The mitochondrially targeted peptide elamipretide (SS-31) improves ADP sensitivity in aged mitochondria by increasing uptake through the adenine nucleotide translocator (ANT)

Aging muscle experiences functional decline in part mediated by impaired mitochondrial ADP sensitivity. Elamipretide (ELAM) rapidly improves physiological and mitochondrial function in aging and binds directly to the mitochondrial ADP transporter ANT. We hypothesized that ELAM improves ADP sensitivity in aging leading to rescued physiological function. We measured the response to ADP stimulation in young and old muscle mitochondria with ELAM treatment, in vivo heart and muscle function, and compared protein abundance, phosphorylation, and S-glutathionylation of ADP/ATP pathway proteins. ELAM treatment increased ADP sensitivity in old muscle mitochondria by increasing uptake of ADP through the ANT and rescued muscle force and heart systolic function. Protein abundance in the ADP/ATP transport and synthesis pathway was unchanged, but ELAM treatment decreased protein s-glutathionylation incuding of ANT. Mitochondrial ADP sensitivity is rapidly modifiable. This research supports the hypothesis that ELAM improves ANT function in aging and links mitochondrial ADP sensitivity to physiological function. ELAM binds directly to ANT and ATP synthase and ELAM treatment improves ADP sensitivity, increases ATP production, and improves physiological function in old muscles. ADP (adenosine diphosphate), ATP (adenosine triphosphate), VDAC (voltage-dependent anion channel), ANT (adenine nucleotide translocator), H+ (proton), ROS (reactive oxygen species), NADH (nicotinamide adenine dinucleotide), FADH2 (flavin adenine dinucleotide), O2 (oxygen), ELAM (elamipretide), -SH (free thiol), -SSG (glutathionylated protein).

Older-aged C57BL/6 mice fed a diet high in saturated fat and sucrose for ten months show decreased resilience to aging

The ability to respond to physical stress that disrupts normal physiological homeostasis at an older age embraces the concept of resilience to aging. A physical stressor could be used to induce physiological responses that are age-related, since resilience declines with increasing age. Increased fat and sugar intake is a nutritional stress with a high prevalence of obesity in older people. In order to determine the effect of this type of diet on resilience to aging, 18-month-old C57BL/6J male mice were fed a diet high in saturated fat (lard) and sucrose (HFS) for ten months. At the end of the 10-month study, mice fed the HFS diet showed increased cognitive impairment, decreased cardiac function, decreased strength and agility, and increased severity of renal pathology compared to mice fed a rodent chow diet low in saturated fat and sucrose (LFS). The degree of response aligned with decreased resilience to the long-term adverse effects of the diet with characteristics of accelerated aging. This observation suggests additional studies could be conducted to investigate the relationship between an accelerated decline in resilience to aging and enhanced resilience to aging under different dietary conditions.

Elamipretide Improves ADP Sensitivity in Aged Mitochondria by Increasing Uptake through the Adenine Nucleotide Translocator (ANT)

Aging muscle experiences functional decline in part mediated by impaired mitochondrial ADP sensitivity. Elamipretide (ELAM) rapidly improves physiological and mitochondrial function in aging and binds directly to the mitochondrial ADP transporter ANT. We hypothesized that ELAM improves ADP sensitivity in aging leading to rescued physiological function. We measured the response to ADP stimulation in young and old muscle mitochondria with ELAM treatment, in vivo heart and muscle function, and compared protein abundance, phosphorylation, and S-glutathionylation of ADP/ATP pathway proteins. ELAM treatment increased ADP sensitivity in old muscle mitochondria by increasing uptake of ADP through the ANT and rescued muscle force and heart systolic function. Protein abundance in the ADP/ATP transport and synthesis pathway was unchanged, but ELAM treatment decreased protein s-glutathionylation incuding of ANT. Mitochondrial ADP sensitivity is rapidly modifiable. This research supports the hypothesis that ELAM improves ANT function in aging and links mitochondrial ADP sensitivity to physiological function.

Abstract Figure

Lifespan benefits for the combination of rapamycin plus acarbose and for captopril in genetically heterogeneous mice

Mice bred in 2017 and entered into the C2017 cohort were tested for possible lifespan benefits of (R/S)-1,3-butanediol (BD), captopril (Capt), leucine (Leu), the Nrf2-activating botanical mixture PB125, sulindac, syringaresinol, or the combination of rapamycin and acarbose started at 9 or 16 months of age (RaAc9, RaAc16). In male mice, the combination of Rapa and Aca started at 9 months and led to a longer lifespan than in either of the two prior cohorts of mice treated with Rapa only, suggesting that this drug combination was more potent than either of its components used alone. In females, lifespan in mice receiving both drugs was neither higher nor lower than that seen previously in Rapa only, perhaps reflecting the limited survival benefits seen in prior cohorts of females receiving Aca alone. Capt led to a significant, though small (4% or 5%), increase in female lifespan. Capt also showed some possible benefits in male mice, but the interpretation was complicated by the unusually low survival of controls at one of the three test sites. BD seemed to produce a small (2%) increase in females, but only if the analysis included data from the site with unusually short-lived controls. None of the other 4 tested agents led to any lifespan benefit. The C2017 ITP dataset shows that combinations of anti-aging drugs may have effects that surpass the benefits produced by either drug used alone, and that additional studies of captopril, over a wider range of doses, are likely to be rewarding.

Long-term treatment with Elamipretide enhances healthy aging phenotypes in mice

Background

Disruption of metabolic and bioenergetic homeostasis related to mitochondrial dysfunction is a key driver of aging biology. Therefore, targeting mitochondrial function would be a rational approach to slowing aging. Elamipretide (Elam, a.k.a. SS-31) is a peptide known to target mitochondria and suppress mammalian signs of aging. The present study was designed to examine the phenotypic effects of long-term Elam treatment on aging in C57BL/6 mice starting at 18 months of age.

Methods

Mice were fed regular chow (RC diet) or a diet high in fat and sugar (HF diet) and treated with 3 mg/kg of Elam or saline subcutaneously 5 days per week for 10 months. Physiological performance assessments were conducted at 28 months of age.

Results

Elam improved the physical performance of males but not females, while in females Elam improved cognitive performance and enhanced the maintenance of body weight and fat mass. It also improved diastolic function in both males and females, but to a greater extent in males. The HF diet over 10 months had a negative effect on health span, as it increased body fat and decreased muscle strength and heart function, especially in females.

