Weight Loss-Independent Effect of Liraglutide on Insulin Sensitivity in Individuals With Obesity and Prediabetes

Metabolic effects of glucagon-like peptide 1 (GLP-1) receptor agonists are confounded by weight loss and not fully recapitulated by increasing endogenous GLP-1. We tested the hypothesis that GLP-1 receptor (GLP-1R) agonists exert weight loss-independent, GLP-1R-dependent effects that differ from effects of increasing endogenous GLP-1. Individuals with obesity and prediabetes were randomized to receive for 14 weeks the GLP-1R agonist liraglutide, a hypocaloric diet, or the dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin. The GLP-1R antagonist exendin(9-39) and placebo were administered in a two-by-two crossover study during mixed-meal tests. Liraglutide and diet, but not sitagliptin, caused weight loss. Liraglutide improved insulin sensitivity measured by HOMA for insulin resistance (HOMA-IR), the updated HOMA model (HOMA2), and the Matsuda index after 2 weeks, prior to weight loss. Liraglutide decreased fasting and postprandial glucose levels, and decreased insulin, C-peptide, and fasting glucagon levels. In contrast, diet-induced weight loss improved insulin sensitivity by HOMA-IR and HOMA2, but not the Matsuda index, and did not decrease glucose levels. Sitagliptin increased endogenous GLP-1 and GIP values without altering insulin sensitivity or fasting glucose levels, but decreased postprandial glucose and glucagon levels. Notably, sitagliptin increased GIP without altering weight. Acute GLP-1R antagonism increased glucose levels in all groups, increased the Matsuda index and fasting glucagon level during liraglutide treatment, and increased endogenous GLP-1 values during liraglutide and sitagliptin treatments. Thus, liraglutide exerts rapid, weight loss-independent, GLP-1R-dependent effects on insulin sensitivity that are not achieved by increasing endogenous GLP-1.

ARTICLE HIGHLIGHTS

Metabolic benefits of glucagon-like peptide 1 (GLP-1) receptor agonists are confounded by weight loss and are not fully achieved by increasing endogenous GLP-1 through dipeptidyl peptidase 4 (DPP-4) inhibition. We investigated weight loss-independent, GLP-1 receptor (GLP-1R)-dependent metabolic effects of liraglutide versus a hypocaloric diet or the DPP-4 inhibitor sitagliptin. GLP-1R antagonism with exendin(9-39) was used to assess GLP-1R-dependent effects during mixed meals. Liraglutide improved insulin sensitivity and decreased fasting and postprandial glucose prior to weight loss, and these benefits were reversed by exendin(9-39). GLP-1R agonists exert rapid, weight loss-independent, GLP-1R-dependent effects on insulin sensitivity not achieved by increasing endogenous GLP-1.

Bradykinin B2 receptor blockade and intradialytic hypotension

INTRODUCTION

Intradialytic hypotension (IDH) is a common clinical complication and is associated with increased morbidity and mortality in patients undergoing maintenance hemodialysis (MHD). The pathogenesis of IDH has been attributed to the rapid reduction of plasma volume during hemodialysis and the inadequate compensatory mechanisms in response to hypovolemia, such as the lack of vasoconstriction. This may be due to the increased production of vasodilators, such as bradykinin. In this study we test the hypothesis that bradykinin B2 receptor blockade prevents intradialytic hypotension.

METHODS

We performed a post-hoc analysis of a double-blind, placebo-controlled, randomized, 2 × 2 crossover clinical trial comparing the continuous infusion of icatibant, a bradykinin B2 receptor blocker, and placebo during hemodialysis. Icatibant or placebo was infused for 30 min before and during hemodialysis in 11 patients on MHD.

RESULTS

Seven of the patients had IDH, defined as a reduction of systolic blood pressure equal to or greater than 20 mmHg during hemodialysis. Stratified analysis, based on the presence of IDH, revealed that icatibant prevented the decrease in blood pressure compared to placebo in patients with IDH [blood pressure at average nadir (2.5 h after hemodialysis): Placebo,114.3 ± 8.9 vs. icatibant, 125.6 ± 9.1 mmHg, mean ± S.E.M]. Icatibant did not affect blood pressure in the group of patients without IDH.

CONCLUSION

Bradykinin B2 receptor blocker may prevent the occurrence of IDH. Further studies should evaluate the hemodynamic effects of icatibant during hemodialysis and the symptomatology associated with IDH.

APOL1 and the risk of adverse renal outcomes in patients of African ancestry with systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) disproportionately affects individuals of African ancestry (AA) compared to European ancestry (EA). In the general population, high risk (HR) variants in the apolipoprotein L1 (APOL1) gene increase the risk of renal and hypertensive disorders in individuals of AA. Since SLE is characterized by an interferon signature and APOL1 expression is driven by interferon, we examined the hypothesis that APOL1 HR genotypes predominantly drive higher rates of renal and hypertensive-related comorbidities observed in SLE patients of AA versus those of EA.

METHODS

We performed a retrospective cohort study in patients with SLE of EA and AA using a genetic biobank linked to de-identified electronic health records. APOL1 HR genotypes were defined as G1/G1, G2/G2, or G1/G2 and low risk (LR) genotypes as 1 or 0 copies of the G1 and G2 alleles. To identify renal and hypertensive-related disorders that differed in prevalence by ancestry, we used a phenome-wide association approach. We then used logistic regression to compare the prevalence of renal and hypertensive-related disorders in EA and AA patients, both including and excluding patients with the APOL1 HR genotype. In a sensitivity analysis, we examined the association of end stage renal disease secondary to lupus nephritis (LN-related ESRD) with ancestry and the APOL1 genotype.

RESULTS

We studied 784 patients with SLE; 195 (24.9%) were of AA, of whom 27 (13.8%) had APOL1 HR genotypes. Eighteen renal and hypertensive-related phenotypes were more common in AA than EA patients (p-value ≤ 1.4E-4). All phenotypes remained significantly different after exclusion of patients with APOL1 HR genotypes, and most point odds ratios (ORs) decreased only slightly. Even among ORs with the greatest decrease, risk for AA patients without the APOL1 HR genotype remained significantly elevated compared to EA patients. In the sensitivity analysis, LN-related ESRD was more prevalent in SLE patients of AA versus EA and AA patients with the APOL1 HR genotype versus LR (p-value < .05 for both).

CONCLUSION

The higher prevalence of renal and hypertensive disorders in SLE patients of AA compared to those of EA is not fully explained by the presence of APOL1 high risk variants.

Ancestry, ACKR1 and leucopenia in patients with systemic lupus erythematosus

OBJECTIVE

SLE is more prevalent in populations of African (AA) than European ancestry (EA) and leucopenia is common. A homozygous variant in ACKR1 (rs2814778-CC) is associated with lower white cell counts; the variant is common in AA but not EA populations. We hypothesised that in SLE: (1) leucopenia is more frequent in patients of AA than EA, and (2) the ACKR1-CC genotype accounts for the higher frequency of leucopenia in AA patients.

METHODS

We performed a retrospective cohort study in patients with SLE at a tertiary care system. Ancestry was defined by genetic principal components. We compared the rate of leucopenia, thrombocytopenia and anaemia between (a) EA and AA patients, and (b) ACKR1-CT/TT and CC genotype in AA patients.

RESULTS

The cohort included 574 patients of EA and 190 of AA; ACKR1-CC genotype was common in AA (70%) but not EA (0%) patients. Rates of leucopenia for ancestry and genotype were AA 60.0% vs EA 36.8 % (p=1.9E-08); CC 67.7% vs CT/TT 42.1% (p=9.8E-04). The rate of leucopenia did not differ by ancestry comparing EA patients versus AA with CT/TT genotype (p=0.59). Thrombocytopenia (22.2% vs 13.2%, p=0.004) and anaemia (88.4% vs 66.2%, p=3.7E-09) were more frequent in AA patients but were not associated with ACKR1 genotype (p=0.82 and p=0.84, respectively).

CONCLUSIONS

SLE of AA had higher rates of anaemia, leucopenia, and thrombocytopenia than those of EA; only the difference in leucopenia was explained by ACKR1-CC genotype. This genotype could affect clinical practice.

