Publications by year
Ahmed U, Anwar A, Savage RS, Costa ML, Mackay N, Filer A, Raza K, Watts RA, Winyard PG, Tarr J, et al
(2015). Biomarkers of early stage osteoarthritis, rheumatoid arthritis and musculoskeletal health. Sci Rep
Biomarkers of early stage osteoarthritis, rheumatoid arthritis and musculoskeletal health.
There is currently no biochemical test for detection of early-stage osteoarthritis (eOA). Tests for early-stage rheumatoid arthritis (eRA) such as rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibodies require refinement to improve clinical utility. We developed robust mass spectrometric methods to quantify citrullinated protein (CP) and free hydroxyproline in body fluids. We detected CP in the plasma of healthy subjects and surprisingly found that CP was increased in both patients with eOA and eRA whereas anti-CCP antibodies were predominantly present in eRA. A 4-class diagnostic algorithm combining plasma/serum CP, anti-CCP antibody and hydroxyproline applied to a cohort gave specific and sensitive detection and discrimination of eOA, eRA, other non-RA inflammatory joint diseases and good skeletal health. This provides a first-in-class plasma/serum-based biochemical assay for diagnosis and type discrimination of early-stage arthritis to facilitate improved treatment and patient outcomes, exploiting citrullinated protein and related differential autoimmunity. Abstract
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Holley JE, Bremer E, Kendall AC, de Bruyn M, Helfrich W, Tarr JM, Newcombe J, Gutowski NJ, Eggleton P (2013). CD20+inflammatory T-cells are present in blood and brain of multiple sclerosis patients and can be selectively targeted for apoptotic elimination. Multiple Sclerosis and Related Disorders
Ellis TP, Choudhury RH, Kaul K, Chopra M, Kohner EM, Tarr JM, Chibber R
(2013). Diabetic retinopathy and atherosclerosis: is there a link?. Curr Diabetes Rev
Diabetic retinopathy and atherosclerosis: is there a link?
Diabetic retinopathy (DR) is the leading cause of blindness amongst the working-age population, and diabetes accelerated cardiovascular disease (CVD) the commonest cause of death in diabetic patients. Although, there is evidence suggesting a close association between DR and CVD, particularly in patients with Type 2 diabetes, the pathophysiology underlying the link is unclear. Here we review common risk factors and pathogenic mechanisms linking DR and CVD, and aim to highlight the need for a more holistic view of the management of diabetes and its complications. The understanding of the link between the two complications could eventually lead to refined management strategies and improved patient outcomes in the expanding diabetes epidemic. Abstract
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Tarr JM, Kaul K, Chopra M, Kohner EM, Chibber R
(2013). Pathophysiology of diabetic retinopathy. ISRN Ophthalmol
Pathophysiology of diabetic retinopathy.
Diabetes is now regarded as an epidemic, with the population of patients expected to rise to 380 million by 2025. Tragically, this will lead to approximately 4 million people around the world losing their sight from diabetic retinopathy, the leading cause of blindness in patients aged 20 to 74 years. The risk of development and progression of diabetic retinopathy is closely associated with the type and duration of diabetes, blood glucose, blood pressure, and possibly lipids. Although landmark cross-sectional studies have confirmed the strong relationship between chronic hyperglycaemia and the development and progression of diabetic retinopathy, the underlying mechanism of how hyperglycaemia causes retinal microvascular damage remains unclear. Continued research worldwide has focussed on understanding the pathogenic mechanisms with the ultimate goal to prevent DR. The aim of this paper is to introduce the multiple interconnecting biochemical pathways that have been proposed and tested as key contributors in the development of DR, namely, increased polyol pathway, activation of protein kinase C (PKC), increased expression of growth factors such as vascular endothelial growth factor (VEGF) and insulin-like growth factor-1 (IGF-1), haemodynamic changes, accelerated formation of advanced glycation endproducts (AGEs), oxidative stress, activation of the renin-angiotensin-aldosterone system (RAAS), and subclinical inflammation and capillary occlusion. New pharmacological therapies based on some of these underlying pathogenic mechanisms are also discussed. Abstract
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Tarr JM, Ding N, Kaul K, Antonell A, Pérez-Jurado LA, Chibber R
(2012). Cellular crosstalk between TNF-α, NADPH oxidase, PKCβ2, and C2GNT in human leukocytes. Cell Signal
Cellular crosstalk between TNF-α, NADPH oxidase, PKCβ2, and C2GNT in human leukocytes.
