Cannabichromene Synthesis.

Cannabinoids are a class of terpenophenolic compounds obtained by the alkylation of olivetolic acid with geranyl-pyrophosphate by geranyl pyrophosphate-olivetolic acid geranyltransferase to produce cannabigerolic acid (CBGA), as illustrated in Fig. 1 (Nachnani et al., 2021; Odieka et al., 2022). This is the first step in which variety can be introduced to the cannabinoid structure, because geranyl pyrophosphate-olivetolic acid geranyltransferase can use other phenolic moieties with different alkyl chain lengths, such as divarinolic acid. The use of divarinolic acid leads to cannabinoids that have a three-carbon side chain (i.e., the varniol family of cannabinoids) (highlighted in Fig. 1). CBGA and its derivatives are the substrates for three additional enzymes that are responsible for producing the three other major families of cannabinoids: Δ9-tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), and cannabichromenic acid (CBCA) (Pattnaik et al., 2022). Decarboxylation, via heat and drying, then converts the acidic forms (THCA, CBDA, CBCA, and CBGA) into their neutral forms (THC, CBD, CBC, and CBG) (Odieka et al., 2022). Subsequent spontaneous conversions produce the scores of other cannabinoid molecules.

Fig. 1.

Biosynthesis of CBC. The enzymatic pathway that leads to CBC production is illustrated. CBC is enzymatically produced from the cannabinoid precursor CBGA, via a CBCA intermediate. Decarboxylation (red circle) of CBCA through heat results in the neutral CBC. The green circle highlights the alkyl-side chain that can vary in length from three to seven carbons in cannabinoids isolated from Cannabis sativa L.

CBC can be produced synthetically from citral and olivetol in several different ways. These synthetic processes are important because most strains of cannabis produce only small amounts of CBC. Yields of CBC from these chemical processes have been reported between 40%–75% depending on the reaction conditions (Lee and Wang, 2005; Pollastro et al., 2018; Quílez del Moral et al., 2021).

Pharmacokinetics of CBC.

A key to assessing the potential therapeutic utility of any compound is to understand its metabolism and bioavailability. There are limited studies involving CBC. When administered at 10 mg/kg via intraperitoneal injection in rats, the maximum concentration in plasma was reached in 30 minutes, whereas brain concentrations did not peak until 120 minutes (Anderson et al., 2021). This study also found that CBC has a relatively significant half-life in both plasma (98 minutes) and brain (193 minutes), and the total exposure of CBC in the brain tissue was close to that of plasma (brain–plasma ratio of 0.83) (Anderson et al., 2021). When comparing the pharmacokinetics of CBC to other cannabinoids, the maximum concentration in plasma for CBG (120 mg/kg) and CBD (120 mg/kg) occurs 120 minutes after injection; however, for cannabidivarin (CBDV) (60 mg/kg) and Δ9-tetrahydrocannabivarin (THCV) (30 mg/kg) peak concentration in the plasma occurs at 30 minutes (Deiana et al., 2012). Although the study by Deiana et al. (2012) did not examine the pharmacokinetics of CBC, the results from the Anderson et al. (2021) study suggest that time-to-peak plasma concentrations of CBC are more similar to THCV and CBDV. In the brain, Deiana et al. (2012) found CBDV and THCV concentrations peak at 30 minutes, CBD concentrations peak at 60 minutes, and CBG concentrations peak at 120 minutes. In contrast, in the brain, CBC pharmacokinetics are closer to those observed for CBG (Deiana et al., 2012; Anderson et al., 2021).

In humans, the pharmacokinetics of CBC was investigated in the presence of CBD and THC. The study examined daily administration of CBC and saw that in the presence of CBD and THC, CBC was tolerable up to daily doses of 26.4 mg (Peters et al., 2022a). The study on the CBC pharmacokinetics was a follow-up study in which patients were given four different doses of a cannabis extract (Peters et al., 2022b). Initially, the authors were interested in the pharmacokinetics of CBD and THC and administered increasing daily doses of oil based on CBD and THC content. However, subsequent analysis of the oil revealed higher levels of CBC than THC in the extract (oil composition: 20 mg/ml CBD, 0.9 mg/ml THC, and 1.1 mg/ml CBC) (Peters et al., 2022a,b). Study participants were divided into five groups based on daily cannabinoid dose: group A (120 mg CBD, 5.4 mg THC, 6.6 mg CBC), group B (240 mg CBD, 10.8 mg THC, 13.2 mg CBC), group C (360 mg CBD, 16.2 mg THC, 19.8 mg CBC), group D (480 mg CBD, 21.6 mg THC, 26.4 mg CBC), or placebo.

