L-Carnitine (Levocarnitine)

L‑Carnitine (also called levocarnitine) is a quaternary ammonium compound that functions primarily as a carrier molecule for long‑chain fatty acids. In humans it is synthesized from the amino acids lysine and methionine and is essential for transporting these fatty acids across the inner mitochondrial membrane where they undergo β‑oxidation to generate ATP.

• Exercise performance: Meta‑analyses of 12‑plus randomized trials show that 2–3 g/day of L‑carnitine can modestly improve endurance (≈5 % increase in VO₂max) and reduce post‑exercise muscle soreness.
• Fat oxidation & weight management: In overweight adults, 2 g/day for 12 weeks lowered body fat percentage by ≈1 % and increased resting fat oxidation.
• Cognitive function: Small pilot studies indicate that 1–2 g/day may improve attention and memory in older adults, possibly via enhanced cerebral mitochondrial metabolism.
• Cardiovascular health: In patients with chronic heart failure, 2–4 g/d for 12 weeks improved left‑ventricular ejection fraction and reduced NT‑proBNP levels.
• Metabolic disease: In type‑2 diabetes, supplementation (2 g/d) modestly lowered fasting glucose and triglycerides, likely through enhanced fatty‑acid oxidation.

• Carnitine Shuttle: L‑carnitine’s primary role is the “carnitine shuttle.”
• Process: In the cytosol, carnitine palmitoyl‑transferase I (CPT‑I) attaches L‑carnitine to long‑chain acyl‑CoA, forming acyl‑carnitine.
• Transport: This complex is transported across the inner mitochondrial membrane by carnitine‑acylcarnitine translocase (CACT) and reconverted to acyl‑CoA by CPT‑II inside the matrix, where β‑oxidation enzymes break the fatty acid down to acetyl‑CoA, feeding the TCA cycle and ATP synthesis.
• Buffering: L‑carnitine also buffers excess acetyl‑CoA by forming acetyl‑carnitine, facilitating removal of excess acetyl groups and supporting the acetyl‑CoA/CoA ratio needed for optimal metabolism.
• Antioxidant: Additionally, L‑carnitine acts as a mild antioxidant, scavenging reactive oxygen species in mitochondria.

• L‑carnitine is a zwitterionic molecule with the formula C₇H₁₅NO₃ and a molecular weight of 161.20 g·mol⁻¹.
• IUPAC Name: Its IUPAC name is (3R)-3‑hydroxy‑4‑trimethylazaniumylbutanoate.
• Structure: The structure features a quaternary ammonium (‑N⁺(CH₃)₃) group attached to a 2‑hydroxy‑4‑carboxylic acid chain, giving it both a positive charge (on the nitrogen) and a negative charge (on the carboxylate).
• Solubility: This confers high water solubility (≈1 g mL⁻¹) and a pKa of ~9.5 for the carboxyl group.
• Stereochemistry: The stereochemistry is R‑configuration at C‑3, essential for biological activity; the S‑enantiomer (D‑carnitine) is inactive in humans.

• Natural Sources: Naturally, L‑carnitine is abundant in red meat, dairy, and fish (≈30–50 mg per 100 g).
• Commercial Production: Commercially, it is produced either by extraction from animal tissues (e.g., bovine kidney) or via microbial fermentation (e.g., Corynebacterium glutamicum), which yields a highly pure, racemic‑free L‑enantiomer.
• Synthetic Routes: Synthetic chemical routes (e.g., condensation of β‑hydroxy‑γ‑butyrolactone with trimethylamine) are also used.
• Supplement Grade: For supplements, pharmaceutical‑grade L‑carnitine is typically produced by fermentation, providing >98 % purity and minimal contaminants.
• Quality Considerations: Quality considerations include verification of enantiomeric purity (R‑form), absence of heavy metals, and compliance with GMP or USP monographs for dietary supplements.