Edible Members of the Solanum Genus Outline

Introduction to Toxicology

EV 460/660 & BI 460/660

Fall 2014

Presentation by Philip Eaton

I. Introduction

A. The Nightshade family (Solanaceae)

1. Infamous for their toxicity from glycoalkaloids and other assorted compounds such as nicotine.

2. Not all nightshades form glycoalkaloids, such as tobacco.

3. These compounds are for defense of the plant as glycoalkaloids are effective as anti-fungal agents and nicotine is an insecticide

II. Staple Nightshade Crops

A. Potatoes

1. Toxins involved

i. Solanine

ii. Chaconine

iii. Nicotine

2. Plant morphology

i. Plant and berries (if present) are green in color with smooth-edged leaves shaped like spades.

ii. Vine-like growth

iii. Below ground is a root system with connected tubers for nutrient sequestering

3. Location of toxins

i. Greenery and berries always contain glycoalkaloids and are avoided as foodstuffs.

ii. tubers are edible provided they have not started growing “eyes”

iii. Amount of toxin production in tubers can vary greatly depending on the type of potato in question.

iv. Sunlight and damage accelerates the rate at which potatoes begin producing glycoalkaloids

B. Tomatoes

1. Toxins involved

i. Solanine

ii. Tomatine

iii. Nicotine

2. Plant morphology

i. Plant is green with leaflets on the edges of the leaves

ii. Vine growth pattern

iii. Berries are green, but turn red as they grow and ripen

3. Location of toxins

i. Greenery contains toxins permanently while fruit loses toxins as it ripens

C. Eggplants

1. Toxins involved

i. Solanine

ii. Nicotine

2. Plant morphology

i. Green plant with ruffled edges on leaves that can sometimes form into leaflets

ii. Typically shrub-like growth

iii. Berries start out white (usually) and egg shaped, and ripen typically into a deep purple or sometimes yellow

iv. They also will elongate during growth.

3. Location of toxins

i. Mainly sequestered in the vegetative material, but some is found in the fruit in very low levels

D. Others

1. There are other Solanum plants used as crops, but they are not as ubiquitous as the three listed above

III. Toxins

A. Glycoalkaloids: Steroid-like alkaloids bonded to sugars, created from cholesterols

1. Solanine and Chaconine: Found in most nightshades (potatoes specifically in the case of chaconine) and can break down into solanidine over time or by bioactivation after ingestion

2. Tomatine: Glycoalkaloid specific to tomatoes, can break down into tomatidine

B. Nicotine: Alkaloid found in several members of the nightshade family in minute amounts

IV. Effects on Organisms

A. Humans: Glycoalkaloids have a bitter taste that is often encountered in aged potatoes or in the attempt to eat the vegetable matter from nightshade plants

1. Bioactivation, Solanine/chaconine to solanidine: The sugar of these chemicals may be processed off of them leaving solinidine (the alkaloid)

2. Nicotine: Present, but in such low amounts in the food products that it would take in inordinate amount of the fruits/tubers to amount to a tangible toxic effect.

3. Acetylcholinesterase inhibition: Glycoalkaloids have an effect on Acetylcholinesterase leading to a syndrome typically known as SLUDGE, referring to its symptoms of salivation, lacrimation, urination, defecation, gastrointestinal upset and emesis

i. This effect is typical of organophosphate poisoning due to inhibition, but it also crops up for glycoalkaloids

4. Glycoalkaloids and their byproducts are hydrophobic, and capable of mixing with the cell membrane of cells

i. This action tends to disrupt the stability of the cell and can cause lysis at higher concentrations

5. Several of these effects can be mitigated by processing the various food products

i. Toxin levels in potatoes are reduced drastically simply by peeling and cooking them

V. Use of chemicals by humans

A. Fungicide

1. Solanum plants produce glycoalkaloids as natural deterrents to fungal growth

i. Testing has been done on extraction of these compounds (specifically tomatine) for use in fighting fungal growth in other crops

ii. This work has shown to be effective at removing some types of fungus entirely, and at least mitigating other types

B. Pesticide

1. The chemicals are not as widely used as pesticides as they once were, however, as these plants produce them naturally, they still remain useful as the plants natural deterrent, and thus, help the overall crop thrive

C. Clinical uses

1. Cancer

i. Tomatine has been found to have an inhibitive effect on pathways necessary for metastasis of breast cancer

a. If used on a patient with breast cancer, this could stall the progression of the cancer until treatment could be completed

ii. Solanine was tested on pancreatic cancer cells to see if it could induce apoptosis

a. The test was quite successful, as the rate of apoptosis had a very strong correlation with solanine dose

2. Nicotine has been correlated with a decrease in probability to contract mental degenerative disorders when taken in small amounts

Study Questions

1. What is the main group of secondary metabolites produced by the nightshade family for defense against herbivores?

2. What are the two main pathways in which glycoalkaloids create a toxic effect?

3. What are the symptoms caused by acetylcholinesterase inhibition by glycoalkaloids?

4. What organisms do the secondary metabolites of the nightshade family protect against most effectively?

5. What factors accelerate glycoalkaloid creation in potatoes?