Synthesis, Physicochemical Properties, and Preliminary Biological Characterizations of a Novel Amphoteric Agmatine-Based Poly(amidoamine) with RGD-Like Repeating Units

Abstract

A linear, amphoteric poly(amidoamine) nicknamed AGMA1, based on 4-aminobutylguanidine, or agmatine, was successfully prepared by Michael-type polyaddition of monoprotonated agmatine and 2,2-bis(acrylamido)acetic acid (BAC). Copolymers between AGMA1 and the biocompatible poly(amidoamine) ISA23 (deriving from the polyaddition of 2-methylpiperazine with BAC) were also prepared. Acid-base titrations gave for AGMA1 three acid dissociation constants, with pKa values of 2.25, 7.45, and >or=12.1, corresponding to a strong acid, a medium-weak base, and a strong base, respectively. The charge distribution profiles show that this polymer is prevailingly cationic at all physiological pH values, the positive net average charge per unit varying from about 0.5 at pH 7.4 to about 1.0 at pH 5, with an isoelectric point at pH approximately 10. Zeta-potential measurements confirmed this. Despite that, AGMA1 is nontoxic and nonhemolytic in vitro within all pH ranges tested (4-7.5). This is in contrast with the previously observed behavior of amphoteric PAAs, for instance ISA23, that are weakly hemolytic at pH 7.4 but highly hemolytic at pH 5/5.5. The lack of hemolytic activity of AGMA1 even at acidic pH values seems typical of the agmatine-BAC sequences and may be ascribed to their RGD-like structure. In fact, AGMA1-ISA23 copolymers behave in a way increasingly similar to that of ISA23; that is, they become hemolytic at low pH values as their ISA23 content increases.

Direct Microfabrication of Topographical and Chemical Cues for the Guided Growth of Neural Cell Networks on Polyamidoamine Hydrogels

“…On the left an array of 9 small squares correspond to the irradiated areas (10  10 mm 2 ) at increasing doses (going from the left to the right and from the top to the bottom). These doses are multiples (3,4,5,6,7,8,10,15,20) of a unitary value, chosen to be 140 mA s Á cm À2 . On the right of the optical images (see à indication) the irradiated area is complementary to the previous one (the squares are not irradiated) and exposed to a constant dose of 1 120 mA s Á cm À2 .…”

“…PAAs containing as side substituents other chemical functions, such as additional tertiary amino groups, carboxyl groups, hydroxyl groups and allyl groups, can be easily obtained using suitably functionalized monomers, for instance aminocarbohydrate derivatives. [8] Despite their very promising properties, synthetic hydrogels are characterized by poor cell adhesion and a number of chemical and physical modifications have been proposed to overcome this problem. [4] In order to increase cell biocompatibility of PAAs hydrogels, functional comonomers, such as 4-aminobutyl guanidine (agmatine), have been introduced in order to build a functional amphoteric repeating unit structurally similar to the tripeptide arginin-glycin-aspartic acid (RGD), present in several extra cellular matrix (ECM) proteins.…”

“…[4] In order to increase cell biocompatibility of PAAs hydrogels, functional comonomers, such as 4-aminobutyl guanidine (agmatine), have been introduced in order to build a functional amphoteric repeating unit structurally similar to the tripeptide arginin-glycin-aspartic acid (RGD), present in several extra cellular matrix (ECM) proteins. [8] PAAs hydrogels incorporating RGD-mimicking units have shown a superior cell adhesion capability when compared to plain amphoteric PPAs. [9] The control of the chemical structure of artificial materials in the bulk, however, is only the preliminary step for controlling the evolution of cellular structures on their surface, since cell-substrate signalling is regulated by topographical and chemical patterns organized on scales ranging from the nanometer to the micrometer, [1,10] as observed for the extracellular matrix where cells are aligned and guided via micro and nanotopographies formed by the hierarchical organization of collagen molecules.…”

Prevailingly Cationic Agmatine-Based Amphoteric Polyamidoamine as a Nontoxic, Nonhemolytic, and “Stealthlike” DNA Complexing Agent and Transfection Promoter

“…At pH 7.4 the average excess positive charge is 0.55 per unit. 14 In spite of that, AGMA1 proved nontoxic and nonhemolytic in vitro within the entire pH range tested (4.0-7.4). 14 In this paper, we prepared AGMA1 labeled with fluorescein isothiocyanate (FITC-AGMA1) and studied its biodistribution in rats and intracellular uptake.…”

“…14 In spite of that, AGMA1 proved nontoxic and nonhemolytic in vitro within the entire pH range tested (4.0-7.4). 14 In this paper, we prepared AGMA1 labeled with fluorescein isothiocyanate (FITC-AGMA1) and studied its biodistribution in rats and intracellular uptake. Furthermore, we determined the DNA complexing ability and transfection efficiency of AGMA1 in view of its use as a DNA carrier in vivo.…”