TL neuro

July 19, 2019

Cannabidiol by vapor inhalation in rats

Filed under: Cannabidiol, Cannabis, E-cigarettes, Tobacco/Nicotine, Vapor Inhalation — mtaffe @ 2:37 pm

Cannabidiol is increasingly popular, occurring in a dizzying array of products in a highly unregulated retail market. This includes creams, oils, lotions, capsules and e-cigarette liquids, among many other items. A simple search for CBD on google will give you a taste of what I mean, if this is new to you. Just about every single senior person I talk to, it seems, is using CBD or knows another person who is using CBD  for various ailments.

The following has just been accepted for publication:

Javadi-Paydar, M.,  Creehan, K.M., Kerr, T.M.  and Taffe, M.A. Vapor inhalation of cannabidiol (CBD) in rats.  Pharmacol Biochem Behav, 2019 Jul 20:172741. doi: 10.1016/j.pbb.2019.172741. [ Publisher Site ][ PubMed ]

Figure 1: This figure has been adapted from Taffe et al. 2015. Click to enlarge.

We have been interested in studying the effects of CBD ever since reading a paper [Morgan et al., 2010] that appeared to show that the presence of CBD in cannabis protected users against the memory impairing effects of acute THC intoxication, subsequent to smoking their preferred cannabis. This led to our interest in the potentially interactive effects of CBD and THC and, in particular, tests of the hypothesis that CBD would reduce the effects of THC. Our initial papers on this were Wright et al 2013 and Taffe et al 2015. Of primary relevance for the discussion of our new work, the latter paper showed that CBD did not alter the body temperature (see Figure 1 C, D; blue bars) or activity of rats when injected at doses of 30 or 60 mg/kg, i.p.. Our new work confirms our prior finding that this may be due to the route of administration since, when male or female Wistar rats experience CBD by vapor inhalation, their body temperature does go down, albeit not as severely as when exposed to THC [Javadi-Paydar et al, 2018].

This finding required some follow-up, extraordinary claims requiring extraordinary evidence and all that. Although in the Taffe et al 2015 paper, CBD did appear to increase the magnitude of the hypothermia associated with THC when each were injected, i.p., (red trace and summary bars in Figure 1) there are data suggesting that this may be due to metobolic interference whereby CBD merely prolongs the activity of THC. Another thing that was slightly strange was the fact we observed that CBD reduces temperature of Wistar rats. We used Sprague-Dawley rats for the Taffe et al 2015 paper because initial pilot experiments suggested that perhaps Wistar (male) rats were less sensitive to the body temperature lowering effects of THC [a follow up to that is available in a pre-print]. Yet Javadi-Paydar et al (2018) found effects of vaporized CBD in male and female Wistar rats. Perhaps this is due to the difference between CB1 receptor mediated effects and serotonin 1a (5-HT1a) receptor mediated effects. There is growing evidence that CBD works in part by activating 5-HT1a receptors, and activation of this receptor (e.g., by injecting the agonist 8-OH-DPAT) drops the body temperature of rats precipitously. As an example we had published a figure on this as a positive control in the Wright et al 2012 paper focused on the activity of the cathinone mephedrone [blog post summary]. To further complicate matters, the response of male Wistar rats to 8-OH-DPAT in that paper seemed to be slightly greater than the response of male Sprague-Dawley rats.

Figure 2: Plasma CBD in male and female Wistar rats after vapor inhalation (top panels) or injection (bottom panels).Click to enlarge.

An earlier version of this manuscript was posted as a pre-print on June 04, 2019, and updated with a version almost identical to the final submitted manuscript on Jul 18, 2019.

The first critical thing in this new paper was to get a point of reference for the doses the animals were getting through vaporized CBD versus i.p. injection. This figure shows the plasma levels experienced at the end of vapor sessions are within the range of plasma levels observed 35 minutes after an injection. This was in male and female Wistar rats, making it a follow-up to the thermoregulatory data in the Javadi-Paydar et al (2018) paper. One of the major ways that we control dose with our inhalation model is to alter the concentration of the drug in the e-liquid vehicle (we use propylene glycol; PG), while holding other parameter fixed. So for CBD we have used concentrations of 100 and 400 mg per mL of the PG. Now admittedly we have only published the effects of 30 mg/kg CBD when injected, at the lower end of the dose range. But based on some pilot work I doubt that we’ll find out that lower dose of CBD are causing hypothermia when injected- but it could still be about dose. Our time-point here for injection was designed for comparison with the inhalation model but levels were likely much higher at 5 minutes after injection whereas they were increasing essentially linearly across the inhalation interval. Nevertheless, we are clearly not getting much, much higher plasma loads of CBD via inhalation, at least not in the blood.

The next step for this paper was to replicate the body temperature effect, which we did in a group of male Wistar rats.

