Plasma glycohydrolase levels in patients with type 1 diabetes at onset and in subjects undergoing an intravenous glucose tolerance test

The effect of hyperglycemia and insulin deficiency on the plasma level of lysosomal glycohydrolases, namely N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase, alpha-D-galactosidase, and alpha-D-glucosidase, was investigated. Two patient groups were assessed: (1) 28 children with type 1 diabetes at onset (fasting blood glucose, 444+/-154 mg/100 mL; hemoglobin A1c, 11.9%+/-2.4%; symptom duration, 15.9+/-8 days; and absence of complications), (2) 14 adult subjects undergoing an intravenous glucose tolerance test (IVGTT), consisting of 8 non-obese subjects (body mass index, 26+/-0.04 kg/m2; fasting blood glucose, 82+/-13 mg/100 mL; blood insulin, 6+/-0.04 mU/L) and 6 obese subjects (fasting blood glucose, 97+/-3.5 mg/100 mL; blood insulin, 27+/-6 mU/L, with normal oral glucose tolerance test). Enzyme activity was determined with the fluorimetric method. The mean level of all evaluated enzymes was significantly increased in patients with type 1 diabetes at diagnosis compared with normal controls. Increased enzyme levels were also detected in the group of adults undergoing an IVGTT in whom hyperglycemia was accompanied by insulin resistance (ie, obese subjects). Glycohydrolase abnormalities appear to be related to insulin deficiency rather than hyperglycemia. Lysosomal apparatus abnormalities seem to be an inherent feature of diabetes that is present at disease onset. The possible role of insulin in the regulation of plasma glycohydrolase levels is discussed.

Membrane anchoring and surface distribution of glycohydrolases of human erythrocyte membranes

The membrane anchoring of the following glycohydrolases of human erythrocyte plasma membranes was investigated: alpha- and beta-D-glucosidase, alpha- and beta-D-galactosidase, beta-D-glucuronidase, N-acetyl-beta-D-glucosaminidase, alpha-D-mannosidase, and alpha-L-fucosidase. Optimized fluorimetric methods for the assay of these enzymes were set up. Treatment of the ghost preparation with 1.0 mol/l (optimal concentration) NaCl caused release ranging from 4.2% of alpha-D-glucosidase to 70% of beta-D-galactosidase; treatment with 0.4% (optimal concentration) Triton X-100 liberated 5.1% of beta-D-galactosidase to 89% of alpha-D-glucosidase; treatment with 1.75% (optimal concentration) octylglucoside yielded solubilization from 6.3% of beta-D-galactosidase to 85% of alpha-D-glucosidase. Treatment with phosphoinositide-specific phospholipase C caused no liberation of any of the studied glycohydrolases. These results are consistent with the notion that the above glycohydrolases are differently anchored or associated with the erythrocyte plasma membrane, and provide the methodological basis for inspecting the occurrence of these enzymes in different membrane microdomains.

Alterations in the activity of several glycohydrolases in red blood cell membrane from type 2 diabetes mellitus patients

The erythrocyte membrane in 71 patients with type 2 diabetes mellitus was assessed for glycohydrolase activity: N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase, alpha- and beta-D-galactosidase, alpha- and beta-D-glucosidase, alpha-D-mannosidase, and alpha-L-fucosidase. Only beta-D-glucuronidase, alpha-D-glucosidase, and beta-D-glucosidase showed markedly elevated levels with respect to the controls regardless of the presence of complications. Among the examined patients, those with good metabolic control (not yet submitted to any therapy) showed the same enzyme levels as the reference subjects, while the levels in patients with unsatisfactory metabolic control (treated with oral hypoglycemic and/or insulin) significantly differed from the control levels. For alpha-D-glucosidase and beta-glucosidase, a correlation with glycemia and the parameters of metabolic control was also evidenced. Alterations of beta-D-glucuronidase, alpha-D-glucosidase, and beta-D-glucosidase were also ascertained in the plasma of the same diabetic patients according to the literature; each enzyme correlated with the other, either in plasma or in the erythrocyte membrane. This study shows a correlation between plasma and erythrocyte membrane levels for these three enzymes. The strict parallelism of the glycohydrolases in the two different compartments provides a profile of these enzymes in the pathology of diabetes.

