Risedronate treatment does not increase microdamage in the canine femoral neck.

Cortical and trabecular bone from the femoral neck of 24 adult female beagle dogs was examined for microdamage following 2 years of treatment with risedronate (NE-58095). Specimens of the femoral neck, sectioned between the femoral head and the intertrochanteric groove, were bulk stained in 1% basic fuchsin in graded alcohols and embedded in methylmethacrylate. Five transverse sections of 100 microns from each specimen were examined for microdamage and measurement of cortical and trabecular area, and three sections from each specimen were measured for calculation of trabecular and cortical bone activation frequency (Ac.f) and bone formation rate (BFR/BV) in the superior and anterior regions of the femoral neck. Although no statistical differences were observed among groups for numerical density or length of microcracks, Kruskal-Wallis analysis showed differences among groups for both cortical and trabecular bone area (p < 0.05). Ac.f was significantly lower in both cortical bone (p < 0.05) and trabecular bone (p < 0.005) of the femoral neck at all dosage levels. No significant difference was observed among groups for trabecular mean wall thickness. The hypothesis that microdamage accumulation increases following reduction in Ac.f was not supported for the canine femoral neck in this experiment. This result could be explained by the fact that microdamage does not accumulate following treatment; that transient increases in microdamage at the beginning of the study period had been repaired; or finally, that the canine femoral neck does not reflect weight-bearing conditions of clinical relevance to humans for assessment of microdamage.

Development of an acute model for the study of chloromethanediphosphonate nephrotoxicity.

Chloromethanediphosphonate (Cl2MDP), a cation chelator, is used as a therapeutic for hypercalcemia of malignancy. Cl2MDP exhibits nephrotoxic potential. Thus, a useful model has been developed to study the mechanism of injury. Intraperitoneal administration of highly exaggerated dosages, specifically 200 mg/kg b.i.d., resulted in a consistent mild to moderate extent of kidney damage after the third day of treatment in rats. Proteinuria and lowered serum phosphorus levels occur prior to onset of histopathologic changes. Injury was characterized as necrosis of proximal tubular epithelium with predilection for pars recta. Unlike many renal toxicity models, the necrosis occurs as cell lysis only after 24 to 48 hours of treatment. However, this model significantly reduces the time required to induce renal toxicity observed in routine toxicity studies from months of treatment to less than 1 week and will, thus, serve as a baseline for subsequent pathogenetic studies.

A new pyrrolizidine alkaloid metabolite, 19-hydroxysenecionine isolated from mouse hepatic microsomes in vitro.

The in vitro mouse hepatic microsomal metabolism of the macrocyclic pyrrolizidine alkaloid senecionine was studied by high-performance liquid chromatography. A muBondapak-C18 reverse-phase system was developed to study the senecionine metabolites over a wide range of polarities. Methods were further developed for the isolation of each individual metabolite. Senecic acid, senecionine N-oxide, and 19-hydroxysenecionine, a new metabolite, were isolated from the microsomal enzyme system of BALB/c mice. The metabolite, dehydroretronecine, which had previously been isolated from rat hepatic microsomes, was not detected, and minor metabolites were not identified.

Covalent binding of two pyrrolizidine alkaloids, senecionine and seneciphylline, to hepatic macromolecules and their distribution, excretion, and transfer into milk of lactating mice.

Two macrocyclic 14C-pyrrolizidine alkaloids (PA's), senecionine an seneciphylline, were studied regarding the distribution, excretion, transfer into milk, and covalent binding to hepatic macromolecules in BALB/c mice. After injection, radioactivity was rapidly excreted in the urine and feces (84% or greater) within 16 hr. The liver contained over 1.5% of the dose at 16 hr. A small amount, 0.04%, of the dose was transferred into the milk in 16 hr; the majority of radioactivity was found in the skim-milk fraction, suggesting that the PA's were transferred to the milk as water-soluble metabolites. Both PA's covalently bound to liver macromolecules (DNA, RNA, and protein). The binding to calf thymus DNA and microsomal macromolecules was measured in vitro. The binding was diminished in the absence of O2 or a NADPH-generating system or by boiling the microsomes. No inhibition of the binding by KCN was observed.

Effects of the pyrrolizidine alkaloids senecionine, retrorsine and seneciphylline on aminopyrine N-demethylase activity on the rat liver S-10 fraction.

The effects of individual pyrrolizidine alkaloids on the mixed-function oxidase (MFO) enzyme aminopyrine N-demethylase were determined in rat liver 10 000 X g supernatant. The pyrrolizidine alkaloids, senecionine, seneciphylline and retrorsine were obtained from Senecio vulgaris. Senecionine and seneciphylline were found to be linear mixed-type inhibitors while retrorsine was found to be a competitive inhibitor of aminopyrine N-demethylase. The average Ki's +/- S.E. for senecionine, seneciphylline and retrorsine were 0.18 +/- 0.02, 0.33 +/- 0.06 and 0.92 +/- 0.05 mM, respectively.

The effect of pyrrolizidine alkaloids (Senecio vulgaris) on the liver mixed-funcion oxidase system.

A model system to detect the toxicity of pyrrolizidine alkaloids (PAs) was explored. Using the liver S-10 fraction, the effect of PAs on aniline hydroxylase and aminopyrine N-demethylase was examined. PAs were toxic to the aminopyrine N-demethylase enzyme system while exerting no toxicity on the aniline hydroxylase enzyme system.