Inhibitory effects of a cyclosporin derivative, SDZ PSC 833, on transport of doxorubicin and vinblastine via human P-glycoprotein

The inhibitory effects of SDZ PSC 833 (PSC833), a non-immunosuppressive cyclosporin derivative, on the P-glycoprotein (P-gp)-mediated transport of doxorubicin and vinblastine were compared with those of cyclosporin A (Cs-A). The transcellular transport of the anticancer drugs and PSC833 across a monolayer of LLC-GA5-COL150 cells, which overexpress human P-gp, was measured. Both PSC833 and Cs-A inhibited P-gp-mediated transport of doxorubicin and vinblastine in a concentration-dependent manner and increased the intracellular accumulation of doxorubicin and vinblastine in LLC-GA5-COL150 cells. The values of the 50%-inhibitory concentration (IC50) of PSC833 and Cs-A for doxorubicin transport were 0.29 and 3.66 microM, respectively, and those for vinblastine transport were 1.06 and 5.10 microM, respectively. The IC50 of PSC833 for doxorubicin transport was about 4-fold less than that for vinblastine transport, suggesting that the combination of PSC833 and doxorubicin might be effective. PSC833 itself was not transported by P-gp and had higher lipophilicity than Cs-A. These results indicated that the inhibitory effect of PSC833 on P-gp-mediated transport was 5- to 10-fold more potent than that of Cs-A, and this higher inhibitory effect of PSC833 may be related to the absence of PSC833 transport by P-gp and to the higher lipophilicity of PSC833.     

Characterization of a novel bisacridone and comparison with PSC 833 as a potent and poorly reversible modulator of P-glycoprotein

Novel compounds, composed of two acridone moieties connected by a propyl or butyl spacer, were synthesized and tested as potential modulators of P-glycoprotein (P-gp)-mediated multidrug resistance. The propyl derivative 1,3-bis(9-oxoacridin-10-yl)-propane (PBA) was extremely potent and, at a concentration of 1 microM, increased steady state accumulation of vinblastine (VLB) approximately 9-fold in the multidrug-resistant cell line KB8-5. In contrast to the readily reversible effects of VRP and cyclosporin A on VLB uptake and similar to the effects of the cyclosporin analog PSC 833, this modulation by PBA was not fully reversed 6-8 hr after transfer of cells to PBA-free medium. Continuous exposure to 3 microM PBA was nontoxic and could completely reverse VLB resistance in KB8-5 cells. Consistent with its effects on VLB transport, the drug resistance-modulating effect of PSC 833 was significantly more persistent than that of VRP. However, the effect of PBA was, like that of VRP, rapidly reversed once the modulator was removed from the extracellular environment. PBA was able to compete with radiolabeled azidopine for binding to P-gp and to stimulate P-gp ATPase activity. However, both the steady state accumulation of PBA and the rate of efflux of PBA were similar in drug-sensitive KB3-1 and drug-resistant KB8-5 cells, suggesting that this compound is not efficiently transported by P-gp. These results indicate that PBA represents a new class of potent and poorly reversible synthetic modulators of P-gp-mediated VLB transport.     

Modulation of the tumor disposition of vinca alkaloids by PSC 833 in vitro and in vivo

