Dimorphic effect of 17β-oestradiol on pathology and oxidative stress in experimental malaria

Testosterone Modulates Oxidative Stress in a Sexually Dimorphic Manner in CBA/Ca Mice Infected with Plasmodium berghei ANKA

Malaria, the deadliest parasitic disease in the world, is sexually dimorphic, inflammatory, and oxidative. Males experience more severe symptoms and mortality than females do; therefore, the roles of 17β-estradiol and testosterone in this phenomenon have been studied. Both hormones affect oxidative stress, the primary mechanism of Plasmodium elimination. Estradiol has antioxidant activity, but the role of testosterone is controversial. Testosterone increases oxidative stress by reducing superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) activities, which increase lipoperoxidation in the testis. However, the antioxidant properties of testosterone in prostate and nervous tissue have also been reported. The discrepancies are probably because when testosterone levels increase, the aromatase enzyme transforms testosterone into estrogens that possess antioxidant activity, which masks the results. Therefore, it is unknown whether testosterone is involved in the sexual dimorphism that occurs in oxidative stress in malaria. In this work, we administered testosterone and simultaneously inhibited aromatase with letrozole to evaluate the role of testosterone in the sexually dimorphic pattern of oxidative stress that occurs in the blood, spleen, and brain of male and female CBA/Ca mice infected with Plasmodium berghei ANKA (P. berghei ANKA). Testosterone triggers parasitemia in males, who also display more oxidative stress than females in the absence of infection, leading to sexually dimorphic patterns. Interestingly, increasing testosterone levels in infected mice reduced oxidative stress in males and increased oxidative stress in females, reversing or eliminating the dimorphic patterns observed. Oxidative stress varies in each tissue; the brain was the most protected, while the blood was the greatest damaged. Our findings highlight the role of testosterone as a regulator of oxidative stress in a tissue and sex-specific manner; therefore, understanding the role of testosterone in malaria may contribute to the development of sex-specific personalized antimalarial therapies.

The Immunomodulatory Role of Estrogen in Malaria: A Review of Sex Differences and Therapeutic Implications

BACKGROUND

Malaria remains a significant global health challenge, with substantial mortality rates, particularly in tropical and subtropical regions. A notable sexual dimorphism exists in malaria, with males often experiencing higher infection and mortality rates compared to females.

OBJECTIVE

This review explores the role of estrogen in modulating immune responses to malaria, potentially explaining the observed sex differences. Estrogen, through its receptors, influences immune cell activation and cytokine production, which are critical in the immune response to malaria.

RESULTS

Utilizing data from the Global Burden of Disease (GBD) study, we analyzed sex differences in malaria burden in Central Sub-Saharan Africa from 2000 to 2021, revealing a significantly lower mortality burden for females compared to males. Epidemiological data and animal model results support the notion that estrogen plays a significant role in modulating immune responses to malaria. Estrogen receptors are widely expressed in immune cells, and estrogen can influence the activation, proliferation, and differentiation of these cells, thereby affecting cytokine production and immune response type. Additionally, selective estrogen receptor modulators (SERMs) show potential as therapeutic agents, with some studies demonstrating their efficacy in reducing parasitemia and improving malaria outcomes.

CONCLUSION

Understanding the sex differences in the pathogenesis of malaria is crucial for its prevention, treatment, and vaccine development. Estrogen's role in immune regulation highlights the need for sex-specific approaches in disease management.

Hormones in malaria infection: influence on disease severity, host physiology, and therapeutic opportunities

Human malaria, caused by Plasmodium parasites, is a fatal disease that disrupts the host's physiological balance and affects the neuroendocrine system. This review explores how malaria influences and is influenced by hormones. Malaria activates the Hypothalamus-Pituitary-Adrenal axis, leading to increased cortisol, aldosterone, and epinephrine. Cortisol, while reducing inflammation, aids parasite survival, whereas epinephrine helps manage hypoglycemia. The Hypothalamus-Pituitary-Gonad and Hypothalamus-Pituitary-Thyroid axes are also impacted, resulting in lower sex and thyroid hormone levels. Malaria disrupts the renin-angiotensin-aldosterone system (RAAS), causing higher angiotensin-II and aldosterone levels, contributing to edema, hyponatremia and hypertension. Malaria-induced anemia is exacerbated by increased hepcidin, which impairs iron absorption, reducing both iron availability for the parasite and red blood cell formation, despite elevated erythropoietin. Hypoglycemia is common due to decreased glucose production and hyperinsulinemia, although some cases show hyperglycemia due to stress hormones and inflammation. Hypocalcemia, and hypophosphatemia are associated with low Vitamin D3 and parathyroid hormone but high calcitonin. Hormones such as DHEA, melatonin, PTH, Vitamin D3, hepcidin, progesterone, and erythropoietin protects against malaria. Furthermore, synthetic analogs, receptor agonists and antagonists or mimics of hormones like DHEA, melatonin, serotonin, PTH, vitamin D3, estrogen, progesterone, angiotensin, and somatostatin are being explored as potential antimalarial treatments or adjunct therapies. Additionally, hormones like leptin and PCT are being studied as probable markers of malaria infection.

