Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease

Pial microvascular responses to transient bilateral common carotid artery occlusion: effects of hypertonic glycerol

OBJECTIVE: The aim of the study was to assess the rat pial microvessel alterations due to transient bilateral common carotid artery occlusion (BCCAO) and to investigate the mechanism of 10% hypertonic glycerol neuroprotection. Our suggestion was that 10% glycerol solution infusion could dilate pial arterioles through nitric oxide release and/or stimulation of ATP-sensitive potassium (K(ATP)) channels. Therefore, we studied the effects of hypertonic glycerol after inhibition of nitric oxide synthase, with N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine, or K(ATP) channels with glibenclamide. METHODS: Pial microcirculation of male Wistar rats was visualized by a fluorescent microscopy technique through an open cranial window, using fluorescein isothiocyanate bound to dextran (molecular weight 70 kDa). BCCAO was induced for 30 min and reperfusion lasted 60 min. The arterioles were classified according to the Strahler ordering scheme. Permeability increase was quantified by normalized grey levels (NGL). Leucocytes were stained with rhodamine 6G. Perfused capillary length and capillary red blood cell (RBC) velocity were measured by computer-assisted methods. RESULTS: The arterioles were assigned 5 orders of branchings, from order 1 (diameter 16.0 +/- 2.5 microm) to order 5 (62.0 +/- 5.0 microm). BCCAO caused inhomogenous changes in diameter of arterioles and leakage of fluorescent dextran, that was further enhanced by reperfusion (0.45 +/- 0.05 NGL, p < 0.01). Adhesion of leukocytes to venules was marked and capillary perfusion was reduced by 39.2 +/- 6.0% of baseline as well as capillary RBC velocity. 10% glycerol solution caused an increase in diameter of all arterioles within 25 +/- 2 min of administration (by 20 +/- 5% in order 4, 25 +/- 4% in order 3 and 18 +/- 3% in order 2; p < 0.01). Leakage (0.19 +/- 0.03 NGL, p < 0.01), leukocyte adhesion (2.0 +/- 1.0/100 microm of venular length, p < 0.01) and capillary occlusion (reduction by 13.0 +/- 5.5% of baseline) were prevented compared with controls. Capillary RBC velocity increased compared with controls. N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine infused prior to glycerol caused vasoconstriction and reduced the protective effects of hypertonic glycerol on permeability increase. The number of adherent leukocytes and perfused capillary length decreased, while capillary RBC velocity was higher than baseline. Glibenclamide prior to 10% glycerol solution blunted glycerol-induced vasodilatation, but did not affect protection by hypertonic glycerol on blood-brain barrier disruption, leukocyte adhesion and capillary perfusion, preserving high capillary RBC velocity. Papaverine (20 mg/kg body weight) induced an increase in arteriolar diameter, enhancing interstitial edema; adhesion of leukocytes was marked as well as capillary occlusion, while capillary RBC velocity increased. CONCLUSIONS: 10% glycerol solution was able to prevent microvascular alterations due to BCCAO protecting cerebral tissue. The effects appear to be due to hyperosmolality causing stimulation of K(ATP) channels, increase in vessel wall shear stress and release of nitric oxide

Melatonin induces membrane conductances changes in isolated retinal rod receptor cells

Experiments were conducted to verify whether the neurohormone melatonin influences the membrane conductance of photoreceptors isolated from the frog retina. It has been found that 20 microM melatonin decreases membrane conductances both in the linear and non linear ranges by <0.4 nS. These actions are estimated to produce in dark adapted photoreceptors an increase of the response to a dim light induced change of the dark current of about 21%, i.e. from 1.3 to 1.62 mV/pA

Molecular steps involved in light-induced oxidative damage to retinal rods

PURPOSE. To define the molecular mechanism underlying light-induced oxidative damage to retinal photoreceptors. METHODS. Oxidative stress was induced in isolated rod photoreceptors by bright 470- to 490-nm light and monitored by measuring the conversion of dihydrorhodamine 123 to rhodamine, with fluorescence microscopy. The effect of the wavelength on oxidant generation was investigated by applying prebleaching stimuli of either 485- or 520-nm light before the bright 470- to 490-nm light. The role of internal messengers in photooxidative stress and membrane damage by bright 470- to 490-nm light was investigated by patch-clamp recording. RESULTS. Constant illumination with bright 470- to 490-nm light caused a rapid increase in generation of oxidants, which peaked after approximately 60 seconds, and a decrease in membrane resistance, eventually producing irreversible membrane damage. The time course and extent of oxidant generation were not affected by the absence of intracellular guanosine triphosphate (GTP) or adenosine triphosphate (ATP), suggesting that oxidative stress and membrane damage induced by 470- to 490-nm light do not require coupling to a GTP-binding protein. Prebleaching exposure to 520-nm light suppressed oxidative stress and membrane damage by subsequent application of bright 470- to 490-mn light, and the extent of suppression increased with prebleaching duration. CONCLUSIONS. Oxidative stress and damage induced in rods in response to 470- to 490-nm light require rhodopsin activation, but not visual transduction steps downstream of active rhodopsin. Prebleaching with 485- or 520-nm light has a different effect on the level of a transient rhodopsin intermediate required for lipid peroxidation by 470- to 490-nm light

Geometric characteristics of arterial network of rat pial microcirculation

OBJECTIVE: The aim of the study was to assess the geometric characteristics of rat pial microcirculation and describe the vessel bifurcation patterns by 'connectivity matrix'. METHODS: Male Wistar rats were used to visualize pial microcirculation by a fluorescent microscopy technique through an open cranial window, using fluorescein isothiocyanate bound to dextran (molecular weight 70 kDa). The arteriolar network was mapped by stop-frame images. Diameters and lengths of arterioles were measured with a computer-assisted method. Pial arterioles were classified according to a centripetal ordering scheme (Strahler method modified according to diameter) from the smallest order 1 to the largest order 5 arterioles in the preparation. A distinction between arteriolar segments and elements was used to express the series-parallel features of the pial arteriolar networks. A connectivity matrix was used to describe the connection of blood vessels from one order to another. RESULTS: The arterioles were assigned 5 orders of branching by Strahler's ordering scheme, from order 1 (diameter: 16.0 +/- 2.5 microm) to order 5 (62 +/- 5.0 microm). Order 1 arterioles gave origin to capillaries, assigned order 0. The diameter, length and branching of the 5 arteriolar orders grew as a geometric sequence with the order number in accordance with Horton's law. The segments/elements ratio was the highest in order 4 and 3 arterioles, indicating the greatest asymmetry of ramifications. Finally, the branching vessels in the networks were described in details by the connectivity matrix. Fractal dimensions of arteriolar length and diameter were 1.75 and 1.78, respectively. CONCLUSIONS: The geometric characteristics of rat pial microcirculation indicate that distribution of vessels is fractal. The connectivity matrix allowed us to describe the number of daughter vessels spreading from parent vessels. This ordering scheme may be useful to describe vessel function, according to diameter, length and branching