Diabetes & Nutritional Sciences (Research Division)
|MPhil/PhD
|Part Time, Full Time
The Diabetes Research Group has as its remit the improvement of outcomes in diabetes care from the bench through the bedside to the community. It comprises several inter-related research Groups:
- Experimental Medicine: investigates human metabolism in vivo and application of technology to explore the pathophysiology of and find better treatments for two major problems in diabetes – the issue of treatment-related hypoglycaemia and the global pandemic of obesity-related diabetes and insulin resistance. The Experimental Medicine Group has a collaborative Metabolic Neuroimaging programme, investigating hypoglycaemia unawareness and appetite dysregulation. A clinical programme of intensified insulin therapy in Type 1 diabetes is backed up by basic research into technologies for glucose sensing and insulin delivery.
- Diabetes and Mental Health: includes community-based studies, including interventions, on the impact of depression on diabetes outcomes and the potential for psychologically-based therapies to improve such outcomes.
- Islet Biology: investigates islet function and pathways regulating islet development and expansion, and the potential for new therapies based on greater understanding of how insulin secreting beta-cells recognise and respond to changes in the environment. Experimental approaches range from cellular molecular biology through to animal models of diabetes. The researchers in the Islet Biology Group work closely with clinical colleagues, including those in the King's islet transplantation programme.
The Research Groups interact with each other and with colleagues in the Nutritional Sciences section of the Division, developing a focus on understanding the pathophysiology of Type 2 diabetes and obesity, and applying that knowledge to new preventive and therapeutic interventions.
Novel candidate biomarkers of diabetic nephropathy, Mitochondrial dysfunction in oxidative stress disorders
Another problems with islet transplantation is that the side effects of the anti-rejection drugs (immunosuppression) outweigh the benefits of improved glucose control in most patients. Therefore, most patients are not suitable for islet transplantation therapy and therefore must rely on insulin injections to control their diabetes. Microencapsulation of islets may allow transplantation of islets in the absence of immunosuppression. The islets are encapsulated in alginate, a polysaccharide derived from seaweed. The alginate forms a network around the islets, which is tight enough to prevent immune cells from making contact with the islets and killing them. The alginate network is, however, open enough to allow the diffusion of nutrients into the capsule and insulin out from the capsule. Therefore this can allow transplantation in the absence of immunosuppression therapy.
Diabetes and reproductive function: effects of kisspeptin and pregnancy on islet function.
Pregnancy and β-cell proliferation
During normal healthy pregnancy insulin sensitivity decreases and the insulin-secreting β-cells in the islets of Langerhans increase in number in response. Under normal physiological conditions β-cells proliferate at an extremely low rate and pregnancy is one of the few physiological states in which β-cells proliferate much more rapidly and islet size increases significantly. Gestational diabetes occurs when the mother is unable to increase insulin release sufficiently to compensate for insulin resistance, possibly caused by insufficient beta-cell proliferation. The mechanisms that cause this increase in proliferation are currently poorly understood and a better understanding would be extremely valuable for the treatment of both gestational diabetes and type 2 diabetes. My current research involves the use of in vitro and in vivo models to investigate the control of islet structure and function during pregnancy, and examining whether these physiological mechanisms could be used therapeutically to stimulate β-cell proliferation.
Kisspeptin and the regulation of islet function
Kisspeptin is a recently-discovered molecule that is found, along with its receptor, in a few areas of the human body – the hypothalamic area of the brain, the placenta and the endocrine pancreas. One important function of kisspeptin in the brain is to control when the process of puberty starts, but the function(s) of kisspeptin in the placenta and the pancreas are mostly unknown. I have previously shown that both kisspeptin and its receptor are expressed within pancreatic islets and that kisspeptin potentiates glucose-induced insulin release, both in vitro and in vivo. I am now investigating the physiological role of the kisspeptin system in islets. Given the vital role of kisspeptin in other tissues in regulating reproductive function I am particularly interested in a possible role of kisspeptin in regulating islet function during states such as puberty and pregnancy.
The aim of the research is to understand the molecular basis and anatomical pathways involved in leptin and insulin action and the role of the immune system and inflammation in obesity and the metabolic syndrome using both in vitro and in vivo models.
