Currently available HIV-1 protease inhibitors are potent agents in the therapy of HIV-1 infection. However, limited oral absorption and variable tissue distribution, both of which are largely unexplained, complicate their use. We tested the hypothesis that P-glycoprotein is an important transporter for these agents. We studied the vectorial transport characteristics of indinavir, nelfinavir, and saquinavir in vitro using the model P-glycoprotein expressing cell lines L-MDR1 and Caco-2 cells, and in vivo after intravenous and oral administration of these agents to mice with a disrupted mdr1a gene. All three compounds were found to be transported by P-glycoprotein in vitro. After oral administration, plasma concentrations were elevated 2-5-fold in mdr1a (-/-) mice and with intravenous administration, brain concentrations were elevated 7-36-fold. These data demonstrate that P-glycoprotein limits the oral bioavailability and penetration of these agents into the brain. This raises the possibility that higher HIV-1 protease inhibitor concentrations may be obtained by targeted pharmacologic inhibition of P-glycoprotein transport activity.

BACKGROUND: Over the past decade, the safety of anesthetic agents in children has been questioned after the discovery that immature animals exposed to anesthesia display apoptotic neurodegeneration and long-term cognitive deficiencies. We examined the association between exposure to anesthesia in children under age 3 and outcomes in language, cognitive function, motor skills, and behavior at age 10. METHODS: We performed an analysis of the Western Australian Pregnancy Cohort (Raine) Study, which includes 2868 children born from 1989 to 1992. Of 2608 children assessed, 321 were exposed to anesthesia before age 3, and 2287 were unexposed. RESULTS: On average, exposed children had lower scores than their unexposed peers in receptive and expressive language (Clinical Evaluation of Language Fundamentals: Receptive [CELF-R] and Expressive [CELF-E]) and cognition (Colored Progressive Matrices [CPM]). After adjustment for demographic characteristics, exposure to anesthesia was associated with increased risk of disability in language (CELF-R: adjusted risk ratio [aRR], 1.87; 95% confidence interval [CI], 1.20–2.93, CELF-E: aRR, 1.72; 95% CI, 1.12–2.64), and cognition (CPM: aRR, 1.69; 95% CI, 1.13–2.53). An increased aRR for disability in language and cognition persisted even with a single exposure to anesthesia (CELF-R aRR, 2.41; 95% CI, 1.40–4.17, and CPM aRR, 1.73; 95% CI, 1.04–2.88). CONCLUSIONS: Our results indicate that the association between anesthesia and neuropsychological outcome may be confined to specific domains. Children in our cohort exposed to anesthesia before age 3 had a higher relative risk of language and abstract reasoning deficits at age 10 than unexposed children.

The Arg16 polymorphism of the beta2-adrenergic receptor is associated with enhanced agonist-mediated desensitization in the vasculature, and the Glu27 polymorphism is associated with increased agonist-mediated responsiveness. Therefore, polymorphisms of the beta2-adrenergic receptor are potentially important determinants of the vascular response to stress.

CYP2C9 is a polymorphic gene for which there are four known allelic variants; CYP2C9*1, CYP2C9*2, CYP2C9*3, and CYP2C9*4. In the present study, DNA from 140 European Americans and 120 African Americans was examined by single-strand conformational polymorphism and restriction fragment length polymorphism analyses, resulting in the identification of a new CYP2C9 variant, CYP2C9*5. This variant is derived from a C1080G transversion in exon 7 of CYP2C9 that leads to an Asp360Glu substitution in the encoded protein. The CYP2C9*5 variant was found to be expressed only in African Americans, such that approximately 3% of this population carries the CYP2C9*5 allele. The variant was expressed in, and purified from, insect cells infected with a recombinant baculovirus. Comparative kinetic studies using the purified wild-type protein CYP2C9*1; the Ile359Leu variant, CYP2C9*3; and the Asp360Glu variant, CYP2C9*5 were carried out using (S)-warfarin, diclofenac, and lauric acid as substrates. The major effect of the Asp360Glu mutation was to increase the K(m) value relative to that of CYP2C9*1 for all three substrates: 12-fold higher for (S)-warfarin 7-hydroxylation, 5-fold higher for the 4'-hydroxylation of diclofenac, and 3-fold higher for the omega-1 hydroxylation of lauric acid. V(max) values differed less than K(m) values between the CYP2C9*1 and CYP2C9*5 proteins. In vitro intrinsic clearances for CYP2C9*5, calculated as the ratio of V(max)/K(m), ranged from 8 to 18% of CYP2C9*1 values. The corresponding ratio for CYP2C9*3 was 4 to 13%. Accordingly, the in vitro data suggest that carriers of the CYP2C9*5 allele would eliminate CYP2C9 substrates at slower rates relative to persons expressing the wild-type protein.

