Mitochondrial metabolism of sexual and asexual blood stages of the malaria parasite Plasmodium falciparum

Background

The carbon metabolism of the blood stages of Plasmodium falciparum, comprising rapidly dividing asexual stages and non-dividing gametocytes, is thought to be highly streamlined, with glycolysis providing most of the cellular ATP. However, these parasitic stages express all the enzymes needed for a canonical mitochondrial tricarboxylic acid (TCA) cycle, and it was recently proposed that they may catabolize glutamine via an atypical branched TCA cycle. Whether these stages catabolize glucose in the TCA cycle and what is the functional significance of mitochondrial metabolism remains unresolved.

Results

We reassessed the central carbon metabolism of P. falciparum asexual and sexual blood stages, by metabolically labeling each stage with ¹³C-glucose and ¹³C-glutamine, and analyzing isotopic enrichment in key pathways using mass spectrometry. In contrast to previous findings, we found that carbon skeletons derived from both glucose and glutamine are catabolized in a canonical oxidative TCA cycle in both the asexual and sexual blood stages. Flux of glucose carbon skeletons into the TCA cycle is low in the asexual blood stages, with glutamine providing most of the carbon skeletons, but increases dramatically in the gametocyte stages. Increased glucose catabolism in the gametocyte TCA cycle was associated with increased glucose uptake, suggesting that the energy requirements of this stage are high. Significantly, whereas chemical inhibition of the TCA cycle had little effect on the growth or viability of asexual stages, inhibition of the gametocyte TCA cycle led to arrested development and death.

Conclusions

Our metabolomics approach has allowed us to revise current models of P. falciparum carbon metabolism. In particular, we found that both asexual and sexual blood stages utilize a conventional TCA cycle to catabolize glucose and glutamine. Gametocyte differentiation is associated with a programmed remodeling of central carbon metabolism that may be required for parasite survival either before or after uptake by the mosquito vector. The increased sensitivity of gametocyte stages to TCA-cycle inhibitors provides a potential target for transmission-blocking drugs.

Spatial and temporal mapping of the PfEMP1 export pathway in Plasmodium falciparum

The human malaria parasite, Plasmodium falciparum, modifies the red blood cells (RBCs) that it infects by exporting proteins to the host cell. One key virulence protein, P. falciparum Erythrocyte Membrane Protein-1 (PfEMP1), is trafficked to the surface of the infected RBC, where it mediates adhesion to the vascular endothelium. We have investigated the organization and development of the exomembrane system that is used for PfEMP1 trafficking. Maurer's cleft cisternae are formed early after invasion and proteins are delivered to these (initially mobile) structures in a temporally staggered and spatially segregated manner. Membrane-Associated Histidine-Rich Protein-2 (MAHRP2)-containing tether-like structures are generated as early as 4 h post invasion and become attached to Maurer's clefts. The tether/Maurer's cleft complex docks onto the RBC membrane at ~20 h post invasion via a process that is not affected by cytochalasin D treatment. We have examined the trafficking of a GFP chimera of PfEMP1 expressed in transfected parasites. PfEMP1B-GFP accumulates near the parasite surface, within membranous structures exhibiting a defined ultrastructure, before being transferred to pre-formed mobile Maurer's clefts. Endogenous PfEMP1 and PfEMP1B-GFP are associated with Electron-Dense Vesicles that may be responsible for trafficking PfEMP1 from the Maurer's clefts to the RBC membrane.

Origin, composition, organization and function of the inner membrane complex of Plasmodium falciparum gametocytes

The most virulent of the human malaria parasites, Plasmodium falciparum, undergoes a remarkable morphological transformation as it prepares itself for sexual reproduction and transmission via mosquitoes. Indeed P. falciparum is named for the unique falciform or crescent shape of the mature sexual stages. Once the metamorphosis is completed the mature gametocyte releases from sequestration sites and enters the circulation making it accessible to feeding mosquitoes. Early ultrastructural studies showed that gametocyte elongation is driven by the assembly of a system of flattened cisternal membrane compartments underneath the parasite plasma membrane and a supporting network of microtubules. Here we describe the molecular composition and origin of the sub-pellicular membrane complex, and show that it is analogous to the inner membrane complex, an organelle with structural and motor functions that is well conserved across the apicomplexa. We identify novel cross-linking elements that may help stabilize the inner membrane complex during gametocyte development. We show that changes in gametocyte morphology are associated with an increase in cellular deformability and postulate that this enables the gametocytes to circulate in the blood stream without being detected and removed by the mechanical filtering mechanisms in the host's spleen.

