Humans have shared a special bond with a certain animal since the time of Aristotle. Artworks as early as 1500 BC depicted interactions with this fascinating creature. Members of this species have assisted the US Navy, and have also been used as therapy animals for patients with Down syndrome and autism. These amiable beings are none other than dolphins.
Along with other marine mammals such as whales and porpoises, dolphins fall into the order Cetacea, and are further grouped under the Delphinus genus. Despite living in an entirely different habitat, they share striking neural similarities with humans, such as specialized brain cells dedicated to intelligence, advanced social skills, empathy, and problem solving. The two mammals also share many common biochemical pathways. This has spiked an interest in studying dolphins as an animal model for diseases such as Alzheimer’s and diabetes.
The Alzheimer’s connection
Dolphins have large brains, coming second to humans in brain size to body mass ratio, that share similar molecular machinery and pathology as human brains. Dolphins sometimes even develop Alzheimer’s disease, a progressive brain disorder that impairs memory and cognitive ability. This disease is characterized by the accumulation of beta amyloid and tau proteins that disrupt neural cell functions.
Both mammals have been found to be uniquely susceptible to Alzheimer’s due to altered insulin function. Like humans, dolphins have a long post-fertility life span that is associated with decreasing sensitivity to insulin. This hormone regulates blood glucose levels and initiates a cascade of chemical reactions known as insulin signaling. Scientists speculate that disrupted insulin signaling can alter the function of specialized brain cells called astrocytes, which supply nerve cells with essential nutrients and maintain pH and ionic balance in the brain environment. This contributes to nerve cell degeneration and Alzheimer’s progression.
Similar alterations to insulin signaling allows us to draw analogies between dolphins and humans, not only in Alzheimer’s research, but potentially in other related diseases such as diabetes as well.
Diabetes in Dolphins
Research at the National Marine Mammal Foundation (NMMF) has revealed that bottlenose dolphins could be the first natural animal model for Type 2 diabetes. Diabetes is a condition where the blood glucose levels are elevated to dangerous levels. People with diabetes either don’t produce insulin (Type 1) or their body’s cells are resistant to insulin (Type 2).
According to the NMMF, dolphins have a genetic fasting switch that allows them to involuntarily turn on and off a diabetic-like condition. Dolphins’ large brains demand high amounts of glucose, yet their fish-laden, high protein diet is low in sugar. To counter this, they show a kind of insulin resistance during sleep that helps to maintain blood sugar levels in the body, ensuring the brain is well fed. As soon as they eat breakfast, they revert from this ‘diabetes-like state’ to a normal metabolic state.
Scientists believe that there may be an analogous “switch” for insulin resistance in the human genome If so, this type of research could ultimately lead to new therapies or potentially even a cure for this disease.
Treatment for Hypoxia in Humans
Dolphins also produce protective proteins that could provide clues for treating hypoxia. Hypoxia is a condition where the body is deprived of oxygen, and can severely affect the brain, liver, heart, and kidneys. In humans, hypoxia can occur during a heart attack, stroke, or kidney injury; this induces the release of free radicals that can cause severe organ damage.
Dolphins, however, can survive underwater dives as long as 90 minutes. During these dives, dolphins undergo hypoxia followed by reoxygenation as they resurface. Dolphin serum has been found to contain high levels of a protein called vanin-1, which is believed to protect their kidneys from the injurious effects of free radicals that are generated from this process. Humans have also been found to possess vanin-1, although in much smaller amounts. Scientists are currently investigating whether these findings can be applied to human medicine, specifically to protect against kidney failure.
Humans and dolphins share many disease pathologies in common. By continuing research into the Delphinus genome, we might be able to develop improved treatments for conditions like Alzheimer’s, type 2 diabetes and hypoxia. Alzheimer’s and Diabetes are two of the leading causes of death in the United States, with about 83,564 and 121,404 deaths in 2017, respectively. Dolphins are proving to be valuable models for identifying genes and metabolic processes that may be relevant to the progression of these diseases. So it’s time to ‘dive deeper’ into the Homo-Delphinus disease connection.