The effect of the enantiomers of ibuprofen and flurbiprofen on the beta-oxidation of palmitate in the rat

Dose-dependent effects of acetaminophen and ibuprofen on mitochondrial respiration of human platelets

Acetaminophen and ibuprofen are widely used over-the-counter medications to reduce fever, pain, and inflammation. Although both drugs are safe in therapeutic concentrations, self-medication is practiced by millions of aged patients with comorbidities that decrease drug metabolism and/or excretion, thus raising the risk of overdosage. Mitochondrial dysfunction has emerged as an important pathomechanism underlying the organ toxicity of both drugs. Assessment of mitochondrial oxygen consumption in peripheral blood cells is a novel research field Cu several applications, including characterization of drug toxicity. The present study, conducted in human platelets isolated from blood donor-derived buffy coat, was aimed at assessing the acute, concentration-dependent effects of each drug on mitochondrial respiration. Using the high-resolution respirometry technique, a concentration-dependent decrease of oxygen consumption in both intact and permeabilized platelets was found for either drug, mainly by inhibiting complex I-supported active respiration. Moreover, ibuprofen significantly decreased the maximal capacity of the electron transport system already from the lowest concentration. In conclusion, platelets from healthy donors represents a population of cells easily available, which can be routinely used in studies assessing mitochondrial drug toxicity. Whether these results can be recapitulated in patients treated with these medications is worth further investigation as potential peripheral biomarker of drug overdose.

Transcriptional and cellular effects of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) in experimentally exposed mussels, Mytilus galloprovincialis

The aim of the present investigation was to provide new insights on accumulation and possible adverse effects of various non-steroidal anti-inflammatory drugs (NSAIDs) in mussels, Mytilus galloprovincialis, exposed to an environmentally realistic concentration (0.5μg/L) of individual compounds, Acetaminophen (AMP), Diclofenac (DIC), Ibuprofen (IBU), Ketoprofen (KET) or Nimesulide (NIM). The measurement of drugs in mussel tissues was integrated with both functional alterations at cellular level and transcriptomic responses. Results indicated the capability of mussels to accumulate DIC and NIM, while AMP, IBU and KET were always below detection limit. A large panel of ecotoxicological biomarkers revealed the early onset of alterations induced by tested NSAIDs on immunological responses, lipid metabolism and DNA integrity. The gene transcription analysis through DNA microarrays, supported cellular biomarker results, with clear modulation of a large number of genes involved in the arachidonic acid and lipid metabolism, immune responses, cell cycle and DNA repair. The overall results indicated an ecotoxicological concern for pharmaceuticals in M. galloprovincialis, with transcriptional responses appearing as sensitive exposure biomarkers at low levels of exposure: such changes, however, are not always paralleled by corresponding functional effects, suggesting caution when interpreting observed effects in terms of perturbed cellular pathways. Fascinating similarities can also be proposed in the mode of action of NSAIDs between bivalves and vertebrate species.

Ecotoxicological potential of non-steroidal anti-inflammatory drugs (NSAIDs) in marine organisms: Bioavailability, biomarkers and natural occurrence in Mytilus galloprovincialis

Pharmaceuticals represent a major environmental concern since the knowledge on their occurrence, distribution and ecotoxicological potential is still limited particularly in coastal areas. In this study, bioaccumulation and cellular effects of various non steroidal anti-inflammatory drugs (NSAIDs) were investigated in mussels Mytilus galloprovincialis to reveal whether common molecules belonging to the same therapeutic class might cause different effects on non target organisms. Organisms exposed to environmental concentrations of acetaminophen (AMP), diclofenac (DIC), ibuprofen (IBU), ketoprofen (KET) and nimesulide (NIM) revealed a significant accumulation of DIC, IBU and NIM, while AMP and KET were always below detection limit. Nonetheless, for all tested NSAIDs, measurement of a large panel of ecotoxicological biomarkers highlighted impairment of immunological parameters, onset of genotoxicity and modulation of lipid metabolism, oxidative and neurotoxic effects. Laboratory results were integrated with a field study which provided the first evidence on the occurrence of DIC, IBU and NIM in tissues of wild mussels sampled during summer months from an unpolluted, touristic area of Central Adriatic Sea. Overall results demonstrated M. galloprovincialis as a good sentinel species for monitoring presence and ecotoxicological hazard of pharmaceuticals in the Mediterranean.

