Glomerular Injury Induced by Hydrogen Peroxide: Modifying Influence of Ace Inhibitors

The sensitivity of isolated glomeruli from normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SHR) strains to oxidant stress was studied by determining the incidence of pyknosis, karyohexis and karyolysis after incubation with different concentrations of hydrogen peroxide (H2O2) (4.7 × 10^-9-10^-3 M). Even though the proportion of glomeruli containing nuclei that demonstrated these features increased progressively with increasing concentrations of H2O2, the number of severely damaged glomeruli was relatively small even at concentrations of 4.7 × 10^-3 M.

Examination of the surface epithelial cells of glomeruli using scanning electron microscopy revealed no evidence of disturbance of the macroscopic or podocyte structure or, of increased blebbing after H2O2-treatment. These data suggest damage to nuclei is an early result of ROS stress on glomeruli.

Preincubation of WKY glomeruli with captopril or lisinopril resulted in a significant drop in the proportion of WKY glomeruli demonstrating structural damage after oxidant stress. In contrast, preincubation of SHR glomeruli with lisinopril had no effect on oxidant-induced changes in the morphology of SHR glomeruli, whereas captopril effected a significant increase in the proportion of glomeruli demonstrating damage at all concentrations of H2O2.     

Structural Evidence for a Copper-Bound Carbonate Intermediate in the Peroxidase and Dismutase Activities of Superoxide Dismutase

Copper-zinc superoxide dismutase (SOD) is of fundamental importance to our understanding of oxidative damage. Its primary function is catalysing the dismutation of superoxide to O₂ and H₂O₂. SOD also reacts with H₂O₂, leading to the formation of a strong copper-bound oxidant species that can either inactivate the enzyme or oxidise other substrates. In the presence of bicarbonate (or CO₂) and H₂O₂, this peroxidase activity is enhanced and produces the carbonate radical. This freely diffusible reactive oxygen species is proposed as the agent for oxidation of large substrates that are too bulky to enter the active site. Here, we provide direct structural evidence, from a 2.15 Å resolution crystal structure, of (bi)carbonate captured at the active site of reduced SOD, consistent with the view that a bound carbonate intermediate could be formed, producing a diffusible carbonate radical upon reoxidation of copper. The bound carbonate blocks direct access of substrates to Cu(I), suggesting that an adjunct to the accepted mechanism of SOD catalysed dismutation of superoxide operates, with Cu(I) oxidation by superoxide being driven via a proton-coupled electron transfer mechanism involving the bound carbonate rather than the solvent. Carbonate is captured in a different site when SOD is oxidised, being located in the active site channel adjacent to the catalytically important Arg143. This is the probable route of diffusion from the active site following reoxidation of the copper. In this position, the carbonate is poised for re-entry into the active site and binding to the reduced copper.     

Studies in the rat on the hepatic subcellular distribution and billary excretion of lithocholic acid.

1. A compartmental model has been used to derive the in vivo subcellular distribution of lithocholic acid in rat liver. The model is based on the values of the partition coefficients for the distribution of lithocholic acid between subcellular fractions and buffer. It also permits calculation of the amount of lithocholic acid which is in free solution in cytosol. 2. The hypothesis that the rate of biliary excretion of a bile acid depends on the proportion in free solution was investigated by comparing the rates of biliary excretion of lithocholic acid and glycocholic acid. The rate for lithocholic acid was substantially less than for glycocholic acid while the percentages of each bile acid in free solution were 0.8% and 10%, respectively. 3. The validity of the model was supported by the observation that the amounts of lithocholic acid predicted to be present in the nuclear and cytosolic fractions were similar to the amounts found after intravenous injection of the bile acid.     

Substantial genetic divergence and lack of recent gene flow support cryptic speciation in a colour polymorphic bumble bee (Bombus bifarius) species complex

Phenotypic polymorphism can constitute an inherent challenge for species delimitation. This issue is exemplified in bumble bees (Bombus), where species can exhibit high colour variation across their range, but otherwise exhibit little morphological variation to distinguish them from close relatives. We examine the species status of one of the most abundant North American bumble bees, Bombus bifarius Cresson, which historically comprised two major taxa, bifarius s.s. and nearcticus. These lineages are recognized primarily by red and black variation in their mid-abdominal coloration; however, a continuum from black (nearcticus) to red (bifarius s.s.) variation has led to their historic synonymization. Integrating mitochondrial and nuclear data and whole-genome sequencing, we reveal a high level of both mitochondrial and nuclear divergence delimiting two morphologically cryptic species – the red bifarius s.s. and the colour-variable (black to red) nearcticus. Population genomic analysis supports an absence of recent genomic admixture and a strong population structure between the two clades, even in sympatry. Species distribution models predict partially differentiated niches between the genetically inferred clades with annual precipitation being a leading differentiating variable. The bifarius s.s. lineage also occupies significantly higher elevations, with regions of sympatry being among the highest elevations in nearcticus. Our data also support a subspecies-level divergence between the broadly distributed nearcticus and the island population vancouverensis. In this paper, we formally recognize the two species, Bombus bifarius Cresson and Bombus vancouverensis Cresson, the latter including the subspecies B. vancouverensis vancouverensis comb.n. and B. vancouverensis nearcticus comb.n ., with vancouverensis the name bearer due to year priority.