Behaviour of some lysosomal enzymes in the plasma of insulin dependent diabetic patients during artificial pancreas treatment

Isoenzyme pattern and partial characterization of hexosaminidases in the membrane and cytosol of human erythrocytes

OBJECTIVES

Hexosaminidase activity is present in lysosomes, plasma membrane and cytosol of many human cells. Plasma membrane and cytosolic hexosaminidase is not well characterized, particularly as regards their isoenzyme forms and their relationship with the lysosomal ones.

DESIGN AND METHODS

Erythrocyte hexosaminidase isoforms were chromatographically separated, characterized and compared to those in the plasma of healthy individuals and in the erythrocytes of a Tay-Sachs patient.

RESULTS

Hexosaminidase isoenzymes were found in plasma membrane and cytosol and were composed of the same alpha- and beta-subunits as the lysosomal and plasma hexosaminidase A and B isoenzymes, though with some structural and kinetic differences. In addition, the cytosol contained a hexosaminidase that is a specific N-acetyl-beta-D-glucosaminidase, the one involved in the removal of N-acetylglucosamine residues O-linked to proteins, named O-GlcNAcase.

CONCLUSIONS

This work provides an additional step in the characterization of hexosaminidases helping better understand their role in non-lysosomal compartments and their involvement in physiological or pathological situations.

Low levels of occupational exposure to arsenic and antimony: effects on lysosomal glycohydrolase levels in plasma of exposed workers and in lymphocyte cultures

BACKGROUND

Heavy metals have been shown to alter the mechanism and release of lysosomal enzymes. In the present study, the activities of lysosomal glycohydrolases were determined in order to evaluate the asymptomatic toxic effects of low levels of exposure to arsenic (As) and antimony (Sb) in art glass workers.

METHODS

N-acetyl-beta-D-glucosaminidase (NAG), beta-D-glucuronidase (GCR), alpha- and beta-D-galactosidase, alpha-D-glucosidase, and alpha-D-mannosidase were determined by a fluorimetric assay in the plasma of 26 art glass workers. Lymphocytes cultured in the presence of different species of As and Sb served as an in vitro model for the study of the protective action of selenium and zinc.

RESULTS

No significant difference in the plasma levels of the various enzymes was detected in art glass workers or control subjects. The in vitro experiments demonstrated that secretion of lysosomal glycohydrolases was increased by Sb (225%) and decreased by As (57%) at the same concentration of elements (200 microg/L). The addition of bivalent selenium to the culture neutralized the effects of both metals, while zinc chloride did not show any protective effect.

CONCLUSIONS

As for the plasma glycohydrolases, no praecox signs of toxicity related to a low concentration of As and Sb was evident in art glass workers. This may be due to the antagonistic effects demonstrated by these two metals in vitro. Their different mechanism of action on release of glycohydrolases is being discussed.

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.

beta-Hexosaminidase isoenzymes A and B in middle-aged and elderly subjects: determinants of plasma levels and relation to vascular disease

Plasma/serum beta-hexosaminidase (Hex) activity is known to be increased in chronic alcoholism, liver disorders, pregnancy and diabetes mellitus. Hex activity also shows an association with risk factors for vascular disease and heredity for arteriosclerosis. There are several isoenzymes of Hex. Using an enzyme immunoassay for Hex isoenzymes (Hex A and Hex B) we studied possible determinants of Hex isoenzymes and their relation to vascular disease in randomly invited (n = 244) 35-95-year-old men and women. In both sexes there were significant age-related increases in Hex activities and men exhibited higher activity of both isoenzymes. Both Hex isoenzymes correlated with age, systolic blood pressure, serum triglycerides and liver enzymes, whereas Hex A was distinguished from Hex B by its stronger correlation with blood glucose. In multiple linear regression analysis Hex A was explained to 20.7% by blood glucose, age, serum aspartate aminotransferase and glutamyl transpeptidase. Hex B was explained to 14% by age, serum glutamyl transpeptidase and serum triglycerides. There was no significant increase in Hex isoenzymes in subjects with hypertension, diabetes mellitus or myocardial disease, nor did current smokers exhibit any increase of these enzymes compared to non-smokers. The main conclusion in that liver function, as reflected by the level of liver enzymes and glucose metabolism, is the major determinant for Hex isoenzymes in plasma.

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.

