Richard G. Cutler

Human longevity and aging: possible role of reactive oxygen species.

A brief overview has been given of the biological nature of human aging processes, where it has been emphasized that, in addition to the diseases of aging, there is also great economic loss as a result of human aging processes that began many years before medical costs related to aging begin to escalate. Because of the ubiquitous nature of aging, reducing the function of essentially all physiological processes, it appears that the only long-term solution to human aging problems is to decrease uniformly the aging rate of the entire body. Although the uniform decrease of aging rate has usually been considered impossible, where emphasis has consequently been placed on diseases of aging by the medically-orientated investigator, there is now at least one theoretical argument, accompanied by some experimental data, that suggests that progress can be made in achieving this goal. This progress has been based on the longevity determinant gene hypothesis predicting the existence of a relatively few key regulatory factors governing aging rate of the entire organism. If this hypothesis is not true, then indeed the prospect for significant intervention into human aging would appear impossible in the near future. Experiments have been briefly reviewed testing the longevity determinant gene hypothesis, the possibility that aging may be a result of dysdifferentiation and if aging rate is determined by mechanisms acting to stabilize the differentiated state of cells. In testing the dysdifferentiation hypothesis of aging, there is not yet much data one way or the other. It is evident, however, that changes in gene expression do occur with age, sometimes involving endogenous retroviruses or oncogenes. Other morphological evidence shows an increase with age in unusual cell type such as metaplasia cells. However, there is considerably more evidence indicating that aging may be a result of genetic instability (as it is in cancer) and that longer-lived species appear to have a more stable genetic apparatus and superior protective mechanisms against reactive oxygen species. There is a striking similarity in this model of aging and models of cancer, and much might be gained in bringing together these two fields of research. Taking all of these data together, as summarized in Table 14, it appears we may be on the right track and that mechanisms acting to protect DNA against oxidative damage may be one class of longevity determinant mechanisms. There is of course much work remaining to be done, some of which is listed in Table 15 in terms of our knowledge and our gaps of knowledge in this field.

Urate and ascorbate: their possible roles as antioxidants in determining longevity of mammalian species

Urate has been shown to be a major antioxidant in human serum and was postulated to have a biological role in protecting tissues against the toxic effects of oxygen radicals and in determining the longevity of primates. This possibility has been tested by determining if the maximum lifespan potentials of 22 primate and 17 non-primate mammalian species are positively correlated with the concentration of urate in serum and brain per specific metabolic rate. This analysis is based on the concept that the degree of protection a tissue has against oxygen radicals is proportional to antioxidant concentration per rate of oxygen metabolism of that tissue. Ascorbate, another potentially important antioxidant in determining longevity of mammalian species, was also investigated using this method. The results show a highly significant positive correlation of maximum lifespan potential with the concentration of urate in serum and brain per specific metabolic rate. No significant correlation was found for ascorbate. These results support the hypothesis that urate is biologically active as an antioxidant and is involved in determining the longevity of primate species, particularly for humans and the great apes. Ascorbate appears to have played little or no role as a longevity determinant in mammalian species.

Quantification of 8-iso-prostaglandin-F2α and 2,3-dinor-8-iso-prostaglandin-F2α in human urine using liquid chromatography-tandem mass spectrometry

Abstract Quantification of 8-iso-prostaglandin F2α (8-iso-PGF2α) has been suggested to be a reliable indicator of lipid peroxidation that may be related to in vivo free radical generation, oxidative damage, and antioxidant deficiency. We have developed a LC-MS/MS method to quantify 8-iso- PGF2α and its dinor metabolite, 2,3-dinor-8-iso-prostaglandin F2α (2,3-dinor-8-iso-PGF2α), in human urine samples. After an initial purification step using an automated C18 solid phase extraction procedure, the urine sample was injected directly into a liquid chromatography (LC) system and detected with tandem mass spectrometry. The detection limit of the assay was 9 pg for 8-iso-PGF2α and 3 pg for 2,3-dinor-8-iso-PGF2α with both inter- and intraday variations of less than 12%. The inaccuracies were less than 3% for both analytes at three different levels. The urinary excretion rate of 2,3-dinor-8-iso-PGF2α was higher than that of 8-iso-PGF2α, and changed in proportion to the parent compound (R = 0.70, n = 60). Values obtained with this method showed good linear correlation to duplicate 8-iso-PGF2α measurements performed with GCMS (R = 0.97, n = 15). The mean excretion rates of 8-iso-PGF2α and 2,3-dinor-8-iso-PGF2α were significantly higher in smokers than in nonsmokers (0.53 ± 0.37 vs. 0.25 ± 0.15 μg/g creatinine, p = 0.002 for 8-iso-PGF2α and 8.9 ± 3.8 vs. 4.6 ± 2.6 μg/g creatinine, p = 0.003 for 2,3-dinor-8-iso-PGF2α, respectively). The excellent accuracy, reproducibility, and high throughput of this method should permit it to be used in large clinical studies and standard clinical laboratories.

