Drug enterocyte adducts: possible causal factor for diclofenac enteropathy in rats

Integrated multi-biomarker responses of juvenile rainbow trout (Oncorhynchus mykiss) to an environmentally relevant pharmaceutical mixture

Pharmaceuticals are emerging pollutants of concern for aquatic ecosystems where they are occurring in complex mixtures. In the present study, the chronic toxicity of an environmentally relevant pharmaceutical mixture on juvenile rainbow trout (Oncorhynchus mykiss) was investigated. Five pharmaceuticals (paracetamol, carbamazepine, diclofenac, naproxen and irbesartan) were selected based on their detection frequency and concentration levels in the Meuse river (Belgium). Fish were exposed for 42 days to three different concentrations of the mixture, the median one detected in the Meuse river, 10-times and 100-times this concentration. Effects on the nervous, immune, antioxidant, and detoxification systems were evaluated throughout the exposure period and their response standardized using the Integrated Biomarker Response (IBRv2) index. IBRv2 scores increased over time in the fish exposed to the highest concentration. After 42 days, fish exposed to the highest concentration displayed significantly higher levels in lysozyme activity (p < 0.01). The mixture also caused significant changes in brain serotonin turnover (p < 0.05). In short, our results indicate that the subchronic waterborne exposure to a pharmaceutical mixture commonly occurring in freshwater ecosystems may affect the neuroendocrine and immune systems of juvenile rainbow trout.

Glycomacropeptide Ameliorates Indomethacin-Induced Enteropathy in Rats by Modifying Intestinal Inflammation and Oxidative Stress

Nonsteroidal anti-inflammatory drug (NSAID)-induced enteropathy is considered a serious and increasing clinical problem without available treatment. Glycomacropeptide (GMP) is a 64-amino acid peptide derived from milk κ-casein with numerous biological activities. The aim of this study was to investigate the protective effect of GMP on NSAID enteropathy in rats. Enteropathy was induced by seven days oral indomethacin administration. Rats were orally GMP treated from seven days previous and during the establishment of the enteropathy model. Changes in metabolism, hematological and biochemical blood alterations, intestinal inflammation and oxidative damage were analyzed. Integrity barrier markers, macroscopic intestinal damage and survival rate were also evaluated. GMP treatment prevented anorexia and weight loss in animals. Furthermore, prophylaxis with GMP ameliorated the decline in hemoglobin, hematocrit, albumin and total protein levels. The treatment had no therapeutic efficacy on the decrease of occludin and mucin (MUC)-2 expression in intestinal tissue. However, GMP markedly decreased neutrophil infiltration, and CXCL1, interleukin-1β and inducible nitric oxide synthase expression. Nitric oxide production and lipid hydroperoxide level in the small intestine were also diminished. These beneficial effects were mirrored by preventing ulcer development and increasing animal survival. These results suggest that GMP may protect against NSAID enteropathy through anti-inflammatory and antioxidant properties.

Identification and Characterization of Efflux Transporters That Modulate the Subtoxic Disposition of Diclofenac and Its Metabolites

In the present work, in vivo transporter knockout (KO) mouse models were used to characterize the disposition of diclofenac (DCF) and its primary metabolites following a single subtoxic dose in mice lacking breast cancer resistance protein (Bcrp) or multidrug resistance-associated protein (Mrp)3. The results indicate that Bcrp acts as a canalicular efflux mediator for DCF, as wild-type (WT) mice had biliary excretion values that were 2.2- to 2.6-fold greater than Bcrp KO mice, although DCF plasma levels were not affected. The loss of Bcrp resulted in a 1.8- to 3.2-fold increase of diclofenac acyl glucuronide (DCF-AG) plasma concentrations in KO animals compared with WT mice, while the biliary excretion of DCF-AG increased 1.4-fold in WT versus KO mice. Furthermore, Mrp3 was found to mediate the basolateral transport of DCF-AG, but not DCF or 4'-hydroxy diclofenac. WT mice had DCF-AG plasma concentrations 7.0- to 8.6-fold higher than Mrp3 KO animals; however, there were no changes in biliary excretion of DCF-AG. Vesicular transport experiments with human MRP3 demonstrated that MRP3 is able to transport DCF-AG via low- and high-affinity binding sites. The low-affinity MRP3 transport had a V _max and K _m of 170 pmol/min/mg and 98.2 µM, respectively, while the high-affinity V _max and K _m parameters were estimated to be 71.9 pmol/min/mg and 1.78 µM, respectively. In summary, we offer evidence that the disposition of DCF-AG can be affected by both Bcrp and Mrp3, and these findings may be applicable to humans.

Experimental study of diclofenac and its biliary metabolites on anastomotic healing

Background

Diclofenac increases the risk of anastomotic leakage, but the underlying mechanism is unknown. As diclofenac is excreted largely as biliary metabolites, the aim of this study was to determine the effect of these metabolites on intestinal anastomoses.

Methods

This was a randomized controlled blinded experiment using 210 male Wistar rats to assess the effect of ‘diclofenac bile’ on the anastomotic complication score, leak rate and anastomotic strength following oral and parenteral administration of diclofenac. Bile duct and duodenal catheterization techniques were used for diversion and replacement of bile, and biliary diclofenac metabolites were determined.

Results

Replacement of control bile with diclofenac bile resulted in higher anastomotic complication scores (P = 0·006) and leakage in five of 18 animals, compared with one of 18 controls (P = 0·089). In turn, following oral diclofenac administration, replacement of diclofenac bile with control bile reduced anastomotic complications (P = 0·016). The leak rate was seven of 15 versus 13 of 17 without replacement (P = 0·127). After intramuscular administration of diclofenac, the reduction in anastomotic complications was not significant when bile was replaced with control bile (P = 0·283), but it was significant when bile was drained without replacement (P = 0·025). Diclofenac metabolites in bile peaked within 2 h after administration. Administration of diclofenac bile resulted in nearly undetectable plasma levels of diclofenac (mean(s.d.) 0·01(0·01) μg/ml) after 120 min. Following oral diclofenac, bile replacement with control bile did not affect the plasma concentration of diclofenac (0·12(0·08) μg/ml versus 0·10(0·05) μg/ml with diclofenac bile; P = 0·869).

Conclusion

Altered bile composition as a result of diclofenac administration increases the ileal anastomotic complication rate in rats.

Microbial Glucuronidase Inhibition Reduces Severity of Diclofenac-Induced Anastomotic Leak in Rats

BACKGROUND

The non-steroidal anti-inflammatory drug diclofenac has been associated with intestinal anastomotic leakage, although the underlying pathophysiology is unclear. Previous data suggest that reactivation of biliary diclofenac metabolites by microbial β-glucuronidases in the gut plays a role in harming the intestinal mucosa, and that microbiome-targeted glucuronidase inhibition prevents this damage. Here, the microbial glucuronidase inhibitor Inh1 was examined for its ability to reduce diclofenac-induced anastomotic leakage in rats.

