Digoxin Inhibits Induction of Experimental Autoimmune Uveitis in Mice, but Causes Severe Retinal Degeneration

Digoxin Exhibits Neuroprotective Properties in a Rat Model of Dementia

Alzheimer's disease (AD) is by far the most common cause of cognitive impairment in older adults. Current treatments are entirely focused on the symptoms of AD. A complex etiology for AD has been proposed recently, in which AD leads in elevated levels of inflammation. We previously studied digoxin's involvement in the sporadic-AD intracerebroventricular (ICV)-streptozotocin (STZ) animal model due to its anti-inflammatory and neuroprotective characteristics. 18 adult sprague-dawley rats were split into three groups: control (n = 6), STZ + Saline (n = 6), and STZ + Digoxin (n = 6). Twelve AD-induced rats were split into two groups using stereotaxy five days after STZ injection (3 mg/kg) into both lateral ventricles: one group got digoxin (0.1 mg/kg/day, i.p.) for three weeks, while the other group received saline. Following treatment, each subject was subjected to a passive avoidance learning (PAL) test, followed by brain tissue harvesting. The levels of tumor necrosis factor-alpha (TNF-α) and choline acetyl transferase (ChAT) were measured in the brain, and neurons were counted using Cresyl violet staining in cornu ammonis-1 (CA1) and cornu ammonis-3 (CA3) cornu ammonis (CA3). ICV-STZ significantly shortened PAL latency, increased brain TNF-α levels, decreased brain ChAT activity, and decreased hippocampus neuron number. On the other hand, digoxin significantly reduced all of these STZ-induced deleterious effects. Digoxin significantly rescued rats from memory loss caused by ICV-STZ by decreasing hippocampal cell death, neuroinflammation, and cholinergic deficiency. These findings suggest that digoxin may be beneficial in treating cognitive impairment and Alzheimer's disease.

Frugoside delays osteoarthritis progression via inhibiting miR-155-modulated synovial macrophage M1 polarization

OBJECTIVES

Direct inhibition of M1 polarization of synovial macrophages may be a useful therapeutic treatment for OA and OA-associated synovitis. Frugoside (FGS) is a cardiac glycoside compound isolated and extracted from Calotropis gigantea. Cardiac glycosides possess interesting anti-inflammatory potential. However, the corresponding activity of FGS has not been reported. Therefore, our aim was to find direct evidence of the effects of FGS on synovial macrophage M1 polarization and OA control.

METHODS

Collagenase was used to establish an experimental mouse OA model (CIOA) with considerable synovitis. Then, FGS was intra-articular administered. The mRNA and protein levels of iNOS were analysed by real-time PCR and Western blotting in vitro. Immunohistochemical and immunofluorescence staining were used to measure the expression of F4/80, iNOS, Col2α1 and MMP13 in vivo. The levels of pro-inflammatory cytokines in FGS-treated M1 macrophage culture supernatants were analysed by flow cytometry.

RESULTS

FGS attenuates synovial inflammation and delays the development of OA in CIOA mice. Further results demonstrate that FGS inhibits macrophage M1 polarization in vitro and in vivo, which subsequently decreases the secretion of IL-6 and TNF-α, in turn delaying cartilage and extracellular matrix (ECM) degradation and chondrocyte hypertrophy. FGS inhibits macrophage M1 polarization by partially downregulating miR-155 levels.

CONCLUSION

This study demonstrates that intra-articular injection of FGS is a potential strategy for OA prevention and treatment, even at an early stage of disease progression. This is a novel function of FGS and has promising future clinical applications.

Tofacitinib inhibits the development of experimental autoimmune uveitis and reduces the proportions of Th1 but not of Th17 cells

Purpose

Tofacitinib is a pan-Janus kinase (JAK) inhibitor that suppresses cytokine signaling and in turn, the cells that participate in inflammatory immunopathogenic processes. We examined the capacity of tofacitinib to inhibit the induction of experimental autoimmune uveitis (EAU) and related immune responses.

Methods

EAU was induced in B10.A mice with immunization with bovine interphotoreceptor retinoid-binding protein (IRBP), emulsified in complete Freund's adjuvant (CFA), and a simultaneous injection of pertussis toxin. Tofacitinib, 25 mg/kg, was administered daily, and the vehicle was used for control. EAU development was assessed by histological analysis of the mouse eyes, and related immune responses were assessed by (i) the levels of interferon (IFN)-γ and interleukin (IL)-17, secreted by spleen cells cultured with IRBP; (ii) flow cytometric analysis of intracellular expression by spleen, or eye-infiltrating CD4 or CD8 cells of IFN-γ, IL-17, and their transcription factors, T-bet and RORγt. In addition, the inflammation-related cell markers CD44 and CD62L and Ki67, a proliferation marker, were tested. The proportions of T-regulatory cells expressing FoxP3 were determined by flow cytometric intracellular staining, while levels of antibody to IRBP were measured with enzyme-linked immunosorbent assay (ELISA).

