A More Oxidized Plasma Albumin Redox State and Lower Plasma HDL Particle Number Reflect Low-Protein Diet Ingestion in Adult Rats.

<bold>Background: </bold>Plasma albumin (ALB) redox state reflects protein nutritional status, but how it differs from other protein nutrition biomarkers remains to be fully elucidated.<bold>Objective: </bold>This study aimed to delineate the characteristics of plasma ALB redox state as a protein nutrition biomarker.<bold>Methods: </bold>Adult male Wistar rats were maintained on an AIN-93 M [14% casein, control (CT)] diet or an AIN-93 M-based 5% casein [low protein (LP)] diet ad libitum for 4 wk. Plasma samples were repeatedly obtained from the same rats at weeks 0-4, ALB redox state was determined by HPLC, and the concentrations of conventional protein nutrition biomarkers, ALB and transthyretin (TTR), were compared between the groups by Student t test. Body mass, relative muscle masses, plasma proteome, and plasma lipids at week 4 were also compared.<bold>Results: </bold>Plasma ALB redox state shifted to a more oxidized state in the LP diet group compared with the CT diet group at weeks 1-4. The LP diet group also showed significantly lower plasma ALB concentrations at weeks 1 and 2 (13% and 11% lower, respectively) and significantly lower TTR concentration at week 1 (21% lower) compared with the CT diet group, but these concentrations did not differ significantly at weeks 3 and 4. After 4 wk, body mass and relative soleus and gastrocnemius muscle masses did not differ, but the relative plantaris muscle mass tended to be 4% lower (1.75 compared with 1.68 g/kg body mass) in the LP diet group compared with the CT group (P = 0.06). The LP diet group also had a significantly lower HDL particle number than the CT group (30% lower).<bold>Conclusions: </bold>A more oxidized plasma ALB redox state and lower plasma HDL particle number reflect LP diet ingestion in adult rats, which did not exhibit changes of plasma ALB and TTR concentrations. [ABSTRACT FROM AUTHOR]