Faecal bacterial and short-chain fatty acids signature in hypercholesterolemia

Gut microbiota has been suggested to affect lipid metabolism. The objective of this study was to characterize the faecal microbiota signature and both short chain fatty acids (SCFAs) and bile acids (BA) profile of hypercholesterolemic subjects. Microbiota composition, SCFAs, BA and blood lipid profile from male volunteers with hypercholesterolemia (HC) and normocholesterolemia (NC) were determined by 16S rDNA sequencing, HPLC, GC and NMR, respectively. HC subjects were characterized by having lower relative abundance of Anaeroplasma (0.002% vs 0.219%, p-value = 0.026) and Haemophilus (0.041% vs 0.078%, p-value = 0.049), and higher of Odoribacter (0.51% vs 0.16%; p-value = 0.044). Correlation analysis revealed that Anaeroplasma and Haemophilus were associated to an unfavourable lipid profile: they correlated negatively to cholesterol and triglycerides related biomarkers and the ratio total to high density lipoprotein (HDL) cholesterol, and positively to HDL size. Odoribacter displayed an opposite behaviour. Faecal SCFAs profile revealed higher abundance of isobutyric (2.76% vs 0.82%, p-value = 0.049) and isovaleric acid (1.32% vs 0.06%, p-value = 0.016) in HC. Isobutyric acid correlated positively with Odoribacter and lipid parameters indicative of an unfavourable profile. BA profile did not show differences between groups. It was concluded that HC subjects showed a particular faecal bacterial signature and SCFAs profile associated with their lipid profile.

A low degree of fatty acid unsaturation leads to lower lipid peroxidation and lipoxidation-derived protein modification in heart mitochondria of the longevous pigeon than in the short-lived rat

Birds have a maximum longevity (MLSP) much greater than mammals of similar metabolic rate and body size. Thus, they are ideal models to identify longevity characteristics not linked to low metabolic rates. In this investigation, we show that the fatty acid double bond content of total lipids and phosphatidylcholine, phosphatidylethanolamine and cardiolipin fractions of heart mitochondria is intrinsically lower in pigeons (MLSP = 35 years) than in rats (MLSP = 4 years). This is mainly due to a lower content of the most highly unsaturated docosahexaenoic acid (22:6n-3) and in some fractions arachidonic acid (20:4n-6). The lower double bond content leads to a lower sensitivity to in vitro lipid peroxidation, and is associated with a lower concentration of lipid peroxidation products in vivo, and a lower level of malondialdehyde-lysine protein adducts in heart mitochondria of pigeons than rats. These results, together with those previously obtained in other species or tissues, suggest that a low degree of fatty acid unsaturation is a general characteristic of longevous homeothermic vertebrate animals both when they have low metabolic rates (mammals of large body size) or high metabolic rates (small sized birds). This constitutive trait helps to protect their tissues and mitochondria against lipid peroxidation and oxidative protein modification and can be a factor contributing to their slow rate of aging. The results also show, for the first time in a physiological model, that lipid peroxidizability is related to lipoxidative protein damage.

Impaired mitochondrial oxidative phosphorylation in the peroxisomal disease X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited metabolic disorder of the nervous system characterized by axonopathy in spinal cords and/or cerebral demyelination, adrenal insufficiency and accumulation of very long-chain fatty acids (VLCFAs) in plasma and tissues. The disease is caused by malfunction of the ABCD1 gene, which encodes a peroxisomal transporter of VLCFAs or VLCFA-CoA. In the mouse, Abcd1 loss causes late onset axonal degeneration in the spinal cord, associated with locomotor disability resembling the most common phenotype in patients, adrenomyeloneuropathy. We have formerly shown that an excess of the VLCFA C26:0 induces oxidative damage, which underlies the axonal degeneration exhibited by the Abcd1(-) mice. In the present study, we sought to investigate the noxious effects of C26:0 on mitochondria function. Our data indicate that in X-ALD patients' fibroblasts, excess of C26:0 generates mtDNA oxidation and specifically impairs oxidative phosphorylation (OXPHOS) triggering mitochondrial ROS production from electron transport chain complexes. This correlates with impaired complex V phosphorylative activity, as visualized by high-resolution respirometry on spinal cord slices of Abcd1(-) mice. Further, we identified a marked oxidation of key OXPHOS system subunits in Abcd1(-) mouse spinal cords at presymptomatic stages. Altogether, our results illustrate some of the mechanistic intricacies by which the excess of a fatty acid targeted to peroxisomes activates a deleterious process of oxidative damage to mitochondria, leading to a multifaceted dysfunction of this organelle. These findings may be of relevance for patient management while unveiling novel therapeutic targets for X-ALD.

