High prevalence of the GSTM3*A/B polymorphism in sub-Sarahan African populations

A 3-bp insertion/deletion polymorphism in intron 6 of GSTM3 (rs1799735, GSTM3*A/*B) affects the activity of the phase 2 xenobiotic metabolizing enzyme GSTM3 and has been associated with increased cancer risk. The GSTM3*B allele is rare or absent in Southeast Asians, occurs in 5-20 percent of Europeans but was detected in 80 percent of Bantu from South Africa. The wide genetic diversity among Africans led us to investigate whether the high frequency of GSTM3*B prevailed in other sub-Saharan African populations. In 168 healthy individuals from Angola, Mozambique and the São Tomé e Príncipe islands, the GSTM3*B allele was three times more frequent (0.74-0.78) than the GSTM3*A allele (0.22-0.26), with no significant differences in allele frequency across the three groups. We combined these data with previously published results to carry out a multidimensional scaling analysis, which provided a visualization of the worldwide population affinities based on the GSTM3 *A/*B polymorphism.

Pharmacogenetic polymorphisms in Brazilian-born, first-generation Japanese descendants

Brazil hosts the largest Japanese community outside Japan, estimated at 1.5 million individuals, one third of whom are first-generation, Brazilian-born with native Japanese parents. This large community provides a unique opportunity for comparative studies of the distribution of pharmacogenetic polymorphisms in native Japanese versus their Brazilian-born descendants. Functional polymorphisms in genes that modulate drug disposition (CYP2C9, CYP2C19 and GSTM3) or response (VKORC1) and that differ significantly in frequency in native Japanese versus Brazilians with no Japanese ancestry were selected for the present study. Healthy subjects (200 native Japanese and 126 first-generation Japanese descendants) living in agricultural colonies were enrolled. Individual DNA was genotyped using RFLP (GSTM3*A/B) or TaqMan Detection System assays (CYP2C9*2 and *3; CYP2C19*2 and *3; VKORC1 3673G>A, 5808T>G, 6853G>C, and 9041G>A). No difference was detected in the frequency of these pharmacogenetic polymorphisms between native Japanese and first-generation Japanese descendants. In contrast, significant differences in the frequency of each polymorphism were observed between native or first-generation Japanese and Brazilians with no Japanese ancestry. The VKORC1 3673G>A, 6853G>C and 9041G>A single nucleotide polymorphisms were in linkage disequilibrium in both native and first-generation Japanese living in Brazil. The striking similarity in the frequency of clinically relevant pharmacogenetic polymorphisms between Brazilian-born Japanese descendants and native Japanese suggests that the former may be recruited for clinical trials designed to generate bridging data for the Japanese population in the context of the International Conference on Harmonization.

A new model for the population pharmacokinetics of didanosine in healthy subjects

Didanosine (ddI) is a component of highly active antiretroviral therapy drug combinations, used especially in resource-limited settings and in zidovudine-resistant patients. The population pharmacokinetics of ddI was evaluated in 48 healthy volunteers enrolled in two bioequivalence studies. These data, along with a set of co-variates, were the subject of a nonlinear mixed-effect modeling analysis using the NONMEM program. A two-compartment model with first order absorption (ADVAN3 TRANS3) was fitted to the serum ddI concentration data. Final pharmacokinetic parameters, expressed as functions of the co-variates gender and creatinine clearance (CL CR), were: oral clearance (CL = 55.1 + 240 x CL CR + 16.6 L/h for males and CL = 55.1 + 240 x CL CR for females), central volume (V2 = 9.8 L), intercompartmental clearance (Q = 40.9 L/h), peripheral volume (V3 = 62.7 + 22.9 L for males and V3 = 62.7 L for females), absorption rate constant (Ka = 1.51/h), and dissolution time of the tablet (D = 0.43 h). The intraindividual (residual) variability expressed as coefficient of variation was 13.0 percent, whereas the interindividual variability of CL, Q, V3, Ka, and D was 20.1, 75.8, 20.6, 18.9, and 38.2 percent, respectively. The relatively high (>30 percent) interindividual variability for some of these parameters, observed under the controlled experimental settings of bioequivalence trials in healthy volunteers, may result from genetic variability of the processes involved in ddI absorption and disposition.

Limited-sampling strategy models for estimating the pharmacokinetic parameters of 4-methylaminoantipyrine, an active metabolite of dipyrone

Bioanalytical data from a bioequivalence study were used to develop limited-sampling strategy (LSS) models for estimating the area under the plasma concentration versus time curve (AUC) and the peak plasma concentration (Cmax) of 4-methylaminoantipyrine (MAA), an active metabolite of dipyrone. Twelve healthy adult male volunteers received single 600 mg oral doses of dipyrone in two formulations at a 7-day interval in a randomized, crossover protocol. Plasma concentrations of MAA (N = 336), measured by HPLC, were used to develop LSS models. Linear regression analysis and a "jack-knife" validation procedure revealed that the AUC0- and the Cmax of MAA can be accurately predicted (R²>0.95, bias <1.5 percent, precision between 3.1 and 8.3 percent) by LSS models based on two sampling times. Validation tests indicate that the most informative 2-point LSS models developed for one formulation provide good estimates (R²>0.85) of the AUC (0-infinity) or Cmax for the other formulation. LSS models based on three sampling points (1.5, 4 and 24 h), but using different coefficients for AUC(0-infinity) and Cmax, predicted the individual values of both parameters for the enrolled volunteers (R²>0.88, bias = -0.65 and -0.37 percent, precision = 4.3 and 7.4 percent) as well as for plasma concentration data sets generated by simulation (R²>0.88, bias = -1.9 and 8.5 percent, precision = 5.2 and 8.7 percent). Bioequivalence assessment of the dipyrone formulations based on the 90 percent confidence interval of log-transformed AUC(0-infinity) and Cmax provided similar results when either the best-estimated or the LSS-derived metrics were used

