Leptin is a growth factor in cancer

[Evaluation of serum cytokines in small cell lung cancer and its clinical significance]

背景与目的

已有的研究表明：小细胞肺癌（small cell lung cancer, SCLC）患者可出现血清细胞因子表达水平的变化，本研究通过检测SCLC患者血清中细胞因子的差异改变，探讨其在SCLC中的诊断价值。

方法

首先使用Reybiotech G6/G7细胞因子芯片对4例SCLC患者、4例健康人和4例炎症患者血清进行细胞因子差异表达筛查，进一步应用酶联免疫吸附法（ELISA试剂盒）对197例SCLC患者、180例正常对照血清以及97例炎性病变患者血清进行验证。

结果

芯片检测120种细胞因子，从有明显差异的细胞因子中选出最有研究价值的4种进行验证，包括尿激酶型纤溶酶原激活剂受体（urokinase plasminogen activator receptor, uPAR）、人瘦素（Leptin）、巨噬细胞刺激蛋白（macrophage stimulating protein α, MSP-α）和巨噬细胞炎症蛋白1β（macrophage inflammatory protein 1β, MIP-1β）。采用ELISA法验证上述结果，SCLC患者血清uPAR较健康人群以及炎症患者增高（P < 0.05），诊断的敏感度为52.93%，特异度为83.36%。Leptin在无体重变化SCLC组较健康人群以及炎症患者增高，诊断的敏感度为50.11%，特异度86.77%；而Leptin在体重下降组较对照组无明显差异。此外，血清MSP-α、MIP-1β水平在三组之间比较无明显差异。

结论

血清uPAR升高在SCLC中具有一定的诊断价值，而Leptin在无体重变化的SCLC中可能具有诊断意义。

Body mass index and survival after breast cancer diagnosis in Japanese women

BACKGROUND

Body mass index (BMI) may be an important factor affecting breast cancer outcome. Studies conducted mainly in Western countries have reported a relationship between higher BMI and a higher risk of all-cause death or breast cancer-specific death among women with breast cancer, but only a few studies have been reported in Japan so far. In the present prospective study, we investigated the associations between BMI and the risk of all-cause and breast cancer-specific death among breast cancer patients overall and by menopausal status and hormone receptor status.

METHODS

The study included 653 breast cancer patients admitted to a single hospital in Japan, between 1997 and 2005. BMI was assessed using a self-administered questionnaire. The patients were completely followed up until December, 2008. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated according to quartile points of BMI categories, respectively: <21.2, ≥21.2 to <23.3 (reference), ≥23.3 to <25.8 and ≥25.8 kg/m2.

RESULTS

During the follow-up period, 136 all-cause and 108 breast cancer-specific deaths were observed. After adjustment for clinical and confounding factors, higher BMI was associated with an increased risk of all-cause death (HR = 2.61; 95% CI: 1.01-6.78 for BMI ≥25.8 vs. ≥21.2 to <23.3 kg/m²) among premenopausal patients. According to hormonal receptor status, BMI ≥25.8 kg/m² was associated with breast cancer-specific death (HR = 4.95; 95% CI: 1.05-23.35) and BMI <21.2 kg/m2 was associated with all-cause (HR = 2.91; 95% CI: 1.09-7.77) and breast cancer-specific death (HR = 7.23; 95% CI: 1.57-33.34) among patients with ER + or PgR + tumors. Analysis by hormonal receptor status also showed a positive association between BMI and mortality risk among patients with ER + or PgR + tumors and with BMI ≥21.2 kg/m² (p for trend: 0.020 and 0.031 for all-cause and breast cancer-specific death, respectively).

CONCLUSIONS

Our results suggest that both higher BMI and lower BMI are associated with an increased risk of mortality, especially among premenopausal patients or among patients with hormonal receptor positive tumors. Breast cancer patients should be informed of the potential importance of maintaining an appropriate body weight after they have been diagnosed.

Leptin promotes glioblastoma

The hormone leptin has a variety of functions. Originally known for its role in satiety and weight loss, leptin more recently has been shown to augment tumor growth in a variety of cancers. Within gliomas, there is a correlation between tumor grade and tumor expression of leptin and its receptor. This suggests that autocrine signaling within the tumor microenvironment may promote the growth of high-grade gliomas. Leptin does this through stimulation of cellular pathways that are also advantageous for tumor growth and recurrence: antiapoptosis, proliferation, angiogenesis, and migration. Conversely, a loss of leptin expression attenuates tumor growth. In animal models of colon cancer and melanoma, a decline in the expression and secretion of leptin resulted in a reduction of tumor growth. In these models, positive mental stimulation through environmental enrichment decreased leptin secretion and improved tumor outcome. This review explores the link between leptin and glioblastoma.

Antibody colocalization microarray: a scalable technology for multiplex protein analysis in complex samples

DNA microarrays were rapidly scaled up from 256 to 6.5 million targets, and although antibody microarrays were proposed earlier, sensitive multiplex sandwich assays have only been scaled up to a few tens of targets. Cross-reactivity, arising because detection antibodies are mixed, is a known weakness of multiplex sandwich assays that is mitigated by lengthy optimization. Here, we introduce (1) vulnerability as a metric for assays. The vulnerability of multiplex sandwich assays to cross-reactivity increases quadratically with the number of targets, and together with experimental results, substantiates that scaling up of multiplex sandwich assays is unfeasible. We propose (2) a novel concept for multiplexing without mixing named antibody colocalization microarray (ACM). In ACMs, both capture and detection antibodies are physically colocalized by spotting to the same two-dimensional coordinate. Following spotting of the capture antibodies, the chip is removed from the arrayer, incubated with the sample, placed back onto the arrayer and then spotted with the detection antibodies. ACMs with up to 50 targets were produced, along with a binding curve for each protein. The ACM was validated by comparing it to ELISA and to a small-scale, conventional multiplex sandwich assay (MSA). Using ACMs, proteins in the serum of breast cancer patients and healthy controls were quantified, and six candidate biomarkers identified. Our results indicate that ACMs are sensitive, robust, and scalable.

Leptin promoter G-2548A genotypes and associated serum leptin levels in childhood acute leukemia at diagnosis and under high-dose steroid therapy

Genotype/allele distributions of leptin promoter G-2548A polymorphism, serum leptin and insulin levels and body weight were not significantly different between 72 children (39 male/33 female; age range 1.08-16, median 6 years) with acute leukemia (56 acute lymphoblastic leukemia [ALL]/16 acute non-lymphoblastic leukemia [ANLL]) at diagnosis and 70 age- and sex-matched controls (p > 0.05). The - 2548GG genotype was associated with the highest leptin levels in controls and patients with acute leukemia after 7-day high-dose methylprednisolone (HDMP) therapy (p < 0.05), while no significant association of genotype with leptin levels was detected in patients at diagnosis (p > 0.05). One-week HDMP therapy in patients carrying the - 2548G allele caused a significant increase in leptin levels and body weight (p < 0.001), whereas increases in those carrying the - 2548AA genotype were insignificant (p > 0.05). Decreases in white blood cell counts of patients after therapy were insignificant in - 2548GG (p > 0.05) yet significant in - 2548GA and - 2548AA (p < 0.05) genotypes. These results revealed no association of leptin genotype with the etiology of childhood acute leukemia but a possible association with leptin levels and effects of HDMP therapy.

Visceral obesity, metabolic syndrome, insulin resistance and cancer

This paper presents emerging evidence linking visceral adiposity and the metabolic syndrome (MetSyn) with carcinogenesis. The link between obesity and cancer has been clearly identified in a multitude of robust epidemiological studies. Research is now focusing on the role of visceral adipose tissue in carcinogenesis; as it is recognised as an important metabolic tissue that secretes factors that systemically alter the immunological, metabolic and endocrine milieu. Excess visceral adipose tissue gives rise to a state of chronic systemic inflammation with associated insulin resistance and dysmetabolism, collectively known as the MetSyn. Prospective cohort studies have shown associations between visceral adiposity, the MetSyn and increased risk of breast cancer, colorectal cancer and oesophageal adenocarcinoma. Furthermore, visceral adiposity and the MetSyn have been associated with increased tumour progression and reduced survival. The mechanisms by which visceral adiposity and the MetSyn are thought to promote tumorigenesis are manifold. These include alterations in adipokine secretion and cell signalling pathways. In addition, hyperinsulinaemia, subsequent insulin resistance and stimulation of the insulin-like growth factor-1 axis have all been linked with visceral adiposity and promote tumour progression. Furthermore, the abundance of inflammatory cells in visceral adipose tissue, including macrophages and T-cells, create systemic inflammation and a pro-tumorigenic environment. It is clear from current research that excess visceral adiposity and associated dysmetabolism play a central role in the pathogenesis of certain cancer types. Further research is required to elucidate the exact mechanisms at play and identify potential targets for intervention.

