Induction of vascularisation by an aqueous extract of the flowers of Calendula officinalis L. the European marigold.

Calendula officinalis L. (calendula) is a plant whose recorded history is indicative of intrinsic wound healing capabilities. The wound healing process involves several distinct phases in which the formation of new blood vessels plays an essential role. This report describes the angiogenic activity of a freeze-dried aqueous extract of the flowers of Calendula officinalis L. (the European marigold) utilizing the chick chorioallantoic membrane (CAM) assay. The CAM assay is a standard and well established method for assessing the angiogenic activity in impure and pure preparations and is suitable for studies requiring examination of large numbers of sample test materials. The angiogenic activity of calendula was measured by examination of CAMs using stereomicroscopy. Further histological investigation and quantification of neovascularization was performed utilizing microvascular counts. The histological sections of CAMs were also examined for the presence of hyaluronan (HA), a tissue glycosaminoglycan associated with neovascularization, by hyaluronidase digestion and staining of tissue sections by alcian blue. All calendula treated CAMs were positive for HA; no HA could be demonstrated in control CAMs. The numbers of microvessels in calendula-treated CAMs were statistically significantly higher than in the control CAMs (p < 0.0001). Thin layer chromatography indicated that the calendula extract contained water-soluble compounds such as flavonoids, but the exact nature of the active angiogenic component(s) has not yet been identified.