Johannes F. Petersen

Surface modification of PAMAM dendrimer improves its biocompatibility

Modification of dendrimer surface groups is one of the methods available to obtain compounds characterized by reduced toxicity. This article reports results of preliminary biocompatibility studies of a modified polyamidoamine dendrimer of the fourth generation. Reaction with dimethyl itaconate resulted in transformation of surface amine groups into pyrrolidone derivatives. Interaction of the modified dendrimer with human serum albumin (HSA) was analyzed. The influence of the dendrimer on mouse neuroblastoma cell line viability and its hemolytic properties were also investigated. The binding constant between analyzed dendrimer and HSA was found to be equal to 1.2 × 10(5) ± 0.2 × 10(5) M(-1). Small changes in HSA secondary structure were observed. The analyzed dendrimer revealed minor toxic activity, as diminishment in cell viability was observed only for dendrimer concentrations higher than 2 mg/mL. Moreover, under the applied experimental conditions, no hemolytic activity was observed. Those observations point to the potential of the analyzed compound for further studies toward its applicability in nanomedicine.

Modified PAMAM dendrimer with 4-carbomethoxypyrrolidone surface groups reveals negligible toxicity against three rodent cell-lines

UNLABELLED Modification of the surface groups of dendrimers is one of the methods to improve their biocompatibility. This article presents results of experiments related to the toxicity of a modified polyamidoamine (PAMAM) dendrimer of the fourth generation with 4-carbomethoxypyrrolidone surface groups (PAMAM-pyrrolidone dendrimer). The cytotoxic activity of the dendrimer was tested on Chinese hamster fibroblasts (B14), embryonic mouse hippocampal cells (mHippoE-18) and rat liver derived cells (BRL-3A). The same cell lines were used to investigate the influence of pyrrolidone dendrimer on the mitochondrial membrane potential, intracellular ROS level and its ability to induce apoptosis or necrosis. The analyzed dendrimer showed only minor toxicity and no ability to induce apoptosis. The most important finding is the lack of influence of the PAMAM-pyrrolidone dendrimer on intracellular ROS level and mitochondrial membrane potential. FROM THE CLINICAL EDITOR The authors demonstrate that pyrrolidone-functionalized PAMAM dendrimers have very low toxicity in the tested cell lines, as evidenced by no alteration of mitochondrial membrane potential and no increase of ROS production.

Copper(II) complexes with 4-carbomethoxypyrrolidone functionalized PAMAM-dendrimers: an EPR study.

The internal flexibility and interacting ability of PAMAM-dendrimers having 4-carbomethoxypyrrolidone-groups as surface groups (termed Gn-Pyr), which may be useful for biomedical purposes, and ion traps were investigated by analyzing the EPR spectra of their copper(II) complexes. Increasing amounts (with respect to the Pyr groups) of copper(II) gave rise to different signals constituting the EPR spectra at room and low temperature corresponding to different coordinations of Cu(2+) inside and outside the dendrimers. At low Cu(2+) concentrations, CuN4 coordination involving the DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a CuN3O coordination. CuN2O2 coordination into the external dendrimer layer was also contributing to G3- and G4-Pyr spectra. The structures of the proposed copper-dendrimer complexes were also shown. G4-Pyr displays unusual binding ability toward Cu(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr and its peculiar binding ability leads to a potential use in biomedical fields.

PAMAM dendrimer with 4-carbomethoxypyrrolidone—In vitro assessment of neurotoxicity

Cytotoxicity of cationic amino-terminated PAMAM dendrimer and modified PAMAM-pyrrolidone dendrimer was compared. LDH assay and cell visualization technique were employed. Mouse embryonic hippocampal cells (mHippoE-18) were used. The experiments were performed in FBS-deprived medium. Pyrrolidone-modification significantly diminished toxicity of PAMAM dendrimer. The absence of FBS did not reveal significant impact on the toxic effect. Results from LDH assay and MTT test were in good consistency. Low cytotoxicity of PAMAM-pyrrolidone dendrimer increases reliability of the results showing a small impact of this dendrimer on cell viability.

Modified PAMAM dendrimer with 4-carbomethoxypyrrolidone surface groups-its uptake, efflux, and location in a cell

Traditional amine terminated PAMAM dendrimers may be readily surface engineered by a facile one-pot conversion with dialkyl itaconate esters into 4-carbomethoxypyrrolidone terminated PAMAM (G=0-4) dendrimers. These terminated dendrimers are uniquely characterized by exhibiting blue fluorescence emissions (λexc=370nm, λmaxem=440nm). Thanks to this property they can be directly analyzed by confocal microscopy and flow cytometry without additional fluorescence labeling, treatment of dendrimers with chemicals or adjusting pH. These intrinsically fluorescent dendrimers were shown to be very effective for assessing important biological cell features such as cellular entry, intracellular trafficking/localization and efflux properties. For example, all tested cell lines (e.g., B14, BRL-3A, and mHippoE-18) rapidly accumulated PAMAM-pyrrolidone dendrimer. The BRL-3A cell line exhibited both cytoplasmic and nuclear localization patterns; whereas in B14 cells and mHippoE-18 cells, the blue dendrimer fluorescence could only be detected in intracellular endosome-like structures. The dendrimer was observed to be released from all three cell lines during the first 24h; however, efflux was substantially slower from the B-14 cell line. The highest efflux rate was observed for the mHippoE-18 cells. This first successful biological experiment opens a broad spectrum of using these dendrimers as new bioimaging agents for extensive biological cell characterizations.

