Association between exaggerated blood pressure response to exercise and serum asymmetric dimethylarginine levels

Effects of AGXT2 variants on blood pressure and blood sugar among 750 older Japanese subjects recruited by the complete enumeration survey method

Background

Alanine:glyoxylate aminotransferase 2 (AGXT2; EC 2.6.1.44) is the only enzyme that degrades the R-form of 3-aminoisobutyrate, an intermediate metabolite of thymine. AGXT2, as well as diaminoarginine dimethylaminohydrolase 1 (DDAH1; EC 3.5.3.18), works as an enzyme that degrades asymmetric dimethylarginine (ADMA), which competitively inhibits the nitric oxide synthase family. Thus, these two enzyme activities may change vascular vulnerability for a lifetime via the nitric oxide (NO) system. We investigated the association between vascular conditions and diseases such as hypertension and diabetes mellitus and polymorphisms of these two genes in 750 older Japanese subjects (mean age ± standard deviation, 77.0 ± 7.6 years) recruited using the complete enumeration survey method in the Nakayama study. Demographic and biochemical data, such as blood pressure (BP) and casual blood sugar (CBS), were obtained. Four functional single nucleotide polymorphisms (SNPs; rs37370, rs37369, rs180749, and rs16899974) of AGXT2 and one functional insertion/deletion polymorphism in the promotor region with four SNPs (rs307894, rs669173, rs997251, and rs13373844) of DDAH1 were investigated. Plasma ADMA was also analyzed in 163 subjects.

Results

The results of multiple regression analysis showed that a loss of the functional haplotype of AGXT2, CAAA, was significantly positively correlated with BP (systolic BP, p = 0.034; diastolic BP, p = 0.025) and CBS (p = 0.021). No correlation was observed between DDAH1 and either BP or CBS. ADMA concentrations were significantly elevated in subjects with two CAAA haplotypes compared with subjects without the CAAA haplotype (p = 0.033).

Conclusions

Missense variants of AGXT2, but not DDAH1, may be related to vulnerability to vascular diseases such as hypertension and DM via the NO system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07612-3.

Effect of high-altitude trekking on blood pressure and on asymmetric dimethylarginine and isoprostane production: Results from a Mount Ararat expedition

The study aimed at exploring the mechanisms behind blood pressure and heart rate changes upon acute altitude exposure utilizing urinary excretion of biochemical factors involved in cardiovascular regulation. The study was conducted on 12 lowlander native male mountain climbers, living at sea level, exposed to altitudes ranging from 1800 to 5147 m above sea level over 4 days, during their ascent to Mount Ararat (Turkey). Blood pressure (measured by oscillometric method), heart rate, and blood oxygen saturation (SpO₂ ) were recorded at rest (on awakening before food intake), in hypoxic conditions at 4200 m and at sea level before and after the altitude expedition. In the same study conditions (ie before-during-after the expedition), first-voided urinary samples were collected and assayed for 8-iso-prostaglandin F_2α (8-iso-PGF_2α ) and asymmetric dimethylarginine (ADMA) determination. Heart rate, and systolic and diastolic blood pressures were higher (P < .05) at high altitude than at the sea level. Furthermore, both urinary 8-iso-PGF_2α and ADMA were significantly elevated (P < .01) at high altitude and returned to normal levels soon after returning to sea level. A 4-day exposure to high-altitude hypoxia induced a temporary increase in blood pressure and heart rate, confirming previous findings. Blood pressure increase at high altitude was associated with significantly enhanced production of biochemical mediators such as 8-iso-PGF2α, catecholamines, and ADMA, although we could not demonstrate a direct link between these parallel significant changes probably due to the forcefully limited sample size of our study, carried out in challenging environmental conditions at very high altitude.

An exaggerated blood pressure response to exercise is associated with nitric oxide bioavailability and inflammatory markers in normotensive females

This study was designed to examine the associations of an exaggerated systolic blood pressure (SBP) response to exercise with the indices of nitric oxide (NO) bioavailability, oxidative stress, inflammation and arterial stiffness in normotensive females. The subjects included 84 normotensive females without a history of cardiovascular disease or stroke who were not taking any medications. Each subject performed a multistage graded submaximal exercise stress test using an electric bicycle ergometer, and their blood pressure was measured at rest and during the last minute of each stage. The brachial-ankle pulse wave velocity, plasma nitrate/nitrite (NO_x), plasma thiobarbituric acid-reactive substances, high-sensitivity C-reactive protein (hs-CRP) and fibrinogen levels and the white blood cell count were measured. An exaggerated SBP response to exercise was defined according to the criteria of the Framingham Study (peak SBP: ⩾190 mm Hg). An exaggerated SBP response to exercise was observed in 27 subjects. A multiple logistic regression analysis revealed that the hs-CRP (odds ratio (OR): 1.05, 95% confidence interval (CI): 1.03-1.07, P=0.015) and plasma NO_x levels (OR: 0.92, 95% CI: 0.87-0.98, P=0.014) were significantly associated with an exaggerated SBP response to exercise. Furthermore, the percent change in SBP was found to be significantly associated with an increase in the hs-CRP (P for trend=0.006) and a decrease in the plasma NO_x levels (P for trend=0.001). These results suggest that an exaggerated SBP response to exercise was associated with the NO bioavailability and inflammatory status in normotensive females.

