Critical Quality Attributes

Although lipid nanoparticles show many advantages for stable and efficient drug delivery, they introduce many challenges in analytical characterization due to their unique preparation processes and complex physicochemical properties. Creative Biolabs provides comprehensive critical quality attributes characterization services to help our customers develop lipid nanoparticle-formulated drugs.

Drug Incorporation and Entrapment Efficiency

The lipid crystalline structure related to the chemical nature of the lipid is a key factor to determine whether a drug would be expelled or firmly incorporated into the carrier systems. In the nanoparticle structure, the lipid forming a highly crystalline state with a perfect lattice would lead to drug expulsion. On the other hand, the imperfection (lattice defects) of the lipid structure could offer space to accommodate the drugs. As a result, the structure of less ordered arrangement in the nanoparticles would be beneficial to the drug loading capacity.

The entrapment efficiency (EE) is determined by the spectrophotometric method after centrifugation of the aqueous dispersion. Briefly, the amount of free drug was detected in the supernatant and the amount of incorporated drug was determined as a result of the initial drug minus the free drug.

Fig. 1. Critical quality attributes (CQAs) of lipid nanoparticle-based pharmaceutical formulations. (Fan, 2021)

Cytotoxicity

Cellular damage results in loss of metabolic cell function. The tetrazolium salt MTT is widely used to quantitate the cytotoxicity of preparations by colorimetric assay. The tetrazolium salt MTT is widely used to quantify the cytotoxicity of preparations by colorimetry. The tetrazolium salts are metabolically reduced to highly colored end-products called formazans. The colorless MTT is cleaved to formazan by the succinate-tetrazolium reductase system which belongs to the mitochondrial respiratory chain and is active only in viable cells.

In Vitro Drug Release

Stable nanoparticle formulations should retain the loaded drug during their in vitro storage and in vivo circulation before delivering the drug to the target. Until now, lots of efforts have been made to develop reliable in vitro release testing methods and predict in vivo behaviors of nanoparticle formulations. These methods can be generally categorized by using sampling and separation (SS), dialysis membrane (DM), continuous flow (CF), or combined approaches.

• Separate (SS)

The SS approach is the simplest and involves samples in the release media, sampling, and separating the released API from intact nanoparticles usually by stand-alone ultracentrifugation or filtration, followed by offline API quantification. Important factors include choices of physiology-relevant release media and appropriate sampling time window.

• Dialysis Membrane (DM)

Compared to SS, DM is more popular and versatile for in vitro drug release studies of nanoparticle formulations. DM approaches mainly include dialysis sac (regular dialysis) and reverse dialysis. The dialysis sac holds nanoparticle formulations inside, achieving simultaneous release and separation of the released API. Key parameters for this method include choices of the dialysis membrane, volume ratios between the sample and release media, and agitation conditions.

• Continuous Flow (CF)

The CF method features dynamic circulation/change of the release media and is often operated by using the USP apparatus IV. To be applied to nanoparticle formulations, a dialysis sac could be used to hold nanoparticle formulations on top of the glass beads in the sample chamber. Compared to the conventional dialysis sac method, the combined DM-CF strategy better discriminated dexamethasone release profiles from liposomes with different lipid compositions.

Reference

1. Fan, Y.; et al. Analytical characterization of liposomes and other lipid nanoparticles for drug delivery. J Pharm Biomed Anal. 2021, 192: 113642.