Michael D. Sharpe

Introduction: Intravenous(IV) immunoglobulin(Ig) treatment is known to alleviate behavioral deficits in the experimentally induced model of sepsis. To delineate the mechanisms by which IVIg treatment prevents neuronal dysfunction, an array of immunological and apoptosis markers was investigated. Methods: Sepsis was induced by cecal ligation perforation(CLP) in rats. The animals were divided into five groups; sham, control, CLP + saline, CLP + immunoglobulin G IgG(250 mg/kg,iv), and CLP + immunoglobulins enriched with immunoglobulin M-IgGAM(250 mg/kg,iv). Blood and brain samples were taken in two sets of experiments after CLP to see the early(24 hrs) and late(10 days) effects of treatment. Total complement activity, complement 3(C3) and soluble complement C5b-9 levels were measured in sera of rats using ELISA-based methods. Cerebral complement content was analyzed by Western Blot. Immune cell infiltration and gliosis were examined by immunohistochemistry using cluster of differentiation 3, CD4, CD8, CD11b, CD19 and glial fibrillary acidic protein antibodies. Apoptotic neuronal death was investigated by TUNEL staining and Western Blot-based semi-quantitative evaluation of brain homogenates by bax and bcl-2 antibodies. Results: IV IgG and IgGAM administration significantly reduced systemic complement activity but increased serum C3 and soluble C5b-9 levels. Likewise, Western Blot data showed slightly increased C5b-9 expression and significantly reduced C1q expression in brain samples of IgGAM-treated but not IgG-treated septic rats especially in the first day of administration. No cerebral cellular infiltrates were observed in treated and non-treated septic rats. By contrast, IV IgG and IgGAM treatment induced considerable amelioration in glial cell proliferation which was increased in non-treated rats. IgG and IgGAM treated rats exhibited significantly reduced numbers of apoptotic neurons and cerebral expression levels of bax and bcl-2 as compared to nontreated rats. Conclusions: We suggest that IV IgG and IgGAM administration ameliorates neuronal dysfunction and behavioral deficits by reducing apoptotic cell death and glial cell proliferation. IgGAM treatment might be suppressing classical complement pathway by reducing C1q expression.

Erythrocyte deformability has been recognized as a determinant of microvascular perfusion. Because nitric oxide (NO) is implicated in the modulation of red blood cell (RBC) deformability and NO levels increase during sepsis, we tested the hypothesis that a NO-mediated decrease in RBC deformability contributes to decreased functional capillary density (CD) in remote organs. With the use of a peritonitis model of sepsis in the rat [cecal ligation and perforation (CLP)] and aminoguanidine (AG) to prevent increases in NO, we measured CD in skeletal muscle (intravital microscopy), mean erythrocyte membrane deformability (; micropipette aspiration), systemic NO production [plasma nitrite/nitrate (NO(x)) chemiluminescence], and NO accumulation in RBC [NO bound to hemoglobin (HbNO) detected by electron paramagnetic resonance spectroscopy]. In untreated CLP animals relative to sham, NO(x) increased 254% (P < 0.05), stopped flow capillaries increased 149% (P < 0.05), and decreased 12.7% (P < 0.05), with a subpopulation (5%) of RBC with deformabilities below the normal range. AG prevented increases in NO(x), accumulation of HbNO, and decreases in both and functional CD. We found no evidence of leukocyte plugging postcapillary venules. Our findings suggest that decreased functional CD during sepsis resulted from a NO-mediated decrease in erythrocyte deformability.

The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.

Inherent in the remote organ injury caused by sepsis is a profound maldistribution of microvascular blood flow. Using a 24-h rat cecal ligation and perforation model of sepsis, we studied O(2) transport in individual capillaries of the extensor digitorum longus (EDL) skeletal muscle. We hypothesized that erythrocyte O(2) saturation (SO(2)) levels within normally flowing capillaries would provide evidence of either a mitochondrial failure (increased SO(2)) or an O(2) transport derangement (decreased SO(2)). Using a spectrophotometric functional imaging system, we found that sepsis caused 1) an increase in stopped flow capillaries (from 10 to 38%, P < 0.05), 2) an increase in the proportion of fast-flow to normal-flow capillaries (P < 0.05), and 3) a decrease in capillary venular-end SO(2) levels from 58.4 +/- 20.0 to 38.5 +/- 21.2%, whereas capillary arteriolar-end SO(2) levels remained unchanged compared with the sham group. Capillary O(2) extraction increased threefold (P < 0.05) and was directly related to the degree of stopped flow in the EDL. Thus impaired O(2) transport in early stage sepsis is likely the result of a microcirculatory dysfunction.