Renal vascular effects of leukotriene C4 in the isolated perfused kidney of the rat

Histamine, leukotriene C4 and interleukin-2 increase antibody uptake into a human carcinoma xenograft model

Systemically administered radiolabelled anti-tumour antibody is ineffective in treating the majority of patients with liver metastasis from colorectal carcinoma. We have assessed whether agents which increase capillary permeability can increase tumour uptake of antibody isotope conjugate. We developed a xenograft model of colorectal carcinoma using an antibody directed against carcinoembryonic antigen (CEA). Tumours were grown subcutaneously in the hind limbs of athymic rats to derive their circulation from the femoral artery. Cannulae were placed in the common iliac artery and iliolumbar vein. Antibody was delivered systemically, regionally and regionally with histamine, leukotriene C4 and interleukin-2. Regionally administered anti-CEA antibody resulted in a significantly greater (P = 0.004) tumour to normal tissue ratio (1.66, s.d. = 0.68) compared to systematically administered antibody (1.25, s.d. = 0.73). The addition of vasoactive drugs produced an approximately 3-fold increase with an increase to a mean tumour:liver ratio of 3.24 (s.d. = 1.39) for histamine (P less than 0.001 compared to systemic delivery), 3.21 (s.d. = 1.13, P less than 0.001) for leukotriene C4 and 3.80 (s.d. = 1.53, P less than 0.001) for interleukin-2. The addition of histamine significantly (P = 0.004) increased the mean tumour to liver ratio (1.73, s.d. = 0.44) of non-specific antibody uptake compared with either systemic (1.12, s.d. = 0.24) or regional delivery (1.25, s.d. = 0.54) of non-specific antibody alone. Increasing tumour capillary permeability can produce a significant clinically useful increase in tumour uptake of antibody-isotope conjugate.

Metabolism of cysteinyl leukotrienes by the isolated perfused rat kidney

The metabolism of cysteinyl leukotrienes by the isolated perfused rat kidney was investigated. For this purpose LTC4, LTD4 or LTE4 were studied in separate experiments. The isolated perfused rat kidney metabolized all cysteinyl leukotrienes to the final metabolite N-acetyl-LTE4. In the presence of 5% albumin 50% of LTC4 was metabolized to LTD4 (22%), LTE4 (15%) and N-acetyl-LTE4 (13%) within 60 min. Excretion of radioactivity into urine was less than 1%. In contrast, in the absence of albumin, LTC4 was completely metabolized within 45 min to N-acetyl-LTE4, the sole and final metabolite of LTC4 found in the perfusion medium as well as in urine. After 60 min 19% and 42% of total radioactivity were found in the perfusion medium and in urine, respectively. Isolated glomeruli metabolized LTC4 to LTD4 and to LTE4 but not to N-acetyl-LTE4 at a rate comparable to the rate observed by the isolated perfused kidney in the absence of albumin. In contrast to isolated glomeruli isolated tubuli metabolized LTE4 to N-acetyl-LTE4 at a rate comparable to that observed by the isolated perfused kidney in the absence of albumin. The present study shows that the isolated perfused rat kidney metabolizes cysteinyl leukotrienes to the sole and final metabolite N-acetyl-LTE4. In the presence of albumin metabolism is slowed down and excretion of N-acetyl-LTE4 into urine is prevented.

Enhanced renal leukotriene production in murine lupus: role of lipoxygenase metabolites

To investigate the potential role of leukotrienes in murine lupus, we measured renal hemodynamics and renal leukotriene production in MRL-lpr/lpr mice at 12 and 20 weeks of age. Over this age range, these animals develop overt manifestations of autoimmune disease with nephritis similar to human SLE. In the current study, we demonstrated that glomerular filtration rate (GFR) and PAH clearance (CPAH) deteriorated with age in MRL-lpr/lpr mice, but not in MRL(-)+/+ controls. Impaired renal hemodynamic function in MRL-lpr/lpr mice was associated with enhanced ionophore-stimulated production of both leukotriene B4 (LTB4) and leukotriene C4 (LTC4) by preparations of renal cortex. There was a significant inverse correlation between GFR and in vitro production of both LTC4 and LTB4 in kidneys from MRL-lpr/lpr mice, but not in control animals. In addition, in vitro LTC4 production was correlated with the severity of renal histomorphologic abnormalities. Administration of the specific peptidoleukotriene receptor antagonist SKF104353 to 20 week old MRL-lpr/lpr mice significantly improved both GFR and CPAH, whereas this agent had no effect of renal hemodynamics in MRL(-)+/+ controls. These results suggest that renal production of LTC4 and LTB4 is increased in MRL-lpr/lpr mice with nephritis, and that enhanced production of peptidoleukotrienes causes reversible renal dysfunction. Increased leukotriene production within the kidney may therefore be important in the pathogenesis of lupus nephritis.

