Sesamum indicum Oleosin L improves oil packaging in Nicotiana benthamiana leaves

Plant oil production has been increasing continuously in the past decade. There has been significant investment in the production of high biomass plants with elevated oil content. We recently showed that the expression of Arabidopsis thaliana WRI1 and DGAT1 genes increase oil content by up to 15% in leaf dry weight tissue. However, triacylglycerols in leaf tissue are subject to degradation during senescence. In order to better package the oil, we expressed a series of lipid droplet proteins isolated from bacterial and plant sources in Nicotiana benthamiana leaf tissue. We observed further increases in leaf oil content of up to 2.3-fold when we co-expressed Sesamum indicum Oleosin L with AtWRI1 and AtDGAT1. Biochemical assays and lipid droplet visualization with confocal microscopy confirmed the increase in oil content and revealed a significant change in the size and abundance of lipid droplets.

Development of a Brassica napus (Canola) Crop Containing Fish Oil-Like Levels of DHA in the Seed Oil

Plant seeds have long been promoted as a production platform for novel fatty acids such as the ω3 long-chain (≥ C20) polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) commonly found in fish oil. In this article we describe the creation of a canola (Brassica napus) variety producing fish oil-like levels of DHA in the seed. This was achieved by the introduction of a microalgal/yeast transgenic pathway of seven consecutive enzymatic steps which converted the native substrate oleic acid to α-linolenic acid and, subsequently, to EPA, docosapentaenoic acid (DPA) and DHA. This paper describes construct design and evaluation, plant transformation, event selection, field testing in a wide range of environments, and oil profile stability of the transgenic seed. The stable, high-performing event NS-B50027-4 produced fish oil-like levels of DHA (9-11%) in open field trials of T3 to T7 generation plants in several locations in Australia and Canada. This study also describes the highest seed DHA levels reported thus far and is one of the first examples of a deregulated genetically modified crop with clear health benefits to the consumer.

How tightly controlled do fluctuations in blood glucose levels need to be to reduce the risk of developing complications in people with Type 1 diabetes?

In 2011, the James Lind Alliance published a 'top 10' list of priorities for Type 1 diabetes research based on a structured consultation process. Whether reducing fluctuations in blood glucose can prevent long-term microvascular and macrovascular complications was one of these. In this narrative review, 8 years on, we have assessed the updated evidence for the assertion that increased glucose variability plays an independent and clinically important role in the complications of Type 1 diabetes, over and above mean blood glucose and the effects of hypoglycaemia: the 'glucose variability hypothesis'. Although studies in cultured cells and ex vivo vessels have been suggestive, most studies in Type 1 diabetes have been small and/or cross-sectional, and based on 'finger-prick' glucose measurements that capture glucose variability only in waking hours and are affected by missing data. A recent analysis of the Diabetes Control and Complications Trial that formally imputed missing data found no independent effect of short-term glucose variability on long-term complications. Few other high-quality longitudinal studies have directly addressed the glucose variability hypothesis in Type 1 diabetes. We conclude that there is little substantial evidence to date to support this hypothesis in Type 1 diabetes, although increasing use of continuous glucose monitoring provides an opportunity to test it more definitively. In the meantime, we recommend that control of glycaemia in Type 1 diabetes should continue to focus on the sustained achievement of target HbA_1c and avoidance of hypoglycaemia.

Proteomics reveals the in vitro protein digestibility of seven transmembrane enzymes from the docosahexaenoic acid biosynthesis pathway

The measurement of protein digestibility is one of the key steps in determining the safety of a genetically modified crop that has been traditionally accomplished using antibodies. Membrane proteins are often extremely difficult to express with replicated authentic tertiary structure in heterologous systems. As a result raising antibodies for use in safety assessment may not be feasible. In this study, LC-MS based proteomics was used to characterise seven transmembrane enzymes from the docosahexaenoic acid biosynthetic pathway that had been introduced into canola. The application of a two-stage digestion strategy involving simulated gastric fluid followed by trypsin enabled the measurement of protein digestibility in vitro. Tryptic peptide markers that spanned the length of each desaturase protein were monitored and showed that these proteins were readily degraded (>95% within 5 min) and highlighted regions of the elongase enzymes that showed limited resistance to simulated gastric digestion. Traditional gel-based and Western blotting analysis of ω3-desaturase and Δ6-elongase revealed rapid hydrolysis of the intact proteins within seconds and no fragments (>3 kDa) remained after 60 min, complementing the novel approach described herein. The LC-MS approach was sensitive, selective and did not require the use of purified proteins.

Identification of Genes Involved in Lipid Biosynthesis through de novo Transcriptome Assembly from Cocos nucifera Developing Endosperm

Cocos nucifera (coconut), a member of the Arecaceae family, is an economically important woody palm that is widely grown in tropical and subtropical regions. The coconut palm is well known for its ability to accumulate large amounts of oil, approximately 63% of the seed weight. Coconut oil varies significantly from other vegetable oils as it contains a high proportion of medium-chain fatty acids (MCFA; 85%). The unique composition of coconut oil raises interest in understanding how the coconut palm produces oil of a high saturated MCFA content, and if such an oil profile could be replicated via biotechnology interventions. Although some gene discovery work has been performed there is still a significant gap in the knowledge associated with coconut's oil production pathways. In this study, a de novo transcriptome was assembled for developing coconut endosperm to identify genes involved in the synthesis of lipids, particularly triacylglycerol. Of particular interest were thioesterases, acyltransferases and oleosins because of their involvement in the processes of releasing fatty acids for assembly, esterification of fatty acids into glycerolipids and protecting oils from degradation, respectively. It is hypothesized that some of these genes may exhibit a strong substrate preference for MCFA and hence may assist the future development of vegetable oils with an enriched MCFA composition. In this study, we identified and confirmed functionality of five candidate genes from the gene families of interest. This study will benefit future work in areas of increasing vegetable oil production and the tailoring of oil fatty acid compositions.

Quantitation of seven transmembrane proteins from the DHA biosynthesis pathway in genetically engineered canola by targeted mass spectrometry

Examining tissue-specific expression and the measurement of protein abundance are important steps when assessing the performance of genetically engineered crops. Liquid chromatography-mass spectrometry offers many advantages over traditional methods for protein quantitation, especially when dealing with transmembrane proteins that are often difficult to express or generate antibodies against. In this study, discovery proteomics was used to detect the seven transgenic membrane-bound enzymes from the docosahexaenoic acid (DHA) biosynthetic pathway that had been engineered into canola. Subsequently, a targeted LC-MS/MS method for absolute quantitation was developed and applied to the simultaneous measurement of the seven DHA biosynthetic pathway enzymes in genetically modified canola grown across three sites. The results of this study demonstrated that the enzymatic proteins that drive the production of DHA using seed-specific promoters were detected only in mature and developing seed of DHA canola. None of the DHA biosynthesis pathway proteins were detected in wild-type canola planted in the same site or in the non-seed tissues of the transgenic canola, irrespective of the sampling time or the tissues tested. This study describes a streamlined approach to simultaneously measure multiple membrane-bound proteins in planta.

