Is 2-Hydroxypropyl-ß-cyclodextrin a Suitable Carrier for Central Administration of Δ9 -Tetrahydrocannabinol? Preclinical Evidence.

Preclinical Research Δ9 -Tetrahydrocannabinol (THC) is a hydrophobic compound that has a potent antinociceptive effect in animals after intrathecal (IT) or intracerebroventricular (ICV) administration. The lack of a suitable solvent precludes its IT administration in humans. 2-Hydroxypropyl-ß-cyclodextrin (HPßCD) increases the water solubility of hydrophobic drugs and is approved for IT administration in humans. To investigate whether HPßCD might be a suitable carrier for ICV administration of THC in rats, two formulations containing THC complexed with HPßCD (30 and 135 µg of THC per animal) and vehicle were administered to Wistar rats. The antinociceptive effect (using the tail flick test), locomotor activity, and body temperature were evaluated. ICV injection of 135 µg of THC/HPßCD complex increased tail flick latency, reduced locomotor activity, and had a dual effect on body temperature. The 30 µg THC/HPßCD formulation only produced a hyperthermic effect. All animals appeared healthy, with no difference between the groups. These results were similar to those obtained in other preclinical studies in which THC was administered centrally using solvents that are unsuitable for IT administration in humans because of their toxicity. Our findings suggest that HPßCD may be a useful carrier for IT administration of THC in humans. Drug Dev Res 78 : 411-419, 2017. © 2017 Wiley Periodicals, Inc.

Sudden death in epilepsy: an experimental animal model.

INTRODUCTION: The physiopathogenetic mechanisms possibly involved in sudden unexplained epileptic death (SUDEP), were investigated in the hemispherectomized rat. METHODS: For this purpose, paroxysmal activity, vagal nerve firing, systemic blood pressure (BP), pulmonary artery pressure, and ECG were simultaneously recorded in an experimental animal model of epilepsy. Recordings were performed in basal conditions and during paroxysmal activity induced by topical application of penicillin-G at hypothalamic and mesencephalic level. During the experiment were also performed hemogas analysis and at end, samples of lung tissue were processed for histology. RESULTS: Activation of hypothalamic (HEF) and mesencephalic (MEF) epileptic foci induced a significant increase of spontaneous vagal nerve firing that was strictly correlated to ECG impairments and hypotension. When paroxysmal activity extinguished, vagal nerve activity and cardiovascular parameters returned to basal conditions. However, in 25% of the animals, co-activation of HEF and MEF always triggered a vagal hypertone which was temporally correlated to cardiac arrhythmias, but also to hyperkalemia, acidosis, pulmonary hypertension and to animal death. Histological control in lungs of deceased animals showed an alveolar and perivessel oedema with an oedematous infiltration in the alveolar and bronchial spaces and mucous secretion. During ictal activity, comparison between survived and deceased animals showed significant differences in the incidence of ECG impairment of pulmonary artery pressures, pO2, and pCO2 pressures, and [K+], [HCO3-], and [pH], concentrations. DISCUSSION: A possible explanation of the above observations is discussed in relationship to SUDEP physiopathogenesis.

Autonomic nervous system activity and life threatening arrhythmias in experimental epilepsy.

In the present study the possible derangement of the autonomic system and its influence in life threatening arrhythmias were analysed during paroxysmal activity. In hemispherectomized rats a paroxysmal activation of the hypothalamic and mesencephalic cardioarrhythmogenic triggers was performed by topical application of penicillin-G. Blood gas parameters and electrical activity of the thalamus, hypothalamus, vagal nerve fibre, ECG and arterial blood pressure were simultaneously monitored in basal conditions and repeated after the appearance of paroxysmal activity. Temporal correlation analysis was carried out. Results showed that during activation of these triggers, the spontaneous vagal nerve fibre activity significantly increased and triggered the appearance of cardiac arrhythmias which could become life threatening and induce animal death when blood gas and electrolytic parameters were simultaneously impaired. These experiments suggest that fatal evolution of the heart impairment is related not only to an autonomic cardiac trigger, but also to a concomitant metabolic derangement, which most likely shares the same autonomic origin.

Epileptic discharge of cortical, subcortical and spinal neurons in penicillin induced experimental epilepsy.

The sensitivity and electrophysiological patterns of paroxysmal activity induced in different brain structures by topical application of penicillin-G were evaluated in the rat. Recordings were carried out in five groups of animals, in telencephalon, diencephalon, mesencephalon, rombencephalon and spinal cords. The following analysis were carried out: frequency distribution histograms, latency and time course duration of paroxysmal activity, duration and amplitude of epileptic bursts. The results obtained showed that the nervous structures tested with penicillin-G had a different epileptogenic sensitivity and response pattern which significantly changed along the cerebral cortex-spinal cord axis. The highest epileptic sensitivity was observed in somatosensory cortex (SI) at 500-600 microns depth; in the other cortical layers, a significant lenghtening in latency was observed. Among the other structures, the spinal cord seemed to be the most sensitive target to the epileptogenic action of penicillin-G, whereas in the remaining structures, sensitivity significantly decreased in rostro-caudal direction. As far as the features of the paroxysmal activity are concerned, significant differences among tested structures were observed. In particular, within the SI cortex, the main differences were represented by the gradual increase in burst frequency and voltage from the surface to the IVth layer and by their subsequent decrease in deeper layers (V-VI). In the diencephalon, the paroxysmal activity was similar to that observed in more superficial and deeper cortical layers even though epileptic bursts showed a lower amplitude. Mesencephalon and rombencephalon displayed a paroxysmal activity with a distinctive feature, characterized by long lasting bursts of low amplitude, although bulbar outbursts showed a shorter duration than the mesencephalic ones. In the spinal cord, the epileptiform activity displayed a different paroxysmal pattern, characterized by the longest duration and the highest amplitude. The different sensitivities of the investigated brain structures to penicillin-G and the characteristics of the induced paroxysmal activity have been extensively discussed.

The brainstem cardioarrhythmogenic triggers and their possible role in sudden epileptic death.

The cardiovascular effects of simultaneous activation of hypothalamic and mesencephalic cardioarrhythmogenic triggers were studied in hemispherectomized rats. Paroxysmal activity of hypothalamic neurons (HEF), elicited by topical application of penicillin G on the thalamus, triggered short-lasting bradyarrhythmic episodes, up to a maximum of 6 s, and alterations in repolarization. In the hypothalamic neurons, an additional penicillin G epileptic focus at mesencephalic level (MEF) induced the enhancement of paroxysmal activity by a recruitment of new units and potentiation of their background activity. HEF+MEF triggered second-degree 2:1-8:1 atrioventricular (A-V) blocks, impairment of the A-V conduction, alterations in the recovery phase and bundle branch blocks. After HEF, the arterial blood pressure decreased by 4-6%. HEF+MEF induced a further reduction of 17% in systolic pressure only. It is possible that the enhancement of the HEF following MEF could depend on MEF spreading upward. The HEF, in turn, by spreading downward could influence the MEF and so activate, between HEF and MEF, a circuitry with reciprocal co-excitation that could explain the more serious cardiovascular alterations observed during HEF+MEF compared with those observed during HEF only or during MEF only. However, this cardiovascular impairment, which must be neurogenic in origin as it was observed in animals with normal acid-base and blood parameter values, did not induce heart death. Thus, additional concomitances must be considered, such as metabolic derangement which can occur during seizures, to explain sudden death in epileptic patients. Some aspects of metabolic complications in cardiac activity during epilepsy are also discussed.