The Frog Vaccine

“The frog vaccine” (Phyllomedusa bicolor

The anuran skin displays great morphofunctional diversity adapted to a number of adverse factors present in the species habitat environment. (CALDERON, 2010). The skin of the neotropical and South American frogs contains large amounts of a wide range of biologically active peptides that are either identical or highly homologous to hormones or neurotransmitters of the nervous system and diffuse endocrine system of the higher vertebrates (LACOMBE et al, 2000).

Ultrastructural characterization of the Phyllomedusa species skin demonstrated that the profile of skin glands are composed by lipid, mucous, and serous glands that lie deep in the skin and subcutaneous connective tissue (LACOMBE et al. 2000; CALDERON et al., 2010). These glands produce a wide variety of noxious or toxic substances with various pharmacological effects on microorganisms, vertebrate, and invertebrate species (LACOMBE et al. 2000).

Some indigenous people in southwestern Amazonia use these secretions from P. bicolor for medicinal purposes. Indians of the language “Pano” on the border between Brazil and Peru are the ones who originally used this vaccine. In Acre, the Katukina Indians call these frogs of "Kampo" or "Kambô" and apply its secretions to remove the "panema" (a kind of weakness or bad luck), giving more force to huntersWhile Indians use the "frog vaccine" to ward off "panema" and various ailments, making a ritual with spiritual meaning, non-Indian users tried this treatment for some specific problems (gastritis, rheumatism, diabetes, allergies, etc.) and curiosity (BERNARDE; SANTOS, 2009; DALY, 1992).

The method of application of the secretion of Phyllomedusa bicolor in humans is known as "frog vaccine", "frog injection" or "Kambô" (BERNARDE; SANTOS, 2009).
The skin secretion is mixed with saliva and introduced into a line of fresh burns on the arms or chest. This induces within minutes violent illness, including rapid pulse, incontinence and vomiting, after which the recipient lapses into a state of listlessness and, finally, into a state perhaps to be described as euphoric; he later claims to be a better hunter, with improved stamina and keener senses (BERNARDE; SANTOS, 2009; DALY, 1992).

The intensity of human reactions to frog secretion is doubtless dose-dependent. The period of intense illness (<1 hr) is followed by a state of listlessness and sleep lasting from one to several days (DALY, 1992).

"frog vaccine"

Phyllomedusa skin peptides

Phyllomedusa skin peptides include: dermaseptin, dermatoxin, distinctin, phylloseptin, phylloxin, plasticin and skin polypeptide YY.
These peptides are synthesized as prepropeptides that are processed into mature peptides after removal of the peptide signal and the acidic propiece. These are then stored in the granules (CALDERON et al., 2010).

The Phyllomedusa skin peptides are grouped in to three main groups according to their ‘‘primary’’ activity: antimicrobial peptides (AMPs); smooth muscle active peptides; and nervous system active peptides. The first group acts as a skin anti-infective passive defense barrier, the second and the third groups cause the disruption of the predator homeostasis balance (CALDERON et al., 2010). Also, skin extracts from this species have been previously studied and are known to contain a variety of vasoactive peptides, including high levels of phyllocaerulein, phyllokinin, and phyllomedusin and moderate levels of sauvagine. (DALY, 1992).

The biological significance of such a complex mixture of antibiotic peptides with different specificity and potency in Phyllomedusa skin is possibly related to a greater protection against a wide range of potential invaders at a minimum metabolic cost, e.g., dermaseptins exhibit synergy of action upon combination with other antibiotic molecules or AMPs, resulting in a 100-fold increase in antibiotic activity (CALDERON et al., 2010).

The ensuing effects depend on the antimicrobial peptide and the severity of the damage, and usually include dissipation of ionic gradients across the PM, leakage of nutrients and/or larger cytoplasmic components, and finally, a collapse of the parasite bioenergetics and osmotic lysis (CALDERON et al., 2010). This killing mechanism acts promptly by destroying their PM, promoting the reduction of log orders of pathogens in a few minutes. This mechanism is unlikely to induce antibiotic-resistance in microorganisms due to a great metabolic change in the PM composition. Two elements seem to be relevant to the antimicrobial action: the selectiveness, and the ability to destabilize PMs (CALDERON et al., 2010). 

Therapeutic peptide antibiotics

Many efforts have been carried out in order to use the AMPs in the development of new infection-fighting drugs applicable to new treatments of nosocomial infections and multidrug-resistant infections, due to the skill of the AMPs to kill drug resistant strains by a mechanism unlikely to induce antibiotic-resistance. The sources from the biodiversity, such as the skin of several frogs’ species, e.g., as Phyllomedusa and other vertebrate and invertebrate animals, plants, and microorganisms, have proved to be an inexorable source of antimicrobial molecules, with a broad spectra of activity, in which the AMPs have highlights in their potential therapeutical application. In order to develop new peptide antibiotics, synthetic changed peptides might offer significant advantages over native AMPs as therapeutical agents. Compared with conventional antibiotics, these bacteria-killing peptides are extremely rapid and attack multiple bacterial cellular targets.

Even with the expected advantages in the use of AMPs as antibiotics, several impediments to therapeutic peptides arise. The main problems at the present moment are the cost of manufacturing peptides, which is economically unfeasible for the amounts of AMPs needed compared to other antibiotics, preventing the widespread clinical use of AMPs as a common antibiotic, and the shortage of studies thoroughly examining systemic peptide  pharmacodynamic and pharmacokinetic issues, including peptide aggregation problems, the in vivo halflife of peptides (and particularly their susceptibility to mammalian proteases), and the required dosing frequency. Due to the specific characteristics of the AMPs, that differentiate them from other antibiotics, the development of new strategies for the therapeutic use of AMPs in medicine are necessary in order to reduce the amount of AMPs necessary to promote the therapeutic infection suppression effect, including the addition of striking affinity to specific targets, efficiency at very low concentrations and negligible toxicity. In this way, nanotechnology has become an efficient and viable alternative to promote the therapeutic application of AMPs. It is expected that in the forthcoming years nanotechnology will promote the emergence of new products for control and prevention of multidrug-resistance microbe infection arising from the identification and analysis of AMPs from South American frog biodiversity (CALDERON et al., 2010).

Bernarde, P. S.; Santos, R. A. (September-2009) Medicinal use of secretions (“the frog vaccine”) from the kambô frog (Phyllomedusa bicolor) by non-indigenous peoples in Rondônia, Brazil. Biotemas, 22 (3): 213-220.

Calderon L. A. et al. (2010) Antimicrobial peptides from Phyllomedusa frogs: from biomolecular diversity to potential nanotechnologic medical applications. Springer-Verlag, 3, 120-141.

Daly, J. W. (November 1992) Frog secretions and hunting magic in the upper Amazon: Identification of a peptide that interacts with an adenosine receptor. Proc. Nati. Acad. Sci. USA Vol. 89, pp. 10960-10963.

Lacombe, C. et al. (September-2000) Peptide secretion on the cutaneous glands of south American tree frog Phyllomedusa bicolor: an ultrastructural study. European Journal of Cell Biology, 79, 631-641.