Conclusions

Elam enhanced healthy aging and cardiac function in both male and female mice, although the specific effects on function differed between sexes. In females, the treatment led to better cognitive performance and maintenance of body composition, while in males, performance on a rotating rod was preserved. These overall observations have translational implications for considering additional studies using Elam in therapeutic or preventive approaches for aging and age-related diseases.

Reduction of Elevated Proton Leak Rejuvenates Mitochondria in the Aged Cardiomyocyte

Rational: Aging-associated diseases, including cardiac dysfunction, are increasingly common in the population. However, the mechanisms of physiologic aging in general, and cardiac aging in particular, remain poorly understood. While effective medical interventions are available for some kinds of heart failure, one age-related impairment, diastolic dysfunction in Heart Failure with Preserved Ejection Fraction (HFpEF) is lacking a clinically effective treatment. Methods and Results: Using the pH indicator cpYFP in the model of naturally aging mice and rats, we show direct evidence of increased mitochondrial proton leak in aged heart mitochondria following a pH gradient stress. Furthermore, we identified Adenine Nucleotide Translocator 1 (ANT1) as mediating the increased proton permeability of old cardiomyocytes. Most importantly, acute (2 hours) in vitro treatment with the tetra-peptide drug SS-31 (elamipretide) reverses age-related excess proton entry, decreases the mitochondrial flash activity and mitochondrial permeability transition pore (mPTP) opening and rejuvenates mitochondrial function. Moreover, we show that SS-31 benefits the old mitochondria by direct association with ANT1 and stabilization of the mitochondrial ATP synthasome, leading to substantial reversal of diastolic dysfunction. Conclusion: Our results uncover excessive mitochondrial proton leak as a novel mechanism of age-related cardiac dysfunction and elucidate how SS-31 is able to reverse this clinically important complication of cardiac aging.

Targeting cPLA2 derived lipid hydroperoxides as a potential intervention for sarcopenia

Defects in neuromuscular innervation contribute significantly to the age-related decline in muscle mass and function (sarcopenia). Our previous studies demonstrated that denervation induces muscle mitochondrial hydroperoxide production (H2O2 and lipid hydroperoxides (LOOHs)). Here we define the relative contribution of mitochondrial electron transport chain (ETC) derived H2O2 versus cytosolic phospholipase A2 (cPLA2) derived LOOHs in neurogenic muscle atrophy. We show that denervation increases muscle cPLA2 protein content, activity, and metabolites downstream of cPLA2 including LOOHs. Increased scavenging of mitochondrial H2O2 does not protect against denervation atrophy, suggesting ETC generated H2O2 is not a critical player. In contrast, inhibition of cPLA2 in vivo mitigates LOOH production and muscle atrophy and maintains individual muscle fiber size while decreasing oxidative damage. Overall, we show that loss of innervation in several muscle atrophy models including aging induces generation of LOOHs produced by arachidonic acid metabolism in the cPLA2 pathway contributing to loss of muscle mass.

Late-life restoration of mitochondrial function reverses cardiac dysfunction in old mice

Diastolic dysfunction is a prominent feature of cardiac aging in both mice and humans. We show here that 8-week treatment of old mice with the mitochondrial targeted peptide SS-31 (elamipretide) can substantially reverse this deficit. SS-31 normalized the increase in proton leak and reduced mitochondrial ROS in cardiomyocytes from old mice, accompanied by reduced protein oxidation and a shift towards a more reduced protein thiol redox state in old hearts. Improved diastolic function was concordant with increased phosphorylation of cMyBP-C Ser282 but was independent of titin isoform shift. Late-life viral expression of mitochondrial-targeted catalase (mCAT) produced similar functional benefits in old mice and SS-31 did not improve cardiac function of old mCAT mice, implicating normalizing mitochondrial oxidative stress as an overlapping mechanism. These results demonstrate that pre-existing cardiac aging phenotypes can be reversed by targeting mitochondrial dysfunction and implicate mitochondrial energetics and redox signaling as therapeutic targets for cardiac aging.

AGED MICE ARE SUSCEPTIBLE TO CARDIAC HYPERTROPHY AFTER 1 WEEK OF CONSUMING A HIGH SUGAR DIET

Over 80% of American adults exceed their daily recommended intake of sugar (<10% kcal). While habitual sugar consumption is associated with an increased risk for diabetes and cardiovascular disease, less is known about the effects of short-term sugar consumption on metabolic health, particularly in the elderly. The purpose of this study was to test whether aged hearts are more susceptible to pathology following a short-term high sucrose (HS) diet. Specific goals were to: A) determine the effects of a 1-week HS diet exposure on the hearts of 5 month-old and 24 month-old mice; and B) test if the mitochondrial targeted peptide SS-31 can protect against HS-diet induced effects. Male CB6F1 mice were placed either on standard chow or HS diet after 1 week of receiving saline (control) or SS-31 through osmotic pumps. Heart function was assessed in vivo through echocardiography before and after treatments. One week of HS induced significant cardiac hypertrophy in the old mice compared to age-matched chow controls. Treatment with SS-31 prevented this HS induced hypertrophy. Young hearts were smaller than in the old, but size was unaffected by diet or SS-31. We observed no effect of HS (with or without SS-31) on respiration or H2O2 production in isolated mitochondria from hearts using high-resolution respirometry. These data indicate that only 1-week exposure to HS diet is enough to exacerbate cardiac hypertrophy in aging mice, but factors other than heart mitochondrial ROS may mediate this effect.

Abstract 903: Rapamycin Treatment Reduces Myocardial Stiffness and Promotes Cardiomyocyte Relaxation to Restore Diastolic Function in Old Murine Hearts

Aging is associated with a decline in diastolic function and is a strong risk factor for heart failure with preserved ejection fraction (HFpEF), which has no effective treatment. We previously showed that late-life rapamycin treatment can reverse age-related cardiac dysfunction in mice. However, the mechanisms of the reversal of diastolic dysfunction have not been established. The objective of this study is to determine the mechanisms by which rapamycin reverses age-related diastolic dysfunction.

