Naloxone-reversible antinociceptive activity of cathinone, the active principle of khat, in the mouse and rat

Disposition Kinetics of Cathinone and its Metabolites after Oral Administration in Rats

BACKGROUND

Cathinone is a natural stimulant found in the Catha edulis plant. Its derivatives make up the largest group of new psychoactive substances. In order to better understand its effects, it is imperative to investigate its distribution, pharmacokinetics, and metabolic profile. However, the existing literature on cathinone remains limited.

OBJECTIVE

This study aimed to investigate the disposition kinetics and metabolic profile of cathinone and its metabolite cathine through a single oral dose of cathinone administration in rats.

METHODS

Cathinone and cathine concentrations were identified and quantified using ion trap liquid chromatography- mass spectrometry (LC-IT/MS). The metabolic profile in the serum, brain, lung, liver, kidney, and heart was analyzed at specific time points (0, 0.5, 2.5, 6, 12, 24, 48, and 72 hours) using the ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS) method.

RESULTS

The highest concentration of cathinone was found in the kidney (1438.6 μg/L, which gradually decreased to 1.97 within 48 h and disappeared after 72 h. Cathinone levels in the lungs, liver, and heart were 859, 798.9, and 385.8 μg/L, respectively, within half an hour. However, within 2.5 hours, these levels decreased to 608.1, 429.3, and 309.1 μg/L and became undetectable after 24 h. In the rat brain, cathinone levels dropped quickly and were undetectable within six hours, decreasing from 712.7 μg/L after 30 min. In the brain and serum, cathine reached its highest levels at 2.5 hours, while in other organs, it peaked at 0.5 hours, indicating slower conversion of cathinone to cathine in the brain and serum.

CONCLUSION

This study revealed a dynamic interplay between cathinone disposition kinetics and its impact on organ-specific metabolic profiles in rats. These results have significant implications for drug development, pharmacovigilance, and clinical practices involving cathinone. Investigating the correlation between the changes in biomarkers found in the brain and the levels of cathinone and cathine is essential for informed decision- making in medical practices and further research into the pharmacological properties of cathinone.

Characterization of the Antinociceptive Mechanisms of Khat Extract (Catha edulis) in Mice

This study investigated the antinociceptive mechanisms of khat extract (100, 200, and 400 mg/kg, i.p.) in four pain models: two thermic (hot plate, tail-flick) and two chemical (acetic acid, formalin) models. Male mice were pretreated intraperitoneally (i.p.) with the opioid receptor blocker naloxone (5 mg/kg), the cholinergic antagonist atropine (2 mg/kg), the selective α₁ blocker prazosin (1 mg/kg), the dopamine D₂ antagonist haloperidol (1.5 mg/kg), or the GABA_A receptor antagonist, bicuculline (1 mg/kg) 15 minutes prior to i.p. injection of khat extract (400 mg/kg). Khat extract reduced the nociceptive response of mice in the four pain tests. Naloxone significantly inhibited the antinociceptive effect of khat extract in the hot plate, tail-flick, and the first phase of formalin tests. Bicuculline significantly antagonized the antinociceptive effect of khat extract on the hot plate and tail-flick tests. Haloperidol significantly reversed the antinociceptive effect of khat extract on the tail-flick test and the first phase of formalin test. These results provide strong evidence that the antinociceptive activity of khat extract is mediated via opioidergic, GABAergic, and dopaminergic pathways. The mechanism of the antinociceptive action of khat may be linked to the different types of pain generated in animal models.

A review of the neuropharmacological properties of khat

BACKGROUND

The psychostimulant khat (Catha edulis Forsk), is a herbal drug cultivated and chewed as a recreational and socializing drug in East Africa and the Arabian Peninsula for centuries. Due to increasing air transportation and the loosening of customs restrictions, it is now readily available in the Western Countries mainly used by immigrants from khat growing areas causing a concern to policy-makers.

OBJECTIVE

We conducted this review to further gain an insight to the neuropharmacological effects of khat.

METHODOLOGY

PubMed search engine with key terms 'khat' or 'qat' or 'mirra' or'qaad/jaad' or 'cathinone' was used to obtain articles relevant to khat chewing. In total 284 English written articles published from 1959 to 2007 were screened.

RESULTS

Most of the studies focused on cathinone, the postulated active psychostimulant alkaloid in khat. There were few studies which investigated the entire plant extract in either in vitro or animal studies. In the majority of the studies it was reported that both cathinone and cathine, another psychoactive constituent, have actions that are similar to those of amphetamine.

