The Natural Presence of Gold
For centuries, the idea of gold within the human body was a mystery, but modern scientific analysis has confirmed its existence. The 0.2 milligrams of gold present in an average human is part of the body's overall metallome—the complete collection of metal ions and their interactions with biomolecules. This tiny amount is not accumulated by specific, purposeful absorption but rather is an incidental collection from the environment, primarily through our diet. It is important to distinguish this from the gold used intentionally in medicine. The gold that naturally occurs is mostly found in the blood and is gradually excreted over time. Its presence, while fascinating, does not currently have a known essential biological purpose, such as a role in enzyme cofactors or structural support, unlike other trace minerals like iron or zinc.
Historical and Modern Therapeutic Uses
Ancient Remedies to Modern Ailments
Historically, gold was used in ancient medicine, where cultures like the Egyptians and Chinese incorporated it into remedies, believing it held curative or mystical powers. These early uses lacked scientific rigor, yet they established a long-standing fascination with the metal's purported healing properties. In the early 20th century, modern medicine began to explore its therapeutic potential more seriously.
Chrysotherapy for Rheumatoid Arthritis
One of the most well-documented medical uses of gold was chrysotherapy, the administration of gold compounds to treat rheumatoid arthritis (RA). In the 1930s, injectable gold salts like gold sodium thiomalate were found to be effective in reducing inflammation and slowing joint damage in RA patients. The mechanism is complex, but it's believed to involve gold ions inhibiting immune cell activation and inflammatory responses. While effective for some, chrysotherapy's use declined in favor of newer, less toxic drugs due to significant side effects, including kidney damage, skin rashes, and blood disorders.
Gold in Biomedical Implants
Due to its high biocompatibility and inertness in its metallic form, gold has been used in various medical implants. Dental alloys for fillings and crowns have long included gold. It has also been used for specialized implants, such as eyelid weights to correct lagophthalmos and components in middle ear reconstruction, where its inertness minimizes adverse tissue reactions.
The Age of Nanotechnology: Gold's New Medical Role
Targeted Drug Delivery and Imaging
The advent of nanotechnology has unlocked a new dimension for gold in medicine. Gold nanoparticles (GNPs) can be synthesized in various sizes and shapes, giving them unique optical and electronic properties. These tiny particles can be engineered to carry drugs, antibodies, or DNA and deliver them with high precision to targeted cells, such as those in a tumor. The surface of GNPs can be functionalized with specific molecules that act as homing beacons, guiding them to diseased tissue. This targeted approach minimizes harm to healthy cells and enhances the drug's effectiveness.
Cancer Therapy and Diagnostics
GNPs have shown significant promise in cancer treatment. In a technique called plasmonic photothermal therapy (PPTT), GNPs that accumulate in a tumor are heated using a laser, destroying the cancerous cells while leaving surrounding healthy tissue unharmed. GNPs are also used in advanced diagnostic imaging. They can act as contrast agents in imaging techniques like computed tomography (CT) and photoacoustic imaging, providing higher resolution and specificity than conventional agents. Furthermore, GNPs can be conjugated with antibodies to detect disease markers, revolutionizing diagnostic tools with faster, more sensitive, and more specific results.
Comparing Forms of Gold in Medicine
| Feature | Bulk Metallic Gold (Implants) | Gold Salts (Chrysotherapy) | Gold Nanoparticles (Nanomedicine) |
|---|---|---|---|
| Form | Solid, pure metal | Soluble ionic compounds | Colloidal particles |
| Mechanism | Physical biocompatibility and inertness | Biochemical inhibition of immune cells | Nanoscale interactions, targeted delivery, and optical properties |
| Medical Use | Dental fillings, implants, prosthetics | Rheumatoid arthritis (largely historical) | Cancer therapy, diagnostics, targeted drug delivery, imaging |
| Reactivity | Highly inert and stable | Chemically reactive, especially with thiols | Reactivity depends on size, shape, and surface chemistry |
| Toxicity | Very low toxicity, minimal tissue reaction | Significant side effects due to systemic toxicity | Toxicity is size- and surface-dependent; requires careful engineering |
| Clinical Status | Established and widely used | Largely superseded by newer drugs | Experimental, undergoing clinical trials |
Toxicology and Future Prospects
Safety and Biocompatibility
While bulk metallic gold is very inert and non-toxic, the toxicity of gold-based compounds and nanoparticles is a critical area of research. Gold ions released from reactive gold compounds can cause side effects. For nanoparticles, factors like size, shape, surface coating, and concentration influence their toxicity. The body’s ability to clear nanoparticles depends on their size, with smaller particles (under 8nm) more likely to be cleared by the kidneys. Careful engineering is required to minimize potential harm, and ongoing research is focused on creating safe, biocompatible nanoparticles for long-term use.
The Future of Gold in Medicine
The future of medical gold lies in the precise control offered by nanotechnology. Researchers are exploring gold nanoclusters and other advanced forms for tracking cells, enhancing vaccines, and creating new diagnostic platforms. As research continues to unravel the complexities of gold's biological interactions, its role is poised to evolve from a historical treatment into a cornerstone of next-generation medical technology.
Conclusion
The human body does not have a biological requirement for gold, containing only trace, non-functional quantities. However, the story of gold in medicine is far from over. From its historical use in treating rheumatoid arthritis to the cutting-edge field of nanotechnology, gold has demonstrated remarkable potential. Gold nanoparticles, with their unique properties for targeted delivery, advanced imaging, and photothermal therapy, are now at the forefront of medical innovation, opening new frontiers in disease diagnosis and treatment.
For more detailed information on the specific use of gold nanoparticles in clinical applications, explore the comprehensive review on gold-based nanomedicine available on the National Institutes of Health website: GOLD NANOPARTICLES: A REVIVAL IN PRECIOUS METAL THERAPY AND MEDICAL DIAGNOSTICS.