Dissection of metabolic, vascular, and nerve conduction interrelationships in experimental diabetic neuropathy by cyclooxygenase inhibition and acetyl-L-carnitine administration

Alterations in cyclooxygenase (COX) pathway activity have been implicated in the pathogenesis of experimental diabetic neuropathy (EDN). These studies explore the relationships between COX-mediated and acetyl-L-carnitine (ALC)-sensitive defects that contribute to functional, metabolic, and vascular abnormalities of EDN. The effects of nonselective COX inhibition with flurbiprofen were contrasted with selective COX-2 inhibition with meloxicam, administered alone and in combination with ALC in nondiabetic (ND) and streptozotocin-induced diabetic (STZ-D) rats. Flurbiprofen treatment of ND rats replicated many of the biochemical and physiological abnormalities of EDN, i.e., reduced motor nerve conduction velocity (MNCV), total and endoneurial nerve blood flow (NBF), Na,K-ATPase activity, and myo-inositol (MI) and taurine content. In STZ-D rats, however, flurbiprofen paradoxically prevented endoneurial NBF deficits but not MNCV slowing. Coadministration of 50 mg x kg(-1) x day(-1) ALC prevented reductions in MNCV, Na,K-ATPase activity, and endoneurial NBF in flurbiprofen-treated ND and STZ-D rats. In contrast, selective COX-2 inhibition with meloxicam was without effect on MNCV, NBF, or MI content in ND rats and prevented MNCV slowing and NBF deficits in STZ-D rats. Western blot analysis showed unchanged sciatic nerve COX-1 protein but increased COX-2 protein abundance in STZ-D versus ND rats. These results imply 1) a tonic role of the COX-1 pathway in the regulation of nerve osmolytes and Na,K-ATPase activity and the maintenance of NBF in ND animals and 2) activation of the COX-2 pathway as an important mediator of NBF and MNCV deficits in EDN.

Chiral inversion of (R)-ketoprofen: influence of age and differing physiological status in dairy cattle

The chiral inversion of ketoprofen has been previously demonstrated in cattle, but no studies have been performed on different ages and metabolic situations in the animals. The aim of this work was to study any modifications of the stereoconversion of ketoprofen that occur by reason of age, lactation or gestation in dairy cows. Holando Argentino cattle were divided into three groups: 8 cows in early lactation, 8 pregnant cows and 8 newborn calves. Four animals from each group received the enantiomer R-(-)-ketoprofen by intravenous administration; the other four animals received the S-(+) enantiomer, all at doses of 0.5 mg/kg. Blood samples were collected at standardized times after dosing and assayed for ketoprofen by high-performance reversed-phase liquid chromatography (HPLC). The percentage inversion of R-(-)-ketoprofen to S-(+)-ketoprofen was 50.5% (SD +/- 2.4) in the preruminants, 33.3% (SD +/- 1.7) in cows in early lactation and 26.0% (SD +/- 5.1) in cows in gestation. These results indicate a differing enantioselective metabolic behaviour for one compound in one species under different physiological situations.

Expression of rat liver long-chain acyl-CoA synthetase and characterization of its role in the metabolism of R-ibuprofen and other fatty acid-like xenobiotics

Our investigations of fatty acid metabolism and epimerization of the 2-arylpropionic acid derivative, R-ibuprofen, resulted in the successful purification of an acyl-CoA synthetase from rat liver microsomes that catalyzes the formation of both palmitoyl-CoA and R-ibuprofenoyl-CoA. To investigate whether R-ibuprofenoyl-CoA synthetase and long-chain acyl-CoA synthetase (LACS) are identical enzymes, we cloned the cDNA from LACS into the pQE30 expression vector and transformed the construct into Escherichia coli M15[pREP4]. Induction of the bacterial protein synthesis with 0.2 mM isopropyl-beta-D-galactoside resulted in a strong, time-dependent increase in LACS protein as determined by Western blot analysis using a polyclonal rabbit anti-LACS antibody. Incubations of the recombinantly expressed protein with palmitic acid as physiological LACS substrate or R-ibuprofen in the presence of Mg2+, ATP, and CoA resulted in a 5-fold increase in the thioesterification of both substrates. Western blot analysis using tissue homogenates of rat liver, heart, kidney, lung, brain, and ileum showed that LACS was found in every tissue investigated, with the greatest expression in the liver. Similar results were obtained with activity measurements using R-ibuprofen and palmitic acid as substrates. Northern blot analysis revealed a hybridization with a 3.8-kb mRNA transcript in rat liver, heart, and kidney, but no signal was observed in lung, brain and ileum, suggesting the expression of different LACS isoform(s) in these organs. In summary, our results further show that R-ibuprofenoyl-CoA synthetase and long-chain acyl-CoA synthetase are identical enzymes that are involved in the metabolism of various xenobiotics.

