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Piotr Witkowski

Publications and source records attributed to Piotr Witkowski.

11 recordsLinked to original sources
PubMed2026

Diabetes related genetics and outcomes after total pancreatectomy with islet autotransplantation.

CONTEXT: Approximately 20% of patients with chronic pancreatitis achieve insulin independence one year after total pancreatectomy with islet autotransplantation (TPIAT), an outcome associated with younger age and lower pre-transplant HbA1c. The contribution of diabetes-related genetics to TPIAT outcomes is unknown. Genetic risk scores (GRS) are associated with C-peptide levels in type 1 (T1D) and type 2 (T2D) diabetes. OBJECTIVE: To evaluate whether T1D and T2D GRS and partitioned metabolic polygenic scores (PGS) are associated with diabetes before TPIAT and metabolic outcomes one year after transplant. METHODS: We genotyped 318 patients with chronic pancreatitis undergoing TPIAT in the multicenter "Advancing Treatment for Pancreatitis: A Prospective Observational Study of TPIAT" using a global screening array. Regression models assessed associations of T1D- and T2D-GRS and metabolic PGS with diabetes outcomes one year after TPIAT. RESULTS: Participants were 29±17 years old, 61% female, 84% non-Hispanic White, and 13% had diabetes prior to transplant. T2D-GRS was higher among those with pre-TPIAT diabetes (-0.6±0.3 versus -0.8±0.2, p=0.003) and was associated with higher pre-transplant HbA1c (β=0.19 % per 1-SD [95% CI:0.04, 0.33], p = 0.011). Adjusted for genotype-derived ancestry and islet equivalents/kg, the beta-cell PGS was associated with higher insulin dose (β=0.05 units/kg/day per 1-SD, [95%CI:0.01, 0.09], p=0.016) and higher insulin dose adjusted A1c (IDAA1c) (β=0.34[95%CI:0.03, 0.67], p=0.029) 1-year post-transplant. The lipodystrophy PGS was associated with higher IDAA1c (β=0.38 [95%CI:0.06, 0.69], p=0.019) and lower fasting C-peptide (β=-0.09 [95%CI:-0.18, 0], p=0.041) at 1 year. CONCLUSIONS: T2D genetic risk is associated with diabetes prior to TPIAT, and beta cell and lipodystrophy PGS are associated with post-TPIAT diabetes outcomes. Diabetes-related genetics may influence transplantation outcomes and inform metabolic heterogeneity.

C-peptide↗
PubMed2006

Visualizing pancreatic beta-cell mass with [11C]DTBZ.

Beta-cell mass (BCM) influences the total amount of insulin secreted, varies by individual and by the degree of insulin resistance, and is affected by physiologic and pathologic conditions. The islets of Langerhans, however, appear to have a reserve capacity of insulin secretion and, overall, assessments of insulin and blood glucose levels remain poor measures of BCM, beta-cell function and progression of diabetes. Thus, novel noninvasive determinations of BCM are needed to provide a quantitative endpoint for novel therapies of diabetes, islet regeneration and transplantation. Built on previous gene expression studies, we tested the hypothesis that the targeting of vesicular monoamine transporter 2 (VMAT2), which is expressed by beta cells, with [11C]dihydrotetrabenazine ([11C]DTBZ), a radioligand specific for VMAT2, and the use of positron emission tomography (PET) can provide a measure of BCM. In this report, we demonstrate decreased radioligand uptake within the pancreas of Lewis rats with streptozotocin-induced diabetes relative to their euglycemic historical controls. These studies suggest that quantitation of VMAT2 expression in beta cells with the use of [11C]DTBZ and PET represents a method for noninvasive longitudinal estimates of changes in BCM that may be useful in the study and treatment of diabetes.

Animals↗
PubMed2005

Catalytic degradation of vitamin D up-regulated protein 1 mRNA enhances cardiomyocyte survival and prevents left ventricular remodeling after myocardial ischemia.

Vitamin D3 up-regulated protein 1 (VDUP1) is a key mediator of oxidative stress on various cellular processes via downstream effects on apoptosis signaling kinase 1 (ASK1) and p38 mitogen-activated protein kinase (MAPK). Here, we report that VDUP1 expression is significantly increased in rat hearts following acute myocardial ischemia, suggesting it may have important regulatory effects on cardiac physiological processes during periods of oxidative stress. Transfection of H9C2 cardiomyoblasts with a sequence-specific VDUP1 DNA enzyme to down-regulate VDUP1 mRNA expression significantly reduced apoptosis and enhanced cell survival under conditions of H(2)O(2) stress, and these effects involved inhibition of ASK1 activity. Direct intracardiac injection of the DNA enzyme at the time of acute myocardial infarction reduced myocardial VDUP1 mRNA expression and resulted in prolonged reduction in cardiomyocyte apoptosis and ASK1 activity. Moreover, down-regulation of VDUP1 was accompanied by significant reduction in cardiac expression of pro-collagen type I alpha2 mRNA level, as well as marked reduction in myocardial scar formation. These features were accompanied by significant improvement in cardiac function. Together, these results suggest a direct role for VDUP1 in the adverse effects of ischemia and oxidative stress on cardiomyocyte survival, left ventricular collagen deposition, and cardiac function. Strategies to inhibit VDUP1 expression and/or function during acute ischemic events may be beneficial to cardiac functional recovery and prevention of left ventricular remodeling.

