Elevated concentrations of Neu5Ac and Neu5,9Ac2 in human plasma: potential biomarkers of cardiovascular disease.

Cardiovascular disease (CVD) is a group of health conditions affecting the heart and vascular system with very high prevalence and mortality rates. The presence of CVD is characterised by high levels of inflammation which have previously been associated with increased plasma concentrations of N-acetyl neuraminic acid (Neu5Ac). While Neu5Ac has been studied in the context of CVD, Neu5,9Ac2 has not, despite being the second most abundant sialic acid in human plasma. A small-scale pilot study of thirty plasma samples from patients with diagnosed CVD, and thirty age and sex-matched healthy controls, was designed to gain insight into sialic acids as biomarkers for CVD and potential future areas of study. Each sample was assayed for Neu5Ac and Neu5,9Ac2 concentrations. Mean Neu5Ac and Neu5,9Ac2 concentrations were significantly elevated in patients with CVD compared to healthy controls (Neu5Ac: P < 0.001; Neu5,9Ac2: P < 0.04). Receiver operator curve (ROC) analysis indicated that both Neu5Ac and Neu5,9Ac2 have reasonable predictive power for the presence of CVD (Neu5Ac AUC: 0.86; Neu5,9Ac2 AUC: 0.71). However, while Neu5Ac had both good sensitivity (0.82) and specificity (0.81), Neu5,9Ac2 had equivalent specificity (0.81) but very poor sensitivity (0.44). A combination marker of Neu5Ac + Neu5,9Ac2 showed improvement over Neu5Ac alone in terms of predictive power (AUC: 0.93), sensitivity (0.87), and specificity (0.90). Comparison to a known inflammatory marker, high sensitivity c-reactive protein (hs-CRP: P-value: NS, ROC:0.50) was carried out, showing that both Neu5Ac and Neu5,9Ac2 outperformed this marker. Further to this, hs-CRP values were combined with the three different sialic acid markers to determine any effect on the AUC values. A slight improvement in AUC was noted for each of the combinations, with Neu5Ac + Neu5,9Ac2 + hs-CRP giving the best AUC of 0.97 overall. Thus, Neu5Ac would appear to offer good potential as a predictive marker for the presence of CVD, which the addition of Neu5,9Ac2 predictive power improves, with further improvement seen by the addition of hs-CRP.

Biomolecular Corona Stability in Association with Plasma Cholesterol Level.

Biomolecular corona is spontaneously formed on the surface of nanoparticles (NPs) when they are in contact with biological fluids. It plays an important role in the colloidal stability of NPs, which is of importance for most of their medical applications and toxicity assessment. While typical studies use either blood plasma or serum from a pooled biobank, it is unclear whether differences in the media, such as cholesterol level or protein concentration, might affect the NP colloidal stability and corona composition. In this study, the silica corona was prepared at particularly low plasma concentrations (3%, v/v-1.98 mg/mL) to identify the critical roles of the protein mass/NP surface ratio and the level of plasma cholesterol on the corona protein pattern and particle stability. While depending on the plasma dilution factor, the corona protein composition could be controlled by keeping the protein/NP constant. The NP colloidal stability was found to strongly correlate with the level of cholesterol in human plasma, particularly due to the high enrichment of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) in the corona. A cohort study on plasma samples from individuals with known cholesterol levels was performed to highlight that association, which could be relevant for all corona systems enriched with the LDL.

Quantitative Standards of 4-O-Acetyl- and 9-O-Acetyl-N-Acetylneuraminic Acid for the Analysis of Plasma and Serum.

N-Acetylneuraminic acid (sialic acid, Neu5Ac) is one of a large, diverse family of nine-carbon monosaccharides that play roles in many biological functions such as immune response. Neu5Ac has previously been identified as a potential biomarker for the presence and pathogenesis of cardiovascular disease (CVD), diabetes and cancer. More recent research has highlighted acetylated sialic acid derivatives, specifically Neu5,9Ac2 , as biomarkers for oral and breast cancers, but advances in analysis have been hampered due to a lack of commercially available quantitative standards. We report here the synthesis of 9-O- and 4-O-acetylated sialic acids (Neu5,9Ac2 and Neu4,5Ac2 ) with optimisation of previously reported synthetic routes. Neu5,9Ac2 was synthesised in 1 step in 68 % yield. Neu4,5Ac2 was synthesised in 4 steps in 39 % overall yield. Synthesis was followed by analysis of these standards via quantitative NMR (qNMR) spectroscopy. Their utilisation for the identification and quantification of specific acetylated sialic acid derivatives in biological samples is also demonstrated.

Sialic acid as a potential biomarker for cardiovascular disease, diabetes and cancer.

Cardiovascular disease (CVD), diabetes and cancer pose increasing global healthcare burdens. New biomarkers could enable earlier diagnosis of these diseases, leading to more effective treatment and lower associated healthcare burden. Elevated sialic acid concentration in plasma and serum has been positively correlated with the presence of CVDs, diabetes and the development of malignant tumors. This article reviews the use of total sialic acid (TSA), bound sialic acid (BSA) and free sialic acid (FSA) as potential biomarkers for these diseases and makes a comparison with existing markers. Elevated sialic acid has been shown to be indicative of the pathogenesis of CVD, diabetes and malignant tumors. While not a specific marker for one disease there is promise in utilizing sialic acid as a marker for monitoring disease progression and effectiveness of treatment programs.

Assays for the identification and quantification of sialic acids: Challenges, opportunities and future perspectives.

N-Acetyl neuraminic acid (sialic acid) is a monosaccharide generally found as the terminating unit on glycans, which in turn are found on the surface of cells and glycoproteins. These glycans aid in a variety of biological functions such as cell interactions and immune response. Sialic acid has been identified as a biomarker for cardiovascular disease, diabetes and a range of other inflammatory and degenerative conditions. It has also been identified as a marker for different types of cancer. Sialic acid levels vary depending on the level of inflammation present during the course of an inflammatory disease and it is overexpressed by tumours as a shield against the immune system. Since the discovery of sialic acid, numerous assays have been developed for the identification and quantification of different sialic acid derivative monosaccharides and these assays fall into four main groups: colorimetric, fluorometric, enzymatic and chromatographic/mass spectrometric, with much overlap between these. Given the importance of sialic acids in biological pathways, this review article critically appraises assays that are used to detect and quantify sialic acid and its derivatives. Thus it details the method, sensitivity, specificity and wider scope of a range of assays, and concludes by suggesting some future directions for assay development and application. In this way, insight is provided into assays that allow for the accurate quantitation of sialic acid in biological samples, which may facilitate identification of the roles of sialic acid in healthy and disease pathways.