Vitamin C for preventing atrial fibrillation in high risk patients: a systematic review and meta-analysis.

BACKGROUND: Atrial fibrillation (AF), a common arrhythmia contributing substantially to cardiac morbidity, is associated with oxidative stress and, being an antioxidant, vitamin C might influence it. METHODS: We searched the Cochrane CENTRAL Register, MEDLINE, and Scopus databases for randomised trials on vitamin C that measured AF as an outcome in high risk patients. The two authors independently assessed the trials for inclusion, assessed the risk of bias, and extracted data. We pooled selected trials using the Mantel-Haenszel method for the risk ratio (RR) and the inverse variance weighting for the effects on continuous outcomes. RESULTS: We identified 15 trials about preventing AF in high-risk patients, with 2050 subjects. Fourteen trials examined post-operative AF (POAF) in cardiac surgery patients and one examined the recurrence of AF in cardioversion patients. Five trials were carried out in the USA, five in Iran, three in Greece, one in Slovenia and one in Russia. There was significant heterogeneity in the effect of vitamin C in preventing AF. In 5 trials carried out in the USA, vitamin C did not prevent POAF with RR = 1.04 (95% CI: 0.86-1.27). In nine POAF trials conducted outside of the USA, vitamin C decreased its incidence with RR = 0.56 (95% CI: 0.47-0.67). In the single cardioversion trial carried out in Greece, vitamin C decreased the risk of AF recurrence by RR = 0.13 (95% CI: 0.02-0.92). In the non-US cardiac surgery trials, vitamin C decreased the length of hospital stay by 12.6% (95% CI 8.4-16.8%) and intensive care unit (ICU) stay by 8.0% (95% CI 3.0-13.0%). The US trials found no effect on hospital stay and ICU stay. No adverse effects from vitamin C were reported in the 15 trials. CONCLUSIONS: Our meta-analysis indicates that vitamin C may prevent post-operative atrial fibrillation in some countries outside of the USA, and it may also shorten the duration of hospital stay and ICU stay of cardiac surgery patients. Vitamin C is an essential nutrient that is safe and inexpensive. Further research is needed to determine the optimal dosage protocol and to identify the patient groups that benefit the most.

STK39 variation predicts the ambulatory blood pressure response to losartan in hypertensive men.

Large-scale genome-wide association studies (GWASs) have identified significant associations of common genetic variants with blood pressure (BP) levels. To obtain more evidence for the role of these variants in BP regulation, we studied their association with BP responses to four different antihypertensive drug monotherapies. We selected 19 single-nucleotide variants based on data from five GWASs. The study group consisted of more than 200 hypertensive Finnish men from the GENRES study. Ambulatory BP responses to 4-week treatments with losartan, bisoprolol, hydrochlorothiazide and amlodipine were the primary targets of the study. Secondarily, baseline indicators of the activity of the renin-angiotensin-aldosterone system were studied. After correction for multiple comparisons, the variant rs6749447 in the STK39 gene was significantly associated with BP responses. Thus, the minor rs6749447 allele was associated with a lower systolic and diastolic BP response to losartan (P=0.0005 and 0.0002, respectively). rs6749447 minor allele homozygotes had marginally higher serum aldosterone/plasma renin activity (PRA) ratios (P=0.04) than those without this allele. In a replication study on aldosterone and renin levels, another cohort of hypertensive patients (n=311) showed a similar trend. When the two cohorts were combined, the aldosterone level (P=0.02) and the aldosterone/PRA ratio (P=0.01) were higher in subjects homozygous for the minor rs6749447 allele than in other subjects. The present study shows that pharmacogenetic approaches may provide evidence that complements systematic genome-wide strategies by identifying gene loci that not only affect the BP level but also might modify its response to pharmacologic interventions.

Common genetic variation of beta1- and beta2-adrenergic receptor and response to four classes of antihypertensive treatment.

Varying results have been reported on the association of beta-adrenergic receptor polymorphisms with blood pressure (BP) response to beta-blockers. We investigated the influence of ADRB1 Ser49Gly and Arg389Gly, and ADRB2 Gly16Arg and Glu27Gln polymorphisms on ambulatory BP response to bisoprolol and three other antihypertensive drug monotherapies in a placebo-controlled, double-blind, cross-over study with 233 moderately hypertensive men. ADRB1 Ser49Ser homozygotes tended to have a better ambulatory BP response to bisoprolol but the difference was statistically nonsignificant. ADRB1 Arg389Arg homozygotes did not show better BP response to bisoprolol than the other genotypes. There were no significant associations of ADRB2 polymorphisms with BP responses to any of the study drugs. The results from this controlled study in hypertensive men do not support clinical use of common polymorphisms in ADRB1 and ADRB2 in predicting BP responses to beta-blockers or to three other antihypertensive drugs.

