cbd inflammation ncbiDecember 15, 2021
Cannabidiol (CBD) is one of the main pharmacologically active phytocannabinoids of Cannabis sativa L. CBD is non-psychoactive but exerts a number of beneficial pharmacological effects, including anti-inflammatory and antioxidant properties. The chemistry and pharmacology of CBD, as well as various molecular targets, including cannabinoid receptors and other components of the endocannabinoid system with which it interacts, have been extensively studied. In addition, preclinical and clinical studies have contributed to our understanding of the therapeutic potential of CBD for many diseases, including diseases associated with oxidative stress. Here, we review the main biological effects of CBD, and its synthetic derivatives, focusing on the cellular, antioxidant, and anti-inflammatory properties of CBD.
Keywords: cannabidiol; cannabidiol synthetic derivatives; endocannabinoids; inflammation; lipid peroxidation; membrane receptors; oxidative stress.
Other natural and synthetic cannabinoid compounds (CBD, AEA, ajulemic acid [AjA] and JWH-015), whose structures are depicted in Table 1 , have also been shown to induce apoptosis in murine and human T lymphocytes. Cannabidiol, the nonpsychoactive ingredient in cannabis, induced apoptosis in CD4 + and CD8 + T cells at 4–8-μM concentrations by increasing reactive oxygen species (ROS) production as well as caspase 3 and 8 activity .
Cannabinoids also exert their immunosuppressive effects on astrocytes. Astrocytes make up 60–70% of brain cells in the CNS and play important roles in neuronal growth, neuronal signaling, glucose metabolism and glutamate removal . During disease progression, astrocytes are activated to secrete cytokines, chemokines and nitric oxide, thereby contributing to the overall inflammatory response. Because astrocytes express both CB1 and CB2 receptors, several studies investigated the inhibitory role of cannabinoids on this cell population in the context of MS. One study investigated the effects of AEA on TMEV-activated primary murine astrocytes. This study showed that AEA stimulated astrocytes and triggered the production of IL-6 in a CB1-mediated pathway . The precise role of IL-6 in the CNS is still unclear; however, it has been reported that IL-6 secretion potentiates neuronal growth factor production. In addition, IL-6 has been shown to inhibit TNF-α production by IFN-γ/IL-1β-stimulated glial cells . In a different study, Molina-Holgado and coworkers showed that AEA and the synthetic CB1 agonist CP-55940 inhibited nitric oxide production by LPS-stimulated astrocytes isolated from 1-day-old mice in a CB1-dependent manner . In 2005, Sheng et al. demonstrated that human fetal astrocytes express both CB1 and CB2 receptors and that treatment of IL-1β-stimulated astrocytes with WIN55,212-2 decreased inflammatory products including nitric oxide, TNF-α, CXCL10, CCL2 and CCL5 ( Figure 1 ) .
The three main cell types that are involved in demyelination of the nerve fibers and axons in the CNS include activated T-cells, microglia and astrocytes. In activated T-cells, treatment with WIN 55,212-12, AEA and JWH-015 has been shown to inhibit cytokine production, infiltration of cells into the spinal cord and in vitro recall response to myelin oligodendrocyte glycoprotein by T-cells. Cannabinoids also inhibit the antigen presenting abilities of microglia by downregulating MHCII expression, costimulatory molecule CD40 expression, as well as cytokine secretion. Astrocytes, the major cell population in the brain, are also affected, as cannabinoid binding to the receptors leads to inhibition of inflammatory molecules, such as nitric oxide, cytokines and chemokines. In addition, anandamide binding leads to secretion of neural growth factor secretion and protection of the neurons in the CNS.
Apoptotic effects of cannabinoids on immune cell populations.
ACEA: Arachidonyl-2-ethylamide; NGF: Neuronal growth factor.
In the later stages of disease, microglial cells secrete IL-12, IL-13 and IL-23, nitric oxide and glutamate and contribute to myelin sheath destruction. IL-12 drives the proliferation of Th1 cells while IL-23 is important in the maintenance of Th17 cells. A recent study by Correa et al. showed that the endogenous cannabinoid AEA inhibited the expression of IL-12 as well as IL-23 in LPS/IFN-γ-activated human and murine microglia. This inhibition of cytokine production occurred via activation of CB2 and signaling through ERK1/2 and JNK pathways . Palazuelos et al. also showed that the CB2 receptor is involved in myeloid progenitor trafficking, which is necessary for microglia replenishment and activation during MS. Their studies demonstrated that CB2 −/− mice had exacerbated EAE symptoms and CD34 + myeloid progenitor cells had greatly infiltrated into the spinal cords of these animals. As an explanation for the mechanism, they showed that, in the bone marrow, CB2 receptor manipulation with HU-308 increased the expression of chemokines and their receptors (CCL2, CCL3, CCL5, CCR1 and CCR2), which are important in trafficking of progenitor cells into the neuroinflamed tissue .
