Maternal dietary omega-3 deficiency worsens the deleterious effects of prenatal inflammation on the gut-brain axis in the offspring across lifetime.

Maternal immune activation (MIA) and poor maternal nutritional habits are risk factors for the occurrence of neurodevelopmental disorders (NDD). Human studies show the deleterious impact of prenatal inflammation and low n-3 polyunsaturated fatty acid (PUFA) intake on neurodevelopment with long-lasting consequences on behavior. However, the mechanisms linking maternal nutritional status to MIA are still unclear, despite their relevance to the etiology of NDD. We demonstrate here that low maternal n-3 PUFA intake worsens MIA-induced early gut dysfunction, including modification of gut microbiota composition and higher local inflammatory reactivity. These deficits correlate with alterations of microglia-neuron crosstalk pathways and have long-lasting effects, both at transcriptional and behavioral levels. This work highlights the perinatal period as a critical time window, especially regarding the role of the gut-brain axis in neurodevelopment, elucidating the link between MIA, poor nutritional habits, and NDD.

Essential omega-3 fatty acids tune microglial phagocytosis of synaptic elements in the mouse developing brain.

Omega-3 fatty acids (n-3 PUFAs) are essential for the functional maturation of the brain. Westernization of dietary habits in both developed and developing countries is accompanied by a progressive reduction in dietary intake of n-3 PUFAs. Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental diseases in Humans. However, the n-3 PUFAs deficiency-mediated mechanisms affecting the development of the central nervous system are poorly understood. Active microglial engulfment of synapses regulates brain development. Impaired synaptic pruning is associated with several neurodevelopmental disorders. Here, we identify a molecular mechanism for detrimental effects of low maternal n-3 PUFA intake on hippocampal development in mice. Our results show that maternal dietary n-3 PUFA deficiency increases microglia-mediated phagocytosis of synaptic elements in the rodent developing hippocampus, partly through the activation of 12/15-lipoxygenase (LOX)/12-HETE signaling, altering neuronal morphology and affecting cognitive performance of the offspring. These findings provide a mechanistic insight into neurodevelopmental defects caused by maternal n-3 PUFAs dietary deficiency.

Dietary omega-3 deficiency exacerbates inflammation and reveals spatial memory deficits in mice exposed to lipopolysaccharide during gestation.

Maternal immune activation (MIA) is a common environmental insult on the developing brain and represents a risk factor for neurodevelopmental disorders. Animal models of in utero inflammation further revealed a causal link between maternal inflammatory activation during pregnancy and behavioural impairment relevant to neurodevelopmental disorders in the offspring. Accumulating evidence point out that proinflammatory cytokines produced both in the maternal and fetal compartments are responsible for social, cognitive and emotional behavioral deficits in the offspring. Polyunsaturated fatty acids (PUFAs) are essential fatty acids with potent immunomodulatory activities. PUFAs and their bioactive derivatives can promote or inhibit many aspects of the immune and inflammatory response. PUFAs of the n-3 series ('n-3 PUFAs', also known as omega-3) exhibit anti-inflammatory/pro-resolution properties and promote immune functions, while PUFAs of the n-6 series ('n-6 PUFAs' or omega-6) favor pro-inflammatory responses. The present study aimed at providing insight into the effects of n-3 PUFAs on the consequences of MIA on brain development. We hypothesized that a reduction in n-3 PUFAs exacerbates both maternal and fetal inflammatory responses to MIA and later-life defects in memory in the offspring. Based on a lipopolysaccharide (LPS) model of MIA (LPS injection at embryonic day 17), we showed that n-3 PUFA deficiency 1) alters fatty acid composition of the fetal and adult offspring brain; 2) exacerbates maternal and fetal inflammatory processes with no significant alteration of microglia phenotype, and 3) induces spatial memory deficits in the adult offspring. We also showed a strong negative correlation between brain content in n-3 PUFA and cytokine production in MIA-exposed fetuses. Overall, our study is the first to address the deleterious effects of n-3 PUFA deficiency on brain lipid composition, inflammation and memory performances in MIA-exposed animals and indicates that it should be considered as a potent environmental risk factor for the apparition of neurodevelopmental disorders.