Blood pressure response to exercise in young athletes aged 10 to 18 years

The aim of the study was to determine arterial blood pressure response to exercise in young athletes. The study group comprised 711 young athletes (457 boys, 254 girls) aged 10 to 18 years (mean 13.41 ± 3.12 years) who had been training for an average of 7.62 ± 4.2 h per week for an average of 4.01 ± 2.5 years. Participants with elevated arterial blood pressure above the 90th percentile at rest were excluded from investigation. A symptom-limited, multistage exercise test to exhaustion was performed using a Monark cycle ergometer. Arterial blood pressure was measured with an aneroid manometer in the third minute of each stage of the test. Mean systolic arterial blood pressure during peak exercise was significantly higher in boys than in girls: 183.21 ± 27.97 mm Hg and 170.97 ± 21.4 mm Hg, respectively (p = 0.03). Multivariate linear regression analysis showed that age and workload had significant effects on arterial blood pressure during the test. Systolic arterial blood pressure during the exercise can be described with the following equations: boys, SBPex (mm Hg) = -1.92 × age (years) + 0.55 × workload (W) + 120.84; girls, SBPex (mm Hg) = -0.88 × age (years) + 0.48 × workload (W) + 111.22. The study results describe reference values of arterial blood pressure during the exercise test. The presented equations and figures can help to assess whether the arterial blood pressure at each stage of the exercise test exceeds the normal range or not.

Exaggerated Exercise Blood Pressure Response and Future Cardiovascular Disease

Exaggerated blood pressure (BP) response to exercise predicts future hypertension. However, there is considerable lack of understanding regarding the mechanism of how this abnormal response is generated, and how it relates to the future establishment of cardiovascular disease. The authors studied 82 healthy male volunteers without cardiovascular risk factors. The participants were categorized into two age-matched groups depending on their exercise systolic BP (ExSBP) rise after 3 minutes of exercise using a submaximal step test: exaggerated ExSBP group (hyper-responders [peak SBP ≥ 180 mm Hg]) and low ExSBP responder group (hypo-responders [peak SBP <180 mm Hg]). Forearm venous occlusion plethysmography and intra-arterial infusions of acetylcholine (ACh), N(G)-monomethyl-L-arginine (L-NMMA), sodium nitroprusside (SNP), and norepinephrine (NE) were used to assess vascular reactivity. Proximal aortic compliance was assessed with ultrasound, and neurohormonal blood sampling was performed at rest and during peak exercise. The hyper-responder group exhibited a significantly lower increase in forearm blood flow (FBF) with ACh compared with the hypo-responder group (ΔFBF 215% [14] vs 332.3% [28], mean [standard error of the mean]; P<.001), as well as decreased proximal aortic compliance. The vasoconstrictive response to L-NMMA was significantly impaired in the hyper-responder group in comparison to the hypo-responder group (ΔFBF -40.2% [1.6] vs -50.2% [2.6]; P<.05). In contrast, the vascular response to SNP and NE were comparable in both groups. Peak exercise plasma angiotensin II levels were significantly higher in the hyper-responder group (31 [1] vs 23 [2] pg/mL, P=.01). An exaggerated BP response to exercise is related to endothelial dysfunction, decreased proximal aortic compliance, and increased exercise-related neurohormonal activation, the constellation of which may explain future cardiovascular disease.

Missense variants of the alanine:glyoxylate aminotransferase 2 gene are not associated with Japanese schizophrenia patients

Alanine:glyoxylate aminotransferase 2 (AGXT2) is the only enzyme that degrades D-3-aminoisobutyrate (D-AIB), which is an intermediate product of thymine, and 30-40% of Japanese lack AGXT2 activity genetically and excrete high amounts of D-AIB in their urine. Recently, AGXT2 is reported to metabolize asymmetric dimethyl arginine (ADMA), a competitive inhibitor of nitric oxide (NO) synthase. Since AGXT2 is expressed in the central nervous system, the loss of AGXT2 activity will be related to the vulnerability for neuropsychiatric disorders related to the NO system. In this study, we recruited 85 Japanese subjects to discover loss variants of the AGXT2 gene with the amount of D-AIB excretion in their urine. From the statistical relevance between them, we found three missense polymorphisms (rs37370, rs37369, and rs180749) independently related to AGXT2 activity (P<0.0001). Then, we performed a case-control association analysis of its missense polymorphisms with 1136 schizophrenia and 1908 control subjects because the NO system may be involved in the vulnerability of schizophrenia processes. We could not find any associations of three functional SNPs with schizophrenia pathogenesis in the analyses of either genotypic or allelic models. We concluded that the AGXT2 gene is not associated with schizophrenia in Japanese subjects.