Clinical Pharmacokinetics of Dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the (S)-(+)-enantiomer (dexketoprofen), while the (R)-(-)-enantiomer is devoid of such activity. The racemic ketoprofen exhibits little stereoselectivity in its pharmacokinetics. Relative bioavailability of oral dexketoprofen (12.5 and 25mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50mg, respectively), as measured in all cases by the area under the concentration-time curve values for (S)-(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the (S)-(+)-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. The drug does not accumulate significantly when administered as 25mg of free acid 3 times daily. The profile of absorption is changed when dexketoprofen is ingested with food, reducing both the rate of absorption (tmax) and the maximal plasma concentration. Dexketoprofen is strongly bound to plasma proteins, particularly albumin. The disposition of ketoprofen in synovial fluid does not appear to be stereoselective. Dexketoprofen trometamol is not involved in the accumulation of xenobiotics in fat tissues. It is eliminated following extensive biotransformation to inactive glucuroconjugated metabolites. No (R)-(-)-ketoprofen is found in the urine after administration of dexketoprofen, confirming the absence of bioinversion of the (S)-(+)-enantiomer in humans. Conjugates are excreted in urine, and virtually no drug is eliminated unchanged. The analgesic efficacy of the oral pure (S)-(+)-enantiomer is roughly similar to that observed after double dosages of the racemic compound. At doses above 7mg, dexketoprofen was significantly superior to placebo in patients with moderate to severe pain. A dose-response relationship between 12.5 and 25mg could be seen in the time-effects curves, the superiority of the 25mg dose being more a result of an extended duration of action than of an increase in peak analgesic effect. A plateau in the analgesic activity of dexketoprofen trometamol at the 25mg dose is suggested. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol. The drug was well tolerated.

Chiral inversion of R(-) fenoprofen and ketoprofen enantiomers in cats

The chiral inversion process is a characteristic metabolic pathway for different aryl-2-propionic acids or profens. Important variations have been observed between these individual compounds as well as between animal species. In this study, R(-) fenoprofen [R(-)FPF] and R(-) ketoprofen [R(-) KTF] were used to investigate their comparative stereoconversion in cats. After intravenous (i.v.) administration of R(-) FPF, the percentage of chiral inversion was 93.20+/-13.70%. A highly significant correlation (r: 0.978) was observed between the clearance of R(-) FPF and the chiral inversion process. After i.v. administration of R(-) KTF, the percentage of inversion was only 36.73+/-2.8%. No correlation between the clearance of R(-) KTF and this process was observed. R(-) FPF was metabolized by the pathways of thioesterification - chiral inversion processes. For R(-) KTF, the competitive metabolic pathways, glucuronidation and hydroxylation may be involved. However, these metabolic steps are saturable or less functional in cats. Moreover, the thioesterification of R(-) KTF in in vitro studies has been shown to be important in carnivores. The lack of correlation between clearance and chiral inversion process of R(-) KTF may be finally explained by deviation of thioesterification to other metabolic pathways of lipids and/or aminoacid conjugation, particulary glicine derivatives.

Do NSAIDs contribute to acute fatty liver of pregnancy?

