Antioxidants do not explain the disparate longevity between mice and the longest-living rodent, the naked mole-rat

Vascular aging in the longest-living rodent, the naked mole rat

The naked mole rat (NMR; Heterocephalus glaber) is the longest-living rodent known [maximum lifespan potential (MLSP): >28 yr] and is a unique model of successful aging showing attenuated declines in most physiological function. This study addresses age-related changes in endothelial function and production of reactive oxygen species in NMR arteries and vessels of shorter-living Fischer 344 rats (MLSP: approximately 3 yr). Rats exhibit a significant age-dependent decline in acetylcholine-induced responses in carotid arteries over a 2-yr age range. In contrast, over a 10-yr age range nitric oxide (NO)-mediated relaxation responses to acetylcholine and to the NO donor S-nitrosopencillamine (SNAP) were unaltered in NMRs. Cellular superoxide anion (O(2)(*-)) and H(2)O(2) production significantly increased with age in rat arteries, whereas they did not change substantially with age in NMR vessels. Indicators of apoptotic cell death (DNA fragmentation rate, caspase 3/7 activity) were significantly enhanced ( approximately 250-300%) in arteries of 2-yr-old rats. In contrast, vessels from 12-yr-old NMRs exhibited only a approximately 50% increase in apoptotic cell death. In the hearts of NMRs (2 to 26 yr old), expression of endothelial NO synthase, antioxidant enzymes (Cu,Zn-SOD, Mn-SOD, catalase, and glutathione peroxidase), the NAD(P)H oxidase subunit gp91(phox), and mitochondrial proteins (COX-IV, ATP synthase, and porin, an indicator of mitochondrial mass) did not change significantly with age. Thus long-living NMRs can maintain a youthful vascular function and cellular oxidant-antioxidant phenotype relatively longer and are better protected against aging-induced oxidative stress than shorter-living rats.

An anti-aging drug today: from senescence-promoting genes to anti-aging pill

Numerous mutations increase lifespan in diverse organisms from worms to mammals. Most genes that affect longevity encode components of the target of rapamycin (TOR) pathway, thus revealing potential targets for pharmacological intervention. I propose that one target, TOR itself, stands out, simply because its inhibitor (rapamycin) is a non-toxic, well-tolerated drug that is suitable for everyday oral administration. Preclinical and clinical data indicate that rapamycin is a promising drug for age-related diseases and seems to have anti-tumor, bone-sparing and calorie-restriction-mimicking 'side-effects'. I also discuss other potential anti-aging agents (calorie restriction, metformin, resveratrol and sirtuins) and their targets, interference with the TOR pathway and combination with antioxidants.

Comparison of endothelial function, O2-* and H2O2 production, and vascular oxidative stress resistance between the longest-living rodent, the naked mole rat, and mice

Vascular aging is characterized by decreased nitric oxide (NO) bioavailability, oxidative stress, and enhanced apoptotic cell death. We hypothesized that interspecies comparative assessment of vascular function among rodents with disparate longevity may offer insight into the mechanisms determining successful vascular aging. We focused on four rodents that show approximately an order of magnitude range in maximum longevity (ML). The naked mole rat (NMR; Heterocephalus glaber) is the longest-living rodent known (ML > 28 yr), Damara mole rats (DMRs, Cryptomys damarensis; ML approximately 16 yr) and guinea pigs (GPs, Cavia porcellus; ML approximately 6 yr) have intermediate longevity, whereas laboratory mice are short living (ML approximately 3.5 yr). We compared interspecies differences in endothelial function, O(2)(-)* and H(2)O(2) production, and resistance to apoptotic stimuli in blood vessels. Sensitivity to acetylcholine-induced, NO-mediated relaxation was smaller in carotid arteries from NMRs, GPs, and DMRs than in mouse vessels. Measurements of production of O(2)(-)* (lucigenin chemiluminescence and ethidium bromide fluorescence) and H(2)O(2) (dichlorofluorescein fluorescence) showed that free radical production in vascular endothelial and smooth muscle cells is comparable in vessels of the three longer-living species and in arteries of shorter-living mice. In mouse arteries, H(2)O(2) (from 10(-6) to 10(-3) mol/l) and heat exposure (42 degrees C for 15-45 min) enhanced apoptotic cell death, as indicated by an increased DNA fragmentation rate and increased caspase 3/7 activity. In NMR vessels, only the highest doses of H(2)O(2) enhanced apoptotic cell death, whereas heat exposure did not increase DNA fragmentation rate. Interspecies comparison showed there is a negative correlation between H(2)O(2)-induced apoptotic cell death and ML. Thus endothelial vasodilator function and vascular production of reactive oxygen species do not correlate with maximal lifespan, whereas increased lifespan potential is associated with an increased vascular resistance to proapoptotic stimuli.

