Dexamethasone Receptor Research Articles

Safety and efficacy of intratympanic histamine injection as an adjuvant to dexamethasone in a noise-induced murine model

The safety and efficacy of intratympanic (IT) histamine (HIS) injection as an adjuvant to increase the inner ear penetration of dexamethasone (DEX) was investigated in this study. IT injections of DEX-only, 1% HIS+DEX and 4% HIS+DEX were performed in mice with noise-induced hearing loss. An inflammatory reaction in the middle ear was observed only in the 4% HIS+DEX group although no serious cytotoxic effects on the organ of Corti (OC) were observed at that concentration. Compared with the DEX-only group, the perilymphatic concentration of DEX was approximately two times higher in the 1% HIS+DEX group and approximately five times higher in the 4% HIS+DEX group. The expression of the DEX receptor in the cochlea was significantly increased in the 4%-HIS+DEX group. HIS appeared to induce transient damage the microstructure of the RWM with recovery observed within 3 weeks. The 1 and 4% HIS + DEX groups showed a significant recovery of the OC compared with the control group and they also achieved significantly better hearing restoration at 8 kHz in the DPOAE hearing test (P < .05) when compared to the DEX-only group. IT HIS temporarily disrupts the structure of the RWM and middle ear mucosa and significantly enhances the inner ear penetration of DEX. Therefore, IT HIS injection could be a simple and effective adjuvant therapy to increase perilymph concentration of DEX and achieve OC recovery after cochlear damage.

English

BACKGROUND Chemotherapy-induced nausea and vomiting (CINV) is a frequent and feared adverse effect of cancer chemotherapy. International guidelines recommend combinations of 5-hydroxytryptamine type 3 (5-HT3) receptor antagonists, dexamethasone, and/or neurokinin-1 (NK1) receptor antagonists for the control of CINV in patients receiving highly emetogenic chemotherapy (HEC) as a part of their treatment. Even though, nausea in delayed period is less controlled and poses a major concern for these patients. METHODS This open label, prospective study was conducted in a rural medical college in Etawah District in Uttar Pradesh, India from November 2017 to November 2018 over a period of 1 year to observe the efficacy of low dose (5 mg OD) olanzapine in combination with standard anti-emetic regimen for the prevention of CINV. Olanzapine is a food and drug administration (FDA) approved antipsychotic drug that has anti-emetic activity and has shown to improve CINV. Low dose olanzapine along with a standard combination of ondansetron, dexamethasone and aprepitant was given to patients receiving highly emetogenic chemotherapy (Cisplatin &gt;70 mg/m2 or doxorubicin-cyclophosphamide combination). CINV was assessed using common toxicity criteria of adverse events (CTCAE) version 5.0. RESULTS Complete response to nausea was observed in 90.90 %, 60.60 % and 54.54 % in acute, delayed and overall period respectively. Complete response to vomiting was observed in 96.96 %, 69.69 % and 66.66 % in acute, delayed and overall period respectively. Complete response to Grade-2 (or above) nausea was observed in 96.96 %, 93.93 % and 90.90 % in acute, delayed and overall period, respectively. Daytime Grade -3 somnolence which was seen in 2/33 patients (6.06 %) was attributable to olanzapine. Patients receiving olanzapine were more likely to have complete response of nausea and emesis in the early, late, and overall assessment periods especially of higher grade (G2 and G3). CONCLUSIONS The authors concluded that low dose olanzapine 5 mg OD combined with an NK1- receptor antagonist, a 5-HT3–receptor antagonist, and dexamethasone is safe and efficacious in the prevention of CINV in patients receiving HEC. KEYWORDS Olanzapine, Low Dose, CINV, HEC

A phase II study of the safety of olanzapine for oxaliplatin based chemotherapy in coloraectal patients

