Methods for inducing and monitoring liver autophagy relative to aging and antiaging caloric restriction in rats.

The functioning of macroautophagy declines with increasing age in the liver of ad libitum fed animals, whereas it is preserved in rats submitted to antiaging caloric restriction. In this perspective, monitoring autophagy during aging may provide a useful biomarker of aging. Here we describe a procedure for the quantification of the ex vivo functioning of autophagy by the use of single-pass liver perfusion to measure the rate of degradation of prelabeled long-lived proteins. The maximum rate of autophagy can be measured after the pharmacological suppression of the supply of free fatty acids during fasting, which intensifies the activation of autophagy by a physiological mechanism. The effects of treatment on the plasma level of branched chain amino acids may be used as a minimally invasive indicator of the intensification of autophagy. The effects of aging on autophagic proteolysis and on amino acid and hormone control can also be assessed by measuring the rate of the 3-methyladenine-sensitive valine released from isolated liver cells incubated in vitro.