Δ 9 -THC and its apoptotic effects on immune cell populations have been studied extensively: in 1998, Zhu et al. demonstrated that in vitro THC induced apoptosis in murine macrophages and T cells. This study also showed that the process was mediated via activation of Bcl-2 and caspases . It was difficult to demonstrate the apoptotic effects of THC on lymphocytes, in vivo , and our laboratory speculated that this might be due to rapid clearance of dead cells by phagocytic cells. Therefore, we exposed C57BL/6 mice to 10 mg/kg bodyweight THC and, after several time points, (4, 6, 24 and 72 h), obtained lymphocytes from the thymus and spleen of these animals. The cells were incubated for 12–24 h ex vivo and, since the phagocytosis was excluded in the cultures, we detected significant levels of THC-induced apoptosis in T cells, B cells and macrophages . We have also demonstrated that THC induced higher levels of apoptosis in naive lymphocytes, when compared with mitogen-activated lymphocytes, because activated cells downregulated the levels of CB2 on their cell surface . Several studies also reported THC-induced apoptosis in antigen-presenting cells. In bone marrow-derived dendritic cells (DCs), THC induced apoptosis via ligation of both CB1 and CB2 and activation of caspases such as caspase 2, 8 and 9. In vivo , THC administration decreased the number of splenic DCs, as well as MHCII expression by DCs [18,19]. Furthermore, THC increased Bcl-2 and caspase 1 activity in naive and lipopolysaccharide (LPS)-activated macrophages isolated from the peritoneal cavity of mice .
Endocannabinoids may also regulate liver cirrhosis by acting as mediators of vascular and cardiac functions. Endocannabinoids can trigger vasorelaxation, while an upregulated CB1-mediated cannabinoid tone causes enhanced mesenteric vasodialation leading to portal hypertension [73,75]. A recent in vivo study by Batkai et al. in rats with CCl 4 -induced cirrhosis, indicated that increased local production of AEA mediated the inhibition of β-adrenergic responsiveness. Further improvement in contractile function of isolated papillary muscles was observed following treatment with AM251, a CB1 receptor antagonist, suggesting therapeutic potential against cirrhotic cardiomyopathy .
Cannabinoids are a group of compounds that mediate their effects through cannabinoid receptors. The discovery of Δ 9 -tetrahydrocannabinol (THC) as the major psychoactive principle in marijuana, as well as the identification of cannabinoid receptors and their endogenous ligands, has led to a significant growth in research aimed at understanding the physiological functions of cannabinoids. Cannabinoid receptors include CB1, which is predominantly expressed in the brain, and CB2, which is primarily found on the cells of the immune system. The fact that both CB1 and CB2 receptors have been found on immune cells suggests that cannabinoids play an important role in the regulation of the immune system. Recent studies demonstrated that administration of THC into mice triggered marked apoptosis in T cells and dendritic cells, resulting in immunosuppression. In addition, several studies showed that cannabinoids downregulate cytokine and chemokine production and, in some models, upregulate T-regulatory cells (Tregs) as a mechanism to suppress inflammatory responses. The endocannabinoid system is also involved in immunoregulation. For example, administration of endocannabinoids or use of inhibitors of enzymes that break down the endocannabinoids, led to immunosuppression and recovery from immune-mediated injury to organs such as the liver. Manipulation of endocannabinoids and/or use of exogenous cannabinoids in vivo can constitute a potent treatment modality against inflammatory disorders. This review will focus on the potential use of cannabinoids as a new class of anti-inflammatory agents against a number of inflammatory and autoimmune diseases that are primarily triggered by activated T cells or other cellular immune components.
