Parasites influence cannibalistic and predatory interactions within and between native and invasive amphipods

In Northern Ireland, the amphipods Gammarus duebeni celticus (native) and G. pulex (invasive) coexist in some places, whilst in others the native species has been replaced by the invader. We explored the role of parasites in mediating interactions between these amphipods, which demonstrate mutual intraguild predation (IGP: predation between animals that also compete for prey). IGP and cannibalism can be important factors in structuring populations and communities. We investigated the effects of parasitism on rates of IGP between G. d. celticus and G. pulex and on cannibalism within each species by comparing functional responses (FRs: relationships between the use of a prey resource and its availability). Infection with the microsporidian Pleistophora mulleri caused an increase in IGP and cannibalism by G. d. celticus, which showed increased attack rates and reduced prey handling times. In contrast, infection with the acanthocephalan parasite Echinorhynchus truttae did not alter IGP or cannibalism by G. pulex. A prey preference experiment revealed that both amphipods were more likely to feed on heterospecific rather than conspecific prey, and this was also corroborated by the fact that overall IGP FRs were higher than cannibalism FRs. This may be selectively advantageous, as feeding on heterospecific prey removes possible competitors without the risk of consuming juvenile kin or acquiring parasites from infected conspecifics. Infection of the native G. d. celticus with P. mulleri enhanced IGP on the invasive G. pulex, which is likely to facilitate the coexistence of the 2 species.

Eaten alive: cannibalism is enhanced by parasites

Cannibalism is ubiquitous in nature and especially pervasive in consumers with stage-specific resource utilization in resource-limited environments. Cannibalism is thus influential in the structure and functioning of biological communities. Parasites are also pervasive in nature and, we hypothesize, might affect cannibalism since infection can alter host foraging behaviour. We investigated the effects of a common parasite, the microsporidian Pleistophora mulleri, on the cannibalism rate of its host, the freshwater amphipod Gammarus duebeni celticus. Parasitic infection increased the rate of cannibalism by adults towards uninfected juvenile conspecifics, as measured by adult functional responses, that is, the rate of resource uptake as a function of resource density. This may reflect the increased metabolic requirements of the host as driven by the parasite. Furthermore, when presented with a choice, uninfected adults preferred to cannibalize uninfected rather than infected juvenile conspecifics, probably reflecting selection pressure to avoid the risk of parasite acquisition. By contrast, infected adults were indiscriminate with respect to infection status of their victims, probably owing to metabolic costs of infection and the lack of risk as the cannibals were already infected. Thus parasitism, by enhancing cannibalism rates, may have previously unrecognized effects on stage structure and population dynamics for cannibalistic species and may also act as a selective pressure leading to changes in resource use.

Trait-Mediated Effects of Parasites on Invader-Native Interactions

Parasites have a variety of behavioural effects on their hosts, which can in turn affect species with which the host interacts. Here we review how these trait-mediated indirect effects of parasites can alter the outcomes of invader-native interactions, illustrating with examples from the literature and with particular regard to the invader-native crustacean systems studied in our laboratories. Parasites may potentially inhibit or exacerbate invasions via their effects on host behaviour, in addition to their direct virulence effects on hosts. In several crustacean systems, we have found that parasites influence both host predation rates on intra- and inter-guild prey and host vulnerability to being preyed upon. These trait effects can theoretically alter invasion impact and patterns of coexistence, as they indirectly affect interactions between predators and prey with the potential for further ramifications to other species in the food web. The fitness consequences of parasite-induced trait-mediated effects are rarely considered in traditional parasitological contexts, but demand attention in the context of ecological communities. We can regard these trait effects as a form of cryptic virulence that only becomes apparent when hosts are examined in the context of the other species with which they interact.

A permanent fish cell line (EPC) for genotoxicity testing of marine sediments with the comet assay

Genotoxicity and cytotoxicity were evaluated in an in vitro system with a permanent cell line Epithelioma papulosum cyprini (EPC) derived from a skin tumour of carp (Cyprinus carpio L.). EPC cells were exposed to different concentrations of organic sediment extracts from the North Sea for 24h. After incubation the cells were analysed for viability and DNA strand breaks with the comet assay or single cell gel electrophoresis (SCGE). The results confirm the sensitivity of this assay. Out of 10 marine sediment samples from the North Sea, 9 showed a dose-dependent genotoxic effect. The EC(50) of sediment extracts ranged from 7 to 307 mg sediment dry weight/ml assay volume. Hepatic microsomal enzymes from dab (Limanda limanda L.) was proposed for enzymatic activation of benzo[a]pyrene (BAP) or sediment extracts, respectively. The suitability of this in vitro test system for assessing genotoxic and cytotoxic effects of marine sediment extracts on EPC cells could be demonstrated.

