Metabolic disturbances in Plasmodium coatneyi-infected rhesus monkeys

A Review of Plasmodium coatneyi-Macaque Models of Severe Malaria

Malaria remains one of the most significant public health concerns in the world today. Approximately half the human population is at risk for infection, with children and pregnant women being most vulnerable. More than 90% of the total human malaria burden, which numbers in excess of 200 million annually, is due to Plasmodium falciparum. Lack of an effective vaccine and a dwindling stockpile of antimalarial drugs due to increased plasmodial resistance underscore the critical need for valid animal models. Plasmodium coatneyi was described in Southeast Asia 50 years ago. This plasmodium of nonhuman primates has been used sporadically as a model for severe malaria, as it mimics many of the pathophysiologic features of human disease. This review covers the reported macroscopic, microscopic, ultrastructural, and molecular pathology of P. coatneyi infection in macaques, specifically focusing on the rhesus macaque, as well as describing the critical needs still outstanding in the validation of this crucial model of human disease.

Tumor necrosis factor-induced cerebral insulin resistance in Alzheimer's disease links numerous treatment rationales

The evident limitations of the amyloid theory of the pathogenesis of Alzheimer's disease are increasingly putting alternatives in the spotlight. We argue here that a number of independently developing approaches to therapy-including specific and nonspecific anti-tumor necrosis factor (TNF) agents, apolipoprotein E mimetics, leptin, intranasal insulin, the glucagon-like peptide-1 mimetics and glycogen synthase kinase-3 (GSK-3) antagonists-are all part of an interlocking chain of events. All these approaches inform us that inflammation and thence cerebral insulin resistance constitute the pathway on which to focus for a successful clinical outcome in treating this disease. The key link in this chain presently absent is a recognition by Alzheimer's research community of the long-neglected history of TNF induction of insulin resistance. When this is incorporated into the bigger picture, it becomes evident that the interventions we discuss are not competing alternatives but equally valid approaches to correcting different parts of the same pathway to Alzheimer's disease. These treatments can be expected to be at least additive, and conceivably synergistic, in effect. Thus the inflammation, insulin resistance, GSK-3, and mitochondrial dysfunction hypotheses are not opposing ideas but stages of the same fundamental, overarching, pathway of Alzheimer's disease pathogenesis. The insight this provides into progenitor cells, including those involved in adult neurogenesis, is a key part of this approach. This pathway also has therapeutic implications for other circumstances in which brain TNF is pathologically increased, such as stroke, traumatic brain injury, and the infectious disease encephalopathies.

Glycemic control and chronic dosing of rhesus monkeys with a fusion protein of iduronidase and a monoclonal antibody against the human insulin receptor

Hurler's syndrome, or mucopolysaccharidosis type I, is a lysosomal storage disorder caused by mutations in the gene encoding the lysosomal enzyme iduronidase (IDUA). The disease affects both peripheral tissues and the central nervous system (CNS). Recombinant IDUA treatment does not affect the CNS, because IDUA does not cross the blood-brain barrier (BBB). To enable BBB penetration, human IDUA was re-engineered as an IgG-IDUA fusion protein, where the IgG domain is a genetically engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb penetrates the brain from the blood via transport on the endogenous BBB insulin receptor and acts as a molecular Trojan horse to deliver the fused IDUA to the brain. Before human testing, the HIRMAb-IDUA fusion protein was evaluated in a 6-month weekly dosing toxicology study at doses of 0, 3, 9, and 30 mg/kg/week of the fusion protein administered to 40 rhesus monkeys. The focus of the present study is the effect of chronic high dose administration of this fusion protein on plasma glucose and long-term glycemic control. The results show that the HIRMAb has weak insulin agonist activity and causes hypoglycemia at the high dose, 30 mg/kg, after intravenous infusion in normal saline. When dextrose is added to the saline infusion solution, no hypoglycemia is observed at any dose. An intravenous glucose tolerance test performed at the end of the 6 months of chronic treatment showed no change in glucose tolerance at any dose of the HIRMAb-IDUA fusion protein.