Lysosomal enzymes in preterm infants with bronchopulmonary dysplasia: a potential diagnostic marker

Some lysosomal glycohydrolases (N-acetyl-beta-D-glucosaminidase and their major isoenzymes, beta-D-glucuronidase, alpha-D-galactosidase, beta-D-galactosidase and alpha-D-glucosidase) were investigated in the plasma of 36 preterm infants with respiratory distress, 11 of whom developed bronchopulmonary dysplasia (BPD), in order to evaluate the role of the lysosomal apparatus in the disease. Enzyme activity was assayed fluorimetrically; the major N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes were separated using a routine chromatofocusing procedure; the diagnostic efficiency was evaluated by Bayes theorem. The mean levels of almost all glycohydrolases considered were significantly higher in BPD than in non-BPD infants. Among NAG major isoenzymes, an increase was found only in form A. No variation was evident in the plasma levels of glycohydrolases during dexamethasone therapy. Data from a retrospective analysis performed in all preterms considered, show that alpha-D-galactosidase and beta-D-galactosidase differentiate a posteriori BPD and non-BPD subjects. These enzymes, after a priori verification of their diagnostic potential in preterm infants at risk of BPD development, could acquire an important predictive value.

Effects of lead and manganese on the release of lysosomal enzymes in vitro and in vivo

In this study we evaluated the effects of two heavy metals, lead and manganese, on the release of some glycohydrolases of lysosomal origin. N-acetyl-beta-D-glucosaminidase and its major isoenzymes, beta-D-glucuronidase and alpha-D-galactosidase. We have studied release of these enzymes in vitro from peripheral mitogen-activated lymphocytes from healthy subjects after addition of Pb or Mn to the medium and their plasma levels in individuals exposed at work to Pb (31 subjects) or to manganese (36 subjects), versus matched controls. We also determined the plasma levels in a general population (417 subjects). The enzymatic activities were assayed fluorimetrically with 4-methylumbelliferyl-glycosides as substrates. Particular attention was given to some technical aspects: enzymatic activity was preserved by addition of ethylene glycol and stable liquid material was employed for calibration purposes. N-acetyl-beta-D-glucosaminidase isoenzymes were separated by a routine chromatofocusing procedure on PBE 94. The addition of both metals to lymphocytes inhibits lysosomal enzyme release. These data were supported by the plasma levels for the exposed subjects, in which enzyme levels were significantly decreased after either type of exposure. In the general population of subjects not professionally exposed, the effect of lead appears to be masked by concomitant effects of alcohol consumption. Undoubtedly, some heavy metals can alter distribution of glycohydrolases of lysosomal origin between the intra- and extracellular environment, probably interfering with membrane mechanisms. Lysosomal enzymes seem to behave as sensitive biomarkers for early subclinical changes that might later lead to clinical disease.

Plasma lysosomal glycohydrolases in a general population

In this study we evaluated the differences in plasma levels of some glycohydrolases of lysosomal origin that appear to be the most interesting for possible usefulness for diagnosis (N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase, alpha-D-galactosidase, beta-D-galactosidase, alpha-L-fucosidase and alpha-D-mannosidase) in a general population of 417 subjects, as related to age and sex and also to body mass and to some habits, such as smoking and consumption of alcohol. The enzymatic activities were assayed by fluorimetric techniques with 4-methylumbelliferyl-glycosides as substrates. Particular attention was given to some technical aspects. Enzymatic activity was preserved by addition of ethylene glycol and stable liquid material was employed for calibration purposes. Blood was sampled rigorously at the same time of day and all the samples were obtained within a short period of time to exclude effects of the circadian and circannual rhythms. beta-Glucuronidase levels were the most affected by sex and body mass. beta-D-Galactosidase was not affected by differences in age, sex, body mass or by smoking, but appeared to be the most sensitive to modification by alcohol consumption. The data in this report emphasize that, whenever changes or differences in the levels of lysosomal enzymes in body fluids are studied, it is essential to have a reference population rigorously correlated with the study population. When possible, repetitive measurements in the same subject could better indicate a clinical trend.

Automated fluorimetric assay procedure for glucohydrolases using a routine centrifugal analyser assay of enzymes of lysosomal origin in plasma, II

The manual fluorimetric procedure, considered as a reference method for the determination of N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase and beta-D-galactosidase in human plasma, was automated as a routine method, using the IL Monarch centrifugal analyser. Using a liquid standard with a known enzyme content, the automated assay correlated fairly well with the reference manual method (r values very close to 1). Its analytical imprecision was much lower than that of the manual method. The automated assay of N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase and beta-D-galactosidase gave coefficients of variation of 5.7-6.9, 3.6-5.0 and 3.8-4.2%, respectively, detection limits of 4, 2 and 1 mU/l plasma respectively, and linear responses of up to 73, 8.4 and 0.9 U/l of plasma respectively. Furthermore, the method required only small volumes of undiluted plasma (4-10 microliters). This method appears to be reliable, sensitive, simple enough for routine analyses and as cost effective as the most common routine serum enzyme assays.