Autoimmunity in Type 1 diabetes: Type 1 diabetes is the result of the destruction of insulin-secreting pancreatic beta cells by a process in which autoimmune recognition of beta cell proteins is implicated. My research group has long-standing interests in the identification and characterisation of beta cell targets of the autoimmune response in Type 1 diabetes, with the view of developing strategies to identify individuals at risk for disease, and to apply antigen specific immune intervention to prevent disease progression in high-risk subjects. My group was the first to detect circulating autoantibodies to a tyrosine phosphatase-like protein, IA-2, in diabetic patients, and this antibody marker is now widely used for the prediction and diagnosis of disease. We have subsequently identified a region of the IA-2 molecule that is very commonly recognised by both ciirculating autoantibodies and T-cells in Type 1 diabetes. We are currently investigating the relationships between T- and B-cell responses to this and other regions of the IA-2 molecule, and the potential for this region to form the basis of antigen-specific vaccination protocols to prevent disease.
Development and function of pancreatic beta cells: IA-2 is a tyrosine phosphatase-like protein localised to secretory granules of pancreatic beta cells, as well as to secretory vesicles of a number of other neuroendocrine organs, including the pituitary. Our recent studies have shown that IA-2 is an important regulator of beta cell secretory granule content and insulin secretion. IA-2 is poorly expressed in fetal life, but is up-regulated after birth, in parallel with increases in islet insulin secretion in response to glucose. We are currently interested in understanding the changes in beta cell gene expression that occur during the functional maturation of pancreatic beta cells during their development, and the influences of hormones and environmental factors, particularly diet, on the development and function of the endocrine pancreas. These studies will aid our understanding of how early exposure to environmental factors can influence susceptibility to Type 1 and Type 2 diabetes later in life.
Experimental medicine programme in diabetes
Hypoglycaemia unawareness: pathogenesis and prevention
Up to 50% of people with established type 1 (insulin dependent) diabetes mellitus lose their ability to recognise the onset of a falling blood glucose concentration and so are at greatly increased risk of severe hypoglycaemia, in which confusion, abnormal behaviour, coma , seizure and, very rarely, death, occur because of inadequate glucose supply to the brain. This damages quality of life, with impact on the patient and his or her family and friends. Professor Amiel demonstrated defective stress responses to hypoglycaemia, which are reversible by strict hypoglycaemia avoidance. She also showed abnormal brain responses, with failure to activate aversive pathways or de-activate hedonic brain pathways in hypoglycaemia unaware patients, helping explain the difficulties people face in changing behaviour to avoid future hypoglycaemia. Currently, her group uses techniques ranging from semi-structured interviewing to collaborative neuroimaging, seeking to discover which of the abnormal brain responses to hypoglycaemia in unawareness are inducible and reversible, and which are innate and potentially useful as a biomarker of risk. A parallel clinical workstream focuses on optimising patient education to avoid hypoglycaemia and the use of new technologies in insulin delivery and glucose sensing (pumps and sensors) to improve hypoglycaemia protection, in a stepped programme that culminates in islet transplantation and cell therapy for type 1 diabetes patients.
Studies in insulin resistance, type 2 diabetes and obesity.
Prof Amiel’s group are also applying physiological investigative techniques such as insulin clamping, stable isotope measurement of substrate turnover and brain and other organ imaging to questions related to type 2 diabetes, in which insulin resistance plays a role. Current studies include use of different modalities of brain imaging to look at the impact of insulin resistance, insulin sensitization, and weight reducing treatments such as gastric bypass on the central mechanisms of appetite control. With liaison psychiatrist, Prof Khalida Ismail, the group run the South London Diabetes study, recruiting people with newly diagnosed diabetes into research, with a particular interest in understanding ethnic and other socio-demographic influences on the metabolic abnormalities that cause type 2 diabetes.
The group have also pioneered research into the effect of triglyceride structure on postprandial lipid metabolism. More recently we have been investigating the effect of different types of fat and food structure on the release of gut hormones that promote insulin secretion and have effects on satiety.