To study the effects of rapamycin on myocardial stiffness, we assessed the passive length-tension relationship of demembranated trabecular muscle from young, old control and old rapamycin-treated mice. We observed a substantial increase in the slope of the length-tension curve with aging, indicating an age-related increase in myocardial stiffness. The age-related increase in myocardial stiffness was significantly reduced by rapamycin treatment, by a mechanism independent of titin isoform shift. We measured the force-calcium relationship of the demembranated trabeculae and revealed an age-related increase in Ca 2+ sensitivity, as indicated by a left-shift of the force-pCa curve, which was partially restored after rapamycin treatment (pCa50: 5.59±0.04 for young controls; 5.76±0.04 for old controls; and 5.65±0.04 for old rapamycin-treated group). To investigate the changes at myofibril level, we assessed kinetic properties of control and rapamycin-treated myofibrils following maximal (pCa 4.0) and submaximal (pCa 5.6) Ca 2+ activation. Myofibrils from rapamycin-treated mice displayed increased rate of the fast phase of relaxation (kREL, fast) compared to old control at both maximal and submaximal Ca 2+ levels, potentially due to reduced myofibril Ca 2+ sensitivity. Studies have detected age-related reductions in expression and activity of SERCA2, which is responsible for SR calcium reuptake during diastole. In this study, we showed that rapamycin increased SERCA2 expression, which may improve cardiomyocyte relaxation.

In summary, our results suggest that rapamycin normalizes age-related increases in myocardial stiffness and Ca 2+ sensitivity and improves myofibril relaxation kinetics, therefore, improving diastolic function.

A New Preclinical Paradigm for Testing Anti-Aging Therapeutics

Testing drugs for anti-aging effects has historically been conducted in mouse life-span studies, but are costly and time consuming, and more importantly, difficult to recapitulate in humans. In addition, life-span studies in mice are not well suited to testing drug combinations that target multiple factors involved in aging. Additional paradigms for testing therapeutics aimed at slowing aging are needed. A new paradigm, designated as the Geropathology Grading Platform (GGP), is based on a standardized set of guidelines developed to detect the presence or absence of low-impact histopathological lesions and to determine the level of severity of high-impact lesions in organs from aged mice. The GGP generates a numerical score for each age-related lesion in an organ, summed for total lesions, and averaged over multiple mice to obtain a composite lesion score (CLS). Preliminary studies show that the platform generates CLSs that increase with the age of mice in an organ-dependent manner. The CLSs are sensitive enough to detect changes elicited by interventions that extend mouse life span, and thus help validate the GGP as a novel tool to measure biological aging. While currently optimized for mice, the GGP could be adapted to any preclinical animal model.

Grip strength is potentially an early indicator of age-related decline in mice

The hand grip test has been correlated with mobility and physical performance in older people and has been shown to be a long-term predictor of mortality. Implementation of new strategies for enhancing healthy aging and maintaining independent living are dependent on predictable preclinical studies. The mouse is used extensively as a model in these types of studies, and the paw grip strength test is similar to the hand grip test for people in that it assesses the ability to grip a device with the paw, is non-invasive and easy to perform, and provides reproducible information. However, little has been reported on how grip strength declines with increasing age in mice. This report shows that grip strength was decreased in C57BL/6 (B6) NIA and C57BL/6×BALB/c F1 (CB6F1) NIA male mice at 12 months of age compared to 8-month-old mice, and continued a robust decline to 20 months and then 28 months of age, when the study was terminated. The decline was not related to lean muscle mass, but extensive age-related carpal and digital exostosis could help explain the decreased grip strength times with increasing age. In conclusion, the grip strength test could be useful in mouse preclinical studies to help make translational predictions on treatment strategies to enhance healthy aging.

Measures of Healthspan as Indices of Aging in Mice-A Recommendation

Over the past decade, a large number of discoveries have shown that interventions (genetic, pharmacological, and nutritional) increase the lifespan of invertebrates and laboratory rodents. Therefore, the possibility of developing antiaging interventions for humans has gone from a dream to a reality. However, it has also become apparent that we need more information than just lifespan to evaluate the translational potential of any proposed antiaging intervention to humans. Information is needed on how an intervention alters the "healthspan" of an animal, that is, how the physiological functions that change with age are altered. In this report, we describe the utility and the limitations of assays in mice currently available for measuring a wide range of physiological functions that potentially impact quality of life. We encourage investigators and reviewers alike to expect at minimum an overall assessment of health in several domains across several ages before an intervention is labeled as "increasing healthspan." In addition, it is important that investigators indicate any tests in which the treated group did worse or did not differ statistically from controls because overall health is a complex phenotype, and no intervention discovered to date improves every aspect of health. Finally, we strongly recommend that functional measurements be performed in both males and females so that sex differences in the rate of functional decline in different domains are taken into consideration.

Harnessing the Power of Integrated Mitochondrial Biology and Physiology: A Special Report on the NHLBI Mitochondria in Heart Diseases Initiative

Mitochondrial biology is the sum of diverse phenomena from molecular profiles to physiological functions. A mechanistic understanding of mitochondria in disease development, and hence the future prospect of clinical translations, relies on a systems-level integration of expertise from multiple fields of investigation. Upon the successful conclusion of a recent National Institutes of Health, National Heart, Lung, and Blood Institute initiative on integrative mitochondrial biology in cardiovascular diseases, we reflect on the accomplishments made possible by this unique interdisciplinary collaboration effort and exciting new fronts on the study of these remarkable organelles.

Mitochondrial catalase suppresses naturally occurring lung cancer in old mice

Lung cancer is generally difficult to detect until the late stages of disease, when it is much more difficult to treat because of the more aggressive and invasive behavior. Advanced lung cancer is much more common in older adults making it even more challenging to treat. Adenocarcinoma belongs to a category of non-small cell lung cancers, which comprise up to 40% of all lung cancers, and about half of these have an activating K-ras mutation. Because treatment relapses are common, more effective unconventional treatment and prevention methods are needed. In this regard, the antioxidant enzyme catalase targeted to mitochondria (mCAT) has been shown to delay aging and cancer in mice, and the progression of transgenic oncogene and syngeneic tumors was suppressed, helping support the notion that attenuation of mitochondria-generated hydrogen peroxide signaling is associated with an antitumor effect. In order to determine if mCAT has any effect on naturally occurring lung cancer of the adenocarcinoma type in old mice, the tumor incidence and progression were examined in the lungs of old mCAT transgenic and wild-type (WT) mice with a CB6F1 (Balb/c X C57BL/6) background. CB6F1 mice with a WT genotype were found to have a high incidence of adenomas at 24 months of age, which progressed to adenocarcinomas at 32 months of age. CB6F1 mice with the mCAT genotype had significantly reduced incidence and severity of lung tumors at both ages. Fibroblasts isolated from the lungs of old mCAT mice, but not WT mice, were shown to secrete soluble factors that inhibited lung tumor cell growth suggesting that stromal fibroblasts play a role in mediating the antitumor effects of mCAT. The aged CB6F1 mouse, with its high incidence of K-ras mutant lung cancer, is an excellent model to further study the anticancer potential of mitochondria-targeted therapy.