Arachidonic acid metabolites have been shown to exhibit properties similar to compounds found in Cannabis sativa . These metabolites are hence referred to as endocannabinoids. These ubiquitous endogenous cannabinoids act as natural ligands for the cannabinoid receptors expressed in mammalian tissue, thus constituting an important lipid-signaling system termed the endocannabinoid system. The endocannabinoid system is an important biological regulatory system that has been shown to be highly conserved from lower invertebrates to higher mammals . Other than the lipid transmitters that serve as ligands for the cannabinoid receptors, the endocannabinoid family also comprises the enzymes for biosynthesis and degradation of the ligands. The endocannabinoids include N -arachidonoylethanolamine, anandamide (AEA), 2-arachidonoyl glycerol (2-AG), N -arachydonoyldopamine, noladin ether and virodhamine. AEA was discovered by Devane et al . and is an amide formed from arachidonic acid and ethanolamine . AEA binds to brain CB1 with high affinity and mimics the behavioral actions of exogenous cannabinoid Δ 9 -tetrahydrocannabinol (THC) when injected into rodents. 2-AG was discovered independently 3 years later by Mechoulam et al .  and Sugiura et al . . It was found to exist in much higher concentration in serum and brain than AEA. 2-AG has similar affinities for both CB1 and CB2 receptors, as does AEA, but it exhibits higher efficacy. Endocannabinoids are derivatives of arachidonic acid conjugated with either ethanolamine or glycerol. They are synthesized on demand from phospholipid precursors residing in the cell membrane in response to a rise in intracellular calcium levels. Inside cells, endocannabinoids are catalytically hydrolyzed by the aminohydrolase fatty acid amide hydrolase (FAAH), which degrades AEA into arachidonic acid and ethanolamine . 2-AG is hydrolyzed into AEA and glycerol by either FAAH or by monoacyl glycerol lipase (MAGL). Fatty acid-binding proteins (FABPs) have been reported to play an important role as intracellular carriers in the transport of AEA from the plasma membrane to FAAH for their subsequent inactivation . Studies to date indicate that the main pharmacological function of the endocannabinoid system is in neuromodulation: controlling motor functions, cognition, emotional responses, homeostasis and motivation. However, in the periphery, this system is an important modulator of the ANS, immune system and microcirculation . Some well-known natural and synthetic cannabinoids and endocannabinoids are depicted in Table 1 .
Cannabinoids & multiple sclerosis.
Fatty acid amide hydrolase is the major enzyme involved in the degradation of several bioactive fatty amides, in particular anandamide , and its genetic deletion in mice leads to a strongly decreased ability to degrade this endocannabinoid and an increase of anandamide levels in several tissues . FAAH-deficient mice showed significant protection against DNBS treatment. However, because anandamide is believed to act not only through cannabinoid receptors but also through other targets, including the peripheral vanilloid receptor TRPV1 , the decreased inflammation in FAAH −/− mice could also be due to the activation of targets other than cannabinoid receptors.
Pharmacological stimulation of cannabinoid receptors with the potent agonist HU210 also induced a reduction of experimental colitis. It has been reported that cannabinoid receptor stimulation could have a beneficial effect on experimental colitis . Intraperitoneal application of ACEA, a CB1-selective agonist, and JWH-133, a CB2-selective agonist, inhibited oil of mustard (OM)-induced colitis and subsequent symptoms such as induced distal colon weight gain, colon shrinkage, inflammatory damage, diarrhea and histological damage. This study demonstrated a role for CB2 activation in experimental colitis. The fact that both CB1 and CB2 agonists are active in colitis models lends additional support to the theory that signaling through cannabinoid receptors may mediate protective mechanisms in colitis.
During chronic inflammation, IL-6 suppression can decrease tissue injury . AjA has been reported to prevent joint-tissue injury in animal models of adjuvant arthritis . Recent studies showed that addition of AjA to human monocyte-derived macrophages in vitro reduced the secretion of IL-6 from activated cells, suggesting that AjA may have a value for treatment of joint inflammation in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and osteoarthritis . It has been observed that the CB2 agonist HU-308 attenuated the hepatic ischemia/reperfusion injury by decreasing the levels of TNF-α, MIP-1α and MIP-2 in the serum and in liver homogenates . Recent in vitro studies have also shown the potent anti-inflammatory effect of synthetic cannabinoids (CP55,940 and WIN55,212-2). Both CP55,940 and WIN55,212-2 downregulated IL-6 and IL-8 cytokine production from IL-1β-stimulated rheumatoid fibroblast-like synoviocytes (FLS), via a non-CB1/CB2-mediated mechanism .
Selected cannabinoid molecules.
