Peripheral but not central leptin prevents the immunosuppression associated with hypoleptinemia in rats

Serum and Tissue Expression Levels of Leptin and Leptin Receptor Are Putative Markers of Specific Feline Mammary Carcinoma Subtypes

Obesity is an established risk factor for breast cancer in post-menopausal women, being associated with elevated serum levels of leptin. Although overweight is a common condition in cat, the role of leptin and its receptor in feline mammary carcinoma remains unsettled. In this study, serum leptin and leptin receptor (ObR) levels were investigated in 58 cats with mammary carcinoma and compared with those of healthy animals, as were the expression levels of leptin and ObR in tumor tissues. The results showed that the Free Leptin Index is significantly decreased in cats with mammary carcinoma (p = 0.0006), particularly in those with luminal B and HER2-positive tumors, and that these animals also present significantly lower serum leptin levels (p < 0.0001 and p < 0.005, respectively). Interestingly, ulcerating tumors (p = 0.0005) and shorter disease-free survival (p = 0.0217) were associated to serum leptin levels above 4.17 pg/mL. In contrast, elevated serum ObR levels were found in all cats with mammary carcinoma (p < 0.0001), with levels above 16.89 ng/mL being associated with smaller tumors (p = 0.0118), estrogen receptor negative status (p = 0.0291) and increased serum levels of CTLA-4 (p = 0.0056), TNF-α (p = 0.0025), PD-1 (p = 0.0023), and PD-L1 (p = 0.0002). In tumor samples, leptin is overexpressed in luminal B and triple-negative carcinomas (p = 0.0046), whereas ObR is found to be overexpressed in luminal B tumors (p = 0.0425). Altogether, our results support the hypothesis that serum levels of leptin and ObR can be used as biomarkers of specific feline mammary carcinoma subtypes, and suggests the use of leptin antagonists as a therapeutic tool, reinforcing the utility of the cat as a cancer model.

Leptin in autoimmune diseases

The past twenty years of research on leptin has provided crucial information on the link between metabolic state and immune system function. Adipocytes influence not only the endocrine system but also the immune response, through several cytokine-like mediators known as adipokines, which include leptin. Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence hematopoiesis, thermogenesis, reproduction, angiogenesis, and more importantly immune homeostasis. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-α). Leptin links nutritional status and proinflammatory T helper 1 (Th1) immune responses and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. Conversely, elevated circulating leptin levels in obesity appear to contribute to the low-grade inflammatory background which makes obese individuals more susceptible to increased risk of developing cardiovascular diseases, diabetes, or degenerative disease including autoimmunity and cancer. In this review, we provide an overview of recent advances on the role of leptin in the pathogenesis of several autoimmune disorders that may be of particular relevance in the modulation of the autoimmune attack through metabolic-based therapeutic approaches.

Leptin as an immunomodulator

Leptin is an adipocyte-derived hormone/cytokine that links nutritional status with neuroendocrine and immune functions. In humans, leptin influences energy homeostasis and regulates neuroendocrine function primarily in states of energy deficiency. Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence basal metabolism, hematopoiesis, thermogenesis, reproduction, and angiogenesis. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-α). Leptin links nutritional status and proinflammatory T helper 1 (Th1) immune responses and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. Similar to other pro-inflammatory cytokines, leptin promotes Th1-cell differentiation and can modulate the onset and progression of autoimmune responses in several animal models of disease. Here, we review the advances and controversy for a role of leptin in the pathophysiology of immune responses and discuss novel possible therapeutic implications for leptin modulators.

Sex-dependent alterations in response to maternal deprivation in rats

We review here our latest results regarding short- and long-term effects of a neonatal maternal deprivation (MD) stress [24h at postnatal day (PND) 9] on diverse psychoneuroimmunoendocrine parameters, pointing out the existence of numerous sexual dimorphisms. Behavioral changes observed in MD animals might be at least in part attributable to neurodevelopmental effects of MD-induced elevated corticosterone levels. Our findings of short-term effects of MD on hippocampal and cerebellar neurons and glial cells appear to support this hypothesis. However, it is important to note that these cellular effects were more marked in males than in females. Moreover, in analyzing the effects of this neonatal stress on the endocannabinoid system (hippocampal endocannabinoid levels and CB1 receptors) we have also found that males were more affected by MD. Since all these sexual dimorphisms were found at an early neonatal age (PND 13), they are attributable to organizational effects of gonadal steroids. We discuss the potential implications of the elevated corticosterone and decreased leptin levels shown by MD animals in their diverse functional alterations, including the above mentioned neural effects as well as the intriguing persistent deficit in their immunological system. We also emphasize the necessity of analyzing the important influence of sex as regards the specific consequences of early life stress.

