Stearoyl-L-carnitine is a naturally occurring long-chain acylcarnitine [1]. It inhibits sodium-dependent [3H]carnitine uptake in human proximal convoluted tubular (HPCT) cells by 52% when used at a concentration of 500 μM [2] It also inhibits lecithin:cholesterol acyltransferase activity in rat, but not human, plasma when used at a concentration of 500 μM/ml of plasma. [3] Plasma levels of stearoyl-L-carnitine are decreased in patients with chronic fatigue syndrome and increased in patients with end-stage renal disease.[1][4]

Reference:
[1]. Reuter, S.E., Evans, A.M., Faull, R.J., et al. Impact of haemodialysis on individual endogenous plasma acylcarnitine concentrations in end-stage renal disease. Ann. Clin. Biochem. 42(Pt 5), 387-393 (2005).
[2]. Huang, W., Shaikh, S.N., Ganapathy, M.E., et al. Carnitine transport and its inhibition by sulfonylureas in human kidney proximal tubular epithelial cells. Biochem. Pharmacol. 58(8), 1361-1370 (1999).
[3]. Bell, F.P. Carnitine esters: Novel inhibitors of plasma lecithin: Cholesterol acyltransferase in experimental animals but not in man (Homo sapiens). Int. J. Biochem. 15(2), 133-136 (1983).
[4]. Reuter, S.E., and Evans, A.M. Long-chain acylcarnitine deficiency in patients with chronic fatigue syndrome. Potential involvement of altered carnitine palmitoyltransferase-I activity. J. Intern. Med. 270(1), 76-84 (2011).