METHODS

Ninety male Wistar rats were allocated to five groups. In the two diclofenac groups, group DCF received diclofenac (3 mg/kg per day) and group DCF-Inh1 additionally received 800 mcg/kg per day of glucuronidase inhibitor Inh1 solution orally. In non-diclofenac groups, animals received either Inh1 (800 mcg/kg per day; group Inh1) solution, the vehicle (methylcellulose; group Veh), or no solution (group Ctrl). All solutions were provided from the day of surgery until sacrifice on day three. Plasma concentrations of diclofenac were determined. Outcomes were anastomotic leakage, leak severity, and anastomotic strength.

RESULTS

Anastomotic leak rates were 89% in group DCF and 44% in group DCF-Inh1 (p = 0.006). Leak severity was reduced in group DCFic-Inh1 (p = 0.029). In non-diclofenac cohorts, mostly minor leakage signs were observed in 25% in group Ctrl, 39% in group Inh1 (0.477), and 24% in group Veh (p = 1.000). Bursting pressure and breaking strength were not significantly different. Plasma concentrations of diclofenac were not changed by Inh1.

CONCLUSION

Microbial glucuronidase inhibitor reduces diclofenac-induced anastomotic leakage severity, which suggests a harmful effect of diclofenac metabolite reactivation in the gut. This finding improves the understanding of the pathogenesis of anastomotic leakage.

Ciprofloxacin blocked enterohepatic circulation of diclofenac and alleviated NSAID-induced enteropathy in rats partly by inhibiting intestinal β-glucuronidase activity

AIM

Diclofenac is a non-steroidal anti-inflammatory drug (NSAID), which may cause serious intestinal adverse reactions (enteropathy). In this study we investigated whether co-administration of ciprofloxacin affected the pharmacokinetics of diclofenac and diclofenac-induced enteropathy in rats.

METHODS

The pharmacokinetics of diclofenac was assessed in rats after receiving diclofenac (10 mg/kg, ig, or 5 mg/kg, iv), with or without ciprofloxacin (20 mg/kg, ig) co-administered. After receiving 6 oral doses or 15 intravenous doses of diclofenac, the rats were sacrificed, and small intestine was removed to examine diclofenac-induced enteropathy. β-Glucuronidase activity in intestinal content, bovine liver and E coli was evaluated.

RESULTS

Following oral or intravenous administration, the pharmacokinetic profile of diclofenac displayed typical enterohepatic circulation, and co-administration of ciprofloxacin abolished the enterohepatic circulation, resulted in significant reduction in the plasma content of diclofenac. In control rats, β-glucuronidase activity in small intestinal content was region-dependent: proximal intestine<distal intestine<ileal valve. Administration of ciprofloxac caused significant reduction of β-glucuronidase activity in distal small intestine, and particularly in ileal valve. Furthermore, ciprofloxacin (10-2000 μmol/L) dose-dependently inhibited β-glucuronidase activity in distal small intestine content or E coli incubated in vitro, but did not affect that in proximal small intestine content or bovine liver incubated in vitro. After receiving 6 oral doses or 15 intravenous doses of diclofenac, typical enteropathy was developed with severe enteropathy occurred in distal small intestine. Co-administration of ciprofloxacin significantly alleviated diclofenac-induced enteropathy.

CONCLUSION

Co-administration of ciprofloxacin attenuated enterohepatic circulation of diclofenac and alleviated diclofenac-induced enteropathy in rats, partly via the inhibition of intestinal β-glucuronidase activity.

Elucidation of the Mechanisms through Which the Reactive Metabolite Diclofenac Acyl Glucuronide Can Mediate Toxicity

We have previously reported that mice lacking the efflux transporter Mrp3 had significant intestinal injury after toxic diclofenac (DCF) challenge, and proposed that diclofenac acyl glucuronide (DCF-AG), as a substrate of Mrp3, played a part in mediating injury. Since both humans and mice express the uptake transporter OATP2B1 in the intestines, OATP2B1 was characterized for DCF-AG uptake. In vitro assays using human embryonic kidney (HEK)-OATP2B1 cells demonstrated that DCF-AG was a substrate with a maximal velocity (Vmax) and Km of 17.6 ± 1.5 pmol/min per milligram and 14.3 ± 0.1 μM, respectively. Another key finding from our in vitro assays was that DCF-AG was more cytotoxic compared with DCF, and toxicity occurred within 1-3 hours of exposure. We also report that 1 mM DCF-AG caused a 6-fold increase in reactive oxygen species (ROS) by 3 hours. Investigation of oxidative stress through inhibition of superoxide dismutase (SOD) revealed that DCF-AG had 100% inhibition of SOD at the highest tested dose of 1 mM. The SOD and ROS results strongly suggest DCF-AG induced oxidative stress in vitro. Lastly, DCF-AG was screened for pharmacologic activity against COX-1 and COX-2 and was found to have IC50 values of 0.620 ± 0.105 and 2.91 ± 0.36 μM, respectively, which represents a novel finding. Since cyclooxygenase (COX) inhibition can lead to intestinal ulceration, it is plausible that DCF-AG can also contribute to enteropathy via COX inhibition. Taken in context, the work presented herein demonstrated the multifactorial pathways by which DCF-AG can act as a direct contributor to toxicity following DCF administration.

Multidrug Resistance-Associated Protein 3 Plays an Important Role in Protection against Acute Toxicity of Diclofenac

Diclofenac (DCF) is a nonsteroidal anti-inflammatory drug commonly prescribed to reduce pain in acute and chronic inflammatory diseases. One of the main DCF metabolites is a reactive diclofenac acyl glucuronide (DCF-AG) that covalently binds to biologic targets and may contribute to adverse drug reactions arising from DCF use. Cellular efflux of DCF-AG is partially mediated by multidrug resistance-associated proteins (Mrp). The importance of Mrp2 during DCF-induced toxicity has been established, yet the role of Mrp3 remains largely unexplored. In the present work, Mrp3-null (KO) mice were used to study the toxicokinetics and toxicodynamics of DCF and its metabolites. DCF-AG plasma concentrations were 90% lower in KO mice than in wild-type (WT) mice, indicating that Mrp3 mediates DCF-AG basolateral efflux. In contrast, there were no differences in DCF-AG biliary excretion between WT and KO, suggesting that only DCF-AG basolateral efflux is compromised by Mrp3 deletion. Susceptibility to toxicity was also evaluated after a single high DCF dose. No signs of injury were detected in livers and kidneys; however, ulcers were found in the small intestines. Furthermore, the observed intestinal injuries were consistently more severe in KO compared with WT. DCF covalent adducts were observed in liver and small intestines; however, staining intensity did not correlate with the severity of injuries, implying that tissues respond differently to covalent modification. Overall, the data provide strong evidence that (1) in vivo Mrp3 plays an important role in DCF-AG disposition and (2) compromised Mrp3 function can enhance injury in the gastrointestinal tract after DCF treatment.

