Minimal analytical characterization of engineered nanomaterials needed for hazard assessment in biological matrices

This paper presents the outcomes from a workshop of the European Network on the Health and Environmental Impact of Nanomaterials (NanoImpactNet). During the workshop, 45 experts in the field of safety assessment of engineered nanomaterials addressed the need to systematically study sets of engineered nanomaterials with specific metrics to generate a data set which would allow the establishment of dose-response relations. The group concluded that international cooperation and worldwide standardization of terminology, reference materials and protocols are needed to make progress in establishing lists of essential metrics. High quality data necessitates the development of harmonized study approaches and adequate reporting of data. Priority metrics can only be based on well-characterized dose-response relations derived from the systematic study of the bio-kinetics and bio-interactions of nanomaterials at both organism and (sub)-cellular levels. In addition, increased effort is needed to develop and validate analytical methods to determine these metrics in a complex matrix.     

Approaches to the safety assessment of engineered nanomaterials (ENM) in food

A systematic, tiered approach to assess the safety of engineered nanomaterials (ENMs) in foods is presented. The ENM is first compared to its non-nano form counterpart to determine if ENM-specific assessment is required. Of highest concern from a toxicological perspective are ENMs which have potential for systemic translocation, are insoluble or only partially soluble over time or are particulate and bio-persistent. Where ENM-specific assessment is triggered, Tier 1 screening considers the potential for translocation across biological barriers, cytotoxicity, generation of reactive oxygen species, inflammatory response, genotoxicity and general toxicity. In silico and in vitro studies, together with a sub-acute repeat-dose rodent study, could be considered for this phase. Tier 2 hazard characterisation is based on a sentinel 90-day rodent study with an extended range of endpoints, additional parameters being investigated case-by-case. Physicochemical characterisation should be performed in a range of food and biological matrices. A default assumption of 100% bioavailability of the ENM provides a ‘worst case’ exposure scenario, which could be refined as additional data become available. The safety testing strategy is considered applicable to variations in ENM size within the nanoscale and to new generations of ENM.     

Microemulsions for improved peptide absorption from the gastrointestinal tract

Results on gastrointestinal absorption of three peptides, insulin, cyclosporin from microemulsions, obtained from studies in our laboratories during the past years have been summarized. The routes of administration were period, intralumenal or rectal. The experiments were carried out in dogs, rabbits and rats. An absorption model for peptides using microemulsions as delivery systems is presented.     

Kinetics of piretanide absorption from the gastrointestinal tract

In a recent report, it was shown that the loop diuretic piretanide is rapidly absorbed after placement of a piretanide solution in the duodenum, while the rate of absorption is definitely slower when the drug is instilled into the ascending colon (5). When piretanide is instilled into the stomach, the absorption process does not differ significantly from that after placement in the duodenum, neither with respect to amount nor rate (5). However, it was not clear from this study whether piretanide is directly absorbed from the stomach or rapidly released into the duodenum. In a study with five volunteers piretanide was instilled into the stomach via a gastroscope. The volunteers took part in two trial phases in a randomized cross-over design: in one phase the administration of 6 mg piretanide was preceded by intravenous administration of 40 mg hyoscine-N-butylbromide (HNB) to immobilize the stomach while in the alternative phase this coadministration of HNB was omitted. Furthermore, the volunteers were lying on their left side to avoid the gastric fluid leaking out into the intestine by gravity. From the concentration-time-curves monitored it can be concluded that piretanide is absorbed directly from the stomach for almost all subjects but with different rates. The rate of absorption increases clearly when the immobilizing effect of HNB disappears. It is most probable that returning peristaltic waves and succeeding gastric emptying results in enhanced absorption from the upper intestinal tract. Furthermore, a pharmacokinetic model which takes into account the differences in the rate of absorption along the gastrointestinal tract was adjusted to the data.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mathematical modeling of oral absorption and bioavailability of a fluoroquinolone after its precipitation in the gastrointestinal tract

Abstract

1. The objective was to characterize the in vivo absorption and bioavailability (BA) of a low solubility, high permeability fluoroquinolone (CNV97101) that precipitates in the gastrointestinal (GI) tract by mathematical modeling approach.

2. In situ rat intestinal perfusion studies were performed to characterize the absorption mechanism. The oral fraction absorbed in vivo was lower than the predicted based on the in situ intestinal permeability. Two additional routes of administration, intraduodenal (ID) and intraperitoneal (IP) were investigated to explore if precipitation in stomach and subsequent partial re-dissolution were the causes of the lower in vivo BA. Ex vivo precipitation studies with the stomach content of fasted rats were also carried out. Fitting procedures were performed with NONMEM VII 1.2.

3. The in situ experiments confirmed simultaneous passive and carrier-mediated absorption processes. The ex vivo experiments confirmed precipitation in stomach lowering in vivo the oral fraction absorbed compared with the IP and ID administrations. Due to the almost complete availability of CNV97101 following IP administration, a first hepatic pass could be excluded. The ex vivo assay results and the pharmacokinetic modeling of in vivo data supported the hypothesis of precipitation in the stomach and partial re-dissolution. Nevertheless, other factors such as residence time in the GI may reduce the fraction absorbed even for low oral doses for which re-dissolution was almost complete in vivo.     