Leptin receptor isoforms mRNA expression in peripheral blood mononuclear cells from patients with chronic viral hepatitis

There is accumulating evidence that leptin has a pleiotropic role in hematopoiesis, immune response, fibrogenesis, and hepatocarcinogenesis. We investigated the expression of leptin and leptin receptor (OB-R) at the protein level by flow cytometry and also quantified by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) the two major leptin receptor isoforms (OB-Rl, OB-Rs) in peripheral blood mononuclear cells (PBMCs) of patients with hepatitis B (HBV; n = 31), hepatitis C (HCV; n = 34), and nonviral liver disease (n = 25), and healthy controls (n = 36), as well as in liver tissues of HBV (n = 8), HCV (n = 7), and healthy individuals (n = 6). Serum leptin levels were measured in all participants (N = 126). We observed significantly lower OB-Rl and OB-Rs mRNA levels in PBMCs of HBV and HCV patients compared with healthy controls and nonviral liver disease patients (P < 0.05). Flow cytometry analysis confirmed the real-time RT-PCR results. Expression of leptin and OB-Rl was significantly increased in viral hepatitis liver tissues compared with healthy tissues (P < 0.01). OB-Rl mRNA levels were not associated with hepatitis patients' clinical status (inactive, chronic hepatitis, or cirrhosis). We also found decreased serum leptin in HBV and HCV patients compared with healthy individuals and the nonviral liver disease group. Leptin was expressed in 3 of 34 HCV (8.8%) and 19 of 25 (76%) nonviral liver disease patients. Moreover, expression of OB-Rl and OB-Rs were associated when all individuals were grouped together (r = 0.78, P < 0.001). In conclusion, our findings may suggest the involvement of the leptin system in the immunopathology of chronic viral hepatitis.

Hyperleptinemia and its relation with peripheral C34(+)CD7(+) stem cells in renal transplant recipients

OBJECTIVES

Leptin, the Ob gene product, centrally regulates weight control. Transplant recipients are exposed to many factors affecting body mass. Leptin has been reported to activate the peripheral immune system. In this study, we evaluated serum leptin levels and factors contributing to hyperleptinemia; the relationship between serum leptin levels and lymphoid stem and mature cells; and their role in the rejection process in renal transplant recipients.

MATERIALS AND METHODS

Sixty-three renal transplant recipients were included in the study. Patients were grouped according to serum leptin percentiles as hypoleptinemic (n=17), normoleptinemic (n=32), and hyperleptinemic (n=14). We determined serum leptin levels by radioimmunoassay and absolute number of CD34(+), CD7(+), CD34(+)CD7(+) lymphoid stem cells, CD4(+) and CD8(+) lymphocytes in peripheral blood by flow cytometry.

RESULTS

The hyperleptinemic patients constituted 22.3% of the transplant patient. The mean peripheral blood CD34(+)CD7(+) lymphocyte count was significantly higher in hyperleptinemic patients than in normo- or hypoleptinemic patients (6.9, 6.1, and 44.3 cells/mm(3), respectively, P<0.05). There were no significant differences in the mean CD34(+), CD7(+), CD8(+), and CD4(+) lymphocyte count and CD4/CD8 ratio among the groups with respect to serum leptin levels. CD34(+)CD7(+) lymphocyte count was positively correlated with serum leptin levels (r=0.416, P<0.05).

CONCLUSIONS

Hyperleptinemia is not rare during the posttransplant period. Our data support the results of previous experimental studies that have demonstrated the effect of the leptin hormone on lymphoid stem cells. The central and peripheral effects of leptin may differ on lymphoid stem cells and a serum threshold level may apply for the central effects.

Leptin in immunology

Leptin is an adipokine which conveys information on energy availability. In humans, leptin influences energy homeostasis and regulates neuroendocrine function primarily in states of energy deficiency. As a cytokine, leptin also affects thymic homeostasis and, similar to other proinflammatory cytokines, leptin promotes Th1 cell differentiation and cytokine production. We review herein recent advances on the role of leptin in the pathophysiology of immune responses.

The weight of leptin in immunity

Leptin is an adipocyte-derived hormone/cytokine that links nutritional status with neuroendocrine and immune functions. As a hormone, leptin regulates food intake and basal metabolism, and is sexually dimorphic - that is, its serum concentration is higher in females than in males with a similar body fat mass. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 and tumour-necrosis factor. Similar to other pro-inflammatory cytokines, leptin promotes T helper 1 (TH1)-cell differentiation and can modulate the onset and progression of autoimmune responses in several animal models of disease. Here, we review the advances and controversy for a role of leptin in the pathophysiology of immune responses.