Effects of peroxidative stress and age on the concentration of a deoxyguanosine-malondialdehyde adduct in rat DNA

Ribose-induced advanced glycation end products reduce the lifespan in Drosophila melanogaster by changing the redox state and down-regulating the Sirtuin genes

Advanced Glycation End (AGE) products are one such factor that accumulates during aging and age-related diseases. However, how exogenous AGE compounds cause aging is an area that needs to be explored. Specifically, how an organ undergoes aging and aging-related phenomena that need further investigation. The intestine is the most exposed area to food substances. How AGEs affect the intestine in terms of aging need to be explored. Drosophila melanogaster, a well-known model organism, is used to decode aging and age-associated phenomena. In this study, we fed Ribose induced Advanced Glycation End products (Rib-AGE) to D. melanogaster to study the aging mechanism. The Rib-AGE-induced aging was checked in Drosophila. We found a series of changes in Rib-AGE-fed flies. Reactive oxygen species (ROS) and nitric oxide species (NOs) were higher in the Rib-AGE-fed flies, and the antioxidant level was lower. The intestinal permeability was altered. The microorganism load was higher inside the gut. The structural arrangement of the gut's microfilament was found to be damaged, and the nuclear shape was found to be irregular. Cell death within the gut was elevated in comparison to control. The food intake was found to be reduced. The relative mRNA expression of the Sirtuin 2 and Sirtuin 6 gene of D. melanogaster was downregulated in Rib-AGE-fed flies compared to the control. All these findings strongly suggest that Rib-AGE accelerates aging and age-related disorders in D. melanogaster.

Dietary Supplementation of Carob and Whey Modulates Gut Morphology, Hemato-Biochemical Indices, and Antioxidant Biomarkers in Rabbits

This study aimed to evaluate the influence of the carob powder (CP) and sweet whey powder (WhP) inclusion into weaning feed on the gut morphology, hemato-biochemical parameters, and antioxidant biomarkers. The addition of 10 g/kg (basal diet +10 g/kg of CP, of WhP) or the mixture (5 g/kg of CP and 5 g/kg of WhP) in the rabbit's standard diet was assessed. A total of 40 weaned New Zealand White rabbits (4 weeks old) was distributed according to body weight (BW) into four treatments (n = 10) and the feed additives were provided for 7 weeks. Tissue samples and blood were obtained after slaughter. Final BW, daily weight gain, feed conversion ratio, intestinal morphology, and carcass dressing were positively affected by CP-WhP treatments compared with the control diet. Also, CP-WhP treatments significantly increased total proteins, calcium and iron levels, fecal cholesterol excretion, total antioxidants capacity, superoxide dismutase, and catalase in different tissues and significantly decreased total cholesterol, triglycerides, and glucose in blood serum. These changes were associated with a diminution of blood tumor necrosis factor alpha, lipid peroxidation, and carbonyl proteins in rabbit tissues. Both the additives separately and especially in the mix may enhance productive performance, protein profile, gut function, immunity, and antioxidant activity, with reducing lipid peroxidation, essential inflammatory mediator, and protein-carbonyl residues of growing rabbits. These findings suggest that CP-WhP dietary supplementation provides novel insights into a variety of bioactive compound mixtures with different beneficial modes of actions.

The Advanced Lipoxidation End-Product Malondialdehyde-Lysine in Aging and Longevity

The nonenzymatic adduction of malondialdehyde (MDA) to the protein amino groups leads to the formation of malondialdehyde-lysine (MDALys). The degree of unsaturation of biological membranes and the intracellular oxidative conditions are the main factors that modulate MDALys formation. The low concentration of this modification in the different cellular components, found in a wide diversity of tissues and animal species, is indicative of the presence of a complex network of cellular protection mechanisms that avoid its cytotoxic effects. In this review, we will focus on the chemistry of this lipoxidation-derived protein modification, the specificity of MDALys formation in proteins, the methodology used for its detection and quantification, the MDA-lipoxidized proteome, the metabolism of MDA-modified proteins, and the detrimental effects of this protein modification. We also propose that MDALys is an indicator of the rate of aging based on findings which demonstrate that (i) MDALys accumulates in tissues with age, (ii) the lower the concentration of MDALys the greater the longevity of the animal species, and (iii) its concentration is attenuated by anti-aging nutritional and pharmacological interventions.