Double bond content of phospholipids and lipid peroxidation negatively correlate with maximum longevity in the heart of mammals

Free radical damage is currently considered a main determinant of the rate of aging. Unsaturated fatty acids are the tissue macromolecules most sensitive to oxidative damage. Therefore, the presence of relatively low degrees of fatty acid unsaturation is expected in the tissues of longevous animals. In agreement with this prediction, fatty acid analyses of heart phospholipids in eight mammals ranging in maximum life span (MLSP) from 3.5 to 46 years showed that their total number of double bonds is negatively correlated with MLSP (r = -0.78, P < 0.02). The low double content of longevous mammals was not due to a low polyunsaturated fatty acid content. Instead, it was mainly due to a redistribution between types of polyunsaturated fatty acids from the highly unsaturated docosahexaenoic acid (22:6n-3) to the less unsaturated linoleic acid (18:2n-6) in longevous animals (r = -0.89, P < 0.003 for 22:6n-3 and r = 0.91, P < 0.002 for 18:2n-6 versus MLSP), where n = number of different animals in each species. This redistribution suggests that one of the mechanisms responsible for the low number of fatty acid double bonds is the presence of low desaturase activities in longevous animals, although other causing factors must be involved. In agreement with the low degree of fatty acid unsaturation of longevous mammals, the sensitivity to lipid peroxidation (r = -0.87; P < 0.005) and the in vivo lipid peroxidation (r = -0.86, P < 0.005) in the heart were also negatively correlated with MLSP across species. These results, together with previous ones obtained in rodents, birds, and humans, suggest that the low degree of tissue fatty acid unsaturation of longevous homeothermic animals could have been selected during evolution to protect the tissues against oxidative damage.

Low fatty acid unsaturation: a mechanism for lowered lipoperoxidative modification of tissue proteins in mammalian species with long life spans

Carbonyl compounds generated by the nonenzymatic oxidation of polyunsaturated fatty acids react with nucleophilic groups in proteins, leading to their modification. It has not been tested whether fatty acid unsaturation is related to steady-state levels of lipoxidation-derived protein modification in vivo. A low fatty acid unsaturation, hence a low protein lipoxidation, in tissues of longevous animals would be consistent with the free radical theory of aging, because membrane lipids increase their sensitivity to oxidative damage as a function of their degree of unsaturation. To evaluate the relationship between fatty acid composition, protein lipoxidation, and maximum life span (MLSP), we analyzed liver fatty acids and proteins from seven mammalian species, ranging in MLSP from 3.5 to 46 years. The results show that the peroxidizability index of fatty acids and the sensitivity to in vitro lipid peroxidation are negatively correlated with the MLSP. Based on gas chromatography and mass spectroscopy analyses, liver proteins of all these species contain malondialdehyde-lysine and Nepsilon-carboxymethyllysine adducts, two biomarkers of protein lipoxidation. The steady-state levels of malondialdehyde-lysine and Nepsilon-carboxymethyl lysine are directly related to the peroxidizability index and inversely related to the MLSP. We propose that a low degree of fatty acid unsaturation may have been selected in longevous mammals to protect their tissue lipids and proteins against oxidative damage while maintaining an appropriate environment for membrane function.