Leptin activates STAT3 and ERK1/2 pathways and induces endometrial cancer cell proliferation

Obesity is an established risk factor for endometrial cancer. Leptin, a secreted protein of the ob gene by white adipose tissue, plays an important role in the regulation of food intake and energy consumption in the brain and acts as a potential growth stimulator in normal and neoplastic cancer cells. However, a direct role for leptin in endometrial cancer has not been demonstrated. In the present study, the effect of leptin on the proliferation of Ishikawa endometrial cancer cells was investigated as well as the possible mechanism(s) underlying this action in endometrial cancers which express both short and long isoforms of leptin receptors. The expression of leptin receptor (ObRb) in Ishikawa cells was detected by RT-PCR and Western blotting. The cells after serum starvation, were treated by leptin with various concentrations (0, 10, 50, 100, 150 ng/mL) for different durations (6, 12, 24 h). The effect of leptin treatment on cell proliferation was examined by MTT assay. Meanwhile, inhibitory effect of Janus tyrosine kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) inhibitor AG490 or extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor PD98059 on the proliferation of Ishikawa cells induced by leptin was also studied. Ishikawa cells were treated with 100 ng/mL leptin for various periods (0, 20, 40, 60 min), and the levels of STAT3 phosphorylation and ERK1/2 phosphorylation were examined by Western blotting. The results showed that leptin induced the phosphorylation of STAT3 and the activation of ERK1/2 in a time- and dose-dependent manner in the Ishikawa endometrial cancer cells. Blocking STAT3 phosphorylation with the inhibitor AG490, or blocking ERK1/2 activation by the specific ERK1/2 kinase inhibitor, PD98059, abolished leptin-induced proliferation of Ishikawa cells. In addition, leptin was found to potently induce the invasion of endometrial cancer cells in a Matrigel invasion assay. Leptin-stimulated invasion was effectively blocked by pharmacological inhibitors of STAT3 (AG490) and ERK1/2 kinase (PD98059). These results suggested that leptin promotes endometrial cancer growth and invasiveness by activating STAT3 and ERK1/2 signaling pathways and therefore blocking its action at the receptor level can be a rational therapeutic strategy.

Metformin reduces the stimulatory effect of obesity on in vivo Walker-256 tumor development and increases the area of tumor necrosis

AIMS

The objective of this study was to analyze the influence of obesity and insulin resistance on tumor development and, in turn, the effect of insulin sensitizing agents.

MAIN METHODS

Male offspring of Wistar rats received monosodium glutamate (400mg/kg) (obese) or saline (control) from the second to sixth day after birth. Sixteen-week-old control and obese rats received 5×10(5) Walker-256 tumor cells, subcutaneously injected into the right flank. Some of the obese and control rats received concomitant treatment with metformin (300mg/kg) by gavage. At the 18th week, obesity was characterized. The percentage of rats that developed tumors, the tumor relative weight and the percentage of cachexia incidence were analyzed. The tumor tissue was evaluated histologically by means of hematoxylin and eosin staining.

KEY FINDINGS

Metformin did not correct the insulin resistance in obese rats. The tumor development was significantly higher in the obese group, whereas metformin treatment reduced it. After pathological analysis, we observed that the tumor tissues were similar in all groups except for adipocytes, which were found in greater quantity in the obese and metformin-treated obese groups. The area of tumor necrosis was higher in the group treated with metformin when compared with the untreated one.

SIGNIFICANCE

Metformin reduced Walker-256 tumor development but not cachexia in obese rats. The reduction occurred independently of the correction of insulin resistance. Metformin increased the area of necrosis in tumor tissues, which may have contributed to the reduced tumor development.

Cellular signal transduction pathways by leptin in colorectal cancer tissue: preliminary results

The aim of the study was to analyse genes typing with the use of the oligonucleotide microarray technique (HG-U133A, Affymetrix) differentiating colorectal cancer tissues from tissues assessed histopathologically as healthy ones among a panel of 91 mRNA of genes encoding proteins involved in activation of cellular signal transduction pathways by leptin. Frozen tumor specimens from 11 colon cancer patients in various stages of clinical progression of the disease in an I-IV stage scale according to the TNM staging were used in molecular tests. Among the genes participating in the cascade of signal transfer in cell activated by leptin, the following ones: AKT1, STAT3, MCL1 were qualified as differentiating stage I and II and VEGFC, CCNDI the encoding genes respectively as differentiating III and IV stage neoplasm. It is necessary to extend studies of analysis of cellular signal transduction pathways by leptin in colorectal cancer initiation and transformation processes.

Feeling too hot or cold after breast cancer: is it just a nuisance or a potentially important prognostic factor?

There is widespread recognition among both patients and caregivers that breast cancer patients often experience debilitating deficiencies in their ability to achieve thermal comfort, feeling excessively hot or cold under circumstances when others are comfortable. However, this symptom receives little clinical or scientific attention beyond identification and testing of drugs that minimise menopausal-like symptoms. Could some of these symptoms represent an important prognostic signal? Could thermal discomfort be among other cytokine-driven sickness behaviour symptoms seen in many breast cancer patients? While the literature reveals a strong link between treatment for breast cancer and some menopausal vasomotor symptoms (e.g. hot flashes also known as "hot flushes"), there is little data on quantitative assessment of severity of different types of symptoms and their possible prognostic potential. However, recent, intriguing studies indicating a correlation between the presence of hot flashes and reduced development of breast cancer recurrence strongly suggests that more study on this topic is needed. In comparison to reports on the phenomenon of breast cancer-associated hot flashes, there is essentially no scientific study on the large number of women who report feeling excessively cold after breast cancer treatment. Since similar acquired thermal discomfort symptoms can occur in patients with cancers other than breast cancer, there may be as yet unidentified cancer- or treatment-driven factor related to temperature dysregulation. In general, there is surprisingly little information on the physiological relationship between body temperature regulation, vasomotor symptoms, and cancer growth and progression. The goal of this article is twofold: (1) to review the scientific literature regarding acquired deficits in thermoregulation among breast cancer survivors and (2) to propose some speculative ideas regarding the possible basis for thermal discomfort among some of these women. Specifically, we suggest a potential association with excessive pro-inflammatory cytokine activity, similar to other cytokine-driven symptoms experienced after breast cancer, including fatigue and depression. We highlight the similarity of some breast cancer-associated thermal discomfort symptoms to those which occur during fever, suggesting the possibility that there may be common underlying changes in pro-inflammatory cytokine activity in both conditions. We anticipate that this contribution will stimulate additional scientific interest among researchers in identifying potential mechanisms and prognostic significance of this under-studied aspect of breast cancer biology and survivorship.

Estrogen receptor alpha pathway is involved in leptin-induced ovarian cancer cell growth

Previously, we demonstrated that leptin, a pleiotropic hormone produced by adipocytes, stimulates the growth of BG-1 ovarian cancer cells via the extracellular signal-regulated kinase signaling pathway. In this study, we further investigated the involvement of estrogen receptor (ER) pathway in the mechanism of leptin-induced ovarian cancer cell growth. Treatment with leptin (100 ng/ml) resulted in a significant increase in the cell growth of ERα-transfected OVCAR-3 and A2780 cells, whereas no significant difference was observed in ERβ-transfected cells. Downregulation of ERα using small interfering RNA completely reversed leptin-induced growth of BG-1 cells. Treatment with leptin resulted in ER transcriptional activation, i.e. nuclear localization of ER and increased expression of pS2, an estrogen-dependent gene. Luciferase reporter assay revealed that treatment of BG-1 cells with leptin (100 ng/ml) stimulated the expression of the reporter gene in the absence of estradiol (E2). To examine an involvement of Janus kinase 2/signal transducers and activators of transcription 3 (STAT-3) and phosphatidyl-inositol 3-kinase (PI3K)/Akt in leptin-induced pathway, we demonstrated that leptin increased phosphorylation of STAT-3 and Akt in BG-1 cells in a time- and dose-dependent manner. On the other hand, leptin-induced cell growth and ER transactivation were effectively blocked by specific STAT-3 inhibitor AG490 and, to a lesser extent, by PI3K inhibition. Further study with coimmunoprecipitation assay revealed that stimulation with leptin induced STAT-3 binding to ERα. Taken together, these results indicate that the stimulation of ovarian cancer cell growth by leptin involves, at least in part, ER transcriptional activation via the STAT-3 signaling pathways.