Chemical Characterization of Bioactive Components of Rosa canina Extract and Its Protective Effect on Dextran Sulfate Sodium-Induced Intestinal Bowel Disease in a Mouse Model

Rosa canina is a well-known medicinal plant used in folk remedy that alleviates various disorders, including inflammation, gastritis, and diarrhea. The objective of this investigation was to identify and quantify the phenolic components of R. canina methanolic extract (RCME) and to determine its protective action with dextran sulfate sodium (DSS)-generated mice colitis model. RCME chemical analysis was done using Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry, and experimental animals received RCME at different doses before colitis induction by oral DSS administration during 7 days. Another group received sulfasalazine as a positive control. Colitis damages and RCME benefits were assessed using histopathological and biochemical changes and improvements. Many phenolic compounds have been identified. In addition, the DSS intoxication induced an alteration of colonic epithelium associated with an oxidative stress state. DSS administration led to an increase or decrease of intracellular mediators such as free iron and ionizable calcium. RCME consumption effectively protected against colonic histological/biochemical alterations induced by DSS intoxication providing support for the traditional use of this plant.

Gastroprotective mechanism of Bauhinia thonningii Schum

ETHNOPHARMACOLOGICAL RELEVANCE

Bauhinia thonningii Schum. (Cesalpiniaceae) is locally known as Tambarib and used to treat various diseases including gastric ulcer.

AIM OF THE STUDY

The current study aims to evaluate the gastroprotecive mechanism(s) of methanolic (MEBT) and chloroform (CEBT) extracts of Bauhinia thonningii leaves on ethanol-induced gastric ulceration.

MATERIALS AND METHODS

Gastric acidity, quantification and histochemistry of mucus, gross and microscopic examination, nitric oxide, lipid peroxidation, 2D gel electrophoresis, mass spectroscopy and biochemical tests were utilized to assess the mechanism(s) underlying the gastroprotective effects of MEBT and CEBT. Effect of these extracts into lipopolysaccharide/interferon-γ stimulated rodent cells were done in vitro. In vitro and in vivo toxicity studies were also conducted. Antioxidant activities of MEBT and CEBT were examined using DPPH, FRAP and ORAC assays. Phytochemical analyses of MEBT and CEBT were conducted using chemical and spectroscopic methods.

RESULTS

Gross and histological features confirmed the anti-ulcerogenic properties of Bauhinia thonningii. Gastroprotective mechanism of MEBT was observed to be mediated through the modulation of PAS-reactive substances, MDA and proteomics biomarkers (creatine kinase, malate dehydrogenase, ATP synthase, actin and thioredoxin). MEBT and CEBT showed no significant in vitro and in vivo effects on nitric oxide. Methanolic extract (MEBT) showed superior gastroprotective effects, polyphenolic content and antioxidant activities compared to CEBT. The plant extracts showed no in vitro or in vivo toxicity.

CONCLUSION

It could be concluded that MEBT possesses anti-ulcer activity, which could be attributed to the inhibition of ethanol-induced oxidative damage and the intervention in proteomic pathways but not the nitric oxide pathway.

The role of DNA damage and repair in aging through the prism of Koch-like criteria

Since the first publication on Somatic Mutation Theory of Aging (Szilárd, 1959), a great volume of knowledge in the field has been accumulated. Here we attempted to organize the evidence "for" and "against" the hypothesized causal role of DNA damage and mutation accumulation in aging in light of four Koch-like criteria. They are based on the assumption that some quantitative relationship between the levels of DNA damage/mutations and aging rate should exist, so that (i) the longer-lived individuals or species would have a lower rate of damage than the shorter-lived, and (ii) the interventions that modulate the level of DNA damage and repair capacity should also modulate the rate of aging and longevity and vice versa. The analysis of how the existing data meets the proposed criteria showed that many gaps should still be filled in order to reach a clear-cut conclusion. As a perspective, it seems that the main emphasis in future studies should be put on the role of DNA damage in stem cell aging.

