Blood-stage malaria infection in diabetic mice

Ethanolic extract of Camellia sinensise licited hypoglycemic but lacked antimalarial properties in Plasmodium berghei-infected diabetic mice

The in vivo antimalarial and antidiabetic activity of extract of Camellia sinensis (ECS) in alloxan-induced diabetic and Plasmodium berghei-infected mice were investigated. Eighty-four BALB/c mice divided into sets 1 & 2 infected with P. berghei and 2 & 3 injected with alloxan received either distilled water, ECS (300mg/kg), Chloroquine (CQ-10mg/kg) or Metformin (250mg/kg). Results showed significant increases (p<0.05) in percentage parasitaemia of P. berghei-infected mice treated with ECS and P. berghei-diabetic mice. Furthermore, ECS significantly decreased (p<0.05) blood glucose and PCV in diabetic and P. berghei-diabetic mice.  ECS regenerated pancreatic islet cells in P. berghei-infected-diabetes but lacked appreciable antimalarial activity.

The plasma membrane calcium ATPase 4 does not influence parasite levels but partially promotes experimental cerebral malaria during murine blood stage malaria

BACKGROUND

Recent genome wide analysis studies have identified a strong association between single nucleotide variations within the human ATP2B4 gene and susceptibility to severe malaria. The ATP2B4 gene encodes the plasma membrane calcium ATPase 4 (PMCA4), which is responsible for controlling the physiological level of intracellular calcium in many cell types, including red blood cells (RBCs). It is, therefore, postulated that genetic differences in the activity or expression level of PMCA4 alters intracellular Ca2+ levels and affects RBC hydration, modulating the invasion and growth of the Plasmodium parasite within its target host cell.

METHODS

In this study the course of three different Plasmodium spp. infections were examined in mice with systemic knockout of Pmca4 expression.

RESULTS

Ablation of PMCA4 reduced the size of RBCs and their haemoglobin content but did not affect RBC maturation and reticulocyte count. Surprisingly, knockout of PMCA4 did not significantly alter peripheral parasite burdens or the dynamics of blood stage Plasmodium chabaudi infection or reticulocyte-restricted Plasmodium yoelii infection. Interestingly, although ablation of PMCA4 did not affect peripheral parasite levels during Plasmodium berghei infection, it did promote slight protection against experimental cerebral malaria, associated with a minor reduction in antigen-experienced T cell accumulation in the brain.

CONCLUSIONS

The finding suggests that PMCA4 may play a minor role in the development of severe malarial complications, but that this appears independent of direct effects on parasite invasion, growth or survival within RBCs.

Seasonality in diabetes in Yaounde, Cameroon: a relation with precipitation and temperature

Background

Diabetes is a growing health concern in developing countries, with Cameroon population having an estimated 6% affected. Of note, hospital attendees appear to be increasing all over the country, with fluctuating numbers throughout the annual calendar. The aim of the study was to investigate the relationship between diabete hospitalization admission rates and climate variations in Yaounde.

Methods

A retrospectively designed study was conducted in four health facilities of Yaounde (Central Hospital, University teaching hospital, Biyem-Assi and Djoungolo District Hospitals), using medical records from 2000 to 2008. A relationship between diabetes (newly diagnosed diabetes patients or decompensated diabetics) hospitalization admissions and climate variations was determined using the “2000–2008” national meteorological database (precipitation and temperature).

Results

The monthly medians of precipitation and temperature were 154mm and 25 °C, respectively. The month of October received 239mm of precipitation. The monthly medians of diabetic admissions rates (newly diagnosed or decompensated diabetes patients) were 262 and 72 respectively. October received 366 newly diagnosed diabetics and 99 decompensated diabetics. Interestingly, diabetic hospitalization admissions rates were higher during the rainy (51 %, 1633/3232) than the dry season, though the difference was non-significant. The wettest month (October) reported the highest cases (10 %, 336/3232) corresponding to the month with the highest precipitation level (239mm). Diabetes hospitalization admissions rates varied across health facilities [from 6 % (189/3232) in 2000 to 15 % (474/3232) in 2008].

