In vitro models for neuropathic pain phenotypic screening in brain therapeutics.

The discovery of brain therapeutics faces a significant challenge due to the low translatability of preclinical results into clinical success. To address this gap, several efforts have been made to obtain more translatable neuronal models for phenotypic screening. These models allow the selection of active compounds without predetermined knowledge of drug targets. In this review, we present an overview of various existing models within the field, examining their strengths and limitations, particularly in the context of neuropathic pain research. We illustrate the usefulness of these models through a comparative review in three crucial areas: i) the development of novel phenotypic screening strategies specifically for neuropathic pain, ii) the validation of the models for both primary and secondary screening assays, and iii) the use of the models in target deconvolution processes.

Burden of itch in ichthyosis: a multicentre study in 94 patients.

BACKGROUND: From clinical experience, we know that itch is a major concern for many ichthyosis patients. Nonetheless, no previous studies specifically addressed the issue of itch in ichthyosis. OBJECTIVE: The objective of this study was to specifically address the burden of itch and all its dimensions in ichthyosis patients. METHODS: Ninety-four ichthyosis patients from four different centres were recruited to participate in this cross-sectional, questionnaire-based study. All participants completed the Leuven Itch Scale, a multidimensional self-report instrument that quantifies the frequency, duration, severity, distress, consequences and surface area of itch. RESULTS: Participants included 18 keratinopathic types, 55 autosomal recessive congenital ichthyoses, 11 X-linked recessive ichthyoses (XLRIs), 6 Netherton's ichthyoses, 1 Sjögren-Larsson type, 1 Iocrin ichthyosis and 2 unknown subtypes. Itch occurred in 93% of all patients. In patients with itch, 63% reported that it was often or always present, although most itch episodes were short in duration. Itch, in all its dimensions, was worst in patients with Netherton syndrome. Patients with XLRI had in general a lower itch profile. About half of all ichthyosis patients reported to experience flares during a change in weather, in a hot environment or in stressful situations, whereas a cold environment led to itch in only 26% of patients. The most significant consequences of itching were lesions from scratching, difficulties in falling asleep, bad mood and loss of concentration. CONCLUSIONS: Itch is a major concern in patients with ichthyosis, with significant impact on daily life. Research on future treatments should therefore take itch into consideration and itch should be evaluated in clinical studies. Among the studied subgroups, Netherton patients experienced the most severe consequences.

Creation and pilot test results of the dermatology-specific proxy instrument: the Infants and Toddlers Dermatology Quality of Life.

BACKGROUND: Until now, there was no validated dermatology-specific health-related quality of life (HRQoL) instrument to be used in youngest patients. OBJECTIVE: To create dermatology-specific proxy instrument for HRQoL assessment in children from birth to 4 years. METHODS: International focus groups, item selection and pilot tests were utilized. In order to avoid the problem of cross-cultural inequivalence, focus group work and pilot tests were planned simultaneously in all national centres of the project. Comprehensibility, clarity, acceptance and internal consistency of new instrument were checked. RESULTS: The title 'Infants and Toddlers Dermatology Quality of Life' was chosen for our new instrument with the proposed acronym 'InToDermQoL'. Focus group work was completed in seven national centres (Croatia, Germany, Greece, Malta, Poland, Romania and Ukraine). A total of 170 families of children with different skin diseases were interviewed, and a pilot version of the instrument was created. Centres from France, Denmark and Spain have joined the project at this stage. Parents of 125 children with skin diseases filled in the pilot versions of the instrument. Good comprehensibility, clarity, acceptance and internal consistency of the InToDermQoL were confirmed. The pilot test results showed that the InToDermQoL questionnaire well differentiates severity-dependent differences. It was also checked and confirmed during the pilot test that no significant information was missed in the questionnaire. Three age-specific versions of the InToDermQoL questionnaire with 10, 12 and 15 items, respectively, were approved for field tests. CONCLUSION: The pilot test results showed that the InToDermQoL questionnaire has good comprehensibility, clarity, acceptance and internal consistency and well differentiates severity-dependent differences. Further validation of the InToDermQoL during international field test will be performed.

Defense related phytohormones regulation in arbuscular mycorrhizal symbioses depends on the partner genotypes.

