Accumulating evidence for a drug-drug interaction between methotrexate and proton pump inhibitors.

BACKGROUND: A number of medications are known to interact with methotrexate through various mechanisms. The aim of this article is to apprise practitioners of a new labeling change based on the accumulating evidence for a possible drug-drug interaction between methotrexate (primarily at high doses) and proton pump inhibitors (PPIs). METHODS: The U.S. Food and Drug Administration (FDA) Adverse Event Reporting System (AERS) database of spontaneous adverse event reports and the published literature were searched for cases reporting an interaction between methotrexate and PPIs. RESULTS: A search of the AERS database and existing literature found several individual case reports of drug-drug interactions and three additional supportive studies that suggest potential underlying mechanisms for the interaction. CONCLUSION: There is evidence to suggest that concomitant use of methotrexate (primarily at high doses) with PPIs such as omeprazole, esomeprazole, and pantoprazole may decrease methotrexate clearance, leading to elevated serum levels of methotrexate and/or its metabolite hydroxymethotrexate, possibly leading to methotrexate toxicities. In several case reports, no methotrexate toxicity was found when a histamine H2 blocker was substituted for a PPI. Based on the reviewed data, the FDA updated the methotrexate label to include the possible drug-drug interaction between high-dose methotrexate and PPIs. Physicians should be alerted to this potential drug-drug interaction in patients receiving concomitant high-dose methotrexate and PPIs.

Effect of dose escalation on the in vivo oral absorption and disposition of glycylsarcosine in wild-type and Pept1 knockout mice.

This study evaluated the in vivo absorption and disposition of glycylsarcosine (GlySar), after escalating oral doses, in wild-type and peptide transporter 1 (Pept1) knockout mice. [(3)H]GlySar was administered to mice at doses of 1, 10, 100, 1000, and 5000 nmol/g b.wt. Serial blood samples were obtained over 480 min, the plasma was harvested, and the area under the plasma concentration-time curve (AUC) was determined. It was observed that the GlySar AUC was 60, 45, and 30% lower in knockout than wild-type mice when evaluated over 2, 4, and 8 h, respectively (p < 0.01). Plasma levels of GlySar reached a plateau at 90 min in knockout mice and then rose to a second plateau at 240 min. In wild-type mice, the plasma levels rose continuously to reach a single plateau at 90 min. When partial AUC (0-120 min) was used as an indicator for rate of absorption, there was a 60% reduction in GlySar absorption rate in knockout mice compared with wild-type animals. Tissue distribution studies were also performed after 10 nmol/g oral doses of [(3)H]GlySar. When sampled 1 h after dosing, GlySar tissue concentrations were significantly lower in knockout versus wild-type mice and, with the exception of intestines, reflected differences in the systemic exposure of dipeptide between these two genotypes. Overall, PEPT1 ablation in mice resulted in significant reductions, in vivo, in the rate and extent of GlySar absorption. The AUC of GlySar was proportional to dose in both genotypes over 1 to 100 nmol/g, with minor decrements at the two highest doses.

Significance and regional dependency of peptide transporter (PEPT) 1 in the intestinal permeability of glycylsarcosine: in situ single-pass perfusion studies in wild-type and Pept1 knockout mice.

The purpose of this study was to evaluate the role, relevance, and regional dependence of peptide transporter (PEPT) 1 expression and function in mouse intestines using the model dipeptide glycylsarcosine (GlySar). After isolating specific intestinal segments, in situ single-pass perfusions were performed in wild-type and Pept1 knockout mice. The permeability of [(3)H]GlySar was measured as a function of perfusate pH, dipeptide concentration, potential inhibitors, and intestinal segment, along with PEPT1 mRNA and protein. We found the permeability of GlySar to be saturable (K(m) = 5.7 mM), pH-dependent (maximal value at pH 5.5), and specific for PEPT1; other peptide transporters, such as PHT1 and PHT2, were not involved, as judged by the lack of GlySar inhibition by excess concentrations of histidine. GlySar permeabilities were comparable in the duodenum and jejunum of wild-type mice but were much larger than that in ileum (approximately 2-fold). A PEPT1-mediated permeability was not observed for GlySar in the colon of wild-type mice (<10% residual uptake compared to proximal small intestine). Moreover, GlySar permeabilities were very low and not different in the duodenum, jejunum, ileum, and colon of Pept1 knockout mice. Functional activity of intestinal PEPT1 was confirmed by real-time polymerase chain reaction and immunoblot analyses. Our findings suggest that a loss of PEPT1 activity (e.g., due to polymorphisms, disease, or drug interactions) should have a major effect in reducing the intestinal absorption of di-/tripeptides, peptidomimetics, and peptide-like drugs.