During inflammation, several different cellular pathways are activated in the intestinal tract, leading to a pathological state . Functional CB1 receptor has been shown to be expressed in the human ileum and colon and the number of CB1-expressing cells was found to be significantly increased after inflammation [59,60]. A protective role for these CB1 receptors during inflammation has been shown in a study analyzing the role of the endogenous cannabinoid system in the development of experimental colitis in mice, induced by intrarectal 2,4-dinitrobenzene sulfonic acid (DNBS) treatment or oral dextran sodium sulfate (DSS) administration . The DSS model, originally reported by Okayasu et al., has been used to investigate the role of leukocytes in the development of colitis . Oral administration of 5% DSS in drinking water can induce acute colitis due to chemical injury in the colon. Furthermore, long-term DSS administration produces colorectal carcinoma, which is similar to the dysplasia–carcinoma sequence seen in the course of cancer development in human ulcerative colitis . On the other hand, intestinal inflammation induced by the intrarectal administration of DNBS has many of the characteristic features of Crohn’s disease in humans, involving induction of an IL-12-driven inflammation with a massive Th1-mediated response . The involvement of the endogenous cannabinoid system in the modulation of the acute phase of DNBS-induced colitis was further supported by the increased levels of transcripts coding for CB1 in wild-type mice after induction of inflammation. It was observed that genetic ablation of CB1 receptors rendered mice more sensitive to inflammatory insults. Furthermore, similar to results observed in CB1-deficient mice, pharmacological blockade of CB1 with the specific antagonist SR141716A led to a worsening of colitis . The protective role of the endogenous cannabinoid system was observed 24 h after DNBS treatment and became more evident on days 2 and 3. However, increased spontaneous spiking activity of smooth muscle cell membrane in DNBS-treated colons from CB1 −/− mice was already visible 8 h after DNBS treatment, indicating that inflammation-induced irritation of smooth muscle occurred at an earlier stage than in wild-type mice. This gives further support to the notion that the endogenous cannabinoid system is protective against inflammatory changes. These data indicated that the activation of CB1 and the endogenous cannabinoid system is an early and important physiological step in self-protection of the colon against inflammation.
Ajulemic acid, a side-chain synthetic analog of Δ(8)-THC-11-oic acid, has been shown to induce apoptosis in human peripheral blood T lymphocytes via the intrinsic pathway at concentrations of 1, 3 and 10 μM . In addition, the use of synthetic CB2 agonist JWH-015 treatment in vitro led to cell death via both the death-receptor pathway and the intrinsic pathway. When JWH-015 was administered in vivo , the antigen-specific response to Staphylococcal enterotoxin A was inhibited significantly .
Endocannabinoids have also been reported to affect the cytokine biology of various cell systems. Antiproliferative effects of endocannabinoids on cancer cell lines are well established and are discussed in the later section of the review. However, AEA has also been reported to increase cytokine-induced proliferation. Mouse bone marrow cells, when cultured in the presence of IL-3 and AEA, were observed to produce more hematopoietic colonies than with IL-3 alone . Significant suppression of IL-2 expression by 2-AG and the nonhydrolyzable 2-AG ether was observed in leukocytes via activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) . Furthermore, in undifferentiated and macrophage-like differentiated HL-60 cells, 2-AG induced CB2-dependent acceleration in the production of IL-8 . In Theiler’s virus immune-mediated demyelinating disease, inactivation of endocannabinoids through the use of two selective inhibitors of their transport; ( R )- N -oleoyl-(1′-hydroxybenzyl)-2′-ethanolamine] (OMDM2) and [( S )- N -oleoyl-(1′-hydroxybenzyl)-2′-ethanolamine (OMDM1) led to decreased production of the proinflammatory cytokines IL-1β and IL-12 . On a contrary note, cytokines have also been shown to affect the endocannabinoid system. IL-12 and IFN-γ have been shown to reduce FAAH activity and protein expression of FAAH, whereas IL-4 or IL-10 stimulated FAAH activity . Table 2 provides a summary of the effect of cannabinoids on cytokines and chemokines in various cell models [26,28,29,32–34,37,40,41].
It is important to note that, unlike in immune cells, cannabinoids can protect from apoptosis in nontransformed cells of the CNS, which can play a protective role in autoimmune conditions such as multiple sclerosis. Cannabinoids protect against apoptosis of oligodendrocytes via CB1 and CB2 receptors, by signaling through the PI3K/AKT pathway. In vivo and in vitro exposure to arachidonyl-2-ethylamide (ACEA) and WIN55,212-12 protected the cells, while pretreatment with CB1 receptor antagonist SR141716A and CB2 receptor antagonist SR144528 blocked the action of these cannabinoids . In a different study by Jackson et al. , 3D mouse brain aggregate cell cultures were compared between wild-type mice and CB1 receptor knockout mice. IFN-γ treatment led to decrease in the neurofilament-H expression in knockout cultures but not in wild-type cultures. In addition, caspase 3 activation was higher in knockout cultures, indicating a protective role of CB1 in neuronal cells .
Effect of cannabinoids on cytokine and chemokine production.