book reviews

Miscellaneous toxin books
Reviewed by: T.J. Nelson

Natural toxicants in food
D.H. Watson, ed

U neven collection of reviews of toxic molecules associated in one way or another with food. Discusses secondary metabolite toxins such as pyrrolizidine alkaloids, glucosinolates, and natural estrogenic compounds, and food-contaminating toxins such as botulinum toxin, mycotoxins, and phycotoxins. The chapters on mycotoxins and seafood phycotoxins are well-written reviews, oriented toward the chemistry and toxicology of the toxins, while the chapters on nut allergens and botulinum toxin are oriented toward environmental health issues, and discuss the prevalence and epidemiology of the toxin in various foods, without discussing their chemistry. The chapter on botulinum and S. aureus toxins is particularly weak, considering the tremendous volume of biochemical information known about the various bacterial toxins. The last third of the book is oriented toward food quality control specialists and contains little information of scientific interest to biochemists.

Unfortunately, there are few books that discuss endogenous toxins in food, and almost none that discuss marine biotoxins. This book makes little attempt at comprehensiveness or consistency, and completely ignores the vast literature on important classes of food toxins such as solanine, oxalate, selenium, saponins, hemagglutinins or protease and amylase inhibitors, antinutrients such as polyphenols (including tannins and tannic acid derivatives), lectins, or phytate, barely touches on cyanogenic compounds or genetically-modified foods, and barely scratches the surface of the vast literature on toxic alkaloids. With a little effort (well, okay, a lot of effort), the editor could have created a unique, valuable, and much-needed authoritative work on this important subject. The book would have benefited from better proofreading. Also, like most books from CRC Press, this book is vastly overpriced.

The Comprehensive Sourcebook of Bacterial Protein Toxins, 2nd ed
J.E. Alouf and J.H. Freer
Academic Press, 1999, 718 pp

A familiarity with the biochemistry of bacterial toxins is essential for understanding the pathophysiology of bacterial diseases, which still affect millions of people annually. The recent outbreaks of E. coli food poisoning in hamburgers in America and the discovery that Iraq has stockpiled large amounts of Bacillus anthracis have also served to bring the ancient problem of pathogenic bacteria to public attention.

This book is a collection of review articles by various authors on bacterial toxins, divided into three sections: toxins acting on cytosolic targets, membrane-damaging toxins, and other toxins of clinical, pharmacological, immunological, and therapeutic interest.

The first section discusses toxins such as ADP-ribosylating toxins, diphtheria toxins, clostridial toxins (such as the various zinc endopeptidase-containing Botulinum toxins), Shiga toxins, and anthrax toxin. Most of these proteins have been extensively studied and many have been crystallized, so the information is quite detailed on the molecular level.

The second section focuses on cytolytic toxins such as Vibrio cholerae toxins, staphylococcal leucocidins, and RTX toxins, while the last section covers other, miscellaneous topics.

Because toxins have evolved exquisitely precise mechanisms over millions of years for targeting specific proteins in specific types of cells of a particular species, they have found use as powerful tools for research and as potential therapeutic agents. For example, diphtheria toxin is cytotoxic at concentrations as low as 10-13 M. The chapter "Diphtheria toxin-based interleukin-2 fusion proteins" discusses the use of mutagenized diphtheria toxins for cancer treatment and describes attempts to target diphtheria toxin to cancer cells. Streptolysin O, a cholesterol-binding toxin from Streptococcus pyogenes, has found widespread use for permeabilization of cultured cells, to allow the introduction of exogenous proteins for experimentation. However, only a few of the chapters discuss potential uses of these molecules.

Even so, most of the articles are exceptionally well written, for example, the chapter "Structural and genomic features of clostridial neurotoxins", which compares the molecular biology of tetanus and botulinum toxins. The pathophysiological properties of these toxins are discussed in the subsequent chapter. A few chapters are slightly less well organized, although still interesting, but contain sentences like:

This model leaves unexplained two main experimental findings: (a) the membrane-inserted A chain is in contact with the fatty acid chains of phospholipids, i.e. it is not shielded from lipids inside the B protomer tunnel; (b) although there is no direct relationship between channel size and conductance, values of the order of units - tens of picosiemens - do not fit with the dimensions expected for a protein channel chain with its lateral groups.

Maybe it was just getting late, but I had to read that particular sentence several times. Better editing could have improved passages like this. There is also considerable overlap and repetition among the chapters due to lack of coordination among contributors. For example, the various S. aureus toxins are described numerous times in different articles, in varying levels of detail. This is perhaps understandable in a "sourcebook", but it can make for tiring reading. For such a mature field as this, it would have better to write a comprehensive textbook.

Some of the explanatory diagrams are also a bit cryptic. On the other hand, I did not find a single typographical error.

The book strictly adheres to the topic of bacterial toxins. Toxic shock toxins, Helicobacter pylori toxins (which cause stomach ulcers), anthrax, Shiga toxins (which were originally found in Shigella dysenteriae and later discovered in E. coli), and RTX and other classes of hemolytic toxins, are thoroughly discussed. Plant toxins, such as ricin (which bears a remarkable resemblance to Shiga toxins), and Legionella, are discussed only in passing. Snake toxins, cyanobacteria, toxin-producing algae such as Pfiesteria piscicida, and viruses, are not discussed at all.

Altogether, this book is an excellent summary of bacterial toxins.