Propofol and Fentanyl Pharmacokinetics and Pharmacodynamics in Extracorporeal Membrane Oxygenation.

RATIONALE: Despite the potential risks associated with sedation, there is a paucity of pharmacokinetic/pharmacodynamic (PK/PD) data for propofol and fentanyl in patients supported with veno-venous extracorporeal membrane oxygenation (V-V ECMO). OBJECTIVE: Describe propofol and fentanyl PK/PD profiles in V-V ECMO patients. METHODS AND MEASUREMENTS: Prospective, single-center, open-label PK/PD study at the Toronto General Hospital ICU between July 2022 and January 2023. Using high-performance liquid chromatography-tandem mass spectrometry, propofol and fentanyl total concentrations were measured during V-V ECMO. Sequential PK/PD modeling, using sex as a covariate, was conducted with processed electroencephalography (PSI) for sedation, and expiratory occlusion pressure (Pocc), and airway occlusion pressure during the first 0.1 seconds (P0.1) for respiratory effort. MAIN RESULTS: Eleven patients underwent 106 evaluations over a median (IQR) follow-up of 146 (116-146) hours. Patient's average (±SD) age was 43 (±13) years, and 55% were female. Propofol and fentanyl PK were best described by a two-compartment model. Propofol-PSI PD was described using an effect compartment, with a coefficient of determination (ρ2) of 0.78. There was a significant increase in propofol (p=0.01) and fentanyl (p=0.03) clearance within 10 minutes of ECMO initiation, plateauing after 8 hours of ECMO support. Despite this, patient over-sedation (PSI<40) occurred in 74% of the observations. Females exhibited higher sedative central volume of distribution and lower propofol clearance. CONCLUSION: ECMO initiation resulted in a time-limited increased sedative clearance. PSI accurately described sedative PD, but variable respiratory effort was observed irrespective of sedative plasma concentrations. Sex-based differences were found in sedative PK/PD parameters.

After 50 Years of Hepatic Clearance Models, Where Should We Go from Here? Improvements and Implications for Physiologically Based Pharmacokinetic Modeling.

There is overwhelming preference for application of the unphysiologic, well-stirred model (WSM) over the parallel tube model (PTM) and dispersion model (DM) to predict hepatic drug clearance, CLH , despite that liver blood flow is dispersive and closer to the DM in nature. The reasoning is the ease in computation relating the hepatic intrinsic clearance ( CLint ), hepatic blood flow ( QH ), unbound fraction in blood ( fub ) and the transmembrane clearances ( CLin and CLef ) to CLH for the WSM. However, the WSM, being the least efficient liver model, predicts a lower EH that is associated with the in vitro CLint ( Vmax / Km ), therefore requiring scale-up to predict CLH in vivo. By contrast, the miniPTM, a three-subcompartment tank-in-series model of uniform enzymes, closely mimics the DM and yielded similar patterns for CLint versus EH , substrate concentration [S] , and KL / B , the tissue to outflow blood concentration ratio. We placed these liver models nested within physiologically based pharmacokinetic models to describe the kinetics of the flow-limited, phenolic substrate, harmol, using the WSM (single compartment) and the miniPTM and zonal liver models (ZLMs) of evenly and unevenly distributed glucuronidation and sulfation activities, respectively, to predict CLH For the same, given CLint ( Vmax and Km ), the WSM again furnished the lowest extraction ratio ( EH,WSM = 0.5) compared with the miniPTM and ZLM (>0.68). Values of EH,WSM were elevated to those for EH, PTM and EH, ZLM when the Vmax s for sulfation and glucuronidation were raised 5.7- to 1.15-fold. The miniPTM is easily manageable mathematically and should be the new normal for liver/physiologic modeling. SIGNIFICANCE STATEMENT: Selection of the proper liver clearance model impacts strongly on CLH predictions. The authors recommend use of the tank-in-series miniPTM (3 compartments mini-parallel tube model), which displays similar properties as the dispersion model (DM) in relating CLint and [ S ] to CLH as a stand-in for the DM, which best describes the liver microcirculation. The miniPTM is readily modified to accommodate enzyme and transporter zonation.

