Isozymes of ribonuclease in human serum and urine. I. Methodology and a survey of a control population

Possible impact of plasma RNase activity on immune dysfunction in juvenile diabetes mellitus

AIM

The ribonuclease (RNase) family represents important enzymes used widely in biomedical and biotechnological applications, as well as for diagnostic and therapeutic purposes. This study was undertaken to test the possibility that plasma alkaline RNase (free or inhibitory bound) determination may be useful in studying the dysregulation of nucleic acid and oligonucleotide metabolism as a possible pathogenetic mechanism in development of immune dysfunction in juvenile diabetes mellitus.

PATIENTS AND METHODS

Children with type 1 diabetes (n=32, age group of 5--14 yr), together with age-matched control subjects (n=35), were enrolled in the study. None had microvascular complications. According to the metabolic regulation of the disease and the hemoglobin A1c (HbA1c) level, all patients were divided into two groups (HbA1c<7.5% and HbA1c>7.5%). According to the duration of diabetes, diabetic children were divided into two groups: duration of diabetes less than 1 yr and duration of diabetes greater than 1 yr. The control group consisted of age-matched subjects (n=35; 15 girls and 20 boys) who were clinically healthy. The activity of free and inhibitory-bound RNase and the level of acid soluble nucleotides were measured in heparinized plasma.

RESULTS

The inhibitory-bound enzyme activity was higher in diabetic children, followed by sharply decreased free enzyme, especially in the group with the level of HbA1c above 7.5%. Recent-onset diabetic patients had lower free RNase activity compared with those with longer duration of the disease. The amount of pre-existing acid-soluble oligonucleotides was significantly increased in diabetic children, especially in those with poor metabolic control.

CONCLUSION

Our observed preliminary results may suggest a hypothesis that a persistent increase of oligonucleotide fragments, most probably due to insufficient RNase activity, may lead to T-cell hyperactivity in type 1 diabetes through the activation of toll-like receptors (TLRs). The measurement of RNase(s) activity (free, inhibitory-bound, or specific toward different substrates), together with the well-known immunobiochemical parameters of diabetes, may help further efforts in identifying a disease-specific early biological marker of immunity dysfunction in juvenile diabetes.

The zymogram method for detection of ribonucleases after isoelectric focusing: analysis of multiple forms of human, bovine, and microbial enzymes

A zymogram method for detection of in situ ribonuclease (RNase) activity, combined with isoelectric focusing in a thin layer of polyacrylamide gel (IEF-PAGE), has been developed. After incubation with a dried agarose film containing substrate RNA, ethidium bromide, and an appropriate reaction buffer, which was placed tightly on the top of the focused gel, sharp and distinct dark bands corresponding to RNase isoenzymes on a fluorescent background appeared under uv light. Addition of urea to the IEF-PAGE gel at a final concentration of 4.8 M permitted optimal focusing of the RNases. This method had not only a high sensitivity of less than 0.1 ng purified RNase A, but also a high band resolution compared with the immunostaining method. It was also useful for analysis of purified enzymes, including bovine pancreatic RNases and two types of human urine RNase as mammalian enzymes, and RNases T1 and T2 as microbial enzymes, as well as for detection of RNases present in crude tissue extracts, resulting in more detailed elucidation of the multiplicity of these enzymes.

Purification and characterization of a human urine ribonuclease (RNAase 1) showing genetic polymorphism

A ribonuclease (RNAase) was isolated and purified from the urine of a 45-year-old man by column chromatographies on DEAE-Sepharose CL-6B, cellulose phosphate and CM-cellulose followed by gel filtrations on Bio-Gel P-100 and Sephadex G-75, and finally to a homogeneous state by SDS-polyacrylamide gel electrophoresis. The enzyme was designated RNAase 1. It was possible to detect RNAase 1 isozymes in urine and serum without difficulty using isoelectric focusing electrophoresis followed by immunoblotting with a rabbit antibody specific to RNAase 1. The existence of genetic polymorphism of RNAase 1 was detected in human serum utilizing this technique (Yasuda, T. et al. (1988) Am. J. Hum. Genet., in press). RNAase 1 in serum and urine seemed to exist in multiple forms with regard to molecular weight and pI value. Genetically polymorphic RNAase 1 was a glycoprotein, containing three mannose, one fucose, four glucosamine and no sialic acid residues per molecule, with a molecular weight of 16,000 and 17,500 determined by gel filtration and SDS-polyacrylamide gel electrophoresis, respectively. The enzyme was most active at pH 7.0 on yeast RNA substrate and inhibited remarkably by Cu2+, Hg2+ and Zn2+. It also showed definite substrate preference for poly(C) and poly(U), but much less activity against poly(A) and poly(G). Thus, the enzyme is a pyrimidine-specific RNAase.

Diuresis-dependent excretions of low-molecular mass proteins in urine: beta 2-microglobulin, lysozyme, and ribonuclease

An investigation was carried out into how the low-molecular mass proteins beta 2-microglobulin, lysozyme, and ribonuclease were excreted over 8 h after high fluid intake (22 ml/kg of body weight in 15 min). With increasing urine flow rate the amount of lysozyme excreted per hour or per millimole creatinine increased more markedly than that of beta 2-microglobulin while at the same time the excretion rate of ribonuclease decreased. The effect of urinary flow upon the excretion rates of the various low-molecular mass proteins has to be considered as a preanalytical factor when these proteins are used as indicators of tubular dysfunction.

Sialic acid residues contribute to the heterogeneity of human serum ribonuclease: demonstration by isoelectric focusing and neuraminidase treatment of serum

Ribonuclease (RNase) activity from human serum appears as multiple zones of activity following isoelectric focusing in thin layer polyacrylamide gel. At least one but not all of these zones is cross reactive with rabbit antibovine pancreatic RNase A antiserum. Treatment of serum or partially purified serum RNase with neuraminidase reduces the complexity of the serum RNase banding pattern to a major band which focuses at a pH of 9.5 or greater and a minor zone of activity which focuses at about pH 6.0-6.2. Trypsin does not affect the pattern. Thus, sialic acid residues account for a large portion of the heterogeneity of human serum RNase. Neuraminidase treatment is requisite for evaluating RNase from serum and certain other sources.

Clinical significance of acidic pI isoenzyme of ribonuclease in human serum

Employing isoelectric focusing with an Ampholine column, the presence of three major pI isoenzymes (basic, neutral and acidic) of human ribonuclease (RNase) is demonstrated. The acidic pI isoenzyme was observed in pancreatic and hepatic cancer cells and in fetal pancreas and liver tissues, and was frequently detected in the sera of patients with pancreatic and hepatic cancer. This isoenzyme was not, however, detected in the sera of non-cancerous patients. In pancreatic cancer tissues, other pI isoenzymes, except for the acidic one, were markedly suppressed and the isoelectrophoretic patterns of the cancerous tissues closely resembled those obtained from fetal pancreatic tissue. These results suggest that the acidic pI isoenzyme could represent one of the carcinofetal proteins and that the detection of this pI isoenzyme in the patient's serum may be useful for the diagnosis of pancreatic and hepatic cancer.

Isozymes of ribonuclease in human serum and urine. II. A survey of patients with cystic fibrosis

A comparison of serum and urine RNase isozymes from CF patients, heterozygotes, and control subjects demonstrated that the major RNase isozymes are not abnormal in CF. Some preliminary evidence indicated that RNase activity of the pancreatic extracts administered to CF patients may appear in the urine and result in a slightly different urine isozyme pattern. In addition, the mean serum RNase activities of the CF patients and heterozygotes were significantly greater than the mean activity of the controls, but there was much overlap in values between the groups.