CXCR4antagonism as a therapeutic approach to prevent acute kidney injury.

We examined whether antagonism of the CXCR4receptor ameliorates the loss of renal function following ischemia-reperfusion. CXCR4is ubiquitously expressed on leukocytes, known mediators of renal injury, and on bone marrow hematopoietic stem cells (HSCs). Plerixafor (AMD3100, Mozobil) is a small-molecule CXCR4antagonist that mobilizes HSCs into the peripheral blood and also modulates the immune response in in vivo rodent models of asthma and rheumatoid arthritis. Treatment with plerixafor before and after ischemic clamping ameliorated kidney injury in a rat model of bilateral renal ischemia-reperfusion. Serum creatinine and blood urea nitrogen were significantly reduced 24 h after reperfusion, as were tissue injury and cell death. Plerixafor prevented the renal increase in the proinflammatory chemokines CXCL1 and CXCL5 and the cytokine IL-6. Flow cytometry of kidney homogenates confirmed the presence of significantly fewer leukocytes with plerixafor treatment; additionally, myeloperoxidase activity was reduced. AMD3465, a monocyclam analog of plerixafor, was similarly renoprotective. Four weeks postreperfusion, long-term effects included diminished fibrosis, inflammation, and ongoing renal injury. The mechanism by which CXCR4inhibition ameliorates AKI is due to modulation of leukocyte infiltration and expression of proinflammatory chemokines/cytokines, rather than a HSC-mediated effect. The data suggest that CXCR4antagonism with plerixafor may be a potential option to prevent AKI.

A pharmacokinetic-pharmacodynamic model for the mobilization of CD34+ hematopoietic progenitor cells by AMD3100.

BACKGROUND: AMD3100 is a small-molecule CXCR4 antagonist that has been shown to induce the mobilization of CD34 + hematopoietic progenitor cells from bone marrow to peripheral blood. AMD3100 has also been shown to augment the mobilization of CD34 + cells in cancer patients when administered in combination with granulocyte colony-stimulating factor (G-CSF) (filgrastim). The purpose of this study was to characterize the exposure-response relationship of AMD3100 in mobilizing CD34 + cells when administered as a single agent in healthy volunteers. METHODS: AMD3100 concentrations and CD34 + cell counts obtained from 29 healthy subjects in a single-dose, intensively sampled pharmacokinetic/pharmacodynamic (PK-PD) study were analyzed by use of nonlinear mixed effects regression with the software NONMEM. FOCE (first order conditional estimation) with interaction was the estimation method, and simultaneous PK-PD fitting was adopted. RESULTS: The pharmacokinetics of AMD3100 was described by a 2-compartment model with first-order absorption. The population estimates (+/-SE) for clearance and central volume of distribution were 5.17 +/- 0.49 L/h and 16.9 +/- 3.79 L, respectively. CD34 + cell mobilization was best described by an indirect effect model that stimulates the entry process of CD34 + from bone marrow to peripheral blood in the form of a sigmoid maximum effect model. The population estimates (+/-SE) of maximum effect, concentration causing 50% of maximum response, and equilibration time were 12.6 +/- 4.89, 53.6 +/- 11.9 mug/L, and 5.37 +/- 1.31 hours, respectively. CONCLUSIONS: This study characterizes the exposure-response relationship of AMD3100 in mobilizing CD34 + cells after subcutaneous administration. This PK-PD model will be useful in assessing relevant covariates and for optimizing the use of AMD3100 in various patient populations.

Pharmacokinetics and safety of AMD-3100, a novel antagonist of the CXCR-4 chemokine receptor, in human volunteers.

AMD-3100, a bicyclam, is a novel agent that uniquely inhibits the entry of human immunodeficiency virus type 1 (HIV-1) into CD4(+) T cells via selective blockade of the chemokine CXCR-4 receptor. Twelve healthy volunteers were given AMD-3100 as a single 15-min intravenous infusion at 10, 20, 40, or 80 microg/kg. Five subjects also received a single subcutaneous injection of AMD-3100 (40 or 80 microg/kg). Three subjects received two escalating oral doses each (80 and 160 microg/kg). All subjects tolerated their dose(s) well without any grade 2 toxicity or dose adjustment. Six subjects experienced mild, transient symptoms, primarily gastrointestinal in nature and not dose related. All subjects experienced a dose-related elevation of the white blood cell count, from 1.5 to 3.1 times the baseline, which returned to the baseline 24 h after dosing. AMD-3100 demonstrated dose proportionality for the maximum drug concentration in serum (C(max)) and the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) over the entire dose range. At the highest intravenous dose (80 microg/kg), the median C(max) was 515 (range, 470 to 521) ng/ml and the AUC(0-infinity) was 1,044 (range, 980 to 1,403) ng-h/ml. The median systemic absorption after subcutaneous dosing was 87% (range, 67 to 106%). No drug was detectable in the blood following oral dosing. Using a two-compartment model, the median pharmacokinetic parameter estimates (ranges) were as follows: volume of distribution, 0.34 (0. 27 to 0.36) liter/kg; clearance, 1.30 (0.97 to 1.34) liters/h; elimination half-life, 3.6 (3.5 to 4.9) h. After a single, well-tolerated intravenous dose of AMD-3100, concentrations were sustained for 12 h above the in vitro antiretroviral 90% inhibitory concentrations and for 8 h above antiviral concentrations identified in the SCID-hu Thy/Liv mouse model of HIV infection.