PSC 833, a nonimmunosuppressive cyclosporin, is able to inhibit the efflux of antitumor drugs mediated by P-glycoprotein (P-gp). The purpose of the present study is to compare the effect of PSC 833 on the tumor disposition of [3H]vincristine ([3H]VCR) and [3H]vinblastine ([3H]VBL) in in vitro and in vivo experiments from a pharmacokinetic point of view. In in vitro experiments, the effect of PSC 833 was investigated on the cellular uptake of [3H]VCR and [3H]VBL by HCT-15 and COLO 205, human colorectal tumor cell lines with extensive and minimal expression of P-gp, respectively. PSC 833 (2 microM) increased the cellular uptake of [3H]VCR and [3H]VBL by HCT-15 cells, but not that by COLO 205 cells, 8- and 6-fold, respectively, without affecting the initial influx rates. In addition, 2 microM PSC 833 reduced the efflux of [3H]VCR from HCT-15 cells to a level comparable with that from COLO 205 cells. Furthermore, the effect of PSC 833 on the tumor disposition of intravenously administered [3H]VCR and [3H]VBL was studied in tumor inoculated mice. Infusion of PSC 833 (10 microg/hr/mouse) increased the HCT-15 tumor disposition of [3H]VBL and [3H]VCR in vivo to a level comparable with that observed in vitro. These findings demonstrate that PSC 833 enhances the tumor disposition of vinca alkaloids by inhibition of P-gp-mediated efflux not only in vitro but also in vivo in a solid tumor model.     

Cyclosporin A and PSC 833 prevent up-regulation of MDR1 expression by anthracyclines in a human multidrug-resistant cell line

We have previously demonstrated that within 24 h of exposure of the CEM/A7R cell line to epirubicin (EPI), MDR1 gene expression is induced. The aim of the current study was to investigate the role of cyclosporin A (CyA) and PSC 833, two biochemical modulators of the classical multidrug-resistant phenotype, in this model. CEM/A7R cells were exposed to EPI in the presence or absence of various concentrations of CyA or PSC 833. MDR1 expression was assessed using Northern blot analysis and quantitated using a phosphorimager. P-glycoprotein (P-gp) expression was analyzed by the determination of MRK16 binding using flow cytometry. P-gp function was measured in an assay of [3H]daunomycin accumulation. The coincubation of CyA or PSC 833 with EPI prevented the increase in MDR1 gene expression induced by EPI alone. This effect of the two modulators was dose dependent. Neither modulator alone had any significant effect on the expression of MDR1. In these experiments, changes in MDR1 expression correlated with changes in P-gp levels (based on MRK16 binding) and P-gp function. Thus, both PSC 833 and CyA appear to prevent the induction of MDR1 gene expression caused by the short-term exposure of CEM/A7R cells to EPI.     

Changes in doxorubicin distribution and toxicity in mice pretreated with the cyclosporin analogue SDZ PSC 833

SDZ PSC 833 (PSC 833) is a cyclosporin A analogue that is under clinical investigation in combination with doxorubicin (Dx) or other anticancer agents as a type-1 multidrug resistance (MDR-1)-reversing agent. The present study was focused on the effects of PSC 833 on the distribution and toxicity of Dx in non-tumor-bearing CDF1 male mice. Mice were given PSC 833 i.p. at 30 min before i.v. Dx treatment. Dx levels were determined by a high-performance liquid chromatography (HPLC) assay at different times during a 72-h period following Dx treatment in the serum, heart, intestine, liver, kidney, and adrenals of mice. In all tissues, Dx area under the concentration-time curve (AUC) values were much greater in mice receiving 10 mg/kg Dx in combination with 12.5 or 25 mg/kg PSC 833 than in mice receiving Dx alone. The highest increase in Dx concentrations was found in the intestine, liver, kidney, and adrenals. Lower, albeit significant, differences were found in the heart. PSC 833 did not appear to influence either urinary or fecal Dx elimination or Dx metabolism to a great extent. Doses of PSC 833 devoid of any toxicity potentiated the acute and delayed toxicity of Dx dramatically. The mechanism responsible for this enhanced toxicity has not yet been elucidated but is likely to be related to an increased tissue retention of Dx due to inhibition of the P-glycoprotein (Pgp) pump by PSC 833, as has recently been proposed for cyclosporin A.     