Conclusion

Diabetes is an important epidemiological disease in the city of Yaounde. The variation in the prevalence of diabetes is almost superimposed to that of precipitation; and the prevalence seems increasing during raining seasons in Yaoundé.

Enhanced transmission of malaria parasites to mosquitoes in a murine model of type 2 diabetes

Background

More than half of the world’s population is at risk of malaria and simultaneously, many malaria-endemic regions are facing dramatic increases in the prevalence of type 2 diabetes. Studies in murine malaria models have examined the impact of malaria infection on type 2 diabetes pathology, it remains unclear how this chronic metabolic disorder impacts the transmission of malaria. In this report, the ability type 2 diabetic rodents infected with malaria to transmit parasites to Anopheles stephensi mosquitoes is quantified.

Methods

The infection prevalence and intensity of An. stephensi mosquitoes that fed upon control or type 2 diabetic C57BL/6 db/db mice infected with either lethal Plasmodium berghei NK65 or non-lethal Plasmodium yoelii 17XNL murine malaria strains were determined. Daily parasitaemias were also recorded.

Results

A higher percentage of mosquitoes (87.5 vs 61.5 % for P. yoelii and 76.9 vs 50 % for P. berghei) became infected following blood feeding on Plasmodium-infected type 2 diabetic mice compared to mosquitoes that fed on infected control animals, despite no significant differences in circulating gametocyte levels.

Conclusions

These results suggest that type 2 diabetic mice infected with malaria are more efficient at infecting mosquitoes, raising the question of whether a similar synergy exists in humans.

Malaria and obesity: obese mice are resistant to cerebral malaria

Background

The relationship between malaria and obesity are largely unknown. This is partly due to the fact that malaria occurs mainly in tropical areas where, until recently, obesity was not prevalent. It now appears, however, that obesity is emerging as a problem in developing countries. To investigate the possible role of obesity on the host-parasite response to malarial infection, this study applied a murine model, which uses the existence of genetically well characterized obese mice.

Methods

The receptivity of obese homozygous ob/ob mice was compared to the receptivity of control heterozygous ob/+ lean mice after a single injection of Plasmodium berghei ANKA sporozoites. Both parasitaemia and mortality in response to infection were recorded.

Results

The control mice developed the expected rapid neurological syndromes associated with the ANKA strain, leading to death after six days, in absence of high parasitaemia. The obese mice, on the other hand, did not develop cerebral malaria and responded with increasing parasitaemia, which produced severe anemia leading to death 18–25 days after injection.

Conclusion

The observed major differences in outward symptoms for malarial infection in obese versus control mice indicate a link between obesity and resistance to the infection which could be addressed by malariologists studying human malaria.

Tuberculosis susceptibility of diabetic mice

Increased susceptibility to infections, including tuberculosis (TB), is a major cause of morbidity and mortality in patients with diabetes. Despite the clinical importance of this problem, little is known about how diabetes impairs protective immunity. We modeled this phenomenon by infecting acute (< or = 1 mo) or chronic (> or = 3 mo) diabetic mice with a low aerosol dose of Mycobacterium tuberculosis (Mtb) Erdman. Diabetes was induced by streptozotocin (STZ) treatment of C57BL/6 mice, while another mouse strain and diabetes model were used to confirm key observations. Lungs from acute diabetic and euglycemic mice had similar bacterial burdens, cytokine expression profiles, and histopathology. In contrast, chronic diabetic mice had > 1 log higher bacterial burden and more inflammation in the lung compared with euglycemic mice. The expression of adaptive immunity was delayed in chronic diabetic mice, shown by reduced early production of IFN-gamma in the lung and by the presence of fewer Mtb antigen (ESAT-6)-responsive T cells compared with euglycemic mice within the first month of infection. However, after 2 months of TB disease proinflammatory cytokines levels were higher in chronic diabetic than euglycemic mice. Here we show that Mtb infection of STZ-treated mice provides a useful model to study the effects of hyperglycemia on immunity. Our data indicate that the initiation of adaptive immunity is impaired by chronic hyperglycemia, resulting in a higher steady-state burden of Mtb in the lung.

