Dissociation rate constants of human fibronectin binding to fibronectin-binding proteins on living Staphylococcus aureus isolated from clinical patients

Staphylococcus aureus is part of the indigenous microbiota of humans. Sometimes, S. aureus bacteria enter the bloodstream, where they form infections on implanted cardiovascular devices. A critical, first step in such infections is a bond that forms between fibronectin-binding protein (FnBP) on S. aureus and host proteins, such as fibronectin (Fn), that coat the surface of implants in vivo. In this study, native FnBPs on living S. aureus were shown to form a mechanically strong conformational structure with Fn by atomic force microscopy. The tensile acuity of this bond was probed for 46 bloodstream isolates, each from a patient with a cardiovascular implant. By analyzing the force spectra with the worm-like chain model, we determined that the binding events were consistent with a multivalent, cluster bond consisting of ~10 or ~80 proteins in parallel. The dissociation rate constant (k(off), s(-1)) of each multibond complex was determined by measuring strength as a function of the loading rate, normalized by the number of bonds. The bond lifetime (1/k(off)) was two times longer for bloodstream isolates from patients with an infected device (1.79 or 69.47 s for the 10- or 80-bond clusters, respectively; n = 26 isolates) relative to those from patients with an uninfected device (0.96 or 34.02 s; n = 20 isolates). This distinction could not be explained by different amounts of FnBP, as confirmed by Western blots. Rather, amino acid polymorphisms within the Fn-binding repeats of FnBPA explain, at least partially, the statistically (p < 0.05) longer bond lifetime for isolates associated with an infected cardiovascular device.     

Synthesis and evaluation of in vitro antioxidant capacities of some benzimidazole derivatives

New, except 1d, melatonin analogue benzimidazole derivatives were synthesized and characterized in the present study. The potential role of melatonin as an antioxidant by scavenging and detoxifying ROS raised the possibility that compounds that are analogous to melatonin can also be used for their antioxidant properties. Therefore the antioxidant effects of the newly synthesized compounds were investigated in vitro by means of their inhibitory effect on hydrogen peroxide-induced erythrocyte membrane lipid peroxidation (EMLP) and on various erythrocyte antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT) and glucose-6-phosphate dehydrogenase (G6PD). The synthesized benzimidazole derivatives showed remarkable antioxidant activity in vitro in the H₂O₂-induced EMLP system. Furthermore their effects on various antioxidant enzymes are discussed and evaluated from the perspective of structure- activity relationships.     

