Systematic process evaluation of the conjugation of proteins to gold nanoparticles

Long-Lasting Exendin-4-Coated Gold Nanoparticles: Synthesis and In Vivo Evaluation of Hypoglycemic Activity

BACKGROUND

Gold nanoparticles (NPs) have drawn great attention in the area of biomedical research with their relatively safe and versatile properties. This study aimed to synthesize long-lasting exendin-4-coated gold NPs (EX-ABD-AFF-GoldNPs) and evaluate their anti-diabetic effects in vivo.

METHODS

In the present study, EX-ABD-AFF-GoldNPs were synthesized using a simple one-step aqueous reduction method. The physical characterization of the prepared particles verified the successful formation of the EX-ABD-AFF-GoldNPs through dynamic light scattering (DLS), transmission electron microscopy (TEM), ultraviolet-visible (UV-VIS) light spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The anti-hyperglycemic and anti-obesity effects were assessed in high-fat diet (HFD)-fed obese diabetic mice. Additionally, pharmacokinetics (PK) and biodistribution studies were performed to verify the long-lasting properties.

RESULTS

The EX-ABD-AFF-GoldNPs were conglomerates of smaller globular-shaped particles, and the average size was 110(±14) nm, based on the TEM images. Safety assessments using Min6, HepG2, and B16F10 cell lines demonstrated low cytotoxicity, with over 80% cell viability up to the highest tested concentration of 150 μg/mL (as EX-ABD-AFF). Notably, the animal studies showed that the EX-ABD-AFF-GoldNPs exhibited significant hypoglycemic activity, comparable to the EX-ABD-AFF, in the HFD-fed mice. A 4-week treatment with EX-ABD-AFF-GoldNPs produced similar reductions in blood glucose and body weight to the EX-ABD-AFF, without any apparent toxicity. Furthermore, the PK and biodistribution study results confirmed the long-lasting properties (plasma half-life: 43.6 h) of the particles.

CONCLUSIONS

Overall, this study demonstrated that the preparation of therapeutic protein-loaded gold NPs is feasible and, despite their much larger size compared with the protein, EX-ABD-AFF-GoldNPs can be successfully absorbed through the subcutaneous route and show nearly equivalent hypoglycemic activity to the EX-ABD-AFF protein. Finally, this study showed that long-lasting properties could be acquired by only coating EX-ABD-AFF onto gold NPs.

Development of gold nanoparticle-based lateral-flow strips for NGAL protein detection in urine samples

This study focuses on enhancing the sensitivity of lateral-flow strips (LFSs) based on gold nanoparticles (AuNPs) for the detection of Neutrophil Gelatinase-Associated Lipocalin (NGAL) protein in urine samples. Several sizes of AuNP-based LFS biosensors were tested to optimize colorimetric signals for NGAL detection based on improved conjugation conditions. AuNPs of 39.8 nm diameter at pH 8 were the most sensitive for the detection of NGAL. Through systematic enhancements to the AuNP-based LFS, the study significantly improves the sensitivity, enabling the reliable detection of NGAL protein in urine samples at a level as low as 12.5 ng mL-1. These advances contribute to the refinement of diagnostic tools for the early detection of kidney injury, specifically in cases associated with the presence of NGAL protein, offering a more precise and effective screening approach.

Investigating and Optimizing Insulin Partitioning with Conjugated Au Nanoparticles in Aqueous Two-Phase Systems Using Response Surface Methodology

This study investigated the impact of bioconjugation on the partitioning of insulin, a clinically valuable protein, in an aqueous two-phase system. Gold nanoparticles of different sizes were synthesized and conjugated with insulin. Analysis of the conjugated insulin showed that the insulin remains fully active. Conjugated gold nanoparticles (AuNPs/insulin) were used in polyethylene glycol (PEG)-dextran aqueous two-phase systems to investigate the effect of pH, PEG and dextran molecular weights, PEG and dextran concentrations, AuNPs/insulin dosage, and nanoparticle size on the partition coefficient. These systems were chosen for their biocompatibility and low toxicity. Response surface methodology with D-optimal design was used to model and optimize these systems and their affected parameters. At the optimum condition of a pH = 8 system containing 21% PEG 4000, 5% dextran 100,000, and 100 IU AuNPs/insulin, the partition coefficient of AuNPs/insulin was found to be 192.96, which is in agreement with the empirical partition coefficient of 189.2. This is significantly higher than the partition coefficient of free insulin in a similar system. This approach could be used to overcome limitations in the feasibility of aqueous two-phase systems for industrial-scale purification of biomolecules and biopharmaceuticals.