Over the years, we have acquired a high level of expertise in carrying out dietary intervention trials. Our current goal is to determine the optimum dietary intervention on the cardiovascular disease risk factors associated with the metabolic syndrome. We are investigating whether maternal obesity can programme the offspring to develop metabolic syndrome. We are particularly interested in why obesity causes metabolic syndrome in some people and not others.
The gut mucosa is the first responder to ingested nutrients. During the digestive process complex CHO are broken down to simple sugars, which are then transported across the small intestine.
My research has been focussed on establishing the molecular mechanisms of intestinal sugar transport. Published data show sugar is transported across the small intestine via SGLT1, GLUT2 and GLUT5. In addition these transporters are subject to regulation by diet, drugs, hormones, and disease, such as diabetes. Recent data has also shown that following meal ingestion the gut senses luminal CHO levels, resulting in the release of hunger/satiety peptides which control energy (food) intake and expenditure.
Using tissue culture and in vivo models of the small intestine, I work on regulation of intestinal sugar transport by dietary CHOs; and the metabolic consequences of elevations in post-prandial flux of sugars. In addition, I study the molecular mechanisms by which dietary CHO, especially industry processed sugars and artificial sweeteners, are sensed by the gut, controlling the release of GI satiety peptides. These preclinical studies will pave the way towards human studies on dietary CHO in the gut and the development of metabolic syndrome.
The ability of fatty acids and retinoids to cross the placenta is critically important for proper fetal growth and development. A protein mediated multi-step mechanism by which essential lipids are selectively transported from maternal to fetal circulation via the trophoblast layer is proposed. To investigate, a combination of mathematical, biochemical, cell and molecular biological approaches are being used.
In vivo function of zinc-alpha2 glycoprotein (ZAG)
ZAG is believed to participate in the chronic weight loss and muscle wasting exhibited by certain cancer patients. ZAG's true in vivo function is as yet undetermined although given that the protein binds long chain fatty acids, it is likely that ZAG participates in lipid homeostasis. Using a series of biochemical and molecular biology based techniques attempts are being made to identify and characterize ZAG's cell surface receptor. Possible clinical applications of this research would be the development of drugs that inhibit or modulate ZAG:receptor binding, thus reducing or eliminating the drastic weight loss exhibited by some cancer patients during physiologically demanding therapies.
Subsequently I undertook a series of cross-sectional studies to measure intramyocellular lipid storage in human subjects characterised by insulin resistance or sensitivty, for example type 2 diabetic subjects, vegan subjects and subjects undergoing weight loss.
Furthermore, I performed human intervention studies to investigate the effects of low glycaemic index dietary manipulations on insulin sensitivity and intramyocellular lipid. This work showed that intramyocellular lipid storage is elevated in insulin resistant subjects compared to insulin sensitive subjects. Dietary manipulations were shown to impact on insulin sensitivity and muscle lipid storage but not in a dependent manner.
My postdoctoral research at Imperial College involved running a large multi-centre, dietary intervention trial; the RISCK trial, in which the effects of dietary manipulations of quantity and quality of dietary fat and carbohydrate on insulin sensitivity and cardiovascular risk were investigated in 650 subjects.
1. Effect of diet-gene interaction on lipid profile and insulin sensitivity in large intervention studies (in collaboration with Prof Tom Sanders).
My main interest is in dietary influence on expression of the peroxisome proliferator-activated receptor genes, PPARα and PPARγ and the PPARγ target gene adiponectin ADIPOQ. Adiponectin enhances insulin sensitivity and protects against cardiovascular disease and suboptimal levels predispose to development of the metabolic syndrome. We have explored the effect of dietary fatty acid interaction with PPARG and PPARA gene variants on plasma lipids in the RISCK study, a randomised control trial in which a high intake of saturated fat was replaced with monounsaturated fats or carbohydrates. We found significant interaction between dietary fatty acid intake, ADIPOQ gene variants and age as a determinant of serum adiponectin concentration, with possible utility for targeted dietary therapy for reducing risk of late-onset disease. Interaction between the intake ratio of polyunsaturated:saturated fatty acids and PPARG gene variants and between dietary fat, PPARA and PPARG gene variants in determination of plasma lipids has also been shown. Ongoing investigations are centred on interaction between genetic variants and intake of n3-PUFA from fish oil in the MARINA study. We have completed studies on n-3 PUFA interaction with ADIPOQ variants which parallel similar age-dependent relationships found with MUFA intake in the RISCK study. Ongoing investigations concern the fatty acid desaturase genes FADS1 and FADS2, and variants are strongly associated with activity in the n-6 and n-3 PUFA synthetic pathways. We are currently investigating the impact of FADS SNP variant and haplotype carriage on plasma fatty acid proportions in response to intake of n-3 PUFA. The aim is to provide evidence of genetic susceptibility to disturbances of plasma fatty acids and lipids that predispose to metabolic and cardiovascular disease and to identify those who may benefit most from dietary modification.
