“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 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 hunters. While 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
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).
References:
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.