Effect of cholestyramine on the fecal excretion of intravenously administered cholesterol-4-14C and its degradation products in a hypercholesterolemic patient.

The effect of cholestyramine on the fecal excretion of bile acids and neutral sterols was measured in a hypercholesterolemic patient on a low fat, high polyunsaturated fatty acid-containing diet after the intravenous injection of cholesterol-4-(14)C. A significant (16%) lowering of serum cholesterol concentration was accompanied by a 3.2-fold increase in fecal bile acid excretion but no change in neutral sterol output. The increased bile acid loss was adequate to account for the observed fall in serum cholesterol level. The implications of these findings were discussed.

Effect of dietary fat on the fecal excretion of cholesterol and its degradation products in man.

Fecal bile acid and neutral sterol excretion rates were determined in five healthy young men when serum cholesterol changes were induced by isocaloric substitution of an unsaturated (safflower oil) for a saturated fat (butter). The isotope balance method was used after the intravenous injection of cholesterol-4-(14)C. A feces extraction method is presented which permits essentially complete separation of fecal neutral sterols and bile acids. There was a significant increase in the total excretion of the fecal end products of cholesterol metabolism from 966 +/- 42 mg/day on saturated fat to 1147 +/- 45 mg/day on unsaturated fat, and the increase was equally distributed between the neutral sterol and bile acid fractions. With the substitution of dietary fats, regardless of the sequence of their feeding, there was a 28% reduction in serum cholesterol concentration during ingestion of the unsaturated fat. There were reciprocal changes in serum cholesterol levels and fecal steroid excretion with the substitution of one type of fat for the other. The changes in plasma cholesterol content were more than adequately balanced by the reciprocal changes in fecal cholesterol end product excretion. The findings in this study agree with several previous reports in supporting the hypothesis that the hypocholesteremic action of dietary unsaturated fatty acids is associated with an increase in the fecal loss of bile acids and neutral sterols.

Thyroid hormone regulation of the pulsatile discharges of luteinizing hormone in ovariectomized rats.

The pulsatile discharges of luteinizing hormone (LH) were characterized in ovariectomized rats in the presence or absence of thyroid hormone. LH secretion in ovariectomized rats with intact thyroid glands and thyroidectomized-ovariectomized rats receiving daily physiological doses of thyroxine (2 mug/100 g BW/day for 8 days) showed equivalent periodic discharges with frequencies between 15 and 45 min. Though the frequency of the plasma LH rhythm in untreated athyroid-ovariectomized rats was normal, the maximum and minimum concentrations were 2- to 3-fold higher than those of euthyroid-ovariectomized animals. On the other hand, treatment of athyroid-ovariectomized rats with a daily hyperthyroid dose of thyroxine (20 mug/100 g BW) for 8 days, attenuated pulsatile discharges of LH. The LH measured in the sera of these animals each gave dose-response curves by radioimmunoassay which were identical to the authentic rat LH reference preparation. Furthermore, neither the molecular profile nor the metabolic clearance rate of LH was affected by alterations in thyroid status. These results suggest that altered thyroid status does not influence the synthesis and metabolism of LH but does exert a profound effect on the secretion of this hormone by presumably acting directly on the hypothalamo-pituitary axis.

Effect of thyroid status on spontaneous and induced surges of luteinizing hormone.

This study was designed to describe the effects of thyroid status on the preovulatory surge of LH and to determine the site(s) at which these effects are exerted. The treatment of normal 4-day cycling rats with a hyperthyroid dose of thyroxine (T4, 20 mug/100 g BW/day) for 8 days resulted in surges of LH on proestrus which were depressed to 25% of control levels. In ovariectomized (OV) or ovariectomized-thyroidectomized (OV-Tx) rats maintained on a physiological regimen of T4 (2 mug/100 gBW/day), the amount of estrogen required to induce an LH surge was far greater than that required in OV-TX rats receiving no T4 replacement. These data suggest that T4 attenuates preovulatory surges of LH by acting at the hypothalamic-pituitary axis. However, the pituitary might be eliminated as a site of action since hyerthyroid proestrous rats responded to a challenge of LH-releasing hormone (500 ng) by secreting a quantity of LH equivalent to that in euthyroid animals. Similarly, there was no difference in the quantity of LH released by hyperthyroid and euthyroid proestrous rats in response to electrochemical stimulation (100 muA, 60 sec) of the medial preoptic area of the hypothalamus. On the other hand, hyperthyroid rats secreted significantly less LH in response to stimulation of the arcuate nucleus-median eminence area (ARN-ME) than did controls. Thus, T4, apparently modifies LH release by depressing the response of the ARN.

