Glycated haemoglobin and the association with long-term survival among patients evaluated for stable angina – a prospective Norwegian cohort

Background and methods

Recent guidelines have included glycated haemoglobin (HbA1c) ≥48 mmol/L as a diagnostic criterion for diabetes mellitus (DM) in addition to plasma glucose (PG) concentrations, mainly based on the relationship between hyperglycemia and microvascular disease [1]. However, increased HbA1c may stem not only from hyperglycemia, and the risk association between HbA1c and long-term survival in patients with stable coronary heart disease and HbA1c ≥48 mmol/L but no previous DM according to PG is uncertain. We explored the relationship between HbA1c and survival among patients with and without DM who were evaluated for stable angina in the period 2000–2004. Endpoints were obtained from the Norwegian Cause of Death Registry.

Results

In total, 4164 patients were evaluated by cardiac cathetherization, of whom 576 patients (13.8%) had DM (median HbA1c 55 mmol/L) according to self-report and/or baseline PG concentrations. Of the remaining 3588 patients 1026 had HbA1c ≥48 mmol/L; however, HbA1c did not correlate with the HOMA2 insulin resistance index or fasting PG in these patients. During median (25–75 percentile) follow-up time of 14.0 (12.1–15.4) years a total of 1328 patients (31.9%) died, of whom 582 from cardiovascular causes. In patients with DM according to PG, HbA1c trended towards positive associations with all-cause and CVD mortality when adjusted for age and gender (HRs (95% CIs) 1.13 (0.99–1.28) and 1.16 (0.98–1.39) per 1SD, respectively). However, HbA1c was not associated with survival in either the group of patients without DM and HbA1c <48 mmol/L (median HbA1c 38 mmol/L) (HRs (95% CIs) 0.99 (0.92–1.06) and 0.96 (0.86–1.08) for all-cause and CVD mortality, respectively) or patients without DM but having HbA1c ≥48 mmol/L (median HbA1c 53 mmol/L) (HRs (95% CIs) 0.99 (0.88–1.12) and 1.04 (0.88–1.22)).

Conclusion

In patients evaluated for stable angina pectoris about two decades ago, almost a third of patients with no history of DM according to PG still had HbA1c concentrations indicating DM according to current guidelines. Including these patients in the DM category yielded similar percentages of patients with DM as observed in recent populations with stable coronary disease [2]. However, as opposed to what we observed in patients with DM, HbA1c did not show any association with very long-term survival among patients without DM. Our findings therefore question the use of HbA1c in the diagnosis of DM, especially in terms of risk assessment for longevity among patients with chronic coronary syndrome.

Funding Acknowledgement

Type of funding sources: None.

Ttrimetyllysine and risk of new-onset atrial fibrillation in two large norwegian cohorts

Funding Acknowledgements

Type of funding sources: None.

Background/Aim

Increased plasma trimetyllysine (TML), a methylated amino acid, has recently been linked to higher risk of acute myocardial infarction (AMI). TML is also a precursor of trimethylamine-N oxide (TMAO), which has been linked to increased cardiovascular risk, including that of  atrial fibrillation (AF). We investigated the association between TML and new-onset AF in two large Norwegian cohorts.

Methods

The primary cohort consisted of 6396 participants in the community-based Hordaland Health Study (HUSK). The validation cohort consited of 2027 patients who underwent coronary angiography due to suspected stable angina pectoris in the Western Norway Coronary Angiography Cohort (WECAC). Information on new-onset AF was obtained by linking patient data to Norwegian public health registries. Risk associations were explored by Cox regression.

Results

During median (25th-75th percentile) follow-up of 10.9 (10.6-11.3) and 7.0 (6.3-8.6) years, 560 (8.8%) patients in the HUSK and 210 (10.4%) in the WECAC was diagnosed with AF.

In the HUSK, the age and gender adjusted HR (95 % CI) for the 4th vs. 1st plasma TML quartiles 1.84 (1.37-2.48) p < 0.001. In multivariable models the association was only slightly attenuated. Correspondingsly, the age and gender adjusted HR (95% CI) for the 4th vs. 1st TML quartiles in the WECAC was 1.48 (0.96-2.27) p = 0.07.

Testing for collinearity between TMAO and TML revealed variance inflation factors between 1.0-1.1 in HUSK and WECAC, thus ruling out collinearity.

Conclusion

Plasma TML was associated with new-onset AF among subjects from the general population, and the relationship was independent from established AF risk factors. A similar trend was also seen in patients with suspected stable angina pectoris, strengthening our findings, which motivate further studies to explore potential pathophysiological relationships between one-carbon metabolism and cardiac arrhythmias

Circulating trimethyllysine and risk of acute myocardial infarction in patients with suspected stable coronary heart disease

BACKGROUND

The carnitine precursor trimethyllysine (TML) is associated with progression of atherosclerosis, possibly through a relationship with trimethylamine-N-oxide (TMAO). Riboflavin is a cofactor in TMAO synthesis. We examined prospective relationships of circulating TML and TMAO with acute myocardial infarction (AMI) and potential effect modifications by riboflavin status.

