Dose-dependency of Life Span Prolongation of F344/DuCrj Rats Injected with (−)deprenyl

What is hormesis and its relevance to healthy aging and longevity?

This paper provides a broad overview of hormesis, a specific type of biphasic dose response, its historical and scientific foundations as well as its biomedical applications, especially with respect to aging. Hormesis is a fundamental component of adaptability, neutralizing many endogenous and environmental challenges by toxic agents, thereby enhancing survival. Hormesis is highly conserved, broadly generalizable, and pleiotrophic, being independent of biological model, endpoint measured, inducing agent, level of biological organization and mechanism. The low dose stimulatory hormetic response has specific characteristics which defines both the quantitative features of biological plasticity and the potential for maximum biological performance, thereby estimating the limits to which numerous medical and pharmacological interventions may affect humans. The substantial degrading of some hormetic processes in the aged may profoundly reduce the capacity to respond effectively to numerous environmental/ischemic and other stressors leading to compromised health, disease and, ultimately, defining the bounds of longevity.

Hormesis: Toxicological foundations and role in aging research

The field of toxicology adopted the threshold dose response in the early decades of the 20th century. The model was rapidly incorporated into governmental regulatory assessment procedures and became a central feature of chemical evaluation and assessment. The toxicological community never validated the capacity of this model to make accurate predictions throughout the remainder of the 20th century. A series of recent investigations have demonstrated that the threshold and linear dose response model failed to make accurate predictions in the low dose zone. Such findings demonstrate a profound failure by the toxicology community on the central pillar of its discipline and one with profound public health, medical and economic implications. Ironically, the hormetic dose response, which was rejected by the toxicology community during the early decades of the 20th century, accurately predicted responses in the low dose zone in the same three large-scale validation assessments. Within the past two decades hormetic dose responses have been frequently reported in the experimental biogerontology literature, associated with endpoints associated enhancing healthy aging and longevity. The low dose stimulatory response of the hormetic dose response model represents the quantification of enhanced biological performance in the experimental facilitation of aging quality via multiple endpoints and mechanisms and in the extension of lifespan in such animal models research.

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity.

Hormesis, cellular stress response and vitagenes as critical determinants in aging and longevity

Understanding mechanisms of aging and determinants of life span will help to reduce age-related morbidity and facilitate healthy aging. Average lifespan has increased over the last centuries, as a consequence of medical and environmental factors, but maximal life span remains unchanged. Extension of maximal life span is currently possible in animal models with measures such as genetic manipulations and caloric restriction (CR). CR appears to prolong life by reducing reactive oxygen species (ROS)-mediated oxidative damage. But ROS formation, which is positively implicated in cellular stress response mechanisms, is a highly regulated process controlled by a complex network of intracellular signaling pathways. By sensing the intracellular nutrient and energy status, the functional state of mitochondria, and the concentration of ROS produced in mitochondria, the longevity network regulates life span across species by co-ordinating information flow along its convergent, divergent and multiply branched signaling pathways, including vitagenes which are genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as carnosine, carnitines or polyphenols, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. The hormetic dose-response, challenges long-standing beliefs about the nature of the dose-response in a lowdose zone, having the potential to affect significantly the design of pre-clinical studies and clinical trials as well as strategies for optimal patient dosing in the treatment of numerous diseases. Given the broad cytoprotective properties of the heat shock response there is now strong interest in discovering and developing pharmacological agents capable of inducing stress responses. In this review we discuss the most current and up to date understanding of the possible signaling mechanisms by which caloric restriction, as well hormetic caloric restriction-mimetics compounds by activating vitagenes can enhance defensive systems involved in bioenergetic and stress resistance homeostasis with consequent impact on longevity processes.

Clorgyline and other propargylamine derivatives as inhibitors of succinate-dependent H(2)O(2) release at NADH:UBIQUINONE oxidoreductase (Complex I) in brain mitochondria

Complex I is the main O(2)(-) producer of the mitochondrial respiratory chain. O(2)(-) release is low with NAD-linked substrates and increases strongly during succinate oxidation, which increases the QH(2)/Q ratio and is rotenone sensitive. We show that the succinate dependent O(2)(-) production (measured as H(2)O(2) release) is inhibited by propargylamine containing compounds (clorgyline, CGP 3466B, rasagiline and TVP-1012). The inhibition does not affect membrane potential and is unaffected by DeltapH modifications. Mitochondrial respiration is similarly unaffected. The propargylamines inhibition of O(2)(-)/H(2)O(2) production is monitored also in the presence of the Parkinson's disease toxin dopaminochrome which stimulates O(2)(-) release. Propargylamine-containing compounds are the first pharmacological inhibitors described for O(2)(-) release at Complex I.

