Dharamainder Choudhary
Dr. Choudhary is an Assistant Professor in the Department of Surgery since 2006. He joined the Schenkman laboratory in the Pharmacology Department as a Postdoctoral fellow in 2000 after successfully completing studies toward the Ph.D. in the field of toxicology. He was recipient of two Research Fellowship awards from University Grants Commission, India during his PhD training. His PhD was based on characterization of new physiological roles for the glyoxalase system. His work on describing the toxic effects of methylglyoxal on redox status (toxicol Lett, 1997) was been well received by the scientific community and has been cited at least 20 times in peer reviewed journals. Methylglyoxal, belongs to a class of cytotoxic compounds called a-oxoaldehydes and is metabolized into a non-toxic lactic acid by the two enzymes glyoxalase I and glyoxalase II. The a-oxoaldehydes are involved in free radical generation and cell killing. They are known to be associated in mutagenesis and cancer by modifying DNA / proteins and forming crosslinked adducts similar to advanced glycylation end products (AGE) which are known to contributing to several pathophysiological conditions, e.g., cancer, diabetes, arthritis. The glyoxalase system holds significant importance in regulating allowable levels of toxic oxoaldehydes.
Dr. Choudhary’s work with medicinal plant based extracts was instrumental in demonstrating the modulation of glyoxalase system. eg. Fenugreek seeds administration enahnced Glyoxalase I activity and hence decreases the level of toxic a-oxoaldehydes, and delineated the possible mechanism for hypoglycemic property for fenugreek seeds and the dose response data of fenugreek seeds presented in this study will be helpful in designing the improved methods and efficient therapy-planning strategies for diabetes (Food Chem Toxicol. (2001). In another study employing curcumin, a compound present in the spice, turmeric, and in treatment of inflammatory diseases he demonstrated the compound to possess radioprotective activity by oral administration to pre-irradiated animals (J Ethanopharmacol, 2001) an indication that this phytochemical’s can contribute towards protection against background irradiation to which mankind is exposed. His findings, thus, indicate that curcumin could be employed as a chemopreventive agent against radiation induced pathological effects like cancer. Interestingly, much attention is being paid to curcumin today as a potential aid in prevention of Alzhemer’s disease.
Dr Choudhary has been working with Dr. Schenkman in a collaboration with Prof. Mansoor Sarfarazi, in studies focused on understanding the role of a cytochrome P450 hemoprotein, CYP1B1, in primary congenital glaucoma (PCG). PCG is a disease manifesting during neonatal and early infantile periods of development (0-3 yrs) and is characterized by high intraocular pressure (IOP), which if uncontrolled results to optic nerve damage and permanent loss of vision. It occurs due to abnormal development of the anterior chamber angle of the eye (especially the trabecular meshwork). This developmental anomaly in trabecular meshwork causes obstruction of the proper drainage of aqueous humor outflow resulting in high intraocular pressure (IOP), optic nerve damage, and blindness.
Sarfarazi’s group was the first to show the identification of mutations in CYP1B1 gene in PCG patients. It has now been confirmed in various ethnic populations by different investigators around the world. As CYP1B1 is a member of Cytochrome P450 family, therefore its involvement in ontogeny is expected to be associated with its catalytic activity by either degrading or formation of a critical biomolecule / morphogen involved in morphogenesis. The aim of Dr. Choudhary's research is to identify the critical enzymatic reaction responsible for normal development of trabecular meshwork during fetal and early post-natal ontogeny. As the P450s are considered mainly as xenobiotic/drug metabolizing enzymes, their expression during human ontogeny has been explained on the basis of their inducible expression by exposure to xenobiotics. However, whether their presence in humans during ontogeny is constitutive or the result of induction could not be concluded with certainty. We have suggested that CYP1B1, as well as a number of other forms of cytochrome P450 he have found to be present during in utero development of mice and humans to have a possible involvement in some critical physiological function during ontogeny apart from their role in xenobiotic metabolism (Reviews – PINSA 2003; Drug Metabol Rev, 2004).
Since mouse has an orthologous form of CYP1B1, Cyp1b1, Dr. Choudhary has used the mouse as a model for study of the role of CYP1B1 in eye development; in both species the eyes suffer developmental damage when the enzyme is mutated to non-function states. Dr. Choudhary's was the first to show the comparative retinoid metabolism patterns of human and mouse CYP1B1 orthologs (Drug Metab Disp, 2004). His hypothesis is that since very similar orthologs are present in both species, both must have a common evolutionary role in eye development. He showed that both orthologs can synthesize retinoic acid but cannot degrade the active morphogen, retinoic acid. This suggested that CYP1B1 may be involved in generating the retinoic acid during a specific time point when the morphogen is necessary for trabecular meshwork development. He examined another putative endogenous substrate, arachidonic acid, for metabolism to a potential substance for morphogenic activity, as its metabolites (HETEs, EETs) are known to have very potent biological activities with a range of cellular responses. Human CYP1B1 was capable of metabolizing arachidonic acid but activity of the mouse ortholog, Cyp1b1, was extremely low, ruling out the arachidonic acid as the critical molecule during CYP1B1 associated eye development.