CONCLUSIONS

It seems that the well investigated khat alkaloids have many features similar to amphetamines; however there is a need for a more thorough examination of khat itself in well designed in vitro, animal and human studies with a range of comparator drugs before confirming the claim that khat is a "natural amphetamine".

Khat chewing from the pharmacological point of view: an update

Khat chewing is deeply rooted in the every day life of people living in the Horn of Africa and in South Arabia, where Catha edulis is endemic. Considered little more than an exotic habit producing just mild pharmacological effects, systematic investigations on its active principles have instead lead to the isolation and chemical characterization of cathinone, a compound structurally related to amphetamine. Three decades of intense experimental and clinical research on khat have depicted a consistently clear picture of its pharmacological and toxicological effects.

The potential adverse effects of habitual use of Catha edulis (khat)

The habit of Catha edulis Forsk (khat) chewing has prevailed for centuries among populations in the horn of Africa and the Arabian peninsula. Fresh leaves of Catha edulis are customarily chewed to attain a state of stimulation. The fact that cathinone has a closer structural similarity with amphetamine, and both share common pharmacodynamic features, led to the conclusion that cathinone is the most important active ingredient of Catha edulis, which causes the major pharmacological effects. Problems associated with repeated consumption of Catha edulis leaves are becoming evident. Literature surveys and clinical diagnostic studies revealed an association with prevalence of psychiatric morbidity. Repeated intermittent oral administration of Catha edulis to laboratory animals lead to development and expression of locomotor sensitisation. Catha edulis also leads to several peripheral effects that include increases in blood pressure and has been associated with the increased incidence of acute coronary vasospasm and myocardial infarction. Catha edulis also accounts for a number of gastrointestinal tract problems, oesophagitis, gastritis and delay intestinal absorption, as well as the development of oral keratotic white lesions at the site of chewing. Administration of Catha edulis extracts showed a deranged systemic capacity to handle oxidative radicals and induces cytotoxic effects in cells of liver and kidney, as well as induction of cell death in various human leukaemia cell lines and in peripheral human blood leukocytes.

Khat (Catha edulis)-an updated review

The habit of chewing fresh leaves and twigs of khat (Catha edulis) for their stimulating amphetamine-like effects is highly prevalent in East Africa and southwest on the Arabic peninsula. There is an extensive literature on khat providing information about its history, botany, production, geographical distribution, chemistry and pharmacology, and exploring the social, economic, medical, psychological and oral aspects related to its use. Some of this literature dates as early as the 11th century; however, most of it appeared after the first scientific description of khat by Peter Forskal in 1775. This review provides a panorama of khat and the various aspects of its use. A non-technical description of the plant chemistry and pharmacology is included. The medical, psychological and oral aspects are emphasized, and the current knowledge about the microbiological effects of khat is also presented.

Effect of khat, its constituents and restraint stress on free radical metabolism of rats

The leaves of khat (Catha edulis) are found to have stimulating and pleasurable effect and are chewed habitually by people of East Africa and Arabian Peninsula. Due to various toxic and psychostimulative effect of khat the present study was undertaken to evaluate the effect of intragastric khat alone or its major constituents flavonoids/alkaloids administration and before and after 4 h of immobilization stress in terms of alteration of free radical scavenging/metabolizing enzymes, uric acid and glucose in rats. Oral khat, alkaloid administration or 4 h restraint stress resulted in the decrease of the circulating levels of superoxide dismutase, catalase, glutathione-S-transferase and glucose with enhanced uric acid concentrations as compared with control rats. Oral treatment with flavonoid fraction of khat was found to enhance the activities of GST and catalase but showed no effect on SOD while the level of glucose was decreased and uric acid increased. The levels of these biochemical parameters were more altered in post stress khat/alkaloid treated rats than pre stress khat/alkaloid treated rats. The alteration in the levels of SOD, GST, catalase and uric acid in the pre stress khat treated rats were comparable with that of khat alone, except the level of glucose which was further decreased in pre stress khat treated rats. The flavonoid fraction of khat reduced the stress induced oxidative stress in terms of above mentioned biochemical parameters. The present study suggests that khat alone or khat/alkaloid consumption preceding stress may significantly decrease the levels of free radical metabolizing/scavenging enzymes and glucose leading to enhanced free radical concentration and toxicity of khat, which could be due to its alkaloid fraction as flavonoids were found to show antioxidant properties for oxidative stress generated during restraint stress.