METHODS

By Cox modelling, risk associations were examined amongst 4098 patients (71.8% men) with suspected stable angina pectoris. Subgroup analyses were performed according to median plasma riboflavin.

RESULTS

During a median follow-up of 4.9 years, 336 (8.2%) patients experienced an AMI. The age- and sex-adjusted hazard ratio (HR) (95% CI) comparing the 4th vs. 1st TML quartile was 2.19 (1.56-3.09). Multivariable adjustment for traditional cardiovascular risk factors and indices of renal function only slightly attenuated the risk estimates [HR (95% CI) 1.79 (1.23-2.59)], which were particularly strong amongst patients with riboflavin levels above the median (P_int  = 0.035). Plasma TML and TMAO were strongly correlated (r_s  = 0.41; P < 0.001); however, plasma TMAO was not associated with AMI risk in adjusted analyses [HR (95% CI) 0.81 (0.58-1.14)]. No interaction between TML and TMAO was observed.

CONCLUSION

Amongst patients with suspected stable angina pectoris, plasma TML, but not TMAO, independently predicted risk of AMI. Our results motivate further research on metabolic processes determining TML levels and their potential associations with cardiovascular disease. We did not adjust for multiple comparisons, and the subgroup analyses should be interpreted with caution.

B vitamin treatments modify the risk of myocardial infarction associated with a MTHFD1 polymorphism in patients with stable angina pectoris

BACKGROUND

Methylenetetrahydrofolate dehydrogenase (MTHFD1) catalyzes three sequential reactions that metabolize derivatives of tetrahydrofolate (THF) in folate-dependent one-carbon metabolism. Impaired MTHFD1 flux has been linked to disturbed lipid metabolism and oxidative stress. However, limited information is available on its relation to the development of atherothrombotic cardiovascular disease.

METHODS AND RESULTS

We explored the association between a MTHFD1 polymorphism (rs1076991 C > T) and acute myocardial infarction (AMI), and potential effect modifications by folic acid/B12 and/or vitamin B6 treatment in suspected stable angina pectoris patients (n = 2381) participating in the randomized Western Norway B Vitamin Intervention Trial (WENBIT). During the median follow-up of 4.9 years 204 participants (8.6%) suffered an AMI. After adjusting for established CVD risk factors, the MTHFD1 polymorphism was significantly associated with AMI (HR: 1.49; 95% CI, 1.23-1.81). A similar association was observed among patients allocated to treatment with vitamin B6 alone (HR: 1.53; 95% CI, 1.01-2.31), and an even stronger relationship was seen in patients treated with both vitamin B6 and folic acid/B12 (HR: 2.35; 95% CI, 1.55-3.57). However, no risk association between the MTHFD1 polymorphism and AMI was seen in patients treated with placebo (HR: 1.29; 95% CI, 0.86-1.93) or folic acid/B12 (1.17; 95% CI, 0.83-1.65).

CONCLUSION

A common and functional MTHFD1 polymorphism is associated with increased risk of AMI, although the risk seems to be dependent on specific B vitamin treatment. Further studies are warranted to elucidate the possible mechanisms, also in order to explore potential effect modifications by nutritional factors.

Vitamin B6 status and interferon-γ-mediated immune activation in primary hyperparathyroidism

OBJECTIVES

Primary hyperparathyroidism (PHPT) has been associated with low-grade inflammation and elevated risk of cardiovascular disease (CVD). In inflammatory conditions, interferon-γ (IFN-γ) activity is enhanced and a decreased circulating concentration of vitamin B6 is often observed. Such changes in IFN-γ activity or vitamin B6 levels have been associated with increased incidence of CVD. The aim of the study was to investigate systemic markers of IFN-γ-mediated immune activation, such as neopterin, the kynurenine-to-tryptophan ratio (KTR) and kynurenine pathway metabolites, as well as B6 vitamers in patients with PHPT.

DESIGN/SUBJECTS

A total of 57 patients with PHPT and a control group of 20 healthy blood donors were included in this study. PHPT patients who responded positively to parathyroidectomy were followed for 6 months. Forty-three patients participated in the longitudinal study in which blood samples were taken at inclusion and 1, 3 and 6 months after surgery.

RESULTS

Plasma concentrations of the B6 vitamers pyridoxal 5'-phosphate (PLP) (P = 0.007) and pyridoxal (P = 0.013) were significantly lower in the patient group compared to healthy control subjects. An increase in the KTR indicated that the kynurenine pathway of tryptophan metabolism was altered in PHPT patients (P = 0.015). During the initial 6 months after surgery, levels of PLP (P < 0.001) and anthranilic acid (P < 0.001) increased significantly, whereas neopterin decreased (P = 0.018).

CONCLUSIONS

The results of this study demonstrate altered levels of vitamin B6 and the KTR in PHPT patients, both of which may reflect cellular immune activation. These abnormalities should be considered in relation to the increased risk of CVD previously observed in patients with PHPT.