Further acatalasemia mutations in human patients from Hungary with diabetes and microcytic anemia

In blood, the hydrogen peroxide concentration is regulated by catalase. Decreased activity of catalase may lead to increased hydrogen peroxide concentration, which may contribute to the manifestation of age-related disease. The aim of this study is to examine association of decreased blood catalase activity and catalase exon mutations in patients (n=617) with diabetes (n=380), microcytic anemia (n=58), beta-thalassemia (n=43) and presbycusis (n=136) and in controls (n=295). Overall, 51 patients (8.3%) had less than half of normal blood catalase activity. Their genomic DNA was used for mutation screening of all exons and exon/intron boundaries with polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and PCR-heteroduplex analyses, and mutations were verified with nucleotide sequencing. Seven patients (type 2 diabetes (n=3), gestational diabetes (n=1), microcytic anemia (n=2)) had four novel catalase exon mutations namely, c.106_107insC, p.G36Afs*5(n=3, Hungarian type G1), c.379C>T, p.R127Y (n=2, Hungarian type H1), c.390T>C, p.R129L, (n=1, Hungarian type H2) and c.431A>T, p.N143V (n=1, Hungarian type H3). In patients with decreased blood catalase, the incidence of acatalasemia mutations was significantly high (P<0.0002) in microcytic anemia, type 2 and gestational diabetes. The four novel mutations were probably responsible for low blood catalase activity in 7/51 patients. In the remainder of the cases, other polymorphisms and epigenetic/regulatory factors may be involved.

Characterization of acatalasemic erythrocytes treated with low and high dose hydrogen peroxide. Hemolysis and aggregation

The effects of hydrogen peroxide on normal and acatalasemic erythrocytes were examined. Severe hemolysis of acatalasemic erythrocytes and a small tyrosine radical signal (g = 2.005) associated with the formation of ferryl hemoglobin were observed upon the addition of less than 0.25 mM hydrogen peroxide. However, when the concentration of hydrogen peroxide was increased to 0.5 mM, acatalasemic erythrocytes became insoluble in water and increased the tyrosine radical signal. Polymerization of hemoglobin and aggregation of the erythrocytes were observed. On the other hand, normal erythrocytes exhibited only mild hemolysis by the addition of hydrogen peroxide under similar conditions. From these results, the scavenging of hydrogen peroxide by hemoglobin generates the ferryl hemoglobin species (H-Hb-Fe(IV)=O) plus protein-based radicals (*Hb-Fe(IV)=O). These species induce hemolysis of erythrocytes, polymerization of hemoglobin, and aggregation of the acatalasemic erythrocytes. A mechanism for the onset of Takarara disease is proposed.

Simple PCR heteroduplex, SSCP mutation screening methods for the detection of novel catalase mutations in Hungarian patients with type 2 diabetes mellitus

BACKGROUND

The enzyme catalase is the main regulator of hydrogen peroxide metabolism. Deficiency of catalase may cause high concentrations of hydrogen peroxide and increase the risk of the development of pathologies for which oxidative stress is a contributing factor, for example, type 2 diabetes mellitus. Catalase deficiency has been reported to be associated with increased frequency of diabetes mellitus in a cohort of patients in Hungary. In this cohort, the majority of mutations in the catalase gene occur in exon 2.

METHODS

Type 2 diabetic patients (n=308) were evaluated for mutations in intron 1 (81 bp), exon 2 (172 bp) and intron 2 (13 bp) of the catalase gene. Screening for mutations utilized PCR single-strand conformational polymorphism (SSCP) and PCR heteroduplex methods. Verification of detected mutations was by nucleotide sequence analysis.