Results

Treatment with tofacitinib significantly suppressed the development of EAU and reduced the levels of secreted IFN-γ, but not of IL-17. Further, treatment with tofacitinib reduced in the spleen and eye-infiltrating cells the intracellular expression of IFN-γ and its transcription factor T-bet. In contrast, treatment with tofacitinib had essentially no effect on the intracellular expression of IL-17 and its transcription factor, RORγt. The selective effect of tofacitinib treatment was particularly evident in the CD8 population. Treatment with tofacitinib also increased the population of CD44, but reduced the populations of cells producing CD62L and Ki67. Treatment with tofacitinib had no effect on the proportion of FoxP3 producing regulatory cells and on the antibody production to IRBP.

Conclusions

Treatment with tofacitinib inhibited the development of EAU, reduced the production of IFN-γ, but had essentially no effect on the production of IL-17.

Retinoschisin and Cardiac Glycoside Crosstalk at the Retinal Na/K-ATPase

Purpose

Mutations in the RS1 gene, which encodes retinoschisin, cause X-linked juvenile retinoschisis, a retinal dystrophy in males. Retinoschisin specifically interacts with the retinal sodium–potassium adenosine triphosphatase (Na/K-ATPase), a transmembrane ion pump. Na/K-ATPases also bind cardiac glycosides, which control the activity of the pump and have been linked to disturbances in retinal homeostasis. In this study, we investigated the crosstalk between retinoschisin and cardiac glycosides at the retinal Na/K-ATPase and the consequences of this interplay on retinal integrity.

Methods

The effect of cardiac glycosides (ouabain and digoxin) on the binding of retinoschisin to the retinal Na/K-ATPase was investigated via western blot and immunocytochemistry. Also, the influence of retinoschisin on the binding of cardiac glycosides was analyzed via enzymatic assays, which quantified cardiac glycoside-sensitive Na/K-ATPase pump activity. Moreover, retinoschisin-dependent binding of tritium-labeled ouabain to the Na/K-ATPase was determined. Finally, a reciprocal effect of retinoschisin and cardiac glycosides on Na/K-ATPase localization and photoreceptor degeneration was addressed using immunohistochemistry in retinoschisin-deficient murine retinal explants.

Results

Cardiac glycosides displaced retinoschisin from the retinal Na/K-ATPase; however, retinoschisin did not affect cardiac glycoside binding. Notably, cardiac glycosides reduced the capacity of retinoschisin to regulate Na/K-ATPase localization and to protect against photoreceptor degeneration.

Conclusions

Our findings reveal opposing effects of retinoschisin and cardiac glycosides on retinal Na/K-ATPase binding and on retinal integrity, suggesting that a fine-tuned interplay between both components is required to maintain retinal homeostasis. This observation provides new insight into the mechanisms underlying the pathological effects of cardiac glycoside treatment on retinal integrity.

Intoxication with Ornithogalum arabicum is a potential cause of visual impairment and irreversible blindness in dogs

We describe two dogs with persistent visual impairment after initially mild intoxication signs following ingestion of Ornithogalum arabicum plant material. Additionally, a 12-year analysis of the Dutch Poisons Information Centre database additionally reveals that ingestion of Ornithogalum plant material can be potentially life-threatening to companion animals. Further studies are necessary to confirm the involvement of cardiac glycoside-like toxins present in Ornithogalum arabicum and the toxicity of these substances to the retina.

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Intoxication with Ornithogalum arabicum leads to visual impairment and irreversible blindness in dogs.

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Intoxication with Ornithogalum arabicum may be life-threatening in companion animals.

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Ornithogalum arabicum and other species are suspected to contain heart glycosides.

Cardiac glycosides with target at direct and indirect interactions with nuclear receptors

Cardiac glycosides are compounds isolated from plants and animals and have been known since ancient times. These compounds inhibit the activity of the sodium potassium pump in eukaryotic cells. Cardiac glycosides were used as drugs in heart ailments to increase myocardial contraction force and, at the same time, to lower frequency of this contraction. An increasing number of studies have indicated that the biological effects of these compounds are not limited to inhibition of sodium-potassium pump activity. Furthermore, an increasing number of data have shown that they are synthesized in tissues of mammals, where they may act as a new class of steroid hormones or other hormones by mimicry to modulate various signaling pathways and influence whole organisms. Thus, we discuss the interactions of cardiac glycosides with the nuclear receptor superfamily of transcription factors activated by low-weight molecular ligands (including hormones) that regulate many functions of cells and organisms. Cardiac glycosides of endogenous and exogenous origin by interacting with nuclear receptors can affect the processes regulated by these transcription factors, including hormonal management, immune system, body defense, and carcinogenesis. They can also be treated as initial structures for combinatorial chemistry to produce new compounds (including drugs) with the desired properties.