Interstitial pericytes decrease in aged mouse kidneys

With increasing age, the kidney undergoes characteristic changes in the glomerular and tubulo-interstitial compartments, which are ultimately accompanied by reduced kidney function. Studies have shown age-related loss of peritubular vessels. Normal peritubular vessel tone, function and survival depend on neighboring pericytes. Pericyte detachment leads to vascular damage, which can be accompanied by their differentiation to fibroblasts and myofibroblasts, a state that favors matrix production. To better understand the fate of pericytes in the aged kidney, 27 month-old mice were studied. Compared to 3 month-old young adult mice, aged kidneys showed a substantial decrease in capillaries, identified by CD31 staining, in both cortex and medulla. This was accompanied by a marked decrease in surrounding NG2+ / PDGFRβ+ pericytes. This decrease was more pronounced in the medulla. Capillaries devoid of pericytes were typically dilated in aged mice. Aged kidneys were also characterized by interstitial fibrosis due to increased collagen-I and -III staining. This was accompanied by an increase in the number of pericytes that acquired a pro-fibrotic phenotype, identified by increased PDGFRβ+ / αSMA+ staining. These findings are consistent with the decline in kidney interstitial pericytes as a critical step in the development of changes to the peritubular vasculature with aging, and accompanying fibrosis.

Changes in glomerular parietal epithelial cells in mouse kidneys with advanced age

Kidney aging is accompanied by characteristic changes in the glomerulus, but little is known about the effect of aging on glomerular parietal epithelial cells (PECs), nor if the characteristic glomerular changes in humans and rats also occur in very old mice. Accordingly, a descriptive analysis was undertaken in 27-mo-old C57B6 mice, considered advanced age. PEC density was significantly lower in older mice compared with young mice (aged 3 mo), and the decrease was more pronounced in juxtamedullary glomeruli compared with outer cortical glomeruli. In addition to segmental and global glomerulosclerosis in older mice, staining for matrix proteins collagen type IV and heparan sulfate proteoglycan were markedly increased in Bowman's capsules of older mouse glomeruli, consistent with increased extracellular matrix production by PECs. De novo staining for CD44, a marker of activated and profibrotic PECs, was significantly increased in aged glomeruli. CD44 staining was more pronounced in the juxtamedullary region and colocalized with phosphorylated ERK. Additionally, a subset of aged PECs de novo expressed the epithelial-to-mesenchymal transition markers α-smooth muscle and vimentin, with no changes in epithelial-to-mesenchymal transition markers E-cadherin and β-catenin. The mural cell markers neural/glial antigen 2, PDGF receptor-β, and CD146 as well as Notch 3 were also substantially increased in aged PECs. These data show that mice can be used to better understand the aging kidney and that PECs undergo substantial changes, especially in juxtamedullary glomeruli, that may participate in the overall decline in glomerular structure and function with advancing age.

Metabolic damage and premature thymus aging caused by stromal catalase deficiency (LYM2P.722)

T lymphocytes are essential mediators of immunity produced by the thymus in proportion to mass. The thymus atrophies rapidly with age, resulting in diminished new T cell production. Decreased thymic output is compensated by duplication of existing cells, but results in progressive dominance by memory T cells, and decreased ability to respond to new pathogens or vaccines. We find that accelerated thymic atrophy results from stromal deficiency in the reducing enzyme catalase, leading to increased damage by reactive oxygen species (ROS) generated during aerobic metabolism. Genetic complementation of catalase diminished atrophy, as did chemical antioxidants, providing a mechanistic link between antioxidants, metabolism, and normal immune function. Progenitor lymphoblasts represent the primary source of thymic ROS, likely acting on stromal cells in trans. We propose that thymic atrophy represents a conventional aging process that is accelerated by stromal catalase deficiency in the context of an intensely metabolic lymphoid environment.

Change in peripheral blood leukocyte telomere length and mortality in breast cancer survivors

BACKGROUND

Progressive telomere shortening with cell division is a hallmark of aging. Short telomeres are associated with increased cancer risk, but there are conflicting reports about telomere length and mortality in breast cancer survivors.

METHODS

We measured peripheral blood leukocyte telomere length at two time points in women enrolled in a multiethnic, prospective cohort of stage I to stage IIIA breast cancer survivors diagnosed between 1995 and 1999 with a median follow-up of 11.2 years. We evaluated associations between telomere length measured at mean 6 (baseline; LTL0; n = 611) and 30 months (LTL30; n = 478) after diagnosis and the change between those time points (n = 478), with breast cancer-specific and all-cause mortality using Cox proportional hazards models adjusted for possible confounders. Statistical tests were two-sided.

RESULTS

There were 135 deaths, of which 74 were due to breast cancer. Neither baseline nor 30-month telomere length was associated with either all-cause or breast cancer-specific mortality (LTL0: hazard ratio [HR] = 0.83, 95% confidence interval [CI] = 0.67 to 1.02; HR = 0.88; 95% CI = 0.67 to 1.15; LTL30: HR = 0.78, 95% CI = 0.59 to 1.05; HR = 0.86; 95% = CI = 0.58 to 1.26, respectively). However, participants whose telomeres shortened between baseline and 30 months were at a statistically significantly increased risk of breast cancer-specific (HR = 3.03; 95% CI = 1.11 to 8.18) and all-cause mortality (HR = 2.38; 95% CI = 1.28 to 4.39) compared with participants whose telomeres lengthened. When follow-up was censored at 5-years after diagnosis, LTL0 (HR = 0.66; 95% CI = 0.45 to 0.96), LTL30 (HR = 0.51; 95% CI = 0.29 to 0.92), and change in telomere length (HR = 3.45; 95% CI = 1.11 to 10.75) were statistically significantly associated with all-cause mortality.

