Piscirickettsia salmonis is the aetiological agent of piscirickettsiosis, a disease which affects a variety of teleost species and that is particularly severe in salmonid fish. Bacterial-free supernatants, obtained from cultures of three isolates of Piscirickettsia salmonis, were inoculated in Atlantic salmon, Salmo salar L., and in three continuous cell lines in an effort to determine the presence of secretion of extracellular products (ECPs) by this microorganism. Although steatosis was found in some liver samples, no mortalities or clinical signs occurred in the inoculated fish. Clear cytotoxicity was observed after inoculation in the cell lines CHSE-214 and ASK, derived from salmonid tissues, but not in MDBK, which is of mammalian origin. The degree of cytotoxicity of the ECPs was different among the P. salmonis isolates tested. The isolate that evidenced the highest cytotoxicity in its ECPs exhibited only an intermediate virulence level after challenging fish with bacterial suspensions of the three P. salmonis isolates. Almost complete inhibition of the cytotoxic activity of ECPs was seen after proteinase K treatment, indicating their peptidic nature, and a total preclusion of the cytotoxicity was shown after their incubation at 50 °C for 30 min. Results show that P. salmonis can produce ECPs and at least some of them are thermolabile exotoxins that probably play a role in the pathogenesis of piscirickettsiosis.

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In order to determine oxidative stress in equine joints with degenerative processes, we analyzed synovial fluid (SF) antioxidant capacity and the concentration of oxidative damage biomarkers in healthy and chronically damaged metacarpophalangeal joints. SF samples were collected from joints of thirty 2-5 year-old crossbreed male equine, macroscopically classified at post mortem inspection and later histologically confirmed. The antioxidant capacity was determined measuring uric acid and the concentration of sulfhydryl groups and the total radical trapping antioxidant potential (TRAP). The oxidative damage was determined by assessing malondialdehyde (MDA) and carbonyl protein concentration. TRAP was significantly higher (p < 0.05) in the group with chronic damage (CD). The sulfhydryl groups and concentration of uric acid did not show significant difference between the groups (p > 0.05). Although carbonyl concentration did not show significant difference between groups, it was slightly higher in the group with CD (p = 0.05009). Concentration of MDA did not show significant difference (p > 0.05) between groups. The observed significant increase in TRAP in the group with CD could be related to the participation of components other than protein, sulfhydryl groups, or uric acid coming from degenerating joint tissues. These findings could be helpful for a better understanding of the oxidative stress role in equine joints with chronic degenerative process.

To improve the understanding of the piscirickettsiosis pathogenesis, the in vivo apoptosis modulation of peritoneal macrophages and lymphocytes was studied in juvenile Salmo salar intraperitoneally injected with Piscirickettsia salmonis. Five fish were sampled at post-exposure days 1, 5, 8 (preclinical), 20 (clinical) and 40 (post-clinical period of the disease), and the leucocytes of their coelomic washings were analysed by flow cytometry (using the JC-1 cationic dye), TUNEL and cytology to detect apoptotic cells. A selective and temporal pattern of apoptosis modulation by P. salmonis infection was observed. Apoptosis in lymphocytes was not affected, whereas it was inhibited in macrophages but only during the preclinical stage of the induced piscirickettsiosis. Hence, it is postulated that P. salmonis inhibits macrophage apoptosis at the beginning of the disease development to survive, multiply and probably be transported inside these phagocytes; once this process is complete, macrophage apoptosis is no longer inhibited, thus facilitating the exit of the bacteria from the infected cells for continuing their life cycle.

The antioxidant mechanisms associated with the response to metacarpophalangeal joint damage in horses appeared to act on different targets, depending on whether the damage was acute or chronic.

Extracellular nucleotides interact with specific receptors on the cell surface and are locally metabolized by ecto‐nucleotidases. Biochemical characterization of the ATPase and ADPase activities detected in rat heart sarcolemma, under conditions where mitochondrial ATPase and adenylate kinase were blocked, supports our proposal that both activities correspond to a single enzyme, known as ATP‐diphosphohydrolase or apyrase. The physiological function of this enzyme could be dephosphorylation of the nucleotides present in the interstitial heart compartment acting together with 5′‐nucleotidase. Both hydrolytic activities have similarities in: sarcolemma localization, bivalent metal ion dependence, optimum pH, effect of several amino acid residue modifiers, competitive inhibition of nucleotide analogs, and broad nucleoside di‐and triphosphate specificity. The ATPase activity could not be separated from the ADPase either through isoelectrofocusing or electrophoresis under acid conditions.

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