Acute fatty liver of pregnancy (AFLP) and the childhood encephalopathy known as Reye's syndrome are both characterised by microvesicular steatosis. Mothers with AFLP are frequently heterozygous for a mutation which reduces the activity of the trifunctional protein (TP) of fatty-acid oxidation. Several lines of evidence suggest that blockade of fatty-acid oxidation may also be the underlying cause of Reye's syndrome, and epidemiological studies have identified aspirin taken during a viral illness as a contributing factor to the development of the disease. The hypotheses are presented:* that children with Reye's syndrome may also be heterozygous for TP mutation, and* that inhibition of the residual long-chain fatty-acid oxidation by NSAIDs including aspirin precipitates the similar symptoms observed in patients with Reye's syndrome and AFLP. Identification of NSAIDs as candidates for the unidentified factor which precipitates AFLP suggests that avoidance of NSAIDs during pregnancy may lead to a reduction in the incidence of this life-threatening disease.

Stereoselective and substrate-dependent inhibition of hepatic mitochondria beta-oxidation and oxidative phosphorylation by the non-steroidal anti-inflammatory drugs ibuprofen, flurbiprofen, and ketorolac

Non-steroidal anti-inflammatory drugs (NSAIDs) cause a range of adverse effects, some of which have been associated with perturbances of lipid metabolic pathways. Previous data demonstrating stereoselective formation of the CoA thioester of R-ibuprofen in particular were suggestive of possible stereoselective effects on lipid metabolism. Our aim was to characterise the relative stereoselectivity of the effects of ibuprofen, flurbiprofen, and ketorolac (0.01-1.0 mM) on both the beta-oxidation of palmitate and oxidative phosphorylation in rat hepatic mitochondria as a means of dissecting prostaglandin related from non-prostaglandin-related events. Beta-oxidation was inhibited stereoselectively by R-ibuprofen (P = 0.015), non-stereoselectively by R- and S-flurbiprofen (P = 0.002 and P = 0.004, respectively), and was essentially unaffected by either enantiomer of ketorolac. At 0.25 mM, inhibition by R-ibuprofen and both flurbiprofen enantiomers was partially reversed by increasing CoA concentrations (0-200 microM). Mitochondrial respiration was moderately inhibited by both enantiomers of ibuprofen and flurbiprofen (P < 0.01), but only by high concentrations (> or = 1 mM) of the enantiomers of ketorolac (P < 0.01). Uncoupling of oxidative phosphorylation measured as stimulation of State 4 respiration contributed to these effects. The data support interactions involving both stereoselective CoA-dependent and non-CoA-dependent mechanisms. The plasma drug concentrations required to achieve these effects are not likely to be attained in the majority of patients, although these concentrations are achievable in the gastrointestinal tract and may contribute to the well-known spectrum of adverse effects in this organ. Some patients do experience systemic adverse events which may be mediated by these mechanisms.

Effect of clofibrate on the chiral inversion of ibuprofen in healthy volunteers

OBJECTIVES

To determine the influence of the hypolipidemic drug clofibrate on the stereoselective metabolism of ibuprofen in humans.

METHODS

Healthy male subjects (n = 12) ingested a dose of 400 mg pseudoracemic ibuprofen (200 mg R-ibuprofen, 160 mg S-ibuprofen, and 40 mg 13C-S-ibuprofen) on two occasions after either pretreatment with clofibrate (2 gm/day over 1 week) or no pretreatment in a randomized order.

RESULTS

When subjects were pretreated with clofibrate, clearances of R-ibuprofen and 13C-S-ibuprofen increased significantly from 55.0 and 66.4 ml/min to 186.2 and 106.7 ml/min (p < 0.01), respectively. This increase was similarly reflected in the clearance by inversion of R-ibuprofen (control, 36.0 ml/min; treated, 118.8 ml/min; p < 0.01), as well as in the clearance by noninversion (control, 19.0 ml/min; treated, 67.4 ml/min; p < 0.01). Unbound clearance values significantly increased for R-ibuprofen (control, 19.5 L/min; treated, 38.7 L/min) but not for 13C-S-ibuprofen (11.8 versus 10.6 L/min, respectively). The fractional inversion of ibuprofen calculated from the urinary metabolite data was increased after clofibrate pretreatment (clofibrate group, 66.4%; control, 53.5%; p < 0.01). However, this was not evident when fractional inversion was calculated from the plasma concentration-time data for the unmetabolized drug.