CONCLUSIONS

Telomere shortening was associated with increased risk of breast cancer-specific and all-cause mortality, suggesting that change in blood telomere length over time could be a biomarker of prognosis. Research on determinants of telomere length and change is needed.

Measuring telomere length for the early detection of precursor lesions of esophageal squamous cell carcinoma

Background

Esophageal cancer is the sixth leading cause of cancer death worldwide; current early detection screening tests are inadequate. Esophageal balloon cytology successfully retrieves exfoliated and scraped superficial esophageal epithelial cells, but cytologic reading of these cells has poor sensitivity and specificity for detecting esophageal squamous dysplasia (ESD), the precursor lesion of esophageal squamous cell carcinoma (ESCC). Measuring telomere length, a marker for chromosomal instability, may improve the utility of balloon cytology for detecting ESD and early ESCC.

Methods

We examined balloon cytology specimens from 89 asymptomatic cases of ESD (37 low-grade and 52 high-grade) and 92 age- and sex-matched normal controls from an esophageal cancer early detection screening study. All subjects also underwent endoscopy and biopsy, and ESD was diagnosed histopathologically. DNA was extracted from the balloon cytology cells, and telomere length was measured by quantitative PCR. A receiver operating characteristic (ROC) curve was plotted for telomere length as a diagnostic marker for high-grade dysplasia.

Results

Telomere lengths were comparable among the low- and high-grade dysplasia cases and controls, with means of 0.96, 0.96, and 0.92, respectively. The area under the ROC curve was 0.55 for telomere length as a diagnostic marker for high-grade dysplasia. Further adjustment for subject characteristics, including sex, age, smoking, drinking, hypertension, and body mass index did not improve the use of telomere length as a marker for ESD.

Conclusions

Telomere length of esophageal balloon cytology cells was not associated with ESCC precursor lesions. Therefore, telomere length shows little promise as an early detection marker for ESCC in esophageal balloon samples.

Abstract 1165: Measuring telomere length for the early detection of precursor lesions of esophageal squamous cell carcinoma

Objectives: Esophageal cancer is the fifth leading cause of cancer death worldwide. The five-year survival is approximately 16%. Patients can be successfully treated if diagnosed early, but current early detection screening tests are inadequate. Balloon cytology is a simple and inexpensive method of retrieving esophageal cells, but traditional cytologic examination of these cells has poor sensitivity and specificity. We examined whether telomere length, a marker for chromosomal instability, in DNA extracted from balloon cytology-collected esophageal cells is associated with precursor lesions of esophageal squamous cell carcinoma.

Methods: The Cytology Sampling Study 2, a population-based esophageal cancer early detection screening study, recruited over 700 healthy subjects from a high-risk population in Linxian, China. The screening study used a mesh-covered balloon to collect esophageal cells. All subjects underwent endoscopy, and precursor lesions were diagnosed by biopsy. Using a nested case-control study design, we examined the association between telomere length and dysplasia in 37 low-grade dysplasia cases, 52 high-grade dysplasia cases, and 92 matched controls. DNA was extracted from cells collected by balloon cytology, and telomere length was measured in triplicate by a quantitative PCR assay. Logistic regression models adjusted for age, sex, smoking tobacco, alcohol intake, and hypertension were used to examine the association between telomere length and risk of low-grade dysplasia and high-grade dysplasia, compared with normal controls.

Results: Telomere lengths were comparable among the low-grade dysplasia cases, high-grade dysplasia cases, and controls, with a median of 0.93 [interquartile range (IQR), 0.84-1.06], 0.94 (IQR, 0.82-1.09), and 0.93 (IQR, 0.78-1.05), respectively. Overall, telomere length was not associated with risk of low-grade dysplasia or high-grade dysplasia, with an odds ratio [OR, 95% confidence interval (CI)] of 1.16 (0.87-1.54) and 1.20 (0.92-1.56), respectively.

Conclusions: Given that esophageal cancers have very poor prognoses, it is of utmost importance to improve early detection. In this study, esophageal cell telomere length was not associated with esophageal precursor lesions and cannot serve as an early detection marker.

Citation Format: Shih-Wen Lin, Christian C. Abnet, Neal D. Freedman, Rosana Risques, Donna Prunkard, Peter Rabinovitch, Ning Lu, You-Lin Qiao, Sanford M. Dawsey. Measuring telomere length for the early detection of precursor lesions of esophageal squamous cell carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1165. doi:10.1158/1538-7445.AM2013-1165

Abstract 3133: Identification and functional validation of novel genetically-linked breast cancer targets through pooled gain-of-function screening

Breast cancer is one of the most common cancer types, with greater than 450,000 deaths reported per year worldwide. Through genome wide sequencing efforts, multiple genetic alterations have been identified, including mutations and amplifications in genes such as v-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (ERBB2), GATA binding protein 3 (GATA3), phosphatidylinositol 3-kinase alpha catalytic subunit (PIK3CA) as well as novel genomic rearrangements such as the recently identified MAGI3-AKT3 fusion. Now that breast cancer can be characterized to an unprecedented level, one of the key challenges remaining is to identify and distinguish critical ‘driver’ events responsible for tumor progression, from neutral ‘passenger’ lesions. In order to achieve this, we utilized high resolution aCGH analysis of 50 purified breast cancer samples (made up of Her2+, estrogen receptor positive (ER+) and triple negative tumors with variable responses to SOC regimens), in combination with a Gain-of-Function transformation screen to identify and validate novel breast targets. 158 genomic regions were found to be recurrently amplified, consisting of 759 genes in total. The top 32 focally amplified genes, along with 12 cancer-relevant mutant alleles were prioritized and a library generated utilizing the pTRIPZ-tetracycline regulated inducible lentiviral vector system. These 44 genes were subsequently combined into 16 different target pools (5-13 targets per pool, co-expressing genes that were co-amplified in the same clinical specimen) and evaluated for their ability to transform immortalized breast epithelial MCF10A cells (both wild-type and p53 -/- cells). Through this screening approach, p21-activated kinase 1 (PAK1) was identified, whose kinase activity was required to robustly transform MCF10A cells through regulating multiple signalling pathways including MAPK. Several other putative oncogenes were also identified and will be presented here, including the glycosyltransferse asparagine-linked glycosylation 8 (ALG8). Interestingly, PAK1 and ALG8 are co-amplified in both breast (8%) and ovarian cancers (11%). Our target validation studies have suggested that ALG8 can support PAK1-induced transformation, as dramatic suppression of soft-agar colony growth was seen in co-amplified breast cancer cell lines upon combined siRNA treatment to both targets. Thus, this combined high resolution aCGH profiling and functional screening approach has enabled the successful identification of novel oncogenic targets in breast cancer.