Dietary Restriction in Nonhuman Primates: Progress Report on the NIA Study

Rhesus and squirrel monkeys have been fed a semisynthetic diet at approximately ad libitum or 30% reduced levels for 3.5 (rhesus group 2) to 4.5 (rhesus group 1 and squirrel) years. Animals have maintained excellent health status as determined by physical examinations, hematology, and blood chemistry. While relative rates of body weight gain in restricted group 1 rhesus and squirrel monkeys have been markedly reduced, DR effects on crown-rump length (body height) have been variable. In addition, numerous physiological and biochemical parameters have been measured, and several exhibit significant cross-sectional age effects. Interestingly, several of these also exhibit possible species and genotype (group 1 and 2 rhesus) differences. A number of physiological parameters are emerging that might be altered by DR; however, further explanation of these effects awaits more extensive and detailed analyses.

Evolution of human longevity: a critical overview.

Evolution of longevity of the ungulates, carnivores and primates is reviewed. Special emphasis is focused on recent evolutionary history of longevity along the hominid ancestral-descendant sequence leading to modern man. Maximum life span potential (MLP) or the change in MLP is predicted in extinct species by (1) a phylogenetic analysis of the MLP of present living species and (2) an empirical equation using brain and body weight estimates from fossils. Both of these methods indicate MLP generally increased during mammalian evolution and at an extremely fast rate during the appearance of the hominid species. These results suggest that relatively few genetic alterations were necessary during the recent evolutionary history of man to significantly extend his innate ability to maintain mental and physical health. Much evidence indicates these genetic alterations principally involve regulatory genes, which control a conserved set of structural genes. Evolution of longevity in man could therefore be a result of simple changes in temporal and quantitative expression. Whether these genetic alterations result from mutational changes and/or chromosomal rearrangement cannot yet be evaluated.

Oxidative Stress Profiling

Many of the most serious human diseases have a strong association with the steady‐state level of oxidative damage in tissues. On an individual level this damage is defined as the patients oxidative stress status (OSS). OSS is associated with many of the major age‐related diseases such as cancer, heart disease, diabetes, and Alzheimers disease, as well as with the aging process itself. In general, the greater the OSS of the individual, the higher the risk for disease development. To further understand the role that OSS has as a causative or an associated factor for these diseases, and to develop more effective personalized therapy to minimize OSS, requires a reliable means to measure the many different components contributing to an individuals OSS. This procedure is called oxidative stress profiling (OSP) and represents a new strategy to simultaneously assess an individuals OSS as well as to identify key physiological parameters, such as the hormone, lipid, antioxidant, or iron profile, that may be responsible for that individuals OSS. The OSP strategy provides physicians with information that enable them to make a more accurate diagnosis of the patients condition and to recommend specific types of therapy based on better scientific data. Follow‐up studies of the patient would then be conducted using these same tests until the OSS of the patient has been minimized. The OSP strategy is particularly well suited for a personalized health optimization program. The procedure is based on measuring both the steady‐state levels of oxidative damage in nucleic acids, proteins, and lipids and the protective and defense processes of these components using blood, urine, and breath samples. Testing individuals before and after a controlled amount of exercise (70% VO2) may also help to obtain greater sensitivity and reproducibility. Evaluation of test results to obtain an integrated calculated OSS result for a patient represents a major challenge. One approach is to present the test results on a percentile bases, allowing results of different tests to be integrated into one or a few parameters, such as an oxidative stress and an antioxidant index. This article presents a general overview and rationale of the concept of the oxidative stress profile, tests to be used, and examples of how it may be applied.

Evolutionary Biology of Senescence

Man’s self-awareness has proven to be uncomfortable to him; he realizes that his life-span is finite, and knows of nothing that will prevent his physical and mental health from slowly declining to the point where death will be unavoidable. Naturally man, with his characteristic curiosity and love of life, wonders why this is so, how it happens, and what can be done, or should be done, about it. Is our life-span sufficient? If we should live any longer, would it be unbearable? An important difference exists between simply living out one’s natural life-span and living the same number of years in an optimum state of vigor and health. Man’s optimum period is from about 14 to 30 years of age, or only about one-fifth of his life-span.

