Research On The Pharmacokinetic Drug-Drug Interaction Between Diallyl Trisulfide And Two Cardiovascular Drugs

Diallyl trisulfide (DATS), called "allitridium", has been demonstrated to be one of the major organosulfur compounds derived from garlic and has been synthesized chemically in China for several years. There are more than 20 kinds of garlic dietary supplements in China and DATS have been increasingly favored by patients for cardiovascular disease and immunity enhancement. The elevating chance of combination with other cardiovascular drugs increased the risk of the occurrence of drug-drug interaction. However, the pharmacokinetic interactions between DATS and other cardiovascular drugs were still unclear and have rarely been reported. The present study aimed to determine whether DATS is able to modify the pharmacokinetics of typical co-medication (nifedipine and dipyridamole) in vivo and in vitro.In the present study, DATS was prepared into aqueous solution using water-soluble vitamin E (TPGS) as a solubilizer, and the stability of the DATS solution was investigated under different conditions. The DATS solution was stable within 24 h under acidic and neutral conditions at room temperature, and degraded rapidly when the environmental pH was greater than 11. There was a great influence on the stability of the solution while exposed to light (4500 Ix×500 Ix) and high temperature (60℃).The pharmacokinetics experiments of the animals were established, and pharmacokinetic parameters of nifedipine and dipyridamole were determined in rats following an oral gavage or intravenous administration with co-administration of DATS and long-term pretreatment of DATS (15 consecutive days). Compared to the respective control groups, pharmacokinetic parameters for intravenous nifedipine and dipyridamole were little changed; slightly higher oral bioavailability of nifedipine was observed for oral gavage of nifedipine after short-term pretreatment of DATS; the oral bioavailability of nifedipine was remarkably enhanced after long-term pretreatment (15 consecutive days) of DATS by an increase from 61.5% to 93.6%; the oral bioavailability of dipyridamole suspension and solution was remarkably decreased after co-administered with DATS, from 61.3% and 70.3% to 25.4% and 45.6% respectively; long-term pretreatment (15 consecutive days) of different doses (10 mg/kg and 20 mg/kg) of DATS caused reductions of the oral bioavailability of dipyridamole suspension, which from 83.6% to 20.2% and 17.7%. the results indicated that there were pharmacokinetics drug-drug interaction between DATS and the two drugs.The equilibrium dialysis was established to investigate the effect of DATS to the plasma protein binding (PPB) of nifedipine and dipyridamole. There were no significant effects of 4μg/ml DATS on the PPB of dipyridamole which would be reduced by 40μg/ml DATS; only slightly decrease of the PPB of high concentration of nifedipine (250 ng/ml) was observed combining with 4μg/ml DATS, while 40μg/ml DATS caused the significant decrease of the PPB of nifedipine. The results indicated that the PPB of the two drugs could be reduced by the high concentrations of DATS, therefore the free-drug concentrations of the two drugs would increase. However, the plasma concentration of DATS with a normal dose should be less than 4μg/ml, the effect of DATS on the distribution of the two drugs could be neglected.An everted gut sac method was established to investigate intestinal absorption of nifedipine and dipyridamole of rat in vitro and the effect of different concentrations of DATS on the intestinal absorption of the two drugs. The mucosal side (bulk solution) to the serosal side (inside sac) transport of dipyridamole was investigated at concentrations ranging from 12.5 to 50μg/ml at different segments of intestines. There were no concentration dependence or saturation observed for the absorptive transport of dipyridamole at concentrations up to 50μg/ml. The cumulative permeation amounts of dipyridamole in ileum and jejunum segments were higher than those in duodenum and colon. The mucosal side (bulk solution) to the serosal side (inside sac) transport of nifedipine was investigated at concentrations ranging from 6.25 to 25μg/ml at different segments of intestines. No concentration dependence or saturation was observed for the absorptive transport of nifedipine at concentrations up to 50μg/ml. The cumulative permeation amounts of dipyridamole in duodenum segments were lower than those in other segments. The results showed that the dipyridamole cumulative amounts in ileum and jejunum were significantly decreased by DATS (P< 0.01) and the nifedipine cumulative amounts in all segments were increased by DATS. The results indicated that passive diffusion was dominated in the absorptive process of the two drugs; DATS may inhibit the intestinal metabolism of nifedipine.Control and different induced (phenobarbital and DATS) rat hepatic and intestinal microsomes were prepared by ultracentrifugation. An in vitro incubation method with rat hepatic and intestinal microsomes was developed to investigate the metabolism of nifedipine and dipyridamole in different microsomes, and the effect of DATS on the metabolism of the two drugs. The P450 enzyme responsible for biotransformation of nifedipine was not significantly induced by DATS; after incubated in the DATS induced hepatic microsomes the value of Km of dipyridamole increased and the Vmax decreased compared with that in the control hepatic microsomes; DATS could be concluded as a weak inhibitor of nifedipine in rat hepatic microsomes with an IC50 of 75.21μmol/L and a Ki of 94.70μmol/L, and also a weak inhibitor of nifedipine in rat intestinal microsomes with an IC50 of 72.37μmol/L and a Ki of 129.90μmol/L; DATS could be concluded as a moderate inhibitor of dipyridamole in rat hepatic microsomes with an IC50 of 34.37μmol/L and a Ki of 20.00μmol/L. The results indicated that DATS significantly enhanced the oral bioavailability of nifedipine likely by the inhibition of intestinal CYP3A2 responsible for biotransformation of nifedipine. DATS played as a moderate inhibitor of CYP enzyme (CYP3A and/or CYP2D) responsible for biotransformation of dipyridamole and the phaseⅠmetabolism of dipyridamole was inhibited by DATS, therefore the phaseⅡmetabolism would be increased. The amount metabolism of dipyridamole would not be significantly changed, so there was no significant metabolism interaction between DATS and dipyridamole.