Benzyl isothiocyanate inhibits oncogenic actions of leptin in human breast cancer cells by suppressing activation of signal transducer and activator of transcription 3

Molecular effects of obesity, a well-established risk factor for breast cancer progression, are mediated by adipocytokine leptin. Given the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of this adipocytokine are much desired. We showed previously that benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables (e.g. garden cress), confers significant protection against mammary carcinogenesis in a transgenic mouse model. The present study provides first evidence for the efficacy of BITC against oncogenic effects of leptin. The BITC treatment circumvented leptin-induced clonogenicity and anchorage-independent growth of MDA-MB-231 and MCF-7 human breast cancer cells. Leptin-stimulated migration and invasion of these cells was also inhibited in the presence of BITC. Analysis of the underlying molecular mechanisms revealed that BITC treatment suppressed leptin-induced Stat3 phosphorylation and cyclin D1 transactivation. The BITC-mediated inhibition of MDA-MB-231 xenograft growth correlated with a modest yet significant decrease in levels of Tyr705 phosphorylated Stat3. The BITC treatment efficiently inhibited Stat3 and SRC1 recruitment to cyclin D1 promoter in a chromatin immunoprecipitation analysis. Furthermore, overexpression of constitutively active Stat3 imparted significant protection against BITC-mediated inhibition of cyclin D1 transactivation, whereas RNA interference of Stat3 resulted in a significant increase in BITC-mediated inhibition of cyclin D1 transactivation in the presence of leptin. These results indicate that Stat3 plays an important role in BITC-mediated inhibition of leptin-induced cyclin D1 transactivation. In conclusion, BITC could potentially be a rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.

Clinical significance of serum vascular endothelial growth factor, endostatin, and leptin levels in children with lymphoma

BACKGROUND

A number of clinical studies conducted in adults have demonstrated the prognostic significance of angiogenic factors in malignancies, however, only a limited number of studies have been conducted in children. The aim of this study was to determine serum vascular endothelial growth factor (VEGF), endostatin, and leptin levels in children with lymphoma and to investigate whether these factors provide prognostic information.

PROCEDURE

Serum samples from 36 children with lymphoma (non-Hodgkin lymphoma (NHL) N = 21, Hodgkin lymphoma (HL) N = 15) were collected at diagnosis and during remission. Serum samples were also collected from 18 healthy children as the control group. Serum VEGF and endostatin levels were quantified by using enzyme-linked immunosorbent assay (ELISA) and serum leptin by immunoradiometric assay.

RESULTS

The serum VEGF levels were found elevated in patients compared to controls (P = 0.033), while endostatin and leptin levels were lower in patients than in controls (endostatin, 43.9 ± 5.8 ng/ml vs. 123.6 ± 13.5 ng/ml, P < 0.001; leptin, 5 ± 1.5 ng/ml vs. 6.7 ± 1.2 ng/ml, P = 0.013). VEGF levels declined (pre, 151.6 ± 55.9 pg/ml vs. post, 16.2 ± 7.9 pg/ml, P = 0.041), while endostatin and leptin levels increased in patients who achieved remission (33 of 36 patients) when compared to pre-treatment levels (endostatin pre, 43.1 ± 5.9 ng/ml vs. post, 65.9 ± 6.8 ng/ml, P = 0.047; leptin, pre, 5.3 ± 1.6 ng/ml vs. post, 9.8 ± 2.7 ng/ml, P = 0.012). Serum VEGF, endostatin, and leptin levels were not predictive of survival.

CONCLUSION

Serial measurement of serum VEGF, endostatin, and leptin levels could potentially be used to predict response to treatment or progressive disease in children with lymphoma.

Insulin resistance and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) accounts for 85-90% of liver cancers and is one of the most frequent carcinomas in the world. HCCs classically develop against the background of chronic liver diseases. Common causes of such liver diseases are viral hepatitis, alcoholic hepatitis, or immune-related diseases; however, 15-50% of patients with HCCs have none of these classic antecedents, especially in developed countries. In this context, obesity and diabetes mellitus have been found to exhibit an increased risk of HCC. Both conditions are associated with insulin resistance. The tumorigenic effects of insulin resistance and complementary hyperinsulinemia could be mediated directly by insulin signaling, or indirectly related to changes in endogeneous hormone metabolism, particularly insulin-like growth factor I. Conversely, insulin resistance may be a consequence of obesity and hepatic inflammation, both of which can themselves promote tumorigenesis, mainly through cytokine production and/or generation of oxidative stress. Because the prevalence of obesity is now increasing throughout the world, insulin resistance is sure to be emphasized as a major factor in hepatocarcinogenesis in the foreseeable future.

Adiponectin antagonizes the oncogenic actions of leptin in hepatocellular carcinogenesis

Obesity is rapidly becoming a pandemic and is associated with increased carcinogenesis. Obese populations have higher circulating levels of leptin in contrast to low concentrations of adiponectin. Hence, it is important to evaluate the dynamic role between adiponectin and leptin in obesity-related carcinogenesis. Recently, we reported the oncogenic role of leptin including its potential to increase tumor invasiveness and migration of hepatocellular carcinoma (HCC) cells. In the present study we investigated whether adiponectin could antagonize the oncogenic actions of leptin in HCC. We employed HCC cell lines HepG2 and Huh7, the nude mice-xenograft model of HCC, and immunohistochemistry data from tissue-microarray to demonstrate the antagonistic role of adiponectin on the oncogenic actions of leptin. Adiponectin treatment inhibited leptin-induced cell proliferation of HCC cells. Using scratch-migration and electric cell-substrate impedance-sensing-based migration assays, we found that adiponectin inhibited leptin-induced migration of HCC cells. Adiponectin treatment effectively blocked leptin-induced invasion of HCC cells in Matrigel invasion assays. Although leptin inhibited apoptosis in HCC cells, we found that adiponectin treatment induced apoptosis even in the presence of leptin. Analysis of the underlying molecular mechanisms revealed that adiponectin treatment reduced leptin-induced Stat3 and Akt phosphorylation. Adiponectin also increased suppressor of cytokine signaling (SOCS3), a physiologic negative regulator of leptin signal transduction. Importantly, adiponectin significantly reduced leptin-induced tumor burden in nude mice. In HCC samples, leptin expression significantly correlated with HCC proliferation as evaluated by Ki-67, whereas adiponectin expression correlated significantly with increased disease-free survival and inversely with tumor size and local recurrence.

CONCLUSION

Collectively, these data demonstrate that adiponectin has the molecular potential to inhibit the oncogenic actions of leptin by blocking downstream effector molecules.

Effect of obesity on survival of women with breast cancer: systematic review and meta-analysis

Obesity is a risk factor for the development of new cases of breast cancer and also affects survival in women who have already been diagnosed with breast cancer. Early studies of obesity and breast cancer survival have been summarised in two meta-analyses, but the latest of these only included studies that recruited women diagnosed as recently as 1991. The primary aim of this study was to conduct a meta-analysis that included the more recent studies. A systematic search of MEDLINE, EMBASE and CINAHL was conducted to identify original data evaluating the effects of obesity on survival in newly diagnosed breast cancer patients. Adjusted hazard ratios (HR) from individual studies were pooled using a random effects model. A series of pre-specified sensitivity analyses were conducted on factors such as overall versus breast cancer survival and treatment versus observational cohort. The meta-analysis included 43 studies that enrolled women diagnosed with breast cancer between 1963 and 2005. Sample size ranged from 100 to 424168 (median 1192). The meta-analysis showed poorer survival among obese compared with non-obese women with breast cancer, which was similar for overall (HR = 1.33; 95% confidence interval (CI): 1.21, 1.47) and breast cancer specific survival (HR = 1.33; 95% CI: 1.19, 1.50). The survival differential varied only slightly, depending on whether body mass index (1.33; 1.21, 1.47) or waist-hip ratio (1.31; 1.08, 1.58) was used as the measure of obesity. There were larger differences by whether the woman was pre-menopausal (1.47) or post-menopausal (1.22); whether the cohort included women diagnosed before (1.31) or after 1995 (1.49); or whether the women were in a treatment (1.22) or observational cohort (1.36), but none of the differences were statistically significant. Women with breast cancer, who are obese, have poorer survival than women with breast cancer, who are not obese. However, no study has elucidated the causal mechanism and there is currently no evidence that weight loss after diagnosis improves survival. Consequently, there is currently no reason to place the additional burden of weight loss on women already burdened with a diagnosis of cancer. Further research should concentrate on assessing whether factors such as diabetes or type of chemotherapy modify the obesity effect and on understanding the causal mechanism, in particular the role of relative under-dosing.

Obesity and gastrointestinal cancer

BACKGROUND

There is emerging evidence of a strong association between obesity and gastrointestinal cancer. This review summarizes the evidence from an epidemiological and pathophysiological perspective.