Aging and brain free cholesterol concentration on amyloid-ß peptide accumulation in guinea pigs.

Alzheimer's disease is a complex multifactorial neurodegenerative disorder wherein age is a major risk factor. The appropriateness of the Hartley guinea pig (GP), which displays high sequence homologies of its amyloid-ß (Aß40 and Aß42) peptides, Mdr1 and APP (amyloid precursor protein) and similarity in lipid handling to humans, was appraised among 9-40 weeks old guinea pigs. Protein expression levels of P-gp (Abcb1) and Cyp46a1 (24(S)-hydroxylase) for Aß40, and Aß42 efflux and cholesterol metabolism, respectively, were decreased with age, whereas those for Lrp1 (low-density lipoprotein receptor related protein 1), Rage (receptor for advanced glycation endproducts) for Aß efflux and influx, respectively, and Abca1 (the ATP binding cassette subfamily A member 1) for cholesterol efflux, were unchanged among the ages examined. There was a strong, negative correlation of the brain Aß peptide concentrations and Abca1 protein expression levels with free cholesterol. The correlation of Aß peptide concentrations with Cyp46a1 was, however, not significant, and concentrations of the 24(S)-hydroxycholesterol metabolite revealed a decreasing trend from 20 weeks old toward 40 weeks old guinea pigs. The composite data suggest a role for free cholesterol on brain Aß accumulation. The decreases in P-gp and Lrp1 protein levels should further exacerbate the accumulation of Aß peptides in guinea pig brain.

Kirchhoff's Laws and Hepatic Clearance, Well-Stirred Model - Is There Common Ground?

Clearance concepts are extensively applied in drug development and drug therapy. The well-stirred model (WSM) of hepatic elimination is the most widely adopted physiologic model in pharmacokinetics owing to its simplicity. A common feature of this organ model is its use to relate hepatic clearance of a compound to the physiologic variables: organ blood flow rate, binding within blood, and hepatocellular metabolic and excretory activities. Recently, Kirchhoff's laws of electrical network have been applied to organ clearance (Pachter et al., 2022; Benet and Sodhi, 2023) with the claim that they yield the same equation for hepatic clearance as the WSM, and that the equation is independent of a mechanistic model. This commentary analyzes this claim and shows that implicit in the application of Kirchhoff's approaches are the same assumptions as those of the WSM. Concern is also expressed in the interpretation of permeability or transport parameters and related equations, as well as the inappropriateness of the corresponding equation defining hepatic clearance. There is no value, and some dangers, in applying Kirchhoff's electrical laws to organ clearance. SIGNIFICANCE STATEMENT: This commentary refutes this claim by Pachter et al. (2022), and Benet and Sodhi, (2023), who suggest that the well-stirred model (WSM) of hepatic elimination, the most widely applied physiologic model of hepatic clearance, provides the same equation as Kirchhoff's laws of electrical network that is independent of a physiologic model. A careful review shows that the claim is groundless and fraught with errors. We conclude that there is no place for the application of Kirchhoff's laws to organ clearance models.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters.

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D3 or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for ß-amyloid peptide efflux and influx, the sodium phosphate transporters (NaPi), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTß) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aß) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

In Defense of Current Concepts and Applications of Clearance in Drug Development and Therapeutics.

Clearance is one of the most widely quoted and applied pharmacokinetic concepts in drug development and therapy. Its foundations and associated models of drug elimination are well embedded and accepted within the scientific community. Recently, however, the prevailing views that have held us in good stead for the past almost 50 years have been challenged with the argument that organ clearance should not be based on elimination rate, now defined by extraction across the liver divided by incoming or systemic concentration, as in current practice, but rather, by the mean concentration of drug within the blood in the organ, which is model-dependent. We argue that all needed parameters already exist, and that the proposed new approach to organ clearance is confusing and unnecessary. SIGNIFICANCE STATEMENT: Clearance concepts are widely applied in drug development and therapy. Historically, hepatic clearance has been defined as the ratio of rate of elimination divided by ingoing blood concentration. Recently, this approach has been challenged arguing that clearance should be referenced to blood concentration within the liver extrapolation (IVIVE). There is no need for additional, a feature that corresponds to intrinsic clearance of the chosen clearance model, a widely accepted parameter in physiologically based pharmacokinetic (PBPK) and in vitro to in vivo extrapolation (IVIVE). There is no need for additional, confusing clearance terms, which offer no material benefit.