The cytochrome P450 3A (CYP3A) subfamily members are the most abundant and important drug-metabolizing enzymes in humans, and wide interindividual variability in CYP3A expression and function is present. CYP3A4 alone cannot fully explain the observed constitutive variability because its genetic variants are relatively uncommon and have limited functional significance, whereas CYP3A5 expression in humans is highly variable and may be contributory. However, it is difficult to delineate the relative contribution of CYP3A4 and CYP3A5, and to differentiate their effects on drug metabolism as their protein structure, function and substrates are so similar. By contrast, molecular biology methods provide the ability to identify CYP3A4 and CYP3A5 genotypes with certainty. This review collates currently available data on CYP3A5 polymorphisms, provides information on the population frequency of each genetic variant in major ethnic groups, and describes in vitro and in vivo studies that have attempted to identify genotype-phenotype associations.

The effect of age on sensitivity to both isoproterenol and propranolol has been investigated in 27 male volunteers aged 21 to 73 yr. The dose of isoproterenol (given as a rapid intravenous injection) required to increase the resting heart rate by 25 bpm (I25) increased with age. The I25 was repeated during an intravenous infusion of propranolol and the dose ratio (I25 after propranolol divided by the control I25) determined. This was related to the concentration of free propranolol in plasma. It was found that the effectiveness of any given free concentration diminished progressively with age. These data are consistent with a diminished responsiveness of the beta-adrenoceptor to both agonist and antagonist drugs with advancing years.

Abstract-Blood pressure reactivity is enhanced in young black subjects through mechanisms that are poorly understood.We compared ␣-adrenergic-mediated vasoconstrictor and ␤-adrenergic vasodilator sensitivity and their relation to sympathetic activity in blacks and whites. Ten healthy black (age, 29.9Ϯ2.4 years) and 10 white (age, 28.3Ϯ1.9 years) men were studied. Forearm blood flow was measured with strain-gauge plethysmography after the intrabrachial artery administration of phenylephrine (1.25 to 20 g/min) and isoproterenol (60 and 400 ng/min) after application of lower-body negative pressure and after a cold pressor test. Forearm and systemic norepinephrine spillover were measured with a radioisotope dilution technique. ␣-Adrenergic vasoconstriction was markedly increased (ANOVA Pϭ0.008) and ␤-adrenergic vasodilation decreased (ANOVA Pϭ0.02) in blacks. Phenylephrine (10 g/min) decreased forearm blood flow by 58.0Ϯ2.5% in blacks but only by 26.6Ϯ6.0% in whites (PϽ0.001). Vasoconstrictor response to endogenous norepinephrine, stimulated by a cold pressor test, resulted in a higher forearm vascular resistance in blacks than in whites (107.3Ϯ13 versus 64.8Ϯ13 mm Hg ⅐ mL Ϫ1 ⅐ 100 mL Ϫ1 , Pϭ0.03). There were no significant ethnic differences in basal or stimulated forearm or systemic norepinephrine spillover. Increased vasoconstrictor and decreased vasodilator responses in blacks were not correlated. Increased sympathetically mediated vascular tone caused by enhanced vasoconstriction and attenuated vasodilation, effects that would be additive, and not increased sympathetic activity could enhance vascular reactivity and may play a role in the pathogenesis of hypertension in blacks.

Opioids have a wide spectrum of P-glycoprotein activity, acting as both substrates and inhibitors, which might contribute to their varying central nervous system-related effects.