Photosensitization by anticancer agents 21: new perylene- and aminonaphthoquinones.

Hypocrellins are under intensive investigation as photosensitizing agents for photodynamic therapy (PDT). A recent advance in the synthesis of hypocrellin congeners resulted in the production of an amino-substituted hypocrellin-B, and its "half chromophore." Both compounds exhibit stronger red light absorption than previously reported hypocrellins, and, therefore, merit investigation as photosensitizers.

Plasma lipoproteins and coronary arteriography in subjects in the program on the surgical control of the hyperlipidemias. Preliminary report.

Coronary arteriographic findings, plasma lipid and lipoprotein levels, and cigarette smoking history are reported for the first 101 male post myocardial infarction survivors who have been entered into the POSCH clinical trial. Estimates of the extent of stenosis in the major coronary arteries were made using 4 models ranging from a simple determination of the number of the 3 major vessels having significant (i.e. 50% or greater stenosis) disease to more complex methods of determining overall extent of disease in 14 major segments of the coronary arteries. Age was shown to be an important factor in the extent of vessel disease. When controlling for age, plasma cholesterol and LDL-cholesterol levels were shown to be related to the extent of disease, especially in Type II hyperlipoproteinemia subjects. Multiple linear regression analysis demonstrated that age and LDL-cholesterol had positive associations and HDL-cholesterol had an inverse association with the coronary artery disease indices. In this comparatively "healthy" subgroup of the overall population of first MI survivors the major CHD risk factors are limited to plasma lipids and cigarette smoking. This preliminary report of 10% of the recruitment objective of the project supports the currently held views of the lipid--atherosclerosis hypothesis regarding the effects of age-total plasma cholesterol, LDL--cholesterol, and HDL--cholesterol on the extent of coronary atherosclerotic plaques, as determined by coronary arteriography.

Clinical angiographic regression of atherosclerosis after partial ileal bypass.

Clinical documentation of atherosclerotic plaque regression has been difficult to obtain. This is a report of a patient with severe and early atherosclerotic cardiovascular disease with regression of at least three major atherosclerotic lesions demonstrated by coronary arteriography 10 years after partial ileal bypass operation. The patient's total plasma cholesterol was reduced over these 10 years, ranging from 40% to 23%, from the preoperative level of 757 mg/dl. Sequential arteriograms were assessed independently by several arteriographers and blindly by the Arteriography Review Panel of the Program on Surgical Control of the Hyperlipidemias (POSCH). The readings were analyzed by 4 grading methods. Unanimously, marked regression was read in the proximal left circumflex artery (70% leads to 20%), middle segment of the right coronary artery (45% leads to 20%), and in the distal right coronary artery (80% leads to 50%). Thus, by any and all of the methods used, there was significant regression of arteriographically demonstrated atherosclerotic lesions.

Measurement of PDT-induced hypoxia in Dunning prostate tumors by iodine-123-iodoazomycin arabinoside.

