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N-acetylaspartate (NAA) is the second most abundant metabolite in the human brain; although it is assumed to be a proxy for a neuronal marker, its function is not fully elucidated. NAA is also detectable in plasma, but its relation to cerebral NAA levels, cognitive performance, or features of cerebral disease has not been investigated. To study whether circulating NAA tracks cerebral NAA levels, and whether circulating NAA correlates with cognitive function and features of cerebral small vessel disease (SVD). Two datasets were analyzed. In dataset 1, structural MRI was acquired in 533 subjects to assess four features of cerebral SVD. Cognitive function was evaluated with standardized test scores (N = 824). In dataset 2, brain 1H-MRS from the occipital region was acquired (N = 49). In all subjects, fasting circulating NAA was measured with mass spectrometry. Dataset 1: in univariate and adjusted for confounders models, we found no correlation between circulating NAA and the examined features of cerebral SVD. In univariate analysis, circulating NAA levels were associated inversely with the speed in information processing and the executive function score, however these associations were lost after accounting for confounders. In line with the negative findings of dataset 1, in dataset 2 there was no correlation between circulating and central NAA or total NAA levels. This study indicates that circulating NAA levels do not reflect central (occipital) NAA levels, cognitive function, or cerebral small vessel disease in man.

Mortality in type 2 diabetes, is determined not only by classical complications, but also by comorbidities, and is linked to hyperglycaemia and apparent even in prediabetes. We aimed to comprehensively investigate, in a population-based cohort, health burden defined as the presence of comorbidities in addition to classical complications and cardiometabolic risk factors, in not only type 2 diabetes but also prediabetes. Such population-based study has not been performed previously. Extensive phenotyping was performed in 3,410 participants of the population-based Maastricht Study (15.0% prediabetes and 28.6% type 2 diabetes) to assess presence of 17 comorbidities, six classical complications, and ten cardiometabolic risk factors. These were added up into individual and combined sum scores and categorized. Group differences were studied with multinomial regression analyses adjusted for age and sex. Individuals with type 2 diabetes and prediabetes, as compared to normal glucose metabolism (NGM), had greater comorbidities, classical complications, cardiometabolic risk factors and combined sum scores (comorbidities sum score ≥ 3: frequencies (95% CI) 61.5% (57.6;65.4) and 41.2% (36.5;45.9) vs. 25.4% (23.5;27.4), p-trend P P = 0.065 vs NGM) vs. 8.0% (6.9;9.3)); cardiometabolic risk factors ≥ 6 (39.7% (35.9;43.4) and 28.5% (24.5;32.6) vs. 14.0% (12.5;15.6); p-trend

Retinopathy and neuropathy in type 2 diabetes are preceded by retinal nerve fibre layer (RNFL) thinning, an index of neurodegeneration. We investigated whether glucose metabolism status (GMS), measures of glycaemia, and daily glucose variability (GV) are associated with RNFL thickness over the entire range of glucose tolerance. We used cross-sectional data from The Maastricht Study (up to 5455 participants, 48.9% men, mean age 59.5 years and 22.7% with type 2 diabetes) to investigate the associations of GMS, measures of glycaemia (fasting plasma glucose [FPG], 2-h post-load glucose [2-h PG], HbA1c, advanced glycation endproducts [AGEs] assessed as skin autofluorescence [SAF]) and indices of daily GV (incremental glucose peak [IGP] and continuous glucose monitoring [CGM]-assessed standard deviation [SD]) with mean RNFL thickness. We used linear regression analyses and, for GMS, P for trend analyses. We adjusted associations for demographic, cardiovascular risk and lifestyle factors, and, only for measures of GV, for indices of mean glycaemia. After full adjustment, type 2 diabetes and prediabetes (versus normal glucose metabolism) were associated with lower RNFL thickness (standardized beta [95% CI], respectively − 0.16 [− 0.25; − 0.08]; − 0.05 [− 0.13; 0.03]; Ptrend = 0.001). Greater FPG, 2-h PG, HbA1c, SAF, IGP, but not CGM-assessed SD, were also associated with lower RNFL thickness (per SD, respectively − 0.05 [− 0.08; − 0.01]; − 0.06 [− 0.09; − 0.02]; − 0.05 [− 0.08; − 0.02]; − 0.04 [− 0.07; − 0.01]; − 0.06 [− 0.12; − 0.01]; and − 0.07 [− 0.21; 0.07]). In this population-based study, a more adverse GMS and, over the entire range of glucose tolerance, greater glycaemia and daily GV were associated with lower RNFL thickness. Hence, early identification of individuals with hyperglycaemia, early glucose-lowering treatment, and early monitoring of daily GV may contribute to the prevention of RNFL thinning, an index of neurodegeneration and precursor of retinopathy and neuropathy.