Mystery toxins in tainted New Zealand honey nabbed

Chemical analysis traces toxic trouble from bees back to a plant’s stealthy biological defense

trail of covert forms of neurotoxin

TOXIC TRAIL  Researchers have discovered a trail of covert forms of tutin, a potent neurotoxin, that goes from tutu shrubs (far left) to passionvine hoppers (center left) to European honeybees (center right) to honey (far right). 

Jon Sullivan/Flickr (CC BY-NC 2.0); Sid Mosdell/Flickr (CC BY 2.0); © Andrea Vannini/ (CC BY-NC); PollyDot/Pixabay

In a sticky sting operation, researchers may have nabbed the last toxic members of a honey-tainting ring in New Zealand.

Cloaked in sugars, two forms of tutin — a potent neurotoxin that can cause delirium and seizures — have been found lurking in poisoned honey, researchers report online May 21 in the Journal of Natural Products. The discovery of the incognito toxins helps to explain puzzling inconsistencies in the timing and severity of symptoms in people who have eaten the spiked syrup.

The new finding will help ensure New Zealand’s honey is safe, says clinical neurologist Andrew Chancellor with the Bay of Plenty District Health Board in Tauranga, New Zealand.  “Sporadic outbreaks of honey poisoning in New Zealand have occurred in low numbers for as long as records have been kept,” he says. For instance, a 2008 outbreak sickened more than 20, including the amateur apiarist who collected the honey.

Tutin has long been a prime suspect in the poisonings, but it has taken decades of detective work to retrace the toxin’s steps and identify accomplices. 

New Zealand’s first report of honey poisoning came in the 1857, shortly after the introduction of the European honeybee (Apis mellifera) to the islands in 1839. Almost a century later, in the 1940s, scientists finally understood the connection. The bees have an unusual taste for the droppings of another insect, the passionvine hopper (Scolypopa australis). This sap-sucking insect, an invader from Australia, likes to feast on the sweet juices of the island’s native tutu shrubs. The honeybees collect passionvine hoppers’ saccharine droppings, which are laced with tutin toxins from the tutu shrubs, researchers found. The bees then carry the toxins back to their honeycombs.

Case closed — but for an unexpected twist: When researchers measured the tutin in toxic honey, the amounts didn’t match the timing and severity of symptoms. Some honey-eaters got sick in half an hour; others fell ill almost a day after eating the same tainted batch.

Last year, researchers found a partial explanation for the delayed symptoms. People who ate toxic honey experienced two waves of tutin in their blood, says toxicologist Barry Fields of Food Standards Australia New Zealand in Barton, Australia. The first wave is from straight-up tutin, which may be in the honey in small quantities and may not cause symptoms; the second wave, researchers speculated, came from a potentially larger but mysterious form of tutin slowly released into the blood.

In collaboration with Fields’ team, researchers led by chemist Nigel Perry at the University of Otago in Dunedin, New Zealand, analyzed samples of tainted honey. Perry’s team reports in the new study that they found two new forms of tutin: tutin glycoside (which has one sugar attached to tutin) and tutin diglycoside (which has two sugars attached to tutin).

More recent, unpublished data from Perry’s lab suggest that the tutu shrub itself might add the sweet shielding. The sugar-coating may act like biological Bubble Wrap, Perry says, keeping the toxic effects of tutin contained until it’s needed to protect the plant from pesky vegetarians.

In the gut of humans, something must unpack the noxious bundle. How that happens and what determines the rate of tutin release into blood remain mysteries.

In the meantime, the New Zealand government has lowered the maximum allowable amount of tutin in honey to compensate for the covert forms of the toxin. 

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