Welcome to the HAB Marketplace

Microcystin-LR: How Toxic Is It? (Part II)

Posted by Stephanie A. Smith, Ph.D. on Mon, Jul 15, 2013 @ 06:00 AM

Microcystis Bloom “I’ve been swimming in that green stuff for years, and I’m fine!”  This is a sentiment I have heard often, usually from people who ignore our Ohio EPA’s warnings to avoid waters that have an active harmful algal bloom (HAB).  The low number of confirmed cases of human illness directly resulting from exposure to HABs and toxins like Microcystin-LR should not be interpreted to mean that HABs are safe to swim in.  Not all adverse health effects are acute, which is why LD50 data that I discussed in my previous blog don’t tell the whole story.  In fact, there are numerous examples in infectious disease and toxicology where confirmed cases of human toxicity have been scant, but when increased exposure risks prompt further studies we discover the risks are higher than we initially thought.  A case in point regards toxins called aflatoxins, and there is one in particular that has important parallels to the HAB toxin Microcystin-LR.

Microcystin-LR is classified by the International Agency for Research on Cancer (IARC) as a Group 2B agent, meaning that it is possibly carcinogenic (cancer-causing) to humans.  It is not hard to find literature where Microcystin-LR is referred to as an agent of liver cancer, but at large, the Group 2B classification overrides that conclusion.  Let’s look at another Group 2B carcinogen to understand what that classification does, or doesn’t, mean.

Aflatoxins are produced by a fungus, and can occur in animal feeds and grains that are stored too long in moist conditions.  One type of aflatoxin, called M1, was originally placed on the Group 2B list like Microcystin-LR.  At some point, it was found that when cows ate aflatoxin-contaminated feeds, M1 could find its way into milk and dairy products, including infant formula.  When this was discovered the carcinogenic properties of M1 were poorly understood, but there were similar aflatoxins that were definitely known to cause cancer.  After scientists took a closer look (thanks to considerable research investments), M1 was reclassified as a Group 1 agent by the IARC.

Motor Boat HABThe increased exposure risks of humans to M1are what prompted increased study, and the effects of global warming and a rise in the incidences of HABs are likewise leading to increased exposures of people to Microcystin-LR, especially in recreational waters.  There are other intriguing parallels between Microcystin-LR and M1, including synergistic effects when ingested by people infected with Hepatitis B, and a cellular mechanism that indicates strong carcinogenic potential (M1 affects the tumor suppressor p53, Microcystin-LR inhibits protein phosphatases involved in signal transduction pathways associated with cellular growth cycles).

Hopefully, recognition of its carcinogenic potential and the increased exposures of people to Microcystin-LR will lead to increased support for toxicological studies, so that we can eventually understand whether it is a Group 1 carcinogen, or alternatively not a carcinogen for humans.  Beagle Bioproducts hopes that our products will help scientists conduct research to better understand the risks of Microcystin-LR exposure.

Footnote:  If you want a good technical review of M1 aflatoxin, this article by Anfossi et al is the place to go!

No comments yet.

Leave a Reply