Genetic ablation of a Maurer's cleft protein prevents assembly of the Plasmodium falciparum virulence complex

The malaria parasite Plasmodium falciparum assembles knob structures underneath the erythrocyte membrane that help present the major virulence protein, P. falciparum erythrocyte membrane protein-1 (PfEMP1). Membranous structures called Maurer's clefts are established in the erythrocyte cytoplasm and function as sorting compartments for proteins en route to the RBC membrane, including the knob-associated histidine-rich protein (KAHRP), and PfEMP1. We have generated mutants in which the Maurer's cleft protein, the ring exported protein-1 (REX1) is truncated or deleted. Removal of the C-terminal domain of REX1 compromises Maurer's cleft architecture and PfEMP1-mediated cytoadherance but permits some trafficking of PfEMP1 to the erythrocyte surface. Deletion of the coiled-coil region of REX1 ablates PfEMP1 surface display, trapping PfEMP1 at the Maurer's clefts. Complementation of mutants with REX1 partly restores PfEMP1-mediated binding to the endothelial cell ligand, CD36. Deletion of the coiled-coil region or complete deletion of REX1 is tightly associated with the loss of a subtelomeric region of chromosome 2, encoding KAHRP and other proteins. A KAHRP-green fluorescent protein (GFP) fusion expressed in the REX1-deletion parasites shows defective trafficking. Thus, loss of functional REX1 directly or indirectly ablates the assembly of the P. falciparum virulence complex at the surface of host erythrocytes.

Data warehousing methods and processing infrastructure for brain recovery research

In order to accelerate translational neuroscience with the goal of improving clinical care it has become important to support rapid accumulation and analysis of large, heterogeneous neuroimaging samples and their metadata from both normal control and patient groups. We propose a multi-centre, multinational approach to accelerate the data mining of large samples and facilitate data-led clinical translation of neuroimaging results in stroke. Such data-driven approaches are likely to have an early impact on clinically relevant brain recovery while we simultaneously pursue the much more challenging model-based approaches that depend on a deep understanding of the complex neural circuitry and physiological processes that support brain function and recovery. We present a brief overview of three (potentially converging) approaches to neuroimaging data warehousing and processing that aim to support these diverse methods for facilitating prediction of cognitive and behavioral recovery after stroke, or other types of brain injury or disease.

Dual labeling with a far red probe permits analysis of growth and oxidative stress in P. falciparum-infected erythrocytes

The malaria parasite, Plasmodium falciparum, develops within human erythrocytes, consuming host hemoglobin to support its own growth. Reactive oxygen species (superoxide and hydrogen peroxide) are by-products of hemoglobin digestion and are believed to exert significant oxidative stress on the parasite. We have characterized a cell permeant, far red fluorescent nucleic acid-binding dye, SYTO 61, that can be used to distinguish between uninfected and infected erythrocytes in a flow cytometric format. The spectral properties of SYTO 61 make it suitable for use in combination with the fluorescent reactive oxygen species reporter 5-(and-6)-chloromethyl-2',7'-dichlorodihydro-fluorescein diacetate acetyl ester. We have used this probe combination to measure oxidative stress in different stages of live P. falciparum. Low levels of the oxidized, fluorescent form of the reporter (2',7'-dichlorofluorescein, DCF) are detected in ring stage parasites; the DCF signal increases as the intraerythrocytic parasite matures into the trophozoite stage where active hemoglobin digestion occurs. Treatment of infected erythrocytes with the cysteine protease inhibitor, E-64, which inhibits hemoglobin digestion, decreases the DCF signal. We show that E-64 prevents schizont rupture but also causes delayed lethal effects when ring stage cultures are exposed to the drug. We also examined cultures of parasites in erythrocytes harboring 98% catalase inactivation and found no effect on growth and only a modest increase in DCF oxidation.

