Zoledronic acid (ZOL) is a highly potent heterocyclic bisphosphonate which has been shown to inhibit bone resorption in short-term experiments in young growing animals. In this investigation we have evaluated the effects of a 1-year administration to mature, ovariectomized (OVX) rats as a model for postmenopausal osteoporosis in order to elucidate (1) the temporal changes in urinary biochemical markers of bone turnover and femoral bone mineral density (BMD), (2) to measure changes of static and dynamic histomorphometric parameters and mechanical strength, and (3) to assess the preventive effects of chronic treatment with ZOL on these parameters. In urine, deoxypyridinoline increased after OVX and was significantly reduced by ZOL administration, indicative of a reduced bone collagen turnover. These changes were accompanied by alterations of tibial cancellous bone: trabecular bone volume and parameters of bone architecture were significantly augmented by ZOL and bone formation rates fell as a consequence of suppressed bone turnover, but were still measurable. No signs of "frozen bone" or osteomalacia could be detected. BMD of the whole femurs rose in sham-operated control animals (SHAM) during the entire experimental period, whereas in OVX animals, BMD plateaued after 32 weeks at a lower level. ZOL at a low dose (0.3 mg/kg/week s.c.) did not alter whole femur BMD, but at higher doses (1.5 and 7.5 mg/kg/week s.c.) BMD increased to the level of the SHAM group. A distinct pattern was noted for the distal quarter of the femur, a region rich in cancellous bone: BMD initially increased in all treatment groups except the OVX group, and at a later stage fell again at a comparable rate irrespective of treatment. Mechanical stability, as assessed by a 3-point bending test, was significantly increased by all doses of ZOL and exceeded OVX and sham-operated controls. The effects on mechanical properties were observed at a low dose which did not measurably increase femoral BMD after 1-year treatment. Multiregression analysis revealed a significant positive correlation between maximum load and BMD, and a significant negative correlation of maximum load with labeled perimeter, a marker of bone formation and turnover. No significant correlation was found with urinary deoxypyridinoline, a marker of bone resorption. The data show that mechanical testing detects improvements of functional bone quality following low dose bisphosphonate treatment which are not identified by standard DXA measurements of BMD.

To study the anti-resorptive effects of zoledronate and pamidronate on growing long bones we have performed a histomorphometric analysis of the three regions of the proximal tibial cancellous bone of bone formed before, during, and after drug treatment. Male rats (190-220 g) were treated subcutaneously for 10 days with zoledronate (0.028-2.8 g/kg) or pamidronate (3.7-370 g/kg) and sacrificed 5 days later. To delineate the three regions of cancellous bone, and for dynamic bone histomorphometry, calcein and demeclocycline were injected at various times. Both bisphosphonates caused a dose-dependent suppression of cancellous bone turnover and resorption to produce an increase in cancellous bone, but zoledronate was 100 times more potent than pamidronate. The increase in the bone amount and connectivity was more pronounced in the bone formed during treatment where transient bone resorption and normal bone formation led to a positive bone balance. In the bone formed before treatment, inhibition of bone resorption associated with reduced bone formation produced a net gain in amount of bone. Although both bone regions showed a positive bone balance, more bone accumulated in the bone formed during treatment probably because its trabecular bone surface was three times greater. In the primary spongiosa formed after treatment, a moderate increase in the bone amount and connectivity was observed only at the highest dose of both bisphosphonates. The bone formed before, during, and after treatment with bisphosphonates responds differently due to differences in bone architecture, rates of modeling and remodeling, and period of drug exposure. Anat. Rec. 249:458-468, 1997. 1997 Wiley-Liss, Inc. Key words: pamidronate; zoledronate; bisphosphonate; rat; bone histomorphometryThe bisphosphonate compound zoledronate (CGP 42446) is a very potent antiresorptive agent in several pharmacological models (Green et al., 1994). In a previous pilot experiment we studied the effects of zoledronate and pamidronate on static histomorphometric parameters of cancellous bone in rat tibia (Pataki et al., 1990). We reported that zoledronate and pamidronate induce a dose-dependent increase in the proximal tibial metaphyseal cancellous bone and that zoledronate was at least 100 times more potent than pamidronate in accumulating bone mass. Both compounds caused a dose-dependent decrease in osteoid perimeter and serum levels of osteocalcin, alkaline phosphates, and tartrate-resistant acid phosphates, suggesting that the increase in bone resulted from depression of bone resorption and formation. In the present study, both static and dynamic morphometric parameters were investigated after administration of zoledronate and compared to the effects of the reference drug pamidronate. In addition to morphometric investigations, the effects on cortical and cancellous bone were also analyzed chemically.Previous investigators characterized the effects of bisphosphonates on the entire metaphysis in growing rats. This is the first report that analyzes the his...