DHEA Induces Sex-Associated Differential Patterns in Cytokine and Antibody Levels in Mice Infected with Plasmodium berghei ANKA

Malaria is the most lethal parasitic disease worldwide; the severity of symptoms and mortality are higher in men than in women, exhibiting an evident sexual dimorphism in the immune response; therefore, the contribution of 17β-estradiol and testosterone to this phenomenon has been studied. Both hormones differentially affect several aspects of innate and adaptive immunity. Dehydroepiandrosterone (DHEA) is the precursor of both hormones and is the sexual steroid in higher concentrations in humans, with immunomodulatory properties in different parasitic diseases; however, the involvement of DHEA in this sexual dimorphism has not been studied. In the case of malaria, the only information is that higher levels of DHEA are associated with reduced Plasmodium falciparum parasitemia. Therefore, this work aims to analyze the DHEA contribution to the sexual dimorphism of the immune response in malaria. We assessed the effect of modifying the concentration of DHEA on parasitemia, the number of immune cells in the spleen, cytokines, and antibody levels in plasma of CBA/Ca mice infected with Plasmodium berghei ANKA (P. berghei ANKA). DHEA differentially affected the immune response in males and females: it decreased IFN-γ, IL-2 and IL-4 concentrations only in females, whereas in gonadectomized males, it increased IgG2a and IgG3 antibodies. The results presented here show that DHEA modulates the immune response against Plasmodium differently in each sex, which helps to explain the sexual dimorphism present in malaria.

Effect of Oxidative Stress-Induced Apoptosis on Active FGF23 Levels in MLO-Y4 Cells: The Protective Role of 17-β-Estradiol

The discovery that osteocytes secrete phosphaturic fibroblast growth factor 23 (FGF23) has defined bone as an endocrine organ. However, the autocrine and paracrine functions of FGF23 are still unknown. The present study focuses on the cellular and molecular mechanisms involved in the complex control of FGF23 production and local bone remodeling functions. FGF23 was assayed using ELISA kit in the presence or absence of 17β–estradiol in starved MLO-Y4 osteocytes. In these cells, a relationship between oxidative stress-induced apoptosis and up-regulation of active FGF23 levels due to MAP Kinases activation with involvement of the transcriptional factor (NF-kB) has been demonstrated. The active FGF23 increase can be due to up-regulation of its expression and post-transcriptional modifications. 17β–estradiol prevents the increase of FGF23 by inhibiting JNK and NF-kB activation, osteocyte apoptosis and by the down-regulation of osteoclastogenic factors, such as sclerostin. No alteration in the levels of dentin matrix protein 1, a FGF23 negative regulator, has been determined. The results of this study identify biological targets on which drugs and estrogen may act to control active FGF23 levels in oxidative stress-related bone and non-bone inflammatory diseases.

Tamoxifen Suppresses the Immune Response to Plasmodium berghei ANKA and Exacerbates Symptomatology

Malaria is the most lethal parasitic disease in the world. Mortality and severity in symptoms are higher in men than women, suggesting that oestrogens, which are in higher concentration in females than in males, may regulate the immune response against malaria. Tamoxifen, a selective oestrogen receptor modulator used in breast cancer treatment due to its antagonistic effect on oestrogen receptors α and β, is also studied because of its potential therapeutic use for several parasitic diseases. However, most studies, including one in malaria, have not addressed the immunomodulatory role of tamoxifen. In this work, we evaluated the effect of tamoxifen on the immune response of CBA/Ca mice against Plasmodium berghei ANKA. This study showed for the first time that tamoxifen increased parasite load, aggravated symptoms by decreasing body temperature and body weight, and worsened anaemia. Additionally, tamoxifen significantly increased the splenic index and the percentages of CD4⁺ and NK⁺ cells on day eight post-infection. By contrast, tamoxifen decreased both CD8⁺ and B220⁺ populations in the spleen and decreased the serum levels of IL-2, IL-6, and IL-17. Our findings support the notion that tamoxifen is a potent immunomodulator in malaria-infected mice and suggest caution when administering it to malaria-infected women with breast cancer.

17β-Estradiol Is Involved in the Sexual Dimorphism of the Immune Response to Malaria

Malaria is the leading cause of parasitic infection-related death globally. Additionally, malaria-associated mortality is higher in men than in women, and this sexual dimorphism reflects differences in innate and adaptive immune responses that are influenced by sex hormones. Normally, females develop more robust immune responses against parasites than males. However, most clinical and laboratory studies related to the immune response to malaria do not consider sex as a variable, and relatively few studies have compared the sex-dependent role of 17β-estradiol in this process. In this study, we decreased in vivo the levels of 17β-estradiol by gonadectomy or administered 17β-estradiol to intact or gonadectomized male and female CBA/Ca mice infected with Plasmodium berghei ANKA. Subsequently, we assessed the effects of 17β-estradiol on parasite load; the percentages of different immune cells in the spleen; the plasma levels of antibodies and pro- and anti-inflammatory cytokines; and the mRNA expression levels of cytokine-encoding genes in the brain. The results showed that the administration of 17β-estradiol increased parasitemia and decreased body weight in intact female mice. Moreover, intact females exhibited higher levels of CD8⁺ T cells and lower levels of NK1.1⁺ cells than their male counterparts under the same condition. Gonadectomy increased IFN-γ and decreased TNF-α concentrations only in intact female mice. Additionally, IL-10 levels were higher in intact females than in their male counterparts. Finally, the mRNA expression levels of cytokines coding genes in the brain showed a dimorphic pattern, i.e., gonadectomy upregulated Tnf, Il1b, and Il10 expression in males but not in females. Our findings explain the sexual dimorphism in the immune response to malaria, at least in part, and suggest potential sex-dependent implications for the efficacy of vaccines or drugs targeting malaria.