Photodynamic therapy (PDT) is known to produce vascular damage in solid tumors resulting in secondary ischemia and tumor cell death from hypoxia. The oxygenation status of both non-treated and PDT-treated Dunning R3327-AT prostate tumors growing in Fischer X Copenhagen rats was investigated with the novel hypoxic marker, 123I-iodoazomycin arabinoside (IAZA). Both qualitative and quantitative data from planar scintigraphy of anesthetized tumor-bearing rats showed increased retention of 123I-IAZA in tumors treated with PDT. Tumor perfusion in the same tumors was measured with 99mTc-hexamethylpropyleneamine oxime (HM-PAO). Region of interest analyses revealed an inverse correlation between tumor hypoxia measured by 123I-IAZA and tumor perfusion as measured by 99mTc-HMPAO (coefficient of correlation, r = -0.72). Planar images of 2-mm frozen sections from a large tumor showed 123I-IAZA selectively retained in the region that had been treated with PDT. This and other iodinated azomycin nucleosides, labeled with 123I, show promise for monitoring tumor oxygenation status non-invasively and, in particular, for monitoring the effectiveness of interstitial PDT treatments where perfusion shutdown is a major mechanism of tumor response.

Directional ST-segment deviation in graded exercise tests correlated with motion of the individual segments of the left ventricular wall.

An exercise test may be characterized as positive because of the production of either electrocardiographic ST-segment depression or elevation. The relationship of exercise-induced ST-segment deviation to the specific motion abnormalities of the individual segments of the left ventricular wall was investigated. The first 280 subjects to enter the Program of Surgical Control of Hyperlipidemia were studied by treadmill exercise testing and left ventriculography. The results showed that exercise-induced ST-segment elevation could occur without evidence in the resting subject of either dyskinesia or aneurysm of the left ventricle, that the area of left ventricular damage was much greater in subjects with exercise-induced ST-segment elevation than in those with ST-segment depression, and that wall motion abnormalities were concentrated in the inferoposterior area in the group with ST-segment elevation, but were generally scattered throughout the left ventricular wall in the group with ST-segment depression.

Evidence for mediation of L-2-chloropropionic acid-induced delayed neuronal cell death by activation of a constitutive nitric oxide synthase.

1. Delayed neuronal cell death elicited by excess excitatory amino acid concentrations has been strongly implicated in many neurological disorders including head trauma, stroke, motor neurone disease and Huntington's disease. We have used the neurotoxin, L-2-chloropropionic acid (L-CPA) to model cellular events in vivo leading to delayed neuronal cell loss which is confined to the cerebellar cortex and can be prevented by inhibitors of nitric oxide synthase such as NG-nitro-L-arginine methyl ester. 2. Experiments were performed to determine whether the constitutive nitric oxide synthase (NOS) or inducible form of NOS (iNOS) was responsible for the neuronal cell death. Activation of NOS was confirmed by a 39% increase in cerebellar total nitrate and nitrite concentrations in L-CPA-treated brains, as compared to controls (controls = 2.53 +/- 0.10; L-CPA treated = 3.51 +/- 0.31 nmol mg-1 protein, P < 0.01 Student's t tests, n = 6, mean +/- s.e.mean). Biochemical measurements of total NOS activity were made in homogenates of cerebellum 6 h and 48 h following L-CPA administration, times at which L-CPA concentrations are maximal in brain and a time when there is a high proportion of cerebellar granule cell death, respectively. NOS activity as measured by the amount of [3H]-arginine converted to [3H]-citrulline, did not reveal any difference between controls (rats dosed with water) and animals dosed with L-CPA at either 6 or 48 h following dosing. Furthermore the ability of three NOS inhibitors, NG-nitro-L-arginine, 7-bromo-3-nitroindazole and S-methylisothiourea to block the conversion of [3H]-citrulline to [3H]-arginine was identical at 6 and 48 h time points in control and L-CPA treated rats. 3. Quantitative autoradiography using [3H]-NG-nitro-L-arginine was used to measure the relative anatomical distribution and amount of NOS enzyme in the cerebellum of controls and L-CPA-treated rats 48 h following dosing. There was no significant alteration in the binding of [3H]-NG-nitro-L-arginine to granular and molecular layers of the cerebellum of control and L-CPA-treated rat brains. 4. Western blotting using antibodies against the inducible NOS enzyme failed to detect the protein in cerebellums of L-CPA-treated rats when measured 48 h after L-CPA dosing. 5. In conclusion, the increase in cerebellar nitrate/nitrite concentrations in L-CPA-treated rats provides further evidence for activation of NOS in the cerebellum following administration of L-CPA. The failure to demonstrate an increase in NOS activity at 6 or 48 h in L-CPA-treated rats as compared to controls suggests that the source of nitric oxide responsible for the granule cell death must originate from the constitutive NOS enzyme, probably the neuronal form which is highly enriched in the cerebellum. This hypothesis was further substantiated by Western blotting and quantitative autoradiography.

