Rj Thomas

Lignin and carbohydrate alteration in particle-size separates of an oxisol under tropical pastures following native savanna

Establishment of improved tropical pastures on acid savanna soils of low fertility can increase the soil organic matter (SOM) content and soil fertility. Our objective was to follow the quantitative and qualitative changes of SOM associated with sand-, silt-and clay-sized separates after establishment of a grass-alone (Brachiaria decumbens) and a grass-legume (Brachiaria decumbens + Pueraria phaseoloides) pasture on isohyperthermic savanna soils of Colombia. Additionally, earthworm casts of anecic and endo-anecic species derived from the grass-legume pasture were investigated. Whole soil and size separates were analyzed for C, N, lignin-derived phenols (alkaline CuO-oxidation) and carbohydrates (4 m trifluoroacetic acid hydrolysis). For native savanna, grass-alone and grass-legume pasture the C content increased in the order sand (1.6–3.3 g C kg−1) < silt (25.8–32.1 g C kg−1) < clay (38.8–43.0 g C kg−1); the C-to-N ratio decreased in the same order. Fifteen years of pasture establishment resulted in an increase of C by factors of ca. 2 (sand), 1.3 (silt) and 1.1 (clay) compared to native savanna. Decreasing yields of phenolic CuO-oxidation products and increasing side-chain oxidation of the remnant lignin indicated progressive lignin alteration with decreasing particle size. Soil under savanna was substantially lower in intact lignin structures than soil under grass-alone and grass-legume pastures. Enrichment factors, E = (mg kg−1 soil under pasture/mg kg−1 soil under savanna), for lignin-derived phenolics after establishment of B. decumbens and B. decumbens + P. phaseoloides were 3.9 and 2.7, 4.3 and 2.4, and 2.6 and 2.6 in sand-, silt-and clay-sized separates, respectively. Clay-bound SOM was rich in microbially-derived sugars, whereas the SOM of the sand-sized separates contained large amounts of plant-derived sugars. Silt-associated SOM had low concentrations of both. Establishment of grass-alone and grass-legume pasture increased the amount of easily-degradable plant-derived sugars by factors of 3.0 and 3.5 (sand), 1.9 and 1.3 (silt), and 1.1 and 1.1 (clay). SOM distribution across size separates suggested an increasing amount of unprotected macro-OM after establishment of grass-alone and grass-legume pastures. Concurrently, lignin and carbohydrate signature indicated higher contents of relatively undergraded plant-derived SOM, notably in the sand-sized separates. It was concluded that the increase of this SOM fraction has beneficial effects on the soil internal N cycle as far as N mineralization and N immobilization is concerned. Earthworm casts were characterized by a tremendous enrichment of C, intact lignin and plant-derived sugars in the sand-sized separates, compared with the surrounding soil. This suggested a pronounced incorporation of fresh litter into the mineral soil (anecic effect), that decomposition processes were dramatically slowed in the casts, and a pool of relatively labile, but physically-protected SOM was built up.

Soil organic matter within earthworm casts of an anecic–endogeic tropical pasture community, Colombia

Large, round-shaped surface casts derived mainly from the anecic Martiodrilus sp., family Glossoscolecidae were investigated for their structural stability and the composition of soil organic matter (SOM) associated with different particle-size separates of the casts. Lignin (CuO oxidation) and carbohydrate (acid hydrolysis) signature of SOM was carried out in addition to 13C nuclear magnetic resonance (NMR) spectroscopy. Data obtained for the casts were compared with those of the surrounding surface soil of an Oxisol under grass/legume pasture following native savanna. Earthworm casts showed significantly higher contents of large (3.15–5 and 5–8 mm) water-stable aggregates than the surrounding soil (765 g kg- 1 vs. 390 g kg−1). This higher structural stability of the casts corresponded with their higher organic C concentration (56 g C kg−1) compared with the surrounding soil (26 g C kg−1). The increase was most pronounced for organic C associated with sand-sized separates, i.e. SOM not involved in organo-mineral complexes. Signature of microbial lignin alteration and carbohydrate composition as well as 13C NMR spectroscopy revealed that organic matter (OM) associated with sand was mainly composed of slightly decomposed plant residues. Hence, higher concentrations of carbohydrates and lignin (primary resources) and lower proportions of C-substituted aromatic C and COOH (humic compounds) observed in whole casts compared with the unfractionated surrounding soil were partly due to the intense mixing of fresh litter into the mineral soil (anecic effect). Microbial products were enriched in clay-bound SOM, and humified organic compounds dominated silt-associated SOM. However, the structural chemical analyses showed that decomposition of SOM bound to silt- and clay-sized particles appeared to be in a more advanced stage in the surrounding soil than in the casts. The data provided evidence that carbohydrate-rich plant debris is responsible for structural stability of earthworm casts, besides mucopolysaccharides derived from microorganisms in the intestines of earthworms and the earthworms themselves. According to Golchin et al. (1994) it was hypothesised that microbial metabolism of notably plant-derived carbohydrates results in the release of mucilage and other metabolites which permeate the coatings of mineral particles and thus stabilise the casts. The consequence of the intimate association of slightly decomposed plant debris with the mineral phase is the build-up of a rather active but physically protected C pool which is released concurrently with the disintegration of the casts.