The esters of p-hydroxy-benzoate (parabens) inhibit the release of lysosomal enzymes by mitogen-stimulated peripheral human lymphocytes in culture

An in vitro test was set up to assess the release of lysosomal enzymes from cells and the effect on this process of the commonly used preservatives, parabens. Human peripheral lymphocytes, cultivated in vitro for 24 h in the presence or absence of phytohaemagglutinin (PHA; 5 mg/l), were used. After 1 day of incubation, PHA treatment caused an increased release (from 220 to 500%) of the lysosomal enzymes N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase, alpha-L-fucosidase and alpha-D-galactosidase. This enhancement was analytically reliable, and detectable with 1-5 micrograms of cell protein. Leakage of lactate dehydrogenase (LDH) underwent only a 20% increase on PHA treatment, indicating that the increased release of lysosomal enzymes was presumably due to secretion, not to cell damage. In PHA-stimulated lymphocytes, methyl-, ethyl-, propyl- and butyl-parabens caused a concentration-dependent diminution of the secretion of lysosomal enzymes. Butyl-paraben appeared to be the most potent inhibitor, causing a 45-50% inhibition at 0.06 mmol/l. With the other parabens, the inhibitory effect became statistically significant at about 0.25 mmol/l for alpha-L-fucosidase and alpha-D-galactosidase, and at 0.5 mmol/l for N-acetyl-beta-D-glucosaminidase and beta-D-glucuronidase. At 1 mmol/l inhibition was greater than 50% for all the enzymes and was more marked with the propyl derivative. Parabens did not influence the release of LDH, suggesting that they affected particularly the secretion of lysosomal enzymes. This supports the hypothesis that parabens are capable of affecting cellular function at concentrations which are likely to be reached in blood or tissues under conditions of common use.

The lysosomal N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes in plasma: study of distribution in a general population by a simple routine chromatofocusing procedure

We have adapted for routine analysis a pre-existing method for separating the three major N-acetyl-beta-D-glucosaminidase (NAG) isoenzyme forms--A, B+I1 and I2--by chromatofocusing followed by fluorimetric assay of the enzyme activity. This method combines good resolution, accurate quantification of the different isoenzymes and high reproducibility with an acceptable degree of analytical precision. We have applied it to studying the isoenzyme levels in the plasma of a general population of 417 subjects and have analysed these enzyme activities as functions of age, sex, body mass and declared alcohol consumption. Unlike the levels of unfractionated enzyme, levels of all the isoenzymes were higher in men than in women at all ages except in the 20-29 year group. Isoenzyme I2 showed the greatest sex difference. On the whole, with increasing age, both sexes showed more or less regular increases in plasma levels of all the isoenzymes. We also found significant correlations for the population as a whole with age and with body mass index. The only significant correlation with alcohol consumption was for B+I1 in men.

Enzymes of lysosomal origin in plasma of twin neonates

The levels of some enzymes of lysosomal origin were assayed during days 2 and 5 of life in plasma from 11 sets of twin neonates and from 25 neonates from single pregnancies (13 of weight appropriate for gestational age and 12 small for their gestational age) as controls. The plasma enzyme levels were also determined in the correspondent twin and control mothers 2 days after delivery. N-Acetyl-beta-D-glucosaminidase isoenzymes were assayed after chromatofocusing separation. All the plasma enzyme levels were higher in the group of twin neonates and of their mothers than in the respective control groups with differences highly statistically significant for two enzymes, beta-D-galactosidase and alpha-D-glucosidase. In neonate plasma lysosomal enzymes are increased at the fifth day of life with respect to the second day. Full term control neonates showed the same enzyme trend. For the N-acetyl-beta-D-glucosaminidase the more significant differences concerned the isoenzyme I2-P (pregnancy). The pattern of the lysosomal enzymes in the twins resembled that of neonates of diabetic mothers who had had no insulin therapy. Since lysosomal enzymes are considered to be particularly sensitive indicators of carbohydrate metabolism abnormalities, we conclude that twin pregnancies are more at risk for these abnormalities than single ones.

Enzymes of lysosomal origin in the cerebrospinal fluid and plasma of patients with multiple sclerosis

Several lysosomal enzymes were determined in 47 and 62 samples of CSF and plasma, respectively, obtained from MS patients. CSF levels of most enzymes considered were significantly lower in patients when compared to those of the controls, whereas the plasma levels vary little and appeared to be influenced by the course of the disease. The most interesting result is the one concerning the beta-D-glucuronidase in the plasma: in relapsing-remitting patients in the still untreated acute phase, the levels remain noticeably diminished in comparison to controls. The data suggest the potential of using this enzyme to monitor the progression of the disease.

