Chapter 7 Herbals and Natural Products
| Abbreviations | |
|---|---|
| DHEA | Dehydroepiandrosterone |
| DNA | Deoxyribonucleic acid |
| DSHEA | Dietary Supplement Health and Education Act |
| FDA | Food and Drug Administration |
| HIV | Human immunodeficiency virus |
| MAOI | Monoamine oxidase inhibitors |
| NE | Norepinephrine |
Therapeutic Overview
Since prehistoric times, humans have used plants as medicines. Of the 520 new prescription drugs approved between 1983 and 1994, 39% were natural products or were derived from plants or animals, with 60% to 80% of antimicrobials and anticancer drugs obtained from such products. Over millions of years, plants have developed the capacity to synthesize a diverse array of chemicals, which attract or repel other organisms, serve as photocollectors or protectants, and respond to environmental challenges. For example, phytochemicals can assist plants in resisting pathogens, make them unpalatable, aid in collecting light energy, protect plants from photo-oxidation, or help dissipate excess light energy as heat. With the advent of modern scientific medicine, phytochemicals have been refined, or altered, to produce a share of the modern pharmacopoeia. Despite the increasing availability of many potent and selective drugs, there remains an increasing interest in folk remedies, including herbal medicines.
acids, vitamins, minerals), often referred to a nutraceuticals, a term coined in 1989 that refers to any substance considered “a food or part of a food that provides medical or health benefits, including the prevention and/or treatment of a disease.”
The Dietary Supplement Health and Education Act (DSHEA), passed by the United States Congress in 1994, defines a dietary supplement as a product that is intended to supplement the diet and contains a vitamin, mineral, amino acid, herb, or other botanical product intended for ingestion in the form of a capsule, powder, or extract. Dietary supplement products must bear an ingredient label that includes the name and quantity of each ingredient or the total quantity of all ingredients (excluding inert ingredients) in a blend. Labeling of products containing herbal or botanical ingredients must state the part of the plant from which the ingredient is derived. Botanicals may be obtained in many formulations listed in Box 7-1.
BOX 7–1 Major Botanical Preparations
Federal regulations provide for the use of various types of statements on the label of dietary supplements, but claims cannot be made about the use of a dietary supplement to diagnose, prevent, mitigate, treat, or cure a specific disease without sufficient clinical evidence. For example, a product may not carry the claim “cures diabetes” or “treats cancer,” unless that claim is supported by clear evidence. Some health claims can be made, if the product has been so approved. For example, the claim that calcium may reduce the risk of osteoporosis has been approved by the Food and Drug Administration (FDA). Products can make claims about classical nutrient deficiency diseases, provided the statements disclose the prevalence of the disease in the United States. In addition, manufacturers may describe the effects of a supplement on “structure or function” of the body or the “well-being” achieved by consuming the dietary ingredient. To use these claims, manufacturers must have substantiation that the statements are truthful and not misleading.
Mechanisms of Action
Like any other drug or chemical, the components of herbal medicines are presumed to exert their effects on physiological or biological systems. One major difference is that botanicals contain large numbers of chemicals, which may interact synergistically or antagonistically. Some remedies consist of mixtures of several herbs, so that the number of chemicals in a single preparation can reach into the hundreds or thousands. The most commonly used botanicals are shown in Box 7-2.
Oxidation of deoxyribonucleic acid (DNA), proteins, carbohydrates, and lipids by reactive oxygen species has been implicated in normal aging and a number of different diseases, including arthritis, cancer, and Alzheimer’s disease. Oxidative stress occurs when there is an imbalance between free radical generation (by the action of reactive oxygen species) and endogenous antioxidants in cells and tissues. Reactive oxygen species are produced by some toxins, ultraviolet light, normal biochemical pathways (e.g., nitric oxide synthase), and pathological events in cells (e.g., free radicals that escaped from the mitochondrial complex). Endogenous antioxidants include reduced glutathione and the enzymes superoxide dismutase, catalase, and glutathione peroxidase. Many plants contain antioxidants (Box 7-3), including several typically used as food; some vitamins also have antioxidant activity. Although there is little clinical evidence that supplementation with dietary antioxidants ameliorates or prevents any disease, there is a wealth of scientific evidence for the free radical scavenging ability of many plant-derived antioxidants; thus interest in this mechanism of action remains strong.
Some herbals are thought to act by modulation of immune function (Box 7-4). This modulation can be indirect, via antioxidant effects, or direct, via effects on immune cells. In general, herbal remedies are thought to enhance immune function by removing toxins from the body (a common concept in herbalism).
The herbal approach to immunomodulation is holistic and focuses on boosting liver function and cleansing the blood. In the herbal philosophy, detoxification by the liver has a crucial role in health and in regulating immune function. Again, there is a dearth of clinical evidence for the efficacy of any herbal medicine in altering the course of disease, but some evidence in animal models and cell cultures suggests possible effects on immune function.
Many plants contain compounds that are used or abused for their psychoactive qualities, usually for sedative, stimulant, or analgesic purposes. These include coffee (caffeine), tobacco (nicotine), coca (cocaine), opium poppy (opiates), marijuana (cannabinoids), and peyote (mescaline). Ethnobotanical studies of shamanism in native populations have revealed many other hallucinogenic plants. A variety of herbal products are commonly used for sedative, stimulant, analgesic, and antiemetic effects (Table 7-1).
TABLE 7–1 Herbs Proposed to Act on the Central Nervous System
| Sedatives | Stimulants |
|---|---|
| Kava | Lobelia |
| Valerian | Coffee |
| Skull cap | Tea |
| Passion flower | Tobacco |
| Lavender | Ginseng |
| Antiemetics | Analgesics |
| Black horehound | Cayenne |
| Lemon balm | White willow bark |
| Cayenne | Feverfew |
| Clove | Jamaican dogwood |
| Dill | St. John’s wort |
| Lavender | Ginseng |
| Meadowsweet | Corydalis (Corydalis yanhusuo) |
| Ginger |
Some herbs contain compounds that mimic or block the actions of hormones, notably estrogen. Currently used products include highly concentrated extracts of phytochemicals, synthetic derivatives, and even steroids like dehydroepiandrosterone (DHEA) and androstenedione, which are classified as dietary supplements because they are produced from plant precursor sterols (Box 7-5).
