Strain differences in aspirin-induced gastric ulceration in rats

Model-based prediction of the acute and long-term safety profile of naproxen in rats

BACKGROUND AND PURPOSE

Despite the increasing importance of biomarkers as predictors of drug effects, toxicology protocols continue to rely on the experimental evidence of adverse events (AEs) as a basis for establishing the link between indicators of safety and drug exposure. Furthermore, biomarkers may facilitate the translation of findings from animals to humans. Combined with a model-based approach, biomarker data have the potential to predict long-term effects arising from prolonged drug exposure. Here, we used naproxen as a paradigm to explore the feasibility of a biomarker-guided approach for the prediction of long-term AEs in humans.

EXPERIMENTAL APPROACH

An experimental toxicology protocol was set up for evaluating the effects of naproxen in rats, in which four active doses were tested (7.5, 15, 40 and 80 mg·kg(-1) ). In addition to AE monitoring and histology, a few blood samples were also collected for the assessment of drug exposure, TXB2 and PGE2 levels. Non-linear mixed effects modelling was used to analyse the data and identify covariate factors on the incidence and severity of AEs.

KEY RESULTS

Modelling results showed that besides drug exposure, maximum PGE2 inhibition and treatment duration were also predictors of gastrointestinal ulceration. Although PGE2 levels were clearly linked to the incidence rates, it appeared that ulceration severity is better predicted by measures of drug exposure.

CONCLUSIONS AND IMPLICATIONS

These results show that the use of a model-based approach provides the opportunity to integrate pharmacokinetics, pharmacodynamics and toxicity data, enabling optimization of the design, analysis and interpretation of toxicology experiments.

Model-based analysis of thromboxane B₂ and prostaglandin E₂ as biomarkers in the safety evaluation of naproxen

The assessment of safety in traditional toxicology protocols relies on evidence arising from observed adverse events (AEs) in animals and on establishing their correlation with different measures of drug exposure (e.g., Cmax and AUC). Such correlations, however, ignore the role of biomarkers, which can provide further insight into the underlying pharmacological mechanisms. Here we use naproxen as a paradigm drug to explore the feasibility of a biomarker-guided approach for the prediction of AEs in humans. A standard toxicology protocol was set up for the evaluation of effects of naproxen in rat, in which four doses were tested (7.5, 15, 40 and 80 mg/kg). In addition to sparse blood sampling for the assessment of exposure, thromboxane B₂ and prostaglandin E₂ were also collected in satellite groups. Nonlinear mixed effects modelling was used to evaluate the predictive performance of the approach. A one-compartmental model with first order absorption was found to best describe the pharmacokinetics of naproxen. A nonlinear relationship between dose and bioavailability was observed which leads to a less than proportional increase in naproxen concentrations with increasing doses. The pharmacodynamics of TXB₂ and PGE₂ was described by direct inhibition models with maximum pharmacological effects achieved at doses >7.5 mg/kg. The predicted PKPD relationship in humans was within 10-fold of the values previously published. Moreover, our results indicate that biomarkers can be used to assess interspecies differences in PKPD and extrapolated data from animals to humans. Biomarker sampling should be used systematically in general toxicity studies.

c-Fos immunoreactivity induced by intraperitoneal LPS administration is reduced in the brain of mice lacking the microsomal prostaglandin E synthase-1 (mPGES-1)

The aim of the present study was to investigate the impact of the deletion of the microsomal prostaglandin E synthase-1 (mPGES-1) gene on lipopolysaccharide (LPS)-induced neuronal activation in central nervous structures. The mPGES-1 catalyses the conversion of COX-derived PGH(2) to PGE(2) and has been described as a regulated enzyme whose expression is stimulated by proinflammatory agents. Using the immediate-early gene c-fos as a marker of neuronal activation, we determined whether deletion of the mPGES-1 gene altered the neuronal activation induced by LPS in structures classically recognized as immunosensitive regions. No significant difference in the c-Fos immunostaining was observed in the brain of saline-treated mPGES-1+/+, mPGES-1+/- and mPGES-1-/- mice. However, we observed that LPS-induced neuronal activation was reduced in most of the centres known as immunosensitive nuclei in mPGES-1-/- mice compared with heterozygous and wild-type mice. The decrease in the number of c-Fos positive nuclei occurred particularly in the caudal ventrolateral medulla, the medial, intermediate and central parts of the nucleus tractus solitarius, area postrema, parabrachial nucleus, locus coeruleus, paraventricular nucleus of the hypothalamus, ventromedial preoptic area, central amygdala, bed nucleus of the stria terminalis and to a lesser extent in the ventrolateral part of the nucleus tractus solitarius and rostral ventrolateral medulla. These results suggest that the mPGES-1 enzyme is strongly needed to provide sufficient PGE(2) production required to stimulate immunosensitive brain regions and they are discussed with regard to the recent works reporting impaired sickness behavior in mPGES-1-/- mice.