2. PPARγ function in mitigation of lipodystrophic effects of anti-retroviral therapy (in collaboration with Dr Anne Mullen).
The use of anti-retroviral therapy can lead to HIV-associated lipodystrophy syndrome (HALS). There is some evidence that the activity of PPARγ is down-regulated by anti-retroviral drugs. Pharmacological PPARγ ligands such as rosiglitazone, have shown positive effects on HALS in some RCTs. We aim to investigate whether pre-treatment of cultured adipocytes with PUFAs alters the level of activated PPARγ extracted from cells exposed to anti-retrovirals. Promising results in vitro are expected to lead to human trials.
Recent publications
AlSaleh A, Sanders TAB, O’Dell SD (2012). Effect of interaction between PPARG, PPARA and ADIPOQ gene variants and dietary fatty acids on plasma lipid profile and adiponectin concentration in a large intervention study. Proc Nutr Soc. 71:141-53.
AlSaleh A, Frost GS, Griffin BA, Lovegrove JA, Jebb SA, Sanders TAB, O’Dell SD(2011). PPARγ2 gene Pro12Ala and PPARα gene Leu162Val SNPs interact with dietary intake of fat in determination of plasma lipid concentrations. J Nutrigenetics Nutrigenomics 4:355-367
AlSaleh A, O’Dell SD, Frost GS, Griffin BA, Lovegrove JA, Jebb SA, Sanders TAB (2011). Interaction of PPAR-γ2 gene Pro12Ala single nucleotide polymorphism with dietary intake of fatty acids in determination of plasma lipids in subjects at cardiometabolic risk. J Lipid Res. 52:2298-2303.
AlSaleh A, O'Dell SD, Frost GS, Griffin BA, Lovegrove JA, Jebb SA, Sanders TA (2011) Single nucleotide polymorphisms at the ADIPOQ gene locus interact with age and dietary intake of fat to determine serum adiponectin in subjects at risk of the metabolic syndrome. Am J Clin Nutr 94:1-8.
Lee AK, Kyriakou T, Weston AJ, O'Dell SD (2010) Functional single nucleotide polymorphism in acetyl-CoA carboxylase ACACB gene promoter. DNA Cell Biol 29:703-12.
Lee AK, Mojtahed-Jaberi M, Kyriakou T, Aldecoa-Otalora Astarloa E, Arno M, Marshall NJ, Brain SD, O'Dell SD (2010) Effect of high-fat feeding on expression of genes controlling availability of dopamine in mouse hypothalamus. Nutrition 26: 411-422.
Liu G, Riese H, Spector TD, O'Dell SD, Stolk R, Snieder H (2009). Bivariate genetic modeling of the response to an oral glucose tolerance challenge: A gene-environment interaction approach. Diabetologia 52:1048-1055.
Goyenechea E, Collins LJ , Parra D, Abete I, Crujeiras AB, O'Dell SD, Alfredo Martínez J. (2009) The -11391 G/A polymorphism of the adiponectin gene promoter is associated with metabolic syndrome traits and the outcome of an energy-restricted diet in obese subjects. Horm Metab Res 41:55-61.
My postdoctoral research involved running a community based dietary trial of increased fruit and vegetable consumption on blood pressure and vascular function in subjects with pre-hypertension/mild hypertension (DRFRUITNVEG). This work involved investigating the potential mechanisms by which fruit and vegetable intake may influence vascular function, including the influence of potassium, which is found in high amounts in fruit and vegetables.
