Seasonal Variation of Phenolic Constituents and Medicinal Activities of Northern Labrador Tea,Rhododendron tomentosumssp.subarcticum, an Inuit and Cree First Nations Traditional Medicine

Abstract

Northern Labrador tea, Rhododendron tomentosum ssp. subarcticum, is one of the most commonly used medicinal plants by Inuit and other First Nations peoples of Canada. The phenolic profile and seasonal variation of this commonly used medicinal plant remains largely unknown. To assess optimal harvesting time, R. tomentosum was collected in accordance with traditional knowledge practices bimonthly throughout the snow-free summer in Iqaluit, Nunavut. The antioxidant potency was measured in a DPPH radical scavenging assay, and the anti-inflammatory activity was determined with a TNF-α production assay. The seasonal variation of phenolic content was assessed with HPLC-DAD for fifteen of the most abundant phenolic compounds; (+)-catechin, chlorogenic acid, PARA-coumaric acid, quercetin 3-O-galactoside (hyperoside), quercetin 3-O-glucoside (isoquercitrin), quercetin 3-O-rhamnoside (quercitrin), quercetin pentoside, myricetin, quercetin, 3 procyanidins, and 3 caffeic acid derivatives. The most abundant constituent was (+)-catechin, which made up 19 % of the total weight of characterized phenolics. There was significant seasonal variation in the quantity of all fifteen constituents assessed, whereas there was no seasonal variation of their total sum. The antioxidant activity was positively correlated with phenolic content and negatively correlated with daylight hours. The anti-inflammatory activity was negatively correlated with caffeic acid derivative 1 and daylight hours. Together these results demonstrate that the timing of harvest of R. tomentosum impacts the plant's phenolic content and its antioxidant and anti-inflammatory activities.

Environmental trends in the variation of biologically active phenolic compounds in Labrador tea, Rhododendron groenlandicum, from northern Quebec, Canada

“…Ferrier et al (2012) showed relationships between total phenolics and glycation end-product inhibition within the Vaccinium genus, which varied with latitude. As well, McIntyre et al (2008) and Black et al (2011) reported variations in pharmacological activities associated with seasonal variations in the phenolic concentrations of plants from Ericaceae, V. angustifolium and R. tomentosum, respectively. Although biologically active constituents in R. groenlandicum were found to vary geographically, pharmacological bioassays need to be performed to properly assess the pharmacological significance of these observations.…”

“…ex Bigelow, Kalmia angustifolia L., Rhododendron tomentosum Harmaja, Vaccinium vitis-idaea L., and Vaccinium angustifolium Aiton (Harris et al 2007;McIntyre et al 2008;Saleem et al 2010;Black et al 2011;Ferrier et al 2012). These species also appear in the CEI pharmacopoeia and, like R. groenlandicum, have been screened by the CIHR Team in Antidiabetic Aboriginal Medicines and shown to possess antioxidant activity and antidiabetic potential (Spoor et al 2006;McIntyre et al 2008;Harbilas et al 2009;Black et al 2011;Ferrier et al 2012). More specifically, three of these compounds, (+)-catechin, (-)-epicatechin, and quercetin, have been found responsible for the adipogenic activity of R. groenlandicum in bioassay-guided fractionation (Ouchfoun 2011).…”

“…Seasonal variation in phenolic concentrations has been detected in other members of the Ericaceae such as V. angustifolium (McIntyre et al 2008) and R. tomentosum (Black et al 2011). Changing the sampling time to a larger window of operation, as was the case for the 2010 harvest, may result in a larger variance, thus explaining smaller R 2 values.…”

Simultaneous determination of flavonoids and triterpenoids in <i>Cyclocarya paliurus</i> leaves using high-performance liquid chromatography

“…Seasonal variations in natural compounds are fairly common and can contribute to variations of the finished products (Chou et al, 2009). Black et al (2011 reported that there were significant seasonal variations in fifteen constituents of Northern Labrador Tea (Rhododendron tomentosum ssp.…”

“…In this study, the content of isoquercitrin was 0.23 mg/g in HHF provenance, and it was much lower than the report from Fang et al (2011), likely caused by seedling ages and extraction methods. Therefore, JXS is selected to be the optimal provenance based on the quantification of seven bioactive compounds.Seasonal variations in natural compounds are fairly common and can contribute to variations of the finished products (Chou et al, 2009). Black et al (2011 reported that there were significant seasonal variations in fifteen constituents of Northern Labrador Tea (Rhododendron tomentosum ssp.…”