Alkaloids are also found in the animal kingdom, especially in millipedes, salamanders, toads, frogs, fish and mammals. They occur particularly in the genera Saxidomus, Salamandra, Phyllobates, Dendrobates, Castor and Moschus. Moreover, alkaloid molecules are found in such genera as Solenopsis, Odon-tomachus, Glomeris and Polyzonium. Many alkaloids have been recently isolated from marine environment, especially from the sponges197. The discovery of ptilomycalin A from the sponges Ptilocaulis spiculifer and Hemimycale spp. preceded the isolation of several analogues from other sponges such as Crambe crambe, Monanchora arbuscula, Monanchora ungiculata as well as from the some starfishes such as Fromia monilis and Celerina heffernani. From the Caribbean sponge Monanchora unguifera the guanidine alkaloids (batzelladine J, ptilomycalin A, ptilocaulin and isoptilocaulin) have been recently isolated197. Many of guanidine alkaloids display ichthyotoxicity, and antibacterial, antifun-gal and antiviral activity. Antiviral activity has been exhibited against Herpes Simplex virus (HSV-1) and also in inhibiting the HIV virus and cytotoxicity against murine leukemia cell lines (L1210) and human colon carcinoma cells (HCT-16). Segraves and Crews198 reported on the isolation of six new brominated tryptophan derived alkaloids from two Thorectidae sponges: Thorectandra and Smenospongia. These alkaloids have also the wide ranging of biological activities and they are attractive compounds for potential applications.
Alkaloids occur in amphibians. These vertebrate animals are reliant on water for their reproduction. Some species live both in and out of water and others are exclusively aquatic species. There are three orders of amphibians: the Anura (syn. Salientia) with more than 4500 species of frogs and toads, the Urodela (syn. Caudata) with 450 species of newts and salamanders, and the Apoda (syn. Gymnophiona) with more than 160 species of worm-like organisms. The skin of amphibians contains alkaloids. Costa et al.199 have reported on bufetenin from Anura species. This tryptamine alkaloid is widely spread as a component of chemical defence system in these species. Bufetenin acts as a potent hallucinogenic factor showing similar activity to LSD upon interaction with the 5HT2 human receptor199. This compound has been isolated from the skin of three arboreal amphibian species, Osteocephalus taurinus, Osteocephalus oophagus and Osteocephalus langsdorfii, from the Amazon and the Atlantic rain forests.
Moreover, it is known that toads belonging to the genus Melanophryniscus contain toxic alkaloids in their skin200. From Melanophryniscus montevidensis, alkaloids of the pumiliotoxin (PTX) group and indolizidines were isolated.
The lady bird (Coccinellidae) and other beetles also contain alkaloids. Examples are mentioned in Table 10. Conversely, some moths, such as the arctiid moth (Utethesia ornatrix), are dependent on alkaloids for defence. Utethesia ornatix, for example, sequesters pyrrolizidine alkaloids as a larva from the food plants of Crotalaria, belonging to the Fabaceae family201. Longitarsus lateripunc-tatus (Coleoptera, Chrysomelidae, Alticidae), a leaf beetle feeding on Pulmonaria abscura leaves, contained readily traceable quantities of pyrrolizidine alkaloids117 202. On the other hand, it is now known that some poisonous frogs (Mantella) digest alkaloids in their food. The ants Anochetum grandidieri and Tetramorium electrum, containing pyrrolizidine alkaloids, have been found in the stomachs of Mantella frogs203. The strawberry poison frog (Dendrobates pumilio) contains dendrobatid alkaloids that are considered to be sequestered through the consumption of alkaloid-containing anthropods distributed in the habitat204. Some pyrroloindole alkaloids, such as pseudophrynaminol, were found in the Australian frog (Pseudophryne coriacea)205. However, it is known that a diverse array of over 800 biologically active alkaloids have been discovered in amphibian skin206. With the exception of the samandarines and pseudophry-namines, all alkaloids appear to be derived from dietary sources. It has been discovered that the beetles are sources for batrachotoxins and coccinelline-like tricyclics and ants and mites for pumiliotoxins. Moreover, ants are sources for decahydroquinolines, izidines, pyrrolidines and piperidines. They are likely sources for histrionicotoxins, lehmizidines and tricyclic gephyrotoxins206.
From North Sea Bryozoan (Flustra foliacea) several, brominated indole alkaloids have been isolated207 208. These include deformylflustramine and flus-tramine. Deformylfrustrabromine A and deformylfrustrabromine B have been shown to have affinities in the lower micromolar range with the neuronal nico-tinic acetylcholine receptor (nAChR). As early as 1973, it was reported151 that erythrinan alkaloids (^-erythroidine and dihydro-^-erythroidine) with neuro-muscular transition blocking activity resembling the effects of curare had been found in the milk of goats (Capra) which grazed the leaves of Erythrinia poeppigiana152. The spectrum of alkaloids in mammals209 ranges from isoquino-line derivatives, via ^-carbolines, through to thiazolidines, arising from vitamin B6, chloral and glyoxylic acid. For a long time, tetrahydroisoquinoline alkaloids were considered to be exclusively of plant origin. Bringmann et al.209 suspected that the formation of such endogenous alkaloids occur naturally in man and mammals. The spontaneous formation of mammalian alkaloids, their further metabolic fate and their biological and medicinal roles are a key not only to a better understanding of metabolic diseases, but also to novel therapeutic concepts. In the case of animal species, it is necessary to check whether alkaloid molecules detected are endogenous or derived from exochemicals of dietary origin. One example of this problem which could be mentioned occurs in the important alkaloid as morphine. The biosynthesis of this alkaloid by plants from the Poppy family (Papaveraceae) is practically resolved, and there are not many research problems. However, the opposite situation occurs in the case of animals. It was reported, and biochemical data was presented to prove, that this alkaloid can occur in animals and humans, in considerable quantities. The only question remaining concerns the origin of this alkaloid in the animal and human body: Is it endogenous? If yes, moreover, the evidence of existing enzymes needed for the biosynthesis of the alkaloid in animals should be presented and biosynthetical activity should be documented. Only after that can the occurrence of alkaloids in the animal species be accepted finally as an endogenous characteristic can without any conditions. On the other hand, there is evidence that animal and human bodies can produce endogenous alkaloids210. Mammalian alkaloids derive from L-tryptophan via biogenic amines such as dopamine, tryptamine and sorotonine. Small amounts of alkaloids are normal in mammals. When disease strikes, alkaloid levels rise steeply. The common mammalian alkaloids are harman, norharman, tetrahydroharman, harmalan, 6-metoxyharman, salsolinol, norlaudanosoline (THP), dideoxynorlaudanosoline 1-carboxylic acid and spinaceamines. Newly detected alkaloids are L-histamine derivatives210 211. Although it is generally accepted or strongly suggested that alkaloids occur in animal species, even as a common matter209'210'211, the genetic origin of these compounds as purely animal is still under discussion. Many research groups are working on this problem. Certainly, alkaloid chemical and biological research is both very challenging and prospectively fascinating. Alkaloids in nature are a part of production and consumer (feeding) chains. Moreover, they contribute to species growth, pleasure and pathology. They are key to the processes of agressivity and defence by the species. Alkaloids are used in nature for many purposes, and by many species. Homo sapiens is just one of them.
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