Cell-mediated effector molecules and complicated malaria

In this review I attempt to advance hypotheses that might help contribute toward understanding the molecular pathogenesis of cerebral malaria (CM) and other complications based on a now widely accepted argument that the illness and pathology occasioned by Plasmodiumfalciparum infection might not necessarily be due to the direct effects of the parasite's 'toxins' and/or exoantigens or even its sequestration and consequent attendant effects in vital organs but rather to the parasite's mediated production of microbicidal molecules by the host. Tumor necrosis factor (TNF)-alpha is implicated in the pathogenesis of complicated malaria. There is a positive correlation between high levels of TNF-alpha and severity of malaria. The role of nitric oxide in the pathophysiology of complicated malaria is not clearly understood. Mononuclear phagocytes by virtue of their capacity to secrete toxic intermediates like reactive oxygen intermediates can inhibit the growth of both murine and human plasmodia. The role of interleukin-10 (IL-10) in malaria is also not well characterized to date. IL-10 is a powerful immunosuppressor factor. It acts as a natural dampener of immunoproliferative and inflammatory responses. Although transforming growth factor-beta has a crucial role in inflammation and repair, its role in complicated malaria is not too clearly understood. Furthermore, the anatomical source of these microbicidal molecules is not precisely known. The role of immune complexes (IC) in the pathophysiology of complicated malaria has hitherto not been tested. I argue here that IC play a critical role in influencing the outcome of malarial disease; IC-mediated stimulation of leukocytes to produce high levels of both TNF-alpha and NO and the fact that leukocytes are probably the principal anatomical source of these microbicidal and other pro-inflammatory mediators in complicated malaria provide a much more plausible explanation for the pathogenesis of CM and other complications. I also review the arguments that help contribute to rationalize hypoglycemia and hyperlactatemia in malarial disease and to some extent severe anemia. I am therefore tempted to conclude that CM and other complications are probably immune-mediated diseases or, at least, they present an inflammatory pathogenesis.

Improvement of glucose homeostasis in obese diabetic db/db mice given Plasmodium yoelii glycosylphosphatidylinositols

We have previously reported that infection with Plasmodium yoelii, Plasmodium chabaudi, or injection of extracts from malaria-parasitized red blood cells induces hypoglycemia in normal mice and normalizes the hyperglycemia in streptozotocin (STZ)-diabetic mice. P yoelii glycosylphosphatidylinositols (GPIs) were extracted in chloroform:methanol:water (CMW) (10:10:3), purified by high-performance thin layer chromatography (HPTLC) and tested for their insulin-mimetic activities. The effects of P yoelii GPIs on blood glucose were investigated in insulin-resistant C57BL/ks-db/db diabetic mice. A single intravenous injection of GPIs (9 and 30 nmol/mouse) induced a significant dose-related decrease in blood glucose (P < .001), but insignificantly increased plasma insulin concentrations. A single oral dose of 2.7 micromol GPIs per db/db mouse significantly lowered blood glucose (P < .01). P yoelii GPIs in vitro (0.062 to 1 micromol/L) significantly stimulated lipogenesis in rat adipocytes in a dose-dependent manner both in the presence and absence of 10(-8) mol/L insulin (P < .01). P yoelii GPIs stimulated pyruvate dehydrogenase phosphatase (PDH-Pase) and inhibited both cyclic adenosine monophosphate (cAMP)-dependent protein kinase A and glucose-6-phosphatase (G6Pase). P yoelii GPIs had no effect on the activity of the gluconeogenic enzymes fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK). This is the first report of the hypoglycemic effect of P yoelii GPIs in murine models of type 2 diabetes. In conclusion, P yoelii GPIs demonstrated acute antidiabetic effects in db/db mice and in vitro. We suggest that P yoelii GPIs, when fully characterized, may provide structural information for the synthesis of new drugs for the management of diabetes.

