Scientists have discovered a biological quirk in bottlenose dolphins that could lead to a treatment for late-onset diabetes in humans. Studies on the marine mammals found that healthy dolphins switch into a diabetic-like state overnight when they are not feeding, but revert to a normal physiology when they eat the following morning.
The extraordinary finding has led scientists to suggest that dolphins have a "genetic switch" that allows them to mimic diabetes while they are fasting, without suffering any ill effects.
If researchers can identify a similar genetic pathway in humans, they may be able to develop drugs to effectively switch off diabetes.
Some 2.2m people in Britain have late onset, or type 2 diabetes, a figure that is expected to reach 4m by 2025 as a consequence of rising levels of obesity.
The tissues of people with type 2 diabetes have become resistant to insulin so they lose the ability to control sugar levels in their blood. The condition can damage the heart, eyes, kidneys and nerves and contributes to 5% of all deaths, according to the World Health Organisation.
Dolphins appear to mimic diabetes to maintain high levels of blood sugar when food is scarce. Like humans, dolphins need some sugar in their blood for their brains to function normally.
"It is our hope that this discovery can lead to novel ways to prevent, treat and maybe even cure diabetes in humans," said Stephanie Venn-Watson, director of clinical research at the National Marine Mammal Foundation in San Diego.
Venn-Watson's team analysed 1,000 blood samples from 52 dolphins while they fasted overnight and fed in the morning. At night time, the dolphins' metabolism changed dramatically and showed similar characteristics to that seen in people with type 2 diabetes.
"What's interesting about this is when you look at dolphins fed in the morning, they revert back to a non-diabetic state, indicating that these animals may have a genetic fasting switch that can turn diabetes on and off," Dr Venn-Watson told the American Association for the Advancement of Science meeting in San Diego yesterday.
Humans and dolphins have the largest brains of all mammals and both have red blood cells that are exceptionally permeable to glucose and able to ferry large amounts of the sugar into the brain.
Scientists believe diabetes emerged in dolphins as an evolutionary adaptation to a high protein and low carbohydrate diet. No other animal apart from humans shows the same complex range of diabetes-like symptoms as dolphins.
"Maybe this is a vestige of something dormant that could be awakened and used as a therapy or cure," Venn-Watson said.
"There is no desire to make a dolphin a lab animal, but what we can do is compare their genes with human genes and look for evidence of a genetic switch," he added.
In 2007, scientists at the Salk Institute in La Jolla, California, identified a genetic switch in mice that lowers blood sugar levels, raising hopes that a similar mechanism exists in humans.
Mark Simmonds, international head of science at the Whale and Dolphin Conservation Society, said the prospect of using dolphins to study diabetes was "a grave concern".
"Dolphins are intelligent and sophisticated animals which are vulnerable to stress and suffering when confined and removed from their natural environment and societies," he said. "The fact that dolphins in captivity experience ongoing stress adds to questions about the validity of studies of physiological processes that are intimately connected with the animals' well-being."