Cyclosporin A and cyclosporin SDZ PSC 833 enhance anti-CD5 ricin A-chain immunotoxins in human leukemic T cells

Recent studies have shown that cyclosporin A (CsA) may affect ricin A-chain immunotoxin (RTA-IT) therapy. In this study, we evaluated the ability of CsA and its nonimmunosuppressive analog, SDZ PSC 833, to enhance anti-CD5 T101 RTA-ITs in vitro. Both 4 mumol/L CsA and 4 mumol/L SDZ PSC 833 significantly and specifically enhanced the cytotoxic activity of T101 RTA-IT on the human lymphoblastic T-cell line, CEM III (101-fold and 105-fold, respectively). Furthermore, these Cs also enhanced the cytotoxicity of the more potent T101 F(ab')2 RTA-IT (ninefold and eightfold, respectively). The effect of human plasma, originating from four patients enrolled in a phase I high-dose CsA regimen, was examined on T101 RTA-IT cytotoxicity on CEM III cells. In each case, with plasma CsA levels between 3,090 and 4,860 ng/mL (2.5 to 4 mumol/L), a significant increase in T101 RTA-IT-mediated cytotoxicity was observed ranging from 31% to 60%. Neither CsA nor SDZ PSC 833 affected the rate of RTA-IT binding, internalization, intracellular trafficking, or degradation. Analysis of internalized T101 RTA-IT molecules showed that these were essentially intact, which suggests that these enhancers may act only on a small population of RTA-ITs that escapes present investigational techniques. In conclusion, because the concentrations used are clinically achievable, Cs appear to be promising agents for in vivo enhancement of RTA-ITs.     

Analysis of the interactions of SDZ PSC 833 ([3'-keto-Bmt1]-Val2]-Cyclosporine), a multidrug resistance modulator, with P-glycoprotein

Multidrug resistance (MDR) is considered to be an important impediment to the effective treatment of cancer. P-glycoprotein, the drug efflux pump that mediates this resistance, can be inhibited by a wide variety of pharmacological agents, resulting in the circumvention of the MDR phenotype. SDZ PSC 833 ([3'-keto-Bmt1]-Val2]-cyclosporine), a nonimmunosuppressive cyclosporine D derivative, was identified to be a potent MDR modulator (Gaveriaux et al. J. Cell Pharmacol. 2:225-234; 1991). In this study, the interactions of P-glycoprotein with two cyclosporine derivatives, SDZ PSC 833 and cyclosporine A (CsA, Sandimmune), were analyzed. SDZ PSC 833 enhanced the sensitivity of the MDR cells to anticancer drugs by increasing the accumulation and inhibiting the efflux of cytotoxic agents from resistant cells more efficiently than CsA. The two cyclosporine analogs competed with the labeling of P-glycoprotein by a photoactive cyclosporine derivative. In addition, membrane vesicles derived from resistant cells bound SDZ PSC 833. However, CsA was transported by P-glycoprotein, whereas SDZ PSC 833 was not actively transported. This resulted in a prolonged inhibitory effect by SDZ PSC 833. The studies suggest that the binding of SDZ PSC 833 to P-glycoprotein in the absence of its transport from MDR cells mediated its high potency as an MDR reversing agent. In addition, the comparison of the two cyclosporine analogs indicated that limited chemical modifications of MDR reversing agents can affect their potential to inhibit P-glycoprotein function.     

Full blockade of intestinal P-glycoprotein and extensive inhibition of blood-brain barrier P-glycoprotein by oral treatment of mice with PSC833

