Abstract
The development of solid materials that deliver nitric oxide (NO) are of interest for several therapeutic applications. Nevertheless, due to NO’s reactive nature, rapid diffusion and short half-life, reporting their NO delivery characteristics is rather complex. The full knowledge of this parameter is fundamental to discuss the therapeutic utility of these materials, and thus, the NO quantification strategy must be carefully considered according to the NO-releasing scaffold type, to the expected NO-releasing amounts and to the medium of quantification. In this work, we explore and discuss three different ways of quantifying the release of NO in different biological fluids: haemoglobin assay, Griess assay and NO electrochemical detection. For these measurements, different porous materials, namely zeolites and titanosilicates were used as models for NO-releasing platforms. The oxyhaemoglobin assay offers great sensitivity (nanomolar levels), but it is only possible to monitor the NO release while oxyhaemoglobin is not fully converted. On the other hand, Griess assay has low sensitivity in complex biological media, namely in blood, and interferences with media make NO measurements questionable. Nevertheless, this method can measure micromolar amounts of NO and may be useful for an initial screening for long-term release performance. The electrochemical sensor enabled real-time measurements in a variety of biological settings. However, measured NO is critically low in oxygenated and complex media, giving transient signals, which makes long-term quantification impossible. Despite the disadvantages of each method, the combination of all the results provided a more comprehensive NO release profile for these materials, which will help to determine which formulations are most promising for specific therapeutic applications. This study highlights the importance of using appropriate NO quantification tools to provide accurate reports.
Highlights
Nitric oxide (NO) is endogenously produced by nitric oxide synthase (NOS) enzymes, acting as a signalling messenger in many physiological processes including neuronal signalling, immune and inflammatory response, cardiovascular homeostasis and wound repair [1]
As in other NO-release strategies, a full control over the NO release kinetics (i.e., NO flux and half-life) and NO payloads are key parameters to develop useful therapies because the biological action of NO is manifested via several chemical reactions that strongly depend on its concentration [7]
33 of inorganic porous materials selected for the NO-releasing assessment that had previously shown potential potential for for NO
Summary
Nitric oxide (NO) is endogenously produced by nitric oxide synthase (NOS) enzymes, acting as a signalling messenger in many physiological processes including neuronal signalling, immune and inflammatory response, cardiovascular homeostasis and wound repair [1]. Titanosilicates and metal-organic frameworks (MOFs) are examples of successful carriers capable of storing therapeutic NO amounts [3,4,5] They release it in its pure form by exposing the material to aqueous biological environments [6]. Given the complexity of NO chemistry, its quantification is complex and its use for pharmacological purposes is yet very limited This gaseous molecule contains an unpaired electron that makes it very unstable when in contact with air and in biological environments since it reacts with oxygen and free radical species such as thiols, superoxide, lipid peroxyls and metal-containing proteins (e.g., haemoglobin), giving a very short biological half-life ranging from a few seconds to a few minutes [8,9]. The use of sensitive and efficient analytical methods to quantify NO is essential
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