Allopurinol absorption from different sites of the rat gastrointestinal tract

Allopurinol exhibits good bioavailability (78-90%) after administration of oral dosage forms to humans and rabbits; however, it is not absorbed rectally from any of the dosage forms to any significant extent. Oral administration of allopurinol in a polyethylene glycol suspension, to which allopurinol may be reversibly complexed, to rabbits has been shown to produce erratic and poor absorption of allopurinol. This suggests the possibility of differential absorption of allopurinol from various sites of the GI tract. The mechanism of allopurinol absorption was investigated in rats using the in situ Levine technique. The allopurinol absorption rate was 0.56 +/- 0.10 microgram/min/cm from the upper portion of the small intestine and was 0.48 +/- 0.12 microgram/min/cm from the midgut. The absorption from the lower portion of the small intestine was 0.33 +/- 0.14 microgram/min/cm and from the upper and lower large intestine segments was negligible (0.04 +/- 0.06 microgram/min/cm). The normalization of these absorption rates for surface area yielded flux values (normalized absorption rate as microgram/min/cm2) with significant differences in permeability between small and large intestine for allopurinol. The allopurinol absorption rate increased with increases in the dose, and there was a linear relationship between dose and absorption rate. Thus, allopurinol absorption, although specific to particular sites, is not dose dependent in the dose range from 0.25 to 2.5 mg/mL. Differences in the rates of absorption may be due to anatomical differences of the various parts of the GI tract or due to physicochemical properties of the drug itself.     

从鲐巴鱼消化道中提取蛋白酶的条件比较

本实验条件下,从鲐巴鱼消化道中提取蛋白酶的有关因素的最适条件是:提取温度20℃、时间2h、pH7.5、活化时间16h、乙醇沉淀浓度为65%。     

Fish cell lines as a tool for the ecotoxicity assessment and ranking of engineered nanomaterials

Risk assessment of engineered nanomaterials (ENMs) is being hindered by the sheer production volume of these materials. In this regard, the grouping and ranking of ENMs appears as a promising strategy. Here we sought to evaluate the usefulness of in vitro systems based on fish cell lines for ranking a set of ENMs on the basis of their cytotoxicity. We used the topminnow (Poeciliopsis lucida) liver cell line (PLHC-1) and the rainbow trout (Oncorhynchus mykiss) fibroblast-like gonadal cell line (RTG-2). ENMs were obtained from the EU Joint Research Centre repository. The size frequency distribution of ENM suspensions in cell culture media was characterized. Cytotoxicity was evaluated after 24 h of exposure. PLHC-1 cells exhibited higher sensitivity to the ENMs than RTG-2 cells. ZnO-NM was found to exert toxicity mainly by altering lysosome function and metabolic activity, while multi-walled carbon nanotubes (MWCNTs) caused plasma membrane disruption at high concentrations. The hazard ranking for toxicity (ZnO-NM > MWCNT ≥ CeO₂-NM = SiO₂-NM) was inversely related to the ranking in size detected in culture medium. Our findings reveal the suitability of fish cell lines for establishing hazard rankings of ENMs in the framework of integrated approaches to testing and assessment.     

Influence of food on the absorption of phenytoin in man

Summary The influence of food intake on the absorption of phenytoin was examined in eight healthy volunteers, by study of single-dose kinetics following ingestion of phenytoin 300 mg either with a standardized breakfast or on an empty stomach. Blood samples were collected at regular intervals from 0 to 48 h, and serum concentrations of unmetabolized phenytoin were determined by gas chromatography. Serum concentrations of the major metabolite of phenytoin, 4-hydroxyphenytoin, were measured by mass fragmentography. Concurrent intake of food and phenytoin appeared to accelerate absorption of the drug from the formulation used, and the peak concentrations were significantly higher (mean increase 40%) in the postprandial than in the preprandial state. As reflected by the AUC (area under the curve), the amount of drug absorbed was increased during postprandial conditions, although the difference only reached borderline significance. It is suggested that phenytoin should always be taken in a defined relation to meals.     

Rhythm of digestion: keeping time in the gastrointestinal tract

1. The best characterized mammalian circadian rhythms follow a light-entrained central master pacemaker in the suprachiasmatic nucleus and are associated with fluctuations in the activities of clock genes, including Clock , Bmal1 , Per and Cry , the products of which bind to sequences in the promoters of effector genes. This is the central clock.
2. In the present review, we discuss evidence for an independent, but interacting, gut-associated circadian clock, the peripheral clock, which is entrained by food.
3. Disruption of circadian rhythms is associated with a wide range of pathologies, most prominently metabolism linked, but the effects of disruption of circadian rhythms on the digestive system are less well studied, although also likely to lead to functional consequences. There are clues suggestive of links between gastrointestinal disorders related to inflammation, cancer and motility and disruption of peripheral rhythms. Research aimed at understanding these links is still in its infancy.
4. We also discuss practical aspects of the presence of circadian rhythms in gastrointestinal tissues for researchers related to experimental design, data interpretation and the choice of animal models.
5. There is currently sufficient evidence to suggest that circadian rhythms are important to gut function, metabolism and mucosal defence and that further investigation will uncover connections between disordered rhythms and gastrointestinal malfunction.     