Mice lacking mdr1-type P-glycoproteins (mdr1a/1b [-/-] mice) display large changes in the pharmacokinetics of digoxin and other drugs. Using the kinetics of digoxin in mdr1a/1b (-/-) mice as a model representing a complete block of P-glycoprotein activity, we investigated the activity and specificity of the reversal agent SDZ PSC833 in inhibiting mdr1-type P-glycoproteins in vivo. Oral PSC833 was coadministered with intravenous [3H]digoxin to wild-type and mdr1a/1b (-/-) mice. The direct excretion of [3H]digoxin mediated by P-glycoprotein in the intestinal mucosa of wild-type mice was abolished by administration of PSC833. Hepatobiliary excretion of [3H]digoxin was markedly decreased in both wild-type and mdr1a/1b (-/-) mice by PSC833, the latter effect indicating that in vivo, PSC833 inhibits not only mdr1-type P-glycoproteins, but also other drug transporters. Upon coadministration of PSC833, brain levels of [3H]digoxin in wild-type mice showed a large increase, approaching (but not equaling) the levels found in brains of PSC833-treated mdr1a/1b (-/-) mice. Thus, orally administered PSC833 can inhibit blood-brain barrier P-glycoprotein extensively, and intestinal P-glycoprotein completely. These profound pharmacokinetic effects of PSC833 treatment imply potential risks, but also promising pharmacological applications of the use of effective reversal agents.     

Effect on cell kill of addition of multidrug resistance modifiers cyclosporin A and PSC 833 to cytotoxic agents in acute myeloid leukaemia

Multidrug resistance (MDR) mediated by the drug efflux pump P-glycoprotein (Pgp), may cause remission failure and relapse in patients with acute myeloid leukaemia (AML) by extruding cytotoxic agents such as anthracyclines from leukaemic cells thus allowing them to survive. Cell line data suggest that reversal of MDR is possible using modifying drugs such as cyclosporin A (CSA) and its analogue PSC 833. We have investigated the effects on cell kill of the addition of CSA and PSC 833 to daunorubicin, idarubicin, mitozantrone, etoposide and cytarabine in 52 fresh cell samples from AML patients using an MTT assay. Pgp status was determined by using monoclonal antibodies JSB-1 and MRK-16 and by assessment of rhodamine efflux. Although overall each cytotoxic-modifier combination produced significant improvements in cell kill compared to cytotoxic alone (P values ranged from P < 0.001 to P = 0.017), modifiers also produced significant cytotoxicity in their own right, and no consistent difference was seen between responses in Pgp-positive and negative groups. Up to one in three Pgp-positive samples failed to show any improvement in cell kill with the addition of CSA or PSC 833, possibly owing to co-expression of alternative resistance mechanisms not affected by the MDR modifiers. The best responses were seen when PSC 833 was added to idarubicin, with 7 out of 22 Pgp-positive cases (32%) showing five-fold improvements in cell kill or better compared to idarubicin alone. Comparison of equimolar concentrations of the two modifiers in the Pgp positive group failed to show a significant difference in cell kill, though PSC 833 was markedly superior to CSA in a minority of highly responsive samples which demonstrated clear evidence of MDR reversal. Our in vitro data suggest that MDR modifiers such as CSA and PSC 833 could play an important role in the therapy of AML and indicate the need for prospective randomised trials to assess their clinical efficacy.     

Reversal of multidrug resistance by SDZ PSC 833, combined with VAD (vincristine, doxorubicin, dexamethasone) in refractory multiple myeloma. A phase I study