Olanzapine has exhibited efficacy as an antiemetic agent when used with 5-HT3 receptor antagonists, dexamethasone, and NK1 receptor antagonists for patients receiving highly emetogenic chemotherapy. In addition, several studies have reported the efficacy or safety of olanzapine in patients receiving moderately emetogenic chemotherapy, including carboplatin, irinotecan, and oxaliplatin. However, no reports of olanzapine use have focused on patients receiving oxaliplatin-based chemotherapy. Therefore, we analyzed the safety of antiemetic therapy using olanzapine, palonosetron, aprepitant, and dexamethasone in colorectal cancer patients undergoing oxaliplatin-based chemotherapy. This study was a prospective phase II single-institution study of 40 patients (median age 60 years, 23 patients were male). The primary endpoint was the incidence of adverse events, and the exploratory endpoints were the rate of chemotherapy-induced nausea and vomiting. Almost all patients (90%) had a performance status of 0. All patients received the scheduled antiemetic therapy. The most common adverse event was somnolence (n = 7 patients, 17.5%). All adverse events were grade 1. Thirty-six patients were included in the exploratory analysis of efficacy. No patients experienced vomiting during the first 120 h after chemotherapy, and complete response and complete control were both 86.1%. The rate of total control was 55.6% during the same time period. Olanzapine use with 5-HT3 receptor antagonists, dexamethasone, and NK1 receptor antagonists was safe for colorectal cancer patients receiving oxaliplatin-based chemotherapy.

Effect of Antiemetic Agents on Hiccups during Chemotherapy in Patients with Lung Cancer

Hiccups commonly occur in patients undergoing chemotherapy for lung cancer and may diminish their motivation for treatment. Therefore, it is important to characterize the hiccups and their risk factors. We examined the medical records of 120 patients with lung cancer during their initial chemotherapy and extracted data on the patients’ profiles and the onset, duration, and severity of their hiccup episodes. We found the incidence of hiccups to be 19.2% among the patients. Hiccups appeared within 3 days of beginning the chemotherapy and disappeared within 4 days. Hiccups hindered sleep in two patients. The characteristics of the hiccups episodes in our study were not different from those of previous studies. We also investigated distinctive features of the patients who developed hiccups. The occurrence of hiccups was associated with gender, age, and the treatment with platinum agents. Antiemetic agents, dexamethasone and neurokinin-1 receptor antagonists, also showed significant effects on hiccup episodes. Although the dose-responsive effect of dexamethasone on hiccups was insignificant and the effects of two neurokinin-1 receptor antagonists, aprepitant and fosaprepitant, on hiccups appeared identical. From these results, we suggest that a high incidence of hiccups may be anticipated with a prophylactic use of antiemetic agents, dexamethasone and neurokinin-1 receptor antagonists.

Evaluation of the Efficacy and Safety of Ramosetron versus Ondansetron for prevention of postoperative nausea and vomiting in gynaecological surgery

Context: Postoperative Nausea and Vomiting (PONV) is a frequent and distressing complication after anaesthesia and surgery with a reported incidence of 20-30% and up to 80% in high-risk cases. It results in increased morbidity, prolonged hospital stay and increased healthcare costs. The multifactorial aetiology of PONV necessitates a combination of prophylactic antiemetic agents to prevent it. Aims: In our study, we compared the efficacy of a combination of dexamethasone and 5HT3 receptor antagonist (Ondansetron or Ramosetron) in preventing PONV in patients undergoing gynaecological surgeries under subarachnoid block. Settings and Design: Prospective, randomised, double blind controlled clinical study. Methods and Material:60 patients between the ages of 20 and 60 years with ASA physical status class I and II, undergoing elective total abdominal hysterectomy under subarachnoid block were selected and divided randomly into two groups of 30 members each. Group OD received Inj. Ondansetron 4 mg IV and Group RD received Inj. Ramosetron 0.3 mg IV, 20 minutes before completion of surgery. Inj. Dexamethasone 8 mg IV was given to patients in both groups immediately before spinal anaesthesia. PONV was assessed using a 4-point scoring system for 0-6, 6-12, 12-18 and 18-24 hours observational periods postoperatively. Incidence of nausea, vomiting, retching and other adverse effects were recorded. Statistical analysis used: analysis of variance, x2 test, two-tailed Fisher’s exact probability test, or the Mann-Whitney U-test, as appropriate. Results: Both groups of patients had significantly low incidence of PONV across all four observation periods with no statistically significant difference between groups OD and RD. In the overall 24 hour postoperative period, 84% of subjects in group OD and 94% in group RD showed a complete response to the prophylactic combination antiemetic therapy with no n

Chemotherapy-Induced Delayed Emesis: What is the Role of 5-HT3Antagonists?

