Elevated uptake of low density lipoprotein by drug resistant human leukemic cell lines

Cholesterol metabolism in pancreatic cancer and associated therapeutic strategies

Pancreatic cancer remains one of the most lethal cancers due to late diagnosis and high chemoresistance. Despite recent progression in the development of chemotherapies, immunotherapies, and potential nanoparticles-based approaches, the success rate of therapeutic response is limited which is further compounded by cancer drug resistance. Understanding of emerging biological and molecular pathways causative of pancreatic cancer's aggressive and chemoresistance is vital to improve the effectiveness of existing therapeutics and to develop new therapies. One such under-investigated and relatively less explored area of research is documenting the effect that lipids, specifically cholesterol, and its metabolism, impose on pancreatic cancer. Dysregulated cholesterol metabolism has a profound role in supporting cellular proliferation, survival, and promoting chemoresistance and this has been well established in various other cancers. Thus, we aimed to provide an in-depth review focusing on the significance of cholesterol metabolism in pancreatic cancer and relevant genes at play, molecular processes contributing to cellular cholesterol homeostasis, and current research efforts to develop new cholesterol-targeting therapeutics. We highlight the caveats, weigh in different experimental therapeutic strategies, and provide possible suggestions for future research highlighting cholesterol's importance as a therapeutic target against pancreatic cancer resistance and cancer progression.

Atorvastatin improves cisplatin sensitivity through modulation of cholesteryl ester homeostasis in breast cancer cells

BACKGROUND

Acquired treatment resistance is a significant problem in breast cancer management, and alterations in lipid metabolism have been proposed to contribute to the development of drug resistance as well as other aspects of tumor progression. The present study aimed to identify the role of cholesterol metabolism in MCF-7 and MDA-MB-231 breast cancer cell response to cisplatin (CDDP) treatment in the acute setting and in a model of CDDP resistance.

METHODS

MCF-7 (luminal A), MDA-MB-231 (triple-negative) and CDDP-resistant MDA-MB-231 (MDACR) cell lines were grown in the presence or absence of CDDP in combination with atorvastatin (ATV), lipid depletion or low-density lipoprotein loading and were analyzed by a variety of biochemical and radiometric techniques.

RESULTS

Co-administration of CDDP and ATV strongly reduced cell proliferation and viability to a greater extent than CDDP alone, especially in MDA-MB-231 cells. These findings were associated with reduced cholesteryl ester synthesis and storage in MDA-MB-231 cells. In MDACR cells, acetyl-CoA acetyltransferase 1 (ACAT-1) was upregulated compared to naïve MDA-MB-231 cells and ATV treatment restored CDDP sensitivity, suggesting that aberrant ACAT-1 expression and associated changes in cholesterol metabolism contribute to CDDP resistance in MDA-MB-231 cells.

CONCLUSION

These findings indicate that the elevated susceptibility of MDA-MB-231 cells to co-administration of CDDP and ATV, is associated with an increased reliance on cholesteryl ester availability. Our data from these cell culture-based studies identifies altered cholesterol homeostasis as an adaptive response to CDDP treatment that contributes to aggressiveness and chemotherapy resistance.

Cholesterol metabolism and lipid droplet vacuoles; a potential target for the therapy of aggressive lymphoma

Cholesterol uptake via LDL receptor (LDLR) is increased in some malignant tumors, and incorporated LDL contribute to lipid droplet formation. Burkitt's lymphoma is known to have a large number of vacuoles in the cytoplasm, however, intracellular vacuoles are also seen in high-grade lymphomas such as adult T-cell leukemia/lymphoma, diffuse large B-cell lymphoma and primary central nervous system lymphoma. Recent studies have shown that esterified cholesterol is the main component of these vacuoles and the expression of cholesterol metabolism-related molecules such as LDLR, acetyl-CoA acetyltransferase 1 (ACAT1) which esterifies free cholesterol, and scavenger receptor class B type I (SR-BI) which effluxes free cholesterol, was significantly upregulated in lymphoma cells. Moreover, negative feedback of LDLR was not regulated even under cholesterol-rich conditions in lymphoma cells. We found that cytoplasmic free cholesterol was increased by ACAT and SR-BI inhibitors (CI-976 and BLT-1, respectively), and the accumulation of free cholesterol induced lymphoma cell apoptosis. In addition, overexpression of lipid droplet surface proteins has been correlated with poor prognosis in several malignant tumor such as ovarian cancer and clear cell renal cell carcinoma, and it is important to evaluate lipid droplet formation in malignant tumors including lymphomas.

Ferredoxin reductase and p53 are necessary for lipid homeostasis and tumor suppression through the ABCA1-SREBP pathway

p53 is known to modulate metabolism and FDXR is required for steroidogenesis. Given that FDXR is a target/regulator of p53, the FDXR–p53 axis may play a unique role in lipid metabolism. Here, we found that expression of ABCA1, a cholesterol-efflux pump, was suppressed by loss of FDXR and/or p53, leading to activation of master lipogenic regulators SREBP1/2. Accordingly, lipid droplets, cholesterol, and triglycerides were increased by loss of FDXR or p53, which were further increased by loss of both FDXR and p53. To explore the biological significance of the FDXR–p53 axis, we generated a cohort of mice deficient in Fdxr and/or Trp53. We found that Fdxr^+/−, Trp53^+/−, and Fdxr^+/−;Trp53^+/− mice had a short life span and were prone to spontaneous tumors and liver steatosis. Moreover, the levels of serum cholesterol and triglycerides were significantly increased in Fdxr^+/− and Trp53^+/− mice, which were further increased in Fdxr^+/−;Trp53^+/− mice. Interestingly, loss of Fdxr but not p53 led to accumulation of serum low-density lipoprotein. Together, our findings reveal that the FDXR–p53 axis plays a critical role in lipid homeostasis and tumor suppression.

Advances in Management of Bladder Cancer-The Role of Photodynamic Therapy

Photodynamic therapy (PDT) is a non-invasive and modern form of therapy. It is used in the treatment of non-oncological diseases and more and more often in the treatment of various types of neoplasms in various locations including bladder cancer. The PDT method consists of local or systemic application of a photosensitizer, i.e., a photosensitive compound that accumulates in pathological tissue. Light of appropriate wavelength is absorbed by the photosensitizer molecules, which in turn transfers energy to oxygen or initiates radical processes that leads to selective destruction of diseased cells. The technique enables the selective destruction of malignant cells, as the photocytotoxicity reactions induced by the photosensitizer take place strictly within the pathological tissue. PDT is known to be well tolerated in a clinical setting in patients. In cited papers herein no new safety issues were identified. The development of anti-cancer PDT therapies has greatly accelerated over the last decade. There was no evidence of increased or cumulative toxic effects with each PDT treatment. Many modifications have been made to enhance the effects. Clinically, bladder cancer remains one of the deadliest urological diseases of the urinary system. The subject of this review is the anti-cancer use of PDT, its benefits and possible modifications that may lead to more effective treatments for bladder cancer. Bladder cancer, if localized, would seem to be a good candidate for PDT therapy since this does not involve the toxicity of systemic chemotherapy and can spare normal tissues from damage if properly carried out. It is clear that PDT deserves more investment in clinical research, especially for plant-based photosensitizers. Natural PS isolated from plants and other biological sources can be considered a green approach to PDT in cancer therapy. Currently, PDT is widely used in the treatment of skin cancer, but numerous studies show the advantages of related therapeutic strategies that can help eliminate various types of cancer, including bladder cancer. PDT for bladder cancer in which photosensitizer is locally activated and generates cytotoxic reactive oxygen species and causing cell death, is a modern treatment. Moreover, PDT is an innovative technique in oncologic urology.

