Detecting metabolites of different transition metal-lithospermate B complexes after intravenous injection in rats

Lithospermate B (LSB) isolated from the traditional Chinese medicine danshen (Salvia miltiorrhiza) is an effective Na(+)/K(+)-ATPase inhibitor and used to treat congestive heart failure. The inhibition of LSB on Na(+)/K(+)-ATPase is potentiated by forming complexes with transition metal ions. Here we investigated the safety and metabolites of different transition metal-LSB complexes in rats.

LSB complexed with six different transition metal ions (Mg(2+), Zn(2+), Cr(3+), Co(2+), Ni(2+) and Mn(2+)) were prepared. Adult male SD rats were injected with the different metal-LSB complexes (50 mg/kg, iv), and their bile and blood samples were collected. The metabolites of the metal-LSB complexes in the samples were analyzed using mass spectroscopy.

In rats injected with LSB complexed with Mg(2+), Zn(2+), Cr(3+), Ni(2+) or Mn(2+), LSB and its four putative metabolites were equivalently detected in their bile samples. Mn(2+)-LSB exhibited distinct metabolite profiles compared with the other four metal-LSB complexes. The four putative metabolites were identified as 3-monomethyl-LSB, 3,3''-dimethyl-LSB, 3,3'''-dimethyl-LSB and 3,3'',3'''-trimethyl-LSB. The tracking of successive bile samples of rats injected with Mg(2+)-LSB, Zn(2+)-LSB and Mn(2+)-LSB concurrently demonstrated that LSB was firstly methylated at position 3, then at position 3'', and, finally, the 3''' hydroxyl group. All rats injected with Co(2+)-LSB died.

Zn(2+)-LSB, Cr(3+)-LSB, Ni(2+)-LSB or Mn(2+)-LSB produces identical four methylated metabolites of LSB in rats, and seemed to be as safe as LSB or Mg(2+)-LSB.