Position 16 of the steroid nucleus modulates glucocorticoid-induced apoptosis at the transcriptional level in murine T-lymphocytes

Anti-inflammatory effects of dexamethasone in COVID-19 patients: Translational population PK/PD modeling and simulation

Dexamethasone (DEX) given at a dose of 6 mg once-daily for 10 days is a recommended dosing regimen in patients with coronavirus disease 2019 (COVID-19) requiring oxygen therapy. We developed a population pharmacokinetic and pharmacodynamic (PopPK/PD) model of DEX anti-inflammatory effects in COVID-19 and provide simulations comparing the expected efficacy of four dosing regimens of DEX. Nonlinear mixed-effects modeling and simulations were performed using Monolix Suite version 2021R1 (Lixoft, France). Published data for DEX PK in patients with COVID-19 exhibited moderate variability with a clearance of about half that in healthy adults. No accumulation of the drug was expected even with daily oral doses of 12 mg. Indirect effect models of DEX inhibition of TNFα, IL-6, and CRP plasma concentrations were enacted and simulations performed for DEX given at 1.5, 3, 6, and 12 mg daily for 10 days. The numbers of individuals that achieved specified reductions in inflammatory biomarkers were compared among the treatment groups. The simulations indicate the need for 6 or 12 mg daily doses of DEX for 10 days for simultaneous reductions in TNFα, IL-6, and CRP. Possibly beneficial is DEX given at a dose of 12 mg compared to 6 mg. The PopPK/PD model may be useful in the assessment of other anti-inflammatory compounds as well as drug combinations in the treatment of cytokine storms.

Pharmacokinetic/Pharmacodynamic Modeling of Dexamethasone Anti-Inflammatory and Immunomodulatory Effects in LPS-Challenged Rats: A Model for Cytokine Release Syndrome

Dexamethasone (DEX) is a potent synthetic glucocorticoid used for the treatment of variety of inflammatory and immune-mediated disorders. The RECOVERY clinical trial revealed benefits of DEX therapy in COVID-19 patients. Severe SARS-CoV-2 infection leads to an excessive inflammatory reaction commonly known as a cytokine release syndrome that is associated with activation of the toll like receptor 4 (TLR4) signaling pathway. The possible mechanism of action of DEX in the treatment of COVID-19 is related to its anti-inflammatory activity arising from inhibition of cytokine production but may be also attributed to its influence on immune cell trafficking and turnover. This study, by means of pharmacokinetic/pharmacodynamic modeling, aimed at the comprehensive quantitative assessment of DEX effects in lipopolysaccharide-challenged rats and to describe interrelations among relevant signaling molecules in this animal model of cytokine release syndrome induced by activation of TLR4 pathway. DEX was administered in a range of doses from 0.005 to 2.25 mg·kg-1 in LPS-challenged rats. Serum DEX, corticosterone (CST), tumor necrosis factor α, interleukin-6, and nitric oxide as well as lymphocyte and granulocyte counts in peripheral blood were quantified at different time points. A minimal physiologically based pharmacokinetic/pharmacodynamic (mPBPK/PD) model was proposed characterizing the time courses of plasma DEX and the investigated biomarkers. A high but not complete inhibition of production of inflammatory mediators and CST was produced in vivo by DEX. The mPBPK/PD model, upon translation to humans, may help to optimize DEX therapy in patients with diseases associated with excessive production of inflammatory mediators, such as COVID-19. SIGNIFICANCE STATEMENT: A mPBPK/PD model was developed to describe concentration-time profiles of plasma DEX, mediators of inflammation, and immune cell trafficking and turnover in LPS-challenged rats. Interrelations among DEX and relevant biomarkers were reflected in the mechanistic model structure. The mPBPK/PD model enabled quantitative assessment of in vivo potency of DEX and, upon translation to humans, may help optimize dosing regimens of DEX for the treatment of immune-related conditions associated with exaggerated immune response.