SDZ PSC 833, a non-immunosuppressive cyclosporin analogue reverses multidrug resistance (MDR) in vitro by inhibiting P-glycoprotein (P-gp) mediated drug efflux. We performed a dose escalation study of SDZ PSC 833 combined with VAD chemotherapy in refractory multiple myeloma (MM). Twenty-two MM patients who were refractory to doxorubicin/vincristine/dexamethasone (VADr, n=11) or had failed multiple regimens (n=6) or were melphalan-refractory (MELr, n=5), were treated with one to three cycles of VAD combined with oral SDZ PSC 833, which was administered at escalating dosages starting at 5 mg/kg/day to 15 mg/kg/day for 7 days. The median trough and peak blood levels of SDZ PSC 833 ranged from 461/1134 ng/ml at 5 mg/kg/day to 821/2663 ng/ml at 15 mg/kg, respectively. With addition of SDZ PSC 833 (5 mg/kg) the mean plasma AUC 0-->96 h of doxorubicin as compared with control patients treated with VAD increased from 779 to 1510 ng/ml/h (P=0.0071), while the doxorubicin clearance was reduced from 47.6 to 27.8 l/h/m2 (P=0.0002). The clearance of doxorubicinol was reduced accordingly. Because of the increased plasma AUC, the dose of doxorubicin and vincristine had to be reduced in 13 patients to 50% (n=1) or 75% (n=12). A further dose-escalation of SDZ PSC 833 did not lead to a proportional increase of doxorubicin AUC. Toxicity WHO CTC grade 2 or 3 included hypoplasia (18/22), constipation (10/22), hyponatremia (3/22) and infections (6/22). A partial response or stable disease was achieved in eight and six patients, respectively. In 17 evaluable patients the mean percentage of pretreatment bone marrow plasma cells which expressed P-glycoprotein was 40%. The pretreatment in vitro rhodamin retention in CD38++ myeloma cells was reversible by 2 microM SDZ PSC 833 with 15-98% in 7/9 tested patients. In 4/5 responding patients analyzed before and after treatment with VAD + SDZ PSC 833, a reduction of P-gp + plasma cells was observed. It is concluded, that the blood concentrations of SDZ PSC 833 attained in MM patients increase with dose after oral administration. It can be safely combined with VAD chemotherapy. SDZ PSC 833 diminishes the clearance of doxorubicin, leading to an increase of the plasma AUC of doxorubicin. In addition, it is an effective inhibitor of P-gp mediated efflux of doxorubicin in myeloma tumor cells in vitro. Therefore, a proportional dose-reduction of doxorubicin and vincristine is warranted. Phase II/III studies in refractory MM are in progress to evaluate the therapeutic efficacy of SDZ PSC 833 with VAD.     

Treatment of refractory and relapsed acute myelogenous leukemia with combination chemotherapy plus the multidrug resistance modulator PSC 833 (Valspodar)

A potential mechanism of chemotherapy resistance in acute myeloid leukemia (AML) is the multidrug resistance (MDR-1) gene product P-glycoprotein (P-gp), which is often overexpressed in myeloblasts from refractory or relapsed AML. In a multicenter phase II clinical trial, 37 patients with these poor risk forms of AML were treated with PSC 833 (Valspodar; Novartis Pharmaceutical Corporation, East Hanover, NJ), a potent inhibitor of the MDR-1 efflux pump, plus mitoxantrone, etoposide, and cytarabine (PSC-MEC). Pharmacokinetic (PK) interactions of etoposide and mitoxantrone with PSC were anticipated, measured in comparison with historical controls without PSC, and showed a 57% decrease in etoposide clearance (P =.001) and a 1.8-fold longer beta half-life for mitoxantrone in plasma (P <.05). The doses of mitoxantrone and etoposide were substantially reduced to compensate for these interactions and clinical toxicity and in Cohort II were well tolerated at dose levels of 4 mg/m2 mitoxantrone, 40 mg/m2 etoposide, and 1 g/m2 C daily for 5 days. Overall, postchemotherapy marrow hypoplasia was achieved in 33 patients. Twelve patients (32%) achieved complete remission, four achieved partial remission, and 21 failed therapy. The PK observations correlated with enhanced toxicity. The probability of an infectious early death was 36% (4 of 11) in patients with high PK parameters for either drug versus 5% (1 of 20) in those with lower PK parameters (P =.04). P-gp function was assessed in 19 patients using rhodamine-123 efflux and its inhibition by PSC. The median percentage of blasts expressing P-gp was increased (49%) for leukemic cells with PSC-inhibitable rhodamine efflux compared with 17% in cases lacking PSC-inhibitable efflux (P =.004). PSC-MEC was relatively well tolerated in these patients with poor-risk AML, and had encouraging antileukemic effects. The Eastern Cooperative Oncology Group is currently testing this regimen versus standard MEC chemotherapy in a phase III trial, E2995, in a similar patient population.     

