Low-Cost Peptide Kills Bacteria and Breaks Up Plaque



Overall healthcare has relied on protein drugs such as insulin, which are derived from biological sources, for decades. Yet dental medicine has not employed them as much due to their high costs and invasive delivery mechanisms. The University of Pennsylvania School of Dental Medicine, however, has developed a new approach for delivering protein drugs to treat and prevent oral diseases including caries.

Using plants to produce antimicrobial peptides, the researchers rapidly killed the bacteria that causes caries and thwarted their ability to form biofilms on a tooth-like surface with a single topical treatment. The peptides were even more effective when combined with an enzyme that degrades the matrix surrounding and protecting the bacteria residing inside of biofilms.

Additionally, periodontal and gingival cells could take up these peptides, which are produced cost-effectively in plants. This delivery method then could be useful in treating diseases that affect gum tissue, perhaps by promoting wound healing or bone regeneration, the researchers said. It’s also a low-cost platform compared to current biopharmaceutical production, they added, while potentially leading to affordable therapies that simultaneously attack plaque and promote gum health.

“What makes this approach so exciting is not only the science but, because the production costs are so low, the feasibility of getting the therapy to the population who truly needs yet can’t afford it,” said Hyun (Michel) Koo, DDS, MS, PhD, co-corresponding author of the study and professor with the department of orthodontics and divisions of pediatric dentistry and community oral health at Penn Dental Medicine.

Previous research has identified antimicrobial peptides that kill the bacteria that causes caries, but these agents are expensive to make and have had limited success at killing the bacteria protected by the extracellular matrix. Also, other research has investigated the enzymes that can break down the biofilm matrix, with limited success at preventing dental caries by themselves.

The Penn researchers combined the antimicrobial peptides with the matrix-degrading enzyme. To address the potentially prohibitive cost of antimicrobial peptide production, the researchers turned to a plant-based protein drug production platform developed by Henry Daniell, PhD, co-corresponding author of the study, director of translational research, and professor at Penn Dental Medicine’s department of biochemistry.

The process entails bombarding a plant leaf with gold particles coated in a cloned gene to reprogram the chloroplasts to synthesize the associated protein. In this case, the researchers coaxed plants to produce a pair of different antimicrobial peptides, retrocyclin and protegrin. Both have complex secondary structures, making them expensive to produce by traditional means.

However, the researchers found they could literally grow these peptides in Daniell’s greenhouse and faithfully replicate their unique secondary structures in the plant’s leaves. Next, they tested whether the plant-made agents could prevent the creation of a biofilm.

The researchers exposed a saliva-coated tooth-like surface to the plant-made protegrin for 30 minutes. Then, they exposed the surface to Streptococcus mutans cells along with sugar and found that it significantly impaired the ability of the bacterium to form a biofilm compared to an untreated surface.

To see if the antimicrobials could act preventively and therapeutically, the researchers exposed a preformed biofilm on the tooth-mimicking surface to either protegrin alone or a combination of protegrin and a matrix-degrading enzyme. The enzyme alone had no effect on the biofilm. And while the antimicrobial alone killed some bacteria, the combination degraded 60% of the matrix and killed even more bacteria.

“A single topical treatment was capable of disrupting the biofilm,” said Koo. “Its effectiveness was comparable to chlorexhidine, which is considered the gold standard for oral antimicrobial therapy.”

Daniell also has been investigating molecular tags to route protein drugs to human cells to treat several diseases. For example, growth hormones and similar drugs could be delivered to gum tissues for wound healing or bone regeneration, enhancing oral health. The recent study confirmed that human cells could take up the plant-made antimicrobial peptides in the oral cavity.

“This was unexpected,” Daniell said. “The antimicrobials didn’t harm any of the human cells in gum tissues but had an unusual ability to go across the cell membranes of periodontal and gingival cells. This opens up a completely new field for drug delivery with a topical agent.”

By collaborating with Johnson & Johnson Consumer Inc, the researchers will continue optimizing their antimicrobial-enzyme production system. For example, chewing gum could be laced with antimicrobial peptides that could be slowly released as one chews. Or, peptides may be grown in betel leaf, which is commonly chewed in some Asian cultures.

The study, “Topical Delivery of Low-Cost Protein Drug Candidates Made in Chloroplasts for Biofilm Disruption and Uptake by Oral Epithelial Cells,” was published by Biomaterials.

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