Population pharmacodynamic modeling of intramuscular and oral dexamethasone and betamethasone effects on six biomarkers with circadian complexities in Indian women

Population pharmacokinetic/pharmacodynamic (PK/PD) analysis was performed for extensive data for differing dosage forms and routes for dexamethasone (DEX) and betamethasone (BET) in 48 healthy nonpregnant Indian women in a partial and complex cross-over design. Single doses of 6 mg dexamethasone phosphate (DEX-P), betamethasone phosphate (BET-P), or 1:1 mixture of betamethasone phosphate and acetate (BET-PA) were administered orally (PO) or intramuscularly (IM) where each woman enrolled in a two-period cross-over study. Plasma concentrations collected over 96 h were described with a two-compartment model with differing PO and IM first-order absorption inputs. Overall, BET exhibited slower clearance, similar volume of distribution, faster absorption, and longer persistence than DEX with BET acetate producing extremely slow absorption but full bioavailability of BET. Six biomarkers were assessed over a 24-h baseline period with four showing circadian rhythms with complex baselines. These baselines and the strong responses seen after drug dosing were fitted with various indirect response models using the Laplace estimation methods in NONMEM 7.4. Both the PK and six biomarker responses were well-described with modest variability likely due to the homogeneous ages, weights, and ethnicities of the women. The drugs either inhibited or stimulated the influx processes with some models requiring joint inclusion of drug effects on circadian cortisol suppression. The biomarkers and order of sensitivity (lowest IC₅₀/SC₅₀ to highest) were: cortisol, T-helper cells, basophils, glucose, neutrophils, and T-cytotoxic cells. DEX sensitivities were generally greater than BET with corresponding mean ratios for these biomarkers of 2.86, 1.27, 1.72, 1.27, 2.69, and 1.06. Overall, the longer PK (e.g. half-life) of BET, but lesser PD activity (e.g. higher IC₅₀), produces single-dose response profiles that appear quite similar, except for the extended effects from BET-PA. This comprehensive population modeling effort provides the first detailed comparison of the PK profiles and six biomarker responses of five commonly used dosage forms of DEX and BET in healthy women.

Nfil3 is a glucocorticoid-regulated gene required for glucocorticoid-induced apoptosis in male murine T cells

Glucocorticoids (GCs) have essential roles in the regulation of development, integrated metabolism, and immune and neurological responses, and act primarily via the glucocorticoid receptor (GR). In most cells, GC treatment results in down-regulation of GR mRNA and protein levels via negative feedback mechanisms. However, in GC-treated thymocytes, GR protein levels are maintained at a high level, increasing sensitivity of thymocytes to GCs, resulting in apoptosis termed glucocorticoid-induced cell death (GICD). CD4(+)CD8(+) double-positive thymocytes and thymic natural killer T cells in particular are highly sensitive to GICD. Although GICD is exploited via the use of synthetic GC analogues in the treatment of hematopoietic malignancies, the intracellular molecular pathway of GICD is not well understood. To explore GICD in thymocytes, the authors performed whole genome expression microarray analysis in mouse GR exon 2 null vs wild-type thymus RNA 3 hours after dexamethasone treatment. Identified and validated direct GR targets included P21 and Bim, in addition to an important transcriptional regulator Nfil3, which previously has been associated with GICD and is essential for natural killer cell development in vivo. Immunostaining of NFIL3 in whole thymus localized NFIL3 primarily to the medullary region, and double labeling colocalized NFIL3 to apoptotic cells. In silico analysis revealed a putative GC response element 5 kb upstream of the Nfil3 promoter that is strongly conserved in the rat genome and was confirmed to bind GR by chromatin immunoprecipitation. The knockdown of Nfil3 mRNA levels to 20% of normal using specific small interfering RNAs abrogated GICD, indicating that NFIL3 is required for normal GICD in CTLL-2 T cells.

FoxO3 mediates antagonistic effects of glucocorticoids and interleukin-2 on glucocorticoid-induced leucine zipper expression

We have analyzed the promoter of human gilz (glucocorticoid-induced leucine zipper), a dexamethasone-inducible gene that is involved in regulating apoptosis, and identified six glucocorticoid (GC)-responsive elements and three Forkhead responsive elements (FHREs). Promoter deletion analysis and point mutations showed that individual mutation of the GC-responsive elements does not affect GC-induced transcription and that FHRE-1 and FHRE-3 elements contribute to the effects of GCs. Furthermore, overexpression of the Forkhead transcription factor FoxO3 enhances GC-induced gilz mRNA expression. The functional significance of the interaction between FoxO3 and GC receptor was established in T lymphocytes. Indeed, we show that GCs failed to induce GILZ expression in the presence of IL-2, a cytokine known to antagonize GC effects in T cells. Using a constitutive active mutant of protein kinase B that inactivates FoxO3 or a FoxO3 mutant that cannot be inactivated by protein kinase B, we demonstrate that IL-2 inhibitory effects on GILZ expression are mediated through inhibition of FoxO3 transcriptional activity. Therefore, FoxO3 appears to be a key factor mediating GC and IL-2 antagonism for gilz regulation in T lymphocytes. This regulation of GILZ expression was placed in a meaningful context in evaluating the effects of GILZ on GC-induced apoptosis in T lymphocytes.