Transport mechanisms of carnosine in SKPT cells: contribution of apical and basolateral membrane transporters.

PURPOSE: The aim of this study was to investigate the transport properties of carnosine in kidney using SKPT cell cultures as a model of proximal tubular transport, and to isolate the functional activities of renal apical and basolateral transporters in this process. METHODS: The membrane transport kinetics of 10 microM [3H]carnosine was studied in SKPT cells as a function of time, pH, potential inhibitors and substrate concentration. A cellular compartment model was constructed in which the influx, efflux and transepithelial clearances of carnosine were determined. Peptide transporter expression was probed by RT-PCR. RESULTS: Carnosine uptake was 15-fold greater from the apical than basolateral surface of SKPT cells. However, the apical-to-basolateral transepithelial transport of carnosine was severely rate-limited by its cellular efflux across the basolateral membrane. The high-affinity, proton-dependence, concentration-dependence and inhibitor specificity of carnosine supports the contention that PEPT2 is responsible for its apical uptake. In contrast, the basolateral transporter is saturable, inhibited by PEPT2 substrates but non-concentrative, thereby, suggesting a facilitative carrier. CONCLUSIONS: Carnosine is expected to have a substantial cellular accumulation in kidney but minimal tubular reabsorption in blood because of its high influx clearance across apical membranes by PEPT2 and very low efflux clearance across basolateral membranes.

Targeted disruption of peptide transporter Pept1 gene in mice significantly reduces dipeptide absorption in intestine.

PEPT1 is a high-capacity, low-affinity peptide transporter that mediates the uptake of di- and tripeptides in the intestine and kidney. PEPT1 also has significance in its ability to transport therapeutic agents and because of its potential as a target for anti-inflammatory therapies. To further understand the relevance of specific peptide transporters in intestinal physiology, pharmacology and pathophysiology, we have generated Pept1 null mice by targeted gene disruption. The Pept1 gene was disrupted by insertion of a lacZ reporter gene under the control of the endogenous Pept1 promoter. Phenotypic profiling of wild-type and Pept1 null mice was then performed, along with in vitro intestinal uptake, in situ intestinal perfusion and in vivo pharmacokinetic studies of glycylsarcosine (GlySar). Pept1 null mice lacked expression of PEPT1 protein in the intestine and kidney, tissues in which this peptide transporter is normally expressed. Pept1-deficient mice were found to be viable, fertile, grew to normal size and weight, and were without any obvious abnormalities. Nevertheless, Pept1 deletion dramatically reduced the intestinal uptake and effective permeability of the model dipeptide GlySar (i.e., by at least 80%), and its oral absorption following gastric gavage (i.e., by about 50%). In contrast, the plasma profiles of GlySar were almost superimposable between wild-type and Pept1 null animals after intravenous dosing. These novel findings provide strong evidence that PEPT1 has a major role in the in vivo oral absorption of dipeptides.

Effect of hydrophobic structure on the catalysis of nitric oxide release from zwitterionic diazeniumdiolates in surfactant and liposome media.

The effect of phospholipid liposomes and surfactant micelles on the rate of nitric oxide release from zwitterionic diazeniumdiolates, R1R2N[N(O)NO]-, with significant hydrophobic structure, has been explored. The acid-catalyzed dissociation of NO has been examined in phosphate-buffered solutions of sodium dodecylsulfate (SDS) micelles and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-[phospho-(1-glycerol)] sodium salt (DPPG) phospholipid liposomes. The reaction behavior of dibenzylamine-, monobenzylamine-, and dibutylamine-derived substrates [1]: R1 = C6H5CH2, R2 = C6H5CH2 NH2+(CH2)2, 2: R1 = C6H5CH2, R2 = NH3+(CH2)2, and 3: R1 = n-butyl, R2 = n-butyl-NH2+(CH2)6] has been compared with that of SPER/NO, 4: R1 = H2N(CH2)3, R2 = H2N(CH2) 3NH2+(CH2)4]. Catalysis of NO release is observed in both micellar and liposome media. Hydrophobic interactions contribute to micellar binding for 1-3 and appear to be the main factor facilitating catalysis by charge neutral DPPC liposomes. Binding constants for the association of 1 and 3 with SDS micelles were 3-fold larger than those previously obtained with comparable zwitterionic substrates lacking their hydrophobic structure. Anionic DPPG liposomes were much more effective in catalyzing NO release than either DPPC liposomes or SDS micelles. DPPG liposomes (at 10 mM total lipid) induced a 30-fold increase in the NO dissociation rate of SPER/NO compared to 12- and 14-fold increases in that of 1 and 3.