Lipoproteins as Markers for Monitoring Cancer Progression

Lipoproteins are among the contributors of energy for the survival of cancer cells. Studies indicate there are complex functions and metabolism of lipoproteins in cancer. The current review is aimed at providing updates from studies related to the monitoring of lipoproteins in different types of cancer. This had led to numerous clinical and experimental studies. The review covers the major lipoproteins such as LDL cholesterol (LDL-C), oxidized low-density lipoprotein cholesterol (oxLDL-C), very low-density lipoprotein cholesterol (VLDL-C), and high-density lipoprotein cholesterol (HDL-C). This is mainly due to increasing evidence from clinical and experimental studies that relate association of lipoproteins with cancer. Generally, a significant association exists between LDL-C with carcinogenesis and high oxLDL with metastasis. This warrants further investigations to include Mendelian randomization design and to be conducted in a larger population to confirm the significance of LDL-C and its oxidized form as prognostic markers of cancer.

Low serum cholesterol levels predict inferior prognosis and improve prognostic index scoring for peripheral T-cell lymphoma, unspecified

Peripheral T-cell lymphomas, unspecified (PTCL-U) is a heterogeneous group of non-Hodgkin lymphomas, arising from the transformation of mature, post-thymic T-cells. Prognostic index for PTCL-U (PIT) is based on Europeans and may not be applicable for Chinese PTCL-U patients. Besides, low circulating cholesterol concentration is associated with elevated cancer incidence and mortality. The purpose of our study was to assess the prognostic value of serum lipid levels in PTCL-U and improve PIT. We screened the prognostic factors associated with progression-free survival (PFS) and overall survival (OS) by multivariate Cox regression analysis in ninety-one enrolled patients. The results showed that low-level high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) were associated with unfavorable OS. Furthermore, we developed a new risk model, PITC, based on low-level HDL-C, LDL-C and PIT. In Chinese PTCL-U, PITC was superior to PIT in PFS and OS. In conclusion, serum cholesterol levels may be good candidates for predicting prognosis in PTCL-U.

Cholesterol Review: A Metabolically Important Molecule

OBJECTIVE

Cholesterol is an important molecule in humans and both its excess and its deficiency cause disease. Most clinicians appreciate its role in stabilizing cellular plasma membranes but are unaware of its myriad other functions.

METHODS

This review highlights cholesterol's newly recognized important roles in human physiology and pathophysiology.

RESULTS

The basis for cholesterol's ubiquitous presence in eukaryote organisms is its three part structure involving hydrophilic, hydrophobic, and rigid domains. This structure permits cholesterol to regulate multiple cellular processes ranging from membrane fluidity and permeability to gene transcription. Cholesterol not only serves as a molecule of regulation itself, but also forms the backbone of all steroid hormones and vitamin D analogs. Cholesterol is responsible for growth and development throughout life and may be useful as an anticancer facilitator. Because humans have a limited ability to catabolize cholesterol, it readily accumulates in the body when an excess from the diet or a genetic abnormality occurs. This accumulation results in the foremost cause of death and disease (atherosclerosis) in the Western world. Identification of cholesterol's disease-producing capabilities dates back 5,000 years to the Tyrolean iceman and more recently to ancient mummies from many cultures throughout the world. In contrast, a deficiency of cholesterol in the circulation may result in an inability to distribute vitamins K and E to vital organs with serious consequences.

CONCLUSION

Understanding the benefits and hazards of cholesterol in the clinical setting will improve the endocrinologist's ability to control diseases associated with this unique molecule.

ABBREVIATIONS

CVD = cardiovascular disease; HDL = high-density lipoprotein; LDL = low-density lipoprotein; NPC1L1 = Niemann-Pick C-1-like-1 protein; U.S. = United States; USDA = U.S. Department of Agriculture.

Low-Density Lipoproteins, High-Density Lipoproteins (HDL), and HDL-Associated Proteins Differentially Modulate Chronic Myelogenous Leukemia Cell Viability

Cellular lipid metabolism, lipoprotein interactions, and liver X receptor (LXR) activation have been implicated in the pathophysiology and treatment of cancer, although findings vary across cancer models and by lipoprotein profiles. In this study, we investigated the effects of human-derived low-density lipoproteins (LDL), high-density lipoproteins (HDL), and HDL-associated proteins apolipoprotein A1 (apoA1) and serum amyloid A (SAA) on markers of viability, cholesterol flux, and differentiation in K562 cells-a bone marrow-derived, stem-like erythroleukemia cell model of chronic myelogenous leukemia (CML). We further evaluated whether lipoprotein-mediated effects were altered by concomitant LXR activation. We observed that LDL promoted higher K562 cell viability in a dose- and time-dependent manner and increased cellular cholesterol concentrations, while LXR activation by the agonist TO901317 ablated these effects. LXR activation in the presence of HDL, apoA1 and SAA-rich HDL suppressed K562 cell viability, while robustly inducing mRNA expression of ATP-binding cassette transporter A1 (ABCA1). HDL and its associated proteins additionally suppressed mRNA expression of anti-apoptotic B-cell lymphoma-extra large (BCL-xL), and the erythroid lineage marker 5'-aminolevulinate synthase 2 (ALAS2), while SAA-rich HDL induced mRNA expression of the megakaryocytic lineage marker integrin subunit alpha 2b (ITGA2B). Together, these findings suggest that lipoproteins and LXR may impact the viability and characteristics of CML cells.

Cholesterol, Oxysterols and LXRs in Breast Cancer Pathophysiology

Breast cancer is the most frequent cancer among women. In 2018, it is estimated that 627,000 women died from breast cancer. This is approximately 15% of all cancer deaths among women (WHO 2018). Breast cancer is a multifactorial chronic disease. While important progress has been made to treat patients, many questions regarding aspects of this disease relating to carcinogenesis are still open. During carcinogenesis, cells exhibit cholesterol homeostasis deregulation. This results in an accumulation of intracellular cholesterol, which is required to sustain their high growth rate. Cholesterol efflux and influx are two metabolic pathways that are necessary to prevent cholesterol accumulation in the cells. Liver X receptors (LXRs) are nuclear receptors that, upon activation, induce the expression of ABC transporters, responsible for promoting cholesterol efflux, and the expression of IDOL (inducible degrader of low-density lipoprotein receptor), in charge of reducing cholesterol influx. Oxysterols, oxygenated derivatives of cholesterol formed through different pathways, have been discovered as LXR-specific ligands. Some oxysterols are involved in tumor formation while others are considered anti-tumor agents. In the present review, we discuss the involvement of cholesterol, oxysterols and LXRs in breast cancer pathophysiology, with an emphasis on the biological effects of LXR ligands.