Genetic Architecture of Plasma Alpha-Aminoadipic Acid Reveals a Relationship With High-Density Lipoprotein Cholesterol

Background Elevated plasma levels of alpha-aminoadipic acid (2-AAA) have been associated with the development of type 2 diabetes and atherosclerosis. However, the nature of the association remains unknown. Methods and Results We identified genetic determinants of plasma 2-AAA through meta-analysis of genome-wide association study data in 5456 individuals of European, African, and Asian ancestry from the Framingham Heart Study, Diabetes Prevention Program, Jackson Heart Study, and Shanghai Women's and Men's Health Studies. No single nucleotide polymorphisms reached genome-wide significance across all samples. However, the top associations from the meta-analysis included single-nucleotide polymorphisms in the known 2-AAA pathway gene DHTKD1, and single-nucleotide polymorphisms in genes involved in mitochondrial respiration (NDUFS4) and macrophage function (MSR1). We used a Mendelian randomization instrumental variable approach to evaluate relationships between 2-AAA and cardiometabolic phenotypes in large disease genome-wide association studies. Mendelian randomization identified a suggestive inverse association between increased 2-AAA and lower high-density lipoprotein cholesterol (P=0.005). We further characterized the genetically predicted relationship through measurement of plasma 2-AAA and high-density lipoprotein cholesterol in 2 separate samples of individuals with and without cardiometabolic disease (N=98), and confirmed a significant negative correlation between 2-AAA and high-density lipoprotein (rs=-0.53, P<0.0001). Conclusions 2-AAA levels in plasma may be regulated, in part, by common variants in genes involved in mitochondrial and macrophage function. Elevated plasma 2-AAA associates with reduced levels of high-density lipoprotein cholesterol. Further mechanistic studies are required to probe this as a possible mechanism linking 2-AAA to future cardiometabolic risk.

Effects of caloric restriction and aerobic exercise on circulating cell-free mitochondrial DNA in patients with moderate to severe chronic kidney disease

Circulating cell-free mitochondrial DNA (ccf-mtDNA) may induce systemic inflammation, a common condition in chronic kidney disease (CKD), by acting as a damage-associated molecular pattern. We hypothesized that in patients with moderate to severe CKD, aerobic exercise would reduce ccf-mtDNA levels. We performed a post hoc analysis of a multicenter randomized trial (NCT01150851) measuring plasma concentrations of ccf-mtDNA at baseline and 2 and 4 mo after aerobic exercise and caloric restriction. A total of 99 participants had baseline ccf-mtDNA, and 92 participants completed the study. The median age of the participants was 57 yr, 44% were female and 55% were male, 23% had diabetes, and 92% had hypertension. After adjusting for demographics, blood pressure, body mass index, diabetes, and estimated glomerular filtration rate, median ccf-mtDNA concentrations at baseline, 2 mo, and 4 mo were 3.62, 3.08, and 2.78 pM for the usual activity group and 2.01, 2.20, and 2.67 pM for the aerobic exercise group, respectively. A 16.1% greater increase per month in ccf-mtDNA was seen in aerobic exercise versus usual activity (P = 0.024), which was more pronounced with the combination of aerobic exercise and caloric restriction (29.5% greater increase per month). After 4 mo of intervention, ccf-mtDNA increased in the aerobic exercise group by 81.6% (95% confidence interval: 8.2-204.8, P = 0.024) compared with the usual activity group and was more marked in the aerobic exercise and caloric restriction group (181.7% increase, 95% confidence interval: 41.1-462.2, P = 0.003). There was no statistically significant correlation between markers of oxidative stress and inflammation with ccf-mtDNA. Our data indicate that aerobic exercise increased ccf-mtDNA levels in patients with moderate to severe CKD.NEW & NOTEWORTHY The effects of prolonged exercise on circulating cell-free mitochondrial DNA (ccf-mtDNA) have not been explored in patients with chronic kidney disease (CKD). We showed that 4-mo aerobic exercise is associated with an increase in plasma ccf-mtDNA levels in patients with stages 3 or 4 CKD. These changes were not associated with markers of systemic inflammation. Future studies should determine the mechanisms by which healthy lifestyle interventions influence biomarkers of inflammation and oxidative stress in patients with CKD.

Effects of long-term intradialytic oral nutrition and exercise on muscle protein homeostasis and markers of mitochondrial content in patients on hemodialysis

Patients with end-stage kidney disease on maintenance hemodialysis commonly develop protein-energy wasting, a syndrome characterized by nutritional and metabolic abnormalities. Nutritional supplementation and exercise are recommended to prevent protein-energy wasting. In a 6-mo prospective randomized, open-label, clinical trial, we reported that the combination of resistance exercise and nutritional supplementation does not have an additive effect on lean body mass measured by dual-energy X-ray absorptiometry. To provide more mechanistic data, we performed a secondary analysis where we hypothesized that the combination of nutritional supplementation and resistance exercise would have additive effects on muscle protein accretion by stable isotope protein kinetic experiments, muscle mass by MRI, and mitochondrial content markers in muscle. We found that 6 mo of nutritional supplementation during hemodialysis increased muscle protein net balance [baseline: 2.5 (-17.8, 13.0) µg·100 mL-1·min-1 vs. 6 mo: 43.7 (13.0, 98.5) µg·100 mL-1·min-1, median (interquartile range), P = 0.04] and mid-thigh fat area [baseline: 162.3 (104.7, 226.6) cm2 vs. 6 mo: 181.9 (126.3, 279.2) cm2, median (interquartile range), P = 0.04]. Three months of nutritional supplementation also increased markers of mitochondrial content in muscle. Although the study is underpowered to detected differences, the combination of nutritional supplementation and exercise failed to show further benefit in protein accretion or muscle cross-sectional area. We conclude that long-term nutritional supplementation increases the skeletal muscle anabolic effect, the fat cross-sectional area of the thigh, and markers of mitochondrial content in skeletal muscle.

Mechanisms Regulating Muscle Protein Synthesis in CKD

BACKGROUND

CKD induces loss of muscle proteins partly by suppressing muscle protein synthesis. Muscles of mice with CKD have increased expression of nucleolar protein 66 (NO66), as do muscle biopsy specimens from patients with CKD or those undergoing hemodialysis. Inflammation stimulates NO66 expression and changes in NF-κB mediate the response.

METHODS

Subtotal nephrectomy created a mouse model of CKD with BUN >80 mg/dl. Crossing NO66^flox/flox with MCK-Cre mice bred muscle-specific NO66 (MCK-NO66) knockout mice. Experiments assessed the effect of removing NO66.

RESULTS

Muscle-specific NO66 knockout in mice blocks CKD-induced loss of muscle mass and improves protein synthesis. NO66 suppression of ribosomal biogenesis via demethylase activity is the mechanism behind these responses. In muscle cells, expression of NO66, but not of demethylase-dead mutant NO66, decreased H3K4me3 and H3K36me3 and suppressed pre-rRNA expression. Knocking out NO66 increased the enrichment of H3K4me3 and H3K36me3 on ribosomal DNA. In primary muscle cells and in muscles of mice without NO66, ribosomal RNA, pre-rRNA, and protein synthesis all increased.

CONCLUSIONS

CKD suppresses muscle protein synthesis via epigenetic mechanisms that NO66 mediates. Blocking NO66 could suggest strategies that counter CKD-induced abnormal muscle protein catabolism.

Skeletal Muscle Mitochondrial Dysfunction Is Present in Patients with CKD before Initiation of Maintenance Hemodialysis

BACKGROUND AND OBJECTIVES

Patients with CKD suffer from frailty and sarcopenia, which is associated with higher morbidity and mortality. Skeletal muscle mitochondria are important for physical function and could be a target to prevent frailty and sarcopenia. In this study, we tested the hypothesis that mitochondrial dysfunction is associated with the severity of CKD. We also evaluated the interaction between mitochondrial function and coexisting comorbidities, such as impaired physical performance, intermuscular adipose tissue infiltration, inflammation, and oxidative stress.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Sixty-three participants were studied, including controls (n=21), patients with CKD not on maintenance hemodialysis (CKD 3-5; n=20), and patients on maintenance hemodialysis (n=22). We evaluated in vivo knee extensors mitochondrial function using ³¹P magnetic resonance spectroscopy to obtain the phosphocreatine recovery time constant, a measure of mitochondrial function. We measured physical performance using the 6-minute walk test, intermuscular adipose tissue infiltration with magnetic resonance imaging, and markers of inflammation and oxidative stress in plasma. In skeletal muscle biopsies from a select number of patients on maintenance hemodialysis, we also measured markers of mitochondrial dynamics (fusion and fission).

RESULTS

We found a prolonged phosphocreatine recovery constant in patients on maintenance hemodialysis (53.3 [43.4-70.1] seconds, median [interquartile range]) and patients with CKD not on maintenance hemodialysis (41.5 [35.4-49.1] seconds) compared with controls (38.9 [32.5-46.0] seconds; P=0.001 among groups). Mitochondrial dysfunction was associated with poor physical performance (r=0.62; P=0.001), greater intermuscular adipose tissue (r=0.44; P=0.001), and increased markers of inflammation and oxidative stress (r=0.60; P=0.001). We found mitochondrial fragmentation and increased content of dynamin-related protein 1, a marker of mitochondrial fission, in skeletal muscles from patients on maintenance hemodialysis (0.86 [0.48-1.35] arbitrary units (A.U.), median [interquartile range]) compared with controls (0.60 [0.24-0.75] A.U.).

CONCLUSIONS

Mitochondrial dysfunction is due to multifactorial etiologies and presents prior to the initiation of maintenance hemodialysis, including in patients with CKD stages 3-5.

