Associations between total mercury, trace minerals, and blood health markers in Northwest Atlantic white sharks (Carcharodon carcharias).

The ecology and life-histories of white sharks make this species susceptible to mercury bioaccumulation; however, the health consequences of mercury exposure are understudied. We measured muscle and plasma total mercury (THg), health markers, and trace minerals in Northwest Atlantic white sharks. THg in muscle tissue averaged 10.0 mg/kg dry weight, while THg in blood plasma averaged 533 µg/L. THg levels in plasma and muscle were positively correlated with shark precaudal length (153-419 cm), and THg was bioaccumulated proportionally in muscle and plasma. Nine sharks had selenium:mercury molar ratios in blood plasma >1.0, indicating that for certain individuals the potential protective effects of the trace mineral were diminished, whereas excess selenium may have protected other individuals. No relationships between plasma THg and any trace minerals or health markers were identified. Thus, we found no evidence of negative effects of Hg bioaccumulation, even in sharks with very high THg.

Reprint of: 1-Aminocyclopropanecarboxylate Synthase, a Key Enzyme in Ethylene Biosynthesis.

1-Aminocyclopropanecarboxylate (ACC) synthase, which catalyzes the conversion of S-adenosylmethionine (SAM) to ACC and methylthioadenosine, was demonstrated in tomato extract. Methylthioadenosine was then rapidly hydrolyzed to methylthioribose by a nucleosidase present in the extract. ACC synthase had an optimum pH of 8.5, and a Km of 20 µM with respect to SAM. S-Adenosylethionine also served as a substrate for ACC synthase, but at a lower efficiency than that of SAM. Since S-adenosylethionine had a higher affinity for the enzyme than SAM, it inhibited the reaction of SAM when both were present. S-Adenosylhomocysteine was, however, an inactive substrate. The enzyme was activated by pyridoxal phosphate at a concentration of 0.1 µM or higher, and competitively inhibited by aminoethoxyvinylglycine and aminooxyacetic acid, which are known to inhibit pyridoxal phosphate-mediated enzymic reactions. These results support the view that ACC synthase is a pyridoxal enzyme. The biochemical role of pyridoxal phosphate is catalyzing the formation of ACC by α,γ-elimination of SAM is discussed.

Mercury and selenium levels in lemon sharks (Negaprion brevirostris) in relation to a harmful red tide event.

Tissue levels of mercury (Hg; total, organic) and selenium (Se) were assessed in juvenile lemon sharks (Negaprion brevirostris) from Florida nearshore waters collected during a harmful algal bloom (HAB, brevetoxin) event and compared with sharks not exposed to HABs. In all sharks studied, total Hg levels in the muscle were generally present in a molar excess over Se (which may protect against Hg toxicity) and mean muscle Hg levels (0.34 microg/g) exceed safe human consumption guidelines. While there was generally no difference in tissue Hg and Se levels following exposure of sharks to HABs, hepatic Hg levels were significantly lower (56% reduction) in the HAB-exposed sharks compared to controls. As Hg and HABs are globally increasing in scope and magnitude, further work is warranted to assess their interactions and biotic impacts within aquatic ecosystems, especially for a species such as the lemon shark that is classified as a near-threatened species by the International Union for the Conservation of Nature.

Leg joint power output during progressive resistance FES-LCE cycling in SCI subjects: developing an index of fatigue.

