Kim Zarse

Antioxidants prevent health-promoting effects of physical exercise in humans

Exercise promotes longevity and ameliorates type 2 diabetes mellitus and insulin resistance. However, exercise also increases mitochondrial formation of presumably harmful reactive oxygen species (ROS). Antioxidants are widely used as supplements but whether they affect the health-promoting effects of exercise is unknown. We evaluated the effects of a combination of vitamin C (1000 mg/day) and vitamin E (400 IU/day) on insulin sensitivity as measured by glucose infusion rates (GIR) during a hyperinsulinemic, euglycemic clamp in previously untrained (n = 19) and pretrained (n = 20) healthy young men. Before and after a 4 week intervention of physical exercise, GIR was determined, and muscle biopsies for gene expression analyses as well as plasma samples were obtained to compare changes over baseline and potential influences of vitamins on exercise effects. Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals. This was paralleled by increased expression of ROS-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, peroxisome-proliferator-activated receptor gamma (PPARγ), and PPARγ coactivators PGC1α and PGC1β only in the absence of antioxidants (P < 0.001 for all). Molecular mediators of endogenous ROS defense (superoxide dismutases 1 and 2; glutathione peroxidase) were also induced by exercise, and this effect too was blocked by antioxidant supplementation. Consistent with the concept of mitohormesis, exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.

How increased oxidative stress promotes longevity and metabolic health: The concept of mitochondrial hormesis (mitohormesis)

Recent evidence suggests that calorie restriction and specifically reduced glucose metabolism induces mitochondrial metabolism to extend life span in various model organisms, including Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans and possibly mice. In conflict with Harmans free radical theory of aging (FRTA), these effects may be due to increased formation of reactive oxygen species (ROS) within the mitochondria causing an adaptive response that culminates in subsequently increased stress resistance assumed to ultimately cause a long-term reduction of oxidative stress. This type of retrograde response has been named mitochondrial hormesis or mitohormesis, and may in addition be applicable to the health-promoting effects of physical exercise in humans and, hypothetically, impaired insulin/IGF-1-signaling in model organisms. Consistently, abrogation of this mitochondrial ROS signal by antioxidants impairs the lifespan-extending and health-promoting capabilities of glucose restriction and physical exercise, respectively. In summary, the findings discussed in this review indicate that ROS are essential signaling molecules which are required to promote health and longevity. Hence, the concept of mitohormesis provides a common mechanistic denominator for the physiological effects of physical exercise, reduced calorie uptake, glucose restriction, and possibly beyond.

Impaired Insulin-/IGF1-Signaling Extends Life Span by Promoting Mitochondrial L-Proline Catabolism to Induce a Transient ROS-Signal

Impaired insulin and IGF-1 signaling (iIIS) in C.xa0elegans daf-2 mutants extends life span more than 2-fold. Constitutively, iIIS increases mitochondrial activity and reduces reactive oxygen species (ROS) levels. By contrast, acute impairment of daf-2 in adult C.xa0elegans reduces glucose uptake and transiently increases ROS. Consistent with the concept ofxa0mitohormesis, this ROS signal causes an adaptive response by inducing ROS defense enzymes (SOD, catalase), culminating in ultimately reduced ROS levels despite increased mitochondrial activity. Inhibition of this ROS signal by antioxidants reduces iIIS-mediated longevity by up to 60%. Induction of the ROS signal requires AAK-2 (AMPK), while PMK-1 (p38) and SKN-1 (NRF-2) are needed for the retrograde response. IIIS upregulates mitochondrial L-proline catabolism, and impairment of the latter impairs the life span-extending capacity of iIIS while L-proline supplementation extends C.xa0elegans life span. Taken together, iIIS promotes L-proline metabolism to generate a ROS signal for the adaptive induction of endogenous stress defense to extend life span.