Possible role of nitric oxide in the development of L-2-chloropropionic acid-induced cerebellar granule cell necrosis.

1. L-2-Chloropropionic acid (L-CPA) produces selective neuronal cell necrosis in rat cerebellum when administered orally at 750 mg kg-1 that is mediated in part through activation of N-methyl-D-aspartate (NMDA) receptors. Cerebellar granule cell death occurs between 30 and 36 h following L-CPA administration exhibiting a number of features in common with excitatory amino acid-induced cell death. We have used this in vivo model to examine the neurochemical processes following L-CPA-induced activation of NMDA receptors leading to neuronal cell death in the rat cerebellum. 2. The effects of a number of compounds which potently block nitric oxide synthase in vitro were examined on L-CPA-induced neurotoxicity 48 h following L-CPA dosing, to discover whether the neuronal cell death is mediated in part by excessive nitric oxide generation. Four inhibitors were studied, NG-nitro-L-arginine (L-NOARG), NG-nitro-L-arginine methyl ester (L-NAME), NG-iminoethyl-L-ornithine (L-NIO) and 3-bromo-7-nitroindazole (BrNI). 3. L-NAME (50 mg kg-1, i.p. twice daily) and BrIN (50 mg kg-1, i.p. twice daily) administration prevented the L-CPA-induced loss of granule cells which can reach up to 80-90% of the total cell number in rats treated with L-CPA alone. L-NOARG (50 mg kg-1, i.p. twice daily) and L-NIO administered at either 25 or 100 mg kg-1, twice daily did not produce any significant protection against L-CPA-induced neurotoxicity. 4. Both L-NAME and BrIN also prevented the L-CPA-induced increase in cerebellar water content and sodium concentrations. L-NIO when administered at the highest doses prevented the increase in cerebellar sodium concentration but not water content. L-NIO and L-NOARG were ineffective in preventing the L-CPA-induced increases in cerebellar water and sodium concentrations. 5. L-CPA-induced reductions in cerebellar aspartate and glutamate concentrations and increases in glutamine and GABA concentrations were prevented by L-NAME and BrIn, but not by L-NIO or L-NOARG. Also reductions in L-[3H]-glutamate binding to glutamate ionotrophic and metabotrophic receptors in the granule cell layer of rat cerebellum was prevented by L-NAME and BrIN, but not L-NIO or L-NOARG. 6. In conclusion, the neuroprotection offered by L-NAME and BrIN suggests that L-CPA-induced cerebellar granule cell necrosis is possibly mediated by or associated with excessive generation of nitric oxide. The inability of nitric oxide synthase inhibitors, L-NOARG and L-NIO to afford protection may result from their limited penetration into the brain (L-NIO) or rapid dissociation from the enzyme.

The Program on the Surgical Control of the Hyperlipidemias: a status report.

The Program on Surgical Control of the Hyperlipidemias (POSCH) is a multicentered secondary coronary heart disease intervention trial utilizing maximal plasma lipid reduction as achieved by the partial ileal bypass operation. With over 500 patients recruited into this trial at present, the 4-year sequential lipid changes are statistically highly significant and include an approximate 30% plasma total cholesterol and 40% low density lipoprotein (LDL)-cholesterol reduction, with a slight increase in the high density lipoprotein (HDL)-cholesterol and a marked increase in the HDL-cholesterol:LDL-cholesterol ratio of about 75% or higher. A definitive answer to the lipid-atherosclerosis theory corollary--whether a decrease in the plasma cholesterol engenders a reduction in the incidence or severity of atherosclerotic cardiovascular disease--can be expected from these marked lipid changes in POSCH.