Bovine serum albumin potentiates caffeine - or ATP - induced tension in human skinned skeletal muscle fibers

Human skinned muscle fibers were used to investigate the effects of bovine serum albumin (BSA) on the tension/pCa relationship and on the functional properties of the Ca2+- release channel of the sarcoplasmic reticulum (SR). In both fast-and slow-type fibers, identified by their tension response to pSr 5.0, BSA (0.7-15 muM) had no effect on the Ca2+ affinity of the contractile proteins and elicited no tension per se in Ca2+-loaded fibers. In contrast, BSA (>1.0 muM) potentiated the caffeine induced tension in Ca2+-loaded fibers, this effect being more intense in slow-type fibers. Thus, BSA reduced the threshold caffeine concentration required for eliciting detectable tension, and increased the amplitude, the rate of rise and the area under the curve of caffeine-induced tension BSA also potentiated the tension elicited in Ca2+-loaded fibers by low-Mg2+ solutions containing 1.0 mM free ATP. These results suggest that BSA modulates the response of the human skeletal muscle SR Ca2+-release channel to activators such as caffeine and ATP.

Comparative pharmacokinetics of different oral nifedipine preparations in healthy brazilian volunteers

The pharmacokinetics of different pharmaceutical preparations of oral nifedipine-Adalat (capsule), Oxcord and Cardalin (tablets)-was determined after administration of single oral doses of 10 mg to nine healthy young Brazilian volunteers (7 men). There no significant changes in heart rate or systolic and diastolic blood pressure measured in the sitting position within 8 h of nifedipine administration to these normotensive volunteers. No side effects were reported by the volunteers or observed by the attending physicians during the study. No significant differences were observed among the three preparations in relation to the following pharmacokinetic parameters obtained from the plasma concentration-time curves: area under the curve (AUC), slope (beta) and half-life (T½) of the elimination phase, volume of distribution (Vd/F) and total body clearance (CL/F), both expre4ssed as functions of the oral bioavailability (F) of nifedipine. The peak, plasma concentration of nifedipine (C max) and the time to reach C max (T max) were not different for the rwo tablet preparations. However, C max was significantly higher, and T max was significantly shorter for the capsule. These data indicate that the capsule and the tablet preparations are not bioequivalent

Release of creatine kinase from skeletal muscles by Bothrops venoms: heparin potentiation of inhibition by antivenin

The glycosaminoglycan, heparin (50 microng/ml) inhibited the increase in creatine kinase (CK) released from rat extensor digitorum longus (EDL) muscles exposed to Bothrops jararaca venom (150 microng/ml). Heparin (2 microng/ml) and polyvalent antivenin (0.5 micronl/ml) did not affect the increase in CK release induced by exposure of the muscles to 50 microng/ml B. jararacussu venom. Simultaneous exposure of the muscles to venom plus heparin (2 microng/ml) plus antivenin (0.5 or micronl/ml) reduced CK release after 160 min by 50% and 80% compared to that induced by venom alone. These changes in CK release from rat EDL muscle show that heparin inhibits the myotoxic effects of Bothrops venoms and increases the potency of their antivenin

Effects of dichlorobenzamil, a sodium-calcium exchange inhibitor, on the calcium paradox and the sodium withdrawal contractures of frog atrial muscle

The effects of dichlorobenzamil (DCB), an amiloride derivative and potent inhibitor of Na-Ca exchange in cardiac sarcolemmal vesicles and isolated cardiac myocytes, were investigated in two paradigms involving Na-Ca exchange, namely the Ca2+ paradox and the Na + - withdrawal contractures of frog atrial muscle strips. Pretreatment with DCB (10-100 micronM) inhibited in a dose-dependent manner the contractures elicited by reexposure of the atrial strips to the control Ringer solution after a 5-20 min equilibration with a Ca2 + - free saline (Ca2 + - readmission contractures; Ca2 + paradox). These contracture were not inhibited, however, when DCB was applied after the preparation had been exposed to the Ca2 + - free saline, but before the reexposure to the control Ringer solution. DCB (10-100 micronM) did not inhibit the contractures elicited by Na + - deficient saline (Na + - withdrawal contractures) in atrial strips pretreated or not with acetylstrophantydin. This result suggests that, under our experimental conditions, DCB falied to substantially inhibit the Ca2 + influx mediated by Na-Ca exchange. The duration of the plateu of the action potentials of atrial cells equilibrated with Ca2 + - free saline was reduced from 1,42 ñ 0,27 s to 0,61 ñ 0,13 s by 50 micronM DCB (P<0.001). This was atributed to blockade of Na + currents through modified L-type Ca2 + channels. It is proposed that shortening of the Na + - dependent action potentials can account for the inhibition of the Ca2 + - readmission contractures, because these contractures have a steep dependence on the Na + influx and intracellular Na + accumulation that occurs during the Ca2 + - free period. The results of this study support the conclusion thatDCB has multiple effects on heart muscle, including a potent blockade of Ca2 + channels, and its use as a selective inhibitor of Na-Ca exchange in cellular systems in un unwarranted