METHODS

Relevant medical literature was identified from searches of PubMed and references cited in appropriate articles were identified. Selection of articles was based on peer review, journal and relevance.

RESULTS

Numerous epidemiological studies consistently identified an increased risk of developing oesophageal adenocarcinoma and colorectal carcinoma in the obese. The association between obesity and other gastrointestinal malignancies was less robust. Sex seems important with respect to cancer risk. Adipose tissue, particularly viscerally located fat, is metabolically active and exerts systemic endocrine effects. Putative pathophysiological mechanisms linking obesity and carcinogenesis include the insulin-like growth factor axis, adipocytokines and sex steroids.

CONCLUSION

A better understanding of the mechanisms that link obesity and cancer may uncover targets for intervention. Tackling obesity may result in a reduction in the incidence in addition to mortality of certain cancers in future.

Calorie restriction and cancer prevention: metabolic and molecular mechanisms

An important discovery of recent years has been that lifestyle and environmental factors affect cancer initiation, promotion and progression, suggesting that many malignancies are preventable. Epidemiological studies strongly suggest that excessive adiposity, decreased physical activity, and unhealthy diets are key players in the pathogenesis and prognosis of many common cancers. In addition, calorie restriction (CR), without malnutrition, has been shown to be broadly effective in cancer prevention in laboratory strains of rodents. Adult-onset moderate CR also reduces cancer incidence by 50% in monkeys. Whether the antitumorigenic effects of CR will apply to humans is unknown, but CR results in a consistent reduction in circulating levels of growth factors, anabolic hormones, inflammatory cytokines and oxidative stress markers associated with various malignancies. Here, we discuss the link between nutritional interventions and cancer prevention with focus on the mechanisms that might be responsible for these effects in simple systems and mammals with a view to developing chemoprevention agents.

Insulin resistance and hyperinsulinaemia in the development and progression of cancer

Experimental, epidemiological and clinical evidence implicates insulin resistance and its accompanying hyperinsulinaemia in the development of cancer, but the relative importance of these disturbances in cancer remains unclear. There are, however, theoretical mechanisms by which hyperinsulinaemia could amplify such growth-promoting effects as insulin may have, as well as the growth-promoting effects of other, more potent, growth factors. Hyperinsulinaemia may also induce other changes, particularly in the IGF (insulin-like growth factor) system, that could promote cell proliferation and survival. Several factors can independently modify both cancer risk and insulin resistance, including subclinical inflammation and obesity. The possibility that some of the effects of hyperinsulinaemia might then augment pro-carcinogenic changes associated with disturbances in these factors emphasizes how, rather than being a single causative factor, insulin resistance may be most usefully viewed as one strand in a network of interacting disturbances that promote the development and progression of cancer.

Estimation of serum leptin in oral squamous cell carcinoma

BACKGROUND

Cachexia contributes significantly to mortality in cancer patients; role of cytokines in inducing cachexia is an emerging view. Leptin, a homologous protein of cytokine family, is found to be decreased in serum with cachexia. The purpose of this study was to compare serum leptin levels of oral squamous cell carcinoma patients with that of control group and correlate it with body mass index.

METHOD

Serum samples of 31 oral squamous cell carcinoma patients and that of 28 healthy individuals were subjected to evaluation of serum leptin levels (ng/ml) using enzyme-linked immunosorbent assay.

RESULTS

A significant reduction in leptin level of oral squamous cell carcinoma patients was observed. Definite correlation between body mass index and serum leptin and also between serum leptin levels of various histopathological variants of oral squamous cell carcinoma was observed.

CONCLUSION

The results of this study suggest that evaluation of serum leptin level can provide status of cachexia in oral squamous cell carcinoma patients.

Leptin and its receptor are overexpressed in brain tumors and correlate with the degree of malignancy

Although leptin and its receptor (ObR) have emerged as important cancer biomarkers, the role of the leptin system in brain tumor development remains unknown. We screened 87 human brain tumor biopsies using immunohistochemistry and detected leptin and ObR in 55.2% and 60.9% cases, respectively. In contrast, leptin and ObR were absent in 14 samples of normal brain tissue. The presence of leptin correlated with ObR with overall concordance 80.5%. The leptin/ObR system was highly expressed in glioblastomas and anaplastic astrocytomas, while lower expression of both markers was noted in low-grade astrocytomas and gangliogliomas. The association between leptin/ObR and the degree of tumor malignancy was highly significant (P < 0.001). Using double immunofluorescence of glioblastoma tissues, we found co-expression of leptin with ObR and with the proliferation marker Ki-67 in 87% and 64% of cells, respectively. The leptin/ObR-positive tissues also expressed activated forms of STAT3 and Akt. In line with this finding, ObR-positive glioblastoma cells responded to leptin with cell growth and induction of the STAT3 and Akt pathways as well as inactivation of the cell cycle suppressor Rb. In summary, our data demonstrate that the leptin/ObR system is expressed in malignant brain tumors and might be involved in tumor progression.

Leptin receptor expression in Middle Eastern colorectal cancer and its potential clinical implication

We investigated the role of leptin receptor (Ob-R) and its relationship with phosphatidylinositol 3-kinase (PI3K)/AKT activation in colorectal carcinomas (CRCs) tissues followed by in vitro studies using a panel of CRC cell lines. Obesity serves an important risk factor of several cancers including CRC that ranks as the second most common cancer in Saudi Arabia. High levels of adipokine leptin (Ob) and its Ob-R are seen in obesity and also in various carcinomas including CRC. We investigated the proliferative and antiapoptotic effect of Ob on human CRC cell lines Caco-2, HT-29 and SW-840 and the role of PI3K/AKT-signaling pathway in mediating these actions. Then the expression of Ob-R and its relationship with clinicopathological features was analyzed in 448 CRC, 229 normal colon mucosa and 24 colorectal adenomas using tissue microarray technology. Treatment with Ob resulted in increased proliferation of CRC cell lines and involved activation of PI3K/AKT-signaling pathway. Pretreatment with Ob-R small interfering RNA or PI3K inhibitor inhibited these responses. Ob-R was significantly overexpressed in primary CRC relative to adenomas and normal colonic mucosa. In primary CRC, Ob-R significantly correlated with Ob expression, early stage and well-differentiated tumors. Intriguingly, patient with Ob-R positive tumors showed significantly better overall survival (P = 0.0098). Ob plays a critical role in CRC carcinogenesis through PI3K/AKT pathway via Ob-R. Ob-R is a prognostic marker associated with better survival.

Risk factors for Barrett's esophagus among patients with gastroesophageal reflux disease: a community clinic-based case-control study

OBJECTIVES

Our aim was to measure the relative risks of Barrett's esophagus (BE) associated with demographic factors, measures of adiposity, and smoking among patients with gastroesophageal reflux disease (GERD).

METHODS

Patients newly diagnosed with specialized intestinal metaplasia (SIM) (n=197) were compared with patients with GERD (n=418) in a community clinic-based case-control study. Case subgroups included those with any visible columnar epithelium (VBE) (n=97), and those with a long segment (>or=2 cm) of columnar epithelium (LSBE) (n=54).

RESULTS

Risks increased with older age (adjusted odds ratio (aOR) per decade for SIM=1.3, 95% confidence interval (CI)=1.1-1.5; VBE aOR=1.4, CI=1.1-1.6; LSBE aOR=1.5, CI=1.2-1.9), male gender (SIM aOR=1.5, CI=1.1-2.2; VBE aOR=2.7, CI=1.6-4.5; LSBE aOR=3.9, CI=1.9-8.1), and possibly Asian race. Increased risk of BE was observed with high waist-to-hip ratio (WHR, male high: >or=0.9, female high: >or=0.8) (SIM aOR=1.3, CI=0.9-2.1; VBE aOR=1.9, CI=1.0-3.5; LSBE aOR=4.1, CI=1.5-11.4). These associations were independent of body mass index (BMI) for the VBE and LSBE case groups but not for SIM, which was the only case group in which BMI was a significant risk factor. Ever having smoked cigarettes increased risk similarly for all case groups (SIM aOR=1.8, CI=1.2-2.6; VBE aOR=1.6, CI=1.0-2.6; LSBE aOR=2.6, CI=1.3-4.9), although a dose-response relationship was not detected for duration or intensity of smoking.

CONCLUSIONS

Older age, male gender, and history of smoking increased risk of SIM and BE among GERD patients independent of other risk factors for BE. Central adiposity was most strongly related to risk of VBE and LSBE. These results may be useful in the development of risk profiles for screening GERD patients.

