Pneumocystis jirovecii colonisation in HIV-positive and HIV-negative subjects in Cameroon.

OBJECTIVE: To determine the prevalence of Pneumocystis pneumonia (PCP), a major opportunistic infection in AIDS patients in Europe and the USA, in Cameroon. MATERIALS AND METHODS: Induced sputum samples from 237 patients without pulmonary symptoms (126 HIV-positive and 111 HIV-negative outpatients) treated at a regional hospital in Cameroon were examined for the prevalence of Pneumocystis jirovecii by specific nested polymerase chain reaction (nPCR) and staining methods. CD4 counts and the history of antiretroviral therapy of the subjects were obtained through the ESOPE database system. RESULTS AND CONCLUSION: Seventy-five of 237 study participants (31.6%) were colonised with Pneumocystis, but none showed active PCP. The Pneumocystis colonisation rate in HIV-positive subjects was more than double that of HIV-negative subjects (42.9% vs. 18.9%, P < 0.001). In the HIV-positive group, the colonisation rate corresponds to the reduction in the CD4 lymphocyte counts. Subjects with CD4 counts >500 cells/µl were colonised at a rate of 20.0%, subjects with CD4 counts between 200 and 500 cells/µl of 42.5%, and subjects with CD4 counts <200 cells/µl of 57.1%. Colonisation with Pneumocystis in Cameroon seems to be comparable to rates found in Western Europe. Prophylactic and therapeutic measures against Pneumocystis should be taken into account in HIV care in western Africa.

Regional vascular responses to ATP and ATP analogues in the rabbit kidney in vivo: roles for adenosine receptors and prostanoids.

BACKGROUND AND PURPOSE: Our knowledge of the effects of P2-receptor activation on renal vascular tone comes mostly from in vitro models. We aimed to characterise the pharmacology of ATP in the renal circulation in vivo. EXPERIMENTAL APPROACH: In pentobarbitone anaesthetized rabbits, we examined total renal and medullary vascular responses to ATP (0.2 and 0.8 mg kg(-1)), beta, gamma-methylene ATP (beta, gamma-mATP, 7 and 170 microg kg(-1)), alpha, beta-mATP (0.2 and 2 microg kg(-1)) and adenosine (2 and 6 microg kg(-1)) using transit-time ultrasound and laser Doppler flowmetry, respectively. We also determined whether adenosine receptors, NO or prostanoids contribute to the actions of the purinoceptor agonists. KEY RESULTS: Renal arterial boluses of ATP, beta,gamma-mATP, and adenosine produced biphasic changes; ischaemia followed by hyperaemia, in total renal and medullary blood flow. alpha,beta-mATP induced only ischaemia. The adenosine receptor antagonist 8-(p-sulphophenyl)theophylline reduced the responses to adenosine and the hyperaemic responses to ATP and beta,gamma-mATP only. NO synthase inhibition (Nomega-nitro-L-arginine) did not significantly alter responses to the P2 receptor agonists. Subsequent cyclooxygenase inhibition (ibuprofen) reduced the ATP- and beta, gamma-mATP-induced increases in renal blood flow. All other responses remained unchanged. CONCLUSIONS AND IMPLICATIONS: In the rabbit kidney in vivo, alpha, beta-mATP sensitive receptors mediate vasoconstriction. beta,gamma-mATP and ATP induce vasodilation at least partly through adenosine receptors. ATP induced renal vasodilatation is independent of NO and partly dependent on prostanoids in the bulk of the kidney, but not in the vasculature controlling medullary blood flow.

Lack of contribution of P2X receptors to neurally mediated vasoconstriction in the rabbit kidney in vivo.