Objective: To review the current literature assessing the efficacy of different antiemetics, with a focus on comparison between serotonin (5-HT3) antagonists and other antiemetics, in the treatment of delayed emesis induced by either cisplatin or non-cisplatin cytotoxic agents. Data Sources: A MEDLINE search (1966–July 2002) was performed using delayed emesis, vomiting, nausea, chemotherapy, cisplatin, moderately emetogenic, selective serotonin subtype-3 (5-HT3) receptor antagonists, metoclopramide, domperidone, corticosteroids, dexamethasone, prognostic factors, risk factors, and neurokinin-1 (NK1) receptor antagonists as key words or subject headings. Only English-language articles were identified and included. Additional references were retrieved from selected articles. Data Synthesis: Various antiemetic consensus guidelines have recommended the use of different pharmacologic treatment, including the use of 5-HT3 antagonists, for the prevention of chemotherapy-induced delayed emesis. In some instances, it has been suggested that combinations containing a 5-HT3 antagonist may be superior to others. Current data have been synthesized in an attempt to demonstrate the efficacy of 5-HT3 antagonists in the treatment of chemotherapy-induced delayed emesis. Conclusions: Dexamethasone has consistently shown its antiemetic efficacy for delayed emesis induced by cisplatin and non-cisplatin agents, whereas the role of 5-HT3 antagonists alone remains controversial. Metoclopramide has been shown to be as efficacious as 5-HT3 antagonists when combined with dexamethasone for the prevention of delayed emesis. As a result, 5-HT3 antagonists should be reserved as second-line agents to metoclopramide in addition to dexamethasone. NK1 receptor antagonists have shown some early promising results. However, many questions need to be addressed before their extensive use in clinical practice.

Low dose latrunculin-A inhibits dexamethasone-induced changes in the actin cytoskeleton and alters extracellular matrix protein expression in cultured human trabecular meshwork cells

We determined the effects of a low dose of the actin-disrupting agent latrunculin (LAT)-A on dexamethasone (DEX)-induced changes in actin organization, focal adhesions, and production of extracellular matrix proteins in cultured human trabecular meshwork (HTM) cells. HTM cells were cultured to a highly confluent stage with stable endothelium-like morphology and incubated with 0·1 or 0·2 μ m DEX and/or 0·1 μ m LAT-A. Changes in the actin cytoskeleton and vinculin-containing focal contacts were evaluated by immunofluorescence microscopy. Expression of thrombospondin-1 (TSP1) and fibronectin (FN) in HTM cells was evaluated by Western blot analysis. The results showed that DEX induced morphological changes and actin reorganization in HTM cells. The cells partly recovered after DEX withdrawal, but the addition of low dose LAT-A hastened the recovery. In addition, DEX failed to induce changes when co-incubated with LAT-A for at least 4 weeks, and for at least 2 weeks when cells were pre-treated with LAT-A for 2 weeks. HTM cells treated with 0·1 μ m LAT-A only for 5 days showed mild disorganization of the actin cytoskeleton and focal adhesions, which persisted during the 4 weeks of treatment. DEX stimulated production of FN in HTM cells independent of LAT-A treatment. LAT-A and, to a lesser extent, DEX inhibited production of TSP1 by HTM cells. Although LAT-A is not a DEX receptor antagonist, it is able to prevent the effects of DEX on the actin cytoskeleton in cultured HTM cells at a dose subthreshold for increasing outflow facility in monkeys. This suggests that LAT-A at low doses may be useful in treating steroid and other glaucomas. TSP1 may be an important target of LAT-A in HTM cells and modulation of TSP may influence the actin cytoskeleton of the trabecular meshwork (TM), and consequently, intraocular pressure.

