Kupffer cell function during the erythocytic stage of malaria.

BACKGROUND AND AIM: Previous studies using isolated perfused rat liver in vivo have suggested that during the erythrocytic phase of malaria infection, overall phagocytosis by Kupffer cells is enhanced. The aim of the present study was to further investigate the individual phagocytic capacity and prostaglandin E(2) (PGE(2)) secretion of isolated Kupffer cells in vitro, and the immunohistochemical characteristics of Kupffer cells in vivo. METHODS: Malaria was induced in male Sprague-Dawley rats (n = 12) by inoculation with parasitized red cells containing Plasmodium berghei. Kupffer cells were isolated by centrifugal elutriation. RESULTS: A significantly increased yield of Kupffer cells was obtained from malaria-infected livers compared to controls (36.7 +/- 4.5 vs 11.8 +/- 1.1 x10(6) cells, P < 0.0001, n = 12). There was an increased internalization by phagocytosis of [(3)H]-BSA latex microspheres after 60 min in malaria-infected Kupffer cells compared to controls (65.05 +/- 1.5 vs 48.6 +/- 0.7, P < 0.001, n = 12). PGE(2) secretion into the cell culture medium was significantly suppressed in malaria-infected Kupffer cells compared to controls (1167 +/- 88 vs 4537 +/- 383 pg per 10(6) cells, P < 0.001, n = 5). Staining of ED1, ED2 and PCNA was greater in malaria-infected livers compared to control. CONCLUSION: The results indicate that the number of Kupffer cells is significantly increased and their phagocytic activity on a cell-by-cell basis is enhanced during the erythrocytic stage of malaria.

Differential bidirectional transfer of indinavir in the isolated perfused human placenta.

The protease inhibitor (PI) indinavir may be used in the management of human immunodeficiency virus (HIV) infection during pregnancy. Poor maternal-to-fetal transfer of indinavir has been reported previously, but the mechanisms of transfer remain unknown. The bidirectional transfer of indinavir was assessed in dually perfused, isolated human placentae. Term placentae (n = 5) were obtained from non-HIV-infected pregnant women. To investigate transport mechanisms, the steady-state transfer of indinavir was compared to those of antipyrine (a marker of passive diffusion) and [(3)H]vinblastine (a marker of P-glycoprotein [P-gp] transport) in the maternal-to-fetal and fetal-to-maternal directions in each placenta. Indinavir and antipyrine perfusate concentrations were determined by using reverse-phase, high-performance liquid chromatography; [(3)H]vinblastine concentrations were measured by liquid scintillation. The antipyrine transfer clearance in each direction did not differ (P = 0.76), a finding consistent with passive diffusion. However, the maternal-to-fetal transfer clearance of vinblastine, normalized to that of antipyrine (clearance index) (0.31 +/- 0.05), was significantly lower than the fetal-to-maternal clearance index of vinblastine (0.67 +/- 0.17; P = 0.017), suggesting the involvement of placental P-gp. Similarly, the maternal-to-fetal clearance index of indinavir (0.39 +/- 0.09) was significantly lower than its fetal-to-maternal clearance index (0.97 +/- 0.12; P < 0.001). These results represent the first evidence for differential transfer of a xenobiotic in the intact human placenta. The use of transport modulators to increase the maternal-to-fetal transfer of PIs as a possible strategy to reduce mother-to-child transmission of HIV warrants investigation.

Reduced tubular cation transport in diabetes: prevented by ACE inhibition.

BACKGROUND: The renal clearance of organic cations is important for the homeostasis of a number of exogenous and endogenous compounds. The organic cation transporters (OCTs) situated on the basolateral surface of proximal tubular cells mediate active cation excretion. Alterations of cation transport may occur in diabetes, although the role of the OCTs has not been previously assessed. METHODS: Experimental diabetes was induced in rats with streptozotocin (55 mg/kg) and animals were randomly assigned to receive ramipril (3 mg/mL) in drinking water for 24 weeks. In a second protocol, rats were infused with angiotensin II (Ang II) at a dose of 58.3 ng/kg/min for 2 weeks via an implanted osmotic pump. Expression of the OCTs and renal clearance of the endogenous cation N-methyl-nicotinamide (NMN) was assessed. RESULTS: Diabetes was associated with a reduction in gene and protein expression of both OCT-1 and OCT-2 and a reduction in NMN clearance. These effects were prevented by ramipril, associated with the prevention of albuminuria and tubular injury as demonstrated by the expression of osteopontin and glutathione peroxidase 3 (GPX-3). An infusion of Ang II also reduced NMN clearance but without altering the renal expression of OCTs. CONCLUSION: We hypothesize that reduced expression of OCTs in diabetes may be a marker of tubular injury. However, Ang II may also directly augment renal cation clearance independent of changes in transporter expression. Together these effects may provide additional mechanism to explain treatment-related improvements in creatinine clearance and renoprotection in diabetes following blockade of the renin-angiotensin system (RAS).