Increasing evidence suggests that chronic, sub-clinical inflammation plays an important role in the pathogenesis of diabetic retinopathy. We have established the potential role of the inflammatory enzyme, core 2 β-1, 6-N-acetylglucosaminyltransferase (C2GNT) in diabetic retinopathy. The present study was designed to explore the NADPH oxidase signaling pathway in the tumor necrosis factor-alpha (TNF-α)-induced activity of C2GNT in leukocytes. Human leukocytes (U937 cells) and an Epstein-Barr-transformed lymphoblastoid cell line deficient in p47phox (F10007 cells) were used for the study. Cells were exposed to TNF-α for 24h in the presence and absence of 1) NADPH oxidase inhibitors (apocynin and scrambled and unscrambled gp91ds-tat), 2) LY379196 (specific protein kinase C β1/2 (PKCβ1/2) inhibitor), and 3) the antioxidant tiron. Subsequent C2GNT and NADPH activity was measured and the adhesion of U937 and F10007 cells to endothelial cells was assessed. TNF-α-induced C2GNT activity (1813±326 pmol/h/mg protein) (mean±SEM) in human leukocytes was significantly reversed with apocynin (153±82 pmol/h/mg protein), unscrambled gp91ds-tat (244±122 pmol/h/mg protein) and tiron (756±87 pmol/h/mg protein). We further supported this C2GNT-NADPH oxidase link using p47phox-deficient leukocytes. The deficiency in p47phox prevented TNF-α-induced NADPH oxidase and C2GNT activity and adherence to endothelial cells. The response to TNF-α was restored by transfection with an expression plasmid containing a p47phox cDNA inserted in the sense direction. Our results demonstrate for the first time a novel signaling crosstalk between TNF-α, NADPH oxidase, PKCβ1/2 and C2GNT in leukocytes. Abstract
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Kaul K, Tarr JM, Ahmad SI, Kohner EM, Chibber R
(2012). Introduction to diabetes mellitus. Adv Exp Med Biol
Introduction to diabetes mellitus.
The chronic metabolic disorder diabetes mellitus is a fast-growing global problem with huge social, health, and economic consequences. It is estimated that in 2010 there were globally 285 million people (approximately 6.4% of the adult population) suffering from this disease. This number is estimated to increase to 430 million in the absence of better control or cure. An ageing population and obesity are two main reasons for the increase. Furthermore it has been shown that almost 50% of the putative diabetics are not diagnosed until 10 years after onset of the disease, hence the real prevalence of global diabetes must be astronomically high. This chapter introduces the types of diabetes and diabetic complications such as impairment of immune system, periodontal disease, retinopathy, nephropathy, somatic and autonomic neuropathy, cardiovascular diseases and diabetic foot. Also included are the current management and treatments, and emerging therapies. Abstract
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Szabó-Taylor K, Eggleton P, Turner CAL, Lo Faro ML, Tarr JM, Tóth S, Whiteman M, Haigh RC, Littlechild JA, Winyard PG, et al
(2012). Lymphocytes from rheumatoid arthritis patients have elevated levels of intracellular
peroxiredoxin 2, and a greater frequency of cells with exofacial peroxiredoxin 2,
compared with healthy human lymphocytes. The International Journal of Biochemistry and Cell Biology
Lymphocytes from rheumatoid arthritis patients have elevated levels of intracellular
peroxiredoxin 2, and a greater frequency of cells with exofacial peroxiredoxin 2,
compared with healthy human lymphocytes
Peroxiredoxin 2 has immune regulatory functions, but its expression in human peripheral blood Abstract
lymphocytes and extracellular fluid in healthy subjects and rheumatoid arthritis patients is poorly
described. In the present study, the median intracellular peroxiredoxin 2 protein content of
lymphocytes from rheumatoid arthritis patients was more than two-fold higher compared with
healthy subjects’ lymphocytes. Flow cytometry detected peroxiredoxin 2 on the surface of ca.