Abstract 107: Bradykinin B 2 Receptor Blockade Prevents Excessive Blood Pressure Reduction During Hemodialysis

Intradialytic hypotension (IDH) is a common clinical complication of hemodialysis in patients with end-stage renal disease and it is associated with increased morbidity and mortality. The pathogenesis of IDH has been attributed to a rapid removal of plasma volume during hemodialysis and the inadequate compensatory mechanisms to hypovolemia, such as the lack of vasoconstriction. This may be due to the removal of vasoconstrictors or the increased production of vasodilators, such as bradykinin. Thus, we tested the hypothesis that bradykinin B 2 receptor blockade prevents intradialytic hypotension. For this purpose, we conducted a double-blind, placebo controlled, randomized, 2x2 crossover clinical trial comparing the continuous infusion of icatibant, a bradykinin B 2 receptor blocker, and placebo during hemodialysis. We evaluated 11 patients who underwent adequate hemodialysis thrice weekly for at least 6 consecutive months. Icatibant or placebo were infused for 30 minutes before and during hemodialysis. Seven of the patients have IDH, defined as a reduction of systolic blood pressure equal or greater than 20 mmHg during hemodialysis. Stratified analysis, based on the presence of IDH, revealed that icatibant prevents the decrease in blood pressure compared to placebo in patients with IDH (change in blood pressure from baseline: Placebo -13.0±9.8 vs . icatibant 1.8±18.8 mmHg, mean±S.D, Figure 1 ). Icatibant has no effect on blood pressure in the group of patients without IDH. Further studies should evaluate not only the hemodynamics effect of icatibant during hemodialysis, but also its efficacy on preventing the symptomatology associated with IDH.

Chronic kidney disease attenuates the plasma metabolome response to insulin

Chronic kidney disease (CKD) leads to decreased sensitivity to the metabolic effects of insulin, contributing to protein energy wasting and muscle atrophy. Targeted metabolomics profiling during hyperinsulinemic-euglycemic insulin clamp testing may help identify aberrant metabolic pathways contributing to insulin resistance in CKD. Using targeted metabolomics profiling, we examined the plasma metabolome in 95 adults without diabetes in the fasted state (58 with CKD, 37 with normal glomerular filtration rate [GFR]) who underwent hyperinsulinemic-euglycemic clamp. We assessed heterogeneity in fasting metabolites and the response to insulin to identify potential metabolic pathways linking CKD with insulin resistance. Baseline differences and effect modification by CKD status on changes with insulin clamp testing were adjusted for confounders. Mean GFR among participants with CKD was 37.3 compared with 89.3 ml/min per 1.73 m2 among controls. Fasted-state differences between CKD and controls included abnormalities in tryptophan metabolism, ubiquinone biosynthesis, and the TCA cycle. Insulin infusion markedly decreased metabolite levels, predominantly amino acids and their metabolites. CKD was associated with attenuated insulin-induced changes in nicotinamide, arachidonic acid, and glutamine/glutamate metabolic pathways. Metabolomics profiling suggests disruption in amino acid metabolism and mitochondrial function as putative manifestations or mechanisms of the impaired anabolic effects of insulin in CKD.

Angiotensin receptor blocker vs ACE inhibitor effects on HDL functionality in patients on maintenance hemodialysis

BACKGROUND AND AIMS

Angiotensin receptor blockers (ARB) and angiotensin converting enzyme inhibitors (ACEI) reduce cardiovascular events in the general population. Maintenance hemodialysis (MHD) patients are at high cardiovascular risk but few studies have directly addressed the comparative efficacy of these drugs. MHD disrupts the normally atheroprotective actions of high density lipoprotein (HDL), therefore, we compared ACEI or ARB treatment on HDL functions in MHD.

METHODS AND RESULTS

HDL was isolated at the starting point (pre) and 3-6 months later (post) in 30 MHD randomly assigned to placebo, ramipril or valsartan. Outcomes included cholesterol efflux, inflammatory cytokine response, effects on Toll-like receptors (TLR), superoxide production, methylarginine and serum amyloid A (SAA) levels. HDL from ARB- or ACEI-treated subjects was more effective in maintaining efflux than HDL of placebo. HDL from ARB- or ACEI-treated subjects but not placebo lessened cellular superoxide production. In contrast, neither ARB nor ACEI improved HDL anti-inflammatory effect. Indeed, HDL of ACEI-treated subjects potentiated the cytokine responses in association with activation of TLR but did not alter the HDL content of methylarginines or SAA.

CONCLUSION

Both ACEI and ARB stabilized HDL cholesterol acceptor function and sustained cellular anti-oxidative effects but not anti-inflammatory effects, and ACEI-treatment instead amplified the HDL inflammatory response. The findings reveal possible utility of antagonizing angiotensin actions in MDH and suggest a possible mechanism for superiority of ARB vs ACEI in the setting of advanced kidney disease.

Excessive Erythrocytosis and Cardiovascular Risk in Andean Highlanders

Corante, Noemí, Cecilia Anza-Ramírez, Rómulo Figueroa-Mujíca, José Luis Macarlupú, Gustavo Vizcardo-Galindo, Grzegorz Bilo, Gianfranco Parati, Jorge L. Gamboa, Fabiola León-Velarde, and Francisco C. Villafuerte. Excessive erythrocytosis and cardiovascular risk in Andean highlanders. High Alt Med Biol. 19:221–231, 2018.—Cardiovascular diseases are the main cause of death worldwide. Life under high-altitude (HA) hypoxic conditions is believed to provide highlanders with a natural protection against cardiovascular and metabolic diseases compared with sea-level inhabitants. However, some HA dwellers become intolerant to chronic hypoxia and develop a progressive incapacitating syndrome known as chronic mountain sickness (CMS), characterized by excessive erythrocytosis (EE; Hb ≥21 g/dL in men, Hb ≥19 g/dL in women). Evidence from HA studies suggests that, in addition to CMS typical signs and symptoms, these highlanders may also suffer from metabolic and cardiovascular disorders. Thus, we hypothesize that this syndrome is also associated to the loss of the cardiometabolic protection observed in healthy highlanders (HH), and therefore to a higher cardiovascular risk (CVR). The aim of the present work was to evaluate the association between EE and CVR calculated using the Framingham General CVR Score and between EE and CVR factors in male highlanders. This cross-sectional study included 342 males from Cerro de Pasco, Peru at 4340 m (HH = 209, CMS = 133). Associations were assessed by multiple logistic regressions adjusted for potential confounders (BMI, pulse oxygen saturation and age). The adjusted models show that the odds of high CVR (>20%) in highlanders with EE was 3.63 times the odds in HH (CI 95%:1.22–10.78; p = 0.020), and that EE is associated to hypertension, elevated fasting serum glucose, insulin resistance, and elevated fasting serum triglycerides. Our results suggest that individuals who suffer from EE are at increased risk of developing cardiovascular events compared with their healthy counterparts.

Response to unfairness across the suicide risk spectrum

Suicidal behavior is frequently triggered by social crises, such as familial, romantic, social or work-related conflict. A variety of cognitive and social functioning impairments has been associated with suicidal thoughts and acts. One of the precipitating and perpetuating factors of social conflict is the desire for retribution after a perceived offense, even at one's own detriment. We utilized the Ultimatum Game-a behavioral economic task which examines the behavioral response to perceived unfairness-in order to characterize the response to unfairness across the acute suicide risk spectrum. We examined five groups of adult individuals of both genders (n = 204): High- and Low-Lethality recent Suicide Attempters, Suicidal Ideators, Non-Suicidal Depressed Patients; and Healthy Controls. We also measured demographic and clinical variables. Even though all depressed groups showed similar rejection rates in the Ultimatum Game, there was a higher likelihood of rejecting offers in the low stakes condition in all acutely suicidal groups compared with healthy controls. Stake size, offer, education, and gender of the proposer were significantly associated with rejection rates. Acutely suicidal patients may be more vulnerable to adverse interpersonal interactions. Further characterization of social behavior may provide targets for secondary and tertiary prevention for high-risk individuals.

Systemic inflammation is associated with exaggerated skeletal muscle protein catabolism in maintenance hemodialysis patients

BACKGROUND

Systemic inflammation and muscle wasting are highly prevalent and coexist in patients on maintenance hemodialysis (MHD). We aimed to determine the effects of systemic inflammation on skeletal muscle protein metabolism in MHD patients.

METHODS

Whole body and skeletal muscle protein turnover were assessed by stable isotope kinetic studies. We incorporated expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue from integrin β1 gene KO CKD mice models.

RESULTS

Among 129 patients with mean (± SD) age 47 ± 12 years, 74% were African American, 73% were male, and 22% had diabetes mellitus. Median high-sensitivity C-reactive protein (hs-CRP) concentration was 13 (interquartile range 0.8, 33) mg/l. There were statistically significant associations between hs-CRP and forearm skeletal muscle protein synthesis, degradation, and net forearm skeletal muscle protein balance (P < 0.001 for all). The associations remained statistically significant after adjustment for clinical and demographic confounders, as well as in sensitivity analysis, excluding patients with diabetes mellitus. In attempting to identify potential mechanisms involved in this correlation, we show increased expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue obtained from an animal model of chronic kidney disease.