Citation Format: Krishna Vasudevan, Axel Hernandez, Zhongwu Lai, Yonghong Xiao, Nin Guan, Carolyn Hardy, Robert Godin, Christopher Denz, Minwei Ye, Elizabeth Lenkiewicz, Stephanie Savage, Michael T. Barrett, Donna Prunkard, Peter Rabinovitch, Mark Basik, Ewa Przybytkowski, Kevin Webster, Michael Zinda, Emma-Louise Jenkins. Identification and functional validation of novel genetically-linked breast cancer targets through pooled gain-of-function screening. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3133. doi:10.1158/1538-7445.AM2013-3133

Ex vivo imaging of excised tissue using vital dyes and confocal microscopy

Vital dyes routinely used for staining cultured cells can also be used to stain and image live tissue slices ex vivo. Staining tissue with vital dyes allows researchers to collect structural and functional data simultaneously and can be used for qualitative or quantitative fluorescent image collection. The protocols presented here are useful for structural and functional analysis of viable properties of cells in intact tissue slices, allowing for the collection of data in a structurally relevant environment. With these protocols, vital dyes can be applied as a research tool to disease processes and properties of tissue not amenable to cell culture-based studies.

Abstract 1129: Mitochondrial dysfunction precedes tumor progression in ulcerative colitis, but it is restored in advanced dysplasia and cancer

Ulcerative colitis (UC) is an inflammatory disease of the colon that predisposes to colorectal cancer. Dysplasia and cancer arise in pre-cancerous fields of inflammed epithelium, which harbor molecular alterations in spite of histologically normal appearance. We previously demonstrated that these molecular alterations include telomere shortening and the loss of cytochrome C oxidase (COX, Complex IV, subunit I), which is a marker of mitochondrial dysfunction. COX loss was more frequent in UC progressors (patients with dysplasia or cancer) than in UC non progressors (patients without dysplasia). Interestingly, COX expression reappeared in dysplasia and cancer, suggesting that the recovery of mitochondrial function is essential for further tumor progression. We are confirming and extending these preliminary results by: (1) analyzing the expression of additional electron transport chain proteins (complexes II, III, IV subunit II, and IV subunit Va), mitochondrial fusion proteins (Opa1 and Mfn1), and PGC1α, the master regulator of mitochondrial biogenesis; (2) investigating the potential association between mitochondrial abnormalities and telomere shortening; (3) quantifying mitochondrial copy number in areas of COX loss; and (4) validating the original COX results in a second, larger set of UC patients. The expression of mitochondrial proteins was analyzed by immunohistochemistry from serial sections of UC colon. Lightly-fixed paraffin-embedded colon biopsies were used for telomere FISH and laser capture microdissection with subsequent mitochondrial copy number quantification by Q-PCR. A tissue microarray including all grade biopsies from 38 UC non progressors and 37 UC progressors was immunostained with COX to validate the original COX results. The serial staining of the four mitochondrial respiratory proteins showed a striking correlation amongst them and with the original COX pattern: loss early in progression and focal gain in later dysplasia. Interestingly, Opa1, Mfn1, and PGC1α also showed very similar expression patterns. Telomere shortening, however, was not associated with COX loss. Preliminary quantification of mitochondrial copy number indicated that the areas with COX loss had normal amounts of mitochondrial DNA. The analysis of a larger number of biopsies in tissue microarrays confirmed previous findings. In conclusion, our results indicate that a severe loss of mitochondrial components, including all complexes of the respiratory transport chain, occur early in UC progression. That loss is likely to be of epigenetic origin, as it is reversible in later progression. Downregulation of mitochondria biogenesis by PGC1α might be the underlying mechanism, but it is not secondary to telomere shortening and it does not appear to be accompanied by mitochondrial DNA loss. Further experiments are warranted to unveil these intriguing results.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1129. doi:1538-7445.AM2012-1129

Mitochondrial oxidative stress mediates induction of autophagy and hypertrophy in angiotensin-II treated mouse hearts

Autophagy is characterized by recycling of cellular organelles and can be induced by several stimuli, including nutrient deprivation and oxidative stress. As a major site of free radical production during oxidative phosphorylation, mitochondria are believed to be primary targets of oxidative damage during stress. Our recent study demonstrated that angiotensin II increases cardiac mitochondrial reactive oxygen species (ROS) production, causes a decline of mitochondrial membrane potential in cardiomyocytes and increases cardiac mitochondrial protein oxidative damage and mitochondrial DNA deletions. The deleterious effects of angiotensin II on mitochondria are associated with an increase in autophagosomes and increased signaling of mitochondrial biogenesis, interpreted as an attempt to replenish the damaged mitochondria and restore energy production. Direct evidence for the central role of mitochondrial ROS was investigated by comparing the effect on mice overexpressing catalase targeted to mitochondria (mCAT) and mice overexpressing peroxisomal targeted catalase (pCAT, the natural site of catalase) challenged by angiotensin II or Gαq overexpression. The mCAT, but not pCAT, mice are resistant to cardiac hypertrophy, fibrosis and mitochondrial damage, biogenesis and autophagy induced by angiotensin II, as well as heart failure induced by overexpression of Gαq.

A mitochondrial view of aging, reactive oxygen species and metastatic cancer

This perspective article highlights the growing evidence placing mitochondria and mitochondrial function at the center of cancer as an age-related disease. The discussion starts from the mitochondrial free radical hypothesis that predicts the involvement of endogenous mitochondrial reactive oxygen species (ROS) in cancer development and summarizes studies demonstrating the impact of the modulation of ROS levels on cancer development and metastasis. Cancer is fundamentally a complex interplay of cell growth, division, metastasis and death- processes connected to mitochondria through energy metabolism. Based on this evidence, therapeutics focused on mitochondrial function and mitochondrial ROS production are an attractive approach to modulating the progression of metastatic cancer and the general improvement of human health span.