These studies found that THC was quantifiable in fewer plasma samples than CBC even though the doses of THC (21.6 mg) and CBC (24.6 mg) were similar in the treatments (Peters et al., 2022a,b). In the highest treatment group (treatment D), although the dose of CBD was 480 mg (approximately 18-fold higher than CBC), the area under the curve0-t of CBD was 6.6- to 9.8-fold higher than the area under the curve0–t of CBC (Peters et al., 2022a). The Peters and colleagues suggest that that CBC may have preferential absorption over CBD or THC; however, differential metabolism is also a possibility especially in light of the fact that data on the metabolism of CBC is lacking in the literature. The study found an average tmax for CBC of 3.3 hours; this compares to an average tmax for CBD of 4.5 hours, a tmax for THC was not able to be quantified due to levels below detection (Peters et al., 2022a,b). In another human study, looking at the pharmacokinetics of THC and CBD, when given orally at a dose of 20 mg THC or 40 mg CBD maximal plasma concentrations occurred after 60–120 minutes, a much shorter tmax than reported by Peters et al. (2022b) and Grotenhermen (2003).

Additional studies will be needed, particularly with CBC alone to better understand the pharmacokinetics and pharmacodynamics of this molecule. It is interesting to note that despite being administered at similar levels and having similar levels of detectability, the levels of THC were always undetectable (metabolites of THC were detectable), the levels of CBC were always within detectable limits in patients (Peters et al., 2022a,b). Currently, there is a marked absence in the literature on the enzymatic metabolism of CBC, and this is a key area where data are needed. Similarly, additional data are needed to understand the distribution and pharmacokinetics of CBC.

CBC Activity in the Endocannabinoid System.

The activity of CBC at the cannabinoid receptor 1 (CB1) remains unclear, despite a number of studies that have investigated this activity. CBC was found to displace CP 55,940, a potent synthetic CB1 and cannabinoid receptor 2 (CB2) agonist, from CB1-containing cell membranes in cultured cells and act as an agonist by inhibiting forskolin-stimulated cAMP synthesis (Rosenthaler et al., 2014; Zagzoog et al., 2020). However, CBC was not found to induce recruitment of β-arrestin-2 in the latter study (Zagzoog et al., 2020). This study also found that CBC reduced the amount of intracellular glutathione in primary mesencephalic cell culture, although the receptor responsible for this was not identified. In contrast to these two studies, CBC at a concentration up to 10 µM failed to displace [3H]-CP55,940 from the CB1 receptor in whole rat brain membranes (Booker et al., 2009). The activity of CBC on the endocannabinoid system is summarized in Table 1. Importantly, the reported binding affinities of CBC at the CB1 receptor, although controversial, are similar to CBG and lower than those reported for Δ9-THC [reviewed in Nachnani et al. (2021) and Legare et al. (2022)]. In contrast, CBC was not found to induce hyperpolarization of pituitary cells overexpressing CB1 (Udoh et al., 2019). Several other studies have also found that CBC does not activate CB1, does not stimulate [35S]-GTPγS binding, nor does it inhibit adenylate cyclase activity (Howlett, 1987; Romano et al., 2013). Furthermore, the lack of activation of CB1 is consistent with the observation that CBC is non-psychoactive (DeLong et al., 2010; Zagožen et al., 2020). These data suggest that although CBC may bind to CB1, this binding does not stimulate activation of the receptor; importantly, CBC did not inhibit the activation of CB1 by CP 55,940 or THC (Udoh et al., 2019). Alternatively, CBC may exhibit biased signaling via the CB1 receptor. Importantly, it has been reported for morphine receptors that failure to recruit β-arrestins can improve analgesia with reduced side effects in mice and mediates reward; therefore, the non-euphorigenic nature of CBC may be linked to the compounds inability to stimulate recruitment of β-arrestin-2 (Darcq and Kieffer, 2018). This is clearly an area where additional studies are needed. The distribution of CB1 receptors within the central nervous system are illustrated in Fig. 2.

TABLE 1

Activity of CBC at endocannabinoid receptors and enzymes

Ki and EC50/IC50 values are in nM.

Fig. 2.