CONCLUSION

These data suggest that systemic inflammation is a strong and independent determinant of skeletal muscle protein homeostasis in MHD patients, providing rationale for further studies using anticytokine therapies in patients with underlying systemic inflammation.

FUNDING

This study was in part supported by NIH grants R01 DK45604 and 1K24 DK62849, the Clinical Translational Science Award UL1-TR000445 from the National Center for Advancing Translational Sciences, the Veterans Administration Merit Award I01 CX000414, the SatelliteHealth Normon Coplon Extramural Grant Program, and the FDA grant 000943.

Sirt3 Impairment and SOD2 Hyperacetylation in Vascular Oxidative Stress and Hypertension

RATIONALE

Clinical studies have shown that Sirt3 (Sirtuin 3) expression declines by 40% by 65 years of age paralleling the increased incidence of hypertension and metabolic conditions further inactivate Sirt3 because of increased NADH (nicotinamide adenine dinucleotide, reduced form) and acetyl-CoA levels. Sirt3 impairment reduces the activity of a key mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2) because of hyperacetylation.

OBJECTIVE

In this study, we examined whether the loss of Sirt3 activity increases vascular oxidative stress because of SOD2 hyperacetylation and promotes endothelial dysfunction and hypertension.

METHODS AND RESULTS

Hypertension was markedly increased in Sirt3-knockout (Sirt3^-/-) and SOD2-depleted (SOD2^+/-) mice in response to low dose of angiotensin II (0.3 mg/kg per day) compared with wild-type C57Bl/6J mice. Sirt3 depletion increased SOD2 acetylation, elevated mitochondrial O₂^· -, and diminished endothelial nitric oxide. Angiotensin II-induced hypertension was associated with Sirt3 S-glutathionylation, acetylation of vascular SOD2, and reduced SOD2 activity. Scavenging of mitochondrial H₂O₂ in mCAT mice expressing mitochondria-targeted catalase prevented Sirt3 and SOD2 impairment and attenuated hypertension. Treatment of mice after onset of hypertension with a mitochondria-targeted H₂O₂ scavenger, mitochondria-targeted hydrogen peroxide scavenger ebselen, reduced Sirt3 S-glutathionylation, diminished SOD2 acetylation, and reduced blood pressure in wild-type but not in Sirt3^-/- mice, whereas an SOD2 mimetic, (2-[2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino]-2-oxoethyl) triphenylphosphonium (mitoTEMPO), reduced blood pressure and improved vasorelaxation both in Sirt3^-/- and wild-type mice. SOD2 acetylation had an inverse correlation with SOD2 activity and a direct correlation with the severity of hypertension. Analysis of human subjects with essential hypertension showed 2.6-fold increase in SOD2 acetylation and 1.4-fold decrease in Sirt3 levels, whereas SOD2 expression was not affected.

CONCLUSIONS

Our data suggest that diminished Sirt3 expression and redox inactivation of Sirt3 lead to SOD2 inactivation and contributes to the pathogenesis of hypertension.

Cytochrome P450 epoxygenase-derived epoxyeicosatrienoic acids contribute to insulin sensitivity in mice and in humans

AIMS/HYPOTHESIS

Insulin resistance is frequently associated with hypertension and type 2 diabetes. The cytochrome P450 (CYP) arachidonic acid epoxygenases (CYP2C, CYP2J) and their epoxyeicosatrienoic acid (EET) products lower blood pressure and may also improve glucose homeostasis. However, the direct contribution of endogenous EET production on insulin sensitivity has not been previously investigated. In this study, we tested the hypothesis that endogenous CYP2C-derived EETs alter insulin sensitivity by analysing mice lacking CYP2C44, a major EET producing enzyme, and by testing the association of plasma EETs with insulin sensitivity in humans.

METHODS

We assessed insulin sensitivity in wild-type (WT) and Cyp2c44 ^-/- mice using hyperinsulinaemic-euglycaemic clamps and isolated skeletal muscle. Insulin secretory function was assessed using hyperglycaemic clamps and isolated islets. Vascular function was tested in isolated perfused mesenteric vessels. Insulin sensitivity and secretion were assessed in humans using frequently sampled intravenous glucose tolerance tests and plasma EETs were measured by mass spectrometry.

RESULTS

Cyp2c44 ^-/- mice showed decreased glucose tolerance (639 ± 39.5 vs 808 ± 37.7 mmol/l × min for glucose tolerance tests, p = 0.004) and insulin sensitivity compared with WT controls (hyperinsulinaemic clamp glucose infusion rate average during terminal 30 min 0.22 ± 0.02 vs 0.33 ± 0.01 mmol kg^-1 min^-1 in WT and Cyp2c44 ^-/- mice respectively, p = 0.003). Although glucose uptake was diminished in Cyp2c44 ^-/- mice in vivo (gastrocnemius R_g 16.4 ± 2.0 vs 6.2 ± 1.7 μmol 100 g^-1 min^-1, p < 0.01) insulin-stimulated glucose uptake was unchanged ex vivo in isolated skeletal muscle. Capillary density was similar but vascular K_ATP-induced relaxation was impaired in isolated Cyp2c44 ^-/- vessels (maximal response 39.3 ± 6.5% of control, p < 0.001), suggesting that impaired vascular reactivity produces impaired insulin sensitivity in vivo. Similarly, plasma EETs positively correlated with insulin sensitivity in human participants.

CONCLUSIONS/INTERPRETATION

CYP2C-derived EETs contribute to insulin sensitivity in mice and in humans. Interventions to increase circulating EETs in humans could provide a novel approach to improve insulin sensitivity and treat hypertension.

Mitochondrial dysfunction and oxidative stress in patients with chronic kidney disease

Mitochondria abnormalities in skeletal muscle may contribute to frailty and sarcopenia, commonly present in patients with chronic kidney disease (CKD). Dysfunctional mitochondria are also a major source of oxidative stress and may contribute to cardiovascular disease in CKD. We tested the hypothesis that mitochondrial structure and function worsens with the severity of CKD. Mitochondrial volume density, mitochondrial DNA (mtDNA) copy number, BNIP3, and PGC1α protein expression were evaluated in skeletal muscle biopsies obtained from 27 subjects (17 controls and 10 with CKD stage 5 on hemodialysis). We also measured mtDNA copy number in peripheral blood mononuclear cells (PBMCs), plasma isofurans, and plasma F2‐isoprostanes in 208 subjects divided into three groups: non‐CKD (eGFR>60 mL/min), CKD stage 3–4 (eGFR 60–15 mL/min), and CKD stage 5 (on hemodialysis). Muscle biopsies from patients with CKD stage 5 revealed lower mitochondrial volume density, lower mtDNA copy number, and higher BNIP3 content than controls. mtDNA copy number in PBMCs was decreased with increasing severity of CKD: non‐CKD (6.48, 95% CI 4.49–8.46), CKD stage 3–4 (3.30, 95% CI 0.85–5.75, P = 0.048 vs. non‐CKD), and CKD stage 5 (1.93, 95% CI 0.27–3.59, P = 0.001 vs. non‐CKD). Isofurans were higher in patients with CKD stage 5 (median 59.21 pg/mL, IQR 41.76–95.36) compared to patients with non‐CKD (median 49.95 pg/mL, IQR 27.88–83.46, P = 0.001), whereas F2‐isoprostanes did not differ among groups. Severity of CKD is associated with mitochondrial dysfunction and markers of oxidative stress. Mitochondrial abnormalities, which are common in skeletal muscle from patients with CKD stage 5, may explain the muscle dysfunction associated with frailty and sarcopenia in CKD. Further studies are required to evaluate mitochondrial function in vivo in patients with different CKD stages.

Comparative effects of immediate‐release and extended‐release aspirin on basal and bradykinin‐stimulated excretion of thromboxane and prostacyclin metabolites

A goal of aspirin therapy is to inhibit thromboxane production and platelet aggregation without inhibiting endothelial production of the vasodilator and anti‐thrombotic prostacyclin. This study tested the hypothesis that extended‐release aspirin (NHP‐554C) would have increased selectivity for inhibition of basal and simulated thromboxane formation compared to immediate‐release aspirin (ASA). Thirty‐six healthy subjects were randomized to NHP‐554C or ASA groups. Within each group, subjects were randomized to 5‐day treatment with 81 mg/d, 162.5 mg/d and placebo in a crossover design in which treatment periods were separated by 2‐week washout. On the fifth day of treatment, 81 mg/d and 162.5 mg/d ASA reduced basal urinary excretion of the stable thromboxane metabolite 11‐dehydro‐thromboxane B2 62.3% and 66.2% and basal excretion of the stable prostacyclin metabolite 2,3‐dinor‐6‐keto‐PGF1α 22.8% and 26.5%, respectively, compared to placebo. NHP‐554C 81 mg/d and 162.5 mg/d reduced 11‐dehydro‐thromboxane B2 53% (P = 0.03 vs. ASA 81 mg/d) and 67.9% and 2,3‐dinor‐6‐keto‐PGF1α 13.4% and 18.5%, respectively. NHP‐554C 81 mg/d did not significantly reduce basal excretion of the prostacyclin metabolite. Both doses of ASA and NHP significantly reduced excretion of both thromboxane and prostacyclin metabolites following intravenous bradykinin. During NHP‐554C 162.5 mg/d, but not during ASA, bradykinin significantly increased urinary 2,3‐dinor‐6‐keto‐PGF1α. Nevertheless, 11‐dehydro‐thromboxane B2 and 2,3‐dinor‐6‐keto‐PGF1α responses to bradykinin were statistically similar during ASA and NHP‐554C. In conclusion, at doses of 81 and 162.5 mg/d immediate‐ and extended‐release aspirin selectively decrease basal thromboxane production. Both forms of aspirin decrease bradykinin‐stimulated thromboxane and prostacyclin production, but some stimulated prostacyclin production remains during treatment with NHP‐554C.