Metabolic engineering for enhanced oil in biomass

The world is hungry for energy. Plant oils in the form of triacylglycerol (TAG) are one of the most reduced storage forms of carbon found in nature and hence represent an excellent source of energy. The myriad of applications for plant oils range across foods, feeds, biofuels, and chemical feedstocks as a unique substitute for petroleum derivatives. Traditionally, plant oils are sourced either from oilseeds or tissues surrounding the seed (mesocarp). Most vegetative tissues, such as leaves and stems, however, accumulate relatively low levels of TAG. Since non-seed tissues constitute the majority of the plant biomass, metabolic engineering to improve their low-intrinsic TAG-biosynthetic capacity has recently attracted significant attention as a novel, sustainable and potentially high-yielding oil production platform. While initial attempts predominantly targeted single genes, recent combinatorial metabolic engineering strategies have focused on the simultaneous optimization of oil synthesis, packaging and degradation pathways (i.e., 'push, pull, package and protect'). This holistic approach has resulted in dramatic, seed-like TAG levels in vegetative tissues. With the first proof of concept hurdle addressed, new challenges and opportunities emerge, including engineering fatty acid profile, translation into agronomic crops, extraction, and downstream processing to deliver accessible and sustainable bioenergy.

Up-regulation of lipid biosynthesis increases the oil content in leaves of Sorghum bicolor

Synthesis and accumulation of the storage lipid triacylglycerol in vegetative plant tissues has emerged as a promising strategy to meet the world's future need for vegetable oil. Sorghum (Sorghum bicolor) is a particularly attractive target crop given its high biomass, drought resistance and C₄ photosynthesis. While oilseed-like triacylglycerol levels have been engineered in the C₃ model plant tobacco, progress in C₄ monocot crops has been lagging behind. In this study, we report the accumulation of triacylglycerol in sorghum leaf tissues to levels between 3 and 8.4% on a dry weight basis depending on leaf and plant developmental stage. This was achieved by the combined overexpression of genes encoding the Zea mays WRI1 transcription factor, Umbelopsis ramanniana UrDGAT2a acyltransferase and Sesamum indicum Oleosin-L oil body protein. Increased oil content was visible as lipid droplets, primarily in the leaf mesophyll cells. A comparison between a constitutive and mesophyll-specific promoter driving WRI1 expression revealed distinct changes in the overall leaf lipidome as well as transitory starch and soluble sugar levels. Metabolome profiling uncovered changes in the abundance of various amino acids and dicarboxylic acids. The results presented here are a first step forward towards the development of sorghum as a dedicated biomass oil crop and provide a basis for further combinatorial metabolic engineering.

Increased DHA Production in Seed Oil Using a Selective Lysophosphatidic Acid Acyltransferase

Metabolic engineering of the omega-3 (ω3) long chain polyunsaturated fatty acid biosynthesis pathway has generated fish oil-like levels of pharmaceutically and nutritionally important docosahexaenoic acid (DHA) in plant seeds. However, the majority of DHA has been accumulated at the sn-1 and sn-3 positions of triacylglycerol (TAG) in these engineered seeds, leaving only a minor amount (∼10%) at sn-2 position and indicating a strong discrimination (or, a very poor specificity) for DHA by seed lysophosphatidic acid acyltransferases (LPAATs), which mediate the acylation of sn-2 position of glycerol backbone. In order to increase the level of DHA at sn-2 position of TAG and to increase overall DHA level in seeds, we attempted to discover DHA-preferring LPAATs. Several LPAATs for acylation of the sn-2 position of the TAG glycerol backbone were investigated for substrate preference for DHA. In transiently expressing these LPAATs in Nicotiana benthamiana, a Mortierella alpina LPAAT had the highest substrate specificity for accumulating DHA onto oleoyl-lysophosphatidic acid (oleoyl-LPA), while the plant LPAATs tested showed lower preference for DHA. In a competition assay with a pool of four ω3 acyl-Coenzyme A (CoA) substrates involved in the DHA biosynthesis pathway, LPAATs from both M. alpina and Emiliania huxleyi showed a high preference for DHA-CoA acylation onto oleoyl-LPA. When docosahexaenoyl-LPA was used as the acyl receiver, M. alpina LPAAT also showed a high preference for DHA-CoA. Stable overexpression of M. alpina LPAAT in an Arabidopsis line that expressed the DHA biosynthesis pathway significantly increased both the total DHA levels and the distribution of DHA onto the sn-2 position of seed TAG. LC-MS analysis of the seed TAG species also confirmed that overexpression of M. alpina LPAAT increased di-DHA and tri-DHA TAGs, suggesting that the M. alpina LPAAT could enrich DHA at the TAG sn-2 position, leading to a metabolic engineering of oil seed for channeling DHA into the sn-2 position of TAG and to a higher DHA level.

A reconfigured Kennedy pathway which promotes efficient accumulation of medium-chain fatty acids in leaf oils

Medium-chain fatty acids (MCFA, C6-14 fatty acids) are an ideal feedstock for biodiesel and broader oleochemicals. In recent decades, several studies have used transgenic engineering to produce MCFA in seeds oils, although these modifications result in unbalance membrane lipid profiles that impair oil yields and agronomic performance. Given the ability to engineer nonseed organs to produce oils, we have previously demonstrated that MCFA profiles can be produced in leaves, but this also results in unbalanced membrane lipid profiles and undesirable chlorosis and cell death. Here we demonstrate that the introduction of a diacylglycerol acyltransferase from oil palm, EgDGAT1, was necessary to channel nascent MCFA directly into leaf oils and therefore bypassing MCFA residing in membrane lipids. This pathway resulted in increased flux towards MCFA rich leaf oils, reduced MCFA in leaf membrane lipids and, crucially, the alleviation of chlorosis. Deep sequencing of African oil palm (Elaeis guineensis) and coconut palm (Cocos nucifera) generated candidate genes of interest, which were then tested for their ability to improve oil accumulation. Thioesterases were explored for the production of lauric acid (C12:0) and myristic (C14:0). The thioesterases from Umbellularia californica and Cinnamomum camphora produced a total of 52% C12:0 and 40% C14:0, respectively, in transient leaf assays. This study demonstrated that the introduction of a complete acyl-CoA-dependent pathway for the synthesis of MFCA-rich oils avoided disturbing membrane homoeostasis and cell death phenotypes. This study outlines a transgenic strategy for the engineering of biomass crops with high levels of MCFA rich leaf oils.

Fludrocortisone therapy for persistent hyperkalaemia

BACKGROUND

Type 4 renal tubular acidosis causes hyperkalaemia, for which diabetes and medications commonly used in this patient group are aetiological factors. Here we describe the novel use of fludrocortisone in this difficult condition.

CASE REPORT

A 55-year-old woman with complex co-morbidities, including Type 2 diabetes (HbA_1c 37 mmol/mol 5.5%), was admitted with renal failure. Bloods on admission: eGFR 25 ml/min, creatinine 184 ?mol/L, urea 35.9 mmol/L, sodium 128 mmol/L, potassium 5.6 mmol/L, bicarbonate 15 mmol/L, and albumin 30 g/L. Her admission was prolonged, complicated by hospital-acquired sepsis (lower respiratory tract, urinary tract, and infected leg ulcers), poor venous access and severe depression. She had recurrent hyperkalaemia and deteriorating renal function, from presumed Type 4 renal tubular acidosis and excessive fluid losses from leg ulcers. Her renal function recurrently deteriorated, despite conventional treatment methods. After 69 days, she was commenced on fludrocortisone 50 mcg/day. Her renal function and serum potassium stabilized and she was discharged with potassium 4.3 mmol/L, eGFR 42 ml/min, and bicarbonate 23 mmol/L. She has remained stable on this treatment, without requiring further hospital admission for over 6 months, with eGFR 40 ml/min, and potassium 5.5 mmol/L, and albumin 26 g/L.