Research strategies for safety evaluation of nanomaterials, part IV: risk assessment of nanoparticles.

Nanoparticles are small-scale substances (<100 nm) with unique properties and, thus, complex exposure and health risk implications. This symposium review summarizes recent findings in exposure and toxicity of nanoparticles and their application for assessing human health risks. Characterization of airborne particles indicates that exposures will depend on particle behavior (e.g., disperse or aggregate) and that accurate, portable, and cost-effective measurement techniques are essential for understanding exposure. Under many conditions, dermal penetration of nanoparticles may be limited for consumer products such as sunscreens, although additional studies are needed on potential photooxidation products, experimental methods, and the effect of skin condition on penetration. Carbon nanotubes apparently have greater pulmonary toxicity (inflammation, granuloma) in mice than fine-scale carbon graphite, and their metal content may affect toxicity. Studies on TiO2 and quartz illustrate the complex relationship between toxicity and particle characteristics, including surface coatings, which make generalizations (e.g., smaller particles are always more toxic) incorrect for some substances. These recent toxicity and exposure data, combined with therapeutic and other related literature, are beginning to shape risk assessments that will be used to regulate the use of nanomaterials in consumer products.     

Risk assessment of engineered nanomaterials: a review of available data and approaches from a regulatory perspective

Abstract

It has been largely recognised that substantial limitations and uncertainties make the conventional risk assessment (RA) of chemicals unfeasible to apply to engineered nanomaterials (ENMs) today, which leaves the regulators with little support in the near term. The aim of this paper is to discuss the state of the art in the area of the RA of nanomaterials, focusing on the available data and approaches. There is a paucity of reliable information in the online safety databases and the literature is dominated by (eco)toxicity studies, while the nano-exposure research lags behind. Most of the reviewed nano-RA approaches are designed to serve as preliminary risk screening and/or research prioritisation tools and are not intended to support regulatory decision making. In this context, we recommend to further study the possibilities to apply complementary/alternative tools for near-term RA of ENMs in order to facilitate their timely regulation, using the data that are currently available in the literature.     

基于胃肠道生理模型的口服药物吸收预测

药物的口服吸收受到许多生理因素的影响,如胃肠液成分、pH、肠道内传输、转运和代谢等。在进行非临床和临床体内试验之前,如果仅仅依靠体外数据能够准确地预测药物的口服吸收,将会大大提高新药研发的效率。在深入理解口服吸收过程的基础上发展起来的胃肠道生理模型为从事新药研发的科研工作者提供了这种机会。这些生理模型可以与经典的药动学模型紧密衔接,用于预测药物的口服吸收速度和程度。本文综述了胃肠道生理模型的最新进展,并对不同的模型进行了比较和讨论。     

Characterization of drug absorption from the gastrointestinal tract with the use of numeric deconvolution

The present investigation is concerned with the absorption of drugs from the gastrointestinal tract. The duration of absorption of drugs was calculated using numerical deconvolution. Clinical data were obtained from the literature. The absorption of 36 different drugs is characterized. The results show that the duration of absorption is not uniform. Penicillins and tetracyclines are absorbed for about 3 hours after application. Most drugs are absorbed during 4 to 6 hours. A few drugs, e.g. theophylline or metoprolol, are absorbed for more than 12 hours from the gastrointestinal tract.     

Investigation of nifedipine absorption in different regions of the human gastrointestinal (GI) tract after simultaneous administration of 13C- and 12C-nifedipine

Objective: To evaluate the absorption of nifedipine in man from four different sites of the gastrointestinal tract. Methods: On separate occasions, nifedipine solution was administered locally to the stomach, the small intestine and two sites in the colon in 4 healthy male volunteers (age 29–34 y weight 73–82 kg, non-smokers) using a remote controlled drug delivery device (HF-capsule). In order to assess absolute and relative bioavailabilities, an intravenous infusion was given on a separate occasion and all treatments were accompanied by a simultaneous oral dose of a stable-isotope labelled nifedipine solution. This allowed to minimise the influence of intra-individual variability. Plasma samples were collected up to 24 h post dose and faeces for 72 h. A new method of analysis of nifedipine in plasma and faeces using gas chromatography with mass-selective detection (GCMS) was employed. Results: Dissolved nifedipine was found to enter the systemic circulation completely along the intestine, being absorbed from jejunum to colon. Absorption was less rapid from the colon than from the upper part of the gut, but this was not associated with a decrease in absorption and/or bioavailability: Absolute bioavailability, calculated from the normalised AUC values, ranged from 42 to 56%, and bioavailability relative to oral solution was 100 to 126% (medians of the application sites). Conclusion: The absence of an absorption window in the intestinal tract suggests that nifedipine is well suited for use in controlled-release formulations. Received: 7 July 1995/Accepted in revised form: 8 January 1996