B1 but not B2 bradykinin receptor agonists promote DU145 prostate cancer cell proliferation and migration.

BACKGROUND: The kallikrein-kinin system (KKS) is an endogenous pathway involved in angiogenesis and tumourigenesis, both vital for cancer growth and progression. OBJECTIVES: To investigate the effect of two bradykinin receptor (B1R and B2R) agonists on growth and motility of prostate tumour (DU145) and micro-vascular endothelial cells (dMVECs). METHODS: Increasing concentrations of selective B1R and B2R agonists were added to cultured cells. Cell proliferation and migration were assessed using the 3-[4,5 dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) and modified Boyden Chamber assays, respectively. Where significant stimulation was found, the influence of an antagonist was also investigated. RESULTS: Neither growth nor motility of endothelial cells was affected by either agonist. In DU145 cells, while the B2R agonist was without any significant effect, the B1R agonist stimulated proliferation and migration at concentrations of 10nM and 50nM respectively. Further, this effect was abrogated when cells were pre-incubated with a B1R antagonist. CONCLUSIONS: Unlike the physiologically-active B2R, the pathologically-inducible B1R may be implicated in prostate tumourigenic events. The involvement of the KKS in malignant prostate pathology supports on-going exploration of bradykinin receptor antagonists as target candidates in the development of alternate approaches to cancer therapy.

Population pharmacokinetics of gentamicin in South African newborns.

OBJECTIVE: Gentamicin population pharmacokinetics in newborns were studied with special reference to possible gender effects. METHODS: Steady-state serum levels ( n=139) were obtained from 79 neonates with a mean birth weight of 2.1 kg, mean gestational age of 35.1 weeks and mean age at the time of sampling of 4.2 days. The data were analysed using the non-linear mixed effects model (NONMEM). A one-compartment model was used to fit the data. RESULTS: The final models for clearance (CL) and volume of distribution (V) were: CL(l/h)=0.001xWGTxGAxP and V(l)=0.472xWGT, where WGT=birth weight (kg), GA=gestational age (weeks) and P=1.2 for girls and 1.0 for boys. The values of inter-individual variability in CL and V were 34% and 35%, respectively. Intra-individual variability was 5% (proportional) and 7.2% (additive). Mean (95% confidence interval) values of CL and half-life were 0.042 l h(-1) kg(-1) (0.041, 0.043 l h(-1) kg(-1)) and 8.0 h (7.7, 8.3 h), while V was 0.472 (0.428, 0.516) l/kg for all patients. CONCLUSION: Mean population pharmacokinetic values were similar to those obtained with NONMEM for gentamicin in other neonates of similar age. Gender was found to be a determinant of CL, with girls clearing faster than boys.

The pharmacokinetics of theophylline in premature neonates during the first few days after birth.

The aims of the study were to estimate the pharmacokinetic parameters, clearance rate (CL), and volume of distribution (V) of theophylline in premature neonates during the first few days after birth, and to identify factors contributing to interindividual variability. The authors obtained 263 serum concentrations from 105 apneic premature neonates receiving intravenous (IV) theophylline. Mean (SD) birth weight and postnatal ages were 1.3 (0.3) kg and 1.1 (0.3) days, respectively. The data were analyzed using the nonlinear mixed effects model (NONMEM). A one-compartment model with first order elimination was used. The final models were: CL (L/h) = 0.006 * WGT 0.75 * P, V (L) = 0.63 * WGT, WGT = weight (kg) P = 1.47 with oxygen support and 1.0 without oxygen support. The CL in the study population was low, resulting in long half-lives. After inclusion of the above covariates, as well as interoccasion variability, the interindividual variability in CL was 56% and in V was 47%. Interoccasion variability in CL and V was 34% and 35% respectively. Theophylline pharmacokinetics are variable in the premature neonate during the first week of life, and this high variability makes it difficult to predict drug concentrations with the same degree of accuracy as in other populations.

A model for the determination of carbamazepine clearance in children on mono- and polytherapy.