CONCLUSION

This woman was presumed to have Type 4 renal tubular acidosis and recurrent hyperkalaemia due to renal insufficiency, in the context of underlying diabetes and chronic kidney disease, which was poorly responsive to conventional management. There is limited evidence for using fludrocortisone in this setting. Our case suggests that fludrocortisone might offer a novel therapeutic strategy when conventional management is not working.

Comparative Lipidomics and Proteomics of Lipid Droplets in the Mesocarp and Seed Tissues of Chinese Tallow (Triadica sebifera)

Lipid droplets (LDs) are composed of a monolayer of phospholipids (PLs), surrounding a core of non-polar lipids that consist mostly of triacylglycerols (TAGs) and to a lesser extent diacylglycerols. In this study, lipidome analysis illustrated striking differences in non-polar lipids and PL species between LDs derived from Triadica sebifera seed kernels and mesocarp. In mesocarp LDs, the most abundant species of TAG contained one C18:1 and two C16:0 and fatty acids, while TAGs containing three C18 fatty acids with higher level of unsaturation were dominant in the seed kernel LDs. This reflects the distinct differences in fatty acid composition of mesocarp (palmitate-rich) and seed-derived oil (α-linoleneate-rich) in T. sebifera. Major PLs in seed LDs were found to be rich in polyunsaturated fatty acids, in contrast to those with relatively shorter carbon chain and lower level of unsaturation in mesocarp LDs. The LD proteome analysis in T. sebifera identified 207 proteins from mesocarp, and 54 proteins from seed kernel, which belong to various functional classes including lipid metabolism, transcription and translation, trafficking and transport, cytoskeleton, chaperones, and signal transduction. Oleosin and lipid droplets associated proteins (LDAP) were found to be the predominant proteins associated with LDs in seed and mesocarp tissues, respectively. We also show that LDs appear to be in close proximity to a number of organelles including the endoplasmic reticulum, mitochondria, peroxisomes, and Golgi apparatus. This comparative study between seed and mesocarp LDs may shed some light on the structure of plant LDs and improve our understanding of their functionality and cellular metabolic networks in oleaginous plant tissues.

Step changes in leaf oil accumulation via iterative metabolic engineering

Synthesis and accumulation of plant oils in the entire vegetative biomass offers the potential to deliver yields surpassing those of oilseed crops. However, current levels still fall well short of those typically found in oilseeds. Here we show how transcriptome and biochemical analyses pointed to a futile cycle in a previously established Nicotiana tabacum line, accumulating up to 15% (dry weight) of the storage lipid triacylglycerol in leaf tissue. To overcome this metabolic bottleneck, we either silenced the SDP1 lipase or overexpressed the Arabidopsis thaliana LEC2 transcription factor in this transgenic background. Both strategies independently resulted in the accumulation of 30-33% triacylglycerol in leaf tissues. Our results demonstrate that the combined optimization of de novo fatty acid biosynthesis, storage lipid assembly and lipid turnover in leaf tissue results in a major overhaul of the plant central carbon allocation and lipid metabolism. The resulting further step changes in oil accumulation in the entire plant biomass offers the possibility of delivering yields that outperform current oilseed crops.

Thioesterase overexpression in Nicotiana benthamiana leaf increases the fatty acid flux into triacylgycerol

Increasing the oil content of leafy biomass is emerging as a sustainable source of vegetable oil to meet global demand. Transient gene expression in leaf provides a reproducible platform to study the effect of transgenes on lipid biosynthesis. We first generated a transgenic Nicotiana benthamiana line containing high levels of triacylglycerol in the leaf tissue (31.4% by dry weight) by stably expressing WRI1, DGAT1 and OLEOSIN. We then used this line as a platform to test the effect of three Arabidopsis thaliana thioesterases (FATA1, FATA2 and FATB). Further increases in leaf oil content were observed with biochemical and lipid assays revealing an increase in the export of fatty acids from the chloroplast and a modification in the oil profile.

Reduced Triacylglycerol Mobilization during Seed Germination and Early Seedling Growth in Arabidopsis Containing Nutritionally Important Polyunsaturated Fatty Acids

There are now several examples of plant species engineered to synthesize and accumulate nutritionally important polyunsaturated fatty acids in their seed triacylglycerols (TAG). The utilization of TAG in germinating seeds of such transgenic plants was unknown. In this study, we examined the TAG utilization efficiency during seed germination in transgenic Arabidopsis seeds containing several examples of these fatty acids. Seed TAG species with native fatty acids had higher utilization rate than the TAG species containing transgenically produced polyunsaturated fatty acids. Conversely, quantification of the fatty acid components remaining in the total TAG after early stages of seed germination revealed that the undigested TAGs tended to contain elevated levels of the engineered polyunsaturated fatty acids (PUFA). LC-MS analysis further revealed asymmetrical mobilization rates for the individual TAG species. TAGs which contained multiple PUFA fatty acids were mobilized slower than the species containing single PUFA. The mobilized engineered fatty acids were used in de novo membrane lipid synthesis during seedling development.

Deep Sequencing of the Fruit Transcriptome and Lipid Accumulation in a Non-Seed Tissue of Chinese Tallow, a Potential Biofuel Crop

Chinese tallow (Triadica sebifera) is a valuable oilseed-producing tree that can grow in a variety of conditions without competing for food production, and is a promising biofuel feedstock candidate. The fruits are unique in that they contain both saturated and unsaturated fat present in the tallow and seed layer, respectively. The tallow layer is poorly studied and is considered only as an external fatty deposition secreted from the seed. In this study we show that tallow is in fact a non-seed cellular tissue capable of triglyceride synthesis. Knowledge of lipid synthesis and storage mechanisms in tissues other than seed is limited but essential to generate oil-rich biomass crops. Here, we describe the annotated transcriptome assembly generated from the fruit coat, tallow and seed tissues of Chinese tallow. The final assembly was functionally annotated, allowing for the identification of candidate genes and reconstruction of lipid pathways. A tallow tissue-specific paralog for the transcription factor gene WRINKLED1 (WRI1) and lipid droplet-associated protein genes, distinct from those expressed in seed tissue, were found to be active in tallow, underpinning the mode of oil synthesis and packaging in this tissue. Our data have established an excellent knowledge base that can provide genetic and biochemical insights for engineering non-seed tissues to accumulate large amounts of oil. In addition to the large data set of annotated transcripts, the study also provides gene-based simple sequence repeat and single nucleotide polymorphism markers.

Cardiovascular safety of the glucagon-like peptide-1 receptor agonist taspoglutide in people with type 2 diabetes: an individual participant data meta-analysis of randomized controlled trials

AIMS

To study the short-term cardiovascular effects of the once-weekly glucagon-like peptide-1 receptor agonist taspoglutide.

