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Under the direction of Rafat A. Siddiqui, PhD, the Cellular Biochemistry laboratory is actively involved in research on:
- Impact of Trans- and Omega-3 fatty acids on vascular modeling
- Modulation of cellular functions by dietary fatty acids
- Cellular effects of Omega-3 fatty acids on cardiomyoctes
Cancer Cell Biology
- Characterization of cellular and molecular processes for the anti-cancer effects of Omega-3 fatty acids
- Synthesis and characterization of novel lipid conjugates for anti-cancer activity
- Metabolomics of cancer cachexia
Impact of Trans- and Omega-3 Fatty Acids on Vascular Modeling
Our long-range goal is to understand the mechanism(s) by which omega-3 polyunsaturated fatty acids (n-3 PUFAs) and Trans fatty acids (TFAs) modulate endothelial cell function leading to vascular remodeling.
Coronary artery disease is the leading cause of myocardial infarctions, and more than 12.4 million Americans have clinically significant coronary artery disease. Epidemiological studies, prospective randomized clinical trials, and laboratory investigations have reported a decrease in morbidity and mortality from heart disease in patients with diets supplemented with n-3 PUFAs. In contrast, it has been estimated that partially hydrogenated fat, the major dietary source of TFAs, may be responsible for 30,000 to 100,000 premature coronary deaths per year in the U.S. alone. We found from our 6-month survival studies, following coronary ligation and feeding rats diet rich in either TFAs or n-3 PUFAs, that only 50% of the animals survived on a TFA diet, whereas 85% of the animals survived on an n-3 PUFA diet (1). n-3 PUFAs inhibit oxidative stress-mediated changes in endothelial cells that function to resist and/or inhibit pathological vascular remodeling and promote compensatory vascular remodeling whereas TFAs promote oxidative stress-mediated changes in endothelial cells that stimulate pathological vascular remodeling and inhibit compensatory vascular remodeling. Our recent data indicate that TFAs promote inflammatory conditions that also contribute to increased risk of cardiovascular diseases (2).
Modulation of Cellular Functions by Dietary Fatty Acids
Our long-range goal is to understand the mechanisms by which dietary fatty acids impact the development of inflammatory, cancer, and cardiovascular disease, and to develop new therapies and dietary recommendations to improve outcomes.
Treating critically ill patients with rapid delivery of much needed calories was recognized as early as 1930 by Studley who demonstrated a strong link between the presence of malnutrition and the development of postoperative mortality. This led in exploration of better ways to deliver adequate fuel calories to malnutrition patients. It took another 30 years when finally Schuberth and Wretlind developed a nontoxic lipid emulsion prepared from soybean oil (SO) (Intralipid, Fresenius-Kabi, Bad Homburg, Germany) for delivering fuel to malnurished patients. Later Ivelip (Baxter, Maurepas, France) was developed which was also based on SO. In order to decrease the high content of n-6 PUFAs in Intralipid, Lipofundin (B Braun, Melsungen, Germany) was introduced consisting of mixtures of soybean oil and coconut oil containing triglycerides of medium chain saturated fatty acids (MCTs). Later Baxter (Maurepas, France) introduced Clinoleic, an olive oil base emulsion, in late 1990s for use in total parenteral nutrition (TPN). In Clinoleic 80% of SO was replaced by olive oil (OO), which is rich in oleic acid (18:1) a long-chain n-9 monounsaturated fatty acid (MUFA). Omegaven (Fresenius-Kabi), an n-3 PUFAs enriched preparation was recently introduced. More recently Lipiplus (also known as Lipidm) containing mixtures of SO, CO, and FO and SMOFlipid containing SO, CO, OO, and FO were introduced by Fresenius-Kabi (Bad Homburg Germany). Although the newer products contained n-3 PUFAs, their ratios are varied from product to product. These lipid products also contain significant amounts of saturated fatty acids, which have some harmful effects (1). Furthermore, recent data also suggest that instead of n-6/n-3 ratios, the total amount of n-3 PUFAs in lipid products are perhaps more important. Unquestionably, there is a gap in the knowledge about an optimum fatty acid mixture for modulating biological activities in order to make lipid infusion product more therapeutic and beneficial to patients. This research will help understand the role of different classes of fatty acid present in lipid emulsions and will help to better formulate lipid emulsions to treat critically ill patients.
- Zaloga, GP., Pavlina, T., Harvey, K., Walker, C., Siddiqui, RA. Long chain saturated fatty acids induce growth inhibition and inflammation in endothelial cells. European Society of Parenteral and Enteral Nutrition-Congress, Florence, Italy, September 13-16, 2008.
Cellular Effects of Omega-3 Fatty Acids on Cardiac Function
The long range goal of this research is to understand the mechanism by which omega-3 fatty acids provide beneficial protective effect to heart functions.
Epidemiological evidence from Greenland Eskimos and Japanese fishing villages suggests that eating fish oil and marine animals can prevent coronary heart disease. Dietary studies from various laboratories have similarly indicated that regular fish oil intake affects several humoral and cellular factors involved in atherogenesis and may prevent atherosclerosis, arrhythmia, thrombosis, cardiac hypertrophy, and sudden cardiac death. The beneficial effects of fish oil are attributed to their n-3 polyunsaturated fatty acid (also known as omega 3-fatty acids) content, particularly, eicosapentaenoic acid (EPA, 20:5,n-3) and docosahexaenoic acid (DHA; 22:6 9,n-3). Dietary supplementation of DHA and EPA influences the fatty acid composition of plasma phospholipids that, in turn, may affect cardiac cell functions in vivo (1). Recent studies have demonstrated that long chain omega 3-fatty acids may exert beneficial effects by affecting a wide variety of cellular signaling mechanisms. Pathways involved in calcium homeostasis in the heart may be of particular importance. L-type calcium channels, the Na+-Ca2+ exchanger, and mobilization of calcium from intracellular stores are the most obvious key signaling pathways affecting the cardiovascular system; however, recent studies now suggest that other signaling pathways involving activation of phospholipases, synthesis of eicosanoids, regulation of receptor-associated enzymes, and protein kinases also play very important roles in mediating n-3 PUFAs effects on cardiovascular health (2). This research is therefore focused on the molecular targets and signaling pathways that are regulated by n-3 PUFAs in relation to their cardio protective effects.