Figure 3: Temperature responses to vapor inhalation of CBD and nicotine in male Sprague-Dawley rats. Open and grey symbols depict statistical differences summarized in the manuscript. Adapted from Javadi-Paydar et al 2019. Click to enlarge.

We then went on to evaluate the effect of CBD inhalation on body temperature in male Sprague-Dawley rats and found a similar (perhaps slightly increased relative to the Wistar male rats) degree of hypothermia under identical vaping conditions.

Figure 3 shows that CBD concentration-dependent reductions in body temperature are found in male Sprague-Dawley rats (blue data series), thereby replicating and extending to an additional rat strain. The next experiment showed that the effect of CBD (at the 100 mg/mL concentration) is attenuated when animals are pre-treated with the 5-HT1a antagonist WAY 100,635. This shows that the 5-HT1a receptor is very likely involved in the hypothermic response to vaporized CBD, further adding to the growing evidence that CBD acts at this receptor.

You may have noticed that the top two panels of Figure 3 include a nicotine inhalation condition and a CBD + nicotine inhalation condition. There are a couple of reasons for this. Most generally, CBD has been shown to attenuate relapse to alcohol and cocaine self-administration in rats and may reduce the salience of cigarette-associated cues in humans. Reviews of the potential of CBD as an anti-drug abuse treatment can be found here and here. The second rationale is that human substance users often use more than one drug at a time. THC and CBD co-occur in cannabis. People frequently use cannabis along with tobacco and/or alcohol. Our work in Javadi-Paydar et al 2019 examined potential interactive effects of THC with nicotine thus it was an obvious followup to see if CBD interacted with nicotine. As you can see in Figure 3, the effect of nicotine alone on body temperature is not obvious in this group (although it did enhance locomotor activity). Nicotine did, however, increase the effect of CBD when the two were co-administered. Interestingly CBD also suppressed the locomotor activating effects of vaporized nicotine inhalation in this study. So the combined effect appears to be independent, not interactive- i.e., an opposition when the two independent drug effects are in the opposite direction (locomotor activity) and add together when the two independent drug effects are in the same direction (see Javadi-Paydar et al 2019 for more on this interactive drug logic and on the hypothermia caused by nicotine inhalation).

CBD is often described as non-psychoactive constituent of cannabis because it does not appear to have the same dramatic subjective properties as delta-9-tetrahydrocannabinol. Also because there are a lot of studies where it does not appear to do much to a rodent when administered by itself. There are exceptions, but I think a fair take away is that often enough it has been found inactive. This may very well be due to investigating CBD in assays that are tuned to detect THC-like effects that are presumably mediated by the CB1 or CB2 receptors. Our thermoregulatory assay, fortunately, is sensitive to both CB1 and 5-HT1a agonists. It may also be the case that the route of administration is a fundamental contributor to observing or not observing effects of CBD in a rat. There are several pharmacokinetic possibilities that may explain this. Our plasma data are fairly limited in a temporal sense and we don’t know from plasma levels what the kinetics look like in the brain. It could be that there is a much different blood/brain ratio associated with the two routes of administration. It may be that the speed of initial brain entry of a threshold amount of drug varies as well. Additional work will be necessary to full determine how the route of administration alters the effects of CBD in rats and how this might translate to the human condition.



July 18, 2015

Prevalence of E-cigarette use in 8th-12th graders

Filed under: E-cigarettes, Tobacco/Nicotine, Vape inhalation — mtaffe @ 5:47 pm

The Monitoring the Future survey added electronic cigarettes to its survey for the first time in 2014. The summary tables and figures and full monographs are available for the clicking.

Results show show that 17.1% of high school seniors reported using an E-cigarette at least once in the past 30 days. Rates were almost as high for 10th grade students (16.2%) and somewhat lower for 8th graders (8.7%).

To put this in perspective the 30 day prevalence for cigarettes was 13.6% for 12th graders, 7.2% for 10th and 4.0% for 8th graders. So twice as many 8th and 10th grade students have at least tried an E-cigarette as have tried a regular cigarette.

6.8% of 12th grade students report smoking one or more cigarettes per day. The rate for 10th graders is only 3.3% and 1.4% for 8th graders. One way to put together the E-cigarette/cigarette ratios from the three grade ranges is to observe that daily smoking is more likely with older students. These individuals may either have less need to resort to E-cigarettes for availability reasons or they may reflect the fact that E-cigarettes may not produce good nicotine levels until smokers are motivated to learn to use them.

For those that are unfamiliar with drug use rates in these grade levels, E-cigarette use is high. The percentage of respondents who used any illicit drug other than marijuana in the past 30 days was 7.7%, 5.6% and 3.3% for 12th, 10th and 8th graders respectively. Marijuana rates were 21.2%, 16.6% and 6.5%. The 30 day rates for 12th graders for individual drugs of interest are much lower: 1.0% cocaine or LSD, 1.4% Ecstasy, 0.4% heroin or PCP, 6.4% for any prescription drug.

