Snyder, Eric M.

Duchenne muscular dystrophy (DMD) is an inheritable disease that presents itself in diminished respiratory function and is the main contributor to mortality in these patients. The main respiratory concerns in DMD are reduced diaphragmatic function, reduced mucocilliary clearance, increased muscle proteolysis, and increased inflammation. The Gly16 variant of the β 2 ‐adrenergic receptor (ADRB2) has been identified as providing a protective effect for respiratory weakness. The aim of this study was to identify the influence of ADRB2 genotype on the age of use for nocturnal ventilatory assistance in DMD. Data from CINRG‐DNHS including 175 DMD patients (ages 3–25 years) with up to 9.7 years follow‐up were analyzed focusing on ADRB2 functional variants. We performed Cox proportional hazard and Kaplan‐Meier time to event analyses for the age of nocturnal ventilation use. There were no differences between genotype groups in age, height, weight, corticosteroid use, number of ambulatory patients, or age of loss of ambulation. The genotype groups differed significantly in the age at which nocturnal ventilation use was prescribed with the Gly16 demonstrating a 2.77‐fold increased risk of using nocturnal ventilation at any given age. These data suggest that genetic variations in the ADRB2 gene may influence the age of nocturnal ventilation use in DMD. Specifically, the Gly16 polymorphism of the ADRB2 may have a deleterious effect on age of nocturnal ventilation use in DMD. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Background Hypertension (HTN) has a strong heritable component and the effectiveness of the treatment for HTN has been shown to be influenced by monogenic guidance. Each of the common HTN pharmacotherapies is ~50% effective in the population and layering blood pressure (BP) medications increases side effects and decreases medication adherence. HTN is a complex disease with primary interactions between the heart, vasculature, and kidney. Known and common genetic variants of each these organs have well‐described mechanisms. Despite the established bell‐curve response to treatment, the complexity of HTN, and functional variants of the major organ systems in HTN: no guidance, to date, utilizes a multi‐gene approach to guide BP therapy. Purpose To assess the association between a weighted multi‐gene algorithm and BP control in patients with HTN. Methods Non‐smokers with a family history of HTN were included in the analysis (n=384; age=61.0±0.9, 11% non‐white). 17 genotypes (ADRB1(2 SNPs), ADRB2 (2SNPs), CYP2D6, WNK (3SNPs), SLC12A3, SCNN1A, alpha‐adducin, renin, angiotensin (3 SNPs), ACE, and the angiotensin receptor) were weighted according to previous effect size in the literature (ΔBP when on the target therapy vs. not) as well as the number of peer‐reviewed papers of quality supporting each functional variant. After weighting, each genotype was entered into an algorithm that assessed pairing (e.g. homozygosity of functional ADRB1 is responsive to β‐blockade, heterozygosity is less responsive, and homozygosity of non‐functional is least responsive) within and between organ systems to predict the pharmacotherapy with greatest impact for each individual patient. Each pharmacotherapy was ranked from 1–4 as most to least likely to respond based on the algorithmic assessment of individual patient's genotypes. Three‐years of data was assessed at six‐month intervals for BP and medication history. Current and past pharmacotherapies were also assessed via chart review. Results There was no difference in initial BP at diagnosis between groups matching the top drug recommendation using the multi‐gene weighted algorithm (n=92) vs. those who did not match (n=292). However, from diagnosis to nadir, patients who matched the primary recommendation had a significantly greater drop in BP when compared to patients who did not (ΔSBP= −39.2±2.4 vs. −32.1±1.3mmHg , ΔDBP= −19.4±1.1 vs. −14.0±1.3mmHg , ΔMAP= −24.4±2.1 vs. −19.0±1.2mmHg, respectively, p<0.05 for SBP and DBP). Further, the difference between diagnosis to current 1yr. average BP was lower in the group that matched the top recommendation (ΔSBP= −33.2±2.3 vs. −27.4±1.2mmHg, ΔDBP=−14.8±1.1 vs. −11.5±1.2, ΔMAP= −21.2±2.3 vs. −15.6±1.8, respectively, p<0.05 for SBP and MAP). Conclusions These data suggest an association between a weighted multi‐gene algorithm on the BP response to pharmacotherapy. This magnitude of difference has previously been shown to be associated with a significant reduction in heart attack and stroke risk. Support or Funding Information Geneticure, Inc. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