Arbuscular mycorrhizal (AM) symbioses are mutualistic associations between soil fungi and most vascular plants. Modulation of the hormonal and transcriptional profiles, including changes related to defense signalling, has been reported in many host plants during AM symbioses. These changes have been often related to the improved stress tolerance common in mycorrhizal plants. However, results on the alterations in phytohormones content and their role on the symbiosis are controversial. Here, an integrative analysis of the response of phylogenetically diverse plants (i.e., tomato, soybean, and maize) to two mycorrhizal fungi -Funneliformis mosseae and Rhizophagus irregularis- was performed. The analysis of the defense-related hormones salicylic acid, abscisic acid, and jasmonates, and the expression of marker genes of the pathways they regulate, revealed significant changes in the roots of mycorrhizal plants. These changes depended on both the plant and the AM fungus (AMF) involved. However, general trends can be identified: roots associated with the most effective colonizer R. irregularis showed fewer changes in these defense-related traits, while the colonization by F. mosseae led to significant modifications in all plants tested. The up-regulation of the jasmonate pathway by F. mosseae was found to be highly conserved among the different plant species, suggesting an important role of jasmonates during this AM interaction. Our study evidences a strong influence of the AMF genotype on the modulation of host defense signalling, and offers hints on the role of these changes in the symbiosis.

Blockade of sigma 1 receptors alleviates sensory signs of diabetic neuropathy in rats.

BACKGROUND: E-52862 (S1RA, 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]-morpholine), a novel selective sigma 1 receptor (σ1R) antagonist, has demonstrated efficacy in nociceptive and neuropathic pain models. Our aim was to test if σ1R blockade with E-52862 may modify the signs of neuropathy in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model. METHODS: Mechanical and thermal response thresholds were tested on 7-, 13-, 14- and 15-week-old ZDF rats treated with saline or with E-52862 acutely administered on week 13, followed by sub-chronic administration (14 days). Axonal peripheral activity (skin-saphenous nerve preparation) and isolated aorta or mesenteric bed reactivity were analysed in 15-week-old ZDF rats treated with saline or E-52862 and in LEAN rats. RESULTS: Zucker diabetic fatty rats showed significantly decreased thermal withdrawal latency and threshold to mechanical stimulation on week 13 compared to week 7 (prediabetes) and with LEAN animals; single-dose and sub-chronic E-52862 administration restored both parameters to those recorded on week 7. Regarding axonal peripheral activity, E-52862 treatment increased the mean mechanical threshold (77.3 ± 21 mN vs. 19.6 ± 1.5 mN, saline group) and reduced the response evoked by mechanical increasing stimulation (86.4 ± 36.5 vs. 352.8 ± 41.4 spikes) or by repeated mechanical supra-threshold steps (39.4 ± 1.4 vs. 83.5 ± 0.9). E-52862 treatment also restored contractile response to phenylephrine in aorta and mesenteric bed. CONCLUSIONS: E-52862 administration reverses neuropathic (behavioural and electrophysiological) and vascular signs in the ZDF rat. SIGNIFICANCE: Blockade of σ1R avoids the development of diabetic neuropathy in rats, and may represent a potentially useful therapeutic approach to peripheral neuropathies in diabetic patients. WHAT DOES THIS STUDY ADD?: This study presents evidences for the potential usefulness of sigma receptor blockade on diabetic neuropathy in rats. The methodology includes behavioural evidences, electrophysiological data and vascular-isolated models.

Effects of centrally acting analgesics on spinal segmental reflexes and wind-up.

BACKGROUND: The spinal cord is a prime site of action for analgesia. Here we characterize the effects of established analgesics on segmental spinal reflexes. The aim of the study was to look for the pattern of action or signature of analgesic effects on these reflexes. METHODS: We used a spinal cord in vitro preparation of neonate mice to record ventral root responses to dorsal root stimulation. Pregabalin, clonidine, morphine and duloxetine and an experimental sigma-1 receptor antagonist (S1RA) were applied to the preparation in a cumulative concentration protocol. Drug effects on the wind-up produced by repetitive stimulation of C-fibres and on responses to single A- and C-fibre intensity stimuli were analysed. RESULTS: All compounds produced a concentration-dependent inhibition of total spikes elicited by repetitive stimulation. Concentrations producing ∼50% reduction in this parameter were (in µM) clonidine (0.01), morphine (0.1), pregabalin (1), duloxetine (10) and S1RA (30). At these concentrations clonidine, pregabalin and S1RA had significant effects on the wind-up index and little depressant effects on responses to single stimuli. Morphine and duloxetine did not depress wind-up index and showed large effects on responses to single stimuli. None of the compounds had strong effects on the amplitude of the non-nociceptive monosynaptic reflex. CONCLUSIONS: morphine and duloxetine had general depressant effects on spinal reflexes, whereas the effects of clonidine, pregabalin and S1RA appeared to be restricted to signals originated by strong repetitive activation of C-fibres. Results are discussed in the context of reported behavioural effects of the compounds studied.