Oxidation-Induced Increase In Photoreactivity of Bovine Retinal Lipid Extract.

The mammalian retina contains a high level of polyunsaturated fatty acids, including docosahexaenoic acid (22:6) (DHA), which are highly susceptible to oxidation. It has been shown that one of the products of DHA oxidation-carboxyethylpyrrole (CEP), generated in situ, causes modifications of retinal proteins and induces inflammation response in the outer retina. These contributing factors may play a role in the development of age-related macular degeneration (AMD). It is also possible that some of the lipid oxidation products are photoreactive, and upon irradiation with blue light may generate reactive oxygen species. Therefore, in this work we analysed oxidation-induced changes in photoreactivity of lipids extracted from bovine neural retinas. Lipid composition of bovine neural retinas closely resembles that of human retinas making the bovine tissue a convenient model for studying the photoreactivity and potential phototoxicity of oxidized human retinal lipids. Lipid composition of bovine neural retinas Folch' extracts (BRex) was determined by gas chromatography (GC) and liquid chromatography coupled to an electrospray ionization source-mass spectrometer (LC-ESI-MS) analysis. Liposomes prepared from BRex, equilibrated with air, were oxidized in the dark at 37 °C for up to 400 h. The photoreactivity of BRex at different stages of oxidation was studied by EPR-oximetry and EPR-spin trapping. Photogeneration of singlet oxygen (1O2, 1Δg) by BRex was measured using time-resolved detection of the characteristic phosphorescence at 1270 nm. To establish contribution of lipid components to the analysed photoreactivity of Folch' extract of bovine retinas, a mixture of selected synthetic lipids in percent by weight (w/w %) ratio resembling that of the BRex has been also studied. Folch's extraction of bovine neural retinas was very susceptible to oxidation despite the presence of powerful endogenous antioxidants such as α-tocopherol and zeaxanthin. Non-oxidized and oxidized BRex photogenerated singlet oxygen with moderate quantum yield. Blue-light induced generation of superoxide anion by Folch' extract of bovine neural retinas strongly depended on the oxidation time. The observed photoreactivity of the studied extract gradually increased during its in vitro oxidation.

Branched-chain fatty acids, increased in tears of blepharitis patients, are not toxic for conjunctival cells.

AIM: The composition of the meibum of blepharitis patients is characterised by increased levels of branched-chain fatty acids (BCFAs) that return to normal values in patients treated with cyclins and lid hygiene. The aim of this study was to determine if BCFAs had toxic effects on conjunctival cells related to the disease. METHODS: Chang and IOBA-NHC conjunctival human cells were treated with BCFAs (isoC16 and isoC20) or palmitic acid as a control for 4 h or 24 h at 50 microM or 100 microM. Morphological and functional changes were investigated by measuring mitochondrial dehydrogenase activity, cell permeability, mitochondrial depolarisation, chromatin condensation, IL-1beta and reactive oxygen species production. RESULTS: None of the fatty acids modified the parameters of cytotoxicity in conjunctival cells in Chang or IOBA-NHC cell lines. Only the mitochondrial dehydrogenase activity was significantly decreased in relation to the isoC20 concentration increase. CONCLUSIONS: The increase in BCFAs in the tears of blepharitis patients does not consistently participate in the conjunctival cell changes throughout the course of the disease. Instead, it is likely an adaptive response of the ocular surface to the lack of tears, possibly increasing meibum fluidity, thus enhancing lacrimal film stability.

Changes in meibomian fatty acids and clinical signs in patients with meibomian gland dysfunction after minocycline treatment.