The contribution of cholesterol and epigenetic changes to the pathophysiology of breast cancer

Breast cancer​ is one of the most commonly diagnosed cancers in women. Accumulating evidence suggests that cholesterol plays an important role in the development of breast cancer. Even though the mechanistic link between these two factors is not well understood, one possibility is that dysregulated cholesterol metabolism may affect lipid raft and membrane fluidity and can promote tumor development. Current studies have shown oxysterol 27-hydroxycholesterol (27-HC) as a critical regulator of cholesterol and breast cancer pathogenesis. This is supported by the significantly higher expression of CYP27A1 (cytochrome P450, family 27, subfamily A, polypeptide 1) in breast cancers. This enzyme is responsible for 27-HC synthesis from cholesterol. It has been shown that 27-HC can not only increase the proliferation of estrogen receptor (ER)-positive breast cancer cells but also stimulate tumor growth and metastasis in several breast cancer models. This phenomenon is surprising since 27-HC and other oxysterols generally reduce intracellular cholesterol levels by activating the liver X receptors (LXRs). Resolving this paradox will elucidate molecular pathways by which cholesterol, ER, and LXR are connected to breast cancer. These findings will also provide the rationale for evaluating pharmaceutical approaches that manipulate cholesterol or 27-HC synthesis in order to mitigate the impact of cholesterol on breast cancer pathophysiology. In addition to cholesterol, epigenetic changes including non-coding RNAs, and microRNAs, DNA methylation, and histone modifications, have all been shown to control tumorigenesis. The purpose of this review is to discuss the link between altered cholesterol metabolism and epigenetic modification during breast cancer progression.

Low level of serum HDL-cholesterol with increased sIL-2R predicts a poor clinical outcome for patients with malignant lymphoma and adult T-cell leukemia-lymphoma

Low concentrations of high-density lipoprotein cholesterol (HDL-C) have been reported in patients with hematological malignancies. However, the proof of decreased HDL-C in hematological malignancies and its association with clinical outcomes remain unclear. We analyzed 140 Japanese patients with malignant lymphoma (ML) and adult T-cell leukemia-lymphoma (ATLL). HDL-C, LDL-C and soluble interleukin-2 receptor (sIL-2R) were measured. Treatment decisions were determined with established protocols. HDL-C was 0.98 ± 0.45 mmol/l in patients and 1.51 ± 0.35 mmol/l in controls (P < 0.001). LDL-C was lower in patients than in controls (2.76 ± 0.96, 3.16 ± 0.76 mmol/l, respectively, P < 0.001). HDL-C was the lowest in ATLL (0.81 ± 0.37 mmol/l), modest in non-Hodgkin lymphoma (1.09 ± 0.42 mmol/l) and the highest in Hodgkin's disease (1.14 ± 0.68 mmol/l), (P = 0.0019). Inverse correlation was found between HDL-C and sIL-2R (r = -0.6584, P < 0.001). Categorized patients into 3 subgroups according to HDL-C (<0.52, 0.52-1.02 and ≥1.03 mmol/l), sIL-2R were the highest (median, 36,675; IQR, 17,180-92,600 U/mL) in patients with HDL-C < 0.52 mmol/l, modest (2386, 1324-8340) in HDL-C 0.52-1.02 mmol/l and the lowest (761, 450-1596) in HDL-C ≥ 1.03 mmol/l (P < 0.001). In Cox regression model, the lowest HDL-C levels, <0.52 mmol/l, were associated with poorer clinical outcome and the hazard ratio was 5.73 (95%CI, 3.09-10.50; P < 0.001). In Kaplan-Meier analysis according to HDL-C tertiles (<0.78, 0.78-1.10 and ≥1.11 mmol/l), patients with lowest HDL-C tertile showed inferior overall survival with a median follow-up of 23 months (P < 0.001). We concluded that cytokine-induced low levels of HDL-C in patients with ML and ATLL has independent prognostic significance, and suggesting an early indicator of poorer outcome.

Acute Myelogenous Leukemia Cells Secrete Factors that Stimulate Cellular LDL Uptake via Autocrine and Paracrine Mechanisms

Leukemic cells isolated from most patients with acute myelogenous leukemia (AML) have higher low density lipoprotein (LDL) uptake than normal mononuclear blood cells. Little is known, however, about the mechanism behind the elevated LDL uptake. We investigated if AML cells secrete factors that stimulate cellular LDL uptake. Mononuclear blood cells were isolated from peripheral blood from 42 patients with AML at diagnosis. Cellular LDL uptake was determined from the degradation rate of ¹²⁵I-labelled LDL. Conditioned media from AML cells stimulated the LDL degradation in the leukemic cell lines KG1 and HL60, and in isolated AML cells. The stimulatory effect correlated with the LDL degradation in the AML cells directly after isolation from blood. Conditioned media also autostimulated LDL degradation in the AML cells themselves. Concentrations of IL-6 and IL-8 in AML cell conditioned media correlated with the LDL degradation in AML cells directly after isolation from blood. Addition of R-TNF-α, but not IL-6 or IL-8, stimulated LDL degradation in HL60, KG1, and AML cells. The LDL degradation in AML cells could be inhibited by a LDL receptor blocking antibody. AML cells secrete factors that stimulate LDL uptake in a paracrine and autocrine pattern which open up therapeutic possibilities to inhibit the uptake of LDL by administration of antibodies to these factors.

Elucidating the structural organization of a novel low-density lipoprotein nanoparticle reconstituted with docosahexaenoic acid

Low-density lipoprotein nanoparticles reconstituted with unesterified docosahexaenoic acid (LDL-DHA) is promising nanomedicine with enhanced physicochemical stability and selective anticancer cytotoxic activity. The unique functionality of LDL-DHA ultimately relates to the structure of this nanoparticle. To date, however, little is known about the structural organization of this nanoparticle. In this study chemical, spectroscopic and electron microscopy analyses were undertaken to elucidate the structural and molecular organization of LDL-DHA nanoparticles. Unesterified DHA preferentially incorporates into the outer surface layer of LDL, where in this orientation the anionic carboxyl end of DHA is exposed to the LDL surface and imparts an electronegative charge to the nanoparticles surface. This negative surface charge promotes the monodisperse and homogeneous distribution of LDL-DHA nanoparticles in solution. Further structural analyses with cryo-electron microscopy revealed that the LDL-DHA nanostructure consist of a phospholipid bilayer surrounding an aqueous core, which is distinctly different from the phospholipid monolayer/apolar core organization of plasma LDL. Lastly, apolipoprotein B-100 remains strongly associated with this complex and maintains a discrete size and shape of the LDL-DHA nanoparticles similar to plasma LDL. This preliminary structural assessment of LDL-DHA now affords the opportunity to understand the important structure-function relationships of this novel nanoparticle.