OBJECTIVE: To derive a model describing carbamazepine (CBZ) clearance in children, in terms of individual patient characteristics. METHODS: One hundred and eighteen steady-state serum carbamazepine concentration measurements were gathered during normal routine care of 72 compliant outpatients (2.3-16.3 years old). Levels were obtained from patients receiving monotherapy (55%), concomitant valproate (26%), or concomitant inducers (phenytoin, phenobarbitone; 19%). A one-compartment model was used to fit the data with the computer programme Nonlinear Mixed Effects Model (NONMEM). RESULTS: Weight, age and concomitant medication were all important determinants of clearance. The final model for clearance (1.h-1) was: CL = [0.7(WT) 0.4] . M, where WT is patient weight (kg) and M is a scaling factor for concomitant medication, with a value of 1 for patients on CBZ monotherapy or concomitant valproate and 1.4 for those receiving concomitant inducers. For the purposes of this analysis, bioavailability (f) was assumed to be complete, i.e., f is thus included in the term CL. CONCLUSIONS: CBZ clearance decreased with increasing age. As age and weight were correlated, either variable was a satisfactory predictor. The influence of both the inducers and valproate on CBZ clearance was as expected. This model, which describes clearance in terms of patient-specific details, can be used when predicting the maintenance dose required to achieve a target mean steady-state CBZ concentration in children.

Determination of population pharmacokinetic parameters for amikacin in neonates using mixed-effect models.

OBJECTIVE: The population pharmacokinetics of amikacin, in neonates, was investigated using the nonlinear mixed effects model (NONMEM). METHODS: One hundred and six steady-state amikacin serum levels were obtained from 53 black neonates with a mean gestational age of 35.1 weeks and mean age at the start of treatment of 3.1 days. A one-compartment model was used to fit the data. RESULTS: The final models for clearance (CL) and volume of distribution (V) were: CL(l.h(-1)) = 0.031WT(1.45) x P and V(l) = 0.316WT(1.44) where WT = birth weight (kg) and P = 1.28 for girls and 1.0 for boys. Inclusion of other fixed effect parameters in the model did not significantly improve the fit of the data. The inter-individual variability for CL and V were 18% and 13%. respectively. Intra-individual variability was 29%. Mean (95% CI) values of CL, V and half-life were 0.048 (0.045, 0.051) l.h(-1).kg(-1), 0.434 (0.414, 0.453) l.kg(-1) and 6.4 (6.2, 6.6) h respectively. CONCLUSION: Birth weight was an important determinant of both CL and V and, in this data set, gender was also found to influence CL. Mean population pharmacokinetic values were within the range of those previously derived for other neonatal populations using traditional methods.

The effect of theophylline on apnoea and hypoxaemic episodes in the premature neonate during the 1st 3 days after birth.

Although the effect of theophylline on apnoea is well documented, its influence on hypoxaemic episodes in premature neonates is less well known. To investigate the influence of the drug on both parameters, 37 apnoeic neonates were monitored before and after theophylline treatment. Incidents and densities of pathological apnoea (cessation of nasal airflow > or = 20 seconds) were recorded. A fall of > or = 10% for > 10 seconds in peripheral oxygen saturation was classified as a hypoxaemic episode. Ethical constraints precluded the inclusion of a control group. Each infant served as its own control. Theophylline serum concentrations were 5.6 (3.4), 8 (7.1) and 8 (5.3) mg/l on days 1, 2 and 3, respectively. The apnoea incidents and densities decreased significantly (p = 0.0001) from baseline on all 3 days. The total number of hypoxaemic episodes, as well as those not associated with pathological apnoea, decreased, though not significantly. However, those hypoxaemic episodes associated with pathological apnoea and a fall in pulse rate of > or = 20% decreased significantly from baseline on day 2 only. Throughout the study period, over 80% of hypoxaemic episodes were not associated with apnoea. It is concluded that in the doses used, theophylline was more effective in reducing apnoea than hypoxaemic episodes in premature neonates.

A comparison of two amikacin dosing regimens in paediatric surgical patients.

This investigation aimed to compare the efficacy and toxicity of two amikacin dosing regimens in seriously ill paediatric surgical patients. Children (0.6-12 years old) received amikacin intravenously either once daily (15 mg/kg, n = 27) or twice daily (7.5 mg/kg, n = 27). Concomitant medication was given as prescribed. Mean (SD) peak serum amikacin levels were significantly different (p < 0.05) between the once and twice daily groups (37.7 (6.9) mg/l and 19.5 (3.7) mg/l, respectively). Cumulative dose and duration of therapy were also significantly higher in the once-daily group. Regimen efficacy (favourable, unfavourable or indeterminate outcome) was assessed by patient temperatures, clinical improvement and white cell counts. Serum creatinine measurements and post-therapy, pure tone air conduction audiometry assessed nephro- and ototoxicity, respectively. No statistically significant differences were found between the groups in terms of outcome (18/24 and 22/25 patients in the once- and twice-daily groups had favourable outcomes; there were no unfavourable outcomes), nephrotoxicity (none of the patients assessed developed nephrotoxicity) or ototoxicity (2/20 and 5/20 patients, respectively, had mild high frequency hearing deficits which were predominantly unilateral and reversible). Although the regimens were similar in this study, other investigations will further clarify the optimal dosing approach in paediatric patients.