Since this was only added to the MtF survey recently, we cannot make much from a single point estimate of E-cigarette use. Maybe this was the peak of a new fad, maybe the beginning of a sustained trend.

What we do know is that substantial numbers of adolescents are sampling the use of these devices.

June 30, 2015

Smokers have to adapt to e-cigarettes to maximize nicotine yield

Filed under: Cannabis, Public Health, Tobacco/Nicotine — mtaffe @ 1:20 pm

One of the reasons that smoked/inhaled drug delivery is highly associated with addiction is that this route allows humans to exquisitely titrate their dosing. Thus for drugs like nicotine that become aversive at higher doses, smoking tobacco in several punctate inhalations over a short interval of time permits the user to avoid unpleasant dose levels.

This contrasts, for example, with buccal administration. If anyone recalls sampling chewing tobacco as a youth, you will understand what I mean. The relatively slowed onset and the larger available dose of the wad of tobacco or snuff packed up against the gums is frequently associated with severe nausea in the naive user.

A similar situation obtains with cannabis for which smoking has been the preferred route of administration. There is, however, relatively familiar use of cannabis via the oral route- think pot brownies. Increasingly, the medical marijuana entities are also selling a variety of edibles for oral administration of marijuana. Again, it is relatively common for naive consumers of edible products to overdose because the subjective effects hit long after a ballistic, irreversible drug administration has been accomplished.

A recent paper on the use of e-cigarettes for cannabis delivery (Etter, 2015) piqued my interest because it suggested that experienced cannabis smokers did not really like the e-cigarette delivery all that much.

Presentations at the recent CPDD meeting referred to the fact that nicotine seekers who use e-cigarette devices have to learn to adjust their inhalation behavior relative to their tobacco smoking. This is described in a paper that I located:

Farsalinos KE, Spyrou A, Stefopoulos C, Tsimopoulou K, Kourkoveli P, Tsiapras D, Kyrzopoulos S, Poulas K, Voudris V. Nicotine absorption from electronic cigarette use: comparison between experienced consumers (vapers) and naïve users (smokers). Sci Rep. 2015 Jun 17;5:11269. doi: 10.1038/srep11269.

Farsalinos15-nicotine-experiencedvapersThe authors examined e-cigarette (EC) use in groups of ex-smokers who had quit and had been using ECs for at least a month and another group of smokers who were not EC users (available for free at PMC here). Subjects were asked to take 10 puffs from a standardized EC device in the first five minutes and then use it at their own discretion for another hour. The study sampled their blood for nicotine levels that were achieved across the study and the key figure from this paper is depicted here. As you can see, the experienced EC users (vapers) reached higher plasma nicotine levels than did the EC-inexperienced smokers. Each group averaged the same number of puffs, around 85-90, but the experience vapers took longer puffs (3.5 vs 2.3 seconds).

The simple interpretation is that if nicotine amount is a function of vapor cloud volume, and delivery across the lungs depends on retention time within the lungs, then longer puffs would result in greater nicotine delivery. The slightly more complex issue, mentioned at the CPDD annual meeting but not addressed in this paper, is that the rate at which a user inhales can be important. The idea is that if you pull too much of the EC vehicle across the heating element it can cool the element, resulting in lower nicotine yield.

Bottom line, EC inhalation for maximum nicotine yield and tobacco smoke inhalation for maximum nicotine yield may require a different inhalation approach.

This then reminds us that when ECs are adapted for crude cannabis extracts or even other drugs, it will require users to learn to adapt their behavior for idealized drug yield before we truly understand the risks. An initial report like Etter (2015) showing cannabis users don’t like to use ECs to deliver THC as well as they like to smoke cannabis need to be viewed in that light

June 28, 2013

RFAs for Tobacco Control “Regulatory Science”

Filed under: NIH, Tobacco/Nicotine — Tags: , — mtaffe @ 10:33 am

One of the more interesting symposia at the recent CPDD meeting focused on a new drive by the FDA and NIH to respond to the 2009 Family Smoking Prevention and Tobacco Control Act.

In short, the FDA is seeking to generate scientific information to guide and justify any steps they take to regulate tobacco products in the future. The money is apparently coming from taxes on said products so this will not involve any new appropriates to the NIH…from what I understood the NIH will simply be administering the research process.

There are now a flurry of RFAs:

are the standard R-mechanism ones.

For the R01s, due dates are January 15, 2014; June 17, 2014, January 16, 2015 and they anticipate devoting $11 Million to 20 awards.

It gets even better since they’ve thrown up some RFAs for K mechanisms

including the K99/R00. Serious stuff.

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