PACA nanoparticles target and deliver sildenafil to rejuvenate aged mouse liver sinusoidal endothelial cells

Ageing is established as the most significant risk factor for disease. About 75% of people over 75 years have diabetes or pre-diabetes and/or hyperlipidaemia which are established risk factors for cardiovascular outcomes, and risk factors for age-related conditions such as dementia, sarcopenia, frailty and osteoporosis. Age-related changes in the liver microcirculation, in particular relating to the cells lining the blood vessels, the liver sinusoidal endothelial cells (LSEC), are a potential cause for dyslipidaemia and insulin resistance in old age. There is also loss of LSEC mediated waste clearance functions essential for homeostasis. Finding ways to reverse these age-related changes in the LSEC will fill a significant gap in therapeutic options available for the treatment of ageing disorders. Such therapies may also benefit patients with fibrotic livers, since LSEC changes in this disease resemble those seen in the ageing LSEC in many aspects. Nanoparticles that access systemic circulation frequently accumulate in the liver. This could be utilized as a promising strategy for targeted drug delivery to the liver. The present study assessed if poly(alkyl-cyanoacrylate) nanoparticles (PACA NPs) are a suitable vector for the targeted transport of such therapeutics to LSEC, to reverse age-related changes such as fenestration/porosity loss. Mice were co-injected with PACA NPs and formaldehyde denatured serum albumin (FSA) and their livers were then examined by microscopy. PACA and FSA co-localised to LSEC, including at the sub-cellular level in endocytic vesicles. Isolated LSEC were challenged with Nile Red (NR668) labelled PACA NPs, which were rapidly internalized. HEK293 cells overexpressing stabilin-2 internalized PACA NPs, suggesting that stabilin-2 mediates PACA uptake on LSEC. Cultured LSEC from aged mice were challenged with PACA NPs containing sildenafil and examined with scanning electron microscopy to determine effects on fenestrations. Sildenafil PACA reversed age-related changes LSEC fenestration frequency and porosity at 3-fold lower sildenafil concentrations than sildenafil alone. If sildenafil PACA induces similar changes in vivo, age-related reduction of LSEC porosity could be reversed by the targeted delivery of sildenafil via PACA NPs.