Inhibition of rat liver microsomal fatty acid chain elongation by gemfibrozil in vitro.

Gemfibrozil, a hypolipidemic drug mainly used in the treatment of hypertriglyceridemic states, strongly inhibits the rat hepatic microsomal fatty acid chain elongation system in vitro. The inhibition is independent on the reducing cofactor used in the assay. Furthermore, gemfibrozil seems to act by inhibiting the rate-limiting step of the elongation process, the condensing reaction, without discriminating among the proposed three different condensing enzymes, devoted to condensation of saturated, mono-unsaturated and polyunsaturated acyl-CoA substrates.

Disubstituted tetrahydrofurans and dioxolanes and PAF antagonists.

A new series of disubstituted tetrahydrofuran and dioxolane derivatives were prepared and evaluated for their PAF antagonist activity in the PAF-induced in vitro platelet-aggregation and in vivo hypotension tests. Several of these compounds exhibited more potent activity than the structurally related 2-[N-acetyl-N-[[[[2-methoxy-3-[(octadecylcarbamoyl) oxy]propoxy]carbonyl]amino]methyl]-1-ethylpyridinium chloride (CV-6209, 3) in the in vitro assay, whereas all showed less potency in the in vivo test. The role of both the substituent nature and the placement and number of oxygen atoms in the ring are discussed. A quantitative SAR study carried out on these nuclei.

(Pyridylcyanomethyl)piperazines as orally active PAF antagonists.

A series of (pyridylcyanomethyl)piperazines was prepared and evaluated for PAF-antagonist activity. Compounds were tested in vitro in a PAF-induced platelet aggregation assay and in vivo in a PAF-induced hypotension test in normotensive rats. Oral activity was ascertained through a PAF-induced mortality test in mice. The main structure-activity trends of the series were established. Activity was mainly found in four skeletons: 1-acyl-4-(3-pyridylcyanomethyl)piperazine, 1-acyl-4-(4-pyridylcyanomethyl)piperazine, 1-acyl-4-(3-pyridylcyanomethyl)piperidine, and 1-acyl-4-cyano-4-(3-pyridylamino)piperidine. The acyl substituents, diphenylacetyl and 3,3-diphenylpropionyl, provided the most active compounds, and the introduction of an amine or hydroxy group in the 3,3-diphenylpropionyl substituent led to further improvement in oral activity. As a result, three of the most active compounds (100, 114, and 115) have been selected for further pharmacological development.

Design, synthesis, and structure-activity relationship studies of novel 1-[(1-acyl-4-piperidyl)methyl]-1H-2- methylimidazo[4,5-c]pyridine derivatives as potent, orally active platelet-activating factor antagonists.

Replacement of the polar head of our previous series of 1-acyl-4-[(2-methyl-3-pyridyl)-cyanomethyl]piperazines with a 2-methylimidazo[4,5-c]pyridine group has led to the identification of a new series of 1-[(1-acyl-4- piperidyl)methyl]-1H-2-methylimidazo[4,5-c]pyridine derivatives as potent, orally active platelet-activating factor (PAF) antagonists. On the basis of the general structure--activity relationship trends found for the acyl substituent in our earlier series, five groups of compounds were tested, diaryl- or alkylarylpropanoyl derivatives, their 3-hydroxy-substituted analogues, and urea, carbamate and amino acid derivatives. The optimal compound 19 UR-12670), bearing the 3,3-diphenylpropanoyl moiety, exhibited very high in vitro and in vivo potency IC50 = 0.0076 microM for the in vitro PAF-induced platelet aggregation assay, ID50 = 0.0086 mg/kg for the in vivo PAF-induced hypotension test in normotensive rats, and ID50 = 0.092 mg/kg po and 0.0008 mg/kg i.v. for the PAF-induced mortality test in mice). Compound 19 also showed long duration of activity. It gave 100% protection against PAF-induced mortality in mice 7 h after i.v. administration of a single dose of 1 mg/kg and also provided 100% inhibition of PAF-induced aggregation in dog whole blood 6 h after i.v. administration of the same dose. The lead structure 19 has been selected for in-depth pharmacological evaluation.

