Preserved antilipolytic insulin action is associated with a less atherogenic plasma lipid profile in healthy centenarians

ROLE of IGF-1 System in the Modulation of Longevity: Controversies and New Insights From a Centenarians' Perspective

Human aging is currently defined as a physiological decline of biological functions in the body with a continual adaptation to internal and external damaging. The endocrine system plays a major role in orchestrating cellular interactions, metabolism, growth, and aging. Several in vivo studies from worms to mice showed that downregulated activity of the GH/IGF-1/insulin pathway could be beneficial for the extension of human life span, whereas results are contradictory in humans. In the present review, we discuss the potential role of the IGF-1 system in modulation of longevity, hypothesizing that the endocrine and metabolic adaptation observed in centenarians and in mammals during caloric restriction may be a physiological strategy for extending lifespan through a slower cell growing/metabolism, a better physiologic reserve capacity, a shift of cellular metabolism from cell proliferation to repair activities and a decrease in accumulation of senescent cells. Therefore, understanding of the link between IGF-1/insulin system and longevity may have future clinical applications in promoting healthy aging and in Rehabilitation Medicine.

Association of mtDNA haplogroup F with healthy longevity in the female Chuang population, China

Human longevity is a complex heritable genetic trait. Based on substantial evidence from model organisms, it is clear that mitochondria play a pivotal role in aging and lifespan. However, the effects that mitochondrial genome variations have upon longevity and longevity-related phenotypes in Chuang people in China have yet to be established. By genotyping 15 variants for 10 haplogroups in 738 Chuang subjects, including 367 long-lived individuals and 371 controls, we found that haplogroup F was significantly associated with longevity in females of Zhuang population of China (p=0.003, OR: 2.01, 95%CI: 1.263-3.197). Additionally, haplogroup F was related to higher HDL levels (p<0.05) in long-lived individuals. Further analysis suggests that the non-synonymous variant m.13928G>C in haplogroup F was also associated with longevity in female Zhuang Chinese which might account for the beneficial effect of F.

Metabolic syndrome and risk factors for cardiovascular disease: are nonagenarians protected?

This study assessed cardiovascular disease risk factors in three groups of human subjects aged 20-34 [young, 20 male (M)/33 female (F)], 60-74 (aged, 29M/29F), and > 90 years (nonagenarian, 47M/50F). Components of the metabolic syndrome, cardiovascular disease, and markers of inflammation and oxidative stress were assessed. Nonagenarians weighed less than the two other groups (P < 0.001); however, there was no difference in percent fat among the three groups. Aged individuals had the highest prevalence of the metabolic syndrome (P < 0.001) according to the Adult Treatment Panel III classification. Both fibrinogen and homocysteine concentrations were significantly higher in the nonagenarians compared to younger groups. However, there were no significant differences between groups in fasting insulin, high sensitive C-reactive protein, and plasminogen activator inhibitor 1 concentrations. There were also no relationships between inflammation/ oxidative stress and the metabolic syndrome or cardiovascular disease although nonagenarians appear to be protected from oxidative damage to DNA.

The impact of mitochondrial DNA on human lifespan: a view from studies on centenarians

The role of inherited and somatic mutations of mitochondrial DNA (mtDNA) in aging and longevity is complex and highly controversial, owing to its peculiar genetics, including the phenomenon of heteroplasmy. Most of the data on mtDNA and longevity have been obtained on humans and particularly on centenarians, i. e., people who escaped or delayed the major age-related pathologies and reached the extreme limit of human lifespan. In this review we summarize the most recent advances in this field that suggest a consistent role in human longevity of both germ-line inherited and somatically acquired mutations. The particular case of the association with longevity of the somatic C150T mutation is extensively discussed, challenging the tenet that mtDNA mutations are basically detrimental. We also stress several limitations of our present knowledge, regarding the difficulty in extrapolating to humans the results obtained in animal models, owing to a variety of biological differences, including the very limited genetic variability of mtDNA in the strains used in laboratory experiments. The use of high-throughput technologies and the extensive analysis, possibly at the single cell level, of different tissues and cell types derived from the same individual will help in disentangling the complexity of mtDNA in aging and longevity.