Comparison of analgesic effects of khat (Catha edulis Forsk) extract, D-amphetamine and ibuprofen in mice

We have compared the analgesic properties of khat (Catha edulis Forsk) extract, amphetamine and ibuprofen in mice. After intragastric administration of the drugs analgesia was measured relative to water-injected controls using the hot-plate, the tail-flick, and abdominal-constriction tests. At the highest doses examined (amphetamine 1.8 mg kg(-1), ibuprofen 90 mg kg(-1), khat extract 1800 mg kg(-1)), all three substances produced analgesia, but the order of efficacy varied with the test. Khat and ibuprofen were significantly different from the control in the hot-plate assay at three or more time points post-injection. In the tail-flick test, khat and amphetamine were efficacious; ibuprofen means were somewhat lower but still significantly different from control. Higher doses of the drugs decreased the number of responses in the acetic acid-induced abdominal-constriction assay. We conclude that khat, like amphetamine and ibuprofen, can relieve pain. Differences in assay results may reflect differences in modes and sites of action, as well as in the type of pain generated by the chemical and thermal stimuli for nociception.

(-)-Norpseudoephedrine, a metabolite of cathinone with amphetamine-like stimulus properties, enhances the analgesic and rate decreasing effects of morphine, but inhibits its discriminative properties

Like psychomotor stimulants, a weak amphetamine-like agent, such as phenylpropanolamine, enhances the analgesic effects of morphine (MOR). Thus, it is possible that full psychomotor stimulant potency is not required to increase the analgesic action of opiates. The validity of this assumption is here tested by studying the ability of (-)-norpseudoephedrine (NPE), an enantiomer of phenylpropanolamine and a metabolite of cathinone, to influence both the analgesic effects of MOR and its discriminative stimulus properties. In mice NPE (5.6-10.0-17.0 mg/kg i.p.) did not prolong the latency to lick or to remove paws from a plate warmed at 54 degrees C. However, it significantly potentiated the analgesic effect of 3.2 mg/kg of MOR. These results were replicated in rats by use of the formalin test, which measures the numbers of hind paw flinches produced by injecting 50 microl of formalin into the dorsal surface of the paw. The higher dose of NPE (17 mg/kg) increased the effect of sub-analgesic doses of MOR (0.56 and 1.0 mg/kg). In rats trained to discriminate between 0.5 mg/kg of amphetamine and solvent in a two-lever operant behavior reinforced by water access. NPE induced a dose-dependent increment of drug lever responding from 0% at 1.0 mg/kg to 100% at 32.0 mg/kg. In contrast, NPE did not generalize for the MOR cue up to the dose of 56.0 mg/kg, which produced a substantial reduction of the response rate. However, when given in combination, NPE attenuated the discriminative effects of MOR and potentiated its inhibitory action on the response rate. These results exclude a direct action of NPE on the mu opiate system. In conclusion, NPE preserves amphetamine-like properties and these properties are probably responsible for the interaction of the drug with the analgesic and discriminative effects of MOR. Therefore, this study contradicts the assumption that the analgesic effects of MOR can be enhanced by a sympathomimetic drug that lacks significant psychostimulant actions.

Cathinone, a natural amphetamine

Cathinone is an alkaloid that has been discovered some fifteen years ago in the leaves of the khat bush. This plant grows in East Africa and in southern Arabia, and the inhabitants of these regions frequently chew khat because of its stimulating properties. Cathinone, which is S(-)-alpha-aminopropiophenone, was soon found to have a pharmacological profile closely resembling that of amphetamine; indeed, in a wide variety of in vitro and in vivo experiments it was demonstrated that cathinone shares the action of amphetamine on CNS as well as its sympathomimetic effects; thus, for example, drug-conditioned animals will not distinguish between cathinone and amphetamine. These various observations were confirmed by a clinical experiment showing that cathinone also in humans produces amphetamine-like objective and subjective effects. Finally, it was demonstrated that cathinone operates through the same mechanism as amphetamine, i.e. it acts by releasing catecholamines from presynaptic storage sites. Thus, much experimental evidence indicates that cathinone is the main psychoactive constituent of the khat leaf and that, in fact, this alkaloid is a natural amphetamine.

Pharmacological properties of the stimulant khat

The chewing of the stimulant leaf khat is a habit that is widespread in certain countries of East Africa and the Arabian peninsula. During the last decade, important progress has been made in understanding the pharmacological basis for the effects of khat. It is now known that the CNS action of this drug is due to the presence of the alkaloid cathinone, and the results of various in vitro and in vivo experiments indicate that this substance must be considered a natural amphetamine. It is the purpose of the present review to describe briefly the khat habit and to summarize the pharmacology of khat and of its active constituents.

