Shi-Kaung Peng

Transport of cholesterol autoxidation products in rabbit lipoproteins

Radiolabeled pure [4-14C]cholesterol was kept at 60 degrees C under air to autoxidize for 5 weeks, after which approximately 12% cholesterol oxidation products were formed. The mixture, suspended in gelatin, was given to rabbits by gastric gavage. Rabbits were killed 4, 24, and 48 h after treatment. Cholesterol and its autoxidation products were separated by thin-layer chromatography into 5 fractions and radioactivities of each fraction were measured. Percentages of each fraction of cholesterol oxidation products and cholesterol in the original mixture before administration and in the rabbit sera after administration were similar, suggesting that the rates of absorption of cholesterol oxidation products are not significantly different from that of cholesterol. Lipoproteins were fractionated by ultracentrifugation into VLDL, LDL and HDL. Radioactivities of each fraction in lipoproteins separated by thin layer chromatography showed that fractions containing cholestane-3 beta,5 alpha,6 beta-triol, 7 alpha- and 7 beta-hydroxycholesterol and 7-ketocholesterol were more selectively transported in VLDL, whereas most of the 25-hydroxycholesterol was present in LDL. HDL contained only minute amounts of cholesterol oxidation products.

Laser Vascular Welding - How Does It Work ?

This study evaluated the histology and electron microscopy of four samples of 2 cm long venotomies and artery-vein anastomoses formed in canine femoral arteries and veins using the argon laser (0.5 W power, 1 800 J/cm2, 4 min exposure/1 cm length of anastomosis). Welds were continuously irrigated with saline during the procedure to limit maximal temperatures to 44.2 +/- 1.6 degrees C (mean +/- SD), and the specimens were removed immediately following fusion and preserved for examination. Histologic and electron microscopic examination of different areas of the welds revealed various mechanisms of fusion including a) apposition of denatured collagen and elastin in the media and adventitia; b) bonding of vein medial collagen and elastin to the internal elastic membrane of the artery; and c) fusion consisting of a coagulum of platelets and fibrin depending on the alignment and apposition of the vessel edges. This study demonstrates that vascular tissue fusion by the argon laser occurs by various mechanisms. Future experiments should delineate which types of seal produce the optimal strength at the time of fusion, and enhance long-term healing.

Effects of cholesterol oxidation derivatives on cholesterol esterifying and cholesteryl ester hydrolytic enzyme activity of cultured rabbit aortic smooth muscle cells

The effects of 5 μg/ml of 25-hydroxycholesterol; cholestane-3β, 5α,6β-triol; and cholesterol on acyl CoA cholesterol acyltransferase, acid cholesteryl ester hydrolase and neutral cholesteryl ester hydrolase was studied in cultured rabbit aortic smooth muscle cells. After 1 hour incubation, 25-hydroxycholesterol resulted in a fourfold stimulation of acyl CoA cholesterol acyltrans-ferase activity. No stimulation by 25-hydroxycholesterol was noted before 15 minutes or after 5 hours of incubation. Neither cholestane-3β,5α,6β-triol nor cholesterol influenced acyl CoA cholesterol acyltransferase activity at any time interval. No significant effects of any of the sterols were noted on acid cholesteryl ester hydrolase or neutral cholesteryl ester hydrolase activity. The imbalance between acyl CoA cholesterol acyl trans-ferase and hydrolase activities induced by 25-hydroxycholesterol could result in cholesteryl ester accumulation by arterial smooth muscle cells, which may be associated with atherosclerosis.

Congenital gastrointestinal pacemaker cell tumor.

The interstitial cells of Cajal complex within the gut wall function as a pacemaker to direct peristalsis. Their neoplastic counterpart is the gastrointestinal pacemaker cell tumor, a spindle and/or epithelioid cell mesenchymal tumor previously known as gastrointestinal stromal tumor or incorrectly called leiomyosarcoma in some cases of older reports. Although numerous cases of gastrointestinal leiomyosarcomas have been documented in the English-language literature, no pediatric case of gastrointestinal stromal tumor or gastrointestinal pacemaker cell tumor has, to our knowledge, been recorded. Herein, we report a case of congenital gastrointestinal pacemaker cell tumor confirmed by immunohistochemistry and electron microscopy in a full-term male newborn.

Influence of Cholesterol Oxidation Derivatives on Membrane Bound Enzymes in Cultured Aortic Smooth Muscle Cells

Abstract Cholestane-3β,5α,6β-triol and 25-hydroxycholesterol are two of the most cytotoxic and also relatively abundant of the autoxidation derivatives of cholesterol. Cultured aortic smooth muscle cells which were incubated with 10 μg/ml of either sterol for 24 to 48 hr showed a marked decrease of 5′-nucleotidase activity in isolated crude membranes. It was further demonstrated that 5′-nucleotidase activity was also markedly decreased in plasma membrane-enriched fractions when cells were incubated with cholestane-3β,5α,6β-triol. Na+, K+-ATPase activity in crude membranes showed a significant decrease (32%) only in cells incubated with cholestane-3β,5α,6β-triol for 48 hr. There was no effect on Na+, K+-ATPase activity in cells incubated for 24 hr with either sterol.