BACKGROUND: The purpose of this study was to investigate the biomechanics of the hip, knee and ankle during a progressive resistance cycling protocol in an effort to detect and measure the presence of muscle fatigue. It was hypothesized that knee power output can be used as an indicator of fatigue in order to assess the cycling performance of SCI subjects. METHODS: Six spinal cord injured subjects (2 incomplete, 4 complete) between the ages of twenty and fifty years old and possessing either a complete or incomplete spinal cord injury at or below the fourth cervical vertebra participated in this study. Kinematic data and pedal forces were recorded during cycling at increasing levels of resistance. Ankle, knee and hip power outputs and resultant pedal force were calculated. Ergometer cadence and muscle stimulation intensity were also recorded. RESULTS: The main findings of this study were: (a) ankle and knee power outputs decreased, whereas hip power output increased with increasing resistance, (b) cadence, stimulation intensity and resultant pedal force in that combined order were significant predictors of knee power output and (c) knowing the value of these combined predictors at 10 rpm, an index of fatigue can be developed, quantitatively expressing the power capacity of the knee joint with respect to a baseline power level defined as fatigue. CONCLUSION: An index of fatigue was successfully developed, proportionalizing knee power capacity during cycling to a predetermined value of fatigue. The fatigue index value at 0/8th kp, measured 90 seconds into active, unassisted pedaling was 1.6. This indicates initial power capacity at the knee to be 1.6 times greater than fatigue. The fatigue index decreased to 1.1 at 2/8th kp, representing approximately a 30% decrease in the knee's power capacity within a 4 minute timespan. These findings suggest that the present cycling protocol is not sufficient for a rider to gain the benefits of FES and thus raises speculation as to whether or not progressive resistance cycling is an appropriate protocol for SCI subjects.

Effect of platelet-rich plasma with autogenous bone graft for maxillary sinus augmentation in a rabbit model.

PURPOSE: To evaluate the effect of platelet-rich plasma (PRP) on autogenous bone graft remodeling during sinus augmentation in a rabbit model. MATERIALS: Twelve New Zealand White rabbits were divided randomly into 3 groups based on their time of sacrifice (2, 4, and 8 weeks). All animals underwent a general anesthetic and harvesting of an autogenous bone graft from the right iliac crest with subsequent bilateral maxillary sinus augmentation. PRP was prepared via standard approved technique by acquiring 21 cc of autogenous blood and performing differential centrifugation to obtain PRP. One cc of PRP was produced that was mixed with bovine topical thrombin and calcium chloride. The left maxillary sinus received only autogenous bone, while the right maxillary sinus received a mixture of PRP mixed with autogenous bone, thus each animal acted as its own control. Equal volumes of bone were inserted in each maxillary sinus. Animals were sacrificed at 2, 4, and 8 weeks and all specimens were harvested for peripheral quantitative computed tomography (pQ-CT), static, and dynamic and histomorphometric analysis. RESULTS: Student t tests were performed comparing bone density via pQ-CT analysis, histomorphometric parameters of total bone area, and bone apposition rate. PRP had no statistically significant effect on bone graft healing in maxillary sinus augmentation when compared using standard pQ-CT, static, and dynamic histologic criteria. CONCLUSION: This study fails to find a direct stimulatory effect of PRP on healing of autogenous bone grafts using pQ-CT, static, and dynamic histomorphometric analyses.

Aviglycine and propargylglycine inhibit conidial germination and mycelial growth of Fusarium oxysporumf. sp. luffae.

Two inhibitors, aviglycine and propargylglycine, were tested for their ability to suppress methionine synthesis thus inhibit conidial germination and mycelial growth of Czapek-Dox liquid medium grown Fusarium oxysporum f. sp. luffaemuM. The linear inhibition range for mycelial growth was about 7.6-762.9 microM. Although aviglycine did not completely inhibit both conidial germination and mycelial growth, it showed significant inhibitory effect at 1.5 microM. The inhibition range for propargylglycine against conidial germination and mycelial growth were from 0.08 to 8841 microM and from 0.8 to 884.1 microM, respectively. Propargylglycine inhibited conidial germination and mycelial growth at a concentration of 8841 muM. The EC(50) values of aviglycine were 1 microM for conidial growth and 122 microM for mycelial growth, and the EC(50) values of propargylglycine were 47.7 microM for conidial growth and 55.6 muM for mycelial growth. Supplement of methionine released inhibition of aviglycine or propargylglycine to conidial germination. In addition, a mixture of aviglycine (1.5 microM) and propargylglycine (8841 microM) showed additive inhibitive effect than applied alone on 10 isolates. From these results, both aviglycine and propargylglycine exhibited inhibitory activity, and suggest that they can provide potential tools to design novel fungicide against fungal pathogens.