Gene therapy: a lipofection approach for gene transfer into primary endothelial cells.

Despite the great potential of gene therapy to become a new treatment modality in future medicine, there are still many limitations to overcome before this gene approach can pass to the stage of human trial. The foremost obstacle is the development of a safe, efficient, and efficacious vector system for in vivo gene application. This study evaluated the efficacy of lipofection as a gene delivery vehicle into primary endothelial cells. Transfection efficiency of several lipid-based reagents (Effectene, Fugene 6, DOTAP) was examined at experimental temperatures of 37 degrees C, 24 degrees C, and 6 degrees C. Human umbilical vein endothelial cells (HUVECs) were transfected with the enhanced green fluorescent protein (EGFP) using precise amounts of DNA (Effectene, 0.2 microg; Fugene 6, 0.5 microg; DOTAP, 2.5 microg) and lipids (Effectene, 10 microl; Fugene 6, 6 microl; DOTAP, 15 microl) optimized in our laboratory. Duration of incubation in the DNA/lipid transfection mixture varied for each lipid transfectant as follows: 5 h for both Fugene 6 and DOTAP and 3 h for Effectene. Efficiency of transfection was quantified by microscopic evaluation of EFGP expression in a minimum of 100 cells per group. Transfection efficiencies achieved with these lipofection agents were 34 +/- 1.3% (mean +/- SEM), 33 +/- 1.4%, and 18 +/- 1.5% for Effectene, Fugene 6, and DOTAP, respectively, at 37 degrees C. Transfection results were lower at 24 degrees C with mean efficiencies of 26 +/- 2.4% for Effectene, 14 +/- 2.9% for Fugene 6, and 15 +/- 3.2% for DOTAP. Furthermore, mean efficiencies at 6 degrees C were 6 +/- 0.5%, 8 +/- 1.5%, and 6 +/- 0.0% for Effectene, Fugene 6, and DOTAP, respectively. Efficiency of transfection appeared to be temperature dependent (ANOVA; p < 0.0001). In spite of a significant decrease (37 degrees C vs. 24 degrees C: p < 0.0001; 37 degrees C vs. 6 degrees C: p < 0.0001; 24 degrees C vs. 6 degrees C: p < 0.0115) in transfection efficiency at low temperatures, the successful in vitro gene manipulation renders lipofection a potential gene delivery strategy for in vivo gene therapy.

Assessment of different transfection parameters in efficiency optimization.

Achieving optimal transfection efficiency is the most critical step in overcoming the primary obstacle to success in nonviral-mediated gene therapy. Several transfection parameters were being examined including the effects of different types of transfection media, glucose concentration, reporter DNA concentration, and incubation time in lipotransfectant. Efficiency of transfection obtained was highest for Opti-MEM I (29 +/- 2.28%; p = 0.001) followed by M199 (24 +/- 1.54%; p = 0.009), both of which performed significantly better than DMEM (14 +/- 0.28%) as a transfection medium. The rate of transfection was affected by glucose levels in only DMEM with higher efficiency achieved using low glucose containing DMEM (17 +/- 0.38%) than its counterpart. Furthermore, transfection rate and cell viability were severely hampered by lengthened exposure to transfection complexes, leading to an overall mean efficiency of 5 +/- 0.87%. However, doubling the DNA content in the transfection mixture did not significantly change the mean rate of transfection in M199 medium (24 +/- 1.54% to 27 +/- 1.54%; p = 0.273). The overall range of mean efficiency acquired with our protocol under different transfection conditions was between 14% and 29%. Hopefully results from this study will further potential success in nonviral-mediated gene transfer.

Hypocrellins as photosensitizers for photodynamic therapy: a screening evaluation and pharmacokinetic study.

