Microscopic Sleuthing

In 1775, British botanist and physician William Withering (1741-1799; Figure 1.12) was asked his opinion of a family herbal recipe for dropsy (edema), consisting of approximately 20 botanicals, used by a Shropshire herbalist, Mrs. Hutton. Presumably, Mrs. Hutton's secret formula was succeeding, whereas treatment by conventional physicians was failing (Withering 1785). Withering laboriously separated the leaf fragments of the prescription and identified fragments of Digitalis leaves through microscopic examination (Leake 1975). More than 200 years earlier, the famed German botanist-physician Leonhart Fuchs (1542) reported on the use of Digitalis for "the scattering of dropsy." Withering was familiar with the work of Fuchs and quickly surmised Digitalis to be the putative active ingredient, which subsequently led to the isolation and introduction of digitalis glycosides into modern medicine (Lee 2005) (Figure 1.13).

FIGURE 1.12 William Withering (1741-1799) was a British botanist and physician who, in 1775, through laborious microscopic examination, identified the leaves of the purple foxglove (Digitalis purpurea) as the putative active ingredient in a prescription of a Shropshire herbalist, Mrs. Hutton, for dropsy (edema). (Illustration by William Bond, after a painting by Carl Fredrik van Breda, London.)

FIGURE 1.12 William Withering (1741-1799) was a British botanist and physician who, in 1775, through laborious microscopic examination, identified the leaves of the purple foxglove (Digitalis purpurea) as the putative active ingredient in a prescription of a Shropshire herbalist, Mrs. Hutton, for dropsy (edema). (Illustration by William Bond, after a painting by Carl Fredrik van Breda, London.)

In 1997, history more or less repeated itself. Two American consumers used a 14-ingredient herbal "internal cleansing" product and, upon consuming it, experienced persistent nausea and irregular heartbeat requiring emergency medical care. The symptoms were consistent with cardiac glycoside intoxication (Slifman et al. 1998). Serum analysis revealed blood levels of digitalis glycosides, suggesting consumption of something that contained Mrs. Hutton's Digitalis. Chemical analysis of the product using a color reaction (Kedde reaction) and thin-layer chromatography (TLC) confirmed the presence of digitalis glycosides and demonstrated that the product had been contaminated.

Analysis of the raw material further confirmed the contamination. Microscopic analysis of the product (14 finely powdered botanical ingredients) was not useful in identifying which of the ingredients was the contaminant. However, microscopic analysis of the individual unpow-dered ingredients obtained from retention samples of the supplier indicated the presence of specific structural elements (glandular trichomes) characteristic of Grecian foxglove (Digitalis lanata) (Figure 1.14).

Thus, with microscopic analysis, the researchers were able to clearly distinguish that, what should have been plantain (Plantago lanceolata), which does not contain digitalis glycosides, was in fact Digitalis. Both Digitalis lanata and plantain have long, lanceolate, similarly colored leaves, which makes misidentification possible. Thus, botanical microscopy was instrumental in determining the adulterating plant's true identity and allowing investigators at the U.S. Food and Drug Administration (FDA) to identify distributors who had received the adulterated material, leading to a recall of specific products. Had microscopy been used as a quality assurance tool by the supplier of the ingredient at the beginning of the supply chain, this episode might have been avoided. This case provides a good example of a classical pharmacognostic investigation that

Digitalis Adulteration

FIGURE 1.13 Purple foxglove (Digitalis purpurea). The original source for Digitalis-related cardiac glycosides that have been in continued use in modern medicine for more than 230 years. (From Curtis's Flora Londinensis originally inserted in Withering's An Account of the Foxglove. Illustration courtesy of Hunt Institute for Botanical Documentation, Carnegie Mellon University, Pittsburgh, PA.)

FIGURE 1.13 Purple foxglove (Digitalis purpurea). The original source for Digitalis-related cardiac glycosides that have been in continued use in modern medicine for more than 230 years. (From Curtis's Flora Londinensis originally inserted in Withering's An Account of the Foxglove. Illustration courtesy of Hunt Institute for Botanical Documentation, Carnegie Mellon University, Pittsburgh, PA.)

utilized the botanical skills of pharmacognosy—specifi-cally, botanical microscopy.

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