Effect of different degrees of caloric restriction on AOPPs and AGEs formation in healthy obese ponies

It is recognized that caloric restriction (CR) decreases oxidative stress1. Since proteins are highly susceptible to oxidative damage by glycoxidation (with the formation of advanced glycation end products (AGEs) like pentosidine (PENT) and carboxymethyllysine (CML)) or oxidation (with the formation of advanced oxidation protein products (AOPPs)2) the analyses of this compounds could be useful to evaluate the cumulative metabolic burden and oxidative stress. We hypothesized that weight loss by CR has an effect on AGEs and AOPPs. Eighteen obese Shetland geldings (BCS:8/9±1) were studied. After a 4 weeks adaption period to maintain stable obese body weight (BW), ponies were randomly divided in three groups for a 16.5 weeks weight loss program (WLP): control group was fed 100% of individual MER to maintain stable obese BW (C, 0.17±0.02 MJ/kgBW), a 'slow' weight loss group, 80% of the MER (S, 0.14±0.01 MJ/kgBW) and a 'rapid' weight loss group 60% of the MER (R, 0.10±0.01 MJ/kgBW). Ponies received low energy hay (8.08 MJ/kg DM) and an equal amount of a balancer (Spillers Gro'n Win®, MARS Horsecare) to meet protein, mineral and vitamin requirements . Plasma was collected at the beginning (T0), after 8 weeks (T1) and at the end (T2) of WLP to evaluate PENT (HPLC)3, CML and AOPP (immunoassay kit). Statistical analysis was based on a linear model to identify differences between treatment*time periods. During the WLP BW was reduced by 3.10±2.03% for C; 5.10 ±2.01% for S; 12.56±2.06% for R based on initial BW. No significant effect was recorded for CML. For AOPP, significant lower values were recorded for C and S (P=0.04) and C and R (P<0.01) between the T0 and T1. For PENT, a trend for an increased concentration for R compared to C at T2 compared to and T1 was noted (P=0.08). Different levels of energy restriction and consequently weight loss appear to affect the levels of AOPPs; also a trend for an altered AGEs formation was observed. This could be related to the higher oxidative state and production of by-products of oxidative metabolism4. The accumulation of these end products serves as a measure of cumulative metabolic and oxidative stress5.

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