A model for estimating individualized valproate clearance values in children.

To evaluate the population pharmacokinetics of valproic acid in children, 97 steady-state serum valproate concentration measurements were gathered during normal, routine, outpatient care of 52 children with epilepsy (1.2-16 years of age). Levels were obtained from patients receiving valproate monotherapy (49%) or valproate with concomitant carbamazepine (32%), phenytoin (11%), or phenobarbitone (8%). A one-compartment model was used to fit the data with the Nonlinear Mixed Effects Model (NONMEM) computer program. The final model for clearance (L/hr) was CL = [EXP (0.022WT-1.38)] X M, where EXP = the base of the natural logarithm, WT = patient weight (kg) and M = a scaling factor for concomitant medication with a value of 1 for patients on valproate monotherapy and 1.61 for those receiving concomitant carbamazepine. Although phenytoin and phenobarbitone also were expected to increase valproate clearance, this could not be demonstrated, possibly because of the small number of samples taken from patients receiving these agents. Weight-adjusted values of valproate clearance decreased with increasing age. The actual mean value of 0.021 L/hr/kg for children taking monotherapy was slightly higher than values shown in most previously published reports, whereas the mean value of 0.028 L/hr/kg for patients taking concomitant carbamazepine was similar to those found previously in children taking other antiepileptic drugs.

Determination of phenobarbitone population clearance values for South African children.

Non-liner Mixed Effects Modelling (NON-MEM) was used to estimate phenobarbitone population clearance values for South African children, using 52 serum levels gathered from 32 patients during their routine care. NONMEM was also used to evaluate the influence of fixed effects such as weight, age and concomitant medication. The final model describing phenobarbitone clearance was CL = [Exp(0.0288 Wt - 2.53)]M, where CL clearance (l x h(-1)), Exp = the base of the natural logarithm, Wt = patient weight (kg) and M = a scaling factor for concomitant medication with a value of 1 for patients on phenobarbitone monotherapy, 0.62 for those receiving concomitant valproate and 0.87 for those patients receiving concomitant carbamazepine or phenytoin. Mean (95% confidence interval) phenobarbitone clearance values were 7.6 ml x h(-1) x kg(-1) (6.2, 9.0 ml x h(-1) x kg(-1) for the monotherapy group, 5.0 ml x h(-1) x hg(-1) (4.0, 6.0 ml x h(-1) x kg(-1)) in the presence of concomitant valproate and 6.8 ml x h(-1) x kg(-1) (5.6, 8.0 ml x h(-1) x kg(-1)) in the presence of concomitant carbamazepine or phenytoin. These values are similar to those previously reported from both traditional and NONMEM pharmacokinetic studies.

Intravenous and intramuscular magnesium sulphate regimens in severe pre-eclampsia.

Patients with severe pre-eclampsia were randomised to receive magnesium sulphate according to an intramuscular (IM) (N = 9) or an intravenous (i.v.) (N = 8) regimen. The IM regimen consisted of a loading dose of 14 g (4 g i.v. and 10 g IM) followed by 5 g 4-hourly. Patients given the IV regimen received a 6 g i.v. loading dose followed by a maintenance infusion of 2 g/h. Clinical outcome, laboratory parameters and serum magnesium levels were recorded for both groups. There were no significant differences between groups with regard to clinical outcome of either mother or child. Similar average serum magnesium concentrations were produced by the regimens the only significant difference was that fluctuations in magnesium levels were greater with the IM than the i.v. regimen. None of the patients had seizures despite levels mostly below 2 mmol/l.

Determination of theophylline clearance in South African children.

Theophylline clearance values in South African children were determined using 400 serum theophylline concentration measurements gathered from 109 compliant outpatients during their normal routine care. Population pharmacokinetic analysis was done using the Non-Linear Mixed Effects Model (Nonmem) to analyse the data. Nonmem was also used to estimate the influence of fixed effects (weight, age, race, gender etc) on clearance and its interindividual variability. Gender, age, and weight raised to an iterated exponent were found to be the most important demographic fixed effect parameters influencing clearance. Race was not found to be important. The weight-adjusted values of theophylline clearance decreased with increasing age. The actual values expressed in l.h-1.kg-1 were 0.0949 for children aged 1-5 y; 0.0813 for children aged 5-9 y, and 0.0660 for children of 9-16 y. The values are similar to those reported in other studies.

Pharmacokinetic consultation program in a pediatric asthma clinic.

