Intoxicação por Brachiaria spp. em ruminantes no Brasil / Brachiaria spp. poisoning of ruminants in Brazil

Brachiaria spp. são as forrageiras mais importantes para a pecuária brasileira. Entretanto, um fator limitante para sua utilização é a sua toxicidade. A maioria dos surtos de fotossensibilização hepatógena é causada por Brachiaria decumbens; porém, B. brizantha, B. humidicola e B. ruziziensis podem também causar intoxicação. A intoxicação afeta bovinos, ovinos, caprinos e bubalinos. Os ovinos são mais susceptíveis que as outras espécies, e os animais jovens são mais susceptíveis que os adultos. Existem diferenças na susceptibilidade entre animais da mesma espécie e tem sido sugerido que esta resistência é genética. Sugere-se, também, que búfalos e provavelmente alguns ovinos são resilientes (quando intoxicados apresentam lesões histológicas e aumento das concentrações séricas de GGT, mas não apresentam sinais clínicos). Em geral, a concentração de saponinas é maior nas plantas em crescimento, mas surtos ocorrem durante todo o ano, provavelmente por aumento da concentração de saponinas na planta por alguma causa ainda desconhecida. Uma síndrome clínica com progressiva perda de peso e morte, sem fotossensibilização, tem sido descrita em bovinos intoxicados por B. decumbens. As principais medidas preventivas são baseadas na seleção de animais resistentes ou resilientes e o desenvolvimento de espécies ou variedades de Brachiaria com menores concentrações de saponinas.

Brachiaria species are the most important grasses for cattle production in Brazil. However, a limiting factor for the use of Brachiaria spp. is their toxicity. Most outbreaks of hepatogenous photosensitization are caused by B. decumbens; however B. brizantha, B. humidicola and B. ruziziensis can also cause poisoning. The poisoning affects cattle, sheep, goats and buffalo. Sheep are more susceptible than other animal species and the young are more susceptible than adults. There are differences in susceptibility among animals of the same species and it has been suggested that this resistance is genetic. Also has been suggested that buffalo and probably some sheep are resilient, i.e. when poisoned these animals have histologic lesions and high GGT serum concentrations, but do not show clinical signs. In general, saponin concentrations are higher in growing plants, but outbreaks occur all over the year, probably due to unexplained rise in saponin concentration in the plant. A clinical syndrome of progressive weight loss and death, without photosensitization, has been reported in cattle poisoned by B. decumbens. Main preventive measures are based on the selection of resistant or resilient animals and on the development of Brachiaria species or varieties with low saponin concentration.

In vitro study of biosynthesis of protoporphyrin IX induced by Ù-Aminolevulinic acid in normal and cancerous cells of the human cervix

Bxkground. Ù-Aminolevulinic acid (ALA) is recognized as the starter in the biosynthesis of the heme group, the structural basis of cytochromes, chlorophylls, biliary pigments, and other porphyrins. It is the first intermediary in the biosynthesis of protoporphyrin IX (PpIX), and of ther heme group. PpIX is present in low concentration in normal cells, and in high concentration in tumor cells. Methods. The accumulation of protoporhyrin IX (PpIX) induced by Ù-aminolevulinic acid (ALA) was tested in two cervico-uterine cancer cell lines (HeLa and CaLo), and in normal human cervical epithelial (NHCE) cells. Results. The optimal concentration of ALA that induced maximum levels of intra- and extracellular accumulation of PpIX in both HeLa and NHCE cells was 300 µg of ALA/mL, and for CaLo cells, 150 µg/mL. The viability of HeLa, CaLo, and NHCE cells exposed to ALA measured 81, 98 and 84 percent, respectively. The optimale time for accumulation of PpIX, both intra- and extracellular, was 4 h for HeLa and NHCE cells and 5 h for CaLo cells per 24 h of expusure to optimal concentrations of ALA. After the maximum level of PpIX accumulation was reached, there was a gradual decrease until there was only a small quantity. A statistically significant difference (p <0.0001) was foundf in the accumulation of PpIX, depending on the concentrations of ALA used as well as between cervical cancer cell lines and 1:7, and for NHCE and CaLo cells. 1:5. Conclusions. These results are important for determining the usefulness of the sensitizer (PpIX)

The photodynamic and non-photodynamic actions of porphyrins

Porphyrias are a family of inherited diseases, each associated with a partial defect in one of the enzymes of the heme biosynthetic pathway. In six of the eight porphyrias described, the main clinical manifestation is skin photosensitivity brought about by the action of light on porphyrins, which are deposited in the upper epidermal layer of the skin. Porphyrins absorb light energy intensively in the UV region, and to a lesser extent in the long visible bands, resulting in transitions to excited electronic states. The excited porphyrin may react directly with biological structures (type I reactions) or with molecular oxygen, generating excited singlet oxygen (type II reactions). Besides this well-known photodynamic action of porphyrins, a novel light-independent effect of porphyrins has been described. Irradiation of enzymes in the presence of porphyrins mainly induces type I reactions, although type II reactions could also occur, further increasing the direct non-photodynamic effect of porphyrins on proteins and macromolecules. Conformational changes of protein structure are induced by porphyrins in the dark or under UV light, resulting in reduced enzyme activity and increased proteolytic susceptibility. The effect of porphyrins depends not only on their physico-chemical properties but also on the specific site on the protein on which they act. Porphyrin action alters the functionality of the enzymes of the heme biosynthetic pathway exacerbating the metabolic deficiencies in porphyrias. Light energy absorption by porphyrins results in the generation of oxygen reactive species, overcoming the protective cellular mechanisms and leading to molecular, cell and tissue damage, thus amplifying the porphyric picture