Animals↗
PubMed2005

Downregulated expression of plasminogen activator inhibitor-1 augments myocardial neovascularization and reduces cardiomyocyte apoptosis after acute myocardial infarction.

OBJECTIVES: The aim of this study was to examine whether selective plasminogen activator inhibitor type 1 (PAI-1) downregulation in the acutely ischemic heart increases the myocardial microvasculature and improves cardiomyocyte (CM) survival. BACKGROUND: Endogenous myocardial neovascularization is an important process enabling cardiac functional recovery after acute myocardial infarction. Expression of PAI-1, a potent inhibitor of angiogenesis, is induced in ischemic heart tissue. METHODS: A sequence-specific catalytic deoxyribonucleic acid (DNA) enzyme was used to reduce PAI-1 levels in cultured endothelial cells and in ischemic myocardium. At the time of coronary artery ligation, rats were randomized into three groups, each receiving an intramyocardial injection (IMI) of a single dose at three different sites of the peri-infarct region consisting, respectively, of DNA enzyme E2 targeting rat PAI-1 (E2), scrambled control DNA enzyme (E0), or saline. Cardiomyocyte apoptosis, capillary density, and echocardiography were studied two weeks following infarction. RESULTS: The E2 DNA enzyme, which efficiently inhibited rat PAI-1 expression in vitro, induced prolonged suppression (>2 weeks) of PAI-1 messenger ribonucleic acid and protein in rat heart tissues after a single IMI. At two weeks, hearts from experimental rats had over five-fold greater capillary density, 70% reduction in apoptotic CMs, and four-fold greater functional recovery compared with controls. CONCLUSIONS: These results imply a causal relationship between elevated PAI-1 levels in ischemic hearts and adverse outcomes, and they suggest that strategies to reduce cardiac PAI-1 activity may augment neovascularization and improve functional recovery.

Animals↗
PubMed2005

Additive effects of endothelial progenitor cells combined with ACE inhibition and beta-blockade on left ventricular function following acute myocardial infarction.

Animal studies have demonstrated the efficacy of endothelial progenitor cells (EPCs) in preventing left ventricular (LV) remodelling following myocardial infarction (MI). Preliminary human studies are underway, yet no studies have demonstrated efficacy in combination with standard medical therapy, i.e. angiotensin-converting enzyme (ACE) inhibitors and beta-blockers. Nude rats underwent left anterior descending coronary artery ligation to induce MI. Animals were randomised to receive no treatment (MI, n = 5), quinapril 200 mg/L + metoprolol 2 g/L (ACE/BB, n = 5), two million EPCs intravenously (EPC, n = 5)or both (ACE/BB + EPC [n = 5]), then sacrificed after two weeks treatment. ACE/BB resulted in a 75% reduction in fibrosis in the region remote from the MI (p < 0.05), but EPC therapy had little effect here. Conversely, EPC therapy induced neovascularisation at the peri-infarct rim, thereby preventing peri-infarct apoptosis by 81% (p < 0.05). Acting via different but complementary mechanisms, the combination of ACE/BB + EPCs resulted in a greater overall improvement in LV function on echocardiography than either therapy alone. Clinical trials using stem cell therapy in conjunction with standard medical treatment are warranted.

Adrenergic beta-Antagonists↗
PubMed2004

Identification of tissue-restricted transcripts in human islets.

The purpose of our study was to identify transcripts specific for tissue-restricted, membrane-associated proteins in human islets that, in turn, might serve as markers of healthy or diseased islet cell masses. Using oligonucleotide chips, we obtained gene expression profiles of human islets for comparison with the profiles of exocrine pancreas, liver, and kidney tissue. As periislet presence of type 1 interferon is associated with the development of type 1 diabetes, the expression profile of human islets treated ex vivo with interferon-alpha2beta (IFNalpha2beta) was also determined. A set of genes encoding transmembrane- or membrane-associated proteins with novel islet-restricted expression was resolved by determining the intersection of the islet set with the complement of datasets obtained from other tissues. Under the influence of IFNalpha2beta, the expression levels of transcripts for several of the identified gene products were up- or down-regulated. One of the islet-restricted gene products identified in this study, vesicular monoamine transporter type 2, was shown to bind [3H]dihydrotetrabenazine, a ligand with derivatives suitable for positron emission tomography imaging. We report here the first comparison of gene expression profiles of human islets with other tissues and the identification of a target molecule with possible use in determining islet cell masses.