Toxicity associated with combination oxaliplatin plus fluoropyrimidine with or without cetuximab in the MRC COIN trial experience

We present the preliminary toxicity data from the MRC COIN trial, a phase III randomised controlled trial of first-line therapy in advanced colorectal cancer, with particular reference to the addition of cetuximab to an oxaliplatin-fluoropyrimidine combination. A total of 804 patients were randomised between March 2005 and July 2006 from 78 centres throughout the United Kingdom. Patients were allocated to oxaliplatin plus fluoropyrimidine chemotherapy with or without the addition of weekly cetuximab. The choice of fluoropyrimidine (either 5-fluorouracil (5FU) or capecitabine) was decided by the treating physician and patient before randomisation. Toxicity data were collected from all patients. Two hundred and three patients received 5FU plus oxaliplatin (OxMdG, 25%), 333 oxaliplatin+capecitabine (Xelox, 41%), 102 received OxMdG+cetuximab (OxMdG+C, 13%) and 166 Xelox+cetuximab (21%). Percent grade 3/4 toxicities included diarrhoea 6, 15, 13 and 25%, nausea/vomiting 3, 7, 7 and 14% for OxMdG, Xelox, OxMdG+C and Xelox+C, respectively. Sixty-day all-cause mortality was 6, 5, 5 and 7%. Statistically significant differences were evident for patients receiving Xelox+cetuximab vs Xelox alone: diarrhoea relative risk (RR) 1.69 (1.17, 2.43, P=0.005) and nausea/vomiting RR 2.01 (1.16, 3.47, P=0.012). The excess toxicity observed in the oxaliplatin-, capecitabine-, cetuximab-treated patients led the trial management group to conclude that a capecitabine dose adjustment was required to maintain safety levels when using this regimen.

Calcium and zinc ion release from polyalkenoate cements formed from zinc oxide/apatite mixtures

Calcium and zinc ion release from hydroxyapatite-zinc oxide-poly(acrylic acid) (HAZnO-PAA) composite cements into deionised water was investigated as a function of HA content, PAA concentration, PAA molecular weight and maturation time. At any given maturation time, zinc ion release was constant until the HA content was at the maximum loading (60 wt%) resulting in the cement matrix breaking up, allowing exacerbated ion release. The calcium ion release increased with increased HA content in the composite until the maximum loading where the release drops off. Up to this point, the release of both ionic species was proportional to square root time for the initial 24 hour period, indicating that the release is diffusion controlled. In agreement with related data from conventional Glass Polyalkenoate Cements (GPCs), it is the concentration of the PAA, not the molecular weight, that influences ion release from these materials. However, unlike GPCs, the release of the active ions results in a pH rise in the deionised water, more conventionally seen with Bioglass and related bioactive glasses. It is this pH rise, caused by the ion exchange of Zn(2+) and Ca(2+) for H(+) from the water, leaving an excess of OH(-), that should result in a favourable bioactive response both in vitro and in-vivo.

Nutrition in the community - an exploratory study of oral nutritional supplements in a health board area in Ireland

BACKGROUND

A review of the General Medical (Payments) Scheme data in the Midland Health Board (MHB) Ireland identified a spend of just over euro 0.5 million on enteral nutritional supplements (oral and tube feeds) in an 11-month period in 1998 [General Medical Services (Payments) Board, 1998, MHB Clinical Nutritional Products: January-December 1998, Dublin]. In 2000, a figure of euro5 million was reported as the annual spend (oral and tube feeds) [General Medical Services (Payments) Board, 2000, MHB Clinical Nutritional Products: January-December 2000, Dublin]. Research has shown that a high proportion of Oral Nutritional Supplements (ONS) are inappropriately prescribed by primary care practitioners (Gall et al., 2001). The role of General Practitioners (GPs) and Public Health Nurses (PHNs) in prescribing ONS to patients aged 65 years and older was examined, as they are directly involved in the delivery of primary health care.

AIM

(i) Assess current trends, decision-making processes and monitoring procedures in the use of ONS for older patients in the community. (ii) Identify whether nutritional assessments and appropriate nutritional criteria are standard practice in determining selection of ONS.

METHODS

A study was conducted among 99 GPs and 120 PHNs in the MHB. All GPs were selected to participate and 50% (60) of PHNs were randomly selected. A telephone questionnaire was administered to each subject over a 2-week period.

RESULTS

Both GPs (78%) and PHNs (47%) reported that their prescription of/recommendations for ONS had increased in the last 4 years. None conducted a full nutritional assessment, but 25% of PHNs used a Nutrition Screening Tool when trying to ascertain whether a patient requires an ONS. Only 19.6% of GPs and 6.8% of PHNs surveyed were aware of the calorie content of a standard 200 mL ONS (sip-feed). In addition, a very significant proportion of both GPs and PHNs do not appear to give appropriate dietary advice to patients who may be at risk of malnutrition. Only 55% of GPs stated that they would specifically review a patient's ONS prescription. All GPs said that they would not conduct a full nutritional assessment at the review appointment.

CONCLUSION

The results of this study raise concerns as to the appropriateness of current ONS prescription and monitoring in the community. They also highlight the need for further intervention in the primary care setting in order to ensure that elderly malnourished patients are detected, treated and monitored in an appropriate and cost-effective manner.