Effect of thyroid status on lipid composition and peroxidation in the mouse liver

In order to analyze the possible relationship between metabolic rate and oxidative stress, OF1 female mice were rendered hyper- or hypothyroid for 4-5 weeks by administration of 0.0012% L-thyroxine (T4) or 0.05% 6-n-propyl-2-thiouracil (PTU), respectively, in their drinking water. Treatment with T4 resulted in increased basal metabolic rate measured by oxygen consumption and liver cytochrome oxidase activity without altering the glutathione redox system. Endogenous lipid peroxidation, sensitivity to lipid peroxidation and fatty acid unsaturation were decreased in the hyperthyroid group. Hypothyroidism also decreased phosphatidylcholine and cardiolipin fatty acid unsaturation but not in total lipids, and thus lipid peroxidation was not altered. Cardiolipin, a mainly mitochondrial lipid, was the most profoundly altered fraction by both hyper- and hypothyroidism. It is suggested that the lipid changes observed in hyperthyroid animals can protect them against an increased oxidative attack to tissue lipids due to their increased mitochondrial activities.

Effects of fasting on oxidative stress in rat liver mitochondria

While moderate caloric restriction has beneficial effects on animal health state, fasting may be harmful. The present investigation was designed to test how fasting affects oxidative stress, and to find out whether the effects are opposite to those previously found in caloric restriction studies. We have focused on one of the main determinants of aging rate: the rate of mitochondrial free radical generation. Different parameters related to lipid and protein oxidative damage were also analyzed. Liver mitochondria from rats subjected to 72 h of fasting leaked more electrons per unit of O(2) consumed at complex III, than mitochondria from ad libitum fed rats. This increased leak led to a higher free radical generation under state 3 respiration using succinate as substrate. Regarding lipids, fasting altered fatty acid composition of hepatic membranes, increasing the double bond and the peroxidizability indexes. In accordance with this, we observed that hepatic membranes from the fasted animals were more sensitive to lipid peroxidation. Hepatic protein oxidative damage was also increased in fasted rats. Thus, the levels of oxidative modifications, produced either indirectly by reactive carbonyl compounds (N(epsilon)-malondialdehyde-lysine), or directly through amino acid oxidation (glutamic and aminoadipic semialdehydes) were elevated due to the fasting treatment in both liver tissue and liver mitochondria. The current study shows that severe food deprivation increases oxidative stress in rat liver, at least in part, by increasing mitochondrial free radical generation during state 3 respiration and by increasing the sensitivity of hepatic membranes to oxidative damage, suggesting that fasting and caloric restriction have different effects on liver mitochondrial oxidative stress.

Diabetes induces an impairment in the proteolytic activity against oxidized proteins and a heterogeneous effect in nonenzymatic protein modifications in the cytosol of rat liver and kidney

It is assumed that increased oxidative stress contributes to the development of complications in diabetes. In this study, several markers of protein structural modifications directly induced by free radicals were investigated in the liver and kidney cytosolic fractions of rats with streptozotocin-induced diabetes. Sulfydryl residue and side-chain amino group analyses, as well as immunoblotting and chromatographic measurements of protein-bound carbonyl, suggest that protein oxidative modification is not increased by diabetes, with the exception of sulfydryl groups in renal cytosol. The levels of the glycation-derived carbonyl N epsilon-fructosyl-lysine are significantly increased by diabetes. Furthermore, unchanged proteolytic activity against in vivo-oxidized proteins, significant decreases both in activity against H2O2-modified proteins and in proteasome activity, measured by the degradation of a specific fluorogenic substrate, suggest that the unchanged oxidative protein modification in the diabetic state cannot be attributed to an increased cytosolic proteolytic activity in these tissues. These results provide evidence against a generalized increase in protein oxidative damage and demonstrate a diabetes-induced alteration in cytosolic proteolytic pathways, suggesting that proteasome activity may be impaired in these organs.

