By David N. Leff
Whenever a virus, a bacterium or any other intruder penetrates the body, there's an antibody poised to pounce on it. Never mind that the immune system may have never seen this antigen before in its life. It has fashioned and filed an estimated 10 million antibody-making B cells, custom-designed to grab any halfway water-soluble antigen.
But what about a man-made molecule, never seen before in nature?
Fullerenes are a trendy example.
These weirdly shaped chemical compounds bear the name of a prodigal American inventor, Richard Buckminster Fuller (1895-1983). His best-known creation is the geodesic dome, a hemispherical structure composed of light girders and trusses, interwoven in an array of hexagons and pentagons.
Soccer balls and basketballs are reduced spherical versions of these polygonal forms.
Fullerenes are submicroscopic versions. A fullerene molecule consists of 60 pure carbon atoms interlaced in the geodesic patchwork of hexagons and pentagons.
Pure carbon existed in only two elemental forms, diamonds and graphites, until the fullerenes came along. "I don't think anyone has ever found fullerene in nature," observed chemist and immunologist Bernard Erlanger, of Columbia University, in New York. "Now they are artificially made by high-temperature reactions with carbon dust — like soot — in electric-arc furnaces."
Erlanger, a professor of microbiology at Columbia, said, "The person who discovered fullerenes, Richard Smalley, shared the 1996 Nobel Prize in chemistry. He named them because their molecular structures looked like Buckminster Fuller's geodesic domes.
"Fullerenes have interesting electronic properties," Erlanger told BioWorld Today. "For example, their compounds have been used to make nanotubes, for miniaturizing electronic apparatus down to the molecular level."
And so far, fullerenes have one interesting biological property, he added. "They have the ability to absorb activated oxygen. Fullerene itself, and compounds made with a fullerene base, pick up oxygen very easily.
"In an animal or a human," Erlanger said, "this is carried out by superoxide dismutase — SOD. It's believed that multiple sclerosis and some other nervous diseases are caused by oxygen free radicals that SOD has not sopped up and inactivated."
What got him intrigued with fullerenes was a report that some of their compounds can protect a mouse model for Lou Gehrig's disease (amyotrophic lateral sclerosis), to some extent, from developing ALS.
Erlanger is senior author of a paper in the current Proceedings of the National Academy of Sciences (PNAS), dated Sept. 1, 1998. It bears the title: "Antigenicity of fullerenes: Antibodies specific for fullerenes and their characteristics."
Two Motivations: Curiosity, Utility
"There were really two reasons why I wanted to make antibodies," Erlanger recounted. The first motive: "I was curious to see if the immune system could recognize this unusual compound, so far not found in nature, and make antibodies to it.
"And second, to see if these antibodies would be clinically useful. If a patient is being treated with fullerene compounds, you want to know their levels in tissues, and also circulating in serum or urine. The easiest, most accurate and most sensitive way — because it measures very low quantities — is with antibodies specific for these fullerenes."
He said that "at the time fullerenes were discovered, a number of people had begun making fullerene compounds. One of them for example is Stephen Wilson, co-author of this PNAS paper. He and his colleagues at Sphere Biosystems Inc., in New Brunswick, N.J., supplied me the fullerene compounds I ordered, and also some others suggested by them."
Erlanger and his co-authors reported in PNAS their finding that although neither fullerene nor any structure like it is found in nature, "they are capable of being recognized by the immune system, and then processed intracellularly. This takes place inside the cells, so it was by no means understood that once the fullerenes got into the cell they wouldn't screw up anything"
He explained: "In the processing that occurs in most cases, the B cell recognizes the fullerene on its surface. The fullerene is attached to a protein, in our experiments to bovine thyroglobulin (TG). By chemical reactions, we attached 15 or so fullerene compounds to this TG protein. That's what we immunized our mice with. This pulled the fullerene into the cell mass and digested the protein/fullerene conjugate into small peptides, 6 to 8 amino acids long.
"The fact that it can do that even though the fullerenes, which are completely unnatural, are in there," Erlanger pointed out, "is an important finding. Then," he said, "it presents the peptide on the cell surface to T cells, which then are induced to produce factors that cause multiplication of the B cells.
From Form To Structure
"The next thing that's of interest to me even beyond the use of fullerenes in therapeutic situations," Erlanger added, "is just how the antibody recognizes this weird structure."
To this end, he and X-ray crystallographer Bradford Braden at Bowie State University, in Bowie, Md., are seeking a joint research grant. "We're going to make monoclonal antibodies, and fragments of them, and give these to the people in Bowie State. He is going to crystallize these antibodies together with fullerene compounds. That way, we'll discover the molecular structure of the antibody/fullerene complex.
"From that," he said, "since fullerenes are so unusual, we hope to find some very unusual things. Their only functions that have been identified at the moment are their antioxidant reactions. We don't know much more than that. But I'll know a hell of a lot more when we get these complexes and see what their structures are."
As for the clinical potential, Erlanger noted that "a number of these fullerene compounds can be tested in the various disease states where SOD is deficient, and in other systems too. The biotech industry has a lot of drug discovery programs where they screen compounds at random.
"What our work here says," he suggested, "is that they screen some of our compounds, of which there are many many more than we have in our paper. Then," Erlanger said, "if any of them work, we have an immune assay system to measure them in patients." *