Circadian Oscillations: The 24-hour day-night cycle plays an important role in mammalian physiology and behavior and, as most travelers are well aware, there is an intimate link between our in-built circadian clocks and metabolic rhythms. This link is in part forged by the protein deacetylase SIRT1, which regulates the clock's molecular circuitry. SIRT1 uses as a cofactor the cellular metabolite NAD ⁺ , which is synthesized through a salvage pathway that includes the enzyme nicotinamide phosphoribosyltransferase (NAMPT) (see the Perspective by Wijnen ). Ramsey et al. (p. 651 ; published online 19 March) and Nakahata et al. (p. 654 , published online 12 March) now show that NAMPT and NAD ⁺ levels oscillate during the daily 24-hour cycle and that this oscillation is regulated by the circadian clock. Furthermore, the oscillations in NAD ⁺ modulate the activity of SIRT1 feeding back into the circadian clock.

Palmitoylethanolamide (PEA), the naturally occurring amide of palmitic acid and ethanolamine, reduces pain and inflammation through an as-yet-uncharacterized mechanism. Here, we identify the nuclear receptor peroxisome proliferator-activated receptor-α (PPAR-α) as the molecular target responsible for the anti-inflammatory properties of PEA. PEA selectively activates PPAR-α in vitro with an EC₅₀ value of 3.1 ± 0.4 μM and induces the expression of PPAR-α mRNA when applied topically to mouse skin. In two animal models, carrageenan-induced paw edema and phorbol ester-induced ear edema, PEA attenuates inflammation in wild-type mice but has no effect in mice deficient in PPAR-α. The natural PPAR-α agonist oleoylethanolamide (OEA) and the synthetic PPAR-α agonists GW7647 and Wy-14643 mimic these effects in a PPAR-α–dependent manner. These findings indicate that PPAR-α mediates the anti-inflammatory effects of PEA and suggest that this fatty-acid ethanolamide may serve, like its analog OEA, as an endogenous ligand of PPAR-α.

Nerve cells mould the lipid fabric of their membranes to ease vesicle fusion, regulate ion fluxes and create specialized microenvironments that contribute to cellular communication. The chemical diversity of membrane lipids controls protein traffic, facilitates recognition between cells and leads to the production of hundreds of molecules that carry information both within and across cells. With so many roles, it is no wonder that lipids make up half of the human brain in dry weight. The objective of neural lipidomics is to understand how these molecules work together; this difficult task will greatly benefit from technical advances that might enable the testing of emerging hypotheses.