Distribution of D-3-aminoisobutyrate-pyruvate aminotransferase in the rat brain

Background

D-3-aminoisobutyrate, an intermediary product of thymine, is converted to 2-methyl-3-oxopropanoate using pyruvate as an amino acceptor by D-3-aminoisobutyrate-pyruvate aminotransferase (D-AIB AT; EC 2.6.1.40). A large amount of D-AIB AT is distributed in the kidney and liver; however, small amounts are found in the brain. Recently, D-AIB AT was reported to metabolize asymmetric dimethylarginine (ADMA) in vivo and was suggested to be an important enzyme for nitric oxide metabolism because ADMA is a competitive inhibitor for nitric oxide synthase. In this study, we examined the distribution of D-AIB AT in the rat brain further to understand its role. We measured D-AIB AT mRNA and protein expression using quantitative RT-PCR and Western blotting, and monitored its distribution using immunohistochemical staining.

Results

D-AIB AT was distributed throughout the brain, with high expression in the cortex and hippocampus. Immunohistochemical staining revealed that D-AIB AT was highly expressed in the retrosplenial cortex and in hippocampal neurons.

Conclusion

Our results suggest that D-AIB AT is distributed in the examined- just the regions and may play an important role there.

The relationship between exercise capacity and masked hypertension in sedentary patients with diabetes mellitus

AIM

Although exaggerated blood pressure responses (EBPR) to exercise have been related to future hypertension and masked hypertension (MHT), the relationship between exercise capacity and MHT remains unclear. A sedentary life style has been related to increased cardiovascular mortality, diabetes mellitus (DM), and hypertension. In this study, we aimed to examine the relationship between exercise capacity and MHT in sedentary patients with DM.

METHODS

This study included 85 sedentary and normotensive patients with DM. Each patient's daily physical activity level was assessed according to the INTERHEART study. All patients underwent an exercise treadmill test, and exercise duration and capacity were recorded. Blood pressure (BP) was recorded during all exercise stages and BP values ≥ 200/110 mmHg were accepted as EBPR. MHT was diagnosed in patients having an office BP <140/90 mmHg and a daytime ambulatory BP >135/85 mmHg. Patients were divided into two groups according to their ambulatory BP monitoring (MHT and normotensive group).

RESULTS

The prevalence of MHT was 28.2%. Exercise duration and capacity were lower in the MHT group than in the normotensive group (p<0.05) and were negatively correlated with age, HbA1c, mean daytime BP, and mean 24 hour BP. Peak exercise systolic BP and the frequency of EBPR were both increased in the MHT group (25.0% and 8.1%, respectively, p=0.03). According to a multivariate regression, exercise capacity (OR: 0.61, CI95%: 0.39-0.95, p=0.03), EBPR (OR: 9.45, CI95%: 1.72-16.90, p=0.01), and the duration of DM (OR: 0.84, CI95%: 0.71-0.96, p=0.03) were predictors of MHT.

CONCLUSION

Exercise capacity, EBPR, and the duration of DM were predictors of MHT in sedentary subjects with DM.

Metabolic syndrome and exaggerated blood pressure response to exercise in newly diagnosed hypertensive patients

Background: Running evidence supports a prognostic value of an exaggerated blood pressure response to exercise (EBPR). The impact of the metabolic syndrome (MS) on EBPR in hypertensive patients has not been investigated.

Design: A cross-sectional study in the setting of an outpatient hypertension clinic.

Methods: In total, 325 non-diabetic patients with newly diagnosed hypertension were divided into two groups based on the presence ( n = 95) or absence ( n = 230) of the MS as defined with NCEP-ATP III criteria. All subjects underwent ambulatory blood pressure monitoring, echocardiography and exercise treadmill testing.

Results: Hypertensive patients with MS exhibited higher prevalence of EBPR (by 17%, p = 0.002) and peak exercise systolic BP (by 10.4 mmHg, p = 0.001) irrespectively of confounders. Metabolic equivalents were higher in hypertensives with MS (by 0.6 ml/kg/min, p = 0.048), but the difference lost significance after adjusting for confounders, including body mass index. Logistic regression analysis identified the MS as an independent predictor of an EBPR ( p = 0.016). Hypertensive patients with MS had a 2.3-fold risk of exhibiting EBPR compared to those without MS. However, individual components of MS altogether as well as each one separately failed to predict EBPR.

Conclusions: Presence of MS in newly diagnosed hypertensive patients is associated with increased peak exercise BP and a higher frequency of EBPR over and above its separate elements.