Reflections on the OECD guidelines for in vitro skin absorption studies.

At the 8th conference of Occupational and Environmental Exposure of the Skin to Chemicals (OEESC) (16-18 September 2019) in Dublin, Ireland, several researchers performing skin permeation assays convened to discuss in vitro skin permeability experiments. We, along with other colleagues, all of us hands-on skin permeation researchers, present here the results from our discussions on the available OECD guidelines. The discussions were especially focused on three OECD skin absorption documents, including a recent revision of one: i) OECD Guidance Document 28 (GD28) for the conduct of skin absorption studies (OECD, 2004), ii) Test Guideline 428 (TGD428) for measuring skin absorption of chemical in vitro (OECD, 2004), and iii) OECD Guidance Notes 156 (GN156) on dermal absorption issued in 2011 (OECD, 2011). GN156 (OECD, 2019) is currently under review but not finalized. A mutual concern was that these guidance documents do not comprehensively address methodological issues or the performance of the test, which might be partially due to the years needed to finalize and update OECD documents with new skin research evidence. Here, we summarize the numerous factors that can influence skin permeation and its measurement, and where guidance on several of these are omitted and often not discussed in published articles. We propose several improvements of these guidelines, which would contribute in harmonizing future in vitro skin permeation experiments.

Differences in locomotor response to an inescapable novel environment predict sensitivity to aversive effects of amphetamine.

Differences in locomotor response to an inescapable novel environment have previously been shown to predict sensitivity to amphetamine reward, where high responders (HR), compared to low responders (LR), showed greater initial sensitivity to amphetamine self-administration. The present experiments sought to extend these findings and assessed the relationship between locomotor response to an inescapable novel environment and conditioned taste aversion (CTA) with amphetamine and lithium chloride (LiCl). Male Sprague-Dawley rats were tested for their locomotor response to an inescapable novel environment and divided into high (HR) or low (LR) responders, based on whether their locomotor scores were above or below the median activity level of the subject sample. After several days, the animals were tested in a CTA procedure and conditioned with either amphetamine or lithium chloride. Compared to HR rats, LR rats showed greater sensitivity to amphetamine CTA at the doses tested. In contrast, the results with LiCl showed no relationship between locomotor response to an inescapable novel environment and CTA. Taken together, the present results suggest that LR, compared to HR, rats show less sensitivity to the rewarding effects of amphetamine because they are more sensitive to aversive effects of amphetamine, as reflected in CTA. In contrast, HR rats display less sensitivity to aversive effects of amphetamine, which may explain their greater propensity to self-administer amphetamine.

The sharing of injecting paraphernalia by intravenous drug users (IDUs) within a Worcestershire cohort, with specific reference to water and filters.

Britain continues to have a drug misuse health strategy that is HIV led. Because of this, little attention has been paid to other blood-borne viruses such as hepatitis. Moreover, while the provision of needle exchange schemes has been particularly successful in containing the spread of HIV, they have had less impact on the prevalence of hepatitis within IDU cohorts. Thus, it is necessary to understand more about the potential pathways through which the hepatitis viruses can be transmitted. One way of achieving this is to assess the propensity of IDUs to share other items of injecting paraphernalia such as water and filters. In addition, it is useful to gauge the level of opinion with respect to health hazards associated with sharing such items, amongst injecting drug users. This study reports on a small pilot project initiated to assess the degree of sharing of filters and water among 40 needle exchange service users in Worcestershire. Results based on questionnaires show that sharing of water and filters is very high within the sample group. Indeed, only 10% of clients reported never sharing either water or filters. The study also demonstrates that although injectors are aware of the health risks associated with sharing (including hepatitis transmission), they continue to participate in high risk sharing activities. Moreover, the majority of IDUs questioned have a mis-conception with respect to the most hygienic sources of water for injecting. For example, only 10% consider sterile water to be the most hygienic source for injecting, with >70% considering tap water in one form or another to be safe. The study is important because it highlights the value of providing sterile water and filters to IDUs to meet their basic and fundamental needs. It is hoped that the findings from this small project will have a wider transferability to other IDU cohorts throughout the UK and beyond.

Augmentation of corticosterone release by means of a caffeine-ethanol interaction in rats.

We examined whether the acute treatment with caffeine delivered before an ethanol injection would augment plasma corticosterone (CORT) levels. The effect of caffeine on blood ethanol levels was also assessed. After 10 days of acclimatization to the colony room conditions, male Wistar rats were injected with either caffeine (5 mg/kg, ip) or saline 30 min before the delivery of ethanol (0.8 g/kg, ip) or saline, respectively. Trunk blood was then collected at 15 and 30 min after the ethanol injection for determination of plasma CORT and blood ethanol levels. CORT was measured with the use of radioimmunoassay, and blood ethanol levels were determined with the use of gas chromatography. The results showed that although caffeine and ethanol delivered singly failed to augment plasma CORT levels, the combination of both drugs produced elevations in plasma CORT levels at 15 and 30 min. These findings were found to be unrelated to changes in ethanol metabolism as caffeine failed to alter blood ethanol levels within the period tested. It was argued that the present elevations in plasma CORT levels observed in animals administered caffeine and ethanol may play a role in the caffeine-induced elevations in ethanol drinking observed elsewhere.

Caffeine promotes ethanol drinking in rats. Examination using a limited-access free choice paradigm.

