Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are newly identified endogenous lipids regulated by fasting and high-fat feeding and associated with insulin sensitivity. Structurally, these esters are comprised of a C-16 or C-18 fatty acid (e.g., palmitoleic, palmitic, oleic, or stearic acid) linked to a hydroxylated C-16 or C-18 lipid. 9-PAHSA is a FAHFA in which palmitic acid is esterified to 9-hydroxy stearic acid. PAHSAs are the most abundant forms of FAHFA in serum as well as white and brown adipose tissues of glucose tolerant AG4OX mice, which overexpress Glut4 specifically in adipose tissue. 9-PAHSA is the predominant isomer of PAHSA in wild type and AG4OX mice. It is found in humans and is reduced in the serum and adipose tissues of insulin-resistant humans. 9-PAHSA improves glucose tolerance, stimulates insulin secretion, and has anti-inflammatory effects in mice.
