Dosing algorithm to target a predefined AUC in patients with primary central nervous system lymphoma receiving high dose methotrexate

There is no consensus regarding optimal dosing of high dose methotrexate (HDMTX) in patients with primary CNS lymphoma. Our aim was to develop a convenient dosing algorithm to target AUC(MTX) in the range between 1000 and 1100 µmol l(-1) h.

Antinociceptive effects, metabolism and disposition of ketamine in ponies under target-controlled drug infusion

Ketamine is widely used as an anesthetic in a variety of drug combinations in human and veterinary medicine. Recently, it gained new interest for use in long-term pain therapy administered in sub-anesthetic doses in humans and animals. The purpose of this study was to develop a physiologically based pharmacokinetic (PBPk) model for ketamine in ponies and to investigate the effect of low-dose ketamine infusion on the amplitude and the duration of the nociceptive withdrawal reflex (NWR). A target-controlled infusion (TCI) of ketamine with a target plasma level of 1 microg/ml S-ketamine over 120 min under isoflurane anesthesia was performed in Shetland ponies. A quantitative electromyographic assessment of the NWR was done before, during and after the TCI. Plasma levels of R-/S-ketamine and R-/S-norketamine were determined by enantioselective capillary electrophoresis. These data and two additional data sets from bolus studies were used to build a PBPk model for ketamine in ponies. The peak-to-peak amplitude and the duration of the NWR decreased significantly during TCI and returned slowly toward baseline values after the end of TCI. The PBPk model provides reliable prediction of plasma and tissue levels of R- and S-ketamine and R- and S-norketamine. Furthermore, biotransformation of ketamine takes place in the liver and in the lung via first-pass metabolism. Plasma concentrations of S-norketamine were higher compared to R-norketamine during TCI at all time points. Analysis of the data suggested identical biotransformation rates from the parent compounds to the principle metabolites (R- and S-norketamine) but different downstream metabolism to further metabolites. The PBPk model can provide predictions of R- and S-ketamine and norketamine concentrations in other clinical settings (e.g. horses).

Aromatase in zebrafish: a potential target for endocrine disrupting chemicals

In zebrafish, two isoforms of the aromatase gene exist, namely cyp19a1 and cyp19a2, expressed predominantly in the gonads and brain, respectively. In this study, we focus on characterizing the specificity of antibodies against the aromatase isoforms, and on (xeno)estrogen-induced changes of individual cyp19a2 mRNA concentrations in the brains of adult male zebrafish. Among three polyclonal antibodies studied, the one against CYP19A2 was found to be specific in Western blots and immunohistochemistry. Real-time RT-PCR analyses revealed strong interindividual variation of cyp19a2 levels in the brains of adult male zebrafish. After a three-week-exposure to (xeno)estrogens, mean values of cyp19a2 mRNA levels tended to increase, with significant induction at 200 ng 17beta-estradiol/L, but interindividual variation of cyp19a2 expression was maintained.

Nuclear receptor and target gene mRNA abundance in duodenum and colon of dogs with chronic enteropathies

Nuclear receptors (NR), such as constitutive androstane receptor (CAR), pregnane X receptor (PXR) and peroxisome proliferator-associated receptors alpha and gamma (PPARalpha, PPARgamma) are mediators of inflammation and may be involved in inflammatory bowel disease (IBD) and food responsive diarrhea (FRD) of dogs. The present study compared mRNA abundance of NR and NR target genes [multi drug-resistance gene-1 (MDR1), multiple drug-resistance-associated proteins (MRD2, MRD3), cytochrome P450 (CYP3A12), phenol-sulfating phenol sulfotransferase (SULT1A1) and glutathione-S-transferase (GST A3-3)] in biopsies obtained from duodenum and colon of dogs with IBD and FRD and healthy control dogs (CON; n=7 per group). Upon first presentation of dogs, mRNA levels of PPARalpha, PPARgamma, CAR, PXR and RXRalpha in duodenum as well as PPARgamma, CAR, PXR and RXRalpha in colon were not different among groups (P>0.10). Although mRNA abundance of PPARalpha in colon of dogs with FRD was similar in both IBD and CON (P>0.10), PPARalpha mRNA abundance was higher in IBD than CON (P<0.05). Levels of mRNA of MDR1 in duodenum were higher in FRD than IBD (P<0.05) or CON (P<0.001). Compared with CON, abundances of mRNA for MRP2, CYP3A12 and SULT1A1 were higher in both FRD and IBD than CON (P<0.05). Differences in mRNA levels of PPARalpha and MRP2 in colon and MDR1, MRP2, CYP3A12 and SULT1A1 in duodenum may be indicative for enteropathy in FRD and (or) IBD dogs relative to healthy dogs. More importantly, increased expression of MDR1 in FRD relative to IBD in duodenum may be a useful diagnostic marker to distinguish dogs with FRD from dogs with IBD.

