Fatty Acids: Definition, Structure, Synthesis, Oxidation, Metabolism and Function

Long aliphatic hydrocarbon chains with a carboxyl group at one end are known as fatty acids. It is the primary component of neutral fats, phospholipids, and glycolipids and is made up of three elements: carbon, hydrogen, and oxygen. Based on the length of their carbon chains, fatty acids can be classified as short-, medium-, or long-chain fatty acids. Since most fatty acids are biosynthesized from 2-carbon units, they often have an even number of carbon atoms. Nowadays, the production of industrial fatty acid salts, daily cosmetics, detergents, coatings, paints, rubber, soap, and other materials all uses fatty acids.

Fatty Acid Definition

Fatty acid (FC) is a type of carboxylic acid compound, consisting of a hydrocarbon group composed of carbon and hydrogen connected to a carboxyl group. It is a colorless, odorless, tasteless lipid with a relative density less than 1. In the presence of sufficient oxygen supply, fatty acids can be oxidized and decomposed into carbon dioxide and water, releasing a large amount of energy, so it is one of the body's main sources of energy. There are about 40 different fatty acids in nature, which are the main components of neutral fats, phospholipids and glycolipids. The physical properties of many lipids depend on the degree of saturation of fatty acids and the length of the carbon chain. Only fatty acids with an even number of carbon atoms can be absorbed and utilized by the body. Short-chain fatty acids can be classified according to their structure, properties and nutritional value to the human body.

Fatty Acid Structure

Fatty acids are carboxylic acids composed of a long hydrocarbon chain ("tail") and a terminal carboxyl group ("head"), mostly linear. The carboxylic acid group contains a double bonded oxygen atom and a hydroxyl group, which gives it acidic properties. The hydrocarbon chain is nonpolar, which means it does not interact well with water molecules. This property makes fatty acids insoluble in water but soluble in organic solvents such as ether or chloroform. The hydrophobic nature of fatty acids also enables them to form lipid bilayers, an important component of cell membranes. Fatty acid carbon chains can vary in length, with most fatty acids containing 12 to 24 carbon atoms. According to the length of the carbon chain, it can be divided into:

Short Chain Fatty Acids

Short-chain fatty acids have less than 6 carbon atoms in the carbon chain and are also called volatile fatty acids. Common short-chain fatty acids include: acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, and caproic acid.

Medium Chain Fatty Acids

Medium-chain fatty acids refer to fatty acids with 6-12 carbon atoms in the carbon chain. Common medium-chain fatty acids include: caprylic acid, capric acid, undecanoic acid, dodecanoic acid, etc.

Long Chain Fatty Acids

Long-chain fatty acids have more than 12 carbon atoms in the carbon chain. Common long-chain fatty acids include: myristic acid, myristoleic acid, palmitoleic acid, stearic acid, oleic acid, etc. Most of the fatty acids contained in general food are long-chain fatty acids.

Saturated vs Unsaturated Fatty Acids

Saturated Fatty Acids

Saturated fatty acids (SFA) refer to acids containing saturated hydrocarbon groups, with only saturated C-C single bonds or C-H single bonds on the carbon chain. Animal fats contain more saturated fatty acids, which are one of the basic components of lipids. Generally, the more common ones include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, etc. The main sources of saturated fatty acids are livestock meat and milk, which are found in the fat of cattle, sheep, pigs and other animals. A few plants such as coconut oil, cocoa butter, palm oil, etc. also contain such fatty acids. The main function of saturated fatty acids is to provide energy to the human body. If the intake of saturated fat is insufficient, people's blood vessels will become brittle, which can easily lead to cerebral hemorrhage, anemia, tuberculosis, neurological disorders and other diseases. At the same time, saturated fatty acids can increase cholesterol and neutral fat in the human body. Excessive intake of saturated fatty acids will lead to an increase in blood cholesterol, triacylglycerol, and LDL-C, which will subsequently cause narrowing of the arterial lumen, form atherosclerosis, and increase the risk of coronary heart disease.

Unsaturated Fatty Acids

Unsaturated double bonds can be found in the hydrocarbon chains of unsaturated fatty acids. They can be separated into monounsaturated and polyunsaturated fatty acids based on the quantity of double bonds. Monounsaturated fatty acids, which have just one unsaturated bond, can be found in a number of foods, including nuts, seeds, avocados, olive oil, and avocados. Omega-3 and omega-6 fatty acids are the two main subgroups of polyunsaturated fatty acids. The main sources of omega-3 fatty acids are fatty fish like sardines, mackerel, and salmon. Vegetable oils including corn oil, sunflower oil, and soybean oil are rich in omega-6 fatty acids. Unsaturated fatty acids support cell structure and function, regulate inflammation, and fend off chronic disease. They are crucial for maintaining healthy cell membranes and fostering the immune system's optimal operation.