This study investigated the protective effect of long-term treatment with the bisphosphonate zoledronic acid on bone mass, structure, and strength in adult, estrogen-deficient rats. Rats were ovariectomized (OVX) at the age of 4 months and divided into four groups of 20 rats: one group of saline-treated OVX controls, and three groups of OVX rats treated with 0.3, 1.5, or 7.5 microg/kg/week s.c. zoledronic acid (ZOL). An additional group of sham-operated, saline-treated rats served as normal controls. Biochemical assays were performed after 16 and 51 weeks, respectively, and bone mineral density (BMD) determinations after 17 and 52 weeks, respectively. Before the end of the experiment animals were injected with tetracyclines for the determination of dynamic bone indexes. Finally, animals were sacrificed after 52 weeks, and vertebral bones (LV5) were subjected to mechanical compression testing. LV4 were used for histology and LV2 for microcomputed tomography. ZOL treatment abolished the rise of osteocalcin and reduced urinary deoxypyridinoline excretion. BMD was reduced in the OVX group in comparison to sham controls, and the decline was dose-dependently prevented by ZOL treatment. Tetracycline labeling showed a significant increase in bone formation rate (BFR) in OVX rats which was abolished by ZOL treatment. The same was observed for osteoid perimeter (Os.Pm) suggesting that ZOL diminished the high bone turnover associated with estrogen deficiency. Architectural parameters (BV/TV, Tb.Th*, Tb.N*, Tb.Sp*, SMI, CD) underwent the expected changes toward structural deterioration which was completely prevented by ZOL administration at doses of 1.5 and 7.5 microg/kg/week s.c. Similar results were obtained in compression testing: maximum stress fell significantly after OVX, and this effect was effectively prevented by ZOL treatment. Regression analysis suggests that in this rat model, SMI and Tb.Th* significantly contribute to compressive strength, albeit to a smaller degree than total cross-sectional area. The data further suggest that in the aged OVX rat, SMI and TB.Th* change in an interdependent way. ZOL prevents this process by inhibiting plate thinning and the transition into rod-shaped trabeculae.

The cerebroprotective properties of the competitive NMDA antagonist D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 40116) were evaluated in a rat model of focal cerebral ischemia. CGP 40116 (5-40 mg/kg i.v.) was injected immediately following permanent occlusion of the left middle cerebral artery (MCA). MK 801 (1 or 3 mg/kg i.v.), D-CPPene (20 mg/kg i.v.), and CGS 19755 (40 mg/kg i.v.) were used for comparison. Lesion volume was assessed using in vivo magnetic resonance imaging, which in initial experiments with parallel histological determinations proved to be an accurate method for the measurement of brain infarction and the determination of a cerebroprotective drug effect. CGP 40116 dose-dependently reduced the volume of cortical infarction, with an ED50 of 11 mg/kg i.v. and a maximal effect equivalent to a 62% reduction in cortical edema volume. Its cerebroprotective efficacy was thus comparable to that of MK 801. The rank order of potency for the NMDA antagonists was MK 801 > CGP 40116 approximately D-CPPene > CGS 19755. Neuroprotection by CGP 40116 was still apparent when treatment was started 30 min after MCA occlusion. It is concluded that CGP 40116 is an effective cerebroprotectant with potential clinical utility for amelioration of focal cerebral ischemic damage.

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