AIMS: To assess the changes in ocular surface abnormalities and meibomian fatty acid composition in patients suffering from meibomian gland dysfunction (MGD) after treatment with oral minocycline associated with lid hygiene versus lid hygiene only. METHODS: We evaluated the break-up time, corneal staining and quality of meibomian excreta, and collected meibomian oil in 20 individuals suffering from MGD before and after 8 weeks of minocycline associated with lid hygiene (n = 10) or lid hygiene only (n = 10). Meibomian fatty acids were directly transmethylated and analysed by gas chromatography (GC) and GC mass spectrometry. RESULTS: The meibomian fatty acid composition was slightly modified after 8 weeks in both groups. The decrease in a branched-chain fatty acid (isoC20) was greater after minocycline treatment than after lid hygiene only (-65% and -25%, respectively; p<0.05). Other fatty acids were unchanged. A significant improvement in the BUT was observed after minocycline treatment (p = 0.03). CONCLUSION: This study showed better tear film stability after minocycline treatment and a biological effect on meibomian fatty acid composition in MGD patients. Minocycline was more effective than lid hygiene alone. Both interventions partly corrected fatty acid composition abnormalities. Among the fatty acids, isoC20 could be a biological marker of MGD.

Differences in meibomian fatty acid composition in patients with meibomian gland dysfunction and aqueous-deficient dry eye.

AIMS: To evaluate the differences in meibomian fatty acid composition in healthy subjects and in patients suffering from meibomian gland dysfunction or aqueous-deficient dry eye. METHODS: We collected meibomian oil using a sterile Schirmer paper in healthy individuals (n = 20), dry eye patients (aqueous-deficient) (n = 32) and meibomian gland dysfunction (MGD) patients (n = 25) after gentle massage of the lid margin. Meibomian fatty acids were directly transmethylated and analysed using gas chromatography (GC) and GC mass spectrometry. RESULTS: Meibomian fatty acids were similar in healthy individuals and in dry eye patients but were different in MGD patients, who showed significantly higher levels of branched-chain fatty acids (29.8% vs 20.2%) (p<0.0001) and lower levels of saturated fatty acids (9.3 vs 24.6%) (p<0.0001), in particular lower levels of palmitic (C16) and stearic (C18) acids. CONCLUSION: The increase in branched-chain fatty acids may reflect greater quantities of wax and cholesterol esters and triglycerides in meibomian gland excreta. Since wax and cholesterol esters are the main lipids of meibum, these differences may have physical consequences for tear-film lipid-layer fluidity and stability. Meibomian fatty acid composition and particularly the increase in branched chains could be a marker for meibomian gland dysfunction.

Dietary cyclic fatty acids derived from linolenic acid do not exhibit intrinsic toxicity in the rat during gestation.

Heating oils and fats may lead to cyclization of polyunsaturated fatty acids, especially those showing multiple double bonds like linolenic acid. Cyclohexenyl and cyclopentenyl fatty acids are subsequently present in some edible oils and these were suspected to induce metabolic disorders. When fed during gestation in the rat, cyclic fatty acids were historically reported to induce high mortality of the neonates. Nevertheless, none of these studies have been performed with cyclic fatty acids fed as triacylglycerols, limiting the nutritional value of the conclusions. Therefore, we assessed the toxicity of a diet containing 0.7% of cyclic fatty acids fed as triacylglycerols during gestation and the first days of life in the rat. In this work, we report no deleterious effect of cyclic fatty acids in the mothers and neonates. However, cyclic fatty acids induced a tremendous insulinopenia in the mothers and pups that was associated with the reduction of food intake in the gestating females. Such a finding may be a plausible explanation for the adverse effects of cyclic fatty acids observed previously with higher doses of cyclic fatty acids. Based on present data, on previous ones showing elimination of cyclic fatty acids, and considering their low amounts in the diet, we suggest that cyclic fatty acids formed from cyclization of linolenic acid are not a major concern for human safety.