Reversal of type 2 diabetes in mice by products of malaria parasites. II. Role of inositol phosphoglycans (IPGs)

We have previously shown that infection with Plasmodium yoelii malaria or injection of extracts from malaria-parasitized red cells induces hypoglycemia in normal mice and normalizes the hyperglycemia in mice made moderately diabetic with streptozotocin. Inositol phosphoglycans (IPGs) are released outside cells by hydrolysis of membrane-bound glycosylphosphatidylinositols (GPIs), and act as second messengers mediating insulin action. The C57BL/Ks-db/db and C57BL/6J-ob/ob mice offer good models for studies on human obesity and Type 2 diabetes. In the present study, we show that a single iv injection of IPG-A or IPG-P extracted from P. yoelii significantly (P < 0.02) lowers the blood glucose in STZ-diabetic, db/db, and in ob/ob mice for at least 4--6 h. Using rat white adipocytes, IPG-P increased lipogenesis by 20--30% in the presence and absence of maximal concentrations of insulin (10(-8) M) (P < 0.01) and stimulated pyruvate dehydrogenase (PDH) phosphatase in a dose-related manner. Both IPG-A and IPG-P inhibited c-AMP-dependent protein kinase (PKA) in a dose-related manner. Compositional analysis of IPGs after 24 h hydrolysis revealed the presence of myo-inositol, phosphorus, galactosamine, glucosamine, and glucose in both IPG-A and IPG-P. However, hydrolysis of IPGs for 4 h highlighted differences between IPG-A and IPG-P. There are some functional similarities between P. yoelii IPGs and those previously described for mammalian liver. However, this is the first report of the hypoglycemic effect of IPGs in murine models of Type 2 diabetes. We suggest that IPGs isolated from P. yoelii, when fully characterized, may provide structural information for the synthesis of new drugs for the management of diabetes mellitus.

Macrophage function in alloxan diabetic mice: expression of adhesion molecules, generation of monokines and oxygen and NO radicals

The increased incidence of bacterial and mycotic infections in poorly controlled diabetic patients or animals is frequently attributed to impaired activities of professional phagocytes (granulocytes, macrophages) in hypoinsulinaemic milieu. We measured production of monokines (IL-6 and tumour necrosis factor-alpha (TNF-alpha)), active NO and reactive oxygen intermediates (ROIs), as well as expression of several cell surface adhesion molecules (Mac-1, -2 and -3, intercellular adhesion molecule-1 (ICAM-1) and Fc gammaRII), by thioglycollate medium-induced peritoneal macrophages of normoglycaemic and alloxan diabetic CBA/J mice (blood glucose level in the range 300 or 500 mg/dl). Macrophages of animals with moderate diabetes (300 mg/dl) produced significantly more IL-6 and TNF-alpha and ROIs than cells of control mice and showed an increased expression of all cell surface molecules, except Mac-3. NO/NO2 production was not affected. Administration of insulin restored enhanced values to normal levels, except for the production of ROIs which remained unusually high. We conclude that two separate mechanisms influence macrophage physiology in diabetes--lack of saturation of insulin receptors on macrophages and an indirect effect due to formation of advanced glycosylation endproducts (AGE) on their surfaces. The latter is possibly responsible for increased generation of ROIs, since it cannot be down-regulated by prolonged insulin treatment. How the increased activity of macrophages of moderately diabetic mice (enhanced production of proinflammatory monokines and oxygen radicals as well as expression of molecules) is related to their ability to kill bacteria is now under investigation.