4-substituted 2-alkoxytetrahydrofurans as potent and long-lasting PAF antagonists.

A series of 4-substituted 2-alkoxytetrahydrofuran derivatives featuring an acetal group were prepared and evaluated for PAF antagonist activity in the PAF-induced in vitro platelet-aggregation and in vivo hypotension tests. Compound 2-[[N-acetyl-N-[[[2-(octadecyloxy)tetrahydrofuran-4- yl]methoxy]carbonyl]amino]methyl]-1-ethylpyridinium chloride (4e, UR-11353) was selected for further development on the basis of its high activity and long-lasting action. The compound maintained a significant activity even 24 h after administration of a single dose of 1 mg/kg iv in the PAF-induced mortality test in mice and 10 h after administration of the same dose in the PAF-induced hypotension test in rats. Comparison with previously reported carba analogues suggests that the presence of the acetal group is the structural characteristic that confers its long-lasting activity.

Synthesis and structure-activity relationships of 1-acyl-4-((2-methyl-3-pyridyl)cyanomethyl)piperazines as PAF antagonists.

A second generation of (cyanomethyl)piperazines, 1-acyl-4-((2-methyl-3-pyridyl)cyanomethyl)-piperazines, with increased oral activity was prepared and evaluated in vitro in a PAF-induced platelet aggregation assay (PAG) and in vivo in a PAF-induced hypotension test in normotensive rats (HYP). Oral activity was ascertained through a PAF-induced mortality test in mice (MOR). Attachment of a methyl group at position 2 of our earlier pyridine derivatives resulted in an improvement of 1 order of magnitude or greater in the ID50 of the oral test. Three different types of acyl substituents of similar potency emerge from this work: N-(diphenylmethylamino)acetyl, 3-substituted 3-hydroxy-3-phenylpropionyl, and N-substituted 3-amino-3-phenylpropionyl groups. The most interesting compounds, 26 (UR-12460, PAG IC50 = 0.040 microM, HYP, ID50 = 0.021 mg/kg i.v., MOR, ID50 = 0.30 mg/kg po) and 58 (UR-12519, PAG IC50 = 0.041 microM, HYP, ID50 = 0.015 mg/kg i.v., MOR, ID50 = 0.044 mg/kg po), compare favorably with WEB-2086. Compounds 26 and 58 were also tested in active anaphylactic shock (AAS) and endotoxin-induced mortality (EIM) tests. On the basis of these data, compounds 26 and 58 have been selected for further pharmacological development.

[(3-Pyridylalkyl)piperidylidene]benzocycloheptapyridine derivatives as dual antagonists of PAF and histamine.

A series of [(3-pyridylalkyl)piperidylidene]- and (nicotinoylpiperidylidene)benzocycloheptapyridine derivatives, Ia,b, were prepared and evaluated for PAF antagonist and H1 antihistamine activity. PAF antagonist activity was investigated by the in vitro PAF-induced platelet aggregation assay (PPA) and the in vivo PAF-induced hypotension test in rats (PH) and mortality test in mice (PM). For the evaluation of H1 antihistamine activity, the in vitro histamine-induced contraction of the guinea-pig ileum assay (HC) and the in vivo histamine-induced hypotension test (HH) in normotensive rats were used. The potential antiallergic activity of the compounds was evaluated using the active anaphylactic shock test in mice. These compounds are structurally related to loratadine (1) and were generated by replacement of the ethoxycarbonyl group of 1 with substituted 3-pyridylmethyl and nicotinoyl moieties. Both anti-PAF and H1 antihistamine activities have shown a high dependence on the exact nature and position of the substituent in the pyridine ring. Optimum structure 19 (UR-12592) incorporating a (5-methyl-3-pyridyl)methyl radical displayed an unique dual activity inhibiting both PAF-induced effects (PPA, IC50 = 3.7 microM; PH, ID50 = 0.44 mg/kg iv; PM, ID50 = 1.9 mg/kg po) and histamine-induced effects (HC, IC50 = 3.9 nM; HH, ID50 = 1.4 mg/kg iv). Furthermore, 19 was highly active in the passive cutaneous anaphylactic shock in rats (ID50 = 1.2 mg/kg po) and strongly protected mice and rats from mortality induced by endotoxin (ID50 = 1.2 and 0.5 mg/kg iv, respectively). Compound 19 showed itself to be devoid of CNS depressant effects, neither modifying spontaneous motor activity nor prolonging barbiturate-sleeping time in mice at a dose of 100 mg/kg po, and is now under development.