Oxidative stress profiling: part I. Its potential importance in the optimization of human health.

Steadily accumulating scientific evidence supports the general importance of oxidative damage of tissue and cellular components as a primary or secondary causative factor in many different human diseases and aging processes. Our goal has been to develop sensitive and reliable means to measure the oxidative damage and defense/repair status of an individual that could be easily used by a physician to determine whether there is an immediate or long‐term increased health risk to their patients with regard to oxidative damage. We also sought to try to determine how this risk can best be reduced, and whether the prescribed therapy is working and how it might be best adjusted to optimize benefits. We have found that combining both an oxidative damage profile with a defense/repair profile produces the most reliable set of information to meet these objectives. Success is indicated by demonstrating the expected inverse correlation of oxidative stress vs. antioxidant status of a population of several hundred individuals. We also find support that oxidative stress status is under tight regulatory control for most individuals over a wide range of lifestyle variables including diet and exercise. Indeed only about 10% of the individuals analyzed appear to have unusually high oxidative stress levels. Only these individuals having the higher than normal levels of oxidative stress are the best responders to antioxidant supplements to lower their oxidative stress status to normal levels. We discuss the implications of these results for human application and review how current clinical studies are carried out to evaluate the benefits of antioxidant supplements in reducing the incidence of specific age‐dependent disease.

EVALUATING MEASURES OF HEMATOLOGY AND BLOOD CHEMISTRY IN MALE RHESUS MONKEYS AS BIOMARKERS OF AGING

Reliable and valid biomarkers of aging can provide valuable tools for examining the effectiveness of interventions that may influence the rate of aging processes. However, a standardized method for identifying biomarkers of aging has yet to be developed. The current analysis focused on hematology and blood chemistry variables obtained from a 5-year longitudinal study of male rhesus monkeys (N = 29) on a diet restriction regime known to retard aging processes and extend lifespan in laboratory rodents (70% of the diet intake of controls). For the current analysis, the major screening criteria for identifying candidate biomarkers of aging were cross-sectional and longitudinal correlation with chronological age (CA) and stability of individual differences. Six potential variables from the battery of blood chemistry tests were identified: 1) serum glutamic oxalacetic transaminase; 2) alkaline phosphatase; 3) total protein; 4) globulin; 5) blood urea nitrogen to creatinine ratio; and 6) phosphates. When submitted to principle component analysis, these variables loaded onto a single component that accounted for over 50% of the total variance to indicate marked covariance among them. By applying the factor score coefficients from the first principle component, an equation was derived for estimating a biological age score (BAS) for each individual monkey. A comparison of BAS between control and diet-restricted monkeys revealed no statistically significant difference at present; however, the slope of the regression of BAS onto CA appeared steeper for the control group compared to the experimental group. Thus, while demonstration of the validity of the candidate biomarkers awaits further evidence, a strategy by which additional biomarkers of aging can be identified is proposed as an improvement over past approaches.

High concentrations of antioxidants may not improve defense against oxidative stress.

It is often assumed that the oxygen radical defense could be further improved by higher concentration of antioxidants. But this has not been demonstrated over a wide range of concentrations. There are different types of oxygen radicals produced in the body and the antioxidant protection against them may not positively related to their concentrations. We report here that by using H(2)O(2) with Cu(2+) as an hydroxyl-radical generator in vitro, ascorbic acid shows no oxygen-radical absorbing capacity. We also found that the net hydroxyl-radical absorbing capacity of a water soluble alpha-tocopherol analogue (Trolox) and uric acid increases with concentration only when the concentration is lower than the normal value found for alpha-tocopherol and uric acid in human serum. At higher concentrations, the hydroxyl-radical absorbing capacity of the alpha-tocopherol analogue and uric acid decreases. The mechanism involved in the decrease of hydroxyl radical absorbance capacity of Trolox and uric acid at high concentration may be related to their reaction with hydroxyl radicals or other oxygen radicals produced in the presence of both H(2)O(2) and Cu(2+). This kind of reaction could lead to the formation of additional many Trolox or uric acid radicals at the same time. These results may be important not only in evaluating antioxidant activities of antioxidants in vitro but also in studying the potential efficiency of antioxidants in vivo in affecting oxidative stress status.