Zinc ion release from novel hard tissue biomaterials

Zinc polyalkenoate cements (ZPCs) and glass polyalkenoate cements (GPCs) are used routinely in dentistry, but have potential for orthopaedic applications as they set at body temperature without shrinkage or significant heat evolution. However, the materials have drawbacks; ZPCs are biocompatible in implant studies, but a fibrous collagen capsular layer forms adjacent to the cement. GPCs are bioactive in the bone environment as a result of the release of calcium, phosphate and fluoride ions, as well as the formation of a silicious gel phase, but research has shown that aluminum ions released result in defective bone mineralisation and as a consequence the ability of these cements to chemically bond to bone is lost. Two approaches have been developed to overcome these problems. The ZPC route considers a ZnO : hydroxyapatite (HA) : poly(acrylic acid) (PAA) mixture, the HA incorporated to improve bioactivity. The GPC route employs a calcium zinc silicate glass; the zinc taking the role that aluminum plays in conventional GPCs. This study has shown that cements can be formulated by an acid base reaction between PAA and both calcium zinc silicate glasses (GPCs) and a mixture of hydroxyapatite and zinc oxide (ZPCs). The moduli of these cements are comparable to both bone and conventional acrylic cements, highlighting their potential for biomedical applications. Unfortunately, both materials have previously been shown to be toxic by cell culture methods, as a result of high zinc ion release, and so it is necessary to study ion release profiles of the cements in order to determine the magnitude of this release. Considering the ZPCs, the modulus of the cement has an inversely proportional relationship to the zinc ion release. From the data presented it is clear that increases in polymer concentration results in lower amounts of zinc ions being released, whilst molar mass of the PAA has no influence. Therefore it would appear that polymer concentration has a significant influence over ion release. Generally, the amount of Zn(2+) released decreases with increasing HA content and/or decreasing ZnO content. Considering the GPCs, the materials are all seen to release large amounts of the active ion, when compared to the commercial versions. The extent of this release increases with temperature and agitation. The release could be minimised by an increased P : L mixing ratio, and an increased PAA concentration, which would produce a more cross-linked cement matrix. Minimising the release of the active ion should improve the in vitro bioactivity of both materials. However, for a full understanding of the clinical benefits of such materials, an in vivo study would be required.

The influence of hydroxyapatite: zinc oxide ratio on the setting behavior and mechanical properties of polyalkenoate cements

The influence of hydroxyapatite (HA) content on the setting behavior and mechanical properties of hydroxyapatite-zinc oxide-poly(acrylic acid) (HA-ZnO-PAA) composite cements were investigated as a function of HA content. The working time increased with HA content up to 45 wt % HA and then decreased whilst the setting time increased with increasing HA content. Mechanical properties were determined after storage in water at 37 degrees C for 1, 7 and 28 days. Young's moduli and compressive strength go through a maximum at approximately 30 and 45 wt % HA. Young's modulus increases with time, which is consistent with an ongoing crosslinking reaction.

The influence of poly(acrylic acid) molar mass on the properties of polyalkenoate cements formed from zinc oxide/apatite mixtures

The influence of poly(acrylic acid) molar mass was investigated on cements formed from zinc oxide-apatite mixtures at three aging times; one, seven and 28 days. Cements based on both hydroxyapatite and fluorapatite were investigated. The compressive strength, un-notched fracture strength and fracture toughness increased markedly with poly(acrylic acid) molar mass. The fracture toughness and un-notched fracture strength increased with aging time for the two highest molar mass cements, but decreased with time for the two lowest molar mass cements. The greater chain entanglement density present in the higher molar mass cements is thought to contribute significantly to the cement stability in addition to the crosslinking of the polyacrylate chains by calcium and zinc ions. Substitution of hydroxyapatite by fluorapatite had no significant influence on the mechanical properties of the cements at aging times longer than one day.