Lipoprotein (a) concentrations in patients with various dyslipidaemias

The results of operative treatment of 45 flexible flat feet (29 patients) using the sinus tarsi spacer are reported. Although radiological improvement in both the talar declination and the ground-navicular distance was found, our patients suffered from pain and functional impairment for an average period of 5 months. An unacceptably high rate of spacer dislocation was noted. Furthermore, the literature indicates spontaneous improvement as the natural history of flexible flat feet. We therefore no longer advise the sinus tarsi spacer as a routine treatment for flexible flat feet.     

Steady-state kinetic mechanism, stereospecificity, substrate and inhibitor specificity of Enterobacter cloacae nitroreductase

Enterobacter cloacae nitroreductase (NR) is a flavoprotein which catalyzes the pyridine nucleotide-dependent reduction of nitroaromatics. Initial velocity and inhibition studies have been performed which establish unambiguously a ping-pong kinetic mechanism. NADH oxidation proceeds stereospecifically with the transfer of the pro-R hydrogen to the enzyme and the amide moiety of the nicotinamide appears to be the principal mediator of the interaction between NR and NADH. 2,4-Dinitrotoluene is the most efficient oxidizing substrate examined, with a kcat/KM an order of magnitude higher than those of p-nitrobenzoate, FMN, FAD or riboflavin. Dicoumarol is a potent inhibitor competitive vs. NADH with a Ki of 62 nM. Several compounds containing a carboxyl group are also competitive inhibitors vs. NADH. Yonetani-Theorell analysis of dicoumarol and acetate inhibition indicates that their binding is mutually exclusive, which suggests that the two inhibitors bind to the same site on the enzyme. NAD+ does not exhibit product inhibition and in the absence of an electron acceptor, no isotope exchange between NADH and 32P-NAD+ could be detected. NR catalyzes the 4-electron reduction of nitrobenzene to hydroxylaminobenzene with no optically detectable net formation of the putative two-electron intermediate nitrosobenzene.     

Partial characterization of a cell-directed inhibitor of leukotaxis in human serum

A leukotactic defect is described in a man with a low cerebrospinal fluid leukocyte count in the presence of an acute listeria meningitis. On the basis of subsequent studies with his serum and normal human serum, a leukotactic inhibitor has been identified. This inhibitor, termed the cell-directed inhibitor (CDI), is relatively heat stable and nondialyzable. By ultracentrifugal analysis in sucrose density gradient, the inhibitor has been resolved into two activities with estimated sedimentation coefficients of 7 and 10 S. It interacts directly with neutrophils and monocytes to render them chemotactically defective. CDI also impairs the phagocytic function of neutrophils. Evidence is presented that an antagonist to the inhibitor is present in normal serum. CDI and its antagonist are probably normally occurring regulators of leukotaxis. In the patient studied, an elevated CDI serum level may be related to the development of the listeria infection and failure of cutaneous response to skin test antigens.     

Chemo-enzymatic synthesis of galactosylmaltooligosaccharidonolactone as a substrate analogue inhibitor for mammalian alpha-amylase

We performed chemo-enzymatic transformation of maltooligosaccharides into both end-modified oligosaccharidonolactones of potential use as substrate analogue inhibitors for mammalian alpha-amylases. Enzymatic modification of the non-reducing end glucosyl residue of the maltooligosaccharide was first performed by transglycosylation with beta-D-galactosidase from Bacillus circulans. When maltotriose and maltotetraose were the acceptors, the enzyme regioselectively synthesized 4(3)-O-beta-D-galactosyl maltotriose (LG3) and 4(4)-O-beta-D-galactosyl maltotetraose (LG4) from lactose as a donor. LG4 was further selectively hydrolyzed with a specific alpha-amylase to afford 4(2)-O-beta-D-galactosyl maltose (LG2). The anomer hydroxyl groups of LG2 and LG3 were chemically oxidized to give the corresponding lactones, 4(2)-O-beta-D-galactosyl maltobionolactone (LG2O) and 4(3)-O-beta-D-galactosyl maltotrionolactone (LG3O), respectively. LG2O and LG3O, which are competitive inhibitors for mammalian alpha-amylases, exhibited Ki values of the order of 2.8-18.0 microM, with p-nitrophenyl alpha-maltopentaoside (G5P) as the substrate. On 1H-NMR analysis, these oligosaccharidonolactones were shown to be transformed into the corresponding aldonic acid forms with time in an aqueous solution. In this case, the lactone form was essential for the occurrence of the alpha-amylase inhibitor.     