Mitochondrial oxidative stress and mammalian healthspan

Aging of the American society is leading to a growing need for disease-modifying interventions to treat age-related diseases and enhance healthspan. Mitochondria and mitochondrially generated reactive oxygen species appear to play a central role in these processes and are a likely target for interventions. Conventional, untargeted antioxidants have not demonstrated a clear benefit in human studies. As a result, approaches have been developed to target antioxidants specifically to mitochondria. Studies have employed a wide array of targeted molecules including antioxidant enzymes such as catalase, peroxiredoxin, superoxide dismutases and small molecular compounds which recapitulate the antioxidant activities of these enzymes. Lifespan and healthspan effects differ between interventions suggesting varied roles for specific mitochondrial reactive oxygen species and their impact on usual aging. Consistent findings in myocardial protection across various interventions support a focus on the impact of cardiac aging on healthspan. The advancement of mitochondrially targeted small-molecule antioxidants suggests the prospect of swift translation to human use.

Lifespan extension in genetically modified mice

Major advances in aging research have been made by studying the effect of genetic modifications on the lifespan of organisms, such as yeast, invertebrates (worms and flies) and mice. Data from yeast and invertebrates have been the most plentiful because of the ease in which genetic manipulations can be made and the rapidity by which lifespan experiments can be performed. With the ultimate focus on advancing human health, testing genetic interventions in mammals is crucial, and the mouse has proven to be the mammal most amenable to this task. Lifespan studies in mice are resource intensive, requiring up to 4 years to complete. Therefore, it is critical that a set of scientifically-based criteria be followed to assure reliable results and establish statistically significant findings so other laboratories can replicate and build on the data. Only then will it be possible to confidently determine that the genetic modification extends lifespan and alters aging.

Age-related cataract progression in five mouse models for anti-oxidant protection or hormonal influence

Five mouse models with known alterations of resistance to oxidative damage were compared by slit lamp examination for the presence and degree of advancement of age-related cataract in young adult and old animals along with wild type controls. A group of young and old normal C57BL/6Jax mice were examined first to constitute a standard, and they were found to exhibit age-related cataract development. Following this, four models on the C57BL/6 background with imposed genetic alterations affecting anti-oxidant enzyme presence or activity, and one outbred model in which a deletion blocked the growth hormone/IGF-1 axis, were similarly examined. There was no evidence of foetal or juvenile cataract development in any of these models, and an age-related severity for lens opacities was shown between young adult and old mice in all groups. Model 1, mice null for the anti-oxidant gene glutathione peroxidase-1 (GPX1) had significantly advanced cataracts in older mice vs. same age controls. In mouse model 2 hemizygous knockout of SOD2 (MnSOD) did not affect age-related cataract development. In model 3 combining the GPX1 and SOD2 deficiencies in the same animal did not advance cataract development beyond that of the GPX1 null alone. In model 4 the addition of anti-oxidant protection in the lens by transfection of human catalase targeted only to the mitochondria resulted in a significant delay in cataract development. The 5th model, growth hormone receptor knockout (GHR-/-) mice, also demonstrated a significant reduction in age-related cataract development, as well as dwarfism. These findings, in general, support the oxidative theory of age-related cataract development. The exception, the partial deletion of SOD2 in the hemizygous KO model, probably did not represent a sufficiently severe deprivation of anti-oxidant protection to produce pathologic changes in the lens.

Peptide conjugates for chromosomal gene targeting by triplex-forming oligonucleotides

Triplex-forming oligonucleotides (TFOs) are DNA-binding molecules, which offer the potential to selectively modulate gene expression. However, the biological activity of TFOs as potential antigene compounds has been limited by cellular uptake. Here, we investigate the effect of cell-penetrating peptides on the biological activity of TFOs as measured in an assay for gene-targeted mutagenesis. Using the transport peptide derived from the third helix of the homeodomain of antennapedia (Antp), we tested TFO-peptide conjugates compared with unmodified TFOs. TFOs covalently linked to Antp resulted in a 20-fold increase in mutation frequency when compared with 'naked' oligonucleotides. There was no increase above background in mutation frequency when Antp by itself was added to the cells or when Antp was linked to mixed or scrambled sequence control oligonucleotides. In addition, the TFO-peptide conjugates increased the mutation frequency of the target gene, and not the control gene, in a dose-responsive manner. Confocal microscopy using labeled oligonucleotides indicated increased cellular uptake of TFOs when linked to Antp, consistent with the gene-targeting data. These results suggest that peptide conjugation may enhance intranuclear delivery of reagents designed to bind to chromosomal DNA.

Pleomorphic xanthoastrocytoma: DNA flow cytometry and outcome analysis of 12 patients

BACKGROUND

Pleomorphic xanthoastrocytoma (PXA) is an astrocytic tumor occurring primarily in childhood and adolescence with some malignant histologic features but a relatively slow clinical course. However, some tumors progress more rapidly and can undergo malignant degeneration. The authors attempted to determine whether various histologic features or tumor cell proliferative indices might help identify lesions at risk for early progression and distinguish PXAs from malignant gliomas.

METHODS

In a retrospective study of 12 patients with PXA, the tumor's histologic features and DNA flow cytometric parameters were compared with their clinical course. DNA flow cytometry values for the S- and G2-phase of the PXAs also were compared with control group samples of malignant and low grade astrocytomas.

RESULTS

Of the 12 tumors at initial diagnosis, 5 were considered typical PXAs whereas 7 had some atypical features (4 with paucity of reticulin fibers, 1 with focal necrosis, and 2 with both atypical reticulin and focal necrosis). During the follow-up period (range, 3.75-11 years; mean, 6.8 years), 2 patients had recurrences; 1 atypical reticulin PXA progressed to glioblastoma after 6.5 years and the 1 tumor with focal necrosis recurred at 6 months and again at 2 years with typical histologic features. DNA flow cytometry parameters of the typical PXA group were similar to values for malignant astrocytoma and significantly higher than values for control specimens of low grade astrocytomas. There were no distinctive DNA flow cytometric features that could distinguish this last tumor from others with a more benign clinical course.

CONCLUSIONS

Measurements of the S-phase and G2-phase obtained from DNA flow cytometry and atypical histologic features cannot reliably identify PXA patients at risk for early progression and overall are significantly higher than values obtained for low grade gliomas. Therefore, frequent (i.e., two to three times per year) postoperative clinical and radiologic examinations are necessary to judge the appropriateness of adjuvant therapy in patients with PXA. The paradox of slow growth but DNA flow cytometry consistent with aggressive malignant lesions may represent a cell-cycle arrest mechanism in these lesions that could be verified in subsequent studies.