Increased production of cysteinyl leukotrienes in hepatorenal syndrome

The cysteinyl leukotrienes C4 and D4 are potent renal vasoconstrictors which may modulate glomerular function in vivo, and may therefore be important in the pathogenesis of hepatorenal syndrome. Urinary leukotriene E4, the major metabolite of leukotrienes C4 and D4, was elevated in patients with hepatorenal syndrome (17.8 ng/h) when compared with normal controls (5.1 ng/h) or subjects with renal failure alone (1.9 ng/h). Urinary leukotriene E4 was also elevated in subjects with decompensated liver disease (cirrhosis with ascites 28.6 ng/h, severe hepatocellular dysfunction 57.5 ng/h), but normal in compensated liver disease (6.7 ng/h). In the early stages of hepatorenal syndrome, leukotriene E4 excretion rate was up to 100-fold higher (560 ng/h) than in normals, and fell in parallel with creatinine clearance, indicative of the glomerular filtration rate-dependent renal excretion. Following correction for creatinine clearance, leukotriene E4, excretion was considerably higher in hepatorenal syndrome (54.1 pg/ml creatinine clearance) compared with normals (1.0 pg/ml creatinine clearance), chronic renal failure (3.2 pg/ml creatinine clearance), decompensated liver disease (ascites 7.7 pg/ml creatinine clearance, and severe hepatocellular dysfunction 11.0 pg/ml creatinine clearance), and compensated liver disease (1.9 pg/ml creatinine clearance). To interpret the significance of these findings, we determined renal clearance and endogenous metabolism of the cysteinyl leukotrienes by infusion of [3H]leukotriene C4 into a single subject with hepato-renal syndrome and two control subjects. Renal clearance of leukotriene E4, was reduced in hepatorenal syndrome (2.4 ml/min) compared with controls (greater than 17 ml/min) which together with the increased excretion rate of leukotriene E4 demonstrates that there is increased cysteinyl leukotriene production in hepatorenal syndrome. This may be one of the factors involved in its pathogenesis.

Leukotrienes cause mesenteric vasoconstriction and hemoconcentration in rats without activating thromboxane receptors

Thromboxane A2/prostaglandin H2 (TP)-receptor activation has been reported to participate in some of the responses to peptide leukotrienes (LT). We examined the effect of TP-receptor antagonism on LT-induced mesenteric vasoconstriction and hemoconcentration in anesthetized rats. The antagonist used in these studies, SQ 30,741, was shown to have high selectivity and potency for vascular TP-receptors in the rat. Arterial (i.a.) injection of LTC4 and D4 elicited dose-dependent and transient reductions in mesenteric blood flow without changes in arterial blood pressure. These responses were unaffected by a dose of SQ 30,741 which produced approximately 99% inhibition of similar responses to U-46,619. In contrast, LT-induced mesenteric vasoconstriction was inhibited approximately 90% by two LT antagonists, LY 171,883 and SKF 104,353. In other experiments i.v. infusion of LTD4 caused increases in hematocrit and reductions in arterial blood pressure that were not influenced by SQ 30,741. These data suggest that increases in mesenteric vascular resistance and hemoconcentration in response to LTs are not the result of TP-receptor activation.

Cardiovascular effects of leukotrienes

Leukotrienes have been shown to significantly influence coronary vascular resistance, infarct size, pulmonary vascular resistance, bronchial tone, and renal vascular resistance either directly or indirectly. There is a notable dearth of data on human pathophysiologic conditions. With the advent of specific inhibitors of the synthesis and action of leukotrienes and, more importantly, of methods on the in-vivo synthesis of these potentially important mediators, these gaps in our understanding will be closed.