High concentrations of a cGMP-stimulated phosphodiesterase mediate ANP-induced decreases in cAMP and steroidogenesis in adrenal glomerulosa cells.

An adrenal cGMP-stimulated phosphodiesterase (cGS-PDE) has been shown to mediate atrial natriuretic peptide (ANP)-induced reductions in aldosterone secretion and cAMP levels in primary bovine glomerulosa cells. High concentrations of cGS-PDE have been localized to the zona glomerulosa cell layer of the adrenal cortex using biochemical and immunological techniques. Immunoblot analysis using an affinity-purified, isozyme-specific antiserum revealed a single band that comigrated with a purified cGS-PDE (105 kDa) (1) and that was most highly concentrated in the outermost 1-2 mm of the cortex, representing the capsule and zona glomerulosa regions. Greater than 90% of the overall phosphodiesterase activity present in tissue extracts prepared from these regions was immunoprecipitated using a solid-phase monoclonal antibody reagent, indicating the cGS-PDE as the predominant phosphodiesterase isozyme. Immunohistochemical staining experiments of frozen thin sections of intact adrenal tissue revealed that the cGS-PDE present in this region was localized in the glomerulosa cells themselves. The role of this isozyme as a mediator of ANP-induced decreases in intracellular cAMP concentrations and aldosterone production was tested in primary cultures of bovine adrenal glomerulosa cells. In cells stimulated by ACTH, ANP treatment produced dose-dependent reductions in aldosterone secretion and cellular cAMP content over the same concentration range. Increases in aldosterone production elicited by three cell-permeable cAMP derivatives (8-bromo-cAMP, 8-p-chlorophenylthio-cAMP, and N6-2'-O-dibutyryl-cAMP) were antagonized by ANP, indicating a site of action distal to adenylate cyclase for this hormone. Because the relative magnitude of the ANP effect differed depending upon the derivative used, the three derivatives were compared with respect to their relative rates of in vitro hydrolysis by adrenal cGS-PDE. A positive correlation between their rates of hydrolysis and the degree to which the steroidogenic response produced by these derivatives was antagonized by ANP was demonstrated, further suggesting an ANP-induced activation of the cGS-PDE as being responsible for this effect. The possible contribution of an additional pathway mediated by an inhibitory guanine nucleotide binding regulatory protein (Gi) acting on adenylate cyclase was tested by pretreatment of primary glomerulosa cells with pertussis toxin. Levels of pertussis toxin sufficient to inhibit subsequent in vitro ribosylation did not significantly alter the ANP effect on aldosterone production, although a partial reduction in the ANP effect on cAMP levels was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug interactions with Ethmozine (moricizine HCl).

Moricizine HCl, a phenothiazine derivative synthesized in the USSR in 1964, has been shown to be an orally effective antiarrhythmic drug. Moricizine HCl has demonstrated a low incidence of generally mild and transient side effects. Studies of possible drug interaction between it and other drugs most likely to be administered to cardiovascular patients are currently being conducted in US drug trials. Possible interactions between moricizine HCl and cimetidine, and between moricizine HCl and digoxin, are reviewed. The coadministration of moricizine HCl had no effect on the pharmacokinetics of cimetidine; in contrast, cimetidine administration slowed the elimination of moricizine HCl. The implications of greater therapeutic and/or toxic effects of moricizine HCl must be considered for patients receiving cimetidine and moricizine HCl concomitantly. No significant interactions were observed when monitoring serum levels of moricizine HCl and digoxin in patients with normal renal function receiving digoxin therapy for congestive heart failure or atrial fibrillation. Moricizine HCl in therapeutic dosages (10 mg/kg daily) demonstrated antiarrhythmic efficacy without significant alterations in serum digoxin levels.

Assessment of the potential pharmacokinetic interaction between digoxin and ethmozine.