Health span extension by later-life caloric or dietary restriction: a view based on rodent studies

In spite of the potential benefit of lifelong food restriction to retard aging and extend life span, it is unrealistic in human. The restriction late in life may be more practical. There are, however, only limited studies on the effect of late onset caloric or dietary restriction. We and other investigators have shown that the late life restriction rejuvenates some parameters that decline with age in rats and mice. Although such studies may provide a basis for human application of late-life caloric or dietary restriction, the prolongation of maximum life span would not be expected in view of the current status of the long-lived population in which maximum life span potential appears to have already been achieved. The late life caloric restriction, however, could extend the health span if the extent were appropriate.

What really declines with age? The Hayflick Lecture for 2006 35th American Aging Association

In order to understand the basic mechanisms underlying the organismic aging process, considerable efforts have been devoted in the last half-century to biochemical (enzyme activity) alterations in specific tissues and organs of various organisms associated with aging. When a decline in enzyme activities with age has been found in a study, especially for key enzymes such as antioxidant enzymes, the results have often been interpreted as a cause for the aging of the entire body. Retrospectively, however, these changes turned out to be so variable--depending on species, strains and sexes of animals--that the interpretation of these results in general terms of aging became invalid. Further, unlike the prediction for the whole human body, many enzyme activities in a vital organ, such as the liver, remained unchanged, as long as the old subjects remained healthy. However, enzyme activities in old animals and humans are often more susceptible to morbidities and frailties, which themselves are often accompanied by infections and malnutrition. Despite the rather stable enzyme functions in the liver with age, a distinct and progressive decline in the lateral diffusion coefficient of proteins of hepatocyte plasma membranes has been demonstrated by fluorescence recovery after photobleaching (FRAP), which was implicated as the cause for the decline of hepatocyte functions such as ouabain (and taurocholate) hepatic uptake and their eventual biliary excretion. Since a similar decline in protein diffusion coefficients was observed in brain and muscle cells, it is likely that these changes are occurring in common with many cell types of the body, thus causing a delay in transmembrane transport of endogenous and exogenous substances whose transports are mediated by membrane proteins. In attempts to prolong the life spans of animals other than by calorie restriction, but instead using deprenyl or tetrahydrocurcumin, works by the author and coworkers are introduced and discussed. Despite limited success along these lines thus far, further attempts are encouraged, primarily to understand the mechanisms underlying organismic aging processes and to find a practical way to prolong the health span of the elderly.

The Necessity of Having a Proper Dose of (-)Deprenyl (D) to Prolong the Life Spans of Rats Explains Discrepancies among Different Studies in the Past

(-)Deprenyl (D) has been shown to be effective in prolonging life span in experimental animals, although, there are some discrepancies in its effect on the life span the even within the same species (rats). The present study aims to clarify the reason for these discrepancies. Male F344/DuCrj rats began receiving subcutaneous (s.c.) injections of D at the age of 18 months. Doses used were 0.25, 0.50, and 1.0 mg/kg/injection (inj.), three times a week. Average life spans of animals were significantly longer in male rats given 0.25 and 0.5 mg/kg/inj.; however, rats given a 1.0 mg/kg dose began dying earlier than control rats, leading to an inverse U-shaped dose-efficacy relationship, a hormesis. Old (27-month-old) rats given different doses of D for 1 month showed a typical hormetic response for antioxidant enzyme activities, indicating a significant increase in superoxide dismutase (SOD) and catalase (CAT) activities in brain dopaminergic regions with four lower doses (0.25 to 2 mg/kg/inj., 3 times a week), but a significantly negative response with the highest dose (4 mg/kg/inj.). Our results clearly indicate that a proper dose of D within a certain dose range can significantly increase the life span of rats, but that a greater dose becomes less effective and may actually adversely affect the life span of rats. A similar hormetic response for its effect on antioxidant enzyme activities and the parallel between the two different effects of D suggest a possible causal relationship between these two effects of D. The presence of this effective dose range of D may explain previously reported discrepancies in the effect of D on the life span of animals.