AIM: The contribution of adenosine triphosphate (ATP) to the neural control of regional renal perfusion in vivo remains unknown. We therefore examined whether P2X receptors mediate renal vascular responses to electrical stimulation of the renal nerves (RNS) in pentobarbitone anaesthetized rabbits. METHODS: Responses to RNS were tested before and during renal arterial infusion of alpha,beta-methylene ATP (alpha,beta-mATP, 7-56 microg kg(-1) min(-1)) to desensitize P2X1 receptors. RNS consisted of 3 min trains at graded frequencies and short trains of RNS (4-32 pulses). RESULTS: Three-minute trains of RNS reduced renal blood flow (RBF), cortical laser Doppler flux (CLDF), and medullary LDF (MLDF) by -90 +/- 3%, -89 +/- 3% and -31 +/- 11%, respectively, at 4 Hz. MLDF was reduced less than CLDF or RBF. During short train RNS, RBF, CLDF and MLDF were reduced by -22 +/- 2%, -15 +/- 2% and -12 +/- 2%, respectively, for 32 s at 1 Hz. CLDF and MLDF were reduced to a similar extent. Infusion of alpha,beta-mATP induced transient reductions in RBF, CLDF and MLDF, but within 5 min these variables had recovered to control levels. Vascular responses to RNS were not significantly altered by alpha,beta-mATP treatment. CONCLUSIONS: In the rabbit kidney in vivo, alpha,beta-mATP-sensitive receptors mediate vasoconstriction and reduce perfusion in both cortical and medullary vascular beds. However, these receptors do not mediate neurally induced reductions in renal perfusion.

The return of glomerular filtered albumin to the rat renal vein--the albumin retrieval pathway.

BACKGROUND: Recent studies have demonstrated that the normal glomerular capillary wall (GCW) is not charge selective to albumin. This means that albumin flux across the GCW is high. This has been confirmed in studies where albumin uptake by the tubules has been inhibited. Therefore, there must be a high capacity postglomerular retrieval pathway in normal kidneys that returns filtered albumin back to the blood supply. METHODS: This study identifies the presence of glomerular filtered albumin in the renal vein from the analysis of the decrease of radioactivity in the venous effluent after the injection of a pulse of tritium labeled albumin into the renal artery in vivo and in the isolated perfused kidney (IPK). RESULTS: The glomerular filtered albumin is returned to the blood supply by a high capacity pathway that transports this albumin at a rate of 1830+/-292 microg/min rat kidney (n= 14) (mean+/-SEM). This pathway has been identified under physiological conditions in vivo and in the IPK. The pathway is specific for albumin as it does not occur for horseradish peroxidase (HRP). The pathway is inhibited in a non-filtering kidney. The pathway is also inhibited by NH4Cl, an inhibitor of protein uptake. CONCLUSIONS: The high capacity retrieval pathway for albumin is most likely associated with transtubular cell transport. It is also apparent that most albuminuric states could be accounted for by the malfunctioning of this pathway without resorting to any change in glomerular permselectivity.

Immuno-unreactive albumin excretion increases in streptozotocin diabetic rats.

We previously showed that albumin is fragmented (>90%) during renal passage to low-molecular-weight (<10 kd) peptides. The aim of the present study was to document the renal handling of albumin in experimental diabetes. Tritium-labeled albumin was infused into control and streptozotocin (STZ) diabetic rats during 7 days. Urinary radioactivity, assessed by size exclusion chromatography, revealed a major peak corresponding to low-molecular-weight, albumin-derived fragments and a minor peak corresponding to intact albumin or high-molecular-weight, albumin-derived protein. The fractional clearance of albumin, calculated from total radioactivity measurements, was at least 100-fold greater than the fractional clearance of albumin determined by radioimmunoassay (RIA) for control and diabetic rats. This result was mainly because low-molecular-weight, albumin-derived fragments were not detected by RIA. The fractional clearance of high-molecular-weight, albumin-derived protein was 2- to 10-fold greater than the fractional clearance determined by RIA. The immuno-unreactive high-molecular-weight, albumin-derived protein (called ghost albumin), characterized by size exclusion chromatography and high-performance liquid chromatography, was present in control and diabetic rat urine. Ghost albumin excretion rate was enhanced 11-fold after 8 weeks of STZ diabetes as compared with aged-matched controls. This study shows that renal modification resulting in low-molecular-weight and high-molecular-weight components of albumin is a major contributor to the renal handling of albumin. The results indicate that excretion of modified albumin is increased in STZ rats as compared with albumin detected by conventional RIA. Long-term studies are necessary to evaluate the potential of ghost albumin as a new marker for the assessment of urinary albumin in diabetes.