Life and death: metabolic rate, membrane composition, and life span of animals

Maximum life span differences among animal species exceed life span variation achieved by experimental manipulation by orders of magnitude. The differences in the characteristic maximum life span of species was initially proposed to be due to variation in mass-specific rate of metabolism. This is called the rate-of-living theory of aging and lies at the base of the oxidative-stress theory of aging, currently the most generally accepted explanation of aging. However, the rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span. Recently, it has been discovered that the fatty acid composition of cell membranes varies systematically between species, and this underlies the variation in their metabolic rate. When combined with the fact that 1) the products of lipid peroxidation are powerful reactive molecular species, and 2) that fatty acids differ dramatically in their susceptibility to peroxidation, membrane fatty acid composition provides a mechanistic explanation of the variation in maximum life span among animal species. When the connection between metabolic rate and life span was first proposed a century ago, it was not known that membrane composition varies between species. Many of the exceptions to the rate-of-living theory appear explicable when the particular membrane fatty acid composition is considered for each case. Here we review the links between metabolic rate and maximum life span of mammals and birds as well as the linking role of membrane fatty acid composition in determining the maximum life span. The more limited information for ectothermic animals and treatments that extend life span (e.g., caloric restriction) are also reviewed.

Modification of the longevity-related degree of fatty acid unsaturation modulates oxidative damage to proteins and mitochondrial DNA in liver and brain

Previous studies have shown that tissue fatty acid unsaturation correlates inversely with maximum longevity. However, it is unclear if this is related to the effects of fatty acid unsaturation only on lipids, or also on proteins and DNA, specially on mitochondrial DNA (mtDNA) oxidative damage. In this investigation the degree of fatty acid unsaturation of liver and brain was successfully manipulated in Wistar rats by chronic feeding with specially designed semipurified diets rich in saturated or unsaturated fats. The brain, an organ of special relevance for aging, was most profoundly affected by the increase in fatty acid unsaturation, and showed significant increases in malondialdehyde (MDA)-lysine, aminoadipic semialdehyde (a protein carbonyl), N(epsilon)-(carboxymethyl)lysine, and N(epsilon)-(carboxyethyl)lysine in proteins, as well as in 8-oxo,7,8-dihydro-2'-deoxyguanosine (8-oxodG) in mtDNA without changes in nuclear DNA (nDNA). In the liver 8-oxodG was also increased in mtDNA and not in nDNA. These DNA results are consistent with the presence of a high density of mitochondrial inner membranes (rich in lipids and in reactive oxygen species generation capacity) near mtDNA but not near nDNA. Among the protein markers analyzed, MDA-lysine was most consistent and responsive to fatty acid unsaturation, since it increased in both organs and showed the highest increase. These results, together with previous data from our laboratories, show that increasing the degree of fatty unsaturation of postmitotic tissues in vivo can raise not only lipid but also protein and mtDNA oxidative damage. This is mechanistically relevant in relation to the constitutively low tissue fatty acid unsaturation of long-lived animals.

