Measurement of urinary excretion of nonisomerized and beta-isomerized forms of type I collagen breakdown products to monitor the effects of the bisphosphonate zoledronate in Paget's disease.

OBJECTIVE: We have previously shown that the woven pagetic bone in patients with Paget's disease is characterized by an impaired degree of beta-isomerization of C-telopeptides of type I collagen molecules, which results in a preferential urinary excretion of nonisomerized type I collagen C-telopeptide breakdown products (CTX). The aim of this study was to measure the urinary excretion of nonisomerized (alpha) and beta-isomerized (beta) CTX in patients with Paget's disease treated with a bisphosphonate. METHODS: We studied 28 patients with active Paget's disease of bone who were a part of a randomized, double-blind, placebo-controlled study comparing the effects of several doses of a single injection of zoledronate, a new potent bisphosphonate. Serum bone alkaline phosphatase (BAP) and type I collagen C-terminal extension propeptide (PICP) and urinary excretion of free deoxypyridinoline (free D-Pyr), N-telopeptide breakdown products (NTX), alphaCTX, and betaCTX were measured at baseline and 5, 10, 30, and 60 days after injection. RESULTS: At baseline, all markers were significantly increased in the patients compared with a group of 97 sex- and age-matched controls, with a greater increase in BAP (12-fold), NTX (19-fold), and alphaCTX (10-fold) compared with PICP (2.2-fold), free D-Pyr (2.5-fold), and betaCTX (3-fold). The ratio of alphaCTX to betaCTX was about 3-fold higher than in controls (2.1 versus 0.76; P < 0.001). After a single intravenous injection of zoledronate (200 or 400 microg), all markers decreased within 5 days, except for BAP and free D-Pyr, which decreased on day 10. The maximum decrease was greater and occurred faster for NTX, alphaCTX (-55% after 10 days), and betaCTX (-42% after 10 days) than for free D-Pyr (-25% after 30 days). After the initial decrease, the urinary excretion of betaCTX increased between days 10 and 30 and returned to pretreatment levels after 2 months, in contrast to the sustained decrease in alphaCTX and NTX that was maintained up to 60 days. The urinary ratio of alphaCTX to betaCTX decreased significantly between days 10 and 60, and returned to within the normal range in most patients after 2 months of treatment, probably reflecting the progressive replacement of woven bone by a lamellar bone with a higher and normal degree of beta-isomerization of type I collagen, as previously documented by histology. CONCLUSION: The determination of the urinary ratio of alphaCTX to betaCTX could be useful for monitoring the effect of bisphosphonate treatment in restoring bone quality in patients with Paget's disease.

Chronic thromboxane synthase inhibition with CGS 12970 in human cyclosporine nephrotoxicity.

CsA nephrotoxicity in rats is associated with an increase in renal thromboxane production. Treatment with selective thromboxane synthase inhibitors or receptor antagonists improves renal function in these animal models. In humans, it is unclear whether intervention aimed at reducing the effects of thromboxane on the kidney will be clinically useful. However, we reported previously that thromboxane metabolite excretion is increased in CsA-treated renal allograft recipients with evidence of CsA toxicity and that 48-hr intravenous infusion of the selective thromboxane synthase inhibitor CGS 13080 improves renal function in such patients. We undertook the present study to determine the effect of more prolonged treatment with an oral thromboxane synthase inhibitor, CGS 12970, in renal transplant recipients taking CsA. We measured glomerular filtration rate and p-aminohippurate clearance before and after 4 weeks of treatment with CGS 12970 in 13 patients with renal allografts who had been treated with CsA for a mean 6.3 months and had mild renal insufficiency. Baseline serum creatinine was 1.8 +/- 0.3. Treatment with CGS 12970 resulted in 83% inhibition of urinary thromboxane B2 (TXB2), 93% inhibition of 2,3-dinor-TXB2, and 89% inhibition of 11-dehydro-TXB2, but no change in the urinary excretion of prostacyclin metabolites. However, suppression of urinary thromboxane metabolites to these levels did not significantly affect renal function. Glomerular filtration rate was 45 +/- 4 ml/min/1.73 m2 at baseline and 43 +/- 4 ml/min/1.73 m2 after 4 weeks of treatment with CGS 12970. Estimated renal plasma flow was 272 +/- 21 ml/min/1.73 m2 at baseline and 251 +/- 38 ml/min/1.73 m2 with thromboxane synthase inhibition. Thus, substantial suppression of thromboxane production with CGS 12970 did not improve renal function in CsA-treated renal allograft recipients.

Uricosuric effect of CGS-12970, a new thromboxane synthase inhibitor.

3-Methyl-2-(3-pyridyl)-1-indoleoctanoic acid (CGS-12970) is a reversible thromboxane synthase inhibitor that was noted to lower serum uric acid during preliminary trials in humans. Our clinical research unit studied 20 healthy male volunteers who received two doses of CGS-12970 12 hours apart (100, 200, 300, or 400 mg twice a day). Four subjects received placebo as a control. Serum uric acid concentrations decreased between 34% and 47%. Urinary excretion of uric acid increased between 28% and 134% within 12 hours of the first dose. Urinary excretion of uric acid returned to baseline within 24 hours after the last dose. In vitro study of bovine-creme xanthine oxidase inhibitor activity revealed minimal inhibition of xanthine oxidase by either CGS-12970 or its metabolite, CGS-12961. CGS-12970 appears to be a potent reversible uricosuric agent. We hypothesize that the uricosuric effect may be attributable to the acidic properties of CGS-12970 rather than to its inhibition of thromboxane synthase.

