Magnolol (M) is a polyphenol antioxidant abundant in the bark of Magnolia officinalis Rehder & E. Wilson, a popular Chinese herb. To understand the pharmacokinetics and bioavailability of M, Sprague-Dawley rats were intravenously injected with a bolus of M (20 mg/kg) and orally given a single dose and seven doses of M (50 mg/kg). Blood samples were withdrawn via cardiopuncture at specific times. Organs including the liver, kidney, brain, lung, and heart were collected at 30 min after the 7th oral dose. The serum and tissue specimens were assayed by HPLC before and after hydrolysis with β-glucuronidase and sulfatase. The results showed that after intravenous bolus, the systemic exposure of magnolol glucuronides (MG) was comparable with that of M while after oral administration, magnolol sulfates/glucuronides (M S/G) were predominant in the bloodstream. Conversely, M was predominant in the liver, kidney, brain, lung, and heart. Among the studied organs, the liver contained the highest concentrations of M and MG. In conclusion, M S/G was the major form in circulation, whereas M was predominant in the liver, kidney, brain, lung, and heart after oral administration of M; among these organs, the liver contained the highest concentrations of M and MG.

Scutellariae Radix (root of Scutellaria baicalensis, SR) contains numerous flavonoids such as baicalin, baicalein, and wogonin. This study investigated the pharmacokinetics and tissue distribution of flavonoids and their metabolites in rats after repeated dosing of a SR decoction. Sprague-Dawley rats were orally administered SR at 2 g/kg for seven doses. After the 7th dose, blood samples were withdrawn at specific times and organs, including the liver, kidney, lung, and brain, and collected. The concentrations of baicalein and wogonin in the serum and various tissues were assayed by HPLC before and after hydrolysis with glucuronidase and sulfatase. Baicalein and wogonin were not detected in the serum, and the molecules found were their glucuronides/sulfates. In tissues, the free forms of baicalein and wogonin appeared in the liver, kidney, and lung in addition to their glucuronides/sulfates. Baicalein was the major form in the lung, whereas baicalein glucuronides/sulfates were the major forms in the liver and kidney. Wogonin was the major form in the liver, kidney, lung, and traces of wogonin glucuronides/sulfates were detected in the kidney and liver. Neither baicalein and wogonin nor their glucuronides/sulfates were detected in the brain. In conclusion, the glucuronides/sulfates of baicalein and wogonin were exclusively present in the circulation, whereas their free forms appeared in the lung, liver, and kidney.

Background: Naringin is a major antioxidant in Citrus fruits and herbs. To clarify molecular forms distributed to various tissues, we investigated tissue distribution of naringin and relevant metabolites in rats after repeated dosing. Methods: Male Sprague-Dawley rats were orally administered naringin (210 mg/kg) twice daily for eight days. At 6 h post the 17^th dose, various tissues including liver, kidney, heart, spleen and brain were collected and analyzed by HPLC method before and after hydrolysis with β-glucuronidase and sulfatase, individually. Results: The free forms of naringin and naringenin were not detected in all the tissues assayed. Liver contained the highest concentration of naringenin sulfates, followed by spleen, heart, brain and kidney. Naringenin glucuronides were present in liver and kidney, but not in spleen, brain and heart. Conclusion: The bioavailability of naringenin glucuronides and sulfates supported its application for personalized medicine.