Humans in the Baltic countries have used ancient amber (fossilized tree resin) for medicinal purposes for centuries. Infants there today are given amber necklaces that they chew to relieve teething pain, and people put pulverized amber in elixirs and ointments for its purported anti-inflammatory and anti-infective properties.
Now researchers from the University of Minnesota (U of M) have pinpointed compounds that help explain Baltic amber’s therapeutic effects and that could lead to new medicines to combat antibiotic-resistant infections.
“New drug scaffolds are urgently needed for pain, inflammation, and infectious disease,” said Elizabeth Ambrose, PhD, associate professor, department of medicinal chemistry, U of M, during a session at the online spring meeting of the American Chemical Society yesterday. “Molecules in fossils, often from extinct species, undergo biotransformations over millions of years that lead to novel structures.”
Ambrose and her team say they knew from previous research that there were substances in Baltic amber that might lead to new antibiotics, but they had not been systematically explored. “We have now extracted and identified several compounds in Baltic amber that show activity against gram-positive, antibiotic-resistant bacteria,” she continues, calling Baltic amber a “med chem treasure trove.”
Each year in the U.S., at least 2.8 million people get antibiotic-resistant infections, leading to 35,000 deaths, according to the U.S. CDC.
Ambrose’s interest originally stemmed from her Baltic heritage. While visiting family in Lithuania, she collected amber samples and heard stories about their medicinal uses. The Baltic Sea region contains the world’s largest deposit of the material, which is fossilized resin formed about 44 million years ago. The resin oozed from now-extinct pines in the Sciadopityaceae family and acted as a defense against microorganisms such as bacteria and fungi, as well as herbivorous insects that would become trapped in the resin.
Ambrose and graduate student Connor McDermott analyzed commercially available Baltic amber samples, in addition to some that Ambrose had collected.
“One major challenge was preparing a homogeneous fine powder from the amber pebbles that could be extracted with solvents,” McDermott explains. He used a tabletop jar rolling mill, in which the jar is filled with ceramic beads and amber pebbles and rotated on its side. Through trial and error, he determined the correct ratio of beads to pebbles to yield a semi-fine powder.
Then, using various combinations of solvents and techniques, he filtered, concentrated and analyzed the amber powder extracts by gas chromatography-mass spectrometry (GC-MS).
Dozens of compounds were identified from the GC-MS spectra. The most interesting were abietic acid, dehydroabietic acid, and palustric acid—20-carbon, three-ringed organic compounds with known biological activity. Because these compounds are difficult to purify, the researchers bought pure samples and sent them to a company that tested their activity against nine bacterial species, some of which are known to be antibiotic resistant.
“The most important finding is that these compounds are active against gram-positive bacteria, such as certain Staphylococcus aureus strains, but not gram-negative bacteria,” McDermott says, adding that gram-positive bacteria have a less complex cell wall than gram-negative bacteria. “This implies that the composition of the bacterial membrane is important for the activity of the compounds,” continues McDermott, who also obtained a Japanese umbrella pine, the closest living species to the trees that produced the resin that became Baltic amber.
McDermott extracted resin from the needles and stem and identified sclarene, a molecule present in the extracts that could theoretically undergo chemical transformations to produce the bioactive compounds the researchers found in Baltic amber samples.
“We are excited to move forward with these results,” Ambrose says. “Abietic acids and their derivatives are potentially an untapped source of new medicines, especially for treating infections caused by gram-positive bacteria, which are increasingly becoming resistant to known antibiotics.”