Influence of rosuvastatin on the NAD(P)H oxidase activity in the retina and electroretinographic response of spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: Retinal complications may be encountered during the development of hypertension as a response to oxidative stress. Statins may reduce the risk of developing hypertension and ocular diseases. We evaluate the effects of rosuvastatin (ROSU) on retinal functionality and oxidative stress levels in normotensive and spontaneously hypertensive rats (SHR). EXPERIMENTAL APPROACH: Wistar Kyoto (WKY) and SHR were treated for 3 weeks with rosuvastatin (10 mg kg(-1) day(-1)). Electroretinograms (ERG) were recorded before and after rosuvastatin treatment. Reactive oxygen species (ROS) were determined in the retina with dihydroethidium staining and NAD(P)H oxidase activity was evaluated. KEY RESULTS: Retinal ganglion cell ROS and retinal NAD(P)H oxidase activity were higher in SHR than in WKY rats, respectively (17.1+/-1.1 vs 10.2+/-1.2 AU, P<0.01; 38095+/-8900 vs 14081+/-5820 RLU mg(-1); P<0.05). The ERG b-wave amplitude in SHR was significantly lower than that in WKY rats. Rosuvastatin reduced SBP in SHR but did not change plasma lipid levels. Rosuvastatin treatment in SHR significantly decreased ROS levels (11.2+/-1.3, P<0.01), NAD(P)H activity in retinal ganglion cells (9889+/-4290; P<0.05), and increased retinal plasmalogen content in SHR, but did not modify the ERG response. CONCLUSIONS AND IMPLICATIONS: Rosuvastatin, beyond lowering cholesterol levels, was able to lower ROS in the retina induced by hypertension, but without improving retinal function in SHR. These findings point to a complex relationship between ROS in the pathogenesis of retinal disease and hypertension.

Might analysis, synthesis and metabolism of CLA contribute to explain the biological effects of CLA?

Conjugated Linoleic Acids (CLA) are of great interest for analysts since techniques have been developed to determine the dietary occurrence of CLA with a good accuracy. CLA is found in animal products from ruminant sources as the result of biohydrogenation of polyunsaturated fatty acids in the rumen and as the consequence of the delta-9 desaturation of vaccenic acid in animal tissues. CLA can also be obtained in the laboratory by isomerisation of linoleic acid or by total chemical synthesis. While the "natural" isomer is rumenic acid (9c,11t-18:2), synthetic mixtures contain mainly two isomers: the 9c,11t- and the 10t,12c-18:2. Although CLA have been shown to be metabolized into desaturated and chain elongated products, it remains unclear whether these so-formed conjugated metabolites may be involved in the effects of CLA on fatty acid metabolism. Experiments carried out on animal models with CLA have shown different health benefits: anticarcinogenic, antiatherosclerotic effects, modulation of body composition , the "natural" CLA (9c,11t-18:2) being closely related to the protection against cancer and the 10t,12c-18:2 to the reduction of the fat mass. Nevertheless, recent findings have suggested adverse effects in mice. Most of the studies carried out on humans concern the influence of CLA on body composition and its possible inverse association with cancer. Since the results are still controversial and since very few data dealing with the safety of using CLA in long term feeding studies have so far been published, further works are warranted to consider the benefits of CLA for humans.

On the turnover of brain cholesterol in patients with Alzheimer's disease. Abnormal induction of the cholesterol-catabolic enzyme CYP46 in glial cells.

Evidence is accumulating for a link between cerebral cholesterol metabolism and Alzheimer's disease (AD). Here we focus on a possible relationship between AD and a newly discovered mechanism for cholesterol efflux from the brain, involving conversion of brain cholesterol into 24S-hydroxycholesterol by the neuronal oxidative enzyme CYP46. There was a marked difference in the distribution of CYP46 in brains of control and AD patients. The neuronal cells were less stained in AD brains than in controls while marked positive staining was found in glial cells in AD but not in controls. The dynamic changes in the mechanisms for cholesterol efflux from the brain are of interest in relation to the link between brain cholesterol and amyloid beta-protein in AD.

Antiepileptic drugs increase plasma levels of 4beta-hydroxycholesterol in humans: evidence for involvement of cytochrome p450 3A4.