Measuring Amyloid-ß Peptide Concentrations in Murine Brain with Improved ELISA Assay.

The amyloid-ß (Aß) peptides of 40 and 42 amino acids that are implicated in Alzheimer's disease may potentially aggregate into toxic oligomers and form neuritic plaques. The enzyme-linked immunosorbent assay (ELISA) is a facile method used for the determination of Aß concentrations in biological matrices, namely plasma, cerebrospinal fluid, and brain. The method is mostly used for the measurement of Aß concentrations in transgenic mice, but it is unknown whether the ELISA method is suitable for measuring low, endogenous levels of Aß in the brains of wild-type mice. The Aß ELISA kit manufacturer recommends use of 5 M guanidine hydrochloride (GuHCl), a protein-denaturing agent, for homogenization of the brain tissue, followed by dilution back down to 0.1 M to avoid quenching by GuHCl. Components of brain matrices and GuHCl that could interfere with the quantitation have not been investigated. In this article, we describe an improved method involving homogenization of mouse brain with 1 M instead of 5 M GuHCl, reducing the dilution factor by 5× to provide a higher sensitivity. The modified ELISA assay is improved for the quantitation of brain Aß peptides in wild-type mice, where Aß peptide levels are much lower than those in transgenic mouse models. © 2021 Wiley Periodicals LLC.

Impact of age, hypercholesterolemia, and the vitamin D receptor on brain endogenous ß-amyloid peptide accumulation in mice.

Age, hypercholesterolemia, and vitamin D deficiency are risk factors that increase the brain accumulation of pathogenic ß-amyloid peptides (40 and 42), precursors leading to Alzheimer's disease (AD) in humans. The relative changes accompanying aging, high cholesterol, and/or treatment of calcitriol, active vitamin D receptor (VDR) ligand, under normal physiology are unknown. We examined these relative changes in C57BL/6 mice of ages 2, 4-8, and more than 10 months old, which were fed a normal or high fat / high cholesterol diet and treated with calcitriol, active ligand of the vitamin D receptor (0 or 2.5 µg/kg ×4, intraperitoneally, every other day to elicit cholesterol lowering in liver). Aß40 but not Aß42 accumulation in brain and lower P-glycoprotein (P-gp) and neprilysin protein expressions for Aß efflux and degradation, respectively, were found to be associated with aging. But there was no trend for BACE1 (ß-secretase 1, a cholesterol-sensitive enzyme) toward Aß synthesis with age. In response to calcitriol treatment, P-gp was elevated, mitigating partially the age-related changes. Although age-dependent decreasing trends in mRNA expression levels existed for Cyp46a1, the brain cholesterol processing enzyme, whose inhibition increases BACE1 and ApoE to facilitate microglia Aß degradation, mRNA changes for other cholesterol transporters: Acat1 and Abca1, and brain cholesterol levels remained unchanged. There was no observable change in the mRNA expression of amyloid precursor protein (APP) and the influx (RAGE) and efflux (LRP1) transporters with respect to age, diet, or calcitriol treatment. Overall, aging poses as a risk factor contributing to Aß accumulation in brain, and VDR-mediated P-gp activation partially alleviates the outcome.

Human Amyloid-ß40 Kinetics after Intravenous and Intracerebroventricular Injections and Calcitriol Treatment in Rats In Vivo.

