Effect of cortisone and thyroxine on acid beta-glycosidases in the liver and kidney of suckling and adult rats

Insulin-dependent changes in lysosomal cathepsin D activity in rat liver, kidney, brain and heart

Streptozotocin-induced diabetes resulted in a decrease in the cathepsin D activity (free and total) in rat liver, kidney, brain and heart with a concomitant increase in tissue protein content and amino acids pool size. Treatment with insulin brought about the restoration of the cathepsin D activity to normal or greater than normal levels; tissue protein content and amino acids pool size also returned to normal values.

Serum lysosomal acid hydrolase activities in Graves' disease

The activities of seven lysosomal enzymes (alpha-D-glucosidase, beta-D-galactosidase, beta-D-glucuronidase, hexosaminidase, alpha-L-fucosidase, alpha-D-mannosidase, acid phosphatases) were studied in the serum of 31 untreated patients with Graves' disease, 30 treated hyperthyroid patients whose clinical abnormalities had disappeared and whose hormones had returned to euthyroid levels, and 34 controls. The hyperthyroid state is characterized by increased serum levels of alpha-D-glucosidase, beta-D-glucuronidase, hexosaminidase and especially of alpha-L-glucosidase and alpha-D-mannosidase. In contrast, neither beta-D-galactosidase nor acid phosphatases serum levels were significantly modified. After antithyroid treatment, the activities of these enzymes returned to normal levels, except for alpha-D-mannosidase. The interpretation of these changes in serum acid hydrolases activities is controversial.

Properties of hexosaminidases in cell-free extracts of rainbow trout livers and effects of thyroid hormones

1. The kinetic and physical properties of hexosaminidase (EC 3.2.1.30) activity were studied in liver extracts of juvenile rainbow trout. 2. Differential centrifugation studies failed to unequivocally demonstrate the sub-cellular localization of hexosaminidase, but indicated that the hexosaminidase activity was associated with the mitochondrial and lysosomal fractions. 3. Cell-free, Triton X-100 liver extracts indicated a pH optimum and activation energies comparable to those of mammals, but for other properties trout hepatic hexosaminidase differed markedly from its mammalian counterpart. 4. In contrast to the situation in rats, trout hexosaminidase was uninfluenced by a wide range of T4 and T3 doses administered by either injection or immersion routes. 5. T4 administration increased plasma T4 with minor change in plasma T3, indicating inhibition of T4 to T3 conversion by high T4 levels.

Hydrolase activities in the rat aorta. V. Comparison to activities in liver and kidney after thyroidectomy and relation to dynamic clearance of circulating low density lipoproteins

Thyroid hormones influence circulating low density lipoprotein (LDL) levels in humans; they could have an effect on LDL catabolism. Male rats were thyroidectomized (H); half were treated for 7 days with 2 micrograms triiodothyronine/100 g body weight (T) and both groups were compared to controls (C). Aorta, liver, and kidney were assayed for cellular marker enzymes, including lysosomal acid cholesteryl esterase (ACE). Specific activities of ACE (mU/mg DNA; mean +/- SD) were: Aorta, C, 0.19 +/- 0.01; H, 0.16 +/- 0.01; T, 0.21 +/- 0.01; Liver: C, 15.55 +/- 1.49; H, 9.16 +/- 1.54; T, 15.43 +/- 2.28; Kidney: C, 1.70 +/- 0.23; H, 1.04 +/- 0.13; T, 2.08 +/- 0.35. Half lives for injected unmodified 125I-labeled human LDL were 11.5 +/- 0.7 hour in C, 16.2 +/- 3.1 in H, and 12.9 +/- 0.9 in T groups. Fractional catabolic rates (FCR) of LDL in %/hr were 6.5 +/- 0.6 in C; 4.8 +/- 0.5 in H, and 6.0 +/- 0.3 in T. Reductively methylated 125I-labeled human LDL had half-lives of 14.9 +/0 1.4 hour in C and 15.1 +/- 1.6 hour in H and the FCR of this modified LDL was 5.3 +/- 0.5 %/hr in C and 5.2 +/- 0.7 %/hr in H groups. Thus, thyroidectomy results in marked decreases in ACE specific activity of liver and kidney and a marked decrease in FCR and prolonged half-life of non-modified LDL (all P less than 0.05). On the other hand, methylated LDL showed a similarly reduced FCR and prolonged half-life in control and thyroidectomized rats (P less than 0.05). This suggests a major effect of thyroid deficiency on receptor-mediated uptake of LDL in vivo and demonstrates the influence of hormonal status on dynamic clearance and catabolism of LDL.

Changes in serum N-acetyl-beta-hexosaminidase levels after treatment of hypothyroid and hyperthyroid individuals with L-thyroxine and propylthiouracil

