Miodrag Radulovacki

Proof of concept trial of dronabinol in obstructive sleep apnea

Study Objective: Animal data suggest that Δ9-TetraHydroCannabinol (Δ9THC) stabilizes autonomic output during sleep, reduces spontaneous sleep-disordered breathing, and blocks serotonin-induced exacerbation of sleep apnea. On this basis, we examined the safety, tolerability, and efficacy of dronabinol (Δ9THC), an exogenous Cannabinoid type 1 and type 2 (CB1 and CB2) receptor agonist in patients with Obstructive Sleep Apnea (OSA). Design and Setting: Proof of concept; single-center dose-escalation study of dronabinol. Participants: Seventeen adults with a baseline Apnea Hypopnea Index (AHI) ≥15/h. Baseline polysomnography (PSG) was performed after a 7-day washout of Continuous Positive Airway Pressure treatment. Intervention: Dronabinol was administered after baseline PSG, starting at 2.5 mg once daily. The dose was increased weekly, as tolerated, to 5 mg and finally to 10 mg once daily. Measurements and Results: Repeat PSG assessments were performed on nights 7, 14, and 21 of dronabinol treatment. Change in AHI (ΔAHI, mean ± SD) was significant from baseline to night 21 (−14.1 ± 17.5; p = 0.007). No degradation of sleep architecture or serious adverse events was noted. Conclusion: Dronabinol treatment is safe and well-tolerated in OSA patients at doses of 2.5–10 mg daily and significantly reduces AHI in the short-term. These findings should be confirmed in a larger study in order to identify sub-populations with OSA that may benefit from cannabimimetic pharmacologic therapy.

Role of adenosine in sleep and temperature regulation in the preoptic area of rats

We have examined the effects on sleep and brain temperature of bilateral microinjections of adenosine and adenosine analogs to the preoptic area (PO) of rats. Administration of adenosine (12.5 nmoles), a nonselective adenosine A1/A2 receptor agonist NECA (N-ethyl-carboxamido-adenosine, 1.0 nmole), and the selective adenosine A1 receptor agonist CPA (cyclopentyladenosine, 0.25, 0.5 nmoles) increased total sleep primarily through an enhancement in deep slow-wave sleep (SWS2), while adenosine also increased REM sleep. Administration of 12.5 nmoles adenosine and 0.25 nmoles CPA did not affect brain temperature, while 1.0 nmole NECA and 0.5 nmoles CPA caused a transient and prolonged hypothermia, respectively. Administration of the selective adenosine A2 receptor agonist CV-1808 (2-phenylaminoadenosine, 5, 10 nmoles) had no effect on sleep or brain temperature. The present results demonstrate a site for the central hypnotic action of adenosine, and a functional role for adenosine A1 receptors in the hypothalamus.

N6 (L-Phenylisopropyl)adenosine (L-PIA) increases slow-wave sleep (S2) and decreases wakefulness in rats

Abstract Rats implanted with electrodes for polygraphic recording were administered with L-PIA (0.115 mg/kg, i.p.), caffeine (15 mg/kg, i.p.) or L-PIA (0.115 mg/kg, i.p.) + caffeine (15 mg/kg, i.p.) and recorded for 6 h. The results show that administration of L-PIA increased S2 by 54 min suggesting that stimulation of adenosine receptors promotes deep sleep. Administration of L-PIA failed to produce the same effect in the presence of caffeine, a finding consistent with the hypothesis that the CNS stimulant effect of caffeine and other methylxanthines is due to their ability to antagonize depressant effects of endogenous adenosine.

Low-frequency oscillations of cortical oxidative metabolism in waking and sleep.

To study the changes in cortical oxidative metabolism and blood volume during behavioral state transitions, we employed reflectance spectrophotometry of the cortical cytochrome c oxidase (cyt aa3) redox state and blood volume in unanesthetized cats implanted with bilateral cortical windows and EEG electrodes. Continuous oscillations in the redox state and blood volume (∼9/min) were observed during waking and sleep. These primarily metabolic oscillations of relatively high amplitude were usually synchronous in homotopic cortical areas, and persisted during barbiturate-induced electrocortical silence. Their mean amplitude and frequency did not vary across different behavioral/EEG states, although the mean levels of cyt aa3 oxidation and blood volume during rapid eye movement (REM) sleep significantly exceeded those during waking and slow-wave sleep. These data suggest the existence of a spontaneously oscillating metabolic phenomenon in cortex that is not directly related to neuroelectric activity. A superimposed increase in cortical oxidative metabolism and blood volume occurs during REM sleep. Experimental data concerning cerebral metabolism and blood flow that are obtained by clinical methods that employ relatively long sample acquisition times should therefore be interpreted with caution.