The poor accuracy of indirect measurements of cadaveric donor kidney weights

Reports that examined the issue of whether transplantation of inadequate nephron mass may be a risk factor for long-term allograft failure yielded conflicting results. One of the more accurate methods of estimating glomerular mass is kidney weight. Most of the clinical studies used body surface area (BSA) or kidney length as estimates of kidney weight. To test the hypothesis that indirect measures of kidney weight are accurate estimates of kidney weight, we compared the kidney weight of 41 consecutive cadaveric kidneys to donor BSA, dimensions measured with calipers at the time of transplantation, and dimensions supplied by the Organ Procurement Agency (OPA). Linear regression analysis was used with kidney weight as the dependent variable and BSA, kidney length, or kidney volume as the independent variable. Kidney length measured with calipers was also compared to kidney length supplied by the OPA. Kidney weight had the best correlation with kidney volume and kidney length determined by caliper measurements (r = 0.640 and 0.646, respectively). The regression analysis showed that the correlation of kidney weight with BSA was 0.487. The correlation of OPA-provided kidney length with kidney weights was poor (r = 0.410). The linear regression of caliper-measured kidney length versus OPA length yielded a slope of 0.360, instead of an ideal slope of 1. The assumption has been made that kidney weight or a surrogate of kidney weight has an excellent correlation with nephron mass. Some of the variability in studies that attempted to examine the effect of transplanted nephron mass on allograft outcome may be due to inaccurate estimates used for kidney weight. Our data suggest that surrogate measurements of kidney weight may not be accurate. We recommend that measured kidney weight should be used in studies examining the effect of donor renal mass on allograft outcomes.

Risk factors for peritonitis in long-term peritoneal dialysis: the Network 9 peritonitis and catheter survival studies. Academic Subcommittee of the Steering Committee of the Network 9 Peritonitis and Catheter Survival Studies

To determine factors involved in peritoneal dialysis-associated peritonitis and catheter loss, all point prevalent peritoneal dialysis patients in Health Care Finance Administration (HCFA) end-stage renal disease (ESRD) Network 9 were followed throughout 1991 for peritonitis events and throughout 1991 to 1992 for catheter survival. Data were collected by questionnaires compiled by the dialysis facility and validated by network staff. Peritonitis was reported 1,168 times in 729 of the 1,930 patients. By gamma-Poisson regression, a significantly increased risk for peritonitis was observed for patients with previous peritonitis, black race, and those dialyzing with standard connectors or cyclers compared with disconnect systems. Decreased risks were observed for patients with longer ESRD experience and when prophylactic antibiotics were administered before catheter insertion. Postinsertion leakage, diabetes, visual problems, previous or current immunosuppression, and physical activity were not risk factors. Infection of any kind caused the removal of 68% of the 414 catheters lost. Patients with downward-directed tunnels were less likely to experience concomitant exit site/tunnel infections associated with peritonitis. Peritonitis episodes with Staphylococcus epidermidis-like organisms were more likely to resolve with a single course of antibiotics. Perhaps because of their higher infection rate, blacks were more likely than whites to use a disconnect system. In general, the outcome of peritonitis in blacks was similar to that in whites, except that blacks were less likely to be hospitalized and were less likely to die.

Pseudomonas peritonitis in peritoneal dialysis patients: the Network #9 Peritonitis Study

To determine risk factors for the development of Pseudomonas peritonitis (PsP) and outcomes of PsP, the authors compared peritoneal dialysis patients who developed PsP with peritoneal dialysis patients who developed non-Pseudomonas bacterial peritonitis (non-PsP). The authors also sought to determine if there were differences in patients who had resolution of PsP compared with those patients whose PsP did not resolve. The data were derived from the prospective Tristate Renal Network Peritonitis and Catheter Survival Study. Resolution in this study was defined as clearing of peritoneal dialysate on visual inspection, with up to three courses of antibiotic therapy allowed. Catheter removal, switch to hemodialysis, or death were outcomes that were considered separately from resolution because of the study design. There were 31 cases of PsP in 28 patients and 886 cases of non-PsP identified in 667 adult patients. There were no differences in race, gender, age, or incidence of diabetes between the groups. The PsP group had a 25% incidence of previous exposure to immunosuppressive agents, whereas it was 10.6% in the non-PsP group (P = 0.028). PsP infections were more frequently associated with concomitant exit and tunnel infections, higher hospitalization rates, increased incidence of catheter loss, switch to hemodialysis, and a worse rate of resolution when compared with non-PsP (all, P < 0.05). Logistic regression could not identify patients at increased risk of PsP. PsP resolved with antibiotic therapy only in 10 of 31 episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

An improved glomerular filtration rate in cardiac transplant recipients with once-a-day cyclosporine dosing