Oxidative damage to nuclear DNA in hyperthyroid rat liver: inability of vitamin C to prevent the damage

The effects of hyperthyroidism on oxidative DNA damage in liver tissue and modification by vitamin C supplementation were investigated in rats. Animals were rendered hyperthyroid by administration of L-thyroxine (0.4 mg/100 g food) for 25 d. In the plasma samples, T(3), T(4), and thyroid-stimulating hormone (TSH) were measured by radioimmunoassay and ascorbate spectrophotometrically. Oxidative damage to hepatic nuclear DNA was determined by measuring deoxy-guanosine (dG) and 8-oxodG by high-performance liquid chromatography with diode array detector electrochemical detection (HPLC-DAD-ECD). In hyperthyroidism, 8-oxodG/(10(5) dG) levels were significantly higher and plasma vitamin C levels lower than in control rats. The results of this experimental study show that oxidative damage to hepatic nuclear DNA increases in the hyperthyroid state and that vitamin C was not effective in preventing this damage.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Membrane fatty acid unsaturation, protection against oxidative stress, and maximum life span: a homeoviscous-longevity adaptation?

Aging is a progressive and universal process originating endogenously that manifests during postmaturational life. Available comparative evidence supporting the mitochondrial free radical theory of aging consistently indicates that two basic molecular traits are associated with the rate of aging and thus with the maximum life span: the presence of low rates of mitochondrial oxygen radical production and low degrees of fatty acid unsaturation of cellular membranes in postmitotic tissues of long-lived homeothermic vertebrates in relation to those of short-lived ones. Recent research shows that steady-state levels of free radical-derived damage to mitochondrial DNA (mtDNA) and, in some cases, to proteins are lower in long- than in short-lived animals. Thus, nonenzymatic oxidative modification of tissue macromolecules is related to the rate of aging. The low degree of fatty acid unsaturation in biomembranes of long-lived animals may confer advantage by decreasing their sensitivity to lipid peroxidation. Furthermore, this may prevent lipoxidation-derived damage to other macromolecules. Taking into account the fatty acid distribution pattern, the origin of the low degree of membrane unsaturation in long-lived species seems to be the presence of species-specific desaturation pathways that determine membrane composition while an appropriate environment for membrane function is maintained. Mechanisms that prevent or decrease the generation of endogenous damage during the evolution of long-lived animals seem to be more important than trying to intercept those damaging agents or repairing the damage already inflicted. Here, the physiological meaning of these findings and the effects of experimental manipulations such as dietary stress, caloric restriction, and endocrine control in relation to aging and longevity are discussed.

Mechanisms linking diet and colorectal cancer: the possible role of insulin resistance

Diet is clearly implicated in the origin of colorectal cancer, with risk factors for the disease including reduced consumption of vegetables, fiber, and starch and increased consumption of red meat and animal fat. Several hypotheses have been developed to explain these associations. Most recently, McKeown-Eyssen and Giovannucci noted the similarity of the risk factors for colorectal cancer and those for insulin resistance and suggested that insulin resistance leads to colorectal cancer through the growth-promoting effect of elevated levels of insulin, glucose, or triglycerides. We briefly review the evidence from observational, epidemiological, and experimental animal studies linking diet with insulin resistance and colorectal cancer. The evidence suggests that diets high in energy and saturated fat and with high glycemic index carbohydrate and low levels of fiber and n-3 fatty acids lead to insulin resistance with hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. We then consider how insulin, the related insulin-like growth factors, triglycerides, and nonesterified fatty acids could lead to increased growth of colon cancer precursor lesions and the development of colorectal cancer. Finally, we consider the implications of this scheme on possible future research directions, including studies of satiety and clinical tests of the importance of insulin resistance in the colon carcinogenesis process.

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.