The major cholesterol oxidation products in the human circulation are 27-hydroxycholesterol, 24-hydroxycholesterol, and 7alpha-hydroxycholesterol. These oxysterols are formed from cholesterol by specific cytochrome P450 enzymes, CYP27, CYP46, and CYP7A, respectively. An additional oxysterol present in concentrations comparable with 7alpha- and 24-hydroxycholesterol is 4beta-hydroxycholesterol. We now report that patients treated with the antiepileptic drugs phenobarbital, carbamazepine, or phenytoin have highly elevated levels of plasma 4beta-hydroxycholesterol. When patients with uncomplicated cholesterol gallstone disease were treated with ursodeoxycholic acid, plasma 4beta-hydroxycholesterol increased by 45%. Ursodeoxycholic acid, as well as the antiepileptic drugs, are known to induce cytochrome P450 3A. Recombinant CYP3A4 was shown to convert cholesterol to 4beta-hydroxycholesterol, whereas no conversion was observed with CYP1A2, CYP2C9, or CYP2B6. The concentration of 4alpha-hydroxycholesterol in plasma was lower than the concentration of 4beta-hydroxycholesterol and not affected by treatment with the antiepileptic drugs or ursodeoxycholic acid. Together, these data suggest that 4beta-hydroxycholesterol in human circulation is formed by a cytochrome P450 enzyme.

Isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men.

Human lipid intake contains various amounts of trans fatty acids. Refined vegetable and frying oils, rich in linoleic acid and/or alpha-linolenic acid, are the main dietary sources of trans-18:2 and trans-18:3 fatty acids. The aim of the present study was to compare the oxidation of linoleic acid, alpha-linolenic acid, and their major trans isomers in human volunteers. For that purpose, TG, each containing two molecules of [1-(13)C]linoleic acid, alpha-[1-(13)C]linolenic acid, [1-(13)C]-9cis,12trans-18:2, or [1-(13)C]-9cis,12cis,15trans-18:3, were synthesized. Eight healthy young men ingested labeled TG mixed with 30 g of olive oil. Total CO(2) production and (13)CO(2) excretion were determined over 48 h. The pattern of oxidation was similar for the four fatty acids, with a peak at 8 h and a return to baseline at 24 h. Cumulative oxidation over 8 h of linoleic acid, 9cis,12trans-18:2, alpha-linolenic acid, and 9cis,12cis,15trans-18:3 were, respectively, 14.0 +/- 4.1%, 24.7 +/- 6.7%, 23.6 +/- 3.3%, and 23.4 +/- 3.7% of the oral load, showing that isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men.

No effect of dietary trans isomers of alpha-linolenic acid on platelet aggregation and haemostatic factors in european healthy men. The TRANSLinE study.

The aim of this study was to investigate the effect of trans alpha-linolenic acid on platelet aggregation and blood haemostasis. A randomized, double blind dietary intervention trial was carried out with healthy male volunteers (n=88) in three European centers. After a 6-week washout period where subjects avoided foods containing all trans fats, subjects either continued for 6 weeks with a low trans diet or a diet where trans alpha-linolenic acid provided 0.6% of energy (supplied as oil, margarine, cheese, muffins, and biscuits). At the end of the washout period the intake of trans polyunsaturated fats was 58+/-115 mg/day; this increased in patients on the high trans diet by +1344+/-328 mg/day, compared with +10+/-67 mg/day in patients on the low trans diet (p<0.01). The change in trans alpha-linolenic acid in plasma cholesteryl esters was 0.26+/-0. 20 on the high trans and 0.00+/-0.07% of fatty acids on the low trans diet (p<0.001). No effect of the high trans diet was observed on platelet aggregation: collagen EC(50) high trans 157+/-100, low trans 152+/-90 ng/mL (NS); U44619 EC(50) high trans 81+/-61, low trans 59+/-27 nM (NS). The high trans diet did not affect platelet thromboxane production, fibrinogen levels, factor VII, activated factor VIIa, or plasminogen activator inhibitor activity. There were no center-specific differences in response to the high trans diet. A relatively high amount of trans alpha-linolenic acid for 6 weeks does not increase the risk of coronary heart disease by promoting platelet aggregation and blood coagulation.

Plasma levels of 24S-hydroxycholesterol in patients with neurological diseases.