Treatment with Sildenafil Improves Insulin Sensitivity in Prediabetes: A Randomized, Controlled Trial

CONTEXT

Sildenafil increases insulin sensitivity in mice. In humans, phosphodiesterase 5 inhibition improves disposition index, but the mechanism of this effect has not been elucidated and may depend on duration. In addition, increasing cyclic GMP without increasing nitric oxide could have beneficial effects on fibrinolytic balance.

OBJECTIVE

The objective was to test the hypothesis that chronic phosphodiesterase 5 inhibition with sildenafil improves insulin sensitivity and secretion without diminishing fibrinolytic function.

DESIGN

This was a randomized, double-blind, placebo-controlled study.

SETTING

This trial was conducted at Vanderbilt Clinical Research Center.

PARTICIPANTS

Participants included overweight individuals with prediabetes.

INTERVENTIONS

Subjects were randomized to treatment with sildenafil 25 mg three times a day or matching placebo for 3 months. Subjects underwent a hyperglycemic clamp prior to and at the end of treatment.

MAIN OUTCOME MEASURES

The primary outcomes of the study were insulin sensitivity and glucose-stimulated insulin secretion.

RESULT

Twenty-one subjects completed each treatment arm. After 3 months, the insulin sensitivity index was significantly greater in the sildenafil group compared to the placebo group by 1.84 mg/kg/min per μU/mL*100 (95% confidence interval, 0.01 to 3.67 mg/kg/min per μU/mL*100; P = .049), after adjusting for baseline insulin sensitivity index and body mass index. In contrast, there was no effect of 3-month treatment with sildenafil on acute- or late-phase glucose-stimulated insulin secretion (P > .30). Sildenafil decreased plasminogen activator inhibitor-1 (P = .01), without altering tissue-plasminogen activator. In contrast to placebo, sildenafil also decreased the urine albumin-to-creatinine ratio from 12.67 ± 14.67 to 6.84 ± 4.86 μg/mg Cr. This effect persisted 3 months after sildenafil discontinuation.

CONCLUSIONS

Three-month phosphodiesterase 5 inhibition enhances insulin sensitivity and improves markers of endothelial function.

Angiotensin converting enzyme inhibition increases ADMA concentration in patients on maintenance hemodialysis--a randomized cross-over study

Background

Endothelial dysfunction occurs in patients with end-stage renal disease (ESRD) and is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA) contributes to endothelial dysfunction in ESRD. In the general population, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) decrease ADMA levels, but no study has compared the effect of these drugs in patients with ESRD on maintenance hemodialysis (MHD).

Methods

We evaluated the effect of 1-week treatment with ramipril (5 mg/d), valsartan (160 mg/d), and placebo on ADMA levels in 15 patients on MHD in a double-blind, placebo-controlled, three x three cross-over study.

Results

We found that ADMA levels were increased at baseline and throughout the dialysis session during ramipril treatment (p < 0.001 compared to both, placebo and valsartan). Ramipril did not increase ADMA levels in a study of patients without ESRD, suggesting that factors related to ESRD or hemodialysis contribute to the ACE inhibitor-induced increase in ADMA. We have previously shown that ACE inhibition increases bradykinin (BK) levels during hemodialysis. We therefore evaluated the effect of bradykinin on ADMA production in A549 cells; a cell line that expresses BK receptors. Incubation with BK increased intracellular ADMA concentration through BK B2-receptor stimulation.

Conclusion

These data indicate that short-term ACE inhibition increases ADMA in patients on MHD whereas ARBs do not. In vitro studies further suggest that this may occur through BK-mediated increase in ADMA production during ACE inhibition.

Trial registration

Clinicaltrials.gov NCT00732069 August 6 2008 and NCT00607672 February 4 2008

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-015-0162-x) contains supplementary material, which is available to authorized users.

Abstract 119: The Imbalance of Mitochondrial Superoxide Dismutase Activity and Superoxide Production in Endothelial Dysfunction and Hypertension

Clinical studies have shown that Sirt3 expression declines by 40% by age 65 paralleling the increased incidence of hypertension and metabolic conditions further inactivate Sirt3 due to increased NADH and Acetyl-CoA. Sirt3 activates a major mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2) by deacetylation of specific lysine residues. We hypothesized that loss of Sirt3 activity increases vascular oxidative stress due to SOD2 hyperacetylation and this promotes endothelial dysfunction and hypertension. Indeed, Western blot analysis showed 3-fold increase in SOD2 acetylation and 1.5-fold decrease in Sirt3 level in hypertensive human subjects. Infusion of angiotensin II (0.7 mg/kg/day) in C57Bl/6J mice increased acetylation of vascular SOD2 by 2-fold, reduced SOD2 activity to 52% and raised blood pressure to 156 mm Hg. We have tested if Sirt3 depletion exacerbates endothelial dysfunction and hypertension. Indeed, Western blot analysis of Sirt3-/- mice showed SOD2 hyperacetylation and reduced SOD2 activity, however, blood pressure and superoxide production was normal. Angiotensin II infusion in Sirt3-/- mice increased blood pressure to 182 mm Hg, increased superoxide, reduced endothelial nitric oxide and impaired acetylcholine-mediated vasodilatation compared with angiotensin II infused wild type mice. Treatment of hypertensive Sirt3-/- mice with SOD2 mimetic mitoTEMPO (1.4 mg/kg/day) after onset of angiotensin II-induced hypertension normalized blood pressure and restored endothelial dependent vasodilatation. We suggest that mitochondrial superoxide does not contribute to the basal vasodilation and blood pressure regulation however high salt, angiotensin II and inflammation increase mitochondrial superoxide. Indeed, superoxide production by complex I in submitochondrial particles was significantly increased in hypertensive mice and this was associated with complex I S-glutathionylation. Interestingly, SOD2 overexpression in transgenic mice prevents complex I S-glutathionylation, reduces superoxide production by complex I and attenuates hypertension. These data indicate that imbalance of SOD2 activity and mitochondrial superoxide production contributes to endothelial dysfunction and hypertension.

Abstract P253: Angiotensin Converting Enzyme Inhibition vs. Angiotensin II Receptor Blockade in Marfan Mouse: Role of Bradykinin

Angiotensin receptor blockers (ARB) decrease aortic root aneurysm progression in a mouse model of Marfan syndrome, by interfering with angiotensin II (Ang II) activation of transforming growth factor beta (TGF-β) signaling. Angiotensin converting-enzyme inhibitors (ACEi) decrease the formation of Ang II, but also increase bradykinin (BK) which can activate the TGF-β pathway. We tested the hypothesis that ACEi and ARBs differ in their effect on aortic aneurysm development in Fbn1C1039G/+ mice due to different effects on BK. We compared the effect of 12-week treatment with telmisartan (3 and 24 mg/L), ramipril (30mg/L) or placebo in the presence or absence of the BK B2 receptor antagonist HOE140 (0.1 mg/Kg/day). ARB and ACEi reduced blood pressure similarly. ARB and ACEi reduced aortic root diameter (by 17.3±3% and 19.1±5%) but only ARB prevented elastin disruption (Figures 1A and 1B), decreased mast cell infiltration and P-ERK immunoreactivity in the ascending aorta. HOE-140 alone did not reduce the aortic root diameter but diminished the aortic elastin disruption. In the lung, ARB compared to ACEi treatment, prevented the development of emphysematous changes (Figure 1C), decreased mast cell infiltration (4.87±0.98% vs. 9.12±1.23%, p=0.012), and decreased MMP12 (1.02±0.08 vs. 1.52±0.13 A.U, p=0.002) and MMP9 (1.32±0.08 vs. 1.69±0.11 A.U, p=0.006) activity. HOE-140 alone prevented emphysematous changes and decreased MMP12 activity. Endogenous BK contributes to elastin disruption in the aortic root and lung by promoting activation of P-ERK and increasing MMP12 activity, respectively. Clinical studies are required to compare the efficacy of ACEi and ARB in Marfan syndrome.