Amyloid-ß peptides of 40 and 42 amino acid lengths, which are synthesized in neurons and degraded in the brain and liver, have the potential to aggregate and form neuritic plaques in Alzheimer disease. The kinetics of human amyloid-ß (hAß) 40 were examined in the rat pursuant to intravenous and intracerebroventricular administration after pretreatment with calcitriol, the active vitamin D receptor ligand (6.4 nmol·kg-1 in 0.3 ml corn oil every other day for four intraperitoneal doses) to induce P-glycoprotein (P-gp) and enhance hAß40 brain efflux. The interference of hAß40 by media matrix that suppressed absorbance readings in the ELISA assay was circumvented with use of different calibration curves prepared in Standard Dilution Buffer, undiluted, 10-10,000 or 5-fold diluted plasma, or artificial cerebrospinal fluid. Simultaneous fitting of hAß40 plasma and cerebrospinal fluid (CSF) data after intravenous and intracerebroventricular administration were described by catenary-mammillary models comprising of a central and two peripheral compartments, the brain, and one to four CSF compartments. The model with only one CSF compartment (model I) best fitted the intravenous data that showed a faster plasma decay t1/2 and slower equilibration between plasma and brain/CSF. Calcitriol induction increased the brain efflux rate constant, k41 (1.8-fold), at the blood-brain barrier when compared with the control group, as confirmed by the 2-fold (P < 0.05) increase in brain P-gp relative protein expression. SIGNIFICANCE STATEMENT: An accurate description of the kinetic behavior of human amyloid-ß (hAß) 40 is needed in defining the toxic peptide as a biomarker of Alzheimer disease. Modeling of hAß40 data after intravenous and intracerebroventricular administration to the rat revealed an initially faster plasma half-life that reflected faster peripheral distribution but slower equilibration between plasma and brain/cerebrospinal fluid even with calcitriol pretreatment that increased P-glycoprotein protein expression and enhanced efflux clearance from brain.

The Segregated Intestinal Flow Model (SFM) for Drug Absorption and Drug Metabolism: Implications on Intestinal and Liver Metabolism and Drug-Drug Interactions.

The properties of the segregated flow model (SFM), which considers split intestinal flow patterns perfusing an active enterocyte region that houses enzymes and transporters (<20% of the total intestinal blood flow) and an inactive serosal region (>80%), were compared to those of the traditional model (TM), wherein 100% of the flow perfuses the non-segregated intestine tissue. The appropriateness of the SFM model is important in terms of drug absorption and intestinal and liver drug metabolism. Model behaviors were examined with respect to intestinally (M1) versus hepatically (M2) formed metabolites and the availabilities in the intestine (FI) and liver (FH) and the route of drug administration. The %contribution of the intestine to total first-pass metabolism bears a reciprocal relation to that for the liver, since the intestine, a gateway tissue, regulates the flow of substrate to the liver. The SFM predicts the highest and lowest M1 formed with oral (po) and intravenous (iv) dosing, respectively, whereas the extent of M1 formation is similar for the drug administered po or iv according to the TM, and these values sit intermediate those of the SFM. The SFM is significant, as this drug metabolism model explains route-dependent intestinal metabolism, describing a higher extent of intestinal metabolism with po versus the much reduced or absence of intestinal metabolism with iv dosing. A similar pattern exists for drug-drug interactions (DDIs). The inhibitor or inducer exerts its greatest effect on victim drugs when both inhibitor/inducer and drug are given po. With po dosing, more drug or inhibitor/inducer is brought into the intestine for DDIs. The bypass of flow and drug to the enterocyte region of the intestine after intravenous administration adds complications to in vitro-in vivo extrapolations (IVIVE).

Noteworthy idiosyncrasies of 1α,25-dihydroxyvitamin D3 kinetics for extrapolation from mouse to man: Commentary.

