Myotoxicity and nephrotoxicity by Micrurus venoms in experimental envenomation.

Micrurus venoms are essentially neurotoxic but other activities, such as myotoxicity, may be apparent under experimental conditions. Although this myotoxicity has been occasionally reported, there are no studies addressing it systematically across the genus, particularly in its relationship to other systemic manifestations such as renal impairment. The lethal potency of Micrurus fulvius, Micrurus nigrocinctus, Micrurus surinamensis, Micrurus altirostris, Micrurus balyocoriphus and Micrurus pyrrhocryptus venoms determined by us were in the range described for the genus and all venoms exhibited phospholipase activity, albeit at significantly different levels. Intramuscular venom injection caused variable local inflammation-edema; myotoxicity (as determined by plasma creatine kinase levels and histopathology) was apparent only in those venoms with highest phospholipase activity, namely M. fulvius, M. nigrocinctus and M. pyrrhocryptus. Kidneys of animals injected with these strongly myotoxic venoms showed lesions consisting in extensive tubular necrosis with nuclear fragmentation, destruction of the brush border, rupture of basal membrane and epithelial exfoliation of tubular cells, granular cast and thickening of tubules. The histological characteristics of the lesions suggest an important role for indirect glomerular damage by myoglobin deposits. Phospholipase and myotoxic activities did not correlate significantly to the lethal potency; renal lesions were, however, evident only in those venoms that caused extensive muscular damage. Although kidney lesions have not been described in clinical cases of Micrurus envenomation, the potential for nephrotoxicity of some of these venoms should be considered in the overall toxicological picture, at least in experimental conditions.

Neutralization of Bothrops alternatus regional venom pools and individual venoms by antivenom: a systematic comparison.

In this study we report that variation in lethality, hemorrhagic potency and procoagulation between individual samples of Bothrops alternatus venom from a single region, and variation between regional pools at the national level are comparable in range. Furthermore, the range of relative neutralization potencies of individual venoms within a region overlaps, and sometimes exceeds, the range of neutralization of regional venom pools throughout the country. Thus, the potency of neutralization of a national venom pool is poorly predictive of the potencies of neutralization of its constituent regional venom pools and, furthermore, the potency of neutralization of a regional venom pool is poorly predictive of the potencies of neutralization of its individual venom constituents. The efficiencies of neutralization of each of these effects (lethality, hemorrhage and procoagulation) were not significantly related to each other and did not correlate to the corresponding toxic potency of each venom or venom pool. Some implications of these findings are discussed in the context of the distinction between experimental quantitation of antivenom potency and the amount of antivenom that might be actually required to successfully treat two apparently comparable B. alternatus envenomations.

Selective inhibition of inducible cyclo-oxygenase-2 expression by antisense peptide nucleic acids in intact murine macrophages.

Prostaglandins are important molecules involved in inflammation and immunomodulation. The rate-limiting step in the synthesis of these potent mediators is the expression of the enzyme cyclo-oxygenase (COX). The isoform responsible, COX-2, is encoded by an immediate-early gene induced by various pro-inflammatory agents in macrophages. Selective blockade of COX-2 by the use of an antisense strategy would overcome the undesirable side effects of conventional inhibitors. Here we describe cellular internalization and activity of a novel class of oligonucleotide analogues named peptide nucleic acids (PNAs) as inhibitors of COX-2 translation. In particular, we designed two antisense murine COX-2 PNA molecules, directed against a mRNA region spanning the AUG translation-initiation codon and a homopurinic sequence inside the COX-2 mRNA reading frame. These two PNA sequences, used separately or mixed together, demonstrated the capacity to inhibit the translation of murine COX-2 enzyme in a cell-free translation model using a rabbit retculocyte lysate model. Since PNAs display very low natural permeability across lipids bilayers, the two molecules were also re-synthesized, modified to be used in intact cells by means of linkage to a hydrophobic peptide to obtain membrane-diffusable PNA chimaerae. Finally, stimulated macrophages were found to be affected strongly by these two compounds, used separately or together, monitoring inhibition of COX-2 synthesis by Western blot analysis of total lysates and enzymic activity via radioactive assay on the microsomal fractions.