Since ancient times, humans have been preoccupied with extending life. Mythology has since given way to science fiction, with futuristic technology often imagined to bring eternal youth. These fantasies were lent credibility when a study successfully used young blood to revitalise the brains of old mice.
In 2014, using a rather unusual technique known as ‘parabiosis’, the blood vessels of two mice – one young, one old - were fused together. Blood was continuously exchanged between the two mice, not unlike the circulatory systems of conjoined twins.
The parabiosis experiment produced substantial changes in the aged mouse’s hippocampus. This region of the brain is involved in the storage of memories and is particularly vulnerable to age-related damage. During the experiment, expression of a subset of genes increased. These genes regulate the process by which the strength of communication between pairs of neurons is modified, called synaptic plasticity. Synaptic plasticity is thought to be the neurological basis of learning, and improving it holds promise for treatment of age-related cognitive decline.
If it is difficult to envision a future in which humans are stitched together to cure disease, more recent studies have provided a more feasible solution. Blood plasma from human umbilical cords has been injected into old mice, not only altering gene expression, but actually reversing the age-related decline in learning and memory. This points to the existence of restorative factors in human blood which decline with age. As blood plasma is already regularly used in medicine, the hurdles towards approving young blood plasma as a treatment would be significantly lower than development of a brand-new drug. Researchers have also begun to pinpoint specific proteins in blood plasma linked to ageing, providing a whole host of new drug targets against neurodegeneration.
Treating neurodegeneration alone would be a huge step forward, but the brain is not the only organ rejuvenated by young blood. Tests in mice have shown that young blood can repair damage to almost every tissue and organ tested – including the muscles, liver and heart. This opens up the possibility that parabiosis may not only treat specific diseases, but could in fact extend life. However, safety concerns have stalled the use of young blood in humans; parabiotic mice are prone to unexpected death and rejuvenating cells leads to an inevitable increase in cancer risk. Despite this, a real-life ‘fountain of youth’ seems closer than ever.
The possibility of a cure for ageing brings hope to people suffering from life-altering diseases, but also presents a host of ethical issues. The line between treating disease and striving for immortality is not so clear-cut, and advancements in parabiosis will have to focus on improving quality, not length of life. Another issue is access to life-extending treatment: we could be faced with a future where the poor sell their blood while the rich chase immortality. Sounds far-fetched? It’s already happening. In a number of ‘trials’ – with no controls – people paid thousands of dollars to be injected with the blood plasma of teenagers, obtained from donors receiving only $20-50 compensation. Maybe vampires too are becoming a reality.