The ability to work efficiently at altitude is impaired by the reduced arterial oxygen tension. Acetazolamide may improve systemic saturation (SaO 2 ) by stimulating ventilation but increases the work of breathing. Efforts have focused on the potential role of sildenafil in improving exercise performance in high altitude environment. The purpose of this study was to determine the effects of acetazolamide and sildenafil on oxygen uptake (VO 2 ) and breathing efficiency during submaximal hypoxic exercise. Sixteen volunteers received sildenafil 40 mg (S), acetazolamide 125 mg (A) or matching placebo (P) tid × four doses in double‐blind fashion starting 8 hours prior to hypoxic exposure over 3 separate overnight stays in an altitude tent with an O 2 concentration of 12.5%, and then performed hypoxic submaximal exercise on a stationary bicycle for 10 min at a workload of 40% of VO 2 peak. SaO 2 decreased with exercise but there was no difference in exercising SaO 2 or VO 2 between conditions. As expected, acetazolamide increased ventilation compared to placebo and sildenafil. Breathing efficiency as measured by Ve/VCO 2 decreased with acetazolamide in comparison to placebo and sildenafil (P: 42.6±1.2, S: 41.9±1.6, A: 46.7±1.1, p<0.01). Sildenafil did not change breathing efficiency while acetazolamide reduced breathing efficiency during hypoxic exercise. This study was funded by Mayo Foundation and NIH Grant No. HL71478.

Reduced partial pressures of inspired O 2 may influence the bronchial circulation through a number of mechanisms (e.g. altered pulmonary and systemic vascular pressures, lung fluid regulation, airway cooling & drying from increased ventilation). The present study examined the impact of acute, graded hypoxia on bronchial blood flow (Q aw ) in eight healthy adults (28 ± 9 years). Subjects were exposed to inspired O 2 levels resulting in arterial O 2 saturation (SaO 2 ) values of 90% and 80% for 15 min each. To control for the mild hyperventilation that accompanies hypoxia, subjects then mimicked the 80% SaO 2 ventilation (V E ) rate with 21% FIO 2 and again with CO 2 added to the inspirate to maintain normocapnia. Q aw and cardiac output (CO) were measured using soluble gas techniques. Also measured were alveolar‐capillary conductance (D m , index of lung fluid balance), pulmonary capillary blood volume (V c ), and systemic mean (MAP) and pulmonary arterial pressures (PAP). Hypoxia resulted in minimal change in MAP, a small rise in PAP, minimal change in CO and V c , and a rise in D m . There was also a non significant decrease in Q aw with hypoxia. Mild hyperventilation resulted in a significant fall in Q aw , but when normocapnia was maintained, Q aw returned to baseline values. These data suggest that acute, graded hypoxic exposure does not significantly impact Q aw , however, the hypocapnia associated with mild hyperventilation reduces Q aw .

Epinephrine is a sympathomimetic which is derived from phenylalanine and tyrosine. The final step of epinephrine synthesis, the conversion from norepinephrine, relies on phenylethanolamine N‐methyltransferase (PNMT). The beta‐2 adrenergic receptor (ADRB2) binds to epinephrine and has several common functional polymorphisms including a Glycine (Gly) for Arginine (Arg) substitution at amino acid 16. We assessed the effect of the gene‐to‐gene interaction of these proteins on the ventricular response to exercise in healthy humans (n=69, age=29±6yrs, ht=174±10cm, wt=71±13kg). We found that within the 2*1 haplotype of the 5′FR, which has previously demonstrated greater epinephrine synthesis compared to 2*7 haplotype, the Arg16 genotype demonstrates lower stroke volume (SV) than the Gly16 genotype despite similar epinephrine levels and synthesis rates (Arg16= 75±5, Gly16=89±6ml/beat). Similarly, within the 2*7 haplotype of the 5′FR, which has demonstrated attenuated epinephrine synthesis compared to 2*1, the Arg16 genotype demonstrates a smaller SV than the Gly16 genotype (Arg16= 59±3, Gly16=78±6ml/beat). Additionally, the Arg16 and Gly16 subjects within the 2*1 haplotype of PNMT have greater stroke volume than their ADRB2 counterparts of the 2*7 haplotype of PNMT. These data demonstrate an interaction between the genes that encode PNMT and ADRB2 on the ventricular response to exercise.