8% of T cells and ca. 56% of B cells (median % values) of all subjects analyzed. In the total
lymphocyte population from rheumatoid arthritis patients, few cells (median, 6%) displayed
surface peroxiredoxin 2. In contrast, a significantly increased proportion of interleukin-17+ve
lymphocytes were peroxiredoxin 2+ve (median, 39%). We suggest that crucial inflammatory cell
subsets, i.e. interleukin-17+ve T cells, exhibit increased exofacial redox-regulating enzymes and
that peroxiredoxin 2 may be involved in the persistence of pro-inflammatory cells in chronic
Stamp LK, Khalilova I, Tarr JM, Senthilmohan R, Turner R, Haigh RC, Winyard PG, Kettle AJ
(2012). Myeloperoxidase and oxidative stress in rheumatoid arthritis. Rheumatology (Oxford)
Myeloperoxidase and oxidative stress in rheumatoid arthritis.
OBJECTIVE: to determine whether MPO contributes to oxidative stress and disease activity in RA and whether it produces hypochlorous acid in SF. METHODS: Plasma and where possible SF were collected from 77 RA patients while 120 healthy controls supplied plasma only. MPO and protein carbonyls were measured by ELISAs. 3-Chlorotyrosine in proteins and allantoin in plasma were measured by mass spectrometry. RESULTS: Plasma MPO concentrations were significantly higher in patients with RA compared with healthy controls [10.8 ng/ml, inter-quartile range (IQR): 7.2-14.2; P3.2) and those with low disease activity (LDA; DAS-28 ≤ 3.2) (HDA 27.9 ng/ml, 20.2-34.1 vs LDA 22.1 ng/ml, 16.9-34.9; P>0.05). There was a significant relationship between plasma MPO and DAS-28 (r=0.35; P=0.005). Plasma protein carbonyls and allantoin were significantly higher in patients with RA compared with the healthy controls. MPO protein was significantly higher in SF compared with plasma (median 624.0 ng/ml, IQR 258.4-2433.0 vs 30.2 ng/ml, IQR 25.1-50.9; P Abstract
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Chopra M, Kaul K, Tarr J, Choudhury R, Kohner EM, Chibber R (2012). Oxidative stress in diabetic neuropathy: source of reactive oxygen species. Endocrinology Studies, 2(2).
Tarr JM, Kaul K, Wolanska K, Kohner EM, Chibber R
(2012). Retinopathy in diabetes. Adv Exp Med Biol
Retinopathy in diabetes.
With the incidence, and prevalence of diabetes mellitus increasing worldwide, diabetic retinopathy is expected to reach epidemic proportions. The aim of this chapter is to introduce diabetic retinopathy, a leading cause of blindness in people of the working age. The clinical course of retinopathy, anatomical changes, its pathogenesis and current treatment are described, followed by an overview of the emerging drug therapies for the potential treatment of this sight-threatening complication of diabetes. Abstract
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Tarr JM, Kaul K, Kohner EM, Chibber R (2011). Diabetic retinopathy: major unmet medical challenge. Endocrinology Studies, 1(1).
Eggleton P, Bremer E, Tarr J, De Bruyn M, Helfrich W, Kendall K, Haigh R, Viner N, Winyard PG (2011). Frequency of Th17 CD20+ cells in the peripheral blood of rheumatoid arthritis patients is higher compared to healthy subjects. Arthritis research and therapy
Tarr JM, Young PJ, Morse R, Shaw DJ, Haigh R, Petrov PG, Johnson SJ, Winyard PG, Eggleton P
(2010). A mechanism of release of calreticulin from cells during apoptosis. J Mol Biol
A mechanism of release of calreticulin from cells during apoptosis.
