Natalia O Litbarg

Publications of Natalia O Litbarg

• Omentum facilitates liver regeneration.

  Authors: Ashok K Singh, Nishit Pancholi, Jilpa Patel, Natalia O Litbarg, Krishnamurthy P Gudehithlu, Perianna Sethupathi, Mark Kraus, George Dunea, Jose Al Arruda

  World journal of gastroenterology : WJG. 04/2009; 15(9):1057-64.

  AIM: To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats wereAIM: To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats were omentectomized; in another group the omentum was left in situ and was not activated, and in the third group the omentum was activated by polydextran particles. METHODS: We pre-activated the omentum by injecting polydextran particles and then made a small wedge wound in the rat liver to allow the omentum to fuse to the wound. We monitored the regeneration of the liver by determining the ratio of liver weight/body weight, by histological evaluation (including immune staining for cytokeratin-19, an oval cell marker), and by testing for developmental gene activation using reverse transcription polymerase chain reaction (RT-PCR). RESULTS: There was no liver regeneration in the omentectomized rats, nor was there significant regeneration when the omentum was not activated, even though in this instance the omentum had fused with the liver. In contrast, the liver in the rats with the activated omentum expanded to a size 50% greater than the original, and there was histologically an interlying tissue between the wounded liver and the activated omentum in which bile ducts, containing cytokeratin-19 positive oval cells, extended from the wound edge. In this interlying tissue, oval cells were abundant and appeared to proliferate to form new liver tissue. In rats pre-treated with drugs that inhibited hepatocyte growth, liver proliferation was ongoing, indicating that regeneration of the liver was the result of oval cell expansion. CONCLUSION: Activated omentum facilitates liver regeneration following injury by a mechanism that depends largely on oval cell proliferation.

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• Stromal cells cultured from omentum express pluripotent markers, produce high amounts of VEGF, and engraft to injured sites.

  Authors: Ashok K Singh, Jilpa Patel, Natalia O Litbarg, Krishnamurthy P Gudehithlu, Perianna Sethupathi, Jose A L Arruda, George Dunea

  Cell and tissue research. 05/2008; 332(1):81-8.

  When rat omentum becomes activated by intraperitoneal injection of inert polydextran particles, these particles are rapidly surrounded by cells that express markers of adult stem cells (SDF-1alpha,When rat omentum becomes activated by intraperitoneal injection of inert polydextran particles, these particles are rapidly surrounded by cells that express markers of adult stem cells (SDF-1alpha, CXCR4, WT-1) and of embryonic pluripotent cells (Oct-4, Nanog, SSEA-1). We have cultured such cells, because they may offer a convenient source of adult stem cells, and have found that they retain stem cell markers and produce high levels of vascular endothelial growth factor for up to ten passages. After systemic or local injection of these cultured cells into rats with acute injury of various organs, the cells specifically engraft at the injured sites. Thus, our experiments show that omental stromal cells can be cultured from activated omentum, and that these cells exhibit stem cell properties enabling them to be used for repair and possibly for the regeneration of damaged tissues.

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• Activated omentum becomes rich in factors that promote healing and tissue regeneration.

  Authors: Natalia O Litbarg, Krishnamurthy P Gudehithlu, Perianna Sethupathi, Jose A L Arruda, George Dunea, Ashok K Singh

  Cell and tissue research. 07/2007; 328(3):487-97.

  In order to study the mechanism by which an omental pedicle promotes healing when applied to an injured site, we injected a foreign body into the abdominal cavity to activate the omentum. One weekIn order to study the mechanism by which an omental pedicle promotes healing when applied to an injured site, we injected a foreign body into the abdominal cavity to activate the omentum. One week after the injection, we isolated the omentum and measured blood vessel density, blood content, growth and angiogenesis factors (VEGF and others), chemotactic factors (SDF-1 alpha), and progenitor cells (CXCR-4, WT-1). We found that the native omentum, which consisted mostly of adipose tissue, expanded the mass of its non-adipose part (milky spots) 15- to 20-fold. VEGF and other growth factors increased by two- to four-fold, blood vessel density by three-fold, and blood content by two-fold. The activated omentum also showed increases in SDF-1 alpha, CXCR-4, and WT-1 cells (factors and cells positively associated with tissue regeneration). Thus, we propose that an omentum activated by a foreign body (or by injury) greatly expands its milky-spot tissue and becomes rich in growth factors and progenitor cells that facilitate the healing and regeneration of injured tissue.

