Lipid Nanoparticles

What are Lipid Nanoparticles?

Lipid nanoparticles (LNPs) are molecules nano-sized made of lipid molecules, which might harbor all kinds of bioactive molecules (proteins, RNA, DNA, tiny molecules). They are nanoparticles, 10-1000 nanometers in size, that are increasingly used for the transport of drugs, vaccines and gene therapies. Because lipid nanoparticles are biocompatible, biodegradable and can accommodate both hydrophilic and hydrophobic molecules, they are the perfect drug delivery material.

These are the latest hot claims made by LNPs to be able to deliver RNA therapies, in the form of mRNA vaccines. The ability to protect nucleic acids from degradation, to promote cellular absorption, and to control release of the encapsulated compound transformed medicine, not least for vaccine delivery, for treating cancers, and for gene therapy.

Lipid Nanoparticle Structure

LNPs are formulated with an optimal design to deliver therapeutic payloads such as mRNA or drugs to the cell of interest. LNPs' fundamental building blocks can be classified into four structural units: ionizable lipids, phospholipids, cholesterol, and the payload in encapsulation (e.g., mRNA).

Ionizable Lipids

Ionizable lipids are required for LNPs to work, especially to deliver mRNA. These lipids are unique in one respect: they shift charge in relation to the environment's pH. In a more acidic environment (like in the endosome following cell absorption), these lipids can get protonated (positively charged). They are positively charged because of this, and in turn they can be more easily reacted to negatively charged mRNA in order to form stable lipid-RNA complexes. Ionizable lipids can also dislodge the endosomal membrane upon entry to the cell so that the payload can be pushed into the cytoplasm.

Phospholipids

Phospholipids are what help to build the bilayer structure of the LNP. These molecules are hydrophilic (water-saturating) and hydrophobic (water-draining) molecules that readily form a bilayer on their own. The hydrophilic heads are open to the watery outside and inside, and the hydrophobic tails are embedded within the bilayer. This phospholipid bilayer is necessary to hold the nanoparticle in place and contain the payload. Apart from structural stability, phospholipids also support biological compatibility with the target cells' membranes.

Cholesterol

Cholesterol is built into the lipid nanoparticles for stability and flow in the membrane. It works by controlling the stiffness of the lipid bilayer, so that the LNP remains less flexible than before, but is stable enough to fuse to the cell membrane during endocytosis. Cholesterol also keeps the encapsulated payload from escaping too early, keeping the LNP intact throughout circulation and cellular transport for the best possible delivery.

Encapsulated Payload

The encapsulated payloads, such as mRNA, protein, and drugs, are all therapeutic substances delivered by LNP to target cells. For mRNA vaccines or drugs, the LNP keeps the mRNA from being damaged by ribonucleases in the blood and helps it be safe to go into cells. Inside the cell, the mRNA escapes from the LNP and is translated into the desired protein. Because the lipid nanoparticle is built so that it gets to the right places in the cell, such as the cytoplasm, where the payload will have time to be expressed.

These components act in tandem to economize on therapeutic molecules, shield the payload from damage, and enable cellular capture and release of the active ingredient. Design and ratio of these lipid elements can be adapted depending on the desired function (e.g., gene delivery, drug delivery, etc.).

Fig.1 The structure of the Lipid Nanoparticle. (Forchette, Lauren, et al., 2021)

Lipid Nanoparticle Characterization

It's necessary to characterize lipid nanoparticles for their therapeutic potential. A number of parameters are important for the quality control and optimization of LNPs: size, charge, stability, and encapsulation efficiency.

Size and Size Distribution: The size of the lipid nanoparticles is the most important parameter that determines how they behave biologically, for example, how they can pass through biological barriers like the cell membranes or blood-brain barrier. LNPs are typically 50 to 200 nanometers in diameter, and a size that balances both therapeutic activity and stability is the ideal size.

Surface Charge (Zeta Potential): Lipid nanoparticles surface charge has an effect on how they will interact with cell membranes, the immune system, and other interacting biological materials. Negative zeta potential usually stabilizes nanoparticles in suspension, so that they don't form conglomerates. But surface charge also impacts cellular absorption, and neutral or slightly positive charges are better for internalization by cells.

Efficiency of Encapsulation: In addition to therapeutic potential, lipid nanoparticles must be able to capture and preserve their payload in an efficient way. It is typically measured by removing the unencapsulated drug from the nanoparticle mixture and measuring how much material was absorbed into it.

Morphology: Shape and surface properties of LNPs can be measured with electron microscopy (scanning electron microscopy or transmission electron microscope). Such images are used to check that the nanoparticle geometry is consistent and solid.

Stability: Stability tests are required to make sure the LNPs keep their structure and encapsulation function in storage. Stability experiments usually focus on the effects of temperature, pH and other environmental parameters on the nanoparticle size, charge and release profile.