New utility of an old marker: serum low-density lipoprotein predicts histopathological response of neoadjuvant chemotherapy in locally advanced gastric cancer

Background

Although the correlation between metabolic abnormality and gastric cancer has been extensively investigated, the question of whether metabolic parameters might influence the efficacy of chemotherapy in locally advanced gastric cancer is still unanswered. In our present study, we investigated the relationship between serum fasting glucose, lipid levels, and histopathological response of neoadjuvant chemotherapy (NAC) in locally advanced gastric cancers.

Patients and methods

A total of 128 patients were identified from a prospectively maintained database of patients with locally advanced gastric cancer who received NAC between July 2004 and December 2012. Histopathological response after NAC was analyzed according to Becker’s tumor-regression grade. Univariate analyses and multivariable regression analyses were performed to determine the correlation between tumor size, differentiation, fasting glucose, lipid levels, and tumor histopathological response after NAC.

Results

Univariate analysis revealed that low-density lipoprotein level and total cholesterol, as well as tumor size and differentiation, correlated significantly with histopathological response. Low-density lipoprotein levels and tumor size were found to be independent predictors for histopathological response, according to multivariable regression analyses.

Conclusion

In this observational, hypothesis-generating study, serum low-density lipoprotein measurement was found to be useful in predicting chemosensitivity to locally advanced gastric cancer patients undergoing NAC. Incorporation of serum low-density lipoprotein levels into individualized treatment protocols could be considered in clinical practice.

[Lipid metabolism in patients with hematologic cancers]

It is considered that hypercholesterolemia is life-threatening and low cholesterol levels are a positive factor. However, taking into consideration the fact that cholesterol plays a key role in cell proliferation, it should be remembered that its low blood level may be linked to high cholesterol demands from neoplastic cells. The literature review analyzes the results of recent investigations of lipid metabolism in patients with hematologic cancers and their other types. All given investigations show a significant reduction in the serum levels of total cholesterol and high-density lipoproteins in patients with hematological disease at its onset. The data for other indicators of the lipid transport system are ambiguous. Such changes have been elucidated to be associated with the accumulation of cholesterol in the leukemia cells due to enhanced synthesis de novo, a more active absorption from circulation and blocked release of its surplus. If the disease runs a favorable course, lipid metabolic parameters become normalized and, in case of remission, correspond to those seen in healthy individuals. They continue to decline in patients with disease progression. This allows the consideration of cholesterol, its fractions, and apolipoproteins as biochemical prognostic markers in hematological cancer patients and as indicators for assessment of treatment results. In addition, there is evidence for the effect of chemotherapeutic agents on lipid metabolism. Recent attempts to elaborate new treatment strategies, by using the current knowledge on the role of lipid metabolism in cancers, are considered.

Obesity and Diabetes: The Increased Risk of Cancer and Cancer-Related Mortality

Obesity and type 2 diabetes are becoming increasingly prevalent worldwide, and both are associated with an increased incidence and mortality from many cancers. The metabolic abnormalities associated with type 2 diabetes develop many years before the onset of diabetes and, therefore, may be contributing to cancer risk before individuals are aware that they are at risk. Multiple factors potentially contribute to the progression of cancer in obesity and type 2 diabetes, including hyperinsulinemia and insulin-like growth factor I, hyperglycemia, dyslipidemia, adipokines and cytokines, and the gut microbiome. These metabolic changes may contribute directly or indirectly to cancer progression. Intentional weight loss may protect against cancer development, and therapies for diabetes may prove to be effective adjuvant agents in reducing cancer progression. In this review we discuss the current epidemiology, basic science, and clinical data that link obesity, diabetes, and cancer and how treating obesity and type 2 diabetes could also reduce cancer risk and improve outcomes.

Cholesterol uptake disruption, in association with chemotherapy, is a promising combined metabolic therapy for pancreatic adenocarcinoma

The malignant progression of pancreatic ductal adenocarcinoma (PDAC) is accompanied by a profound desmoplasia, which forces proliferating tumor cells to metabolically adapt to this new microenvironment. We established the PDAC metabolic signature to highlight the main activated tumor metabolic pathways. Comparative transcriptomic analysis identified lipid-related metabolic pathways as being the most highly enriched in PDAC, compared with a normal pancreas. Our study revealed that lipoprotein metabolic processes, in particular cholesterol uptake, are drastically activated in the tumor. This process results in an increase in the amount of cholesterol and an overexpression of the low-density lipoprotein receptor (LDLR) in pancreatic tumor cells. These findings identify LDLR as a novel metabolic target to limit PDAC progression. Here, we demonstrate that shRNA silencing of LDLR, in pancreatic tumor cells, profoundly reduces uptake of cholesterol and alters its distribution, decreases tumor cell proliferation, and limits activation of ERK1/2 survival pathway. Moreover, blocking cholesterol uptake sensitizes cells to chemotherapeutic drugs and potentiates the effect of chemotherapy on PDAC regression. Clinically, high PDAC Ldlr expression is not restricted to a specific tumor stage but is correlated to a higher risk of disease recurrence. This study provides a precise overview of lipid metabolic pathways that are disturbed in PDAC. We also highlight the high dependence of pancreatic cancer cells upon cholesterol uptake, and identify LDLR as a promising metabolic target for combined therapy, to limit PDAC progression and disease patient relapse.

Oxidized low density lipoprotein and inflammation in gout patients

To analyze the levels of oxidized low density lipoprotein (ox-LDL) and inflammatory cytokines in the plasma of gout patients. The levels of ox-LDL, hypersensitive C-reactive protein (hs-CRP), interleukin-1β, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were measured in the plasma of 41 gout patients [28 in acute phase episode, 13 in intermittent phase (IP)], and in 40 healthy controls. The relationship between ox-LDL and inflammation was also explored by measuring the levels of several pro-inflammatory cytokines in the plasma. The plasma levels of ox-LDL, hs-CRP, IL-6 and TNF-α were significantly increased in patients with gout in the acute phase compared to those in the IP group and healthy controls (P < 0.05), but the levels of TGF-β were significantly lower in the acute phase group than in the IP group and healthy controls (P < 0.01). The levels of ox-LDL in the gout patients in the IP were significantly higher than those in healthy controls (P < 0.05). Correlation analysis indicated that the levels of ox-LDL were positively correlated with hs-CRP, IL-6 and TNF-α (r = 0.343, r = 0.386, r = 0.659, P < 0.01, respectively), but negatively correlated with TGF-β levels in patients in the acute phase (r = -0.240, P < 0.05). The levels of ox-LDL in gout patients were significantly higher than those in healthy controls. The changes in ox-LDL levels may be associated with enhanced inflammation in gout patients.

