Melatonin in edible plants identified by radioimmunoassay and by high performance liquid chromatography‐mass spectrometry

Abstract

Melatonin, the chief hormone of the pineal gland in vertebrates, is widely distributed in the animal kingdom. Among many functions, melatonin synchronizes circadian and circannual rhythms, stimulates immune function, may increase life span, inhibits growth of cancer cells in vitro and cancer progression and promotion in vivo, and was recently shown to be a potent hydroxyl radical scavenger and antioxidant. Hydroxyl radicals are highly toxic by-products of oxygen metabolism that damage cellular DNA and other macromolecules. Herein we report that melatonin, in varying concentrations, is also found in a variety of plants. Melatonin concentrations, measured in nine different plants by radioimmunoassay, ranged from 0 to 862 pg melatonin/mg protein. The presence of melatonin was verified by gas chromatography/mass spectrometry. Our findings suggest that the consumption of plant materials that contain high levels of melatonin could alter blood melatonin levels of the indole as well as provide protection of macromolecules against oxidative damage.

Putative regulatory molecules in plants: evaluating melatonin

“…Although we and others have consistently detected appreciable quantities of melatonin in plants both by chromatography and immunological methods [Van Tassel et al, 1993;Kolar and Machackova, 1994;Dubbels et al, 1995;Hattori et al, 1995;Kolar et al, 1995;Manchester et al, 2000], we argue here that neither method is reliable on its own.…”

“…By this method, we have found melatoninlike immunoreactivity in P. nil, Arabidopsis, tobacco cotyledons/leaves, tomato fruit, black tea, coffee, red and white wines, mushrooms, and the unicells Spirulina and baker's yeast [Van Tassel, 1997]. Melatonin values have been published for a number of other angiosperm species, also based on RIA or HPLC [Dubbels et al, 1995;Hattori et al, 1995].…”

“…These findings invalidate any identification or quantification of melatonin in plant species based on either RIA or HPLC alone, unless they have been validated by more stringent methods than the standard methods commonly used. Some of the melatonin values cited in the literature [Van Tassel et al, 1993;Dubbels et al, 1995;Hattori et al, 1995] should therefore be reexamined because we found that a number of the plant materials that were reported to contain high levels of melatonin, e.g., oats and ginger [Hattori et al, 1995], actually had only trace amounts [Van Tassel, 1997]. The overestimates can be attributed to substantial levels of unidentified cross-reacting substances.…”

“…Fortunately, gas chromatography -mass spectrometry (GC -MS) or liquid chromatographymass spectrometry (LC -MS), when used with an internal standard such as deuterated melatonin, is self-validating for each sample and provides an alternative to RIA, HPLC, or both. The presence of melatonin in the plant kingdom has been demonstrated qualitatively by its identification in three different species by independent GC -MS or LC-MS analyses [Van Tassel et al, 1993;Dubbels et al, 1995;Kolar et al, 1995Kolar et al, , 1997. Preliminary measurements, in which melatonin was quantified in P. nil by GC -MS with selected ion monitoring using an internal standard, indicated that melatonin in the cotyledons of this plant are indeed 1.6-to 4-fold higher in the dark than during the day [S.D.…”

Phytoremediative Capacity of Plants Enriched with Melatonin

“…In 1995, two groups independently found that melatonin indeed exists in plants including fruits, vegetables and cereals. 4,5 Thereafter, numerous publications have confirmed melatonin's presence in the plant kingdom. [6][7][8][9] It seems that melatonin's presence in plants is a universal phenomenon.…”