My current research continues in the broad theme of diet and cardiovascular risk, with particular focus on dietary lipids and the effects and mechanisms by which dietary fat acutely affects endothelial function, in collaboration with the Cardiovascular Division at St Thomas' Hospital.
Wherever possible, we try to take a holistic view with regard to dietary intake and are interested in the effects of overall dietary patterns. We have a long-standing interest in comparing the health of vegans with vegetarians, who consume milk and eggs, and omnivores, who eat meat/or fish in addition to milk and eggs. We also have an interest in the acute effects resulting from the consumption of certain foods as well as the longer term effects.
Our group has specific expertise in the measurement of polyunsaturated fatty acids and other lipids including eicosanoids. Perhaps what differentiates the work of our group from other groups working on dietary lipids is that we have tended to focus on the interaction between the effects of dietary lipids and changes in haemostasis. Our work was among the first to show that meals high in fat induce activation of clotting factor VII and impair endothelial function. Our most recent work in this area indicates that meals high in oleic acid may have adverse effects on procoagulant activity and endothelial function compared with meals containing stearic acid.
We endeavour to foster cross-disciplinary research and seek to work with people with expertise that complements our own. We have much experience in the design and execution of controlled dietary intervention trials.
Examples of dietary approaches include:
- Probiotics and prebiotics;
- Modification of fibre and fermentable carbohydrate consumption;
- Development of gluten-free dietary interventions.
In addition, we use proteomic techniques to study the effects of trauma and alcohol on protein turnover and tissue repair, and the effects of oxidative stress on these processes.
Research in the Diet and Gastrointestinal Health Group is funded by the European Union, the BBSRC, industry and various medical research charities.
In 1999, I completed a postgraduate diploma in Systematic Reviews Methodology at University College London and subsequently completed a major systematic review of nutritional support in the management of weight loss, focusing particularly on food-based interventions. This is published in the Cochrane Library and is updated annually.
My PhD was completed in 2002-2006, and involved conducting a series of patient-focused studies examining aspects of nutritional support in the management of weight loss in patients with advanced cancers. The principal project during this period was a major intervention study, which necessitated recruitment, dietetic support and follow-up of more than 300 subjects.
My current research interests are split between using systematic review methodology to examine the role of interventions designed to enhance food intake in the management of patients with weight loss and, studies of the factors affecting patient compliance with oral nutritional interventions which focus on assessment of compliance and patient understanding of simple dietary interventions.
Numerous disorders of the GI tract are associated with alterations in the microbiota they harbour, a term called dysbiosis. Whether dysbiosis is a cause or consequence of disease is unclear, an issue we are currently investigating. The GI microbiota can be modified through dietary manipulation, including the use of probiotics (e.g. lactobacilli, bifidobacteria) and prebiotics (e.g. fructo-oligosaccharides). There is significant potential that such dietary substances may be therapeutic for GI disorders, an area we are keenly researching.
Our research translates findings from the basic sciences and tests them in the clinical environment, whilst our clinical trials always include endpoints for both efficacy and mechanistic evaluation. Our laboratory utilises molecular microbiological techniques such as fluorescent in situ hybridisation (FISH) and quantitative PCR in order to investigate various aspects of the GI microbiota.
In collaboration with both clinical researchers (e.g. gastroenterologists, dietitians) and basic scientists (e.g. immunologists, microbiologists) we have undertaken multi-centre investigations of the GI microbiota in patients with inflammatory bowel disease, irritable bowel syndrome and patients receiving artificial nutrition. Our findings indicate marked dysbiosis in such patients and further trials have investigated the efficacy of probiotics and prebiotics in these groups.
Further to this, many patients with GI disorders have disturbances across the spectrum of nutrition, including alterations in nutrient intake, digestion, absorption and metabolism. We are involved in investigating both the causes and consequences of these disturbances in order that malnutrition can be minimised. This involves research on barriers to food intake and the effect of disease on energy expenditure (indirect calorimetry), as well as the development and validation of clinical tools to assist in their detection.