Preparation of a stable liquid material for calibration and quality control for lysosomal enzymes in plasma. Assay of enzymes of lysosomal origin in plasma, I

Several lysosomal enzymes present in human plasma (N-acetyl-beta-glucosaminidase, beta-glucuronidase, beta-galactosidase, alpha-galactosidase, alpha-L-fucosidase, alpha-mannosidase, beta-glucosidase) were maintained in a fully active state for at least 8 months by the addition of ethylene glycol (300 milligrams final concentration) to freshly prepared plasma and storage at -20 degrees C. Pools of human plasma from healthy humans, stabilized and stored as above, and containing a low, medium or high content of the above enzymes, were used to establish the analytical imprecision (within-run, day-to-day and total imprecision) of the fluorimetric assay. Ten replicates in ten different analytical series, covering a period of two months, were performed. The total imprecision (expressed as coefficient of variation) was in general lower than 10%; in a few cases, particularly plasma samples with a low enzyme content, the total imprecision was 18%. The isozymes A, B, I1, and I2 of N-acetyl-beta-glucosaminidase displayed the same stability upon storage as the unfractionated enzyme. It is concluded that pools of human plasma containing known amounts of lysosomal enzymes, stabilized by the addition of 300 micrograms ethylene glycol and stored at -20 degrees C, are suitable liquid materials for calibration and quality control for the assay of the same enzymes.

The lysosomal beta-D-N-acetylglucosaminidase isozymes in human plasma during pregnancy: separation and quantification by a simple automated procedure

beta-D-N-Acetylglucosaminidase isozymes were separated and assayed in the plasma of control healthy individuals and pregnant women by an automated method consisting in chromatofocusing on polybuffer exchanger PBE-94 column, flow-through fluorimetric determination of activity and computer assisted quantification. Under the established optimal conditions the method fractionated beta-D-N-acetylglucosaminidase into four isozymes. A, I2, I1 and B, with the analytical coefficients of variation of 1.8, 2.2, 6.4 and 4.1%, respectively. Duration of a single analysis was 25 min including washing, and 10-15 successive runs could be performed on the same column with good reproducibility. A linear activity response was observed from 1-5 microliters of plasma (depending on the individual isozyme) to 50 microliters, and the detection limit was 0.016 mUnits. Isozyme A was heat labile. Upon sialidase treatment, isozymes A, I2 and I1 released sialic acid and were eluted from the column at less acidic pHs. In healthy individuals isozymes A, I2, I1 and B covered about 62.8, 6.9, 15.0 and 15.1% of the total beta-D-N-acetyl-glucosaminidase activity, respectively. During pregnancy the plasma concentration of all isozymes increased. Isozyme I2 showed the highest enhancement (30-fold), followed by I1 (8-fold), B (5.6-fold) and A (3-fold). Interruption of pregnancy by either physiological delivery or ambulatory abortion was followed by a sharp fall of the concentration of all isozymes reaching, in a few days, the control levels.

Enzymes of lysosomal origin in the serum of infants of diabetic mothers behavior in the first days after birth

The serum levels of the two enzymes of lysosomal origin, beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase, and the isozyme pattern of the former, were determined in control infants and in infants of diabetic mothers (IDM) on the 1st and 5th day after birth. IDM were divided into three groups. Group 1: class A diabetic mothers treated dietetically; Groups 2 and 3: class A and classes B, C, D diabetic mothers, respectively, treated with insulin. All, but one, diabetic mothers were in excellent metabolic control. In the controls the serum levels of both enzymes were quite elevated on the 1st day after birth, reflecting the condition of the mothers at the end of pregnancy, and increased further on the 5th day, presumably as a result of the concurrent burst of antiinsulin hormones. In Group 1 IDM the serum levels of the two enzymes were higher than in controls, on the 1st day, probably reflecting the higher concentrations present in the mothers at the end of pregnancy than in controls, but equalling the condition of normal neonates on the 5th day. This indicates that IDM of this group had a normal post-natal response of the lysosomal apparatus to hormone stress. In Groups 2-3 IDM the enzyme levels on the 1st day could not be distinguished from those of controls, while on the 5th day a decrease was seen, suggesting reduced effect of the antiinsulin hormone burst on the lysosomal apparatus. The isozyme pattern of beta-N-acetyl-D-glucosaminidase in all IDM was similar to that of controls. The behavior of serum lysosomal enzymes of Groups 2-3 IDM is a further indication that the lysosomal apparatus is extremely sensitive to even small metabolic perturbations occurring in diabetic mothers during pregnancy.