Toxicological effects of clofibric acid and diclofenac on plasma thyroid hormones of an Indian major carp, Cirrhinus mrigala during short and long-term exposures

In the present investigation, the toxicity of most commonly detected pharmaceuticals in the aquatic environment namely clofibric acid (CA) and diclofenac (DCF) was investigated in an Indian major carp Cirrhinus mrigala. Fingerlings of C. mrigala were exposed to different concentrations (1, 10 and 100μgL(-1)) of CA and DCF for a period of 96h (short term) and 35 days (long term). The toxic effects of CA and DCF on thyroid hormones (THs) such as thyroid stimulating hormone (TSH), thyroxine (T4) and triiodothyronine (T3) levels were evaluated. During the short and long-term exposure period TSH level was found to be decreased at all concentrations of CA (except at the end of 14(th) day in 1 and 10μgL(-l) and 21(st) day in 1μgL(-l)) whereas in DCF exposed fish TSH level was found to be increased when compared to control groups. T4 level was found to be decreased at 1 and 100μgL(-l) of CA exposure at the end of 96h. However, T4 level was decreased at all concentrations of CA and DCF during long-term (35 days) exposure period. Fish exposed to all concentrations of CA and DCF had lower level of T3 in both the treatments. These results suggest that both CA and DCF drugs induced significant changes (P<0.01 and P<0.05) on thyroid hormonal levels of C. mrigala. The alterations of these hormonal levels can be used as potential biomarkers in monitoring of pharmaceutical drugs in aquatic organisms.

Diclofenac toxicity in human intestine ex vivo is not related to the formation of intestinal metabolites

The use of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is associated with a high prevalence of gastrointestinal side effects. In vivo studies in rodents suggested that reactive metabolites of DCF produced by the liver or the intestine might be responsible for this toxicity. In the present study, precision-cut intestinal slices (PCIS) prepared from the jejunum of 18 human donors were used as an ex vivo model to investigate whether DCF intestinal metabolites are responsible for its intestinal toxicity in man. PCIS were incubated with a concentration range of DCF (0-600 µM) up to 24 h. DCF (≥400 µM) caused direct toxicity to the intestine as demonstrated by ATP depletion, morphological damage, caspase 3 activation, and lactate dehydrogenase leakage. Three main metabolites produced by PCIS (4'-hydroxy DCF, 5-hydroxy DCF, and DCF acyl glucuronide) were detected by HPLC. Protein adducts were detected by immunohistochemical staining and showed correlation with the intestinal metabolites. DCF induced similar toxicity to each of the samples regardless of the variation in metabolism among them. Less metabolites were produced by slices incubated with 400 µM DCF than with 100 µM DCF. The addition of the metabolic inhibitors such as ketoconazole, cimetidine, or borneol decreased the metabolite formation but increased the toxicity. The results suggest that DCF can induce intestinal toxicity in human PCIS directly at therapeutically relevant concentrations, independent of the reactive metabolites 4'-OH DCF, 5-OH DCF, or diclofenac acylglucuronide produced by the liver or formed in the intestine.

Short and long-term effects of clofibric acid and diclofenac on certain biochemical and ionoregulatory responses in an Indian major carp, Cirrhinus mrigala

Extensive use of pharmaceuticals in human and veterinary medicine and aquaculture practices pose a serious threat to aquatic organisms. In the present investigation, Cirrhinus mrigala an Indian major carp was exposed to different concentrations of clofibric acid (CA) and diclofenac (DCF) and certain biochemical and ionoregulatory responses were assessed under short and long term exposures. During short-term (96h) exposure period, plasma glucose and sodium (Na(+)) levels were increased at all concentrations (1, 10 and 100μgL(-1)) of CA and DCF treated fish. Plasma protein and chloride (Cl(-)) levels were found to be decreased at all concentrations of CA and DCF exposed fish comparatively to control groups. Meanwhile an increase in plasma potassium (K(+)) level was noted in fish exposed to CA treatments alone and in DCF treatments it was decreased. In long-term exposure (35d), plasma Na(+) and Cl(-) levels were found to be significantly increased at all concentration of CA and DCF. However, a biphasic trend was observed in plasma glucose, protein and K(+) levels. In both the treatments, a significant (P<0.01 and P<0.05) changes were observed in all parameters measured in fish exposed to different concentrations of CA and DCF. The results of the present investigation indicate that both the drugs caused significant changes in biochemical and ionoregulatory responses of fish at all concentrations. The alterations of these parameters can be useful in monitoring of pharmaceutical residues present in aquatic environment.

Mechanisms, prevention and clinical implications of nonsteroidal anti-inflammatory drug-enteropathy

This article reviews the latest developments in understanding the pathogenesis, detection and treatment of small intestinal damage and bleeding caused by nonsteroidal anti-inflammatory drugs (NSAIDs). With improvements in the detection of NSAID-induced damage in the small intestine, it is now clear that this injury and the associated bleeding occurs more frequently than that occurring in the stomach and duodenum, and can also be regarded as more dangerous. However, there are no proven-effective therapies for NSAID-enteropathy, and detection remains a challenge, particularly because of the poor correlation between tissue injury and symptoms. Moreover, recent studies suggest that commonly used drugs for protecting the upper gastrointestinal tract (i.e., proton pump inhibitors) can significantly worsen NSAID-induced damage in the small intestine. The pathogenesis of NSAID-enteropathy is complex, but studies in animal models are shedding light on the key factors that contribute to ulceration and bleeding, and are providing clues to the development of effective therapies and prevention strategies. Novel NSAIDs that do not cause small intestinal damage in animal models offer hope for a solution to this serious adverse effect of one of the most widely used classes of drugs.