• Impaired integration of endothelial progenitor cells in capillaries of diabetic wounds is reversible with vascular endothelial growth factor infusion.

  Authors: Ashok K Singh, Krishnamurthy P Gudehithlu, Shreya Patri, Natalia O Litbarg, Perianna Sethupathi, Jose A L Arruda, George Dunea

  Translational research : the journal of laboratory and clinical medicine. 06/2007; 149(5):282-91.

  To understand impaired angiogenesis in diabetic wounds, polyvinyl tubes were implanted subcutaneously in rats to form a granulation tissue for 2 weeks and the granulation tissue was studied afterTo understand impaired angiogenesis in diabetic wounds, polyvinyl tubes were implanted subcutaneously in rats to form a granulation tissue for 2 weeks and the granulation tissue was studied after inducing diabetes with streptozotocin. By 1 week of diabetes, the granulation tissue was bloody and thinner than controls, its medial layer was depleted of microvessels, and the surviving vessels appeared dehisced. Vascular endothelial growth factor (VEGF) in the diabetic granulation tissue was reduced by 50% compared with control granulation tissue. After 3 days of diabetes, the diabetic tissue showed a greater degree of apoptosis in the microvessels. Chemotactic factors [stromal cell-derived factor-1alpha and chemokine receptor-4 (CXCR-4)], responsible for attracting bone marrow cells, showed equal intensity in control and diabetic tissues. As expected, progenitor endothelial CD-34 cells were observed in abundance in both the control and the diabetic granulation tissues. However, although the CD-34-positive cells appeared mostly to be integrated in the blood vessels of the control tissue, fewer such cells were present in the blood vessels of the diabetic tissues, suggesting that CD-34 failed to integrate into new blood vessels. Infusion of VEGF in the granulation tissue of diabetic rats for 1 week resulted in complete prevention of the microvascular defect compared with the contralateral granulation tissue that showed the typical diabetic changes. It was concluded that diabetes causes reduction of VEGF in the wound, resulting in loss of blood vessels by apoptosis and possible failure of CD-34 cells to integrate into the vessel structure.

• Transplanting fragments of diabetic pancreas into activated omentum gives rise to new insulin producing cells.

  Authors: Ashok K Singh, Krishnamurthy P Gudehithlu, Natalia O Litbarg, Perianna Sethupathi, Jose A L Arruda, George Dunea

  Biochemical and biophysical research communications. 04/2007; 355(1):258-62.

  To determine if pancreatic progenitor cells can be induced to form insulin producing cells in vivo, we auto-transplanted fragments of streptozotocin-induced diabetic pancreas into omentumTo determine if pancreatic progenitor cells can be induced to form insulin producing cells in vivo, we auto-transplanted fragments of streptozotocin-induced diabetic pancreas into omentum pre-injected with a foreign material. As shown previously, omentum pre-activated in this manner becomes rich in growth factors and progenitor cells. After auto-transplanting diabetic pancreas in the activated omentum, new insulin secreting cells appeared in the omentum in niches surrounding the foreign particles--a site previously shown to harbor progenitor cells. Extracts of these omenta contained measurable insulin. Four of eight diabetic animals treated in this manner became normoglycemic. This shows that new insulin producing cells can be regenerated from diabetic pancreas by auto-transplanting pancreatic fragments into the activated omentum, an environment rich in growth factors and progenitor cells.

• Antagonism of vascular endothelial growth factor results in microvessel attrition and disorganization of wound tissue.

  Authors: Krishnamurthy P Gudehithlu, Naila Ahmed, Henry Wu, Natalia O Litbarg, Sandra L Garber, Jose A L Arruda, George Dunea, Ashok K Singh

  The Journal of laboratory and clinical medicine. 05/2005; 145(4):194-203.