We tested the hypothesis that there would be a difference in the unwanted side effects of cyclosporine (CsA) when heart transplant patients received CsA once a day versus half the dose twice a day. Eight stable cardiac transplant patients (> 6 months posttransplant) were administered their dose of CsA either as a once-a-day dose or half the dose b.i.d. for 21 days in a random fashion. After 21 days the patients were crossed over to the other regimen. Patients underwent inulin and PAH clearances at CsA trough on each arm of the study. Each patient collected several 24-hr urines for determination of creatinine clearance, and had ambulatory blood pressure monitoring done during each arm of the study. Serum chemistries and lipid profiles were performed at the end of each arm of the study. The CsA dose was 1.9-7.2 mg/kg/day. All patients were hypertensive and on calcium channel antagonists. Once-a-day CsA dosing resulted in a 29% decrease in trough CsA levels. A significant increase in glomerular filtration rate, as estimated by the clearance of inulin, (65.16 +/- 24.4 q. day vs. 54.62 +/- 19.0 b.i.d. (ml/min) P < .02) and a significant increase in renal plasma flow, as estimated by the clearance of PAH, occurred with once-a-day dosing when compared with b.i.d. dosing (P = .02). Creatinine clearances were not different between the 2 arms of the study and significantly overestimated glomerular filtration rates (P = .01). CsA dosing b.i.d. resulted in significantly higher nocturnal blood pressures (91.2 +/- 8.3 b.i.d. vs. 86.4 +/- 8.1 q. day, mmHg, P = .015) when compared with once-a-day dosing. A significant increase in LDL cholesterol and a significant decrease in HDL cholesterol were noted during the b.i.d. dosing arm when compared with q. day CsA dosing. We conclude that in stable heart transplant patients once-a-day CsA dosing results in better GFR and renal plasma flow, a lower nocturnal blood pressure, and an improved lipid profile when compared with dosing CsA twice a day.

Effect of erythropoietin on renal excretion of a sodium load

To determine whether erythropoietin alters the renal excretion of a sodium load in humans, we administered either erythropoietin (150 units/kg) or vehicle intravenously in a randomized crossover design to six normal white men on day 4 of a controlled sodium diet. After erythropoietin administration, the subjects were given 2 L normal saline solution intravenously over 4 hours. All urine was collected for 4 days after drug administration. Serum sodium and creatinine levels and blood pressure were determined 0, 4, 8, and 24 hours after drug administration. Peripheral renin activity and aldosterone levels were determined 0, 4, and 8 hours after drug administration. Erythropoietin significantly decreased total sodium excretion during the 4 days after drug administration (erythropoietin = 784 +/- 46 mEq/4 days versus control = 840 +/- 41 mEq/4 days; p < 0.001). Erythropoietin did not alter creatinine clearance, blood pressure, or the changes in plasma renin activity and aldosterone caused by the saline load. We conclude that erythropoietin decreases urine sodium excretion after a sodium load in normal human subjects without altering glomerular filtration rate, blood pressure, or plasma renin activity.

Effect of calcium channel antagonists on renal function in hypertensive heart transplant recipients

Orthotopic heart transplant recipients treated with immunosuppressive regimens based on cyclosporine have a high incidence of hypertension. Cyclosporine-induced nephrotoxicity characterized by afferent glomerular arteriolar vasoconstriction also develops in these patients. Calcium channel antagonists produce afferent glomerular arteriolar vasodilation. Angiotensin-converting enzyme inhibitors (ACEI) dilate the efferent arteriole and have been suggested to decrease glomerular filtration rate in subjects taking cyclosporine. To test the hypothesis that calcium channel antagonists would improve glomerular filtration rate in heart transplant patients receiving ACEI treatment, we reviewed the charts of our patients whose treatment for hypertension had been changed from an ACEI to a calcium channel antagonist. A change in renal function was assessed by the average of serum creatinine level, blood urea nitrogen, and creatinine clearance within 3 months before and after the change from ACEI to calcium channel antagonist. Blood pressure was assessed on two different occasions before and after conversion to calcium channel antagonist. The data were analyzed by a paired Student t test. Serum blood urea nitrogen and creatinine levels decreased significantly when patients were treated with calcium channel antagonists (p < 0.05). Creatinine clearance increased in all patients when the treatment was converted to a calcium channel antagonist (CCA) (ACEI = 56.4 +/- 19.3 ml/min versus CCA = 71.06 +/- 23.77, N = 9; p < 0.005). A 5-mm Hg decrease occurred in mean arterial pressure when treatment was changed from ACEI to calcium channel antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of glomerular filtration rate by the thromboxane receptor antagonist L655,240 during low dose cyclosporine administration

