Metabolism of delta-1-tetrahydrocannabinol by the rat in vivo and in vitro

Combined effects of marijuana and nicotine on memory performance and hippocampal volume

Combined use of marijuana (MJ) and tobacco is highly prevalent in today's population. Individual use of either substance is linked to structural brain changes and altered cognitive function, especially with consistent reports of hippocampal volume deficits and poorer memory performance. However, the combined effects of MJ and tobacco on hippocampal structure and on learning and memory processes remain unknown. In this study, we examined both the individual and combined effects of MJ and tobacco on hippocampal volumes and memory performance in four groups of adults taken from two larger studies: MJ-only users (n=36), nicotine-only (Nic-only, n=19), combined marijuana and nicotine users (MJ+Nic, n=19) and non-using healthy controls (n=16). Total bilateral hippocampal volumes and memory performance (WMS-III logical memory) were compared across groups controlling for total brain size and recent alcohol use. Results found MJ and MJ+Nic groups had smaller total hippocampal volumes compared to Nic-only and controls. No significant difference between groups was found between immediate and delayed story recall. However, the controls showed a trend for larger hippocampal volumes being associated with better memory scores, while MJ+Nic users showed a unique inversion, whereby smaller hippocampal volume was associated with better memory. Overall, results suggest abnormalities in the brain-behavior relationships underlying memory processes with combined use of marijuana and nicotine use. Further research will need to address these complex interactions between MJ and nicotine.

The Urinary Disposition of Intravenously Administered 11-Nor-9-carboxy-delta-9-Tetrahydrocannabinol in Humans

The objective of this study was to investigate the fraction of an administered dose of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH) that is actually excreted into urine and to determine its urinary half-life independent of the parent compound. Ten healthy, male marijuana nonusers who were enrolled in the study were administered a single dose of 5 mg THCCOOH by the intravenous route. Urine specimens were collected up to 96 hours after administration. Samples were extracted before and after alkaline hydrolysis. The concentration of unconjugated and total THCCOOH was determined using gas chromatography-mass spectrometry. Most of the THCCOOH found in urine was conjugated, with only 0.14 +/- 0.08% of the dose present as unconjugated THCCOOH. The amount of conjugated THCCOOH ranged from 149.3 to 559.8 (mean +/- SD, 342.8 +/- 117.3) microg, representing a recovery of 3% to 11% of the administered dose. The measured amounts of total THCCOOH were low and highly varied among individuals. Renal excretion does not appear to be the preferred elimination pathway for THCCOOH. Urinary elimination half-life of unconjugated and conjugated THCCOOH ranged from 9.0 to 27.4 (mean +/- SD, 17.3 +/- 5.3) hours and from 10.7 to 27.6 (mean +/- SD, 16.0 +/- 5.0) hours, respectively. Although preliminary in nature, the actual urinary elimination half-life of THCCOOH appears to be significantly shorter than its apparent or terminal half-life reported from single or multiple dosing of delta-9-tetrahydrocannabinol (THC).

Pharmacokinetics of 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (CTHC) after intravenous administration of CTHC in healthy human subjects

After cannabis consumption there is only limited knowledge about the pharmacokinetic (PK) and metabolic properties of 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (CTHC), which is formed by oxidative breakdown from Delta(9)-tetrahydrocannabinol (THC). Despite widely-varying concentrations observed in smoking studies, attempts have been made to interpret consumption behavior with special regard to a cumulated or decreasing concentration of CTHC in serum. Ten healthy nonsmoking white male individuals received 5 mg CTHC intravenously over 10 min. Highest serum concentrations of CTHC were observed at the end of the infusion (336.8+/-61.7 microg/l) followed by a quick decline. CTHC concentration could be quantified up to 96 h after administration, with a terminal elimination half-life of 17.6+/-5.5 h. Total clearance was low (91.2+/-24.0 ml/min), with renal clearance having only a minor contribution (0.136+/-0.094 ml/min). This first metabolite-based kinetic approach will allow an advanced understanding of CTHC PKs data obtained in previous studies with THC.