The Gly allele of the Arg16/Gly β 2 ‐adrenergic receptor polymorphism has been associated with hypertension in a linkage analysis in Rochester, MN. Gly homozygotes have greater forearm β 2 ‐receptor mediated vasodilation than Arg after a normal Na + diet (150 mmol/day), and the difference is mediated by endothelial NO. To test the hypothesis that dietary Na + restriction affects β 2 ‐mediated dilation in these groups, we measured forearm blood flow (FBF, plethysmography) during brachial arterial infusion of isoproterenol (ISO) after 5 days of low dietary Na + (10 mmol/day), in healthy subjects homozygous for Arg (n=15, 8 women, 29 ± 8 yrs, mean ± SD) vs. Gly (n=17, 7 women, 31 ± 7 yrs). Baseline FBF did not differ between groups. ISO caused a significant increase in FBF that was not different based on genotype (P = 0.51, main effect of genotype; P = 0.72, genotype‐by‐ISO‐interaction). For example, the highest response to ISO was 10.3 ± 5.5 in Arg and 12.0 ± 4.4 ml/100 ml forearm vol/min in Gly (P t‐test = 0.33). NO inhibition with L‐NMMA decreased baseline FBF, and significantly blunted the response to ISO, but there was no evidence to suggest the responses were influenced by genotype (P = 0.89, genotype‐by‐ISO‐by‐L‐NMMA interaction). We conclude that greater NO‐mediated β 2 ‐receptor vasodilation in Gly homozygotes is no longer apparent following dietary Na + restriction, suggesting that greater dilator function in Gly homozygotes during normal Na + intake may be a protective vascular mechanism in a population where the Gly allele is associated with hypertension. Support: HL‐63328, GCRC RR‐00585, NCRR K23‐17520.

Pulmonary hypertension is common in patients with heart failure (HF); however, for a given degree of left ventricular dysfunction, the range in pulmonary artery pressures (PAP) is large. Polymorphisms of a number of candidate genes have been implicated in contributing to smooth muscle dysfunction and remodeling of the pulmonary vasculature, including the serotonin transporter (5HTT) gene. Patients with HF may have mild tissue hypoxia, which may alter expression of 5HTT. This study examined the influence of a repeat length polymorphism in the promoter region of the 5HTT gene on differences in PAP in HF patients. Ninety HF patients (age=55±14yrs; LVEF=28±10%; NYHA=2.0±0.9) and 90 age and gender matched controls (CTL, age=51±15yrs; LVEF=63±7%) were recruited. Heart failure and CTL subjects were divided into 3 genotype groups, SS‐homozygotes for the short variant, LL‐homozygotes for the long variant and LS‐heterozygous condition. For both HF and CTL, SS n=20; LS n=41; LL n=29). PAP was calculated from the tricuspid regurgitant velocity. Age and gender did not differ between HF and CTL or among genotype groups. PAP was higher in HF compared to CTL (38.9±12.5 vs 27.7±8.2 mmHg, p<0.01, respectively) with a significant genotype effect in HF (SS=34.2±8.6 vs LS=38.2±11.4 vs LL=43.2±15.2 mmHg, p<0.05), but not in CTL. The HF group also demonstrated elevated left atrial diameter compared to CTL (HF 48.0±8.7 vs 32.8±4.8 mm, p<0.01, respectively) although no difference was seen within the HF group across genotypes. These results suggest that the LL variant of 5HTT is associated with elevated PAP in HF but not CTL. HL71478 and HL07111.

Pulmonary artery capacitance (Pa CAP ) is the ability of the pulmonary artery to accept a volume of blood at a given pressure. Measured invasively with heart catheterization; Pa CAP can be estimated non‐invasively through the measurement of end‐tidal CO 2 (P ETCO2 ) and stroke volume (SV), known as gas‐exchange capacitance (GX CAP ). We have shown that GX CAP is decreased at rest as well as during peak exercise in patients with cystic fibrosis (CF), when compared to healthy subjects. To determine whether GX CAP is different in CF and controls at a workload that matches for SV. 9 CF patients (age=22±3yrs, BMI=23±1kg/m 2 , VO 2 =19±1mL/kg/min, FEV 1 =81±8%pred.) and 13 healthy subjects (age=28±3yrs, BMI=25±1kg/m 2 , VO 2 =23±2L/min, FEV 1 =93±3%pred.) were studied. Exercise testing was performed on a cycle ergometer. P ETCO2 was assessed using a metabolic cart, SV was calculated from heart rate and cardiac output (Q) using the acetylene rebreathe technique and GX CAP was calculated as the product of P ETCO2 and SV. When matched for workload which sought to match SV, there was a significant difference in CF and healthy subjects in workload (Watts=72±6 vs. 90±4W), but no difference in percent of max watts (%MaxW=63±4 vs. 66±5W), Q (11±1 vs. 13±1L/min), or SV (89±4 vs. 90±4ml/beat). When matched, the previous difference in GX CAP in healthy and CF was abolished (GX CAP =32±2 vs. 32±2mL/BEAT • min). P ETCO2 was similar between CF and healthy subjects (P ETCO2 36±1 and 35±1mmHg). When matched for SV, GX CAP was statistically similar in CF. In relatively healthy CF there is no evidence of pulmonary vasculature dysfunction. NIH RO1 HL108962‐02

