Corneal endothelial toxicity secondary to Asclepias fruticosa

Abstract

Listen

Translate article

Sir, A single layer of endothelial cells covers the posterior surface of Descemet's membrane of the cornea. Corneal hydration and consequently transparency is primarily a function of the sodium–potassium adenosine triphosphatase (Na+/K+-ATPase) pump, expressed in the basolateral membrane of corneal endothelial cells. If this pump is impaired, corneal oedema results.1 Cardenolides, also known as cardiac glycosides, are a group of C23 steroids produced in nature by several plant families. These natural toxins protect plants and insects from predation. In humans, they have a cardiotonic activity, which is the basis for much of their pharmacological uses. A receptor for cardenolides is the integral membrane protein Na+/K+-ATPase. Cardenolides bind the enzyme region of this protein at the endothelial cell surface and inhibit the pump's activity.2 Asclepias fruticosa is a small perennial shrub about 1–1.5 m in height, containing a milky latex with cardiac glycosides and proteolytic activity (Figure 1).3 Plants of the genus Asclepias (milkweed family) are widely distributed, mainly in the tropics and subtropics, and are well known causes of death in sheep and cattle in open-range grazing.4, 5 It is common in grassland and is often planted in gardens because it attracts butterflies. Figure 1 Asclepias fruticosa (copyright permission given by Karlheinz Knoch at the Botanical Garden of Karlsruhe). There has been one previous case report describing painless blurring of vision and corneal oedema following contact with the milky latex of A. curassavica.1 Herein, we describe the self-limited effects of A. fruticosa latex components on the cornea. We also discuss the mechanism of endothelial cell toxicity and provide an update on the current literature on the regulation of the Na+/K+-ATPase activity and pump function in corneal endothelial cells.