Congo red is not the nickname of a Central African communist.
Rather, it's an industrial dye for coloring cotton cloth. "Congo red," explained molecular biologist Junying Yuan at Harvard Medical School, "is a dye that people have been using for 150 years to stain postmortem brains for amyloid pathologic tissue, and diagnosing amyloidosis."
Yuan is senior author of a paper in Nature, dated Jan. 23, 2003. It's title: "Pivotal role of oligomerization in expanded polyglutamine neurodegenerative disorders."
One such disorder is Huntington's disease (HD).
"The key finding in this Nature paper," Yuan told BioWorld Today, "is that the expanded glutamine aggregation of CAG repeat sequences is neurotoxic. That should be a promising target for therapeutics to treat Huntington's disease.
"CAG is a triplet DNA codon," Yuan explained, "composed of cytosine-adenosine-guanine. It codes for glutamine, an essential amino acid that's a normal component of protein. Proteins are made of amino acids; DNA is made of nucleic acid. Sometimes the CAG number of copies increases in Huntington's disease. Healthy people have multiple copies of glutamine in the HD gene, for example. They have far fewer CAG repeat copies than do HD patients - 35 copies or less, whereas the HD patients have 40 or more.
"The role of expanded polyglutamine aggregation in the neuronal dysfunction and degeneration of HD is very controversial," Yuan continued. "Three years ago most people probably would have believed that the CAG repeat aggregation is either a bystander effect or even beneficial. These opinions were mostly because of limited understanding of the phenomena at the time, or just indirect evidence interpreted incorrectly.
"Most significant," Yuan pointed out, "is the fact that multiple neurodegenerative diseases such as Parkinson's, Alzheimer's, amyotrophic lateral sclerosis - including the prion-caused mad cow disease, bovine spongiform encephalopathy - all have abnormal protein aggregates as common features."
CAG Repeats Cause Eight Maladies - Count 'Em
"As for normal protein aggregation," Yuan continued, "our study implied that the nonpathological aggregation of a protein can be a therapeutic target for these diseases. Those patients also develop diabetes, because their body cells have these extended polyglutamine repeats. All told so far, polyglutamine accounts for eight neurological diseases, which are expanded polyglutamine-related. They include five different kinds of spinal cerebellar atrophy, Kennedy's disease, and other types of neurodegeneration leading to selective neuronal death - also caused by polyglutamine repeats."
In an overview, Yuan summed up the in vitro experiments she and her team reported in the Nature paper: "We had a cell model for extended polyglutamine-induced cell death. So we asked what can we do to prevent a cell from dying? We tried a whole bunch of compounds, and Congo red [CR] was the only agent that could do that. Its mode of action is to insert itself into anti-parallel beta sheets, a kind of protein structure. As we described in this journal article, we found out that CR disrupts the beta sheets.
"One thing we found is that it can disrupt polyglutamine. So then we asked whether it can disrupt the aggregation in vitro, and what CR does to the cells. Then we found out that it maintains normal ATP [adenosine triphosphate] levels, and the protein synthesis of protein degradation machinery, which prevents deactivation of an apoptotic cell-death protease - namely caspase-8.
"This discovery might have suggested that Congo red is a candidate therapeutic," Yuan observed. "However, CR cannot cross the blood-brain barrier, so it can t be used as a drug directly. But there are research programs to develop CR-like compounds that can penetrate the barrier, and have actions similar to CR. I don't know their status. Some look like CR; some don't, but have a similar action, based on beta-sheet disruption of proteins."
To study HD in vivo, Yuan and her co-authors turned to a well-established murine animal that mimics the human disease closely. "This mouse model has a truncated exon-1 expressing 169 expanded polyglutamine CAG repeats," she recounted. "It's a piece of the HD protein from a patient, which expresses a piece of the gene that encodes a mutant protein. Like human symptoms, these transgenic mice developed motor dysfunction, severe weight loss, diabetes owing to the presence of polyglutamine aggregates in the pancreas, curtailed life span, and eventually died. They had significantly shorter survival, and the Congo red treatment helped prolong that, as long as we kept up the CR treatments, by either intracerebroventricular cannula or intraperitoneally."
Dangled By Tail - Briefly - To Test HD Model
"One form of behavioral testing was dyskinesia of the hind limbs," Yuan went on. "It consisted of holding up a mouse by the tail - very briefly. The wild-type animals simply extended their feet while the HD model curled up very typical of motor dysfunction. Then we measured their irregular gait, and they walked around like a drunk. The transgenic mice formed the CAG aggregation with the expanded polyglutamine, whereas those receiving CR treatment didn't have aggregation.
"Our present ongoing work," Yuan volunteered, "involves screening for other compounds that inhibit polyglutamine induction, and we've found a variety of such compounds. We're now trying to sort out these inhibitory agents; whether they act like CR or are blocking a different step. In finding compounds useful for treating HD, it appears that the same therapeutics might also act in treating some other neurodegenerative diseases. Congo red has been shown to disrupt amyloid beta, which is the toxic culprit of Alzheimer's disease. In that regard CR may prevent the amyloid beta peptide.
"CR has also been shown to alter prion proteins that make mad cow disease, but it has not been tested as to whether if one treated mice with models of bovine spongiform encephalopathy CR would be helpful or not. It would be very interesting to test that. However," Yuan noted, "we are not allowed to work on mad cow disease, which requires a higher level of research facilities.
"The university has applied to patent our discoveries," she allowed, "with myself as principal inventor. It claims something like, For treatment of neurodegenerative diseases, and usage of compounds in Huntington's disease therapy,'" Yuan concluded.