Effect of RenaGel, a non-absorbable, cross-linked, polymeric phosphate binder, on urinary phosphorus excretion in rats.

BACKGROUND: Normalization of serum phosphorus is critical in the treatment of End Stage Renal Failure patients. Aluminum or calcium based phosphate binders, while efficacious, are associated with potential adverse side effects and toxicities. We have developed RenaGel, a novel, non-absorbed hydrogel which binds dietary phosphate leading to increased fecal excretion, decreased absorption and decreased serum phosphorus levels. In this paper, we present results from both in vitro and in vivo studies in which we examined the efficacy of this novel phosphate binder. METHODS: In vitro, RenaGel was suspended in the test solution, and the mixture was stirred for 1 hour at room temperature. The solid was then filtered off, and the residual liquid analyzed for phosphate. In vivo, RenaGel was mixed in rodent feed at different concentrations and fed to normal rats for up to 4 days. Urine was collected and analysed for phosphate content. RESULTS AND CONCLUSIONS: In vitro binding studies demonstrate that RenaGel has an extremely high phosphate binding capacity. At an estimated physiological concentration of 5 mM phosphate, RenaGel binds 2.6 mmole phosphate/g of phosphate binder. The in vivo binding study shows that RenaGel mixed into the diet decreased urinary phosphorus excretion in a dose dependent manner. RenaGel particles with a 23 microns mean diameter are more efficacious than the larger ones. In conclusion, the above studies indicate that RenaGel is a potent phosphate binder. RenaGel contains no calcium or aluminum and offers an alternative to existing phosphate binder treatments.

Absorption, distribution and excretion of GT31-104, a novel bile acid sequestrant, in rats and dogs after acute and subchronic administration.

The absorption, distribution, and excretion of GT31-104, a novel bile acid sequestrant, was studied in rats and dogs after both acute and subchronic oral administration. The polyallylamine backbone of GT31-104 was labeled with tritium and one of the alkyl side chains was labeled with 14C. The mean blood and plasma concentration of [3H, 14C]GT31-104 in rats, in both treatment regimens, was negligible at all time points, with the highest amount observed being 0.69 microgram eq/g blood; in dogs the mean blood and plasma concentration of [3H, 14C]GT31-104 was below the limit of quantitation (< 0.001% total dose) at all time points. In both rats and dogs, the mean total urinary excretion of [3H, 14C]GT31-104 was approximately 0.06% of the total dose. The fecal excretion data indicates that both 3H- and 14C-derived radioactivity was excreted entirely in the feces. Mean total radioactivity excreted in the feces ranged from approximately 95 to 105% in the rats and 92 to 102% in the dogs. Across the different treatment regimens, in both species, tissue concentrations were negligible (< 0.01% total dose) and no differences in tissue profile were noted, indicating that there was no effect of pretreatment on [3H, 14C]GT31-104 absorption. GT31-104 was extracted with water, and the water-soluble portion contained radioactivity that would correlate to approximately 0.19% of the 3H dose and 0.41% of the 14C dose; this portion probably accounted for the negligible radioactivity observed systemically. Analysis of gastrointestinal (GI) tract tissues with contents indicated that GT31-104 is rapidly cleared from the GI tract. These data indicate that GT31-104 is not absorbed from the GI tract in rats and dogs.

Characteristics of students who bring weapons to school.

PURPOSE: This study explores the relationships between social, demographic, and behavioral characteristics and self-reported carrying of a weapon to school among middle school students. The results provide a statistical profile of youth most likely to bring weapons to school and help to identify characteristics that are only spuriously related to this behavior. METHODS: Study respondents were part of an ongoing randomized evaluation of a school-based drug use prevention program in Illinois. Self-administered questionnaires were completed by 1,503 seventh and eighth graders in the spring of 1992. RESULTS: Fifteen percent of respondents brought some type of weapon to school in the past month. In a multivariate logistic regression model, being male, not living with both parents, not feeling close to parents, drinking heavily, participating in fights, damaging school property, and perceiving that at least a few other students brought weapons to school, were significantly associated with weapon carrying. Victimization and fear for safety in school were not significantly associated with weapon carrying in the multivariate model. CONCLUSIONS: Study results suggest that both the structure and the dynamics of the family play an important role in weapon carrying behavior. Weapon carrying also appears to cluster with other deviant behaviors. Furthermore, the findings suggest that weapons are not brought to school because of a heightened need for protection, but rather may be in response to normative influences in school.

Long-term evaluation of drug abuse resistance education.

Project DARE (Drug Abuse Resistance Education) is the most prevalent school-based drug-use prevention program in the United States, but there is little evidence of its effectiveness. Results from a longitudinal evaluation of the program in 36 schools in Illinois provide only limited support for DARE's impact on student's drug use immediately following the intervention, and no support for either continued or emerging impact on drug use 1 or 2 years after receiving DARE instruction. In addition, DARE had only limited positive effects on psychological variables (i.e., self-esteem) and no effect on social variables (e.g., peer resistance skills). Possible substantive and methodological explanations for the relative lack of DARE's effectiveness observed in this study are discussed.

Enantiomers of 7-(2,3-epoxypropoxy)actinomycin D as dual-action DNA-acting antitumor agents.

