Traditional Chinese medicine (TCM) is one of the important complementary and alternative approaches to treat osteoporosis1,2. Water decoction is the basic and most commonly used form of the formula3. However, drawbacks also exist: bad taste, inconvenience for carriage, short shelf life and inconsistent protocols, limiting the uses as well as the curative effects. To avoid the above disadvantages as well as to pursue better effects, granules were developed and have been widely used4. Although many studies have explored the pharmacological mechanisms of one or more effective components from the granules5,6,7, the exact mechanisms and underlying pharmacological processes are still difficult to identify. This is because too many effective components from one granule may simultaneously exert similar or opposed effects4. Therefore, the development of one standard protocol to prepare the granules before delivering to the body not only would have a great impact on the therapeutic outcomes but is also required for both in vivo and in vitro assays.
Moreover, the curative effects of granules in the clinic are difficult to confirm and exactly identify using in vitro or ex vivo studies, which creates a challenge because the pharmacological mechanisms are too complex. To resolve this, the preparation of drug-containing serum was first proposed by Tashino in 1980s8. From then on, numerous researchers applied drug-containing serum to herbal medicine, including granules9,10,11. Currently, the choice of drug-containing serum for in vitro investigations is regarded as one strategy that closely mimics physiological conditions.
Gushukang (GSK) granules were developed to treat postmenopausal osteoporosis (POP) based on clinical practice in light of the theory of TCM. GSK granules prevent bone loss in ovariectomized (OVX) mice in vivo, inhibit osteoclastic bone resorption, and stimulate osteoblastic bone formation4. Consequently, Li et al.12 found that GSK granules have bone protective effects in OVX mice by enhancing the activities of calcium receptor to stimulate bone formation. To confirm the bone-protective effects as well as the pharmacological effects of GSK granules, the authors here provide a detailed procedure for preparation of working solutions and drug (GSK granule)-containing serum. Moreover, this article describes the application of GSK granules in an OVX-induced osteoporotic mouse model and GSK granule-containing serum for in vitro osteoclastogenesis/osteoblastogenesis.
GSK granules are composed of several herbs13,14 and can be completely dissolved in saline easily. Therefore, saline serves as the vehicle. Sham-operated mice (Sham) and OVX mice were administered the same volume of saline as the granule-administered mice. The equivalent doses of GSK granules for the mouse were calculated based on the Meeh-Rubner equation15. This equation not only has the advantage of obtaining safe dosages but also guarantees pharmacological effects15. The three dosages of GSK granules were generated as the follows: (1) GSKL: OVX + low-dose GSK granules, 2 g/kg/day. (2) GSKM: OVX + medium-dose GSK granules, 4 g/kg/day. (3) GSKH: OVX + high-dose GSK granules, 8 g/kg/day. Mice in the GSKL, GSKM and GSKH groups were intragastrically administered GSK granules. Calcium carbonate (600 mg/tablet) with vitamin D3 (125 international unit/tablet), for example, in a mature and marketed product (e.g., Caltrate [CAL]) for treating and preventing osteoporosis, was used as a positive control.