ABSTRACT
Introduction The many roles of carnitine in metabolism make carnitine homeostasis in humans critically important for maintaining health and treating disease. We are now beginning to recognize that there is also a critically important role of carnitine in human homeostasis. Homeostasis is a self-regulating process that maintains stability while adjusting to changing conditions. Ideally the carnitine metabolite pool and the metabolic processes of the body exist in their own dynamic equilibrium. They reach a balance in which internal change continuously compensates for external change. Thus, the concentrations and locations of the different carnitine metabolites in the body must change to meet the changing sources of carnitine, the interconversion of different acylcarnitines, and the removal of carnitine from the body. Carnitine likely functions in maintaining homeostasis
Introduction ........................................................................................................ 3 Sources of carnitine ............................................................................................ 4
Endogenous biosynthesis of carnitine ........................................................ 4 Exogenous sources of carnitine ................................................................... 4
Interconversion of different acylcarnitines ..................................................... 5 Conversion of acylCoAs to acylcarnitines and back again ..................... 5 Fatty acid metabolism ................................................................................... 6 Carboxylic acids in metabolism .................................................................. 7
Carnitine metabolites......................................................................................... 7 Interorgan carnitine homeostasis and fuel homeostasis .............................. 8 Conclusions ......................................................................................................... 9
What we think we know .............................................................................. 9 What we think might be (exciting hypotheses) ........................................ 9
References .......................................................................................................... 10
in many metabolic pathways and physiological conditions, with carnitine’s role in energy metabolism homeostasis being the best studied. The following chapters provide details concerning carnitine transport and metabolism in specific tissues under various physiological conditions, including health, exercise, and disease. The purpose of this chapter is to provide a brief overview of some of the basics of carnitine synthesis, transport, and function, but more importantly, to step back and look at the gestalt of carnitine and then to stand on tiptoes to try to see over the horizon of established carnitine information.