Enantiomeric forms of (+/-)-EPA [racemic 7-(2,3-epoxypropoxy)actinomycin D] have been synthesized; these are (R)-(+)- and (S)-(-)-EPA, which are active against a range of actinomycin resistant and marginally responsive tumors. The R-(+) enantiomer is uniformly superior to the other forms in all the tumor lines tested. These enantiomers act by binding to DNA, both by intercalation and alkylation at the guanine base of DNA. They are superior to actinomycin D in their in vitro activity against mouse leukemias (L1210 and P388/ADR) and mouse melanoma B16. This superior activity is also evident against all the preceding mouse leukemias and against solid tumors B16 and C26 in vivo. In biochemical action, the enantiomers behave similarly and act primarily by inhibiting DNA synthesis in tumor cells; the only difference found was in their preference for sites in DNA bases during alkylation. The R-(+) enantiomer generates an adduct that is believed to be bonded to the N7-site of guanosine; conversely, the S-(-) isomer forms two adducts with DNA that are different from the preceding one by HPLC and are tentatively assigned O6-guanosine-substituted structures on the basis of their UV, CD, and other chemical behaviors.

Synthesis and biological properties of actinomycin D chromophoric analogues substituted at carbon 7 with aziridine and cyclopropyl functions.

The growing importance of functionalized tricyclic rings, e.g., cyclopropyl and aziridine, in numerous organic biomolecules led us to develop syntheses of novel actinomycin D (AMD) analogues substituted with aziridine and cyclopropyl functions. Reaction of 7-hydroxyactinomycin D with 1-aziridineethyl iodide and bromomethylcycloporopane afforded the desired 7-[2-(1-aziridinyl)ethoxy] and cyclopropylmethoxy analogues, respectively. Calf thymus DNA binding of these analogues was comparable to that of AMD as examined by UV-vis difference spectral measurements, CD techniques, and relaxation of supercoiled closed circular SV40 DNA, indicating an intercalative mode of binding to the DNA duplex. Thermal denaturation of DNA experiments employing higher temperatures than room temperature exhibit a thermal lability of the DNA analogue complexes, suggestive of a probable covalent bond formation with DNA bases. The analogues were found to be 1/4-1/40 as cytotoxic to human lymphoblastic CCRF-CEM leukemia and B16 melanoma cells in vitro as AMD, with ID50 values in the nanomolar concentration range.

Synthesis and biological properties of actinomycin D chromophoric analogues substituted at the 7-carbon with aziridine and aminopropoxy functions.

The growing importance of functionalized aziridines in numerous organic biomolecules led us to develop syntheses of novel actinomycin D (AMD) analogues substituted with an aziridine. Reaction of 7-hydroxyactinomycin D with 2-(iodomethyl)aziridine produced the desired 7-(2-aziridinylmethoxy)actinomycin analogue. In an attempt to develop an alternate route to this analogue, 7-(2-azido-3-iodopropoxy)actinomycin was subjected to reduction with dimethylamine-borane complex; the reaction did not produce the three-membered aziridine; instead the reaction product was found to be linear 7-(2-aminopropoxy)actinomycin D. Calf-thymus-DNA binding of these analogues was comparable to that of AMD as examined by UV-visible difference spectral measurements, thermal denaturation of DNA, and CD techniques. The analogues were found to be about 1/4 to 1/30 as cytotoxic to human lymphoblastic CCRF-CEM leukemia and B16 melanoma cells in vitro as AMD.

In vitro binding of mirex by mouse hepatocytes.

Mirex (dodecachlorooctahydro-1,3,4-metheno-2H-cyclobuta[cd]+ ++pentalene) is a hepatic tumorigen that is shown to cause marked disturbances in hepatic cell ploidy in rodents. Kinetic measurements of [14C]mirex binding were performed in freshly prepared diploid (DP) and polyploid (PP) hepatocytes, as well as in erythrocytes, under controlled conditions. The binding of mirex to hepatocytes, irrespective of their ploidy, was partially Na+-dependent and totally Ca2+-independent. Variations in temperature and pH appeared to significantly inhibit mirex binding; the optimum binding was seen at 37 degrees C under physiological pH. The saturation kinetic data revealed that PP cells were saturated at a very low concentration of mirex (two- to threefold) compared to DP, exhibiting a high-affinity binding of mirex to PP with a low Km (347 nM) and Vmax (102 nmol/mg X min). The Km (550 nM) and Vmax (340 nmol/mg X min) values determined for DP cells were of higher magnitude, like those of erythrocytes (Km, 819 nM; Vmax, 330 nmol/mg X min), indicating that distinct differences exist in the binding affinities of three cell types. However, erythrocytes and DP cells showed close similarity in their Vmax values. Interestingly, mirex levels in the lipid compartments of DP and PP cells revealed no apparent differences. The results are discussed in terms of the possible susceptibility of PP cells and their role in the initiation of toxic response leading to hepatotumorigenesis in rodents.

Uptake and disposition of mirex in hepatocytes and subcellular fractions in CD1 mouse liver.

In vivo uptake and disposition of [14C]mirex by CD1 mouse liver subcellular fractions and cells of different nuclear ploidy were examined following single or multiple doses of mirex injected intraperitoneally. Significant amounts of mirex were rapidly taken up by liver (21-29%), suggesting that liver is one of the primary sites of accumulation of the chemical. Among subcellular fractions, mirex was predominantly distributed in mitochondria and microsomes in the irreversibly bound form (about 20%), although its levels fluctuated considerably with time. Mirex was completely dissociated with trichloroacetic acid treatment from both nuclear and plasma membrane fractions, although the total uptake by these fractions was markedly high. The time course of uptake and concentration-dependent disposition of mirex revealed that polyploid hepatocytes selectively accumulated higher amounts of the chemical (two to three times) compared to diploid hepatocytes. The increased affinity of polyploid cells to mirex may indicate a greater susceptibility of this cell type to the chemical insult and also may suggest a possible early involvement of polyploids in the tumorigenic process in rodent livers.