Cellular proliferative effect of dexamethasone in immortalized trabecular meshwork cell (TM5) line.

Dexamethasone (DEX), one of the corticosteroid hormones, is one of the most common therapeutic strategies in ophthalmological treatment. Despite its widespread use and clinical efficiency, little is known regarding the specific effects of DEX on cell growth, differentiation and cell death in human trabecular meshwork cells. The presence of the glucocorticoid receptor (GR, dexamethasone receptor) in TM-5 cell line, which was derived from the primary human trabecular meshwork cells, was verified by RT-PCR and western blot analysis. The effects of DEX on the cellular proliferation of TM5 cells were measured by a BrdU incorporation assay. Western blot analysis were used to examine the effects of DEX on the Ras/MEK/ERK signaling pathway. The total Ras, MEK1/2 and ERK1/2 protein levels as well as the levels of activated (phosphorylated) form were both significantly increased by the DEX treatment for 5 days. Both MEK1/2 and ERK1/2 were significantly activated by phosphorylation after 10 minutes. The dependence of this increased cell proliferation on GR activation by DEX and the sustained activation of ERK was examined using RU486 (a GR inhibitor) and U0126 (a MEK inhibitor). Both RU486 and U0126 prevented the induction of cell proliferation by the DEX treatment in the TM5 cells. In conclusion this study demonstrated that GR is expressed in TM5 cells. Secondly, DEX treatment for 5 days stimulates cell proliferation in TM5 cells, and that this increased proliferation effect is mediated by the Ras/MEK/ERK pathway.

Transgenerational effect of a single neonatal benzpyrene treatment on the glucocorticoid receptor of the rat thymus.

Hormonal imprinting is provoked perinatally by the appropriate hormone on its receptor, causing a life-long adjustment of the connection between the two participants. Faulty imprinting is caused by the presence of molecules similar to the hormone in this critical period, which results in a persistent alteration of the receptor. In the present experiment the transgenerational imprinting effect of a steroid-like environmental pollutant, benzpyrene, on the receptor binding capacity of filial thymic dexamethasone and uterine estrogen receptors was studied. The receptor density (Bmax) of the thymic glucocorticoid receptors of the males was reduced up to the third (F2) generation. In females this reduction was observed only in the F1 generation of treated animals. There was no change in receptor affinity (Kd). Uterine estrogen receptors were not subjected to transgenerational imprinting. The experiments demonstrate (1) the possibility of the transgenerational transmission of imprinting effect, (2) the differences of steroid receptors in different organs, and (3) the differences of male's and female's reactions from this aspect. The results call attention to the dangers of perinatal aromatic hydrocarbon exposition to the progeny generations.

Dexamethasone receptors and their distribution in the brain of the red tilapia

Cytosolic extracts of liver and brain showed specific, saturable binding with [3H]dexamethasone: Scatchard plots were linear. Cortisol and 11-deoxycortisol acted as competitors, whilst 17α,20α-dihydroxy-4-pregnen-3-one was relatively much less effective. There was a four-fold range of differences in specific binding capacity between dissected brain regions, the order being telencephalon > hypothalamus > rhombencephalon > optic tectum ≃ (thalamus + tegmentum + torus semicircularis) when Nmax was calculated in terms of DNA content. There was no evidence for any binding of [3;H]dexamethasone with membrane fractions.

Induction of18A2/mts1Gene Expression and Its Effects on Metastasis and Cell Cycle Control

