Targeting components of the stress system as potential therapies for the metabolic syndrome: the peroxisome-proliferator-activated receptors.

The three peroxisome-proliferator-activated receptor (PPAR) subtypes PPAR-alpha, PPAR-gamma, and PPAR-delta are ligand-activated transcription factors of the nuclear receptor family. PPARs form obligate heterodimers with the retinoid X receptor, which bind to peroxisome-proliferator-response elements (PPREs). PPAR-alpha is expressed mainly in liver, brown fat, kidney, heart, and skeletal muscle; PPAR-gamma in intestine and adipose tissue; PPAR-alpha and PPAR-gamma are both expressed in vascular endothelium, smooth muscle cells, macrophages, and foam cells; PPAR-delta in skeletal muscle, human embryonic kidney, intestine, heart, adipose tissue, developing brain, and keratinocytes. Intense interest in the development of drugs with new mechanisms of action for the metabolic syndrome has focused attention on nuclear receptors, such as PPARs that function as regulators of energy homeostasis. Agonists of PPAR-alpha and PPAR-gamma are currently used to treat diabetic dyslipidemia and type 2 diabetes. Dual PPAR-alpha/gamma agonists and PPAR-alpha/gamma/delta pan-agonists are under investigation for treatment of cardiovascular disease and the metabolic syndrome. Selective PPAR modulators (SPPARMs) are PPAR ligands that possess desirable efficacy and improved tolerance. Efforts are being made to identify novel partial agonists or antagonists for PPAR-gamma in order to combine their antidiabetic and antiobesity effects. Glucocorticoids are major mediators of the stress response and could be the link between stress and PPAR activator signaling and thus may affect the downstream metabolic pathways involved in fuel homeostasis.