Background Although lower vs. healthy individuals, diffusion capacity of lungs for carbon monoxide (DL CO ) and nitric oxide (DL NO ) (may influence oxygen uptake, VO 2 ) are higher during exercise vs. rest in cystic fibrosis patients (CF). Thus, because the Fick equation suggests cardiac output (Q) increases linearly with VO 2 , we sought to study relationships between VO 2 with cardiac function from rest to peak exercise as increases in Q, DL CO and DL NO occur during exercise in CF. Methods 50 individuals participated (ages 22 ± 2 vs. 27 ± 2, BSA = 1.7 ± 0.1 vs. 1.8 ± 0.0 m 2 , VO 2peak = 24 ± 2 vs. 35 ± 2 ml/kg/min, CF (n = 19) vs. controls (CTL, n = 31), mean ± SEM, p<0.05 for all). Acetylene rebreathe was used to assess Q and calculate stroke volume (SV), and standard gas‐exchange was used to assess VO 2 (mL/kg/min). Cardiac power (CP, Q i × MAP) and stroke work (SW, SV i × MAP) were calculated. Q and SV were indexed to BSA (Q i and SV i ). Results Linear regression (R 2 ) between VO 2 with SV i , Q i , CP, and SW at rest were similarly negligible for CF vs. CTL (p=ns). At 50 % VO 2peak , R 2 between VO 2 with SV i (0.25 and 0.43, p<0.05), Q i (0.37 and 0.41, p<0.05), CP (0.18, p=ns and 0.25, p<0.05), and SW (0.12 and 0.30, p=ns) improved for CF and CTL, respectively. At VO 2peak , stronger R 2 between VO 2 with SV i (0.41, p<0.05), Q i (0.47, p<0.05), CP (0.24, p<0.05), and SW (0.19, p=ns) occurred in CF; but, R 2 weakened in CTL (0.28, p<0.05; 0.33, p<0.05; 0.07, p=ns; 0.02, p=ns, respectively). Conclusions From rest to VO 2peak the relationship between VO 2 with cardiac function improves in CF patients. Participation in exercise may benefit relationships between gas‐transfer with cardiac hemodynamics in CF patients.

Mutations in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) lead to altered ion regulation, resulting in CF. CFTR also plays an important role in cardiac function. We have shown that β‐agonist inhalation results in increased cardiac output (Q), stroke volume (SV), and decreased systemic vascular resistance (SVR) in healthy humans, suggesting stimulation of the β‐adrenergic receptors via inhalation. We have also shown that this cardiovascular (CV) response is attenuated in CF, which could be due to receptor desensitization or inhibited drug delivery to the blood stream due to mucus build‐up. This study sought to determine the effects of epinephrine (EPI) and norepinephrine (NE) on CV function in CF. 11 CF patients and 27 controls completed a cycle ergometery test with measures of Q, SV, SVR, and HR along with EPI and NE. CF patients had lower Q corrected for NE at 50% and peak exercise (rest: Q/NE= 0.012 ±0.002 vs 0.017 ±0.002; 50%: Q/NE= 0.026 ±0.004 vs 0.045 ±0.004; peak: Q/NE= 0.03 ±0.004 vs 0.05 ±0.005, CF vs healthy, p<0.05) and lower SV corrected for NE at rest, 50%, and peak (rest: SV/NE= 0.12 ±0.03 vs 0.22 ±0.02; 50%: SV/NE= 0.17 ±0.04 vs 0.32 ±0.03; peak: SV/NE= 0.18 ±0.04 vs 0.35 ±0.03, CF vs healthy, p<0.05), no difference in SVR when corrected for EPI (rest: SVR/EPI= 53 ±13 vs 33 ±4; 50%: SVR/EPI= 28 ±7 vs 15 ±2; peak: SVR/EPI= 22 ±5 vs 15 ±3; in CF vs healthy). These results suggest that CF patients have lower cardiac function relative to circulating NE, no difference in SVR relative to EPI, indicating impairment in cardiac function, likely as a result from a loss of CFTR function.