Hypocrellin compounds were selected as potential photosensitizers for photodynamic therapy (PDT) owing to their high quantum yields of singlet oxygen (1O2), and facility for site-directed chemical modification to enhance phototoxicity, pharmacokinetics, solubility, and light absorption in the red spectral region, among other properties. Parent hypocrellins A and B share an absorption peak at 658 nm. These molecules may therefore be considered useful progenitors of derivatives which absorb more strongly in the red, considering that the ideal sensitizer should absorb in the 650-800 nm range, beyond the absorption range of hemoglobin and melanin, and where light penetration in tissues is maximized through reduced scattering. A series of pure, monomeric hypocrellin derivatives was tested for properties of dark cytotoxicity and photosensitizing potential by clonogenic assay in monolayer cultures of EMT6/Ed murine tumor cells. Their respective toxicities are reported on a molar basis. The in vitro screening assay has, to date, resulted in the selection of four hypocrellin derivatives for further development as photosensitizers for PDT. Cellular uptake for photosensitizing doses of selected compounds was determined by fluorimetry. Dose escalation studies in rodents indicate that potentially photosensitizing doses promote no demonstrable systemic toxicity.

Uptake kinetics and intracellular localization of hypocrellin photosensitizers for photodynamic therapy: a confocal microscopy study.

Hypocrellins are naturally occurring compounds with photosensitizing properties in biological systems. We have prepared synthetic derivatives of hypocrellin B, which have promise as photosensitizers in the clinical application of photodynamic therapy. The intracellular localization and uptake kinetics of hypocrellin B and several selected hypocrellin congeners were determined semiquantitatively by fluorescence confocal microscopy in monolayer cultures of EMT6/Ed murine tumor cells. Each compound had unique uptake kinetics. Although no compound tested to date has demonstrated nuclear labeling, most could be detected in lysosomes, Golgi, endoplasmic reticulum and, to a minor extent, in cellular membranes. No two compounds gave identical labeling distributions. The differences are assumed to originate in physicochemical properties characteristic of each compound, which may ultimately impact upon the primary modality of phototoxicity.

Biodistribution of Photofrin II and 5-aminolevulinic acid-induced protoporphyrin IX in normal rat bladder and bladder tumor models: implications for photodynamic therapy.

Photodynamic therapy (PDT) has been considered as a potential therapy for superficial bladder carcinomas. Cutaneous photosensitivity and reduction of bladder capacity are the two well-known complications following systemic administration of the commonly used photosensitizer, Photofrin II (PII). The objective of the present study was to evaluate whether intravesical (i.b.) instillation of photosensitizers for PDT of bladder cancer might be a more suitable treatment method. Female Fischer rats were utilized to develop orthotopic and heterotopic bladder tumor models. Rats bearing orthotopic bladder tumors were treated either intravesically or intravenously with graded doses of 5-aminolevulinic acid (ALA) or PII. Normal rats received the same doses of ALA or PII. As well, rats bearing heterotopic tumor were studied for comparison. The biodistribution times (times allowed for tissue uptake and bioconversion following drug administration) were 2, 4 or 6 h. Porphyrin fluorescence intensities within tumor, urothelium, submucosa, bladder muscularis and abdominal muscle were quantitated by confocal laser scanning microscopy. Following intravenous (i.v.) injection of ALA, tumor protoporphyrin IX (PpIX) levels peaked at 4 h and diminished by 6 h. The PpIX ratios of tumor-to-bladder mucosa, submucosa and muscle layers were 3:1, 5:1 and 8:1, respectively, 4 h following 1000 mg/kg ALA injection. After ALA instillation, the optimal biodistribution time appeared to be 4 h. Bladder instillation provided comparable tumor labeling with the i.v. route, but lost selectivity of PpIX accumulation between tumor and normal urothelium. The PpIX ratio of tumor-to-bladder muscularis was 5:1. After i.b. instillation of PII, porphyrin fluorescence was detected only within tumor and urothelium, while porphyrin fluorescence was mainly located in bladder submucosa following i.v. injection. Intravesical administration of ALA or PII might be feasible for PDT of superficial bladder cancers.