[Review of the association between obesity and gastroesophageal reflux and its complications]

Esophageal adenocarcinoma and its precursor Barrett's esophagus are increasing in incidence in western populations. Gastroesophageal reflux and high body mass index (BMI) are known risk factors. Studies about Barrett's esophagus in obese patients have emphasised the role of central adiposity as a stronger risk factor than BMI in the development of specialized intestinal metaplasia and subsequently esophagus adenocarcinoma. The proinflammatory impact of adipocytokines of the abdominal fat associated with the metabolic syndrome is also relevant. Except cardiovascular diseases, type 2 diabetes and non alcoholic steatohepatitis, abdominal obesity and metabolic syndrome are responsible of an increase of prevalence of esophageal adenocarcinoma, but also other cancer sites. In this review, we study the up to date main epidemiologic and physiopathologic data concerning this association that could be important in future for a preventive action in obese patients, especially when metabolic syndrome is present.

IL-1 family in breast cancer: potential interplay with leptin and other adipocytokines

Obesity is associated with an increased risk of breast cancer. interleukin-1 (IL-1), a pro-inflammatory cytokine secreted by adipose tissue, is involved in breast cancer development. There is also convincing evidence that other adipocytokines including leptin not only have a role in haematopoiesis, reproduction and immunity but are also growth factors in cancer. Therefore, IL-1 family and leptin family are adipocytokines which could represent a major link between obesity and breast cancer progression. This minireview provides insight into recent findings on the prognostic significance of IL-1 and leptin in mammary tumours, and discusses the potential interplay between IL-1 family members and adipocyte-derived hormones in breast cancer.

Leptin regulation of proangiogenic molecules in benign and cancerous endometrial cells

Several proangiogenic/proinflammatory factors involved in endometrial cancer are regulated by leptin, but the signaling mechanisms responsible for these leptin-induced actions are largely unknown. Here, we report that in benign (primary and HES) and cancerous-endometrial epithelial cells (EEC) (An3Ca, SK-UT2 and Ishikawa), leptin in a dose-dependent manner regulates vascular endothelial growth factor, (VEGF); interleukin-1 beta, (IL-1beta); leukemia inhibitory factor, (LIF) and their respective receptors, VEGFR2, IL-1R tI and LIFR. Remarkably, leptin induces a greater increase in VEGF/VEGFR2 and LIF levels in cancer than in benign cells. However, IL-1beta was only increased by leptin in benign primary-EEC. Cancer-EEC expressed higher levels of leptin receptor (full-length OB-Rb and short isoforms) in contrast to benign primary-EEC. Leptin-mediated activation of JAK2 (janus kinase 2) was upstream to the activation of PI-3K (phosphatidylinositol-3 kinase) and/or MAPK (mitogen-activated protein kinase) signaling pathways. Leptin induction of cytokines/receptors generally involved JAK2 and MAPK activation, but PI-3K phosphorylation was required for leptin increase of LIF, IL-1/IL-1R tI. Leptin-mediated activation of mTOR (mammalian target of Rapamycin), mainly linked to MAPK, played a central role in leptin regulation of all cytokines and receptors. These results suggest that leptin's effects are cell-specific and could confer a proliferative or cell survival advantage or possibly promote endometrial thickness. Leptin's effects on proangiogenic molecules were more evident in malignant versus benign cells and may imply that there is an underlying shift in leptin-induced cell signaling pathways in endometrial cancer cells.

Barrett's esophagus

Barrett's esophagus is an important step in the pathway to esophageal adenocarcinoma. Since most patients with Barrett's esophagus are undiagnosed and patients present with advanced adenocarcinoma de novo, prognosis for this disease remains poor. To identify those people with Barrett's esophagus who are at particular risk many new technologies are being developed. In association with these advances in risk stratification, progress is being made in the endoscopic treatment of Barrett's. Chemoprevention is also an area of interest and trials are underway.

Quantitative and morphometric evaluation of the angiogenic effects of leptin

Angiogenesis is a dynamic process that requires an interaction of pro-and antiangiogenic factors. It is known that the cytokine leptin stimulates endothelial cell growth and angiogenesis, but further quantitative analysis is necessary to understand leptin angiogenic effects. The quail chorioallantoic membrane (CAM) assay has been used to study angiogenesis in vivo by focusing on morphometric parameters that quantify vascular complexity and density. We quantify the angiogenic activity of leptin using the CAM assay by digital morphometry and a computer-assisted image analysis to evaluate more precisely vessel length, diameter, branching, and tortuousity. CAM images are obtained from ex ovo cultures of E8-E9 quail embryos. MATLAB and custom software are used for our analysis. The effects of leptin, vascular endothelial growth factor-165 (VEGF(165)), and their corresponding neutralizing antibodies are compared. Our results show that CAM treated with leptin and VEGF(165) has a significant increase in vascular complexity and density. A corresponding decrease is observed using neutralizing antibodies. Notably, leptin induced more significant changes than VEGF in vessel length and tortuousity. Conversely, VEGF induced a greater increase in vessel branching than leptin. These results underscore the importance of using multiparametric quantitative methods to assess several aspects of angiogenesis and enable us to understand the proangiogenic effects of leptin.

Differential effects of leptin on the invasive potential of androgen-dependent and -independent prostate carcinoma cells

Obesity has been linked with an increased risk of prostate cancer. The formation of toxic free oxygen radicals has been implicated in obesity mediated disease processes. Leptin is one of the major cytokines produced by adipocytes and controls body weight homeostasis through food intake and energy expenditure. The rationale of the study was to determine the impact of leptin on the metastatic potential of androgen-sensitive (LNCaP) cells as well as androgen-insensitive (PC-3 and DU-145) cells. At a concentration of 200 nm, LNCaP cells showed a significant increase (20% above control; P < .0001) in cellular proliferation without any effect on androgen-insensitive cells. Furthermore, exposure to leptin caused a significant (P < .01 to P < .0001) dose-dependent decrease in migration and invasion of PC3 and Du-145 prostate carcinoma cell lines. At the molecular level, exposure of androgen-independent prostate cancer cells to leptin stimulates the phosphorylation of MAPK at early time point as well as the transcription factor STAT3, suggesting the activation of the intracellular signaling cascade upon leptin binding to its cognate receptor. Taken together, these results suggest that leptin mediates the invasive potential of prostate carcinoma cells, and that this effect is dependent on their androgen sensitivity.

Association between BMI and metabolic syndrome and adenomatous colonic polyps in Korean men

Obesity and insulin resistance are associated with the risk of colon cancer. Adenomatous colonic polyps are precancerous lesions of colon cancer. We investigated whether BMI and the metabolic syndrome are associated with the presence of adenomatous colonic polyps in Korean men. Anthropometric measurements, metabolic risk factors, and colonoscopic pathologic findings were assessed in 1,898 men who underwent routine colonoscopy at the Health Promotion Center of Asan Medical Center in 2005. The modified National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) and International Diabetes Federation (IDF) criteria were used for the definition of the metabolic syndrome. Multiple logistic regression analysis was used to evaluate the association between BMI and the metabolic syndrome and adenomatous polyps. Compared with men in the 1st quintile of the BMI, the adjusted odds ratio (OR) and 95% confidence interval (CI) for adenomatous polyps in men in the 2nd, 3rd, 4th, and 5th quintiles of the BMI were 1.55 (1.10-2.19), 1.57 (1.10-2.24), 1.94 (1.34-2.81), and 1.99 (1.31-3.01), respectively (P for trend <0.0001). Men with triglycerides (TGs) > or = 150 mg/dl were significantly more likely to have adenomatous polyps than were men with TG <150 mg/dl (OR 1.29; 95% CI 1.03-1.62). As a function of the number of metabolic risk factors, the ORs for adenomatous polyps were 1.41 (1.03-1.93), 1.52 (1.08-2.12), 1.46 (1.01-2.12), and 1.77 (1.08-2.90) for 1, 2, 3, and > or = 4 risk factors, respectively (P for trend <0.05). Adenomatous colonic polyps were significantly associated with increased BMI levels. Subjects with even one component of the metabolic syndrome had a significantly higher risk for developing adenomatous polyps compared to those subjects without any component in Korean men.

Mitogenic and anti-apoptotic actions of adipocyte-derived hormone leptin in prostate cancer cells

OBJECTIVE

To investigate the proliferative and anti-apoptotic effects of leptin on human prostate cancer cells, and the role of related signalling pathways in mediating these actions, as obesity is a possible risk factor for prostate cancer and leptin, an adipocyte-derived hormone, has mitogenic action in various cell types.

