Chunxian Chen

Mechanism-based inhibition of human cytochrome P450-3A activity by grapefruit hybrids having low furanocoumarin content.

A citrus breeding program aimed at developing low furanocoumarin (FC) grapefruit cultivars provided 40 grapefruit juice (GFJ) samples containing variable concentrations of FC derivatives, established as being mechanism-based (irreversible) inhibitors of human CYP3A isoforms. The principal inhibitory FCs were identified as 6′,7′-dihydroxybergamottin, along with a series of dimeric compounds (spiroesters) having high inhibitory potency. A random subset of the GFJ samples (n = 25) were tested as CYP3A inhibitors using an in vitro model based on human liver microsomal metabolism of the index substrate triazolam. The reciprocal values of in vitro 50% inhibitory concentrations (IC50) were highly correlated with concentrations of inhibitory FCs in the GFJ samples (r2 = 0.96). However the correlations were driven mainly by a few samples having high FC content and high reciprocal IC50 (corresponding to low IC50). Among the rest of the samples, the relationship was less robust. Further study is needed to determine how low the FC content needs to be (or how high the IC50 needs to be) to assure minimal risk of clinical interactions involving GFJ and CYP3A substrate drugs.

IDENTIFICATION OF AFLP MARKERS ASSOCIATED WITH CITRUS CANKER RESISTANCE WITHIN CITRUS

Asian Citrus Canker (ACC) is an immediate threat to the entire Florida citrus industry. The recent results of phenotyping the individuals of a mapping family, designated as 9100 family, derived from a cross between susceptible Palestine sweet lime (Citrus limettoides) and the resistant Ichang papeda (C. ichangensis), revealed a normal distribution from the most resistant to the most susceptible individuals. In order to identify molecular markers linked to the citrus canker resistance gene(s) and develop a genetic map based on these results, we applied a combination of the amplified fragment length polymorphism (AFLP) technique and bulked segregant analysis (BSA) to an F1 population and their parents for subsequent work. Ninety-three pairs of AFLP primer combinations were screened. A total of 89, from the determined 950 polymorphic bands (present in the resistant parent and absent in the susceptible parent), were found tightly associated with the resistant individuals. These markers were mapped by Joinmap v. 2.0 in a co-segregation group.