A model to quantify the influence of treatment patterns and optimize outcomes in nAMD.

Neovascular age-related macular degeneration (nAMD) is a progressive retinal disease that often leads to severe and permanent vision loss. Early initiation of anti-vascular endothelial growth factor (anti-VEGF) therapy has been shown to preserve vision in nAMD patients. Concurrently, treatment outcomes in real-world are inferior to those reported in clinical trials. The most likely reasons observed are fewer treatment-intensity in routine clinical practice than in clinical trials. The other possibility could be the delay in starting treatment and the re-treatment interval. Although a negative impact of aforementioned parameters seems obvious, quantitative impact measures remain elusive in a real-world setting due to a lack of an 'optimal treatment' control group. To overcome this shortcoming, we developed, validated, and applied a model to assess and quantify the impact of anti-VEGF administration variables on visual acuity development in a prospective nAMD patient cohort. The model was further applied to probe the impact of the COVID-19 pandemic on visual progressions in nAMD patients. The presented model paves the way to systematically explore and evaluate realistic interventions in the current treatment paradigm, that can be adopted in routine clinical care.

Solubilisation and properties of the sialate-4-O-acetyltransferase from guinea pig liver.

The O-acetylation of sialic acids turns out to be one of the most important modifications that influence the diverse biological and pathophysiological properties of glycoconjugates in animals and microorganisms. To understand the functions of this esterification, knowledge of the properties, structures and regulation of expression of the enzymes involved is essential. Attempts to solubilise, purify or clone the gene of one of the sialate-O-acetyltransferases have failed so far. Here we report on the solubilisation of the sialate-4-O-acetyltransferase from guinea pig liver, the first and essential step in the purification and molecular characterisation of this enzyme, by the zwitterionic detergent CHAPS. This enzyme O-acetylates sialic acids at C-4 both free and bound to oligosaccharides, glycoproteins and glycolipids with varying activity, however, gangliosides proved to be the best substrates. Correspondingly, a rapid enzyme test was elaborated using the ganglioside GD3. The soluble O-acetyltransferase maximally operated at 30 degrees C, pH 5.6, and 50-70 mM KCl and K2HPO4 concentrations. The Km values were 3.6 microM for AcCoA and 1.2 microM for GD3. CoA inhibits the enzyme with a Ki value of 14.8 microM. A most important discovery enabling further enzyme purification is its need for an unknown low molecular mass and heat-stable cofactor that can be separated from the crude enzyme preparation by 30 kDa ultrafiltration.

Characterization of the sialate-7(9)-O-acetyltransferase from the microsomes of human colonic mucosa.

Sialic acids present on human colonic mucins are highly O-acetylated, however, little is known about the underlying enzymatic activity required for O-acetylation in this tissue. Here we report on the substrate specificity, subcellular localization and characterization of the sialate-7(9)-O-acetyltransferase in normal human colonic mucosa. Using CMP-Neu5Ac, the most efficient acceptor substrate of all those tested, the enzymatic activity was found to be optimal at 37 degrees C, with a pH optimum of 7.0. Activity was also found to be dependent on protein, CMP-Neu5Ac (Km: 59.2 microM) and AcCoA (Km: 6.1 microM) concentrations, as well as membrane integrity. The enzyme's activity could be inhibited by CoA with a Ki of 11.9 microM. In addition, enzymatic activity was found to be localized in the Golgi-enriched membrane fraction. The nature of the O-acetylated products formed were verified with the aid of chromatographic and enzymatic techniques. The main product was 9-O-acetylated Neu5Ac, with a significant amount of oligo-O-acetylated Neu5Ac also being detected. The utilization of CMP-Neu5Ac as the acceptor substrate was confirmed by the isolation and characterization of the putative product, CMP-Neu5,9Ac2, using ion-exchange chromatography. The ability of CMP-Neu5,9Ac2 to act as a sialic acid donor for sialyltransferases represents the conclusive demonstration for the formation of CMP-Neu5,9Ac2.