Clinical associations of striae gravidarum

Striae gravidarum are a common finding in the abdominal skin of pregnant women. This study of 128 pregnant women examined factors which are associated with their occurrence. It is clear that women with higher body mass indices have more striae and that striae are also more common in younger women. These findings may be explained by the greater degrees of stretch applied to the skin in obese women with larger babies, and by changes in skin collagen and connective tissue that are age-related and affect its tendency to tear.

Brain choline concentration Early quantitative marker of ischemia and infarct expansion

Objective: Better prediction of tissue prognosis in acute stroke might improve treatment decisions. We hypothesized that there are metabolic ischemic disturbances measurable noninvasively by proton magnetic resonance spectroscopy (1H MRS) that occur earlier than any structural changes visible on diffusion-tensor imaging (DTI), which may therefore serve for territorial identification of tissue at risk. Methods: We performed multivoxel 1H MRS plus DTI within a maximum of 26 hours, and DTI at 3–7 days, after ischemic stroke. We compared choline, lactate, N-acetylaspartate, and creatine concentrations in normal-appearing voxels that became infarcted (infarct expansion) with normal-appearing voxels around the infarct that remained “healthy” (nonexpansion) on follow-up DTI. Each infarct expansion voxel was additionally classified as either complete infarct expansion (infarcted tissue on follow-up DTI covered ≥50% of the voxel) or partial infarct expansion (<50% of voxel). Results: In 31 patients (NIH Stroke Scale score 0–28), there were 108 infarct nonexpansion voxels and 113 infarct expansion voxels (of which 80 were complete expansion and 33 partial expansion voxels). Brain choline concentration increased for each change in expansion category from nonexpansion, via partial expansion to complete expansion (2,423, 3,843, 4,158 IU; p < 0.05). Changes in lactate, N-acetylaspartate, and creatine concentrations in expansion category were insignificant although for lactate there was a tendency to such association. Conclusions: Choline concentration measurable with 1H MRS was elevated in peri-ischemic normal-appearing brain that became infarcted by 3–7 days. The degree of elevation was associated with the amount of infarct expansion. 1H MRS might identify DTI-normal-appearing tissue at risk of conversion to infarction in early stroke.

A grid overlay framework for analysis of medical images and its application to the measurement of stroke lesions

AbstractObjectivesTo create and evaluate an interactive software tool for measuring imaging data in situations where hand-drawn region-of-interest measurements are unfeasible, for example, when the structure of interest is patchy with ill-defined boundaries.MethodsAn interactive grid overlay software tool was implemented that enabled coding of voxels dependent on their imaging appearance with a series of user-defined classes. The Grid Analysis Tool (GAT) was designed to automatically extract quantitative imaging data, grouping the results by tissue class. Inter- and intra-observer reproducibility was evaluated by six observers of various backgrounds in a study of acute stroke patients.ResultsThe software tool enabled a more detailed classification of the stroke lesion than would be possible with a region-of-interest approach. However, inter-observer coefficients of variation (CVs) were relatively high, reaching 70% in “possibly abnormal” tissue and around 15–20% in normal appearing tissues, while intra-observer CVs were no more than 13% in “possibly abnormal” tissue and generally less than 1% in normal-appearing tissues.ConclusionsThe grid-overlay method overcomes some of the limitations of conventional Region Of Interest (ROI) approaches, providing a viable alternative for segmenting patchy lesions with ill-defined boundaries, but care is required to ensure acceptable reproducibility if the method is applied by multiple observers.Key Points• Computer software developed to overcome limitations of conventional regions of interest measurements • This software is suitable for patchy lesions with ill-defined borders • Allows a more detailed assessment of imaging data

Clinical Trial: Heme Arginate in patients planned for Cardiac Surgery (HACS)

Acute kidney injury (AKI) is a significant complication of cardiac surgery and is associated with increased morbidity and mortality [1]. Despite much research, there is no specific therapy available. Although AKI can be multifactorial, ischaemia reperfusion injury (IRI) often plays a key role. Thus, cardiac surgery offers an attractive opportunity for translational AKI research given the predictive haemodynamic challenge to renal perfusion. Hemeoxygenase-1 (HO-1) is a key inducible anti-inflammatory enzyme that catalyses the breakdown of the pro-oxidant protein heme ubiquitously found at inflamed sites. The drug heme arginate has been in use for over 20 years in the treatment of porphyria but also upregulates HO-1 in peripheral blood mononuclear cells (PBMCs) [2] and ameliorates calf muscle ischaemia [3]. In addition, treatment of mice with heme arginate prior to renal IRI strongly upregulates renal HO-1 expression and protects from AKI [4]. We therefore hypothesise that HA may offer a prophylactic therapy for human renal IRI via the upregulation of HO-1.