CONCLUSIONS

Clofibrate altered the stereoselective disposition of ibuprofen in healthy volunteers by increased formation of R-ibuprofenoyl-coenzyme A rather than by an effect on oxidative metabolism of ibuprofen. This interaction has potential therapeutic implications.

Blockade of long chain fatty acid oxidation by non-steroidal anti-inflammatory drugs may contribute to inhibition of proliferation of human colorectal carcinoma cell lines

Non-steroidal anti-inflammatory drugs (NSAIDs) reduce the growth of colorectal carcinoma (CRC) cell lines. Although the mechanism appears to be independent of cyclooxygenases, the inhibitory target has not previously been defined. We now report for the first time that NSAIDs inhibit oxidation of the long chain fatty acid palmitate in human CRC cell lines with potencies which are in good agreement with the potencies of NSAIDs as inhibitors of cell proliferation. The absence of inhibition of acetate oxidation rules out an effect on mitochondrial functions. We conclude that the long chain fatty acid oxidation pathway may be a novel target for some of the inhibitory effects of NSAIDs on the growth of CRC cell lines.

New insights into the site and mode of antinociceptive action of flurbiprofen enantiomers

The S-enantiomer of flurbiprofen has been shown to have both antiinflammatory and antinociceptive effects, whereas R-flurbiprofen is antinociceptive but not antiinflammatory. Importantly, only S-flurbiprofen inhibited prostaglandin biosynthesis in vitro at therapeutic concentrations. R-flurbiprofen did not undergo significant chiral inversion to S-flurbiprofen in rats and humans. A study was conducted to gain new insight into the possible sites and modes of action of flurbiprofen enantiomers. In a modified Randall Selitto assay, both enantiomers were antinociceptive in a dose-dependent manner after systemic administration. After local administration into the inflamed paw, only S-flurbiprofen produced significant dose-related antinociception. In a physiologic study, we recorded extracellularly from nociceptive spinal cord neurons that were rendered hyperexcitable. Intravenous administration of R- and S-flurbiprofen reduced responses of neurons to pressure applied to the inflamed knee and the noninflamed ankle and paw in a dose-dependent manner. When injected directly into the knee joint, only S-flurbiprofen but not R-flurbiprofen reduced responses to pressure. These results suggest a central site of antinociceptive action for R- and S-flurbiprofen and an additional peripheral site for S-flurbiprofen. The findings may be of clinical relevance, as it was demonstrated that both enantiomers also were antinociceptive in humans. Because R-flurbiprofen caused less toxicity in rats than the S-enantiomer or the racemic compound, a reduction in the quantitatively most important side effects in the gastrointestinal tract might be achieved with the use of R-flurbiprofen for pain therapy.

Clofibric acid increases the undirectional chiral inversion of ibuprofen in rat liver preparations

1. The formation of (S)-ibuprofen from (R)-ibuprofen was monitored in perfused rat livers and in rat hepatocytes and the rate constants calculated. 2. Pre-treatment of animals for three days with clofibric acid markedly increased the (R)-to-(S) inversion of ibuprofen in both preparations. In contrast, clofibric acid did not elicit such a reaction with flurbiprofen, an analogue that does not undergo inversion under control conditions. 3. An increase in the chiral inversion was also seen when clofibric acid was added to the perfusion medium or to hepatocyte suspensions. In the latter system this increase was shown to be concentration dependent. 4. Pre-treatment of rat combined with addition of clofibric acid to the perfusion medium produced a cumulative stimulation of (R)-to-(S) inversion of ibuprofen. 5. Clofibric acid added to hepatocyte suspensions transiently increased intracellular concentrations of coenzyme A whereas (R)-ibuprofen transiently decreased CoA concentrations. The two effects cancelled each other upon co-incubation of the two compounds. 6. It is postulated that the metabolic interaction observed between clofibric acid and (R)-ibuprofen may be due to changes in intracellular concentrations of CoA.

