Differential effects of di-isopropylfluorophosphate poisoning and its treatment on opioid antinociception in the mouse

Fabrication of Tip-Dissolving Microneedles for Transdermal Drug Delivery of Meloxicam

Dissolving microneedles (MNs) offered a simple, minimally invasive method for meloxicam (MX) delivery to the skin. However, the fabrication of dissolving MNs still faced some challenges, such as significant time consumption, loss of drug activity, and difficulty in regulating MN drug loading. To address these issues, we developed the tip-dissolving (TD) MNs. Several kinds of drugs were encapsulated successfully, and the quantity of MX ranged from 37.23 ± 8.40 to 332.53 ± 13.37 μg was precisely controlled. The effects of fabrication process on biomacromolecules stability were studied, and it was found that tyrosinase kept 90.4% activity during the fabrication process. The whole process for the fabrication of MNs only takes approximately 1 h. In order to further evaluate the potential of the TD MNs, MX TD MNs were prepared for in vitro release experiments, in vivo release experiments, safety evaluation, pharmacokinetic studies, and pharmacodynamic studies. The results demonstrated that MX TD MNs offered several advantages, including rapid release of the encapsulated drug (91.72% within 30 min), efficient drug delivery to skin (79.18%), no obvious skin irritation, decent relative bioavailability (122.3%), and strong anti-inflammatory and analgesic effects. Based on these results, we envisage that the TD MNs have promising potential for transdermal drug delivery of MX.

Further studies on the antinociceptive effects of delta 6-THC-7-oic acid

The antinociceptive effects of delta 6-THC-7-oic (THC-7-oic) acid have been investigated further with particular regard to the influence of certain experimental parameters in the hot plate test. These included the degree of the thermal stimulus, the nature of the vehicle and a possible role for copper in the response. A temperature effect similar to that seen with nonsteroidalantiinflammatory drugs (NSAIDs) was observed, 55 degrees produced observable antinociception, however, at a surface temperature of 58 degrees C no drug effect was seen. Non-aqeous vehicles such as peanut oil increased the potency of THC-7-oic acid. Finally, the substitution of purified water for tap water reduced the drug response which could be partially restored by adding copper to the purified drinking water. An increase in the inhibitory effect when copper was added was also seen in vitro in a cell culture model where the acid reduced prostaglandin synthesis induced by THC. Our findings suggest that THC-7-oic acid probably acts by mechanisms similar to the NSAIDs and that the above mentioned experimental conditions can greatly influence the outcome of studies with this agent.

Interactions between anticholinesterase poisoning and opioid analgesia and locomotion in mice

Interactions between anticholinesterases and opioid drugs on antinociception and locomotor behaviour have been studied in the mouse. The anticholinesterase di-isopropylfluorophosphate (DFP) (1 mg/kg), pyridostigmine (1 mg/kg) and neostigmine (200 micrograms/kg) or drugs used to treat anticholinesterase poisoning (atropine, pralidoxime and diazepam) were not antinociceptive. DFP, at doses which produced marked neurotoxicity (2 mg/kg), produced antinociception which was not mediated by opioid receptors. The antinociceptive effects of alfentanil, but not fentanyl or morphine, were potentiated by DFP, whereas pyridostigmine and neostigmine were without effect. The potentiating activity of DFP was unaffected by atropine, pralidoxime and diazepam. DFP (1 mg/kg) produced a small degree of hypolocomotion whilst atropine and pralidoxime produced marked hyperlocomotion. Diazepam alone and with DFP, atropine, pralidoxime or opioid drugs produced marked motor incapacitation. Hyperlocomotion induced by morphine and alfentanil was reduced by DFP but fentanyl hyperlocomotion was unaffected. Treatment of DFP toxicity with atropine and pralidoxime reversed the effects on alfentanil locomotion but failed to alter DFP's action upon morphine or fentanyl locomotion. Atropine and pralidoxime treatment alone did not affect fentanyl hyperlocomotion, attenuated alfentanil hyperlocomotion and produced marked hypolocomotion in morphine-treated mice. Opioids and anticholinesterases do not exhibit common interactions and their effects are dependent on both opioid, anticholinesterase and the behaviour studied.

Differential displacement of opioids from plasma protein binding sites by di-isopropylfluorophosphate in the mouse

Di-isopropylfluorophosphate (DFP) displaced the opioid drug, alfentanil, from plasma proteins in-vivo and in-vitro in mice but was without effect on the structurally related compound, fentanyl. This action probably accounts for the enhanced entry of alfentanil into the brain of DFP-treated animals and its enhanced antinociceptive activity.

A modified hot-plate test sensitive to mild analgesics

The present study compares a modified hot-plate test in which the temperature is slowly increased from non-noxious levels with a standard constant temperature hot-plate test. In both tests, hindpaw lick was found to be a more reliable criterion response than forepaw lick, and was employed throughout the experiments. In the constant temperature hot-plate test, 1-min exposure to the test apparatus the day before testing significantly reduced the response latencies of both rats and mice. No effect of pre-exposure was found in the increasing temperature test. In both tests and in both species, sessions of repeated testing were conducted with only insignificant alterations in responsiveness between trials. In both rats and mice, dose-related increases in response temperature were obtained in the increasing temperature hot-plate test after administration of morphine, paracetamol and acetylsalicylic acid, whereas only morphine had consistent effects in the constant temperature test. Thus, the increasing temperature hot-plate is a useful analgesimetric test in both rats and mice, superior to the conventional hot-plate test with regard to consistency of results and sensitivity to non-narcotic analgesics.

Different effects of di-isopropylfluorophosphate on the entry of opioids into mouse brain

Di-isopropylfluorophosphate (DFP) potentiates the antinociceptive activity of alfentanil but has no effect on the activity of morphine or fentanyl. We have studied the effect of DFP on the distribution of these three opioids in the brain. Distribution studies were carried out using 3H-labelled opioids administered subcutaneously to mice. Animals were killed at times of peak antinociceptive activity and 3H-opioid measured in plasma and in eight brain regions. DFP pretreatment (1 mg kg-1) caused a significant increase in the brain:plasma ratio of alfentanil in all brain regions but had no effect on brain:plasma ratios for morphine or fentanyl. The enhanced entry of alfentanil into the brain of DFP-treated mice probably accounts for the increased antinociception observed with this opioid. This drug interaction appears to be opioid specific.

Assessment of the hot-plate antinociceptive test in mice. A new method for the statistical treatment of graded data

The use of graded data from hot-plate antinociceptive tests is complicated by the problem of how to treat responses that are greater than the cut-off time. This paper describes a statistical procedure for analysis of antinociceptive data that circumvents this problem. The method is based upon the likelihood function and the data is assumed to follow a Weibull distribution. The technique can be implemented with the use of a computer and provides a more comprehensive assessment of antinociceptive data.