Fighting Pain with Gold Nanorods

Japanese researchers from the Institute for Integrated Cell-Material Sciences (iCeMS) at Kyoto University have developed a novel technique that could lead to therapies for pain relief in patients with intractable pain, possibly including cancer-related pain.

The technique uses gold nanorods—tiny rods that are 1-100 nanometers wide and long—to target pain receptors. Coating the gold nanorods with a lipoprotein allowed the nanorods to bind efficiently to nerve cell membranes bearing the pain receptor TRPV1 (transient receptor potential vanilloid type 1). Applying near-infrared light to the nanorod-coated pain receptors heated up the nanorods, in turn activating the paint receptors, which allowed for an influx of calcium ions through the membrane. Previous studies have shown that prolonged activation of TRPV1 subsequently leads to desensitization of the receptor and therefore brining pain relief. Heating the gold nanorods safely activated the TRPV1 pain receptors only, without affecting the membrane in which they lie.

Prior research shows that magnetic nanoparticles (particles in the nano-range that are made from magnetic materials) are also successful in activating TRPV1 receptors by applying a magnetic field. For TRPV1 receptor activation using magnetic nanoparticles to be successful, the target cells require genetic modification. With the lipoprotein-coated gold nanorods, genetic modification of the target cells is not required for the method to be successful. The nanorods studied by the iCeMS team were also shown to be 1,000 times more efficient than magnentic nanoparticles in generating heat and in TRPV1 receptor activation.

“The gold nanorods can be retained in the body for a prolonged period,” said principal investigator Tatsuya Murakami, an assistant professor in the iCeMS. “Local injection of our gold nanorods might enable repetitive and on-demand treatment for people experiencing intractable pain because prior genetic engineering of the target cells is unnecessary.”

The study was published in Angewandte Chemie International Edition on August 6, 2015, where Murakami and colleagues concluded, “Our method provides an optogenetic platform without the need for prior genetic engineering of the target cells and might be useful for novel TRPV1-targeted phototherapeutic approaches.”