Preclinical and clinical development of dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the S(+)-enantiomer (dexketoprofen), while the R(-)-enantiomer is devoid of such activity. The pharmacokinetic profile of ketoprofen and its enantiomers was assessed in several animals species and in human volunteers. In humans, the relative bioavailability of oral dexketoprofen trometamol (12.5 and 25 mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50 mg, respectively), as measured in all cases by the area under the concentration-time curve values for S(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the S-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. Peak plasma concentrations of 1.4 and 3.1 mg/L are reached after administration of dexketoprofen trometamol 12.5 and 25 mg, respectively. From 70 to 80% of the administered dose is recovered in the urine during the first 12 hours, mainly as the acyl-glucuronoconjugated parent drug. No R(-)-ketoprofen is found in the urine after administration of dexketoprofen [S(+)-ketoprofen], confirming the absence of bioinversion of the S(+)-enantiomer in humans. in animal studies, the anti-inflammatory potency of dexketoprofen was always equivalent to that demonstrated by twice the dose of ketoprofen. Similarly, animal studies showed a high analgesic potency for dexketoprofen trometamol. The R(-)-enantiomer demonstrated a much lower potency, its analgesic action being apparent only in conditions where the metabolic bioinversion to the S(+)-enantiomer was significant. The gastric ulcerogenic effect of dexketoprofen at various oral doses (1.5 to 6 mg/kg) in the rat do not differ from those of the corresponding double doses (3 to 12 mg/kg) of racemic ketoprofen. Repeated (5-day) oral administration of dexketoprofen as the trometamol salt causes less gastric ulceration than was observed after the acid form of both dexketoprofen and the racemate. In addition, single dose dexketoprofen as the free acid at 10 to 20 mg/kg does not show a significant intestinal ulcerogenic effect in rats, while racemic ketoprofen 20 or 40 mg/kg is clearly ulcerogenic to the small intestine. The analgesic efficacy of oral dexketoprofen trometamol 10 to 20 mg is superior to that of placebo and similar to that of ibuprofen 400 mg in patients with moderate to serve pain after third molar extraction. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol than in those treated with ibuprofen 400 mg. Dexketoprofen trometamol was well tolerated, with a reported incidence of adverse events similar to that of placebo.

In vitro fenoprofenyl-coenzyme A thioester formation: interspecies variations

In vitro coenzyme A thioester formation from (-)-(R)-fenoprofen (FPF) and palmitic acid has been studied using liver microsomes from rat, guinea pig, sheep, and dog. In every species with both palmitic acid or (-)-(R)-fenoprofen, the Lineweaver-Burk plot was linear in the substrate concentration range used and as a consequence agrees with the involvement of only one isoenzyme (or different isoenzymes of similar Km values). The Vmax values for the thioesterification of (-)-(R)-fenoprofen present large species variations from 2.1 +/- 1.0 with sheep liver microsomes to 60.6 +/- 11 nmol/min/mg with dog liver microsomes. These values statistically significantly correlate (r = 0.94) to the Vmax values observed when palmitic acid was used as a substrate. Furthermore palmitic acid inhibited (-)-(R)-fenoprofen-CoA formation in the same extent in all animal species. The stereoselectivity of the thioesterification was also species dependent.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

The role of coenzyme A in the biotransformation of 2-arylpropionic acids

A number of 2-arylpropionic acid non-steroidal anti-inflammatory drugs ('profens') undergo highly enantioselective inversion from the (R)- to (S)-enantiomer. The mechanism of this inversion reaction involves the initial enantioselective formation of a coenzyme A thioester followed by epimerization and finally hydrolysis to regenerate free acids. Long-chain fatty acyl-CoA synthetase appears to mediate the initial thioester formation and an epimerase of an unknown physiologic function effects the second step. The hydrolases mediating the final step are poorly defined. Available evidence suggests that the liver is quantitatively the most important tissue site of inversion but local tissue inversion may influence the pharmacological and toxicological response of a given organ. Data from isolated rat hepatocytes indicate that other xenobiotics can modulate the formation and hydrolysis of ibuprofenyl-CoA by influencing inversion pathways, non-inversion pathways or both. Interactions between xenobiotics may therefore accentuate inter-individual variability in response to 2-aryl-propionic acids. The formation of 2-arylpropionyl-CoA thioesters in vivo has the potential to disrupt numerous biochemical pathways in addition to enhancing individual exposure to the potent anti-inflammatory (S)-enantiomers.