The dose-response effects of caffeine on sleep in rats

Caffeine at doses of 0.125, 1.25, 12.5 and 25 mg/kg was administered to rats and the subsequent effects on the sleep-wake cycle were measured. The 12.5 and 25 mg/kg doses of caffeine increased wakefulness, and decreased slow wave sleep-1 (SWS1), SWS2, rapid eye movement (REM) sleep and total sleep time (P less than or equal to 0.05). The 0.125 and 1.25 mg/kg doses of caffeine increased SWS1 at the expense of SWS2 (P less than or equal to 0.05), and did not affect total sleep time in any time period measured. Adenosine or adenosine agonists have been shown to increase SWS2 at the expense of waking or SWS1 with an increase in total sleep time. The effects of caffeine on sleep reported in this study suggest that caffeine administration not only antagonizes the effects of adenosine at the receptor level, but also at the behavioral level.

Effects of chronic administration of caffeine on adenosine A1 and A2 receptors in rat brain

Chronic administration of caffeine (75 mg/kg/day) to rats for 12 days increased [3H]R-PIA binding in the cerebral cortex and cerebellum and [3H]NECA binding to high affinity receptor sites in the striatum. The results indicate that both adenosine A1 and A2 receptor subtypes possess mechanisms of adaptation to chronic caffeine treatment. In addition, adenosine A1 receptor binding shows heterogenous neuroanatomical pattern indicating that the A1 response to caffeine treatment presents regional variation in the rat brain.

Hypnotic effects of deoxycorformycin in rats.

Rats implanted with EEG and EMG electrodes were treated with deoxycoformycin (0.5 or 2.0 mg/kg, i.p.), and polygraphically recorded for 6 h. Deoxycoformycin is a potent inhibitor of adenosine deaminase and would be expected to elevate the levels of adenosine in the central nervous system. The 0.5 mg/kg dose of the drug increased REM sleep and reduced REM sleep latency while the dose of 2.0 mg/kg increased deep slow-wave sleep (S2). These results appear to be consistent with those reported previously for the adenosine analog, N6-(L-phenylisopropyl)-adenosine (L-PIA) and indicate a hypnotic role for adenosine.

REM sleep deprivation up-regulates adenosine A1 receptors

Adenosine receptor binding was determined in the brains of rats deprived of rapid eye movement (REM) sleep for 48 and 96 h using [3H]L-phenylisopropyladenosine. Adenosine A1 receptors (Bmax) were significantly increased in the cortex and corpus striatum, and this increase was sleep-specific. Endogenous adenosine was assayed in microwave-fixed brain tissue and no significant changes were found in REM-deprived rats.

Effect of tryptophan on sleep in the rat

Abstract Rats implanted with EEG and EMG electrodes were injected intraperitoneally with 30 or 120 mg/kg of l -tryptophan and a recording was made for 6 hr. The 30 mg/kg dose decreased the latency to the first slow-wave sleep (SWS) episode by 15 min (43%) and to the first rapid eye movement (REM) sleep episode by 18 min (27%). There were no changes in wakefulness. SWS or REM sleep during the 6hr of EEG recording. In contrast, the 120 mg/kg dose did not affect sleep latencies but increased wakefulness and decreased REM sleep during the second hour of EEG recording. The reduction of SWS latency produced by the 30 mg/kg tryptophan occurred at a time when the level of 5-hydroxyindoleacctic acid (5-HIAA) was elevated in the cortex and pons-medulla (i.e. 15 min post-injection). At the same time, hippocampal and cortical dopamine levels decreased while that of homovanillic acid did not change. The level of norepinephrine, also, decreased in the hippocampus. Whereas these changes in brain calecholamines were not observed 45 min after tryptophan administration, there was an elevation of 5-hydroxytryptamine in the pons-medulla and cortex as well as of 5-HIAA in the pons-medulla and hippocampus. Present data suggest that the hypnotic effect of tryptophan may involve the normal sleep mechanism, since similar neurochemical findings were reported during natural SWS. However, the effect may be limited to a certain dose range because a high dose produced waking rather than sleep.

Effect of ondansetron on moderate obstructive sleep apnoea, a single night, placebo-controlled trial.