The aims of the research in coeliac disease are:
- To develop strains of wheat, rye and barley that retain the baking and nutritional qualities of the original cultivars but which do not exacerbate coeliac disease.
- To characterise epitopes within wheat and related cereals that exacerbate coeliac disease.
- To raise monoclonal antibodies to the toxic epitopes in order to
- Develop improved assays to quantify the gluten content of foods for individuals with coeliac disease and
-To improve our understanding the pathogenesis of the condition
- To Investigate the pathogenesis and genetics of coeliac disease, the latter of which may permit developing a cDNA diagnostic test kit
The work in pouchitis is to investigate the pathogenesis of this condition. This involves investigating the role of the antibiotics, metronidazole and ciprofloxacin which can be used to treat the condition. We are concomitantly studying the effect of the probiotics (VSL#3) which can be used to treat the condition. We are attempting to characterise the intestinal flora by 35S-DNA molecular fingerprinting and sequencing in collaboration with the Sanger Institute in Cambridge. This is as a prelude to developing improved treatment modalities to improve our understanding of the pathogenetic role that bacteria have in this condition. In parallel work we are studying the role of immune cells and cytokines in the pathogenesis of the condition with immunohistochemistry of mucosal biopsies.
An important part of this work is to perform structure-function studies in order to:
1. Understand the role of dietary NSP in the prevention and treatment of disease. More specifically, this has involved investigating polysaccharide function in relation to gastrointestinal (GI) events, especially the physico-chemical processes that influence carbohydrate digestion and absorption. This is of considerable importance in evaluating the role of starch and non-starch polysaccharides ('dietary fibre') in the aetiology and treatment of disease, such as diabetes and cardiovsacular disease.
2. Facilitate the development of 'functional foods' with enhanced medical or nutritional benefits.
The main experimental approaches being used at present are proteomic techniques including 2-dimensional gel electrophoresis to separate proteins and mass spectrometry to identify the separated proteins. A method is currently being developed to measure the rate of synthesis of individual proteins in vivo.
We discovered and characterised several genes involved in iron homeostasis including Dcytb (ferric-reductase), ferroportin (iron exporter) and HCP1/PCFT (haem importer). We demonstrated that hepcidin inhibits intestinal iron transport through down-regulation of DMT1 and ferroportin.
We study molecules involved in cellular zinc homeostasis; the control of cellular zinc ion fluxes in signalling, antioxidant and stress (glucocorticoid) responses; and how cellular metal ions are buffered and compartmentalized.
A particular strength is our multidisciplinary approach:
- Animal models to study the physiology of metal absorption and homeostasis;
- Cell culture models to determine metal bioavailability and nutrient-gene interactions;
- Genomics, proteomics and bioinformatics to build interaction pathways for metal regulation;
- Inorganic chemical biology to investigate cellular metal ion fluxes with fluorescent probes.
Collaborations: London Iron Metabolism Group; Zinc-UK; several national and international institutes, including University College London, Institute Cochin, Paris, and National Institute of Nutrition and Seafood Research, Norway.
Funding: BBSRC, MRC (NC3Rs), NERC, EU and Industry.
Major advances have been made in this area in recent years and our group has been at the forefront of these, identifying two genes (Ireg1/ferroportin and Dcytb) encoding proteins directly involved in the process of duodenal non-heme iron absorption. The genes were isolated from a mutant mouse (hypotransferrinaemic, HPX) which develop anaemia due to lack of a functional transferrin. Due to the anaemia, circulating levels of the iron regulatory peptide hepcidin are low or undetectable in HPX mice, leading to increased iron absorption through the gut (over 10 times higher than wild type mice).
We identified several candidate genes highly over expressed in the gut cells of HPX mice which when tested by Northern blot were highly iron regulated. The first gene to be described from these studies, Ireg11 (or ferroportin) encodes the protein responsible for iron efflux out of intestinal cells, macrophages and other cells and seems to be a universal pathway for iron efflux in all cells in which it is found. In humans Ireg1 mutations have been found in patients with an iron overload disease similar to haemochromatosis referred to as ‘ferroportin’ disease2.