Urinary aldehydes as indicators of lipid peroxidation in vivo

The excretion of malondialdehyde (MDA), lipophilic aldehydes and related carbonyl compounds in rat and human urine was investigated. MDA was found to be excreted mainly in the form of two adducts with lysine, indicating that its predominant reaction in vivo is with the lysine residues of proteins. Adducts with the phospholipid bases serine and ethanolamine and the nucleic acid bases guanine and deoxyguanosine also were found. Except for the adduct with deoxyguanosine (dG-MDA), the excretion of these compounds increased with peroxidative stress imposed in the form of vitamin E deficiency or the administration of iron or carbon tetrachloride. Marked differences in the concentration of dG-MDA in different tissues were correlated with their content of fatty acids having three or more double bonds, the putative source of MDA. Fourteen nonpolar and eleven polar lipophilic aldehydes and other carbonyl compounds were identified as their 2,4-diphenylhydrazine derivatives in rat urine. The excretion of five nonpolar and nine polar compounds was increased under conditions of peroxidative stress. The profile of lipophilic aldehydes obtained for human urine resembled that for rat urine. Except for a reported 4-hydroxynon-2-enal conjugate with mercapturic acid, the conjugated forms of the lipophilic aldehydes excreted in urine remain unidentified. Aldehyde excretion is influenced by numerous factors that affect the formation of lipid peroxides in vivo such as energy status, physical activity and environmental temperature, as well as by wide variations in the intake of peroxides in the diet. Consequently, urinalysis for aldehydic products of lipid peroxidation is an unreliable indicator of the general state of peroxidative stress in vivo.

Effect of thyroid hormones on mitochondrial oxygen free radical production and DNA oxidative damage in the rat heart

Mitochondria seem to be involved in oxygen radical damage and aging. However, the possible relationships between oxygen consumption and oxygen radical production by functional mitochondria, and oxidative DNA damage, have not been studied previously. In order to analyze these relationships, male Wistar rats of 12 weeks of age were rendered hyper- and hypothyroid by chronic T(3) and 6-n-propyl-2-thiouracil treatments, respectively. Hypothyroidism decreased heart mitochondrial H(2)O(2) production in States 4 (to 51% of controls; P<0.05) and 3 (to 21% of controls; P<0.05). In agreement with this, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) decreased in the heart genomic DNA of hypothyroid animals to 40% of controls (P<0.001). Studies with respiratory inhibitors showed that the decrease in oxygen radical generation observed in hypothyroidism occurred at Complex III (mainly) and at Complex I; that decrease was due to the presence of a lower free radical leak in the respiratory chain (P<0.05). Hyperthyroidism did not significantly change heart mitochondrial H(2)O(2) production since the increase in State 4 oxygen consumption in comparison with control and hypothyroid animals (P<0.05) was compensated by a decrease in the free radical leak in relation to control animals (P<0.05). In agreement with this, heart 8-oxodG was not changed in hyperthyroid animals. The lack of increase in H(2)O(2) production per unit of mitochondrial protein will protect mitochondria themselves against self-inflicted damage during hyperthyroidism.

Age and organ dependent spontaneous generation of nuclear 8-hydroxydeoxyguanosine in male Fischer 344 rats

8-Hydroxydeoxyguanosine (8-OHdG) is a major oxidative DNA adduct playing roles in senescence, carcinogenesis and various disease processes. High-performance liquid chromatography with an electrochemical detection (HPLC-ECD) method has been widely used to assess organ levels of 8-OHdG, and a recently introduced immunohistochemical approach has made it possible to clarify intra-organ localization. In the present study, these methods were employed to reveal age-dependent changes in nuclear 8-OHdG within various tissues of male Fischer 344 rats between 18 fetal days and 104 weeks of age. 8-OHdG was detected in the nuclei of cerebellar small granule and small cortical cells, cerebral nerve cells, and choroid plexus epithelia of the brain and ependymal cells of the spinal cord; parenchymal cells in the anterior lobe of the pituitary and adrenal glands (mainly cortex); bronchial epithelium of the lung; intra-hepatic bile duct, pancreatic duct, glandular gastric and intestinal epithelial cells; renal tubular epithelial cells (mainly medulla); and spermatogonia and spermatocytes of the testis and seminal vesicle epithelia. The nuclear 8-OHdG levels were high (more than two lesions per 10(6) deoxyguanosines) from 7 days to 104 weeks of age in the brain, 3 to 6 weeks in the adrenal gland, 6 to 104 weeks in the lung, and 3 to 52 weeks in the testis. In the other organs, the nuclear 8-OHdG levels remained low throughout. These findings provide a basis for research dealing with oxidative stress by indicating organ-specific and age- but not aging-dependent changes in the localization of spontaneously generated nuclear 8-OHdG in intact rats. The immunohistochemical approach has advantages for assessing variation of 8-OHdG formation at the cellular level not accessible to the HPLC-ECD method.