METHODS

We conducted a meta-analysis of individual-participant data from nine randomized controlled trials in the T-Emerge programme, which assessed the efficacy and safety of taspoglutide in type 2 diabetes. Our primary outcome was a composite of death from cardiovascular disease (CVD) and acute myocardial infarction, stroke and hospitalization for unstable angina.

RESULTS

Overall, 7056 individuals were included in the analysis, and there were 67 primary endpoint events during 7478 person-years of follow-up (40 vs 27 events in the intervention vs control groups, respectively). The odds ratio for the composite endpoint among people randomized to taspoglutide was 0.94 (95% confidence interval 0.57-1.56), which was robust across multiple subgroups. Longer-term data were not available as the development of taspoglutide was stopped because of gastrointestinal intolerance and serious hypersensitivity reactions.

CONCLUSIONS

The available data suggest that short-term, once-weekly administration of taspoglutide was not associated with an excess risk of CVD, and provide insights relevant to the development of other novel once-weekly incretin mimetics.

Metabolic engineering of medium-chain fatty acid biosynthesis in Nicotiana benthamiana plant leaf lipids

Various research groups are investigating the production of oil in non-seed biomass such as leaves. Recently, high levels of oil accumulation have been achieved in plant biomass using a combination of biotechnological approaches which also resulted in significant changes to the fatty acid composition of the leaf oil. In this study, we were interested to determine whether medium-chain fatty acids (MCFA) could be accumulated in leaf oil. MCFA are an ideal feedstock for biodiesel and a range of oleochemical products including lubricants, coatings, and detergents. In this study, we explore the synthesis, accumulation, and glycerolipid head-group distribution of MCFA in leaves of Nicotiana benthamiana after transient transgenic expression of C12:0-, C14:0-, and C16:0-ACP thioesterase genes. We demonstrate that the production of these MCFA in leaf is increased by the co-expression of the WRINKLED1 (WRI1) transcription factor, with the lysophosphatidic acid acyltransferase (LPAAT) from Cocos nucifera being required for the assembly of tri-MCFA TAG species. We also demonstrate that the newly-produced MCFA are incorporated into the triacylglycerol of leaves in which WRI1 + diacylglycerol acyltransferase1 (DGAT1) genes are co-expressed for increased oil accumulation.

Expression of Mouse MGAT in Arabidopsis Results in Increased Lipid Accumulation in Seeds

Worldwide demand for vegetable oil is projected to double within the next 30 years due to increasing food, fuel, and industrial requirements. There is therefore great interest in metabolic engineering strategies that boost oil accumulation in plant tissues, however, efforts to date have only achieved levels of storage lipid accumulation in plant tissues far below the benchmark to meet demand. Monoacylglycerol acyltransferase (MGAT) is predominantly associated with lipid absorption and resynthesis in the animal intestine where it catalyzes monoacylglycerol (MAG) to form diacylglycerol (DAG), and then triacylglycerol (TAG). In contrast plant lipid biosynthesis routes do not include MGAT. Rather, DAG and TAG are either synthesized from glycerol-3-phosphate by a series of three subsequent acylation reactions, or originated from phospholipids via an acyl editing pathway. Mouse MGATs 1 and 2 have been shown to increase oil content transiently in Nicotiana benthamiana leaf tissue by 2.6 fold. Here we explore the feasibility of this approach to increase TAG in Arabidopsis thaliana seed. The stable MGAT2 expression resulted in a significant increase in seed oil content by 1.32 fold. We also report evidence of the MGAT2 activity based on in vitro assays. Up to 3.9 fold increase of radiolabeled DAG were produced in seed lysate which suggest that the transgenic MGAT activity can result in DAG re-synthesis by salvaging the MAG product of lipid breakdown. The expression of MGAT2 therefore creates an independent and complementary TAG biosynthesis route to the endogenous Kennedy pathway and other glycerolipid synthesis routes.

The multiply-operated total knee replacement patient: salvage options

Although the vast majority of patients that undergo total knee replacement have satisfactory outcomes with a generally low complication rate, occasionally a patient will be encountered that has had multiple failed surgeries, and now reaches a crossroad as to whether limb salvage will be acceptable or not.

Lipidomic analysis of Arabidopsis seed genetically engineered to contain DHA

Metabolic engineering of omega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA) in oilseeds has been one of the key targets in recent years. By expressing a transgenic pathway for enhancing the synthesis of the ω3 LC-PUFA docosahexaenoic acid (DHA) from endogenous α-linolenic acid (ALA), we obtained the production of fish oil-like proportions of DHA in Arabidopsis seed oil. Liquid chromatography-mass spectrometry (LC-MS) was used to characterize the triacylglycerol (TAG), diacylglycerol (DAG) and phospholipid (PL) lipid classes in the transgenic and wild type Arabidopsis seeds at both developing and mature stages. The analysis identified the appearance of several abundant DHA-containing phosphatidylcholine (PC), DAG and TAG molecular species in mature seeds. The relative abundances of PL, DAG, and TAG species showed a preferred combination of LC-PUFA with ALA in the transgenic seeds, where LC-PUFA were esterified in positions usually occupied by 20:1ω9. Trace amounts of di-DHA PC and tri-DHA TAG were identified and confirmed by high resolution MS/MS. Studying the lipidome in transgenic seeds provided insights into where DHA accumulated and combined with other fatty acids of neutral and phospholipids from the developing and mature seeds.

Characterization of oilseed lipids from "DHA-producing Camelina sativa": a new transformed land plant containing long-chain omega-3 oils

New and sustainable sources of long-chain (LC, ≥C₂₀) omega-3 oils containing DHA (docosahexaenoic acid, 22:6ω3) are required to meet increasing demands. The lipid content of the oilseed of a novel transgenic, DHA-producing land plant, Camelina sativa, containing microalgal genes able to produce LC omega-3 oils, contained 36% lipid by weight with triacylglycerols (TAG) as the major lipid class in hexane extracts (96% of total lipid). Subsequent chloroform-methanol (CM) extraction recovered further lipid (~50% polar lipid, comprising glycolipids and phospholipids) and residual TAG. The main phospholipid species were phosphatidyl choline and phosphatidyl ethanolamine. The % DHA was: 6.8% (of total fatty acids) in the TAG-rich hexane extract and 4.2% in the polar lipid-rich CM extract. The relative level of ALA (α-linolenic acid, 18:3ω3) in DHA-camelina seed was higher than the control. Major sterols in both DHA- and control camelina seeds were: sitosterol, campesterol, cholesterol, brassicasterol and isofucosterol. C₁₆-C₂₂ fatty alcohols, including iso-branched and odd-chain alcohols were present, including high levels of iso-17:0, 17:0 and 19:0. Other alcohols present were: 16:0, iso-18:0, 18:0 and 18:1 and the proportions varied between the hexane and CM extracts. These iso-branched odd-chain fatty alcohols, to our knowledge, have not been previously reported. These components may be derived from wax esters, or free fatty alcohols.