Khat consumption: a pharmacological review

The present review deals with the considerable body of evidence gathered in the last ten years on the clinical and experimental pharmacology of Khat. Khat effects are generally agreed to be of amphetamine-like type. In particular, Khat ingestion, like amphetamine ingestion, produces sympathetic activation, anorexia, euphoria, increased intellectual efficiency and alertness. These effects are mainly mediated by phenylalkylamines, such as cathinone and cathine, because the pharmacological actions of these agents and those produced by amphetamine almost overlap. In infra-human species cathinone is an effective positive reinforcer (i.e., it maintains self-administration). However, it would be inappropriate to infer from cathinone and cathine effects assessed in animals a high potential of abuse for Khat in humans; apart from other reasons the bulk volume of Khat leaves, limits the ingestion of high quantities of the active principles. Accordingly, in habitual consumers Khat dependence is probably mild, because craving and tolerance to the sympathomimetic and neuroendocrine effects of Khat are present, but there is no definite abstinence syndrome. Therefore, in our opinion, policies restricting the use of Khat should be adopted with caution, lest they simply change the pattern of drug abuse and increase the spread of more dangerous drugs.

The role of opiate mechanisms in the development of tolerance to the anorectic effects of amphetamines

To study the role played by opiate mechanisms in the tolerance to the anorectic effects of amphetamines, the influence of chronic treatment with d,1-amphetamine (AMPH) on the effects of the selective kappa opiate agonist U50488H (U50), of morphine (MORPH) and of diazepam (DZP) on food and water intake was evaluated in rats. Since diuresis is selectively enhanced by kappa agonists, its sensitivity to chronic AMPH was also evaluated. On the first day of AMPH treatment the feeding response to U50 was depressed. On day 9, when tolerance to the anorectic effects of AMPH had developed, this response was enhanced and prolonged. U50-mediated diuresis was not increased in the AMPH group. AMPH however produced diuresis by itself and this effect may be responsible for the increased water intake that developed during chronic treatment. The administration of MORPH (on day 17), but not of DZP (on day 13), produced a similar pattern of response. Interruption of AMPH treatment brought about a slow normalization of response to U50, that appeared to be completed after 17 days. An increase in feeding response to U50 was also obtained after 14 days of cathinone administration, confirming the amphetamine-like properties of this drug. In order to evaluate the possibility that preventing sensitization of opiate mechanisms could also prevent tolerance to anorectic effects of AMPH, we chronically administered MORPH in combination with AMPH, obtaining a further reduction of feeding and an apparent slowing in tolerance development. However, such a reduction was also obtained acutely, although MORPH alone produced feeding stimulation. We suggest that opiates may both activate and inhibit feeding and that AMPH inhibits the activatory branch and works synergically with the inhibitory branch. The prolonged inhibition of the activatory branch causes its compensatory hypertrophy resulting in hypersensitivity to exogenous opiates.

Dopaminergic mediation of a behavioral effect of l-cathinone

Ten male rats were trained to discriminate between the stimulus properties of 0.6 mg/kg l-cathinone and saline in a two-lever food-motivated operant task. Once trained, rats showed a dose-dependent increase in discrimination over a dosage range of 0.15-1.2 mg/kg l-cathinone. Analysis of this dose-response relationship indicated an ED50 of 0.27 mg/kg. Pretreatment with 0.2 mg/kg of the specific dopamine blocking drug haloperidol increased this ED50 to 0.47 mg/kg and significantly decreased discriminative performance when co-administered with either 0.15, 0.3, or 0.6 mg/kg l-cathinone. Since the dose-effect curves for cathinone with and without haloperidol pre-treatment were parallel, it is suggested that l-cathinone, the active constituent in khat, produces its discriminative properties, in part, by mediation of dopaminergic neuronal systems.

Comparative discriminative stimulus properties of dl-cathinone, d-amphetamine, and cocaine in rats

The discriminative stimulus properties of dl-cathinone (dl-CAT), d-amphetamine (d-A), and cocaine (COC) were compared and effects of haloperidol pretreatment on these properties were studied in rats. The ED50's of each drug were also determined. Stimulus generalization (i.e., greater than 75% of responses occurring on the drug lever) occurred with each of the three training drugs to all three test drugs. The degree of generalization was less between d-amphetamine and dl-cathinone than between d-amphetamine and cocaine or between cocaine and dl-cathinone. No significant differences were observed among the ED50's of each test drug obtained in all three training groups. Pretreatment with haloperidol failed to alter the stimulus properties of dl-cathinone. Haloperidol administration did partially antagonize the stimulus complex induced by d-amphetamine and cocaine. It is concluded that all three agents share somewhat similar but not identical, stimulus properties. The stimulus properties of the training dose of d-amphetamine may be somewhat different from those of dl-cathinone and may be more dependent on functional dopaminergic pathways.