Membrane expression of platelet calpain

Platelet calpain has many platelet substrates, including external membrane proteins. We thus investigated whether platelet calpain II was associated with platelet membranes in unstimulated and thrombin- activated platelets. A monospecific, goat polyclonal antibody was reared to purified platelet calpain II. Sixteen whole platelet lysates were found to contain 4.5 +/- 0.7 micrograms calpain antigen II per 10(8) platelets (mean +/- SEM) as determined by a competitive enzyme- linked immunosorbent assay. Using the dipeptide fluorogenic substrate, Suc-Leu-Tyr-MCA, 17 human platelet lysates contained 3.6 +/- 0.4 micrograms calpain activity per 10(8) platelets. Platelet calpain II was associated with the Triton X-100 insoluble platelet cytoskeletons from both unstimulated and thrombin-activated platelets. When compared with the total cell content of platelet calpain II, calpain antigen (10% to 13%) and calpain activity (24% to 28%) was associated with platelet cytoskeletons in unstimulated and thrombin-activated platelets, respectively. On immunoblot, the heavy chain (80 Kd) of calpain II was detected in platelet cytoskeletons. Subcellular fractionation studies on both unstimulated and thrombin-activated platelets, revealed that half of the total platelet calpain II antigen was associated with cytosol, and the other half was associated with the membrane fraction. Platelet calpain II was not seen on the surface of unstimulated, paraformaldehyde fixed platelets by immunofluorescence. However, on thrombin-activated platelets, rim immunofluorescence was seen, indicating that activated platelets externalize their calpain. This observation was confirmed by the finding that about 2,000 molecules per platelet of an 125I-anti-calpain II Fab' specifically bound to thrombin-activated but not unstimulated platelets. Both dibucaine (1 mmol/L) and platelet activating factor (1.86 mumol/L) in the absence of external Ca++, but not collagen (5 micrograms/mL) or ionophore A23187 (2.5 mumol/L) in the absence of external Ca++, were also able to externalize platelet calpain II antigen, as indicated by a similar level of specific 125I-anti-calpain II Fab'-platelet binding. These combined studies indicate that platelet calpain II is a major protein, comprising 2% of total platelet protein, a substantial portion of which is membrane-associated. When platelets are activated by thrombin and platelet activating factor, calpain II antigen also becomes present on the external platelet surface.     

High-dose combination alkylating agents with autologous bone marrow support: a Phase 1 trial

Twenty-nine patients were treated with 31 courses of high-dose combination cyclophosphamide, cisplatin, and carmustine (BCNU) with and without melphalan with autologous bone marrow support. Toxicity was dose related. The maximum tolerated dose for cyclophosphamide, cisplatin, and BCNU in this combination in mg/m2 was 5,625, 165, and 600, respectively. Further dose escalation was precluded by the development of multiple organ toxicity, including venoocclusive disease, refractory thrombocytopenia, and hypertension. Melphalan added to the three-drug combination produced excessive renal and gastrointestinal toxicity. Objective tumor regression occurred in 21 of 25 evaluable cases. The results suggest that selected alkylating agents can be combined in full or nearly full doses before nonmyelosuppressive dose-limiting toxicity precludes further escalation.     

Familial glucocorticoid deficiency in a girl with familial hypophosphatemic rickets

Familial glucocorticoid deficiency is a rare multisystem disorder characterized by glucocorticoid deficiency with normal mineralocorticoid activity, achalasia of the cardia, and alacrima. Familial hypophosphatemic rickets is characterized by selective renal phosphate wasting with subsequent hypophosphatemia and an inappropriately low 1,25-dihydroxyvitamin D concentration for the degree of hypophosphatemia. A 6-year-old girl with both disorders is described. A biochemical relationship between familial glucocorticoid deficiency and familial hypophosphatemic rickets could not be defined; the influence of cortisol on her serum calcium level, phosphorus level, and rickets, as well as the natural history of these two entities, is described.