Metabolic engineering of biomass for high energy density: oilseed-like triacylglycerol yields from plant leaves

High biomass crops have recently attracted significant attention as an alternative platform for the renewable production of high energy storage lipids such as triacylglycerol (TAG). While TAG typically accumulates in seeds as storage compounds fuelling subsequent germination, levels in vegetative tissues are generally low. Here, we report the accumulation of more than 15% TAG (17.7% total lipids) by dry weight in Nicotiana tabacum (tobacco) leaves by the co-expression of three genes involved in different aspects of TAG production without severely impacting plant development. These yields far exceed the levels found in wild-type leaf tissue as well as previously reported engineered TAG yields in vegetative tissues of Arabidopsis thaliana and N. tabacum. When translated to a high biomass crop, the current levels would translate to an oil yield per hectare that exceeds those of most cultivated oilseed crops. Confocal fluorescence microscopy and mass spectrometry imaging confirmed the accumulation of TAG within leaf mesophyll cells. In addition, we explored the applicability of several existing oil-processing methods using fresh leaf tissue. Our results demonstrate the technical feasibility of a vegetative plant oil production platform and provide for a step change in the bioenergy landscape, opening new prospects for sustainable food, high energy forage, biofuel and biomaterial applications.

Metabolic engineering Camelina sativa with fish oil-like levels of DHA

BACKGROUND

Omega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are critical for human health and development [corrected].. Numerous studies have indicated that deficiencies in these fatty acids can increase the risk or severity of cardiovascular, inflammatory and other diseases or disorders. EPA and DHA are predominantly sourced from marine fish although the primary producers are microalgae. Much work has been done to engineer a sustainable land-based source of EPA and DHA to reduce pressure on fish stocks in meeting future demand, with previous studies describing the production of fish oil-like levels of DHA in the model plant species, Arabidopsis thaliana.

PRINCIPAL FINDINGS

In this study we describe the production of fish oil-like levels (>12%) of DHA in the oilseed crop species Camelina sativa achieving a high ω3/ω6 ratio. The construct previously transformed in Arabidopsis as well as two modified construct versions designed to increase DHA production were used. DHA was found to be stable to at least the T5 generation and the EPA and DHA were found to be predominantly at the sn-1,3 positions of triacylglycerols. Transgenic and parental lines did not have different germination or seedling establishment rates.

CONCLUSIONS

DHA can be produced at fish oil-like levels in industrially-relevant oilseed crop species using multi-gene construct designs which are stable over multiple generations. This study has implications for the future of sustainable EPA and DHA production from land-based sources.

Transcriptional and biochemical responses of monoacylglycerol acyltransferase-mediated oil synthesis and associated senescence-like responses in Nicotiana benthamiana

Triacylglycerol (TAG) accumulates in plant seeds as a major renewable source of carbon for food, fuel and industrial feedstock. Approaches to enhance TAG content by altering lipid pathways and genes in vegetative parts have gained significant attention for biofuel and other applications. However, consequences of these modifications are not always studied in detail. In an attempt to increase TAG levels in leaves we previously demonstrated that a novel substrate, monoacylglycerol (MAG), can be used for the biosynthesis of diacylglycerol (DAG) and TAG. Transient expression of the Mus musculus monoacylglycerol acyltransferases MGAT1 and 2 in the model plant Nicotiana benthamiana increased TAG levels at 5 days post-infiltration (dpi). Here we show that increased TAG and DAG levels can be achieved as early as 2 dpi. In addition, the MGAT1 infiltrated areas showed senescence-like symptoms from 3 dpi onwards. To unravel underlying molecular mechanisms, Illumina deep sequencing was carried out (a) for de-novo assembling and annotation of N. benthamiana leaf transcripts and (b) to characterize MGAT1-responsive transcriptome. We found that MGAT1-responsive genes are involved in several processes including TAG biosynthesis, photosynthesis, cell-wall, cutin, suberin, wax and mucilage biosynthesis, lipid and hormone metabolism. Comparative analysis with transcript profiles from other senescence studies identified characteristic gene expression changes involved in senescence induction. We confirmed that increased TAG and observed senescence-symptoms are due to the MAG depletion caused by MGAT1 activity and suggest a mechanism for MGAT1 induced TAG increase and senescence-like symptoms. The data generated will serve as a valuable resource for oil and senescence related studies and for future N. benthamiana transcriptome studies.

Insulin resistance in type 1 diabetes: what is 'double diabetes' and what are the risks?

In this review, we explore the concept of 'double diabetes', a combination of type 1 diabetes with features of insulin resistance and type 2 diabetes. After considering whether double diabetes is a useful concept, we discuss potential mechanisms of increased insulin resistance in type 1 diabetes before examining the extent to which double diabetes might increase the risk of cardiovascular disease (CVD). We then go on to consider the proposal that weight gain from intensive insulin regimens may be associated with increased CV risk factors in some patients with type 1 diabetes, and explore the complex relationships between weight gain, insulin resistance, glycaemic control and CV outcome. Important comparisons and contrasts between type 1 diabetes and type 2 diabetes are highlighted in terms of hepatic fat, fat partitioning and lipid profile, and how these may differ between type 1 diabetic patients with and without double diabetes. In so doing, we hope this work will stimulate much-needed research in this area and an improvement in clinical practice.

AtDGAT2 is a functional acyl-CoA:diacylglycerol acyltransferase and displays different acyl-CoA substrate preferences than AtDGAT1

Demonstration of the function of the Arabidopsis thaliana acyl-CoA:diacylglycerol acyltransferase 2 (AtDGAT2) has remained elusive despite biochemical testing of genetic mutants and overexpression lines. We show that transiently expressed AtDGAT2 in the Nicotiana benthamiana leaf resulted in an increase in triacylglycerol twice as great as the increase observed following parallel expression of AtDGAT1. AtDGAT2 showed higher conversion from labeled diacylglycerol to triacylglycerol compared to AtDGAT1, and was acyl-CoA dependent. In addition, AtDGAT2 had different acyl-CoA substrate preference than AtDGAT1. These results allow us to conclude that AtDAGT2 is a functional acyl-CoA:diacylglycerol acyltransferase enzyme that can catalyse substantial increase in TAG synthesis.

Synergistic effect of WRI1 and DGAT1 coexpression on triacylglycerol biosynthesis in plants

Metabolic engineering approaches to increase plant oil levels can generally be divided into categories which increase fatty acid biosynthesis ('Push'), are involved in TAG assembly ('Pull') or increase TAG storage/decrease breakdown ('Accumulation'). In this study, we describe the surprising synergy when Push (WRI1) and Pull (DGAT1) approaches are combined. Co-expression of these genes in the Nicotiana benthamiana transient leaf expression system resulted in TAG levels exceeding those expected from an additive effect and biochemical tracer studies confirmed increased flux of carbon through fatty acid and TAG synthesis pathways. Leaf fatty acid profile also synergistically shifts from polyunsaturated to monounsaturated fatty acids.

Metabolic engineering plant seeds with fish oil-like levels of DHA

Background

Omega-3 long-chain (≥C₂₀) polyunsaturated fatty acids (ω3 LC-PUFA) have critical roles in human health and development with studies indicating that deficiencies in these fatty acids can increase the risk or severity of cardiovascular and inflammatory diseases in particular. These fatty acids are predominantly sourced from fish and algal oils, but it is widely recognised that there is an urgent need for an alternative and sustainable source of EPA and DHA. Since the earliest demonstrations of ω3 LC-PUFA engineering there has been good progress in engineering the C₂₀ EPA with seed fatty acid levels similar to that observed in bulk fish oil (∼18%), although undesirable ω6 PUFA levels have also remained high.