Low Density Lipid Nanoparticles for Solid Tumor Targeting

One of the most significant characteristics of cancer cells is their rapid dividing ability and overexpression of LDL receptors, which offers an opportunity for the selective targeting of these cells. 5-Fluorouracil (5-FU)-encapsulated low density lipid nanoparticles (LDLN) were prepared by the emulsion congealing method which mimics the plasma-derived LDL by acquiring the apolipoprotein B-100 from the blood. The average particle size, transmission electron microscope (TEM), and drug content of the prepared LDLN dispersion were found to be 161±3.5 nm, with spherical shape, and 0.370±0.05 mg/mL, respectively. In vitro release studies revealed a sustained profile which decreased with a lapse of time. In vivo studies of 5-FU serum concentration and biodistribution revealed a 5-FU serum concentration of 8.5% in tumor cells and about 2.1% in the liver at the end of 24 hr from LDLN. Tumor growth suppression studies showed 185.42% average tumor growth and 89.76% tumor height as compared to the control exhibiting tumor growth at 1166.47% and tumor height at 176.07%. On the basis of these collective data, it is suggested that a higher accumulation of LDLN, when given as an IV, in solid tumors is attributed to the active uptake of LDLN via LDL receptors via apolipoprotein B-100.

Contrast agents for preclinical targeted X-ray imaging

Micro-computed tomography (micro-CT) is an X-ray based instrument that it is specifically designed for biomedical research at a preclinical stage for live imaging of small animals. This imaging modality is cost-effective, fast, and produces remarkable high-resolution images of X-ray opaque skeleton. Administration of biocompatible X-ray opaque contrast agent allows delineation of the blood vessels, and internal organs and even detection of tumor metastases as small as 300 μm. However, the main limitation of micro-CT lies in the poor efficacy or toxicity of the contrast agents. Moreover, contrast agents for micro-CT have to be stealth nanoparticulate systems, i.e. preventing their rapid renal clearance. The chemical composition and physicochemical properties will condition their uptake and elimination pathways, and therefore all the biological fluids, organs, and tissues trough this elimination route of the nanoparticles will be contrasted. Furthermore, several technologies playing on the nanoparticle properties, aim to influence these biological pathways in order to induce their accumulation onto given targeted sites, organs of tumors. In function of the methodologies carried out, taking benefit or not of the action of immune system, of the natural response of the organism like hepatocyte uptake or enhanced permeation and retention effect, or even accumulation due to ligand/receptor interactions, the technologies are called passive or active targeted imaging. The present review presents the most recent advances in the development of specific contrast agents for targeted X-ray imaging micro-CT, discussing the recent advance of in vivo targeting of nanoparticulate contrast agents, and the influence of the formulations, nature of the nanocarrier, nature and concentration of the X-ray contrasting materials, effect of the surface properties, functionalization and bioconjugation. The pharmacokinetic and versatility of nanometric systems appear particularly advantageous for addressing the versatile biomedical research needs. State of the art investigations are on going to propose contrast agents with tumor accumulating properties and will contribute for development of safer cancer medicine having detection and therapeutic modalities.

Development of synthetic peptide-modified liposomes with LDL receptor targeting capacity and improved anticancer activity

In this study, we report an active targeting liposomal formulation directed by a novel peptide (AA13) that specifically binds to the low density lipoprotein receptor (LDLR) overexpressed on acute myeloid leukemia (AML) cells. The objectives of this study were to evaluate the in vitro and in vivo tumor drug targeting delivery of AA13-anchored liposomes on AML cells. AA13 conjugated to the distal end of DSPE-PEG2000-maleimide was incorporated into the liposomes via a postinsertion method. To study the effect of the peptide decoration and density on tumor cell targeting and internalization by AML cells (THP-1 and NB4), stealth liposomes bearing 3% (peptide/S100PC, molar ratio, LL) and 7% (peptide/S100PC, molar ratio, HL) AA13 were prepared, respectively. Higher uptake of LL (1.9- and 2.6-fold) and HL (2.3- and 3.6-fold) targeted liposomes occurred in THP-1 and NB4 cells, respectively, compared to untargeted liposomes. An LDLR inhibitor was used to confirm inhibition of the receptor-mediated cellular association of AA13 modified liposome in both cells. Daunorubicin (DNR) demonstrated a 2.2- and 3.5-fold higher cytotoxicity with the HL formulation and a 1.2- and 2.0-fold higher cytotoxicity with the LL formulation compared to the unmodified liposomal formulation in THP-1 and NB4 cells, respectively. Tumor drug accumulation of DNR-loaded HL was greater than that of the untargeted liposome in the biodistribution assay. The in vivo efficacy study in BALB/c nude mice bearing NB4 xenografts treated with DNR loaded HL also showed more tumor volume inhibition and a longer survival time compared to the untargeted formulation. In conclusion, the AA13-anchored liposomes demonstrated desirable potential as a promising vector for enhanced AML tumor drug targeting.

Atypical plasma lipid profile in cancer patients: cause or consequence?

The aberrant blood lipoprotein levels in cancer patients are reported to be associated with cancer risk and mortality incidents however, there are several discrepancies in the previous reports. Hence the clinical usefulness of plasma/serum levels in risk stratification of a variety of cancers remains elusive. The present review highlights and compiles findings from different research groups regarding association of plasma lipoprotein levels with the risk of developing various types of cancer. We will discuss some prospective underlying mechanisms for this reported association. In addition to that the potential roles of plasma lipids in promoting carcinogenesis will be conferred.

The role of cholesterol metabolism and cholesterol transport in carcinogenesis: a review of scientific findings, relevant to future cancer therapeutics

While the unique metabolic activities of malignant tissues as potential targets for cancer therapeutics has been the subject of several recent reviews, the role of cholesterol metabolism in this context is yet to be fully explored. Cholesterol is an essential component of mammalian cell membranes as well as a precursor of bile acids and steroid hormones. The hypothesis that cancer cells need excess cholesterol and intermediates of the cholesterol biosynthesis pathway to maintain a high level of proliferation is well accepted, however the mechanisms by which malignant cells and tissues reprogram cholesterol synthesis, uptake and efflux are yet to be fully elucidated as potential therapeutic targets. High and low density plasma lipoproteins are the likely major suppliers of cholesterol to cancer cells and tumors, potentially via receptor mediated mechanisms. This review is primarily focused on the role(s) of lipoproteins in carcinogenesis, and their future roles as drug delivery vehicles for targeted cancer chemotherapy.

The epidemiology and molecular mechanisms linking obesity, diabetes, and cancer

The worldwide epidemic of obesity is associated with increasing rates of the metabolic syndrome and type 2 diabetes. Epidemiological studies have reported that these conditions are linked to increased rates of cancer incidence and mortality. Obesity, particularly abdominal obesity, is associated with insulin resistance and the development of dyslipidemia, hyperglycemia, and ultimately type 2 diabetes. Although many metabolic abnormalities occur with obesity and type 2 diabetes, insulin resistance and hyperinsulinemia appear to be central to these conditions and may contribute to dyslipidemia and altered levels of circulating estrogens and androgens. In this review, we will discuss the epidemiological and molecular links between obesity, type 2 diabetes, and cancer, and how hyperinsulinemia and dyslipidemia may contribute to cancer development. We will discuss how these metabolic abnormalities may interact with estrogen signaling in breast cancer growth. Finally, we will discuss the effects of type 2 diabetes medications on cancer risk.