Variability of standard clinical protein assays in the analysis of a model urine solution of fragmented albumin.

OBJECTIVES: This study investigates the sensitivity of various standard clinical techniques in the detection of albumin fragments. The significance of this work is in the detection of urinary proteins, such as albumin, which has recently been discovered to be excreted as mainly peptide fragments as a result of filtered albumin undergoing degradation during renal passage. All filtered proteins undergo a similar degradation process. DESIGN AND METHODS: Albumin digested with trypsin was used as a model urine solution. The solution was assayed for albumin concentration by various methods including the biuret assay that is known to detect urinary albumin fragments. The digest solution was also analyzed by various clinically used chromagen assays, electrophoretic and chromatographic methods to determine whether they are able to detect the fragmented protein. RESULTS: The benzethonium chloride, Coomassie blue, and pyrogallol red assays for urine protein, the immunoassay for human albumin and sodium dodecyl sulfate polyacrylamide gel electrophoresis with Coomassie blue staining were unable to detect the albumin fragments. Capillary electrophoresis was sensitive to the fragments but with low resolution. High-performance liquid chromatography gave the best results. CONCLUSIONS: Many techniques utilized to assay patient urine samples are unable to detect fragmented albumin and, hence, will severely underestimate albumin and protein excretion.

Characteristics of albumin processing during renal passage in anti-Thy1 and anti-glomerular basement membrane glomerulonephritis.

Recent studies have shown that glomerular-filtered albumin appears to be processed by two distinct cellular pathways. The major pathway, a high-capacity retrieval pathway, returns most of the filtered albumin to the blood supply intact. The albumin not taken up by the retrieval pathway is degraded by lysosomes during renal passage and excreted as fragments in urine. We studied the interplay of the albumin retrieval pathway and the degradation pathway in the disease models of anti-Thy1 nephritis, a model of mild proteinuria, and anti-glomerular basement membrane (anti-GBM) disease, a model of severe proteinuria. This is achieved by investigating the integrity of urinary albumin and its excretion rate. Total albumin excretion (intact plus fragments) did not change significantly in the rats with anti-Thy1 nephritis. However, it was established that intact albumin excretion had a strong positive correlation with increasing total-protein excretion, which showed that the degradation pathway was being predominantly affected in this disease. For the rats with anti-GBM disease, total protein excretion increased 26-fold compared with the control group, and intact albumin excretion increased 250-fold. The profound changes in albumin excretion in anti-GBM disease are consistent with inhibition primarily of the retrieval pathway.

The return of glomerular-filtered albumin to the rat renal vein.

BACKGROUND: Recent studies have demonstrated that the normal glomerular capillary wall (GCW) is not charge selective to albumin. This means that albumin flux across the GCW is high, and this has been confirmed in studies in which albumin uptake by the tubules has been inhibited. Therefore, there must be a high-capacity postglomerular retrieval pathway in normal kidneys that returns filtered albumin back to the blood supply. METHODS: This study identifies the presence of glomerular-filtered albumin in the renal vein from the analysis of the decrease of radioactivity in the venous effluent after the injection of a pulse of tritium-labeled albumin into the renal artery in vivo and in the isolated perfused kidney. RESULTS: The postglomerular filtered albumin is returned to the blood supply by a high-capacity pathway that transports this albumin at a rate of 1830 +/- 292 micrograms/min.rat kidney (N = 14, mean +/- SEM). This pathway has been identified under physiological conditions in vivo and in the isolated perfused kidney. The pathway is specific for albumin, as it does not occur for horseradish peroxidase. The pathway is inhibited in a nonfiltering kidney. The pathway is also inhibited by ammonium chloride (an agent that inhibits tubular protein uptake but does not alter glomerular size selectivity) and by albumin peptides (which compete for the tubular albumin receptor). CONCLUSIONS: The high-capacity retrieval pathway for albumin is most likely associated with transtubular cell transport. It is also apparent that most albuminuric states could be accounted for by the malfunctioning of this pathway without resorting to any change in glomerular permselectivity.