Fatty acids, palm-oil, hydrogenated

Endpoint summary

Additional information

Fatty acids

Upon ingestion, fatty acids are directly taken up intothe cells lining the intestines (enterocytes), then transported mainly in the form of triglycerides via the lymph to various tissues (see below). The fatty acids may then be stored in the form of triglycerides as a source of energy or redistributed to phospholipids and sterol esters (conversion mainly in the liver) (Mead and Fillerup, 1957; McArthur et al., 1999).

The extent of absorption in the gastro-intestinal system varies depending on the chain length of the fatty acids and their degree of saturation. Generally, short-chain fatty acids are better absorbed than the long chain counterparts. Also, absorption decreases with increasing saturation (MacDonald, 1973; Robinson, 1973; Chen and Farese, 2002). In an overview by the Cosmetic Ingredient Review Panel (CIR, 1987), stearic acid (C18) was cited as being the most poorly absorbed of the common fatty acids.

Only limited information could be located on dermal penetration of fatty acids. In dermal application studies in the rat (Butcher, 1951), linoleic acid was shown to penetrate the epithelium rapidly and reach the vascular system. Oleic acid was also reported to penetrate the epithelium of rats, possibly via hair follicles, but only minute amounts were seen in the blood vessels. Ricinoleic acid on the other hand was retained mainly in the outer strata of the epidermis. Other authors have noted that skin permeability increases with the lipophilic nature of a compound (Scheuplein, 1965; CIR, 1987). Dermal uptake of fatty acids has also been studied with fatty acid soaps. The C₁₀and C₁₂soaps show the greatest skin penetration of human epidermis. Also, percutaneous absorption of sodium laurate is greater than that of most other anionic surfactants (HERA, 2002).

Glycerides

When taken up orally, glycerides are split in the intestinal lumen into glycerol and fatty acids with the help of lipases and bile secretions, then move into enterocytes. The triglycerides are rebuilt in the enterocytes from their fragments and packaged together with cholesterol and proteins to form chylomicrons. These are excreted from the cells, collected by the lymph system and transported to the large vessels near the heart before entering the blood.Eventually, the triglycerides bind to the membranes of hepatocytes, adipocytes or muscle fibers, where they are either stored or oxidized for energy. When the body requires fatty acids as a source of energy, the hormone glucagon signals the breakdown of the triglycerides by hormone-sensitive lipases to release free fatty acids. The fatty acids are then broken down by stepwise elimination of C2-units in the mitochondrial β-oxidation.Alternate oxidation pathways can be found in the liver (ω-oxidation) and the brain (α-oxidation) (HERA, 2002).The C2-units are esterified to acetyl-coenzyme A which directly enters the citric acid cycle where it is converted to carbon dioxide and energy (MacDonald, 1973; Robinson, 1973; Chen and Farese, 2002). Not all fatty acids present as triglycerides are used for energy production: after metabolisation in the liver, redistribution tophospholipids and sterol esters may for example also occur (Mead and Fillerup, 1957; McArthur et al., 1999).

Glycerides with alkyl chain lengths between C8 to18, including C18-unsatd. are generally poorly water soluble have an estimated log Pow > 6 and molecular weights > 500. As such,uptake into the stratum corneum of skin and further transfer into the epidermis are likely to be low (REACH guidance document R7.C (May 2008).