Essential vs Nonessential Fatty Acids

Essential Fatty Acids

Essential fatty acids are fatty acids that the body cannot synthesize on its own. It is also a necessary nutrient for the synthesis of various hormones and endogenous substances in the body. It must be supplemented by food to allow the body's physiological functions to operate normally. Essential fatty acids include omega-3 and omega-6. Essential fatty acids are the main components of biological membrane lipids such as cell membranes, mitochondrial membranes and plasma membranes. They play a key role in the properties of most membranes and are also involved in the synthesis of phospholipids. The concentration, chain length and degree of unsaturation of fatty acids in phospholipids largely determine physical properties such as cell membrane fluidity and softness. These physical properties in turn affect how biological membranes perform their structural functions.

Nonessential Fatty Acids

Non-essential fatty acids are fatty acids that the body can synthesize by itself without relying on food supply. They include saturated fatty acids and monounsaturated fatty acids. For example, oleic acid, a non-essential fatty acid, is a monounsaturated fatty acid commonly found in olive oil, avocados, and nuts. Oleic acid plays a key role in reducing inflammation and improving heart health by lowering LDL cholesterol levels and increasing HDL cholesterol levels. It also contributes to healthy cell membranes and aids in the absorption of fat-soluble vitamins. Another important non-essential fatty acid is palmitic acid, a saturated fatty acid that is synthesized primarily by the body from carbohydrates and stored as fat for energy. While excessive consumption of palmitic acid can have negative health effects, such as weight gain and increased risk of heart disease, it is essential for hormone production and maintaining healthy skin and hair.

Fatty Acid Synthesis

Fatty acids in animals are mainly synthesized from carbohydrates in adipose tissue, liver and lactating mammary gland. Carbohydrates are converted into acetyl-CoA through glycolysis, and acetyl-CoA is converted into citric acid through the TCA cycle. Citric acid is regenerated into acetyl-CoA in the cytoplasm by ATP-citrate lyase, and then through a series of iterative reactions, the fatty acid chain is extended by two carbons. Catalyzed by fatty acid synthase, seven malonyl-CoA and one acetyl-CoA are condensed to generate palmitic acid (FA16:0). Palmitic acid (FA16:0) undergoes C chain extension and desaturation through SCD, ELOVLs and FADs to produce other types of fatty acids such as stearic acid (FA18:0), oleic acid (FA18:1).

Fatty Acid Molecule

BOC Sciences produces and supplies a wide range of lipid and fatty acid compounds, which can be derived from natural sources such as vegetable oils, animal fats and seaweed, or synthesized through chemical reactions in the laboratory. We offer fatty acids in a variety of forms, including pure compounds, mixtures, derivatives and conjugates with other molecules such as proteins, carbohydrates or lipids. These products are produced using state-of-the-art manufacturing processes and analytical techniques to ensure their purity, stability and consistency. BOC Sciences' fatty acid compounds are tested for identity, potency and impurities to meet the most stringent quality standards and regulatory requirements. In addition to an extensive catalog of ready-to-use fatty acid compounds, BOC Sciences offers fatty acid analysis services to meet specific customer requirements.

Fatty Acid Oxidation

Fatty acid oxidation (FAO) is a key metabolic process in the body that breaks down fatty acids and supports energy production, redox homeostasis, and biosynthetic reactions. FAO utilizes fatty acid-converted acetyl-CoA (CoA) subunits to generate nicotinamide adenine dinucleotide (NADH), acetyl-CoA, and adenosine triphosphate (ATP) to support energy production, redox homeostasis, and biosynthetic reactions. Dysregulated FAO enhances tumor metastasis, drug resistance, and immune evasion. In recent years, there has been increasing interest in fatty acid oxidation as a potential therapeutic strategy for the treatment of various diseases, including cancer, diabetes, and metabolic disorders. Therefore, fatty acid oxidation has become a promising target for drug discovery and development.

Fatty Acid Metabolism

Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules belonging to the lipid macronutrient category. These processes can be mainly divided into (1) catabolic processes that produce energy and (2) anabolic processes.