RESULTS

A total of 11 catalase gene mutations were detected in the 308 subjects (3.57%, p<0.001). Five of the 11 were at two previously reported mutation sites: exon 2 (79) G insertion and (138) GA insertion. Six of the 11 were at five previously unreported catalase mutation sites: intron 1 (60) G-->T; intron 2 (7) G-->A and (5) G-->C; exon 2 (96) T-->A; and exon 2 (135) T-->A. The novel missense mutations on exon 2 (96 and 135) are associated with 59% and 48% decreased catalase activity, respectively; the novel G-->C mutation on intron 2 (5) is associated with a 62% decrease in catalase activity. Mutations detected on intron 1 (60) and intron 2 (7) showed no change in catalase activity. The G-->C mutation on intron 2 (5) might be a splicing mutation. The two missense mutations on exon 2 (96) and (135) cause substitutions of amino acids 53 (Asp-->Glu) and 66 (Glu-->Cys) of the catalase protein. These are close to amino acids that are important for the binding of heme to catalase, 44 (Val) and 72-75 (Arg, Val, Val, His). Changes in heme binding may be responsible for the activity losses.

CONCLUSION

Mutations that cause decreased catalase activity may contribute to susceptibility to inherited type 2 diabetes mellitus. Exon 2 and neighboring introns of the catalase gene may be minor hot spots for type 2 diabetes mellitus susceptibility mutations.

Inhibitory effects of prior low-dose X-ray irradiation on carbon tetrachloride-induced hepatopathy in acatalasemic mice

The catalase activities in blood and organs of the acatalasemic (C3H/AnLCs(b)Cs(b)) mouse of C3H strain are lower than those of the normal (C3H/AnLCs (a)Cs(a)) mouse. We examined the effects of prior low-dose (0.5 Gy) X-ray irradiation, which reduced the oxidative damage under carbon tetrachloride-induced hepatopathy in the acatalasemic or normal mice. The acatalasemic mice showed a significantly lower catalase activity and a significantly higher glutathione peroxidase activity compared with those in the normal mice. Moreover, low-dose irradiation increased the catalase activity in the acatalasemic mouse liver to a level similar to that of the normal mouse liver. Pathological examinations and analyses of blood glutamic oxaloacetic and glutamic pyruvic transaminase activity and lipid peroxide levels showed that carbon tetrachloride induced hepatopathy was inhibited by low-dose irradiation. These findings may indicate that the free radical reaction induced by the lack of catalase and the administration of carbon tetrachloride is more properly neutralized by high glutathione peroxidase activity and low-dose irradiation in the acatalasemic mouse liver.

Characterization of hydrogen peroxide removal reaction by hemoglobin in the presence of reduced pyridine nucleotides

Hydrogen peroxide removal rates by hemoglobin were enhanced in the presence of reduced pyridine nucleotides. The species which had the activity to oxidize pyridine nucleotides was purified from human blood and identified as hemoglobin A. Hydrogen peroxide removal rates by hemoglobin A without reduced pyridine nucleotides at 0.2 mM hydrogen peroxide were 0.87+/-0.11 micromol/s/g hemoglobin, and the removal rates using 0.2 mM NADH and NADPH were 2.02+/-0.20 and 1.96+/-0.31 micromol/s/g hemoglobin, respectively. We deduced that the removal reaction by hemoglobin included formations of methemoglobin and the ferryl radical and reduction of the latter with pyridine nucleotides. The hydrogen peroxide removal ability by hemoglobin was less than that by catalase but was larger than that by glutathione peroxidase-glutathione reductase system at 0.2 mM hydrogen peroxide. Under acatalasemic conditions, it was suggested that NAD(P)H were important factors to prevent the oxidative degradation of hemoglobin.

Tissue and organ expression of catalase in acatalasemic beagle dogs

Acatalasemic Beagle dogs which were maintained in our laboratories showed no sign of catalase activity at all in the erythrocytes, and glutathione peroxidase and superoxide dismutase were at normal levels. Immunoblotting analysis demonstrated that no catalase protein is detectable in their erythrocytes. On the other hand, catalase activity was detected in other tissues and organs, albeit at varying, lower levels than in normal dogs. Quantitative immunoblotting analysis consistently demonstrated that the catalase protein is expressed in the liver and kidneys of acatalasemic dogs in proportion to the activity in these organs. The catalase mRNA expressions in the blood, liver and kidneys in acatalasemic dogs were almost the same as those in normal dogs. These results suggested that catalytically normal catalase protein is translated from mRNA in the tissues and organs including erythrocytes, but in erythrocytes this enzyme protein is disposed of by an unknown mechanism.