Microsomal incubation test of potentially hemolytic drugs for glucose-6-phosphate dehydrogenase deficiency.

The in vitro metabolizing method was modified and its ability to correctly identify eight known hemolytic and nine known nonhemolytic drugs of glucose-6-phosphate (G6PD)-deficient erythrocytes was evaluated. The technique is based on inducing in vitro drug metabolism by incubation of red cells and drug with a reduced NADP-generating system in the presence of phenobarbital-induced mouse liver microsomes. Thus, this system provides a model for in vivo metabolic function. The hemolytic potential of tested drugs is indicated by the extent of loss of reduced glutathione of G6PD-deficient erythrocytes during 60-min incubations. Complete agreement between the test and literature for nonhemolytic compounds was observed. The test also correctly identified six of the eight known hemolytic drugs and failed to identify two known hemolytic drugs (acetanilide and sulfacetamide). The test was also applied to 14 drugs about which there is uncertainty regarding hemolytic potential. Of the latter, DL-alpha-methyldopa; alpha-naphthol; beta-naphthol; 2,3, dimercaptopropanol; phenacetin; and menadione were found to react positively. We conclude that this in vitro assay system will be useful in predicting which new drugs will be hemolytic in G6PD-deficient patients.

Melting, glass transition, and apparent heat capacity of α-D-glucose by thermal analysis.

The thermal behaviors of α-D-glucose in the melting and glass transition regions were examined utilizing the calorimetric methods of standard differential scanning calorimetry (DSC), standard temperature-modulated differential scanning calorimetry (TMDSC), quasi-isothermal temperature-modulated differential scanning calorimetry (quasi-TMDSC), and thermogravimetric analysis (TGA). The quantitative thermal analyses of experimental data of crystalline and amorphous α-D-glucose were performed based on heat capacities. The total, apparent and reversingheat capacities, and phase transitions were evaluated on heating and cooling. The melting temperature (T(m)) of a crystalline carbohydrate such as α-D-glucose, shows a heating rate dependence, with the melting peak shifted to lower temperature for a lower heating rate, and with superheating of around 25K. The superheating of crystalline α-D-glucose is observed as shifting the melting peak for higher heating rates, above the equilibrium melting temperature due to of the slow melting process. The equilibrium melting temperature and heat of fusion of crystalline α-D-glucose were estimated. Changes of reversing heat capacity evaluated by TMDSC at glass transition (T(g)) of amorphous and melting process at T(m) of fully crystalline α-D-glucose are similar. In both, the amorphous and crystalline phases, the same origin of heat capacity changes, in the T(g) and T(m) area, are attributable to molecular rotational motion. Degradation occurs simultaneously with the melting process of the crystalline phase. The stability of crystalline α-D-glucose was examined by TGA and TMDSC in the melting region, with the degradation shown to be resulting from changes of mass with temperature and time. The experimental heat capacities of fully crystalline and amorphous α-D-glucose were analyzed in reference to the solid, vibrational, and liquid heat capacities, which were approximated based on the ATHAS scheme and Data Bank.

Interactions of glucose-6-phosphate dehydrogenase deficiency with drug acetylation and hydroxylation reactions.

We hypothesize that the bimodal distribution of hemolytic response by G6PG-deficient individuals to particular drugs such as sulfones may be due to the genetically determined acetylation rate of those drugs. Since metabolism, e.g., hydroxylation, may be required for these drugs to become hemolytic, genetically and environmentally determined variation in hydroxylation of a drug may also contribute to this variability in hemolytic response. To test the possibilities that acetylation and hydroxylation alter the hemolytic potential of these drugs, we incubated G6PG-deficient and normal red cells with mouse liver microsomes at two states of hydroxylase activity (uninduced and induced), an NADPH-generating system, and acetylated or unacetylated drug. We then measured GSH depletion in the cells as an indicator of prelytic cell damage. We found that in the presence of induced (high hydroxylase activity) microsomes, thiazolsulfone (Promizole) or DDS in unacetylated form caused the highest level of GSH depletion in G6PD-deficient red cells. Acetylation protected against GSH depletion. The specificity of the hydroxylation reaction in producing marked GSH depletion was shown by the protective effect of a specific hydroxylation inhibitor. Our results indicate that G6PD-deficient, genetically slow acetylators, having high microsomal activity, would be most susceptible to Promizole- or DDS-induced hemolysis, compared to other metabolic phenotypes. In addition, the bimodality in hemolytic response to Promizole probably corresponds to the bimodal distribution of acetylator phenotype in the population.

Pharmacogenetic interactions in G6PD deficiency and development of an in vitro test to predict a drug's hemolytic potential.

To summarize our results and their implications, by adding induced mouse liver microsomes to an in vitro test for the hemolytic potential of a drug in G6PD deficiency, we found that: 1) Hydroxylation appears to play an important role in activating the hemolytic potential of many drugs. 2) Use of an in vitro test system combining drug, hydroxylation system and red cell, appears to be very reliable in ruling out hemolytic potential, when it is in fact absent, and about 80% effective in identifying hemolytic potential when it is present. 3) Acetylation seems to markedly reduce the hemolytic potential of two drugs studied: promizole and DDS. The genetic polymorphism in acetylation may explain the bimodal response to promizole. 4) These studies suggest that interaction among three pharmacogenetic systems produces a given hemolytic result. Variability of hydroxylation and acetylation rates can be expected to contribute to variability in individual responses to certain hemolytic drugs.

Stereochemical elucidation and total synthesis of dihydropacidamycin D, a semisynthetic pacidamycin.

Hydrogenation of the C(4') exocyclic olefin of the pacidamycins has been shown to produce a series of semisynthetic compounds, the dihydropacidamycins, with antimicrobial activity similar to that of the natural products. Elucidation of stereochemistry in the pacidamycins has been completed through a campaign of natural product degradation experiments in combination with the total synthesis of the lowest-molecular weight dihydropacidamycin, dihydropacidamycin D. The stereochemical identities of the tryptophan and two alanine residues contained in pacidamycin D have been shown to be of the natural (S) configuration, and the unique 3-methylamino-2-aminobutyric acid contained in this series of antibiotics has been shown to be of the (2S,3S) configuration. Finally, the stereochemistry obtained by hydrogenation of the C(4')-C(5') exocyclic olefin has been shown to be (R) at the C(4') nucleoside site.