Preclinical assessment of hypocrellin B and hypocrellin B derivatives as sensitizers for photodynamic therapy of cancer: progress update.

Hypocrellins are perylenequinone pigments with substantial absorption in the red spectral region and high singlet oxygen yield. They are available in pure monomeric form and may be derivatized to optimize properties of red light absorption, tissue biodistribution and toxicity. In vitro screening of synthetic derivatives of the naturally occurring compound, hypocrellin B (HB), for optimal properties of cyto-(dark) toxicity and phototoxicity resulted in selection of three compounds for preclinical evaluation: HBEA-R1 (ethanolaminated HB), HBBA-R2 (butylaminated HB) and HBDP-R1 [2-(N,N-dimethylamino)-propylamine-HB]. Extinction coefficients at 630 nm (epsilon 630) are 6230, 6190 and 4800, respectively; and 1O2 quantum yields, phi, 0.60, 0.32 and 0.42. Intracellular uptake is essentially complete within 2 h (HBEA-R1, HBBA-R2) and 20 h (HBDP-R1). Greatest uptake is associated with lysosomes and Golgi. The HBEA-R1 and HBBA-R2 elicit phototoxicity in vitro primarily via the type II mechanism, with some type I activity under stringently hypoxic conditions. Transcutaneous phototherapy with HBEA-R1 permanently ablates EMT6/Ed tumors growing in the flanks of Balb/c mice, with minimal cutaneous effects. The HBBA-R2 does not elicit mutagenic activity in strains TA98 and TA100 of Salmonella typhimurium. Further development of selected hypocrellin derivatives as photosensitizers for photodynamic therapy is warranted.

Competition for polyamine uptake into rat lung slices by WR2721 and analogues.

The objective of these studies was to determine whether a series of structurally related radioprotective agents could act as substrates for the recently identified polyamine system in the lung. We have shown that WR2721 (S-2(3-aminopropylamino)ethyl phosphorothioate), S-2(4-aminobutylamino)ethyl phosphorothioate (S-ABEP or WR2822) and S-2(7-aminoheptylamino)ethyl phosphorothioate (S-AHEP) competitively inhibit the uptake of putrescine into rat lung slices. The ability of the radioprotectors to act as substrates for the polyamine uptake system was expressed as the Ki for each compound. The Ki values for WR2721, S-ABEP and S-AHEP in the absence of dithiothreitol were 48, 57 and 7 mumol dm-3 compared to 155, 88 and 15 mumol dm-3 in the presence of dithiothreitol, indicating that the disulphide form may have a higher affinity for the transport system. By analogy with other substrates for the polyamine uptake system we have concluded that it should be possible to target radioprotectors to the alveolar epithelial type I and II cells and the Clara cells in the lung, as they prossess this uptake system, and thus protect these cells from oxidative stress.

Radiance modelling using the P3 approximation.

Light dosimetry is an essential component of effective photodynamic therapy (PDT) of tumours. Present PDT light dosimetry techniques rely on fluence-based models and measurements. However, in a previous paper by Barajas et al, radiance-based light dosimetry was explored as an alternative approach. Although successful in demonstrating the use of Monte Carlo (MC) simulations of radiance in tissue optical characterization, the MC proved time consuming and impractical for clinical applications. It was proposed that an analytical solution to the transport equation for radiance would be desirable as this would facilitate and increase the speed of tissue characterization. It has been found that the P3 approximation is one such potential solution. Radiance and fluence expressions based on the P3 approximation were used to optically characterize an Intralipid-based tissue phantom of varying concentration of scatterer (Intralipid) and absorber (methylene blue) using a plane wave illuminated, semi-infinite medium geometry. The results obtained compare favourably with the Grosjean approximation of fluence (a modified diffusion theory) using the same optical parameters (mu(a), mu(s), g). The results illustrate that radiance-based light dosimetry is a viable alternative approach to tissue characterization and dosimetry. It is potentially useful for clinical applications because of the limited number of invasive measurements needed and the speed at which the tissue can be characterized.