New azole antifungals. 2. Synthesis and antifungal activity of heterocyclecarboxamide derivatives of 3-amino-2-aryl-1-azolyl-2-butanol.

A series of 92 azole antifungals containing an amido alcohol unit was synthesized. The nature and substitution of the amide portion was systematically modified in search of improved antifungal activity, especially against filamentous fungi. The compounds were tested in vitro against a variety of clinically important pathogens and in vivo (po) in a murine candidosis model. Thiazole and thiophene carboxamides carrying both a substituted phenyl ring and a small alkyl group were best suited for activity against filamentous fungi. In a subset of these compounds, the amide portion was conformationally locked by means of a pyrimidone ring and it was proven that only an orthogonal orientation of the phenyl ring yields bioactive products. A tendency to display long plasma elimination half-lives was observed in both series. Two compounds, 74 and 107, representative of the open and cyclic amides, respectively, were chosen for further studies, based on their excellent activity in in vivo murine models of candidosis and aspergillosis. This work describes the SARs found within this series. The next paper displays the results obtained in a related series of compounds, the quinazolinones.

New azole antifungals. 3. Synthesis and antifungal activity of 3-substituted-4(3H)-quinazolinones.

A series of azole antifungal agents featuring a quinazolinone nucleus have been subjected to studies of structure-activity relationships. In general, these compounds displayed higher in vitro activities against filamentous fungi and shorter half-lives than the structures described in our preceding paper. The most potent products in vitro carried a halogen (or an isostere) at the 7-position of the quinazolinone ring. Using a murine model of systemic candidosis, oral activity was found to be dependent on hydrophobicity, which, in turn, modulated the compound's half-life. The 7-Cl derivative, (1R,2R)-7-chloro-3-[2-(2, 4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2, 4-triazol-1-yl)propyl]quinazolin-4(3H)-one (20, UR-9825), was selected for further testing due to its high in vitro activity, low toxicity, good pharmacokinetic profile, and ease of obtention. Compound 20 is the (1R,2R) isomer of four possible stereoisomers. The other three isomers were also prepared and tested. The enantiomer (1S,2S) and the (1R,2S) epimer were inactive, whereas the (1S,2R) epimer retained some activity. In vitro 20 was superior to fluconazole, itraconazole, SCH-42427, and TAK-187 and roughly similar to voriconazole and ER-30346. In vivo, 20 was only moderately active in a mouse model of systemic candidosis when administration was limited to the first day. This was attributed to its short half-life in that species (t1/2 = 1 h po). Protection levels comparable to or higher than those of fluconazole, however, were observed in systemic candidosis models in rat and rabbit, where the half-life of the compound was found to be 6 and 9 h, respectively. Finally, 20 showed excellent protection levels in an immunocompromised rat model of disseminated aspergillosis. The compound showed low toxicity signs when administered to rats at 250 mg/kg qd or at 100 mg/kg bid during 28 days.

Synthesis and SAR of a new series of COX-2-selective inhibitors: pyrazolo[1,5-a]pyrimidines.

The synthesis and pharmacological activity of a series of bicyclic pyrazolo[1,5-a]pyrimidines as potent and selective cyclooxygenase-2 (COX-2) inhibitors are described. The new compounds were evaluated both in vitro (COX-1 and COX-2 inhibition in human whole blood) and in vivo (carrageenan-induced paw edema and air-pouch model). Modification of the pyrimidine substituents showed that 6,7-disubstitution provided the best activity and led to the identification of 3-(4-fluorophenyl)-6,7-dimethyl-2-(4-methylsulfonylphenyl)pyrazolo[1,5-a]pyrimidine (10f) as one of the most potent and selective COX-2 inhibitor in this series.

Novel azo derivatives as prodrugs of 5-aminosalicylic acid and amino derivatives with potent platelet activating factor antagonist activity.

