Pharmacokinetics and Pharmacodynamics of (+)-Primaquine and (?)-Primaquine Enantiomers in Rhesus Macaques (Macaca mulatta)

Primaquine (PQ) remains the sole available drug to prevent relapse of Plasmodium vivax malaria more than 60 years after licensure. While this drug was administered as a racemic mixture, prior studies suggested a pharmacodynamic advantage based on differential antirelapse activity and/or toxicities of its enantiomers. Oral primaquine enantiomers prepared using a novel, easily scalable method were given for 7 days to healthy rhesus macaques in a dose-rising fashion to evaluate their effects on the blood, liver, and kidneys. The enantiomers were then administered to Plasmodium cynomolgi-infected rhesus macaques at doses of 1.3 and 0.6 mg/kg of body weight/day in combination with chloroquine. The (−)-PQ enantiomer had higher clearance and apparent volume of distribution than did (+)-PQ and was more extensively converted to the carboxy metabolite. There is evidence for differential oxidative stress with a concentration-dependent rise in methemoglobin (MetHgb) with increasing doses of (+)-PQ greater than that seen for (−)-PQ. There was a marked, reversible hepatotoxicity in 2 of 3 animals dosed with (−)-PQ at 4.5 mg/kg. (−)-PQ in combination with chloroquine was successful in preventing P. cynomolgi disease relapse at doses of 0.6 and 1.3 mg/kg/day, while 1 of 2 animals receiving (+)-PQ at 0.6 mg/kg/day relapsed. While (−)-PQ was also associated with hepatotoxicity at higher doses as seen previously, this has not been identified as a clinical concern in humans during >60 years of use. Limited evidence for increased MetHgb generation with the (+) form in the rhesus macaque model suggests that it may be possible to improve the therapeutic window for hematologic toxicity in the clinic by separating primaquine into its enantiomers.     

Monitoring and evaluation of a model demonstration project for the control of cervical cancer in Nakhon Phanom province, Thailand

Cancer of the uterine cervix is the second most common cancer in females in the world with about half a million new patients per year. Since the introduction by Papanicolaou of cervical smear screening, the incidence of cervical cancer has declined in many developed countries. The decrease in the incidence of and mortality from cervical cancer is mainly due to the organized mass screening using Pap smear programmes. Uterine cervical cancer is the leading cancer among women in Thailand with age-standardized incidence rates of 24.7 per 100,000 in 1999. Most cases present at advanced stages with poor prognoses of survival and cure. In the present study, cervical cancer screening programme with cervical cytology was organized for Nakhon Phanom province, Thailand. The specific objectives were: 1) to evaluate the reduction in incidence and mortality from cervical cancer in the province by means of an organised low-intensity cervical cytology programme. 2) to demonstrate the different aspects of programme implementation as a potential model for nationwide implementation. The screening activities were integrated in the existing health care system. Organized screening for women in the target population (aged 35-54 years) at 5-year intervals was free of charge. Sample taking was done by trained nurses (midwives) and primary health care personnel in the local health care centers. Sample quality was under continuous controlled by the cytology laboratories and pathologists. Confirmation and treatment were integrated into the normal health care routines. The screening results of the programme, including histologically confirmed diagnosis, were registered at the National Cancer Institute using PapReg and CanReg 4 programmes. A population-based cancer registry in Nakhon Phanom province was also set up in 1997. In the period 1999-2002, 32,632 women aged 35-54 years were screened. Women with low-grade lesions returned for routine follow-up smears. High-grade preinvasive disease was further evaluated by repeating Pap smear, conization or biopsy and subsequent treatment through surgical removal or ablation. This organized low-intensity cervical cytology programme showed a considerable increase in early carcinoma in situ and CIN II -III cases and should reduce incidence of and mortality from cervical cancer in Nakhon Phanom province in the future. Screening with the Papanicolaou smear plus adequate follow-up diagnosis and therapy can achieve major reductions in both incidence and mortality rates.     

Circadian rhythm of cytochrome P4502E1 and its effect on disposition kinetics of chlorzoxazone in rats

The aim of this report is to study the circadian rhythm of cytochrome P4502E1 (CYP2E1) and its effect on the disposition kinetics of chlorzoxazone in male Wistar rats. The rats were housed under a 12-h light/dark cycle (lights from 9:00 to 21:00) with food and water ad libitum for 3 months. It was found that the expression of microsomal CYP2E1 mRNA in the liver during the dark phase was significantly lower than during the light phase, whereas the content of CYP2E1 protein and its hydroxylation activity were significantly higher. Therefore, chlorzoxazone 20 mg/kg was intravenously administered at 12:00 (light phase group) or 24:00 (dark phase group) to determine the effect on the disposition kinetics. The value of the area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) of chlorzoxazone showed no significant difference between the two groups. However, the value of chlorzoxazone half-life in plasma of the light phase group was significant longer than the dark phase group. The AUC(0-8 h) of 6-hydroxychlorzoxazone, a metabolite formed from chlorzoxazone mainly by CYP2E1, was significantly higher in the dark phase than in the light phase. In conclusion, microsomal CYP2E1 shows a substantial circadian variation in rats, and this was associated with a decrease of chlorzoxazone half life, and an increase of 6-hydroxychlorzoxazone production. Therefore, the temporal variations of therapeutic response and toxicological effects may have to be taken into consideration for other xenobiotics that are predominantly metabolized by CYP2E1, particularly those with a short half-life.     

Effects of Vernonia cinerea Compounds on Drug‐metabolizing Cytochrome P450s in Human Liver Microsomes

Vernonia cinerea has been widely used in traditional medicines for various diseases and shown to aid in smoking abstinence and has anticancer properties. V. cinerea bioactive compounds, including flavonoids and hirsutinolide‐type sesquiterpene lactones, have shown an inhibition effect on the nicotine‐metabolizing cytochrome P450 2A6 (CYP2A6) enzyme and hirsutinolides reported suppressing cancer growth. In this study, V. cinerea ethanol extract and its bioactive compounds, including four flavonoids and four hirsutinolides, were investigated for an inhibitory effect on human liver microsomal CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 using cocktail inhibition assays combined with LC‐MS/MS analysis. Among tested flavonoids, chrysoeriol was more potent in inhibition on CYP2A6 and CYP1A2 than other liver CYPs, with better binding efficiency toward CYP2A6 than CYP1A2 (K_i values in competitive mode of 1.93 ± 0.05 versus 3.39 ± 0.21 μM, respectively). Hirsutinolides were prominent inhibitors of CYP2A6 and CYP2D6, with IC₅₀ values of 12–23 and 15–41 μM, respectively. These hirsutinolides demonstrated time‐dependent inhibition, an indication of mechanism‐based inactivation, toward CYP2A6. Quantitative prediction of microsomal metabolism of these flavonoids and hirsutinolides, including half‐lives and hepatic clearance rate, was examined. These findings may have implications for further in vivo studies of V. cinerea. Copyright © 2017 John Wiley & Sons, Ltd.