Correlation of fatty acid unsaturation of the major liver mitochondrial phospholipid classes in mammals to their maximum life span potential

Free radical damage is considered a determinant factor in the rate of aging. Unsaturated fatty acids are the tissue macromolecules that are most sensitive to oxidative damage. Therefore, the presence of low proportions of fatty acid unsaturation is expected in the tissues of long-lived animals. Accordingly, the fatty acid compositions of the major liver mitochondrial phospholipid classes from eight mammals, ranging in maximum life span potential (MLSP) from 3.5 to 46 yr, show that the total number of double bonds is inversely correlated with MLSP in both phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) (r = 0.757, P < 0.03, and r = 0.862, P < 0.006, respectively), but not in cardiolipin (P = 0.323). This is due not to a low content of unsaturated fatty acids in long-lived animals, but mainly to a redistribution between kinds of fatty acids on PtdCho and PtdEtn, shifting from arachidonic (r = 0.911, P < 0.002, and r = 0.681, P = 0.05, respectively), docosahexaenoic (r = 0.931 and r = 0.965, P < 0.0001, respectively) and palmitic (r = 0.944 and r = 0.974, P < 0.0001, respectively) acids to linoleic acid (r = 0.942, P < 0.0001, for PtdCho; and r = 0.957, P < 0.0001, for PtdEtn). For cardiolipin, only arachidonic acid showed a significantly inverse correlation with MLSP (r = 0.904, P < 0.002). This pattern strongly suggests the presence of a species-specific desaturation pathway and deacylation-reacylation cycle in determining the mitochondrial membrane composition, maintaining a low degree of fatty acid unsaturation in long-lived animals.

Influence of hyper- and hypothyroidism on lipid peroxidation, unsaturation of phospholipids, glutathione system and oxidative damage to nuclear and mitochondrial DNA in mice skeletal muscle

While the biochemical literature on free radical metabolism is extensive, there is little information on the endocrine control of tissue oxidative stress, and in the case of thyroid hormones it is mainly limited to liver tissue and to short-term effects on a few selected biochemical parameters. In this investigation, chronic hypothyroidism and hyperthyroidism were successfully induced in mice, and various oxidative-stress-related parameters were studied in skeletal muscle. In vivo and in vitro lipid peroxidation significantly increased in hyperthyroidism and did not change in the hypothyroid state. The fatty acid composition of the major phospholipid classes was affected by thyroid hormones, leading to a significant decrease in total fatty acid unsaturation both in hypothyroid and hyperthyroid muscle in phosphatidylcholine and phosphatidylethanolamine fractions. In cardiolipin, however, the double bond content significantly increased as a function of thyroid status, leading to a 2.7 fold increase in the peroxidizability index from euthyroid to hyperthyroid muscle. Cardiolipin content was also directly and significantly related to thyroid state across the three groups. Glutathione system was not modified by thyroid state. The oxidative damage marker 8-oxo-7,8-dihydro-2'-deoxyguanosine did not change in mitochondrial DNA, and decreased in genomic DNA both in hypothyroid and hyperthyroid muscle. The results indicate that chronic alterations in thyroid status specially affect oxidative damage to lipids in skeletal muscle, with a probably stronger effect on mitochondrial membranes, whereas the cytosolic redox potential and DNA are better protected possibly due to homeostatic compensatory reactions on the long-term.

Effect of the degree of fatty acid unsaturation of rat heart mitochondria on their rates of H2O2 production and lipid and protein oxidative damage

Previous comparative studies have shown that long-lived animals have lower fatty acid double bond content in their mitochondrial membranes than short-lived ones. In order to ascertain whether this trait protects mitochondria by decreasing lipid and protein oxidation and oxygen radical generation, the double bond content of rat heart mitochondrial membranes was manipulated by chronic feeding with semi-purified AIN-93G diets rich in highly unsaturated (UNSAT) or saturated (SAT) oils. UNSAT rat heart mitochondria had significantly higher double bond content and lipid peroxidation than SAT mitochondria. They also showed increased levels of the markers of protein oxidative damage malondialdehyde-lysine, protein carbonyls, and N(e)-(carboxymethyl)lysine adducts. Basal rates of mitochondrial oxygen radical generation were not modified by the degree of fatty acid unsaturation, but the rates of H2O2 generation stimulated by antimycin A were higher in UNSAT than in SAT mitochondria. These results demonstrate that increasing the degree of fatty acid unsaturation of heart mitochondria increases oxidative damage to their lipids and proteins, and can also increase their rates of mitochondrial oxygen radical generation in situations in which the degree of reduction of Complex III is higher than normal. These observations strengthen the notion that the relatively low double bond content of the membranes of long-lived animals could have evolved to protect them from oxidative damage.

