Review of antiviral and immunomodulating properties of plants of the peruvian rainforest with a particular emphasis on una de gato and sangre de grado

Alternative Medicine Review, Dec, 2001 by James E. Williams

Abstract

Viral diseases, including emerging and chronic viruses, are an increasing worldwide health concern. As a consequence, the discovery of new antiviral agents from plants has assumed more urgency than in the past. A number of native Amazonian medicines of plant origin are known to have antimicrobial and anti-inflammatory activity, although only a few have been studied for their antiviral properties and immunomodulating effects. Those most studied include: sangre de grado (drago) (Croton lechleri) in the Euphorbiaceae family and una de gato (Uncaria tomentosa) in the Rubiaceae family. This article reviews the chemical composition, pharmacological properties, state of current research, clinical use, and potential antiviral and immunomodulating activity of these and other plants from the Peruvian Amazon. (Altern Med Rev 2001;6(6):567-579)

Introduction

Co-evolution between plants and their natural enemies -- including insects, bacteria, fungi, nematodes, animals, humans, and viruses -- is considerably more far reaching than current theories of reciprocal interactions suggest. Counter-resistance, genetic adaptability, polymorphic immune capacity, and pleomorphism among microbial agents allow for immense diversity of species and endless biochemical possibilities. (1) In order to adapt to environmental insults, plants produce a vast number of natural products that have antimicrobial and immunomodulating potential. (2) These include isoflavonoids, indoles, phytosterols, polysaccharides, sesquiterpenes, alkaloids, glucans, tannins, a variety of vitamins and trace minerals that function as antioxidants and co-enzymes, and many other phytochemical substances. In addition, there are a number of parallels between plant immunological activity and the immune systems of mammals, including adaptive mechanisms for viral resistance. (3)

Both the attribute of reciprocal natural co-evolution and the concept of shared chemistry among species are characteristics that allow humans to use plants as antiviral and immunomodulating medicines. (4) In an age of emerging new viruses with stunning virulence, natural antiviral and immunomodulating substances could play a significant role in human disease prevention and treatment.

Amazonian Ethnobotany

The Amazonian region of northwestern Peru is among the earth's richest zones of biodiversity. It includes plants, animals, insects, as well as microbial organisms, and is one of nature's perfect evolutionary laboratories for plant biology. Ethnobotany has a long and distinguished history throughout the Amazon basin and its tributaries. Richard Evans Schultes (1915-2001), a tireless supporter of Amazonian ethnobotany, (5) began his investigation in the northwestern Amazon in 1941. (6) In previous centuries much of our knowledge of Amazonian flora is credited to Alexander von Humboldt of Germany (1769-1859) and Richard Spruce of England (1849-1863), as well as to Henry Hurd Rusby of Columbia University (1885-1928). Contemporary authorities on Amazonian ethnobotany include James Duke (7) and Mark Plotkin. (8)

Natural Product Selection

There are two ways natural products are selected for investigation. The classical method is laboratory based and relies on previous taxonomic findings, phytochemical factors, immunopharmacological studies, and random screening methods. The other, which is gaining popularity among investigators, is searching traditional texts and herbal medicine usage, including oral interviews with traditional indigenous healers -- the ethnobotanical route. (9,10) In one study, researchers found that an ethnobotanically driven approach led to a higher percentage of active compounds isolated than the standard high volume random screening method, reporting a 125-630 times more effective yield depending on the type of virus, (11) In another screening, 207 plants were tested for antiviral activity with 64 percent showing in vitro activity, 42 percent with strong activity. (12)

Antiviral Activity of Peruvian Plants

Largely due to the AIDS epidemic, an imperative for developing effective antivirals has generated considerable activity in antiviral screening during the last two decades. However, the search for antiviral compounds has not been easy. Relatively few antiviral drugs are available, and those approved for use often have high side-effect profiles and exhibit the potential to cause rapid resistance among targeted viral strains. According to Colegate, an antiviral must meet three criteria: (1) it must inhibit the virus completely without affecting the host cells, (2) it must have a broad range of activity, and (3) it must not be immunosuppressive (Table 1). (13)

A number of plant substances have been found to meet the basic criteria, and screenings have been performed on several thousand plant extracts and other natural products. However, considering the overwhelming volume of medicinal plants in the upper Amazon and the near epidemic prevalence of hepatitis B, (14) as well as the high incidence of hepatitis A, D, C, E, (15) and G, (16) and other viruses like dengue strains in Peru, surprisingly few herbs from this region are listed in the literature as having traditional uses for viral diseases.