Health Effects of Long-Term Rapamycin Treatment: The Impact on Mouse Health of Enteric Rapamycin Treatment from Four Months of Age throughout Life

May Health Effects of Long-Term Rapamycin Treatment: The Impact on Mouse Health of Enteric Rapamycin Treatment from Four Months of Age throughout Life Kathleen E. Fischer 0 1 2 Jonathan A. L. Gelfond 0 1 2 Vanessa Y. Soto 0 1 2 Chul Han 0 1 2 Shinichi Someya 0 1 2 Arlan Richardson 0 1 2 Steven N. Austad 0 1 2 0 a Current address: Department of Biology, University of Alabama at Birmingham , Birmingham , Alabama, United States of America b Current address: University of Oklahoma Health Science Center & Oklahoma City Veteran Administration Medical Center , Oklahoma City, Oklahoma , United States of America 1 1 Barshop Institute for Longevity & Aging Studies, University of Texas Health Science Center San Antonio , San Antonio, Texas , United States of America, 2 Department of Physiology, University of Texas Health Science Center San Antonio , San Antonio, Texas , United States of America, 3 Department of Epidemiology & Biostatistics, University of Texas Health Science Center San Antonio , San Antonio, Texas , United States of America, 4 Departments of Aging and Geriatric Research, University of Florida, Gainesville, Florida, United States of America, 5 Department of Cellular & Structural Biology, University of Texas Health Science Center San Antonio , San Antonio, Texas , United States of America 2 Academic Editor: Christoph Englert, Leibniz Institute for Age Research - Fritz Lipmann Institute (FLI) , GERMANY Rapamycin, an mTOR inhibitor, has been shown to extend lifespan in a range of model organisms. It has been reported to extend lifespan in multiple strains of mice, administered chronically or acutely early or late in life. The ability of rapamycin to extend health (healthspan) as opposed to life is less well documented. To assess the effects chronic rapamycin treatment on healthspan, enteric rapamycin was given to male and female C57BL/6J mice starting at 4 months of age and continued throughout life. Repeated, longitudinal assessments of health in individual animals were made starting at 16 months of age (=12 months of treatment) until death. A number of health parameters were improved (female grip strength, female body mass and reduced sleep fragmentation in both sexes), others showed no significant difference, while at least one (male rotarod performance) was negatively affected. Rapamycin treatment affected many measures of health in a highly sex-specific manner. While sex-specific phenotypic effects of rapamycin treatment have been widely reported, in this study we document sex differences in the direction of phenotypic change. Rapamycin-fed males and females were both significantly different from controls; however the differences were in the opposite direction in measures of body mass, percent fat and resting metabolic rate, a pattern not previously reported. - RFA-OD-09-004.html), and NIH training grant (T32 AG 021890) to SNA (http://www.nia.nih.gov/research/ dea/institutional-training-grants). Competing Interests: The authors have declared that no competing interests exist. Rapamycin, a potent mTOR inhibitor, has been reported to extend lifespan in both vertebrate and invertebrate model organisms. In at least 7 previous studies mouse lifespan has been shown to be extended in both sexes, in heterogeneous and several inbred strains, with rapamycin administered in food (enteric rapamycin) or via injection, chronically or acutely, at a variety of ages [111]. However complete loss of mTOR signaling causes significant defects in growth and/or development in worms (C. elegans) and flies (D. melanogaster), and is embryonic lethal in mice [10]. The mTOR signaling network plays a pivotal role in promoting anabolic and inhibiting catabolic processes. mTOR activation stimulates ribosome biogenesis, protein synthesis and the import of nutrients into cells [12]; conversely, reduction or inhibition of mTOR activity decreases mRNA translation, increases autophagy, retards protein synthesis, slows cell growth and proliferation and enhances stress responsive transcription. Because rapamycin treatment increases longevity across phylogenetically distant groups and is already FDA-approved for use in humans, it may represent a viable intervention to extend human life as well. Its effects on health have been less well documented. Recent evidence suggests that rapamycin may improve resistance to multiple, age-associated degenerative processes in mice. This offers the tantalizing possibility that rapamycin could extend the length of healthy human life. In mouse models rapamycin has been shown to delay the onset of Alzheimers pathology [13, 14], reduce the incidence of some cancers [4, 1517], inhibit the development of atherosclerotic plaques [18], maintain cardiac function [1], enhance vaccine response in aged animals [5], delay age-related cognitive decline [1921], and maintain some aspects of activity, motor function and behavior [1, 4, 11, 15, 16, 2123]. On the other hand, rapamycin has been reported to have deleterious effects in mice, such as glucose intolerance and insulin resistance [24], testicular degeneration, increased cataract severity [15] and nephrotoxicity [21]. In some cases, results from different studies are inconsistent. For instance, some the beneficial effects on age-related changes found in one study (e.g. improved cardiac function with age [1] or increased insulin sensitivity [25]) have not been found in others (e.g. cardiac function [21], insulin sensitivity [24]). The potential use of rapamycin to address age-related diseases is promising, but the lack of consistent findings with respect to health in mice is reason for concern. There are additional reasons for caution in considering rapamycin as a potential aging intervention. The use of rapamycin as part of immunosuppressive therapy after organ transplantation may be a reason for concern given age-related decline in immune function [26, 27]; however, recent research suggests that, in mice and primates, enterically delivered rapamycin may enhance rather than suppress some aspects of immune response (e.g. [28, 29]). Secondly, because it inhibits protein synthesis, cellular processes requiring de novo protein synthesis such as growth, tissue repair and regeneration may be compromised by chronic rapamycin administration. For example, some rodent studies have observed that mTOR inhibition retards recovery from skeletal [30] or cardiac muscle injury [31]. Additionally, rapamycin has been reported to negatively affect neuronal long-term potentiation and memory consolidation [32, 33]. Both human and rodent studies have associated inhibition of mTOR with insulin resistance [34]; however recent studies have suggested that these effects are transitory and diminish as duration of chronic treatment increases [1, 22]. Extending lifespan without delaying or diminishing age-related morbidity is not a desirable goal and rapamycins effects on healthspan were anything but clear. We therefore initiated a longitudinal s (...truncated)