Multiple NSAID-induced hits injure the small intestine: underlying mechanisms and novel strategies

Nonsteroidal anti-inflammatory drugs (NSAIDs) can cause serious gastrointestinal (GI) injury including jejunal/ileal mucosal ulceration, bleeding, and even perforation in susceptible patients. The underlying mechanisms are largely unknown, but they are distinct from those related to gastric injury. Based on recent insights from experimental models, including genetics and pharmacology in rodents typically exposed to diclofenac, indomethacin, or naproxen, we propose a multiple-hit pathogenesis of NSAID enteropathy. The multiple hits start with an initial pharmacokinetic determinant caused by vectorial hepatobiliary excretion and delivery of glucuronidated NSAID or oxidative metabolite conjugates to the distal small intestinal lumen, where bacterial β-glucuronidase produces critical aglycones. The released aglycones are then taken up by enterocytes and further metabolized by intestinal cytochrome P450s to potentially reactive intermediates. The "first hit" is caused by the NSAID and/or oxidative metabolites that induce severe endoplasmic reticulum stress or mitochondrial stress and lead to cell death. The "second hit" is created by the significant subsequent inflammatory response that would follow such a first-hit injury. Based on these putative mechanisms, strategies have been developed to protect the enterocytes from being exposed to the parent NSAID and/or oxidative metabolites. Among these, a novel strategy already demonstrated in a murine model is the selective disruption of bacteria-specific β-glucuronidases with a novel small molecule inhibitor that does not harm the bacteria and that alleviates NSAID-induced enteropathy. Such mechanism-based strategies require further investigation but provide potential avenues for the alleviation of the GI toxicity caused by multiple NSAID hits.

Role of intestinal cytochrome p450 enzymes in diclofenac-induced toxicity in the small intestine

The aim of this study was to determine the role of small intestinal (SI) cytochrome P450 (P450) enzymes in the metabolic activation of diclofenac (DCF), a widely used nonsteroidal anti-inflammatory drug, and DCF-induced intestinal toxicity. DCF induces intestinal ulcers in humans and mice, but the underlying mechanisms, including the necessity for drug bioactivation in the target tissues and the sources and identities of reactive intermediates, are not fully understood. We found that the number of DCF-induced (at 50 mg/kg p.o.) intestinal ulcers was significantly smaller in an intestinal epithelium (IE)-specific P450 reductase (CPR) knockout (IE-Cpr-null) mouse model, which has little P450 activity in the IE, than in wild-type (WT) mice, determined at 14 h after DCF administration. The involvement of intestinal P450 enzymes was confirmed by large reductions (>80-90%) in the rates of in vitro formation, in SI microsomal reactions, of hydroxylated DCF metabolites and reactive intermediates, trapped as DCF-glutathione (GSH) conjugates, in the IE-Cpr-null, compared with WT mice. The SI levels of DCF-GSH conjugates (at 4 h after dosing) and DCF-protein adducts (at 14 h after dosing) were significantly lower in IE-Cpr-null than in WT mice. In additional experiments, we found that pretreatment of mice with grapefruit juice, which is known to inhibit SI P450 activity, ameliorated DCF-induced intestinal toxicity in WT mice. Our results not only strongly support the notion that SI P450 enzymes play an important role in DCF-induced intestinal toxicity, but also illustrate the possibility of preventing DCF-induced intestinal toxicity through dietary intervention.

A protective effect of melatonin on intestinal permeability is induced by diclofenac via regulation of mitochondrial function in mice

AIM

This study investigated the effect of intragastrically administered melatonin on intestinal mucosal permeability induced by diclofenac in mice.

METHODS

Intestinal mucosal permeability was induced in mice by intragastric administration of diclofenac (2.5 mg/kg). Melatonin was given intragastrically (10 mg/kg) once per day for 3 d after diclofenac administration. The small intestine was examined macroscopically and microscopically for pathologic injury to the intestinal mucosa. Intestinal mucosal permeability was evaluated by Evans blue and FITC-dextran methods. Mitochondrial functional parameters, including mitochondrial membrane potential, mitochondrial ATPase and succinate dehydrogenase (SDH) activity, were assessed. The malondialdehyde (MDA) and myeloperoxidase (MPO) levels were determined from small intestinal mucosal homogenates.

RESULTS

As compared with control mice, the permeability, pathologic score, MDA and MPO levels and ulceration of the intestinal mucosa were increased significantly by diclofenac treatment, and a broadened junctional complex and enlarged intercellular space were observed by transmission electron microscopy (TEM). Melatonin treatment significantly reduced the intestinal mucosal permeability, pathologic score, MDA, and MPO levels and ulceration of the intestinal mucosa. By TEM, the small intestine villus morphology and intercellular spaces were nearly normal in melatonin-treated mice. At the level of the mitochondria, melatonin treatment significantly restored the activities of ATPase and SDH.

CONCLUSION

The intestinal damage and increased intestinal permeability induced by diclofenac in mice was limited by melatonin; moreover, melatonin preserved several aspects of mitochondrial function.

LC-MS/MS for immunosuppressant therapeutic drug monitoring

Due to their narrow therapeutic indices and highly variable pharmacokinetics, therapeutic drug monitoring is necessary to individualize immunosuppressant dosage following organ transplantation. Until recently, monitoring was performed primarily using immunoassays, however, there is an increasing shift to HPLC coupled with MS/MS, due to its greater sensitivity and specificity. Online sample clean-up with either a single analytical column or with 2D chromatography significantly reduces manual handling and is essential to minimize matrix effects and maximize specificity and, coupled with rapid chromatography, allows the simultaneous analysis of the major immunosuppressants, with rapid sample throughput. Thus, LC-MS/MS is an attractive and versatile technique that facilitates rapid development of analytical methods, including new immunosuppressants as they become approved for clinical use.

Acyl glucuronides: the good, the bad and the ugly

Acyl glucuronidation is the major metabolic conjugation reaction of most carboxylic acid drugs in mammals. The physiological consequences of this biotransformation have been investigated incompletely but include effects on drug metabolism, protein binding, distribution and clearance that impact upon pharmacological and toxicological outcomes. In marked contrast, the exceptional but widely disparate chemical reactivity of acyl glucuronides has attracted far greater attention. Specifically, the complex transacylation and glycation reactions with proteins have provoked much inconclusive debate over the safety of drugs metabolised to acyl glucuronides. It has been hypothesised that these covalent modifications could initiate idiosyncratic adverse drug reactions. However, despite a large body of in vitro data on the reactions of acyl glucuronides with protein, evidence for adduct formation from acyl glucuronides in vivo is limited and potentially ambiguous. The causal connection of protein adduction to adverse drug reactions remains uncertain. This review has assessed the intrinsic reactivity, metabolic stability and pharmacokinetic properties of acyl glucuronides in the context of physiological, pharmacological and toxicological perspectives. Although numerous experiments have characterised the reactions of acyl glucuronides with proteins, these might be attenuated substantially in vivo by rapid clearance of the conjugates. Consequently, to delineate a relationship between acyl glucuronide formation and toxicological phenomena, detailed pharmacokinetic analysis of systemic exposure to the acyl glucuronide should be undertaken adjacent to determining protein adduct concentrations in vivo. Further investigation is required to ascertain whether acyl glucuronide clearance is sufficient to prevent covalent modification of endogenous proteins and consequentially a potential immunological response.