CYP2C9 genotype modifies activity of the renin-angiotensin-aldosterone system in hypertensive men.

BACKGROUND: Two variants of the CYP2C9 gene, CYP2C9*2 and CYP2C9*3, have been indicated to have impaired enzyme function, and thus suspected to reduce the formation of the active metabolite of losartan. Cytochrome P450 (CYP) enzymes are also involved in eicosanoid biosynthesis and regulation of blood pressure (BP) and sodium homeostasis. METHODS: We studied the impact of these variants on BP response to losartan and three other antihypertensive drugs and on baseline indicators of the activity of the renin-angiotensin-aldosterone system. The participants were 217 moderately hypertensive Finnish men that participated in the double-blind, cross-over, placebo-controlled GENRES Study. RESULTS: BP responses to losartan did not differ between CYP2C9*2 or CYP2C9*3 allele carriers and CYP2C9*1*1 patients. A suggestive finding of less pronounced ambulatory BP response to losartan in CYP2C9*1*3 patients with low-normal kidney function was made. At baseline of the GENRES Study, CYP2C9*1*3 patients had significantly lower plasma renin activity and aldosterone levels than CYP2C9*1*1 patients (both P values 0.004). In a replication study in patients with treatment-resistant hypertension, men with CYP2C9*3 allele also had lower plasma renin activity (P = 0.03) and aldosterone levels (P = 0.18). In addition, these men had attenuated renin and aldosterone responses in captopril challenge test (P = 0.29 and 0.006, respectively). CONCLUSION: The CYP2C9*3 allele was associated with lower activity of the renin-angiotensin-aldosterone system in hypertensive men, which may reflect a more efficient sodium reabsorption capacity. CYP2C9*2 and CYP2C9*3 alleles do not influence the antihypertensive effect of losartan in men with essential hypertension and normal kidney function.

Renin-angiotensin system and alpha-adducin gene polymorphisms and their relation to responses to antihypertensive drugs: results from the GENRES study.

BACKGROUND: Polymorphisms in genes coding for components of the renin-angiotensin system (RAS) and alpha-adducin (ADD1) have been reported to be associated with blood pressure (BP) responses to antihypertensive agents. The results, however, have not been consistent and most of the earlier studies have been small and lacked placebo-control. Therefore, the association of common polymorphisms in these genes with BP responses to four different antihypertensive drugs was analyzed in a controlled study. METHODS: The study included 208 hypertensive Finnish men from the GENRES study. All of them used amlodipine 5 mg, bisoprolol 5 mg, hydrochlorothiazide (HCT) 25 mg, and losartan 50 mg daily, each for 4 weeks as a monotherapy in a double-blind, randomized, study. The treatment periods were separated by 4-week placebo periods. Both 24-h ambulatory (ABP) and office BP (OBP) measurements were carried out. The polymorphisms analyzed were ADD1 Gly460Trp, angiotensinogen (AGT) Met235Thr, angiotensin converting enzyme (ACE) insertion/deletion (I/D), and angiotensin II type 1 receptor (AGTR1) 1166A/C. RESULTS: The presence of 460Trp allele of ADD1, previously suggested to be a marker of thiazide responsiveness, did not predict a better response to HCT. There was no significant association of AGT Met235Thr, ACE I/D, and AGTR1 1166A/C polymorphisms with BP responses to the study drugs. ADD1 460Trp and AGT 235Thr alleles were associated with higher systolic white coat effect (WCE) during the placebo periods (P values 0.03 and 0.01, respectively). CONCLUSIONS: Common polymorphisms of ADD1, AGT, ACE, and AGTR1 do not markedly predict BP responses to amlodipine, bisoprolol, HCT, and losartan, at least in white hypertensive men.

Short-term electrophysiological effects of losartan, bisoprolol, amlodipine, and hydrochlorothiazide in hypertensive men.