Antinociceptive actions of R(-)-flurbiprofen--a non-cyclooxygenase inhibiting 2-arylpropionic acid--in rats

Intraperitoneal administration of R(-)- and S(+)-flurbiprofen resulted in dose dependent antinociceptive behavior in the rat paw formalin test. S(+)-flurbiprofen was significantly more potent than the non-cyclooxygenase inhibiting R(-)-enantiomer with a potency ratio of about 3 to 1. Chiral inversion was very low and does not seem to account for the action of R(-)-flurbiprofen. In a modified Randall Selitto assay also both enantiomers were active in a dose dependent manner following systemic administration. Following local administration into the inflamed paw only S(+)-flurbiprofen showed significant dose related antinociceptive effects. R(-)-flurbiprofen was unable to block prostaglandin E2 induced hyperalgesia following local administration. Consequently, a central site of action independent of prostaglandin synthesis inhibition has to be discussed with respect to antinociceptive activity following systemic administration.

Evaluation of human blood lymphocytes as a model to study the effects of drugs on human mitochondria. Effects of low concentrations of amiodarone on fatty acid oxidation, ATP levels and cell survival

Human lymphocytes were assessed as a cellular model for determining the effects of drugs on human mitochondria. Formation of total oxidized 14C-products was maximal with 1 mM [U-14C]palmitic acid, was linear for 90 min, linear with the number of lymphocytes, and decreased by 95% and 77% in the presence of 30 microM rotenone and 2 mM KCN. Seven drugs were tested which had previously been shown to inhibit beta-oxidation in animals; all decreased formation of total oxidized 14C-products by human lymphocytes, but with different IC50 values: 35 microM with amiodarone, 2.75 mM with tetracycline and amineptine, 3.75 mM with tianeptine, and more than 10 mM for valproic acid and the ibuprofen enantiomers. Formation of [14C]CO2 either increased or decreased, in relation to the various effects of these drugs on coupling, beta-oxidation, and the tricarboxylic acid cycle. There was a general trend for some relationship between inhibition of fatty acid oxidation and loss of cellular ATP. Those compounds, however, which uncoupled oxidative phosphorylation (2,4-dinitrophenol, amiodarone, ibuprofen) and/or inhibited the mitochondrial respiratory chain (amiodarone, rotenone, KCN) resulted in comparatively higher ATP depletion. Amiodarone, a drug which produces several effects (uncoupling, inhibition of beta-oxidation, of the tricarboxylic acid cycle and of the respiratory chain), caused a dramatic decrease in cellular ATP and cell viability at low concentrations (20-100 microM). Both these effects were prevented by the addition of 5 mM glucose, a substrate for anaerobic glycolysis. We conclude that human lymphocytes may be a useful model for assessing the effects of drugs on human mitochondrial function. IC50 values determined with this model may not necessarily apply, however, to other cells.

Pure enantiomers of 2-arylpropionic acids: tools in pain research and improved drugs in rheumatology

The mode of action of aspirinlike drugs in pain is widely referred to as inhibition of prostaglandin synthesis. Salicylic acid, however, at low doses, is an analgesic but not a potent anti-inflammatory agent. This "enigma" may be resolved by recent findings employing 2-arylpropionic acids. Pure enantiomers of these chiral drugs show a different pharmacodynamic and pharmacokinetic profile. Using pure enantiomers of flurbiprofen, ibuprofen, and ketoprofen, we could show that (1) R-enantiomers of these drugs are inverted to S-enantiomers to a different degree in different species, including humans, (2) the pharmacokinetic parameters of both pure enantiomers differ in a drug- and a species-specific manner, and (3) both enantiomers exert differential analgesic effects. It appears particularly interesting that R-flurbiprofen, for instance, which is not or only to a small extent inverted in humans and rats, is practically devoid of prostaglandin synthesis inhibition in vitro. Consequently, in line with current thinking, R-flurbiprofen is not toxic to the gastrointestinal tract and shows no anti-inflammatory effects. In contrast to current concepts, however, this enantiomer does exert analgesic activity in different models of pain and nociception. It is concluded that R-flurbiprofen and, possibly, other R-enantiomers of 2-arylpropionic acids may exert novel analgesic effects independently of peripheral prostaglandin synthesis inhibition in inflamed tissue.