The influence of nanomaterial uptake on small arterial function

The emergence of nanomedicine, involving the intravenous injection of tracking agents (such as dyes and nanoparticles) and drug-loaded nanoparticles (NPs) for diagnostic and therapeutic purposes may display a biosafety concern specifically to the circulating blood and the vascular system. Dye-encapsulated silica nanoparticles (SiNPs) are one of the most popular NPs recently being explored for medical intervention. However, there are limited studies investigating their biocompatibility and biosafety with regards to blood vessels. Our group’s previous findings suggest that SiNPs of 100 and 200 nm in size have no detrimental effect on conduit arterial function. However, their direct effect on small size arteries, which play an important role in controlling blood flow into tissues, has not been investigated previously. Aim To investigate the direct influence of SiNPs on small arterial function and contractility. Methodology Mono-dispersed dye-encapsulated SiNPs of defined diameters (98 nm) were fabricated using a modified Stober method and characterised using the Malvern Zetasizer and transmission electron microscopy (TEM). NP characteristics (size and charge) were monitored over a 15-month period in various media. Small mesenteric arteries (MAs) (150-300 μm in diameter) from male Wistar rats were isolated, mounted between two glass cannulae and superfused in gassed physiological salt solution (PSS) at 37℃. Vasoconstrictor (high potassium [KPSS], Phenylephrine [Phe]) and vasodilator (Acetylcholine [ACh], Sodium nitroprusside [SNP] and papaverine [PAPA]) responses were assessed using pressure myography before and 30 minutes after the intravascular infusion of SiNPs under static conditions at intravascular pressure of 60 mmHg. SiNPs were also injected intravenously and mesenteric vessels isolated after a 2-hour period, for assessment of vascular reactivity. Results and Conclusion Our findings show that SiNPs are rapidly taken up into ECs lining small mesenteric arteries and were freely localised in the cytoplasm, with no evidence of uptake into the nucleus or the smooth muscle cell layer. SiNPs (calculated at 5.32 x 1011 NP/mL) attenuated Phe contractile responses, but did not alter the responses to KPSS ex vivo, suggesting that the contractile machinery is unaffected by SiNP uptake. There was an attenuated endothelium dependent (ACh) dilator response following the incubation with SiNPs ex vivo. In contrast, the lower dose of SiNPs (at 1.01 x 1011 NP/mL) had no overall effect on ACh responses. The endothelium-independent (SNP) vasodilator responses were unaffected by the incubation in SiNPs. When injected intravenously in vivo, SiNPs only had a detrimental effect on constrictor (Phe) and endothelial dependent (ACh) dilator responses, at the lower agonist concentrations. At high agonist concentrations, however, the injected SiNPs did not seem to alter the constriction or dilation response, suggesting that possible corona formation may have been protective in vivo. SiNPs injected in vivo, significantly reduced SNP-induced dilator responses at a lower dosage. This may have clinical implications on the use of SNP drugs for patients with heart disease. A small fraction of the SiNPs administered in vivo (6%) were localised within various tissues including; lungs, heart, aorta, mesentery, liver, spleen and kidney, with the MA accounting for the majority of uptake (approximately 5% of total injected SiNPs). Inhibition studies (using L-NNA and potassium channel blockers), demonstrated that both nitric oxide (NO) and endothelial-derived hyperpolarising factors (EDHFs) contribute to the vasodilator component in MAs. The co-incubation of SiNPs in the presence of L-NNA completely abolished the dilator responses to ACh, suggesting the direct effect of SiNPs on the EDHF pathway. The co-incubation in SOD did not reverse the actions of the SiNPs, indicating that a reactive oxygen species (ROS)-independent mechanism may mediate SiNPs actions in small arteries. The reduction of ERK and Akt phosphorylation ex vivo may underpin the mechanisms of SiNPs effects on rat mesenteric arteries. Depending on their dosage, we demonstrate that SiNPs uptake and accumulation in ECs have detrimental effects on the function of small arteries.