Methodology/Principal Findings

The transgenic seed production of the particularly important C₂₂ DHA has been problematic with many attempts resulting in the accumulation of EPA/DPA, but only a few percent of DHA. This study describes the production of up to 15% of the C₂₂ fatty acid DHA in Arabidopsis thaliana seed oil with a high ω3/ω6 ratio. This was achieved using a transgenic pathway to increase the C₁₈ ALA which was then converted to DHA by a microalgal Δ6-desaturase pathway.

Conclusions/Significance

The amount of DHA described in this study exceeds the 12% level at which DHA is generally found in bulk fish oil. This is a breakthrough in the development of sustainable alternative sources of DHA as this technology should be applicable in oilseed crops. One hectare of a Brassica napus crop containing 12% DHA in seed oil would produce as much DHA as approximately 10,000 fish.

Area-based socioeconomic status, type 2 diabetes and cardiovascular mortality in Scotland

AIMS/HYPOTHESIS

The aim of this study was to explore the relationships between type 2 diabetes mellitus, area-based socioeconomic status (SES) and cardiovascular disease mortality in Scotland.

METHODS

We used an area-based measure of SES, Scottish national diabetes register data linked to mortality records, and general population cause-specific mortality data to investigate the relationships between SES, type 2 diabetes and mortality from ischaemic heart disease (IHD) and cerebrovascular disease (CbVD), for 2001-2007. We used negative binomial regression to obtain age-adjusted RRs of mortality (by sex), comparing people with type 2 diabetes with the non-diabetic population.

RESULTS

Among 216,652 people aged 40 years or older with type 2 diabetes (980,687 person-years), there were 10,554 IHD deaths and 4,378 CbVD deaths. Age-standardised mortality increased with increasing deprivation, and was higher among men. IHD mortality RRs were highest among the least deprived quintile and lowest in the most deprived quintile (men: least deprived, RR 1.94 [95% CI 1.61, 2.33]; most deprived, RR 1.46 [95% CI 1.23, 1.74]) and were higher in women than men (women: least deprived, RR 2.84 [95% CI 2.12, 3.80]; most deprived, RR 2.04 [95% CI 1.55, 2.69]). A similar, weaker, pattern was observed for cerebrovascular mortality.

CONCLUSIONS/INTERPRETATION

Absolute risk of cardiovascular mortality is higher in people with diabetes than in the non-diabetic population and increases with increasing deprivation. The relative impact of diabetes on cardiovascular mortality differs by SES, and further efforts to reduce cardiovascular risk both in deprived groups and people with diabetes are required. Prevention of diabetes may reduce socioeconomic health inequalities.

Hospitalised hip fracture risk with rosiglitazone and pioglitazone use compared with other glucose-lowering drugs

AIMS/HYPOTHESIS

Current drug labels for thiazolidinediones (TZDs) warn of increased fractures, predominantly for distal fractures in women. We examined whether exposure to TZDs affects hip fracture in women and men and compared the risk to that found with other drugs used in diabetes.

METHODS

Using a nationwide database of prescriptions, hospital admissions and deaths in those with type 2 diabetes in Scotland we calculated TZD exposure among 206,672 individuals. Discrete-time failure analysis was used to model the effect of cumulative drug exposure on hip fracture during 1999-2008.

RESULTS

There were 176 hip fractures among 37,479 exposed individuals. Hip fracture risk increased with cumulative exposure to TZD: OR per year of exposure 1.18 (95% CI 1.09, 1.28; p = 3 × 10(-5)), adjusted for age, sex and calendar month. Hip fracture increased with cumulative exposure in both men (OR 1.20; 95% CI 1.03, 1.41) and women (OR 1.18; 95% CI 1.07, 1.29) and risks were similar for pioglitazone (OR 1.18) and rosiglitazone (OR 1.16). The association was similar when adjusted for exposure to other drugs for diabetes and for other potential confounders. There was no association of hip fracture with cumulative exposure to sulfonylureas, metformin or insulin in this analysis. The 90-day mortality associated with hip fractures was similar in ever-users of TZD (15%) and in never-users (13%).

CONCLUSIONS/INTERPRETATION

Hip fracture is a severe adverse effect with TZDs, affecting both sexes; labels should be changed to warn of this. The excess mortality is at least as much as expected from the reported association of pioglitazone with bladder cancer.

Recruiting a new substrate for triacylglycerol synthesis in plants: the monoacylglycerol acyltransferase pathway

BACKGROUND

Monoacylglycerol acyltransferases (MGATs) are predominantly associated with lipid absorption and resynthesis in the animal intestine where they catalyse the first step in the monoacylglycerol (MAG) pathway by acylating MAG to form diacylglycerol (DAG). Typical plant triacylglycerol (TAG) biosynthesis routes such as the Kennedy pathway do not include an MGAT step. Rather, DAG and TAG are synthesised de novo from glycerol-3-phosphate (G-3-P) by a series of three subsequent acylation reactions although a complex interplay with membrane lipids exists.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrate that heterologous expression of a mouse MGAT acyltransferase in Nicotiana benthamiana significantly increases TAG accumulation in vegetative tissues despite the low levels of endogenous MAG substrate available. In addition, DAG produced by this acyltransferase can serve as a substrate for both native and coexpressed diacylglycerol acyltransferases (DGAT). Finally, we show that the Arabidopsis thaliana GPAT4 acyltransferase can produce MAG in Saccharomyces cerevisiae using oleoyl-CoA as the acyl-donor.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates the concept of a new method of increasing oil content in vegetative tissues by using MAG as a substrate for TAG biosynthesis. Based on in vitro yeast assays and expression results in N. benthamiana, we propose that co-expression of a MAG synthesising enzyme such as A. thaliana GPAT4 and a MGAT or bifunctional M/DGAT can result in DAG and TAG synthesis from G-3-P via a route that is independent and complementary to the endogenous Kennedy pathway and other TAG synthesis routes.

Do men develop type 2 diabetes at lower body mass indices than women?

AIMS/HYPOTHESIS

To describe the associations between age, sex and BMI at diagnosis of type 2 diabetes, and test the hypothesis that men are diagnosed with diabetes at lower average BMI than women of similar age.

METHODS

Linear regression was used to estimate and compare the relationship between age and BMI at diagnosis among 51,920 men and 43,137 women included in a population-based diabetes register in Scotland for whom an index BMI measurement was taken within 1 year of diabetes diagnosis. We also examined HbA(1c) values by sex within the same timescale.

RESULTS

Mean BMI closest to date of diagnosis of type 2 diabetes mellitus was 31.83 kg/m(2) (SD 5.13) in men and 33.69 kg/m(2) (SD 6.43) in women. The inverse relationship between age and BMI at diagnosis of type 2 diabetes mellitus was significantly steeper in women than in men (slope estimate in men -0.12 kg/m(2) per year [95% CI -0.13, -0.12] women -0.18 kg/m(2) per year [95% CI -0.18, -0.17], p < 0.0001 for formal test of interaction). Mean BMI difference was most marked at younger ages and narrowed with advancing age. However, HbA(1c) levels within 1 year of diagnoses were broadly similar in men and women.