High oxidative damage levels in the longest-living rodent, the naked mole-rat

Oxidative stress is reputed to be a significant contributor to the aging process and a key factor affecting species longevity. The tremendous natural variation in maximum species lifespan may be due to interspecific differences in reactive oxygen species generation, antioxidant defenses and/or levels of accrued oxidative damage to cellular macromolecules (such as DNA, lipids and proteins). The present study tests if the exceptional longevity of the longest living (> 28.3 years) rodent species known, the naked mole-rat (NMR, Heterocephalus glaber), is associated with attenuated levels of oxidative stress. We compare antioxidant defenses (reduced glutathione, GSH), redox status (GSH/GSSG), as well as lipid (malondialdehyde and isoprostanes), DNA (8-OHdG), and protein (carbonyls) oxidation levels in urine and various tissues from both mole-rats and similar-sized mice. Significantly lower GSH and GSH/GSSG in mole-rats indicate poorer antioxidant capacity and a surprisingly more pro-oxidative cellular environment, manifested by 10-fold higher levels of in vivo lipid peroxidation. Furthermore, mole-rats exhibit greater levels of accrued oxidative damage to lipids (twofold), DNA (approximately two to eight times) and proteins (1.5 to 2-fold) than physiologically age-matched mice, and equal to that of same-aged mice. Given that NMRs live an order of magnitude longer than predicted based on their body size, our findings strongly suggest that mechanisms other than attenuated oxidative stress explain the impressive longevity of this species.

Disparate patterns of age-related changes in lipid peroxidation in long-lived naked mole-rats and shorter-lived mice

A key tenet of the oxidative stress theory of aging is that levels of accrued oxidative damage increase with age. Differences in damage generation and accumulation therefore may underlie the natural variation in species longevity. We compared age-related profiles of whole-organism lipid peroxidation (urinary isoprostanes) and liver lipid damage (malondialdehyde) in long living naked mole-rats [maximum lifespan (MLS) > 28.3 years] and shorter-living CB6F1 hybrid mice (MLS approximately 3.5 years). In addition, we compared age-associated changes in liver non-heme iron to assess how intracellular conditions, which may modulate oxidative processes, are affected by aging. Surprisingly, even at a young age, concentrations of both markers of lipid peroxidation, as well as of iron, were at least twofold (P < 0.005) greater in naked mole tats than in mice. This refutes the hypothesis that prolonged naked mole-rat longevity is due to superior protection against oxidative stress. The age-related profiles of all three parameters were distinctly species specific. Rates of lipid damage generation in mice were maintained throughout adulthood, while accrued damage in old animals was twice that of young mice. In naked mole-rats, urinary isoprostane excretion declined by half with age (P < 0.001), despite increases in tissue iron (P < 0.05). Contrary to the predictions of the oxidative stress theory, lipid damage levels did not change with age in mole-rats. These data suggest that the patterns of age-related changes in levels of markers of oxidative stress are species specific, and that the pronounced longevity of naked mole-rats is independent of oxidative stress parameters.

Oxidation-Resistant Membrane Phospholipids Can Explain Longevity Differences Among the Longest-Living Rodents and Similarly-Sized Mice

Underlying causes of species differences in maximum life span (MLS) are unknown, although differential vulnerability of membrane phospholipids to peroxidation is implicated. Membrane composition and longevity correlate with body size; membranes of longer-living, larger mammals have less polyunsaturated fatty acid (PUFA). We determined membrane phospholipid composition of naked mole-rats (MLS > 28.3 years) and similar-sized mice (MLS = 3-4 years) by gas-liquid chromatography to assess if the approximately 9x MLS difference could be explained. Mole-rat membrane composition was unchanged with age. Both species had similar amounts of membrane total unsaturated fatty acids; however, mice had 9 times more docosahexaenoic acid (DHA). Because this n-3PUFA is most susceptible to lipid peroxidation, mole-rat membranes are substantially more resistant to oxidative stress than are mice membranes. Naked mole-rat peroxidation indices, calculated from muscle and liver mitochondrial membranes, concur with those predicted by MLS rather than by body size, suggesting that membrane phospholipid composition is an important determinant of longevity.

The naked mole-rat: a new long-living model for human aging research

Tremendous variation in maximum life span among species overshadows modest increases in longevity resulting from experimental manipulation. Few aging studies focus on long-lived mammals even though these species may expose mechanisms involved in resisting aging. Naked mole-rats (NMRs approximately 35 grams) are the longest-living (>28.3 years) rodents known. This review describes their biology and potential use in aging research. Lifestyle features concur with most evolutionary theories with the exception of the disposable soma theory. Indeed, maximum life span is similar in breeders and nonbreeders, and these highly fecund animals reproduce until they die. Shared characteristics with calorie-restricted, methionine-restricted, and dwarf mice models of extended longevity include reduced body temperature; reduced thyroid, and blood glucose concentrations; and low glycated hemoglobin; in addition to reduced incidence of cancer. Young naked mole-rats surprisingly have high levels of accrued oxidative damage. With their similar longevity quotient to humans, these rodents may provide a novel opportunity to examine mechanisms modulating aging.