Gender-specific effects of depression and suicidal ideation in prosocial behaviors

Background

Prosocial behaviors are essential to the ability to relate to others. Women typically display greater prosocial behavior than men. The impact of depression on prosocial behaviors and how gender interacts with those effects are not fully understood. We explored the role of gender in the potential effects of depression on prosocial behavior.

Methods

We examined prosocial behaviors using a modified version of the Trust Game in a clinical population and community controls. Study participants were characterized on the severity of depression and anxiety, presence of suicidal ideation, history of childhood trauma, recent stressful life events, and impulsivity. We correlated behavioral outcomes with gender and clinical variables using analysis of variance and multiple regression analysis.

Results

The 89 participants comprised four study groups: depressed women, depressed men, healthy women and healthy men (n = 16–36). Depressed men exhibited reciprocity more frequently than healthy men. Depression induced an inversion of the gender-specific pattern of self-centered behavior. Suicidal ideation was associated with increased reciprocity behavior in both genders, and enhancement of the effect of depression on gender-specific self-centered behavior.

Conclusions

Depression, particularly suicidal ideation, is associated with reversal of gender-specific patterns of prosocial behavior, suggesting abnormalities in sexual hormones regulation. This explanation is supported by known abnormalities in the hypothalamus-pituitary-adrenal and hypothalamus-pituitary-gonadal axes found in depression.

Abstract 230: Angiotensin-Converting Enzyme Inhibition Increases ADMA Concentration in Patients on Hemodialysis

Endothelial dysfunction occurs commonly in patients with end-stage renal disease (ESRD) and is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA), an inhibitor of nitric oxidase synthase, is elevated in patients with chronic kidney disease and contributes to endothelial dysfunction in ESRD. In the general population, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) decrease ADMA levels, but no study has compared the effect of these drugs in patients with ESRD on hemodialysis. We therefore evaluated the effect of one-week treatment with ramipril (5 mg/d), valsartan (160 mg/d) and placebo on ADMA levels in fifteen patients on hemodialysis in a previously published double-blind, placebo-controlled, 3X3 cross-over study. We found that ADMA levels were increased at baseline and throughout the dialysis session during ramipril treatment (Figure 1, p<0.001 compared to both placebo and valsartan). Ramipril did not increase ADMA levels in a study of patients without ESRD, suggesting that factors related to ESRD or hemodialysis contribute to the ACE inhibitor-induced increase in ADMA levels. We have previously shown that ACE inhibition increases bradykinin (BK) levels during hemodialysis. Therefore, we evaluated the effect of BK on ADMA production in A549 cells; incubation with BK increased intracellular ADMA concentration through bradykinin B2- receptor (B2R) stimulation (Figure 2). In conclusion, ACE inhibition increases ADMA in patients on hemodialysis. Studies in vitro suggest that this could occur through a bradykinin-mediated increase in ADMA production.

Whole genome sequencing of Ethiopian highlanders reveals conserved hypoxia tolerance genes

BACKGROUND

Although it has long been proposed that genetic factors contribute to adaptation to high altitude, such factors remain largely unverified. Recent advances in high-throughput sequencing have made it feasible to analyze genome-wide patterns of genetic variation in human populations. Since traditionally such studies surveyed only a small fraction of the genome, interpretation of the results was limited.

RESULTS

We report here the results of the first whole genome resequencing-based analysis identifying genes that likely modulate high altitude adaptation in native Ethiopians residing at 3,500 m above sea level on Bale Plateau or Chennek field in Ethiopia. Using cross-population tests of selection, we identify regions with a significant loss of diversity, indicative of a selective sweep. We focus on a 208 kbp gene-rich region on chromosome 19, which is significant in both of the Ethiopian subpopulations sampled. This region contains eight protein-coding genes and spans 135 SNPs. To elucidate its potential role in hypoxia tolerance, we experimentally tested whether individual genes from the region affect hypoxia tolerance in Drosophila. Three genes significantly impact survival rates in low oxygen: cic, an ortholog of human CIC, Hsl, an ortholog of human LIPE, and Paf-AHα, an ortholog of human PAFAH1B3.

CONCLUSIONS

Our study reveals evolutionarily conserved genes that modulate hypoxia tolerance. In addition, we show that many of our results would likely be unattainable using data from exome sequencing or microarray studies. This highlights the importance of whole genome sequencing for investigating adaptation by natural selection.

Whole-genome sequencing uncovers the genetic basis of chronic mountain sickness in Andean highlanders

The hypoxic conditions at high altitudes present a challenge for survival, causing pressure for adaptation. Interestingly, many high-altitude denizens (particularly in the Andes) are maladapted, with a condition known as chronic mountain sickness (CMS) or Monge disease. To decode the genetic basis of this disease, we sequenced and compared the whole genomes of 20 Andean subjects (10 with CMS and 10 without). We discovered 11 regions genome-wide with significant differences in haplotype frequencies consistent with selective sweeps. In these regions, two genes (an erythropoiesis regulator, SENP1, and an oncogene, ANP32D) had a higher transcriptional response to hypoxia in individuals with CMS relative to those without. We further found that downregulating the orthologs of these genes in flies dramatically enhanced survival rates under hypoxia, demonstrating that suppression of SENP1 and ANP32D plays an essential role in hypoxia tolerance. Our study provides an unbiased framework to identify and validate the genetic basis of adaptation to high altitudes and identifies potentially targetable mechanisms for CMS treatment.

Comparative effects of angiotensin-converting enzyme inhibition and angiotensin-receptor blockade on inflammation during hemodialysis

Biomarkers of oxidative stress and inflammation predict cardiovascular events in maintenance hemodialysis patients. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin-receptor blockers (ARBs) reduce cardiovascular mortality in the general population, but their benefit in maintenance hemodialysis patients is not fully explored. To test whether ACE inhibitors and ARBs differentially affect markers of oxidative stress, inflammation, and fibrinolysis during hemodialysis, we conducted a randomized, double-blind, placebo-controlled 3×3 crossover study. We randomly assigned 15 participants undergoing hemodialysis to placebo, ramipril (5 mg/d), and valsartan (160 mg/d) for 7 days, with a washout period of 3 weeks in between the treatments. On the morning of the seventh day of drug treatment, participants underwent serial blood sampling during hemodialysis. Neither ramipril nor valsartan affected BP during hemodialysis. Ramipril increased IL-1β concentrations (P=0.02) and decreased IL-10 concentrations (P=0.04) compared with placebo. Valsartan and ramipril both lowered IL-6 levels during dialysis (P<0.01 for each compared with placebo). Valsartan increased F(2)-isoprostane levels, and ramipril suggested a similar trend (P=0.09). Valsartan and ramipril both lowered D-dimer levels (P<0.01 for both), whereas only ramipril seemed to prevent a rise in vWf levels (P=0.04). In summary, during hemodialysis, valsartan induces a greater anti-inflammatory effect compared with ramipril, although ramipril seems to prevent dialysis-induced endothelial dysfunction as measured by levels of vWf. A prospective clinical trial is necessary to determine whether ACE inhibitors and ARBs also differ with respect to their effects on cardiovascular mortality in this population.

Muscle endurance and mitochondrial function after chronic normobaric hypoxia: contrast of respiratory and limb muscles

Skeletal muscle adaptation to chronic hypoxia includes loss of oxidative capacity and decrease in fiber size. However, the diaphragm may adapt differently since its activity increases in response to hypoxia. Thus, we hypothesized that chronic hypoxia would not affect endurance, mitochondrial function, or fiber size in the mouse diaphragm. Adult male mice were kept in normoxia (control) or hypoxia (hypoxia, FIO(2) = 10%) for 4 weeks. After that time, muscles were collected for histological, biochemical, and functional analyses. Hypoxia soleus muscles fatigued faster (fatigue index higher in control, 21.5 ± 2.6% vs. 13.4 ± 2.4%, p < 0.05), but there was no difference between control and hypoxia diaphragm bundles. Mean fiber cross-sectional area was unchanged in hypoxia limb muscles, but it was 25% smaller in diaphragm (p < 0.001). Ratio of capillary length contact to fiber perimeter was significantly higher in hypoxia diaphragm (28.6 ± 1.2 vs. 49.3 ± 1.4, control and hypoxia, p < 0.001). Mitochondrial respiration rates in hypoxia limb muscles were lower: state 2 decreased 19%, state 3 31%, and state 4 18% vs. control, p < 0.05 for all comparisons. There were similar changes in hypoxia diaphragm: state 3 decreased 29% and state 4 17%, p < 0.05. After 4 weeks of hypoxia, limb muscle mitochondria had lower content of complex IV (cytochrome c oxidase), while diaphragm mitochondria had higher content of complexes IV and V (F (1)/F (0) ATP synthase) and less uncoupling protein 3 (UCP-3). These data demonstrate that diaphragm retains its endurance during chronic hypoxia, apparently due to a combination of morphometric changes and optimization of mitochondrial energy production.