Drug-induced Injury of the Gastrointestinal Tract

The effects of drugs on the gastrointestinal tract are diverse and depend on numerous factors. Diagnosis is centered on histologic findings, with mostly nonspecific patterns of injury that must be interpreted in the correct clinical context. Nonsteroidal antiinflammatory drugs are a common cause of drug-induced gastrointestinal injury, with effects primarily in the gastric mucosa but also throughout the gastrointestinal tract. Another common class of drugs causing a variety of pathologic findings in the gut is chemotherapeutic agents. This article discusses the differential diagnosis of the various patterns of injury, including ischemic damage, and the histologic findings specific for certain drugs.

Inflammatory stress and idiosyncratic hepatotoxicity: hints from animal models

Adverse drug reactions (ADRs) present a serious human health problem. They are major contributors to hospitalization and mortality throughout the world (Lazarou et al., 1998; Pirmohamed et al., 2004). A small fraction (less than 5%) of ADRs can be classified as "idiosyncratic." Idiosyncratic ADRs (IADRs) are caused by drugs with diverse pharmacological effects and occur at various times during drug therapy. Although IADRs affect a number of organs, liver toxicity occurs frequently and is the primary focus of this review. Because of the inconsistency of clinical data and the lack of experimental animal models, how IADRs arise is largely undefined. Generation of toxic drug metabolites and induction of specific immunity are frequently cited as causes of IADRs, but definitive evidence supporting either mechanism is lacking for most drugs. Among the more recent hypotheses for causation of IADRs is that inflammatory stress induced by exogenous or endogenous inflammagens is a susceptibility factor. In this review, we give a brief overview of idiosyncratic hepatotoxicity and the inflammatory response induced by bacterial lipopolysaccharide. We discuss the inflammatory stress hypothesis and use as examples two drugs that have caused IADRs in human patients: ranitidine and diclofenac. The review focuses on experimental animal models that support the inflammatory stress hypothesis and on the mechanisms of hepatotoxic response in these models. The need for design of epidemiological studies and the potential for implementation of inflammation interaction studies in preclinical toxicity screening are also discussed briefly.

Intrinsic versus idiosyncratic drug-induced hepatotoxicity--two villains or one?

"Intrinsic" and "idiosyncratic" drug-induced liver injury reactions are commonly thought to arise by different modes of action. Intrinsic toxicity is reproducible in animals and occurs dose-dependently at sublethal doses. Environmental and genetic sensitivity factors can influence the toxicity of intrinsic hepatotoxicants. Among these is inflammatory stress. For example, exposure of mice to inflammatory bacterial lipopolysaccharide (LPS) causes a leftward shift in the dose-response relationship for acetaminophen hepatotoxicity; that is, acetaminophen toxicity is enhanced by LPS-induced inflammatory stress. Idiosyncratic reactions present themselves very differently than intrinsic ones; they happen in a minority of patients, with variable time of onset and no obvious relationship to drug dose, and they are not reproducible in usual animal tests. Although these characteristics seem to distinguish them from intrinsic reactions, consideration of fundamental principles of dose response can explain the differences. For a drug that causes idiosyncratic hepatotoxicity, the liver may not be a typical target for toxicity because the dose-response curve for hepatotoxicity lies to the right of the lethal dose. However, a sporadically occurring sensitivity factor, such as an inflammatory episode, could shift the dose-response curve for hepatotoxicity to the left, thereby bringing hepatotoxic doses into the therapeutic range. This hypothesis can account for the bizarre characteristics of idiosyncratic reactions and is supported by recent results showing that several drugs associated with human idiosyncratic reactions can be rendered hepatotoxic to rodents upon interaction with an inflammatory stimulus. In light of this view, intrinsic and idiosyncratic reactions may not be that different after all.

Protection from diclofenac-induced small intestinal injury by the JNK inhibitor SP600125 in a mouse model of NSAID-associated enteropathy

Small intestinal ulceration, bleeding, and inflammation are major adverse effects associated with the use of diclofenac (DCF) or other nonsteroidal anti-inflammatory drugs (NSAIDs). The underlying mechanisms of DCF enteropathy are poorly understood, but there is increasing evidence that topical effects are involved. The aim of this study was to explore the role of c-Jun-N-terminal kinase (JNK) in DCF-induced enterocyte death because JNK not only regulates mitochondria-mediated apoptosis but also is a key node where many of the proximal stress signals converge. Male C57BL/6J mice were injected intraperitoneally with DCF or vehicle (Solutol HS-15), and the extent of small intestinal ulceration was determined. A single dose of DCF (60 mg/kg) produced numerous ulcers in the third and fourth quartiles of the jejunum and ileum, with maximal effects after 18 h and extensive recovery after 48 h. To study the molecular pathways leading to enterocyte injury, we isolated villi-enriched mucosal fractions from DCF-treated mice. Immunoblot studies with a phosphospecific JNK antibody revealed that JNK1/2 (p46) was activated at 6 h, leading to phosphorylation of the downstream target c-Jun. The levels of the JNK-regulated proapoptotic transcription factor C/EBP homologous protein (CHOP) were also increased after DCF. The selective JNK inhibitor SP600125 (30 mg/kg ip), given both 1 h before and 1 h after DCF, blocked JNK kinase activity and afforded significant protection against DCF enteropathy. In conclusion, these data demonstrate that the JNK pathway is critically involved in the pathogenesis of DCF-induced enteropathy and suggest a potential application of JNK inhibitors in the prevention of NSAID-induced enteropathy.

Suppression of gastric acid increases the risk of developing immunoglobulin E-mediated drug hypersensitivity: human diclofenac sensitization and a murine sensitization model

BACKGROUND

Hypersensitivity reactions towards non-steroidal anti-inflammatory drugs (NSAID) are common, although true allergies are detectable only in a subgroup of patients. The current study was prompted by a case observation, where a patient experienced generalized urticaria following his second course of diclofenac and proton pump inhibitor medication, and was found to have diclofenac-specific IgE. During recent years, our group has been investigating the importance of gastric digestion in the development of food allergies, demonstrating anti-acid medication as a risk factor for sensitization against food proteins.

OBJECTIVE

Here, we aimed to investigate whether the mechanism of food allergy induction described can also be causative in NSAID allergy, using diclofenac as a paradigm.

METHODS

We subjected BALB/c mice to several oral immunization regimens modelled after the patient's medication intake. Diclofenac was applied with or without gastric acid suppression, in various doses, alone or covalently coupled to albumin, a protein abundant in gastric juices. Immune responses were assessed on the antibody level, and functionally examined by in vitro and in vivo crosslinking assays.

RESULTS

Only mice receiving albumin-coupled diclofenac under gastric acid suppression developed anti-diclofenac IgG1 and IgE, whereas no immune responses were induced by the drug alone or without gastric acid suppression. Antibody induction was dose dependent with the group receiving the higher dose of the drug showing sustained anti-diclofenac titres. The antibodies induced triggered basophil degranulation in vitro and positive skin tests in vivo.

