Transient bleomycin-induced thrombocytopenia. A clinical study

Serotonin-deficient neonatal mice are not protected against the development of experimental bronchopulmonary dysplasia or pulmonary hypertension

Serotonin (5-hydroxytryptamine, 5-HT) is a potent pulmonary vasoconstrictor and contributes to high pulmonary vascular resistance in the developing ovine lung. In experimental pulmonary hypertension (PH), pulmonary expression of tryptophan hydroxylase-1 (TPH1), the rate limiting enzyme in 5-HT synthesis, and plasma 5-HT are increased. 5-HT blockade increases pulmonary blood flow and prevents pulmonary vascular remodeling and PH in neonatal models of PH with bronchopulmonary dysplasia (BPD). We hypothesized that neonatal tph1 knock-out (KO) mice would be protected from hypoxia-induced alveolar simplification, decreased vessel density, and PH. Newborn wild-type (WT) and tph1 KO mice were exposed to normoxia or hypoxia for 2 weeks. Normoxic WT and KO mice exhibited similar alveolar development, pulmonary vascular density, right ventricular systolic pressures (RVSPs), and right heart size. Circulating (plasma and platelet) 5-HT decreased in both hypoxia-exposed WT and KO mice. Tph1 KO mice were not protected from hypoxia-induced alveolar simplification, decreased pulmonary vascular density, or right ventricular hypertrophy, but displayed attenuation to hypoxia-induced RVSP elevation compared with WT mice. Tph1 KO neonatal mice are not protected against hypoxia-induced alveolar simplification, reduction in pulmonary vessel density, or RVH. While genetic and pharmacologic inhibition of tph1 has protective effects in adult models of PH, our results suggest that tph1 inhibition would not be beneficial in neonates with PH associated with BPD.

Early-onset thrombocytopenia during combination chemotherapy in testicular cancer is induced by vinblastine

Platelet kinetics were studied in 70 patients with testicular cancer to elicit the agent responsible for chemotherapy-induced transient early-onset thrombocytopenia; 204 treatment courses were analyzed using three different therapy protocols, which contained vinblastine and bleomycin either alone or in combination with cisplatin. Platelet count decreased significantly from the start of vinblastine administration reaching its nadir on the third day of therapy in each of the three treatment groups. Between day 4 and day 10 of the treatment cycle, platelet counts steadily increased even in patients still receiving continuous bleomycin infusions. The conclusion that the observed early-onset thrombocytopenia was caused by vinblastine was substantiated by the outcome of two additional examinations. Platelet half-life was significantly shortened 24 hours after vinblastine administration and electron microscopy revealed a dissolution of cytoplasmatic microtubules with loss of the typical discoid shape of platelets within 15 minutes after the start of therapy. Both findings occurred irrespective of the specific treatment protocol, i.e., even after nothing but vinblastine had been given. These results strongly suggest that vinblastine is the main cytostatic agent responsible for the transient early-onset thrombocytopenia observed during chemotherapy of testicular cancer.

Transient vinblastine-induced thrombocytopenia during chemotherapy with vinblastine, cis-platinum and bleomycin

An early, transient drop in peripheral blood platelets to a mean nadir value of 49% (range 31-83%) of the pretreatment value was seen in 31 patients during chemotherapy with cis-platinum, vinblastine and bleomycin (PVB). The mean number of platelets dropped by 22% during the first 24 h after the start of chemotherapy, nadir value was seen after 3 d, with recovery to 107% of pretreatment level on d 14-15. Platelet survival studies during PVB chemotherapy showed shortened platelet survival time and indicated increased destruction of platelets. Identical patterns of early, transient thrombocytopenia were seen in 6 patients treated with vinblastine only. The early fall in circulating platelets did not predict subsequent serious thrombocytopenia. There were no bleeding episodes in the 37 patients studied here, but the early thrombocytopenia seen after vinblastine therapy may possibly be of clinical importance in critically ill patients at risk for bleeding episodes. In rats, an early drop in circulating platelets occurred after a high dose of vinblastine, but not after bleomycin. Addition of bleomycin to vinblastine did not increase the vinblastine-induced thrombocytopenia. It is concluded that the early drop in peripheral blood platelets during chemotherapy with PVB is due to vinblastine.

Endothelial injury caused by antineoplastic agents

The vascular lining of the blood vessels to normal organs and malignant tissues would be expected to reflect the functional demands placed upon it. These functional requirements may be accomplished by specific biochemical macromolecules, some of which are localized on the plasma membrane of the endothelium. Considerable evidence exists that toxicity to at least some normal organs caused by antineoplastic agents is heralded by endothelial damage. This endothelial damage may reflect a specific drug-endothelium interaction, the mechanism and basis of which are not yet understood. The possibility also exists that destruction of solid tumors by currently employed antitumor agents is mediated in part by local loss of essential vasculature. Selective destruction of the tumor endothelium could be a rational and novel target to which drugs could be designed.