Culture Techniques↗
PubMed2004

Rat CD8+ FOXP3+ T suppressor cells mediate tolerance to allogeneic heart transplants, inducing PIR-B in APC and rendering the graft invulnerable to rejection.

Human CD8+ FOXP3+ T suppressor cells (TS) were previously shown to induce the expression of the inhibitory receptors, Immunoglobulin-like transcript (ILT) 3 and ILT4 on dendritic and endothelial cells, rendering them tolerogenic to allogeneic T cells. We have demonstrated the importance of CD8+ TS in a rat model of heart allo-transplantation. Tolerance was induced in ACI recipients by multiple transfusions of UVB-irradiated blood from Lewis heart donors. CD8+ T cells from tolerant ACI rats expressed FOXP3, transferred tolerance to naive secondary hosts and induced the upregulation of the inhibitory receptor, paired immunoglobulin-like receptor (PIR)-B, an ILT4 orthologue, in Lewis dendritic cells (DC) and heart endothelial cells (EC). When long-term surviving Lewis heart allografts with PIR-B+ EC were retransplanted from a primary to a secondary ACI recipient they did not elicit rejection. This study focuses attention on the need to develop agents that act directly on graft EC in order to achieve tolerance.

Animals↗
PubMed2003

Immature rat myeloid dendritic cells generated in low-dose granulocyte macrophage-colony stimulating factor prolong donor-specific rat cardiac allograft survival.

BACKGROUND: Because the differential polarization of T cells in response to antigen presentation is dependent on the maturational state of dendritic cells (DCs), we hypothesized that the adoptive transfer of immature myeloid DCs (iMDCs) would prolong graft survival. METHODS: To evaluate this hypothesis, we studied the effects of transfer of iMDCs and mature myeloid DCs (mMDCs) on rat cardiac allograft survival. RESULTS: Whereas iMDCs that do not express costimulatory molecules induce allogeneic T-cell hyporesponsiveness in coculture studies, mMDCs that express high levels of major histocompatibility complex class II costimulatory and maturation molecules induce a robust allostimulatory T-cell response. Adoptive transfer of Wistar Furth iMDCs, unlike mMDCs, 7 days before cardiac transplantation significantly prolonged graft survival. It was important that adoptive transfer of iMDCs combined with 0.5 mL antilymphocyte serum (ALS) transient immunosuppression on day -7 led to donor-specific permanent graft survival in 50% of recipients. In contrast, adoptive transfer of mMDCs combined with ALS led to graft survival similar to that in recipients treated with ALS alone. Stimulation of CD4 T cells isolated from the spleen of unresponsive allograft recipients with donor antigen resulted in donor-specific hyporesponsiveness and production of interleukin (IL)-10 and transforming growth factor-beta but not IL-4 and interferon-gamma. The tolerant T-cell unresponsiveness was reversed by the addition of IL-2. CONCLUSION: Our data confirming the immunoregulatory effect of immature DCs indicate that induction of transplant tolerance by iMDCs is partly dependent on in vivo generation of regulatory T cells. This finding suggests that immunization with immature donor DCs has therapeutic potential for the induction of transplant tolerance and treatment of autoimmune diseases.

Adoptive Transfer↗
PubMedDate not supplied

CD4+CD25+ regulatory T cells mediate acquired transplant tolerance.

The Holy Grail of clinical organ transplantation is the safe induction of allograft tolerance. Transplant tolerance has been successfully induced in animal models. Since T cells play a pivotal role in graft rejection, modulating T cell function has been the primary focus of studies aimed at inducing transplant tolerance. Rodent models of transplant tolerance induction include central deletion and peripheral mechanisms involving activation-induced cell death (AICD), anergy, immune deviation, and production of regulatory T cells. These mechanisms are not mutually exclusive. Although clonal deletion and anergy limit self-reactive T cells in the thymus, these mechanisms alone are not sufficient for controlling self-reactive T cells in the periphery. There is now evidence that the adult animal harbors two functionally distinct populations of CD4(+) T cells; one mediates autoimmune disease and the other dominantly inhibits it. The latter cells express CD4, CD25 and CTLA-4. These thymus-derived T cells have recently been shown to mediate the induction and maintenance of transplant tolerance. These CD4(+)CD25(+) T cells are similar in origin, phenotype, and function to those that maintain natural self-tolerance and T cell homeostasis in the periphery. Against this background, is it possible that alloantigen specific regulatory T cells might be generated and expanded ex vivo before organ transplantation and then infused to induce long-term tolerance, perhaps without the need for chronic immunosuppression?

Animals↗