Effects of thromboxane synthase inhibition with CGS 13080 in human cyclosporine nephrotoxicity.

Cyclosporine is a potent immunosuppressive agent, however, its use is limited by nephrotoxicity. Increased production of the potent vasoconstrictor thromboxane A2 contributes to cyclosporine nephrotoxicity in animal models, but the role of thromboxane in human cyclosporine nephrotoxicity has not been established. We therefore studied cyclosporine-treated renal allograft recipients who had evidence of toxicity manifested by decreased renal function. We measured GFR and PAH clearance (CPAH) before, during, and one week after a 48-hour intravenous infusion of the thromboxane synthase inhibitor CGS 13080. At baseline, the urinary excretion of TXB2 and 2,3-dinor-TXB2 was elevated in the study patients compared to healthy subjects. CGS 13080 infusion caused selective and nearly complete inhibition of thromboxane metabolite excretion in all patients. Mean CPAH improved 33% from 223 +/- 45 to 298 +/- 59 ml/min/m2 (P = 0.055) during infusion, while mean GFR improved 9% from 50.1 +/- 3.9 at baseline to 54.6 +/- 4.5 ml/min/1.73 m2 (P = 0.111). The effect on GFR occurred primarily in those patients taking calcium channel blockers. The mean increase in GFR in these 5 patients was 10.0 +/- 2.8 versus -1.0 +/- 2.8 ml/min/m2 in the remainder. We conclude that thromboxane synthase inhibitors may be useful in attenuating the nephrotoxic effects of cyclosporine following renal transplantation.

Comparison of thromboxane synthetase inhibitor and methylprednisolone effects on protamine responses in dogs.

Neutralization of heparin anticoagulation by protamine produces catastrophic hemodynamic reactions in some patients. Using a canine model, we tested effects of thromboxane synthetase inhibition (CGS-13080) and glucocorticoid pretreatment on the cardiorespiratory effects of protamine. In control dogs, protamine decreased mean arterial pressure and cardiac output and increased mean pulmonary artery pressure, systemic and pulmonary vascular resistances (SVR, PVR), and airway pressure. Both CGS-13080 and methylprednisolone ameliorated some effects of protamine. CGS-13080 infusion decreased mean pulmonary artery pressure, SVR, and airway pressure after protamine injection relative to controls. Cardiac output and PVR were unaffected by the drug, whereas the decrease in mean arterial pressure was prolonged. Plasma thromboxane A2 metabolite (TXB2) concentrations were lower and prostacyclin metabolite (6-keto PGF1 alpha) concentrations were higher compared with that of controls. These experiments support a role for TXA2 in the response to protamine. Methylprednisolone pretreatment produced larger cardiac output and lower airway pressure after protamine injection compared with controls. Mean arterial pressure was improved, but not significantly. Mean pulmonary artery pressure, SVR, and PVR were not different from that of controls; TXB2 and 6-keto PGF1 alpha were unaffected. The effects of methylprednisolone appear unrelated to arachidonic acid metabolism, as TXB2 and 6-keto PGF1 alpha levels were unaffected.

Pharmacokinetics of CGS 12970 and inhibition of thromboxane synthesis after oral administration in healthy adults.

The pharmacokinetics and pharmacodynamics of biochemical effect of a selective thromboxane synthase inhibitor, CGS 12970, were studied in healthy male volunteers after a dosing scheme of either 200 mg once daily or 100 mg twice a day for 6 days. The peak plasma concentration appeared 1 to 2 hours after administration, followed by a biexponential decline with half life values of about 1 and 7 hours, respectively. The mean oral clearance was 16 L/hr. Biochemically, the capacity of the platelets to form thromboxane A2 ex vivo (serum) was inhibited greater than 90% at both doses. In contrast to the short plasma half-life, the suppression of ex vivo serum thromboxane production was maintained greater than 70% to 80% at 48 hours after dosing. Inhibition of the thromboxane production in vivo (urine) was also substantial, but incomplete at both doses (200 mg daily; thromboxane B2, 75%; 2,3-dinor-thromboxane B2, 83%; 11-dehydrothromboxane B2, 90%). The urinary excretion, however, returned to the predose level at the end of a 1-week follow-up period after the last dosing. In conclusion, CGS 12970 is an orally active, reversible inhibitor of thromboxane synthase with a prolonged duration of action in humans.

Fetal and maternal response to intravenous infusion of a thromboxane synthetase inhibitor.

Pharmacologic inhibition of thromboxane synthetase activity has reversed the clinical manifestations of toxemia in the ovine model. To investigate placental transfer and fetal effects of a selective thromboxane synthetase inhibitor, CGS13080 (Ciba-Geigy, Summit, N.J.) was intravenously infused into eight singleton- or twin-bearing ewes near term. During CGS 13080 infusion (0.1 mg/kg/hr), maternal steady-state CGS 13080 levels of 102 +/- 18 ng/ml were achieved within 30 minutes and maternal serum thromboxane generation decreased significantly (13 +/- 3 to 4 +/- 1 ng/ml). However, fetal serum levels of CGS 13080 were only 4% of peak maternal concentrations and fetal serum thromboxane generation did not change. There was no evidence of change in uterine blood flow, maternal or fetal blood pressure, heart rate, blood gas values, or fetal or maternal metabolites of prostacyclin or prostaglandin E2 during the study. We speculate that CGS 13080 may be efficacious in the treatment of human pregnancy-induced hypertension.