Lipoproteins, vascular-related genetic factors, and human longevity

The relationships among lipoprotein metabolism, genetic vascular factors, vascular disease, and Alzheimer's disease suggest that the examination of centenarian populations in relation to certain genes or lipoprotein metabolism provide insights into human longevity. The findings on the higher frequency of the apolipoprotein E epsilon4 allele in middle-aged subjects than in centenarians were substantially confirmed. On the contrary, recent findings did not confirm previous data on increased prevalence of the high-risk angiotensin I converting enzyme D allele in French centenarians. The variability in the strength of association between angiotensin I converting enzyme polymorphism and longevity could be related to regional differences in angiotensin I converting enzyme D allele frequency in Europe recently showed, as also recently reported for apolipoprotein Eepsilon2 and epsilon4 allele in centenarians. Indeed some studies of lipoprotein profiles in centenarians have also had contradictory outcomes, with evidence of lower serum levels of high-density lipoprotein cholesterol, with higher high-density lipoprotein 2 cholesterol subfraction, larger high-density lipoprotein and low-density lipoprotein particle sizes, and higher lipoprotein(a) concentration in centenarians, which is apparently disadvantageous for human longevity. Elevated lipoprotein(a) serum levels, increasing the risk for cerebrovascular disease, may play a role in determining clinical Alzheimer's disease, but lipoprotein(a) elevation in centenarians, in the absence of other coronary artery disease risk factors, appears as a positive survival factor. In different populations, there are significant trends in the reduction of serum apolipoprotein E levels from apolipoprotein E epsilon2- to epsilon4-carriers and significant differences in serum apolipoprotein E levels with respect to age in epsilon4-carriers but only after adjustment for high-density lipoprotein cholesterol. While further studies are needed to confirm the possible role of apolipoprotein E concentration as putative longevity factor this paper provides an overview of many of the investigated vascular factors with respect to longevity.

Metabolic aspects of the extreme longevity

Starting from young to very old subjects, aging is associated with a progressive remodeling. Such an age-dependent remodeling process mainly affects anthropometrics, endocrine and thus, also metabolic factors. Interestingly, it occurs in some individuals successfully, while in others unsuccessfully. Centenarians in good health conditions are a very selected group of subjects representing an exceptional condition. Why the centenarians reach the extreme human life span is still unknown. Thus, in this article we will review the best known causes of age-related insulin resistance, outline the main metabolic differences between aged subjects and healthy centenarians, underline the clinical relevance of insulin resistance in the elderly and finally, we will try to propose a unifying hypothesis for explaining the development of insulin resistance with aging.

Evaluation of neuroendocrine status in longevity

It is well known that physiological changes in the neuroendocrine system may be related to the process of aging. To assess neuroendocrine status in aging humans we studied a group of 155 women including 78 extremely old women (centenarians) aged 100-115 years, 21 early elderly women aged 64-67 years, 21 postmenopausal women aged 50-60 years and 35 younger women aged 20-50 years. Plasma NPY, leptin, glucose, insulin and lipid profiles were evaluated, and serum concentrations of pituitary, adrenal and thyroid hormones were measured. Our data revealed several differences in the neuroendocrine and metabolic status of centenarians, compared with other age groups, including the lowest serum concentrations of leptin, insulin and T3, and the highest values for prolactin. We failed to find any significant differences in TSH and cortisol levels. On the other hand, LH and FSH levels were comparable with those in the elderly and postmenopausal groups, but they were significantly higher than in younger subjects. GH concentrations in centenarians were lower than in younger women. NPY values were highest in the elderly group and lowest in young subjects. We conclude that the neuroendocrine status in centenarians is markedly different from that found in early elderly or young women.

More favorable midlife cardiovascular risk factor levels in male twins and mortality after 25 years of follow-up is related to longevity of their parents

BACKGROUND

Genetic studies of life span in humans have used broad survival measures, most commonly longevity, which is moderately correlated between parents and offspring. We examined whether genetic cardiovascular disease risk factors in male twin offspring are related to longevity of their parents in the National Heart, Lung, and Blood Institute twin study.

METHODS

Cholesterol levels, body mass index, blood pressures, and pulmonary function measured over the first three examinations (average subject age 48, 58, and 63 years, respectively) were compared with the twins' paternal, maternal, and parental mean longevity divided into upper versus lower quintiles. The presence of an apolipoprotein E epsilon 4 allele typed from DNA collected at Exam 3 and mortality in the twin cohort through 1997 were also examined in relation to parental longevity quintiles.

RESULTS

Twins, particularly whose fathers died at younger ages, had significantly higher total cholesterol (p <.05), ratio of total cholesterol to high-density lipoprotein (p <.01), and blood pressures (p <.01) in middle age. This relationship decreased at the subsequent two examinations, but consistently, twins with longer-lived parents tended to have better risk factor profiles. A twin death (mean age 65) was significantly more common in families with mothers (p <.001) and, to a lesser extent, fathers who died early. An apolipoprotein epsilon 4 allele was more common in families with parents' age at death in the lowest quintile (p <.05).

CONCLUSIONS

Systolic blood pressures, cholesterol levels, and the presence of the apolipoprotein E epsilon 4 allele likely contribute to the observed familial correlations in longevity that have been reported in the literature.