Anticancer activity of the cholesterol exporter ABCA1 gene

The ABCA1 protein mediates the transfer of cellular cholesterol across the plasma membrane to apolipoprotein A-I. Loss-of-function mutations in the ABCA1 gene induce Tangier disease and familial hypoalphalipoproteinemia, both cardiovascular conditions characterized by abnormally low levels of serum cholesterol, increased cholesterol in macrophages, and subsequent formation of vascular plaque. Increased intracellular cholesterol levels are also frequently found in cancer cells. Here, we demonstrate anticancer activity of ABCA1 efflux function, which is compromised following inhibition of ABCA1 gene expression by oncogenic mutations or cancer-specific ABCA1 loss-of-function mutations. In concert with elevated cholesterol synthesis found in cancer cells, ABCA1 deficiency allows for increased mitochondrial cholesterol, inhibits release of mitochondrial cell death-promoting molecules, and thus facilitates cancer cell survival, suggesting that elevated mitochondrial cholesterol is essential to the cancer phenotype.

Drug delivery via lipoprotein-based carriers: answering the challenges in systemic therapeutics

Plasma lipoproteins are transporters of lipids and other hydrophobic molecules in the mammalian circulation. Lipoproteins also have a strong potential to serve as drug-delivery vehicles due to their small size, long residence time in the circulation and high-drug payload. Consequently, lipoproteins and synthetic/reconstituted lipoprotein preparations have been evaluated with increasing interest towards clinical applications, particularly for cancer diagnostics/imaging and chemotherapy. In this review, past and current studies on lipoproteins and similar alternative drug carriers are discussed regarding their suitability as agents to deliver drugs, primarily to cancer cells and tumors. A lipoprotein-based delivery strategy may also provide a novel platform for improving the therapeutic efficacy of drugs that have previously been judged unsuitable or had only limited application due to poor solubility. An additional, and perhaps the most important aspect of the drug-delivery process via lipoprotein-type carriers, is the receptor-mediated uptake of the payload from the lipoprotein complex. Monitoring the expression of specific receptors prior to treatment could, thus, give rise to efficient selection of optimally responsive patients, resulting in a successful personalized therapy regimen.

Consensus-phenotype integration of transcriptomic and metabolomic data implies a role for metabolism in the chemosensitivity of tumour cells

Using transcriptomic and metabolomic measurements from the NCI60 cell line panel, together with a novel approach to integration of molecular profile data, we show that the biochemical pathways associated with tumour cell chemosensitivity to platinum-based drugs are highly coincident, i.e. they describe a consensus phenotype. Direct integration of metabolome and transcriptome data at the point of pathway analysis improved the detection of consensus pathways by 76%, and revealed associations between platinum sensitivity and several metabolic pathways that were not visible from transcriptome analysis alone. These pathways included the TCA cycle and pyruvate metabolism, lipoprotein uptake and nucleotide synthesis by both salvage and de novo pathways. Extending the approach across a wide panel of chemotherapeutics, we confirmed the specificity of the metabolic pathway associations to platinum sensitivity. We conclude that metabolic phenotyping could play a role in predicting response to platinum chemotherapy and that consensus-phenotype integration of molecular profiling data is a powerful and versatile tool for both biomarker discovery and for exploring the complex relationships between biological pathways and drug response.

Resistance to chemotherapy drugs in cancer sufferers is very common. Using a panel of 59 cell lines obtained from different types of cancer we study the links between the genes and metabolites measured in these cells and the resistance the cells show to common cancer drugs containing platinum. In order to combine the information given by the genes and metabolites we introduce a new pathway-based approach, which allows us to explore synergy between the different types of data. We then extend the procedure to look at a wider panel of drugs and show that the pathways we found were associated with platinum are not just the pathways which are frequently selected for a large number of drugs. Given the increasing use of multiple sets of measurements (genes, metabolites, proteins etc.) in biological studies, we demonstrate a powerful, yet straightforward method for dealing with the resulting large datasets and integrating their knowledge. We believe that this work could contribute to developing a personalised medicine approach to treating tumours, where the genetic and metabolic changes in the tumour are measured and then used for prediction of the optimal treatment regime.

Role of cholesterol in the development and progression of breast cancer

Diet and obesity are important risk factors for cancer development. Many studies have suggested an important role for several dietary nutrients in the progression and development of breast cancer. However, few studies have specifically addressed the role of components of a Western diet as important factors involved in breast cancer initiation and progression. The present study examined the role of cholesterol in the regulation of tumor progression in a mouse model of mammary tumor formation. The results suggest that cholesterol accelerates and enhances tumor formation. In addition, tumors were more aggressive, and tumor angiogenesis was enhanced. Metabolism of cholesterol was also examined in this mouse model. It was observed that plasma cholesterol levels were reduced during tumor development but not prior to its initiation. These data provide new evidence for an increased utilization of cholesterol by tumors and for its role in tumor formation. Taken together, these results imply that an increase in plasma cholesterol levels accelerates the development of tumors and exacerbates their aggressiveness.

Uptake of synthetic Low Density Lipoprotein by leukemic stem cells--a potential stem cell targeted drug delivery strategy

Chronic Myeloid Leukemia (CML) stem/progenitor cells, which over-express Bcr-Abl, respond to imatinib by a reversible block in proliferation without significant apoptosis. As a result, patients are unlikely to be cured owing to the persistence of leukemic quiescent stem cells (QSC) capable of initiating relapse. Previously, we have reported that intracellular levels of imatinib in primary primitive CML cells (CD34+38(lo/⁻)), are significantly lower than in CML progenitor cells (total CD34+) and leukemic cell lines. The aim of this study was to determine if potentially sub-therapeutic intracellular drug concentrations in persistent leukemic QSC may be overcome by targeted drug delivery using synthetic Low Density Lipoprotein (sLDL) particles. As a first step towards this goal, however, the extent of uptake of sLDL by leukemic cell lines and CML patient stem/progenitor cells was investigated. Results with non-drug loaded particles have shown an increased and preferential uptake of sLDL by Bcr-Abl positive cell lines in comparison to Bcr-Abl negative. Furthermore, CML CD34+ and primitive CD34+38(lo/⁻) cells accumulated significantly higher levels of sLDL when compared with non-CML CD34+ cells. Thus, drug-loading the sLDL nanoparticles could potentially enhance intracellular drug concentrations in primitive CML cells and thus aid their eradication.

In vitro assessment of poly-iodinated triglyceride reconstituted low-density lipoprotein: initial steps toward CT molecular imaging

RATIONALE AND OBJECTIVES

Targeted molecular probes offer the potential for greater specificity in cancer imaging with contrast-enhanced computed tomography (CT). We investigate a low-density lipoprotein (LDL) nanoparticle loaded with poly-iodinated triglyceride (ITG) in a proof of concept study of targeted x-ray imaging. LDLs are targeted to the LDL cell surface receptor (LDLR), which is overexpressed in several tumor types. The LDL-LDLR pathway presents a high-capacity and self-renewing transport system for molecular imaging in CT.

