. Sharma, et al. Activation of the Peripheral Endocannabinoid System in Human Obesity Diabetes, October 1, 2005; 54(10): 2838 - 2843. [Abstract] [Full Text] [PDF] |
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J. L. Shoemaker, B. K. Joseph, M. B. Ruckle, P. R. Mayeux, and P. L. Prather The Endocannabinoid Noladin Ether Acts as a Full Agonist at Human CB2 Cannabinoid Receptors J. Pharmacol. Exp. Ther., August 1, 2005; 314(2): 868 - 875. [Abstract] [Full Text] [PDF] |
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J. C. Sipe, N. Arbour, A. Gerber, and E. Beutler Reduced endocannabinoid immune modulation by a common cannabinoid 2 (CB2) receptor gene polymorphism: possible risk for autoimmune disorders J. Leukoc. Biol., July 1, 2005; 78(1): 231 - 238. [Abstract] [Full Text] [PDF] |
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S. Kishimoto, M. Muramatsu, M. Gokoh, S. Oka, K. Waku, and T. Sugiura Endogenous Cannabinoid Receptor Ligand Induces the Migration of Human Natural Killer Cells J. Biochem., February 1, 2005; 137(2): 217 - 223. [Abstract] [Full Text] [PDF] |
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S. Oka, S. Ikeda, S. Kishimoto, M. Gokoh, S. Yanagimoto, K. Waku, and T. Sugiura 2-Arachidonoylglycerol, an endogenous cannabinoid receptor ligand, induces the migration of EoL-1 human eosinophilic leukemia cells and human peripheral blood eosinophils J. Leukoc. Biol., November 1, 2004; 76(5): 1002 - 1009. [Abstract] [Full Text] [PDF] |
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C. A. Newton, T. Lu, S. J. Nazian, I. Perkins, H. Friedman, and T. W. Klein The THC-induced suppression of Th1 polarization in response to Legionella pneumophila infection is not mediated by increases in corticosterone and PGE2 J. Leukoc. Biol., October 1, 2004; 76(4): 854 - 861. [Abstract] [Full Text] [PDF] |
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