Biomedical subjects

Andrew Evan

Publications and source records attributed to Andrew Evan.

4 recordsLinked to original sources

PubMed2006

Pathophysiological correlates of two unique renal tubule lesions in rats with intestinal resection.

Rats with small bowel resection fed a high-oxalate diet develop extensive deposition of calcium oxalate (CaOx) and calcium phosphate crystals in the kidney after 4 mo. To explore the earliest sites of renal crystal deposition, rats received either small bowel resection or transection and were then fed either standard chow or a high-oxalate diet; perfusion-fixed renal tissue from five rats in each group was examined by light microscopy at 2, 4, 8, and 12 wk. Rats fed the high-oxalate diet developed birefringent microcrystals at the brush border of proximal tubule cells, with or without cell damage; the lesion was most common in rats with both resection and a high-oxalate diet (10/19 with the lesion) and was significantly correlated with urine oxalate excretion (P < 0.001). Rats with bowel resection fed normal chow had mild hyperoxaluria but high urine CaOx supersaturation; four of these rats developed birefringent crystal deposition with tubule plugging in inner medullary collecting ducts (IMCD). Two rats fed a high-oxalate diet also developed this lesion, which was correlated with CaOx supersaturation, but not oxalate excretion. Tissue was examined under oil immersion, and tiny birefringent crystals were noted on the apical surface of IMCD cells only in animals with IMCD crystal plugging. In one animal, IMCD crystals were both birefringent and nonbirefringent, suggesting a mix of CaOx and calcium phosphate. Overall, these animals demonstrate two distinct sites and mechanisms of renal crystal deposition and may help elucidate renal lesions seen in humans with enteric hyperoxaluria and stones.

Animals↗

PubMed2005

A concerted protocol for the analysis of mineral deposits in biopsied tissue using infrared microanalysis.

The mechanism(s) by which crystals are retained in the kidney resulting in stone disease remains unclear. Intratubular aggregation as well as crystal cell binding, or internalization and translocation, or alternatively nucleation and growth in the interstitial fluid are possible models. Our group is testing the hypothesis that calcium phosphate deposits in kidneys of patients with calcium renal stones arise in unique anatomical regions of the kidney. Furthermore, we believe that their formation is conditioned by specific stone forming pathophysiologies. To test this hypothesis, we performed intra-operative renal papillary biopsies during percutaneous nephrolithotomy of kidneys from 15 idiopathic calcium stone formers as well as kidney tissue from a patient who ingested ethylene glycol, and developed a new protocol to accurately identify the composition of the calcium deposits located in the renal tissue. We developed a new histological approach that incorporated a low-energy (low-E) reflective slide substrate that has similar characteristics to a common microscope slide and infrared absorption microspectroscopy. Infrared absorption microspectroscopy revealed the crystal deposits in the idiopathic calcium oxalate stone formers to be hydroxyapatite in composition with an occasional region of calcium carbonate, while calcium oxalate was the predominant mineral in the kidney of the patient who had ingested ethylene glycol. The results demonstrate that mixed sample types containing tissue and mineralized deposits are easily analyzed while mounted on a low-E slide using the attenuated total internal reflectance (ATR) method. Reflection/absorption (R/A) analysis allows one to quickly survey a tissue section and provides qualitative information about its components. Once interesting sites have been identified by R/A analysis, ATR analysis can then be used to collect the best data possible. ATR analysis provides spectra free from many of the artifacts associated with transmission and R/A analysis, and completes the full picture of the components contained in the crystal deposits and tissue. We present a method of analysis for mineralized materials embedded in kidney tissue that uses readily or easily obtainable materials and instrumentation. The sensitivity of this method allows tissue sections to remain unstained, alleviating the tedious and time-consuming constraints of earlier methods of visual analysis. The present method will save time and training, while simultaneously offering an unbiased analysis of mineralized components that is more accurate and conducive to patient treatments than previous methods.

Biopsy↗

PubMed2005

Kidney stone disease.

About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. Stones ultimately arise because of an unwanted phase change of these substances from liquid to solid state. Here we focus on the mechanisms of pathogenesis involved in CaOx, CaP, UA, and cystine stone formation, including recent developments in our understanding of related changes in human kidney tissue and of underlying genetic causes, in addition to current therapeutics.

Animals↗

PubMed2002

The TRQQKRP motif located near the C-terminus of Rac2 is essential for Rac2 biologic functions and intracellular localization.

Rac GTPases regulate a wide variety of cellular processes including actin cytoskeleton organization, gene expression, cell-cycle progression, and apoptosis. Here we report that the TRQQKRP motif of Rac2 located near the C-terminus, a region of sequence disparity among Rac proteins, is essential for complementation of Rac2 function in Rac2-deficient cells. Deletion of this sequence can also intragenically suppress the dominant-negative Rac2(D57N) mutation in a variety of functional assays. In Rac2-deficient cells, expression of TRQQKRP-deleted Rac2 protein is unable to completely rescue migration and nicotinamide adenine dinucleotide phosphate oxidase deficiencies previously described in these cells. In fibroblasts, the Rac2(D57N) mutant phenotypes of abnormal proliferation, cell morphology, and membrane ruffling are suppressed by the TRQQKRP motif deletion. In myeloid hematopoietic cells, the deletion of the TRQQKRP motif eliminates a Rac2(D57N)-induced block in in vitro differentiation of neutrophils not previously described with this mutant. Mechanistically, deletion of the TRQQKRP motif results in diminished geranylgeranylation and delocalization of intracellular Rac2 protein. Taken together, these results indicate that the TRQQKRP motif in Rac2 protein is required for efficient prenylation and correct intracellular localization of Rac2 protein and is essential for Rac2 to mediate a variety of its biologic functions. These data suggest that precise localization of Rac2 protein in intracellular compartments and/or with other proteins/lipids is a prerequisite for its diverse functions.

3T3 Cells↗