Immunochemical characterization of a cytochrome P450 isozyme and a protein purified from liver microsomes of male guinea pigs and their roles in the oxidative metabolism of delta 9-tetrahydrocannabinol by guinea pig liver microsomes

A protein (designated as protein-B) was purified from liver microsomes of adult male guinea pigs by an affinity chromatography with omega-aminooctyl Sepharose 4B, followed by HPLC using DEAE-5PW and hydroxyapatite columns which had been used to purify a cytochrome P450 (P450) isozyme (P450-A) from the same subcellular fraction (Narimatsu et al., Biochem Biophys Res Commun 172: 607-613, 1990). Protein-B had a molecular mass of 49 kDa in SDS-PAGE, but did not show absorbance at 417 nm for heme. Further, it did not show any oxidative activities towards aniline (AN), d-benzphetamine (d-BP), p-nitroanisole (p-NA) or delta 9-tetrahydrocannabinol (delta 9-THC) in a reconstituted system including dilauroylphosphatidylcholine, NADPH-P450 reductase, and cytochrome b5. However, antiserum against protein-B raised in rabbits suppressed liver microsomal oxidative activities towards d-BP and p-NA dose-dependently. The antibody decreased delta 9-THC oxidative activity most effectively, but did not decrease AN hydroxylation activity. Antiserum against P450-A suppressed all the activities towards these four substrates, especially towards delta 9-THC, in liver microsomes of male guinea pigs. Moreover, reconstitution with hemin made it possible for protein-B to produce some oxidative activity toward delta 9-THC. These results suggest that protein-B is also a cytochrome P450 isozyme which has lost a heme moiety during purification steps. Both P450-A and protein-B could have a role as cytochrome P450 isozymes in the oxidative metabolism of drugs, especially that of delta 9-THC by the liver microsomes of adult male guinea pigs.

Sex difference in the oxidative metabolism of delta 9-tetrahydrocannabinol in the rat

Oxidative metabolism of delta 9-tetrahydrocannabinol (THC), one of the major components of marihuana, was studied using liver microsomes of adult male and female rats. There was no significant difference in the rates of the cannabinoid oxidation in terms of nmol per min per nmol of liver microsomal cytochrome P450 or of nmol per min per mg of microsomal protein between male and female rats. delta 9-THC was biotransformed to various metabolites including 11-hydroxy-delta 9-THC (11-OH-delta 9-THC), 8 alpha-OH-delta 9-THC, 8 alpha,11-diOH-delta 9-THC, 3'-OH-delta 9-THC by liver microsomes of male rats, while it was oxidized selectively to 11-OH-delta 9-THC by liver microsomes of female rats. After intraperitoneal administration of delta 9-THC, various metabolites were again found in the liver of the male rat, while in the female rat oxidation of the methyl group at the 9-position was a major metabolic pathway. These results demonstrate that an apparent sex-related difference exists in the oxidative metabolism of delta 9-THC in the rat.

Cross-tolerance between delta9-tetrahydrocannabinol and ethanol: the role of drug disposition

Acute challenge doses of delta9-tetrahydrocannabinol (THC), 10.1 mg/kg, administered intragastrically by gavage (IG), or ethanol, 1.24 g/kg, IP, reduced the rotarod performance of female rats by 50%. Daily treatment of the animals with THC, 10.1 mg/kg, IG, or ethanol, 4 g/kg, IG, resulted in tolerance development to the impairing effects of the challenge doses of each drug on rotarod performance. THC-tolerant animals were cross-tolerant to the challenge dose of ethanol, but ethanol-tolerant rats did not show complete cross-tolerance to the challenge dose of THC. THC-tolerant animals initially had higher blood levels of 14C-THC than controls after IG drug administration. Following IV injection, the rates of 14C-THC disappearance were equivalent in the latter groups. 14C-THC disappearance was not altered in ethanol-tolerant animals. The rates of ethanol disappearance were not significantly modified in THC- or ethanol-tolerant animals. In conclusion, THC-tolerant female rats demonstrated cross-tolerance to ethanol as shown previously for males. Furthermore, the development of tolerance and cross-tolerance was not a function of changes in drug disappearance.

