title: Metabolic and genomic response to dietary isocaloric protein restriction in the rat.
abstract: We have examined hepatic, genomic, and metabolic responses to dietary protein restriction in the non-pregnant Sprague-Dawley rat. Animals were pair-fed either a 6 or 24% casein-based diet for 7-10 days. At the end of the dietary period, a microarray analysis of the liver was performed, followed by validation of the genes of interest. The rates of appearance of phenylalanine, methionine, serine, and glucose and the contribution of pyruvate to serine and glucose were quantified using tracer methods. Plasma and tissue amino acid levels, enzyme activities, and metabolic intermediates were measured. Protein restriction resulted in significant differential expression of a number of genes involved in cell cycle, cell differentiation, transport, transcription, and metabolic processes. RT-PCR showed that the expression of genes involved in serine biosynthesis and fatty acid oxidation was higher, and those involved in fatty acid synthesis and urea synthesis were lower in the liver of protein-restricted animals. Free serine and glycine levels were higher and taurine levels lower in all tissues examined. Tracer isotope studies showed an ∼50% increase in serine de novo synthesis. Pyruvate was the primary (∼90%) source of serine in both groups. Transmethylation of methionine was significantly higher in the protein-restricted group. This was associated with a higher S-adenosylmethionine/S-adenosylhomocysteine ratio and lower cystathione β-synthase and cystathionine γ-lyase activity. Dietary isocaloric protein restriction results in profound changes in hepatic one-carbon metabolism within a short period. These may be related to high methylation demands placed on the organism and caused by possible changes in cellular osmolarity as a result of the efflux of the intracellular taurine.
authors.affiliation: Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio 44195, USA. sck@case.edu
authors.forename: Satish C
authors.initials: SC
authors.lastname: Kalhan
authors.forename: Sonal O
authors.initials: SO
authors.lastname: Uppal
authors.forename: Jillian L
authors.initials: JL
authors.lastname: Moorman
authors.forename: Carole
authors.initials: C
authors.lastname: Bennett
authors.forename: Lourdes L
authors.initials: LL
authors.lastname: Gruca
authors.forename: Prabhu S
authors.initials: PS
authors.lastname: Parimi
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Dasarathy
authors.forename: David
authors.initials: D
authors.lastname: Serre
authors.forename: Richard W
authors.initials: RW
authors.lastname: Hanson
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D002453:Cell Cycle; D002454:Cell Differentiation; D018753:Diet, Protein-Restricted; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D008099:Liver / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013654:Taurine / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D013654:Taurine