Protein modification by advanced Maillard adducts can be modulated by dietary polyunsaturated fatty acids

Advanced Maillard adducts, such as N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine, can be formed efficiently in vitro from both peroxidation of polyunsaturated fatty acids and glycolysis intermediates. In an attempt to differentiate the in vivo influence of the two pathways in these modifications, Wistar rats were chronically fed with specially designed diets rich in saturated or unsaturated fats. The degree of fatty acid unsaturation of all analysed organs (liver, kidney, brain) was altered by these dietary stresses. Protein glycoxidative and lipoxidative modifications were measured by GC/MS. In accordance with fatty acid profiles, concentrations of N∊-(malondialdehyde)lysine in these tissues were significantly increased in animals fed the unsaturated fat diet. In contrast, N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine concentrations were strongly dependent on the tissue analysed; although the unsaturated fat diet increased their levels significantly in brain, levels were unchanged in kidney and decreased in liver. These later results could be interpreted on the basis that polyunsaturated fatty acids decrease the expression of several glycolytic enzymes in liver. Globally, these data suggest that tissue-specific metabolic characteristics play a key role in the degree of cellular protein modification by Maillard reactions, e.g. by modulation of the concentration of glycolysis intermediates or via specific defensive systems 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.

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.

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.

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.

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.

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.

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.

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.

Evidence for the Maillard reaction in rat lung collagen and its relationship with solubility and age

This study investigated age-related changes in collagen solubility and collagen-linked fluorescence, and their relationship with the Maillard reaction. As a result of the collagen purification of rat lung samples, we obtained two pools of collagen with different degrees of solubility. The relative distribution of collagen between these two fractions was time-dependent, and the proportion of the smaller and less soluble fraction increased with time (r = 0.73, P < 0.0001). In this fraction, the intensity of fluorescence at Exc 335 nm/Em 385 nm, and the total amount of pentosidine increased with age (r = 0.66, P < 0.002, and r = 0.69, P < 0.01, respectively). The mean values for fluorescence and pentosidine per milligram of collagen were, respectively, six and ten times greater in the less soluble fraction. In this fraction the pentosidine per milligram of collagen increased with age (r = 0.59, P < 0.03). Our results demonstrated the presence of pentosidine in rat lung collagen. Moreover, its accumulation in the less soluble fraction suggested a relationship between Maillard reaction products, physico-chemical changes in collagen solubility, and the ageing process in rat lungs.

Chromatographic evidence for Amadori product formation in rat liver aminophospholipids

This work presents data which indicates the presence of Amadori product derived from Maillard reaction in aminophospholipids. The presence of 5-HMF, a stable derivative of acid-treated Amadori product, in the phospholipidic fraction from cell membranes was established by HPLC-UV and subsequent GC/MS analysis. The assay for 5-HMF in rat liver phospholipid revealed the presence of this molecule in membrane phospholipids of euglycemic rats, and showed increased glycation levels in membrane phospholipids from streptozotocin-induced diabetic rats (p < 0.001). This gives a new insight to cell membrane physiology and physiopathology.

Age-related fluorescence in rat lung collagen

Mechanical lung properties are impaired with age. In other organs an age-related increase in collagen-linked fluorescence, attributable to advanced glycation endproducts (AGE), or other nonenzymatic reactions such as those related to lipid peroxidation derivatives has been described. Moreover, oxidative processes accelerate some of these reactions. In several tissues, these AGE products have been found to be responsible for protein cross-linking and lack of elasticity. We have evaluated the fluorescence levels of lung collagen in rats aged from 1 to 25 months at two distinct wavelengths: the standard AGE fluorescence (Exc 370 nm/Em 440 nm) and the pentosidine fluorescence (Exc 335 nm/Em 395 nm). In pulmonary tissue fluorescence at both 370/440 nm (p < 0.05) and 335/395 nm (p < 0.001) increases with age. However, a relative stabilization of values is seen in the 25 months group that could be related to the kinetics of fluorescent products in vivo. So, as observed in other tissues, AGE products may increase in pulmonary tissues with time. This may explain the age-associated decline in pulmonary compliance.

Mechanisms of glycation in atherogenesis

Non-enzymatic glycation may affect the arterial wall altering its connective tissue and promoting LDL accumulation. Its recognition by specific receptors and growth factor release, as well as possible alteration of DNA, may stimulate smooth muscle cell proliferation. Free radical generation may favour non-enzymatic PUFA degradation and quench NO, which would alter vascular relaxation. All of these aspects may participate in atherogenesis.

Receptors to agglutinin from Dolichus biflorus (DBA) at the synaptic basal lamina of rat neuromuscular junction. A histochemical study during development and denervation

The binding of agglutinin from Dolichus biflorus (DBA) and other lectins (Concanavalin A, agglutinin from wheat germ and lectin from Bandeiraea simplicifolia) to synaptic and extrasynaptic portions of the basal lamina of muscle fibers, was studied with histochemical methods. In rat muscle, DBA-binding is specifically detected at the basal lamina of neuromuscular junction. However, long-term (6 months) denervated end-plate in adult rat muscle failed to bind DBA. During normal development, synaptic DBA receptors appear later than acetylcholine receptors or acetylcholinesterase at the rat neuromuscular junction. Generalized DBA-binding to motor end-plates is first visualized in 3-day-old rats, but section of sciatic nerve in 1-day-old rats prevents the appearance of synaptic DBA-binding on the leg end-plates. It is suggested, therefore, that the synaptic DBA receptors could be related to the postnatal stabilization of rat neuromuscular synapses.