The metastasis associated 18A2/mtsI gene was inserted into the mammalian expression vector pMAMneo placing it under the control of the dexamethasone-inducible MMTV promoter. The construct was transfected into dexamethasone receptor negative F1 and receptor positive F10 cells of the B16 murine melanoma. The transferred gene was switched on in two transfectant clones of F10, by exposure to 10(-6) M dexamethasone, but not in clones of the receptor negative F1 line. One of the F10 transfectant clones (F10-192/10) was characterized further. A 13.5-fold increase in 18A2/mts1 transcripts was found in this clone upon exposure to dexamethasone. There was also a seven-fold increase in lung colonization in an experimental metastasis assay, together with increased expression of depolymerized tubulin and enhanced detection of p53 protein. The number of cells in the S phase increased by 2.5-fold following dexamethasone treatment of the clone. These data suggest a direct involvement of the 18A2/mts1 gene in lung colonization by the tumor cells. The 18A2/mts1 protein promotes tubulin depolymerization, sequesters the p53 phosphoprotein, and induces the cells to enter the S phase, but the relevance of these in the metastatic process remains to be elucidated.

Involution of rat thymus: characterization of cytoplasmic glucocorticoid receptors, evidence of glucocorticoid resistant dexamethasone receptor-positive cells.

In rats, thymic relative weight increased after birth reaching maximum values between days 15-30 and then decreased markedly in a similar way in both sexes, while the organ's absolute weight continued to increase until days 80-90 and declined slowly with apparent sex differences from day 30 onward. Scatchard analysis revealed that the [3H] dexamethasone (Dexa) receptor sites concentration showed a pattern comparable to that found in relative thymic weight, with no change in the apparent KD. The reduction of lymphocytes mitotic activity resulting in reduction of immature thymocytes production must be accompanied by a fall of the number of glycocorticoid receptors in ageing thymuses. Despite the profound decrease in the glucocorticoid receptor sites levels, the thymus sensitivity to Dexa remained unchanged during development. Indeed, in prepuberal and adult rats, the steroid administration was followed 4 days after by a transient thymic weight loss of about 70-80% which was mainly linked to the reduction in the cortical area. In contrast, the density of [3H] Dexa binding sites was reduced unexpectedly by 25% only after steroid treatment. These findings provided evidence that Dexa receptor-positive population cells in thymus was formed in a large part by relatively glucocorticoid resistant cells.

Determination of the lethal dose of dexamethasone for early passage in vitro human glioblastoma cell cultures.

Previous investigators have supported the idea that glucocorticoids may be oncolytic. In this study, the percentage of cell death in two human glioblastoma cell cultures was related to the concentration of dexamethasone that was administered. It was determined that for Cell line 1, the median lethal dose was approximately 500-800 micrograms/ml and the completely lethal dose was about 900-1000 micrograms/ml; the 3H-thymidine uptake to approximate the mitotic rate was 16,607 cpm, and the dexamethasone receptor activity was 228 fmol/mg protein. The median lethal dose and completely lethal dose for Cell line 2 was approximately 500-600 micrograms/ml and 700-1000 micrograms/ml, respectively; the 3H-thymidine uptake was 8402 cpm, and the dexamethasone receptor activity was 137 fmol/mg protein. These lethal concentrations of dexamethasone are probably higher than can be tolerated by systemic delivery. However, it remains to be seen whether the interstitial administration of dexamethasone could achieve local concentrations resulting in the oncolysis of malignant gliomas. The clinical significance of these findings will depend on the local tolerance of normal brain parenchyma to very high doses of dexamethasone. A review of some of the literature is included.

Duration of antagonizing effect of RU486 on the agonist induction of tyrosine aminotransferase via glucocorticoid receptor

The duration of the antagonizing activity of RU486 on tyrosine aminotransferase (TAT) induction and the glucocorticoid receptor in rat liver was studied. A single dose of RU486 (10 mg/kg) caused occupation of the cytosol glucocorticoid receptor in rat liver at 1h. During this time no nuclear binding of [ 3H]dexamethasone ([ 3H]Dex) receptor complex was recorded, and TAT induction was completely blocked. TAT inducibility recovery parallelled receptor binding in both the cytosol and the nuclei, reaching maximum at 12 h. In contrast, nuclear binding recovered in 24 h, and [ 3H]Dex receptor binding in cytosol 48 h after RU486 application. It is concluded that the inhibitory effect of a single dose of RU486 on TAT induction is of rather short duration. At concomitant presence of agonist and antagonist in vivo, no direct correlation between agonist receptor occupancy and TAT induction could be observed.