CONCLUSIONS/INTERPRETATION

Men are diagnosed with type 2 diabetes at lower BMI than women across the age range. This observation may help explain why type 2 diabetes is more common among middle-aged men in populations of European extraction. Whether the same pattern is also observed in other ethnic groups requires confirmation.

Inpatient costs for people with type 1 and type 2 diabetes in Scotland: a study from the Scottish Diabetes Research Network Epidemiology Group

AIMS/HYPOTHESIS

The rising prevalence of diabetes worldwide has increased interest in the cost of diabetes. Inpatient costs for all people with diabetes in Scotland were investigated.

METHODS

The Scottish Care Information-Diabetes Collaboration (SCI-DC), a real-time clinical information system of almost all diagnosed cases of diabetes in Scotland, UK, was linked to data on all hospital admissions for people with diabetes. Inpatient stay costs were estimated using the 2007-2008 Scottish National Tariff. The probability of hospital admission and total annual cost of admissions were estimated in relation to age, sex, type of diabetes, history of vascular admission, HbA(1c), creatinine, body mass index and diabetes duration.

RESULTS

In Scotland during 2005-2007, 24,750 people with type 1 and 195,433 people with type 2 diabetes were identified, accounting for approximately 4.3% of the total Scottish population (5.1 million). The estimated total annual cost of admissions for all people diagnosed with type 1 and type 2 diabetes was £26 million and £275 million, respectively, approximately 12% of the total Scottish inpatient expenditure (£2.4 billion). Sex, increasing age, serum creatinine, previous vascular history and HbA(1c) (the latter differentially in type 1 and type 2) were all associated with likelihood and total annual cost of admission.

CONCLUSIONS/INTERPRETATION

Diabetes inpatient expenditure accounted for 12% of the total Scottish inpatient expenditure, whilst people with diabetes account for 4.3% of the population. Of the modifiable risk factors, HbA(1c) was the most important driver of cost in type 1 diabetes.

Expanding the docosahexaenoic acid food web for sustainable production: engineering lower plant pathways into higher plants

BACKGROUND

Algae are becoming an increasingly important component of land plant metabolic engineering projects. Land plants and algae have similar enough genetics to allow relatively straightforward gene transfer and they also share enough metabolic similarities that algal enzymes often function in a plant cell environment. Understanding metabolic systems in algae can provide insights into homologous systems in land plants. As examples, algal models are currently being used by several groups to better understand starch and lipid metabolism and catabolism, fields which have relevance in land plants. Importantly, land plants and algae also have enough metabolic divergence that algal genes can often provide new metabolic traits to plants. Furthermore, many algal genomes have now been sequenced, with many more in progress, and this easy access to genome-wide information has revealed that algal genomes are often relatively simple when compared with plants.

SCOPE

One example of the importance of algal, and in particular microalgal, resources to land plant research is the metabolic engineering of long-chain polyunsaturated fatty acids into oilseed crops which typically uses microalgal genes to extend existing natural plant biosynthetic pathways. This review describes both recent progress and remaining challenges in this field.

What to add in with metformin in type 2 diabetes?

This review considers the therapeutic choices currently faced by people with type 2 diabetes and those caring for them when glucose levels initially controlled with lifestyle management and metformin start to rise. While sulphonylureas are familiar agents and cheaper than other alternatives, they cause hypoglycaemia and modest weight gain, and robust outcome data are still lacking. Dipeptidyl peptidase 4 inhibitors ('gliptins') have an attractive pharmacological and adverse effect profile, but their effects on the cardiovascular system are also uncertain. Thiazolidinediones ('glitazones') are effective glucose-lowering agents, but cause weight gain and increase the risk of fracture, while the cardiovascular benefits hoped for in association with 'insulin-sensitization' have not been as expected. Glucagon-like peptide-1 agonists will not be acceptable as initial second-line agents for many people as they are injectable rather than oral. Well-powered 'head-to-head' clinical trials of adequate duration are therefore required to allow evidence-based decisions on second-line therapy.

Isolation and characterisation of a high-efficiency desaturase and elongases from microalgae for transgenic LC-PUFA production

The production of long-chain polyunsaturated fatty acids from precursor molecules linoleic acid (LA; 18:2omega6) and alpha-linolenic acid (ALA; 18:3omega3) is catalysed by sequential desaturase and elongase reactions. We report the isolation of a front-end Delta6-desaturase gene from the microalgae Ostreococcus lucimarinus and two elongase genes, a Delta6-elongase and a Delta5-elongase, from the microalga Pyramimonas cordata. These enzymes efficiently convert their respective substrates when transformed in yeast (39-75% conversion for omega3 substrate fatty acids), and the Delta5-elongase in particular displays higher elongation efficiency (75% for conversion of eicosapentaenoic acid (20:5omega3) to docosapentaenoic acid (22:5omega3)) than previously reported genes. In addition, the Delta6-desaturase is homologous with acyl-CoA desaturases and shows a strong preference for the omega3 substrate ALA.

Microemulsions for oral delivery of insulin: design, development and evaluation in streptozotocin induced diabetic rats

Insulin loaded microemulsions were developed adopting a low shear reverse micellar approach using didoceyldimethylammonium bromide (DMAB) as the surfactant, propylene glycol (PG) as the co-surfactant, triacetin (TA) as the oil phase and insulin solution as the aqueous phase. A ternary phase diagram was constructed based on multiple cloud point titration to highlight the reverse micellar region. The droplet sizes of the microemulsions were 161.7±24.7nm with PDI of 0.447±0.076 and insulin entrapment of ∼85%. Transmission electron microscopy (TEM) revealed the spherical nature and size homogeneity of the microemulsion droplets. The conformational stability of the entrapped insulin within microemulsions was confirmed by fluorescence spectroscopy and circular dichroism. The microemulsions displayed a 10-fold enhancement in bioavailability compared with plain insulin solution administered per oral in healthy rats. The short-term in vivo efficacy in STZ induced diabetic rats provided the proof of concept by a modest glucose reduction at a dose of 20IU/kg. Together this preliminary data indicate the promise of microemulsions for oral delivery of insulin.

The use of metformin in type 1 diabetes: a systematic review of efficacy

AIMS/HYPOTHESIS

As adding metformin to insulin therapy has been advocated in type 1 diabetes, we conducted a systematic review of published clinical trials and clinical trial databases to assess the effects on HbA(1c), weight, insulin-dose requirement and adverse effects.

METHODS

We constructed evidence tables and fitted a fixed-effects model (inverse variance method) in order to assess heterogeneity between studies and give a crude measure of each overall treatment effect.

RESULTS

Of 197 studies identified, nine involved randomisation with informed consent of patients with type 1 diabetes to metformin (vs placebo or comparator) in either a parallel or crossover design for at least 1 week. We noted marked heterogeneity in study design, drug dose, age of participants and length of follow-up. Metformin was associated with reductions in: (1) insulin-dose requirement (5.7-10.1 U/day in six of seven studies); (2) HbA(1c) (0.6-0.9% in four of seven studies); (3) weight (1.7-6.0 kg in three of six studies); and (4) total cholesterol (0.3-0.41 mmol/l in three of seven studies). Metformin was well tolerated, albeit with a trend towards increased hypoglycaemia. Formal estimates of combined effects from the five trials which reported appropriate data indicated a significant reduction in insulin dose (6.6 U/day, p < 0.001) but no significant reduction in HbA(1c) (absolute reduction 0.11%, p = 0.42). No reported trials included cardiovascular outcomes.