  Vascular endothelial growth factor (VEGF) is a potent growth factor that is indispensable for the development of blood vessels in the fetus and for wound healing in adults. VEGF likely plays a roleVascular endothelial growth factor (VEGF) is a potent growth factor that is indispensable for the development of blood vessels in the fetus and for wound healing in adults. VEGF likely plays a role in maintaining the blood vessels once they have been formed. It is not clear, however, whether a low tissue VEGF (caused either by disease or by systemic administration of VEGF antagonists) can cause abnormalities in preexisting blood vessels, especially of wound tissue that requires high local levels of VEGF for healing. The present study investigated the effect of VEGF antagonism on blood vessels of foreign-body granulomas (a model of wound-healing tissue). Granulomas were induced by implanting perforated polyvinyl tubes into the subcutaneous tissue of rats and allowed to develop for 14 days, at which time the implanted tubes were completely encapsulated by the subcutaneous tissue. The encapsulated granulomas consisted of 3 distinct histological layers, of which the middle layer was well perfused by a rich supply of microvessels. Morphologically, the granuloma remained "stable" after developing for 14 days. At 1 week, VEGF levels in the granuloma fluid, which is in equilibrium with the interstitial fluid, were 25 times higher than in the plasma. VEGF levels in the granuloma fluid continued to increase for up to 3 weeks, reflecting the high dependence of the wound tissue on ambient VEGF levels. After injection of the VEGF receptor antagonist in the fully formed granuloma, the preexisting blood vessels in the middle layer regressed and underwent apoptosis, accompanied by expansion of the extracellular matrix (predominately collagen I) into areas normally devoid of matrix. We conclude that wound tissue is sensitive to ambient VEGF levels, and that a low VEGF condition resulting from VEGF receptor antagonism can disrupt the healing of wound tissue.

• Decreased urinary peptide excretion in patients with renal disease.

  Authors: Ashok Singh, Krishnamurthy P Gudehithlu, Gigi Le, Natalia O Litbarg, Viorica Khalili, Jane Vernik, Peter Hart, Jose A L Arruda, George Dunea

  American journal of kidney diseases : the official journal of the National Kidney Foundation. 01/2005; 44(6):1031-8.

  BACKGROUND: Normal urine contains low-molecular-weight peptides or protein fragments that have been poorly studied, primarily because of the technical difficulty of measuring peptides in the presenceBACKGROUND: Normal urine contains low-molecular-weight peptides or protein fragments that have been poorly studied, primarily because of the technical difficulty of measuring peptides in the presence of proteins. We studied these substances in healthy subjects and patients with renal disease and varying degrees of proteinuria to understand the factors that determine their excretion. METHODS: We estimated these substances as the difference between results using the Lowry method (which detects both proteins and peptides) and those obtained using the dye-binding Bradford (Biorad) method (Biorad Laboratories Inc, Hercules, CA; which detects only proteins). RESULTS: We validated this 2-assay approach to measure peptide levels by showing that such proteins as immunoglobulin G, albumin, and lysozyme were measured equally by the Lowry and Biorad methods, whereas degraded proteins were recognized by the Lowry method only, but not by the Biorad method. We found that healthy subjects excreted less than 200 mg of protein, but 3 to 4 g of peptides/g creatinine; thus, peptides constituted approximately 95% of total protein material excreted in urine. Patients with renal disease and proteinuria had a progressive decrease in peptide excretion, ranging from 3 to 0 g/g creatinine. Twenty-five percent of nephrotic patients (18 of 72 patients) excreted very small amounts of peptides in urine (0% to 10% of total protein material). CONCLUSION: We found that healthy persons excrete substantial amounts of peptides in urine, and this excretion decreases in the presence of proteinuric renal disease. It is possible that these peptides in urine arise from the tubular degradation of filtered proteins and exocytosis of protein fragments toward the urinary side, a process that becomes increasingly impaired as proteinuria increases.