Thyroid status modulates glycoxidative and lipoxidative modification of tissue proteins

Steady state protein modification by carbonyl compounds is related to the rate of carbonyl adduct formation and the half-life of the protein. Thyroid hormones are physiologic modulators of both tissue oxidative stress and protein degradation. The levels of the glycation product N(epsilon)-fructoselysine (FL) and those of the oxidation products, N(epsilon)-(carboxymethyl)lysine (CML) and malondialdehyde-lysine (MDA-lys), identified by GC/MS in liver proteins, decreased significantly in hyperthyroid rats, as well as (less acutely) in hypothyroid animals. Immunoblotting of liver proteins for advanced glycation end-products (AGE) is in agreement with the results obtained by GC/MS. Cytosolic proteolytic activity against carboxymethylated foreign proteins measured in vitro was significantly increased in hypo- and hyperthyroidism. Oxidative damage to DNA, estimated as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8oxodG), did not show significant differences between groups. The results suggests that the steady state levels of these markers depend on the levels of thyroid hormones, presumably through their combined effects on the rates of protein degradation and oxidative stress, whereas DNA is more protected from oxidative damage.

The gut mycobiome composition is linked to carotid atherosclerosis

The mycobiotic component of the microbiota comprises an integral, yet under-researched, part of the gastrointestinal tract. Here, we present a preliminary study of the possible contribution of gut mycobiota to sub-clinical atherosclerosis in a well-characterised group of obese and non-obese subjects in association with the Framingham Risk Score (FRS) and carotid intima-media thickness (cIMT). From all taxa identified, the relative abundance of the phylum Zygomycota, comprising the family Mucoraceae and genus Mucor, was negatively associated with cIMT and this association remained significant after controlling for false discovery rate. Obese subjects with detectable Mucor spp. had a similar cardiovascular risk profile as non-obese subjects. Interestingly, the relative abundance of Mucor racemosus was negatively associated both with FRS and cIMT. Partial least square discriminant analyses modelling, evaluating the potential relevance of gut mycobiota in patients stratified by mean values of cIMT, showed that even a 1 component model had a high accuracy (0.789), with a high R2 value (0.51). Variable importance in projection scores showed that M. racemosus abundance had the same impact in the model as waist-to-hip ratio, high-density lipoprotein-cholesterol, fasting triglycerides or fasting glucose, suggesting that M. racemosus relative abundance in the gut may be a relevant biomarker for cardiovascular risk.

Carboxymethylated phosphatidylethanolamine in mitochondrial membranes of mammals--evidence for intracellular lipid glycoxidation

The non-enzymatic modification of aminophospholipids with lipoperoxidation-derived aldehydes and glycoxidation-derived products have been reported previously. However, it remains unknown whether intracellular membranes are damaged by these glycoxidation-derived products. To investigate this issue, we tested whether aminophospholipids from mitochondrial membranes are damaged by glycoxidative stress the mitochondrion being identified as the major site of reactive-species production in the cell. We have used a selected-ion-monitoring/gas-chromatography/mass-spectrometry assay for carboxymethylethanolamine (CM-Etn) detection, and provide evidence for the presence of CM-Etn in mitochondrial phospholipids. Further, as a physiological approach to evaluate the influence of mitochondrial oxidative stress in CM-Etn formation, we also present the comparative levels of CM-Etn in mitochondrial membranes of ten mammalian species ranging in maximum life-span from 3.5 years to 100, since the rate of mitochondrial reactive-oxygen-species production is inversely correlated to the maximum life-span. Our results show that CM-Etn levels correlate in a logarithmic fashion with the maximum-life-span [[CM-Etn] = 0.51 + 0.50 x', where x' = log(maximum-life-span); r = 0.81, P < 0.004]. The data demonstrate the intracellular occurrence of glycoxidative processes affecting membrane lipids. Moreover, these data show that longer-lived mammals contain higher levels of CM-Etn in mitochondrial membrane aminophospholipids. This trend could result from differences in rates of CM-Etn accumulation and/or phospholipid turnover.