Rat diaphragm mitochondria have lower intrinsic respiratory rates than mitochondria in limb muscles

The mitochondrial content of skeletal muscles is proportional to activity level, with the assumption that intrinsic mitochondrial function is the same in all muscles. This may not hold true for all muscles. For example, the diaphragm is a constantly active muscle; it is possible that its mitochondria are intrinsically different compared with other muscles. This study tested the hypothesis that mitochondrial respiration rates are greater in the diaphragm compared with triceps surae (TS, a limb muscle). We isolated mitochondria from diaphragm and TS of adult male Sprague Dawley rats. Mitochondrial respiration was measured by polarography. The contents of respiratory complexes, uncoupling proteins 1, 2, and 3 (UCP1, UCP2, and UCP3), and voltage-dependent anion channel 1 (VDAC1) were determined by immunoblotting. Complex IV activity was measured by spectrophotometry. Mitochondrial respiration states 3 (substrate and ADP driven) and 5 (uncoupled) were 27 ± 8% and 24 ± 10%, respectively, lower in diaphragm than in TS (P < 0.05 for both comparisons). However, the contents of respiratory complexes III, IV, and V, UCP1, and VDAC1 were higher in diaphragm mitochondria (23 ± 6, 30 ± 8, 25 ± 8, 36 ± 15, and 18 ± 8% respectively, P ≤ 0.04 for all comparisons). Complex IV activity was 64 ± 16% higher in diaphragm mitochondria (P ≤ 0.01). Mitochondrial UCP2 and UCP3 content and complex I activity were not different between TS and diaphragm. These data indicate that diaphragm mitochondria respire at lower rates, despite a higher content of respiratory complexes. The results invalidate our initial hypothesis and indicate that mitochondrial content is not the only determinant of aerobic capacity in the diaphragm. We propose that UCP1 and VDAC1 play a role in regulating diaphragm aerobic capacity.

Chronic hypoxia increases insulin-stimulated glucose uptake in mouse soleus muscle

People living at high altitude appear to have lower blood glucose levels and decreased incidence of diabetes. Faster glucose uptake and increased insulin sensitivity are likely explanations for these findings: skeletal muscle is the largest glucose sink in the body, and its adaptation to the hypoxia of altitude may influence glucose uptake and insulin sensitivity. This study tested the hypothesis that chronic normobaric hypoxia increases insulin-stimulated glucose uptake in soleus muscles and decreases plasma glucose levels. Adult male C57BL/6J mice were kept in normoxia [fraction of inspired O₂ = 21% (Control)] or normobaric hypoxia [fraction of inspired O₂ = 10% (Hypoxia)] for 4 wk. Then blood glucose and insulin levels, in vitro muscle glucose uptake, and indexes of insulin signaling were measured. Chronic hypoxia lowered blood glucose and plasma insulin [glucose: 14.3 ± 0.65 mM in Control vs. 9.9 ± 0.83 mM in Hypoxia (P < 0.001); insulin: 1.2 ± 0.2 ng/ml in Control vs. 0.7 ± 0.1 ng/ml in Hypoxia (P < 0.05)] and increased insulin sensitivity determined by homeostatic model assessment 2 [21.5 ± 3.8 in Control vs. 39.3 ± 5.7 in Hypoxia (P < 0.03)]. There was no significant difference in basal glucose uptake in vitro in soleus muscle (1.59 ± 0.24 and 1.71 ± 0.15 μmol·g⁻¹·h⁻¹ in Control and Hypoxia, respectively). However, insulin-stimulated glucose uptake was 30% higher in the soleus after 4 wk of hypoxia than Control (6.24 ± 0.23 vs. 4.87 ± 0.37 μmol·g⁻¹·h⁻¹, P < 0.02). Muscle glycogen content was not significantly different between the two groups. Levels of glucose transporters 4 and 1, phosphoinositide 3-kinase, glycogen synthase kinase 3, protein kinase B/Akt, and AMP-activated protein kinase were not affected by chronic hypoxia. Akt phosphorylation following insulin stimulation in soleus muscle was significantly (25%) higher in Hypoxia than Control (P < 0.05). Neither glycogen synthase kinase 3 nor AMP-activated protein kinase phosphorylation changed after 4 wk of hypoxia. These results demonstrate that the adaptation of skeletal muscles to chronic hypoxia includes increased insulin-stimulated glucose uptake.

Mitochondrial content and distribution changes specific to mouse diaphragm after chronic normobaric hypoxia

Chronic hypoxia reduces aerobic capacity (mitochondrial content) in limb skeletal muscles, and one of the causes seems to be decreased physical activity. Diaphragm and other respiratory muscles, however, may have a different pattern of adaptation as hypoxia increases the work of breathing. Thus, we hypothesized that chronic hypoxia would not reduce mitochondrial content in mouse diaphragm. Adult male C57BL/6J mice were kept in normoxia (Fi(O(2)) = 21%, control) or normobaric hypoxia (Fi(O(2)) = 10%, hypoxia) for 1, 2, and 4 wk. Mice were then killed, and the diaphragm and gastrocnemius muscles collected for analysis. In the diaphragm, cytochrome c oxidase histochemistry showed less intense staining in the hypoxia group. The total content of subunits from the electron transport chain, pyruvate dehydrogenase kinase 1 (PDK1), and voltage-dependent anion channel 1 (VDAC1) was evaluated by Western blot. These proteins decreased by 25-30% after 4 wk of hypoxia (P < 0.05 vs. control for all comparisons), matching a comparable decrease in diaphragmatic mitochondrial volume density (control 33.6 +/- 5.5% vs. hypoxia 26.8 +/- 6.7%, P = 0.013). Mitochondrial volume density or protein content did not change in gastrocnemius after hypoxia. Hypoxia decreased the content of peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgamma cofactor 1-alpha (PGC-1alpha) in diaphragm but not in gastrocnemius. PGC-1alpha mRNA levels in diaphragm were also reduced with hypoxia. BCL2/adenovirus E1B interacting protein 3 (BNIP-3) mRNA levels were upregulated after 1 and 2 wk of hypoxia in diaphragm and gastrocnemius, respectively; BNIP-3 protein content increased only in the diaphragm after 4 wk of hypoxia. Contrary to our hypothesis, these results show that chronic hypoxia decreases mitochondrial content in mouse diaphragm, despite the increase in workload. A combination of reduced mitochondrial biogenesis and increased mitophagy seems to be responsible for the decrease in mitochondrial content in the mouse diaphragm after hypoxia.

Lower respiratory capacity in extraocular muscle mitochondria: evidence for intrinsic differences in mitochondrial composition and function

PURPOSE

The constant activity of the extraocular muscles is supported by abundant mitochondria. These organelles may enhance energy production by increasing the content of respiratory complexes. The authors tested the hypothesis that extraocular muscle mitochondria respire faster than do mitochondria from limb muscles because of the higher content of respiratory complexes.

METHODS

Inner mitochondrial membrane density was determined by stereological analysis of triceps surae (a limb muscle) and extraocular muscles of adult male Sprague-Dawley rats. The authors measured respiration rates of isolated mitochondria using a Clark-type electrode. The activity of respiratory complexes I, II, and IV was determined by spectrophotometry. The content of respiratory complexes was estimated by Western blot.

RESULTS

States 3, 4, and 5 respiration rates in extraocular muscle mitochondria were 40% to 60% lower than in limb muscle mitochondria. Extraocular muscle inner mitochondrial membrane density was similar to that of other skeletal muscles. Activity of complexes I and IV was lower in extraocular muscle mitochondria (approximately 50% the activity in triceps), but their content was approximately 15% to 30% higher. There was no difference in complex II content or activity or complex III content. Finally, complex V was less abundant in extraocular muscle mitochondria.

CONCLUSIONS

The results demonstrate that extraocular muscle mitochondria respire at slower rates than mitochondria from limb muscles, despite similar mitochondrial ultrastructure. Instead, differences were found in the activity (I, IV) and content (I, IV, V) of electron transport chain complexes. The discrepancy between activity and content of some complexes is suggestive of alternative subunit isoform expression in the extraocular muscles compared with limb muscles.

Abnormal energy regulation in early life: childhood gene expression may predict subsequent chronic mountain sickness

BACKGROUND

Life at altitude depends on adaptation to ambient hypoxia. In the Andes, susceptibility to chronic mountain sickness (CMS), a clinical condition that occurs to native highlanders or to sea level natives with prolonged residence at high altitude, remains poorly understood. We hypothesized that hypoxia-associated gene expression in children of men with CMS might identify markers that predict the development of CMS in adults. We assessed distinct patterns of gene expression of hypoxia-responsive genes in children of highland Andean men, with and without CMS.

METHODS

We compared molecular signatures in children of highland (HA) men with CMS (n = 10), without CMS (n = 10) and in sea level (SL) children (n = 20). Haemoglobin, haematocrit, and oxygen saturation were measured. Gene expression in white cells was assessed at HA and then, in the same subjects, within one hour of arrival at sea level.