CONCLUSIONS/INTERPRETATION

Metformin reduces insulin-dose requirement in type 1 diabetes but it is unclear whether this is sustained beyond 1 year and whether there are benefits for cardiovascular and other key clinical outcomes.

Rapid expression of transgenes driven by seed-specific constructs in leaf tissue: DHA production

BACKGROUND

Metabolic engineering of seed biosynthetic pathways to diversify and improve crop product quality is a highly active research area. The validation of genes driven by seed-specific promoters is time-consuming since the transformed plants must be grown to maturity before the gene function can be analysed.

RESULTS

In this study we demonstrate that genes driven by seed-specific promoters contained within complex constructs can be transiently-expressed in the Nicotiana benthamiana leaf-assay system by co-infiltrating the Arabidopsis thaliana LEAFY COTYLEDON2 (LEC2) gene. A real-world case study is described in which we first assembled an efficient transgenic DHA synthesis pathway using a traditional N. benthamiana Cauliflower Mosaic Virus (CaMV) 35S-driven leaf assay before using the LEC2-extended assay to rapidly validate a complex seed-specific construct containing the same genes before stable transformation in Arabidopsis.

CONCLUSIONS

The LEC2-extended N. benthamiana assay allows the transient activation of seed-specific promoters in leaf tissue. In this study we have used the assay as a rapid preliminary screen of a complex seed-specific transgenic construct prior to stable transformation, a feature that will become increasingly useful as genetic engineering moves from the manipulation of single genes to the engineering of complex pathways. We propose that the assay will prove useful for other applications wherein rapid expression of transgenes driven by seed-specific constructs in leaf tissue are sought.

A leaf-based assay using interchangeable design principles to rapidly assemble multistep recombinant pathways

The assembly of multistep recombinant pathways in stably transformed plants is a cornerstone of crops producing new products yet can be a laborious and time-consuming process. Any heterologous expression platform capable of providing a rapid estimation of the functional assembly of an entire pathway would guide the design of such transgenic traits. In this study, we use a Nicotiana benthamiana transient leaf expression system to simultaneously express five genes, from five independent T(DNA) binary vectors, to assemble a complete recombinant pathway in five days. In this study, we demonstrate the production of long-chain polyunsaturated fatty acids (LC-PUFA) requiring five transgene-encoded reactions to convert endogenous fatty acids to LC-PUFA. The addition of a triacylglycerol assembly enzyme, Arabidopsis thaliana diacylglyceride-O-acyltransferase, and fractionation of the total lipid profile demonstrated that leaf oils contained 37% newly synthesised LC-PUFA, including 7% arachidonic acid (AA), 6% eicosopentaenoic acid and 3% docosahexaenoic acid. The calculation of enzymatic conversion efficiencies at each step of LC-PUFA synthesis suggests that this transient assembly of a complicated multistep pathway is highly efficient. Unlike experiments using stably transformed plants our assembly of an intricate pathway maintained full gene-for-gene interchangeability and required a fraction of the time and glasshouse space. Furthermore, an exogenous LC-PUFA fatty acid substrate, AA, was fed and metabolised by a transiently expressed Delta17-desaturase enzyme, and provided results similar to those obtained in yeast feeding experiments. Although the assay was ideal for LC-PUFA pathways, this assay format may become a powerful tool for the characterisation and step-wise improvement of other recombinant pathways and multigenic traits.

Isolation and characterisation of a delta5-fatty acid elongase from the marine microalga Pavlova salina

The marine microalga Pavlova salina (Haptophyta, Pavlovophyceae) produces lipids containing approximately 50% n-3 long-chain polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A full-length cDNA sequence, designated PsElo5, was isolated from P. salina. Sequence alignment showed that the gene was homologous to corresponding ELO-type elongases from other microalgae. Heterologous expression of PsElo5 in yeast and in higher plants confirmed that it encodes a specific Delta5-elongase activity as predicted and, furthermore, within the n-3 pathway, the elongation activity was confined exclusively to EPA.

Endothelium-dependent relaxation is resistant to inhibition of nitric oxide synthesis, but sensitive to blockade of calcium-activated potassium channels in essential hypertension

In human essential hypertension (EH), endothelium-dependent relaxation can occur independent of nitric oxide (NO) and prostacyclin (PGI(2)). Recent in vivo data suggest that rapid compensatory upregulation of endothelial cytochrome P450 epoxygenase 2C9 occurs to preserve vasorelaxation under conditions of decreased NO bioavailability. As one of the vascular actions of CYP2C9 is to modulate small and intermediate conductance endothelial calcium-activated potassium channels (SK(Ca) and IK(Ca)), we examined whether endothelium-dependent relaxation is sensitive to inhibitors of these channels (apamin and charybdotoxin) in resistance-sized vessels from human with EH. Subcutaneous gluteal biopsies were performed on 12 humans with EH and 12 matched control subjects. Resistance arteries were dissected and relaxation responses to carbachol were assessed ex vivo using wire myography in the presence of: (i) N(G)-nitro-L-arginine (L-NOARG)/indomethacin; and (ii) apamin/charybdotoxin. Maximal carbachol relaxation was impaired in EH vs control subjects. No differences in responses were observed with the endothelium-independent agonist, S-nitroso-N-acetyl-penicillamine. Relaxation to carbachol was attenuated following incubation with L-NOARG/indomethacin in vessels from control subjects (P<0.01 analysis of variance (ANOVA)), but not in vessels from patients with EH. The reverse pattern was seen following apamin/charybdotoxin with carbachol relaxation attenuated only in EH vessels (P<0.001 ANOVA). Endothelium-dependent relaxation is resistant to endothelial nitric oxide synthase inhibition but sensitive to blockade of calcium-activated potassium channels in human EH. Studies with more specific inhibitors are required to determine whether this response is mediated by endothelial potassium channel subtypes (SK(Ca) and IK(Ca)).

Isolation and characterization of genes from the marine microalga Pavlova salina encoding three front-end desaturases involved in docosahexaenoic acid biosynthesis

The marine microalga Pavlova salina produces lipids containing approximately 50% omega-3 long chain polyunsaturated fatty acids (LC-PUFA) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Three cDNA sequences, designated PsD4Des, PsD5Des, PsD8Des, were isolated from P. salina and shown to encode three front-end desaturases with Delta4, Delta5 and Delta8 specificity, respectively. Southern analysis indicated that the P. salina genome contained single copies of all three front-end fatty acid desaturase genes. When grown at three different temperatures, analysis of fatty acid profiles indicated P. salina desaturation conversions occurred with greater than 95% efficiency. Real-Time PCR revealed that expression of PsD8Des was higher than for the other two genes under normal growth conditions, while PsD5Des had the lowest expression level. The deduced amino acid sequences from all three genes contained three conserved histidine boxes and a cytochrome b(5) domain. Sequence alignment showed that the three genes were homologous to corresponding desaturases from other microalgae and fungi. The predicted activities of these three front-end desaturases leading to the synthesis of LC-PUFA were also confirmed in yeast and in higher plants.