MATERIALS AND METHODS

Two human prostate cancer cell lines, DU145 and PC-3, were treated with leptin (5-100 ng/mL) for up to 48 h. Under serum-free conditions, cell proliferation was measured using a colorimetric tetrazolium assay and apoptosis by an enzyme-linked immunosorbent assay measuring cell death. Also, the phosphorylation of ERK1/2 and Akt was detected by Western blotting, and specific inhibitors of mitogen-activated protein kinase (MAPK) (PD98059; 40 microm) and phosphatidylinositol 3-kinase (PI3-K, LY294002; 40 microm) were used to evaluate the role of these signalling pathways.

RESULTS

Leptin dose-dependently increased the cell number in both cell lines for up to 48 h of incubation, the mean (sem) percentage of the control being 189 (4.3)% for DU145 and 173 (7.5)% for PC-3 (100 ng/mL leptin, 48 h; P < 0.01). Leptin also significantly reduced the number of apoptotic cells after 24 h of treatment, dose-dependently caused ERK1/2 and Akt phosphorylation; pretreatment with inhibitors of MAPK and PI3-K inhibited these responses.

CONCLUSION

These results show that chronic increases in leptin might enhance the growth of prostate cancer via the MAPK and PI3-K pathways. Further studies are needed to investigate whether the ability of leptin to stimulate mitogenic/anti-apoptotic signal transduction pathways could represent a target for anticancer drug discovery.

Reproducibility of serum leptin, insulin-like growth factor-I, and insulin-like growth factor-binding protein-3 measurements

BACKGROUND

Many epidemiologic studies examine the effects of single measurements of hormones, including those related to obesity such as insulin-like growth factors (IGFs) or leptin, on disease associations; however, few studies have determined whether these single values accurately reflect measurements over time.

METHODS

We examined the reproducibility of hormones associated with obesity, specifically leptin, IGF-I, and IGF-binding protein-3 (IGFBP-3). Two fasting blood samples, approximately four months apart, were collected from 38 participants from the Seattle metropolitan area; leptin, IGF-I, and IGFBP-3 concentrations were measured in previously unthawed serum samples. Unadjusted and adjusted intraclass correlation coefficients (ICC) were calculated to assess reproducibility.

RESULTS

Adjusting for age and sex, the ICCs for leptin, IGF-I, and IGFBP-3 were 0.73, 0.83 and 0.60, respectively. Weighted kappas yielded similar results.

CONCLUSION

These data suggest that for leptin, IGF-I, and IGFBP-3, a single fasting serum measurement can fairly reliably reflect the hormonal milieu over periods of months.

Adiposity, type 2 diabetes and the metabolic syndrome in breast cancer

Upper body obesity and the related metabolic disorder type 2 diabetes have been identified as risk factors for breast cancer, and associated with late-stage disease and a poor prognosis. Components of the metabolic syndrome, including visceral adiposity, insulin resistance, hyperglycemia and hyperinsulinemia, with or without clinically manifest diabetes mellitus, low serum high-density lipoprotein cholesterol and hypertension have all been related to increased breast cancer risk. The biochemical mechanisms include extraglandular oestrogen production, reduced sex hormone-binding globulin with consequent elevation of the bioactive plasma free oestradiol and increased insulin biosynthesis, all of which exert mitogenic effects on both untransformed and neoplastic breast epithelial cells. Obesity, type 2 diabetes and the metabolic syndrome also have in common an increased production of leptin and a decreased production of adiponectin by adipose tissue, with consequent elevations and reductions, respectively, in the circulating levels of these two adipokines. These changes in plasma leptin and adiponectin, acting through endocrine and paracrine mechanisms, have been associated in several studies with an increase in breast cancer risk and, perhaps, to more aggressive tumours; studies in vitro showed that leptin stimulates, and adiponectin inhibits, tumour cell proliferation and the microvessel angiogenesis which is essential for breast cancer development and progression.

Central adiposity and risk of Barrett's esophagus

BACKGROUND AND AIMS

Aside from chronic reflux, the etiology of Barrett's esophagus (BE) remains largely unknown. This case-control study investigated body mass index (BMI), central adiposity, and cigarette smoking and risk of BE.

METHODS

Washington residents newly diagnosed with specialized intestinal metaplasia on at least 1 of 4 esophageal biopsy specimens taken at community gastroenterology clinics (cases [n = 193]) were compared with matched population controls (n = 211). Case subgroups included those with any visible columnar epithelium (visible BE) and those with at least 2 cm of columnar epithelium (long-segment BE [LSBE]). Interviewers conducted personal interviews and took anthropometric measurements.

RESULTS

All measures of central adiposity were strongly related to BE risk, particularly for LSBE. For the high category of waist-to-hip ratio (WHR), the adjusted odds ratios were 2.4 (95% confidence interval [CI]: 1.4-3.9) for all cases, 2.8 (95% CI: 1.5-5.1) for visible BE, and 4.3 (95% CI: 1.9-9.9) for LSBE. In contrast, the associations with BMI were weaker. When BMI and WHR were modeled simultaneously, the associations with BMI were greatly attenuated, whereas those with WHR remained strong. Further adjustment for frequency of heartburn did not change these results. Cigarette smoking moderately increased risk but with no evidence of a dose-dependent response or increasing strength by case group.

CONCLUSIONS

These observations indicate the importance of identifying the mechanisms underlying obesity's role in BE and esophageal adenocarcinoma, and suggest that weight loss might be a fruitful approach to the prevention of these diseases.

Expression of leptin, leptin receptor, and hypoxia-inducible factor 1 alpha in human endometrial cancer

Recent studies suggested that Ob (Ob) and its receptor (ObR) could be involved in the pathogenesis of various human malignancies, among others in endometrial cancer. Moreover, hypoxia, which is associated with solid tumors, might stimulate, through hypoxia-inducible factor 1alpha (HIF-1alpha), expression of Ob and ObR. In this article, we analyzed by immunohistochemistry the expression of Ob, ObR, and HIF-1alpha in 60 cases of human endometrial cancer tissues as well as in 25 cases of normal endometria. Additionally, we assessed correlations among studied proteins as well as relationships with selected clinicopathological features of endometrial cancer. Immunoreactivity for Ob, ObR, and HIF-1alpha protein was observed in 56.7%, 30.0%, and 78.3% of endometrial cancers, respectively. The expression of HIF-1alpha showed a significant positive correlation with Ob (P < 0.0001, r = 0.573) and ObR (P = 0.020, r = 0.299). Moreover, we noted positive correlation between Ob and ObR (P = 0.001, r = 0.429). No statistically significant relationship was revealed between Ob, ObR, and HIF-1alpha protein in regard to patient's age, histological grade, and extent of tumor growth (pT). In conclusion, HIF-1alpha, which is related to tissue hypoxia in endometrial cancer, seems to be associated with overexpression of Ob and ObR. Ob could exert autocrine effect to stimulate endometrial cancer progression. Thus the autocrine Ob loop should be taken into consideration as a novel potential target in endometrial cancer prevention and treatment.

Concomitant activation of the JAK/STAT, PI3K/AKT, and ERK signaling is involved in leptin-mediated promotion of invasion and migration of hepatocellular carcinoma cells

Various epidemiologic studies have shown that obesity is associated with hepatocellular carcinoma. Leptin, the key player in the regulation of energy balance and body weight control, also acts as a growth factor on certain organs in both normal and disease states. It is plausible that leptin acts to promote hepatocellular carcinogenesis directly affecting malignant properties of liver cancer cells. However, a direct role for leptin in hepatocellular carcinoma has not been shown. In this study, we analyzed the role of leptin and the mechanism(s) underlying its action in hepatocellular carcinoma cells, which express both short and long isoforms of leptin receptors. Treatment with leptin resulted in increased proliferation of both HepG2 and Huh7 cells and involves activation of signal transducers and activators of transcription 3 (STAT3), AKT, and extracellular signal-regulated kinase (ERK) signaling pathways. Leptin-induced phosphorylation of ERK and AKT was dependent on Janus-activated kinase (JAK)/STAT activation. Intriguingly, we also found that leptin potently induces invasion of hepatocellular carcinoma cells in Matrigel invasion and electric cell-substrate impedance-sensing assays. Leptin-stimulated invasion was effectively blocked by pharmacologic inhibitors of JAK/STAT and, to a lesser extent, by ERK and phosphatidylinositol 3-kinase (PI3K) inhibition. Importantly, leptin also induced the migration of both HepG2 and Huh7 cells on fibronectin matrix. Inhibition of JAK/STAT, ERK, and PI3K activation using pharmacologic inhibitors effectively blocked leptin-induced migration of HepG2 and Huh7 cells. Taken together, these data indicate that leptin promotes hepatocellular carcinoma growth, invasiveness, and migration and implicate the JAK/STAT pathway as a critical mediator of leptin action. Our findings have potential clinical implications for hepatocellular carcinoma progression in obese patients.

