Steryl glucoside concentration declines with Cycas micronesica seed age

Abstract

Neurotoxins contained in the seeds of Cycas micronesica K.D. Hill have been implicated in the Guam neurological disease cluster, amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS-PDC). Some of these neurotoxins remain in the washed cycad seed flour that was historically an important part of the Chamorro diet. Of these, variant steryl glucosides have been identified by us as a possible etiological factor in the disease. In vitro and in vivo animal studies have strongly supported a role for these molecules in some forms of neurodegeneration. As part of a series of studies, we have now determined the concentrations of several steryl glucosides and their sterol precursors as affected by the age of C. micronesica seeds. The concentration of these molecules declined with seed age from 2.0 to 30.5 months. Following log-transformation of both axes, the decline was linear. Similarly, concentration of all but one of the molecules declined with age when samples were restricted to gametophyte tissue. Factors suspected of influencing phenotypic plasticity must be addressed when interpreting plant physiology data. Our results confirm for the first time that tissue age must be documented and reported in cycad seed biochemistry studies to remove ambiguities from results. Past studies in this important area of research have failed to account for the potential impact of seed age, rendering previous outcomes and interpretations of cycad neurotoxins in their impact on ALS-PDC ambiguous.

Chronic Exposure to Dietary Sterol Glucosides is Neurotoxic to Motor Neurons and Induces an ALS–PDC Phenotype

“…Seed maturity appears to be the most crucial factor with younger seeds having higher concentrations by up to several orders of magnitude (Marler et al 2006). Similar variations for stigmasterol glucoside and other phytosterol glucosides have also been measured (Marler et al 2005).…”

Chemical Constituents of Cycas aenigma

“…and C. circinalis L. yielded lariciresinol, naringenin and biflavonoids (Ferreira et al, 2009). β-Sitosterol β-D-glucoside, stigmasterol β-D-glucoside, β-sitosterol, and stigmasterol were obtained from the seeds of C. micronesica K. D. Hill (Marler et al, 2006), while C. beddomei afforded a new biflavonoid, along with pinoresinol, hinokiflavone, and amento flavones (Das et al, 2006;Das et al, 2005). The leaves of C. panzhihuaensis yielded a new flavone, along with 2,3-dihydrohinokiflavone, a biflavone, vanillic acid, sitosterol and daucosterol (Zhou et al, 2002).…”

Free and glycosylated sterol bioaccumulation in developing Cycas micronesica seeds

“…We have mentioned that prior studies of Cycas seed chemistry have been of limited utility because response variables were restricted to concentration of various compounds (Marler et al, 2006), such that the pattern of changes in bioaccumulation of compounds has remained unreported. We have now addressed this deficiency to reveal that C. micronesica seed sink activity for sterol and steryl glucoside compounds or the net biosynthesis of these compounds in seeds is consistently sustained throughout their development up to 24 months.…”

“…We have begun to address this paucity of information by determining that concentration of sterols was greatest in young Cycas micronesica seeds, and declined log–log linearly throughout seed development and maturation (Marler, Lee, Chung, & Shaw, 2006). This nonlinear decline in concentration was dependent on intact import/export relations, as evidenced by a stable concentration in detached seeds during extended storage (Marler, Lee, & Shaw, 2007b).…”