Role of Sirtuins in Lifespan Regulation is Linked to Methylation of Nicotinamide

Sirtuins, a family of histone deacetylases, have a fiercely debated role in regulating lifespan. In contrast with recent observations, here we find that overexpression of sir-2.1, the ortholog of mammalian SirT1, does extend Caenorhabditis elegans lifespan. Sirtuins mandatorily convert NAD(+) into nicotinamide (NAM). We here find that NAM and its metabolite, 1-methylnicotinamide (MNA), extend C. elegans lifespan, even in the absence of sir-2.1. We identify a previously unknown C. elegans nicotinamide-N-methyltransferase, encoded by a gene now named anmt-1, to generate MNA from NAM. Disruption and overexpression of anmt-1 have opposing effects on lifespan independent of sirtuins, with loss of anmt-1 fully inhibiting sir-2.1-mediated lifespan extension. MNA serves as a substrate for a newly identified aldehyde oxidase, GAD-3, to generate hydrogen peroxide, which acts as a mitohormetic reactive oxygen species signal to promote C. elegans longevity. Taken together, sirtuin-mediated lifespan extension depends on methylation of NAM, providing an unexpected mechanistic role for sirtuins beyond histone deacetylation.

Mitochondrial hormesis links low-dose arsenite exposure to lifespan extension.

Arsenite is one of the most toxic chemical substances known and is assumed to exert detrimental effects on viability even at lowest concentrations. By contrast and unlike higher concentrations, we here find that exposure to low‐dose arsenite promotes growth of cultured mammalian cells. In the nematode C. elegans, low‐dose arsenite promotes resistance against thermal and chemical stressors and extends lifespan of this metazoan, whereas higher concentrations reduce longevity. While arsenite causes a transient increase in reactive oxygen species (ROS) levels in C. elegans, co‐exposure to ROS scavengers prevents the lifespan‐extending capabilities of arsenite, indicating that transiently increased ROS levels act as transducers of arsenite effects on lifespan, a process known as mitohormesis. This requires two transcription factors, namely DAF‐16 and SKN‐1, which employ the metallothionein MTL‐2 as well as the mitochondrial transporter TIN‐9.1 to extend lifespan. Taken together, low‐dose arsenite extends lifespan, providing evidence for nonlinear dose‐response characteristics of toxin‐mediated stress resistance and longevity in a multicellular organism.

Cannabinoid type 1 receptor blockade induces transdifferentiation towards a brown fat phenotype in white adipocytes.

Aim: The endocannabinoid (EC) system is a major component in the control of energy homeostasis. It mediates a positive energy balance via central and peripheral pathways. Blockade of the cannabinoid type 1 receptor induces weight reduction and improves cardiovascular risk factors in overweight patients. Cannabinoid receptor type 1 (CB1R)‐deficient mice are resistant to diet‐induced obesity. The mechanisms responsible for these effects remain only partially elucidated. We hypothesized peripheral effects via direct modulation of adipocyte function to be an integral part of EC action on energy metabolism and insulin sensitivity.

D -Glucosamine supplementation extends life span of nematodes and of ageing mice

D-Glucosamine (GlcN) is a freely available and commonly used dietary supplement potentially promoting cartilage health in humans, which also acts as an inhibitor of glycolysis. Here we show that GlcN, independent of the hexosamine pathway, extends Caenorhabditis elegans life span by impairing glucose metabolism that activates AMP-activated protein kinase (AMPK/AAK-2) and increases mitochondrial biogenesis. Consistent with the concept of mitohormesis, GlcN promotes increased formation of mitochondrial reactive oxygen species (ROS) culminating in increased expression of the nematodal amino acid-transporter 1 (aat-1) gene. Ameliorating mitochondrial ROS formation or impairment of aat-1-expression abolishes GlcN-mediated life span extension in an NRF2/SKN-1-dependent fashion. Unlike other calorie restriction mimetics, such as 2-deoxyglucose, GlcN extends life span of ageing C57BL/6 mice, which show an induction of mitochondrial biogenesis, lowered blood glucose levels, enhanced expression of several murine amino-acid transporters, as well as increased amino-acid catabolism. Taken together, we provide evidence that GlcN extends life span in evolutionary distinct species by mimicking a low-carbohydrate diet.