BACKGROUND AND AIM: Hypertension-induced left ventricular structural remodelling associates with repolarization abnormalities. We investigated if antihypertensive drugs can modulate ventricular repolarization. METHODS: A total of 183 hypertensive men received for 4 weeks drugs (losartan 50 mg, bisoprolol 5 mg, amlodipine 5 mg, hydrochlorothiazide (HCTZ) 25 mg) in a randomized order, separated by 4-week placebo periods. Electrocardiograms (ECG) were recorded at the end of placebo and drug periods. Measurements of repolarization duration (QT intervals), repolarization heterogeneity (T-wave peak to T-wave end (TPE) intervals), and T-wave morphology (T-wave principal component analysis (PCA) ratio, T-wave morphology dispersion (TMD), and total cosine R-to-T (TCRT)) during each drug were compared to placebo measurements. RESULTS: Losartan and bisoprolol shortened maximum and mean rate-adjusted QT intervals as well as mean TPE interval, decreased TMD, and increased TCRT. Losartan also shortened precordial maximum TPE interval and decreased PCA ratio. Amlodipine had no repolarization effects, whereas HCTZ prolonged precordial maximum TPE interval and mean TPE interval. CONCLUSION: Losartan and bisoprolol have beneficial short-term ECG repolarization effects. Amlodipine seems to have no repolarization effects. HCTZ seems to prolong the ECG TPE interval, potentially reflecting increased repolarization heterogeneity. These findings show that antihypertensive drugs may relatively rapidly and treatment-specifically modulate ECG markers of ventricular repolarization.

Laboratory tests as predictors of the antihypertensive effects of amlodipine, bisoprolol, hydrochlorothiazide and losartan in men: results from the randomized, double-blind, crossover GENRES Study.

OBJECTIVE: Individual blood pressure responses to antihypertensive therapy are difficult to predict. To improve optimization of antihypertensive therapy, we analyzed correlations of relevant laboratory tests with blood pressure responses to four antihypertensive monotherapies. METHODS: In the GENRES study, 208 Finnish men aged 35-60 years with moderate hypertension used amlodipine 5 mg, bisoprolol 5 mg, hydrochlorothiazide 25 mg and losartan 50 mg daily, each for 4 weeks as a monotherapy in a double-blind, randomized, placebo-controlled crossover study; that is, each subject received each type of monotherapy in a random order. The treatment periods were preceded and separated by 4-week placebo periods. Ambulatory 24-h and office blood pressure measurements were carried out after all study periods. Data from several biochemical tests were correlated to antihypertensive drug responses. RESULTS: Serum total calcium concentration was negatively correlated with blood pressure responses to amlodipine (P values 0.001-0.002). Plasma renin activity was positively correlated with blood pressure responses to losartan (P values 0.001-0.005) and bisoprolol (P values 0.03-0.17), and negatively with blood pressure responses to hydrochlorothiazide (P values 0.01-0.07). Daily urinary excretion of sodium was negatively correlated with ambulatory blood pressure responses to amlodipine (P values 0.001-0.01). CONCLUSIONS: In this carefully controlled study, marked individual variations in antihypertensive drug responsiveness were found to correlate to several baseline laboratory parameters. The negative correlation between serum calcium levels and amlodipine responses is intriguing and suggests an underlying mechanistic association. Collectively, our data imply that laboratory tests may have some value in prediction of the efficacy of various antihypertensive drug therapies, although great patient-to-patient variation remains an obstacle for exact predictive classification.

Predictors of antihypertensive drug responses: initial data from a placebo-controlled, randomized, cross-over study with four antihypertensive drugs (The GENRES Study).

BACKGROUND: Only a minority of hypertensive individuals is adequately controlled for their hypertension, partially because reliable predictors for efficient antihypertensive drug therapy are lacking. METHODS: In a prospective, randomized, double-blind, cross-over, placebo-controlled study (The GENRES Study), 208 moderately hypertensive Finnish men (aged 35 to 60 years) were treated for 4 weeks with antihypertensive drugs from four different classes: amlodipine (5 mg), bisoprolol (5 mg), hydrochlorothiazide (25 mg), or losartan (50 mg) daily. Each individual received each of the four monotherapies in a randomized order. Four-week placebo periods were included before and between drug treatment periods. Antihypertensive responses were assessed with 24-h ambulatory and office measurements and analyzed according to age, body mass index, triceps skin fold thickness, waist-to-hip ratio, duration of hypertension, number of previous antihypertensive drugs, number of affected parents, and blood pressure (BP) levels, and profiles during placebo periods. RESULTS: The median BP responses in 24-h ambulatory recordings (systolic/diastolic) were 11/8 mm Hg for bisoprolol, 9/6 mm Hg for losartan, 7/5 mm Hg for amlodipine, and 5/2 mm Hg for hydrochlorothiazide. The highest pairwise within-subject correlations in BP responses were seen for the combinations of bisoprolol-losartan and amlodipine-hydrochlorothiazide. The BP responses to bisoprolol and losartan did not vary according to the variables. Amlodipine and hydrochlorothiazide responses were positively correlated with age, placebo BP level, and lower night-time dipping on placebo. CONCLUSIONS: Baseline clinical and BP parameters may be used to predict the efficacy of antihypertensive therapies. The GENRES Study material should provide an excellent platform for future pharmacogenetic analyses of antihypertensive drug responsiveness.