Porcine reproductive and respiratory syndrome virus: origin hypothesis

Porcine reproductive and respiratory syndrome is a serious swine disease that appeared suddenly in the midwestern United States and central Europe approximately 14 years ago; the disease has now spread worldwide. In North America and Europe, the syndrome is caused by two genotypes of porcine reproductive and respiratory syndrome virus (PRRSV), an arterivirus whose genomes diverge by approximately 40%. My hypothesis, which explains the origin and evolution of the two distinct PRRSV genotypes, is that a mutant of a closely related arterivirus of mice (lactate dehydrogenase-elevating virus) infected wild boars in central Europe. These wild boars functioned as intermediate hosts and spread the virus to North Carolina in imported, infected European wild boars in 1912; the virus then evolved independently on the two continents in the prevalent wild hog populations for approximately 70 years until independently entering the domestic pig population.     

Effects of rhein on human articular chondrocytes in alginate beads

This study was designed to investigate the effects of rhein, the active metabolite of diacerhein, on the metabolic functions of human chondrocytes cultured in alginate beads.Enzymatically isolated osteoarthritic (OA) chondrocytes were cultured in alginate beads in a well-defined culture medium for 12 days. Rhein was tested in a range of concentrations comprised between 10(-7) and 4 x 10(-5)M, in the presence or absence of 10(-10)M IL-1beta. Interleukin (IL)-6 and -8, macrophage inflammatory protein (MIP-1beta), stromelysin-1 (MMP-3), aggrecan (AGG), tissue inhibitor of metalloproteinases-1 (TIMP-1), prostaglandin E(2) (PGE(2)) and nitric oxide (NO) productions were assayed. Cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS) mRNA steady-state levels were also quantified. In the basal condition, 10(-5)M rhein increased by 46.5% the production of AGG, decreased by 17-30% the production of IL-6, MMP-3, NO and MIP-1beta but enhanced by 50% the production of PGE(2). IL-1beta increased IL-6, IL-8, MIP-1beta, NO, PGE(2) and MMP-3 productions, but inhibited AGG and TIMP-1 synthesis. Rhein partially reversed the effect of IL-1beta on TIMP-1 and NO production, had no effect on AGG, IL-6 and MIP-1beta production, but up-regulated the IL-1beta stimulated PGE(2) production. The COX-2 and iNOS mRNA levels and IL-8 production were not modified by rhein.Overall, these results contribute to explain the clinical efficiency of rhein and give new information on its mechanisms of action.     

Antioxidant and pro-oxidant properties of pyrroloquinoline quinone (PQQ): implications for its function in biological systems

Pyrroloquinoline quinone (PQQ) is a novel redox cofactor recently found in human milk. It has been reported to function as an essential nutrient, antioxidant and redox modulator in cell culture experiments and in animal models of human diseases. As mitochondria are particularly susceptible to oxidative damage we studied the antioxidant properties of PQQ in isolated rat liver mitochondria. PQQ was an effective antioxidant protecting mitochondria against oxidative stress-induced lipid peroxidation, protein carbonyl formation and inactivation of the mitochondrial respiratory chain. In contrast, PQQ caused extensive cell death to cells in culture. This surprising effect was inhibited by catalase, and was shown to be due to the generation of hydrogen peroxide during the autoxidation of PQQ in culture medium. We conclude that the reactivities of PQQ are dependent on its environment and that it can act as an antioxidant or a pro-oxidant in different biological systems.     

Enhancement of proteolytic processing of the beta-amyloid precursor protein by hyperforin

We studied the effect of hyperforin, a component of St. John's wort (Hypericum perforatum) extracts, on the processing of the amyloid precursor protein (APP) in rat pheochromocytoma PC12 cells, stably transfected with human wildtype APP. We observed transiently increased release of secretory APP fragments upon hyperforin treatment. Unique features, like a strong reduction of intracellular APP and the time course of soluble APP release, distinguished the effects of hyperforin from those of alkalizing agents and phorbol esters, well known activators of secretory processing of APP. Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), a protonophore, induced an almost identical decrease in intracellular pH in PC12 cells as does hyperforin. Despite this, FCCP induced a less pronounced release of soluble APP fragments and only slightly reduced intracellular APP levels. These results suggest that hyperforin is an activator of secretory processing of APP with a novel mechanism of action not solely dependent on its effects on intracellular pH.     