More recently Ireg1 has been shown to be the target and receptor for the regulatory peptide hepcidin3 which binds to the transporter and causes its internalisation and degradation thus providing a mechanism of how hepcidin controls iron metabolism. Dcytb encodes a highly iron-regulated apical ferric4 or DHA5 reductase that is required to reduce dietary ferric iron to the ferrous form which is transported into the enterocyte by DMT1. No mutations have yet been found in Dcytb which cause disease in humans. In 2005 we identified a gene implicated in duodenal heme transport (HCP1)6. Recently HCP1 has also been shown to transport folate7.
Our group continue to work on identifying other new genes involved in iron metabolism as well as characterising the biochemical function of Ireg1, Dcytb, HCP1 and other genes of iron metabolism.
Another area of interest is the effects of environmental pollutants on biological processes in mammalian models and in aquatic organsims of ecological relevance. Among other technologies, post-genomic and proteomics methods are deployed as tools for class prediction (diagnosis of effects from specific contaminants) and to mechanistically relate effects on phenotype to affected molecular networks. In collaboration with Dr Nic Bury, we have also developed a fish cell culture based method to detect and quantify toxicity of metals in natural waters and shown that this could be used as an ecotoxicological biomonitoring tool. We are continuing this work in a current project in which we are extending the gill cell culture system into a tool to replace fish in safety assessment of pharmaceuticals to the environment.
Metal homeostasis and toxicity
A. Iron and zinc metabolism
Recently, we have shown that freshwater fish are able to acquire iron from water and that marine fish acquire iron from their diet. This is of significance as in both environments; iron would not be expected to be bioavailable in significant quantities. This is because in well oxygenated circumneutral freshwaters, iron is predominantly bound into insoluble ferric (hydro)oxides and in marine fish, secretion of large amounts of bicarbonate in the intestine would be predicted to chelate divalent ions. The specialised mechanisms by which the gills and gut of fish are able to acquire iron is the focus of current investigations.
In addition, we are currently exploring how stress influence cellualr zinc uptake, signalling and buffering.
B. Metal toxicity
Maintaining essential metal homeostasis and excreting non-essential metals when exposed to elevated metals in the environment are important for health. Recently, we have shown that diets with elevated concentrations of metals do impair reproductive performance in fish. What is of interest is that these contaminated diets were natural, comprising polychaetes from estuaries with a history of elevated concentrations of metal mixtures. However, the only element to be implicated in the toxicty was arsenic. This result is of interest to researchers throughout the world who are assessing the contribution dietary metals make to the overall ecological impact of metal pollution. We are currently assessing metal assimilation efficiency in dietary-exposed fish and linking this to metal homeostasis by measuring the changes in the expression of the key metal transport proteins (DMT, CTR1, Zip, IREG, ZnT1) in epithelial tissues.
C. Gill cell culutre - The gills of fish are constantly bathed in water and are thus always exposed to pollutants. We have developed a technique to culture gill cells on permabale supports enabling water to be placed on the outside and media on the inside. Thus, mimicking the exposure route for fish. This system has been shown to mimic the resposne of whole organisms to metal pollution. Two new projects will test the versatiltiy of this system. The first will determine if it repsonds well to natural waters and thus can be used in investigative pollution monitoring programmes. The second will assess the response of the cells to a suite of pharmaceuticals. The aim is assess if this cell based system can replace the large numbers of fish thata re currently used in toxicity testing experiments.
Corticosteriod receptor functioning and evolution:
In mammals there are two corticosteroid receptors (CRs), glucocorticoid (GRs) and mineralocorticoid (MRs) receptors that control or influence a vast array of cellular functions. For example they are involved in the stress response, mineral balance, immune system and development. We have recently made an intriguing discovery - teleost fish have two GRs and an MR, the extra GR apparently being retained following the whole genome duplication that occurred in the actinopterygian lineage around 350MYA. These two receptors have very differing sensitivities in transactivation studies to cortisol, the main corticosteroid hormone in fish. This suggests a mechanism for neofunctionalisation of the duplicated GR. We are currently identifying the molecular basis for this difference in sensitivity, as this may be an important feature relating to the evolution of GR and MR characteristics in the early actinopterygians and teleost fish.