Calreticulin (CRT) is an endoplasmic reticulum (ER) chaperone responsible for glycoprotein folding and Ca(2+) homeostasis. CRT also has extracellular functions, e.g. tumor and apoptotic cell recognition and wound healing, but the mechanism of CRT extracellular release is unknown. Cytosolic localization of CRT is determined by signal peptide and subsequent retrotranslocation of CRT into the cytoplasm. Here, we show that under apoptotic stress conditions, the cytosolic concentration of CRT increases and associates with phosphatidylserine (PS) in a Ca(2)(+)-dependent manner. PS distribution is regulated by aminophospholipid translocase (APLT), which maintains PS on the cytosolic side of the cell membrane. APLT is sensitive to redox modifications of its SH groups by reactive nitrogen species. During apoptosis, both CRT expression and the concentration of nitric oxide (NO) increase. By using S-nitroso-l-cysteine-ethyl-ester, an intracellular NO donor and inhibitor of APLT, we showed that PS and CRT externalization occurred together in an S-nitrosothiol-dependent and caspase-independent manner. Furthermore, the CRT and PS are relocated as punctate clusters on the cell surface. Thus, CRT induced nitrosylation and its externalization with PS could explain how CRT acts as a bridging molecule during apoptotic cell clearance. Abstract
Whiteman M, Haigh R, Tarr JM, Gooding KM, Shore AC, Winyard PG
(2010). Detection of hydrogen sulfide in plasma and knee-joint synovial fluid from rheumatoid arthritis patients: relation to clinical and laboratory measures of inflammation. Ann N Y Acad Sci
Detection of hydrogen sulfide in plasma and knee-joint synovial fluid from rheumatoid arthritis patients: relation to clinical and laboratory measures of inflammation.
Blood concentrations of hydrogen sulfide (H(2)S) are markedly elevated in several animal models of inflammation. Pharmacological inhibition of H(2)S synthesis reduces inflammation and swelling, suggesting that H(2)S is a potential inflammatory mediator. However, it is currently unknown whether H(2)S synthesis is perturbed in human inflammatory conditions or whether H(2)S is present in synovial fluid. We analyzed paired plasma and synovial fluid (SF) aspirates from rheumatoid arthritis (RA; n= 20) and osteoarthritis (OA; n= 4) patients and plasma from age matched healthy volunteers (n= 20). Median plasma H(2)S concentrations from healthy volunteers and RA and OA patients were 37.6, 36.6, and 37.6 microM, respectively. In RA patients, median synovial fluid H(2)S levels (62.4 microM) were significantly higher than paired plasma (P= 0.002) and significantly higher than in synovial fluid from OA patients (25.1 microM; P= 0.009). SF H(2)S levels correlated with clinical indices of disease activity (tender joint count, r= 0.651; P < 0.05) and markers of chronic inflammation; Europhile count (r=-0.566; P < 0.01) and total white cell count (r=-0.703; P < 0.01). Our study shows for the first time that H(2)S is present in synovial fluid and levels correlated with inflammatory and clinical indices in RA patients. Abstract
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Tarr JM, Winyard PG, Haigh R, Viner N, Eggleton P (2010). Extracellular calreticulin accumulates in the joints of rheumatoid arthritis patients and inhibits FasL (CD95L) mediated apoptosis of T cells. Arthritis and Rheumatism, 62(10), 2919-2929.
Kaul K, Hodgkinson A, Tarr JM, Kohner EM, Chibber R
(2010). Is inflammation a common retinal-renal-nerve pathogenic link in diabetes?. Curr Diabetes Rev
Is inflammation a common retinal-renal-nerve pathogenic link in diabetes?