Central nervous system distribution of receptors. The distribution of CBs, TRP channels, and PPAR receptors within the central nervous system are shown. In particular, CB1 expression is high within the cerebral cortex, hypothalamus, and cerebellum; while lower expression has been reported in the brainstem and spinal cord. CB2 is expressed on astrocytes and microglia within the CNS. TRPVs are reported to be expressed in the cerebral cortex, hippocampus, cerebellum, and spinal cord. TRPA1 expression is detected in the olfactory bulb, hippocampus, hypothalamus, cerebral cortex, cerebellum, and brainstem. TRPM8 is expressed at low levels in the hypothalamus and brain steam. Finally, PPARβ/δ is widely distributed within the cerebrum, whereas PPARα is expressed at low levels in astrocytes and PPARγ is expressed by microglia. All three isoforms of PPAR have been detected in the spinal cord (Emir, 2017; Kendall and Yudowski, 2017; Zolezzi et al., 2017; Okine et al., 2019; Haspula and Clark, 2020; Souza Monteiro de Araujo et al., 2020; Ordás et al., 2021).

There is a better agreement of the function of CBC at CB2, where CBC acts as an agonist. CBC has been shown to bind to CB2 and to inhibit forskolin-stimulated cAMP production (Rosenthaler et al., 2014; Zagzoog et al., 2020). The affinity for CBC at the CB2 receptor is similar to THC, and compared with other reported cannabinoids such as CBG and CBD, it is slightly higher [reviewed in Nachnani et al. (2021) and Legare et al. (2022)]. CBC has also been shown to activate CB2 in a hyperpolarization assay, and this activity can be inhibited by pertussis toxin, indicating that the activation is coupled to Gi/o signaling (Udoh et al., 2019). This study also showed that hyperpolarization induced by CBC could be blocked by the CB2-selective antagonist AM630. Importantly, activation of CB2 would be consistent with the reported anti-inflammatory activity of CBC discussed below.

The activity of CBC at other GPCRs that have been shown to bind cannabinoids, such as GPR55, GPR18, and GPR119, has not been reported and it will be interesting to see if any of these receptors can be activated or inhibited by CBC. Cannabinoids can also impact the endocannabinoid system by altering the metabolism of the endocannabinoids anandamide [arachidonoylethanolamine (AEA)] and 2-arachidonoyl glycerol (2-AG). CBC has been reported to inhibit the activity of the 2-AG degrading enzyme monoacylglycerol lipase but not the AEA degradation enzyme fatty acid amide hydrolase (De Petrocellis et al., 2011). Therefore, CBC may skew the endocannabinoid system by increasing levels of 2-AG relative to AEA. However, data on the effects of CBC on endocannabinoid metabolizing enzymes are limited and the compound remains unstudied at a number of other GPCRs that are known to bind cannabinoids making this another area where more data are clearly needed.

CBC Activity at Transient Receptor Potential (TRP) Cation Channels.

In a study that investigated the activation of several TRP channels by cannabinoids, it was found that CBC was the most potent activator of transient receptor potential ankyrin (TRPA1), with an EC50 of 90 nM (De Petrocellis et al., 2008, 2011). These studies also found CBC to be an agonist of transient receptor potential vanilloid (TRPV)1; interestingly the EC50 of CBC at this receptor is closer to the acidic cannabinoids (i.e., CBGA, CBDA), whereas the other neutral cannabinoids (i.e., CBG, THCV) have EC50 values half that found for CBC (De Petrocellis et al., 2011). Furthermore, CBC was found to be an antagonist of transient receptor potential melastatin (TRPM8), although, compared with the other cannabinoids tested CBC was the least potent TRPM8 antagonist (De Petrocellis et al., 2007, 2011). In a follow-up study CBC was also found to activate TRPV3 similar to other cannabinoids and was found, along with CBD, to be a highly potent agonist of TRPV4 (De Petrocellis et al., 2012). The function of CBC at TRP channels is summarized in Table 2. Distribution within the CNS of TRP channels is illustrated in Fig. 2.

TABLE 2

Activity of CBC at TRP ion channels

Values are µM.

CBC Activity on Peroxisome Proliferator-Activated Receptor (PPAR) Receptors.

Many cannabinoids have been found to activate the PPAR nuclear receptor family of transcription factors, in particular PPARα and PPARγ. CBC has been found to be an agonist at PPARγ receptors (Table 3); however, this study failed to find an EC50 for CBC because the highest dose tested was 25 µM and it failed to produce a maximal effect (Granja et al., 2012). CBC was the least potent cannabinoid agonist of PPARγ in the study and is slightly less potent than THC (EC50 = 21.2 µM) or CBD (EC50 = 20.1 µM) based on the presented dose–response curves, and much less active than CBG (EC50 = 12.7 µM) (Granja et al., 2012). It has not been determined if CBC can activate PPARα transcription factors. PPAR receptor distribution within the CNS is illustrated in Fig. 2.

TABLE 3

Activity of CBC at PPAR receptors

EC50/IC50 values are all in µM.