For the first time, scientists have images of something that's heretofore only been known about in theory, and what seems like a tiny step to capture microscopic blood vessels may also be a giant leap in bone health research.
A vascular system within the bones has long been theorized, but until recently, no one has found it. Using advanced imaging technology, scientists have finally uncovered a complex network of microscopic blood vessels. What they found inside that network has offered insight into degenerative diseases of the bone, including osteoporosis and chronic arthritis. What we're now learning, as a result, is revealing new science about bones and that could well make a major difference to arthritis or osteoporosis sufferers.
Doctors have understood from as early as the 1920s that the bones have a circulatory structure. In World War II, medics were taught to inject emergency medications into a patient’s leg bone for hemorrhagic injuries when intravenous therapy was otherwise impossible. This process, called IO infusion, is just as effective at delivering intravenous medications and can be a life-saver in cases where a person is in shock, dehydrated or the blood pressure is too low to find a vein.
Still, despite knowing about their existence for nearly a century, researchers have only just captured the first images of bones’ microscopic blood vessels. As reported in a study recently published in Nature, researchers used a combination of techniques to gain the images. First, they soaked the bone for seven days in a detergent called Tween20 and cleaned it in ethyl cinnamate, which made the bones transparent. Then they stained the samples to reveal circulatory tissue and examined them under a high-powered electroscope.
The study’s researchers found a massive network of blood vessels, called trans-cortical vessels (TCVs), which they believe neutrophils, leukocytes and other immune cells use to travel from the bone marrow into the bloodstream. But these networks may also possess a supportive role in the vascular system’s structure: More than 80% of the blood in the arteries also filters through TCVs, along with nearly 60% of blood moving through the veins.
The researchers also found evidence that osteoclasts, cells that dissolve bone tissue to make way for new bone growth, are vital to TCV maintenance. As they eat through the bone, osteoclasts create microscopic passages that become the framework for new TCV passages. This finding led to a better understanding of how bone density actually works.
Osteoporosis occurs when osteoclasts become hyperactive, or when the body doesn’t have enough calcium to replace all the osteoclasts have dissolved. When osteoclasts become depressed, such as when a person takes bisphosphonates to reduce bone loss, this appears to inhibit the growth of new pathways for TCVs, effectively reducing bone circulation. This may be why, paradoxically, larger bones can be at a higher risk of fracture in people taking bisphosphonates.
Too much circulation isn’t any better. Chronic arthritis appears to trigger an overabundance of TCVs in affected areas. Along with increased circulation (which means increased osteoclast activity, and therefore, decreased bone density), this increases the number of immune cells coming in from the bone marrow. Because chronic arthritis is caused by too many immune cells to begin with, this can leave bones even more vulnerable to erosion and damage.
The discovery of TCVs has led to a wealth of understanding about how bones interact with the circulatory system. Future studies may be able to shed light on potential treatments for degenerative bone diseases like osteoporosis and chronic arthritis. More is likely to come to light as researchers dig deeper into this incredible breakthrough.