Identification of Organic Anion Transporter 2 Inhibitors: Screening, Structure-Based Analysis, and Clinical Drug Interaction Risk Assessment

Organic anion transporter 2 (OAT2 or SLC22A7) plays an important role in the hepatic uptake and renal secretion of several endogenous compounds and drugs. The goal of this work is to understand the structure activity of OAT2 inhibition and assess clinical drug interaction risk. A single-point inhibition assay using OAT2-transfected HEK293 cells was employed to screen about 150 compounds; and concentration-dependent inhibition potency (IC₅₀) was measured for the identified "inhibitors". Acids represented about 65% of all inhibitors, and the frequency of bases-plus-zwitterions approximately doubled for "non-inhibitors". Interestingly, 9 of 10 most potent inhibitors (low IC₅₀) are acids (pK_a ∼ 3-5). Additionally, inhibitors are significantly larger and lipophilic than non-inhibitors. In silico (binary) models were developed to identify inhibitors and non-inhibitors. Finally, in vivo risk assessed via static drug-drug interaction models identified several inhibitors with potential for renal and hepatic OAT2 inhibition at clinical doses. This is the first study assessing the global pattern of OAT2-ligand interactions.

Evaluation of Prediction Accuracy for Volume of Distribution in Rat and Human Using In Vitro, In Vivo, PBPK and QSAR Methods

Volume of distribution at steady state (V_ss) is an important pharmacokinetic parameter of a drug candidate. In this study, V_ss prediction accuracy was evaluated by using: (1) seven methods for rat with 56 compounds, (2) four methods for human with 1276 compounds, and (3) four in vivo methods and three Kp (partition coefficient) scalar methods from scaling of three preclinical species with 125 compounds. The results showed that the global QSAR models outperformed the PBPK methods. Tissue fraction unbound (f_u,t) method with adipose and muscle also provided high V_ss prediction accuracy. Overall, the high performing methods for human V_ss prediction are the global QSAR models, Øie-Tozer and equivalency methods from scaling of preclinical species, as well as PBPK methods with Kp scalar from preclinical species. Certain input parameter ranges rendered PBPK models inaccurate due to mass balance issues. These were addressed using appropriate theoretical limit checks. Prediction accuracy of tissue Kp were also examined. The f_u,t method predicted Kp values more accurately than the PBPK methods for adipose, heart and muscle. All the methods overpredicted brain Kp and underpredicted liver Kp due to transporter effects. Successful V_ss prediction involves strategic integration of in silico, in vitro and in vivo approaches.

Opioid-prescribing patterns, storage, handling, and disposal in postoperative pediatric urology patients

BACKGROUND

Emerging research on surgeons and the opioid epidemic have focused on the adult population. Consequently, little is known regarding opioid-prescribing practices in the pediatric population. The goal of this study is to examine postoperative opioid-prescribing and consumption patterns, as well as storage and disposal trends for specific pediatric urologic procedures.

STUDY DESIGN

Patients undergoing surgery associated with specified Current Procedural Terminology codes were retrospectively identified, and details regarding opioid medications were obtained through our pharmacy database. Patients' guardians were contacted two weeks postoperatively to determine opioid usage. Opioids were prescribed at a standard dosing of 0.1 mg/kg per dose or the equivalent.

RESULTS

Of the 171 identified patients, 117 patients were successfully contacted, with 67 (39%) completing telephone surveys. The 3 most common pediatric urology procedures were inguinal hernia repair (N = 39), circumcision (N = 27), and cystoscopy (N = 16). Across all procedures, there was an average excess of 9.8 doses prescribed, corresponding to an overprescription rate of 64%. Of the patients prescribed opioids, 41 (62%) had leftover opioid medication two weeks postoperatively. Thirty-two of 41 (78%) patients did not dispose of their leftover medication. Only 13 patients received perioperative counseling on appropriate storage and disposal of opiates.

DISCUSSION

Prescribing practices for an array of pediatric urologic procedures are non-standardized and often generously excessive. We show universal overprescribing for all our reviewed urologic procedures. Sixty-two percent of pediatric urology patients did not use their entire prescribed opiate, leaving a significant pool of medicine within the pediatric family home. Given the low incidence of perioperative education, unsurprisingly a majority of our patients improperly handled and disposed off excess opioid medication.

CONCLUSION

There is general overprescription of postoperative opioids and poor perioperative opioid education in the pediatric urology population.

Lifetime of charge carriers in multiwalled nanotubes

The nature of low-energy excitations in multiwalled nanotubes (MWNTs) is investigated by means of two-color time-resolved photoemission. A careful analysis of the ballistic transport, secondary excitations, and band structure effects was employed in order to extract single electron lifetimes from the observed relaxation trend. It is demonstrated that in the vicinity of the Fermi level the energy dependence of e-e scattering times is inversely proportional to approximately the square of the excitation energy. This result provides strong evidence that electron transport in MWNTs exhibits a Fermi-liquid behavior, indicating that long-range e-e interaction along the tube vanishes due to screening.

Time-resolved photoimaging of image-potential states in carbon nanotubes

The first experimental evidence for the existence of image-potential states in carbon nanotubes is presented. The observed features constitute a new class of surface image states due to their quantized centrifugal motion. Measurements of binding energies and the temporal evolution of image state electrons were performed using femtosecond time-resolved photoemission. The associated lifetimes are found to be significantly longer than those of n=1 image state on graphite, indicating a substantial difference in electron decay dynamics between tubular and planar graphene sheets.