Fatty Acid Catabolism

In catabolism, fatty acids are metabolized to produce energy, primarily in the form of adenosine triphosphate (ATP). Compared to other macronutrient categories (carbohydrates and proteins), the most ATP is produced on a per gram energy basis when fatty acids are completely oxidized to CO₂ and water through beta oxidation and the citric acid cycle. Therefore, fatty acids (mainly in the form of triglycerides) are the most important form of fuel storage in most animals and to a lesser extent in plants.

Fatty Acid Anabolism

Most of the fatty acids in the human body come from food and are exogenous fatty acids that can be used by the human body through transformation and processing in the body. At the same time, the body can also use sugar and protein to convert into fatty acids called endogenous fatty acids, which are used to generate triglycerides and store energy. The main organs that synthesize fatty acids are the liver and lactating mammary glands. In addition, fatty tissues, kidneys, and small intestines can also synthesize fatty acids. The direct raw material for synthesizing fatty acids is acetyl CoA, which consumes ATP and NADPH. First, sixteen-carbon palmitate is generated, which is processed to generate various fatty acids in the human body. The synthesis takes place in the cytoplasm.

Fatty Acid Function

Fatty Acids for Inflammatory and Autoimmune Diseases

One area where fatty acids show particular promise in drug discovery is in the treatment of inflammatory and autoimmune diseases. Inflammation is the immune system's natural response to infection or injury, but when this response is dysregulated, chronic inflammation can lead to a range of diseases, including rheumatoid arthritis, inflammatory bowel disease and asthma. Fatty acids such as omega-3 and omega-6 polyunsaturated fatty acids have been shown to have anti-inflammatory properties and may help modulate the immune response in these conditions. For example, the anti-inflammatory effects of omega-3 fatty acids found in fish oil have been extensively studied and have shown potential in treating rheumatoid arthritis. One study found that omega-3 fatty acids can reduce joint pain and stiffness in patients with rheumatoid arthritis, suggesting these molecules may be a promising option for treating the disease.

Fatty Acids for Obesity and Diabetes

In addition to their anti-inflammatory properties, fatty acids have been studied for their potential in treating metabolic diseases such as obesity and diabetes.  Obesity is a major risk factor for a range of chronic diseases, including type 2 diabetes, cardiovascular disease and certain types of cancer. Fatty acids play a crucial role in energy metabolism, and increasing evidence suggests that alterations in fatty acid metabolism may contribute to the development of obesity and related metabolic disorders. For example, studies have shown that abnormalities in fatty acid oxidation (the process by which fatty acids are broken down to produce energy) are associated with insulin resistance and type 2 diabetes. Additionally, it has been suggested that inhibition of enzymes involved in fatty acid synthesis may help reduce fat accumulation and improve insulin sensitivity in obese individuals. Fatty acid derivatives that mimic the effects of natural fatty acids, such as PPAR agonists, have also shown promise in preclinical studies as potential treatments for metabolic disorders.

Fatty Acids for Neurological Disorders

Fatty acids are also being explored as potential drug candidates for treating neurological diseases, including Alzheimer's disease, Parkinson's disease and multiple sclerosis. Research suggests that changes in brain fatty acid composition may contribute to neurodegenerative diseases, and targeting fatty acid metabolism may provide new treatment options for these diseases. For example, omega-3 fatty acids have been studied for their potential neuroprotective effects in Alzheimer's disease. Omega-3 fatty acids are abundant in the brain and have been shown to have anti-inflammatory and antioxidant properties that may help protect neurons from damage and improve cognitive function in Alzheimer's patients.

Fatty Acids for Drug Delivery

In addition to their therapeutic potential, fatty acids are also being studied as drug delivery vehicles to improve the bioavailability and efficacy of existing drugs. Fatty acids are amphipathic molecules, meaning they have both hydrophilic and hydrophobic regions, which allows them to interact with a variety of pharmaceutical compounds and increase their solubility and stability. One common approach is to combine fatty acids with existing drugs to create prodrugs that can be more efficiently delivered to target tissues. For example, fatty acid conjugates have been used to increase the oral bioavailability of poorly water-soluble drugs, such as paclitaxel, a chemotherapeutic agent used to treat various types of cancer. By attaching a fatty acid moiety to paclitaxel, the researchers were able to enhance its absorption in the gastrointestinal tract and improve its therapeutic efficacy.

PEGylated Stearic Acid