Living longer--but better?

The highest attained age has increased by about 20 years since the beginning of the 19th century. In the course of the 1990s, more than ten individuals reached 115 years or more, including Jeanne Calment who attained the age of 122 years. In low-mortality countries, the number of centenarians has doubled every decade since 1950. This dramatic increase was mainly due to periodical effects related to the drastic fall in mortality among the elderly. The fact that centenarians are survivors does not mean that they are healthy. A high prevalence of comorbidity is found, and many centenarians have survived major diseases thanks to medical treatment and surgery. It is, however, possible that the comorbidity is less serious than in younger elderly. Certain personality traits may also be important in surviving health-threatening conditions. Furthermore, a number of biological and cognitive functions seem to be well-preserved in several centenarians. The influence of the apoE-gene and other genes involved in fundamental mechanisms illustrates that with advancing age and increasing mortality even small risks may have a substantial effect on survival to 100 years. A small proportion of long-livers may be considered as relatively autonomous, and this proportion will probably increase in the future. We are living longer and seem to postpone the terminal dependent phase to higher ages. Longevity may thus be perceived as part of our postmodern condition with its mix of pleasure and suffering.

Elevated plasma activator inhibitor 1 is not related to insulin resistance and to gene polymorphism in healthy centenarians

Previous studies demonstrated a relationship between the degree of insulin resistance and plasma plasminogen activator inhibitor type-1 (PAI-1) levels. We aim at investigating the relationship between the degree of insulin resistance and plasma PAI-1 levels in aged subjects (n=83) and in healthy centenarians (n=42). In all subjects the degree of insulin resistance was assessed by HOMA method. Our data demonstrated that healthy centenarians have higher plasma PAI-1 levels (73.1+/-13.9 vs 23.7+/-14.7 ng/ml, P<0.001) and lower degree of insulin resistance (1.4+/-0.5 vs 3.3+/-1.3, P<0.001) than aged subjects. In aged subjects plasma PAI-1 levels correlated with the degree of insulin resistance (r=0.61, P<0.001), fasting plasma triglycerides (r=0.74, P<0.001) and age (r=0.33, P<0.001). All such associations were lost in centenarians. Plasma PAI-1 Ag levels were also similar in aged subjects and centenarians even after categorization for PAI gene polymorphism. In multivariate analysis, a model made by age, sex, body mass index, fasting plasma triglycerides, HOMA and PAI-1 gene explained 65 and 50% of plasma PAI-1 level variations in aged subjects and centenarians, respectively. Nevertheless, HOMA (P<0.001) was significantly and independently associated with plasma PAI-1 levels only in aged subjects. In conclusion, our data demonstrates that in healthy centenarians, plasma PAI-1 were not associated with the degree of insulin resistance as in aged subjects. Frequency of PAI-1 genotype does not provide an explanation for such differences between aged subjects and centenarians.

Age-related insulin resistance: is it an obligatory finding? The lesson from healthy centenarians

It is widely known that advancing age is associated with impaired glucose handling. A unifying hypothesis explaining the relationship between aging and insulin resistance might encompass four main pathways, namely: (a) anthropometric changes (relative and absolute increase in body fat combined with a decline in fat free mass) which could be the anatomic substrate for explaining the reduction in active metabolic tissue; (b) environmental causes, mainly diet style and physical activity; (c) neuro-hormonal variations [decline in plasma dehydroepandrosterone sulphate (DHEAS) and IGF-1]; and finally (d) the rise in oxidative stress. Indeed previous studies have also investigated the occurrence and the degree of insulin resistance in healthy centenarians. Such data demonstrated that age-related insulin resistance is not an obligatory finding in the elderly and that healthy centenarians have a preserved insulin action compared to aged subjects. Why insulin action is preserved in centenarians is still not known. Nevertheless, a possible approach to the question is to outline the centenarians' anthropometric, endocrine and metabolic characteristics in order to design a clinical picture of such metabolic "successful aging". According to the remodeling theory of age, the preserved insulin action in centenarians might be the net result of the continuous adaptation of the body to the deleterious changes that occur over time. Nevertheless, only future longitudinal studies specifically designed to investigate the relationship between extreme old age and degree of insulin sensitivity will provide a conclusive answer with regard to the pathophysiology of adaptive metabolic changes occurring in the elderly.

