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Phospholipids

Introduction

All lipids that contain phosphorus are called phospholipids. Phospholipids also known as phosphatides, are molecules in which hydrophilic head group and hydrophobic acyl chains are linked to the alcohol. The variation in head groups, aliphatic chains and alcohols leads to the existence of a wide variety of phospholipids. As main components of cellular membrane, phospholipids have excellent biocompatibility. In addition, phospholipids are renowned for their amphiphilic structures. The amphiphilicity confers phospholipids with self-assembly, emulsifying and wetting characteristics. These unique properties make phospholipids with a very wide range of applications, especially in the pharmaceutical industry.

Fig.1 The structure of phospholipids

Classification

(1) According to the structure of alcohols contained in the phospholipids, they can be divided into glycerophospholipids and sphingomyelins.

Glycerophospholipids: Glycerophospholipids refer to the phospholipids in which glycerol is the backbone. Variation in the head group of glycerophospholipids leads to different glycerophospholipids, such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol (PG) and cardiolipin (CL). The structure and properties of above glycerophospholipids are shown in Table 1 ^[1].

Table 1. The structure and property of glycerophospholipids

Phospholipids	Group (-X)	Physiological properties	Net charge in pH 7
PC		PC is an important substrate of synthesis of the neurotransmitter acetylcholine, and has the function of nourishing the brain and improving intelligence.	0
PE		PE plays an important role in membrane fusion.	0
PS		PS can improve the function of nerve cells, regulate the conduction of nerve impulse, and enhance the memory function of brain.	-1
PA		-	-1
PI		PI is the precursor of second messenger, which plays a very important role in the process of transmission of messages in neural system.	-1
PG		-	-1
CL		CL, a phospholipid of unusual structure, is localized almost exclusively to inner mitochondrial membrane, is particularly rich in unsaturated fatty acids. This phospholipid plays an important role in mitochondrial bioenergetics by affecting the activity of key proteins of mitochondrial inner membrane.	-2

Sphingomyelins: The sphingomyelins with structure of N-acylsphingosine-1-phosphatidylcholine are an important component of animal cell membranes. In 1962, researchers confirmed that all sphingomyelins of biological sources are D-erythro configuration.

Fig.2 The structure of sphingomyelins

(2) According to the sources, phospholipids can be divided into natural phospholipids and synthetic phospholipids.

Natural phospholipid: Natural phospholipids are defined as phospholipids isolated from natural sources like vegetable (e.g., soybeans, rape (canola) seed, wheat germ, sunflower, and flax seed) and animal material (e.g., egg yolk, bovine brain, milk, or krill). However, different natural sources have differences in the contents and species of phospholipids. In terms of production, egg yolk and soybean are the most important sources for phospholipids. In addition, phospholipids isolated from plants and animals can be purified into different levels, including food and pharmaceutical grade according to the specific uses.
Synthetic phospholipids: Since the single component of naturally occurring phospholipids are not readily accessible, chemical synthesis are developed to get an access to phospholipids with defined structure and configuration. The synthesis of phospholipids can be divided into semi-synthesis and total synthesis. Semi-synthesis refers to the changing of head, tail groups or both on the basis of natural phospholipids. The total synthesis of involves the formation of ester or ether bonds linking a polar moiety to glycerol backbone, and the attachment of polar head group.

Applications

Phospholipids are well-established excipients for pharmaceutical applications, and have been widely used to prepare liposome, ethosomes and other nano-formulations of topical, oral and parenteral drugs for differing reasons like improved bio-availability, reduced toxicity and increased permeability across membranes. And phospholipids offer manifold possibilities to be used as excipients in drug delivery systems, which can deliver both hydrophilic and lipophilic drugs. In addition, purified phospholipids are produced commercially and have found applications in nanotechnology and materials science.

Fig.3 Schematic representation of liposome by using phospholipid

Alfa Chemistry can offer various phospholipids such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol (PG) cardiolipin (CL), natural phospholipids and others. You can click on our product list for a detailed view. If you do not find the product you want, we also provide you with custom synthesis service. Please contact us, if you are in need of assistance.

Reference

Li, J., et al. A review on phospholipids and their main applications in drug delivery systems[J]. Asian journal of pharmaceutical sciences, 2015, 10(2): 81-98.