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.

The effect of dietary fat on malondialdehyde concentrations in Fischer 344 rats

The effects of dietary fat and age on the level of malondialdehyde (MDA), a product of lipid peroxidation, were investigated in cerebellum, kidney, and liver tissues of female Fischer 344 rats. Groups of rats were fed diets containing various levels of corn oil (3, 5, 10, 15, or 20%), starting at 57 days of age, for a duration of 2, 10, or 20 weeks. High fat diets are thought to promote tumor formation, diabetes, and cardiovascular diseases via induction of oxidation stress, and this can begin early in the lifespan. However, it was observed that rats chronically consuming 3 and 5% corn oil diets yielded significantly higher levels of MDA, as analyzed by high-performance liquid chromatography, compared with those fed higher fat diets. After 20 weeks of feeding, the concentration of MDA in each of the three organs studied showed no significant differences among rats consuming diets containing 10, 15, or 20% corn oil. The levels of MDA were highest in the cerebellum, followed by kidney, and lowest in liver. Over the 20-week feeding period, a decrease in MDA level in both cerebellum and liver was observed.

Age-dependent sensitization to oxidative stress by dietary fatty acids

Experiments were designed to test the hypothesis that short-term feeding of a high polyunsaturated fatty acid (PUFA) diet would increase susceptibility to lipid peroxidation in an age-dependent manner. Young (6 month) and old (24 month) male B6C3F1 mice were fed modified AIN-76 diets containing either 5% corn oil (CO, N = 5 per age group) or 19% fish oil plus 1% corn oil (FO, N = 20 per age group) for two weeks. Five CO and five FO diet mice per age received an intraperitoneal injection of normal saline and were sacrificed one hour later; the remaining FO diet mice (N = 15 per age) were challenged with an acute systemic oxidative stress by intraperitoneal injection of 125 mg iron/kg body weight as iron dextran, and were sacrificed 1, 5, and 24 hours post-injection. Microsomal membrane fatty acid analysis revealed that increased age and a FO diet significantly increased membrane PUFA content. Serum iron levels increased significantly following iron treatment, peaking at 5 hours in both age groups. Formation of microsomal malondialdehyde (MDA), a product of lipid peroxidation, was significantly greater in the livers of the young mice. The temporal patterns of serum iron and microsomal MDA concentrations were significantly correlated in young mice, but not in old mice. Histochemical examination showed that liver iron accumulation following iron injection was similar in both age groups, but was associated with a significant temporal increase in liver apoptotic cells in young mice, but not in old mice. Thus, both age groups had similar iron exposure and iron accumulation, and the liver microsomal membranes of old mice were more unsaturated, yet there was significantly greater peroxidative damage (MDA formation) and cell death (apoptosis) in the young mouse livers. These findings suggest that the older animals have upregulated antioxidant defenses.

Lipid peroxidation, antioxidant protection and aging

The free radical hypothesis of aging proposes that deleterious actions of oxygen-derived radicals are responsible for the functional deterioration associated with aging. Because cellular membranes house the production apparatus of these radicals and because membranes suffer great damage from these radicals, modification of membrane lipids has been proposed to play a major role in the process of aging. Although the relationships between lipid peroxidation and aging have been investigated extensively, the studies have produced conflicting results. Increased lipid peroxidation and decreased antioxidant protection frequently occur, but they are not universal features of aging. Instead, age-dependent changes in these parameters appear to be species-, strain-, sex- and tissue specific. Potential correlations between lipid peroxidation and transition metal concentrations or between lipid peroxidation and declining antioxidant protection have been obscured by the contradictory nature of the findings. Future studies should focus on new approaches for the measurement in vivo lipid peroxidation and on identification of the critical targets of lipid peroxidation.