Measurement and prediction of the short-term response of soft tissue sarcomas to chemotherapy

BACKGROUND

Preoperative chemotherapy has been advocated for the treatment of soft tissue sarcomas, yet there is little information about how these tumors respond pathologically to therapy or whether tumor response can be predicted from a pretreatment biopsy.

METHODS

Biopsy was done of 25 intermediate- or high-grade soft tissue sarcomas before they were treated with three cycles of doxorubicin and cisplatin and resected. The authors compared the pathologic features of the treated tumors with clinical and radiologic evidence of response to identify the pathologic features that best reflected chemotherapeutic effect. They analyzed the pretreatment biopsy specimens by light microscopic study and flow cytometry to identify parameters that predict short-term response to chemotherapy.

RESULTS

In the treated tumors, the clearest indicator of early chemotherapeutic effect was the percentage of the resected mass composed of viable neoplasm. Eleven of 25 resection specimens contained less than 15% viable neoplasm (patients with pathologic response); 9 of these had 5% or less. Flow cytometric estimates of the proliferative rate in the initial biopsy specimen predicted early chemotherapeutic effect; 7 of 10 tumors with S-phase fractions (SPF) greater than 6% responded pathologically, whereas only 3 of 12 tumors with lower SPF responded (P = 0.041). Initial tumor grade, cell type, percent tumor necrosis, mitotic rate, cellularity, and ploidy did not predict chemotherapy response.

CONCLUSION

These results indicate that soft tissue sarcomas often respond dramatically to chemotherapy, that the amount of residual viable sarcoma is an indicator of short-term effect, and that flow cytometric estimates of cell proliferation predict early response to chemotherapy.

Prenatal diagnosis of tetraploidy: a case report

We report on the second trimester prenatal diagnosis of an apparently nonmosaic tetraploid fetus, 92,XXYY. Indications for cytogenetic studies of the fetus included abnormal ultrasound findings and abnormal maternal serum levels of alpha-fetoprotein (AFP)/estriol. Chromosome analysis of amniocytes documented tetraploidy, a finding confirmed by flow cytometry of several fetal tissues. Autopsy findings in the fetus are compared with those of other cases of tetraploidy. To our knowledge this is the first reported prenatal diagnosis of a tetraploid fetus. Additionally, it illustrates the value of flow cytometric analysis of products of conception in which polyploidy is suspected.

Effects of sodium butyrate on proliferation-dependent insulin gene expression and insulin release in glucose-sensitive RIN-5AH cells

A rat islet tumor subclone, RIN-5AH-T2-B, was cultured with 2 mmol/liter of the proliferation-arresting compound sodium butyrate (NaB). Insulin gene expression and glucose-stimulated insulin release were analyzed and compared with logarithmically proliferating and confluent control cells cultured without NaB. Logarithmically proliferating control cells revealed high insulin gene expression. In the presence of amino acids, these cells showed a dose-dependent insulin response to glucose with a half-maximal and maximal 6.5-fold stimulation by 0.8 and 5.6 mmol/liter D-glucose, respectively. However, as the control cells approached growth arrest, insulin gene expression subsided to below detectability, an occurrence that is associated with decreased insulin release and accumulation of cells in the G1 phase of the cell cycle. In contrast, NaB-arrested cells showed continuous insulin gene expression throughout the experiment. Despite this, insulin release in response to glucose was lost. NaB revealed a biphasic effect on the cell-cycle: after an initial leaky G1 arrest during the first 24 h, the 5AH-B cells were arrested in G2 during the following 3 days. These data suggest that insulin gene expression and glucose-stimulated insulin release are affected by the cell cycle. These glucose-sensitive RIN-5AH-T2-B cells may be useful in studies of insulin secretion and gene regulation.

Mitogen-induced hyperproliferation response of peripheral blood mononuclear cells from patients with severe generalized periodontitis: lack of correlation with proportions of T cells and T-cell subsets

Severe generalized periodontitis (SGP) is a localized inflammatory disease which differs clinically from common periodontitis in that it leads to remarkable extensive alveolar bone loss in relatively young adults. There is evidence that B-cell responses to bacterial substances may play a major role in the pathogenesis of this disease. In the present report, we show that a B-cell mitogen from Actinomyces viscosus (AVIS) bacteria provokes a hyperproliferation response of peripheral blood mononuclear cells (PBMNC) from these patients. In addition, AVIS-stimulated PBMNC from SGP patients proliferate for longer periods in culture than do PBMNC from control subjects. There were, however, no differences between patients and controls in the numbers of immunoglobulin-secreting cells in these cultures as determined by an indirect plaque-forming cell assay. The possibility that differences in numerical proportions of regulatory T-cell subsets may play a role in the mitogen-induced hyperproliferation phenomenon is examined. PBMNC were stained with fluorescein isothiocyanate-conjugated monoclonal antibodies OKT3, OKT4, and OKT8 in order to identify, respectively, total T cells, helper/inducer, and suppressor/cytotoxic subsets. Flow cytometric analysis of such specifically stained cell preparations from 14 control subjects and 14 SGP patients did not reveal any significant differences between the proportions of total T cells or T-cell subsets of the two groups. Furthermore, there were no statistically significant correlations between the magnitude of proliferation responses and the proportions of total T cells or either of the T-cell subsets.

Acceleration forces at eye level experienced with rotation on the horizontal bar

Negative acceleration forces (-Gz) experienced at eye level have been associated with preretinal hemorrhage and headache. These signs and symptoms were found in individuals who experienced negative (toward the head) force while rotating on a horizontal bar or hanging from a trapeze. Lightweight accelerometers were used to measure -Gz experienced at eye level in children and adult gymnasts performing a single-knee backswing on a horizontal bar. Rate of onset of -Gz, peak -Gz, time experiencing -Gz, area of curve (G.second), and mean force (area/time) were calculated. There was no significant difference between the children and the adult gymnasts in any of the above parameters. The best gymnast had a maximum rate of onset of 38.15 G/s and the maximum negative force experienced was 5.52 G. The maximum rate of onset for a child was 41.56 G/s and the maximum negative force experienced was 5.73 G. Compared with -Gz tolerance curves generated on a centrifuge the best gymnast would have become symptomatic while performing this maneuver in 6 s. The best child would have become symptomatic in 25 s. These tolerance limits can be easily exceeded by gymnasts and by the monkey-bar enthusiast.