Activation of sirtuin 1 as therapy for the peroxisomal disease adrenoleukodystrophy

Oxidative stress and mitochondrial failure are prominent factors in the axonal degeneration process. In this study, we demonstrate that sirtuin 1 (SIRT1), a key regulator of the mitochondrial function, is impaired in the axonopathy and peroxisomal disease X-linked adrenoleukodystrophy (X-ALD). We have restored SIRT1 activity using a dual strategy of resveratrol treatment or by the moderate transgenic overexpression of SIRT1 in a X-ALD mouse model. Both strategies normalized redox homeostasis, mitochondrial respiration, bioenergetic failure, axonal degeneration and associated locomotor disabilities in the X-ALD mice. These results indicate that the reactivation of SIRT1 may be a valuable strategy to treat X-ALD and other axonopathies in which the control of redox and energetic homeostasis is impaired.

Urinary pyrraline as a biochemical marker of non-oxidative Maillard reactions in vivo

The presence of pyrraline, a non-oxidative glucose-derived Maillard reaction product in plasma proteins has been established previously. In this study we have investigated the presence of pyrraline in human urine to determine whether pyrraline-containing proteins are metabolized or selectively retained. Pyrraline was detected by means of HPLC, and its presence was confirmed by UV and electrospray-mass spectrometry. The quantification of pyrraline in urine from healthy individuals showed 1.21 +/- 0.4 micrograms/mg creatinine. In urine from diabetic patients, pyrraline levels varied considerably, although the mean level was higher than in healthy subjects (1.37 +/- 0.6 micrograms/mg creatinine). These data further support the presence of a catabolic pathway for advanced non-oxidative Maillard reaction products in vivo and suggest their role in the pathogenesis of diabetes.

Glycaemic control and in vivo non-oxidative Maillard reaction: urinary excretion of pyrraline in diabetes patients

The presence of pyrraline in human urine has recently been described. Using reversed-phase high-performance liquid chromatography, we measured urinary pyrraline in 45 insulin-treated diabetic patients with preserved renal function and in 30 age- and sex-matched healthy subjects. The relationship between urinary pyrraline and metabolic control parameters in the diabetic population (glycaemia, fructosamine, haemoglobin A1c, and 1-year mean haemoglobin A1c) was evaluated. The mean urinary level of pyrraline in diabetic patients with poor glycaemic control (HbA1c > 9.5%) was higher than that in healthy subjects (1.12 +/- 0.35 vs. 0.75 +/- 0.2 mumol mmol-1 creatinine, P < 0.04), whereas in patients with good to moderate glycaemic control (HbA1c < 9.5) it was slightly but not significantly higher than in healthy subjects (0.80 +/- 0.3 mumol mmol-1 creatinine vs. 0.75 +/- 0.2 mumol mmol-1 creatinine). There is a significant correlation between urinary pyrraline level and glycaemia (P < 0.008), haemoglobin A1c (P < 0.01) and 1-year mean haemoglobin A1c values (P < 0.007), but not with fructosamine. The results of the present work prove, for the first time, that glycaemic status influences circulating levels of advanced Maillard reaction products.