The role of glycosyl-phosphatidylinositol in signal transduction

Glycosyl-phosphatidylinositol (GPI) lipids have a structural role as protein anchors to the cell surface. In addition, they are implicated in hormone, growth factor and cytokine signal transduction. Their phosphodiesteric hydrolysis mediated by an activated phospholipase results in the generation of water soluble oligosaccharide species termed the inositol phosphoglycan (IPG). This product has been demonstrated to possess biological properties when added exogenously to cells mimicking the biological effects of a variety of extracellular ligands. This may be accomplished since IPG is generic for a family of closely related species which are released in a tissue-specific manner and additionally have cell-specific targets. Micro-organic synthesis has recently been able to shed new light on this topic by the introduction of defined oligosaccharide analogues of IPG for the assessment of their biological activity. These have complemented the findings observed with purified IPG from biological sources thus strengthening the belief that the GPI/IPG signalling system represents a truly novel aspect of transmembrane signalling.

The biological basis of malarial disease

In this review we summarise the arguments that inflammatory cytokines, triggered by material released from the parasite at schizogony (malarial toxin), might induce the illness and pathology seen in malaria. These pro-inflammatory cytokines can generate inducible nitric oxide synthase and cause nitric oxide to be released, as can low concentrations of malarial toxin itself provided interferon-gamma, which has only low activity in the absence of malarial toxin, is present. We suggest here that recently described hypermetabolic functions of these mediators provide a much more plausible explanation for malarial hyperlactataemia and hypoglycaemia, the chief prognostic indicators in falciparum malaria, than does hypoxia secondary to mechanical blockage of vessels by sequestering parasites, which is the dominant current theory. We also review the arguments that rationalise, through these mediators, the reversibility of the coma of cerebral malaria. Although not yet tested at a cellular level, the proposal that nitric oxide generated in cerebral vascular walls contributes to this coma continues to gather indirect support. In addition, new evidence incriminating nitric oxide in the mechanism of tolerance to endotoxin rationalises the raised nitric oxide generation seen in malarial tolerance.

Cell signalling by inositol phosphoglycans from different species

The discovery of glycosyl-phosphatidylinositol (GPI) molecules and their products has given new insight into the field of signal transduction. In the last decade a novel mechanism of protein attachment to membranes has emerged, which involves a covalent linkage of the protein to the glycan moiety of a GPI. The discovery that GPI-anchored proteins are ubiquitous throughout the eukaryotes was followed by the observation that uncomplexed GPI molecules are implicated in signal transduction for a diversity of hormones and growth factors. The hydrolysis of free-GPI generates a novel second messenger: the inositol phosphoglycan (IPG). The aim of this article is to review the role of IPG and IPG-like molecules in signal transduction and to discuss future research directions.

Reversal of hypoglycaemia in murine malaria by drugs that inhibit insulin secretion

We have investigated the metabolic disturbances in 2 murine models of blood-stage malaria, Plasmodium chabaudi and Plasmodium yoelii. Blood glucose, plasma insulin and parasitaemia were measured in normal and infected mice before and after treatment with diazoxide, adrenaline, Sandostatin and quinine. Severe hypoglycaemia and marked hyperinsulinaemia developed during both infections. A single injection of diazoxide (25 mg/kg i.p.) or adrenaline (0.03 mg s.c.) lowered insulin concentrations in normal mice, reversed the hypoglycaemia in both infections and significantly reduced the hyperinsulinaemia in P. chabaudi-infected mice (P < 0.0001). Higher doses of Sandostatin (500 micrograms/kg s.c.) were required to reverse hypoglycaemia. Quinine (25 mg/kg i.p.) significantly increased blood glucose in normal and infected mice (P < 0.0010 and no hypoglycaemia was observed in mice with normal blood glucose for more than 3 h. This study shows that the major cause of hypoglycaemia in murine malaria is hyperinsulinaemia rather than high consumption of glucose by host and parasites or chemotherapy with quinine, and that hypoglycaemia can be reversed by correcting the hyperinsulinaemia.