Epidermal dexamethasone receptors in dogs with confirmed hyperadrenocorticalism, hypothyroidism or undiagnosed hormonal alopecia

Low capacity, high affinity [ 3H] dexamethasone binding receptors were identified in cytosolic preparations of the skin (mean number 42·0 ± 25·2 mg −1 protein, apparent dissociation constant (1 nM ± 0·23) of clinically normal dogs. No [ 3H] dexamethasone binding was observed in the skin of nine out of 10 dogs with confirmed spontaneous hyperadrenocorticism or in the skin of three out of six dogs with undiagnosed hormonal alopecia. A reduction was detected in the number of [ 3H] dexamethasone binding receptors in the skin of one dog with confirmed hypothyroidism. This study provides evidence for the susceptibility of canine glucocorticoid receptors to down regulation by imbalances of endogenous hormones, particularly increased glucocorticoid concentrations.

Dexamethasone Receptor Levels in Palatal and Lung Fibroblasts of Adult A/J and C57BL/6J Mice: Relationship to Glucocorticoid-Induced Cleft Palate

Glucocorticoid-induced cleft palate (CP) has been used as an animal model for hormonal teratogenesis. In mice, the susceptibility to glucocorticoid-induced CP varies with the strain, A/J being very sensitive and C57/BL6J relatively resistant. Studies in adult and embryonic murine tissues have attempted to correlate the number of glucocorticoid receptors and CP susceptibility, with conflicting results. The relative quantities of dexamethasone receptors were now studied in established palatal and lung fibroblast cell cultures obtained from adult C57 and A/J mice. A rapidly saturable, stable binding system was demonstrated. Scatchard plots were linear indicating a single class of high affinity receptors. The glucocorticoid receptor number ranged from 6.2 x 10(-16) mole/microgram prot to 8.6 x 10(-16) mole/microgram prot, while the KD varied from 1.0 x 10(-8) M to 2.8 x 10(-8) M. The differences in receptor characteristics between murine strains were not significant (p greater than 0.05). The absence of a difference in receptor number between the two strains may reflect the limitation of fibroblast cell culture in assessing glucocorticoid binding in vivo. Alternatively, if a difference in palatal dexamethasone receptor levels between mice strains exists, it may occur only in the embryo.

Dexamethasone Receptor Levels in Palatal and Lung Fibroblasts of Adult A/J and C57BL/6J Mice: Relationship to Glucocorticoid-Induced Cleft Palate

Dexamethasone Receptor Levels in Palatal and Lung Fibroblasts of Adult A/J and C57BL/6J Mice: Relationship to Glucocorticoid-Induced Cleft Palate

Abnormal Induction of Aromatase Activity by Dexamethasone in Fibroblasts from a Patient with Cortisol Resistance*

Cortisol resistance is a rare condition due to abnormal glucocorticoid receptor function. Stimulation of aromatase activity by dexamethasone (DEX) in cultured human skin fibroblasts provides a model for studying the biological activity of glucocorticoid receptors in cells. Skin fibroblasts derived from an affected father and his less severely affected son with cortisol resistance were used for this study. Saturation analysis of DEX receptor binding was performed after incubation of cells with various DEX concentrations (1-50 nmol/L). In normal cells, the mean maximal binding capacity (Bmax) and dissociation constant (Kd) were 24 +/- 3 pmol/mg DNA and 14 +/- 3 nmol/L, respectively. Although the Bmax in cells of the father (33 +/- 2 pmol/mg DNA) was normal, the Kd (31 +/- 7 nmol/L) was abnormally elevated. By contrast, both the Bmax and Kd in cells of the son were normal. The dose response of aromatase activity to DEX stimulation was determined by assay of aromatase activity after incubation of cells in the absence or presence of DEX (0.25-500 nmol/L) for 14 h. In three strains of normal fibroblasts, the mean concentration of DEX that produced a half-maximal response was 6 +/- 1 nmol/L). In cells from the father, the mean concentration of DEX that produced half-maximal stimulation of aromatase (27 +/- 4 nmol/L) was abnormally elevated. By contrast, the concentration of DEX that half-maximally stimulated aromatase activity (6.0 and 5.9 nmol/L) was normal in cells from the son. These data provide additional evidence of abnormal glucocorticoid action in the father, but not in his son, and demonstrate the potential usefulness of determining aromatase induction by DEX as a means of assessing the biological activity of the glucocorticoid receptor.

