Chemical Structure of Cationic Groups in Amphiphilic Polymethacrylates Modulates the Antimicrobial and Hemolytic Activities

Abstract

A library of amphiphilic random copolymers containing cationic and hydrophobic side chains were prepared by copolymerization of amine-functionalized methacrylate monomers with various ratios of an alkyl methacrylate. Primary or tertiary amine groups, or quaternary ammonium groups, were utilized as the source of cationic charge in each copolymer series. The antimicrobial and hemolytic activities of these copolymers are reported, enabling a systematic assessment of the effect different amine groups exert on the biological activity of the polymers. It was shown that the copolymer composition of amphiphilic copolymers containing primary or tertiary amine groups can be tuned to achieve potent antimicrobial activity while minimizing red blood cell lysis. On the other hand, the copolymers containing quaternary ammonium groups required a greater amount of hydrophobic comonomer to express activity and showed generally lower selectivity for E. coli versus human red blood cells. Potentiometric titration data revealed the fraction of the primary or tertiary amine groups in the polymers, which are deprotonated (basic) at physiological pH. Measurements of the bactericidal and hemolytic activities in buffers of pH varying from 6 to 8 showed the impact of polymer ionization on biological activity. A decrease in the fraction of amine groups that are cationic, from alpha = 1.0 to 0.7, caused an enhancement of antimicrobial and hemolytic activity. As this value was decreased further to alpha = 0.5, loss of activity was observed. The activities of polymers containing quaternary ammonium groups were shown to be pH-independent.

Poly (hydroxyethyl methacrylate-glycidyl methacrylate) films modified with different functional groups: In vitro interactions with platelets and rat stem cells

“…The chemical formulation of the amine groups also seems to play a critical role in the polymer-cell interaction, as evidenced by HMDA modified hydrogels, has a higher amount of hemolytic activity compared to other tested hydrogels formulated with differently amine groups. Palermo and Kuroda [47] prepared methacrylate based copolymer contained primary or tertiary amine groups, or quaternary ammonium groups, and were utilized as the source of cationic charge in each copolymer series. Measurements of the bactericidal and hemolytic activities in buffers of pH varying from 6 to 8 showed the impact of polymer ionization on biological activity.…”

Antimicrobial Polymers: Mimicking Amino Acid Functionali ty, Sequence Control and Three-dimensional Structure of Host-defen se Peptides

“…15 Amino ethyl methacrylate was usually used as charge generating unit and copolymerized with methacrylates bearing various hydrophobic side chains (methyl, 16 butyl, 17 ethyl, 18 hexyl 18 and phenyl 18 ) (Fig. 3).…”

“…If the copolymer was too hydrophobic, selectivity for bacterial cell membranes was lost, leading to increased haemolysis, while an excess of cationic charges resulted in high MIC values, which indicates that the polymers were not able to destabilize the target bacterial cell membrane. 16 In a direct comparison of different side chain length /archit ecture s it was found that more hydrophobic monomers require a higher amount of cationic comonomer in order to be effective/selective, and for methacrylate based polymers, the methyl side chain was identified to achieve the highest selectivity when the amphiphilic balance is matched, 19 which also holds true when tertiary amines are used as a hydrophobic component (dimethylamine vs. diethylamine). 20 It becomes obvious how fragile that balance is when small changes in the backbone architecture (met hacy lami de inste ad of methacylate) require much higher ratios of hydrophobic comonomer to work.…”

“…20 It becomes obvious how fragile that balance is when small changes in the backbone architecture (met hacy lami de inste ad of methacylate) require much higher ratios of hydrophobic comonomer to work. 16 Detailed investigations on quarternized poly (vinyl pyridine)/ methacrylate copolymer systems revealed that one alkyl chain per quarternized amine obtains the best results, and that butyl chain perform best in this type of system. 21…”

“…16,41 It was found that for similar polymeric architectures, polymers having quarternized amines are more hydrophilic than polymers with the same amount of primary amines at pH 6,19 which is attributed to the fact that neighbouring amines in a polymer chain influence each other's pK a values in dependence on their state of protonation. While it is reported that primary amine containing polymers have an increased tendency to induce haemolysis, 19 highest selectivity was achieved using primary amines.…”