Missense mutations in the gp91-phox gene encoding cytochrome b558 in patients with cytochrome b positive and negative X-linked chronic granulomatous disease

Chronic granulomatous disease (CGD) is a disorder of host defense due to genetic defects of the superoxide (O2-) generating NADPH oxidase in phagocytes. A membrane-bound cytochrome b558, a heterodimer consisting of gp91-phox and p22-phox, is a critical component of the oxidase. The X-linked form of the disease is due to defects in the gp91-phox gene. We report here biochemical and genetic analyses of patients with typical and atypical X-linked CGD. Immunoblots showed that neutrophils from one patient had small amounts of p22-phox and gp91-phox and a low level of O2- forming oxidase activity, in contrast to the complete absence of both subunits in two patients with typical CGD. Using polymerase chain reactions (PCR) on cDNA and genomic DNA, we found novel missense mutations of gp91-phox in the two typical patients and a point mutation in the variant CGD, a characteristic common to two other patients with similar variant CGD reported previously. Spectrophotometric analysis of the neutrophils from the variant patient provided evidence for the presence of heme of cytochrome b558. Recently, we reported another variant CGD with similar amounts of both subunits, but without oxidase activity or the heme spectrum. A predicted mutation at amino acid 101 in gp91-phox was also confirmed in this variant CGD by PCR of the genomic DNA. These results on four patients, including those with two variant CGD, are discussed with respect to the missense mutated sites and the heme binding ligands in gp91-phox.

Physiological production of singlet molecular oxygen in the myeloperoxidase-H2O2-chloride system

The putative role of singlet oxygen (1O2) in the respiratory burst of neutrophils has remained elusive due to the lack of reliable means to study its quantitative production. To measure 1O2 directly from biological or chemical reactions in the near infrared region, we have developed a highly sensitive detection system which employs two InGaAs/InP pin photodiodes incorporated with a dual charge integrating amplifier circuit. Using this detection system, we detected light emission derived from a myeloperoxidase (MPO)-mediated reaction in physiological conditions: pH 7.4, 1-30 nM MPO, 10-100 microM H2O2 and 100-130 mM CI in place of Br without the use of deuterium oxide. The MNPO-H2O2-CI(-) system exhibited a single emission peak at 1.27 microm with a spectral distribution identical to that of delta singlet oxygen. Our results suggest physiological production of 1O2 in the MPO-H2O2-CI(-) system at an intravacuolar neutral pH. The MPO-mediated generation of 1O2, which may have an important role in host defense mechanisms, is discussed in connection with previous results.

A novel mutation at a probable heme-binding ligand in neutrophil cytochrome b558 in atypical X-linked chronic granulomatous disease

A membrane-bound cytochrome b558, a heterodimer consisting of gp91-phox and p22-phox, is a critical component of the superoxide (O2-)-generating reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in phagocytes. Chronic granulomatous disease (CGD) is characterized by recurrent bacterial infection caused by a defect of the oxidase. Both subunits are absent from phagocytes in typical X-linked recessive CGD patients who are primarily defective in gp91-phox. We report here an atypical case of X-linked CGD in which neutrophils showed a complete absence of O2--forming NADPH oxidase activity, but a small amount (about 10% of control) of both subunits was detected by immunoblot analysis. Spectrophotometric studies of the neutrophils with a recently developed sensitive method gave no evidence for the heme spectrum in the cytochrome b558, of this CGD. Reverse transcription/polymerase chain reaction and sequence analysis revealed a C to T transition replacing histidine at amino acid position 101 (His101) by tyrosine in gp91-phox. These results provide evidence that His101 of gp91-phox is the one of the heme-binding ligands of cytochrome b558.

Spectrophotometric determination of neutrophil cytochrome b558 of chronic granulomatous disease

BACKGROUND

Chronic granulomatous disease (CGD) is an inherited disease characterized clinically by severe recurrent bacterial infections from infancy. This disease is a disorder of the formation of superoxide (O2-) by the neutrophil NADPH oxidase system, mostly due to defects in cytochrome b558 (cyt b558), which is one of the oxidase components. Diagnosis of CGD has been performed by the assay of the O2- forming activity, immunological determination of defects in the oxidase components, and or spectrophotometry of cyt b558. However, spectrophotometric analysis of the b-type heme is difficult with small amounts of blood from infant CGD patients, as the limited amounts of neutrophils are contaminated with a relatively high ratio of hemoglobin (Hb) that interferes with the heme spectrum of cyt b558. This report presents an accurate method for the spectrophotometric analysis of cyt b558 in a small amount of CGD neutrophils that were treated with CO gas in a safe procedure instead of the previously reported CO-bubbling method.

METHODS AND RESULTS

The difference of the reduced minus oxidized cyt b558 spectrum was measured under no interference from oxy Hb at the alpha and beta bands and differentiated as d[delta A]/d lambda (lambda = wavelength) to obtain further evidence for the defects of the cyt b558 heme spectrum. The interference from CO-insensitive met Hb was eliminated by subtracting the absorption peak at the Soret (gamma) band of the contaminating met Hb, which was estimated from the CO-treated and untreated spectra of the same, hemolyzed sample.

CONCLUSIONS

This spectrophotometric method is feasible for the determination of abnormality and heme content of cyt b558 with a small amount of CGD neutrophils in 10-20 mL of blood even in the presence of contaminating Hb.

Comparison of systemic and renal hemodynamics measured by Doppler ultrasonography in canine experimental hypovolemia

The aim of this study was to examine renal hemodynamics at the hypovolemic and recovery phases in two different hypovolemic shock models using Doppler ultrasonography, and to compare this with systemic hemodynamics. In experiment 1, the hypovolemic phase was induced in 6 mongrel dogs by removing arterial blood at 30 ml/kg for 60 min. In the recovery phase, this blood was reinfused at 30 ml/kg over 60 min. In experiment 2, hypovolemia was induced in 12 beagle dogs by rapid blood removal until blood pressure decreased to 40 mmHg and was maintained at this pressure for 30 min. Six of the dogs were then infused with 20 ml/kg hydroxyethyl starch over 5 min, and the other 6 were infused with 60 ml/kg lactated Ringer's solution also over 5 min. Parameters for systemic and renal hemodynamics were measured by using a polygraph and the Doppler method, respectively. The decrease of diastolic blood flow, resulted in an increase of vessel resistance, and was detected in the hypovolemic kidney by the Doppler method. The rapid and large volume infusion of resuscitation fluids was effective for the recovery of both systemic circulation and renal blood flow, however this induced an increase of kidney vessel resistance, a result of the autoregulation mechanism of the kidney. The changes in these parameters at the main renal artery and interlobar artery were similar.