Metabolic age modelling: the lesson from centenarians

Evolutionary theories of ageing, and data emerging from cellular and molecular biology of ageing, suggested that animals and humans capable of reaching an age close to the extreme limit of the life span should be equipped with a very efficient network of anti-ageing mechanisms. Indeed several evidences have demonstrated that starting from young to very old subjects, ageing is associated with a progressive remodelling. Thus, a new paradigm, the remodelling theory of age, was proposed. This theory, focusing on the human immune system, suggested that immunosenescence is the net result of the continuous adaptation of the body to the deteriorative changes occurring over time. According to this hypothesis, body resources are continuously optimized, and immunosenescence must be considered a very dynamic process including both loss and gain. Whether the metabolic pathways and the endocrine functions are also part of the age remodelling is not investigated. The aim of this review is to focus on the age-related changes in metabolic pathways and endocrine functions and to demonstrate that healthy centenarians (HC) represent the best living example of successful age-remodelling in whom the age remodelling has occurred without problems. In order to design the clinical picture of such successful ageing, anthropometric, endocrine and metabolic characteristics of healthy centenarians (HC), compared with aged subject, have been outlined.

The network and the remodeling theories of aging: historical background and new perspectives

Two general theories, i.e. "the network theory of aging" (1989) and "the remodeling theory of aging" (1995), as well as their implications, new developments, and perspectives are reviewed and discussed. Particular attention has been paid to illustrate: (i) how the network theory of aging fits with recent data on aging and longevity in unicellular organisms (yeast), multicellular organisms (worms), and mammals (mice and humans); (ii) the evolutionary and experimental basis of the remodeling theory of aging (immunological, genetic, and metabolic data in healthy centenarians, and studies on the evolution of the immune response, stress and inflammation) and its recent development (the concepts of "immunological space" and "inflamm-aging"); (iii) the profound relationship between these two theories and the data which suggest that aging and longevity are related, in a complex way, to the capability to cope with a variety of stressors.

Effects of glucose ingestion on cardiac autonomic nervous system in healthy centenarians: differences with aged subjects

BACKGROUND

Spectral analysis of heart rate variability (HRV) investigates the cardiac autonomic nervous system (ANS) activity. In particular, low frequency/high frequency (LF/HF) is considered an index of cardiac sympatho-vagal balance and is stimulated by glucose ingestion in healthy subjects. No studies have evaluated the effect of glucose ingestion on cardiac ANS in centenarians.

MATERIALS AND METHODS

In 30 healthy centenarians (HC) and 25 aged subjects (AS) power spectral analysis of HRV was investigated during an oral glucose ingestion.

RESULTS

Glucose ingestion rose LF/HF ratio in both groups studied. Such stimulatory effects were restrained to the first 60 min of the study. Independent of age, gender, body mass index (BMI) and fasting plasma norepinephrine and FT3 concentrations, HC had basal total power (1318 +/- 546 vs. 1918 +/- 818 msec2, P < 0.01), lower low frequency (LF) (33 +/- 21 vs. 50 +/- 11 n.u., P < 0. 03), and higher high frequency (HF) (74 +/- 18 vs. 43 +/- 15 n.u., P < 0.05) than AS. Consequently, LF/HF ratio (0.43 +/- 0.07 vs. 0.91 +/- 0.05, P < 0.02) was also lower in HC than in AS. In AS, but not in HC, the baseline LF/HF ratio correlated significantly with BMI (r = 0.48, P < 0.01), waist-hip-ratio (WHR) (r = 0.45, P < 0.02), fasting plasma insulin (r = 0.49, P < 0.01) and norepinephrine (r = 0.57, P < 0.02) concentration. Glucose ingestion was associated with a significant rise in LF/HF ratio in both groups studied but per cent changes in glucose mediated stimulation of LF/HF was lower in HC than in AS. In a control study, water administration did not affect power spectral parameters of HRV.

CONCLUSION

Our study demonstrates that basal- and glucose-stimulated LF/HF, an indirect index of cardiac sympatho-vagal balance, are lower in HC than in AS.

Advancing age and insulin resistance: new facts about an ancient history

The relationship between advancing age and insulin resistance is widely known, but the cause(s) of such association are less well understood. Age-related changes in anthropometric characteristics and environmental factors (changes in diet habits and decline in physical activity) have been hypothesized as being among the main causes. More recently, the role of plasma insulin-like growth factor I (IGF-I), dehydroepiandrosterone sulphate (DHEAS) and tumour necrosis factor alpha (TNF-alpha) concentrations as well as the degree of oxidative stress have also been evaluated. As far as the anthropometric changes are concerned, a decline in fat-free mass and a relative or absolute increase in fat mass are common findings in aged subjects. Such changes are combined with a decline in plasma DHEAS and IGF-I concentration and a rise in plasma TNF-alpha concentrations and oxidative stress, which, in turn, may interact with the anthropometric changes determining the worsening in insulin-mediated glucose uptake. Finally, age-related environmental factors (changes in diet quality and decline in the degree of physical activity) might be a common factor allowing anthropometric factors and age-related remodelling to accelerate their negative impact on insulin action.