The effect of a clinical pharmacokinetic consultation program for theophylline on the outcomes of pediatric patients with asthma was studied. The program was established in 1989 at a pediatric asthma clinic. For each patient visit, a clinical pharmacist recorded demographic, clinical, and medication-related information and counseled the parents. When an adjustment in the theophylline dosage was indicated, the pharmacist calculated the appropriate dosage using population pharmacokinetic values. If the pediatrician requested a measurement of the serum theophylline concentration, the time when the blood sample was drawn relative to the last dose was recorded, an average serum theophylline concentration at steady state and individualized pharmacokinetic values were calculated, and the dosage was adjusted accordingly. Patient data were compared among three stages: (1) the month before and the month of entry into the program, (2) months 5 and 6 after entry, and (3) months 11 and 12 after entry. A total of 44 patients were studied during each of stages 1 and 2, and 29 patients were reviewed during stage 3. There was a significant improvement in wheezing from stage 1 to stage 2 and in exercise tolerance and nocturnal coughing from stage 1 to stage 2 and stage 1 to stage 3. Forced expiratory volume in one second improved significantly from stage 1 to stage 2, and there was a significant reduction in the necessity for hospital visits for the treatment of exacerbations of asthma between stages 1 and 2. The daily weight-adjusted dose of theophylline increased significantly after the program began. Asthmatic children taking theophylline had improvements in outcome variables after pharmacokinetic consultation and medication counseling were initiated.

Levels of catecholamine in plasma and cerebrospinal fluid in aneurysmal subarachnoid hemorrhage.

Despite intensive investigation into the cause of cerebral vasospasm (focal ischemic deficit) after subarachnoid hemorrhage, the morbidity and mortality associated with this condition remain high. Various studies have shown levels of catecholamine in plasma and cerebrospinal fluid (CSF) to be increased in subarachnoid hemorrhage, and it is possible that these vasoactive substances play an important role in the subsequent vasospasm. In an attempt to elucidate this possibility, the study presented here was undertaken to investigate the relationship between catecholamine levels in plasma and CSF and focal ischemic deficit (FID); the rupture of aneurysms on blood vessels supplying the hypothalamus as compared with the rupture of aneurysms on blood vessels supplying other areas of the brain; and the clinical outcome of the patients. Concentrations of adrenaline and noradrenaline in plasma and CSF samples obtained from 21 patients who had suffered aneurysmal subarachnoid hemorrhage were determined by a radioenzymatic technique. Significantly higher levels of adrenaline were found at the time of surgery in the CSF of patients with FID. A similar trend, though not statistically significant, was also observed for plasma. Patients with a rupture of aneurysms on blood vessels supplying the hypothalamus showed a tendency towards higher catecholamine levels in plasma and CSF. Subjects with a bad clinical outcome (i.e., those who were severely disabled or had died) had significantly higher levels of catecholamine in plasma than did those with a good clinical outcome (i.e., those with moderate or no disability). Further detailed analysis of the interrelationships showed that, within the group of patients with FID, those with rupture of aneurysms on blood vessels supplying the hypothalamus had significantly higher catecholamine levels in plasma than did those with rupture of aneurysms on other cerebral vessels. Furthermore, in the group of patients with rupture of aneurysms on blood vessels supplying the hypothalamus, those with a bad clinical outcome had significantly higher catecholamine levels in plasma than did those with a good clinical outcome. These findings lend support to the possibility that damage to the hypothalamus and subsequent elevations in catecholamine levels may be associated with FID and poor clinical outcome.

The role of prostaglandins in the inhibition of cultured carcinoma cell growth produced by gamma-linolenic acid.

The growth of the cultured human breast carcinoma cell line NUB 1 as well as that of other cultured malignant cells has been shown to be inhibited by addition of gamma-linolenic acid (GLA) to the culture medium. It has previously been suggested that these findings may be attributed to correction of a GLA deficiency in malignant cells, with supplementation of this fatty acid leading to increased prostaglandin (PG) production and consequent growth inhibition. To test this hypothesis the effect of 50 micrograms/ml concentrations of GLA and its sequential metabolite dihomo-gamma-linolenic acid (DGLA) and cell growth, morphology and prostaglandin (PGE and PGF) production by NUB 1 cells was investigated. GLA increased PGE and PGF production, inhibited cell growth and caused accumulation of lipid containing cytoplasmic granules. While treatment with DGLA increased PG production to a significantly greater extent than GLA administration it had no apparent effect on cell growth of morphology and did not inhibit cell growth. These findings suggest that some action other than the ability to increase PG production may be responsible for the inhibitory effects produced by GLA in malignant cells.

Human esophageal carcinoma cell lines: prostaglandin production, biological properties, and behavior in nude mice.