Plasma beta-hexosaminidase isoenzymes A and B exhibit different relations to blood glucose levels in a population of Type 1 diabetic patients

The activity of lysosomal enzymes, such as beta-hexosaminidase (Hex), is increased in the plasma and serum of diabetic patients. A positive association has been shown between enzyme activity and glycated proteins, indicating an association with the degree of metabolic control. Several isoenzymes of Hex exist. Studies have reported different proportions of the isoenzymes in plasma from diabetic patients, compared with healthy subjects. In the present study, Hex isoenzymes were examined in 76 Type 1 diabetic patients, of mean age 37.4 years (SD 12.9) compared with 38 age- and sex-matched healthy control subjects in an attempt to evaluate the influence of long- and short-term changes in blood glucose levels on these isoenzymes. The results show that Hex A activity (p<0.01), but not Hex B activity, was higher in the diabetic patients. Hex A activity was positively associated with both the actual blood glucose levels (r = 0.48, p<0.001) and haemoglobin A1c (HbA1c) (r = 0.43, p<0.001), while Hex B activity was associated with the level of HbA1c only (r = 0.42, p<0.001). Both Hex A and B activities were also positively associated with early signs of diabetic nephropathy (e.g. urinary excretion of Hex, fractional albumin excretion ratio and urinary albumin). There was no association between Hex A and B activities and different degrees of retinopathy. In conclusion, the present study demonstrates an association between Hex A and B and metabolic parameters in diabetes as well as with clinical signs of early diabetic nephropathy, but no association with the degree of retinopathy. Furthermore, Hex A seems to be more influenced than Hex B by short-term changes in blood glucose levels.

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.

Serum beta-hexosaminidase isoenzymes are related to risk factors for atherosclerosis in a large population of postmenopausal women

Lysosomes are involved in atherogenesis. Therefore we have studied the level of serum beta-hexosaminidase isoenzymes (Hex A and Hex B) in relation to risk factors for atherosclerosis in a homogeneous population of 886 post-menopausal women. We found a relation with several risk factors such as serum triglycerides, diastolic and systolic blood pressure, blood glucose, waist/hip ratio and body mass index but not with serum cholesterol. Also, the mean values for Hex A and Hex B were higher in smokers than in non-smokers but only the mean value for Hex A differed significantly. The relation of serum beta-hexosaminidase isoenzymes to risk factors might be due to lysosomal over-loading, which gives rise to increased enzyme synthesis and enhanced secretion of lysosomal enzymes to circulation. The subjects in the 95-100 percentile of Hex A showed significantly increased frequency of myocardial infarction of their fathers and of stroke in their mothers and the subjects in the 95-100 percentile of Hex B showed increased frequency of stroke in their mothers. Thus the findings of a relation between Hex isoenzymes and heredity for vascular disease further stress the significant relation between Hex isoenzymes and risk factors. Since Hex B is a sensitive marker for alcohol abuse, we also investigated its serum level in subjects that could be suspected of alcohol abuse. However, we did not find any differences in these subjects compared with the others, possibly due to the relatively short half-life of Hex B after alcohol withdrawal.

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.

The association between plasma beta-hexosaminidase and its isoenzyme patterns and retinopathy in type 1 diabetes mellitus

beta-Hexosaminidase and its isoenzyme patterns were investigated in plasma from patients with Type 1 diabetes mellitus. The patients were divided into three main groups matched for duration of diabetes: (a) proliferative retinopathy (b), progress of retinopathy within a two-year period (c) and with no background retinopathy. When all patients were compared to a reference group, a significant increase of plasma beta-hexosaminidase activity was found. Patients with proliferative retinopathy had significantly increased activity of plasma beta-hexosaminidase compared to the reference group but not compared to the other diabetic patients. The isoenzyme distribution was not different in any of the diabetic subgroups compared to the reference group. It was also shown that various degrees of diabetic nephropathy did not influence total plasma Hex or the isoenzyme pattern.

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.

Serum enzymes of lysosomal origin as indicators of the metabolic control in non-insulin-dependent diabetics

Several lysosomal enzymes (beta-N-acetyl-D-glucosaminidase, beta-D-glucuronidase, alpha-D-galactosidase, beta-D-galactosidase, alpha-D-glucosidase, beta-D-glucosidase, alpha-L-fucosidase and alpha-D-mannosidase) were determined in the serum of 54 non-insulin-dependent diabetics with different degrees of metabolic control and without complications and in 18 non-insulin-dependent diabetics with complications. The serum levels of beta-N-acetyl-D-glucosaminidase, beta-D-glucuronidase, alpha-D-galactosidase, and alpha-D-mannosidase were significantly (p less than 0.01) higher in the diabetics without complications. The levels of beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase were inversely proportional to the degree of metabolic control, in a statistically significant manner. Moreover the levels of these enzymes decreased to normal values during a 2-month period of controlled oral hypoglycemic drug-diet therapy resulting in metabolic compensation. The presence of complications was indicated by a further increase of serum beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase; however the portion of lysosomal enzyme activities due to complications remained unchanged after controlled therapy aimed at compensating the metabolism. The conclusion is drawn that in non-insulin-dependent diabetics, as already shown for insulin dependent-diabetics, serum lysosomal enzymes, especially beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase, are good intraindividual indicators of the metabolic control of the disease.