Proteinuria and mortality in diabetes: the WHO Multinational Study of Vascular Disease in Diabetes

The relation between proteinuria and mortality was investigated in 1188 patients with Type 1 diabetes and 3234 patients with Type 2 diabetes, aged 35-55 at baseline and followed up for a mean of 9.4 +/- 3.1 years in the WHO Multinational Study of Vascular Disease in Diabetes. Baseline prevalence of light or heavy proteinuria was the same (25%) in both types of diabetes after adjustment for differences in diabetes duration. Compared with patients with no proteinuria, all cause mortality ratios were 1.5 (95% confidence interval 1.1-2.0) and 2.9 (2.2-3.8) for Type 1 patients with light and heavy proteinuria, respectively, and 1.5 (1.2-1.8) and 2.8 (2.3-3.4) for Type 2 patients, after adjustment for age, duration of diabetes, blood pressure, cholesterol, and smoking. Proteinuria was associated with significantly increased mortality from renal failure, cardiovascular disease, and all other causes of death. In both types of diabetes, the association was strongest for renal deaths, and of similar magnitude for cardiovascular and all other causes of death. In conclusion, proteinuria is a common, important, and rather non-specific risk factor for increased morbidity and mortality in diabetes. The relation of proteinuria to mortality is similar for both types of diabetes. The benefits and risks of proteinuria reduction should be examined in large randomized trials with clinical endpoints.

New home-delivered training prospects for people with disabilities

The 'Home-Delivered Training Project' set out to test the viability of providing training in Information Technology to people with physical disabilities in their homes, using computers and modem links. The course included core modules on business applications software and optional modules on more specialist applications. The computer-based approach to instruction included computerized monitoring of student progress, the provision of on-line tutorial support as well as computerized test administration and marking. The 20 course participants, who lived in locations throughout Ireland, were unable to attend conventional training centres because of their limited mobility or other restrictions arising from their disabilities. They differed considerably in terms of disability type, educational qualifications and experience with computers. All but one of them completed the course successfully and were awarded certificates which are recognized in Ireland and the United Kingdom. Overall, they were very positive about the course, mainly because they could undertake it in their homes at a flexible pace to suit their learning patterns and the requirements of their disabilities. They recognized, however, that studying at home required a self-disciplined study routine which was not always easy to maintain. The fact that they were awarded an internationally recognized qualification on completion of the course was an important motivating factor, as it made the course relevant in terms of their employment aspirations.

A follow-up study of diabetic Oklahoma Indians. Mortality and causes of death

OBJECTIVE

To determine the mortality rates and causes of death for diabetic Oklahoma Indian adults by sex and age.

RESEARCH DESIGN AND METHODS

This was a cohort follow-up study with baseline examination between 1972-1980 and the mortality follow-up between 1986 and 1989. Mean follow-up time was 10 +/- 4 yr. A quasi-random sample of 1012 (379 men and 633 women) NIDDM American Indians in Oklahoma was performed. Mean age was 52 yr and duration was 7 yr at baseline. Mean degree of Indian blood was 92% (77% full blood). At follow-up, 548 (54%) were alive, 452 (45%) were decreased, and 12 (1%) could not be traced.

RESULTS

Death certificates were obtained and coded (ICD-9) for 439 (97%) of the deceased. Mean annual mortality rates were 4.99% for men and 4.17% for women, with an increasing trend with age for both sexes. Compared with the general population of Oklahoma, the observed/expected ratios for number of deaths were 2.92 for men and 4.09 for women (P < 0.0001). The three leading causes of death were circulatory disease (38%), diabetes (24%), and malignant neoplasms (12%).

CONCLUSIONS

There is an excessively high mortality among diabetic Oklahoma Indians compared with the general population in the state and with diabetic patients in other populations.

Effects of secretin and caerulein on enzymes of cultured pancreatic acinar cells

We examined the effects of secretin (0 to 200 nM) and caerulein (0 to 100 nM) on rat pancreatic acinar cells cultured 0 to 48 h in serum-free medium. The effects of 100 nM secretin with 1 nM caerulein were also studied because secretin may potentiate the effects of caerulein. Cellular and media (secreted) lipase and amylase were analyzed as were cellular DNA and protein content. Cellular lipase and amylase activities significantly decreased (P less than 0.0001) over time in all treatment groups, whereas media amylase and lipase significantly increased (P less than 0.0001). Neither secretin nor caerulein affected cellular lipase or media amylase. However, secretin significantly increased (P less than 0.04) and caerulein tended to increase (P less than 0.08) media lipase in a dose-dependent manner. At 12 h, 10 nM secretin maximally increased media lipase (58%) suggesting that cultured acinar cells remain responsive to secretin in vitro. Caerulein, at all concentrations, significantly decreased (P less than 0.001) cellular amylase but exhibited a dose-dependent effect only at 24 h when 100 nM caerulein maximally decreased cellular amylase (34%). Secretin (100 nM) did not alter these effects of caerulein. These results support the proposed role of caerulein in the regulation of amylase but not a direct role of secretin in the regulation of lipase.