A new mutation responsible for severe G6PD deficiency in two ethnic Chinese with different clinical presentations: determination by a direct PCR sequencing technique

To test the hypothesis that clinical manifestation in G6PD deficiency correlates with a molecular lesion, we investigated the G6PD gene of two Chinese Americans both of whom had G6PD deficiency, but who manifested different clinical presentations. In this study, we have developed a direct PCR sequencing protocol to examine the human G6PD gene. By using optimized PCR conditions with internal primers, we were able to amplify a 4.2 kb DNA fragment (covering exon 3 through 13 of the G6PD gene) of consistently high quality. From this we were then able to generate high quality single-stranded DNA templates by asymmetric PCR for subsequent sequencing. We also overcame the crossband problem by using internal primers, high temperature reaction with Taq I DNA polymerase, and/or sequencing with gene 32 protein. We could consistently amplify exons 1 and 2 despite their high G/C content by substituting 75% of dGTP with deoxy-7-deaza-guanosine triphosphate. By using this novel approach, we have identified a new mutation at cDNA position 1376 from G to T, which causes substitution of Leu for Arg at amino acid position 459. This mutation has not been reported in other ethnic groups. It is the only genetic defect in the coding regions of the G6PD gene of these two G6PD deficient individuals. We speculate that in addition to a defect in the G6PD gene, other factors also play a role in the clinical manifestation of G6PD deficiency.

A to G substitution identified in exon 2 of the G6PD gene among G6PD deficient Chinese

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Two commonly occurring nucleotide base substitutions in Chinese G6PD variants

Using a direct PCR sequencing technique, we have identified two DNA base substitutions in 8 different biochemical G6PD variants of Chinese origin. Neither one of these abnormalities has been reported in other ethnic groups. An abnormality (C1) of G to T substitution at cDNA 1376 causing an amino acid change from Arg to Leu has been found in 3 variants. Another abnormality (C2) of G to A substitution at cDNA 1388 causing an amino acid change from Arg to His has been found in 5 variants. Both C1 and C2 are located in exon 12 of the G6PD gene and are only 12 base pairs apart. However, C1 is associated with a significant increase in the deamino-NADP utilization rate, whereas C2 is not. Taken together, our data suggest that C1 and C2 are very common among Chinese with a G6PD deficiency and exon 12 may define an important functional domain of the human G6PD.

Erythrocyte defense against hydrogen peroxide: preeminent importance of catalase

To investigate the relative importance of catalase and glutathione in erythrocyte oxidant defense, human and mouse (normal and acatalasemic) erythrocytes were reversibly lysed and resealed in the presence of exogenous catalase or glutathione. This resulted in an increase in intracellular catalase activity or glutathione concentration in the resealed erythrocytes while normal cellular structure, hemoglobin concentration, cell volume, cellular deformability, and adenosine triphosphate concentration were maintained. Resealing alone had no effect on oxidant sensitivity. In human cells, a threefold increase in catalase activity resulted in the maintenance of glutathione levels in response to hydrogen peroxide (H2O2) challenge. Reconstitution of congenitally acatalasemic mouse erythrocytes, which were extremely sensitive to even micromolar concentrations of H2O2 with purified catalase resulted in complete protection against H2O2. Indeed, the catalase-reconstituted acatalasemic cells were less sensitive to H2O2-mediated damage than were normal, catalase-replete mouse cells. In contrast, alteration of the glutathione status of human and mouse (normal and acatalasemic) cells had no significant effect on oxidant sensitivity. Even a five-fold increase in intracellular glutathione concentration (greater than 30 micromoles glutathione per gram of hemoglobin) in normal or catalase-deficient (azide-treated or acatalasemic) red blood cells had no protective effect against H2O2-mediated lipid peroxidation or methemoglobin generation. Similarly, depletion of glutathione by 1-chloro-2,4-dinitrobenzene also had no effect on erythrocyte H2O2 sensitivity. These results suggest an important role for catalase in protection against H2O2-mediated damage at physiologic levels and that catalase is as at least as important as glutathione in cellular defense against H2O2.

NADPH, not glutathione, status modulates oxidant sensitivity in normal and glucose-6-phosphate dehydrogenase-deficient erythrocytes

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is characterized by the loss of NADPH and enhanced erythrocyte oxidant sensitivity. Historically, it has been theorized that the elevated oxidant sensitivity of G6PD-deficient erythrocytes arises as the direct consequence of decreased intracellular glutathione (GSH) concentrations. To directly investigate the basis of G6PD deficiency oxidant sensitivity, the effects of altered GSH and NADPH concentrations were examined in normal and G6PD-deficient erythrocytes. The results of this study demonstrated that GSH depletion, by 1-chloro-2,4-dinitrobenzene (CDNB), had no effect on hemoglobin oxidation in response to hydrogen peroxide (H2O2) generating systems (phenazine methosulfate and menadione bisulfite) in either normal or G6PD-deficient cells. Furthermore, a fourfold to sixfold increase in intracellular GSH concentration also did not protect against H2O2-generating systems in the normal or G6PD-deficient erythrocytes. Conversely, introduction of an NADPH-generating system (purified G6PD) into G6PD-deficient cells resulted in a significant decrease in oxidant sensitivity and an ability to cycle GSH. Further experiments demonstrated that the reduced oxidant sensitivity of the G6PD-reconstituted erythrocytes was not due to the maintenance of GSH levels because CDNB-mediated depletion of GSH did not alter this protective effect. Analysis of these results demonstrated a direct correlation between NADPH, but not GSH, concentration and hemoglobin oxidant sensitivity.

Conditioned taste aversion but not adrenal activity develops to ICV administration of interleukin-1 in rats

In a previous investigation with mice, the paired presentation of either odor or taste cues with the peripheral (IP) administration of the immunoactive peptide interleukin-1 (IL-1) led to the conditioned enhancement of glucocorticoid production. The present study found that an initial central infusion of IL-1 in the presence of saccharin cues produced a robust taste aversion but not a conditioned elevation of either ACTH or corticosterone production. These results indicate that the glucocorticoid response induced by centrally administered IL-1 in rats is independent of the behaviorally aversive properties of this cytokine which are conditionable. The differential effects of IP versus ICV administration of IL-1 on glucocorticoid conditioning requires a clearer specification of the respective signaling mechanisms and pathways activated by these two routes of administration.