Goldilocks,vitamin D and sarcoidosis

While low levels of vitamin D can increase the risk for osteoporosis, excessive amounts of vitamin D may also be problematic. Hypercalcemia and hypercalcuria due to increased vitamin D activity occur in a significant proportion of sarcoidosis patients. Saidenberg-Kermanac’h and colleagues compared vitamin D levels with bone fragility fractures in their sarcoidosis clinic. They found that a 25-(OH) vitamin D level between 10 and 20 ng/ml was associated with the lowest risk of bone fractures and paradoxically higher levels increased the risk of bone fractures. Using less vitamin D supplementation may simultaneously lower the risk for bone fracture and hypercalcemia in sarcoidosis.In the previous issue, Saidenberg-Kermanac’h and colleagues provide more information regarding the complexity of vitamin D activity in sarcoidosis [1]. A few years ago, vitamin D was declared the nutrient of the decade. This was heady stuff for a sterol that was originally felt important only in preventing rickets. Studies have demonstrated its key role in calcium absorption and bone growth. Beyond that, vitamin D has been considered an important sterol in various aspects of health. Low levels of vitamin D have been associated with increased risk for cancer, type 2 diabetes, and heart disease.Most of these observations have been based on measurements of 25-(OH)-vitamin D3 (ergocalcitrol). This sterol is converted by 1-alpha hydroxylase to 1,25-(OH)2-vitamin D3 (calcitrol), the active form of vitamin D. This conversion occurs in the kidney and patients with chronic renal failure require calcitrol replacement.In tuberculosis, vitamin D supplementation has been recommended in patients because vitamin D is crucial in the granulomatous reaction against the organism. However, what may be good for tuberculosis eradication may not be good for sarcoidosis. It has been noted that excessive amounts of vitamin D are associated with a worse clinical outcome in sarcoidosis [2]. In granulomas, there may be increased activity of 1-alpha hydroxylase. As part of the Th-1 immune response, calcitrol has a paracrine effect within the granuloma. In some cases, this leads to excessive calcitrol, resulting in hypercalcuria or hypercalcemia [3]. At least 10% of sarcoidosis patients have hypercalcemia, half of whom can develop associated renal dysfunction [3,4]. In some cases, hypercalcemic renal failure can be reversed by simply withdrawing vitamin D supplementation [3]. There are case reports of excessive vitamin D replacement leading to hypercalcemia in patients with mycobacterial infections [5].The sarcoidosis patient may be treated with glucocorticoids, sometimes for years. Obviously, long-term glucocorticoid administration places the patient at risk for developing osteoporosis [6,7]. In rheumatoid arthritis, patients undergoing prolonged glucocorticoid treatment are recommended to receive calcium and vitamin D replacement [8]. While this is the cornerstone of prevention of osteoporosis, the role of calcium and vitamin D replacement in sarcoidosis remains unclear [9].Into this quandary comes the study by Saidenberg-Kermanac’h and colleagues reported in the previous issue of Arthritis Research & Therapy[1]. After studying a large cohort of sarcoidosis patients from their clinic, the authors found that fragility fractures occurred in nearly a quarter of them. The fracture risk was increased for those treated with corticosteroids. Although low levels of ergocalcitrol was an independent risk for osteoporosis, ironically high levels of ergocalcitrol were also associated with an increased risk for osteoporosis. They found that ergocalcitrol levels of 10 to 20 ng/ml was associated with the lowest fracture risk for patients. This J shaped risk for bone fragility has been noted in non-sarcoidosis patients, although the proposed target levels are higher for these patients [10]. For the clinician treating sarcoidosis, one has to balance not only the risk for osteoporosis, but also the risk for hypercalcemia and renal failure (Figure 1).Open in a separate windowFigure 1Schematic depicting vitamin D metabolism in the body from ergocalcitrol to calcitrol. The conversion is enhanced by increased activity of 1-alpha hydroxylase activity in the granuloma of sarcoidosis patients. The untoward consequences of low or high vitamin D activity are summarized at the bottom of the figure.One possible explanation for the lower ideal ergocalcitrol level in sarcoidosis is the enhanced activity of 1-alpha hydroxylase in sarcoidosis granulomas. The authors did not provide information regarding calcitrol levels in their patients. The proportion of calcitrol to ergocalcitrol appears to be higher in sarcoidosis compared to non-sarcoidosis conditions. In one study of 270 sarcoidosis patients, 80% had low ergocalcitrol levels, but less than 1% had low calcitrol levels. In fact, that study found that 10% of patients had elevated calcitrol levels [3]. Those with elevated calcitrol were more likely to have a history of hypercalcemia or hypercalcuria. Higher levels of calcitrol have been associated with more advanced pulmonary sarcoidosis [2].The other potential benefits of vitamin D replacement in sarcoidosis are unclear. Should sarcoidosis patients with low ergocalcitrol but normal calcitrol levels be prescribed vitamin D supplementation to reduce their risk for cancer and type 2 diabetes? If so, do they increase their risk for hypercalcemia or hypercalcuria? Could this increased vitamin D intake raise the functional level of vitamin D even higher and therefore increase the risk for osteoporosis?To paraphrase Goldilocks, one does not want too little or too much vitamin D. You want just the right amount.     

