Vitamin D3 and its metabolites in tomato, potato, egg plant and zucchini leaves
Introduction
Many plant species are known to cause calcinosis in grazing animals that ingest them. Calcinogenic activity is claimed to be attributed to the presence of vitamin D-like activity in these plants1, 2, 3. It is now well-established that the leaves of Solanum malacoxylon and Cestrum diurnum, two calcinogenic plants belonging to the family Solanaceae, contain the glycoside of calcitriol (1α,25-(OH)2 D3) which is the most potent hormonal form of vitamin D3 (cholecalciferol) responsible for maintenance of calcium and phosphorus homeostasis in higher animals[4]. In addition to calcitriol glycoside, S. malacoxylon contains vitamin D3 glycoside and the glycoside of 25-(OH)D35, 6, 7. Prema et al.[8]. reported the occurrence of free vitamin D3, its metabolites and their glycosides in Cestruim diurnum leaves. They also reported the presence of vitamin D-like activity in Lycopersicon esculentum leaves[9]. This activity is claimed to be due to the presence of vitamin D3 and its hydroxylated metabolites 25-OH D3 and 1α,25-(OH)2 D3 both free and in the glycosidic form. These effects were established in vitamin D3-deficient rats.
In our previous work on cell cultures derived from S. malacoxylon leaves[10], we investigated the presence of different precursors of the vitamin D3 biosynthtic pathway. The presence of cholesterol and 7-dehydrocholesterol was established. In addition, the occurrence of vitamin D3 and its hydroxylated metabolites 25-OH D3 and 1α,25-(OH)2 D3 was also reported. Most of the known calcinogenic plants so far screened belong mainly to the Solanaceae. In the present study, we investigated the occurrence of vitamin D3 and its hydroxylated metabolites in leaves of some members of the Solanaceae. Among these are Lycopersicon esculentum (tomato), Solanum tuberosum (potato) and Solanum melongena (egg plant). Moreover, the presence of the above mentioned constituents was also investigated in Cucurbita pepo (zucchini), family Cucurbitaceae. The results show the presence of free vitamin D3 in the leaves of tomato, potato, zucchini but not in egg plant leaves. Only tomato leaves were found to contain 25-OH D3. However, neither the other vitamin D3 hydroxylated metabolites, namely 1α-OH D3 and 1α,25-(OH)2 D3, nor the glycosidic form of vitamin D3 or any of its metabolites were detected in any of the above tested plant extracts.
Section snippets
Results and discussion
Leaves of the four species were extracted with chloroform and then with ethanol. Ethanolic extracts expected to contain the glycosides of vitamin D3 and/or any of its hydroxylated metabolites were hydrolyzed enzymically with mixed glycosidases prior to analysis as chloroform extracts. Chromatographic analysis on reverse-phase HPLC of the chloroform extracts of tomato, potato and zucchini but not egg plant revealed the presence of free vitamin D3. The extract of each species was partially
Extraction and analysis
Fresh young apical leaves (2 kg) of L. esculeutum, S., S. melongena, and C. pepo, were cut into fine pieces and then extracted in the dark with CHCl3 (0.6 l×3) by percolation. The CHCl3 extracts were dried (Na2SO4), filtered and the solvent removed under red. pres. The residues were then extracted with EtOH (0.6 l×3). The EtOH extracts were dried (Na2SO4), filtered and the solvents were removed under red. pres. The EtOH extracts were hydrolyzed enzymically using a mixed glycosidases preparation
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