Jir S. Tsai

Increased Peroxidation and Reduced Antioxidant Enzyme Activity in Alzheimer's Disease☆

The overall peroxidation activity in brain tissue by region from patients with Alzheimers disease (AD) and age-matched controls was determined employing the thiobarbituric acid-reactive substances (TBARS) assay, a measure of lipid peroxidation, followed by a determination the activities of the antioxidant enzymes Cu/Zn superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), in the frontal, temporal, and cerebellar cortex of 10 AD and 9 control brains. The level of TBARS was elevated in all regions, with particular statistical significance in the temporal cortex when compared to age-matched controls. SOD activity was significantly decreased in AD frontal and AD temporal cortex, while catalase activity was significantly decreased in AD temporal cortex. There was no significant difference in GSH-Px activity found in any of the regions examined. This study supports the theory that in AD the brain is affected by increased oxidative stress which, when combined with a decrease in SOD activity, produces oxidative alterations, seen most significantly in temporal cortex in AD, where the pathophysiologic changes are most severe.

Thyroid Hormone Action IN VITRO CHARACTERIZATION OF SOLUBILIZED NUCLEAR RECEPTORS FROM RAT LIVER AND CULTURED GH1 CELLS

We previously reported that putative nuclear receptors for thyroid hormone can be demonstrated by incubation of hormone either with intact GH(1) cells, a rat pituitary tumor cell line, or with isolated GH(1) cell nuclei and rat liver nuclei in vitro. We characterized further the kinetics of triiodothyronine (T3) and thyroxine (T4) binding and the biochemical properties of the nuclear receptor after extraction to a soluble form with 0.4 M KCl. In vitro binding of [(125)I]T3 and [(125)I]T4 with GH(1) cell and rat liver nuclear extract was examined at 0 degrees C and 37 degrees C. Equilibrium was attained within 5 min at 37 degrees C and 2 h at 0 degrees C. The binding activity from GH(1) cells was stable for at least 1 h at 37 degrees C and 10 days at - 20 degrees C. Chromatography on a weak carboxylic acid column and inactivation by trypsin and Pronase, but not by DNase or RNase, suggested that the putative receptor was a nonhistone protein. The estimated equilibrium dissociation constants (K(d)) for hormone binding to the solubilized nuclear binding activity was 1.80 x 10(-10) M (T3) and 1.20 x 10(-9) M (T4) for GH(1) cells and 1.57 x 10(-10) M (T3) and 2.0 x 10(-9) M (T4) for rat liver. These K(d) values for T3 are virtually identical to those which we previously reported with isolated rat liver nuclei and GH(1) cell nuclei in vitro. The 10-fold greater affinity for T3 compared to T4 in the nuclear extract is also identical to that observed with intact GH(1) cells. In addition, the [(125)I]T3 and [(125)I]T4 high-affinity binding in the nuclear extract were inhibited by either nonradioactive T3 or T4, which suggests that the binding activity in nuclear extract was identical for T3 and T4. In contrast, the binding activity for T4 and T3 in GH(1) cell cytosol was markedly different from that observed with nuclear extract (K(d) values were 2.87 x 10(-10) M for T4 and 1.13 x 10(-9) M for T3). Our results indicate that nuclear receptors for T3 and T4 can be isolated in a soluble and stable form with no apparent change in hormonal affinity. This should allow elucidation of the mechanisms of thyroid hormone action at the molecular level.

Thyroid Hormone Action: A Cell-Culture System Responsive to Physiological Concentrations of Thyroid Hormones

Cells from a rat pituitary tumor cell line will respond in vitro to physiological concentrations of L-thyroxine and L-triiodothyronine. The cells are grown in a cultutre medium that contains serum from a hypothyroid calf. Dose-response relationships of a vacriety of thyronine derivatives indicate that this system has a specificity of response which is similar to that observed in vitro.

Thyroid hormone action: Stimulation of growth hormone and inhibition of prolactin secretion in cultured GH1 cells

Summary Triiodothyronine induces a 3-fold increase in the rate of growth of cultured GH 1 cells, a growth hormone and prolactin producing pituitary cell line. Associated with the increased rate of cell replication is an increase in the rate of growth hormone secretion and a decrease in prolactin secretion. The Thyrotropin Releasing Hormone mediated increase in prolactin secretion was also inhibited by triiodothyronine. Half-maximal inhibition of prolactin secretion occurred at a free triiodothyronine concentration of 3 × 10 −11 M. This value is identical to the equilibrium dissociation constant for binding of triiodothyronine with nuclear receptors for the thyroid hormones. This suggests that the thyroid hormone inhibition of prolactin secretion is mediated by control of regulatory events at the level of the cell nucleus.