Leptin acts as a mitogenic and antiapoptotic factor for colonic cancer cells

BACKGROUND

Obesity is associated with increased levels of leptin. The mitogenic actions of leptin have been identified in various cell types. Because obesity may be a risk factor for colonic cancer, the proliferative and antiapoptotic effects of leptin on colonic cancer cells and the role of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-K) signalling were investigated.

METHODS

Three human colonic cancer cell lines (T(84), HT29/Cl.19A and Caco-2) were treated with leptin. Cell proliferation was measured using the XTT colorimetric assay and apoptosis by a cell death enzyme-linked immunosorbent assay. Inhibitors of MAPK and PI3-K were used to evaluate the role of these signalling pathways. Phosphorylation of the downstream components extracellular signal-regulated kinase (ERK) 1/2 and Akt was detected by western blotting.

RESULTS

Leptin increased cell number in all cell lines in a dose-dependent manner and reduced the number of apoptotic cells in a cell line-dependent manner. Leptin also caused ERK1/2 and Akt phosphorylation. Pretreatment with inhibitors of MAPK and PI3-K inhibited these responses, attenuated the mitogenic action of leptin and abolished its antiapoptotic effects.

CONCLUSION

Chronic increases in leptin concentration may enhance the growth of colonic cancers via MAPK and PI3-K pathways. These effects of leptin could provide a link between obesity and colonic cancer, and may represent a target for anticancer drug development.

Molecular interactions between breast cancer cells and the bone microenvironment drive skeletal metastases

Breast cancer cells preferentially spread to bone. Bone metastases are currently incurable and therefore better treatments need to be developed. Metastasis is an inefficient, multi-step process. Specific aspects of both breast cancer cells and the bone microenvironment contribute to the development of bone metastases. Breast cancers express chemokine receptors, integrins, cadherins, and bone-resorbing and bone-forming factors that contribute to the successful and preferential spread of tumor to bone. Bone is rich in growth factors and cell types that make it a hospitable environment for breast cancer growth. Once breast cancer cells enter the bone, a highly complex vicious cycle develops, in which breast cancer cells secrete factors that act on bone cells and other cells within the bone (stem cells, T cells, platelets, adipocytes, fibroblasts, and endothelial cells), causing them to secrete factors that act on adjacent cancer cells. The steps in the metastatic cascade and the vicious cycle within bone offer unique targets for adjuvant treatments to treat and cure bone metastases.

Anorexia in cancer: role of feeding-regulatory peptides

Anorexia is one of the most common symptoms in advanced cancer and is a frequent cause of discomfort for cancer patients and their families. The pathogenesis of cancer anorexia is multi-factorial and involves most of the hypothalamic neuronal signalling pathways modulating energy homeostasis. It is considered to be the result of a failure of usual appetite and satiety signals. Loss of appetite can arise from decreased taste and smell of food, as well as from dysfunctional hypothalamic signalling pathways and cytokine production. Cytokines in particular, appear to play a key role in energy balance through persistent activation of the melanocortin system and inhibition of the neuropeptide Y pathway. The imbalance between anorexigenic and orexigenic peptides leads to suppression of appetite, and increased satiety and satiation associated with marked weight loss and decline in physical performance. High levels of serotonin also appear to contribute to these effects and recent findings implicate corticotropin-releasing factor in the pathogenesis of cancer anorexia as well. Despite significant advances in our understanding of the regulation of food intake and energy expenditure, few effective therapies are available. A better appreciation of the molecular and neuronal mechanisms that control body weight homeostasis may lead to the development of new therapies for improving the survival and quality of life of these patients.

Plasma levels of leptin and mammographic density among postmenopausal women: a cross-sectional study

Introduction

Obesity has been linked to increased risk of breast cancer in postmenopausal women. Increased peripheral production of estrogens has been regarded as the main cause for this association, but other features of increased body fat mass may also play a part. Leptin is a protein produced mainly by adipose tissue and may represent a growth factor in cancer. We examined the association between leptin plasma levels and mammographic density, a biomarker for breast cancer risk.

Methods

We included data from postmenopausal women aged 55 and older, who participated in a cross-sectional mammography study in Tromsø, Norway. Mammograms, plasma leptin measurements as well as information on anthropometric and hormonal/reproductive factors were available from 967 women. We assessed mammographic density using a previously validated computer-assisted method. Multiple linear regression analysis was applied to investigate the association between mammographic density and quartiles of plasma leptin concentration. Because we hypothesized that the effect of leptin on mammographic density could vary depending on the amount of nondense or fat tissue in the breast, we also performed analyses on plasma leptin levels and mammographic density within tertiles of mammographic nondense area.

Results

After adjusting for age, postmenopausal hormone use, number of full-term pregnancies and age of first birth, there was an inverse association between leptin and absolute mammographic density (P_trend = 0.001). When we additionally adjusted for body mass index and mammographic nondense area, no statistically significant association between plasma leptin and mammographic density was found (P_trend = 0.16). Stratified analyses suggested that the association between plasma leptin and mammographic density could differ with the amount of nondense area of the mammogram, with the strongest association between leptin and mammographic absolute density in the stratum with the medium breast fat content (P_trend = 0.003, P for interaction = 0.05).

Conclusion

We found no overall consistent association between the plasma concentration of leptin and absolute mammographic density. Although weak, there was some suggestion that the association between leptin and mammographic density could differ with the amount of fat tissue in the breast.

The metabolic syndrome: A high-risk state for cancer?

The metabolic syndrome is composed of cardiovascular risk factors including increased body mass index/waist circumference, blood pressure, plasma glucose, and triglycerides, as well as decreased high-density lipoprotein cholesterol. The essence of the metabolic syndrome lies in the clustering of these risk factors, which are associated with cardiovascular disease. Interestingly, most of the components of the metabolic syndrome have individually been linked in some way to the development of cancer. However, epidemiological studies linking the metabolic syndrome to cancer are scarce. Nevertheless, two such studies indicate that the clustering of metabolic syndrome components significantly increases the risk of colon cancer mortality compared with the individual components. The purpose of this review is to further explore the potential relationship between the metabolic syndrome and cancer risk. Specifically, we examine the hypothesis that individual components of the metabolic syndrome contribute to the development of several processes, including insulin resistance, aromatase activity, adipokine production, angiogenesis, glucose utilization, and oxidative stress/DNA damage, which can work together to increase cancer risk beyond that of the individual components alone. We propose that the metabolic syndrome be considered as a high-risk state for certain types of cancer and that this relationship should be systematically explored across cancer types.

Preparation of Leptin Antagonists by Site-Directed Mutagenesis of Human, Ovine, Rat, and Mouse Leptin's Site III

Six muteins of human, ovine, rat, and mouse leptins mutated to Ala in amino acids 39-41 or 39-42 were prepared by site-directed mutagenesis of the putative site III, which does not affect binding but is necessary for receptor activation, then expressed, solubilized in 4.5 M urea, at pH 11.3 in presence of cysteine, refolded and purified to homogeneity by anion-exchange chromatography on Q-Sepharose or combination of anion-exchange chromatography followed by gel filtration. The overall yields were 400-800 mg from 5 L of fermentation. All proteins were >98% pure as evidenced by SDS-PAGE and contained at least 95% monomers as documented by gel-filtration chromatography under nondenaturing conditions. Circular dichroism analysis revealed that all six muteins have identical secondary structure characteristic of nonmutated leptins, namely 52-63% of alpha helix content. All muteins formed a 1:1 complex with chicken leptin binding domain, (chLBD) and bound chLBD or membrane-embedded leptin receptor with affinity identical to WT leptins. Muteins were devoid of any biological activity in several bioassays but were potent competitive antagonists. Some muteins were pegylated using 40 kDa PEG. Although pegylation decreased the in vitro activity, increasing circulation half-life can recompensate this deficit, so pegylated antagonists are expected to be more potent in vivo.

Long-term low-protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk

BACKGROUND

Western diets, obesity, and sedentary lifestyles are associated with increased cancer risk. The mechanisms responsible for this increased risk, however, are not clear.

OBJECTIVE

We hypothesized that long-term low protein, low calorie intake and endurance exercise are associated with low concentrations of plasma growth factors and hormones that are linked to an increased risk of cancer.

DESIGN

Plasma growth factors and hormones were evaluated in 21 sedentary subjects, who had been eating a low-protein, low-calorie diet for 4.4 +/- 2.8 y (x +/- SD age: 53.0 +/- 11 y); 21 endurance runners matched by body mass index (BMI; in kg/m2); and 21 age- and sex-matched sedentary subjects eating Western diets.