There is growing evidence that caffeine may alter the pattern of intake of a variety of drugs. The present study was designed to assess the effect of caffeine pretreatment on voluntary ethanol consumption. The first experiment examined the effect of caffeine on the acquisition of ethanol intake in a limited-access-choice procedure in which water and ethanol were presented concurrently. Male Wistar rats, exposed to food and water ad lib, were presented with a daily 1-h choice session between water and progressively increasing concentrations of ethanol (2-10%). Each ethanol concentration was made available for 4-6 days for a total of 20 days of access to ethanol. Intraperitoneal injections of caffeine (5 or 10 mg/kg) or saline were administered to the rats 30 min prior to each choice session. Caffeine produced a dose-related facilitation in ethanol drinking whereby the lower caffeine dose produced enhancement in ethanol drinking. The second experiment examined the effect of caffeine on the maintenance of established ethanol consumption. Male Wistar rats, initially acclimatized to increasing concentrations of ethanol (2%-10), were presented with an additional 18 ethanol (10%) presentations, comprised of a 6-day baseline period followed by 6 days of treatment where animals were given one of three doses of caffeine (2.5, 5 or 10 mg/kg) or saline prior to ethanol presentation. A final 6-day post-treatment period followed treatment. These results revealed an inverted-U effect of caffeine dose on ethanol ingestion where the low and high caffeine doses produced no effect but the moderate dose of 5 mg/kg enhanced ethanol drinking that persisted throughout the post-treatment period. A third experiment revealed that caffeine did not alter levels of blood ethanol within the time period used for the ethanol drinking session.

Preexposure effects of nicotine and acetaldehyde on conditioned taste aversion induced by both drugs.

Previous assessments have demonstrated an interaction between ethanol and nicotine in the conditioned taste-aversion (CTA) paradigm. The present study assessed whether acetaldehyde, the primary reinforcing metabolite of ethanol, would interact with nicotine as well. In six experiments, water-deprived male Wistar rats were preexposed to either acetaldehyde (0.2 or 0.3 g/kg, IP) or nicotine (0.8, 1.2, or 2 mg/kg, SC) for 3 consecutive days and then subsequently conditioned, 24 h later, with either nicotine (0.8, 1.2, or 2 mg/kg, SC) or acetaldehyde (0.2 or 0.3 g/kg, IP), respectively. There were 4 conditioning days and 4 drug-free test days, each spaced 72 h apart. On test days, animals were offered a free choice between water and saccharin. The results of the following set of experiments demonstrated a dose-related interaction between nicotine and acetaldehyde, where lower doses of each drug failed to attenuate CTA induced by one another, but a higher nicotine dose (2 mg/kg) attenuated the formation of a CTA induced by acetaldehyde (0.3 g/kg). It was argued that the primary metabolite of ethanol may play a role in the interaction between nicotine and ethanol previously observed.

Exposure to nicotine enhances acquisition of ethanol drinking by laboratory rats in a limited access paradigm.

Observations in humans suggest that the initial use of tobacco occurs in close temporal proximity to experimentation with alcohol. There have been relatively few research reports, however, examining possible interactions between these two agents. The present experiments examined the effect of nicotine exposure on the acquisition of ethanol drinking behavior in a limited access procedure. In experiment 1, rats were presented with 1-h access to ethanol solutions of increasing concentration for a period of 20 days. Subcutaneous injections of nicotine (0.6 or 1.2 mg/kg salt) or vehicle were administered 30 min prior to each ethanol presentation. Experiment 2 used a similar method, but rats were presented with water along with ethanol during the 1-h test session. Mecamylamine, a nicotinic receptor antagonist, was administered 30 min prior to the nicotine treatment. Nicotine was seen to produce a dose-dependent increase in ethanol drinking behavior which commenced at the 5% ethanol concentration and continued at 8% and again at 10%. In the second experiment, mecamylamine was observed to block completely the nicotine-induced increase in ethanol drinking behavior. The findings suggest that exposure to nicotine can facilitate the acquisition of ethanol drinking behavior in naive rats and that this effect is mediated by nicotine's interaction at the nicotinic-cholinergic receptor.

Type characterisation and antibiotic susceptibility of Burkholderia (Pseudomonas) cepacia isolates from patients with cystic fibrosis in the United Kingdom and the Republic of Ireland.

The spread of Burkholderia cepacia among cystic fibrosis (CF) patients in the UK prompted an investigation into whether an epidemic strain was responsible. A total of 366 B. cepacia isolates from 178 CF patients in 17 centres was examined by ribotyping and pulsed-field gel electrophoresis (PFGE). Associations were also sought between antibiotic resistance and strain type. More than 50 ribotype patterns were found but one, termed ribotype 1, was identified from 68 patients in eight centres. One centre had a single patient with this type while, in others, most or all patients harboured this organism. Small clusters of apparent cross-colonisation within centres were also evident for some other ribotypes. PFGE confirmed that ribotype 1 isolates were genetically similar. Ribotype 1 isolates were not markedly more resistant to antimicrobial agents than were other isolates, and the MICs of individual antibiotics were no more tightly clustered for ribotype 1 isolates than for others. Most isolates were resistant to ciprofloxacin, amikacin, gentamicin, tobramycin, carbenicillin, cefuroxime, cefotaxime, imipenem, biapenem, chloramphenicol, tetracycline, trimethoprim and sulphamethoxazole, but > or = 77% were susceptible to ceftazidime, piperacillin, piperacillin/ tazobactam and meropenem. We conclude that numerous strains of B. cepacia colonise CF patients in the UK and Ireland but that one epidemic strain has spread in at least eight centres. Isolates of this strain appear homogenous in total genomic profile but very variable in antibiotic susceptibility.