The carbonyl scavenger carnosine ameliorates dyslipidaemia and renal function in Zucker obese rats

Abstract

The metabolic syndrome is a risk factor that increases the risk for development of renal and vascular complications. This study addresses the effects of chronic administration of the endogenous dipeptide carnosine (β-alanyl-L-histidine, L-CAR) and of its enantiomer (β-alanyl-D-histidine, D-CAR) on hyperlipidaemia, hypertension, advanced glycation end products, advanced lipoxidation end products formation and development of nephropathy in the non-diabetic, Zucker obese rat. The Zucker rats received a daily dose of L-CAR or D-CAR (30 mg/kg in drinking water) for 24 weeks. Systolic blood pressure was recorded monthly. At the end of the treatment, plasma levels of triglycerides, total cholesterol, glucose, insulin, creatinine and urinary levels of total protein, albumin and creatinine were measured. Several indices of oxidative/carbonyl stress were also measured in plasma, urine and renal tissue. We found that both L- and D-CAR greatly reduced obese-related diseases in obese Zucker rat, by significantly restraining the development of dyslipidaemia, hypertension and renal injury, as demonstrated by both urinary parameters and electron microscopy examinations of renal tissue. Because the protective effect elicited by L- and D-CAR was almost superimposable, we conclude that the pharmacological action of L-CAR is not due to a pro-histaminic effect (D-CAR is not a precursor of histidine, since it is stable to peptidic hydrolysis), and prompted us to propose that some of the biological effects can be mediated by a direct carbonyl quenching mechanism.

Fig 1

Comparison of the best pose for L- (white) and D- (red) carnosine. The figure shows that the imidazole ring is accommodated in a very similar mode, but the charged groups assume totally different arrangements, thus explaining the incapacity of D-carnosine to assume a pose conducive to the catalysis.

Fig 2

In vitro studies: kinetics of the enzymatic hydrolysis of L-CAR (triangle) and D-CAR (square) in (A) human serum, (B) rat kidney and (C) human liver.

Fig 3

Time course of L-CAR (triangle) and D-CAR (square) in rat plasma, after oral administration of 100 mg/kg.

Fig 4

Body weight and plasma analytical determinations in LN, ZK and Zucker treated animals (ZK + L; ZK + D). Values are expressed as mean ± S.E.M. relative to six animals/group. All ZK values statistically different from LN (P < 0.001), except for glucose (not statistically different). All ZK + L and ZK + D values not statistically different. *P < 0.05 versus ZK, ***P < 0.001 versus ZK.

Fig 5

Evolution of SBP, during the study, in LN (circle), ZK (square) and Zucker treated animals (ZK + L, triangle up; ZK + D, triangle down). (A) P < 0.001 versus LN; (B) P < 0.001 versus ZK; (C) P < 0.05 versus LN. ZK + L and ZK + D values not statistically different.

Fig 6

Renal functions and histological alterations in LN, ZK and Zucker treated animals (ZK + L; ZK + D). Values are expressed as mean ± S.E.M. relative to six animals/group. All ZK values statistically different from LN (P < 0.001). All ZK + L and ZK + D values not statistically different. *P < 0.05 versus ZK, **P < 0.01 versus ZK, ***P < 0.001 versus ZK.

Fig 7

Glomerular capillary loops in LN (A), ZK (B) and Zucker treated animals (ZK + L, C; ZK + D, D). Arrows point to GBM. Up left: LN rat with normal GBM thickness, podocyte and foot processes; up right: ZK rat with thick GBM, edematous podocyte and foot processes; down left and down right: ZK + L and ZK + D rats with almost normal GBM thickness, podocyte and foot processes. GBM: glomerular basement membrane; P: podocyte, FP: foot processes.

Fig 8

Selected Reaction Monitoring (SRM) chromatogram, relative to CAR-HNE parent ion → product ions transition, in LN (A), ZK (B) and Zucker treated animals (ZK + D, C; ZK + L, D) and CAR-HNE structure.