Fever as a cause of hypophosphatemia in patients with malaria

Hypophosphatemia occurs in 40 to 60% of patients with acute malaria, and in many other conditions associated with elevations of body temperature. To determine the prevalence and causes of hypophosphatemia in patients with malaria, we retrospectively studied all adults diagnosed with acute malaria during a 12-year period. To validate our findings, we analyzed a second sample of malaria patients during a subsequent 10-year period. Serum phosphorus correlated inversely with temperature (n = 59, r = −0.62; P<0.0001), such that each 1°C increase in body temperature was associated with a reduction of 0.18 mmol/L (0.56 mg/dL) in the serum phosphorus level (95% confidence interval: −0.12 to −0.24 mmol/L [−0.37 to −0.74 mg/dL] per 1°C). A similar effect was observed among 19 patients who had repeat measurements of serum phosphorus and temperature. In a multiple linear regression analysis, the relation between temperature and serum phosphorus level was independent of blood pH, PCO2, and serum levels of potassium, bicarbonate, calcium, albumin, and glucose. Our study demonstrates a strong inverse linear relation between body temperature and serum phosphorus level that was not explained by other factors known to cause hypophosphatemia. If causal, this association can account for the high prevalence of hypophosphatemia, observed in our patients and in previous studies of patients with malaria. Because hypophosphatemia has been observed in other clinical conditions characterized by fever or hyperthermia, this relation may not be unique to malaria. Elevation of body temperature should be added to the list of causes of hypophosphatemia.

Plasmodium coatneyi: differential clinical and immune responses of two populations of Macaca fascicularis from different origins

Two species of macaques, including two Macaca fascicularis from the Philippines, two M. fascicularis from Mauritius, and one Macaca mulatta, were experimentally infected with blood stages of Plasmodium coatneyi and followed during their clinical, parasitological, biological, and immunological evolution. Plasma cytokine (TNF-alpha, IL-1beta, IL-6, IFN-gamma) production peaked for all monkeys 11 days after inoculation, concomitantly with peaks of parasitemia. Only the M. fascicularis from the Philippines survived the infection. The main features, which discriminated nonfatal from fatal cases, were the observation in M. fascicularis from the Philippines of a mean CD4+/CD8+ ratio below I and of their ability, as revealed by mitogenic stimulation of whole blood, to produce increasing amounts of IFN-gamma as infection evolved. The contribution of environmental and genetic factors, which may differentiate the three groups of monkeys and therefore explain fatal or nonfatal evolution of the infection among them, is discussed.

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.

The metabolism of platelet-activating factor in severe and cerebral malaria

In order to examine the effects of platelet-activating factor (PAF) in complicated Plasmodium falciparum infections, plasma concentrations of lyso-PAF, stable metabolite and principal precursor of PAF, were measured in 25 Vietnamese adults with severe malaria. The concentration of PAF in the cerebrospinal fluid (CSF) was determined in a sub-group of 23 comatose patients and, together with that of lyso-PAF, in the plasma of 20 patients on recovery of consciousness. The concentration of lyso-PAF in the plasma was depressed on admission to hospital (median [range]; 21 [8-143] vs. 293 [215-410] ng/ml in 10 controls; P < 0.001). There was, however, no change in plasma activity of acetylhydrolase which converts PAF to lyso-PAF (P > 0.01 vs. controls) while simultaneous reduction in the concentration of lipoproteins associated with lyso-PAF were less than those of lyso-PAF per se in the plasma. The plasma concentration of lyso-PAF on admission was associated with parasitaemia and the concentration of serum triglycerides (rs = -0.42, P = 0.04 in each case), the latter being consistent with hepatic effects of PAF reported in previous studies. CSF concentrations of PAF on admission were low (2.3 [0.5-7.7] vs. 0.9 [0-2.5] ng/ml after recovery, P < 0.01) compared with values reported previously in bacterial meningitis. Plasma concentrations of lyso-PAF after recovery lay between admission and control values. While increased availability of PAF may reflect parasite burden and may modulate liver-mediated metabolic disturbances such as hypoglycaemia and lactic acidosis, the role of PAF in cerebral malaria is uncertain.

Hypoglycemia and hyperinsulinemia in rodent models of severe malaria infection

Severe hypoglycemia developed during nonlethal Plasmodium chabaudi and lethal P. yoelii blood stage malaria infection in mice, always in association with hyperinsulinemia. Supernatants of lethal P. yoelii incubated overnight induced hypoglycemia and hyperinsulinemia in normal mice. In murine malaria, hypoglycemia may be largely secondary to increased insulin secretion.