There has been conflicting data on the part played by 5-HT neurotransmission pathways in the pathogenesis of obstructive sleep apnoea (OSA) (Horner 2000). 5-HT controls some aspects of the hypoglossal neurones supplying genioglossus, and is likely to stimulate upper airway muscle activity (Jelev et al. 2001). Reduction in upper airway tone during non-rapid eye movement (NREM) sleep is thought to result from withdrawal of 5-HT activity, but the mechanism of further reduced upper airway muscle activity during rapid eye movement (REM) sleep is far from clear. In addition stimulation of vagal afferent C fibres in anaesthetized cats can produce central apnoeas (Vardhan et al. 1993) and this effect can be replicated by stimulation of the nodose ganglion with 5-HT (Sutton 1981). The administration of 5-HT3 receptor antagonists prevents these apnoeas (Yoshioka et al. 1992). In rats ondansetron, a 5-HT3 antagonist, also blocks this peripherally mediated central apnoea in REM sleep (Carley and Radulovacki 1999; Radulovacki et al. 1998). Recently in the journal Sleep, it has been shown in a single dose study that ondansetron influences apnoea activity in English bulldogs with OSA, mainly during REM sleep, but also to some extent in NREM sleep (Veasey et al. 2001). It is unclear whether this is due to purely peripheral effects, or additional central effects. This present study was designed to assess whether this effect of a single dose of ondansetron in the bulldog model of OSA could be replicated in humans with OSA. We studied subjects with moderate sleep apnoea, as we hypothesized that in these subjects it would be easier to influence their OSA, in comparison with patients with severe disease where pharyngeal collapsing forces are greatest. Ten patients with symptomatic OSA awaiting nasal continuous positive air pressure (CPAP) were asked to take part in this study if they had moderate disease (>4% SaO2 dips h )1 of between 10 and 40), and lived in or near Oxford (for reasons of convenience). The diagnostic sleep studies were performed using a five-channel respiratory polysomnography system, oximetry, heart rate, body movement, snoring and pulse transit time (providing indices of arousal and respiratory effort; Visi-Laboratory, Stowood Scientific Systems, Oxford, UK). The experimental sleep studies were carried out with conventional polysomnography according to standard criteria (Anonymous 1999) (Embla Medical, Flaga, Iceland). The tracings were analysed to provided separate values for apnoeas per hour, hypopnoeas per hour (HI), combined (AHI), and >4% SaO2 desaturations per hour (ODI). Patients were admitted at 20:00 h for overnight studies on two occasions a week apart. They were asked to refrain from alcohol, sedatives or coffee on the day of admission. All other drugs were allowed and they were asked not to change any regular medications during the week between studies. One hour before the patients chosen bedtimes they were randomized to receive either ondansetron 16 mg or matching placebo. Results from the two nights were compared using paired t-tests. This study was passed by the Oxfordshire Clinical Research Ethics Committee (application no. C01.005) who allowed a maximum oral dose of 16 mg. All 10 patients (one woman) completed the protocol and reported no side-effects. The patients had a mean (SD) age of 53.1 (11.4), mean body mass index of 33.7 (4.9) and their AHI values ranged from 17 to 62. The results are shown in the Table 1. The sleep structure was chaotic, as would be expected, and there were no significant differences between the two groups for percentage or absolute amounts of stages 1 and 2, or 3 and 4, or REM. In addition, there were no significant differences in respiratory indices between the two groups when expressed according to the individual sleep stages. This study has found no effect of ondansetron on moderate OSA, contrary to that found in the English bulldog with mild OSA (Veasey et al. 2001). This could be for several reasons. First, the dose of ondansetron we administered was significantly lower than that used in the bulldogs, 20 and 40 mg, which approximated to 1 and 2 mg kg, respectively. In our study, a dose of 16 mg approximated to 0.15 mg kg. We used this dose as it is the highest recommended single oral dose for nausea control, according to its licensed indication. Secondly, it could be that a longer period of dosing would be appropriate, as there is some evidence in patients with bulimia nervosa that the therapeutic effect may take up to 4 weeks to appear (Faris et al. 2000). Alternatively, it may be that the study was too under-powered to demonstrate an effect. However, the correlation coefficients between night 1 and night 2 for AI, AHI, HI and ODI were 0.64, 0.88, 0.27 and Correspondence: John Stradling, Oxford Centre for Respiratory Medicine, Oxford University, Churchill Hospital, Oxford, OX3 7LJ, UK. Tel.: 44 1865225236; fax: 44 1865225221; e-mail: john.stradling@orh.nhs.uk J. Sleep Res. (2003) 12, 169–170