Thyroid Hormone Action: In vitro Demonstration of Putative Receptors in Isolated Nuclei and Soluble Nuclear Extracts

Saturable binding activities for triiodothyronine were demonstrated in vitro with isolated nuclei and soluble nuclear extracts of rat liver, kidney, and cultured GH1 cells. The binding activity can be extracted from nuclei in soluble form with no significant change in hormone affinity and has properties of a nonhistone protein.

In vitro characterization of the mechanism of insulin degradation and the effect of chloroquine.

The cultured rat hepatoma cell line, MH1C1, inactivates 125I-labeled insulin by a temperature dependent mechanism. The estimated Km for insulin degradation is 1.4 . 10(-7) M and the V is 2.5 . 10(-10) mol/10(6) cells/h. The iodocompounds released from cells preincubated at 0 degrees C with 125I-labeled insulin are immunoreactive with anti-insulin antibody, while the iodocompounds released from the cells incubated at 37 degrees C only reacts to a very small degree with anti-insulin antibody. The degradation products were analyzed by Sephadex gel chromatography. Sephadex G-75 gel filtration of iodocompounds derived from cells incubated at 37 degrees C with 125I-labeled insulin for 5, 20 min and 1 h showed a progressive decrease in intact insulin, and an increase in the peak representing insulin breakdown products. Treatment with chloroquine, a lysosomal enzyme inhibitor, resulted in a large increase of cell-associated insulin compared to control cells. However, chromatographic studies of iodocompounds extracted from cells incubated with or without chloroquine show a similar pattern but differ in the size of the peak which represents the degradation products of 125I-labeled insulin. Furthermore, the iodocompounds released from the chloroquine treated cells were not immunoreactive with anti-insulin antibody. These results suggest that chloroquine inhibits the release of insulin degradation products from the cells.

Nocturnal Monitoring of Growth Hormone, Insulin, C-Peptide, and Glucose in Patients With Acromegaly

Circulating growth hormone, insulin, C-peptide, and glucose levels were compared during the sleep state in adults with acromegaly and healthy control subjects. Growth hormone secretion was episodic in both groups, with the sleep-related growth hormone peak noticeably absent in the acromegalic subjects. The mean nocturnal plasma insulin concentration was greater in the acromegalics. There was no significant difference in the C-peptide between the two groups. Insulin and glucose levels did not show an early morning rise in either acromegalics or healthy subjects. The authors conclude that there is a marked difference in the circulating levels of growth hormone and insulin between the acromegalic and the healthy groups during the sleep state, and there is no sleep-related nocturnal growth hormone peak in the acromegalic subjects. The hyperinsulinism of patients with acromegaly cannot be attributed to excess secretion of insulin.

Airway Obstruction due to Goiter in Older Patients

It has been shown that goiters can progressively enlarge to compress the surrounding trachea or esophagus and result in incapacitating obstructive symptoms or potentially fatal airway obstruction. 1–3 The potential of a goiter to become hyperactive also exists. Recently, we have seen three older patients with longstanding untreated “benign” goiters who presented difficult management decisions. Given the likelihood of progressive growth of a goiter and the increased life expectancy of these patients with goiters, it is essential to perform flow‐volume loop studies while following these patients.

Growth hormone-releasing factor releases ACTH from an AtT-20 mouse pituitary tumor cell line but not from normal pituitary cells.

Corticotropin-releasing factor (CRF) and both human pancreatic growth hormone-releasing factor (hp-GRF) and rat hypothalamic GRF (rh-GRF) stimulated ACTH release from neoplastic AtT-20 mouse pituitary tumor cells in a dose-dependent fashion, with CRF inducing a 10-fold increase and GRF a maximal increment of approximately one-half that of CRF. Neither rh-GRF nor hp-GRF induced ACTH release in normal anterior pituitary cells. Pretreatment with either dexamethasone or somatostatin prior to the addition of rh-GRF inhibited the increase in ACTH release. Both ovine CRF and rh-GRF stimulated adenosine 3,5-monophosphate production in AtT-20 cells. The weak but clearly discernible effect of GRF on ACTH release from AtT-20 cells may be due to an abnormality in the AtT-20 cell receptor.