Redox reactions and fluorescence spectroscopic behaviour of trifluoperazine at the surface of colloidal silica

A high pressure study of calmodulin-ligand interactions using small-angle X-ray and elastic incoherent neutron scattering

Calmodulin (CaM) is a Ca²⁺ sensor and mediates Ca²⁺ signaling through binding of numerous target ligands. The binding of ligands by Ca²⁺-saturated CaM (holo-CaM) is governed by attractive hydrophobic and electrostatic interactions that are weakened under high pressure in aqueous solutions. Moreover, the potential formation of void volumes upon ligand binding creates a further source of pressure sensitivity. Hence, high pressure is a suitable thermodynamic variable to probe protein-ligand interactions. In this study, we compare the binding of two different ligands to holo-CaM as a function of pressure by using X-ray and neutron scattering techniques. The two ligands are the farnesylated hypervariable region (HVR) of the K-Ras4B protein, which is a natural binding partner of holo-CaM, and the antagonist trifluoperazine (TFP), which is known to inhibit holo-CaM activity. From small-angle X-ray scattering experiments performed up to 3000 bar, we observe a pressure-induced partial unfolding of the free holo-CaM in the absence of ligands, where the two lobes of the dumbbell-shaped protein are slightly swelled. In contrast, upon binding TFP, holo-CaM forms a closed globular conformation, which is pressure stable at least up to 3000 bar. The HVR of K-Ras4B shows a different binding behavior, and the data suggest the dissociation of the holo-CaM/HVR complex under high pressure, probably due to a less dense protein contact of the HVR as compared to TFP. The elastic incoherent neutron scattering experiments corroborate these findings. Below 2000 bar, pressure induces enhanced atomic fluctuations in both holo-CaM/ligand complexes, but those of the holo-CaM/HVR complex seem to be larger. Thus, the inhibition of holo-CaM by TFP is supported by a low-volume ligand binding, albeit this is not associated with a rigidification of the complex structure on the sub-ns Å-scale.

Placental profiling of UGT1A enzyme expression and activity and interactions with preeclampsia at term

Placental UDP-glucuronosyltransferase (UGT) enzymes have critical roles in hormone, nutrient, chemical balance and fetal exposure during pregnancy. Placental UGT1A isoforms were profiled and differences between preeclamptic (PE) and non-PE placental UGT expression determined. In third trimester villous placenta, UGT1A1, 1A4, 1A6 and 1A9 were expressed and active in all specimens (n = 10), but UGT1A3, 1A5, 1A7, 1A8 and 1A10 were absent. The UGT1A activities were comparable to human liver microsomes per milligram, but placental microsome yields were only 2 % of liver (1 mg/g of tissue vs. 45 mg/g of tissue). For successful PCR, placental collection and processing within 60 min from delivery, including DNAse and ≥300 ng of RNA in reverse transcription were essential and snap freezing in liquid nitrogen immediately was the best preservation method. Although UGT1A6 mRNA was lower in PE (P < 0.001), there were no other significant effects on UGT mRNA, protein or activities. A more comprehensive tissue sample set is required for confirmation of PE interactions with UGT. Placental UGT1A enzyme expression patterns are similar to the liver and a detoxicative role for placental UGT1A is inferred.

Inhibitory effects of commonly used herbal extracts on UDP-glucuronosyltransferase 1A4, 1A6, and 1A9 enzyme activities

The aim of this study was to investigate the effect of commonly used botanicals on UDP-glucuronosyltransferase (UGT) 1A4, UGT1A6, and UGT1A9 activities in human liver microsomes. The extracts screened were black cohosh, cranberry, echinacea, garlic, ginkgo, ginseng, milk thistle, saw palmetto, and valerian in addition to the green tea catechin epigallocatechin gallate (EGCG). Formation of trifluoperazine glucuronide, serotonin glucuronide, and mycophenolic acid phenolic glucuronide was used as an index reaction for UGT1A4, UGT1A6, and UGT1A9 activities, respectively, in human liver microsomes. Inhibition potency was expressed as the concentration of the inhibitor at 50% activity (IC(50)) and the volume in which the dose could be diluted to generate an IC(50)-equivalent concentration [volume/dose index (VDI)]. Potential inhibitors were EGCG for UGT1A4, milk thistle for both UGT1A6 and UGT1A9, saw palmetto for UGT1A6, and cranberry for UGT1A9. EGCG inhibited UGT1A4 with an IC(50) value of (mean ± S.E.) 33.8 ± 3.1 μg/ml. Milk thistle inhibited both UGT1A6 and UGT1A9 with IC(50) values of 59.5 ± 3.6 and 33.6 ± 3.1 μg/ml, respectively. Saw palmetto and cranberry weakly inhibited UGT1A6 and UGT1A9, respectively, with IC(50) values >100 μg/ml. For each inhibition, VDI was calculated to determine the potential of achieving IC(50)-equivalent concentrations in vivo. VDI values for inhibitors indicate a potential for inhibition of first-pass glucuronidation of UGT1A4, UGT1A6, and UGT1A9 substrates. These results highlight the possibility of herb-drug interactions through modulation of UGT enzyme activities. Further clinical studies are warranted to investigate the in vivo extent of the observed interactions.

Pediatric development of glucuronidation: the ontogeny of hepatic UGT1A4

This article reports on the development of UDP-glucuronosyltransferase (UGT) enzyme activity in pediatric livers. The substrates 4-methylumbelliferone (4MU) and trifluoperazine (TFP) were used as probes for general glucuronidation and specific UGT1A4 activity, respectively. The activity of hepatic beta-glucuronidase enzymes was also determined so as to investigate the balance between glucuronide clearance and systemic recirculation. UGT activity toward 4MU reached maximum levels by 20 months of age, whereas the activity of beta-glucuronidase was highest in the neonatal liver and decreased to steady-state adult levels by 4 months. The average V(max) and K(m) values for UGT1A4 in pediatric samples were 151.9 +/- 63.5 pmol/min/mg protein and 14.4 +/- 9.6 muM, respectively. Average V(max) was understandably low because of developmental dynamics, but K(m) was similar to values reported elsewhere. When a constant rate of enzyme development is assumed, maximum activity of UGT1A4 occurs at 1.4 years of age. When the intrinsic hepatic clearance of TFP was scaled with an allometric model, hepatic clearance of TFP by UGT1A4 did not reach maximum levels until 18.9 years of age and scaled results underestimated reported in vivo clearances in adult males. No significant differences in UGT activities or hepatic clearance were observed with gender or ethnicity. The developmental dynamics of most drug-metabolizing enzymes are unknown, and this article contains, to our knowledge, the first description of the development of a single UGT isoform in childhood. Ultimately, work such as this is important for predicting drug responses and for developing and evaluating new medications in children.