Kinetic studies on the hepatic microsomal metabolism of dimethylnitrosamine, diethylnitrosamine, and methylethylnitrosamine in the rat.

The oxidative dealkylation of dimethylnitrosamine (DMN), diethylnitrosamine (DEN), and methylethylnitrosamine (MEN) by Sprague-Dawley rat liver microsomes was studied by a colorimetric assay for the simultaneous analysis of formaldehyde and acetaldehyde. Dealkylation in each instance followed Michaelis-Menten kinetics, but the Michaelis constant (Km) for DEN was an order of magnitude smaller than the Km for DMN. Km values for demethylation and deethylation of MEN were intermediate between those for DMN and DEN. DMN inhibited-deethylase, and DEN inhibited DMN-demethylase activity. The inhibition was of a mixed type in both instances.

The effects of serum albumin and phospholipid on sterol excretion in tissue culture cells.

Serum albumin was as effective as whole serum or alpha-globulins in facilitating sterol release from strain L mouse fibroblasts. Commercial bovine serum albumin preparations, however, had markedly different absolute effects in this regard. These differences were attributable to the variation in phospholipid content of these products. All but one of these albumins enhanced sterol release when supplemented with phospholipid. The exception was fatty acid-poor albumin which contained an adequate amount of phospholipid. Among the phospholipids examined, lecithin proved to be most effective, while phosphatidylethanolamine had little potentiating influence. As the unsaturation of the test lecithins increased, enhancement of sterol release decreased. The potentiating effect of the phospholipid was in turn dependent on the protein used, since the phenomenon was not observed with non-serum proteins like ovalbumin or with non-transport serum proteins such as gamma-globulins. The results of these studies raise the possibility that serum albumin together with phospholipid can play an important role in sterol release in tissue culture cells.

Inhibition of rat hepatic dimethylnitrosamine demethylase by cyclic and acyclic nitrosamines and secondary amines.

Inhibition of hepatic dimethylnitrosamine (DMN) metabolism by a variety of cyclic and acyclic nitrosamines was demonstrated. Nitrosoproline, a noncarcinogenic nitrosamine, behaved differently from the carcinogenic nitrosamines as an inhibitor for DMN-demethylase. Secondary amines corresponding to the nitrosamines inhibited DMN-demethylase in a manner similar to the nitrosamines.

Antibody response to Escherichia coli L-asparaginase. Prognostic significance and clinical utility of antibody measurement.

By using a modification of the microtiter solid-phase radioimmunoassay, we have measured Escherichia coli L-asparaginase (L-ASP) specific IgG, IgG4, and IgE antibodies in children who received L-ASP as part of their chemotherapy for leukemia and lymphoma. In 13 children with acute lymphoblastic leukemia induced with vincristine, prednisone, and L-ASP (10,000 IU/M2 i.v. each week for 3 weeks), seven developed high titer specific IgG antibodies. Four of the seven relapsed at the time of their peaking IgG response (6-10 months). None of the six with low or absent L-ASP antibody response have relapsed (followed for 20-35 months). In six children with allergic reactions to L-ASP reinduction, all had high titers of L-ASP specific IgG4 (greater than or equal to 20 U/ml) at the time of their reaction. In 16 other children with low L-ASP IgG4 (less than 13 U/ml), none demonstrated allergic reactions to rechallenge. Specific IgE was not consistently detectable in either group. In 21 patients with leukemia or lymphoma on L-ASP with cyclophosphamide-containing regimens, none developed significant IgG antibody response, compared with seven of 13 not receiving cyclophosphamide (p less than 0.001). We conclude: (a) development of L-ASP antibodies may have prognostic significance; (b) the detection of specific IgG4 can predict L-ASP allergy; and (c) cyclophosphamide-containing regimens reduce antibody formation to L-ASP and may allow repetitive (without anaphylaxis) and more effective (avoiding neutralizing antibodies) use of L-ASP.