Cyclosporin A (CsA) alters the production of prostaglandins (PG) by the kidney. CsA causes an increase in renal vascular resistance, a decrease in renal blood flow, a decrease in glomerular filtration rate (GFR), and increases the renal production of the vasoconstrictor thromboxane. Recently, low dose CsA has been utilized in the treatment of refractory autoimmune diseases. To determine if low dose CsA administration could produce renal hemodynamic alterations and to determine if the thromboxane receptor antagonist L655,240 could prevent these alterations, we administered groups of rats either CsA, 5 mg/kg, subcutaneously and the L655,240 vehicle NaHCO3 (CsA-NaHCO3), or CsA and L655,240 (CsA-L655,240), or CsA vehicle and L655,240. The rats were administered the drugs for 7 days and then subjected to inulin and PAH clearances or kidneys were harvested for prostaglandin production studies. CsA significantly depressed GFR and renal plasma flow when compared to the L655,240 treated groups. There was no difference in inulin or PAH clearance between the CsA-L655,240 and CsA vehicle L655,240 groups. Glomerular prostaglandin production including thromboxane was depressed by CsA administration. No histologic alterations were noted in the glomeruli or the medullary portions of the kidney. We conclude that administration of low dose CsA, 5 mg/kg, for 7 days results in a decrease in renal blood flow and GFR without histologic alterations. Administration of the thromboxane receptor antagonist L655,240 prevents the renal hemodynamic alterations induced by CsA in this rat model.

The effect of cyclosporine on agonist-stimulated glomerular and mesangial cell vasodilatory prostaglandin production

Cyclosporine A administration produces an increase in renal vascular resistance and a decrease in glomerular filtration rate in both human and animal models. CsA usage in humans has also been shown to alter the ability of the kidney to adapt to alterations in renal hemodynamics. CsA alters the production of prostaglandins by isolated rat glomeruli. Normally, vasoconstrictive agents stimulate the production of vasodilatory glomerular and mesangial cell PG. To determine if CsA alters glomerular and mesangial cell (MC) vasodilatory PG production in response to vasoconstrictive agents, we administered CsA, 20 mg/kg, or vehicle to rats for 7 days, or incubated mesangial cells with CsA 1 mcg/ml for 24 hr. Ex vivo glomerular PGE2 and 6-keto-PGF1a production was determined in the presence or absence of angiotensin II 10(-6) M and norepinephrine 10(-5)M. CsA administration decreased glomerular production of both eicosanoids in the basal and stimulated state. Incubation of MC with CsA markedly suppressed PGE2 and 6-keto-PGF1a production in response to stimulation with 200 nM angiotensin II. To determine if CsA inhibits angiotensin II-stimulated PG production prior to protein kinase C, we incubated glomeruli and MC with the diacylglycerol mimetic OAG. CsA depressed OAG-stimulated glomerular and MC PGE2 and 6-keto-PGF1a production. Conversely, CsA stimulated the production of PGE2 by renal medullary slices. We conclude that CsA blunts the vasoconstrictor-induced increase in glomerular and mesangial cell vasodilatory PG production, thereby removing a compensatory mechanism that maintains GFR in states of vasoconstrictor excess.

Urinary excretion and renal production of prostaglandins E2, F2 alpha, and thromboxane B2 in experimental diabetes mellitus

To delineate the urinary excretion of prostaglandins E2 (PGE), F2 alpha (PGF), and thromboxane B2 (TxB) in diabetic rats, we treated male Sprague-Dawley rats with streptozocin 60 mg/kg or with vehicle. Plasma glucose and creatinine concentration and 24-hour urine collections for determination of TxB, PGE, PGF, creatinine, and protein excretion were measured at 2, 8, and 14 weeks after streptozocin. Creatinine clearance was significantly decreased in diabetic rats at 2 and 8 weeks, whereas the urinary protein excretion was three to five times that of control animals at all times. The 24-hour excretion of TxB was elevated twofold to threefold in diabetic rats, whereas PGE and PGF excretion were both significantly decreased. This alteration in excretion was not caused by increased urine flow rate, inasmuch as mannitol-induced osmotic diuresis caused an increase in PGE and PGF excretion. Eight weeks after streptozocin, a group of diabetic and control rats were sacrificed, and the production of PGE, PGF, and TxB by the renal papillae and glomeruli determined. An additional five diabetic rats were treated with protamine zinc insulin for 1 week before sacrifice to determine the effect of insulin treatment on the production of PGE, PGF, and TxB by the glomeruli and renal papillae. Papillary production of PGE, PGF, and TxB was decreased in diabetic rats, as was glomerular production of PGE and PGF. Insulin treatment increased PGF production by the renal papillae and increased PGE, PGF, and TxB production by glomeruli. These results indicate that changes in prostaglandin excretion accompany the development of marked proteinuria and a decrease in creatinine clearance.(ABSTRACT TRUNCATED AT 250 WORDS)