Calcitriol or 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ] is the active ligand of the vitamin D receptor (VDR) that plays a vital role in health and disease. Vitamin D is converted to the relatively inactive metabolite, 25-hydroxyvitamin D3 [25(OH)D3 ], by CYP27A1 and CYP2R1 in the liver, then to 1,25(OH)2 D3 by a specific, mitochondrial enzyme, CYP27B1 (1α-hydroxylase) that is present primarily in the kidney. The degradation of both metabolites is mostly carried out by the more ubiquitous mitochondrial enzyme, CYP24A1. Despite the fact that calcitriol inhibits its formation and degradation, allometric scaling revealed strong interspecies correlation of the net calcitriol clearance (CL estimated from dose/AUC∞ ), production rate (PR), and basal, plasma calcitriol concentration with body weight (BW). PBPK-PD (physiologically based pharmacokinetic-pharmacodynamic) modeling confirmed the dynamic interactions between calcitriol and Cyp27b1/Cyp24a1 on the decrease in the PR and increase in CL in mice. Close scrutiny of the literature revealed that basal levels of calcitriol had not been taken into consideration for estimating the correct AUC∞ and CL after exogenous calcitriol dosing in both animals and humans, leading to an overestimation of AUC∞ and underestimation of the plasma CL. In humans, CL was decreased in chronic kidney disease but increased in cancer. Collectively, careful pharmacokinetic data analysis and improved definition are achieved with PBPK-PD modeling, which embellishes the complexity of dose, enzyme regulation, and disease conditions. Allometric scaling and PBPK-PD modeling were applied successfully to extend the PBPK model to predict calcitriol kinetics in cancer patients.

Current Evidence and Future Directions of Tranexamic Acid Use, Efficacy, and Dosing for Major Surgical Procedures.

Tranexamic acid reduces blood loss and transfusion requirements with no significant thrombotic adverse effects. Postoperative seizures have been seen in cardiac surgical patients in association with patient (advanced age, underlying neurologic disease, chronic kidney disease); surgical (open cardiac procedures, long bypass times); and drug (high tranexamic acid dose) risk factors. Tranexamic acid dosing regimens should be decreased in patients with chronic kidney dysfunction secondary to reduced clearance and drug accumulation. Optimal dosing for cardiac surgical patients has been recommended. Additional research is required to determine dosing regimens in major noncardiac surgery and plasma concentration levels associated with inducing seizures.

Hepatic clearance concepts and misconceptions: Why the well-stirred model is still used even though it is not physiologic reality?

The liver is the most important drug metabolizing organ, endowed with a plethora of metabolizing enzymes and transporters to facilitate drug entry and removal via metabolism and/or biliary excretion. For this reason, much focus surrounds the development of clearance concepts, which are based on normalizing the rate of removal to the input or arterial concentration. By so doing, some authors have recently claimed that it implies one specific model of hepatic elimination, namely, the widely used well-stirred or venous equilibration model (WSM). This commentary challenges this claim and aims to provide a comprehensive discussion of not only the WSM but other currently applied hepatic clearance models - the parallel tube model (PTM), the dispersion model (DM), the zonal liver model (ZLM), and the heterogeneous capillary transit time model of Goresky and co-workers (GM). The WSM, PTM, and DM differ in the patterns of internal blood flow, assuming bulk, plug, and dispersive flows, respectively, which render different degrees of mixing within the liver that are characterized by the magnitudes of the dispersion number (DN), resulting in different implications concerning the (unbound) substrate concentration in liver (CuH). Early models assumed perfusion rate-limited distribution, which have since been modified to include membrane-limited transport. The recent developments associated with the misconceptions and the sensitivity of the models are hereby addressed. Since the WSM has been and will likely remain widely used, the pros and cons of this model relative to physiological reality are further discussed.

Theoretical consideration of the properties of intestinal flow models on route-dependent drug removal: Segregated Flow (SFM) vs. Traditional (TM).

The intestine is endowed with a plethora of enzymes and transporters and regulates the flow of substrate to the liver. Physiologically-based pharmacokinetic models have surfaced to describe intestinal removal. The traditional model (TM) describes the intestinal flow as a whole perfusing the entire tissue that contains the intestinal transporters and enzymes. The segregated flow model (SFM) describes that only a fraction (fQ  < 0.2) of the intestinal blood flow perfuses the enterocyte region where the intestinal enzymes and transporters are housed, rendering a lower drug distribution/intestinal clearance when drug enters via the circulation than from the gut lumen. As shown by simulations, a higher intestinal clearance and extraction ratio (EI,iv ) exists for the TM than for SFM after iv dosing. By contrast, the EI,po after po dosing is higher for the SFM, due to the smaller volume of distribution for the enterocyte region and a lower flow rate that result in increased mean residence time and higher drug extraction. Under MBI (mechanism-based inhibition), the AUCR,po after oral bolus is the highest for drug when inhibitor is given orally, with SFM > TM. Competitive inhibition of intestinal enzymes leads to higher liver metabolism; again, when both drug and inhibitor are given orally, changes in the SFM > TM. However, less definitive patterns result with inhibition of both intestinal and liver enzymes. In conclusion, differences exist for EI and drug-drug interaction (DDI) between the TM and SFM. The fractional intestinal blood flow (fQ ) is a key factor affecting different extents of intestinal/liver metabolism of the drug after oral as well as intravenous administration.