MATERIALS AND METHODS

ITG was synthesized and loaded into the core of LDL particles to form a reconstituted nanoparticle, hereafter referred to as (rITG)LDL. Particle size was measured by dynamic light scattering. The x-ray attenuation of the (rITG)LDL solution was measured with CT imaging and signal enhancement was calibrated for equivalent iodine concentration. Cultured human hepatoblastoma G2 (HepG2) cells, which overexpress LDLR, were incubated with (rITG)LDL with or without native LDL. The cells were imaged with CT to characterize particle sequestration.

RESULTS

Reconstitution of LDL with ITG was successful and did not compromise the targeting function of the particle. Measurement of the x-ray attenuation properties of the (rITG)LDL solution revealed an effective iodine concentration of 0.78 mg/mL. In vitro studies of HepG2 cells demonstrated a significant increase in CT image intensity over control cells when incubated with (rITG)LDL.

CONCLUSION

The in vitro results of this study suggest that (rITG)LDL can provide adequate image enhancement for CT molecular imaging. Potential applications include breast imaging and small animal imaging at low x-ray energies. In vivo experiments will be required to verify that tumor uptake of (rITG)LDL is sufficient for enhanced detection. Use at higher x-ray energies, as used in conventional CT, will require a further increase in iodine loading.

Prospects and challenges of the development of lipoprotein-based formulations for anti-cancer drugs

This review evaluates drug delivery systems that involve intact plasma lipoproteins or some of their components. These complex macromolecules transport highly water-insoluble compounds (cholesteryl esters and triacylglycerols) in their natural environment - a property that renders them ideal carriers of hydrophobic drugs. Particular emphasis is placed on the application of lipoproteins as drug delivery agents in cancer chemotherapy. The history and present activity regarding lipoprotein-based formulations are reviewed, with the primary focus on the smaller sized (low and high density) lipoprotein-based formulations and their potential clinical and commercial value. The use of both native and synthetic lipoproteins as drug delivery agents are discussed from the standpoint of therapeutic efficacy, as well as commercial feasibility. The advantages of lipoprotein-based drug delivery formulations are compared with other drug delivery models, with the primary focus on liposomal preparations. Finally, an expert opinion is provided, regarding the potential use of lipoprotein-based formulations in cancer treatment, taking into consideration the major advantages (biocompatibility, safety, drug solubility) and the barriers (manufacturing protein components, financial interest, investments) to their commercial development.

Plasma LDL cholesterol has no impact on P-glycoprotein (MDR1/ABCB1) activity in human peripheral blood mononuclear cells

Several studies have demonstrated that the adenosine triphosphate-binding cassette transporter P-glycoprotein (P-gp) is at least partly located in cholesterol- and sphingolipid-enriched parts of the plasma membrane called "lipid rafts" and that modification of cellular cholesterol content has an impact on the activity of P-gp in vitro and ex vivo. Cholesterol modulation in vitro does not closely reflect the in vivo situation. The aim of our study was therefore to investigate whether differences in individual plasma low-density lipoprotein (LDL) cholesterol levels in humans have an impact on cholesterol content in peripheral blood mononuclear cells (PBMCs) and thereby on individual activity of P-gp. PBMCs of 20 ambulatory patients with elevated LDL cholesterol (173.9 +/- 22.4 mg/dl; range 151.0-234.4 mg/dl) and 28 controls (125.2 +/- 16.9 mg/dl; range 74.6-149.6 mg/dl) were isolated. Cellular cholesterol was measured by an enzymatic fluorimetric assay, efflux activity of P-gp in PBMCs was determined by a flow cytometric method (rhodamine123 efflux), and messenger ribonucleic acid expression was quantified by reverse transcriptase real-time polymerase chain reaction (RT-PCR). There was no difference in cellular cholesterol or P-gp activity between the two groups suggesting that high plasma LDL cholesterol concentration as observed in dyslipidemic patients does not correlate with cellular cholesterol content or P-gp activity in PBMCs. There was, however, a significant negative relationship between age and P-gp efflux activity indicating that P-gp activity in PBMCs decreases with advancing age. These results need further confirmation because investigation of age dependency of P-gp activity was not the primary aim of the study.

All-trans-retinoic acid nanodisks

Nanodisks are nanoscale, disk-shaped phospholipid bilayers whose edge is stabilized by association of apolipoprotein molecules. Self-assembled ND particles enriched with all-trans-retinoic acid (ATRA) (phospholipid:ATRA molar ratio = 5.5:1) were generated wherein all reaction components were solubilized. ATRA-ND migrated as a single band (Stokes' diameter approximately 20 nm) on native gradient polyacrylamide gel electrophoresis. ATRA, phospholipid and apolipoprotein co-eluted from a Sepharose 6B gel filtration column, consistent with stable integration of ATRA into the ND particle milieu. Spectroscopic analysis of ATRA-ND in buffer yielded an absorbance spectrum characteristic of ATRA. ATRA-ND mediated time-dependent inhibition of cultured HepG2 cell growth more effectively than free ATRA. The nanoscale size of the formulation particles and the stable integration of biologically active ATRA suggest ND represent a potentially useful vehicle for solubilization and in vivo delivery of ATRA.

Low-density lipoprotein nanoparticles as magnetic resonance imaging contrast agents

Low-density lipoproteins (LDLs) are a naturally occurring endogenous nanoplatform in mammalian systems. These nanoparticles (22 nm) specifically transport cholesterol to cells expressing the LDL receptor (LDLR). Several tumors overexpress LDLRs presumably to provide cholesterol to sustain a high rate of membrane synthesis. Amphiphilic gadolinium (Gd)-diethylenetriaminepentaacetic acid chelates have been incorporated into the LDL to produce a novel LDLR-targeted magnetic resonance imaging (MRI) contrast agent. The number of Gd chelates per LDL particle ranged between 150 and 496 Gd(III). In vitro studies demonstrated that Gd-labeled LDL retained a similar diameter and surface charge as the native LDL particle. In addition, Gd-labeled LDL retained selective cellular binding and uptake through LDLR-mediated endocytosis. Finally, Gd-labeled LDLs exhibited significant contrast enhancement 24 hours after administration in nude mice with human hepatoblastoma G2 xenografts. Thus, Gd-labeled LDL demonstrates potential use as a targeted MRI contrast agent for in vivo tumor detection.

Cytotoxic effect of a lipophilic alkylating agent after incorporation into low density lipoprotein or emulsions: Studies in human leukemic cells

The use of low density lipoprotein (LDL) as drug carrier in acute myeloblastic leukemia chemotherapy is attractive due to high LDL uptake by leukemic cells. Lipid-based formulations, such as liposomes or microemulsions are promising alternatives. In the current study, we incorporated N-trifluoroacetyl-adriamycin-14-valerate (AD32), a lipophilic derivative of daunorubicin (DNR), and WB4291, a lipophilic alkylating agent, into LDL or lipid microemulsions and evaluated their cytotoxic activities towards leukemic cell lines using as references DNR and melphalan. The incorporation of AD32 into LDL or emulsion resulted in complexes with poor cytotoxicity. WB4291-LDL and WB4291-emulsion exerted, on the other hand, promising cytotoxic effects towards parental and resistant K562 and HL60 cell lines.

