Sequential Extraction as Novel Approach to Compare 12 Medicinal Plants From Kenya Regarding Their Potential to Release Chromium, Manganese, Copper, and Zinc

Abstract

This study is focusing on a novel approach to screen a large number of medicinal plants from Kenya regarding their contents and availability of selected metals potentially relevant for treatment of diabetes patients. For this purpose, total levels of zinc, chromium, manganese, and copper were determined by flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry as well as BCR sequential extraction to fractionate the elemental species in anti-diabetic medicinal plants collected from five natural locations in two sub counties in Nyamira County, Kenya. Solanum mauense had the highest zinc level of 123.0 ± 3.1 mg/kg while Warburgia ugandensis had the lowest level of 13.9 ± 0.4 mg/kg. The highest level of copper was in Bidens pilosa (29.0 ± 0.6 mg/kg) while the lowest was in Aloe vera (3.0 ± 0.1 mg/kg). Croton macrostachyus had the highest manganese level of 1630 ± 40 mg/kg while Clerodendrum myricoides had the lowest (80.2 ± 1.2 mg/kg). The highest level of chromium was in Solanum mauense (3.20 ± 0.06 mg/kg) while the lowest (0.04 ± 0.01 mg/kg) were in Clerodendrum myricoides and Warburgia ugandesis among the medicinal plants from Nyamira and Borabu, respectively. The levels of the elements were statistically different from that of other elements while the level of a given element was not statistically different in the medicinal plants from the different sub counties. Sequential extraction was performed to determine the solubility and thus estimate the bioavailability of the four investigated essential and potentially therapeutically relevant metals. The results showed that the easily bioavailable fraction (EBF) of chromium, manganese, zinc, and copper ranged from 6.7 to 13.8%, 4.1 to 10%, 2.4 to 10.2%, and 3.2 to 12.0% while the potentially bioavailable fraction (PBF) ranged from 50.1 to 67.6%, 32.2 to 48.7%, 23.0 to 41.1%, and 34.6 to 53.1%, respectively. Bidens pilosa, Croton macrostachyus, Ultrica dioica, and Solanum mauense medicinal plants used to treat diabetes by 80 % of the herbalists in Nyamira County were found to be rich in chromium, manganese, copper, and zinc. The EBF of zinc, manganese, and chromium constitutes adequate amounts recommended for daily intake not exceeding the ADI and delivered a low percentage of RDA when estimating daily intake during therapy from typically applied doses. The plants did not show any significant differences at p < 0.05 in terms of concentrations of the elements between the two study areas though the levels of the different elements were statistically significant. Another major observation was that high total levels of the metals in a given plant did not necessarily translate to high bioavailable levels, and hence the need to determine bioavailable form as it is the one accessible to the patient.

Assessment of bio-availability of Cd, Pb, As and Tl via Gastric/Intestinal Digestion in Plants Collected From Different Kenyan Regions

“…This increases the plant safety as low amounts of As, Cd, Tl and Pb elements are absorbed. The results are contrary to those we reported for Zn, Mn, Cr and Cu in the sequential extraction as novel approach to compare 12 medicinal plants from Kenya regarding their potential to release chromium, manganese, copper and zinc (Mogwasi et al 2018). The low molecular mass species enhanced the absorption of the therapeutic elements while the existence of the toxic elements in large molecular weight species means less amounts are absorbed, lowering their toxicity.…”

“…The details on herbalist recruitment in Manga and Borabu sub-counties were as described in our previous works (Nischwitz et al 2017;Mogwasi et al 2018;Mogwasi et al 2019). Based on the herbalist information he most commonly used herbal plants and the protocols used in their preparations were established.…”

“…The modi ed Mogwasi et al (2018) sequential ultra-ltration method was used to determine bio accessibility of Cd, Pb, As and Tl from the plants. Approximately 140 mg of ground plant material was mixed with 40 mL deionised hot water in a polypropylene tube and shaken for 13 hours in the dark using a horizontal shaker at 100 motions per minute (n=3).…”

“…This requirement is not observed in the third world countries where the use of plants is neither controlled nor regulated by quality assurance parameters (Annan et al 2010;Khan 2013;Ogunbanjo et al 2016;Adie and Adekunle 2017). Though the determination of the total content of the heavy metal in the plants give an indication of the levels of toxicity much more information can be obtained by measuring the bioavailability and bio accessibility (Arpadjan et al 2008;Intawongse and Dean 2008;Musa Özcan et al 2008;Yemane et al 2008;Jayawardene et al 2010;Lv et al 2013;Zhu et al 2013;Okem et al 2014;Čadková et al 2015;Parviz et al 2015;Bolan et al 2016;Pizarro et al 2016;Yang et al 2016;Nischwitz et al 2017;Mogwasi et al 2018;Zhou et al 2018;Mogwasi et al 2019).…”

Trace Elements in Medicinal Plants Traditionally Used in the Treatment of Diabetes—Do They Have a Role in the Claimed Therapeutic Effect?

“…A comprehensive compilation of literature data on the elemental content (macrominerals and trace elements) of medicinal plants and their tisanes, as well as the percentage of element release into infusions and decoctions, is provided by Pohl et al [ 23 ]. For highly relevant elements, such as Cr, Mn, Zn and Cu, it has been shown that the “easily bioavailable fraction” can typically be less than 10% [ 24 ].…”