Absorption, metabolism, and serum concentrations of cholesterol in vegetarians: effects of cholesterol feeding

Serum concentrations and metabolism of cholesterol were studied in vegetarians basally and during a dietary cholesterol load. Cholesterol absorption efficiency was normal and synthesis was slightly enhanced, even though serum cholesterol precursors were not increased. The serum concentrations of total and low-density-lipoprotein cholesterol were decreased proportionally to the reduced intake and absolute absorption of cholesterol. Fecal plant sterols were negatively correlated with the absorption efficiency of cholesterol and positively with fecal sterols and cholesterol synthesis, suggesting interference of high plant sterol intakes with cholesterol absorption. Cholesterol saturation and bile acid composition of the bile were not changed. The increased serum plant sterol-cholesterol ratios were positively related to the intake and negatively to the biliary secretion of plant sterols. Cholesterol feeding increased absolute cholesterol absorption and serum concentrations of total and low-density-lipoprotein cholesterol, did not change absorption efficiency or synthesis of cholesterol, but increased fecal cholestanol excretion.     

Salicylic acid is a reducing substrate and not an effective inhibitor of ascorbate peroxidase

This communication describes the interactions of salicylic acid (SA) with plant ascorbate peroxidase (APX). Contrary to a recent report (Durner, J., and Klessig, D. F. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 11312-11316) we show conclusively that ascorbate oxidation by APX is not inhibited by SA (10 mM), but that SA is a slow reducing substrate of this enzyme. The suggestion that SA-dependent inhibition of APX in planta may result in the elevation of H2O2 levels, which in turn acts as a second messenger in systemic acquired resistance signaling, is therefore not tenable. We conclude that APX remains a key antioxidant during systemic acquired resistance following pathogenic infection of plants. The transient products of SA oxidation by APX appear to be SA free radicals that undergo subsequent chemistry. APX-dependent oxidation of SA could be essential for diminishing the detrimental effects of this phenolic acid on plant cells.     

Use of REMEDi HS in emergency toxicology for a rapid estimate of drug concentrations in urine, serum, and gastric samples

The REMEDi HS is a broad spectrum drug identification system, designed for emergency toxicology screening and forensic applications. The total analysis time is about 20 min. The current library has 555 drugs and metabolites. The system has a software routine that uses an internal standard (IS) to perform quantitative analysis for target compounds when calibrators are available; further, response factors (RF) are supplied for a rapid estimate of drug concentrations when calibrators are unavailable. In the present study, The concentrations of six drugs (bromisovalum, ephedrine, hydroxyzine, diphenhydramine, ranitidine, and lidocaine) and a metabolite of lidocaine (glycinexylidide) were determined using both methods. The slopes of the regression lines between the rapid estimate method and the IS method were generally within 20% of unity, in agreement with the manufacturer's claim. Semiquantitative estimates based on RF also showed good agreement with results obtained using multipoint calibration. These estimates were sufficient for clinical differentiation of routine and toxic levels. Our study demonstrated that the REMEDi HS is particularly useful for a rapid estimate of drug concentrations in the samples from emergency cases when calibrators are not readily available. Our study also showed that this system can be used for the therapeutic monitoring of ranitidine, bromisovalum, lidocaine, and diphenhydrmine.