Cellular metal ion homeostasis requires multiple proteins for transport, sensing, chaperoning, and other functions in a network of tightly controlled interactions and with full integration into metabolism and signaling. The metal-regulatory proteins employ specific molecular mechanisms. One mechanism is the sulfur-ligand centered reactivity in zinc/thiolate coordination environments. Sulfur donors confer redox activity on the otherwise biologically redox-inert zinc ion. This coupling between zinc and redox metabolism provides a way of controlling zinc binding and protein functions.
Fundamental insights into the control of transition metal ion homeostasis will lead to an understanding of the pharmacological activity and toxic actions of metal ions, and aid in developing strategies for optimizing human health and for preventing, diagnosing, and treating human diseases.
Dietary iron intake is a key homeostatic step in iron metabolism, and a deficiency or excess absorption of iron is associated with disorders in a significant proportion of the UK population. The spectrum of these ailments ranges from iron deficiency anaemia (insufficiency in the diet) and hereditary haemochromatosis (dysregulatory absorption) to colorectal carcinogenesis (mutagenic and genotoxic propensities). Iron is present in diets in two forms: non-haem iron derived from cereals and vegetables and haem iron derived from animal protein. Investigating iron bioavailability from foods and in supplemental iron is an approach towards the treatment and the prevention of iron deficiency anaemia. Non-haem iron in food iron is reduced to the ferrous (Fe2+) ion prior to uptake by duodenal enterocytes. This is achieved by luminal ascorbate and the duodenal iron-regulated ferric reductase protein (Dcytb, Cybrd1). The regulation of Dcytb under different modulators of iron absorption is an active research area in our laboratory. On-going projects include the interactions of ascorbic acid with Dcytb in the generation of reducing equivalents in the process of ferrireduction. The involvement of Hif 2α in the expression and regulation of Dcytb is also being investigated and explored.
While many advances have been made in understanding how non-haem iron is absorbed, understanding of how haem is taken up has lagged behind. Dietary haem iron from animal products is much more bioavailable than non-haem iron and therefore can provide a relatively larger amount of iron to the body. The mechanism of its absorption remains a major question in the field of iron research. My research interest in this area involves the elucidation of potential haem transport proteins in the gastrointestinal tract.
Hepcidin is a 25-amino acid peptide that regulates systemic iron homeostasis. It binds to ferroportin and induces its internalisation and degradation, thereby decreasing iron export from enterocytes. The effects of iron and flavonoids on the regulation and expression of hepcidin in cell culture and mice models of iron disorders are also areas of my research interest.
Subsequently I undertook a series of cross-sectional studies to measure intramyocellular lipid storage in human subjects characterised by insulin resistance or sensitivty, for example type 2 diabetic subjects, vegan subjects and subjects undergoing weight loss.
Furthermore, I performed human intervention studies to investigate the effects of low glycaemic index dietary manipulations on insulin sensitivity and intramyocellular lipid. This work showed that intramyocellular lipid storage is elevated in insulin resistant subjects compared to insulin sensitive subjects. Dietary manipulations were shown to impact on insulin sensitivity and muscle lipid storage but not in a dependent manner.
My postdoctoral research at Imperial College involved running a large multi-centre, dietary intervention trial; the RISCK trial, in which the effects of dietary manipulations of quantity and quality of dietary fat and carbohydrate on insulin sensitivity and cardiovascular risk were investigated in 650 subjects.
Cellular metal ion homeostasis requires multiple proteins for transport, sensing, chaperoning, and other functions in a network of tightly controlled interactions and with full integration into metabolism and signaling. The metal-regulatory proteins employ specific molecular mechanisms. One mechanism is the sulfur-ligand centered reactivity in zinc/thiolate coordination environments. Sulfur donors confer redox activity on the otherwise biologically redox-inert zinc ion. This coupling between zinc and redox metabolism provides a way of controlling zinc binding and protein functions.
Fundamental insights into the control of transition metal ion homeostasis will lead to an understanding of the pharmacological activity and toxic actions of metal ions, and aid in developing strategies for optimizing human health and for preventing, diagnosing, and treating human diseases.