- Siddiqui, R., Harvey, K., Zaloga, G., Stillwell, W. Modulation of lipid rafts by omega-3 fatty acids in inflammation and cancer: Implication for use of lipids during nutritional support. Nutrition in Clinical Practice 2007; 22:74-88
- Siddiqui, RA., Harvey, KA., Zaloga, GP. Modulation of Enzymatic Activities by n-3 Polyunsaturated Fatty Acids to Support Cardiovascular Health. J. Nutrition Biochemistry 2008; 19: 417-437
Characterization of Cellular and Molecular Processes for the Anti-cancer Effects of Omega-3 Fatty Acids
The long term goal of this study is to elucidate the cellular and molecular mechanisms for the anticancer effects of n-3 PUFAs in cancer cells.
DHA has a well-documented role in inhibiting or preventing cancer. Early epidemiological evidence strongly links fish oil [rich in DHA and eicosapentaenoic acid (EPA)] and low incidence of several types of cancer, including breast cancer. In addition to strong epidemiological studies, dietary studies on many types of animals, including humans, and on numerous cultured cells have also substantiated DHA's role as an anticancer agent for breast cancer. For the past 15 years, our laboratory has investigated the relationship between DHA's alteration of membrane structure and its effects on cell signaling and apoptosis.
DHA induces apoptosis in cancer cells through multiple mechanisms. Among other mechanisms, we demonstrated that DHA induces cell cycle arrest in Jurkat cells via hypophosphorylation of pRb through p21-mediated inhibition of cdk2 kinase activity and stimulates protein phosphatase activity (1). These effects appear to be mediated through ceramide formation from activation of neutral sphingo-myelinase (N-SMYase) in both Jurkat leukemic (1) and breast cancer (2) cells. The effects were mediated through enhanced expression of p21. In addition, transport of DHA and other fatty acids to the nucleus and binding to nuclear receptors such as peroxisome proliferator-activated receptor (PPAR) and retinoid X receptors (RXRs) have been reported. DHA is a general ligand of PPARs, but binds more selectively to RXR transcription factors. RXRs form homo- or heterodimers with PPAR and other nuclear hormone receptor super-families that include receptors for steroids, thyroid hormones, retinoic acid and vitamin D and involved in the regulation of p21 expression. This recent research focuses to determine if DHA plays a role in attenuation of breast cancer growth through PPARg/RXR-mediated p21 expression.
- Siddiqui, R.A., Jenski, L.J., Harvey, K., Wiesehan, J., Stillwell, W., Zaloga, G. (2003). Cell cycle arrest in Jurkat leukemic cells: a possible role for dososahexaenoic acid. Biochem. J., 371, 621-629.
- Wu, M., Harvey, K.A., Ruzmetov, N., Welch, Z., Sech, L., Jackson, K., Stillwell, W., Zaloga, G.P., Siddiqui, RA.. Omega-3 polyunsaturated fatty acids attenuate breast cancer growth through activation of aneutral sphingomyelinase-mediated pathway. Intl. J. Cancer 2005;117: 340-348
Synthesis and Characterization of Novel Lipid Conjugates for Anti-cancer Activity
The long term goal of this investigation is to enhance properties of anti-cancer drugs by making novel conjugates with lipids.
The major obstacles to the successful use of nutrients as preventive or therapeutic agents are their efficacy and bioavailability. In some cases these problems can be overcome by using more frequent or larger doses of bioactive nutrients. However in most cases this approach causes undesirable side effects, increase in cost and also leads to serious practical difficulties in formulation. One approach to overcoming the problem of drug uptake is to link water-soluble drugs to lipophilic carriers. As a proof of principle we have carried out conjugation of DHA with 2,6 diisopropyl phenol (1) and our initial data (2), which have received worldwide attention in the press (reported in over 100 news Web sites and attained highly accessed status) have shown that the DHA-propofol conjugate exerts synergistic effects in inducing apoptosis in breast cancer cells. We are currently synthesizing novel conjugates of polyphenols with fatty acids and are testing their effects on various cancers.
1. Fatty acid phenolic conjugates (20040254357) Patent Pending.
- Siddiqui, R.A., Zerouga, M., Wu, M., Castillo, A., Harvey, K., Zaloga, G.P., and Stillwell, W. Anticancer Properties of Propofol-Docosahexaenoate and Propofol-Eicosapentaenoate on Breast Cancer Cells. Breast Cancer Research 2005; R645-R654
Metabolomics of Cancer Cachexia
The long term goal of this study is to identify metabolite(s) for possible biomarker for the induction and/or progression of cachexia.
Cachexia represents a complex metabolic process wherein there is progressive loss of tissue mass that primarily affects muscle and adipose tissue due to drastic changes in the intermediary metabolism of organs and tissues of the cancer patients (1). The objective of this proposal is to identify pathway(s) that are differentially operated in cachectic and non-cachectic animals. Such information is desired for the clinical management of cachexia and the well being of cancer patients.
- Siddiqui, R.A., Pandya, D., Harvey, K., and Zaloga, G.P. Nutrition modulation of cachexia/proteolysis. Nutrition in Clinical Practice. 2006; 21 (2): 155-167.