Regulation of the bioavailability of thioredoxin in the lens by a specific thioredoxin-binding protein (TBP-2)

Thioredoxin (TRx) is known to control redox homeostasis in cells. In recent years, a specific TRx binding protein called thioredoxin binding protein-2 (TBP-2) was found in other cell types and it appeared to negatively regulate TRx bioavailability and thereby control TRx biological function. In view of the sensitivity of lens transparency to redox status, proper regulation of TRx bioavailability is of the utmost importance. This study was conducted to examine the presence and function of TBP-2 in human lens epithelial cells (HLE B3). We cloned human lens TBP-2 from a human cDNA library (GenBank accession number AY 594328) and showed that it is fully homologous to the human brain TBP-2 gene. The recombinant TBP-2 protein was partially purified and mass spectrometric analysis confirmed its sequence homology to that of brain TBP-2. Immunoprecipitates obtained from HLE B3 cells using anti-TRx and anti-TBP-2 antibodies showed the presence of TRx and TBP-2 in immunoprecipitates indicating the formation of a TRx-TBP-2 complex in vivo. Furthermore, under H(2)O(2)-stress conditions, TRx gene expression was transiently up-regulated while TBP-2 gene expression was inversely down-regulated as seen in both HLE B3 cells and in the epithelial cell layers from cultured pig lenses. Cells with overexpressed TBP-2 showed lower TRx activity, grew slower and were more susceptible to oxidative stress-induced apoptosis. This is the first report of the presence of a TRx-specific binding protein in the lens. Our data suggest that TBP-2 is likely a negative regulator for the bioavailability, and therefore, the overall function of TRx in the lens.

Pharmacokinetics/pharmacodynamics of nondepleting anti-CD4 monoclonal antibody (TRX1) in healthy human volunteers

PURPOSE

TRX1 is a nondepleting anti-CD4 monoclonal IgG1 antibody being developed to induce tolerance by blocking CD4-mediated functions. The purpose of this study is to describe the pharmacokinetics (PK) and pharmacodynamics (PD) of TRX1 and to develop a receptor-mediated PK/PD model that characterizes the relationships between serum TRX1 concentration and total and free CD4 expression in healthy male volunteers.

METHODS

Nine subjects from three dosing cohorts in double-blinded, placebo-controlled phase I clinical study was included in the analysis. Serum TRX1 levels were determined using enzyme-linked immunosorbent assay. Blood total and free CD4 receptor levels were determined by using flow cytometric analyses. The receptor-mediated PK/PD model was developed to describe the dynamic interaction of TRX1 binding with CD4 receptors.

RESULTS AND CONCLUSIONS

TRX1 displayed nonlinear pharmacokinetic behavior and the CD4 receptors on T cells were saturated and down-modulated following treatment with TRX1. Results from in vitro studies using purified human T cells suggested that CD4-mediated internalization may constitute one pathway by which CD4 is down-modulated and TRX1 is cleared in vivo. The developed receptor-mediated PK/PD model adequately described the data. This PK/PD model was used to simulate PK/PD time profiles after different dosing regimens to help guide the dose selection in future clinical studies.

Recombinant human thioredoxin suppresses lipopolysaccharide-induced bronchoalveolar neutrophil infiltration in rat

Human thioredoxin (TRX) is a multifunctional redox-active protein. We previously reported that the intraperitoneal administration of recombinant human thioredoxin (rhTRX) attenuates inflammatory cytokine- or bleomycin-induced lung injury in mice. In this study, the effect of rhTRX injected intravenously after lipopolysaccharide (LPS) injection was analyzed in rats. Rats were injected with LPS followed by treatment with rhTRX. Although the bolus injection exerted no protective effect, continuous intravenous administration of rhTRX significantly suppressed percentage number of neutrophils in bronchoalveolar lavage fluid. Histological examination also showed that rhTRX decreased neutrophil infiltration in the lung tissues. Administered rhTRX was mainly excreted into the urine and the tissue accumulation of rhTRX in the lung was marginal. LPS-induced oxidative stress in the lung was slight in this model. These results demonstrated that continuous intravenous administration of rhTRX suppresses LPS-induced bronchoalveolar neutrophil infiltration by an anti-chemotactic effect. Administration of rhTRX did not promote the tumor growth nor affect chemosensitivity in the xenotransplantation model, suggesting the safety of rhTRX therapy for cancer patients.

Effects of transdermal and oral estrogen supplementation on endothelial function, inflammation and cellular redox state

The incidence of ischemic heart disease shows a sharp rise after menopause. However, the effects of hormone replacement therapy (HRT) on cardiovascular disease are still controversial. Not only oxidative stress, but also inflammation has been suggested to play an important role in the pathogenesis of cardiovascular events. We compared the effects of HRT on endothelial function, cellular antioxidant system and inflammation between oral and transdermal administration in mild hypercholesterolemic postmenopausal women. Transdermal estradiol replacement was administrated to 12 patients (mean age 53 years) for 12 weeks, and oral conjugated equine estrogen was administrated to 12 patients (mean age 54 years) for 12 weeks. The flow-mediated endothelium-dependent dilation of the brachial artery, serum levels of thioredoxin as a marker of the cytoprotective antioxidant system, and high-sensitivity C-reactive protein (hs-CRP) were measured every 4 weeks. The flow-mediated vasodilation increased with HRT (oral, baseline 4.9 +/- 0.5, 4-week 8.9 +/- 0.7*, 8-week 9.9 +/- 0.6*, 12-week 9.4 +/- 0.7*; transdermal, 4.7 +/- 0.6, 8.3 +/- 0.7*, 9.1 +/- 0.8*, 8.9 +/- 0.9%*, * = p < 0.01 versus baseline). The thioredoxin levels decreased with HRT (oral, 26.1 +/- 7.2, 24.1 +/- 8.2, 22.1 +/- 7.8, 19.1 +/- 7.0*; transdermal, 26.9 +/- 7.4, 23.4 +/- 8.7, 21.1 +/- 7.9, 19.2 +/- 7.2 ng/ml*, * = p < 0.01 versus baseline). There were no differences in the variation of the flow-mediated vasodilation or thioredoxin concentrations between the 2 groups. The hs-CRP levels increased with oral HRT (0.32 +/- 0.12, 0.72 +/- 0.17*, 0.86 +/- 0.23*, 0.88 +/- 0.21 mg/dl*, * = p < 0.01 versus baseline), while transdermal HRT did not elicit any changes (0.35 +/- 0.15, 0.34 +/- 0.17, 0.38 +/- 0.20, 0.36 +/- 0.22 mg/dl). The differences of hs-CRP concentrations between the 2 groups analyzed by 2-way ANOVA were significant (p < 0.01). Oral HRT instigated inflammation, but transdermal did not. Both oral and transdermal HRT, however, improved endothelial function and decreased oxidative stress through affecting the cellular redox state. These differentials in the effects caused by the course of administration may affect the future cardiovascular events.