CPT1i

CPT1i is a designation used in the biochemical literature to refer to inhibitors of carnitine palmitoyltransferase 1 (CPT1). CPT1 is the outer mitochondrial membrane enzyme that catalyzes the conversion of long-chain fatty acyl-CoA to acyl-carnitine, enabling transport into mitochondria for beta-oxidation. By inhibiting CPT1, CPT1i reduces mitochondrial uptake of long-chain fatty acids and decreases fatty acid oxidation, often shifting cellular energy metabolism toward glucose oxidation.

CPT1 exists in several isoforms: CPT1A in liver, CPT1B in muscle and adipose tissue, and CPT1C in the brain. Inhibitors vary in potency and isoform selectivity; some are nonselective across CPT1 isoforms. Etomoxir is among the best-characterized CPT1 inhibitors and has been widely used in laboratory settings, though it can have off-target effects and safety concerns at higher doses. Other compounds, including some investigational molecules, are referred to collectively as CPT1 inhibitors or CPT1i and differ in efficacy and pharmacokinetic properties.

In research, CPT1i are used to study metabolic flexibility, the role of fatty acid oxidation in energy homeostasis, and the pathophysiology of metabolic diseases such as obesity and type 2 diabetes. They are also employed in cellular and animal models of ischemia-reperfusion to understand how shifts in energy substrate utilization affect outcomes.

Limitations include potential toxicity, reliance on animal models for interpretation, and the essential role of CPT1 in normal physiology—particularly in the liver and heart. Therefore, the use of CPT1i requires careful consideration of dosing and tissue-specific effects.

See also: carnitine palmitoyltransferase, fatty acid oxidation, etomoxir, metabolic flexibility.