Application of a Biomimetic Nanoparticle-Based Mock Virus to Determine SARS-CoV-2 Neutralizing Antibody Levels in Blood Samples Using a Lateral Flow Assay

The presence of neutralizing antibodies against SARS-CoV-2 in blood, acquired through previous infection or vaccination, is known to prevent the (re)occurrence of outbreaks unless the virus mutates. Therefore, the measurement of neutralizing antibodies constitutes an indispensable tool in assessing an individual's and a population's immunity against SARS-CoV-2. For this reason, we have developed an innovative lateral flow assay (LFA) capable of detecting blood-derived neutralizing antibodies using a biomimetic SARS-CoV-2 mock virus system. Here, functionalized gold nanoparticles (AuNPs) featuring the trimeric spike (S) protein at its surface imitate the virus's structure and are applied to monitor the presence and efficacy of neutralizing antibodies in blood samples. The detection principle relies on the interaction between mock virus and the immobilized angiotensin-converting enzyme 2 (ACE2) receptor, which is inhibited when neutralizing antibodies are present. To further enhance the sensitivity of our competitive assay and identify low titers of neutralizing antibodies, an additional mixing pad is embedded into the device to increase the interaction time between mock virus and neutralizing antibodies. The developed LFA is benchmarked against the WHO International Standard (21/338) and demonstrated reliable quantification of neutralizing antibodies that inhibit ACE2 binding events down to a detection limit of an antibody titer of 59 IU/mL. Additional validation using whole blood and plasma samples showed reproducible results and good comparability to a laboratory-based reference test, thus highlighting its applicability for point-of-care testing.

A novel lateral flow immunochromatographic assay using a recombinant VP2 antigen for total antibody detection of canine parvovirus-2

Canine parvovirus-2 (CPV-2) is a viral disease of dogs causing acute hemorrhagic gastroenteritis and myocarditis with high morbidity and mortality rates. The infection is still widespread all over the world. Vaccines developed against infection have great importance in preventing infection. However, it is difficult to recommend a practical vaccination program without knowing the antibody level of a puppy. Despite widespread vaccination, difficulties in detecting the maternal antibodies in puppies remain the main cause of vaccination failure. The hemagglutination inhibition (HAI) test is the gold standard to determine the immune status of dogs for canine parvovirus 2, but the HAI test has several disadvantages such as the need for fresh porcine blood, well-equipped laboratory, and long incubation periods. In this study, for the first time we developed a colloidal gold-based competitive lateral flow assay (cLFA) system for the rapid detection of total antibodies in canine serum using CPV-2b-VP2 derived from field isolates. The recombinantly expressed capsid protein of CPV-2 in the prokaryotic expression system was used as a labeled molecule in cLFA. We carried out studies on our cLFA system using the standard antibody solution and the clinical samples from vaccinated puppy serum. We compared the results of the LFAs with the HAI test. Competitive lateral flow assay results showed good correlation with the gold standard method, the HAI test. In the developed platform, the limit of detection of the standard antibody was determined to be 375 ng mL-1, while the cut-off level of antibodies was observed to be 1 : 40 HAI titer in clinical samples. Our reported system will be a strong alternative for CPV-2 antibody-based detection applications.

AF4-UV/VIS-MALS-ICPMS/MS for the characterization of the different nanoparticulated species present in oligonucleotide-gold nanoparticle conjugates

In-depth characterization of functionalized nanomaterials is still a remaining challenge in nanobioanalytical chemistry. In this work, we propose the online coupling of Asymmetric Flow Field-Flow Fractionation (AF4) with UV/Vis, Multiangle Light Scattering (MALS) and Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) detectors to carry out, in less than 10 min and directly in the functionalization reaction mixture, the complete characterization of gold nanoparticles (AuNPs) functionalized with oligonucleotides and surface-modified with polyethylene glycol (PEG). AF4 separation provided full separation of the bioconjugates from the original AuNPs while P/Au and S/Au ICP-MS/MS ratios in the bioconjugate fractographic peaks could be used to compute the corresponding stoichiometries, oligonucleotide/AuNP and PEG/AuNPs. MALS detection clearly showed the coexistence of two distinct nanoparticulated populations in the bioconjugation mixture, which were demonstrated to be different not only in size but in functionality as well. The major bioconjugate population showed lower hydrodynamic ratios (18 nm) with higher and steadier oligonucleotides/AuNPs (92) and PEG/AuNPs (2350) stoichiometries, in comparison to the minor abundant population (54 nm, 51 and 1877, respectively). Moreover, the ratio between the absorbance signals measured at 520 nm and 650 nm reflects a lower AuNP aggregation in the major (10.5) than in the minor (4.5) population. Results obtained prove the benefits of a detailed characterization to find out if subsequent purification of functionalized AuNP-oligonucleotides is required to design more efficiently their final bioanalytical application.