RESEARCH PROJECTS

1. Investigation into whether the lipoprotein binding of drugs (i.e. Amphotericin B) modify their pharmacological toxicity and plasma disposition(i.e. pharmacokinetics).

Collectively our research in this area has been cited over 350 times in the past decade. A number of key papers with several compounds (i.e. Amphotericin B, Cyclosporine, Halofantrine, Nystatin, E5564, Clozapine) have been published demonstrating the importance of drug association with plasma lipoproteins.

Several key papers are highlighted below:

1. Impact of lipoproteins on the biological activity and disposition of hydrophobic drugs: implications for drug discovery .Published in Nature Reviews Drug Discovery in January 2008. This paper highlights the historical perspective and summarizes our latest research in the area of lipoprotein-drug interactions.
2. Enhanced Amphotericin B Nephrotoxicity in Intensive Care Patients with Elevated Levels of Low-Density Lipoprotein Cholesterol Clinical Infectious Diseases 24:78-80; 1997). This is the first published paper to suggest that patients with higher serum LDL cholesterol concentrations are more susceptible to amphotericin B-induced kidney toxicity.
3. Pharmacokinetics, Lipoprotein Distribution and Renal Toxicity of Amphotericin B (AmpB) and Amphotericin B Lipid Complex(ABLC) in Cholesterol-Fed Rabbits (Antimicrob. Agents Chemother. 1998). This is the first in a set of papers published to demonstrate rabbits with a higher total and LDL cholesterol concentrations are more susceptible to amphotericin B-induced renal toxicity following Fungizone but not ABLC administration.
4. Lipid Transfer Protein I Facilitated Transfer of Cyclosporine from Low- to High-Density Lipoproteins is only partially dependent on its Cholesteryl Ester Transfer Activity (JPET 1998; Pharmaceutical Research 1999 & 2002; Biochemical Pharmacology 2002) This research suggests that a novel plasma transfer protein, Lipid Transfer Protein, facilitates the transfer of different drugs (i.e. amphotericin, cyclosporine A) among different lipoprotein subclasses. This is the first set of papers with empirical evidence of the role of LTP in redistribution of drug into the lipoprotein subclasses.

 

2. Investigating the cardiovascular effects of a novel class of breast cancer agents called aromatase inhibitors in post-menopausal women.

1. Study which reported that the aromatase inhibitor, Letrozole, does not significantly alter serum cholesterol, HDL cholesterol, LDL cholesterol, triglycerides or Lp(a) in non-hyperlidiemic postmenopausal women with primary breast cancer treated up to 36 months following at least 5 years of adjuvant tamoxifen therapy. These findings further support the tolerability of extended adjuvant letrozole in postmenopausal women following standard tamoxifen therapy (Ann Oncol. 2005; 16(5):707-15.).

 

3. Published research investigating the role of lipid profiles in schizophrenia therapy.

1. Study which reported that Risperidone augmentation of clozapine for treatment resistant schizophrenia offered no benefit for severity of symptoms, and may increase the risk for cognitive impairment and glucose dysregulation.(Accepted in The New England Journal of Medicine, November8th 2005; In Press February 2006).
2. Study which reported that modified in vitro lipid profiles can modify the lipoprotein distribution of clozapine.(Am. J. Psychiatry 158:949-951, June 2001)\

 

4. Amphotericin B for treatment of Visceral Leishmaniasis

5. Physiological Role of P-Glycoprotein in Regulating the Gastrointestinal (GI) Absorption and Cellular Transport of Cholesterol.

Introduction: Despite an increase in research, treatment options and public awareness of risk factors, cardiovascular disease remains the leading cause of death in Canada. Elevated plasma cholesterol levels, smoking and hypertension are some of the major contributing risk factors in this fatal disease. Although cessations of smoking and pharmaceutical treatment of hypertension are both effective means of reducing the risk of cardiovascular disease, a universally effective cholesterol-lowering treatment regime remains elusive. The development of HMG-CoA reductase inhibitors (statins) in the early ‘80s was heralded as a solution to hypercholesterolemia, yet the rate of decrease in average total cholesterol levels among North Americans over the last decade has failed to meet expectations. Despite the widespread acceptance of dietary therapy and use of statins as means of reducing plasma cholesterol, the clinical promise of statins remains largely unfulfilled, indicating a need for alternate target mechanisms. Cholesterol homeostasis in the cell is regulated by a complex set of mechanisms that include cholesterol biosynthesis, hydrolysis from lipoproteins internalized into lysosomes and bidirectional transport of cholesterol to the endoplasmic reticulum (ER) where cholesterol undergoes esterification, and from the ER to the plasma membrane (PM). Unlike any other cell type within the body, the intestinal absorptive cell is bathed at its apical surface with both dietary and biliary cholesterol. Transport of dietary cholesterol into the enterocyte contributes significantly to the plasma cholesterol pool and to maintaining whole body cholesterol balance. Since absorbed cholesterol is likely the major source of cholesterol for the intestinal cell, understanding its transport and utilization is of importance and will provide valuable insights into the regulatory pathways of cholesterol. With the continuous influx of cholesterol at the apical membrane, cholesterol synthesis and low-density lipoprotein receptor expression are suppressed. Understanding the regulation of enterocyte cholesterol levels and the associated mechanisms of suppression may provide alternate targets for pharmaceutical lipid-lowering therapies. Class I P-glycoproteins [Pgp; encoded by the MDR-1 (humans) & MDR-1a/1b (mice) genes] are integral cell membrane proteins that were originally identified in multidrug-resistant tumor cells. The original functions elucidated were to reduce intracellular concentrations of structurally diverse chemotherapeutic agents and to act as efflux transporters of xenobiotics from the small intestine enterocytes back into the intestinal lumen resulting in decreased drug bioavailability. Preliminary studies have reported that nonspecific inhibitors of Pgp inhibit synthesis and esterification of cholesterol putatively by blocking trafficking of cholesterol from the PM to ER and that relative increases in Pgp within a given cell type are associated with increased accumulation of cholesterol. These findings provide indirect evidence supporting a physiologic function for Pgp in regulating cholesterol homeostasis. However, direct evidence is required. Therefore, this grant proposal will test the hypothesis “that class I Pgp has a direct physiological function in regulating the gastrointestinal absorption and intracellular transport of cholesterol” by completing two specific aims: a) determining the cholesterol GI absorption and tissue distribution in MDR1a-/-/1b-/- knock-out mice fed low, standard and high cholesterol and fat enriched diets and b) determining whether modulation of MDR-1 Pgp expression and activity results in altered cholesterol uptake and intracellular transport from the PM to the ER within human intestinal cells.

Experimental Design: Aim 1: We will determine [3H]cholesterol GI absorption and tissue distribution in MDR1a-/-/1b-/- knock-out mice after chronic feeding of low, standard and high cholesterol and fat enriched diets. Aim 2: We will determine cholesterol cellular uptake and intracellular transport from the PM to the ER within Caco-2 (intestinal) cells with either enhanced or reduced MDR-1 Pgp expression or activity using gene transfection or small interfering RNA technologies respectively. Additional cholesterol studies will use purified enterocytes obtained from MDR1a-/-/1b-/- knock-out mice. Significance: The funding of this project would specifically aid in our understanding of a potentially unique mechanism responsible for the gastrointestinal absorption and intracellular transport of cholesterol. Elucidation of this mechanism could provide the core data required for the development of novel pharmaceutical agents that have cholesterol lowering capabilities by inhibiting a unique pathway of cholesterol transport and synthesis.