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Antibiotic properties of amber

Chemicals in fossilised Baltic amber resin have antibiotic properties, and may be useful for treating antibiotic resistance.

Amber has long been used medicinally in Baltic nations. Traditionally, crushed amber is added to elixirs and ointments, and babies are given amber necklaces to relieve teething pain.

“Amber … has been used medicinally for centuries due to its immune-boosting, wound-healing, analgesic, anti-inflammatory, anti-infective, antifungal and anticancer properties,” write Elizabeth Ambrose and Connor McDermott, from the University of Minnesota, US.

“Despite its well-established use in folk medicine, a comprehensive study of the bioactive constituents of Baltic amber has yet to be conducted to explain its therapeutic effects.”

Ambrose led a team that extracted and identified the bioactive compounds in amber. They are presenting their findings at the online Spring 2021 American Chemical Society (ACS) Conference.

The amber compounds show “activity against gram-positive, antibiotic resistant bacteria,” says Ambrose. This has promise for addressing antibiotic-resistant infections which affect at least 2.8 million people and kill about 35,000 in the US each year.

The Baltic Sea area has the world’s largest amber bounty, sticky resin from now-extinct pine trees from the Sciadopityaceae family which became fossilised around 44 million years ago. The resin protected the trees against bacteria, fungi, and herbivorous insects that became trapped in it.

With a Baltic heritage, Ambrose was intrigued by her family’s stories about amber’s medicinal uses and collected samples while visiting them in Lithuania.

The team analysed these samples along with commercially available versions.

“One major challenge was preparing a homogenous fine powder from the amber pebbles that could be extracted with solvents,” says McDermott. He achieved this by rolling a jar filled with ceramic beads and amber pebbles and then filtered, concentrated and analysed the powder using gas chromatography-mass spectrometry.

The analysis revealed dozens of compounds, including three with known biological activity – abietic, dehydroabietic and palustric acid. These complicated organic molecules are difficult to purify, so the researchers purchased pure samples and tested them against nine bacterial species 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,” says McDermott.

Gram-positive bacteria have a less complex cell wall, he explains. “This implies that the composition of the bacterial membrane is important for the activity of the compounds.”

Extracting resin from the needles of the extinct pine trees’ closest living relative, the Japanese umbrella pine, McDermott identified a molecule, sclarene, that could potentially undergo chemical transformation to produce the bioactive compounds in the amber.

“We are excited to move forward with these results,” says Ambrose. “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.”

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