Dr. Choudhary has carried out the first systematic investigation of gestational age-dependent cytochrome P450 expression patterns. Using normalized cDNA panels and uniform RT-PCR based techniques he was able to examine 40 of the 93 known forms of cytochrome P450 in mouse, and show the presence of cDNA of 27 different cytochrome P450 forms appeared at one or another stage of in utero development (Arch Biochem Biophys, 2003). The data also answered an obvious question as to why other members of CYP1 family, which have broad, overlapping substrates, do not compensate for CYP1B1 deficiency during trabecular meshwork development. Data indicated that CYP1A1, CYP1A2 and CYP1B1 have non-overlapping expression patterns during mouse development. Hence, CYP1A1, CYP1A2 cannot compensate for CYP1B1 deficiency during embryonic development, as they are not expressed at the same developmental period.
In furtherance of his hypothesis that cytochrome P450 expression during ontogeny is associated with performance of a key biological function, Dr. Choudhary focused on other forms of cytochrome P450 with possess high sequence identity and other indications of being evolutionary conserved. Dr. Choudhary’s recent report (Arch Biochem Biophys, 2005) encompasses a complete characterization of the comparative expression levels of the cytochrome P450 orthologs between mouse and human during ontogeny and levels in the respective adult tissues. The expression pattern of 10 CYP orthologs (families 1-4) in human and mouse adult tissue and during ontogeny were determined. The study showed positive expression of all the ten CYP orthologs except CYP1A2 during ontogeny in mouse and human. The expression of the different CYP transcripts in developing mouse fetus suggested their presence may not be associated only with detoxification of the xenobiotics, but might also be associated with normal development. Hence, the presence of the ortholog CYPs may indicate retention of some physiological function necessary for normal development that is maintained in the many different species.
Dr. Choudhary is currently constructing mutations of wild type CYP1B1 that have been identified in human PCG patients. These mutants will be expressed and the protein will be characterized by performing stability and different substrate metabolism reactions. This may provide explanation as to the potential mechanism of PCG phenotype occurrence in these patients. Some of the mutations are homozygous in PCG family members who do not have the PCG disease phenotype, a phenomena called incomplete penetrance. In a study in which he participated, (Pharmacogenetics, 2001) an emerging concept points to environmental factors impact on levels of CYP1B1 and can overcome effects of compromised activities of cytochrome P450 forms due to mutations by a process of induction. Dr. Choudhary's future findings with newly constructed CYP1B1 mutants is expected to be significant in solving some of the mysteries of this blindness-causing disease.
Dr. Choudhary is extremely gifted researcher, has performed outstanding work, provided critical and original ideas to the planning and execution of scientific problems. His contributions resulted in a number of peer reviewed significant research papers from my laboratory and 2-3 will be forthcoming this year. He has published a total of twenty two papers in high reputed journals. He has presented oral talks and posters in international conferences during his post-doctoral period and all were well received by the attending scientific community. He has established his name in Cytochrome P450 field by assigning new role of P450s in ontogeny, a function distinct from their established roles in drug detoxification.
Recent papers
D. Choudhary., I. Jansson, J.B.
Schenkman, M Sarfarazi., and I Stoilov. Comparative expression profiling of 40 mouse
cytochrome p450 genes in embryonic and adult tissues. Arch Biochem. Biophys. 414: 91-100
(2003).
D. Choudhary, I. Jansson, I. Stoilov, M. Sarfarazi and J. B. Schenkman. Metabolism of retinoids and arachidonic acid by human and mouse cytochrome P450 1B1. Drug Metab. Dispos. 32: 840-847 (2004).
D.
Choudhary, I.Jansson, I. Stoilov, M.Sarfarazi, and J.B. Schenkman. Expression patterns of
mouse and human CYP orthologs (families 1-4) during development and in different adult
tissues. Arch. Biochem. Biophys. 436:50-61 (2005).
Recent Reviews
J.B. Schenkman,
D. Choudhary, I. Jansson, M. Sarfarazi and I. Stoilov. Involvement of cytochromes P450 in
Development. Proc. Indian Natn. Sci. Acad. B69:917-929 (2003).
D. Choudhary,
I. Jansson, M. Sarfarazi, and J.B. Schenkman. Xenobiotic-metabolizing cytochromes P450 in
ontogeny: evolving perspective. Drug Metab. Reviews:36: 549-568 (2004).
D.
Choudhary, I. Jansson, M. Sarfarazi and J.B. Schenkman. Physiological Significance and
Expression of P450s in the developing eye. Drug Metabolism Reviews 38(1): 337-352 (2006).