Composite porosity of expanded polytetrafluoroethylene vascular prosthesis

Polytetrafluoroethylene (PTFE) prostheses were modified to produce two types of composite porosity PTFE grafts: type I--inner 60 microns/outer 20 microns and type II--inner 20 microns/outer 60 microns. These composite porosity PTFE designs were investigated for bleed through, graft healing and patency and compared with high porosity PTFE (60 microns) and standard PTFE (20 microns) grafts. The grafts were implanted into the carotid and femoral arteries of dogs and retrieved after 4, 12 and 18 weeks. Both composite porosity grafts showed significantly less bleed through than standard and high porosity grafts after reperfusion. In composite grafts, the 60-microns layer allowed fibrovascular tissue and histiocyte ingrowth from perigraft tissue, but the 20-microns layer did not. Neointima formation occurred earlier and endothelialization was more extensive in high porosity grafts, but seroma formation occurred in 25% of cases. In type I composite porosity grafts, smooth muscle cells of neointima migrated into the pores of the graft, providing a firmly anchored intima. Type II composite porosity grafts allowed better ingrowth of fibrovascular tissue at the outer layer from the perigraft tissue; however, endothelialization was not completed. Composite porosity grafts should be considered for evaluation in specific clinical situations.

In Vivo Study of a High-Porosity Polytetrafluoroethylene Graft: Endothelialization, Fluid Leakage, and the Effect of Fibrin Glue Sealing

Standard polytetrafluoroethylene (PTFE) grafts (30-microns internodal distance, ID) (ST grafts), high-porosity PTFE grafts (90 microns ID) (HP grafts), high-porosity PTFE grafts preclotted with autogenous blood (BHP grafts), and high-porosity PTFE grafts presealed with fibrin glue (FHP grafts) were implanted in both common carotid and femoral arteries of 18 dogs. Of the three high-porosity groups, the FHP graft showed the shortest bleeding time. Seromas and/or hematomas occurred as follows: ST grafts 1, HP grafts 7 (P < .05 vs ST), BHP grafts 5 and 2 with FHP grafts. Fibrin glue was observed in all histological sections of 1-week samples, but by 4 weeks it was almost totally absorbed. No endothelialization (ET) was measurable at 2 weeks. By 4 weeks ET extended for a short distance from each anastomosis and there were no significant differences between the four graft groups. At 18 weeks, the HP, BHP, and FHP grafts showed a significant increase in ET compared with the ST graft (P < .01) but there were no significant differences between the three types of high-porosity graft. The differences in patency rates and neointimal thicknesses did not reach statistical significance. High-porosity PTFE grafts showed superior endothelialization in dogs; however, the enlarged ID of PTFE grafts increased intraoperative bleeding and postoperative seroma formation. Fibrin glue sealant controlled bleeding through the graft wall without affecting graft healing, but its sealant effect was not enough to prevent late fluid leakage.

Experimental and early clinical evaluation of vascular anastomoses with argon laser fusion and the use of absorbable guy sutures: A preliminary report

This study investigated the feasibility of forming vascular anastomoses by use of argon laser tissue fusion and absorbable, monofilament polydimethylsiloxane guy sutures. In initial animal studies femoral arteriovenous fistulas approximately 1.5 cm in length were created bilaterally in each of 10 dogs and were studied histologically at 2, 4, 8, 16, and 24 weeks (two animals in each interval). In each animal, one anastomosis (control) was formed with continuous 6-0 polypropylene suture, and the contralateral anastomosis (experimental) was performed with an argon laser (0.5 watt, 5 to 7 minutes exposure, energy fluence 1100 to 1500 joules/cm2 per 1 cm length) with stay sutures of 5-0 polydimethylsiloxane at 0.5 to 0.65 cm intervals. At removal, all anastomoses were patent without hematomas, aneurysms, or luminal narrowing. Histologic examination at 2 to 16 weeks demonstrated resorption of the biodegradable suture material by a local inflammatory reaction. By 24 weeks, laser-fused specimens had no evidence of suture material at the anastomotic line, and healing consisted of a bond between artery and vein wall tissues. Control suture specimens at the same intervals exhibited an organized fibrous tissue response to the suture. Clinical adaptability of this technology has subsequently been evaluated in five patients at 10 to 27 months (21.6 +/- 5.8) by physical examination and duplex scanning and demonstrate no evidence of abnormal healing. This study establishes the experimental and preliminary clinical feasibility of laser-fused anastomoses aligned by biodegradable guy sutures and supports further investigation and refinement of the technique.

Effects of cholesterol autoxidation derivatives on hexose transport in cultured aortic smooth muscle cells

Several cholesterol autoxidation derivatives known to be cytotoxic to arterial smooth muscle cells both in vivo and in vitro were shown to inhibit hexose transport in these cells in culture. Cholestane-3 beta, 5 alpha, 6 beta-triol was the most potent inhibitory sterol. The rapid onset of inhibition (15 min) and the reversibility of the effect upon removal of the sterol from the tissue culture medium suggests that the effect may be due to incorporation of the sterol into the plasma membrane. 25-Hydroxycholesterol, a potent inhibitor of sterol biosynthesis in cultured arterial smooth muscle cells, did not affect hexose transport up to 8 hr of incubation. The cytotoxic effect of 25-hydroxycholesterol, therefore, may be a consequence of the reduced sterol biosynthesis caused by this sterol.

Coinfection of Visceral Leishmaniasis and Mycobacterium in a Patient With Acquired Immunodeficiency Syndrome

We report a case of coinfection of visceral leishmaniasis and Mycobacterium avium-intracellulare in the same lesions in the small bowel and bone marrow of a 33-year-old man with acquired immunodeficiency syndrome who complained of abdominal pain and chronic diarrhea. The duodenal mucosa and bone marrow biopsy specimens showed numerous foamy macrophages packed with two forms of microorganisms that were identified histologically and ultrastructurally as Leishmania and Mycobacterium species. Visceral leishmaniasis is rarely suspected in patients residing in nonendemic countries including the United States. It should be included in the differential diagnosis for opportunistic infection in patients with acquired immunodeficiency syndrome. An appropriate travel history is important. To our knowledge, this is the first reported case showing coinfection of visceral leishmaniasis and Mycobacterium avium-intracelluulare in the same lesion in a patient with acquired immunodeficiency syndrome.