The brain is the exclusive or almost exclusive site of formation of 24S-hydroxycholesterol and we have shown that the circulating level of 24S-hydroxycholesterol is dependent upon the relation between cerebral production and hepatic clearance. In the present work we determined plasma levels of 24S-hydroxycholesterol in patients with various neurological diseases. Eleven subjects with brain death occurring 6-10 h before collection of the plasma samples had markedly reduced circulating levels of 24S-hydroxycholesterol (-43%, P<0.001). Patients with advanced Alzheimer's disease and cerebral inflammatory diseases had slightly lower levels of 24S-hydroxycholesterol in plasma when compared to matched controls. Patients with acute ischemic stroke, multiple sclerosis and primary brain tumors had levels not significantly different from those of controls. The conditions leading to reduced plasma levels of 24S-hydroxycholesterol had no significant effect on plasma levels of another side-chain oxidized oxysterol, 27-hydroxycholesterol. Except for conditions characterized by very marked destruction of the central nervous system, different severe neurological diseases seem to have relatively small effects on the flux of 24S-hydroxycholesterol from the brain.

Plasma levels of 24S-hydroxycholesterol reflect the balance between cerebral production and hepatic metabolism and are inversely related to body surface.

We have previously presented evidence that most of the 24S-hydroxycholesterol present in the circulation originates from the brain and that most of the elimination of this oxysterol occurs in the liver. Plasma 24S-hydroxycholesterol levels decline by a factor of about 5 during the first decades of life. The concentration of the enzyme cholesterol 24S-hydroxylase in the brain is, however, about constant from the first year of life, and reduced enzyme levels thus cannot explain the decreasing plasma levels during infancy. In the present work we tested the hypothesis that the plasma levels of 24S-hydroxycholesterol may reflect the size of the brain relative to the capacity of the liver to eliminate the substance. It is shown here that the age-dependent changes in absolute as well as cholesterol-related plasma level of 24S-hydroxycholesterol closely follow the changes in the ratio between estimated brain weight and estimated liver volume. The size of the brain is increased only about 50% whereas the size of the liver is increased by about 6-fold after the age of 1 year. Liver volume is known to be highly correlated to body surface, and in accordance with this the absolute as well as the cholesterol-related plasma level of 24S-hydroxycholesterol was found to be highly inversely correlated to body surface in 77 healthy subjects of varying ages (r(2) = 0.74). Two chondrodystrophic dwarves with normal size of the brain but with markedly reduced body area had increased levels of 24S-hydroxycholesterol when related to age but normal levels when related to body surface. It is concluded that the balance between cerebral production and hepatic metabolism is a critical determinant for plasma levels of 24S-hydroxycholesterol at different ages and that endocrinological factors are less important. The results are discussed in relation to the possibility to use 24S-hydroxycholesterol in the circulation as a marker for cholesterol homeostasis in the brain.

Effects of conjugated linoleic acid isomers on the hepatic microsomal desaturation activities in vitro.

The influence of individual conjugated linoleic acid (CLA) isomers on the delta6 desaturation of linoleic and alpha-linolenic acids and on the delta9 desaturation of stearic acid was investigated in vitro, using rat liver microsomes. The delta6 desaturation of 18:2n-6 was decreased from 23 to 38% when the ratio of 9cis,11trans-18:2 to 18:2n-6 increased from 0.5 to 2. The compound 10trans,12cis-18:2 exhibited a similar effect only at the highest concentration. The delta6 desaturation of alpha-linolenic acid was slightly affected by the presence of CLA isomers. The sole isomer to induce an inhibitory effect on the delta9 desaturation of stearic acid was 10trans,12cis-18:2.

Desaturation and chain elongation of [1-14C]mono-trans isomers of linoleic and alpha-linolenic acids in perfused rat liver.

