Acetylation has recently emerged as an important mechanism for controlling a broad array of proteins mediating cellular adaptation to metabolic fuels. Acetylation is governed, in part, by SIRTs (sirtuins), class III NAD⁺-dependent deacetylases that regulate lipid and glucose metabolism in liver during fasting and aging. However, the role of acetylation or SIRTs in pathogenic hepatic fuel metabolism under nutrient excess is unknown. In the present study, we isolated acetylated proteins from total liver proteome and observed 193 preferentially acetylated proteins in mice fed on an HFD (high-fat diet) compared with controls, including 11 proteins not previously identified in acetylation studies. Exposure to the HFD led to hyperacetylation of proteins involved in gluconeogenesis, mitochondrial oxidative metabolism, methionine metabolism, liver injury and the ER (endoplasmic reticulum) stress response. Livers of mice fed on the HFD had reduced SIRT3 activity, a 3-fold decrease in hepatic NAD⁺ levels and increased mitochondrial protein oxidation. In contrast, neither SIRT1 nor histone acetyltransferase activities were altered, implicating SIRT3 as a dominant factor contributing to the observed phenotype. In Sirt3^−/− mice, exposure to the HFD further increased the acetylation status of liver proteins and reduced the activity of respiratory complexes III and IV. This is the first study to identify acetylation patterns in liver proteins of HFD-fed mice. Our results suggest that SIRT3 is an integral regulator of mitochondrial function and its depletion results in hyperacetylation of critical mitochondrial proteins that protect against hepatic lipotoxicity under conditions of nutrient excess.

Pyrroloquinoline quinone (PQQ) is associated with biological processes such as mitochondriogenesis, reproduction, growth, and aging. In addition, PQQ attenuates clinically relevant dysfunctions (e.g., those associated with ischemia, inflammation and lipotoxicity). PQQ is novel among biofactors that are not currently accepted as vitamins or conditional vitamins. For example, the absence of PQQ in diets produces a response like a vitamin-related deficiency with recovery upon PQQ repletion in a dose-dependent manner. Moreover, potential health benefits, such as improved metabolic flexibility and immuno-and neuroprotection, are associated with PQQ supplementation. Here, we address PQQ’s role as an enzymatic cofactor or accessory factor and highlight mechanisms underlying PQQ’s actions. We review both large scale and targeted datasets demonstrating that a neonatal or perinatal PQQ deficiency reduces mitochondria content and mitochondrial-related gene expression. Data are reviewed that suggest PQQ’s modulation of lactate acid and perhaps other dehydrogenases enhance NAD+-dependent sirtuin activity, along with the sirtuin targets, such as PGC-1$\mathsf{\alpha }$, NRF-1, NRF-2 and TFAM; thus, mediating mitochondrial functions. Taken together, current observations suggest vitamin-like PQQ has strong potential as a potent therapeutic nutraceutical.

Amino acids in biological fluids have previously been shown to be detectable using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) with perfluorinated acids as ion‐pairing agents. To date, these studies have used precursor mass, retention time and tandem mass spectrometry (MS/MS) to identify and quantify amino acids. While this is a potentially powerful technique, we sought to adapt the method to time‐of‐flight (TOF)MS. A new application of a recently described liquid chromatographic separation method was coupled with TOFMS to employ accurate mass for qualitative identification; resulting in additional qualitative data not available with standard single quadrupole data. In the current study, we evaluated 25 physiological amino acids and one dipeptide that are routinely quantified in human plasma. Accuracy and precision of the method was evaluated by spiking human plasma with a mix of the 25 amino acids; in addition, the inclusion of a cation‐exchange cleanup step was evaluated. The calibration curves were linear over a range from 1.56 to 400 µM. The dynamic range was found to be within physiological levels for all amino acids analyzed. Accuracy and precision for most of the amino acids was between 80–120% spike recovery and <10% relative standard deviation (RSD). The LC/MS technique described in this study relies on mass accuracy and is suitable for the quantitation of free amino acids in plasma. Copyright © 2007 John Wiley & Sons, Ltd.