Interactions between delta9-tetrahydrocannabinol and phencyclidine hydrochloride in rats

delta9-Tetrahydrocannabinol (THC; 2.5, 5.0, 10.0 mg/kg, PO) impaired avoidance and rotarod performance, and caused bradycardia and hypothermia. Phencyclidine (PCP; 1.25, 2.5, 5.0 mg/kg, IP) impaired avoidance and rotarod performance and caused a marked increase in photocell activity. When combined, the depressant properties of each drug were enhanced and the stimulation of photocell activity cg/kg THC and its interactions with PCP followed subacute treatment for six days, whereas many of the effects of PCP were enhanced after subacute treatment with a dose of 2.5 mg/kg. Open-field behavior was affected by each drug alone and in combination in a similar way as photocell activity, but the depression caused by their interaction was greater; both drugs caused an increase in urination. Response rates on an FR-10 schedule of food reinforcement were decreased by 2.5 mg/kg PCP, but not by 5.0 mg/kg THC; the combination caused greater response suppression than either drug alone. The functional interactions between THC and PCP were not related to changes in the concentrations of 14C or 3H in plasma or brain derived from 14C-delta9-THC and 3H-PCP, respectively.

Ethanol and delta-9-tetrahydrocannabinol: mechanism for cross-tolerance in mice

The pharmacological interaction between equipotent doses of ethanol (1.35 g/kg) and delta-9-tetrahydrocannabinol (THC, 17 mg/kg) was evaluated in mice using rotarod performance as a measure of drug action. Tolerance ot the effects of ethanol and THC as well as a symmetrical cross-tolerance between these two drugs was demonstrated. Ethanol elimination was not altered by previous treatment with either ethnaol or THC as determined by measuring blood ethanol concentrations with an enzymatic assay. THC metabolite ratios in blood, brain and liver tissues determined after a dose of 3H-THC demonstrated that THC treatment had no effect upon THC metabolism or disposition. Ethanol treatment altered the distribution of THC and also altered hepatic THC metabolism as evidence by the occurrence of increased proportions of polar THC metabolites. No treatment regimens produced lower whole brain levels of subsequent ethanol or THC suggesting that tolerance to ethanol or THC and cross-tolerance between these two drugs does not develop due to lower brain concentrations. A vehicle effect was shown when treatment with a mixture of propylene glycol and Tween-80 altered the metabolic and behavioral effects of subsequently administered THC.

Effects of various psychoative drugs on the metabolism of delta-tetrahydrocannabinol by rats in vitro and in vivo

Metabolism of 14C-tetrahydrocannabinol (14C-THC) by rat liver microsomal preparations in vitro was studied in the absence and presence of other psychoative drugs. Disappearance of 14C-THC, and changes in metabolite patterns as shown by thin layer chromatography, were studied. SKF 525-A, pentobarbital, phenobarbital and amphetamine all produced an apparently non-competitive inhibition of THC metabolism. The inhibition produced by meprobamate was at least partly competitive. Morphine and mescaline had no evident effect. SKF 525-A and the barbiturates markedly decreased the concentrations of all the major THC metabolites found in the incubation media. In contrast, none of the drugs tested in vivo, with the exception of SKF 525-A, had any effect on the biliary 14C-excretion or metabolite pattern, or on final tissue levels of 14C, when administered in doses comparable to those used for studies of interaction with THC in vivo. SKF 525-A, however, did markedly decrease the excretion of total 14C and alter the pattern of THC metabolities in the bile, and increased the final tissue 14C levels. It is concluded that in vivo interactions between THC and other psychoactive drugs are probably not explainable primarily on the basis of altered THC metabolism.