Mitochondrially targeted tamoxifen alleviates markers of obesity and type 2 diabetes mellitus in mice
Eliska Vacurova, Jaroslava Trnovska, Petr Svoboda, Vojtech Skop, Vendula Novosadova, David Pajuelo Reguera, Silvia Petrezselyová, Benoit Piavaux, Berwini Endaya, Frantisek Spoutil, Dagmar Zudova, Jan Stursa, Magdalena Melcova, Zuzana Bielcikova, Lukas Werner, Jan Prochazka, Radislav Sedlacek, Martina Huttl, Sona Stemberkova Hubackova, Martin Haluzik & Jiri Neuzil
Abstract
Type 2 diabetes mellitus represents a major health problem with increasing prevalence worldwide. Limited efficacy of current therapies has prompted a search for novel therapeutic options. Here we show that treatment of pre-diabetic mice with mitochondrially targeted tamoxifen, a potential anti-cancer agent with senolytic activity, improves glucose tolerance and reduces body weight with most pronounced reduction of visceral adipose tissue due to reduced food intake, suppressed adipogenesis and elimination of senescent cells. Glucose-lowering effect of mitochondrially targeted tamoxifen is linked to improvement of type 2 diabetes mellitus-related hormones profile and is accompanied by reduced lipid accumulation in liver. Lower senescent cell burden in various tissues, as well as its inhibitory effect on pre-adipocyte differentiation, results in lower level of circulating inflammatory mediators that typically enhance metabolic dysfunction. Targeting senescence with mitochodrially targeted tamoxifen thus represents an approach to the treatment of type 2 diabetes mellitus and its related comorbidities, promising a complex impact on senescence-related pathologies in aging population of patients with type 2 diabetes mellitus with potential translation into the clinic.
Introduction
The increasing prevalence of type 2 diabetes mellitus (T2DM) with its chronic debilitating complications represents one of the most significant health threats worldwide1. Diabetes, currently affecting 422 million people around the globe, is expected to become the seventh leading cause of death by 20301. This is particularly evident in elderly patients, where it can affect as many as 30–40% of the population compared to ~6–25% of patients under 65 years of age2.
A combination of genetic predisposition, sedentary lifestyle, and excessive intake of calorie-rich food leads to obesity that, in turn, considerably increases the risk of T2DM development3,4. Excessive accumulation of adipose tissue and its functional changes largely contribute to the etiopathogenesis of T2DM and accompanying diseases, such as arterial hypertension, dyslipidemia, non-alcoholic fatty liver disease (NAFLD), and many other pathologies5. In patients with obesity, markedly enlarged adipocytes, in particular in the visceral fat compartment, are more prone to apoptosis that stimulates mobilization of pro-inflammatory macrophages and other immunocompetent cells into visceral fat6. As a result, adipose tissue produces excessive amounts of pro-inflammatory factors that are released into the circulation and contribute to the development of sub-clinical inflammation, typically present in patients with T2DM and obesity7. Furthermore, chronic/enhanced ectopic lipid accumulation in non-adipose tissues contributes to the development of insulin resistance in the liver and muscles, and to increased apoptosis of insulin-producing β-cells in the pancreas8.
Changes induced by long-standing, poorly controlled obesity followed by the development of T2DM are linked to premature senescence in various tissues, contributing to further deterioration of their function and eventually to the development of chronic irreversible complications9. Cellular senescence is a form of cell cycle arrest that limits the proliferative potential of cells10. Despite the arrest, senescent cells are metabolically active and produce various cytokines, chemokines, proteases, and growth factors (collectively referred to as “senescence-associated secretory phenotype”, SASP) that affect the surrounding environment11. The inability of immune cells to eliminate senescent cells from the organism results in chronic inflammation and gradual tissue damage, as seen in the panoply of age-related pathologies, including T2DM12.
Senescent cells play an important role in the induction of T2DM pathogenesis13. Considering that metabolic and signaling changes associated with T2DM can promote senescence, senescent cells are components of the “pathogenic loop” in diabetes. In obese and diabetic mice, visceral adipose tissue (VAT) is the most prominent compartment of senescent cells accumulation. VAT, therefore, presents the nexus of mechanisms involved in longevity and age-related metabolic dysfunctions14. A close relationship between visceral fat content and the risk of T2DM and cardiovascular complications has also been demonstrated in humans. Components of SASP secreted by adipose‐derived senescent cells confer insulin resistance to metabolic tissues and attract immune cells that can exacerbate the effects of insulin resistance14,15. Moreover, there is a close relationship between senescence and fat accumulation in hepatocytes followed by the development of steatosis in diabetic mice16.
Senolytic agents may improve glucose control and obesity- and diabetes-related pathologies14, supporting the idea that targeting senescent cells may be a promising strategy for T2DM management. Mitochondrial function is an important determinant of the aging process (reviewed in ref. 17), and we have recently reported that targeting mitochondria in senescent cells presents a plausible way to eliminate such cells in the context of pathological senescence as well as senescence-associated diseases18. Using mitochondrially targeted tamoxifen (MitoTam), our proprietary agent with anticancer activity19 that has recently undergone Phase 1/1b clinical trial (EudraCT 2017-004441-25), we have achieved specific elimination of senescent cells. Treatment with MitoTam effectively reduces oxidative phosphorylation (OXPHOS) and mitochondrial membrane potential in senescent cells, and severely affects mitochondrial morphology based on a low level of the ADP/ATP translocation channel ANT2 (adenine nucleotide translocase 2). These cells cannot, therefore, pump ATP inside mitochondria in order to maintain mitochondrial potential by cleavage of ATP by ATPase, resulting in the collapse of mitochondrial integrity and function18. Based on these results, we reasoned that MitoTam may present a non-cannonical therapeutic modality to treat senescence-associated pathologies, such as T2DM.
Here we show that MitoTam considerably improves glucose control, decreases body weight, and reduces diabetic markers as well as diabetic comorbidities in mice with diet-induced obesity and prediabetes. These improvements are associated not only with a reduction of food intake (FI) and a drop in the number of senescent cells in the organism but also with rejuvenation of the adipose tissue, suggesting the role of MitoTam in T2DM treatment and prevention of chronic diabetic complications.
