Biotin and Avidin Are Used in Many Diagnostic Tests

Because of the molecular attraction and strong bonding between biotin and avidin, medical researchers began exploring its use for diagnostic and therapeutic applications. In addition to using avidin, researchers also use avidin conjugates and streptavidin to bind to biotin. Streptavidin is often used because although biotin bonds as strongly to streptavidin as to avidin, it releases up to 30 times faster. This method may be chosen when a biotinylated treatment molecule is attached to a carrier molecule.⁹

Although there are complex variations involved in each separate diagnostic test, the basic mechanism involves attaching biotin to the molecule used as a probe to detect whatever is being looked for in the body (a process called biotinylation), applying this biotinylated probe to the tissue being tested, and then detecting the bound biotinylated probe molecules-substance with labeled avidin molecules. Other treatments and tests take advantage of the fact that avidin/streptavidin molecules accumulate wherever there is inflammation or infection.^{9, 12}

Some of the innovative biomedical uses of the biotin-avidin bonding mechanism include:

• Detection of GAD65 Antibodies in Autoimmune Disease. Biotinylated GAD65-based enzymes are used with avidin derivatives to successfully detect GAD65 antibodies - typically more prevalent in patients with type-1 diabetes. These antibodies are considered a marker for predisposition to type-1 diabetes and also for a number of autoimmune disorders that may occur in these diabetic patients. GAD65 tests are also used to test for GAD65 antibodies patients with stiff-man syndrome, autoimmune cerebellitis, and other nervous system disorders (e.g., epilepsy and myasthenia gravis).^13-14
• Test for Vertebral Osteomyelitis. Clinical studies demonstrate that using a biotin-streptavidin testing mechanism is significantly more accurate than either MRI or CT scan in early diagnosis of suspected vertebral osteomyelitis - a type of bone infection. In one investigation involving 55 men and women within two weeks of first reporting symptoms of osteomyelitis, one group was given an MRI, another a CT, and then all underwent a streptavidin/111In-biotin scintigraphy. This entailed IV-administered streptavidin followed four hours later with biotin tagged with a low-dose, short half-life isotope of the element indium. The streptavidin/111In-biotin scintigraphy test accurately detected osteomyelitis in 32 of the 34 patients and correctly reported negative results in 19 of 21 uninfected patients - compared to between 35 and 55% accurate positive and 57-75% correct negative results with the MRI/CT scans.¹²
• Virus-Like Particles (VLPs). A common use of VLPs is for vaccines - non-replicating, noninfectious molecules that deliver an antigen of a particular virus that stimulates the body's immune system response to build antibodies against the actual infectious, replicating virus. Another benefit of VLPs with therapeutic potential for cancer and chronic viral infections is their stimulatory effect on the immune system's T-cell responses. To boost this effect, researchers use the bonding mechanism between biotin and streptavidin to attach multiple beneficial molecules to VLP walls.¹⁵