The potential for a pharmacokinetic interaction between the investigational antiarrhythmic drug ethmozine (moricizine HCl, the generic name that is infrequently used in existing literature) and digoxin was evaluated in nine healthy male adults. Serum and urinary digoxin concentrations were measured by radioimmunoassay following intravenous digoxin administration before and during steady-state ethmozine dosing. Plasma ethmozine levels following a single oral dose were measured before and after a single intravenous dose of digoxin. A mean elimination half-life of 45.6 hours was determined for digoxin alone, compared to 43.1 hours in combination with ethmozine. Average values for digoxin systemic clearance, apparent volume of distribution, and renal clearance were 2.87 mL/min/kg, 11.3 L/kg, and 2.44 mL/min/kg, respectively for digoxin alone, compared to 3.01 mL/min/kg, 11.3 L/kg, and 2.64 mL/min/kg, respectively for digoxin with ethmozine. A mean half-life of 2.0 hours was determined for ethmozine alone, compared with 1.8 hours following a single intravenous dose of digoxin. No change was observed in the oral pharmacokinetics of ethmozine following a single intravenous dose of digoxin, as indicated by the area under the plasma concentration versus time curve, Cmax or Tmax. These findings suggest that no pharmacokinetic interaction occurs when single intravenous doses of digoxin are co-administered with multiple oral doses of ethmozine.

Bioavailability of the bis- and monodigitoxosides of digitoxigenin.

The pharmacokinetic behavior of digitoxigenin is affected by the number of glycosides present. This study was conducted to compare the bioavailabilities of the bis- and monodigitoxosides of digitoxigenin in man. Intravenous and oral doses of the two drugs were administered to six normal volunteers. Blood samples were collected up to 28 days after each dose, and assayed for the specific drug administered and for total radioassayable drug. Both drugs were virtually completely absorbed, based on serum concentrations of administered drug plus metabolites. However, the mean bioavailability of unchanged bisdigitoxoside was only 56.3% indicating that substantial metabolism occurred prior to entry into the systemic circulation. Monodigitoxoside was virtually completely metabolized prior to entry into the systemic circulation.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in normal subjects.

The kinetics of digitoxin and two of its metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six normal subjects. Mean t 1/2s and total body clearances were 134.4, 15.4, and 0.59 hr and 2.66, 27.3, and 1071 ml/min. Mean renal clearance of the monodigitoxoside was more rapid (7.24 ml/min) than those of digitoxin (0.81 ml/min) or the bisdigitoxoside (0.94 ml/min). The volumes of distribution were of the same order, 0.45 l/kg for digitoxin, 0.57 l/kg for the bisdigitoxoside, and 0.83 l/kg for the monodigitoxoside. The short t 1/2 of monodigitoxoside would make it unsuitable for clinical use, but the bisdigitoxoside of digitoxigenin has a t 1/2 of an intermediate length and may have significant therapeutic advantages.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in renal insufficiency.

The kinetics of digitoxin and two of its major metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six subjects with renal insufficiency and compared to those in six age- and sex-matched normal control subjects. No significant differences between the two groups were found in elimination t 1/2, total body clearance, or volume of distribution. Average renal clearances of all three drugs were reduced in subjects with renal failure, but the differences were significant only in the case of digitoxin. The bis-digitoxoside of digitoxigenin has kinetic properties that offer clinical advantages.

Extra-hepatic GSH-dependent metabolism of 1,2-dibromoethane (DBE) and 1,2-dibromo-3-chloropropane (DBCP) in the rat and mouse.

Although DBE is metabolized by both microsomal and cytosolic pathways, it is the latter, GSH-dependent route, that may lead to hepatic and extra-hepatic genotoxicity and mutagenicity. As both DBE and DBCP exhibit predominantly extra-hepatic toxicity, their in vitro GSH-dependent debromination was measured in cytosolic fractions prepared from liver, kidney, testes and stomachs of Sprague-Dawley rats and Swiss-Webster mice. There was a marked species difference between the rat and mouse, with the rat metabolizing DBCP more rapidly than DBE, and the mouse metabolizing DBE more rapidly than DBCP. Hepatic rates exceeded those seen in extra-hepatic tissues in every case. Extra-hepatic rates of debromination represented as much as 84% of the hepatic rates, and generally followed the order: kidney greater than testes greater than stomach. Rates of metabolism for DBE and DBCP represented only a small fraction of the total cytosolic GSH S-transferase activity. These findings suggest significant levels of GSH-dependent metabolism may occur within those tissues associated with the in vivo toxicity of DBE and DBCP.

Pharmacokinetics and bioavailability of digitoxin by a specific assay.

The pharmacokinetics and bioavailability of digitoxin were examined in six normal human subjects using an assay that separates digitoxin from its metabolites. After intravenous administration, the mean systemic clearance was 2.44 ml/min; the volume of distribution was 0.47 l/kg; and the elimination half-life was 6.5 days. After oral administration, the elimination half-life was 5.8 days. The bioavailability was 81.5% using the specific assay. Using a non-specific, direct serum digitoxin radioimmunoassay the bioavailability was 98.0%. Assay of aqueous fractions from extracted serum samples indicated higher levels of water-soluble metabolites following oral compared to intravenous digitoxin administration. These findings suggest that previously reported values for digitoxin bioavailability using non-specific methods may be falsely elevated due to the presence of digitoxin metabolites in serum.