Novel boronated derivatives of 5,10,15,20-tetraphenylporphyrin: synthesis and toxicity for drug-resistant tumor cells

We have developed the synthesis of boronated porphyrins for potential application in cancer treatment, based on the functional derivatives of 5,10,15,20-tetraphenylporphyrin. Boronated amide derivatives starting from 5,10,15,20-tetra(p-aminophenyl)porphyrin and 9-o- and 9-m-carborane carboxylic acid chlorides were prepared. Also, the reaction of 2-formyl-5,10,15,20-tetraphenylporphyrin with closo-C-lithium-o- and m-carboranes, as well as with closo-C-lithium monocarbon carborane, yielded neutral and anionic boronated hydroxy derivatives of 5,10,15,20-tetraphenylporphyrin, respectively. Water-soluble forms of neutral compounds were prepared by deboronation of closo-polyhedra with Bu4NF into nido-7,8- and nido-7,9-dicarbaundecaborate anions. Monocarbon carborane conjugated with copper (II) complex of 5,10,15,20-tetraphenylporphyrin was active for a variety of tumor cell lines (IC50 approximately 5 microM after 48-72 h of exposure) but was inert for non-malignant fibroblasts at up to 100 microM. At low micromolar concentrations, this compound caused the death of cells that express P-glycoprotein and other mechanisms of resistance to conventional anticancer drugs.

Proteomic Profiling of Hepatic Endoplasmic Reticulum-associated Proteins in an Animal Model of Insulin Resistance and Metabolic Dyslipidemia

Hepatic insulin resistance and lipoprotein overproduction are common features of the metabolic syndrome and insulin-resistant states. A fructose-fed, insulin-resistant hamster model was recently developed to investigate mechanisms linking the development of hepatic insulin resistance and overproduction of atherogenic lipoproteins. Here we report a systematic analysis of protein expression profiles in the endoplasmic reticulum (ER) fractions isolated from livers of fructose-fed hamsters with the intention of identifying new candidate proteins involved in hepatic complications of insulin resistance and lipoprotein dysregulation. We have profiled hepatic ER-associated proteins from chow-fed (control) and fructose-fed (insulin-resistant) hamsters using two-dimensional gel electrophoresis and mass spectrometry. A total of 26 large scale two-dimensional gels of hepatic ER were used to identify 34 differentially expressed hepatic ER protein spots observed to be at least 2-fold differentially expressed with fructose feeding and the onset of insulin resistance. Differentially expressed proteins were identified by matrix-assisted laser desorption ionization-quadrupole time of flight (MALDI-Q-TOF), MALDI-TOF-postsource decay, and database mining using ProteinProspector MS-fit and MS-tag or the PROWL ProFound search engine using a focused rodent or mammalian search. Hepatic ER proteins ER60, ERp46, ERp29, glutamate dehydrogenase, and TAP1 were shown to be more than 2-fold down-regulated, whereas alpha-glucosidase, P-glycoprotein, fibrinogen, protein disulfide isomerase, GRP94, and apolipoprotein E were all found to be up-regulated in the hepatic ER of the fructose-fed hamster. Seven isoforms of ER60 in the hepatic ER were all shown to be down-regulated at least 2-fold in hepatocytes from fructosefed/insulin-resistant hamsters. Implications of the differential expression of positively identified protein factors in the development of hepatic insulin resistance and lipoprotein abnormalities are discussed.

MR and fluorescent imaging of low-density lipoprotein receptors

RATIONALE AND OBJECTIVES

Over-expression of low-density lipoprotein receptors (LDLRs) occurs in many types of malignancies and is related to the requirement for lipids for rapid proliferation of the tumors. On the other hand, LDLRs that are unable to bind LDL are found on hepatocytes of patients with familial hypercholesterolemia (FH), a genetic disease that leads to premature atherosclerosis and death. The highly selective binding of LDL to LDLR makes these particles ideal carriers of therapeutic and diagnostic contrast agents into the targeted cells. The objectives of this paper are to examine whether a prototype contrast agent (PTIR267) with dual detection properties is suitable for labeling of LDL particles for in vivo detection of LDLR by magnetic resonance imaging (MRI) and for in vitro monitoring of cellular localization by confocal fluorescence microscopy.

MATERIALS AND METHODS

PTIR267 is a lipophilic GdDTPA derivative conjugated to a fluorescent dye. The conjugated dye molecule makes the probe sufficiently water soluble to allow labeling of LDL by a brief incubation of LDL with PTIR267 dissolved in PBS at 37 degrees C (mole ratio LDL: PTIR267 = 0.09:1). The molar relaxivity of PTIR267 in saline is 26 mM(-1)s(-1). Specific LDLR-mediated uptake of PTIR267-labeled LDL was demonstrated in vitro by confocal fluorescence imaging of B16 melanoma cells using confocal fluorescence imaging. In vivo uptake of PTIR267-labeled LDL by a subcutaneously implanted B16 melanoma in mice leads to 30% decrease in longitudinal relaxation time (T(1)) in the tumor. In vivo uptake of PTIR267-labeled LDL leads to 70% decrease in T(1) in a normal C57BL/6 mouse liver; however, in the liver of LDL receptor gene knockout (LDLr-/-) mice with C57BL/6 background, only 12% decrease in T(1) is observed.

CONCLUSIONS

The dual fluorescence and MR imaging properties of PTIR267, combined with the ease of LDL labeling, suggest that it will be a useful tool for optimization of LDLR-targeted cancer diagnosis or therapy and for monitoring the efficacy of gene therapy of FH.

Cholesterol and prostate cancer

Cholesterol is a neutral lipid that accumulates in liquid-ordered, detergent-resistant membrane domains called lipid rafts. Lipid rafts serve as membrane platforms for signal transduction mechanisms that mediate cell growth, survival, and a variety of other processes relevant to cancer. A number of studies, going back many years, demonstrate that cholesterol accumulates in solid tumors and that cholesterol homeostasis breaks down in the prostate with aging and with the transition to the malignant state. This review summarizes the established links between cholesterol and prostate cancer (PCa), with a focus on how accumulation of cholesterol within the lipid raft component of the plasma membrane may stimulate signaling pathways that promote progression to hormone refractory disease. We propose that increases in cholesterol in prostate tumor cell membranes, resulting from increases in circulating levels or from dysregulation of endogenous synthesis, results in the coalescence of raft domains. This would have the effect of sequestering positive regulators of oncogenic signaling within rafts, while maintaining negative regulators in the liquid-disordered membrane fraction. This approach toward examining the function of lipid rafts in prostate cancer cells may provide insight into the role of circulating cholesterol in malignant growth and on the potential relationship between diet and aggressive disease. Large-scale characterization of proteins that localize to cholesterol-rich domains may help unveil signaling networks and pathways that will lead to identification of new biomarkers for disease progression and potentially to novel targets for therapeutic intervention.