Ontogeny of mRNA abundance of nuclear receptors and nuclear receptor target genes in young cattle

After birth the development of appropriate detoxification mechanisms is important. Nuclear receptors (NR), such as constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor-alpha (PPARalpha), retinoid receptors (RAR, RXR), and NR target genes are involved in the detoxification of exogenous and endogenous substances. We quantified abundances of hepatic mRNA of NR and several NR target genes (cytochromes, CYP; cytochrome P450 reductase, CPR; UDP-glucuronosyl transferase, UDP) in calves at different ages. Gene expression was quantified by real-time RT-PCR. Abundance of mRNA of CAR and PXR increased from low levels at birth in pre-term calves (P0) and full-term calves (F0) to higher levels in 5-day-old calves (F5) and in 159-day-old veal calves (F159), whereas mRNA levels of PPARalpha did not exhibit significant ontogenetic changes. RARbeta mRNA levels were higher in F5 and F159 than in F0, whereas no age differences were observed for RARalpha levels. Levels of RXRalpha and RXRbeta mRNA were lower in F5 than in P0 and F0. Abundance of CYP2C8 and CYP3A4 increased from low levels in P0 and F0 to higher levels in F5 and to highest levels in F159. Abundance of CPR was transiently decreased in F0 and F5 calves. Levels of UGT1A1 mRNA increased from low levels in P0 and F0 to maximal level in F5 and F159. In conclusion, mRNA levels of NR and NR target genes exhibited ontogenetic changes that are likely of importance for handling of xeno- and endobiotics with increasing age.

Nuclear receptor and nuclear receptor target gene messenger ribonucleic acid levels at different sites of the gastrointestinal tract and in liver of healthy dogs

Nuclear receptors (NR) are ligand-activated transcription factors that regulate different metabolic pathways by influencing the expression of target genes. The current study examined mRNA abundance of NR and NR target genes at different sites of the gastrointestinal tract (GIT) and the liver of healthy dogs (Beagles; n = 11). Samples of GIT and liver were collected postmortem and homogenized, total RNA was extracted and reverse transcribed, and gene expression was quantified by real-time reverse-transcription PCR relative to the mean of 3 housekeeping genes (beta-actin, glyceraldehyde-3-phosphate dehydrogenase, and ubi-quitin). Differences were observed (P < or = 0.05) in the mRNA abundance among stomach (St), duodenum (Du), jejunum (Je), ileum (Il), and colon (Col) for NR [pregnane X receptor (Du, Je > Il, Col > St), peroxisome proliferator-associated receptor gamma (St, Du, Col > Je, Il), constitutive androstane receptor (Je, Du > Il, Col), and retinoid x receptor alpha (Du > Il)] and NR target genes [glutathione-S-transferase A3-3 (Du > Je > St, Il; St > Col), phenol-sulfating phenol sulfotransferase 1A1 (Du, Je > Il, St; Col > St), cytochrome P450 3A12 (Du, Je > St, Il, Col), multiple drug resistance gene 1 (Du, Je, Il, Col > St), multiple drug resistance-associated protein 2 (Je, Du > Il > St, Col), multiple drug resistance-associated protein 3 (Col > St > Il; Du > Je, Il; St > Il), NR corepressor 2 (St > Il, Col), and cytochrome P450 reductase (St, Du, Je > Il, Col)], but not for peroxisome proliferator-associated receptor alpha. Differences (P > 0.05) in mRNA abundance in the liver relative to the GIT were also observed. In conclusion, the presence of numerous differences in expression of NR and NR target genes in different parts of the GIT and in liver of healthy dogs may be associated with location-specific functions and regulation of GIT regions.

Effectively Selecting a Target Population for a Future Comparative Study

When comparing a new treatment with a control in a randomized clinical study, the treatment effect is generally assessed by evaluating a summary measure over a specific study population. The success of the trial heavily depends on the choice of such a population. In this paper, we show a systematic, effective way to identify a promising population, for which the new treatment is expected to have a desired benefit, using the data from a current study involving similar comparator treatments. Specifically, with the existing data we first create a parametric scoring system using multiple covariates to estimate subject-specific treatment differences. Using this system, we specify a desired level of treatment difference and create a subgroup of patients, defined as those whose estimated scores exceed this threshold. An empirically calibrated group-specific treatment difference curve across a range of threshold values is constructed. The population of patients with any desired level of treatment benefit can then be identified accordingly. To avoid any ``self-serving'' bias, we utilize a cross-training-evaluation method for implementing the above two-step procedure. Lastly, we show how to select the best scoring system among all competing models. The proposals are illustrated with the data from two clinical trials in treating AIDS and cardiovascular diseases. Note that if we are not interested in designing a new study for comparing similar treatments, the new procedure can also be quite useful for the management of future patients who would receive nontrivial benefits to compensate for the risk or cost of the new treatment.