Atherosclerosis prevention by nutritional factors: a meta-analysis in small animal models

BACKGROUND AND AIMS

Atherosclerosis prevention in small laboratory models has been used as a preclinical stage in the development of functional foods with claimed antiatherogenic properties. However, a high heterogeneity of experimental atherosclerosis models as well as species-specific differences in lipoprotein metabolism could limit the usefulness of these developments. To solve this, we have performed a meta-analysis on the effects of nutritional complements (i.e. less than 2% of diet) with potential antiatherogenic properties in mice, rabbits and hamsters, and compared the outcomes with those obtained in humans.

METHODS AND RESULTS

A meta-analysis comprising works dealing with dietary prevention of experimental atherosclerosis (i.e. macroscopic and/or pathological evidences of atheromatosis in aorta) has been performed (n = 110 works). Quality criteria were applied resulting in selection of 16 works comprising 511 animals. Despite high heterogeneity, there is a significant effect of nutritional interventions reducing atheroma globally (mean effect 24.38% (95% CI: 13.24-35.51%) of prevention). In mouse studies (20.64% (95% CI: 8.38-32.90%)) and in rabbits (40.48% (95% CI: 6.73-74.23%)) this effect was significant, in contrast with hamster-based works (95% CI: 13.66-49.48%). Meta-regression showed that reduction of atheroma plaque formation was not linked to changes either in total circulating cholesterol or LDL cholesterol levels.

CONCLUSION

Nutritional addition of selected compounds significantly prevents experimental atheromatosis, but the reproduction of positive effects observed in humans was very limited. These analyses reinforce the need for adequate standardization of atherosclerosis studies in preclinical models and for human intervention trials.

Heart fatty acid unsaturation and lipid peroxidation, and aging rate, are lower in the canary and the parakeet than in the mouse

Despite their high metabolic rates, birds have a much higher maximum longevity (MLSP) than mammals of similar body size, and thus represent ideal models for identifying longevity characteristics not linked to low metabolic rates. This study shows that the fatty acid double bond content of both canary (MLSP = 24 years) and parakeet (MLSP = 21 years) hearts is intrinsically lower than in mouse (MLSP = 3.5 years) heart. This is caused by a redistribution between types of unsaturated fatty acids, mainly due to a lower content of the most highly unsaturated docosahexaenoic acid (22:6n-3) in the two birds in relation to the mammal. The lower double bond content leads to a lower sensitivity to lipid peroxidation, and to a lower level of in vivo lipid peroxidation in the heart of parakeets and canaries than in that of mice. Similar results have been previously found comparing liver mitochondria of rats and pigeons and tissues of different mammalian species. All these results taken together suggest that a low degree of fatty acid unsaturation is a general characteristic of longevous homeothermic vertebrate animals, both when they have low metabolic rates (mammals of large body size) or high metabolic rates (the studied birds); this constitutive trait protects their tissues and organelles against free radical mediated lipid peroxidation, and can contribute to their slow aging rate.

Mitochondrial membrane peroxidizability index is inversely related to maximum life span in mammals

The oxidative stress theory of aging predicts a low degree of fatty acid unsaturation in tissues of longevous animals, because membrane lipids increase their sensitivity to oxidative damage as a function of their unsaturation. Accordingly, the fatty acids analyses of liver mitochondria from eight mammals, ranging in maximum life span from 3.5 to 46 years, show that the total number of double bonds and the peroxidizability index are negatively correlated with maximum life span (r = -0. 88, P < 0.003; r = -0.87, P < 0.004, respectively). This is not due to a low content of unsaturated fatty acids in longevous animals, but mainly to a redistribution between kinds of the polyunsaturated n-3 fatty acids series, shifting from the highly unsaturated docosahexaenoic acid (r = -0.89, P < 0.003) to the less unsaturated linolenic acid (r = 0.97, P < 0.0001). This redistribution pattern strongly suggests the presence of a constitutively low delta6-desaturase activity in longevous animals (r = -0.96, P < 0.0001). Thus, it may be proposed that, during evolution, a low degree of fatty acid unsaturation in liver mitochondria may have been selected in longevous mammals in order to protect the tissues against oxidative damage, while maintaining an appropriate environment for membrane function.