RESULTS

HA children showed higher expression levels of genes regulated by HIF (hypoxia inducible factor) and lower levels of those involved in glycolysis and in the tricarboxylic acid (TCA) cycle. Pyruvate dehydrogenase kinase 1(PDK1) and HIF prolyl hydroxylase 3 (HPH3) mRNA expressions were lowest in children of CMS fathers at altitude. At sea level the pattern of gene expression in the 3 children's groups was indistinguishable.

CONCLUSION

The molecular signatures of children of CMS patients show impaired adaptation to hypoxia. At altitude children of CMS fathers had defective coupling between glycolysis and mitochondria TCA cycle, which may be a key mechanism/biomarker for adult CMS. Early biologic markers of disease susceptibility in Andeans might impact health services and social planning.

Adaptation and mal-adaptation to ambient hypoxia; Andean, Ethiopian and Himalayan patterns

The study of the biology of evolution has been confined to laboratories and model organisms. However, controlled laboratory conditions are unlikely to model variations in environments that influence selection in wild populations. Thus, the study of “fitness” for survival and the genetics that influence this are best carried out in the field and in matching environments.

Therefore, we studied highland populations in their native environments, to learn how they cope with ambient hypoxia. The Andeans, African highlanders and Himalayans have adapted differently to their hostile environment.

Chronic mountain sickness (CMS), a loss of adaptation to altitude, is common in the Andes, occasionally found in the Himalayas; and absent from the East African altitude plateau.

We compared molecular signatures (distinct patterns of gene expression) of hypoxia-related genes, in white blood cells (WBC) from Andeans with (n = 10), without CMS (n = 10) and sea-level controls from Lima (n = 20) with those obtained from CMS (n = 8) and controls (n = 5) Ladakhi subjects from the Tibetan altitude plateau. We further analyzed the expression of a subset of these genes in Ethiopian highlanders (n = 8). In all subjects, we performed the studies at their native altitude and after they were rendered normoxic.

We identified a gene that predicted CMS in Andeans and Himalayans (PDP2). After achieving normoxia, WBC gene expression still distinguished Andean and Himalayan CMS subjects.

Remarkably, analysis of the small subset of genes (n = 8) studied in all 3 highland populations showed normoxia induced gene expression changes in Andeans, but not in Ethiopians nor Himalayan controls. This is consistent with physiologic studies in which Ethiopians and Himalayans show a lack of responsiveness to hypoxia of the cerebral circulation and of the hypoxic ventilatory drive, and with the absence of CMS on the East African altitude plateau.

Plasma catecholamines and blood volume in native Andeans during hypoxia and normoxia

Plasma catechols and blood volume were measured in 20 male, native high-altitude residents of Cerro de Pasco, Peru (4338 m), while hypoxic and subsequently while normoxic at sea level. Ten subjects were healthy controls,with hematocrits lower than 61%, and ten had chronic mountain sickness (CMS), a syndrome of maladaptation to altitude, characterized by polycythemia (hematocrit > 61%), profound hypoxemia, and neurologic symptoms. The main aim of the study was to evaluate the chronic effects of hypoxia on plasma catechols and on blood volume, by studying these parameters during hypoxia at high altitude (HA) and shortly after exposure to normoxia at sea level (SL). Subjects were first studied at HA in their habitual hypoxic environment, and measurements were repeated within 4 hours of arrival at SL (Lima, Peru, 150 m). All subjects had higher plasma norepinephrine (NE), dopamine (DA), and dihydroxyphenylglycol (DHPG) levels in HA (NE in controls and CMS: 414+/-47 and 514+/-35 pg/mL; DA: 9+/-1 and 13+/-1 pg/mL, DHPG: 817+/-48 and 972+/-77 pg/mL) than at SL (NE: 164+/-9 and 243+/-28 pg/mL; DA: 4+/-0.5 and 5+/-1 pg/mL DHPG: 502+/-23 and 649+/-39 pg/mL). Group differences were statistically significant only for NE in the CMS group. Plasma volume was higher in HA in both groups (p<0.05); red cell volume was higher in HA only in the CMS group. The results indicate sympathetic nervous stimulation by chronic ambient hypoxia at altitude in Andean natives, independent of maladaptation to their native environment.

Peroxisome proliferator-activated receptor-γ ligands reduce inflammation and infarction size in transient focal ischemia

Newly developed insulin-sensitizing agents, which target the nuclear receptor peroxisome proliferator-activated receptor-gamma have recently been appreciated to exhibit potent anti-inflammatory actions. Since stroke is associated with an intense inflammatory response, we reasoned that these agents may ameliorate injury from stroke. We report that administration of troglitazone or pioglitazone 24 h before and at the time of cerebral infarction dramatically reduced infarction volume and improved neurological function following middle cerebral artery occlusion in rats. Furthermore, we find that delayed therapy also significantly reduced infarct volume. The brains of the drug-treated animals displayed reduced inflammation as evidenced by decreased immunoreactivity for microglial/macrophage markers and reduced protein and mRNA for interleukin-1beta, cyclooxygenase-2 and inducible nitric oxide synthase. We argue that the beneficial effects of these drugs are likely due to reduced expression of these inflammatory mediators, which are known to exacerbate ischemic injury following stroke. These results are of particular relevance to diabetic patients chronically treated with these agents who may benefit from the neuroprotective actions of these drugs.

Neuronal migration is transiently delayed by prenatal exposure to intermittent hypoxia

BACKGROUND

Neonatal neurodevelopment is influenced by a variety of external factors, although the mechanisms responsible are poorly understood. Prenatal hypoxia, from physiological or chemical sources, can have no discernible effect, or can result in a broad spectrum of abnormalities.

METHODS

To mimic some of the maternal effects of smoking, we developed a model that investigates the effects of intermittent hypoxia (IH), with or without concurrent nicotine in timed pregnant Sprague-Dawley rats.

RESULTS

We found no significant differences between litter sizes or birthweight of pups from any treatment group, but animals exposed to IH (with or without nicotine) showed long term diminished body weights. Animals subjected to IH consistently showed a transient delay in neuronal migration early in the postpartum period, which was amplified by concurrent nicotine administration. We observed increased c-Abl protein levels in animals from the IH treatment groups. Multiple proteins involved in the intricate control of neuronal migration were also altered in response to this treatment, primarily the downstream targets of c-Abl: Cdk5, p25, and the cytoskeletal elements neurofilament H and F-actin and catalase. Catalase activity and protein levels, already elevated in response to IH, were further amplified by simultaneous nicotine exposure.

CONCLUSIONS

This new model provides a novel system for investigating the effects of low grade IH in the developing brain and suggests that concurrent nicotine further aggravates many of the deleterious effects of IH.

Acral paresthesias in the Andes and neurology at sea level

BACKGROUND

Thirty-nine percent of permanent altitude dwellers in the Andes experience acral paresthesias.

METHODS

Clinical examinations, sural nerve biopsies, and electrodiagnostic studies on peripheral nerves were performed on 15 men. Ten Cerro de Pasco (CP) natives living at 4,338 meters were biopsied. Three of these subjects had no burning feet/burning hands (BF/BH); three had BF/BH; and four had chronic mountain sickness (CMS), a maladaptation syndrome resulting from living in the Andes, all with BF/BH. Three patients with CMS were biopsied in Lima within hours after leaving CP. Two normal Lima natives were biopsied in Lima. Symptom scores for BF/BH and CMS score ratings were used. The nerves were assayed for Na+, K+ adenosine triphosphatase (ATPase), cytochrome oxidase (CO), substance P (SP), and endothelin (ET).

RESULTS

Low ATPase was inversely related to symptom scores and CMS scores (p < 0.001). Patients with CMS biopsied in normoxia (Lima) had ATPase levels similar to those of controls. Nerve motor conduction velocities and sensory action potentials were normal. CO was inversely related to age (p < 0.03) and no relation of SP to any variable was found. ET levels were lower in sea level natives (p = 0.04).

CONCLUSIONS

Acral paresthesias are associated with low ATPase in peripheral nerves. Lower ET levels of sea level natives likely reflect lowered release from vasa nervorum.

Energetic metabolism in mouse cerebral cortex during chronic hypoxia

We measured the activities of Na(+)K(+) ATPase and of enzymes of the glycolytic pathway, Krebs cycle, and the respiratory chain in cerebral cortex of mice exposed to chronic hypoxia for three weeks and compared their values with those of sea level controls. There were no differences in Na(+)K(+) ATPase activity or in the activity of glycolytic enzymes. In the Krebs cycle, a 66% increase of succinate dehydrogenase activity was found due to a lower Km. In contrast, respiratory chain cytochrome oxidase activity was reduced by 12% in mice exposed to hypoxia. This suggested that the metabolic demand would be satisfied despite the respiratory chain depression (cytochrome oxidase), probably due to anaerobic energy production within the mitochondria (succinate dehydrogenase).