Dexamethasone inhibition of rat hepatoma cell growth and cell cycle traverse is reversed by insulin

(1) The growth of 7800 C1 Morris hepatoma cells was inhibited by dexamethasone. The inhibition was detectable at 1 nM and half-maximal effect was obtained with approx. 13 nM dexamethasone. About 80% growth inhibition was obtained with 250 nM of the hormone and the growth rate was normalized on cessation of treatment. (2) These hepatoma cells contain dexamethasone receptors with equilibrium dissociation constant of 0.24 nM and a capacity of 24 fmol/mg cell protein. Treatment of the cells with insulin did not change these dexamethasone binding properties. Binding experiments showed that 2, 10 and 100% of the receptors were occupied when the cells were incubated with 1 nM, 7 nM and 250 nM dexamethasone, respectively. (3) Insulin completely counteracted the growth inhibition by dexamethasone and antagonized the induction of peroxisomal acyl-CoA oxidase and tyrosine aminotransferase caused by the glucocorticoid. (4) Micro-flow fluorometry showed that the cultures had a major diploid DNA stem line and a minor tetraploid stem line. Changes in diploid, tetraploid and S phase cells of the diploid stem line were scored. Dexamethasone reduced the proportion of cells in S phase and of tetraploid cells. Insulin partly reversed the action of dexamethasone in S phase, but prevented the reduction in tetraploid cells caused by dexamethasone. (5) The mitotic rate was significantly reduced by dexamethasone and this effect was reversed by insulin. (6) Continuous [ 3H]methylthymidine labelling showed a growth fraction of unity in all treatment groups. (7) It is concluded that dexamethasone induces growth inhibition by reducing the G 1-S transition. Insulin is able to counteract this effect and increase the rate of DNA synthesis.

Uptake and receptor binding of dexamethasone in cultured 7800 C 1 hepatoma cells in relation to regulation of cell growth and peroxisomal β-oxidation

1. 1. Uptake and binding of dexamethasone to glucocorticoid receptor has been studied in Morris hepatoma 7800 C 1 cells in relation to its effect on cell growth and peroxisomal β-oxidation. 2. 2. Intact cells showed saturable, specific dexamethasone binding of limited capacity and Scatchard analysis revealed one single class of binding sites with equilibrium dissociation constant ( K d) of 0.24 nM similar to other glucocorticoid receptors. However, the binding capacity of 24 fmol/mg cell protein is < 5% of previously reported values. 3. 3. Uptake of [ 3H]dexamethasone by intact cells was temperature dependent giving a linear Arrhenius plot with a calculated energy of activation of 58.5 kJ mol −1 × degree −1. 4. 4. Cytosol fractions had specific binding proteins for glucocorticoid hormones with sedimentation coefficient of ca 7S. No specific binding sites for [ 3H]dexamethasone was demonstrated in purified membrane fractions. 5. 5. Dexamethasone and the synthetic fatty acid analogue tetradecylthio acetic acid (TTA) both inhibited the growth of the 7800 C 1 cells and induced the peroxisomal acyl-CoA oxidase activity. A combination of the two compounds gave additive effects. Both these effects of dexamethasone and TTA were counteracted by insulin. 6. 6. We conclude that dexamethasone induces growth inhibition and enzyme induction by binding to functional intracellular glucocorticoid receptors. The action of dexamethasone is consistent with a dissolution in the membrane from where it diffuses passively into the cell and binds to specific receptors in an energy dependent step. 7. 6. The synergistic action of dexamethasone and TTA and the counteraction exerted by insulin are not due to changes in the dexamethasone receptor affinity or binding capacity.