Multiple serum samples were obtained from six hypothyroid and six hyperthyroid females, 11--17 years of age, over the course of their corrective treatment with L-thyroxine (LT4) and propylthiouracil (PTU), respectively. Sera were assayed for total N-acetyl-beta-hexosaminidase (HEX), the A (heat-labile) and B (heat-stable) isozymes, and total T4. HEX activity (total HEX A) in sera from hypothyroid (< 4 micrograms/dl T4) patients (total HEX: 518 +/- 66 nmol/60 min/ml, mean +/- S.D.; HEX A: 325 +/- 55; n = 5) was significantly lower than that of the euthyroid control group (total HEX: 638 +/- 77 (p < 0.005); HEX A: 420 +/- 76 ( p < 0.01); n = 23); no difference in HEX B levels was noted. Serum samples from patients successfully treated for hypothyroidism via oral administration of LT4 (n = 12) displayed levels of total HEX (722 +/- 113) and HEX A (491 +/- 91) significantly higher than those of the control group (p < 0.01 in both cases); again, no change in levels of HEX B was observed. HEX activity in sera from hyperthyroid (> 13 micrograms/dl T4) individuals (total HEX: 839 +/- 96; HEX A: 540 +/- 74; HEX B: 299 +/- 52; n =20) was significantly higher than that of the control group (p < 0.005 in all cases). The depression of hormone activity to the euthyroid range by PTU was accompanied ay a decrease in enzyme activity to control levels (total HEX: 632 +/- 92; HEX A: 400 +/- 55; HEX B: 232 +/- 52; n = 16). Non-parametric analysis of the data shows highly significance differences between pre- and post-treatment enzyme levels (alpha < 0.001) in both hyper- and hypothyroid groups. Alteration of thyroid status, and specifically T4 level is, therefore, indicated to be a contributing factor in the regulation of serum HEX activity in humans, as evidenced by individual responsiveness to oral administration of this hormone, or inhibitors of its peripheral metabolism.

Sex differences in serum levels of N-acetyl-beta-hexosaminidase in infancy: correlation of enzyme activity with testosterone levels

Serum levels of N-acetyl-beta-hexosaminidase (HEX) (EC 3.2.1.30) activity in infants display a sexual dimorphism. Total HEX activity in males between 1 and 3 months of age is significantly elevated over female levels (male (M), 1535 +/- 300 nmol/60 min/ml; female (F), 1150 +/- 203, P < 0.0005), and the A (labile) isozyme constitutes a significantly lower proportion of the total activity present (M, 56.0 +/- 4.2, N = 24; F, 64.3 +/- 4.6, N = 21, P < 0.0005). These findings led us to investigate the relationship between testosterone concentration and HEX activity in serum. Samples from male (N = 36) and female (N = 33) infants between 1 and 6 months of age were included. In both sexes, a high degree of correlation (P < 0.0005) was observed between testosterone and total HEX (M, r = 0.71; F, r = 0.73), HEX A (M, r = 0.68; F, r = 0.56) and HEX B (M, r = 0.68; F, r = 0.72). An inverse relationship exists between testosterone levels and % A: M, r = -0.56; F, r = -0.38 (P < 0.0025 and 0.025, respectively). In contrast, no correlation between HEX levels and testosterone was evident in either male or female adults (r = 0.20 and 0.18, respectively). These data implicate testosterone in the regulation of HEX activity during the early months of human development.

Effects of cortisone and thyroxine on suckling rat liver N-acetyl-beta-glucosaminidase isozymes. Comparison with adult reactivity

Suckling rat liver N-acetyl-beta-glucosaminidase (hexosaminidase) activity undergoes considerable fluctuation during the first two weeks of life. As two major forms of hexosaminidase (A, heat-labile, and B, heat-stable) are known to exist in both human and adult rat liver, we choose to examine the effect of the maturative hormones, thyroxine and cortisone, upon these isozymes during the suckling period. Between days 7 and 15, the observed developmental change is attributable solely to an increase in the 'A-like' (heat-labile) form of the enzyme; an enhanced response is seen in thyroxine-injected 11-15-day old animals. The response may be considered 'age-independent', as adult animals react in the same manner. In contrast, cortisone-injected sucklings show a decrease in both A and B isozymes, while in adults no changes in total activity or isozyme distribution are evoked. The ratio of hexosaminidase A to hexosaminidase B in suckling rat liver appears to shift in favor of the labile (A) isozyme early in development.

Relationship of thyroid status and serum N-acetyl-beta-glucosaminidase isoenzyme activities in humans

Serum from 28 hyperthyroid, hypothyroid, and euthyroid pre- or early puberty females was examined for N-acetyl-beta-glucosaminidase (HEX) activity. Total, isoenzyme A (labile), and isoenzyme B (stable) levels were determined for this enzyme. A high degree of correlation (r = 0.76; p less than 0.001) exists between total hexosaminidase activity and thyroid hormone levels (as reflected by the Free Thyroxine Index). Examining each isoenzyme individually, A is selectively enhanced (r = 0.84; p less than 0.0005) whereas B displays no significant change regardless of thyroid activity. In hyperthyroid individuals, levels of total hexosaminidase (730 +/- 67 units) (mean +/- S.D.) and isoenzyme A (516 +/- 46) were significantly higher than levels found in either the hypothyroid (total: 547 +/- 30; isoenzyme A: 352 +/- 31) or euthyroid (total: 620 +/- 81; isoenzyme A: 423 +/- 45) groups. However, no change was observed in levels of isoenzyme B among hypothyroid (195 +/- 19), euthyroid (197 +/- 43) and hyperthyroid (215 +/- 32) groups. These data substantiate our earlier findings in the rat, wherein thyroxine administration evoked a similar response in the liver. They are of particular interest in light of the deficiency of HEX A in variants of GM2 gangliosidosis.

Increase in liver acid lipase of thyroidectomized rats by thyroid hormones and its inhibition by actinomycin D

Acid lipase activity in the livers of thyroidectomized rats is increased by administration of L-thyroxine. The response is dose-dependent and can be demonstrated within 12 h after treatment. L-Triiodothyronine also evokes a rapid increase in acid lipase activity, and this increase can be inhibited by coadministration of actinomycin D.