Trans polyunsaturated fatty acids are produced during heat treatment of oils, such as deodorization and frying. The detailed metabolic pathways of these trans isomers are not fully understood. In the present work, the desaturation and chain elongation of [1-14C]linoleic acid, 9cis,12trans -18:2, 9trans,12cis -18:2, alpha-linolenic acid, 9cis, 12cis,15trans -18:3 and 9trans,12cis, 15cis -18:3 were studied using a perfused rat liver model. After perfusion with both trans isomers of 18:2n-6, the 14C was equally distributed between phospholipids and triacylglycerols, compared to the 70:30 distribution (phospholipids:triacylglycerols) observed after infusing linoleic acid. The corresponding distribution of 14C after perfusion with both trans isomers of 18:3n-3 was comparable to what was obtained for alpha-linolenic acid. The products of conversion were analyzed by combination of different radio chromatographic methods. 9cis,12trans -18:2 was 16 times more converted into a C18:3n-6 fatty acid than linoleic acid into gamma-linolenic acid. Trans -18:2 isomers were more elongated into "dead-end products" when compared to the conversion of linoleic acid into 20:2n-6 (from 2- to 5-times more). 9cis,12cis,15trans -18:3 and 9trans,12cis, 15cis-18:3 were 2- and 10-times less converted to trans -20:5, respectively, than alpha-linolenic acid into eicosapentaenoic acid. Moreover, 9cis,12cis,15trans -18:3 and 9trans, 12cis, 15cis -18:3 were equally and 2.5-times more elongated into "dead-end products", respectively, than alpha-linolenic acid into 20:3n-3. The partitioning of the conversion between formation of desaturated and chain elongated products on the one hand and production of "dead-end products" on the other was also calculated. Compared to their cis analogs, 9trans,12cis -18:2 and 9trans,12cis, 15cis -18:3 were elongated into trans "dead-end products" rather than being converted to desaturated and chain elongated trans-metabolites. On the other hand 9cis,12cis,15trans -18:3 was more desaturated and chain elongated into 17trans 20:5 rather than elongated into 17trans -20:3.

In vitro desaturation or elongation of monotrans isomers of linoleic acid by rat liver microsomes.

Several nutritional studies have shown the in vivo conversion of the 9c, 12t-18:2 and 9t, 12c-18:2 into long chain polyunsaturated fatty acids (PUFA) containing 20 carbons (geometrical isomers of eicosadienoic and eicosatetraenoic acids). In the present work, some in vitro studies were carried out in order to have precise information on the conversion of these two isomers. In a first set of experiments, studies were focused on the in vitro delta6 desaturation, the first regulatory step of the biosynthesis of n-6 long chain PUFA, from 9c, 12c-18:2. Rat liver microsomes were prepared and incubated under desaturation conditions with [1-14C]-9c, 12c-18:2 in presence of unlabelled 9c, 12t-, 9t, 12c- or 9t, 12t-18:2. The data show that each trans isomer induced a decrease of the delta6 desaturation of the [1-14C]-9c, 12c-18:2, but the 9c, 12t-18:2 was the most potent inhibitor (up to 63%). Rat liver microsomes were also incubated with [1-14C]-9c, 12c-18:2, [1-14C]-9c, 12t-18:2 or [1-14C]-9t, 12c-18:2 under desaturation conditions. The results indicated that 18:2 delta9c, 12t is a much better substrate for desaturase than 9t, 12c-18:2. Moreover, the conversion levels of [1-14C]-9c, 12t-18:2 was similar to what was observed for its all cis homologue, at low substrate concentration only. In a second set of experiments, in vitro elongation studies of each mono-trans 18:2 isomer and 9c, 12c-18:2 were carried out. For that purpose, rat liver microsomes were incubated with [1-14C]-9c, 12c-18:2, [1-14C]-9c, 12t-18:2 or [1-14C]-9t, 12c-18:2 underelongation conditions. The data show that [1-14C]-9t, 12c-18:2 is betterelongated than 9c, 12c-18:2 while the amount of product formed from [1-14C]-9c, 12t-18:2 was lower than was produced from the 9c, 12c-18:2. Thus, the desaturation enzymes presented a higher affinity for the 9c, 12t-18:2 whereas the elongation enzyme presented a higher affinity for the 9t, 12c-18:2.