RESULTS

BMI was lower in the low-protein, low-calorie diet (21.3 +/- 3.1) and runner (21.6 +/- 1.6) groups than in the Western diet (26.5 +/- 2.7; P < 0.005) group. Plasma concentrations of insulin, free sex hormones, leptin, and C-reactive protein were lower and sex hormone-binding globulin was higher in the low-protein, low-calorie diet and runner groups than in the sedentary Western diet group (all P < 0.05). Plasma insulin-like growth factor I (IGF-I) and the concentration ratio of IGF-I to IGF binding protein 3 were lower in the low-protein, low-calorie diet group (139 +/- 37 ng/mL and 0.033 +/- 0.01, respectively) than in the runner (177 +/- 37 ng/mL and 0.044 +/- 0.01, respectively) and sedentary Western (201 +/- 42 ng/mL and 0.046 +/- 0.01, respectively) diet groups (P < 0.005).

CONCLUSIONS

Exercise training, decreased adiposity, and long-term consumption of a low-protein, low-calorie diet are associated with low plasma growth factors and hormones that are linked to an increased risk of cancer. Low protein intake may have additional protective effects because it is associated with a decrease in circulating IGF-I independent of body fat mass.

Obesity, adipokines, and prostate cancer in a prospective population-based study

BACKGROUND

The purpose of this investigation was to examine the association of obesity and the adipokines leptin, adiponectin, and interleukin-6 (IL-6) with prostate cancer risk and aggressiveness.

METHODS

One hundred twenty-five incident prostate cancer cases and 125 age-matched controls were sampled from among participants in the original San Antonio Center for Biomarkers of Risk of Prostate Cancer cohort study. The odds ratios (OR) of prostate cancer and high-grade disease (Gleason sum >7) associated with the WHO categories of body mass index (kg/m(2)) and with tertiles of serum concentrations of adiponectin, leptin, and IL-6 were estimated using multivariable conditional logistic regression models.

RESULTS

Body mass index was not associated with either incident prostate cancer [obese versus normal; OR, 0.75; 95% confidence interval (95% CI), 0.38-1.48; P(trend) = 0.27] or high-grade versus low-grade disease (OR, 1.17; 95% CI, 0.39-3.52; P(trend) = 0.62). Moreover, none of the three adipokines was statistically significant associated with prostate cancer risk or high-grade disease, respectively: leptin (highest versus lowest tertile; OR, 0.77; 95% CI, 0.28-1.37; P(trend) = 0.57; OR, 1.20; 95% CI, 0.48-3.01; P(trend) = 0.85); adiponectin (OR, 0.87; 95% CI, 0.46-1.65; P(trend) = 0.24; OR, 1.93; 95% CI, 0.74-5.10; P(trend) = 0.85); IL-6 (OR, 0.84; 95% CI, 0.46-1.53; P(trend) = 0.98; OR, 0.84; 95% CI, 0.30-2.33; P(trend) = 0.17).

CONCLUSIONS

Findings from this nested case-control study of men routinely screened for prostate cancer and who had a high prevalence of overweight and obesity do not provide evidence to support that prediagnostic obesity or factors elaborated by fat cells strongly influence prostate cancer risk or aggressiveness. However, due to the small sample population, a small or modest effect of obesity and adipokines on these outcomes cannot be excluded.

Development of leptin antagonists and their potential use in experimental biology and medicine

Leptin is a pleotropic hormone that acts both centrally and peripherally. Whereas leptin exhibits positive effects on several physiological functions, such as regulation of energy metabolism, reproductive function and immune responses, negative actions, such as enhancement of undesired immune responses in autoimmune diseases, tumorigenesis, elevated blood pressure and cardiovascular pathologies, have also been documented. The recent development of leptin muteins with antagonistic properties and other proteins that block leptin activity opens up new possibilities for their use in research and, eventually, therapy.

The evolving role of leptin and adiponectin in chronic liver diseases

Leptin and adiponectin, the main metabolic products of adipose tissue, have been implicated in a wide spectrum of human diseases. Given the frequent presence of hepatic steatosis in several chronic liver diseases, there is currently increasing interest in the role of these adipokines in the development of hepatic steatosis and also in necroinflammation and fibrosis, mostly in patients with nonalcoholic fatty liver disease or chronic hepatitis C. According to experimental data, reduced adiponectin levels and increased leptin levels associated with leptin resistance, which are usually observed in obese patients with or without metabolic syndrome, may result in fat accumulation in the liver and in the enhancement of liver inflammation and mostly fibrogenesis. Increased leptin and decreased adiponectin serum levels have been detected initially in patients with nonalcoholic steatohepatitis and more recently in patients with chronic hepatitis C compared to healthy controls in most but not all studies, while the data on the associations between these adipokine levels and the severity of hepatic steatosis or fibrosis are still rather conflicting. However, several potential confounding parameters were not evaluated in all studies. Therefore, the associations between adipokines and liver histological lesions and their effects on liver cells should be evaluated further in prospective, carefully designed studies, including larger cohorts of patients with detailed assessment of metabolic and other potential confounding factors.

Leptin Signaling Promotes the Growth of Mammary Tumors and Increases the Expression of Vascular Endothelial Growth Factor (VEGF) and Its Receptor Type Two (VEGF-R2)

To gain insight into the mechanism(s) by which leptin contributes to mammary tumor (MT) development we investigated the effects of leptin, kinase inhibitors, and/or leptin receptor antagonists (LPrA2) on 4T1 mouse mammary cancer cells in vitro and LPrA2 on 4T1-MT development in vivo. Leptin increases the expression of vascular endothelial growth factor (VEGF), its receptor (VEGF-R2), and cyclin D1 through phosphoinositide 3-kinase, Janus kinase 2/signal transducer and activator of transcription 3, and/or extracellular signal-activated kinase 1/2 signaling pathways. In contrast to leptin-induced levels of cyclin D1 the changes in VEGF or VEGF-R2 were more dependent on specific signaling pathways. Incubation of 4T1 cells with anti-VEGF-R2 antibody increased leptin-mediated VEGF expression suggesting an autocrine/paracrine loop. Pretreatment of syngeneic mice with LPrA2 prior to inoculation with 4T1 cells delayed the development and slowed the growth of MT (up to 90%) compared with controls. Serum VEGF levels and VEGF/VEGF-R2 expression in MT were significantly lower in mice treated with LPrA2. Interestingly, LPrA2-induced effects were more pronounced in vivo than in vitro suggesting paracrine actions in stromal, endothelial, and/or inflammatory cells that may impact the growth of MT. Although all the mechanism(s) by which leptin contributes to tumor development are unknown, it appears leptin stimulates an increase in cell numbers, and the expression of VEGF/VEGF-R2. Together, these results provide further evidence suggesting leptin is a MT growth-promoting factor. The inhibition of leptin signaling could serve as a potential adjuvant therapy for treatment of breast cancer and/or provide a new target for the designing strategies to prevent MT development.

Leptin-induced growth of human ZR-75-1 breast cancer cells is associated with up-regulation of cyclin D1 and c-Myc and down-regulation of tumor suppressor p53 and p21WAF1/CIP1

Obesity has been recognized as a risk factor for breast cancer. Adipocyte-derived leptin may play as a paracrine regulator on the growth of breast cancer cells. Expression of both leptin and its OB-Rb receptor was detected in human breast cancer ZR-75-1 cells and further induced by leptin, suggesting that both expression and message mediation of leptin were autoregulated by itself. With cell counting and MTT assay, we had observed leptin stimulated ZR-75-1 growth in dose- and time-dependent manners. To study what steps of cell cycle progression leptin may involve in, we analyzed cell-cycle profile with flow cytometric analysis, mRNA and protein expressions of four cell-cycle regulators with RT-PCR and Western blotting analysis. Under the treatment of leptin, the G1 arrest of cells was reduced accompanied with up-regulation of G1 phase-specific cyclin D1 and proto-oncogene c-Myc, but down-regulation of cyclin-dependent kinase inhibitor p21(WAF1/CIP1) and tumor suppressor p53. Furthermore, JAK2 inhibitor AG490, PI3K/Akt inhibitor Wortmannin, and MEK/ERK1/2 inhibitor PD98059 were efficiently prevented leptin-promoted cell growth. Effect of cooperation between leptin and estrogen on ZR-75-1 growth had been observed. Collectively, the results showed that the proliferative effect of leptin on ZR-75-1 was associated with the up-regulation of cyclin D1 and c-Myc and down-regulation of tumor suppressor p53 and p21(WAF1/CIP1) plausibly through a hypothesized JAK2-PI3K/Akt-MEK/ERK pathway. The leptin- and OB-Rb-expressing capability of ZR-75-1 created a possible autocrine control of leptin, in which signal could be effectively amplified by itself, on cell growth.