Local host ant specificity of Phengaris (Maculinea) teleius butterfly,an obligatory social parasite of Myrmica ants

1. Phengaris butterflies are obligatory social parasites of Myrmica ants. Early research suggested that there is a different Myrmica host species for each of the five European Phengaris social parasites, but more recent studies have shown that this was an oversimplification. 2. The pattern of host ant specificity within a Phengaris teleius metapopulation from southern Poland is reported. A combination of studying the frequency distribution of Phengaris occurrence and morphometrics on adult butterflies were used to test whether use of different host species is reflected in larval development. 3. Phengaris teleius larvae were found to survive in colonies of four Myrmica species: M. scabrinodis, M. rubra, M. ruginodis, and M. rugulosa. Myrmica scabrinodis was the most abundant species under the host plant but the percentage of infested nests was similar to other host ant species at two sites and lower in comparison to nests of M. rubra and M. ruginodis at the other two sites. Morphometric measurements of adult butterflies reared by wild colonies of M. scabrinodis and M. ruginodis showed that wing size and number of wing spots were slightly greater for adults eclosing from nests of M. ruginodis. 4. Our results suggest that P. teleius in the populations studied is less specialised than previously suggested. The results are consistent with the hypothesis that P. teleius is expected to be the least specific of the European Phengaris species, as it has the largest and best defended fourth‐instar caterpillars and, as a predatory species, it spends less time in the central larval chambers of the host colonies. The fact that individuals reared by M. ruginodis had wider hind wings may suggest that P. teleius had better access to resources in M. ruginodis than in M. scabrinodis colonies.     

Disease-associated glycosylated molecular variants of human C-reactive protein activate complement-mediated hemolysis of erythrocytes in tuberculosis and Indian visceral leishmaniasis

Human C-reactive protein (CRP), as a mediator of innate immunity, removed damaged cells by activating the classical complement pathway. Previous studies have successfully demonstrated that CRPs are differentially induced as glycosylated molecular variants in certain pathological conditions. Affinity-purified CRPs from two most prevalent diseases in India viz. tuberculosis (TB) and visceral leishmaniasis (VL) have differential glycosylation in their sugar composition and linkages. As anemia is a common manifestation in TB and VL, we assessed the contributory role of glycosylated CRPs to influence hemolysis via CRP-complement-pathway as compared to healthy control subjects. Accordingly, the specific binding of glycosylated CRPs with erythrocytes was established by flow-cytometry and ELISA. Significantly, deglycosylated CRPs showed a 7–8-fold reduced binding with erythrocytes confirming the role of glycosylated moieties. Scatchard analysis revealed striking differences in the apparent binding constants (10⁴–10⁵ M⁻¹) and number of binding sites (10⁶–10⁷sites/erythrocyte) for CRP on patients’ erythrocytes as compared to normal. Western blotting along with immunoprecipitation analysis revealed the presence of distinct molecular determinants on TB and VL erythrocytes specific to disease-associated CRP. Increased fragility, hydrophobicity and decreased rigidity of diseased-erythrocytes upon binding with glycosylated CRP suggested membrane damage. Finally, the erythrocyte-CRP binding was shown to activate the CRP-complement-cascade causing hemolysis, even at physiological concentration of CRP (10 μg/ml). Thus, it may be postulated that CRP have a protective role towards the clearance of damaged-erythrocytes in these two diseases.     

The role of F-series prostaglandins as reproductive priming pheromones in the brown trout

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F-series prostaglandins (PGFs) PGF_1α and PGF_2α, with detection threshold concentrations of 10⁻¹¹ M. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF_2α (threshold 10⁻⁸ m), but did not detect a further metabolite, 13,14,-dihydro-15-ketoPGF_2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF_1α and PGF_2α (concentration 10⁻⁸ m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one whilst exposure to urine increased the levels of expressible milt. In addition, PGF_2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F-series prostaglandins have a role as priming pheromones in male brown trout.