Types of Lipid Nanoparticles

There are different lipid nanoparticles of different characteristics and use:

Solid Lipid Nanoparticles (SLNs): Made of solid lipids at body temperature, these aren't as effective at hydrophilic drug encapsulation. SLNs are also stable, release controlled and low toxicity, which allows for oral, topical and parenteral drug administration.

Nanostructured Lipid Carriers (NLCs): NLCs, are SLNs but consist of both solid and liquid lipids. This design optimizes the nanoparticles' loading capacity and drug release profiles for a more broad range of drugs.

Liposomes: Liposomes are hollow vesicles with a lipid bilayer, which are used to package hydrophilic drugs in their aqueous interior. They are common in parenteral drug delivery and can also encapsulate hydrophilic and hydrophobic medications.

Polymeric-Lipid Hybrid Nanoparticles (PLNs): These particles bring together the best of lipids and polymers in the form of greater stability, drug release and bioavailability. PLNs can be targeted and loaded with larger therapeutic molecules.

Lipid-Cemented Nanoparticles: They are made of a hard nanoparticle core (usually a polymer or metal) sandwiched between a lipid shell. This lipid coating makes the core bio-compactible and prevents it from oxidizing so that the therapeutic ingredient can be delivered in controlled quantities.

Lipid Nanoparticles Synthesis

The synthesis of lipid nanoparticles is typically achieved through various methods, each offering advantages depending on the desired characteristics of the particles. The main techniques include:

High-Pressure Homogenization: This method involves forcing a lipid and drug mixture through a high-pressure homogenizer to create nanoparticles. The shear forces break the lipid aggregates into small particles, resulting in a uniform size distribution. This technique is widely used for producing SLNs and NLCs.

Microemulsion Method: In this method, a mixture of oil, water, and surfactant is used to create small droplets containing the drug. The microemulsion is then processed to form lipid nanoparticles. This approach is ideal for preparing liposomes and lipid-coated nanoparticles.

Solvent Evaporation: Solvent evaporation techniques involve dissolving lipids and drugs in an organic solvent, which is then evaporated to form nanoparticles. This method is used in the preparation of SLNs and liposomes, offering simplicity and scalability.

Extrusion: In this method, lipid mixtures are forced through a membrane with small pores to create uniform nanoparticles. This process is particularly useful for producing liposomes and NLCs.

Film Hydration: Lipid films are hydrated with aqueous solutions containing drugs, forming nanoparticles upon hydration. This method is commonly used for the synthesis of liposomes.

FDA-Approved Lipids for Nanoparticles

The U.S. Food and Drug Administration (FDA) has approved multiple lipid nanoparticles for drug delivery and therapy. These lipid nanoparticles are typically composed of four main lipids: ionizable cationic lipids, helper lipids (e.g., 1, 2-distearoyl-SN-glycerol-3-phosphate choline, DSPC), cholesterol, and polyglycol (PEG) -conjugated lipids. Currently, FDA-approved lipid-based nanoparticle formulations include Doxil (the liposomal form of Doxorubicin) for cancer therapy, the first FDA-approved nanomaterial for the treatment of metastatic ovarian cancer and AIDS-related Kaposi's sarcoma. In addition, there is Onpattro for the treatment of polyneuropathy in patients with hereditary transthyroxin-mediated amyloidosis, a siRNA drug that utilizes DLin-MC3-DMA ionized lipids.

These lipid nanoparticles are favored for their high biocompatibility, low toxicity, and ability to efficiently transport hydrophobic and hydrophilic drugs. For example, Doxil significantly improves drug bioavailability and reduces systemic toxicity by encapsulating doxorubicin in liposomes. Onpattro enables efficient nucleic acid delivery and intracellular release through its unique ionized lipid structure.

Advantages of Lipid Nanoparticles

Lipid nanoparticles offer several advantages that make them highly attractive for therapeutic applications:

Biocompatibility and Biodegradability: LNPs are composed of naturally occurring lipids or lipid-like materials, which are generally safe and can be broken down by the body after they have fulfilled their therapeutic role.

Protection of Encapsulated Payloads: LNPs effectively protect sensitive payloads, such as RNA, from degradation by enzymes in the bloodstream, thus ensuring that the therapeutic agents reach their target cells intact.

Controlled Release: Lipid nanoparticles offer the potential for controlled and sustained release of therapeutic agents, improving the overall efficacy of treatments and minimizing side effects.

Enhanced Cellular Uptake: The lipid composition of LNPs allows for efficient interaction with cell membranes, facilitating the internalization of the encapsulated cargo into target cells. This makes LNPs an ideal delivery system for RNA-based therapeutics, vaccines, and small molecules.

Scalability and Flexibility: The synthesis methods for LNPs are scalable, and the formulation can be easily adapted to deliver a wide variety of therapeutic agents, making them versatile for a range of medical applications.

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BOC Sciences offers a wide range of lipid nanoparticle products as well as customized products in different types to meet a variety of research and application needs. Below is the list of products we can provide, if you have more needs, please contact us to customize the synthesis of your lipid nanoparticles.

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