Nanopar­ti­cles to man­age big prob­lem: snakebites

San Antonio Express-News (Sunday) - - Health | Science - By Don­ald G. McNeil Jr.

An Epi-Pen to treat a snakebite?

It is a dis­tant dream, but a Cal­i­for­nian chemist and Costa Ri­can venom ex­pert are re­port­ing progress in a novel ef­fort to make in­jectable nanopar­ti­cles that can neu­tral­ize snake venom and can be car­ried in back­packs.

In a re­cent study in PLOS Ne­glected Trop­i­cal Dis­eases, their par­ti­cles pro­tected mice against tis­sue dam­age from spit­ting-co­bra venom with­out trig­ger­ing al­ler­gic re­ac­tions.

In wealthy coun­tries, snakes are an abid­ing threat to an un­lucky few, among them hik­ers, ranch hands, sol­diers, zookeep­ers and rep­tile col­lec­tors.

But in the trop­ics of Africa, Asia and Latin Amer­ica, they are a ma­jor cause of death and dis­abil­ity in ru­ral ar­eas: More than 2 mil­lion peo­ple are bit­ten each year. About 100,000 of them die, and an­other 400,000 are left with se­ri­ous dis­abil­i­ties, in­clud­ing am­pu­ta­tions or nerve dam­age so ex­ten­sive a leg or hand is per­ma­nently use­less.

An­tivenins ex­pen­sive

An­tivenins have ex­isted for decades, of course, but they are ex­pen­sive, po­ten­tially dan­ger­ous and used only rarely in poor coun­tries. The medicines con­tain an­ti­bod­ies har­vested from the blood of sheep or horses that have been in­jected with di­luted venom and al­lowed to re­cover.

The process is cum­ber­some, and the an­ti­bod­ies must be kept re­frig­er­ated. Few drug com­pa­nies bother to make an­tivenins, so the prices are high.

Be­cause they con­tain horse or sheep pro­teins, an­tivenins also can trig­ger life-threat­en­ing ana­phy­lac­tic shock or hem­or­rhag­ing. They must be given in­tra­venously in an emer­gency room, and many bite vic­tims die be­fore they can reach hos­pi­tals.

More­over, an­tivenins are species-spe­cific: A treat­ment for co­bra bites, for ex­am­ple, will not help against rat­tlesnake or asp bites. Hos­pi­tals must keep many kinds of an­tivenins on hand, and vic­tims must be able to pro­duce or de­scribe the snake that bit them.

“They have a lot of is­sues, but they’re the only show in town,” said Ken­neth J. Shea, a chemist at the Univer­sity of Cal­i­for­nia, Irvine.

Shea’s lab is cre­at­ing hy­dro­gel nanopar­ti­cles coated with poly­mers — the build­ing blocks of plas­tics — small enough to at­tach to pro­teins.

While screen­ing them against com­mon ven­oms, he iso­lated some nanopar­ti­cles that bind with and neu­tral­ize two poi­sons pro­duced by snakes such as co­bras, kraits, co­ral snakes, sea snakes and mam­bas.

A stop­gap mea­sure

José María Gu­tiér­rez, a venom spe­cial­ist at the Univer­sity of Costa Rica, in­jected dozens of mice with the venom of the black­necked spit­ting co­bra. He found that Shea’s nanopar­ti­cles sig­nif­i­cantly re­duced tis­sue dam­age in the mice. Im­por­tantly, the nanopar­ti­cles did not ap­pear to in­ter­fere with nor­mal pro­teins or to trig­ger dan­ger­ous al­ler­gic re­ac­tions.

It would not com­pletely re­place an­tivenins. But since the nanopar­ti­cles are rel­a­tively easy to make and need no re­frig­er­a­tion, they could be car­ried in the field and in­jected into the site of a bite, re­duc­ing tis­sue dam­age and stop­ping the poi­son from spread­ing. That would buy time to reach bet­ter treat­ment.

The path to reg­u­la­tory ac­cep­tance might be a long one. Use of nanopar­ti­cles in medicine is rel­a­tively new, and for clin­i­cal tri­als in­volv­ing snakebites, “there aren’t many vol­un­teers,” Shea said.

Shan­non Tomp­kins / Staff file photo

Many in­ci­dents of snakebite oc­cur when a per­son tries to catch, kill or in­ter­act with a ven­omous snake. Sim­ply leav­ing the rep­tile alone is the surest way to avoid a po­ten­tially dan­ger­ous en­counter.

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