Realizing when proteins go bad

Just as some plastics warp when left out in the heat and sun, some proteins are destroyed under suboptimal conditions. Knowing when changes in proteins are caused by poor conditions and not disease is critical. In a paper recently published in the journal Molecular & Cellular Proteomics, researchers have demonstrated that changes in two major blood proteins, considered by some scientists to be signs of cardiovascular disease, actually correlate with improper handling and storage.

Chad Borges
Borges

Chad Borges at Arizona State University was interested in albumin and apolipoprotein A-I as possible markers for cardiovascular disease in patients with type 2 diabetes. “There is a track record in the literature suggesting that the oxidized forms of both of these proteins are associated with diseases involving oxidative stress,” says Borges. ”Some researchers are supporters of this hypothesis for one or both proteins, and other researchers remain unconvinced.”
 
When Borges and colleagues started to look more closely at the changes in oxidation of albumin and apoA-1, they started to notice trends that had nothing to do with patient medical histories or diagnoses. When they analyzed the two proteins by liquid chromatography-mass spectrometry, which are common in clinical analyses laboratories, they discovered that these proteins spontaneously oxidize if they are not completely frozen below −30°C. “This point will not come as a surprise to most chemists,” says Borges. “But it has three major ramifications for clinical investigators.”
 
First, he states, validating protein oxidation as a biomarker of disease requires differentiating between biochemical effects caused by disease from artifacts brought on by improper handling and storage.
 
Second, says Borges, it would be naïve to think that albumin and apo A-I are the only proteins to get damaged under incorrect storage and handling conditions. It’s very likely that most proteins with free cysteine and methionine residues, which are most susceptible to oxidation, will break down under suboptimal conditions. “When these chemical modifications occur on proteins, they may very well affect the manner in which the protein interacts with antibodies employed in clinical test kits designed to quantify the protein,” explains Borges. ”In other words, protein oxidation may invalidate some clinical assays – and it may be the molecular root cause behind the eventual disappearance of other candidate markers of biospecimen integrity that simply disappear when a sample has gone bad.”
 
Third, Borges says the oxidation phenomenon could be turned around to benefit clinicians: It could be used to monitor how well blood samples are handled and stored and determine whether results from assays are reliable.
 
This aspect goes beyond the clinic. Laboratories that test for performance-enhancing substances in athletes have to prove that samples were properly handled and stored whenever their data are disputed in legal courts. The finding by Borges and colleagues that some key proteins oxidize under suboptimal conditions could be applied in sports doping.

Rajendrani MukhopadhyayRajendrani Mukhopadhyay (rmukhopadhyay@asbmb.org) is the senior science writer and blogger for ASBMB. Follow her on Twitter (www.twitter.com/rajmukhop), and read her ASBMB Today blog, Wild Types.

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