The global diabetes burden is predicted to rise to 380 million by 2025 and would present itself as a major health challenge. However, both Type 1 and Type 2 diabetes increase the risk of developing micro-vascular complications and macro-vascular complications which in turn will have a devastating impact on quality of life of the patients and challenge health services Worldwide. The micro-vascular complications that affect small blood vessels are the leading cause of blindness (diabetic retinopathy) in the people of the working-age, end-stage renal disease (diabetic nephropathy) the most common cause of kidney failure today, and foot amputation (diabetic neuropathy) in patients with Type 1 and Type 2 diabetes. It is accepted that hyperglycemia is a major causative factor for the development of these complications, there is also growing evidence for the role of inflammation. Here we discuss low-grade inflammation as a common retinal-renal-nerve pathogenic link in patients with Type 1 and Type 2 diabetes. This review summarizes evidence showing a link between circulating and locally produced inflammatory biomarkers, such as cell adhesion molecules (vascular adhesion cell molecule-1, VCAM-1; intracellular adhesion molecule-1, ICAM-1), pro-inflammatory cytokines (interleukin-6, IL-6; tumour necrosis factor-alpha, TNF-α; C-reactive protein, CRP) with the development and progression of diabetic micro-vascular complications. Abstract
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Chibber R, Mustapha NM, Tarr J, Kohner EM (2010). NADPH oxidase versus mitochondria derived ROS in glucose induced apoptosis of pericytes in early diabetic retinopathy. Journal of Opthalmology
Szabo-Taylor KE, Lo Faro ML, Eggleton P, Turner CAL, Tarr JM, Haigh RC, Littlechild JA, Whiteman M, Winyard PG
(2010). Peroxiredoxin 2 in Human Inflammatory Joint Disease. Author URL
Bailey SJ, Winyard P, Vanhatalo A, Blackwell JR, Dimenna FJ, Wilkerson DP, Tarr J, Benjamin N, Jones AM
(2009). Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol (1985)
Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans.
Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O2 cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19-38 yr) consumed 500 ml/day of either BR (containing 11.2 +/- 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of "step" moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4-6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 +/- 44 vs. PL: 140 +/- 50 nM; P < 0.05), and systolic blood pressure was significantly reduced (BR: 124 +/- 2 vs. PL: 132 +/- 5 mmHg; P < 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O2 extraction (as estimated using near-infrared spectroscopy). The gain of the increase in pulmonary O2 uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 +/- 0.7 vs. PL: 10.8 +/- 1.6 ml.min(-1).W(-1); P < 0.05). During severe exercise, the O2 uptake slow component was reduced (BR: 0.57 +/- 0.20 vs. PL: 0.74 +/- 0.24 l/min; P < 0.05), and the time-to-exhaustion was extended (BR: 675 +/- 203 vs. PL: 583 +/- 145 s; P < 0.05). The reduced O2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans. Abstract
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Tarr JM, Eggleton P, Winyard PG
(2006). Nitric oxide and the regulation of apoptosis in tumour cells. Curr Pharm Des
Nitric oxide and the regulation of apoptosis in tumour cells.
Nitric oxide (NO) is a small, highly reactive, diffusible free radical which has been implicated in many physiological and pathophysiological processes. It has either pro-apoptotic or anti-apoptotic effects on cells, depending upon a host of factors. This review outlines some of the regulatory molecules and organelles involved in the apoptotic pathways that can be influenced by the presence of NO, including p53, Bcl-2, caspases, mitochondria, and heat shock proteins. The effects of NO on the apoptosis of tumour cells are also examined. Abstract
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Tarr J, Eggleton P
(2005). Immune function of C1q and its modulators CD91 and CD93. Crit Rev Immunol
Immune function of C1q and its modulators CD91 and CD93.
C1q is a subcomponent of the first component of complement C1, which is a multimolecular complex comprising one molecule of C1q and two molecules each of the autoreactive proteases, C1r and C1s. This multimolecular complex triggers the classical pathway of complement. Advances in the past several years have provided a partial crystal structure of the C1q subunit. This, together with gene deletion of C1q, has allowed further insight into the multifunctional immune aspects of this molecule. Two C1q-mediated functions that have received intense scrutiny recently are C1q-mediated apoptotic clearance of cell debris and phagocytosis. This has led to a heightened search for specific receptors for the collagen-like region (CLR) as well as the globular heads. Two transmembrane proteins, CD91 and CD93, have been proposed to interact indirectly with the CLR of C1q, promoting apoptotic clearance and phagocytosis, respectively. The aim of this article is to provide an overview of the structural and functional information that implicates CD91 and CD93 in C1q-mediated functional effects. Abstract
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