Finding Tmax and Cmax in Multicompartmental Models.

Drug absorption data are critical in bioequivalence comparisons, and factors such as the maximum drug concentration (Cmax), time to achieve Cmax (or Tmax), as well as the area under the curve (AUC) are important metrics. It is generally accepted that the AUC is a meaningful estimate of the extent of absorption, and Tmax or Cmax may be used for assessing the rate of absorption. But estimation of the rate of absorption with Tmax or Cmax is not always feasible, as explicit solutions relating Tmax and Cmax to the absorption (ka) and elimination rate (k) constants exist only for the one and not multicompartmental oral model. Therefore, the determination of Tmax or Cmax for multicompartmental models is uncertain. Here, we propose an alternate, numerical approach that uses the point-slope method for the first and second derivative(s) of the concentration-versus-time profiles and the Newton-Raphson iteration method for the determination of Tmax and Cmax We show that the method holds for multicompartmental oral dosing under single or steady-state conditions in the absence of known microconstants, even for flip-flop (ka < ß) models. Simulations showed that the Cmax and Tmax estimates obtained with the Newton-Raphson method were more accurate than those based on the noncompartmental, observation-based method recommended by the US Food and Drug Administration. The %Bias attributable to sampling frequency and assay error were less than those determined by the noncompartmental method, showing that the Newton-Raphson method is viable for the estimation of Tmax and Cmax.

Strategies and limitations associated with in vitro characterization of vitamin D receptor activators.

In vitro cell-based assays are common screening tools used for the identification of new VDR ligands. For 25-hydroxyvitamin D3 [25(OH)D3] and 1α-hydroxyvitamin D3 [1α(OH)D3], protein expressions of CYP2R1 and CYP27B1, respectively, that form the active 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] ligand were detected in human embryonic kidney (HEK293) cells expressing the GAL4-hVDR, the human brain microvessel endothelial (hCMEC/D3) and adenocarcinoma colonic (Caco-2) cells. The impact of bioactivation enzymes was shown upon the addition of ketoconazole (10 µM KTZ), a pan-CYP inhibitor, which reduced the apparent potency of 25(OH)D3 and increased the EC50 from 272 to 608 nM in HEK293 cells. EIA assays verified that 1,25(OH)2D3 was formed and contributed to VDR activity independently of its precursors. In hCMEC/D3 cells where enzyme protein levels were lowest, changes in MDR1/P-gp expression with KTZ were minimal. In Caco-2 cells, the induction of TRPV6 (calcium channel), CYP24A1, CYP3A4, OATP1A2 and MDR1 mRNA expression was 1,25(OH)2D3 > 1α(OH)D3 > 25(OH)D3, with the magnitude of change being blunted by KTZ. Upon inclusion of KTZ in the cell-based assays, high transcriptional activities were observed for synthetic VDR activators from Teijin Pharma. Cyclopentanone derivatives: TPD-003, TPD-005, TPD-006, TPD-008 and TPD-009 (EC50s 0.06 to 67 nM, unchanged with KTZ) were found more potent over straight chain and lactone derivatives (antagonists). Most TPD compounds activated OATP1A2, CYP24A1, CYP3A4, and MDR1 (28-67%) and TRPV6 transcriptionally in Caco-2 cells. The results identified that cell-based assays with added KTZ could accurately identify new VDR activators, although these may be hypercalcemic with strong TRPV6 inducing properties.