Prophylactic digoxin treatment reduces IL-17 production in vivo in the neonatal calf and moderates RSV-associated disease

Respiratory syncytial virus (RSV) is a leading cause of morbidity and mortality in human infants. Bovine RSV infection of neonatal calves is pathologically and immunologically similar to RSV infection in infants, and is therefore a useful preclinical model for testing novel therapeutics. Treatment of severe RSV bronchiolitis relies on supportive care and may include use of bronchodilators and inhaled or systemic corticosteroids. Interleukin-17A (IL-17) is an inflammatory cytokine that plays an important role in neutrophil recruitment and activation. IL-17 is increased in children and rodents with severe RSV infection; and in calves with severe BRSV infection. It is currently unclear if IL-17 and Th17 immunity is beneficial or detrimental to the host during RSV infection. Digoxin was recently identified to selectively inhibit IL-17 production by antagonizing its transcription factor, retinoid-related orphan receptor γ t (RORγt). Digoxin inhibits RORγt binding to IL-17 and Th17 associated genes, and suppresses IL-17 production in vitro in human and murine leukocytes and in vivo in rodent models of autoimmune disease. We demonstrate here that in vitro and in vivo digoxin treatment also inhibits IL-17 production by bovine leukocytes. To determine the role of IL-17 in primary RSV infection, calves were treated prophylactically with digoxin and infected with BRSV. Digoxin treated calves demonstrated reduced signs of clinical illness after BRSV infection, and reduced lung pathology compared to untreated control calves. Digoxin treatment did not adversely affect virus shedding or lung viral burden, but had a significant impact on pulmonary inflammatory cytokine expression on day 10 post infection. Together, our results suggest that exacerbated expression of IL-17 has a negative impact on RSV disease, and that development of specific therapies targeting Th17 immunity may be a promising strategy to improve disease outcome during severe RSV infection.

TMP778, a selective inhibitor of RORγt, suppresses experimental autoimmune uveitis development, but affects both Th17 and Th1 cell populations

Experimental autoimmune uveitis (EAU), an animal model for severe intraocular inflammatory eye diseases, is mediated by both Th1 and Th17 cells. Here, we examined the capacity of TMP778, a selective inhibitor of RORγt, to inhibit the development of EAU, as well as the related immune responses. EAU was induced in B10.A mice by immunization with interphotoreceptor retinoid-binding protein (IRBP). Treatment with TMP778 significantly inhibited the development of EAU, determined by histological examination. In addition, the treatment suppressed the cellular immune response to IRBP, determined by reduced production of IL-17 and IFN-γ, as well as lower percentages of lymphocytes expressing these cytokines, as compared to vehicle-treated controls. The inhibition of IFN-γ expression by TMP778 is unexpected in view of this compound being a selective inhibitor of RORγt. The observation was further confirmed by the finding of reduced expression of the T-bet (Tbx21) gene, the transcription factor for IFN-γ, by cells of TMP778-treated mice. Thus, these data demonstrate the capacity of TMP778 to inhibit pathogenic autoimmunity in the eye and shed new light on its mode of action in vivo.

Digoxin-induced retinal degeneration depends on rhodopsin

Na,K-ATPases are energy consuming ion pumps that are required for maintaining ion homeostasis in most cells. In the retina, Na,K-ATPases are especially important to sustain the dark current in photoreceptor cells needed for rapid hyperpolarization of rods and cones in light. Cardiac glycosides like digoxin inhibit the activity of Na,K-ATPases by targeting their catalytic alpha subunits. This leads to a disturbed ion balance, which can affect cellular function and survival. Here we show that the treatment of wild-type mice with digoxin leads to severe retinal degeneration and loss of vision. Digoxin induced cell death specifically in photoreceptor cells with no or only minor effects in other retinal cell types. Photoreceptor-specific cytotoxicity depended on the presence of bleachable rhodopsin. Photoreceptors of Rpe65 knockouts, which have no measurable rhodopsin and photoreceptors of Rpe65^R91W mice that have <10% of the rhodopsin found in retinas of wild-type mice were not sensitive to digoxin treatment. Similarly, cones in the all-cone retina of Nrl knockout mice were also not affected. Digoxin induced expression of several genes involved in stress signaling and inflammation. It also activated proteins such as ERK1/2, AKT, STAT1, STAT3 and CASP1 during a period of up to 10 days after treatment. Activation of signaling genes and proteins, as well as the dependency on bleachable rhodopsin resembles mechanisms of light-induced photoreceptor degeneration. Digoxin-mediated photoreceptor cell death may thus be used as an inducible model system to study molecular mechanisms of retinal degeneration.