Low-dose lithium uptake promotes longevity in humans and metazoans

PurposeLithium is a nutritionally essential trace element predominantly contained in vegetables, plant-derived foods, and drinking water. Environmental lithium exposure and concurrent nutritional intake vary considerably in different regions. We here have analyzed the possibility that low-dose lithium exposure may affect mortality in both metazoans and mammals.MethodsBased on a large Japanese observational cohort, we have used weighted regression analysis to identify putative effects of tap water-derived lithium uptake on overall mortality. Independently, we have exposed Caenorhabditis elegans, a small roundworm commonly used for anti-aging studies, to comparable concentrations of lithium, and have quantified mortality during this intervention.ResultsIn humans, we find here an inverse correlation between drinking water lithium concentrations and all-cause mortality in 18 neighboring Japanese municipalities with a total of 1,206,174 individuals (βxa0=xa0−0.661, pxa0=xa00.003). Consistently, we find that exposure to a comparably low concentration of lithium chloride extends life span of C. elegans (pxa0=xa00.047).ConclusionsTaken together, these findings indicate that long-term low-dose exposure to lithium may exert anti-aging capabilities and unambiguously decreases mortality in evolutionary distinct species.

Impaired respiration is positively correlated with decreased life span in Caenorhabditis elegans models of Friedreich Ataxia

Impaired expression of mitochondrial genes causes alterations in life span of the nematode Caenorhabditis elegans. Intriguingly, although some of these genes have been shown to extend life expectancy and reduce aging processes, others are known to shorten life span in the same model organism. Reduced expression of a mitochondrial protein called frataxin causes a neurodegenerative disorder named Friedreich Ataxia, which decreases life span in humans. Surprisingly, reduced expression of the C. elegans frataxin homologue frh‐1 has been associated with both increased as well as decreased life span by different laboratories. To further elucidate these conflicting findings, here we show that different RNA interference (RNAi) constructs directed against frh‐1 reduce C. el‐egans life span. Moreover, we show that frh‐1‐inhibiting RNAi impairs oxygen consumption and that respiratory rate is positively correlated with life span in this multi‐cellular eukaryote (r= 0.8566), suggesting that >73% of life span variance in C. elegans is explained by changes in respiratory rate. Taken together, impaired mitochon‐drial metabolism due to RNAi‐mediated inhibition of the frataxin homologue frh‐1 causes both impaired respiration as well as decreased life span in the multi‐cellular eukaryote C. elegans.—Zarse, K., Schulz, T. J., Birringer, M., Ristow, M. Impaired respiration is positively correlated with decreased life span in Caenorhabditis elegans models of Friedreich Ataxia. FASEB J. 21, 1271–1275 (2007)

Inhibition of Alanine Aminotransferase in Silico and in Vivo Promotes Mitochondrial Metabolism to Impair Malignant Growth

Cancer cells commonly exhibit increased nonoxidative d-glucose metabolism whereas induction of mitochondrial metabolism may impair malignant growth. We have first used an in silico method called elementary mode analysis to identify inhibition of ALAT (l-alanine aminotransferase) as a putative target to promote mitochondrial metabolism. We then experimentally show that two competitive inhibitors of ALAT, l-cycloserine and β-chloro-l-alanine, inhibit l-alanine production and impair d-glucose uptake of LLC1 Lewis lung carcinoma cells. The latter inhibition is linked to an initial energy deficit, as quantified by decreased ATP content, which is then followed by an activation of AMP-activated protein kinase and subsequently increased respiration rates and mitochondrial production of reactive oxygen species, culminating in ATP replenishment in ALAT-inhibited LLC1 cells. Moreover, we observe altered phosphorylation of p38 MAPK (mitogen-activated protein kinase 14), ERK (extracellular signal-regulated kinase 1/2), and Rb1 (retinoblastoma 1) proteins, as well as decreased expression of Cdc25a (cell decision cycle 25 homolog A) and Cdk4 (cyclin-dependent kinase 4). Importantly, these sequelae of ALAT inhibition culminate in similarly reduced anchorage-dependent and anchorage-independent growth rates of LLC1 cells, together suggesting that inhibition of ALAT efficiently impairs cancer growth by counteracting the Warburg effect due to compensatory activation of mitochondrial metabolism.