HBOC vaguely resemble blood. They are very dark red or burgundy and are made from real, sterilized hemoglobin, which can come from a variety of sources:
- RBCs from real, expired human blood
- RBCs from cow blood
- Genetically modified bacteria that can produce hemoglobin
- Human placentas
However, doctors can't just simply inject hemoglobin into the human bloodstream. When it's inside blood cells, hemoglobin does a great job of carrying and releasing oxygen. But without the cell's membrane to protect it, hemoglobin breaks down very quickly. Disintegrating hemoglobin can cause serious kidney damage. For this reason, most HBOCs use modified forms of hemoglobin that are sturdier than the naturally-occurring molecule. Some of the most common techniques are:
- Cross-linking portions of the hemoglobin molecule with an oxygen-carrying hemoglobin derivative called diaspirin
- Polymerizing hemoglobin by binding multiple molecules to one another
- Conjugating hemoglobin by bonding it to a polymer
Scientists have also researched HBOCs wrap hemoglobin in a synthetic membrane made from lipids, cholesterol or fatty acids. One HBOC, called MP4, is made from hemoglobin coated in polyethylene glycol.
HBOCs work much like ordinary RBCs. The molecules of the HBOC float in the blood plasma, picking up oxygen from the lungs and dropping it off in the capillaries. The molecules are much smaller than RBCs, so they can fit into spaces that RBCs cannot, such as into extremely swollen tissue or abnormal blood vessels around cancerous tumors. Most HBOCs stay in a person's blood for about a day -- far less than the 100 days or so that ordinary RBCs circulate.
However, HBOCs also have a few side effects. The modified hemoglobin molecules can fit into very small spaces between cells and bond to nitric oxide, which is important to maintaining blood pressure. This can cause a patient's blood pressure to rise to dangerous levels. HBOCs can also cause abdominal discomfort and cramping that is most likely due to the release of free radicals, harmful molecules that can damage cells. Some HBOCs can cause a temporary, reddish discoloration of the eyes or flushed skin.
Next, learn about PFC blood and how it is different from HBOCs.