Model-based integration and interpretation of data

Data integration and interpretation plays a crucial role in supervisory control. The paper defines a set of generic inference steps for the data integration and interpretation process based on a three-layer model of system representations. The three-layer model is used to clarify the combination of constraint and object-centered representations of the work domain throwing new light on the basic principles underlying the data integration and interpretation process of Rasmussens abstraction hierarchy as well as other model-based approaches combining constraint and object-centered representations. Based on these results some implications for interface design are outlined

Two for the Price of One: PAMAM-Dendrimers with Mixed Phosphoryl Choline and Oligomeric Poly(Caprolactone) Surfaces

The application of dendrimers for biological and medical purposes is highly dependent on the type of surface group in relation to cytotoxicity. Since amine terminated PAMAM dendrimers have been shown to have toxic properties and thereby limited applications in the medical field, the discovery of a new nontoxic surface coating is of great interest. In the present work, amine terminated DAB-PAMAM dendrimers from generation zero to four have been coated with statistical surface functionalization giving a dendrimer surface consisting of an approximately 1:1 mixture of zwitterionic phosphoryl choline hexanamide and 6-((6-hydroxyhexanoyl)oxy)hexanamide. The cytotoxic properties of generation two to four were tested on three different human cancer cell lines, SKBR3 human breast cancer cells, HeLa human cervical cancer cells, and Hep G2 human hepatocellular liver carcinoma cells and compared to the toxicity of amine terminated PAMAM dendrimers. In addition to lower cytotoxicity than observed for amine terminated dendrimers, the coated dendrimers showed minor cytotoxicity against all three human cell lines, negligible influence on ROS generation and mitochondrial membrane potential. These observations support the conclusion that the analyzed group of phosphorylcholine dendrimers may be suitable for medical applications.

Being two is better than one - Catalytic reductions with dendrimer encapsulated copper - And copper-cobalt-subnanoparticles

Copper and copper-cobalt subnanoparticles have been synthesized using 4-carbomethoxypyrrolidone terminated PAMAM-dendrimers as templates. The metal particles were applied in catalytic reduction reactions. While Cu subnanoparticles were only capable of reducing conjugated double bonds, enhancing the Cu particles with Co led to a surprising increase in catalytic activity, reducing also isolated carbon double and triple bonds.

Study of the complexation of oxacillin in 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers.

The complexation of oxacillin to three generations of 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied with NMR in CD3OD and CDCl3. The stochiometries, which were determined from Job plots, were found to be both solvent- and generation-dependent. The dissociation constants (K(d)) and Gibbs energies for complexation of oxacillin into the 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimer hosts were determined by (1)H NMR titrations and showed weaker binding of oxacillin upon increasing the size (generation) of the dendrimer.

Pyrrolidone Modification Prevents PAMAM Dendrimers from Activation of Pro-Inflammatory Signaling Pathways in Human Monocytes

The biological features of dendrimers are affected by the character of highly reactive terminal moieties. In some polyamine dendrimer types the surface charge makes them bioincompatible and prevent their direct medical application. Moreover, foreign particles can induce the immune response which is undesirable due to the adverse side effects in vivo. The reduction of cytotoxicity of positively charged macromolecules is possible through chemical modifications of terminal groups. In our study, we have developed new derivatives of PAMAM dendrimers modified with 4-carbomethoxypyrrolidone and evaluated their immunomodulatory properties. The experiments were conducted on two human cancer myeloid cell lines: THP-1 and U937. To evaluate the cytotoxicity of dendrimers, the reasazurin assay was applied. The expression level of NF-κB targets (NFKBIA, BTG2) and cytokine genes (IL1B, TNF) was determined by quantitative real-time RT-PCR. The measurement of binding of NF-κB to a consensus DNA probe was determined by electrophoretic mobility shift assay. The ELISA cytokine assay was performed to measure protein concentration of IL-1β and TNFα. We have found that PAMAM-pyrrolidone dendrimers did not impact THP-1 and U937 viability even at high concentrations (up to 200 μM). The surface modification prevented PAMAM dendrimers from stimulating NF-κB-related signal transduction, which have been determined on the level of nuclear translocation, gene expression and protein secretion. Pyrrolidone modification efficiently prevents PAMAM dendrimers from stimulating pro-inflammatory response in human cancer myeloid cell lines, thus it can be used to improve the biocompatibility of positively charged dendrimers and to broaden the scope of their biological applications.