Species-specific differences in the glucocorticoid receptor transactivation function upon binding with betamethasone-esters

Glucocorticoids (GCs) are the most effective drugs for anti-inflammatory diseases. A number of adverse side effects, however, limit chronic treatment with GCs. To improve their therapeutic usefulness, attempts have been made to dissociate the two main actions of the glucocorticoid receptor (GR), transactivation and transrepression, which are believed to be responsible for the side effects and anti-inflammatory effects, respectively. We report here species-specific differences in the transactivation response mediated by GR. Dexamethasone (DEX), betamethasone (BM), and their esterified-derivatives had full transrepression agonistic activity in a reporter assay using CV-1 cells transfected with either human or rat GR. These GCs also had full transactivation agonistic activity in CV-1 cells transfected with human GR. The esterified-BM, however, had only partial transactivation agonistic activity in cells transfected with rat GR, whereas BM and esterified-DEX had full transactivation agonistic activity. Moreover, in rat hepatoma H4-II-E cells, the esterified-BM failed to induce tyrosine aminotransferase, which is regulated by GR-mediated transactivation activity. There were no significant differences between the binding affinity of these GCs to human and rat GR. Consistent with the weak transactivation activity of esterified-BM mediated by rat GR, there were few side effects, evaluated by thymus involution and body weight loss, in an antigen-induced asthmatic model in rats. These results suggest that the potency of esterified-BM to induce transactivation activity is different between species and that this difference is not due to differences in receptor binding.

Interleukin-2 inhibits glucocorticoid receptor transcriptional activity through a mechanism involving STAT5 (signal transducer and activator of transcription 5) but not AP-1

Cytokines and glucocorticoids (GCs) signaling pathways interfere with each other in the regulation of apoptosis and gene expression in the immune system. Interleukin-2 (IL-2), through the Janus kinase/signal transducers and activators of transcription (Jak/STAT) and mitogen-activated protein kinase (MAPK) pathways, activates STAT5 and activated protein-1 (AP-1) transcription factors, respectively, which are known to repress glucocorticoid receptor (GR) activity, at least in part, through protein-protein interactions. In this work, we have analyzed the mechanisms whereby IL-2 down-regulates the GC-induced transactivation of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in murine CTLL-2 T lymphocytes. Mutagenesis studies revealed that the MMTV-LTR STAT5 binding site (-923/-914) was not required for IL-2-mediated inhibition but identified both glucocorticoid response elements (GREs) and the -104/+1 region as critical elements for this negative response. The DNA binding activities of transcription factors required for GC-mediated activation of the MMTV-LTR promoter and that bind to the -104/+1 region (nuclear factor-1, Oct-1) were not affected by IL-2 treatment. Overexpression of wild-type STAT5B enhanced the effect of IL-2 on MMTV-LTR activity, and a dominant negative form of STAT5B (Y699F) abolished the IL-2-mediated MMTV-LTR inhibition, whereas AP-1 activation had no effect in this system. Direct interaction between liganded GR and STAT5 was observed in CTLL-2 cells in a STAT5 phosphorylation-independent manner. Overexpression of nuclear coactivators CBP (CREB-binding protein) or SRC-1a (steroid receptor coactivator 1a) did not blunt IL-2 inhibitory effects. We suggest that the STAT5-repressive activity on the GC-dependent transcription may involve direct interaction of STAT5 with GR, is dependent on the promoter context and STAT5 activation level, and occurs independently of coactivators levels in T cells.

The glucocorticoid receptor and STAT6 physically and functionally interact in T-lymphocytes

In lymphocytes, glucocorticoids (GC)- and interleukin-4-signaling pathways are known to interact, as evidenced by inhibition of IL-4-mediated proliferation by dexamethasone or suppression of GC-induced apoptosis by IL-4. In this study, we characterized the molecular basis for this reciprocal interference. We report that, in murine CTLL-2 cells, IL-4 inhibits GC-induced MMTV (mouse mammary tumor virus) promoter transactivation, and that GC suppress IL-4-induced transactivation of a STAT6 (signal transducers and activators of transcription 6)-responsive promoter without affecting IL-4-stimulated STAT6 DNA-binding. Moreover, we evidenced a physical association between GC receptor and STAT6, which proved to be functionally relevant, since STAT6 overexpression increased the IL-4 inhibitory effect on GC-induced MMTV transactivation.