The protective role of peroxisome proliferator-activated receptor gamma in lipotoxic podocytes.

Podocytes are specialized epithelial cells that maintain the glomerular filtration barrier. These cells are susceptible to lipotoxicity in the obese state and irreversibly lost during kidney disease leading to proteinuria and renal injury. PPARγ is a nuclear receptor whose activation can be renoprotective. This study examined the role of PPARγ in the lipotoxic podocyte using a PPARγ knockout (PPARγKO) cell line and since the activation of PPARγ by Thiazolidinediones (TZD) is limited by their side effects, it explored other alternative therapies to prevent podocyte lipotoxic damage. Wild-type and PPARγKO podocytes were exposed to the fatty acid palmitic acid (PA) and treated with the TZD (Pioglitazone) and/or the Retinoid X receptor (RXR) agonist Bexarotene (BX). It revealed that podocyte PPARγ is essential for podocyte function. PPARγ deletion reduced key podocyte proteins including podocin and nephrin while increasing basal levels of oxidative and ER stress causing apoptosis and cell death. A combination therapy of low-dose TZD and BX activated both the PPARγ and RXR receptors reducing PA-induced podocyte damage. This study confirms the crucial role of PPARγ in podocyte biology and that their activation in combination therapy of TZD and BX may be beneficial in the treatment of obesity-related kidney disease.

Regulation of adipogenesis through retinoid X receptor and/or peroxisome proliferator-activated receptor by designed lignans based on natural products in 3T3-L1 cells.

We previously synthesized two retinoid X receptor (RXR) agonists, 4'-hydroxy-3'-propyl-[1,1'-biphenyl]-3-propanoic acid ethyl ester (4'OHE) and 6-hydroxy-3'-propyl-[1,1'-biphenyl]-3-propanoic acid ethyl ester (6OHE), based on the structure of magnaldehyde B, a natural product obtained from Magnolia obovata. 4'OHE and 6OHE exhibited different selectivities for peroxisome proliferator-activated receptor (PPAR)/RXR heterodimers. To examine the regulatory effects of these compounds in adipogenesis, 3T3-L1 mouse preadipocytes were treated with a differentiation cocktail with or without test compounds to induce differentiation, and subsequently treated with test compounds in insulin-containing medium every alternate day. Lipid droplets were stained with Oil Red O to examine lipid accumulation. In addition, adipogenesis-related gene expression was measured using RT-qPCR and immunoblotting. The results showed that a PPARγ agonist, 4'OHE, which exerts agonistic effects on PPARγ and RXRα, enhanced adipogenesis similar to rosiglitazone. However, unlike GW501516, a PPARδ agonist, 6OHE and its hydrolysis product (6OHA), which exert agonistic effects on PPARδ and RXRα, suppressed adipogenesis. In a manner similar to 6OHE and 6OHA, bexarotene, an RXR agonist, suppressed adipocyte differentiation, and its anti-adipogenic effect was reversed by an RXR antagonist. Furthermore, 6OHA and bexarotene inhibited the increase in Pparγ2 and Cebpa mRNA levels 2 days after the induction of differentiation. We demonstrated the adipogenic effect of 4'OHE and anti-adipogenic effects of 6OHE and 6OHA in 3T3-L1 cells. Previously, RXR agonists have been reported to positively regulate the differentiation of mesenchymal stem cells into adipocytes, but our current data showed that they inhibited the differentiation of preadipocytes, at least 3T3-L1 cells, into adipocytes.

Inhibition of Integrin αVß3 Signaling Improves the Antineoplastic Effect of Bexarotene in Cutaneous T-Cell Lymphoma.

Bexarotene is a specific retinoid X receptor agonist that has been used for the treatment of cutaneous T-cell lymphoma (CTCL). Because bexarotene causes hypothyroidism, it requires the administration of levothyroxine. However, levothyroxine, in addition to its ubiquitous nuclear receptors, can activate the αVß3 integrin that is overexpressed in CTCL, potentially interfering the antineoplastic effect of bexarotene. We thus investigated the biological effect of levothyroxine in relation to bexarotene treatment. Although in isolated CTCL cells levothyroxine decreased, in an αVß3-dependent manner, the antineoplastic effect of bexarotene, levothyroxine supplementation in preclinical models was necessary to avoid suppression of lymphoma immunity. Accordingly, selective genetic and pharmacologic inhibition of integrin αVß3 improved the antineoplastic effect of bexarotene plus levothyroxine replacement while maintaining lymphoma immunity. Our results provide a mechanistic rationale for clinical testing of integrin αVß3 inhibitors as part of CTCL regimens based on bexarotene administration. TEASER: Inhibiting αVß3 integrin improves the antineoplastic effect of bexarotene while maintaining lymphoma immunity.

Discovery of the FDA-approved drugs bexarotene, cetilistat, diiodohydroxyquinoline, and abiraterone as potential COVID-19 treatments with a robust two-tier screening system.

Coronavirus Disease 2019 (COVID-19) caused by the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with a crude case fatality rate of about 0.5-10 % depending on locality. A few clinically approved drugs, such as remdesivir, chloroquine, hydroxychloroquine, nafamostat, camostat, and ivermectin, exhibited anti-SARS-CoV-2 activity in vitro and/or in a small number of patients. However, their clinical use may be limited by anti-SARS-CoV-2 50 % maximal effective concentrations (EC50) that exceeded their achievable peak serum concentrations (Cmax), side effects, and/or availability. To find more immediately available COVID-19 antivirals, we established a two-tier drug screening system that combines SARS-CoV-2 enzyme-linked immunosorbent assay and cell viability assay, and applied it to screen a library consisting 1528 FDA-approved drugs. Cetilistat (anti-pancreatic lipase), diiodohydroxyquinoline (anti-parasitic), abiraterone acetate (synthetic androstane steroid), and bexarotene (antineoplastic retinoid) exhibited potent in vitro anti-SARS-CoV-2 activity (EC50 1.13-2.01 µM). Bexarotene demonstrated the highest Cmax:EC50 ratio (1.69) which was higher than those of chloroquine, hydroxychloroquine, and ivermectin. These results demonstrated the efficacy of the two-tier screening system and identified potential COVID-19 treatments which can achieve effective levels if given by inhalation or systemically depending on their pharmacokinetics.