[Frontiers in Bioscience 7, a109-116, May 1, 2002]

DECREASED MITOCHONDRIAL CARNITINE TRANSLOCASE IN SKELETAL MUSCLES IMPAIRS UTILIZATION OF FATTY ACIDS IN INSULIN-RESISTANT PATIENTS

Gianfranco Peluso1, Orsolina Petillo1, Sabrina Margarucci1, Gertrude Mingrone2, Aldo Virgilio Greco2, Cesare Indiveri3, Ferdinando Palmieri3, Mariarosa Anna Beatrice Melone4 Emilia Reda5, and Menotti Calvani5

1Institute of Protein Biochemistry and Enzymology, CNR, Naples, Italy and Department of Experimental Oncology, National Cancer Institute, Naples, Italy. 2Department of Internal Medicine, Catholic University, School of Medicine, Rome, Italy, 3department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Bari, Italy,4Department of Neurological Sciences, Second University of Naples;5Scientific Department, Sigma Tau SpA, Rome, Italy

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and methods
3.1.Clinical Characteristics of Patients
3.2. Body composition
3.3.Euglycemic hyperinsulinemic clamp
3.4.Skeletal muscle lipid analysis
3.5. Northern blot analysis.
3.6.Isolation of mitochondria
3.7. Western blot analysis
3.8.Carnitine-acylcarnitine translocase and carnitine palmytoyltransferase II assays
3.9. Statistical Analysis
4. Results
4.1. Skeletal muscle lipid levels in Patients and Normal Individuals
4.2.CACT mRNA and protein levels
4.3. Carnitine-acylcarnitine translocase activity
5. Discussion
6. Acknowledgements
7. References

1. ABSTRACT

Insulin resistance (IR) and its health consequences (diabetes, hypertension, cardiovascular disease, obesity etc.) affect between 25 and 35% of Westernized populations. Decreased fatty acid (FA) oxidation in skeletal muscle is implicated in obesity-related IR. Carnitine-acylcarnitine translocase (CACT) transports long-chain FAs both into mitochondria (as carnitine esters for energy-generating processes) and out of mitochondria. To determine whether CACT activity correlates with decreased FA oxidation we measured CACT concentrations in cellular and mitochondrial extracts from the skeletalmuscle of 19 obese IR individuals and of 19 lean controls. We also evaluated carnitine transport in skeletal muscle mitochondria in both groups. Mitochondrial CACT was decreased at translational and transductional level, and carnitine-carnitine and acylcarnitine-carnitine exchange rates were significantly lower in IR subjects. Aberrant acylcarnitine flux into mitochondria was not correlated with decreased activity of other components of the mitochondrial carnitine system (i.e., carnitine palmitoyl transferase-I and II). Our data suggest that by restraining entry of FA-coenzyme A into mitochondria, low CACT levels increase cytosolic FA levels and their incorporation into glycerolipids. The low level of CACT in IR muscle may contribute to the elevated muscle concentrations of triglycerides, diacylglycerol, and FA-coenzyme A characteristic of IR muscle.