This paper describes the synthesis of a series of azo compounds able to deliver 5-aminosalicylic acid (5-ASA) and a potent platelet activating factor (PAF) antagonist in a colon-specific manner for the purpose of treating ulcerative colitis. We found it possible to add an amino group on the aromatic moiety of our reported 1-[(1-acyl-4-piperidyl)methyl]-1H-2-methylimidazo[4,5-c]pyridine derivatives or on British Biotech compounds BB-882 and BB-823 maintaining a high level of activity as PAF antagonist. A selected compound UR-12715 (49c) showed an IC(50) of 8 nM in the in vitro PAF-induced aggregation assay, and an ID(50) of 29 microg/kg in the in vivo PAF-induced hypotension test in normotensive rats. Through attachment of 49c to the 5-ASA via azo functionality we obtained UR-12746 (70). Pharmacokinetics experiments with [14C]-70 allow us to reach the following conclusions, critical in the design of these new prodrugs of 5-ASA. Neither the whole molecule 70 nor the carrier 49c were absorbed after oral administration of [14C]-70 in rat as was demonstrated by the absence of plasma levels of radioactivity and the high recovery of it in feces. Effective cleavage of azo bond (84%) by microflora in the colon is achieved. These facts ensure high topical concentrations of 5-ASA and 49c in the colon. Additionally, 70 exhibited a potent anticolitic effect in the trinitrobenzenesulfonic acid-induced colitis model in the rat. This profile suggests that UR-12746 (70) provides an attractive new approach to the treatment of ulcerative colitis.

Cold ischemia in the absence of alloreactivity induces chronic transplant nephropathy through a process mediated by the platelet-activating factor.

BACKGROUND: Ischemia-reperfusion injury is considered a risk factor for the development of chronic transplant nephropathy (CTN) although the mechanisms that mediate its effects have not been completely established. We have previously shown that treatment with a platelet-activating factor (PAF) receptor antagonist (UR12670) protected kidneys from the progression to chronic nephropathy induced by warm ischemia. Here we examine the contribution of cold ischemia to the development of late functional and structural kidney changes in rats subjected to syngeneic renal transplantation and the role of PAF in this chronic nephropathy. SUBJECTS AND METHODS: Lewis rats were used as kidney donors and recipients, which were transplanted either immediately or after a cold ischemia period of 5 hr. Contralateral nephrectomy was performed on the seventh day after transplantation. Cyclosporine was administered for 15 days after transplantation. Groups were as follows: Sy, immediate transplantation; SyI, transplantation after 5 hr of cold ischemia; SyIUr, transplantation after 5 hr of cold ischemia plus UR12670 from the transplantation day to the end of the study, at 24 weeks. Serum creatinine, creatinine clearance, and proteinuria were determined every 4 weeks. Urinary

Decreased susceptibility to copper-induced oxidation of rat-lipoproteins after fibrate treatment: influence of fatty acid composition.

1. The effect of clofibrate (CFB), bezafibrate (BFB), and gemfibrozil (GFB) on plasma lipoprotein (VLDL and LDL) concentration, composition and resistance to copper-induced oxidation has been studied in male Sprague-Dawley rats after a 15 day treatment. 2. Plasma triglyceride levels were reduced by CFB (41%) and BFB (39%). This effect was related to a significant reduction (67% for CFB and 56% for BFB) in the amount of circulating VLDL-protein. 3. Plasma total cholesterol was reduced by 28% and 45% in CFB- and BFB-treated animals, respectively, mainly by modification of the cholesteryl ester fraction. In contrast, GFB significantly increased total cholesterol (27%). No modification in the LDL protein or lipid content was introduced by fibrates, although GFB decreased the proportion of LDL-triglycerides, at the expense of an increase in total cholesterol. 4. The fatty acid species carried by VLDL and LDL were affected after fibrate treatment. In general, both particles showed an increase in monounsaturated fatty acids (MUFA) (18:1) and a decrease in polyunsaturated fatty acids (PUFA) species (18:2 n-6, 20:4 n-6, 18:3 n-3, 20:5 n-3). As a consequence, the ratio of PUFA/(SFA+MUFA) for the whole lipoproteins was markedly reduced. 5. The degree of copper-induced VLDL- and LDL-oxidation was assessed by means of the analysis of lysine content, thiobarbituric acid reactive substances (TBARS) production and conjugated dienes formation. Lipoproteins obtained from fibrate-treated rats were more resistant to the oxidative challenge. For each lipoprotein, BFB was the most effective drug, followed by CFB and GFB. 6. The observed antioxidant effect can be ascribed to two independent phenomena produced by fibrates: the reduction of the amount of substrate for the oxidation process due to their hypolipidemic activity, and the alteration in the type of fatty acids transported by the lipoproteins towards an enrichment in species resistant to the oxidation process. 7. As similar lipoprotein fatty acid changes have been reported after fibrate treatment in human subjects, an antioxidant effect of fibrates in human therapy, independent of their well known hypolipidaemic activity, should be expected.