Prostaglandin production by two continuous human esophageal carcinoma cell lines HCU 18 and HCU 39 derived from poorly and moderately differentiated source tumors, respectively, was investigated. Behavior of both lines in vitro and upon sc inoculation into athymic randombred BALB/c nude mice was also assessed. Approximately half the xenografts induced by HCU 18 cells were invasive, whereas those initiated by HCU 39 cells were all well encapsulated. Although metastases were not detected in mice given injections of HCU 39 cells, metastatic tumors developed in 2 mice inoculated with HCU 18 cells. In addition, HCU 18 cells produced significantly more prostaglandin E (PGE) and prostaglandin F (PGF) than HCU 39 cells. These findings suggest a relationship between PGE and PGF production by human esophageal carcinoma cells and their invasive and metastatic potential in athymic mice.

Effects of gamma-linolenic acid, dihomo-gamma-linolenic acid and ethanol on cultured human mammary carcinoma cells.

A number of fatty acids have been shown to inhibit the growth of malignant cells in vitro. In particular, gamma-linolenic acid (GLA) has been proposed to act as a precursor for the production of prostanoids especially prostaglandin E1 (PGE1). To test this hypothesis, the effects of GLA on cultured human breast carcinoma cells were compared with those of dihomo-gamma-linolenic acid (DGLA) the metabolite of GLA and the immediate precursor of PGE1. The influence of ethanol (which has been shown to enhance conversion of DGLA to PGE1) on the actions of each of the fatty acids was also investigated. In contrast to the inhibitory effects observed with all concentrations of GLA cell growth was promoted by the presence of 50 micrograms DGLA. Ethanol reduced the action of both GLA and DGLA possibly due to some physicochemical reaction between the alcohol and the fatty acids. The fact that the actions of GLA were not mimicked by DGLA which is the next step towards PG production casts doubt upon the role of PGE1 as mediator of the effects which have been observed with GLA in malignant cells.

Effects of gamma-linolenic acid on murine cells in vitro and in vivo.

The effects of gamma-linolenic acid (GLA) on growth of cells of the continuous murine sarcoma line M52B were investigated in vitro. Prostaglandin (PG) production by these cells after GLA treatment was also measured. GLA inhibited the growth of M52B cells and became overtly toxic at high doses or after long periods of exposure to lower doses. The inhibitory effects of GLA were accompanied by an increase in PGE production by M52B cells. However, the rise in PGE was not statistically significant. Accordingly the extent to which PGE may contribute to the inhibition observed with GLA remains unclear. In order to establish whether these in vitro effects could be reproduced in vivo, athymic nude mice bearing murine sarcoma allografts were fed either standard laboratory diets or diets supplemented with 35% evening primrose oil, which contains 10% GLA. As there was no significant difference in tumour volumes between the two groups at the end of the treatment period, the oil-enriched diet was concluded to be without effect on tumour growth in this in vivo model.

The response of human carcinoma cell lines to gamma-linolenic acid with special reference to the effects of agents which influence prostaglandin and thromboxane synthesis.

Recently, addition of gamma linolenic acid (GLA) which is a precursor of prostaglandin E1 (PGE1) to cell cultures, has been shown to inhibit growth of various carcinoma cells (1,2,3,4). These findings are consistent with Horrobin's proposal that some of the metabolic abnormalities of malignant cells may be due to deficiencies of certain prostanoids. To determine whether the observed effects of GLA are in fact mediated by increasing levels of its metabolites, this study investigated the influence of various inhibitors and stimulants of prostaglandin (PG) synthesis on the effects of GLA on carcinoma cells in vitro. Most of the agents used (aspirin, imidazole, lithium carbonate and ascorbic acid) produced results consistent with the idea that elevation of levels of thromboxane A2 (TxA2) and/or PGE1 may be important as regards the actions of GLA. In sharp contrast was the result obtained with indomethacin. This drug, which could be expected to block conversion of GLA to PGE1 and therefore protect cells against the effects of GLA, actually exaggerated the effects of this fatty acid, thereby causing cell death and desquamation.

Parenteral gamma-linolenic acid administration in nude mice bearing a range of human tumour xenografts.

The nude mouse human tumour xenograft system was used as an in vivo model to investigate the possible effect of gamma-linolenic acid (GLA) both on established tumour xenografts and as a prophylactic agent prior to tumour induction. Eighty-nine nude mice bearing a range of different human tumours were studied and two solvents (each of which presented certain practical problems) were used to deliver GLA parenterally to the animals. GLA treatment was found to have no significant effect on the growth of any of the tumour xenografts investigated.