Protection by aspirin of indomethacin-induced small intestinal damage in rats: mediation by salicylic acid

Most of non-steroidal anti-inflammatory drugs (NSAIDs) except aspirin (ASA) produce intestinal damage in rats. In the present study, we re-examined the intestinal toxic effect of ASA in rats, in comparison with various NSAIDs, and investigated why ASA does not cause damage in the small intestine, in relation to its metabolite salicylic acid (SA). Various NSAIDs (indomethacin; 10 mg/kg; flurbiprofen; 20 mg/kg; naproxen; 40 mg/kg; dicrofenac; 40 mg/kg; ASA; 20-200 mg/kg) were administered s.c., and the small intestinal mucosa was examined macroscopically 24 h later. All NSAIDs tested, except ASA, caused hemorrhagic lesions in the small intestine, with a decrease of mucosal PGE(2) contents. ASA did not provoke any damage, despite inhibiting (prostaglandin) PG production, and prevented the occurrence of intestinal lesions induced by indomethacin, in a dose-related manner. This protective action of ASA was mimicked by the equimolar doses of SA (17.8-178 mg/kg). Indomethacin caused intestinal hypermotility, in preceding to the occurrence of lesion, and this event was followed by increases of enterobacterial translocation in the mucosa. Both ASA and SA prevented both the intestinal hypermotility and the bacterial translocation seen after indomethacin treatment. In addition, the protective effect of SA was not significantly influenced by either the adenosine deaminase or the adenosine receptor antagonists. Following administration of ASA, the blood SA levels reached a peak within 30 min and remained elevated for more than 7 h. These results suggest that SA has a cytoprotective action against indomethacin-induced small intestinal lesions, and this action may be associated with inhibition of the intestinal hypermotility and the bacterial translocation, but not mediated by endogenous adenosine. Failure of ASA to induce intestinal damage may be explained, at least partly, by a protective action of SA, the metabolite of ASA.

Depressive behavior and stress ulcer in Wistar Kyoto rats

Wistar Kyoto (WKY) rats, as compared to several other rat strains, are hypoactive in the open field test and in the defensive burying test. WKY rats readily acquire a learned helplessness task as well as a passive avoidance tasks. WKY rats also reveal a greater susceptibility to restraint-induced stress ulcer. The behavioral tests suggest the presence of depressive behavior in WKY rats. When exposed to the Porsolt forced-swim test of 'behavioral despair', WKY rats are judged as exhibiting more depressive behavior. Desipramine not only reduced immobility in the forced-swim test, but also diminished the severity of restraint-induced stress ulcer. These data suggested a heightened activity of the hypothalamic-pituitary axis. Basal plasma ACTH levels did not differ between WKY rats and Wistar rats, but serial plasma ACTH response to restraint stress was significantly greater for WKY rats. These data suggest that depressive behavior is a characteristic of WKY rats and this strain is a valuable model for studying depression which may be induced by an exaggerated stress response.

Gastric mucus glycoprotein in different rat strains

The extent of gastric damage induced by aspirin was found to differ according to rat strain. The occurrence of ulcers varied, from high to low, in the following strain order: Donryu, Sprague-Dawley (SD) and Wistar. The content of corpus mucus glycoprotein was essentially the same in all the strains: about 6 mg as hexose of dry tissue. Antral mucus glycoprotein content increased in the order Wistar, SD and Donryu: 7.1, 8.3 and 9.1 mg, respectively. Gastric mucus glycoprotein carbohydrate composition was essentially the same in all three strains. The relatively low proportions of N-acetylglucosamine, galactose and sialic acid from the antrum was a characteristic feature in contrast to mucus glycoprotein from the corpus which contained a high proportion of these sugars.

Environmental and genetic effects on food-deprivation induced stomach lesions in male rats

When Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rats were individually housed in plastic cages with sawdust bedding and food-deprived (F-D) for 4-5 days, it was found that F-D RHA/Verh rats had more lesions than their unfasted controls and more lesions than F-D RLA/Verh rats. The lesions were mostly petechial in nature and located in the glandular portion of the stomach. Also, F-D RHA/Verh rats which were housed in the same room as the controls, as well as F-D RHA/Verh rats which were housed in a separate room with a strong food odor present, had more lesions than F-D RHA/Verh rats housed in the same separate room when there was no food odor, and when none of the rats present had access to food. When F-D RHA/Verh and F-D RLA/Verh rats were individually housed in metal cages with grid floors, however, a general increase in lesion scores resulted and differences between the two rat lines disappeared, as did differences among the room conditions. Also, many lesions were of an ulcerative nature and were located in the rumenal portion of the stomach. It was concluded that sensory (in this case olfactory, at least) and genetic factors are capable of playing roles in the induction of stomach lesions in rats, and that the type, extent and location of the lesions can depend upon whether or not the animals have access to sawdust bedding.

Effect of proglumide on glycoprotein synthesis in aspirin-induced gastric erosions in rats

The effect of proglumide on the rate of incorporation of (3H)-N-acetylglucosamine into glycoproteins (GP synthesis) in the glandular stomach in normal, fasting and aspirin-treated rats was studied. GP synthesis was significantly reduced by fasting. In Donryu rats, administration of aspirin (100 mg/kg) significantly decreased GP synthesis and induced the concurrent development of gastric erosions in the corpus, but not in the antrum, where no erosion was detected. Meanwhile, in Wistar rats little or no decrease of GP synthesis was observed in the glandular stomach and only slight erosions were found in the corpus. A negative linear correlation was found between the area of erosions and GP synthesis in the corpus of Donryu rats. Pretreatment with proglumide accelerated GP synthesis in the normal glandular stomach and restored the GP decrease caused by fasting. Gastric erosions induced by aspirin were also inhibited by proglumide and the GP decrease in the corpus was prevented. These results suggest that decreased synthesis of glycoproteins may be associated with the development of erosions induced by aspirin and that proglumide may partly exert its anti-erosive activity by stimulating glycoprotein synthesis in the glandular stomach.