Potencies of vitamin D analogs, 1α-hydroxyvitamin D3 , 1α-hydroxyvitamin D2 and 25-hydroxyvitamin D3 , in lowering cholesterol in hypercholesterolemic mice in vivo.

Vitamin D3 and the synthetic vitamin D analogs, 1α-hydroxyvitamin D3 [1α(OH)D3 ], 1α-hydroxyvitamin D2 [1α(OH)D2 ] and 25-hydroxyvitamin D3 [25(OH)D3 ] were appraised for their vitamin D receptor (VDR) associated-potencies as cholesterol lowering agents in mice in vivo. These precursors are activated in vivo: 1α(OH)D3 and 1α(OH)D2 are transformed by liver CYP2R1 and CYP27A1 to active VDR ligands, 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ] and 1α,25-dihydroxyvitamin D2 [1,25(OH)2 D2 ], respectively. 1α(OH)D2 may also be activated by CYP24A1 to 1α,24-dihydroxyvitamin D2 [1,24(OH)2 D2 ], another active VDR ligand. 25(OH)D3 , the metabolite formed via CYP2R1 and or CYP27A1 in liver from vitamin D3 , is activated by CYP27B1 in the kidney to 1,25(OH)2 D3 . In C57BL/6 mice fed the high fat/high cholesterol Western diet for 3 weeks, vitamin D analogs were administered every other day intraperitoneally during the last week of the diet. The rank order for cholesterol lowering, achieved via mouse liver small heterodimer partner (Shp) inhibition and increased cholesterol 7α-hydroxylase (Cyp7a1) expression, was: 1.75 nmol/kg 1α(OH)D3  > 1248 nmol/kg 25(OH)D3 (dose ratio of 0.0014) > > 1625 nmol/kg vitamin D3 . Except for 1.21 nmol/kg 1α(OH)D2 that failed to lower liver and plasma cholesterol contents, a significant negative correlation was observed between the liver concentration of 1,25(OH)2 D3 formed from the precursors and liver cholesterol levels. The composite results show that vitamin D analogs 1α(OH)D3 and 25(OH)D3 exhibit cholesterol lowering properties upon activation to 1,25(OH)2 D3 : 1α(OH)D3 is rapidly activated by liver enzymes and 25(OH)D3 is slowly activated by renal Cyp27b1 in mouse.

Tranexamic Acid Dosing for Cardiac Surgical Patients With Chronic Renal Dysfunction: A New Dosing Regimen.

BACKGROUND: Tranexamic acid (TXA) is a common antifibrinolytic agent used to minimize bleeding in cardiac surgery. Up to 50% cardiac surgical patients have chronic renal dysfunction (CRD). Optimal dosing of TXA in CRD remains poorly investigated. This is important as TXA is renally eliminated with accumulation in CRD. High TXA doses are associated with postoperative seizures. This study measures plasma TXA concentrations in CRD cardiac surgical patients for pharmacokinetic modeling and dose adjustment recommendations. METHODS: This prospective cohort study enrolled 48 patients with stages 1-5 CRD, classified by Kidney Disease Outcome Quality Initiative. Patients were separated into 2 treatment groups. A "low-risk" group underwent simple aortocoronary bypass or single-valve repair/replacement and received a 50 mg/kg TXA bolus. A "high-risk" group underwent redo, aortic, multiple valve or combination surgery and received the Blood Conservation Using Anti-fibrinolytics Trial dosing regimen (loading dose 30 mg/kg, infusion 16 mg/kg/h with 2 mg/kg in pump prime). Primary outcome identified changes in TXA clearance and distribution volume, which provided the rationale for dose adjustment. Descriptive clinical outcomes assessed postoperative seizures, blood loss, ischemic-thrombotic complications, in-hospital mortality, and length of hospital stay. RESULTS: TXA concentrations were elevated and sustained above the therapeutic threshold for approximately 12 hours in high-risk stages 3-5 groups, in accordance to CRD severity. CONCLUSIONS: Using a pharmacokinetic model, we propose a simple new TXA dosing regimen that optimizes maximal antifibrinolysis and avoids excessive drug dosing.