CONCLUSION

Gastric acid suppression was found to be a causative mechanism in the induction of IgE-mediated diclofenac allergy.

Exacerbation of inflammatory bowel diseases associated with the use of nonsteroidal anti-inflammatory drugs: myth or reality?

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs), conventional and selective cyclooxygenase-2 (COX-2) inhibitors, are among the most widely used medications for the treatment of various inflammatory conditions. There is strong evidence of a possible association between the use of these drugs and the relapse of inflammatory bowel diseases (IBD).

OBJECTIVE

Our objective was to examine the literature regarding the exacerbation of IBD associated with the use of conventional NSAIDs and selective COX-2 inhibitors and the underlying pathogenetic mechanisms.

STUDY DESIGN

We reviewed articles, including original papers, controlled trials, case reports, reviews, and editorials published in English at the PubMed, Scopus Database, and Science Direct database, searching with the following keywords: nonsteroidal anti-inflammatory drugs (NSAIDs), COX-2 inhibitors, Coxibs, inflammatory bowel diseases (IBD), ulcerative colitis (UC), Crohn's disease (CD).

RESULTS

There is substantial evidence that exacerbation of IBD happens after treatment with NSAIDs, but the available data remain conflicting, and it is not clear whether selective COX-2 inhibitors are safer than traditional NSAIDs. However, there is some evidence that selective COX-2 inhibition and COX-1 inhibition (with low-dose aspirin) appear to be well-tolerated in the short term. Regarding the mechanisms of relapse, the reduction of prostaglandins appears to be the hallmark of the NSAIDs adverse effects.

CONCLUSIONS

Further randomized, double-blind, controlled trials should be performed to address this issue, and more in vitro studies to identify the pathways involved are required.

Distribution of intraperitoneally injected diclofenac in brown trout (Salmo trutta f. fario)

The detection of low levels of pharmaceuticals in aquatic environments has lately raised concerns regarding possible adverse effects of these highly active substances on aquatic organisms. The non-steroidal anti-inflammatory drug diclofenac (DCF) is one of the pharmaceutical substances regularly detected in surface waters and has lately been demonstrated to elicit adverse effects in salmonid species at environmentally relevant concentrations. The aim of the present study was to investigate the distribution of DCF in indigenous brown trout (Salmo trutta f. fario) following intraperitoneal (i.p.) injection of a single dose of (14)C-labelled DCF. A distribution kinetic over 36 h provides information on possible accumulation of DCF in different organs as well as on DCF detoxification in trout, possibly enabling identification of sites of preferential toxicity. Approximately 57% of the total single DCF dose appeared in the bile 6 h after i.p. application. Subsequently, DCF was observed to undergo enterohepatic cycling with an amount of (14)C-activity comparable to the 6 h bile values reappearing in bile 36 h after application. Results for (14)C-activity in intestine and pylori support the observation of enterohepatic cycling with a small peak in intestine at 3 h post i.p. injection and a low peak in intestine and pylori at 6 h post i.p. injection, reflecting presence of the drug substance in bile. The highest activity in intestine was found 24 h post-injection coinciding with low levels in bile, followed by a gradual decrease of activity in intestine mirroring the re-uptake of DCF into bile. The finding of enterohepatic cycling of DCF in brown trout is suggestive of a prolonged retention of DCF in brown trout.

Acute effects of diclofenac and DMSO to Daphnia magna: immobilisation and hsp70-induction

To determine the toxicity of the anti-rheumatic drug diclofenac to Daphnia magna, acute toxicity tests according to the OECD guideline 202 were combined with biochemical investigations of the hsp70 level as a biomarker for proteotoxicity. Particular attention was paid to the impact of the solvent DMSO as a confounding factor to diclofenac toxicity by means of testing different variations of producing stock solutions. In the acute immobilisation tests, diclofenac was most toxic as a singular test substance, with indication of a slight antagonistic interaction between the two substances. The highest EC50 values were obtained in those approaches using diclofenac pre-dissolved in DMSO. Thus, the observed antagonism seems to be intensified by pre-dissolution. Hsp70 levels of 12- to 19-days-old D. magna were determined after 48h exposure using a highly reproducible immunological protocol. Hsp70 induction occurred at a LOEC of 30mgl(-1) diclofenac plus 0.6mll(-1) DMSO, and at a LOEC of 40mgl(-1) for diclofenac alone. In summary, DMSO showed only slight confounding effects on diclofenac action in the applied range of concentrations.

Plasma concentrations of mycophenolic acid acyl glucuronide are not associated with diarrhea in renal transplant recipients

The aim of this study was to determine whether plasma concentrations of the acyl (AcMPAG) and phenolic (MPAG) glucuronide metabolites of mycophenolic acid (MPA) were related to diarrhoea in renal transplant patients on mycophenolate mofetil (MMF) with cyclosporine (CsA) or tacrolimus (TCL). Blood samples (0, 30, 120 min) were taken at days 3, 10, week 4, months 3, 6 and 12 for determination of MPA, MPAG and AcMPAG. MPA-AUC was estimated using validated algorithms. Two hour AUCs were calculated for MPAG and AcMPAG. Immunosuppressive therapy consisted of CsA/MMF (n= 110) and of TCL/MMF (n= 180). In 70/290 (24%) patients 86 episodes of diarrhoea were recorded during 12 months. Significantly more patients on TCL (31.1%) suffered from diarrhea compared to CsA (12.7%). MMF dose, MPA-AUC and the 2 h AUCs of MPAG and AcMPAG did not differ between patients with and without diarrhoea. Plasma AcMPAG and MPAG concentrations were substantially higher in patients on CsA compared with TCL, while MPA-AUC was lower in the former group. These data support the concept that CsA inhibits the biliary excretion of MPAG and AcMPAG, thereby potentially reducing the risk of intestinal injury through enterohepatic recycling of MPA and its metabolites.

Intestinal tract injury by drugs: Importance of metabolite delivery by yellow bile road

Drug secretion into bile is typically considered a safe route of clearance. However, biliary delivery of some drugs or their reactive metabolites to the intestinal tract evokes adverse consequences due to direct toxic actions or indirect disruption of intestinal homeostasis. Biliary concentration of the chemotherapy agent 5-fluorodeoxyuridine (FUDR) and other compounds is associated with bile duct damage while enterohepatic cycling of antibiotics contributes to the disruptions of gut flora that produce diarrhea. The goal of this review is to describe key evidence that biliary delivery is an important factor in the intestinal injury caused by representative drugs. Emphasis will be given to 3 widely used drugs whose reactive metabolites are plausible causes of small intestinal injury, namely the nonsteroidal anti-inflammatory drug (NSAID) diclofenac, the immunosuppressant mycophenolic acid (MPA), and the chemotherapy agent irinotecan. Capsule endoscopy and other sensitive diagnostic techniques have documented a previously unappreciated, high prevalence of small intestinal injury among NSAID users. Clinical use of MPA and irinotecan is frequently associated such severe intestinal injury that dosage must be reduced. Observations from clinical and experimental studies have defined key events in the pathogenesis of these drugs, including roles for multidrug resistance-associated protein 2 (MRP2) and other transporters in biliary secretion and adduction of enterocyte proteins by reactive acyl glucuronide metabolites as a likely mechanism for intestinal injury. New strategies for minimizing the adverse intestinal consequences of irinotecan chemotherapy illustrate how basic information about key events in the biliary secretion of drugs and the nature of their proximate toxicants can lead to safer protocols for drugs.