A novel method for determining hepatic sinusoidal oxygen permeability in the isolated perfused rat liver using [15O]O2.

Measurement of hepatic sinusoidal permeability of oxygen and other substrates may help elucidate the mechanisms responsible for impaired liver function in cirrhosis. However studies of sinusoidal oxygen permeability in normal liver and various disease states have been limited due to the considerable technical difficulties involved in the use of standard techniques. We have developed a new method for measuring sinusoidal oxygen permeability in the isolated perfused rat liver that overcomes the difficulties of previous methods by using [(15)O]O(2) and an in-line fluid monitor. This method uses data obtained from impulse response curves of radiolabelled red cells, albumin and oxygen that are fitted mathematically using the axial dispersion model to yield rate constants that describe oxygen transit through the liver. We have demonstrated the utility and reproducibility of this method by comparing multiple injections and permeability determinations in the same preparation. This approach could be used in isolated perfused organs to study oxygen permeability in a range of disease states.

Hepatic Kupffer cell phagocytotic function in rats with erythrocytic-stage malaria.

BACKGROUND: In the erythrocytic phase of malaria, Kupffer cells show marked hypertrophy and hyperplasia and are filled with malarial pigment. However, phagocytic function in this state has not been well characterized. The aim of the present study was to use mouse Plasmodium berghei to infect rats with malaria and study the phagocytic function and morphology of Kupffer cells. METHODS: We used a recirculating isolated perfused rat liver (IPRL) to quantitate Kupffer cell phagocytic clearance of radiolabeled albumin-latex over 120 min in high parasitemia (53 +/- 6%; n = 7) and low parasitemia (approximately 1%; n = 4) malaria-infected rats and littermate controls (n = 7 and n = 4, respectively). In a further group of high-parasitemic rats, perfusion was ceased after 7 min and liver radioactivity also measured. Electron microscopy was performed after perfusions. RESULTS: In high-parasitemia malaria rats, clearance of radiolabeled latex from IPRL perfusate over 120 min was significantly (P < 0.01) faster than in controls, with a lower area under the curve (0.19 +/- 0.02 vs 0.43 +/- 0.07 /mL per min, respectively) and shorter half-life (t1/2k; 2.4 +/- 0.6 vs 10.0 +/- 2.3 min, respectively). Low-parasitemia rats were identical to controls. After 7 min perfusion in high-parasitemic rats (n = 4), total radioactivity in liver homogenates was higher than in controls (n = 4; 33.1 +/- 6.2 vs 18.4 +/- 1.9% of injected radiolabel; P < 0.05). Electron microscopy showed latex in Kupffer cells, more abundantly seen in high-parasitemic animals. CONCLUSIONS: Total Kupffer cell phagocytic activity of the liver is markedly increased in rats with a high parasitemic load of malarial P. berghei infection. This is presumed to reflect an upregulation of scavenger activity phagocytosing erythrocytes and their breakdown products.

The effect of oxygen supplementation on the arterial ketone body ratio in human cirrhosis.

BACKGROUND/AIMS: Data from studies in experimental models have suggested that the impairment of mitochondrial function and altered redox state that occur in cirrhosis may be due to impaired hepatic oxygenation. Since interventions that improve oxygen delivery to hepatocytes may improve mitochondrial functions, we studied the effects of oxygen supplementation on the arterial ketone body ratio (AKBR) in normal volunteers and patients with cirrhosis. METHODS: After a 2-hour fast, ketone bodies were measured in arterial blood taken from patients and controls while breathing room air and then after breathing oxygen via a face mask at 12 liters/min for 60 min. RESULTS: The AKBR was reduced in cirrhotic patients compared with controls, 0.74 +/- 0.23 and 1.51 +/- 0.4, respectively (p = 0.002). Oxygen supplementation significantly improved the AKBR in cirrhotic patients, from 0.74 +/- 0.23 to 1.04 +/- 0.28 (p = 0.001) but did not affect the AKBR in controls. CONCLUSION: These findings suggest that reduced hepatocyte oxygenation contributes to impaired hepatic mitochondrial function in cirrhosis. Strategies at increasing hepatic oxygen delivery may improve hepatic mitochondrial function in patients with chronic liver disease.