Protein Chemistry: Organelle isolation, protein purification, protein association with artificial membranes, chemical labelling, protein digestion and peptide analysis, structure-function analysis.

Enzymology: Cytochrome P450scc catalysis and mechanism, substrate specificity, steady state and rapid reaction kinetics.

Recombinant DNA Technology: Cloning, bacterial expression, site-directed mutagenesis, PCR.

Steroid and vitamin D Biochemistry/Endocrinology: Steroid and lipid extraction and analysis, radioimmunoassay, TLC, GLC and HPLC analysis of steroids and vitamin D.

Cell Biology: Placental cell culture

Vitamin D Synthesis and Metabolism

Current research primarily involves the metabolism of vitamin D by cytochrome P450scc (CYP11A1), and the activation and inactivation of vitamin D by other cytochromes P450 including CYP27A1, CYP27B1, CYP24A1 and CYP2R1. With collaborators we are trying to develop new forms of vitamin D which are non-toxic and have therapeutic potential for the treatment of immune disorders, fibrosis and cancer.

Vitamin D synthesis in the skin

Vitamin D3 is produced by the action of UV radiation on 7-dehydrocholesterol (7-DHC) in the skin.  The initial event is the photochemical breaking of the C9-C10 bond in the B ring of 7-DHC resulting in the formation of previtamin D3. Once formed, previtamin D3 undergoes thermal isomerization in the skin over several hours to form vitamin D3. With further exposure to UV radiation, previtamin D3 undergoes photoisomerization to lumisterol and tachysterol which become the major photoisomers observed in human skin after prolonged UV irradiation.  This was assumed to be a mechanism to prevent vitamin D intoxication with excessive UV-radiation.  It had been believed that lumisterol and tachysterol were inactive end-products of excessive UV radiation with their formation preventing excessive vitamin D production. Recently however, we discovered that lumisterol can be metabolised by CYP11A1 and CYP27A1 to biologically active products, such as 24-hydroxylumisterol, that may confer protection to the skin against further UV damage. For example, 24-hydroxylumisterol induces DNA repair enzymes which reduce the damage to the DNA and thus has anti-cancer properties. This compound can be applied to the skin after the radiation to achieve this outcome and thus provides the possibility of an “after sunburn” treatment to reduce the incidence of skin cancer.  Some of the products of CYP27A1 action on lumisterol are still to be isolated, identified and their biological activity characterized. 

Vitamin D activation

There are 4 mitochondrial cytochrome P450 enzymes and one microsomal P450 that catalyse the hydroxylation of vitamin D and its metabolites, CYP11A1, CYP27A1, CYP27B1, CYP24A1 and CYP2R1. CYP27A1 and CYP2R1 catalyse the first step in the classical pathway for activation of vitamin D which is hydroxylation at the C25 position, producing 25-hydroxyvitamin D3.  CYP27B1 catalyses the second step in this activation, 1α-hydroxylation of 25-hydroxyvitamin D3 to produce 1,25-dihydroxyvitamin D3, the major hormonally active form of vitamin D. 1,25-Dihydroxyvitamin D3 not only regulates calcium metabolism required for strong healthy bones, but also has many other important effects including inhibiting proliferation and promoting differentiation of a range of normal and cancer cells, plus regulating the immune system including reducing inflammation. CYP24A1 acts on 1,25-dihydroxyvitamin D3, hydroxylating it at C24 which causes its inactivation.

In collaboration with Professor Andrzej Slominski at the University of Alabama, Birmingham, we discovered that CYP11A1 can also metabolize vitamin D3. We found that CYP11A1 hydroxylates the side chain of vitamin D3 producing 20-hydroxyvitamin D3 and 20,23-dihydroxyvitamin D3, and that these compounds also display the benificial anti-cancer properties of 1,25-dihydroxyvitamin D3 but without elevating serum calcium. Thus, unlike 1,25-dihydroxyvitamin D3 they can be administered at high doses without causing toxic hypercalcaemia, and therefore have great therapeutic potential for the treatment of cancer and immune disorders.

We are expressing CYP27A1, CYP27B1, CYP24A1 and CYP2R1 in E. coli, and studying their catalytic properties in a reconstituted system that utilizes phospholipid vesicles to mimic the inner-mitochondrial membrane.  We are also using these enzymes to hydroxylate the CYP11A1-derived vitamin D analogues such as 20-hydroxyvitamin D3, to see if 1-, 24- or 25-hydroxylation of these compounds enhances their potency without causing them to display calcaemic activity, with the aim of further improving their therapeutic properties. 

Current research involves  metabolism of vitamins D2 and D3 and their precursors by cytochromes P450 and the enzymatic synthesis of novel vitamin D derivatives with therapeutic potential for the treatment of cancers and immune disorders.