Combined effects of bovine colostrum and glutamine in diclofenac-induced bacterial translocation in rat

BACKGROUND AND AIMS

The aim of this study was to examine whether the combined administration of bovine colostrum and glutamine was able to prevent the non-steroidal anti-inflammatory drug (NSAID)-induced gut damage and bacterial translocation (BT) in the rats.

METHODS

The animal model population of the study consisted of six groups; control group, diclofenac group, diclofenac with milk group, diclofenac with colostrum group, diclofenac with glutamine group and diclofenac with colostrum and glutamine group. The animals with milk, colostrum or glutamine were fed with low fat milk, liquid colostrum or glutamine by orogastric gavage for 5 days before the diclofenac administration. Intestinal permeability, serum biochemical profiles and intestinal adhesion for assessment of the gut damage, and enteric bacterial overgrowth and BT at the mesenteric lymph nodes, liver, spleen and systemic blood were measured.

RESULTS

Diclofenac caused the increase in gut damage, enteric bacterial numbers and BT. Supplements with colostrum or glutamine reduced these changes induced by diclofenac, but this result was not seen for supplementation with low fat milk. Combined administration of colostrum and glutamine reduced diclofenac-induced gut damage and BT as compared to the use of bovine colostrum alone or glutamine alone.

CONCLUSIONS

This study suggested that the combined administration of bovine colostrum and glutamine might effectively reduce NSAID-induced gut damage and BT in the rat.

Efficient high performance liquid chromatograph/ultraviolet method for determination of diclofenac and 4′-hydroxydiclofenac in rat serum

A rapid and sensitive high-performance liquid chromatographic method was developed for determination of diclofenac and its major metabolite, 4'-hydroxydiclofenac, in serum from rats treated with diclofenac. The method is simple with a one-step extraction procedure, isocratic HPLC separation, and UV detection at 280 nm. Use of N-phenylanthranilic acid as the internal standard provided good accuracy without interference by endogenous compounds or 5-hydroxydiclofenac, another metabolite of interest. Limits of detection for diclofenac and 4'-hydroxydiclofenac were 0.0225 and 0.0112 microg/ml, respectively. Average extraction efficiencies of diclofenac, 4'-hydroxydiclofenac, and the internal standard were >/=76%. The method was applied to serum collected at 3h after rats were treated with an experimentally useful dosage range of 3, 10 and 50mg/kg diclofenac. Recovery (as a percentage of dose) for the 4'-hydroxy metabolite in serum was found to consistently average from 0.10 to 0.12% following each dosage, whereas recovery of diclofenac in serum declined from 0.45 to 0.37%. Thus, the method is suitable for measurement of a major diclofenac metabolite in experimental studies.

Glucuronidation in therapeutic drug monitoring

BACKGROUND

Glucuronidation is a major drug-metabolizing reaction in humans. A pharmacological effect of glucuronide metabolites is frequently neglected and the value of therapeutic drug monitoring has been questioned. However, this may not always be true.

METHODS

In this review the impact of glucuronidation on therapeutic drug monitoring has been evaluated on the basis of a literature search and experience from the own laboratory.

RESULTS

The potential role of monitoring glucuronide metabolite concentrations to optimize therapeutic outcome is addressed on the basis of selected examples of drugs which are metabolized to biologically active/reactive glucuronides. Furthermore indirect effects of glucuronide metabolites on parent drug pharmacokinetics are presented. In addition, factors that may modulate the disposition of these metabolites (e.g. genetic polymorphisms, disease processes, age, and drug-drug interactions) are briefly mentioned and their relevance for the clinical situation is critically discussed.

CONCLUSION

Glucuronide metabolites can have indirect as well as direct pharmacological or toxicological effects. Although convincing evidence to support the introduction of glucuronide monitoring into clinical practice is currently missing, measurement of glucuronide concentrations may be advantageous in specific situations. If the glucuronide metabolite has an indirect effect on the pharmacokinetics of the parent compound, monitoring of the parent drug may be considered. Furthermore pharmacogenetic approaches considering uridine diphosphate (UDP) glucuronosyltransferases polymorphisms may become useful in the future to optimize therapy with drugs subject to glucuronidation.

Water-borne diclofenac affects kidney and gill integrity and selected immune parameters in brown trout (Salmo trutta f. fario)

The detection of residues of various pharmaceuticals in surface waters during the last two decades has prompted concerns about possible adverse effects of this kind of pollution on aquatic organisms. The objective of the present study was to investigate effects of the non-steroidal anti-inflammatory drug diclofenac, one of the pharmaceuticals most prevalent in surface waters, on brown trout (Salmo trutta f. fario), a salmonid species native to German rivers. Brown trout were exposed to 0.5, 5 and 50 microg/L diclofenac for 7, 14 and 21 days, whereby the lowest exposure concentration is comparable with concentrations commonly found in the aquatic environment. Fish exposed to diclofenac displayed significantly reduced haematocrit levels after 7 and 14 days of exposure. After 21 days, trout were examined for histopathological alterations, whereby diclofenac exposure resulted in increased monocyte infiltration in the liver, telangiectasis in gills, and the occurrence of interstitial hyaline droplets, interstitial proteinaceous fluid and mild tubular necrosis in trunk kidney. Concurrent immunohistological analysis revealed an increase of granulocyte numbers in primary gill filaments, as well as granulocyte accumulation and increased major histocompatibility complex (MHC) II expression in kidney, suggestive of an inflammatory process in these organs. Moreover, the ability of diclofenac to hinder the stimulation of prostaglandin E2 synthesis was shown in head kidney macrophages of brown trout in vitro. These findings support the hypothesis that environmental exposure of fish to diclofenac provokes the same mechanism of action in these non-target organisms as previously described for mammalian species and can thus lead to similar (possibly adverse) effects. In general, the present study suggests that exposure of brown trout to diclofenac in concentration ranges commonly found in the environment can result in adverse effects in various organs and possibly compromise the health of affected fish populations.