No difference in net uptake or disposal of lactate by trained and untrained forearms during incremental sodium lactate infusion

A number of training adaptations in skeletal muscle might be expected to enhance lactate extraction during hyperlactataemia. The aim of the present study was to determine whether resting endurance-trained forearms exhibit an increased net lactate removal during hyperlactataemia. Six racquet-sport players attended the laboratory for two experiments, separated by 2 weeks. In the first experiment incremental handgrip exercise to fatigue was performed to identify trained (TRFA, n=6) and untrained (UTFA, n=5) forearms. In the second experiment net forearm lactate exchange was compared between TRFA and UTFA during an incremental infusion of sodium lactate. TRFA performed more work than UTFA during handgrip exercise [mean (SE) TRFA, 66.1 (9.5) J·100 ml^–1; UTFA, 35.1 (2.3) J·100 ml^–1; P=0.02] and UTFA exhibited a greater increase in net lactate output relative to work load (P=0.003). During lactate infusion net lactate uptake across the resting forearms increased linearly with the arterial lactate concentration in both groups (TRFA, r=–0.95 (0.03); UTFA, r=–0.92 (0.04); P<0.02], with no difference in the regression slopes [TRFA, –1.06 (0.13); UTFA, –1.07 (0.27); P=0.97] or y-intercepts [TRFA, 0.67 (0.20); UTFA, 1.36 (0.67); P=0.37] between groups. Almost all of the lactate taken up was disposed of by both groups of forearms [TRFA, 99.6 (0.2)%; UTFA, 98.5 (1.0)%; P=0.37]. It was concluded that the net uptake and removal of lactate by resting skeletal muscle is a function of the concentration of lactate in the blood perfusing the muscle rather than the muscle training status. Electronic Publication     

Multiple compartments with different metabolic characteristics are involved in biosynthesis of intracellular and released glutamine and citrate in astrocytes

The metabolism of glucose and lactate was investigated in cultured mouse cerebellar astrocytes, a culture preparation consisting of a homogeneous population of cells, by incubating the cells in a medium containing either [U-(13)C]glucose or [U-(13)C]lactate in combination with unlabeled lactate and glucose, respectively. After the incubation, cell extracts and media were analyzed by GC/MS (gas chromatography/mass spectrometry) for labeling patterns in aspartate, glutamate, and glutamine, as well as the tricarboxylic acid (TCA) cycle constituents citrate and fumarate. Triple labeling of extracellular citrate exceeded that of double labeling from [U-(13)C]glucose. This was not the case when lactate was the labeled precursor. These results indicate that pyruvate carboxylation in biosynthesis of releasable citrate was less prominent from lactate compared with glucose. As observed in the case of extracellular citrate, triple labeling of intracellular aspartate was higher than double labeling when [U-(13)C]glucose was the precursor, but not with [U-(13)C]lactate as precursor. The pattern of labeling in citrate was different intra- and extracellularly and the extent of labeling extracellularly was 10 times higher using [U-(13)C]glucose compared with [U-(13)C]lactate. However, the intracellular citrate labeling from [U-(13)C]glucose only exceeded that originating from labeled lactate by a factor of two. This is in contrast to the labeling pattern obtained for glutamine, since intracellularly this was equally prominent using [U-(13)C]glucose and [U-(13)C]lactate as substrates. Moreover, extracellularly the labeling was only slightly higher when using [U-(13)C]glucose compared with [U-(13)C]lactate. Intracellular glutamate and extracellular glutamine exhibited similar incorporation patterns with regard to double compared with triple labeling and the extent of incorporation of label from [U-(13)C]lactate compared with [U-(13)C]glucose. It should be noted that the main intracellular pools of citrate and glutamine were compartmentalized; i.e., releasable citrate and glutamine exhibited a labeling pattern distinctly different from that of their intracellular pools. Moreover, carboxylation of pyruvate using glucose as the precursor was more important for biosynthesis of releasable glutamine and citrate, compared with their intracellular pools. Based on the results a model of multiple compartments is suggested. The compartments differ with regard to utilization of lactate and glucose, synthetic pathways for TCA cycle intermediates and amino acids, particularly citrate and glutamine, as well as the contents of different metabolites.     

Changes in regional energy metabolism after closed head injury in the rat

We examined in the present investigation regional ATP, glucose, and lactate content in the cortical and subcortical structures, in a rat model of closed head injury (CHI). In serial tissue sections bioluminescence imaging of ATP, glucose, and lactate was performed at 4 h, 12 h and 24 h (n=4/5 per time point with) after the induction of CHI or sham surgery. Bioluminescence images were analyzed by computer-assisted densitometry, at the lesion site, in remote cortical areas, and in the subcortical structures (thalamus and caudate nucleus). ATP content was significantly decreased at the lesion site after 4 h and in the remote cortex at 12 h post-injury. At 12 h, the ATP content reached baseline levels on the ipsilateral side and at 24 h also at remote lateral parietal sites. In the contralateral cortex, ATP increased transiently above the baseline at 12 h. No significant changes in ATP were found in the thalamus and caudate nucleus. Cortical glucose and lactate contents could not be discerned over time. Following CHI there is an acute and progressive, yet transient, ischemic cortical profile, which is not reflected in subcortical areas.