Drug delivery: from needles to nanorods?

Gold nanorods warmed by beams of infrared light could be the ideal way to deliver drugs through the skin, researchers in Japan have discovered. Even the bulky proteins often used in vaccines can efficiently pass through the skin this way, the team has found.

Delivering drugs or vaccines through the skin can offer many advantages over pills or injections, say Dakrong Pissuwan, Takuro Niidome and colleagues at Kyushu University. Drugs delivered this way can avoid being quickly broken down by the liver, while vaccines can generate a stronger immune response because of the many antigen-recognising immune cells present in the skin.

However, large hydrophilic proteins tend to be poorly absorbed through the skin, being halted by the stratum corneum, the hydrophobic barrier layer of dead cells that make up the skin’s outer surface. Pissuwan and Niidome have now shown how gold nanorods can help just such a protein, ovalbumin (OVA), to cross this barrier and enter the body. 

The team exploited the fact that gold nanorods heat up when irradiated with near-infrared (NIR) light - a property known as the photothermal effect. The researchers mixed together OVA, the nanorods and a surfactant into an oil-based dispersion that could be applied to the skin. When hit by NIR light, the warmed nanorods erode the stratum corneum, allowing the protein to pass through. Tests using mice showed that the protein successfully triggered an immune response when delivered in this way.

’We believe that the induced immune response is strong enough to be used as a vaccination technique,’ Pissuwan says. The team is yet to study in detail whether the process damages the skin, but preliminary studies on the mice treated so far have not revealed any severe side effects, Pissuwan adds.  

If it works as well in humans as it does in mice, the technique could offer a good way to deliver proteins through the skin, says Tom Robertson, who investigates transdermal drug delivery at the University of South Australia. ’Obviously this would be appealing to the consumer - the fear of needles has been side-stepped,’ he says. ’If that leads to better compliance with vaccination programmes then that would be a big step.’ The process could also be much cheaper than a competing vaccine delivery technology, microneedle patches, because of all the fabrication steps involved in making them, he adds.  

Pissuwan and Niidome are currently investigating other types of drug that can be delivered through the skin using gold nanorods. ’The penetration of the gold nanorods through the skin also needs to be studied before we move to try it at the clinical level,’ Pissuwan adds. 

James Mitchell Crow