Complications intestinales liées aux AINS

Chronic use of non-salicylate NSAIDs causes in most individuals an asymptomatic enteropathy involving the small bowel, particularly its distal part. This enteropathy is characterised by an increase in intestinal permeability and a mild mucosal inflammation. Hypoalbuminemia and iron deficiency may occur. In addition, non-salicylate NSAIDs may cause focal lesions of the small intestine. Ulcerations and ulcers, that can be accidentally discovered during an ileoscopy, may cause acute or chronic bleeding. Deep ulcers may provoke sudden peritonitis. Small bowel diaphragms are rare fibrotic lesions, specifically associated with the use of non-salicylate NSAIDs or salicylates (duodenal diaphragms only). NSAID use is not associated with a constant toxicity on colonic mucosa. NSAID-induced colonic ulcers and diaphragms are rare. In patients with colonic diverticulosis, NSAID intake is a risk factor for severe attacks of diverticulitis. Acute or chronic use of non-salicylate NSAIDs increases the risk for ischemic colitis and flare-ups of inflammatory bowel disease. De novo colitis caused by non-salicylate NSAIDs are rare. The definite diagnosis of this entity relies on the absence of recurrence of colitis in the 2-3 following years. Such a recurrence would lead to the post-hoc diagnosis of first attack of inflammatory bowel disease triggered by NSAID use. Experimental data suggest that selective COX-2 inhibitors do not alter constantly mucosa of the small intestine. Pilot epidemiological works suggest that severe intestinal lesions are less frequent in association with COX-2 inhibitor use than in association with conventional NSAIDs. However, COX-2 appears as playing a beneficial role in mucosal healing, and it seems that COX-2 inhibitors, like conventional NSAIDs, may trigger flare-ups of inflammatory bowel disease.

Acyl glucuronide reactivity in perspective: biological consequences

The metabolic conjugation of exogenous and endogenous carboxylic acid substrates with endogenous glucuronic acid, mediated by the uridine diphosphoglucuronosyl transferase (UGT) superfamily of enzymes, leads to the formation of acyl glucuronide metabolites. Since the late 1970s, acyl glucuronides have been increasingly identified as reactive electrophilic metabolites, capable of undergoing three reactions: intramolecular rearrangement, hydrolysis, and intermolecular reactions with proteins leading to covalent drug-protein adducts. This essential dogma has been accepted for over a decade. The key question proposed by researchers, and now the pharmaceutical industry, is: does or can the covalent modification of endogenous proteins, mediated by reactive acyl glucuronide metabolites, lead to adverse drug reactions, perhaps idiosyncratic in nature? This review evaluates the evidence for acyl glucuronide-derived perturbation of homeostasis, particularly that which might result from the covalent modification of endogenous proteins and other macromolecules. Because of the availability of acyl glucuronides for test tube/in vitro experiments, there is now a substantial literature documenting their rearrangement, hydrolysis and covalent modification of proteins in vitro. It is certain from in vitro experiments that serum albumin, dipeptidyl peptidase IV, tubulin and UGTs are covalently modified by acyl glucuronides. However, these in vitro experiments have been specifically designed to amplify any interference with a biological process in order to find biological effects. The in vivo situation is not at all clear. Certainly it must be concluded that all humans taking carboxylate drugs that form reactive acyl glucuronides will form covalent drug-protein adducts, and it must also be concluded that this in itself is normally benign. However, there is enough in vivo evidence implicating acyl glucuronides, which, when backed up by in vivo circumstantial and documented in vitro evidence, supports the view that reactive acyl glucuronides may initiate toxicity/immune responses. In summary, though acyl glucuronide-derived covalent modification of endogenous macromolecules is well-defined, the work ahead needs to provide detailed links between such modification and its possible biological consequences.

Acyl glucuronide drug metabolites: toxicological and analytical implications

Although glucuronidation is generally considered a detoxification route of drug metabolism, the chemical reactivity of acyl glucuronides has been linked with the toxic properties of drugs that contain carboxylic acid moieties. It is now well documented that such metabolites can reach appreciable concentrations in blood. Furthermore, they are labile, undergo hydrolysis and pH-dependent intramolecular acyl migration to isomeric conjugates of glucuronic acid, and may react irreversibly with plasma proteins, tissue proteins, and with nucleic acids. This stable binding causes chemical alterations that are thought to contribute to drug toxicity either through changes in the functional properties of the modified molecules or through antigen formation with subsequent hypersensitivity and other immune reactions. Whereas in vitro data on the toxicity of acyl glucuronides have steadily accumulated, direct evidence for their toxicity in vivo is scarce. Acyl glucuronides display limited stability, which is dependent on pH, temperature, nature of the aglycon, and so on. Therefore, careful sample collection, handling, and storage procedures are critical to ensure generation of reliable pharmacologic and toxicologic data during clinical studies. Acyl glucuronides can be directly quantified in biologic specimens using chromatographic procedures. Their adducts with plasma or cell proteins can be determined after electrophoretic separation, followed by blotting. ELISA techniques have been used to assess the presence of antibodies against acyl glucuronide-protein adducts. This review summarizes the most recent evidence concerning biologic and toxicologic effects of acyl glucuronide metabolites of various drugs and discusses their relevance for drug monitoring. A critical evaluation of the available methodology is included.

Mechanisms of NSAID-induced hepatotoxicity: focus on nimesulide

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been associated with idiosyncratic hepatotoxicity in susceptible patients. The molecular mechanisms underlying this toxicity have not yet been fully elucidated. However, experimental evidence suggests that they include increased concentration of the drugs in the hepatobiliary compartment, formation of reactive metabolites that covalently modify proteins and produce oxidative stress, and mitochondrial injury. Genetic and/or acquired patient factors can either augment the pathways leading to hepatic toxicity or impede the protective and detoxifying pathways. An example is nimesulide, a selective cyclo-oxygenase-2 inhibitor widely used for the treatment of inflammatory and pain conditions, which has been recently associated with rare but serious and unpredictable adverse reactions in the liver (increases in serum aminotransferase activities, hepatocellular necrosis, and/or intrahepatic cholestasis). Similar to other drugs causing idiosyncratic hepatotoxicity, both the molecule and the patient contribute to the hazard. Here, the weakly acidic sulfonanilide drug undergoes bioreductive metabolism of the nitroarene group to reactive intermediates that have been implicated in oxidative stress, covalent binding, and mitochondrial injury. It is only in a small number of susceptible patients, however, that genetic or nongenetic factors will cause this potential toxicity to become clinically manifest. In view of the very large recipient population, the incidence of nimesulide-induced liver injury has been low (approximately 0.1 per 100,000 patients treated). Although this estimation is based on spontaneous reporting data versus sales units and needs correction due to the classical bias of this system, the type and incidence of these rare but severe hepatic adverse reactions are comparable to that of other NSAIDs.